What is max diaphragm size / shearline spacing - Wood light frame SDC D

[Jrswett]

I swear I saw this in the code somewhere that the there was a limit to the maximum distance between shearlines or a maximum diaphragm dimension, maybe specifically unblocked diaphragms. This is for SDC D structures in California. I think it was 50 feet. I should have book marked that or noted it. I think it was in the ASCE 7 when I was looking at redundancy maybe? Anyone know if there is a code specified the limit on this? I tried to find it again in the ASCE 7 or the AWC SDPWS and couldn't spot it. Thanks

 

[jittles]

SPDWS has some aspect ratio limitations

 

[Jrswett]

Yeah there are the aspect ratio limits for the various diaphragm types, it wasn't that. It might have been in the CBC in the structural section for Wood or something similar. There was some kind of upper limit on wood frame diaphragm dimensions. It may have been for the distance between shearlines. I tend to max out at about 50 ft anyways. I saw it somewhere.

 

[jittles]

If you find it, make sure to follow up here. I don't know of a hard limit, just the aspect ratio limits, limits on open fronts and cantilevers. Perhaps in the prescriptive section of the code or the IRC side of things, neither of which I venture into.

There is probably a practical limit related to diaphragm shear capacity...

 

[Jrswett]

Will do. It was a specific kind of note like.. flexible unblocked wood diaphragms in Seismic Design Category D shall not exceed 50 feet in any dimension. Something like that. It may have been somewhere else that essentially specified this limitation for typical design. Like the redundancy factor... that might be where it is. Maybe the redundancy factor shall be 1.3 etc etc limitation on diaphragm size. Which would make sense, I think it might be in redundancy somewhere.

 

[DoubleStud]

It is not controlled by the chord force on your top plate? I never see any limit. But then again I don't do California.

 

[Jrswett]

There isn't really a functional limit. Eventually you would start having to use more steel is all. But I think there was a limit for the redundancy factor maybe. Which again just hits the functional limit by adding a 1.3 multiplier to the base shear.

 

[bones206]

Maybe you were thinking of IBC 1613.3.5.1(4):

https://codes.iccsafe.org/s/IBC2015P4/chapter-16-structural-design/IBC2015P4-Ch16-Sec1613.3.5.1