ASCE 7-05 Canopy Pressures 1

[wallerdf]

I have a 9 ft deep canopy and am trying to figure out what wind pressures are appropriate for the face of the canopy. I can get the roof pressures easily using the tables. And typically I have been using those roof pressures and calculating the pressure on the face assuming it to act as a solid sign above ground. Resently I have been thinking that might not be totally right. Shouldn't there be some windward and leeward pressures on the front and back faces? Any thoughts?

 

[hsustersic]

I agree with you that the force coefficients for solid signs might not be the best approach. If you read the commentary to Fig. 6-20 of ASCE7-05, you find that these force coefficients were derived using wind tunnel tests on solid signs and free-standing walls that, presumably, are very thin in the plane of the wind load.

What is the configuration of your canopy (gabled? flat? troughed?) If it is flat, I would probably use components and cladding wall pressure coefficients evaulated at the highest point of the canopy.

 

[wallerdf]

It's flat. What steered me away from that was the tables say that the coefficients are for enclosed or partially enclosed. It seems you could use the external pressure coefficients and not the internal to get what I'm looking for. Thanks.

 

[JLNJ]

Be careful. Canopies seem to be the first thing to fly away in a strong storm, leading me to believe that we don't have a handle on the design pressures.

The British and Canadians have some info in their codes which might be a helpful addition to ASCE 7.

 

[vmirat]

I'm also designing a canopy with similar conditions. Mine has a flat roof with soffit panels underneath. The fascia is vertical with a height of 3 feet. For vertical wind loads, I used ASCE 7-05, Figure 6-18A, with a slope of 0 degrees. For horizontal wind, I used Figure 6-20, Cases A and B only. I decided that Case C was unique to signs because of the aerodynamics of flow around a flat plate. I decided to use Figure 6-20 instead of assuming this was a fully enclosed building because of the height to length ratio (the canopy dimensions are 40'x45'). I decided that this situation could be evaluated similar to the simplified method where you use just the projected area of the structure versus calculating the positive and negative pressures on the windward and leeward sides.

 

[wannabeSE]

See ASCE 7-05 section 6.5.13.2. Open buildings with flat roofs should use parapet wind pressures on the fascia for MWFRS calcs.

 

[wallerdf]

Perfect. Never read that before. Thanks.