ASCE 7-10 30.10 Roof Overhangs

[StrEng007]

This section of ASCE, in addition to Figure 30.10-1, indicate that the GCp values for roof overhangs include the contribution from the top and bottom surfaces of the roof overhang.

If this GCp, which considers top and bottom surfaces, is to be used with equation 30.10-1, why does this equation consider the GCpi? This would be analogous to the calculations for overall lateral loads (MWFRS) on a structure. Cp is considered from the windward and leeward sides, (+Cp)+|-Cp|, giving the overall load and illustrating the point that GCpi should cancel out. ASCE doesn't provide a commentary on section 30.10. I didn't think GCp could consider "both" surfaces of a component and then subtract either (+0.18) or (-0.18).

 

[wannabeSE]

For a rafter that cantilevers, the internal wind pressure will cancel-out. But, the cladding often times receives wind load from only one side. You need to look at a section though the overhang and determine which elements need to be designed with the internal pressure coefficient.