ILE Technical Report No 7 2002 With 2003 Aemndments (2) (4)

The Institution of Lighting Engineers

Technical Report Number 7 High Masts for Lighting and CCTV

2000 Edition (amended 2003)

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The Institution of Lighting Engineers

Technical Report Number 7

HIGH MASTS FOR LIGHTING AND CCTV

2000 Edition Amended 2003

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High Masts for Lighting and CCTV

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HIGH MASTS FOR LIGHTING AND CCTV

Specification for design, manufacture, assembly, erection, painting, testing and maintenance.

(2000 EDITION, Amended 2003)

Copyright 2003 ILE

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without permission

in writing of the Institution of Lighting Engineers.

Institution of Lighting Engineers Regent House Regent Place

Rugby Warwickshire

CV21 2PN

Tel: (01788) 576492 Fax: (01788)540145 Email: [email protected]

Registered Charity Number 268547

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FOREWORD This report relates specifically to conventional raising and lowering high mast systems using winches and wire ropes. Other systems such as bottom, mid-hinged or hydraulically operated masts are not precluded, as many aspects of this report will be relevant with modifications to the operating procedures.

The report covers the aspects of safety, design, erection and maintenance. It is intended to be used as an industrial standard for specifying purposes in the absence of any other specification. It is recognized that, as with any structural design, there will be aspects, which will be the subject of individual specification, and adaptation of this report to suit proven details, materials or principles is implied.

Section 2.6 gives guidance on the design wind loads based on existing information and BS 6399: Part 2: 1977, "Code of Practice for wind loads" for the U K in particular. The Eurocode for wind loads was still under development at the t ime of drafting. Future amendment may be necessary based on the principles included in this report.

Several organisations have been involved in the development of this report and they are listed in the section entitled 'Drafting History and Contr ibutors ' , which also indicates the involvement and the Chairmanship of each drafting committee.

The Health & Safety Executive was also consulted during the preparation of the operational parts of the draft and some amendments were included as a result of the discussions.

This Publication has been prepared 1w the 1LE Technical committee for study and application. The document reports on current knowledge and experience within the specific field of light and lighting described and is intended to be

used by the ILE Membership and other interested parties. It should be noted, however, that the status of this document is advisory and not mandatory. The ILE should be consulted regarding possible subsequent amendments,

Any mention of organizations or products does not imply endorsement by the ILE. Whilst ever care has been taken in the compilation of any lists, up to the time of going to press, these may not he comprehensive.

Compliance with any recommendations does not of itself confer immunity from legal obligations.


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CONTENTS FOREWORD 4

CONTENTS 5

DRAFTING HISTORY AND CONTRIBUTORS 9

ORIGINAL PANEL MEMBERS 9 First Edition (1976) 9

SECTION 2 REVISION (1984) 10

REVIEW PANEL MEMBERS 10 Second Edition (1996) 10

STRUCTURAL TEST PROGRAM (1995) 10

2000 EDITION 10

SECTION 1 - GENERAL 11

1.1 SCOPE 11

1.2 MATERIALS WORKMANSHIP AND DESIGN 11

1.3 STANDARDS, SPECIFICATIONS AND REGULATIONS 11

1.4 DEFINITIONS 12

1.5 SCHEDULE OF DETAILS TO BE SUPPLIED BY PURCHASER AND MANUFACTURER 14

SECTION 2 - DESIGN OF MAST STRUCTURE AND FOUNDATION 17

2.1 SCOPE 17

2.2 METHOD OF DESIGN 17

2.3 LIMIT STATE REQUIREMENTS 17 2.3.1 Ultimate Limit State 17 2.3.2 Serviceability Limit States 18 2.3.2.1 General 18 2.3.2.2 Lighting Masts 18 2.3.2.3 CCTV Masts 18

2.4 SAFETY FACTORS FOR LOADS 18

2.5 SAFETY FACTORS FOR MATERIALS 19

2.6 WIND LOADING 19 2.6.1 General 19 2.6.2 Wind Speeds 20 2.6.2.1 Basis for Calculating Wind Speeds 20 2.6.2.2 Design Wind Speed 20 2.6.2.3 Hourly Mean Wind Speed 20

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2.6.3 Reference Pressure 21 2.6.4 Peak Equivalent Static Pressure 21

2.6.4.1 General 21 2.6.4.2 Size Reduction Factor, 8 21 2.6.4.3 Response Factor, p 21

2.6.5 Force Coefficients 23 2.6.6 Characteristic Wind Loads 26

2.7 MAST CONSTRUCTION 26 2.7.1 Steel 26 2.7.2 Welding 26 2.7.3 Door Opening 26 2.7.4 Site Joints in Mast 27 2.7.5 Ventilation 27 2.7.6 Winch and Equipment Mountings within the Base Compartment 27 2.7.7 Tolerances 28

2.8 CONNECTION BETWEEN MAST AND SUBSTRUCTURE 28

2.9 FOUNDATIONS AND SUBSTRUCTURE 29 2.9.1 Basic Wind Loads 29 2.9.2 Foundation Design 29 2.9.3 Overtuming29 2.9.4 Substructure Design 29

2.10 PROTECTION AGAINST CORROSION 30 2.10.1 General Requirements : Steel Masts 30 2.10.2 Performance Requirements 30 2.10.3 Environment 30 2.10.4 Protective Systems 31 2.10.5 Suggested Systems 31

2.11 METAL COATINGS 34

2.12 APPENDIX (EXPLANATORY NOTES) 34 2.12.1 Symbols 34 2.12.2 Explanatory Note on the Derivation of the P and 8 Factors 35 2.12.3 Typical Calculation of the Bending Moment at the Foot of a Mast 36

2.13 APPENDIX A - METHOD FOR CALCULATION OF DAMPING 42 2.13.1 Total Damping 42 2.13.2 Aerodynamic Damping 42 2.13.3 Structural Damping 43

SECTION 3 - WINCHES AND MECHANICS 45

3.1 SCOPE 45

3.2 LUMINAIRE/CCTV CARRIAGE 45 3.4.1 Mechanical Details 45

3.4.2 Electrical Details 46

3.3 HEAD FRAME ASSEMBLY 46

3.4 WINCH 47 3.4.1 General 47 3.4.2 Safe Working Load 48

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3.4.3 Design 48 3.4.4 Drive & Speed of Operation 48 3.4.5 Security Against Runaway 48 3.4.6 Drive Shaft Positive Locking Device 49 3.4.7 Winch Drum 50 3.4.8 Gearing 50 3.4.9 Power Tool Drive 51 3.4.10 Winch Tests 51

3.4.10.1 Type Tests 51 3.4.10.2 Demonstration Tests 52 3.4.10.3 Proof Test 52

3.4.11 Nameplate 52

3.5 WIRE ROPES 53

3.6 SECURITY CONNECTOR 53

3.7 LIGHTNING PROTECTION 54

3.8 POWER TOOL AND TRANSFORMER 55

3.9 MAINTENANCE CARRIAGE 55

3.10 MAINTENANCE CARRIAGE SAFETY DEVICE 55

3.11 SITE MAST TESTS 55

SECTION 4 - LUMINAIRES AND ELECTRICS 57

4.1 SCOPE 57

4.2 CONSTRUCTION OF LUMINAIRES 57

4.3 PHOTOMETRIC 57

4.4 LAMPS 58

4.5 CONTROL GEAR 58

4.6 ELECTRICAL WIRING - LUMINAIRES AND LUMINAIRE CARRIAGE 59

4.7 MAST CABLE 60

4.8 SWITCHING CONTROL 60

SECTION 5 - ASSEMBLY, ERECTION AND TESTING 61

5.1 SCOPE 61

5.2 SCHEDULE 61

5.3 COMMISSIONING 61

5.4 FUTURE OPERATION 62


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SECTION 6 - MAINTENANCE 63

6.1 INTRODUCTION 63

6.2 SCOPE 63

6.3 DEFINITIONS 64

6.4 TYPICAL MAINTENANCE AND INSPECTION SCHEDULE AND CERTIFICATE 64

6.5 USE OF MAINTENANCE CARRIAGE SCHEDULE AND CERTIFICATE 68

6.6 POINTS TO BE OBSERVED IN THE LOWERING AND RE-ERECTION OF HIGH MASTS 71

BRITISH STANDARDS AND CODES OF PRACTICE AND OTHER REFERENCES 76

FIGURE 1 - R E S P O N S E FACTOR 0 v RATIO r)o/Vio 22 FIGURE 2 - SIZE REDUCTION F A C T O R 5 v H E I G H T h 23 FIGURE 3 - F O R C E COEFFICIENTS FOR S Q U A R E SECTIONS 24 FIGURE 4 - E X A M P L E BENDING M O M E N T S C A L C U L A T I O N 40

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DRAFTING HISTORY AND CONTRIBUTORS This Report is the summation of experience contributed by all those listed below, who, together with their supporting staff, have monitored the design, installation and maintenance of high mast lighting and CCTV schemes.

