communication structures

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Communicationstructures

Brian W. Smith



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

Distributors for Thomas Telford books areUSA: 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 andPatents Act 1988, no part of this publication may be reproduced, stored in a retrieval system ortransmitted 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 statementsmade and opinions expressed in it and that its publication does not necessarily imply that suchstatements and/or opinions are or reect the views or opinions of the publishers. While everyeffort has been made to ensure that the statements made and the opinions expressed in thispublication 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, BristolPrinted and bound in Great Britain by MPG Books, Bodmin, Cornwall



Contents

Foreword

Preface xi

Acknowledgements xiii

Chapter 1 Introduction 1

Chapter 2 History 6

Chapter 3 Design considerations 193.1 General, 193.2 Choice of site, 203.3 Choice of structure, 243.4 Economic considerations, 273.5 Environmental considerations, 273.6 Electronic considerations, 30

3.6.1 General, 303.6.2 Antenna characteristics, 333.6.3 Low-frequency antennas, 373.6.4 Medium-frequency antenna systems, 413.6.5 VHF and UHF antennas, 443.6.6 Digital audio broadcasting, 493.6.7 Mobile phone antennas, 513.7 Effect on existing services of subsequent additional

antennas, 54

Chapter 4 Failures of masts and towers 564.1 General, 56

iii



4.2 Icing failures, 594.3 Design/detail failures, 614.4 Maintenance failures, 634.5 Aircraft damage, 654.6 Vandal damage, 684.7 Lessons to be learned, 69

Chapter 5 Forms of structure 715.1 General, 715.2 Timber towers, 715.3 Concrete towers, 715.4 Lattice steel towers, 75

5.5 Lattice guyed masts, 815.6 Tubular guyed masts, 875.7 Concrete guyed masts, 905.8 Other forms of communication structures, 91

Chapter 6 Meteorological parameters 936.1 General, 936.2 Wind, 936.2.1 Wind climate, 956.2.2 Boundary layer, 996.2.3 Serviceability wind speeds, 1026.3 Atmospheric icing, 1046.3.1 General, 1046.3.2 Physics and theoretical modelling of ice accretion, 1076.3.3 Empirical models to estimate ice loads on

structures, 1096.4 Earthquakes, 1136.5 Temperature, 1146.6 Other meteorological aspects, 115

Chapter 7 Wind resistance 1177.1 General, 1177.2 Symmetrical structures without ancillaries, 1227.3 Symmetrical structures with limited ancillaries, 1287.4 General method for structures containing

ancillaries, 129

7.5 Linear ancillaries, 1337.6 Discrete ancillaries, 1337.7 Cables, 133

iv

Communications structures



7.8 Measurements on scale model of communicationstower, 134

7.9 Discrepancy between wind tunnel tests and full-scalemeasurements, 137

7.10 Icing, 140

Chapter 8 Response 1478.1 General, 1478.2 Lattice towers, 1488.3 Guyed masts, 1508.3.1 General, 1508.3.2 Frequency domain analysis, 152

8.3.3 Time domain analysis, 1578.3.4 Simplied methods, 1598.3.5 Summary, 176

Chapter 9 Strength 1779.1 Introduction, 1779.2 Design against buckling — individual members, 1789.2.1 General, 1789.2.2 Inuence of local and torsional buckling, 1809.2.3 Angle leg members, 1819.2.4 Angle bracing members, 1829.2.5 Tubular leg members, 1849.2.6 Tubular bracing members, 1849.2.7 Solid round members, 1849.3 Secondary members (‘redundants’), 1859.4 Bracing types, 1869.5 Compound members, 1899.6 Tension, 1909.7 Connections, 1909.7.1 General, 1909.7.2 Flange joints in tubular or solid round leg

members, 1909.7.3 Guy connections, 192

Chapter 10 Cables 19510.1 General, 195

10.2 Types of cables, 19510.3 Strength of guy ropes, 20210.4 Rotational characteristics of steel ropes, 202

v

Contents



10.5 Modulus of elasticity, 20310.6 Prestretching, 20310.7 Still air tension, 20610.8 Terminations, 20610.8.1 General, 20610.8.2 Types of terminations, 207

Chapter 11 Aerodynamic stability 21011.1 General, 21011.2 Vortex shedding, 21111.2.1 General, 21111.2.2 Background and critical wind speed, 211

11.2.3 Practical implications, 21311.2.4 Damping devices, 21411.3 Galloping, 21611.3.1 General, 21611.3.2 Critical wind speed, 21611.3.3 Damping devices, 219

Chapter 12 Fatigue 22012.1 General, 22012.2 Lattice towers, 22312.3 Lattice masts, 22312.4 Guys, 226

Chapter 13 Foundations 22813.1 General, 22813.2 Foundation types, 22813.2.1 Type I: to resist uplift, 22813.2.2 Type II: to resist overturning, 23113.2.3 Type III: to resist down thrust, 23313.2.4 Type IV: guy anchorages, 233

Chapter 14 Codes and standards 23914.1 History, 23914.1.1 General, 23914.1.2 Wind loading, 23914.1.3 Ice loading, 242

14.1.4 Strength, 24314.1.5 Other aspects, 24314.2 Current codes, 244

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14.2.1 General, 24414.2.2 Comparison of current Codes, 245

Chapter 15 Access and safety 24615.1 General, 24615.2 IASS Recommendations for safe access, 249

Chapter 16 Fabrication and erection 25116.1 Materials and fabrication, 25116.1.1 Steel for towers and mast columns, 25116.1.2 Aluminium, 25716.1.3 Timber, 257

16.1.4 Plastics, 25816.2 Erection, 25816.2.1 General, 25816.2.2 Erection of lattice towers, 25916.2.3 Erection of guyed masts, 259

