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RE: Rigid diaphragm with framed shear walls and concrete shear walls

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I believe there is a limitation about the thickness of concrete on floors supported by wood to 4" or less. If your average deck topping thickness is 4" or less average, you should be fine.

Mark E. Deardorff, SE
R & S Tavares Associates, Inc
9815 Carroll Canyon Road
Suite 206
San Diego, CA 92131
Phone: 858-444-3344
Phone: 209-863-8928



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From: Jeff Hedman [mailto:jeff_h(--nospam--at)]
Sent: Tuesday, August 21, 2007 9:56 AM
To: seaint(--nospam--at)
Subject: Re: Rigid diaphragm with framed shear walls and concrete shear walls


According to IBC 2305.1.5, wood members shall not be used to resist horizontal seismic forces contributed by masonry or concrete walls.  It doesn’t say anything about concrete filled decks, it specifically says walls.  If the concrete diaphragm is also a limitation please let me know where it is located so I can change the building design as I am currently not aware of this limitation.  The concrete walls on small portions of the bottom floor has affected my choice for the lateral system in an attempt to save the owner some money as he can get a pretty good discount on steel studs.  I understand that many times when you try to save someone money, it takes you down the wrong path and you end up changing the building design anyway.  But as far as my shear wall loads go, they are well within the range the unit shear loads divided by the safety factor in the AISI Standard for cold formed steel framing lateral design.   Of course this is in concert with the few concrete shear walls that have now been spaced symmetrically around the building on the bottom floor.  The concrete walls end up doing all of the work for the most part, which is why my steel shear walls are not being overloaded.  This structure steps in on every floor, like a ziggurat pyramid, which is why I decided to try to use the system I am using.  All discontinuous shear walls can be located on top of steel beams which transfer the uplift forces thorough the structure to the foundation.  All walls are bolted to the concrete floor and screwed into the bottom flange of the steel beam located above to keep the load path continuous.  However, because I am still learning, all criticism and input is welcome, smug or notJ


Jeff Hedman



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