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RE: Plated Truss Lateral Frame

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The lateral resistance from wood panels over wood framing is based on the behavior of nails being deformed by rigid panels rotating on a very flexible frame.  This system results in a very ductile and somewhat flexible system. 
 
It is my personal opinion (since we've never done the cyclic tests) that panels over a truss frame is NOT the same thing.  I would not anticipate that the underlying truss frame would have the inherent flexibility (and in this case ductility) as the code listed system.  This would likely effect R, Cd and Omega_O.
 
I don't have a suggestion on the correct R value (other than a very conservative R = 2 or so), but I don't think R = 6 is appropriate.
 
Just my $0.02 worth.
 
Tom
 

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Thomas D. Skaggs, Ph.D., P.E.
Senior Engineer
APA - The Engineered Wood Association
7011 S. 19th Street
Tacoma, WA 98466
ph: 253/565-6600
fx: 253/620-7235
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From: Jason W. Kilgore [mailto:jkilgore(--nospam--at)leok.com]
Sent: Friday, July 09, 2004 13:28
To: seaint(--nospam--at)seaint.org
Subject: Plated Truss Lateral Frame

Here’s a good question for a Friday afternoon:

 

I’ve got a client with a 4-story commercial building.  He wants to build it with exterior wood bearing walls (steel beams and columns on the interior), but he’s not giving me enough room for shear walls.  He wants to use a system he’s used before, which is a plated wood truss frame.  They are apparently much cheaper than Simpson shear walls.

 

The design consist of me putting the loads on the plans and elevations, the truss manufacturer designing the trusses and connections, (floor, roof, and frame), then me approving the shop drawings.

 

The question is, what seismic “R” value should I use?  While not designed as a traditional wood shear wall I am going to specify wood exterior sheathing, which would imply that R should be 6.

 

 

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Jason Kilgore

Leigh & O'Kane, LLC

Kansas City, Missouri