AS 1170.2 - 1989 - Wind Loads

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AS 1170.2—1989

Australian Standard 

SAA Loading Code

Part 2: Wind loads

This Australian Standard was prepared by Committee BD/6, Loading on Structures. It was approved on behalf of the Council of Standards Australia on 19 December 1988 and published on 20 March 1989.

The following interests are represented on Committee BD/6: Association of Consulting Engineers, Australia Association of Consulting Structural Engineers, Australia Australian Clay Brick Association Australian Construction Services (Department of Administrative Services) Australian Council of Local Government Associations Australian Federation of Construction Contractors Australian Institute of Steel Construction Australian Mining Industry Council Building Management Authority, W.A. Bureau of Meteorology Bureau of Steel Manufacturers of Australia CSIRO, Division of Building, Construction and Engineering Department of Local Government, Qld Electricity Supply Association of Australia Engineering and Water Supply Department, S.A. James Cook University of North Queensland

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Master Builders’ Construction & Housing Association, Australia Monash University National Association of Australian State Road Authorities Public Works Department, N.S.W. University of Melbourne University of Newcastle Additional interests participating in preparation of Standard: Road Construction Authority University of Sydney University of Western Australia

Review of Australian Standards. To keep abreast of progress in industry, Australian Standards are subject to periodic review and are kept up to date by the issue of amendments or new editions as necessary. It is important therefore that Standards users ensure that they are in possession of the latest ed ition, and any amendments thereto. Full details of all Australian Standards and related publications will be found in the Standards Australia Catalogue of Publications; this information is supplemented each month by the magazine ‘The Australian Standard’, which subscribing members receive, and which gives details of new publications, new editions and amendments, and of withdrawn Standards. Suggestions for improvements to Australian Standards, addressed to the head office of Standards Australia, are welcomed. Notification of any inaccuracy or ambiguity found in an Australian Standard should be made without delay in order that the matter may be investigated and appropriate action taken.

This Standard was issued in draft form for comment as DR 87163.

AS 1170.2—1989

Australian Standard  Minimum design loads on structures (known as the SAA Loading Code)

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Part 2: Wind loads

First published as part of SAA Int. 350—1952. Revised and redesignated AS CA 34.2—1971. Revised and redesignated AS 1170.2 — 1973. Second edition 1975. Third edition 1981. Fourth edition 1983. Fifth edition 1989. Incorporating: Amdt 1 — 1991 Amdt 2 — 1993 Amdt 3 — 1993

PUBLISHED BY STANDARDS AUSTRALIA (STANDARDS ASSOCIATION OF AUSTRALIA) 1 THE CRESCENT, HOMEBUSH, NSW 2140 ISBN 0 7262 5485 1

AS 1170.2—1989

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PREFACE This Standard was prepared by the Standards Australia Committee for Loading on Structures to supersede AS 1170 — 1983, Minimum design loads on structures, Part 2 — Wind forces. This Standard is intended to be used for the determination of the minimum wind loads in structural design, and is in a limit states format. It provides a simplified procedure (Section 2) for the determination of wind loads on a limited range of small buildings and structures, and a detailed procedure (Sections 3 and 4) for determination of wind loads on a wide range of structures, varying from those less sensitive to wind action, to those for which dynamic response must be taken into consideration. It permits wind tunnel tests or similar determinations of wind loads on structures. Explanatory material for this Standard are given in Appendices C to F, which correspond to Sections 1 to 4. The Standards Australia Committee has considered exhaustive research and testing information from Australian and overseas sources in the preparation of this Standard with a view to reducing the design wind loads by the maximum extent consistent with safety. The design wind loads prescribed in this Standard are the minimum for the general cases. These will be circumstances arising in particular cases, which will result in additional loads requiring to be taken note of in the design of structures in those cases. Designers must be alert to the conditions to which their particular structure is exposed and must take note of all the provisions in clauses and notes under the clauses. This Standard differs from the previous Standard as follows: (a) Windspeeds are specified for the serviceability and ultimate strength/stability limit states, and for permissible stress design. (b) Return periods and windspeed contours (isopleths) have been deleted. (c) Regional boundaries have been included (boundaries of the tropical cyclone regions are slightly modified). (d) Direct shielding allowance is separately identified and extended. (e) A more rational system of multipliers for wind speed and external pressures is provided. (f) Methods of calculating wind loads on cantilevered roofs, attached canopies, awnings, carports, circular cross-sections, such as bins, silos and tanks, and lattice towers have been added. Existing data on pressure and force coefficients have been revised in the light of recent research. (g) Dynamic analysis has been expanded (replaces Annex: ‘Notes on Wind Forces on Tall Buildings’ in the previous edition). (h) References to other publications are listed numerically at the end of this document. (i) Statements expressed in mandatory terms in Notes to tables and figures are deemed to be requirements of this Standard. Notwithstanding the general copyright provisions applicable to all Australian Standards as detailed below, this Standard contains intellectual material provided by another party and permission to reproduce that material may be conditional on an appropriate royalty payment to Standards Australia, or the other party, or both. Details of the clauses applicable and the right to reproduce them either in printed or electronic form can be obtained from the Head Office of Standards Australia.  Copyright STANDARDS AUSTRALIA Users of Standards are reminded that copyright subsists in all Standards Australia publications and software. Except where the Copyright Act allows and except where provided for below no publications or software produced by Standards Australia may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in writing from Standards Australia. Permission may be conditional on an appropriate royalty payment. Requests for permission and information on commercial software royalties should be directed to the head office of Standards Australia. Standards Australia will permit up to 10 percent of the technical content pages of a Standard to be copied for use exclusively in-house by purchasers of the Standard without payment of a royalty or advice to Standards Australia. Standards Australia will also permit the inclusion of its copyright material in computer software programs for no royalty payment provided such programs are used exclusively in-house by the creators of the programs. Care should be taken to ensure that material used is from the current edition of the Standard and that it is updated whenever the Standard is amended or revised. The number and date of the Standard should therefore be clearly identified. The use of material in print form or in computer software programs to be used commercially, with or without payment, or in commercial contracts is subject to the payment of a royalty. This policy may be varied by Standards Australia at any time.

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AS 1170.2—1989

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CONTENTS Page

SECTION 1. SCOPE AND APPLICATION 1.1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 DESIGN PROCEDURES—SIMPLIFIED OR DETAILED 1.4 DESIGN REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . 1.5 DETERMINATION OF WIND LOADS . . . . . . . . . . . . . 1.6 DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 NOTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4 4 4 4 4 5 6

SECTION 2. SIMPLIFIED PROCEDURE 2.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 LIMITATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 BASIC PRESSURES (p′) . . . . . . . . . . . . . . . . . . . . . . . 2.5 MULTIPLYING FACTORS . . . . . . . . . . . . . . . . . . . . . 2.6 FATIGUE LOADING . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 SERVICEABILITY DESIGN LOADS . . . . . . . . . . . . . . 2.8 FARM BUILDINGS AND TEMPORARY STRUCTURES

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9 9 10 10 13 17 17 17

SECTION 3. DETAILED PROCEDURE: STATIC ANALYSIS 3.1 LIMITATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 GUST WIND SPEED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 DYNAMIC WIND PRESSURE (q z ) . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 FORCES (F) AND PRESSURES (pz ) ON ENCLOSED BUILDINGS, FREE ROOFS AND WALLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 FORCES ON EXPOSED STRUCTURAL MEMBERS . . . . . . . . . . . . . . 3.6 FATIGUE LOADING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23 33 35

SECTION 4. DETAILED PROCEDURE: DYNAMIC ANALYSIS 4.1 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 HOURLY MEAN WIND SPEED . . . . . . . . . . . . . . . . . 4.3 DYNAMIC WIND PRESSURE (qz ) . . . . . . . . . . . . . . . . 4.4 PROCEDURE AND DERIVATION . . . . . . . . . . . . . . .

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36 36 42 42

......

48

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53 59 61 62 77

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

90

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

93

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APPENDICES A ADDITIONAL PRESSURE COEFFICIENTS . . . . . . . . . . . . . . . B SECTIONAL DRAG FORCE AND FORCE COEFFICIENTS AND ASPECT RATIO CORRECTION FACTORS . . . . . . . . . . . . . . . . C EXPLANATORY MATERIAL TO SECTION 1 . . . . . . . . . . . . . D EXPLANATORY MATERIAL TO SECTION 2 . . . . . . . . . . . . . E EXPLANATORY MATERIAL TO SECTION 3 . . . . . . . . . . . . . F EXPLANATORY MATERIAL TO SECTION 4 . . . . . . . . . . . . .

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AS 1170.2—1989

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STANDARDS AUSTRALIA Australian Standard Minimum design loads on structures Part 2: Wind loads

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SECTION 1. SCOPE AND APPLICATION 1.1 SCOPE. This Standard sets out procedures for determining design wind speeds and wind loads to be used in structural design of all buildings and components of buildings, bridges (minimum design wind speed only), and other structures subjected to wind. For bridges, the design wind loads shall be determined in accordance with the AUSTROADS Bridge Design Code. Major offshore structures remote from the coast and transmission lines are not covered, nor are the effects of tornadoes which are special-event winds. The design wind loads for structures containing high risk contaminants, such as some nuclear or biological materials is considered outside the scope of this Standard. This Standard does not attempt to account for possible future climatic changes. 1.2 APPLICATION. This Standard applies to structures, other than bridges, designed to Australian Standards using both limit state and permissible stress design rules. 1.3 DESIGN PROCEDURES — SIMPLIFIED OR DETAILED. 1.3.1 Simplified procedure. For the determination of wind loads on a limited range of small buildings and structures, including domestic buildings, a simplified procedure is given in Section 2 with limitations given in Clause 2.2. Simplified and detailed procedures shall not be mixed. (See Paragraph C1.3.1 of Appendix C.) 1.3.2 Detailed procedure — static and dynamic analysis. For the determination of wind loads on a wide range of structures, detailed procedures are given in Section 3 (Static analysis) and Section 4 (Dynamic analysis). These structures vary from those less sensitive to wind action to those in which dynamic response must be taken into consideration. The dynamic analysis shall be undertaken for the calculation of overall forces for any structure with both a height-(or length)-to-breadth ratio greater than five and the first mode frequency is less than 1 Hz. (See Paragraph C1.3.2 of Appendix C.) 1.4 DESIGN REQUIREMENTS. 1.4.1 General. Wind loads associated with any limit state or permissible stress design requirement, which is relevant to the safe and proper functioning of the

structure or its components, shall be determined from the appropriate clauses in this Standard. 1.4.2 Stability limit state. Wind loads acting alone or in combination with other loads, which cause failure or overturning of the structure as a whole, uplift or sliding, shall be calculated using ultimate limit states design wind speeds (V u). 1.4.3 Strength limit state. Wind loads acting on a structure and its components, which are required to be withstood without failure during the life of the structure, shall be calculated using ultimate limit states design wind speeds (V u). 1.4.4 Ultimate limit states. For the purpose of this Standard, stability and strength limit states are together called ultimate limit states. 1.4.5 Serviceability limit state. Serviceability limit state wind speeds (V s) are given to calculate wind loads acting on a structure and its components for serviceability limit states, such as excessive deflection, cracking and vibration. 1.4.6 Permissible stress design procedure. Where an Australian Standard has adopted a permissible stress design procedure, the wind loads acting on a structure or its components shall be calculated using permissible stress design wind speeds (V p). (See Paragraph C1.4 of Appendix C.) 1.5 DETERMINATION OF WIND LOADS. 1.5.1 Methods of determination of wind loads. Wind loads on a structure or part of a structure shall be determined by one or more of the following: (a) The applicable clauses of this Standard. (b) Reliable references used consistently with the clauses of this Standard. (c) Reliable data on wind speed and direction. The use of uncorrected anemometer data is not permitted. (d) As an alternative to the methods outlined in Clauses 3.2.3 and 4.2.3, the use of a detailed probability analysis for the effects of wind direction is allowed. (e) Wind tunnel or similar tests carried out for a specific structure or reference to such tests on a similar structure (see Clauses 1.5.2. and 1.5.3), together with applicable clauses of this Standard. (See Paragraph C1.5.1 of Appendix C.)

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1.5.2 Wind tunnel tests or similar determinations. For the purposes of determining forces and pressures, wind tunnel tests or similar tests employing a fluid other than air, shall be considered properly conducted only if the natural wind has been modelled for the appropriate terrain categories to take account of — (a) the variation of wind speed with height; and (b) the scale and intensity of the longitudinal component of turbulence. Notice shall be taken of — (i) the effects of Reynolds number where curved shapes are involved; (ii) the appropriate frequency response of force and pressure measuring systems; and (iii) scaling of mass, length, stiffness, and damping, where measurements of dynamic response are involved. (See Paragraph C1.5.2 of Appendix C.) 1.5.3 Wind tunnel tests on a specific structure. Where properly conducted wind tunnel tests on a specific structure have been carried out, or when reference to such tests on a similar structure is used, the loads thus determined shall be used instead of those determined through the provisions of this Standard. 1.6 DEFINITIONS. For the purpose of this Standard, the definitions below apply. Awnings — a roof-like structure, usually of limited extent, projecting from a wall of a building. Canopy — a roof adjacent to or attached to a building, generally not enclosed by walls. Cladding — the material which forms the external surface over the framing of an element of a building or structure. Dominant opening — an opening in the external surface of an enclosed building which directly influences the average internal pressure in response to external pressures at that particular opening. Dominant openings need not be large. Drag — a force acting in the direction of the windstream. Enclosed buildings — buildings which have full perimeter walls (nominally sealed) from floor to roof level. Escarpment — a long (steeply sloping) face between nominally level lower and upper plains with average slopes of not greater than 5%. Force coefficient — a coefficient which when multiplied by the incident wind pressure and an appropriate area (defined in the text), gives the force in a specific direction. Free roof — a roof (of any type) with no enclosing walls underneath, e.g. freestanding carport. Freestanding walls — walls which are exposed to the wind on both sides, with no roof attached, e.g. fences. Freestream dynamic pressure — the theoretically computed incident pressure of a uniform air stream of known density q = 0.0006 x V 2 (at ambient temperature and barometric pressure).

AS 1170.2—1989

Gable roof — a ridged roof with end walls triangular from lowest points up to the ridge. Hip roof — a traditional roof with sloping ridges rising up from external corners (valleys rise up from any return corners). Hoardings — free standing (rectangular) signboards, etc, supported clear of the ground. Immediate supports (cladding) — those supporting members to which cladding is directly fixed (e.g. battens, purlins, girts, studs). Lattice towers — three-dimensional frameworks comprising three or more linear boundary members interconnected by linear bracing members joined at common points (nodes), enclosing an open area through which the wind may pass. Lift — a force acting at 90° to the windstream. Major offshore structures — major navigation structures, drilling platforms and major structures on small islands, reefs or shoals. Monoslope roof — a planar roof with no ridge, which has a constant slope. Obstructions — natural or man-made objects which generate turbulent windflow, ranging from single trees to forests and from isolated small structures to closely spaced multi-storey buildings. Permeability — an aggregation of small openings and cracks etc, which allows air to pass through walls or roofs etc, under the action of a pressure differential. Pitched roof — a bi-fold, bi-planar roof with a ridge at its highest point. Porosity (of cladding) — the ratio of the area of openings divided by the total surface area. Pressure — air pressure in excess of ambient. Negative values are less than ambient, positive values exceed ambient. Net pressures act normal to a surface in the direction specified within the text. Pressure coefficient — the ratio of the average pressure acting at the point on a surface, to the freestream pressure of the incident wind. Reliable data (wind speeds and directions) — it is the professional responsibility of the user to assess data other than that presented within this Standard. Reliable references (wind pressures and loads) — reference material or other material judged to be reliable by the professional user. Ridge (topographic feature) — a long crest or chain of hills which have a nearly linear apex, with sloping faces on either side of the crest. Roughness length — a theoretical quantification of the (wind) turbulence inducing nature of a particular type of terrain. Sufficient (meteorological information) — the assessment of an appropriately qualified and experienced professional. Terrain — the surface roughness condition when considering the size and arrangement of obstructions to the wind. Topography — major land surface features comprising hills, valleys and plains which strongly influence wind flow patterns.

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AS 1170.2—1989

6

Tornado — a violently rotating column of air, pendant from the base of a convective cloud, and often observable as a funnel cloud attached to the cloud base. Tributary area — the area of building surface contributing to the force being considered. Tropical cyclone — an intense low-pressure centre accompanied by heavy rain and gale-force winds or greater. It forms over warm tropical oceans and decays rapidly over land. In the southern hemisphere, winds spiral clockwise into the centre. Troughed roof — a bi-fold, bi-planar roof with a valley at its lowest point.

CF,x =

1.7 NOTATION. Unless a contrary intention is stated, the notation used in this Standard shall have the following meanings with respect to a structure, or member, or condition to which a Clause is applied. The SI system of units is used throughout. A = the surface area of the element or the tributary area which transmits wind forces to the element A r = the gross plan area of the roof including eaves, canopies, awnings etc A z = the area of a structure or a part of a structure, at height z, upon which the design wind pressure (p z) operates, being — (a) when used in conjunction with the pressure coefficient (C p), the area upon which the pressure acts, which may not always be normal to the windstream; (b) when used in conjunction with a drag force coefficient (C d), the projected area normal to the windstream; and (c) when used in conjunction with a force coefficient, (C F,x ) or (CF,y ), the areas as defined in applicable clauses. a = the dimension used in defining the extent of application of local pressure factors B = a background factor, which is a measure of the slowly varying background component of the fluctuating response caused by the lower frequency wind speed variations B 1 = a regional multiplying factor B 2 = a terrain and height multiplying factor B 3 = a topographic multiplying factor B 4 = an area reduction factor for roofs b = the horizontal breadth of a vertical structure normal to the windstream; or the average breadth of a vertically tapered structure over the top half of the structure; or the nominal average breadth of a horizontal structure; or the average diameter of a circular section bs = the average breadth of shielding buildings, normal to the windstream. Cd = the drag force coefficient for a structure or member in the direction of the windstream Fd = A zq z

Cp = Cp,c =

= CF,y =

= Cf = Cfs =

Cp,e = Cp,i = Cp,l = Cp,n = Cp,w = Cp1 = c

=

D d

= =

da

=

E

=

e

=

F

=

Fd

=

Fd = Ff

=

Fx

=

Fy

=

Fz = f

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=

the force coefficient for a structure or member, in the direction of the member’s x-axis Fx A zq z the force coefficient for a structure or member, in the direction of the member’s y-axis Fy A zq z a frictional drag force coefficient the cross-wind force spectrum coefficient generalized for a linear mode a pressure coefficient a pressure coefficient for the windward edge of a roof supported by a cantilevered beam an external pressure coefficient an internal pressure coefficient a net pressure coefficient for the leeward half of a free roof a net pressure coefficient for canopies, free standing roofs, walls, etc a net pressure coefficient for the windward half of a free roof an external pressure coefficient for a bin, silo or tank of unit aspect ratio the net height of a hoarding, bin, silo or tank a building spacing parameter the minimum roof plan dimension or, the depth or distance to which the plan or cross-section of a structure or shape extends parallel to the wind stream the along-wind depth of a porous wall or roof surface a spectrum of turbulence in the approach windstream; or the modulus of elasticity the base of Napierian logarithms (≈ 2.71828) the wind force acting normal to the surface of a building element the drag force acting parallel to the wind stream the hourly mean drag force acting parallel to the windstream the resultant frictional force acting parallel to the windstream the wind force component resolved along the x-axis of a body the wind force component resolved along the y-axis of a body the hourly mean net horizontal force acting on a building or structure at height z a friction stress

7

G gf gv

= = =

H h hc

= = =

he hi

= =

hs ht

= =

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I = Ka = Kar = Ki

=

Kl Kp Ksh Kt k kc

= = = = = =

Lh

=

Lu

=

L*

=

l

=

ls = Ma = Ma = ^ = M a Mc = Mc = ^ = M c Mi = Mo = Mo = MR =

a gust factor a peak factor (fluctuating response) a peak factor for the upwind velocity fluctuation the height of a hill, ridge or escarpment the height of a structure above ground the height from ground to the attached canopy, etc the eaves height of building the developed height of the inner layer, which is equal to z for the calculation of x i the average height of shielding buildings the height to the top of a structure above ground the second moment of area an area reduction factor an aspect ratio correction factor for individual member forces a factor to account for the angle of inclination of the axis of members to the wind direction a local pressure factor a reduction factor for porous cladding a shielding factor for multiple open frames a type factor for topography a mode shape power exponent a multiplier for Cp,e (on circular tanks, bins and silos) a measure of the effective turbulence length scale the horizontal distance upwind from the crest of a hill, ridge or escarpment to a level half the height below the crest the effective horizontal length of the upwind slope of a hill, ridge or escarpment the length of a frame member; or the length of a cantilevered roof beam the average spacing of shielding buildings the along-wind base overturning moment the mean base overturning moment for a structure in the along-wind direction the design peak base overturning moment for a structure in the along-wind direction the cross-wind base overturning moment the mean base overturning moment for a structure in the cross-wind direction the design peak base overturning moment for a structure in the cross-wind direction a structure importance multiplier the upstream terrain category gust wind speed multiplier at the beginning of each new terrain inner layer for height z the upstream terrain category hourly mean wind speed multiplier at the beginning of each new terrain inner layer for height z the resultant vector base overturning moment

AS 1170.2—1989

^ M R

=

Ms

=

Mt

=

Mt

=

Mx

=

Mx

=

M (z,cat)

=

M (z,cat)

=

Mα

=

m mo

= =

N n

= =

na

=

nc

=

ns

=

pc

=

pd

=

pe pi pn pz p′ qh

= = = = = =

qh

=

qz

=

qz

=

R Re

= =

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the peak resultant vector base overturning moment a shielding multiplier for both gust and hourly mean wind speeds a topographic multiplier for gust wind speeds a topographic multiplier for hourly mean wind speeds the gust wind speed multiplier at a distance x from the start of new terrain category for height z the hourly mean wind speed multiplier at a distance x from the start of the new terrain category for height z a gust wind speed multiplier for a terrain category at height z (for upwind distance of at least (2500 + x i) m) an hourly mean wind speed multiplier for a terrain category at height z (for upwind distance of at least (1500 + x i) m) a component of the base overturning moment acting in the α direction the mass per unit length the average mass per unit height of a structure an effective reduced frequency the number of spans of a multi-span roof; or the first mode frequency of a structure the first mode frequency of a structure in along-wind direction the first mode frequency of a structure in cross-wind direction the number of upwind shielding buildings within a 45° sector of radius 20ht the maximum design wind pressure at the leading edge of a roof supported by a cantilevered beam the ultimate limit state design wind pressure the external wind pressure the internal wind pressure the net wind pressure the design wind pressure at height z the net basic wind pressure the free stream gust dynamic wind pressure at the top of a structure the free stream hourly mean dynamic wind pressure at height h the free stream gust dynamic wind pressure resulting from V z the free stream hourly mean dynamic wind pressure resulting from V z the return period the Reynolds number

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AS 1170.2—1989

r

=

S Sr s u* V V V crit Vh Vh

= = = = = = = = =

Vp

=

Vs

=

Vu

=

Vz Vz

= =

w

=

wc

=

x

=

x x^ xi

= = =

ÿ^

=

z

=

zg

=

zo z1, z2

= =

zo,r

=

α

=

8

the corner radius of a structural shape, or a roughness factor, or the rise of a curved roof a size factor the Strouhal number a position factor for topographic effects the friction velocity the basic wind speed the hourly mean wind speed the critical wind speed, for ‘Lock-in’ the design gust wind speed at height h the design hourly mean wind speed at height h the basic wind speed for permissible stress methods the basic wind speed for serviceability limit state the basic wind speed for ultimate strength limit state the design gust wind speed at height z the design hourly mean wind speed at height z a factor to account for the second order effects of turbulence intensity the width of canopy, etc, from the face of the building the distance downwind from a change in terrain category to the structure under consideration; or the horizontal distance from a structure to the crest of a hill or a ridge the mean value of random variables the peak value of random variables the distance downstream from the start of the new terrain roughness to the developed height of the inner layer (h i) the peak acceleration at the top of a structure in cross-wind direction the distance or height above the ground; or the effective height of an escarpment the gradient height, at which terrain influence ceases a characteristic terrain roughness length the effective heights of a hill, on each side of it the larger of the two roughness lengths, at the change in terrain the angle of slope of a roof; or the direction of a resultant vector base overturning moment with respect to the along-wind direction

αmax

=

β

=

δ

=

δe

=

εa

=

εc

=

ε^c

=

ε^t

=

ζ

=

η

=

the angle to the along-wind direction of the plane of the maximum resultant vector base overturning moment the fractional porosity of a wall; or the angle from the wind direction to a point on the wall of a circular bin, silo or tank the actual solidity ratio for an open frame the effective solidity ratio for an open frame a structural load effect derived from the mean along-wind dynamic response a structural load effect derived from the mean cross-wind dynamic response a structural load effect derived from the peak cross-wind response, and proportional to the peak cross-wind base overturning moment M^ c the total combined peak load scalar effect a fraction of the critical damping capacity of a structure a multiplier, used to calculate σ v

= θ

=

λ υ ρ σv

= = = =

σv /V z

=

σx

=

τo φ

= =

φd

=

φ′ ψ (z)

= =

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the angle of deviation of the wind stream from the axis of a structural section a spacing ratio for open frames the kinematic viscosity the atmospheric density the standard deviation of a wind gust component the turbulence intensity in the approach flow at height z the standard deviation of a set of values of variable ‘x’ the surface friction shear stress the upwind slope of a hill, ridge or escarpment or the angle between the windstream and the plane of a structural member the average downwind slope measured from the crest of a hill, ridge or escarpment to the ground level at a distance of 5H the lesser value of φ or 0.3 a mode shape

9

SECTION 2.

