AS 4055-2012 Wind loads for housing.pdf

(1)

AS 4055—2012

Australian Standard

®

Wind loads for housing

AS 405

5—2

01

(2)

This Australian Standard® was prepared by Committee BD-099, Wind Loads for Housing. It was approved on behalf of the Council of Standards Australia on 23 November 2012. This Standard was published on 24 December 2012.

The following are represented on Committee BD-099: • Australian Building Codes Board

• Australian Window Association

• Concrete Masonry Association of Australia • Cyclone Testing Station

• Engineers Australia

• Forest and Wood Products Australia • Housing Industry Association • Master Builders Association • Roofing Tile Association of Australia • Think Brick Australia

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

Standards Australia wishes to acknowledge the participation of the expert individuals that contributed to the development of this Standard through their representation on the Committee and through the public comment period.

Keeping Standards up-to-date

Australian Standards® are living documents that reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued.

Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments that may have been published since the Standard was published.

Detailed information about Australian Standards, drafts, amendments and new projects can be found by visiting www.standards.org.au

Standards Australia welcomes suggestions for improvements, and encourages readers to notify us immediately of any apparent inaccuracies or ambiguities. Contact us via email at [email protected], or write to Standards Australia, GPO Box 476, Sydney, NSW 2001.

(3)

AS 4055—2012

Australian Standard

®

Wind loads for housing

Originated as AS 4055—1992. Previous edition 2006. Third edition 2012.

(4)

PREFACE

This Standard was prepared by the Standards Australia Committee BD-099, Wind loads for housing to supersede AS 4055—2006.

This Standard will be referenced in the National Construction Code (NCC) 2013 edition, thereby superseding in part the previous edition, AS 4055—2006, which will be withdrawn 12 months from the date of publication of this edition.

The objective of this Standard is to provide designers, builders and manufacturers of building products that are affected by wind loading with a range of wind speed classes that can be used to design and specify such products for use in housing that are within the limitations in this Standard.

This revision aims to improve modelling of topographic effects and also to harmonize with recent changes to AS/NZS 1170.2:2011, including Amendments No.1 and No.2. This edition differs from the previous edition as follows:

(a) The Scope of the Standard has been revised to include the limitation to Class 1 and Class 10 buildings as defined by the NCC. This has always been the intention of this Standard as reflected in the definition of ‘house’, but the limitation is more obvious when presented in the Scope.

(b) Table 2.1 presenting wind speeds for each wind classification has been split into a Non-Cyclonic regions table and a Cyclonic regions table for clarification. The wind speeds for each wind classification remain unchanged.

(c) Table 2.2 presenting the Wind Classification for sites has been changed to include a new Topographic Class T0 and to harmonize with changes adopted by AS/NZS 1170.2, terrain category multipliers.

(d) Definitions for terrain categories have been revised to be compatible with those in AS/NZS 1170.2:2011 (as amended). The revised definitions are intended to clarify the differences between the categories. International research has shown that the wind speeds over water are appropriate for Terrain Category 1 multipliers, so AS/NZS 1170.2 has included water bodies in Terrain Category 1 for all wind regions. In the case of wind blowing over large bodies of water, including seas and oceans, shoaling waves can introduce a near-shore roughness that means this water can be considered as Terrain Category 1.5. This change has followed through to this Standard. Terrain Category 4 is not applicable to this Standard as in Terrain Category 4, a house is embedded within the Terrain Category 4 roughness and its wind force evaluation may require special techniques.

(e) The calculation of topographic class had previously used the average of the maximum and minimum slope on a topographic feature to determine an average slope. While the average slope characterized a conical hill well, it significantly underestimated the slope of a ridge or escarpment. The maximum slope is now used to characterize the topographic feature. This will better represent the slope of a ridge or escarpment without significantly changing the characterization of a conical hill. This change was recommended as a result of observation of significantly higher levels of wind damage on ridges and escarpments in cyclonic and non-cyclonic wind storms.

(f) In AS/NZS 1170.2:2011, the topographic multiplier for flat land applies to hill slopes of less than 1:20 and this revision introduces a new Topographic Class T0 to represent slopes from 0 to 1:20. This Class has a topographic multiplier of 1.0. The topographic multiplier for T1 has been changed to 1.1 and includes wind for slopes from 1:20 to 1:10. Hill slopes have also been expressed in degrees.

(5)

(g) Shielding classifications have been harmonized with those in AS/NZS 1170.2 as appropriate for houses. For Regions A and B, large trees and heavily wooded areas can offer shielding and have been explicitly included, whereas in Regions C and D, the long duration of the wind event means that trees will be denuded before the arrival of the peak gust.

(h) Shielding classifications are linked to the topographic classes. AS/NZS 1170.2:2011 also links shielding with topography by allowing shielding only on slopes of less than 1:5. This has also been incorporated into this Standard by allowing full shielding only for those topographic classes with slopes of less than 1:5. This change in both Standards are based on wind-field models of hills and damage surveys following cyclonic and non-cyclonic wind events.

(j) Houses in the first row adjacent to wide, open areas are classed as ‘Not Shielded’, the second row from wide open areas is classed as ‘Partial Shielding’ and subsequent rows as ‘Full Shielding’ where there are sufficient houses.

(k) Pressure zones on roofs and walls have been defined, named and illustrated on diagrams. Edge and corner zones are subject to higher pressures due to the local pressure factors defined in AS/NZS 1170.2. An additional zone on the windward corners of low slope roofs allows for the RC1 zone introduced to AS/NZS 1170.2:2011 based on recent international research.

(l) The combination factor (K_c) from AS/NZS 1170.2:2011 has been applied to all pressures for walls and roofs. This has reduced some of the design pressures in the Standard.

(m) A more detailed commentary has been added (Appendix A) to clarify the relationship of this Standard to AS/NZS 1170.2 and to give background to some of the clauses. (n) The example of topographic classes (Appendix B) has been changed to reflect the

changes to definition of topographic classes.

(o) The example of terrain categories and shielding (Appendix C) has been changed to reflect the changes to definition of terrain categories and Shielding.

