Maximum deflection for canopy

[Jared Joseph]

I am designing a canopy for a small stadium in an open field. The cantilever beams are w24x76 . They are 36 feet 10 inches long and 14 feet apart. A fixed end support on the far end and a pin support at 13 feet 10 inches . Using ASCE 7-16 section for canopies , I found the wind load during storms with 200mph winds ( I live in the Caribbean ) to be 115 psf. Attached is a photo of the moment and shear diagrams yielded.

I get a maximum deflection of 2.5 inches, this is L/110. Is this acceptable since it's just a canopy roof and not a member people walk on? It doesn't matter if it deflects so much the galvume sheeting deforms and needs replacing, I just want to make sure the beams don't fail.

 

[HDStructural]

That is a long cantilever with a small backspan. I'm guessing there isn't much you can do to make that a better ratio.

The allowable deflection depends on the final use of the structure and any governing codes which I am not familiar with for stadiums. You may be trying to keep your deflection under a certain ratio (L/240, L/360), or under a certain amount of deflection (1", 1/2"). Not sure what your limits should be.

However, IBC allows you to effectively cut the deflection ratio in half for cantilevers (table 1604.3, footnote i), so for a 22' cantilever, you would do 22' * 12"/' * 2 / 2.5" => L/220
People also typically use a 10 year wind event to calculate deflection which is mentioned in the IBC deflection table. It says to use 0.42 * the components and cladding force for deflection (table 1604.3, footnote f).

 

[Harbringer80]

I'd be more concerned with any wind oscillation effects (galloping, etc) for this type of structure than deflection under a static load.