AS 4055-2012 Wind loads for housing.pdf

AS 4055—2012

Australian Standard®

Wind loads for housing

AS

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This Australian Standard® was prepared by Committee BD-099, Wind Loads for Housing. It

was approved on behalf of the Council of Standards Australia on 23 November 2012.

This Standard was published on 24 December 2012.

The following are represented on Committee BD-099:

• Australian Building Codes Board

• Australian Window Association

• Concrete Masonry Association of Australia

• Cyclone Testing Station

• Engineers Australia

• Forest and Wood Products Australia

• Housing Industry Association

• Master Builders Association

• Roofing Tile Association of Australia

• Think Brick Australia

This Standard was issued in draft form for comment as DR AS 4055.

Standards Australia wishes to acknowledge the participation of the expert individuals that

contributed to the development of this Standard through their representation on the

Committee and through the public comment period.

Keeping Standards up-to-date Australian Standards® are living documents that reflect progress in science, technology and

systems. To maintain their currency, all Standards are periodically reviewed, and new editions

are published. Between editions, amendments may be issued.

Standards may also be withdrawn. It is important that readers assure themselves they are

using a current Standard, which should include any amendments that may have been

published since the Standard was published.

Detailed information about Australian Standards, drafts, amendments and new projects can

be found by visiting www.standards.org.au

Standards Australia welcomes suggestions for improvements, and encourages readers to

notify us immediately of any apparent inaccuracies or ambiguities. Contact us via email at

[email protected], or write to Standards Australia, GPO Box 476, Sydney, NSW 2001.

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AS 4055—2012

Australian Standard®


Originated as AS 4055—1992. Previous edition 2006.

Third edition 2012.

COPYRIGHT

© Standards Australia Limited

All rights are reserved. No part of this work may be reproduced or copied in any form or by

any means, electronic or mechanical, including photocopying, without the written

permission of the publisher, unless otherwise permitted under the Copyright Act 1968.

Published by SAI Global Limited under licence from Standards Australia Limited, GPO Box

476, Sydney, NSW 2001, Australia

ISBN 978 1 74342 323 3

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AS 4055—2012 2

PREFACE

This Standard was prepared by the Standards Australia Committee BD-099, Wind loads for

housing to supersede AS 4055—2006.

This Standard will be referenced in the National Construction Code (NCC) 2013 edition,

thereby superseding in part the previous edition, AS 4055—2006, which will be withdrawn

12 months from the date of publication of this edition.

The objective of this Standard is to provide designers, builders and manufacturers of

building products that are affected by wind loading with a range of wind speed classes that

can be used to design and specify such products for use in housing that are within the

limitations in this Standard.

This revision aims to improve modelling of topographic effects and also to harmonize with

recent changes to AS/NZS 1170.2:2011, including Amendments No.1 and No.2. This

edition differs from the previous edition as follows:

(a) The Scope of the Standard has been revised to include the limitation to Class 1 and

Class 10 buildings as defined by the NCC. This has always been the intention of this

Standard as reflected in the definition of ‘house’, but the limitation is more obvious

when presented in the Scope.

(b) Table 2.1 presenting wind speeds for each wind classification has been split into a

Non-Cyclonic regions table and a Cyclonic regions table for clarification. The wind

speeds for each wind classification remain unchanged.

(c) Table 2.2 presenting the Wind Classification for sites has been changed to include a

new Topographic Class T0 and to harmonize with changes adopted by

AS/NZS 1170.2, terrain category multipliers.

(d) Definitions for terrain categories have been revised to be compatible with those in

AS/NZS 1170.2:2011 (as amended). The revised definitions are intended to clarify

the differences between the categories. International research has shown that the wind

speeds over water are appropriate for Terrain Category 1 multipliers, so

AS/NZS 1170.2 has included water bodies in Terrain Category 1 for all wind regions.

In the case of wind blowing over large bodies of water, including seas and oceans,

shoaling waves can introduce a near-shore roughness that means this water can be

considered as Terrain Category 1.5. This change has followed through to this

Standard. Terrain Category 4 is not applicable to this Standard as in Terrain

Category 4, a house is embedded within the Terrain Category 4 roughness and its

wind force evaluation may require special techniques.

(e) The calculation of topographic class had previously used the average of the maximum

and minimum slope on a topographic feature to determine an average slope. While the

average slope characterized a conical hill well, it significantly underestimated the

slope of a ridge or escarpment. The maximum slope is now used to characterize the

topographic feature. This will better represent the slope of a ridge or escarpment

without significantly changing the characterization of a conical hill. This change was

recommended as a result of observation of significantly higher levels of wind damage

on ridges and escarpments in cyclonic and non-cyclonic wind storms.

(f) In AS/NZS 1170.2:2011, the topographic multiplier for flat land applies to hill slopes

of less than 1:20 and this revision introduces a new Topographic Class T0 to

represent slopes from 0 to 1:20. This Class has a topographic multiplier of 1.0. The

topographic multiplier for T1 has been changed to 1.1 and includes wind for slopes

from 1:20 to 1:10. Hill slopes have also been expressed in degrees.

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3 AS 4055—2012

(g) Shielding classifications have been harmonized with those in AS/NZS 1170.2 as

appropriate for houses. For Regions A and B, large trees and heavily wooded areas

can offer shielding and have been explicitly included, whereas in Regions C and D,

the long duration of the wind event means that trees will be denuded before the

arrival of the peak gust.

(h) Shielding classifications are linked to the topographic classes. AS/NZS 1170.2:2011

also links shielding with topography by allowing shielding only on slopes of less than

1:5. This has also been incorporated into this Standard by allowing full shielding only

for those topographic classes with slopes of less than 1:5. This change in both

Standards are based on wind-field models of hills and damage surveys following

cyclonic and non-cyclonic wind events.

(j) Houses in the first row adjacent to wide, open areas are classed as ‘Not Shielded’, the

second row from wide open areas is classed as ‘Partial Shielding’ and subsequent

rows as ‘Full Shielding’ where there are sufficient houses.

(k) Pressure zones on roofs and walls have been defined, named and illustrated on

diagrams. Edge and corner zones are subject to higher pressures due to the local

pressure factors defined in AS/NZS 1170.2. An additional zone on the windward

corners of low slope roofs allows for the RC1 zone introduced to

AS/NZS 1170.2:2011 based on recent international research.

(l) The combination factor (Kc) from AS/NZS 1170.2:2011 has been applied to all

pressures for walls and roofs. This has reduced some of the design pressures in the

Standard.

(m) A more detailed commentary has been added (Appendix A) to clarify the relationship

of this Standard to AS/NZS 1170.2 and to give background to some of the clauses.

(n) The example of topographic classes (Appendix B) has been changed to reflect the

changes to definition of topographic classes.

(o) The example of terrain categories and shielding (Appendix C) has been changed to

reflect the changes to definition of terrain categories and Shielding.

(p) In checking Tables 5.2 to 5.13, some minor discrepancies were found between values

in the previous edition and those calculated from the formulae in Appendix A. These

discrepancies were corrected and while there may be small differences in racking

forces between this document and AS 1684, this will not affect the use of AS 1684.

(q) References to the differential pressures on photovoltaic solar panels in

AS/NZS 1170.2 were included.

The term ‘informative’ has been used in this Standard to define the application of the

Appendix to which it applies. An ‘informative’ appendix is only for information and

guidance.

Notes to the text contain information and guidance. They are not an integral part of the

Standard.

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AS 4055—2012 4

CONTENTS

Page

SECTION 1 SCOPE AND GENERAL

1.1 SCOPE ......................................................................................................................... 5

1.2 LIMITATIONS ............................................................................................................ 5

1.3 NORMATIVE REFERENCES .................................................................................... 5

1.4 DEFINITIONS ............................................................................................................. 6

1.5 NOTATION ................................................................................................................. 7

SECTION 2 WIND LOADS

2.1 CLASSIFICATION ..................................................................................................... 9

2.2 RELATIONSHIP TO WIND REGION AND SITE CONDITIONS ............................ 9

2.3 SELECTION OF TERRAIN CATEGORY ................................................................ 12

2.4 SELECTION OF TOPOGRAPHIC CLASS .............................................................. 13

2.5 SELECTION OF SHIELDING CLASS ..................................................................... 14

SECTION 3 CALCULATION OF PRESSURES AND FORCES

3.1 PRESSURE ZONES .................................................................................................. 16

3.2 PRESSURE COEFFICIENTS .................................................................................... 17

3.3 CALCULATION OF PRESSURES ........................................................................... 20

3.4 CALCULATION OF FORCES .................................................................................. 21

3.5 PRESSURES FOR TYPICAL APPLICATIONS ....................................................... 21

SECTION 4 UPLIFT FORCES .............................................................................................. 24

SECTION 5 RACKING FORCES

5.1 RACKING FORCES ................................................................................................. 25

5.2 AREA OF ELEVATION ........................................................................................... 25

APPENDICES

A COMMENTARY ....................................................................................................... 42

B WORKED EXAMPLE FOR THE DETERMINATION OF TOPOGRAPHIC

CLASS ....................................................................................................................... 53

C WORKED EXAMPLES FOR THE SELECTION OF TERRAIN CATEGORY

AND SHIELDING CLASS ........................................................................................ 57

D WORKED EXAMPLE FOR RACKING FORCES .................................................... 61

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5 AS 4055—2012

www.standards.org.au © Standards Australia

STANDARDS AUSTRALIA

Australian Standard


S E C T I O N 1 S C O P E A N D G E N E R A L

1.1 SCOPE

This Standard specifies site wind speed classes for determining design wind speeds and

wind loads for NCC buildings Classes 1 and 10 within the geometric limits given in

Clause 1.2. The classes are for use in the design of housing and for design, manufacturing

and specifying of building products and systems used for housing.

Wind loads for houses not complying with the geometric limits given in Clause 1.2 are

outside the scope of this Standard.

NOTES:

1 Commentary on the clauses of this Standard is given in Appendix A.

2 A worked example for the determination of topography is given in Appendix B.

3 Worked examples for the determination of terrain category and shielding class are given in

Appendix C.

4 A worked example for racking forces is given in Appendix D.

5 Where houses do not comply with the geometric and other limitations of this Standard, use

AS/NZS 1170.2.

1.2 LIMITATIONS

For the purpose of this Standard, the following conditions (geometric limits) shall apply

(see Figure 1.1):

(a) The distance from ground level to the underside of eaves shall not exceed 6.0 m. The

distance from ground level to the highest point of the roof, not including chimneys,

shall not exceed 8.5 m.

(b) The width (W) including roofed verandas, excluding eaves, shall not exceed 16.0 m,

and the length (L) shall not exceed five times the width.

(c) The roof pitch shall not exceed 35°.

The tables in Section 5 are based on floor to ceiling height of 2.4 m and a floor depth of

0.3 m (floor level down to ceiling below).

If wind loads on houses are determined using this Standard, design parameters shall be

derived from this Standard only. Where wind loads on buildings are determined using

AS/NZS 1170.2, design parameters in that Standard only must be used.

NOTE: Clause 3.2.3 in this Standard refers to pressures on solar panels given in AS/NZS 1170.2.

These parameters are referenced in this Standard.

1.3 NORMATIVE REFERENCES

The following are the normative documents referenced in this Standard:

AS/NZS

1170 Structural design actions

1170.2 Part 2: Wind actions

ABCB

NCC National Construction Code

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AS 4055—2012 6

© Standards Australia www.standards.org.au

Height totop of roof,

r idge or gableand 8.5 m max.

One ortwo storey

Roof pi tch35° max.

Roof pi tch35° max.

16.0 m max.

Height to eaves exceptgable ends 6.0 m max.

16.0 m max.

Height at any sect ionthrough the house 8.5 m max.

Height f rom groundlevel to unders ide

of eaves exceptfor gable ends

6.0 m max.

Eaves 900 mm max.

(a) Sect ions

(b) Plan view

W16.0 m max.

Edge of eaves

External wal l

W16.0 m max.

L

L

W16.0 m max.

L 5W

L

L

FIGURE 1.1 GEOMETRY

1.4 DEFINITIONS

For the purpose of this Standard, the definitions below apply.

1.4.1 Bottom of hill, ridge or escarpment

Area at the base of the hill, ridge or escarpment, where the average slope is less than 1 in

20.

1.4.2 Height

Distance from ground level to the underside of eaves or to the highest point of the roof

neglecting chimneys; or the height of each storey at external walls (see Figure 1.1).

1.4.3 House

Class 1 or 10 building as defined by the National Construction Code (NCC) with the

geometric limitations specified in Clause 1.2.

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7 AS 4055—2012


1.4.4 Length

Maximum overall distance between outside edges of the external walls of a house or shape

(see Figure 1.1).

1.4.5 Obstruction

Natural or man-made objects that generate turbulent wind flow, ranging from single trees to

forests and from isolated small structures to closely spaced multi-storey buildings.

1.4.6 Plan

Basic rectangular, square or L-shaped layout, or simple combinations of these (see

Figure 1.1).

1.4.7 Racking forces

Forces that occur in walls parallel to the wind direction.

1.4.8 Width

Maximum distance from wall to wall in the direction perpendicular to the length, including

roofed verandas but excluding eaves (see Figure 1.1).

