Appraisal of existing structures (Third edition) October 2010
Appraisal of Existing Structures.indd 1 22/10/2010 10:22 Membership of Task Group for third edition B C Bell MA MSc DIC CEng FIStructE FICE (Bell Johnson Ltd) Chairman C J Bolton BSc CEng FIStructE MICE (Sellafield Ltd) Vice Chairman K S K Chan BSc CEng MIStructE (Phoenix Consulting Engineers Ltd) S L Matthews BEng PhD CEng CSci FIStructE FICE MCIWEM (BRE) R Stagg BSc CEng FIStructE MICE (Conisbee Ltd) F E Weare MSc DIC CEng FIStructE MICE MIMMM DMS MIHT (Consultant) J G M Wood BSc PhD CEng FIStructE MICE FIAgrE (Structural Studies & Design Ltd)
Secretary to the Task Group B H G Cresswell Riol BEng (Institution of Structural Engineers)
Acknowledgements Thanks also to Dr Florian Block, Dr Chris Burgoyne, Mr Michael Bussell, Dr John Cairns, Mrs Ann Campbell, Mr George Faller, Mr Mike Grantham, Mr Michael Green, Dr Susan Halliwell, Mr Peter Harris, Mr Richard Harris, Mr Chris Holland, Mr Chris Jofeh, Mr Martin Kealy, Mr Michael Kightley, Mr Hirohisa Koga, Mrs Deborah Lazarus, Mr Ian Liddell, Dr John Menzies, Dr John Morlidge, Mr Ian Morrison, Mr Brian Neale, Mr Chris Newman, Dr Rupert Pool, Mr Clive Richardson, Mr Norman Seward, Dr Bob de Vekey and Dr Martyn Webb for their contributions.
Membership of Task Groups for previous editions E Happold* RDI BSc DSc FEng FIStructE FICE FCIOB J H R Haswell†† BSc CEng FIStructE FICE Chairman to First and Second Editions R A Heaton CEng FIStructE FICE MIMuNE A P Backler BSC(Eng) DLC CEng MICE I J Hume DIC DiplConsAA CEng MIStructE J A Baird CEng FIStructE FIWSc P K Jaitly BSc MA LLB CEng FIStructE P R Bartle CEng FIStructE M Law BSc FIFireE W D Biggs§ QBE PhD CEng FIStructE FCIOB S L Matthews BEng PhD CEng CSCI FIStructE FICE MCIWEM W A Black MSc CEng MIStructE FICE FRICS J B Menzies FREng, PhD, BSc(Eng), FIStructE, DipCU P Beckmann MSc(Eng) CEng FIStructE MICE HonRIBA Vice-Chairman to Second Edition G A Bettany MSc CEng MIStructE FRICS R J W Milne‡ BSc Secretary to Second Edition J L Clarke MA CEng MICE R M Moss BSc PhD DIC CEng MIStructE MICE M S G Cullimore# BSc PhD CEng FIStructE F Myerscough CEng MIStructE R J Currie BSc(Eng) CEng FIStructE MICE A L Randall CEng FIStructE W G Curtin† MEng CEng FIStructE FICE W H Sharp CEng FIStructE D K Doran DIC BSc(Eng) CEng FIStructE FICE FCGI R Stagg BSc CEng FIStructE MICE D L Eckett A Stevens CEng FIStructE FICE R J Evans MA(Cantab) LLB CEng MICE MHKIE FCIArb R J M Sutherland FREng BA CEng FIStructE FICE K W Gibson BSc CEng MIStructE MICE Fritz Wenzel M G Green BE CEng MIStructE MICE C J K Williams MA PhD CEng MIStructE
† deceased December 1991 †† deceased October 1994 * deceased January 1996 § deceased March 1998 ‡ deceased August 2002 # deceased April 2007
Published by The Institution of Structural Engineers International HQ, 11 Upper Belgrave Street, London SW1X 8BH Telephone: +44 (0)20 7235 4535 Fax: +44 (0)20 7235 4294 Email: [email protected] Website: www.istructe.org First published 2010 ISBN 978-1-906335-04-5
© 2010 The Institution of Structural Engineers
The Institution of Structural Engineers and those individuals who contributed to the publication of all editions of this Report have endeavored to ensure the accuracy of its contents. However, the guidance and recommendations given in the Report should always be reviewed by those using the Report in the light of the facts of their particular case and specialist advice obtained as necessary. No liability for negligence or otherwise in relation to this Report and its contents is accepted by the Institution, the members of the Task Group, their servants or agents.
In this Report, the words 'ensure', 'must' and 'should' are not intended to imply legal obligations but are intended to convey the weight of the advice given. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without prior permission of the Institution of Structural Engineers, who may be contacted at 11 Upper Belgrave Street, London SW1X 8BH.
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Tablesi v 3.14 Moisture ingress 18 3.14.1 Salt crystallisation 18 Glossary vii 3.14.2 Freezing 18 Foreword to the third edition ix 3.14.3 Organic degradation 18 3.15 Deleterious materials 18 1 Introduction 1 3.16 Fungal and insect infestation 19 1.1 Scope 1 3.17 Atmospheric conditions 19 1.2 Reasons for structural appraisal 1 3.18 Abrasion and erosion 19 1.3 Principles 1 3.19 Vandalism 19 1.4 F ormat of third edition 2 3.20 References 19 1.5 ‘Structural surveys’ 3 1.6 References 3 4 The appraisal process 22 1.7 Bibliography 3 4.1 General 22 4.2 Basic questions 22 2 The brief, legal implications and the report 4 4.2.1 Relevance of codes of practice 23 2.1 Introduction 4 4.2.2 Serviceability and structural safety 23 2.2 The brief 5 4.2.3 Acceptable level of risk 25 2.3 Commercial aspects 5 4.2.4 Limitations of calculations 25 2.4 Legal responsibilities 6 4.2.5 International standards 25 2.4.1 Introduction 6 4.3 P ath of appraisal 25 2.4.2 Law of contract 6 4.4 I nitial stage of appraisal (see Figure 4.5) 26 2.4.3 L aw of tort 7 4.5 S econd stage of appraisal (see Figure 4.6) 28 2.4.4 G eneral 7 4.6 Third stage of appraisal (see Figure 4.7) 28 2.5 Appraisal findings 7 4.6.1 Principles behind third stage assessment 28 2.6 Report 7 4.6.2 F urther on-site investigation work 31 2.6.1 Introduction 7 4.6.3 C omposition of partial safety factors 32 2.6.2 Caveats 8 4.6.4 R igorous analysis further to distribute the load 32 2.6.3 General considerations 8 4.7 Future performance 32 2.6.4 Practical aspects 8 4.8 C alculations requiring special consideration 32 2.6.5 Format 9 4.8.1 G eneral 32 2.7 References 11 4.8.2 Brittle materials 33 2.8 Bibliography 11 4.8.3 C ombined stresses 33 4.8.4 F atigue 33 3 P reparation and influencing factors 12 4.8.5 Buckling 33 3.1 General 12 4.8.6 C onnections 33 3.2 Desk study 12 4.8.7 B olted and riveted connections 33 3.3 R econnaissance and site inspection 12 4.8.8 W elded joints 34 3.4 Dimensions 13 4.8.9 A ssessment of the effects of fire 34 3.5 S tructural arrangements and materials of 4.8.10 Non code based assessments 34 construction 14 4.9 R eferences 34 3.6 Condition 14 3.7 A ctions and loadings 15 5 Testing and monitoring 35 3.7.1 I ntroduction 15 5.1 C ommissioning of testing and monitoring works 35 3.7.2 D ead loads 15 5.2 Determination of testing and monitoring 3.7.3 I mposed loads 15 requirements 35 3.7.4 S torage loads 15 5.3 Simple on-site testing 37 3.7.5 D ynamic loads 15 5.4 M aterials testing 38 3.7.6 D ynamic crowd loads 15 5.5 Load testing 43 3.7.7 L oads arising from machinery, appliances and 5.6 M onitoring of structures 43 equipment 15 5.7 References 43 3.7.8 W ind loads 16 3.7.9 S now and ice loads 16 6 U se and properties of materials 44 3.7.10 F oundations 16 6.1 I ntroduction 44 3.7.11 H ighway and railway loads 16 6.2 M asonry 44 3.7.12 E xtreme events 16 6.2.1 Natural stone 44 3.7.13 F ire 16 6.2.2 Bricks and blocks 49 3.7.14 E arthquake loads 17 6.2.3 M ortars 51 3.7.15 S trains induced by fabrication, assembly, 6.2.4 Masonry construction 51 erection and movement 17 6.2.5 S trength of masonry, characteristic strength, 3.8 Lateral stability 17 c-factors 53 3.9 Soil pressures and ground movement 17 6.2.6 O ther walling materials 54 3.10 A ggressive ground conditions 17 6.3 Timber 55 3.11 T hermal effects 18 6.3.1 General 55 3.12 C hanges of humidity 18 6.3.2 S trength of timber, permissible stresses 56 3.13 Creep 18 6.3.3 P eriod of fire resistance 56
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6.4 M etals and alloys 57 7 Health and safety considerations 89 6.4.1 F errous alloys 57 7.1 Introduction 89 6.4.2 B rittle fracture 59 7.2 Risk management 90 6.4.3 Appraisal of structural ironwork and 7.3 Hazards 91 steelwork 60 7.4 UK legislation 91 6.4.4 S tainless steels 61 7.5 Personal protective equipment (PPE) 92 6.4.5 Aluminium alloys 62 7.6 Specialist training 93 6.4.6 B ronzes and brasses 63 7.7 C hecklist – what the engineer should consider 93 6.4.7 Ropes and cables 64 7.8 R eferences 93 6.5 Concrete 66 6.5.1 History of modern use 66 Appendix 1 Sources of UK-based information on design, 6.5.2 Identification 67 construction and history 95 6.5.3 Mechanical properties 67 A1.1 Introduction 95 6.5.4 Durability 67 A1.2 Building-specific information: primary sources 97 6.5.5 Plain (mass) concrete 67 A1.2.1 Points to note 97 6.5.6 Reinforced concrete 68 A1.3 Building-specific information: secondary sources 97 6.5.7 Prestressed concrete 69 A1.4 Explanatory information 98 6.5.8 Precast concrete 70 A1.4.1 Trade literature and Third Party Certification 98 6.5.9 Glassfibre reinforced concrete (GRC) 70 A1.4.2 Contemporary Codes of Practice 98 6.6 Steel/concrete composite construction 71 A1.4.3 Contemporary textbooks, papers, and 6.6.1 D efinition and history of use 71 periodicals 99 6.6.2 T ypes and properties 71 A1.4.4 Guides to the identification and appraisal of 6.6.3 A ppraisal of composite action 72 systems, products and particular structures 99 6.7 P olymeric materials 72 A1.5 Record sources 99 6.7.1 H istory of use 72 A1.5.1 Possible record sources 99 6.7.2 I dentification 72 A1.5.2 National record centres for ancient monuments and 6.7.3 M echanical properties 72 historic buildings 101 6.7.4 Durability 73 A1.6 Materials 102 6.8 Fibre-reinforced polymer composites 73 A1.7 Government agencies 103 6.8.1 H istory of use 73 A1.8 Other organisations 103 6.8.2 P roperties 73 6.8.3 D urability 73 Appendix 2 Acceptable risk levels for existing 6.9 A dvanced composite materials 73 structures 106 6.9.1 I ntroduction and history of use 73 A2.1 Acceptable risk levels for existing structures 106 6.9.2 I dentification 74 A2.2 References 108 6.9.3 P roperties 74 6.9.4 D urability 74 Appendix 3 Types of defect 109 6.10 Polymers and adhesives 74 A3.1 Introduction 109 6.10.1 Introduction and history of use 74 A3.2 Tables of defects 109 6.10.2 Identification 75 A3.3 References / Bibliography 118 6.10.3 Properties 75 A3.3.1 General 118 6.10.4 Laminated timber (‘glulam’) 76 A3.3.2 Concrete 118 6.10.5 Durability 76 A3.3.3 Masonry 119 6.11 Protective materials 76 A3.3.4 Steel, cast iron and wrought iron 119 6.11.1 Bituminous materials 76 A3.3.5 Timber 120 6.11.2 Lead 76 6.11.3 Paints 77 Appendix 4 Damage due to extreme events 121 6.11.4 Sealants 77 A4.1 Introduction 121 6.12 Glass 78 A4.2 Sources of severe damage 122 6.12.1 Introduction and history 78 A4.2.1 Explosions due to deflagration 122 6.12.2 Identification 80 A4.2.2 Explosions due to detonation 122 6.12.3 Mechanical properties 80 A4.2.3 I mpact of massive objects such as vehicles or 6.12.4 Durability 80 aircraft 123 6.12.5 Safety 80 A4.2.4 Earthquake resistance 123 6.13 Fabric 81 A4.3 Engineering advice in relation to explosion damage 124 6.13.1 Yarns 81 A4.3.1 Pre-event advice 124 6.13.2 Weaves 81 A4.3.2 Post-event 125 6.13.3 Coated fabrics 81 A4.4 References 125 6.13.4 Properties 81 A4.5 Bibliography 126 6.13.5 Ageing and degradation 81 6.14 References 82 Appendix 5 Performance of existing structures 6.15 Bibliography 86 before fire 127 6.15.1 Building construction 86 A5.1 Introduction 127 6.15.2 Particular structural forms 86 A5.1.1 Legislation (England and Wales) 127 6.15.3 Concrete 87 A5.1.2 Non-compliance 128 6.15.4 Masonry 87 A5.1.3 Common failures 128 6.15.5 Metals 88 A5.2 Procedure for fire safety appraisal 128 6.15.6 Timber 88 A5.3 Fire safety requirements of structural elements 128 6.15.7 Glass 88 A5.3.1 Statutory requirements 128 6.15.8 Plastics and polymers 88 A5.3.2 Design approaches 128 A5.3.3 Definition of fire resistance 129 A5.4 Fire performance of existing structures 129
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A5.4.1 Structural fire engineering approach 129 A8.6 E lectrical and other indirect methods of moisture A5.4.2 Management plan and housekeeping 130 measurement of concrete and masonry products 168 A8.7 I nfrared thermography and Transient pulse A5.5 Materials 130 thermography 169 A5.5.1 Reinforced and prestressed concrete 130 A8.8 D etection of cracks in stone or concrete materials 169 A5.5.2 Timber 130 A8.9 B ond wrench 169 A5.5.3 Brickwork and masonry 130 A8.10 Acoustic pulse velocity 170 A5.5.4 Steelwork 130 A8.11 Ultrasonics – timber 170 A5.5.5 Cast Iron 131 A8.12 Drilling energy test 170 A5.5.6 Aluminium 131 A8.13 Crack opening displacement test 170 A5.6 References 132 A8.14 Time domain reflectometry 170 A5.7 Bibliography 132 A8.15 Acoustic emission 171 A8.16 Stiffness damage test 171 Appendix 6 Performance of existing structures A8.17 Radiographic techniques for non-metallic material 171 after fire 133 A8.18 Oxygen diffusion 171 A6.1 Introduction 133 A8.19 Carbon dioxide diffusion 172 A6.2 Procedure for appraisal 133 A8.20 Subsurface radar 172 A6.3 Site visit and desk study 133 A8.21 Resistivity 172 A6.4 Collection of detailed evidence 133 A8.22 Linear polarisation resistance 172 A6.5 Damage assessment 135 A8.23 Eddy currents 173 A6.5.1 Reinforced concrete 135 A8.24 Hall-effect test 173 A6.5.2 Prestressed concrete 136 A8.25 Air test for prestressing ducts 173 A6.5.3 Timber 136 A8.26 Dynamic testing of structures 173 A6.5.4 Brickwork 137 A8.27 Impact echo (also ‘sonic echo’ and ‘stress wave’) A6.5.5 Steelwork 137 technique 174 A6.5.6 Cast iron 140 A8.28 Capacity of existing isolated piled foundations 175 A6.5.7 Wrought iron 140 A6.6 References 141 Appendix 9 Methods of monitoring structures 176 A6.7 Bibliography 141 A9.1 Visual and manual methods 176 A9.2 P hotogrammetric methods 177 Appendix 7 Conventional test techniques 142 A9.3 Automatic and autonomous monitoring systems 177 A7.1 I ntroduction 142 A9.3.1 Instrumentation for measuring actions on A7.2 Tests T1 to T62 144 structures 177 A7.3 Collated references 160 A9.3.2 Instrumentation for measuring responses of A7.3.1 M ethods of test for concrete structures 160 structures 177 A7.3.2 M ethods of test for ferrous metal A9.4 Surveying using global navigation satellite systems structures 161 (GNSS) 178 A7.3.3 Methods of test for masonry structures 162 A9.5 Surveying using total station methods 179 A7.3.4 M ethods of test for timber structures 162 A9.6 Bibliography (for whole Appendix) 179 A7.3.5 Methods of test for polymers and fibre reinforced polymers 163 Appendix 10 Safety factors 180 A7.3.6 S tructural load testing 163 A10.1 Composition of safety factors 180
A7.4 Bibliography 163 A10.2 Load factors, cf 180 A7.4.1 G eneral 163 A10.2.1 General 180
A7.4.2 M ethods of test for concrete structures: General A10.2.2 Load variation factor, cf1 181 guidance 163 A10.2.3 Load combination and sensitivity factor, cf2 181 A7.4.3 Methods of test for concrete structures: Further A10.2.4 Structural performance factor, cf3 181 test methods 164 A10.3 Material factor, cm 181 A7.4.4 F errous metal structures: General A10.4 Permissible stresses 182 guidance 164 A10.5 References 182 A7.4.5 Methods of test for ferrous metal structures: A10.6 Bibliography 182 Further test methods 164 A7.4.6 M asonry structures: General guidance 165 Appendix 11 Residual service life 183 A7.4.7 M ethods of test for masonry structures: Further A11.1 Introduction 183 test methods 165 A11.2 Identifying risk of decay and structural A7.4.8 T imber structures: General guidance 165 consequences 184 A7.4.9 M ethods of test for polymers and fibre reinforced A11.3 Estimating residual service life 184 polymers: General guidance 165 A11.4 Maintain or re-establish stable conditions 184 A7.4.10 Methods of test for polymers and fibre reinforced A11.4.1 Stage 1: Determine stability 184 polymers: Further test methods 165 A11.4.2 Stage 2: Determine deterioration rates 184 A11.5 References 186 Appendix 8 Specialist test techniques 166 A11.6 Detailed investigations of deterioration 187 A8.1 I ntroduction 166 A11.7 Bibliography 187 A8.2 D imensional measurements 166 A8.3 Strain and movement measurements 166 A8.3.1 M echanical: Demec gauges and studs 166 A8.3.2 E lectrical resistance 166 A8.3.3 A coustic 166 A8.3.4 I nductive displacement transducers 166 A8.3.5 O ptical 167 A8.4 I n situ stress measurement 167 A8.5 Fatigue tests of material samples 168
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Table 5.1 Equipment for simple on-site testing and inspection techniques 37 Table 5.2 Concrete structures 38 Table 5.3 Iron, steel and other metal structures 40 Table 5.4 Masonry 41 Table 5.5 Timber structures 42 Table 5.6 Polymers and Fibre Reinforced Polymers 42 Table 6.1 Materials and/or form of construction and period of availability/use in UK 46 Table 6.2 Indicative properties of structural stone originating in the UK 48 Table 6.3 Brick sizes 50 Table 6.4 Indicative values of compressive strength of bricks 50 Table 6.5 Characteristic strengths of stone masonry 54 Table 6.6 Timber species 55 Table 6.7 Chronology of developments in structural iron and steel in the UK 57 Table 6.8 Features that may assist in identification 58 Table 6.9 Indicative physical properties of cast iron, wrought iron and early mild steel 59 Table 6.10 Design stresses and partial safety factors 59 Table 6.11 Mechanical properties of stainless steels 62 Table 6.12 History of use of aluminium 63 Table 6.13 Mechanical properties for aluminium alloys (as at 1957) 63 Table 6.14 Typical properties of wrought bronze containing 8% tin 64 Table 6.15 Typical mechanical properties for cables 65 Table 6.16 History of modern use of concrete 66 Table 6.17 Indicative properties of the main types of concrete 67 Table 6.18 Key dates in the development of polymers 72 Table 6.19 Indicative properties of common polymers 72 Table 6.20 Physical properties of typical products used in concrete repairs 75 Table 6.21 Development of glass-making 79 Table 6.22 Development of 20th century glass types 79 Table 6.23 Typical mechanical properties of annealed glass 80 Table 6.24 Typical design tensile strengths in annealed glass 80 Table A3.1 Building components: concrete 109 Table A3.2 Building components: masonry 113 Table A3.3 Building components: structural steel, cast iron and wrought iron 115 Table A3.4 Building components: timber 117 Table A6.1 Effect of temperature on selected substances 134 Table A6.2 Ignition temperatures of various materials (average values) 134 Table A6.3 Classes of damage after fire, characterisation and description 135 Table A7.1 List of tests described in Appendix 7 142 Table A8.1 List of tests described in Appendix 8 166 Table A10.1 Combinations of ULS loading in BS 8110 180
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Conversion table (to 3 significant figures)
Measure Imperial to si units SI to imperial units 3 Length 1yd = 0.914m 1m = 1.09yd = 3.28ft (= 3'-3 /8") 1ft (1') = 0.305m 1cm = 0.394in 1in (1") = 25.4mm 1mm = 0.0394in Area 1yd2 = 0.836m2 1m2 = 1.20yd2 = 10.8ft2 1ft2 = 0.09290m2 1cm2 = 0.155in2 1in2 = 645mm2 1mm2 = 0.00155in2 Volume 1yd3 = 0.765m3 1m3 = 1.31yd3 = 35.3ft3 1ft3 = 0.0283m3 1cm3 = 0.0610in3 1in3 = 16400mm3 1 litre = 0.220 UK gallon 1 UK gallon = 4.55 litres Mass 1 ton = 1020kg = 1.020 tonne 1 tonne = 0.984 ton 1cwt = 50.8kg 1kg = 2.20lb 1lb = 0.454kg Density 1lb/ft3 = 16.0kg/m3 1kg/m3 = 0.0624lb/ft3 Force 1tonf = 9.96kN 1N = 0.225lbf 1lbf = 4.45N 1kN = 225lbf = 0.100tonf Pressure 1tonf/ft2 = 107kN/m2 1kN/m2 (1kPa) = 0.00932tonf/ft2 1tonf/in2 = 15.4N/mm2 1kN/m2 (1kPa) = 20.9lbf/ft2 1lbf/in2 = 0.00689N/mm2 1N/mm2 (1MPa) = 145lbf/in2
For more detailed information on conversion from Imperial to SI units and vice versa see BS 350: 2004: Conversion factors for units. London: BSI, 2004. In this book, the MPa (Megapascal) is used in preference to N/mm2.
Glossary Term / Words in full Definition/explanation First used abbreviation in text AAR Alkali-aggregate reaction A reaction between the aggregate and alkali hydroxides in concrete, causing 4.7 expansion and cracking over a period of many years. This alkali-aggregate reaction has two forms; alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR) ACR Alkali-carbonate reaction See AAR ALARP ‘as low as reasonably A legal term in the UK to imply that the responsible individual has a duty to A2.1 practicable’ eliminate or reduce all risks, unless to do so [i.e. the cost of doing so] is grossly disproportionate to the benefit. See also ‘SFARP’ ASR Alkali-silica reaction See Alkali-aggregate reaction 6.5.1 CDM Construction (Design 7.4 and Management) Regulations 2007 CFRP Carbon fibre reinforced See FRP 6.10.1 plastic Clevis A U-shaped coupler with a bolt or pin passing through its holes to complete the 6.4.7 coupling Corrosion The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties Ductility The ability to undergo inelastic deformations without significant loss of capacity 1.3 Durability The ability to resist weathering action, chemical attack, and abrasion Fabric In the context of 6.13 of this Report, Fabric is made from woven or knitted yarns 6.13 that form a two-dimensional cloth Failure The inability to continue to sustain the limit state under consideration Fire resistance The ability of a structure to prevent fire from spreading from one part of a building to another, while maintaining structural integrity FRP Fibre reinforced polymer A composite material comprising a polymer matrix reinforced with fibres usually of 6.8 glass, carbon, or aramid (and even cotton or wool). The term FRP is a more general description of materials like GRP. The polymer is usually an epoxy, vinyl ester or polyester thermosetting plastic
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Term / Words in full Definition/explanation First used abbreviation in text GPS Global positioning system A satellite based navigation system providing accuracy usable for surveys on a 3.4 worldwide basis. GPS has become a universal, reliable positioning system; it is used in surveying and other applications where precise positioning is necessary GRC Glass reinforced Concrete that uses alkali-resistant glass fibres for reinforcement as opposed 6.5.9 concrete to traditional steel. It is possible to make lightweight elements that have good structural qualities GRP Glass reinforced See FRP 6.7.3 plastic (polymer and/or polyester) HAC High alumina cement Cement made with bauxite, with a high percentage of alumina. It sets to a high 6.5.1 strength in 24 hours HACC High alumina cement See HAC 6.5.1 concrete HSFG bolt High strength friction A bolt using the friction generated between the faying surfaces clamped by the bolt 4.8.7 grip bolt to achieve the required shear capacity Hydraulic lime A lime mortar (q.v.) containing pure lime with some clay or silt content, which sets mortar chemically when mixed with water. It is known as ‘hydraulic’ lime as it can set under water in the absence of atmospheric oxygen Lime mortar Mortar made with lime as the binder, with no cement content 6.2.3 Lime putty Quicklime which has been slaked with an excess of water Metastability A state of equilibrium which is stable for small perturbation but unstable for large NDT Non destructive testing Testing methods usually performed on in situ construction materials that do not cause any damage to the materials being tested Permissible A design philosophy where the designer ensures that the stresses developed in stress a structure due to service loads do not exceed the elastic limit, or more usually a proportion of the elastic limit (usually determined through the use of implied factors of safety). The permissible stress design approach has generally been replaced by limit state design (also known as ultimate stress design) as far as structural engineering is concerned, although it remains relevant to the assessment of brittle structural materials such as cast iron (see 6.4.3) PTFE Polytetrafluoroethylene A thermoplastic resin that is resistant to heat and chemicals, has an extremely low 6.13.3 coefficient of friction, and is used in applications where friction is to be reduced Pure lime A lime mortar (q.v.) containing pure lime with no clay or silt content; it hardens 6.2.3 mortar slowly by carbonation from adsorption of atmospheric carbon dioxide PVC Polyvinyl chloride A thermoplastic material composed of polymers of vinyl chloride. PVC is a colourless solid with outstanding resistance to water, alcohols, and concentrated acids and alkalis Reeving Passing a rope round a pulley 6.4.7 Robustness The ability to absorb damage without disproportionate collapse 1.3 Serviceability The functioning of the structure under normal use, giving consideration to its general appearance and to users’ comfort SFARP ‘so far as is reasonably A legal term used in the UK; in CDM 2007 Regulations, with respect to the Duties of 1.3 practicable’ Designers, 11 (3) and (4). See also 'ALARP' 7.4 SI Système International The International System of Units (abbreviated SI from the French phrase) is the d’Unités most widely used system of units of measurement. It is the most common system for everyday commerce in the world, and is almost universally used in the realm of science Strength A very general term that may be applied to a material or a structure. In a material, strength refers to a level of stress at which there is a significant change in the state of the material, e.g. yielding or rupture. In a structure, strength refers to a level of loading which produces a significant change in the state of the structure, e.g. inelastic deformations, buckling, or collapse Stress The combined action of a specific corrodant and applied stresses that may result in 6.4.4 corrosion spontaneous cracking of some metals, where the corrodant alone would only have cracking caused mild corrosion Stress grading The visual, or more usually mechanical, grading of individual timber elements after sawing for their ability to withstand flexural stress Structural A term that is no longer recommended for use in the context of any aspects of a 1.5 survey structural appraisal Survey Where unqualified, an inspection 1.5
viii The Institution of Structural Engineers Appraisal of existing structures
Appraisal of Existing Structures.indd 8 22/10/2010 10:22 Foreword to the third edition
The first edition of the Appraisal of Existing The re-use of existing structures has taken on a new Structures was published in 1980 as a result of importance through sustainability. This has however four years’ work carried out by a multi-disciplined to be tempered by a ‘whole life’ approach not only and highly talented Committee, under the to service life but also to energy conservation and enthusiastic chairmanship of my first employer, carbon emissions, subjects which are relatively in Professor Sir Edmund Happold, or ‘Ted’ as he was their infancy and which must mature rapidly. The affectionately known. At 60 pages’ length it was Task Group for the fourth e-edition may need to commendably brief, and informal in style. start now.
The second edition, sixteen years later, was able to It is reassuring to know our legacy of structures incorporate a greater knowledge of materials, testing remains in such good hands, as witnessed by for and diagnosis, and assessment of fire resistance example traffic on the Civil Engineering Heritage before and after fire. Ted was sadly stricken by Exchange forum; and the internet is an excellent cardiomyopathy during its preparation and the Task medium for the dissemination of information and Group dedicated the revised report to his memory. advice, but the note at the start of the American The report now stood at 106 pages. It has become Petroleum Institute’s code of practice for offshore the most popular of the Institution’s reports, relied structures is relevant: “This publication is intended to upon by newcomers and dipped into as a reminder supplement rather than replace individual engineering of good practice by the more experienced: it has judgement.” been out of print for some time.
In 2003, the Institution convened a new Task Group charged with: –– incorporating the latest knowledge; –– adding information about newer materials such as glass, cables and fabrics; and –– thoroughly updating the references.
Little modification to the text was expected but it was hoped the report could be enhanced by Brian Bell coloured illustrations. Task Group Chairman
In the event, the text has been fairly extensively revised, particularly as a result of Health and Safety legislation, of developments in testing and in fire engineering, of our currently rather more litigious climate and of the impact of the internet. Greater legal precision has become necessary and, with it, a reduction in informality and increase in circumlocution. Hyperlink references have been added. As a result, the report has grown to some 187 pages.
In 2006, when 927 comments were made on the draft, the Task Group realised it had reached a false summit. However, under the tactful cajoling of its Secretary, Ben Cresswell Riol (to whom I am most grateful but whose patience I have tested to the limit), the Task Group manfully responded to this ‘wish list’, thanks especially to one of the commentators, Michael Bussell, who has shared his vast experience. I am grateful to all the members of the Task Group but in particular to Dr Stuart Matthews, and his colleagues at BRE, for the meticulous work on testing and to Chris Bolton for sharing the editorial rôle. I am also grateful to the Institution’s Librarian, Rob Thomas, for his work in helping the Secretary with the references and to the staff of the Institution for their support, in particular to Dr John Littler.
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The Foreword by the present Chairman refers to The group who wrote the report are not the fount “Ted” and the esteem in which he was held, as of all current wisdom. The report will hopefully be witnessed by the tribute in the second edition. The amended and improved, and it is our wish that Foreword to the first edition continues to be relevant engineers who read it will comment, draw the and is reproduced below. Institution’s attention to omissions and add to the useful references. Foreword to the first edition (1980) The Chairman thanks the members of the committee In 1742 Pope Benedict XIV, concerned with the and those other engineers who commented on this state of the dome of St Peter’s, requested three report. men, Le Seur, Jacquier and Boscowich to carry out a structural survey to determine the causes The committee enjoyed and learnt from their meeting, of distress and to devise remedial measures. The and we are all grateful for the experience. But our report, published the following year, was prefaced respect and thanks go most of all to Mr R J W Milne, by an apology that said they had assessed it with Assistant Secretary (Technical), whose constant theoretical mathematical reflection only because the attendance and help gave much to us all. building was so unique. Then followed a detailed survey of the dimensions and a discussion on possible explanations for the damage and named the yielding of the tie rings at the circumference as E. Happold the cause. But the interesting part of this report was Chairman (first and second editions) the second part because an attempt was made to calculate the horizontal thrust and to prove that the two rings built in at the time of erection were no longer able to carry this thrust.
The report caused a furore. One comment at the time stated: ‘If it were possible to design and build St Peter’s dome without mathematics and especially without the new fangled mathematics of our time, it will also be possible to restore it without the aid of mathematicians and mathematics ... Michelangelo knew no mathematics and yet was able to build the dome ... Heaven forbid that the calculation is correct. For, in that case, not a minute would have passed before the entire structure would have collapsed.’ Certainly the analysis contained some errors. But in spite of disagreements as to the causes of the damage most people were agreed on the measures to be taken, and in 1743 five additional rings were built in the cupola.
The importance of this event was that, contrary to tradition, the stability of a structure had not been based on empirical rules and opinions but on a detailed survey and mathematical analysis.
Today we are even more interested in developing the art of structural appraisal. We have a large stock of structures and buildings representing successive deposits of human imagination, which we are reluctant to discard for emotional or hard economic reasons. Urban renewal is a rapidly expanding exercise.
The art of appraisal of structures is different from design. In design the forces follow the choice of form and the analysis follows that. In appraisal the engineer is left face to face with an existing structure of definable qualities and must determine its condition and suitability of use. This is not an easy task. In defining the structure’s qualities the engineer may gain from the experience of other engineers’ methods, available testing procedures and current developments in analytical techniques, and this report hopes to assist him.
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1.1 Scope –– determination of the strength of a structure, its components and constituent materials, now and in the future This Report is particularly concerned with the –– derivation of suitable methods for calculating structural appraisal of buildings, but it is relevant in structural behaviour parts to the appraisal of other structures for which –– consideration of future maintenance. specialist assessment advice and guidance is also available, such as bridges, masts, chimneys, cooling towers, cranes and gantries, docks and harbour works, underground structures, containment 1.3 Principles structures, liquid-excluding structures and pipelines.
The process of appraisal follows sequential stages Structural adequacy can be examined in relation to: which this Report reflects in its layout of Chapters: –– overall stability 1 Introduction –– strength 2 The brief, legal implications and the report –– robustness 3 Preparation and influencing factors –– ductility 4 The appraisal process –– geometric permanence (effect of creep and other 5 Testing and monitoring of structures long-term deformations) 6 Use and properties of materials –– stiffness all underpinned by: –– dynamic response 7 Health and safety considerations. –– resistance to fire and other accidental loading –– weather-tightness It is intended for this Report initially to be read –– durability through, not for extracts to be read selectively. Where –– apparent condition. the term ‘engineer’ is used it is meant to refer to a qualified structural engineer or other such competent Structural appraisal is an activity different from structural professional, or to one under competent supervision. design. It is aimed at appraising the actual condition Advice on refurbishment and renovation, although and adequacy of an existing structure as opposed to sometimes requested by a client, is outside the designing a structure which has not yet been built, and scope of this Report. therefore much of the uncertainty present at the design stage is absent. This greater certainty can be taken into The Institution of Structural Engineers has produced account in the appraisal, provided sufficient information this Report as a guide to supplement but not to is gathered. On the other hand, some different replace individual engineering judgement. It is not uncertainties, such as those caused by deterioration, intended to provide the definitive approach in any may need to be taken into account. situation, as in all circumstances the party best placed to decide on the appropriate course of action The questions to be answered will usually be: will be the engineer undertaking the appraisal. –‘– Is the structure adequately safe now and will it remain so in the future?’ –‘– Can it be used for its intended purpose now and in the future?’ 1.2 Reasons for structural appraisal
Appraisal is checking the adequacy of an existing structure, which sometimes becomes necessary for reasons of: –– purchase, insurance, or legal purposes –– change of use or loading regime –– defects in design and construction –– deterioration with time or from being in service –– accidental, fire or other damage –– assuring safety and/or serviceability for future use –– structural alterations –– change of environmental conditions.
Experience in the appraisal of buildings has led to the development of methods for assessing the ever changing strength and serviceability of existing construction, requiring: –– consideration of the levels of safety appropriate to the use of the construction –– assessment of loading Figure 1.1 Ferniehill subsidence study © Arup
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There is no absolute measure of adequate safety. failure of a small mass of material can lead directly However, there does exist a generally accepted to loss of support for a large mass of material. This level of safety provided by design and construction is hazardous because the trigger for failure requires in accordance with current regulations and codes little energy, but there are high levels of energy of practice. This level of safety may provide a useful stored in the structure which can feed the failure datum, but, when assessing existing structures, mechanism, enabling widespread damage to occur mature engineering judgement may need to take rapidly. In these circumstances visual feedback precedence over compliance with the detailed through inspections is unlikely to be useful, and a clauses of codes of practice for structural design. high level of confidence is therefore required in any Serviceability is even more subjective, although some assessment. aspects can be measured. Serviceability is seond in importance to safety. The design process currently in use achieves an acceptable level of reliability by using a combination The processes for design of new structures and of explicit and implicit means. The use of partial for appraisal of existing structures are also quite factors (c-values) is the most important explicit different. The philosophical basis for appraisal method. These factors are assigned to both sides of needs to be different from that adopted in the the load-resistance equation. Those assigned to the design process, even though many of the detailed load side are intended to cover the uncertainties in calculation steps may be similar. It is often necessary the load values, while those on the resistance side to work from first principles. are intended to cover uncertainties in the strengths of the structure, which are usually given in terms All structures are exposed to a range of hazards of tests on material samples. This approach gives which have the potential to threaten their structural an overall factor that experience suggests leads to adequacy. The risk to structures has two distinct reliable structures, provided that appropriate loading components: the probability of failure and the conditions have been considered. consequence of failure. Safety is ultimately judged subjectively and is the perception of the combination Implicit in design are conservative assumptions of these two components. that may be upper- or lower-bound values inherent in the design equations and the neglect in analysis The safety of a structure is dominated by the of such realities as infill walls or stiff cladding behaviour of the whole. Structural form dictates how and three-dimensional behaviour. Such usually loads may be distributed and the consequences of conservative assumptions have influenced judgement local weakness or failure to perform adequately in about the overall factors of safety that have become a structural sense. Current UK design processes considered appropriate. consider these issues largely at the component level through the partial factors of safety (c-factors). Conventional design prejudges the variability of loads Conscious assessment and decision on these and materials. It reduces the problem to its simplest c-factors is one of the most important judgements form, prescribing, where possible, parameters and made by the engineer and requires an appreciation factors in order that values can be obtained for the not only of the significance of components but also of strength and load sides of the equations to answer the overall behaviour of the structure. the question ‘Is the structure adequately safe?’ (Or, summarising CDM legislation in the UK; ‘Have the Two questions to be asked when assessing the hazards been eliminated so far as is reasonably safety of a structure: practicable and the risks from any remaining hazards –B– y what mechanism or mechanisms can the been reduced so far as is reasonably practicable?’1.1). structure become inadequate? –W– hat are the consequences for the overall structure The approach of appraisal has to be quite different of a local failure (avoiding ‘disproportionate from that of design because one is seeking to collapse’) and what are the implications for the assess the real condition of the built structure. It safety of the building users and third parties? involves interpreting records and observations of, and measurements obtained directly from, the Asking these questions should focus the mind on structure. The information thus obtained is of the the level of assurance the engineer seeks from actual condition and the variability of the structure as different parts of the structure, which will depend opposed to what a designer might have assumed. on how likely the failure mechanism is to occur and the consequences of such a failure. For example, in a case where a series of short columns support a continuous beam, which at ultimate stresses is 1.4 Format of third edition capable of spanning across one or two columns, the failure of one column would not lead to immediate collapse. Furthermore, compressive failure of even The third edition has been slightly re-formatted so a single column will usually involve crushing a that the chapters, while following the chronological considerable amount of material which would give process that takes place during an appraisal, refer some warning prior to total loss of capacity. In such a to larger volumes of information which have been system, deterioration or loss of strength would have to transferred to the appendices in order to maintain be widespread and severe to pose a safety problem. the flow of the text. Some chapter and appendix headings have been altered from the Second Edition An important factor in determining the consequences the better to reflect their content. of a potential structural hazard is the rate at which local failure may lead to more widespread damage or Following this introduction, Chapter 2 examines collapse, e.g. brittle cast iron or buckling/overturning. the brief, legal implications and the structure of the In general, the situation is most hazardous where Report. Chapter 3 studies in detail the preparation
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required and the various factors influencing the 1.6 References appraisal: that is, those arising from studies carried out beforehand and from the geometric, loading and environmental factors affecting the structure. 1.1 Institution of Civil Engineers. A Review of, and commentary Chapter 4 steps through the appraisal process, on, the legal requirement to exercise a duty ‘so far as is with flow charts to illustrate key features. Testing reasonably practicable’ with specific regard to designers and monitoring are discussed in Chapter 5, while in the construction industry. Available at: http://www.ice. Chapter 6 is devoted to the use and properties of org.uk/downloads//SFARP%20Report-v12-January10.doc materials. [Accessed: 26 January 2010]
In view of the importance of health and safety, the 1.2 Construction Industry Council. Definitions of inspections subject has been promoted from an appendix to a and surveys of buildings. Available at: http://www.cic.org. full chapter in this edition. To avoid the re-numbering uk/services/definitionsofinspectionsandsurveysofbuildings. of existing chapters and possible corruption of pdf [Accessed: 9 September 2009] references, it has become Chapter 7 and carries further references to relevant UK legislation. 1.3 IStructE. Guide to surveys and inspections of buildings and associated structures. London: IStructE, 2008 Much useful data is presented in the appendices, including new ones on damage due to extreme 1.4 Royal Institution of Chartered Surveyors. Building surveys events, on factors of safety and on residual service and inspections of commercial and industrial property. life. Appendix 2 previously held the health and safety 3rd ed. Coventry: RICS Books, 2005 information, and now considers the much narrower issue of acceptable risk levels for existing structures. References, and often a Bibliography, are given at the end of each chapter. 1.7 Bibliography
In this Report, the words ‘ensure’, ‘must’ and ‘should’ are not intended to imply legal obligations but are Beckmann, P. and Bowles, R. Structural aspects of building intended to convey the weight of the advice given. conservation. 2nd ed. Oxford: Elsevier Butterworth-Heinemann, 2004 References are generally given to BSI codes and standards and occasionally to others. CEN standards Bonshor, R.B. and Bonshor, L.L. Cracking in buildings. BRE Report are only referred to in order to illustrate a particular 292. London: CRC, 1996 point. Structures designed to CEN standards are unlikely to require appraisal in the near future. BS 8210: 1986: Guide to building maintenance management. However CEN standards may contain the results of London: BSI, 1986 recent research which may never be incorporated in the BSI standards they supersede and so should IStructE. Guide to inspection of underwater structures. London: be consulted where appropriate. Many references IStructE, 2001 originating from earlier Editions of the Appraisal of Existing Structures are to documents current at the Oxley, R. Survey and repair of traditional buildings: a sustainable time. In order to maintain the validity of the reference, approach. Shaftesbury: Donhead, 2003 the documents’ details have been preserved. Where a document has been updated, superseded or Richardson, C. AJ guide to structural surveys. London: replaced, the latest reference has been cited in curly Architectural Press, 1985 brackets {thus}. Robson, P. Structural appraisal of traditional buildings. 2nd ed. Shaftesbury: Donhead, 2005
1.5 ‘Structural surveys’ Robson, P. Structural repair of traditional buildings. Shaftesbury: Donhead, 1999
A structural appraisal may require surveys to be Watt, D. and Swallow, P. Surveying historic buildings. Shaftesbury: carried out. Some of these surveys may be of Donhead, 1996 structure. However, the Institution of Structural Engineers believes the phrase ‘structural survey’ to have been so widely misused and misunderstood that it should no longer be employed, ‘inspection’ being the preferred replacement. Indeed, the Construction Industry Council (CIC) has issued a leaflet1.2 explaining to the client who is not a construction professional what types of inspections and surveys of a building are available. Similarly the Institution1.3 and RICS1.4 have produced guidance. The Report returns to this topic in Chapter 3. (Where the word ‘survey’ is used unqualified in this Report, it is intended as ‘inspection’ and is not intended to imply ‘structural survey’.)
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2.1 I ntroduction many will contain procedures for checking appraisal reports, errors are harder to detect. An omission in design calculations will typically It is important to ensure that any commission taken be obvious by its absence, whereas, if a defect by an engineer, and the responsibilities which flow in a structure is unnoticed during the inspection from it, are clearly understood. This applies to all work, no amount of checking of the report will engineering work but is particularly relevant in the pick it up. Repetition of the inspection work is not field of appraising existing structures. a viable form of quality management: inspection requires competence and adequate resources, Compared to a design commission, appraisal work including time. tends to be small with a commensurately small fee. An appraisal can however carry relatively onerous In today’s design environment, rightly or responsibilities. wrongly, engineering judgement is in many ways conditioned by requirements given, for example, Appraisals often involve other specialists yet the by Building Regulations or in codes of practice. client may be unaware of the distinctions between Owing to the variety of forms of construction, and their work and that of the engineer. Some clients, to the quality of their execution, the appraisal of if not informed otherwise, will expect a structural existing structures relies heavily on engineering appraisal to cover all aspects of a building. In judgement, however well guided and informed addition, many clients now expect the engineer to by publications such as this and others, and is take on the appraising team as sub-consultants therefore more open to question than is design. or sub-contractors and to be responsible for an all-encompassing report. Many appraisals of existing ‘structures’ occur within a ‘building’. The engineer is thus required Many appraisals are informally arranged, at least to use judgement as to exactly what is and is initially. Briefs are often given over the telephone, not included in the appraisal and how much requiring an urgent visit in a day or so, with a verbal exposure and/or testing of the structure is summary there and then and a written report a day needed. Some elements of building fabric are or so later. non-structural and can reasonably be ignored. Many however are sufficiently relevant to the Engineers’ quality management systems tend to structure that their inclusion in the appraisal is be more aligned to the design process. Whilst necessary.
Figure 2.1 Structural neglect © Arup
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The vast majority of existing buildings do not responsibilities, confidentiality and so on. It may meet current Building Regulations. It may not be appropriate to state in general terms how be helpful to the client to emphasise every slight the engineer will proceed with the appraisal. It is transgression of original or current codes of particularly important to clarify the physical extent practice if it does not materially affect the safety of of the appraisal, for example whether exploratory the structure or its serviceability in relation to the opening-up and excavations will be required, whether client’s requirements. local making good is required, etc.
Definite conclusions should be reached and The brief should be regularly reviewed during recommendations given clearly in a written report. the appraisal process, and, if necessary, further If the appraisal has highlighted a need for further discussed with the client to seek approval or appraisal work, beyond the current brief, the report agreement in modifying the brief. It is sensible to should explain this as part of the conclusions and include the final brief in the report. recommendations. Many appraisals require input from others, such as The engineer must always both satisfy their testing houses, specialists, etc. Their roles should professional responsibilities and act in the client’s be clearly defined in the brief and understood by best interests, retaining professional independence the client. Ideally the client should appoint them in reaching conclusions and avoiding being swayed directly which will ensure that the testing house by commercial or similar pressures, whether from or specialist is directly responsible to the client the client or from others. Unless within the engineer’s for their performance. Alternatively, if the engineer experience, commercial judgements should be left to takes them on as part of the appraising team, others. the responsibility for their performance ordinarily lies with the engineer. Such an arrangement is Whilst much of the guidance in this chapter can be often favoured by clients since it simplifies their applicable to large, possibly complex, appraisals, the arrangements. The engineer should, however, be principles outlined apply to all appraisals and should aware of the liability implications and ensure that be considered in that light. a sub-contract with terms and conditions back to back with the engineer’s appointment is in place, where appropriate, and that the sub-contractor’s insurance cover (for both professional indemnity and 2.2 The brief public liability) is adequate. In such circumstances it would be reasonable for the engineer to agree a ‘handling charge’ which would include some The first stage of an appraisal is the establishment recognition of the additional risk, responsibility and of a brief for the engineer to work to. However insurance liability taken on by the engineer. The informal an initial request to carry out an appraisal, legal implications of sub-contract arrangements can a written brief should be prepared and agreed by be complicated and legal advice may be advisable both parties. Prudently, this should be carried out, before entering into them. wherever possible, before significant appraisal work is undertaken. It is sometimes appropriate for the If an appraisal is to be carried out jointly with another engineer to develop the brief and explain it to and engineer employed by another client or if the discuss it with the client to ensure that it covers the appraisal is to be done by one engineering practice client’s requirements. It is often prudent to insist on a representing more than one client, as for example in site visit before finalising the brief and thus the scope some expert witness work2.1, the division and extent of the appraisal. of responsibilities should be carefully defined and appropriate safeguards put in place. The written An engineer may be called in by a client who does brief is the correct place for such safeguards to be not fully understand the need for, or cannot fully recorded. There are additional duties placed on define the extent of, the appraisal. It is essential to expert witnesses by Civil Procedure Rules2.2 (CPR), find out at the start exactly what the client needs, Part 35 in particular, which are outside the scope of what aspects are to be considered and in what detail, this Report. and to what use the report is to be put and by whom. The client should be informed by the engineer what scope of appraisal work is being proposed and what the report will cover, clearly defining the ‘structural’ 2.3 Commercial aspects aspects. Some building elements will clearly be beyond the remit of a structural appraisal, such as building services. Other elements are less clearly Although they should not form part of the brief itself, within, or beyond, the scope; items of building fabric the conditions of the engineer’s appointment and such as roof tiles and partition walls are examples the fee arrangement should also be clearly stated of where misunderstandings may occur unless their and recorded in writing. The engineer must be inclusion or exclusion is stated in the brief. aware how and when the contract of appointment is formed and what terms are incorporated. It is best The extent of the appraisal and the subsequent for the engineer to be appointed using a written report should be appropriate to the client and may agreement clearly setting out each party’s rights and be partly influenced by the client’s status (e.g. owner, obligations; this may be in the form of a simple letter tenant, potential buyer, etc.). If so, due account referring to standard Forms of Agreement2.3 such should be taken of this when preparing the brief. as those of the Association for Consultancy and Engineering (ACE). The commercial arrangements In addition the brief may usefully include other between the client and engineer would normally not details such as programme, the need for specialists, be included in the report.
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By its very nature, the amount of work involved is significantly more onerous than required under in appraisal is unknown and therefore the most common law, e.g. a strict obligation or a warranty of equitable fee arrangement would be a time charge fitness for purpose, is inadvisable. In particular, the basis with perhaps a budget and an absolute ceiling engineer should check whether the PII covers work identified, neither of which would be exceeded that is subject to such an obligation. without good reason and the client’s prior approval. Such an arrangement requires trust between the two Unless a specialist in a certain type of appraisal parties. If that trust does not exist, the commission work, and intending to exercise such specialist skill in should not be accepted. If the client requires the fee the appraisal, engineers should be careful not to hold to be quoted as a lump sum, the risks inherent in themselves out, or accept terms of appointment, as predicting the amount of work involved in appraisal specialists. Otherwise, they will be measured against work should be recognised by the engineer and the a higher standard of care. fee quotation prepared accordingly. Clients who try to pass risk on to other parties do not always Engineers need to exercise the required standard of understand that they are likely to pay for the risk, skill and care at every stage of the appraisal process whether the risk is realised or not. It should be noted (including planning the survey, site observations, that even if an appraisal has been undertaken without recording and analysing data, writing and checking payment it still carries liability. the report and recommending any further appraisal work). Failure to do so may make them liable to The Housing Grants, Construction and Regeneration pay damages in breach of contract (or in the tort of Act 19962.4 contains minimum provisions for a negligence: see Section 2.4.3). payment timetable and mechanism and may be applicable. Under the law of contract, the engineer is normally only liable to the client for whom the appraisal Whilst professional indemnity (PI) insurance is work is being carried out and the report is being not currently compulsory for structural engineers, prepared. The engineer may be liable to this client practising within the construction industry without for any losses incurred as a result of the incorrect adequate PI cover is inadvisable. Again this applies to conclusion or recommendations in, or omissions all engineering work but is particularly relevant in the from, the report, provided that such conclusions, field of appraisal. The engineer should be sure to hold recommendations or omissions are a result of the insurance covering the engineer’s potential liabilities engineer’s negligence and/or breach of the terms of arising from the work undertaken. The engineer must the appointment. be alert to any limits to insurance cover, particularly in relation to pollution, contamination, asbestos, If the client is allowed to assign the benefit of the fungus and mould. The Institution of Structural report to another party, then the engineer may be Engineers requires any member practising without liable to this other party for any losses suffered as a PI cover to inform the client accordingly. Many result of reliance upon the report and as a result of clients commissioning appraisals will be laymen the engineer’s negligence and/or breach of contract. and probably unaware of such insurance and the implications; this issue will need to be managed A third party is not normally entitled to rely on the carefully in such circumstances. report unless the engineer knows of the existence and interest of that party at the time of the appraisal The engineer is advised to limit total liability by a and report preparation and that such third party will contract term agreed with the client which should read and rely on the report. The engineer should reflect a realistic assessment of the potential therefore consider this carefully before re-addressing consequences of any negligence or breach. A the report to a named third party, particularly if the starting point for such an assessment may be to limit interest and requirement of the client and of the liability to a multiple of the fee. named third party are not the same and may even conflict. The engineer should identify such a conflict and may need to re-negotiate the contract for the additional cost of resolving the conflict. 2.4 Legal responsibilities The Contracts (Rights of Third Parties) Act 19992.6 sets out third party rights. In some situations, third 2.4.1 Introduction parties may be able to enforce the terms of the original appointment and thus rely on the report by Engineers cannot avoid responsibility for their actions virtue of this Act. The engineer will need to consider and statements2.5. Those in breach of legislation may the interests and requirements of such third parties. attract criminal sanctions (see Chapter 7). However, claims against engineers are normally civil claims The engineer can seek to reduce the liability to third either via a breach of contract or negligence under parties by excluding rights of third parties and strictly the law of tort. controlling any assignment by express contractual terms in the appointment or by careful use of caveats 2.4.2 Law of contract in the brief and in the report. Such provisions should be used with care as they will be interpreted ‘strictly’ The normal common law standard of care expected (e.g. contra proferentum [against the offeror] rule) from the engineer will be ‘reasonable skill and care’, by the courts and need to pass the ‘reasonableness i.e. the skill and care reasonably to be expected test’ under the Unfair Contract Terms Act 19772.7 and of a competent engineer performing an appraisal Unfair Terms in Consumer Contracts Regulations of the type in question. However, the contract can 19992.8. Therefore, they may not always give the require a different standard of care, and the engineer engineer as much protection as wished for. (See also needs to check this. Accepting any obligation which Section 2.6.2.)
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2.4.3 L aw of tort 2.5 Appraisal findings
Under the law of tort, the engineer owes a duty of care to the client and to certain third parties. If a To many engineers, the uncertainty inherent in claim in the tort of negligence is pursued against the appraisal work is one of its attractions but the client engineer, the court will first have to decide whether must be kept informed of unexpected findings during the engineer owes the claimant a duty of care; then the appraisal where they have relevance. It may be the court will decide whether there has been a failure necessary to give an interim report and perhaps even to meet the duty of care, normally assessed by alter the brief. This must be agreed in advance with reference to the ‘standard of the ordinary skilled man the client however, particularly if there are financial exercising and professing to have that special skill’ – implications such as a need for additional inspection, Bolam Test2.9. research, testing, access equipment and so on.
In appraisal work, the engineer may be liable in tort, If a client requires advice on items beyond the for negligence, to all persons who are physically structural appraisal, such as building services, the injured or whose property is damaged by the engineer may reasonably suggest to the client that engineer’s actions in carrying out the appraisal or such advice is sought from an appropriate source because of a negligent appraisal. Pure economic but should not give the advice unless competent to losses (such as diminution of value in property) do so. If a building services engineer for example is may be recoverable from the engineer in certain also commissioned to appraise the building, liaison cases. The injury, damage or losses recoverable are between the engineers can be helpful to plan and normally those which are reasonably foreseeable at co-ordinate the on-site survey work. If the building the time of the appraisal as a consequence of such is occupied, such an approach becomes even more actions or negligence. important.
The engineer owes a duty of care to the public An engineer has a responsibility for the safety of the which includes passers-by, neighbours and public including anyone in or around the structure. adjacent owners. The engineer has a duty to raise If any hint of significant danger is discovered with any issues regarding hazards discovered during the structure being appraised, the engineer must the appraisal that might be outside the brief or inform the client immediately and act accordingly, for represent dangers to the public. This can include example ensuring only controlled access is allowed notifying local authorities or others, as well as the and propping is introduced. This applies even if the client, about dangerous or potentially dangerous danger is not relevant to the brief, for example the structures. Providing this is handled sensitively and suspected presence of asbestos or defective wiring. expeditiously, it need not be unduly onerous. It will In that case the engineer should again avoid giving be sensible for the engineer to record such actions advice unless professionally competent but should in writing. highlight the potential danger and advise the client clearly to seek such advice as may be necessary and 2.4.4 G eneral with the appropriate urgency. Chapter 7 gives further advice in the unlikely scenario of a client ignoring The engineer is unlikely to have the professional what appear to be critical health and safety matters. expertise to advise the client on the legal implications of the appraisal. If for example defects are found which could be considered to be someone’s fault, this opinion could be included in the report but the 2.6 Report engineer should avoid advising the client to seek legal advice. If, based on the evidence contained within the report, the client does decide to then that 2.6.1 Introduction is the client’s prerogative. Every appraisal will have a report describing the An engineer who is commissioned to comment brief, what was done, the findings, the conclusions on the work of others should always maintain and the recommendations as its end result. It is professional standards, in particular avoiding essential to employ as much care and expertise in its irrelevant or derogatory statements whether made preparation as has been used in the appraisal work in writing or orally. The Institution of Structural and, above all, the report must answer the brief. This Engineers’ Code of Conduct and its Guidance fundamental need highlights the requirement for Notes2.10 includes the requirement for those whose a realistic brief at the start. The care and diligence work is being reviewed to be consulted and notified required when preparing a report are generally not where feasible. related to the size or complexity of the structure to be appraised, but will be influenced by the On becoming aware of circumstances that might consequences of failure. give rise to a claim under their PII policy, engineers should, as required by the policy, notify insurers It is recommended that the report is a written one. immediately and keep them updated. Most insurers If an oral report is given in advance of the written provide legal advice but, if not, the engineer should report, the client is entitled to rely on it in the same consider seeking it at the earliest opportunity and way as a written one. In law there is no difference. certainly before responding to any possible claim. However, disputes as to the substance of an oral report may arise so it is essential to confirm the This section contains only a very brief synopsis of contents of an oral report in writing as soon as some legal aspects of appraisal work. Care must possible. The advice given below applies primarily to always be taken when considering legal aspects written reports, but some of it is equally applicable to since the law is constantly developing. oral reports.
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2.6.2 Caveats The report should include appropriate background information to allow a stranger to the structure to It is important for the engineer to define become aware of the full situation by reading the responsibilities by quoting the authority for report. This approach also ensures that, if a report the inspection and the brief, and the physical, is left for some period or if personnel changes administrative, timing and other limitations on the occur within the client’s or engineer’s organisations, appraisal, including, where required, areas with repeated familiarisation work is minimised. limited need for inspection, restricted access or not inspected. It may also be prudent to discuss the The conclusions should be definite, reasoned, accuracy of the methods employed in the appraisal engineering judgements, reached after careful and the relevant significance of the findings. Any consideration of the information obtained. Each reservations or limitations implicit in the appraisal conclusion should be based on the information in methods, techniques employed or interpretations of the report and be expressed explicitly without the results should be clearly stated. use of vague generalities. Where there is insufficient information or the results of the survey and/or tests Excessive use of caveats in a report is not helpful to are inconclusive, this should be clearly stated and the the client nor, in reality, to the engineer; it is unlikely conclusions qualified accordingly. to be well received in the courts. The employment of a professional engineer, capable of using reasonable Any recommendations should be based only on skill and care, entitles the client to expect a clear the conclusions. They may include proposals response to the brief. It is considered reasonable for remedial work, regular maintenance work, however to include two important caveats: monitoring, inspections or further appraisal work. If a report includes a recommendation that advice from (1) The report has been prepared for the other experts should be sought, it is imperative that client alone and no third party should rely the report does not contain any advice beyond the on it. This caveat is particularly important expertise of the author. following the Contracts (Rights of Third Parties) Act 19992.6. If the engineer is If the recommendations from the appraisal leave the made aware during the briefing stage that client with a choice as to a future course of action, a third party will rely on the report, such a it is important that the report provides sufficient caveat needs to reflect the fact. An example information, or indicates that (and preferably how) occurs when a report is commissioned by a such information should be obtained, for the potential purchaser but is to be passed on client to make a valid decision. Only if required to a provider of finance. by the brief, the recommendations may include appropriate engineering solutions, with their (2) Short of the whole structure involved being advantages and disadvantages and the engineer’s dismantled, an appraisal can only ever be recommendation(s) for these solutions. Advice based on the areas investigated in the belief regarding the design of remedial schemes however they are representative. is beyond the remit of an appraisal and is not considered further in this publication. The engineer should also consider restricting any ‘assignment’ of the report, as discussed in Some clients may wish to make comments on the Section 2.4.2. report at draft stage. This is acceptable provided the engineer remains confident that the final report is a 2.6.3 General considerations true record of the appraisal and continues to follow the advice given in this section. Since the report will be When writing the report the engineer should consider issued under the engineer’s name and the engineer will the potential readers, e.g. owners, tenants, financiers, remain responsible for it, the final decision in the event etc, and their probably limited familiarity with of a disagreement over content must be the engineer’s. technical issues and any (essential) jargon. Drafting requires careful thought, review and redrafting. 2.6.4 P ractical aspects The meaning of each sentence must be examined critically. Whilst many reports remain largely unread The report will be in hard copy and, quite likely by the client other than for their synopsis and nowadays, in electronic format. Both should be recommendations, other parties such as lawyers and presented in a professional manner, the latter in a checking engineers are likely to assess each word format which cannot be altered. Elaborate use of with rigour if a difficulty arises. graphics is not usually required. Hard copies should have durable bindings since reports often circulate The report should be as simple and clear as within clients’ organisations and suffer in handling possible. At the same time it must be technically as a consequence. A client may wish to receive an accurate. If it is necessary to use symbols or unbound copy for ease of copying, particularly if an abbreviations, these must be generally understood electronic version is not available. or should be defined in the text so as to avoid confusion. The report’s format should be logical, Photographs are likely to be helpful but any included have continuity and be easy to follow. should be referred to in the text. Their excessive use in the report should be avoided unless the brief The engineer should, when writing the report, keep specifically requires a comprehensive photographic observed facts and hypothetical interpretations record. Typical defects only should be illustrated, clearly distinguished. This can be achieved by together with general informative photographs of the allocating separate sections of the report to each, structure. The subject matter should be intelligible to although this process can lead to repetition. a reader who has not inspected the real-life situation.
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Photographs should show general views of the Title page structure as well as detail. Detail on its own is often This should normally read ‘Structural appraisal of confusing. It is often helpful for reference, and for
In the format considered below, the report is Brief essentially subdivided thus: The brief, or a summary of it, should set out the –T– itle page requirements of the appraisal, as agreed by the client –S– ynopsis and engineer. Correspondence defining the brief in –C– ontents detail, with dates, names and status of signatories –I– ntroduction, dealing with: should be referred to and relevant parts may be –– the brief quoted. If an extensive brief is involved, briefing –– the investigative procedures documentation should be reproduced in an appendix. –– a guide to the report Communications such as telephone conversations –– background description of the structure modifying the brief should also be noted. –S– ections on ‘specific issues’ –S– ummary of recommendations Investigative procedures –A– ppendices. This section should be short but it is important, enabling the engineer to list exactly what has The engineer would need to consider what been done in response to the brief detailed in the constitutes a ‘specific issue’ worthy of its own preceding section. It is essential in this section not to section. describe the findings of the investigations but rather just what procedures were used during the appraisal. An alternative is to follow the introduction with a section on findings, a discussion section, followed If other specialists have been involved in the by conclusions and finally recommendations. This appraisal, this section should be used to explain what approach neatly separates matter of fact from the they did. If their appraisal work is to be included in engineer’s judgement but requires careful discipline the report, their findings will come later, probably to avoid judgement creeping into reported facts. In summarised by the engineer in the main part but with practice this can be very difficult. It also is likely to the specialists’ full reports included as appendices. lead to some repetition as for example the discussion section inevitably repeats some of the factual The dates of the inspection(s) should be recorded, also information from the previous section. factors such as the weather and lighting conditions and any factors which could have affected the survey work, In either format, the use of an ‘introduction’ as follows such as the vantage points, range of observations is worthwhile. In essence the introduction explains to and use of binoculars or other aids. The name of the reader at the very start exactly what the engineer the engineer who carried out the inspections should was asked to do, i.e. the brief; how the engineer be stated, together with any who may have been in responded, i.e. the investigative procedures; and attendance, for example a client representative. then guides the reader to the answer, i.e. the guide to the report. This approach becomes particularly Information obtained from the desk study should be helpful if there were to be any question over whether mentioned here, and a full list of those documents the engineer had responded correctly to the brief, included as an appendix. If an archive search was e.g. using ‘reasonable skill and care’ and working to attempted but did not find anything, or if particularly ‘the standard of the ordinary skilled man exercising relevant material was not found, this should also be and professing to have that special skill’. recorded here.
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If information was received orally, perhaps from Each section should report the findings of the the client or an occupier of the building, that fact appraisal work although there is no need to repeat should be noted. If possible, the name and role of the details given in the ‘investigative procedures’ the source, together with the date of the interview earlier in the report. A concise description of should be given. The engineer’s assessment of the what was seen or done on each occasion should information and its credibility will be covered later in be recorded or, if necessary, an appendix with the report. a schedule of individual observations can be referred to. If at all possible, the inference or If samples were taken from the structure or tests significance of the observations should, however, carried out, the nature and number of samples or not be included with the reporting of the findings tests should be stated along with relevant dates. The themselves. findings of the sampling/testing will be reported later in the report and, if extensive, a full set of results may The section continues with interpretation and/ best be included as an appendix. If a testing house or or opinions. The report will be safer to use and laboratory is involved, its name should be given. If other easier to defend in a possible conflict if ‘facts’ parties are involved in the appraisal it may be important and ‘opinions’ are clearly separated. The extent that samples are taken or in situ tests carried out in the of discussion of the findings’ implications and the presence of their representatives. The names of both overlap with the conclusions depend very much testers and observers should be given. on the size and complexity of the appraisal. There may come a point where extensive theoretical Any calculations that have been carried out as part discussions not essential to understanding the basic of the appraisal should be referred to here. It may message would be better placed in an appendix, be useful to clarify here the detail to which those available to the reader if required. calculations were prepared but, as elsewhere in this section, any conclusions should not be given. Conclusions Any uncertainties remaining after the investigation, It may be useful to note the chronological order in and any need for further checks, should be stated which activities have been done, particularly when here. Conclusions should be firm, reasoned the appraisal is complex, e.g. an initial inspection judgements reached after careful assessments of followed by a detailed inspection. Any limitations the information obtained. It is prudent to discuss on the appraisal, e.g. limited access or lack of briefly the accuracy and limitations of the methods time, should also be recorded here with a succinct employed and the true significance of the findings. explanation if appropriate. Every conclusion should be based on matters contained in the report. Guide to report This section guides the reader through the report If required by the brief, a short description of the and is an appropriate section for the two caveats courses of action available to the client derived mentioned in Section 2.6.2 and for any other caveats. from the conclusions should follow, with the It could give background to what information is recommended action highlighted if appropriate included in the report and where. It can also be used and only if required by the brief. Recommendations to explain if some information is not included in the should probably cover broad principles only, report and why. described in clear, plain language, intelligible to the lay reader, e.g. the one who has to see to the Background description of the structure implementation. Details of that implementation are It should be assumed that a reader is unfamiliar unlikely to have been commissioned as part of the with the structure and needs to have a clear picture appraisal brief, but, if so, should be placed in an of what the engineer was investigating. Even if the appendix. first intended reader knows the structure well, the report may be used in the future by people who do Summary of recommendations not. The section should be brief and may include Although each section on specific issues will include selected images and diagrams, a summarised recommendations, in a lengthy report it can be history of the structure’s original construction and useful to summarise them in a final section. In reality subsequent alterations, and past and present use. most readers look for the recommendations first Any information significant to the purpose of the and may then look into the background of how appraisal need only be briefly mentioned here since it those recommendations were reached when and if will be covered in depth later in the report. time allows. This section should give more details of the recommendations than the synopsis but should Sections on specific issues not include the other information necessary in the The brief, and consideration of the client’s synopsis such as brief, caveats etc. requirements, will determine which issues warrant a full section and which a sub-section. It is likely Appendices that a client would find a report more useful if sub- The report alone should answer the brief but divided into relatively broad sections containing appendices should be included for information from sub-sections dealing with specific issues. A general which the reader may gain a greater understanding. appraisal may neatly divide into sections on structural A copy of the full brief is certainly worthwhile as integrity, durability, defects and future maintenance an appendix. A list of archive information seen is for example. Within the section on durability, for important, particularly if the appraisal relies on it. If example regarding reinforced concrete, sub-sections further information comes to light after the appraisal, would deal with carbonation, cover, chloride content, which perhaps brings into question the appraisal etc. A report containing dozens of small sections, findings, the effort in listing individual documents is sometimes covering specific issues about which the well repaid. client has little understanding, is not helpful.
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2.1 IStructE. Expert evidence: a guide for expert witnesses and their clients. 2nd ed. London: IStructE, 2003
2.2 Ministry of Justice. Civil Procedure Rules. Part 35: Experts and assessors. Available at: http://www.justice. gov.uk/civil/procrules_fin/contents/parts/part35.htm [Accessed: 4 January 2010]
2.3 Association for Consultancy and Engineering. ACE Agreement 2: advise and report or Agreement 5: homeowner. London: ACE, 2009 [Replace ACE Short Form of Agreement 2002]
2.4 Housing Grants, Construction and Regeneration Act 1996. Chapter 53. London: The Stationery Office, 1996
2.5 Wright, I. ‘Risk and liability for the structural engineer: a legal perspective’. The Structural Engineer, 81(14), 15 July 2003, pp23-35
2.6 Contracts (Rights of Third Parties) Act 1999: Chapter 31. London: The Stationery Office, 1999
2.7 Unfair Contract Terms Act 1977: Chapter 50. London: HMSO, 1977
2.8 The Unfair Terms in Consumer Contracts Regulations 1999. [s.l.]: The Stationery Office, 1999 (SI 1999/2083)
2.9 Bolam v Friern Hospital Management Committee [1957] 1 WLR 582
2.10 IStructE. Code of conduct and guidance notes. London: IStructE, 2007
2.8 Bibliography
Dugdale, A.M. and Stanton, K.M. Professional negligence. 3rd ed. London: Butterworths, 1996
‘Duty of care and professional responsibility’. The Structural Engineer, 57A(5), May 1979, p168
Halsbury’s laws of England. Vol 33. 4th ed. London: Butterworths, 1997
Jackson, R.M. Jackson & Powell on professional negligence. 5th ed. London: Sweet & Maxwell, 2002 [and later supplements]
Scott, W. Communication for professional engineers. London: Thomas Telford, 1984 {Since superseded by Scott, W. and Billing, P. Communication for professional engineers. 2nd ed. London: Thomas Telford, 1998}
Wallace, I.N.D. Hudson’s building and engineering contracts. 11th ed. London: Sweet & Maxwell, 1994, sections 1.273 to 1.390 {Since superseded by Atkin Chambers. Hudson’s building and engineering contracts. 12th ed. London: Sweet & Maxwell, 2010 [Due for publication in 2010]}
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3.1 General time, expense, and disruption can be saved if documentary information can be obtained, before any physical investigation of the structure – other The information required for the first stage of a than visual inspection – is undertaken. For notifiable structural appraisal includes knowledge of both the projects constructed in the UK since 1994 there construction and the conditions of service to which should be a Health and Safety File available to the building has been, or is likely to be, subjected. which reference may be made. This information is gathered from documents, any site inspection in support of the appraisal, and oral Information from documents is of particular accounts. importance where the structure is unconventional, or the opportunity for comprehensive opening-up The character and scope of the inspection may be is limited. For example, in a ‘suspended’ office limited by the dictates of time and money, but it building, the perimeter ‘columns’ may in fact be should seek as far as possible all relevant information ‘hangers’ supported from a cantilevered structure about geometry, dimensions and condition. The at a higher level. Hanger loads increase towards inspection may range from a brief visit to examine the top of the building, while loads on the central one building component to a complete survey of core structure will be grossly underestimated if it is condition and dimensions, including a programme of not recognised that it supports the entire building materials testing. Precisely what is done will depend load. Such a building, when new, would have been on the reason for the appraisal. a notable construction: owners, tenants, and many building professionals would have been conscious Where a contractor is required to undertake work of its novel structure. But decades later, with new in connection with the appraisal reference should owners and tenants and with elevations re-clad, be made to Section 5.1. If the engineer appoints such a building may appear to be just ‘ordinary’. the contractor directly the engineer is responsible for the work and any damage that the contractor Possible sources of such information are discussed may cause. in Appendix 1.
3.2 Desk study 3.3 Reconnaissance and site inspection
It is important, as noted in the next section, to Before a site inspection for appraisal is carried out, establish at the outset and certainly before any the engineer needs to establish site conditions and exposure is contemplated whether the structure requirements for access and to decide if finishes is Listed, in a Conservation Area or otherwise the have to be removed to expose the structure. It may subject of interest to Local Authorities or other be necessary to arrange for the attendance of a bodies such as English Heritage, Cadw or Historic contractor who can provide means of access, carry Scotland. out the necessary exposure work, and make good after the inspection. Valuable information on the design, construction and history of the structure can often be obtained If exposure is required to assess the structural from documents prepared for the original design arrangement and condition of the structure, and construction and for subsequent modifications. permission should be obtained in advance from the Substantial time can be saved if dimensioned building owner/user and the appropriate authorities. drawings can be found. Information on other This is particularly important in the case of a construction in the locality may also be useful. structure that is a listed building or a scheduled Names may be a useful pointer – ‘Lakeside …’ or ancient monument. Failure to comply with statutory ‘spring’, for example, may offer some clues as to requirements, and the requirements of local present or past features. authorities and certain other bodies such as English Heritage, can result in criminal proceedings against An engineer will rarely be presented with a dossier the engineer. of structural drawings and other documents that provides a complete description of the original While carrying out the desk study of Section 3.2, structure as built and of its subsequent alterations risks to the health and safety of personnel carrying and repairs. Even if such information is provided, out the inspection and risks to building occupants the engineer should check critical aspects as far as and members of the public will need to be possible against the evidence from the structure itself considered. The engineer has a responsibility by inspection, opening-up, and testing. for safety (see Chapter 7). Inexperienced people working on their own should not carry out site work. In most cases, the engineer will have to search for If work is carried out alone, a system of ‘reporting such information. The structure itself is of course in’ at specified intervals during the day should be the primary source of information, but much adopted.
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Figure 3.1 Site with unusual conditions/features © Andy Chopping/Museum of London Archaeology Service
The site inspection will usually include visual structure, and not all of this information may be observation and measurement to determine necessary. The process should therefore be to dimensions of the structure, structural arrangements examine the structure for potential weaknesses and materials of construction and the condition of which should be investigated more closely. If or the structure. A set of drawings, preferably reduced when it is obvious that dimensional accuracy is to A3 size, is an invaluable aid during inspection important, it will be worthwhile making the effort work. Voids should be inspected; if inaccessible, to obtain dimensions. a borescope or similar device may sometimes be useful. A photographic record of the initial condition The dimensions of the structure may be available on should be obtained before any interventions are existing drawings. If so, critical dimensions should made. It can be very useful to meet and collect be checked on site for accuracy. If dimensions are information from people who have been involved not available, appropriate measurements should with the structure, particularly over time. However, be carried out. Specialist surveying companies can people’s memories are not always correct, and undertake complete measured surveys, if they are statements should be checked and verified. required, accurately, economically and often without requiring access scaffold. Work on site should be carried out systematically, and a diary of site work kept. The engineer, who A survey should, as necessary, measure the site, should be prepared to inspect neglected voids building, the relevant rooms and structural elements and spaces, should be appropriately dressed and and establish their levels. Structural dimensions can properly trained and equipped. Chapter 7 and be measured by tapes, plumb-bobs, the ‘Giraffe’ Table 5.1 indicate possible requirements. (see Appendix 7), callipers and optical equipment, e.g. lasers, photogrammetry, GPS, etc.
The standard grid and level datum, national 3.4 Dimensions or local, to which the survey refers, should be specified. It may be necessary to establish and protect survey stations and level points for later re- A staged approach should be taken when use. The form and content of the final dimensional considering the detailed dimensions required for record should be decided in advance and agreed the appraisal; it may be difficult and expensive with the survey contractor, if the engineer is not to obtain accurate dimensions of the whole carrying out the survey.
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Appraisal of Existing Structures.indd 13 22/10/2010 10:22 3.5 Preparation and influencing factors 3.5 S tructural arrangements and materials 3.6 Condition of construction The assessment of the condition of a structure Exposure of the structure may be necessary to should be approached with an open mind without establish the structural arrangements, materials of prejudging the cause of any apparent defects. construction, joint details, etc. If such information is The complexity of a structure’s behaviour and its found on existing drawings, selected items should be history often prevents all possible combinations of carefully checked. As-built details can be significantly defects and their causes being understood on first different from those illustrated on design drawings, inspection. There is a danger that a defect beyond and many structures have been altered after the experience of the engineer will be missed or construction. that effort will be expended in attempting to find a defect known to the engineer but not actually Where services have been installed at a later date present. the structure should be checked to ensure that any cutting or modification, including the installation The primary task on site should be to describe the of new lift shafts or more commonly notching of conditions adequately so that the situation can be timber joists, has not compromised the original reviewed back in the office. However the engineer’s structure. Service loads from tanks, pipework, previous experience of defects, such as those valves, ductwork, etc. should be examined in order described in Appendix 3, should not be ignored, to confirm that adequate allowances are used in the and appropriate checks should be made. Facts and appraisal. opinions should be separated.
If it is necessary to expose structural details, In most inspections the engineer will need to take engineering judgement is required to decide on how a broad view of the building before concentrating comprehensive such work needs to be. This decision on specific structural aspects. The engineer is often difficult because of damage to finishes, the should be aware of defects that can be repetitive. cost of making good, the disruption to building users, A brief inspection of adjacent similar buildings etc. If constraints prevent the engineer from obtaining is often helpful in this regard but care should be all the information considered necessary, this should exercised not to disturb third parties, such as be reported to and discussed with the client, and the neighbours. outcome stated in the report (see Section 2.3). In many low-rise unframed buildings, the individual If the brief requires the presence or absence of components are predominantly held together by certain materials to be ascertained, the degree friction and gravity. This lack of continuity theoretically of assurance that can be given will depend on leaves the structure vulnerable to disproportionate the extent of the investigation carried out. It is not collapse but these two forces have been fundamental possible to give an unequivocal assurance of the to building construction throughout history and absence of a specific material – or of a specific concern should only be expressed if there is deleterious condition. For some materials, specialist evidence of distress, such as serious cracking in advice may be required. brickwork.
Figure 3.2 Opening up to expose details © AECOM (formerly Maunsell)
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In developing the plan for the appraisal, it may be 3.7.5 Dynamic loads useful to consider that the current condition of an existing building can be appraised with regard to For a number of structures, dynamic loading ‘as-designed’ or ‘rule-of-thumb’ conditions, to ‘as- represents a significant load case in addition to built’ conditions and to ‘as-degraded’ conditions. the normal static loads, and dynamic response These may be related to its ‘durability to date’ and will need to be considered. Different forms of its ‘durability in the future’. The relationships are loading may result in different types of problem, for explored more fully in Appendix 11. example: –V– ibrations produced by pedestrians or traffic can often be felt by people, and this problem of human perception may prove to be a critical 3.7 Actions and loadings factor in assessment of some structures such as long-span floors3.18, 3.19, 3.20. –L– oading induced by coordinated movement of 3.7.1 Introduction groups of people can lead to both serviceability and safety problems. Existing permanent loadings can be established –L– oads from explosions, vehicle impacts or on site; it may be necessary to make enquiries to earthquakes, may lead to different types of safety establish transient loadings. Intended future loadings problems involving either local or global damage should be derived from the client’s brief. Historical (see Appendix 4). loadings may be obtained from archive records –L– oads from wind or waves may also result in or from evidence on site, including talking to the further problems, e.g. resonance due to vortex building’s occupants, neighbours of long standing shedding, fatigue due to the repeated loads, etc. and others with a previous or current involvement –F– atigue failure, usually in metals, where the such as facilities managers, etc. Changes in load number and amplitude of vibration cycles are may have occurred owing to structural alterations excessive. – upwards, downwards or sideways – or owing to –C– hurch bells or other forms of vibrating equipment adjacent new or demolished structures. (flour sifters, presses, stamping machines, etc.). –I– ncreased horizontal loads, such as on 3.7.2 Dead loads balustrades in public buildings. –C– onnections between adjacent structural Dead loads may initially be estimated on the basis of members may become loosened due to vibration 3.1 dimensions and codes of practice and standards or unexpected load reversal. such as BS 6483.2. Differences between design and actual loads may arise from variations in the The eventual result of repeated dynamic response dimensions, and the density and moisture content of may be fracture caused by resonance in building materials. components with insufficient damping. Engineers will be aware that some forms of structures, such 3.7.3 I mposed loads as barriers to resist vehicle-borne attack, rely on ductility to resist dynamic loading. Since imposed loads depend on the use of the building a specification of the original, the current The large variety of loads cannot be considered and proposed usage should be obtained from the in detail here, although a number of situations are building user. This should be confirmed as far as discussed in the clauses below. possible by the inspection. The appropriate future loads can be derived from statutory requirements3.3, 3.7.6 D ynamic crowd loads 3.4, 3.5, 3.6, codes of practice3.1, Eurocodes3.7 or the results of loading surveys3.8, 3.9, 3.10, 3.11. Dynamic loads will be significant when any crowd movement (swaying, dancing, jumping, rhythmic Consideration of crowd loading will be necessary stamping, etc.) is synchronised. Movement of the for some structures. Information may be found in crowd can generate both horizontal and vertical BS 6399: Part 1, BS 61803.12 Temporary demountable loads. If the synchronised movement excites a structures3.13 and Dynamic performance requirements natural frequency of the structure, resonance will for permanent grandstands subject to crowd action3.14 occur3.18. Resonance will greatly amplify structural (see Section 3.7.6). response of the structure and its connections.
3.7.4 Storage loads Where significant dynamic loads are to be expected, safety may be achieved by ensuring that Attention should be paid to the current and proposed the structure will withstand the dynamic loads or by methods and patterns of storage. Mechanical avoiding resonance effects. For grandstands, the stacking and moveable shelving may induce dynamic recommendations in publications on temporary3.13 effects and increase loading. or permanent3.14 structures may be applied, as appropriate. It is necessary to confirm that materials stored in structural containers are of the same characteristics as 3.7.7 Loads arising from machinery, appliances and those assumed in the original design. Overloading is equipment common during stockpiling and alteration works. Skips and other waste containers used during alteration Static and dynamic loadings applied by plant and should not be located within the structure except on equipment to the structure may be obtained by ground-bearing slabs, unless a specially designed reference to the user or manufacturer. Attention supporting structure is in place. The design of hoppers should be paid to the loads applied during the and silos is covered by references 3.15, 3.16 and 3.17. installation, relocation or replacement of plant
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and equipment. The size, location and direction A design carried out before the issue of of application of point loads from lifting or pulling BS 6399-33.30 in 1988 would include uniformly equipment may be of significance. distributed and concentrated loading allowances greater than or equal to the minimum specified Dynamic effects of mobile equipment, e.g. forklift currently to allow for loads due to people, sheet trucks, cranes, bagging plant and vibrators, etc., ice and rainwater, etc. This design may, however, should be investigated. Account should be taken of not be adequate to cover the current snow loading impact from presses, hammers, compressors and requirements for geographical and local variation similar equipment producing cyclic loads that may of ground and roof snow load distributions3.31, 3.32, induce a dynamic response of the structure. It may particularly local drift loadings. prove necessary to measure dynamic effects and to assess the fatigue properties of the materials 3.7.10 Foundations and structural connections, possibly using the bridge design codes3.21 or bridge assessment Some existing buildings will have foundations advice notes3.22. Structures such as crash barriers that do not satisfy current design requirements. or mooring dolphins which rely on deformation If there is no evidence in the superstructure of to absorb energy should be recognised. Where significant foundation movement and no increase structures are interconnected the effects on in superstructure load is envisaged, and if there and from adjacent structures may need to be is no foreseeable risk of significant changes in appraised. ground conditions and/or ground water regime, the foundations may be adequate. However, changes When new mezzanine floors are fitted into existing of pore water pressures in cohesive soils (clays) and buildings and connected to the existing structure of water table levels in cohesionless soils (sands to provide them with sway resistance and stability, and gravels) due to new construction, land drainage if appropriate the original and adjacent structures or the planting or removal of trees, should be should be checked for the consequential effects of considered and, if necessary, monitored: mitigation horizontal force and dynamic vibrations. measures may then be proposed with greater confidence. 3.7.8 Wind loads Reference should be made to the Institution of Simple analysis may show that lightweight roofs (19th Structural Engineers publications Subsidence of low century ones in particular) do not satisfy current rise buildings3.33 and Soil-structure interaction3.34. wind codes for uplift yet have performed well for many decades. In such cases all possible load paths 3.7.11 Highway and railway loads should be considered in appraisal and judgement be based on past history, condition and potential The frequency, weight and distribution of actual consequences. These structures should also be road and rail traffic, particularly on private roads appraised for overall stability, and bracing added if and sidings, may have to be determined3.35, 3.36. necessary. The dynamic effects of road and rail traffic may be significant. For the UK, the Network Rail guidance UK wind load codes were changed with the on assessment of underbridges is available for introduction of CP 3: Chapter V: 19723.23. Structures purchase3.37, and the Highways Agency Design designed before 1972 are likely to have been Manual for Roads and Bridges (‘DMRB’) may designed for lower wind loads than are now required be downloaded free of charge3.38. As stated in in design. The replacement, BS 6399: Part 23.24, was Chapter 1, bridges are considered outside the scope issued in 1995 with more specific detail and was of this Report, but walls retaining ground on which updated in 1997. This will in turn be withdrawn, after vehicles are travelling may impart load on adjacent a period of co-existence, by BS EN 1991-1-4: 2005 structures and guidance is given in DMRB. (Eurocode 1)3.25. 3.7.12 Extreme events Additional information on wind loads and localised effects may be obtained from, for example, the Statutory requirements and codes of practice cover Building Research Establishment and Engineering general provisions for accidental damage: the Sciences Data Unit or the Centre for Window and resistance required for explosions (see Appendix 4) Cladding Technology (CWCT) at Bath University, or impact loads may need to be determined from contact information for which may be found in first principles. Vulnerable parts – damage to which Appendix 1. might lead to disproportionate collapse – should be protected. The dynamic effects of wind on structures such as canopies, masts, towers and buildings of flexible Barriers to contain vehicles may need specific construction – and the effects on their connections – consideration. It is probably better, where practicable, will require special consideration3.26, 3.27, 3.28, 3.29. to re-align roadways to remove or lessen the risk of impact. 3.7.9 S now and ice loads 3.7.13 Fire There have been considerable changes in requirements for designing for snow loads, mainly Advice on appraisal of safety in the event of fire to take account of drifting. Most roofs before 1988 is given in Appendix 5 and on assessment of the will have been designed for a snow load of no more effects of an actual fire in Appendix 6. If the engineer than 0.75kN/m2. Roof extensions and modifications has adequate knowledge of fire engineering, and has creating valleys should be checked for local loads accepted a brief requiring this, the inspection should from drifting snow. include details of compartmentation, means of
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In older structures the questions of lateral support and restraint were not considered in such great detail as under present codes and Building Regulations.
