AS 1170.2 - 1989 - Wind Loads

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AS 1170.21989

Australian Standard

SAA Loading Code

Part 2: Wind loads

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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

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

Revi ew of Austr alia n Stand ard s. To keep abreast of progress in industry, Australian Standards are subjectto periodic review and are kept up to date by the issue of amendments or new editions as necessary. It isimportant therefore that Standards users ensure that they are in possession of the latest edition, and anyamendments thereto.

Full details of all Australian Standards and related publications will be found in the Standards AustraliaCatalogue of Publications; this information is supplemented each month by the magazine The AustralianStandard, which subscribing members receive, and which gives details of new publications, new editionsand amendments, and of withdrawn Standards.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 madewithout 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.Accessedb

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AS 1170.21989

Australian Standard

Minimum design loads onstructures (known as the SAALoading Code)

Part 2: Wind loads

First published as part of SAA Int. 3501952.Revised and redesignated AS CA 34.21971.Revised and redesignated AS 1170.2 1973.Second edition 1975.Third edition 1981.Fourth edition 1983.Fifth edition 1989.

Incorporating:Amdt 1 1991Amdt 2 1993Amdt 3 1993

PUBLISHED BY STANDARDS AUSTRALIA(STANDARDS ASSOCIATION OF AUSTRALIA)1 THE CRESCENT, HOMEBUSH, NSW 2140

ISBN 0 7262 5485 1Accessedb

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AS 1170.21989 2

PREFACE

This Standard was prepared by the Standards Australia Commit tee for Loading on Structuresto 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 instructural design, and is in a limit states format.

It provides a simplified procedure (Section 2) for the determination of wind loads on alimited 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 lesssensitive to wind action, to those for which dynamic response must be taken intoconsideration. It permits wind tunnel tests or similar determinations of wind loads onstructures.

Explanatory material for this Standard are given in Appendices C to F, which correspond toSections 1 to 4.

The Standards Australia Committee has considered exhaustive research and testinginformation from Australian and overseas sources in the preparation of this Standard with aview to reducing the design wind loads by the maximum extent consistent with safety. Thedesign wind loads prescribed in this Standard are the minimum for the general cases. Thesewill be circumstances arising in particular cases, which will result in additional loadsrequiring to be taken note of in the design of structures in those cases. Designers must bealert to the conditions to which their particular structure is exposed and must take note of allthe 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/stabilitylimit 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 areslightly 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 havebeen added. Existing data on pressure and force coefficients have been revised in thelight of recent research.

(g) Dynamic analysis has been expanded (replaces Annex: Notes on Wind Forces on TallBuildings 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 tobe requirements of this Standard.

Notwithstanding the general copyright provisions applicable to all Australian Standards asdetailed below, this Standard contains intellectual material provided by another party and

permission to reproduce that material may be conditional on an appropriate royalty paymentto Standards Australia, or the other party, or both. Details of the clauses applicable and theright to reproduce them either in printed or electronic form can be obtained from the HeadOffice of Standards Australia.

Copyright STANDARDS AUSTRALIA

Users of Standards are reminded that copyright subsists in all Standards Australia publications and software. Except where theCopyright Act allows and except where provided for below no publications or software produced by Standards Australia may bereproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in writing fromStandards Australia. Permission may be conditional on an appropriate royalty payment. Requests for permission and information oncommercial 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 useexclusively 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 theStandard 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 incommercial contracts is subject to the payment of a royalty. This policy may be varied by Standards Australia at any time.

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3 AS 1170.21989

CONTENTS

PageSECTION 1. SCOPE AND APPLICATION

1.1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.2 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.3 DESIGN PROCEDURESSIMPLIFIED OR DETAILED . . . . . . . . . . . 4

1.4 DESIGN REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5 DETERMINATION OF WIND LOADS . . . . . . . . . . . . . . . . . . . . . . . . 4

1.6 DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.7 NOTATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

SECTION 2. SIMPLIFIED PROCEDURE

2.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2 LIMITATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.3 PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.4 BASIC PRESSURES (p) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.5 MULTIPLYING FACTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.6 FATIGUE LOADING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.7 SERVICEABILITY DESIGN LOADS . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.8 FARM BUILDINGS AND TEMPORARY STRUCTURES . . . . . . . . . . . 17

SECTION 3. DETAILED PROCEDURE: STATIC ANALYSIS

3.1 LIMITATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2 GUST WIND SPEED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.3 DYNAMIC WIND PRESSURE (qz ) . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.4 FORCES (F) AND PRESSURES (pz) ON ENCLOSED BUILDINGS,FREE ROOFS AND WALLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.5 FORCES ON EXPOSED STRUCTURAL MEMBERS . . . . . . . . . . . . . . 33

3.6 FATIGUE LOADING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

SECTION 4. DETAILED PROCEDURE: DYNAMIC ANALYSIS

4.1 APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.2 HOURLY MEAN WIND SPEED . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.3 DYNAMIC WIND PRESSURE (qz) . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4.4 PROCEDURE AND DERIVATION . . . . . . . . . . . . . . . . . . . . . . . . . . 42

APPENDICES

A ADDITIONAL PRESSURE COEFFICIENTS . . . . . . . . . . . . . . . . . . . . . 48

B SECTIONAL DRAG FORCE AND FORCE COEFFICIENTS ANDASPECT RATIO CORRECTION FACTORS . . . . . . . . . . . . . . . . . . . . . . 53

C EXPLANATORY MATERIAL TO SECTION 1 . . . . . . . . . . . . . . . . . . . 59

D EXPLANATORY MATERIAL TO SECTION 2 . . . . . . . . . . . . . . . . . . . 61

E EXPLANATORY MATERIAL TO SECTION 3 . . . . . . . . . . . . . . . . . . . 62

F EXPLANATORY MATERIAL TO SECTION 4 . . . . . . . . . . . . . . . . . . . 77

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

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AS 1170.21989 4

STANDARDS AUSTRALIA

Australian StandardMinimum design loads on structures

Part 2: Wind loads

SECTION 1. SCOPE AND APPLICATION

1.1 SCOPE. This Standard sets out procedures fordetermining design wind speeds and wind loads to beused in structural design of all buildings andcomponents of buildings, bridges (minimum designwind speed only), and other structures subjected towind.

For bridges, the design wind loads shall be

determined in accordance with the AUSTROADSBridge Design Code.

Major offshore structures remote from the coast andtransmission lines are not covered, nor are the effectsof tornadoes which are special-event winds.

The design wind loads for structures containing highrisk contaminants, such as some nuclear or biologicalmaterials is considered outside the scope of thisStandard.

This Standard does not attempt to account forpossible future climatic changes.

1.2 APPLICATION. This Standard applies tostructures, other than bridges, designed to Australian

Standards using both limit state and permissible st ressdesign rules.

1.3 DESIGN PROCEDURES SIMPLIFIED ORDETAILED.

1.3.1 Simplified procedure. For the determinationof wind loads on a limited range of small buildingsand structures, including domestic buildings, asimplified procedure is given in Section 2 withlimitations given in Clause 2.2. Simplified anddetailed 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 awide range of structures, detailed procedures aregiven in Section 3 (Static analysis) and Section 4(Dynamic analysis). These structures vary from thoseless sensitive to wind action to those in whichdynamic response must be taken into consideration.The dynamic analysis shall be undertaken for thecalculation of overall forces for any structure withboth a height-(or length)-to-breadth ratio greaterthan five and the first mode frequency is less than1 Hz.

(See Paragraph C1.3.2 of Appendix C.)

1.4 DESIGN REQUIREMENTS.

1.4.1 General. Wind loads associated with any limitstate or permissible stress design requirement, whichis relevant to the safe and proper functioning of the

structure or its components, shall be determined fromthe appropriate clauses in this Standard.

1.4.2 Stability limit state. Wind loads acting aloneor in combination with other loads, which causefailure or overturning of the structure as a whole,uplift or sliding, shall be calculated using ultimatelimit states design wind speeds (Vu).

1.4.3 Strength limit state. Wind loads acting on astructure and its components, which are required tobe withstood without failure during the life of thestructure, shall be calculated using ultimate limitstates design wind speeds (Vu).

1.4.4 Ultimate limit states. For the purpose of thisStandard, stability and strength limit states aretogether called ultimate limit states.

