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RE: FNDT: Shearwall and slab foundation question

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Started using YOUR abbreviations again, eh?

IMHO, sounds like grade beam time to me. If this question came into my office, I would have a hard time justifying the (free) time to do a questionable analysis just to save the owner some bucks. I could always respond "sorry about the grade beam, it was required due to a plan check correction". Keep in mind, once you start distributing the forces a long distance away, you will need additional reinforcement (in the slab, etc.) anyway. I would question the capability of the slab/thickened edge to resist uplift forces requiring an HD8A (6k +/-).

My $1.50
Bill Allen

-----Original Message-----
From:	wish [SMTP:wish(--nospam--at)]
Sent:	Wednesday, February 04, 1998 1:06 PM
To:	seaoc(--nospam--at)
Subject:	FNDT: Shearwall and slab foundation question

 << File: ATT00001.html >> A recent plan check correction stated "For holddowns HD8A or above, please provide a gross stability calculation of the holddown and bearing pressure calculation under the shearwall footing."

If the wall is supported independently on a grade beam, I would have not problems with this. However, the walls are supported by either a continuous thickened edge around the slab and the slab itself which contributes resistance by nature of the tensile connection through the wire mesh. A wall in the center of the slab which rests upon a foundation monolithically poured should also be able to consider the effect of the slab connection to the grade-beam to resist sliding and uplift.

I would like some opinions on this issue. If anyone has done an analysis that they can share with me that takes the slab and friction between soil and slab into consideration for both resistance to uplift and protection from over-bearing soil pressures, I would be appreciative.

Finally, I do not mind increasing the foundation size as though it were independent of the slab, however, I would still question this in order to save the client some money.

Dennis Wish PE