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# Re: Concrete in uplift

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• To: seaint(--nospam--at)seaint.org
• Subject: Re: Concrete in uplift
• From: Chris Tse <cyltse(--nospam--at)pacbell.net>
• Date: Fri, 19 Oct 2001 00:15:25 -0700

You are concerned about how much a concrete slab area will take to resist
that
1500 lb. uplift load!
Assume that 4" thick is reliable enough, you need approx. 6.5 feet diameter
of
slab to resist it. Next you check the concrete slab capacity by rupture
strength
of concrete, assuming some low value to it, such as f'c=2000.0 . The
diameter may be reduced when considering 1/3 increase against uplift caused
by wind or earthquake. You can pick out moment coefficients to derive
moments at the 'virtual'
fixed edge of the slab from any concrete text book or if you like, go
through yield line theory to obtain those moments.
Not sure if you have any access to test existing concrete strength or you
want
to guess (not recommended) something and are willing to take uneccessary
responsibility. If nothing seems to fly, your first plan already answers for
you.

Chris Tse,
Sunnyvale, CA

Drew Morris wrote:

> We were having a discussion at work on anchorage to a concrete slab.
> The uplift force is 1500 # and the slab is at least 4" thick.  We have
> no information on the slab thickness or reinforcing (if present).  What
> tributary area can I use for resisting the uplift (if any at all)?  I'm
> planning on using a helical screw anchor or saw cut the slab and use the
> "blob of concrete as dead load" concept.
>
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