Wind Load on Canopies 1

[peinapod]

Can anyone help me out and tell me where I might find information on the component and cladding wind load on canopies? Specifically, I have a canopy with a cold-formed steel framed soffit and a structural steel framed roof with metal decking. I have designed the structure assuming an open building. I am looking for the wind pressure on the cold-formed steel soffit. ASCE 7 very clearly states that you can separate the Cn value and use only portion acting on the portion of roof you're designing (i.e. the soffit or roof decking). It says this, but doesn't tell you how to do it or what portion of Cn is from the roof and what portion is from the soffit. Does anyone have a reference for this?

I know that I can conservatively just use Cn, but I would like to see what the value is for each surface.

Thanks.

 

[hokie66]

Pressure on the canopy soffit would be the same as on the abutting wall exterior surface, at least where the two surfaces meet.

 

[zcp]

Is this an open canopy / structure with a soffit or is it next to / attached to a building that is larger in size?

ZCP

http://www.phoenix-engineer.com

 

[peinapod]

Hokie66 where did you find that reference?

 

[xez]

PEINAPOD- I don't believe ASCE 7 is clear on that topic. Experimental data can be found in a paper by Peter Vickery, Journal of Structural Engineering, 2008, Vol. 134, Issue 5, Pg. 846-853. The abstract for this paper will also explain that the results of the soffit tests correlate to wall pressures.

 

[MillR]

I agree with hokie66 - we have a typical note on our drawings that says "design soffits for adjacent wall component and cladding wind pressures" and yes, it is unclear in the code.

 

[hokie66]

It is fundamental that pressure at a given point is exerted in all directions equally.

 

[peinapod]

HOKIE66 - Yes, that's a fundamental given. However, my calculations are being reviewed and a lot of reviewing engineers don't deal in reality ;-). They want to see a code reference. I appreciate the information.

BCNG - Very helpful. Thanks.

 

[Huaxingxing]

Actually, i am working on a canopy design, and I realized using the formula on page 72 is not that suitable, because you will have a really big reaction at the bottom of the column, just take them as MWFRS, it will be much easier.

 

[peinapod]

Huaxingxing - I have no idea what you're trying to say. Page 72 varies depending upon which code and which code version you have. My ASCE 7-05 page 72 is a table. Additionally, it is unconservative to design cladding using MWFRS loads. However, for some reason, you mention a column? Your statement is so confusing.

 

[Ron]

Design the soffit as an overhang per ASCE 7

 

[MillR]

Ron, I disagree. Designing the soffit as an overhang is too much load. The total canopy (top and bottom) can be designed as an overhang, but the component and cladding pressure for just the underside of the overhang, the soffit, is the same as an adjacent wall pressure.

 

[peinapod]

I agree MillR. Overhang loads are not the correct value to use here. While it would certainly be conservative, the loads are too high. My canopy is quite large as well. To apply a pressure related to edge vortices over the entire surface would be a huge cost.

 

[Ron]

Maybe I'm missing something here......

peinapod....what version of ASCE 7 are you using?
Canopies have been treated somewhat differently in ASCE 7 with various revisions (as have other structures!). How are you defining your soffit? Is it an entire underslung "ceiling" or is it confined to some portion of the edge of the canopy?