Chapter 17 Maintenance 26417.1 General, 26417.2 Constraints, 26417.3 Minimizing maintenance at the design stage, 26517.4 Manuals, 267

Chapter 18 Seismic response 26918.1 General, 26918.2 Seismicity and earthquake-resistance performance levels, 27018.3 Prediction of seismic response of structures, 27118.3.1 General, 27118.3.2 Self-supporting lattice towers, 27218.3.3 Monopoles, 27318.3.4 Guyed masts, 27318.3.5 Antennas and ancillary components, 27518.4 Geotechnical considerations, 275

Annex A Codes of Practice and Design Standards 276A.1 General, 276A.2 Comparisons of National Codes, 277

A.3 Scope, 277A.4 Limit states/reliability classes, 277A.5 Wind structure, 279

vii

Contents



A.5.1 General, 279A.5.2 Wind resistance, 286A.6 Ice loading, 292A.7 Displacements/serviceability, 293A.8 Partial safety factors, 295A.9 Strength, 298A.9.1 Compressive strength, 298A.9.2 Tensile strength, 303A.9.2.1 Steel structure, 303A.9.2.2 Guys, 303A.10 Guy assemblies, 304A.10.1 General, 304

A.10.2 Prestretching, 304A.10.3 Terminations, 304A.10.4 Initial tensions, 305A.11 Erection, 305A.12 Insulators, 305A.13 Access, 307

Annex B IASS Working Group Number 4: Masts andTowers 308

B.1 Brief history, 308B.2 Role in the future, 308B.3 The members of the Group, 309

References 311

Index 327

viii




Foreword

Today none of us can enjoy modern life even for a single day withoutmaintaining communication with others or receiving informationfrom radio and TV. Nevertheless, very few of us recognize that thesemodern conveniences are literally supported by structures properlydesigned, constructed and maintained for that particular purpose.

Although some of the tasks of terrestrial antennas have been takenover 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 topof Mount Fuji, which had served for 35 years for weather forecasting,was dismantled and replaced by satellites in 1999. Meanwhile, thedemand for a new Tokyo Tower for the ground digital communicationnetworks, which may be twice as tall as the existing one, is now underdiscussion. A remarkably high structure like a TV tower often incorpo-rates a viewing platform or restaurant for people at its top, and plays animportant role as a tourist centre in the locality, too.

Brian Smith’s book on communication structures is a thorough studyof the technology of structures supporting communication systems forour society. It covers a very wide range of tower and mast structures,and looks at them from their history, forms, loads, analysis anddesign, codes and standards, fabrication and erection to their mainte-nance. The book also deals with access and safety of masts andtowers, part of which has already been published within the IASS(International Association for Shell & Spatial Structures). I am surethat engineers who are working in the elds of design, analysis, fabrica-

tion and construction of masts and/or towers will accomplish their taskswith condence by making good consultation with the book, which alsocontains comprehensive references for further study.

ix



Brian Smith and I have been good friends for more than fteen years,mainly through activities in the IASS. He has been a member of theIASS for a long time, and is currently one of the most activemembers of the IASS Executive Council. In 1997 he was conferredthe IASS Tsuboi Award for his excellent joint paper on ‘SimpliedDynamic analysis Methods for Guyed masts in Turbulent Winds’presented in the IASS Journal.

The IASS Working Group 4 for Masts and Towers, in which Brianhas played the leading role, is the most animated working group inthe Association. According to Brian he has received a great deal of help and advice from members of Working Group 4. On behalf of theIASS 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 bookon 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 statusthat 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 bequite 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 haveprevented local governments knowing the level and scope of casualtiescaused by the disaster; as we know, this is crucial for the rescue of injured people from collapsed buildings in the rst few critical hours.

On behalf of the IASS Technical Activities Committee, I would liketo congratulate Brian for his endeavor in making this book a reality, andWG4 for their backing of such an endeavor. We believe that with thisbook, engineers and researchers working on communication structuresand the like can benet greatly from the huge amount of informationprovided.

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

x




Preface

Communication structures, in the modern sense — masts and towers — arenow familiar to everybody as these structures are situated in the openlandscape as well as in the middle of our cities. The tall masts andtowers for broadcasting of radio and TV have gradually been acceptedby 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 engineeringchallenges and specialisms behind these common structures. They arenot aware that ‘a guyed-mast is one of the most complicated structuresan engineer may be faced with’ when driving by in their cars they see a300m broadcast mast; and nobody worries or gets nervous when theysee on their TV screens the message ‘temporary deterioration of thesignal due to icing of the Emley Moor antenna’. It is of course wrongto say ‘nobody’ because there is a group of people — structural engineers,scientic 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, exchangingexperiences, launching new designs, presenting numerous technicalpapers etc. worldwide, but have not until now systematically accumu-lated or gathered their knowledge into one work. This has led to asituation where analysis and design of communication structures hasnot appeared as part of the syllabus for structual engineers at technicalunversities; and young engineers starting on their professional careerhave had no introduction to this eld 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

xi



the new generation of engineers — whether they study at technicaluniversities 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 rst work of its kind, which in aninstructive and clear way expounds the background of communicationstructures, taking into account all the issues involved in the analysis,design, fabrication, construction and maintenance. It is fully illustratedwith excellent photographs and gures throughout and makes referencesto 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 allthe British codes and standards directly related to masts and towers,and for those with inuence on masts and towers. Internationally,Brian has been a very active member of the IASS (InternationalAssociation for Shell and Spatial Structures) Working Group for Mastsand Towers since its formation in 1969, and for ten years he waschairman of the group. Perhaps, most signicant, is Brian’s inuenceon the new common Eurocode for Towers and Masts, a work he haschaired and steered from its inception in 1993 to the nal draft whichwas accepted unanimously by all the European states in 2003.

