DESIGNERS’ GUIDES TO THE EUROCODES

DESIGNERS’ GUIDE TO EN 1991-1-4 EUROCODE 1: ACTIONS ON STRUCTURES, GENERAL ACTIONS PART 1–4: WIND ACTIONS

Eurocode Designers’ Guide Series Designers’ Guide to EN 1990. Eurocode: Basis of Structural Design. H. Gulvanessian, J.-A. Calgaro and M. Holicky´. 0 7277 3011 8. Published 2002. Designers’ Guide to EN 1994-1-1. Eurocode 4: Design of Composite Steel and Concrete Structures. Part 1.1: General Rules and Rules for Buildings. R. P. Johnson and D. Anderson. 0 7277 3151 3. Published 2004. Designers’ Guide to EN 1997-1. Eurocode 7: Geotechnical Design – General Rules. R. Frank, C. Bauduin, R. Driscoll, M. Kavvadas, N. Krebs Ovesen, T. Orr and B. Schuppener. 0 7277 3154 8. Published 2004. Designers’ Guide to EN 1993-1-1. Eurocode 3: Design of Steel Structures. General Rules and Rules for Buildings. L. Gardner and D. Nethercot. 0 7277 3163 7. Published 2004. Designers’ Guide to EN 1992-1-1 and EN 1992-1-2. Eurocode 2: Design of Concrete Structures. General Rules and Rules for Buildings and Structural Fire Design. A. W. Beeby and R. S. Narayanan. 0 7277 3105 X. Published 2005. Designers’ Guide to EN 1998-1 and EN 1998-5. Eurocode 8: Design of Structures for Earthquake Resistance. General Rules, Seismic Actions, Design Rules for Buildings, Foundations and Retaining Structures. M. Fardis, E. Carvalho, A. Elnashai, E. Faccioli, P. Pinto and A. Plumier. 0 7277 3348 6. Published 2005. Designers’ Guide to EN 1995-1-1. Eurocode 5: Design of Timber Structures. Common Rules and for Rules and Buildings. C. Mettem. 0 7277 3162 9. Forthcoming: 2007 (provisional). Designers’ Guide to EN 1991-4. Eurocode 1: Actions on Structures. Wind Actions. N. Cook. 0 7277 3152 1. Forthcoming: 2007 (provisional). Designers’ Guide to EN 1996. Eurocode 6: Part 1.1: Design of Masonry Structures. J. Morton. 0 7277 3155 6. Forthcoming: 2007 (provisional). Designers’ Guide to EN 1991-1-2, 1992-1-2, 1993-1-2 and EN 1994-1-2. Eurocode 1: Actions on Structures. Eurocode 3: Design of Steel Structures. Eurocode 4: Design of Composite Steel and Concrete Structures. Fire Engineering (Actions on Steel and Composite Structures). Y. Wang, C. Bailey, T. Lennon and D. Moore. 0 7277 3157 2. Forthcoming: 2007 (provisional). Designers’ Guide to EN 1993-2. Eurocode 3: Design of Steel Structures. Bridges. C. R. Hendy and C. J. Murphy. 0 7277 3160 2. Forthcoming: 2007 (provisional). Designers’ Guide to EN 1991-2, 1991-1-1, 1991-1-3 and 1991-1-5 to 1-7. Eurocode 1: Actions on Structures. Traffic Loads and Other Actions on Bridges. J.-A. Calgaro, M. Tschumi, H. Gulvanessian and N. Shetty. 0 7277 3156 4. Forthcoming: 2007 (provisional). Designers’ Guide to EN 1991-1-1, EN 1991-1-3 and 1991-1-5 to 1-7. Eurocode 1: Actions on Structures. General Rules and Actions on Buildings (not Wind). H. Gulvanessian, J.-A. Calgaro, P. Formichi and G. Harding. 0 7277 3158 0. Forthcoming: 2007 (provisional). Designers’ Guide to EN 1994-2. Eurocode 4: Design of Composite Steel and Concrete Structures. Part 2: General Rules and Rules for Bridges. C. R. Hendy and R. P. Johnson. 07277 3161 0. Published 2006.

