SELECTION PROCEDURE
To identify a Rationalised Gust Wind Speed for a proposed 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 CATEGORY
The wind speed at a structure is influenced by the terrain it flows over as it approaches the structure. The terrain category classifications 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 flat, 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 classification 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)
TOPOGRAPHIC EFFECT
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 classification.
Topographic classification 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 FACTOR
Shielding classification is required because the wind speeddatasheet-15-6
at a structure is influenced by any upwind obstructions of similar size to the structure that are close to the building. The three shielding classifications are defined 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 first two rows of houses or single houses abutting open water, airfields and open parklands.
DESIGN FACTORS
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.
NOTE
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.
WIND SPEED EXAMPLES
The examples below show typical applications of the rationalised gust wind speeds. For a full analysis refer to AS/NZS1170.2:2002.
QUEENSLAND
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
NEW SOUTH WALES
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
AUSTRALIAN CAPITAL TERRITORY
FYSHWICK Ph: (02) 6280 5905 25 Tennant St
VICTORIA
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
SOUTH AUSTRALIA
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
WESTERN AUSTRALIA
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
NORTHERN TERRITORY
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