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Re: Collector elements and precpmpression force

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Samir,
Precompression from unbonded tendons may be used to resist seismic forces in
diaphragms, refer to UBC 1921.6.12.

We typically limit the contribution of the precompression by balancing this
against the DL and reduced LL requirement in combination with seismic.  For
the Em level forces this would be equivalent to checking the slab span for
the 1612.4 combinations, or specifically 1.2D + .5L + Em as opposed to the
typical governing gravity load case 1.4D + 1.7L.  The difference in the DL
and LL demand would be the reserve capacity available to contribute to Em.

A similar methodology is used to calculate the contribution of the
precompression to the chord forces.


Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
----- Original Message -----
From: "Samir Ghosn" <sghosn(--nospam--at)harris-assoc.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, December 17, 2002 3:25 PM
Subject: Collector elements and precpmpression force


> Another question to the experts:
> Thanks for all those whe participated earlier, Gerard, Ben, Jan , others,
> Now I have a new question, Can a precompression force in a post tension
> slab be utilized as a way to reduce the collector element force in a sense
> of reducing the required mild reinforcing steel criteria.  Is there a
limit
> to the reduction allowed if it is allowed at all.  Can any body direct me
a
> code sepcific section that permits precompression force utililization?
How
> do others deal with this?
> Thanks for your help in advance.
> Samir Ghson, PE
> harris & Associates
> (800) 827-4901 xt 360
>
>
>
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