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DESIGNERS’ GUIDES TO THE EUROCODES

DESIGNERS’ GUIDE TO EN 1991-1-4 EUROCODE 1: ACTIONS ON STRUCTURES, GENERAL ACTIONS PART 1–4: WIND ACTIONS

N. COOK

Published by Thomas Telford Publishing, Thomas Telford Ltd, 1 Heron Quay, London E14 4JD URL: http://www.thomastelford.com

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First published 2007

Eurocodes Expert Structural Eurocodes offer the opportunity of harmonized design standards for the European construction market and the rest of the world. To achieve this, the construction industry needs to become acquainted with the Eurocodes so that the maximum advantage can be taken of these opportunities Eurocodes Expert is a new ICE and Thomas Telford initiative set up to assist in creating a greater awareness of the impact and implementation of the Eurocodes within the UK construction industry Eurocodes Expert provides a range of products and services to aid and support the transition to Eurocodes. For comprehensive and useful information on the adoption of the Eurocodes and their implementation process please visit our website or email [email protected]

A catalogue record for this book is available from the British Library ISBN: 978-0-7277-3152-4

# The authors and Thomas Telford Limited 2007

All rights, including translation, reserved. Except as permitted by the Copyright, Designs and Patents Act 1988, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior written permission of the Publishing Director, Thomas Telford Publishing, Thomas Telford Ltd, 1 Heron Quay, London E14 4JD. This book is published on the understanding that the author is solely responsible for the statements made and opinions expressed in it and that its publication does not necessarily imply that such statements and/or opinions are or reflect the views or opinions of the publishers. While every effort has been made to ensure that the statements made and the opinions expressed in this publication provide a safe and accurate guide, no liability or responsibility can be accepted in this respect by the author or publishers.

Typeset by Academic þ Technical, Bristol Printed and bound in Great Britain by MPG Books, Bodmin

Preface EN 1991-1-4, Eurocode 1: Actions on Structures – General Actions – Part 1–4: Wind Actions, is the head code for wind actions on structures and describes the principles and requirements for calculating design wind loads on structures. It complies with the requirements of Eurocode EN 1990, Eurocode: Basis of Structural Design, and provides the wind actions necessary to implement the structural design Eurocodes 2 to 9.

Aims and objectives of this guide The principal aim of this book is to provide the user with guidance on the interpretation and use of EN 1991, Eurocode 1: Actions on Structures – General Actions – Part 1–4: Wind Actions, and on the expected changes that will be introduced by the associated National Annexes. In particular, the opportunity has been taken to add a commentary on the changes introduced in the UK National Annex (Draft for public comment). Some of the remaining issues with the UK NAD may be resolved before publication.

Layout of this guide EN 1991-1-4 has a foreword and eight sections together with six annexes. Chapters 1 to 8 of this guide correspond to the eight sections of EN 1991-1-4. The numbering sequence of these chapters mirrors the clause numbers of the EN. Chapter 9 corresponds to the six annexes. In addition, the relevant clause numbers of EN 1991-1-4 and of the UK National Annex appear in the margins against the corresponding commentary. Text which has been directly reproduced from the EN is set in italics. Expressions and figures repeated from EN 1994-1-4 retain their number. The author’s expressions, where numbered and figures have numbers prefixed by D (for Designers’ Guide); for example, equation (D4.1) in Chapter 4.

Acknowledgements This guide would not have been possible without the analysis and calibrations of EN 19911-4 undertaken by the other members of the UK National Application Document drafting panel, who have given their time and expertise freely to assist the British Standards Institution to prepare for the implementation of the Eurocode in the UK.

Contents Preface Aims and objectives of this guide Layout of this guide Acknowledgements

v v v v

Chapter 1.

General 1.1. Scope 1.2. Normative references 1.3. Assumptions 1.4. Distinction between Principles and Application Rules 1.5. Design assisted by tests and measurements 1.6. Definitions 1.6.1. Fundamental basic wind velocity 1.6.2. Basic wind velocity 1.6.3. Mean wind velocity 1.6.4. Pressure coefficient 1.6.5. Force coefficient 1.6.6. Background response factor 1.6.7. Resonance response factor 1.7. Symbols

1 1 3 3 4 5 5 6 6 6 6 6 6 6 7

Chapter 2.

Design situations 2.1. Persistent situations 2.2. Transient situations 2.3. Accidental situations 2.4. Fatigue

9 9 10 10 11

Chapter 3.

Modelling of wind actions 3.1. Nature 3.2. Representation of wind actions 3.3. Classification of wind actions 3.4. Characteristic values 3.5. Models

13 13 14 14 14 14

Chapter 4.