1.5 NOTATION

Unless otherwise stated, the notation used in this Standard shall have the following

meaning:

C1 to C4 = cyclonic wind classes

C1serv to C4serv = cyclonic wind classes for serviceability

Cp = pressure coefficient (external, internal or net, as appropriate)

Cp,e = external pressure coefficient

Cp,i = internal pressure coefficient

Cp,n = net pressure coefficient

d = average horizontal distance measured from the crest of the

escarpment or hill to the near top-third zone, in metres

FS, PS, NS = shielding classes, full shielding, partial shielding and no

shielding

G = dead load; or permanent action (self-weight), in kPa

G = wind pressure zone more than 1200 mm from edges of roofs or

external corners of walls

H = height of a hill, ridge or escarpment, in metres

H0 = maximum distance from the ground to the underside of the

bearer in the lower floor, in metres

h = average roof height, in metres

h0 = half the height of the wall (half of the floor to ceiling height) in

metres

Kc = combination factor

Kl = local pressure factor

L, M, T, O = lower, middle and top third of hill, ridge or escarpment and

over-top zone for escarpments

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AS 4055—2012 8


L = length of a house; or lower part of a hill, ridge or escarpment,

in metres

Ms = shielding multiplier

Mt = topographic multiplier

M6.5,cat = terrain category multiplier at height (h)

N1 to N6 = non-cyclonic wind classes

N1serv to N6serv = non-cyclonic wind classes for serviceability

p = design wind pressure acting normal to a surface, in kilopascals

qu = free stream dynamic gust pressure, in kilopascals

NA = Not applicable

RC = pressure zone on roofs within 1200 mm of external corners

RE = pressure zone on roofs within 1200 mm of roof panel edges

SC = pressure zone on walls within 1200 mm of external corners of

the house

TC1 to TC3 = terrain categories

T0 to T5 = topographic classes

Vh = design gust wind speed at height (h), in metres per second

Vh,s = design gust wind speed at height (h) for serviceability limit

state, in metres per second

Vh,u = design gust wind speed at height (h) for ultimate strength limit

state, in metres per second

W = width of a house, in metres

Ws = serviceability wind action, in kPa

Wu = ultimate wind action in kPa

α = angle of roof pitch

φa = maximum slope through the top half of the hill, ridge or

escarpment

γ = load factor

ρair = density of air, which shall be taken as 1.2 kg/m3

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9 AS 4055—2012


S E C T I O N 2 W I N D L O A D S

2.1 CLASSIFICATION

The system of 10 classes is set out in Tables 2.1A and B together with the associated design

gust wind speeds (Vh) for the serviceability and ultimate limit states. This incorporates both

non-cyclonic (N) and cyclonic (C) winds.

TABLE 2.1A

DESIGN GUST WIND SPEED (Vh) FOR NON-CYCLONIC REGIONS A AND B

Wind class

Design gust wind speed (Vh) at height (h)

m/s

Serviceability limit state

(Vh,s)

Ultimate limit state

(Vh,u)

N1

N2

N3

26

26

32

34

40

50

N4

N5

N6

39

47

55

61

74

86

TABLE 2.1B

DESIGN GUST WIND SPEED (Vh) FOR CYCLONIC REGIONS C AND D

Wind class

Design gust wind speed (Vh) at height (h)

m/s

Serviceability limit state

(Vh,s)

Ultimate limit state

(Vh,u)

C1

C2

C3

C4

32

39

47

55

50

61

74

86

NOTE: Section 3 may present different pressures for the same wind speed depending on classification.

2.2 RELATIONSHIP TO WIND REGION AND SITE CONDITIONS

The selection of wind speed class for a house depends on the conditions at the site of the

house. The class shall be determined from Table 2.2 using the following site conditions

determined as stated:

(a) Geographic wind speed region of the site as defined in Figure 2.1 (Region A, B, C or

D, as given in AS/NZS 1170.2).

(b) The terrain category that surrounds or is likely to surround the site within the next 5

years, as defined in Clause 2.3 (TC1, TC2, TC2.5 or TC3).

(c) The topographic class of the site, as defined in Clause 2.4 (T0, T1, T2, T3, T4 or T5).

(d) The shielding class of the house, as defined in Clause 2.5 (FS, PS or NS).

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AS 4055—2012 10


TABLE 2.2

WIND CLASSIFICATION FROM WIND REGION AND SITE CONDITIONS

Wind

region

TC Topographic class

T0 T1 T2 T3 T4 T5

FS PS NS FS PS NS FS PS NS PS NS NS NS

A 3 N1 N1 N1 N1 N2 N2 N2 N2 N2 N3 N3 N3 N4

2.5 N1 N1 N2 N1 N2 N2 N2 N3 N3 N3 N3 N4 N4

2 N1 N2 N2 N2 N2 N3 N2 N3 N3 N3 N3 N4 N4

1.5 N2 N2 N2 N2 N3 N3 N3 N3 N3 N3 N4 N4 N5

1 N2 N3 N3 N2 N3 N3 N3 N3 N4 N4 N4 N4 N5

B 3 N2 N2 N3 N2 N3 N3 N3 N3 N4 N4 N4 N4 N5

2.5 N2 N3 N3 N3 N3 N3 N3 N4 N4 N4 N4 N5 N5

2 N2 N3 N3 N3 N3 N4 N3 N4 N4 N4 N5 N5 N6

1.5 N3 N3 N4 N3 N4 N4 N4 N4 N4 N5 N5 N5 N6

1 N3 N4 N4 N4 N4 N4 N4 N5 N5 N5 N5 N6 N6

C 3 C1 C1 C2 C1 C2 C2 C2 C2 C3 C3 C3 C3 C4

2.5 C1 C2 C2 C2 C2 C2 C2 C3 C3 C3 C3 C4 NA

2 C1 C2 C2 C2 C2 C3 C2 C3 C3 C3 C4 C4 NA

1.5 C2 C2 C3 C2 C3 C3 C3 C3 C4 C4 C4 NA NA

1 C2 C3 C3 C3 C3 C3 C3 C4 C4 C4 NA NA NA

D 3 C2 C3 C3 C2 C3 C3 C3 C4 C4 C4 C4 NA NA

2.5 C2 C3 C3 C3 C3 C4 C3 C4 C4 C4 NA NA NA

2 C3 C3 C4 C3 C4 C4 C4 C4 NA NA NA NA NA

1.5 C3 C4 C4 C4 C4 NA C4 NA NA NA NA NA NA

1 C3 C4 C4 C4 NA NA NA NA NA NA NA NA NA

LEGEND:

FS = Full shielding

PS = Partial shielding

NS = No shielding

N = Non-cyclonic

C = Cyclonic

N/A = Not applicable, that is, beyond the scope of this Standard (use AS/NZS 1170.2)

TC = Terrain category

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11 AS 4055—2012


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rum

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his

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A

, B

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AN

D D

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AS 4055—2012 12


2.3 SELECTION OF TERRAIN CATEGORY

The terrain category for a housing site is a measure of the lowest effective surface

roughness from any radial direction within a distance of 500 m of the proposed housing

site. It shall be based on the likely terrain five years after design. Substantial well-

established trees may be considered as obstructions for evaluation of terrain category in all

wind regions.

The terrain category for a housing site shall be identified by the notation TC1, TC1.5, TC2,

TC2.5 or TC3 and shall be determined as follows:

(a) Terrain Category 1 (TC1) Very exposed open terrain with few or no obstructions

and enclosed limited sized water surfaces at serviceability and ultimate wind speeds

in all wind regions, e.g. flat, treeless, poorly grassed plains, or river, canals, lakes and

enclosed bays, extending less than 10 km in the wind direction.

(b) Terrain Category 1.5 (TC1.5) Open water surfaces subjected to shoaling waves at

serviceability and ultimate wind speeds in all wind regions, e.g. near-shore water,

large unenclosed bays on seas and oceans, lakes and enclosed bays extending greater

than 10 km in the wind direction.

(c) Terrain Category 2 (TC2) Open terrain including grassland with well-scattered

obstructions having heights generally from 1.5 m to 5 m with no more than two

obstructions per hectare, e.g. farmland and cleared subdivisions with isolated trees

and uncut grass.

(d) Terrain Category 2.5 (TC2.5) Terrain with a few trees or isolated obstructions. This

category is intermediate between TC2 and TC3 and represents the terrain in

developing outer urban areas with scattered houses, or large acreage developments

with fewer than 10 buildings per hectare.

(e) Terrain Category 3 (TC3) Terrain with numerous closely spaced obstructions having

heights generally from 3 m to 10 m. The minimum density of obstructions shall be at

least the equivalent of 10 house-size obstructions per hectare, e.g. suburban housing

or light industrial estates.

In urban situations, roads, rivers, small lakes or canals less than 200 m wide shall be

considered to form part of normal ‘Terrain Category 3’ terrain. Parks and other open spaces

less than 250 000 m2 in area shall also be considered to form part of normal ‘Terrain

Category 3’ terrain provided they are not within 500 m of each other, or not within 500 m

of open country. Housing sites less than 200 m from the boundaries of open areas larger

than 250 000 m2, e.g. golf courses, that are completely surrounded by urban terrain, shall be

considered to have the terrain category applicable to the open area itself. Shielding

provisions may still apply to these sites.

Housing sites less than 500 m from the edge of a development shall be classified as the

applicable terrain that adjoins the development, i.e. TC1, TC1.5, TC2, TC2.5 or TC3, as

applicable.

NOTES:

1 For commentary on terrain categories, see Appendix A.

2 For worked examples, see Appendix C.

3 Terrain Category 4, as defined in AS/NZS 1170.2, is not applicable to this Standard.

4 The terrain categories are the same as those in AS/NZS 1170.2.

5 Vegetation is considered differently for terrain categories in this Clause and for shielding

classes in Clause 2.5.

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13 AS 4055—2012


2.4 SELECTION OF TOPOGRAPHIC CLASS

The topographic class determines the effect of wind on a house because of its location on a

hill, ridge or escarpment and the height and maximum slope of the hill, ridge or escarpment.

The topographic class for a housing site shall be identified by the notation T0, T1, T2, T3,

T4 or T5 and shall be determined from Table 2.3 and Figure 2.2 for all sites in the top two

thirds of a ridge, hill or escarpment.

NOTES:

1 The method defined in Table 2.3 and Figure 2.2 is suitable for the purpose of either mapping

the wind classes of an area or assessing the wind class of an individual site.

2 For a worked example to determine topographic class, see Appendix B.

The bottom of a hill, ridge or escarpment shall be that area at the base of the hill, ridge or

escarpment where the average slope is less than 1 in 20, e.g. creek, river valley or flat area.

The maximum slope of a hill, ridge or escarpment (φa) shall be the slope measured as the

steepest slope through the top half of the hill, ridge or escarpment.

NOTES:

1 Often the maximum slope will not occur at the actual proposed housing site and should be

appraised by considering the adjacent topography

2 For an example of the classification of topography, see Appendix B.

The top-third zone (T) extends for an equal distance (d) either side of the crest of an

escarpment as shown in Figure 2.2. The value of d is the average horizontal distance

measured from the crest of the escarpment to the near top-third zone.

A rise in terrain shall be considered an escarpment where the maximum slope on one side of

the ridge is greater than 1 in 10 and on the other side is less than 1 in 20 (see Figure 2.2(b)).

The over-top zone (O) of an escarpment shall be taken to extend to a distance of 4H past the

crest of an escarpment.

TABLE 2.3

TOPOGRAPHIC CLASSIFICATION FOR HILLS, RIDGES OR ESCARPMENTS

Maximum slope

(φa)

Site location (see Figure 2.2)

Lower-

third

zone

(L)

Mid-

third

zone

(M)

Top-third zone

(T)

Over-top zone

(O)

(for 4H past

crest of

escarpments

only) H ≤ 10 m 10 m < H ≤ 30 m H > 30 m

<1:20

(<2.9°)

T0 T0 T0 T0 T0 T0

≥1:20

(≥2.9°)

<1:10

(<5.7°)

T0 T0 T1 T1 T1 T0

≥1:10

(≥5.7)

<1:7.5

(<7.6°)

T0 T1 T1 T2 T2 T0

≥1:7.5

(≥7.6°)

<1:5

(<11.3°)

T0 T1 T2 T2 T3 T1

≥1:5

(≥11.3°)

<1:3

(<18.4°)

T0 T2 T2 T3 T4 T2

≥1:3

(≥18.4°)

T0 T2 T3 T4 T5 T3

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AS 4055—2012 14


H/3

H/3

H/3

M

L

d d

T O

Average s lope 1:20

Average s lope 1:10

4H

Average s lope 1:20

(b) Escarpments

LEGEND:

Hd

LMTO

� ==

====

height of the hi l l , r idge or escarpmentaverage hor izonta l distance measured f rom thecrest of the escarpment to the near top-thi rd zonelower thi rd of the hi l l , r idge or escarpmentmiddle thi rd of the hi l l , r idge or escarpmenttop thi rd of the hi l l , r idge or escarpmentover top zone (for escarpment only)

H/3

H/3

H/3

M

L

d d

T

Average s lope 1:20

(a) Hi l ls

FIGURE 2.2 TOPOGRAPHIC ZONES FOR AVERAGE SLOPE

2.5 SELECTION OF SHIELDING CLASS

Where the wind speed on a house is influenced by obstructions of similar size to the house,

shielding shall be considered and shall be based on the likely shielding five years hence.

In Regions A and B trees or groups of trees with similar face area to houses may be

considered as shielding elements. In Regions C and D trees and vegetation shall not be

considered as shielding elements.

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15 AS 4055—2012


The shielding class for a housing site shall be identified by the notation FS, PS or NS, and

shall be determined as follows:

(a) Full shielding (FS) Full shielding shall apply where at least two rows of houses or

similar size permanent obstructions surround the house being considered. In Regions

A and B, permanent heavily wooded areas within 100 m of site provide full shielding.

Full shielding is only possible for houses within Topographic Classes T0, T1, and T2.

The application of full shielding shall be appropriate for typical suburban

development greater than or equal to 10 houses, or similar size obstructions per

hectare.

The effects of roads or other open areas with a distance measured in any direction of

less than 100 m shall be ignored. However, the first two rows of houses abutting

permanent open areas with a least dimension greater than 100 m, such as parklands,

large expanses of water and airfields, shall be considered to have either partial

shielding or no shielding.

(b) Partial shielding (PS) Partial shielding shall apply to intermediate situations where

there are at least 2.5 houses or sheds per hectare, such as acreage type suburban

development or wooded parkland. Partial shielding is only possible for houses within

Topographic Classes T0, T1, T2, and T3. The second row of houses abutting open

parkland, open water or airfields may be classified as having partial shielding.

(c) No shielding (NS) No shielding shall apply where there are no permanent

obstructions or where there are less than 2.5 obstructions per hectare, such as the row

of houses or single houses abutting open parklands, open water or airfields.

