Wind Loading, Case A or Case B? 1

[spud22]

In ASCE 7-10, under wind loading Table27.4-5 shows Cn factors for Pitched Free Roofs, Open Buildings. There is a column listing values for Case A and Case B. Can someone tell me what Case A and Case B refer to?

 

[SlideRuleEra]

Case A and Case B are explained in the ASCE 7-10 Commentary, page 552 in my copy:

Two load cases, A and B, are given in Figs. 27.4-4 through 27.4-6. These pressure distributions provide loads that envelop the results from detailed wind-tunnel measurements of simultaneous normal forces and moments. Application of both load cases is required to envelop the combinations of maximum normal forces and moments that are appropriate for the particular roof shape and blockage configuration.

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