So when Brian gives credit for the book to the IASS WG 4 — it is forall members of this Group a great honour — an honour that none of usreally deserve.

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

xii




Acknowledgements

The author has received a great deal of help and advice during thepreparation of this manuscript. Working Group 4 (WG4) of the Inter-national Association of Shell and Spatial Structures (IASS) hasprovided both much of the source material as well as support for thisventure. In particular, the following members of IASS WG4 haveprovided both advice and technical input to certain chapters asbelow:

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)

Miros 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 valuablecomments on all chapters. A full list of the current active members of IASS WG4 is given in Annex B.

xiii



Material which appears in Chapters 18 and Annex A is reproducedwith the permission of Canadian Standards Association. Material isreproduced from CSA Standard CSA-537-01 Antennas, Towers andAntenna Supporting Structures, which is copyrighted by CanadaStandards 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 ispresented, nor for any interpretations thereof.

Permission to reproduce extracts from BS 8100-4: 1995 is granted byBSI British Standards and can be obtained from BSI Customer Services,389 Chiswick High Road, London W4 4AL. Tel: þ 44 (0)208996 9001.email: [email protected]

The support of the IASS through the President, Professor MamoruKawaguchi, 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 colleaguesDavid MacKenzie and John Rees for reviewing the draft and providingvaluable comments, and to Helen Cartwright for patiently typing themanuscript.

All gures are reproduced with the kind permission of Flint & NeillPartnership unless otherwise accredited.

xiv




3Design considerations

3.1 GeneralFrequently the design and construction of the antenna supportstructure is, in terms of costs, a relatively small element in a complexproject 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 thesedisciplines. However, the specication for each discipline is oftenproduced independently, in spite of the inter-relationships with otherdisciplines. Generally the fundamental parameters are the availablefrequency at which the signal is transmitted, and the proposedservice 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 todeliver the signal. This proposed radiated power, in turn, denes theoptions for the physical size and disposition of the antenna andfeeders, which in their turn dene the weights and wind resistance to

be carried by the structure. These data are then incorporated intothe 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. Forexample, in broadcasting the transmitted signal strength or effectiveradiated power (erp) is a function of the transmitter power and the gainof the antenna array. By increasing the transmitter power the gain (andthus the length of the antenna aperture) can be reduced, savingantenna cost and signicantly reducing the structural loading. Unfortu-

nately this increases the initial cost of the transmitters and also thepower consumption and running costs. Broadcast project engineershence have to try to optimize the combination of transmitter and

19



antenna costs but, unless they are alerted by the structural designer, rarelyconsider the potential reduction in structure cost which a smaller antennamight permit. For example, a slight reduction in antenna loading mightallow a standard ‘off-the-shelf ’ structure to be used rather than a morecostly ‘special’ design. More commonly on existing structures, a smallerantenna may be possible without the need for structural strengtheningwhereas a larger antenna could necessitate signicant strengthening.

3.2 Choice of siteThe selection of the site must take into account:

. The area to be served by the installation; clearly this is dependent onthe 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 affectthe directionality needed of the antenna system and, possibly, theorientation in plan of the structure itself (see section 3.6).

. The general nature of the terrain; this will affect the height of thestructure (see below).

.

The presence, or otherwise, of high ground in the locality; this canagain alter the height of the structure, and the viability of sites in theshadow of the high ground.

. The radiation pattern from the proposed antenna; for example forTV broadcasting whether the horizontal pattern of radiationshould be omnidirectional or shaped to provide increased powertowards more distant parts of the served area. On occasions thepattern needs to be shaped to protect an adjacent service on thesame frequency.

. For telecommunication structures used for mobile phone services,the principal concern is the aesthetics of the structures, particularlyin suburban areas. Novel lattice structures are often needed toplacate local Authority demands and residents’ concerns (seesection 3.5).

The nal choice is invariably a compromise between economics of the proposed service and the demands of other services in differentfrequency bands that could enable co-siting to be considered.

The range of a broadcast signal, and hence the service area covered, isgoverned not only by the erp from the antenna but also by a combinationof the height of the antenna and the nature of the terrain and the

20

Communication structures



broadcast frequency. The higher the broadcast frequency the more theservice area will be restricted to line of sight from the antenna.

For TV and FM radio the height of the antenna above the meanground between the transmitter and receiver is a crucial factor in deter-mining the strength of the signal received. This height depends partlyon the elevation of the chosen site, and partly on the height of theantenna above the site ground level. Generally speaking, high supportsare required when the terrain is level (effective site height small) (seeFig. 3.1(a)), and in such cases conditions will normally favour the erec-tion of high structures, whereas in mountainous regions, where theelevation of the site is signicant but erection conditions difcult,lower supports can be used (see Fig. 3.1(b)). This is well illustratedby comparing Denmark and the Netherlands where mean site eleva-tions are practically zero and antenna structures over 250 m high arecommon, with Spain and Portugal where sites often exceed 500 m inelevation and the average structure is some 60 m high.

