unbonded precompression ranges

[CTSeng]

I've been designing unbonded PT condo flat plate slabs with precompression ranges in the 200 to 250 psi ranges as recommended by several references.

Recently a project with large irregular spans (~40') has pushed required precompression to well over 500psi in some spans to get the stresses to work out. Are these published ranges just for economy or are there other reasons I should keep them down?

Thanks,

 

[JGrubb]

With greater precompression forces you'll certainly increase the likelihood of blow-outs and increase congestion of rebar/tendons. You might want to choose a concrete mix design with higher strength and lower viscosity.

 

[rapt]

As the precompression increases more attention needs to be given to the effects of restraint on slab shortening and the stresses induced by this.

Logical solutions are varied slab depths and short tendons in critical areas.