A SPON PRESS BOOK

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vContents

Preface to the rst edition xvPreface to the second edition xviiPreface to the third edition xixAuthor xxi

1 T he nture of wind stors nd wind-indued dge 1

1.1 Introduction 11.2 Meteorological aspects 1

1.2.1 Pressure gradient 21.2.2 Coriolis force 21.2.3 Geostrophic wind 41.2.4 G radient wind 41.2.5 Frictional effects 5

1.3 Types of wind storms 61.3.1 Gales from large depressions 61.3.2 Tropical cyclones 71.3.3 Thunderstorms 101.3.4 Tornadoes 111.3.5 Downbursts 121.3.6 Downslope winds 13

1.4 Wind damage 131.4.1 Recent history of wind loss and damage 15

1.5 Wind-generated debris 171.5.1 Threshold of ight 171.5.2 Trajectories of compact objects 191.5.3 Trajectories of sheet and rod objects 201.5.4 Standardised missile-testing criteria 21

1.6 Wind storm damage and loss prediction 221.6.1 H azard models 221.6.2 Vulnerability curves 231.6.3 Damage produced by ying debris 25

1.7 Hurricane-damage modelling 271.8 Predicted effects of climate change 281.9 Summary 28

vi Contents

1.10 The following chapters and appendices 29References 29

2 Predition of design wind speeds nd struturl sfety 33

2.1 Introduction and historical background 332.2 Principles of extreme value analysis 34

2.2.1 The GEV Distribution 342.2.2 Return period 352.2.3 Separation by storm type 352.2.4 Simulation methods for tropical cyclone wind speeds 362.2.5 Compositing data from several stations 362.2.6 Correction for gust duration 362.2.7 Wind direction effects and wind direction multipliers 37

2.3 Extreme wind estimation by the Type I D istribution 392.3.1 G umbels method 392.3.2 G ringortens method 402.3.3 Method of Moments 402.3.4 Example of tting the Type I D istribution to annual maxima 412.3.5 General penultimate distribution 41

2.4 The peaks-over-threshold approach 452.4.1 Example of the use of the peaks over threshold method 462.4.2 Extreme winds by direction sector 48

2.5 Parent wind distributions 482.6 Wind loads and structural safety 49

2.6.1 Limit states design 502.6.2 Probability of failure and the safety index 502.6.3 Nominal return period for design wind speeds 522.6.4 Uncertainties in wind load specications 53

2.7 Wind load factors 542.8 Summary 55References 55

3 Strong wind hrteristis nd turbulene 57

3.1 Introduction 573.2 Mean wind speed proles 58

3.2.1 The Logarithmic Law 583.2.2 The Power Law 603.2.3 Mean wind proles over the ocean 603.2.4 Relationship between upper level and surface winds 623.2.5 Mean wind proles in tropical cyclones 623.2.6 Wind proles in thunderstorm winds 633.2.7 Wind proles in tornadoes 63

3.3 Turbulence 643.3.1 Turbulence intensities 653.3.2 Probability density 66

Contents vii

3.3.3 G ust wind speeds and gust factors 673.3.4 Wind spectra 693.3.5 Correlation 703.3.6 Co-spectrum and coherence 713.3.7 Turbulence in a downdraft 72

3.4 Modication of wind ow by topography 733.4.1 General effects of topography 743.4.2 Topographic multipliers 753.4.3 Shallow hills 753.4.4 Steep hills, cliffs and escarpments 763.4.5 Effect of topography on tropical cyclones andthunderstormwinds 77

3.5 Change of terrain 783.6 Weakening of a tropical cyclone after a coast crossing 793.7 O ther sources 803.8 Summary 80References 81

4 Bsi bluff-body erodynis 83

4.1 Flow around bluff bodies 834.2 Pressure and force coefcients 83

4.2.1 Bernoullis equation 834.2.2 Force coefcients 854.2.3 Dependence of pressure and force coefcients 854.2.4 Reynolds Number 86

4.3 Flat plates and walls 874.3.1 Flat plates and walls normal to the ow 874.3.2 Flat plates and walls inclined to the ow 90

4.4 Rectangular prismatic shapes 924.4.1 D rag on two-dimensional rectangular prismatic shapes 924.4.2 Effect of aspect ratio 924.4.3 Effect of turbulence 934.4.4 D rag and pressures on a cube and nite-height prisms 954.4.5 Jensen Number 97

4.5 Circular cylinders 974.5.1 Effects of Reynolds Number and surface roughness 974.5.2 Effect of aspect ratio 101

4.6 Fluctuating forces and pressures 1024.6.1 Introduction 1024.6.2 The Q uasi-steady assumption 1024.6.3 Body-induced pressure uctuations andvortex-sheddingforces 1034.6.4 Fluctuating pressure and force coefcients 1054.6.5 Correlation length 1074.6.6 Total uctuating forces on a slender body 108

4.7 Summary 110References 111