The broadcast frequency also has a signicant inuence on the rangeof the signal. Lower frequency signals have greater ability to diffractaround obstructions and hence the amount of shadowing from a xed

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

Design considerations



Index

Page numbers in italics refer to diagrams and illustrations.

accesscodes and standards 307denition 247safety 33

climb duration 247climber competency 250guidelines 246ÿ 247ladder types 249

system sophistication 248aerodynamic responses see galloping;

vortex sheddingaesthetics 2

cellular phone antennas 52, 54, 92, 92

aircraftdamage to guyed masts 65 ÿ 66, 66 , 67 ,

68mast warning lights 66, 265painted warnings 265

altitude, and wind speeds 282 ÿ 284, 283aluminium, uses of 257angle leg members

angle bracing 182ÿ 183eccentricities 183

compound cruciform bracingbolted 182, 182

welded 182, 182

symmetric bracing 181, 181

unsymmetric bracing 181 ÿ 182, 181

angled sections, buckling curves178ÿ 180, 178 , 179

antenna aperture, denition 44

antennassee also masts and antennas by typeband specic 78digital audio broadcasting 49 ÿ 51gain 44ÿ 45interference between 54 ÿ 55low-frequency systems 37ÿ 41, 39

medium-frequency systems 41 ÿ 44, 42 ,43

multi-purpose, compromises 26 ÿ 27,33ÿ 34

radiation patternshorizontal 35 ÿ 37, 37 , 38 , 44vertical 34 ÿ 35, 35 , 36

seismic responses 275tilt/height effect 34, 35

VHF/UHF systems 44 ÿ 49, 45 ÿ 49

Australiacodes and standards 276, 292

reliability classes 280

Batsfjord cylindrical mast (Norway) 88bending moment responses, guyed masts

165, 165

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

bracing systems 299see also connectionscompound members 189 ÿ 190, 189

327



bracing systems (continued )cross-bracing 186ÿ 187, 186

with horizontals at centreintersections 186 , 187ÿ 188

with redundants 186 , 187K 188, 188

cranked 188 ÿ 189, 188

multiple lattice 188 , 189portal frame 188 , 189single lattice 186, 186

tension 186 , 187in tension 190

British Broadcasting Corporation (BBC),wind loading curves 239 ÿ 240, 240

broadcast frequencyidentifying 19signal range 21ÿ 23, 22

broadcastsearly

France 12UK 13ÿ 14

future developments 18Marconi’s experiments 12 ÿ 13

bucklingcurves, angle sections 178 ÿ 180, 178 ,

179local and torsional 178 , 180ÿ 181

building mounted lattice towers, seismicresponses 272

Canadacodes and standards 276

reliability classes 280cantilevers

guyed mastserection 263guy tensions 174, 175

patch load analysis 170 ÿ 171lattice steel towers 86

capacitance discs, low-frequencyantennas 41

cellular phonesantennas 27, 52, 53 , 54, 54

aesthetics 52, 54, 92, 92

design objectives 92

disguised as trees 30, 30rst generation systems 51 ÿ 52second generation systems 52

services 18third generation systems 52

Charpy V-notch tests, normalization 252252

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

250CN Tower Toronto (Canada) 72, 73

lightning strikes 115 , 116codes and standards

access 307Australia 276Canada 276, 279comparisons 277, 278deection angles 295drag coefcients 286 ÿ 287, 288 ÿ 291 ,

292erection tolerances 305, 306Eurocode 3 244, 276, 279, 282Germany 244guy assemblies 303ÿ 305guyed masts 279

deection limits 243 ÿ 244ice loadings 242, 292insulators 305 ÿ 306lattice steel towers 279national 3partial safety factors 295ÿ 298reliability classes 280ÿ 281serviceability factors 293ÿ 295, 294

strength 243compressive 298, 300 ÿ 303tensile 303 ÿ 304

UK 245, 276USA 244, 276, 279wind loadings, early 239ÿ 242, 240 , 241wind speeds

and altitude 282 ÿ 284, 283

and gust speeds 282

and topography 283 ÿ 284, 284 , 285 ,286

wind structures 279, 282 ÿ 284, 285 ,286

collapses see failurescommunication towers, environmental

impact 28 ÿ 29, 29compound members, bracing systems

189ÿ 190, 189

328




compression strengthsangle leg members

angle bracing 182ÿ 183compound cruciform bracing 182,

182

symmetric bracing 181, 181

unsymmetric bracing 181 ÿ 182, 181

angle sections, buckling curves178ÿ 180, 178 , 179

codes and standards 298, 300 ÿ 303round sections 83, 184 ÿ 185tubular bracing members 184, 184

tubular leg members 184concrete guyed masts

advantages 90disadvantages 90 ÿ 91

concrete towersantenna mounting 72deection advantages 72drag factors 72rst 28 , 71ÿ 72height-to-base ratios 76public access 72steel topmasts, height-to-base ratios 76structure 72 ÿ 73weight 72

connectionsange joints

solid round legs 190ÿ 191, 191

tubular round legs 191 ÿ 192, 191

guy cablesfreedom of rotation 193 , 194, 194

stay plates 192, 192 , 194corrosion

bi-metallic 266concrete 90humidity 94, 115pollution 94

corrosion protectionexternal 86 ÿ 87galvanizing 88, 265, 266guy cables 65

galvanizing 266, 267greasing 266zinc-rich paste 267

tubes, internal 81crack detection, fatigue damage

225ÿ 226, 226

cranked K-bracing systems 188 ÿ 189,188

critical wind speedsgalloping 216ÿ 219, 217vortex shedding 211 ÿ 212

cross-bracing, bracing systems, withhorizontals at centre intersections186 , 187ÿ 188

cross-bracing systems 186ÿ 187, 186

with horizontals at centreintersections 186 , 187ÿ 188

with redundants 186 , 187cross-lays, wire ropes 198Crystal Palace Tower 78, 79

cylindersdrag 120, 121 , 137ÿ 138, 138vortex shedding 213 ÿ 214

strake damping 214, 215

tuned mass dampers 214 ÿ 215

DAB see digital audio broadcastingDanish standard towers 79, 80

guy cables, articulation 104, 193

dead loads 2ÿ 3deection angles, codes and standards

295delta-type low-frequency antennas 40design, corrosion protection, galvanizing

88, 265, 266design faults, guyed masts, failures due

to 61, 62 , 63digital audio broadcasting (DAB)

antenna requirements 33multimedia potential 51multiplex carriers 50reception 50transmitter spacing 51