It is very important to determine the lateral support afforded to gable walls which are adjacent to open stairwells. High, unsupported and thin brick walls often found in older buildings would not be permitted today and may not have the factor of safety against collapse required in modern design. In assessing the suitability of walls in older buildings modern principles, supplemented by engineering judgement, may be useful to verify that they are safe.
Imposed movement, e.g. because of differential settlement, can cause significant stresses and instability in the structure.
3.9 Soil pressures and ground movement
Actions from soils depend on the nature of the material, its condition and ground movements3.33, 3.34, 3.43 – 3.48. The engineer should look for movements not only in the structure but in the surrounding ground Figure 3.3 Fire damaged building © AECOM (formerly and adjacent buildings that may be caused by: Maunsell) –– failure of load bearing soil strata –– total and differential settlement due to consolidation of normally and overconsolidated clays, resulting escape, fire load and the provisions for fire detection from additional loading or changes in water tables and fire fighting in order to determine the resistance levels and thereby influencing effective stresses of the structure to fire. –– pumping ground water or decline in aquifer pumping Structural alterations and changes to the layout of –– slope erosion or instability non-structural walls or partitions in a building, any of –– earth tremor, earthquakes which may have a negligible effect on strength, may –– mineral extraction, tunnelling considerably reduce resistance to fire. –– soil compaction due to vibration from machinery or pile driving 3.7.14 Earthquake loads –– settlement due to the collapse of culverts or cavities The zones in which significant earthquakes are –– movement due to construction on the site or in the likely to occur and the design criteria are usually locality given by local building regulations3.39, 3.40 and in –– settlement due to combustion in coal seams Eurocode 83.41. The UK is not considered a seismic –– subsurface erosion from faulty drains, water supply zone for most buildings, but earth tremors do occur. or land drainage Special attention should be paid to structures –– swelling of unsuitable hardcore and fill materials, accommodating hazardous processes or materials, and heave due to frost to which Eurocode 8 does not apply. –– settlement due to planting, growth or removal of trees or vegetation. 3.7.15 Strains induced by fabrication, assembly, erection and movement
Forced assembly of badly fitting components or 3.10 Aggressive ground conditions local deformations during fabrication (e.g. caused by welding or by excessive local deflection of temporary works) may cause strains and forces within the Certain constituents in the ground may degrade parts structure during construction that can affect its of the building such as foundations and ground floor strength and serviceability3.42. slabs, e.g. sulfate attack on concrete elements3.49. The effects of contaminated land can be significant, Structures involving differing primary structural and the engineer should be aware of this potential materials (or structural materials in contact with non- source of deterioration: see for example Lower structural, but stiff, materials) should be appraised for Swansea Valley Project study3.50. compatibility of movement, strength and stability. For example, rigid infill panels would not be compatible An historical survey of previous land and building with timber frames which rely on their flexibility to uses, usually from local authority records, can be accommodate differential settlement where on useful. If necessary, expert advice should be sought shallow foundations. on the implications of the findings, and appropriate
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A change of relative humidity will lead to change of moisture content of most materials. This will cause dimensional changes and may affect the strength and durability of some materials, e.g. timber. It may be useful to calculate the position of the dewpoint in specified circumstances and its relation to any vapour barrier; guidance is available from BRE and BISRIA.
3.13 Creep
Creep – the increase in strain with time under constant load – can occur with certain materials. The level of stress and the period of its application are important factors3.59, 3.60.
3.14 Moisture ingress Figure 3.4 Contaminated land © Arup
The ingress of moisture should be prevented as far as possible, to eliminate the primary causes of decay precautions should be taken if trial pits are to be of the structure: frost damage to masonry, timber dug or other work undertaken on site where the decay, rusting of iron and steel members, and sulfate presence of contaminants is suspected. Generally attack of cement and concrete. the structural appraisal will be concerned only with contaminants that may affect or have affected the 3.14.1 Salt crystallisation structural integrity of the existing building or that may pose a hazard to the inspector or to future Moisture entering materials may cause or encourage occupants. (The engineer will need to be familiar with various forms of deterioration. Water may import salts any limitations of Professional Indemnity Insurance into material and these may cause damage where regarding insurance cover, including those for salt crystallisation occurs below the ‘dry’ surface matters relating to pollution, contamination, asbestos from which the water evaporates. and mould: the brief should reflect such limitations. See Chapter 2.) 3.14.2 Freezing
In freezing conditions, the wind may remove subsurface water from masonry by evaporation or 3.11 T hermal effects sublimation, giving the masonry the appearance of being dry. Water held in porous materials under surfaces sheltered from the wind, particularly in Diurnal and seasonal variations in ambient masonry with impermeable mortar or pointing, may temperature cause expansion and contraction of freeze and cause spalling of stone, crumbling of the structure and its components. The ambient mortar and deterioration of low quality concrete or temperature range to which a structure in the UK concrete lacking air-entrainment. is subjected may be obtained by reference to the Meteorological Office. The effects of heat gain and 3.14.3 Organic degradation loss from radiation may be established by transient heat flow analysis and by reference to published solar Moisture encourages organic degradation, radiation data3.51. particularly in timber.
Significant temperature variations3.52 in the structure may arise from building use, inadequately insulated furnaces and cold rooms and stores, even from 3.15 Deleterious materials kitchens in large hotels, etc. The variations may need to be measured on site. Extremes of temperature may affect the performance of materials3.53, 3.54, e.g. A limited number of materials used for buildings brittle fracture of steel. have been found to have characteristics that can be inherently detrimental to structure performance, Variations in moisture content in most building exacerbated when moisture intrudes. The engineer materials give rise to dimensional changes that can should be aware of the construction materials under affect structural conditions. examination and any history of inherent defects that may be associated with such materials, e.g. calcium A change in temperature may increase the chloride used in concrete to accelerate hardening in rate of corrosion or the deterioration in building winter conditions. Lists of proscribed materials may materials3.55 – 3.58. be consulted with circumspection3.61.
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Organic materials are susceptible to fungal and 3.1 BS 6399-1: 1996: Loading for buildings – Part 1: Code of insect infestation. Forms of attack are described in practice for dead and imposed loads. London: BSI, 1996 the literature3.62, 3.63, 3.64, but the engineer will again need to be familiar with any limitations of Professional 3.2 BS 648: 1964: Schedule of weights of building materials. Indemnity Insurance regarding insurance cover in London: BSI, 1964 respect of spores and mould (fungal infection). 3.3 Greater London Council. Constructional by-laws, London Building Acts 1930-1939, London Building (Constructional) By-Laws, 1972. London: GLC, 1973 3.17 Atmospheric conditions 3.4 The Building Regulations 2000. London: HMSO, 2000 (SI 2000/2531) Normal atmospheric conditions give rise to corrosion of steel and surface weathering of 3.5 Building Standards (Scotland) Regulations 2004. London: concrete. For structures designed, constructed and The Stationery Office, 2004 (SSI 2004/406) maintained in accordance with the relevant codes of practice the rate of corrosion and/or weathering 3.6 Building Regulations (Northern Ireland) 2000. London: is usually acceptable. Exceptions include bridges HMSO, 2000. (Statutory Rules of Northern Ireland and multi-storey car parks where de-icing salt 2000/389) has taken its toll; and the exposed parts of heavily ventilated underground structures such as cut-and- 3.7 BS EN 1991: Eurocode 1: Actions on structures [10 parts] cover tunnels and stations where carbonation has de-passivated the reinforcement and accelerated 3.8 Mitchell, G.R. and Woodgate, R.W. Floor loadings in office chloride attack3.65. Various classes of environment buildings: the results of a survey. BRS Current Paper may be recognised – internal, marine, external, CP 3/71. Garston: BRS, 1971 sheltered, exposed, etc. Account should be taken of moisture, corrosive materials, gases, discharges, 3.9 Mitchell, G.R. and Woodgate, R.W. Floor loadings in retail etc. The rate or incidence of corrosion may be premises: the results of a survey. BRS Current Paper CP affected in some materials by the level of stress. 25/71. Garston: BRS, 1971
Adverse atmospheric conditions3.66 such as chemical 3.10 Mitchell, G.R. and Woodgate, R.W. Floor loadings in pollution may be indicated by the deterioration of domestic premises: the results of a survey. BRS Current materials in the locality if not on the building itself. Paper CP 2/77. Garston: BRS, 1977 Investigation of possible local sources of pollution may indicate the corrosive agent. Further information 3.11 English Heritage. Office floor loading in historic buildings. may be available in the UK from offices of the Health London: English Heritage, 1994 & Safety Executive or the Environment Agency (EA). For historical records, the Alkali Inspectorate 3.12 BS 6180: 1995: Barriers in and about buildings – code of regulated atmospheric pollution from 1863 to 1987, practice. London: BSI, 1995 {Since superseded by 1999 when it became HM Inspectorate of Pollution, in turn version} becoming part of the EA in 1996. 3.13 IStructE. Temporary demountable structures: guidance on Atmospheric sulfates can accelerate the corrosion of procurement, design and use. 3rd ed. London: IStructE, zinc; the life of galvanised coatings can be shortened 2007 significantly. 3.14 IStructE. Dynamic performance requirements for Ultraviolet rays contained in sunlight cause permanent grandstands subject to crowd action: deterioration of many polymer based materials used Recommendations for management, design and in buildings such as paints, sealants and GRP. assessment. London: IStructE, 2008
3.15 CEN TC 250/SC1/PT8: Eurocode 1: Basis of design and actions on structures. Part 4: Actions in silos and 3.18 Abrasion and erosion tanks, 1992 {Since superseded by BS EN 1991-4: 2006: Eurocode 1: Actions on structures. Part 4: Silos and tanks. London: BSI, 2006} In time a structure may be damaged by abrasion or erosion, and a significant reduction in strength and 3.16 Gorenc, B.E and other eds. Guidelines for the assessment serviceability may result. Abrasion from vehicles of loads on bulk solids containers. Barton: Institution of or equipment and erosion by wind and water are Engineers, Australia, 1986 examples. 3.17 Rotter, J. Guide for the economic design of circular metal silos. London: Spon, 2001
3.19 Vandalism 3.18 Littler, J.D. ‘Frequencies of synchronised human loading from jumping and stamping’. The Structural Engineer, 81(22), 18 November 2003, pp27-35 Vandalism may create other forms of damage.
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3.19 Ellis, B.R ‘The Influence of crowd size on floor vibrations 3.37 Network Rail. The Structural assessment of underbridges. induced by walking’. The Structural Engineer, 81(6), NR/GN/CIV/25, Issue 3 June 2006. Available 18 March 2003, pp20-27 through: http://uk.ihs.com/products/rail [Accessed: 10 September 2009] 3.20 Willford, M.R. and Young, P. A Design guide for footfall induced vibration of structures: a tool for designers to 3.38 Highways Agency. Design manual for roads and bridges. engineer the footfall vibration characteristics of buildings Available at: http://www.standardsforhighways.co.uk or bridges. CCIP-016. Camberley: The Concrete Society, [Accessed: 10 September 2009] 2006 3.39 Structural Engineers Association of California. 3.21 BS 5400-10: 1980: Steel, concrete and composite bridges Recommended lateral force requirements and – Part 10: Code of practice for fatigue. London: BSI, 1980; commentary. Sacramento, CA: SEAOC, 1975 {Since BS 5400-10C: 1999: Steel, concrete and composite superseded by Structural Engineers Association of bridges – Part 10C: Charts for classification of details for California. Recommended lateral force requirements and fatigue. London: BSI, 1999 commentary. 7th ed. Sacramento, CA: SEAOC, 1999}
3.22 Highways Agency. Design manual for roads and bridges. 3.40 Dowrick, D.J. Earthquake resistant design and risk Volume 3. Section 4: Assessment. Available at: http:// reduction. Chichester: Wiley, 1997 {Since superseded www.standardsforhighways.co.uk/dmrb/vol3/section4.htm by Dowrick, D.J. Earthquake resistant design and risk [Accessed: 10 September 2009] reduction. 2nd ed. Chichester: Wiley, 2009}
3.23 CP 3: Chapter V: Part 2: 1972: Code of basic data for 3.41 Eurocode 8: Structures in seismic regions – design. Part the design of buildings. Chapter V: Loading: Part 2: Wind 1: General and building, 1988 {Since superseded by loads. London: BSI, 1972 BS EN 1998-1: 2004: Eurocode 8: Design of structures for earthquake resistance – Part 1: General rules, seismic 3.24 BS 6399-2: 1995: Loading for buildings – Part 2: Code actions and rules for buildings. London: BSI, 2005} of practice for wind loads. London: BSI, 1995 {Since superseded by 1997 version} 3.42 Welding Institute. Proceedings of conference on fatigue in welded structures, Cambridge, July 1970. Cambridge: 3.25 BS EN 1991-1-4: 2005: Eurocode 1: Actions on structures Welding Institute, 1970 – Part 1-4: General actions – wind actions. London: BSI, 2005 3.43 BS 8004: 1986: Code of practice for foundations. London: BSI, 1986 3.26 Building Research Establishment. The Assessment of wind loads. Digest 346 [8 parts] 3.44 Building Research Station. Soils and foundations: I. BRS Digest 63. London: HMSO, 1965 3.27 Building Research Establishment. Wind loads on canopy roofs. BRE Digest 284. Garston: BRE, 1986 3.45 Building Research Station. Soils and foundations: 2. BRS Digest 64. London: HMSO, 1965 3.28 Cook, N.J. The designer’s guide to wind loading of building structures. Part 1: Background, damage survey, wind data 3.46 Building Research Station. Soils and foundations: 3. and structural classification. London: Butterworth, 1985; BRS Digest 67. London: HMSO, 1966 Part 2: Static structures. London: Butterworth, 1990 3.47 National Coal Board. Subsidence engineers’ handbook. 3.29 BS 8100-1: 1986: Lattice towers and masts. Part 1: Code 2nd ed. London: NCB, 1975 of practice for loading. London: BSI, 1986 3.48 IStructE. Design and construction of deep basements. 3.30 BS 6399-3: 1988: Loading for buildings. Part 3: Code of London: IStructE, 1975 {Superseded by IStructE. Design practice for imposed roof loads. London: BSI, 1988 and construction of deep basements and cut-and-cover structures. London: IStructE, 2004} 3.31 BS EN 1991-1-3: 2003: Eurocode 1: Actions on structures – Part 1-4: General actions – Snow loads. London: BSI, 3.49 Building Research Establishment. Concrete in aggressive 2005 ground. BRE Special Digest 1. 3rd ed. Garston: BRE, 2005
3.32 Currie, D.M. Handbook of imposed roof loads: commentary 3.50 The Lower Swansea Valley Project. Available at: http:// on British Standard BS 6399 ‘Loading for buildings’, www.swanseaheritage.net/themes/industry/swanval.asp Part 3. BRE Report BR 247. Garston: BRE, 1994 [Accessed: 10 September 2009]
3.33 IStructE. Subsidence of low rise buildings. London: 3.51 Chartered Institution of Building Services Engineers. Solar IStructE, 1994 {Since superseded by 2nd ed, 2000} heating: design and installation guide. London: CIBSE, 2007 3.34 IStructE. Structure-soil interaction: the real behaviour of structures. London: IStructE, 1989 3.52 American Concrete Institute. Temperature and concrete. ACI Special Publication SP 25, Detroit, MI: ACI, 1971 3.35 BS 5400-2: 1978: Steel, concrete and composite bridges – Part 2: Specification for loads. London: BSI, 1978 3.53 Wells, A.A. ‘Fracture mechanics, notched bars tests and {Since superseded by 2006 version} the brittle strengths of welded structures’. British Welding Journal, 12(1), January 1965 3.36 BS EN 1991-2: 2003: Eurocode 1: Actions on structures – Part 2: Traffic loads on bridges. London: BSI, 2003 3.54 Building Research Station. Environment changes, temperature, creep and shrinkage in concrete structures. BRS Current Paper CP 7/70. London: HMSO, 1970
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3.55 Building Research Establishment. Why do buildings crack? BRE Digest 361. Garston: BRE, 1991
3.56 Building Research Establishment. Clay brick work: 1. BRE Digest 164. London: HMSO, 1974
3.57 Building Research Establishment. Clay brick work: 2. BRE Digest 165. London: HMSO, 1974
3.58 Princes Risborough Laboratory. The Movement of timbers. Technical Note no 38. Garston: BRE, 1982
3.59 Illston, J.A., and England, L. ‘Creep and shrinkage of concrete and their influence on structural behaviour’. The Structural Engineer, 48(7), July 1970, pp283-292
3.60 Concrete Society. The creep of structural concrete. Technical paper 101. London: Concrete Society, 1974
3.61 Ove Arup and Partners. Good practice in the selection of construction materials. Reading: British Council for Offices; London: British Property Federation, 1997
3.62 BRE. Recognising wood rot and insect damage in buildings. Garston: BRE, 1987 {Superseded by Bravery, A.F. et al. Recognising wood rot and insect damage in buildings. BRE Report BR453. 3rd ed. London: BRE Bookshop, 2003}
3.63 Building Research Establishment. Wet rot: recognition and control. BRE Digest 345. Garston: BRE, 1989
3.64 Building Research Establishment. Dry rot: its recognition and control. BRE Digest 299. Garston: BRE, 1985
3.65 IStructE. Design and construction of deep basements including cut-and-cover structures. London: IStructE, 2004
3.66 Wilson, J.G. ‘Concrete’, in Simpson, J.W., and Horrobin, P.J. eds. The Weathering and performance of building materials. Aylesbury: Medical and Technical Publishing Co, 1970, pp41-104
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4.1 G eneral 4.2 Basic questions
As mentioned in the Introduction, structural By definition, structural appraisals are carried out appraisal is an activity quite different from design. on existing buildings or structures. Chapters 1 and It is aimed at assessing the real condition and the 2 already discuss the objectives and reasons for adequacy of an existing structure. the appraisal. The following questions can often be used to form the technical basis for the brief for the The adequacy of a structure is assessed by appraisal: the exercise of engineering judgement on –W– as the structure designed and constructed for its information obtained from the study of drawings current and/or proposed uses? and calculations, and of the results of surveys, –H– ow well did the structure meet those inspections and possibly testing. Each of these requirements? activities should be taken no further than is –H– as the passage of time reduced the strength, necessary for a conclusion to be reached. stiffness and robustness of the structure (e.g. carbonation, shrinkage, creep, corrosion, fatigue)? Such engineering judgement derives from ‘well- –I– s the structure behaving as designed? winnowed’ experience4.1, gained from assessments –A– re there any external factors (current or proposed) successfully completed and knowledge of the that have affected or will affect adversely the fundamental principles. loading, strength, stiffness, and/or robustness of the structure (e.g. subsidence, corrosion, change/ As described in Section 2.2, it is of the utmost addition to building/structure under consideration importance to understand, define and agree the or to surrounding buildings)? client’s brief. Only upon the agreement of such a brief can the appraisal process be carried out The importance of assessing loads adequately is effectively. vital, especially if there is risk of overloading arising from change of use. It is also important to take account of the seriousness of any structural or service failure (e.g. economic consequences, danger to community etc.).
Figure 4.1 Bankside Power Station – now Tate Modern © Arup
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Knowledge of the history and social background of there is evidence to suggest that the structure is the building and the era of its construction is often inadequate as a result. It should also be ascertained very useful in answering the above questions. It will if there is any evidence from other structures that give clues to the material used for the construction, earlier recommendations have failed to lead to structural form, workmanship etc. CIRIA report 1114.2 safe and durable structures. For example, see the and Appendix 1 of this Report provide useful starting Merrison rules4.4 following the collapse of two box points. The internet forum CEHX (see Appendix A1.5) girder bridges, the Regan rules4.5 following shear may be able to provide valuable data on unusual failure in concrete, and the rules for robustness materials and structures. against disproportionate collapse following the collapse of Ronan Point4.6. Given this information, the path or strategy of appraisal of the particular building or structure can Codes applicable at the time of design may be used be specifically formulated to answer the client’s brief as a basis for the first assessment, which should with the resources available. indicate if any major oversights or omissions have occurred, or provide assurance that the structure had 4.2.1 Relevance of codes of practice a satisfactory professional input at its original design stage. There are very few codes of practice dating Codes of practice are intended for use with the from before the 1930s. materials and construction methods of their day. They may contain implicit or explicit assumptions that 4.2.2 Serviceability and structural safety are not valid for the structure being appraised. It may, therefore, occasionally be necessary to take a code Serviceability is very much ‘in the eye of the user’. For formula and work back, using first principles and the existing structures, the requirements of serviceability source research, to find the assumptions made in should be stipulated by the user in consultation with its derivation. Codes must, for practical reasons, be the engineer. Similarly, structural safety cannot be limited in length and complexity and cannot allow for prescribed in absolute terms, but is certainly less the infinite number of possible variations in structural subjective than serviceability. form and layout. Sometimes, innovative forms of construction were designed outside the scope of Deflection calculations are notoriously unreliable. these design standards (e.g. large-panel construction Calculating deflections and comparing these with in the 1960s: see notes in Appendix 4). code recommendations is rarely of much value when appraising an existing structure. Therefore in the It is often relevant to consult out-of-date codes of situations where there is no proposed change of use practice and engineering publications that were and no identifiable significant deterioration of the current at the time of construction. A check on this structure, the performance to date provides a better basis will provide one view on the adequacy of the yardstick for serviceability performance. structure and will indicate if the original design was carried out competently. If the design is shown to be When appropriate, an estimate should be made of in accordance with good practice of the time, it may deflections to be expected, and the effect on the provide some indication that detailing and stability intended use should be assessed. Care should be issues have been considered. Superseded codes taken to distinguish between deflections caused by and designers’ manuals may also be consulted to permanent load and those arising from fluctuations investigate the basis for the original design and the in imposed load. Similarly, the effects of creep loadings that might have been assumed. However, it deflections on finishes should be considered. Special should be remembered that such codes may contain care should be taken when heavy partitions are information and criteria (such as those for concrete moved or new ones inserted. shear strength, wind loading and robustness against disproportionate collapse) that are now considered If the engineer is satisfied that the structure has inappropriate. They also sometimes use different already been subjected to a high proportion (and sometimes reduced) design safety factors of its design load without excessive cracking, when compared with modern design codes. A deflection or vibration, the structure may be useful account of the development of codes and assumed to be serviceable even if it does not their application to appraisal of historic buildings is comply with code requirements. A guiding available in The Structural Engineer4.3. principle is sometimes stated as: ‘If it works, leave it alone’. So if the structure has performed The combined use of clauses from superseded well for say over 100 years, it would then be and current codes should be avoided. A code is foolish to ignore the established evidence that the a self-contained set of rules, based on a variety of structure is sound, and it can cope with what is conditions and practices of the day. A very cautious required of it (referred to as the 100-Year Rule4.7). approach should be taken to isolated values or Past performance may, however, not always recommendations from one code being considered be a satisfactory guide, as many deterioration in conjunction with values or recommendations in mechanisms are progressive, while others are another code. For example, concrete cover given in a self-limiting. later code should not be treated as applying to earlier construction because the concrete mix and cover It is therefore essential to establish the full specifications and compaction standards might have circumstances and causes of any deterioration been quite different. where there is a requirement for a structure to remain serviceable for an extended period. It is also It is sometimes useful, however, to compare the important to obtain from the client the expected latest code requirements with those in use when service life required and the level of acceptable the building was constructed. Wherever there are maintenance since the needs for remedial action will differences, the main issue will be to determine if depend on these factors.
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Figure 4.2 Leaning timber framed structure – serviceability is in the eye of the user © Peter Ross
Serviceability problems not envisaged in the original design may arise through deterioration. Some may have safety implications for people in and around the building e.g. spalling of concrete or masonry at high level, fragmentation of asbestos insulation or cladding and cracks due to creep deformation of components allowing the transmission of fire and gases.
When assessing structural safety or serviceability, the data obtained from a structure should be viewed critically against the following criteria: –D– o the data enable possible performance failure mechanisms to be identified and assessed? –A– re the data reliable in themselves? –H– ow sensitive is the assessment of the performance failure mechanism to the accuracy of the data?
For the concrete columns and continuous beam previously discussed in Section 1.3, isolated low Figure 4.3 Dynamic testing of the Millennium Bridge, London strengths from small diameter cores taken from the columns would not be significant provided that no visual signs of distress were present, since both the risk of sudden performance failure and the consequences of failure would be very low.
On the other hand, certain phenomena require extra care in the formulation of the assumptions for their calculation and the interpretation of the results, e.g. if the mode of failure of a structure or member is likely to be sudden as may occur in the failure of cast iron beams4.8 or over-reinforced concrete beams. Similarly, the collapse of a member that could lead to loss of life should be treated with a heightened level of concern compared with a local failure merely affecting serviceability.
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4.2.3 Acceptable level of risk 4.3 Path of appraisal
Every structure carries some risk of failure. Modern design codes, through the safety factors, already The path and stages of appraisal are iterative (see Figures take the risk into consideration: for the design of new 4.5, 4.6 and 4.7, their notes and their legend at Figure 4.4). buildings, the designer does not need to judge the They lead to a series of assessments of the strength acceptable level of risk. As long as the requirements and future serviceability of the structure. For each stage, of the relevant code of practice are met, the risk of information is collected and assessed. If the result of structural failure is considered to be acceptably low. the assessment shows that the structure is adequate and the client’s brief does not need to be expanded, the By contrast, for the appraisal of existing structures, process should stop there. If the result is inconclusive, it needs to be appreciated that many do not meet more information can be collected and assessed more current code requirements. This does not necessarily thoroughly and a further review made. The same iterative mean these structures are unsafe. The engineer process will also apply if the investigation work shows should therefore be prepared to make appropriate that the client’s brief will need to be modified. Then the professional judgements to assess the acceptable engineer should carefully explain the issues with the client level of risks of these structures, and make suitable to seek agreement to modify the brief. The action required recommendations to the client. (Such judgements may be taken in stages, each stage depending on the are common in industries with risk assessments findings of the previous one. Early site visit is always useful falling outside the usual criteria, such as offshore oil within the appraisal process. drilling, railways and nuclear power.) In addition to the technical issues, it is important for the engineer There are three stages: to understand the legal framework used to judge, in consultation with the client, the acceptability of risks. (1) A preliminary, broad assessment of Appendix 2 describes the legal position in the UK, appropriateness for the intended use and and similar legal principles are often applicable in apparent physical condition, robustness and other countries. strength of the structure, including simple calculations where necessary. If these checks 4.2.4 Limitations of calculations are satisfactory no further investigation is required. If these checks indicate a dangerous It is easy to get so involved with the details of a particular situation, some temporary safety measure may calculation that other equally important considerations have to be taken, pending further investigation. are given only a small amount of time or omitted completely. For example, a considerable amount of time (2) A detailed assessment including, but not and effort might be put into a computer analysis of a exclusively based on, numerical checks on steel-framed building, and the joints then analysed using stability and integrity of the whole structure a highly simplified method. The time would have been as well as of the strength of each member. far better spent obtaining references to establish how Conventional limit state design calculations such joints really behave and checking the joints using will usually be used for these checks, although forces and moments from a simplified but reasonably ‘working stresses’, calculated using unfactored representative analysis of the building as a whole. service loads, may, when compared with failure stresses of the materials, give a quick It is therefore useful to set out a list of the calculations appreciation of the likely margin of safety. envisaged and to check the refinement of each operation against that of the others before carrying out (3) If (1) and (2) are not conclusive, a more in-depth any numerical work. analysis is required. This should be based on the best knowledge of loads and material When failures are investigated, they are usually found strengths that can be practically obtained, either to be caused by combinations of several factors. It by measurements and tests, or if appropriate, is rare for defects and failures to be attributable to by other investigations. Such more precise shortcomings that would be shown up by conventional knowledge, used with an understanding of how design calculations. This should be borne in mind (partial) safety factors are derived, may justify when planning the appraisal. reduction of the factors used in the calculations.
4.2.5 International standards The flow charts (Figures 4.5, 4.6 and 4.7) illustrate the path of appraisal. They will not apply to all appraisals, Principles on the assessment of existing structures are and they may not be complete in some situations. given in ISO 13822–20014.9 where a useful flowchart is There will be occasions when deviations from the also given. sequence will be justified. For example, when a member shows visible signs of distress, a simple check This standard allows assessment to be based on on this member should be carried out first. satisfactory past performance provided that certain appraisals and reviews are carried out to the engineer’s It is not unusual for the engineer to be asked only to satisfaction. Where design calculations are used in appraise certain parts of the structure or even certain appraisal work, the conclusion should withstand particular structural elements. The basic principles a plausibility check. Accordingly, where design of the flow charts still apply, but the engineer will calculations indicate insufficient safety, whilst the real need to use experience to plan and carry out the structural condition shows no signs of distress, the works needed to satisfy this more constricted brief, discrepancy should be explained. The engineer should considering carefully whether the constrictions to note that the engineering models used for design the brief are advisable. Sometimes, the engineer calculations are often conservative, and this may be the will need to discuss the findings with the client and first area to be checked to try to explain the discrepancy. advise that the appraisal work should be extended.
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4.4 Initial stage of appraisal In such preliminary calculations there is little (see Figure 4.5) to choose between partial factor or working load methods, so long as the corresponding permissible stresses have the necessary factors The information to hand should be studied and of safety built into them. Alternatively one can analysed. Initial checks on possible mechanisms of make approximate calculations of overall factors failure, load bearing capacity and margins of safety of safety by comparing the likely ranges of load- should be made. These checks should be partly induced member forces with the probable levels qualitative and partly by very simple calculations. of corresponding member strengths. Whichever In particular, the inherent stability, robustness and approach is used, it is essential that it is used adequacy of the structure should be examined. consistently. When detailed calculations are required and where the reserve of safety is The approach may need to be varied depending marginal, it is more appropriate to use limit state on the reason for the appraisal. For example, a methods (see Section 4.6). structure being appraised because of distress should be treated differently from one being appraised for The accuracy of the information available in the change of use. early stages of an appraisal does not justify any agonising over, for example, the shape of the stress It is important that the engineer does not rely too block or the exact length of lever arm, nor usually much on calculations, particularly using those does time permit it. It may be adequate, having methods of analysis and design intended for new sketched the cross-section, to estimate the areas structures: a balance between calculation and in compression and tension and with an informed judgement based on experience must be struck, and guess at the lever arm, calculate average stresses the proportion of each will vary from case to case. in those areas.
The engineer should also consider ‘often found’ Similarly, bending in columns (or ties) may be ignored defects of this type and era of buildings in the at first and its significance evaluated after the direct assessment. Appendix 3 provides a list of defects, stress has been estimated. some of which may reduce the load-carrying capacity of the structure or structural elements. The important point is to acquire and use a knowledge of and feeling for real structural behaviour When previous repair work has been uncovered and not rely on rigid analytical routines. during the investigation work, the effectiveness of the repair should be considered. The investigation work When the aim is to arrive at the order of overstress may need to be expanded to check for other similar in service or, say, the effect of severe section loss or related situations. through corrosion, simple but conservative estimates should be made of the actual loads and the If during the first inspection some element of the calculated stresses compared with both serviceability structure looks inadequate or shows signs of and ultimate values. distress, the engineer should first assess how significant these signs are. Consideration should be If these simple checks show sufficient margins of given to how failure might occur and what warning, if safety, even when conservative assumptions have any, there would be of impending collapse. Likewise been made, and if an increase in loading does not in the case of failure of a member, consideration have to be considered due to a proposed change be given to the possibility of alternative paths for of use, no further investigations or calculations the loads, e.g. ‘if the beam fails, would the window should be necessary, although some repairs may be framing below prevent complete collapse, or would required. the floor span the other way?’ If these simple estimates suggest inadequacy, If the immediate answers to these questions are possible alternative load-carrying mechanisms negative there may be no alternative to propping should be considered. When alternative mechanisms or cordoning-off the area in question. Usually the have been taken into account and the structure is still condition will call for some quick numerical checks found to be inadequate, temporary propping followed and commonsense considerations before preventive by remedial work should be considered. action is taken.
In the flowcharts the following conventions have been used:
A directive in a rectangle indicates an activity which procures or increases the information about the structure. (This is an activity which can often be delegated.) A question in a diamond indicates an assessment of the information available at that stage. The next step in the process depends on whether the answer to the question is ‘Yes’ or ‘No’. (Answering the question involves the exercise of judgement and is therefore the duty of the engineer in charge of the appraisal.)
A statement in a hexagon or circle indicates a conclusion.
Weak points are as common at connections as in members. Where the flow charts read ‘element’, this Element should therefore be interpreted as ‘member and/or connections’.
Figure 4.4 Legend to Figures 4.5, 4.6 and 4.7
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Agree brief with client, study documentation received from client, etc., then carry out initial inspection identifying nature of construction
No Yes Are any parts visibly in distress? Simple calculations of suspect parts, Check on site again if using estimated or actual loads taking Study further documents necessary into account any structural deterioration
Yes
Do site Are Yes observations No Can other suspect parts confirm paper documents be ‘safe’? evidence? found?
No Yes No Carry out further survey/opening up work if necessary Is Take preventive action information No before further appraisal now adequate for assessment?
Yes
Does Uncover samples of No ‘new’ use impose hitherto hidden details heavier loads than designed for?
Yes
Are all structural details No in good condition? Are No Yes defects easy to mend?
Yes
Propose repairs
Is No robustness established?
Defect No Yes easy to remedy?
Propose Consider the need to Yes repairs carry out full assessment, calculations etc, see Structure adequate for Figure 4.6 unchanged use, subject to Note repairs, if proposed Indicates appraisal not requiring calculations
Figure 4.5 Initial stage of appraisal
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Appraisal of Existing Structures.indd 27 22/10/2010 10:22 4.5 The appraisal process 4.5 Second stage of appraisal 4.6 Third stage of appraisal (see Figure 4.6) (see Figure 4.7)
When the initial stage check indicates stresses The second stage appraisal has been based on of the same order as those used in design today conventional design assumptions. If the calculations or even higher, the engineer should discuss the indicate a moderate shortfall in load bearing capacity, findings with the client, and if necessary clarify or it may be worthwhile to review and seek to improve extend the brief. It is probably then necessary to the accuracy of the conventional design assumptions carry out a conventional check of robustness of the in the following ways: whole structure and of the resistance of individual (a) further on-site investigation work members, with consideration of their current state of (b) consideration of the composition of the safety factors structural deterioration. This may lead to one of three (c) rigorous analysis to distribute the load further. possible conclusions: The third stage appraisal (see Figure 4.7) should be (1) The calculations show that the structure has carried out with great care. Often, the objective of this an adequate margin of safety according to stage of assessment is to see if the present condition the relevant code of practice or other relevant of the particular structure warrants taking load beyond standard or guidance documents. the load-carrying capacity of the same structure designed under the current design guidelines. There If the engineer is satisfied that relevant code may also be some risk in its structural performance, recommendations are adequate for the e.g. under wind and snow loading. The engineer likely use of the structure, and if the visual should consider discussing these with the client examination of the structure has not revealed and also consider the alternatives such as repair or any signs of distress, it should be necessary upgrading the existing structure. only to recheck the assumptions to guard against gross error before pronouncing the 4.6.1 Principles behind third stage assessment structure safe. The possibility of such modes of failure as fatigue or unseen corrosion should, Most common design calculations use very however, be considered. If the structure shows simplified (mostly two-dimensional) models, and the signs of distress, a more thorough recheck mechanical properties of the materials are simulated of the survey and the calculations should be by fairly coarse approximations. As a consequence undertaken. the secondary contributions to the load-carrying capacity of a member and the reductions in the loads (2) The calculations indicate that the structure acting on a particular member or part of member, is grossly overloaded to the extent that the which arise from static indeterminacies, are ignored. calculated overall factor of safety is unity or less. Furthermore, at the time of design the actual dimensions If the structure nevertheless is carrying the load and material properties of the structure to be built are, without any signs of overstress and generally to some degree, uncertain. Design calculations have to appears in good order, the calculations and the include an allowance for these uncertainties. assumptions, on which they are based, must be examined for error. Partial safety factors are introduced to take account of the above factors. If the structure is seen to be badly cracked, grossly deflected or collapsed, the observed However, once a structure has been built, some mode(s) of impending failure should be of the uncertainty present at the design stage has compared to that (those) predicted by the been removed. The strength of the materials and calculations. their variability can be assessed on site and it may therefore be possible to adjust the safety factors If the observed mode of possible failure based on the in situ assessments of the materials. does not correspond to that predicted, further investigation should be carried out; if There are two alternative strategies for dealing observation and prediction tally, remedial action with variability. The first is to use statistical should be considered. characterisation to provide a degree of certainty about the data. The second is to accept the variability (3) The calculations indicate a factor of safety and produce upper- and lower-bound solutions greater than unity but less than that within which one can be confident that the correct recommended by the codes and the structure solution lies. shows little if any indication of overload. A point to remember is that the only facts are the In this case a revised calculation is called direct measurements. Any extrapolation, using for (i.e. the third stage of appraisal), using a statistical models, does not add information but more refined mathematical model that takes merely characterises the existing information in account of diverging (alternative) load paths a, possibly, more understandable way. Extensive and secondary load-carrying mechanisms, if manipulation of the basic data is therefore not a cost- any. It may also be necessary to see whether effective exercise in reaching engineering judgements the assumptions made on the loadings and and can lead to an exaggerated faith in the load-carrying capacities of the structural judgements. (Techniques to obtain 95% confidence members are appropriate. levels such as Latin hypercube sampling4.10 are beyond the scope of this Report.)
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START Define the structure or from Yes Figure 4.5 Is it a Can the mechanism Yes structure be No as defined? redefined? [1]
No Has it Yes collapsed? Assess forces on structure as a whole and check stability Yes No
Can forces Is robustness No No Investigate or safety factors Consider adequate? other possible be reconsidered? further [2] causes of support collapse Yes
Will ‘removal’ of Can Protect or single critical element(s) Yes critical element(s) No strengthen endanger robustness resist accidental critical of whole structure forces? elements [3] or parts?
No Yes
Assess actual loads on each element and in situ strength(s) of materials Reassess assumptions and loads on element considered Conventional check Reassess strength(s), calculation size and/or assumptions No [4]
Do in situ Element Check Yes Yes satisfied? conditions justify is all assumptions? adequate [5] [6] No
Are real Is deficiency Yes Yes Can element No of element conditions as bad shed loads to drastic? as assumed? others? [7] [6] No Element No Yes is inadequate
Will early yield of Recheck robustness of Yes Yes Can other No element affect robustness structure and/or parts elements carry of other parts of their share? structure? [8]
Robustness No Robustness still Yes Recheck element: is adequate? see Figure 4.7 adequate Are past No assumptions too Yes conservative?
No
Robustness is inadequate Figure 4.7
Figure 4.6 Second stage of appraisal
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From Figure 4.6
Is Yes mathematical model too crude, as so far defined? Refine mathematical model, reconsider assumptions. Make accurate analysis of redefined structure No
[10]
Make accurate analysis of element(s) and sections
Is Have Yes calculated material strengths Yes capacity been checked adequate? in situ ?
No No
Measure dead loads and materials’ strengths in situ
Element(s) adequate
Are loads and/or Yes Reconsider safety factors strengths known more where appropriate accurately than at design? [9]
No Final ULS analysis
Is Yes Reject, test load or No calculated continually monitor capacity adequate? element where appropriate
Figure 4.7 Further stages of appraisal
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Notes For Figures 4.6 and 4.7 the number in square brackets refers to the corresponding note below.
[1] A mechanism is a system which, because of the disposition and number of members and/or the freedom of the joints to deform without increase in moment (energy), is inherently unstable. A system stable for small displacements may become unstable for large displacements (i.e. metastable) as a result of P-Delta effects.
[2] At this stage the check is for overall robustness (see Glossary), stability having been satisfied. (See also [4/5]).
[3] This is equivalent to the check for ‘resistance to disproportionate collapse’ according to Building Regulation A3.
[4/5] ‘Conventional’ refers to the absence of assumptions and/or procedures beyond those normally used in initial design. The ‘frame analysis’ may at first include no more than reasonable estimates of support moments, but a proper analysis may be necessary when iterating.
‘Check satisfied’ means that the calculations indicate (possibly by inference) that the recommendations of a relevant code of practice could be shown to be observed.
The checks referred to in note [2] may depend on the outcome of some of the calculations referred to under [4] and [5] and these latter are obviously repeated for each element in turn.
[6] A visit to the site should be made again at this stage to confirm the parameters used in the calculations.
[7] ‘Drastic’ deficiency means that the calculated overall load factor is less than 1.1 for dead load only.
[8] If, for example, the element under consideration provides lateral restraint on which a compression member (or just a compression flange) relies to prevent it buckling, then early yielding (say, as a prerequisite for load-sharing) could deprive the possibly more essential compression member of some of its lateral restraint.
[9] See Section 4.6.3.
[10] Refinement of the mathematical model may involve the basic arrangement of the structural system and its mode of behaviour as well as its geometric dimensions. It may also include reassessment of load paths and load sharing. This may lead to several iterations of trial and error which for reasons of space and because they will be different for each structure have not been shown in the flow charts. It may also at this stage be worth checking whether the results of previous calculations are sensitive to changes in the assumptions of strength and stress/strain relations.
The appropriate use of the approaches outlined Appraisal based on detailed dimensional in Sections 4.5 and 4.6 will depend on the degree measurements on site may allow a more accurate to which one can model the problem. In cases estimate of dead load to be made. Hence the such as the flexural behaviour of an isolated beam, normally accepted level of overall safety will the mathematical model is probably sufficiently be achieved with a lower nominal value for the developed to enable the use of a statistical factor of safety being used in the assessment approach when applying the data to predict the calculations. failure capacity. For more complicated assemblies, such as walls and floors, involving many structural The use of factors different from those normally used interactions, and most massive masonry, an in design should, however, be considered with care. accurate mathematical model will not be available, It should be resorted to only when the additional and one should seek to establish the boundaries information is adequate to demonstrate that the of possible behaviour based on a series of resulting level of safety matches that which results assumptions that cannot be proved. from normal design and sound building practice. (See Appendix 10.) Appraising levels of safety is thus the art of accurately assessing the boundaries within which the correct 4.6.2 Further on-site investigation work solution lies. The better the data and mathematical model available, the narrower the bounds become. The objective of this further on-site investigation However, the engineer should be aware of the work (Section 4.6(a)) is to provide accurate data sensitivity of the structure to the data and model for the third stage assessment calculations to be taken or to the parameters assumed. carried out.
In some cases all that will be necessary is an The work will typically include taking measurements assessment of the worst credible condition since, if (e.g. establishing the exact structural geometry and this is satisfactory, the structure will fulfil its function. the actual thickness and densities of the materials Specific advice can be found in BD 44/954.11 that make up the dead load), testing (on site or in the for concrete bridges, and for other structures in laboratory to ascertain the strengths of the structural Section 2 of BS 8110: Part 2: 19854.12. However, even materials – see Chapter 5 for guidance) and in these cases, setting of an upper boundary is still checking on the extent and effect of any structural valuable in giving a measure of how sensitive the deterioration. Load testing can also be used (see solution is to the accuracy of the data. Section 5.4 for guidance).
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4.6.3 Composition of partial safety factors of the strategy to develop a ‘Life-Care Plan’ for the particular structure. The current British design codes effectively use four partial factors. The structural performance The data on the current condition of the structure, requirements to be met are: i.e. the ‘as-deteriorated’ strength, may be used to provide a basis for extrapolation to predict future
Function [cf1, cf2, cf3, effects of Fk ] G function [fk / cm ] performance. The extrapolation needs to take into account when there have been significant where: changes in the environment (e.g. when de-icing
Fk represents the characteristic loads salt was applied or when a roof started to leak). fk represents the characteristic strengths It should also be recognised that future strength cf1 takes account of the possibility of unfavourable is not a process of simple linear extrapolation. deviation of loads from the characteristic external Corrosion damage tends to accelerate with time. loads, thus allowing to some extent for abnormal Frost damage can develop suddenly when wet or unforeseen actions weather filling cracks is followed by sudden frost.
cf2 takes account of the reduced probability that In concrete structures, AAR crack growth generally various loadings acting together will all be increases steadily with time. simultaneously at their characteristic value
cf3 is intended to allow for possible adverse Rates of future deterioration can be significantly modification of loading effects due to incorrect reduced by cladding or improved rain shedding. design assumptions, constructional discrepancies Electro-chemical techniques can be used to reduce such as dimensions of cross section, deviation of and control corrosion rates in some conditions. columns from vertical and accidental eccentricities Cutting out carbonated or chloride-contaminated
cm is intended to allow for all possible reductions concrete can locally restore control of corrosion in the strength of the materials in the structure but care should be taken so that these measures as a whole compared with the characteristic will not weaken the structure and introduce further value deduced from the control test specimens serviceability problems (i.e. spalling of concrete including (except in BS81104.12) the effect of the repairs). deterioration of the materials. As a result of the many concrete structures built With sufficient on-site investigation work the in the 1950s, 60s and 70s, and the problems engineer may review the above partial safety factors associated with these structures, certain methods and reduce or increase the respective values as have been developed for the appraisal of residual
appropriate. While cf2 remains unaltered, it is not service life. For a five or ten year period, it is possible unusual to be able to reduce the values of cf1, cf3 to make reasonable estimates on future performance, and cm but deterioration of the structure can lead but these predictions will need to be checked by to an increase in the value of cm or changes to the regular future monitoring of the structure as part of characteristic strengths being required. the Life-Care Plan. Longer term predictions are very difficult so the uncertainties of these exercises, and See Appendix 10 for further discussion on this the cost of acquiring sufficient data, need to be made subject. clear to clients before this type of appraisal work is embarked on. 4.6.4 Rigorous analysis further to distribute the load See Appendix 11 for further discussion about The second stage assessment calculations are residual service life appraisals, the advancement usually carried out on a two-dimensional elastic of this subject being most developed for concrete model. A three-dimensional model will often allow structures. the load to be distributed further. Plastic analysis and finite element analysis are sometimes useful in this further distribution of load. 4.8 Calculations requiring special The analysis will usually be carried out by suitable consideration computer programs. Care should be taken in interpreting the results. The results should also be checked against the actual structural behaviour on 4.8.1 General site to verify the validity of the computer model and the boundary conditions assumed. Useful papers on Perhaps the greatest danger is the use of a formula these topics have been published in The Structural in a situation where it is not directly applicable. If Engineer4.13, 4.14. the formula is obtained from a code or standard, there should, however, be no danger provided It is also important to check whether the existing that the formula is used exactly as intended in connections will sustain the redistribution of loading the document. Sometimes, other assessment assumed or derived. techniques can be used which are not based on ‘code compliance’.
Formulae from textbooks have usually been derived 4.7 Future performance for idealised, simplified conditions and will give values applicable for those conditions only. The Euler formula, for example, will give the exact elastic The engineer is sometimes asked to provide critical load for a straight pin-ended bar, but does not information on the likely future performance of the include parameters such as yield strength and initial structure. This work should be carried out as part bow which are necessary to calculate the buckling
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load of a real strut. A textbook formula will not, calculations will entail an analysis of the variations generally, contain safety factors. Any factors must be in stress to which the structure has already been chosen to take account of what the formula is based subjected and those anticipated, together with an on and what it expresses. analysis to obtain the spectrum of stress variations for the areas of stress concentration of the joints Most engineering design calculations do not under consideration, summing these through Miner’s accurately represent the real structural behaviour but Rule4.15 as appropriate. Existing fatigue test data nevertheless result in structures that are safe and may be used for the ‘potential damage’ calculation. serviceable. Certain types of structural behaviour, Methods of carrying out these calculations are set such as brittle behaviour and metastability, are, out in references 4.15, 4.16, 4.17, 4.18, 4.19, 4.20, however, not predictable by conventional calculation, 4.21 and 4.22. In some circumstances a fracture- so safety factors alone will not ensure safety. mechanics crack propagation analysis may be an Unfortunately, the types of failure that are most equally acceptable approach. difficult to predict accurately also tend to be the most sudden, and therefore present the most danger to 4.8.5 Buckling life: these situations require special consideration. Buckling depends on member stiffness and 4.8.2 Brittle materials geometric imperfections together with any end moments and lateral loads. Material strength is Some materials, e.g. plain concrete, cast iron and unlikely to be very significant once buckling has been stone, are inherently brittle and fail with little or no initiated; yield or fracture is likely. plastic deformation. Brittle structure should therefore always be assessed under service loading using Questions that need to be asked before starting a permissible stress criteria. The energy-absorbing buckling calculation include: capacity of a brittle component is much lower than –W– ill the structure suddenly collapse as a whole or that of a similar component made from a ductile in part following buckling of a single member? If so, material. Particular care should be taken in the initial imperfections will have a greater effect on the consideration of dynamic and accidental loads. collapse load. Imposed displacements, such as temperature –I– s the material subject to creep? If so, this is movement and foundation settlements, are unlikely equivalent to a reduction in stiffness and should be to cause rupture (or failure) of a ductile structure, taken into account. whereas the reverse may be true of a brittle structure –I– f the component is assumed to be restrained by or component. adjacent elements, are these elements stiff and strong enough? Flexural failure of over-reinforced concrete members –I– f a code of practice or British Standard formula may occur in the concrete: such failures may be is used to check buckling, does the accuracy of sudden and brittle. construction of the structure correspond to that assumed in the code or standard? In some cases it may be impossible to carry out calculations with any confidence, e.g. the strength of 4.8.6 C onnections fixings cast into or drilled into concrete can be verified only from test data. The rigorous analysis of connections is extremely difficult. It is often only the ductility of most 4.8.3 C ombined stresses engineering materials that enable calculations to give results that predict actual failure loads. The simplest states of a stress are uniaxial tension, uniaxial compression and shear. The strengths of a Certain connections have to be checked for imposed material in these modes may be estimated by tests. displacements caused by temperature movements, Loading in practice may not be unidirectional. Direct foundation settlement, etc. This applies particularly and shear stress components may be present in when the connection is the ‘weakest link in the chain’ two or three planes. In such cases the principal so that movement is concentrated at the connection, stresses should be calculated. The failure criterion for example in old timber framed structures. appropriate to the material, often expressed in terms of an ‘equivalent stress’, should then be applied to If, as is often the case, connections are hidden so determine the limiting load. that their condition cannot be fully ascertained by inspection, no reduction of safety factors should be It follows, therefore, that in quoting the results of tests contemplated. made to determine the ‘strength’ of a material, the stress conditions in which the data were obtained 4.8.7 Bolted and riveted connections must be stated precisely. The orientation, size and shape of the test specimen must be given as they The calculation of the capacity of bolted and riveted also influence the test results. More care is therefore connections is clearly dependent on the state of the needed in checking structural elements which fasteners. Confidence is required that they are in experience combined stresses in different directions good condition and of a type and number adequate particularly if the value of cm has been altered. to transmit the service loading. This may require the removal and replacement of samples. 4.8.4 Fatigue Confidence is also required that high-strength Fatigue calculations may be necessary when friction-grip (HSFG) bolted joints have satisfactory considering the remaining life of a structure, contact of the faying surfaces and that corrosion particularly a metal one, that is and has been between these is absent. This may require subjected to repeated fluctuating loads. The the dismantling of the joint for full confidence,
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remembering that slackening of an HSFG bolt 4.8 Standing Committee on Structural Safety. Failure of cast requires its replacement with a new bolt (and iron beams. SCOSS Safety Advisory Note SC/02/88. new nut). Available at: http://www.scoss.org.uk/publications/rtf/ CIBeamFailure.doc [Accessed: 11 September 2009] 4.8.8 Welded joints 4.9 ISO 13822: 2001: Bases for design of structures: The calculation of the capacity of welded joints assessment of existing structures. Geneva: ISO, 2001 is similarly dependent on the state of the joints, which need the welds to be of a size and type 4.10 Latin hypercube sampling. Available at http://en.wikipedia. adequate to transmit the required loads taking into org/wiki/Latin_hypercube_sampling [Accessed: account cracking or other signs of deterioration. 18 January 2010] Transverse load-carrying fillet welds normally fail from the weld root. Cracking may not therefore be 4.11 Highways Agency. The assessment of concrete highway detected by visual inspection only. Dye penetrant bridges and structures. BD 44/95. Available at: http:// (T27 in Appendix 7) cannot be used for the weld www.standardsforhighways.co.uk/dmrb/vol3/section4/ root (except during welding) but is a reliable test for bd4495.pdf [Accessed: 11 September 2009] surface-breaking flaws and therefore requires surface preparation. 4.12 BS 8110-1: 1985: Structural use of concrete – Part 1: Code of practice for design and construction. London: BSI, 4.8.9 Assessment of the effects of fire 1985 {Since superseded by 1997 version}; BS 8110-2: 1985: Structural use of concrete. Part 2: Code of practice An appraisal of a structure may have to include an for special circumstances. London: BSI, 1985 assessment of its fire resistance. Information on this is given in Appendix 5. 4.13 Burgoyne, C. ‘Are structures being repaired unnecessarily?’ The Structural Engineer, 82(1), 6 January 2004, pp22-26 After an actual fire an assessment of the effects on the adequacy of structural elements on the basis of 4.14 Mann, A.P. and May, I. ‘The interpretation of computer the residual section with an allowance for charring analysis’. The Structural Engineer, 84(7), 4 April 2006, deducted may be required before decisions on repair pp29-32 and/or replacement are taken (see Appendix 6). 4.15 Maddox, S.J. Fatigue strength of welded structures. 2nd ed. 4.8.10 Non code based assessments Cambridge: Abingdon Publishing, 1991
For some structure, e.g. masonry arches, massive 4.16 BS 7608: 1993: Code of practice for fatigue design and masonry structures, it may be more appropriate to assessment of steel structures. London: BSI, 1993 use other assessment techniques such as line of thrust determination. 4.17 BS 5400-10: 1980: Steel, concrete and composite bridges – Part 10: Code of practice for fatigue. London: BSI, 1980; BS 5400-10C: 1999: Steel, concrete and composite bridges – Part 10C: Charts for classification of details for 4.9 References fatigue. London: BSI, 1999
4.18 BS 3518: Methods of fatigue testing. Parts 1-3 and 5 4.1 Burland, J.B. ‘The interaction between geotechnical and structural engineers’. The Structural Engineer, 84(8), 4.19 ASTM E466-07: Standard practice for conducting force 18 April 2006, pp29-37 controlled constant amplitude axial fatigue tests of metallic materials. West Conshohocken, PA: ASTM, 2007 4.2 Construction Information Research and Information Association. Structural renovation of existing buildings. 4.20 ASTM E467-08: Standard practice for verification of CIRIA Report 111. London: CIRIA, 1994 constant amplitude dynamic forces in an axial fatigue testing system. West Conshohocken, PA: ASTM, 2007 4.3 Yeomans, D. ‘The Safety of historic structures’. The Structural Engineer, 84(6), 21 March 2006, pp18-22 4.21 Gurney, T.R. Fatigue of welded structures. Cambridge: University Press, 1968 {superseded by Gurney, T.R. Fatigue 4.4 Inquiry into the basis of design and method of erection of welded structures. 2nd ed. Cambridge: University Press, of steel box girder bridges: report of the [Merrison] 1979} Committee. Appendix 1: Interim design and workmanship rules. Parts 1 and 2. London: HMSO, 1973 4.22 Frost, N.E., Marsh, E.L., and Pook, L.P. Metal fatigue. Oxford: Clarendon Press, 1974 4.5 Regan, P.E. Behaviour of reinforced concrete flat slabs. CIRIA Report 89. London: CIRIA, 1981
4.6 Building Research Establishment. The Structure of Ronan Point and other Taylor Woodrow-Anglian buildings. BRE Report 63. Garston: BRE, 1985
4.7 Ross, P. Appraisal and repair of timber structures. London: Thomas Telford, 2002
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5.1 Commissioning of testing and is technically knowledgeable, it is possible that the monitoring works client may define a brief for testing. This approach can pose difficulties should the engineer consider the client’s brief to be inadequate for the purpose Testing and monitoring works may be commissioned of establishing the information needed for a proper by the engineer or directly by the client on the appraisal of the structure. The engineer should recommendation of the engineer. Whilst the latter not knowingly work from data considered to be arrangement has contractual and legal advantages inappropriate or inadequate for the purposes. for the engineer and the client, it may pose practical difficulties in the process of undertaking the There may be no need for testing where the following investigation and associated assessment. Conflicts apply: can also arise if there are differences in opinion –T– he structure is fully inspectable and clearly in a between the specialists undertaking the testing or sound condition without apparent defects, the monitoring works and the engineer in respect of the physical dimensions determined in the survey interpretation of the results. allow calculations to confirm the suitability of the structure for its intended future use and the Before any site works concerned with inspection, assessment relates to the currently observable testing, monitoring or related activities are condition only. commenced, it is imperative that appropriate –L– ower-bound values of strength give an assurance consideration be given to health and safety issues for of adequacy, for example in the case of cast and not only those involved in undertaking the task, but wrought iron by the use of values given in BD215.1 possibly also for the users of the building or structure or the SCI guide to the appraisal of existing iron and involved or the general public. Consideration should steel structures5.2. be given to issues such as the presence of asbestos –V– isual defects or the poor condition of the or other harmful materials which could affect the structure point to obvious conclusions that meet proposed site works. There could be concerns the requirements of the brief (e.g. the structure is about the contamination of surfaces by hazardous clearly unsatisfactory or clearly inadequate for the substances. Reference should be made to Chapter 7 proposed use). for discussion of health and safety issues. –T– here is no requirement to assess latent problems or related issues (such as discovering whether For listed buildings it may be necessary to obtain high alumina cement was used in construction or listed building consent for testing and investigative whether the structure contains significant levels of works. chlorides).
There may be need for testing where one or more of the following concerns exist: 5.2 Determination of testing and –T– here is a lack of information on the nature and monitoring requirements properties of the materials in the structure. –T– he presence of deteriorated or deleterious materials is known or suspected. In many cases a visual inspection and a desk study –T– he brief requires a prognosis of the future life of will enable satisfactory conclusions to be reached, the structure. and there will be no need to carry out testing. This –T– he structure has been recalculated to and fails to is most likely to be true where the structure has comply with more onerous codes of practice (e.g. performed well and has had appropriate professional EN19915.3 versus BS63995.4 or CP35.5) imposed by input to its original design and construction. Some new owners, insurers etc. additional assurance may also be gained if the –T– he expected loading may change either structure is one of many similar structures with a temporarily during adjacent new works or good service history. permanently due to changes of circumstances (e.g. water table rises, wind load increases due to It is important that testing and monitoring works adjacent demolition etc.). are targeted to provide specific information for the appraisal. The risk of structural damage should be Available tests cover a wide range of cost and minimised and the work should be carried out safely. complexity. Some tests cause little disturbance For these reasons detailed inspection, sampling, to the structure itself or to the occupants, while testing and monitoring programmes should always others cause major disruption and require a degree be checked and approved by the engineer. There are of making good afterwards. Prior to making a considerable practical advantages if this is directly recommendation as to what testing is required, controlled by the engineer. the engineer should weigh up the advantages of proposed tests against the consequences and the In most circumstances the client’s brief for the costs. It may be appropriate to discuss these issues assessment is likely to adopt the approach of with the client prior to making a recommendation, defining the performance demanded of the structure. particularly where the engineer is dealing with In such circumstances it will be for the engineer to a technically knowledgeable client. In some recommend what testing is required. Where the client circumstances the cost of testing can be such that
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remedial action or some other form of intervention theory can all be used to optimise test programmes without testing provides a more economic solution. to give an appropriate degree of confidence.
The deterioration of structural details that cannot The concept of ‘characteristic values’ is embodied practically be inspected or tested can pose in design codes. A value for appraisal purposes may particularly severe difficulties in terms of obtaining be established through testing. It is more useful to suitable information for an assessment to be made regard testing as an aid to establishing the most or when seeking to make a prognosis of future likely performance of a structure within certain durability. For example, such issues have been performance boundaries. It is nearly always more highlighted in reports upon car park structures and in effective to target sampling at critical locations respect of certain types of joints in bridges. than to adopt a random sampling regime and draw general conclusions from oversimplified statistical The purpose of and procedure for each type of test analysis. and the information that it can provide should be understood so that the correct test regime can be Where testing is targeted at establishing structural specified. The engineer may need to witness the performance (e.g. static or dynamic load testing), testing and depending upon the commissioning the worst circumstances should be identified so that arrangements may need to provide direction for a minimum number of tests (possibly of different the testing; this will generally require appropriate type) can be used to set a lower boundary on the experience. It may be necessary for the engineer to structure’s performance. Issues concerned with load seek guidance upon the selection of appropriate test testing are discussed in more detail in Section 5.4. or inspection methods from competent specialists or test houses. The engineer should seek to ensure that Testing is expensive compared with desk studies. the advice or recommendations given are objective Thus it should be targeted to yield the maximum and take account of the ability of the test procedure information contributing directly to engineering to assist in the particular situation, bearing in mind decisions. It is therefore important to use all the the limitations of the equipment and procedure and available facts about the structure when devising a the potential difficulties of interpretation of results. test regime.
Tests can be divided into those that give information Generally, the lower the level of performance on properties, e.g. the material strength, and those required, the less the testing that will be needed. The that give information on the condition or performance first stage in developing a test regime is to consider of a structure or structural element. the minimum necessary. Further tests should be carried out only if the assessment of the first tests Some uses of testing are to: shows that a more advantageous course of action –C– onfirm assumptions that have been made or need can be taken as a result. to be made in carrying out desk studies, e.g. the quality or strength of a material, its reinforcement Where there is reason to suspect substandard configuration and type, etc. quality in construction (e.g. from wide variation –D– etermine the frequency and distribution of a locally in cover depth, patched honeycombing or poor identified defect, e.g. reinforcement corrosion. compaction adjacent to joints in concrete structures; –I– dentify mechanisms responsible for apparent misalignments and distortion at connections; poorly deterioration, e.g. carbonation, the presence of made welds), initial inspection or testing should be chlorides or alkali-silica reaction. directed to establishing the facts. Further testing –I– dentify susceptibility to future deterioration, e.g. should be directed to quantifying the defects, but embrittlement of polymers. only if such quantification is necessary. –S– how by test that performance is adequate for structures built with materials that are of uncertain The number of tests and locations will depend on the quality or type or where there is a high natural particular circumstances and should be decided by variability (and consequently a need for high factors the engineer taking account of factors including: of safety). –T– he likely variation in material properties within and between parts of the structure. Whatever the motive for testing, the engineer should –T– he probable critical locations. have a clear picture of what can and cannot be –T– he possible errors in the test procedure and achieved, and how the results are to be interpreted to associated deviations in the results obtained. enable decisions to be made. –T– he fact that different techniques may measure properties of different volumes (e.g. in concrete, Before any tests are commissioned, the influence of ultrasonic-pulse-velocity measurements indicate the test results on the subsequent decisions should the average quality through the depth whereas be established. If the decisions would remain the core tests only provide a measure of the properties same, testing is not justified. For example, if the tie- in the sampled zone which is typically only rods of bowstring trusses are so badly corroded that 100-300mm depth: but of course sampling can be they need replacing, there is no point in testing their taken significantly deeper if circumstances demand strength. and permit). –T– he fact that similar tests or procedures may Testing is sometimes extended in the misguided produce results that are not directly comparable, belief that greater numbers will automatically provide e.g. test methods for assessing the surface a more valid conclusion. This is not so. Sampling and properties of concrete. testing, however comprehensive, cannot define the structure fully. But targeted comprehensive sampling Some of these factors could affect the consistency of limited sets of representative areas, statistical of the results. When seeking to characterise the test analysis of the variability and the use of sampling results, which will include evaluation of their scatter,
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it may be necessary to consider the appropriateness Table 5.1 Equipment for simple on-site testing and inspection techniques of standard statistical procedures (e.g. the data Function Associated equipment distributions may not be Gaussian in nature). Personal protective Hard hat*, safety footwear*, high visibility vest or jacket, overalls*, Caution needs to be exercised when relying on tests clothing mask, goggles, gloves, ear protectors conducted previously by others, especially where (see also Chapter 7) results have been quoted in more general reports Safety equipment Air quality monitor when working in confined spaces, harness when and only these are available for consideration. It working at height†, life jacket (when working over water), charged is important to check the validity of existing data mobile phone* before proceeding with further work that relies on Access** Collapsible ladder*, manhole keys*, demountable tower, cradle, mobile them. These issues, along with the basis upon which access equipment, scissor platform, abseiling equipment‡ conclusions have been reached and including the reasons why more testing may be required, may General Claw hammer*, screwdrivers*, club hammer*, pliers*, floorboard saw, need to be discussed with the client. Otherwise the bolster, chisels, crowbar, jemmy, brushes, metal detector, sample client may think they are being asked to pay for the bags*, cleaning cloths*, electrical cable detector, spray paints, chalk same thing twice. Observation Mirror*, telescope, binoculars*, torch*, endoscope (borescope) Recording and Dictating machine*, pencil* (with sharpener or spare leads), pen, dimensional survey paper*, clipboard*, scale rule*, tape*, camera with flash*, clipboard, 5.3 Simple on-site testing folding rule, wax crayons/chalk, electronic measuring device, video recorder Plumb, line and level Spirit level*, plumb line*, string line, water level, surveyor’s level and It is useful to have the capability to conduct simple staff, theodolite, electronic distance measuring equipment (e.g. laser on-site tests during visits to site. Although it is distance measuring instrument), Giraffe (refer Appendix 7) becoming more common for engineers to have Crack measurement Crack width gauge*, suitable tell-tales, vernier calipers, Demec gauge, relatively sophisticated test instrumentation available measuring microscope to them, it is appropriate to sound a note of warning. Dampness Hand held dampmeter* (e.g. Protimeter), carbide moisture meter Modern equipment, particularly where electronics- based, may be easy to operate. With very little Structural steelwork Hammer, spanners§, penetrating fluid training or experience, sets of numbers can be Reinforcement Covermeter (various proprietary brands of equipment), potential generated that purport to measure some parameter wheels about the materials or structure. The engineer should Concrete Phenolphthalein plus spray bottle, drill and dust collection device, feel competent to understand and interpret correctly Schmidt hammer, BRE internal fracture test, Pundit the numbers produced by the equipment, and know its limits of applicability. The source data for Masonry Wall-tie detector* calibration should be understood and, if practicable, Timber Penknife*, bradawl, decay detecting drill be checked. Soil Spade*, hand auger*, hand penetrometer, vane tester, hand sampling equipment, unconfined compression tester When planning an investigation the engineer also needs to bear in mind: * Items that may be particularly useful for the survey of small commercial, industrial buildings –T– he limitations of the testing or inspection or traditional domestic property procedures adopted and any requirement for ** Excluding access to confined spaces which requires specialist training and equipment on-site calibration of the instrumentation. † Other provisions such as nets or airbags may be appropriate. Access provisions need –T– he difficulty of carrying out the tests and the to comply with the provision of relevant legislation (in the UK the Work at Height reliability of the results. Regulations5.7). The use of most access equipment requires some form of training and –T– he type of premises and the provision of safe certification, particularly for powered equipment such as mobile access platforms, ‘cherry access and egress, appropriate equipment and pickers’, etc. Companies hiring out such equipment may need to provide it with a trained protective clothing. operator. In addition, training is also required for the erection of various other items of access equipment, such as demountable access towers. Refer to Chapter 7 for discussion Comprehensive risk assessments should be of health and safety issues undertaken and documented through the risk ‡ Access by abseiling is generally considered to be a specialist area because of the register. Further information relating to health and associated health and safety issues. It is typically sub-contracted to specialist firms. safety requirements is given in HSE publication The engineer will need to consider how to interpret these observations, how to direct HSG1505.6 and in Chapter 7. the inspection and how the outcomes are to be reported. Alternatively if the engineer is frequently involved in these activities training could be undertaken to become an abseiler A list of equipment is given in Table 5.1 but it does (refer Industrial Rope Access Trade Association – see Appendix A) not attempt to be comprehensive. The equipment § Spanners are listed to allow the removal and replacement of a bolt / selected bolts to check necessary for any programme of on-site testing and their precise nature, or to evaluate their condition, existence of damage or yielding. Clearly inspection is naturally dependent on the scope and such activities would need first to be thoroughly assessed and undertaken with great care depth of investigation required in the brief. bearing in mind potential consequences Notes There are also other techniques which prove to be a During the course of undertaking on-site testing and inspections, spare batteries may be useful in providing supplementary information, such needed for various types of electronic equipment employed. This might include some of as the facility to obtain overview images/photographs the following – endoscope (borescope), camera and flash, audio recorder, video recorder, from adjacent vantage points or from a high location, electronic distance measuring equipment, covermeter, wall tie detector, etc. perhaps via a camera on a tall mast. b The list of equipment given above does not attempt to be comprehensive but is intended simply as a guide.
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5.4 Materials testing The lists of techniques are not exhaustive. Other techniques are available that may be appropriate in unusual circumstances. They generally require Materials evaluation usually involves a combination specialist expertise and are briefly described in of on-site non-destructive testing and laboratory Appendix 8. Some of these techniques are still under analysis or testing of samples taken from the development. structure. Non-destructive testing in this context is defined as that which will not significantly damage the Where metal samples are required and can be structural member. However, some methods cause removed from a structure, many of the tests localised damage; such tests may be described described can be carried out on a comparatively as partially destructive. Many tests require surface small sample of material. The largest pieces required preparation, and the removal of surface finishes is are likely to be for standard tensile test specimens often necessary to expose the structure. or for weld test specimens. When it is possible to obtain only non-standard size test specimens (i.e. There are tests that can be performed in the field, miniature pieces of different shapes) the results but these will usually only be indicative. For accurate should be carefully considered since they may not quantitative results the use of proper laboratory be representative nor give a true indication of in situ facilities is usually needed. properties.
It is unlikely that the engineer carrying out an Some types of non-destructive test can be carried appraisal will themselves undertake tests that require out on material without removing it from the specialist equipment or laboratory procedures. The structure. engineer should, however, be present to observe and, if appropriate, direct the work to ensure that For all materials it is clearly important that appropriate the inspection, sampling and testing programmes consideration be given to the structural effects are being followed and varied where circumstances of removing samples for testing, with their extent dictate. and location being carefully considered. Clearly it is important to label all samples with a reference Conventional test techniques are listed in Tables 5.2 number and to note their origin, along with other to 5.6, with remarks to assist selection. Further pertinent details about their context and any details of the techniques are given in Appendix 7. particular reason for taking the sample.
Table 5.2 Concrete structures Information sought Techniques available a Selection Remarks c Guide b Mix proportions, cement content, T8 Petrographic examination V 1, 2, 3, 6 cement type T9 Chemical analysis of samples (crushed cores and drillings) D 2 Type of aggregate and grading T8 Petrographic examination V (susceptibility to alkali-silica T9 Chemical analysis of samples D 2, 5 reaction) Presence, position of, and cover T20 Covermeter, Ferroscan etc. V 2 to steel reinforcement T21 Physical exposure V Presence and position of deeply No simple technique available, but see Appendix 8 embedded metal objects Mechanical properties of steel See Table 5.3 Strength T1 Rebound hammer D 6 T3 Examination and crushing of cores V 2 T4 Internal fracture test D 2, 6 T5 Windsor probe D 2, 6 T6 Break-off test D 2, 6 T8 Petrographic examination H 2, 3, 6 Quality of placed concrete T2 Ultrasonic pulse velocity V 2, 6 T3 Examination of cores V 2 T8 Petrographic examination D 2, 3 Depth of carbonation T7 Phenolphthalein test V (not applicable to HAC concretes) T8 Petrographic examination D 1, 2, 3, 6 Free lime content T8 Petrographic examination H 1, 2 Water/cement ratio T8 Petrographic examination V 2, 3 T11 Chemical analysis H 1, 2, 5
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Table 5.2 Continued
Information sought Techniques available a Selection Remarks c Guide b Permeability T12 Initial Surface Absorption Test (ISAT) D 2, 6 T13 Water and gas permeability tests V 2 T14 Absorption test on intact cores D 2, 6 Presence of chlorides T15 Tests for chlorides – laboratory methods for chemical D 2 analysis of samples (crushed cores and drillings) are preferred, but field based tests are possible (HACH and QUANTAB) Presence of sulfates T16 Laboratory based chemical analysis of samples (crushed V 2 cores and drillings) Presence of admixtures and T16 Laboratory based chemical analysis of samples (crushed H 1, 2, 3, 7 contaminants cores and drillings) Moisture content T17 Direct moisture measurement D 1 Monitoring – see Appendix 9 H Presence of voids No simple technique available, but see Appendix 8 Abrasion resistance T18 Accelerated wearing test V 2 Air entrainment T19 Microscopy V 2, 3 Risk of corrosion of T22 Electrical potential by half cell V 2, 6 reinforcement Areas experiencing corrosion of T21 Physical exposure D 3 reinforcement T22 Electrical potential by half cell V 2, 6 Severity of reinforcement T21 Physical exposure V 3 corrosion and rate of corrosion Corrosion rate measurements and monitoring – see D 2, 3, 5 Appendices 8 and 9 Delamination Sounding surveys (tapping, chain drag etc.) V T2 Ultrasonic pulse velocity D 2, 5, 6 T3 Core examination D 3 T8 Petrographic examination H 3 Other specialist techniques available such as Radar and Thermal D 2, 3, 6 Imaging, see Appendix 8 Defective grouting of post- T23 Borescope V 1, 2, 6 tensioning tendon-ducts Air test for void volume or duct integrity – see Appendix 8 D 1, 2 Notes a The techniques are described in Appendix 7 using these references. b Simplified Selection Guide V Extremely valuable: test which would usually be employed where circumstances permit D Desirable in some circumstances but not usually deemed to be essential H May be helpful in some cases. c Remarks 1 Not in common use 2 Specialist equipment and / or expertise required 3 Relatively expensive 4 Special safety precautions required 5 Check probable performance for particular application 6 Provides indirect measurement or assessment only 7 Reliability of results may be of concern. Use with care: validation checks likely to be required.
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Table 5.3 Iron, steel and other metal structures Information sought Techniques available a Selection Remarks c Guide b Identification of metal T24 Visual examination V 5 T25 Chemical analysis of small samples (drilling swarf) D 2 Identification of metal and internal T26 Metallographic microscopy D 2, 5 structure Tensile strength T30 Hardness tests: in situ or on small samples V, D 2, 5, 6 T31 Laboratory tests on samples D 2 T28 Ultrasonic NDT determination V, D 2 Strength, E-value, yield point T22 Laboratory tests on samples V 2 Ductility d T34 Impact tests on samples V 2, 5 Wall thickness of hollow sections Measurement in small drill hole e V, D T28 Ultrasonics D 2, 5, 6 Tensile strength of cast iron f T32 Wedge penetration test on disc sample H 1 T33 Split cylinder test H 1 Integrity: presence of cracks, casting T27 Dye pentetrants – surface cracks V 5 flaws, delaminations (in parent metal, e.g. T28 Ultrasonics D 2, 5 cast and wrought iron) T29 Radiography D 2, 3, 4, 5 Weld defects, e.g. cracks, lack of T27 Dye penetrants – surface defects D 2 penetration, porosity, etc. T28 Ultrasonics D 2, 5 T29 Radiography D 2, 3, 4, 5 T35 Visual examination V T36 Magnetic particle test D 1, 2, 5 Partial cracks in bolts T19 Ultrasonics D 2, 5, 6 T35 Visual examination V Corrosion of encased sections T21 Physical exposure V Stress corrosion and presence of cracking T27 Dye penetrants D 2, 5, 6 T28 Ultrasonics D 2, 5, 6 T29 Radiography H 1, 4 T35 Visual examination V T37 Accelerated in situ tests H 1 Condition of cables T38 Visual examination of cables V Notes a, b and c See Table 5.2 for explanatory footnotes. d It is not appropriate for ductility testing techniques to be applied to a brittle cast iron. e Should be made using a non-percussive drilling technique in cast iron. f Although the quoted tests exist which permit the determination of the tensile strength of cast iron, the assessment of cast iron elements is typically based upon the use of ‘prescriptive’ strength values such as those given in BD215.1. Thus the need and desirability of undertaking such tests on cast iron is usually limited.
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Testing and monitoring 5.4
Table 5.4 Masonry Information sought Techniques available a Selection Remarks c Guide b Identification of type of clay or concrete T24 Visual examination V unit/natural stone block Strength of clay units and of natural stone T39 Crushing of units V 2 blocks T39 Crushing of cores V 2, [6 if hollow] Strength of cement-based units T1 Rebound hammer H 5, 6 NB. Anisotropic units may need to be T4 Internal fracture test D 2, 6 tested in particular orientations T5 Windsor probe D 2, 6 T39 Crushing of units or cores V 2, [6 for cores if units perforated] Strength of low strength range cement- T40 Helix pull-out (in situ) V 1, 2, 5, 6 based units and mortars up to around 8MPa Mortar mix proportions, presence and T9 Chemical analysis of samples (0.5 to 1kg) V 2, 5 concentration of deleterious ingredients and/or contaminants Compressive strength of masonry. T39 Crushing strength of unit combined with mortar mix V 5, 6 NB. Anisotropic units may need to be proportions according to BS 56285.8 tested in particular orientations T41 Split cylinder tests on horizontal cores with and H 1, 2, 5 [needs without horizontal diametric bed-joints calibration] T42 Flatjack test D 1, 2, 5 T39 Laboratory test on (large) sawn-out sample D 1, 2, 5 Young’s modulus of masonry T42 Flatjack test V 1, 2, 5 Moisture content T17 Direct moisture measurement V 1 Flexural bond strength No simple technique available, but see Appendix 8 Shear resistance of masonry (mainly for T43 Shove test V 1, 2, 3, 5, 6 seismic conditions) Presence of wall ties T44 Metal detector V 5, 6 Presence and condition of wall ties, T23 Borescope V blockages of wall cavity T21 Physical exposure V Presence of deeply-embedded metal No simple technique available, but see Appendix 8 1, 2, 3, 4, 5 (wrought iron ties in old masonry) or voids Presence of voids, internal structure, T21 Visual examination of core holes V thickness of retaining walls Other techniques available, such as subsurface D radar – see Appendix 8 In situ flexural resistance of panels T60 Air bag test with temporary timber or similar V 1, 2, 3, 4 reaction wall Reason for the appearance of cracks d T42 Flatjack test to assess whether local over-stressing D 2, 3 is occurring Should be used in conjunction with materials tests to D establish whether the cracking results from excessive expansion, contraction or cyclic movement of masonry components (e.g. retrospective clay masonry moisture expansion test, moisture movement tests and chemical analysis of units/mortars) Notes a, b and c See Table 5.2 for explanatory footnotes. d The potential reasons for the appearance of cracks should be considered before embarking upon a programme of mechanical and physical tests. It is generally most effective if an investigation is hypothesis driven, that is to gather data / information to confirm or deny what is perceived to be the probable cause.
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Table 5.5 Timber structures Information sought Techniques available a Selection Remarks c Guide b Species of timber T45 Visual examination through magnifying glass or a V [probably 2] core for microscopic examination Type and condition of bolt T45 Visual examination of temporarily unloaded and V 3 connectors dismantled joint T29 Radiography H 1, 2, 3, 4, 6 Type of glue T50 Chemical analysis of small samples V 1, 2, 5 Type of preservative T51 Chemical analysis of small samples V 1, 2, 5 Moisture content T48 Moisture meter D 6 T17 Direct measurement V T48 Drying of sample and weighing V 2 Strength grade T45 Visual examination V BS49785.9 (softwoods) BS57565.10 (hardwoods). Use CP1125.11 where BS4978 and BS5756 are not applicable Mechanical properties T49 Species and grading V 6 T49 Dry density of small sample V 5, 6 T49 Tensile or bending tests on clear specimen V 1, 2, 3 Delamination of glue line T45 Knife blade V 5 Insect attack d T46 Visual examination and use of decay detecting V [identification: probably 2] drill or screwdriver/bradawl Fungal attack d T47 Visual examination and use of decay detecting V [identification: probably 2] drill or screwdriver/bradawl Notes a, b and c See Table 5.2 for explanatory footnotes. d The determination of the existence of severe insect or fungal attack is generally fairly straightforward and may be made visually or by the means indicated. If the member concerned is severely and extensively damaged, this is likely to be apparent. However the identification of the type of insect or fungal attack will generally require an expert, as will decisions on treatments and related matters.
Table 5.6 Polymers and Fibre Reinforced Polymers Information sought Techniques available a Selection Remarks c Guide b Identification of type of polymer T52 Visual examination through magnifying glass d V 2, 5 T52 Heating D Trade names often give a good guide to chemical T52 Effect of flame D composition and spread-of- T52 Chemical analysis, infra red spectroscopy V flame characteristics Mechanical properties T54 Tensile strength V 2, 5 T55 Fatigue D 2, 5 T56 Impact strength D 2, 5 Water absorption T57 Laboratory test V 2, 5 Delamination and void detection T53 Ultrasound – in situ D 2, 5 Transient pulsed thermography, see Appendix 8 D 2, 5 Effects of weathering T58 Laboratory test to predict durability V 2, 3, 5 T59 Visual inspection V 6 Notes a, b and c See Table 5.2 for explanatory footnotes. d Supported by laboratory based determination. The identification of the type of polymer will generally require an expert.
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5.5 Load testing The initial classification of purpose helps in the formulation of the requirements for a monitoring system. Guidance on methods of monitoring building Load testing can provide useful data for the structures is given in Appendix 9 (but see also estimation of load-carrying capacity. Load testing of Table 5.1). individual elements of a structure, such as rafters, can be of modest cost and yield valuable results. A load test of a complete structure is a costly and time-consuming operation with various potential 5.7 References risks. Generally it cannot be repeated because of the disruption involved. Load testing will usually be adopted only after other approaches based on References and guidance on specific tests are calculation, survey and local tests on materials have contained in Appendix 7. failed to demonstrate an adequate margin of safety of the structure under the loads likely to be imposed on 5.1 Highways Agency. The Assessment of highway bridges it. Refer to T61 in Appendix 7 for further details about and structures. BD 21/01. Available at: http://www. structural load testing procedures. standardsforhighways.co.uk/dmrb/vol3/section4/bd2101. pdf [Accessed: 15 September 2009]
5.2 Bussell, M. Appraisal of existing iron and steel structures. 5.6 Monitoring of structures SCI Publication 138. Ascot: SCI, 1997
5.3 BS EN 1991-1-4: 2005: Eurocode 1: Actions on structures It is necessary to give careful consideration to – Part 1-4: General actions – wind actions. London: BSI, the purpose and benefits to be gained before 2005 embarking on structural monitoring, which may involve significant expenditure. The definition of the 5.4 BS 6399-2: 1997: Loading for buildings – Part 2: Code of purpose is the most important part of the process; it practice for wind loads. London: BSI, 1997 establishes what is to be done with the information collected, how it will be interpreted and how this will 5.5 CP 3: Chapter V: Part 2: 1972: Code of basic data for aid decision-making. The limitations of any monitoring the design of buildings. Chapter V: Loading. Part 2: Wind scheme should also be considered. Clients may loads. London: BSI, 1972 not appreciate that monitoring can be a long-term activity, potentially with significant attendant costs. 5.6 Health and Safety Executive. Health and safety in It may be appropriate for the engineer to ensure that construction. HSG150. 3rd ed. Sudbury: HSE Books, 2006 these issues are understood by the client, along with the benefits arising from these activities. 5.7 The Work at Height Regulations 2005. Norwich: The Stationery Office, 2005 (SI 2005/735) Monitoring needs to be closely related to the predicted behaviour from the structural analysis. 5.8 BS 5628-1: 1992: Code of practice for the use of masonry It is essential to establish that the frequency and – Part 1: Structural use of unreinforced masonry. London: accuracy of measurements will identify a developing BSI, 1992 {Since superseded by 2005 version} failure mode in time for suitable action to be taken. General performance monitoring can be highly 5.9 BS 4978: 1973: Specification for timber grades for effective where structures of uncertain strength structural use. London: BSI, 1973 [Revised 1983 as characteristics, despite this uncertainty and if Specification for softwood grades for structural use, overloaded, would exhibit measurable deformation in 1996 as Specification for visual strength grading of without risk of becoming unsafe. softwood and in 2007 as Visual strength grading of softwood – Specification] Where failure modes are likely to be sudden and brittle with little warning sign (e.g. corrosion of 5.10 BS 5756: 1997: Specification for visual strength grading prestressing tendons or punching shear failure) of hardwood. London: BSI, 1997 {Since superseded general performance monitoring of deflections and by BS 5756: 2007: Visual grading of hardwood – the like is unlikely to provide a suitable safeguard. Specification. London: BSI, 2007} However specialist techniques (e.g. acoustic emission), carefully researched and implemented, 5.11 CP 112-2: 1971: The Structural use of timber. Part 2: may be of assistance in these difficult circumstances. Metric units. London: BSI, 1971, British Standards Institution, London {Since superseded by BS 5268-2: Effective and appropriately targeted monitoring is 1984, see ref 6.34} able to provide better knowledge of a structure’s behaviour. It can help demonstrate that an apparently defective structure continues to perform adequately, thereby avoiding costly and disruptive remedial works. It can also provide a method by which confidence in a structure’s performance can be gained in a safe and controlled manner. Contingency plans for various trigger levels need to be in place to ensure that the appropriate action is taken if the results of the monitoring show that the structure is not performing as was expected.
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6.1 I ntroduction Prior to about 1900 (and in many cases up to 1914) clients such as the Admiralty or the Office of Works had their own individual specifications, and This chapter offers only general guidance on the materials were supplied to satisfy these. There was use of materials, their mechanical properties and great variation in requirements and duplication in the processes of deterioration. It is not intended specifications. Conversely any structures built after to replace the relevant specifications, codes of 1960 should have materials that conform to the practice, etc. applicable in new work. The treatment British Standards of the time. It must not, however, is largely historical since it is essential that the be unquestioningly assumed that what was specified engineer has some understanding of the conditions was actually built. under which a structure was designed and built. Table 6.1 gives some background information on The fact that materials do not conform to a availability and periods of use of common structural British Standard, particularly those pre-dating the materials in the UK, but does not cover all materials standards, does not necessarily mean that they are and forms of construction. (The density of the inadequate for their purpose. shading indicates the extent of the use.) Many old buildings, particularly those that have been Two important factors should always be borne in in constant use, may have been repaired or altered mind when reviewing the materials in an existing several times in the past. It is therefore important that structure. The first is that the mechanical properties the engineer is aware of what should be found in a of many materials change with the passage of building of a given age, and what should not; e.g. a time6.1. Examples are the drying-out of timber building from the late 19th century would not include and the progressive hydration of concrete with steel (except as a result of alterations or repairs) but consequent changes in strength. Thus the use of could include wrought or cast iron, neither of which data defining properties of materials when new may would have been welded at the time of construction. need to be considered carefully. Both are difficult to weld even now, and if a weld is spotted then a later repair or alteration has been Some such changes are dimensional and may carried out. It is generally advisable to investigate the cause loads to be transmitted to other parts of the reasons for such welding. structure, which are less able to accommodate them. There may be an incompatibility between BSI has archives of all material based British the dimensional changes, e.g. as concrete cures Standards issued since 1901 available for it shrinks, at the same time as ceramic tiles, consultation. Trade Associations, e.g. Aluminium emerging dry from the kiln, absorb moisture Federation, Brick Development Association, etc. also and expand. Some materials (e.g. concrete, have archival material. The Institution’s own library polymers and timber) have properties that are time contains a limited set of archival specifications and dependent, and/or they creep under constant load. codes. This behaviour is influenced by ambient conditions such as temperature and humidity, and is largely References 6.2, 6.3 and 6.4 may be used as source irreversible. documents to support this chapter but in order to avoid constant repetition are not quoted on each The second factor is that most materials deteriorate relevant occasion. with time, some faster than others, even in ‘normal’ atmospheric conditions. Cycles of wetting and drying cause swelling and shrinking in porous materials such as brick; when restrained this can 6.2 Masonry result in stresses leading to spalling and cracking. Most metals corrode, and a loss of strength may be associated with a reduction of cross-section. 6.2.1 Natural stone Extremes of temperature may lead to fundamental changes in performance, e.g. brittle fracture in 6.2.1.1 History of use steel, or loss of strength in polymers. Bi-metallic Stone has been used from earliest times. Load- contact may encourage corrosion: a reference, bearing stonework was used up to about the late applicable to all metals, is given in Section 6.4.4.5. 19th century, but many earlier structures were built of rubble or brick faced with stone ashlar. Since Aggressive conditions may arise from the use of the about 1900 stone has been mostly used as facing to structure. Examples are the use of floor-cleaning cheaper masonry or as cladding for other materials agents containing chlorides; the spillage of fats, including steel frames. However it is interesting to oils and acids; and the action of acid gases. Most note that load bearing stone (and masonry) has been of these effects are difficult to quantify without the chosen for selected structural elements (columns) in benefit of lengthy testing. The engineer may need a number of recent buildings, and, in the case of e.g. to rely on experience when assessing a structural the Queen’s Building, Emmanuel College (Figure 6.1), material in such circumstances. post-tensioned.
