Communication Structures

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Communication

structures

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Distributors for Thomas Telford books are

USA: ASCE Press, 1801 Alexander Bell Drive, Reston, VA 20191-4400

Japan: Maruzen Co. Ltd, Book Department, 3—10 Nihonbashi 2-chome, Chuo-ku, Tokyo 103 Australia: DA Books and Journals, 648 Whitehorse Road, Mitcham 3132, Victoria

First published 2007

A catalogue record for this book is available from the British Library ISBN: 978-0-7277-3400-6

#Brian W. Smith 2006

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 Academicþ Technical, Bristol

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Contents

Foreword

ix

Preface

xi

Acknowledgements

xiii

Chapter 1

Introduction

1

Chapter 2

History

6

Chapter 3

Design considerations

19

3.1

General, 19

3.2

Choice of site, 20

3.3

Choice of structure, 24

3.4

Economic considerations, 27

3.5

Environmental considerations, 27

3.6

Electronic considerations, 30

3.6.1

General, 30

3.6.2

Antenna characteristics, 33

3.6.3

Low-frequency antennas, 37

3.6.4

Medium-frequency antenna systems, 41

3.6.5

VHF and UHF antennas, 44

3.6.6

Digital audio broadcasting, 49

3.6.7

Mobile phone antennas, 51

3.7

Effect on existing services of subsequent additional

antennas, 54

Chapter 4

Failures of masts and towers

56

4.1

General, 56

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4.2

Icing failures, 59

4.3

Design/detail failures, 61

4.4

Maintenance failures, 63

4.5

Aircraft damage, 65

4.6

Vandal damage, 68

4.7

Lessons to be learned, 69

Chapter 5

Forms of structure

71

5.1

General, 71

5.2

Timber towers, 71

5.3

Concrete towers, 71

5.4

Lattice steel towers, 75

5.5

Lattice guyed masts, 81

5.6

Tubular guyed masts, 87

5.7

Concrete guyed masts, 90

5.8

Other forms of communication structures, 91

Chapter 6

Meteorological parameters

93

6.1

General, 93

6.2

Wind, 93

6.2.1

Wind climate, 95

6.2.2

Boundary layer, 99

6.2.3

Serviceability wind speeds, 102

6.3

Atmospheric icing, 104

6.3.1

General, 104

6.3.2

Physics and theoretical modelling of ice accretion, 107

6.3.3

Empirical models to estimate ice loads on

structures, 109

6.4

Earthquakes, 113

6.5

Temperature, 114

6.6

Other meteorological aspects, 115

Chapter 7

Wind resistance

117

7.1

General, 117

7.2

Symmetrical structures without ancillaries, 122

7.3

Symmetrical structures with limited ancillaries, 128

7.4

General method for structures containing

ancillaries, 129

7.5

Linear ancillaries, 133

7.6

Discrete ancillaries, 133

7.7

Cables, 133

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7.8

Measurements on scale model of communications

tower, 134

7.9

Discrepancy between wind tunnel tests and full-scale

measurements, 137

7.10

Icing, 140

Chapter 8

Response

147

8.1

General, 147

8.2

Lattice towers, 148

8.3

Guyed masts, 150

8.3.1

General, 150

8.3.2

Frequency domain analysis, 152

8.3.3

Time domain analysis, 157

8.3.4

Simplified methods, 159

8.3.5

Summary, 176

Chapter 9

Strength

177

9.1

Introduction, 177

9.2

Design against buckling — individual members, 178

9.2.1

General, 178

9.2.2

Influence of local and torsional buckling, 180

9.2.3

Angle leg members, 181

9.2.4

Angle bracing members, 182

9.2.5

Tubular leg members, 184

9.2.6

Tubular bracing members, 184

9.2.7

Solid round members, 184

9.3

Secondary members (‘redundants’), 185

9.4

Bracing types, 186

9.5

Compound members, 189

9.6

Tension, 190

9.7

Connections, 190

9.7.1

General, 190

9.7.2

Flange joints in tubular or solid round leg

members, 190

9.7.3

Guy connections, 192

Chapter 10

Cables

195

10.1

General, 195

10.2

Types of cables, 195

10.3

Strength of guy ropes, 202

10.4

Rotational characteristics of steel ropes, 202

v

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10.5

Modulus of elasticity, 203

10.6

Prestretching, 203

10.7

Still air tension, 206

10.8

Terminations, 206

10.8.1

General, 206

10.8.2

Types of terminations, 207

Chapter 11

Aerodynamic stability

210

11.1

General, 210

11.2

Vortex shedding, 211

11.2.1

General, 211

11.2.2

Background and critical wind speed, 211

11.2.3

Practical implications, 213

11.2.4

Damping devices, 214

11.3

Galloping, 216

11.3.1

General, 216

11.3.2

Critical wind speed, 216

11.3.3

Damping devices, 219

Chapter 12

Fatigue

220

12.1

General, 220

12.2

Lattice towers, 223

12.3

Lattice masts, 223

12.4

Guys, 226

Chapter 13

Foundations

228

13.1

General, 228

13.2

Foundation types, 228

13.2.1

Type I: to resist uplift, 228

13.2.2

Type II: to resist overturning, 231

13.2.3

Type III: to resist down thrust, 233

13.2.4

Type IV: guy anchorages, 233

Chapter 14

Codes and standards

239

14.1

History, 239

14.1.1

General, 239

14.1.2

Wind loading, 239

14.1.3

Ice loading, 242

14.1.4

Strength, 243

14.1.5

Other aspects, 243

14.2

Current codes, 244

vi

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14.2.1

General, 244

14.2.2

Comparison of current Codes, 245

Chapter 15

Access and safety

246

15.1

General, 246

15.2

IASS Recommendations for safe access, 249

Chapter 16

Fabrication and erection

251

16.1

Materials and fabrication, 251

16.1.1

Steel for towers and mast columns, 251

16.1.2

Aluminium, 257

16.1.3

Timber, 257

16.1.4

Plastics, 258

16.2

Erection, 258

16.2.1

General, 258

16.2.2

Erection of lattice towers, 259

16.2.3

Erection of guyed masts, 259

Chapter 17

Maintenance

264

17.1

General, 264

17.2

Constraints, 264

17.3

Minimizing maintenance at the design stage, 265

17.4

Manuals, 267

Chapter 18

Seismic response

269

18.1

General, 269

18.2

Seismicity and earthquake-resistance performance levels, 270

18.3

Prediction of seismic response of structures, 271

18.3.1

General, 271

18.3.2

Self-supporting lattice towers, 272

18.3.3

Monopoles, 273

18.3.4

Guyed masts, 273

18.3.5

Antennas and ancillary components, 275

18.4

Geotechnical considerations, 275

Annex A

Codes of Practice and Design Standards

276

A.1

General, 276

A.2

Comparisons of National Codes, 277

A.3

Scope, 277

A.4

Limit states/reliability classes, 277

A.5

Wind structure, 279

vii

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A.5.1

General, 279

A.5.2

Wind resistance, 286

A.6

Ice loading, 292

A.7

Displacements/serviceability, 293

A.8

Partial safety factors, 295

A.9

Strength, 298

A.9.1

Compressive strength, 298

A.9.2

Tensile strength, 303

A.9.2.1 Steel structure, 303

A.9.2.2 Guys, 303

A.10

Guy assemblies, 304

A.10.1

General, 304

A.10.2

