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Re: Shear wall w/ plywood on both sides

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In a message dated 1/23/99 3:37:14 AM EST, suresh(--nospam--at)ynn.com writes:

<< I would appreciate your comments on the following --
 When one of the several shear walls in a given line is provided with
 plywood on both sides, I have seen that some people consider the double
 sided shear wall equivalent to 2 times the actual length of the wall
 while calculating unit shear along that line.[i.e. v=V/(sum of length of
 single sided wall + 2*sum of double sided wall].  I feel little bit
 uneasy in buying this method of calculating unit shears in wood shear
 walls. Anybody has experience with this kind of situation? Thanks.
 
 Suresh
 Berkeley, Calif >>


If I understand the problem correctly (as an example:  a 4 foot wall w/
plywood one side, a 8 foot wall  w/ plywood both sides, and a 6 foot wall w/
plywood one side all along the same wall line), this single line of shear
walls will resist a total load, but not necessarily in the proportions most
likely assummed (example: assuming average plywood shear is 300#/ft, therefore
average distribution would be 4 foot wall: 300#.ft, 8 foot wall: 2x 300# /ft,
6 foot wall: 300#/ft.) .  The plywood wall with plywood both sides in your
case will most likely be stiffer than the walls with plywood on one side only
depending upon actual wall lengths, gravity loads, holdown sizes, nail size
and spacing on each wall, etc.  

You can calculate the plywood shear wall deflection for these walls to see how
much load they actually take.    All walls must have the same deflection since
they are in the same line and tied together by the diaphragm.  If you do the
calculation, then you can have some walls with plywood both sides, and other
walls with plywood one side along the same wall line.  From what I understand,
more building departments in the very near future are going to be requiring
wood shear wall deflection calculations be included in the submitted calc's
for plan check.

I think the more common design practice would be to sheath either one side or
both sides for all the shear walls along a given single wall line, using the
same nail spacing for all plywood sheathing along this wall line.    

Mike Cochran