SIMPLIFIED PROCEDURE

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2.1 INTRODUCTION. This Section sets out a simplified procedure for the determination of wind loads on a limited range of small buildings and structures, which satisfy the limitations set out in Clause 2.2. This Section must not be used in conjunction with other sections of this Standard except where specific reference to other sections is made (see Clause 1.3.1). The loads specified in this Section are ultimate strength limit state design wind loads. If loads are required for permissible stress design, the ultimate strength loads given in this Section shall be divided by 1.5. If loads are required for serviceability limit state design, the ultimate strength loads specified in this Section shall be multiplied by the serviceability multiplying factors given in Table 2.7. (See Paragraph D2.1 of Appendix D.) 2.2 LIMITATION. The simplified procedure shall only be applied to the determination of wind loads on buildings, their attachments, and miscellaneous structures which satisfy all of the relevant following conditions: (a) The overall height does not exceed 15.0 m.

FIGURE 2.2(A)

AS 1170.2—1989

(b) The buildings are rectangular in plan, or a combination of rectangular units. (c) The roof pitch of buildings does not exceed 30°. (d) The ratio of the height (ht) to the minimum roof plan dimension (d) is less than five for enclosed buildings, and less than one for free standing roofs. (e) The gross roof plan area of buildings does not exceed 1000 m 2. (f) The consequences of failure of the building in social and economic terms is not high relative to that normally associated with small buildings. Structures that have special post-disaster functions, e.g. hospitals and communications buildings, shall not be designed using this Section. The minimum roof plan dimension of a building is the minimum width of the roof in plan (see Figure 2.2(A)). The height (ht) is the height from the lowest point at ground level to the highest point of the structure (see Figure 2.2(B)). The gross roof plan area of buildings is the total area of the roof in plan, including any attached canopies, awnings, carports, etc.

MINIMUM PLAN DIMENSION (d ) FOR DIFFERENT ROOF PLANS

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2.3 PROCEDURE. 2.3.1 General. The ultimate limit state design wind pressures (pd ) shall be obtained by multiplying the net basic wind pressures (p′ ) given in Clause 2.4 by the appropriate multiplying factors given in Clause 2.5, using Equation 2.3.1. pd = p′B 1 B2 B3 B4 . . . . . . . . . . . . . . (2.3.1) where pd = the ultimate limit state design wind pressure, in kilopascals p′ = the net basic wind pressure, in kilopascals B1 = a regional multiplying factor (see Table 2.5.1) B2 = a terrain and height multiplying factor (see Table 2.5.2) B3 = a topographic multiplying factor (see Table 2.5.3) B4 = an area reduction factor for external pressures on roofs (see Table 2.5.4). The net basic wind pressure (p′ ) shall be the worst case of combined internal and external basic pressures, or windward and leeward basic wall pressures, as appropriate. In combining external and internal basic pressures, the worst combination of the basic pressures prescribed within the limits given in this Section shall be used. Where only one limit of basic pressure is given, it shall be assumed that the other limit is zero. 2.3.2 Forces (F) on elements of buildings. The wind force (F) due to wind pressure acting on an element of a structure shall be calculated from Equation 2.3.2. F = pdA . . . . . . . . . . . . . . . . . . . (2.3.2) where F = the wind force acting normal to the surface of a building element pd = the ultimate limit state design wind pressure, in kilopascals A = the surface area of the element or the tributary area which transmits wind forces to the element, in square metres. Resultant forces on complete buildings shall be computed from the summation of forces acting normal to all the individual surfaces of the building. 2.4 BASIC PRESSURES. 2.4.1 External pressures on rectangular buildings. 2.4.1.1 General. The basic external pressures on buildings are a function of the location of the building, the direction of the wind relative to the orientation of the building, and the geometry of the building. The geometry of the building is defined in terms of the windward roof slope in the direction of the wind and the following factors: (a) ht = the height of the building, as described in Clause 2.2. (b) d = the minimum roof plan dimension in the direction of the wind (see Figure 2.4.1.1).

2.4.1.2 Windward sections of roofs. For the windward sections of roofs the basic pressures given in Table 2.4.1.2 shall be used. TABLE 2.4.1.2 EXTERNAL BASIC PRESSURES FOR WINDWARD SECTIONS OF ROOFS Windward roof slope (α) degrees

Basic pressure, kPa

max.neg. ≤10 15 20 25 30

-0.95 -0.75 -0.45 -0.35 -0.25

max.pos. 0 0 0.25 0.35 0.35

max.neg.

max. pos.

-1.4 -1.1 -0.75 -0.55 -0.35

0 0 0 0 0.25

NOTE: For intermediate values of α and ht/d, linear interpolation is permitted.

The windward section of the roof is the windward half of the roof, or the section windward of the highest horizontal ridge at right angles to the wind direction where such ridges are present. Where the windward roof slope varies, the basic pressures used in the design vary according to the roof slope in the direction of the wind, otherwise the minimum roof slope in the direction of the wind on the windward section of the roof shall be used for negative pressures, and the maximum roof pitch shall be used for positive pressures. The basic pressures given in Table 2.4.1.2 shall be assumed to act over the whole of enclosed monoslope roofs, and over all of the area of roofs having slopes in the direction of the wind which are nominally zero. 2.4.1.3 Leeward sections of roofs. For the leeward sections of roofs the basic pressures given in Table 2.4.1.3 shall be used. TABLE 2.4.1.3 EXTERNAL BASIC PRESSURES FOR LEEWARD SECTIONS OF ROOFS Leeward roof slope (α) degrees ≤ 15 ≥ 20

Basic pressure, kPa

-0.55 -0.65

-0.75 -0.65

NOTE: For intermediate values of α and ht/d, linear interpolation is permitted.

2.4.1.4 Walls and undersides of eaves. For walls and undersides of eaves, the basic pressures given in Table 2.4.1.4 shall be used. TABLE 2.4.1.4 EXTERNAL BASIC PRESSURES FOR WALLS AND UNDERSIDES OF EAVES Location Windward: (a) normal building (b) highset building Leeward Side

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Basic pressure, kPa 0.75 0.85 -0.55 -0.7

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NOTE: α ≤ 30°; h t ≤ 15 m. NOTE: For wind blowing end-on to a gable roof, the windward roof slope shall be taken as zero.

FIGURE 2.4.1.1

MINIMUM PARAMETERS USED IN CLAUSES 2.4.1.2 TO 2.4.1.6 COPYRIGHT

AS 1170.2—1989

AS 1170.2—1989

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A highset building is an elevated building with a clear, unwalled space underneath the first floor level, with a height from ground to underside of floor of at least one third of the total height of the building. For the design of unenclosed eaves, the use of net basic pressures obtained from Clauses 2.4.3.2 and 2.4.3.3 is permitted. 2.4.1.5 Local negative external pressures. Cladding and its immediate supports within 0.2√A r of edges, corners, ridges, etc, shall also be designed for the external local basic pressures given in Table 2.4.1.5, where A r is the gross plan area of the roof including attached canopies, awnings, etc. TABLE 2.4.1.5 BASIC LOCAL NEGATIVE EXTERNAL PRESSURES FOR CLADDING AND ITS IMMEDIATE SUPPORTS Basic pressure, kPa

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Location

Tributary area (A) m2

Roof

0.04Ar

-1.9 -1.45 -0.95

-2.1 -2.1 -1.4

Walls

0.04A

-1.4 -1.05 -0.7

-1.4 -1.05 -0.7

The tributary area is the area contributing to the force being considered. For example, the tributary area for a cladding fastener will be the area of cladding supported by a single fastener; for a purlin it will be the span between supporting rafters times the distance between purlins. 2.4.1.6 Local positive external pressures. Wall elements with tributary areas less than 0.01A r, as defined in Clause 2.4.1.5, shall be designed for the following basic local positive external pressures: (a) For normal buildings: 0.9 kPa. (b) For highset buildings: 1.05 kPa. For definition of highset building, see Clause 2.4.1.4. 2.4.1.7 Under floor pressures of highset buildings. Highset buildings shall be designed for under floor basic pressures of 0.85 kPa and - 0.65 kPa. 2.4.2 Internal pressures. Both cladding and structure shall be designed for the internal basic pressures given in Table 2.4.2. TABLE 2.4.2 INTERNAL BASIC PRESSURES Basic pressure, kPa Openings max. neg.

max. pos.

No dominant openings

-0.35

0.25

Dominant openings: (a) Normal building (b) Highset building

-0.7 -0.7

0.75 0.85

Internal pressures based on dominant openings shall be used when the area of a permanent opening in one

wall exceeds 4 times the sum of the permanent openings in other walls and the roof. In tropical cyclone-prone regions C and D, as defined in Clause 2.5.1, internal pressures based on dominant openings shall be used for calculating both ultimate strength and permissible stress design loads unless windows are protected against impact of debris by screens or shutters capable of resisting a 4 kg piece of timber of 100 mm × 50 mm cross-section striking them at any angle at a speed of 15.0 m/s. This requirement does not apply to the calculation of serviceability design loads. For definition of high set buildings, see Clause 2.4.1.4. 2.4.3 Unenclosed attached canopies, awnings, carports and eaves. 2.4.3.1 General. Unenclosed attached canopies, awnings and carports with a roof slope of less than 5° and attached to buildings satisfying the limitations in Clause 2.2, shall be designed using the basic pressures given in Clauses 2.4.3.2 and 2.4.3.3. For the design of unenclosed eaves, the use of net basic pressures given in these Clauses is also permitted. 2.4.3.2 Main structural components. The main structural components shall be designed for the net basic pressures given in Table 2.4.3.2 acting on the roof. TABLE 2.4.3.2 NET BASIC PRESSURES (p′ ) FOR UNENCLOSED CANOPIES, AWNINGS, CARPORTS AND EAVES Net basic pressure (p′), kPa Upwards Downwards

2500 m the distance downstream, in metres, from the start of the new terrain to the developed height of the inner layer (h i), given by Equation 3.2.6(1) the larger of the two roughness lengths, in metres, given in Table 3.2.4, at the change in terrain the developed height of the inner layer, in metres, which is equal to z for the ca lcul a ti on o f xi, gi v en b y Equation 3.2.6(2) the wind speed multiplier at a distance x from the start of new terrain category for height z

Mo

the upstream terrain category gust wind speed multiplier at the beginning of each new terrain for height z = the downstream terrain category gust M (z,cat) wind speed multiplier for each new terrain for height z and (x - x i) > 2500 m, given in Tables 3.2.5.1 and 3.2.5.2 x = the distance downwind, in metres, from a change in terrain category to the structure under consideration Fully developed gust windspeed multipliers M (z,cat) only apply at a structure site when the terrain category at the site is uniform upstream for a distance greater than (2500 + x i) metres. When there is terrain of more than one roughness length upwind of the structure site, corrected wind speed mul tipl iers (M x ) shall be comput ed using Equation 3.2.6(3). The extent of upwind terrain to be considered need not exceed the larger of either 2500 m or 50 times the structure height (h t), provided that the terrain at that limit is Terrain Category 3 or less rough, (assume the windspeed multiplier (M o) to be the value for fully developed terrain at that limit). If the terrain at that point is rougher than Terrain Category 3, the upwind limit shall be extended until Terrain Category 3 or terrain of less roughness is encountered, or alternatively fully developed Terrain Category 3 may be arbitrarily assumed upwind of that point.

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where xi

. . . (3.2.6(3))

AS 1170.2—1989

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=

AS 1170.2—1989

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3.2.7 Shielding multiplier (M s ). Shielding buildings are those upwind buildings within a 45° sector of radius 20ht, whose heights are greater than or equal to z. The shielding multiplier (M s ) is given in Table 3.2.7. Without shielding, M s = 1.0. To determine the shielding multiplier (M s ) from Table 3.2.7, the following procedures shall be used: (i) Each wind direction being considered shall be assessed for upwind shielding buildings within a 45° sector of radius 20h t. (ii) The building spacing parameter (D) in any sector shall be calculated using Equation 3.2.7(1).

TABLE 3.2.8 TOPOGRAPHIC MULTIPLIER AT CREST (x = 0) FOR GUST WIND SPEEDS Topographic multiplier (M t) Upwind slope (φ)

0.05 0.1 0.2 ≥ 0.3

Escarpments φd ≤ 0.05

Hills and ridges φd ≥ 0.10 (see Notes 1 and 2)

1.04 1.08 1.16 1.24

1.09 1.18 1.36 1.54

LEGEND:

. . . . . . . . . . . . . . . . . . (3.2.7(1))

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where D ls

= =

the building spacing parameter the average spacing of shielding buildings, in metres

=

. . . . . . . . . . . . (3.2.7(2))

hs

=

bs

=

ht

=

ns

=

the average height of shielding buildings, in metres the average breadth of shielding buildings, normal to the windstream, in metres the height to the top of the structure being shielded, in metres the number of upwind shielding buildings within a 45° sector of radius 20h t and with height h ≥ z.

TABLE 3.2.7 SHIELDING MULTIPLIER (M s ) Building spacing parameter (D) ≤1.5 3.0 6.0 ≥ 12.0

Shielding multiplier (Ms )

φ

=

the upwind slope, calculated from φ =

φd

=

the average downwind slope, measured from the crest of a hill, ridge or escarpment to the ground level at a distance of 5H

H

=

the height of the hill, ridge or escarpment, in metres

Lu

=

the horizontal distance upwind from the crest to a level half the height below the crest, in metres.

NOTES: 1. An escarpment has a value of downwind slope (φd) ≤ 0.05. A hill or a ridge has a value of downwind slope (φd) > 0.05. The values given in Table 3.2.8 are applicable only to those hills and ridges with downwind slope ≥ 0.10. 2. For hills and ridges with downwind slope 0.05 < (φd) < 0.10, linear interpolation between the Mt values for escarpments and, hills and ridges in Table 3.2.8 is permitted. 3. For intermediate values of upwind slope (φ) and downwind slope (φd ), linear interpolation is permitted.

M t may also be obtained by the following methods: (a) The use of an appropriate equation based upon experimental and theoretical results, such as that given in Paragraph E3.2.8 of Appendix E. (b) Correctly-scaled wind tunnel test. (c) Full-scale measurements at site. 3.2.9 Structure importance multiplier (M i). For special structures, the design gust wind speed shall (or may in the case of reductions) be adjusted with a multiplier (M i) given in Table 3.2.9.

0.7 0.8 0.9 1.0

TABLE 3.2.9 STRUCTURE IMPORTANCE MULTIPLIER (M i)

NOTE: For intermediate values of D, interpolation is permitted.

(See Paragraph E3.2.7 of Appendix E.) 3.2.8 Topographic multiplier (M t). If the structure under consideration is located within a local topographic zone, the topographic multiplier (M t) shall be obtained by interpolation from the values of M t at the crest of a hill, ridge or escarpment given in Table 3.2.8 and the value of M t = 1 at the boundary of the zone. Interpolation shall be linear with horizontal distance from the crest, and with height above the local ground level. The local topographic zones are shown in Figures 3.2.8.1 and 3.2.8.2. A topographic multiplier of M t = 1 shall be used for all sites outside a local topographic zone or if the upwind slope (φ) is less than 0.05.

Class of structure

Structure importance multiplier (M i )

Structures which have special post-disaster functions, e.g. hospitals and communications buildings

1.1

Normal structures

1.0

Structures presenting a low degree of hazard to life and other property in the case of failure, e.g. isolated towers in wooded areas, farm buildings

0.9

Structures of temporary nature and which are to be used for less than 6 months

0.8

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AS 1170.2—1989

NOTE: Figures 3.2.8.1 and 3.2.8.2 are cross-sections through the structure site for a particular wind direction

FIGURE 3.2.8.2 ESCARPMENTS

(See Paragraph E3.2.8 of Appendix E.) WARNING: The wind speeds in this Standard do not include any specific allowance for the effects of tornadoes. The design wind loads for structures containing high risk contaminants such as some nuclear or biological materials are also considered outside the scope of this Standard.

(See Paragraph E3.2.9 of Appendix E.) 3.3 DYNAMIC WIND PRESSURE (q z). The gust dynamic wind pressure (q z) at a height z shall be calculated using Equation 3.3. qz = . . . . . . . . . . . . . . . . (3.3) where qz = the free stream gust dynamic wind pressure at height z, in kilopascals V z = the design gust wind speed at height z, in metres per second.

(See Paragraph E3.3 of Appendix E.) 3.4 FORCES (F) AND PRESSURES (p z) ON ENCLOSED BUILDINGS, FREE ROOFS AND WALLS. 3.4.1 General. This Clause sets out procedures for determining wind pressures, forces and moments on the overall structures and on components, using the ‘Static Analysis’. 3.4.1.1 Procedure. Design wind pressures or forces shall be determined from pressure coefficients multiplied by the basic wind pressure computed from the gust wind speed. The design wind forces and moments on the whole or part shall be determined from the integration of pressures.

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AS 1170.2—1989

24

3.4.1.2. Forces (F) on building elements. The forces (F) on building elements, such as a wall or a roof, shall be taken to be the resultant of the pressures acting over the external and internal surfaces of the element and shall be calculated using Equation 3.4.1.2. F = ∑pzA z . . . . . . . . . . . . . . . . . (3.4.1.2) where F = the wind force acting normal to the surface of a building element pz = the design wind pressure at height z, in kilopascals = (p e - p i) for enclosed buildings or (p n) where net pressure is applicable A z = the area at height z, upon which the design wind pressure (p z) operates, in square metres pe = the external pressure determined in accordance with Clause 3.4.2 and Appendix A = the internal pressure determined in pi accordance with Clause 3.4.7 pn = the net pressure determined in accordance with Clauses 3.4.9 and 3.4.10

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NOTE: If the surface pressure (pz) varies because of height, the area may be subdivided so that the specified pressures are taken over appropriate areas.

3.4.1.3 Calculation of forces and moments on complete buildings. The total resultant forces and overturning moments on a complete building shall be taken to be the summation of the effects of the pressures on all surfaces of the building. 3.4.2 External pressures (p e). The external wind pressure (pe) on a surface of an enclosed structure shall be calculated using Equation 3.4.2. pe = Cp,e KaKlKpq z . . . . . . . . . . . . . . (3.4.2) where pe = the external wind pressure, in kilopascals Cp,e = the external pressure coefficient obtained from Tables 3.4.3.1 and 3.4.3.2 for rectangular enclosed buildings, and from Tables A1.1, A1.2, A2 and Paragraph A3 of Appendix A, and Figures A4.1 and A4.2 for other shapes Ka = the area reduction factor for roofs and side walls, given in Clause 3.4.4 Kl = the local pressure factor applicable to cladding and immediate supporting structure only, given in Clause 3.4.5 Kp = the reduction factor for porous cladding, given in Clause 3.4.6 qz = the free stream gust dynamic wind pressure at height z, given in Clause 3.3. Unless stated otherwise, q z shall be taken as q h, where h is either h e or ht, as defined in Clause 3.4.3 or Appendix A. The building as a whole, the walling, and roofing elements of such buildings or structures shall be assumed to be subject to the most severe possible combination of wind forces associated with these

coefficients and, except where shown otherwise, these forces shall be assumed to be distributed uniformly over the surface concerned. Where interaction is possible, these external pressures (pe) shall be assumed to act simultaneously with the internal pressures (p i) given in Clause 3.4.7 and under eaves pressures, which shall be taken as the pressure on the adjoining wall faces below the surface under consideration, according to Table 3.4.3.1. 3.4.3 External pressure coefficients (C p,e) for rectangular enclosed buildings. The external pressure coefficients for walls and roofs of rectangular enclosed buildings are given in Tables 3.4.3.1(A)(B)(C) and 3.4.3.2(A)(B)(C). The parameters referred to in these tables are shown in Figure 3.4.3. In Tables 3.4.3.1(A)(B)(C) and 3.4.3.2(A)(B)(C), the height h shall be taken as the height to eaves level (h e), except for θ = 0°, α ≥ 60°; and θ = 90°, all α, where the value of h shall be taken as the height to the top of the building (ht). The external pressure coefficients (C p,e) for non-rectangular enclosed buildings are given in Appendix A. The external pressure coefficient (C p,e) on the underside of highset buildings shall be taken as 0.8 and -0.6. For other buildings elevated above the ground, interpolation between these values and 0.0, according to the ratio of clear unwalled height underneath first floor level to total building height, is permitted. For the calculation of underside external pressures, take q z = qh . A highset building is an elevated building with a clear, unwalled space underneath the first floor level, with a height from ground to underside of floor of at least one-third of the total height of the building. (See Paragraph E3.4.3 of Appendix E.) TABLE 3.4.3.1 WALLS: AVERAGE EXTERNAL PRESSURE COEFFICIENTS (Cp,e ) FOR RECTANGULAR ENCLOSED BUILDINGS TABLE 3.4.3.1(A) WINDWARD WALL (W) Average external pressure coefficient (Cp, e) h ≤ 25.0 m

h > 25.0 m

For highset buildings: 0.8, used with qz = q h For all other buildings: 0.8, when qz varies with height or 0.7, when used with qz = q h

0.8, when q z varies with height

TABLE 3.4.3.1(B) LEEWARD WALL (L) Average external pressure coefficient (Cp,e ) θ = 90°, for all α θ = 0°, with α < 10°

θ = 0°

10° ≤ α ≤ 15° -0.5

-0.3

-0.2

-0.3

α = 20° α ≥ 25° -0.4

-0.5

NOTE: For intermediate values of d/b and α, linear interpolation is permitted.

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AS 1170.2—1989

TABLE 3.4.3.1(C) SIDE WALLS (S)

TABLE 3.4.3.2(B) DOWNWIND SLOPE (U) For: θ = 0° and α ≥ 10°

Horizontal distance from windward edge

Average external coefficient (Cp,e )

0 to 1h 1h to 2h 2h to 3h > 3h

Average external pressure coefficient (Cp,e)

Ratio

-0.65 -0.5 -0.3 -0.2

NOTE: For the leeward and sidewalls, qz shall be taken as qh in all cases.

Roof pitch (α) degrees 10

15

20

25

30

35

45

≥60

≤0.25

-0.7 -0.3

-0.5 -0.0

-0.3 0.2

-0.2 0.3

-0.2 0.3

0.4

0.5

0.01α

0.5

-0.9 -0.4

-0.7 -0.3

-0.4 0.0

-0.3 0.2

-0.2 0.2

-0.2 0.3

0.4

0.01α

≥1.0

-1.3 -0.6

-1.0 -0.5

-0.7 -0.3

-0.5 0.0

-0.3 0.2

-0.2 0.2

0.3

0.01α

TABLE 3.4.3.2 ROOFS: AVERAGE EXTERNAL PRESSURE COEFFICIENTS (C p,e) FOR RECTANGULAR ENCLOSED BUILDINGS

TABLE 3.4.3.2 (C) DOWNWIND SLOPE (D) For: θ = 0° and α ≥ 10° Average external pressure coefficient (Cp,e)

TABLE 3.4.3.2(A) UPWIND SLOPE (U) AND DOWNWIND SLOPE (D)

Ratio

θ = 0°, for α < 10° θ = 90°, for all α. Horizontal distance from windward edge

≤0.25 0.5

Average external pressure coefficient (C p,e)

≥1.0

Roof pitch (α) degrees 10

15

≥20

-0.3 -0.5 -0.7

-0.5 -0.5 -0.6

-0.6 -0.6 -0.6

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NOTES: 0 to 1/2h 1/2h to 1h 1h to 2h 2h to 3h > 3h *

-

0.9, 0.9, 0.5, 0.3, 0.2,

- 0.4 - 0.4 0.0 0.2 0.3

- 1.3, - 0.6 - 0.7, - 0.3 (- 0.7)*,(- 0.3) * — —

1.

