Volume 3 Inspection and Maintenance Section 2 Maintenance
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DESIGN MANUAL FOR ROADS AND BRIDGES VOLUME 3 INSPECTION AND MAINTENANCE SECTION 2 MAINTENANCE PART 5 BD 54/15 MANAGEMENT OF POST-TENSIONED CONCRETE BRIDGES SUMMARY This standard provides the requirements and guidance for the management of post-tensioned concrete bridges. It implements a risk based approach to management and includes advice on Special Inspections, monitoring, repairs and strengthening. INSTRUCTIONS FOR USE 1. Remove existing contents pages for Volume 3 and insert new Contents pges for Volume 3 dated February 2015 2. Remove BD 54/93 from Volume 3, Section 1, which is superseded by BD 54/15 and archive as appropriate. 3. Insert BD 54/15 into Volume 3, Section 2 after Part 4. 4. Archive this sheet as appropriate. Note: A quarterly index with a full set of Volume Contents Pages is available separately from The Stationery Office Ltd. February 2015 DESIGN MANUAL FOR ROADS AND BRIDGES BD 54/15 THE HIGHWAYS AGENCY Volume 3, Section 2, Part 5 TRANSPORT SCOTLAND LLYWODRAETH CYMRU WELSH GOVERNMENT THE DEPARTMENT FOR REGIONAL DEVELOPMENT NORTHERN IRELAND Management of post-tensioned concrete bridges Summary: This standard provides the requirements and guidance for the management of post-tensioned concrete bridges. It implements a risk based approach to management and includes advice on Special Inspections, monitoring, repairs and strengthening. Volume 3 Section 2 Part 5 BD 54/15 Register of amendments REGISTER OF AMENDMENTS Amend No Page No Signature & Date of incorporation Amend No Page No Signature & Date of incorporation of amendments of amendments February 2015 Volume 3 Section 2 Register of amendments Part 5 BD 54/15 REGISTER OF AMENDMENTS Amend No Page No Signature & Date of incorporation Amend No Page No Signature & Date of incorporation of amendments of amendments February 2015 DESIGN MANUAL FOR ROADS AND BRIDGES VOLUME 3 INSPECTION AND MAINTENANCE SECTION 2 MAINTENANCE PART 5 BD 54/15 MANAGEMENT OF POST-TENSIONED CONCRETE BRIDGES Contents Chapter 1 Introduction 2 Risk Review 3 Risk Assessment 4 Risk Management 5 PTSI – Organisation 6 PTSI – Site Inspection 7 PTSI – Site Investigation 8 Monitoring 9 Repair 10 Strengthening 11 Normative References 12 Informative References 13 Enquiries Annexes A Example Risk Assessment Report B Case Studies C Advice on severe localized corrosion (crevice corrosion) D List of TPB Contributing Organisations February 2015 Volume 3 Section 2 Chapter 1 Part 5 BD 54/15 Introduction 1. INTRODUCTION Background 1.1 Generally post-tensioned concrete bridges give good service and few have significant problems. However, they are particularly vulnerable to corrosion and severe deterioration where internal grouting of tendon ducts is incomplete and moist air, water or de-icing salts can enter the ducting system. The ingress of water and salts into tendon ducts is most likely at joints in segmental construction, other construction joints, at anchorages and over intermediate supports when the deck is continuous. 1.2 A programme of Post-tensioned Concrete Bridge Special Inspections (PTSI) undertaken in the UK in the 1990s showed that the condition of the post-tensioning system in most cases was satisfactory although many contained voids in the ducts and light corrosion of tendons. A small number were less satisfactory and needed repair work. Others are likely to need attention in the future (Woodward R, 2001). 1.3 Since the 1990s PTSI programme Overseeing Organisations have tended to rely on the principal and general inspection programme to identify signs of deterioration. Experience has shown that it is the construction detail and practices that are of the greatest significance in affecting deterioration of post- tensioned concrete bridges. However, these inspections do not identify the internal conditions of the post- tensioning system so as time elapses beyond the original PTSI, the level of uncertainty about the internal condition of tendons increases. Whereas for most forms of construction, defects tend to be relatively easy to interpret and result in ductile modes of failure, safety critical defects in post-tensioned concrete are typically hidden, very difficult to detect and may result in a brittle mode of failure.The primary problem with PT bridges which sets them apart from other types is the difficulty of establishing the internal condition of the tendons because outward signs of distress are not generally expected to occur. For this reason the most vulnerable bridges need monitoring and reinspection after an appropriate interval. Visual inspection methods alone cannot give warning of imminent collapse and internal inspections can be expensive and potentially damaging for the structure and should only be carried out if there is a clear need. It is essential that a combination of techniques and procedures be adopted as part of a system of risk assessment and risk management, to assist bridge managers in decisions as to when to undertake further intrusive investigations and when to use other risk management measures. 