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RE: Hold Downs With No Plywood Ductility

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Totally agree.  I have directly supervised and witnessed literally hundreds of wood frame shear wall tests, and I've never seen load factors as high as stated below.  That's not to say there isn't something there, but the rumor looks fishy, and I'm not going to comment any more w/o seeing more information.

Tom


Thomas D. Skaggs, Ph.D., P.E.
Manager, Product Evaluation
APA
7011 S. 19th Street
Tacoma, WA 98466
253-620-7479 (office)
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tom.skaggs(--nospam--at)apawood.org
www.apawood.org



-----Original Message-----
From: Ehrlich, Gary [mailto:gehrlich(--nospam--at)nahb.com]
Sent: Friday, May 09, 2008 13:18
To: seaint(--nospam--at)seaint.org
Subject: RE: Hold Downs With No Plywood Ductility

It's almost impossible to comment without knowing a LOT more details about the testing. Really, one can't comment without reading a full report.

Buddy Showalter, Tom Skaggs, and I could likely fill your e-mail inboxes to overflowing with a discussion of boundary conditions, wall/panel configurations, and their effects on test results. 8-)

Gary

Gary J. Ehrlich, PE
Program Manager, Structural Codes & Standards
National Association of Home Builders (NAHB)
1201 15th Street, NW, Washington, DC 20005
ph: 202-266-8545  or 800-368-5242 x8545
fax: 202-266-8369
gehrlich(--nospam--at)nahb.com

-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint2(--nospam--at)truesdellengineering.com]
Sent: Friday, May 09, 2008 3:12 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Hold Downs With No Plywood Ductility

How long had the assembly been in place before the testing was done. 2
weeks or 20 years?  Not that this is definitely the case, but it would
seem that the frictional interface between the plywood and the studs
would add significantly to the stiffness of the assembly until the studs
and sheathing reduced in size due to moisture-loss related shrinkage.
Maybe they should test some assemblies after running them a few months
in a kiln?

Of course, that would require a 2-5 year waiting period from the time of
construction to time of safe occupancy. That might not sit well with the
NAHB. ;-)

Jordan



David Merrick, SE wrote:
> Just heard a rumor out of San Jose State University.
>
> The ASD Hold Down capacity was 30% higher than the Plywood shear wall
> and yet the Hold Down failed by ripping the screws out of the stud.
> The plywood showed no obvious signs of distortion relative to the
> studs. So the wall must have lifted off the base still square in shape.
>
> Ultimate load was 4.7 times the sheathing design capacity and 3.5
> times the holdown capacity.
>
> Something is seriously wrong. This is the second event I have heard of
> where the HD failed before the plywood.
>
> Ultimate strength of plywood needs to be reconsidered to not first
> fail the HD, Resulting in little plywood ductility. You know, the
> stuff that allows the very high rho of 6.5
>
> David Merrick, SE
>
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