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drywall, seismic

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Who nails drywall? Wouldn't this leave a lot of hammer dings to cover with
compound? I thought it was only screwed.

I have used double sheathed interior drywall shear walls only one time, for
a bearing wall on an interior wall where the contractor and the truss fab
mistakenly assumed the interior wall was bearing when it was not intended to
be bearing. I had to redesign the interior wall for bearing and shear, due
to wind (I am in FL, no seismic). I would avoid it at all costs for reasons
stated previously, plus my own doubts of gyp board's capacity in shear. But
it was pretty much unavoidable for architectural reasons, and seeing as the
building was mostly built when the decision was made.

These discussions about California building codes and seismic design are way
over my head, as I am down here in FL and the key word is uplift, followed
by shear. I have done very limited design in lower NE seismic regions. What
I have picked up on is the discussion of flexible versus rigid horizontal
diaphragm design. Now have I missed out on something? When have plywood and
metal deck roofs and floors been considered rigid? Is this a seismic or Cal
thing? Pardon my ignorance, but this has me worried. The Steel Deck
Institute and the NDS say nothing about this. So if you do consider plywood
diaphragms as rigid, and you have a wood frame wall, then do you have to
calculate relative stiffness values like in masonry to distribute the shear?
Include effects of rotational shear?

Follow up question on diaphragms. What is the treatment of a FLEXIBLE
diaphragm supported on three sides by shear walls, your average rectangular
plan? From everything we have read in SDI and elsewhere, you do NOT consider
rotational shear (as a flex diaphragm cannot transmit rotational shear), but
you just treat the lone wall and diaphragm as cantilevered, so the lone wall
will have shear = V, not V/2. I know this may seem trivial, but I have not
found one source that spells this out. This is what I have assumed based on
SDI and other sources. I am sure you can cantilever flex diaph., but am I
missing anything? Oh, I know you have to design the border/chord members for
T/C.

Thanks in advance!

Andrew Kester, EI
Longwood, FL



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