Holmes Structural Engineering “A fine text for a wind engineering course… A must for any wind engineer’s library. –Leighton Cochran, consulting engineer “The first book I recommend to the many customers I have who—as practicing structural engineers Wind not wind engineers—are in need of a comprehensive yet understandable reference text.” –Daryl Boggs, CPP, Inc Wind Loading of Structures “I highly recommend this book by Dr John Holmes for use in graduate and senior undergraduate studies, structural engineering design against wind actions, and other professional design Loading of practices.” –Kenny Kwok, University of Western Sydney Wind forces from various types of extreme wind events continue to generate ever-increasing damage to buildings and other structures. The third edition of this well-established book fills an Structures important gap as an information source for practising and academic engineers alike, explaining the principles of wind loads on structures, including the relevant aspects of meteorology, bluff- body aerodynamics, probability and statistics, and structural dynamics. Among the unique features of the book are its broad view of the major international codes and Third Edition standards, and information on the extreme wind climates of a large number of countries of the world. It is directed towards practising (particularly structural) engineers, and academics and graduate students. The main changes from the earlier editions are: • Discussion of potential global warming effects on extreme events • More discussion of tornados and tornado-generated damage • A rational approach to gust durations for structural design • Expanded considerations of wind-induced fatigue damage • Consideration of Aeolian vibrations of suspended transmission lines • Expansion of the sections on the cross-wind response of tall slender structures • Simplified approaches to wind loads on “porous” industrial, mining, and oil/gas structures • A more general discussion of formats in wind codes and standards John Holmes draws on 40 years of international experience in research, teaching, and consulting Edition Third on the wind loading of structures; has acted as an expert witness in several legal actions; and has been a radio and television commentator after severe wind events. John D. Holmes K22609 6000 Broken Sound Parkway, NW Suite 300, Boca Raton, FL 33487 ISBN: 978-1-4822-2919-6 711 Third Avenue 90000 an informa business New York, NY 10017 2 Park Square, Milton Park www.crcpress.com Abingdon, Oxon OX14 4RN, UK 9 781482 229196 www.sponpress.com A SPON PRESS BOOK K22609 mech-rev.indd 1 12/18/14 8:52 AM Wind Loading of Structures Third Edition Wind Loading of Structures Third Edition John D. Holmes JDH Consulting, Australia A SPON PRESS BOOK CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2015 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Version Date: 20141205 International Standard Book Number-13: 978-1-4822-2922-6 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. 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Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Contents Preface to the first edition xv Preface to the second edition xvii Preface to the third edition xix Author xxi 1 The nature of wind storms and wind-induced damage 1 1.1 Introduction 1 1.2 Meteorological aspects 1 1.2.1 Pressure gradient 2 1.2.2 Coriolis force 2 1.2.3 Geostrophic wind 4 1.2.4 Gradient wind 4 1.2.5 Frictional effects 5 1.3 Types of wind storms 6 1.3.1 Gales from large depressions 6 1.3.2 Tropical cyclones 7 1.3.3 Thunderstorms 10 1.3.4 Tornadoes 11 1.3.5 Downbursts 12 1.3.6 Downslope winds 13 1.4 Wind damage 13 1.4.1 Recent history of wind loss and damage 15 1.5 Wind-generated debris 17 1.5.1 Threshold of flight 17 1.5.2 Trajectories of compact objects 19 1.5.3 Trajectories of sheet and rod objects 20 1.5.4 Standardised missile-testing criteria 21 1.6 Wind storm