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Roof Pressure in Design Wind Load Cases (Simultaneously 75%)

Roof Pressure in Design Wind Load Cases (Simultaneously 75%)

Roof Pressure in Design Wind Load Cases (Simultaneously 75%)

(OP)
There was an older tread two years back but was unfortunately was closed. See Roof Pressure in Design Wind Load Cases thread507-322346: Roof Pressure in Design Wind Load Cases

It looks like ASCE 7-10 didn't do much more explaining than 7-05 did. In my view, it seems to be fair not to add the roof wind pressure up, but to rearrange them so they reflect the new wind direction. The intent of this additional load case is not to over-design the roof structural members by 1.5 at selected locations, but to ensure columns have enough biaxial and torsional capacity (for a simple structure anyways).

If anything, using 0.75 Px and 0.75 Py implies the wind velocity pressure remains the same: 0.75 * sqrt(2) = 1.06 = 1.0, which again proves my point that roof wind pressure shouldn't be added up.

Thoughts?

RE: Roof Pressure in Design Wind Load Cases (Simultaneously 75%)

I have 2 thoughts:

The gravity framing for the roof is not part of the Main Wind Force Resisting System and needs to be designed for the Components and Cladding wind loads.

Per footnote 1 on figure 27.4-8 (and 6-7 in ASCE7-05), the wind loads are acting on the "projected area perpendicular to each principle axis". The uplift or vertical component of the roof wind load will not act on these projected areas.

RE: Roof Pressure in Design Wind Load Cases (Simultaneously 75%)

I have never doubled up the roof winds for that condition

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