72782287-AS-4055-2006

AS 4055—2006

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 7 November 2005. This Standard was published on 6 January 2006.

The following are represented on Committee BD-099:

Australian Building Codes Board

Australian Glass and Glazing Association

Australian Institute of Building Surveyors

Australian Windows Association

Building Designers Association of Australia

Clay Brick and Paver Institute

Concrete Masonry Association of Australia

Cyclone Testing Station (JCU)

Housing Industry Association

Master Builders Australia

National Timber Development Council

Roofing Tile Association of Australia

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This Standard was issued in draft form for comment as DR 04347. Acc

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AS 4055—2006

Australian Standard™


First published as AS 4055—1992. Second edition 2006.

COPYRIGHT

© Standards Australia

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.

Published by Standards Australia, GPO Box 476, Sydney, NSW 2001, Australia

ISBN 0 7337 7087 8

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AS 4055—2006 2

PREFACE

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

housing to supersede AS 4055—1992.

This Standard will be referenced in the Building Code of Australia 2006 edition

(BCA 2006), thereby superseding in part the previous edition, AS 4055—1992, 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be withdrawn 12 months from the date of publication of this edition.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 edition differs from the previous edition as follows:

(a) Wind speeds are specified for the serviceability and ultimate strength/stability limit

states only. Permissible stress has been omitted.

(b) The Standard has been updated to reflect the latest technical knowledge on wind

forces as represented by the 2002 edition of AS/NZS 1170.2.

(c) The table of classes for site conditions has been updated.

(d) Pressure factors have been made normative and calculation methods given for

determining pressures and forces.

(e) New racking tables have been included in limit states format.

(f) 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.

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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3 AS 4055—2006

CONTENTS

Page

SECTION 1 SCOPE AND GENERAL

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

1.2 LIMITATIONS ........................................................................................................... 4

1.3 NORMATIVE REFERENCES.................................................................................... 4

1.4 DEFINITIONS ............................................................................................................ 5

1.5 NOTATION ................................................................................................................ 6

SECTION 2 WIND LOADS

2.1 CLASSIFICATION ..................................................................................................... 8

2.2 RELATIONSHIP TO WIND REGION AND SITE CONDITIONS ............................ 8

2.3 SELECTION OF TERRAIN CATEGORY................................................................ 11

2.4 SELECTION OF TOPOGRAPHIC CLASS .............................................................. 11

2.5 SELECTION OF SHIELDING CLASS..................................................................... 13

SECTION 3 CALCULATION OF PRESSURES AND FORCES

3.1 PRESSURE COEFFICIENTS ................................................................................... 15

3.2 CALCULATION OF PRESSURES........................................................................... 16

3.3 CALCULATION OF FORCES ................................................................................. 16

3.4 PRESSURES FOR TYPICAL APPLICATIONS....................................................... 17

SECTION 4 UPLIFT FORCES.............................................................................................. 19

SECTION 5 RACKING FORCES

5.1 RACKING FORCES ................................................................................................. 20

5.2 AREA OF ELEVATION ........................................................................................... 20

APPENDICES

A COMMENTARY....................................................................................................... 37

B WORKED EXAMPLE FOR THE DETERMINATION OF TOPOGRAPHY ........... 46

C WORKED EXAMPLES FOR THE SELECTION OF TERRAIN CATEGORY AND

SHIELDING CLASS................................................................................................. 48

D WORKED EXAMPLE FOR RACKING FORCES ................................................... 50

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AS 4055—2006 4

Standards Australia www.standards.com.au

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 housing 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 1170.0 and 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 from

ground level to the highest point of the roof, neglecting 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).

1.3 NORMATIVE REFERENCES

The following referenced documents are indispensable for the application of this Standard:

AS/NZS

1170 Structural design actions

1170.0 Part 0: General principles

1170.2 Part 2: Wind actions

ABCB

BCA Building Code of Australia

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5 AS 4055—2006

www.standards.com.au Standards Australia

Height totop of roof,

r idge or gableand 8.5 m max.

One ortwo storey

Roof pitch35° max.

Roof pitch35° max.

16.0 m max.