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Figure 6.1 Queen’s Building, Emmanuel College, Cambridge © Buro Happold
Stone as a material is geographically widespread. 6.2.1.3 Mechanical properties of stone Its use in structures is often confined to indigenous Precise strength data are rarely required for materials from a nearby quarry, but imported material appraisal of traditional load-bearing stone is commonly found, e.g. Canterbury Cathedral masonry, as wall and pier sections were typically was built of stone from Normandy and prestigious sized by rules of thumb and were usually quite buildings in London were usually faced with stone lightly stressed by comparison with their crushing from Portland, Dorset. strength. In addition, the strength of stonework is influenced by mortar strength and by the frequency 6.2.1.2 Identification of bed-joints (see Section 6.2.5). If strength data are Recognition of the type of rock is generally easy; considered necessary, for example in establishing visual examination is often adequate. Identification the structural adequacy of thin stone cladding of the origin of the particular stone can, however, be panels subject to flexure under wind loading, then difficult. testing of samples from the structure may be the only reliable answer. There are three general types of rocks used for building. The properties of many types of stone have probably ––Igneous: e.g. granites. Crystallised from molten not even been measured, and even if they have, the rock, and have low porosity. properties from small laboratory samples may not ––Sedimentary: e.g. limestones and sandstones. reflect the properties of large blocks. Produced by cementation of sediments such as fragments of earlier rock (sand grains), animal Indicative properties of structural stone from various skeletons, etc. Their chemical composition and parts of the UK are shown in Table 6.2. More porosity vary greatly. specific properties of particular stones can be found ––Metamorphic: Produced from sedimentary in contemporary building construction text-books, deposits by recrystallisation under heat and for example reference 6.13. The properties can vary pressure, e.g. true marble (from limestones) and from quarry to quarry even in a fairly small area, slate (from mudstones). and within each quarry (Figure 6.2). They may be affected by the quarrying process: stone extracted All rocks of one type contain roughly the same by blasting will contain more micro-defects than mineral constituents but in different forms and blocks extracted by sawing and wedging. (Blasting proportions. Chemical analysis is therefore of no is no longer acceptable within the UK for the use for identification. Petrographic examination extraction of building stone.) may be necessary to ascertain the exact type and nature of the stone, particularly if it is heavily The properties of sedimentary and metamorphic weathered. If possible, the source of the stone stones are significantly affected by the moisture should be ascertained, as this may be a pointer to its content and the orientation of the bedding planes properties. Old records and accounts can provide relative to the loading direction. information on the quarry and hence identify the stone. Quarries are well documented6.5 – 6.12 and many publish the properties of their stone.
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Table 6.1 Materials and/or form of construction and period of availability/use in UK 6.2 Period of availability/major use in the UK (density of shading indicates extent of use) Material and/or form of construction 1600 1700 1750 1800 1850 1900 1925 1950 1975 2000 2010
Natural stone masonry Loadbearing walls and piers; solid or with rubble cores Subsequent facing to timber frames and loadbearing brickwork Use and properties of materials of properties and Use 46 Bonded facing to brickwork backing Cladding to steel, or reinforced concrete, construction
Appraisal of existing structures existing of Appraisal Engineers Structural of Institution The Brickwork and blockwork Loadbearing walls: clay bricks in lime mortar Loadbearing walls: clay bricks in cement* mortar Loadbearing walls: calcium-silicate bricks in cement* mortar Loadbearing walls: concrete blocks and bricks in cement* mortar Infill to timber frames: clay bricks in lime mortar Infill/cladding to steel, or concrete, frames: clay bricks, cement* mortar Infill/cladding to steel, or concrete, frames: calcium-silicate bricks Infill/cladding to steel, or concrete, frames: concrete blocks Wood based Timber frame with clay or brickwork infill: home-grown hardwood Timber frame with brickwork, or tile-cladding, softwood Timber frame and inner leaf with brickwork cladding Roof trusses and floors on masonry walls: home-grown hardwood Roof trusses and floors on masonry walls: softwood Bolted, and/or glued, laminated beams and frames** Plywood – web and similar beams Cast iron Beams Roof truss components Columns Components for special structures: S.G. (ductile) cast irons Water and gas mains, drain pipes, etc. Wrought iron Tie rods, straps and bolts in timber structures Tie rods, chains, cramps and dowels in masonry Rolled strip, L and T sections Rolled I and [ sections Rivetted, built-up sections Wire for bridge suspensions cables (chains used earlier) Corrugated sheet (superseded by steel from 1890-1900) Structural steel Plates and tie rods Rolled L, T, I and [ sections (Is up to 610 deep) Rivetted, built up sections Structural tubes Rolled ‘parallel-flange’ I sections and sections up to 1100mm deep Welded, built-up sections Other steel products Corrugated sheet, galvanised Profiled sheet, plastic-coated Tubes for plumbing, etc. Mild steel reinforcing bars, smooth High-tensile reinforcing bars, cold twisted square High-tensile reinforcing bars, cold twisted ribbed High-tensile reinforcing bars, hot-rolled smooth High-tensile reinforcing bars, hot-rolled ribbed Wire for suspension cables and for pre-stressing tendons High-tensile pre-stressing bars Stainless steel (structural, fixings, cladding) 22/10/2010 10:22 Appraisal ofExisting Structures.indd 47
Period of availability/major use in the UK (density of shading indicates extent of use) Material and/or form of construction 1600 1700 1750 1800 1850 1900 1925 1950 1975 2000 2010
Non-ferrous metals Aluminium: alloys in structural sections Aluminium: sheeting, flat and corrugated, for roofs and wall cladding
Copper and zinc: roof sheeting Copper and copper alloys: plumbing and roof drainage Copper alloys: fixings
Lead: plumbing Lead: dowels in masonry, roofing and guttering Lead: underlay for heavy bearings on masonry Lead: dampproof coursing in masonry Cement and concrete based Mass concrete: lime or pre-Portland cement based Mass concrete: Portland cement based Clinker aggregate concrete in filler-joist floors Reinforced concrete: early patent systems Reinforced concrete Precast concrete Pre-tensioned concrete Post-tensioned concrete Lightweight structural concrete, blocks and screeds Asbestos-fibre-reinforced cement sheet materials Glass-fibre-reinforced cement (cladding and permanent formworks) Other fibre-reinforced concretes (screeds and ground floors) Polymer-fibre-reinforced concrete Appraisal of existing structures existing of Appraisal Engineers Structural of Institution The Steel-concrete composite construction Composite steel deck – concrete slabs Composite steel – concrete beams Organic polymer-based Glass-fibre-reinforced plastic Polymer sheeting
Structural glass materials of properties and Use
Miscellaneous Rammed earth ‘Cob’ (revival from late twentieth century) Wattle and daub Asphalt roofing, guttering and waterproofing Bituminous felt roofing
* Includes cement/lime mortars ** 'Bolt-lam' used 1820–1920
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Table 6.2 Indicative properties of structural stone originating in the UK
Type and location Density Compressive strength Water absorption (kg/m3) (MPa) (% of dry weight) Granites Devon and Cornwall 1800 – 2650 140 – 200 0.30 + Cumbria and Scotland 2600 – 2900 170 – 250 0.19 – 0.24 Sandstones Derby, Glos and Notts 2200 – 2600 40 – 65 3.5 – 5 Lancs, Shrops and Staffs 1950 – 2350 25 – 40 Not available Northumberland 2150 – 2350 35 – 60 5 – 10 W. Yorks, Durham and Scotland 2200 – 2750 40 – 70 2.4 – 2.8 Limestones Avon (Bath) and Devon (Beer) 2200 – 2400 17 – 35 7 – 15 Cumbria and N. Yorks 2400 – 2700 80 – 100 Not available Glos (Cotswold) 1800 – 2300 16 – 120 1 – 4 Leics (Clipsham) and Lincs 1800 – 2200 20 – 35 4.5 – 10 Portland 2000 – 2300 35 – 55 4.5 – 10
6.2.1.4 Deterioration The agents of decay of natural stone may be chemical, physical and organic. Chemical decay is mostly associated with atmospheric pollutants, especially carbon dioxide and sulfurous gases. Limestones are especially vulnerable and, in addition to surface erosion, may exhibit exfoliation. Sulfur dioxide from atmospheric pollution may cause gypsum crystals to grow in the pores of limestones resulting in crumbling of the surface.
Within the UK physical damage from frost or thermal stress is comparatively rare except in conditions of extreme exposure. The use of a repointing mortar less permeable than the stone may exacerbate frost damage. Severe and widespread spalling can occur where a sedimentary stone (i.e. formed in near- horizontal layers) has been face bedded (i.e. with the natural bedding planes parallel to the vertical face). This is more commonly found in ashlared work using stone extracted from a seam too small to provide blocks for proper bedding.
Abrasion by windborne sand generally occurs near the coast together with windborne salt solutions. Artificial abrasion by grit-blasting and other cleaning processes, including chemical ones, have sometimes disfigured the face of the stone.
Rainwater running off one type of stone to another may accelerate damage. For example runoff from limestone or any lime-based product, e.g. concrete or reconstituted stone, will damage sandstone and even some granite. Similar effects can occur if the properties of the mortar used for re-pointing do not match those of the stone itself.
Organic growth (lichens and mosses (Figure 6.3)) is widespread, although atmospheric pollution discourages it. Lichens and mosses are an indicator of wet conditions and sometimes point to more serious decay. They are difficult to remove without the use of treatments that might seriously damage the stone and make it susceptible to accelerated decay6.14, 6.15, 6.16. However English Heritage6.5 describe an apparently satisfactory method for the Figure 6.2 Jura blocks quarried © Arup control of organic growth on masonry.
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Figure 6.3 Lichen growing out of masonry
6.2.2 Bricks and blocks 19th century, and by the second half of that century brick had become the universal building material, 6.2.2.1 History of use although, where the stone tradition was strong, Brick is the oldest man-made building material. bricks were used only for internal walls. Examples of sun-dried bricks (adobe) date back to 8000 BC and fired bricks were in use by 2500 BC. The brick taxes which were imposed from 1784 The Romans brought the art of firing and the use of until the 1850s were largely responsible for the bricks as a structural material to an advanced level. development of various types of hollow bond. Many of these, e.g. rat trap, were the forerunners of the Clay bricks were traditionally made locally. cavity wall, which is now used for altogether different Large-scale brick production dates from the early reasons.
Figure 6.4 Tapia and adobe brick barn with modern brick repair at base. Matanza de los Oteros, Spain © ML Riol Riol
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6.2.2.2 Identification 6.2.2.3 Mechanical properties Although features may be more reliable as a dating It is essential to recognise that the compressive aid, brickwork may sometimes be approximately strength of the bricks is not in itself a true guide to dated by the brick size, as indicated in Table 6.3 the strength of brickwork, which is influenced by the below. There are however regional variations which presence of the mortar and its strength. A formula may be greater than those relating to age; for for brickwork strength given in BS EN 19966.17 instance 3" (76mm) bricks were used in the North demonstrates this: simultaneously with 25/8" (67mm) in the South. a b fk = K fb . fm The first and essential point to be established is whether the bricks are fired clay, calcium-silicate where:
(sand-lime), or concrete. fk = c haracteristic compressive strength of masonry Clay bricks exhibit long-term initial moisture K = a constant obtained from BS EN 1996-1-1
expansion, because they emerge desiccated from fb = n ormalised mean compressive strength of the kiln and subsequently take up moisture from the masonry unit
atmosphere over a period of months and years. fm = compressive strength of mortar a and b = values obtained from BS EN 1996-1-1, Calcium-silicate and concrete bricks have significant typically, for commons in lime mortar, initial drying shrinkage. 0.65 and 0.25 respectively.
Calcium-silicate bricks are unlikely to be found in The frequent and closely-spaced bed-joints in buildings dating from before 1900. They are usually brickwork result in a lower masonry strength than recognisable by their combination of a sandy surface for blockwork or stonework which have larger units texture and an originally uniform colour. They have and correspondingly more widely-spaced bed-joints. very sharp and true arrises without any trace of the This is reflected in the variety of strengths for units of small irregularities in colour and texture that arise different geometry given in Table 2 of BS 5628-16.18. from the forming and firing of clay bricks. Indicative values of the compressive strength of bricks (alone) are given in Table 6.4.
Table 6.3 Brick sizes Period Imperial size (h × l × w)in Metric size (h × l × w)mm 1300 – 1430 1¾ × 12 × 6 (44 × 305 × 152) 1430 – 1650 2 × 9 × 4½ (51 × 229 × 114) 1650 – 1750 2¼ to 2½ × 9 × 4½ (57 to 64 × 229 × 114) 1784 – 1803 3¼ × 11 × 5 (due to brick tax) (83 × 280 × 127) 3¼ × 12 × 6 (83 × 305 × 152) 1803 – 1850 3 × 10 × 5 (maximum under brick tax) (76 × 254 × 127) 1850 – 1930 3 × 9 × 4½ (76 × 229 × 114)
1930 – 1950 27/8 × 9 × 4½ (73 × 229 × 114)
1950 – 1973 25/8 × 9 × 4½ (67 × 229 × 114) 1978 – date (2½ × 8½ × 4) 65 × 215 × 103
Table 6.4 Indicative values of compressive strength of bricks Type of clay brick Compressive strength b (MPa) Extruded 20 – 200 Machine moulded 3.5 – 175 Engineering H 70 Commons 2 – 20 Flettons (normal) 15 – 28 London stocks 7 – 20 Calcium silicate bricks 7 – 35 (commonly 14 – 28) Concrete bricks 7 – 40 Notes a Table taken from reference 6.19. b When tested in accordance with BS 3921: 19856.20.
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6.2.2.4 Deterioration Deterioration of clay bricks is nearly always caused by the presence of water. Efflorescence of soluble salts is unsightly but generally harmless structurally. More important is frost damage where freeze-thaw cycles create spalling either by general crumbling of the surface or by the flaking of the surface layer (Figure 6.5). Water-absorption tests do not give a reliable indication of susceptibility to frost attack, which depends on the clay, on firing conditions and on conditions of exposure.
Clay bricks also suffer from salt crystallisation and occasionally contain inclusions of (quick) lime; both of these cause surface spalling.
Calcium-silicate bricks can be susceptible to chloride salts.
6.2.3 Mortars
Mortars normally consist of sand and a binder and in rare cases some clay. The binder can be cement, lime or a mix of both. Some mortars, used in the past, contained ash to give a dark colour. The ash might act as a pozzolan, but could Figure 6.5 Frost damage and efflorescence on masonry also, because of its content of sulfates, corrode embedded metal.
Lime, burnt lime or quick lime is calcium oxide The strength of the mortar influences the strength (CaO) produced when chalk or limestone (calcium of the masonry in compression, tension and flexure
carbonate, CaCO3) is heated, driving off the carbon but not to a great degree. Lime:sand mortars were dioxide (CO2). When the lime is later slaked with traditionally used. They were able to accommodate water (CaO + H2O), slaked lime, lime putty or calcium movement, both from the bricks themselves and hydroxide (Ca(OH)2) is produced. from the structure as a whole. It was considered good practice that the mortar should never be Pure lime mortars, containing no clay or silt, harden stronger than the brick. In specifying repair of by carbonation of the calcium hydroxide. This can older, normally weaker, brickwork, the use of a take many years, depending on the porosity of the stronger mortar should be avoided for the reasons stone or brick and on the thickness of the wall. above. Further, strong cement-rich mortars tend In mortars made from hydraulic lime, where the to shrink, which can lead to poor bonding and limestone is ground and fired with some clay or silt, water ingress into the wall. It should perhaps be the lime reacts with water for initial strength gain, remembered that generally the purpose of mortar supplemented subsequently by carbonation of any is to transfer the gravitational force uniformly free lime. through the brickwork, the tying effect being achieved by friction and the staggered pattern of Pure lime mortars (lime:sand) are relatively weak and the bricks. flexible. Pure cement mortars (cement:sand) may be stronger and stiffer than the stone or brick. If the The compressive strength of mortar in existing mortar is too strong, any cracks in the masonry from joints cannot be measured directly (but see helix whatever cause may therefore go through the stones pull-out test. Appendix 7, T40). The ratios of or bricks rather than follow the joints. ‘Masonry cement:lime:sand can be established by chemical cement’ is Portland cement with an equal part of analysis of mortar samples taken from the joints. inert filler, such as stone dust, added to improve the These ratios can be related to the strengths of workability of the mortar. modern mortars of similar compositions. This approach tends to underestimate the strength of pure Cement-lime mortars (cement:lime:sand) have lime mortars, but where these have been identified in intermediate strengths; the greater the proportion of an old building the mortar compressive strength may cement, the stronger the mortar. Small additions of be assumed to be in the region of 0.5-1.0MPa. cement to lime mortars increase the strength marginally but reduce the permeability significantly. This can result 6.2.4 Masonry construction in frost damage in porous stone or brick. 6.2.4.1 G eneral Mortar joints are eroded by rain running down Cracks in masonry construction may arise from a faces of walls. This effect is aggravated by chemical number of causes including unbalanced thrusts from breakdown of the binder, because of the acidity of the arches and vaults, foundation movements, corrosion rainwater. The resistance to this weathering increases of embedded structural framing, and thermal and with the total proportion of binder to sand. Sulfates, moisture movements of the masonry itself or of other from whatever source, can cause the expansion and structural elements. When movement in cracks is disintegration of mortar. Some bricks contain sulfates seasonal (because of climatic fluctuations) or diurnal which may be leached out into the mortar. Unlined and not progressive then it may not be necessary to flues can suffer serious sulfate attack. carry out major repairs.
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6.2.4.2 Brickwork Cavity walls pre-1900 will probably be 15½" (394mm) Examples of brick bond laying patters are given in thick, having 9" (229mm) inner leaf of common Figure 6.6. Stretcher bond leaves require ties to be brickwork, 2" (52mm) cavity, and 4½" (114mm) outer leaf considered transversely bonded. for decorative purposes and weathering. Alternatively, some 15½" cavity walls have 4½" inner leaf, 2" cavity and Solid bonded walls, where fair faced, are usually a 9" outer leaf with various bonding patterns. recognised by the presence of headers, but a check should be made that they are not snap (or snapped) Cavity walls post-1930 will probably be 11" (279mm) headers (brick cut in half to imitate bond work). In thick having 4½" outer leaf, 2" cavity and inner leaf older work, there may be a few through headers, but of 4½" or 4" block. Where fair-faced, they are usually no metal ties. However, metal ties were widely used recognisable by being in stretcher bond. Some walls, in railway architecture of the mid-1800s, usually in the which show stretcher bond on the face, may however form of a flat strip in every fourth to sixth bed-joint. be solid with ties in lieu of headers. The ties can sometimes be identified by slight but regular cracking at these joints because of expansion In cavity walls the corrosive expansion of inadequately due to corrosion. protected ferrous metal ties can cause stress concentrations, leading to spalling or cracking, and In Victorian times snap headers were often used to complete corrosion of wire ties can cause loss of form patterns in the outer leaf, often using different structural integrity. Surface treatments against water coloured bricks. penetration are not generally effective and, indeed, may often prove detrimental by inhibiting drying-out Solid walls and piers of thickness greater than by evaporation: in making an appraisal the engineer 18" (457mm) may consist of two skins of properly should review the presence or absence of details such bonded whole bricks, with a random infill of mortar as cavity trays, DPCs, air bricks and weep holes. The with brickbats (fragments of brick). advice of an architect or surveyor may be required.
Cavity walls are usually post-1850 and most are Some buildings, while appearing to be of load- post-1930. bearing brickwork, may in fact have iron or steel frames with brickwork infill. Corrosion of the metal may cause cracking: see stone masonry below.
Stretcher bond* Header bond English bond
Flemish bond English garden wall bond
Monk bond Flemish garden wall
* Leaves not bonded unless by ties
Figure 6.6 Common solid brickwork bonds
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6.2.4.3 B lockwork Many buildings from the end of the 19th and first The term ‘blockwork’ is usually synonymous with half of the 20th century, while appearing to be ‘concrete blockwork’. However, hollow clay blocks of traditional masonry construction, are in fact were quite common in the UK between 1930 and masonry cladding on iron and/or steel frames, 1960 and still are in mainland Europe. usually consisting of a stone facing with brickwork backing. Corrosion of the frame can occur from Concrete blocks were first used in the early 1900s. ingress of moisture arising, for example, from However, the period 1918-39 saw a noticeable erosion of masonry mortar joints aggravated by growth in production to support the house building poor maintenance. The masonry cladding may programme. During that time the material was mainly be cracked by pressure exerted by the build-up clinker blocks, which were used for partition walls. of rust. The cracking usually occurs along lines Since World War II the use of concrete blockwork parallel to and within the width of the iron or steel increased dramatically because of the promotion members. Absence of cracks, however, does not of cavity walls and the need for improved thermal necessarily mean that the frame is not corroded insulation, which was achieved by the use of since the corrosion may have built up in any gap lightweight concrete blocks for the inner skin. between the back of the cladding and the frame member. Block sizes vary from 390 × 190 × 60mm to 590 × 215 × 250mm. Warland6.24 illustrates typical steel-framed masonry-clad construction from the 1920s, while Blocks may be solid, cellular (with formed holes the potential problems and possible treatments are which do not wholly pass through the block) or considered in Gibbs6.25. hollow. Three basic types of concrete are used in block production. 6.2.5 Strength of masonry, characteristic strength, –A– utoclaved aerated – compressive strengths c-factors 2.8 – 7.0MPa. –L– ightweight aggregate – compressive strengths There is currently no simple way of assessing the 3.5 – 10.5MPa. basic compressive strength of masonry in situ. –D– ense aggregate – compressive strengths up to 35MPa. BS 5628: Part 16.18 is aimed at the design of new structures to be constructed with modern materials. Densities vary in the range 475kg/m3 (autoclaved It does however contain information which, if suitably aerated) to 2000kg/m3 (normal aggregate) with interpreted, can provide the basis for appraisal as lightweight aggregate blocks in the mid-range. Some discussed below. blocks now incorporate additional insulation in their cavities or on one face. It is assumed in design that if the compressive strengths of the units (stone, bricks or blocks) and of 6.2.4.4 S tone masonry the mortar are known, the compressive strength of the masonry at right angles to the bedjoints can be Stone masonry construction may be of ashlar, determined. In practice design recommendations in squared/coursed rubble, random rubble, etc. BS 5628 combine strength of the units with the mix Composite rubble/ashlar walls have often been proportions of the mortar to arrive at a ‘characteristic used. It cannot be assumed that a pier or wall with compressive strength’ (ignoring slenderness) for ashlar facing is of solid construction through its the masonry. Tables 2a to 2d of BS 5628-16.18 give entire section; often the core will be of very weak characteristic strengths for masonry using bricks, material6.21, 6.22, 6.23 (see Figure 6.7). blocks and, by inference, natural stone laid in mortars of varying mix proportions, but not in pure lime mortar.
This approach tends to penalise existing masonry laid in pure lime mortar and reference should be made to the advice at the end of Section 6.2.3. Masonry can still be laid in pure lime mortar but few modern structures, for which design codes are written, are built this way. The assessment of masonry laid in lime mortar is a good example of the difficulty of using a design code for assessment. An appraisal does not have to use the design code, but there should be a logical justification for whatever assumptions are used instead, as illustrated by e.g. Appendix A3 of CIRIA Guide C5796.26.
Techniques are available for measuring the in situ compressive strength, but these are partially destructive, require specialist equipment and are not usually justified for ordinary appraisals.
6.18 The cm-factors in BS 5628-1 depend on the brick manufacturer’s quality control, workmanship on site and the site control of the mortar. While these Figure 6.7 Section through ashlar and rubble-core wall factors are difficult to quantify after the event, it is
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however usually possible to assess the consistency 6.2.6 Other walling materials of the brick strength and mortar composition by sampling and testing. Further, it can be assumed Some other forms of walling that are not strictly
that the tabulated cm-values included some inbuilt masonry are sometimes found, such as those listed allowances for deviations from the design such as as follows. laying bricks ‘frog’ down, future cutting of horizontal chases and raking out of joints prior to pointing 6.2.6.1 M athematical tiles with soft mortar. Detailed site information on these Mathematical tiles (brick tiles or wall tiles) are like points may allow some reduction of the appropriate vertically-hung roofing tiles and shaped like the cm-factor. header or stretcher of a brick. They were nailed to timber boarding or hung on laths with joints painted
The strengths and cm-factors quoted in BS5628 in mortar. They are quite widely found in the south refer primarily to present-day construction practice, east of the UK where their use persisted well into where wall thickness rarely exceeds 350mm and the 19th century. They are usually confined to the where it is assumed that chases for electrical front elevation of the building with plain tiles over conduits, etc. may be cut after construction. For the sides and rear. Their presence if suspected can existing walls, where subsequent cutting of chases be confirmed by tapping the face, when a hollow or can be controlled, or where a greater wall thickness ringing sound will distinguish them from the dullness makes the weakening by a standard 40mm deep of brickwork, invariably much thicker6.29. chase proportionally much less than in a 220mm
wall, it may be acceptable to reduce the cm- factors 6.2.6.2 R ammed earth by about 12% for 330mm walls and about 25% for The tradition of using earthen materials was formerly a walls 440mm or thicker. good deal more widespread than is generally imagined. Although architectural tradition in Europe is most often CP1116.27 gave permissible stresses for pure lime thought of as being masonry based, in many places mortars (hydraulic and non-hydraulic). Modern (notably France and Germany) there are still many codes of practice have withdrawn reference made examples of monumental earthen buildings of great to brickwork laid in lime mortar, possibly motivated age. England, despite the damp and humid climate, by a requirement to limit the squeezing-out of has some examples. Walls could be built of cob the mortar and the resulting settlement of the (clay, pressed down in layers and often strengthened brickwork in the period following the construction. with straw), wichert (crushed chalk similarly laid), or This consideration is not relevant when assessing blocks of clay ‘lump’. With adequate protection against an existing building. The increase in stress that rain by a generously overhanging roof, and set on a might be allowed is, however, difficult to assess in stone base to guard against rising damp, such walls the absence of further information, such as may can be surprisingly long-lived6.30. Once rendered or sometimes be obtained by split-cylinder tests on whitewashed it is not easy to establish, visually, what cores, in situ flat-jack tests or by sawing out prisms type of structural units were used. of brickwork and testing them intact.
BS 5628 allows the tabulated strengths for natural stone masonry to be enhanced, when the units are large, carefully cut to regular shape and laid with very thin joints.
Standard BD 21/936.28 has a graph of characteristic compressive strengths of stone masonry for different stone strengths, types, and mortars; covering masonry such as ashlar (precisely worked stone with very thin joints); squared rubble stone in 1:2:9 mortar; through to random rubble with lime mortar. The values given are similar, although not identical, to the strengths of stonework that can be derived from BS 5628-16.18.
Table 6.5 shows characteristic strengths of stone Figure 6.8 Palace constructed from rammed earth, Toral de masonry derived from the graph in BD21/936.28. los Guzamanes, Spain © ML Riol Riol
Table 6.5 Characteristic strengths of stone masonry Type Strengths of masonry units (MPa) 40 80 120 160 200 Ashlar 7.0 11.0 14.0 16.0 17.5 Squared rubble in 1:2:9 mortar 5.2 8.4 10.5 12.0 13.0 Random rubble in lime mortar 3.5 5.5 6.9 8.0 8.8 Note The strengths given in this table may be conservative if used with the partial factors in BS 5628-16.18; they may, however, be enhanced by reference to clause 23.1.8 of BS 5628-1.
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6.2.6.3 Clunch Blocks of basal chalk laid in a lime putty can be found in southern England in chalky areas. Rendering or regular lime-washing is essential to their maintenance, to avoid damage by frost. A thatched ‘roof’ and a footing of sarsen stone are sometimes used for garden walls: see Figure 6.9. ‘Find Chalk a good hat and shoe and it will serve You well.’6.31 ('Puddingstone' is a regional name for clunch; but care should be taken as, in other regions, the same word is used to refer to conglomerate rock.)
6.3 Timber
6.3.1 General
6.3.1.1 H istory of use Oak was the most common timber in British construction until the end of the 17th century but some elm was also used. Increasing scarcity of native timber and better availability of imported softwood from Baltic countries promoted the change to the use of softwood, particularly near ports and Figure 6.9 Clunch garden wall in Ashwell, Hertfordshire towns on main transport routes. Oak remained in use where the transport of softwood was uneconomic. Subsequently softwood became available from North -6.3.1.2 Identification America. The date of original construction and the location of the structure may give some indication of the origin As a rough guide the eastern districts of England and likely identities of the species of the timber. imported from Scandinavia and Russia (redwood, whitewood, etc.). In western parts of the country, This identification of species is necessary for a first Canadian and American timbers (spruce, yellow indication of strength. Often it will be adequate simply pine, Douglas-fir) were commonly used. to establish whether the timber is hardwood or softwood. Where accurate identification is important, Many structural timber members may have been a small, clean-cut end grain sample should be used more than once, recycled from demolished examined under magnification (10 × hand lens for buildings: such re-use is often detectable from hardwoods; microscope for softwoods). This requires unused notches or rebates or from the timber specialist knowledge (cf BRE’s ‘Wood Library’, where profile. samples of many thousands of species are held) or a specialist advisor (e.g. TRADA). Table 6.6 indicates the likely timber species in relation to the age of the structure. The amount of sapwood (the outer layers of the tree trunk that had not changed into heartwood by the When appraising timber structures, reference can time of felling) should also be assessed as this may usefully be made to Ross6.32 and Yeomans6.33. affect durability (see Durability below).
Table 6.6 Timber species Approximate period Origin Species 1780-1830 UK Oak and other local hardwoods Some softwoods (not very common) Scandinavia/Russia Redwood/whitewoods America/Canada Douglas-fir, pitch pine 1880-1930 Baltic states Redwood/whitewoods Canada/USA Spruce, Douglas-fir, pitch pine UK Scots pine, oak (in selected applications) 1930 onwards Scandinavia/Russia Redwoods, whitewoods Tropical regions Tropical hardwoods Canada/USA Douglas-fir, pitch pine, yellow pine, western hemlock Spruce/pine/fir (from 1970)
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6.3.1.3 Mechanical properties 6.3.2 Strength of timber, permissible stresses The terms ‘hardwood’ and ‘softwood’ refer to a botanical classification and do not relate to the Any structural member is likely to contain natural engineering properties: Balsa is classified as a imperfections such as knots which will reduce the hardwood, while softwoods include yew and strength below that of a clear sample. When assessing Douglas-fir. the strength of a member, this reduction is taken account of by the process of ‘stress-grading’. Timber is anisotropic; the properties parallel to the grain (tension and bending) are far better Timber in post-1950 construction can sometimes be than those perpendicular to the grain (shear and assessed by the markings from machine stress-grading tension). Modern manufacturing processes involve (BS 49786.35, or to the standard of the country of origin). the removal of defects/knots etc and ‘green gluing’ Examining the markings may not always be practicable or finger-jointing to make long lengths of defect- for timber members in situ and for older timbers there free structural timber. (The specialist products will be no markings. manufactured from such timber are beyond the scope of this Report.) If the species can be identified and the timber faces can be seen, members can be visually stress-graded and The mechanical properties depend on the moisture the code design stresses assessed. For softwoods, the content of the timber. When first felled, it has a rules in CP 1126.36 (superseded for the design of new high moisture content (from 80% to over 100% by works) are easier to use than those in BS 5268-26.34. weight of dry matter) but it will eventually dry out to a For temperate hardwoods, the grading rules have moisture content that is in equilibrium with the relative been revised. Visual stress-grading requires skill and humidity of its environment, typically 12% to 20%. experience. Long-term substantial changes in relative humidity will cause changes of the moisture content and As the level of stress reduction depends on the nature, hence of the mechanical properties. extent and location of the imperfections, the procedure of in situ grading has the advantage that the reduction There is a roughly linear relationship between the arising from a local defect (e.g. a knot) need be taken density of a ‘clear’ sample (a sample free from into account only at that location. If the defect is in a defects, e.g. knots, etc.) at 12% moisture content and lightly-stressed part of the member, the load-carrying the basic strength. capacity of the member, as a whole, may not be affected. Such stress-grading requires that at least Timber can be thought of as a visco-elastic some of the timber surfaces are visible, i.e. not obscured material to explain its behaviour with respect by decoration, and experience or specialist assistance is to creep and stress relaxation. A joist may sag necessary. because of overloading, but it is more likely to sag because it has been carrying its (safe) load for a Certain members such as floor joists in old houses are long time. sometimes undersized by today’s standards and have frequently been notched for service pipes, electrical The failure stress for long-term loading is less than wiring, etc. Some traditional craft-based joint details in that for short-term loading. Current British codes of roof trusses, etc. appear not to follow sound engineering practice therefore reduce the permitted stress levels principles. In these cases calculations are likely to prove for long-term loading. unhelpful. Subject to inspection of bearings and joints, the engineer has either to accept ‘structural adequacy 6.3.1.4 Durability by force of habit’, where the load is not increased, or to With historic or significant timber structures, recommend remedial works, or possibly load testing. specialist advice from both professionals and companies may be necessary for the identification The strength of the connections in timber structures is and treatment of species, infections and insect often more significant than that of the timber members attack. themselves. The oak pegs in old structures were usually intended only for location and handling purposes during Biological agencies (fungi and insects) are the erection; their strength is low. predominant cause of deterioration. However, if timber is kept at a moisture content below 20%, it is Ferrous timber connectors (bolts, nails, etc.) may lose immune from fungal infection and the risk of insect strength because of corrosion, particularly in timber attack is reduced. At higher moisture contents, the exposed to saline atmospheres6.37. Oak, when wet, durability of heartwood varies according to species gives off acids that can corrode ferrous connectors. (see BS 5268-26.34); sapwood is not durable. The chemical treatment of softwoods can also corrode ferrous connectors if the wood is allowed to become wet. Fissures occur commonly as a result of natural drying-out; their effects are allowed for in the stress Advice on the adhesive used in laminated timber grading (see Section 6.3.2). (‘glulam’) is given in Section 6.10.4.
It is possible for timber members to appear to be 6.3.3 Period of fire resistance in reasonable condition, but internally to have been subjected to fungal attack (e.g. dry rot) or insect Most roofs (if they do not support or provide stability attack, with little evidence on the external face of the to walls) will not be required to have any specified timber. This can be the case for example in timber period of fire resistance. Other exposed members floor beams close to the bearing in the wall. A probe may be assessed on the basis of charring rates; see of the timber can indicate whether this is the case, Appendix 5. The fire resistance of covered members and specialist advice can be taken. depends largely on the nature, integrity and fixings of the covering/encasement.
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6.4 Metals and alloys Wrought and cast iron were rarely used in new construction after 1914. BS 4496.41 was published in 1932 and revised in 1935, 1937, 1948, 1959 and 6.4.1 Ferrous alloys 1969, with amendments up to 1995. More recent developments include stainless steels, weathering 6.4.1.1 H istory of use steels, high-tensile steels (both weldable and The historical development of structural iron and non-weldable grades), etc. Only the principal varieties steel is shown in Table 6.7. The period from about are considered here. 1880 to about 1900 was the critical one when cast iron, wrought iron and steel were all in use. With 6.4.1.2 I dentification the advent of cheap steel, available in appropriate The only certain method to distinguish between sections, the use of cast iron and wrought iron cast iron, wrought iron and steel is metallographic diminished. examination of a sample, sawn (not flame cut) from the member. This may be done on site by a specialist In summary, cast iron contains 2 to 5% carbon and with the appropriate equipment providing the is formed in a molten state above 1150°C: it is strong circumstances are suitable. in compression but is weak in tension and brittle. Wrought iron is made in batches from cast iron, with All ferrous materials are magnetic except most of the carbon removed, by hammering and for austenitic ‘stainless’ steels and some rolling to a profile: it is ductile but heavily laminated. special-purpose alloys. Steel typically contains 0 to 2% carbon and is made in bulk: it is also ductile, but modern steel is unlikely Other features that may assist identification are to be laminated when below 100mm in thickness. shown in Table 6.8. Not all of the features listed are necessarily found together. Some sample The London Building Act (1909)6.38 gave design rules metallographic sections are shown in Figure 6.10; and permissible stresses for iron and steel structures. these require expert interpretation.
Table 6.7 Chronology of developments in structural iron and steel in the UK Date Cast iron Wrought iron Steel 1770s First beams 1794 First columns c. 1800 First I-beams 1840s First built-up beams (plates and angles) and rolled joists (in France) From 1860 Onset of decline in use for beams 1877 Board of Trade approved use in bridge building 1884–1890 Forth rail bridge 1885 First rolled joist (Dorman Long) 1901–1903 First standard steel sections 1909 London Building Act 6.38 gives rules and permissible stresses 1914 Rarely used in new work 1927 Institution of Structural Engineers' report on design of steelwork6.39 1930s High yield steel 1931 DSIR report on design of steelwork6.40 1932 BS 449 published6.41 1935 First revision of BS 449 1937 Second revision of BS 449 1938 Institution of Structural Engineers' report revised 1939 Wartime emergency amendment to BS 449 increasing allowable stress by 25% 1948 Third revision of BS 449. CP 1136.42 supersedes Institution of Structural Engineers' 1938 report 1950s Decline of riveting. Advance of welding and HSFG bolts 1959 Revised BS 449 (incorporating CP 113) Universal beams introduced 1967 Formation of British Steel Corporation from the UK’s 14 main steel producing companies 1969 Metric version of BS 449 1970 Tension control bolt available c1970 Introduction of metric equivalents for imperial section sizes 1985 BS 59506.43 published c1990 Introduction of hot-rolled sections such as Slimflor and Slimdek and of cold-worked sections such as Metsec 1999 British Steel merger with Hoogovens to form Corus: closure of many rolling mills 2002 Aceralia, Usinor and Arbed merge to form Arcelor 2004 Steel grades: BS EN 10025-1:20046.44 replaced BS 43606.45 and BS EN 10025:1993 2005 BS EN 1993 (Eurocode 3) published 2006 Arcelor merge with Mittal Steel 2007 Corus taken over by Tata Steel
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Low alloy steel Grey cast iron Grey iron
100nm 100nm © Castings Technology International
Figure 6.10 Examples of metallographic examination
Table 6.8 Features that may assist in identification Grey cast iron Wrought iron Structural steel Appearance of member Pitted or ‘gritty’ surface texture Smoother surface than cast iron unless Visually similar to uncorroded wrought iron Thick webs and flanges corroded, when delamination often visible but larger sections available Internal corners rounded: external corners Joists rolled in modest sizes only: larger Maker’s name or section reference often ‘sharp’ sections built up from joists, plates and stamped on web angles riveted together Tension flange often larger than Standardised section sizes compression flange Larger sections built up from joists, plates Flanges often ‘fish-bellied’ on plan or webs and angles riveted together, up to 1950s on elevation Form of structural section Varying beam sections, cast in web- Constant section, since from rolls stiffeners Forged ends to tie-rods Sections built up by riveting and after 1960 Hollow circular or rectangular columns Sections built up by riveting by welding Cruciform columns Integral heads or brackets Integral decoration Generally thicker than wrought iron or steel Connections Bolts or almost invisible socket connections Riveting or bolting Riveting or bolting Welding rare (invariably repair of later date) Welding rare except for forge welding or Welding from 1920s but only in wide use as repair from 1950s Appearance of fracture Clean break, no reduction of area, no Pronounced tearing and ductility; fracture Between cast and wrought iron, depending tearing laminated, fibrous on quality of steel and temperature of test Grey crystalline surface Sometimes shiny in places Ductile necking before tensile fracture
6.4.1.3 Mechanical properties 6.4.1.4 D urability Ironmasters supplied grades, and sections of cast All ferrous alloys deteriorate, by oxidation – even iron, wrought iron and steel prior to 1900 as required in ‘normal’ atmospheric conditions. Wrought by the market6.2. National standards were not iron and cast iron are generally regarded as the available. least vulnerable to corrosion though this is highly dependent on the nature of the environment and Tables 6.9 and 6.10 give some indicative properties. the surface condition of the material. All three are Values for cast iron should be used with great highly susceptible to corrosion by sea water – cast care. BS 43606.45 issued in 1968 was the first iron being the least susceptible in this respect. All comprehensive specification covering steels previously three require protection to endure. ‘Loss of strength’ specified in BS 156.48, 6.49, BS 9686.50, BS 27626.51 and can be a consequence of loss of section due to BS 37066.52. Four groups of steel were included with corrosion. ultimate strengths 26, 28, 32 and 36tonf/in2 (401, 432, 494 and 556MPa) minimum and corresponding yield It should be remembered, however, that rust strengths. Yield strengths have continued to rise since, occupies some 5-10 times the volume of iron from such that steel with bespoke yield strengths and other which it was formed so that even an apparently properties may now be ordered. heavy layer of rust may, when removed, reveal only a small diminution of the section. If the material has
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Table 6.9 Indicative physical properties of cast iron, wrought iron and early mild steel Grey cast iron Wrought iron Mild steel (bars, flats, angles, etc) Ultimate strength Tension 5.8-16.2tonf/in2 21-24tonf/in2 28-32tonf/in2 (90-250MPa) (324-371MPa)6.46 but see also (433-494MPa)6.48 18-38tonf/in2 (278-593MPa)6.47 Compression 50-71tonf/in2 (775-1100MPa) Yield strength No defined yield point or plateau Not specified in BS, but see also First specified as 14.2tonf/in2 15-25tonf/in2 (220MPa)6.28 (232-386MPa)6.49 and 14.9tonf/in2 (230MPa)6.28 Elastic modulus 80-150GPa or 170-220GPa or 190-210GPa or 90-138GPa6.28 200GPa6.28 205GPa6.28
Table 6.10 Design stresses and partial safety factors Cast iron Wrought iron Mild steel Partial factor of safety Effectively BD 21/93 uses working stresses for cast iron Material 1.2 Mean value for range BD 21/93 (depending on dead to live load proportion) – following a Live load 1.5 1.05 to 1.15 plotted curve varying from 24.5 to 46MPa Dead load 1.1 Characteristic yield strength No defined yield point or plateau 220MPa 230MPa BD 21/93 Equivalent working stress Tension MPa Tension and Tension and BD 21/93 LL/DL = 0.5 39 Compression: Compression: LL/DL = 1.0 34 141MPa 147MPa LL/DL = 1.5 32 Compression 154 Working stress MPa Tension and Tension and London Building Act 1909 Tension 23 Compression: Compression: Compression 124 77MPa 116MPa Notes a The design stresses and partial safety factors in this table are taken from Highways Agency’s Departmental Standard BD 21/936.28 and from the London Building Act of 19096.38 b LL/DL = Live load/Dead load
received some sort of protective coating (e.g. paint), –– crack-like defects or severe stress concentrations both the coating and the underlying material should –– material of poor notch ductility or low fracture be inspected carefully for the presence of defects. toughness at service temperature.
A small defect, exposing a local area to the To appraise the risk of failure from brittle fracture it atmosphere, will generally widen and deepen over is important to know the notch ductility or fracture time. It may be worth grit-blasting a small trial area toughness of the iron or steel, the stress levels to reveal the condition of the metal. Generalised present, the presence of stress concentrations or corrosion is often less significant than localised possibility of crack-like defects, and the previous corrosion, especially under dynamic loading. loading history. A structural member subject to Such considerations may be especially important loading in one direction only is unlikely to suffer brittle where a change of use carries with it a change of fracture if in the past it has carried high loads safely. environment. Where the microclimate differs from the This is however subject to there being no increase general environment, corrosion may be significantly in load, no deterioration by fatigue cracks, and no more severe (e.g. built-in ends of roof trusses material changes, e.g. because of fire, etc. otherwise situated in dry air). Pitting corrosion may be found in crevices such as those formed by faying No indication of the notch ductility can be obtained surfaces between riveted and bolted components. from the tensile test: compare tests T31 and T34 in See also Section 6.4.4 with regard to stainless steels. Appendix 7.
6.4.2 B rittle fracture The structure being appraised may be found to have cracks. Fracture-mechanics techniques are now Grey cast iron (‘cast iron’) is more ductile than available to predict the residual life of such structures. modern spheroidal graphite iron: the latter, though Specialist advice should be sought. Brittle fracture more brittle, is stronger. Wrought iron is ductile but and fracture mechanics are discussed in references not as tough as steel. Fracture in structural ironwork 6.53, 6.54, and 6.55. or steelwork is due to a combination of factors, including: Where steel is in contact with liquid metal, liquid –– tensile strength metal embrittlement (LME) can occur. Where steel
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has been in contact with liquid metal which has Cast iron, and then wrought iron, were used now solidified, e.g. galvanising, liquid metal assisted structurally before steel was introduced during the cracking (LMAC) can be induced6.56, 6.57. Such last decades of the 19th century (see Table 6.7). potential cracking may require investigation. These materials will still be found in many structures. 6.4.3 Appraisal of structural ironwork and steelwork Cast iron, used structurally in the grey form with Geometric properties of obsolete sections can often 2-5% carbon mainly in the form of graphite flakes, be found in reference 6.58. is relatively weak and fails in a brittle manner in tension, with no defined yield point. In compression For concrete-encased members some reserve it is at least as strong as mild steel. Its strength is strength may be available, particularly if the variable, depending on carbon content, section casing is reinforced and composite action can be thickness and treatment during the casting process. substantiated. These factors need to be taken into account if reliance is placed on test results for assessment, For steel design, BS 59506.43, which succeeded which should be based on working or permissible BS 4496.41, uses partial safety factors to cover stresses as the material has effectively no ductility variations in material quality, structural performance or capacity for redistribution.
and applied loads. A material factor (cm) of 1.0 has been adopted for structural steel. As far as loading Earlier editions of BD21 for bridge assessment is concerned, the make-up of the partial load factor gave generic values of permissible stresses for grey is as described in Section 4.6.3. The structural cast iron, which have been carried through into the 6.28 performance factor, cf3, takes account of rolling current edition ; the same values are suggested tolerances on the steel, together with inaccuracies for building structures6.47. of design, fabrication and erection. Cast iron is often readily distinguishable from Where, in existing structures, steels to BS 156.48, wrought iron and steel by its appearance. Being BS 5486.59 and BS 9686.50 have been used, the formed in a molten state in a mould, the material strength may be assumed to be comparable to the can take up almost any profile. Columns with equivalent grade of BS 43606.45 or BS EN 100256.44. ornamental heads, and beams with convex web (It should be noted that in these later standards the or flange profiles for structural efficiency, are strength of steel specified is a minimum and not commonly found.
a characteristic value.) In these circumstances cm may be assumed to have a value of 1.0. For other Because of its high carbon content, cast iron steel, and particularly for earlier steel not covered cannot be easily welded; specialist advice should by British Standards, the strength of the material be sought if this is contemplated. should be determined from tests, making reference to the relevant specification (if available). For such Wrought iron, like steel, is ductile. It has virtually 6.47 materials a value of cm of 1.2 should be used ; no carbon, but contains residual slag from the if only one or two specimens can be tested, a manufacturing process. Repeated working and then higher value would be appropriate, especially if the rolling orientates the slag into long threads which strength results are not closely similar. reduce the transverse strength to about two-thirds to three-quarters of the longitudinal strength. It may In situ hardness tests may be used to locate the be difficult to distinguish by eye from steel. Both are weakest material in a structure or small cores formed by rolling through mills, producing constant may be removed for laboratory testing. It may be cross-sections such as angles, tees, channels, possible to correlate the hardness values by tensile tie-rods, H-columns and I-beams. (This will often tests on samples or against standard tables, and distinguish them from cast iron, see above. Both
thus justify values of cm between 1.25 and 1.0. materials were in use during the transition period (Examples of suitable NDT test methods are given from about 1880 to 1900.) in Appendix 7.) For assessment purposes, the yield strength Where welding is to be undertaken on an existing for wrought iron is within 5% of that suggested structure, as part of repair or strengthening, it for mild steel (see Table 6.10) but mild steel has is necessary to check that the original material approximately one-and-a-half times the ultimate is of a suitable composition and condition. BS tensile strength of wrought iron. For structures 51356.60, now withdrawn, contains a useful formula which are only assumed to be stable within their for establishing the weldability of steel in terms elastic limit, a mistake in identification might not be of a ‘carbon equivalent’ value taking account of significant, but for structures which might rely on other elements present including manganese. plastic yielding, wrought iron has a much smaller This is considered in reference 6.47. It will often be margin at ultimate load. worthwhile to seek specialist advice on weldability and welding techniques, particularly for older The presence of slag threads makes fillet welding steel which may contain higher levels of sulfur and of wrought iron unreliable. Butt-welding can be phosphorus than is permitted in more recent steel successfully carried out, but specialist advice is specifications. The welding of cast and wrought iron recommended. is discussed below. The appraisal of iron and steel structures is discussed further in reference 6.47.
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6.4.4 Stainless steels Other austenitic steels have been developed with higher corrosion resistance, but the standard Stainless steels are iron-based alloys which contain ‘18-9’ and ‘17-12-2’ austenitic stainless steels at least 11% of chromium. When present at or (see Table 6.11) are the grades most likely to be above this level, the chromium promotes formation encountered in modern building applications. of a stable, passive oxide film on the surface Stainless steel grade names contain numbers by reaction with the oxygen in the atmosphere, which represent the nominal percentage of conferring corrosion resistance. The steels were chromium, nickel and molybdenum, for example, developed around 1913 and were used in the first ‘17-12-2’. Each grade also has a defined carbon instance primarily for cutlery, high-temperature content, which does not normally appear in the components such as furnace equipment and name, so the numbers may be changed slightly to engine exhaust valves, and in chemical plant. create the extra grades. ‘18-9’ and ‘18-10’ are not Thereafter stainless steels found application in substantially different in nickel content but ‘18-9’ building construction and architecture as decorative has lower carbon. An alternative form of name is cladding. Past and current uses include specialised 5CrNiMo18-9; in this case the leading ‘5’ indicates loaded members and reinforcement in building the approximate maximum carbon content (in preservation projects. Use in building construction hundredths of one percent). has extended to roofing and cladding, including curtain wall systems, shop-fittings, window The martensitic and precipitation hardening components and trims. Structural uses include grades are heat-treatable and will be found mainly stairways/balustrades, reinforcement, wall ties and as specialised components such as high-strength a range of load-bearing members such as lintels, fasteners, pins and yokes. Welding or heat masonry fixings and brick supports. Stainless steels treatment of these steels should not be attempted may also be used for critical fasteners, pins and without specialist advice. tie-rods in support systems where designs call for high-strength durable components. The duplex steels have ferritic-austenitic microstructures and combine corrosion Fuller information on the nature, characteristics, and characteristics equal to, or better than, those of structural applications of stainless steels may be the austenitic steels with a high strength level. found in references 6.61 – 6.64. Their use in construction is comparatively recent, and although it is expected that they will become 6.4.4.1 Types of stainless steels widely used, they are unlikely to be encountered in Four major classes of stainless steels may be buildings requiring appraisal. encountered, distinguished by their microstructures. All current grades of stainless steels are now listed 6.4.4.2 Identification in BS EN 100886.65, and further details are specified Stainless steels will usually have been put into in the later parts of BS EN 10088; references to service with a scale-free, generally bright finish the various superseded British Standards are given and this should be visible after cleaning. Following below for historic reasons. Definitions of steel types removal of any gross adhering matter, it is usually are given in e.g. Baddoo6.66. possible to reveal the surface with a mild non- abrasive cleaner. Testing with a pocket magnet The ferritic steels contain principally from 11% to will give a broad indication of the type of stainless 27% chromium. They are magnetic and they do steel: the greater the ferritic content, the greater the not undergo a structural phase change on normal magnetic attraction. heat treatments. This means that a coarse-grained structure can develop on welding, with a reduction The range of compositions that may be in strength and toughness in sections above about encountered and as shown in Table 6.11 means 3mm. The most widely used ferritic grade is a that chemical analysis, and possibly metallographic 17% chromium steel, 430S17 of BS 1449: Part 2: examination, is necessary for positive identification 19836.67, which may be found in a wide range of and estimation of the original specification of the thin-section components. material. Proprietary staining pastes are available to indicate in situ the presence of molybdenum, The austenitic steels contain 17-19% chromium allowing distinction between the standard and and 8-12% nickel, typified by the BS grade molybdenum-bearing stainless steels. 304S15. They cannot be heat treated, but work- harden on cold deformation. They are non- or 6.4.4.3 Mechanical properties only weakly-magnetic. They are widely used for Typical mechanical properties for selected stainless cladding and roofing and, as welded tubulars or steels meeting the superseded British Standards cold-formed sections, for structural support. In are given in Table 6.11. This shows also the bar form they are used for tie-rods, reinforcement standard designations of the steels as defined in and fasteners. Austenitic stainless steel reinforcing the relevant BS and the current BS EN 10088-26.68 bars may be encountered in concrete structures (The two new forms of designations for each type housing electronic equipment, where the magnetic of steel are shown at the foot of the entries in characteristics of conventional reinforcement are column 1 of Table 6.11.) unacceptable. The strength values shown are those quoted as The austenitic steels are readily weldable and minima in the relevant flat products standards, generally have better corrosion resistance than the except in the case of the martensitic precipitation ferritic steels. An addition of molybdenum further hardening grade. Higher strengths may however be increases corrosion resistance, and steels with achieved in the austenitic steels by cold or warm 2% molybdenum are recommended for exterior working as, for example, the high-strength stainless applications. reinforcing bars (BS 6744:19866.71).
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Table 6.11 Mechanical properties of stainless steels Steel type 0.2% proof stress Tensile strength Standard Application (MPa) (MPa) 17% chromium ferritic, 245 430 BS 1449: Part 2: Sheet, decorative trim, fittings 430S17 19836.67 (interior) [1.4016 × 6Cr17] 18% chromium, 9% nickel austenitic, 195+ 500 BS 1449 (other Cladding, trim, tubulars, 304S15 standards cover reinforcement bars and various. [1.4301 × 5CrNi18-10] bar/rod/wire) (Usually interior or within-leaf) 17% chromium, 12% nickel, 2% 250+ 510 As above As above, for external, more molybdenum austenitic, 316S31 aggressive environment [1.4401 × 5CrNiMo17-12-2] 22% chromium, 5% nickel, 3% 480 680 BS 1501: Part 3: Used since c.1985 in specialist molybdenum duplex, 318S13 19906.69 applications, e.g. process plant. [1.4462 × 2CrNiMoN22-5-3] Combination of strength and corrosion resistance will increase use 14% chromium, 5% nickel, 540-1030 850-1340 Aerospace/ Example of a heat treatable precipitation hardening (PH) defence stainless steel offering very high martensitic ‘520B’ standards such as strength with good corrosion [1.4594 × CrNiMoCuNb14-5] BS 4S1006.70 resistance for specialist fasteners, pins and yokes
6.4.4.4 S tructural design environments at elevated temperatures. However, Very limited use is made of hot-rolled sections in cracking of the lower alloy, standard austenitic stainless stainless steels; most members are either welded steels in the cold-worked, or stressed condition has tubes, cold-formed sections or welded from plate. been observed in the spaces above some indoor swimming pools. This has resulted from a combination 6.4.4.5 D urability of stainless steels of heating and ventilating conditions and liberation into In normal atmospheric conditions, stainless steels the air of aggressive products of reactions between do not suffer from a general loss of section by bather body matter and pool water disinfectants. corrosion, being protected by the self-repairing Duplex alloys, alloys containing molybdenum and nature of the surface oxide film. However, cases of annealed materials are less susceptible to this problem. localised corrosion may be encountered, where a Stainless steel in swimming pools6.72 provides detailed ‘microclimate’ has allowed build-up of aggressive guidance on this issue. substances which have attacked the passive film locally. Where these forms of attack are encountered, Stainless steels in the normal passive state are their causes should be investigated to prevent high in the electrochemical series, and note should recurrence. be taken of the guidelines in PD 6484: 19796.73, concerning bi-metallic corrosion at joints between Pitting attack takes the form of localised surface dissimilar metals. pitting. Freely exposed rain-washed panels of the standard austenitic steels show only micropitting 6.4.5 A luminium alloys to depths of a few tens of microns after 30 years’ exposure to urban atmospheres. However, pitting can 6.4.5.1 H istory of use be severe in the presence of chemical contamination. Aluminium is especially used in structures where The most common cause is concentration of halides, its low density can be exploited, i.e. in those with a especially chlorides. This type of attack may be high ratio of self-weight/imposed load such as roofs, related to the build-up of salt deposits on marine footbridges and long-span structures. structures, or misuse of aggressive cleaning materials used in building maintenance, such as hypochlorite Aluminium readily forms alloys with many elements bleaches and cement removers. such as copper, zinc, magnesium, manganese and silicon (e.g. Duralumin). Aluminium with very low alloy Crevice attack involves widespread pitting in crevices content may frequently be found in the mill-finished created by metal-to-metal contact, leaving fine cracks condition, i.e. without additional protective coatings. open to the environment. The corrosion is related to High strength alloys, e.g. Dural, in externally exposed oxygen concentration differences within and outside conditions are normally treated by anodising. This the crevice and is accelerated by the presence of process also allows a wide range of colours to be chlorides. Crevicing and pitting may be found under produced, e.g. for window and door frames. wetted, chloride-bearing poultices adhering to steel surfaces or at any faying surfaces. Design guidance to The corrosion resistance of aluminium is a frequent avoid creating crevices when specifying replacement reason for its selection as a structural material. In work is available in reference 6.62. addition, the ability of the material to be extruded into complex shapes has promoted its use in such Stress corrosion cracking can result in the fracture applications as curtain walling, pedestrian and of components without significant visual indication of vehicle parapets and glazed structures. corrosion. It is normally encountered only in process plant components, subject to either internally or A summarised history of the use of aluminium is externally applied stresses and exposed to aggressive given in Table 6.12.
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Table 6.12 History of use of aluminium Date Development Comment 1854 Deville process Precious metal use 1885 First production in UK Small scale only 1886 Heroult-Hall process ‘Large scale’ production in UK 1893 Statue of Eros, London Aluminium casting 1913 Heat treatable alloys Duralumin (Al - 4% Cu) 1920 Aircraft specifications only For aircraft use About 1930 First structural use (USA) 1946 to date Inert gas welding 1948 BS 14906.74 First comprehensive specification for general engineering 1960 Institution of Structural Engineers' report on structural use of aluminium6.75 1969 CP 1186.76 Code of Practice on structural use of aluminium 1972 BS 14706.77 (series) Wrought aluminium and aluminium alloys 1991 BS 81186.78 Limit-state code of practice on structural use of aluminium 2006 BS EN 19996.79 Limit-state Eurocode on structural use of aluminium
6.4.5.2 Identification especially in their resistance to severely polluted Chemical analysis or metallographic examinations industrial atmospheres. Deterioration is generally on their own are unlikely to be conclusive. There revealed as pitting associated with the chemical are many alloys each with different heat treatments, composition of the alloy. The higher strength alloys and specifications overlap. Unless the material can are susceptible to stress-corrosion cracking. be identified from drawings, specifications, etc., Aluminium is low in the galvanic series with the result the only safe course is to obtain a specimen large that it tends to corrode sacrificially when in contact enough for mechanical testing (generally in tension), with other metals in the presence of an electrolyte together with metallographic examination and such as ‘acid rain’. chemical analysis if necessary. There is no simple site test. Prior to the development of inert gas welding, Probably the most significant developments since structures were bolted or riveted. The presence of about 1960 have been in the weldable alloys and welding indicates that the construction is at least in welding techniques. Both non heat-treatable post-1945, and, in the UK, more probably post-1950. and heat-treatable alloys suffer a considerable reduction of strength in the heat affected zone of 6.4.5.3 M echanical properties the weld. Only the softer, fully annealed, alloys are Mechanical properties are dependent on immune to this effect, and these are rarely used in composition, previous processing, whether wrought structures. or cast, and whether heat treated or not. Data presented in 1957 are given in Table 6.13: note that 6.4.6 Bronzes and brasses aluminium does not exhibit a yield point. 6.4.6.1 H istory of use Since 1957 the available range of alloys has Simple ‘tin bronze’ (copper with 10% tin) was the increased. Although only three or four alloy types first alloy to be used by mankind for weapons, are now commonly used in structures, the range tools and decorative purposes. The ‘Bronze Age’ in of possible materials is too large to list them fact succeeded the ‘Stone Age’. Bronze founding here. Unless very low stress in the structure can probably reached its peak in the 14th and 15th be demonstrated by calculation, testing may be centuries, the high period of decorative bronze work essential. in Europe. In more recent times many variations have been developed, e.g. phosphor bronze, 6.4.5.4 Durability aluminium bronze, silicon bronze and silicon- The good performance of aluminium and its alloys aluminium bronze, and have been used for cladding in many corrosive situations is attributable to a fixings and glazing bars. ‘Manganese bronze’ (also protective, highly adherent oxide film which in known as ‘delta metal’) is in fact a high-tensile oxidising conditions is self-repairing if damaged. The brass, i.e. a copper-zinc alloy containing manganese various alloys do, however, differ quite significantly, (and sometimes lead).
Table 6.13 Mechanical properties for aluminium alloys (as at 1957) Specific gravity E* 0.1% PS Tensile strength Permissible tension (GPa) (MPa) (MPa) (MPa) (No yield point) 2.7 – 2.8 65 – 70 230 – 280 280 – 310 100 – 150 Note *For shear modulus, G, multiply by 0.38
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6.4.6.2 I dentification ‘Bronze disease’ occurs in old bronzes exposed to It is generally not difficult to identify a copper conditions of high humidity. The normal, uniform alloy – colour alone is often good enough. Specific protective patina of the bronze breaks down to identification, however, requires chemical analysis. produce bright green spots of soluble cuprous salts, unsightly but not structurally dangerous. Specialist There are many varieties; some heat treatable, some advice should be taken. not; some wrought; many cast. It is not practical to list them here. Brasses can be subject to ‘de-zincification’ in aggressive environments; this leaves a porous 6.4.6.3 M echanical properties ‘coppery’ metal. Cast brackets for cladding are likely to be aluminium bronze or silicon bronze. In older buildings a simple Copper is high in the electrochemical potential tin bronze is most likely to be found. Other bronzes series. It will therefore cause corrosion in steel, and brasses are used for fixing cladding, as bolts or zinc, aluminium, etc., if an electrolyte such as rain is as wall ties. present. For example, a galvanised corrugated iron roof was perforated along a line where the drips from The mechanical properties of tin bronzes depend a copper aerial wire fell on it. on the amount of tin present (between 5% and 10%) and on the temper. For a wrought bronze containing 6.4.7 Ropes and cables 8% tin, typical properties are given in Table 6.14. 6.4.7.1 D escription and use Structures using steel cables of spiral strand or wire Table 6.14 Typical properties of wrought bronze rope construction have now found their way well containing 8% tin into the architectural vernacular. The information and Temper Tensile Yield Young’s advice below for the designer represents practice strength stress modulus as at 2005, and may be used as a starting point for (MPa) (MPa) (GPa) assessment. Annealed 400 170 110 Wire rope cables are spun from high tensile wire. Hard 650 600 110 For structural work the cables should be strand Spring 750 725 110 typically 1 × 19 (i.e. a single wire used at the centre, surrounded by 6 single wires, further surrounded by 12 single wires) or 1 × 37, galvanised Class A, and 6.4.6.4 D urability are known as Spiral strand (see Figure 6.11). Many copper alloys including brass and bronze are susceptible to stress-corrosion cracking, especially Multi strand ropes with independent wire rope in the presence of ammonia or in ammoniacal core (IWRC) can be used where the extra stretch is atmospheres. For this reason, high-tensile brasses acceptable and the flexibility is beneficial: these are (manganese bronzes) should not be used for generally known as wire rope. Normal construction load-bearing masonry fixings. There have, however, is 6 × 19 (i.e. 6 wires to form each strand: a single been cases of large precast concrete sandwich strand at the centre, surrounded by 6 strands, further panels where the only connection of outer leaf to the surrounded by 12 strands). Hoisting ropes with fibre inner (supported) leaf is by means of manganese core are usually ungalvanised and heavily greased, bronze ties in lieu of the specified phosphor bronze. and are to be strictly avoided (sulfate reducing
Spiral strand Independent wire rope core
Avoid grease filling
Figure 6.11 Spiral strand and IWRC steel wire rope
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bacteria can feed on the fibre and grease). For Table 6.15 Typical mechanical properties for cables increased corrosion resistance, the largest diameter Spiral strand Wire rope wire should be used and the cables can be filled with zinc powder in a slow-setting polyurethane varnish Nominal diameter, D (mm) 3 to 90 10 to 180 during the spinning process. Young’s Modulus, E (GPa) 150 ± 10 90 ± 10 Ultimate tensile strength (UTS) For still greater corrosion resistance, filled strand of steel (MPa): or locked-coil strand can be used. Such strands can also be fitted with a shrunk-on polyurethane or before 1990 1200 polypropylene sleeve. after 1990 1500 to 1700 2 2 Metallic area, A (mm ) = Fa × r D /4 Stainless steel apparently offers total corrosion where Area factor, F 0.74 0.53 resistance but in some aggressive atmospheres, a or if oxygen is excluded by enclosure of the cable, Minimum breaking load, T (N) = Fs × A × UTS of steel
corrosion may occur which can be more damaging where Stranding factor, Fs 0.88 0.80 and faster developing than with carbon steel cables, possibly dangerously so.
6.4.7.2 T erminations 6.4.7.4 C orrosion and maintenance The simplest and cheapest type of termination Corrosion of galvanised cables in a covered and well is a swaged eye made round a thimble, such as ventilated situation can be considered negligible. the Talurit eye. This connects into a clevis type External cables should be galvanised and filled with connection or onto the pin of a shackle. If it is zinc paste. In this condition a life of 30 years can be required that the shackle body is threaded onto expected in normal environments. For longer life an the eye, then a ‘reeving’ thimble must be used. alloy of zinc which has 5% aluminium added can be Swaged end terminations are the neatest and most used. This is called Galfan and extends the life to streamlined fittings (see Figure 6.12). around 50 years.
Hot-poured zinc terminations (‘sockets’) still have to Maintenance consists of inspecting the cables for be used for very heavy cables, greater than 50mm in corrosion and wire breaks. Wire breaks indicate diameter. They are still occasionally used for smaller fatigue damage and when a critical number has been cables but generally swaged fittings have taken over. reached the cable has to be replaced. This is the Epoxy with steel balls as a filler can be used in place standard approach for lift and hoisting cables. The of zinc. This material offers an improvement in fatigue cables can be further protected against corrosion life at the termination. by painting with zinc-rich paint. The use of plastic sheaths is doubtful. If water and corrosive agents 6.4.7.3 M echanical properties can enter, the resulting corrosion can be worse than Typical mechanical properties are given in Table 6.15. if the cable is unprotected, and the cable cannot be inspected. Cable fittings should be arranged to Construction stretch is that inelastic stretch due allow easy replacement. Additional holes in lugs for to the wires compacting under load, and can be temporary by-pass cables are worth considering if eliminated by pre-stretching and cycling to 45% UTS. the structure is planned to have a very long life.
Talurit swaged loop Talurit swaged termination Talurit doubly swaged without thimble with thimble termination with thimble Thimble
Dee-shackle
Figure 6.12 Terminations
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6.5 Concrete 6.5.1 History of modern use
A summary history of modern use is given in Concrete today is made from cement, water, Table 6.16 below. A more detailed history is given in sand and aggregate, often also incorporating reference 6.80. admixtures. A wide range of formulation is used to enable particular strength and other properties The properties of concrete as a material are to be achieved. More generally concrete could be described below, followed by the properties and described as an artificial conglomerate formed by durability characteristics and problems of the binding together a mass of hard coarse material by different forms of construction: plain (mass) concrete, means of some kind of cementitious material. As reinforced concrete, prestressed concrete and such it is much earlier in its origins: concrete made precast concrete. with lime and pozzolans as binder was used in Roman times.
Table 6.16 History of modern use of concrete Date Development 1796 Roman cement patented by James Parker 1824 Joseph Aspdin’s patent for Portland cement 1845 (approximately) First reliable Portland cement 1854 William B. Wilkinson uses wrought iron flats as reinforcement in floor slabs 1858 Systematic testing of Portland cements for use in construction of London drainage systems 1860s onwards Wide use of filler joist floors in iron-framed buildings. Most common aggregates were coke breeze, clinker or broken brick
1875 Patent 2886 for use of CaCl2 as accelerator 1878 Thaumasite first described, in Sweden 1890 Introduction of use of blastfurnace slag 1898 First Hennebique-Mouchel ‘package’ used in Britain: Weaver warehouse building, Swansea 1908 Hennebique’s patents expire; several new ‘systems’ of special reinforcement bars and arrangements introduced 6.81 1914 High alumina cement concrete (HACC) used for in situ fortifications in France 1916 London County Council: Reinforced concrete regulations 6.82, using modular ratio design for all elements, including columns 1920s Freyssinet develops post-tensioning in France 1934 DSIR code using modular ratio, triangle stress-block for bending; sum of permissible capacities of concrete and steel for columns 1936-1940 Twin-twisted high-tensile bars, welded mesh and Hoyer pre-tensioning system, using cold-drawn high-tensile wire, introduced in Germany 1938 BS 7856.83 specifies ultimate strength for mild steel, medium- and high-tensile steel reinforcement and yield points for medium- and high- tensile steels 1948-1955 First British Standard code of practice CP 114: 19486.84. Square twisted high-tensile bars introduced in Britain; some hot-rolled smooth round high-tensile bars made by Whiteheads. (Hot-rolled ribbed round bars in use in Scandinavia.) 1950s Growth of ready mixed concrete industry in UK. Some use of HACC in situ. [HACC precast piles found ‘rotted’ after shipment as deck cargo to Malaya (Malaysia)] 1957 CP 114 revised, introducing ‘load-factor’ method with rectangular stress-block for bending; also concrete specification now based on strength as an alternative to prescribed mix proportions 1959 First BS code for prestressed concrete: CP 1156.85 1960s Large-scale use of HACC in precast (mainly floor) units Thaumasite identified as becoming problematic 1965 BS code for precast concrete: CP 1166.86 1965-69 Further revisions of CP 114: introducing statistical quality control of concrete strength; first reference to sulfate resisting Portland cement and supersulfated slag. Ribbed round reinforcement bars, both hot-rolled and cold-twisted introduced 1970s Cement manufacture modified to save fuel; this changed the chemistry and the grinding and enabled higher early strength gain of the concrete6.87 1971 ASR6.88 identified in UK (previously identified in the US, 1940) 1972 New code: CP 1106.89 introduced limit state design and partial factor format 1974 Revision to CP 110 removed HACC from the Code, after a number of collapses had occurred 1977 Calcium chloride discontinued as an accelerator, following imposition of limits on total chloride content in reinforced and prestressed concrete 1985 CP 110 superseded by BS 81106.90 1991 BRE Special Digest 1 published: Concrete in aggressive ground 6.91, revised 2005 2002 Eurocode 26.92 published (UK National Annex 2005)
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6.5.2 Identification The main causes of deterioration of Portland cement concrete are: In general terms, identification is not too difficult: –– attack by atmospheric pollutants (sulfurous and concrete is usually distinguishable from rendering nitrous oxides) by the imprint of formwork (except on floated top –– attack on buried structures by sulfate-bearing surfaces). Detection of brick-, clinker- or lightweight (including thaumasite conversion when also in aggregate and HACC requires the removal of a cold conditions and in contact with sulfates) fragment for inspection and analysis. and/or acidic ground water, destructive aggregates, e.g. clinker or ‘breeze’ (cinders), 6.5.3 Mechanical properties metallurgical slag, colliery shale, etc. (see BRE Special Digest 16.91) Listing of the properties of all the types and mixes –– alkali-silica reaction (ASR6.98: generally rare) of concrete, used during the last 30-odd years, is –– mundic (can occur in aggregates from mine- not possible here. They are described in detail in the waste containing sulfur compounds, essentially standard references such as reference 6.93. limited to Devon and Cornwall6.99) –– problems caused by de-icing salts; and Little information is obtainable about concretes made –– frost. earlier than 1909, when the London County Council (LCC) figure for working load design stress was Sulfates, whether from the atmosphere or 2.5MPa rising to 4.5MPa in 1921 and to 5.2MPa in from ground water, cause recrystallisation with 1934 (see however reference 6.94). expansion that results in crumbling of the surface. Some aggregates oxidise and expand and ASR The main types of concrete with indicative properties produces a gel around the aggregate particles are given in Table 6.17. The tensile strength of that sometimes expands and causes cracking. concrete is very low compared with its compressive cube strength and is ignored for checking the Clinker or breeze may contain unburnt coal which strength of reinforced concrete. A nominal value of in a fire could ignite and support combustion, 0.55MPa at the centroid of the reinforcement, in the rather than offering the separation that should be long-term, may be taken for curvature (and hence provided by a concrete floor or wall6.100. deflection) calculations6.95. Apart from ASR and sulfate attack (which includes thaumasite and ettringite formation) the effects of Table 6.17 Indicative properties of the main types chemical contamination are usually superficial and of concrete do not affect the structural integrity of the mass of Aggregate Density 28 day Young’s the concrete, but cracks can allow water, carrying (kg/m3) compressive modulus deleterious substances, to penetrate below the strength (GPa) surface. (MPa) In the 1950s HACC was recommended for Natural, dense foundations in sulfate-bearing ground. It suffers Gravel 2200 – 2500 14 – 70 loss of strength within a few years of casting, Crushed 2200 – 2400 24 – 35 20 – 35 due to an inherent recrystallisation process of Limestone the cement, known as conversion. Unless the Artificial, dense concrete was made with very low water/cement Crushed brick 1700 – 2200 14 – 28 ratio, the strength loss can be significant and can Artificial, lightweight be aggravated if the concrete is wetted by alkaline Foamed slag 1000 – 2000 2 – 24 7 – 20 water, e.g. leaching through Portland cement 6.101 Sintered pfa 1200 – 1800 5 – 40 screeds or toppings . Expanded clay 1200 – 2000 5 – 15 6.5.5 Plain (mass) concrete
For testing of concrete strength see Chapter 5. Plain concrete is considered a brittle material when subjected to tension. The basic cause of Note: It should be remembered that specified cube cracking in plain concrete is tension: anything strength is not the same as the in situ strength of the leading to the development of significant tensile concrete in the structure. If cores are tested in order stresses will lead to cracking. Differential to confirm strength, the ‘raw’ core crushing strengths temperatures, particulary during hydration, and must be converted to in situ strengths according to differential settlement cause bending tensile BS 60896.96 or Concrete Society technical report 116.97 stresses; freezing of water in pores and cracks before being factored to produce design strengths or results in expansion; restrained drying shrinkage permissible stresses for use in calculations. results in tensile cracks. Accidental overload must also be considered. 6.5.4 Durability Establishing the precise cause is not always Properly made and compacted Portland cement easy, and specialist advice may be necessary. concrete, per se, is generally quite durable; the The retro-fitting of post-tensioning may provide a main durability problems encountered in concrete solution. structures are caused by corrosion of reinforcement or prestressing steel.
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6.5.6 Reinforced concrete The corrosion is aggravated in the presence of chlorides, from calcium chloride (used as accelerator), 6.5.6.1 M echanical properties from de-icing salts or from a marine environment. The mechanical properties of concrete depend on Even in highly alkaline concrete, a high concentration the proportions and qualities of the ingredients. of chloride will cause corrosion. Since the chloride ions act as catalysts and are not consumed in the Reinforcement, shown on drawings, may be corrosion process, they can lead to pitting corrosion. confirmed by selective opening up in situ. In the This is a far more serious attack and is much absence of drawings, some electromagnetic and more difficult to remedy than corrosion following sub-surface radar instruments (supplemented by carbonation. artificial neural networks) are claimed to enable bar diameters as well as position and thickness of Much concrete made with clinker or breeze (a concrete cover to be ascertained; this may also be synonym for cinders) was used from the 1860s until confirmed by removal of cover in selected positions. at least the 1920s. These lumpy materials, taken from the grates of coal fires, were a cheap source of For early reinforcement no yield point was specified coarse aggregate, and found wide use in floors and in and references state only the working stresses block walling. However this material contained sulfur recommended at the time and, sometimes, compounds and other aggressive materials. When the ultimate strength. See Tables 5.1 and 5.2 in wetted – for example in a poorly-maintained roof reference 6.80. slab – the resulting acidic matter could aggravate the corrosion of embedded iron or steel sections. The Standard specifications, dating between 1940 and potential combustibility of clinker or breeze has been 1965, usually stipulated a minimum yield point, while noted in Section 6.5.4. later reinforcement standards quote ‘characteristic’ values. The properties of modern reinforcement Problems have occurred with particular forms of steels are given in BS 44496.102, BS 44616.103, concrete construction; four well-known forms are BS 44836.104 and BS EN 100806.105. described here.
When assessing the load-bearing capacity, care Hollow-tile or hollow-block flooring: In situ floor is necessary in establishing which, if any, of the construction in the early to mid-20th century often early ‘patent’ reinforcement systems was used. employed hollow clay blocks laid in rows between Special care is needed in the identification of arched ribs containing longitudinal bar reinforcement (without structures apparently of brickwork, but where the links) and connected by a topping, forming a shallow brickwork may be concealing steel or concrete. T-beam floor. The clay blocks had a castellated surface profile, which ensured bond with the concrete For so-called filler joist construction (plain concrete, and also provided a key for in situ plasterwork on often with coke-clinker aggregate, ‘reinforced’ with the soffit. To maintain this key, so-called ‘slip tiles’ – small I-sections of wrought iron or steel at about thin clay strips with the same surface profile – were 0.6 – 1.2m spacing), BS449: Part 2: 19696.106 gives placed under the ribs. If the ribs were too narrow, the design rules and stresses. concrete might not flow down past the bars to form a solid encasement to the steel. Equally the bars 6.5.6.2 D urability might be knocked off their bottom spacers during The forms of deterioration of concrete, per se, are concreting if not firmly secured, becoming in contact discussed in Sections 6.5.4 and 6.5.5. Corrosion of with the tiles. In either case there might be insufficient the steel reinforcement is however the most common concrete cover for durability or fire protection of the durability failure of concrete structures. Atmospheric steel, or inadequate bond between the two materials. carbon dioxide combines with free moisture in the Opening-up is recommended if such a floor is found, concrete pores to form carbonic acid. This reduces although inadequately-protected steel might occur in the alkalinity of the concrete which otherwise only localised areas and may be hard to find. protects the steel, permitting corrosion to occur. The reduction process, known as ‘carbonation’, proceeds Woodwool formwork: Woodwool – made from waste from the surface, the more porous the concrete the timber shavings bonded together with cement – was faster this occurs. used in thin panels as either temporary or permanent formwork. If woodwool became excessively wet, the Before 1950, concrete cover to reinforcement steel spacer blocks could sink into it, or the bars could was often specified as only 12mm and equally be displaced, with the consequences as described for often turned out to be less, as built. The depth of hollow-block construction above. carbonation is proportional to the square root of the exposure time. Older structures constructed Autoclaved aerated concrete: This material, still with poorly compacted concrete are therefore widely used, is made by introducing air into a mix of particularly susceptible to this deterioration process. fine inert mineral particles which are bound together, Similarly, in the first years after prescribed mixes typically with Portland cement. This is steam-cured were superseded by strength specification, the lower at high temperature to produce lightweight blocks strengths required by design ‘habit’ led to lower or slabs. With reinforcement the slabs can be used cement contents and higher water:cement ratios, as roof, floor or wall panels. There have been some and hence to porous concrete. Carbonation typically serviceability problems – cracking, corrosion of results in widespread and generalised corrosion, reinforcement, excessive deflection and consequent causing spalling of the cover due to the fact that rust water ingress – particularly in roof panels built before occupies some 5 to 10 times the volume of the steel the 1980s, although the material is still being used in from which it was formed. building construction with satisfactory performance6.107.
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No-fines concrete: This type of concrete (known The value of cm of 1.15 for steel given in BS 8110: generically as ‘Wimpey no-fines’) has very little Part 1: 19976.90 is based on a single tensile test by the or no fine granular parting, the coarse granular manufacturer for every 25t (40t for large diameter bars) constituent being bound by cement paste. The and has, in addition, to accommodate rolling tolerance.
resulting concrete is therefore of very low strength In 2002, cm was reduced to 1.05 for steel of Grade and highly porous. In situ cast no-fines concrete 460 in AMD 134686.112 to BS 8110 owing to the higher was used extensively in England and Scotland and strength of steel from the mills. However in 2005, to a lesser degree in Wales, initially from the inter- with the introduction of Grade 500 reinforcement in 6.102 6.113 war years until well into the late 1960s, possibly BS 4449: 2005 , cm was restored to 1.15 . even later. George Wimpey & Co Ltd developed system housing using this type of concrete from Since sampling from a primary member usually leads the mid 1940s, constructing more than 300,000 to substantial loss of structural resistance except low rise units. These buildings were up to five, very in lowly-stressed locations, it is often impractical to occasionally six, storeys high. Typically no–fines extract bar samples for testing. If samples have been concrete walls were either rendered or, to a lesser obtained from a number of representative members extent, brickwork clad, with render or hard plaster and tested and the consistency of the mechanical applied to the internal face. This therefore makes properties of the other bars has been checked using visual identification of the material difficult. Keys to non-destructive means, there may be a case for
the identification of such system housing can be reducing cm for steel to no lower than 1.05. In this found in references 6.108 and 6.109. Some typically case measured effective depths should be used in encountered structural issues can be found in the calculations: the full stress/strain curve should be reference 6.108, while reference 6.109 provides obtained from the tests and it should show adequate case studies of renovation techniques. It should ductility and reserve of strength beyond the yield point. however be noted that reference 6.108 was not an extensive study of potential defects; for example 6.5.7 Prestressed concrete it is known that occasionally, where significant structural movement has occurred in a wall, the 6.5.7.1 M echanical properties cementitious bond in the no-fines concrete can be A history of the early days of prestressing is given extensively disrupted. In such circumstances work in reference 6.114. The earliest applications used to form new openings can encounter difficulties as cold-drawn wires, stressed individually in Hoyer’s the un-bonded gravel can run from the openings, pre-tensioning system and in parallel-wire cables requiring moderately extensive repairs. with cone end anchorages in Freyssinet’s post- tensioning system. BS 2691 laid down the properties 6.5.6.3 Partial material factors for appraisal for these wires. The Lee-McCall system initially used 6.90 In BS 8110 , the factor cm for concrete, is 1.5. It cold-drawn bars. Prestressing was first applied to 6.110 includes the factor cm1 in ISO 2394 which allows any extent in the UK during the Second World War, for the difference between in situ strength and the using pre-tensioning for beams, slabs, and railway strength of the test cubes. The value of 1.5 has sleepers. Post-tensioning was adopted in the late been chosen to take account of uncertainties in the 1940s. In 1985 CIRIA published a useful guide to quality of materials and workmanship, compaction, post-tensioning systems6.115. curing, etc. The properties of modern prestressing steels are If concrete strengths are ascertained by tests on given in BS 58966.116 and BS 44866.117. cores from the actual structure supplemented by ultrasonic pulse velocity or rebound hammer 6.5.7.2 D urability measurements to assess the variability, it may be In most post-tensioned construction the tendons
reasonable to reduce the overall value of cm (but see rely for their corrosion protection on the grout comments in Appendix 10). surrounding them in their sheaths or ducts. There are several documented cases of failures due Where the failure mechanism is well understood and to inadequate grouting and many more where ductile (e.g. bending of under-reinforced beams and inadequate filling of ducts, unsuitable grout mixes
slabs) consideration could be given to reducing cm to and/or admixtures placed tendons at risk of 1.25, particularly where members are continuous and corrosion. Similarly, inadequate protection of the monolithic. Conversely, where the failure mechanism anchorages can lead to corrosion of the tendon is not well understood, e.g. shear, or where members end. Indeed, a moratorium on grouted internal may fail suddenly without warning, e.g. beams in post-tensioned tendons (that is tendons within the shear and columns in compression, greater caution concrete body itself) was imposed by the Highways
is appropriate, and cm = 1.35 may be more prudent. Agency for the design of all its new bridges from For slender columns that cannot be safely cored, 1991 – 1994, it being mandatory for such tendons
even higher values for cm than 1.5 may be required, to be replaceable, unbonded and external: the particularly if corrosion has caused loss of concrete moratorium is still in place for segmental bridges6.118. cover and hence reduced stiffness. It should be remembered that the factor (0.67) by which cube In buildings, grouted tendons and their anchorages are strength is multiplied to give the ‘design strength’ of a so difficult to inspect that, where the risk of corrosion is beam is for a simplified rectangular stress block and high, a view may be needed on the advisability of their
is to be divided further by cm before use. abandonment and possible replacement.
Recent research in Canada has confirmed the Recent methods of corrosion protection for post- vulnerability of slabs without links to brittle failure in tensioned prestressing strands and for ground or shear6.111 and the vulnerability of flat slabs designed rock anchors utilise double corrosion protection to CP 114 to punching shear. Increased factors of (DCP) systems with twin, continuous, convoluted, safety will not improve their brittleness. plastic sheaths.
