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Re: FNDT: Shearwall and slab foundation question

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For HD8 holdown, the allowable force is almost 8 kips, that means you
would need , say a spread footing of 5' x 5' x 24" deep, if your actual
uplift force in that wall corner is 8 kips. I don't think that
conventional thickened edge even connected to the slab-on-grade with WWF
will work. First, you don't have enough slab weight to counteract the
uplift force. Second, the WWF quite often end up at the bottom of the
slab without proper concrete cover and will rust and therefore
ineffective.

Tom Chiu, SE
Thomas Engineering 

> wish wrote:
> 
> 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
>