When two values are listed, the roof shall be designed for both values. In these cases, roof surfaces may be subjected to either values due to turbulence. Alternative combinations of external and internal pressures (see Clause 3.4.7) must be considered to obtain the most severe conditions for design.

2.

To obtain intermediate values for roof slopes and h/d ratios other than those shown, linear interpolation is permitted. Interpolation shall only be carried out between values of the same sign. Where no value of the same sign is given, assume 0.0 for interpolation purposes.

Value is provided for interpolation purposes.

FIGURE 3.4.3 PARAMETERS FOR RECTANGULAR ENCLOSED BUILDINGS COPYRIGHT

AS 1170.2—1989

26

3.4.4 Area reduction factors (K a) for roofs and side walls. For roofs and side walls, the external wind pressure (p e) calculated in accordance with Clause 3.4.2, shall be multiplied by the applicable reduction factor (Ka) as given in Table 3.4.4. For all other cases, take Ka = 1.0. Tributary area is the area contributing to the force being considered. For example, for a cladding fastener it will be the area of cladding supported by a single fastener, for a purlin it will be the span between supporting rafters times the distance between purlins.

3.4.5 Local pressure factors (K l) for cladding. The local pressure factor (K l) for wall and roof claddings, and their immediate supporting members and fixings, shall be obtained from Table 3.4.5 for the cases given in this Table, or taken as 1.0, whichever gives the worst combination of external and internal pressure.

NOTE: Ka = 1.0 for side walls of circular bins, silos and tanks.

Local pressure factors (K l) greater than 1.0 are not applicable in the ridge zone where the roof pitch is less than 10°.

TABLE 3.4.4 AREA REDUCTION FACTORS (K a) FOR ROOFS AND SIDE WALLS ACCORDING TO TRIBUTARY AREA Area (A) m2 ≤ 10 25 ≥100

Where an element of cladding or an immediate supporting member extends beyond the areas given in Table 3.4.5, the local pressure factor (K l) shall be taken as 1.0 on the remainder of that element or member.

When applying the local pressure factor, the negative limit to KlCp,e shall be -2.0.

Reduction factor (Ka) 1.0 0.9 0.8

NOTE: For intermediate values of A, linear interpolation is permitted.

(See Paragraph E3.4.4 of Appendix E.)

TABLE 3.4.5 LOCAL PRESSURE FACTORS (K l)

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Case

Description

Local pressure factors (K 1)

1

Positive pressures on areas of 0.25 a2 or smaller, anywhere on a windward wall, for all buildings

1.25

2

(a) Negative pressures (suctions) on areas of roof of 1.0a2 or less, within a distance 1.0a from a roof edge, from a ridge or hip on a roof with a pitch of 10° or more for building of all ht ; or on areas of wall of 1.0 a2 or less within a distance 1.0a from a windward wall edge, for buildings with h t ≤ 25.0 m (b) Negative pressures (suctions) on areas of wall of 0.25a2 or less, beyond a distance of 1.0a from a windward wall edge, for buildings with ht > 25.0 m

1.5

3

4

1.5

(a) Negative pressures (suctions) on areas of roof of 0.25a2 or less, within a distance 0.5a from a roof edge, from a ridge or hip on a roof with a pitch of 10° or more for buildings of all ht ; or on areas of wall of 0.25a2 or less within a distance 0.5a from a windward wall edge, for buildings with h t ≤ 25.0 m

2.0

(b) Negative pressures (suctions) on areas of wall of 1.0a2 or less, within a distance of 1.0a from a windward wall edge, for buildings ht > 25.0 m

2.0

Negative pressures (suctions) on areas of wall of 0.25a2 or less, on side walls within a distance 0.5a from a windward wall edge, for buildings with ht > 25.0 m

3.0

NOTES: 1. The dimension a is defined in Figure 3.4.5. 2. If more than one case applies, that giving the largest value of K1 should be used. 3. For the roof of podium buildings below tall buildings and on the walls of tall buildings where there are sloping edges or edge discontinuities exposed to conditions of high turbulence, the local pressure factor (K1 ) = 3.0 is not conservative. These situations are outside the scope of this Standard and specialist advice should be sought.

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27

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h t ≤ 25.0 m

AS 1170.2—1989

ht > 25.0 m

NOTE: Dimension ‘a’ is to be taken as the MINIMUM of 0.2b or 0.2d or the height ht as shown in Figure 3.4.3

FIGURE 3.4.5

LOCAL PRESSURE FACTORS (K1 )

(See Paragraph E3.4.5 of Appendix E).

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AS 1170.2—1989

28

3.4.6 Reduction factors (K p) for porous cladding. Where cladding porosity over a main surface exceeds 0.001 and is less than 0.01, the local negative pressure (Cp,e) shall be multiplied by the applicable reduction factors (K p) given in Table 3.4.6. For all other cases, take K p = 1.0. TABLE 3.4.6 PRESSURE REDUCTION FACTOR (K p) FOR CLADDING POROSITY Horizontal distance from windward edge > > > >

0.2d a 0.4d a 0.6d a 0.8d a

LEGEND: Porosity = da

= =

≤ ≤ ≤ ≤ ≤

0.2da 0.4da 0.6da 0.8da 1.0da

values of qz corresponding to those adopted for the external surfaces, using Equation 3.4.7. pi

(Cp,i)qz . . . . . . . . . . . . . . . . . . . (3.4.7)

=

the internal wind pressure, in kilopascals

where pi

Pressure reduction factor (Kp) 0.9 0.8 0.7 0.7 0.8

=

Cp,i =

the internal pressure coefficient, given in Table 3.4.7

qz

the free stream gust dynamic wind pressure at height z, given in Clause 3.3.

=

The internal pressures (p i) so determined shall be assumed to act simultaneously with the external pressures (p e), including the effects of local pressure factors (Kl), and the most severe conditions thus determined shall be selected for purposes of design.

the ratio of the open area over the total area of the surface the along-wind depth of the surface, in metres d, for walls or flat roofs, or the distance from windward edge to the ridge, for a pitched roof.

(See Paragraph E3.4.6 of Appendix E.) 3.4.7 Internal pressures (p i). The internal wind pressures (p i) shall be determined using the internal pressure coefficients (C p,i) given in Table 3.4.7 and the

Dominant openings are openings on a single surface whose combined area exceeds the combined open areas on any other single surface. A dominant opening does not need to be large. In cyclonic regions, windows shall be considered as potential dominant openings, unless capable of resisting impact by a 4 kg piece of timber of 100 mm × 50 mm cross-section, striking them at any angle at a speed of 15 m/s.

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TABLE 3.4.7 AVERAGE INTERNAL-PRESSURE COEFFICIENTS (C p,i) FOR BUILDINGS OF RECTANGULAR PLAN AND OPEN INTERIOR PLAN Condition 1.

2.

3.

Internal pressure coefficient (C p,i)

One wall permeable, other walls impermeable: (a) Wind normal to permeable wall (b) Wind normal to impermeable wall

0.6 - 0.3

Two or three walls equally permeable, other walls impermeable: (a) Wind normal to permeable wall (b) Wind normal to impermeable wall

0.2 - 0.3

All walls equally permeable or openings of equal area on all walls

- 0.3 or 0.0 whichever is the more severe for combined loadings

4. Dominant openings on one wall: (a) Dominant openings on windward wall, giving a ratio of open windward area to total open area (including permeability) of other walls and roofs subject to external suction, equal to — 0.5 or less 1 1.5 2 3 6 or more (b) (c) (d) 5.

Dominant openings on leeward wall Dominant openings on side wall Dominant openings in a roof segment

A building effectively sealed and having non-opening windows

(See Paragraph E3.4.7 of Appendix E.)

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- 0.3 or 0.0 ± 0.1 0.3 0.5 0.6 Windward wall pressure coefficient as in Table 3.4.3.1.(A) Value of C p,e for leeward external wall surface Value of C p,e for side external wall surface Value of C p,e for external surface of roof segment - 0.2 or 0.0, whichever is the more severe for combined loads

29

3.4.8 Frictional drag force (Ff) for rectangular enclosed buildings. The frictional drag force (F f) shall be taken in addition to those loads calculated for rectangular clad buildings only where the ratio d/h or d/b is greater than 4. For roofs, the calculation of frictional drag force is only required for those cases where Table 3.4.3.2(A) is applicable for determining external pressure coefficients for the calculation of external pressures. The frictional drag force (Ff) in the direction of the wind is given by Equations 3.4.8(1) and 3.4.8(2). If h ≤ b, Ff

= Cfqzb(d - 4h) + Cfqz2h(d - 4h) . . . . . . . . . . . . . . . . . . . . . . (3.4.8(1))

If h ≥ b, Ff

= Cfqzb(d - 4b) + Cfqz2h(d - 4b) . . . . . . . . . . . . . . . . . . . . . . (3.4.8(2))

where Ff

=

Cf

=

qz

=

b

=

d

=

h

=

the frictional drag force acting parallel to the windstream the frictional drag force coefficient for the structure or shape in the direction of the windstream the free stream gust dynamic wind pressure at height z, given in Clause 3.3 the breadth of the structure or structural member, normal to the windstream, in metres the depth of the structure parallel to the windstream, in metres the height of the structure, in metres

AS 1170.2—1989

Cf

=

pn

=

0.01 for smooth surfaces without corrugations or ribs, or with corrugations or ribs parallel to wind direction = 0.02 for surfaces with corrugations across the wind direction = 0.04 for surfaces with ribs across the wind direction. 3.4.9 Net pressures (pn) for free roofs. A monoslope, pitched or troughed free roof shall be assumed to be acted on by net pressures on each roof half, derived from the pressure coefficients given in Tables 3.4.9.1 to 3.4.9.3. Coefficients for the windward and leeward halves of each roof are shown in Figures 3.4.9(A), 3.4.9(B), and 3.4.9(C). All values shall be used with the value of q z applying at height h. Where two values are listed, the roof shall be designed for both values, taking the combination from the two roof halves giving the worst effect. The net wind pressure (pn) across the roof surface shall be calculated using Equation 3.4.9.

where Cp,n = Ka

=

Kl

=

qz

=

NOTE: For θ = 0°, take h = he and for θ = 90°, take h = ht.

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The first term in each equation gives the frictional drag force on the roof and the second, the frictional drag force on the walls. The terms are given separately to allow for the use of different values of Cf and qz on the different surfaces. qz shall be taken as qh.

FIGURE 3.4.9(A)

Cp,nKaKlqz . . . . . . . . . . . . . . . . . . . (3.4.9) the windward side net pressure coefficient (Cp,w) or the leeward side net pressure coefficient (Cp,l) the area reduction factor, given in Clause 3.4.4 the local pressure factor applicable to cladding and its immediate supporting structure, given in Table 3.4.9.4 the free stream gust dynamic wind pressure at height z, given in Clause 3.3.

NET PRESSURE COEFFICIENTS FOR MONOSLOPE FREE ROOFS (0.25 ≤ h/d ≤ 1)

TABLE 3.4.9.1(A) NET PRESSURE COEFFICIENTS FOR MONOSLOPE FREE ROOFS (0.25 ≤ h/d ≤ 1) θ = 0°

Roof pitch (α)

θ = 180° Cp,l

Cp,w

Cp,w

Cp,l

degrees

Empty under

Blocked under

Empty under

Blocked under

Empty under

Blocked under

Empty under

Blocked under

0 15 30

–0.6 0.6 –1.0 –2.2

–1.0 0.4 –1.5 –2.7

–0.4 0.2 –0.6 0.0 –1.1 –0.2

–0.8 0.4 –1.0 0.2 –1.3 0.0

–0.6 0.6 0.8 1.6

–1.0 0.4 0.8 1.6

–0.4 0.2 0.4 0.8

–0.8 0.4 –0.2 0.0

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AS 1170.2—1989

30 TABLE 3.4.9.1(B)

NET PRESSURE COEFFICIENTS FOR MONOSLOPE FREE ROOFS WITH α ≤ 5°, θ = 0° AND 90° (0.05 ≤ h/d ≤ 0.25) Horizontal distance from windward edge ≤1h

>1h ≤2h

Net pressure coefficient (C p,n) Values given for Cp,w in Table 3.4.9.1 (A) for α = 0°

FIGUR E 3.4.9(C) NET PRESSURE COEFFICIENTS FOR TROUGHED FREE ROOFS (0.25 ≤ h/d ≤ 1)

Values given for Cp,l in Table 3.4.9.1 (A) for α = 0°

TABLE 3.4.9.3 NET PRESSURE COEFFICIENTS FOR TROUGHED FREE ROOFS (0.25 ≤ h/d ≤ 1)

-0.2, 0.2 for empty under >2h -0.4, 0.2 for blocked under

θ = 0°

Roof pitch (α)

NOTE: For θ = 90° and all configurations, the roof pitch is effectively zero, and Table 3.4.9.1(A) or Table 3.4.9.1(B) with θ = 0° and α = 0° shall be used. For this wind direction, the height (h) should be taken to the highest point of the roof.

degrees 7.5 15 22.5

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Cp,l

Cp,w Empty under -0.6 0.4 -0.6 0.4 -0.7 0.3

Blocked under -0.7 -0.8 -1.0

Empty under 0.3 0.5 0.7

Blocked under -0.3 -0.2 -0.2

NOTES: 1. To obtain intermediate values for roof slopes other than those shown, linear interpolation is permitted. Interpolation shall be carried out only between values of the same sign. Where no value of the same sign is given, assume 0.0 for interpolation purposes 2. For θ = 90° and all configurations, the roof pitch is effectively zero, and Table 3.4.9.1(A) with θ = 0° and α = 0° shall be used. 3. ‘Empty under’ implies goods and materials stored under the roof, blocking less that 50% of the cross-section area exposed to the wind. 4. ‘Blocked under’ implies 75% or more of the cross-section area blocked. 5. For intermediate values of blockage, linear interpolation is permitted.

For free roofs of low pitch with fascia panels, the fascia panel shall be treated as the wall of an elevated building, and pressures obtained from Table 3.4.3.1. For the design of cladding and its immediate supporting structure, the values of local net pressure factors (K l) given in Table 3.4.9.4 shall be used. TABLE 3.4.9.4 LOCAL NET PRESSURE FACTORS (K l) FOR FREE ROOFS AND CANOPIES AND CARPORTS

FIGURE 3.4.9(B) NET PRESSURE COEFFICIENTS FOR PITCHED FREE ROOFS (0.25 ≤ h/d ≤ 1)

TABLE 3.4.9.2

Case

NET PRESSURE COEFFICIENTS FOR PITCHED FREE ROOFS (0.25 ≤ h/d ≤ 1) Roof pitch (α) degrees 7.5 15 22.5 30

1

θ = 0° Cp,w Empty under -0.6 0.4 -0.4 0.6 -0.4 0.8 -0.4 0.9

Cp,l Blocked under -1.4 -1.2 -0.9 -0.5

Empty under -0.7 -1.0 -1.1 -1.2

2 Blocked under -1.0 -1.3 -1.4 -1.5

3

Description Pressures on an area between 0.25a2 and 1.0a2 , within a distance 1.0a from a roof edge, or from a ridge with a pitch of 10° or more Pressures on an area of 0.25a2 or less, within a distance 0.5a from a roof edge, or from a ridge with a pitch of 10° or more Negative pressure (upward net pressures) on an area of 0.25a2 or less, within a distance 0.5a from a windward corner of a free roof with a pitch of less than 10°

Local net pressure factor (K 1) 1.5

2.0

3.0

NOTE: a is 20% of the shortest horizontal plan dimension of the free roof or canopy.

(See Paragraph E3.4.9 of Appendix E.)

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3.4.10 Net pressures (pn) for canopies, awnings and carports, adjacent to enclosed buildings. The net wind pressures (pn) across canopies, awnings or carports adjacent to an enclosed building, and with a roof slope of 5° or less, shall be calculated using Equation 3.4.10. pn = Cp,nKaKlqz . . . . . . . . . . . . . . . . . . (3.4.10) where pn = the net wind pressure, in kilopascals Cp,n = the net pressure coefficient obtained from Tables 3.4.10(A) and (B) or Figure 3.4.10(B) Ka = the area reduction factor, given in Table 3.4.4 Kl = the local pressure factor, given in Table 3.4.9.4 qz = the free stream gust dynamic wind pressure at height z, given in Clause 3.3. The height (z) is either the height of the canopy, awning or carport above the ground, or the height of the building, according to Tables 3.4.10(A) and (B) or Figure 3.4.10(B). The canopies, awnings or carports shall be designed for both downwards (positive) and upwards (negative) net wind pressures, where indicated. TABLE 3.4.10(A) NET PRESSURE COEFFICIENTS (C p,n) FOR CANOPIES AND AWNINGS ADJACENT TO BUILDINGS FOR hc/h < 0.5 and θ = 0° (WIND NORMAL TO WALL) Ratio

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0.1 0.2 0.5

Net pressure coefficient (Cp,n) (qz = qh) Downward

Upward

1.2 0.7 0.4 (see Note)

-0.2 -0.2 -0.2 (see Note)

NOTE: These values are provided for interpolation purposes.

AS 1170.2—1989 NOTE: For canopies attached to side walls, h shall be taken as the height he, and for canopies attached to gable ends ht, as shown in Figure 3.4.10(A).

TABLE 3.4.10 (B) NET PRESSURE COEFFICIENTS (C p,n) FOR CANOPIES AND AWNINGS ADJACENT TO BUILDINGS FOR h c/h ≥ 0.5 and θ = 0° (WIND NORMAL TO WALL) Ratio

0.5 0.75 1.0 *

Downward 0.5 0.4 0.2

Net pressure coefficient (Cp,n) (qz at z = hc) Upward -0.3 [-0.3 - 0.2(h c/wc )] or -1.5* [-0.3 - 0.6(h c/wc )] or -1.5*

Whichever is the lower magnitude. NOTES TO TABLES 3.4.10(A) and 3.4.10(B): 1. hc is the height from ground to the attached canopy, awning or carport. 2. For intermediate values of hc/h, linear interpolation is permitted.

For wind directions parallel to the wall of the adjacent building, the net pressure coefficients (C p,n) on the canopy or awning shall be obtained from Table 3.4.9.1(A) or Table 3.4.9.1(B), as appropriate. For the ratio hc/h < 0.5, the net pressure coefficient (C p,n) shall be used with qz = qh and for hc/h ≥ 0.5, use qz at z = hc. NOTE: In Tables 3.4.9.1(A) and 3.4.9.1(B), the net wind pressures are modified when ‘blocked under’ condition exist under the canopy.

3.4.11 Net pressures (pn) for cantilevered roofs. The design wind loads on cantilevered roofs, such as grandstands, where the cantilever length is greater than 5.0 m, must be determined by taking into account the dynamic response as given in Clause 4.4.4. For cantilevered roofs less than 5.0 m in length, the design wind loads may be obtained as for free roofs (see Clause 3.4.9).

FIGURE 3.4.10(A) NET PRESSURE COEFFICIENTS (CP,N) FOR CANOPIES AND AWNINGS ADJACENT TO BUILDINGS

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AS 1170.2—1989

32

Wind direction (θ)

Net pressure coefficient (C p,n) (upward) (qz at z = hc)

0° 90°

-1.0 -0.7

Wind direction (θ)

Net pressure coefficient (Cp,n) (upward) (qz at z = hc)

0° 90°

-1.2 -0.6

FIGURE 3.4.10 (B) NET PRESSURE COEFFICIENTS (Cpn) FOR PARTIALLY ENCLOSED CARPORTS (hc/wc ≤ 0.5) AND (qz at z = hc)

(See Paragraph E3.4.10 of Appendix E.) 3.4.12 Frictional drag force (Ff) for free roofs and canopies. For cases given in Tables 3.4.9.1 to 3.4.9.3, frictional drag forces acting horizontally in the direction of windstream shall be calculated using Equations 3.4.12(1), 3.4.12(2), and 3.4.12(3). Calculation of frictional drag is not required for wind directions of 0° and 180° for free roofs with pitches of 10° or more, or for attached canopies for wind direction of 0°. For smooth surfaces without corrugations or ribs, or where wind is parallel to corrugations or ribs: Ff = 0.01bdqz . . . . . . . . . . . . . . (3.4.12(1)) where wind is across corrugations: Ff = 0.02bdqz . . . . . . . . . . . . . . (3.4.12(2)) where wind is across ribs: Ff = 0.04bdqz . . . . . . . . . . . . . . (3.4.12(3)) For free roofs or canopies that are clad on top and bottom, the frictional drag on both surfaces shall be computed in accordance with this Clause. For structures

with exposed roof trusses or other exposed members, the loads on these shall be calculated in accordance with Clause 3.5. 3.4.13 Net pressure (pn) for hoardings and free-standing walls. The net wind pressure (p n) across flat rectangular hoardings or free standing walls shall be calculated using Equation 3.4.13. pn = Cp,nKpqh . . . . . . . . . . . . . . . . (3.4.13) where Cp,n = the net pressure coefficient obtained from Table 3.4.13 Kp = the porosity reduction factor given by [1 − (1 − δ)2], where δ is the actual solidity ratio for a wall (ratio of solid area to total surface area) qh = the free stream gust dynamic wind pressure calculated at the top of the hoarding or wall.

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TABLE 3.4.13 NET PRESSURE COEFFICIENTS (C p,n) FOR HOARDINGS (0.5 ≤ b/c ≤ 45) AND FREESTANDING WALLS (0.5 ≤ b/h ≤ 45) TABLE 3.4.13(A) WIND NORMAL TO HOARDING OR WALL (θ = 0°) Net pressure coefficient (Cp,n) Hoardings Free-standing walls

1.5

1.2

TABLE 3.4.13(B) WIND AT 45° TO HOARDING OR WALL (θ = 45°)

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Net pressure coefficient (Cp, n) Free-standing walls Hoardings (5 ≤ b/c < 45) (5 ≤ b/h < 45) Distance from windward Distance from windward free end free end 0 to 2c 2c to 4c >4c 0 to 2h 2h to 4 h > 4h 3.0 1.5 0.75 2.4 1.2 0.6 Free-standing walls Hoardings (0.5 ≤ b/c < 5) (0.5 ≤ b/h < 5) Distance from windward Distance from windward free end free end 0 to b/2 b/2 to b 0 to b/2 b/2 to b 1.7 1.1 1.7 1.1

TABLE 3.4.13(C) WIND PARALLEL TO HOARDING OR WALL (θ = 90°) Net pressure coefficient (Cp,n) Hoardings Free-standing walls Distance from windward free end Distance from windward free end 0 to 2c 2c to 4c > 4c 0 to 2h 2h to 4h > 4h ± 1.2 ± 0.6 ± 0.3 ± 1.0 ± 0.5 ± 0.25

AS 1170.2—1989

3.5 FORCES ON EXPOSED STRUCTURAL MEMBERS. 3.5.1 General. These Clauses set out procedures for determining wind forces and moments on structure and components, consisting of exposed members, such as lattice frames, trusses and towers using the ‘Static Analysis’. 3.5.2 Procedure. The conversion of wind speed to dynamic pressure is as defined in Clause 3.3. Force and drag force coefficients for use in this Section are given in Appendix B. The wind force on an exposed structural member, whose aspect ratio (l/b) is greater than 8, shall be calculated for wind axes from Equation 3.5.2(1). Fd = KiKshKarCdAzqz . . . . . . . . . . . . . (3.5.2(1)) and for body axes from Equations 3.5.2(2) and 3.5.2(3). Fx = KiKshKarCF,xAzqz . . . . . . . . . . . . (3.5.2(2)) Fy = KiKshKarCF,yAzqz . . . . . . . . . . . . (3.5.2(3)) where Fd = the drag force acting in the direction of the windstream Ki = a factor to account for the angle of inclination of the axis of members to the wind direction = 1.0, when the wind is normal to member = sin2φ, when there is an angle φ between the wind direction and the axis of the structural member Ksh = a shielding factor for multiple open frames (see Tables 3.5.4.1 and 3.5.4.2) Kar = an aspect ratio correction factor for individual member forces (see Table B6) Cd = the drag force coefficient for the member in the direction of the windstream Az = a reference area at height z = bl (see Appendix B)

NOTE: When the ratio (c/h) exceeds 0.7, treat the hoarding as a fee-standing wall.