The first Report was drafted in 1976 by separate panels working on each section and much of the original work is still current and relevant and was retained in later revisions. In 1984 a small structural panel was formed to review Section 2 on mast design and to produce a new version with additional explanation. The second edition in 1996 followed a total review prior to reprinting to allow for changes in the current standards and documentation, and to take account of further experience by minor revision.

This 2000 Edition includes C C T V aspects for the first t ime and updates the wind loading design to current standards. The opportunity was taken to include other minor design details for doors and flanges.

ORIGINAL P A N E L M E M B E R S

First Edition (1976)

DRColvin Association of Public Lighting Engineers D G Duncan Association of Public Lighting Engineers AAGFrame Association of Public Lighting Engineers K J Goddard Association of Public Lighting Engineers A Paul Association of Public Lighting Engineers L Riley Association of Public Lighting Engineers R Crowther Concrete Utilities Ltd. K H Twibell Concrete Utilities Ltd. P Elliot Department of Environment S M Phillipson Department of Environment F Shields Department of Environment F A Tuck Department of Environment E M Jordan GEC (Street Lighting) Ltd. M II Mounsdon G E C (Street Lighting) Ltd. E M Haines G E C Hirst Research Centre E B Rhead London Electric Firm J M Clough Outdoor Lighting Ltd. P Harthill Phosco Ltd. G J Glassbrook Scottish Development Department B R McKenna Scott Wilson Kirkpatrick & Partners J S Buyers A McCaig

* Section Chairman


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SECTION 2 REVISION (1984)

E M Haines (Chairman) R T Aitken C R L a n e G W Naylor

GEC Hirst Research Centre British Steel Corporat ion (Tubes Division) Concrete Utilities Ltd. Husband & Co

REVIEW PANEL M E M B E R S

Second Edition (1996)

C R Lane (Chairman) A Jenvey H Pfitzmann R Street P Plackett

CU Lighting Ltd. Abacus Municipal Ltd. Phosco Ltd. Siemens Lighting Ltd. Stainton Metal Co. Ltd.

S T R U C T U R A L T E S T P R O G R A M (1995)

WS Atkins Consultants Ltd. Abacus Municipal Ltd. CU Lighting Ltd. Holophane Europe Ltd. Siemens Lighting Ltd. Stainton Metal Co. Ltd.

2000 EDITION

C R Lane (Chairman) CU Lighting Ltd. B W Smith Flint and Neill Partnership E J Rees Flint and Neill Partnership A Jenvey Abacus Lighting Ltd. D Javes Holophane Europe Ltd. H Pfitzmann Phosco Ltd. P J Plackett Stainton Metal Co . Ltd. A Riley Whitecroft Road & Tunnel Lighting Ltd

The Highways Agency generously contributed to the costs of the Third Edition, but accept no responsibility for its content.


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SECTION 1 - GENERAL 1.1 SCOPE

This Report covers the design, manufacture, assembly, erection, painting, testing and maintenance of an unstayed steel mast, used for the purpose of supporting luminaires or C C T V cameras at heights at, or between, 10 metres and 60 metres.

1.2 MATERIALS W O R K M A N S H I P A N D DESIGN

The workmanship throughout shall be of a high standard and materials new and of the best quality. Care shall be taken in manufacture to ensure that all parts will fit together on erection at site.

All components shall be designed to require the min imum of maintenance and skilled attention and also to allow routine maintenance to be carried out quickly and easily with a minimum use of tools.

All equipment shall be suitable for use in and be rated for the service conditions at site.

Every reasonable precaution and provision shall be incorporated in the design of the equipment for the safety and security of the system and of those concerned with its operation and maintenance.

All materials and practices used and in regard to which Reports , Specifications or Codes of Practice have been issued by the British Standards institution, shall be made and supplied in accordance with such current Reports, Specifications or Codes unless otherwise specified or approved. T h e intent of the Health and Safety at Work Act 1974 shall be observed throughout design, manufacture, assembly and erection and when recommending maintenance routines and standards for the design life of the installation.

The electrical installation shall comply with all appropriate statutory requirements and with the BS 7671 : 1992, "Requirements for electrical installations. IEE Wiring Regulations. Sixteenth edition".

1.3 S T A N D A R D S , S P E C I F I C A T I O N S A N D R E G U L A T I O N S

Any Standard, Specification or Regulation referred to shall be held to be the latest Edition. It is essential to verify if additions or amendments have been made. (The current standards at the t ime of drafting are listed in the References section.)


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1.4 DEFINITIONS

C A B L E

C C T V C A M E R A

C O M P E N S A T I N G PULLEY

D O C K I N G

F L A N G E PLATE

H E A D F R A M E ASSEMBLY

HIGH M A S T

L U M I N A I R E

L U M I N A I R E / C C T V C A R R I A G E

Insulated electricity supply conductors.

Closed circuit television camera.

A compensating device used to maintain the luminaire / CCTV carriage in a horizontal plane.

A term used to describe the correct (home) positioning of a luminaire / C C T V carriage at the top of a high mast.

A structural plate welded to the base of the mast to provide a connection to the foundation bolts.

That part at the top of a mast used to support pulleys, guides, stops, docking or other supporting, limiting or electrical devices, or a combination of them.

An unstayed steel mast supporting luminaires or C C T V cameras.

A lighting fitting or optical device controlling a light source or sources.

The supporting medium on which luminaires or cameras are raised and lowered.

M A I N T E N A N C E C A R R I A G E

M A S T H E I G H T

M O U N T I N G HEIGHT

P O W E R T O O L

R O P E

A cradle designed to carry two operatives with their equipment to the head of the mast.

The mast height (h) is the vertical distance between the base flange and the top of the head frame assembly.

The height of the mast defined as the vertical distance between the base flange and the plane in which the luminaires or C C T V cameras lie when in their operating position.

A device used to raise and lower the carriage via the winch.

A flexible cord of twisted steel strands used to support the carriage.


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SECURITY CONNECTOR A rope or chain used to contain other supporting ropes in the event of the rope from a single drum winch failing.

W I N C H A geared device giving a mechanical advantage to raise and lower the luminaire or CCTV camera carriage.

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1.5 S C H E D U L E OF DETAILS T O B E SUPPLIED BY P U R C H A S E R A N D M A N U F A C T U R E R

DETAILS T O BE SUPPLIED BY P U R C H A S E R T O M A N U F A C T U R E R

a) Mast height or mounting height.

b) Number of luminaires, light source, wattage, type of light distribution, limiting weight and projection (windage) or the number of cameras, pan and tilt requirements, limiting weight and projection (windage).

c) For locations in the U.K. the purchaser should specify: the basic wind speed and topographic increment as defined in BS 6399, Part 2, Clause 3.2, and the wind return period if different from the standard 25 years given in this Specification.

For locations not in the UK, the purchaser should specify the hourly mean wind speed and 3-second gust wind speed at the site for the required return period. Unless data for the site can be obtained from a Code of Practice or other recognized design guide, the purchaser is recommended to seek advice from the relevant meteorological office or building research agency.

d) If lock nuts are required on the foundation bolts.

NOTE. Lock nuts are not essential for a properly maintained mast but may be desirable in areas of high vandalism. However, when used good engineering practice should be followed during tightening.

e) Details of foundations if provided by others or soils data if foundations are to b e designed by manufacturers.

f) Protective system.

g) Requirements, if any, for serviceability limit states.

h) Details of particular electrical switching arrangement.

i) Details of photocell (if required).

j ) Type of winch system and power tool including operating voltage and electrical safety requirements.


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DETAILS T O BE SUPPLIED B Y M A N U F A C T U R E R T O P U R C H A S E R

a) General arrangement drawings showing principal dimensions of mast and details of base, door opening and locking devices, mast head pulleys etc.

b) Calculations or test data to show that masts and foundations (if appropriate) comply with Specification.

c) Details of welding fabrication, joint ing and erection procedure.

d) Details of sub-contractors, if any.

e) Recommendat ions on operation and maintenance of mast and fittings.


