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RE: Elevated post-tensioned slab cracks

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Oshin,

Assuming there are indeed no tendons nor rebar between the banded tendons
(unreinforced middle strip) I would do a slab analysis in the banded
direction assuming a column strip width and assign 100% of the moments to
this column strip with all of the banded PT - basically ignore the CRACKED
middle strip that has no reinforcing. Check ultimate flexure, stresses (it
will be cracked) and cracked deflections. For stress check, do not forget
that the P/A will be the average over the entire panel width, not just the
column strip/band width. For stress check, you will need to make a decision
on what is an appropriate level of precompression remaining in the slab
knowing that restraint/cracking has occurred - maybe that is zero!

It is sort of a moot point to worry about stresses when you know it is
cracked, but at least you can compare the theoretically (some prefer to call
then hypothetically!) calculated values to code-specified maximums.

Mark Geoghegan
Honolulu, HI





             > -----Original Message-----
             > From: Oshin Tosounian [mailto:oshin(--nospam--at)kcematrix.com]
             > Sent: Thursday, January 09, 2003 1:40 PM
             > To: 'seaint(--nospam--at)seaint.org'
             > Subject: RE: Elevated post-tensioned slab cracks
             >
             >
             > Thank you, Roger.
             >
             > So, what do you suggest?
             >
             > Oshin Tosounian, S.E.
             > Los Angeles, CA
             >
             > > -----Original Message-----
             > > From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
             > > Sent: Thursday, January 09, 2003 6:10 AM
             > > To: Oshin Tosounian
             > > Subject: Elevated post-tensioned slab cracks
             > >
             > >
             > > Oshin,
             > >
             > > I have contended for years that post-tensioned
             > concrete slabs
             > > with banded
             > > tendons in one direction is really a one-way slab,
             > spanning
             > > in the direction
             > > of the distributed tendons with the banded tendons
             > creating an
             > > over-compressed in-slab beam.
             > >
             > > It is absurd to believe that banding tendons is
             > the same as
             > > distributing
             > > the tendons.
             > >
             > > If you look at the research that supposedly shows that
             > > two-way action is not
             > > dependent on distribution of tendons, you will see
             > that the
             > > slab fails as a
             > > one-way slab, with cracks first appearing parallel to the
             > > distributed tendons.
             > >
             > > A. Roger Turk, P.E.(Structural)
             > > Tucson, Arizona
             > >
             >
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