Wind velocity and velocity pressure 4.1. Basis for calculation 4.2. Basic values

17 17 18

DESIGNERS’ GUIDE TO EN 1991-1-4

viii

4.2.1. Fundamental value of basic wind velocity 4.2.2. Basic wind velocity 4.3. Mean wind 4.3.1. Variation with height 4.3.2. Terrain roughness 4.3.3. Terrain orography 4.3.4. Large and considerably higher neighbouring structures 4.3.5. Closely spaced buildings and obstacles 4.4. Wind turbulence 4.5. Peak velocity pressure

18 19 20 20 21 25 25 25 26 28

Chapter 5.

Wind actions 5.1. General 5.2. Wind pressures on surfaces 5.3. Wind forces

31 31 31 32

Chapter 6.

Structural factor cs cd 6.1. General 6.2. Determination of cs cd 6.3. Detailed procedure 6.3.1. Structural factor cs cd 6.3.2. Serviceability assessments 6.3.3. Wake buffeting

35 35 36 36 36 37 38

Chapter 7.

Pressure and force coefficients 7.1. General 7.1.1. Choice of aerodynamic coefficient 7.1.2. Asymmetric and counteracting pressures and forces 7.1.3. Effects of ice and snow 7.2. Pressure coefficients for buildings 7.2.1. General 7.2.2. Vertical walls of rectangular plan buildings 7.2.3. Flat roofs 7.2.4. Monopitch roofs 7.2.5. Duopitch roofs 7.2.6. Hipped roofs 7.2.7. Multispan roofs 7.2.8. Vaulted roofs and domes 7.2.9. Internal pressure 7.2.10. Pressures on walls and roofs with more than one skin 7.3. Canopy roofs 7.4. Free-standing walls, parapets, fences and signboards 7.4.1. Free-standing walls and parapets 7.4.2. Shelter factors for walls and fences 7.4.3. Signboards 7.5. Friction coefficients 7.6. Structural elements with rectangular sections 7.7. Structural elements with sharp-edged section 7.8. Structural elements with polygonal section 7.9. Circular cylinders 7.9.1. External pressure coefficients 7.9.2. Force coefficients 7.9.3. Force coefficients for vertical cylinders in a row arrangement

39 39 40 40 41 41 41 42 44 44 44 44 44 44 45 47 48 49 49 50 50 51 52 52 53 53 53 54 54

CONTENTS

7.10. 7.11. 7.12. 7.13.

Spheres Lattice structures and scaffoldings Flags Effective slenderness
and end-effect factor




54 54 55 55

Chapter 8.

Wind actions on bridges 8.1. General 8.2. Choice of the response calculation procedure 8.3. Force coefficients 8.3.1. Force coefficients in the x-direction – general method 8.3.2. Force in x-direction – simplified method 8.3.3. Wind forces on bridge decks in z-direction 8.3.4. Wind forces on bridge decks in y-direction 8.4. Bridge piers 8.4.1. Wind directions and design situations 8.4.2. Wind effects on piers

57 57 58 59 59 60 60 60 60 60 60

Chapter 9.

Annexes 9.1. General comments 9.2. Annex A Terrain effects 9.2.1. A.1 Illustrations of the upper roughness of each terrain category 9.2.2. A.2 Transition between roughness Categories 0, I, II, III and IV 9.2.3. A.3 Numerical calculation of orography coefficients 9.2.4. A.4 Neighbouring structures 9.2.5. A.5 Displacement height 9.3. Annex B Procedure 1 for determining the structural factor cs cd 9.4. Annex C Procedure 2 for determining the structural factor cs cd 9.5. Annex D cs cd values for different types of structure 9.6. Annex E Vortex shedding and aeroelastic instabilities 9.6.1. E.1 Vortex shedding 9.6.2. E.2 Galloping 9.6.3. E.3 Interference galloping 9.6.4. E.4 Divergence and flutter 9.7. Annex F Dynamic characteristics of structures 9.7.1. F.1 General 9.7.2. F.2 Fundamental frequency 9.7.3. F.3 Fundamental mode shape 9.7.4. F.4 Equivalent mass 9.7.5. F.4 Logarithmic decrement of damping

63 63 63 63 64 64 65 65 65 66 66 67 67 67 68 68 68 68 68 69 69 70

Postscript

71

References

73

Index

75

ix

CHAPTER 3

Modelling of wind actions This chapter is concerned with the way that wind actions are represented by the Eurocode. The material in this chapter is covered in Section 3, in the following clauses: . . . . .