1.4.5 Serviceability limit state. Serviceability limitstate wind speeds (Vs) are given to calculate windloads acting on a structure and its components forserviceability limit states, such as excessivedeflection, cracking and vibration.

1.4.6 Permissible stress design procedure. Wherean Australian Standard has adopted a permissiblestress design procedure, the wind loads acting on astructure or its components shall be calculated usingpermissible stress design wind speeds (Vp).

(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 shallbe determined by one or more of the following:

(a) The applicable clauses of this Standard.

(b) Reliable references used consistently with theclauses of this Standard.

(c) Reliable data on wind speed and direction. Theuse of uncorrected anemometer data is notpermitted.

(d) As an alternative to the methods outlined inClauses 3.2.3 and 4.2.3, the use of a detailedprobability analysis for the effects of winddirection is allowed.

(e) Wind tunnel or similar tests carried out for aspecific structure or reference to such tests on asimilar 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 fluidother than air, shall be considered properly conductedonly if the natural wind has been modelled for theappropriate terrain categories to take account of

(a) the variation of wind speed with height; and

(b) the scale and intensity of the longitudinalcomponent of turbulence.

Notice shall be taken of

(i) the effects of Reynolds number where curvedshapes are involved;

(ii) the appropriate frequency response of force andpressure measuring systems; and

(iii) scaling of mass, length, stiffness, and damping,where measurements of dynamic response areinvolved.

(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 aspecific structure have been carried out, or whenreference to such tests on a similar structure is used,the loads thus determined shall be used instead ofthose determined through the provisions of thisStandard.

1.6 DEFINITIONS. For the purpose of thisStandard, the definitions below apply.

Awnings a roof-like structure, usually of limitedextent, projecting from a wall o f a building.

Canopy a roof adjacent to or attached to abuilding, generally not enclosed by walls.

Cladding the material which forms the externalsurface over the framing of an element of a buildingor structure.

Dominant opening an opening in the externalsurface of an enclosed building which directlyinfluences the average internal pressure in response toexternal pressures at that particular opening.Dominant openings need not be large.

Drag a force acting in the direction of thewindstream.

Enclosed buildings buildings which have fullperimeter walls (nominally sealed) from floor to rooflevel.

Escarpment a long (steeply sloping) face betweennominally level lower and upper plains with averageslopes of not greater than 5%.

Force coefficient a coefficient which whenmultiplied by the incident wind pressure and anappropriate area (defined in the text), gives the forcein a specific direction.

Free roof a roof (of any type) with no enclosingwalls underneath, e.g. freestanding carport.

Freestanding walls walls which are exposed tothe wind on both sides, with no roof attached, e.g.fences.

Freestream dynamic pressure the theoretically

computed incident pressure of a unifo rm air stream ofknown density q = 0.0006 x V2 (at ambienttemperature and barometric pressure).

Gable roof a ridged roof with end walls triangularfrom lowest points up to the ridge.

Hip roof a traditional roof with sloping ridgesrising up from external corners (valleys rise up fromany return corners).

Hoardings free standing (rectangular) signboards,etc, supported clear of the ground.

Immediate supports (cladding) those supportingmembers to which cladding is directly fixed (e.g.battens, purlins, girts, studs).

Lattice towers three-dimensional frameworkscomprising three or more linear boundary membersinterconnected by linear bracing members joined atcommon points (nodes), enclosing an open areathrough which the wind may pass.

Lift a force acting at 90to the windstream.Major offshore structures major navigationstructures, drilling platforms and major structures onsmall islands, reefs or shoals.

Monoslope roof a planar roof with no ridge,which has a constant slope.

Obstructions natural or man-made objects whichgenerate turbulent windflow, ranging from singletrees to forests and from isolated small structures toclosely spaced multi-storey buildings.

Permeability an aggregation of small openingsand cracks etc, which allows air to pass through wallsor roofs etc, under the action of a pressuredifferential.

Pitched roof a bi-fold, bi-planar roof with a ridgeat 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, positi ve valuesexceed ambient. Net pressures act normal to a surfacein the direction specified within the text.

Pressure coefficient the ratio of the averagepressure acting at the point on a surface, to thefreestream pressure of the incident wind.

Reliable data (wind speeds and directions) it isthe professional responsibility of the user to assessdata 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 chainof hills which have a nearly linear apex, with slopingfaces on either side of the crest.

Roughness length a theoretical quantification ofthe (wind) turbulence inducing nature of a particulartype of terrain.

Sufficient (meteorological information) theassessment of an appropriately qualified andexperienced professional.

Terrain the surface roughness condition whenconsidering the size and arrangement of obstructionsto the wind.

Topography major land surface featurescomprising hills, valleys and plains which stronglyinfluence wind flow patterns.

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Tornado a violently rotating column of air,pendant from the base of a convective cloud, andoften observable as a funnel cloud attached to thecloud base.

Tributary area the area of building surfacecontributing to the force being considered.

Tropical cyclone an intense low-pressure centreaccompanied by heavy rain and gale-force winds orgreater. It forms over warm tropical oceans anddecays rapidly over land. In the southern hemisphere,winds spiral clockwise into the centre.

Troughed roof a bi-fold, bi-planar roof with avalley at its lowest point.

1.7 NOTATION. Unless a contrary intention isstated, the notation used in this Standard shall havethe following meanings with respect to a structure, ormember, or condition to which a Clause is applied.

The SI system of units is used throughout.A = the surface area of the element or thetributary area which transmits wind forcesto the element

Ar = the gross plan area of the roof includingeaves, canopies, awnings etc

Az = the area of a s truc ture or a part of astructure, at heightz, upon which the designwind pressure (pz) operates, being

(a) when used in conjunction with thepressure coefficient (Cp), the area uponwhich the pressure acts, which may notalways be normal to the windstream;

(b) when used in conjunction with a dragforce coefficient (Cd), the projected areanormal to the windstream; and

(c) when used in conjunction with a forcecoefficient, (CF,x) or (CF,y), the areas asdefined in applicable clauses.

a = the dimension used in defining the extent ofapplication of local pressure factors

B = a background factor, which is a measure ofthe slowly varying background componentof the fluctuating response caused by thelower frequency wind speed variations

B1 = a regional multiplying factor

B2 = a terrain and height multiplying factorB3 = a topographic multiplying factor

B4 = an area reduction factor for roofs

b = the horizontal breadth of a vertical structurenormal to the windstream; or the averagebreadth of a vertically tapered structure overthe top half of the structure; or the nominalaverage breadth of a horizontal structure; orthe 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 ormember in the direction of the windstream

= Fd

Azq

z

CF,x = the force coefficient for a structure ormember, in the direction of the members

x-axis

=F

x

Azq

z

CF,y = the force coefficient for a structure ormember, in the direction of the members

y-axis

=F

y

Azq

z

Cf = a frictional drag force coefficient

Cfs = the cross-wind force spectrum coefficientgeneralized for a linear mode

Cp = a pressure coefficient

Cp,c = a pressure coefficient for the windward edgeof a roof supported by a cantilevered beam

Cp,e = an external pressure coefficient

Cp,i = an internal pressure coefficient

Cp,l = a net pressure coefficient for the leewardhalf of a free roof

Cp,n = a net pressure coefficient for canopies, freestanding roofs, walls, etc

Cp,w = a net pressure coefficient for the windwardhalf of a free roof

Cp1 = an external pressure coefficient for a bin,silo or tank o f unit aspect ratio

c = the net height of a hoarding, bin, silo ortank

D = a building spacing parameter

d = the minimum roof plan dimension or, thedepth or distance to which the plan orcross-section of a structure or shape extendsparallel to the wind stream

da = the along-wind depth of a porous wall orroof surface

E = a spectrum of turbulence in the approachwindstream; or the modulus of elasticity

e = the base of Napierian log arit hms(2.71828)

