47.5 MB - The Whole Building Design Guide

The MWFRS is an assemblage of structuralelements assigned to provide support andstability for the overall structure. The systemgenerally receives wind loading from morethan one surface. The C&C are elements ofthe building envelope that do not qualify aspart of the main wind-force resisting system.In the formula for determining wind pressures,the basic wind speed is squared.Therefore, as the wind speed increases, thepressures are exponentially increased, asillustrated in Figure 3-5. This figure also illustratesthe relative difference in pressuresexerted on the main wind-force resistingsystem (MWFRS) and the components andcladding (C&C) elements.Topography: Abrupt changes in topography, such as isolated hills,ridges, and escarpments, cause wind to speed up. Therefore, abuilding located near a ridge would receive higher wind pressuresthan a building located on relatively flat land. ASCE 7 provides aprocedure to account for topographic influences.Building height: Wind speed increases with height above theground. Taller buildings are exposed to higher wind speeds andgreater wind pressures. ASCE 7 provides a procedure to accountfor building height.Figure 3-5: Wind pressure as a function of wind speed3-10 MAKING CRITICAL FACILITIES SAFE FROM High Wind