Height to eaves exceptgable ends 6.0 m max.

16.0 m max.

Height at any sectionthrough the house 8.5 m max.

Height from groundlevel to undersideof eaves exceptfor gable ends

6.0 m max.

Eaves 900 mm max.

(a) Sections

(b) Plan view

W16.0 m max.

Edge of eaves

External wall

W16.0 m max.

L

L

W16.0 m max.

L 5W

FIGURE 1.1 GEOMETRY

1.4 DEFINITIONS

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

1.4.1 Average slope

Slope measured by averaging the steepest slope and the least slope through the top half of

the hill, ridge or escarpment.

1.4.2 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.

1.4.3 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).

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AS 4055—2006 6


1.4.4 House

Class 1 or 10 building as defined by the Building Code of Australia (BCA) with the

geometric limitations specified in Clause 1.2.

1.4.5 Length

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

(see Figure 1.1).

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

to the near top-third zone

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

G = dead load; or

permanent action (self-weight or ‘dead’ action)

H = height of a hill, ridge or escarpment

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

lower floor

h = average roof height

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

Kl = local pressure factor

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

zone for escarpments

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

Ms = shielding multiplier

Mt = topographic multiplier

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

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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 pascals

qu = free stream dynamic gust pressure, in kilopascals

qz = a reference pressure, in kilopascals

= (0.5 ρair) [Vh,u]2/1000

TC1 to TC3 = terrain categories

T1 to T5 = topographic classes

Vh = design gust wind speed at height (h)

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

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

W = width of a house

Ws = serviceability wind action

Wu = ultimate wind action

α = angle of roof pitch

φa = average slope measured by averaging the steepest slope and the least

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

γ = average weight density, in kilonewton per cubic metre

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

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AS 4055—2006 8


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 Table 2.1 together with the associated design gust

wind speeds (Vh) for the serviceability and ultimate limit states. It incorporates both non-

cyclonic (N) and cyclonic (C) winds.

TABLE 2.1

DESIGN GUST WIND SPEED (Vh) FOR CLASSIFICATION

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

m/s

Regions A and B

(non-cyclonic)

Regions C and D

(cyclonic)

Serviceability limit state

(Vh,s)

Ultimate limit state

(Vh,u)

N1

N2

N3

—

—

C1

26

26

32

34

40

50

N4

N5

N6

C2

C3

C4

39

47

55

61

74

86

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 (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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9 AS 4055—2006


TABLE 2.2

WIND CLASSIFICATION FROM WIND REGION AND SITE CONDITIONS

Wind class

Topographic class

T1 T2 T3 T4 T5 Wind

region TC

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

Region A

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

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

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


Region B


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

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


Region C

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

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

1,2 C2 C2 C2 C2 C3 C3 C3 C4 C4 C3 C4 C4 C4 NA NA

Region D

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

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

1,2 C3 C3 C4 C4 NA NA C4 NA NA NA NA NA NA NA NA

LEGEND:

FS

PS

NS

N

C

N/A

TC

=

=

=

=

=

=

=

full shielding

partial shielding

no shielding

non-cyclonic

cyclonic

not applicable, that is, beyond the scope of this Standard (use AS/NZS 1170.2)

terrain category

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AS 4055—2006 10


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11 AS 4055—2006


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 hence.

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

or TC3 and shall be determined as follows:

(a) Terrain Category 1 (TC1) Exposed open terrain with few or no obstructions. This

condition exists only for isolated houses in flat, treeless, poorly grassed plains of at

least 10 km width. This category is applicable for water surfaces for serviceability

design.

(b) Terrain Category 2 (TC2) Open terrain including sea coast areas, airfields, grassland

with few well-scattered obstructions, such as isolated trees and uncut grass, having

heights from 1.5 m to 10.0 m.

(c) Terrain Category 2.5 (TC2.5) Terrain with a few trees, isolated obstructions, such as

agricultural land, cane fields or long grass, up to 600 mm high. This category is

intermediate between TC2 and TC3 and represents the terrain in developing outer

urban areas.