F = the wind force acting normal to the surfaceof a building element

Fd = the drag force acting parallel to the wind

stream

= the hourly mean drag force acting parallel toFd

the windstream

Ff = the resultant frictional force acting parallelto the windstream

Fx = the wind force component resolved alongthe x-axis of a body

Fy = the wind force component resolved alongthe y-axis of a body

= the hourly mean net horizontal force actingFz

on a building or structure at heightz

f = a friction stress

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G = a gust factor

gf = a peak factor (fluctuating response)

gv = a peak factor for the upwind velocityfluctuation

H = the height of a hill, ridge or escarpment

h = the height of a structure above ground

hc = the height from ground to the attachedcanopy, etc

he = the eaves height of building

hi = the developed height of the inner layer,which is equal to z for the calculation ofx i

hs = the average height of shielding buildings

ht = the height to the top of a structure aboveground

I = the second moment of area

Ka = an area reduction factor

Kar = an aspect ra tio correction factor for

individual member forcesKi = a factor to account fo r the angle o f

inclination of the axis of members to thewind direction

Kl = a local pressure factor

Kp = a reduction factor for porous cladding

Ksh = a shielding factor for multiple open frames

Kt = a type factor for topography

k = a mode shape power exponent

kc = a multiplier for Cp,e(on circular tanks, binsand silos)

Lh = a measure of the effective turbulence length

scaleLu = the horizontal distance upwind from the

crest of a hill, ridge or escarpment to a levelhalf the height below the crest

L* = the effective horizontal length of the upwindslope of a hill, ridge or escarpment

l = the length of a frame member; or the lengthof a cantilevered roof beam

ls = the average spacing of shielding buildings

Ma = the along-wind base overturning moment

Ma = the mean base overturning moment for astructure in the along-wind direction

M^a = the design peak base overturning moment

for a structure in the along-wind directionMc = the cross-wind base overturning moment

Mc = the mean base overturning moment for astructure in the cross-wind direction

M^c = the design peak base overturning momentfor a structure in the cross-wind direction

Mi = a structure importance multiplier

Mo = the upstream terrain category gust windspeed multiplier at the beginning of eachnew terrain inner layer for height z

Mo = the upstream terrain category hourly meanwind speed multiplier at the beginning ofeach new terrain inner layer for height z

MR = the resultant vector base overturningmoment

M^R = the peak resultant vector baseoverturning moment

Ms = a shielding multiplier for both gust andhourly mean wind speeds

Mt = a topographic multiplier for gust wind

speedsMt = a topographic multiplier for hourly mean

wind speeds

Mx = the gust wind speed multiplier at adistance xfrom the start of new terraincategory for heightz

Mx = the hourly mean wind speed multiplierat a distance x from the start of the newterrain category for height z

M(z,cat) = a gust wind speed multiplier for aterrain category at height z(for upwinddistance of at least (2500 + x i) m)

M(z,cat) = an hourly mean wind speed multiplier

for a terrain category at height z (forupwind distance of at least (1500 +

xi) m)

M = a component of the base overturningmoment acting in the direction

m = the mass per unit length

mo = the average mass per unit height of astructure

N = an effective reduced frequency

n = the number of spans of a multi-spanroof; or the first mode frequency of astructure

na

= the first mode frequency of a structurein along-wind d irection

nc = the first mode frequency of a structurein cross-wind direction

ns = the number of upwind shieldingbuildings within a 45 sector of radius20ht

pc = the maximum design wind pressure atthe leading edge of a roof supported bya cantilevered beam

pd = the ultimate limit state design windpressure

pe = the external wind pressure

pi = the internal wind pressurepn = the net wind pressure

pz = the design wind pressure at heightz

p = the net basic wind pressure

qh = the free stream gust dynamic windpressure at the top of a structure

qh = the free stream hourly mean dynamicwind pressure at height h

qz = the free stream gust dynamic windpressure resulting from Vz

qz = the free stream hourly mean dynamicwind pressure resulting from Vz

R = the return period

Re = the Reynolds number

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r = the corner radius of a structural shape,or a roughness factor, or the rise of acurved roof

S = a size factor

Sr = the Strouhal number

s = a position factor for topographic effectsu* = the friction velocity

V = the basic wind speed

V = the hourly mean wind speed

Vcrit = the critical wind speed, for Lock-in

Vh = the design gust wind speed at heighth

Vh = the design hourly mean wind speed atheight h

Vp = the basic wind speed for permissiblestress methods

Vs = the basic wind speed for serviceabilitylimit state

Vu = the basic wind speed for ultimatestrength limit state

Vz = the design gust wind speed at heightz

Vz = the design hourly mean wind speed atheight z

w = a factor to account for the second ordereffects of turbulence intensity

wc = the width of canopy, etc, from the faceof the building

x = the distance downwind from a change interrain category to the structure underconsideration; or the horizontal distancefrom a structure to the crest of a hill or

a ridgex = the mean value of random variables

x = the peak value of random variables

xi = the distance downstream from the startof the new terrain roughness to thedeveloped height of the inner layer (h i)

= the peak acceleration at the top of astructure in cross-wind direction

z = the distance or height above the ground;or the effective height of an escarpment

zg = the gradient height, at which terraininfluence ceases

zo = a characteristic terrain roughness length

z1, z2 = the effective heights of a hill, on eachside of it

zo,r = the larger of the two roughness lengths,at the change in terrain

= the angle of s lope of a roof; or thedirection of a resultant vector baseoverturning moment with respect to thealong-wind direction

max = the angle to the along-wind direction ofthe plane of the maximum resultantvector base overturning moment

= the fractional porosity of a wall; or theangle from the wind direction to a pointon the wall of a circular bin, silo or tank

= the actual solidity ratio for an openframe

e = the effective solidity ratio for an openframe

a = a structural load effect derived from themean along-wind dynamic response

= a structural load effect derived from thec

mean cross-wind dynamic response

c = a structural load effect derived from thepeak c ross -wind response, andproportional to the peak cross-wind baseoverturning moment M^c

t = the total combined peak load scalareffect

= a fraction of the cri tical dampingcapacity of a structure

= a multiplier, used to calculatev

=

= the angle of deviation of the windstream from the axis of a structuralsection

= a spacing ratio for open frames

= the kinematic viscosity = the atmospheric density

v = the standard deviation of a wind gustcomponent

v/Vz = the turbulence intensity in the approachflow at height z

x = the standard deviation of a set of valuesof variable x

o = the surface friction shear stress

= the upwind slope of a hill, ridge orescarpment or the angle between thewindstream and the plane of a structuralmember

d = the average downwind slope measuredfrom the crest of a hil l, r idge orescarpment to the ground level at adistance of 5H

= the lesser value ofor 0.3(z) = a mode shape

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SECTION 2. SIMPLIFIED PROCEDURE

2.1 INTRODUCTION. This Section sets out asimplified procedure for the determination of windloads on a limited range of small buildings andstructures, which satisfy the limitations set out in

Clause 2.2.This Section must not be used in conjunction withother sections of this Standard except where specificreference to other sections is made (see Clause 1.3.1).

The loads specified in this Section are ultimatestrength limit state design wind loads.

If loads are required for permissible stress design, theultimate strength loads given in this Section shall bedivided by 1.5.

If loads are required for serviceability limit statedesign, the ultimate strength loads specified in thisSection 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 shallonly be applied to the determination of wind loads onbuildings, their attachments, and miscellaneousstructures which satisfy all of the relevant f ollowingconditions:

(a) The overall height does not exceed 15.0 m.

(b) The buildings are rectangular in plan, or acombination of rectangular units.

(c) The roof pitch of buildings does not exceed 30.

(d) The ratio of the height (ht) to the minimum roofplan dimension (d) is less than five for enclosedbuildings, and less than one for free standingroofs.

(e) The gross roof plan area of buildings does notexceed 1000 m2.

(f) The consequences of failure of t he building insocial and economic terms is not high relative tothat normally associated with small buildings.Structures that have special post-disasterfunctions, e.g. hospitals and communicationsbuildings, shall not be designed using thisSection.

The minimum roof plan dimension of a building isthe minimum width of the roof in plan (seeFigure 2.2(A)).

The height (ht) is the height from the lowest point atground level to the highest point of the structure (seeFigure 2.2(B)).

The gross roof plan area of buildings is the total areaof the roof in plan, including any attached canopies,awnings, carports, etc.

FIGURE 2.2(A) MINIMUM PLAN DIMENSION (d) FOR DIFFERENT ROOF PLANS

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2.3 PROCEDURE.