1.4 This document provides a process of risk review, risk assessment and risk management for post-tensioned concrete bridges with advice on the activities that may be needed for the successful risk management of post-tensioned concrete bridges. 1.5 This standard supersedes BD 54/93, BA 50/93 and BA 43/94, which are hereby withdrawn. Scope 1.6 This standard is applicable to the management of post-tensioned concrete bridges that are the responsibility of the Overseeing Organisations. The scope includes bridges, any parts of which have been constructed using post-tensioning techniques in which tendons (bars, single strands or multi-strands) are tensioned so as to apply a compressive force to pre-cast concrete or hardened in situ concrete elements. The tendons could be in ungrouted, grouted or greased internal or external ducts, or otherwise protected (eg concrete or mortar surround), or unprotected. The tendons could be in longitudinal, transverse, secondary, vertical or tie down members. February 2015 1/1 Chapter 1 Volume 3 Section 2 Introduction Part 5 BD 54/15 Purpose 1.7 This purpose of this standard is to set out the requirements and advice for risk review, risk assessment and risk management, special inspections, repair, strengthening and monitoring of post-tensioned concrete bridges that are the responsibility of the Overseeing Organisations. Mandatory Sections 1.8 Sections of this document containing mandatory requirements are identified by being contained in boxes. These requirements must be complied with or a prior agreement to a Departure from Standard must be obtained from the Overseeing Organisation. The text outside boxes contains advice and explanation, which is commended to users for consideration. Mutual Recognition 1.9 The requirements and guidance in this document are given on the basis that construction and/or maintenance of post-tensioned concrete bridges will be carried out using the Specification for Highway Works (MCHW Vol.1). However, products conforming to equivalent standards and specifications of other member states of the European Union and tests undertaken in other member states may be acceptable in accordance with the terms of the 104 and 105 Series of Clauses of that Specification. Devolved Administration Issues 1.10 Not Applicable. Implementation 1.11 This Standard must be used forthwith on all projects for the assessment, design, construction, operation and maintenance of motorway and all-purpose trunk roads (and all roads in Northern Ireland) except where procurement of works has reached a stage at which, in the opinion of the Overseeing Organisation, its use would result in significant additional expense or delay progress (in which case the decision must be recorded in accordance with the procedure required by the Overseeing Organisation). Personnel 1.12 The person responsible for overseeing Risk Review, Risk Assessment and PTSI must have specialist experience of post-tensioned bridge design and construction methods, and have proven and demonstrable wide experience of post-tensioned bridge management, inspection, testing and monitoring procedures. 1/2 February 2015 Volume 3 Section 2 Chapter 1 Part 5 BD 54/15 Introduction Definitions and Abbreviations 1.13 For the purpose of this standard, the following definitions apply: Maintaining Organisation – The organisation appointed by the Overseeing Organisation to manage highway assets on its behalf. PTSI Site Inspection – A visual inspection of a bridge in accordance with Chapter 6 of this standard. PTSI Site Investigation – A detailed investigation of a bridge involving, external examination, materials testing, NDT and internal examination, in accordance with Chapter 7 of this standard. Project Manager – The person appointed by the Maintaining Organisation to manage a PTSI in accordance with paras 1.12 and 5.4. Risk Review – an examination of a previous risk assessment and other information with the objective of identifying the need for further risk assessment, in accordance with Chapter 2 of this standard. Risk Review Report – A report on the Risk Review as defined in paras 2.18 to 2.22. Risk Assessment – the identification of hazards, risk events, likelihood, consequences, risk level and Risk Rating in accordance with Chapter 3 of this standard. Risk Assessment Report – A report on the Risk Assessment as defined in para 3.36. Risk Management – The use of various measures to mitigate or remove identified risks in accordance with Chapter 4 of this standard. Risk Management Plan – The application of a set of Risk Management measures to an individual structure. 1.14 The following abbreviations are used in this standard: AADT – Annual Average Daily Traffic ALL – Assessment Live Load ASR – Alkali Silica Reaction NDT – Non-Destructive Testing PTSI – Post-Tensioned concrete bridge Special Inspection SA – Sulfate Attack February 2015 1/3 Chapter 1 Volume 3 Section 2 Introduction Part 5 BD 54/15 1/4 February 2015 Volume 3 Section 2 Chapter 2 Part 5 BD 54/15 Risk Review 2. RISK REVIEW General 2.1 An ongoing system of Risk Review, Risk Assessment and Risk Management will be used to provide assurance on the safety of the stock of post-tensioned concrete bridges.