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RE: Rigid Diaphragm

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4 inches thick sounds pretty darned thin.  Is there a joist system or
something along those lines?  What type of framing supports the 4 inch thick
slab, and if it is concrete (joists for example) how about accounting for
those in your calcs?

It also depends on the configuration of the slab.  What is the aspect ratio?

Depending on the configuration, you may want to :

1) Thicken the slab
2) Create a steel bracing system under the slab using rolled sections to
take the in plane shears to the shear walls

Or a combination of the two.

First place to start I guess would be with the question "on what analytical
basis is the conclusion that the slab is too flexible being based?"

Hope this helps.

T. Eric Gillham PE

-----Original Message-----
From: frp2000 [mailto:frp2000(--nospam--at)]
Sent: Saturday, March 10, 2001 8:31 AM
To: seaint(--nospam--at)
Subject: Rigid Diaphragm

I have a situation where an existing slab is 4" thick. Owners would like to
make it "more" rigid", to distribute seismic loads to new shear walls

Is this possible?? If so, how??

jim k