Analyzing Existing Post Tension Beam and Slab
Analyzing Existing Post Tension Beam and Slab
(OP)
I am trying to analyze the capacity of an existing post tensioned one way slab and beams. I have the existing structural drawings but not the post tensioned shop drawings. The structural drawings specify a required tension strength per foot for the strands (call this value Fp). Should this force be used when solving for the moment capacity as opposed to finding the strand stress using approximate methods or strain compatibility to find fp (the strand stress then the strand force would be Fp=fp*Ap)?
Therefore using Fp the moment capacity would be:
a=Fp+Asfy/(0.85*f'c*b)
Mn=Fp*(dp-a/2)+Asfy*(dt-a/2)
Where As,fy and dt all relate to the nonstressed tension steel.
Thanks.
Therefore using Fp the moment capacity would be:
a=Fp+Asfy/(0.85*f'c*b)
Mn=Fp*(dp-a/2)+Asfy*(dt-a/2)
Where As,fy and dt all relate to the nonstressed tension steel.
Thanks.
EIT






RE: Analyzing Existing Post Tension Beam and Slab
RE: Analyzing Existing Post Tension Beam and Slab
The drawings specify the type of strand (7 wire ASTM 416)and list the ultimate, final, transfer and over stresses. However I'm not sure how to get from a post tension force (given on the drawings) to an effective stress if I don't know how many or what size strands were used (I'm assuming they are half inch but this still does not help). I'm I missing something?
Also another side question - for unbonded tendons would the stress/strain be constant when checking strain compatibly.
EIT
RE: Analyzing Existing Post Tension Beam and Slab
RE: Analyzing Existing Post Tension Beam and Slab
As hokie mentioned, you'll also need the mild-steel, but that should also be on the drawings. I haven't done a ton of P/T jobs, but it my limited experience, it's usually the service level stress that controls the design, not the ultimate moment strength.
RE: Analyzing Existing Post Tension Beam and Slab
Lion - I will have to look into the serviceability checks.
Thanks
EIT
RE: Analyzing Existing Post Tension Beam and Slab
EIT