2.3.1 General. The ultimate limit state design windpressures (pd) shall be obtained by multiplying the netbasic wind pressures (p) given in Clause 2.4 by theappropriate multiplying factors given in Clause 2.5,using Equation 2.3.1.

pd = pB1B2B3B4 . . . . . . . . . . . . . . (2.3.1)where

pd = the ultimate limit state design windpressure, in kilopascals

p = the net basic wind p ressure, inkilopascals

B1 = a regional multiplying factor (seeTable 2.5.1)

B2 = a terrain and height multiplying factor(see Table 2.5.2)

B3 = a topographic multiplying factor (seeTable 2.5.3)

B4 = an area reduction factor for externalpressures on roofs (see Table 2.5.4).

The net basic wind pressure (p) shall be the worstcase of combined internal and external basicpressures, or windward and leeward basic wallpressures, as appropriate. In combining external andinternal basic pressures, the worst combination of thebasic pressures prescribed within the limits given inthis Section shall be used. Where only one limit ofbasic pressure is given, it shall be assumed that theother limit is zero.

2.3.2 Forces (F) on elements of buildings. Thewind force (F) due to wind pressure acting on anelement of a structure shall be calculated fromEquation 2.3.2.

F = pdA . . . . . . . . . . . . . . . . . . . (2.3.2)

where

F = the wind force acting normal to thesurface of a building element

pd = the ultimate limit state design windpressure, in kilopascals

A = the surface area of the element or thetributary area which transmits windforces to the element, in square metres.

Resultant forces on complete buildings shall becomputed 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 onbuildings are a function of the location of thebuilding, the direction of the wind relative to theorientation of the building, and the geometry of thebuilding.

The geometry of the building is defined in terms ofthe windward roof slope in the direction of the windand the following factors:

(a) ht = the height of the building, as described inClause 2.2.

(b) d = the minimum roof plan dimension in thedirection of the wind (see Figure 2.4.1.1).

2.4.1.2 Windward sections of roofs. For thewindward sections of roofs the basic pressures givenin Table 2.4.1.2 shall be used.

TABLE 2.4.1.2EXTERNAL BASIC PRESSURES FORWINDWARD SECTIONS OF ROOFS

Windward

roof slope

()

degrees

Basic pressure, kPa

max .neg . max .pos. max .neg . max . pos.

1015

20

25

30

-0.95

-0.75

-0.45

-0.35

-0.25

0

0

0.25

0.35

0.35

-1.4

-1.1

-0.75

-0.55

-0.35

0

0

0

0

0.25

NOTE: For intermediate values of and ht/d, l inearinterpolation is permitted.

The windward section of the roof is the windwardhalf of the roof, or the section windward of thehighest horizontal ridge at right angles to the winddirection where such ridges are present.

Where the windward roof slope varies, the basicpressures used in the design vary according to theroof slope in the direction of the wind, otherwise theminimum roof slope in the direction of the wind onthe windward section of the roof shall be used fornegative pressures, and the maximum roof pitch shallbe used for positive pressures.

The basic pressures given in Table 2.4.1.2 shall beassumed to act over the whole of enclosed monosloperoofs, and over all of the area of roofs having slopesin the direction of the wind which are nominally zero.

2.4.1.3 Leeward sections of roofs. For the leewardsections of roofs the basic pressures given inTable 2.4.1.3 shall be used.

TABLE 2.4.1.3EXTERNAL BASIC PRESSURES FOR

LEEWARD SECTIONS OF ROOFS

Leeward roof slope ()

degrees

Basic pressure, kPa

1520

-0.55

-0.65

-0.75

-0.65

NOTE: For intermediate values of and ht/d, l inearinterpolation is permitted.

2.4.1.4 Walls and undersides of eaves. For walls andundersides of eaves, the basic pressures given inTable 2.4.1.4 shall be used.

TABLE 2.4.1.4EXTERNAL BASIC PRESSURES FOR WALLS

AND UNDERSIDES OF EAVES

Location Basic pressure, kPa

Windward:

(a) normal building

(b) highset building

Leeward

Side

0.75

0.85

-0.55

-0.7

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NOTE: 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

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A highset building is an elevated building with aclear, unwalled space underneath the first floor level,with a height from ground to underside of floor of atleast one third of the total height of the building.

For the design of unenclosed eaves, the use of netbasic pressures obtained from Clauses 2.4.3.2 and

2.4.3.3 is permitted.

2.4.1.5 Local negative external pressures. Claddingand its immediate supports within 0.2Ar of edges,corners, ridges, etc, shall also be designed for theexternal local basic pressures given in Table 2.4.1.5,where Aris the gross plan area of the roof includingattached canopies, awnings, etc.

TABLE 2.4.1.5BASIC LOCAL NEGATIVE EXTERNALPRESSURES FOR CLADDING AND ITS

IMMEDIATE SUPPORTS

Location Tributary area (A)m2

Basic pressure, kPa

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 forcebeing considered. For example, the tributary area fora cladding fastener will be the area of claddingsupported by a single fastener; for a purlin it will bethe span between supporting rafters times the distancebetween purlins.

2.4.1.6 Local positive external pressures. Wallelements with tributary areas less than 0.01A r, asdefined in Clause 2.4.1.5, shall be designed for thefollowing basic local positive external pressures:

(a) For normal buildings: 0.9 kPa.

(b) For highset buildings: 1.05 kPa.

For definit ion 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 floorbasic pressures of 0.85 kPa and - 0.65 kPa.

2.4.2 Internal pressures. Both cladding andstructure shall be designed for the internal basicpressures given i n Table 2 .4.2.

TABLE 2.4.2INTERNAL BASIC PRESSURES

Openings

Basic pressure, kPa

max. ne g. max. pos.

No dominant openings

Dominant openings:

(a) Normal building

(b) Highset building

-0.35

-0.7

-0.7

0.25

0.75

0.85

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

wall exceeds 4 times the sum of the permanentopenings in other walls and the roof.

In tropical cyclone-prone regions C and D, as definedin Clause 2.5.1, internal pressures based on dominantopenings shall be used for calculating both ultimatestrength and permissible stress design loads unless

windows are protected against impact of debris byscreens or shutters capable of resisting a 4 kg pieceof timber of 100 mm 50 mm cross-section strikingthem at any angle at a speed of 15.0 m/s. Thisrequirement does not apply to the calculation ofserviceability design loads.

For definition of high set bui ldings, seeClause 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 5and attached to buildings satisfying the limitations in

Clause 2.2, shall be designed using the basicpressures given in Clauses 2.4.3.2 and 2.4.3.3. Forthe design of unenclosed eaves, the use of net basicpressures given in these Clauses is also permitted.

2.4.3.2 Main structural components. The mainstructural components shall be designed for the netbasic pressures given in Table 2.4.3.2 acting on theroof.

TABLE 2.4.3.2NET BASIC PRESSURES (p ) FOR

UNENCLOSED CANOPIES, AWNINGS,CARPORTS AND EAVES

Net basic pressure (p), kPa

Upwards

Downwards

1 2 5

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TABLE 2.4.3.3LOCAL NET BASIC PRESSURES (p ) ON

ROOF CLADDING OF CANOPIES, ETC

Tributary area

(A)

m2

Net basic pressure (p), kPa

Upwards

Downwards

5

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FIGURE 2.5.1 MAP OF AUSTRALIA SHOWING BOUNDARIES OF REGIONS

FOR THE CHOICE OF REGIONAL MULTIPLYING FACTOR (B1)

(see Paragraph D2.5.1 of Appendix D)

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2.5.2 Terrain and height multiplying factor (B2).To account for the surrounding terrain and the heightof the building, the terrain and height multiplyingfactors (B2) given in Table 2.5.2 shall be used.

TABLE 2.5.2TERRAIN AND HEIGHT MULTIPLYING

FACTORS (B2)

NOTE: For intermediate values of ht, linear interpolation is

Building

Height

(ht)

m

Factors (B2)

Suburban Open rural terrain

Exposed Sheltered Regions A and B Regions C and D

47

10

15

0.85

0.90

1.00

1.15

0.55

0.60

0.65

0.75

1.15

1.30

1.45

1.60

1.10

1.20

1.30

1.45

permitted.

The height (ht) of the structure or building shall beused when selecting (B2) factors for componentssituated lower on the structures.

Open rural terrain refers to isolated structures indesignated rural areas, and buildings on the edge ofdesignated rural areas or adjacent to the sea or otherlarge expanses of water.

