The Structural Engineer's Corner

Eng. Onorio Francesco Salvatore

Regional wind speed according to AS/NZS 1170:2

Written By: Lexatus - Sep• 14•13

In order to obtain the design wind speed to be used in the calculation of design wind pressure, a regional wind velocity and a site wind velocity must be calculated.

VR, the Regional wind speed, is defined as a 3-second gust wind speed. It is an all-directional basic action because no considerations on direction from which wind gust is originated are made. Its unit of measure is metres/second. In order to obtain this value, a return period R, defined as the reciprocal of the annual probability of exceedance must be evaluated.

A Structural Engineer needs to calculate the return period R and then select the appropriate wind region. Australia is divided in 5 principal regions: A, W, B, C and D. The region A is subdivided in 7 regions (A1, …, A7). The regions C and D are cyclonic, the remaining are non-cyclonic.

For every region, there is a specific formula for the calculation of VR, as follow:

The calculated value shall be rounded to the nearest 1 m/s.

As you can see, the Regional wind speed for tropical cyclones regions C and D takes in account an additional factor to allow uncertainties in the prediction of ultimate design wind speeds.

For any issues or questions, you can contact the author at:

onorio@strutturista.com

Eng. Onorio Francesco Salvatore

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