FIGURE 3.4.13 HOARDINGS AND FREE-STANDING WALLS

(See Paragraph E3.4.13 of Appendix E.) COPYRIGHT

AS 1170.2—1989

34

= the free stream gust dynamic wind pressure at height z, given in Clause 3.3 Fx and Fy = the force components resolved along the member’s x- and y-axes respectively CF,x and CF,y = the force coefficients for the member, in the direction of the member’s x- and y-axes respectively. If the wind speed varies over the height of the member, the area shall be subdivided so that the specified forces are taken over appropriate areas. 3.5.3 Single open frames. The wind force on a structure of open frame type comprising a number of members, lying in a single plane normal to the wind direction, shall be taken as the sum of the wind forces on the individual members from the drag force coefficients for their respective shapes as in Clause 3.5.2. For single open frames the value Ksh = 1.0. (See Paragraph E3.5.3 of Appendix E.) 3.5.4 Multiple open frames. For structures comprising a series of similar open frames in parallel, the force on the second and subsequent frames shall be taken as the force on the windward frame calculated as in Clause 3.5.3, multiplied by a shielding factor (Ksh) obtained from Tables 3.5.4.1 and 3.5.4.2. TABLE 3.5.4.1 SHIELDING FACTORS (K sh) FOR MULTIPLE FRAMES (θ = 0°)

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qz

Effective solidity (δe )

≤0.2

0.5

1.0

2.0

4.0

≥ 8.0

0 0.1 0.2 0.3 0.4 0.5 0.7 1.0

1.0 0.8 0.5 0.3 0.2 0.2 0.2 0.2

1.0 1.0 0.8 0.6 0.4 0.2 0.2 0.2

1.0 1.0 0.8 0.7 0.5 0.3 0.2 0.2

1.0 1.0 0.9 0.7 0.6 0.4 0.2 0.2

1.0 1.0 1.0 0.8 0.7 0.6 0.4 0.2

1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

The effective solidity ratio (δe) in Tables 3.5.4.1 and 3.5.4.2 shall be taken as the actual solidity ratio (δ) which is equal to the solid area divided by the total area for flat-sided members. For circular cross-section members, the effective solidity (δe) shall be obtained from the actual solidity ratio (δ) using Equation 3.5.4. δe = 1.2δ1.75 . . . . . . . . . . . . . . . . . . . . (3.5.4) (See Paragraph E3.5.4 of Appendix E.) 3.5.5 Drag force coefficients (Cd) for lattice towers. The overall drag force coefficients (Cd) for lattice towers are given for various arrangements in Tables 3.5.5.1, 3.5.5.2 and 3.5.5.3. For the wind blowing against any face, the design drag force shall be calculated using Equation 3.5.5. Fd = CdAzqz . . . . . . . . . . . . . . . . . . . . (3.5.5) where Fd = the drag force acting parallel to the wind-stream Cd = the drag force coefficient for the section of the tower in the direction of the windstream Az = the area at height z of members in the front face, projected normal to that face qz = the free stream gust dynamic wind pressure at height z, given in Clause 3.3. TABLE 3.5.5.1 DRAG FORCE COEFFICIENTS (C d) FOR SQUARE AND EQUILATERAL-TRIANGLE PLAN LATTICE TOWERS WITH FLAT-SIDED MEMBERS

Frame spacing ratio (λ)

Actual solidity of front face (δ)

0.1 0.2 0.3 0.4 ≥ 0.5

TABLE 3.5.4.2 SHIELDING FACTORS (K sh) FOR MULTIPLE FRAMES (θ = 45°) Effective solidity (δ e)

Frame spacing ratio (λ) ≤0.5

1.0

2.0

4.0

≥8.0

0 0.1 0.2 0.3 0.4 0.5 0.7 1.0

1.0 0.9 0.8 0.7 0.6 0.5 0.3 0.3

1.0 1.0 0.9 0.8 0.7 0.6 0.6 0.6

1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.6

1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8

1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Drag force coefficient (Cd) Square towers

Equilateral-triangle towers

3.5 2.8 2.5 2.1 1.8

3.1 2.7 2.3 2.1 1.9

TABLE 3.5.5.2 DRAG FORCE COEFFICIENTS (C d) FOR SQUARE PLAN LATTICE TOWERS WITH CIRCULAR MEMBERS

NOTES TO TABLES 3.5.4.1 and 3.5.4.2: 1. λ is equal to frame spacing centre-to-centre divided by the projected frame breadth normal to wind. 2. For intermediate values of δe and λ, interpolation is permitted.

Actual Drag force coefficient (Cd) solidity of Parts of tower in subParts of tower in front face (δ) critical flow super-critical flow bV < 3 m 2/s bV ≥ 6 m 2/s Onto face Onto Onto face Onto corner corner 0.05 2.4 2.5 1.4 1.2 0.1 2.2 2.3 1.4 1.3 0.2 1.9 2.1 1.4 1.6 0.3 1.7 1.9 1.4 1.6 0.4 1.6 1.9 1.4 1.6 ≥0.5 1.4 1.9 1.4 1.6

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TABLE 3.5.5.3 DRAG FORCE COEFFICIENTS (C d) FOR EQUILATERAL-TRIANGLE PLAN LATTICE TOWERS WITH CIRCULAR MEMBERS Actual solidity of front face (δ)

0.05 0.1 0.2 0.3 0.4 ≥0.5

Drag force coefficient (Cd) Parts of tower in sub-critical flow bV < 3 m 2/s (all wind directions)

Parts of tower in super-critical flow bV ≥ 6 m 2/s (all wind directions)

1.8 1.7 1.6 1.5 1.5 1.4

1.1 1.1 1.1 1.1 1.1 1.2

AS 1170.2—1989

coefficient which occurs when the wind blows on to a corner, shall be taken as 1.2 times the force coefficient for the wind blowing against a face. (See Paragraph E3.5.5 of Appendix E.) 3.6 FATIGUE LOADING. In tropical cyclone regions C and D (as defined in Figure 3.2.2) cladding and its connections shall be designed to resist the fatigue loading sequence given in Table 3.6, or from pressure sequences obtained from simulated wind tunnel studies, or full-scale measurements, under cyclonic conditions. (See Paragraph E3.6 of Appendix E.) TABLE 3.6 FATIGUE LOADING SEQUENCE Range

LEGEND TO TABLES 3.5.5.1, 3.5.5.2 AND 3.5.5.3: δ = the actual solidity ratio (solid area divided by the total enclosed area). b = the average member diameter. NOTE: For intermediate values of bV, interpolation is permitted.

0 0 0 0

to to to to

0.40pd 0.50pd 0.65pd 1.00pd

Number of cycles 8 000 2 000 200 1

LEGEND: pd = the ultimate limit state design wind pressure (pe + pi) as calculated from Clause 3.4.2 and 3.4.7.

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For equilateral-triangle lattice towers with flat-sided members, the force coefficient shall be assumed to be constant for any inclination of the wind to a face. For square lattice towers with flat-sided members, the force

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NOTE: This requirement will normally be met by testing three samples each of which should pass. If only one sample is tested, the final cycle should be increased to 1.3pd, and if two samples are tested, it should be increased to 1.2pd.

AS 1170.2—1989

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SECTION 4. DETAILED PROCEDURE: DYNAMIC ANALYSIS 4.1 APPLICATION. The dynamic analysis procedure set out in this Section enables the determination of wind forces and moments on the overall structure. Dynamic analysis is permitted for all classes of structures and must be used for the analysis of wind-sensitive structures. A wind-sensitive structure (building or component) is defined as one in which additional loads occur as a result of the dynamic interaction of the wind and structure. In particular, the dynamic analysis procedure shall be used for the design of main structural components of any structure having both the following properties: (a) Height or length-to-breadth ratio greater than 5. (b) A first-mode frequency of vibration of less than 1 Hz. Pressures and forces on parts of walls, roof cladding, canopies, awnings, windows, doors and their supporting framework shall be determined using the static analysis procedure set out in Section 3. (See Paragraph F4.1 of Appendix F.) 4.2 HOURLY MEAN WIND SPEED. 4.2.1 General. The design hourly mean wind speed (Vz) at height z shall be used to determine wind pressures and forces acting on a structure for the dynamic analysis procedure. 4.2.2 Derivation of design hourly mean wind speed (Vz). The design hourly mean wind speed (Vz) shall be determined from the appropriate basic wind speed given in Figure 4.2.2 for the appropriate limit state using Equation 4.2.2. Vz = VM(z,cat)MsMtMi . . . . . . . . . . . . (4.2.2) where Vz = the design hourly mean wind speed at height z, in metres per second V = the basic wind speed, (V u), (Vp) and (Vs) (see Figure 4.2.2), in metres per second M(z,cat) = an hourly mean wind speed multiplier for a terrain category at height z for upwind distance of at least (1500 + x i) m (see Clause 4.2.6, Tables 4.2.5.1 and 4.2.5.2) Ms = a shielding multiplier (see Table 4.2.7) Mt = a topographic multiplier for hourly mean wind speeds (see Table 4.2.8)

Mi

=

a structure importance multiplier (see Table 4.2.9).

NOTE: M(z,cat) may change from the tabulated values if the structure site is within the transition zone near the edge of a terrain boundary (see Clause 4.2.6).

Irrespective of the calculation in this Clause the design hourly mean wind speed (Vz), determined by Equation 4.2.2, shall not be less than the following: (a) Ultimate limit state . . . . . . . . . . . . . . . . . . 20 m/s. (b) Permissible stress method . . . . . . . . . . . . . 17 m/s. (See Paragraph F4.2.2 of Appendix F.) 4.2.3 Wind direction. At least four wind directions, equally spaced, shall be considered when calculating wind loads on structures using the detailed procedure. Where sufficient meteorological information is available, the basic wind speed (V) at a site may be adjusted for specific wind directions, in region A for V s, Vp and Vu, and in region B for Vs. For some of the major population centres this is given in Table 4.2.3. Directional wind speeds shall be corrected for terrain, height, shielding and local topography, as indicated in Clause 4.2.2. Where the dynamic response data and associated multiplying factors are given for only four orthogonal directions relative to the major axes of the structure, the wind speed for any given orthogonal direction shall be taken to be the largest corrected directional wind speed from a 90° sector, symmetrically positioned about the orthogonal direction being considered. Where dynamic response data and associated multiplying factors are given for eight or sixteen separate wind directions, they shall be used with the corresponding corrected sector wind speeds derived from Table 4.2.3. Where directional wind speed data are not available, or their use is not allowed (as in tropical cyclone regions C and D) or for Vp and Vu in intermediate region B (which includes Brisbane), the basic wind speed may be multiplied by 0.95 for the determination of resultant forces and overturning moments on complete buildings. NOTE: A reduction factor of 0.95 should not be used simultaneously with values from Table 4.2.3, except for Vp and Vu in Brisbane.

TABLE 4.2.3 BASIC WIND SPEEDS (V) IN m/s WITH WIND DIRECTION FOR SOME OF THE MAJOR POPULATION CENTRES Wind direction NE E SE S SW W NW N

Adelaide

Brisbane

Canberra

Melbourne

Sydney

Vs

Vp

Vu

Vs

Vp

Vu

Vs

Vp

Vu

Vs

Vp

Vu

Vs

Vp

Vu

Vs

Vp

Vu

31 30 30 30 38 38 36 33

34 34 33 33 41 41 39 37

42 42 40 40 50 50 48 45

30 30 32 32 38 38 30 30

49 49 49 49 49 49 49 49

60 60 60 60 60 60 60 60

30 30 30 30 30 35 38 30

33 33 33 33 33 38 41 34

40 40 40 40 41 46 50 42

30 30 30 32 35 38 34 37

33 33 33 34 38 41 36 38

40 40 40 42 46 50 44 46

30 31 30 30 34 38 34 30

33 33 33 33 35 41 38 33

40 40 40 40 43 50 46 41

31 30 36 36 35 38 35 30

33 33 39 38 38 41 38 33

40 40 48 47 47 50 47 40

NOTES: 1 2

Perth

Wind direction in this Table indicates the direction from which the wind blows. For intermediate wind directions, linear interpolation is permitted.

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37

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AS 1170.2—1989

AS 1170.2—1989

38

As an alternative to the methods outlined in this Clause, a detailed probability analysis to allow for the directional effects of wind is permitted. (See Paragraph E3.2.3 of Appendix E.) 4.2.4 Terrain category. Terrain, over which the approach wind flows towards a structure shall be assessed on the basis of the following category descriptions (see also Figures E3.2.4(A) to (D) of Appendix E): (a) Category 1 — exposed open terrain with few or no obstructions and water surfaces at serviceability windspeeds (V s) only. (b) Category 2 — open terrain, grassland with few well scattered obstructions having heights generally from 1.5 m to 10.0 m and water surfaces at windspeeds (V u) and (Vp). (c) Category 3 — terrain with numerous closely spaced obstructions having the size of domestic houses (3.0 m to 5.0 m high). (d) Category 4 — terrain with numerous large, high (10.0 m to 30.0 m high) and closely spaced obstructions such as large city centres and well-developed industrial complexes.

Selection of terrain category shall be made with due regard to the permanence of the obstructions which constitute the surface roughness, in particular vegetation in tropical cyclonic regions shall not be relied upon to maintain a wooded terrain roughness. A roughness length (zo) is defined for each terrain category in Table 4.2.4. TABLE 4.2.4 ROUGHNESS LENGTH (zo) Terrain category 1 2 3 4

Roughness length (z o) metres 0.002 0.02 0.2 2.0

(See Paragraph E3.2.4 of Appendix E.) 4.2.5 Terrain and structure height multiplier (M(z,cat)). The variation of terrain multipliers with height (z) shall be taken from Tables 4.2.5.1 and 4.2.5.2. Values for turbulence intensity (σv/Vz) as a function of height and terrain category are given in Table 4.2.5.3. Designers shall take account of probable future changes to terrain roughness in assessment of terrain and structure height multipliers M(z,cat).

TABLE 4.2.5.1 TERRAIN AND STRUCTURE HEIGHT MULTIPLIERS FOR HOURLY MEAN WIND SPEEDS IN FULLY DEVELOPED TERRAINS ULTIMATE LIMIT STATE AND PERMISSIBLE STRESS DESIGN — REGIONS A AND B ONLY SERVICEABILITY LIMIT STATE DESIGN — ALL REGIONS

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Height (z) m

Terrain Category 1 0.61 0.65 0.71 0.74 0.77 0.80 0.83 0.85 0.89 0.92 0.97 1.00 1.03 1.06 1.10 1.14

≤3 5 10 15 20 30 40 50 75 100 150 200 250 300 400 500

Multiplier (M(z,cat)) Terrain Category 2 Terrain Category 3 0.48 0.38 0.53 0.38 0.60 0.44 0.64 0.49 0.66 0.52 0.70 0.57 0.74 0.60 0.76 0.63 0.81 0.68 0.84 0.72 0.89 0.78 0.93 0.82 0.96 0.86 0.99 0.89 1.04 0.94 1.08 0.99

Terrain Category 4 0.35 0.35 0.35 0.35 0.35 0.38 0.40 0.42 0.51 0.55 0.62 0.67 0.71 0.74 0.81 0.86

TABLE 4.2.5.2 TERRAIN AND STRUCTURE HEIGHT MULTIPLIERS FOR HOURLY MEAN WIND SPEEDS IN FULLY DEVELOPED TERRAINS ULTIMATE LIMIT STATE AND PERMISSIBLE STRESS DESIGN — REGIONS C AND D ONLY Height (z) m ≤3 5 10 15 20 30 40 50 75 ≥100

Multiplier (M(z,cat)) Terrain Categories 1 and 2 0.50 0.54 0.60 0.64 0.68 0.75 0.80 0.84 0.93 1.00

Terrain Categories 3 and 4 0.40 0.40 0.47 0.54 0.59 0.67 0.74 0.80 0.91 1.00

NOTE TO TABLES 4.2.5.1 AND 4.2.5.2: For intermediate values of height (z) and terrain category, interpolation is permitted. COPYRIGHT

39

AS 1170.2—1989

TABLE 4.2.5.3 TURBULENCE INTENSITY (σ v/Vz) ULTIMATE LIMIT STATE AND PERMISSIBLE STRESS DESIGN — REGIONS A AND B ONLY SERVICEABILITY LIMIT STATE DESIGN — ALL REGIONS Height (z) m ≤3 5 10 15 20 30 40 50 75 100 150 200 250 300 400 500

Turbulence intensity (σv/Vz) Terrain Category 1 0.171 0.165 0.157 0.152 0.147 0.140 0.133 0.128 0.118 0.108 0.095 0.085 0.080 0.074 0.068 0.058

Terrain Category 2 0.207 0.196 0.183 0.176 0.171 0.162 0.156 0.151 0.140 0.131 0.117 0.107 0.098 0.092 0.082 0.074

NOTES: 1. For intermediate values of height (z) and terrain category, interpolation is permitted. 2. For ultimate limit state and permissible stress calculations, for Terrain Categories 1, 2 and 3 in cyclone regions C and D, use turbulence intensities for Terrain Category 3 in non-cyclone regions A and B. For Terrain Category 4 in cyclone regions C and D, use turbulence intensities for Terrain Category 4 in non-cyclone regions A and B. 3. Turbulence intensities have not been provided for heights below the general roughness height, since these vary enormously with location around the structure.

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(See Paragraph E3.2.5 of Appendix E.) 4.2.6 Changes in terrain category. The wind speed at a site shall be adjusted for change in terrain roughness through a correction to the wind speed multiplier (M(z,cat)). There is an upper limit to the developed height of the inner layer (hi) which is a function of x i and which is independent of whether the flow is from the rougher terrain or to the rougher terrain. With reference to Figure 4.2.6 the corrected wind speed multiplier is given by Equation 4.2.6(3). xi

=

. . . . . . . . . . . . . (4.2.6(1))

Conversely: hi

=

. . . . . . . . . . . . . (4.2.6(2))

For hourly mean wind speeds: For x < xi Mx = Mo For (x - xi) < 1500 m Mx

=

. . . (4.2.6(3))

For (x - xi) > 1500 m Mx = M(z,cat) where xi = the distance downstream, in metres, from the start of the new terrain to the developed height of the inner layer (hi), given by Equation 4.2.6(1)

Terrain Category 3 — 0.271 0.239 0.225 0.215 0.203 0.195 0.188 0.176 0.166 0.150 0.139 0.129 0.121 0.108 0.098

zo,r

Terrain Category 4 — — — — 0.342 0.305 0.285 0.270 0.248 0.233 0.210 0.196 0.183 0.173 0.155 0.141

= the larger of the two roughness lengths, in metres, given in Table 4.2.4. hi = the developed height of the inner layer, in metres, which is equal to z for the cal cul a t i on of x i , gi ven b y Equation 4.2.6(2) Mx = the hourly mean wind speed multiplier at a distance x from the start of new terrain category for height z Mo = the upstream terrain category hourly mean wind speed multiplier at the beginning of each new terrain for height z M(z,cat) = the downstream terrain category hourly mean wind speed multiplier for each new terrain for height z and (x - xi) > 1500 m, g i ven i n Tables 4.2.5.1 and 4.2.5.2 x = the distance downwind, in metres, from a change in terrain category to the structure under consideration. Fully developed hourly mean windspeed multipliers (Mz,cat) only apply at a structure site when the terrain category at the site is uniform upstream for a distance greater than (1500 + xi) metres. When the immediate upstream terrain extent is less than (1500 + xi) metres, corrected windspeed multipliers (Mx) shall be computed using Equation 4.2.6(3). Notwithstanding this requirement, the extent of upwind terrain to be considered need not exceed the larger of either 2500 m or 50 times the structure height (ht), provided that the terrain at that limit is Terrain Category 3 or less rough, (assume the windspeed multiplier (Mo) to be the value for fully developed terrain at that limit). If the terrain at that point is rougher than Terrain Category 3, the upwind limit shall be extended until Terrain Category 3 or terrain of less roughness is encountered, or alternatively fully developed Terrain Category 3 may be arbitrarily assumed upwind of that point.

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AS 1170.2—1989

40

FIGURE 4.2.6 CHANGES IN TERRAIN CATEGORY

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(See Paragraph F4.2.6 of Appendix F.) 4.2.7 Shielding multiplier (Ms). Shielding is permitted when the following conditions are satisfied: (a) The heights of upwind buildings within a 45° sector of a radius 20ht are greater than or equal to ht. (b) Alternatively, if upwind buildings within a radius of 20ht are of lesser height, shielding is permitted only on the upwind face of the building in the area below the average height of shielding buildings. Full loading shall be applied to all other areas. The shielding multiplier (Ms) is given in Table 4.2.7. Without shielding, M s = 1.0. To determine the shielding multiplier (Ms) from Table 4.2.7 the following procedure shall be used: (i) Each wind direction being considered shall be assessed for upwind shielding buildings within a 45° sector of radius 20ht. (ii) The building spacing parameter (D) in any sector shall be calculated using Equation 4.2.7(1). D

=

. . . . . . . . . . . . . . . . . (4.2.7(1))

where D ls

= =

the building spacing parameter the average height of shielding buildings, in metres

=

. . . . . . . . . . . . . (4.2.7(2))

hs

=

bs

=

ht

=

ns

=

the average height of shielding buildings, in metres the average breadth of shielding buildings, normal to the windstream, in metres the height to the top of the structure being shielded, in metres the number of upwind shielding buildings within a 45° sector of radius 20ht and with height h ≥ ht.

TABLE 4.2.7 SHIELDING MULTIPLIER (M s) Building spacing parameter (D) ≤ 1.5 3.0 6.0 ≥12.0

Shielding multiplier (M s) 0.7 0.8 0.9 1.0

NOTE: For intermediate values of D, interpolation is permitted.

(See Paragraph E3.2.7 of Appendix E.) 4.2.8 Topographic multiplier (Mt). If the structure under consideration is located within a local topographic zone, the topographic multiplier (Mt) shall be obtained by interpolation from the values of Mt at the crest of a hill, ridge or escarpment given in Table 4.2.8 and the value of Mt = 1 at the boundary of the zone. Interpolation shall be linear with horizontal distance from the crest, and with height above the local ground level. The local topographic zones are shown in Figures 4.2.8.1 and 4.2.8.2. A topographic multiplier of Mt = 1 shall be used for all sites outside a local topographic zone or if the upwind slope (φ) is less than 0.05. TABLE 4.2.8 TOPOGRAPHIC MULTIPLIER AT CREST (x = 0) FOR HOURLY MEAN WIND SPEEDS Upwind slope (φ)

0.05 0.1 0.2 ≥0.3

Topographic multiplier (Mt ) Escarpments Hills and ridges φd ≤ 0.05 φd ≥ 0.10 (See Notes 1 and 2) 1.07 1.16 1.14 1.32 1.28 1.64 1.42 1.96

LEGEND: φ = the upwind slope, calculated from φ = H/2Lu φd = the average downwind slope, measured from the crest of a hill, ridge or escarpment to the ground level at a distance of 5H. H = the height of the hill, ridge or escarpment, in metres Lu = the horizontal distance upwind from the crest to a level half the height below the crest, in metres.

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Mt may also be obtained by the following methods: (a) The use of an appropriate equation based upon experimental and theoretical results, such as that given in Paragraph F4.2.8 of Appendix F. (b) Correctly-scaled wind tunnel test. (c) Full-scale measurements at site.

AS 1170.2—1989 NOTES: 1. An escarpment has a value of downwind slope (φd) ≤ 0.05. A hill or a ridge has a value of downwind slope (φd) > 0.05. The values given in Table 4.2.8 are only applicable to those hills and ridges with downwind slopes ≥ 0.10. 2. For hills and ridges with downwind slope 0.05 < φd < 0.10, linear interpolation between the Mt values for escarpments, and hills and ridges in Table 4.2.8 is permitted. 3. For intermediate values of upwind slope (φ) and downwind slope (φd), linear interpolation is permitted.

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FIGURE 4.2.8.1 HILLS AND RIDGES

NOTE: Figures 4.2.8.1 and 4.2.8.2 are cross-sections through the structure site for a particular wind direction.

FIGURE 4.2.8.2 ESCARPMENTS

(See Paragraph F4.2.8 of Appendix F.)

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AS 1170.2—1989

42

4.2.9 Structure importance multiplier (Mi). For special structures, the design hourly mean wind speed shall (or may in the case of reductions) be adjusted with a multiplier (M i) given in Table 4.2.9. TABLE 4.2.9 STRUCTURE IMPORTANCE MULTIPLIER (M i) Class of structure

(See Paragraph F4.4.1 of Appendix F.)

Structure importance multiplier (M i )

Structures which have special post-disaster functions, e.g. hospitals and communications buildings Normal structures Structures presenting a low degree of hazard to life and other property in the case of failure, e.g. isolated towers in wooded areas, farm buildings Structures of temporary nature and which are to be used for less than 6 months

1.1 1.0 0.9

0.8

WARNING: The wind speeds in this Standard do not include any specific allowance for the effect of tornadoes. The design wind loads for structures containing high-risk contaminants such as some nuclear or biological materials are considered outside the scope of this Standard.

(See Paragraph E3.2.9 of Appendix E.)

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NOTE: The wind induced dynamic response of a structure and local pressures may be substantially increased by the presence of other structures, both upstream and downstream. Structures found in groups, such as chimney stacks and multiple pipe runs, and tall buildings are most affected. These interference effects from structures of similar size within 10 cross-wind building breadths may be significant and should be investigated in the dynamic analysis with the aid of published material or by means of wind tunnel tests.

4.3 DYNAMIC WIND PRESSURE (qz). The hourly mean dynamic wind pressure (qz) at a height z shall be calculated using Equation 4.3. 2 q z 0.6V z × 10 3 . . . . . . . . . . . . . . . . . . . . (4.3) where = the free-stream hourly mean dynamic wind qz pressure at height z, in kilopascals Vz = the design hourly mean wind speed at height z, in metres per second. (See Paragraph F4.3 of Appendix F.) 4.4 PROCEDURE AND DERIVATION. 4.4.1 General. Response and consequent design-load estimates shall be determined separately for along-wind and cross-wind motions. Derivations shall be based on a design hourly mean wind speed as determined from Clause 4.2.2 with corrections for changes in terrain, local topographic effects, shielding, wind direction and for special structures as appropriate (see Clauses 4.2.3 to 4.2.9). For tall buildings and towers, the derivation shall determine a design base overturning moment and shall contain either explicitly or implicitly a mean and a dynamic component with the latter, for design purposes, being characterized by a peak value which will be the maximum likely to occur on average once during exposure to one hour of the design hourly mean wind speed. Load effects arising from the maximum along-wind response derived from Clause 4.4.2, and from the maximum cross-wind response derived from Clauses 4.4.3 and 4.4.5, shall be determined according to the procedure given in Clause 4.4.6. Structures requiring dynamic analysis and for which insufficient data are available in this Standard shall be analysed to the requirements of this Section with the aid of other published material or through the use of dynamic wind tunnel model studies.

4.4.2 Along-wind response — tall buildings and towers. For all tall buildings and towers, the along-wind response shall be calculated using the gust factor method. ^ ) shall be The design peak base overturning moment (M a determined by multiplying the mean base overturning moment (Ma) by the gust factor (G), i.e. ^ M = GMa . . . . . . . . . . . . . . . . . . (4.4.2(1)) a The mean base overturning moment (Ma) shall be determined by summing the moments resulting from the mean pressures on faces calculated using Equations 4.4.2(2) and 4.4.2(3). Fz = ∑Cp,e qz Az . . . . . . . . . . . . . . . (4.4.2(2)) or for structures with discrete elements: Fd = ∑Cd qz Az . . . . . . . . . . . . . . . . (4.4.2(3)) where Fz = the hourly mean net horizontal force acting on a building or structure at height z Cp,e = the pressure coefficients for both windward and leeward surfaces, of rectangular buildings and these shall be obtained from Table 4.4.2.1 qz = the free stream hourly mean dynamic wind pressure resulting from Vz, in kilopascals = 0.6(Vz)2 × 10 -3 Az = the area of a structure or a part of a structure, at height z, in square metres Fd = the hourly mean drag force acting on discrete elements Cd = the drag force coefficient for an element of the structure of area A z, from Clause 3.5.5 or Appendix B. The gust factor (G) shall be calculated using Equation 4.4.2(4) G

=

where G r

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. . . . (4.4.2(4))

= =

=

a gust factor a roughness factor, twice the longitudinal turbulence intensity at height h evaluated for z = h

NOTE: Values for turbulence intensity (σv/Vz) are to be obtained from Table 4.2.5.3 and the values of the togographic multiplier (Mt) from Clause 4.2.8.

43

gv = a peak factor for the upwind velocity fluctuation = 3.7 B = a background factor, which is a measure of the slowly varying background component of the fluctuating response caused by the lower frequency wind speed variations

AS 1170.2—1989

gf

= a peak factor, the ratio of the expected peak value which occurs once per hour to the standard deviation of the resonant part of the fluctuating response, (e.g. of a force, moment, stress, deflection or accelerations), gf,x =

= = S h

b

Lh

= the height of the building or structure, in metres. For enclosed buildings, the height h shall be taken as the height to eaves level except for θ = 0°, α ≥ 60°; for θ = 90° and all α, the height h shall be taken as the height to the top of the building, where α is the angle of the roof pitch. For significant elevated elements or horizontal structures, h is the height to the centroid of the significant area, in metres = the horizontal breadth of a vertical structure normal to the windstream; or the average breadth of a vertically tapered structure over the top half of the structure; or the nominal average breadth of a horizontal structure, in metres = a measure of the effective turbulence length scale, in metres

=

na Vh E

= the first mode along-wind frequency of the structure, in hertz = the design hourly mean wind speed at height h, in metres per second = a spectrum of turbulence in the approaching wind stream =

N

= an effective reduced frequency =

= w

= a size factor to account for the correlation of pressures over a structure

ζ

= a factor to account for the second order effects of turbulence intensity

= the structural damping capacity as a fraction of the critical damping ratio given in Table 4.4.2.2.

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= TABLE 4.4.2.1 AVERAGE EXTERNAL WALL PRESSURE COEFFICIENTS (C p,e) FOR BUILDINGS WITH RECTANGULAR CROSS-SECTION Leeward wall Windward wall

θ = 90° and for all α θ = 0° and with α < 10°

θ = 0° 10° ≤ α ≤ 15° α = 20°

0.8

−0.5

−0.3

qz varies with height z

−0.2

−0.3

−0.4

α ≥ 25° −0.5

qz = qh for all cases

d = dimension of building parallel to the wind direction.

TABLE 4.4.2.2 VALUES OF FRACTION OF CRITICAL DAMPING OF STRUCTURES (ζ) Stress levels

Fraction of critical damping (ζ)

Serviceability stress levels: Steel frame Reinforced or prestressed concrete

0.005 to 0.010 0.005 to 0.010

Ultimate and permissible stress levels: Steel frame welded Steel frame bolted Reinforced concrete

0.02 0.05 0.05

(See Paragraph F4.4.2 of Appendix F.)

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AS 1170.2—1989

44

4.4.3 Cross-wind response — tall buildings and enclosed towers. The cross-wind design peak base overturning moment (M^c) for enclosed buildings and towers shall be determined from Equation 4.4.3(1). ^ Mc

=

where pc

(4.4.3(1))

qh

and the acceleration (ÿ^c) at the top of a structure with approximately constant mass per unit height shall be determined from Equation 4.4.3(2). ÿ^c where ^ M c gf

=

Cp,c

(4.4.3(2)) =

= the design peak base overturning moment for a structure in cross-wind direction = a peak factor, =

=

in cross-wind direction

= the hourly mean dynamic wind pressure at height h, in pascals b = the breadth of the structure normal to the wind, in metres h = the height of the structure, in metres k = a mode shape power exponent from representation of the fundamental mode shape by ψ(z) = (z/h)k Typical values of the mode shape power exponent (k) are as follows: (a) Uniform cantilever, k = 1.5. (b) Slender framed structure (moment resisting), k = 0.5. (c) Building with a central core and momentresisting facade, k = 1.0. (d) Tower decreasing in stiffness with height, or a tower with a large mass at the top, k = 2.3. Cfs = the cross-wind force spectrum coefficient generalized for a linear mode (see Figures 4.4.3(A) and (B)). Interpolation is permitted ζ = the fraction of critical damping given in Table 4.4.2.2 ^ÿ = the acceleration at the top of the structure in c cross-wind direction, in metres per second squared mo = the average mass per unit height of the structure, in kilograms per metre. nc = the fundamental mode frequency in cross-wind direction, in hertz. (See Paragraph F4.4.3 of Appendix F.) qh

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= the maximum design wind pressure at the leading edge of a roof supported by a cantilevered beam (see Figure 4.4.4), in kilopascals = the hourly mean dynamic wind pressure at height h, in kilopascals = the pressure coefficient for the windward edge of a roof supported by a cantilevered beam

4.4.4 Cross-wind response — cantilevered roofs and canopies. The design wind load on cantilevered roof beams, for which the cantilever length is greater than 5.0 m, shall be determined from Equation 4.4.4, where the maximum design wind pressure (pc) at the leading edge of a triangular pressure distribution is obtained from the pressure coefficient Cp,c, i.e. pc = Cp,cqh . . . . . . . . . . . . . . . . . . . . . . (4.4.4)

Vh

=

nc

=

l

=

5.0

for

for the design hourly mean wind speed at height h, in metres per second the first mode frequency of the cantilevered roof system in cross-wind direction, in hertz the length of the cantilevered roof beam, in metres.

4.4.5 Cross-wind response — lattice towers and masts. The cross-wind response for open lattice towers and masts shall be considered where there are substantial enclosed parts of the structure near the top. NOTE: However the cross-wind response may be neglected provided the actual solidity ratio (δ) is less than 0.3.

4.4.6 Combination of along-wind and cross-wind responses. Scalar structural effects, such as an axial load in a column, when both along-wind and cross-wind responses have been computed, shall be derived from Equation 4.4.6(1). = . . . . . . . . . . . . . . . . . . . . . . . . . . (4.4.6(1))

where = =

= G

= =

the total combined peak load scalar effect (e.g., axial load in a column, etc.) the load effect derived from the mean alongwind response, and proportional to the mean along-wind base overturning moment (Ma) the load effect derived from the mean crosswind response the gust factor for along-wind response the load effect derived from the peak crosswind response, and proportional to the peak ^ c). cross-wind base overturning moment ( M

NOTE : For the data given in this Standard, ε c = 0. However, ε c may be other than zero when any of the following conditions apply: (a) An asymmetric building. (b) Interference from upwind structures. (c) Wind directions which are not normal to a building wall. For these cases, wind tunnel tests should be carried out.

(See Paragraph F4.4.6 of Appendix F.)

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FIGURE 4.4.3(A) VALUES OF THE CROSS-WIND FORCE SPECTRUM COEFFICIENT FOR SQUARE SECTION BUILDINGS

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FIGURE 4.4.3(B) VALUES OF THE CROSS-WIND FORCE SPECTRUM COEFFICIENT FOR 2:1 AND 1:2 RECTANGULAR SECTION BUILDINGS

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FIGURE 4.4.4 CANTILEVERED ROOF AND CANOPY

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(See Paragraph F4.4.4 of Appendix F.)

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APPENDIX A

ADDITIONAL PRESSURE COEFFICIENTS (This Appendix forms an integral part of this Standard.) A1 EXTERNAL PRESSURE COEFFICIENTS (C p,e) FOR MULTI-SPAN BUILDINGS (α < 60°). External pressures (pe) for multi-span buildings, with roofs of pitched or saw-tooth shape (see Figures A1.1 and A1.2), shall be calculated in accordance with Clause 3.4.2. External pressure coefficients (C p,e) for multi-span buildings for wind directions θ = 0° and θ = 180°, shall be obtained from Table A1.1 or Table A1.2. Where two values are listed, the roof shall be designed for both values. The height h shall be taken as the height to eaves (h e) for wind directions of θ = 0° and θ = 180°. For wind direction θ = 90°, the height h shall be taken to the top of the building (h t). External pressure coefficients for wind directions of θ = 90° and θ = 270° shall be obtained from Tables 3.4.3.1 and 3.4.3.2(A), but [-0.05(n-1)] shall be added to the roof pressure coefficients in the region 0 to 1h from the leading edge, where n is the total number of spans. For this calculation, take n = 4, if n is greater than 4.

FIGURE A1.1 EXTERNAL PRESSURE COEFFICIENTS (Cp,e) FOR MULTI-SPAN BUILDINGS — PITCHED ROOFS

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TABLE A1.1 EXTERNAL PRESSURE COEFFICIENTS (C p,e) FOR MULTI-SPAN BUILDINGS — PITCH ROOFS Wind direction (θ) degrees

a

External pressure coefficient (Cp,e)

0

0.7

b

c

Use Table 3.4.3.2(A), (B) or (C) for same (h/d) and α, as appropriate

m

z

-0.3 and 0.2 for α 0.1 years in Region A and for serviceability limit state wind speed in Region B, Equations E3.2.2(2) and (3) are valid for R > 5 years in Regions C and D. A flow chart given in Figure E3.2.2 shows the procedure for the determination of design gust wind speed.

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NOTE: Refer to Clause 3.2.3 for reductions applicable to resultant wind forces on complete buildings.

FIGURE E3.2.2 FLOW CHART FOR DETERMINATION OF DESIGN GUST WIND SPEED USING THE STATIC ANALYSIS PROCEDURE

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E3.2.3 Wind direction. The recommended directional design wind speeds are based on Bureau of Meteorology data analysed by Melbourne (Ref. 14) and Dorman (Ref. 4) to produce probability distributions of gust wind speeds with direction for the main population centres. These directional wind speed data may be used for ultimate limit state or permissible stress design and for serviceability considerations either directly via an approximation or through a full integration process; the methodology of both is given by Melbourne (Ref. 14). For direct use, the data in Table 3.2.3 have been reduced on the basis that the major contributions to the probability of a given load occurring will be confined to two 45° directional sectors. The assumption that contributions will be confined to two 45° directional sectors is based on the directional characteristics typical of rectangular buildings. Such an assumption would not be valid for near-circular structures. The final proof of any such assumption must be in a full integration. The use of the directional wind speeds for three different building orientations is illustrated in Figures E3.2.3(A) to E3.2.3(E). The following examples consider basic wind speeds corrected only for directional characteristics, (in the Melbourne area), prior to the application of any further multipliers. Figure E3.2.3(A) shows the general directional wind speeds obtained from Table 3.2.3.

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FIGURE E3.2.3(A) DIRECTIONAL WIND SPEEDS (Vu)

(a)

Building orientated E—W. The assumed wind speeds for four orthogonal directions are shown in Figure E3.2.3(B).

FIGURE E3.2.3(B) WIND SPEEDS FOR FOUR ORTHOGONAL DIRECTIONS WITH BUILDING ORIENTATED E—W

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(b) Building orientated NW—SE. The assumed wind speeds for four orthogonal directions are shown in Figure E3.2.3(C).

FIGURE E3.2.3(C) WIND SPEEDS FOR FOUR ORTHOGONAL DIRECTIONS WITH BUILDING ORIENTATED NW—SE

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(c) Building orientated NNW—SSE. The orthogonal directions for the building and the 90° sectors are shown in Figure E3.2.3(D).

DIRECTIONAL SECTORS (90°)

FIGURE E3.2.3(D) INTERPOLATED WIND SPEEDS AND DIRECTIONAL SECTORS

The assumed wind speeds for four orthogonal directions are shown in Figure E3.2.3(E).

FIGURE E3.2.3(E) WIND SPEEDS FOR FOUR ORTHOGONAL DIRECTIONS WITH BUILDING ORIENTATED NNW—SSE

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Note that the reduction factor of 0.95 should not be used simultaneously with values from Table 3.2.3, except for Vp, and Vu in Brisbane. The reduction factor was derived from consideration of the average probability of the design wind load being exceeded for structures randomly orientated in azimuth. See Davenport (Ref. 18), Holmes (Ref. 19) and Walker (Ref. 20). Other methods for detailed probability analysis of the effects of wind direction are given by Davenport (Ref. 63), Simiu and Filliben (Ref. 64), and Holmes (Ref. 65). E3.2.4 Terrain category. The four defined terrain categories are the same as those used in the previous edition. To facilitate interpolation between the defined terrain categories, and the calculation of turbulence intensity and the relationship between hourly mean and gust wind speeds, it has been necessary to define these terrain categories in terms of the roughness length, and the best fit was found as given in Table E3.2.4. TABLE E3.2.4 TERRAIN CATEGORY AND ROUGHNESS LENGTH (z o)

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Terrain category

Roughness length (zo) m

1.

Open, no significant obstructions (water surfaces at windspeed Vs)

0.002

2.

Open, grassland, few obstructions (rough open water surfaces at windspeeds Vu and Vp)

0.02

3.

Suburban, wooded terrain

0.20

4.

City buildings (10.0 m to 30.0 m)

2.0

NOTES: 1. For sites with open water (sea or lakes) upwind, the roughness length (zo) varies with wave height and spray density. A general rule would be from extreme winds (ultimate limit state), zo = 0.02 m (Terrain Category 2) and for less winds (serviceability limit state), zo = 0.002 m (Terrain Category 1). Coastal waters are estimated to develop surface roughness equivalent to at least Terrain Category 2 during a tropical cyclone. 2. Terrain Category 4 conservatively covers city centres, where high-rise development of very tall buildings and structures occurs. The only way of determining true design wind speeds and loads in such locations is through specific model or full-scale studies. 3. Design wind speeds and loads may be determined through specific model or full scale studies (see Clause 1.5.2). 4. Interpolation for roughness length (zo) between terrain categories given in Table E3.2.4 is permitted according to Equation E3.2.4. zo = 2 × 10(Terrain category —4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E3.2.4)

A broader description of terrain categories, based on the roughness length, is given in Figure E3.2.4(A). E3.2.5 Terrain and structure height multiplier (M(z,cat)). An engineering wind model for Australia has been developed by Melbourne (Ref. 2) from the Deaves and Harris model (Ref. 3). This model is based on extensive full-scale data and on the classic logarithmic law in which the mean velocity profile in strong winds applicable in noncyclonic Regions A and B (neutral stability conditions) is given by Equation E3.2.5(1).

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E.2.5(1)) For values of z < 30.0 m, the z/zg values become insignificant and Equation E3.2.5(1)) simplifies to — . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E3.2.5(2)) where Vz

=

the design hourly mean wind speed at height z, in metres per second

u*

=

the friction velocity =

z zo zg

= = =

the distance or height above ground, in metres the characteristic terrain roughness length, in metres the gradient height

=

=

, in metres (the value ranges from 2700 m to 4500 m).

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FIGURE E3.2.4(A) ROUGHNESS LENGTH (zo) AND TERRAIN CATEGORIES AS A FUNCTION OF TERRAIN DESCRIPTION OF AN AREA.

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FIGURE E3.2.4(B) TERRAIN CATEGORY 2

FIGURE E3.2.4(C) TERRAIN CATEGORY 3

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FIGURE E3.2.4(D) TERRAIN CATEGORY 4

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The Deaves and Harris model (Ref. 3) provides as a function of the roughness length (z o) a determination of turbulence intensity (σv/V) and then the crucial link between hourly mean and gust wind speeds as follows: V

=

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E3.2.5(3))

σv

=

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E3.2.5(4))

η

=

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E3.2.5(5))

The Deaves and Harris model (Ref. 3) is not valid below the height of the roughness elements (buildings). Designers should take account of probable future changes to terrain roughness in assessment of terrain multiplier. E3.2.6 Changes in terrain category. The influence of a new terrain roughness develops slowly upwards into a volume defined by the developed height of the new inner layer given approximately by Equation 3.2.6(1), Wood (Ref. 8), which is valid for the lower levels up to about a third of the gradient height. Upstream of this developed height, the flow characteristics are those of the upstream terrain roughness and downstream, the flow characteristics at a given height change slowly to those of the new terrain roughness in an asymptotic manner approximated by Equation 3.2.6(3) for gust wind speeds, Melbourne (Ref. 9). Figure 3.2.6 illustrates the rate at which the development proceeds and to facilitate computation, a tabulation of Equation 3.2.6(1) is given in Table E3.2.6. Equation 3.2.6(3) is a simplified (linear) approximation, which is non-conservative by no more than 5% on design wind speed. The maximum error occurs at (x - x i) = 2500 m. TABLE E3.2.6 VALUES OF (xi) FOR THREE TERRAIN CATEGORIES Height (hi)

Values of (xi), m

m

Terrain Category 2 Terrain Category 3 Terrain Category 4 (zo = 0.02 m)

(zo = 0.2 m)

(zo = 2.0 m)

3 5 10

47 90 213

27 50 120

15 28 67

15 20 30

354 507 841

199 285 473

112 160 266

50 100 200

1 592 3 787 9 008

895 2 130 5 066

504 1 198 2 849

300

14 953

8 409

4 729

The flow chart in Figure E3.2.6 illustrates the method for computation of the corrected multiplier M x.

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FIGURE E3.2.6 METHOD FOR ADJUSTING M(z,cat) VALUES AT CHANGES IN TERRAIN ROUGHNESS

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Example calculation: Building is 20 m high located within Terrain Category 3 with city centre. (Terrain Category 4) upwind and ocean (Terrain Category 2) beyond. Region B — Ultimate limit state.

h = 20.0 m Terrain Category 4, zo,r = 2.0 m xi

=

Observations:

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Options:

Table 3.2.4

= (1) (2) (3)

=

160 m

Equation 3.2.6(1)

Terrain Category 3 is not fully developed, i.e. x < (2500 + 160) Nominal upwind ‘limit’ is 2500 m (greater than 50h t = 1000 m) At upwind limit, Terrain Category 4 is rougher than the limit of Terrain Category 3.

(a) Arbitrarily assume fully developed Terrain Category 3 at 2500 m. Mx = 0.94 Table 3.2.5.1 (b) Consider terrain further upwind, extent of Terrain Category 4 is 2000 m, which is not sufficient for full development. Proceed to change in terrain. Mo = 1.08 Table 3.2.5.1 Mx =

Equation 3.2.6(3)

=

Mx

= = = = =

1.08 - 0.26 0.82 (Mo at change into Terrain Category 3) Equation 3.2.6(3) 0.82 + 0.10 0.92 (at top of building)

Conclusion: By considering full effect of Terrain Category 4, a reduction of 2% on wind speed or 4% on wind pressure was obtained. E3.2.7 Shielding multiplier (Ms). The shielding multiplier (Ms) has been based on work by Holmes and Best (Ref. 5), Hussain and Lee (Ref. 6), and Lee (Ref. 7) and is a conservative generalization to accommodate effects of total and local wind loads on structures in a range of shielding configurations. The building spacing parameter (D) for Australian suburbs (Terrain Category 3), is usually in the range from 3 to 6, giving a typical range of M s from 0.8 to 0.9.

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The sector for the determination of the building spacing parameter (D) is shown in Figure E3.2.7.