Prestretching, 304

A.10.3

Terminations, 304

A.10.4

Initial tensions, 305

A.11

Erection, 305

A.12

Insulators, 305

A.13

Access, 307

Annex B

IASS Working Group Number 4: Masts and

Towers

308

B.1

Brief history, 308

B.2

Role in the future, 308

B.3

The members of the Group, 309

References

311

Index

327

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Foreword

Today none of us can enjoy modern life even for a single day without

maintaining communication with others or receiving information

from radio and TV. Nevertheless, very few of us recognize that these

modern conveniences are literally supported by structures properly

designed, constructed and maintained for that particular purpose.

Although some of the tasks of terrestrial antennas have been taken

over by celestial ones, more and more demands for transmission

struc-tures for local and ground communication have emerged in recent

years. In Japan, for instance, the meteorological radar station on top

of Mount Fuji, which had served for 35 years for weather forecasting,

was dismantled and replaced by satellites in 1999. Meanwhile, the

demand for a new Tokyo Tower for the ground digital communication

networks, which may be twice as tall as the existing one, is now under

discussion. A remarkably high structure like a TV tower often

incorpo-rates a viewing platform or restaurant for people at its top, and plays an

important role as a tourist centre in the locality, too.

Brian Smith’s book on communication structures is a thorough study

of the technology of structures supporting communication systems for

our society. It covers a very wide range of tower and mast structures,

and looks at them from their history, forms, loads, analysis and

design, codes and standards, fabrication and erection to their

mainte-nance. The book also deals with access and safety of masts and

towers, part of which has already been published within the IASS

(International Association for Shell & Spatial Structures). I am sure

that engineers who are working in the fields of design, analysis,

fabrica-tion and construcfabrica-tion of masts and/or towers will accomplish their tasks

with confidence by making good consultation with the book, which also

contains comprehensive references for further study.

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Brian Smith and I have been good friends for more than fifteen years,

mainly through activities in the IASS. He has been a member of the

IASS for a long time, and is currently one of the most active

members of the IASS Executive Council. In 1997 he was conferred

the IASS Tsuboi Award for his excellent joint paper on ‘Simplified

Dynamic analysis Methods for Guyed masts in Turbulent Winds’

presented in the IASS Journal.

The IASS Working Group 4 for Masts and Towers, in which Brian

has played the leading role, is the most animated working group in

the Association. According to Brian he has received a great deal of

help and advice from members of Working Group 4. On behalf of the

IASS I am very proud of the Working Group as well as Brian himself,

and would like to congratulate the Working Group and all the

consti-tuent members of the Group on the publication of this remarkable book.

Mamoru Kawaguchi, President of IASS, June, 2006

In preparing the report for the Executive Council meeting held in

Mont-pellier, France on September 19, 2004, I was informed by Ulrik

Støttrup-Andersen, Chairman of IASS Working Group 4 on Masts and Towers,

that Brian Smith has, with the support of WG4, agreed to write a book

on communication structures, and that IASS WG4 will act as the

‘backing group’. By having the research results published in the form of

a book, available in libraries and/or bookshelves is the highest status

that can be achieved by an IASS working group and its members.

The importance of communication structures cannot be

underesti-mated, as the failure of communication facilities can sometimes be

quite destructive. One example was the malfunction of the

communi-cation facilities of a key station in the Kobe area of Japan immediately

after the January 17, 1995 earthquake. This event was said to have

prevented local governments knowing the level and scope of casualties

caused by the disaster; as we know, this is crucial for the rescue of

injured people from collapsed buildings in the first few critical hours.

On behalf of the IASS Technical Activities Committee, I would like

to congratulate Brian for his endeavor in making this book a reality, and

WG4 for their backing of such an endeavor. We believe that with this

book, engineers and researchers working on communication structures

and the like can benefit greatly from the huge amount of information

provided.

Y.B. Yang, Chair, Technical Activities Committee, IASS. Taipei, Taiwan

x

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Preface

Communication structures, in the modern sense — masts and towers — are

now familiar to everybody as these structures are situated in the open

landscape as well as in the middle of our cities. The tall masts and

towers for broadcasting of radio and TV have gradually been accepted

by the public, and now their focus is on the numerous number of

smaller masts, towers and poles primarily used for mobile networks.

However, most of the general public are unaware of the engineering

challenges and specialisms behind these common structures. They are

not aware that ‘a guyed-mast is one of the most complicated structures

an engineer may be faced with’ when driving by in their cars they see a

300 m broadcast mast; and nobody worries or gets nervous when they

see on their TV screens the message ‘temporary deterioration of the

signal due to icing of the Emley Moor antenna’. It is of course wrong

to say ‘nobody’ because there is a group of people — structural engineers,

scientific researchers, mast and tower owners, antenna experts etc.,

which know and ‘worry’. This group, heavily involved in the analysis,

design, construction and operation of communication structures,

have for a long time been discussing new developments, exchanging

experiences, launching new designs, presenting numerous technical

papers etc. worldwide, but have not until now systematically

accumu-lated or gathered their knowledge into one work. This has led to a

situation where analysis and design of communication structures has

not appeared as part of the syllabus for structual engineers at technical

unversities; and young engineers starting on their professional career

have had no introduction to this field other than the experienced

personnel in a company.