(p) In checking Tables 5.2 to 5.13, some minor discrepancies were found between values in the previous edition and those calculated from the formulae in Appendix A. These discrepancies were corrected and while there may be small differences in racking forces between this document and AS 1684, this will not affect the use of AS 1684. (q) References to the differential pressures on photovoltaic solar panels in

AS/NZS 1170.2 were included.

The term ‘informative’ has been used in this Standard to define the application of the Appendix to which it applies. An ‘informative’ appendix is only for information and guidance.

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

(6)

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 NCC buildings Classes 1 and 10 within the geometric limits given in Clause 1.2. The classes are for use in the design of housing and for design, manufacturing and specifying of building products and systems used for housing.

Wind loads for houses not complying with the geometric limits given in Clause 1.2 are outside the scope of this Standard.

NOTES:

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

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

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

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

5 Where houses do not comply with the geometric and other limitations of this Standard, use AS/NZS 1170.2.

1.2 LIMITATIONS

For the purpose of this Standard, the following conditions (geometric limits) shall apply (see Figure 1.1):

(a) The distance from ground level to the underside of eaves shall not exceed 6.0 m. The distance from ground level to the highest point of the roof, not including chimneys, shall not exceed 8.5 m.

(b) The width (W) including roofed verandas, excluding eaves, shall not exceed 16.0 m, and the length (L) shall not exceed five times the width.

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

The tables in Section 5 are based on floor to ceiling height of 2.4 m and a floor depth of 0.3 m (floor level down to ceiling below).

If wind loads on houses are determined using this Standard, design parameters shall be derived from this Standard only. Where wind loads on buildings are determined using AS/NZS 1170.2, design parameters in that Standard only must be used.

(8)

H e i g h t to to p of r o of, r i d g e o r g a b l e a n d 8 . 5 m m a x . O n e o r t wo s to r ey R o o f p i tc h 3 5° m a x . R o o f p i tc h 3 5° m a x . 16 .0 m m a x . H e i g h t to e ave s exc e p t g a b l e e n d s 6 . 0 m m a x . 16 .0 m m a x . H e i g h t a t a ny s e c t i o n t h r o u g h t h e h o u s e 8 . 5 m m a x . H e i g h t f r o m g r o u n d l eve l to u n d e r s i d e of e ave s exc e p t f o r g a b l e e n d s 6 . 0 m m a x . E ave s 9 0 0 m m m a x . (a ) S e c t i o n s ( b) Pl a n v i ew W 16 .0 m m a x . Ed g e o f e ave s E x te r n a l wa l l W 16 .0 m m a x . L L W 16 .0 m m a x . L 5W L L FIGURE 1.1 GEOMETRY 1.4 DEFINITIONS

For the purpose of this Standard, the definitions below apply. 1.4.1 Bottom of hill, ridge or escarpment

Area at the base of the hill, ridge or escarpment, where the average slope is less than 1 in 20.

1.4.2 Height

Distance from ground level to the underside of eaves or to the highest point of the roof neglecting chimneys; or the height of each storey at external walls (see Figure 1.1).

1.4.3 House

Class 1 or 10 building as defined by the National Construction Code (NCC) with the geometric limitations specified in Clause 1.2.

(9)

1.4.4 Length

Maximum overall distance between outside edges of the external walls of a house or shape (see Figure 1.1).

1.4.5 Obstruction

Natural or man-made objects that generate turbulent wind flow, ranging from single trees to forests and from isolated small structures to closely spaced multi-storey buildings.

1.4.6 Plan

Basic rectangular, square or L-shaped layout, or simple combinations of these (see Figure 1.1).

1.4.7 Racking forces

Forces that occur in walls parallel to the wind direction. 1.4.8 Width

Maximum distance from wall to wall in the direction perpendicular to the length, including roofed verandas but excluding eaves (see Figure 1.1).

1.5 NOTATION

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

C1 to C4 = cyclonic wind classes

C1_serv to C4_serv = cyclonic wind classes for serviceability

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

C_p,i = internal pressure coefficient C_p,n = net pressure coefficient

d = average horizontal distance measured from the crest of the escarpment or hill to the near top-third zone, in metres

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

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

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

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

H0 = maximum distance from the ground to the underside of the bearer in the lower floor, in metres

(10)

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

M_s = shielding multiplier

Mt = topographic multiplier

M_6.5,cat = terrain category multiplier at height (h) N1 to N6 = non-cyclonic wind classes

N1_serv to N6_serv = non-cyclonic wind classes for serviceability

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

V_h = design gust wind speed at height (h), in metres per second V_h,s = design gust wind speed at height (h) for serviceability limit

state, in metres per second

V_h,u = design gust wind speed at height (h) for ultimate strength limit state, in metres per second

W = width of a house, in metres

W_s = serviceability wind action, in kPa W_u = ultimate wind action in kPa

α = angle of roof pitch

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

γ = load factor

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

(11)

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

2.1 CLASSIFICATION

The system of 10 classes is set out in Tables 2.1A and B together with the associated design gust wind speeds (V_h) for the serviceability and ultimate limit states. This incorporates both non-cyclonic (N) and cyclonic (C) winds.

TABLE 2.1A

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

Wind class

Design gust wind speed (Vh) at height (h) m/s

Serviceability limit state (Vh,s)

Ultimate limit state (Vh,u) N1 N2 N3 26 26 32 34 40 50 N4 N5 N6 39 47 55 61 74 86 TABLE 2.1B

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

Wind class

Design gust wind speed (Vh) at height (h) m/s

Serviceability limit state (Vh,s)

Ultimate limit state (Vh,u) C1 C2 C3 C4 32 39 47 55 50 61 74 86

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

2.2 RELATIONSHIP TO WIND REGION AND SITE CONDITIONS

The selection of wind speed class for a house depends on the conditions at the site of the house. The class shall be determined from Table 2.2 using the following site conditions determined as stated:

(a) Geographic wind speed region of the site as defined in Figure 2.1 (Region A, B, C or D, as given in AS/NZS 1170.2).

