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Re: Precast Double Tees Diaphragm

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Michael Valley wrote:
 
> Section 1921.6.12 of the 1997 UBC (item 1): "Thickness shall not be
> less than 2 inches (51 mm)."

This is true, however the previous section 1921.6.11 reads:

"A cast-in-place topping on a precast floor system MAY serve as the
diaphragm, provided the cast-in-place topping acting alone is
proportioned and detailed to resist the design forces"

This section seams to hint that the top flange can be designed to carry
the diaphragm forces.  I agree that that the thickness is zero at the
joints.  This is the discrepancy I have been trying to work out. 
Secondly as much as I would love to use ACI 318-99 and FEMA, they have
not been adopted by the UBC and my client is requesting UBC guidelines.
I am only using FEMA to point me the right direction.  Are there any
other place that may prohibit the use of the flanges from double tee's?

Thank you Mr. Valley, I sincerely appreciate your help.

Respectfully,
Jake Watson, E.I.T.
Salt Lake City, UT

P.S. Is California letting these styles of structures be built without a
topping slab?