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FIGURE E3.2.7 SHIELDING IN COMPLEX URBAN SITUATIONS

Reduction in shielding is permitted for pressures on the windward wall of a building, when the average external pressure coefficient (Cp,e) value of 0.8 with qz varying with height in Table 3.4.3.1(A), is used. In this case, for each height z, the height and spacing of shielding buildings, i.e. upwind buildings with heights greater than or equal to z within a 45° section of radius 20h t, should be calculated. Thus, the shielding multiplier (Ms) will depend on the height z. However, if there are no upwind buildings greater than or equal to ht in height, the shielding multiplier (M s) for other parts of the building, i.e. side walls and leeward walls, should be taken as 1.0. For the evaluation of the effective shielding spacing (l s), Equation 3.2.7(2) gives reasonable values for the cases of regular rows of buildings and of randomly distributed shielding buildings within the sector. However the user should beware of ‘corridors’ with no shielding buildings immediately upwind of the structure. Shielding at a building site may change considerably with time as a result of new developments and demolitions. Designers should account for this when determining the shielding multiplier. An assessment of the shielding situation 5 years after the completion of the building, or other structure, would be appropriate. E3.2.8 Topographic multiplier (Mt). The wind speed at any given site is influenced by local topographical features such as funnelling or expansion in valleys, hills and escarpments. Where there is doubt, meteorological advice should be sought or recourse to model or full-scale studies may be made to determine appropriate design wind speeds in the presence of significant local topographical features. The most critical conditions occur near the top of a steep rise, cliff, bluff or escarpment and rules for these situations are given. The rules follow the guidelines given by Taylor and Lee (Ref. 10) and Bowen (Ref. 11), which are based on extensive full-scale and wind tunnel studies, and theoretical work by Jackson and Hunt (Ref. 12). A general equation for the topographic multiplier (M t) is as follows: Mt where kt

s

=

= = = = = =

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E3.2.8)

a type factor for topography 1.4 for escarpments 1.4 + 36(φd - 0.05) with a maximum of 3.2 for hills and ridges a position factor for topographic effects for φ ≤ 0.3 for φ > 0.3 (steep slopes) for negative values of x: L* = Lu L* = 1.67H (for φ > 0.3, steep slopes) COPYRIGHT

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for positive values of x: L* = Lu or 1.67H, whichever is greater (hills and ridges) L* = 2Lu or 3.33H, whichever is greater (escarpments) φ′ = the lesser value of φ or 0.3 φ = the effective upwind slope of a hill, ridge or escarpment. φd = the average downwind slope of a hill, ridge or escarpment σv/Vz = the turbulence intensity in the approach flow at height z x = the horizontal coordinate with origin at the crest, in metres z = the height above local ground level, in metres. The use of turbulence intensity (σv/Vz) as a function of height and terrain category, given in Table E3.2.8 is permitted. The values given in Table 3.2.8 are computed from Equation E3.2.8 with s = 1, and σ v/Vz = 0.207 (Terrain Category 2). TABLE E3.2.8 TURBULENCE INTENSITY (σ v/Vz) FOR COMPUTING TOPOGRAPHIC MULTIPLIER (Mt) ULTIMATE LIMIT STATE AND PERMISSIBLE STRESS DESIGN — REGIONS A AND B ONLY SERVICEABILITY LIMIT STATE DESIGN — ALL REGIONS

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Height (z)

Turbulence intensity (σv/Vz)

m

Terrain Category 1

Terrain Category 2

Terrain Category 3

Terrain Category 4

≤3 5 10

0.171 0.165 0.157

0.207 0.196 0.183

(0.271) 0.271 0.239

(0.448) (0.448) (0.448)

15 20 30

0.152 0.147 0.140

0.176 0.171 0.162

0.225 0.215 0.203

0.448 0.342 0.305

40 50 75

0.133 0.128 0.118

0.156 0.151 0.140

0.195 0.188 0.176

0.285 0.270 0.248

100 150 200

0.108 0.095 0.085

0.131 0.117 0.107

0.166 0.150 0.139

0.233 0.210 0.196

250 300 400

0.080 0.074 0.068

0.098 0.092 0.082

0.129 0.121 0.108

0.183 0.173 0.155

500

0.058

0.074

0.098

0.141

NOTES TO TABLE E3.2.8: 1. For intermediate values of height (z) and terrain category, interpolation is permitted. 2. For Terrain Categories 1 to 3 in cyclone regions C and D, use turbulence intensity values given for Terrain Category 3 for permissible stress design and ultimate limit state design. 3. For Terrain Category 4 in cyclone regions C and D, use turbulence intensity values given for Terrain Category 4 for permissible stress design and ultimate limit state design. 4. The values of σv/Vz in brackets indicate that structures are situated below the height of roughness elements, and conservative assumptions with respect to the calculation of the topographic multiplier (Mt) have been made. These values in brackets should not be used for other purposes.

Example calculation: Escarpment (kt = 1.4) Terrain Category 3 z = 20 m H = 150 m Lu = 750 m x = -200 m (site on upwind slope) H 150 φ = = = 2L u 2 × 750 s

0.10

= =

= 0.822 × 0.973 (L * = Lu)

= 0.8

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σv/Vz

=

74

σv/V20 =

Mt = =

0.215 (from Table E3.2.8) =

= 1 + 0.062

1.06

E3.2.9 Structure importance multiplier (Mi). Structure importance multipliers may be applicable for both methods, static analysis and dynamic analysis. Structures designed with lower importance factors should be positioned such, that if failure occurs at higher wind speeds, resulting debris will not endanger other structures nearby.

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E3.3 DYNAMIC WIND PRESSURE (q z). In Equation 3.3, the conversion constant (0.6) is half the air density, at an air density of 1.20 kg/m3, which is appropriate for air temperatures of approximately 20°C, has been selected for general use in Australian conditions. E3.4 FORCES (F) AND PRESSURES (p z) ON ENCLOSED BUILDINGS, FREE ROOFS AND WALLS. E3.4.1 General. E3.4.1.1 Procedure. E3.4.1.2 Forces (F) on building elements. E3.4.1.3 Calculation of forces and moments on complete buildings. E3.4.2 External pressures (p e). E3.4.3 External pressure coefficients (Cp,e) for rectangular enclosed buildings. For low-rise buildings, a detailed background discussion of pressure coefficients is given by Holmes (Refs 15 and 16). For buildings that are non-rectangular in plan, but are made up of rectangular modules, such as L-shaped and T-shaped buildings, the external wall pressure coefficient may be obtained by drawing the enclosing rectangle, and determining the values on the enclosing surfaces. These values may then be applied to the actual surfaces projected along the principal axes of the rectangle. More detailed information on monoslope roofs is given by Stathopoulos and Mohammadian (Ref. 17). The pressure coefficients given in Tables 3.4.3.1, 3.4.3.2, and in Tables A1.1, A1.2, A2, A3 and A4 in Appendix A are deemed to be related to extremes of wind loads on the wall and roof surfaces of structures of the form illustrated. It should be noted, that in these Tables, a positive pressure denotes pressure towards a surface and a negative pressure denotes suction away from a surface. The pressure coefficients given in these Tables are average values for use in establishing overall wind loads. The values quoted are applicable for sharp-edged rectangular buildings when the wind is blowing normal to one face. Local peak pressures are higher than these average values and the pressure coefficients (with local pressure factors Kl) specified in Clause 3.4.5 should be used for the determination of forces on windows and cladding elements. The values given in Tables 3.4.3.1(A), (B) and (C) take into account the effect of the variation of velocity with height on the pressures produced on a tall building which is relatively isolated and exposed within the particular terrain category. It should be noted that some combinations of isolated tall buildings placed together could lead to local and overall increases in the values of the average pressure coefficients given in Tables 3.4.3.1(A),(B) and (C). Under these conditions the appropriate coefficients can be determined only from correctly scaled wind tunnel tests. The use of qz varying with height, for windward wall pressures, is more appropriate for buildings of slender form (high aspect ratio). However the user may find the use of q h, giving a constant windward wall pressure with height, more convenient in most cases of buildings less than 25.0 m in height. E3.4.4 Area reduction factors (Ka) for roofs and side walls. These factors provide an approximate reduction for the lack of spatial correlation of fluctuating pressures on roofs and side walls, and are for the calculation of loads on the major supporting structure, and on cladding elements, or battens or purlins, etc, to which cladding is directly fixed. The values used in Table 3.4.4 were derived from direct measurements of total roof loads in wind tunnels. (See Davenport, Surry and Stathopoulos, Ref. 21; Holmes and Rains, Ref. 22; Roy and Holmes, Ref. 23; and full scale tests of Kim and Mehta, Ref. 24.) Tributary area is the area contributing to the force being considered. For example, for a cladding fastener it will be the area of cladding supported by a single fastener; for a purlin it will be the span between supporting rafters times the distance between purlins.

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E3.4.5 Local pressure factors (Kl) for cladding. The local pressure factors (Kl) allow for the pressures on small areas compared with the average increase over the surface in question and especially the suction peaks that occur on small areas near windward corners and roof edges on buildings.

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E3.4.6 Reduction factors (Kp) for porous cladding. Negative surface pressures on porous cladding are found to be lower than those on a similar non-porous cladding because air flow through the porous surface induces a negative pressure in the internal volume behind the surface. Cheung and Melbourne (Ref. 26) have quantified a number of configurations resulting in the generalized data given in Table 3.4.6. E3.4.7 Internal pressures (p i). Table 3.4.7 allows the determination of internal pressures by a quasi-steady assumption. The validity of this assumption and possible resonant dynamic effects on internal pressure is discussed by Holmes (Ref. 25). In particular, the designer of tall towers should realize that in the Standard, the treatment of dominant openings in the upper levels is very conservative. Significant savings may be obtained by applying a more correct treatment of these effects based on wind tunnel tests. In determining the most critical loading condition, the designer may use his discretion as to which opening can be relied upon to be closed, with closures capable of withstanding peak wind forces, at the critical loading conditions. Possible debris effects may also require attention. Internal pressures developed within an enclosed structure may be positive or negative depending on the position and size of the openings. In Table 3.4.7 the permeability of a surface is defined as cracks and gaps arising from normal construction tolerances. As a guide, the typical permeability of an office block or house with all windows nominally closed is between 0.01% and 0.2% of the wall area, depending on the degree of draught-proofing. Industrial and farm buildings can have permeabilities of up to 0.5% of wall area. Openings include open doors and windows, vents for air conditioning and ventilation systems, deliberate gaps in cladding, etc. A dominant opening is an opening, whose area exceeds the open areas on any other surface. A dominant opening does not need to be large. The value of Cp,i can be limited or controlled to advantage by deliberate distribution of permeability in the wall and roof, or by the deliberate provision of a venting device at a position having a suitable external pressure coefficient. An example of such is a ridge ventilator on a low-pitch roof, and this, under all directions of wind, can reduce the uplift force on the roof. For buildings where internal pressurization is utilized, this additional pressure must also be considered. In cyclonic areas, windows should be considered as potential dominant openings unless capable of resisting an impact by a 4 kg piece of timber of 100 mm × 50 mm cross-section, striking them at any angle at a speed of 15 m/s. E3.4.8 Frictional drag force (Ff) for rectangular enclosed buildings. E3.4.9 Net pressures (pn) for free roofs. The net pressure coefficients for monoslope, pitched or troughed free roofs are based mainly on wind tunnel tests described by Gumley (Refs 47 and 48). The roof pitches specified are those for which the tests were carried out. Some adjustment to Table 3.4.9.2 has been made based on the full-scale measurements by Robertson, Hoxey and Moran, (Ref. 49). E3.4.10 Net pressures (pn) for canopies, awnings and carports, adjacent to enclosed buildings. The values in Table 3.4.10(B) are derived from wind tunnel tests described by Jancauskas and Holmes (Ref. 54) and that in Table 3.4.10(A) from Jancauskas and Eddleston (Ref. 55). The values given in Figure 3.4.10(B) are from unpublished data. The net wind pressure acting on a canopy for a wind direction normal to the wall to which the canopy is attached, depends on the height of the canopy above ground in relation to the height of the adjacent wall, and on the height/width ratio for the canopy. Short canopies at the top of a building experience similar loads as for overhanging eaves. E3.4.11 Net pressures (pn) for cantilevered roofs. E3.4.12 Frictional drag force (Ff) for free roofs and canopies. E3.4.13 Net pressures (pn) for hoardings and free-standing walls. The main sources of data for the pressure coefficients are wind tunnel studies carried out by Holmes (Ref.56) and Letchford (Ref.57).

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The loads specified for wind blowing parallel to the hoarding or wall in Table 3.4.13(C) are caused by turbulence and unsteady flow effects. In this case, wind loads in both directions must be considered. When an adjacent wall, with a length of greater than 2c for hoardings, or greater than 2h for free-standing walls, runs at right angles to a free end, forming a corner, reduced wind loads may be used for the 45° and 90° directions. It is suggested, that the values given for 2c to 4c, or 2h to 4h, be extended up to the windward corner, i.e. they should apply to a distance of 0 to 4c, or 0 to 4h from the windward corner. E3.5 FORCES ON EXPOSED STRUCTURAL MEMBERS. E3.5.1 General. E3.5.2 Procedure. E3.5.3 Single open frames. This method of calculation will give reasonable results for low solidity ratios. For higher solidity ratios, Equation E3.5.3 has been found to match experimental data well for sharp-edged rectangular or structural sections. Cd = 1.20 + 0.26(1 - δ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E3.5.3) Equation E3.5.3 is due to Georgiou and Vickery (Ref. 27) and is applicable for 0.1 < δ < 1.0. E3.5.4 Multiple open frames. The shielding factors (Ksh) given in Tables 3.5.4.1 and 3.5.4.2 are derived from the study of Georgiou and Vickery (Ref. 27). The effective solidity (δe) for circular cross-section member in Equation 3.5.4 was derived by Whitbread (Ref. 28). This was derived for critical and super-critical flow. E3.5.5 Drag force coefficients (Cd) for lattice towers. The clause gives overall drag force coefficients for lattice towers. The projected area (Az) is calculated for the windward face or faces only. The values in Tables 3.5.5.1 to 3.5.5.3 incorporate the drag forces on the downwind members shielded by the windward face or faces. The values in Table 3.5.5.1 for square towers with flat-sided members are based on Equations E3.5.5(1) and E3.5.5(2) given by Bayar (Ref. 29) — Cd

=

4.2 - 7δ

for 0 < δ < 0.2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E3.5.5(1))

and

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Cd = 3.5 - 3.5δ for 0.2 < δ < 0.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (E3.5.5(2)) More detailed methods for calculating wind forces on lattice towers are given in Ref. 66 and Ref. 67. E3.6 FATIGUE LOADING. When using the fatigue loading sequence given in Table 3.6, the upper limit of pressure in each range should be increased by dividing by the appropriate material capacity reduction factor. If the correct material factor is not available, the pressures should be divided by 0.9.

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APPENDIX F

EXPLANATORY MATERIAL TO SECTION 4 (This Appendix does not form an integral part of this Standard.) F4.1 APPLICATION. The dynamic analysis is the analysis of the response of a structure to wind action which accommodates the true response mechanism. The static analysis procedure of Section 3 is only an artifice and cannot determine wind forces and moments on structures which are flexible, lightweight, slender or lightly damped. The dynamic analysis should take account of the true physical processes and, even with approximations on the aerodynamic side, should include the following: (a) The aerodynamic loading spectrum (or valid approximation of relevant part). (b) The resonance response process for relevant response modes. (c) The inertial loading process which provides the dynamic stress or strain. The possibility of excessive response or incipient instability can be determined, and structures in these categories should be subject to special studies which may involve wind-tunnel testing. An approximate method for calculating the first mode natural frequency (n) of a rectangular plan multi-storey building is given by Equation F4.1(1). 46 n = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (F4.1(1)) h where n = the first mode frequency of the structure, in hertz = na for along-wind response = nc for cross-wind response h = the building height, in metres. More rigorous structural analysis by computer methods may be used as an alternative. ‘Wind sensitive structures’ may also be lightweight or slender structures which possess low natural frequency or low damping properties, making them susceptible to dynamic effects, e.g. tall masts and chimneys and long cantilevered canopies. An approximate method for calculating the first mode natural frequency of a uniform cantilevered mast is by the use of Equation F4.1(2).

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n

=

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (F4.1(2))

where n = the first mode natural frequency of a cantilevered mast, in hertz h = the height of the mast, in metres E = the modulus of elasticity, in pascals I = the second moment of area, in metres to the fourth power m = the mass per unit length, in kilograms per metre. F4.2 HOURLY MEAN WIND SPEED. F4.2.1 General. Accurate data on the full extent of penetration of tropical cyclones inland from the coast of Western Australia, particularly in Region D, is currently not available to the Committee. This is the reason for the substantial step change from Region C to Region A between latitudes 20°S and 25°S. Generally, the step changes shown in basic wind speeds between the regions have been adopted to meet the requirements laid down for the use of Standards in building regulations. In nature, such step changes do not occur and wind speeds in reality vary continuously from point to point. F4.2.2 Derivation of design hourly mean wind speed (Vz). Regional basic design gust wind speeds have been determined from an analysis of long-term records of daily maximum gust wind speed records collected by the Bureau of Meteorology at over 100 anemometer stations in Australia (Dorman, Ref. 4). These data have been corrected for approach terrain, height, and local interference (buildings) with a height of 10.0 m in open country terrain. The basic design gust wind speed is defined in this Standard, as being the maximum 2-second to 3-second gust occurring within 1 hour at a height of 10.0m in terrain with a roughness length, z o = 0.020 m. The design hourly mean wind speed is derived from the regional design gust wind speed through the Deaves and Harris wind model (Ref. 3). For wind storms driven by extensive pressure systems, the hourly mean wind speed so derived is a true hourly mean wind speed within which the defined gust wind speed will be the maximum two to three second mean maximum (gust) wind speed likely to occur, on average, during that hour. However, for shorter duration storms, such as thunderstorms, the hourly mean wind speed so determined, whilst it is artificial, still contains the gust characteristics of the thunderstorm because it is based on the basic wind speed which in its derivation has included data from all storm sources in Australia except tornadoes.

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Having adopted the Deaves and Harris wind model (Ref. 3), it is a simple matter to fit that model to either gust or hourly mean wind speed data. However, when basing design hourly mean wind speeds on the gust wind speed data, it should be appreciated that the resulting hourly mean wind speeds are artificial. The ultimate limit state gust wind speed (V u) and the serviceability limit state wind speed (V s), which have 5% probabilities of being exceeded in a 50-year and 1-year period respectively, were obtained as 1000- and 20-year return period wind speeds from Equations F4.2.2(1), (2) and (3), in which the gust wind speeds can be approximated as a function of return period. Region A: V = 29.2 + 3.0 logeR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (F4.2.2(1)) Region C: V = 26.0 + 6.4 logeR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (F4.2.2(2)) Region D: V = 23.0 + 9.0 logeR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (F4.2.2(3)) where V = the gust wind speed, in metres per second R = the return period, in years. The permissible stress gust wind speed is obtained from . . . . . . . . . . . . . . . . . . . . . . . . (F4.2.2 (4))

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Region B is an intermediate region in which the ultimate limit state wind speed is still dominated by tropical cyclones (weakening and/or less frequent) and for which the design wind speed has been given a value midway between that for Region A and Region C. The serviceability limit state wind speed in Region B is considered to be the same as for Region A which is without tropical cyclone influence and which is controlled by extensive pressure systems and thunderstorms. Equation F4.2.2(1) is valid for R > 0.1 years in Region A and for serviceability limit state wind speed in Region B, Equations F4.2.2(2) and (3) are valid for R > 5 years in Regions C and D. A flow chart given in Figure F4.2.2 shows the procedure for the determination of design hourly mean wind speed. F4.2.3 Wind direction. See Paragraph E3.2.3 of Appendix E. F4.2.4 Terrain category. See Paragraph E3.2.4 and Figures E3.2.4(A), (B), (C) and (D) of Appendix E. F4.2.5 Terrain and structure height multiplier (M(z,cat)). See Paragraph E3.2.5 of Appendix E. F4.2.6 Changes in terrain category. The influence of a new terrain roughness develops slowly upwards into a volume defined by the developed height of the new inner layer given approximately by Equation 4.2.6(1), Wood (Ref. 8), which is valid for the lower levels up to about a third of the gradient height. Upstream of this developed height, the flow characteristics are those of the upstream terrain roughness and downstream, the flow characteristics at a given height change slowly to those of the new terrain roughness in an asymptotic manner approximated by Equation 4.2.6(3) for hourly mean wind speeds, Melbourne (Ref. 9). Figure 4.2.6 illustrates the rate at which the development proceeds and to facilitate computation, a tabulation of Equation 4.2.6(1) is given in Table F4.2.6.1. Equation 4.2.6(3) is a simplified (linear) approximation, which is non-conservative by no more than 5% on design wind speed. The maximum error occurs at (x - x i) = 1500 m. TABLE F4.2.6.1 VALUES OF (xi) FOR THREE TERRAIN CATEGORIES Height (hi) m

Values of (xi), m Terrain Category 2 (zo = 0.02 m)

Terrain category 3 (zo = 0.2 m)

Terrain Category 4 (zo = 2.0 m)

≤3 5 10

47 90 213

27 50 120

15 28 67

15 20 30

354 507 841

199 285 473

112 160 266

50 100 200

1 592 3 787 9 008

895 2 130 5 056

504 1 198 2 849

300 500

14 953 28 317

8 409 15 924

4 729 8 955

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NOTE: Refer to Clause 4.2.3 for reductions applicable to resultant wind forces on complete buildings.

FIGURE F4.2.2 FLOW CHART FOR DETERMINATION OF DESIGN HOURLY MEAN WIND SPEED USING THE DYNAMIC ANALYSIS PROCEDURE

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The flow chart in Figure F4.2.6 illustrates the method for computation of the corrected multiplier Mx.

FIGURE F4.2.6 METHOD FOR ADJUSTING M(z,cat) VALUES AT CHANGES IN TERRAIN ROUGHNESS

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Example calculation: High-rise building is located near edge of Terrain Category 4 with parkland adjacent and suburbs beyond. Region B — Ultimate limit state.

Height of change in terrain where building is located:

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Equation 4.2.6 (2)

At reference height of 20.0 m: Equation 4.2.6 (1) Extent of effective Terrain Category 4: = (300 − 160) = 140 m 1500 m Must consider effect of terrain further upwind. 50ht = 5000 m 2500 m Terrain Category 3 is fully developed at this point, 5000 m upwind. Mo = 0.52 (at change into Terrain Category 2) Mx

=

Table 4.2.5.1 Equation 4.2.6(3)

= = = Mx

0.52 + 0.05 0.57 (Mo for beginning of change into Terrain Category 4)

= = =

Equation 4.2.6(3) 0.57 − 0.02 0.55 (modified hourly mean wind speed multiplier for reference height of 20.0 m).

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F4.2.7 Shielding multiplier (Ms). See Paragraph E3.2.7 of Appendix E. F4.2.8 Topographic multiplier (Mt). The wind speed at any given site is influenced by local topographical features such as funnelling or expansion in valleys, hills and escarpments. Where there is doubt, meteorological advice should be sought or recourse to model or full-scale studies may be made to determine appropriate design wind speeds in the presence of significant local topographical features. The most critical conditions occur near the top of a steep rise, cliff, bluff or escarpment and rules for these situations are given. The rules follow the guidelines given by Taylor and Lee (Ref. 10) and Bowen (Ref. 11), which are based on extensive full-scale and wind tunnel studies and theoretical work by Jackson and Hunt (Ref. 12). A general equation for the topographic multipliers (Mt) is as follows: Mt where kt

s

=

1 + (ktsφ′) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

= = = =

a type factor for topography 1.4 for escarpments 1.4 + 36(φd - 0.05) with a maximum of 3.2 for hills and ridges a position factor for topographic effects

(F4.2.8)

=

=

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L*

= Lu L* = 1.67H (for φ > 0.3, steep slopes) = Lu or 1.67H, whichever is greater (hills and ridges) for positive values of x: L* L* = 2Lu or 3.33H, whichever is greater (escarpments) φ′ = the lesser value of φ or 0.3 φ = the effective upwind slope of a hill, ridge or escarpment φd = the average downwind slope of a hill, ridge or escarpment x = the horizontal coordinate with origin at the crest, in metres z = the height above local ground level, in metres. The values given in Table 4.2.8 are computed from Equation F4.2.8 with s = 1. Example calculation: Escarpment (kt = 1.4) Terrain Category 3 z = 80 m H = 150 m Lu = 750 m x = -200 m (site on upwind slope) for negative values of x:

φ

=

s

=

H 2 Lu

150 2 × 750

0.10

=

Mt

=

0.734

= = =

1 + (ktsφ) 1 + (1.4 × 0.734 × 0.10) 1.10

F4.2.9 Structure importance multiplier (Mi). See Paragraph E3.2.9 of Appendix E. F4.3 DYNAMIC WIND PRESSURE (qz). In Equation 4.3, the conversion constant (0.6) is half the air density, at an air density of 1.20 kg/m3, which is appropriate for air temperatures of approximately 20°C, has been selected for general use in Australian conditions.