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

the size of houses. The minimum density of houses and trees, except for Regions C

and D, shall be the equivalent of 10 house-size obstructions per hectare. Substantial

well-established trees shall be considered as obstructions except in Regions C and D

where a maximum of TC2.5 applies for the equivalent of 10 house-size obstructions

per hectare.

In urban situations, roads, rivers 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 these,

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, TC2, TC2.5 or TC3, as

applicable.

NOTE: For worked examples, see Appendix C.

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 average slope of the hill, ridge or escarpment.

The topographic class for a housing site shall be identified by the notation T1, T2, T3, T4

or T5 and shall be determined from Table 2.3 and Figure 2.2.

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.

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AS 4055—2006 12


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 average slope of a hill, ridge or escarpment (φa) shall be the slope measured by

averaging the steepest slope and the least slope through the top half of the hill, ridge or

escarpment.

NOTES:

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

appraised by considering the adjacent topography

2 For the determination 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 one average slope is less than

1 in 20 and the other average slope is greater than 1 in 10. 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

Site location (see Figure 2.2)

Top-third zone

(T)

Over-top zone

(O) (for 4H past crest

of escarpments only)

Average slope

(φa)

Hill height (H) below which

T1 applies for all sites on

the hill, ridge or

escarpment

(m)

Lower-

third zone

(L)

Mid-third

zone

(M) H ≤30 m H >30 m

<1:10 All H T1 T1 T1 T1 T1

≥1:10 <1:7.5 H < 20 T1 T1 T2 T2 T1

≥1:7.5 <1:5 H < 9 T1 T1 T2 T3 T1

≥1:5 <1:3 — T1 T2 T3 T4 T2

≥1:3 — T1 T2 T4 T5 T3

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13 AS 4055—2006


H /3

H /3

H /3

M

L

d d

T

Average slope 1:20

H /3

H /3

H /3

M

L

d d

T O

Average slope 1:20

NAverage slope 1:10

Average slope 1:20

(a) Hi l ls

(b) Escarpments

LEGEND:

H = height of the hi l l , r idge or escarpmentd = average hor izontal distance measured from the crest of the escarpment to the near top-third zoneL = lower third of the hi l l , r idge or escarpmentM = middle third of the hi l l , r idge or escarpmentT = top third of the hi l l , r idge or escarpmentO = over top zone (for escarpment only)

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.

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, heavily wooded areas provide full shielding. Acc

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AS 4055—2006 14


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, trees or sheds per hectare, such as acreage type suburban

development or wooded parkland. In Regions C and D, heavily wooded areas shall be

considered to have 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 first

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

NOTE: For worked examples, see Appendix C.

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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 COEFFICIENTS

3.1.1 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.

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

(Cp,eKl)

Internal pressure

coefficient

(Cp,i)

Net pressure

coefficient

(Cp,n)

Roof

(a) General, including all trusses and

rafters

−0.9

+0.4

0.2

−0.3

−1.1

+0.7

(b) Cladding, fasteners and immediate

supporting members within 1200 mm

of edges, e.g., battens and purlins

−1.8 0.2 −2.0

Walls

(a) General, including all studs +0.7

−0.65

−0.3

+0.2

+1.0

−0.85

(b) Cladding, fasteners and corner

windows within 1200 mm of edges −1.3 +0.2 −1.5

3.1.2 Wind classes C1 to C4 (cyclonic)

For houses with wind classes C1 to C4 (in Regions C and D) the following pressure

coefficients shall be used:

(a) Internal pressure coefficients—Ultimate strength........................... Cp,i = 0.7 or −0.65.

Serviceability ................................................................................. Cp,i = 0.2 or −0.3.

(b) Net pressure coefficients—Ultimate strength ...................................... (see Table 3.2).

