Component and Cladding - ASCE-7-05

[cgstrucg]

Hello,

I am working on a project in NYC that has 3 different elevation roofs. All roofs are connected together. One roof is 66ft high and another 2 are 32ft and 26ft. When I calculate C&C wind uplift pressure, do I calculate C&C forces separately for lower roofs or is it going to be same value for all roofs?

If the answer is same for all buildings, then in some hypothetical scenario, if one 26ft roof is isolated from two higher roofs. Do we apply different C&C for the 26ft one as its isolated?

Thanks a lot for the help.

 

[JAE]

The value of q in Equation 6-23 is defined, for roofs, as qh (the value of q at the mean height of the roof.

The issue you have is that you have different roofs.
The ASCE 7 procedures are typically based on general type buildings (i.e. buildings that look like a box on the ground).

The uplift roof pressures, from my understanding, are based on the general upward drag from wind hitting the side of the building and creating a vertical vortex upward.

For individual roofs at different levels, it seems rational to use qh for each separate roof level independently.
That said, the irregular shape of your building (as you described it and I imagined it) suggests the need for a wind tunnel - but that might be too much for your project budget.

 

[cgstrucg]

Thank You JAE, I thought the same.