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RE: Crack in Wall Connected to Post-tensioned Slab

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Whenever you post-tension a slab, it compresses.  If the slab is not free to
move differentially to a parallel wall, the slab or wall will crack.  I have
even seen slabs crack on well-detailed slab to wall slip connections.  It is
ugly and expensive to repair (epoxy injection at about $5 per foot), but it
is repairable.  I would wait as long as possible.  The slab shrinkage will
also contribute to the cracking.

To avoid this problem most designers require a pour strip.  The tie to the
parallel wall should be made as late as possible to allow the slab to shrink
and compress as much as possible.  If the structure is given to thermal
cycling (like in the parking garage), the cracking will be forever active.

Regards,
Harold O. Sprague

> -----Original Message-----
> From:	Shahrouri Issam [SMTP:ishahrouri(--nospam--at)lagunabeachcity.net]
> Sent:	Monday, July 02, 2001 10:17 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Crack in Wall Connected to Post-tensioned Slab
> 
> The project is a 5 story hotel in Laguna Beach, under construction. As the
> tendons were being tensioned in the slab, cracks started appearing in some
> of the supporting walls. The direction of the tensioning was parallel to
> the
> wall. The cracks are diagonal starting at the point where the
> post-tensioning begins downs to the ground. The width of the crack varies
> from about 1/8 inch at the top down to almost nothing at the ground. The
> crack occurs on both sides of the wall. The walls are 8 inches thick and
> designed to act as shear walls as well.
> 
> I would appreciate any comments from a similar experience.
> 
> 
> Sincerely,
> 
> 
> Issam Shahrouri, PE, CBO
> Senior Plan Check Engineer
> City of Laguna Beach
> 
> 
> ************************************************************************
> * Tracking #: 79B2D2F5B38D08439BE589C4D6D41990E2FD5B0A
> *
> ************************************************************************
> 

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