Nature Representation of wind actions Classification of wind actions Characteristic values Models

Clause 3.1 Clause 3.2 Clause 3.3 Clause 3.4 Clause 3.5

3.1. Nature In this context ‘modelling’ does not mean the construction of physical or numerical scaled models, as required for wind tunnel testing or computational fluid dynamics (CFD) calculations permitted by clause 1.5. It means the ‘conceptual model’ – the simplified methodology used in the EN to represent the complex processes of wind actions. Wind actions fluctuate in time and in position over the external surfaces of a structure in a complex and apparently random manner. Stiff structures will respond directly to these actions, allowing the use of the static design model, whereby the maximum strain is directly proportional to the maximum load. Dynamic structures selectively amplify their response to wind actions through resonances at the natural frequencies of the structure. In some circumstances, the motion of the structure is sufficient to increase the wind actions and such structures are called aeroelastic. The EN uses mathematical models to represent these static, dynamic and aeroelastic action effects as follows: .

.

.

.

External pressures: normal pressures over the external surfaces of enclosed structures and the internal surfaces of open structures caused directly by the wind actions. Internal pressures: normal pressures over the internal surfaces of enclosed structures caused indirectly by the external pressures acting through porosity of the external surface. Normal forces: forces normal to the surface of the structure cause by the action of the normal pressures. Tangential forces: forces acting tangentially to the surface caused by friction which may be significant when large areas of structures are swept by the wind.

Pressure is actually a scalar quantity that acts equally in all directions. The term ‘normal pressure’ is used to imply that these pressures, applied to the surface of a structure, cause forces which act normal to the surface, as opposed to the tangential forces that are caused by friction.

Clause 3.1(1)

DESIGNERS’ GUIDE TO EN 1991-1-4

3.2. Representation of wind actions Clause 3.2(1)

The EN represents the actual distributions of these pressures and forces by a simplified set of values that give structural loads equivalent to the extreme wind actions, i.e. the most onerous ‘characteristic’ loads. The simplification in the model inevitably involves a degree of conservatism to ensure that the most onerous loading case is included. For this reason, design assisted by testing and measurement, as permitted by clause 1.5, often results in lower design loads and a more efficient structure.

3.3. Classification of wind actions Clause 3.3(1)

These ‘characteristic’ loads should be applied as ‘variable fixed actions’ as specified by EN 1990; that is, as ‘an action for which the variation in magnitude with time is neither negligible nor monotonic’, except where specified. The specified exception is for elective dominant openings (see section 2.3 above) which are treated as ‘accidental actions’. However, in both cases the actions are represented as ‘an upper value with an intended probability of not being exceeded ’.

3.4. Characteristic values Clause 3.4(1)

The wind actions are ‘characteristic values’, i.e. values with a characteristic annual risk of being exceeded of 0.02 in each and every year that the structure remains in service. This level of risk is alternatively described by the mean recurrence interval or ‘return period’ given by the reciprocal of the annual risk, in this case 50 years. The use of the term ‘return period’ is now discouraged because it is often misinterpreted to imply that recurrence is periodic whereas, in reality, recurrence is well described by the Binomial Distribution. If we define P(r, n) as the probability that a wind velocity will be exceeded r times in n years, then: Pðr; nÞ ¼

n! pr ð1
pÞn
r r!ðn
rÞ!

Now with the characteristic annual risk of p ¼ 0:02, the probability of exceedences in a period of n ¼ 50 years is: No exceedences, r ¼ 0:

Pðr; nÞ ¼ 0:9850 ¼ 0:364

One exceedence, r ¼ 1:

Pðr; nÞ ¼

50  0:021  0:9849 ¼ 0:372 1

Two exceedences, r ¼ 2:

Pðr; nÞ ¼

50  49  0:022  0:9848 ¼ 0:186 21

Three exceedences, r ¼ 3: Pðr; nÞ ¼

50  49  48  0:023  0:9847 ¼ 0:061 321

Four exceedences, r ¼ 4:

50  49  48  47  0:024  0:9846 ¼ 0:0145 4321

Pðr; nÞ ¼

The probability of at least one exceedence is found from the value for no exceedences, 1
0:364 ¼ 0:636. Hence the chance that the characteristic value is exceeded at least once in the return period is approximately 64%, i.e. almost twice as likely as not. The mean recurrence interval is maintained because years in which there are no exceedences are balanced by years when there are multiple exceedences, so that the average rate of all exceedences is one per return period.

