PT Diaphragm Shear Strength for Seismic

[InDepth]

Does anyone know where to find papers or design guides that explains and provides examples of how PT increases the shear strength of slabs under seismic loading when designing diaphragms?

1) If you have PT in one direction only, can you increase the diaphragm shear strength only in the orthogonal direction or both?
2) Can Temp PT be used to increase diaphragm shear capacity?
3) Can the ACI-318 shear capacity for presstressed concrete (Chpt 11) be used for diaphragm capacity?

There are papers on how PT affects collectors, but haven't seen any on how PT affects diaphragm shear capacity.

 

[ishvaaag]

In columns the presence of axial force is thought to increase the resistance just because it contributes to difficult the formation of cracking.This, and seeing that in the end PT contributes to keep the whole section in compression would mean your section would have increased shear strength ... because of the standing compression and compressive state along PT strands. This compressive force modifies the strut and tie scheme (angle) by which we determine reinforcement and might innfluence negatively the compressive strut capacity limit (probably at stresses forbidden by the code). In any case I wouldn't count on any gain of shear strength in this direction without looking a chart on how along the beam compressive stresses affect the design. You can give a look on it in

Prestressed Concrete Structures
Michael P. Collins
Denis Mitchell
Response Publications 1997

I think they still have a freely downloadable program calles RESPONSE (it was then free, I don't know now) that may help you to decide.