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Calculating Wind Loads on Buildings

When structural engineers and architects collaborate during the design phase for buildings or structures, one of the most important factors requiring consideration is the velocity and imposed load of wind on the building and the constituent components (such as doors and windows). When calculating these loads, there are several factors that need to be considered.  Some of these factors are not as intuitive as one might think.

The geographical location of the building is the most important factor that should be considered when calculating wind loads. Buildings located on plain flat surfaces face more pressure than those located in a covered neighborhood where the flow of wind in highly obstructed. Similarly, if a building is located on a hill top, it will face more wind pressure than the one located at the bottom. Another consideration which is important is whether the building is located in a hurricane prone area or not.

The wind pressure on different surface areas of a building vary to a large extent depending on several factors. Places where airflow is disrupted are exposed to higher pressure, including the corners and the overhangs of roof; therefore, complex architectural designs must account for these surface area variations of wind pressure on a building.

When determining wind pressure, an important factor that needs to be considered is the direction of the wind. If the wind is blowing against a building surface it is called “windward” pressure which acts in a positive direction.  Negative wind pressure or “leeward” pressure, is generated while winds blow away from the surface in question. Depending on the usual direction of airflow in an area, it can be determined whether the building will have to face negative pressure or positive pressure.

This indicates the pressure created inside a building due to wind sucked inside through wind ports made in the building. Depending on these ports and the direction of airflow, the internal pressure can be positive and negative as well. The pressure coefficients for internal pressure also need to be accounted for during the construction of a building and its components.

Combined together, all these factors give a measure of design pressure, which is the product of all these different pressures a building is exposed to. Using this design pressure as a basic element, architectural designs for building walls, doors and windows are created accordingly.

A handy technical reference which does a great job at summarizing the differences between the “old” ASCE code and the latest ASCE 7-10 code, is the white paper – “Changes to the Wind Speed Maps and Wind Design – 2010 Florida Building Codes” as provided by Building A Safer Florida, Inc.  While this resource is written for and intended to serve as a summary for structural engineers, there is much information contained that can serve the “non-technical” reader.  The basic behavior of these wind load calculation parameters have been summarized below for the casual reader.  You don’t have to be a structural engineer in order to understand how wind loads effect the building components many manufacturers must design for – particularly in the high-velocity hurricane regions of South Florida.

Dash Door’s full-time professional structural engineer is available to provide technical support services as they relate to all products and wind load resistance.