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F4.4 PROCEDURE AND DERIVATION. F4.4.1 General. The exciting forces on a structure due to wind action tend to be random in amplitude and spread over a large range of frequencies. The structural response is dominated by the action of resonant response to energy available in the narrow bands about the natural structural frequencies. In most cases the major part of the exciting energy is at frequencies much lower than the fundamental natural frequencies of structures and decreases with frequency. Hence for design purposes, with respect to wind loading, it is usually only necessary to consider response in the fundamental modes, as the contribution from higher modes is rarely significant, particularly for the largest values of response. The total response of structures can be classified as being those associated with the hourly mean wind speed or low frequency components and those associated with the gustiness or turbulence of the wind which are predominantly dynamic in character. Davenport (Ref. 30) has discussed the gap in the spectra of strong winds which separates the climatic from the higher frequency gust fluctuations which bring about these two classifications of responses. As a consequence it has been found convenient to describe forces, moments, deflections, accelerations, etc, in terms of an hourly mean value plus the average maximum likely to occur in an hour which, when added, can then be used as an average hourly maximum, or peak response as it is sometimes called, to define equivalent static design data. The peak value can be obtained from a probability distribution of the random variables concerned and can be expressed conveniently in terms of the reduced variate, that is the number of standard deviations by which the peak exceeds the mean value. For design purposes it has become practice to define a specific value of this reduced variate and call it a peak factor (gf) whereby the peak value of a variable (x) can be calculated from Equation F4.4.1. x^

x

g fσx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (F 4.4.1)

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where (^x), (x) and (σx) are the peak, mean and standard deviation values of x respectively, usually related to a record period of one hour for the reasons introduced above. This is discussed in detail by Melbourne (Ref. 31). The division of response into along-wind and cross-wind is not just a distinction of convenience. The distinction really relates to the forcing mechanisms rather than the response; in fact, the two motions combine to give overall structure response in approximately elliptical paths. The calculations of response are divided into along-wind and cross-wind to accommodate the totally different mechanisms in the calculation models. A proof of the independence of the along-wind and cross-wind mechanisms is given by Melbourne (Ref. 32) who showed, in model and full scale, that the joint probability distributions of the along-wind and cross-wind motions were symmetrical and similar to a bivariate normal distribution. The wind-induced dynamic response of a slender structure may be substantially increased by the presence of one or more adjacent structures of a similar size (Saunders and Melbourne, Ref. 33; Bailey and Kwok, Ref. 34). The flow around any structure in a group will usually differ from that around a similar isolated structure leading to different forces, both time-averaged and fluctuating. Interference effects can be divided into these following mechanisms (Ref. 34): (a) Modification of the incident turbulence mechanism by an upstream structure. (b) Alteration of the wake excitation mechanism by upstream and downstream structures. (c) Variations in the quasi-static forces on the structure as it oscillates relative to another (wake flutter and wake galloping). Interference effects are prevalent in structures located less than 10b apart where b is the dimension of the structure normal to the wind. Structures found in groups, including chimney stacks, multiple pipe runs in chemical plant and tall slender buildings are most affected. Adverse effects may be decreased by geometrical variations in structural shape and relative placement. An example of interference effects on the cross-wind response of a square sectional tower building is given in Figure F4.4.1.

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FIGURE F4.4.1 TYPICAL PERCENTAGE CHANGE IN CROSS-WIND RESPONSE OF A SQUARE-SECTION BUILDING B DUE TO A SIMILAR BUILDING A AT (X, Y) BUILDING HEIGHT (h) EQUALS 4 BUILDING BREADTHS (b) F4.4.2 Along-wind response — tall buildings and towers. Since the early 1960s from the work primarily of Davenport (Ref. 35) and Vickery (Ref. 36) it can be concluded that the along-wind response of most structures originates almost entirely from the action of the incident turbulence of the longitudinal component of the wind velocity (superimposed on a mean displacement due to the mean drag). The gust factor method, as presented in this Standard, is based on a fundamental mode of vibration which has an approximately linear mode shape. F4.4.3 Cross-wind response — tall buildings and enclosed towers. Cross-wind excitation of modern tall buildings and structures can be divided into three mechanisms (Ref. 32) which are associated with wake; incident turbulence and the cross-wind displacement and its higher time derivatives, which are described as follows: (a) Wake. For buildings and structures under wind action, the most common source of cross-wind excitation is that associated with ‘vortex shedding’. For a particular structure, the shed vortices have a dominant periodicity which is defined by the Strouhal number. Hence the structure is subjected to a periodic pressure loading which results in an alternating cross-wind force. If the natural frequency of the structure coincides with the shedding frequency of the vortices, large amplitude displacement response may occur and this is often referred to as critical velocity effect. In practice, vertical structures are exposed to a turbulent wind in which both the hourly mean wind speed and the turbulence level vary with height, so that excitation due to vortex shedding is effectively broad-band. Therefore the term ‘wake excitation’ is used to include all forms of excitation associated with the wake and not just those associated with the critical wind velocity. In this Standard methods for calculating cross-wind response will be restricted to structures under wake excitation. (b) Incident turbulence. The ‘incident turbulence’ mechanism refers to the situation where the turbulent properties of the natural wind give rise to changing wind speeds and directions which directly induce varying lift and drag forces and pitching moments on the structure over a wide band of frequencies. The ability of incident turbulence to produce significant contributions to cross-wind response depends very much on the ability to generate a cross-wind (lift) force on the structure as a function of longitudinal wind speed and angle of attack (a). In general, this means a section with a high lift curve slope (dCl/da) or pitching moment curve slope (dCm/da) such as a streamline bridge deck section or flat deck roof. No methods for calculating cross-wind response for these structures under incident turbulence excitation will be given in this Standard. (c) Cross-wind displacement. Several cross-wind excitation mechanisms are recognized under the heading of ‘excitation due to displacement’ which more explicitly should read ‘excitation due to cross-wind displacement and higher derivatives of displacement, and rotation’. There are three commonly recognized displacement dependent excitations, ‘galloping’, ‘flutter’ and ‘lock-in’, all of which are also dependent on the effects of turbulence inasmuch as turbulence affects the wake development and hence the aerodynamic derivatives. (i) ‘Galloping excitation’ results in a single degree of freedom motion which depends on the sectional aerodynamic force characteristics and on the rate of cross-wind displacement to produce a force in phase with the displacement. It is mostly two-dimensional structures such as electrical conductors which are prone to this form of excitation in practice (refer to Parkinson and Brooks, Ref. 37). However, galloping excitation can be significant at very high wind velocities for flexible, lightly-damped and slender tower-like structures (Novak and Davenport, Ref. 38; Kwok and Melbourne, Ref. 39).

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Saunders (Ref.40) discusses the relevance of galloping excitation to typical tall buildings and concludes that galloping and the quasi-steady formulation of negative aerodynamic damping do not have a significant effect on the level of response for Vh/ncb less than 10. Saunders also concludes that within the range of experiments, which covers many typical rectangular tall buildings, the cross-wind force spectra are insensitive to the level of displacement.

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ii)

‘Flutter’ as a name is usually used to cover instabilities and excitations having more than one degree of freedom. In the civil engineering field the bridge deck has suffered and is the one most likely to suffer forms of flutter excitation. A series of studies of flutter in this context by Scanlan and Tomko (Ref. 41) with respect to the effect of various aerodynamic derivatives are of particular interest. The motion of a cantilevered roof in which coupling between rotation and displacement can be significant would also fit partly under a flutter heading.

(iii) ‘Lock-in’ is a term commonly used to describe large amplitude cross-wind oscillations of structure which occur at wind velocities at which the vortex shedding frequencies are close to the natural frequency of the structure. The lock-in excitation mechanism is thought to be due to the cross-wind displacement in which the cross-wind response of a structure causes an increase in the excitation forces, which in turn increases the response of the structure. That is, there is an inter-dependence between the excitation and response processes so that once lock-in becomes established, the vortex shedding frequency tends to couple with the natural frequency of the structure, and the large amplitude response persists. Data applicable to modern tall buildings and structures in natural turbulence boundary layer flow are extremely rare. Wind tunnel model studies by Vickery (Ref. 42), Melbourne (Ref. 43) and Kwok and Melbourne (Ref. 44) are the few reported cases in which lock-in has been found to be significant for tall structures under simulated natural wind conditions. Lock-in is only likely to occur for structures which have relatively low stiffness, are lightly-damped, and are operating near the critical wind velocity (Vcrit) given in Equation F4.4.3. nc b Vcrit = . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (F4.4.3) Sr where Vcrit = the critical wind speed, in metres per second nc = the fundamental natural frequency in the cross-wind direction, in hertz b = the breadth of the structure normal to the wind stream, in metres. Sr = the Strouhal number For structures of rectangular cross-section in turbulent flow — Sr = 0.1 for Re > 104 For structures of circular cross-section in turbulent flow — Sr is given in Figure F4.4.3.1, where the Reynolds number Re = 0.67 × 10 5 Vhb. In practice the only common structures affected by lock-in are chimney stacks. The technique employed to calculate the cross-wind response due to wake excitation is to solve the equation of motion for a lightly damped structure in modal form with the forcing function mode generalized in spectral format. The values of the cross-wind force spectrum coefficients given in Figures 4.4.3(A) and (B) are based on a fun damental mode of vibration which has a linear mode shape. Extension of this data to non-linear mode shapes may be obtained by the mode shape correction factor discussed by Holmes (Ref. 45). The factors (1.06 - 0.06k) and (0.76 + 0.24k) in Equations 4.4.3(1) and 4.4.3(2) are conservative linear correction factors to the base overturning moment and tip acceleration, incorporating corrections to the inertia forces and generalized mass as well as that to the spectrum of generalized cross-wind force.

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FIGURE F4.4.3.1 DOMINANT WAKE FREQUENCY ASSOCIATED WITH VORTEX SHEDDING FROM BLUFF BODIES IN TURBULENT FLOW

F4.4.4 Cross-wind response — cantilevered roofs and canopies. The response of a cantilevered roof is dependent on the dynamic response to wind action. This response may be approximately related to the first mode frequency of the cantilevered system as given in Equation 4.4.4. There is obviously dependency on leading edge configurations, and substantial reduction in load can be achieved by using a slotted leading edge. The dependency on mass and damping does not appear to be as much as for many of the other structures in this Section because the response mechanism is not so dependent on the resonance mechanism. (See Melbourne and Cheung (Ref. 46).) For the design of roof cladding, purlins etc, the static analysis procedures set out in Section 3 should be used. F4.4.5 Cross-wind response — lattice towers and masts. F4.4.6 Combination of along-wind and cross-wind responses. As shown by Melbourne (Ref. 68), the dynamic along-wind response and cross-wind response of symmetrical structures each have Gaussian (normal) probability distributions, and are statistically independent of each other. Hence, the joint probability distribution of the along-wind and cross-wind base moment, and their corresponding load effects, is bivariate Gaussian with zero correlation coefficient. It would be conservative therefore, to apply ^ a) and (M ^ c), simultaneously to the structure, as the probability of occurring together, the peak moments (M in an hour of wind run at the design hourly mean wind speed under consideration, is much smaller than the probability of occurring separately. Equation 4.4.6(1) is an excellent approximation to the combined response of scalar structural effects, when the conditions described in the previous paragraph apply, and when the along-wind frequency (n a) and cross-wind frequency (nc) are nearly equal to each other (Ref. 69).

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As shown in Figure F4.4.6.1, the combined along-wind and cross-wind dynamic vector response falls within an elliptic envelope. At different times the resultant base moment can take different magnitudes and directions with approximately equal probability. An alternative method to the use of Equation 4.4.6(1) to determine the maximum of any scalar load effect ( ) is to determine it for a range of resultant vector base moments such as those shown in Figure F4.4.6.1 to find the largest ( ). The peak resultant vector base moment (

) is equal to the largest distance from the origin to any point

on the ellipse. When the mean cross-wind response ( ) is equal to zero, and the dynamic cross-wind response exceeds the along-wind dynamic response (see Figure F4.4.6.2), this distance is given by Equation F4.4.6(1), and the angle (αmax) at which the moment acts is given by Equation F4.4.6(2).

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (F 4.4.6(1))

for

=

0

>

(G − 1)

(F4.4.6(2))

for

= 0 > (G − 1)

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where

G

=

the mean base overturning moment in the along-wind direction

=

the gust factor for along-wind response

=

the peak base overturning moment in the cross-wind direction.

When the mean cross-wind response ( ) is equal to zero and the cross-wind dynamic response is less than or equal to the along-wind dynamic response, (see Figure F4.4.6.3), the peak resultant base moment is equal to the peak along-wind moment, ( ) equal to ( ). Similar equations to F4.4.6(1) and F4.4.6(2) can be used for other vector resultants such as acceleration and deflection. Equation F4.4.6(1) can also be derived by computing the peak base moment ( to the mean wind direction, by setting

equal to

Equation 4.4.6(1), and then finding the largest value of to the largest resultant (

cos α and

) in a plane at an angle α equal to

sin α in

for any angle α. This value (

) is equal

). Note, from Figure F4.4.6.2, that

, being a resultant, has no other

component in the orthogonal direction, but the largest moment at any other angle ( ) acts together with an orthogonal component in a plane at an angle (90° + α) to the mean wind direction. No simple equations like F4.4.6(1) and F4.4.6(2) can be derived for the maximum resultant vector base moment when is not equal to zero, and a graphical or numerical method of solution should be used.

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FIGURE F4.4.6.1 RESULTANT VECTOR BASE MOMENTS

FIGURE F4.4.6.2 PEAK RESULTANT VECTOR RESPONSE WHEN ^ Mc = 0, AND Mc > (G - 1) Ma

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FIGURE F4.4.6.3 PEAK RESULTANT VECTOR RESPONSE WHEN ^ Mc = 0, AND Mc ≤ (G - 1) Ma

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REFERENCES 1. REINHOLD, T. (ed.), ‘Wind Tunnel Modelling for Civil Engineering Applications’, Proceedings, International Workshop on Wind Tunnel Modelling Criteria and Techniques in Civil Engineering Applications, Gaithersburg, Maryland, U.S.A., Cambridge University Press, April 1982. 2. MELBOURNE, W.H.,‘Towards an Engineering Wind Model’, Course Notes on the Structural and Environmental Effects of Wind on Buildings and Structures, Chapter 19, Monash University, 1981. 3. DEAVES, D.M. and HARRIS, R.I., ‘A Mathematical Model of the Structure of Strong Winds’, Construction Industry Research and Information Association (U.K.), Report 76, 1978. 4. DORMAN, C.M.L.,‘Extreme Wind Gust Speeds in Australia Excluding Tropical Cyclones’, Civil Engineering Transactions, The Institution of Engineers, Australia, 1983, pp. 96-106. 5. HOLMES, J.D. and BEST, R.J., A wind tunnel study of wind pressures on grouped tropical houses, James Cook University, Wind Engineering Report 5/79, 1979. 6. HUSSAIN, M. and LEE, B.E., ‘A wind tunnel study of the mean pressure forces acting on large groups of low rise buildings’, Journal of Wind Engineering & Industrial Aerodynamics, Vol 6, 1980, pp. 207-225 7. LEE, B.E., ‘Wind effects on groups of low rise buildings’ (as yet unpublished paper). 8. WOOD, D.H., ‘Internal boundary layer growth following a step change in surface roughness’, Boundary Layer Meteorology, Vol 22 (1982), pp. 241-244. 9. MELBOURNE, W.H., ‘The structure of wind near the ground’, Course notes on the Structural and Environmental Effects of Wind on Buildings and Structures, Chapter 2, Monash Uni, 1981. 10. TAYLOR, P.A. and LEE, R.J., ‘Simple guidelines for estimating windspeed variation due to small scale topographic features’, Climatological Bulletin (Canada), Vol 18, No 22, pp. 3-32, 1984. 11. BOWEN, A.J., ‘The prediction of mean wind speeds above simple 2D hill shapes’, Journal of Wind Engineering and Industrial Aerodynamics, Vol 15, pp. 259-270, 1983. 12. JACKSON, P.S. and HUNT, J.C.R., ‘Turbulent flow over a low hill’, Quarterly Journal of the Royal Meteorological Society, Vol 101, pp. 929-955, 1975. 13. BUILDING RESEARCH ESTABLISHMENT (U.K.), ‘The Assessment of Wind Speed over Topography’, Digest, 283, March 1984. 14. MELBOURNE, W.H.,‘Designing for Directionality’, 1st Workshop on Wind Engineering and Industrial Aerodynamics, Highett, Victoria, July 1984. 15. HOLMES, J.D., Wind Loads on Low-Rise Buildings — A Review, CSIRO Division of Building Research Report, 1983. 16. HOLMES, J.D., ‘Recent developments in the codification of wind loads on lowrise structures’, Proc. Asia-Pacific Symposium on Wind Engineering, Roorkee India, December 1985, pp. iii—xvi. 17. STATHOPOULOS, T., and MOHAMMADIAN, A.R., ‘Code Provisions for Wind Pressures on Buildings with Monosloped Roofs’, Proceedings, Asia-Pacific Symposium on Wind Engineering, Roorkee, India, December, 1985, pp. 337-347. 18. DAVENPORT, A.G., ‘The prediction of risk under wind loading’, Proc. 2nd International Conference on Structural Safety and Reliability, Munich 1977, pp. 511538. 19. HOLMES, J.D., ‘Reduction factors for wind direction for use in codes and standards’, Proc. Colloque, Designing with the Wind, Nantes, France, June 1981. 20. WALKER, G.R., ‘Directionality and risk in respect of overall wind drag forces on a rectangular building’, Unpublished submission to the Standards Association of Australia, 1981. 21. DAVENPORT, A.G., SURRY, D. and STATHOPOULOS, T., ‘Wind loads on low-rise buildings’ Final report of Phases I & II, University of Western Ontario, Boundary Layer Wind Tunnel Report, BLWT SS8 — 1977.

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22. HOLMES, J.D. and RAINS, G.J., ‘Wind loads on flat and curved roof low-rise buildings — Application of the covariance integration approach’, Proc. Colloque, Designing with the Wind, Nantes, France, June 1981. 23. ROY, R.J. and HOLMES, J.D., ‘Total force measurement on wind tunnel models for low-rise buildings’, Proc. Colloque, Designing with the Wind, Nantes, France, June 1981. 24. KIM, S.I. and MEHTA, K.C., Wind loads on flat-roof area through full scale experiment, Texas Tech. University, Institute for Disaster Research report, 1977. 25. HOLMES, J.D., ‘Mean and fluctuating internal pressures induced by wind’, Proc. 5th International Conference on Wind Engineering, Fort Collins, 1979, pp. 435-450. 26. CHEUNG, J.C.J. and MELBOURNE, W.H., ‘Wind loading on porous cladding’, Proc, 9th Australian conference on Fluid Mechanics, Auckland, N.Z., 1986, pp. 308-311. 27. GEORGIOU, P.N., and VICKERY, B.J., ‘Wind Loads on Building Frames’, Proceedings, 5th Int. Conf. on Wind Engineering, Fort Collins, 1979, pp. 421-433. 28. WHITBREAD, R.E., ‘The Influence of Shielding on the Wind Forces Experienced by Arrays of Lattice Frames’, Proceedings, 5th Int. Conf. on Wind Engineering, Fort Collins, 1979, pp. 405-420. 29. BAYAR, D.C., ‘Drag Coefficients of Latticed Towers’, Journal of Structural Engineering, ASCE, Vol 112, 1986, pp. 417-430. 30. DAVENPORT, A.G., ‘The Application of Statistical Concepts to the Wind Loading of Structures’, Proceedings, Institution of Civil Engineers, London, Vol 19, 1961, pp. 449472. 31. MELBOURNE, W.H., ‘Probability Distributions Associated with the Wind Loading of Structures’, Civil Engineering Transactions, Vol CE19, No 1, 1977, pp. 58-67. 32. MELBOURNE, W.H.,‘Cross-wind Response of Structures to Wind Action’, 4th International Conference on Wind Effects on Buildings and Structures, Cambridge University Press, London, 1975. 33. SAUNDERS, J.W. and MELBOURNE, W.H., ‘Buffeting Effects of Upwind Buildings’, Proc. 5th International Conference on Wind Engineering, Fort Collins, 1979, pp. 593606. 34. BAILEY, P.A., and KWOK, K.C.S., ‘Interference Excitation of Twin Tall Buildings’, Journal of Wind Engineering and Industrial Aerodynamics, Vol 21, 1985, pp. 323-338. 35. DAVENPORT, A.G., ‘Gust Loading Factors’, Journal of the Structural Division, ASCE, Vol 93, 1967, pp. 11-34. 36. VICKERY, B.J., ‘On the Reliability of Gust Loading Factors’, Civil Engineering Transactions, I.E. Aust., Vol 13, 1971, pp. 1-9. 37. PARKINSON, G.V., and BROOKS, N.P.H., ‘On the Aeroelastic Instability of Bluff Cylinders’, Transactions, ASME Journal of Applied Mechanics, Vol 28, 1961, pp. 252258. 38. NOVAK, M., and DAVENPORT, A.G., ‘Aeroelastic Instability of Prisms in Turbulent Flow’, Journal of the Engineering Mechanics Division, ASCE, Vol 96, No EM2, Proc. Paper 7076, Feb., 1970, pp. 17-39. 39. KWOK, K.C.S, and MELBOURNE, W.H., ‘Freestream Turbulence Effects on Galloping’, Journal of the Engineering Mechanics Division, ASCE, Vol 106, No EM2, Proc. Paper 15356, April 1980, pp. 273-288. 40. SAUNDERS, J.W., and MELBOURNE, W.H., ‘Tall Rectangular Building Response to Cross-wind Excitation’, Proc. 4th International Conference on Wind Effects on Buildings and Structures, Cambridge University Press, September 1975, pp. 369-379. 41. SCANLAN, R.H., and TOMKO, J.J., ‘Aerofoil and Bridge Deck Flutter Derivatives’, Proceedings, Engineering Mechanics Division of ASCE, Vol 97, No EM6, 1971, pp. 1717-1737. 42. VICKERY, B.J., ‘Wind Induced Vibrations of Towers, Stacks and Masts’, Proc. 3rd International Conference on Wind Effects on Buildings and Structures, Paper IV-2, Saikon Company, Tokyo, 1971. 43. MELBOURNE W.H., ‘Response of a Slender Tower to Wind Excitation’, Proc. 5th Australasian Conference on Hydraulics and Fluid Mechanics, New Zealand, 1974, pp. 251-257.

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44. KWOK, K.C.S., and MELBOURNE, W.H., ‘Wind-induced Lock-in Excitation of Tall Structures’, Journal of The Structural Division, ASCE, Vol 107, No ST1, January, 1981, pp. 57-72. 45. HOLMES, J.D., ‘Mode shape corrections for dynamic response to wind’, Engineering Structures, Vol 9, pp. 210-212, 1987. 46. MELBOURNE, W.H., and CHEUNG, J.C.K, ‘Wind Loads on Grandstand Roofs’, 2nd Workshop on Wind Engineering and Industrial Aerodynamics, Highett, Victoria, August 1985. 47. GUMLEY, S.J., Panel Loading Mean Pressure Study for Canopy Roofs, University of Oxford, Department of Engineering Science, OUEL Report 1380/81, 1981. 48. GUMLEY, S.J., ‘A Parametric Study of Extreme Pressures for the Static Design of Canopy Structures’, Journal of Wind Engineering and Industrial Aerodynamics, Vol 16, 1984, pp. 43-56. 49. ROBERTSON, A.P., HOXEY, R.P. and MORAN, P., ‘A full scale study of wind loads on agricultural canopy structures and proposal for design’, Journal of Wind Engineering and Industrial Aerodynamics, Vol 21, 1985, pp. 167-205. 50. HOLMES, J.D., ‘Determination of Wind Loads for an Arch Roof’, Civil Engineering Transactions, I.E. Aust, Vol CE 26, No 4, pp. 247-253, 1984. 51. HOLMES J.D., ‘Wind Loading of Multi-Span Buildings’, First Structural Engineering Conference, Melbourne, 26-28 August 1987. 52. SABRANSKY, I.J., ‘Wind Pressure Distribution on Cylindrical Storage Silos’, M. Eng. Sc. Thesis, Monash University, 1984. 53. MACDONALD, P.A., KWOK, K.C.S., and HOLMES, J.D., ‘Wind Loads on Storage Bins, Silos and Tanks I, Point Pressure Measurements on Isolated Structures’, Journal of Wind Engineering and Industrial Aerodynamics, Vol 31, 1988, pp. 165-188. 54. JANCAUSKAS, E.D., and HOLMES, J.D., ‘Wind Loads on Attached Canopies’, 5th U.S. National Conference on Wind Engineering, Lubbock, Texas, November 1985. 55. JANCAUSKAS, E.D. and EDDLESTON, J.D., ‘Wind loads on canopies at the base of tall buildings’, James Cook University, Dept of Civil and Systems Engineering Report October 1986. 56. HOLMES J.D., ‘Pressure and Drag on Surface-mounted Rectangular Plates and Walls’, 9th Australian Fluid Mechanics Conference, Auckland, 1986. 57. LETCHFORD, C.W., ‘Wind Loads on Free-standing Walls’, Department of Engineering Science, Oxford University, Report OUEL, 1599-85, 1985. 58. DELANEY, N.K., and SORENSEN, N.E., ‘Low-speed Drag of Cylinders of Various Shapes’, National Advisory Committee for Aeronautics, Technical Note 3038, 1953. 59. SACHS, P., Wind Forces in Engineering, Pergamon Press, 1972. 60. JANCAUSKAS, E.D., ‘The Cross-wind Excitation of Bluff Structures’, Ph.D Thesis, Monash University, 1983. 61. NAKAGUCHI, N., HASHIMOTO, K., and MUTO, S., ‘An Experimental Study on Aerodynamic Drag of Rectangular Cylinders’, Journal Japan Society for Aeronautical and Space Sciences, Vol 16, 1968, pp. 1-5. 62. SIA Technische Normen Nr 160, Normen fur die Belastungsannahmen, die Inbetriebnahme and die Uberwachung Bauten, 1956. 63. DAVENPORT, A.G., ‘On the statistical prediction of structural performance in the wind environment’, A.S.C.E. — National Structural Engineering meeting, Baltimore, Maryland, April 1971. 64. SIMIU, E. and FILLIBEN, J.J., ‘Wind direction effects on cladding and structural loads’, Engineering Structures, Vol 3, pp. 181-186, July 1981. 65. HOLMES, J.D., ‘The application of probability theory to the directional effects of wind’, Proceedings 10th Australasian Conference on the Mechanics of Structures and Materials, Adelaide, 1986, pp. 169174. 66. BS 8100, Part 1, 1986, Lattice Towers and Masts — Part 1, Code of Practice for Loading, British Standards Institution, London. 67. Wind Forces on Tubular Structures — Design Manual, Tubemakers of Australia, August 1987. 68. MELBOURNE, W.H., ‘Probability Distributions of Response of BHP House to Wind Action and Model Comparisons’, Journal of Industrial Aerodynamics, Vol 1, 1975, pp. 167-175. 69. PHAM, L and LEICESTER, R H, Combination of Stochastic Loads’, Proceedings, 7th Australasian Conference on the Mechanics of Structures and Materials, Perth, May 12-14, 1980, pp. 154-158.