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SECTION 2 - DESIGN OF MAST STRUCTURE AND FOUNDATION 2.1 SCOPE

This Section covers the design of a high mast (including foundation) with a mast height equal to or greater than 10 metres but not more than 60 metres. The mast height (h) is defined as the vertical distance between the base flange and the top of the head frame assembly.

2.2 M E T H O D O F DESIGN

Masts shall be designed using limit state principles. The limit states to be considered are:

a) Ult imate b) Serviceability

based on a design wind speed with a return period of 25 years.

Confirmed practical test data and experimental wind tunnel data may be used in place of coefficients given in this Specification.

The loads set out in the Specification are characteristic loads. Each of the characteristic loads shall be multiplied by the appropriate value of a safety factor for loads (yf) to arrive at the design load to be used in the calculation of moments , shears, total forces or other effects for each of the limit states under consideration.

Similarly, the characteristic strength of the materials used in the construction shall be divided by the appropriate value of the safety factor for materials (y m ) to arrive at the design strength to be used in calculations.

2.3 L I M I T S T A T E R E Q U I R E M E N T S

2.3.1 Ult imate Limit State

The strength of the structure shall be sufficient to withstand the design loads. The strength of the structure may, for steels complying with BS EN 10025: 1993, "Hot rolled products of non-alloy structural steels. Technical delivery condi t ions" be assessed using the plastic moment of resistance provided the moment due to the design loads are equal to or less than the moment capacity M as determined in Clause 2.4. Particular attention must be paid to the nature and design of the door opening (Clause 2.7.3).


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Current practice and experience indicates that vibration and fatigue need not be considered as design criteria where the natural frequency of oscillation in the fundamental mode does not exceed 1 Hz.

2.3.2 Serviceability Limit States

2.3.2.1 General

The deflection and the vibration of the structure shall not exceed any limits specified by the Purchaser.

2.3.2.2 Lighting Masts

The limits for deflection for lighting masts may be specified at a wind speed lower than the design wind speed. It is not generally necessary to specify limits for vibration for lighting masts. For example, where deflection is considered critical it may be limited to 1/40 of the mast height at 2/3 of the design wind speed.

2.3.2.3 CCTV Masts

For CCTV applications the mast stiffness shall be such that with loads arising from a gust wind profile, with a wind speed of 22m/sec at 10m above ground level, the torsional rotation at the top of the mast shall not exceed 25 minutes of arc (0.0073 radians) and the linear deflection at the top of the pole shall not exceed 150mm.

2.4 S A F E T Y F A C T O R S F O R L O A D S

The design loads shall be the characteristic loads multiplied by the safety factors for loads (Yf) given in the following table. The safety factor (yf) is a combined factor to allow for wind load and structural variations.

Serviceability Limit States

Ultimate Limit State

Dead Load 1.0 1.0 Wind Load 1.0 1.25

For masts of circular or regular polygonal cross section with 16 or more sides and where the D/t ratio does not exceed 200, the moment capacity of the section (M ) may be calculated as follows:

Note: For N < 16 guidance is given in BS 5649: Part 7: 1985, "Lighting columns. Method of verification of structural design by calculation ".


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For D/t < NE/180a y

M * = M / y m

F o r N E / 1 8 0 a y < D / t < 2 0 0

M* = MP{0.9241 x [(90a yD/NEt)"- 2 8 5 8] - 0.1266}/ym

is the diameter or across flats dimension of the section (mm) is the section wall thickness (mm) is the number of sides, and is to be taken as 20 for circular and polygonal sections with 20 or more sides, and as the actual number of sides for polygonal sections with less than 20 sides is the Young ' s modulus of elasticity (N /mm 2 ) is the characteristic yield strength (N /mm 2 )

is the section design bending resistance (Nm) is the section plastic moment of resistance (Nm)

For door sections refer to Clause 2.7.3

2.5 SAFETY F A C T O R S FOR M A T E R I A L S

The design strengths shall be the characteristic strengths divided by a safety factor for materials y m given in the following table:

Ult imate Limit State

Concrete 1.5 Steel, Reinforcement and Bolts 1.15

The characteristic strength means the value of the cube strength of the concrete (below which not more than 5% of the test results fall), and for steel the specified minimum yield strength or 0 .2% proof stress. For holding down bolts, the characteristic strength in tension shall be the 0 .2% proof stress and for shear (0 .2% proof stress)/V3.

2.6 W I N D L O A D I N G

2.6.1 General

The basis for the structural design of high masts shall be the peak response of the structure to an appropriate wind speed, which has a return period of 25 years at the site where they will be used.

Where : D

t N

M* M


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The peak response is derived from the peak equivalent static pressure which is a function of firstly, the actual wind speed at the site, and secondly, the apparent magnification of the wind pressure which depends on the natural frequency of oscillation of the mast, the mast height and the amount of damping present.

2.6.2 Wind Speeds

2.6.2.1 Basis for Calculating Wind Speeds

The design wind speed and the hourly mean wind speed shall be obtained using BS 6399: Part 2: Clause 3.2: Directional wind speeds, using the following procedure:

When calculating the site wind speed, V s using equation (8) of BS 6399: Part 2, the following assumptions shall be made:

the direction factor, Sd shall be taken as 1.0; the seasonal factor, S s shall be taken as 1.0, the probability factor, S p shall be taken as 0.96 for a 25 year return period. [If other return periods are specified, BS 6399: Part 2 equation D. l shall be used. Note that the annual risk of the basic wind speed being exceeded, Q = 1/(return period). Thus Q = 0.04 for a 25 year return period] .

2.6.2.2 Design Wind Speed

The design wind speed at effective height, H e shall be taken as the effective wind speed, V e obtained using BS 6399: Part 2: Clause 3.2.3. The effective height H e shall be taken as the height in metres above ground level of the centre of the area of the section under consideration. (Note that this definition of H e is conservative for sites in town terrain. The procedure in BS 6399: Part 2: Clause 1.7.3.3 may be used if a more accurate value is required.)

The gust peak factor, g t , shall be taken as 3.44.

NOTE : The size reduction factor 8, given in Figure 2, takes account of the size of the mast in relation to gust dimensions .

2.6.2.3 Hourly Mean Wind Speed

The hourly mean wind speed, V at effective height H e shall be calculated using the direction method given in B S 6399: Part 2 : Clause 3.2, taking the gust peak factor gt = 0.0 (i.e. no gust a l lowance) .

Thus in BS 6399: Part 2, Clause 3.2.3.2.2 equation (28) for sites in country terrain becomes:

Sb = Sc(l + Sh)


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903581Rectangle

903581Rectangle


and equation (29) for sites in town terrain becomes:

Sb = ScTc(l + Sh)

The terms S c , T c and Sh are defined in BS 6399: Part 2, Clause 3.2.3.2.

2.6.3 Reference Pressure

The reference pressure, qn e ( N / m 2 ) at any height H e , shall be derived from the equation:

q H e = 0 . 6 1 3 V e 2

Where V e is the design wind speed calculated in accordance with Clause 2.6.2.2.

2.6.4 Peak Equivalent Static Pressure

2.6.4.1 General

The reference pressure at any height H e shall be multiplied by the response factor p and the size reduction factor 8 to obtain the peak equivalent static pressure, EQH, in N / m 2 .

EqH = P5qHe

(See Clause 2.12.2 for explanatory notes on the deviation of the P and 8 factors).

2.6.4.2 Size Reduction Factor, 8

The size reduction factor 8 is a function of the mast height and shall b e selected from Figure 2.

2.6.4.3 Response Factor, (3

The response factor P depends on the natural frequency, tLj (Hz) and the total damping of the mast at the hourly mean wind speed at a height of 1 Om above ground level, Vio . The value of the response factor, P shall be selected from the curves given in Figure 1. Values of response factor for intermediate values of logarithmic decrement of damping may be obtained by linear interpolation between the curves. Unless evidence can be produced to justify the use of higher values, the logarithmic decrement of the damping shall be assumed to be 0 .1 . If agreed with the Purchaser, the method of assessing damping given in Appendix A may be used.