damage and loss prediction 22 1.6.1 Hazard models 22 1.6.2 Vulnerability curves 23 1.6.3 Damage produced by flying debris 25 1.7 Hurricane-damage modelling 27 1.8 Predicted effects of climate change 28 1.9 Summary 28 v vi Contents 1.10 The following chapters and appendices 29 References 29 2 Prediction of design wind speeds and structural safety 33 2.1 Introduction and historical background 33 2.2 Principles of extreme value analysis 34 2.2.1 The GEV Distribution 34 2.2.2 Return period 35 2.2.3 Separation by storm type 35 2.2.4 Simulation methods for tropical cyclone wind speeds 36 2.2.5 Compositing data from several stations 36 2.2.6 Correction for gust duration 36 2.2.7 Wind direction effects and wind direction multipliers 37 2.3 Extreme wind estimation by the Type I Distribution 39 2.3.1 Gumbel’s method 39 2.3.2 Gringorten’s method 40 2.3.3 Method of Moments 40 2.3.4 Example of fitting the Type I Distribution to annual maxima 41 2.3.5 General penultimate distribution 41 2.4 The peaks-over-threshold approach 45 2.4.1 Example of the use of the ‘peaks over threshold’ method 46 2.4.2 Extreme winds by direction sector 48 2.5 Parent wind distributions 48 2.6 Wind loads and structural safety 49 2.6.1 Limit states design 50 2.6.2 Probability of failure and the safety index 50 2.6.3 Nominal return period for design wind speeds 52 2.6.4 Uncertainties in wind load specifications 53 2.7 Wind load factors 54 2.8 Summary 55 References 55 3 Strong wind characteristics and turbulence 57 3.1 Introduction 57 3.2 Mean wind speed profiles 58 3.2.1 The ‘Logarithmic Law’ 58 3.2.2 The ‘Power Law’ 60 3.2.3 Mean wind profiles over the ocean 60 3.2.4 Relationship between upper level and surface winds 62 3.2.5 Mean wind profiles in tropical cyclones 62 3.2.6 Wind profiles in thunderstorm winds 63 3.2.7 Wind profiles in tornadoes 63 3.3 Turbulence 64 3.3.1 Turbulence intensities 65 3.3.2 Probability density 66 Contents vii 3.3.3 Gust wind speeds and gust factors 67 3.3.4 Wind spectra 69 3.3.5 Correlation 70 3.3.6 Co-spectrum and coherence 71 3.3.7 Turbulence in a downdraft 72 3.4 Modification of wind flow by topography 73 3.4.1 General effects of topography 74 3.4.2 Topographic multipliers 75 3.4.3 Shallow hills 75 3.4.4 Steep hills, cliffs and escarpments 76 3.4.5 Effect of topography on tropical cyclones and thunderstorm winds 77 3.5 Change of terrain 78 3.6 Weakening of a tropical cyclone after a coast crossing 79 3.7 Other sources 80 3.8 Summary 80 References 81 4 Basic bluff-body aerodynamics 83 4.1 Flow around bluff bodies 83 4.2 Pressure and force coefficients 83 4.2.1 Bernoulli’s equation 83 4.2.2 Force coefficients 85 4.2.3 Dependence of pressure and force coefficients 85 4.2.4 Reynolds Number 86 4.3 Flat plates and walls 87 4.3.1 Flat plates and walls normal to the flow 87 4.3.2 Flat plates and walls inclined to the flow 90 4.4 Rectangular prismatic shapes 92 4.4.1 Drag on two-dimensional rectangular prismatic shapes 92 4.4.2 Effect of aspect ratio 92 4.4.3 Effect of turbulence 93 4.4.4 Drag and pressures on a cube and finite-height prisms 95 4.4.5 Jensen number 97 4.5 Circular cylinders 97 4.5.1 Effects of Reynolds Number and surface roughness 97 4.5.2 Effect of aspect ratio 101 4.6 Fluctuating forces and pressures 102 4.6.1 Introduction 102 4.6.2 The Quasi-steady assumption 102 4.6.3 Body-induced pressure fluctuations and vortex-shedding forces 103 4.6.4 Fluctuating pressure and force coefficients 105 4.6.5 Correlation length 107 4.6.6 Total fluctuating forces on a slender body 108 4.7 Summary 110 References 111 viii Contents 5 Resonant dynamic response and effective static load distributions 113 5.1 Introduction 113 5.2 Principles of dynamic response 113 5.3 The random vibration or spectral approach 116 5.3.1 Along-wind response of a single-degree-of-freedom structure 118 5.3.2 Gust response factor 121 5.3.3 Peak factor 122 5.3.4 Dynamic response factor 122 5.3.5