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Re: CMU Wall Supported by Plywood Sheathed Roof Diaphragm and Shearwalls

[Subject Prev][Subject Next][Thread Prev][Thread Next] Thanks for the reply........

dcarroll wrote:

WHY DON'T you have a X-braced vertical lateral system btwn cols just inside
the wall(btwn columns which I assume you will have and not mentioned to this
point?
There are no columns, just bearing walls.  The roof joists span 50'.
 I can't imagine that a 1" defl would hurt a reinforced masonry cmu
wall (and yes, I agree that a cmu wall would be better than a wood sheathed
wall in this area,
You're probably right.  97 UBC Section 2315.2 (which doesn't apply because this
is not over 1 story) limits deflection to 0.005 times story height (1.38") but also limits
story height to 12' instead of 23'.  But, if the deflection calcs out at 6", I don't find a
code section that would limit the deflection.
 Provided that you can manage the FOUNDATION proximity
problem.
Tricky but done.
For that matter,  you may need to study the aforementioned column
fdns Quite carefully as well!!
A good reason for not having columns.
 
On a side note I presume that you are not surcharging the existing bldg fdn
or interfering with existing underground utilities paralleling the same ftg.
Correct.  Both foundations are at the same depth.
 
As for wood clad shear walls------2 points I offer:
               Have you thought about the large tie down force(resistance)
reqd ; usually                             accomodated via Simpson anchors and the associated
fdn space (mass) reqts?
Not a problem.  The except for two doors, there are no openings.  So, the shear walls
are very long (50' and 80').
               Have you thought about "possibly" using a special Simpson
Strong Wall ,, if they             will  work with you in designing such a special?
I don't think they make one that is 23' high  ;0)
 

-----Original Message-----
From: Monty Hart [mailto:montyh(--nospam--at)gci.net]
Sent: Thursday, February 22, 2001 1:48 AM
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