3.5. Models Clause 3.5(1)

14

EN 1991-1-4 models the effect of wind on the structure, depending on its size, shape and dynamic properties. This is essentially a dynamic model in which the accelerations of the

CHAPTER 3. MODELLING OF WIND ACTIONS

structure are significant. However, the EN simplifies this model into quasi-steady pressures and forces by the use of a dynamic factor cd that allows static-based design where this is appropriate – which is exactly the same model as in BS 6399-2,1 where the dynamic augmentation factor Cr is equivalent to cd
1. The EN also models aeroelastic response in those cases where the motion of the structure modifies the aerodynamic forces. Susceptible structures are cables, masts, chimneys and bridges. Design of potentially aeroelastic structures essentially involves eliminating the possibility of aeroelastic response.

Clause 3.5(2)

15

Index Abbreviations: NA ÿ National Annex; UK NA ÿ United Kingdom National Annex. Page numbers in italics refer to diagrams and illustrations. accidental situations combined actions in 10, 11 definitions 10 elective openings in 10ÿ11 open and closed scenarios 11 aerodynamic coefficients, choice of 40 aeroelastic responses elimination of 15 modelling 15 susceptible structures 15 aeroelastic stability, bridges 58 altitude factors, orography 19 Annex A (terrain effects) 3 displacement heights 65 neighbouring structures, wind loads 65 orography coefficients 64ÿ65 roughness transitions 64 upper 63ÿ64 Annex B (structural factor determination, procedure I) 3, 65ÿ66 Annex C (structural factor determination, procedure II) 3, 66 Annex D, UK usage 3, 66 Annex E divergence/flutter 68 galloping 67ÿ68 interference/wake 68 UK usage 3 vortex shedding 67 Annex F (dynamic characteristics of structures) 3, 68 damping, logarithmic decrement 70 equivalent masses, cantilever structures 69ÿ70 fundamental frequencies 68ÿ69 fundamental mode shapes 69, 69, 70 annexes informative status 2ÿ3, 63 new, as non-contradictory complementary information 63

assymetric loads signboards 50 torsional effects EN 1991-1-4 40ÿ41, 40 UK NA 40ÿ41, 40 background response factors, definitions 6 Baker, Benjamin 35 barrel-vault roofs 45 basic velocity pressures, definitions 29 basic wind velocities definitions 6, 18, 19 directional factors 20 National Values 19 probability factor models 20, 20 seasonal factors 20 UK NA variants 20 boundary layers, mean wind velocities 21ÿ23, 22 box-girder bridges 59 bridge piers continuous bridges 61 wind actions 60ÿ61 UK NA 61 bridges see also bridge piers aeroelastic stability 58 box-girder 59 coordinate axes 57 dimensional notation 58 dynamic magnification in 58 expansion joints 60 foot-, cable-stayed 58 force coefficients inclined decks 59 rail bridges 59 road bridges 59 x-direction 59, 60 y-direction 60 z-direction 60

DESIGNERS’ GUIDE TO EN 1991-1-4

bridges (continued ) National Annexes inclusion in 57 limitations 58 parapets 59 reference heights 59 response calculation procedures 58 UK NA 58 solid plate beams 59 wind actions and rail traffic 58 and road traffic 58 wind forces, calculations 57 BS 6399-2 and EN 1991-1-4 wind action parameters 33 wind velocity parameters 30 Building Regulations 5 buildings closely packed, and wind velocities 25ÿ26 demolition and redevelopment, wind exposure during 26 tall, and low-rise buildings 25 cable-stayed bridges foot 58 galloping, rain-induced 68 canopy roofs definitions 48 flat, wind forces 33 internal pressures 45, 48 internal stacking 49 multibays 49 pitched, friction 51ÿ52 cantilevers damping 70 aerodynamic 70 deflections cantilevered from ground 69, 69 self-weight 69, 69 equivalent masses 69ÿ70 characteristic values, annual risk of exceedence 14 chimneys grouped, wake buffeting 38 internal pressure coefficients 47 circular cylinders force coefficients, definitions 54 pressure coefficients, definitions 53 reference areas 53 stacks/flues, roof-mounted 54 cladding loads 39 combined structural factors Davenport method 36 design wind loads, underestimates 37 determination 36 structural factor 36ÿ37, 37 reference heights, terminology confusion 36ÿ37 serviceability assessments 37ÿ38 UK NA 36

