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RE: 2-in conc slab = rigid diaph?

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David,

Especially when you consider the 2" slab in combination with the waffle
slab beam elements.

But, ultimately remember that a "rigid" diaphragm is really an assessment
that determines that the deflection of the diaphragm in plane is less
relative than the lateral deflection/drift of the vertical lateral system
in such a matter that the horizonatal plane rotates as a "rigid" body more
than it deforms.  So, it is not just a function of what your diaphragm is
but also a function of what your vertical lateral system is.

Regards,

Scott
Adrian, MI


On Thu, 14 Dec 2006, David Topete wrote:

> Thanks, Will, for the response.  In the situation I have, the span between
> shearwalls in either direction is not too bad.  I can reasonably assume the
> waffle grid is stiff enough to be considered "rigid."
>
> David Topete, SE
>
>
>
>   _____
>
> From: Will Haynes [mailto:gtg740p(--nospam--at)gmail.com]
> Sent: Thursday, December 14, 2006 4:53 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: 2-in conc slab = rigid diaph?
>
>
>
> ACI 2002 section 21.9.4 gives 2" as the minimum required for a diaphragm. I
> am not sure if it can automatically be considered rigid.
>
>
>
>
>
> Will Haynes
>
>
>
> On 12/14/06, David Topete <dtopete(--nospam--at)gfdseng.com> wrote:
>
> I am doing a peer review.  The structures are masonry, single story.  Some
> have pitched roofs.  Others are flat roofs.  The flat roofs are made of a
> c.i.p. concrete waffle grid, 8" joists, 2 feet c.c. each way in a 12" deep
> system.  The slab itself is only 2-in thick with 6x6 wire mesh
> reinforcement.  Can I assume the slab itself as essentially zero, and depend
> on the grid for diaphragm action to transfer loads to the LFRS?  If anyone
> has a quick answer, it'd be most appreciated.
>
>
>
> David A. Topete, SE
>
> Structural Engineer
>
>
>
> GFDS Engineers
>
> 543 Howard St., First Floor
>
> San Francisco, CA 94105
>
> v : (415) 512-1301 x21
>
> f : (415) 512-1302
>
> dtopete(--nospam--at)gfdseng.com
>
> http://www.gfdseng.com <http://www.gfdseng.com/>
>
>
>
>
>
>

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