NOTES:

1 For commentary on shielding class, see Appendix A.

2 For worked examples, see Appendix C.

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AS 4055—2012 16


S E C T I O N 3 C A L C U L A T I O N O F P R E S S U R E S

A N D F O R C E S

3.1 PRESSURE ZONES

The following external pressure zones (illustrated in Figure 3.1 for roofs and Figure 3.2 for

walls) shall be used in evaluating wind loads on houses:

(a) General (G) Areas of roofs more than 1200 mm from edges, and areas of walls

(including windows and doors) more than 1200 mm from external corners.

(b) Roof edge (RE) Areas of roofs within 1200 mm of all edges except the external

corners of the roof.

(c) Roof corners (RC) Areas of the external corners of roofs within 1200 mm of two

adjacent edges. (This is the overlap area between two RE zones.)

(d) Walls near corners (SC) Walls (including windows and doors) at external corners of

the house within 1200 mm of the corner.

G Roof general area

RE Roof edge

RC Roof edge corner

G

G

G

G

G

LEGEND:

1200

RC

RERC

RE

RC

24

00

2400 RE RC

RE

RC

1200

NOTE: Indicated plan width varies to suit roof pitch.

DIMENSIONS IN MILLIMETRES

FIGURE 3.1 PRESSURE ZONES ON HOUSING—ROOFS (PLAN VIEW)

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17 AS 4055—2012


Wall edgeSC

Wall-genera l areaG

LEGEND:

1200

1200

G

G

SC

SC

G

SC

SC

G

G

G

SC

DIMENSIONS IN MILLIMETRES

FIGURE 3.2 PRESSURE ZONES ON HOUSING—WALLS (PLAN VIEW)

3.2 PRESSURE COEFFICIENTS

3.2.1 Wind classes N1 to N6 (non-cyclonic)

For houses with Wind Classes N1 to N6 (in Regions A and B), the pressure coefficients in

Table 3.1 shall be used.

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AS 4055—2012 18


TABLE 3.1

PRESSURE COEFFICIENTS FOR WIND CLASSES N1 TO N6

(REGIONS A AND B FOR ULTIMATE STRENGTH AND SERVICEABILITY)

Housing component

Factored external

pressure coefficient

(Kl.Cp,e)

Internal pressure

coefficient

(Cp,i)

Net pressure

coefficient

(KC.Cp,n)

Roof—General areas (See Region G in Figure 3.1)

(a) General, including all trusses and

rafters

−0.9

+0.4

+0.2

−0.3

−1.0

+0.63

(b) Cladding, fasteners and immediate

supporting members not within

1200 mm of edges

−0.9

+0.4

+0.2

−0.3

−1.0

+0.63

Roof—Edges

(c)

Cladding, fasteners and immediate

supporting members within 1200 mm

of edges (See Region RE in

Figure 3.1)

−1.8 +0.2 −1.8

(d)

Cladding, fasteners and immediate

supporting members within 1200 mm

of eaves corners (applies to roof

slopes less than 10°) (See Region RC

in Figure 3.1)

−2.7 +0.2 −2.61

Walls

(a) General, including all studs (See

Region G in Figure 3.2)

+0.7

−0.65

−0.3

+0.2

+0.9

−0.77

(b) Cladding, fasteners, doors and

windows not within 1200 mm of

edges (See Region G in Figure 3.2)

−0.65

+0.7

+0.2

−0.3

−0.77

+0.9

(c)

Cladding, fasteners, doors and corner

windows within 1200 mm of edges

(See Region SC in Figure 3.2)

−1.3 +0.2 −1.35

NOTES:

1 Positive internal or external pressures are towards the surface (negative values are away from the

surface—suctions). For net pressures, positive values are inwards net pressures, and negative values

are outwards net pressures.

2 For roofs, immediate supporting members include battens and purlins. Rafters and trusses are not

considered as immediate supporting members.

3 The internal pressures presented in this table may only be used where all cladding elements including

windows demonstrate compliance with the relevant Australian Standard.

4 Net pressure coefficient includes the effect of a combination factor and so will not equal Kl.Cp,e − Cp,i

(see Paragraph A4).

5 Windows and doors with 25% or more of the width of a single panel or pane within 1200 mm of the

building edge are classified as SC not G.

3.2.2 Wind Classes C1 to C4 (cyclonic)

For houses with Wind Classes C1 to C4 (in Regions C and D) the pressure coefficients in

Tables 3.2A and B shall be used.

3.2.3 Wind pressures on photovoltaic solar panels

Pressures on photovoltaic solar panels for designing their connection to the roof structure

shall be obtained from Appendix D in AS/NZS 1170.2.

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TABLE 3.2(A)

PRESSURE COEFFICIENTS FOR WIND CLASSES C1 TO C4

(REGIONS C AND D—CYCLONIC—FOR ULTIMATE STRENGTH)

Housing component

Factored external


(Kl.Cp,e)

Internal pressure

coefficient

(Cp,i)

Net pressure

coefficient

(KC.Cp,n)



rafters

−0.9

+0.4

+0.7

−0.65

−1.44

+0.95



1200 mm of edges

−0.9

+0.4

+0.7

−0.65

−1.44

+0.95

Roof—Edges

(c) Cladding, fasteners and immediate

supporting members within

1200 mm of edges (See Region RE

in Figure 3.1)

−1.8 +0.7 −2.25

(d) Cladding, fasteners and immediate


1200 mm of eaves corners (applies

to roof slopes less than 10°) (See

Region RC in Figure 3.1)

−2.7 +0.7 −3.06

Walls



−0.65

+0.7

+0.7

−0.65

−1.22

+1.22

(b) Cladding, fasteners, doors and

windows not within 1200 mm of

edges (See Region G in Figure 3.2)

−0.65

+0.7

+0.7

−0.65

−1.22

+1.22

(c)

Cladding, fasteners, doors and

corner windows within 1200 mm

of edges (See Region SC in

Figure 3.2)

−1.3 +0.7 −1.8

NOTES:


surface—suctions). For net pressures, positive values are inwards net pressures, and negative values

are outwards net pressures.



3 Net pressure coefficient includes the effect of a combination factor and so will not equal

Kl.Cp,e − Cp,i (see Paragraph A4).



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AS 4055—2012 20


TABLE 3.2(B)

PRESSURE COEFFICIENT FOR WIND CLASSES C1 TO C4

(REGIONS C AND D—CYCLONIC—FOR SERVICEABILITY)

Housing component Factored external


(Kl.Cp,e)

Internal pressure

coefficient

(Cp,i)

Net pressure

coefficient

(KCCp,n)



rafters

−0.9

+0.4

+0.2

−0.3

−1.0

+0.63



1200 mm of edges

−0.9

+0.4

+0.2

−0.3

−1.0

+0.63

Roof—Edges

(c) Cladding, fasteners and immediate


1200 mm of edges (See Region RE

in Figure 3.1)

−1.8 +0.2 −1.8

(d) Cladding, fasteners and immediate


1200 mm of eaves corners (applies

to roof slopes less than 10°) (See

Region RC in Figure 3.1)

−2.7 +0.2 −2.61

Walls



+0.7

−0.65

−0.3

+0.2

+0.9

−0.77

(b) Cladding, fasteners and windows

not within 1200 mm of edges (See


−0.65

+0.7

+0.2

−0.3

−0.77

+0.9

(c) Cladding, fasteners and corner

windows within 1200 mm of edges

(See Region SC in Figure 3.2)

−1.3 +0.2 −1.35

NOTES:


surface—suctions). For net pressures, positive values are inwards net pressures, and negative values are

outwards net pressures.



3 Net pressure coefficient includes the effect of a combination factor and so will not equal Kl.Cp,e − Cp,i (see

Paragraph A4).



3.3 CALCULATION OF PRESSURES

The design wind pressures (p), in kilopascals, shall be determined for structures and parts

of structures as follows:

p = quCp . . . 3.1

where

p = design wind pressure acting normal to a surface, in kilopascals

NOTE: Positive pressures indicate pressures above ambient. Negative pressure

indicate pressures below ambient.

qu = free stream dynamic gust pressure Acc

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21 AS 4055—2012


= 0.5ρair[Vh]2/1000

ρair = density of air, which shall be taken as 1.2 kg/m3

Cp = pressure coefficient, as given in Clause 3.2 (external, internal or net, as

appropriate)

This Standard does not require evaluation of pressures across internal walls. (Where design

requires pressures across internal walls, see AS/NZS 1170.2.)

3.4 CALCULATION OF FORCES

The design wind forces shall be determined for structures and parts of structures by

multiplying the pressure by the area under consideration and applying the resultant force at

the centre of the area normal to the surface.

NOTE: Additional information on calculating pressures and forces may be found in

AS/NZS 1170.2.

Uplift forces are determined by taking the uplift pressure (negative pressure coefficients

indicate outward forces on a surface) by the total area of the roof (see Section 4).

Racking forces are determined for the overall house by taking the appropriate vertical

projected area and applied by distributing the force to the bracing walls or panels (see

Section 5).

3.5 PRESSURES FOR TYPICAL APPLICATIONS

Based on the net pressure coefficients in Tables 3.1 and 3.2, ultimate limit state design

pressures (tabulated as ‘ultimate strength pressure’) for the N and C categories are as given

in Table 3.3. Serviceability limit state design pressures (tabulated as ‘serviceability

pressure’) from N and C categories are as given in Table 3.4.

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AS 4055—2012 22


TABLE 3.3

ULTIMATE STRENGTH PRESSURES (kPa) FOR WIND CLASSIFICATION

FROM THE NET PRESSURE COEFFICIENTS GIVEN IN CLAUSE 3.2

Wind class Walls Roofs

Any

position

Away from

corners

(see Note 3)

Within

1200 mm of

corners

(see Note 3)

Any position General away

from edges

(see Note 2)

Within

1200 mm of

edges

(see Note 2)

At corners (within

1200 mm of both

edges)

(see Note 2)

Pressure

Zone

G, SC

Figure 3.2

G

Figure 3.2

SC

Figure 3.2

G, RE, RC

Figure 3.1

G

Figure 3.1

RE

Figure 3.1

RC

Figure 3.1

KC.Cp,n +0.9 −0.77 −1.35 +0.63 −0.99 −1.8 −2.61

N1 +0.62 −0.53 −0.94 +0.44 −0.69 −1.25 −1.81

N2 +0.86 −0.74 −1.30 +0.60 −0.95 −1.73 −2.51

N3 +1.35 −1.16 −2.03 +0.95 −1.49 −2.70 −3.92

N4 +2.01 −1.72 −3.01 +1.41 −2.21 -4.02 −5.83

N5 +2.96 −2.53 −4.44 +2.07 −3.25 −5.91 −8.58

N6 +3.99 −3.42 −5.99 +2.80 -4.39 −7.99 −11.58

KC.Cp,n +1.2 −1.2 −1.8 +0.95 −1.44 −2.25 −3.06

C1 +1.80 −1.80 −2.7 +1.43 −2.16 −3.38 −4.59

C2 +2.68 −2.68 −4.02 +2.12 −3.21 −5.02 −6.83

C3 +3.94 −3.94 −5.91 +3.12 −4.73 −7.39 −10.05

C4 +5.33 −5.33 −7.99 +4.22 −6.39 −9.98 −13.58

NOTES:

1 All locations must be able to resist both positive and negative net pressures. The positive net pressures apply to any

position on the surface. The negative net pressures are given for each pressure zone defined in Clause 3.1 and illustrated

for roofs in Figure 3.1 and for walls in Figure 3.2.

2 For roofs, net pressures on cladding, fasteners and immediate supporting members (such as battens and purlins) are

specific to the pressure zone. Net pressure effects on trusses and rafters can be taken from the net pressures for general

zones.

3 For walls, net pressures on cladding elements and fasteners (such as wall sheathing, windows and doors) are specific to the

pressure zone. Net pressure effects on wall studs and frames can be taken from the net pressures for general zones.

4 The design net pressures for eaves and soffit linings are taken as equal to the net pressures applied to adjacent wall surface

(e.g. the design pressure for eaves lining within 1200 mm of a corner for a C2 classification is +2.68 kPa and −4.02 kPa)

5 The net pressures for all N wind classifications may only be used where all cladding elements including windows

demonstrate compliance with the relevant Australian Standard. (See Paragraph A4).

6 In order to use the internal pressures in the N classifications in this Table, all of the cladding elements including windows,

doors and garage doors need to be designed to resist the design winds.

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TABLE 3.4

SERVICEABILITY PRESSURES (kPa) FOR WIND CLASSIFICATION

FROM THE NET PRESSURE COEFFICIENTS GIVEN IN CLAUSE 3.2

Wind class

Walls Roofs

Any

position

Away from

corners

(see Note 2)

Within

1200 mm of

corners

(see Note 3)

Any position General away

from edges

(see Note 2)

Within

1200 mm of

edges

(see Note 2)

At corners (within

1200 mm of both

edges)

(see Note 2)

Pressure

Zone

G, SC

Figure 3.2

G

Figure 3.2

SC

Figure 3.2

G, RE, RC

Figure 3.1

G

Figure 3.1

RE

Figure 3.1

RC

Figure 3.1

KC.Cp,n +0.9 −0.77 −1.35 +0.63 −0.99 −1.8 −2.61

N1serv +0.37 −0.31 −0.55 +0.26 −0.40 −0.73 −1.06

N2 serv +0.37 −0.31 −0.55 +0.26 −0.40 −0.73 −1.06

N3 serv +0.55 −0.47 −0.83 +0.39 −0.61 −1.11 −1.60

N4 serv +0.82 −0.70 −1.23 +0.57 −0.90 −1.64 −2.38

N5 serv +1.19 −1.02 −1.79 +0.84 −1.31 −2.39 −3.46

N6 serv +1.63 −1.40 −2.45 +1.14 −1.80 −3.27 −4.74

KC.Cp,n +0.9 −0.77 −1.35 +0.63 −0.99 −1.8 −2.61

C1 serv +0.55 −0.47 −0.83 +0.39 −0.61 −1.11 −1.60

C2 serv +0.82 −0.70 −1.23 +0.57 −0.90 −1.64 −2.38

C3 serv +1.19 −1.02 −1.79 +0.84 −1.31 −2.39 −3.46

C4 serv +1.63 −1.40 −2.45 +1.14 −1.80 −3.27 −4.74

NOTES:

1 All locations are subject to both positive and negative net pressures. The positive net pressures apply to any position on

the surface. The negative net pressures are given for each pressure zone defined in Clause 3.1 and illustrated for roofs

in Figure 3.1 and for walls in Figure 3.2.