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TABLE 3.2

PRESSURE COEFFICIENTS FOR WIND CLASSES C1 TO C4

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

Housing component

Factored external

pressure coefficient

(Cp,eKl)

Internal pressure

coefficient

(Cp,i)

Net pressure

coefficient

(Cp,n)

Roof

(a) General, including all trusses and

rafters

−0.9

+0.4

+0.7

−0.65

−1.6

+1.05

(b) Cladding, fasteners and

immediate supporting members

within 1200 mm of edges, e.g.,

battens and purlins

−1.8 +0.7 −2.5

Walls

(a) General, including all studs −0.65

+0.7

+0.7

−0.65

−1.35

+1.35

(b) Cladding, fasteners and corner

windows within 1200 mm of

edges

−1.3 +0.7 −2.0

3.2 CALCULATION OF PRESSURES

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

structures as follows:

p = qu Cp . . . 3.1

where

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

NOTE: Pressures are taken as positive, indicating pressures above ambient and

negative, indicating pressures below ambient.

qu = free stream dynamic gust pressure

= 0.5ρair [Vh]2

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

Vh = design gust wind speed, as given in Table 2.1

Cp = pressure coefficient, as given in Clause 3.1 (external, internal or net, as

appropriate)

3.3 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).

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3.4 PRESSURES FOR TYPICAL APPLICATIONS

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

pressures for the N and C categories are as given in Table 3.3. Serviceability limit state

design pressures from N and C categories are as given in Table 3.4.

TABLE 3.3

ULTIMATE STRENGTH PRESSURES FOR WIND CLASSIFICATION

FROM THE NET PRESSURE COEFFICIENTS GIVEN IN CLAUSE 3.1

Walls Roofs

Away from

corners(1)

Within 1200 mm

of corners(2) Away from edges(1)

Within 1200 mm

of edges(2) Wind class

Cp,n = 1.0 Cp,n = −1.5 Cp,n = −1.1 Cp,n = 0.7 Cp,n = −2.0

m/s kPa kPa kPa kPa kPa

N1 0.69 1.04 −0.76 0.49 1.39

N2 0.96 1.44 −1.06 0.67 −1.92

N3 1.50 2.25 −1.65 1.05 −3.00

N4 2.23 3.35 2.46 1.56 4.47

N5 3.29 4.93 3.61 2.30 6.57

N6 4.44 6.66 4.88 3.11 8.88

Cp,n = −1.35 Cp,n = −2.0 Cp,n = −1.6 Cp,n = 1.05 Cp,n = −2.5

C1 −2.03 −3.00 −2.40 1.58 3.75

C2 −3.01 4.47 3.57 2.34 5.58

C3 −4.44 6.57 5.26 3.45 8.21

C4 −5.99 −8.88 −7.10 4.66 11.09

NOTES:

1 General areas, including wall studs more than 1200 mm from corners and roof trusses and

rafters more than 1200 mm from edges.

2 Areas of cladding and fasteners within 1200 mm of wall corners or roof edges; windows within

1200 mm of wall corners; immediate supporting members such as battens and purlins within

1200 mm of roof edges.

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TABLE 3.4

SERVICEABILITY PRESSURES FOR WIND CLASSIFICATION

FROM THE NET PRESSURE COEFFICIENTS GIVEN IN CLAUSE 3.1

Walls Roofs

Away from

corners(1)

Within 1200 mm

of corners(2) Away from edges(1)

Within 1200 mm

of edges(2) Wind class

Cp,n = 1.0 Cp,n = −1.5 Cp,n = −1.1 Cp,n = 0.7 Cp,n = −2.0

m/s kPa kPa kPa kPa kPa

N1serv 0.41 −0.61 −0.45 0.28 −0.81

N2serv 0.41 −0.61 −0.45 0.28 −0.81

N3serv 0.61 −0.92 −0.68 0.43 −1.23

N4serv 0.91 −1.37 −1.00 0.64 −1.83

N5serv 1.33 −1.99 −1.46 0.93 −2.65

N6serv 1.82 −2.72 −2.00 1.27 −3.63

C1serv 0.61 −0.92 −0.68 0.43 −1.23

C2serv 0.91 −1.37 −1.00 0.64 −1.83

C3serv 1.33 −1.99 −1.46 0.93 −2.65

C4serv 1.82 −2.72 −2.00 1.27 −3.63

NOTES:

1 General areas, including wall studs more than 1200 mm from corners and roof trusses and

rafters more than 1200 mm from edges.

