(Project ID: 100967) Draft for Public Comment Australian Standard · · 2012-06-21Draft for...

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COMMITTEE BD-099

DR AS 4055

(Project ID: 100967)

Draft for Public Comment

Australian Standard

LIABLE TO ALTERATION—DO NOT USE AS A STANDARD

BEGINNING DATE FOR COMMENT:

4 June 2012

CLOSING DATE FOR COMMENT:

6 August 2012

Important: The procedure for public comment has changed – please

read the instructions on the inside cover of this document.

Wind loads for housing (Revision of AS 4055—2006)

COPYRIGHT

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Australian Standard

The committee responsible for the issue of this draft comprised representatives of organizations interested in the subject matter of the proposed Standard. These organizations are listed on the inside back cover.

Comments are invited on the technical content, wording and general arrangement of the draft.

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STANDARDS AUSTRALIA

Committee BD-099—Wind loads for Housing

DRAFT

Australian Standard

Wind loads for housing

(Revision of AS 4055—2006)

(To be AS 4055—2XXX)

Comment on the draft is invited from people and organizations concerned with this subject.

It would be appreciated if those submitting comment would follow the guidelines given on

the inside front cover.

Important: The procedure for public comment has changed – please read the instructions on the inside cover of this document

This document is a draft Australian Standard only and is liable to alteration in the light of

comment received. It is not to be regarded as an Australian Standard until finally issued as

such by Standards Australia.

DRAFT ONLY 2 DRAFT ONLY

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PREFACE

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

housing to supersede AS 4055—2006.

This Standard incorporates Amendment No. 1 (July 2008). The changes required by the

Amendment are indicated in the text by a marginal bar and amendment number against the

clause, note, table, figure or part thereof affected.

This Standard will be referenced in the Building Code of Australia 2013 edition

(BCA 2006), 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be withdrawn 12 months from the date of publication of this edition.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 harmonise the

standard with recent changes to AS/NZS 1170.2:2011 including Amendment No.1. This

edition differs from the previous edition as follows:

(a) The Scope of the Standard has been amended to include the limitation of the standard

to Class 1 and Class 10 buildings as defined by the BCA. This has always been the

intention of the standard as reflected in its 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 harmonise 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 water flowing over 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 characterised a conical hill well, it significantly

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

to characterise the topographic feature. This will better represent the slope of a ridge

or escarpment without significantly changing the characterisation 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.


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(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.

(g) Shielding classifications have been harmonised 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

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.

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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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 ................................................................ 12

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

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:........................................................................................................................ 52

C WORKED EXAMPLES FOR THE SELECTION OF TERRAIN CATEGORY AND

SHIELDING CLASS ................................................................................................... 56

D WORKED EXAMPLE FOR RACKING FORCES ...................................................... 60


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STANDARDS AUSTRALIA

Australian Standard

Wind loads for housing

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 Class 1 and Class 10 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.

6 Class 1 and 10 buildings are defined in the BCA.

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).

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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Height totop of roof,

r idge or gableand 8 . 5 m ma x .

One ort wo storey

Roof pitch35° ma x .

Roof pitch35° ma x .

16.0 m ma x .

Height to eaves exceptgable ends 6 .0 m ma x .

16.0 m ma x .

Height at any sec tionthrough the house 8 . 5 m ma x .

Height f rom groundlevel to underside

of eaves exceptfor gable ends

6.0 m ma x .

Eaves 9 0 0 mm ma x .

(a) Sec tions

(b) Plan v iew

W16.0 m ma x .

Edge of eaves

E x ternal wal l

W16.0 m ma x .

L

L

W16.0 m ma x .

L 5 W

L

L

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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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 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.

1.4.7 Plan

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

Figure 1.1).

1.4.8 Racking forces

Forces that occur in walls parallel to the wind direction.

