Wind Speed - Design of Structures

Design of Structures

Wind speed is a common factor in the design of structures and buildings around the world. The wind speed is often the governing factor in the "lateral" design of a structure and is used by professional engineers and designers.

In the United States, the wind speed used in design is often referred to as a "3-second gust" which is the highest sustained gust over a 3 second period having a probability of being exceeded per year of 1 in 50 (ASCE 7-05). Windspeedbyzip maps out the design wind speed as suggested by ASCE 7-05 for the United States. This design wind speed is accepted by most building codes in the United States and oftentimes governs the lateral design of buildings and structures. In Canada, reference wind pressures are used in design and are based on the "mean hourly" wind speed having a probability of being exceeded per year of 1 in 50. The reference wind pressure (q) is calculated in Pascals using the following equation (ref: NBC 2005 Structural Commentaries - Part 4 of Div. B, Comm. I): q=(1/2)pV**2 where p is the air density in kg/m**3 and V is wind speed in m/s.

Historically, wind speeds have been reported with a variety of averaging times (fastest mile, 3-second gust, 1-minute and mean hourly for example) which designers may have to take into account. To convert wind speeds from one averaging time to another, the Durst Curve (Ref: ASCE 7-05 commentary Figure C6-4) was developed which defines the relation between probable maximum wind speed averaged over t seconds, V(t), and mean wind speed over one hour V(3600).