With this book, Brian W. Smith has covered the subject very

effectively indeed; and this title will surely be invaluable not only for

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the new generation of engineers — whether they study at technical

universities or they start their professional carreer in engineering

prac-tices, telecom organisations, with contractors or mast and tower

fabri-cators, but also certainly for the established mast and tower experts.

Communication structures is the first work of its kind, which in an

instructive and clear way expounds the background of communication

structures, taking into account all the issues involved in the analysis,

design, fabrication, construction and maintenance. It is fully illustrated

with excellent photographs and figures throughout and makes references

to actual real-life constructions.

Brian W. Smith has been involved in the analysis and design of

communication structures all of his professional life as a partner of

Flint & Neill Partnership. He has been involved as the expert in all

the British codes and standards directly related to masts and towers,

and for those with influence on masts and towers. Internationally,

Brian has been a very active member of the IASS (International

Association for Shell and Spatial Structures) Working Group for Masts

and Towers since its formation in 1969, and for ten years he was

chairman of the group. Perhaps, most significant, is Brian’s influence

on the new common Eurocode for Towers and Masts, a work he has

chaired and steered from its inception in 1993 to the final draft which

was accepted unanimously by all the European states in 2003.

So when Brian gives credit for the book to the IASS WG 4 — it is for

all members of this Group a great honour — an honour that none of us

really deserve.

Ulrik Støttrup-Andersen, Chairman of IASS Working Group No. 4

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Acknowledgements

The author has received a great deal of help and advice during the

preparation of this manuscript. Working Group 4 (WG4) of the

Inter-national Association of Shell and Spatial Structures (IASS) has

provided both much of the source material as well as support for this

venture. In particular, the following members of IASS WG4 have

provided both advice and technical input to certain chapters as

below:

Ondrej Fischer

(Chapter 11)

Duncan Gould

(Chapters 3, 7, 9, 13, 16 and Annex A)

Mark Grant

(Chapter 15)

Tony di Guglielmo

(Chapter 3)

Peter Heslop

(Chapters 2, 3)

Mark Malouf

(Chapter 14 and Annex A)

Don Marshall

(Chapter 16)

Ciro Martoni

(Chapter 10)

Ghyslaine McClure

(Chapter 18)

John Mearns

(Chapters 3, 16, 17)

Mirosˇ Pirner

(Chapter 7)

Bruce Sparling

(Chapter 8)

John Wahba

(Chapter 14 and Annex A)

Simon Weisman

(Chapters 4, 5, 7, 8)

Geoff Wiskin

(Chapters 2, 3, 4)

In addition Ulrik Støttrup-Andersen (Chairman of IASS WG4) and

Mogens Nielsen (Secretary of IASS WG4) reviewed and made valuable

comments on all chapters. A full list of the current active members of

IASS WG4 is given in Annex B.

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Material which appears in Chapters 18 and Annex A is reproduced

with the permission of Canadian Standards Association. Material is

reproduced from CSA Standard CSA-537-01 Antennas, Towers and

Antenna Supporting Structures, which is copyrighted by Canada

Standards

Association, 178 Rexdale

Blvd, Toronto, Ontario,

M9W 1R3, www.csa.ca. While use of this material has been authorized,

CSA shall not be responsible for the manner in which the information is

presented, nor for any interpretations thereof.

Permission to reproduce extracts from BS 8100-4: 1995 is granted by

BSI British Standards and can be obtained from BSI Customer Services,

389 Chiswick High Road, London W4 4AL. Tel:

þ44 (0)208996 9001.

email: cservices@bsi-global.com

The support of the IASS through the President, Professor Mamoru

Kawaguchi, and the Working Bureau is most gratefully acknowledged.

Finally, I would like to thank Flint & Neill Partnership for allowing

me to prepare this document with their support, for my colleagues

David MacKenzie and John Rees for reviewing the draft and providing

valuable comments, and to Helen Cartwright for patiently typing the

manuscript.

All figures are reproduced with the kind permission of Flint & Neill

Partnership unless otherwise accredited.

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3

Design considerations

3.1 General

Frequently the design and construction of the antenna support

structure is, in terms of costs, a relatively small element in a complex

project comprising access roads, buildings, site development,

trans-mitters, monitoring equipment, power supplies, antennas and feeders.

The project management team will need experts in each of these

disciplines. However, the specification for each discipline is often

produced independently, in spite of the inter-relationships with other

disciplines. Generally the fundamental parameters are the available

frequency at which the signal is transmitted, and the proposed

service area (the population targeted to receive the service). A

‘service area plan’ is then developed, which explores available sites,

the height of structure needed and the radiated power necessary to

deliver the signal. This proposed radiated power, in turn, defines the

options for the physical size and disposition of the antenna and

feeders, which in their turn define the weights and wind resistance to

be carried by the structure. These data are then incorporated into

the design brief and passed to the structural engineer.

Frequently the structural engineer is unaware of possible alternatives

that may provide the client with a more economical solution. For

example, in broadcasting the transmitted signal strength or effective

radiated power (erp) is a function of the transmitter power and the gain

of the antenna array. By increasing the transmitter power the gain (and

thus the length of the antenna aperture) can be reduced, saving

antenna cost and significantly reducing the structural loading.

Unfortu-nately this increases the initial cost of the transmitters and also the

power consumption and running costs. Broadcast project engineers

hence have to try to optimize the combination of transmitter and

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antenna costs but, unless they are alerted by the structural designer, rarely

consider the potential reduction in structure cost which a smaller antenna

might permit. For example, a slight reduction in antenna loading might

allow a standard ‘off-the-shelf ’ structure to be used rather than a more

costly ‘special’ design. More commonly on existing structures, a smaller

antenna may be possible without the need for structural strengthening

whereas a larger antenna could necessitate significant strengthening.

3.2 Choice of site

The selection of the site must take into account:

. The area to be served by the installation; clearly this is dependent on

the type of service to be provided — cellular phone, television,

micro-wave networks, etc. — and on the density of population in that area.

This will have economic and environmental implications.