1.4.9 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

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

shielding

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

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

external corners of walls

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)

Kc = Combination factor

Kl = local pressure factor


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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)

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)

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 = 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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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 2.1A

DESIGN GUST WIND SPEED (Vh) FOR NON CYCLONIC CLASSIFICATIONS

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

m/s

Regions A and B

(non-cyclonic)

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 CLASSIFICATION

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

m/s

Regions C and D

(cyclonic)

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 (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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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

Region A

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

Region B

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

Region C

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

Region D

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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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, 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 water surfaces at serviceability and ultimate wind speeds in all Wind

Regions. E.g flat, treeless, poorly grassed plains of at least 10 km width, lakes,

enclosed bays, rivers and canals.

(b) Terrain Category 1.5 (TC1.5) Large open water surfaces at serviceability and

ultimate wind speeds in all Wind Regions. E.g sea and ocean water, large unenclosed

bays.

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

obstructions having heights generally from 1.5 m to 10m. E.g farmland and cleared

subdivisions with isolated trees and uncut grass.

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

agricultural open woodland, 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 with scattered houses, or large acreage developments

with fewer than 10 houses per hectare. In Regions C and D where trees can be

considered the equivalent of 10 house-size obstructions per hectare, the Terrain can

be considered as Terrain Category 2.5.

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

heights generally from 3 m to 10 m (the size of houses). The minimum density

ofobstructions shall be the equivalent of 10 house-size obstructions per hectare. Only

in Regions A and B, substantial well-established trees may be considered as

obstructions.

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, TC1.5, TC2, TC2.5 or TC3, as

applicable.

NOTES:

1 For worked examples, see Appendix C.

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

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.


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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 2.2b)..

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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H /3

H /3

H /3

M

L

d d

T O

Average slop e 1:20

Average slop e 1:10

4 H

Average slop e 1:20

(b) Escarpments

LEGEND:

Hd

LMTO

==

====

height of the hi l l , r idge or escarpmentaverage horizontal distance measured f rom thecrest of the escarpment to the near top -third zonelower third of the hi l l , r idge or escarpmentmiddle third of the hi l l , r idge or escarpmenttop third 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 slop e 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 and vegetation may be considered as shielding elements and in

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

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

shall be determined as follows:


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(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.

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 ZONES

The following external pressure zones (illustrated in Figure 3.1 and 3.2) shall be used in

evaluation of wind loads on housing:

(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

NOTEIndicated plan width var ies to su it roof pitch.

G

G

G

G

G

LEGEND:

1200

RC

RERC

RE

RC

24

00

2400 RE RC

RE

RC

1200

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


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Wall edgeSC

Wall-genera l areaG

LEGEND:

1200

1200

G

G

SC

SC

G

SC

SC

G

G

G

SC

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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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 −1.2

(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 and corner

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 and corner

windows within 1200 mm of edges

(See Region SC in Figure 3.2)

−1.3 +0.2 −1.35

NOTES:

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

considered as immediate supporting members.

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

windows, doors and garage doors demonstrate compliance with the relevant Australian Standard.

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

Table 3.2 shall be used.


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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)

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


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




−0.65

+0.7

+0.7

−0.65

−1.22

+1.22

(c)

Cladding, fasteners and corner



−1.3 +0.7 −1.8

NOTE: For roofs, immediate supporting members include battens and purlins. Rafters and

trusses are not considered as immediate supporting members.


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TABLE 3.2(B)

PRESSURE COEFFICIENT FOR WIND CLASSES C1 TO C4

(REGIONS C AND D—CYLONIC—FOR SERVICIBILITY)

Housing component Factored external


(Cp,eKl)

Internal pressure

coefficient

(Cp,i)

Net pressure

coefficient

(Cp,nKc)

Roof – General areas

(See Region G in Figure 3.1)


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 −1.2

(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




−0.65

+0.7

+0.2

−0.3

−0.77

+0.9

(c) Cladding, fasteners and corner



−1.3 +0.2 −1.35

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

considered as immediate supporting members.