2 Areas of cladding and fasteners within 1200 mm of wall corners or roof edges; windows within

1200 mm of wall corners; immediate supporting members such as battens and purlins within

1200 mm of roof edges.

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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, kPa

Serviceability limit state Ultimate strength limit state

Roof type Wind class

Tile roof Sheet roof

(see Note 2) Tile roof

Sheet roof

(see Note 2)

N1

N2

N3

0

0

0

0.05

0.05

0.28

0.04

0.34

0.93

0.44

0.74

1.33

N4

N5

N6

0.10

0.56

1.10

0.60

1.06

1.60

1.74

2.89

4.16

2.14

3.29

4.56

C1

C2

C3

0.08

0.60

1.22

0.58

1.06

1.72

1.68

2.85

4.54

2.08

3.25

4.94

C4 2.00 2.50 6.38 6.78

NOTES:

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

combinations:

(a) Serviceability limit state: Ws − γG.

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

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

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

3 γG = 0.72 kPa for tile roof; γG = 0.28 kPa for sheet roof.

4 Sheet roof includes metal tile roof.

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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 Tables 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 kilonewtons, 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 (that is, 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.

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Wind direct ion 1

Wind direct ion 2

Gable end

Hip end

Area ofelevation

h0Floor level

Area of elevation(gable ends)

Area ofelevation

h0Floor 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 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.

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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AS 4055—2006 22


h0

h0

h0

h0

h0

Winddirection 2

Wind direct ion 1Gable end

Hip end

Hip end

(a) Plan

Single-storey section


(c) Wind direct ion 2

Floor level

Area ofelevation

Floor level

Area of elevation(gable end)

Upper storey of two-storey section

Upper storey of two-storey section Lower storey of two-storey section

Area of elevation(gable end)

Lower storey of two-storey section h0

Floorlevel

Floor level

Area of elevationArea of elevation

NOTES:

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

2 For lower storey of two-storey section h0 = half the height of the lower storey (i.e., lower storey floor to

lower storey ceiling).



FIGURE 5.2 DETERMINING AREA OF ELEVATION FOR A TWO-STOREY

OR SPLIT LEVEL BUILDING

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23 AS 4055—2006


Wind direct ion 2 Wind direct ion 3

Gable endHip end

Wind direct ion 1

Floor

Area ofelevation

H0h0

Area ofelevation

Floor

Floor

Area ofelevation

h0

h0

(a) Plan


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

In the subfloor of a two-storey construction, the maximum distance (H0) from theground to the underside of the bearer in the lower f loor shal l be 1800 mm.

NOTES:

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

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 5.3 DETERMINING AREA OF ELEVATION FOR SUBFLOORS

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TABLE 5.1

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

PRESSURE (kPa) 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 C1 1.44

N4 C2 2.14

N5 C3 3.16

N6 C4 4.26

NOTE: For derivation of these values, refer to

Paragraph A5.2, Appendix A.

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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

Roof pitch (degrees) Width (m)