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T|o/VlO

r j 0 = natural frequency (Hz)

Vio = hourly mean wind speed (m/s)

F I G U R E 1 - R E S P O N S E F A C T O R p v R A T I O TJO/VIO


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8

1.0

0.9

0.8

0.7

0.6

0.5

3 < h * s 6 0 8 - 1 - 0.006(h - 3)

3 < h * s 6 0 8 - 1 - 0.006(h - 3)

0 10 20 30 40 50 Height (h) of top of structure above flange (metres)

60

F I G U R E 2 - SIZE R E D U C T I O N F A C T O R 8 v H E I G H T h

2.6.5 Force Coefficients

a) Masts

For masts with a paint or smooth galvanized finish the value of the force coefficient shall be as follows:

For Circular masts :

0 < R e 2 x l 0 5 C f = 1.2 2 x l 0 5 < R e 4 x l 0 5 C f = 1 .9-0 .35ReX 10"5

4 x l 0 5 < R e 2 2 x l 0 5 C f = 0.433 + 0.0167ReX 10"5

2 2 x l 0 5 < R e C f = 0.8

For Octagonal masts (8 sided):

0 < R e 2.3 x 10 5 C f = 1.45 2 . 3 x l 0 5 < R e D 3 . 0 x l 0 5 C f - 1.943 - 0 . 2 1 4 3 R e x 10"5

3.0 x l O 5 < R e C f = 1.3


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For Dodecagonal masts (12 sided):

0 2 x 10 5

< R e < 2 x 10 5

< R e < 7 x 10 5

< R e 7 x lcr

For Hexadecagonal masts (16 sided):

Where

0 2 x 10 5

6 x 10 5

14 x 10 5

< R e < 2 x 10 5

r/B

FIGURE 3 - F O R C E C O E F F I C I E N T S F O R S Q U A R E S E C T I O N S


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For masts of other cross-sectional shapes either force coefficients may be obtained from recognized International Standards or they shall be determined from properly conducted wind tunnel tests. Adoption of values from such standards or from wind tunnel tests shall be agreed with the Purchaser. Particular care should be taken to ensure that the values of force coefficients relate to cross-sections of members of infinite length.

Wind tunnel tests to establish force coefficients should be carried out using true-scale specimens, which accurately represent the final proposed column. The forces on the specimen shall be measured in the direction of the airflow and the direction normal to the airflow.

Previous wind tunnel tests have indicated that small angular rotations of specimens can cause considerable differences in force coefficients. The specimens shall therefore be turned in the wind tunnel and measurements taken at angular increments. In the region of each force coefficient the measurements shall be reduced to approximately 1 of rotation. Comparisons shall be made with the values of similar sections given in recognized International Standards as part of the adoption and agreement procedure with the Purchaser set out above.

b) Luminaire /CCTV and Head Frame Assemblies

The force coefficients for luminaries/CCTV and head frame assemblies should be obtained from wind tunnel tests. In the absence of such data, the force coefficient applicable to the projected area in the direction of the wind may be assumed to be equal to unity.

These tests shall be carried out on a full-scale model in a tunnel sufficiently large to reduce side effects to an insignificant level. The surface condition of the specimen shall accurately represent that of the production version.

The test specimen must include all elements of the luminaire, C C T V , head frame assembly and associated equipment

When carrying out wind tunnel tests, forces both in the direction of the air flow and in the direction normal to the air flow shall be measured, as shape and lift coefficients are required for all the directions considered. All shape coefficients shall be based on the projected area normal to the airflow.

Forces shall be measured in increments of rotation of approximately 1 between the limit of 10 to the horizontal. During testing the effects of small plan rotations about the point of fixing shall also be taken into account. Where an increase in shape coefficient is obtained with a rotation within the limits of 10 then this value shall be adopted.


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2.6.6 Characteristic Wind Loads

The characteristic wind loads shall be the product of the peak equivalent static pressures; the force coefficients; and the projected area. See Clause 2.12.3 for typical calculations of the wind moment at the foot of a mast.

2.7 M A S T C O N S T R U C T I O N

2.7.1 Steel Structural steel shall comply with the requirements of BS EN 10025 and shall have a notch toughness appropriate to the proposed location. For the UK, plates over 25mm shall have a Charpy value at -20C of 27 joules min imum; plates 2 5 m m and less need not be Charpy tested.

Notwithstanding the above, special steels may be used if agreed by the purchaser.

When steel tubes are used, they shall comply with the requirements of BS EN 10210-2: 1997 "Tolerances, dimensions and sectional properties", or other agreed specification.

The flange plate shall be free from significant laminations and inclusions. Where required, appropriate non-destructive tests shall be carried out.

2.7.2 Welding

Welding shall comply with the requirements of BS EN 1011-1:1998 "Welding. Recommendations for welding of metallic materials. General guidance for arc welding" and BS E N 1011-2:2001 "Welding. Recommendat ions for welding of metallic materials. Arc welding of ferritic steels".

Detailed procedures and procedure trials, where required, shall be in accordance with BS EN 288-1:1992 "General rules for fusion welding", BS EN 288-2:1992 "Welding procedures specification for arc welding" and BS EN 288-3:1992 "Welding procedure tests for the arc welding of steel". Welding and fabrication details shall be given (Refer to Clauses 16 of BS EN 1011-2:2001).

2.7.3 Door Opening

A vandal resistant weatherproof door shall be provided in the mast with a door opening of min imum size consistent with clear access to equipment mounted therein. A vandal resistant door locking device shall be provided.

The distance from the mast flange plate to the bottom of the door opening shall be a minimum of twice the width of the door opening.

In the detailing of door openings consideration should be given to the need for reinforcement of the edges, buckling, stress concentrations at corners and torsional effects if any. A min imum radius of 20mm is recommended at corners of openings.


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Where the section containing the door opening is circular or polygonal with eight or more sides, design strengths may be calculated by reference to BS 5649:- "Lighting columns" using the following procedure:

M U D 7 = M U 7 x M U D 4 o / M U 4 0

Where Mun7 is the bending strength of the door section to be used in design.

Mij7 is the bending strength of the closed section at the door in accordance with Clause 2.4

MUD40 is m e bending strength of the door section in accordance with BS5649.

Mu4o is the bending strength of the closed section at the door in accordance with BS5649 .

In all other cases the design strength shall either be calculated from first principles, or be based on the results of full-scale load tests.

2.7.4 Site Joints in Mast

Masts may be delivered to site complete or in sections as circumstances allow. However, if masts are constructed in sections, principles and details shall be shown on the drawings. Jointings shall be strictly in accordance with the manufacturer 's instructions.

2.7.5 Ventilation

The mast shall be ventilated: means to achieve this shall be stated.

2.7.6 Winch and Equipment Mountings within the Base Compartment

Brackets or mount ing plates, drilled to template shall b e mounted in the mast to support the winch and mast electrical equipment.

A 12mm diameter stainless steel or brass stud attached to the main body of the mast structure shall be provided in a readily accessible position in the base compartment to provide a lightning and cable earth point.

The stud shall be provided with sufficient brass or stainless steel nuts and washers to allow two separate connect ions to be made for:

a) Earth strip from electrical supply point. b) Lightning protection earth strip.


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2.7.7 Tolerances

i) Length

The length of the mast shall be such as to provide a mast height not less than that specified. Occasionally, in the vicinity of airports, for example, it may be necessary to specify a maximum height.

ii) Diameter

The diameter of circular hollow sections shall comply with the tolerances specified in BS EN 10210: "Hot finished structural hollow sections of non-alloy and fine grain structural s teels" or BS EN 10219: "Cold formed welded structural sections of non-alloy and fine grain steels". The dimension across flats for polygonal sections shall not be less than the value used in the design calculations.

iii) Verticality and Straightness

When measured in still air and even temperature conditions the axis of the mast when erected shall not deviate:

(a) From the vertical by more than 0 . 3 % of the height above the flange plate.

(b) From straightness by more than 0 . 3 % of any length measured at the centre of that length.

2.8 C O N N E C T I O N B E T W E E N M A S T A N D S U B S T R U C T U R E

The mast shall be connected to the substructure by means of a flange plate and holding down bolts (including lock-nuts if specified) or other approved methods.

The flange plate shall be designed for the ultimate limit state using the safety factors for loads and materials given in Clauses 2.4 and 2.5 respectively. The method of design shall be appropriate for the actual fabrication details. Full account shall be taken of the shear stresses around the holding down bolts, and bending strength within the flange by means of yield line analysis, or other suitable method. Alternatively, design may be based upon the results of full-scale load tests.

The diameter of the flange plate shall not be less than the pitch circle diameter of the holding down bolts plus 2.4 t imes the diameter of the bolt holes.