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6.5.8 P recast concrete Several failures resulting from this conversion led to its withdrawal as a structural material in in situ 6.5.8.1 H istory and use and precast construction in 1974. However, many Where site conditions allow or dictate, concrete has floor units made with HACC remain in service, used the ability to be moulded into components away together with hollow pots, sometimes compositely from its final location and then to be incorporated with a structural Portland cement topping. If such into the structure. Such pre-casting has been used, units have been made under properly controlled for example, for cladding panels, where consistency factory conditions, used in dry environments and not of finish has been paramount; for building frames, been repeatedly subjected to alkaline solutions, e.g. where speed of erection on site dictates; for entire leaching from OPC screeds, their residual strength ‘system-built’ dwellings, where complete ‘flat-pack’ has usually been found adequate from investigations panels have been stitched together on site; and for carried out in the 1970s and 1980s6.97, 6.120. ‘tilt-up’ construction, where large panels have been cast face down on the ground and rolled upright. HACC is generally darker in colour that OPC concrete Pre-casting is as old as, and possibly older than, but as the colour of any concrete depends largely in situ casting. on the colour of the aggregate, colour is in itself not a sufficient guide. Current recommendations for the 6.5.8.2 A ssessment of capacity assessment of HACC may be found in reference 6.121. Where precast units are used, the reinforcement may be ascertained as for in situ work. 6.5.9 G lassfibre reinforced concrete (GRC)
In pre-tensioned units, the wires or strands extend 6.5.9.1 H istory and use to the end of the units but some may be de-bonded GRC is strictly speaking glass reinforced mortar: over part of their length. A simple count of tendons, there is no coarse aggregate. It has been in use for plus measurement of their size may therefore allow over 30 years – the Glassfibre Reinforced Concrete the amount of steel to be ascertained, if an end Association (GRCA) was formed in 1976. surface can be uncovered to a reasonable depth of penetration. Unless the tendons have been deflected In a typical section thickness of 6mm to 20mm, GRC in the mould, their position on the end face enables has been used as an alternative to precast concrete, the flexural capacity to be established. sheet metal, timber and asbestos cement, often as permanent formwork: the glass fibres replace Flooring units and early bridge beams tend not to conventional ferrous reinforcement and allow thinner have nominal shear links such as are now required sections. There are many different formulations. The one by current codes. The shear capacity of such units most commonly used in the UK6.122 has 3%-5% glass is however usually adequate, and, providing that no fibre, a sand:cement ratio of between 2 and 1, and a signs of diagonal cracking are present, the units can water:cement ratio of between 0.3 and 0.4. Admixtures be assessed according to BS 81106.90. are frequently used and some manufacturers find advantages in adding polymers. The fibres of glass are Pre-cast units are often vulnerable at their joints with required to be tolerant of the alkalinity of the cement: each other and with in situ concrete, and these joints alkali-resistant fibres are preferred to standard ‘e-glass’ may need careful inspection. Ties across these joints fibres (see also Section 6.9.3). may need to be assessed against modern standards of robustness. 6.5.9.2 P roperties GRC is a modern version of the earliest recorded 6.5.8.3 Durability composite material — clay bricks made with straw In addition to the factors common to both plain to control the propagation of cracks within the brittle and reinforced concrete (Sections 6.5.5 and 6.5.6), matrix. the following are especially important in precast construction. They arise from the commercial The GRC produced in the UK in the 1970s suffered need for rapid stripping of the moulds, which led some failures. The failure mode of GRC is fibrous some manufacturers to adopt the routine use of and ductile when new, but becomes more brittle accelerators, while others were tempted to use high after a number of years. Where failures of GRC alumina cement. cladding elements occurred they were generally to sandwich panels with a filling of cement-polystyrene Calcium chloride is a most efficient accelerator and bead mortar. The dominant effect in these cases has been used as such since about 1875. Chlorides is differential movement (thermal or moisture can however promote rapid corrosion of embedded induced) between the outer and inner skins of the steel6.119 (see Section 6.5.6.2). panel which can produce stresses in the skins if restrained. Both over-rigid fixing and panel shape High alumina cement concrete (HACC) units can give restraint of movement. Rigidity of the filling Concrete made with high alumina cement develops and water uptake after cracking were ancillary its full strength in 24 hours. At that stage the cement factors. Thickness control of the second skin to be has however hydrated to an unstable crystalline sprayed was also difficult and often inadequate and form and it subsequently ‘converts’ to a stable this aggravated the problems. Panels containing form, leaving the concrete matrix more porous and sheet polystyrene tended to delaminate at the weakened. Unless the concrete was made with a interfaces which prevented composite behaviour. water/cement ratio G 0.45 the strength will reduce Curved panels of sandwich construction were at significantly within a few years. In its converted risk of cracking as their shape prevented the bowing form it is more susceptible to chemical attack and which could relieve differential movement between reinforcement corrosion if moisture is present. In the their skins. Surface crazing and staining are absence of comprehensive testing it is prudent to cosmetic problems related to manufacture which assume all the HACC has converted. may become more visible with ageing.
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In the particular case of GRC permanent formwork 6.6.2 Types and properties panels (particularly for bridge decks), a small number of installations used double or triple layer panels in 6.6.2.1 S labs order to increase spanning ability. These were found Even where steel beams rather than composite to be problematic in that only one face was bonded beams form the primary structure, the slabs may to the concrete deck and the lower face was on have been cast on precast, often pre-tensioned, occasions susceptible to delamination. Formwork concrete planks which act as permanent formwork elements of single skin nature, flat or corrugated, and contain the main bottom reinforcement have been used successfully. transverse to the beams. The slab and planks then form a composite slab. The ultimate strength of GRC is essentially dependent on the glass content, the orientation of Profiled metal decking has been widely used the fibres, the method of manufacture (e.g. sprayed since the 1980s, acting as both permanent or vibration cast) and the degree of cure. The formwork and reinforcement. To do so it needs technical literature should be consulted. to be anchored to the concrete: since the manufacturing process tends to leave the (usually 6.5.9.3 D urability zinc-coated) surface very smooth, bond is likely to This is generally as for all concrete-based materials be problematic and anchorage will largely depend but a change of properties of GRC occurs with age on the pattern of profiling. The alkalinity of the and this is accelerated in warm, damp conditions. concrete may attack the zinc unless kept dry, and Ingress of water into the filling of sandwich panels the performance of the formwork as reinforcement is possible after cracking of the outer skin and is when exposed to fire needs careful consideration. a serious secondary problem. In practice most While these aspects are now covered by codes failures have been associated with restraint of natural for composite design such as reference 6.124, shrinkage and thermal movements of the GRC which and guidance is available6.125, early examples were may be a consequence of design or fixing. Where built before the advent of these documents. problems occurred they were often in the first two years of life when loss of ductility is not a significant 6.6.2.2 B eams factor. The magnitude of stresses induced by In old structures with riveted compound beams, restraint can be sufficient to cause problems even in some shear connection may be provided by the rivet young material. The causes can be poor formulation heads protruding into the concrete, but this would (generally inadequate fibre content) and general lack require confirmation. of quality control in manufacture, together with lack of consideration of all design and installation factors. The shear connection between steel beam and concrete slab is usually nowadays achieved by headed steel studs, welded to the top flange of the beam and subsequently enveloped by the concrete. 6.6 Steel/concrete composite construction The efficacy of the shear connection depends on the height and diameter of the studs and their heads and on the spacing of the studs along the beam. 6.6.1 Definition and history of use The spacing is often closer near the supports of the beam, where the shear forces are greater. Where Composite construction, in the general sense, is the metal decking is used, the shear studs are often use of different materials or methods of construction welded through the decking to the beam flange. If within one structural element in a way that utilises moisture is present below the decking, this can result the properties of each to the best advantage. in porous welds which are prone to brittle failure, as The term ‘composite construction’ has, within the reported by CROSS6.126. construction industry, become accepted as meaning the juxtaposition of structural steel and concrete with When appraising composite floors, it should be some shear connection between the two materials remembered that part of any observed deflection to enable composite action within the resulting could have occurred during casting if the steel was structural member. The most common examples not propped when supporting the wet concrete and today are concrete floor slabs (cast on metal its shuttering. New uses for the floor may be sensitive decking as integral and composite formwork and to vibrations and thus to live load deflections (see reinforcement) and steel beams, utilising the concrete Sections 3.7.5 and 3.7.6). slab as the compression flange; composite columns and other forms are also in use. 6.6.2.3 C olumns and frames Making columns composite, either as encased Research into composite steel/concrete construction open sections or filled structural hollow sections, began in Canada in the 1920s. In the UK, 1965 saw with or without reinforcement, not only increases the publication of CP 117: Composite construction the load-carrying capacity of the columns but also in steel and concrete: Part 1: Simply supported improves their fire resistance. beams in buildings6.123. It was not, however, until the introduction of metal decking permanent formwork, A composite frame, where the increased properties in the UK in the early 1980s, that composite floors of each individual element due to composite action became common construction for multistorey can be used to improve the properties of the frame buildings. In the UK, design of composite beams is as a whole, can show further efficiencies. Steel- covered by BS 5950: Part 3: Section 3.1, 19906.43. framed buildings with concrete cores or shear walls The design of floor slabs using metal decking is which provide overall stability could be described as covered by BS 5950: Part 4: 19946.124. behaving compositely.
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6.6.3 Appraisal of composite action Table 6.18 Key dates in the development of polymers
The appraisal of existing steel and concrete Date Development separately has been dealt with earlier, and will not be 1839 First vulcanising of natural rubber repeated here. 1916 First commercial synthetic polymer, Bakelite The appraisal of a composite element or frame must 1920s Chemical structure of polymers established begin with determining whether composite action 1933 Synthetic resin glues produced in Germany exists, and, if so, what degree of interaction is present. 1939 Rapid development in UK, especially as adhesives In a floor system the moment capacity of a typically and for electrical insulation proportioned composite beam will be between 1.6 and 2.0 times the capacity of the steel section alone. 1960s Glass reinforced polymers in common use A complete and accurate assessment can be made only if the steel and concrete strengths as well as the amounts of reinforcement and shear connection are 6.7.2 Identification determined. This information is also required to assess the fire resistance. In general terms recognition is not difficult. Precise identification needs specialist advice. Much advice is given about ‘flame testing’ but different polymer groups display similar characteristics on burning. 6.7 Polymeric materials The converse is also true – similar groups display differences in behaviour. The range is now so wide that even mechanical testing can be misleading. 6.7.1 History of use 6.7.3 Mechanical properties Polymers are nowadays widespread, especially as adhesives, paints, sealants, etc. (see Sections 6.10, Polymers cover such a wide range and are so 6.11.3 and 6.11.4). The first ‘man-made’ polymer dependent on the application that rough guidance may have been vulcanised natural rubber (Charles only is possible. For the more common polymers now Goodyear, 1839). Other key dates are given in in use Table 6.19 gives indicative properties. Table 6.18.
Table 6.19 Indicative properties of common polymers Material Density Maximum Maximum Short-term Behaviour in fire (kg/m3) coefficient temperature tensile of linear recommended for strength at expansion continuous operation 20°C (per °C) (°C) (MPa) Polythene a low density 910 20 × 10-5 80 7 – 16 Melts and burns like paraffin wax candle high density 945 14 × 10-5 104 20 – 38 Polypropylene 900 11 × 10-5 120 34 Melts and burns like paraffin wax candle Polymethyl methacrylate (‘perspex’, ‘plexiglas’) 1185 7 × 10-5 80 70 Melts and burns readily Rigid PVC (uPVC) 1395 5 × 10-5 65 55 Melts but burns only with great difficulty Post-chlorinated PVC 1300-1500 7 × 10-5 100 55 Melts and burns only with great difficulty Plasticised PVC 1200-1450 7 × 10-5 40 – 65 10 – 24 Melts, may burn, depending on plasticiser used Acetal resins 1410 8 × 10-5 80 62 Softens and burns fairly readily ABS 1060 7 × 10-5 90 40 Melts and burns readily Nylon 1120 8 × 10-5 70 – 110 50 – 80 Melts but burns only with great difficulty Polycarbonate 1200 7 × 10-5 110 55 – 70 Melts and burns with difficulty Phenolic laminates 1410 3 × 10-5 110 80 High resistance to ignition GRP laminates (see also section below) 1600 2 – 4 × 10-5 90 – 150 100 Usually burns, but relatively flame retardant grades are available Key uPVC = unplasticised polyvinyl chloride PVC = polyvinyl chloride ABS = acrylonitrile/butadiene/styrene copolymer GRP = glass reinforced plastic
Note a High density (HDPE) and low density polythene (LDPE) differ in their basic physical properties, the former being harder and more rigid than the latter. No distinction is drawn between them in terms of chemical properties or durability. The values shown are for typical materials but may vary considerably, depending on composition and method of manufacture. Both can be fusion welded, unless the polymer chains have been cross-linked during manufacture to increase strength.
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The mechanical properties of the polymers are 6.8.2 Properties significantly affected by temperature, rate and duration of loading, etc. For example, creep can In general the mechanical properties of composite be a serious problem at the maximum operating materials are, like those of timber, dependent on temperatures. The engineer should therefore be environment and age. Some reduction of properties especially cautious. The normal published ‘physical usually occurs over time. Design should have allowed data’ is of only limited use unless the service for the reduction in strength and stiffness over the conditions are known. Furthermore, plastics are service life of the structure or component resulting undergoing continuous development and data taken from thermal and creep effects. from tables only a few years old may be out of date although possibly appropriate to older structures. Types of composites are too numerous to list, but the tensile strengths (on elongation to rupture) of 6.7.4 Durability two widely used examples of glass fibre reinforced polyester resin are: chopped strand mat 20 to The most common cause of deterioration is 69MPa; woven cloth 207 to 305MPa6.127. sunlight – the energy of shortwave ultraviolet light is comparable to the bonding energy of the polymer Where randomly orientated fibres or woven fibre chains and prolonged exposure leads to breakdown cloth is used as reinforcement in sheet or plate and embrittlement. The most usual early sign is a material, the mechanical properties are isotropic change in colour. Mechanical damage can occur in two dimensions. Some materials are however in many ways. Continuous or intermittent stressing ‘pultruded’ (see Section 6.9.1), and their properties can reduce the life of many polymers. Failure may are directional. The density and length of fibres used be accelerated by sunlight (as noted above) and by precludes three-dimensionally uniform [isotropic] water vapour. Dirt, although unsightly, may act as properties. a protective film – but plant growth in the dirt is not desirable owing to the acids, etc., produced. Since the design for many applications is governed by stiffness rather than strength, the reduction in There can be significant variation in properties strength over time is often not critical. between different formulations of the same polymer. If there is a record of the type of polymer used, the The polymers in some composite materials may manufacturer’s advice should be sought. Otherwise, also be affected by ultraviolet radiation. The effects particularly if the polymer is likely to be more than are usually confined to a shallow superficial zone ten years old or appears to have aged, it should be below the surface of the component but this can be regarded as suspect. Its suitability for continued use significant in thin laminates. is best judged on the basis of tests. 6.8.3 Durability
Superficial deterioration, e.g. degradation of the 6.8 Fibre-reinforced polymer composites surface protective gel coat, pits, blisters and voids, can be assessed by visual inspection. If the degradation of the gel coat (‘chalking’) has 6.8.1 History of use progressed to the fibre reinforcement, more rapid breakdown may follow. In some cases As noted above, a composite material may be it may be necessary to assess the integrity of described as one in which two (or more) materials, the material throughout its thickness. Although each having distinctive properties, are combined in many fibre-reinforced composites are reported order to produce better properties than the sum of to be notch sensitive, they have excellent fracture the individual components. They are as old as time toughness and fatigue resistance when properly itself. Nearly all ‘natural’ materials such as bone, horn manufactured. This is in contrast to glass-reinforced and wood are composites. Plywood, chipboard, concrete. adobe, asbestos cement and even plain concrete are also composite materials. The integrity of a structural component may be assessed by comparing the stiffness as determined Current usage of the terminology tends to restrict by a simple load test with the short-term value ‘composite’ to those materials in which a set of expected of the material. If the structural integrity desirable properties (usually mechanical properties) is unimpaired any superficial damage can be made are obtained by deliberately combining two (or more) good by the application of a new surface layer. materials in predetermined ratios. The number of possible combinations is too large, so discussion here is limited to fibre-reinforced polymers (FRP). 6.9 Advanced composite materials The use of fibre-reinforced polymers in construction is relatively recent. They were first used in the 1950s and it was in the 1960s that they became widely 6.9.1 Introduction and history of use accepted for construction purposes – both functional (as cladding, as roof lights where transparent, and as Advanced composites are distinguished from the permanent formwork for columns and beams) and composites covered in Section 6.8 by the fact that decorative. The most widely used type is glass-fibre they can be the primary load-carrying elements. reinforced polyester resin, but other fibres and other They are characterised by long continuous resins are now being used, e.g. carbon and aramid filaments usually, but not always, contained within fibres6.127 and epoxy resins. a resin. Glass fibres are most commonly used for
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economy, but aramid, polyester and carbon fibres 6.9.4 Durability are also used. Various manufacturing techniques are available, including pultrusion (where fibres, Advanced composites are not susceptible to mats and rovings are drawn through a die which corrosion in the same way that metals are, which was shapes and cures the resin), filament winding one of the prime reasons for their adoption. However, (where a continuous fibre is wound round a they may suffer from other deterioration mechanisms mandrel to form a hollow shape), and various which only become evident with use. Some of the moulding techniques based on the use of woven fibres may be susceptible to attack by ultraviolet light, fibre sheets pre-impregnated with resin that or hydrolytic attack by water or certain chemicals. is subsequently cured. These techniques are It is believed that, while the alkalinity of the cement sometimes used in combination. Also included in fibre reinforced concrete will attack bare fibres of would be ropes, in either parallel-lay or low lay- glass or aramid, for composite prestressing tendons angle forms. the resin in the pultrusion or the sheath of a strand is sufficient to prevent direct contact between the fibres Advanced composites have been used since the and the cement matrix. There is the possibility of very 1970s. Stay cables for antennae assemblies are slow hydrolytic attack on naked aramids. Structures often made from polyester or aramid ropes, as being assessed should be inspected to see if there are a number of mooring systems for offshore is any evidence of such deterioration, but not by structures. GRP reinforcement has been used removing the protective layer. in concrete to eliminate corrosion, to eliminate magnetism and to allow tunnelling machines Some pultruded glass fibre handrails and standards to bore out of or into their launch or reception which had been exposed to weather for 20 years chambers. A number of soil-reinforcement were found to have become brittle and lost significant systems use polyester fibre strips behind concrete strength, as well having projecting glass fibres due to face panels to support concrete retaining panels. surface splintering. A number of small GRP structures were also built in the 1980s. There has been a significant When inspecting such structures, attention should increase in the number of applications since be paid to the joints to see if they are behaving as 1990, including some GRP structures, such as designed. Adhesive joints should be inspected for footbridges and bridge enclosures6.128. There evidence of peeling or shearing, while bolted joints are also repair or strengthening applications should be inspected for evidence of failure around where thin plates, usually of carbon fibre, are stress concentrations. The whole system should bonded onto existing structures. The plates can be inspected for evidence of internal delamination. be bonded under beams to improve flexural Ropes should be inspected for evidence of broken strength or on their sides for shear, or sheathes fibres at or near the end fittings. It should be can be wrapped round columns to improve remembered that the resins have to transmit load to containment6.129. and from the internal fibres, so particular attention should be paid to evidence of resin deterioration. 6.9.2 I dentification Structures should be inspected for evidence of fire Identification of the particular type of composite is damage. Glass and carbon fibres are resistant to not easy. Glass fibres are clear, but appear white quite high temperatures, but aramid starts to lose in bulk: aramid fibres (‘kevlarTM’) are yellow: carbon strength at about 200°C. A more likely source of fibres are black. However, the use of pigment in the strength loss is in the resin, which can be damaged resin may alter the apparent colour. Components at much lower temperatures. formed by pultrusion are of necessity prismatic or cylindrical and normally have slight undulations in the surface texture; filament wound structures normally have a helical texture showing the winding 6.10 Polymers and adhesives angle of the surface fibres, while those produced by pressure moulding normally have a smooth surface, sometimes showing mould marks. The 6.10.1 Introduction and history of use internal structure cannot be identified other than by burning off the resin. It should be remembered Adhesives have a wide range of uses in construction, that composites are not normally isotropic, their e.g. joining timber, structural repair of cracked strength being stronger in the direction of the concrete, jointing between precast concrete fibres, significantly lower in the transverse direction elements, and strengthening of structures by bonding and they can be prone to delamination through on steel or CFRP plates6.130, 6.131, 6.132. Polymer and their thickness. Resin types are addressed in epoxy resins are used both as adhesives and as Section 6.10. the matrix in FRP, and the comments in the section above apply to both uses. 6.9.3 P roperties Animal glues (‘horn and hide’ glues) were widely used The tensile strength (on elongation to rupture) from earliest times until the 19th century, and casein perpendicular to the reinforcement, for unidirectional was used from about 1930 in the United Kingdom. fibres, is some 1260MPa for high modulus carbon Modern synthetic adhesives were developed in World fibre and some 1380MPa for polyester resin War Two, initially for use in the aircraft industry. The reinforced by polyaramid fibre6.127. (See Section 6.8 development of synthetic polymer dispersions as for glass fibre reinforced polyester resin.) the basis of many paints dates from about the same period. Major usage for structural engineering dates from around 1960, e.g. the glued segmental post- tensioned columns in Coventry Cathedral6.133.
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6.10.2 Identification 6.10.3 Properties
Generic identification is not difficult. Thickness of At present there are few UK standard test methods joints offers a good guide. for use of adhesives in construction, although test methods are currently being developed by the Specific identification is difficult without chemical European Committee for Standardization (CEN). analysis. There are two main groups currently As a consequence, published data on mechanical in widespread use, epoxy resins and polyester properties may not always reflect the true picture. resins6.131 which are generally supplied as two (or three) component systems. More recently other BS 63196.134 covers ‘testing of resin compositions groups, acrylic resins and polyurethanes, have come for use in construction’ and BS 53506.135 covers into use. ‘methods of test for adhesives’. Very few test procedures provide quantitative data, either 6.10.2.1 Epoxy resins about adhesive material properties or about Epoxy resins are adhesives specially formulated adhesion properties. It is important to note that the for use in construction. Correct proportioning and compressive modulus of epoxy and polyester types careful mixing are essential. The rate of cure is of resin may be as much as an order of magnitude temperature-dependent. For many formulations lower than that of concrete. This difference must be curing stops altogether below 5°C. The rate of taken into account, for example, when designing cure approximately doubles for each 10°C rise in for a repair using these materials (see Table 6.20). temperature. For this reason different formulations Creep behaviour is considered by most authorities as may be necessary for use in different locations and at less of a problem than believed by some designers different times. because adhesives are generally used in thin bond lines. However, as evidenced by the ceiling collapse 6.10.2.2 Polyester resins at Boston I-90 tunnel with fatal results6.136, their Polyester resins are chemically much simpler than use as gap filler and adhesive for anchors without epoxy resins. Mixing and proportioning is less underreams under sustained load needs careful critical although more care is required when mixing assessment. in bulk owing to the exothermal reaction and when curing owing to high thermal gradients. There is also Resin adhesives cured in ambient conditions show shrinkage on curing. These resins should therefore a significant loss of strength at temperatures in the be limited in general to relatively small areas. range 45°C to 60°C6.132. For this reason, structural Provided that they are used with care, their main applications are limited to those where the risk of attraction in repair work is the rapid development of fire is minimal or where the structure is physically strength, e.g. 2 to 6h at 20°C as compared with up to adequate in the short term without depending on the 48h for epoxy resins, and their ability to cure at lower additional strength achieved by the use of an adhesive. temperatures. Alternatively, fire protection can be provided.
Resins also exhibit a small loss of strength (but an increase in strain to failure and fracture toughness) on absorption of small amounts of water. The effect of absorbed water is slightly to plasticise the adhesive material, and may be an advantage in locally highly strained areas in a bonded joint.
Table 6.20 Physical properties of typical products used in concrete repairs Physical property Epoxy resin grouts, Polyester resin Cementitious Polymer modified mortars and grouts, mortars and grouts, mortars and cementitious concretes concretes concretes systems Compressive strength (MPa) 55 – 110 55 – 110 20 – 70 10 – 80 Compressive modulus E-value (GPa) 0.5 – 20 2 – 10 20 – 30 1 – 30 Flexural Strength (MPa) 25 – 50 25 – 30 2 – 5 6 – 15 Tensile strength (MPa) 9 – 20 8 – 17 1.5 – 3.5 2 – 8 Elongation at break (%) 0 – 15 0 – 2 0 0 – 50 Linear coefficient of thermal expansion (/°C) 25 – 30×10-6 25 – 30×10-6 7 – 12×10-6 8 – 20×10-6 Water absoption, 7 days at 25°C (%) 0 – 1 0.2 – 0.5 5 – 15 0.1 – 0.5 Maximum service temperature under 40 – 80 50 – 80 G300 dependent upon mix load (°C) design: 30 – 100 Time to development of strength at 20°C 6 – 48 hours 1 – 2 hours 1 – 4 weeks 1 – 7 days
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6.10.4 Laminated timber (‘glulam’) 6.11.1.2 Properties Tars and bitumens are exceedingly complex The adhesives most widely used in the manufacture chemically. Chemical properties are therefore not of laminated timber are casein and various types discussed here. based on formaldehyde, e.g.: –– urea-formaldehyde All bitumens are viscoelastic, i.e. they creep under –– phenol-formaldehyde a sustained load. For example, the squeezing out of –– resorcinol-formaldehyde. a damp proof course is to be expected and is not necessarily deleterious. These adhesives are specified in BS EN301: 19926.137 which superseded BS 1204: Part 1: 19796.138, with 6.11.1.3 Durability selection based on exposure conditions. Specialist Roof and floor coverings are usually of ‘two-coat’ advice is likely to be required for their appraisal. application. Different grades of asphalt are manufactured for different conditions, i.e. roofing and 6.10.5 Durability flooring grades.
For bonded joints, environmental durability is The main problem for the engineer concerns the dependent on the nature of the polymer as well as ‘ageing’ or hardening of the material, when exposed its adhesion to the substrate surfaces6.132. Water and to the atmosphere. The mechanisms vary with the freezing of trapped moisture can disrupt adhesive composition. Weathering is a surface phenomenon bonds as well as plasticising the polymer itself; only and material below the surface is usually potential disruption of adhesive bonds is by far the unaffected unless exposed by cracking or removal most important aspect. Good surface preparation of the surface layer. Surface cracking can occur, is essential for joints of the highest strength and particularly at corner and upstand details. Roof durability, so that the use of appropriate preparation coverings tend to be sensitive to ultraviolet light procedures which do not damage the substrate and are nowadays often painted to overcome this is seen as the key to promoting long-term bond problem and to reduce solar heating. stability. Some adhesives bond to certain substrates better than others and site adhesion tests are always Bitumens and tars burn at quite low temperatures recommended. Primers are also useful, particularly – mostly by vaporisation of the lighter oily fractions. for conferring enhanced durability on metallic and When these fractions are exhausted the fire usually porous surfaces; any primers should, however, be goes out. At higher temperatures however – such as formulated for bonded joints rather than simply for may be met in a building fire – burning will continue. corrosion inhibition. Outer layers strain more than the Growth of moulds, mosses, etc. is normally inhibited inner layers: in the case of concrete repair materials, by chemicals in the material; if such growth is temperature and moisture changes may cause observed, it can be expected to be rooted in the disruption of bond unless a reasonably close match substrate by penetrating through a crack. It may of parent concrete and repair material properties has also be rooted in a build-up of debris on the roof. It been obtained. is recommended that mastic asphalt work should be regularly inspected by those knowledgeable in the subject.
6.11 Protective materials 6.11.2 Lead
6.11.2.1 History of use An assessment of the condition of protective systems Lead has been used since earliest times – it was forms an essential element of structural appraisal, but one of the first metals to be extracted from its ores. can usefully be highlighted in the brief as a separate Lead sheeting and lead piping were widely used in item, matched to the expertise of the engineer. Roman times and lead sheet roofing was common on Deterioration or breakdown of bitumens, paints, etc. mediaeval churches and later monumental buildings. may lead to ingress of aggressive substances whose Now it is mostly used for flashings, damp-proof effects on the underlying structure may be significant. courses, etc.
6.11.1 Bituminous materials Lead is now recognised as a potential health hazard and, in many applications, is being replaced by 6.11.1.1 History of use other materials. Investigating and working with lead The excellent durability and adhesion of these requires special health, safety and environmental materials have led to their use as waterproofing precautions, particularly in respect to protective agents throughout the ages. Bitumen mastics were clothing, to ingestion (washing of hands before used for sealing reservoirs in Mesopotamia in 3000 eating) and to inhalation (avoidance of fumes). BC and some parts of these constructions are still in Reference should be made, for example, to the Lead existence. Development Association (LDA) and the Control of Lead at Work Regulations, 19986.139, which requires There is some confusion of the terminology – in the suspension of further exposure at a blood level of US and many other parts of the world, bituminous 60ng/100ml and half this for women of reproductive materials are described as asphalt whereas, in the capacity6.140. UK, asphalt is a gap-graded mineral material with a high bitumen content.
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6.11.2.2 Identification and mechanical properties 6.11.3.2 Durability Lead is normally dull grey, but a fresh cut is silvery Durability, while expressed in a single word, bright. It is very soft and can be scored with a thumb nevertheless covers a large number of nail. Its density is very high. processes of paint deterioration. It depends on a combination of environmental conditions which Lead has low ultimate strength (7 – 14MPa) and include attack by sunlight, moisture and oxygen. creeps under low loads: a limit of 2.75MPa in pure The relative importance of these influences compression is advised by the LDA website. It has varies according to the location. For example, however excellent damping capacity. The melting the underside of a steel member has minimal point is low. With other metals, such as bismuth, ultraviolet attack, but maximum moisture and tin and cadmium, it is used in ‘fusible alloys’ as in perhaps salt spray attack, while the topside sprinkler systems, electrical fuses, etc. It is readily might have maximum ultraviolet exposure but welded at comparatively low temperatures. This less moisture. Frequently a cyclic process is is known in the roofing trade as ‘lead burning’ (as more aggressive than a continuous one; hence opposed to soldering, which uses a lead-tin alloy). continuous exposure to moisture may be less damaging than wetting and drying cycles. 6.11.2.3 Durability The durability of lead is generally good. In acid The geographical location is also important in solutions it is cathodic to iron, i.e. the iron is attacked determining the durability of a coating, which at a preferentially. Lead has, however, poor resistance to seaside location may be poor, while at an inland corrosion in alkaline solutions, e.g. if in contact with location might be more than adequate. Paint wet and fresh mortar. Resistance to seawater is good. failure in one location may be different from that in another. While the varying environment produces 6.11.3 Paints varying durability due to the different mechanisms of defect formation, nevertheless continuity of the 6.11.3.1 Background6.141 – 6.143 paint film is crucial for effective protection and Paint consists of a dispersion of fine particles (the this is dependent on the: pigment) in a polymeric matrix (the binder); solvents –– effectiveness of the substrate surface preparation are added to facilitate handling and/or application. –– effectiveness and conditions of application Paints, or surface coatings including powder coatings, –– suitability of the product for the requirement. can be classified in different ways; however, the simplest is based on their film forming process, which 6.11.4 Sealants can be either by solvent loss (lacquer dry) or by chemical reaction (chemical conversion). Many paints 6.11.4.1 Introduction combine the two processes unobtrusively, such as Joints that are subject to movement can be sealed decorative oil-based paints which lose solvent and with gaskets, foams, tapes or sealants. Gaskets react with oxygen to produce the final cured film. are preformed sections of synthetic or natural rubber which are often inserted into joints in a The various chemico-physical properties demanded compressed state and designed to maintain a of a surface coating are rarely met in a single pressure against the sides of a joint to maintain a product, hence paints with different characteristics seal. No adhesion is needed between the gasket are usually applied sequentially to produce a and the joint face but only very limited movement ‘laminate’ of materials to give the desired property, can be accommodated. e.g. a primer for adhesion, followed by an undercoat for opacification and smoothing of the substrate, then Expansive foams and tapes, based on synthetic a topcoat for decorative and durability properties. polymers, are also inserted into joints in a compressed state. Some adhesion to the joint faces Properties such as durability, adhesion, hardness, is required and, as with gaskets, relatively smooth elasticity are primarily determined by the nature of and even surfaces are needed. the binder, which is normally a synthetic resin. The pigment confers mechanical properties such as Sealants form a seal by bonding to both sides of sandability, appearance (gloss or matt) as well as a joint and forming a flexible link between the two colour. Durability is enhanced by the pigment’s ability substances. Adhesion is critical to ensure satisfactory to absorb the harmful actinic radiation (ultraviolet from performance, and movement is accommodated by sunlight) which causes polymer degradation; overall stretching and/or compressing. Hot-poured sealants the pigment and binder generally tend to complement are limited to horizontal joints whereas cold-curing each other. Hard, resistant, durable polymers such gunnable materials can be applied to any joint as acrylics are used in automotive topcoats, and soft, orientation. Modern gunnable sealants come either elastic polymers such as synthetic oil-based resins as single-part or two-part materials. (alkyds) and latex (emulsion) polymers are used on wood where there is a large degree of movement A sealed joint consists of the sealant primer, and in the substrate dependent on the relative humidity. back-up foam or bond breaker tape. The sealant While a hard finish is excellent on metal, it would be should be matched to the joint size, type and totally unsuitable on wood, and, vice versa, a soft frequency of movement and be compatible with elastic finish is unsuitable on metal because of its lack the substrates involved (e.g. staining is a potential of scratch and dirt impaction resistance. problem with some types of sealant on natural stone). The correct sealant profile width-to-depth The large variations in substrate protection, ratios should be used in conjunction with the appearance and application conditions for a paint minimum movement accommodation factor required: mean that specialist advice should be sought see e.g. BS 6093: 19926.144. when appraising or choosing a paint system. When choosing, cost will also feature.
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Good surface preparation and priming is essential and to permanent deformation. Plastic sealants, for promoting adhesion and long-term durability, such as non-curing oil-, butyl- and acrylic-based especially on porous substrates, and for preventing materials, are suitable only for joints subject to staining. Closed-cell polyethylene foam is the small movements and permanent compressive preferred back-up material for controlling joint depth. deformation. In the absence of loading or other Tooling, following sealant preparation, is essential to factors (e.g. damage- or vandal-resistance), low provide compaction. The whole application process modulus sealants are always preferred as they is highly operator-dependent, and there is thus a impose less strain on the substrate bond. considerable potential for defects. Two-part products generally achieve a high degree 6.11.4.2 History of use of cure in a shorter time than an equivalent one-part Building sealants were only developed in the second system. However moisture is required, and the part of the 20th century6.145, 6.146. Prior to 1950, oil- presence of oxygen and elevated temperatures may based caulks such as putty and bitumen were the also accelerate cure development. One-part sealants main materials whose usage was limited largely to rely on atmospheric moisture and oxygen to initiate filling cavities. Modern buildings are characterised cure reactions; cure begins on the surface with the by lighter, thinner and often larger external elements formation of a skin, and the material proceeds to cure than previously, with fewer natural water-shedding inward from the surface. An increase in temperature, features. The cyclic, often frequent, joint movements humidity and air flow can accelerate curing. can be accommodated only by modern synthetic Development of full cure may take anything between sealants. Polysulphide sealants were available to a week and several months depending on generic the building industry from 1957 but their high cost type, sealant mass and atmospheric conditions. restricted widespread usage. 6.11.4.4 Durability The past 50 years has seen intensive development A well designed and executed joint has a life of modern materials with properties to suit the expectancy of perhaps 25 years, a figure that is less performance requirements. In addition to a better than that expected of the structure itself. Resealing understanding of joint behaviour, there is better is therefore necessary at about 20 year intervals and appreciation of the importance of joint design, this is an inherent feature, not a defect. Badly sealed sealant choice and application6.146. Sealant joints are unfortunately common, and may have a materials now play a vital role in maintaining the much shorter useful life. weathertightness of modern building envelopes. High modulus silicone sealants are used in structural Ultraviolet light and oxygen may cause some long- glazing as the primary means of attaching glazed term surface deterioration (e.g. crazing, cracking, units in curtain walling. etc.) and prolonged exposure to, or immersion in, water will lead to adhesion failure. 6.11.4.3 Types and properties ISO 11600: 19936.147 represents the most recent source of information. Gunnable sealants are traditionally referred to as elastic, elastoplastic 6.12 Glass or plastic materials and are based on a variety of polymers and polymer blends. Future classification will be performance-based, and materials will be 6.12.1 Introduction and history designed within a performance class because of the range of properties available in each generic Glass has been used in the external walls, roofs and class. Broadly speaking, elastic sealants such as internal walls of buildings for hundreds of years. It polyethanes and silicones are suitable for joints has been said that the history of architecture is the affected by large, frequent, cyclic movement. history of transparency. Since the 17th century, and Elastoplastic sealants such as polysulphides, and particularly since the early 19th century, greenhouses, some acrylics, epoxies and silicones, are best also known as glasshouses, have made extensive suited to joints affected by slow, cyclic movement use of glass, a notable example being the Palm House at Kew Gardens, near London6.148 (Figure 6.13).
The late 20th century saw the development of new types of glass with improved thermal properties, enabling entire façades of buildings to be made of glass6.149. At the same time, interest grew in glass as a structural material, and a number of buildings may now be found in which glass plays a significant structural role6.150.
While a structural appraisal may be concerned with glass more as a structural material than as a decorative, its use in the façade of buildings, some of great antiquity, makes it useful to be aware of the European history of glass production.
A summary of the development of glass-making is Figure 6.13 Palm House, Kew given in Table 6.21.
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Table 6.21 Development of glass-making Period Country Development 10,000 BC Egypt Oldest finds 100 AD Egypt (Alexandria) Romans invented clear glass. Later developed by Syrians, Venetians, French, Germans and English 680 Britain Glass industry around Jarrow and Wearmouth 13th century Britain (Sussex) Broad Sheet: poor quality, fairly opaque. (Molten glass gathered on a blowpipe, blown to elongated balloon, ends cut off, resulting cylinder split with shears, then flattened on iron plate.) 14th century France (Rouen) Crown Glass. (Molten glass gathered on a blowpipe, blown to balloon, blowpipe removed, solid rod attached, glass spun rapidly until disc formed: outer portion beyond central knob cut into panes.) Used in windows, with some imported cylinder glass, until mid 19th century 17th century Britain (London) Crown Glass was first produced in London. Blown Plate produced by grinding and polishing Broad Sheet by hand France Polished Plate produced by casting glass onto table and grinding and polishing by hand 1670s Britain Ravenscroft invented lead glass 18th century Britain (Ravenshead) English Polished Plate using French process produced France, Germany Cylinder Blown Sheet made by similar process to Broad Sheet, except that larger cylinders produced by swinging cylinder in trench; cylinder is cut, re-heated and flattened, resulting in larger panes and much-improved surface quality 1775 Britain British Plate Glass Company founded 19th century Britain Developments in structural engineering allowed larger openings, stimulating demand for bigger and better panes. Improved Cylinder Sheet manufactured using German process, used extensively until early in 20th century 1800 Britain Steam engines used to carry out grinding and polishing of cast glass 1825 USA Glass-pressing machine patented 1851 Britain Improved Cylinder Sheet used to glaze Crystal Palace in Hyde Park 1890s Britain Pilkingtons introduced Wired Cast Glass (mesh of fine wires cast in centre). Wires weaken glass (by acting as crack inducers) but hold glass together once broken 20th century See Table 6.22
Table 6.22 Development of 20th century glass types Process Description of manufacture Use Machine Drawn Cylinder Sheet Tall cylinder of glass drawn up from bath of Used in UK to 1930 (Invented in USA, made by Pilkington molten glass, annealed, cut into smaller cylinders, in UK 1910-1930) split, flattened Flat Drawn Sheet Continuous sheet of consistent width drawn Commercial production from 1914 (from (Belgium, Fourcault, 1905) vertically from bath 1919 in UK) (Belgium, Bicheroux, c1918) Molten glass poured between two rollers: thickness more even, so grinding and polishing more economical Single and Twin Ground Polished Mechanised improvements on Polished Plate Glass method Float Glass Molten glass fed on top of bath of molten tin, Current standard method (USA, Heal, 1902, patent) drawn into annealing oven in continuous ribbon (UK, Pilkington, 1960, commercially viable process) Laminated Glass (“Triplex”) Originally celluloid layer inserted between two Safety glass: sheets held intact by central (France, Benedictus, 1910) sheets, heated and pressed. Now many different layer(s) types of inter-layers Toughened (Tempered) Glass Annealed glass heated to 620°C and quenched Only cracks that penetrate the surface by cold air: cooling core induces compression in propagate. Glass then fragments into dice. surface Nickel sulphide impurities in the tensile core can cause spontaneous shattering Heat Strengthened Glass Similar to toughened but reduced compression Breaks like annealed glass induced Insulating Glass ‘Double- (or triple-)glazing’: two layers with sealed Better thermal insulation gap filled with dried air or inert gas (e.g. argon) Glass Blocks Two halves sealed at high temperature, annealed Used in walls with mortar and perhaps with to room temperature to reduce internal pressure vertical or horizontal reinforcement and in to 0.3 bar floors supported by gratings
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6.12.2 Identification To compare glass with other, more familiar, structural materials the reader is recommended references Glass is a brittle transparent or translucent 6.150 and 6.152. non-crystalline (i.e. amorphous) solid, composed of silica, lime, soda and small amounts of magnesium, Because glass is brittle and sensitive to tensile aluminium, iron and other elements. It can be coloured stress, any method used to analyse the stresses in or mirrored and may be completely opaque because a piece of glass must take careful account of how of its location (in spandrel panels, for example), or the glass is held or supported. Unlike steel, yielding because it is bonded to an opaque material, such and redistribution of stresses does not occur, so as an interlayer in laminated glass, or because of the analysis method must accurately predict peak impurities or simply because of the build-up of dirt. It stresses, which may be very localised, at a setting may also contain an embedded wire mesh. block or around a bolt hole, for example. The design of many modern bolted glass assemblies is based Glass that is sold in the UK as safety glass (which upon tests conducted by their manufacturers, who may be toughened or laminated) should have should be consulted about the capacities and a small symbol denoting this in one corner6.151. behaviours of their systems and products. There are non-destructive ways of identifying toughened or heat-strengthened glass, which use Glass behaves perfectly elastically until the moment polarised light. One method uses an instrument it fractures. There is no creep, and glass in church known as a differential surface refractometer and windows which is thicker at the bottom than at the another uses the more accurate grazing angle top is so because the glass was made and installed surface polarimeter. that way.
6.12.3 Mechanical properties 6.12.4 Durability
Typical mechanical properties of modern glass are Glass is extremely durable, with excellent resistance given in Table 6.23. to salt water, strong acids, organic solvents, ultra- violet radiation and aerated water. It has poor Table 6.23 Typical mechanical properties of resistance to strong alkalis. It is most susceptible to annealed glass surface flaws or scratches (which may not be visible Property Value(s) to the naked eye), which grow under applied tensile stress until the glass suddenly and without warning 3 Density 2500kg/m fractures. Tensile stresses may arise for thermal or Modulus of elasticity 70GPa impact reasons as well as because of structural load. Poisson’s ratio 0.22 6.12.5 Safety Coefficient of thermal 7.7-8.8 × 10-6/°C expansion Because glass is brittle, it can break without warning. Yield strength Theoretical value is 3600MPa but Annealed and heat-strengthened glass both break behaviour is fracture-governed into jagged sharp-edged pieces which are very Tensile strength >5000MPa but behaviour is fracture- dangerous. Even toughened glass, which is sold as a governed safety glass, can be dangerous if it falls on a person from sufficient height. A 2m × 2m × 6mm pane of Tensile ductility 0 glass weighs 60kg, which can easily knock a person Compressive strength >1000MPa but complementary tensile to the ground. Toughened glass does not always stresses (or buckling) will govern completely disintegrate, and large fragments have been known to remain intact until impact. The use of Because of the growth of cracks under tensile laminated glass does not of itself ensure safety, and stress, annealed glass is weaker under long-term may actually make things worse if the glass can fall loads than under short-term ones. Typical design as a single massive piece. tensile stresses (i.e. for use with factored loads and, where appropriate, non-linear analysis) are given in The principal safety issues associated with glass are: Table 6.24. –O– verhead/sloping glazing: what are the risks if a piece breaks? –G– lass in balustrades: what are the risks if a piece Table 6.24 Typical design tensile strengths in breaks? annealed glass –G– lass used structurally: if a piece of glass breaks or Property Value is removed will progressive collapse follow? –D– amage caused by flying debris in very high winds Permanent loads 7MPa and other extreme events: what are the risks? Medium-term loads 17MPa Short-term (gust) loads 28MPa It should be noted that sometimes glass plays an unacknowledged structural role. Reference 6.148 describes a 20m tall early 19th century dome in which Heat-strengthened glass typically has a surface the glass provided in-plane bracing to the wrought compressive stress of around 30-50MPa. Toughened iron framework. In such a building, and in others such (tempered) glass typically has a surface compressive as those made popular by Buckminster Fuller, if the stress of around 70-150MPa. The effect of these decision were to be made to replace the glass, it is precompressions is to enable the glass to carry entirely possible that removal of certain patterns of larger imposed tensile stresses than would otherwise panes could render the structure unstable, leading to be the case. its collapse.
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6.13 Fabric linear metres. The fabric industry uses ‘dtex’, the mass in grams of 10000 linear metres of fibre.
Tension structures incorporating fabrics are now The amount of fibre in grams in each direction per commonplace and the earlier ones are beginning to square metre of woven cloth is defined by the number require appraisal. The information and advice below of ends/picks per cm multiplied by the appropriate represent current practice, and may be used as a yarn count in dtex /100. (‘Ends’ refer to the warp and starting point. ‘picks’ to the fill.) The strength of the cloth can be calculated using the strength/tex and appropriate 6.13.1 Yarns factors to allow for the twist and crimp. In practice, the strength is measured by strip tensile tests. Fabrics are made from woven or knitted yarns that form a two-dimensional cloth. The yarns are Tear strength is the most important property. The bundles of fibres held together by twist. Natural trapezoidal tear test loads a cut at the edge of a test fibres such as cotton, flax or wool have a relatively strip, so only the few yarns at the end of the cut are short staple length and require twist to generate the loaded. The results depend on how well the yarns friction necessary to get the fibres to work together. can slip to allow them to share the force, but are Artificial fibres are made from continuous filaments not a quantitative guide to the effect on the strength and generally have only sufficient twist to hold the of a fabric of small cuts. For this, it is necessary to fibres together as a yarn. High-twist yarns have carry out wide panel tear tests where the cut is in the lower strength but greater flexibility and are used for centre of the sample. These tests demonstrate that particular applications such as automobile tyres and the tear propagation stress falls off very quickly to hovercraft skirts where flexibility is essential. about 30% of the strip tensile strength and continues to fall to about 15% when the tear reaches 500mm 6.13.2 Weaves or so.
There is a range of different weaves used for The load-extension properties are obtained industrial fabrics. The warp consists of the yarns that from biaxial testing, and are greatly affected by run in long lengths through the weaving machine construction stretch, inelastic extension from the while the weft or fill consists of the yarns that traverse weave and crimp compaction under tension. The the width of the cloth. Plain weave used for traditional properties are also affected by crimp interchange canvas consists of single yarns woven over and which causes an effect similar to Poisson’s ratio but under each other. Panama weave is similar but with is non-linear. pairs or sometimes triple yarns. In satin weave the fill yarns go over and under three or more warp yarns 6.13.5 Ageing and degradation but the bundle of warp yarns moves by one yarn at each row. The aim is to produce a cloth with a PVC coatings start beautifully clean, but with smoother finish. In all the above weaves the yarns are time the plasticiser migrates and dirt sticks to the not straight: the amount of undulation is called crimp surface. This effect is reduced by the application and causes changes to the load-extension properties of surface lacquers which can be acrylic or various of the fabric. The American producer of coated combinations of polyvinylidenefluoride (PVDF). fabrics, Seaman, uses malimo or stitch-bonded The success of the fluoropolymer coatings relies cloth: the fill yarns are laid over the warp and stitched on the integrity of the coating being maintained together thus avoiding the effects of crimp. and its ability to adhere to the surface. If it comes off, the resulting appearance will be worse than 6.13.3 Coated fabrics with standard acrylic coating. Mould growth within the fibres also particularly affects PVC. If moisture Canvas relies on the tightness of the weave and gets into the fabric from cut edges or surface proofing agents that increase its surface tension to scratches, purple or black mould will develop. This make it waterproof. Artificial fibres do not respond spreads along the yarns, supported by nutrients in so well to this treatment, thus coatings are used. the PVC. These problems are extremely disfiguring As well as keeping water out, coatings protect but do not affect the structural properties the fibres from abrasion and ultraviolet light and significantly. provide flame resistance. Coating materials can be thermoplastics such as polyvinylchloride (PVC), With old PVC-coated fabrics, the PVC hardens with polytetrafluoroethylene (PTFE), Hypalon (a type of loss of plasticiser and the tear strength reduces chlorosulfonated polyethylene) and polyurethane because the yarns cannot bunch up at the tear tips. (PU), or rubbers such as Neoprene or ethylene PVC fabric can be repaired with hot air welding but propylene diene monomer (EPDM or Terpolymer), or this will be much less successful with old, hardened Silicone. The commonly used fabric combinations are material. The loss of plasticiser causes noticeable PVC coated polyester and PTFE coated glass. The hardening after 12 years. The oldest PVC structures glass fibres used are 3.5 microns in diameter which have been kept in place for about 22 years but at have better strength and flexibility properties. Fibres this age they are unsightly and are probably much of 6 micron diameter are sometimes used, but with less safe. caution: fibres of 9 micron diameter should never be used since they are too stiff. PTFE/glass fabrics have a better track record for durability and dirt retention; the oldest ones have 6.13.4 Properties lasted over 30 years and are still in place. Tests on 20 year old material indicated that the strip The amount of fibre in a yarn is defined by the Tex tensile strength dropped by about 20 – 25%, while number. This is the mass in grams of 1000 linear the trapezoidal tear strength dropped by about metres of fibre. Denier is the mass in grams of 9000 30 – 40%.
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6.14 References 6.18 BS 5628-1: 1992: Code of practice for the use of masonry – Part 1: Structural use of unreinforced masonry. London: BSI, 1992 {Since superseded by 2005 version} 6.1 Watt, D.S. Building pathology: principles and practice. Oxford: Blackwell, 1999 {Superseded by Watt, D.S. 6.19 Everett, A. Materials. London: Batsford, 1970 [Mitchell’s Building pathology: principles and practice. 2nd ed. Oxford: Building Construction series] Blackwell, 2007} 6.20 BS 3921: 1985: Specification for clay bricks. London: BSI, 6.2 Doran, D.K. ed. Construction materials reference book. 1985 {Since superseded by BS EN 771 and BS EN 772} Oxford: Butterworth-Heinemann, 1992 6.21 Hendry, A.W. ‘Aspects of stability and strength of stone 6.3 Blythe, A. ed. Specification 92. London: MBC Architectural masonry structures’, Proceedings of the British Masonry Press, 1992 Society, no 6, 1994, p212-217
6.4 Illston, J.M. ed. Construction materials: their nature 6.22 Hendry, A.W. ‘Assessment of stone masonry strength and behaviour. London: Spon Press, 1994 {Superseded in existing structures’, Proceedings 5th international by Illston, J.M. and Domone, P.L.J. eds. Construction conference on structural faults and repairs. Vol 3. materials: their nature and behaviour. 3rd ed. London: Spon Edinburgh: Engineering Technics Press, 1993, pp265-268 Press, 2001} 6.23 Beckmann, P. Structural aspects of building conservation. 6.5 Ashurst, J. and Ashurst, N. Practical building conservation. London: McGraw-Hill, 1994, pp103, 105 {Since Vol 1: Stone masonry. English Heritage Technical superseded by Beckmann, P. and Bowles, R. eds. Structural Handbook. Aldershot: Gower, 1988 aspects of building conservation. 2nd ed. Oxford: Elsevier Butterworth-Heinemann, 2004} 6.6 Leary, E. Building limestones of the British Isles. London: HMSO, 1983 6.24 Warland, E.G. Modern practical masonry. London: Batsford, 1929 [Reprinted by Donhead in 2006] 6.7 Leary, E. Building sandstones of the British Isles. Garston: BRE, 1986 6.25 Gibbs, P. Corrosion in masonry clad early 20th century steel framed buildings. Technical Advice Note 20. 6.8 Hart, D. The Building slates of the British Isles. BRE Report Edinburgh: Historic Scotland, 2000 195. Garston: BRE, 1991 6.26 Bussell, M., Lazarus, D. and Ross, P. Retention of masonry 6.9 Hart, D. The Building magnesian limestones of the British facades: best practice guide. CIRIA C579. London: CIRIA, Isles. BRE Report 134. Garston: BRE, 1988 2003
6.10 Natural stone directory. 16th ed. Nottingham: QMJ 6.27 CP111: 1964: Structural recommendations for loadbearing Publishing, 2008 walls. London: BSI, 1964 [With AMD March, 1966 (PD 5804) and May 1967 (PD 6156)] 6.11 Stone Federation Great Britain. Indigenous stone quarries: a specifier’s guide. London: SFGB, 1994 {Since 6.28 Department of Transport et al. Highways Agency. The superseded by Stone Federation Great Britain. Stone Assessment of highway bridges and structures. BD specifier’s guide 2009-2010. Folkestone: SFGB, 2009} 21/93. London: DTp, 1993 {Since superseded by Highways Agency. The Assessment of highway bridges 6.12 Howe, J.A. The Geology of building stones. Shaftesbury: and structures. BD 21/01. Available at http://www. Donhead, 2001 [Reprint of 1910 original] standardsforhighways.co.uk/dmrb/vol3/section4/bd2101. pdf [Accessed: 15 September 2009] 6.13 Smith, P. [Rivington’s] Notes on building construction. Part III: Materials. London: Longmans Green, 1904 [Reprinted 6.29 Melville, I.A. and Gordon, I.A. The Repair and maintenance by Donhead in 2004] of houses. London: Estates Gazette, 1973
6.14 BS 6270: 1982: Code of practice for cleaning and surface 6.30 Williams-Ellis, C. Building in cob, pisé and stabilized earth. repair of buildings – Part 1: Natural stone, cast stone and Cambridge: University Press, 1916 [Reprinted by Donhead clay and calcium silicate brick masonry. London: BSI, 1982 Publishing in 1999] {Since superseded by BS 8221-1: 2000: Code of practice for cleaning and surface repair of buildings – Part 1: 6.31 Brandon, P. The South Downs. Chichester: Philimore, 1998 Cleaning of natural stones, brick, terracotta and concrete and BS 8221-2: 2000: Code of practice for cleaning 6.32 Ross, P. Appraisal and repair of timber structures. London: and surface repair of buildings. Surface repair of natural Thomas Telford, 2002 stones, brick and terracotta. London: BSI, 2000} 6.33 Yeomans, D. The Repair of historic timber structures. 6.15 Building Research Establishment. Control of lichens, London: Thomas Telford, 2003 moulds and similar growths. BRE Digest 370. Garston: BRE, 1992 6.34 BS 5268-2: 1991: Code of practice for the structural use of timber – Part 2: Timber grades for structural use. 6.16 Building Research Establishment. Decay and conservation London: BSI, 1991 {Since superseded by 1996 and 2002 of stone masonry. BRE Digest 177. Garston: BRE, 1975 editions and then by BS EN 1995-1-1: 2004 +A1: 2008: Eurocode 5: Design of timber structures – Part 1-1: 6.17 BS EN 1996-1-1: 2005: Eurocode 6: Design of masonry General – Common rules and rules for buildings. London: structures – Part 1-1: General rules for reinforced and BSI, 2004} unreinforced masonry structures. London: BSI, 2005
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6.35 BS 4978: 1973: Specification for timber grades for 6.52 BS 3706: 1964: Mild steel for general engineering structural use. London: BSI, 1973 [Revised 1983 as purposes. London: BSI, 1964 Specification for softwood grades for structural use, in 1996 as Specification for visual strength grading of 6.53 Maddox, S.J. Fatigue strength of welded structures. 2nd ed. softwood and in 2007 as Visual strength grading of Cambridge: Abingdon Publishing, 1991 softwood – Specification] 6.54 Boyd, G.M. ed. Brittle fracture in steel structures. London: 6.36 CP 112-2: 1971: The Structural use of timber. Butterworths, 1970 Part 2: Metric units. London: BSI, 1971, British Standards Institution, London {Since superseded by BS 5268-2: 6.55 Knott, J.F. Fundamentals of fracture mechanics. London: 1984, see ref 6.34} Butterworths, 1973
6.37 Building Research Establishment. Corrosion of metals by 6.56 Standing Committee on Structural Safety. Liquid metal wood. BRE Digest 301. Garston: BRE, 1985 assisted cracking of galvanised steelwork: SCOSS Topic Paper SC/T/04/02. Available at: www.scoss.org.uk/ 6.38 London County Council (General Powers) Act 1909 publications/rtf/LMAC_Final_Version_3.pdf and update SC/06/59 www.scoss.org.uk/publications/rtf/Liquid Metal 6.39 IStructE. Report on steelwork for buildings. 2 parts. Assisted Cracking.pdf [Accessed: 1 October 2009] London: IStructE, 1927 6.57 British Constructional Steelwork Association and 6.40 Department of Scientific and Industrial Research. First Galvanizers Association. Galvanizing structural steelwork: report of the Steel Structures Research Committee. an approach to the management of liquid metal assisted London: HMSO, 1931 cracking. Publication 40/05. London: BCSA, 2005
6.41 BS 449: 1969: Specification for use of structural steel in 6.58 Bates, W. Historical structural steelwork handbook. London: building. London: BSI, 1969 BCSA, 1984
6.42 CP 113: 1948: The Structural use of steel in buildings. 6.59 BS 548: 1934: British specification for high strength London: BSI, 1948 structural steel for bridges etc and general building construction. London: BSI, 1934 6.43 BS 5950-1: 1985: Structural steelwork in building. Part 1: Code of practice for design in simple and 6.60 BS 5135: 1984: Specification process of arc welding of continuous construction: hot rolled sections. London: BSI, carbon and carbon manganese steel. London: BSI, 1984 1985 {Since superseded by 2000 version} 6.61 Burgan, B.A. Concise guide to the structural design of BS 5950-3.1: 1985: Structural steelwork in building. stainless steel. SCI Publication 123. 2nd ed. Ascot: SCI, Part 3: Design in composite construction. Section 3.1: 1993 Code of practice for design of simple and continuous composite beams. London: BSI, 1985 {Since superseded 6.62 Baddoo, N R. Design of stainless steel fixings and ancillary by 1990 version} components. SCI Publication 119. Ascot: SCI, 1993
BS 5950-4: 1982: Structural steelwork in building. Part 4: 6.63 Chung, K.F., Baddoo, N.R. and Burgan, B.A. Section Code of practice for design of floors with profiled steel property and member capacity tables for cold-formed sheeting. London: BSI, 1982 {Since superseded by 1994 stainless steel with explanatory notes in accordance with version} the ‘Concise guide to the structural design of stainless steel’. SCI Publication 152. Ascot: SCI, 1995 6.44 BS EN 10025-1: 2004: Hot rolled products of structural steels. Part 1: General technical delivery conditions. 6.64 Nickel Development Institute and the European Stainless London: BSI, 2004 Steel Development and Information Group. Design manual for structural stainless steel, 1994 {Since superseded by 6.45 BS 4360: 1968: Specification for weldable structural Euro Inox and Steel Construction Institute. Design manual for steels. London: BSI, 1968 {Since superseded by various structural stainless steel. 3rd ed. Brussels: Euro Inox, 2006} standards} 6.65 BS EN 10088-1: 2005: Stainless steels – Part 1: List of 6.46 BS 51: 1939: Wrought iron for general engineering stainless steels. London: BSI, 2005 purposes. London: BSI, 1939 6.66 Baddoo, N.R, and Gardner, L. Development of the use of 6.47 Bussell, M. Appraisal of existing iron and steel structures. stainless steel in construction. ECSC Project Final report. SCI Publication 138. Ascot: SCI, 1997 Contract no 7210 SA/842. Ascot: SCI, 2000
6.48 BS 15: 1912: British standard specification for structural 6.67 BS 1449-2: 1983: Specification for stainless and heat- steel for bridges, etc., and general building construction. resisting steel plate, sheet and strip. London: BSI, 1983 London: BSI, 1912 {First published in 1906; last published {Since superseded by various standards} in 1948} 6.68 EN 10088-2: 2005: Stainless steels – Part 2: Technical 6.49 BS 15: 1948: Structural steel. London: BSI, 1948 delivery conditions for sheet/plate and strip of corrosion resisting steels for general purposes. London: BSI, 2005 6.50 BS 968: 1962: Specification for high yield stress (welding quality) structural steel. London: BSI, 1962 6.69 BS 1501-3: 1990: Steels for pressure purposes. Specification for corrosion – and heat-resisting steels: 6.51 BS 2762: 1956: Notch ductile steel for general structural plates, sheet and strip. London: BSI, 1990 {Since purposes. London: BSI, 1956 superseded by various standards}
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6.70 BS 4S 100: 1975: Procedure for inspection and testing 6.83 BS 785-1: 1967: Specification for hot rolled bars and hard of wrought steels (other than sheet, strip and tubes. drawn wire for the reinforcement of concrete. Part 1: hot London: BSI, 1975 {Since superseded by BS 5S 100: rolled steel bars. London: BSI, 1967 1993: Procedure for inspection, testing and acceptance of wrought steels (other than plate, sheet, strip and tube). 6.84 CP 114: 1948: The structural use of normal reinforced London: BSI, 1993} concrete in buildings. London: BSI, 1948 [Revised 1957; metric version 1969] 6.71 BS 6744: 1986, Specification for austenitic stainless bars for the reinforcement of concrete, revised 2001, Stainless 6.85 CP 115: 1959: The structural use of prestressed concrete Steel Bars for the Reinforcement of and Use in Concrete, in buildings. London: BSI, 1959 [Metric version 1969] BSI, London 6.86 CP 116: 1965: The structural use of precast concrete. 6.72 Nickel Development Institute. Stainless steel in swimming London: BSI, 1965 [Metric version 1969] pools. NiDI Publication 12010. Birmingham: NiDI, 1995 6.87 Concrete Society. Changes in the properties of ordinary 6.73 PD 6484: 1979: Commentary on corrosion at bimetallic Portland cement and their effects on concrete. Concrete contacts and its alleviation. London: BSI, 1979 Society Technical Report 29. London: Concrete Society, 1987 6.74 BS 1490: 1988: Specification for aluminium and aluminium alloy ingots for general engineering purposes. 6.88 Doran, D.K. Alkali Silica Reaction in Concrete. Available at: London: BSI, 1988 {Since superseded by various http://www.istructe.org/technical/db/280.asp [Accessed: standards} 18 September 2009]
6.75 Institution of Structural Engineers. Report on the structural 6.89 CP 110-1: 1972: Code of practice for the structural use use of aluminium. London: IStructE, 1962 of concrete. Part 1: Design, materials and workmanship. London: BSI, 1972 6.76 CP 118: 1969: The structural use of aluminium. London: BSI, 1969 6.90 BS 8110-1: 1985: Structural use of concrete. Part 1: Code of practice for design and construction. London: BSI, 1985 6.77 BS 1470: 1987: Specifications for wrought aluminium [Revised in 1997] and aluminium alloys for general engineering purposes – Plate, sheet and strip. London: BSI, 1987; BS 1471: 1972: 6.91 Building Research Establishment. Concrete in aggressive Specifications for wrought aluminium and aluminium alloys ground. BRE Special Digest 1. 4 parts. London: CRC, 2001 for general engineering purposes – Drawn tube. London: [Revised 2003 and 2005] BSI, 1972; BS 1472: 1972: Specifications for wrought aluminium and aluminium alloys for general engineering 6.92 BS EN 1992: Eurocode 2: Design of concrete structures purposes – Forging stocks and forgings. London: BSI, [4 parts] 1972; BS 1473: 1972: Specifications for wrought aluminium and aluminium alloys for general engineering 6.93 Neville, A.M. The Properties of concrete. 3rd ed. Harlow: purposes – Rivet, bolt and screw stock. London: BSI, Longman, 1981 {Since superseded by Neville, A.M. The 1972; BS 1474: 1987: Specifications for wrought Properties of concrete. 4th ed. Harlow: Longman, 1995} aluminium and aluminium alloys for general engineering purposes – Bars, extruded round tubes and sections. 6.94 Sutcliffe, G.L. Concrete, its nature and use. 2nd ed. London: BSI, 1987; BS 1475: 1972: Specifications for London: Crosby Lockwood, 1905 wrought aluminium and aluminium alloys for general engineering purposes – Wire. London: BSI, 1972 {All since 6.95 BS 8110-2: 1985: Structural use of concrete. Part 2: Code superseded by various standards} of practice for special circumstances. London: BSI, 1985
6.78 BS 8118-1: 1991: Structural use of aluminium – Part 1: 6.96 BS 6089: 1981: Guide to assessment of concrete strength Code of practice for design. London: BSI, 1991 in existing structures. London: BSI, 1981
6.79 BS EN 1999: Eurocode 9: Design of aluminium structures 6.97 Concrete Society. Concrete core testing for strength. [5 parts] Concrete Society Technical Report 11. London: Concrete Society, 1987 6.80 Sutherland, [R].J.[M]., Chrimes, M. and Humm, D. Historic Concrete: background to appraisal. London: Thomas 6.98 Institution of Structural Engineers. Structural effects of Telford, 2001. {See also Concrete Society. Historical alkali-silica reaction. London: IStructE, 1992 approaches to the design of concrete buildings and structures. Concrete Society Technical Report TR 70. 6.99 Royal Institution of Chartered Surveyors. The mundic Camberley: Concrete Society, 2009} problem: a guidance note. Recommended sampling, examination and classification procedure for suspect 6.81 Jones, B.E. ed. Cassell’s reinforced concrete. 2nd ed. concrete building materials in Cornwall and parts of Devon. London: Waverley Book Co, 1920 2nd ed. London: RICS Books, 1997
6.82 London County Council. Regulations made under the 6.100 Lea, F.M. Investigations on breeze and clinker aggregates. provisions of section 23 of the London County Council DSIR Building Research Technical Paper 7. London: HMSO, (General Powers) Act, 1909, with respect to the 1929 construction of buildings wholly or partly of reinforced concrete. London: LCC, 1916 6.101 Bate, S.C.C. High alumina cement concrete in existing building superstructures. London: HMSO, 1984
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6.102 BS 4449: 1969: Specification for carbon steel bars for the 6.120 Building Regulations Advisory Committee. Report of Sub- reinforcement of concrete. London: BSI, 1969 [Revised Committee P (High Alumina Cement Concrete). London: 1978, 1988, 1997 and 2005] Department of the Environment, 1975 [The Stone Report]
6.103 BS 4461: 1969: Specification for cold worked steel bars 6.121 Dunster, A. HAC concrete in the UK: assessment, durability for the reinforcement of concrete. London: BSI, 1969 management, maintenance and refurbishment. BRE [Revised 1978] Special Digest 3. London: BRE Bookshop, 2002
6.104 BS 4483: 1969: Specification for steel fabric for the 6.122 Moore, J.F.A. The Use of glass-reinforced cement in reinforcement of concrete. London: BSI, 1969 [Revised cladding panels. BRE Report BR49. Watford: BRE, 1984 1985, 1998 and 2005] 6.123 CP 117-1: 1965: Composite construction in steel and 6.105 BS EN 10080: 2005: Steel for the reinforcement of concrete – Part 1: Simply supported beams in building. concrete – Weldable reinforcing steel – General. London: London: BSI, 1965 {Since superseded by BS 5950-3.1: BSI, 2005 1990: Structural use of steelwork in building – Part 3: Design in composite construction – Section 3.1: Code of 6.106 BS 449-2: 1969: Specification for use of structural steel in practice for design of simple and continuous composite building. Part 2: Metric units. London: BSI, 1969 beams. London: BSI, 1990}
6.107 Matthews, S. et al. Reinforced autoclaved aerated concrete 6.124 BS 5950-4: 1994: Structural use of steelwork in building. panels: review of behaviour, and developments in assessment Code of practice for design of composite slabs with and design. BRE Report 445. London: CRC, 2002 profiled steel sheeting. London: BSI, 1994
6.108 Reeves, B.R. and Martin, G.R. The Structural condition of 6.125 SteelBiz Shop. Available at: http://shop.steelbiz.org Wimpey no-fines low-rise dwellings. BRE Report BR153. [Accessed: 18 January 2010] Garston: BRE, 1989 6.126 CROSS – Confidential Reporting on Structural Safety 6.109 Williams, A.W. and Ward, G.C. The Renovation of no-fines Newsletter, no 2, April 2006. Available at: http://www. housing: a guide to the performance and rehabilitation scoss.org.uk/cross/pdf/CROSS_NewsLetter_2A.html of loadbearing no-fines concrete dwellings built using [Accessed: 16 September 2009] the Wimpey and Scottish Special Housing Association systems. BRE Report BR191. Garston: BRE, 1991 6.127 McArthur, H. and Spalding, D. Engineering materials science: properties, uses, degradation, remediation. 6.110 ISO 2394: 1998: General principles on reliability for Chichester: Horwood Publishing, Chichester, 2003 structures. Geneva: ISO, 1998 6.128 Shanmuganathan, S. ‘Fibre reinforced polymer composite 6.111 Vecchio, F.J. and Collins, M.P. ‘The Modified compression materials for civil and building structures – review of the field theory for reinforced concrete elements subjected to state-of-the-art’. The Structural Engineer, 81(13), 1 July shear’, ACI Journal, 83(2), 1986, pp219-231 2003, pp26-33
6.112 BS 8110: 1997: Structural use of concrete – Part 1: Code 6.129 Clarke, J. and Hutchinson A.R. eds. Strengthening concrete of practice for design and construction. London: BSI, 1997. structures using fibre composite materials: acceptance, Amendment AMD 13468: May 27, 2002 inspection and monitoring. Concrete Society Technical Report 57. Crowthorne: Concrete Society, 2003 6.113 BS 8110: 1997: Structural use of concrete – Part 1: Code of practice for design and construction. London: BSI, 1997. 6.130 Mays, G.C. ‘Structural applications of adhesives in civil Amendment AMD 16016: November 30, 2005 engineering’. Materials Science and Technology, 1(11), Nov 1985, pp937-943 6.114 Walley, F. ‘The Childhood of prestressing: an introduction’. The Structural Engineer, 62A(1), January 1984, pp5-10 6.131 Shaw, J.D.N. ‘Adhesives in the construction industry: materials and case studies’. Construction and Building 6.115 Andrew, A.E. and Turner, F.H. Post-tensioning systems Materials, 4(2), June 1990, pp92-97 for concrete in the UK: 1940-1985. CIRIA Report 106. London: CIRIA, 1985 6.132 Mays, G.C. and Hutchinson, A.R. Adhesives in civil engineering. Cambridge: University Press, 1992 6.116 BS 5896: 1980: Specification for high tensile steel wire and strand for the prestressing of concrete. London: BSI, 6.133 ‘The New cathedral at Coventry’. Concrete and 1980 Constructional Engineering, 57(7), July 1962. pp275-281
6.117 BS 4486: 1980: Specification for hot rolled and hot 6.134 BS 6319: Testing of resin and polymer/cement rolled and processed high tensile alloy steel bars for the compositions for use in construction [11 parts] prestressing of concrete. London: BSI, 1980 6.135 BS 5350: Methods of tests for adhesives [Several parts] 6.118 Highways Agency. Design for durability. BD 57/01. Available at: http://www.standardsforhighways.co.uk/ 6.136 Angelo, W.J. ‘Collapse report stirs debate on epoxies’. dmrb/vol1/section3/bd5701.pdf. [Accessed: 18 September Engineering News Record, 23 July 2007, pp10-12 2009] 6.137 BS EN 301: 2006: Adhesives, phenolic and aminoplastic, 6.119 Building Research Establishment. The Structural condition for load-bearing timber structures – Classification and of Intergrid buildings of prestressed concrete. London: performance requirements. London: BSI, 2006 HMSO, 1978, Appendix B
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6.138 BS 1204: 1979: Synthetic resin adhesives (phenolic and 6.15 Bibliography aminosplastic) for wood – Part 1: Specification for gap- filling adhesives. London: BSI, 1979 {Since superseded by 2003 version, now withdrawn} 6.15.1 Building Construction
6.139 The Control of Lead at Work Regulations 1998. London: Brunskill, R.W. Traditional buildings of Britain: an introduction to The Stationery Office, 1998 (SI 1998/543) {Since vernacular architecture. 2nd ed. London: Victor Gollancz, 1992 superseded by The Control of Lead at Work Regulations {Since superseded by Brunskill, R.W. Traditional buildings of 2002. [s.l.]: The Stationery Office, 2002 (SI 2002/2676)} Britain: an introduction to vernacular architecture and its revival. 3rd ed. London: Cassell, 2004} 6.140 Health and Safety Executive. Exposure to lead. Available at: http://www.hse.gov.uk/statistics/causdis/lead/. [Accessed: Clifton-Taylor, A. The Pattern of English building. 4th ed. London: 18 September 2009] Faber, 1987
6.141 Turner, G.P.A. Introduction to paint chemistry. 3rd ed. Concrete Society. Non-structural cracks in concrete. Concrete London: Chapman & Hall, 1983 {Since superseded Society Technical Report 22. 3rd ed. Slough: Concrete Society, 1992 by Bentley, J. and Turner, G.P.A. Introduction to paint chemistry. 4th ed. London: Chapman & Hall, 1998} Innocent, C.F. The Development of English building construction. Shaftesbury: Donhead, 1999 [Reprint of 1916 original] 6.142 Lambourne, R. and Strivens, T.A. eds. Paint and surface coatings: theory and practice. 2nd ed. Cambridge: Jackson, N. and Dhir, R.K, eds. Civil engineering materials. 4th ed. Woodhead Publishing, 1999 London: MacMillan, 1988, pp16-18
6.143 Philbin, T. Painting, staining, and finishing. New York: Jaggard, W.R. and Drury, F.E. Architectural building construction. McGraw-Hill, 1997 3 vols. Cambridge: University Press [Various editions 1916-1946]
6.144 BS 6093: 1981: Code of practice for the design of joints McKay, W.B. McKay’s building construction. Shaftesbury: and jointing in building construction. London: BSI, 1981 Donhead, 2005 [reprint of three volumes published 1938-44] [Revised in 1993 and 2006] Melville, I.A. and Gordon, I.A. Inspections and reports on 6.145 Panek, J.R. and Cook, J.P. Construction sealants and dwellings: assessing age. London: Estates Gazette, 2004 adhesives. 2nd ed. New York: John Wiley, 1984 {Since superseded by Panek, J.R. and Cook, J.P. Construction Melville, I.A. and Gordon, I.A. Inspections and reports on sealants and adhesives. 3rd ed. New York: John Wiley, dwellings: inspecting. London: Estates Gazette, 2005 1992} Melville, I.A. and Gordon, I.A. Inspections and reports on 6.146 Woolman, R. and Hutchinson, A.R. eds. Resealing dwellings: reporting for buyers. London: Estates Gazette, 2007 of buildings: a guide to good practice. Oxford: Butterworth-Heinemann, 1994 Melville, I.A. and Gordon, I.A. Inspections and reports on dwellings: reporting for sellers. London: Estates Gazette, 2009 6.147 BS EN ISO 11600: 2003: Building construction – Jointing products – classification and requirements for sealants. Melville, I.A. and Gordon, I.A. The Repair and maintenance of London: BSI, 2003 houses. 2nd ed. London: Estate Gazette, 1997
6.148 Woods, M. and Warren, A.S. Glass houses: a history of Melville, I.A. and Gordon, I.A. Structural surveys of dwelling greenhouses, orangeries and conservatories. London: houses: including structural surveys of flats and new dwellings. Aurum Press, 1988 London: Estates Gazette, 1992
6.149 Compagno, A. Intelligent glass façades: materials, practice, Mitchell, C.F. Building construction. London: B.T. Batsford [various design. Basel: Birkhäuser, 1996 {Since superseded by editions since 1888] Compagno, A. Intelligent glass façades: materials, practice, design. 5th ed. Basel: Birkhäuser, 2002} Naismith, R.J. Buildings of the Scottish countryside. London: Gollancz, 1985 6.150 Institution of Structural Engineers. Structural use of glass in buildings. London: IStructE, 1999 Smith, P. Rivington’s building construction. Shaftesbury: Donhead, 2004 [Reprint of 1904 edition, excluding volume 4] 6.151 Centre for Window and Cladding Technology. Curtain wall installation handbook. Chapter 7: Glass. Available at: Strike, J. Construction into design: the influence of new materials http://www.cwct.co.uk/construction/installation%20guide/ of construction on architectural design 1690-1990. Oxford: INST-7.pdf [Accessed: 18 September 2009] Butterworth, 1991
6.152 Ashby, M.F. Materials selection in mechanical design. 6.15.2 Particular structural forms Oxford: Pergamon Press, 1987 {Since superseded by Ashby, M.F. Materials selection in mechanical design. Bray, R.N. and Tatham, P.F.B. Old waterfront walls: management, 3rd ed. Oxford: Elsevier Butterworth-Heinemann, 2005} maintenance and rehabilitation. London: E. & F.N. Spon, 1992
BRE. The structural adequacy and durability of large panel systems dwellings. BRE Report BR107. Garston: BRE, 1987
CIRIA. Drystone retaining walls and their modifications: condition appraisal and remedial treatment. CIRIA C676. London: CIRIA, 2009
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CIRIA. Iron and steel bridges: condition appraisal and remedial Pullar-Strecker, P. Concrete reinforcement corrosion: from treatment. CIRIA C664. London: CIRIA, 2006 assessment to repair decisions. ICE Design and Practice Guide. London: Thomas Telford, 2002 CIRIA. Masonry arch bridges: condition appraisal and remedial treatment. CIRIA C656. London: CIRIA, 2008 Sutherland, [R]J.[M]., Humm, D., and Chrimes, M. eds. Historic concrete: background to appraisal. London: Thomas Telford, 2001 CIRIA. Tunnels: condition appraisal and remedial treatment. London: CIRIA, 2010 [Due for publication in 2010] True, G. GRC production and uses. London: Palladium, 1986
Heyman, J. The Masonry arch. Chichester: Ellis Horwood, 1982. 6.15.4 Masonry
Heyman, J. The Stone skeleton: structural engineering of masonry Ashurst, J. and Dimes, F.G. Stone in building. London: Stone architecture. Cambridge: University Press, 1995. Federation, 1984
Institution of Structural Engineers. Aspects of cladding. London: Brick Development Association. Spot the difference. Available at: SETO, 1995 http://www.azobuild.com/downloads/spot_the_difference_BDA. pdf [Accessed: 19 January 2010] Page, J. ed. Masonry arch bridges: state-of-the-art review. Transport Research Laboratory, 1993. BS 5390: 1976: Code of practice for stone masonry. London: BSI, 1976 {Since superseded by BS 5268-3: 2005: Code of practice 6.15.3 Concrete for the use of masonry – Part 3: Materials and components, design and workmanship. London: BSI, 2005} BS 915-2: 1972: Specification for high alumina cement. Part 2: Metric units. London: BSI, 1972 {Since superseded by BS 5628-3: 2001: Structural use of masonry. Part 3: Materials BS EN 14647: 2005: Calcium aluminate cement – Composition, and components, design and workmanship. London: BSI, 2001 specifications and conformity criteria. London: BSI, 2005 and BS 4550-6: 1978: Methods of testing cement – Part 6: Standard BS 8298: 1994: Code of practice for design and installation of sand for mortar cubes. London: BSI, 1978} natural stone cladding and lining. London: BSI, 1994
Building Research Establishment. Properties of GRC: 10 year Brunskill, R.W. Brick building in Britain. London: Victor Gollancz, results. BRE Information Paper IP36/79. Garston: BRE, 1979 1990 {Since superseded by Brunskill, R.W. Brick and clay building in Britain. 2nd ed. New Haven: Yale University Press, 2009} Building Research Establishment. The Structural conditions of prefabricated reinforced concrete houses designed before 1960. Bussell, M., Lazarus, D. and Ross, P. Retention of masonry BRE Information Paper IP 10/84. Garston: BRE, 1984 facades: best practice guide. CIRIA C579. London: CIRIA, 2003
Currie, R. J. and Crammond, N. J. ‘Assessment of existing HAC Clifton-Taylor, A. and Ireson, A.S. English stone building. London: concrete construction in the UK’. ICE Proceedings, Structures and Gollancz, 1994. Buildings, 104(1), February 1994, pp83-92 [Reprinted as BRE Digest 392, now superseded by BRE Special Digest 3 (ref 6.116)] Cowper, A.D. Lime and lime mortars. Shaftesbury: Donhead, 1998 [Reprint of 1927 Building Research Station report] de Courcy, J.W. ‘The Emergence of reinforced concrete 1750-1910’. The Structural Engineer, 65A(9), September 1987, CP 121-1: 1973: Code of practice for walling. Part 1: Brick and pp313-322 block masonry. London: BSI, 1973 [Withdrawn; now replaced by BS 5628-3: 1985] The Durability of steel in concrete. 3 parts. BRE Digests 263, 264, 265. Garston: BRE, 1982 CP 122: 1952: Walls and partitions of blocks and slabs. London: BSI, 1952 [Withdrawn] Hamilton, S.B. A Note on the history of reinforced concrete in buildings. National Buildings Studies Special Report 24. London: Curtin, W.G. et al. Structural masonry designers’ manual. London: HMSO, 1956 Granada, 1982 {Since superseded by Curtin, W.G. et al. Structural masonry designers’ manual. 3rd ed. Oxford: Blackwell, 2006} Intelligent monitoring of concrete structures [News item]. Available at: http://www.buildingtalk.com/news/cir/cir300.html [Accessed: Davey, N., and Thomas, F.G. ‘The Structural uses of brickwork’. 21 September 2009] ICE Engineering Division Papers, 8, 1950
Lancaster, R.I. ‘Current Practice Sheet 64: Steel reinforcement – Hammett, M. ‘The repair and maintenance of brickwork’. production and practice’. Concrete, 15(5), May 1981, pp33-35 Structural Survey, 9(2), 1990, pp153-160
Macdonald, S. ed. Concrete: building pathology. Oxford: Blackwell Handisyde, C.C. and Haseltine, B.A. Bricks and brickwork. Science, 2003 Windsor: Brick Development Association, 1975
Matthews, S., Narayanan, N., and Goodier, A. Reinforced Hendry, A.W. Structural masonry. Basingstoke: Macmillan, 1990 autoclaved aerated concrete panels: review of behaviour and {Since superseded by Hendry, A.W. Structural masonry. 2nd ed. developments in assessment and design. BRE Report BR445. Basingstoke: Macmillan, 1998} London: CRC, 2002 Howe, J.A. The geology of building stones. Shaftesbury: Donhead, Proctor, B.A. ‘Past development and future prospect for grc 2001 [reprint of 1910 original] materials’. Proceedings of the 3rd International Congress on GRC, Paris, 1981. Gerrards Cross: Glass Fibre Reinforced Cement Pearson, G.T. Conservation of clay and chalk buildings. Association, 1981, pp50-67 Shaftesbury: Donhead, 1992
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Roberts, J.J. et al. Concrete masonry designer’s handbook. Latham, B. Timber: its development and distribution. London: Leatherhead: Eyre & Spottiswoode, 1983 {Since superseded Harrap, 1957 by Roberts, J.J. et al. Concrete masonry designer’s handbook. 2nd ed. London: Spon, 2001} Ozelton, E.C. and Baird, J.A. Timber designers’ manual. London: Crosby Lockwood, 1976 {Since superseded by Ozelton, E.C. and Schaffer, R.J. The Weathering of natural building stones. Shaftesbury: Baird, J.A. Timber designers’ manual. 3rd ed. Oxford: Blackwell Donhead, 2004 [Reprint of 1932 Building Research Station report] Science, 2006}
Sowdon A.M. ed. The Maintenance of brick and stone masonry Ridout, B. Timber decay in buildings: the conservation approach structures. London: E. & F.N. Spon, 1990 to treatment. London: E. & F. N. Spon, 2000
Stone Federation Great Britain. Stone Federation handbook Ross, P. Appraisal and repair of timber structures. London: and directory of members. London: SFGB, 2001 {Since ceased Thomas Telford, 2002 publication} Yeomans, D. The Repair of historic timber structures. London: Stratton, M. The Terracotta revival. London: Gollancz, 1993. Thomas Telford, 2003
6.15.5 Metals 6.15.7 Glass
Aluminium Federation. The Properties of aluminium and its alloys. Behling, S. and Behling, S. eds. Glass: Structure and technology 8th ed. West Bromwich: ALFED, 1983 {Since superseded by in architecture. London: Prestel, 2000 Aluminium Federation. The Properties of aluminium and its alloys. West Bromwich: ALFED, 2009} Brown, S. ‘Stained glass’. in Kemp, M. ed. The Oxford history of western art. Oxford: University Press, 2000, pp108-23 Aluminium Stockholders Association. About aluminium, [s.l.]: Aluminium Stockholders Association, 1981 [New edition due Centre for Window and Cladding Technology. Glass in building 2010] conference series
Bates, W. Historical structural steelwork handbook. London: BCSA, Institution of Structural Engineers. Structural use of glass in 1984 buildings. London: IStructE, 1999
Bussell, M. Appraisal of existing iron and steel structures. SCI Nijsse, R. Glass in structures: elements, concepts, designs. Basel: Publication 138. Ascot: SCI, 1997 Birkhäuser, 2003
CIRIA. Iron and steel bridges: condition appraisal and remedial Schittich, C. et al. Glass construction manual. 2nd ed. Basl: treatment. CIRIA C664. London: CIRIA, 2006 Birkhauser, 2007
Elliot, D.A and Tupholme, S.M. An Introduction to steel selection. Sedlacek, G., Blank, K. and Gusgen, J. ‘Glass in structural Part 2: stainless steels. Oxford: University Press, 1981 engineering’. The Structural Engineer, 73(2), 17 January 1995, pp17-22. Gibbs, P. Corrosion in masonry clad early 20th century steel framed buildings. Technical Advice Note 20. Edinburgh: Historic 6.15.8 Plastics and polymers Scotland, 2000 Bank, L.C. Composites for construction: structural design with Hoffman, W. Lead and lead alloys: properties and technology. FRP materials. Hoboken, NJ: Wiley, 2007 Berlin: Springer-Verlag, 1970 [English translation of 2nd revised German edition] Building Research Establishment. Reinforced plastics cladding panels. BRE Digest 161. London: HMSO, 1974 King, F. Aluminium and its alloys. Chichester: Ellis Horwood, 1987 Building Research Station. Applications and durability of plastics. Mann, A.P. ‘The structural use of stainless steel’. The Structural Digest 69. London: HMSO, 1966 Engineer, 71(4), 16 February 1993, pp60-69 Clarke, J.L. ed. Structural design of polymer composites: Porter, S. et al. ‘The Behaviour of cast iron in fire: a review of EUROCOMP design code and handbook. London: Spon, 1996 previous studies and guidance on achieving a balance between improvements in fire protection and the conservation of historic Feldman, D. Polymeric building materials. London: Elsevier structures’. English Heritage Research Transactions, 1: Metals, Applied Science, 1989 1998, pp11-20 Hollaway, L. Glass reinforced plastics in construction: engineering Swailes, T. and Marsh, J. Structural appraisal of iron-framed textile aspects. Glasgow: Surrey University Press, 1978 mills. London: Thomas Telford, 1998 Hollaway, L. ed. Polymers and polymer composites in Walker, B. et al. Corrugated iron and other ferrous cladding. construction. London: Thomas Telford, 1990 Technical Advice Note 29. Edinburgh: Historic Scotland, 2004 Leggatt, A.J. GRP and buildings: a design guide for architects and 6.15.6 Timber engineers. London: Butterworths, 1984
Forest Products Laboratory. Wood handbook: wood as an engineering material. Madison, WI: Forest Products Laboratory, 1987 {Since superseded by Forest Products Laboratory. Wood handbook: wood as an engineering material. General Technical Report FPL-GTR-113. Madison, WI: Forest Products Laboratory, 1999}
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7.1 Introduction an emergency, but should not be relied upon. It should be clear what action must be taken, and by whom, if a scheduled report is missed. HSE publication Appraisal of existing structures may require inspection IND(G)737.6 may be consulted for further guidance. of structures which are not necessarily safe. The engineer in charge of the appraisal must ensure the The engineer should be trained to be aware of likely safety of all those who may be affected, including hazards and safe systems of work and be familiar participants, occupants (if any) and the public. with safety equipment, e.g. safety harnesses, Appraisal often involves unique or short term activities, for working at height and respiratory protective requiring careful planning and risk assessment 7.1. equipment if access to confined spaces 7.7 is involved. Basic first aid knowledge is also desirable. This section provides guidance on health and safety As well as general knowledge, the engineer should during the appraisal. Appendix 2 provides further identify specific hazards which may be encountered advice on matters which should be considered in on the site concerned, and should consider how the appraisal to ensure that future risks from the to eliminate, minimise or protect against them. structure are acceptable. The client’s knowledge of the structure may be important. Review of hazards during the appraisal is Structural inspections often use access equipment recommended, in case anything unexpected arises. and allow little time for the development of awareness of site hazards. The majority of construction It is important to follow the principle that each accidents result from falls from height, and half the activity should be shown to be safe before it may people who die on a construction site have been be commenced. It is bad practice to rely on the working there for less than two weeks 7.2. Structural assumption that an activity is safe unless proven inspections can therefore be as dangerous as unsafe 7.8. construction or demolition work. Appraisal work and preparation for demolition have many aspects There are some activities which cannot safely be in common, and the code of practice for demolition, carried out by a single person. An inspection team BS 61877.3 contains much relevant information, may therefore be required. For example, when particularly sections 10 and 12. working in confined spaces or other potentially dangerous areas, there must be a person on watch The requirements of relevant legislation for health outside, and when using mobile inspection platforms, and safety must be met for all work on site. If some there must be a trained driver in control of the aspect of an inspection appears to involve undue platform. Depending on the risk assessment, it may elements of risk, the engineer must use judgement also be necessary to have a person at ground level. and if necessary refuse to undertake such work and explain why to the client. The occupier of the Before entering a building, a general assessment of premises (which means the persons(s) in control of the condition of the structure should be made and the land, building, premises, etc.), who may or may entry should be made only if the building appears not be the client, has a legal duty of care to anyone adequately safe. The sequence of inspection entering them7.4, but engineers have a responsibility depends on many factors, including the building for their own safety and that of their employees (if form, construction and condition. Where possible, any) and of the public, in respect of their activities. structural elements, such as floor joists, should be inspected before being walked on. If any part of a In general, the findings of an appraisal are building is considered unsafe, the engineer should, confidential to the client. If, however, the structure as soon as practicable, initiate steps to deter access is a danger to the public, both the law in the UK by anyone, including unauthorised persons such as and the Institution’s Code of Conduct7.5 require the squatters and vandals. The client should be kept engineer to take appropriate and timely action in the informed, preferably before action is taken. public interest, in the first instance making the client aware of the situation, with clearly stated reasons. When inspecting occupied buildings, it is essential If the client does not then act promptly to eliminate that the client notifies the occupiers in advance of or minimise the danger, the engineer may have to the inspection work to avoid misunderstandings on act unilaterally, although the client should be given site. The engineer and the client should agree how a further opportunity to act and be kept informed the appraisal will be carried out, in order to meet of any action taken. The local authority’s Building the client’s expectations safely and professionally, Control have the powers to take the necessary highlighting particular aspects affecting building action. The engineer's actions must be reasonable users, such as noise and dust resulting from and necessary. exploratory cutting.