Suburban terrain refers to buildings within designatedurban areas and at least 500 m from the edge ofdesignated rural areas in the case of buildings ofoverall height less than 10 m, and at least 2500 mfrom the edge of designated rural areas in the case ofbuildings of overall height equal to or greaterthan 10 m.

Within suburban terrain, buildi ngs shall be classed assheltered if surrounded to a depth of at least two rowsby buildings of similar or greater height and size atan average density of not less than 10 buildings perhectare; and classed as exposed if adjacent to areas inwhich the average density of buildings of similar orgreater height and size is less than 2.5 buildings per

hectare.

For intermediate densities of buildings and within thetransition region between suburban terrain anddesignated rural areas, linear interpolation of valuesof B2is permitted.

2.5.3 Topographic multiplying factor (B3). Wherestructures are located on the upper levels of hills andridges or near the edges of escarpments, thetopographic multiplying factors (B3) given inTable 2.5.3 shall be applied.

TABLE 2.5.3TOPOGRAPHIC MULTIPLYING FACTORS

(B3)

Topographic

features

Maximum

incline

Lo ca tion Fa ct or s

(B3)

Escarpment

Escarpment

Hill or ridge

Hill or ridge

< 1 in 7.5

< 1 in 15

< 1 in 7.5

< 1 in 10

J

T

J

T

1.0

Escarpment

Escarpment

Hill or ridge

Hill or ridge

1 in 41 in 7.5

1 in 4

1 in 7.5

J

T

J

T

1.3

Escarpment

Hill or ridge

Hill or ridge

1 in 41 in 3

1 in 5

T

J

T

1.6

Hill or ridge

Hill or ridge

> 1 in 1.5

1 in 2

J

T

2.0

Hill or ridge 1 in 1.5 T 2.4

NOTES:

1. The maximum incline is the maximum slope of the hillsidein terms of the average slope over a change in elevation of20% of the effective height of the hill.

2. The effective height is the height of the hill above thegeneral level of the adjacent terrain. In Figure 2.5.3(a),z1and z2 are the effective heights of the hill (in metres), oneach side of it. In Figure 2.5.3(b), zis the effective height ofthe escarpment (in metres).

3. Locations T and J are defined in Figure 2.5.3.

4. For topographic features with effective heights of less than10 m in open rural terrain and 25 m in suburban terrain, it is

permitted to take the topographic multiplying factor (B3)equal to 1 for buildings and their attachments.

5. The topographic multiplying factor (B3) for locations otherthan T and J is equal to 1.

6. For intermediate values of average upwind slopes, linearinterpolation is permitted.

2.5.4 Roof reduction factor (B4). The external windforces on major roof supporting structures, excludingcladding and its immediate supporting members, shallbe multiplied by the roof reduction factor (B4) givenin Table 2.5.4.

TABLE 2.5.4ROOF REDUCTION FACTORS (B4)

NOTES:

Tributary area (A)

m2Factor (B4)

1025

100

1.0

0.9

0.8

1. For intermediate values of tributary area (A), linearinterpolation is permitted.

2. For definition of tributary area, see Clause 2.4.1.5.

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2.6 FATIGUE LOADING. In tropical cycloneregions C and D, as shown in Figure 2.5.1, claddingand its connections shall be designed to resist thefatigue loading sequence given in Table 2.6.

(See Paragraph D2.6 of Appendix D.)

TABLE 2.6

FATIGUE LOADING SEQUENCE

LEGEND:

Range Number of cycles

0 to 0.4pd0 to 0.5pd0 to 0.6pd0 to 1.0pd

8 000

2 000

200

1

pd = the ul timate l imit s ta te design wind pressure , asspecified in Clause 2.3.

NOTE: These requirements will normally be met by testingthree samples each of which should pass. If only one sampleis tested, the final cycle should be increased to 1.3pd, and iftwo samples are tested, it should be increased to 1.2pd.

2.7 SERVICEABILITY DESIGN LOADS. Whereserviceability design loads are required, they shall beobtained by multiplying the ultimate limit state designloads by the multiplying factors given in Table 2.7.

TABLE 2.7

SERVICEABILITY MULTIPLYING FACTORS

Region

Serviceability

multiplying factor

ANormal

BIntermediate

CTropical cyclone

DSevere tropical cyclone

0.6

0.4

0.4

0.35

2.8 FARM BUILDINGS AND TEMPORARYSTRUCTURES.

2.8.1 Farm buildings. In the design of structuressuch as farm buildings, which present a low degree ofhazard to life and other property in the case of

failure, the calculated forces on the structure obtainedfrom Clauses 2.4 to 2.7 may be multiplied by 0.8.

2.8.2 Temporary structures. Where the structure isof a temporary nature and is to be erected for aperiod of less than 6 months, the calculated forces onthe structure obtained from Clauses 2.4 to 2.7 may bemultiplied by 0.65.

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SECTION 3. DETAILED PROCEDURE:

STATIC ANALYSIS

3.1 LIMITATION. Wind pressures, forces, and

moments on structures and components may becalculated by the static analysis procedure set downin this Section unless the structure is wind sensitive.

A wind sensitive structure or component is defined asone in which additional loads occur as a result of thedynamic interaction of the wind and structure. Thedynamic analysis procedure set down in Section 4shall be used for wind sensitive structures.

The static analysis procedure shall not be used for thedesign of main structural components of any structurehaving both the following properties:

(a) Height or length-to-breadth ratio greater than 5.

(b) A first-mode frequency of vibration of less than1 Hz.

Pressures and forces on parts of walls, roof cladding,canopies, awnings, windows, doors and theirsupporting framework shall be determined using thestatic analysis procedure set out in this Section.

(See Paragraph E3.1 of Appendix E.)

3.2 GUST WIND SPEED.

3.2.1 General. The design gust wind speed (Vz) atheight zshall be used to determine wind loads on astructure or part of a structure with the static analysisprocedure set out in this Section.

3.2.2 Derivation of design gust wind speed (Vz

).The design gust wind speeds (Vz) shall be determinedfrom the appropriate basic wind speed shown inFigure 3.2.2 for the appropriate limit state given byEquation 3.2.2.

Vz = VM(z,cat)MsMtMi . . . . . . . . . . . (3.2.2)

where

Vz = the design gust wind speed at height z,in metres per second

V = the basic wind speed, (Vu), (Vp) and (Vs)(see Figure 3.2.2), in metres per second

M(z,cat) = a gust wind speed multiplier for a

terrain category at height z forupwind di stance o f at l east(2500 + xi) m (see also Clause 3.2.6,Tables 3.2.5.1 and 3.2.5.2)

Ms = a sh ield in g mul ti pl ier ( seeTable 3.2.7)

Mt = a topographic multiplier for gustwind speeds (see Table 3.2.8)

Mi = a structure importance multiplier(see Table 3.2.9).

NOTE: M(z,cat)may change from the tabulated values if thestructure site is within the transition zone near the edge of aterrain boundary (see Clause 3.2.6).

Irrespective of the calculation in this Clause, thedes ign gus t wind speed (Vz), determined byEquation 3.2.2, shall be not less than the following:

(a) Ultimate limit state . . . . . . . . . . . . . . 30 m/s.

(b) Permissible stress method . . . . . . . . 25 m/s.

(See Paragraph E3.2.2 of Appendix E.)

3.2.3 Wind direction. At least four wind directions,equally spaced, shall be considered when calculatingwind loads on structures using the detailed procedure.Where sufficient meteorological information isavailable, the basic wind speed (V) at a site may beadjusted for specific wind directions, in region A for

Vs, Vpand Vu, and in region B for Vs. For some of themajor population centres this is given in Table 3.2.3.

Directional wind speeds shall be corrected for terrain,height, shielding and local topography, as indicated inClause 3.2.2.

Where pressure coefficients or force coefficients andassociated multiplying factors are given for only fourorthogonal directions relative to the major axes of thestructure, the wind speed for any given orthogonaldirection shall be taken to be the largest correcteddirectional wind speed from a 90 sector,symmetrically positioned about the orthogonaldirection being considered.

