Can be input in Pryda Software

using THREE methods

Classification Method- Limited to residential or isolated building types only

- Ultimate Design Wind Speeds obtained from AS 4055 -2006

for classifications ranging from N1 to N6 and C1 to C4

- Ridge Height is limited to 8mDirect Entry Method

- Engineer provides the Ultimate Design Wind

Speed and the Internal Pressure Coefficient.

PREFERRED OPTION

Basic Data Method- Engineer provides information for all parameters, and

software computes Ultimate Design Wind Speed

WIND SPEEDS

How is the Ultimate Design Wind Speed determined ?

An Example

Basic Data Method

Topographical Calculation = 1

refers to a building located anywhere

along a flat or rolling countryside or

lower third (near bottom) of a hill, ridge

or escarpment.

Use Mt =1.0

Terrain Category = 2.5

refers to a terrain with a few

trees, isolated obstructions and

generally represents the terrain

in developing outer urban areas.

Region = D

Represents severe cyclonic region –

coastal WA between 20o & 25o latitude.

Use VR = V500 = 88 m/s

Building Type = Residential

Relates to Importance Level of 2 as per

BCA 2011, corresponds to Regional

Wind Speed V500 as per AS1170.2-2011

Shielding = Partial

refers to acreage type suburban

development or woodland parkland.

In Regions C and D, heavily

wooded areas shall be considered

to have partial shielding.

Use Ms = 0.95

Maximum Eaves and Ridge Height

The Average Building Height as

described in AS 1170.2-2011 based on

these two entries

Internal Pressure Coefficient

Provided by the Project Engineer or

taken as +0.7 for cyclonic regionsUltimate Design Wind Speed

Computed by Pryda Build software

based on all the relevant data

provided here

Ultimate Design Wind Speed

Regional Wind Speed, VR = 88 m/s (Table 3.1 AS1170.2:2011)

Wind Direction Multiplier, Md = 1.00 (Table 3.2 AS1170.2:2011)

Terrain/Height Multiplier, Mz,cat = 0.91 (Table 4.1(B) AS1170.2:2011)

(Note: Obtained for an avge building height of 7.5m and Terrain Category 2.5)

Shielding Multiplier, Ms = 0.95 (Table A4; AS4055-2006)

(Note: Table 4.3 AS 1170.2:2011 may also be used if the shielding parameter is known)

Topographic Multiplier, Mt = 1.00 (Table A3; AS4055-2006)

(Note: Clause 4.4 AS 1170.2:2011 may be used if all parameters are know)

Ultimate Design Wind Speed (m/s) = VR Md Mz,cat Ms Mt

= 88 x 1.0 x 0.91 x 0.95 x 1.0

= 76.1 m/s

September 2011

Wind Regions of WA and QLD

September 2011

Building

Type

Importance

Level(as per BCA)

Description

Isolated 1Buildings or structures presenting a low degree of hazard to life and

other property in the case of failure. eg: farm sheds etc

Residential 2Buildings or structures not included in Importance Levels 1, 3 or 4

eg: Normal domestic dwelling, duplexes, small apartments etc

Commercial 3Buildings or structures that are designed to contain a large number of

people. eg: Offices, shops, hotels, aged-care centres

Essential 4Buildings or structures that are essential to post-disaster recovery or

associated with hazardous facilities. eg: Schools, hospitals etc.

Note: Not all schools, hospitals etc need to be classed as ‘Essential’ building type, as only some of them are likely to

serve the ‘post-disaster’ function. Seek advice from local councils

BUILDING TYPE

Bottom Chord Bracing

Suspended or no ceiling or

when ceiling battens clipped-on

Require Bottom Chord ties.

Fabricators only provide cross bracing as per Clause 4.4 AS4440-2004

Important !!AS4440- Bottom Chord ties and bracing are intended only to laterally restrain truss bottom chords and DO NOT provide lateral stability to the building to resist lateral wind loads.

Bottom Chord Bracing

Wind Trusses

Nailplated timber trusses installed in a horizontal

plane.

Resist Lateral Wind loads.

Usually fixed to underside of bottom chord of

roof trusses.

Engineer to provide loadings for fabricator to

design wind trusses.

Connections to supporting walls to be also

provided by the engineer.