Inspections should not be carried out by A vacant building, particularly if it has been inexperienced people working on their own. An vandalised, is more likely to contain the hazards listed engineer, however experienced, visiting a building in Section 7.3. Evidence of significant dilapidation alone should report back at specified intervals, and on resulting from many years of neglect of maintenance completion, to confirm that all is well. A mobile phone would also suggest that particular care must be or radio is useful for this and can be vital in the event of exercised when inspecting.
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7.2 Risk management –– by substitution (replace the hazard with something less dangerous) –– by a safe system of work (provide a formal UK legislation7.7, 7.9, 7.10, 7.11 now spells out the process to minimise the risk) requirements for a suitable and adequate –– by the provision of protective equipment (to assessment of health and safety risks to both mitigate the damage if the risk occurs). employees and others who may be affected by the work. For example, the public may be affected by a In general, ways to reduce the risk to all persons, town-centre façade inspection. The level of detail in and which require no action by the people a risk assessment should be broadly proportional to protected, for example handrails and safety nets the risk, taking into account not only the risks to the or fall bags (see Figure 7.1) have mandatory priority appraisal team, but also to the public, the client’s over those which protect only the individual, or employees and indeed anyone else who may be which require specific action from the user, such as affected. A generic risk assessment may be sufficient a safety harness. For short term activities such as to cover routine inspection tasks in well controlled inspections, however, personal protection may be environments, but in most appraisal situations it will appropriate. For example, erecting safety nets may be necessary to carry out a specific risk assessment require the wearing of safety harnesses, and could to ensure that any risks to health and safety involve more risk than one person using a harness have been identified and eliminated if reasonably to make a brief inspection. Note that roped access practicable, or adequately controlled if not. techniques7.9, which can be the safest overall way to inspect the outside of a structure, are classed as In all cases it is important that a structured approach positioning systems, not protection. is adopted along the following lines. –I– dentify the hazards – physical, chemical, As part of controlling the risk, adequate biological7.10. supervision, training and information should –A– ssess the extent of the risk – a function of the be provided to those involved. The engineer likelihood that harm will occur and its severity. responsible for the appraisal should ensure that –C– ontrol the risk – in order of priority7.12: this has been done, including obtaining adequate –– by elimination (remove the hazard which is the information from the client. cause of the risk)
Figure 7.1 Fall (safety) bags: ‘Soft Landing System’ © Forest Safety Products Limited
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7.3 Hazards (5) Biological hazards may be present, including Weil’s disease (leptospirosis) from rats’ urine, anthrax from old lime plaster including cow The potential site hazards associated with dung and hair, lung infection from the dust appraising existing structures listed below are of pigeon droppings and various diseases offered as preliminary guidance. This list should from medical and organic waste, abandoned be supplemented by specific items relevant to containers, discarded needles, uncovered the project. Subject to the circumstances of each burial sites and decomposing carcasses. individual appraisal, further research and reading may be necessary7.2, 7.13, 7.14. (6) Dangerous animals, (e.g. aggressive dogs) or insects (e.g. wasps nesting in loft spaces) (1) Fire and explosion damaged buildings should be avoided and the client advised. demand specialist attention and may need temporary support before extensive inspection (7) Geotechnical trial holes should be properly is possible. See Appendix 4. Toxic fumes planked and strutted against collapse of and dust hazards may well result from such surrounding ground and/or adjacent structures. damage7.7. If left open and unattended, the holes should be temporarily covered or fenced to prevent (2) Partial demolition or stripping out may have anyone, including unauthorised persons, resulted in a lack of protection to roof edges, falling in accidentally. Excavation of trial holes openings in floors, stairwells, etc. The risk of should be carried out with care (after risk falls through fragile roofs or floors should be assessment) particularly if the ground is likely to anticipated when planning the inspection. be contaminated.
(3) Confined spaces need to be identified and (8) Falls of people, for example from untied the appropriate precautions of testing for poor ladders, and objects falling from scaffold edges air quality taken. Manholes are the classic are likely to give rise to the greatest number of example, but service ducts, unventilated rooms injuries. Specialised training and equipment is or voids which have remained closed for a a prerequisite for the safe erection of scaffolds, long time and basements can also present a including mobile towers, and for the safe use of danger of toxic, flammable or oxygen-deficient powered access equipment and rope access atmospheres7.7. techniques such as abseiling.
(4) Asbestos7.15 or other hazardous materials7.10 (9) Building services, particularly electricity, may may be present. HSE Guidance Note EH407.16 be a hazard, e.g. if live cables are struck during gives the maximum exposure limits (MEL) of exploratory opening-up or excavating of trial various potentially harmful substances and is holes: detectors should be used and services updated regularly. Any affected areas should mapped before excavation. Any electrically be sealed and licensed specialist advice powered equipment used should, where sought. If cores or other structural samples are reasonably practicable, have a 110V power taken, care should be taken in case these are supply. If 240V is used, a residual current device contaminated. at the point of supply should be incorporated. Provision for adequate lighting should be Since May 2004, anyone in control of non- planned, particularly if mains services have domestic premises in the UK has had a been disconnected. duty under the Control of Asbestos at Work Regulations 20027.15 to: (10) Overhead cables can be a hazard during –– assess whether there is any asbestos in their access to roofs or while using mobile access buildings; a licence will be required in the vast equipment. majority of cases of working with asbestos –– depending on the condition of the asbestos, either remove it or manage it, making sure that maintenance activities carried out 7.4 UK legislation subsequently do not expose workers to any avoidable risk –– ensure that information on the location and This section identifies specific legislation which may condition of these materials is given to anyone be relevant to the conduct of an appraisal. likely to disturb them. The principal UK Act regarding safety at work is the This places a duty on the client (if assumed to Health and Safety at Work etc. Act 19747.17. This is be in control of the premises) to provide this supported by secondary legislation in the form of information on asbestos to the engineer. The various Regulations, which can be amended by a engineer should not rely on this information government minister7.7, 7.9, 7.10, 7.15, 7.18, 7.19. It is therefore unless the client can show that it is derived important to consult the latest version. Each set from a comprehensive and competent survey. of Regulations is in turn often supported by an The engineer should also be aware that the Approved Code of Practice (ACoP). Anyone who client may expect such a survey to be carried complies with the ACoP has a good defence against out as part of the appraisal. The brief must be a charge of not complying with the Regulations, clear and the engineer should only accept work whereas those who do not follow the ACoP would within their competence. have to prove that they had complied. Further guidance on construction safety can be found in the HSE guidance booklet7.20.
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A duty is placed on owners of buildings: "Where a 7.5 Personal protective equipment (PPE) workplace is in a building, the building shall have a stability and solidity appropriate to the nature of the use of the workplace" (The Health and Safety It is not possible to eliminate all risks in site (Miscellaneous Amendments) Regulations 20027.19, inspections of structures. Personal protective 6(c): new regulation 4A to be added to Amendment equipment may be required7.21. Safety helmets are of the Workplace (Health, Safety and Welfare) usually required, and in some cases protective Regulations 19927.19). footwear. Goggles for eye protection are necessary if drilling, cutting, welding, chipping, grinding or The Construction (Design and Management) similar work is undertaken and are recommended Regulations7.11 (CDM) impose duties on both if the environment is dusty or if falling debris is designers and clients for construction work, which possible, such as during inspection of a shaft. may be relevant to appraisal. The engineer does not The use of ear protection appropriate to the incur the designer’s duties as a result of making an hazard should be considered, bearing in mind that appraisal, per se: the definition of ‘construction work’ restricting hearing may introduce new dangers. in the regulations does not include appraisal itself: Protective clothing, such as overalls and gloves, should be made available. " ‘construction work’ means the carrying out of any building, civil engineering or engineering When working at height7.22 the engineer must be construction work and includes: properly equipped. Equipment may include a safety harness, lanyard and secure anchorage where a (a) the construction, alteration, conversion, safe working platform is not available. The same fitting out, commissioning, renovation, repair, care is required when working where lack of oxygen upkeep, redecoration or other maintenance may occur, or toxic gases, asphyxiants, etc. may (including cleaning which involves the use be present, e.g. in confined spaces7.7, trial pits in of water or an abrasive at high pressure or contaminated ground, etc. Gas monitors and escape the use of corrosive or toxic substances), sets are usual where such hazards are possible decommissioning, demolition or dismantling of but not expected, while respiratory protective a structure;" equipment will be required if the risk is higher and entry is essential. Adequate training in the use and [followed by (b) to (e), q.v.] maintenance of personal protective equipment should be provided7.21. The CDM regulations may be applicable, however, if any of the following apply: –– the appraisal is part of a notifiable project –– the appraisal requires invasive investigation (‘opening up’) –– temporary works are necessary to provide access –– the scope of the appraisal includes proposals for modifications.
If in doubt, it would be wise to consider as construction work anything which physically alters the building, however small the change. Similarly, anyone who makes a decision about the nature of such a change should be considered a designer. This could include workers opening up the structure for examination (see Section 3.5), if they are given discretion in the way this is carried out. The engineer should therefore specify how any such work should be done.
Starting work only when the client is aware of their (the client's) duties, the designer's primary duties under CDM are, so far as is reasonably practicable, to eliminate hazards which may give rise to risks and to reduce risks from any remaining hazards, so that the construction work being designed can be safely constructed and maintained. For further information see reference 7.11.
CDM can, however, make the appraiser’s job easier. For all construction work carried out since the regulations became law, the owner must retain the Health and Safety File, describing the significant risks arising from the design, including provisions for maintenance and demolition. The engineer can legitimately ask for the Health and Safety File, which should be a valuable source of information, although experience has shown that it is not always available Figure 7.2 Donning PPE © Arup even when legally it should be.
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7.6 Specialist training 7.5 Institution of Structural Engineers. Code of Conduct and guidance notes. Available at: http://www.istructe.org/ AboutIStructE/Pages/Codeofconduct.aspx [Accessed: Specialist training may be necessary for safe working 23 September 2009] on specific types of premises, such as railways, highways or electrical switch rooms. In some cases, 7.6 Health and Safety Executive. Working alone in safety: there may be a specific legal requirement for such controlling the risks of solitary work. INDG73, 1998 {Since training. The engineer should seek the advice of the superseded by Health and Safety Executive. Working alone: client, who should be aware of such requirements, health and safety guidance on the risks of working alone. but should not rely on this exclusively. Restrictions INDG(rev2). Available at: http://www.hse.gov.uk/pubns/ may also apply, such as the requirement to abstain indg73.pdf [Accessed: 23 September 2009]} from alcohol or drugs for a period before working and while working. 7.7 The Confined Spaces Regulations 1997. London: The Stationery Office, 1997 (SI 1997/1713) and Health and Safety Executive. Safe work in confined spaces: Confined Spaces Regulations 1997. Approved code of practice, 7.7 Checklist – what the engineer should regulations and guidance. L101. Sudbury: HSE Books, 2009 consider 7.8 Mason, R.O. ‘Lessons in organizational ethics from the Columbia disaster: can a culture be lethal?’. Organizational At the commission stage, the engineer should, as Dynamics, 33(2), 2004, pp128–142. Available at: http:// appropriate: www-rohan.sdsu.edu/faculty/dunnweb/case.columbia.pdf –A– sk the client for the Health and Safety File. [Accessed: 23 September 2009] –D– ecide whether CDM is applicable to the appraisal. –C– arry out a risk assessment on the proposed work 7.9 The Management of Health and Safety at Work Regulations on site relating to the appraisal and modify the 1999. London: The Stationery Office, 1999 (SI 1999/3242) proposal accordingly. and Health and Safety Executive. Management of health –I– nform the client what is going to be done on site. and safety at work: Management of Health and Safety at –C– larify the division of responsibility between the Work Regulations 1999. Approved code of practice and client, the engineer and any other parties for guidance. L21. 2nd ed. Sudbury: HSE Books, 2000 management of health and safety. –P– re-qualify any contractors and their sub- 7.10 The Control of Substances Hazardous to Health contractors and review their method statements. Regulations 2002. London: The Stationery Office, 2002 –C– heck equipment and training; a licence may (SI 2002/2677) and Health and Safety Executive. Control be required (for example, if investigation may of substances hazardous to health: The Control of encounter asbestos). Substances Hazardous to Health Regulations 2002 (as amended). Approved code of practice and guidance. L5. During the appraisal, the engineer should, as 5th ed. Sudbury: HSE Books, 2005 appropriate: –C– arry out the appraisal safely and not to endanger 7.11 The Construction (Design and Management) Regulations any person. 1994. London: HMSO, 1994 (SI1994/3140), as –C– ontinuously re-appraise the risk assessment amended by the Construction (Design and Management) on site to see if the original assumptions and (Amendment) Regulations 2000. London: The Stationery assessment are still valid. Office, 2000 (SI 2000/2380), and Health and Safety –T– ake action to remove or mitigate any new hazards Executive. Managing health and safety in construction: or risks identified. Construction (Design and Management) Regulations –I– nform the client immediately if the structure 1994. Approved code of practice and guidance. HSG224. presents a significant risk. Initially, use any practical Sudbury: HSE Books, 1995 [Revised by The Construction means, verbal, email, fax, etc, and confirm formally (Design and Management) Regulations 2007. [s.l]: The in writing as soon as possible. Stationery Office, 2007 and Health and Safety Executive. Managing health and safety in construction: Construction (Design and Management) Regulations 2007. Approved code of practice. L144. [Norwich]: HSE Books, 2007] 7.8 References 7.12 Health and Safety Executive. Successful health and safety management. HSG65. 2nd ed. Sudbury: HSE Books, 1997 7.1 Health and Safety Executive. Five steps to risk assessment. INDG163(rev1), 1998 {Since superseded by Health 7.13 Health and Safety Executive. Evaluation and inspection of and Safety Executive. Five steps to risk assessment. buildings and structures. HSG58. London: HMSO, 1990 INDG163(rev2). Available at: http://www.hse.gov.uk/pubns/ indg163.pdf [Accessed: 23 September 2009]} 7.14 Construction Industry Publications. Construction health and safety manual. Bedford: CIP, 2005 7.2 Bielby, S.C. and Read, J.A. Site safety handbook. CIRIA Special Publication 90. 3rd ed. London: CIRIA, 2001 {Since 7.15 The Control of Asbestos at Work Regulations 2002. superseded by Bielby, S. and Gilbertson, A. Site safety London: The Stationery Office, 2002 (SI 2002/2675) handbook. CIRIA C669. 4th ed. London: CIRIA, 2008} and Health and Safety Executive. Work with asbestos which does not normally require a licence. Control of 7.3 BS 6187: 2000: Code of practice for demolition. London: Asbestos at Work Regulations 2002: Approved code of BSI, 2000 practice and guidance. L27. Sudbury: HSE Books, 2002 {Since superseded by The Control of Asbestos at Work 7.4 Occupiers’ Liability Act 1957. London: HMSO, 1957 and Regulations 2006. London: The Stationery Office, 2006 (SI Occupiers’ Liability Act 1984. London: HMSO, 1984 2006/2739)}
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7.16 Health and Safety Executive. Occupational exposure limits. EH40/2002. Sudbury: HSE Books, 2002 and Supplement 2003 {Since superseded by Health and Safety Executive. Workplace exposure limits. EH40/2005. Sudbury: HSE Books, 2005}
7.17 The Health and Safety at Work etc Act 1974. London: HMSO, 1974
7.18 BS 7985: 2002: Code of practice for the use of rope access methods for industrial purposes. London: BSI, 2002
7.19 The Workplace (Health, Safety and Welfare) Regulations 1992. London: The Stationery Office, 1992 (SI 1992/3004) as amended by The Health and Safety (Miscellaneous Amendments) Regulations 2002. London: The Stationery Office, 2002 (SI 2002/2174)
7.20 Construction (Health, Safety and Welfare) Regulations 1996. London: The Stationery Office, 1996 (SI 1996/1592)
7.21 Health and Safety Executive. Health and safety in construction. HSG150. 3rd ed. Sudbury: HSE Books, 2006
7.22 The Personal Protective Equipment at Work Regulations 1992. London: The Stationery Office, 1992 (SI 1992/2966) and Health and Safety Executive. A Short guide to The Personal Protective Equipment at Work Regulations 1992. INDG174(rev1). 3rd ed. Sudbury: HSE Books, 2005
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A1.1 Introduction –B– uilding-specific information is likely to be more valuable for modern buildings, such as office blocks and multistorey buildings which have ‘embedded’ Information of use to the appraisal can be listed structures of reinforced concrete or steel, as under two broad headings of ‘building-specific’ and compared with traditional buildings of masonry ‘explanatory’. and timber and the more exposed structures of modern buildings such as warehouses. In the former Building-specific information describes the structure case, little information on structural form, materials, being appraised. It includes drawings, calculations components and details may be available without and specifications. (A health and safety file may exist major opening-up work. In the latter case, limited under the Construction (Design and Management) opening-up would reveal directions and dimensions Regulations: see Sections 3.2, 7.2 and 7.4 and of timber floor spans, while the ‘naked’ warehouse reference 7.10.) would require only opening-up of concrete or concrete-cased steel, the basic form and dimensions Explanatory information does not describe the of its structure usually being evident by inspection. particular structure, but covers the systems, –B– uilding-specific information of direct use to the components, materials, practices, etc. used in engineer is most likely to be found with those its construction. Examples are contemporary originally or subsequently involved in the design, catalogues of ‘patent’ in situ or precast concrete construction and maintenance. They are listed construction of floors, roofs, walls, houses, etc., below as primary sources. and of proprietary steel purlin or lattice truss –T– he second possible source of building-specific components, contemporary codes of practice, information is technical and professional contemporary textbooks and papers, and guides to publications which will usually identify the original the identification and use of such products. designers and describe notable features of the design and construction. Such publications may In planning and budgeting a search for documentary also deal with ground conditions. They are listed information, the engineer should bear in mind several later as secondary sources. factors: –E– xplanatory information is more likely to be available –M– ore information is likely to survive, and to be from professional institutions and specialised readily available, for ‘recent’ buildings than for sources such as research establishments, trade ‘older’ buildings. There is an unfortunate trend, associations, libraries and manufacturers rather than however, for ‘commercial’ pressures to result from general archive sources. in data for recent buildings not being kept as carefully as used to be the case. It is less likely to Some examples of availability and importance be available for ‘small’ buildings (especially houses) of documentary information are given below. than for larger buildings and structures. [All websites in this Appendix were accessed on 28 January 2010].
A late medieval cottage of stone and timber No original building-specific information will exist. If converted or upgraded in recent years, there may be architect’s drawings of the work. More recent work may be documented. Opening-up is relatively quick, informative and may not be unduly disruptive, though consideration should be given to whether prior consent, such as Listed Building Consent, need be obtained
The Guildhall, Thaxted © Mike Collins An 18th century country house The original architect’s drawings may exist. If not available from the owners or their advisers (solicitors, estate managers, etc.) the most fruitful line of inquiry would be via architectural archives and local record offices. More recent work may be documented. Opening-up (with consent) is relatively quick, informative and may not be unduly disruptive
Buscot Park, Oxfordshire © Buscot Park and the Faringdon Collection
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A mid-19th century cast-iron-framed textile mill Original framing drawings (if they have survived) are most likely to be in a professional engineering institution, reference library, or technological museum or archive. The structure is usually visible, with opening-up necessary only to confirm floor construction, beam profiles and column-beam and wall-beam connections
Murray’s Mills, Manchester © Heritage Works Building Preservation Trust/Building Design Partnership A reinforced concrete warehouse of 1910 Original engineering drawings may have survived, for example with the original designers or their successors. The building may be described in contemporary publications (catalogues, books and technical journals). Load testing of such structures was common, and the basic results are often recorded. ‘Safe load’ signs were often displayed on landings. Contemporary information on material strengths, loadings, reinforced systems, and design principles (elastic, modular-ratio) is often available, particularly if it has been possible to identify a concrete ‘patent’ system. Opening-up is slow and laborious: reinforcement patterns need to be established if documentation is not available, and spot-checked if it is A 1930s stone-clad steel-framed office block Original architects’ and engineers’ drawings have often survived: many professional practices of this period have survived, or have merged but can still be traced. Technical journals may contain description of the buildings or even an engineering paper. Opening- up is slow, laborious and disruptive, especially on stone-clad elevations (in which corrosion of the steelwork is a common occurrence)
Luton Town Hall © N Nessa A prefabricated concrete or steel-framed housing estate of the 1950s, or a late 1960s high-rise ‘systems-built’ block of large-panel precast-concrete floor-and-wall units The drawings for the particular estate or block may survive with the relevant local authority (or successive owner). It should be possible to identify the system(s) used from the original records or more recently published guidance, and fuller details of these systems, including calculations, may be obtainable from the originators, their successors or licensees. Most high-rise blocks were appraised for robustness and strength following the Ronan Point partial collapse in 1968: records of these appraisals may be available from owners, consulting engineers, or building control authority. Opening-up will be slow, laborious and disruptive but may be needed in any event to check for soundness of reinforcement and connections, and for durability of concrete. See references in Appendix 3 (Section A3.3.2) A 1980s ‘post-modern’ clad building block with a steel frame Drawings and calculations should be in the possession of the building control authority and the original structural consultants, or their successors. Parties to the construction should be readily identifiable. Opening-up might only be considered if there are reasons to doubt the reliability of documents, unless there is evidence of distress requiring investigation
Ropemaker Street, London © Arup
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–B– uilding owner (current/previous/original). The following sources may also be useful: –B– uilding occupier(s) if not owner (current/previous/ original). Topographical information: Current Ordnance –O– wners’ and occupiers’ professional advisers Survey maps at large scale are usually accessible in (notably solicitors, managing/estate agents/facilities local authority offices; historical editions of Ordnance managers, consulting architects, engineers, Survey and other plans should be available in the surveyors, insurers). relevant local library or record office. –O– riginal structural designers (consultants, contractors, design-and-build contractor, etc.) e.g Insurance plans: Best known are the Goad plans Samuely offers access to archived jobs. for commercial and industrial areas of most UK cities –O– ther original design team members (architects, and towns, at a large scale usually of 40ft to the inch services consultants, quantity surveyors, building (1:480). They were periodically updated, so that the or party wall surveyors). evolution of a building or site can be traced. A full set –A– djoining owners (party wall agreements). is held at the British Library Map Room. –C– ontractors (site investigation contractor, main/management contractor, sub- and trade Site and building history: In addition to maps, contractors, suppliers and manufacturers of local libraries and record offices contain local structural components). historical studies, old directories (which often reveal –M– aintenance and defects data, including – with earlier uses, owners, and construction dates), appropriate caution – anecdotal accounts (building copies of surveys by local history groups, industrial owner’s staff at all levels of responsibility, managing archaeologists, vernacular architecture study agents, contractors, neighbours). groups, etc. –D– esigners and contractors for refurbishment(s) or major alteration(s) (architects, structural Geological data: Initial inquiries at the building engineers, services consultants, quantity surveyors, control authority may highlight issues such as contractors, suppliers, and manufacturers). mining subsidence, as well as giving access to site –B– uilding control authority (District Surveyor in investigation data, general guidance on ground Inner London, building inspector, National House- conditions and current thinking on bearing pressures, Building Council, other warranty providers, etc.). local groundwater, sulfates, contamination, etc. –P– ublic utilities and statutory undertakers (water, The British Geological Survey publishes maps and sewage, gas, electricity, telephone, cable, memoirs for the UK which give an overall picture railways including underground and metro, local of the geology. Site investigation contractors authorities, etc.). may provide reports on the site in question or its –R– ecord offices and archives in which original neighbours, subject to permission from their original drawings and other documents have been clients. Coalmining operators may be able to provide deposited (Public Record Office, ICE/Institution advice on coalmining areas. of Structural Engineers/Concrete Society/RIBA Drawings Collection), specialist sources. Constructional information: The Royal Institute –C– ommercial aerial photography firms. of British Architects library maintains a database of papers and articles on buildings. Similar records A1.2.1 Points to note of papers are maintained by the Institution of Civil Engineers and the Institution of Structural Engineers. The following advisory and precautionary points The National Register of Archives of the former Royal should be noted: Commission on Historical Manuscripts is useful on –R– ecent years (in particular) have seen many sources of business and architectural history; this is architects, engineers, surveyors and contractors now part of the National Archives, see below. undergoing mergers, changing names, or ceasing to trade altogether. It is often difficult to track The National Monuments Record, www.english- down the original designer or contractor in such heritage.org.uk/nmr (for England), the Royal cases. Useful leads to the successor practices and Commission on the Ancient and Historical companies may be obtained by inquiries to: Monuments of Scotland, www.rcahms.gov.uk –– for architects: RIBA, ARB (for Scotland), the Royal Commission on Ancient –– for consulting engineers: ACE, Institution of and Historical Monuments in Wales, www. Structural Engineers Consultants Tracker (www. rcahmw.gov.uk (for Wales), the Monuments and istructe.org/library/consultanttracker.asp) Building Record, Environment and Heritage –– for surveyors: RICS Service, www.ni-environment.gov.uk/built/build. –– for contractors: Construction Confederation, htm (for Northern Ireland), and Manx National CECA Heritage, www.gov.im/mnh (for the Isle of Man) –T– he building control authority may decline to open may hold relevant information. Other sources its records to third parties (unless requested under include the voluntary conservation groups the Freedom of Information Act), and is also likely (Ancient Monuments Society, Church Monuments to discard records after some time because of Society, Georgian Group, Society for Protection shortage of space or other reasons. of Ancient Buildings, Twentieth Century Society, –I– nformation may sometimes be disclosed only on Victorian Society) and local building preservation, presentation of a letter of authority from the client conservation and history societies. Records and/or building owner, and/or on payment of a are also likely to have been kept by nationalised search or access fee. corporations and/or their successors.
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A1.4 Explanatory information Concrete –C– P 114: 1948 (earlier Reinforced Concrete Regulations introduced in London in 1916; Four principal classes of information are available. Department of Scientific and Industrial Research –C– ontemporary trade literature and Third Party code of 1934) Certification describing products and processes. –C– P 115: 1959 (prestressed) –C– ontemporary codes of practice. –C– P 116: 1965 (precast) –C– ontemporary textbooks, papers and periodicals. –C– P 110: 1972 (superseded CP 114/115/116) –G– uides to the identification and appraisal of –B– S 8110: 1985 (superseded CP 110) systems, products and particular structures. –B– S EN 1992-1, -3 (will supersede BS 8110)
Principal sources are listed below in the following Steel sections. –B– S 449: 1932 (earlier London Building Acts of 1909 onwards, Institution of Structural Engineers Report A1.4.1 Trade literature and Third Party Certification 1927; BS 449 still in use) –T– he British Library (www.bl.uk/catalogues/ –B– S 5950: Part 1: 1985 business) is an extremely valuable source of –B– S 5950-1: 1990 (superseded BS 5950: Part 1: information on proprietary building products of all 1985) periods. –B– S 5950-1: 2000 (superseded BS 5950-1: 1990) –O– riginal designers, manufacturers or suppliers if still –B– S EN 1993 (will supersede BS 5950) trading. A notable example is Mouchel Parkman for information on the Hennebique reinforced concrete Composite construction (beams for buildings) system. Mergers and name changes may often –C– P 117: Part 1: 1965 be traceable through Companies House or the –B– S 5950: Part 3: Section 3.1: 1990 (superseded relevant trade associations. CP 117: Part 1: 1965) –T– echnical libraries and technical/industrial –B– S EN 1994-1 (will supersede BS 5950-3) museums often hold collections of trade literature, sometimes deposited when the original company Composite construction (beams for bridges) ceased trading or cleared out its archives prior to a –C– P 117: Part 2: 1967 move, reorganisation, etc. –B– S 5400: Part 5: 1979 (superseded CP 117: Part 2: –D– irectories such as: 1967) RIBA Product Selector (www.productselector.co.uk), –B– S 5400-5: 2005 (superseded BS 5400: Part 5: Barbour Index (www.barbourproductsearch.info), 1979) Abacus Construction Index –B– S EN 1994-2 (will supersede BS 5400-5) (www.construction-index.com), IHS UK (formerly Technical Indexes) (uk.ihs.com), Loadbearing masonry walls The Building Centre (www.buildingcentre.co.uk), –C– P 111: 1948 Building Information Warehouse (www.biwtech.com), –B– S 5628: Part 1: 1978 (superseded CP 111) Building Products Index (www.bpindex.co.uk) and –B– S 5628-1:1992 (superseded BS 5628: Part 1: UK Civil Engineering (www.ukcivilengineering.co.uk). 1978) All are updated regularly. Earlier editions are a mine –B– S 5628-1: 2005 (superseded BS 5628-1:1992) of useful information both in the editorial text and in –B– S EN 1996 (will supersede BS 5628) the advertisements sometimes included; they may be found in technical libraries (notably at the ICE, Timber Institution of Structural Engineers, RIBA and the British –C– P 112: 1952 Library noted above), often in the reserve collection. –B– S 5268: Part 2: 1984 (superseded CP112) Previous versions of information published on the –B– S 5268: Part 2: 1988 (superseded BS 5268: internet may be available at the Internet Archive: Part 2: 1984) Wayback Machine (www.archive.org/web/web.php). –B– S 5268: Part 2: 1991(superseded BS 5268: –A– grément Certificates provide information on the Part 2: 1988) performance of many construction products and –B– S 5268-2: 1996 (superseded BS 5268: Part 2: materials produced since 1966. Information on 1991) these products and those with the European Union –B– S 5268-2: 2002 (superseded BS 5268-2: 1996) Construction Products Directive’s CE Marking can –B– S EN 1995 (will supersede BS 5628) be found via the British Board of Agrément (www.bbacerts.co.uk). Aluminium –C– P118: 1969 (obsolescent) A1.4.2 Contemporary Codes of Practice –B– S 8118: Part 1: 1991 –B– S EN 1999 (will supersede BS 8118) Old editions of British codes of practice and standards may be found in the BSI library and other Foundations major technical libraries. It may be useful to note –C– ivil Engineering Code of Practice No. 4: 1954 here the earliest appearance dates of the common –C– P 2004: 1972 (superseded CECP4) structural codes of practice, to avoid vain searches –B– S 8004: 1986 (superseded CP 2004) for earlier editions. –B– S EN 1997 (will supersede BS 8004)
Earth retaining structures –C– ivil Engineering Code of Practice No 2: 1951 –B– S 8002: 1994 –B– S EN 1997 (will supersede BS 8002)
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Loadings provided suitable identification is produced, but –C– P4: 1944 some bodies may require prior application.) –C– P3: Chapter V: 1952 (superseded CP4) –I– s a search or access fee payable, and, if so, is it –B– S 648:1964: Schedule of weights of building payable in advance or on arrival? materials –I– s an appointment necessary? (Some sources have –B– S 6399: Part 1: 1984, Dead and imposed loads, very limited working or seating areas.) and BS 6399: Part 3: 1988, Imposed roof loads –W– hat are opening hours if no appointment is (superseded relevant parts of CP3: Chapter V) needed? –B– S 6399-1: 1996 (superseded BS 6399: Part 1: –I– s copying of records permitted? If so, are 1984) photocopying facilities available, and how much do –B– S 6399: Part 2: 1995, Wind loads (ran in parallel copies cost? (Some bodies allow only pencil hand- with CP3: Chapter V: Part 2, Wind loads, first copying or note-taking; others allow use of digital issued in 1970 – withdrawn 15 October 2001) cameras.) –B– S 6399-2: 1997 (superseded BS 6399: Part 2: –C– an records be pre-ordered for study on arrival? 1995) (If so, a first batch of records can be pre-ordered –B– S EN 1990 from an online catalogue or by phone; more can –B– S EN 1991-1 (will supersede BS 6399) be ordered on arrival, to be retrieved while the first batch is being studied.) A1.4.3 Contemporary textbooks, papers, and periodicals –H– ow many records can be accessed at any one –L– ibraries, notably those of the ICE, Institution of time? (This can often be limited to three or four Structural Engineers, and RIBA (see contact details making the process time-consuming.) in A1.5). Inter-library loans and loans from the –I– s an index, database or website available to assist British Library facilitate access to scarce material. effective location of the records sought? (The Catalogues are valuable time-savers when the item entries below include a selection only of such aids.) is not known by name. –B– ook dealers, both general second-hand shops A1.5.1 Possible record sources where bargains may sometimes be obtained due to lack of awareness of scarcity or importance of the ACE – Association for Consultancy and Engineering item, and the few specialist dealers in engineering (formerly Association of Consulting Engineers) history whose prices more reflect the demand for Alliance House, 12 Caxton Street, London SW1H 0QL such material. Good catalogues, notably those Tel: +44 (0)20 7222 6557, published occasionally by Elton Engineering Fax: +44 (0)20 7990 9202 Books, 32 Fairfax Road, London W4 1EW, Website: www.acenet.co.uk Tel: +44 (0)20 8747 0967, provide useful critiques of the significance of particular items. Note that the Architects (British) – Guides: A Biographical Dictionary engineer is competing here with book collectors; of English Architects 1660-1840 by Colvin, H.M. much once common and cheap material, such as (John Murray, 1954); Directory of British Architects early safe load tables, is now both expensive and 1834-1900 compiled by Felstead, A. et al. for the British hard to come by. Architectural Library, RIBA (Mansell, 1993)
A1.4.4 Guides to the identification and appraisal of ARB – Architects Registration Board systems, products and particular structures 8 Weymouth Street, London W1W 5BU –L– ibraries are again a useful starting-point for Tel: +44 (0)20 7580 5861 research, particularly those of the ICE, Institution of Fax: +44 (0)20 7436 5269 Structural Engineers, RIBA, and the British Library Website: www.arb.org.uk noted above. –T– he BRE produces an excellent variety of BRE – Building Research Establishment publications covering identification, constructional Garston, Watford WD25 9XX details, potential defects and assessment of, in Tel: +44 (0)1923 664000 particular, proprietary precast concrete systems for Website: www.bre.co.uk housing (low-, medium- and high-rise) and steel- framed housing systems. British Architectural Library and Drawings Collection – –T– he Highways Agency issues a series of see RIBA documents dealing with appraisal of highway structures. British Geological Survey – BGS Central Enquiries British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, Tel: +44 (0)115 936 3143 A1.5 Record sources Fax: +44 (0)115 936 3276 Website: www.bgs.ac.uk
It is both courteous and efficient to email, telephone, British Library – The British Library fax, or write to a possible record source in the first St Pancras, 96 Euston Road, London NW1 2DB instance. This, or indeed the source’s website, will Tel: +44 (0)870 444 1500 answer the following key questions: Website: www.bl.uk –I– s the source likely to have useful information? –I– s a letter of authority needed from the client and/ BSI – British Standards Institution or building owner, or does the casual user need 389 Chiswick High Road, London W4 4AL a reference, e.g. from an employer or another Tel: +44 (0)20 8996 9000 institution? Fax: +44 (0)20 8996 7001 –I– s a reader’s ticket required? (For example, one Website: www.bsigroup.com. Library (including foreign can be obtained on arrival at the National Archives, and earlier editions of UK codes and standards)
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Building inspectors – see entries in local telephone Dock structures – enquiries should be made to directory under local authorities, building control, etc; the relevant dock authority (e.g. Port of London Websites: Authority; www.pla.co.uk), maritime or local museum www.labc-services.co.uk (England and Wales) (e.g. www.museumindocklands.org.uk for London), or www.londonbuildingcontrol.org.uk (London) local record office(s) www.sabsm.co.uk (Scotland) ICE – Institution of Civil Engineers Canal and waterways structures – One Great George Street, Westminster, National Waterways Museum London SW1P 3AA Llanthony Warehouse, The Docks, Gloucester GLI 2EH Tel: +44 (0)20 7222 7722 Tel: +44 (0)1452 318200 Website: www.ice.org.uk Fax: +44 (0)1452 318202 Library and Archives. Guides: Online Library Website: www.nwm.org.uk. Enquiries may also be Catalogue, Library Catalogue; ICE Publications Index; made to British Waterways regional offices Catalogue of Periodical Publications 1665-1994 (www.britishwaterways.co.uk), and to local record compiled by Lawless, V. (ICE, 1995). The ICE Panel for office(s) Historic Engineering Works may be contacted via the above address, and the Concrete Society Archive is CECA – Civil Engineering Contractors Association held here 55 Tufton Street, London SW1P 3QL Tel: +44 (0)20 7227 4620 Institution of Structural Engineers Fax: +44 (0)20 7227 4621 11 Upper Belgrave Street, London SWIX 8BH Website: www.ceca.co.uk Tel: +44 (0)20 7235 4535 Fax: +44 (0)20 7235 4294 CEHX – Civil Engineering Heritage Exchange: a forum Website: www.istructe.org on the internet subscribed to by many interested in, Library. Online Library Catalogue. The Convener of the and knowledgeable in, history and conservation: Institution’s History Study Group may be contacted via Registration required. knowledgelists.ice.org.uk/ the above address archives/civil-engineering-heritage-l.html Irish architecture – The Irish Architectural Archive CIBSE – Chartered Institution of Building Services 45 Merrion Square, Dublin 2, Eire Engineers Tel: +353 1663 3040 222 Balham High Road, London SW12 9BS Fax: +353 1663 3041 Tel: +44 (0)20 8675 5211 Website: www.iarc.ie Fax: +44 (0)20 8675 5449 Website: www.cibse.org Irish engineering – Guide: Irish Engineering 1760- 1960 (annotated catalogue of material on engineering CIOB – Chartered Institute of Building in Ireland in the library of the Institution of Engineers Englemere, Kings Ride, Ascot, Berkshire SL5 8BJ of Ireland; www.iei.ie) by Hughes, N.J. (Institution of Tel: +44 (0)1344 630700 Engineers of Ireland, 1982) Fax: +44 (0)1344 630777 Website: www.ciob.org.uk London Metropolitan Archives City of London, Guildhall, PO Box 270, London EC2P 2EJ Civil and structural engineers – Institution of Structural Tel: +44 (0)20 7606 3030 Engineers Library; ICE Library and Archives. Contact Website: www.cityoflondon.gov.uk/lma details as below. Guide: A Biographical Dictionary of Catalogue. Records of former London and Middlesex Civil Engineers in Great Britain and Ireland, Volume 1: County Councils, Greater London Council, Inner 1500 – 1830 edited by Skempton, AW et al., Thomas London Education Authority, bomb damage maps, Telford, 2002 English Heritage London records and much more
Copac – Copac service, Mimas London public housing – Guide: Sources for the The University of Manchester, Mezzanine Floor, Study of Public Housing: a London Archives Guide Devonshire House, University Precinct Centre, Oxford by Cox, A. (Guildhall Library and the London Archive Road, Manchester M13 9QH Users’ Forum, 1993) Tel: +44 (0)161 275 6789 Website: copac.ac.uk. A freely available library The National Archives, Ruskin Avenue, Kew, catalogue, giving access to the merged online Richmond, Surrey TW9 4DU catalogues of many major UK and Irish academic and Tel: +44 (0) 20 8876 3444 national libraries, and many specialist libraries Website: www.nationalarchives.gov.uk Formerly known as the Public Record Office, the Construction Confederation National Archives holds records of the UK government, 55 Tufton Street, London SW1P 3QL including such diverse material as railway and canal Tel: +44 (0)870 8989 090 company records, documentation of military and Fax: +44 (0)870 8989 095 supply installations, Board of Trade reports, etc. It also Website: www.constructionconfederation.co.uk houses the National Register of Archives which acts as a clearing-house for information about the repositories Construction History Society – contactable via CIOB and location of non-public records and manuscripts relating to British history kept elsewhere in the UK and District Surveyors – see local authority entries in overseas. telephone directory under (usually) Building Control or Website: www.nationalarchives.gov.uk/a2a District Surveyor
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National Archives of Scotland – National Archives of Public (national) record offices: Scotland, HM General Register House, England and Wales: see National Archives 2 Princes Street, Edinburgh EH1 3YY Scotland: see National Archives of Scotland Tel: +44 (0)131 535 1314 Northern Ireland: Public Record Office of Northern Website: www.nas.gov.uk Ireland, 66 Balmoral Avenue, Belfast BT9 6NY It holds Scottish government records and other Tel: +44 (0)28 9025 5905 material including that of Scottish railway companies Fax: +44 (0)28 9025 5999 and the Scottish National Register of Archives Website: www.proni.gov.uk. Catalogues and Guides Tel: +44 (0)131 535 1405 Fax: +44 (0)131 535 1430 Public utilities structures – enquiries should be made to Website: www.nas.gov.uk the relevant public utility, the local authority, or relevant local record office(s) A1.5.2 National record centres for ancient monuments and historic buildings Railway structures – enquiries for information on railway structures should be directed to Network Rail, English Heritage (includes the National Monuments Kings Place, 90 York Way, London N1 9AG Record Centre), Customer Services Department, Tel: +44 (0)8457 114 141 PO Box 569, Swindon SN2 2YP Fax: +44 (0)20 3356 9245 Tel: +44 (0)870 333 1181 Website: www.networkrail.co.uk Fax: +44 (0)1793 414 926 Regional plan rooms hold large collections of drawings Website: www.english-heritage.org.uk and other reports; accessible to bona fide enquirers by The National Monuments Record is open to the public arrangement. A fruitful source for older structures is the and contains extensive collections of archaeological National Railway Museum, Leeman Road, York Y02 4XJ and building records as well as aerial photographs. Tel: +44 (0)8448 153139 Copies of listed building and scheduled ancient Fax: +44 (0)1904 61112 monument entries are available. The national heritage Website: www.nrm.org.uk database PastScape is available to locate buildings Guide: A Guide to Railway Research and Sources for and sites for which information is held and is accessible Local Railway History by Kay, P. (SSG Publications, online (www.pastscape.org). Advice available 1990). Enquiries may also be made to local record office(s). Royal Commission on Ancient and Historical Monuments in Wales (Comisiwn Brenhinol Henebion RIAS – Royal Incorporation of Architects in Scotland Cymru, National Monuments Record for Wales) 15 Rutland Square, Edinburgh EH1 2BE Plas Crug, Aberystwyth SY23 1NJ Tel: +44 (0)131 229 7545 Tel: +44 (0)1970 621200 Fax: +44 (0)131 228 2188 Fax: +44 (0)1970 627701 Website: www.rias.org.uk Website: www.rcahmw.gov.uk Advice available, collection similar to that of the English RIBA – Royal Institute of British Architects, 66 Portland Heritage National Monuments Centre. Online access is Place, London W1B 4AD available via COFLEIN (www.coflein.gov.uk) Tel: +44 (0)20 7580 5533 Fax: +44 (0)20 7255 1541 Royal Commission on the Ancient and Historical Website: www.architecture.com Monuments of Scotland (National Monuments Record Library, Directories of Members and Practices. of Scotland) Guides: Online Library Catalogue; The Royal Institute John Sinclair House, 16 Bernard Terrace, of British Architects: A Guide to its Archive and Edinburgh EH8 9NX History Collection by Mace, A. (RIBA, 1988); see also Tel: +44 (0)131 662 1456 under Architects above. The Drawings and Archives Fax: +44 (0)131 662 1477 Collections are at the Victoria and Albert Museum, Website: www.rcahms.gov.uk. Cromwell Road, South Kensington, London, SW7 2RL Guide; National Monuments Record of Scotland Tel: +44 (0)20 7942 2563 Jubilee: A Guide to the Collections, 1941-1991. Fax: +44 (0)20 7942 2410 Advice available, collection similar to that of the English Website: www.vam.ac.uk Heritage National Monuments Centre. Online access available through CANMORE and PASTMAP (requires RICS – Royal Institution of Chartered Surveyors, RICS registration through www.rcahms.gov.uk) Contact Centre, Surveyor Court, Westwood Way, Coventry CV4 8JE NHBC – National House-Building Council Tel: +44 (0)870 333 1600 NHBC House, Davy Avenue, Knowlhill, Milton Keynes Fax: +44 (0)20 7334 3811 MK5 8FP Website: www.rics.org Tel: +44 (0)844 633 1000 Fax: +44 (0)1908 747255 Site information and investigations – Guides: Website: www.nhbc.co.uk for general advice and guidance refer to BS EN 1997-2:2007, Geotechnical design. Ground ‘Pevsner’ – the Buildings of England series initiated investigation and testing; and the superseded by the late Sir Nikolaus Pevsner and published by BS 5930: 1999, Code of practice for site investigations. Allen Lane and subsequently Yale University Press, For specific sources of information, a useful if elderly covering English counties and later, Wales, Scotland source is Preliminary Sources of Information for Site and Ireland. Subsequent editions give more attention Investigations in Britain by Dumbleton, M. J. and West, to 19th and 20th century buildings. An invaluable G., TRRL Laboratory Report 403 (Transport & Road source for identifying architects of particular buildings, Research Laboratory, 1976) leading to potentially further useful information (www.pevsner.co.uk)
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A1.6 Materials Concrete Block Association (www.cba-blocks.org.uk)
Aluminium Federation Concrete Centre (www.alfed.org.uk) (www.concretecentre.com)
Brick Development Association Concrete Pipeline Systems Association (www.brick.org.uk) (www.concretepipes.co.uk)
British Aggregates Association Concrete Repair Association (www.british-aggregates.com) (www.cra.org.uk)
British Cement Association Concrete Society (see Mineral Products Association) (www.concrete.org.uk)
British Ceramic Research Ltd (CERAM) Copper Development Association (www.ceram.com) (www.copper.org)
British Ceramic Confederation Corus (www.ceramfed.co.uk) (www.corusgroup.com)
British Coatings Federation Council for Aluminum in Building (www.coatings.org.uk) (www.c-a-b.org.uk)
British Constructional Steelwork Association Engineering Employers Federation (www.steelconstruction.org) (www.eef.org.uk)
British Non-Ferrous Metals Federation European Coil Coating Association (see Copper Development Association) (www.ecca-uk.com)
British Plastics Federation European Phenolic Foam Association (www.bpf.co.uk) (www.epfa.org.uk)
British Precast Concrete Federation Fibre Cement Manufacturers Association (www.britishprecast.org) Flat Glass Manufacturers Association British Rigid Urethane Foam Manufacturers Association (www.brufma.co.uk) Flat Roofing Alliance (www.nfrc.co.uk/fra.aspx) British Rubber & Polyurethane Products Association (www.brppa.co.uk) Glass & Glazing Federation (www.ggf.org.uk) British Stainless Steel Association (www.bssa.org.uk) Glassfibre Reinforced Concrete Association (www.grca.org.uk) British Structural Waterproofing Association (www.bswa.org.uk) Glass Online (www.glassonline.com) British Wood Preserving and Damp Proofing Association Glued Laminated Timber Association (see Property Care Association and Wood Protection (www.glulam.co.uk) Organisation) Gypsum Products Development Association British Woodworking Federation (www.gpda.com) (www.bwf.org.uk) Institute of Materials, Minerals and Mining Builders Merchants Federation (www.iom3.org) (www.bmf.org.uk) International Building Materials Group (CRH) Cast Metals Federation (www.crh.ie) (www.castmetalsfederation.com) International Lead Association Castings Technology International (www.ila-lead.org) (www.castingstechnology.com) Lead Sheet Association Cementitious Slag Makers Association (www.leadsheetassociation.org.uk) (www.ukcsma.co.uk) Medieval Stained Glass in Britain Clay Pipe Development Association (Corpus Vitrearum Medii Aevi) (www.cpda.co.uk) (www.cvma.ac.uk)
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Metal Cladding and Roofing Manufacturers Association Health and Safety Executive (www.mcrma.co.uk) (www.hse.gov.uk)
Mineral Products Association Her Majesty’s Courts Service (www.mineralproducts.org) (www.hmcourts-service.gov.uk)
National Federation of Roofing Contractors Higher Education Funding Council for England (www.nfrc.co.uk) (www.hefce.ac.uk)
Paint Research Association Higher Education Statistics Agency (www.pra-world.com) (www.hesa.ac.uk)
Property Care Association Highways Agency (www.property-care.org) (www.highways.gov.uk)
Quarry Products Association HM Treasury (see Mineral Products Association) (www.hm-treasury.gov.uk)
Single Ply Roofing Association Local Government Association (www.spra.co.uk) (www.lga.gov.uk)
Steel Construction Institute Local Government Technical Advisors Group (www.steel-sci.org) (www.tagonline.co.uk)
Steel Lintel Manufacturers Association Meteorological Office (www.metoffice.gov.uk) Stone Federation Great Britain (www.stone-federationgb.org.uk) Millennium Commission (www.millennium.gov.uk) Timber Trade Federation (www.ttf.co.uk) Office of Government Commerce (www.ogc.gov.uk) Timber Research and Development Association (www.trada.co.uk) Office of Public Sector Information (www.opsi.gov.uk) UK Steel Association (see Engineering Employers Federation) Ordnance Survey (www.ordnancesurvey.co.uk) Wood Protection Organisation (www.wood-protection.org) Parliament (www.parliament.uk)
Scottish Environment Protection Agency A1.7 Government agencies (www.sepa.org.uk)
The Technology and Construction Court Central Office of Information (www.hmcourts-service.gov.uk/infoabout/tcc) (www.coi.gov.uk) The Stationery Office Communities and Local Government (www.tso.co.uk) (www.communities.gov.uk) UK National Statistics Convention of Scottish Local Authorities (www.statistics.gov.uk) (www.cosla.gov.uk) Water Services Regulation Authority Department for Business, Innovation and Skills (www.ofwat.gov.uk) (www.berr.gov.uk)
Department for Environment, Food and Rural Affairs (www.defra.gov.uk) A1.8 Other organisations
Department for Innovation, Universities and Skills (www.dius.gov.uk) Architectural Heritage Society of Scotland (www.ahss.org.uk) Department for Transport (www.dft.gov.uk) Architecture Centre Network (www.architecturecentre.net) Environment Agency (www.environment-agency.gov.uk) Architecturelink (www.architecturelink.org.uk) Foresight (www.foresight.gov.uk)
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Association for Specialist Fire Protection Federation of Master Builders (www.asfp.org.uk) (www.fmb.org.uk)
Association of Drainage Authorities Federation of Piling Specialists (www.ada.org.uk) (www.fps.org.uk)
Association for Project Safety Fire and Blast Information Group (www.associationforprojectsafety.co.uk) (www.fabig.com)
Association of Specialist Underpinning Contractors Galvanizers Association (www.asuc.org.uk) (www.hdg.org.uk)
Basement Information Centre Guild of Builders and Contractors (www.basements.org.uk) (www.buildersguild.co.uk)
British Expertise Hazards Forum for Health and Safety in the workplace (www.britishexpertise.org) (www.hazardsforum.co.uk)
British Geological Survey Industrial Rope Access Trade Association (www.bgs.ac.uk) (www.irata.org)
British Institute of Non-Destructive Testing Institute of Asset Management (www.bindt.org) (www.theiam.org)
British Standards Institution Institute of Concrete Technology (www.bsigroup.com) (ict.concrete.org.uk)
Centre for Construction Innovation and Research Institute of Conservation (sst.tees.ac.uk/ccir) (www.icon.org.uk)
Centre for Window and Cladding Technology Institute of Measurement and Control (www.cwct.co.uk) (www.instmc.org.uk)
Confidential Reporting on Structural Safety Institute of Metal Finishing (www.scoss.org.uk/cross) (www.uk-finishing.org.uk)
Commission for Architecture and the Built Environment Institution of Agricultural Engineers (www.cabe.org.uk) (www.iagre.org)
Conservation Accreditation Register for Engineers Institution of Chemical Engineers (careregister.org.uk) (www.icheme.org)
Construction Industry Council Institution of Civil Engineering Surveyors (www.cic.org.uk) (www.ices.org.uk)
Construction Industry Research and Information Institution of Engineering and Technology Association (www.theiet.org) (www.ciria.org) Institution of Engineering Designers Construction Plant-hire Association (www.ied.org.uk) (www.cpa.uk.net) Institution of Gas Engineers and Managers Construction Products Association (www.igem.org.uk) (www.constructionproducts.org.uk) Institution of Highways and Transportation Corrosion Prevention Association (www.iht.org) (www.corrosionprevention.org.uk) Institution of Mechanical Engineers County Surveyors Society (www.imeche.org) (www.cssnet.org.uk) Looking at Buildings Design and Technology Association (www.lookingatbuildings.org.uk) (www.data.org.uk) National Access and Rescue Centre Energy Institute (www.narc.co.uk) (www.energyinst.org.uk) National Building Specification Engineering Council (UK) (www.thenbs.com) (www.engc.org.uk) National Churches Trust Engineering & Physical Sciences Research Council (www.nationalchurchestrust.org) (www.epsrc.ac.uk)
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National Federation of Demolition Contractors SAVE Britain’s Heritage (www.demolition-nfdc.com) (www.savebritainsheritage.org)
National Joint Utilities Group Standing Committee on Structural Safety (www.njug.org.uk) (www.scoss.org.uk)
National Piers Society Scottish Engineering (www.piers.co.uk) (www.scottishengineering.org.uk)
National Platform for the Built Environment Society for Adhesion and Adhesives (UK) (www.nationalplatform.org.uk) (uksaa-www.me.ic.ac.uk)
National Soil Resources Institute Society of Architectural Historians of Great Britain (www.cranfield.ac.uk/sas/nsri) (www.sahgb.org.uk)
National Trust Society of British Water and Wastewater Industries (www.nationaltrust.org.uk) (www.sbwi.co.uk)
National Trust for Scotland Society of Construction Law (www.nts.org.uk) (www.scl.org.uk)
Network Group for Composites in Construction Society of Operations Engineers (www.ngcc.org.uk) (www.soe.org.uk)
Network on Information Standardisation, Exchanges Sprayed Concrete Association and Management in Construction (www.sca.org.uk) (www.research.scpm.salford.ac.uk/siene) Steelbiz New Construction Research and Innovation Strategy (www.steelbiz.org) Panel (nCRISP) (see National Platform for the Built Environment ) Stone Pages (www.stonepages.com) New Engineering Contract (www.neccontract.com) Transport Planning Society (www.tps.org.uk) Partners in Innovation Limited (www.pinin.org.uk) Twentieth Century Society (www.c20society.org.uk) Permanent Way Institution (www.permanentwayinstitution.com) UK Certification Authority for Reinforcing Steels (www.ukcares.co.uk) Pipe Jacking Association (www.pipejacking.org) UK Irrigation Association (www.ukia.org) Pipeline Industries Guild (www.pipeguild.co.uk) UK Quality Ash Association (www.ukqaa.org.uk) Public Monuments and Sculpture Association (www.pmsa.org.uk) UK Society for Trenchless Technology (www.ukstt.org.uk) Pyramus & Thisbe [specialists in party wall matters] (www.partywalls.org.uk) UK Wind Engineering Society (www.windengineering.org.uk) Royal Academy of Engineering (www.raeng.org.uk) Victorian Society (www.victoriansociety.org.uk) Royal Commission on Environmental Pollution (www.rcep.org.uk) Water Jetting Association (www.waterjetting.org.uk) Royal Institute of British Architects (www.architecture.com) Welding Institute (www.twi.co.uk) Royal Institution of Chartered Surveyors (www.rics.org)
Royal Institution of Naval Architects (www.rina.org.uk)
Royal Society of Chemistry (www.rsc.org)
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A2.1 A cceptable risk levels for existing This is a complex area and this guidance is intended structures to indicate the main considerations. It is not definitive. To make the principles easier to follow, some detail which is not important for understanding has been Good practice for the design of new structures is omitted. well defined. It is generally accepted that meeting the requirements of current legislation and standards will The level of safety which is acceptable to society is result in a structure with a low risk of ‘failure’. Many usually considered to be a matter for government. existing structures (Figure A2.1) were not designed to Thus, the framework used to judge the acceptability meet current requirements, but nevertheless provide of risk is laid down in law. This appendix is based an acceptable level of safety. In conducting an on the legal position in the UK, but similar principles appraisal, therefore, the engineer may need to rely on apply in many countries. making appropriate professional judgements. The law lays duties on employers and building Most of this Report provides advice on the owners to ensure that their structures are ‘safe’. engineering aspects of these judgements. This Every structure, however, carries some risk of failure. appendix provides advice for the engineer on the For a new building, the engineer does not usually level of risk which may be acceptable for existing have to judge the acceptable level of risk explicitly. structures. The principles described are well Provided the design of a new building meets the established in industries with risks which require requirements of the relevant codes of practice, production of a formal safety case, such as offshore applied with engineering common sense, it can oil drilling, railways and nuclear power, but may be normally be taken that the risk is acceptable. unfamiliar to engineers who have not worked in these fields. The engineer has a common law duty of care to those entitled to rely on the appraisal to ensure that recommendations from the appraisal are valid and reasonable (see Sections 2.3 and 2.4). If the structure was adequate by the standards in force at its original construction, but not by those of today, the engineer has to know whether there is any legal obligation to modify it for continued or further use. Legal advice may need to be sought.
Most new structures in the UK should meet the requirements of the Building RegulationsA2.1. These regulations will only apply to existing structures if certain modifications are made, or if there is a material change of use (see BRE Digest 366A2.2). Therefore, if a structure is being appraised for its suitability for a new use, any shortfalls against the current building regulations should be highlighted. In particular, the requirements of the regulations aimed at structural safety, including avoiding disproportionate collapse, should be taken into account (see also Appendix 4).
One of the principal statutes regulating occupational health and safety in the UK is the Health and Safety at Work etc. Act 1974A2.3 (HSWA). This has both specific and general provisions. Many regulations exist under this Act, the majority of which are more relevant to the conduct of an appraisal (see Chapter 7) than to the acceptable risk level in a structure.
The statutory duty on employers is to ensure ‘so far as is reasonable practicable’ the health and safety of all employees. This duty is widely interpreted to mean that, for everyone at work, risks to employees and others should be ‘as low as reasonably practicable’. This is known as the ALARP principle. The legal interpretation of the words ‘reasonably practicable to avoid or prevent breach’ (which correlates with the ALARP principle) can be found in the judgment in Figure A2.1 Central Criminal Court, London Edwards v. The National Coal Board (1949)A2.4:
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"A computation must be made in which the quantum of risk is placed on one scale and the Disproportion line sacrifice, whether in money, time or trouble, involved in the measures necessary to avert the risk is placed in the other; and that, if it be shown that there is a gross disproportion between them, the risk being insignificant in relation to the sacrifice, the person upon
whom the duty is laid discharges the burden Grossly disproportionate of proving that compliance was not reasonably practicable."
Another way to look at this, expressed in engineering rather than legal terms, is that an Cost of measure (’Sacrifice made’) employer has a duty to eliminate or reduce all foreseeable risks, unless the cost of doing so is grossly disproportionate to the benefit. The client for the appraisal may or may not be intending to employ people in the building, but both client and engineer may be liable, however indirectly, if they fail to consider how risks can be reduced as far as reasonably practicable.
The Health and Safety Executive (HSE) document Proportionate Reducing Risks, Protecting PeopleA2.5 (known as R2P2) states that HSE expect duty holders to use ‘good practice’ as a minimum standard. In this case, meeting the accepted standard of Risk reduction: Value of measure (’Benefit gained’) good practice could be taken to demonstrate Cost v Benefit compliance with the ALARP principle. For appraisal of existing structures, ISO 13822A2.6 together with A: Action with greatest value (risk reduction) this Report might perhaps be accepted as good B: Possible action practice. C: Best ‘value for money’ (in risk terms)
For projects where the consequences of failure are Figure A2.2 Illustration of ALARP large, it may be necessary to include consideration of societal risksA2.7, i.e., disruption to the normal way of life. Where there is clearly a risk, but uncertainty about how much risk, the Precautionary PrincipleA2.7 may apply. Society may require action beyond the The concept of gross disproportion is shown in ALARP criterion. Figure A2.2. The slope of the line bounding the area shaded in red is set at the ‘disproportionate’ The benefit of removing or reducing a risk also cost-benefit ratio (see below). Points above the line depends on the severity of the initial risk. For represent risk reduction measures for which the cost example, deafness, dermatitis and major injury are all is grossly disproportionate: no action is required. risks which are covered by ALARP. The points below the line represent risk reduction measures which are not disproportionate; if such Cost benefit analysis (CBA) is one way to review measures can be identified, there would be a legal whether risks are ALARP, and provides a useful obligation to adopt one of them. The law does not model for what is acceptable. However, The HSE state whether A, B or C would be preferred and do not expect that CBA will be used explicitly in opinions differ. For further information see references most cases. CBA is a useful model to develop A2.9 and A2.10, the latter drawing attention to understanding, but ‘good practice’ should be the quandary over the precise meaning of SFARP considered first. CBA attempts to place the risk and (‘so far as is reasonably practicable’), in the CDM the cost of reducing it on a common scale, often but regulations. not necessarily monetary. The factor for ‘gross disproportion’ is usually To demonstrate how a monetary CBA might be taken as at least 2, and can be up to 10 for large carried out, assume that a defect or shortfall in the risks, i.e., the cost would need to be more than structure was judged to have a 1 in 1000 risk of £3,210 – £16,050 to justify taking no action. If it is causing death. Taking a benchmark value of about not reasonably practicable to remove the whole £1,604,880 (June 2005 prices)A2.8 for the value of risk, but only to reduce it, the same test should be preventing a fatality (VPF) as proposed by the HSE, applied to the reduction in risk. In many cases, a the benefit of removing the risk would be valued qualitative argument will be sufficient to show where at £1605. The employer would be legally bound to the balance lies. It is sometimes argued that if a remove the risk unless the cost of doing so would be numerical assessment is necessary, the case is grossly disproportionate to the benefit, i.e., the cost sufficiently ‘borderline’ that action is required. It might was significantly more than £1605. If the cost was be unreasonable to expect the engineer to carry estimated to be, for example, £2400, this would not out a complete ALARP assessment as part of the be considered grossly disproportionate, and the risk appraisal, but any circumstances where ALARP may should be removed. apply should be brought to the client’s notice.
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In some other European countries an employer’s A2.10 Institution of Civil Engineers. A Review of, and commentary legal duty to protect employees is absolute, not on, the legal requirement to exercise a duty ‘so far as is limited to what is reasonably practicable. However, reasonably practicable’ with specific regard to designers the courts in such countries have discretion in the in the construction industry. Available at: http://www.ice. application of the law, which UK courts do not. org.uk/downloads//SFARP%20Report-v12-January10.doc [Accessed: 26 January 2010] In considering the suitability of premises as workplaces, the engineer should be aware of the A2.11 The Workplace (Health, Safety and Welfare) Regulations 2002 update to the Workplace (Health, Safety 1992. London: The Stationery Office, 1992 (SI 1992/3004) and Welfare) RegulationsA2.11 which requires that as amended by The Health and Safety (Miscellaneous "Where a workplace is in a building, the building Amendments) Regulations 2002. London: The Stationery shall have a stability and solidity appropriate to the Office, 2002 (SI 2002/2174) nature of the use of the workplace." This now puts a statutory duty alongside the common law duty of care and reinforces the requirement in the HSWA to provide a safe place of work. There is as yet no case law to help define ‘stability and solidity’, but the 2004 version of Approved Document A to the Building RegulationsA2.1 provides some guidance and further references. The regulations also require that premises "avoid excessive effects of sunlight and be adequately thermally insulated, having regard to the type of work carried out and the physical activity of the persons carrying out the work." The engineer should determine from the client whether these ‘non-structural’ aspects are within the scope of the appraisal.
Failure Modes [Causes] and Effects Analysis (FM[C]EA), using Event Tree Analysis (ETA) and Fault Tree Analysis (FTA), may also be carried out. These techniques are outside the scope of this Report.
A2.2 References
A2.1 The Building Regulations 2000. London: HMSO, 2000 (SI 2000/2531) and amendments
A2.2 Building Research Establishment. Structural appraisal of existing buildings for change of use. BRE Digest 366. Garston, BRE, 1991
A2.3 The Health and Safety at Work etc Act 1974. London: HMSO, 1974
A2.4 Edwards v. The National Coal Board [1949] 1 All ER 743
A2.5 Health and Safety Executive. Reducing risks, protecting people, Sudbury: HSE Books, 2001
A2.6 ISO 13822: 2001: Basis for design of structures – assessment of existing structures. Geneva: ISO, 2001
A2.7 The Royal Academy of Engineering. The Societal aspects of risk. Available at: http://www.raeng.org.uk/news/ publications/list/reports/The_Societal_Aspects_of_Risk.pdf [Accessed: 24 September 2009]
A2.8 Department for Transport. 2005 valuation of the benefits of prevention of road accidents and casualties. Highways Economics Note 1. Available at: www.dft.gov.uk/pgr/ roadsafety/ea/pdfeconnote105.pdf [Accessed: 26 January 2010]
A2.9 Institution of Structural Engineers. Risk in Structural Engineering. London: IStructE, 2011 {Due for publication 2011}
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A3.1 Introduction in the following tables and should be considered when evaluating possible causes and carrying out investigations. Tables of indicators of defects are given for four main building components: Note 2: In the following Tables in this Appendix: –T– able A3.1 Concrete –– under 'Test(s)', T refers to the tests in Appendix 7 –T– able A3.2 Masonry and A8 refers to the tests in Appendix A8 –T– able A3.3 Structural steel, cast iron and wrought –– under 'Reference', G, C, M, S, and Ti refer to the iron General, Concrete, Masonry, Steel and Timber –T– able A3.4 Timber references and bibliography given after the Tables. For each, the following notes apply: Between the Tables, photographic examples are Note 1: Generally, defective material and/or given. After these, general bibliographies and workmanship may be a factor in many of the defects bibliographies specific to materials are given.
A3.2 Tables of defects
Table A3.1 Building components: concrete
Component or Indication Possible cause(s) Investigation suggested Test(s) Reference element General Rust spots on surface Iron compounds in aggregates; Chemical analysis of samples T3, T8 nails/wire left in formwork General Rust stains on surface Corrosion of tying wire/ Check on cover; carbonation T7, T8 C7, C8 reinforcement General (see Cracking of concrete cover/exposure Corrosion of reinforcement (e.g. by Check adequacy of cover; test for T3, T20, C1, C7, C8
Figures A3.1-A3.3) of reinforcement CaCl2); nails/wire from formwork left chlorides T21, T22 in concrete cover Fire Visual examination – concrete white, straw or pink after fire T8 Phenolphthalein test for carbonation T7 General Surface crazing Construction fault: Check extent by small dia. coring T3, T8 C1 Mix too wet Poor curing General Cracks at intervals Restrained shrinkage; reinforcement Check frequency and details of T20, T8 C2, C7, C8, too near surface; corrosion of joints C10 reinforcement Check distribution reinforcement T3 Moisture movement Check for shrinkable aggregate T8 General Random diagonal cracking or lateral Inadequate provision for shrinkage Check reinforcement and spacing C1, C10 cracking at even spacing of joints Over rich/wet mix Analyse samples T3, T8 General Repetitive vertical or horizontal Excessive joint spacing Examine details T3, T8 C2, C10 cracks Shrinkage Check mix and aggregates Link corrosion General Surface abrasion Excessive wear Check plant loading T18 Poor abrasion resistance History of usage General Surface spalling Poor quality concrete Analyse samples T3, T8 C7, C8 Reinforcement corrosion Check reinforcement Chemical attack Frost attack General Wet and damp areas; deterioration Poor compaction Check spacing/detailing of joints of applied finishes, but no obvious Faulty or missing waterbars Check for vapour barrier and water cracking bars Test/analyse concrete T1, T2, T3
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Table A3.1 Continued
Component or Indication Possible cause(s) Investigation suggested Test(s) Reference element General Water penetration at joints or Faulty movement joints Check for vapour barrier and ‘cracks’ Faulty or missing waterbars waterbars Movement resulting from Investigate reason for movement inadequate joints or inadequate reinforcement General Rust staining below mortar covering Tendon corrosion Check location/extent of corrosion T21, A8.25 C8 of external prestressing Poor grouting of tendons General Cracking or spalling with or without Corrosion of tendons or Check condition of embedded steel; T7, T21, C8 rust staining (generally parallel to reinforcement check cover, carbonation, chloride T22, direction of steel) Corrosion of encased steel section content A8.21, A8.22, A8.25 ASR, restrained by reinforcement Check presence of ASR T8, T10 General Map cracking Alkali-silica reaction Check concrete constituents T3, T8, T10 C1, C3, C4, (see Figure A3.4) Petrographic analysis C5 General Map cracking on top surfaces Early drying-out of over-rich mix Remove laitence, check concrete T3, T8 C1 laitence underneath if necessary by coring General Dark colour HAC Analysis of samples T3, T8 C6 General Deflection Shrinkable aggregate Analysis of samples T3, T8 C6 Premature removal of formwork Overloading Design check C6 Ground-bearing Local settlements combined with Poor sub-grade compaction Investigate foundation and substrata C2, G1, G2, slabs diagonal cracks Inadequate reinforcement G3 Ground movement due to water/ erosion/mining/shrinkable clays, peat or other causes RC Beams Vertical or slightly inclined cracks If less than 0.3mm: normal action Compare actual load with design C1 on sides and soffit on central part of RC load of span If wider than 0.5mm: maybe Check span/depth ratios with Code C2 overload, excessive shrinkage of requirements slab, premature removal of props Check temperature gradient RC Beams Diagonally inclined cracks generally Overloading Check actual shear resistance C2 at/or near supports Under-reinforcement against shear against Code allowance Inadequate depth RC Beams Vertical cracks at regular intervals Shrinkage around stirrups/links RC Beams ‘Helical’ cracks in beam face and Torsional shear stresses Check actual torsional shear C2 extending around section perimeters resistance against code allowance RC Beams Excessive deflection Inadequate depth Check span depth/ratios with Code C2 Overloading (long-term) requirements Formwork defect Compare actual and theoretical C2 Inadequate or displaced deflections reinforcement Checking load history Shrinkable aggregate Materials defective or deteriorated Covermeter check T1, T2, Bond slip of reinforcement (possible Test concrete T3, T8, use of woodwool former) Check construction T20, T21 Presstressed Excessive deflection Overloading Check actual against design load T1, T2, T3, C2 Beams Overstressing or poor concrete T20, T21 Loose or defective anchorage Materials defective or deteriorated Check design T21, A8.4, Segment separation Covermeter check A8.25 Grout disturbance Segment shear cracks Prestressed Bowing Distortion during erection; concrete Check loading conditions; check T1, T2, T3, C2 Columns creep or shrinkage design; check for construction fault; T8, T20, Tendon fracture covermeter check T21, A8.4 Inadequate prestress Check tendon condition at any Displaced tendons fracture Materials defective or deteriorated
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Table A3.1 Continued
Component or Indication Possible cause(s) Investigation suggested Test(s) Reference element Slabs Excessive deflection Inadequate depth Check span/depth ratios with Code C2 Overloading (long-term) requirements Formwork defect Compare actual and theoretical C2 Inadequate or displaced deflections reinforcement Check loading history Materials defective or deteriorated Lack of continuity Covermeter check T20 Test concrete T1, T2, T3, T8 Check for shrinkable aggregates T8 Slabs Cracking of slab and/or finishes over Slab designed as simply supported Check design C2 support but constructed as continuous or Covermeter check T20 with fixed supports Inadequate top reinforcement in continuously designed slabs Excessive support moment relaxation Inadequate top steel at supports Top steel displaced Nibs and corbels Spalling Corrosion of reinforcement Covermeter check T20 C7, C8, (see Figures A3.5 Inaccurate positioning of top Check cover against Code C2 and A3.6) reinforcement requirement Check condition of embedded steel Absence of reinforcement Covermeter check Where present: expansion of brick Check actual against design loading C2 infill panels combined with elastic Check adequacy of movement joints shortening/shrinkage of concrete in panel walls frame Nibs and corbels Vertical cracking Inadequacy of top reinforcement Design check C2 Local bond failure Inadequate anchorage of top Check against reinforcement reinforcement drawings Corbels Wide vertical and/or diagonal cracks End rotation and/or thermal Check amount, arrangement and movement of supported beam with position of corbel reinforcement inadequate or displaced corbel Check deflection of beam reinforcement Nibs Horizontal ‘peeling’ crack on vertical Inadequate or displaced Check design, check reinforcement, face reinforcement check loading history Accidental overload Foundations Concrete turned to ‘mush’ Thaumasite (delayed external sulfate [Coring and] chemical analysis attack) Foundations Wide cracks Delayed ettringite formation (internal Coring and chemical analysis C9 sulfate attack)
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Figure A3.1 Spalling of cover/exposure of beam reinforcement Figure A3.5 Exposed concrete in nib
Figure A3.2 Spalling of cover/exposure of beam reinforcement Figure A3.6 Spalling
Figure A3.3 Spalling of cover/exposure of slab soffit reinforcement Figure A3.7 Wall out-of-plumb
Figure A3.4 ASR in foundations Figure A3.8 Diagonal crack following masonry joints
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Table A3.2 Building components: masonry Component or Indication Possible cause(s) Investigation suggested Test(s) Reference element General Wall out of plumb Foundation movement Foundation and subsoil G2, G3, G4, (see Figure A3.7) investigation; check trees; check G5, M2 drainage Lack of lateral restraint Check lateral ties M1, M2 Movement of floors, etc. If relevant check roof spread Horizontal forces not considered in design Cutting of horizontal chases Check construction M2 Sulfate attack on face Chemical tests Crushing of masonry on one face In long buildings with no internal Spread of pitched roof cross-walls: check stability of columns Check lateral tying and restraint General Vertical fractures, Foundation movement Foundation and subsoil G2 (see Figure A3.8) tapering cracks, Slip of sloping ground investigation; check drainage; diagonal cracks check existing trees and roots in following vertical and case of settlement; check removed horizontal masonry trees in case of heave joints Roof spread; overloading Check design; check roof; check M1, M2, M7, construction M9 Cutting of vertical chases Identify chases M2 Sulfate attack on mortar Chemical tests Thermal movement Check movement joints Movement of building frame Check records and compare M4 Previous structural alterations materials in situ General Bulge in wall or pier Inadequate lateral restraint (including tie corrosion) Check lateral ties M1, M2 Inadequate pier or wall bond (skin separation) Check construction Too slender pier Check design M1, M3 If wall is of two leaves with rubble core: inadequate Check if overall thickness increases M2 ties at bulge Core drill to check for rubble core General Spalling Repointing with hard mortar Check compatibility of mortar M2 Sulfate attack on convex face Chemical tests General Parallel horizontal Movement/corrosion of embedded metal Check condition of embedded cracks metal reinforcement, ties, etc. General Parallel vertical Overloading Check design M1, M2 cracks Thermal movement; drying shrinkage Check movement joints Monitor General Hairline fractures at Shrinkage of bricks Check brick type M2 vertical joints with Omission of movement joints Check construction details evidence of hairline Deflection of supporting structure Check adequacy of support cracks along bed- joints General Vertical constant Thermal expansion/contraction Check adequacy of joint provision M2 (see Figure A3.9) width cracks adjacent Corrosion of embedded steel section Check condition of section to return corners General Vertical displacement Ground subsidence Check as appropriate of walls Overloading Movement of supporting structure Cavity walls Bowing of outer leaf Inadequate lateral restraint Check for Code compliance M5 (see Figure A3.10) Inadequate tying of leaves (including tie corrosion) Check frequency, embedment T23 adequacy and condition of ties: borescope Unsuitable materials Check integrity of mortar joints Overloading Check design and details M5 Eccentric loading Check suitability of movement Inadequate detail design joints Creep, shrinkage and elastic shortening of concrete For infill brickwork: examine frame; expansion of brickwork supporting nibs/shelf angles
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Table A3.2 Continued
Component or Indication Possible cause(s) Investigation suggested Test(s) Reference element Cavity walls Horizontal fractures Inadequate support of external skin Check support detail in flank walls at Thermal movement due to underfloor heating Check presence of underfloor concrete floor levels heating Cavity walls Dampness on inside Condensation Check adequacy of cavity (50mm M5 (see Figure A3.11) face of inner leaf minimum recommended) Mortar droppings on ties or in base of cavity; or other Check for cavity bridging; cavity bridging borescope examination Omission of dpcs and/or weepholes in outerleaf Check presence of cavity dpc Faulty cavity insulation trays, weepholes Walls (cavity and Deterioration in Chemical attack (including Mundic) Visual examination; core sampling M1, M4 solid) concrete block work Overload Check design M5, M6 Crushing
Figure A3.9 Vertical crack near corner Figure A3.10 Bowing external wall, Lichfield © Brian Clancy Figure A3.11 Dampness on inside face of inner leaf
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Table A3.3 Building components: structural steel, cast iron and wrought iron
Component or Indication Possible cause(s) Investigation suggested Test(s) Reference element General Excessive deformations Out of plumb columns Check safety, if in doubt consider closure or T24 to S5 Poor fabrication or erection temporary support T36 General Distorted or buckled Overloading or design fault Check design and detailing S1, S5 (see Figure A3.12) members; bowing of Wrong steel grade Check construction against details beams, ties and bracings Inadequate bracing or lateral support Check design Poor fit, slip or failure of supports/ Check connections for lack of bolts, connections inadequate bolt tightness, poor welding Impact Check for accidental damage Fire Check for signs of fire damage, including crystal structure changes General Distortion/damage to Unsatisfactory baseplate arrangements Check geometry of structure against that S5 windows, doors or cladding intended Impact Check for accidental damage Elevated temperature beyond design Investigate possible elevated temperatures range Removal of key members Identify structural system Defective foundations or differential Check foundation adequacy settlement General Unacceptable flexibility/ Wind or out-of-balance machinery Check performance of structure in absence vibration of structure or of wind or operating machinery structural members Check adequacy of anti-vibration mountings Vortex shedding on circular structures Relate natural frequency of structure to that of exciting forces Members inadequately braced Identify structural system General Missing weld or welds of Oversight Check weld quality by NDT T27, T28 poor appearance Unsatisfactory welding General Fractured material Poor welding Check weld quality by NDT T27, T28 which may have surface Fatigue Specialist investigation appearance varying from Brittle fracture Specialist investigation smooth to crystalline General Cracks on surface of welds Poor welding Check weld quality by NDT T27, T28 or heat affected zones General Cracks within thickness Lamellar tearing (caused by high Ultrasonics; at welded connection; not restraint to weld contraction, out of the test coupon for through thickness ductility; usually visible until failure plane of rolling; insufficient preheat; Specialist investigation occurs; sulfide inclusions; steel not specified surface of the fracture is with through thickness ductility.) fibrous and ‘woody’ General Cracks where liquid metal Liquid metal embrittlement: Specialist investigation S4 present (galvanising, brittle fracture accelerated by liquid mercury, etc.) metal General Cracks initiate at stress Fatigue or brittle fracture Design/detail check raisers Specialist investigation General Joint slip; connection Overloading Check loading, size and effectiveness of S2 (see Figure A3.13) tearing; metal distortion Incorrect fastener fasteners adjacent to holes Incorrect bolt tightening Poor hole punching Hole drift during erection General Open holes missing Badly fitting fasteners Replace missing fasteners S5 fasteners; loose rivets, Fasteners not installed Check adequacy of fasteners bolts, nuts Distorted fasteners Misaligned/misplaced holes Check for building sway Uneven head/nut seating Defective fasteners Check hole accuracy Gaps between bearing Defective bolting Check design and detailing plates Deformation due to welding General Corrosion Environmental attack Ascertain type of corrosion (see Figure A3.14) Presence of moisture Identify sources of moisture Failure of protective system Check section sizes for residual adequacy Stress/galvanic corrosion Check protective system
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Table A3.3 Continued
Component or Indication Possible cause(s) Investigation suggested Test(s) Reference element General Cracking of concrete Corrosion of structural steel Check condition of embedded steel casing Corrosion of casing reinforcement General Distortion of bearings Eccentric bearing Check design detail for precast floor units or Twisting of steel section cladding Sheet piling and Severe unexpected Accelerated low water corrosion Check level of corrosion S3 marine structures corrosion near low water (caused by sulfate reducing bacteria Check thickness of steel required level, bright orange colour existing defects on surface electrochemical action)
Figure A3.12 Failure of overloaded member Figure A3.15 Dry rot in timber
Figure A3.13 Severe shear deformation Figure A3.16 Timber deterioration
Figure A3.14 Rust flake detaching from steel Figure A3.17 King rafter having moved stanchion and no longer adequately supported
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Table A3.4 Building components: timber
Component or Indication Possible cause(s) Investigation suggested Test(s) Reference element General Cubic crazing Fungal attack Check water entry T47, T48 (see Figure A3.15) Discolouration Dry rot (red dust useful indicator) Check ventilation Crumbling Mycelium Check tendril spread Fungal growth Water entry Check extent of structural damage Smell Lack of ventilation General Discolouration Wet rot Check extent of inspection and structural T47 Splitting Water entry damage Softening Smell Stringy appearance General Holes 1-3mm Insect attack (death-watch and other Check extent of inspection and structural T46 diameter on surface beetles) damage Dust General Splits Drying-out Check moisture content Ti1, Ti2 (see Figure A3.16) Inadequate seasoning Check design Overloaded bolts/connectors Overloaded 'carpentered' joints Flat roofs Sagging Structural deflection Check design/detailing Ti1, Ti2, Ponding Ti3, TI4 Change of roof cover Check construction G6 Change of loading Check timber condition Lack of falls Timber defects (see general) Joint inadequacy Pitched roofs (see Ridge sag Rafter spread Check design/detailing Figures A3.17 and Walls out-of-plumb Removal of rafter/purlin support Check construction Check timber condition A3.18) Non-planar roof Lack of bracing Check roof bracing surface Change of roof cover Check wall plumb Tile course Rafter/purlin deflection Check roof ties/backing disturbance Timber defects (see general) Check timber condition Joint inadequacy Check roof cover Aircraft wake vortices Valley beam sag Excessive deflection Check design/detailing Ti2, G6 Removal of supporting wall Check construction Timber defects (see general) Check gutter Joint inadequacy Check timber condition Floors Sagging Undersize joists or beams Check design/detailing Ti2 Flexibility Notching Overloading Lack of strutting Check construction Timber defects Check timber condition Joint inadequacy Adhesive breakdown in laminated beams Columns and Buckling Excessive loading As for floors As floors posts (including Twisting Lack of restraint loadbearing stud Crushing Timber defects partitions) Joint inadequacy Beams Excessive deflection Overloading As for floors As floors (see Figure A3.19) Buckling Lack of restraint Twisting Joint inadequacy Adhesive breakdown in laminated construction Timber defects
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Figure A3.18 Damp staining to timbers at hipped end Figure A3.19 Defective joint in purlin
A3.3 References / Bibliography Building Research Establishment. Defect action sheets: the complete set. Garston: BRE, 2001
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S5 Bates, W. Historical structural steelwork handbook. London: BR 218 Weir steel-clad (1920s) houses BCSA, 1984 BR 219 Stuart steel-framed houses BR 221 Riley steel-framed houses Association for Specialist Fire Protection. Fire protection for BR 222 Coventry Corporation steel-framed houses structural steel in buildings. 4th ed. Aldershot: ASFP, 2007 Digest 317: Fire-resistant steel structures
Bates, W. Historical structural steelwork handbook. London: A3.3.5 Timber BCSA, 1984 Ti1 Carmichael, E.N. Timber engineering: practical design Breakell, J.E. et al. Management of accelerated low water studies. London: Spon, 1984 corrosion in steel maritime structures. CIRIA C634. London: CIRIA Ti2 BS 5628: Structural use of timber [Various parts]
IABSE. Remaining fatigue life of steel structures: IABSE Ti3 Flat roofing: a guide to good practice. Tarmac, 1982 workshop, Lausanne, 1990. IABSE Report 59. Zurich: IABSE, 1990 Ti4 Arup Research and Development and British Flat Roofing Council. Flat roofing: a guide to good practice. CIRIA Book Lawson, R.M. Fire resistant design of steel structures: a 15. London: CIRIA, 1993 handbook to BS 5950: Part 8. SCI Publication 80. Ascot: SCI, 1990 Bravery, A.F. et al. Recognising wood rot and insect damage in buildings. Princes Risborough: BRE, 1987 Lawson, R.M. and Newman, G.M. Enhancement of fire {Since superseded by Bravery, A.F. et al. Recognising wood resistance of beams by beam to column connections. SCI rot and insect damage in buildings. BRE Report BR453. 3rd Publication 86. Ascot: SCI, 1990 ed. London: BRE Bookshop, 2003
Moon, J.R. ‘Chapter 5: Steel’. In Doran, D.K. ed. Building Research Establishment. Supplementary Construction materials reference book. Oxford: guidance for assessment of timber framed houses. Part 1: Butterworth-Heinemann, 1992 Examination. BRE Good Building Guide 11. Garston: BRE, 1993 Standing Committee on Structural Safety. Liquid metal assisted cracking of galvanised steelwork: SCOSS Topic Building Research Establishment. Supplementary Paper SC/T/04/02. Available at: www.scoss.org.uk/ guidance for assessment of timber framed houses. Part 2: publications/rtf/LMAC_Final_Version_3.pdf and update Interpretation. BRE Good Building Guide 12. Garston: BRE, SC/06/59 www.scoss.org.uk/publications/rtf/Liquid Metal 1993 Assisted Cracking.pdf [Accessed: 1 October 2009] Damage to roofs from aircraft wake vortices. Digest 391, Building Research Establishment Steel-framed and steel- BRE, 1994 {Since superseded by Blackmore, P. Slate and clad dwellings, BRE Reports dealing with the following tile roofs: avoiding damage from aircraft wake vortices. industrialised systems: BRE Digest 467. London: CRC, 2002} BR 77 BISF steel-framed house BR 78 Howard steel-framed house Ozelton, E.C. and Baird, J.A. Timber designers’ manual. BR 110 Dorlonco steel-framed houses 3rd ed. Oxford: Blackwell Science, 2002 BR 111 Thorncliffe cast-iron panel houses BR 113 Steel-framed and steel-clad houses: inspection Ross, P. Appraisal and repair of timber structures. London: and assessment Thomas Telford, 2002 BR 119 Roften steel-framed houses BR 120 Dennis-Wild steel framed houses Sunley, J.G. ‘Chapter 50: Timber’. in Doran, D.K. BR 132 Cussins steel-framed houses ed. Construction materials reference book. Oxford: BR 133 Livett-Cartwright steel-framed houses Butterworth-Heinemann, 1992 BR 139 Cruden rural steel-framed houses BR 144 Falkiner-Nuttall steel-framed houses Yeomans, D. Repair of historic timber structures. London: BR 145 Crane steel-framed bungalows Thomas Telford, 2003 BR 146 Trusteel MKII steel-framed houses BR 147 Trusteel 3M steel-framed houses BR 148 Atholl steel BR 149 Dorlonco supplement to BR 110 BR 152 Hawthorn Leslie steel-framed houses BR 163 Nissen-Petren steel-framed houses BR 188 Lowton-Cubitt steel-framed houses BR 189 Telford steel-clad houses BR 193 Cranwell steel-framed houses BR 196 Birmingham Corporation steel-framed houses BR 197 Hills Presweld steel-framed houses BR 198 Arcal steel-framed houses BR 199 Homeville industrialised steel-frame houses BR 200 5m steel-framed houses BR 201 Arrowhead steel-framed houses BR 202 British Housing steel-framed houses BR 203 Keyhouse Unibuilt steel-framed houses BR 204 Open system building steel-framed houses BR 205 Steane steel-framed houses BR 217 Comeson steel-clad houses
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A4.1 Introduction
For some years consideration has had to be given to how buildings behave in collapse situations. This has become necessary for a variety of reasons which include accidental damage and deliberate sabotage. Since the events of 11 September 2001, the range of threats which may need to be considered has increased substantially. Appraisal may be necessary in order to establish the resistance of a structure to loads for which it was not designed, or to determine its condition following such an event. In many cases, it will not be expected that the building would remain intact, only that it should remain sufficiently stable to protect the lives of the occupants while they escape.