TABLE 3.2.3BASIC WIND SPEEDS (V) IN (m/s) WITH WIND DIRECTION

FOR SOME OF THE MAJOR POPULATION CENTRES

Winddirection

Adelaide Brisbane Canberra Melbourne Perth Sydney

Vs Vp Vu Vs Vp Vu Vs Vp Vu Vs Vp Vu Vs Vp Vu Vs Vp Vu

NEE

SE

SSWW

NWN

313030

303838

3633

343433

334141

3937

424240

405050

4845

303032

323838

3030

494949

494949

4949

606060

606060

6060

303030

303035

3830

333333

333338

4134

404040

404146

5042

303030

323538

3437

333333

343841

3638

404040

424650

4446

303130

303438

3430

333333

333541

3833

404040

404350

4641

313036

363538

3530

333339

383841

3833

404048

474750

4740

NOTES:1 Wind direction in this Table indicates the directionfromwhich the wind blows.2 For intermediate wind directions, linear interpolation is permitted.

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FIGURE 3.2.2 BOUNDARIES OF REGIONS A, B, C AND D

(see Paragraph E3.2.1 of Appendix E)

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Where pressure coefficients or force coefficients andassociated multiplying factors are given for 8 or 16separate wind directions, they shall be used with thecorresponding corrected sector wind speeds derivedfrom Table 3.2.3.

Where directional wind speed data are not available, or

their use is not allowed (as in tropical cyclone regionsC and D), or for Vpand Vu in intermediate region B(which includes Brisbane), the basic wind speed may bemultiplied by 0.95 for the determination of resultantforces and overturning moments on complete buildingsand major framing elements.

NOTE: A reduction factor of 0.95 should not be usedsimultaneously with values from Table 3.2.3, except for Vpan d

Vuin Brisbane.

As an alternative to the methods outlined in this Clause,a detailed probability analysis to allow for thedirectional effects of wind is permitted.

(See Paragraph E3.2.3 of Appendix E.)

3.2.4 Terrain category. Terrain, over which theapproach wind flows towards a structure, shall beassessed on the basis of the following categorydescriptions (see also Figures E3.2.4(A) to (D) ofAppendix E):

(a) Category 1 exposed open terrain with few or noobstructions and water surfaces atserviceability wind speeds (Vs) only.

(b) Category 2 open terrain, grassland with fewwell scattered obstructions havingheights generally from 1.5 m to10.0 m and water surfaces at windspeeds (Vu) and (Vp).

(c) Category 3 terrain with numerous closelyspaced obstructions having the sizeof domestic houses (3.0 m to 5.0 mhigh).

(d) Category 4 terrain with numerous large, high(10.0 m to 30.0 m high) and closelyspaced obstructions such as largecity centres and well-developedindustrial complexes.

Selection of terrain category shall be made with dueregard to the permanence of the obstructions whichconstitute the surface roughness, in particular vegetationin tropical cyclonic regions shall not be relied upon tomaintain a wooded terrain roughness.

A roughness length (zo) is defined for each terraincategory in Table 3.2.4.

TABLE 3.2.4ROUGHNESS LENGTH (z o)

Terrain category

Roughness length (zo)

metres

1

2

3

4

0.002

0.02

0.2

2.0

(See Paragraph E3.2.4 of Appendix E.)

3.2.5 Terrain and structure height multiplier

(M(z, cat)). The variation of terrain multipliers withheight (z) shall be taken from Tables 3.2.5.1 and3.2.5.2.

Designers shall take account of probable future changesto terrain roughness in assessment of terrain andstructure height multipliers M(z,cat).

TABLE 3.2.5.1TERRAIN AND STRUCTURE HEIGHT

MULTIPLIERS FOR GUST WIND SPEEDS INFULLY DEVELOPED TERRAINSULTIMATE LIMIT STATE AND PERMISSIBLESTRESS DESIGN REGIONS A AND B ONLY

SERVICEABILITY LIMIT STATE DESIGN ALL REGIONS

Height (z)

m

Multiplier (M(z, cat))

TerrainCategory 1

TerrainCategory 2

TerrainCategory 3

TerrainCategory 4

35

10

1520

30405075

100150200

250300400

500

0.991.051.12

1.161.19

1.221.241.251.27

1.291.311.32

1.341.351.37

1.38

0.850.911.00

1.051.08

1.121.161.181.22

1.241.271.29

1.311.321.35

1.37

0.750.750.83

0.890.94

1.001.041.071.12

1.161.211.24

1.271.291.32

1.35

0.750.750.75

0.750.75

0.800.850.900.98

1.031.111.16

1.201.231.28

1.31

TABLE 3.2.5.2TERRAIN AND STRUCTURE HEIGHT

MULTIPLIERS FOR GUST WIND SPEEDS INFULLY DEVELOPED TERRAINS

ULTIMATE LIMIT STATE AND PERMISSIBLESTRESS DESIGN REGIONS C AND D ONLY

Height (z) Multiplier (M(z, cat))

m

Terrain

Categories

1 and 2

Terrain

Categories

3 and 4

35

10

152030

405075

100

0.900.951.00

1.071.131.20

1.251.291.35

1.40

0.800.800.89

0.951.051.15

1.251.291.35

1.40

NOTE TO TABLES 3.2.5.1 AND 3.2.5.2: For intermediate values of

height z and terrain category, interpolation is permitted.

(See Paragraph E3.2.5 of Appendix E.)

3.2.6 Changes in terrain category. The wind speed ata site shall be adjusted for changes in terrain roughnessthrough a correction to the wind speed multiplier(M(z,cat)). There is an upper limit to the developed heightof the inner layer (hi) which is a function of x i, andwhich is independent of whether the flow is from the

rougher terrain or to the rougher terrain. With referenceto Figure 3.2.6 the corrected wind speed multiplier isgiven by Equation 3.2.6(3).

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xi = . . . . . . . . . . . (3.2.6(1))

Conversely:

hi = . . . . . . . . . . . . (3.2.6(2))

For gust wind speeds:

Mx = Mo

for x< x i

Mx = . . . (3.2.6(3))

for 0 < (x- xi) < 2500 m

Mx = M(z,cat)

for (x- xi) > 2500 m

where

xi = the distance downstream, in metres, fromthe s tart of the new terrain to thedeveloped height of the inner layer (h i),given by Equation 3.2.6(1)

zo,r = the larger of the two roughness lengths, inmetres, given in Table 3.2.4, at the changein terrain

hi = the developed height of the inner layer, inmetres, which is equal to z for thec a l c u l a t i o n o f x i , g i v en b yEquation 3.2.6(2)

Mx = the wind speed multiplier at a distance xfrom the start of new terrain category for

height z

Mo = the upstream terrain category gust windspeed multiplier at the beginning ofeach new terrain for height z

M(z,cat) = the downstream terrain category gustwind speed multiplier for each new ter-rain 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, froma change in terrain category to thestructure under consideration

Fully developed gust windspeed multipliersM(z,cat) onlyapply at a structure site when the terrain category at thesite is uniform upstream for a distance greater than(2500 + xi) metres.

When there is terrain of more than one roughness lengthupwind of the structure site, corrected wind speedmul t ip l ie rs (Mx) shall be comput ed u singEquation 3.2.6(3).

The extent of upwind terrain to be considered need notexceed the larger of either 2500 m or 50 times thestructure height (h t), provided that the terrain at that limitis Terrain Category 3 or less rough, (assume thewindspeed multiplier (Mo) to be the value for fullydeveloped terrain at that limit).

If the terrain at that point is rougher than TerrainCategory 3, the upwind limit shall be extended untilTerrain Category 3 or terrain of less roughness isencountered, or alternatively fully developed TerrainCategory 3 may be arbitrarily assumed upwind of thatpoint.

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3.2.7 Shielding multiplier (Ms). Shielding buildingsare those upwind build ings within a 45sector of radius20ht, whose heights are greater than or equal to z.

The shielding multiplier (Ms) is given in Table 3.2.7.Without shielding, Ms= 1.0.

To determine the shielding multiplier (Ms) f romTable 3.2.7, the following procedures shall be used:

(i) Each wind direction being considered shall beassessed for upwind shielding buildings within a45sector of radius 20h t.

(ii) The building spacing parameter (D) in any sectorshall be calculated using Equation 3.2.7(1).

