What is a Design Wind Speed?


To identify a Rationalised Gust Wind Speed for a proposeddatasheet-15-1
building site, there are four variables you must fi rst identify.
They are Region (fi gure 1), Terrain Category, Shielding
Factor and Topographic Classifi cation. The Rationalised
Gust Wind Speed can then determined using table 2.
If the wind classifi cation (as defi ned in AS4055-1992) is
known, the gust wind speed can be taken from table 1.
*This is an approximate method for estimating wind speeds
for residential structures only. For full analysis refer to
Australian Standard AS/NZS1170.2:2002.






TERRAIN CATEGORYdatasheet-15-4

The wind speed at a structure is infl uenced by the terrain
it fl ows over as it approaches the structure. The terrain
category classifi cations can be described as follows:

Category 1
Exposed open terrain with few or no obstructions. This
condition is rare and exists only for isolated buildings in
fl at, treeless, poorly grassed plains of at least 10km width.

Category 2
Open terrain, grassland with few well scattered obstructions
having heights generally from 1.5 metres to 10.0 metres.

Category 2.5
Terrain with few trees and isolated obstructions. This is an
intermediate classifi cation between Category 2 and 3.

Category 3
Terrain with numerous closely spaced obstructions such as
areas of suburban housing. (3.0 metres to 5.0 metres high)




The Equivalent Maximum Surface Slope is the slope of the
steepest 20 metre segment of ground directly downhill from
the proposed building site on the hill, ridge or escarpment
being considered. Often The Equivalent Maximum Surface
Slope will not occur at the actual proposed building site.
In steeply folded topography, the Equivalent Maximum
Surface Slope shall be the direction giving the highest
topographical classifi cation.

Topographic classifi cation T1 shall apply to all hills, ridges
and escarpments if the hills are less than 25 metres high for
Terrain Category 3, 20 metres for Category 2.5, 15 metres
for Category 2 or if the surface inclination is less than 1 in 10.




Shielding classifi cation is required because the wind speeddatasheet-15-6
at a structure is infl uenced by any upwind obstructions of
similar size to the structure that are close to the building.
The three shielding classifi cations are defi ned as follows:

FS - Represents Full Shielding
Full Shielding is where at least two rows of houses or similar
sized permanent obstructions surround the building being
considered. In regions A and B, heavily vegetated areas can
provide Full Shielding. The application of Full Shielding is
considered appropriate for typical suburban development,
equal to or greater than 10 houses and/or similar sized
obstructions per hectare.

PS - Represents Partial Shielding
Partial Shielding applies to intermediate situations where
there are at least 2.5 houses, trees, or sheds per hectare
upwind of the structure. e.g. Typical “acreage” type suburban
development or wooded parklands.

NS - Represents No Shielding
No Shielding occurs where there are no (or less than 2.5
obstructions per hectare) permanent obstructions upwind.
e.g. The fi rst two rows of houses or single houses abutting
open water, airfi elds and open parklands.


DESIGN FACTORSdatasheet-15-8

Wind speeds have been determined using the following factors, in accordance with AS1170.2-2002. 500 year design return period and a maximum ten metre structure height.

Note: Wind speeds have been reduced by a factor of 1.5 from ultimate limit state to give permissible wind gust as is commonly used.




The method used for calculating the design gust wind speeds has been developed by Stratco with the assistance of suitably qualifi ed engineers in order to comply with the requirements of AS1170.2-2002.

Stratco does not accept liability for any loss or damage suff ered as a result of any errors in the interpretation or application of this design guide. Any person wishing to check any  calculations made by them pursuant to this method may wish to seek independent engineering advice.



The examples below show typical applications of the rationalised gust wind speeds. For a full analysis refer to AS/NZS1170.2:2002.



ORMEAU Ph: (07) 3451 4411 1 Mavis Crt
• CRESTMEAD Ph: 3451 4411 179 Magnesium Dve
• TOOWOOMBA Ph: 4638 9322 167 Herries St
• VIRGINIA Ph: 3451 4411 2037 Sandgate Rd
• CABOOLTURE Ph: 5431 4100 17 Concorde Pl
• MAROOCHYDORE Ph: 5351 0100 14 Pike St, Kunda Park
• GOLD COAST Ph: 3451 4411 108 Eastlake St, Carrara
• CAPALABA Ph: 3451 4411 Cnr. Smith St & Redland Bay Rd
• ARCHERFIELD Ph: 3451 4411 Cnr. Beaudesert & Granard Rd
• REDBANK PLAINS Ph: 3451 4411 326 Kruger Pde

HUNTINGWOOD Ph: (02) 8811 7211 15 Liberty Rd
• CAMPBELLTOWN Ph: 8811 7211 22 Blaxland Rd
• PENRITH Ph: 8811 7211 125 Coreen Ave
• NEWCASTLE Ph: 4922 2777 2 Hartley Dve, Thornton

FYSHWICK Ph: (02) 6280 5905 25 Tennant St

EPPING Ph: (03) 9409 9260 17 Scanlon Dr
• DEER PARK Ph: 9409 9260 1027 Western Hwy
• KILSYTH Ph: 9409 9260 73 Canterbury Rd
• DANDENONG Ph: 9409 9260 14 Princes Hwy, Doveton

GEPPS CROSS Ph: (08) 8349 5559 125 Cavan Rd
• RICHMOND Ph: 8349 5559 221 Marion Rd, Marleston
• LONSDALE Ph: 8349 5559 Cnr. Dyson & O’Sullivan Beach Rd
• ST AGNES Ph: 8349 5559 129 Tolley Rd
• GAWLER Ph: 8522 1132 16 Main North Rd, Willaston
• GOOLWA Ph: 8555 2825 29 Hutchinson St
• VICTOR HARBOR Ph: 8551 3400 95 Victoria St
• MURRAY BRIDGE Ph: 8531 9191 15 Hindmarsh Rd
• KADINA Ph: 8828 1555 9 Kennett St
• RIVERLAND Ph: 8582 4666 53 Zante Rd, Berri
• PORT AUGUSTA Ph: 8642 6333 70 Victoria Pde
• WHYALLA Ph: 8645 7344 50 Ian St, Whyalla Norrie

CANNING VALE Ph: (08) 9455 5111
Corner of Bannister Road and Hopewell Street
• MALAGA Ph: 9455 5111 Cnr. Marshall Rd & Energy St
• BALCATTA Ph: 9455 5111 140 Balcatta Rd
• MANDURAH Ph: 9455 5111 11 Fitzgerald Rd
• BUNBURY Ph: 9791 4200 Cnr. Strickland St & Zaknic Pl
• BUSSELTON Ph: 9752 3122 18 Wright St
• KALGOORLIE Ph: 9080 8080 8 Federal Rd
• BROOME Ph: 9191 3800 26 Hunter St

BERRIMAH Ph: (08) 8944 2300 780 Stuart Hwy
• ALICE SPRINGS Ph: 8950 9898 6 Ghan Rd NEW ZEALAND
CHRISTCHURCH Ph: (03) 338 9063 55 Hands Rd
AUCKLAND Ph: (09) 274 6487
Block 4, 22 Harris Rd, East Tamaki


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