The holding down bolts shall be installed with a lower location plate and an upper template to ensure correct vertical and horizontal bolt alignment.

The space between the top of the concrete substructure and the underside of the flange plate shall either be filled with an impervious material after provision of adequate drainage hole or left open. The cable entry duct shall not be obstructed.


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When the weight of the mast is to be carried by nuts beneath the flange plate, the bolts shall be suitably designed to resist all additional stresses arising from the construction detail, and protected against corrosion.

When the weight of the mast is supported directly through the flange plate to the substructure, the space should be packed with dry pack mortar.

2.9 F O U N D A T I O N S A N D S U B S T R U C T U R E

2.9.1 Basic Wind Loads

Because of the difference in the dynamic behaviour of the mast and the foundation it may be assumed, in the absence of more accurate information, that the basic wind loads transferred from the mast to the substructure reduces the values calculated in accordance with Clause 2.6 at the top of the substructure to 1/p of the values at the bottom of the substructure and foundation, where p is the response factor for the mast.

2.9.2 Foundation Design

The design of the foundation shall be based on the principles set out in BS 8004: 1986, "Code of practice for foundations". As BS 8004 is not based on limit state design, the design forces for the purposes of foundation design (in accordance wi th BS 8004) shall b e the appropriate characteristic forces specified herein multiplied by a safety factor for loads yf equal to 1.0.

2.9.3 Overturning

The stability of the mast and substructure shall be considered under the effects of design forces derived from mult iplying the characteristic forces by the safety factors for loads yf corresponding to the ult imate limit state i.e. dead load 1.0 and wind loading 1.25.

The least restoring moment shall be equal to not less than 1.15 t imes the great overturning moment .

2.9.4 Substructure Design

The design of the reinforced concrete substructure shall be based on the principles set out in BS 8110:- "Structural use of concrete" as appropriate. When using BS 8110, the safety factors for loads y f corresponding to the ult imate limit state shall be 1.0 for dead load and 1.25 for wind loads.


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2.10 P R O T E C T I O N A G A I N S T C O R R O S I O N

2.10.1 General Requirements : Steel Masts

Where stainless steel is used no additional corrosion protection is necessary for both internal and external surfaces. For ferrous steels the protective system can be selected from those given in Clause 2.10.5. Other suitable protective systems are available and may be offered as alternatives to those listed. The method of protection of the underside of the flange plate, together with protection afforded to holding down bolts, levelling nuts and associated stress components beneath it, must be given.

2.10.2 Performance Requirements

The protective system shall comprise an external treatment and an internal treatment of the mast. It shall be selected with regard to durability during handling, transport, erection and in service. It shall meet requirements for long term exposure at the site, for ease of maintenance and overcoating and for appearance. Where requirements for durability are incompatible with appearance and choice of colour, a suitable decorative coating may be applied over the protective system. The durability of the chosen system should provide a typical t ime to first maintenance of 10 to 20 years.

2.10.3 Environment

Four types of environment are defined. The corresponding site environment shall be identified and the protection system selected accordingly.

a) Non-polluted inland (Type 1) b) Polluted inland (Type 2) c) Non-polluted coastal (Type 3) d) Polluted coastal (Type 4)

Parts of the mast which may be buried or which will be subjected to the effect of local contaminants such as salt spray from the highway shall have additional protection if specified.


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2.10.4 Protective Systems

The following types of protective systems may be used:

TYPES O F P R O T E C T I V E S Y S T E M

External Surfaces Galvanized and painted Galvanized Metal sprayed and sealed Painted

Internal Surfaces Galvanized Bituminous Paint*

Exposed holding down bolts and nuts

Galvanized Painted Mastic coating Impregnated wrapping

Limited to accessible surfaces when applied by brush or spray.

2.10.5 Suggested Systems

The protective system may be selected from the suggested systems given in the table below. Alternatively other approved systems or methods of protection may be used. An indication of suitability of the suggested systems for the environment types given in Clause 2.10.3 is given but performance and life will vary with local conditions. Further guidance may be obtained by reference to BS 5493: 1977, "Code of practice for protective coating of iron and steel structures against corrosion".

S U G G E S T E D S Y S T E M S E N V I R O N M E N T

i) Galvanized & Painted Types 1 .2,3 and 4 (SB9 in BS 5493)

ii) Galvanized Type 1 (SB1 i n B S 5493)

iii) Aluminium Sprayed and Sealed Types 1,2,3 and 4 (SC5 A in BS 5493)

iv) Zinc Sprayed and Sealed Types 1,2 and 4 (SC5Z in BS 5493)

v) Painted A Types 1 and 3 (SH6 in BS 5493)

vi) Painted B Types 2 and 4 (SH7 in BS 5493)

NOT E: A survey has shown a general requirement for a galvanized finish for high masts . For a hot dipped galvanized process this automatically provides internal and external protection.


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i) G A L V A N I Z E D A N D PAINTED -E N V I R O N M E N T S T Y P E S 1,2,3 and 4

a) Internal and External Surfaces.

Galvanized to BS EN ISO 1461: 1999, "Hot dipped galvanized coatings on fabricated iron and steel articles. Specifications and test me thods" (85 um minimum coating thickness).

b) External Surface only.

Degrease followed by:

1st Coat calcium plumbate types A or C to BS 3698: 1964 (1979) "Specification for calcium plumbate priming paints". (40um min imum dry film thickness).

2nd Coat micaceous iron oxide phenolic tung oil finish (40um min imum dry film thickness).

ii) G A L V A N I Z E D -E N V I R O N M E N T T Y P E 1

a) Internal and External Surfaces.

Galvanized to BS EN ISO 1461 (85 um min imum coating thickness).

N O T E : A uniform appearance cannot b e guaranteed with galvanizing a product the size of a h igh mast together with the changes in material thicknesses involved. Where appearance is very important consideration should be given to a single coat of appropriate paint for aesthetic reasons only.

iii) A L U M I N I U M S P R A Y E D A N D S E A L E D -E N V I R O N M E N T S T Y P E S 1,2,3 and 4

a) External Surfaces.

Metal Spray: Aluminium spray to BS 2569:- "Specification for sprayed metal coatings". (100 u m nominal thickness), sealed.

b) Internal Surfaces.

Paint System: Bi tumen Coating.


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iv) ZINC S P R A Y E D A N D S E A L E D -E N V I R O N M E N T S T Y P E S 1,2 A N D 4


Metal Spray: Zinc spray to BS 2569 (100 u m nominal thickness), sealed.


Paint System: Bi tumen Coating.

v) PAINT S Y S T E M A -E N V I R O N M E N T S T Y P E S l a n d 3


Surface Preparation: Blast clean to 2nd quality BS 7079:-"Preparation of steel substrates before application of paint and related products".

Paint System: Primer: Zinc phosphate (70 u m dry film thickness) Undercoat: Micaceous iron oxide (100 u m dry film

thickness) Finish: Micaceous iron oxide (100 u m dry film

thickness)


Paint System: Bi tumen coating.

vi) PAINT S Y S T E M B ( E N V I R O N M E N T S T Y P E S 2 A N D 4)


Surface Preparation: Blast clean to 2nd quality BS 7079.

Paint System: Primer: Zinc phosphate (100 u m dry film thickness) Undercoat: Micaceous iron oxide (100 u m dry film

thickness) Finish: Micaceous iron oxide (100 u m dry film

thickness)


Paint System: Bitumen coating.

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2.11 M E T A L C O A T I N G S

The preparation for galvanizing and the galvanizing itself shall not adversely affect the mechanical properties of the treated materials.

All welding, drilling, punching, stamping, cutting and bending of parts shall be completed and all burrs removed before the metal coating process is carried out.

Galvanized bolts shall be coated including threads, but the threads of nuts are to be free from excess coating.

Stringent precautions shall be taken to protect parts with metal coatings from injury or damage to the coating during assembly, transit, storage and erection.