(12)

TABLE 2.2

WIND CLASSIFICATION FROM WIND REGION AND SITE CONDITIONS

Wind region TC Topographic class T0 T1 T2 T3 T4 T5 FS PS NS FS PS NS FS PS NS PS NS NS NS A 3 N1 N1 N1 N1 N2 N2 N2 N2 N2 N3 N3 N3 N4 2.5 N1 N1 N2 N1 N2 N2 N2 N3 N3 N3 N3 N4 N4 2 N1 N2 N2 N2 N2 N3 N2 N3 N3 N3 N3 N4 N4 1.5 N2 N2 N2 N2 N3 N3 N3 N3 N3 N3 N4 N4 N5 1 N2 N3 N3 N2 N3 N3 N3 N3 N4 N4 N4 N4 N5 B 3 N2 N2 N3 N2 N3 N3 N3 N3 N4 N4 N4 N4 N5 2.5 N2 N3 N3 N3 N3 N3 N3 N4 N4 N4 N4 N5 N5 2 N2 N3 N3 N3 N3 N4 N3 N4 N4 N4 N5 N5 N6 1.5 N3 N3 N4 N3 N4 N4 N4 N4 N4 N5 N5 N5 N6 1 N3 N4 N4 N4 N4 N4 N4 N5 N5 N5 N5 N6 N6 C 3 C1 C1 C2 C1 C2 C2 C2 C2 C3 C3 C3 C3 C4 2.5 C1 C2 C2 C2 C2 C2 C2 C3 C3 C3 C3 C4 NA 2 C1 C2 C2 C2 C2 C3 C2 C3 C3 C3 C4 C4 NA 1.5 C2 C2 C3 C2 C3 C3 C3 C3 C4 C4 C4 NA NA 1 C2 C3 C3 C3 C3 C3 C3 C4 C4 C4 NA NA NA D 3 C2 C3 C3 C2 C3 C3 C3 C4 C4 C4 C4 NA NA 2.5 C2 C3 C3 C3 C3 C4 C3 C4 C4 C4 NA NA NA 2 C3 C3 C4 C3 C4 C4 C4 C4 NA NA NA NA NA 1.5 C3 C4 C4 C4 C4 NA C4 NA NA NA NA NA NA 1 C3 C4 C4 C4 NA NA NA NA NA NA NA NA NA LEGEND: FS = Full shielding PS = Partial shielding NS = No shielding N = Non-cyclonic C = Cyclonic

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

TC = Terrain category

(13)

D C B th e d line 10 0 k m 10 0 k m BRISBA NE Gasco yne Junct ion C h rist m as Island Re gion B Cocos Islands Re gion C Mill stre a m 50 k m 10 0 k m 15 0 k m io n D 20 ° arn ar v o n Ade la ide Riv e r K u nunur ra Iv anhoe Wyndham ( C ) Burk et o w n Bor roloola Al ice Springs Ma rble Ba r 11 ° 14 2 ° Moret o n 20 ° Ma re e b a Biloe la 25 ° Bundabe rg C o llin s ville W oome ra re m a rk e d w it h t h e l e tt e rs A , B , C a n d D . g io n b o u n d a ri e s a re s m o o th l in e s s e t i n o o th e d c o a s tl in e by 5 0 , 1 0 0, 1 5 0 a n d 20 0 k m . h in 5 0 k m of t h e c o a s t a re d e s ig n a te d i n t h e n a s t h e a d ja c e n t c o a s t. C a ll y tharra Springs Mulle w a Mora w a Head 25 ° 30° 27 ° Gr een Kalgoorl ie 35 ° Nor fol k Island Re gion B Lo rd Ho w e I s la nd Re gion A SY D N E Y CA N B E R R A Corind i Bourk e Ky o g le 30° T o o w oomba 40° 35 ° ADE L AI DE 45 ° Po r t H e d la n d rr atha w Reg io n C P E RTH Espe rance Al b a n y Reg io n A Broome DA R W IN Reg io n C Reg io n C Reg io n C R eg io n B Ca ir n s Ro ck ha mp to n Reg io n A HOB A RT Mount G a mbie r Sale io n B Reg io n B Reg io n B Nhulunbuy Norman to n La u n c e s to n Ce duna n E xmout h Derb y T o rr e s Strait Islands Re gion B Wit tenoom Ge elong Wa g g a Wa g g a W o ll ongong N e w c a s tl e Ne w c ast le At h e r to n M a c k a y Macka y T o wn s ville K a ru m b a Ka ru mba McD o nnell Cre e k NOTE: Th is m a p is fro m AS/ N ZS 1170.2. T h e wind d ire cti on sub-regions of Region A ha ve be en r e mov e d for clar ity. FIGU RE 2.1 BOUNDA R IES OF REGIONS A, B, C AND D

(14)

2.3 SELECTION OF TERRAIN CATEGORY

The terrain category for a housing site is a measure of the lowest effective surface roughness from any radial direction within a distance of 500 m of the proposed housing site. It shall be based on the likely terrain five years after design. Substantial well-established trees may be considered as obstructions for evaluation of terrain category in all wind regions.

The terrain category for a housing site shall be identified by the notation TC1, TC1.5, TC2, TC2.5 or TC3 and shall be determined as follows:

(a) Terrain Category 1 (TC1) Very exposed open terrain with few or no obstructions and enclosed limited sized water surfaces at serviceability and ultimate wind speeds in all wind regions, e.g. flat, treeless, poorly grassed plains, or river, canals, lakes and enclosed bays, extending less than 10 km in the wind direction.

(b) Terrain Category 1.5 (TC1.5) Open water surfaces subjected to shoaling waves at serviceability and ultimate wind speeds in all wind regions, e.g. near-shore water, large unenclosed bays on seas and oceans, lakes and enclosed bays extending greater than 10 km in the wind direction.

(c) Terrain Category 2 (TC2) Open terrain including grassland with well-scattered obstructions having heights generally from 1.5 m to 5 m with no more than two obstructions per hectare, e.g. farmland and cleared subdivisions with isolated trees and uncut grass.

(d) Terrain Category 2.5 (TC2.5) Terrain with a few trees or isolated obstructions. This category is intermediate between TC2 and TC3 and represents the terrain in developing outer urban areas with scattered houses, or large acreage developments with fewer than 10 buildings per hectare.

(e) Terrain Category 3 (TC3) Terrain with numerous closely spaced obstructions having heights generally from 3 m to 10 m. The minimum density of obstructions shall be at least the equivalent of 10 house-size obstructions per hectare, e.g. suburban housing or light industrial estates.