76

construction processes Health and Safety Executive 5 as transient situations 10 Cook–Mayne methodology 17 coordinate axes, bridges 57 cylinders see circular cylinders damping aerodynamic 70 logarithmic decrement of 70 Davenport method, combined structural factors 36 demolition and redevelopment, wind exposure during 26 designers, load and response information 5 dimensional notation, bridges 58 displacement heights Annex A (terrain effects) 65 definitions 21 woodland, permanent 26 divergence Annex E 68 avoidance 68 ‘division by parts rule’, pressure coefficients 42 domes 44ÿ45 dominant elective openings closure protocols 46 consideration of 10ÿ11 definitions 45 internal pressures 45 interpretation of caveats 46 doors see elective openings down-pipes, external 54 drag coefficients, rectangular plan buildings 42ÿ43 drag forces, polygonal-plan buildings 53 duopitch roofs definitions 44 pressure coefficients 44 reference heights 44 Dutch barns 48 internal stacking 49 dynamic characteristics of structures, fundamental frequencies 68ÿ69, 69 dynamic factor, or size factor, NA 35ÿ36 dynamic magnification, bridges 58 dynamic modelling 14ÿ15 effective slenderness, force coefficients 55 elective openings in accidental situations 10ÿ11 open and closed scenarios 11 dominant closure protocols 46 consideration of 10ÿ11 definitions 45 internal pressures 45ÿ46 interpretation of caveats 46 external 31 integrity assumptions 9

INDEX

EN 1990, applicability 3ÿ4 EN 1991-1-4 Annexes acceptance or rejection 3 amalgamation with EN 71 informative status 2ÿ3, 63 assymetric loads, torsional effects 40ÿ41, 40 and BS 6399-2 wind action parameters 33 wind velocity parameters 30 definitions 5ÿ7 errors, correction of 72 exclusions 1 implementation 2 errors of 71ÿ72 limitations 1ÿ2 and National Annexes 2 amalgamation 3 pressure coefficients external local 41 external overall 41 end-effect factors, force coefficients 55 equivalent masses, cantilevers 69ÿ70 Eurocodes (EN) enforcement 5 non-contradictory complementary information, uses of 5 Principle and Application Rule 4ÿ5 reference to 3 ‘vertical’ structure 71 external down-pipes 54 external pressures coefficients 39 definitions 13 local 41 overall 41 roof overhangs 42 external surfaces, wind pressures 31 fatigue due to galloping 68 low-cycle, in transient situations 10 in persistent situations 9 reference to structural Eurocode 11 fences lattice 49 shelter factors 50 end zones 50 solidarity ratios 49 flags, overloading 55 flat roofs canopy structures, wind forces 33 definitions 44 friction 33, 52 pressure coefficients 44 reference heights 44 fluctuating loads, and vibration frequencies 35 flutter Annex E 68 stall

avoidance 68 signboards 50ÿ51 footbridges, cable-stayed 58 force coefficients 40 bridges inclined decks 59 x-direction 59, 60 y-direction 60 z-direction 60 circular cylinders, definitions 54 definitions 6 effective slenderness 55 end-effect factors 55 ice and snow effects 41 lattice structures 54 polygonal section structural elements 53 rectangular section structural elements 52 scaffolding, sheltered 54ÿ55 sharp-edged structural sections 52 slender buildings, tall 43 spheres 54 Forth rail bridge 35 freestanding walls pressure coefficients 49 reference heights 49 shelter factors 50 end zones 50 solidarity ratios 49 friction coefficients 40 BS 6399-2 values 51 definitions 51 reference areas 51ÿ52 reference heights 52 wind forces flat-roofed canopy structures 33 long-span buildings 33 parallel surfaces 33 pitched roofs 33 fundamental basic wind velocity, definitions 6 fundamental frequencies, dynamic characteristics of structures 68ÿ69, 69 funnelling, pressure coefficients 42 galloping Annex E 67ÿ68 definitions 67 fatigue due to 68 interference/wake 68 rain-induced 68 general public, health and safety 10 glazed ‘wind screens’ 48 grandstands, internal pressures 45 Greek and Latin symbol notation, confusion 7, 53 gust speeds, maximum 17 health and safety see safety Health and Safety Executive, construction processes 5