The partial collapse of a high rise block of flats in London (Ronan Point, Figure A4.1) in 1968 showed the need to design against accidental damageA4.1. As a result UK Building Regulations and some codes of practice issued since that time have included provisions relating to disproportionate collapse of buildings.
While the regulations and codes require some buildings not to suffer collapse to an extent disproportionate to the cause of the accident, it was not originally envisaged that these regulations Figure A4.1 Ronan Point, London © HR Cresswell would also be applicable to conditions resulting from deliberate attack by terrorist organisations. Such attacks have however made owners aware of the need for assessment, and possibly protection, of their buildings.
Following the 11 September attacks, a substantial effort has been put into this topic, worldwide. Significant publications for structural engineers are the Institution of Structural Engineers' report on Safety in Tall BuildingsA4.2, the ASCE reportA4.3 on the performance of the Pentagon building and the FEMA report on the World Trade CenterA4.4 (Figure A4.2). Apart from the insight they offer into the performance of buildings, these two US reports are also good examples of forensic structural appraisal. Reference should also be made to the Institution of Structural Engineers’ Practical guide to structural robustness and disproportionate collapse in buildingsA4.5.
Engineers should therefore be aware of the vulnerability and behaviour of buildings in such conditions. Building owners may need advice on measures that can provide protection and limit damage to their business and property, and to reduce casualties among building occupants. UK Building RegulationsA4.6 have for some time included requirements designed to restrict progressive or disproportionate collapse, the scope of which has been revised several times. Whether required by regulations or not, the engineer should inform the client of perceived vulnerabilities which may result in an unacceptable risk of harm to people. Figure A4.2 World Trade Center © Patrick S McCafferty/Arup
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The assessment of potential and actual effects A4.2 Sources of severe damage of explosion on existing buildings in the threat situation, and after an incident has occurred, is considered in this Appendix. The engineer’s advice A4.2.1 Explosions due to deflagration should be based on assessment of the impulses produced by explosive blastwaves or other events, Explosions may be caused by rapid ‘burning’ of the relationship of these to the performance of gas-air mixtures. A deflagration has no ‘shock the building and its structure, and the ways to front’ as occurs in detonation and will only ensure robustness in the structure. It should be generate high pressures if confined. Domestic recognised that this is not an exact science and gas explosions in buildings can result from gas that any predictions are only indicative. leaking from mains, cylinders or appliances into the building; these are usually deflagrations Under UK Building Regulations, design against and are a more likely cause of loading than disproportionate collapse is required for all detonations. Deflagration is generally less new buildings. The 1992 issue of Approved destructive than detonation, although deflagration Document A, StructureA4.7, limited the application in a confined space can nevertheless generate of this requirement to buildings of five or more significant pressure. Compared to detonation, storeys. Earlier versions were limited to buildings a relatively long duration of loading is produced with more than five storeys, i.e., the 1992 issue which can impose large static pressures on brought five storey buildings under the rule. The the adjacent elements of a building. Specific 2004 issue of Approved Document AA4.6 removed explosion hazards may occur in industrial any limitation, so that all buildings are covered. buildings and information should be obtained The approved document provides guidance, for from the client. different classes of building, on how to reduce the sensitivity of buildings to disproportionate collapse. A4.2.2 Explosions due to detonation
There are two principal approaches; to ensure Explosions may also be caused by the detonation that the building has sufficient redundancy that of a high-explosive charge. Such explosions loss of any member can be tolerated, or to design can occur for a number of reasons, including ‘key members’, failure of which would otherwise controlled explosions for blasting or demolition, result in disproportionate damage, to resist all accidental detonation of stored explosives and foreseeable abnormal loads. Such members, wartime relics. However, sabotage or terrorism therefore, have to be either protected from any has now become the main potential cause foreseeable accident or designed for a loading of damage to buildings from high-explosive representing the effect of an accident (which detonations. was notionally related to the risk associated with an explosion arising from an unlimited piped Such detonations are very fast chemical gas supply). This loading has been given as reactions and in an unconfined situation they 34kPa in the approved document and also in give rise to transient air pressure waves travelling BS 6399: Part 1A4.8 to serve as a device so that away from the source of the explosion, and buildings have a suitable level of provision against producing high overpressures. The peak and disproportionate collapse, irrespective of the duration of the overpressures vary with the nature of any gas supply provided at the time of distance from the source of the explosion, the construction. size of charge and packaging.
Existing buildings with five or more storeys An explosion in a street (Figure A4.3) will produce may have to be appraised with regard to the a blast wave which, when resisted or reflected, provision against accidental loading, for example, may build up and impose high pressures on on account of some material alteration to their adjacent structures. It can pass over and around framework or use requiring their compliance with buildings to affect all faces. Buildings may be Building Regulations 2000A4.9. Such appraisal subject to more than one pulse of pressure should depend on the type of construction and because of blast reflection, but the initial pulse is the assessment of risk in an accident which the significant one. could be related to the provision of gas supply in the building. ResearchA4.10 has shown that For a detonation in close proximity to a building, for a building without any piped gas supply the damage is likely from debris impact produced maximum pressure likely to be developed in an by the device and its carrier – disintegrating explosion is 17kPa. If it is certain that such a vehicles, street furniture and adjacent buildings building will remain without any piped gas supply, – in addition to that caused by the increased the loading for the assessment of ‘key’ elements effective blast pressure. Debris is often the (or, in case of large-panel structuresA4.11, for main threat to occupants, and buildings should checking the design of unvented confining surfaces preferably have areas away from windows, of the enclosure as appropriate) may be taken as protected by solid partition walls, where 17kPaA4.12. occupants can shelter if a bomb warning is received.
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Figure A4.3 Devastation following the Manchester Bomb in 1996 © Greater Manchester Police
A4.2.3 Impact of massive objects such as vehicles or A4.2.4 Earthquake resistance aircraft The need for earthquake resistance is related to the The consequences of impact damage will quite location of the building and its importance. In the possibly have not been considered in the design of UK, one of the least seismically active areas of the existing structures. The probability of impact should world, only nuclear installations and some bridges be discussed with the client. The most common are designed to resist earthquakes, but in most of source of impact damage is road vehicles: although the rest of the world, the risk is significant. Although this generally affects only low rise structures, there earthquake engineering is a specialist field, there is no recorded incident of a road vehicle causing are a number of criteria which a non-specialist significant damage to a building of five or more engineer can use to judge whether a building may storeys. Terrorist attack using aircraft is unlikely to be vulnerable to earthquakes, and thus whether be a consideration for most structures, however in specialist advice is required. a preliminary study BRE has found that the risk of greatest damage to large panel structures over five Good features for earthquake resistance: storeys in height arose from aircraft impact. –– steel frame with ductile connections –R– C frame and shear walls (but dependent on good The principal physical mechanisms involved in impact detailing and shear reinforcement, which may be are the transfer of momentum from the impacting difficult to check for) object to the structure, the stresses involved in –– symmetry in plan, elevation, loading and stiffness transmitting this to the ground, and the dissipation of –– foundations piled or bearing on rock kinetic energy at the point of impact. –– redundant load paths –– clear lateral load resisting systems The response of a structure to impact can therefore –– general robustness (as discussed above in relation be considered in terms of global and local behaviour. to Building Regulation A3). Global behaviour is dependent on the mass and natural frequency of the whole structure. The lower Vulnerable features for earthquake resistance the natural frequency, the more chance the structure (Figure A4.4): has of absorbing the impact and transmitting to the –– loadbearing masonry, especially rubble walls foundations over a longer timescale. Local behaviour –– significant changes in building form or stiffness with depends more on the strength of the structure at the height point of impact, and determines whether the object –– irregular plan shape, or re-entrant corners will cause failure of structural members or punch –– soft ground (particularly with a high water table) through the perimeter walls. and pad foundations –– structures close together, or tied with no provision For any vehicle or aircraft carrying fuel, the effects for differential movement of fire are likely to be more significant. The chemical –– adjacent structures with vulnerable features. energy of the fuel in an aircraft may be 1000 times the kinetic energy, and will result in a fire which will No British Standard covers resistance to overwhelm any normal fire fighting system. This will earthquakes. BS EN 1998A4.13 relates specifically to ignite the building contents, which contain more seismic design, but as a design code, is unlikely to be thermal energy, and, as in the World Trade CenterA4.4, relevant to appraisal. Where required, expert advice may lead to collapse. For further information on is recommended. assessing the vulnerability of buildings to fire, see Appendices 5 and 6.
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Figure A4.4 Kobe Earthquake
A4.3 Engineering advice in relation to Typical buildings may resist impact of a light aircraft explosion damage or medium sized vehicle; it is not practical, however, to design any ordinary building to resist the impact of large aircraft and it is necessary to assume that Generally engineering adviceA4.14, A4.15 may be severe damage will occur. For an ordinary building, required to: such damage would not be disproportionate to the –– Evaluate the potential of an existing building to event and would therefore be acceptable. withstand the effects of an agreed explosive blast or impact scenario and to indicate the possible These tasks will require the following: damage level (pre-event advice). –A– n assessment of the risk of the building being –G– ive structural advice on the damage that has been subject to explosion. Such an assessment is caused to a building by an explosion or impact, and usually carried out by a specialist and is based on on the extent of demolition and/or on the repair and such considerations as location, type of occupation remedial works required (post-event advice). and security condition of the building itself and –A– dvise on measures to reduce the risk of explosion adjacent buildings or installations. or impact (e.g. removal of gas supply). –A– n estimate of the size of charge and type of explosive to be considered and its possible A4.3.1 Pre-event advice location(s) relative to the building. –D– etails of the building and its environment, Appraisal of the dynamic performance of the including date of construction, floor plans, design construction of existing buildings, and prediction criteria, structural form, material properties, of blast attenuation and decay around and through current condition and state of maintenance. This the buildings, in the event of an explosion may be information forms part of an ordinary appraisal (see required in order to: Chapters 3 and 4 and Appendix 1). –A– ssess the likelihood of structural collapse and the extent of possible damage to the structure and Some of the factors affecting the ability of a building fabric. to resist a blast are: –A– dvise on protective measures for the building and/ or work necessary to enhance its blast resistance. Disproportionate collapse: Whether the –A– dvise on measures (bollards, barriers, etc.) to building was designed to the requirements of the prevent the placing of devices in close proximity to Building Regulations relating to progressive or the building. disproportionate collapse. Following the collapse –I– dentify vulnerable areas of the building and those of Ronan Point, Ministry of Housing and Local areas suitable for escape routes, shelters and Government circulars 62/68A4.12 and 71/68A4.16 for emergency assembly points for the reasonable large-panel structures six storeys or more in height protection of persons, valuable plant, equipment, prescribed checks and strengthening. documents, etc. –I– dentify openings, such as ventilation louvres, which Form of structure: Framed buildings in ductile could allow blast into the building. materials – steel, reinforced concrete, –A– ssess the likely response to various types of reinforced masonry – tend to behave better in a blast impact, to allow planning of post-event actions. situation than those constructed of unreinforced masonry. The ductility, damping and the natural
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period of vibration determine the response of Work carried out to render a building safe and a building to blast or impact. Continuity of the reusable will need to satisfy the local authority and, structure, the presence of alternative load paths, and in the case of a listed building, the planning authority the ability to arch or to act as a catenary, all enhance and/or the national heritage bodies should be notified the ability of a building to withstand explosive forces as soon as possible of intended work. without disproportionate damage. The immediately obvious indication of an explosion Permeability: Windows, doors, ducts and service is the visible damage to the building. There may, openings are vulnerable points for external blast to however, be hidden damage, for example, to the penetrate buildings. If strengthening glazing in order fixings of cladding panels; and ground shock can to protect the interior of a building, consideration cause damage to buried services. should be given to the transfer of blast loads on to frames, fixings, cladding and structure and the Some typical damage caused by explosives: consequences of such strengthening in the event of an internal or external explosion. Blast dampers Masonry can be fitted to ducts and other openings to restrict –– missing, fractured, bulging, displaced or out-of- the entry of blast into the building and to protect vital plumb walls services. –– vertical fracturing at wall junctions –– fractured or unsupported arches Vulnerable elements: The blast effect of a –– spalling or fracturing of masonry units. detonation can dislodge elements such as external cladding, partitioning, heavy false ceilings and plant. Steel Many people have been injured by glazing fragments –– excessive permanent deformation or distortion from blast loads, but laminated glass is much safer –– buckling or failure of slender members in this situation than annealed or toughened glass. –– failure, distortion or springing of bolted or welded Although glazing is not usually structural, if the connections. client’s requirements include consideration of blast resistance, the engineer would be wise to consider Reinforced and pre-stressed concrete the type of glazing. –– fracturing, cracking, spalling and loss of concrete cover Clients must not be led into false expectations of –– shear and flexural failure, showing as wide cracks the performance of a building in the event of an –– failure in floors and other members because of load explosion or into a false sense of security. The limits reversal of any advice and the limited aims and objectives of –– dislodging of precast units. any proposed measures or work carried out must be clearly pointed out to clients. Timber –– failure of joints –– flexural failure –– displacement of members A4.3.2 Post-event –– lifting and distortion of roof structures.
Health and safety will be the immediate concern The degree of damage and the need to repair or post-eventA4.17: see Chapter 7 regarding the replace will be apparent in the badly damaged parts obligations of the appraising engineer. of a structure. In areas further from the source of explosion, if there is no visible damage, the structure After an explosion, parts of a building may be may well be safe, but the possibility of hidden left standing while being in a dangerous state. damage, such as may have occurred to concealed Emergency works may have to be carried out in fixings, must be considered. order to render the building safe for access and for emergency services to operate. The removal of loose Some examples of damage not immediately and broken glass and loose cladding is usually a high apparent that may require closer investigation and/ priority. or testing are cracked welds, failure of shear studs in composite construction, slip in HSFG bolted The emergency works will have to be arranged in joints, and failure of concealed cladding fixings. The consultation with the emergency services in order subsequent repair or demolition and rebuilding after that they can be coordinated with other operations. damage caused by explosions is straightforward and would be dealt with in the usual way. As with any dangerous structure, a full survey and inspection of the structure will need to be carried out. The survey should be done with extreme care taking into account the survey and safety sections of this A4.4 References Report. It may be wise to carry out initial inspections from a Mobile Elevated Work Platform (MEWP or ‘cherrypicker’) adjacent to the structure, starting from A4.1 Ministry of Housing and Local Government. Report of the the top. From below, a floor slab may appear intact, Inquiry into the Collapse of Flats at Ronan Point, Canning while actually supporting debris from the upper floors Town. London: HMSO, 1968 and being on the point of collapse. A4.2 Institution of Structural Engineers. Safety in tall buildings Instructions may also have to be given for demolition, and other buildings of large occupancy. London: IStructE, removal of debris, shoring and temporary support 2002 works to make a structure safe. First-aid repairs may also be needed to avoid further deterioration.
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A4.3 Mlakar. P.F. et al. The Pentagon building performance A4.5 Bibliography report. Reston, VA: ASCE, 2003
A4.4 FEMA. World Trade Center building performance study. Baker, W.E. Explosion hazards and evaluation. Amsterdam: Available at: http://www.fema.gov/rebuild/mat/wtcstudy. Elsevier, 1983 shtm [Accessed 1 October 2009] Biggs, J.M. Introduction to structural dynamics. New York: A4.5 Institution of Structural Engineers. Practical guide to McGraw-Hill, 1964 structural robustness and disproportionate collapse in buildings. London: IStructE, 2010 [Not yet published] Institution of Structural Engineers. Notes for guidance which may assist in the interpretation of Appendix 1 to Ministry of Housing A4.6 Office of the Deputy Prime Minister. The Building and Local Government Circular 62/68. RP/68/02. London: Regulations 2000. Approved Document A: Structure. IStructE, 1968** Available at: http://www.planningportal.gov.uk/uploads/br/ BR_PDF_AD_A_2004.pdf [Accessed: 1 October 2009] Institution of Structural Engineers. Structural stability and the prevention of progressive collapse. RP/68/01. London: IStructE, A4.7 DETR. The Building Regulations 1991. Approved Document 1968** A: Structure. Available at: http://www.planningportal.gov. uk/uploads/br/BR_PDF_AD_A_1992.pdf [Accessed: 1 Matthews, S.L. and Reeves, B. Assessment of large panel October 2009] buildings under accidental loading. ASELB Spring Seminar, IStructE, London, 7 April, 2006. Available at: http://www.aselb. A4.8 BS 6399-1: 1996: Loading for buildings. Part 1: Code of com/pdf/sem1.pdf [Accessed: 26 January 2010] practice for dead and imposed loads. London: BSI, 1996 Mays, G.C. and Smith, P.D. eds. Blast effects on buildings. A4.9 The Building Regulations 2000. London: The Stationery London: Thomas Telford, 1995 {Since superseded by Cormie, D., Office, 2000 (SI 2000/2531) Available at: http://www. Mays, G.C. and Smith, P.D. eds. Blast effects on buildings. 2nd ed. hmso.gov.uk/si/si2000/20002531.htm [Accessed: 1 London: Thomas Telford, 2009} October 2009] Morton, J. Accidental damage robustness and stability. Design A4.10 Ellis, B.R. and Currie, D.M. ‘Gas explosions in buildings Guide 15. Windsor: Brick Development Association, 1996 in the UK: regulation and risk’. The Structural Engineer, 76(19), 6 October 1998, pp373-380 Smith, P. and Hetherington, J. Blast and ballistic loading of structures. Oxford: Butterworth-Heinemann, 1994 A4.11 Currie, R J., Armer, G.S.T., and Moore, J.F.A. The Structural adequacy and durability of large panel systems. Part 2: US Department of the Army et al. Structures to resist the effects of Guidance on appraisal. Garston: BRE, 1987** accidental explosions. TM5-1300. Available at http://www.dtic.mil under ADA243272 [Accessed: 1 October 2009]. {Superseded by A4.12 Ministry of Housing and Local Government. Flats UFC 3-340-02. Available at: http://www.wbdg.org/ccb/DOD/UFC/ constructed with precast concrete panels. Appraisal and ufc_3_340_02_pdf.pdf [Accessed 1 October 2009]} strengthening of existing high blocks. Design of new blocks. Circular 62/68. London, HMSO, 1968** Yandzio, E. and Gough, M. Protection of buildings against explosions. SCI Publication 244. Ascot, SCI, 1999 A4.13 EN 1998: Eurocode 8: Design of structures for earthquake resistance [6 parts] References and bibliography entries marked ** are expected to be superseded in 2010 by the following new guidance to be A4.14 Elliot, C.L., Mays, G.C., and Smith, P.D. ‘The protection of issued by BRE: Matthews, S.L. and Reeves, B.R. Assessment of buildings against terrorism and disorder’. ICE Proceedings, large panel system (LPS) dwelling blocks for accidental loading: Structures & Buildings, 94(3), August 1992, pp287-292 handbook
A4.15 Walley, F. ‘The effect of explosions on structures’. ICE Proceedings Structures & Buildings, 104(3), August 1994, pp325-334
A4.16 Ministry of Housing and Local Government. Flats constructed with precast concrete panels. Appraisal and strengthening of existing high blocks. Design of new blocks. Circular 71/68. 20 December 1968 London: HMSO, 1968**
A4.17 Institution of Structural Engineers. The structural engineer’s response to explosion damage. London: IStructE, 1995
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A5.1 Introduction fundamental criteria and reasons for the appraisal and the framework within which the procedure will be controlled. Fire is an important accidental load case and thus it is essential that due consideration is given to the This Appendix 5 deals with the performance of robustness of an existing structure in the event of a existing structures before a fire. To appraise the fire and to the life safety of the occupants and the performance of existing structures after a fire, rescue services. In this Appendix 5 and the following on which advice is given in Appendix 6, it is of Appendix 6 the appraisal of the fire performance of course essential that the engineer understands the existing buildings without and with fire damage are background to the fire resistance of undamaged discussed and the scope and motivation for both structures: it is therefore assumed that the reader will parts can be summarised as follows: digest Appendix 5 before tackling Appendix 6.
Appendix 5 – There is often a need to predict the A5.1.1 Legislation (England and Wales) future performance of an existing structure because of changes in occupancy, changes in ownership The Fire Precautions Act 1971A5.6 and many other or the desire to comply with current standards in items of fire safety legislation were repealed and an old structure. Knowledge of the materials used replaced by The Regulatory Reform (Fire Safety) and the assumptions that were made at the time Order 2005A5.7 (RRO), with effect from 1 October are useful. However there is great benefit in being 2006. RRO is, however, intended to consolidate able to reinterpret the structure using a modern fire and clarify the law, not to change the legal view of engineering approach if there are any weak points to what constitutes a safe building, so it has little effect be explored or if there is any redundancy that can be on the advice given in this Report. One significant exploited. change is that fire certificates are no longer required. Instead, the ‘Responsible Person’, as defined in the Appendix 6 – After a fire there is always a chance RRO, must carry out a risk assessment. Enforcement that some or all of a structure can be reused and action may be taken if the risk assessment or the fire therefore determining the degradation of materials precautions are inadequate. is most important. Reinterpreting the structural performance is also important in this respect. All Where there is no ‘material alteration’, as defined in structures that are exposed to a substantial fire are Section 0.20 of Approved Document B Fire SafetyA5.4 likely to deflect substantially or suffer damage or (ADB), to the building (i.e. it is no less compliant), no both. Compliance with tests does not mean that additional fire protection measures will be required. repairs will be unnecessary. However it is important If there is a material alteration, the building must to put the cost of structural repairs into context. In be brought up to the full standard in the Building a highly serviced building with lifts and expensive RegulationsA5.8 and their ADB or BS 9999A5.5. In this cladding which have been affected by fire, it is likely case the enforcing authority is Building Control. that the structural repair costs will be relatively small as long as the structure was designed and built A material alteration includes change of use, for properly. example modifying an office to a residence, and could include modifying the means of escape from a building. The Institution of Structural Engineers has published two guides on the fire safety of structuresA5.1, Where an existing building is modified to such degree A5.2 which give much more information than can that a ‘material alteration’ is caused but its overall be shown here. The guides are mainly focused fire safety is not reduced as a consequence of the on new structures but the considerations and modification, it is reasonable for the fire authorities to principles described in the guides can be adapted allow the modification to go ahead without additional for existing structures as long as the behaviour of fire safety measures or changes. materials and structure during and after a fire are understood. BS 7974: 2001A5.3 gives good guidance Where the building is modified, a material alteration on the procedures to undertake a fire engineered is caused and its overall fire safety is reduced as a assessment of an existing structure. Furthermore, the consequence, the authorities will recommend the Approved Document B (Fire safety)A5.4 and BS 9999: building be brought up to the full standard in the 2008A5.5 give good guidance for the fire safety of codes. However, some flexibility can be expected normal structures. for existing structures as it is not often practical fully to comply with modern standards. This will be The responsibility for an appraisal of fire safety can negotiated on a case by case basis and professional vary depending on the brief. Structural engineers, advice from a fire safety engineer should be sought architects and building services engineers may to maximise value without compromising safety. be involved. Increasingly there is a requirement for the specialist services of a fire safety engineer The risk to the occupants from fire must still be for more complex buildings. It is important to acceptable by the standards of today’s society. The define responsibilities clearly at the outset. Before Regulatory Reform (Fire Safety) OrderA5.7 applies to attempting to carry out a fire safety appraisal of all non-domestic premises and includes requirements an existing building it is necessary to establish the for fire safety arrangements, fire-fighting and fire
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detection, emergency routes and exits and treatment (3) If the initial appraisal is inconclusive, the structure of dangerous substances. Failure to comply may appears to be inadequate or the resulting fire result in enforcement action by the fire service, which protection works would be economically or could include prohibition of use pending alteration. architecturally unacceptable, a structural fire engineering approach could be adopted (see A5.1.2 Non-compliance Section A5.4.1). Materials testing and further detailed site surveys may be required. It is important to report to the client where and how the building does not comply with modern (4) Consider the benefits of carrying out fire standards. It is also important to distinguish resistance testing. between non-compliance with legal requirements and areas where the building, although as safe as is (5) Prepare documentation to support the reasonably practicable, is still less safe than might performance of the existing construction or to be expected of a new building. There may also be specify testing or improvements. areas where fire damage could have a serious effect on the client’s business. In some cases it may be (6) Submit documentation to the stakeholders and, beneficial to consider the possibility of enhancing if applicable, Building Control for approval. the fire protection to sensitive elements that are most at risk. Reducing the risk of large scale failure In the following some guidance is given on how to by careful choice of improvements could benefit the undertake the different tasks described above. overall performance of the building in a fire and offer good value. For example, the improved protection in a high fire risk area of a column supporting a large number of floors or of a transfer beam supporting A5.3 Fire safety requirements of structural columns above, would benefit a substantial part of elements the building.
A5.1.3 Common failures A5.3.1 Statutory requirements
The most common failures occur as a result of the Part B of the Building Regulations 2000A5.4 states installed fire protection systems being compromised the following in relation to the fire performance of during the life of the building. Fire protection (such as elements of structure: board or sprayed systems) may be missing in the first instance, may be removed by contactors undertaking "B3. (1) The building shall be designed and modifications to the building, or may even fall off over constructed so that, in the event of a fire, its time. Fire protection sometimes falls off steel columns, stability will be maintained for a reasonable particularly in the lift shafts of tall buildings where less period." robust spray protection has been used. Tall buildings are also prone to wind movement which may reduce In the UK the Building Regulations are non- the adherence of fire protection products. prescriptive and any reasonable approach can be adopted in order to satisfy the requirements of Although not necessarily the direct concern of the Part B. The most common approaches are described structural engineer, fire safety is also influenced by in the next Sections. protection systems such as sprinklers and alarms and their maintenance, increased fire load from that A5.3.2 Design approaches envisaged, and many other factors. If it appears that fire safety may be a significant factor in the appraisal, There are two fundamentally different approaches to it may be wise to involve other professionals such as satisfy the requirements of the Building Regulations. a fire engineer. The first is to follow prescriptive guidance like ADBA5.4 or BS 9999A5.5, which give an interpretation of Part B of the Building Regulations and specify A5.2 Procedure for fire safety appraisal what is classified as an element of structure as well as what is considered a reasonable period in buildings of various uses and sizes. This approach is The procedure for the fire safety appraisal of an simple to execute and simple for a local authority to existing structure is simplified below. It may require review, but provides no information on the expected several iterations to achieve the optimum in more performance of the structure or the actual safety complex structures: margins in the design.
(1) Make an initial site visit. The second approach is to conduct a performance based design, whose steps are described in great (2) Carry out an initial desk study in parallel detail in the BS 7974 frameworkA5.3. In simplistic with the primary structural appraisal using terms, there are three variants of performance based Approved Documents, the Institution of design: Structural Engineers’ fire safety guidesA5.1, A5.2, fire test data and conclusions from the initial (1) An Equivalent or Comparative approach which site visit. This desk study should establish the substantiates the performance of the structure fire protection requirements of the structural during a fire by logical prediction of its likely elements (see Section A5.3) and make an performance, using the basic principles of appraisal of the fire performance of the building structural fire designA5.1. A simple calculation as it stands (see Section A.5.4). could assist this approach.
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(2) A Deterministic approach which involves a in the publication of the Association for Specialist Fire detailed and calculated assessment based on ProtectionA5.12. research or analytical modelling and possibly on full scale fire tests. In this method, worst If the information provided in these documents does credible case assumptions are made and safety not describe the structure under appraisal or the factors appliedA5.2. structure appears to be inadequate or the resulting fire protection works would be economically or (3) A Probabilistic approach whose objective is architecturally unacceptable, a detailed structural to show that the likelihood of a given event fire engineering approach could be adopted, as occurring is acceptably small. Risks can never described below. be reduced to zero and care should be taken to ensure reliable data is available to carry out this A5.4.1 Structural fire engineering approach approach. The structural fire engineering approach for a In all cases it is important to gain an appreciation, building tends to be unique to each case, but there leading to a practical and reasonable solution, of how are a number of common steps. It is advisable the structure might fail in a fire and the consequences to keep clients and fellow professionals aware of to people in and near the building. what is being done, not only to explain the potential advantages, but also because other disciplines may A5.3.3 Definition of fire resistance need to be involved.
The fire resistance of an element of structure The Institution of Structural Engineers’ two reportsA5.1, is commonly measured against three different A5.2 describe the principles and the various techniques components: of structural fire engineering in detail and it is –– load-bearing capacity recommended that the structural fire appraiser is –– integrity (control of transmission of hot gases) familiar with these documents. The fundamental steps –– insulation (limitation of heat transfer). of a structural fire engineering approach are as follows.
The fire resistance period is reached if any of the (1) Agree the proposed methodology with all relevant failure criteria are exceeded when the stakeholders. element of structure is exposed to the standard fire as described in BS 476A5.9. The detailed requirements (2) Define design fires. for fire resistance are given in ADBA5.4 in Tables A1 and A2 as well as in BS 9999A5.5 Section 31. (3) Develop appraisal criteria and agree with stakeholders. Columns and beams normally are required only to maintain their strength and stability, unlike (4) Consider heat transfer from the fire to the compartment walls and floors which need to achieve structural elements. a defined performance for all three components. However, if, for example, a wall can be shown to be (5) Carry out structural analysis at elevated structurally redundant by analysis of the fire case, no temperatures. This should consider the real fire protection would be necessary unless the wall was building geometry, large deflections, correct still required to resist the transmission of gases and member temperatures and the non-linear heat under B4 of ADBA5.4. Portal framed structures behaviour of materials at elevated temperatures. often require special attention in this regard. (6) List the design assumptions and the results for stakeholders as well as for the approving authorities. A5.4 Fire performance of existing structures (7) Gain Building Control approval if applicable.
The assessment of the fire performance of existing Where a sprinkler system has been introduced, its structures is never easy due to the number of benefits as part of the structural fire engineering uncertainties originating from the often historic approach may be considered. According to building materials and the frequent lack of information BS 9999A5.5 the presence of a sprinkler system allows with regards to the original design assumptions. an increase of travel distances as well as a reduction Therefore, care should be taken to use sufficient of the required fire resistance period, which, where factors of safety in the prediction of the fire significant modifications are planned, could bring the performance of an existing structure. Furthermore, it existing structure into compliance with current fire is important to collect as much data during the site safety legislation. Guidance on and examples of the visits as possible and potentially to conduct material introduction of sprinkler systems in historic buildings testing at elevated temperatures. Additionally, it is can be found in Technical Advice Note 14A5.13. often required to review fire test data of old forms of construction, which can be found in published The engineer should be aware that, in cases where journal papers as well as in selected books on fire the previous structural system did not meet the engineering of structures. For more recent forms required fire resistance standards, it is possible that of construction, the fire performance of structural fire resistant structural elements have been added elements and fire protection can be found in the subsequently which are just sufficient to resist Institution of Structural Engineers’ guides for fire the reduced loads at ‘fire limit state’ without the safety of structures, in the material specific British contribution of those parts of the existing structure Standards [BS 8110A5.10, BS 5950-8A5.11] and in the which are not fire resistant. However, for ultimate and fire parts (1.2) of the structural Eurocodes as well as serviceability limit states, the added and the previous
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structure work compositely. This approach has been with the capacity required (with appropriately used in many situations but is particularly relevant to reduced factors of safety). floor structures. Generally, modern concrete has an inherently good A5.4.2 Management plan and housekeeping resistance to the effects of fire as long as the risk of spalling of the concrete in fire is considered. Care is Most major fire failures have been the result of a required with the appraisal of structures made from series of failures in the building’s management older concrete, particularly if highly stressed or if procedures. This highlights the importance of Fire thermal properties are critical: in such cases, material Safety Management during the whole life of a building testing may need to be considered. as most buildings contain a mixture of active and passive fire protection systems. Part of the total A5.5.2 Timber protection system is the management plan; this fact has not fully been recognised in the recent past, but The effects of fire on timber for the appraisal of advice is now given in CIBSE Guide EA5.14 and in timber structures after fire is described in A6.5.3. BS 9999A5.5. Details of the fire performance of timber can be found in BS EN 1995-1-2A5.21. However some general points on its behaviour are given below.
A5.5 Materials Unless timbers are massive, some form of fire protection is usually required to achieve useful fire resistance. For timber floors with sections up Building fire temperatures can reach 1000°C to to about 75mm thick, a resistance of ½h may be 1200°C, affecting the load bearing capacity of possible in some cases, but there is little chance of structural elements in a number of ways. Each achieving a significant fire resistance period unless material has its own particular characteristics and the sections are lightly loaded. response to high temperature and the duration of applied heat. Much of the available technical If sections are massive, then charring of the data relates to the time/temperature curve of the surface of the timber can leave a substantial bulk of standard fire test which can be used to support the unaffected timber in the centre of the section but with prescriptive and qualitative approaches. When a reduced capacity. Detailed charring rates are given in fire engineering approach is adopted, temperatures Table 3.1 of BS EN 1995-1-2A5.21. are often calculated. A full range of relationships for material properties with respect to temperature is Where steel plates and other steel components have then required unless a correlation with the standard been used to repair or strengthen timber, it may be time/temperature curve as defined in ISO 834A5.15 necessary to provide some protection depending and repeated in Eurocode 1A5.16 is possible. on the level of stress in the steel and the degree of interaction between the steel and timber. Metal bolts For each of the materials discussed in this section the with exposed heads and nuts conduct heat to the normal prescriptive and historical data are defined interior of the timber and may cause internal charring, followed by a description of the data and methods thus weakening the connections. The scatter of that can be used as part of a fire engineering charring depth, which is considerable because of approach. In some cases research data are cracks, knots, condition, humidity, etc., should be insufficient and testing may be required. taken into account.
The influence of high temperature and the rate of A5.5.3 Brickwork and masonry increase of temperature on structural capacity varies significantly between materials. The concern here is Reference should be made to BS 5628A5.22 as well with properties at high temperature and assessment as BS EN 1996-1-2A5.23 and current and historical of the reduction in strength or reduction in effective data on fire resistance periods for brickwork and section, rather than with the resulting capacity after masonry. Where masonry panels are particularly tall cooling (which is the subject of a different type of or long, consideration should be given to the risk appraisal, discussed in A6.1). of differential heating causing bowing and possible collapse. A5.5.1 Reinforced and prestressed concrete Sandstone may spall due to boiling of crystalline The mode of failure and the characteristics of water in the silica. Limestone will calcine and lose concrete subjected to heat are described in detail for strength. relatively new concrete elements in BS EN 1992-1- 2A5.17 as well as in Bulletin 46A5.18. For more historic A5.5.4 Steelwork concrete, test data can be found in LennonA5.19 and NBSR’s Paper No. 12A5.20. There is a substantial amount of research, test data and codified information on the performance in fire of If the concrete is modern and made with natural or protected and unprotected steelwork. Manufacturers lightweight aggregates, and the depth of cover to the of fire protection systems have also developed data reinforcement can be determined, BS 8110A5.10 or on the basis of the standard fire tests. The durability BS EN 1992-1-2A5.18 can be used to justify a simple of these systems and their resistance to damage prescriptive approach. An alternative is to calculate should be an important consideration. Information on the heat transfer through the concrete cover and the properties of steel and steel members in fire may establish the rise in temperature of the steel and be obtained from BS 5950-8A5.11, Reference A5.24 hence the reduced ultimate capacity, for comparison and BS EN 1993-1-2A5.25.
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There are three principal approaches to the protection The thermal stresses resulting from the surrounding system: structure are considered particularly important due to the low tensile strength of cast iron and its propensity (1) Compare the existing fire protection system with to brittle failure. This weakness is not explored in prescriptive specifications in previous and current a standard test where no account of surrounding building control documentation to determine a structure is made. The performance of cast iron notional fire resistance period. It is important to be members in fire cannot therefore readily be related to aware that ‘1 hour fire resistance’ means that the results from members tested in standard fire tests. element will withstand a standard fire for 1 hour, which may bear no relation to how it will behave in Under normal loading in a test, a cast iron column a real fire in the building considered. is unlikely to fail below 600ºC if it contains no major defects. When assessing fire protection for such a (2) Use a structural fire engineering assessment to member, a failure temperature should be defined based determine if no or partial protection is adequate on that member’s particular loading. For example (see Section A5.4). A fire engineering approach where cast iron or steel beams are rigidly connected may typically be beneficial for steelwork where to columns, the temperature of the columns or beams a section is partially encased, e.g. in a filler joist should not be allowed to rise to such an extent as to floor or by masonry between column flanges. cause excessive thermal movements. Barnfield and The concrete or masonry acts as a heat sink Porter recommend that, when steel or cast iron beams and also reduces the area of steel subjected to are connected to a cast iron column, the temperature radiant and convective heat transfer. A higher should not exceed 300ºC and that, when timber fire resistance period will be achieved for small beams are connected to cast iron members, structural ratios of perimeter to cross-sectional area temperatures should not exceed 550ºC. and when stresses are lower. The exposed elements of steelwork may thus be shown to be The behaviour of cast iron at elevated temperatures acceptable. is very similar to that of steel. At 750ºC, up to 50% of the ambient strength is lostA5.28. Figure A5.1 shows the (3) Proprietary systems have been increasingly effect of temperature on the tensile strength of various specified for fire protecting steelwork. They cast ironsA5.29. are slightly more complicated to survey and appraise. Their design has usually been based Intumescent paint is a potential solution to providing on fire resistance tests, the results of which thermal insulation and retaining architectural detail, are published in the form of design tablesA5.12. but continuity of protection during fire fighting activities The assessment of the condition and durability should be considered. of these systems is important. For board and spray systems, assessment of significance of mechanical damage may be all that is required. Grade 20
For intumescent paints and coatings the situation 300 is however less clear. Reference should be made to Grade 17 BS 8202-2A5.26 as well as to the guidance provided by the Association for Specialist Fire Protection (ASFP).
Attempts should be made to determine the original Tensile strength (MPa) supplier, the film thickness and whether a protective 200 sealer coat has been applied. An attempt should also be made to assess the durability of the coating Grade 10 by reference to testing that may have been carried out in the development of the original paint system. It is advantageous to involve the original supplier in 100 the appraisal. Decorative treatment can reduce the effectiveness of the intumescence.
A5.5.5 Cast Iron 0 Cast iron has been found to perform well in standard 0 100 200 300 400 500 600 fire tests owing to its high density and relatively low Temperature (°C) design stresses. However, Barnfield and PorterA5.27 has stated that the standard fire tests for cast iron are Figure A5.1 Tensile properties of cast iron at elevated temperature misrepresentative of their actual performance in fire for two reasons. First, no quenching occurs in the standard test and, second, no account is taken of stress A5.5.6 Aluminium introduced from the surrounding structure. Aluminium has a melting point of 600°C – 660°C, Cast iron is known to crack when cooled rapidly, as and needs to be limited to 200°C – 250°C in order to observed in standard tests followed by quenching carry load. Strength is significantly reduced above this performed by Barnfield and Porter. Columns which temperature. had not cracked during heating were found to crack considerably upon hosing. It is suggested by SmithA5.28 Compared to steel, aluminium has four times the however that during fire fighting activities it is unlikely thermal conductivity and twice the specific heat. Heat that a sufficient volume of water would be in contact is therefore conducted away faster, and a greater with the column long enough to cause the severe heat input is necessary to bring the same mass of thermal gradients necessary to cause major cracks. aluminium to a given temperature compared with
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steel. Where an aluminium structure is exposed to the A5.16 BS EN 1991-1-2: 2002: Eurocode 1: Actions on structures heat of a fire, the relatively high thermal conductivity – Part 1-2: General actions – Actions on structures enables the heat to be conducted rapidly away from exposed to fire. London: BSI, 2002 the exposed area. The extent of dissipation will depend on the degree of thermal insulation provided A5.17 BS EN 1992-1-2: 2004: Eurocode 2: Design of concrete to the aluminium for fire protection. structures – Part 1-2: General rules – Structural fire design. London: BSI, 2005 The reflectivity of weathered aluminium is 80% to 90% compared with 5% for painted steel and 25% A5.18 FIB. Fire design of concrete structures: structural behaviour for stainless steel. This is of considerable benefit in and assessment. FIB Bulletin 46. Lausanne: FIB, 2008 reducing radiation effects. A5.19 Lennon, T. Fire safety of concrete structures: background Available fire protection materials include a range to BS 8110 fire design. BRE Report BR468. Garston: BRE of insulating layers and intumescent coatings. Bookshop, 2004 Thicknesses are usually greater than for steel. Radiation shielding can usefully be considered where A5.20 Davey, N. and Ashton, L.A. Investigations on building fires. the structure is not in the compartment fire zone. Part V: Fire tests on structural elements. National Building Studies Research Paper 12. London: HMSO, 1953
A5.21 BS EN 1995-1-2: 2004: Eurocode 5: Design of timber A5.6 References structures – Part 1-2: General – Structural fire design. London: BSI, 2004
A5.1 Institution of Structural engineers. Introduction to the fire A5.22 BS 5628-2: 2005: Code of practice for the structural safety engineering of structures. London: IStructE, 2003 use of masonry – Part 2: Structural use of reinforced and prestressed masonry. London: BSI, 2005 A5.2 Institution of Structural Engineers. Advanced fire safety engineering of structures. London: IStructE, 2006 A5.23 BS EN 1996-1-2: 2005: Eurocode 6: Design of masonry structures – Part 1-2: General rules – Structural fire A5.3 BS 7974: 2001: Application of fire safety engineering design. London: BSI, 2005 principles to the design of buildings – Code of practice. London: BSI, 2001 A5.24 Lawson, R.M. and Newman, G.M. Fire resistance design of steel structures: a handbook to BS 5950: Part 8. SCI A5.4 Department for Communities and Local Government. The Publication 80. Ascot: SCI, 1990 Building Regulations 2000. Approved Document B: Fire Safety. Vol 1: Dwellinghouses; Vol 2: Buildings other than A5.25 BS EN 1993-1-2: 2005: Eurocode 3: Design of steel dwellinghouses. 2006 ed. London: NBS, 2007 structures – Part 1-2: General rules – Structural fire design. London: BSI, 2005 A5.5 BS 9999: 2008: Code of practice for fire safety in design and management of buildings. London: BSI, 2008 A5.26 BS 8202: Coatings for fire protection [2 parts]
A5.6 The Fire Precautions Act 1971. London: HMSO, 1971 A5.27 Barnfield, J.R. and Porter, A.M. ‘Historic buildings and fire: fire performance of cast-iron structural elements’. The A5.7 The Regulatory Reform (Fire Safety) Order 2005. Norwich: Structural Engineer, 62A(12), December 1984, pp373-380 The Stationery Office, 2005 (SI 2005/1541 A5.28 Smith, C. et al. ‘The Reinstatement of fire damaged steel A5.8 The Building Regulations 2000. London: The Stationery framed structures’. Fire Safety Journal, 4, 1981, pp21-62 Office, 2000 (SI 2000/2531) Available at: http://www. hmso.gov.uk/si/si2000/20002531.htm [Accessed: 1 A5.29 Kirby, B.R., Lapwood, D.G. and Thomson, G. The October 2009] Reinstatement of fire damaged steel and iron framed structures. [Rotherham]: British Steel Corporation Swinden A5.9 BS 476: Fire tests on building materials and structures Laboratories, 1986 [several parts]
A5.10 BS 8110: Structural use of concrete [3 parts] A5.7 Bibliography A5.11 BS 5950-8: 1990: Structural use of steelwork in building. Part 8: Code of practice for fire resistant design. London: BSI, 1990 {Since superseded by 2003 version} Building Research Establishment. Fire resistance steel structures: free-standing blockwork-filled columns and stanchion. BRE A5.12 Association for Specialist Fire Protection. Fire protection for Digest 317. Garston: BRE, 1986 structural steel in buildings. 4th ed. Aldershot: ASFP, 2007 Morris, W.A., Read, R.E.H. and Cooke, G.E.M. Guidelines for the A5.13 Historic Scotland. The Installation of sprinkler systems in construction of fire-resisting structural elements. BRE Report historic buildings. Technical Advice Note 14. Edinburgh: BR128. Garston: BRE, 1988 Historic Scotland, 1998 TRADA. Timber building elements of proven fire resistance. Wood A5.14 Chartered Institution of Building Services Engineers. CIBSE Information Sheet 1-11 [Several parts] Guide E: Fire engineering. 2nd ed. London: CIBSE, 2003
A5.15 ISO 834: Fire resistance tests – Elements of building construction [9 parts]
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A6.1 Introduction In parallel with this, all drawings, calculations, specifications, and information regarding the use of the building should be collected. Witness and Repairability after a fire cannot be simply based fire service reports, photographs and videos are on the assessment of technical feasibility but must important in establishing the fire history. be based on much broader considerations. The aesthetic appearance, the reliability of repairs and the Using the preliminary fire temperature data, the desk views of the insurance company and client all have to study and the evidence from the initial site visit, a be taken into account. However, technical feasibility strategy for the detailed collection of evidence can and a related cost appraisal must be reported as be established. It is important to understand the a datum from which other considerations can be structure in its condition before the fire in order to judged. establish which material characteristics are likely to influence the performance of the structure in its Structural engineers may also be involved in urgent condition after the fire. work to determine the short term stability of a fire-damaged building.
It is of course essential that the engineer understands A6.4 Collection of detailed evidence the background to the fire resistance of structures before attempting to appraise an existing structure which has been damaged by fire, so it is assumed As much evidence as possible should be carefully that the reader has digested Appendix 5 before recorded prior to removal of the debris. The tackling this Appendix 6. position, the condition, the melting and the charring of materials (including non-structural materials) all provide evidence for an estimate of the time/ temperature history of the fire (see Tables A6.1 and A6.2 Procedure for appraisal A6.2). Photographic or video recordings will prove most useful and are quickly acquired.
The appraisal of a fire-damaged structure depends In examining the debris it is important to consider on the particular materials involved and whether whether the evidence gives a true indication of questions of overall stability or the local capability of the exposure of the structure. For instance non- an individual member are relevant. The procedure structural timber may continue to char after primary would generally comprise: extinguishing, particularly following collapse, and –– initial site visit could produce over-estimates of the exposure of –– desk study the structure. –– collection of evidence in detail –– damage assessment Thermal expansion and subsequent contraction –– specification of repairs. can result in permanent or temporary distortions which can lead to damage to connections between The specification of repairs is outside the scope elements of construction. Damage of this type can of this Report. Once the problems have been be well away from the directly heat-damaged zone. understood, there should be sufficient guidance in This is a particularly important assessment where the remainder of this Report. The other elements of tie forces are required for robustness. Distortions, the procedure are discussed below. out-of-plumb and local damage should all be carefully recorded.
If a fire has taken place in a larger building it may A6.3 Site visit and desk study be impractical and unnecessary to examine every element of construction unless obvious damage and distortions are present. To aid the eventual After a fire, a building may be unsafe. Refer to damage appraisal and the development of a repair Chapter 7 and Appendix 4 (A4.3.2) for advice schedule, an attempt should be made to plot before entering such a building, particularly if the fire intensity and the resultant approximate employed to advise the authorities on whether it is isothermal surfaces. From this, zones of damage stable. Following a fire, and once a room or building and related repair can eventually be defined. If an has been declared safe to enter by the fire service extensive appraisal is required, classes of damage or building control authority, it is essential to gather can be defined and adopted to simplify the data all possible clues regarding the history of the fire. An collection and final presentation (see Table A6.3 for initial overview examining the most conspicuously a possible approach). damaged elements is necessary to give an early indication of the likely scale of the damage.
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Table A6.1 Effect of temperature on selected substances
Approximate Substance Typical examples Condition a temperature (°C) 100 Paint Deteriorates 150 Destroyed 120 Polystyrene Thin-wall food containers, foam, light Collapse 120 – 140 shades, handles, curtain hooks, radio Softens 150 – 180 casings Melts and flows 120 Polyethylene Bags, films, bottles, buckets, pipes Shrivels 120 – 140 Softens and melts 130 – 200 Polymethyl Handles, covers, skylights, glazing Softens 250 methacrylate Bubbles 100 PVC Cables, pipes, ducts, linings, profiles, Degrades 150 handles, knobs, houseware, toys, bottles Fumes 200 Browns 400 – 500 Charring 200 – 300 Cellulose Wood, paper, cotton Darkens 240 Wood Ignites 250 Solder Plumber joints Melts 300 – 350 Lead Plumbing Melts, sharp edges rounded 350 – 400 Sanitary installations, toys Drop formation 400 Zinc Sanitary installations, gutters, downpipes Drop formations 420 Melts 400 Aluminium and Fixtures, casings, brackets, small Softens 600 alloys mechanical parts Melts 650 Drop formation 500 – 600 Glass Glazing, bottles Softens, sharp edges rounded 800 Flowing easily, viscous 900 Silver Jewellery, spoons, cutlery, etc. Melts 950 Drop formation 900 – 1000 Brass Locks, taps, door handles, clasps Melts 950 – 1050 (particularly edges) Drop formation 900 Bronze Windows, fittings, doorbells, Edges rounded 900 – 1000 ornamentation Drop formation 1000 – 1100 Copper Wiring, cables, ornaments Melts 1100 – 1200 Cast iron Radiators, pipes Melts 1150 – 1250 Drop formation Note a Can be used to assess (maximum) temperature at the location of these materials. Examples are: wood char patterns; softening and melting (glass, brick, metals, plastics); aggregate, concrete and brick discolouration.
Table A6.2 Ignition temperatures of various materials (average values)
Material Ignition temperature a Auto-ignition temperature b (°C) (°C) Wood 280 – 310 525 Wool 240 – Paper 230 230 Cotton fabrics 230 – 270 255 Polymethylacrylate (Perspex) 280 – 300 450 – 460 Rigid polyurethane foam 310 415 Polyethylene 340 350 Polystyrene 345 – 360 455 – 495 Polyester (glass-fibre filled) 350 – 400 480 Polyvinyl chloride 390 455 Polyamide 420 425 – 450 Phenolic resins (glass-fibre filled) 520 – 540 570 – 580 Notes a The temperature to which material has to be heated for sustained combustion to be initiated from a pilot source. b The temperature at which the heat evolved by a material decomposing under the influence of heat is sufficient to bring about combustion without the application of an external source of ignition. This tends to be higher than the ignition temperature. c Combustion products from some of these materials may be toxic or noxious chemicals.
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Table A6.3 Classes of damage after fire, characterisation and description
Class Characterisation Description '0' No discernible damage Floor remote from fire Equipment remains in working order 1 Cosmetic damage, surface Characterised by soot deposits and discolouration. Uneven distribution of soot deposits may occur Permanent discolouration on high-quality surfaces 2 Technical damage, surface Characterised by damage to surface treatments and coatings Small extent only of concrete spalling or corrosion on uncovered metals Painted surfaces can be repaired. Plastic-coated surfaces need replacing or covering. Minor spalling may remain or can be replastered 3 Structural damage, surface Characterised by some concrete cracking and spalling, lightly charred wood surfaces, some deformation of metal surfaces or moderate corrosion damage 4 Structural damage, cross-section Characterised by major concrete cracking and spalling, deformed flanges and webs of steel (interior) beams, partly charred cross-sections of timber constructions, and degraded plastics. Damage can in many cases be repaired on the existing structure. Within the class are also deformations of structures so large that the load-bearing capacity is reduced, or dimensional alterations prevent proper fitting into building. This applies in particular to metal/steel constructions 5 Structural damage to members Characterised by severely damaged structural members and components, impaired and components materials and large deformations. Concrete constructions are characterised by extensive spalling, exposed reinforcement and impaired compression zone. In steel structures extensive permanent deformations have arisen due to diminished load-bearing capacity caused by high-temperature conditions. Timber structures may have almost fully charred cross-sections. Changes in materials may occur after the fire, so they may display unfavourable properties
A6.5 Damage assessment A6.5.1 Reinforced concrete
Reinforced concrete is varied in its response to fire The damage assessment consists of several parts that temperatures. Its properties after heating depend on are combined to give a qualitative appraisal supported a number of factors including rate of heating, duration by a level of analysis which must be carefully judged of heating, loading regime and mix constituents. and used with caution. The parts are: The damage to a spalled, discoloured or blackened (1) An appraisal of how the original pre-fire concrete surface with exposed reinforcement may be structure ‘worked’ and the loads applied to it. more superficial than may first be suspected. Care (2) The time/temperature profile of the fire should therefore be taken before such a structure is, determined from the evidence collected and or such elements are, condemned. a correlation with the standard fire test or a parametric fire. In 2009 the Concrete Society published a revision of (3) Assessment of the temperature profile of the its Technical Report No 33A6.1, now called TR68A6.2. fire by examining and testing the elements This report gives detailed guidance on fire damaged of the structure under consideration. Where concrete structures, which are therefore not possible this should again be correlated with reproduced here. However, some of the main points the standard fire test or a parametric fire in to consider are given below: combination with a structural fire engineering –– reduction in compressive strength of concrete assessment. –– creep or excessive deflection due to large reduction (4) An assessment of structural capacity and of the elastic modulus the need for repairs, based on temperature –– cracking around heavily reinforced areas data and other evidence. This stage can be –– deep cracks due to restrained cooling or thermal approached with greater confidence if there is shock from water from hoses some degree of agreement between (2) and (3) –– reduced bond between reinforcement and concrete above. –– spalling – explosive or by sloughing –– reduction in strength of steel reinforcement, Other considerations include: structural steel or steel inserts. (See also –H– ave distortions/bowing caused significant Figure A6.1 regarding the behaviour of hot-rolled reduction in capacity and can they be tolerated and cold-worked bars and prestressing tendons without special measures? and Figure A6.2 regarding prestressing wires.) –E– ffects of local eccentricities and moments due to misalignment of members, caused by the fire. Cold-worked bars, when heated, lose their strength –T– he effects of expansive forces on areas in the more rapidly than hot-rolled high-yield and mild-steel region of and remote from the fire. bars. The properties after heating are of interest from –O– verall stability. the point of view of reinstatement. The original yield –R– obustness of the fire-damaged structure. stress is almost completely recovered on cooling from temperatures of 500°C to 600°C for all bars: on The system for defining classes of damage (Table A6.3) cooling from 800°C it is reduced by 5% for hot-rolled can be extended and defined for a particular material bars but 30% for cold-worked bars. as a method for standardising the approach.
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A6.5.2 Prestressed concrete Maximum temperatures reached in the tendons, and their durations, together with the temperature The behaviour of prestressing steel after a fire is distribution, are therefore more critical in the much more critical than that of reinforcing steel. The assessment of fire-damaged prestressed concrete tensile properties of prestressing steels deteriorate members than in the case of reinforced concrete. It more markedly at elevated temperatures, as can be is necessary to consider factors such as the effect of seen in Section 3.2.4 of BS EN 1992-1-2: 2004A6.3. temperature, the exposure time during the hot state, The reduction in the tensile strength of cold-worked the residual characteristic values after cooling, the prestressing steel starts at temperatures between effect on the elastic modulus, creep in the concrete, 100°C and 200°C. Its strength reduces to about 50% the effects of expansion and any restraints against of room temperature strength at 400°C and to less expansion. Assessment of temperature contours, than 10% at around 700°C. Quenched and tempered testing and correlations are as for reinforced concrete. prestressing steel behaves slightly better. Due to the reversal of the strength enhancing treatments A6.5.3 Timber used during the manufacturing of the prestressing tendons, their residual strength upon cooling can be As timber is combustible, it will normally survive only permanently reduced after elevation in temperature localised fires or fires where rapid intervention by the to above about 200°C. The residual strength for fire brigade is successful, unless sections are massive. normal reinforcement and prestressing tendons is given in Figure A6.1. Timber ‘browns’ at about 120-150°C, ‘blackens’ around 200-250°C and evolves combustible vapours Additionally, the reduction of elastic modulus in the at about 300°C. Above a certain temperature concrete, increased relaxation due to creep and 400-450°C (or 300°C if a flame is present) the non-recoverable extension of tensioned steel occur surface of the timber will ignite and char at a steady as a result of increased temperatures. All effects rate. Any charred part of a section must be assumed contribute to losses in tension. The temperature to have lost all strength, but any timber beneath the effects on relaxation of untreated cold-drawn charred layer may be assumed to have no significant prestressing wire are given in Figure A6.2. loss of strength because the thermal conductivity of charred timber is low.
1.2
1.1
1.0
0.9 Relative proportion of room temperature strength 0.8
0.7 Hot-rolled Yield stress Cold-worked Reinforcing 0.6 steel Hot-rolled Tensile Cold-worked strength 0.5 Proof stress and tensile strength – Prestressing steel
0.4 0 200 400 600 Fire simulation temperature (°C)
Figure A6.1 Residual strength properties upon cooling of reinforcing bars and prestressing tendons following fire-simulation requirements
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(a) Relaxation at 100°C (b) Relaxation at 200°C
1100 900
Stress (MPa) 1000 Stress (MPa) 800
900 700 0 2 4 6 0 2 4 6 Duration (h) Duration (h)
(c) Relaxation at 300°C (d) Relaxation at 400°C
700 300
Stress (MPa) 600 Stress (MPa) 200
500 100 0 2 4 6 0 2 4 6 Duration (h) Duration (h)
Figure A6.2 Temperature effects on relaxation of untreated cold-drawn prestressing wire
The repair of timber structures after fire depends Expansion of floor members – slabs and, in on the degree of charring. If the depth of char is particular, unprotected steel beams – can result in insignificant the remaining section may still be able to large expansion forces that may cause significant resist the design loads, although it will have reduced movements of masonry walls, even enough to resistance to any future fire. Local damage around push them over. Out-of-plumb brickwork should steel connectors must be repaired. The problem of be checked, the reason for it ascertained, and the removing the layer of char may be solved either by effectiveness of any lateral restraint provided by floor sandblasting or by the use of a scraping plane. By slabs and beams assessed. Such damage can occur their nature, repairs will depend on circumstances remote from the fire. but could involve combinations of nailing, bolting, screwing, steel plating or gluing. A6.5.5 Steelwork
A6.5.4 Brickwork For steel, the yield strength at room temperature is reduced to about half at 550°C, and at 1000°C The physical properties and mechanisms of failure it is 10% or less. Since steel has a high thermal of brick walls exposed to fire are not known in detail. conductivity the temperature of unprotected internal As with concrete there may be a loss of compressive steelwork locally during a fire will normally be little strength, and unequal thermal expansion of the different from the fire temperature. It is for this reason two faces; and behaviour is influenced by edge that structural steelwork is usually fire protected conditions. For solid bricks, fire resistance is directly by insulation. In addition to losing practically all its proportional to thickness. Perforated bricks and load-bearing capacity in fire conditions, unprotected hollow clay units are more sensitive to thermal shock; steelwork can cause considerable movement, there can be cracking of the connecting webs and the coefficient of expansion being of the order of a tendency for the ‘leaves’ to separate. All types 12 × 10-6/°K. of brick give much better performance if plaster is present, owing to its improved insulation and Young’s modulus decreases with temperature rise reduction of thermal shock. at a slightly higher rate than does yield strength. The decrease in strength upon cooling after fire exposure If brickwork does not show visible damage (e.g. can be estimated from Figures A6.3 and A6.4. appreciable deformation, cracking or spalling), the (TS = tensile strength; LYS = lower yield strength; strength of the bricks may be taken to be similar RT = room temperature.) to the original value, since high temperatures are reached during their manufacture. Mortar containing Cold-drawn and heat-treated steels lose a part sand with a given mineral composition behaves of their strength permanently when heated to similarly to concrete with aggregate of comparable temperatures in excess of about 300°C and 400°C, mineral composition. respectively.
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500
450 TS
Strength (MPa) TS for BS 4360 Grade 43A min (equal to BS EN 10025-2 S275) 400 Not heat-treated 1 hour at temperature 350 4 hours at temperature
300
250 LYS for BS 4360 Grade 43A min LYS (equal to BS EN 10025-2 S275)
RT 100 200 300 400 500 600 700 800 900 1000 Fire simulation temperature (ºC)
Note TS = tensile strength; LYS = lower yield strength; RT = room temperature
Figure A6.3 Effect of laboratory heat treatments on residual strength properties upon cooling of a British Standard mild steel
Not heat-treated 600 1 hour at temperature 4 hours at temperature
550 TS Strength (MPa) 500
450 TS for A 572 Grade 50 min
400
350 LYS for A 572 Grade 50 min LYS
300
RT 300 400 500 600 700 800 900 1000 Fire simulation temperature (ºC)
Note TS = tensile strength; LYS = lower yield strength; RT = room temperature
Figure A6.4 Effect of laboratory heat treatments on residual strength properties upon cooling of an ASTM microalloyed steel
The creep rate of steel is sensitive to higher members. In a severe fire, unprotected steelwork temperatures; it becomes significant for mild steel will distort and will not be suitable for reuse. In a less above 450°C. In fires the rate of temperature rise severe fire, only a limited number of members may while the steel is reaching its critical temperature is be affected, and the straightness, distortion and fast enough to mask any effects of creep. However, mechanical properties of these members can easily where there may be a long cooling-down period, as be checked. The in situ hardness check provides a in prestressed concrete, subsequent creep may have quick and relatively easy means of establishing the some effect in an element that has not reached the approximate tensile strength of the material. Where critical condition. hardness measurements are borderline and the design is critical, metallographic assessment can Generally, in fire-damaged steel-framed buildings, provide a method of determining the steel quality and decisions are required on only a limited number of the thermal cycle that the steelwork has undergone.
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Prior to 1959, bolts and rivets were manufactured Examination of a number of fire-damaged structures from mild steel, and therefore at elevated has revealed several failure mechanisms at bolted temperatures they would be expected to show a connections. These include shear and tensile failure similar response to hot-rolled mild-steel sections. as well as thread stripping. Grade 4.6 and 8.8 bolts Since high-strength friction grip bolts form a critical should give an adequate performance in fire if loaded part of many more recent structures (and hot to normal maximum stresses at temperatures in driven rivets, of older structures), their strength the region of 360°C to 425°C. The residual strength behaviour has to be evaluated to assess whether properties upon cooling show a substantial recovery they would distort, shear or lose their friction grip for grade 4.6 if heated to only 600°C and for at even a moderate rise in temperature. grade 8.8 if heated to only 400°C (see Figures A6.5 and A6.6: PS = proof stress).
Heat Tensile Yield treatment strength stress 600 Maximum tensile strength As received ½ hour 500 4 hours
Strength (MPa) TS 400
Minimum tensile strength 300 LYS
200 Minimum yield stress
100
0 RT 200 400 600 800 1000 Fire-simulation temperature (ºC)
Note TS = tensile strength; LYS = lower yield strength; RT = room temperature
Figure A6.5 Residual strength properties upon cooling of bolts (grade 4.4) following fire-simulation treatment
1000 Maximum tensile strength Heat Tensile Yield treatment strength stress 900 As received
Strength (MPa) ½ hour 800 4 hours Minimum tensile strength 700
TS 600 Minimum 0.2% proof stress
500
400 0.2% PS or LYS 300
RT 200 400 600 800 1000 Fire-simulation temperature (ºC)
Note TS = tensile strength; LYS = lower yield strength; RT = room temperature; PS = proof stress
Figure A6.6 Residual strength properties upon cooling of bolts (grade 8.8) following fire-simulation treatment
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Temperature gradients across a section, end restraints Grey cast iron may crack if it is quenched arising from global structural action or stiffness from temperatures above 350°C rapidly and provided by secondary elements of construction can non-uniformly, for example by fire-fighting water. result in significant residual stresses after cooling. If Even when hot beams are not under load, contact there has been yielding during the hot phase, severe with cold water can also be detrimental as a result weakening of connections and sections is a possibility of the highly uneven stress distribution created that should be assessed. It is common for steel during rapid cooling. sections to yield in compression while softened by the fire, resulting in tension as the member cools. By the As a general guide, grey cast iron columns may time the tensile stress has built up, the yield strength is be reused under direct compressive loading back almost to normal and no yield occurs. This can so long as there are no obvious cracks. It is subject connections to the full tensile capacity of the suggested that cast iron beams are replaced if member, which often leads to connection failure, even there is any indication of them having been heated if the bolts retain their strength. to 350°C since, at some time in the future, fine cracks may open up when full structural loading A6.5.6 Cast iron is reintroduced. Quality and uniformity of the cast iron material and of the sections themselves are The sensitivity of cast iron to heating can be taken to also relevant factors in considering the continuing be similar to that of steelA6.4. No reduction in residual adequacy of a cast iron member, as is the heat strength occurs in cast iron members if they are sink effect offered by masonry or concrete in exposed to temperatures up to 600°C for several jack-arch floors (compare Figure A6.7(a) with hours. However, at higher temperatures, a permanent Figure A6.7(b)). loss in strength will occur after heating to 750°C. This loss in strength can be as great as 50% of the A6.5.7 Wrought iron original value. The data available on wrought iron are still more Because of the heavy mass and relatively low design limited than those for cast iron. The data indicate stresses, cast iron members, particularly columns, that high temperature can be beneficial to the generally perform well in fire. The performance of material’s strength, probably due to the high cast iron members has been evaluated in standard phosphorus content. Provided that a wrought iron fire tests, which have shown that, subjected to section has not deformed there is little justification normal design loads, their inherent fire resistance is for its removal. However, it has to be considered good. They have been known to achieve standard fire that the quality and the strength properties of test ratings of 30min and lh. However, in very severe wrought iron sections are very variable. Therefore, in fire conditions, cast iron columns, like steel, will reinstating a building or element containing wrought buckle when the applied load exceeds the elevated- iron, members must not be stressed beyond their temperature load-bearing capacity of the member. original levels before the fire.
(a) Cast iron beam supporting stone slabs. (b) Cast iron beam with brick jack-arches (bottom Exposed to flame on 3 sides, low thermal flange often shaped as shown, to provide springing mass, so it heats up quickly. for arches). Reduced exposure to flame and floor acts as ‘heat sink’.
Thick stone slabs Flagstones on form floor ash/rubble fill
Figure A6.7 Protection offered by heat sink
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A6.1 Concrete Society. Assessment and repair of fire-damaged concrete structures. Technical Report 33. London: Concrete Society, 1990
A6.2 Concrete Society. Assessment, Design and Repair of Fire-damaged Concrete Structures. Technical Report 68. Camberley: Concrete Society, 2008
A6.3 BS EN 1992-1-2: 2004: Eurocode 2: Design of concrete structures – Part 1-2: General rules – Structural fire design. London: BSI, 2005
A6.4 Barnfield, J.R. and Porter, A.M. ‘Historic buildings and fire: fire performance of cast-iron structural elements’. The Structural Engineer, 62A(12), December 1984, pp373-380
A6.7 Bibliography
Concrete Society. Assessment and repair of fire-damaged concrete structures. Technical Report 33. London: Concrete Society, 1990
FIP. Maintenance, repair and strengthening of concrete structures. State-of-the-art report. Slough: FIP, 1982 {See also FIB. Management, maintenance and strengthening of concrete structures. FIB Bulletin 17. Lausanne: FIB, 2002}
Fisher, R.W. Fire test results on building products: fire resistance. London: Fire Protection Association, 1983
Fisher, R.W. and Smart, P.M.T. Results of fire resistance tests on elements of building construction. 2 vols. Watford: BRE, 1975
Gustaferro, A. ‘Experience from evaluating fire-damaged concrete structures’. Fire safety of concrete. ACI Special Publication SP 80. Detroit, MI: ACI, 1983, pp269-278
Kirby, B.R., Lapwood, D.G. and Thomson, G. The Reinstatement of fire damaged steel and iron framed structures. [Rotherham]: British Steel Corporation Swinden Laboratories, 1986
Malhotra, H.L. Spalling of concrete in fires. CIRIA Technical Note 118. London: CIRIA, 1984
Morris, W.A. CIB 14 Workshop: Repairability after fire. Summary Report from UK. Borehamwood: Fire Research Station, 1987
Placido, F. ‘Thermoluminescence test for fire damaged concrete’. Magazine of Concrete Research, 32(111), June 1980, pp112-116
‘Repair of a reinforced concrete building affected by fire damage’. Building Technology [Japanese], 351, 1980
Smith, C. et al. ‘The Reinstatement of fire damaged steel framed structures’. Fire Safety Journal, 4, 1981, pp21-62
‘Special issue: Repairability of fire damaged structures. CIB W14 report’. Fire Safety Journal, 16(4), 1990
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A7.1 Introduction Percussive or rotary drilling into concrete, masonry, steel or other materials can provide samples for laboratory analyses. Work upon cast iron should This appendix lists the test techniques given in Tables avoid the use of percussive techniques for drilling or 5.2 to 5.6 and briefly describes their use. For detailed other activities. Concrete and masonry samples may information on test procedures the references should also be obtained by taking cores. Drillings or cores be consulted. Specialist expertise may be required can normally be taken from non-critical locations in in a number of cases and accredited laboratories most structures. Minor repairs are required. Cores should be consulted where necessary. are required for certain examinations or tests (e.g. petrographic studies). When selecting test techniques for a particular appraisal, the engineer should first define what Spot tests during sampling can sometimes provide a information is sought, including such requirements useful, but often crude, estimate of compositions or as the number of tests, level of accuracy, etc. The contaminants in structure. number of tests and the level of accuracy should be no more than is required for the assessment. Care must be taken to avoid contamination of Consideration should be given to using techniques samples, e.g. concrete by plaster. Samples should that will directly give the required information. Where be put into clean containers and clearly marked. direct observation or measurement is not practicable In concrete the outer 5mm should generally be or possible, as is often the case, other techniques discarded, except for site tests for chlorides, may indirectly provide the information sought, e.g. sulfates and carbonation (T15 and T16). A drill measurement of ultrasonic pulse velocity to give diameter equivalent to or larger than the maximum indications of the variation of concrete consistency aggregate size is recommended. Vacuum drilling (strength, compaction etc) within or between techniques, which prevent loss of fine particles structural elements. from the sample, can be employed in dry materials. However the equipment may be difficult Clearly the available tests have varying degrees of to obtain. appropriateness depending upon circumstances and the objectives of the investigation. The selection At the end of the description of each test, relevant of testing and investigation procedures may also references are given. A collation of these, sorted be constrained by the available budget. If the by material type and augmented, is provided at circumstances are difficult and not straightforward, it the end of all the test descriptions, followed by a may be advisable to seek expert advice. bibliography.
Table A7.1 List of tests described in Appendix 7
No. Test T1 Rebound (Schmidt) hammer T2 Ultrasonic pulse velocity – concrete T3 Core sampling and testing T4 Internal fracture test for concrete T5 Windsor probe T6 Break-off test (Norwegian method) T7 Phenolphthalein test T8 Microscopy studies T9(a) Cement content and cement / aggregate ratio T9(b) Type of cement T9(c) Type of aggregate T10 Latent expansion test T11 Water / cement ratio T12 Initial surface absorption test (ISAT) T13 Water and gas permeability tests T14 Water absorption test T15 Tests for chloride content T16 Admixtures and contaminants T17 Direct moisture measurement of concrete, masonry products and timber T18 Abrasion resistance testing
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Table A7.1 Continued
No. Test T19 Air entrainment T20 Covermeter T21 Physical exposure T22 Electrical potential T23 Endoprobe and borescope T24 Visual identification of wrought iron and cast iron T25 Chemical analysis of metals T26 Metallography T27 Dye penetrants T28 Ultrasonics – steel and other metals T29 Radiographic techniques for metals T30 Hardness tests T31 Tensile tests T32 Wedge penetration test for cast iron: use not recommended T33 Split-cylinder test for cast iron: use not recommended T34 Impact tests T35 Visual examination for weld and other surface observable defects T36 Magnetic-particle crack detection T37 Accelerated in situ tests for stress corrosion of bronze and other alloys T38 Visual inspection of steel cables T39 Crushing of masonry cores, units or sawn-out samples T40 Helix pull-out test T41 Split-cylinder tests T42 Flatjack test T43 Shove test (in situ shear) T44 Wall-tie detection T45 Visual examination of timber T46 Identification of insect attack T47 Identification of dry rot/wet rot T48 Moisture content of timber T49 Mechanical properties of timber T50 Identification of glues T51 Identification of preservative treatments T52 Identification of type of polymers T53 Ultrasonics – fibre reinforced polymeric (FRP) materials T54 Tensile strength – FRP materials T55 Fatigue – FRP materials T56 Impact strength – FRP materials T57 Water absorption – FRP materials T58 Accelerated weathering – polymers and FRP materials T59 Visual inspection – FRP materials T60 Air bag test T61 Structural load testing T62 ‘Giraffe’ wall profile measuring tool
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A7.2 Tests T1 to T62 by experienced persons as skill is required in the operation of the equipment, in placing of sensors and in the interpretation of results. T1 R ebound (Schmidt) hammer References This is a simple technique used primarily for making BS EN 12504-4:2004: Testing concrete in structures – Part 4: a comparative assessment of the quality of concrete Determination of ultrasonic pulse velocity. London: BSI, 2004 by testing its surface hardness. Light abrasion of the surface is required over an area about 100mm Bungey, J.H. and Millard, S.G. Testing of concrete in structures. square at each test location. Strength can be 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, estimated in existing construction by calibrating J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in against core tests. As the impact on the surface structures. 4th ed. Abingdon: Taylor & Francis, 2006} of the concrete is over a small area, the readings are susceptible to local variations. At least nine Concrete Bridge Development Group. Guide to testing and readings should be taken in each location to obtain monitoring the durability of concrete structures. Technical a representative result and the average value taken. Guide 2. Crowthorne: Concrete Society, 2002 The results are influenced, among other factors, by carbonation of the concrete surface, which increases T3 C ore sampling and testing the hardness of this layer, invalidating strength calibration curves derived for new concrete. The Standard cores of 100mm or 150mm diameter may results sometimes exhibit a wide scatter. In spite of be cut from concrete for measurement of the actual these drawbacks the test appears to be relatively strength and density. They may also be used to commonly used, perhaps because of its simplicity indicate the distribution of materials in the concrete, and cheapness to perform. the concrete quality (voids, honeycombing, etc.), and for petrographic, microscopy and associated studies. Rebound hammer is frequently used to provide a After strength testing, the crushed cores can be useful initial guide as to whether a problem really chemically analysed to determine mix proportions, exists with a batch of recently cast concrete when, presence of admixtures and contaminants, etc. for example, cubes have indicated that a problem Cores may also be used for tests, for measuring the might exist with the concrete. The technique can be shrinkage, expansion and absorption properties of used quickly to provide an indication of consistency the concrete, and the depth of carbonation. However with other elements and batches of notionally similar it is important that coring is undertaken at locations concrete. where it will not significantly weaken the structure.
References As cores are usually drilled to a depth of at least BS EN 12504-2: 2001: Testing concrete in structures – Part 2: 100mm they may pass through reinforcement. Cores Non-destructive testing – Determination of rebound number. can thus be used to give an accurate measure of London: BSI, 2001 the cover and to determine the type and size of steel used. However the consequences of cutting the Bungey, J.H. and Millard, S.G. Testing of concrete in structures. reinforcement should be considered. A covermeter 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, (T20) should be employed prior to coring to minimise J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in the risk of unintentional damage to reinforcement. structures. 4th ed. Abingdon: Taylor & Francis, 2006} Caution is required when interpreting the results of crushing tests on cores containing reinforcement. Concrete Bridge Development Group. Guide to testing and monitoring the durability of concrete structures. Technical For situations where standard cores cannot be Guide 2. Crowthorne: Concrete Society, 2002 obtained, for example in small beams, smaller cores may be taken. The results obtained should T2 U ltrasonic pulse velocity – concrete be subjected to cautious interpretation since the relationship to cube strength will not be the same as The quality and uniformity of concrete can be for standard cores, and the scatter of the results may assessed by measuring the velocity of ultrasonic be greater. pulses through it. Access is generally required to opposite faces of the member under test. The Small diameter cores (50mm diameter or less) method may be used to determine the presence are a convenient means of obtaining samples for of voids, cracks or other imperfections in a inspection and chemical analyses (e.g. for identifying member, and to give indications of variations in the shrinkable aggregates). composition or strength of the concrete in different members or along a given member. Core cutting is normally a ‘wet’ process, although the flush water can sometimes be recirculated with The instrument does not give a direct estimation of little spillage: dry coring techniques can, however, strength. Pulse velocity responds to factors, such be employed in some materials such as brick and as density and elastic modulus, which have an lightweight unreinforced concretes and blocks. influence upon strength. Calibration against cores is required to improve the accuracy of the estimation Remedial action will be required to repair the damage of strength. The test can, however, give useful to the structure; this makes the technique relatively indications of variations in uniformity when comparing expensive. areas of similar concrete construction. The technique requires accurate measurement of the distance References between the two ultrasonic transducers. Moisture BS 6089: 1981: Guide to assessment of concrete strength in variations can affect results. It is suitable for use only existing structures. London: BSI, 1981
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BS EN 12390-6: 2000: Testing hardened concrete – Part 6: surface damage. The cost of cartridges may be Tensile splitting strength of test specimens. London: BSI, 2000 significant.
BS EN 12390-7: 2000: Testing hardened concrete – Part Reference 7: Density of hardened concrete. London: BSI, 2000 {Since Bungey, J.H. and Millard, S.G. Testing of concrete in structures. superseded by 2009 version} 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in BS EN 12504-1: 2001: Testing concrete in structures – Part structures. 4th ed. Abingdon: Taylor & Francis, 2006} 1: Cored specimens – Taking, examining and testing in compression. London: BSI, 2001 {Since superseded by 2009 T6 Break-off test (Norwegian method) version} The test involves applying a transverse force, by Concrete Bridge Development Group. Guide to testing and a hydraulic load cell to the top of a core formed monitoring the durability of concrete structures. Technical Guide by diamond coring 70mm into the surface of No 2. Crowthorne: Concrete Society, 2002 the concrete member. It provides an estimate of the flexural tensile strength of concrete. A result Concrete Society. Concrete core testing for strength. Concrete should be taken as the mean of at least five test Society Technical Report 11. London: Concrete Society, 1987 values. Correlation with compressive strength is less reliable than for tensile strength. The test is T4 Internal fracture test for concrete inexpensive and quick to perform, but remedial repairs are usually required to the concrete surface. This test seeks to provide a measure of the The test should be calibrated against cores from compressive strength of concrete by inducing internal the same concrete. fracture within the material. This can be achieved in a number of ways which are classified as either References ‘pull-out tests’, where an anchor is inserted into the BS 1881-207: 1992: Testing concrete – Part 207: concrete, or ‘pull-off tests’ where a disk is bonded to Recommendations for the assessment of concrete strength near- the concrete surface. The test causes some minor to-surface tests. London: BSI, 1992 damage to the surface, which may require repair. Good surface preparation is required with the ‘pull- Bungey, J.H. and Millard, S.G. Testing of concrete in structures. off tests’ and there will be a time-lag (24h) while the 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, adhesive hardens. Dampness can affect the bond J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in achieved. Compressive strength is estimated from structures. 4th ed. Abingdon: Taylor & Francis, 2006} calibration charts. Multiple tests are required to give a representative result. T7 Phenolphthalein test (not applicable to HAC concretes) This test is no longer recommended for use on high- alumina cement (HAC) concrete over 15 years old. By The internal alkaline environment within concretes this age HAC concrete is likely to be fully converted. and mortars, which affords corrosion protection to The assessment of HAC concrete elements is embedded metal, is degraded by the penetration typically based upon the use of ‘prescriptive’ strength of acidic atmospheric gases. The most common is values given in the BRAC Rules. Thus the need carbon dioxide. The resulting reduction in alkalinity for undertaking this type of test on HAC concrete can be shown by the use of an indicator solution elements is usually limited. sprayed onto a freshly broken concrete surface. Phenolphthalein solution identifies alkaline zones by a References purple red coloration. BS 1881-207: 1992: Testing concrete – Part 207: Recommendations for the assessment of concrete strength near- Where it is not possible to break off pieces of to-surface tests. London: BSI, 1992 concrete or form a broken surface between two closely spaced drill holes, the depth of carbonation BS EN 12504-3: 2005: Testing concrete in structures – Part 3: can be determined by an incremental drilling Determination of pull-out force. London: BSI, 2005 technique, the drilling dust remaining colourless when sprayed with phenolphthalein solution in the Moss, R. and Dunster, A. High alumina cement concrete: carbonated zone. BRAC rules – revised 2002. BRE Report BR451. Garston: BRE Bookshop, 2002 Tests are easy and quick to perform, and where drillings are used surface damage is minor. T5 Windsor probe References This test involves firing a hardened steel pin into BS EN 14630: 2006: Products and systems for the protection concrete using a standard powder cartridge. The and repair of concrete structures. Test methods. Determination of method is a form of hardness testing, the depth carbonation depth in hardened concrete by the phenolphthalein of pin penetration providing an empirical estimate method. London: BSI, 2006 of compressive strength, uniformity and quality of concrete, mortar, bricks and blocks. A representative Building Research Establishment. Carbonation of concrete made test result is obtained from a group of 3 pins. with dense material aggregates. BRE Information Paper IP6/81. Penetration is mainly influenced by aggregate type Garston: BRE, 1981 and hardness. An appropriate calibration chart is required for a particular concrete. The pins should Bungey, J.H. and Millard, S.G. Testing of concrete in structures. be positioned more than 50mm from reinforcing bars 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, and edges of the concrete. Larger diameter pins are J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in available for lightweight concretes. The test causes structures. 4th ed. Abingdon: Taylor & Francis, 2006}
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T8 Microscopy studies by standard chemical analyses of concrete. A complete chemical analysis of the fine material from These techniques involve the petrographic a sample of concrete can be compared with typical examination of polished surfaces or thin sections analyses of various types of cement. A petrological of concrete to study the mineral materials under examination may also be helpful. The use of scanning the microscope. They may be used to determine electron microscopy is a particularly powerful tool, concrete constituents, voids, cracks and other being able to perform chemical identification over structural features, as well as mineralogical formation very small areas (such as an individual cement clinker when used in conjunction with methods such as particle). Portland blast-furnace cement and high- scanning microscopy. Water:cement ratios up alumina cement may be distinguishable in concrete to about 0.6 can be estimated with reasonable visually by the colour of the matrix. However colour accuracy. A reasonably precise indication of the may also be affected by the aggregate used, and progression of the carbonation front into concrete extreme care is necessary. can be given by thin-section microscopy techniques. Although these techniques can be relatively The BRE HAC test provides a simple and rapid way expensive, they often provide greater insight into of identifying high-alumina cement concrete on site. some aspects of the characteristics and deterioration The test may sometimes give false indication of HAC; processes affecting concrete structures. hence, a positive result should be confirmed by laboratory tests. Contamination by plaster must be References avoided. Bungey, J.H. and Millard, S.G. Testing of concrete in structures. 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, References J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in BS EN 197-1: 2000: Cement – Part 1: Composition, structures. 4th ed. Abingdon: Taylor & Francis, 2006} specifications and conformity criteria for common cements. London: BSI, 2000 Concrete Society. Analysis of hardened concrete. Concrete Society Technical Report 32. London: Concrete Society, 1989 Concrete Society. Analysis of hardened concrete. Concrete Society Technical Report 32. London: Concrete Society, 1989 St John, D.A., Poole A.W. and Sims, I. Concrete petrography: a handbook of investigative techniques. London: Arnold, 1998 T9(c) T ype of aggregate
T9(a) C ement content and cement:aggregate ratio The types of aggregate used in concrete may be immediately apparent on visual inspection. Where The determination of cement content of a hardened there is doubt, a petrographic examination of a cut concrete requires the facilities of a chemical slice will identify them and can also give information laboratory. The techniques used depend on whether on hardness, porosity, permeability, specific gravity or not the aggregate grading and content are to be and thermal properties, as well as potentially established as well as the type of cement, cement deleterious substances. content and aggregate used. If, by chance, samples of the materials used to make the concrete are still References available, the inherent errors in chemical analyses BS EN 12620: 2002: Aggregates for concrete. London: BSI, 2002 are considerably reduced. Nevertheless for simple {Since supplemented by +A1: 2008} aggregates such as flint and quartz sands, good results can be obtained, even without controls. Bungey, J.H. and Millard, S.G. Testing of concrete in structures. Igneous rocks, such as granites and basalts present 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, much more difficulty. J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in structures. 4th ed. Abingdon: Taylor & Francis, 2006} Petrographic and thin-section techniques (T8) are also able to estimate mix proportions. These Collis, L. and Fox, R.A. eds. Aggregates, sand, gravel and crushed methods involve a microscopic visual examination rock aggregates for construction purposes. Engineering Geology of specially prepared specimens. They are relatively Special Publication 9. 3rd ed. London: Geological Society, London, more expensive, but do produce a more detailed 2001 understanding of the concrete without some of the potential errors inherent in the chemical analytical Concrete Society. Analysis of hardened concrete. Concrete Society techniques. Technical Report 32. London: Concrete Society, 1989
References T10 Latent expansion test BS 1881-124: 1988: Testing concrete – Part 124: Methods for analysis of hardened concrete. London: BSI, 1988 To confirm suspected alkali-aggregate reactivity, laboratory tests are generally conducted on concrete BS 4551-2: 1998: Methods of testing mortar, screeds and samples taken from cores. These tests establish plasters. Part 2: Chemical analysis and aggregate grading. long-term latent expansion and other characteristics. London: BSI, 1998 Reference Concrete Society. Analysis of hardened concrete. Concrete Society Building Research Establishment. Alkali-silica reaction in Technical Report 32. London: Concrete Society, 1989 concrete. BRE Digest 330. 4 parts. Garston: BRE Bookshop, 2004
T9(b) Type of cement T11 Water:cement ratio
Most concretes are made with Portland cement Following determination of cement content, a – ordinary, rapid-hardening, sulfate-resisting or low- knowledge of the original water content enables the heat. These cements are not normally distinguishable water:cement ratio to be estimated, together with the
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concrete strength. A comparison can also be made been developed to overcome difficulties with the ISAT with the original mix design if known. method (T12). The Figg tests require drilled holes approximately 10mm diameter and 40mm deep. For Analytical methods of determining the original water the CLAM tests a 50mm internal diameter steel ring content of concrete are usually based on saturation is bonded to the concrete to isolate the test area. techniques. They give approximate answers only and Reported field experience is limited, and these tests cannot be used on damaged, poorly compacted or are most suitable for comparative purposes. aerated concretes. References Further guidance can be gained by petrographic and Bungey, J.H. and Millard, S.G. Testing of concrete in structures. thin-section examination. 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in References structures. 4th ed. Abingdon: Taylor & Francis, 2006} BS 1881-124: 1988: Testing concrete – Part 124: Methods for analysis of hardened concrete. London: BSI, 1988 Concrete Bridge Development Group. Guide to testing and monitoring the durability of concrete structures. Technical Concrete Society. Analysis of hardened concrete. Concrete Society Guide 2. Crowthorne: Concrete Society, 2002 Technical Report 32. London: Concrete Society, 1989 Concrete Society. Permeability testing of site concrete: a review St John, D.A., Poole A.W. and Sims, I. Concrete petrography: a of methods and experience. Technical Report 31. Camberley: handbook of investigative techniques. London: Arnold, 1998 Concrete Society, 1988 {Since superseded by Concrete Society. Permeability testing of site concrete: a review of methods and T12 I nitial surface absorption test (ISAT) experience. Technical Report 31. 2nd ed. Camberley: Concrete Society, 2008} This test measures the surface absorption of concrete. Considerable care needs to be taken. Kropp, J. and Hilsdorf, H.K. Performance criteria for concrete The test does not damage the structure. It is most durability: state of the art report. RILEM Report 12. London: Spon, suitable for comparative purposes. The results are 1995 affected by the nature of the surface. Tests on oven- dry samples give reasonably consistent results. T14 W ater absorption test
This test is being used increasingly to assess the Tests are made on small cores, 75mm in diameter, durability of in situ concrete. Tests are very sensitive cut from the concrete. Considerable care needs to to concrete quality and correlate with observed be taken when performing these tests. weathering behaviour. A minimum dry period of 48h is required before the test on surfaces exposed Absorption limits for concrete at different ages are to weather. Inherent variations in initial moisture specified in some British Standards for precast condition of the concrete need to be taken into concrete products. account when interpreting results. References References BS 1881-122: 1983: Testing concrete – Part 122: Method for BS 1881-208: 1996: Testing concrete – Part 208: determination of water absorption. London: BSI, 1983 Recommendations for the determination of the initial surface absorption of concrete. London: BSI, 1996 Concrete Bridge Development Group. Guide to testing and monitoring the durability of concrete structures. Technical Bungey, J.H. and Millard, S.G. Testing of concrete in structures. Guide 2. Crowthorne: Concrete Society, 2002 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in Concrete Society. Permeability testing of site concrete: a review structures. 4th ed. Abingdon: Taylor & Francis, 2006} of methods and experience. Technical Report 31. Camberley: Concrete Society, 1988 {Since superseded by Concrete Society. Concrete Bridge Development Group. Guide to testing and Permeability testing of site concrete: a review of methods and monitoring the durability of concrete structures. Technical Guide experience. Technical Report 31. 2nd ed. Camberley: Concrete 2. Crowthorne: Concrete Society, 2002 Society, 2008}
Concrete Society. Permeability testing of site concrete: a review T15 T ests for chloride content of methods and experience. Technical Report 31. Camberley: Concrete Society, 1988 {Since superseded by Concrete Society. Laboratory-based methods for chemical analysis of Permeability testing of site concrete: a review of methods and samples (eg. crushed cores and dust from drillings) experience. Technical Report 31. 2nd ed. Camberley: Concrete are generally preferred for their greater accuracy Society, 2008} and the assurance provided by the adoption of laboratory procedures, but it is possible to use T13 Water and gas permeability tests commercially available kits to make field-based determinations. These tests are designed to assess the permeability of concrete in the surface zone. The quality of A minimum sample mass of 25g is required to ensure the concrete in this zone is critical to durability. a representative sample. The sampling regime should Laboratory tests on material samples provide the be carefully designed for the particular structure most reliable assessment of permeability. and the nature of the envisaged contamination (i.e. introduced at the time of construction or The Figg and the ‘CLAM’ water and air permeability subsequently by ingress). Field tests provide the tests are relatively simple tests which can be used on flexibility to amend the sampling regime in light of the site to evaluate in situ concrete. These methods have results obtained.
