The design consideration of Wind loads is essential in highly exposed areas, and has become increasingly more important recently with the use of lighter, larger spanning building cladding, facades and structures in contemporary construction techniques.
When wind flows around and over a building, it produces suction pressures. These largely occur along the exposed edges of the building directed towards the wind. Cladding and exterior fixtures must be firmly fastened to the structure to prevent movement or failure. A flat roof will produce higher suction forces that a steeply sloped one. When coupled with the ability for the roof to efficiently shed rainwater, it is essential that the roof cladding is sufficiently rigid, sealed, tied down, and able to maintain its integrity in spit of extreme conditions.
Wind loads determine how the structure will perform under the forces of wind. Unlike Dead loads and Live loads, wind loads are more likely to force a poorly designed building to be pushed over, or lifted up and blown away, as opposed to collapsing under its weight. There are several factors that influence how you for wind loading, necessitating structural bracing and tie-down:
- Local terrain – A building situated on top of a hill or at the edge of an escarpment will have a higher wind load classification than if it is situated in a valley, or in a heavily wooded area.
- Broader geographic location – A site in close proximity to the ocean or at high altitude may be more susceptible to high winds.
Conducting a site inspection and desktop investigation of meteorological data will provide you with a better understanding of the likely wind loading requirements for a building’s siting.
Terrain category
Terrain category classifications provide estimate Wind load calculations.
AS 4055 ‘Wind loads for housing’ sets out four terrain categories:
TC1, TC2, TC2.5, TC3 with TC3 as the worst case.
Wind exerts force on a structure in three ways:
- Uplift load – Strong airflow under a roof pushes upward. Strong airflow over a roof pulls upward.
- Lateral load – Strong horizontal airflow creates pushing and pulling pressure on walls that can cause a building to shift or topple.
- Shear load – Strong horizontal wind pressure can cause racking of walls, making a building tilt, twist and bend.
Regulatory Information
AS1170.2 (2011) Structural design actions Wind actions
AS 4055 (2012) - Wind loads for housing - sets out 10 classifications of wind loads.
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