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Re: FNDT: Shearwall and slab foundation question

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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
> 
Not to attract flames...but, I do not believe the wire mesh has a
significant contribution beyond shrinkage control.  For purposes of
gross stability of the HD8, I would be reluctant to consider more than
the integrity of the grade beam about the anchor.  Can the beam resist
the moment induced by the tension developed?    A shear wall tied to a
grade beam can not rotate about its longitudinal axis (in my universe). 
I would argue that the bearing pressure below the grade beam is of
moderate concern save for vertical load path.  Rotation of the entire
beam is required for failure.  Ewood vs Econc.  No contest.

Paul Reilly PE