In urban situations, roads, rivers, small lakes or canals less than 200 m wide shall be considered to form part of normal ‘Terrain Category 3’ terrain. Parks and other open spaces less than 250 000 m2 in area shall also be considered to form part of normal ‘Terrain Category 3’ terrain provided they are not within 500 m of each other, or not within 500 m of open country. Housing sites less than 200 m from the boundaries of open areas larger than 250 000 m2, e.g. golf courses, that are completely surrounded by urban terrain, shall be considered to have the terrain category applicable to the open area itself. Shielding provisions may still apply to these sites.

Housing sites less than 500 m from the edge of a development shall be classified as the applicable terrain that adjoins the development, i.e. TC1, TC1.5, TC2, TC2.5 or TC3, as applicable.

NOTES:

1 For commentary on terrain categories, see Appendix A. 2 For worked examples, see Appendix C.

3 Terrain Category 4, as defined in AS/NZS 1170.2, is not applicable to this Standard. 4 The terrain categories are the same as those in AS/NZS 1170.2.

5 Vegetation is considered differently for terrain categories in this Clause and for shielding classes in Clause 2.5.

(15)

2.4 SELECTION OF TOPOGRAPHIC CLASS

The topographic class determines the effect of wind on a house because of its location on a hill, ridge or escarpment and the height and maximum slope of the hill, ridge or escarpment. The topographic class for a housing site shall be identified by the notation T0, T1, T2, T3, T4 or T5 and shall be determined from Table 2.3 and Figure 2.2 for all sites in the top two thirds of a ridge, hill or escarpment.

NOTES:

1 The method defined in Table 2.3 and Figure 2.2 is suitable for the purpose of either mapping the wind classes of an area or assessing the wind class of an individual site.

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

The bottom of a hill, ridge or escarpment shall be that area at the base of the hill, ridge or escarpment where the average slope is less than 1 in 20, e.g. creek, river valley or flat area. The maximum slope of a hill, ridge or escarpment (φ_a) shall be the slope measured as the steepest slope through the top half of the hill, ridge or escarpment.

NOTES:

1 Often the maximum slope will not occur at the actual proposed housing site and should be appraised by considering the adjacent topography

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

The top-third zone (T) extends for an equal distance (d) either side of the crest of an escarpment as shown in Figure 2.2. The value of d is the average horizontal distance measured from the crest of the escarpment to the near top-third zone.

A rise in terrain shall be considered an escarpment where the maximum slope on one side of the ridge is greater than 1 in 10 and on the other side is less than 1 in 20 (see Figure 2.2(b)). The over-top zone (O) of an escarpment shall be taken to extend to a distance of 4H past the crest of an escarpment.

TABLE 2.3

TOPOGRAPHIC CLASSIFICATION FOR HILLS, RIDGES OR ESCARPMENTS

Maximum slope

(φ_a)

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

(16)

H/3 H/3 H/3 M L d d T O Ave r a g e s l o p e 1:20 Ave r a g e s l o p e 1:10 4H Ave r a g e s l o p e 1:20 ( b) E s c a r p m e n t s L EG E N D: H d L M T O = = = = = = h e i g h t of t h e h i l l , r i d g e o r e s c a r p m e n t ave r a g e h o r i zo n t a l d i s t a n c e m e a s u r e d f r o m t h e c r e s t of t h e e s c a r p m e n t to t h e n e a r to p -t h i r d zo n e l owe r t h i r d of t h e h i l l , r i d g e o r e s c a r p m e n t m i d d l e t h i r d of t h e h i l l , r i d g e o r e s c a r p m e n t to p t h i r d of t h e h i l l , r i d g e o r e s c a r p m e n t ove r to p zo n e (fo r e s c a r p m e n t o n l y ) H/3 H/3 H/3 M L d d T Ave r a g e s l o p e 1:20 (a ) H i l l s

FIGURE 2.2 TOPOGRAPHIC ZONES FOR AVERAGE SLOPE

2.5 SELECTION OF SHIELDING CLASS

Where the wind speed on a house is influenced by obstructions of similar size to the house, shielding shall be considered and shall be based on the likely shielding five years hence. In Regions A and B trees or groups of trees with similar face area to houses may be considered as shielding elements. In Regions C and D trees and vegetation shall not be considered as shielding elements.

(17)

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

(a) Full shielding (FS) Full shielding shall apply where at least two rows of houses or similar size permanent obstructions surround the house being considered. In Regions A and B, permanent heavily wooded areas within 100 m of site provide full shielding. Full shielding is only possible for houses within Topographic Classes T0, T1, and T2. The application of full shielding shall be appropriate for typical suburban development greater than or equal to 10 houses, or similar size obstructions per hectare.

The effects of roads or other open areas with a distance measured in any direction of less than 100 m shall be ignored. However, the first two rows of houses abutting permanent open areas with a least dimension greater than 100 m, such as parklands, large expanses of water and airfields, shall be considered to have either partial shielding or no shielding.

(b) Partial shielding (PS) Partial shielding shall apply to intermediate situations where there are at least 2.5 houses or sheds per hectare, such as acreage type suburban development or wooded parkland. Partial shielding is only possible for houses within Topographic Classes T0, T1, T2, and T3. The second row of houses abutting open parkland, open water or airfields may be classified as having partial shielding.

(c) No shielding (NS) No shielding shall apply where there are no permanent obstructions or where there are less than 2.5 obstructions per hectare, such as the row of houses or single houses abutting open parklands, open water or airfields.

NOTES:

1 For commentary on shielding class, see Appendix A. 2 For worked examples, see Appendix C.

(18)

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

A N D F O R C E S

3.1 PRESSURE ZONES

The following external pressure zones (illustrated in Figure 3.1 for roofs and Figure 3.2 for walls) shall be used in evaluating wind loads on houses:

(a) General (G) Areas of roofs more than 1200 mm from edges, and areas of walls (including windows and doors) more than 1200 mm from external corners.

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

(c) Roof corners (RC) Areas of the external corners of roofs within 1200 mm of two adjacent edges. (This is the overlap area between two RE zones.)

