Wood Diaphragm with Rafters/Trusses Spaced at >24" o.c.

[wel-eng.]

Hi All,

A discussion was recently brought up within my company regarding wood panel diaphragm in-plane shear capacity for support framing spaced at > 24" o.c.. AWC and the SDPWS doesn't have much information on how the capacity is adjusted to account for framing at a spacing that is atypical. Regarding field nailing, Section 4.2.7.1.1 states, "maximum nail spacing shall be 6" o.c. when support spacing of 48" o.c. is specified and 12" o.c. for closer support spacing". So what if you have framing spaced at 32" o.c.? Or 36" o.c. w/4'x9' panels? It doesn't specify in the commentary or in the standard if there is a capacity reduction, but at the same time only has tabulated values for framing up to 24" o.c., hence my confusion.

I have read from a few sources that having framing spacing > 24" o.c. can increase the deflections of unblocked diaphragms if the aspect ratios are close to 3:1, but that doesn't help quantify the shear capacity.

It should be noted that I am not much interested in discussing out-of-plane loads. That is a bit more clear in the SDPWS.

Any sources or links to more info on this would be greatly appreciated. There is surprisingly little out there on this.

Thanks!

 

[Celt83]

The couple times I've reached out to AWC on diaphragm or shear wall questions it essentially boiled down to the capacity tables are all based on load tested assemblies, so there is no recommended analytical procedure to determine allowable shear capacity in wood diaphragms and shear walls.

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