2.12 A P P E N D I X ( E X P L A N A T O R Y NOTES)

2.12.1 Symbols

p response factor

c f force coefficient c g gust factor 5 size reduction factor

site altitude in metres above sea level Eqh peak equivalent pressure at height H above ground = qn e x (3 x 5

(N /m 2 ) g the ratio of the peak value of the fluctuating component to the

standard deviation gust peak factor

Yf safety factor for loads safety factor for materials

H height above ground level (m) h height of top of structure above flange including head frame

assembly (m) He effective height (m) N the number of sides for polygonal sections no natural frequency of structure (Hz) qtte reference pressure at height H (N/m 2 ) Re Reynolds number S a altitude factor

sb terrain and building factor fetch factor

sd direction factor sh topographic increment SP probability factor S s seasonal factor S, turbulence factor a standard deviation o f the fluctuating component


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u mean value averaged over one hour V e effective wind speed (mis) V s site wind speed (m/s)

V hourly mean design wind speed (mis)

VlO hourly mean design wind speed at height 10 metres above ground (mis)

2.12.2 Explanatory Note on the Derivation of the p and 5 Factors

The response factor P and the size reduction factor 5 given in the design pressure Clause 2.6.4 of this Specification have been derived from a method proposed by Professor A G Davenport.

Davenport shows that the m a x i m u m response of a relatively flexible structure to the randomly varying forces in a turbulent wind can be predicted, if the pressure corresponding to the wind speed averaged over a long t ime (the m e a n hourly wind speed) is multiplied by a 'gust factor' . The resultant peak equivalent static pressure can then be used to calculate the max imum forces and moments in the structure.

The gust factor C g is given by Davenport as Cg = 1 + gcr/jJ, .

Davenport gives various formulae whereby the coefficient of variation of the total loading effect (the factor olfa in the formula) and the peak factor (g in the formula) can be calculated. Both the coefficient of variation o /u and the peak factor g are functions of the natural frequency, the overall height of the structure, the amount of damping present, and the mean hourly wind speed.

Davenport ' s method can be applied directly to the data given in CP 3 : Chapter V provided that the three second gust speeds given are first converted to the mean hourly wind speeds for the site using the ratios given in CP 3: Appendix A.

However, the method requires separate calculations for each combinat ion of natural frequency, height and damping coefficient and it would be convenient for the designer if these effects could be calculated separately. This is the method adopted in the design pressure Clause 2.6.4 in this Specification.

It is well known that if the natural frequency of a structure is large compared to the forcing frequency, no magnification of the input will occur. The value of the gust factor given by Davenport is then simply the ratio of the peak gust pressure to the mean hourly pressure.

If, therefore, the value of Davenpor t ' s gust factor for a structure of fixed height and damping coefficient is divided by the ratio of the peak (3 second gust) pressure to the

mean hourly wind pressure, a response factor P is obtained which depends only on the natural frequency and the mean hourly wind speed.


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It is known that up to a height of about 3 metres, small gusts are fully effective over the structure as a whole and there is no reduction in the response at heights below this value.

It, therefore, values of the response factor are calculated for a range of heights, the ratio of the value of the response factor for each height divided by the value for the min imum height of 3 metres gives a size reduction factor 8 which is dependent only on the overall height of the structure. For a given combination of natural frequency and overall height the magnification is then given by the product of the response factor p, based on a min imum height of 3 metres and the size reduction factor 8 appropriate to the height.

The values of the response factor given in the Specification were calculated using Davenport ' s data to estimate the gust factor C g for a column of 3 metres height and a reference mean hourly wind velocity of 30 m/s for a category 2 roughness situation. The latter corresponds to a map reference speed in CP 3: Chapter V of 55 m/s . The calculation covered a range of frequencies from 0.1 Hertz up to 20 Hertz. The response factor p was then obtained by dividing the gust factor by the square of the ratio of the three second gust speed to the mean hourly wind speed given in CP 3: Chapter V. The calculations were repeated for 3 values of damping coefficients and the results are plotted against the ratio nj VlO in Figure 1.

In order to obtain the value of the size reduction factor 8, the calculations for the response factor were repeated with the overall height increased to 50 metres , and later extrapolated to 60 metres. A straight line relationship between the value of the size reduction factor and the height was assumed and is plotted in Figure 2 for reference.

In practice, the relationship is not linear. However, check calculations show that for values of the height between the levels of 3 metres and 60 metres, the correct value of the size reduction is slightly less than that given by the straight line relationship. For example, for the height of 20 metres , the correct value of 8 is 0.835, whereas the linear relationship gives 0.896 and in consequence, the overall magnification factor is about 7 % greater than the correct value.

It should be noted that the derivation of P and 8 factors remains valid with the adoption of BS 6399: Part 2 as the basis for wind loading.

2.12.3 Typical Calculation of the Bending Moment at the Foot of a Mast

Circular section 30m masts are required for erection at a site near Not t ingham in country terrain. Topography at the site is not significant with respect to wind loading and the site altitude is 45m above mean sea level. The site is 75 km from the sea in the prevailing wind direction. The natural frequency of the mast is 0.21 Hz and the logarithmic decrement of damping is 0 .1 . The headgear has a projected area of 1.4m 2

and the diameter of the shaft is 0.45m at the base reducing to 0.15m at the top.


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Wind Speed:

From BS 6399:Part 2: Clause 3.2.1, the basic wind speed V b is obtained from figure 6.

For Nottingham, Vb = 22m/s.

From BS 6399: Part 2: Clause 3.2.2, the site wind speed V s is calculated using equation (8), following the procedure given in Clause 2.2.2, except for the determination of the altitude factor, S a .

Equation (8) states that Vs = Vb x Sa x Sd x Ss x Sp

Where: S a is an altitude factor (calculated below) S d is a direction factor, taken as 1.0 S s is a seasonal factor, taken as 1.0 S p is a probability factor, taken as 0.96 for a 25 year design life.

From BS 6399: Part 2: Clause 3.2.2, as topography is not significant, the altitude factor S a is calculated using equation (25).

Equation (25) states that Sa = 1 + 0.001 As

Where: A s is the site altitude in metres above sea level For this site A s = 45m above mean sea level, So S a = 1.045

Substituting the above values into Equation (8) gives:

Site wind speed, Vs = 22 m/s x 1.045 x 1.0 x 1.0 x 0.96 = 22.07 m/s

The design wind speed at effective height H e shall be taken as the effective wind speed, V e obtained using BS 6399: Part 2: Clause 3.2.3.

Equation (27) states that Ve = Vs x Sb

Where: Sb is the terrain and building factor. For sites in country terrain, this should be determined from equation (28)

Equation (28) states that Sb = Sc{l + (g t x St) + Sh}

Where: S c is the fetch factor, obtained from table 22. For H e = 10m, S c = 1.02. gt is the gust peak factor, taken as 3.44. S t is the turbulence factor, obtained from table 22 For H e = 10m, S t = 0.178 Sh = the topographic increment. As topography is not significant, Sh =0.


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Substituting the above values into equation (28) gives:

Terrain and building factor, Sb = 1.02 x (1 + (3.44 x 0.178) + 0) = 1.64

And substituting into equation (27) gives:

Effective Wind Speed, V e = 22.07 m/s x 1.64 = 36.2m/s

2 2 Now, dynamic wind pressure, qHe=0.613Ve (in SI units: N / m and m/s)

Therefore, q H e at height of 10m above ground level =

qHe=0.613x36.2 2=803N/m 2

Wind speeds and pressures can be calculated at various heights using variations of fetch factor, S c and turbulence factor, S t with height given in BS 6399: Part 2: Table 22.

For example, when H e = 3 0 m then S c = 1.22 and S t = 0.159.

Substituting into equation (28) gives:

Sb = 1.22 x (1 + (3.44 x 0.159) + 0) = 1.89

Therefore, substituting into equation (27) gives:

V e at 30m height = 2.07 m/s x 1.89 = 41.7 m/s and the corresponding 2 / 2

dynamic wind pressure, qHe=0.613x41.7 =1064N/m .

Peak Equivalent Static Pressure

From Clause 2.6.2.3, when calculating the hourly mean wind speed, V, the terrain and

building factor Sb is amended as follows for country terrain: Sb = Sc(l + Sh).

From the above calculations, S c = 1.02 at 10m height and Sh = 0 for this site.

Thus S b = 1.02

Substituting the amended form of Sb given above into equation (27) gives an hourly mean wind speed, V at 10m height of 22.07m/s x 1.02 = 22.5m/s.

For a natural frequency, T|o =0.21Hz, then T | o / V = 0.21/22.5 = 0.0093

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From Figure 1, the response factor, p = 1.77 for a logarithmic decrement of damping ofO. l .

From figure 2, for a 30m mast, the size reduction factor, 8 = 0.84.