. The distribution of the population in that area; this could affect

the directionality needed of the antenna system and, possibly, the

orientation in plan of the structure itself (see section 3.6).

. The general nature of the terrain; this will affect the height of the

structure (see below).

. The presence, or otherwise, of high ground in the locality; this can

again alter the height of the structure, and the viability of sites in the

shadow of the high ground.

. The radiation pattern from the proposed antenna; for example for

TV broadcasting whether the horizontal pattern of radiation

should be omnidirectional or shaped to provide increased power

towards more distant parts of the served area. On occasions the

pattern needs to be shaped to protect an adjacent service on the

same frequency.

. For telecommunication structures used for mobile phone services,

the principal concern is the aesthetics of the structures, particularly

in suburban areas. Novel lattice structures are often needed to

placate local Authority demands and residents’ concerns (see

section 3.5).

The final choice is invariably a compromise between economics of

the proposed service and the demands of other services in different

frequency bands that could enable co-siting to be considered.

The range of a broadcast signal, and hence the service area covered, is

governed not only by the erp from the antenna but also by a combination

of the height of the antenna and the nature of the terrain and the

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broadcast frequency. The higher the broadcast frequency the more the

service area will be restricted to line of sight from the antenna.

For TV and FM radio the height of the antenna above the mean

ground between the transmitter and receiver is a crucial factor in

deter-mining the strength of the signal received. This height depends partly

on the elevation of the chosen site, and partly on the height of the

antenna above the site ground level. Generally speaking, high supports

are required when the terrain is level (effective site height small) (see

Fig. 3.1(a)), and in such cases conditions will normally favour the

erec-tion of high structures, whereas in mountainous regions, where the

elevation of the site is significant but erection conditions difficult,

lower supports can be used (see Fig. 3.1(b)). This is well illustrated

by comparing Denmark and the Netherlands where mean site

eleva-tions are practically zero and antenna structures over 250 m high are

common, with Spain and Portugal where sites often exceed 500 m in

elevation and the average structure is some 60 m high.

The broadcast frequency also has a significant influence on the range

of the signal. Lower frequency signals have greater ability to diffract

around obstructions and hence the amount of shadowing from a fixed

source increases rapidly with frequency (see Fig. 3.2).

Ideally, however, the transmitting site should provide an unobstructed

line-of-sight over the area to be covered, particularly for UHF services.

21

Coverage (a)

Same coverage as for level terrain, using shorter structure (b)

Fig. 3.1 Aerial coverage

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Index

Page numbers in italics refer to diagrams and illustrations. access

codes and standards 307 definition 247 safety 33 climb duration 247 climber competency 250 guidelines 246ÿ247 ladder types 249 system sophistication 248 aerodynamic responsessee galloping;

vortex shedding aesthetics 2

cellular phone antennas 52, 54, 92,92 aircraft

damage to guyed masts 65ÿ66, 66, 67, 68

mast warning lights 66, 265 painted warnings 265

altitude, and wind speeds 282ÿ284, 283 aluminium, uses of 257

angle leg members angle bracing 182ÿ183

eccentricities 183 compound cruciform bracing

bolted 182,182 welded 182,182 symmetric bracing 181,181 unsymmetric bracing 181ÿ182, 181 angled sections, buckling curves

178ÿ180, 178, 179 antenna aperture, definition 44

antennas

see also masts and antennas by type band specific 78

digital audio broadcasting 49ÿ51 gain 44ÿ45 interference between 54ÿ55 low-frequency systems 37ÿ41, 39 medium-frequency systems 41ÿ44, 42, 43 multi-purpose, compromises 26ÿ27, 33ÿ34 radiation patterns horizontal 35ÿ37, 37, 38, 44 vertical 34ÿ35, 35, 36 seismic responses 275 tilt/height effect 34,35 VHF/UHF systems 44ÿ49, 45ÿ49 Australia

codes and standards 276, 292 reliability classes 280

Ba˚tsfjord cylindrical mast (Norway) 88 bending moment responses, guyed masts

165,165

Berlin Tower (Germany) 72 bi-metallic corrosion 266 bolts, yield strength 257 boundary layer, wind climates 99 bracing systems299

see also connections

compound members 189ÿ190, 189

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bracing systems (continued ) cross-bracing 186ÿ187, 186

with horizontals at centre intersections186, 187ÿ188 with redundants186, 187 K 188,188 cranked 188ÿ189, 188 multiple lattice188, 189 portal frame188, 189 single lattice 186,186 tension186, 187 in tension 190

British Broadcasting Corporation (BBC), wind loading curves 239ÿ240, 240 broadcast frequency identifying 19 signal range 21ÿ23, 22 broadcasts early France 12 UK 13ÿ14 future developments 18 Marconi’s experiments 12ÿ13 buckling

curves, angle sections 178ÿ180, 178, 179

local and torsional178, 180ÿ181 building mounted lattice towers, seismic

responses 272 Canada

codes and standards 276 reliability classes 280 cantilevers

guyed masts erection 263

guy tensions 174,175 patch load analysis 170ÿ171 lattice steel towers 86 capacitance discs, low-frequency

antennas 41 cellular phones antennas 27, 52,53, 54, 54 aesthetics 52, 54, 92,92 design objectives 92 disguised as trees 30,30 first generation systems 51ÿ52 second generation systems 52

services 18

third generation systems 52

Charpy V-notch tests, normalization 252 252

clamped terminations, guy cables 198 climber competency, and access safety

250

CN Tower Toronto (Canada) 72,73 lightning strikes115, 116 codes and standards

access 307 Australia 276 Canada 276, 279 comparisons 277, 278 deflection angles 295 drag coefficients 286ÿ287, 288ÿ291, 292 erection tolerances 305, 306 Eurocode 3 244, 276, 279, 282 Germany 244 guy assemblies 303ÿ305 guyed masts 279 deflection limits 243ÿ244 ice loadings 242, 292 insulators 305ÿ306 lattice steel towers 279 national 3

partial safety factors 295ÿ298 reliability classes 280ÿ281 serviceability factors 293ÿ295, 294 strength 243 compressive 298, 300ÿ303 tensile 303ÿ304 UK 245, 276 USA 244, 276, 279

wind loadings, early 239ÿ242, 240, 241 wind speeds

and altitude 282ÿ284, 283 and gust speeds282

and topography 283ÿ284, 284, 285, 286

wind structures 279, 282ÿ284, 285, 286

collapsessee failures

communication towers, environmental impact 28ÿ29, 29

compound members, bracing systems 189ÿ190, 189

328

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compression strengths angle leg members

angle bracing 182ÿ183

compound cruciform bracing 182, 182

symmetric bracing 181,181 unsymmetric bracing 181ÿ182, 181 angle sections, buckling curves