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

where

D = the building spacing parameter

ls = the average spacing of shielding buildings,

in metres

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

hs = the average height of shielding buildings,in metres

bs = the average breadth of shielding buildings,normal to the windstream, in metres

ht = the height to the top of the structure beingshielded, in metres

ns = the number of upwind shielding buildingswithin a 45sector of radius 20h tand withheight h z.

TABLE 3.2.7SHIELDING MULTIPLIER (Ms)

Building spacing

parameter (D)

Shielding multiplier

(Ms)

1.53.0

6.0

12.0

0.70.80.9

1.0

NOTE: For intermediate values ofD , interpolation is permitted.

(See Paragraph E3.2.7 of Appendix E.)

3.2.8 Topographic multiplier (Mt). If the structureunder consideration is located within a local topographiczone, the topographic multiplier (Mt) shall be obtainedby interpolation from the values ofMtat the crest of ahill, ridge or escarpment given in Table 3.2.8 and thevalue of Mt = 1 a t the boundary of the zone.Interpolation shall be linear with horizontal distancefrom the crest, and with height above the local groundlevel.

The local topograph ic zones are shown inFigures 3.2.8.1 and 3.2.8.2.

A topographic multiplier ofMt= 1 shall be used for allsites outside a local topographic zone or if the upwindslope () is less than 0.05.

TABLE 3.2.8TOPOGRAPHIC MULTIPLIER AT CREST

(x = 0) FOR GUST WIND SPEEDS

Upwind slope ()

Topographic multiplier (Mt)

Escarpments

d 0.05

Hills and ridges

d 0.10(see Notes 1 and 2)

0.050.10.2

0.3

1.041.081.161.24

1.091.181.361.54

LEGEND:

= the upwind slope, calculated from =

d = 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 (d) 0.05. A hillor a ridge has a value of downwind slope (d) > 0.05. The valuesgiven in Table 3.2.8 are applicable only to those hills and ridgeswith downwind slope 0.10.

2. For hills and ridges with downwind slope 0.05 < (d) < 0.10,linear interpolation between the Mtvalues for escarpments and,hills and ridges in Table 3.2.8 is permitted.

3. For intermediate values of upwind slope () and downwind slope(d), linear interpolation is permitted.

Mtmay also be obtained by the following methods:

(a) The use of an appropriate equation based uponexperimental and theoretical results, such as thatgiven 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 (Mi). Forspecial structures, the design gust wind speed shall (ormay in the case of reductions) be adjusted with amultiplier (Mi) given in Table 3.2.9.

TABLE 3.2.9STRUCTURE IMPORTANCE

MULTIPLIER (Mi)

Class of structure

Structure

importance

multiplier (Mi)

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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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 anyspecific allowance for the effects of tornadoes. The design windloads for structures containing high risk contaminants such assome 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 gustdynamic wind pressure (qz) at a height z shall becalculated using Equation 3.3.

qz = . . . . . . . . . . . . . . . . (3.3)

where

qz = the f ree s tream gust dynamic wind

pressure at height z , in kilopascalsVz = the design gust wind speed at heightz, in

metres per second.

(See Paragraph E3.3 of Appendix E.)

3.4 FORCES (F) AND P RE SSURES (pz) ONENCLOSED BUILDINGS, FREE ROOFS ANDWALLS.

3.4.1 General. This Clause sets out procedures fordetermining wind pressures, forces and moments on theoverall structures and on components, using the StaticAnalysis.

3.4.1.1 Procedure. Design wind pressures or forcesshall be determined from pressure coefficients multipliedby the basic wind pressure computed from the gust windspeed. The design wind forces and moments on thewhole or part shall be determined from the integration ofpressures.

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3.4.1.2. Forces (F) on building elements. The forces(F) on building elements, such as a wall or a roof, shallbe taken to be the resultant of the pressures acting overthe external and internal surfaces of the element andshall be calculated using Equation 3.4.1.2.

F = pz

Az

. . . . . . . . . . . . . . . . . (3.4.1.2)

where

F = the wind force acting normal to the surfaceof a building element

pz = the design wind pressure at height z, inkilopascals

= (pe - p i) for enclosed buildings or (pn)where net pressure is applicable

Az = the area at heightz, upon which the designwind pressure (pz) operates, in squaremetres

pe = the external pressure determined inaccordance with Clause 3.4.2 and

Appendix A

pi = the internal pressure determined inaccordance with Clause 3.4.7

pn = the net pressure determined in accordancewith Clauses 3.4.9 and 3.4.10

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 completebuildings. The total resultant forces and overturningmoments on a complete building shall be taken to be thesummation of the effects of the pressures on all surfacesof the building.

3.4.2 External pressures (pe). The external windpressure (pe) on a surface of an enclosed structure shallbe calculated using Equation 3.4.2.

pe = Cp,eKaKlKpqz . . . . . . . . . . . . . . (3.4.2)

where

pe = the external wind pressure, in kilopascals

Cp,e = the external pressure coefficient obtainedfrom Tables 3.4.3.1 and 3.4.3.2 forrectangular enclosed buildings, and fromTables A1.1, A1.2, A2 and Paragraph A3of Appendix A, and Figures A4.1 andA4.2 for other shapes

Ka = the area reduction factor for roofs and sidewalls, given in Clause 3.4.4

Kl = the local pressure factor applicable tocladding and immediate supportingstructure only, given in Clause 3.4.5

Kp = the reduction factor for porous cladding,given in Clause 3.4.6

qz = the f ree st ream gust dynamic windpressure at height z , given in Clause 3.3.

Unless stated otherwise, qzshall be taken as qh, whereh is either he or ht, as defined in Clause 3.4.3 orAppendix A.

The building as a whole, the walling, and roofingelements of such buildings or structures shall beassumed to be subject to the most severe possiblecombination of wind forces associated with these

coefficients and, except where shown otherwise, theseforces shall be assumed to be distributed uniformly overthe surface concerned.

Where interaction is possible, these external pressures(pe) shall be assumed to act simultaneously with theinternal pressures (p

i

) given in Clause 3.4.7 and undereaves pressures, which shall be taken as the pressure onthe adjoining wall faces below the surface underconsideration, according to Table 3.4.3.1.

3.4.3 External pressure coefficients (Cp,e) forrectangular enclosed buildings. The external pressurecoefficients for walls and roofs of rectangular enclosedbuildings are given in Tables 3.4.3.1(A)(B)(C) and3.4.3.2(A)(B)(C). The parameters referred to in thesetables are shown in Figure 3.4.3.

In Tables 3.4.3.1(A)(B)(C) and 3.4.3.2(A)(B)(C), theheight hshall be taken as the height to eaves level (he),except for = 0, 60; and= 90, all , where thevalue ofh shall be taken as the height to the top of the

building (ht).The externa l pressure coeff ic ients (Cp,e) fornon-rectangular enclosed buildings are given inAppendix A.

The external pressure coefficient (Cp,e) on the undersideof highset buildings shall be taken as 0.8 and -0.6. Forother buildings elevated above the ground, interpolationbetween these values and 0.0, according to the ratio ofclear unwalled height underneath first floor level to totalbuilding height, is permitted. For the calculation ofunderside external pressures, take qz= qh.

A highset building is an elevated building with a clear,unwalled space underneath the first floor level, with aheight 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 3.4.3.1WALLS: AVERAGE EXTERNAL PRESSURECOEFFICIENTS (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 q z= q h

For all other buildings:0.8, when q zvaries with height

or

0.7, when used with qz= q h

0.8, when q zvaries with height

TABLE 3.4.3.1(B)LEEWARD WALL (L)

Average external pressure coefficient (Cp,e)

= 90, for all = 0, with < 10

= 0

10 15 = 20 2 5

-0.5 -0.3 -0.2 -0.3 -0.4 -0.5

NOTE: For intermediate values ofd/ban d , linear interpolation

is permitted.

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TABLE 3.4.3.1(C)SIDE WALLS (S)

Horizontal

distance from

windward edge

Average external

coefficient (Cp,e)

0 to 1h

1hto 2h

2hto 3h

> 3h

-0.65

-0.5

-0.3

-0.2

NOTE: For the leeward and sidewalls, qz shall be taken as

qhin all cases.

TABLE 3.4.3.2ROOFS: AVERAGE EXTERNAL PRESSURECOEFFICIENTS (Cp,e) FOR RECTANGULAR

ENCLOSED BUILDINGS

TABLE 3.4.3.2(A)UPWIND SLOPE (U) ANDDOWNWIND SLOPE (D)

= 0, for < 10 = 90, for all .