0 5 10 15 20 25 30 35

N1: Wind on side Wind direct ion Wind direct ion

WW

4 0.61 0.53 0.48 0.44 0.44 0.52 0.56 0.55

5 0.61 0.52 0.46 0.41 0.42 0.50 0.54 0.53

6 0.61 0.50 0.44 0.39 0.42 0.50 0.53 0.54

7 0.61 0.49 0.42 0.38 0.43 0.51 0.53 0.54

8 0.61 0.47 0.40 0.37 0.43 0.51 0.52 0.54

9 0.61 0.46 0.39 0.36 0.44 0.52 0.51 0.54

10 0.61 0.45 0.38 0.35 0.44 0.52 0.51 0.54

11 0.61 0.44 0.36 0.35 0.45 0.52 0.51 0.55

12 0.61 0.42 0.34 0.35 0.45 0.52 0.51 0.55

13 0.61 0.41 0.33 0.36 0.46 0.52 0.52 0.55

14 0.61 0.40 0.31 0.36 0.46 0.53 0.52 0.56

15 0.61 0.39 0.30 0.36 0.47 0.53 0.52 0.56

16 0.61 0.39 0.29 0.37 0.47 0.53 0.52 0.56

N1: Wind on end Wind direct ion Wind direct ion

W W

4 0.67 0.62 0.59 0.55 0.55 0.57 0.59 0.58

5 0.67 0.61 0.57 0.53 0.53 0.56 0.58 0.57

6 0.67 0.60 0.56 0.52 0.53 0.56 0.57 0.57

7 0.67 0.59 0.54 0.50 0.52 0.56 0.56 0.57

8 0.67 0.58 0.53 0.49 0.52 0.56 0.56 0.57

9 0.67 0.57 0.51 0.48 0.52 0.56 0.55 0.57

10 0.67 0.56 0.50 0.47 0.52 0.56 0.54 0.57

11 0.67 0.55 0.49 0.46 0.52 0.56 0.54 0.57

12 0.67 0.55 0.47 0.46 0.52 0.56 0.54 0.57

13 0.67 0.54 0.46 0.46 0.52 0.56 0.55 0.57

14 0.67 0.53 0.45 0.46 0.53 0.56 0.55 0.57

15 0.67 0.52 0.44 0.46 0.53 0.56 0.55 0.58

16 0.67 0.52 0.43 0.46 0.53 0.56 0.55 0.58

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TABLE 5.3



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


W W

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

N1: Wind on end Wind direct ion

W

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 Acc

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TABLE 5.4






0 5 10 15 20 25 30 35


WW

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 Wind direct ion Wind direct ion

W W

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






0 5 10 15 20 25 30 35


W W

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

N2: Wind on end Wind direct ion

W

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 Acc

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TABLE 5.6






0 5 10 15 20 25 30 35

N3, C1: Wind on side Wind direct ion Wind direct ion

WW

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 Wind direct ion Wind direct ion

W W

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






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

N3, C1: Wind on end Wind direct ion

W

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 Acc

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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


W W

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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AS 4055—2006 32


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


W

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 Acc

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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

Wind direct ion Wind direct ionW W

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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AS 4055—2006 34


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


W

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 Acc

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35 AS 4055—2006


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


W W

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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AS 4055—2006 36


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


W

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 Acc

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APPENDIX A

COMMENTARY

(Informative)

A1 COMMENT ON TABLE 2.1—WIND CLASSIFICATION

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 would be assessed for

compliance with geometry and for evaluation of pressures.

The classification was originally based on the permissible stress ‘W’ classes. 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 BCA (the design wind loading level

associated with housing)

NOTE: See Note 1 to Clause 1.1.

(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 trees, 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).

A2 DERIVATION OF TABLE 2.2—WIND CLASSIFICATION

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

given in Table 2.2, the effect of wind events on large numbers of houses, rather than on

individual structures, has been considered. 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.

(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).

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(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 A2).

(f) Topographic multiplier (Mt) has been derived from AS/NZS 1170.2 (see Table A3).

The values chosen for T2 to T5 represent the average of the ranges for each class (T1

is taken as 1.0 to represent the majority of housing on flat terrain). For the top third,

the class changes for slopes greater than 30 m high. The separation zone at the crest

has not been included.

(g) Shielding multiplier (Ms) has been derived from AS/NZS 1170.2 (see Table A4).

TABLE A2

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

Terrain category multiplier (M6.5,cat) Region

Terrain Category 1 Terrain Category 2 Terrain Category 2.5 Terrain Category 3

A 1.07 0.94 0.88 0.83

B 1.07 0.94 0.88 0.83

C 0.97 0.97 0.90 0.83

D 0.97 0.97 0.90 0.83

TABLE A3

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

T1 1.0 1.0 to <1.16

T2 1.2 ≥1.16 to <1.25

T3 1.3 ≥1.25 to <1.36

T4 1.42 ≥1.36 to <1.47

T5 1.57 ≥1.47

TABLE A4

SHIELDING MULTIPLIER (Ms)

Shielding class Shielding multiplier (Ms)

Full shielding (FS) 0.85

Partial shielding (PS) 0.95

No shielding (NS) 1.00

A3 COMMENT ON CLAUSE 1.3—GEOMETRIC LIMITS

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 greater than the 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).

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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.