(d) Walls near corners (SC) Walls (including windows and doors) at external corners of the house within 1200 mm of the corner.

G R o o f g e n e r a l a r e a R E R o o f e d g e R C R o o f e d g e c o r n e r G G G G G L EG E N D: 120 0 R C R E R C R E R C 24 0 0 24 0 0 R E R C R E R C 120 0

NOTE: Indicated plan width varies to suit roof pitch.

DIMENSIONS IN MILLIMETRES

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

(19)

Wa l l e d g e S C Wa l l - g e n e r a l a r e a G L EG E N D: 120 0 120 0 G G S C S C G S C S C G G G S C DIMENSIONS IN MILLIMETRES

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

3.2 PRESSURE COEFFICIENTS

3.2.1 Wind classes N1 to N6 (non-cyclonic)

For houses with Wind Classes N1 to N6 (in Regions A and B), the pressure coefficients in Table 3.1 shall be used.

(20)

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 +0.63 −1.0 (b) Cladding, fasteners and immediate

supporting members not within 1200 mm of edges −0.9 +0.4 +0.2 −0.3 +0.63 −1.0 Roof—Edges

(c) Cladding, fasteners and immediate supporting members within 1200 mm of edges (See Region RE in

Figure 3.1)

−1.8 +0.2 −1.8

(d) Cladding, fasteners and immediate supporting members within 1200 mm of eaves corners (applies to roof slopes less than 10°) (See Region RC in Figure 3.1)

−2.7 +0.2 −2.61

Walls

(a) General, including all studs (See Region G in Figure 3.2)

+0.7

−0.65 −0.3 +0.2

+0.9 −0.77 (b) Cladding, fasteners, doors and

windows not within 1200 mm of edges (See Region G in Figure 3.2)

−0.65 +0.7

+0.2

−0.3 −0.77 +0.9 (c) Cladding, fasteners, doors and corner

windows within 1200 mm of edges (See Region SC in Figure 3.2)

−1.3 +0.2 −1.35

NOTES:

1 Positive internal or external pressures are towards the surface (negative values are away from the surface—suctions). For net pressures, positive values are inwards net pressures, and negative values are outwards net pressures.

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

3 The internal pressures presented in this table may only be used where all cladding elements including windows demonstrate compliance with the relevant Australian Standard.

4 Net pressure coefficient includes the effect of a combination factor and so will not equal K_l.C_p,e− C_p,i (see Paragraph A4).

5 Windows and doors with 25% or more of the width of a single panel or pane within 1200 mm of the building edge are classified as SC not G.

3.2.2 Wind Classes C1 to C4 (cyclonic)

For houses with Wind Classes C1 to C4 (in Regions C and D) the pressure coefficients in Tables 3.2A and B shall be used.

3.2.3 Wind pressures on photovoltaic solar panels

Pressures on photovoltaic solar panels for designing their connection to the roof structure shall be obtained from Appendix D in AS/NZS 1170.2.

(21)

TABLE 3.2(A)

PRESSURE COEFFICIENTS FOR WIND CLASSES C1 TO C4 (REGIONS C AND D—CYCLONIC—FOR ULTIMATE STRENGTH)

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)

−0.9 +0.4

+0.7

−0.65 −1.44 +0.95 (b) Cladding, fasteners and immediate

supporting members not within 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 supporting members within 1200 mm of eaves corners (applies to roof slopes less than 10°) (See Region RC in Figure 3.1)

−2.7 +0.7 −3.06

Walls

−0.65 +0.7

+0.7

−0.65 −1.22 +1.22 (b) Cladding, fasteners, doors and

windows not within 1200 mm of edges (See Region G in Figure 3.2)

−0.65 +0.7

+0.7

−0.65 −1.22 +1.22 (c) Cladding, fasteners, doors and

corner windows within 1200 mm of edges (See Region SC in Figure 3.2)

−1.3 +0.7 −1.8

NOTES:

3 Net pressure coefficient includes the effect of a combination factor and so will not equal Kl.Cp,e− Cp,i (see Paragraph A4).

(22)

TABLE 3.2(B)

PRESSURE COEFFICIENT FOR WIND CLASSES C1 TO C4 (REGIONS C AND D—CYCLONIC—FOR SERVICEABILITY)

Housing component Factored external pressure coefficient (Kl.Cp,e) Internal pressure coefficient (Cp,i) Net pressure coefficient (KCCp,n) Roof—General areas (See Region G in Figure 3.1)

−0.9 +0.4

+0.2

−0.3 +0.63 −1.0 (b) Cladding, fasteners and immediate

supporting members not within 1200 mm of edges −0.9 +0.4 +0.2 −0.3 +0.63 −1.0 Roof—Edges

(c) Cladding, fasteners and immediate supporting members within 1200 mm of edges (See Region RE in Figure 3.1)

−1.8 +0.2 −1.8 (d) Cladding, fasteners and immediate

supporting members within 1200 mm of eaves corners (applies to roof slopes less than 10°) (See Region RC in Figure 3.1)

−2.7 +0.2 −2.61

Walls

+0.7

−0.65 +0.2 −0.3

+0.9 −0.77 (b) Cladding, fasteners and windows

not within 1200 mm of edges (See Region G in Figure 3.2)

−0.65 +0.7

+0.2

−0.3 −0.77 +0.9 (c) Cladding, fasteners and corner

windows within 1200 mm of edges (See Region SC in Figure 3.2)

−1.3 +0.2 −1.35 NOTES:

3 Net pressure coefficient includes the effect of a combination factor and so will not equal K_l.C_p,e− C_p,i(see Paragraph A4).

3.3 CALCULATION OF PRESSURES

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

p = q_uC_p . . . 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.

q_u = free stream dynamic gust pressure

(23)

= 0.5ρ_air[V_h]2/1000

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

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

This Standard does not require evaluation of pressures across internal walls. (Where design requires pressures across internal walls, see AS/NZS 1170.2.)

3.4 CALCULATION OF FORCES

The design wind forces shall be determined for structures and parts of structures by multiplying the pressure by the area under consideration and applying the resultant force at the centre of the area normal to the surface.

NOTE: Additional information on calculating pressures and forces may be found in AS/NZS 1170.2.

