Wind uplift for metal deck on bar joist 1

[yawp1]

thread507-460392
I have designed a low sloped roof (.25/12) to act as a shear diaphram. The metal deck I am using is non-composite. I have specified 3.5 inches of concrete which, by virtue of the dead load, will resist most uplift but not all. Is the bond between the metal deck and the concrete sufficient to resist maybe 10 to 20 psf of uplift. I am in a hurricane prone area.

 

[phamENG]

I wouldn't count on it. Not sure if there have been any studies into how strong or reliable that "bond" would be, but I can't imagine it's much.

How are you applying the wind load? Is this a components and cladding application you're looking at? With 3.5" of concrete, I'm guessing you're going to put some WWR in it. As long as that's properly installed, I'd feel comfortable considering a really large area of the slab as my "tributary area" for determining applicable wind load. It would be far greater than the trib for the joist, deck, or deck to joist fastener, so your uniform loading will be lower. Might give you enough of a reduction to make it work. Otherwise, consider some sort of studs to hold the concrete down, switching to composite deck, or adding another inch of concrete.

 

[r13]

Mathematically it can. Assume 22 gage metal deck, with 1.5" deep flute, and 145 pcf normal weight concrete, the roof weight per square foot is 34 psf. The factored lift load is 32 psf, which is less than the nominal weight available. However, I would suggest to make the overall slab thickness 4", so you can easily get design information from the metal deck supplier's catalog. Link

 

[jayrod12]

Also, when checking the roof uplift, are you including the interior pressure? if so, that doesn't apply to the concrete, just the deck and it's connection to the joists. The concrete itself only actually sees the wind suction on the exterior.

 

[phamENG]

Good insight, jayrod12 - I didn't think about that piece of it.