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INDEX Additional pressure coefficients, Appendix A Along-wind and cross-wind responses, combination, 4.4.6. F4.4.6 Along-wind response, tall buildings and towers, 4.4.2, F4.4.2 Analysis, static (see Limitation), 3.1, E3.1 Application (limitation) detailed procedure, 3.1, 4.1, E3.1, F4.1 of Standard, 1.2 simplified procedure, 2.2 Area reduction factors for roofs and side walls, detailed procedure, 3.4.2, 3.4.4, 3.4.9, 3.4.10, Appendix A, E3.4.4 AUSTROADS, 1.1 Aspect ratio correction factors, Appendix B Awnings adjacent to buildings, net pressure coefficients, 3.4.10 Awnings, definition, 1.6 Awnings, pressures and forces, 3.1 Awnings, unenclosed attached, basic pressures, simplified procedure, 2.4.3.

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Basic pressures, simplified procedure, 2.3.1, 2.4 external, 2.4.1 internal, 2.4.2 Basic wind speed detailed procedure, 3.2.2, 3.2.3, 4.2.2, 4.2.3, E3.2.2, F4.2.2 Bridges, 1.1, 1.2 Building geometry parameters, simplified procedure, 2.4.1.1 Buildings (structures), wind forces, 2.3.2 Calculation of forces and moments on complete buildings, detailed procedure, 3.4.1.3 Canopies adjacent to buildings, net pressure coefficients, 3.4.10 Canopies, frictional drag force, 3.4.12 pressures and forces, 3.1 unenclosed attached, basic pressures, simplified procedure, 2.4.3 Canopy, definition, 1.6 Cantilevered roofs and canopies, cross-wind response, 4.4.4, F4.4.4 Cantilevered roofs, net pressure, 3.4.11 Carports, partially enclosed, net pressure coefficients, 3.4.10, E3.4.10 Carports, unenclosed attached, basic pressures, simplified procedure, 2.4.3 Changes in terrain category, detailed procedure, 3.2.6, 4.2.6, E3.2.6, F4.2.6 Cladding, definition, 1.6 Cladding, immediate supports, definition, 1.6 Cladding in cyclonic regions, fatigue loading, detailed procedure, 3.6 simplified procedure, 2.6 Cladding, internal pressures, simplified procedure, 2.4.2 Cladding, local negative external pressures, simplified procedure, 2.4.1.5 Cladding, local pressure factors for monoslope, pitched or troughed free roofs, detailed procedure, 3.4.9 rectangular enclosed buildings, detailed procedure, 3.4.2, 3.4.5, E3.4.5 Cladding, porosity of, definition, 1.6 Climatic changes, 1.1 Cross-wind response cantilevered roofs and canopies, 4.4.4, F4.4.4 lattice towers and masts, 4.4.5 tall buildings and enclosed towers, 4.4.3, F4.4.3 Definitions, 1.6 Derivation of design gust wind speed, 3.2.2, E3.2.2 Derivation of design hourly mean wind speed, 4.2.2, F4.2.2 Design gust wind speed detailed procedure, 3.2, 3.3 Design hourly mean wind speed detailed procedure, 4.2, 4.3 Design procedures detailed procedure—static and dynamic analysis, 1.3.2, C1.3.2 simplified procedure, 1.3.1, C1.3.1

Design requirements, 1.4 general, 1.4.1, C1.4.1 permissible stress design procedure, 1.4.6 serviceability limit state, 1.4.5 stability limit state, 1.4.2 strength limit state, 1.4.3 ultimate limit states, 1.4.4 Detailed procedure—static and dynamic analysis design procedures, 1.3.2, C1.3.2 Detailed procedure: dynamic analysis, Section 4 application, 4.1, F4.1 changes in terrain category, 4.2.6, F4.2.6 design hourly mean wind speed, derivation, 4.2.2, F4.2.2 dynamic wind pressure, 4.3, 4.4.2, F4.3 hourly mean wind speed, 4.2, 4.3 general, 4.2.1 wind direction, 4.2.3, E3.2.3 limitation (see Application) procedure and derivation, 4.4 along-wind response, tall buildings and towers, 4.4.2, F4.4.2 combination of along-wind and cross-wind responses, 4.4.6, F4.4.6 cross-wind response, cantilevered roofs and canopies, 4.4.4, F4.4.4 cross-wind response, lattice towers and masts, 4.4.5 cross-wind response, tall buildings and towers, 4.4.3, F4.4.3 general, 4.4.1, F4.4.1 shielding multiplier, 4.2.2, 4.2.7, E3.2.7 structure importance multiplier, 4.2.2, 4.2.9, E3.2.9 terrain and structure height multiplier, 4.2.2, 4.2.5, 4.2.6, E3.2.5 terrain category, 4.2.4, E3.2.4 topographic multiplier, 4.2.2, 4.2.8, F4.2.8 Detailed procedure: static analysis, Section 3 application (see Limitation) changes in terrain category, 3.2.6, E3.2.6 design gust wind speed, 3.2 derivation of, 3.2.2, E3.2.2 general, 3.2.1 wind direction, 3.2.3, E3.2.3 dynamic wind pressure, 3.3, 3.4.2, E3.3 fatigue loading, 3.6, E3.6 forces and pressures on enclosed buildings, free roofs and walls, 3.4 area reduction factors for roofs and side walls, 3.4.2, 3.4.4, 3.4.9, 3.4.10, Appendix A, E3.4.4 calculation of forces and moments on complete buildings, 3.4.1.3 external pressure coefficients circular bins, silos and tanks, Appendix A curved (arched) roofs, Appendix A mansard roofs, Appendix A multi-span buildings, Appendix A pitched roofs, Appendix A saw-tooth roofs, Appendix A rectangular enclosed buildings, 3.4.2, 3.4.3, E3.4.3 external pressures, 3.4.1.2, 3.4.2 forces on building elements, 3.4.1.2 frictional drag force for free roofs and canopies, 3.4.12 frictional drag force for rectangular enclosed buildings, 3.4.8 general, 3.4.1 internal pressures, 3.4.1.2, 3.4.7, E3.4.7 local pressure factors for cladding, 3.4.2, 3.4.5, E3.4.5 net pressures for canopies, awnings and carports, 3.4.1.2 3.4.10, E3.4.10 for cantilevered roofs, 3.4.11 for free roofs, 3.4.1.2, 3.4.9, E3.4.9 for hoardings and free-standing walls, 3.4.13, E3.4.13 procedure, 3.4.1.1 reduction factors for porous cladding, 3.4.2, 3.4.6, E3.4.6 forces on exposed structural members, 3.5 aspect ratio correction factors, Appendix B drag force coefficients for lattice towers, 3.5.5, E3.5.5 drag force coefficients for rounded cylindrical shapes, Appendix B drag force coefficients for sharp-edged prisms, Appendix B

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Detailed procedure: static analysis (cont) forces on exposed structural members (cont.) force coefficients for rectangular prismatic sections, Appendix B force coefficients for structural sections, Appendix B general, 3.5.1 multiple open frames, 3.5.4, E3.5.4 procedure, 3.5.2 single open frames, 3.5.3, E3.5.3 limitation, 3.1, E3.1 shielding multiplier, 3.2.2, 3.2.7, E3.2.7 structure importance multiplier, 3.2.2, 3.2.9, E3.2.9 terrain and structure height multiplier, 3.2.2, 3.2.5, 3.2.6, E3.2.5 terrain category, 3.2.4., E3.2.4 topographic multiplier, 3.2.2, 3.2.8, E3.2.8 Determination of wind loads, 1.5 Directional wind speed data, detailed procedure, 3.2.3, 4.2.3 Dominant opening, definition, 1.6 Dominant openings, detailed procedure, 3.4.7, E3.4.7 simplified procedure, 2.4.2 Doors, pressures and forces, 3.1 Drag, definition, 1.6 Drag force coefficient, detailed procedure, 3.5.2, 3.5.5, 4.4.2 Drag force coefficients for lattice towers, 3.5.5, E3.5.5 Drag force coefficients for rounded cylindrical shapes, Appendix B Drag force coefficients for sharp-edged prisms, Appendix B Dynamic analysis design procedure, 1.3.2, C1.3.2 Dynamic analysis, detailed procedure, Section 4 Dynamic response data, 4.2.3 Dynamic wind pressure, detailed procedure, 3.3, 3.4.2, 4.3, 4.4.2, 4.4.3, 4.4.4, E3.3, F4.3 Eaves, unenclosed attached, basic pressures, simplified procedure, 2.4.3 Eaves, basic external pressures simplified procedure, 2.4.1.4 Elements of buildings, wind forces, 2.3.2 Enclosed buildings, definition, 1.6 external pressure coefficients, 3.4.3 parameters, 3.4.3 Escarpment, definition, 1.6 Escarpments, detailed procedure, 3.2.8, 4.2.8, E3.2.8, F4.2.8 Exposed structural members, wind forces, 3.5.2 External pressure, detailed procedure, 3.4.1.2, 3.4.2 External pressure coefficients, circular bins, silos and tanks, Appendix A curved (arched) roofs, Appendix A mansard roofs, Appendix A pitched roofs, multi-span buildings, Appendix A rectangular enclosed building, 3.4.2, 3.4.3, E3.4.3 saw-tooth roofs, multi-span buildings, Appendix A underside of highset buildings, 3.4.3. External pressures on rectangular buildings, 2.4.1

Forces on elements of buildings, simplified procedure, 2.3.2 Forces on exposed structural members detailed procedure, 3.5 Frames, multiple open, 3.5.4, E3.5.4 single open, 3.5.3, E3.5.3 Free roof, definition, 1.6 Free roofs, frictional drag force, 3.4.12 Free roofs, net pressure coefficient, 3.4.9, E3.4.9 Free standing roofs, basic pressures, simplified procedure, 2.4.4 Free standing walls, net pressure, detailed procedure, 3.4.13, E3.4.13 Free standing walls, definition, 1.6 Free standing walls on ground, basic pressures, simplified procedure, 2.4.5 Freestream dynamic pressure, definition, 1.6 Frictional drag force coefficient, detailed procedure, 3.4.8 Frictional drag force for free roofs and canopies, detailed procedure, 3.4.12 Frictional drag force for rectangular enclosed buildings, detailed procedure, 3.4.8 Frictional forces, free standing roofs, simplified procedure, 2.4.4.1, 2.4.4.2 Cable roof, definition, 1.6 Gust dynamic wind pressure, detailed procedure, 3.3, 3.4.2, E3.3. Gust factor, 4.4.2 Gust wind speed, detailed procedure, 3.2, 3.3 Highset building, definition. detailed procedure, 3.4.3 simplified procedure, 2.4.1.4 Highset buildings, 2.4.1.4, 2.4.1.6, 2.4.1.7, 2.4.2, 3.4.3 Hills and ridges detailed procedure, 3.2.8, 4.2.8, E3.2.8, F4.2.8 Hip roof, definition, 1.6 Hoardings and signs, basic pressures, simplified procedure, 2.4.6 Hoardings, definition, 1.6 Hoardings, net pressure, detailed procedure, 3.4.13, E3.4.13 Hourly mean dynamic wind pressure, 4.3, 4.4.2, 4.4.3, 4.4.4, F4.3 Hourly mean wind speed, 4.2, 4.3 Immediate supports, cladding, definition, 1.6 Impact, debris, 3.4.7, E3.4.7 Importance multiplier, 3.2.9, 4.2.9, E3.2.9 Internal pressure coefficients, 3.4.7, E3.4.7 Internal pressures, detailed procedure, 3.4.1.2, 3.4.7, E3.4.7 simplified procedure, 2.4.2

Farm buildings, simplified procedure, 2.8.1 Fatigue loading, detailed procedure, 3.6, E3.6 simplified procedure, 2.6, D2.6 Fences (see Walls) Force coefficient, definition, 1.6 Force coefficients, 3.2.3 Force coefficients for rectangular prismatic sections, Appendix B Force coefficients for structural sections, Appendix B Forces and pressures on complete buildings, calculation, detailed procedure, 3.4.1.3 Forces and pressures on enclosed buildings, free roofs and walls, detailed procedures, 3.4 Forces on building elements detailed procedure, 3.4.1.2

Lattice towers and masts, cross-wind response, 4.4.5 Lattice towers, definition, 1.6 drag force coefficients, 3.5.5, E3.5.5 Leeward sections of roofs, basic external pressures, simplified procedure, 2.4.1.3 Lift, definition, 1.6 Lift force coefficient, 3.5.2 Limitation (Application), detailed procedure, 3.1, 4.1, F3.1, F4.1 of Standard, 1.1, 1.2 simplified procedure, 2.2 Local negative external pressures, simplified procedure, 2.4.1.5 Local net pressure factors for free roofs and canopies, 3.4.9 Local positive external pressures simplified procedure, 2.4.1.6 Local pressure factors for cladding, detailed procedure, 3.4.2, 3.4.5, E3.4.5

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95 Local topographic zones, detailed procedure, 3.2.8, E3.2.8, 4.2.8, F4.2.8 Main structural components, canopies, awnings, carports and eaves, basic pressures, simplified procedure, 2.4.3.2 free standing roofs, basic pressures simplified procedure, 2.4.4.2 Major offshore structures, definition, 1.6 Methods of determination of wind loads, 1.5.1, C1.5.1 Monoslope free roofs, net pressure coefficients, 3.4.9, E3.4.9 Monoslope roof, definition, 1.6 Monoslope roofs, basic external pressures, simplified procedure, 2.4.1.2 Multiplying factors, detailed procedure, 3.2.2, 3.2.5, 3.2.7, 3.2.8, 3.2.9, 4.2.2, 4.2.5, 4.2.7, 4.2.8, 4.2.9 simplified procedure, 2.3.1, 2.5, D2.5.1 Net pressure for hoardings and free standing walls, detailed procedure, 3.4.13, E3.4.13 Net pressures for cantilevered roofs, detailed procedure, 3.4.11 Net pressures for free roofs, detailed procedure, 3.4.1.2, 3.4.9, E3.4.9 Net pressures for canopies, awnings and carports, detailed procedure, 3.4.1.2, 3.4.10, E3.4.10 Notation, 1.7

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Obstructions, definition, 1.6 Offshore structures, 1.1 Open frame structures, wind forces, 3.5.3, 3.5.4, E3.5.3, E3.5.4 Openings, dominant definition, 1.6 detailed procedure, 3.4.7, E3.4.7 simplied procedure, 2.4.2 Permeability, definition, 1.6 Permissible stress design procedure, design requirements, 1.4.6 Permissible stress design, simplified procedure, 2.1 Pitched free roofs, net pressure coefficient, 3.4.9, E3.4.9 Pitched roof, definition, 1.6 Porosity, 3.4.6 Porosity of cladding, definition, 1.6 Porosity reduction factor for hoardings and free standing walls, 3.4.13 Porous cladding, reduction factors, detailed procedure, 3.4.2, 3.4.6, E3.4.6 Pressure coefficient, definition, 1.6 Pressure coefficients, 3.2.3 Pressure coefficients, additional, Appendix A Pressure coefficients, circular bins, silos and tanks, Appendix A curved (arched) roofs, Appendix A mansard roofs, Appendix A external, non-rectangular enclosed buildings, Appendix A pitched roofs, multi-span buildings, Appendix A rectangular enclosed buildings, 3.4.2, 3.4.3, E3.4.3 saw-tooth roofs, multi-span buildings, Appendix A underside of highset buildings, 3.4.3 Pressure, definition, 1.6 Rectangular buildings, external pressure, 2.4.1 Rectangular prismatic sections, force coefficients, Appendix B Reduction factors for porous cladding, detailed procedure, 3.4.2, 3.4.6, E3.4.6 Reduction factors for roofs, simplified procedure, 2.3.1, 2.5.4 Reduction factors for roofs, and side walls, detailed procedure, 3.4.2, 3.4.4, 3.4.9, 3.4.10, Appendix A, E3.4.4 Regional boundaries, basic wind speeds, detailed procedure 3.2.2, 4.2.2, E3.2.2, F4.2.2 Regional boundaries, regional multiplying factor simplified procedure, 2.5.1 Regional multiplying factor, simplified procedure, 2.3.1, 2.5.1 Reliable data, definition, 1.6 Reliable references, definition, 1.6

AS 1170.2—1989 Ridge-topographic feature, definition, 1.6 Roof cladding, canopies, awnings, carports and eaves, basic pressures, simplified procedure, 2.4.3.3 free standing roofs, basic pressures, simplified procedure, 2.4.4.3 Roof cladding, local pressure factors, detailed procedure, 3.4.5 Roof cladding, pressures and forces, 3.1 Roof reduction factors, detailed procedure, 3.4.2, 3.4.4, 3.4.9, 3.4.10, Appendix A, E3.4.4 simplified procedure, 2.3.1, 2.5.4 Roughness length, detailed procedure, 3.2.4, 4.2.4, E3.2.4 Roughness length, definition, 1.6 Rounded cylindrical shapes, drag force coefficients, Appendix B Scope (of Standard), 1.1 Serviceability design loads, simplified procedure, 2.7 Serviceability design, simplified procedure, 2.1 Serviceability limit state design requirements, 1.4.5 Sharp-edged prisms, drag force coefficients, Appendix B Shielding factor for multiple open frames 3.5.2, 3.5.4, E3.5.4 Shielding multiplier, detailed procedure, 3.2.2, 3.2.7, 4.2.2, 4.2.7, E3.2.7 Signs (see Hoardings) Simplified procedure, Section 2, application (see Limitation) basic external pressures general, 2.4.1.1 leeward sections of roofs, 2.4.1.3 local negative external pressures, 2.4.1.5 local positive external pressures, 2.4.1.6 under floor pressures of highset buildings, 2.4.1.7 walls and undersides of eaves, 2.4.1.4 windward sections of roofs, 2.4.1.2 basic internal pressures, 2.4.2 basic pressures, 2.3.1, 2.4 building geometry parameters, 2.4.1.1 design procedures, 1.3.1, C1.3.1 farm buildings, 2.8.1 fatigue loading, 2.6, D2.6 force on elements of buildings, 2.3.2 free standing roofs, basic pressures, 2.4.4 general, 2.4.4.1 main structural components, 2.4.4.2 roof cladding and its immediate supports, 2.4.4.3 free standing walls on ground, basic pressures, 2.4.5 general, 2.3.1 introduction, 2.1, D2.1 limitation, 2.2 multiplying factors, 2.3.1, 2.5, D2.5.1 permissible stress design, 2.1 rectangular hoardings and signs, basic pressures, 2.4.6 regional multiplying factor, 2.3.1, 2.5.1, D2.5.1 roof reduction factors, 2.3.1, 2.5.4 serviceability design, 2.1 serviceability design loads, 2.7 temporary structures, 2.8.2 terrain and height multiplying factor, 2.3.1, 2.5.2 topographic multiplying factor, 2.3.1, 2.5.3 ultimate limit state design wind pressure, 2.3.1, 2.3.2 ultimate strength limit state design, 2.1, 2.3.1 unenclosed attached canopies, awnings, carports and eaves, basic pressures, 2.4.3 general, 2.4.3.1 main structural components, 2.4.3.2 roof cladding and its immediate supports, 2.4.3.3 Single open frames, wind force, 3.5.3, E3.5.3 Small structures and buildings, wind loads, Section 2 Solidity ratio, 3.5.4, 3.5.5, E3.5.4 Stability limit state, design requirements, 1.4.2 Static analysis, design procedure, 1.3.2, C1.3.2 Static analysis, detailed procedure, Section 3

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AS 1170.2—1989

96

Strength limit state, design requirements, 1.4.3 Structural sections, force coefficients, Appendix B Structure importance multiplier, detailed procedure, 3.2.2, 3.2.9, 4.2.2, 4.2.9, E3.2.9 Structures containing high risk contaminants, 1.1 Sufficient-meteorological information, definition, 1.6

Verandahs (see Canopies) Wall cladding, local pressure factors, detailed procedure, 3.4.5 Wall reduction factors, detailed procedure, 3.4.2, 3.4.4 Appendix A, E3.4.4 Walls and undersides of eaves, basic external pressures, simplified procedure, 2.4.1.4 Walls free standing, 3.4.13, E3.4.13 pressures and forces on parts of, 3.1 Wind direction, detailed procedure, 3.2.3, 4.2.3, E3.2.3 Wind forces on complete buildings, 2.3.2 on elements of buildings, 2.3.2 on exposed structural members, 3.5 on open frame structures, 3.5.3, 3.5.4, E3.5.3, E3.5.4 Wind loads, methods of determination, 1.5.1, C1.5.1 Wind loads on small structures and buildings, Section 2 Wind sensitive structure, definition, 3.1, 4.1 Wind speed, basic, regional boundaries, 3.2.2, 4.2.2, E3.2.2, F4.2.2 design gust, 3.2.2, E3.2.2 design hourly mean, 4.2.2, F4.2.2 direction, 3.2.3, 4.2.3, E3.2.3 Wind tunnel tests on a specific structure, 1.5.3 Wind tunnel tests or similar determinations, 1.5.2, C1.5.2 Windows, pressures and forces, 3.1 Windward sections of roofs, basic external pressures, simplified procedure, 2.4.1.2

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Tall buildings and enclosed towers, cross-wind response, 4.4.3, F4.4.3 Tall buildings and towers along-wind response, 4.4.2, F4.4.2 Temporary structures, simplified procedure, 2.8.2 Terrain and height multiplying factor, simplified procedure, 2.3.1, 2.5.2 Terrain and structure height multiplier, detailed procedure, 3.2.2., 3.2.5, 3.2.6, 4.2.2, 4.2.5, 4.2.6, E3.2.5 Terrain category, detailed procedure, 3.2.4, 4.2.4, E3.2.4 Terrain category, changes in, detailed procedure, 3.2.6, 4.2.6, E3.2.6, F4.2.6 Terrain, definition, 1.6 Terrain roughness, detailed procedure, 3.2.6, 4.2.6, E3.2.6, F4.2.6 Topographic multiplier, detailed procedure, 3.2.2, 3.2.8, 4.2.2, 4.2.8, E3.2.8, F4.2.8 Topographic multiplying factor, simplified procedure, 2.3.1, 2.5.3 Topography, definition, 1.6 Tornado, definition, 1.6 Tornadoes,1.1 Transmission lines, 1.1 Tributary area, definition, 1.6 detailed procedure, 3.4.4 simplified procedure, 2.4.1.5 Tropical cyclone, definition, 1.6 Troughed free roofs, net pressure coefficients, 3.4.9, E3.4.9 Troughed roof, definition, 1.6 Turbulence intensity, 4.2.5, E3.2.5, E3.2.8

Ultimate limit states, design requirements, 1.4.4 Ultimate limit states, design wind pressures, simplified procedure, 2.3.1, 2.3.2 Ultimate strength limit state design, simplified procedure, 2.1, 2.3.1 Under floor pressures of highset buildings, simplified procedure, 2.4.1.7

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Accessed by BLUESCOPE STEEL LIMITED on 10 Jun 2005 [AVAILABLE SUPERSEDED]