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RE: CMU Wall Supported by Plywood Sheathed Roof Diaphragm and She arwalls

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Section 2315.2 of UBC addresses this issues. However, this is probably one
of the most overlooked sections of the code when it comes to design or plan
check. I can tell you that you may even find many buildings using masonry
area separation walls up to 4 stories relying entirely of wood shear walls
for lateral resistance. So it doesn't surprise me that the contractor is
claiming he has seen it before. But, if you don't meet the criteria in the
code, it is definitely not compliant. However, if you can convince yourself
and the code authority that the deflections are acceptable, you may want to
try applying for alternate method & material application per section
104.2.8.

Ben Yousefi, SE
San Jose, CA

	-----Original Message-----
	From:	Monty Hart [SMTP:montyh(--nospam--at)gci.net]
	Sent:	Wednesday, February 21, 2001 10:48 PM
	To:	seaint(--nospam--at)seaint.org
	Subject:	CMU Wall Supported by Plywood Sheathed Roof
Diaphragm and Shearwalls

	I'm working on a proposed one story 50' x 80'  warehouse in seismic
zone
	4.  Exterior walls are 8" metal studs sheathed with plywood and are
23'
	high to the roof deck.  Roof is open web wood joists with a plywood
roof
	diaphragm.  One of the 80' long walls is adjacent to (with a 4" gap)
the
	CMU wall of an existing building.   The existing building and the
new
	building are on different lots, so the buildings can not be
connected.
	The new wall needs to be a firewall, and must be finished on the
	interior and exterior sides, with only a 4" clearance for installing
the
	exterior sheathing.  I would prefer to try sheathing a stud wall
flat on
	the slab and then tilting it up, or installing temporary bracing,
sheath
	the studs in a vertical position about 4 ft from the existing wall
and
	then slide the new wall into place.   Neither I nor the contractor
has
	seen a metal stud wall erected in this way, so the contractor is
	insisting on a single 80' long, 23' high CMU wall.  I am extremely
	reluctant to support such a wall with a plywood sheathed roof
diaphragm
	supported by plywood sheathed shear walls because of the potential
for
	excessive deflection at the top of the CMU wall, which may result in
	cracking of the concrete block.    I have not yet calced the
deflection,
	but I assume it would be in the 1" to 2" range at the top of the CMU
	wall.

	The contractor says he has seen other buildings constructed with a
	single CMU fire wall.  Unfortunately, I can not find any section of
the
	'97 ICBO Code that would prevent it or even address the allowable
	out-of-plane deflection for a CMU wall.   I would appreciate any
	comments regarding applicable code requirements or experience with
	failures of similarly constructed buildings.  I would also like any
	recommendations about installing plywood sheathing on a metal stud
wall
	with only 4" of clearance.

	Thanks in advance for any comments,

	Monty Hart
	Associated Design Consultants, Inc.
	Anchorage, Alaska