Wind Loads

In the 1997 edition of the Uniform Building Code (UBC), the wind load provisions are, for the most part, the same technical provisions incorporated into an earlier code, the 1991 UBC. These provisions occurred as a result of the work of the High Winds/Hurricane Design Code Development Committee of the International Conference of Building Officials (ICBO). In addition, the Structural Engineering Associations of Washington and California contributed to this work; producing a practical and logical set of code guidelines. These provisions agreed with the prevailing national standard of the time – American Society of Civil Engineering's ASCE 7-88, Minimum Design Loads for Buildings & Other Structures – except that they are simpler as the result of certain assumptions made about the buildings under consideration.

Wind loads are dynamic in nature, but are treated in the code as quasi-static lateral inward and/or outward acting building forces.

The magnitude of the wind-induced pressure or suction depends upon the complex interrelationship of: wind velocity; air mass density; structural geometry including dimensions, stiffness, orientation, and location; and the surrounding ground surface conditions. The development of the code-based wind pressure diagrams, which are discussed in the next section, required many simplifying assumptions about these complex issues.

The information presented here follows the 1994 UBC guidelines 1613 through 1623 and the 1997 UBC 1615 through 1625. These provisions may not be used for buildings taller than 400 feet above grade or for buildings with height to width ratios greater than or equal to 5.

The design of the primary lateral force resisting system (LFRS), as well as its elements and components, for wind is based upon the appropriate application of the following equation:

P = CeCqqsIw (18-1 of '94 UBC and 20-1 of '97 UBC)
where P is the design pressure in pounds per square foot (psf).

The use of the code pressure equation and the definition and selection of terms are reviewed as you work through this tutorial.

You are now ready to develop wind pressure diagrams for a simple rectangular building.


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Wind Load Calculator