Uplift forces are determined by taking the uplift pressure (negative pressure coefficients indicate outward forces on a surface) by the total area of the roof (see Section 4).

Racking forces are determined for the overall house by taking the appropriate vertical projected area and applied by distributing the force to the bracing walls or panels (see Section 5).

3.5 PRESSURES FOR TYPICAL APPLICATIONS

Based on the net pressure coefficients in Tables 3.1 and 3.2, ultimate limit state design pressures (tabulated as ‘ultimate strength pressure’) for the N and C categories are as given in Table 3.3. Serviceability limit state design pressures (tabulated as ‘serviceability pressure’) from N and C categories are as given in Table 3.4.

(24)

TABLE 3.3

ULTIMATE STRENGTH PRESSURES (kPa) FOR WIND CLASSIFICATION FROM THE NET PRESSURE COEFFICIENTS GIVEN IN CLAUSE 3.2

Wind class Walls Roofs

Any position Away from corners (see Note 3) Within 1200 mm of corners (see Note 3)

Any position General away from edges (see Note 2) Within 1200 mm of edges (see Note 2) At corners (within 1200 mm of both edges) (see Note 2) Pressure Zone G, SC Figure 3.2 G Figure 3.2 SC Figure 3.2 G, RE, RC Figure 3.1 G Figure 3.1 RE Figure 3.1 RC Figure 3.1 KC.Cp,n +0.9 −0.77 −1.35 +0.63 −0.99 −1.8 −2.61 N1 +0.62 −0.53 −0.94 +0.44 −0.69 −1.25 −1.81 N2 +0.86 −0.74 −1.30 +0.60 −0.95 −1.73 −2.51 N3 +1.35 −1.16 −2.03 +0.95 −1.49 −2.70 −3.92 N4 +2.01 −1.72 −3.01 +1.41 −2.21 -4.02 −5.83 N5 +2.96 −2.53 −4.44 +2.07 −3.25 −5.91 −8.58 N6 +3.99 −3.42 −5.99 +2.80 -4.39 −7.99 −11.58 KC.Cp,n +1.2 −1.2 −1.8 +0.95 −1.44 −2.25 −3.06 C1 _{+1.80 −1.80 −2.7} _+1.43 _−2.16 _−3.38 _−4.59 C2 _{+2.68 −2.68 −4.02 +2.12} _−3.21 _−5.02 _−6.83 C3 _{+3.94 −3.94 −5.91 +3.12} _{−4.73 −7.39} _−10.05 C4 _{+5.33 −5.33 −7.99 +4.22} _{−6.39 −9.98} _−13.58 NOTES:

1 All locations must be able to resist both positive and negative net pressures. The positive net pressures apply to any position on the surface. The negative net pressures are given for each pressure zone defined in Clause 3.1 and illustrated for roofs in Figure 3.1 and for walls in Figure 3.2.

2 For roofs, net pressures on cladding, fasteners and immediate supporting members (such as battens and purlins) are specific to the pressure zone. Net pressure effects on trusses and rafters can be taken from the net pressures for general zones.

3 For walls, net pressures on cladding elements and fasteners (such as wall sheathing, windows and doors) are specific to the pressure zone. Net pressure effects on wall studs and frames can be taken from the net pressures for general zones. 4 The design net pressures for eaves and soffit linings are taken as equal to the net pressures applied to adjacent wall surface

(e.g. the design pressure for eaves lining within 1200 mm of a corner for a C2 classification is +2.68 kPa and −4.02 kPa) 5 The net pressures for all N wind classifications may only be used where all cladding elements including windows

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

6 In order to use the internal pressures in the N classifications in this Table, all of the cladding elements including windows, doors and garage doors need to be designed to resist the design winds.

(25)

TABLE 3.4

SERVICEABILITY PRESSURES (kPa) FOR WIND CLASSIFICATION FROM THE NET PRESSURE COEFFICIENTS GIVEN IN CLAUSE 3.2

Wind class Walls Roofs Any position Away from corners (see Note 2) Within 1200 mm of corners (see Note 3)

Any position General away from edges (see Note 2) Within 1200 mm of edges (see Note 2) At corners (within 1200 mm of both edges) (see Note 2) Pressure Zone G, SC Figure 3.2 G Figure 3.2 SC Figure 3.2 G, RE, RC Figure 3.1 G Figure 3.1 RE Figure 3.1 RC Figure 3.1 KC.Cp,n +0.9 −0.77 −1.35 +0.63 −0.99 −1.8 −2.61 N1serv +0.37 −0.31 −0.55 +0.26 −0.40 −0.73 −1.06 N2 serv +0.37 −0.31 −0.55 +0.26 −0.40 −0.73 −1.06 N3 serv +0.55 −0.47 −0.83 +0.39 −0.61 −1.11 −1.60 N4 serv +0.82 −0.70 −1.23 +0.57 −0.90 −1.64 −2.38 N5 serv +1.19 −1.02 −1.79 +0.84 −1.31 −2.39 −3.46 N6 serv +1.63 −1.40 −2.45 +1.14 −1.80 −3.27 −4.74 KC.Cp,n +0.9 −0.77 −1.35 +0.63 −0.99 −1.8 −2.61 C1 serv +0.55 −0.47 −0.83 +0.39 −0.61 −1.11 −1.60 C2 serv +0.82 −0.70 −1.23 +0.57 −0.90 −1.64 −2.38 C3 serv +1.19 −1.02 −1.79 +0.84 −1.31 −2.39 −3.46 C4 serv +1.63 −1.40 −2.45 +1.14 −1.80 −3.27 −4.74 NOTES:

1 All locations are subject to both positive and negative net pressures. The positive net pressures apply to any position on the surface. The negative net pressures are given for each pressure zone defined in Clause 3.1 and illustrated for roofs in Figure 3.1 and for walls in Figure 3.2.

2 For roofs, net pressures on cladding, fasteners and immediate supporting members (such as battens and purlins) are specific to the pressure zone. Net pressure effects on trusses and rafters can be taken from the net pressures for general zones.

