The Structural Engineer's Corner

Eng. Onorio Francesco Salvatore

Orientation factor in wind action evaluation according to Australian Standard 1170.2

Written By: Lexatus - Sep• 14•13

Once obtained the Site wind speed, the Structural Engineer needs a Design wind speed. As said in previous article, the Site wind speed – as the name says – is only related to a specific site, no matter of what structure we are analysing. In order to evaluate the specific wind speed on structure, the Structural Engineer has to consider if the orientation is known or unknown. In the first case, for the specific structural element he wants to analyse, an orientation modified wind speed is needed.

In order to determine the design wind speed, one of the following approaches has to be used:

1. ORIENTATION UNKNOWN – assume Md = 1.0 and take the worst case on site for (Mz,cat Ms Mt) in order to obtain a single value of Vdes to be used in all parts of the structures;

2. ORIETATION KNOWN – in this case, the Structural Engineer has to calculate 8 values of Vsit and obtain the multiple Vdes to be used. There is a Vdes for every direction perpendicular to the structure; for example, for a house we have 8 Vsit and 4 Vdes, one for each of the 4 sides of the house.

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Eng. Onorio Francesco Salvatore

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