178ÿ180, 178, 179

codes and standards 298, 300ÿ303 round sections 83, 184ÿ185 tubular bracing members 184,184 tubular leg members 184

concrete guyed masts advantages 90 disadvantages 90ÿ91 concrete towers antenna mounting 72 deflection advantages 72 drag factors 72 first28, 71ÿ72 height-to-base ratios 76 public access 72

steel topmasts, height-to-base ratios 76 structure 72ÿ73

weight 72 connections

flange joints

solid round legs 190ÿ191, 191 tubular round legs 191ÿ192, 191 guy cables freedom of rotation193, 194, 194 stay plates 192,192, 194 corrosion bi-metallic 266 concrete 90 humidity 94, 115 pollution 94 corrosion protection external 86ÿ87 galvanizing 88, 265, 266 guy cables 65 galvanizing 266, 267 greasing 266 zinc-rich paste 267 tubes, internal 81

crack detection, fatigue damage 225ÿ226, 226

cranked K-bracing systems 188ÿ189, 188

critical wind speeds galloping 216ÿ219, 217 vortex shedding 211ÿ212 cross-bracing, bracing systems, with

horizontals at centre intersections 186, 187ÿ188

cross-bracing systems 186ÿ187, 186 with horizontals at centre

intersections186, 187ÿ188 with redundants186, 187 cross-lays, wire ropes 198 Crystal Palace Tower 78,79 cylinders

drag 120,121, 137ÿ138, 138 vortex shedding 213ÿ214

strake damping 214,215 tuned mass dampers 214ÿ215 DABsee digital audio broadcasting Danish standard towers 79,80

guy cables, articulation 104,193 dead loads 2ÿ3

deflection angles, codes and standards 295

delta-type low-frequency antennas 40 design, corrosion protection, galvanizing

88, 265, 266

design faults, guyed masts, failures due to 61,62, 63

digital audio broadcasting (DAB) antenna requirements 33 multimedia potential 51 multiplex carriers 50 reception 50 transmitter spacing 51 dipoles batwing 45ÿ46, 45

with reflector screens 46,47 screening 36ÿ37

wind effects 36ÿ37

dish antennas, wind resistance 100ÿ101, 118

downthrust resistance, foundations 229, 233,233, 234

downtime, due to wind speeds 102ÿ104, 103

(21)

drag ancillaries 128ÿ132, 129ÿ131, 287 discrete 133 guy cables 133ÿ134, 134, 144ÿ145, 145 linear 133 Australian code 292 circular members 120 codes and standards 286ÿ287,

288ÿ291, 292 crosswinds 127ÿ128

cylinders 120,121, 137ÿ138, 138 dish antennas 118ÿ119

guyed masts, fluctuations 162ÿ163 icing coefficients 141ÿ142, 142 guy cables 140 light 140ÿ141, 141 mean loading 117 round members 83 square structures 117,118

and angle of incidence 125ÿ126, 125, 126

circular section members124, 126 flat-sided members123, 125 wind on corner290 wind on face288 structural ‘panels’ 118,119

and surface roughness 138ÿ139, 139 triangular structures 117ÿ118, 118

ancillaries 129,129, 130 angle of incidence 126ÿ127, 127,

128

circular section members124, 127, 129, 130

flat-sided members123, 131 wind on corner291 wind on face289

and turbulence 124ÿ125, 139 wind tunnel tests 118, 131ÿ132,

134ÿ137, 135, 136 with ancillaries135, 137 discrepancies 137ÿ140, 138, 139 dustfall effects 94, 116

dynamic analysis

see also simplified dynamic analysis guyed masts 150ÿ154, 152

background components 155

bending moment components 156ÿ157, 156

gust factor analysis 168ÿ170, 168 mean components 154ÿ155 non-linearity responses 153ÿ154 resonant components 155ÿ156 and simplified analysis 168,168 time domain 148 simulation 3 dynamic responses calculations 147ÿ148 lattice towers 148,149, 150 earthing systems lightning strikes 44, 116 low-frequency antennas 40 earthquakessee seismic responses economics, balancing 19ÿ20, 69ÿ70 Eddystone lighthouses 8,10

Smeaton’s 8,10 Winstanley’s 8,9

effective radiated power (erp) definitions 19

maximising 33 Eiffel, Gustave 10ÿ12

Eiffel tower (France) 9ÿ12, 11, 17, 27 broadcasts from 12

Electronics Industries Association (EIA) (USA) 244

elevation, sites 21,21, 23 Emley Moor TV transmitter (1st),

failure, icing 60ÿ61, 113 Emley Moor TV transmitter (2nd) 73,

74

Listed Building Status 28, 75 endurance curves, welded details

221ÿ222, 221 environmental impact

Eiffel tower 27 planning permissions 70

tall communications towers 28ÿ29 equal lays, wire ropes 198

erection 4

guyed masts 260ÿ263, 262 lattice towers 259ÿ260, 260 tolerances, codes and standards 305,

306 weather 259

330

(22)

erpsee effective radiated power Eurocode 3 244, 276

reliability classes 280 fabrication 4

bolts, yield strength 257 faults, failures due to 63 poor flange plates 255,256 tubular legs 255ÿ257, 256 slotted holes 257 failures 3ÿ4 by terrorism 68ÿ69 by vandalism 68ÿ69, 69 economic considerations 69ÿ70 fabrication faults 63 guyed masts 56ÿ57, 58 aircraft damage 65ÿ66, 66, 67, 68 design faults 61,62, 63 maintenance 63,64, 65 single guy cables 68 stay plates62, 63 icing 59, 113 triggering mechanisms 60 maintenance, procedures 63,64, 65, 70 fatigue damage assessing 220

endurance curves, welded details 221ÿ222, 221 guy cables 226ÿ227 guyed masts construction standards 223ÿ224 crack detection 225ÿ226, 226 flange joints 224ÿ225, 225 lattice towers 223 low cycle 220 total 222ÿ223 vortex excitation 220ÿ221 wind causes 104, 220

