Communication structures
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 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 Academic þ Technical, Bristol Printed and bound in Great Britain by MPG Books, Bodmin, Cornwall
Contents
Foreword
ix
Preface
xi
Acknowledgements
xiii
Chapter 1
Introduction
1
Chapter 2
History
6
Chapter 3 Design considerations 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
19
Chapter 4 Failures of masts and towers 4.1 General, 56
56
iii
Communications structures
4.2 4.3 4.4 4.5 4.6 4.7
Icing failures, 59 Design/detail failures, 61 Maintenance failures, 63 Aircraft damage, 65 Vandal damage, 68 Lessons to be learned, 69
Chapter 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8
5 Forms of structure General, 71 Timber towers, 71 Concrete towers, 71 Lattice steel towers, 75 Lattice guyed masts, 81 Tubular guyed masts, 87 Concrete guyed masts, 90 Other forms of communication structures, 91
71
Chapter 6.1 6.2 6.2.1 6.2.2 6.2.3 6.3 6.3.1 6.3.2 6.3.3
6 Meteorological parameters General, 93 Wind, 93 Wind climate, 95 Boundary layer, 99 Serviceability wind speeds, 102 Atmospheric icing, 104 General, 104 Physics and theoretical modelling of ice accretion, 107 Empirical models to estimate ice loads on structures, 109 Earthquakes, 113 Temperature, 114 Other meteorological aspects, 115
93
6.4 6.5 6.6 Chapter 7.1 7.2 7.3 7.4 7.5 7.6 7.7 iv
7 Wind resistance General, 117 Symmetrical structures without ancillaries, 122 Symmetrical structures with limited ancillaries, 128 General method for structures containing ancillaries, 129 Linear ancillaries, 133 Discrete ancillaries, 133 Cables, 133
117
Contents
7.8 7.9 7.10
Measurements on scale model of communications tower, 134 Discrepancy between wind tunnel tests and full-scale measurements, 137 Icing, 140
Chapter 8 Response 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
147
Chapter 9 Strength 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
177
Chapter 10 Cables 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
195
v
Communications structures
10.5 10.6 10.7 10.8 10.8.1 10.8.2
Modulus of elasticity, 203 Prestretching, 203 Still air tension, 206 Terminations, 206 General, 206 Types of terminations, 207
Chapter 11.1 11.2 11.2.1 11.2.2 11.2.3 11.2.4 11.3 11.3.1 11.3.2 11.3.3
11 Aerodynamic stability General, 210 Vortex shedding, 211 General, 211 Background and critical wind speed, 211 Practical implications, 213 Damping devices, 214 Galloping, 216 General, 216 Critical wind speed, 216 Damping devices, 219
210
Chapter 12.1 12.2 12.3 12.4
12 Fatigue General, 220 Lattice towers, 223 Lattice masts, 223 Guys, 226
220
Chapter 13.1 13.2 13.2.1 13.2.2 13.2.3 13.2.4
13 Foundations General, 228 Foundation types, 228 Type I: to resist uplift, 228 Type II: to resist overturning, 231 Type III: to resist down thrust, 233 Type IV: guy anchorages, 233
228
Chapter 14.1 14.1.1 14.1.2 14.1.3 14.1.4 14.1.5 14.2
14 Codes and standards History, 239 General, 239 Wind loading, 239 Ice loading, 242 Strength, 243 Other aspects, 243 Current codes, 244
239
vi
Contents
14.2.1 14.2.2
General, 244 Comparison of current Codes, 245
Chapter 15 Access and safety 15.1 General, 246 15.2 IASS Recommendations for safe access, 249
246
Chapter 16 Fabrication and erection 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
251
Chapter 17 Maintenance 17.1 General, 264 17.2 Constraints, 264 17.3 Minimizing maintenance at the design stage, 265 17.4 Manuals, 267
264
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 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
276
vii
Communications structures
A.5.1 A.5.2 A.6 A.7 A.8 A.9 A.9.1 A.9.2 A.9.2.1 A.9.2.2 A.10 A.10.1 A.10.2 A.10.3 A.10.4 A.11 A.12 A.13
General, 279 Wind resistance, 286 Ice loading, 292 Displacements/serviceability, 293 Partial safety factors, 295 Strength, 298 Compressive strength, 298 Tensile strength, 303 Steel structure, 303 Guys, 303 Guy assemblies, 304 General, 304 Prestretching, 304 Terminations, 304 Initial tensions, 305 Erection, 305 Insulators, 305 Access, 307
Annex B IASS Working Group Number 4: Masts and Towers B.1 Brief history, 308 B.2 Role in the future, 308 B.3 The members of the Group, 309
308
References
311
Index
327
viii
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 structures 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 incorporates 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 maintenance. 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, fabrication and construction 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. ix
Communications structures
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 constituent 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 Montpellier, France on September 19, 2004, I was informed by Ulrik StøttrupAndersen, 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 underestimated, as the failure of communication facilities can sometimes be quite destructive. One example was the malfunction of the communication 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
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 accumulated 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 xi
Communications structures
the new generation of engineers — whether they study at technical universities or they start their professional carreer in engineering practices, telecom organisations, with contractors or mast and tower fabricators, 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
xii
Acknowledgements
The author has received a great deal of help and advice during the preparation of this manuscript. Working Group 4 (WG4) of the International 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 Duncan Gould Mark Grant Tony di Guglielmo Peter Heslop Mark Malouf Don Marshall Ciro Martoni Ghyslaine McClure John Mearns
(Chapter 11) (Chapters 3, 7, 9, 13, 16 and Annex A) (Chapter 15) (Chapter 3) (Chapters 2, 3) (Chapter 14 and Annex A) (Chapter 16) (Chapter 10) (Chapter 18) (Chapters 3, 16, 17)
Mirosˇ Pirner Bruce Sparling John Wahba Simon Weisman Geoff Wiskin
(Chapter 7) (Chapter 8) (Chapter 14 and Annex A) (Chapters 4, 5, 7, 8) (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. xiii
Communications structures
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:
[email protected] 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.