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Where chloride is suspected to have been added Other admixtures and contaminants, e.g. organic during construction and assessment of a large admixtures, sugars, metals, can be determined by number of similar components in a structure is laboratory techniques such as X-ray fluorescence required, single samples from 10% of the building spectroscopy, infrared absorption, scanning electron components under investigation will usually microscopy, etc. The assessment of dosage (which determine if significant levels of chloride are present is frequently the prime objective of the test) is in the structure. If significant levels are identified dependent on a precise knowledge of the admixture it may be necessary to undertake further testing used. The tests are difficult, complex and quantitative to arrive at a prognosis of the future life of the methods can be very hard to perform with any components. accuracy. The use of these tests is limited.
There are a number of commercially available kits Reference (e.g. such as HACH titrator and QUANTAB strip Concrete Society. Analysis of hardened concrete. Concrete Society indicator methods) for field tests to determine the Technical Report 32. London: Concrete Society, 1989 chloride contents of drilled concrete and mortar samples. The tests are generally straightforward and T17 Direct moisture measurement of concrete, quick to perform (30 minutes). It is necessary to have masonry products and timber appropriate facilities for sample preparation. The tests are generally of sufficient accuracy to indicate The most direct method is to take a ‘lump’ sample, the presence and level when there is a significant weigh it, dry it in an oven, and weigh it again. The chloride content. However, it is considered prudent moisture content (by mass) is: for these indications to be backed up by a proportion
of laboratory-based determinations. W1 – W2 × 100% There may be particular benefits offered by being W2 able to conduct chloride determinations on site
as an investigation proceeds. For example, this where W1 is the undried weight and W2 is the oven- approach potentially allows the sampling regime to dried weight. be adapted to the circumstances appertaining to the particular site, as revealed by the test results Another approach for concrete and masonry is to obtained. However such potential advantages need take drilled samples from the material ensuring that to be balanced against the potential risks associated overheating of the dust does not occur. Weighed with on-site tests, which can give inaccurate results, quantities of dust and reagent are mixed within especially in the hands of inadequately-skilled a calorimeter. Gas is given off and the pressure people. The fact that laboratory tests can generally generated is proportional to the water content of the be performed rapidly and accurately may negate the sample. The test is simple and quick to perform and need for site-based determinations. is (with care) reasonably accurate. The drilling causes some surface damage. References BS EN 13396: 2004: Products and systems for the protection T18 Abrasion resistance testing and repair of concrete structures – Test methods – Measurement of chloride ion ingress. London: BSI, 2004 Abrasion resistance of concrete is generally only of critical importance for floors within industrial Bungey, J.H. and Millard, S.G. Testing of concrete in structures. premises or warehouses subject to heavy wear 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, and high wheel loads. It may be assessed using an J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in accelerated wear apparatus consisting of a rotating structures. 4th ed. Abingdon: Taylor & Francis, 2006} loaded plate supported by three case hardened steel wheels which wear a groove in the concrete Concrete Bridge Development Group. Guide to testing and surface. The depth of the groove is measured after a monitoring the durability of concrete structures. Technical Guide 15 minute standard test period. The results correlate 2. Crowthorne: Concrete Society, 2002 well with observed deterioration of floors in service.
prEN 14629: 2003: Products and systems for the protection and References repair of concrete structures – Test methods – Determination of BS 8204-2: 2002: Screeds, bases and in situ floorings – Part 2: chloride content in hardened concrete. London: BSI, 2007 {Since Concrete wearing surfaces – Code of practice. London: BSI, 2002 superseded by BS EN 14629: 2007: Products and systems for {Supplemented by +A1: 2009} the protection and repair of concrete structures – Test methods – Determination of chloride content in hardened concrete. London: Bungey, J.H. and Millard, S.G. Testing of concrete in structures. BSI, 2007} 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in T16 A dmixtures and contaminants structures. 4th ed. Abingdon: Taylor & Francis, 2006}
Many varieties of admixtures have been used in T19 A ir entrainment concrete construction. Calcium chloride is the most likely one to be considered in a structural Entrained air voids in concrete are spherical and, for appraisal. The amount of chloride in a sample can effective protection of the cement paste from freezing be determined in the laboratory or a good estimate and thawing cycles, range in size from about 0.2 to can be obtained by a field test with indicator kits 1mm. The percentage of entrained air voids, their size (see T15). The presence of sulfate may also need to and distribution may be established by microscopy be considered in an appraisal. It can be determined point counting methods on prepared samples readily by laboratory analysis of a sample. impregnated with a suitable dye.
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References of the reinforcement. The results are plotted on BS EN 480-11: 1999: Admixtures for concrete, mortar and contour maps of potential enabling localised zones grout – Test methods – Part 11: Determination of air void of corrosion risk to be identified. The method is characteristics in hardened concrete. London: BSI, 1999 {Since susceptible to weather conditions which markedly superseded by 2005 version} influence the absolute values of electrical potential. It does not indicate the degree of corrosion that Concrete Society. Analysis of hardened concrete. Concrete Society has occurred. Care has to be exercised to ensure Technical Report 32. London: Concrete Society, 1989 satisfactory electrical coupling with pore fluids within the concrete. T20 Covermeter References This simple electromagnetic equipment is used to ASTM C876-09: Standard test method for half-cell potentials estimate the depth to steel reinforcement in concrete of uncoated reinforcing steel in concrete. West Conshohocken: and to determine its orientation and distribution. ASTM, 2009 The response of the equipment differs for different diameter bars and is influenced by multiple layers Building Research Establishment. Corrosion of reinforcement in and/or close pitch. Some modern equipment is concrete: electrochemical monitoring. BRE Digest 434. Garston: claimed to identify the diameter of bars. Particular BRE, 1998 care is needed where the meter is used on lightweight concrete or concrete containing crushed Concrete Bridge Development Group. Guide to testing and rock aggregate incorporating magnetic particles. monitoring the durability of concrete structures. Technical Some pozzolans, especially fly ashes, contain Guide 2. Crowthorne: Concrete Society, 2002 magnetic particles and some sands contain particles of magnetite. The performance of some types of Concrete Society. Electrochemical tests for reinforcement equipment, especially older models, may be affected corrosion. Concrete Society Technical Report 60. Camberley: by temperature variations. Concrete Society, 2004
Although the equipment is straightforward to use, Vassie, P.R. The Half-cell potential method of locating corroding considerable care and skill is required to obtain reinforcement in concrete structures. TRRL Application Guide 9. acceptable results. In heavily reinforced members Crowthorne: TRRL, 1991 or members with cover thicker than 60mm it may not be possible to obtain reliable results with older T23 E ndoprobe and borescope equipment. Recent equipment can provide an image (pattern) of the underlying reinforcement provision. It These miniature CCTV devices may be used for the is still prudent to undertake some ‘verification’ either inspection of the integrity of cavity wall ties or other by drilling onto bars (gives indication of cover depth) elements within cavities, e.g. under floors. or by limited opening up, which provides information on cover depth and bar type but causes more They can also be used to inspect the condition of surface damage. ‘Calibration’ may be required for prestressing tendons in ungrouted or poorly grouted some older equipment. ducts in concrete structures. Access is gained either through the duct wall or (rarely) via the end References anchorage blocks. Extreme care is required to avoid BS 1881-204: 1988: Testing concrete – Part 204: damaging the prestressing tendons. Holes are drilled Recommendations on the use of electromagnetic covermeters. into the ducts to provide access for the fibre optic London: BSI, 1988 viewer.
Bungey, J.H. and Millard, S.G. Testing of concrete in structures. References 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, de Vekey, R.C. Corrosion of steel wall ties: recognition and J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in inspection. BRE Information Paper IP 13/90. Garston: BRE, 1990 structures. 4th ed. Abingdon: Taylor & Francis, 2006} Johnson, M.A.E. and Fifield, B.E. ‘Remote visual inspection Concrete Bridge Development Group. Guide to testing and of voids and cavities: practical experience on post-tensioned monitoring the durability of concrete structures. Technical Guide concrete bridges’. In Forde, M.C. ed. Structural faults and repair 2. Crowthorne: Concrete Society, 2002 93. Vol 1: Extending the life of bridges. Edinburgh: Engineering Technics Press, 1993, pp301-303 T21 P hysical exposure T24 Visual identification of wrought iron and cast iron The removal of the cover of concrete, masonry or non-structural finishes using hand tools or The presence of wrought iron and cast iron should hand-operated power tools is a simple technique be expected in all 19th century structures. The for exposing hidden parts of structures locally, structural use of these materials diminished with e.g. reinforcement, structural steel, wall ties, for the introduction of steel in the 1880s and effectively visual examination. See also Appendix A8.25 and ceased by the 1930s. associated reference. Wrought iron is not easily distinguishable chemically T22 E lectrical potential from a low-carbon steel. However, it may often be identified visually by its characteristic laminated This technique involves measuring the electrical structure. If a small area is ground on the surface potential of embedded reinforcing steel relative to a to remove scale and expose the clean metal, which reference half-cell (generally copper/copper sulfate is then polished with fine abrasive paper, filaments or silver/silver chloride) placed on the concrete of slag, visible through a hand magnifying glass, surface. It gives an indication of the risk of corrosion identify the material as wrought iron. In forged
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elements – such as clevises, brackets, eye-bars – T27 D ye penetrants the direction of the lamination should be checked to identify areas in which tensile stress occurs normal to These techniques of inspection of steel structures are the plane of lamination. probably the most commonly employed field method of defect detection. They provide information on the Forge welding of wrought iron was a common surface condition of the steel, i.e. the presence of practice in fabricating structural elements. The cracks and surface imperfections, particularly those presence of welds in, for example, eye-bar ends, associated with welding. large bars with threaded ends, or where there is a marked change in section, should be considered The technique is inexpensive and easily applied and suspect and non-destructive tests made to verify the interpreted. It requires the surface to be cleaned to a soundness of the weld. high standard (grit blasted) over the area of interest. A fluid is placed on the cleaned surface and allowed As the laminations of wrought iron constitute internal to penetrate cracks and surface defects. Excess discontinuities, crack detection techniques are of little penetrant is wiped off and developing fluid (often use in determining its integrity. Visual examination white) applied. The penetrant then seeps from cracks should be used, if possible supplemented by tension and other surface defects and stains the developer tests on samples. The surface of the sample should revealing the presence of cracks. be examined for stamp marks that identify the quality. References Cast iron can usually be identified by its shape, e.g. BS EN 1371-1: 1997: Founding – Liquid penetrant inspection – tapering round columns, and the appearance on Part 1: Sand, gravity die and low pressure die castings. London: its surface of evidence of the casting process, e.g. BSI, 1997 sand marks, mould joints. It may also be identified by drilling, which will result in fragmented swarf. Beams BS EN ISO 12706: 2001: Non-destructive testing – Terminology – with unequal flanges, or of unusually thick section, Terms used in penetrant testing. London: BSI, 2001 should be suspected as being made of cast iron. Hunt, B.J. ‘The use of fluorescent dyes in highlighting some Cast iron members should be examined for cracks construction problems’. Structural Survey, 12(6), 1993-94, pp4-7 and for soundness, i.e. casting defects, by suitable NDT methods. Dimensional accuracy, e.g. constancy T28 U ltrasonics – steel and other metals of wall thickness in a column, should also be checked. Ultrasonics, while providing similar information to References radiographic techniques, will indicate the presence Ashurst, J. and Ashurst, N. Practical building conservation. Vol 4: of laminations in steel and other metals. Lamellar Metals. English Heritage Technical Handbook. Aldershot: Gower, tearing is also revealed. The technique requires the 1988 surface to be cleaned down to bare metal. It is very dependent on the competence of the operator to Bussell, M. Appraisal of existing iron and steel structures. SCI recognise and report indications of defects. Defects Publication 138. Ascot: SCI, 1997 of millimetre dimensions can be detected within the metal. The technique can also be used to measure Morgan, J. ‘The Strength of Victorian wrought iron’. ICE wall thickness of tubes and hollow columns. Proceedings, Structures and Buildings, 134(4), Nov 1999, pp295-300 The coarse grain structures of some cast iron and the laminated structure of wrought iron limits the T25 C hemical analysis of metals application of ultrasound in these materials. Access is required to one face of a member only since Laboratory analysis of samples of metals can be the technique works by reflection of propagated used to provide an indication of type and associated ultrasound pulses. physical properties. The mechanical properties of many non-ferrous alloys show very significant References variations depending on the manufacturing process, BS EN 1330-4: 2000: Non-destructive testing – Part 4: Terms e.g. extrusion and the state of temper. used in ultrasonic testing. London: BSI, 2000
Reference BS EN 1714: 1998: Non destructive examination of welded joints Taylor, J.L. ed. Basic metallurgy for non-destructive testing. – Ultrasonic examination of welded joints. London: BSI, 1998 Northampton: British Institute of Non-Destructive Testing, 1989 {Since superseded by Taylor, J.L. ed. Basic metallurgy for non- BS EN 10160: 1999: Ultrasonic testing of steel flat product destructive testing. 4th ed. Northampton: British Institute of Non- of thickness equal or greater than 6 mm (reflection method). Destructive Testing, 1996} London: BSI, 1999
T26 M etallography BS EN 10228-3: 1998: Non-destructive testing of steel forgings – Part 3: Ultrasonic testing of ferritic or martensitic steel forgings. Metallographic examination can give information London: BSI, 1998 on the internal structure of a material, e.g. it might indicate some chemical segregation that would explain BS EN 10228-4: 1999: Non-destructive testing of steel forgings anomalous response to welding. This requires a sample – Part 4: Ultrasonic testing of austenitic and austenitic-ferritic with one flat surface approximately 10 × 10mm. stainless steel forgings. London: BSI, 1999
Reference BS EN 12680-1: 2003: Founding – Ultrasonic examination – BS 6533: 1984: Guide to macroscopic examination of steel by Part 1: Steel castings for general purposes. London: BSI, 2003 etching with strong mineral acids. London: BSI, 1984
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T29 Radiographic techniques for metals T31 T ensile tests
Radiographic techniques are used to determine the Testing of steel by measuring the tensile load integrity of steel and other metals, i.e. to ascertain required to rupture a standard specimen is the presence and degree of cracks, laminations, probably the best test for the identification of porosity and inclusions, both in parent materials and materials. This type of test is also frequently used welds. Cracks in a plane containing the line joining to obtain measurements of the ductility of the the source (isotope) to the receptor (film) cannot be material in addition to the tensile strength. Other detected. Radiation regulations require operation properties which may be measured include elastic by suitably trained and classified personnel, and limit, yield point, proof stress and modulus of suitable precautions to prevent unnecessary elasticity. Test pieces of standard size (between exposure to radiation. 150 and 250mm long) are usually required, their cross-section may be circular, square, rectangular References or, in special cases, of some other form. Test BS EN 1330-3: 1997: Non-destructive testing – Terminology – pieces should generally be machined to the Part 3: Terms used in industrial radiographic testing. London: BSI, dimensions given in the various Standards, but 1997 some sections, bars, tubes, etc. may in certain circumstances be tested without being machined. BS EN 1435: 1997: Non-destructive examination of welds – However, this type of test is expected to be very Radiographic examination of welded joints. London: BSI, 1997 sparingly used due to the damage involved in taking a sample and the cost involved. T30 Hardness tests Cast iron: The material is fairly variable in strength The hardness number of a material is determined and this is related to the manufacturing process from the size of an indentation made on its surface. and section thickness. The values given in BD21 The surface properties however may differ from for permissible stresses (which are also contained those within the body of the material. For steels, in the Steel Construction Institute (SCI) guide to the an empirical relation exists between the hardness appraisal of existing iron and steel structures) are number and the ultimate (not yield) strength. The considered to be safe but not unduly conservative. result should be regarded as a guide only. If a Accordingly it is unlikely that a ‘better’ strength strength is required for calculations, a tensile test (see would be obtained by testing. In any event, for the T31) should be made if possible. results to be statistically reliable, it is necessary to take 6-10 samples, and for heritage structures The standard laboratory hardness tests are the this amount of cutting about might not be Brinell (ball), Vickers (pyramid diamond) and acceptable. Strength testing of cast iron is seldom Rockwell (ball or diamond cone). They give much warranted, and is expensive and destructive of more reliable results than on-site tests using portable original material. Thus the assessment of cast testing apparatus. Comparative in situ testing may iron elements is typically based upon the use of however be useful for identifying the weakest of a ‘prescriptive’ strength values such as those given large number of members. in BD21.
The ranges of tensile strengths of the various grades Wrought iron: The material is of variable strength, of structural steel overlap. Therefore it may not with acceptable values for yield strength being be possible positively to identify the grade of the given in BD21 and the SCI guide. Accordingly steel solely from its hardness number. The cost of similar comments apply as for cast iron. physically exposing a metal surface for test, e.g. steel reinforcing bars in concrete and the subsequent Steel: Strength testing of steel may be more reinstatement, should therefore be carefully useful, particularly for more recent steels which considered against the value of the results to be may be of specified higher strength than mild steel. obtained. References References BS EN 10002-1: 2001: Tensile testing of metallic materials – BS EN 10003-1: 1995: Metallic materials – Brinell hardness test Part 1: Method of test at ambient temperature. London: BSI, – Part 1: Test method. London: BSI, 1995 {Since superseded by 2001{Since superseded by BS EN ISO 6892-1: 2009: Metallic BS EN ISO 6506-1: 2005: Metallic materials – Brinell hardness materials – Tensile testing – Part 1: Method of test at ambient test – Part 1: Test method. London: BSI, 2005} temperature. London: BSI, 2009}
BS EN 10109-1: 1996: Metallic materials – Hardness test BS EN 10002-5: 1992: Tensile testing of metallic materials – – Part 1: Rockwell test (scales A, B, C, D, E, F, G, H, K) and Part 5: Method of test at elevated temperatures. London: BSI, Rockwell superficial test (scales 15 N, 30 N, 45 N, 15 T, 30 T 1992 and 45 T). London: BSI, 1996 {Superseded by BS EN ISO 6508- 1: 2005: Metallic materials – Rockwell hardness test – Part 1: Bussell, M. Appraisal of existing iron and steel structures. SCI Test method (Scales A, B, C, D, E, F, G, H, K, N, T). London: BSI, Publication 138. Ascot: SCI, 1997 2006} Highways Agency. The Assessment of highway BS EN ISO 6507-1: 1998: Metallic materials – Vickers hardness bridges and structures. BD 21/01. Available at: test – Part 1: Test method. London: BSI, 1998 {Since superseded http://www.standardsforhighways.co.uk/dmrb/vol3/section4/ by 2005 version} bd2101.pdf [Accessed: 14 October 2009]
BS EN ISO 18265: 2003: Metallic materials – Conversion of hardness values. London: BSI, 2003
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T32 W edge penetration test for cast iron References BS 131: 1961: Notched bar tests – Part 1: The IZOD impact test This test is used for quality control of new castings, on metals. London: BSI, 1961 although there has been one application as part of the assessment of the tensile strength of the cast iron BS 7448-1: 1991: Fracture mechanics toughness tests – Part in a bridge. It requires a disc of a diameter between 1: Method for determination of KIc, critical CTOD and critical 25 and 50mm and a thickness of about a third of the J values of metallic materials; BS 7448-2: 1997: Fracture diameter. This is placed between a hardened wedge mechanics toughness tests – Part 2: Method for determination and an anvil. The force on the wedge at which the of KIc, critical CTOD and critical J values of welds in metallic disc splits is measured and divided by the area of the materials. London: BSI, 1991; 1997 split. The correlation between this splitting stress and the tensile strength can be established by calibration. T35 V isual examination for weld and other surface observable defects Note: See comment made for T31 about applicability and need for testing to determine the tensile The surface appearance of welds and other elements strength of cast iron. The need and desirability of may give an indication of quality and the presence of undertaking this type of test on cast iron members defects, e.g. cracking. The surface to be examined is usually limited. Generally testing would not be should be clean. The use of dye penetrants (see T27) recommended. It is suggested that the assessment may be helpful. of cast iron elements should normally be based upon the use of ‘prescriptive’ strength values such as If stress corrosion is suspected a detailed visual those given in BD21. examination should be carried out. This involves the optical examination of the components with a '×10' Reference hand lens to confirm the presence or absence of See Castings Technology International (previously British Cast Iron well established cracks. However, a simple visual Research Association) publications for details of test procedures. examination cannot be relied upon.
T33 S plit-cylinder test for cast iron References BS EN 970: 1997: Non-destructive examination of fusion welds – A small machined cylinder is placed horizontally Visual examination. London: BSI, 1997 between the platens of a testing machine and compressed until it splits along the vertical diametric Shreir, L.L. and other eds. Corrosion. Oxford: Butterworth- plane. For cylinders 11.5mm in diameter and 23mm Heinemann, 1994 {Since superseded by Richardson, T. ed. long, taken from hollow columns, the University Shreir’s corrosion. 4 vols. Oxford: Elsevier Science, 2009} of Karlsruhe has found that the tensile strength is between 1.85 and 1.53 times the cylinder splitting T36 M agnetic-particle crack detection strength, with a mean value from 14 tests of 1.74. This is mainly an inspection tool used during the Note: See comment made for T31 about applicability fabrication and erection of steelwork. The method and need for testing to determine the tensile can detect only surface and near surface defects and strength of cast iron. The need and desirability of is limited to magnetic materials. undertaking this type of test on cast iron members is usually limited. Generally testing would not be The surface must be cleaned, usually by grit blasting. recommended. It is suggested that the assessment A white background paint is applied before an ink of cast iron elements should normally be based upon containing magnetic particles. A magnetic field is the use of ‘prescriptive’ strength values such as introduced across the test area by means of a hand those given in BD21. held (electro-) magnet. Surface defects are revealed by fine lines of magnetic particles and a subsurface Reference defect by a fuzzy build-up of magnetic particles. Only Käpplein, R. ‘Zur Beurteilung des Tragverhaltens alter gußeisener cracks that are largely perpendicular to the magnetic Hohlsäulen’. Berichte der Versuchsanstalt fur Stahl, Holz und field are detectable. Steine der Universität Fridericiana in Karlsruhe, 4 Folge, Heft 23, 1991 [in German] Although it is considered to be a simple technique for smooth flat-plate surfaces with flush welds it is less T34 I mpact tests simple with more complex structural arrangements. The test zone is left in a magnetised condition. Standard impact tests – the Izod (cantilever) and Although rarely a problem this can affect subsequent Charpy (beam) – measure the energy required operations such as welding owing to the straying of to fracture a standard notched specimen with a the welding arc. blow from a pendulum. The Charpy test is the more versatile as it enables results to be obtained References over a range of temperatures. The results enable BS EN 1330-7: 2005: Non-destructive testing – Terminology comparisons of the notch ductility of different – Part 7: Terms used in magnetic particle testing. London: BSI, metals to be made. They also allow checks of the 2005 compliance with standard requirements for adequate resistance to brittle failure. BS EN 1369: 1997: Founding – Magnetic particle inspection. London: BSI, 1997 Sample sizes for the Izod impact tests are 70mm for one notch, 98mm for two notches and 126mm for BS EN ISO 9934-1: 2001: Non-destructive testing – Magnetic 3 notches, the cross-section being 10 × 10mm. For particle testing – Part 1: General principles. London: BSI, 2001 the Charpy impact tests the sample size is 55mm by 10 × 10mm for either a U- or V-notch test piece.
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T37 A ccelerated in situ tests for stress corrosion of Spark tests may indicate the quality of any remaining bronze and other alloys coating, and testing with magnetic fields may highlight broken wires within the body of the cable Chemical analyses of bronze drillings allow the (see also A8.24: but the technique is better than determination of the composition of the metal, but merely ‘experimental’ for this application). this does not automatically indicate the mechanical properties. Special chemical tests on small solid T39 C rushing of masonry cores, units or sawn-out samples can indicate susceptibility to stress- samples corrosion cracking. Dry coring techniques can be used in brick and Stress corrosion cracking is a complex mechanism concrete block masonry (see T3). Samples for testing which requires the combination of specific alloys in may also be obtained by removing individual bricks specific environments. The susceptibility of a given or blocks from the masonry or by sawn-out masonry alloy and environment combination can usually be samples. Strength may be determined by crushing found from the literature. However, it is prudent cores, bricks, blocks or sawn-out masonry samples to carry out accelerated tests in situ, employing in the laboratory. samples of the alloy placed under stress by a testing rig. The results of such tests will indicate the The most reliable techniques for assessing the likelihood that stress corrosion cracking can occur. compressive strength of masonry involve the removal of either components or representative References prisms of composite masonry for laboratory testing. BS EN ISO 7539-1: 1995: Corrosion of metals and alloys – Anisotropic units or masonry may need to be tested Stress corrosion testing – Part 1: General guidance on testing in particular orientations. procedures. London: BSI, 1995 Reference Logan, H.L. Stress corrosion of metals. New York: John Wiley, LUMD1: Removal and testing of specimens from existing 1966 masonry’. In: RILEM. Technical recommendations for the testing and use of construction materials. London: E. & F. N. Spon, 1994, Scalley, J.C. ed. Theory of stress corrosion cracking in alloys. pp501-502 Brussels: NATO Scientific Affairs Division, 1971 T40 Helix pull-out test Shreir, L.L. and other eds. Corrosion. Oxford: Butterworth- Heinemann, 1994 {Since superseded by Richardson, T. ed. This test gives an indication of the compressive Shreir’s corrosion. 4 vols. Oxford: Elsevier Science, 2009} strength of mortar or lightweight aerated concrete blocks. It is fundamentally a measurement of the T38 Visual inspection of steel cables shear strength of a small cylinder or annulus of material (mortar or low density block) which is The comments below refer to structural cables and engaged by a helical self-tapping screw. not to those used to carry moving loads in lifting gear or other mechanical equipment. The test is still under development but work to date shows good correlation with compressive strength If the original specification is available a check of low density aerated concrete blocks. The results should be made to see if the cable was prestretched from use in 10mm mortar joints show a consistent (normally by the manufacturer) before installation. relationship, but variability is high. The test displays Subsequent stretching in service, which may be greatest sensitivity for compressive strengths below checked by measuring the sag or alignment of 10MPa. The damage to the masonry is small and adjacent structural elements and comparison with easily repaired. The common and incorrect practice the original design, normally indicates significant of laying bricks frog down can cause a void to be cable damage. present above the mortar bed. This can influence the test results. Inspection may be made by visual examination. The following should be borne in mind: References –D– amage is most likely to be present at the ends Building Research Establishment. Measuring the compressive (terminations); the outer wires generally fail before strength of masonry materials: the screw pull-out test. BRE the inner ones. Digest 421. London: CRC, 1997 –T– he ends of cables may show signs of relative movement between the cable and socket or end de Vekey, R.C. ‘The Non-destructive evaluation of masonry connection. materials in structures’. Proceedings 8th CIMTEC world ceramics –C– orrosion is more likely to occur at the lower congress, Florence, 1994 end of a cable as it tends to remain wet due to rainwater. Ferguson, W.A. and Skandamoorthy, J. ‘The screw pull-out tests –T– here is frequently a groove at the cable/socket for the in situ measurement of the strength of masonry materials’. junction where water can collect. Proceedings 10th international brick and block masonry –I– f the outside of a cable is painted, the presence conference, Calgary 1994, pp1257-1265 of a broken wire in the outer lay is indicated by a spiral crack in the paint caused by the relative T41 Split-cylinder tests movement between adjacent wires when the tension in the broken wire is released. The so-called compressive failure of masonry is in –A– reas where the lay of the cable or individual reality a lateral tensile failure. It is influenced by the strands are disturbed are potential failure sites. mortar undergoing greater transverse deformation than the units. This behaviour is utilised in the split-cylinder test.
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The compressive strength of the units is determined ‘Test method recommendations of RILEM TC 177-MDT Masonry by direct tests, or tests on (small) ‘vertical’ cores. The durability and on-site testing – D.5: Insitu stress – strain cylinder splitting strength of the units is determined behaviour tests based on the flat jack’. Materials and Structures, by testing (small) cores taken horizontally from the 37(7), August 2004, pp497-501 units. The reduction of the transverse tensile strength of the masonry, due to the mortar, is determined T43 Shove test (in situ shear) by cylinder-splitting tests on horizontal cores, incorporating a bedjoint in the horizontal diametric The in-place bedjoint shear (shove) test is a partially plane. The basic in situ compressive strength of the destructive test designed to measure the sliding masonry is then equal to the compressive strength of shear strength of a masonry joint. It consists of the units multiplied by the ratio between the splitting displacing a single masonry unit horizontally with a strength of the jointed cylinder and the splitting hydraulic jack. It is necessary to remove another unit, strength of the solid cylinder. to provide access for the hydraulic jack. A head joint is removed on the opposite side of the unit under test Reference to isolate it from the adjoining masonry. An improved Berger, F. Zur nachträglichen Bestimmung der Tragfähigkeit technique is to use a small flatjack in place of a von zentrisch gedrücktem Ziegelmauerwerk, Erhalten historisch standard jack, which necessitates the removal only of bedeutsamer Bauwerke. Berlin: Ernst und Sohn, 1987 [in joints at either end of the unit to be tested. German] The test gives a measure of the shear resistance T42 F latjack test of a masonry wall and can be used comparatively as a quality indicator. Some repairable damage This test is used to measure the in situ compressive occurs. The test is relatively straightforward but stress in masonry. Pairs of Demec studs are placed time-consuming, and therefore relatively expensive, vertically above and below a bed-joint. A special to carry out. It is used mainly to assess potential flatjack is inserted into a horizontal slot cut into this behaviour under seismic conditions and as such may bed-joint. The flatjack is progressively pressurised have limited application in the UK. until the distances between the Demec studs return to their original values prior to the stress-relief caused A modified test positions the unit to be displaced by the cutting of the slot. Each flatjack has to be between two horizontal flatjacks (see T42). The calibrated. The method has a long and useful history unit is instrumented to measure horizontal shear (it was originally used in rock mechanics) but is deformation. The horizontal load is increased until the dependent on the competence of the tester. unit continues to displace under constant load. The vertical load is then increased and the test repeated The flatjack test can be used to assess whether local through a number of cycles. over stressing is occurring. These results give the relationship between sliding The deformation properties of masonry may be shear strength and vertical stress. If the quality of the evaluated by employing two parallel flatjacks, one masonry in a building is uniform and consistent with directly above the other and separated by a number the test specimen, the results may be used to verify of courses. The flatjacks are pressurised equally, the local vertical load in the walls of that building. thus imposing load on the intervening masonry. The deformations of the intervening masonry may be Reference related to the imposed loads. ASTM C1197-09: Standard Test Method for In Situ Measurement of Masonry Deformability Properties Using the Flatjack Method. The flat jack can also be used in situ to assess the West Conshohocken, PA, ASTM, 2009 compressive strength of masonry, but is not normally capable of testing to failure due to limitations in the T44 W all-tie detection available reaction from the remainder of the structure: an external reaction frame may be necessary. Metal detectors depend on the interactions between a coil or coils carrying alternating voltage and References conducting or ferromagnetic (or both) materials. ASTM D4729-08: Standard test method for in situ stress The devices are similar to covermeters. Certain and modulus of deformation using flatjack method. West ingredients in the masonry units, such as iron Conshohocken, PA: ASTM, 2008 compounds in bricks, can cause erroneous results. Some experience of operation is Building Research Establishment. Masonry and concrete desirable. They are often used in conjunction with structures: measuring insitu strength and elasticity using flat endoscopes/borescopes (see T23). Stainless steel jacks. BRE Digest 409. London: CRC, 1995 or non-ferrous ties are only detectable with certain types of instrument. de Vekey, R.C. ‘Measurement of load eccentricity using flat jacks’. Masonry (9): Proceedings of the British Masonry Society. 6th References International Masonry Conference, London, 2002. Stoke-on-Trent: de Vekey, R.C. Corrosion of steel wall ties: history of occurrence, British Masonry Society, 2002, pp79-85 background and treatment. BRE Information Paper IP12/90. Garston: BRE, 1990 ‘Test method recommendations of RILEM TC 177-MDT Masonry durability and on-site testing – D.4: Insitu stress tests based de Vekey, R.C. Corrosion of steel wall ties: recognition and on the flat jack’. Materials and Structures, 37(7), August 2004, inspection. BRE Information Paper IP 13/90. Garston: BRE, 1990 pp491-496
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T45 Visual examination of timber The two fungi – dry rot and wet rot – are easier to diagnose in the later stages of development when the The visual examination of timber can provide good fruiting body appears on the surface of the timber. indications of timber species, grade and quality and of insect and fungal attack. Bolted connections can Early signs of dry rot are cracks along the grain, be examined visually for defects or deterioration if followed by cracks at right-angle to the grain (i.e. a temporarily unloaded and dismantled. A magnifying miniature ‘block’ or ‘brick’ appears). A sharp-pointed glass and a knife blade can be useful aids. knife can easily be pushed into the timber. Dry rot usually gives off a smell similar to that of mouldy References cheese. Bravery, A.F. et al. Recognising wood rot and insect damage in buildings. BRE Report BR453. 3rd ed. London: BRE Bookshop, Wet rot continues to develop only on timber that is 2003 wet, whereas dry rot, having established itself on wet timber, will spread to otherwise sound dry timber. The BS 4978: 1996: Specification for visual strength grading of treatments of the two types of decay are different. softwood. London: BSI, 1996 {Since superseded by BS 4978: Accurate identification is therefore important. 2007: Visual strength grading of softwood – Specification. London: BSI, 2007} References Building Research Establishment. Dry rot: its recognition and BS 5756: 1997: Specification for visual strength grading of control. BRE Digest 299. Garston: BRE, 1993 hardwood. London: BSI, 1997 {Since superseded by BS 5756: 2007: Visual grading of hardwood – Specification. London: BSI, Building Research Establishment. Wet rot: recognition and control. 2007} BRE Digest 345. Garston: BRE, 1989
CP 112-2: 1971: The Structural use of timber. Part 2: Metric units. T48 Moisture content of timber London: BSI, 1971, British Standards Institution, London {Since superseded by BS 5268-2: 1984, see ref 6.34} The moisture content of solid untreated timber can usually be determined with sufficient accuracy by T46 Identification of insect attack a portable battery-operated moisture meter. Deep probes should preferably be used, and the moisture The pests most frequently infesting constructional should be checked at several points including, in timber are the common furniture beetle and the particular, those where ventilation is poor. When house longhorn beetle. The latter is prevalent only in using a moisture meter to take moisture readings of a small area of south-east England. plywood or preserved timber, reference should be made to a correction factor for the particular meter It is necessary to distinguish between live insect being used. attack, attack that has died out and emergence holes associated with attack on the timber in the forest, If the moisture content is about 15%-16% it e.g. pinhole borer (Ambrosia beetle) which dies out may prove valuable to check the temperature on conversion of the log to beams or boards. and humidity of the air (with a dry bulb/wet bulb hygrometer) to relate (by available tables) to the It is recommended that insect identification is moisture content. confirmed by a specialist. The engineer should be able to distinguish live attack by evidence of bore References dust around the exit holes. Baird, J.A. and Ozelton, E.C. Timber designers’ manual. 2nd ed. London: Granada, 1984 {Since superseded by Ozelton, E.C. and References Baird, J.A. Timber designers’ manual. 3rd ed. Oxford: Blackwell Bravery, A.F. et al. Recognising wood rot and insect damage in Science, 2002} buildings. BRE Report BR453. 3rd ed. London: BRE Bookshop, 2003 TRADA. Moisture meters for wood. Wood Information Sheet 4-18. High Wycombe: TRADA, 1997 Building Research Establishment. Identifying damage by wood- boring insects. Digest 307. Garston: BRE, 1992 T49 Mechanical properties of timber
TRADA. Pests in houses. Wood Information Sheet 4-17. High To determine the mechanical properties of timber the Wycombe: TRADA Technology, 2005 engineer should first try to establish the stress grade of the timber. With machine stress-graded timber TRADA. Timber: fungi and insect pests. Wood Information Sheet or timber visually stress-graded to BS 4978 or BS 2.3-32. High Wycombe: TRADA Technology, 2004 5756 the timber or component should have been marked. If no marking is visible the engineer should T47 I dentification of dry rot/wet rot measure defects to establish the stress grade. In this process consideration will need to be given to the The early signs of fungal attack of timber are not timber species, and means of identifying the timber easy to spot without specialist laboratory equipment. species are discussed in T45. Reference should be However, given a sufficiently long exposure to damp made to BS 5268: Part 2 for permissible stresses or conditions, any unpreserved timber is likely to to BS 5756 or the TRADA publication. decay. In the early stages the conditions for decay are usually easier to identify than the fungus, i.e. To arrive at the permissible stress of plywood the prolonged moisture content in excess of 20%. type of plywood should be established (either by reference to makers or to specialist organisations) and reference made to BS 5268: Part 2.
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References Beilstein test which detects halogens. Simple heating BS 4978: 1996: Specification for visual strength grading of tests can often determine the class of polymer and softwood. London: BSI, 1996 {Since superseded by BS 4978: are usually carried out before an elemental test 2007: Visual strength grading of softwood – Specification. for nitrogen, sulfur, chlorine, bromine and fluorine. London: BSI, 2007} Infrared spectrographic analysis can also be used to identify polymers and their degradation products, BS 5268-2: 2002: Structural use of timber – Part 2: Code the analysis of which will usually require expert of practice for permissible stress design, materials and knowledge and experience. workmanship. London: BSI, 2002 References BS 5756: 1997: Specification for visual strength grading of British Rubber & Polyurethane Products Association and Others. hardwood. London: BSI, 1997 {Since superseded by BS 5756: Rubber chemicals manual. [Colchester?]: BRPRA, 1999 2007: Visual grading of hardwood – Specification. London: BSI, 2007} Doran, D.K. ed. Construction materials reference book. Oxford: Butterworth-Heinemann, 1992 {2nd edition due 2011} TRADA. Design stresses for members graded insitu for British- grown hardwoods. IS 47. High Wycombe: TRADA, 1985 {See also Forde, M. ed. ICE manual of construction materials. Vol 2: TRADA. British-grown hardwoods: the designers’ handbook. DG3. Metals and alloys; polymers; polymer fibre composites in High Wycombe: TRADA Technology, 1996} civil engineering; timber; glass; non-conventional materials; appendices. London: Thomas Telford, 2009 T50 I dentification of glues Kluckow, P. Rubber and plastic testing. London: Chapman & Hall, Chemical analysis is usually necessary to establish 1963 precisely types of glue used in construction. However, there are guides that can be used. If Saunders, K.J. The Identification of plastics and rubber. London: the glue is dark brown it is likely that the glue is a Chapman & Hall, 1966 weather- and boil-proof glue such as resorcinol. If it is white it could be either a moisture-resistant glue, T53 U ltrasonics – fibre reinforced polymeric (FRP) such as a urea, or an ‘interior’ glue such as casein. If materials clear, it may be a PVA glue. Ultrasonic techniques can be used in reflective mode, Reference i.e. as with metals, to detect laminations, voiding Rodwell, D.F.G. Ageing of wood adhesives: loss in strength with and other defects in fibre reinforced polymeric (FRP) time. BRE Information Paper IP8/84. Garston: BRE, 1984 materials. These defects may be in FRP components or plate bonded carbon fibre strips used for T51 I dentification of preservative treatments strengthening concrete, masonry, metallic or timber structures. Timber treated with creosote has a distinctive odour and brown colour. Green-coloured timber suggests Reference treatment with a copper containing formulation, a Concrete Society. Strengthening concrete structures using fibre pale green-brown colour suggesting the presence of materials: acceptance, inspection and monitoring. Technical copper/chromium/arsenic formulations and a pure Report 57. Camberley: Concrete Society, 2003 green colour the presence of copper carboxylates (e.g. the fungicide acypetacs copper) applied in T54 Static tensile strength – FRP materials organic solvent solutions. Other wood preservative preparations are colourless and odourless. Most The majority of FRP materials fail in a brittle manner reputable manufacturers of preservatives should in tension and may possess significantly different be able to check for the presence of their products, properties in compression from those in tension. or an independent laboratory may be approached. The brittle nature also results in greater sensitivity In both cases a small sample of the treated timber, to stress concentrations, notches, holes etc. than which should include some sapwood, should be would be the case with ductile materials such as submitted for the identification. steel. However, FRPs will often give signs of being over-stressed before catastrophic failure, in the form Reference of crazing, cracking, whitening and delamination. BS 5666-2: 1980: Methods of analysis of wood preservatives and treated timber. Part 2: Qualitative analysis. London: BSI, 1980 Tensile strength tests on coupon samples give an indication of changes in the bulk properties of T52 Identification of type of polymers an FRP product. Other properties which may be measured include elastic limit, yield point, proof Various rigid polymeric materials are used in stress and modulus of elasticity. Test pieces of construction including polyvinylchloride, acrylonitrile standard size (between 150 and 250mm long) are butadiene styrene, acrylics, polystyrene, usually required, their cross-section may be circular, polypropylene, polyesters and epoxides. Polymers square, rectangular or, in special cases, of some may be degraded in use by ultraviolet and infrared other form. Test pieces should generally be machined radiation, moisture, etc. As a result crazing, resin- to the dimensions given in the various Standards, glass interface failure, colour fading and subsequent but some sections, bars, tubes, etc. may in certain diminution of structural properties can occur. circumstances be tested without being machined.
Tests to identify whether the polymer found is a rubber, a flexible thermoplastic, a rigid thermoplastic or a thermosetting polymer are by appearance, bounce, odour, feel, colour, specific gravity and the
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References Reference BS EN ISO 527-4: 1997; BS 2782-3: Method 326F: 1997: ASTM D570-98(2005): Standard test method for Plastics – Determination of tensile properties – Test conditions water absorption of plastics. West Conshohocken, PA: for isotropic and orthotropic fibre-reinforced composites. London: ASTM, 1998 BSI, 1997 T58 Accelerated weathering – polymers and FRP BS EN ISO 527-5: 1997/BS 2782-3: Method 326G: 1997: materials Plastics – Determination of tensile properties – Test conditions for unidirectional fibre-reinforced plastic composites. London: Laboratory trials using Q-UV or xenon-arc based BSI, 1997 {Superseded by BS EN ISO 527-5: 2009: Plastics – equipment can give indicative performance data. The Determination of tensile properties – Part 5: Test conditions for test results are available in a relatively short period of unidirectional fibre-reinforced plastic composites. London: BSI, time. However, the data cannot be used to quantify 2009} behaviour outdoors. Tests themselves are relatively inexpensive, but the capital cost of the equipment BS EN ISO 14126: 1999: Fibre reinforced plastics composites – can be high. Accredited laboratories should be used Determination of compressive properties in the in-plane direction. to carry out the tests. London: BSI, 1999 References BS EN ISO 14129: 1998: Fibre reinforced plastics composites – Halliwell, S. Fibre reinforced polymers in construction: durability. Determination of the in-plane shear stress/shear strain response, BRE Information Paper IP 10/03. Garston: BRE, 2003 including the in-plane shear modulus and strength by the ±45° tension test method. London: BSI, 1998 Halliwell, S. Fibre reinforced polymers in construction: predicting weathering. BRE Information Paper IP 11/03. Garston: BRE, 2003 BS EN ISO 14130: 1998: Fibre reinforced plastic composites. Determination of apparent interlaminar shear strength by short- Halliwell, S.M. and Reynolds, T. FRPs in construction: long-term beam method. London: BSI, 1998 performance in service. BRE Report BR461. Garston: BRE, 2003
T55 Fatigue and other strength properties – FRP T59 Visual inspection – FRP materials materials Visual inspection of FRP components gives early Fatigue is generally defined as the physical warning signs of possible damage, deterioration phenomenon that causes a material or component to of probable failure. Visible signs include blisters, fail after an applied condition (load) for a number of surface crazing, erosion of top surface (gel-coat) and cycles, even though the magnitude of that condition discolouration. Chalking may also be apparent. is not great enough to cause failure on the first cycle of application. Fatigue ‘life’ is usually measured as the If defects are visible, a decision must be made as number of cycles to failure for a given applied level. to whether repair or removal for further testing is The tests are carried out using specialist laboratory necessary. Most visual defects do not represent a equipment by a skilled operator. deterioration in bulk properties of an FRP component and can be repaired. The inspections should be Reference carried out by trained operatives. BS ISO 13003: 2003: Fibre-reinforced plastics – Determination of fatigue properties under cyclic loading conditions. London: BSI, Reference 2003 Halliwell, S.M. Polymer composites in construction. BRE Report 405. Garston: BRE, 2000 T56 Impact strength – FRP materials T60 Air bag test Resistance to damage by impact is determined using laboratory equipment. A tool of known weight This structural loading test uses an incrementally is dropped from a specified height and the effect on pressurised air bag as a loading device to establish the specimen impacted recorded by instrumentation. the in situ flexural resistance of masonry panels to The data can be interpreted to give a measure of the lateral loads. The testing procedure requires the impact strength of a material. The test is commonly creation of a temporary reaction wall at each test site. used for polymer products, and less widely for FRP components. Reference de Vekey, R.C., Ferguson, A. and Edgell, G. ‘Lateral Performance Reference of very wide cavity walls’. Proceedings 9th Canadian masonry BS EN ISO 179-2: 1999; BS 2782-3: Method 359B: 1999: symposium, Fredricton, New Brunswick, Canada, 2001, CDROM Plastics. Determination of Charpy impact properties. Instrumented Paper 22 impact test. London: BSI, 1999 T61 Structural load testing T57 Water absorption – FRP materials Load testing will usually be adopted only after other Water absorption into glass or carbon FRPs is very approaches based on calculation, survey and local slow. Changes occur in the physical properties of tests on materials have failed to demonstrate an the FRP, for example, electrical properties. Water adequate margin of safety of the structure under absorption occurs through exposed fibre ends. the loads likely to be imposed on it. A load test of a Accepted tests are ASTM D570 and ISO 62, both of complete structure is a costly and time-consuming which involve immersion in water for 24hrs or until operation with various hazards. Generally it cannot saturated, or exposure to 50% relative humidity for be repeated because of the disruption involved. 24 hrs. There may, however, be some structures that are not amenable to calculation. In such circumstances
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the only way to assess the load-carrying capacity Where deterioration of the structural components is to carry out load tests. Load testing of individual has occurred, its effect on current and future elements of a structure, such as rafters, can be of structural capacity may need to be assessed. If modest cost and yield valuable results. deterioration is localised and limited in nature, such that it is likely that the deterioration will not Thus the type of testing employed will depend on the have had much structural effect, there will be little objectives of the testing, with three broad categories call for load testing to supplement calculations. If, generally being recognised: however, the deterioration has affected much of –P– roof testing the structural material (e.g. advanced alkali-silica –A– cceptance or compliance testing reaction in concrete) or structurally significant –T– esting aimed at investigating structural behaviour corrosion of reinforcement or prestressing tendons has occurred, the structural effects may be Proof testing, as its name implies, simply provides much more difficult to assess, and there may be evidence that the structure can withstand a given uncertainty as to the validity of standard calculation loading. With this type of testing it may not even be procedures. In such circumstances load testing necessary to instrument the structure. may have an important role to play. However it should be recognised that the use of load testing Acceptance or compliance testing seeks to establish to check the condition of prestressing, especially behaviour under specified loads related to assumed in circumstances where it may have undergone working conditions. Specific measurements of the deterioration, is fraught with difficulties and has response are required so that a comparison with to be undertaken with great care by appropriately acceptance criteria can be made. In many cases experienced engineers. loads to be applied and acceptance criteria to be met will be laid down in codes of practice. Carrying Before load testing is carried out, a check on the out such tests demonstrates only that the structure, response of the structure to loading to above full or the part being tested, complies with the relevant service design load, and the potential consequences, code. should be carried out. Where the structure is likely to be elastic, then ductile, to well above the test load, Testing aimed at investigating structural behaviour load testing may be appropriate. Where the failure seeks to discover the true behaviour and capabilities may be brittle and sudden or the overload may of the structure. The loads to be applied and the weaken the structure, load testing is inappropriate for measurements to be taken can be chosen freely validating that there is a sufficient margin of safety. and can be modified dependent on the structure’s Evaluation of load testing should be based on a own response. This form of testing is much more comparison of the measured deformations under full extensive, requiring a much greater amount of load, under moderate overload, and after recovery on planning and forethought. Information gained from unloading, with those predicted from analysis. such testing will however be much more useful in making a structural appraisal. There are a number of reasons why structural elements forming part of an existing structure behave It should be borne in mind that load testing can differently from the manner assumed in design. usually only demonstrate serviceability behaviour at Particularly significant factors include composite the time of testing and, although useful in providing action between structural and non-structural a datum for assessment, can provide only limited components and modifications of the boundary assurance for future performance. conditions to structural members. Supports may settle inelastically and their displacements and Structural load testing involves the application of recovery should be monitored. physical test loads to a structure (or parts of it), measurement of the response of the structure to When a single component is loaded, adjacent the loads and interpretation of the results. Loads components may also act in resisting the applied may be of a static or dynamic nature, depending on load. This load-sharing is particularly prevalent in floor circumstances. and roof structures. To make sure that the structural components under test are carrying their full As a general guide, a structure or part of a structure intended test load, it is necessary either to eliminate can be considered as behaving statically if its or compensate for the load-distribution effects. The response to a particular loading is not affected most certain way of doing this is physically to isolate significantly by the rate at which the loading is that part of the structure under test. applied. A practical alternative is to eliminate the load-sharing Types of structure or parts of structures that may effect by similarly loading all the components exhibit a dynamic response are large cantilevers, influenced by the testing. Rolling load testing and long-span lightweight construction and temporary, dynamic testing techniques can be employed to tall or slender structures. establish the load-sharing characteristics of floor and roof structures, providing guidance on the extent of Circumstances in which load tests can be useful the area to be load tested. in providing additional evidence include those where deterioration of structural components has Another approach is to determine the load-sharing occurred, where there is a change of structural use, characteristics of the structure and compensate for or where construction has not been carried out to them by applying increased loads to the components specification. Load testing may have a role to play under test. However, considerable care and in calibrating a measurement system installed to experience are required when using such techniques, monitor structural performance. and the advice of a specialist should be sought.
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Composite action between structural and non- T62 Wall profile measuring tool [The Giraffe™] structural components may mean that the structural components appear to perform much better than This is a tool for accurately measuring at ground if they were tested in isolation. Stiffening effects level the (vertical) profile of a wall. It consists of a produced by non-structural floor screeds, for example, telescopic or sectional pole with a small wheel (with can be very considerable. Test data have shown that clean, non-marking tyre) at the top. A quadrant is fourfold increases in stiffness have been produced attached, its centre at the intersection of the wheel when bonded screeds have been used with some with a horizontal axis through the wheel’s centre. forms of floor construction, without commensurate A tape (or string) measure, suitably weighted, is increases in the strength of the floor. In such cases the attached to the quadrant. The tape measure is wider issue of the reliability of such composite action extended to a reference line at ground level or on a effects is raised, and there may be justification for table and plumbed, and the offset from a datum and making acceptance criteria more stringent. the taped height are recorded.
In some cases it may be appropriate to remove Reference components from a structure and test them in Richardson, C. ‘Distorted walls: survey, assessment, repair’. laboratory conditions. Architects’ Journal, 13 January 1988, pp51-52
Some structures, e.g. roofs, will deform considerably under the influence of differential temperatures across the construction. Deflection measurements recorded during load tests may therefore contain elements of temperature-induced deflection and these will need to be compensated for. One way of compensating for these temperature movements is to establish a ‘footprint’ of movement for the structure R for a range of differential temperatures including solar effects. Any temperature movement caused by measured temperature changes occurring during a load test can be predicted and deducted from the total readings taken. The influence of temperature changes on the instrumentation and its supporting structure also needs to be considered. R
It is sometimes necessary to ascertain the dynamic behaviour of a structure or to assess its remaining fatigue life. The dynamic behaviour can be assessed on the basis of measurements of vibration amplitudes at different frequencies in service conditions or under imposed dynamic test loads. Where identical components have been subjected to similar fatigue loading in the past, their remaining fatigue life may be assessed by removing a small number of them for testing in a laboratory. Alternatively, the stresses at the stress raiser in the component may be calculated and the fatigue life estimated from data on specimens with the same stress concentration factor. Specialist advice may be required.
References Fitzsimons, N. and Longinow, A. ‘Guidance for load tests of buildings’, Journal of the Structural Division, ASCE, 101(ST7), July 1975, pp1367-1380
Institution of Structural Engineers. Load testing of structures and structural components. London: IStructE, 1989
Jones P.S. and Oliver C.W. ‘The practical aspects of load testing’. The Structural Engineer, 56A(12), December 1978, pp353-356
Lloyd, R.M. and Wright, H.D. ‘Insitu testing of a composite floor system’. The Structural Engineer, 70(12), June 1992, pp211-219
Menzies J.B. ‘Load testing of concrete building structures’. The Structural Engineer, 56A(12), December 1978, pp347-353
Moss, R.M. ‘Load testing of floors and roofs’. The Structural Engineer, 69(19), October 1991, pp342-344
Moss, R.M. and Currie, R.J. Static load testing of building structures. BRE Information Paper IP 9/89. Garston: BRE, 1989 Figure T62 Wall profile measuring tool ('The Giraffe')
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A7.3 Collated references BS EN 12620: 2002: Aggregates for concrete. London: BSI, 2002 {Since supplemented by +A1: 2008} (T9(c))
The bold tags in brackets denote the specific test to BS EN 13396: 2004: Products and systems for the protection which the reference refers. and repair of concrete structures – Test methods – Measurement of chloride ion ingress. London: BSI, 2004 (T15) A7.3.1 Methods of test for concrete structures BS EN 14630: 2006: Products and systems for the protection ASTM C876-09: Standard test method for half-cell potentials and repair of concrete structures. Test methods. Determination of of uncoated reinforcing steel in concrete. West Conshohocken: carbonation depth in hardened concrete by the phenolphthalein ASTM, 2009 (T22) method. London: BSI, 2006 (T7)
BS 1881-122: 1983: Testing concrete – Part 122: Method for Building Research Establishment. Alkali-silica reaction in determination of water absorption. London: BSI, 1983 (T14) concrete. BRE Digest 330. 4 parts. Garston: BRE Bookshop, 2004 (T10) BS 1881-124: 1988: Testing concrete – Part 124: Methods for analysis of hardened concrete. London: BSI, 1988 (T9(a), T11) Building Research Establishment. Carbonation of concrete made with dense material aggregates. BRE Information Paper IP6/81. BS 1881-204: 1988: Testing concrete – Part 204: Garston: BRE, 1981 (T7) Recommendations on the use of electromagnetic covermeters. London: BSI, 1988 (T20) Building Research Establishment. Corrosion of reinforcement in concrete: electrochemical monitoring. BRE Digest 434. Garston: BS 1881-207: 1992: Testing concrete – Part 207: BRE, 1998 (T22) Recommendations for the assessment of concrete strength near- to-surface tests. London: BSI, 1992 (T4, T6) Building Research Establishment. Masonry and concrete structures: measuring insitu strength and elasticity using flat BS 1881-208: 1996: Testing concrete – Part 208: jacks. BRE Digest 409. London: CRC, 1995 (T42) Recommendations for the determination of the initial surface absorption of concrete. London: BSI, 1996 (T12) Building Research Establishment. Measuring the compressive strength of masonry materials: the screw pull-out test. BRE Digest BS 4551-2: 1998: Methods of testing mortar, screeds and 421. London: CRC, 1997 (T40) plasters. Part 2: Chemical analysis and aggregate grading. London: BSI, 1998 (T9(a)) Bungey, J.H. and Millard, S.G. Testing of concrete in structures. 3rd ed. London: Blackie, 1996 {Since superseded by Bungey, BS 6089: 1981: Guide to assessment of concrete strength in J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in existing structures. London: BSI, 1981 (T3) structures. 4th ed. Abingdon: Taylor & Francis, 2006} (T1, T2, T5, T6, T7, T8, T9(c), T12, T13, T15, T18, T20) BS 8204-2: 2002: Screeds, bases and in situ floorings – Part 2: Concrete wearing surfaces – Code of practice. London: BSI, 2002 Collis, L. and Fox, R.A. eds. Aggregates, sand, gravel and crushed {Supplemented by +A1: 2009} (T18) rock aggregates for construction purposes. Engineering Geology Special Publication 9. 3rd ed. London: Geological Society, London, BS EN 197-1: 2000: Cement – Part 1: Composition, 2001 (T9(c)) specifications and conformity criteria for common cements. London: BSI, 2000 (T9(b)) Concrete Bridge Development Group. Guide to testing and monitoring the durability of concrete structures. Technical BS EN 480-11: 1999: Admixtures for concrete, mortar and Guide 2. Crowthorne: Concrete Society, 2002 (T1,T2, T3, T12, grout – Test methods – Part 11: Determination of air void T13, T14, T15, T20, T22) characteristics in hardened concrete. London: BSI, 1999 {Since superseded by 2005 version} (T19) Concrete Society. Analysis of hardened concrete. Concrete Society Technical Report 32. London: Concrete Society, 1989 (T8, T9(a), BS EN 12390-6: 2000: Testing hardened concrete – Part 6: T9(b), T9(c), T11, T16, T19) Tensile splitting strength of test specimens. London: BSI, 2000 (T3) Concrete Society. Concrete core testing for strength. Concrete Society Technical Report 11. London: Concrete Society, 1987 (T3) BS EN 12390-7: 2000: Testing hardened concrete – Part 7: Density of hardened concrete. London: BSI, 2000 {Since Concrete Society. Electrochemical tests for reinforcement superseded by 2009 version} (T3) corrosion. Concrete Society Technical Report 60. Camberley: Concrete Society, 2004 (T22) BS EN 12504-1: 2001: Testing concrete in structures – Part 1: Cored specimens – Taking, examining and testing in Concrete Society. Permeability testing of site concrete: a review compression. London: BSI, 2001 {Since superseded by 2009 of methods and experience. Technical Report 31. Camberley: version} (T3) Concrete Society, 1988 {Since superseded by Concrete Society. Permeability testing of site concrete: a review of methods and BS EN 12504-2: 2001: Testing concrete in structures – Part 2: experience. Technical Report 31. 2nd ed. Camberley: Concrete Non-destructive testing – Determination of rebound number. Society, 2008} (T12, T13, T14) London: BSI, 2001 (T1) Kropp, J. and Hilsdorf, H.K. Performance criteria for concrete BS EN 12504-3: 2005: Testing concrete in structures – Part 3: durability: state of the art report. RILEM Report 12. London: Spon, Determination of pull-out force. London: BSI, 2005 (T4) 1995 (T13)
BS EN 12504-4:2004: Testing concrete in structures – Part 4: Determination of ultrasonic pulse velocity. London: BSI, 2004 (T2)
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Moss, R. and Dunster, A. High alumina cement concrete: BS EN 10002-1: 2001: Tensile testing of metallic materials – BRAC rules – revised 2002. BRE Report BR451. Garston: BRE Part 1: Method of test at ambient temperature. London: BSI, Bookshop, 2002 (T4) 2001{Since superseded by BS EN ISO 6892-1: 2009: Metallic materials – Tensile testing – Part 1: Method of test at ambient prEN 14629: 2003: Products and systems for the protection and temperature. London: BSI, 2009} (T31) repair of concrete structures – Test methods – Determination of chloride content in hardened concrete. London: BSI, 2007 {Since BS EN 10002-5: 1992: Tensile testing of metallic materials – superseded by BS EN 14629: 2007: Products and systems for Part 5: Method of test at elevated temperatures. London: BSI, the protection and repair of concrete structures – Test methods – 1992 (T31) Determination of chloride content in hardened concrete. London: BSI, 2007} (T15) BS EN 10003-1: 1995: Metallic materials – Brinell hardness test – Part 1: Test method. London: BSI, 1995 {Since superseded by St John, D.A., Poole A.W. and Sims, I. Concrete petrography: a BS EN ISO 6506-1: 2005: Metallic materials – Brinell hardness handbook of investigative techniques. London: Arnold, 1998 (T8, test – Part 1: Test method. London: BSI, 2005} (T30) T11) BS EN 10109-1: 1996: Metallic materials – Hardness test Vassie, P.R. The Half-cell potential method of locating corroding – Part 1: Rockwell test (scales A, B, C, D, E, F, G, H, K) and reinforcement in concrete structures. TRRL Application Guide 9. Rockwell superficial test (scales 15 N, 30 N, 45 N, 15 T, 30 Crowthorne: TRRL, 1991 (T22) T and 45 T). London: BSI, 1996 {Superseded by BS EN ISO 6508-1: 2005: Metallic materials – Rockwell hardness test A7.3.2 Methods of test for ferrous metal structures – Part 1: Test method (Scales A, B, C, D, E, F, G, H, K, N, T). London: BSI, 2006} (T30) Ashurst, J. and Ashurst, N. Practical building conservation. Vol 4: Metals. English Heritage Technical Handbook. Aldershot: Gower, BS EN 10160: 1999: Ultrasonic testing of steel flat product 1988 (T24) of thickness equal or greater than 6 mm (reflection method). London: BSI, 1999 (T28) BS 131: 1961: Notched bar tests – Part 1: The IZOD impact test on metals. London: BSI, 1961 (T34) BS EN 10228-3: 1998: Non-destructive testing of steel forgings – Part 3: Ultrasonic testing of ferritic or martensitic steel forgings. BS 6533: 1984: Guide to macroscopic examination of steel by London: BSI, 1998 (T28) etching with strong mineral acids. London: BSI, 1984 (T26) BS EN 10228-4: 1999: Non-destructive testing of steel forgings BS 7448-1: 1991: Fracture mechanics toughness tests – Part – Part 4: Ultrasonic testing of austenitic and austenitic-ferritic 1: Method for determination of KIc, critical CTOD and critical stainless steel forgings. London: BSI, 1999 (T28) J values of metallic materials; BS 7448-2: 1997: Fracture mechanics toughness tests – Part 2: Method for determination BS EN 12680-1: 2003: Founding – Ultrasonic examination – of KIc, critical CTOD and critical J values of welds in metallic Part 1: Steel castings for general purposes. London: BSI, 2003 materials. London: BSI, 1991; 1997 (T34) (T28)
BS EN 970: 1997: Non-destructive examination of fusion welds – BS EN ISO 6507-1: 1998: Metallic materials – Vickers hardness Visual examination. London: BSI, 1997 (T35) test – Part 1: Test method. London: BSI, 1998 {Since superseded by 2005 version} (T30) BS EN 1330-3: 1997: Non-destructive testing – Terminology – Part 3: Terms used in industrial radiographic testing. London: BSI, BS EN ISO 7539-1: 1995: Corrosion of metals and alloys – 1997 (T29) Stress corrosion testing – Part 1: General guidance on testing procedures. London: BSI, 1995 (T37) BS EN 1330-4: 2000: Non-destructive testing – Part 4: Terms used in ultrasonic testing. London: BSI, 2000 (T28) BS EN ISO 9934-1: 2001: Non-destructive testing – Magnetic particle testing – Part 1: General principles. London: BSI, 2001 BS EN 1330-7: 2005: Non-destructive testing – Terminology (T36) – Part 7: Terms used in magnetic particle testing. London: BSI, 2005 (T36) BS EN ISO 12706: 2001: Non-destructive testing – Terminology – Terms used in penetrant testing. London: BSI, 2001 (T27) BS EN 1369: 1997: Founding – Magnetic particle inspection. London: BSI, 1997 (T36) BS EN ISO 18265: 2003: Metallic materials – Conversion of hardness values. London: BSI, 2003 (T30) BS EN 1371-1: 1997: Founding – Liquid penetrant inspection – Part 1: Sand, gravity die and low pressure die castings. London: Bussell, M. Appraisal of existing iron and steel structures. SCI BSI, 1997 (T27) Publication 138. Ascot: SCI, 1997 (T24, T31)
BS EN 1435: 1997: Non-destructive examination of welds – Highways Agency. The Assessment of highway bridges Radiographic examination of welded joints. London: BSI, 1997 and structures. BD 21/01. Available at: http://www. (T29) standardsforhighways.co.uk/dmrb/vol3/section4/bd2101.pdf [Accessed: 14 October 2009] (T31) BS EN 1714: 1998: Non destructive examination of welded joints – Ultrasonic examination of welded joints. London: BSI, 1998 Hunt, B.J. ‘The use of fluorescent dyes in highlighting some (T28) construction problems’. Structural Survey, 12(6), 1993-94, pp4-7 (T27)
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Käpplein, R. ‘Zur Beurteilung des Tragverhaltens alter gußeisener LUMD1: Removal and testing of specimens from existing Hohlsäulen’. Berichte der Versuchsanstalt fur Stahl, Holz und masonry’. In: RILEM. Technical recommendations for the testing Steine der Universität Fridericiana in Karlsruhe, 4 Folge, Heft 23, and use of construction materials. London: E. & F. N. Spon, 1994, 1991 [in German] (T33) pp501-502 (T39)
Logan, H.L. Stress corrosion of metals. New York: John Wiley, ‘Test method recommendations of RILEM TC 177-MDT Masonry 1966 (T37) durability and on-site testing – D.4: Insitu stress tests based on the flat jack’. Materials and Structures, 37(7), August 2004, Morgan, J. ‘The Strength of Victorian wrought iron’. ICE pp491-496 (T42) Proceedings, Structures and Buildings, 134(4), Nov 1999, pp295- 300 (T24) ‘Test method recommendations of RILEM TC 177-MDT Masonry durability and on-site testing – D.5: Insitu stress – strain Scalley, J.C. ed. Theory of stress corrosion cracking in alloys. behaviour tests based on the flat jack’. Materials and Structures, Brussels: NATO Scientific Affairs Division, 1971 (T37) 37(7), August 2004, pp497-501 (T42)
Shreir, L.L. and other eds. Corrosion. Oxford: Butterworth- A7.3.4 Methods of test for timber structures Heinemann, 1994 {Since superseded by Richardson, T. ed.. Shreir’s corrosion. 4 vols. Oxford: Elsevier Science, 2009} (T35, Baird, J.A. and Ozelton, E.C. Timber designers’ manual. 2nd ed. T37) London: Granada, 1984 {Since superseded by Ozelton, E.C. and Baird, J.A. Timber designers’ manual. 3rd ed. Oxford: Blackwell Taylor, J.L. ed. Basic metallurgy for non-destructive testing. Science, 2002} (T48) Northampton: British Institute of Non-Destructive Testing, 1989 {Since superseded by Taylor, J.L. ed. Basic metallurgy for non- Bravery, A.F. et al. Recognising wood rot and insect damage in destructive testing. 4th ed. Northampton: British Institute of Non- buildings. BRE Report BR453. 3rd ed. London: BRE Bookshop, Destructive Testing, 1996 (T25) 2003 (T45, T46)
A7.3.3 M ethods of test for masonry structures BS 4978: 1996: Specification for visual strength grading of softwood. London: BSI, 1996 {Since superseded by BS 4978: ASTM C1197-09: Standard Test Method for In Situ Measurement 2007: Visual strength grading of softwood – Specification. of Masonry Deformability Properties Using the Flatjack Method. London: BSI, 2007} (T45, T49) West Conshohocken, PA, ASTM, 2009 (T43) BS 5268-2: 2002: Structural use of timber – Part 2: Code ASTM D4729-08: Standard test method for in situ stress of practice for permissible stress design, materials and and modulus of deformation using flatjack method. West workmanship. London: BSI, 2002 (T49) Conshohocken, PA: ASTM, 2008 (T42) BS 5666-2: 1980: Methods of analysis of wood preservatives Berger, F. Zur nachträglichen Bestimmung der Tragfähigkeit and treated timber. Part 2: Qualitative analysis. London: BSI, 1980 von zentrisch gedrücktem Ziegelmauerwerk, Erhalten historisch (T51) bedeutsamer Bauwerke. Berlin: Ernst und Sohn, 1987 [in German] (T41) BS 5756: 1997: Specification for visual strength grading of hardwood. London: BSI, 1997 {Since superseded by BS 5756: de Vekey, R.C. Corrosion of steel wall ties: history of occurrence, 2007: Visual grading of hardwood – Specification. London: BSI, background and treatment. BRE Information Paper IP12/90. 2007} (T45, T49) Garston: BRE, 1990 (T44) Building Research Establishment. Dry rot: its recognition and de Vekey, R.C. Corrosion of steel wall ties: recognition and control. BRE Digest 299. Garston: BRE, 1993 (T47) inspection. BRE Information Paper IP 13/90. Garston: BRE, 1990 (T23, T44) Building Research Establishment. Identifying damage by wood- boring insects. Digest 307. Garston: BRE, 1992 (T46) de Vekey, R.C. ‘Measurement of load eccentricity using flat jacks’. Masonry (9): Proceedings of the British Masonry Society. 6th Building Research Establishment. Wet rot: recognition and control. International Masonry Conference, London, 2002. Stoke-on-Trent: BRE Digest 345. Garston: BRE, 1989 (T47) British Masonry Society, 2002, pp79-85 (T42) CP 112-2: 1971: The Structural use of timber. Part 2: Metric units. de Vekey, R.C. ‘The Non-destructive evaluation of masonry London: BSI, 1971, British Standards Institution, London {Since materials in structures’. Proceedings 8th CIMTEC world ceramics superseded by BS 5268-2: 1984, see ref 6.34} (T45) congress, Florence, 1994 (T40) Rodwell, D.F.G. Ageing of wood adhesives: loss in strength with Ferguson, W.A. and Skandamoorthy, J. ‘The screw pull-out tests time. BRE Information Paper IP8/84. Garston: BRE, 1984 (T50) for the insitu measurement of the strength of masonry materials’. Proceedings 10th international brick and block masonry TRADA. Design stresses for members graded insitu for British- conference, Calgary 1994, pp1257-1265 (T40) grown hardwoods. IS 47. High Wycombe: TRADA, 1985 {See also TRADA. British-grown hardwoods: the designers’ handbook. DG3. Johnson, M.A.E. and Fifield, B.E. ‘Remote visual inspection High Wycombe: TRADA Technology, 1996}(T49) of voids and cavities: practical experience on post-tensioned concrete bridges’. In Forde, M.C. ed. Structural faults and repair TRADA. Moisture meters for wood. Wood Information Sheet 4-18. 93. Vol 1: Extending the life of bridges. Edinburgh: Engineering High Wycombe: TRADA, 1997 (T48) Technics Press, 1993, pp301-303 (T23) TRADA. Timber: fungi and insect pests. Wood Information Sheet 2.3-32. High Wycombe: TRADA Technology, 2004 (T46)
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TRADA. Pests in houses. Wood Information Sheet 4-17. High Saunders, K.J. The Identification of plastics and rubber. London: Wycombe: TRADA Technology, 2005 (T46) Chapman & Hall, 1966 (T52)
A7.3.5 Methods of test for polymers and fibre reinforced A7.3.6 Structural load testing polymers de Vekey, R.C., Ferguson, A. and Edgell, G. ‘Lateral Performance ASTM D570-98(2005): Standard test method for water of very wide cavity walls’. Proceedings 9th Canadian masonry absorption of plastics. West Conshohocken, PA: ASTM, 1998 symposium, Fredricton, New Brunswick, Canada, 2001, CDROM (T57) Paper 22 (T60)
British Rubber & Polyurethane Products Association and Others. Fitzsimons, N. and Longinow, A. ‘Guidance for load tests of Rubber chemicals manual. [Colchester?]: BRPRA, 1999 (T52) buildings’, Journal of the Structural Division, ASCE, 101(ST7), July 1975, pp1367-1380 (T61) BS EN ISO 179-2: 1999; BS 2782-3: Method 359B: 1999: Plastics. Determination of Charpy impact properties. Instrumented Institution of Structural Engineers. Load testing of structures and impact test. London: BSI, 1999 (T56) structural components. London: IStructE, 1989 (T61)
BS EN ISO 527-5: 1997 / BS 2782-3: Method 326G: 1997: Jones P.S. and Oliver C.W. ‘The practical aspects of load testing’. Plastics – Determination of tensile properties – Test conditions The Structural Engineer, 56A(12), December 1978, pp353-356 for unidirectional fibre-reinforced plastic composites. London: (T61) BSI, 1997 {Superseded by BS EN ISO 527-5: 2009: Plastics – Determination of tensile properties – Part 5: Test conditions for Lloyd, R.M. and Wright, H.D. ‘Insitu testing of a composite floor unidirectional fibre-reinforced plastic composites. London: BSI, system’. The Structural Engineer, 70(12), June 1992, pp211-219 2009} (T54) (T61)
BS EN ISO 14126: 1999: Fibre reinforced plastics composites – Menzies J.B. ‘Load testing of concrete building structures’. The Determination of compressive properties in the in-plane direction. Structural Engineer, 56A(12), December 1978, pp347-353 (T61) London: BSI, 1999 (T54) Moss, R.M. ‘Load testing of floors and roofs’. The Structural BS EN ISO 14129: 1998: Fibre reinforced plastics composites – Engineer, 69(19), October 1991, pp342-344 (T61) Determination of the in-plane shear stress/shear strain response, including the in-plane shear modulus and strength by the ±45° Moss, R.M. and Currie, R.J. Static load testing of building tension test method. London: BSI, 1998 (T54) structures. BRE Information Paper IP 9/89. Garston: BRE, 1989 (T61) BS EN ISO 14130: 1998: Fibre reinforced plastic composites. Determination of apparent interlaminar shear strength by short- Richardson, C. ‘Distorted walls: survey, assessment, repair’. beam method. London: BSI, 1998 (T54) Architects’ Journal, 13 January 1988, pp51-52 (T62)
BS ISO 13003: 2003: Fibre-reinforced plastics – Determination of fatigue properties under cyclic loading conditions. London: BSI, 2003 (T55) A7.4 Bibliography
Concrete Society. Strengthening concrete structures using fibre materials: acceptance, inspection and monitoring. Technical A7.4.1 General Report 57. Camberley: Concrete Society, 2003 (T53) Health and Safety Executive. Health and safety in construction. Doran, D.K. ed. Construction materials reference book. Oxford: HSG150. 3rd ed. Sudbury: HSE Books, 2006 Butterworth-Heinemann, 1992 {2nd edition due 2011} (T52) Highways Agency. The Assessment of highway bridges Forde, M. ed. ICE manual of construction materials. Vol 2: and structures. BD 21/01. Available at: http://www. Metals and alloys; polymers; polymer fibre composites in standardsforhighways.co.uk/dmrb/vol3/section4/bd2101.pdf civil engineering; timber; glass; non-conventional materials; [Accessed: 14 October 2009] appendices. London: Thomas Telford, 2009 (T52) Holyoak, J.H. Negligence in building law: materials and Halliwell, S. Fibre reinforced polymers in construction: durability. commentary. Oxford: Blackwell, 1992 BRE Information Paper IP 10/03. Garston: BRE, 2003 (T58) A7.4.2 Methods of test for concrete structures: General Halliwell, S. Fibre reinforced polymers in construction: predicting guidance weathering. BRE Information Paper IP 11/03. Garston: BRE, 2003 (T58) ACI Special Publication 82: Insitu/non-destructive testing of concrete. Detroit, MI: ACI, 1984 Halliwell, S.M. Polymer composites in construction. BRE Report 405. Garston: BRE, 2000 (T59) ACI SP 222R-01: Protection of metals in concrete against corrosion. Farmington Hills, MI: ACI, 2001 Halliwell, S.M. and Reynolds, T. FRPs in construction: long-term performance in service. BRE Report BR461. Garston: BRE, 2003 ACI SP 228.2R-98: Nondestructive test methods for evaluation of (T58) concrete in structures. Farmington Hills, MI: ACI, 1998
Kluckow, P. Rubber and plastic testing. London: Chapman & Hall, Bartlett, F.M. and Sexsmith, R.G. ‘Bayesian technique for 1963 (T52) evaluation of material strengths in existing bridges’. ACI Materials Journal, 88(2), March-April 1991, pp164-169
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Bate, S.C.C. High alumina cement concrete in existing building Neville, A.M. The Properties of concrete. 4th ed. Harlow: Longman, structures. London: HMSO, 1984 1995
BCA: The Diagnosis of alkali-silica reaction. 2nd ed. Slough, BCA, A7.4.4 F errous metal structures: General guidance 1992 BCSA: Historical structural steelwork handbook. London: BCSA, BRE Digest 444: Corrosion of steel in concrete. 4 parts. London: 1984 CRC, 2000 BRE IP14/87: Inspecting steel houses. Garston: BRE, 1987 BRE IP 10/84: The Structural condition of prefabricated reinforced concrete houses designed before 1960. Garston: BRE, 1984 BRE Report 113: Steel-framed and steel-clad houses: inspection and assessment. Garston: BRE, 1987 BRE IP 8/88: Update on assessment of high alumina cement concrete. Garston: BRE, 1988 BRE Report 165: Corrosion of metals in swimming pool buildings. Garston: BRE, 1989 BRE Report 107: The Structural adequacy and durability of large panel systems dwellings. Garston: BRE, 1987 Bussell, M. Appraisal of existing iron and steel structures. SCI ––Part 1 – Investigations of construction Publication 138. Ascot: SCI, 1997 ––Part 2 – Guidance on appraisal Swailes, T. et al. Scottish iron structures. Guide for practitioners 5. BRE Report 114: A Review of carbonation in reinforced concrete. Edinburgh: Historic Scotland, 2006 Garston: BRE, 1987 A7.4.5 M ethods of test for ferrous metal structures: BRE Special Digest 3: HAC Concrete in the UK: assessment, Further test methods durability management, maintenance and refurbishment. London: BRE Bookshop, 2002 BS 6533: 1984: Guide to macroscopic examination of steel by etching with strong mineral acids. London: BSI, 1984 Bungey, J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in structures. 4th ed. Abingdon: Taylor & Francis, 2006 BS EN 875: 1995: Destructive tests on welds in metallic materials – Impact tests – Test specimen location, notch orientation and CEB Bulletin 192: Diagnosis and assessment of concrete examination. London: BSI, 1995 structures: state of the art report. Lausanne: CEB, 1989 BS EN 876: 1995: Destructive tests on welds in metallic materials Concrete Society Technical Report 21: Durability of tendons in – Longitudinal tensile test on weld metal in fusion welded joints. prestressed concrete: recommendations on design, construction, London: BSI, 1995 inspection and remedial measures. London: Concrete Society, 1982 BS EN 895: 1995: Destructive tests on welds in metallic materials – Transverse tensile test. London: BSI, 1995 Concrete Society Technical Report 33: Assessment and repair of fire damaged concrete structures. Slough: Concrete Society, 1990 BS EN 910: 1996: Destructive tests on welds in metallic materials – Bend tests. London: BSI, 1996 FIP. Inspection and maintenance of reinforced and prestressed concrete structures. London: Thomas Telford, 1986 BS EN 1043: Destructive tests on welds in metallic materials ––Part 1: 1996: Hardness testing. Hardness test on arc welded Somerville, C. The Design Life of Concrete Structures, The joints Structural Engineer, V64A, 2, Feb 1986 – p60-70 ––Part 2: 1997: Hardness testing. Micro hardness testing on welded joints A7.4.3 M ethods of test for concrete structures: Further test methods BS EN 1320: 1997: Destructive tests on welds in metallic materials – Fracture tests. London: BSI, 1997 BS 1881: Testing concrete ––Part 121: 1983: Method for determination of static modulus of BS EN 1321: 1997: Destructive test on welds in metallic elasticity in compression materials. Macroscopic and microscopic examination of welds. ––Part 201: 1986: Guide to the use of the non-destructive methods London: BSI, 1997 of test for hardened concrete ––Part 205: 1986: Recommendations for radiography of concrete BS EN ISO 2064: 2000: Metallic and other inorganic coatings. Definitions and conventions concerning the measurement of BS 4550-0: 1978: Methods of testing cements – General thickness. London: BSI, 2000 introduction. London: BSI, 1978 BS EN ISO 3882: 2003: Metallic and other inorganic coatings. BS 5080: Structural fixings in concrete and masonry Review of methods of measurement of thickness. London: BSI, ––Part 1: 1993: Method of test for tensile loading 2003 ––Part 2: 1986: Method for determination of resistance to loading in shear BS EN ISO 7438: 2005: Metallic materials – Bend test. London: BSI, 2005 BS EN 196: Methods of testing cement [10 parts] including: ––Part 2: 2005: Chemical analysis of cement BS EN ISO 9018: 2003: Destructive tests on welds in metallic ––Part 5: 2005: Pozzolanicity test for pozzolanic cement materials – Tensile test on cruciform and lapped joints. London: BSI, 2003 Bungey, J.H., Millard, S.G. and Grantham, M.G. Testing of concrete in structures. 4th ed. Abingdon: Taylor & Francis, 2006 BS M 40: 1972: Methods for measuring coating thickness by non destructive testing. London: BSI, 1972
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A7.4.6 Masonry structures: General guidance A7.4.10 Methods of test for polymers and fibre reinforced polymers: Further test methods BRE GBG 13: Surveying brick or blockwork freestanding walls. Garston: BRE, 1992 BS EN 1013-2: 1999. Light transmitting profiled plastics sheeting for single skin roofing – Specific requirements and test methods BRE Digest 177: Decay and conservation of stone masonry. for sheets of glass fibre reinforced polyester resin (GRP). London: Garston: BRE, 1975 BSI, 1999
BRE Report 141: Durability tests for building stone. Garston: BRE, BS EN 13280: 2001: Specification for glass fibre reinforced 1989 cisterns of one-piece and sectional construction, for the storage, above ground, of cold water. London: BSI, 2001 Schaffer R.J. The Weathering of natural building stones. Shaftesbury: Donhead, 2004 [Reprint of 1932 original] BS EN ISO 75-3: 2004: Plastics – Determination of temperature of deflection under load – Part 3: High-strength thermosetting A7.4.7 Methods of test for masonry structures: Further laminates. London: BSI, 2004 test methods BS EN ISO 1172: 1999: Textile-glass-reinforced plastics. ASTM: C1072-05a: Standard test method for measurement of Prepregs, moulding compounds and laminates – Determination of masonry flexural bond strength. West Conshohocken, PA: ASTM, the textile-glass and mineral-filler content – Calcination methods. 2005 London: BSI, 1999
AS 3700: 1988: Masonry structures. Appendix A7: Flexural BS EN ISO 11667: 2000: Fibre reinforced plastics – Moulding strength by bond wrench. Sydney: Standards Australia, 1988 compounds and prepregs. Determination of resin, reinforcement- {Since superseded by a 2001 version} fibre and mineral-filler content – Dissolution methods. London: BSI, 2000 BS 5080: Structural fixings in concrete and masonry: ––Part 1: 1993: Method of test for tensile loading BS EN ISO 14125: 1998: Fibre reinforced plastics composites – ––Part 2: 1986: Method for determination of resistance to loading Determination of flexural properties. London: BSI, 1998 in shear BS EN ISO 14130: 1998. Fibre reinforced plastic composites A7.4.8 Timber structures: General guidance – Determination of apparent interlaminar shear strength by short- beam method. London: BSI, 1998 BRE IP15/82: Inspection and maintenance of flat and low-pitched timber roofs. Garston: BRE, 1982 BS ISO 3597: Textile-glass-reinforced plastics. Determination of mechanical properties on rods made of roving-reinforced resin A7.4.9 M ethods of test for polymers and fibre reinforced ––Part 1: 2003: General considerations and preparation of rods polymers: General guidance ––Part 2: 2003: Determination of flexural strength ––Part 3: 2003: Determination of compressive strength BS 2782: Methods of testing plastics [several parts] ––Part 4: 2003: Determination of apparent interlaminar shear strength BS 4154-1: 1985: Corrugated plastics translucent sheets made from thermo-setting polyester resin (glass fibre reinforced) – BS ISO 15024: 2001: Fibre-reinforced plastic composites.