dipolesbatwing 45ÿ 46, 45

with reector screens 46, 47

screening 36 ÿ 37wind effects 36ÿ 37

dish antennas, wind resistance 100 ÿ 101,118

downthrust resistance, foundations 229,

233, 233 , 234downtime, due to wind speeds 102 ÿ 104,

103

329

Index



dragancillaries 128ÿ 132, 129 ÿ 131 , 287

discrete 133guy cables 133ÿ 134, 134 , 144ÿ 145,

145

linear 133Australian code 292circular members 120codes and standards 286 ÿ 287,

288 ÿ 291 , 292crosswinds 127ÿ 128cylinders 120, 121 , 137ÿ 138, 138

dish antennas 118 ÿ 119guyed masts, uctuations 162 ÿ 163icing

coefcients 141ÿ 142, 142guy cables 140light 140ÿ 141, 141

mean loading 117round members 83square structures 117, 118

and angle of incidence 125 ÿ 126,125 , 126

circular section members 124 , 126

at-sided members 123 , 125

wind on corner 290wind on face 288

structural ‘panels’ 118, 119

and surface roughness 138 ÿ 139, 139

triangular structures 117 ÿ 118, 118

ancillaries 129, 129 , 130

angle of incidence 126 ÿ 127, 127 ,128

circular section members 124 , 127 ,129 , 130

at-sided members 123 , 131wind on corner 291

wind on face 289

and turbulence 124 ÿ 125, 139wind tunnel tests 118, 131 ÿ 132,

134ÿ 137, 135 , 136

with ancillaries 135 , 137

discrepancies 137 ÿ 140, 138 , 139

dustfall effects 94, 116dynamic analysis

see also simplied dynamic analysisguyed masts 150ÿ 154, 152

background components 155

bending moment components156ÿ 157, 156

gust factor analysis 168ÿ 170, 168

mean components 154 ÿ 155non-linearity responses 153 ÿ 154resonant components 155 ÿ 156and simplied analysis 168, 168

time domain 148simulation 3

dynamic responsescalculations 147 ÿ 148lattice towers 148, 149 , 150

earthing systemslightning strikes 44, 116low-frequency antennas 40

earthquakes see seismic responseseconomics, balancing 19 ÿ 20, 69ÿ 70Eddystone lighthouses 8, 10

Smeaton’s 8, 10

Winstanley’s 8, 9

effective radiated power (erp)denitions 19maximising 33

Eiffel, Gustave 10ÿ 12Eiffel tower (France) 9 ÿ 12, 11 , 17, 27

broadcasts from 12Electronics Industries Association (EIA)

(USA) 244elevation, sites 21, 21 , 23Emley Moor TV transmitter (1st),

failure, icing 60ÿ 61, 113Emley Moor TV transmitter (2nd) 73,

74

Listed Building Status 28, 75endurance curves, welded details

221ÿ 222, 221

environmental impactEiffel tower 27planning permissions 70tall communications towers 28 ÿ 29

equal lays, wire ropes 198erection 4

guyed masts 260ÿ 263, 262

lattice towers 259 ÿ 260, 260

tolerances, codes and standards 305,306

weather 259

330




erp see effective radiated powerEurocode 3 244, 276


fabrication 4bolts, yield strength 257faults, failures due to 63poor

ange plates 255, 256

tubular legs 255 ÿ 257, 256

slotted holes 257failures 3ÿ 4

by terrorism 68ÿ 69by vandalism 68ÿ 69, 69

economic considerations 69 ÿ 70fabrication faults 63guyed masts 56ÿ 57, 58

aircraft damage 65 ÿ 66, 66 , 67 , 68design faults 61, 62 , 63maintenance 63, 64 , 65single guy cables 68stay plates 62 , 63

icing 59, 113triggering mechanisms 60

maintenance, procedures 63, 64 , 65,70

fatigue damageassessing 220endurance curves, welded details

221ÿ 222, 221

guy cables 226ÿ 227guyed masts

construction standards 223 ÿ 224crack detection 225 ÿ 226, 226

ange joints 224 ÿ 225, 225

lattice towers 223low cycle 220total 222 ÿ 223vortex excitation 220 ÿ 221wind causes 104, 220

Finland, icing conditions 140 ÿ 141ange joints

poor fabrication 255, 256

solid round legs 190ÿ 191, 191

tubular round legs 191 ÿ 192, 191

foundationsdownthrust resistance 229, 233, 233 ,

234

guy cablesconventional 233 ÿ 235, 235

inverted T 235, 237

tension rod 237 ÿ 238, 238tie rod 236, 237

two stays 235, 236

guyed lattice masts 85 ÿ 86, 85

lattice steel towers 232

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

uplift resistance 228 ÿ 229, 230 , 231,231

freezing snow, icing due to 104, 106fundamental parameters

service area 19signal frequency 19

Gabin mast (Poland), failure, guyreplacement 64 , 65

gain, TV antennas 44 ÿ 45galloping

calculations 216causes 216ÿ 217, 218ÿ 219damping devices 219denition 216iced cables 216ÿ 217, 217spoilers 217wake 218

galvanizingcorrosion protection 88, 265, 266

guy cables 266, 267geotechnical site considerations 275Germany, codes and standards 244glass-bre cylinders, antenna screening