2 For roofs, net pressures on cladding, fasteners and immediate supporting members (such as battens and purlins) are

specific to the pressure zone. Net pressure effects on trusses and rafters can be taken from the net pressures for general

zones.

3 For walls, net pressures on cladding elements and fasteners (such as wall sheathing, windows and doors) are specific to

the pressure zone. Net pressure effects on wall studs and frames can be taken from the net pressures for general zones.

4 The design net pressures for eaves and soffit linings is taken as equal to the net pressures applied to adjacent wall

surface

5 The net pressures for all N wind classifications may only be used where all cladding elements including windows

demonstrate compliance with the relevant Australian Standard. (See Paragraph A4).

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AS 4055—2012 24


S E C T I O N 4 U P L I F T F O R C E S

Table 4.1 gives net design uplift pressures for the determination of anchoring requirements

at tops of walls. The pressures shall be applied as uplift on the entire roof surface.

TABLE 4.1

NET DESIGN UPLIFT PRESSURES FOR DETERMINATION

OF ANCHORING REQUIREMENTS AT TOP OF WALLS

kilopascals

Wind class

Serviceability limit state Ultimate strength limit state

Tile roof Sheet roof

(see Note 4) Tile roof

Sheet roof

(see Note 4)

N1 0 0.04 0 0.33

N2 0 0.04 0.14 0.59

N3 0 0.25 0.68 1.13

N4 0 0.54 1.40 1.85

N5 0.42 0.95 2.44 2.89

N6 0.90 1.44 3.58 4.03

C1 0 0.25 1.35 1.80

C2 0 0.54 2.40 2.85

C3 0.41 0.95 3.92 4.37

C4 0.90 1.44 5.58 6.03

NOTES:

1 Positive values in this Table indicate a net upward pressure that is to be resisted by tie

down details.

2 The net design uplift pressures given in Table 4.1 are based on the following load

combinations:

(a) Serviceability limit state: Ws – G.

(b) Ultimate strength limit state: Wu – γG.

3 Wu and Ws have been calculated as set out in Section 3 where Vh = Vh,u or Vh,s as

appropriate, using the pressure coefficients as given in Section 3.

4 Load combination factor γ = 0.9.

5 The values for G = 0.9 kPa for tile roof, G = 0.4 kPa for sheet roof have been taken

from AS 1684.

6 Sheet roof includes metal tile roof.

7 The net uplift pressures presented in this table may only be used where all cladding

elements including windows demonstrate compliance with the relevant Australian

Standard.

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25 AS 4055—2012


S E C T I O N 5 R A C K I N G F O R C E S

5.1 RACKING FORCES

Racking forces are lateral (horizontal) forces transferred to the foundations through bracing

provided for each storey of the house and the subfloor.

The forces occur in walls parallel to the wind direction and are calculated from the

horizontal component of wind blowing on the external envelope of the house and resisted

by bracing walls.

Racking forces shall be calculated as follows:

(a) Determine the wind class as given in Section 2.

(b) Determine area of elevation of the house as given in Clause 5.2.

(c) Determine the wind pressure as given in Table 5.1 for buildings presenting a flat

vertical surface to the wind.

(d) Determine the wind pressure as given in Tables 5.2 to 5.13 using the width (shorter

dimension) of the building and roof pitch of the building being designed. Pressures

are given for single storey and upper storey of two storeys for both long and short

sides of the building, and for lower storey of two storeys or subfloor for both long

and short sides of the building.

(e) Calculate racking force, in kN, as follows:

Total racking force = Area of elevation (m2) × Lateral wind pressure (kPa).

The racking force shall be calculated for both directions (long and short sides) of the

building. The total racking force for each storey or level of the building shall be determined

as the sum of the forces on each of the areas facing the direction being considered. Racking

forces shall be calculated to address the most adverse loading situation.

NOTES:

1 For intermediate values between those given in Tables 5.1 to 5.13, use linear interpolation.

2 For the explanation of Tables 5.1 to 5.13, see Appendix A.

3 For worked examples, see Appendix D.

5.2 AREA OF ELEVATION

Area of elevation appropriate for calculation of racking forces shall be as shown in

Figures 5.1 to 5.3.

The wind direction used shall be that resulting in the greatest load for the length and width

of the building, respectively. As wind can blow from any direction, the elevation used shall

be that for the worst direction. In the case of a single-storey house with a gable at one end

and a hip at the other, the gable end facing the wind will result in a greater amount of load

at right angles to the width of the house than the hip end facing the wind.

For complex building shapes, buildings that are composed of a combination of storeys or

rectangles (i.e., L, H or U shapes) the shapes may be considered individually and forces

added together later or the total area as a whole can be calculated. Irrespective of which

method is used, racking forces shall be calculated to address the most adverse situation.

If a veranda, or the like, is present and is to be enclosed, it shall be included in the ‘area of

elevation’ calculations.

Where there is more than one floor level in a building, each level shall be considered

separately for the purpose of calculating the racking forces at each level. Acc

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AS 4055—2012 26


Wind direct ion 1

Wind direct ion 2

Gable end

Hip end

Area ofe levat ion

Floor level

Area of e levat ion(gable ends)

Area ofe levat ion

h0

h0

Floor level

(a) Plan

(b) Wind direct ion 1


NOTES:

1 h0 = half the height of the wall (half of the floor to ceiling height).

2 For lower storey of two-storey section ho = half the height of the lower storey (i.e., lower storey floor to

lower storey ceiling).

3 The area of elevation of the triangular portion of eaves overhang up to 1000 mm wide may be ignored in

the determination of area of elevation.

FIGURE 5.1 DETERMINING AREA OF ELEVATION FOR A

SINGLE-STOREY BUILDING

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(a) Plan


(c) Wind direct ion 2

Wind direct ion 1

Winddirect ion 2

Gable end

Hip end

Hip end

h0

h0

h0

Floor level

Cei l inglevelFloor level

Upper storey of two-storey sect ion

Single-storey sect ion

Area of e levat ion(gable end)

Lower storey of two-storey sect ion

Area ofe levat ion

Area of e levat ion(gable end)

Area of e levat ionArea of e levat ion

h0

h0

Lower storey of two-storey sect ionUpper storey of two-storey sect ion

Cei l inglevel

Upperf loorlevelFloor level

NOTES:

1 h0 = half the height of the wall (half of the floor to ceiling height).

2 For houses on sloping ground, the area of elevation will vary depending upon the wind direction or

elevation being considered. The racking force calculated for the worst case should be selected.



FIGURE 5.2 DETERMINING AREA OF ELEVATION FOR A TWO-STOREY OR SPLIT

LEVEL BUILDING

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AS 4055—2012 28


Wind direct ion 2 Wind direct ion 3

Gable endHip end

Wind direct ion 1

Floor

Area ofe levat ion

H0 h0

Area ofe levat ion

Floor

Floor

Area ofe levat ion

h0

h0

(a) Plan


(c) Wind direct ion 2—Hip end (d) Wind direct ion 3—Gable end

In the subf loor of a two-storey construct ion, the maximum distance (H0) f rom theground to the unders ide of the bearer in the lower f loor shal l be 1800 mm.

FIGURE 5.3 DETERMINING AREA OF ELEVATION FOR SUBFLOORS

NOTES:

1 h0 = half the height from the ground to the lower-storey floor.

2 For wind direction 2, the pressure on the gable end is determined from Table 5.1 and the pressure on the

hip section of the elevation is determined from Tables 5.2 to 5.13. The total of racking forces is the sum of

the forces calculated for each section.



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TABLE 5.1

VERTICAL SURFACES (FLAT WALLS, GABLE ENDS AND SKILLION ENDS)—

PRESSURE ON AREA OF ELEVATION

Wind direct ion Wind direct ion

Wind direct ion

Wind direct ion

Wind direct ion

Wind direct ion

Wind direct ion

Wind direct ion

Wind direct ion

Wind class Pressure

kPa

N1 0.66

N2 0.92

N3 1.44

N4 2.14

N5 3.16

N6 4.26

C1 1.44

C2 2.14

C3 3.16

C4 4.26

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TABLE 5.2

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—PRESSURE (kPa) ON AREA

OF ELEVATION—SINGLE STOREY OR UPPER FLOOR OF TWO STOREYS

Single storey or upper floor of two storeys, 2.4 m storey, 0.3 m floor

Width (m) Roof pitch (degrees)

0 5 10 15 20 25 30 35

Wind di rect ion Wind di rect ion

WW

N1: Wind on side

4 0.61 0.53 0.48 0.45 0.49 0.56 0.56 0.57

5 0.61 0.52 0.46 0.44 0.49 0.56 0.55 0.57

6 0.61 0.50 0.43 0.44 0.50 0.56 0.55 0.57

7 0.61 0.49 0.41 0.44 0.50 0.56 0.55 0.58

8 0.61 0.47 0.39 0.44 0.51 0.56 0.55 0.58

9 0.61 0.46 0.37 0.44 0.51 0.56 0.55 0.58

10 0.61 0.45 0.35 0.43 0.51 0.56 0.55 0.58

11 0.61 0.44 0.34 0.43 0.51 0.55 0.55 0.58

12 0.61 0.42 0.32 0.42 0.50 0.55 0.54 0.58

13 0.61 0.41 0.31 0.41 0.50 0.55 0.54 0.58

14 0.61 0.40 0.30 0.41 0.50 0.54 0.54 0.58

15 0.61 0.39 0.29 0.40 0.49 0.54 0.54 0.58

16 0.61 0.39 0.28 0.40 0.49 0.54 0.53 0.57

Wind di rect ion Wind di rect ionW W

N1: Wind on end

4 0.67 0.62 0.59 0.56 0.60 0.57 0.59 0.60

5 0.67 0.61 0.57 0.55 0.59 0.56 0.58 0.60

6 0.67 0.60 0.55 0.54 0.59 0.56 0.58 0.60

7 0.67 0.59 0.53 0.54 0.59 0.56 0.58 0.60

8 0.67 0.58 0.52 0.54 0.59 0.56 0.58 0.60

9 0.67 0.57 0.50 0.53 0.59 0.56 0.58 0.60

10 0.67 0.56 0.49 0.53 0.58 0.56 0.57 0.60

11 0.67 0.55 0.47 0.52 0.58 0.56 0.57 0.60

12 0.67 0.55 0.46 0.51 0.58 0.56 0.57 0.60

13 0.67 0.54 0.45 0.50 0.57 0.56 0.56 0.59

14 0.67 0.53 0.44 0.50 0.57 0.56 0.56 0.59

15 0.67 0.52 0.43 0.49 0.57 0.56 0.56 0.59

16 0.67 0.52 0.42 0.48 0.56 0.56 0.56 0.59

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TABLE 5.3


OF ELEVATION—LOWER STOREY OF TWO STOREYS

Lower storey of two storeys, 2.4 m storey, 0.3 m floor


0 5 10 15 20 25 30 35

Wind direction Wind direction

W W

N1: Wind on side

4 0.61 0.58 0.56 0.54 0.54 0.60 0.62 0.61

5 0.61 0.58 0.55 0.53 0.53 0.59 0.61 0.60

6 0.61 0.57 0.54 0.52 0.52 0.59 0.60 0.59

7 0.61 0.57 0.53 0.51 0.52 0.59 0.59 0.59

8 0.61 0.56 0.53 0.50 0.52 0.58 0.58 0.59

9 0.61 0.55 0.52 0.49 0.52 0.58 0.58 0.59

10 0.61 0.55 0.51 0.48 0.52 0.58 0.57 0.59

11 0.61 0.54 0.50 0.48 0.52 0.58 0.57 0.59

12 0.61 0.54 0.49 0.48 0.52 0.58 0.57 0.59

13 0.61 0.53 0.48 0.48 0.52 0.58 0.57 0.59

14 0.61 0.53 0.47 0.48 0.52 0.58 0.57 0.59

15 0.61 0.52 0.46 0.48 0.53 0.58 0.57 0.59

16 0.61 0.52 0.45 0.48 0.53 0.58 0.57 0.59

Wind direction

W

N1: Wind on end

4 0.67 0.65 0.64 0.63 0.62 0.63 0.64 0.63

5 0.67 0.65 0.63 0.62 0.61 0.62 0.63 0.63

6 0.67 0.64 0.63 0.61 0.61 0.62 0.63 0.62

7 0.67 0.64 0.62 0.60 0.61 0.62 0.62 0.62

8 0.67 0.64 0.62 0.60 0.61 0.62 0.62 0.62

9 0.67 0.63 0.61 0.59 0.60 0.62 0.61 0.62

10 0.67 0.63 0.60 0.58 0.60 0.61 0.61 0.61

11 0.67 0.63 0.60 0.58 0.60 0.61 0.60 0.61

12 0.67 0.62 0.59 0.58 0.60 0.61 0.60 0.61

13 0.67 0.62 0.58 0.58 0.60 0.61 0.60 0.61

14 0.67 0.62 0.58 0.58 0.60 0.61 0.60 0.61

15 0.67 0.61 0.57 0.57 0.60 0.61 0.60 0.61

16 0.67 0.61 0.57 0.57 0.60 0.61 0.60 0.61

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TABLE 5.4





0 5 10 15 20 25 30 35


WW

N2: Wind on side

4 0.84 0.74 0.67 0.61 0.61 0.72 0.77 0.76

5 0.84 0.71 0.64 0.57 0.58 0.69 0.75 0.74

6 0.84 0.69 0.61 0.55 0.59 0.70 0.74 0.74

7 0.84 0.67 0.58 0.53 0.59 0.70 0.73 0.74

8 0.84 0.65 0.56 0.51 0.60 0.71 0.72 0.75

9 0.84 0.64 0.54 0.49 0.61 0.71 0.71 0.75

10 0.84 0.62 0.52 0.48 0.61 0.72 0.70 0.75

11 0.84 0.60 0.50 0.48 0.62 0.72 0.71 0.75

12 0.84 0.59 0.47 0.49 0.63 0.72 0.71 0.76

13 0.84 0.57 0.45 0.49 0.63 0.73 0.71 0.77

14 0.84 0.56 0.43 0.50 0.64 0.73 0.72 0.77

15 0.84 0.55 0.42 0.50 0.65 0.73 0.72 0.77

16 0.84 0.53 0.40 0.51 0.65 0.73 0.72 0.78


N2: Wind on end

4 0.92 0.86 0.81 0.77 0.76 0.79 0.82 0.81

5 0.92 0.84 0.79 0.74 0.73 0.77 0.81 0.79

6 0.92 0.83 0.77 0.72 0.73 0.77 0.79 0.79

7 0.92 0.82 0.75 0.70 0.73 0.77 0.78 0.79

8 0.92 0.80 0.73 0.68 0.72 0.77 0.77 0.79

9 0.92 0.79 0.71 0.66 0.72 0.77 0.76 0.79

10 0.92 0.78 0.69 0.65 0.72 0.77 0.75 0.78

11 0.92 0.77 0.68 0.64 0.72 0.77 0.75 0.79

12 0.92 0.76 0.66 0.64 0.72 0.77 0.75 0.79

13 0.92 0.75 0.64 0.64 0.73 0.77 0.75 0.79

14 0.92 0.73 0.62 0.64 0.73 0.77 0.76 0.79

15 0.92 0.72 0.60 0.64 0.73 0.77 0.76 0.80

16 0.92 0.71 0.59 0.64 0.73 0.77 0.76 0.80

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TABLE 5.5




Width

(m)