3 For walls, net pressures on cladding elements and fasteners (such as wall sheathing, windows and doors) are specific to the pressure zone. Net pressure effects on wall studs and frames can be taken from the net pressures for general zones. 4 The design net pressures for eaves and soffit linings is taken as equal to the net pressures applied to adjacent wall

surface

5 The net pressures for all N wind classifications may only be used where all cladding elements including windows demonstrate compliance with the relevant Australian Standard. (See Paragraph A4).

(26)

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

Table 4.1 gives net design uplift pressures for the determination of anchoring requirements at tops of walls. The pressures shall be applied as uplift on the entire roof surface.

TABLE 4.1

NET DESIGN UPLIFT PRESSURES FOR DETERMINATION OF ANCHORING REQUIREMENTS AT TOP OF WALLS

kilopascals

Wind class

Serviceability limit state Ultimate strength limit state

Tile roof Sheet roof

(see Note 4) Tile roof

Sheet roof (see Note 4) N1 0 0.04 0 0.33 N2 0 0.04 0.14 0.59 N3 0 0.25 0.68 1.13 N4 0 0.54 1.40 1.85 N5 0.42 0.95 2.44 2.89 N6 0.90 1.44 3.58 4.03 C1 0 0.25 1.35 1.80 C2 0 0.54 2.40 2.85 C3 0.41 0.95 3.92 4.37 C4 0.90 1.44 5.58 6.03 NOTES:

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

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

(a) Serviceability limit state: W_s – G. (b) Ultimate strength limit state: W_u – γG.

3 W_u and W_s have been calculated as set out in Section 3 where V_h = V_h,u or V_h,s as appropriate, using the pressure coefficients as given in Section 3.

4 Load combination factor γ = 0.9.

5 The values for G = 0.9 kPa for tile roof, G = 0.4 kPa for sheet roof have been taken from AS 1684.

6 Sheet roof includes metal tile roof.

7 The net uplift pressures presented in this table may only be used where all cladding elements including windows demonstrate compliance with the relevant Australian Standard.

(27)

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

5.1 RACKING FORCES

Racking forces are lateral (horizontal) forces transferred to the foundations through bracing provided for each storey of the house and the subfloor.

The forces occur in walls parallel to the wind direction and are calculated from the horizontal component of wind blowing on the external envelope of the house and resisted by bracing walls.

Racking forces shall be calculated as follows:

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

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

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

(d) Determine the wind pressure as given in Tables 5.2 to 5.13 using the width (shorter dimension) of the building and roof pitch of the building being designed. Pressures are given for single storey and upper storey of two storeys for both long and short sides of the building, and for lower storey of two storeys or subfloor for both long and short sides of the building.

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

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

The racking force shall be calculated for both directions (long and short sides) of the building. The total racking force for each storey or level of the building shall be determined as the sum of the forces on each of the areas facing the direction being considered. Racking forces shall be calculated to address the most adverse loading situation.

NOTES:

1 For intermediate values between those given in Tables 5.1 to 5.13, use linear interpolation. 2 For the explanation of Tables 5.1 to 5.13, see Appendix A.

3 For worked examples, see Appendix D.

5.2 AREA OF ELEVATION

Area of elevation appropriate for calculation of racking forces shall be as shown in Figures 5.1 to 5.3.

The wind direction used shall be that resulting in the greatest load for the length and width of the building, respectively. As wind can blow from any direction, the elevation used shall be that for the worst direction. In the case of a single-storey house with a gable at one end and a hip at the other, the gable end facing the wind will result in a greater amount of load

(28)

W i n d d i r e c t i o n 1 W i n d d i r e c t i o n 2 G a b l e e n d H i p e n d A r e a o f e l eva t i o n F l o o r l eve l A r e a o f e l eva t i o n ( g a b l e e n d s) A r e a o f e l eva t i o n h0 h0 F l o o r l eve l (a ) Pl a n ( b) W i n d d i r e c t i o n 1 ( b) W i n d d i r e c t i o n 2 NOTES:

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

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

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

FIGURE 5.1 DETERMINING AREA OF ELEVATION FOR A SINGLE-STOREY BUILDING

(29)

(a ) Pl a n ( b) W i n d d i r e c t i o n 1 (c) W i n d d i r e c t i o n 2 W i n d d i r e c t i o n 1 W i n d d i r e c t i o n 2 G a b l e e n d H i p e n d H i p e n d h0 h0 h0 F l o o r l eve l C e i l i n g l eve l F l o o r l eve l U p p e r s to r ey o f t wo - s to r ey s e c t i o n S i n g l e - s to r ey s e c t i o n A r e a o f e l eva t i o n ( g a b l e e n d ) L owe r s to r ey o f t wo - s to r ey s e c t i o n A r e a o f e l eva t i o n A r e a o f e l eva t i o n ( g a b l e e n d ) A r e a o f e l eva t i o n A r e a o f e l eva t i o n h0 h0 L owe r s to r ey o f t wo - s to r ey s e c t i o n U p p e r s to r ey o f t wo - s to r ey s e c t i o n C e i l i n g l eve l U p p e r f l o o r l eve l F l o o r l eve l

(30)

W i n d d i r e c t i o n 2 W i n d d i r e c t i o n 3 G a b l e e n d H i p e n d W i n d d i r e c t i o n 1 F l o o r A r e a of e l eva t i o n H0 h0 A r e a of e l eva t i o n F l o o r F l o o r A r e a of e l eva t i o n h0 h0 (a ) Pl a n ( b) W i n d d i r e c t i o n 1 (c) W i n d d i r e c t i o n 2—H i p e n d (d ) W i n d d i r e c t i o n 3—G a b l e e n d I n t h e s u bf l o o r of a t wo - s to r ey c o n s t r u c t i o n , t h e m a x i m u m d i s t a n c e (_H₀) f r o m t h e g r o u n d to t h e u n d e r s i d e of t h e b e a r e r i n t h e l owe r f l o o r s h a l l b e 18 0 0 m m .

FIGURE 5.3 DETERMINING AREA OF ELEVATION FOR SUBFLOORS NOTES:

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

2 For wind direction 2, the pressure on the gable end is determined from Table 5.1 and the pressure on the hip section of the elevation is determined from Tables 5.2 to 5.13. The total of racking forces is the sum of the forces calculated for each section.