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

= 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 3.1 (external, internal or net, as

appropriate)


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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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TABLE 3.3

ULTIMATE STRENGTH PRESSURES FOR WIND CLASSIFICATION

FROM THE NET PRESSURE COEFFICIENTS GIVEN IN CLAUSE 3.1

Wind class Walls Walls Walls Roofs Roofs Roofs Roofs

Any

position

Away from

corners

(3)

Within

1200 mm of

corners(3)

Any position General away

from edges(2)

Within

1200 mm of

edges(2)

At corners (within

1200 mm of both

edges)(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 -0.765 −1.35 +0.63 −0.99 -1.8 −2.61

kPa kPa kPa kPa kPa kPa kPa

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

N2 +0.86 -0.73 -1.30 +0.60 -0.95 -1.73 -2.51

N3 +1.35 -1.15 -2.03 +0.95 -1.49 -2.70 -3.92

N4 +2.01 -1.71 -3.01 +1.41 -2.21 -4.02 -5.83

N5 +2.96 -2.51 -4.44 +2.07 -3.25 -5.91 -8.58

N6 +3.99 -3.39 -5.99 +2.80 -4.39 -7.99 -11.58

KC.Cp,n +1.215 −1.215 −1.8 Cp,n = 0.945 −1.44 −2.35 −3.06


C1 +1.82 −1.82 −2.7 +1.42 −2.16 −3.53 −4.59

C2 +2.71 −2.71 −4.2 +2.11 −3.21 −5.25 −6.83

C3 +3.99 −3.99 −5.91 +3.10 −4.73 −7.72 −10.05

C4 +5.39 −5.39 −7.99 +4.19 −6.39 −10.43 −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 +2.71 kPa and -4.02 kPa)

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

and garage doors demonstrate compliance with the relevant Australian Standard


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TABLE 3.4

SERVICEABILITY PRESSURES FOR WIND CLASSIFICATION

FROM THE NET PRESSURE COEFFICIENTS GIVEN IN CLAUSE 3.1

Wind class Walls Walls Walls Roofs Roofs Roofs Roofs

Any

position

Away from

corners(3)

Within

1200 mm of

corners(3)

Any position General away

from edges(2)

Within

1200 mm of

edges(2)

At corners (within

1200 mm of both

edges)(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 -0.765 −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 -1.01 -1.79 +0.84 -1.31 -2.39 -3.46

N6 serv +1.63 -1.39 -2.45 +1.14 -1.80 -3.27 -4.74

KC.Cp,n +0.9 −0.765 −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 −1.01 −1.79 +0.84 −1.31 −2.39 −3.46

C4 serv +1.63 −1.39 −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,

doors and garage doors demonstrate compliance with the relevant Australian Standard.


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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 FOR DETERMINATION OF ANCHORING

REQUIREMENTS AT TOP OF WALLS, kPa

Wind class Serviceability limit state Ultimate strength limit state

Roof type Roof type

Tile roof Sheet roof

(see Note 4) Tile roof

Sheet roof

(see Note 4)

N1 0 −0.08 0 −0.37

N2 0 −0.08 −0.23 −0.63

N3 0 −0.30 −0.77 −1.17

N4 −0.18 −0.58 −1.50 −1.90

N5 −0.60 −1.00 −2.53 −2.93

N6 −1.08 −1.48 −3.67 −4.07

C1 0 −0.30 −1.44 −1.84

C2 −0.18 −0.58 −2.50 −2.90

C3 −0.60 −1.00 −4.00 −4.40

C4 −1.08 −1.48 −5.67 −6.07

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 = Vh,u or Vh,s as

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

3 Load combination factor γ = 0.8.

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

from AS 1684.

5 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 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 (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 of

e levat ion

Floor level

Area of e levat ion

(gable ends)

Area of

e levat ion

h0

h0

Floor level

(a) Plan

(b) Wind direct ion 1


FIGURE 5.1 DETERMINING AREA OF ELEVATION FOR A

SINGLE-STOREY BUILDING

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.


