Wood Diaphragm Gravity Design 4

[reverbz]

Hey Guys,

Just wondering if you actually check your wood diaphragm for gravity loads(outside of special cases with extreme loads) and how you do it? I've looked around and it seems like everything assumes lateral controls the design. Is span rating just always controlled by lateral?

Thank you!

 

[EngDM]

In the Canadian Wood Design Manual there are some crude span tables for what thickness is required for a specified live load. I've typically back calculated the moment resistance of the panel based on the tablated span and design load, and then compared it to the moment (assuming simply supported) generated by my larger load and my span. High snow loads can govern the design over shear.

 

[JoshPlumSE]

I've never checked a diaphragm for gravity loading..... Only wind or seismic.

That being said, if I had an internal mezzanine in a non-seismic area, then I would design it for some nominal "notional" loads.... even if there isn't a specific code requirement. Something like a 0.2% notional load like we see in AISC's direct analysis method. Maybe more if I have design criteria suggesting something more than 1/500 out of plumb.... Say a Forklift accident or something along those lines.

 

[lexpatrie]

Huh?

 

[Celt83]

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[jayrod12]

Canadian Wood Design Manual

CSA O86 has the formulas needed to design for plywood in bending. And they honestly aren't that onerous.

 

[driftLimiter]

Seems like there is a terminology problem that may be confusing you.

I've looked around and it seems like everything assumes lateral controls the design

Probably because when you use the term 'diaphragm' it implies that the loads are in the plane of the element.

Pretty much all diaphragms in buildings also resist loads normal to their plane. (dead loads, live loads, snow loads, etc). We would always say that the roof sheathing resists these loads. But generally were not calling it a diaphragm in this case.

There may be a rare case where the roof diaphragm resists gravity loads applied in it's plane. And frankly I'm not sure if this is what you are asking about or rather just loads applied normal to the diaphragm. I'm also not sure if your even talking about wood. But regardless of material the decking needs to resist all applied loading, if it has normal loading then it needs to be checked for flexure, shear, and deflection, and if it has in plane loads then it needs to be checked for shear, and chord forces.