Thus the magnification factor, 5 x p = 0.84 x 1.77 = 1.49

From Clause 2.6.4.1, the peak equivalent static pressure, EqH = C[He x p x 5

For He = 10m, EqH = 803 N / m 2 x 1.49 = 1196 N / m 2

F o r H e = 30m, EqH = 1 0 6 4 N / m 2 x 1.49 = 1 5 8 5 N / m 2

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Bending Moments at Foot of Mast

Calculations of bending moments at the foot of the mast for the example given are listed in Figure 4 below.

FIGURE 4 - E X A M P L E BENDING M O M E N T S C A L C U L A T I O N

A B C D E Item Height

(m) V e

(m/s) qHe

(N/m 2 ) EqH

(N/m 2 ) Lantern Assembly 30 41.7 1,064 1,585

Mast 27.5 41.4 1,051 1,566 Mast 22.5 40.6 1,013 1,509 Mast 17.5 39.4 949 1,414 Mast 12.5 37.7 874 1,302 Mast 7.5 34.9 746 1,112 Mast 2.5 29.6 537 800

A B F G H I J Item Height

(m) ] Mast

Diameter (m)

Reynolds Number ReX 10 5

c f Projected Area (m 2 )

Wind Resistance

( m 2 ) Lantern Assembly 30 - - 1.000 1.400 1.400

Mast 27.5 0.175 4.993 0.516 0.875 0.452 Mast 22.5 0.225 6.381 0.540 1.125 0.607 Mast 17.5 0.275 7.656 0.561 1.375 0.771 Mast 12.5 0.325 8.760 0.579 1.625 0.941 Mast 7.5 0.375 9.696 0.595 1.875 1.115 Mast 2.5 0.425 10.155 0.603 2.125 1.280

A K L B M N Item Section

(m) EqH (N

x C f / m 2 )

Lever arm (to mid

height of section)

(m)

Wind Load (N)

Ground Level

Bending Moment

(Nm) Lantern Assembly 30 1, 585 30 2,218 66,555

Mast 25-30 8 08 27.5 707 19,454 Mast 20-25 814 22.5 916 20,608 Mast 15-20 793 17.5 1,091 19,088 Mast 10-15 754 12.5 1,225 15,316 Mast 5 - 10 661 7.5 1,240 9,299 Mast 0-5 482 2.5 1,024 2,560

T O T A L S 8,422 152,880 =153 k N m


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D = 0.613 x C E = D x P x 8 G = C x F / ( 1 . 4 6 x l O " 5 ) I = F x length of section (5 metres in this example) J = H x I M= E x J (Sum of this column represents horizontal shear at base flange) N = B x M (Sum of this column represents total wind moment at base flange) L = E x H For design add moment due to dead load at max imum deflection

NOTE: It is usual for the mast to be subdivided into increments of length no greater than 5 metres for the purpose of calculating the loads and bending moments .


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2.13 APPENDIX A - M E T H O D FOR C A L C U L A T I O N O F D A M P I N G

2.13.1 Total Damping

The logarithmic decrement to be used is the combination of aerodynamic and structural damping. A method for calculating this combined logarithmic decrement is given as follows:

The total damping available, Su , should be taken as:

= U-a + Jis

where:

[ia is the logarithmic decrement of aerodynamic damping. u s is the logarithmic decrement of structural damping.

2.13.2 Aerodynamic Damping

The logarithmic decrement of aerodynamic damping, u a , for vibrations in the plane of the wind should be calculated as:

O a Z R w T V | T a = P

2no2JlTlT

where:

ZRWT is the product of the force coefficient and projected areas in the direction of wind, in the top third of the height of the mast (in m 2 )

E m j is the total mass of the top third of the height of the high mast (in kg) V is the hourly mean wind speed at the level of the top of the high mast,

determined in accordance with the method given in Clause 2.6.2.3 (in m/s)

no is the fundamental natural frequency of the high mast (in Hz); p a is the density of air, taken as 1.22 kg /m 3 .

Calculation of aerodynamic damping may be illustrated with the example mast used in section 2.12.3:

E R W T is the wind resistance of the lantern assembly and the top third of the mast column. It is obtained from Figure 4 by summing the first three numbers in column J (1.400+0.452+0.607) = 2 .459m 2 .

E m T is the mass of the lantern assembly and the top third of the mast and equals 1385kg in this example.


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V is calculated at 30m height, using the method given in the example in Clause 2.12.3.

Thus V = V s x S c (1 + Sh) for a mast in country terrain. For this example , Sh= 0 and when H e = 30m, S c = 1.22. Thus V = 22.07m/s x 1.22 (1 + 0) = 26.93m/s .

riois given as 0.21 Hz for this example.

Substituting these values into the equation for aerodynamic damping gives:

_ 1.22kg/m 3 x 2.459m 2 x 26.93ms' 1

2 x 0.21Hz x 1385kg

Where aerodynamic damping is calculated by the above method, the force coefficients for the luminaires and head frame assemblies shall be obtained from wind tunnel tests.

2.13.3 Structural Damping

The structural damping should be assessed by reference to measurements in calm air on existing structures having size, form of construction and foundation conditions similar to the high mast under consideration. Alternatively, the logari thmic decrement of structural damping, p s may b e taken as:

(Is = Kn x ur

where:

U-T is the logarithmic decrement for the superstructure to be taken as 0.015 for high masts;

is a factor to allow for the influence of foundation characteristics, to be obtained from Table 1.

Type of foundation Factor K ,

Piled foundation or spread-footing on stiff soil or rock 1.0 Spread-footing on m e d i u m stiff soil 1.5 Spread-footing on soft soil 3.0

Table 1 - Damping factor, K M , for various types of foundation

NOTE: The logarithmic decrement p. T of 0.015 given above, whilst low, is appropriate to all-welded steel structures. High masts may contain other details, which dissipate energy (e.g. lap joints) and contribute to the overall structural damping. If agreed with the Purchaser, then the overall structural damping may be obtained by testing.


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SECTION 3 - WINCHES AND MECHANICS 3.1 S C O P E

This Specification covers the design of raising and lowering gear including associated mechanical and electrical details.

3.2 L U M I N A I R E / C C T V C A R R I A G E

3.4.1 Mechanical Details

The luminaire/CCTV carriage shall b e of robust construction comprising a min imum of separate small components. If required for maintenance purposes, the frame of the carriage shall be capable of being fitted to and removed from the mas t after erection of the mast.

The design of the carriage shall b e such that the structure embodies as far as possible, the necessary mountings and housings for the equipment, control gear units and terminal boxes. The design shall also take account of the appropriate section of this Specification regarding the provisions for embodying wiring into the carriage structure.

The carriage assembly shall be protected against corrosion by hot dip galvanizing or be processed or finished by plastic coat ing or otherwise to achieve an equivalent protection.

The suspension points on the carriage shall be designed to avoid local flexing of the wire rope either in service or if the carriage is at any t ime inadvertently suspended below the final raised position due to stretching of the wire rope or other reason. The suspension points and the structure of the carriage shall b e such that they cannot be damaged or cause danger of total failure even if the winch is overwound. The design of the suspension points shall be such that inspection of the wire rope on the carriage including its termination point, the suspension point and the fixing be tween the termination and suspension point can be carried out with the min imum of dismantling of components and drawings shall be included to show how this is achieved.

The design of the whole suspension system shall be such that the wire ropes can be removed and replaced from ground level without the necessity of lowering the mast or the use of special equipment.

Particular care shall be taken to ensure that the wire rope and electrical cable cannot abrade against any components at any t ime.


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To prevent damage to paintwork during raising and lowering, and where necessary to assist in the location of the carriage in the raised position, it shall be fitted with rollers or suitable rubbing surfaces. Where these are fitted, rollers shall have bearings of a type which will not require further attention during the life of the mast and the rubbing surfaces shall be designed on a similar basis.

The carriage shall be arranged to locate firmly against stops when in the service position and these stops shall be of adequate strength to ensure that they cannot be damaged by over-winding of the winch. They shall be of stiff enough construction to provide an immediately recognizable increase in winch drive effort when they make contact and to withstand the full pretensioning of the wire rope and the varying forces which will occur in service.

The fixings for the equipment shall be such that the units can be readily removed.

3.4.2 Electrical Details

The luminaire/CCTV carriage shall have provision made on it for supporting and gripping the weight of the supply cable without causing damage to the sheathing of the cable and fixings or a guide tube shall be provided to ensure that the cable cannot at any t ime m a k e abrading contact with the cable suspension points or other components. Any tube shall be bushed where the cable enters or leaves and the cable shall be glanded by an approved type of weather-proof metal gland into a terminal box. All electrical wiring shall be in accordance with BS 7671 : "Requirements for electrical installations. IEE Wiring Regulations. Sixteenth edition".