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

(e) 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 the local pressures known to occur in these areas of buildings. AS/NZS 1170.2

includes a local pressure factor to account for this effect.

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.

A5.1.2 Notation

Notation symbols for this Section are 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)

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)

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AS 4055—2006 40


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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41 AS 4055—2006


Hips(i f hip-end roof)

Rid

ge L

W

Plan

0°

90°

End elevation Side elevation

Ceil ing

Floor

Floor

Projected areasfor determinationof single or upperstorey racking loads

Hips(i f hip-end roof)

Ceil ing

Hu

HL

HF

Hul2

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 θ = 0° and for hip ends, θ = 90°

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AS 4055—2006 42


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

TABLE A5.3

COMBINED PRESSURE COEFFICIENTS FOR ROOFS—

WIND DIRECTION PARALLEL TO ROOF SLOPE*

Cpt,roof

Roof pitch (α) Ratio h/d

<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 θ = 0° and for hip ends, 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 A5.2 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 A5.2 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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43 AS 4055—2006


Wind direct ion

Wind direct ionWind direct ion

W

W W

WW

W

Wind direct ion

Wind direct ionWind 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:

( ) ( )[ ]( ) ( ) α

α

tan2/2/

tan2/2/

u

roofpt,uwallpt,cu

WH

WCHCKqp

+

+

= . . . 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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AS 4055—2006 44


( ) ( )[ ]( ) ( ) α

α

tan2/2/

tan2/2/

LFu

roofpt,LFuwallpt,uu

WHHH

WCHHHCKqp

+++

+++=

. . . A5.2(3)

where

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

Cpt,roof = value determined 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 hip- or gable-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.

( ) ( )[ ]( ) ( ) α

α

tan4/2/

tan4/2/

u

roofpt,uwallpt,cu

WH

WCHCKqp

+

+

= . . . 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 Acc

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45 AS 4055—2006


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:

( ) ( )[ ]( ) ( ) α

α

tan4/2/

tan4/2/

LFu

roofpt,LFuwallpt,cu

WHHH

WCHHHCKqp

+++

+++=

. . . A5.2(5)

where

Cpt,wall = 1.2

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

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

(a) 1 m/s × 3.6 = 1 km/h.

(b) 1 m/s × 1.94 = 1 knot.

(c) 1 m/s × 2.24 = 1 mile/h.

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AS 4055—2006 46


APPENDIX B

WORKED EXAMPLE FOR THE DETERMINATION OF TOPOGRAPHY

(Informative)

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

example is provided, which relates to Figure B1.

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

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

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

Step 4 Identify the steepest and least slope in the top half of the hill:

(i) Least slope = (110 − 75)/350 = 0.10.

(ii) Steepest slope = (110 − 75)/130 = 0.27.

Step 5 Calculate average slope: (0.1 + 0.27)/2 = 0.185 which relates to a slope of

1 in 5.4, (i.e., 1/0.185 = 5.4).

Step 6 Identify the location of the house. If the house at site A is located in the mid-

third of the hill, the topographic class for an average slope of 1 in 5.4 is T1

(see Table 2.3).

As the house at site B is in closer proximity to the peak of hill 1 than hill 2, the topographic

effect of hill 1 is considered to predominate. Therefore, if the house at site B is located in

the near top-third of the hill, the topographic class for an average slope of 1 in 5.4 is T3

(see Table 2.3).

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47 AS 4055—2006


Creek40

50

60

8090

100Housingsite B

Neartop 1/3contour

Hil l 2

110

90

100

110

Hil l 1

Steepest

slopeLeast

slope

8070

Mid 1/3band

80

70

6050 60

Housingsite A

Mid heightcontour

60

50

Lower 1/3contour

Creek

50

Creek

Cre

ek

80

Scale (m)

0 100 200 300 400

FIGURE B1 DETERMINATION OF TOPOGRAPHIC CLASS

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AS 4055—2006 48


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, which is 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 from Table C1 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 to clarify the use of Table C1.

Example A:

As the house at location A is sited more than 500 m from the open sea and surrounded for a

distance of more than 500 m by a minimum surface roughness greater than 10 houses per

hectare except for a small park of less than 500 m in width, the terrain category of the site

is TC3.