xiv
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, transmitters, 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. Unfortunately 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 19
Communication structures
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, microwave 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 20
Design considerations
Coverage (a)
Same coverage as for level terrain, using shorter structure (b)
Fig. 3.1 Aerial coverage
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 determining 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 erection 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 elevations 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
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 responses see 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 systems 299 see also connections compound members 189ÿ190, 189
327
Communication structures bracing systems (continued ) cross-bracing 186ÿ187, 186 with horizontals at centre intersections 186, 187ÿ188 with redundants 186, 187 K 188, 188 cranked 188ÿ189, 188 multiple lattice 188, 189 portal frame 188, 189 single lattice 186, 186 tension 186, 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 torsional 178, 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
328
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 strikes 115, 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 speeds 282 and topography 283ÿ284, 284, 285, 286 wind structures 279, 282ÿ284, 285, 286 collapses see failures communication towers, environmental impact 28ÿ29, 29 compound members, bracing systems 189ÿ190, 189
Index 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 first 28, 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 rotation 193, 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 intersections 186, 187ÿ188 with redundants 186, 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 DAB see 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
329
Communication structures 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 members 124, 126 flat-sided members 123, 125 wind on corner 290 wind on face 288 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 members 124, 127, 129, 130 flat-sided members 123, 131 wind on corner 291 wind on face 289 and turbulence 124ÿ125, 139 wind tunnel tests 118, 131ÿ132, 134ÿ137, 135, 136 with ancillaries 135, 137 discrepancies 137ÿ140, 138, 139 dustfall effects 94, 116 dynamic analysis see also simplified dynamic analysis guyed masts 150ÿ154, 152 background components 155
330
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 earthquakes see 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
Index erp see 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 plates 62, 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 towers 232 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 replacement 64, 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, mediumfrequency systems 41 gust response factors lattice steel towers 148, 149 terrain categories 148, 149 gust speeds, and wind speeds 282 guy cables see also galloping; guy insulators; vortex shedding aircraft damage to 66, 67 anchorages conventional 233ÿ235, 235
331
Communication structures guy cables anchorages (continued ) inverted T 235, 237 tension rod 237ÿ238, 238 tie rod 236, 237 two stays 235, 236 connections freedom of rotation 193, 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
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loops 208, 209 preformed grips 208ÿ209 wind resistance 133ÿ134, 134 guy insulators costs 27 installing 263 guy sockets, terminations 207, 207, 208 guyed lattice masts 82 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 masts 17 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
Index erection 258ÿ261, 260 failures 56ÿ57, 58 bracing rods 63, 65 during guy replacement 64, 65 ice loading 59ÿ61 stay plates 62, 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 safety see 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 IASS see 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
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Communication structures 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 foundations 232 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
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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 buckling 178, 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 phones see cellular phones modulus of elasticity ropes 203, 203 variability 204
Index monopoles, seismic responses 273 Moscow Tower (Russia) 72 Mount Sutro Tower (USA) 47, 48 multi-purpose antennas, compromises 26ÿ27, 33ÿ34 multiple lattice bracing systems 188, 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 systems 188, 189 Post Office Tower 74 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 redundants see 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 ice 105, 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
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Communication structures 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
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multi-purpose structures 22 parameters 23 selection parameters 20 service area 20ÿ21 Sjællands Odde tower (Denmark) 130, 132 skywave components, medium-frequency systems 41 snow see 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 standards see codes and standards static, medium-frequency systems 43 stayplates, failure of 62, 63 steel see also fabrication; ropes (steel) angle 254, 300 buckling curves 178ÿ180, 178, 179 strength 301ÿ302, 302 Charpy V-notch tests normalization252 252 specifications 253ÿ254 chemical composition 253, 254 circular 300 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
Index tubes costs 79 diagonal connections to 79, 80, 81 welding, fracture toughness 253 still air tensioning, guy cables 206 strength components 4 strengths see 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 systems 186, 187 terrain categories, gust response factors 148, 149 terrorism, risk assessments 69 Teutoberger mast (Germany), design faults 62, 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 buckling 178, 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 masts 88 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
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Communication structures turbulence modes (continued ) simulation, time domain analysis 158ÿ159, 159 and wind resistance 124ÿ125, 139 UHF systems see 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
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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 resistance see drag wind speeds and altitude 282ÿ284, 283 downtime due to 102ÿ104, 103 and gust speeds 282 and topography 283ÿ284, 284, 285, 286 wind tunnels drag tests 118, 131ÿ132, 134ÿ137, 136 with ancillaries 135, 137 discrepancies 137ÿ140, 138, 139 early use of 11ÿ12 wire ropes see guy cables; lays Ylla¨s mast (Finland), failure, icing 60, 61, 113