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(a) Plan

(b) Wind direc t ion 1

(c) Wind direc t ion 2

Wind direc t ion 1

Winddirec tion 2

Gable end

Hip end

Hip end

h o

h o

h o

Floor level

Cei l inglevelFloor level

Upp er s torey of t wo -storey sec tion

Single -storey sec tion

Area of e levation(gable end)

Lower storey of t wo -storey sec tion

Area ofelevation

Area of e levation(gable end)

Area of e levationArea of e levation

h o

h o

Lower storey of t wo -storey sec tionUpp er s torey of t wo -storey sec tion

Cei l inglevel

Upp erfloorlevelFloor level

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

LEVEL BUILDING

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.




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Wind direct ion 2 Wind direct ion 3

Gable endHip end

Wind direct ion 1

Floor

Area of

e levat ion

H0

h0

Area of

e levat ion

Floor

Floor

Area of

e 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 the

ground 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 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.




DR_AS_4055.doc - 28/05/2012 15:05:11

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 1.44

N4 2.14

N5 3.16

N6 4.26

C1 1.44

C2 2.14

C3 3.16

C4 4.26


DR_AS_4055.doc - 28/05/2012 15:05:11

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 0.44 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

Wind di rect ion Wind di rect ionW W

N1: Wind on end

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


DR_AS_4055.doc - 28/05/2012 15:05:11

TABLE 5.3


OF ELEVATION—LOWER STOREY OF TWO STOREYS

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


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


DR_AS_4055.doc - 28/05/2012 15:05:11

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


DR_AS_4055.doc - 28/05/2012 15:05:11

TABLE 5.5



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

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


DR_AS_4055.doc - 28/05/2012 15:05:11

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


DR_AS_4055.doc - 28/05/2012 15:05:11

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


DR_AS_4055.doc - 28/05/2012 15:05:11

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


DR_AS_4055.doc - 28/05/2012 15:05:11

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


DR_AS_4055.doc - 28/05/2012 15:05:11

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


DR_AS_4055.doc - 28/05/2012 15:05:11

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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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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APPENDIX A

COMMENTARY

(Informative)

A1 COMMENTARY ON SCOPE AND GENERAL

A1.1 Genereal

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 BCA (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 A2).

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

AS/NZS 1170.2 (see Table A3). 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 A4).

TABLE A2

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

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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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

T0 1.0 ≥1 to <1.08

T1 1.1 ≥1.04 to <1.16

T2 1.2 ≥1.14 to <1.25

T3 1.3 ≥1.21 to <1.37

T4 1.42 ≥1.29 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

A3.2 Terrain category

The definitions of Terrain Category in AS 4055 are consistent with those in

AS/NZS 1170.2:2011 (amendment 1).

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

the top off 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 metres wide. However, 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 is a Terrain Category that specifically addresses the roughness of near

shore open waterbodies such as seas and oceans adjoining housing land.

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. In wind regions A and B, very strong winds are

frequently of short enough duration to allow the trees to remain as obstructions throughout

the event. However, in tropical cyclone events in Regions C and D, strong winds act over a

sufficiently long duration to denude trees and reduce their effectiveness as obstructions.

Hence in Regions A and B, very large trees with a frequency of more than 10 large trees per

hectare can be considered as Terrain Category 3, but in Regions C and D, trees with that

frequency can only be counted as Terrain Category 2.5. In all regions, land with fewer than

10 large trees per hectare should be classed as Terrain Category 2.

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.


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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 A3.

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 permanent shielding. If only one full row of housing is available on one side, then

the site is categorised 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.

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.