Roof pitch (degrees)

0 5 10 15 20 25 30 35


W W

N2: Wind on side

4 0.84 0.81 0.78 0.75 0.75 0.83 0.85 0.84

5 0.84 0.80 0.77 0.73 0.73 0.82 0.84 0.83

6 0.84 0.79 0.75 0.72 0.73 0.81 0.83 0.82

7 0.84 0.78 0.74 0.70 0.72 0.81 0.82 0.82

8 0.84 0.78 0.73 0.69 0.72 0.81 0.81 0.82

9 0.84 0.77 0.71 0.68 0.72 0.81 0.80 0.81

10 0.84 0.76 0.70 0.67 0.72 0.81 0.79 0.81

11 0.84 0.75 0.69 0.66 0.72 0.80 0.79 0.81

12 0.84 0.74 0.68 0.66 0.72 0.80 0.79 0.81

13 0.84 0.74 0.66 0.66 0.72 0.80 0.79 0.82

14 0.84 0.73 0.65 0.66 0.73 0.80 0.79 0.82

15 0.84 0.72 0.64 0.66 0.73 0.80 0.79 0.82

16 0.84 0.72 0.63 0.66 0.73 0.80 0.79 0.82

Wind direction

W

N2: Wind on end

4 0.92 0.90 0.89 0.87 0.86 0.87 0.88 0.87

5 0.92 0.90 0.88 0.85 0.85 0.86 0.87 0.87

6 0.92 0.89 0.87 0.84 0.85 0.86 0.87 0.86

7 0.92 0.89 0.86 0.84 0.84 0.86 0.86 0.86

8 0.92 0.88 0.85 0.83 0.84 0.85 0.85 0.86

9 0.92 0.88 0.84 0.82 0.84 0.85 0.84 0.85

10 0.92 0.87 0.84 0.81 0.83 0.85 0.84 0.85

11 0.92 0.87 0.83 0.80 0.83 0.85 0.84 0.85

12 0.92 0.86 0.82 0.80 0.83 0.85 0.83 0.85

13 0.92 0.86 0.81 0.80 0.83 0.84 0.83 0.85

14 0.92 0.85 0.80 0.80 0.83 0.84 0.83 0.85

15 0.92 0.85 0.79 0.79 0.83 0.84 0.83 0.85

16 0.92 0.85 0.78 0.79 0.83 0.84 0.83 0.85

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TABLE 5.6

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—

PRESSURE (kPa) ON AREA OF ELEVATION—

SINGLE STOREY OR UPPER FLOOR OF TWO STOREYS



0 5 10 15 20 25 30 35


WW

N3, C1: Wind on side

4 1.30 1.20 1.00 0.95 0.96 1.10 1.20 1.20

5 1.30 1.10 1.00 0.89 0.91 1.10 1.20 1.20

6 1.30 1.10 0.95 0.85 0.91 1.10 1.20 1.20

7 1.30 1.10 0.91 0.82 0.93 1.10 1.10 1.20

8 1.30 1.00 0.88 0.79 0.94 1.10 1.10 1.20

9 1.30 0.99 0.84 0.77 0.95 1.10 1.10 1.20

10 1.30 0.97 0.81 0.75 0.95 1.10 1.10 1.20

11 1.30 0.94 0.78 0.75 0.97 1.10 1.10 1.20

12 1.30 0.92 0.74 0.76 0.98 1.10 1.10 1.20

13 1.30 0.90 0.71 0.77 0.99 1.10 1.10 1.20

14 1.30 0.87 0.68 0.78 1.00 1.10 1.10 1.20

15 1.30 0.85 0.65 0.79 1.00 1.10 1.10 1.20

16 1.30 0.83 0.62 0.79 1.00 1.10 1.10 1.20


N3, C1: Wind on end

4 1.40 1.30 1.30 1.20 1.20 1.20 1.30 1.30

5 1.40 1.30 1.20 1.20 1.10 1.20 1.30 1.20

6 1.40 1.30 1.20 1.10 1.10 1.20 1.20 1.20

7 1.40 1.30 1.20 1.10 1.10 1.20 1.20 1.20

8 1.40 1.30 1.10 1.10 1.10 1.20 1.20 1.20

9 1.40 1.20 1.10 1.00 1.10 1.20 1.20 1.20

10 1.40 1.20 1.10 1.00 1.10 1.20 1.20 1.20

11 1.40 1.20 1.10 1.00 1.10 1.20 1.20 1.20

12 1.40 1.20 1.00 1.00 1.10 1.20 1.20 1.20

13 1.40 1.20 1.00 1.00 1.10 1.20 1.20 1.20

14 1.40 1.10 0.97 1.00 1.10 1.20 1.20 1.20

15 1.40 1.10 0.94 1.00 1.10 1.20 1.20 1.20

16 1.40 1.10 0.92 1.00 1.10 1.20 1.20 1.20

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TABLE 5.7



LOWER STOREY OF TWO STOREYS



0 5 10 15 20 25 30 35


W W


4 1.30 1.30 1.20 1.20 1.20 1.30 1.30 1.30

5 1.30 1.20 1.20 1.10 1.10 1.30 1.30 1.30

6 1.30 1.20 1.20 1.10 1.10 1.30 1.30 1.30

7 1.30 1.20 1.20 1.10 1.10 1.30 1.30 1.30

8 1.30 1.20 1.10 1.10 1.10 1.30 1.30 1.30

9 1.30 1.20 1.10 1.10 1.10 1.30 1.20 1.30

10 1.30 1.20 1.10 1.00 1.10 1.30 1.20 1.30

11 1.30 1.20 1.10 1.00 1.10 1.30 1.20 1.30

12 1.30 1.20 1.10 1.00 1.10 1.30 1.20 1.30

13 1.30 1.20 1.00 1.00 1.10 1.30 1.20 1.30

14 1.30 1.10 1.00 1.00 1.10 1.30 1.20 1.30

15 1.30 1.10 1.00 1.00 1.10 1.20 1.20 1.30

16 1.30 1.10 0.98 1.00 1.10 1.20 1.20 1.30

Wind direction

W

N3, C1: Wind on end

4 1.40 1.40 1.40 1.40 1.30 1.40 1.40 1.40

5 1.40 1.40 1.40 1.30 1.30 1.30 1.40 1.40

6 1.40 1.40 1.40 1.30 1.30 1.30 1.40 1.30

7 1.40 1.40 1.30 1.30 1.30 1.30 1.30 1.30

8 1.40 1.40 1.30 1.30 1.30 1.30 1.30 1.30

9 1.40 1.40 1.30 1.30 1.30 1.30 1.30 1.30

10 1.40 1.40 1.30 1.30 1.30 1.30 1.30 1.30

11 1.40 1.40 1.30 1.30 1.30 1.30 1.30 1.30

12 1.40 1.30 1.30 1.30 1.30 1.30 1.30 1.30

13 1.40 1.30 1.30 1.20 1.30 1.30 1.30 1.30

14 1.40 1.30 1.30 1.20 1.30 1.30 1.30 1.30

15 1.40 1.30 1.20 1.20 1.30 1.30 1.30 1.30

16 1.40 1.30 1.20 1.20 1.30 1.30 1.30 1.30

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AS 4055—2012 36


TABLE 5.8





0 5 10 15 20 25 30 35


WW


4 2.00 1.70 1.60 1.40 1.40 1.70 1.80 1.80

5 2.00 1.70 1.50 1.30 1.30 1.60 1.80 1.70

6 2.00 1.60 1.40 1.30 1.40 1.60 1.70 1.70

7 2.00 1.60 1.40 1.20 1.40 1.60 1.70 1.70

8 2.00 1.50 1.30 1.20 1.40 1.60 1.70 1.70

9 2.00 1.50 1.30 1.10 1.40 1.70 1.70 1.70

10 2.00 1.40 1.20 1.10 1.40 1.70 1.60 1.70

11 2.00 1.40 1.20 1.10 1.40 1.70 1.60 1.80

12 2.00 1.40 1.10 1.10 1.50 1.70 1.70 1.80

13 2.00 1.30 1.10 1.10 1.50 1.70 1.70 1.80

14 2.00 1.30 1.00 1.20 1.50 1.70 1.70 1.80

15 2.00 1.30 0.97 1.20 1.50 1.70 1.70 1.80

16 2.00 1.20 0.93 1.20 1.50 1.70 1.70 1.80


N4, C2: Wind on end

4 2.10 2.00 1.90 1.80 1.80 1.80 1.90 1.90

5 2.10 2.00 1.80 1.70 1.70 1.80 1.90 1.80

6 2.10 1.90 1.80 1.70 1.70 1.80 1.80 1.80

7 2.10 1.90 1.70 1.60 1.70 1.80 1.80 1.80

8 2.10 1.90 1.70 1.60 1.70 1.80 1.80 1.80

9 2.10 1.80 1.70 1.50 1.70 1.80 1.80 1.80

10 2.10 1.80 1.60 1.50 1.70 1.80 1.80 1.80

11 2.10 1.80 1.60 1.50 1.70 1.80 1.80 1.80

12 2.10 1.80 1.50 1.50 1.70 1.80 1.80 1.80

13 2.10 1.70 1.50 1.50 1.70 1.80 1.80 1.80

14 2.10 1.70 1.40 1.50 1.70 1.80 1.80 1.80

15 2.10 1.70 1.40 1.50 1.70 1.80 1.80 1.90

16 2.10 1.70 1.40 1.50 1.70 1.80 1.80 1.90

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TABLE 5.9






0 5 10 15 20 25 30 35


W W


4 2.00 1.90 1.80 1.70 1.70 1.90 2.00 2.00

5 2.00 1.90 1.80 1.70 1.70 1.90 2.00 1.90

6 2.00 1.80 1.80 1.70 1.70 1.90 1.90 1.90

7 2.00 1.80 1.70 1.60 1.70 1.90 1.90 1.90

8 2.00 1.80 1.70 1.60 1.70 1.90 1.90 1.90

9 2.00 1.80 1.70 1.60 1.70 1.90 1.90 1.90

10 2.00 1.80 1.60 1.60 1.70 1.90 1.80 1.90

11 2.00 1.70 1.60 1.50 1.70 1.90 1.80 1.90

12 2.00 1.70 1.60 1.50 1.70 1.90 1.80 1.90

13 2.00 1.70 1.50 1.50 1.70 1.90 1.80 1.90

14 2.00 1.70 1.50 1.50 1.70 1.90 1.80 1.90

15 2.00 1.70 1.50 1.50 1.70 1.90 1.80 1.90

16 2.00 1.70 1.50 1.50 1.70 1.90 1.80 1.90

Wind direction

W

N4, C2: Wind on end

4 2.10 2.10 2.10 2.00 2.00 2.00 2.10 2.00

5 2.10 2.10 2.00 2.00 2.00 2.00 2.00 2.00

6 2.10 2.10 2.00 2.00 2.00 2.00 2.00 2.00

7 2.10 2.10 2.00 1.90 2.00 2.00 2.00 2.00

8 2.10 2.10 2.00 1.90 2.00 2.00 2.00 2.00

9 2.10 2.00 2.00 1.90 1.90 2.00 2.00 2.00

10 2.10 2.00 1.90 1.90 1.90 2.00 2.00 2.00

11 2.10 2.00 1.90 1.90 1.90 2.00 1.90 2.00

12 2.10 2.00 1.90 1.90 1.90 2.00 1.90 2.00

13 2.10 2.00 1.90 1.90 1.90 2.00 1.90 2.00

14 2.10 2.00 1.90 1.90 1.90 2.00 1.90 2.00

15 2.10 2.00 1.80 1.80 1.90 2.00 1.90 2.00

16 2.10 2.00 1.80 1.80 1.90 2.00 1.90 2.00

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AS 4055—2012 38


TABLE 5.10






0 5 10 15 20 25 30 35


WW


4 2.90 2.50 2.30 2.10 2.10 2.50 2.60 2.60

5 2.90 2.40 2.20 1.90 2.00 2.40 2.60 2.50

6 2.90 2.40 2.10 1.90 2.00 2.40 2.50 2.50

7 2.90 2.30 2.00 1.80 2.00 2.40 2.50 2.50

8 2.90 2.20 1.90 1.70 2.10 2.40 2.50 2.60

9 2.90 2.20 1.80 1.70 2.10 2.40 2.40 2.60

10 2.90 2.10 1.80 1.60 2.10 2.50 2.40 2.60

11 2.90 2.10 1.70 1.70 2.10 2.50 2.40 2.60

12 2.90 2.00 1.60 1.70 2.10 2.50 2.40 2.60

13 2.90 2.00 1.60 1.70 2.20 2.50 2.40 2.60

14 2.90 1.90 1.50 1.70 2.20 2.50 2.50 2.60

15 2.90 1.90 1.40 1.70 2.20 2.50 2.50 2.60

16 2.90 1.80 1.40 1.70 2.20 2.50 2.50 2.70


N5, C3: Wind on end

4 3.20 2.90 2.80 2.60 2.60 2.70 2.80 2.80

5 3.20 2.90 2.70 2.50 2.50 2.60 2.80 2.70

6 3.20 2.80 2.60 2.40 2.50 2.60 2.70 2.70

7 3.20 2.80 2.60 2.40 2.50 2.60 2.70 2.70

8 3.20 2.80 2.50 2.30 2.50 2.60 2.60 2.70

9 3.20 2.70 2.40 2.30 2.50 2.60 2.60 2.70

10 3.20 2.70 2.40 2.20 2.50 2.60 2.60 2.70

11 3.20 2.60 2.30 2.20 2.50 2.60 2.60 2.70

12 3.20 2.60 2.20 2.20 2.50 2.60 2.60 2.70

13 3.20 2.50 2.20 2.20 2.50 2.60 2.60 2.70

14 3.20 2.50 2.10 2.20 2.50 2.60 2.60 2.70

15 3.20 2.50 2.10 2.20 2.50 2.60 2.60 2.70

16 3.20 2.40 2.00 2.20 2.50 2.60 2.60 2.70

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TABLE 5.11





0 5 10 15 20 25 30 35


W W


4 2.90 2.80 2.70 2.60 2.60 2.80 2.90 2.90

5 2.90 2.70 2.60 2.50 2.50 2.80 2.90 2.80

6 2.90 2.70 2.60 2.50 2.50 2.80 2.80 2.80

7 2.90 2.70 2.50 2.40 2.50 2.80 2.80 2.80

8 2.90 2.70 2.50 2.40 2.50 2.80 2.80 2.80

9 2.90 2.60 2.40 2.30 2.50 2.80 2.70 2.80

10 2.90 2.60 2.40 2.30 2.50 2.80 2.70 2.80

11 2.90 2.60 2.40 2.30 2.50 2.80 2.70 2.80

12 2.90 2.50 2.30 2.30 2.50 2.70 2.70 2.80

13 2.90 2.50 2.30 2.30 2.50 2.70 2.70 2.80

14 2.90 2.50 2.20 2.30 2.50 2.70 2.70 2.80

15 2.90 2.50 2.20 2.30 2.50 2.70 2.70 2.80

16 2.90 2.50 2.10 2.30 2.50 2.70 2.70 2.80

Wind direction

W

N5, C3: Wind on end

4 3.20 3.10 3.00 3.00 3.00 3.00 3.00 3.00

5 3.20 3.10 3.00 2.90 2.90 2.90 3.00 3.00

6 3.20 3.10 3.00 2.90 2.90 2.90 3.00 2.90

7 3.20 3.00 2.90 2.90 2.90 2.90 2.90 2.90

8 3.20 3.00 2.90 2.80 2.90 2.90 2.90 2.90

9 3.20 3.00 2.90 2.80 2.90 2.90 2.90 2.90

10 3.20 3.00 2.90 2.80 2.90 2.90 2.90 2.90

11 3.20 3.00 2.80 2.80 2.80 2.90 2.90 2.90

12 3.20 3.00 2.80 2.70 2.80 2.90 2.90 2.90

13 3.20 2.90 2.80 2.70 2.80 2.90 2.80 2.90

14 3.20 2.90 2.70 2.70 2.80 2.90 2.80 2.90

15 3.20 2.90 2.70 2.70 2.80 2.90 2.80 2.90

16 3.20 2.90 2.70 2.70 2.80 2.90 2.80 2.90