77

DESIGNERS’ GUIDE TO EN 1991-1-4

hipped roofs definitions 44 pressure coefficients 44 reference heights 44 ice and snow effects force coefficients 41 lattice structures 41 pressure coefficients 41 interference galloping 68 internal partitions, net pressures across 31 internal pressures canopy roofs 45, 48 causes 45 coefficients 39 silos 47 definitions 13 elective openings, dominant 45ÿ46 grandstands 45 ‘most onerous’ 45 open-sided buildings 45 reference heights 47 uniformly distributed openings 46ÿ47, 47 internal surfaces, wind pressures 32 Latin and Greek symbol notation, confusion 7, 53 lattice structures fences 49 force coefficients 54 ice and snow effects 41 vortex shedding 67 lift effects, plate-like sections 52 load and response information, obtaining 5 long-span buildings, wind forces, friction 33 low-cycle fatigue, in transient situations 10 low-rise buildings, adjacent tall buildings, effects of 25 mathematical symbol notations 7 mean wind velocities boundary layers 21ÿ23, 22 calculation of 20ÿ21 definitions 6, 20ÿ21 terrain roughness factors 21ÿ24, 22 UK NA orographic variant 21 modelling aeroelastic responses 15 definitions 13 dynamic 14ÿ15 monopitch roofs pressure coefficients 44 reference heights 44 multi-skin roofs examples 47 pressure differences 47ÿ48 UK NA 48 multi-skin walls examples 47 pressure differences 47ÿ48 UK NA 48

78

multispan roofs, pressure coefficients 44 National Annexes (NA) see also UK National Annexes amalgamation with EN 1991-4-1 71 bridges inclusion of 57 limitations 58 drafting rules 1ÿ2 and EN 1991 2 amalgamation 3 exceptions and additions 3 roles of 71 size factor, or dynamic factor 35ÿ36 status 2 variants basic wind velocity 18ÿ19 orography 18ÿ19, 19 peak velocity pressures 29ÿ30, 29 wind loads 18 net pressure coefficients 40 non-contradictory complementary information Eurocodes, uses of 5 new annexes 63 normal forces, definitions 13 normal pressures, definitions 13 open-sided buildings, internal pressures 45 orography see also terrain; terrain roughness coefficients, Annex A (terrain effects) 64ÿ65 UK NA rules 18ÿ19, 19 altitude factor 19 wind velocity effects, assessments 25 over-ground pipelines 54 parapets bridges 59 pressure coefficients 49 reference heights 49 partitions internal, net pressures across 31 internal and external 31 peak velocity pressures averaging periods 29 definitions 28ÿ29 NA variants 29ÿ30, 29 UK NA 29ÿ30, 29 persistent situations combined loadings 9 definitions 9 fatigue factors 9 pipelines, over-ground 54 pitched roofs canopy, friction 51ÿ52 wind forces, friction 33 plate-like sections, lift effects 52 polygonal section structural elements, force coefficients 53 polygonal-plan buildings, drag forces 53

INDEX

pressure coefficients circular cylinders, definitions 53 definitions 6 ‘division by parts rule’ 42 external 39 local 41 overall 41 funnelling 42 ice and snow effects 41 internal 39 leeward faces 42 net 40 parapets 49 roofs duopitch 44 flat 44 hipped 44 monopitch 44 multispan 44 walls, freestanding 49 windward faces 42 Principle and Application Rule, Eurocodes 4ÿ5 probability factor models, basic wind velocities 20, 20 rail bridges, wind and traffic actions 58, 59 rectangular plan buildings drag coefficients 42ÿ43 pressure coefficients, UK NA 43 reference heights, definitions 42 windward walls, pressure coefficients 42 rectangular section structural elements force coefficients 52 reference areas 52 reference areas circular cylinders 53 friction 51ÿ52 reference heights bridges 59 friction 52 internal pressures 47 parapets 49 rectangular plan buildings definitions 42 ‘division by parts rule’ 42 roofs duopitch 44 flat 44 hipped 44 monopitch 44 terminology confusion 36ÿ37 walls, freestanding 49 windward faces 42 response factors background, definitions 6 resonance, definitions 6ÿ7 road bridges, wind and traffic actions 58, 59 roofs barrel-vault 45 domes 44ÿ45

duopitch definitions 44 pressure coefficients 44 reference heights 44 flat definitions 44 friction 52 pressure coefficients 44 reference heights 44 hipped definitions 44 pressure coefficients 44 reference heights 44 monopitch definitions 44 pressure coefficients 44 reference heights 44 multi-skin examples 47 pressure differences 47ÿ48 multispan, pressure coefficients 44 overhangs, external pressures 42 uplift loads, elective openings damaged 10 vaulted 44ÿ45 safety construction processes 5 general public 10 walls, falling 50 workforce 10 scaffolding, sheltered, force coefficients 54ÿ55 seasonal factors, basic wind velocities 20 serviceability assessments, combined structural factors 37ÿ38 sharp-edged structural sections, force coefficients 52 shelter factors end zones 50 fences 50 walls, freestanding 50 signboards assymetry of load 50 definitions 50 stall flutter (stall-limited divergence) 50ÿ51 silos, internal pressure coefficients 47 size factor, or dynamic factor, NA 35ÿ36 slender buildings tall, force coefficients 43 wake buffeting 38 snow see ice and snow effects solidarity ratios fences 49 freestanding walls 49 spheres, force coefficients 54 stacks/flues, roof-mounted 54 stall flutter see flutter structural elements polygonal section, force coefficients 53 rectangular section, force coefficients 52 sharp-edged, force coefficients 52