If the house is located within the first two rows of houses adjacent to the park, no shielding

is provided by this open space.

Example B:

The house at location B is within a residential subdivision but immediately adjoins a large

acreage subdivision.

As the least surface roughness for a distance of 500 m in any direction of the site is

between 10 and 2.5 houses per hectare, the terrain category at location B is TC2.5.

As the site immediately abuts a large acreage subdivision with a surface roughness of

between 10 and 2.5 houses per hectare, only partial shielding is provided.

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TA

BL

E

C1

TE

RR

AIN

CA

TE

GO

RY

AN

D S

HIE

LD

IN

G C

LA

SS

IF

IC

AT

IO

N F

OR

RE

GIO

NS

A A

ND

B

Lo

ca

tio

n '

A'

Lo

ca

tio

n '

B'

Desc

rip

tio

n

W

ate

r-

fro

nt

sub

urb

ia

Resi

den

tia

l

sub

urb

ia,

well

-

wo

od

ed

co

un

try

Sm

all

op

en

pa

rk

lan

d

or l

ak

e

<2

50

00

0 m

2

an

d c

an

al

<2

00

m w

ide

Resi

den

tia

l su

bu

rb

ia,

well

-wo

od

ed

co

un

try

Acrea

ge s

ub

urb

ia,

iso

late

d b

uil

din

gs,

few

trees,

ca

ne f

ield

s,

lon

g g

ra

ss

Air

field

iso

late

d t

rees,

larg

e

ex

pa

nse

s,

op

en

wa

ter

Resi

den

tia

l su

bu

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ia,

well

-

wo

od

ed

co

un

try

Su

rface

rou

gh

ness

≥1

0

Ho

use

s, e

tc.

per

hecta

re

Neg

lig

ible

≥

10

Ho

use

s, e

tc.

per

hecta

re

≥1

0

Ho

use

s, e

tc.

per

hecta

reN

eg

lig

ible

≥

10

Ho

use

s, e

tc.

per

hecta

re

Terr

ain

cate

go

ry:

Dev

elo

pm

en

t

len

gth

50

0 m

50

0 m

50

0 m

50

0 m

Cla

ssif

icati

on

TC

2

TC

3

TC

3

TC

3

TC

2.5

T

C2

.5

TC

2

TC

2

TC

2

TC

3

Sh

ield

ing

:

Dev

elo

pm

en

t

len

gth

2 r

ow

s o

f

ho

use

s

2 r

ow

s o

f

ho

use

s

2 r

ow

s o

f

ho

use

s

2 r

ow

s o

f

ho

use

s

2 r

ow

s o

f

ho

use

s

2 r

ow

s o

f

ho

use

s

Cla

ssif

icati

on

No

shie

ldin

g

Fu

ll

shie

ldin

g

No

shie

ldin

g

N

o

shie

ldin

g

P

art

ial

shie

ldin

g

Part

ial

shie

ldin

g

No

shie

ldin

g

N

o

shie

ldin

g

Fu

ll

shie

ldin

g


49 AS 4055—2006

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AS 4055—2006 50


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 class 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

are determined: (1.2 + 1.4)/2 = 1.3.

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).


are determined: (1.6 + 1.7)/2 = 1.65.



force.

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


are determined: (1.6 + 1.7)/2 = 1.65.



force.

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


are determined: (1.9 + 2.0)/2 = 1.95.



force.

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51 AS 4055—2006

NOTES

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AS 4055—2006 52

NOTES

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Standards Australia

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most of the voluntary technical and commercial standards used in Australia. These standards are

developed through an open process of consultation and consensus, in which all interested parties are

invited to participate. Through a Memorandum of Understanding with the Commonwealth government,

Standards Australia is recognized as Australia’s peak national standards body. For further information

on Standards Australia visit us at

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Administration Phone (02) 8206 6000 Fax (02) 8206 6001 Email [email protected]

Customer Service Phone 1300 65 46 46 Fax 1300 65 49 49 Email [email protected]

Internet www.standards.org.au

ISBN 0 7337 7087 8 Printed in Australia

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