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Re: Post tensioned concrete floors

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1) If the tensile stress exceeds 2sqrt(f'c) in positive moment areas, the total tensile force must be carried by bonded reinforcement..It's not hard to keep that tensile stress low enough to eliminate the bonded reinforcement in residential applications, given a span of 18' or less.
2) The drape profile is important for determining the balanced load and the compression induced in the concrete. The net load then becomes the total load minus the balanced load,  with the Fe/A  (tendon stress/area) staying around the 200 psi range or less.

Walter DeVore

Anantha Narayan C.K. wrote:
I am working on designing post tensioned floors for mixed use and residential buildings. I am relatively new to this and I had a few questions.
1) Is it really possible to decrease the bottom reinforcement by increasing the prestress in the strands or is there a limit to the reduction. Are there any design tips for that ? Say if you attain a certain P/A, you can reach a point of minimum bottom reinforcement
2) Does adding more tendons to reduce bottom reinforcement cause additional negative reinforcement? Is it essentially a give and take situation.
Thank you

Graduate Student
Structural Engineering and Materials (SEM)
Virginia Tech,  VA - 24061

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