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A5.1.2 Notation

Notation symbols for this Section are closer to the notation in AS/NZS 11702. This is so

that its origin in that document can be followed to the source. The notation in this Section 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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Hips

( i f h ip-end roof )

Hips


Rid

ge L

W

Plan

0°

90°

noitavele ediSnoitavele dnE

Cei l ing

Floor

Floor

Projected areas

for determinat ion

of s ingle or upper

storey racking loads

Hips


Cei l 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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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*

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 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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Wind direct ion

Wind direct ionWind direct ion

W

W W

WW

W

Wind direct ion

Wind direct ion

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 = ( ) ( )[ ]( ) ( ) α

αtan22

tan22C

u

roofptwallptcu

//

//,,

WH

WCHKqu

++

. . .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.


W

W

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

following equation:


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p = ( ) ( )[ ]( ) ( ) α

αtan22

tan22C

LFu

roofptLFwallptcu

//

//,,

WHHH

WCHHHKqu

++++++

. . .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 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.

p = ( ) ( )[ ]( ) ( ) α

αtan42

tan42C

u

roofptwallptcu

//

//,,

WH

WCHKqu

++

. . .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



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Wind direct ionW

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

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 = ( ) ( )[ ]( ) ( ) α

αtan42

tan42C

LFu

roofptLFwallptcu

//

//,,

WHHH

WCHHHKqu

++++++

. . .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.

(c) 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 x ⅓ = 53 m

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

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


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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 400300200100

10m contour interval

10

10

S i te BSite BSite ASite A

20

20

30

30

40

40 5

05

0 60

60

70

70 8

08

09

09

01

00

10

0

11

011

0

120

120

Middle third

(shaded)

Steepest s lope Steepest s lope


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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 x ⅓ = 63 m

Top third zone will be above contour 40 + 70 x 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.


DR_AS_4055.doc - 28/05/2012 15:05:11

Creek40

50

60

80

90

100Housing

site D

Housing

si te D

Near

top 1/3

contour

Hi l l 2

110

90

100

110

Hi l l 1

80807070

Mid 1/3

band

Mid 1/3

band

80

70

6050

60

Mid height

contour

60

50

Lower 1/3

contour

Cre

ek

50

Cre

ek

Cre

ek

80

Scale (m)

0 400300200100

5m contour interval

Ste

epest slo

pe

Ste

epest slo

pe

Housing

site C

Housing

si te C

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


DR_AS_4055.doc - 28/05/2012 15:05:11

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 TC 1.)

(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 TC 3.


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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 250000 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 (<250000 m2) to allow the wind to speed up as it passes over. The 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.

DR

_A

S_

40

55

.do

c - 2

8/0

5/2

01

2 1

5:0

5:1

1

58

D

RA

FT

ON

LY

D

RA

FT

ON

LY

TABLE C1

TERRAIN CATEGORY AND SHIELDING CLASSIFICATION FOR REGIONS A AND B

EXAMPLE WHERE THERE IS OPEN WATER, SUBURBAN

HOUSING AND A LARGE PARK

Description

Ocean Waterfront suburbia

Location A

Residential suburbia

Location B

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

DR

_A

S_

40

55

.do

c - 2

8/0

5/2

01

2 1

5:0

5:1

1

59

D

RA

FT

ON

LY

D

RA

FT

ON

LY

TABLE C1

TERRAIN CATEGORY AND SHIELDING CLASSIFICATION FOR REGIONS A AND B

EXAMPLE WHERE THERE IS CLOSED WATER AND SUBURBAN AND ACREAGE HOUSING

Description Lake Waterfront

suburbia


Location C

Small park <

250,000 m2,

150 m across


Location D

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


DR_AS_4055.doc - 28/05/2012 15:05:11

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).





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.

*** END OF DRAFT ***

PREPARATION OF AUSTRALIAN STANDARDS

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Australian Standards may be derived from existing industry Standards, from established

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The following interests are represented on the committee responsible for this draft

Australian Standard:

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

Masters Builder Association

Roofing Tile Association of Australia

Think Brick Australia

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