46, 47

glaze icing, formation 104, 106groundwave components, medium-

frequency systems 41gust response factors

lattice steel towers 148, 149

terrain categories 148, 149

gust speeds, and wind speeds 282

guy cablessee also galloping; guy insulators;

vortex shedding

aircraft damage to 66, 67anchorages

conventional 233 ÿ 235, 235

331

Index



guy cablesanchorages ( continued )

inverted T 235, 237

tension rod 237 ÿ 238, 238tie rod 236, 237

two stays 235, 236

connectionsfreedom of rotation 193 , 194, 194

stay plates 192, 192 , 194corrosion 65corrosion protection

galvanizing 266, 267greasing 266zinc-rich paste 267

fatigue damage 226ÿ 227icing 107, 107

accretion 144 ÿ 145, 145

assymetric loadings due to 109assymetric shedding 113drag coefcient 145formation 108 ÿ 109, 109

wind drag 140ideal parameters 195nomenclature 196, 196

ropesclamped terminations 198core 196lays 196, 197 , 198, 201, 202 , 203locked-coil 199ÿ 200, 199 , 202,

203 , 205

modulus of elasticity 203, 203

non-metallic 201parallel laid wires in a strand 200polypropylene impregnated

200ÿ 201, 201 , 267prestretching 203 ÿ 204, 205 , 206,

304rotational characteristics 202 ÿ 203,

202

spiral strands 198 ÿ 199, 199 , 202 ,203, 205

strength 202use of standard 196

slope, optimum 25still air tensioning 206

temperature effects 114terminations 206 ÿ 207, 304ÿ 305

guy sockets 207, 207 , 208

loops 208, 209

preformed grips 208ÿ 209wind resistance 133 ÿ 134, 134

guy insulatorscosts 27installing 263

guy sockets, terminations 207, 207 , 208

guyed lattice masts 82

failures, maintenance 63, 65foundations, xed 85 ÿ 86, 85

guy cablesdirections 83inclination 83spacing 81ÿ 82, 83twin 84ÿ 85, 84

leg sections 82ÿ 83omnidirectional antennas 82top sections 82torsional restraint

arms 85, 85

twin guys 84ÿ 85, 84

vertical thrust 82weight 89ÿ 90

guyed masts 17see also concrete guyed masts; guy

cables; guyed lattice masts;tubular guyed masts

aircraft damage 65 ÿ 66, 66 , 67 , 68bases, pinned 167cantilevers

erection 263guy tensions 174, 175

patch load analysis 170 ÿ 171codes and standards, deection limits

243ÿ 244design faults, failures due to 61, 62 ,

63dynamic analysis 150ÿ 154, 152

see also guyed masts, simpliedanalysis

background components 155bending moment components

156ÿ 157, 156

gust factor analysis 168ÿ 170, 168

mean components 154 ÿ 155

non-linearity responses 153 ÿ 154resonant components 155 ÿ 156and simplied analysis 168, 168

332




erection 258 ÿ 261, 260

failures 56ÿ 57, 58

bracing rods 63, 65during guy replacement 64 , 65ice loading 59ÿ 61stay plates 62 , 63

fatigue damageconstruction standards 223 ÿ 224crack detection 225 ÿ 226, 226


guy supports, analysis 173, 173

guy tensionsgust factors 174patch load methods 174 ÿ 175

height, determinants 25 ÿ 26multi-purpose, compromises 26 ÿ 27seismic responses 91, 273ÿ 274simplied analysis 159ÿ 161

bending moment responses 165,165

and dynamically sensitive masts 167patch load methods 160 ÿ 164, 162 ,

167ÿ 168, 168 , 169ÿ 172, 171 ,172

static procedures 164 ÿ 165, 166 ,167

single cable failure 68square 24, 25

stay lanes, elevation 24 ÿ 25time domain analysis 148, 157 ÿ 159,

159

advantages 157aerodynamic damping 158turbulence simulation 158 ÿ 159,

159

triangular 24, 25turbulance, modes 150, 151

vandalism 68 ÿ 69, 69

vortex shedding, damping 215warning lights 66weight 17wind load uctuations 162 ÿ 163

hail effects 94health and safety see safety

height-to-base ratiosconcrete towers 76

with steel topmasts 76

lattice steel towers 75 ÿ 76horizontal radiation patterns,

omni-directional 35 ÿ 37, 37 , 38 ,44

Houston mast (USA), maintenancefailure 63

humidity effects, corrosion 94, 115hybrid connections 184, 184

IASS see International Association of Shell and Spatial Structures

icing 2, 94, 110

codes and standards 242, 292drag

coefcients 141ÿ 142, 142

radiused corners 143 ÿ 144, 143failures due to 59

guyed masts 59ÿ 61triggering mechanisms 60

freezing snow 104, 106galloping 216ÿ 217, 217

glaze 104, 106

growth rates 107 ÿ 108guy cables 107, 107

accretion 144 ÿ 145, 145

assymetric loadings due to 109assymetric shedding 113formation 108 ÿ 109, 109

wind drag 140lattice towers 59, 59

light, drag 140ÿ 141, 141

loadings, codes 242loads due to 106 ÿ 107

estimating 110 ÿ 111precipitation 59 ÿ 60rime 104, 105 , 106

formation 108hard 104, 105 ÿ 106soft 104ÿ 105

risk assessments 111and vortex shedding 60 ÿ 61zoning map, UK 111 ÿ 112, 112

inspection programmes 70insulators

codes and standards 305 ÿ 306

guy, costs 27lightning strikes 116

interference, between antennas 54 ÿ 55

333

Index



International Association of Shell andSpatial Structures (IASS) 244

access safety recommendations248ÿ 250, 249

masts and towers 308 ÿ 310reliability classes 281

International Aviation Organization(IAO), aircraft warnings 66, 265

international frequency rangesradio 31, 32 , 37television 31, 32

K-bracing systems 188, 188

cranked 188 ÿ 189, 188

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

see also guyed lattice mastsantenna attachments 77 ÿ 78building mounted, seismic responses