Finland, icing conditions 140ÿ141 flange joints

poor fabrication 255,256 solid round legs 190ÿ191, 191 tubular round legs 191ÿ192, 191 foundations downthrust resistance 229, 233,233, 234 guy cables conventional 233ÿ235, 235 inverted T 235,237 tension rod 237ÿ238, 238 tie rod 236,237 two stays 235,236 guyed lattice masts 85ÿ86, 85 lattice steel towers232

overturning resistance 229,230, 231 tubular guyed masts 88,89

uplift resistance 228ÿ229, 230, 231, 231

freezing snow, icing due to 104, 106 fundamental parameters

service area 19 signal frequency 19

Gabin mast (Poland), failure, guy replacement64, 65 gain, TV antennas 44ÿ45 galloping calculations 216 causes 216ÿ217, 218ÿ219 damping devices 219 definition 216 iced cables 216ÿ217, 217 spoilers 217 wake 218 galvanizing corrosion protection 88, 265, 266 guy cables 266, 267

geotechnical site considerations 275 Germany, codes and standards 244 glass-fibre cylinders, antenna screening

46,47

glaze icing, formation 104,106 groundwave components,

medium-frequency systems 41 gust response factors

lattice steel towers 148,149 terrain categories 148,149 gust speeds, and wind speeds282 guy cables

see also galloping; guy insulators; vortex shedding

aircraft damage to 66,67 anchorages

conventional 233ÿ235, 235

(23)

guy cables anchorages (continued ) inverted T 235,237 tension rod 237ÿ238, 238 tie rod 236,237 two stays 235,236 connections freedom of rotation193, 194, 194 stay plates 192,192, 194 corrosion 65 corrosion protection galvanizing 266, 267 greasing 266 zinc-rich paste 267 fatigue damage 226ÿ227 icing 107,107 accretion 144ÿ145, 145 assymetric loadings due to 109 assymetric shedding 113 drag coefficient 145 formation 108ÿ109, 109 wind drag 140 ideal parameters 195 nomenclature 196,196 ropes clamped terminations 198 core 196 lays 196,197, 198, 201, 202, 203 locked-coil 199ÿ200, 199, 202, 203, 205 modulus of elasticity 203,203 non-metallic 201

parallel laid wires in a strand 200 polypropylene impregnated 200ÿ201, 201, 267 prestretching 203ÿ204, 205, 206, 304 rotational characteristics 202ÿ203, 202 spiral strands 198ÿ199, 199, 202, 203,205 strength 202 use of standard 196 slope, optimum 25 still air tensioning 206 temperature effects 114 terminations 206ÿ207, 304ÿ305 guy sockets 207,207, 208 loops 208,209 preformed grips 208ÿ209 wind resistance 133ÿ134, 134 guy insulators costs 27 installing 263

guy sockets, terminations 207,207, 208 guyed lattice masts82

failures, maintenance 63, 65 foundations, fixed 85ÿ86, 85 guy cables directions 83 inclination 83 spacing 81ÿ82, 83 twin 84ÿ85, 84 leg sections 82ÿ83 omnidirectional antennas 82 top sections 82 torsional restraint arms 85,85 twin guys 84ÿ85, 84 vertical thrust 82 weight 89ÿ90 guyed masts17

see also concrete guyed masts; guy cables; guyed lattice masts; tubular guyed masts aircraft damage 65ÿ66, 66, 67, 68 bases, pinned 167

cantilevers erection 263

guy tensions 174,175 patch load analysis 170ÿ171 codes and standards, deflection limits

243ÿ244

design faults, failures due to 61,62, 63

dynamic analysis 150ÿ154, 152 see also guyed masts, simplified

analysis

background components 155 bending moment components

156ÿ157, 156

gust factor analysis 168ÿ170, 168 mean components 154ÿ155 non-linearity responses 153ÿ154 resonant components 155ÿ156 and simplified analysis 168,168

332

(24)

erection 258ÿ261, 260 failures 56ÿ57, 58

bracing rods 63, 65

during guy replacement64, 65 ice loading 59ÿ61 stay plates62, 63 fatigue damage construction standards 223ÿ224 crack detection 225ÿ226, 226 flange joints 224ÿ225, 225 guy supports, analysis 173,173 guy tensions

gust factors 174

patch load methods 174ÿ175 height, determinants 25ÿ26 multi-purpose, compromises 26ÿ27 seismic responses 91, 273ÿ274 simplified analysis 159ÿ161

bending moment responses 165, 165

and dynamically sensitive masts 167 patch load methods 160ÿ164, 162,

167ÿ168, 168, 169ÿ172, 171, 172

static procedures 164ÿ165, 166, 167

single cable failure 68 square 24,25

stay lanes, elevation 24ÿ25 time domain analysis 148, 157ÿ159,

159 advantages 157 aerodynamic damping 158 turbulence simulation 158ÿ159, 159 triangular 24,25 turbulance, modes 150,151 vandalism 68ÿ69, 69 vortex shedding, damping 215 warning lights 66

weight 17

wind load fluctuations 162ÿ163 hail effects 94

health and safetysee safety height-to-base ratios

concrete towers 76 with steel topmasts 76

lattice steel towers 75ÿ76 horizontal radiation patterns,

omni-directional 35ÿ37, 37, 38, 44

Houston mast (USA), maintenance failure 63

humidity effects, corrosion 94, 115 hybrid connections 184,184 IASSsee International Association of

Shell and Spatial Structures icing 2, 94,110

codes and standards 242, 292 drag coefficients 141ÿ142, 142 radiused corners 143ÿ144, 143 failures due to 59 guyed masts 59ÿ61 triggering mechanisms 60 freezing snow 104, 106 galloping 216ÿ217, 217 glaze 104,106 growth rates 107ÿ108 guy cables 107,107 accretion 144ÿ145, 145 assymetric loadings due to 109 assymetric shedding 113 formation 108ÿ109, 109 wind drag 140 lattice towers 59,59 light, drag 140ÿ141, 141 loadings, codes 242 loads due to 106ÿ107 estimating 110ÿ111 precipitation 59ÿ60 rime 104,105, 106 formation 108 hard 104, 105ÿ106 soft 104ÿ105 risk assessments 111 and vortex shedding 60ÿ61 zoning map, UK 111ÿ112, 112 inspection programmes 70 insulators

codes and standards 305ÿ306 guy, costs 27

lightning strikes 116

interference, between antennas 54ÿ55

(25)