Specification for material and performance requirements. London: Determination of mode I interlaminar fracture toughness, G ic, for BSI, 1985 [obsolescent] unidirectionally reinforced materials. London: BSI, 2001
BS 6564-3: 1990: Polytetrafluoroethylene (PTFE) materials and ISO 9782: 1993: Plastics – Reinforced moulding compounds products. Specification for E-glass fibre filled PTFE. London: BSI, and prepregs – Determination of apparent volatile matter content. 1990 Geneva: ISO, 1993
BS EN 13706: Reinforced plastics composites – Specifications for ISO 15039: 2003: Textile-glass rovings – Determination of pultruded profiles solubility of size. Geneva: ISO, 2003 ––Part 1: 2002: Designation ––Part 2: 2002: Method of test and general requirements ––Part 3: 2002: Specific requirements
BS EN ISO 10350-2: 2001: Plastics – Acquisition and presentation of comparable single-point data – Long-fibre- reinforced plastic. London: BSI, 2001
BS EN ISO 13002: 1999: Carbon fibre – Designation system for filament yarns. London: BSI, 1999
ISO 4899: 1993: Textile glass reinforced thermosetting plastics; properties and test methods. Geneva: ISO, 1993
ISO 14127: 2008: Carbon-fibre-reinforced composites: determination of the resin, fibre and void contents. Geneva: ISO, 2008
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A8.1 I ntroduction A8.2 Dimensional measurements
The techniques listed in Table A8.1, some of which Sophisticated optical methods are available which, are not widely used, may be appropriate in particular in appropriate circumstances, may be used to check circumstances. They generally require specialist on dimensions. For example, laser and optical expertise. equipment may be employed to establish overall structural dimensions, whereas X- and c-rays can be Table A8.1 List of tests described in Appendix 8 used to help establish dimensions of hidden internal A8.2 Dimensional measurements elements such as the size of reinforcing bars or voids within concrete. A8.3 Strain and movement measurements A8.3.1 Mechanical: Demec gauges and studs A8.3.2 Electrical resistance A8.3 Strain and movement measurements A8.3.3 Acoustic
A8.3.4 Inductive displacement transducers There are a number of different techniques for A8.3.5 Optical measuring strain in materials depending on the circumstances, nature and duration of measurement. A8.4 In situ stress measurement Some common methods are briefly described below. A8.5 Fatigue tests of material samples The choice of method needs careful consideration. A8.6 Electrical and other indirect methods of moisture A8.3.1 Mechanical: Demec gauges and studs measurement of concrete A8.7 Infrared thermography and transient pulse Over the gauge length of the instrument (typically, thermography mm) strain produces a displacement, which is measured using a dial gauge system. Although the A8.8 Detection of cracks in stone or concrete equipment is inexpensive, it is a manual method with materials some dependence on operator skill. It is often used A8.9 Bond wrench on site for infrequent monitoring of structures over a A8.10 Acoustic pulse velocity long timescale. A8.11 Ultrasonics – timber A8.3.2 Electrical resistance A8.12 Drilling energy test Generally of wire or foil design, electrical resistance A8.13 The crack opening displacement test strain gauges require skilled installation. They use the A8.14 Time domain reflectometry principle that changes in strain in the substrate alter the resistance of the gauges. The gauges can be made A8.15 Acoustic emission very small and read remotely. The technique is best A8.16 Stiffness damage test suited for use on metal structures and for short-term (including dynamic) measurements of strain. A8.17 Radiographic techniques for non-metallic material A8.3.3 Acoustic A8.18 Oxygen diffusion These gauges, sometimes called vibrating-wire A8.19 Carbon dioxide diffusion gauges, are based on the principle that the resonant A8.20 Subsurface radar frequency of a taut wire varies with changes in A8.21 Resistivity tension brought about by changes in strain in the substrate over the length of the gauge (150-300mm). A8.22 Linear polarisation resistance The tensioned wire is sealed with a protective tube A8.23 Eddy currents incorporating an electromagnet to pluck the wire and record its vibrations. Skilled installation is necessary. A8.24 Hall-effect test These gauges have good long-term stability and can A8.25 Air test for prestressing ducts be read remotely. Accuracy of ±10 microstrain has been reported. A8.26 Dynamic testing of structures A8.27 Impact echo (also ‘sonic echo’ and ‘stress wave’) A8.3.4 Inductive displacement transducers technique These transducers use an armature moving within A8.28 Capacity of isolated piled foundations two electrical coils to sense the position of the armature. They are very accurate, but require signal conditioning equipment. They can be read remotely and require specialist installation.
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A8.3.5 Optical Fibre optic sensors can be joined in various configurations to form distributed or multiplexed An optical fibre sensor consists of a thin glass fibre sensing systems. In a multiplexed system, a single as the sensor, typically 5 micron diameter, with a instrument transmits to and analyses light received thicker plastic coating and jacket to protect it from from many separate sensors. In a distributed system, physical damage and chemical attack. Such sensors separate sensing points are located along a single are increasingly used for monitoring both strains optic fibre. Bragg grating and microbend sensors can and displacements in structures as they can offer form combined multiplexed and distributed systems, significant advantages over conventional strain whereas other fibre optic sensors can form only gauges. These advantages include the ability to multiplexed systems. measure strain at discrete points along the length of a single sensor and also over potentially extremely References long sensor lengths (depends on the type of optical Buenfeld N.R. et al. Intelligent monitoring of concrete structures. fibre sensor used), immunity from electromagnetic CIRIA Report C661. London: CIRIA, 2008 interference, low signal loss, long life and ease of installation. Some types of optical fibre sensor are Gawthorpe, P. Code of practice for the installation of electrical more sensitive than other sensors, reportedly being strain gauges. [s.l.]: British Society for Strain Measurement, 1992 able to measure strains as small as 0.1 microstrain. {Superseded by British Society for Strain Measurement. Code of practice for the installation of electrical strain gauges. CP1. 2nd Change in the geometry of the optical fibre (e.g. ed. [s.l.]: British Society for Strain Measurement, 2009} bending, stretching, compression) affects the light signal transmitted. Bending a fibre results in some Inaudi, D. et al. ‘Lessons learned in the use of fiber optic sensor loss of transmitted light (attenuation) and stretching for civil structural monitoring’. Proceedings of the conference the fibre causes a shift in the wavelength of the on The Present and the future in health monitoring, Weimar, transmitted light. These changes in the light signal Germany, June 2000. Available at: http://www.smartec.ch/ form the basis of fibre optic sensing. Bibliography/PDF/C47.pdf [Accessed: 23 October 2009]
There are various types of fibre optic sensors, each Lau, K.T. ‘Fibre-optic sensors and smart composites for concrete has its advantages and limitations. Those most applications’. Magazine of Concrete Research, 55(1), February commonly used in civil engineering are: 2003, pp19-34 –I– nterferometric (e.g. SOFO, Fabry-Perot) which mostly measure strain at a single point on a fibre Leung, C.K.Y. ‘Fibre optic sensors in concrete: the future?’. NDT & (some sensors can also be joined in series along a E International, 34, 2001, pp85-94 single fibre). This type provides localised sensing, albeit that the sensing length might be perhaps Moss, R.M. and Matthews, S.L. ‘In-service structural monitoring: a 20m and are reported to be able to achieve a state of the art report’. The Structural Engineer, 73(2), 17 January resolution of ±0.01 microstrain. 1995, pp23-31 –B– ragg grating sensors measure the change in wavelength (hence the spectrum) in a single fibre Scott, R.H. and Gill, P.A.T. ‘Measurement of internal concrete at discrete points where gratings (typically 10mm strains using embedded strain gauges’. Magazine of Concrete long) are created. This type provides localised Research, 39(139), 1987, pp109-112 sensing and have a maximum resolution of ±10 microstrain. –B– rillouin sensors measure frequency or refractive index change due to strain along the fibre length. A8.4 In situ stress measurement They can measure strain or temperature variations in fibres with lengths up to 50km with spatial resolution down to less than one metre. The ‘absolute’ stresses within the concrete of a –M– icrobending sensors, which consist of an optic structure are a combination of internal stresses and fibre twisted with other fibres or metallic wires, external stresses. The ‘internal stresses’ are those measure displacement at locations along the caused by internal phenomena such as shrinkage, full length of the fibre, and hence is a distributed creep and non-uniform temperature distributions. The sensor. This has advantages over point or localised ‘external stresses’ are caused by externally applied sensors. Resolution is typically 30 microns for short loads, including self-weight, deformations and other periods, and 100 microns for longer periods. Thus behaviours such as restrained thermal response. If they are more suitable for short-term, dynamic the intention of the engineer is to determine the factor monitoring. By comparing the light passing of safety against yield or cracking (which might cause through the sensor with that passing through a failure of a brittle structure), the absolute stress within reference optical fibre, an electrical signal can be the concrete is of interest. This can be obtained by continuously generated from which the overall in situ stress measurement techniques. strain level can be derived, using what is known as the light attenuation method. This electrical signal However, if the intention is to determine the amount is logged and an alarm can be triggered if the of prestress that remains, or the ability of a ductile recorded strain is out of limits. structure as a whole to resist external loads, then what is required is to find the external stress Alternatively an optical time domain reflectrometry caused purely by the particular forces. This is more (OTDR) record of reflected light pulses against a time complicated as it requires the elimination of internal base can be taken at discrete time intervals. The stresses, dead load stresses, thermal stresses, locations of the major fluctuations of strain along the imposed load stresses and stresses caused by sensor length, which can be many metres long, can imposed deformations from the absolute in situ be determined by comparing changes in the traces stresses determined by measurement. taken at different times.
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There are two generally accepted methods for the Abdunur, C. and Eymard, R. ‘Stress redistribution and structural determination of in situ concrete stresses. They are: reserves in prestressed concrete bridges’. In Harding, J.E. and other eds. Bridge Management 3: inspection, maintenance, (1) The hole-drill, or centre-hole, technique which assessment and repair. London: E. & F.N. Spon, 1996, was developed by mechanical engineers pp761-768 concerned with the in situ stresses in metallic plates and structures. Begg, D.W. et al. ‘Determination of concrete properties in situ’. In Carlomango, G.M. and Brebbia, C.A. eds. Computational methods (2) The partial stress release method, which uses and experimental measurement VII. Southampton: Computational flat jacks to re-establish the original stress field Mechanics Publications, 1995, pp537-544. in the member being evaluated. Begg, D.W., Huang, W. and Owens, A. ‘Practical application of the The application of the hole-drill method to determine centre hole technique to insitu stress determination of concrete in situ stresses within concrete structures was structures’. In Virdi, K.S. et al. Structural assessment: the role pioneered by Owens, who further developed the of large and full-scale testing. London: E. & F. Spon, 1997, method with Begg and other co-workers. A similar pp442-451 method has been developed in parallel by Lindsell at the University of Surrey. The technique involves Building Research Establishment. Masonry and concrete measuring changes in strain at the surface of the structures: measuring in-situ strength and elasticity using flat specimen as a stress relieving hole or slot is made in jacks. BRE Digest 409. Garston: BRE, 1995 the specimen. Lindsell, P. ‘Evaluation from structural tests’. Proceedings of the The following points give an indication of the general seminar on the role of load testing in the assessment and repair issues associated with the hole drilling technique: of bridges, New College, Oxford, 1997. [s.l.]: Peter Lindsell & –B– eyond a drilling depth equal to the diameter of the Associates], 1997, pp61-69 hole, the strain variation at the surface is negligible. –I– t is very important to use the strain gauge Owens, A. et al. ‘A new in-situ stress determination technique techniques correctly and with great accuracy, and for concrete bridges’. In Barr, B.I.G. and other eds. Bridge to introduce data smoothing. assessment, management and design. Amsterdam: Elsevier, –T– he accuracy of the technique is a function 1994, pp423-428 of the gauge and hole geometry, the depth increment over which the stress is determined, Owens, A. ‘In-situ stress determination used in structural the mechanical properties of the material and the assessment of concrete structures’. Strain, 4, November 1993, consistency of the stress field. Local stresses occur pp115-123 between the aggregate and the matrix. The large core diameter and depths used help to minimise the effect of these localised stresses upon the measurements. A8.5 Fatigue tests of material samples –T– he average error for strain measurement techniques on site is estimated to be 3%. In many applications materials are subjected to The partial stress release method can be used to vibrating or oscillating forces. The behaviour of determine the in situ stresses within concrete and materials under such load conditions differs from masonry. The method, developed by Abdunur, can the behaviour under a static load. Since the material be used not only to determine the absolute stresses is subjected to repeated load cycles (fatigue) in within the concrete but also the elastic modulus of actual use, designers are faced with predicting the (assumed) isotropic material. fatigue life, which is defined as the total number of cycles to failure under specified loading conditions. In essence, this method uses a narrow slot (4mm in This procedure requires specialist expertise and width to a maximum depth of 80mm), with a semi- equipment. circular shape at the bottom, cut in the concrete. An internal pressure is applied to the slot using a flat Reference jack. The pressure needed to cancel the effects of BS 3518-1:1993: Methods of fatigue testing – Part 1: Guide to the creation of the slot provides the average absolute general principles. London: BSI, 1993 stress that was previously present.
De Vekey developed the technique further for use in masonry structures: refer to BRE Digest 409. A8.6 Electrical and other indirect methods of moisture measurement of concrete and References Abdunur, C. ‘Direct access to stresses in concrete and masonry masonry products bridges’. In Harding, J.E and other eds. Bridge Management 2: inspection, maintenance, assessment and repair. London: A range of electrical methods is available. One Thomas Telford, 1993, pp217-226 range of devices utilises the change in dielectric properties of building materials with moisture Abdunur, C. ‘Testing and modelling to assess the capacity of content. They are based on the measurement of prestressed bridges’, IABSE Report on Remaining Structural dielectric constant and dissipation factor. Field Capacity of Prestressed Bridges, Remaining structural capacity: devices require calibration charts for each type IABSE colloquium, Copenhagen, 1993. IABSE Report 67. Zurich: of building product. They are most appropriate IABSE, 1993, pp353-360 for making assessments of moisture variation. Other equipment measures the relative humidity of air. Internal moisture measurements are made
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by sealing a probe into a hole drilled into the particular circumstances. The technique allows rapid material. Such probes can be employed for remote scanning and is generally easy to apply on site. As monitoring. Accuracy varies with relative humidity, the technique is not invasive there is no surface or but is generally within 5%. other type of damage.
A number of hand-held resistivity measuring The technique has been used in laboratory trials instruments (moisture meters) are available which and field studies to determine the size and position use surface contacting probes. These devices can of ‘critical defects’ introduced during the application be subject to large errors because of problems of carbon fibre reinforced plates (CFRP) as with contact resistance and the influence of strengthening plates to concrete substrates. TPT has soluble salts. demonstrated an ability to detect areas of debonding between the concrete substrate and the CFRP Neutron moisture gauges are commercially available strengthening (both plates and wrapping sheets). and are fairly widely used in soils testing. Accuracy It could provide a basis for rapid monitoring and is not good at the lower moisture levels generally evaluation of the long-term performance under load encountered in building materials. Radiation of CFRP strengthening systems exposed to harsh regulations require operation by suitably trained and and changing environmental conditions, or say to classified personnel. evaluate the condition of CFRP seismic strengthening after minor or modest earthquake events. Reference Ahmet, K. et al. The Long-term monitoring of moisture in concrete Reference structures: report for the Concrete Bridge Development Group. Yong, J.C.M. and Morlidge, J.R. ‘The rapid, non-destructive Luton: University of Luton, 2000 assessment of ‘critical defects’ in composite structural strengthening systems using transient pulsed thermography’. In Forde, M.C. ed. Structural faults and repair 2001, London, 4-6 July 2001. Edinburgh: Engineering Technics Press, 2001 A8.7 Infrared thermography and Transient pulse thermography A8.8 Detection of cracks in stone or Infrared photographs or video views taken during concrete materials the cooling of a heated structure (or vice-versa) can be used to identify temperature differences, often relatively small, across an elevation. The differences While larger cracks may be detected most simply by indicate the heat fluxes that are present. The visual or photographic means during the drying of technique often utilises insolation (solar heating) as a a plain wetted surface, fine cracks in mottled stone means of providing the required thermal input. There such as granite may be detected using ultraviolet light are some practical limitations which may arise when if the surface is specially treated with fluorescent flaw using the sun as the energy source. detector. Extreme care must be taken in interpreting the observed pattern to differentiate between This technique has been used to detect voiding, shrinkage and thermal cracks and those caused by delamination and damp areas of the surface of applied loads. bridge decks, render on building façades and the position of hidden construction features such as wall Reference ties in masonry buildings. Hunt, B.J. ‘The Use of fluorescent dyes in highlighting some construction problems’. Structural Survey, 12(6), 1993-94, pp4-7 Thermography provides rapid coverage and is totally non-destructive, although the method is sensitive to weather conditions. A permanent record is provided by means of a photograph, pseudo-colour plot or A8.9 Bond wrench magnetic media.
This technique potentially provides a means for rapid This is a simple lever test for measuring the bond identification of areas warranting further investigation strength between a masonry unit and the mortar joint by other techniques. immediately below it. The masonry unit is first isolated by removing units above it, and cutting the perpend Transient pulse thermography (TPT) is an ongoing joints either side and the joint behind it in the case of development of the methodology described above. walls thicker than one unit. The lever is clamped on The basic TPT technique involves pulse heating the to the unit and the moment required to cause failure surface under investigation with powerful flash lamps measured. The equipment associated with the test and recording the subsequent transient thermal (lead shot, balance, etc.) is cumbersome. decay of the flash heated surface using an infrared (IR) camera. The thermal decay is generally recorded The BRENCH is a development of the test and as a timed-sequence of thermographic images employs electronic force measurement making the which can be examined using various image analysis equipment more portable and convenient to use by techniques. This approach has advantages over the technical staff after minimal training. general methodology described previously in that it enables investigations to be made under controlled The test produces some repairable damage. conditions with the thermal input (flux) being adjusted to suit the particular circumstances and the nature of Reference the target feature sought. Thus the approach enables Building Research Establishment. Testing bond strength of the investigation methodology to be optimised for the masonry. BRE Digest 360. Garston: BRE, 1991
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This technique is similar to ultrasonic pulse velocity In this test the power consumption of a drill is but it employs lower frequency acoustic pulses monitored as it is driven into the material. The (kHz). It can be used in masonry construction to consumption potentially can be related to the establish details of the internal construction and properties of a homogeneous material by calibration major flaws, voids and cracks. It may be used to tests based upon drilling a standard diameter and investigate construction uniformity and condition. depth hole. The method might be used to test existing mortar joints in situ. This method is also The pulse will travel through considerable known by the term PNT-G. thicknesses of construction (metres). The technique has a lower resolution than ultrasonic pulse velocity References because of the lower frequency used. It has been de Vekey, R.C. and Sassu, M. ‘Comparison of non-destructive used successfully in comparative surveys on insitu mechanical tests on masonry mortars: the PNT-G method bridge piers, harbour walls and similar massive and the Helix method’, Proceedings, 11th International brick and construction. It requires specialist equipment and block masonry conference, Shanghai, 1997. Vol 1, pp376-384 personnel. ‘RILEM recommendation MDT. D.1 – Indirect determination of the Variations of the technique using a transducer in a surface strength of unweathered hydraulic cement mortar by the borehole have been used for determination of the drill energy method’. Materials and Structures, 37(271), Aug-Sep lengths of foundation piles and steel sheet piling, 2004, pp485-487 and, using a transducer and receiver in separate holes, for determination of the integrity of piles, ‘RILEM TC 177-MDT: Masonry durability and on-site testing’. barrettes and diaphragm wall panels. See also Test Materials and Structures, 37(271), Aug-Sep 2004, pp485-501 A8.27 – Impact or sonic echo.
References Fenning, P. and McCann, D. ‘Sea defences: geophysical and NDT A8.13 Crack opening displacement test investigation techniques’. In Forde, M.C. ed. Structural faults and repair 93. Vol 2: Extending the life of civil and building structures. Edinburgh: Engineering Technics Press, 1993, pp11-19 This test determines the value of the critical crack opening displacement at the tip of the defect in Veness, K.J. ‘Structural investigation of coastal defences’. a metal sample at the onset of stable or unstable Construction Maintenance and Repair, 5(3), May-June 1991, crack extension. It is not suitable for general pp36-38 application in structural appraisal but, in exceptional circumstances, it may be helpful. Specialist advice on its use should be sought.
A8.11 Ultrasonics – timber References BS 6729: 1987: Determination of the dynamic fracture toughness of metallic materials. London: BSI, 1987 {Since superseded by Ultrasonic pulse velocity responds to changes in BS 7448-3: 2005: Fracture mechanics toughness tests – Part 3: density and elastic modulus of the material being Method for determination of fracture toughness of metallic interrogated. As such the technique can be used to materials at rates of increase in stress intensity factor greater than assist identification of internal decay and defects in 3.0MPa m0.5 s-1. London: BSI, 2005} timber, as well as comparative variations in stiffness and strength in a member. The inherent variability BS 7910: 2005: Guide on methods for assessing the in the properties of timber gives considerable acceptability of flaws in metallic structures. London: BSI, 2005 uncertainty in interpreting the results. See also comments on subsurface radar.
The technique is less widely used for examining A8.14 Time domain reflectometry timber than for concrete or steel. Access is required to opposite faces of the member under test. Low frequency probes are used (kHz). Most of the This technique seeks to provide information on the information regarding the technique that is available condition of post-tensioned construction. A high- is understood to appear in manufacturer’s literature. frequency electrical impulse is introduced into the end See also Test A8.27 – Impact or sonic echo. of the prestressing tendon (comprising multiple strands) via the anchorage and reflections are produced from Reference interfaces and changes in electrical characteristics, TRADA Technology. Non-destructive testing of timber. Wood such as voiding within grouting and damage to the Information Sheet 4-23. High Wycombe: TRADA, 2004 tendon. Experience within the UK appears to be minimal. Although it has developed significantly, the technique must be considered to be experimental and requires further development and validation.
Reference Chajes, M. et al. ‘Void detection in grouted post-tensioned bridges using time domain reflectometry’. Proceedings of the Transportation Research Board 82nd Annual Meeting. Washington, DC, 2003
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As a structure is loaded, localised points may be The stiffness damage test provides a comparative strained beyond their elastic limit and crushing or means of assessing the development of damage microcracking may occur. The energy released within concretes experiencing expansive internal propagates small amplitude elastic stress reactions, such as ASR. The test involves the waves through the structure, known as acoustic measurement of the strain response of concrete emissions. The waves are generally not in the cores under low level cyclic axial loading. Measured audible range, but may be detected as small test parameters include chord (secant) stiffness, displacements by transducers mounted on the unloading stiffness, damage index (area of surface. normalised hysteresis loops), plastic strain and a non-linearity index. In most materials no emission takes place on subsequent loading until previous stress levels Reference are exceeded. However, concrete has the ability Chrisp, T.M., Crouch, R.S., and Wood, J.G.M. ‘The stiffness to recover many aspects of its precracked internal damage test: a quantitative method of assessing damaged structure within a matter of hours by continued concrete’. In Armer, G.S.T. and other eds. The Life of structures: hydration and energy released on reloading. During physical testing. London: Butterworth, 1989, pp127-136 loading the emission rate and signal level increase slowly and consistently until failure approaches (80-90% of ultimate) and then there is a rapid increase. This behaviour allows crack initiation and A8.17 Radiographic techniques for non- propagation to be monitored. metallic material The method has been used to monitor behaviour during load testing. It has also been used in c- and X-rays may be used to examine the interior structures subject to fatigue damage as an of concrete members to check for the presence indicator of increasing levels of damage. Monitoring of voids, poor compaction, continuity of grouting of reinforcement corrosion and predicting its in prestressing ducts, layout of reinforcement, intensity have also used this method. Application etc. These techniques are expensive and require of the technique has been limited but has been specialist equipment and experience. Each growing in popularity over recent years and is radiograph covers a relatively small area of concrete. available commercially from a number of specialist The test requires access to two opposite faces of organisations. components.
References Care has to be taken to ensure that personnel and ‘Advice Note 3.6: Acoustic Emission (AE)’ In Highways third parties are not exposed to harmful radiation. Agency. Advice notes on the non-destructive testing of X-ray techniques have also been used to investigate highway structures. BA 86/06. Available at: http://www. the internal condition of timber and masonry standardsforhighways.co.uk/dmrb/vol3/section1/ba8606.pdf construction, although rarely, because of cost and [Accessed: 26 October 2009] safety issues.
Lim, M.K. and Koo, T.K. ‘Acoustic emission from reinforced Reference concrete beams’. Magazine of Concrete Research, 41(149), Pullen, D.A.W. and Clayton, R.P. ‘The Radiography of Swaythling December 1989, pp229-234 Bridge’. British Journal of NDT, September 1981, pp227-232
Ohtsu, M., Okamoto, T. and Yuyama, S. ‘Moment tensor analysis of acoustic emission for cracking mechanisms in concrete’. ACI Structural Journal, 95(2), March-April 1998, pp87-95 A8.18 Oxygen diffusion
Pullin, R. et al. ‘Bridge integrity assessment by acoustic emission: global monitoring’, Proceedings 2nd International A concrete sample is sealed in a circular steel ring conference on identification on engineering systems, Swansea, such that the cut faces are exposed. Oxygen at a March 1999. Swansea: University of Wales, 1999, pp392-400 known pressure, temperature and flow rate is passed over one side of the specimen and helium gas is Pullin, R. et al. ‘Bridge integrity assessment by acoustic purged over the opposite face at the same pressure, emission: local monitoring’, Proceedings 2nd International temperature and flow rate. The helium gas stream is conference on identification on engineering systems, Swansea, analysed by gas chromatography for oxygen and the March 1999. Swansea: University of Wales, 1999, pp401-409 time taken to reach equilibrium determined (generally 24-48h). The diffusion coefficient for oxygen can Yuyama, S. et al. ‘A Proposed standard for evaluating structural then be calculated. This provides a measure of the integrity of reinforced concrete beams by acoustic emission’. maximum theoretical corrosion rate for embedded In Vahaviolos, S.J. ed. Acoustic emission: standards and steel (ignoring the influence of cracks, etc.). technology update. ASTM STP 1353. West Conshohocken: ASTM, 1998 Reference Lawrence, C.D. ‘Measurements of permeability’, Proceedings of the 8th International congress on the chemistry of cement, Rio de Janeiro, 1986. Vol 5, pp29–34
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A8.19 Carbon dioxide diffusion References Concrete Society. Guidance on the radar testing of concrete structures. Concrete Society Technical Report 48. Camberley: This is conducted in a similar manner as for oxygen Concrete Society, 1998 diffusion (see A8.18) except that carbon dioxide is introduced instead of oxygen. The measured carbon Matthews, S.L. Application of subsurface radar as an investigative dioxide diffusion rate can be used to estimate the technique. BRE Report BR340. Garston: BRE, 1998 rate of carbonation and hence the time-scale before possible reinforcement corrosion.
Reference A8.21 Resistivity BS EN 1062-6: 2002: Paints and varnishes – Coating materials and coating systems for exterior masonry and concrete – Part 6: Determination of carbon dioxide permeability. London: BSI, 2002 The technique seeks to measure the ability of electrical corrosion currents to flow through concrete. It is used to identify areas of greatest corrosion risk. The resistivity of the concrete A8.20 Subsurface radar surface layer is measured by either 2 probe or 4 probe (Wenner) methods. In the case of the latter approach, four equally spaced probes are High-frequency electromagnetic impulses are held firmly on the surface of the concrete and an transmitted from an antenna traversed over the alternating current is passed between the outer surface under investigation. Reflections are received electrodes. The resultant potential difference from internal features and boundaries between between the inner probes is measured enabling materials of differing electrical properties. This the average resistivity to be calculated. When used technique may be used on concrete and masonry in conjunction with a half-cell potential survey the structures to establish subsurface construction measurements give an indication of the general details and below ground to identify shallow likelihood of corrosion and its likely extent. geological structure. Radar has been used to locate rot in timber structures (such as utility poles). The technique does not give any guide as to the degree of corrosion damage that has taken place. The equipment is moderately expensive and requires Difficulties arise when a significant thickness of the experienced personnel to operate and interpret the cover concrete is carbonated, owing to the higher results. The technique can be very powerful and resistivity of carbonated concrete. This can be works best in simple planar construction e.g. slabs. avoided by drilling shallow holes at the surface of the As it operates in reflection mode, it needs access to concrete, into which the probes are inserted. only one face of a structure. For concrete structures it may be used to estimate element thickness, A variation on the technique is used to detect leakage reinforcement cover, orientation and spacing. in waterproof membranes. It measures the resistance between the surface and reinforcement. The technique is completely non-destructive, although exploratory holes are required physically References to identify anomalies. Resolution and penetration Building Research Establishment. Corrosion of reinforcement depends on the frequency of radiation employed; in concrete: electrochemical monitoring. BRE Digest 434. each is obtainable at the expense of the other, Garston: BRE, 1998 and expert advice is required to achieve a good compromise. Moisture affects the behaviour. It Concrete Bridge Development Group. Guide to testing and can also provide information on a number of other monitoring the durability of concrete structures. Technical parameters (chlorides, corrosion, moisture, density, Guide 2. Crowthorne: Concrete Society, 2002 etc.) in certain circumstances. Millard, S.G. ‘Reinforced concrete resistivity measurement The engineer should seek objective advice from a techniques’. ICE Proceedings, Part 2, 91, March 1991, radar specialist as to the ability of radar to assist pp71-88 in particular situations. The radar specialist should be able to explain the limitations of the equipment Rodriguez, J. et al. ‘On-site corrosion rate measurements in and any potential difficulties in the interpretation of concrete structures using a device developed under the Eureka the results, allowing these factors to be carefully Project EU-401’, International conference on Concrete across considered before deciding to employ the technique. borders, Odense, Denmark, June 1994. Vol 1, pp215-226 It is possible that a considerable degree of other testing will be required to supplement the radar data. It should be borne in mind there may be great uncertainty amongst even experienced radar A8.22 Linear polarisation resistance specialists as to whether the technique will do the job required, simply because of the lack of information about the circumstances concerned. Some A series of polarisation resistance measurements specialists have the ability to investigate the likelihood from a structure provide an indication of the rate of success of a radar survey by undertaking some of corrosion of metal embedded in the concrete. preparatory modelling based upon this information. It can be used for assessing the comparative Accordingly the client and engineer should be corrosion risk between different areas of a structure. prepared to provide as much information about the Determination of the polarisation resistance involves survey circumstances as possible. measuring the half-cell potential and then applying a small potential shift of the order of 10 to 20mV to the
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reinforcing bar and measuring the resulting current wires or corrosion, and other causes of disturbance, flow. This enables an estimate of the corrosion such as pieces of tie wire embedded in the concrete. current to be made. The method must still be considered as experimental.
Various designs of equipment are available. In the Reference simplest form two nominally equivalent electrodes Ausenberger, F.N. and Barton, J.R. Detection of flaws in are used. Some systems incorporate a third reinforcing steel in prestressed concrete. Report RD-81/087. electrode in which the electrode of interest (working Washington, DC: Federal Highways Administration, 1981 electrode) is measured relative to a reference electrode as in a half-cell potential measurement and the third electrode (auxiliary) is used simply to complete the circuit to allow current flow. A major A8.25 Air test for prestressing ducts difficulty with measurements made from the surface of the concrete is defining the area of embedded metal (reinforcement) which is participating in the The most direct method of inspecting inside measurement. One approach adopted to overcome ungrouted ducts in post-tensioned concrete this is to confine the measurement to a known area structures is carefully to drill into the duct and use an by the use of a guard ring electrode. endoscope (see T23). However, if a series of holes is drilled and a vacuum applied at one, the pressure References drop at the others gives an indication of the continuity Building Research Establishment. Corrosion of reinforcement in of any voids present. An approximate estimate of void concrete: electrochemical monitoring. BRE Digest 434. Garston: volume can be obtained by measuring the drop in BRE, 1998 pressure within a container of known volume when connected to the void. Concrete Bridge Development Group. Guide to testing and monitoring the durability of concrete structures. Technical . An indication of the ease with which moisture, Crowthorne: Concrete Society, 2002 atmospheric gases and other deleterious materials can enter the duct can be gained by applying a small pressure to the duct and measuring the rate of leakage. A8.23 Eddy currents These procedures are not suitable for use during routine inspections. They may be useful on post- Eddy current testing is based on the principle of tensioned concrete structures exhibiting some electromagnetic induction. It makes use of the degree of deterioration or distress. magnetic field generated by a coil carrying an alternating current. The magnetic field interacts with Reference a test object brought near to the coil, and the effect Stain, R.T. and Dixon, S. ‘Inspection of cables in post- of the field depends, inter alia, on the electrical and tensioning bridge: what techniques are available’. In Forde, magnetic properties of the test object. Variations M.C. ed. Structural Faults and Repair 93. Vol 1: Extending the in voltage across the coil reflect variations in the life of bridges. Edinburgh: Engineering Technics Press, 1993, characteristics of the test object within the coil. pp297-300 Eddy current testing provides a simple and rapid way of distinguishing between objects with different characteristics. A simple example is the checking of bolts. The characteristics of a bolt that is cracked will A8.26 Dynamic testing of structures be different from those of one that is sound.
References The vibration response of whole or parts of BS EN 1330-5: 1998: Non-destructive testing – Terminology – structures to excitation can be used to estimate Part 5: Terms used in eddy current testing. London: BSI, 1998 structural parameters, including natural frequency, stiffness of members and overall stiffness, and to Rudlen, J.R. ‘A Beginner’s guide to eddy current testing’. British evaluate support conditions. The technique may Journal of NDT, 31(6), June 1989, p314 be used to compare the measured response with analytical models.
Dynamic tests have an advantage over static tests A8.24 Hall-effect test in that they are quicker and easier to undertake. However, they cannot always provide the same information as static tests, especially those Defects, such as breaks and local changes in cross- concerned with strength assessments. As with sectional area, of tendons within structural cables any type of testing it is essential to know what may be detected by measurement of the magnetic information is required and whether the selected anomaly fields produced around the cable when a test procedure is likely to yield that information. It strong magnetic field is induced in the cable. is also important to know that the equipment to be used is appropriate, both for range and accuracy, For pre- and post-tensioned concrete construction, that it is correctly calibrated and that it will be a constant magnetic field is applied to the beam operated in a correct manner. under test. A ‘hall-effect’ probe is used to scan the surface of the beam parallel to the direction of the Excitation of the structure can be by vibrators, prestressing tendons. There are, however difficulties impact hammers, or on large structures by ambient in distinguishing between defects, such as broken wind effects. The structural response is generally
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monitored by accelerometers or geophones. The A8.27 Impact echo (also ‘sonic echo’ and dynamic characteristics of the structure may be ‘stress wave’) technique established using signal analysers or model analysis procedures. The equipment is expensive and experienced personnel are required to perform tests The test involves the propagation of an ultrasonic and interpret the results. stress wave through the body of a concrete element and the detection of energy reflected Changes in the dynamic characteristics with time may back to the surface. This provides information on be used to monitor changes in structural parameters. the member thickness and the presence of major The sensitivity of the technique is reduced for internal voids, delaminations or other defects. structures with a greater degree of redundancy. The Mapping of the results enables the existence of technique is unlikely to be sensitive to local defects, thickness variations and the location and extent some of which may be of considerable structural of defects to be established. The stress wave significance (e.g. localised severe corrosion of is typically generated by a single impact on the reinforcement or prestressing steel). surface from a specialised hammer. Calibration of the propagation velocity is necessary to obtain Damage to structures sometimes results in a reduction absolute determinations of thickness variations and of stiffness and hence a change of frequency, and depths to internal features; otherwise comparisons monitoring can identify such changes. However, are made on a relative basis. frequencies also vary with temperature and other factors and it may be difficult to separate effects These techniques have also been used on timber due to damage from other effects. Also damage members to assist in the identification of internal may not necessarily lead to measurable changes in decay and defects in timber, as well as comparative stiffness: hence it is not usually practicable to assess variations in stiffness and strength in a member. damage from this type of test, unless the mechanism The inherent variability in the properties of timber of damage is known and thought to be linked with gives considerable uncertainty in interpreting the measurable changes in stiffness. results. Guidance appears to be provided only by manufacturer’s and trade literature – no consensus The most common application of dynamic testing guidance appears to be available. Some conference techniques is to foundation piles. Typically an impact papers are believed to have made reference to the is applied to the top of the pile shortly after forming use of the impact echo technique in this context, but and before the pile cap has been constructed. could not be identified.
Transient dynamic response (TDR) techniques utilise References vibration characteristics to estimate the length of See A8.26 references and: pile, damage within shaft, the presence of bulbs or inclusions and pile head stiffness. Pulse-echo ANSYS user’s manual for version 5.0a. Vol 1. Houston, PA: techniques employ time-flight methods to estimate Swanson Analysis Systems, Inc, 1992 {Since superseded by similar characteristics. TDR techniques have been version 5.6, 2003} used to investigate voiding beneath ground bearing slabs. Derivations of these techniques can be used Ghorbanpoor, A. Evaluation of post tensioned concrete bridge to investigate piling supporting existing structures structures by the impact-echo technique. FHWA-RD-92-096. (see A8.28). Washington, DC: Federal Highway Administration, 1993
References Jaeger, B.J., Sansalone, M.J., and Poston, R.W. ‘Detecting voids Ellis, B.R. ‘Chapter 5: Dynamic testing’. In Moore, J.F.A. ed. in grouted tendon ducts of post-tensioned concrete structures Monitoring building structures. Glasgow: Blackie, 1991 using the impact-echo method’, ACI Structural Journal, 93(4), July-August 1996, pp462-473 Likins, G. and Rausche, F. ‘Recent advances and proper use of PDI low strain pile integrity testing’, 6th International conference Lin, Yinching. Impact response of bars with applications to on the application of stress-wave theory to piles, São Paulo, concrete beams, columns and shafts. Cornell University PhD Brazil, September 11-13, 2000. Rotterdam: A.A. Balkema, 2000 thesis, 1992
Massoudi, N. and Teffera, W. ‘Non-destructive testing of piles Lin, Y. and Sansalone, M. ‘Detecting flaws in concrete beams and using the low strain integrity method’, Proceedings of the 5th columns using the impact-echo method’. ACI Materials Journal, International conference on case histories in geotechnical 89(4), July-August 1992, pp394-405 engineering, New York, 13-17 April 2004. Rolla, Missouri: University of Missouri-Rolla, 2004 Lin,Y.C. and Sansalone, M. ‘Transient response of thick circular and square bars subjected to transient elastic impact’. Journal Rausche, F., Likins, G. and Ren Kung, S. ‘Pile integrity testing of the Acoustic Society of America, 91(2), February 1992, and analysis’, Proceedings of the 4th International conference on pp885-893 the application of stress-wave theory to piles, The Netherlands, September 1992. Rotterdam: A.A. Balkema, 1992 Lin, Y. and Sansalone, M. ‘Transient response of thick rectangular bars subjected to transverse elastic impact’. Journal of the Rausche, F., Robinson, B. and Likins, G. ‘Economy, benefits and Acoustic Society of America, 91(5), May 1992, pp2674-2685 limitations of NDT for augered-cast-in-place-piles’, Proceedings from the Michael Wayne O’Neill auger cast-in-place pile sessions: Martin, J. et al. ‘Impact-echo assessment of post-tensioned recent experiences & advancements in the U.S. and abroad on concrete bridge beams’. In Forde, M.C. ed. Structural faults the use of auger cast-in-place piles. 83rd Annual Transportation and repair 97. Vol 1: Extending the life of bridges. Edinburgh: Research Board Meeting, Washington, DC, January 13, 2004 Engineering Technics Press, 1997, pp341-353
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Martin, J. et al. ‘Quantifying the defects in post-tensioned bridges References using the impulse ultrasonics’, Structural faults and repair 95. Vol Davis, R.A., Mure, J.N. and Kightley, M.L. ‘The dynamic analysis 1: Extending the life of bridges. Edinburgh: Engineering Technics of piled foundations using the CAPWAPC method’. Ground Press, pp209-216 Engineering, 20(8), November 1987
Mindlin, R.D. and Fox, E.A. ‘Vibrations and waves in elastic bars Klingmüller, O. ‘Sonic echo pile integrity testing and quality of rectangular cross section’. Journal of Applied Mechanics, 27, control’. Ground Engineering, 26(10), December 1993 March 1960, pp152-158 Rausche, F., Moses, F. and Goble, G.G. ‘Soil resistance predictions Sansalone, Mary Jane. Flaw detection in concrete using transient from pile dynamics’, Journal of the Soil Mechanics and stress waves. Cornell University PhD thesis, 1986 Foundation Division, ASCE, 98(SM9), September 1972
Sansalone, M. ‘Impact-echo: the complete story’, ACI Structural Journal, 94(6), November-December 1997, pp777-786
Sansalone, M. and Carino, N.J. Impact-echo: a method for flaw detection on concrete using transient stress waves. NBSIR 86- 3452. Washington, DC: National Bureau of Standards, 1986
Sansalone, M. and Carino, N.J. ‘Impact-echo method: detecting honeycombing, the depth of surface-opening, cracks, and ungrouted ducts’, Concrete International, 10(4), 1988, pp38-46
Sansalone, M. and Streett, W.B. Impact-echo: nondestructive testing of concrete and masonry. Ithaca, NY: Bullbrier Press, 1996
Woodward, R.J. and Williams, F.W. ‘Collapse of Ynys-y-Gwas bridge, West Glamorgan’. ICE Proceedings, Part 1, 84, August 1988, pp635-69
Woodward, R.J. and Wilson, D.L.S. ‘Deformation of segmental post-tensioned precast bridges as a result of corrosion of the tendons’. ICE Proceedings, Part 1, 90, April 1991, pp397-419
A8.28 Capacity of existing isolated piled foundations
As urban sites are re-developed progressively, space for new foundations is at a premium. There is considerable pressure to re-use existing pad or piled foundations, from consideration of economy, congestion, buildability and sustainability. The capacity of a pad foundation can be assessed from its area and a presumed bearing value, with appropriate checks for its reinforcement. The capacity of piles can likewise be assessed from geotechnical consideration.
However Pile Driving Analysis (PDA), employing stress-wave methods, can be carried out if a hammer or drop weight can be used to drive the existing pile sufficiently to mobilise the required working load. Accelerometers and strain transducers are attached to the pile head and the characteristics of the percussive wave recorded. The pattern of the recording is synthesised, usually off-site, by assuming pile and soil parameters at intervals down the pile, putting these into a mass-spring-damper program, and varying the parameters until a good match with the measured pattern is obtained. These parameters are used to estimate the ultimate capacity of the pile. It is usually sufficient to test only a percentage of the piles using this high strain method. In situ piles in the UK have been tested to loads in excess of 7MN by this technique.
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Monitoring may be a control or a diagnostic process To achieve such discrimination will require data but is not an end in itself. Monitoring should have a to be taken at intervals which are less than half specified purpose and time limit (the latter possibly the period of the effect with the shortest period subject to the results obtained). A definition for influencing the observed behaviour. Should this be monitoring is given below: necessary, some form of automatic monitoring (see Appendix A9.3) will usually be required. To keep watch over, recording progress and changes with time; possibly also involving The techniques may be quite sophisticated, and they the control of the functioning or working of may employ modern computational techniques. The an entity or process. Structural monitoring techniques include: typically involves gathering information by a –V– isual inspections: range of techniques and procedures to aid –– noting cracks, deterioration, dampness, damage, the management of an individual structure etc. or class of structures. It often involves the –– photographs or other images, including those automatic recording of performance data for taken in normal light and at other frequencies – the structure and possibly also some degree of such as infra-red for thermographic imaging associated data processing, although there is –V– ertical movement: a variety of means of gathering and processing –– levelling surveys (precise or otherwise) appropriate data. –– hydrostatic level indicators or similar –– global positioning systems (GPS) (if movements In this Appendix, discussion of monitoring sufficiently large) methods will be restricted to visible structure –– laser devices and so will not include geotechnical methods –V– erticality measurements: using instruments such as inclinometers and –– theodolite, plumb-bobs, optical plumb, total piezometers. station measurement, laser devices etc. –H– orizontal movement: There are also other techniques which prove to –– triangulation by theodolite, total station be useful in providing supplementary information, measurement etc. such as the facility to obtain overview images or –– trilateration by tapes or electronic distance photographs from adjacent vantage points or from measurement (EDM) equipment a high location, perhaps via a camera on a tall –G– PS (if movements sufficiently large) mast. –– laser devices –M– ovement across cracks: –D– emec gauges or similar devices –– calibrated (graticule) tell-tales A9.1 Visual and manual methods –– laser devices –C– rack propagation: –– marking ends of visible cracks These methods rely primarily on visual inspections –R– einforcement corrosion: or observation with instrumentation to obtain a –– half-cell potential mapping, resistivity and measurement of length or some other parameter corrosion current measurements. from which movement or change may be deduced. Such methods generally require the In addition many of the instruments (or manual presence of an observer on site at the time of versions thereof) described in Appendix A9.3 can measurement. also be employed using a manual read-out of data. Only a limited number of instruments is likely to be Manual methods have relatively low initial set-up employed in this way, when the short duration of the costs (compared to automatic or autonomous monitoring period or the long time between readings systems), but incur relatively high costs each time a makes it more economical to employ people to read set of measurements is taken. Manual methods are them than to invest in automation. therefore likely to be employed when the programme of monitoring is expected to be short and not involve Any technique that involves measurement of a much instrumentation, e.g. a small-scale load test, or parameter can usually be implemented either as where monitoring of a limited number of instruments a computer-based automated monitoring system will take place over a longer time-scale with repeat or a ‘manual’ method. Whilst this generally might measurements taken infrequently. be taken to exclude visual survey and inspection, automatic computer-based techniques exist for the Such limited measurements do not generally comparison of visual images, and the detection of allow the influence of different contributing small differences between two images taken from the factors to be separated. Accordingly it is unlikely same camera position is eminently practicable. This to be possible to discriminate diurnal (probably provides a monitoring methodology depending upon thermally induced), seasonal (possibly moisture the fineness of the digitisation of the image (i.e. a induced) and longer term effects (possibly higher number of pixels giving a finer digitisation and structural and most likely the topic of interest). so greater resolution).
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A9.2 Photogrammetric methods Instrumentation for monitoring structural behaviour can be broadly categorised into instrumentation that measures actions on the structure (e.g. imposed Photogrammetry is defined as the ‘science of loads, wind loads and temperature changes) and measurement from photographs’. It has been that which measures the response of the structure to employed to obtain accurate positional data in those actions (e.g. deflections, vibrations, rotations many situations and, by comparing records taken at and strains). different times, has been used to monitor movements of parts of structures or even complete structures. A9.3.1 Instrumentation for measuring actions on structures The basic principle of obtaining three-dimensional information requires the combination of a minimum In existing construction it is likely to be difficult to of two [stereo] photographs taken from different install instrumentation to measure imposed loads survey stations using precision ‘metric’ cameras. directly. Pressure transducers are available for The coordinates of identifiable parts of the image are measurement of wind pressures. Temperature measured on each resulting negative. Targets are measuring devices likely to be suitable for sometimes mounted on the structures. monitoring purposes are resistance thermometers, thermocouples, thermistors and transducers In ideal conditions in-plane displacements can be incorporated into optical fibres. measured to an accuracy within 1 in 105 of the field of view: i.e. accuracies to within 1 to 2mm can be A9.3.2 Instrumentation for measuring responses of obtained. structures
The long-term stability of the camera stations and Deflection reference points is important, since their displacements There is a range of direct and indirect methods that reduce the accuracy of the method. The problem may be employed to measure long-term deflections. can be reduced when there is sufficient redundancy Direct methods are preferable as they reduce the in the measurements to allow the coordinates of the number of assumptions necessary to interpret the camera positions to be treated as additional unknowns. data. However, direct methods require a frame Typically photographs from six different vantage of reference to be established for the individual points are required for this purpose. More recent measurement points. developments use video cameras or scanning lasers, ––Direct methods: the results from which can be processed to produce a –– potentiometers and linear variable displacement three-dimensional computer model. transducers (LVDTs) (or similar instruments) –– hydraulic levelling systems Photogrammetry is a flexible monitoring technique, –– laser systems and total station surveying but it does require specialist equipment and a high equipment level of expertise. The advantages of the method –G– PS (for larger structures) – see specific section are the documentary value of the photographs below and the relative speed and simplicity of the ––Indirect methods: measurements. Stereo-photogrammetry, producing –– slope measurement devices (e.g. electrolevels): three-dimensional information, does however require relatively expensive and may need calibration substantial work in processing the ‘raw’ images. trials.
Rotation Devices generally sense the movement of a A9.3 Automatic and autonomous monitoring conducting fluid in response to rotation. Devices systems include various designs of electrolevel and tilt transducer. Other devices include pendulums, inclinometers and laser based instruments. The frequency and extent of measurements that can be taken using manual or traditional methods are Vibration limited. They may not allow a suitable body of data to Devices are available that sense particle acceleration be obtained. Automatic systems, on the other hand, (accelerometers), velocity (geophones) and are able to collect data frequently and for extended displacement (LVDTs or similar). They have different periods of monitoring, and may have lower costs operating frequency ranges, with accelerometers of data collection. However, installation and initial extending to the highest frequencies and costs associated with data-processing systems are displacement measurements (which require an generally high compared to manual systems. Many independent frame of reference) to the lowest. automatic systems can be controlled remotely and Laser and electro-optical equipment can be used this facility can reduce the need for visits to site. for vibration measurements, possibly including devices such as total station theodolites. GPS and Automatic systems also enable systematic its derivative technologies may be able to provide presentation and processing of data, reducing the useful information for larger structures in some potential for human error. They can also reduce the circumstances. data to a form suitable for interpretation, enabling the operator to concentrate on understanding Strain what is happening, rather than being absorbed Three designs of strain gauges are commonly used: in the processing of the data. The engineer –E– lectrical resistance gauges (foil or wire designs) needs to determine the form in which the data which have good dynamic characteristics, but are are presented; this should not be left to the prone to drift in the longer term. instrumentation technician.
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–V– ibrating wire gauges which have good long-term An increase in the number of satellites used in the stability and can measure strain over longer gauge process of determining position can reduce the lengths (up to 300mm). This type of gauge has magnitude of the uncertainty or error margin in the some dynamic capability (< 5Hz). estimated position. Uncorrected positions determined –O– ptical fibre strain sensors of various designs from GPS satellite signals produce accuracies in the can be utilised in a number of ways and may be range of perhaps 50 to 100 metres. When using a employed as a very long base length (perhaps 5km technique called differential correction, users can or more) transducer chain, with perhaps 50 or more determine their position to within perhaps 1 to 5 sensing locations, measuring changes in length metres, or possibly even less. It should be realised that (strain) and possibly other related information (e.g. GPS accuracy is both time and location dependent. temperature) across a structure. For example, they may be utilised as a helical winding around the full Differential correction requires a second GPS height of (say) a concrete cooling tower. receiver, a base station, collecting data at a stationary position for a precisely known point – typically this In addition to the above, instrumentation is also might be a surveyed bench mark. As the physical available for monitoring various aspects of structural location of the base station is known a correction degradation, seeking to record directly the progress factor can be calculated. The differential correction of the deterioration process. technique reduces some of the various sources of error which affect GPS determinations. Most of the instruments for monitoring structural degradation and moisture content are more The latest method of providing better accuracy from appropriate for incorporation within buildings at the GPS constellation of satellites is the use of a Space the time of construction, and are therefore not Based Augmentation System (SBAS). This technology necessarily appropriate for application to existing avoids the need for a second GPS receiver required structures. by the differential correction technique. Instead of a beacon receiver, the correction data is sent from a geostationary satellite and is decoded by one of the regular channels present in the GPS receiver. The A9.4 Surveying using global navigation system utilises a network of ground stations to obtain satellite systems (GNSS) the necessary correction data. There are a number of these regional systems. In Europe the system is known as EGNOS (European Geostationary Navigation Global navigation satellite systems (GNSS) is a Overlay) and consists of three geostationary satellites generic technology for determining spatial position, and a network of Europe-wide ground stations. To use that is the location of a point in space or anywhere the system in the northern hemisphere GPS receivers on the earth’s surface. It has numerous mapping and will need a clear view of the portion of the southern related applications. The currently available systems sky required to be able to see the geostationary were developed for military use, but the technology satellite of interest. This may limit the use of the now has a wide and increasing range of civil uses for system by ground based receivers and its greatest a diverse number of purposes. Both the American use may be for navigation of planes and boats. It is GPS and the Russian GLONASS (Global Orbiting understood that some of these difficulties can be Navigation Satellite System) systems have been overcome by obtaining correction data via an Internet operational for some years. The GPS technology link, or possibly via radio or phone modems. In the uses a constellation of satellites orbiting the earth at USA the system is operational and is known as WAAS an altitude of some 11,000 miles. Currently Europe is (Wide Area Augmentation System), while in Asia the developing its own civil system (Galileo). What follows Japanese system is called MTSAS and the Indian is described in terms of GPS technology but is largely system will be known as GAGAN. applicable to both systems and the generic GNSS concept. There are various types of GPS receiver available which offer different levels of accuracy. Essentially GPS is based upon satellite ranging –C– oarse Acquisition (CA) Code Receivers: Typically (trilateration), which involves calculating the distances providing 1-5 metre accuracy with differential between the receiver (at the location where the correction and an occupation time (how long it position information is required) and the known is necessary to be at the point to determine its position of 3 or more satellites. At least 4 satellites location) of 1 second. Longer occupation times (up are needed if elevation is required. The information to 3 minutes) can improve accuracy to within 1-3 supplied to civil users of the American GPS was metres. Recent advances in GPS receiver design designed to be degraded if necessary for military will allow CA Code Receivers to achieve accuracy reasons. This mechanism was known as selective down to about 30cm. availability and was officially discontinued from –C– arrier Phase Receivers: Typically providing 1 January 2000, so that the full accuracy is available 10-30cm accuracy with differential correction, to all. It was intended to limit the accuracy which but require a significantly greater occupation can be achieved by non-military users of the system. time. When initialising using a known point the Similar considerations apply to the GLONASS. occupation time will be about 5 minutes. However when using an unknown point the occupation time GPS receivers require a direct line of sight to the could be about 30-40 minutes, which may limit satellites they are using and any object in that path, their application. such as the tree canopy, buildings and terrain –D– ual Frequency Receivers: Work by receiving GPS features, has the potential to interfere with the signals on two frequencies simultaneously. Typically reception of the GPS signal. GPS receivers will not providing sub-centimetre accuracy with differential work inside buildings or other facilities where there is correction. Such accuracy is required to undertake no satellite visibility. survey work.
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The use of GNSS, which gives a unique address to A9.6 Bibliography (for whole Appendix) each spatial position i.e. ‘the where’, may make its greatest contribution when used in conjunction with Geographic Information Systems (GIS), which give Buenfeld N.R. et al. Intelligent monitoring of concrete structures. information about the particular place i.e. ‘the what’. CIRIA Report C661. London: CIRIA, 2008 Potentially this combination provides a very powerful tool. Building Research Establishment. Simple measuring and monitoring of movement in low-rise buildings. Part 1: Cracks. References BRE Digest 343. Garston: BRE, 1989 Background Guide to GPS and GNSS. Available at: www.ice.org. uk/downloads/GPS_v0.1.pdf [Accessed: 26 October 2009] Building Research Establishment. Simple measuring and monitoring of movement in low-rise buildings. Part 2: Settlement, Brown, C.J. et al. ‘Monitoring of structures using the global heave and out-of-plumb. BRE Digest 344. Garston: BRE, 1989 positioning system’. ICE Proceedings, 134(1), February 1999, pp97-105 Burland, J.B., Standing, J.R. and Jardine, F.M. eds. Building response to tunnelling: case studies from construction of the Jubilee Line Extension. Vol 1: projects and methods; Vol 2: case studies. CIRIA Special Publication 200. London: CIRIA, 2001 A9.5 Surveying using total station methods Concrete Bridge Development Group. Guide to testing and monitoring the durability of concrete structures. Technical Total stations integrate the measurement of angles, Guide 2. Crowthorne: Concrete Society, 2002 as traditionally undertaken using a theodolite, with distance measurement, as traditionally undertaken Fédération Internationale du Béton. Management, maintenance using a steel tape (or similar) but latterly using and strengthening of concrete structures. FIB Bulletin 17. laser-based Electronic Distance Measurement Lausanne: FIB, 2002 (EDM) devices. All readings are digitised, facilitating subsequent automated data processing and Fédération Internationale du Béton. Monitoring and safety reporting of survey outcomes. Measurements are evaluation of existing concrete structures. FIB Bulletin 22. made by laser via a series of survey points that Lausanne: FIB, 2003 require line of sight between a minimum number of survey points. The measurement target is Jardine, F.M. ed. Response of buildings to excavation-induced often a survey prism, especially at longer ranges ground movements: proceedings of the international conference, (up to about 7500m). However at shorter ranges Imperial College, 17-18 July 2001. CIRIA Special Publication (probably at distances of over 500m) the laser- 1999. London: CIRIA, 2003 based measurements can often be made directly of building features without the use of a reflector. Overall Longworth, T.I. Techniques for monitoring ground movement distance measurement accuracies are in the order of above abandoned limestone mines. BRE Information Paper IP 2-5mm plus 2ppm. Thus for a measurement distance 1/88. Garston: BRE, 1988 of 1000m the accuracy would be 2-5mm plus 2mm. Matthews, S.L. ‘Deployment of instrumentation for in-service Total station survey techniques are increasingly monitoring’. The Structural Engineer, 78(13), 4 July 2000, being used in conjunction with real-time kinematic pp28-32 GPS (RTK GPS) to produce highly accurate surveys, particularly where overhead obstructions limit the use Moore, J.F.A. ed. Monitoring building structures, Glasgow: Blackie, of GPS. RTK GPS is a form of the GPS differential 1992 correction technique utilising dual frequency GPS receivers (see Appendix A9.4) which is understood Moss, R.M. and Matthews, S.L. ‘In-service structural monitoring: a to deliver centimetre-level position accuracy. In state of the art report’. The Structural Engineer, 73(2), 17 January these circumstances the combined total station and 1995, pp23-31 GPS receiver utilise a remote reference GPS station (up to 50km from the measurement location). It is understood that these techniques can yield positional accuracies of the following orders: –H– orizontal position accuracy: 10mm + 1ppm –V– ertical position accuracy: 20mm + 1ppm
References Dias, P. et al. ‘Combining intensity and range images for 3D architectural modelling’, International symposium on virtual and augmented architecture, Trinity College of Dublin, 21-22 June 2001, pp139–145
Irvine, W. and Maclennan, F. Surveying for construction. 5th ed. Maidenhead: McGraw-Hill, 2006
The following non-commercial websites have useful guidance on 3D laser scanning: –– www.heritage3d.org –– www.englishheritage.org/servers/show/nav.1155 –– www.pastperfect.info/archaeology/totalstatn.html
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A10.1 Composition of safety factors A10.2 Load factors, cf
When considering the factors of safety (partial A10.2.1 General or global) to be used in the further stage of A10.1 assessment calculations, it may be helpful to The [combined] cf factors in BS 8110 and similar examine the broad principles of the partial factor codes are composed of three elements: approach and the composition of the safety
factors. cf1 Load variation factor. This takes account of the possibility of unfavourable deviation of the According to the partial factor format used in load from the value considered in deriving the British structural design codes, such as BS characteristic load. A10.1 A10.2 8110 (concrete), BS 5628 (masonry), cf2 Load combination and sensitivity factor. This BS 5950A10.3 (structural steel) and BS 8118A10.4 takes into account the reduced probability that (aluminium), the basic design equation is written: various loads acting together will all be at their characteristic values simultaneously, but also structural resistance the increased safety margin which is required for c (load effects) G load combinations in which some forces have a f c m beneficial effect and some an adverse.
cf3 Structural performance factor. This takes where cf is the [combined] partial factor for loads into account possibly inaccurate assessment of and load effects and cm is the partial factor for the overall effects of loading, unforeseen stress material strength, etc. redistribution within the structure, variations in the dimensional accuracy achieved in the structure so As Eurocodes are now becoming available for far as they affect its response, and the importance design, the Eurocode system of partial factors can of the limit state being considered. be used as an equally valid basis from which to derive safety factors for appraisal. As the partial For the design of ordinary structures for strength (‘the
factors in the two systems are different (although ultimate limit state’), a value of cf3 = 1.2 is implied. the principles are similar), consistent factors from one system should be used throughout to ensure The general equation for design loads:
that the overall factor is adequate. Design load effect = Function [cf1, cf2, cf3 , Effects of characteristic loads] In both British design codes and the Eurocodes,
cf and cm between them cover the seven partial can be re-written in summary, e.g. for BS 8110, as: factors listed in ISO 2394: 1988A10.5. (These seven
partial factors took on a different form in the later Design load effect = (cf1 cf2 G & cf1 cf2 Q & cf1 cf2 W) cf3 ISO 2394: 1998.) where '&' here means 'in combination with'.
The combinations of ultimate limit state (ULS) loading prescribed by BS 8110A10.1 are reproduced in Table A10.1.
Table A10.1 Combinations of ULS loading in BS 8110
Effects of Dead Imposed Wind characteristic load G Q W
Partial load factor cf1 cf2 cf1 cf2 cf1 cf2 cf3 Load combinations Load acting Dead load alone Adversely 1.15 1.0 1.2 Beneficially 0.85 1.0 Dead and imposed load Adversely 1.15 1.0 1.35 1.0 1.2 Beneficially 0.85 1.0 0 1.0 Dead and wind load Adversely 1.15 1.0 1.2 Beneficially 0.85 0.9 Dead, imposed and wind load Adversely 1.15 0.9 1.35 0.75 1.15 0.9 1.2 Beneficially
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A10.2.2 Load variation factor, cf1 therefore may be allowed to fail in less exceptional winds should cf1 be reduced. With the prediction that Dead loads wind speeds may rise in the next decade due to global It is sometimes feasible in buildings to measure weather changes, caution is advisable. structural dimensions and densities accurately so that it may be possible to calculate the weight of Reference should also be made to Section 3.7.8. the structure with an accuracy that will justify the
reduction of the load variation factor cf1 for dead The statistical basis for the snow loads in BS 6399: loads from 1.15 to say 1.05. A possible exception Part 3A10.9 is similar to that for wind in CP3: may be thin slabs, where 1.10 may be appropriate for Chapter V: Part 2A10.10. Except for very short life
thickness of 100mm or less. expectancies for the structure, no reduction of cf1 is justified. Clause 4.4 of the Code points out the If the thickness and density of screeds and partitions importance of considering partial snow loading on
are measured to calculate actual loads, cf1 = 1.05 arched and domed structures. Recent amendments may be appropriate. If screeds and/or partitions are have highlighted the loading from drifting snow
to be renewed the normal design value of cf1 = 1.15 at parapets and steps in roof level; specific should be used. consideration may be necessary.
Imposed loads A10.2.3 Load combination and sensitivity factor, cf2 If proper ‘characteristic’ values were used for imposed
loads there would be little justification for reducingc f1.Q As the considerations that govern this factor are not for separate elements. Reduction factors for multi- affected by the difference between the design of a storey columns, such as those in BS 6399: Part 1A10.6 new structure and the design of an existing structure, should take adequate care of the reduced probability of c remains unaltered for appraisal calculations, unless f2 all floors being fully loaded simultaneously. there is a change of use from the original design.
It is the experience of most engineers that floors are A10.2.4 Structural performance factor, cf3 very rarely subjected to the imposed loads stipulated
by BS 6399: Part 1 and in reference A10.7. Gross The design factor cf3 = 1.2 covers inaccuracies overloading from storage, etc. does however occur of construction, inaccuracies of analysis and the occasionally, particularly on floors originally intended severity of the consequences of failure of the element for dwelling use. The engineer must assess the in the relevant limit state. suitability of floors for their intended use. If measured dimensions, including eccentricities caused Even in situations where BS 6399: Part 1 by building inaccuracy, are used in an assessment loadings, which are deemed to satisfy the Building of an existing structure and realistic or conservative Regulations, do not apply, extensive safeguards assumptions are made about the mechanics of load on the foreseeable future use (as opposed to the transfer, the following values of c could be used: f3 immediately intended use) would be needed before ––cf3 = 1.15 for primary members supporting other contemplating reducing the imposed loads from parts of the structure, and for secondary members the values of the Code. Similar reservations apply failure of which might cause loss of life and/or
to the alternative approach of reducing cf1 since the substantial material damage. probability of exceeding the load usually remains ––cf3 = 1.05 for secondary elements, failure of which the same. In some circumstances it may even be will not lead to disproportionate collapse.
necessary to increase the imposed loads or cf1.
For arched structures and for portal frames, imposed load on part of the span is often more critical than full A10.3 Material factor, cm loading.
A10.1 Liquid pressures in storage tanks can be calculated The factor cm, in BS 8110 and other design as accurately as the weight of the structure provided codes, allows for the probable difference between that denser liquids are excluded from future use. the strength of the material actually in the structure
A combined cf factor of 1.05 may be appropriate if and the strength of the test specimens. It also applied to the pressure corresponding to the highest allows for the variation between different parts of possible head including any dynamic effects. the structure, and for the accuracy of the formulae
used for predicting behaviour. cm therefore varies for Similar considerations might apply to the weight different modes of failure. of existing earth fill but not to lateral earth
pressures. Overloading due to roof gardens does For possible reductions of cm appropriate to each sometimes occur due to the accumulation of soil material, see Chapter 6. and to water logging. If material strengths are measured by tests on BS 6399: Part 2A10.8 wind loads are not ‘characteristic’ an appropriate number of specimens taken from loads but those applied by gusts. It is possible to obtain the actual structural members and these tests, if
an understanding of the physical implications of cf1, necessary, are supplemented by non-destructive however, by multiplying the wind load corresponding tests to assess the variability of the material, a A10.1 to S1 = 1 by cf1 = 1.15, as a result of which a wind reduction of the overall value of cm may be load corresponding to a return period of 140 years justified. For this purpose, the test results should is obtained. This is probably a reasonable ultimate be statistically processed to give a lower 95% value for most buildings. Only for exceptional elements confidence limit (= ‘characteristic strength’) (see or structures that cannot cause injury on failure and Chapter 5).
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The reduction in cm that can be permitted depends A10.9 BS 6399-3: Loading for buildings – Part 2: Code of on how well the failure mechanism is understood, practice for imposed roof loads and on the amount of visual warning of impending failure that can be expected. If the failure will be A10.10 CP3: Chapter V: Part 2: Code of basic data for the ductile and the member is visible and will give design of buildings – Chapter 5: Loading – Part 2: warning by excessive deflection, a significant Wind loads reduction may be acceptable. If the member is hidden and/or the failure will be brittle, little or no reduction should be allowed. A10.6 Bibliography For example, for a visible ‘under-reinforced’ concrete beam it could be reasonable to reduce
cm for bending in concrete from 1.5 to 1.25, or Institution of Structural Engineers. Manual for the design of even to 1.20. For an over-reinforced beam, where building structures to Eurocode 1 and basis of structural design. a beam is hidden by a false ceiling or particularly if London: IStructE, 2010 shear is the governing criterion, it is doubtful if any reduction should be contemplated.
For a secondary member that carries only a limited area of floor, which by its failure would not endanger life or the overall integrity of the structure, a greater reduction of c can be m permitted than for a primary member, which by its failure may kill or injure a large number of persons and/or bring down substantial other parts of the structure.
The engineer should assess the deterioration of the structure to see whether there is even a need to increase the value of c and/or whether it is m necessary to reduce the material’s characteristic strength values.
A10.4 Permissible stresses
When permissible stresses are used for assessment calculations, similar arguments apply to adjusting the permissible working stresses. To do so rationally requires consideration of what proportion of the ratio of applied to permissible
stress (the overall factor) corresponds to cm and what to cf .
A10.5 References
A10.1 B S 8110: Structural use of concrete [3 parts]
A10.2 BS 5628: Code of practice for the use of masonry [3 parts]
A10.3 BS 5950: Structural use of steelwork in building [9 parts]
A10.4 BS 8118: Structural use of aluminium [2 parts]
A10.5 ISO 2394: General principles on reliability for structures
A10.6 BS 6399-1: Loading for buildings – Part 1: Code of practice for dead and imposed loads
A10.7 English Heritage Office floor loading in historic buildings, London, English Heritage, 1994
A10.8 BS 6399-2: Loading for buildings – Part 2: Code of practice for wind loads
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A11.1 I ntroduction must be made fully aware of these uncertainties and their sensitivity to inspection and maintenance procedures. These estimates need regular updating Residual service life appraisal aims to predict the based on inspection and monitoring of the condition future condition of the structure in order to assess of the structure. the need for repair/maintenance actions that will enable the structure to continue to serve its function. The materials in structures can deteriorate due to In other words, it deals with the structure’s ability to corrosion, frost damage, fatigue, rot or physical and/ meet requirements of the ultimate and serviceability or chemical changes (UV degradation of polymers limit states throughout the remainder of its required and sealants, ASR and sulfate attack in concrete, service life, as opposed to its capacity in its present fatigue or hydrogen embrittlement of steel, etc.). condition, which is the concern of most of the rest of Best practice in construction has been to ensure that these Appendices. the environment in a structure maintains materials in uncontaminated conditions of low and stable Knowledge of the present condition is, however, of moisture availability, low temperature range and prime importance because of the information it can low stress range, so that they do not deteriorate provide on the progress and rate of the degradation (Figure A11.1). Materials as unstable as cob or processes which, to a greater or lesser degree, affect wattle and daub have survived for centuries in these all materials and structures. It is a task increasingly conditions. being undertaken within a framework of service life planning and an ongoing maintenance management However, not all structures have been designed, system (MMS) rather than as a one-off check. detailed and/or maintained in accordance with best However, it might also be used as a measure to practice. Some past ‘good practice’, like the use of control financial risk prior to transfer of ownership or Calcium Chloride, HAC, galvanised wall ties etc, is operational responsibility. now known to create severe problems of premature deterioration in adverse conditions. Some structures are Predictions of the residual service life can be carried in severe environments or are exposed to aggressive out assuming a range of remedial works options, so ground conditions. Blocked gutters can trigger that the cost effectiveness of different management corrosion, rot, frost damage and plant growth, to initiate strategies can be compared. This is an essential the deterioration. Where the structure is neglected for a element in developing a ‘Life-Care Plan’ for a long period of time, it may no longer be cost effective to structure. repair the structure, and this will eventually lead to the demolition of the structure. The development of a ‘Life-Care Plan’ for a structure provides: –– early indication of the need for remedial action, allowing a wider range of remedial actions to be considered –– the potential for optimising a maintenance strategy through Life Cycle Costing –– more accurate budget forecasting through advanced notice of the need for expenditure on inspection, maintenance and repair; and –– a basis for minimising disruption to occupants and/or users through better planning, timing and conduct of interventions.
As a broad rule, early intervention to tackle degradation provides the best chance for reducing Figure A11.1(a) Consequences of neglect life cycle costs.
The methodologies for prediction of residual service life are being developed, with associated procedures for ‘Whole Life Costing’. They are still subject to debate and there is considerable research in progressA11.1–A11.6, chiefly in the behaviour of concrete. The severity of deterioration problems with car parks has led to specific recommendationsA11.7 for developing ‘Life-Care Plans’ and detailed studies of deterioration and its consequencesA11.8, A.11.9.
Because of the inherent variability of most construction materials and the variability of conditions to which they are subjected, only broad estimates of Figure A11.1(b) Aftermath of appraisal: timber checked by long-term future performance are possible. Clients bradawl
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The range of materials used and forms of This approach to ‘Structural Severity Rating’ was deterioration found in construction materials are so developed for concrete structures with ASR and diverse that only general principles can be set out has been further developed for other forms of here. Sections 3.8 to 3.19 of this Report discuss concrete deterioration in CONTECVETA11.10. The the conditions which give rise to deterioration and same type of procedure can be followed for other Chapter 6 sets out some of the sensitivities of materials. materials to deterioration. Traditional construction often has large reserves of For some common forms of deterioration, strength, so that the early stages of deterioration specialist guidance, bringing together the results of are of little consequence. With the refinement fundamental research and detailed investigations of of modern design and because few codes deteriorating structures, is available and the more include a strength reserve for deterioration, important are listed as references in Chapters 3 many 20th Century structures are sensitive to and 6. When unusual and/or severe deterioration is even minor deterioration. Careful consideration found, the engineer will need to consult the specialist is required to establish the extent to which literature critically and work with materials science design factors of safety can be allowed to fall (if professionals, so that they understand the particular at all), as deterioration develops, before action processes which are contributing to the loss of is required. This needs to be related to type and strength and serviceability. consequences of failure. (See Appendix 2).
A11.2 Identifying risk of decay and A11.3 E stimating residual service life structural consequences The prediction of service life of the structure can be The investigation of current condition, as set split into: out in this Report, is the essential starting point –– parts where stable conditions to prevent for collecting the much more comprehensive deterioration can be established and maintained information needed for predicting future behaviour. –– parts where, due to the configuration of the In extrapolating from current condition, it must be structure, the exposure conditions and the inherent born in mind that deterioration and strength loss characteristics of the materials, progressive decay are not linear processes with time and that various will develop, creating structural risks. deterioration processes interact. When a breakdown in waterproofing or development of condensation from change of use occurs, deterioration can start rapidly. A11.4 Maintain or re-establish stable conditions The first step in estimating residual service life is to categorise the elements of the structure where decay risk may shorten service life. A11.4.1 Stage 1: Determine stability –M– aterials in conditions which prevent any risk The first stage in residual service life prediction is of deterioration, giving a potentially unlimited to consider the following for each element of the service life. structure. –M– aterials which do not normally deteriorate but are –I– s the current strength and serviceability adequate sensitive to a change in conditions (e.g. leakage for future use? or condensation initiating decay, or corrosion of –C– an stable conditions be maintained or re- connections, in timber or corrosion in carbonated established, so that no significant further concrete). deterioration will occur? –M– aterials whose primary protection is degrading but where no adverse structural effects have If positive answers can be achieved, then started (e.g. galvanising thinning; paint beginning the residual service life is only limited by the to break down; carbonation of damp concrete effectiveness of inspection and maintenance in approaching reinforcement). maintaining stable conditions. For many structures, –M– aterials where deterioration is actively reducing drying-out will provide the best route to stabilising structural effectiveness (e.g. active corrosion of materials to prevent further deterioration. Some reinforcement in concrete leading to spalling; loss broad trends for concrete deterioration are of containment or strength at laps; corrosion of indicated in Figure A11.2. The deterioration rate is steel; decay of timber). expressed as a percentage of that in 100% relative humidity conditions. Temperature will also influence For each material, maintenance and protective deterioration rate. As RH varies within a material measures to prevent the initiation of deterioration and with seasonal changes, deterioration rates will or to slow the rate of deterioration need to be vary, with most deterioration arising during damp identified for consideration in estimating the residual periods. service life and for the inspection and maintenance recommendations. A11.4.2 Stage 2: Determine deterioration rates If stability cannot immediately be achieved the next This risk of decay needs to be related to the questions are: potential risks to the strength and serviceability –C– an local areas of severe deterioration be of the structure. Where decay risk and structural repaired, replaced or upgraded so there is a risk coincide, the consequences of failure and any sufficient reserve of strength and serviceability to surplus reserve of strength need to be identified. make a further period of deterioration acceptable?
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–C– an the rate of further deterioration be reduced to give a sufficient residual service life for the client’s specified needs, defined as a ‘Limit’ to acceptable deterioration: –– in areas of repair and remedial works? 100 –– in areas where deterioration has started but has yet to cause sufficient damage to justify repair Chlorides 80 or pre-emptive measures? AAR Residual service life is usually limited by the 60 Frost performance of a few critical elements where decay risk and structural risk coincide. 40
For these it is necessary to: 20
–– estimate the rate and form of deterioration, with or Detrioration rate (% of 100% RH) without intervention 0 –– determine the effects on strength and serviceability; and 60 70 80 90 100 –– compare this to the acceptable ‘Limit’ in the Relative humidity (%) critical elements, as indicated in Figure A11.3.
For many materials there is a two-stage deterioration process with a loss of protection followed by a decay stage (e.g. loss of zinc on Figure A11.2 Influence of moisture on deterioration rate, for concrete subject to frost, AAR galvanised steel or carbonation of cover concrete or corrosion from chlorides to reinforcement, followed by corrosion). ‘Proactive intervention’ can be applied to improve the primary protection by painting or by anti-carbonation coating to delay the start of corrosion. Remedial measures applied after corrosion has started Intervention: constitute reactive intervention. None The essential difficulty is in predicting rate of deterioration and its consequences for No intervention serviceability and strength. Often deterioration Limit state arises where there was poor construction quality. Reactive The variability of construction quality needs to be Reactive evaluated in the investigation of a structure. This Corrosion of reinforcement intervention variability needs explicit consideration in residual service life prediction. Proactive Proactive For concrete, the Eurocode on concrete repairA11.11 intervention and guides to good practiceA11.12 give the basis for a range of approaches to intervention, remedial works and controlling the rate of further deterioration. Simplified theoretical models for Time predicting the development of carbonation and chloride ingress to initiate corrosion and the subsequent rate of corrosion exist for idealised constant conditions. These models need to be Figure A11.3 Influence of intervention on service life compared and calibrated against the data from the investigation of the structure where environment and construction quality will be highly variable. Comprehensive testing is needed to determine this variability and limited spot checks will not provide the data required for residual service life prediction. Figure A11.4 shows the variability of carbonation depth, cover to reinforcement and spalling after 30 years in 4 typical pours of exposed concrete in a prestige structure. Similar data on variability of chloride ingress and consequent corrosion is availableA11.8, A11.13.
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50
45 Max. carbonation 40
Rebar cover 35
30
25 Depth of reinforcement cover and carbonation (mm) 20
15
10
5
0 Pour 1 Pour 2 Pour 3 Pour 4 Spalls Spalls No spalls Severe spalls
Figure A11.4 Spalling relative to variation in carbonation and cover depth for four pours on one structure
A11.5 R eferences A11.8 Henderson, N.A, Johnson, R.A. and Wood, J.G.M. Enhancing the whole life cycle structural performance of multi-storey car parks. Available at: http://www. A11.1 Somerville, G. The Design life of structures. Glasgow: planningportal.gov.uk/uploads/odpm/4000000009277. Blackie, 1991 pdf [Accessed: 2 November 2009]
A11.2 Glanville, J. and Neville, A.M. eds. Prediction of concrete A11.9 Wood, J.G.M. ‘Pipers Row car park collapse: identifying durability: proceedings of STATS 21st anniversary risk’. Concrete, 37(9), October 2003, pp29-31 conference. London: E. & F.N. Spon, 1997 A11.10 GEOCISA and Torroja Institute. CONTECVET: a validated A11.3 ISO 13822: 2001: Bases for design of structures – users manual for assessing the residual service life of Assessment of existing structures. Geneva: ISO, 2001 concrete structures. Manual for assessing corrosion- affected concrete structures. Available at: http:// A11.4 ISO 15686: Buildings and constructed assets – Service life www.ietcc.csic.es/fileadmin/Ficheros_IETcc/Web/ planning [9 parts] EventosPublicaciones/PublicacionesElectronicas/ manual_ingles.pdf [Accessed: 2 November 2009] A11.5 Cairns, J., Du, Y. and Law, D.W. ‘Structural assessment of corrosion damaged bridges’, Structural Faults and Repair A11.11 BS EN 1504: Products and systems for the protection 2003. Edinburgh: Engineering Technics Press, 2003 and repair of concrete structures [9 parts]
A11.6 Frangopol, D.M. et al. ‘Bridge management based on A11.12 Pullar-Strecker, P. Concrete reinforcement corrosion: lifetime reliability and whole life costing’. In Ryall, M.J. from assessment to repair decisions. ICE Design and and other eds. Bridge Management 4: inspection, Practice Guide. London: Thomas Telford, 2002 maintenance, assessment and repair. London: Thomas Telford, 2000, pp392-399 A11.13 Wood, J.G.M. and Crerar, J. ‘Analysis of chloride ingress variability and prediction of long term deterioration: a A11.7 National Steering Committee for the Inspection of Multi review of data for the Tay Road Bridge’. In Forde, M.C. Storey Car Parks. Recommendations for the inspection, ed. Structural faults and repair 95. Vol 1: Extending the maintenance and management of car park structures. life of bridges. Edinburgh: Engineering Technics Press, London: Thomas Telford, 2002 1995, pp41-46
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A11.6 D etailed investigations of deterioration GEOCISA and Torroja Institute. CONTECVET: a validated users manual for assessing the residual service life of concrete structures. Manual for assessing corrosion-affected Harrison, H. and other eds. Non-traditional houses: identifying concrete structures. Available at: http://www.ietcc.csic. non-traditional houses in the UK 1918-75. BRE Report BR469. es/fileadmin/Ficheros_IETcc/Web/EventosPublicaciones/ Garston: BRE Bookshop, 2004 PublicacionesElectronicas/manual_ingles.pdf [Accessed: 2 November 2009] Wood, J.G.M. Pipers Row Car Park, Wolverhampton: quantitative study of the causes of the partial collapse on 20th March 1997. ISO 13822: 2001: Bases for design of structures – Assessment Available at: http://www.hse.gov.uk/research/misc/pipersrow.htm of existing structures. Geneva: ISO, 2001 [Accessed: 2 November 2009] ISO 15686: Buildings and constructed assets – Service life Wood, J.G.M. ‘Pipers Row Car Park collapse: identifying planning [several parts] risk. Some lessons on the appraisal, inspection and repair of deteriorating concrete’. In Forde, M.C. Structural faults and repair Law, D. et al. ‘Measurement of Loss of Steel from Reinforcing 2003. Edinburgh: Engineering Technics Press, 2003 Bars in Concrete Using Linear Polarisation Resistance Measurements’. NDT & E International, 37(5), July 2004, Wood, J.G.M. and Johnson, R.A. ‘The Appraisal and maintenance pp381-388 of structures with alkali silica reaction’. The Structural Engineer, 71(2), 19 January 1993, pp19-23 NIST. BridgeLCC: life-cycle costing software for preliminary bridge design. Version 2.0. Available at: http://www.bfrl.nist.gov/ bridgelcc/download.html [Accessed: 2 November 2009]
A11.7 Bibliography Roberts, M.B. et al. ‘A Proposed empirical corrosion model for reinforced concrete’. ICE Proceedings, Structures and Buildings, 140(1), Feb 2000, pp1-11 Alonso, C. et al. ‘Chloride threshold to depassivate reinforcing bars embedded in a standardised OPC mortar. Cement and Sarja, A. and Vesikari, E. eds. Durability design of concrete Concrete Research, 30(7), July 2000, pp1047-1055 structures. RILEM Report Series 14. London: E. & F.N. Spon, 1996
Anderson, H. ed. Diagnosis and assessment of concrete Schiessl, P. Durable concrete structures. Comité Euro-International structures. CEB Bulletin 192. Lausanne: CEB, 1989 du Béton (CEB) Design Guide. CEB Bulletin 182. 2nd ed. Lausanne: CEB, 1989 ASTM E 917-05. Standard practice for measuring life-cycle costs of buildings and building systems. West Conshohocken, PA: Schiessl, P. New approach to durability design: an example for ASTM, 2005 carbonation induced corrosion. CEB Bulletin 238. Lausanne: CEB, 1997 BS EN 206-1: 2000: Concrete – Part 1: Specification, performance, production and conformity. London: BSI, 2001 Söderqvist, M-K., Veijola, M. ‘Finnish Project Level Bridge Management System. Proceedings of the TRB International Cady, P.D. et al. Condition evaluation of concrete bridges relative Bridge Management Conference, Denver Colorado, 26-28 April to reinforcement corrosion. Vol 2: Method for measuring the 1999. Available at: http://onlinepubs.trb.org/onlinepubs/circulars/ corrosion rate of steel in concrete. SHRP-S-324. Washington, DC: circ498/v2_F05.pdf [Accessed: 2 November 2009] National Research Council, 1992 Soderqvist, M-K.and Vesikari, E. Generic Technical Handbook Cairns, J. and Law, D. ‘Prediction of the ultimate limit state of for a Predictive Life Cycle Management System of Concrete degradation of concrete structures’. Proceedings of the 2nd Structures (LMS). LIFECON deliverable D 1.1. Available at: http:// International Symposium on Integrated Life-time Engineering of lifecon.vtt.fi/d11.pdf [Accessed: 2 November 2009] Buildings and Civil Infrastructures, Kuopio, Finland, December 2003. Helsinki: VTT Technical Research Centre of Finland, 2003, Thompson, P.D. et al. ‘The Pontis bridge management system’. pp169-174 Structural Engineering International, 4, 1998, pp303-308
Concrete Corrosion Inhibitors Association. LIFE-365: software for Wood, J.G.M. FICK2ND user manual: fitting chloride ingress data service life and life-cycle cost calculation. Version 2.0. Available to a Fick’s 2nd law diffusion curve. Godalming: Structural Studies at: http://www.corrosioninhibitors.org/life365intro.htm [Accessed: & Design, 1995 2 November 2009] The following series of Conferences contain many DuraCrete. Brite EuRam III Project BE95-1347. Report R3: Models papers on deterioration of and remedial works to for Environmental Actions on Concrete Structures. 1999 deteriorating and damaged structures.
DuraCrete. Brite EuRam III Project BE95-1347. Report R4-5: Structural faults and repair conferences. See http://www. Modelling of degradation. 1998 structuralfaultsandrepair.com [Accessed: 1 November 2009]
Fédération Internationale du Béton. Management, maintenance The series of biennial conferences on concrete organised by the and strengthening of concrete structures. FIB Bulletin 17. Concrete Technology Unit of the University of Dundee. See http:// Lausanne: FIB, 2002 www.ctucongress.co.uk [Accessed: 2 November 2009]
The series of international conferences on bridge management organised by the University of Surrey
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