272cantilevers 86codes and standards 279costs 27cylindrical sections 86Danish standard 79, 80

diagonals, bolted connections 79, 81,81

dynamic responses 148, 149, 149

gusts 148, 149

erection 258 ÿ 260, 260

fatigue damage 223foundations 232

height-to-base ratios 75 ÿ 76heights 75icing 59, 59

internal corrosion 81as relay stations 76ÿ 77, 77

sections 78ÿ 79round bars 86 ÿ 87tubular connections 79, 80

seismic responses 272ÿ 273torsional rigidity 76, 77turbulence modes 150, 151

vortex shedding 212 ÿ 213lattice towers, glass reinforced plastic

259

layswire ropes 196, 197 , 198

cross- 198equal 198Lang’s 198, 201ordinary 198

lighthouses, Eddystone 8, 9 , 10

lightning strikes 94, 115 , 116earthing 44, 116insulators 116medium-frequency systems 43

Lisnagarvey mast 43, 43

Listed Building Status, Emley Moor TVtransmitter 28, 74 , 75

local and torsional buckling 178 ,180ÿ 181

locked-coil ropes 199ÿ 200, 199

prestretching 204, 205 , 206loop terminations, guy cables 208, 209

low temperature embrittlement, steel 115low-frequency antennas 37 ÿ 40, 38 , 39

capacitance discs 41delta-type 40design objectives 38earthing systems 40T-type 40, 40umbrella designs 38ÿ 40, 39

maintenance 5, 70constraints 264 ÿ 265failures during, clamp failures 63manuals 267 ÿ 268minimizing, at design stages 265ÿ 267programmes 70

Marconi, Guglielmo 12 ÿ 13medium-frequency systems

column length, base impedance 43current distributions 42 ÿ 43, 42

groundwave components 41lightning strikes 43 ÿ 44skywave components 41static 43

microwave dish antennas, plan rotation36

mobile phones see cellular phones

modulus of elasticityropes 203, 203

variability 204

334




monopoles, seismic responses 273Moscow Tower (Russia) 72Mount Sutro Tower (USA) 47, 48

multi-purpose antennas, compromises26ÿ 27, 33ÿ 34

multiple lattice bracing systems 188 ,189

multiplex carriers, digital audiobroadcasting 50

ordinary lays, wire ropes 198overturning resistance, foundations 229,

230 , 231

panel antennas 48, 49

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

standards 295 ÿ 298planning permissions, environmental

impact 70plastics

lattice structures 259shell radomes 259ÿ 260sunlight degradation 94, 115‘tree’ communication towers 30, 30 ,

258pollution effects, corrosion 94polypropylene impregnated ropes

200ÿ 201, 201 , 267portal frame bracing systems 188 , 189Post Ofce Tower 74

bomb attack 68structure 73

precipitation icing 59 ÿ 60preformed grip terminations, guy cables

208ÿ 209

radiation patternshorizontal, omni-directional 35 ÿ 37,

37 , 38 , 44vertical 34ÿ 35, 35 , 36

radiodigital broadcasting, antenna

requirements 33France 12

international frequency ranges 31, 32 ,37

relay stations 76 ÿ 77, 77

timber towers 71UK 13ÿ 15

redundants see stabilizing membersrelay stations

directional importance 77, 78

lattice steel towers 76 ÿ 77, 77 , 78

Reynold’s numberdenition 120icing, drag coefcients 141ÿ 142, 142

rime ice 105 , 106

formation 108, 108

hard 104, 105 ÿ 106soft 104ÿ 105

risk assessmentsicing 111terrorism 69

ropes, non-metallic 201ropes (steel)

clamped terminations 198core 196lays

cross-ropes 198equal 198Lang’s 198, 201ordinary 198, 202 , 203, 205

wire 196, 197 , 198locked-coil 199ÿ 200, 199 , 202 , 203

prestretching 204, 205 , 206modulus of elasticity 203, 203

variability 204parallel laid wires in a strand 200polypropylene impregnated 200 ÿ 201,

201

prestretchingconstructional 203, 304curves 204, 205cyclical 204

rotational characteristics 202 ÿ 203,202

spiral strands 198 ÿ 199, 199 , 202 , 203prestretching 204, 205 , 206

strength 202use of standard 196

round sectionssee also tubes

compression strength 83, 184 ÿ 185solid, ange joints 191, 191

wind resistance 83, 86, 120

335

Index



safetyaccess 33

climb duration 247climber competency 250guidelines 246ÿ 247ladder types 249sophistication of 248

IASS recommendations 248 ÿ 250, 249

legal requirements 5training schemes 246

security, sites, vandalism 68 ÿ 69, 69

seismic responses 3, 94, 113ÿ 114,269ÿ 270

antennas 275categories 270ÿ 271geotechnical site considerations 275guyed masts 91, 273ÿ 274lattice towers 272 ÿ 273monopoles 273peak ground accelerations 271sensitivity predictions 271 ÿ 272

service area, plan 19serviceability components 4serviceability factors, codes and

standards 293 ÿ 295, 294

serviceability limits, and windpredictions 102 ÿ 104, 103

shadow effects, VHF/UHF systems 49shell radomes, plastic 258signal range, broadcast frequency 21 ÿ 22,

22

simplied dynamic analysisguyed masts 159ÿ 161

bending moment responses 165,165

and dynamically sensitive masts167

and full analysis 168, 168

patch load methods 160 ÿ 164, 162 ,167ÿ 168, 168 , 169ÿ 172, 171 ,172

static procedures 164 ÿ 165, 166 ,167

single lattice bracing systems 186, 186

sites

broadcast frequency 21 ÿ 23, 22elevation 21, 21 , 23geotechnical considerations 275

multi-purpose structures 22parameters 23selection parameters 20service area 20ÿ 21