International Association of Shell and Spatial Structures (IASS) 244 access safety recommendations

248ÿ250, 249 masts and towers 308ÿ310 reliability classes 281

International Aviation Organization (IAO), aircraft warnings 66, 265 international frequency ranges

radio 31,32, 37 television 31,32 K-bracing systems 188,188

cranked 188ÿ189, 188 ladder types, access safety 249 Lang’s lay, wire ropes 198, 201 lattice steel towers

see also guyed lattice masts antenna attachments 77ÿ78 building mounted, seismic responses

272 cantilevers 86

codes and standards 279 costs 27

cylindrical sections 86 Danish standard 79,80

diagonals, bolted connections 79, 81, 81 dynamic responses 148, 149,149 gusts 148,149 erection 258ÿ260, 260 fatigue damage 223 foundations232 height-to-base ratios 75ÿ76 heights 75 icing 59,59 internal corrosion 81 as relay stations 76ÿ77, 77 sections 78ÿ79 round bars 86ÿ87 tubular connections 79,80 seismic responses 272ÿ273 torsional rigidity 76, 77 turbulence modes 150,151 vortex shedding 212ÿ213 lattice towers, glass reinforced plastic

259 lays wire ropes 196,197, 198 cross- 198 equal 198 Lang’s 198, 201 ordinary 198 lighthouses, Eddystone 8,9, 10 lightning strikes 94,115, 116 earthing 44, 116 insulators 116 medium-frequency systems 43 Lisnagarvey mast 43,43

Listed Building Status, Emley Moor TV transmitter 28,74, 75

local and torsional buckling178, 180ÿ181

locked-coil ropes 199ÿ200, 199 prestretching 204,205, 206 loop terminations, guy cables 208,209 low temperature embrittlement, steel 115 low-frequency antennas 37ÿ40, 38, 39 capacitance discs 41 delta-type 40 design objectives 38 earthing systems 40 T-type 40,40 umbrella designs 38ÿ40, 39 maintenance 5, 70 constraints 264ÿ265

failures during, clamp failures 63 manuals 267ÿ268

minimizing, at design stages 265ÿ267 programmes 70

Marconi, Guglielmo 12ÿ13 medium-frequency systems

column length, base impedance 43 current distributions 42ÿ43, 42 groundwave components 41 lightning strikes 43ÿ44 skywave components 41 static 43

microwave dish antennas, plan rotation 36

mobile phonessee cellular phones modulus of elasticity

ropes 203,203 variability 204

334

(26)

monopoles, seismic responses 273 Moscow Tower (Russia) 72 Mount Sutro Tower (USA) 47,48 multi-purpose antennas, compromises

26ÿ27, 33ÿ34

multiple lattice bracing systems188, 189

multiplex carriers, digital audio broadcasting 50

ordinary lays, wire ropes 198

overturning resistance, foundations 229, 230, 231

panel antennas 48,49

parallel laid wires in a strand 200 partial safety factors, codes and

standards 295ÿ298

planning permissions, environmental impact 70

plastics

lattice structures 259 shell radomes 259ÿ260 sunlight degradation 94, 115 ‘tree’ communication towers 30,30,

258

pollution effects, corrosion 94 polypropylene impregnated ropes

200ÿ201, 201, 267

portal frame bracing systems188, 189 Post Office Tower74

bomb attack 68 structure 73

precipitation icing 59ÿ60

preformed grip terminations, guy cables 208ÿ209 radiation patterns horizontal, omni-directional 35ÿ37, 37, 38, 44 vertical 34ÿ35, 35, 36 radio

digital broadcasting, antenna requirements 33 France 12

international frequency ranges 31,32, 37

relay stations 76ÿ77, 77

timber towers 71 UK 13ÿ15

redundantssee stabilizing members relay stations

directional importance 77,78 lattice steel towers 76ÿ77, 77, 78 Reynold’s number

definition 120

icing, drag coefficients 141ÿ142, 142 rime ice105, 106 formation 108,108 hard 104, 105ÿ106 soft 104ÿ105 risk assessments icing 111 terrorism 69 ropes, non-metallic 201 ropes (steel) clamped terminations 198 core 196 lays cross-ropes 198 equal 198 Lang’s 198, 201 ordinary 198,202, 203, 205 wire 196,197, 198 locked-coil 199ÿ200, 199, 202, 203 prestretching 204,205, 206 modulus of elasticity 203,203 variability 204

parallel laid wires in a strand 200 polypropylene impregnated 200ÿ201, 201 prestretching constructional 203, 304 curves 204,205 cyclical 204 rotational characteristics 202ÿ203, 202 spiral strands 198ÿ199, 199, 202, 203 prestretching 204,205, 206 strength 202 use of standard 196 round sections

see also tubes

compression strength 83, 184ÿ185 solid, flange joints 191,191 wind resistance 83, 86, 120

(27)

safety access 33 climb duration 247 climber competency 250 guidelines 246ÿ247 ladder types 249 sophistication of 248 IASS recommendations 248ÿ250, 249 legal requirements 5 training schemes 246

security, sites, vandalism 68ÿ69, 69 seismic responses 3, 94, 113ÿ114,

269ÿ270 antennas 275 categories 270ÿ271

geotechnical site considerations 275 guyed masts 91, 273ÿ274

lattice towers 272ÿ273 monopoles 273

peak ground accelerations 271 sensitivity predictions 271ÿ272 service area, plan 19

serviceability components 4 serviceability factors, codes and

standards 293ÿ295, 294 serviceability limits, and wind

predictions 102ÿ104, 103 shadow effects, VHF/UHF systems 49 shell radomes, plastic 258

signal range, broadcast frequency 21ÿ22, 22

simplified dynamic analysis guyed masts 159ÿ161

bending moment responses 165, 165

and dynamically sensitive masts 167

and full analysis 168,168

patch load methods 160ÿ164, 162, 167ÿ168, 168, 169ÿ172, 171, 172

static procedures 164ÿ165, 166, 167

single lattice bracing systems 186,186 sites broadcast frequency 21ÿ23, 22 elevation 21,21, 23 geotechnical considerations 275 multi-purpose structures 22 parameters 23 selection parameters 20 service area 20ÿ21