Horizontal

distance from

windward edge

Average external pressure

coefficient (Cp,e)

0 to 1/2h

1/2hto 1h

1hto 2h

2hto 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)*

* Value is provided for interpolation purposes.

TABLE 3.4.3.2(B)DOWNWIND SLOPE (U)

For: = 0 a nd 1 0

RatioAverage external pressure coefficient (Cp,e)

Roof pitch ()degrees

10 15 20 25 30 35 45 60

0.25

0.5

1.0

-0.7-0.3

-0.9-0.4

-1.3-0.6

-0.5-0.0

-0.7-0.3

-1.0-0.5

-0.30.2

-0.40.0

-0.7-0.3

-0.20.3

-0.30.2

-0.50.0

-0.20.3

-0.20.2

-0.30.2

0.4

-0.20.3

-0.20.2

0.5

0.4

0.3

0.01

0.01

0.01

TABLE 3.4.3.2 (C)DOWNWIND SLOPE (D)

For: = 0 a nd 1 0

Ratio

Average external pressure coefficient (Cp,e

)

Roof pitch ()

degrees

10 15 20

0.25

0.5

1.0

-0.3

-0.5

-0.7

-0.5

-0.5

-0.6

-0.6

-0.6

-0.6

NOTES:

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 toturbulence. Alternative combinationsof external and internal pressures(see Clause 3.4.7) must be considered to obtain the most severeconditions for design.

2. To obtain intermediate values for roof slopes andh/dratios other thanthose shown, linear interpolation is permitted. Interpolation shall onlybe carried out between values of the same sign. Where no value of

the same sign is given, assume 0.0 for interpolation purposes.

FIGURE 3.4.3 PARAMETERS FOR RECTANGULAR ENCLOSED BUILDINGS

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3.4.4 Area reduction factors (Ka) for roofs and sidewalls. For roofs and side walls, the external windpressure (pe) 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, takeKa= 1.0.

Tributary area is the area contribut ing to the force beingconsidered. For example, for a cladding fastener it willbe the area of cladding supported by a single fastener,for a purlin it will be the span between supportingrafters times the distance between purlins.

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

TABLE 3.4.4AREA REDUCTION FACTORS (Ka) FOR

ROOFS AND SIDE WALLS ACCORDING TOTRIBUTARY AREA

(See Paragraph E3.4.4 of Appendix E.)

Area (A)m2

Reduction factor (Ka)

1025100

1.00.90.8

NOTE: For intermediate values ofA, linear interpolation is permitted.

3.4.5 Local pressure factors (Kl) for cladding. Thelocal pressure factor (Kl) for wall and roof claddings, andtheir immediate supporting members and fixings, shall beobtained from Table 3.4.5 for the cases given in thisTable, or taken as 1.0, whichever gives the worstcombination of external and internal pressure.

Where an element of cladding or an immediatesupporting member extends beyond the areas given inTable 3.4.5, the local pressure factor (Kl) shall be takenas 1.0 on the remainder of that element or member.

Local pressure factors (Kl) greater than 1.0 are notapplicable in the ridge zone where the roof pitch is lessthan 10.

When applying the local pressure factor, the negativelimit to KlCp,eshall be -2.0.

TABLE 3.4.5LOCAL PRESSURE FACTORS (Kl)

Case Description Local pressurefactors (K1)

1 Positive pressures on areas of 0.25a2 or smalle r, anywhere on a windward wa ll, for a ll bui ld ings 1 .25

2 (a) Negative pressures (suctions) on areas of roof of 1.0a2 or less, within a distance 1.0afrom a roofedge, from a ridge or hip on a roof with a pitch of 10or more for building of all ht; or on areas ofwall of 1.0 a2 or less within a distance 1.0afrom a windward wall edge, for buildings withht 25.0 m

(b) Negative pressures (suctions) on areas of wall of 0.25a2 or less, beyond a distance of 1.0afrom awindward wall edge, for buildings with h t> 25.0 m

1.5

1.5

3 (a) Negative pressures (suctions) on areas of roof of 0.25a2 or less, within a distance 0.5afrom a roofedge, from a ridge or hip on a roof with a pitch of 10or more for buildings of all ht; or on areas ofwall of 0.25a2 or less within a distance 0.5afrom a windward wall edge, for buildings withht 25.0 m

(b) Negative pressures (suctions) on areas of wall of 1.0a2 or less, within a distance of 1.0afrom a

windward wall edge, for buildings h t> 25.0 m

2.0

2.0

4 Negative pressures (suctions) on areas of wall of 0.25a2 or less, on side walls within a distance 0.5afrom 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 ofK1should 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 edgediscontinuities exposed to conditions of high turbulence, the local pressure factor ( K1) = 3.0 is not conservative. These situations areoutside the scope of this Standard and specialist advice should be sought.

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ht 25.0 m ht > 25.0 m

NOTE: Dimension a is to be taken as the MINIMUMof 0.2bor 0.2dor the height htas 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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3.4.6 Reduction factors (Kp) for porous cladding.Where cladding porosity over a main surface exceeds0.001 and is less than 0.01, the local negative pressure(Cp,e) shall be multiplied by the applicable reductionfactors (Kp) given in Table 3.4.6. For all other cases,take Kp= 1.0.

TABLE 3.4.6

PRESSURE REDUCTION FACTOR (Kp) FORCLADDING POROSITY

(See Paragraph E3.4.6 of Appendix E.)

Horizontaldistance from

windward edgePressure reduction factor (Kp)

0.2da> 0.2da 0.4da> 0.4da 0.6da> 0.6da 0.8da> 0.8da 1.0da

0.90.80.70.70.8

LEGEND:

Porosity = the ratio of the open area over the total area ofthe surface

da = 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.

3.4.7 Internal pressures (pi). The internal windpressures (pi) shall be determined using the internalpressure coefficients (Cp,i) given in Table 3.4.7 and the

values of qz corresponding to those adopted for theexternal surfaces, using Equation 3.4.7.

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

where

pi = the internal wind pressure, in kilopascals

Cp,i = the internal pressure coefficient, given inTable 3.4.7

qz = the free stream gust dynamic wind pressureat height z, given in Clause 3.3.

The internal pressures (p i) so determined shall beassumed to act simultaneously with the externalpressures (pe), including the effects of local pressurefactors (Kl), and the most severe conditions thusdetermined shall be selected for purposes of design.

Dominant openings are openings on a single surfacewhose combined area exceeds the combined open areason any other single surface. A dominant opening doesnot need to be large.

In cyclonic regions, windows shall be considered aspotential dominant openings, unless capable of resistingimpact by a 4 kg piece of timber of 100 mm 50 mmcross-section, striking them at any angle at a speed of15 m/s.

TABLE 3.4.7

AVERAGE INTERNAL-PRESSURE COEFFICIENTS (Cp,i) FOR BUILDINGSOF RECTANGULAR PLAN AND OPEN INTERIOR PLAN

Condition Internal pressurecoefficient (Cp,i)

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

0.6- 0.3

2. 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

3. All walls equally permeableoropenings of equal area on all walls

- 0.3 or 0.0 whichever is the more severe forcombined 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) ofother walls and roofs subject to external suction, equal to 0.5 or less11.5236 or more

(b) Dominant openings on leeward wall(c) Dominant openings on side wall(d) Dominant openings in a roof segment

- 0.3 or 0.00.1

0.30.50.6

Windward wall pressure coefficient as inTable 3.4.3.1.(A)Value ofCp,e for leeward external wall surfaceValue ofCp,e for side external wall surfaceValue ofCp,e for external surface of roof segment

5. A building effectively sealed and having non-opening windows - 0.2 or 0.0, whichever is the more severe forcombined loads

(See Paragraph E3.4.7 of Appendix E.)

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29 AS 1170.21989

3.4.8 Frictional drag force (Ff) for rectangular enclosedbuildings. The frictional drag force (Ff) shall be taken inaddition to those loads calculated for rectangular cladbuildings only where the ratio d/h or d/b is greater than 4.For roofs, the calculation of frictional drag force is onlyrequired for those cases where Table 3.4.3.2(A) is

applicable for determining external pressure coefficients forthe calculation of external pressures. Th