Open Buildings

[NITTANYRAY]

ASCE 7-05 has tables for Open Buildings for pitched roofs.
All the MWFRS tables for open roofs have values for Load Case A and Load Case B. I can not find anywhere in the document where they define what Load Case A and B are and why the values differ so much. Does anyone know what these load cases are?

 

[UcfSE]

They represent two different possibilities of pressure coefficients that could occur at a given time. You have to check both.

 

[Taro]

Check the footnotes. I don't have it in front of me, but going from memory I believe one case is for unobstructed wind flow beneath the roof and the other is for when objects below the roof disrupt the wind flow.

 

[NITTANYRAY]

They show both unobstructed and obstructed load conditions in the table and Load case A & B for both.