The directionality factor (Kd) used in the ASCE 7 wind load provisions for components and cladding is a load reduction factor intended to take into account the less than 100% probability that the design event wind direction aligns with the worst case building aerodynamics.
 
Per ASCE 7-10,Section 26.6, the Directionality Factor Kd is defined as a parameter that makes the design more rational by considering the dependencies of the wind speed, the frequency of occurrence of extreme wind and the aerodynamic property on wind direction. The wind Directionality Factor Kd is affected by the frequency of occurrence and the routes of typhoons, climatological factors, large-scale topographic effects and so on.
 
See Table 26.6-1 below for the Wind Directionality Factors required per structure type.

kd values

 

The question then comes as to whether load combinations exist for windows & doors.  According to a declaratory statement published by the state of Florida, they do exist and the above can be used.

 

Additionally, Broward County publishes a ‘deemed to comply’ document inside the HVHZ allowing Kd=0.85 to be used for windows and doors.

 

Last, ASCE 7-16 has addressed this issue and clarified the use of Kd=0.85 for component and cladding design in a revised table.

 

Jul 27, 2016   5602    Codes & Standards    
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