Wind load on a structure depends on several factors including wind velocity, surrounding terrain, and the size, shape, and dynamic response of the structure. Traditional theory assumes that horizontal wind load pressures act normally on the face of the structure. Computations for wind in all directions are calculated to find the most critical loading condition. Consideration of suction from pressure differential forces caused by wind is also typically estimated in the case of sidewalls and leeward walls. Typically, building codes allow for either calculated wind loads or wind loads determined by testing of models in a terrain setting equivalent to that of the building site.
Determine the basic wind speed for the location of the structure. If no data is available for the site, use the following approximate values for basic wind speed in the United States:
Coastal and mountainous areas 110 mph Northern and central U.S. 90 mph Other areas of the U.S. 80 mph
Select the category of terrain for the structure. Choose category “A” for city centers with other structures nearby over 70 feet . Choose “B” for wooded or urban areas with structures under 70 feet. Choose “C” for flat areas with obstructions under 30 feet in height. Choose “D” for flat, unobstructed areas.
Use the following to find the coefficient of exposure (K) using the terrain category. For exposure “A” use .000307. For exposure “B” use .000940. For exposure “C” use .002046. For exposure group “D” use .003052.
Use the following calculation to estimate wind pressure on a structure: q = K x V^2 = coefficient of exposure x basic wind velocity c basic wind velocity.
Multiply the wind pressure by 1.15 for important structures such as schools, hospitals, high-occupancy buildings, vital communication buildings, or tall or slender structures.
Multiply the wind pressure by 1.05 for buildings subject to hurricanes along the Gulf of Mexico or the Atlantic coast.
Multiply the calculated wind pressure times the surface area, in square feet, of the structure exposed to wind in each specific direction. Use the largest surface area exposed to wind for the highest wind loading.
The basic wind speed for a location is the fastest wind speed recorded 10 meters (32.8 feet) above open level terrain over a 50-year interval.
-The calculation steps above provide a simple approximation of the wind load on a structure. Having detailed data about the specific site and a model of the structure will result in much more accurate wind load results. Specifically, structure walls need to be checked for ASCE-7 code for positive and negative pressures resulting from wind.
-Check with a qualified structural engineer or architect in order to qualify actual wind load calculations on a structure.
-Check the local building code to determine the wind load requirements for the specific site of the structure.