The Structural Engineer's Corner

Eng. Onorio Francesco Salvatore

Site wind speed according to AS/NZS 1170.2

Written By: Lexatus - Sep• 14•13

In order to obtain the Design wind velocity, the Structural Engineer needs to define the Site wind velocity. This value is substantially defined as the Regional wind velocity modified taking into account the direction and the exposure of the site.

The formula used is:

Md is a wind directional multiplier for the 8 cardinal directions (b). The values in the brackets are used to take into account the exposure of the site, as said before. These last three coefficients are named as Terrain/height multiplier, Shielding multiplier and Topographic multiplier.

The design height, z, at which the site and design wind speeds are calculated is the height of the average roof level. That said, the Structural Engineer should take into account that for very high structures a variable z should be considered. Lattice towers of 25-30 m in height are typical examples.

It is important to note that when the orientation of a building is not know, the regional wind speed shall be assumed to act from any cardinal direction (i.e. Md = 1.0 for all directions).

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

Eng. Onorio Francesco Salvatore

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