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AS 4055—2012 40


TABLE 5.12






0 5 10 15 20 25 30 35


WW


4 3.92 3.38 3.11 2.84 2.84 3.38 3.51 3.51

5 3.92 3.24 2.97 2.57 2.70 3.24 3.51 3.38

6 3.92 3.24 2.84 2.57 2.70 3.24 3.38 3.38

7 3.92 3.11 2.70 2.43 2.70 3.24 3.38 3.38

8 3.92 2.97 2.57 2.30 2.84 3.24 3.38 3.51

9 3.92 2.97 2.43 2.30 2.84 3.24 3.24 3.51

10 3.92 2.84 2.43 2.16 2.84 3.38 3.24 3.51

11 3.92 2.84 2.30 2.30 2.84 3.38 3.24 3.51

12 3.92 2.70 2.16 2.30 2.84 3.38 3.24 3.51

13 3.92 2.70 2.16 2.30 2.97 3.38 3.24 3.51

14 3.92 2.57 2.03 2.30 2.97 3.38 3.38 3.51

15 3.92 2.57 1.89 2.30 2.97 3.38 3.38 3.51

16 3.92 2.43 1.89 2.30 2.97 3.38 3.38 3.65


N6, C4: Wind on end

4 4.32 3.92 3.78 3.51 3.51 3.65 3.78 3.78

5 4.32 3.92 3.65 3.38 3.38 3.51 3.78 3.65

6 4.32 3.78 3.51 3.24 3.38 3.51 3.65 3.65

7 4.32 3.78 3.51 3.24 3.38 3.51 3.65 3.65

8 4.32 3.78 3.38 3.11 3.38 3.51 3.51 3.65

9 4.32 3.65 3.24 3.11 3.38 3.51 3.51 3.65

10 4.32 3.65 3.24 2.97 3.38 3.51 3.51 3.65

11 4.32 3.51 3.11 2.97 3.38 3.51 3.51 3.65

12 4.32 3.51 2.97 2.97 3.38 3.51 3.51 3.65

13 4.32 3.38 2.97 2.97 3.38 3.51 3.51 3.65

14 4.32 3.38 2.84 2.97 3.38 3.51 3.51 3.65

15 4.32 3.38 2.84 2.97 3.38 3.51 3.51 3.65

16 4.32 3.24 2.70 2.97 3.38 3.51 3.51 3.65

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TABLE 5.13






0 5 10 15 20 25 30 35


W W


4 3.92 3.78 3.65 3.51 3.51 3.78 3.92 3.92

5 3.92 3.65 3.51 3.38 3.38 3.78 3.92 3.78

6 3.92 3.65 3.51 3.38 3.38 3.78 3.78 3.78

7 3.92 3.65 3.38 3.24 3.38 3.78 3.78 3.78

8 3.92 3.65 3.38 3.24 3.38 3.78 3.78 3.78

9 3.92 3.51 3.24 3.11 3.38 3.78 3.65 3.78

10 3.92 3.51 3.24 3.11 3.38 3.78 3.65 3.78

11 3.92 3.51 3.24 3.11 3.38 3.78 3.65 3.78

12 3.92 3.38 3.11 3.11 3.38 3.65 3.65 3.78

13 3.92 3.38 3.11 3.11 3.38 3.65 3.65 3.78

14 3.92 3.38 2.97 3.11 3.38 3.65 3.65 3.78

15 3.92 3.38 2.97 3.11 3.38 3.65 3.65 3.78

16 3.92 3.38 2.84 3.11 3.38 3.65 3.65 3.78

Wind direction

W

N6, C4: Wind on end

4 4.32 4.19 4.05 4.05 4.05 4.05 4.05 4.05

5 4.32 4.19 4.05 3.92 3.92 3.92 4.05 4.05

6 4.32 4.19 4.05 3.92 3.92 3.92 4.05 3.92

7 4.32 4.05 3.92 3.92 3.92 3.92 3.92 3.92

8 4.32 4.05 3.92 3.78 3.92 3.92 3.92 3.92

9 4.32 4.05 3.92 3.78 3.92 3.92 3.92 3.92

10 4.32 4.05 3.92 3.78 3.92 3.92 3.92 3.92

11 4.32 4.05 3.78 3.78 3.78 3.92 3.92 3.92

12 4.32 4.05 3.78 3.65 3.78 3.92 3.92 3.92

13 4.32 3.92 3.78 3.65 3.78 3.92 3.78 3.92

14 4.32 3.92 3.65 3.65 3.78 3.92 3.78 3.92

15 4.32 3.92 3.65 3.65 3.78 3.92 3.78 3.92

16 4.32 3.92 3.65 3.65 3.78 3.92 3.78 3.92

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AS 4055—2012 42


APPENDIX A

COMMENTARY

(Informative)

A1 COMMENTARY ON SCOPE AND GENERAL

A1.1 General

This Standard has been derived for houses as a group or large numbers of buildings. In

general, the level of reliability for the group is similar to that found by applying

AS/NZS 1170.2. However, it is recognized that a correct application of this Standard may

lead to some houses with more conservative design loads, and others with less conservative

design loads.

It is important to categorize each building on a case-by-case basis. Each site should be

assessed individually for its wind classification. Each building must be assessed for

compliance with geometry and for evaluation of pressures.

A1.2 Comment on Clause 1.3—Geometric Limits

The geometric limits presented in Clause 1.3 have been provided to enable some

simplifications to the AS/NZS 1170.2 methods for the most common geometries of housing.

It is intended that 16 m width limit be applied to the width of the tallest section of the

house. For example, in many cases the various sections of a house (that is the basic

rectangular box shapes) may be displaced horizontally with respect to each other. This

could make the overall floor plan dimension greater than the 16 m limit even though none

of the sections of roof might be wider than 16 m.

Such a house should be within the limits provided that none of the roof sections parallel to

the wind direction being considered are greater than 16 m (neglecting the width of eaves).

A2 COMMENT ON TABLE 2.1—WIND CLASSIFICATION

An approximate 50% increase in wind pressures occurs from one class to the next higher

one, that is, N2 to N3, N3 to N4, etc.

Once a particular building site has been classified using the methods set out in Section 2,

the ultimate wind speed for that class represents the design wind speed for the house and

includes the effects of—

(a) the importance level which is set by the NCC (the design wind loading level

associated with housing);

(b) directionality (the likelihood of wind occurring at its maximum from the direction for

which the house is most vulnerable in terms of the pressures on the envelope);

(c) height (of the building above the ground);

(d) terrain roughness (sizes of the obstructions in the wider area around the building site

such as water, grass, open space and size of buildings);

(e) topography (the position of the site on hills or in valleys); and

(f) shielding (the effect of specific buildings and other obstructions near to the proposed

building).

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A3 DERIVATION OF TABLE 2.2—WIND CLASSIFICATION

A3.1 Wind classification

In determining the application of the N and C classes to the selected site criteria that are

given in Table 2.2, a number of simplifications of the methods in AS/NZS 1170.2 were

made. The classifications were derived from a range of design scenarios that were evaluated

using AS/NZS 1170.2. The following criteria were selected:

(a) Annual probability of exceedance has been taken as 1/500.

(b) A 0.95 factor on wind speed was allowed to account for the variation of orientation of

houses within suburbs and groups of suburbs and the fact that the peak wind gust will

only come from a single direction. There will be few for which this direction is the

critical one with respect to terrain, topography and the house orientation.

(c) A 5% margin has been allowed on the wind speed for the assigning of the N and C

classes.

(d) Average roof height has been taken as 6.5 m (selected as not the worst case but

covering the majority of average housing being constructed within the limitations

given in Figure 1.1).

(e) The terrain/height multiplier (M6.5,cat) has been derived from AS/NZS 1170.2 with h

(average roof height) taken as 6.5 m (see Table A1).

(f) Topographic multiplier (Mt) has been derived from the hill shape multiplier defined in

AS/NZS 1170.2 (see Table A2). The values chosen for T1 to T5 represent the average

of the ranges for each class (T0 is taken as 1.0 to represent housing on flat or nearly

flat topography). For the top third, the class changes for slopes greater than 30 m

high. A column has also been included for hill heights of less than 10 m to facilitate

correct classification of topography on small hills (with a height the same order as the

height of houses). The separation zone at the crest has not been included, but for

escarpments only, a zone immediately over the crest is included.

Shielding multiplier (Ms) has been derived from AS/NZS 1170.2 (see Table A3).

TABLE A1

TERRAIN CATEGORY MULTIPLIER (M6.5,cat) AT HEIGHT 6.5 m

Region

Terrain category multiplier (M6.5,cat)

Terrain

Category 1

Terrain

Category 1.5

Terrain

Category 2

Terrain

Category 2.5

Terrain

Category 3

All regions 1.07 1.00 0.94 0.88 0.83

NOTE: Terrain category multipliers for intermediate Terrain Categories (1.5 and 2.5) were found by interpolation.

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AS 4055—2012 44


TABLE A2

TOPOGRAPHIC MULTIPLIER (Mt)

Topographic class

Value of topographic multiplier

(Mt) applied in calculation of the

N and C categories

Range of values calculated using

AS/NZS 1170.2 that are included

in the class

T0 1.0 ≥1 <1.08

T1 1.1 ≥1.04 <1.16

T2 1.2 ≥1.14 <1.25

T3 1.3 ≥1.21 <1.37

T4 1.42 ≥1.29 <1.47

T5 1.57 ≥1.47

TABLE A3

SHIELDING MULTIPLIER (Ms)

Shielding class Shielding multiplier (Ms)

Full shielding (FS) 0.85

Partial shielding (PS) 0.95

No shielding (NS) 1.00

A3.2 Terrain category

The definitions of terrain category in this Standard are consistent with those incorporated

into AS/NZS 1170.2:2011 by its Amendment 2 (2012).

At serviceability and ultimate limit states wind speeds, the very strong winds tend to blow

the top off short-wavelength waves and the water surface can be quite smooth. Closed

waterbodies such as lakes, rivers and enclosed bays, therefore have minimal roughness and

can be classed as Terrain Category 1 where they are more than 200 m but less than 10 km

wide. However, larger water bodies such as open oceans and seas can have long wavelength

waves which rise as they enter the shallower near-shore water. This gives these waterbodies

a slightly rougher surface near the land and they can therefore be classified as Terrain

Category 1.5 in their effect on one and two storey houses.