3.3 H E A D F R A M E A S S E M B L Y

The assembly shall comprise the capping unit for the mast and it shall embody the pulley wheels and other associated equipment for the luminaire/CCTV carriage wire ropes and the electric cable, where used. The assembly shall either in itself comprise a protection cover for the pulley assembly and the top of the mast or be arranged to support a separate canopy unit. The assembly shall be equipped with the necessary guides and stops for the carriage and, where required, it shall also be fitted with an attachment point for the external safety ropes for the maintenance carriage or for direct attachment of the carriage.

The head frame assembly shall be arranged to fit on to the top of the mast and approved arrangements shall be provided for locking it to the mast and to prevent rotation about the mast. Arrangements shall also be made to ensure that the head frame is correctly located in relation to the door of the mast.

The whole of the head frame assembly shall be designed and constructed for operation over the life of the mast without the necessity for maintenance attention. It shall be of welded steel construction and all components shall be relatively large and robust. Where stainless steel is used no additional protection is necessary but ferrous steel shall be protected by hot dip galvanizing or other approved finish.


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Pulley wheels shall be made of corrosion resistant material and fitted with maintenance free bearings protected from the ingress of moisture or dirt and designed for operation over the life of the mast without further attention. The diameter of pulleys and the formation of the pulley grooves shall be in accordance with the requirements of the appropriate British Standard or otherwise, as may be agreed. The pulley wheels for the electric cable shall be so designed that the groove dimensions and pulley diameter are such that the cable will not be adversely affected in use.

The shafts on which the pulley wheels revolve shall be of approved corrosion resistant material and they shall be of large diameter to reduce the bearing loadings below normal design ratings. The shafts shall b e positively secured in the head frame assembly to prevent rotation.

Close fitting guards shall be provided to prevent wire ropes or cables from entanglement or from leaving the pulleys when operating either loaded or slack and these guards shall b e securely located against movement . Their position relative to the pulley wheels and other components shall be checked to a known clearance prior to erection of the mast.

Where the head frame forms the capping unit for the mast, it shall be provided with a removable cover which shall overlap the body of the head frame to provide a rain shed. The use of covers depending only on the security of gaskets for weather-proofing will not be accepted. The fixing arrangements for the cover shall be securely locked but these shall be of simple corrosion resistant construction to allow removal to be effected with the min imum of difficulty and use of tools at any time.

The head frame assembly shall be dispatched to site fully protected against weather and damage, the min imum protection to comprise enclosure within a strong waterproof bag. The assembly shall remain so protected until it is erected on the mast.

3.4 W I N C H

3.4.1 General

Each mast shall be provided with a single or mult iple drum winch suitable for the following duties:

a) Raising and lowering the luminaire /CCTV carriage. b) Supporting the luminaire/CCTV carriage in the raised position, unless a

mechanical docking and support mechanism is used. c) Raising and lowering the equipment and the maintenance carriage, if

required, and at the stated working and test loads.

Particular care shall be exercised in all aspects of the design, manufacture, testing and installation arrangements of the winch to ensure safety under all operating conditions.


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3.4.2 Safe Working Load

The winch shall have a safe working load not less than whichever is the greater of:

a) The max imum weight of the equipment and luminaire/CCTV carriage.

b) The weight of a maintenance carriage plus 250 kg (representing the weight of two men and tools).

When requested, a separate Test Certificate shall be issued with each winch, which shall be suitably identified in a permanent manner to correspond with the numbering of its Test Certificate.

3.4.3 Design

Components shall be designed for an estimated operating life of 25 years and due allowance shall be made for reduction in section as a result of wear and corrosion during the operating life.

The winch shall be designed to be suitable for operation under the conditions of dampness and dirt, which can occur inside a mast, and suitable fixed covers shall be provided over parts, which could be damaged by falling dirt. In addition, a plastic or canvas cover of approved type shall be supplied with each winch to protect the whole unit from dirt and moisture when the winch is in the service position.

The winch shall be provided with a self-contained lubrication system and shall not require any attention in service other than the recharging of the lubricant at intervals.

The design of the winch shall be such that it can be installed in or removed from the mast through the door opening.

3.4.4 Drive & Speed of Operation

The winch shall be suitable for both hand and power operation.

For the convenience of use during maintenance work on the mast, the speed of operation of the winch, when operated by power drive, shall provide as short raising and lowering times as are consistent with safety and with the practical operating speed of the winch and other moving parts.

The winch shall be rated to carry out one uninterrupted cycle of operations of raising and lowering at any of the speed/load conditions put forward without causing over-heating or excessive wear. The average rate of raising and lowering shall be not less than 3 metres per minute .

3.4.5 Security Against Runaway

The winch shall be self-sustaining as a result of gear ratio or other direct mechanical means supplemented by the provision of a brake or other restraining device.

Institution oj Lighting Engineers 4S

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The winch shall be entirely self-sustaining under all normal circumstances and it shall not be so dependent on the brake or restraining device that uncontrolled or dangerous runaway speeds will occur in the event of the total failure of this device.

The brake or other device shall satisfy the following requirements:

a) It must be self-adjusting and not require any attention during the life of the winch.

b) It must be unaffected by oil and/or water. c) It must be so arranged that it cannot be interfered with at site. d) It shall not depend on manual operation for use.

3.4.6 Drive Shaft Positive Locking Device

A positive locking device shall be incorporated in the system to ensure security of the luminaire carriage during the in service condition. It shall prevent the unintentional gradual lowering or sudden release of the carriage in service.

The device shall meet the following requirements:

a) Where the luminaire/CCTV carriage is held at the top of the mast by a locking device, it shall be robust and corrosion resistant and allow smooth engagement and disengagement during the life of the structure.

The device shall remain effective with the carriage out of level to the maximum degree that can occur in practice.

b) Where the luminaire/CCTV carriage is held at the top of the mast by the wire ropes, the winch shall be fitted with a posit ive locking device, which shall remain engaged to prevent rotation in the Tower ' direction when the mast is in service.

The device shall operate automatically under gravity to the locked position whenever the operating handle or driving tool is removed. The device shall preferably move automatically to the " o f f posit ion when the handle or tool is engaged but it is essential that the locking feature shall remain operative until the handle or tool has made a secure engagement with the driving device on the operating shaft and the locking feature shall re-establish before disengagement of the handle or tool from the driving device.

The device shall be so designed that it will engage more firmly with increasing applied torque from the driving shaft but it shall not be dependent on this torque for engagement or for remaining in engagement. The device shall be so arranged that it will effect correct engagement if applied to a shaft, which is already rotating. The device shall be sufficiently robust to ensure that it shall not be so damaged as to become inoperative should it be applied by the accidental withdrawal of the


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driving tool or handle when the winch is being operated under any condition or load including failure of the brake or friction device.

The device shall be of a simple nature, unaffected by dirt or corrosion in service. Springs shall not be used.

3.4.7 Winch Drum

The drum and flanges shall be of cast iron, ductile iron, mild steel or cast aluminium alloy L M 6 M construction, designed to be entirely suitable for the application.

Where multiple layering of the rope occurs, the drum flanges shall be designed to withstand the forces that this will impose on them. The type test on the drum shall include winding on the full numbers of layers of rope at a tension not less than that equivalent to five times the safe working load of the winch and after complet ing the top layer, increasing this tension with the rope adjacent to a flange until failure of the rope occurs. The flanges shall remain intact and shall not be so distorted as to be incapable of further use. Flanges shall be rim stamped to indicate that they have withstood, or will withstand this loading.

The drum shall be grooved except that in the case of applications where the first layer remains fully applied during all normal operations of the winch, a plain drum may be provided.

The drum shall be so designed as to prevent the rope layers from stacking one on top of the other against the flange and also to prevent rope on any layer forcing its way down into lower layers.

The rope anchorage shall be arranged so that it shall be possible to remove the rope end from the drum without drawing the whole length of the rope through a hole in the drum. The fixing arrangements shall present the rope into the first turn on the drum witho

ILE Technical Report No 7 2002 With 2003 Aemndments (2) (4)

Documents

Transcript of ILE Technical Report No 7 2002 With 2003 Aemndments (2) (4)