Sjællands Odde tower (Denmark) 130, 132

skywave components, medium-frequency systems 41

snowsee icing solar heating 114

tilt effect 35

spiral strand ropes 198ÿ199, 199, 202, 203,205 prestretching 204,205, 206 square structures wind effects 100,100 wind resistance 117,118 stabilizing members K bracing 185 triangular structures 185ÿ186 value of 185

standardssee codes and standards static, medium-frequency systems 43 stayplates, failure of62, 63

steel

see also fabrication; ropes (steel) angle 254,300

buckling curves 178ÿ180, 178, 179 strength 301ÿ302, 302

Charpy V-notch tests normalization252252 specifications 253ÿ254 chemical composition 253, 254 circular300 corrosion protection 86ÿ87 galvanising 88, 265, 266 low temperature embrittlement 115 mild

high-yeild stress 253 strengths 251 plates, cutting 257

rapid loading, brittle fractures 252 round 254ÿ255 brittle failures 255 compression resistance 83 residual stresses 255 wind resistance 83, 86, 120 temperatures, service 251, 253,254

336

Communication structures

(28)

tubes costs 79

diagonal connections to 79,80, 81 welding, fracture toughness 253 still air tensioning, guy cables 206 strength components 4

strengthssee compression strengths; local and torsional buckling Stuttgart Tower (Germany)28, 71 sunlight degradation, plastics 94, 115 T-type low-frequency antennas 40,40 television

antennas

see also guyed masts maximum service area 24 digital broadcasting, antenna

requirements 33 early

France 13 UK 15ÿ17, 16

international frequency ranges 31,32 temperature effects 94 guy cables 114 low extremes 114ÿ115 steel embrittlement 115, 251 solar heating 114 tilt effect 35

tensile strength, codes and standards 303ÿ304

tension, strength in 190 tension bracing systems186, 187 terrain categories, gust response factors

148,149

terrorism, risk assessments 69 Teutoberger mast (Germany), design

faults62, 63

tilt, antennas, due to solar heating 35 timber towers 71, 257ÿ258

radio transparency 71, 257 time domain analysis

guyed masts 148, 157ÿ159, 159 advantages 157 aerodynamic damping 158 turbulence simulation 158ÿ159, 159 topography aerial coverage 21,21

and wind speeds 283ÿ284, 284, 285, 286

Torre de Collserola (Spain) 29,29 construction 91

torsional and local buckling178, 180ÿ181

torsional restraint arms 85,85 twin guys 84ÿ85, 84

torsional rigidity, lattice steel towers 76, 77

Tower of Babel 6,7 Tower of Pharos 6,7, 8 towers

see also communication towers; concrete towers; lattice steel towers; timber towers church 8

in history 6,7, 8 lighthouses 8,9, 10

‘tree’ communication towers 30,30, 258 triangular structures stabilizing members 185ÿ186 wind effects 100,100 wind resistance 117ÿ118, 118 tubes costs 79 diagonal connections to 79,80, 81 internal corrosion 81

tubular bracing members 184,184 tubular guyed masts88

advantages 87 corrosion protection 88 disadvantages 87 foundations 88,89 guy planes 88 internal access lifts 88 structure 87ÿ88 weight 89ÿ90 tubular leg members

compression strengths 184 fabrication, poor 255ÿ257, 256 flange joints 191ÿ192, 191 turbulence modes guyed masts 150,151 lattice towers 150,151

337

(29)

turbulence

modes (continued )

simulation, time domain analysis 158ÿ159, 159

and wind resistance 124ÿ125, 139 UHF systemssee VHF/UHF systems ultimate loads, wind effects, probability

of exceedance 97ÿ98, 98 United Kingdom

broadcasting development radio 13ÿ15

television 15ÿ17, 16 codes and standards 245, 276

reliability standards 281 ice zoning map 111ÿ112, 112 uplift resistance, foundations 228ÿ229,

230, 231, 231 USA

codes and standards 244, 276 reliability classes 281 vandalism, guyed masts 68ÿ69, 69 vertical radiation patterns 34ÿ35, 35,

36 VHF/UHF systems antenna mountings candelabra type 47,48 dipoles 45ÿ46, 45, 46 glass-fibre cylinders 46,47 maintenance 46 panels 48,49 shadow effects 49 verticality, importance of 48ÿ49 vortex excitation, fatigue 220ÿ221 vortex shedding

causes 211ÿ212, 212 critical wind speeds 211ÿ212 cylindrical masts 213ÿ214 damping devices

strakes 214,215

tuned mass dampers 214ÿ215 guyed masts, damping 215 and ice loading 60ÿ61

wake galloping 218

welded details, endurance curves 221ÿ222, 221

welding, steel, fracture toughness 253 wind climates 93ÿ94

atmospheric circulation 95ÿ97, 95 boundary layer 99

extreme speeds 96, 97ÿ98, 98 wind directions, critical 100,100 wind loadings 2

see also drag curves BBC 239ÿ240, 240 early 241ÿ242, 241 dipoles 36 dish antennas 100ÿ101 fatigue damage 104 height relationships 99ÿ100 square structures 100,100 topographical factors 101ÿ102 triangular structures 100,100 turbulence 99

ultimate, probability of exceedance 97ÿ98, 98

vertical wind profile 101 vortex shedding, ice 60ÿ61 wind predictions 102

and serviceability limits 102ÿ104, 103 wind resistancesee drag

wind speeds

and altitude 282ÿ284, 283 downtime due to 102ÿ104, 103 and gust speeds282

and topography 283ÿ284, 284, 285, 286 wind tunnels drag tests 118, 131ÿ132, 134ÿ137, 136 with ancillaries135, 137 discrepancies 137ÿ140, 138, 139 early use of 11ÿ12

wire ropessee guy cables; lays Ylla¨s mast (Finland), failure, icing 60,

61, 113

338

Figure

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