Terrain Category 1.5 specifically addresses the roughness of near shore open waterbodies

such as seas and oceans adjoining housing land.

Where a water body is less than 200 m wide (i.e. the wind blows for less than 200 m across

the top of the water in order to pass over the site under consideration) the wind does not

have sufficient time over the water to increase its velocity enough for the terrain category to

change. However, where the wind passes over the water body for more than 200 m, the time

over smooth terrain is sufficient to increase the wind velocity to that of smooth terrain (i.e.

Terrain Category 1). Where the water body is large (i.e. the wind has been blowing over the

water for more than 10 km), then wind has the chance to develop long wavelength waves

that will shoal on reaching the shore irrespective of the wind. Hence:

(a) Water bodies less than 200 m wide in the direction that the wind is blowing to affect a

site do not affect the terrain category.

(b) Water bodies greater than 200 m wide, but less than 10 km wide in the direction that

the wind is blowing to affect a site are deemed to be Terrain Category 1.

(c) Only water bodies greater than 10 km wide in the direction that the wind is blowing

to affect a site are deemed to be Terrain Category 1.5.

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Terrain Category 2.5 addresses acreage subdivisions where the house density is less than 10

per hectare. This level of roughness is also appropriate for some wooded agricultural land

or farms with very high crops such as sugar cane.

Large trees offer some surface roughness. Even if they are denuded in very strong winds,

the standing trees contribute to the surface roughness. This is a very different concept to

shielding where a denuded tree is not able to offer protection to a nearby structure. The

density of trees is important in assigning terrain categories. Where trees are large and

robust (similar size to houses) then wooded areas with:

(i) Fewer than 2 large trees per hectare can be categorized as TC2.

(ii) Between 2 and 10 large trees per hectare can be categorized as TC2.5.

(iii) More than 10 large trees per hectare can be categorized as TC3.

In some cases, the 500 m radius circle may contain combinations of smooth features. For

example, a small lake with diameter less than 200 m may be adjoined by a park also with

width less than 200 m. However, the combine width of smooth features is greater than

200 m and the lake should be considered as part of the park, giving limiting terrain category

for the building at the centre of the 500 m radius circle as Terrain Category 2.

Other combinations of smooth features may be less apparent. For example, a freeway

reserve of width 150 m may be adjacent to a creek and reserve of width 100 m. Here the

total width of smooth features is greater than 200 m, so must be considered as a region of

Terrain Category 2.

Where the smooth features do not adjoin they do not have to be combined. For example, a

freeway reserve of width 150 m and a creek reserve of width 100 m separated by two rows

of houses can be treated as two separate smooth features, each with a width of less than

200 m. The two separated features do not affect the terrain category.

Appendix C has some illustrations of the application of terrain classification. It shows that

within 500 meters of a change in terrain category, the lowest terrain category applies to all

housing.

A3.3 Topographic class

The topographic class in AS 4055 is derived from the topographic multipliers used in

AS/NZS 1170.2 as shown in Table A2.

A3.4 Shielding

In assessing shielding, permanent obstructions of the same size as the house designed with a

frequency of more than 10 per hectare within 100 m of the site, can be considered as

providing full shielding. This means that two full rows of housing are required on all sides

to give full shielding. If only one full row of housing is available on one side, then the site

is categorized as ‘partially shielded’. If there are no shielding obstructions on at least one

side, then it is classified as ‘not shielded’.

In assessing shielding, a reasonable estimate should be made about infill development in the

next five years, as it is the anticipated development five years after construction that is

assessed.

Consistent with the classification of trees for terrain categories, large trees in Regions A

and B can be treated as obstructions, but not in Regions C and D. This is because the long

duration of the wind events in tropical cyclones can denude the trees and reduce their

effectiveness as obstructions.

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Recent amendments of AS/NZS 1170.2 provide that where buildings are situated on steeply

rising land, the roof of a building being designed will not be shielded by the roof of a

similar-sized building lower on the slope. This Standard has simplified the AS/NZS 1170.2

provisions by relating the shielding to the topographic class. Higher topographic classes are

associated with steeper slopes, for which full shielding is not appropriate. Hence, full

shielding may only be used on slopes corresponding to Topographic Classes T0, T1, and

T2. It is recognized that some partial shielding may be possible for slightly higher slopes,

so partial shielding is appropriate for Topographic Classes T0, T1, T2, and T3. No shielding

can be recognized where the slope is sufficient for T4 or T5.

A4 COMMENTARY ON PRESSURE COEFFICIENTS (SECTION 3)

The pressure coefficients given in Section 3 have been based on AS/NZS 1170.2. The

following criteria were used:

(a) The house comprises basically rectangular bluff bodies within the geometric shape

limits given in Clause 1.5.

(b) Roofs are of normal shape (for example, not arched).

(c) Net pressure coefficients comprise the addition of internal and external pressures on

the building envelope. The combination factor (Kc in AS/NZS 1170.2) is included to

take account of the fact that peak pressures occur on different surfaces at slightly

different times.

(d) Pressures include the effects of dominant openings for Regions C and D only.

(e) In order to justify the use of lower internal pressures in Regions A and B, all elements

of the cladding need to be designed to withstand the design winds.

(f) Pressures include the effects of local high-pressure zones on the leading edges of

surfaces of the building envelope.

The pressure factors given for the 1200 mm zones near corners and near edges of roofs

reflect a simplification of the AS/NZS 1170.2 factors for peak local pressures known to

occur in these areas of buildings. Comparisons of pressure coefficients from the simplified

local pressure model in this Standard and the more complex model in AS/NZS 1170.2

showed that the underestimations and overestimations were relatively small.

The local pressure model in this Standard recognizes that the high local pressure factor

must act on around 25% of a structural unit in order to classify it as attracting higher

pressures. Hence, windows with 25% or more width of a single pane within 1200 mm of the

building edge are classified for pressures as SC (corner). A single pane will respond

independently of the rest of the elements in the window. For doors, the single element is the

opening leaf on a single door, one opening leaf on a double door. Hence, doors with 25% or

more of the width of one opening leaf within 1200 mm of the building edge are classified as

SC not G.

A5 COMMENTARY ON PRESSURES FOR DETERMINATION OF RACKING

FORCES (SECTION 5)

A5.1 General, notation and assumptions

A5.1.1 General

This Paragraph describes how the equivalent pressures tabulated in Section 5 for use with

projected areas, for the calculation of racking loads to be resisted by bracing have been

derived. The methods of determination of equivalent pressures for the calculation of racking

forces in orthogonal directions for single or upper storey, for lower of two storeys and for

subfloor level are given.

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A5.1.2 Notation

Notation symbols for Paragraph A5 are closer to the notation in AS/NZS 1170.2. This is so

that its origin in that document can be followed to the source. The notation in Paragraph A5

is as follows:

b = plan dimension of building or part of building perpendicular to wind direction,

in metres (see AS/NZS 1170.2)

Cpt,roof = combined pressure coefficient for the windward and leeward roof areas

Cpt,wall = combined pressure coefficient for the windward and leeward walls

d = plan dimension of building or part of building parallel to the wind direction, in

metres (see AS/NZS 1170.2)

HF = depth of upper floor, in metres

HL = height, floor to ceiling for lower storey of two storeys, in metres

Hu = height, floor to ceiling for single or upper storey, in metres

h = height to eaves, in metres (see AS/NZS 1170.2)

Ka = area reduction factor

Kc = pressure combination factor

L = length of building, in metres (see Figure A5.1)

qu = free stream dynamic gust pressure, in kPa, for the ultimate limit state in

accordance with Clause 3.2

W = width of building, in metres (see Figure A5.1)

α = roof pitch, in degrees (see AS/NZS 1170.2 and Figure A5.1)

θ = wind direction, in degrees (see AS/NZS 1170.2)

A5.1.3 Assumptions

The following assumptions have been made in the derivation of equivalent pressures for use

with projected areas for the determination of racking forces:

(a) The geometry assumed is a simple outline of the building, which ignores eaves

overhangs, fascias and gutters. The projected area for the roof is taken as the area

above ceiling level for the single or upper storey (see Figure A5.1).

(b) Buildings are assumed enclosed underneath the lower floor.

(c) The floor depth of upper floors (HF) is assumed to be 0.3 m.

(d) Hu = HL = 2.4 m. Pressures calculated for 2.4 m floor to ceiling heights are assumed

to apply for walls up to 3.0 m high.

(e) A pressure combination factor Kc = 0.8 is applied where the load effect is the result of

the combination of pressures on two or more surfaces. [Kc is not applied in

combination with the area reduction factor (Ka).]

(f) The assumed combined pressure coefficients for the windward and leeward walls

(Cpt,wall) for wind directions θ = 0° and θ = 90° are given in Table A5.1 and

Table A5.2 respectively.

(g) The assumed combined pressure coefficients for the windward and leeward roofs

(Cpt,roof) for wind parallel to the slope (pitch) of roof are given in Table A5.3.

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AS 4055—2012 48


Hips( i f h ip-end roof )Hips( i f h ip-end roof )

Rid

ge L

W

Plan

0°

90°

noitavele ediSnoitavele dnE

Cei l ing

Floor

Floor

Projected areasfor determinat ionof s ingle or upperstorey racking loads

Hips( i f h ip-end roof )

Cei l ing

H u

H L

H F

H u l2

FIGURE A5.1 NOTATION

TABLE A5.1

COMBINED PRESSURE COEFFICIENTS FOR WALLS—

WIND DIRECTION PARALLEL TO ROOF SLOPE*

Roof pitch (α) α < 10° 10° ≤ α ≤ 15° α = 20° α ≥ 25°

Cpt,wall 1.1 1.1 1.1 1.2

* For all roofs, wind is parallel to the roof slope for θ = 0° and for hip ends also for θ = 90°.

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TABLE A5.2

COMBINED PRESSURE COEFFICIENTS FOR WALLS—

WIND DIRECTION PERPENDICULAR TO ROOF SLOPE*

d/b ≤1 2 ≥4

Cpt,wall 1.2 1.0 0.9

* For θ = 90° for gable or skillion roof ends the wind is perpendicular to the roof slope.

TABLE A5.3

COMBINED PRESSURE COEFFICIENTS FOR ROOFS—

WIND DIRECTION PARALLEL TO ROOF SLOPE*

Ratio h/d

Cpt,roof

Roof pitch (α)

<10° 10° 15° 20° 25° 30° 35°

≤0.25 0 0 +0.5 +0.8 +0.9 +0.9 +1.0

0.5 0 +0.1 +0.2 +0.6 +0.8 +0.8 +0.9

≥1.0 0 +0.1 +0.1 +0.3 +0.6 +0.8 +0.8

* For all roofs, wind is parallel to the roof slope for θ = 0° and for hip ends also for θ = 90°.

A5.2 Equivalent pressures on projected areas

A5.2.1 For flat wall surfaces, gable or skillion roof ends

The equivalent pressure (p) on the projected area shown in Figure A4.2 for calculation of

the racking load for bracing in single or upper storey, or the lower of two-storey or subfloor

walls is determined from the following equation:

p = qu Cpt,wall Kc . . .A5.2(1)

where

Cpt,wall = 1.2, as given in Table A4.2 for d/b = 1

Kc = 0.8, pressure combination factor applicable for the combined effect of

pressure on two or more surfaces

NOTE: The assumption that d = b, i.e., L = W corresponds to the maximum combined pressure

coefficient for the walls.

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AS 4055—2012 50


Wind direct ion

Wind direct ionWind direct ion

W

W W

WW

W

Wind direct ion


FIGURE A5.2 FLAT WALL SURFACES—GABLE AND SKILLION ROOF ENDS

A5.2.2 For side elevations, single or upper storey, gable- or hip-ended roofs

The equivalent pressure (p) for the projected areas shown in Figure A5.3 for calculation of

the racking load for bracing in single or upper storey walls is determined from the

following equation:

p = ( ) ( )[ ]( ) ( ) αW//H

αW/C/HCKq

tan22

tan22

u

roofpt,uwallpt,cu

++

. . .A5.2(2)

where

Cpt,wall = value from Table A5.1 for roof pitch, α

Cpt,roof = value from Table A5.3, for roof pitch α, and assuming (h/d) = (Hu/W)

Kc = 0.8, pressure combination factor

NOTES:

1 The assumption that h/d = Hu/W maximizes the assumed combined pressure coefficients for

the roof.

2 The reduction in projected area for hip-ended roofs has been ignored in the determination of

the equivalent pressures to be applied to the projected areas corresponding to either gable- or

hip-ended roofs.


WW

FIGURE A5.3 SIDE ELEVATIONS—SINGLE OR UPPER STOREY—

GABLE- OR HIP-ENDED ROOFS

A5.2.3 Side elevation, lower storey of two storeys or subfloor, gable- or hip-ended roof

The design wind pressure (p) on the projected area shown in Figure A5.4 for calculation of

the racking force for bracing in the lower storey of two-storey walls is determined from the

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51 AS 4055—2012


p = ( ) ( )[ ]( ) ( ) α

αtan2/2/

tan2/2/

LFu

roofpt,LFuwallpt,cu

WHHH

WCHHHCKq

++++++

. . .A5.2(3)

where

Cpt,wall = value determined from Table A5.1 for roof pitch (α)

Cpt,roof = value from Table A5.3, for roof pitch α, and assuming

(h/d) = (Hu + HF + HL)/W


NOTES:

1 The assumption that (h/d) = (Hu + HF + HL)/W maximizes the assumed combined pressure

coefficients for the roof.

2 The reduction in projected area for hip-ended roofs has been ignored in the determination of

equivalent pressures to be applied for projected areas for either gable or hip-ended roofs.

