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Re: cracking of concrete in post-tension

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Gil Brock wrote:

. > The way the ACI code minimum reinforcement rules work for unbonded slabs
. > (especially 2 way slabs), it is very possible to have large areas of slab 
. > in tension and cracked and there will be no unprestressed reinforcement or
. > bonded reinforcement to limit the crack width. 

The ACI provisions for a two-way prestressed slab that permit the tendons to 
be banded in one direction means that you end up with a one-way slab spanning 
in the direction of the distributed tendons.  The only reason that this 
method "works" is because it was based on analysis using the equivalent frame 
method:  *ALL* of the loads are supported by an equivalent frame in one 
direction, AND, *ALL* of the loads are supported by an equivalent frame in 
the other direction.  The crack pattern in the tests that were conducted to 
justify banding tendons in one direction clearly show that the failure 
occurred as a one-way slab.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona