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FW: doubled plywood sheathing on one side of shear wall to increa se capacity?

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Hope you don't mind Tom.

-----Original Message-----
From: Tom Skaggs [mailto:tom.skaggs(--nospam--at)apawood.org]
Sent: Wednesday, September 19, 2001 7:15 AM
To: 'HaanSM(--nospam--at)ci.anchorage.ak.us'
Cc: John Rose (E-mail); Help
Subject: RE: doubled plywood sheathing on one side of shear wall to
increa se capacity?


Mr. Haan,
John Rose, a former APA engineer, forwarded your question to me.  Below is
the "standard answer" from our help-desk.

### standard response ###

"Test results and a design analysis method for diaphragms sheathed in the
high shear areas with two layers of plywood on one side are provided in APA
Research Report 138, Plywood Diaphragms, (Diaphragm No. 2).

Section 2315.3.3 and 2319.3 of the 1997 Uniform Building Code provide for
wood structural panel wall sheathing on both sides of shear walls and
permits the calculation of diaphragm values "...by principles of mechanics
without limitation by using values of nail strength and wood structural
panel shear values..."  This section refers to "Horizontal and vertical
diaphragms..."

Even though two layer shear walls aren't directly addressed in the UBC,
there is no technical reason to prohibit their use provided that the
calculated design capacities can take the calculated loads and a load path
is provided. The calculated design capacities could be developed using the
principles established in the high shear load diaphragm noted above.  The
capacity of the wall hold downs should be given careful consideration, their
ability to resist overturning may be the limiting factor."

### end standard response ###

To my knowledge, this particular system has never been tested either
monotonically (static) or cyclically.  I've discussed this issue with
several of the APA Engineers, and if:

1.) minimum fastener penetration into the framing is met
2.) panel vertical edges are staggered to help minimize lumber splitting
3.) consideration is given to top and bottom plate nailing
4.) overturning, including hold down and bottom plate crushing is studied

Then we see no reason why this system could not be used similar to the
double sided shear wall or a double sheathed diaphragm (as discussed in APA
Report 138).

I would also like to state John Rose's suggestion.  He said that he used to
suggest using 50% of the shear capacity of the top layer as additional
capacity.  It would appear, that this approach would be a conservative
alternative.  However, if care is taken in nailing the top layer, this
approach might be too conservative.

Hope this helps,
Tom
-----------------------------------------------------------------------
Thomas D. Skaggs, Ph.D., P.E.
Senior Engineer
APA - The Engineered Wood Association
P.O. Box 11700
Tacoma, WA 98411-0700
ph: 253/565-6600
fx: 253/565-7265
-----------------------------------------------------------------------


> -----Original Message-----
> From: Haan, Scott M. [mailto:HaanSM(--nospam--at)ci.anchorage.ak.us]
> Sent: Tuesday, September 18, 2001 9:17
> To: Seaint list (E-mail)
> Subject: doubled plywood sheathing on one side of shear wall 
> to increase
> c apacity?
> 
> 
> 1997 UBC 2319.3 says "Where wood structural panel is applied 
> to both faces
> of a shear wall ..., allowable shear for the wall may be 
> taken as twice  the
> tabulated shear for one side, except that where the shear 
> capacities are not
> equal, the allowable shear shall be either the shear for the 
> side with the
> higher capacity or twice the shear of the side with the lower 
> capacity,
> whichever is greater."
> 
> I have seen several designers try to increase the capacity of 
> a wall by
> applying two layers of sheathing on one side of the wall. 
> 
> Is doubling the sheathing on one side of a wood structural 
> panel shearwall
> an acceptable way of increasing the capacity? Has there ever been any
> testing for this assembly? How come the code does not mention it?
> 
> 
> Thanks,
> 
> Scott M Haan P.E.
> Plan Review Engineer
> Building Safety Division 
> Development Services Department
> Municipality of Anchorage
> http://www.muni.org/building
> phone:907-343-8183  
> fax:907-249-7399
> mailto:haansm(--nospam--at)ci.anchorage.ak.us
> 
> 
> 
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