W W


FIGURE A5.4 SIDE ELEVATION—LOWER STOREY OF TWO STOREYS

OR SUBFLOOR—GABLE- OR HIP-ENDED ROOF

A5.2.4 End elevation, single or upper storey, hip-ended roof

The design wind pressure (p) on the projected area shown in Figure A5.5 for calculation of

racking loads for bracing in single or upper storey walls is determined from the following

equation.

p = ( ) ( )[ ]( ) ( ) α

αtan4/2/

tan4/2/

u

roofpt,uwallpt,cu

WH

WCHCKq

++

. . .A5.2(4)

where

Cpt,wall = 1.2

Cpt,roof = value obtained from Table A5.3 for roof pitch (α) with h/d = Hu/L and

assuming L = W


Wind direct ionW

FIGURE A5.5 END ELEVATION—SINGLE OR UPPER STOREY—HIP-ENDED ROOF

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AS 4055—2012 52


A5.2.5 End elevation, lower storey of two storeys, hip-ended roof

The equivalent pressure (p) on the projected area shown in Figure A5.6 for calculating

racking loads for bracing in walls of the lower storey of two-storey walls is determined

from the following equation:

p = ( ) ( )[ ]( ) ( ) αW//HHH

αW/C/HHHCKq

tan42

tan42

LFu

roofpt,LFuwallpt,cu

++++++

. . .A5.2(5)

where

Cpt,wall = 1.2

Cpt,roof = value from Table A5.3, for roof pitch α, and assuming

(h/d) = (Hu + HF + HL)/L and = 1.5W


Wind direct ion

W

FIGURE A5.6 END ELEVATION—LOWER STOREY OF TWO STOREYS—

HIP-ENDED ROOF

A6 CONVERTING WIND SPEEDS

Wind speeds may be approximately converted from metres per second (m/s) to other

commonly reported measures of speed as follows:

1 m/s × 3.6 = 1 km/h.

1 m/s × 1.94 = 1 knot.

1 m/s × 2.24 = 1 mile/h.

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APPENDIX B

WORKED EXAMPLE FOR THE DETERMINATION OF TOPOGRAPHIC CLASS

(Informative)

B1 GENERAL

In order to illustrate how to determine the appropriate topographic class, the following two

examples are provided:

(a) Houses on an escarpment which relates to Figure B1.

(b) Houses on more complex topography which relates to Figure B2.

Each example has two individual house sites shown to illustrate the use of the Standard. In

practice, the Standard will generally be used for one house site at a time.

B2 HOUSES ON AN ESCARPMENT

Figure B1 shows an escarpment with the slope rising steadily from 20 m to around 120 m at

the top.

The first steps in the process focus on the escarpment and in this case, the section line will

be drawn as close as practical to the site being considered. This is because the slope

anywhere on the side of the escarpment will be much the same and so the slope through the

house sites is of most relevance to the houses.

The later steps (Steps 6 and 7) take into account the location of the house site relative to the

top of the topographic feature.

Step 1 Identify the top of the escarpment: RL 120 m.

Step 2 Identify the bottom of the escarpment: RL 20 m (Bottom of the slope where

the contours spread out indicating a slope of less than 1 in 20 – 10 m contours

around 200 m apart).

Calculate height of the feature as 120 m – 20 m = 100 m.

Step 3 Calculate the mid-height of the escarpment: (120 + 20)/2 = RL 70 m.

Step 4 Identify the steepest slope in the top half of the escarpment:

(a) As shown on Figure B1, the distance across the contours from the top of

the escarpment to the mid height of the escarpment is 380 metres.

(b) Steepest slope of top half of escarpment = (120 – 70)/380 = 0.131

(c) This can be expressed as 1:run by taking the inverse 1/0.131 = 1:7.6 or

as an angle by finding the angle with a tan of 0.131, tan-1 (0.131) = 7.5°

Step 5 Identify the three zones of the escarpment:

(a) Bottom third zone will be below contour 20 + 100 × ⅓ = 53 m

(b) Top third zone will be above contour 20 + 100 × ⅔ = 87 m

(c) Middle third zone will be between contour 53 m and 87 m

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AS 4055—2012 54


Step 6 Identify the location of the house.

Site A is located above the 87 m contour and is therefore in the top third of the

escarpment with the feature 100 m high.

Site B is located below the 53 m contour and is therefore in the bottom third of

the escarpment.

Step 7 Use Table 2.3 to assign a topographic classification:

(a) The escarpment has a maximum slope of 1:7.6 or 7.5° which is just

inside the range of the third row of figures in Table 2.3.

(b) Site A is in the top third of the escarpment with the feature 100 metres

high and Table 2.3 gives a topographic classification of T2.

(c) Site B is in the bottom third of the escarpment and Table 2.3 gives a

topographic classification of T0.

Scale (m)

0 40030020010010m contour interval

10

10

S i te BSite BSite ASite A

20

20

30

30

40

40 5

05

0 60

60 7

07

0 80

80

90

90

100

100

110

110

120

120

Middle third(shaded)

Steepest s lope Steepest s lope

FIGURE B1 EXAMPLE—TOPOGRAPHIC CLASS—SITES

A AND B ON AN ESCARPMENT

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B3 HOUSES ON A HILL

Figure B2 shows more complex terrain, with a number of hills. The two house sites (C and

D) are on the flanks of Hill 1

The first steps in the process focus on the geometry of Hill 1, and the location of the houses

isn’t considered at all until the later steps.

The later steps (Steps 6 and 7) take into account the location of the house site relative to the

top of the topographic feature.

Step 1 Identify the top of Hill 1: RL 110 m.

Step 2 Identify the bottom of the hill: RL 40 m (RL of creek).

Hill has a height of 110 – 40 = 70 m.

Step 3 Calculate the mid-height of the hill: (110 + 40)/2 = RL 75 m.

Step 4 Identify the steepest slope in the top half of the hill. This will be where the 75 m

contour is closest to the top of the hill:

Steepest slope = (110 – 75)/130 = 0.27

This can be expressed as 1:run by taking the inverse 1/0.27 = 1:3.7 or as an

angle by finding the angle with a tan of 0.27, tan-1 (0.27) = 15.1°

Step 5 Identify the three zones of the hill.

Bottom third zone will be below contour 40 + 70 × ⅓ = 63 m

Top third zone will be above contour 40 + 70 × ⅔ = 86 m

Middle third zone will be between contour 63 m and 86 m

Step 6 Identify the location of the house.

(a) Site C is located above the 63 m contour and below the 86 m contour and

is therefore in the middle third of the hill.

(b) Site D is located above the 86 m contour and is therefore in the top third

of the hill.

Step 7 Use Table 2.3 to assign a topographic classification:

(a) The hill has a maximum slope of 1:3.7 or 15.1° which is inside the range

of the fifth row of figures in Table 2.3.

(b) Site C is in the middle third of the hill and Table 2.3 gives a topographic

classification of T2.

(c) Site D is in the top third of the hill with a height of 70 m and Table 2.3

gives a topographic classification of T4.

Housing site D is between Hill 1 and Hill 2 as shown in Figure B2. The site itself is to the

right of the saddle between the two hills and so is geographically part of Hill 1 rather than

Hill 2.

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AS 4055—2012 56


Creek40

50

60

8090

100Housingsite DHousingsi te D

Neartop 1/3contour

Hi l l 2

110

90

100

110

Hi l l 1

80807070

Mid 1/3bandMid 1/3band

80

70

6050 60

Mid heightcontour

60

50

Lower 1/3contour

Creek

50

Creek

Cre

ek

80

Scale (m)

0 4003002001005m contour interval

Steepest slope

Steepest slope

Housingsite CHousingsi te C

FIGURE B2 EXAMPLE—TOPOGRAPHIC CLASS—SITES C AND D ON A HILL

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APPENDIX C

WORKED EXAMPLES FOR THE SELECTION OF TERRAIN CATEGORY AND

SHIELDING CLASS

(Informative)

The typical surface roughness types encountered in an urban area are represented in Table

C1, and in outer suburban areas in Table C2. These examples are provided to assist in the

selection of terrain categories and shielding classes of particular sites.

In conjunction with deriving the correct topographic class from Table 2.3, the terrain

category and shielding class selected for each site are applied to Table 2.2 for the

appropriate geographic region to determine the rationalized wind class for the design of

houses or structures.

The following examples are provided.

Example A:

The house at Location A, shown in Table C1, is sited in the second row of houses facing

open water such as an ocean or larger bay. The site may be thought of as a part of suburbia,

but the terrain and shielding are classified as follows:

(a) A 500 m radius circle centred on the house site will take in some of the open water.

The smoothest terrain within the circle will be the water with a terrain category (TC)

of 1.5. Here the water is given TC1.5 as it is open water. (Had the water been in an

enclosed bay or lake, it would have been TC1.)

(b) For shielding, this site has at least one side (the side facing the water) which has only

one row of houses that can be regarded as shielding. It is therefore classified as

‘partially shielded’ (PS). Even though there may have been three sides of the site that

had many rows of houses, it is the side with the least shielding that dictates the

shielding class.

The terrain category of the site is therefore TC1.5 and the Shielding Class PS.

Note that houses must be more than 500 m from the ocean shore before the site can be

classed as TC 3.

Example B:

The house at Location B, shown in Table C1, is sited more than two rows back from the

edge of a very large area of parkland. While the house is surrounded by normal suburban

housing, the terrain and shielding are classified as follows:

(a) A 500 m radius circle centred on the house site will take in some of the large park.

The smoothest terrain within the circle will be the open terrain of the park with a

terrain category (TC) of 2.

(b) For shielding, this site has all sides with at least two rows of houses that can be

regarded as shielding. It is therefore classified as ‘fully shielded’ (FS).

The terrain category of the site is therefore TC2 and the Shielding Class FS.

Note that sites must be more than 500 m from the park before they can be classed as TC3.

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Example C:

The house at Location C, shown in Table C2, is sited immediately adjacent to a small park

with a width of 150 m, but an area of less than 250 000 m2. Because the park is relatively

small, the house is still regarded as being within normal suburbia.

(a) A 500 m radius circle centred on the house site will take in the small park, but it is

too small (<250 000 m2) to allow the wind to speed up as it passes over. This

Standard ignores small parks in classifying terrain. The smoothest terrain within the

circle will therefore be the suburban housing with a terrain category (TC) of 3.

(b) For shielding, this site has at least one side with no houses that can be regarded as

shielding (the side facing the small park). It is therefore classified as Not Shielded

(NS).

The terrain category of the site is therefore TC3 and the Shielding Class NS.

Note that the small park in this case was big enough to affect the shielding (more than

100 m wide), but small enough not to affect the terrain roughness (less than 200 m wide).

Example D:

The house site at Location D, shown in Table C2, is to be sited within an acreage

development with fewer than 10 houses per hectare anticipating development in five years

time.

(a) A 500 m radius circle centred on the house site will take in the acreage development

and some nearby suburban housing. The smoothest terrain within the circle will be

the acreage development with a terrain category (TC) of 2.5.

(b) For shielding, this site will have houses on all sides, but as they are sparse, it is

therefore classified as ‘partially shielded’ (PS).

The terrain category of the site is therefore TC2.5 and the Shielding Class PS.

Note that the first row of housing in the normal suburban development has some shielding

on the side of the acreage development, so even though it is the first row of suburbia, it

takes the same shielding as the acreage development.

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TABLE C1

TERRAIN CATEGORY AND SHIELDING CLASSIFICATION

EXAMPLE WHERE THERE IS OPEN WATER, SUBURBAN

HOUSING AND A LARGE PARK

Description Ocean Waterfront suburbia Residential suburbia Large park > 250 000 m2

Surface roughness Open Water (TC1.5)

Houses >10 per hectare (TC3)

Scattered trees (TC2)

Design TC for

houses in this area N/A

500 m

TC1.5 TC3

500 m

TC2 N/A

Shielding for houses

in this area N/A 1st row NS 2nd row PS FS FS FS 2nd row PS 1st row NS N/A

Design criteria for

houses in this area N/A TC1.5, NS TC1.5, PS TC1.5, FS TC3, FS TC2, FS TC2, PS TC2, NS N/A

A B

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TABLE C2

TERRAIN CATEGORY AND SHIELDING CLASSIFICATION

EXAMPLE WHERE THERE IS CLOSED WATER AND SUBURBAN AND ACREAGE HOUSING

Description Lake Waterfront

suburbia

Residential suburbia Small park

< 250 000 m2,

150 m across

Residential suburbia Acreage suburbia

Surface

roughness Closed

Water

(TC1)

Houses >10 per hectare (TC3) Scattered trees

in small area Houses > 10 per hectare (TC3)

Houses < 10 per

hectare (TC2.5)

Design TC for

houses in this

area N/A

500 m

TC1

TC3

N/A

TC3 500 m

TC2.5

TC2.5

Shielding for

houses in this

area N/A

1st row

NS

2nd row

PS FS FS

2nd row

PS

1st row

NS N/A

1st row

NS

2nd row

PS FS FS

1st row

PS PS

Design Criteria

for houses in this

area N/A

TC1,

NS

TC1,

PS N/A

TC3,

FS

TC3,

PS

TC3,

NS N/A TC3, NS TC3, PS

TC3,

FS

TC2.5,

FS

TC2.5,

PS TC2.5, PS

C D

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61 AS 4055—2012


APPENDIX D

WORKED EXAMPLE FOR RACKING FORCES

(Informative)

The example given in this Appendix, using ultimate limit states design, illustrates the

method of determining racking forces on a two-storey house located in Region B, Terrain

Category 2.5, having partial shielding and a topographic classification T2.

For the example, assume that the house is 16 m long, 8 m wide and has a 17.5° pitched,

gable-end roof.

Step 1 From Table 2.2 (for Region B, TC2.5, T2 and PS) the wind class is N4.

Step 2 Calculate the upper storey racking for wind normal to ridge.

From Table 5.8, for W = 8 m and roof slope = 17.5°, the pressure for wind on

side is determined: (1.4 + 1.6)/2 = 1.5 kPa.

Determine area on which the pressure is to be applied and multiply the area by

the pressure to give the racking force in kN. Provide bracing appropriate to

resist this force.

Step 3 Calculate the upper storey racking for wind parallel to ridge (wind on end).





resist this force.

Step 4 Calculate lower storey racking for wind normal to ridge.





resist this force.

Step 5 Calculate lower storey racking for wind parallel to ridge (wind on end).





resist this force.

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Documents

AS 4055-2012 Wind loads for housing.pdf