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.

(31)

TABLE 5.1

VERTICAL SURFACES (FLAT WALLS, GABLE ENDS AND SKILLION ENDS)— PRESSURE ON AREA OF ELEVATION

W i n d d i r e c t i o n W i n d d i r e c t i o n W i n d d i r e c t i o n W i n d d i r e c t i o n W i n d d i r e c t i o n W i n d d i r e c t i o n W i n d d i r e c t i o n W i n d d i r e c t i o n W i n d d i r e c t i o n

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

(32)

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 W i n d d i r e c t i o n W i n d d i r e c t i o n W W N1: Wind on side 4 0.61 0.53 0.48 0.45 0.49 0.56 0.56 0.57 5 0.61 0.52 0.46 0.44 0.49 0.56 0.55 0.57 6 0.61 0.50 0.43 0.44 0.50 0.56 0.55 0.57 7 0.61 0.49 0.41 0.44 0.50 0.56 0.55 0.58 8 0.61 0.47 0.39 0.44 0.51 0.56 0.55 0.58 9 0.61 0.46 0.37 0.44 0.51 0.56 0.55 0.58 10 0.61 0.45 0.35 0.43 0.51 0.56 0.55 0.58 11 0.61 0.44 0.34 0.43 0.51 0.55 0.55 0.58 12 0.61 0.42 0.32 0.42 0.50 0.55 0.54 0.58 13 0.61 0.41 0.31 0.41 0.50 0.55 0.54 0.58 14 0.61 0.40 0.30 0.41 0.50 0.54 0.54 0.58 15 0.61 0.39 0.29 0.40 0.49 0.54 0.54 0.58 16 0.61 0.39 0.28 0.40 0.49 0.54 0.53 0.57 W i n d d i r e c t i o n W i n d d i r e c t i on W W N1: Wind on end 4 0.67 0.62 0.59 0.56 0.60 0.57 0.59 0.60 5 0.67 0.61 0.57 0.55 0.59 0.56 0.58 0.60 6 0.67 0.60 0.55 0.54 0.59 0.56 0.58 0.60 7 0.67 0.59 0.53 0.54 0.59 0.56 0.58 0.60 8 0.67 0.58 0.52 0.54 0.59 0.56 0.58 0.60 9 0.67 0.57 0.50 0.53 0.59 0.56 0.58 0.60 10 0.67 0.56 0.49 0.53 0.58 0.56 0.57 0.60 11 0.67 0.55 0.47 0.52 0.58 0.56 0.57 0.60 12 0.67 0.55 0.46 0.51 0.58 0.56 0.57 0.60 13 0.67 0.54 0.45 0.50 0.57 0.56 0.56 0.59 14 0.67 0.53 0.44 0.50 0.57 0.56 0.56 0.59 15 0.67 0.52 0.43 0.49 0.57 0.56 0.56 0.59 16 0.67 0.52 0.42 0.48 0.56 0.56 0.56 0.59

(33)

TABLE 5.3

HIP ROOFS AND SIDE WIND ON GABLE ROOFS—PRESSURE (kPa) ON AREA OF ELEVATION—LOWER STOREY OF TWO STOREYS

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

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

(34)

TABLE 5.4

0 5 10 15 20 25 30 35 W i n d d i r e c t i o n W i n d d i r e c t i o n W W 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 W i n d d i r e c t i o n W i n d d i r e c t i on W W 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

(35)

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

(36)

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 W i n d d i r e c t i o n W i n d d i r e c t i o n W W 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 W i n d d i r e c t i o n W i n d d i r e c t i on W W 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

(37)

TABLE 5.7

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

LOWER STOREY OF TWO STOREYS

0 5 10 15 20 25 30 35

W W N3, C1: Wind on side 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

(38)

TABLE 5.8

(39)

TABLE 5.9

0 5 10 15 20 25 30 35

(40)

TABLE 5.10

(41)

TABLE 5.11

0 5 10 15 20 25 30 35

W W N5, C3: Wind on side 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

(42)

TABLE 5.12

(43)

TABLE 5.13

0 5 10 15 20 25 30 35

(44)

APPENDIX A

COMMENTARY

(Informative) A1 COMMENTARY ON SCOPE AND GENERAL A1.1 General

This Standard has been derived for houses as a group or large numbers of buildings. In general, the level of reliability for the group is similar to that found by applying AS/NZS 1170.2. However, it is recognized that a correct application of this Standard may lead to some houses with more conservative design loads, and others with less conservative design loads.

It is important to categorize each building on a case-by-case basis. Each site should be assessed individually for its wind classification. Each building must be assessed for compliance with geometry and for evaluation of pressures.

A1.2 Comment on Clause 1.3—Geometric Limits

The geometric limits presented in Clause 1.3 have been provided to enable some simplifications to the AS/NZS 1170.2 methods for the most common geometries of housing. It is intended that 16 m width limit be applied to the width of the tallest section of the house. For example, in many cases the various sections of a house (that is the basic rectangular box shapes) may be displaced horizontally with respect to each other. This could make the overall floor plan dimension greater than the 16 m limit even though none of the sections of roof might be wider than 16 m.

Such a house should be within the limits provided that none of the roof sections parallel to the wind direction being considered are greater than 16 m (neglecting the width of eaves). A2 COMMENT ON TABLE 2.1—WIND CLASSIFICATION

An approximate 50% increase in wind pressures occurs from one class to the next higher one, that is, N2 to N3, N3 to N4, etc.

Once a particular building site has been classified using the methods set out in Section 2, the ultimate wind speed for that class represents the design wind speed for the house and includes the effects of—

(a) the importance level which is set by the NCC (the design wind loading level associated with housing);

(b) directionality (the likelihood of wind occurring at its maximum from the direction for which the house is most vulnerable in terms of the pressures on the envelope);

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

(d) terrain roughness (sizes of the obstructions in the wider area around the building site such as water, grass, open space and size of buildings);

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

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

AS 4055-2012 Wind loads for housing.pdf

AS 4055—2012

Australian Standard

®

Wind loads for housing

AS 4055—2012

Australian Standard

®

Wind loads for housing

PREFACE

CONTENTS

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

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

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

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

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

COMMENTARY