Wind Loads: Explained in 1-minute

Wind Loading is not taught in great detail at most universities but it is an important design factor for the design of a buildings lateral force resisting systems. Hopefully this article can help shed some slight on the very basic aspects of wind loading.

Wind Pressure on Buildings

When wind blows over a building, there are areas of low pressure (suction, air moving away from the surface i.e. negative pressure) and high pressure (overpressure, air moving towards the surface i.e. positive pressure).

An example for wind on a house is shown below:

The wind pressure on surface A, is a uniformly distributed pressure, expressed in kN/m2 or N/mm2.

A simplified 3d example is shown below, with colours representing the pressure magnitudes (darker colours indicate higher magnitudes). Of course the real pressure variation is much more sophisticated.

The wind pressure represents the maximum dynamic pressure during a 3-second gust. It can be calculated by using the following equation:

Dynamic Pressure,

ρ is the air pressure, generally taken as 1.225 kg/m3. U is the Wind Speed (usually at a reference height such as the top of the building). Cnet is the net pressure coefficient and is defined as follows:

Net Pressure Coefficient,

Where Cpe and Cpi are the external and internal pressure coefficients, respectively. These values are widely available in building codes for different building shapes and pressure regions.

※ How to obtain the external pressure coefficient for wind loading?

※ How to obtain the internal pressure coefficient for wind loading?

Wind Force on Buildings 

Knowing the dynamic pressure, we can calculate the force acting on an area as follows:

Force,

Where Q is the pressure and A is the tributary area.

※ What is the tributary area for wind loading? Explained in 1-minute.

Using this information as a basis, we can do simple calculations for:

- Determining overall structural wind loads

- Determining local wind loads for cladding 

For tall buildings, the wind pressure varies with height, so the wind force can be calculated on a storey-by-storey basis. In this case, the tributary heights for each storey can be considered as half the distance to the storeys above and below... as shown in the image below.

Example Calculation for Tall Building

Coming soon...!