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structural Eurocode, fatigue 11 structural factors combined determination 36ÿ37, 37 serviceability assessments 37ÿ38 UK NA 36 determination Annex B procedure I 65ÿ66 Annex C procedure II 66 grouped buildings, wake buffeting 38 size factors, and dynamic factors 35ÿ36 subscript indices 7 symbol notations Greek and Latin, confusion 7, 53 mathematical 7 reuse of 47 subscript indices 7 tall buildings low-rise buildings, effects on 25 slender, force coefficients 43 vortex shedding 43 tangential forces, definitions 13 tanks, internal pressure coefficients 47 terrain see orography; terrain roughness Terrain Categories 0 23 I 23 II 18, 23 wind turbulence 27ÿ28, 27 coastal 28, 28 III 23 IV 23 terrain roughness categories, Annex A 63ÿ64 factors affecting 23ÿ24 mean wind velocities 21ÿ24, 22 sea-to-land transitions 22ÿ23, 22 transition effects, boundaries 23ÿ24, 23 UK NA 23ÿ24, 24 torsional effects assymetric loads EN 1991-1-4 40ÿ41, 40 UK NA 40ÿ41, 40 transient situations construction processes 10 definitions 10 fatigue, low-cycle 10 health and safety 10 partial loadings 10 UK National Annex (UK NA) Annex D 3, 66 Annex E 3, 67ÿ68 assymetric loads, torsional effects 40ÿ41, 40 basic wind velocities 20 probability factors models 20, 20 seasonal factors 20 bridge piers, wind actions 61 bridges, response calculation procedures 58

80

continuous bridges 61 EN 1991-1-4 errors corrected 72 orography 18ÿ19, 19 altitude factor 19 mean wind velocities 21 wind velocity increases 25 peak velocity pressures 29ÿ30, 29 pressure coefficients funnelling 42 isolated buildings 42 rectangular plan buildings 43 roofs, multi-skin 48 structural factors, combined 36 structure 2 terrain roughness 23ÿ24, 24 walls, multi-skin 48 vaulted roofs 44ÿ45 velocity pressures basic, definitions 29 peak averaging periods 29 definitions 28ÿ29 NA variants 29ÿ30, 29 vibration frequencies, and fluctuating loads 35 vortex shedding Annex E 67 definitions 67 lattice structures 67 tall buildings 43 wake buffeting grouped buildings 38 grouped chimneys 38 wake galloping 68 walls see also parapets freestanding pressure coefficients 49 reference heights 49 shelter factors 50 solidarity ratios 49 multi-skin examples 47 pressure differences 47ÿ48 UK NA 48 porous 49 wind actions bridge piers 60ÿ61 UK NA 61 bridges and rail traffic 58 and road traffic 58 as characteristic values, annual risk of exceedence 14 extreme, most onerous loads 14 fluctuations 13 representation of 14 wind forces bridges, calculations 57

INDEX

determination direct 32 indirect 32 friction effects 33 wind loads Annex A (terrain effects), neighbouring structures 65 design, underestimates 37 maximum 17ÿ18 NA variants 18 wind pressures external surfaces 31 internal surfaces 32 non-simultaneous gusts 35 wind turbulence Category II terrain 27ÿ28, 27 coastal 28, 28 equilibrium factors 26ÿ27, 27 and height 26ÿ27, 27 intensity, definitions 26 wind velocities basic definitions 6, 18, 19 directional factors 20 National Values 19

probability factor models 20, 20 seasonal factors 20 buildings, closely packed 25ÿ26 calculation, basis for 17ÿ18 fundamental basic, definitions 6 low-rise buildings, and adjacent tall buildings 25 and maximum gust speeds 17 mean boundary layers 21ÿ23, 22 calculation of 20ÿ21 definitions 6, 20ÿ21 terrain roughness 21ÿ24, 22, 23 UK NA orographic variant 21 NA variants 18ÿ19 orographic effects, assessments 25 windows see also elective openings glazed ‘wind screens’ 48 windward faces pressure coefficients 42 reference heights 42 woodland, permanent, displacement height 26 workforce, safety 10

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