Sjællands Odde tower (Denmark) 130,132

skywave components, medium-frequencysystems 41

snow see icingsolar heating 114

tilt effect 35spiral strand ropes 198 ÿ 199, 199 , 202 ,

203, 205

prestretching 204, 205 , 206square structures

wind effects 100, 100wind resistance 117, 118

stabilizing membersK bracing 185triangular structures 185 ÿ 186value of 185

standards see codes and standardsstatic, medium-frequency systems 43stayplates, failure of 62 , 63steel

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

buckling curves 178 ÿ 180, 178 , 179

strength 301 ÿ 302, 302

Charpy V-notch testsnormalization252 252

specications 253 ÿ 254chemical composition 253, 254circular 300

corrosion protection 86 ÿ 87galvanising 88, 265, 266

low temperature embrittlement 115mild

high-yeild stress 253strengths 251

plates, cutting 257rapid loading, brittle fractures 252round 254 ÿ 255

brittle failures 255compression resistance 83

residual stresses 255wind resistance 83, 86, 120

temperatures, service 251, 253, 254

336




tubescosts 79diagonal connections to 79, 80 , 81

welding, fracture toughness 253still air tensioning, guy cables 206strength components 4strengths see compression strengths;

local and torsional bucklingStuttgart Tower (Germany) 28 , 71sunlight degradation, plastics 94, 115

T-type low-frequency antennas 40, 40

televisionantennas

see also guyed mastsmaximum service area 24

digital broadcasting, antennarequirements 33

earlyFrance 13UK 15ÿ 17, 16

international frequency ranges 31, 32

temperature effects 94guy cables 114low extremes 114 ÿ 115

steel embrittlement 115, 251solar heating 114tilt effect 35

tensile strength, codes and standards303ÿ 304

tension, strength in 190tension bracing systems 186 , 187terrain categories, gust response factors

148, 149

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

faults 62 , 63tilt, antennas, due to solar heating 35timber towers 71, 257 ÿ 258

radio transparency 71, 257time domain analysis

guyed masts 148, 157ÿ 159, 159

advantages 157aerodynamic damping 158turbulence simulation 158 ÿ 159,

159topography

aerial coverage 21, 21

and wind speeds 283 ÿ 284, 284 , 285 ,286

Torre de Collserola (Spain) 29, 29

construction 91torsional and local buckling 178 ,

180ÿ 181torsional restraint

arms 85, 85

twin guys 84ÿ 85, 84

torsional rigidity, lattice steel towers 76,77

Tower of Babel 6, 7

Tower of Pharos 6, 7 , 8towers

see also communication towers;concrete towers; lattice steeltowers; timber towers

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

‘tree’ communication towers 30, 30 ,258

triangular structuresstabilizing members 185ÿ 186wind effects 100, 100

wind resistance 117 ÿ 118, 118tubes

costs 79diagonal connections to 79, 80 , 81internal corrosion 81

tubular bracing members 184, 184

tubular guyed masts 88

advantages 87corrosion protection 88disadvantages 87foundations 88, 89guy planes 88internal access lifts 88structure 87 ÿ 88weight 89ÿ 90

tubular leg memberscompression strengths 184fabrication, poor 255 ÿ 257, 256


turbulence

modesguyed masts 150, 151

lattice towers 150, 151

337

Index



turbulencemodes (continued )simulation, time domain analysis

158ÿ 159, 159and wind resistance 124 ÿ 125, 139

UHF systems see VHF/UHF systemsultimate loads, wind effects, probability

of exceedance 97 ÿ 98, 98

United Kingdombroadcasting development

radio 13ÿ 15television 15 ÿ 17, 16

codes and standards 245, 276reliability standards 281

ice zoning map 111 ÿ 112, 112uplift resistance, foundations 228 ÿ 229,

230 , 231, 231

USAcodes and standards 244, 276


vandalism, guyed masts 68ÿ 69, 69

vertical radiation patterns 34 ÿ 35, 35 ,36

VHF/UHF systemsantenna mountings

candelabra type 47, 48

dipoles 45ÿ 46, 45 , 46

glass-bre cylinders 46, 47

maintenance 46panels 48, 49

shadow effects 49verticality, importance of 48 ÿ 49

vortex excitation, fatigue 220 ÿ 221vortex shedding

causes 211ÿ 212, 212

critical wind speeds 211 ÿ 212cylindrical masts 213ÿ 214damping devices

strakes 214, 215

tuned mass dampers 214 ÿ 215guyed masts, damping 215and ice loading 60ÿ 61

wake galloping 218welded details, endurance curves

221ÿ 222, 221

welding, steel, fracture toughness 253wind climates 93 ÿ 94

atmospheric circulation 95 ÿ 97, 95

boundary layer 99extreme speeds 96, 97 ÿ 98, 98

wind directions, critical 100, 100

wind loadings 2see also dragcurves

BBC 239ÿ 240, 240

early 241ÿ 242, 241

dipoles 36dish antennas 100 ÿ 101fatigue damage 104height relationships 99 ÿ 100square structures 100, 100

topographical factors 101 ÿ 102triangular structures 100, 100

turbulence 99ultimate, probability of exceedance

97ÿ 98, 98

vertical wind prole 101vortex shedding, ice 60 ÿ 61

wind predictions 102and serviceability limits 102 ÿ 104, 103

wind resistance see dragwind speeds

and altitude 282 ÿ 284, 283

downtime due to 102 ÿ 104, 103

and gust speeds 282

and topography 283 ÿ 284, 284 , 285 ,286

wind tunnelsdrag tests 118, 131 ÿ 132, 134ÿ 137, 136

with ancillaries 135 , 137

discrepancies 137 ÿ 140, 138 , 139

early use of 11ÿ 12wire ropes see guy cables; lays

Yllas mast (Finland), failure, icing 60,61, 113

338


communication structures

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