POST TENSIONED CIP LONG SPAN CONSTRUCTION
POST TENSIONED CIP LONG SPAN CONSTRUCTION
(OP)
Post-tension design experts, when you model your structure with your software of choice, do you somehow represent the dead load balancing effects of the post tensioning in your model? When you have long span (60 ft) beams with substantial dead loads, parking garages for instance, you get large column moments and at the top level minimal axial loads so your column reinforcing could get rather large. Or do you just model it as regular reinforced, and design for full moments?
Comments/recommendations are greatly appreciated.
Comments/recommendations are greatly appreciated.






RE: POST TENSIONED CIP LONG SPAN CONSTRUCTION
A clear conscience is usually the sign of a bad memory
RE: POST TENSIONED CIP LONG SPAN CONSTRUCTION
You seem to be implying that the column moments will be larger with the prestress!
The prestress effects will normally reduce the column moments. The effects are real so why not allow for them.
If you add in shortening effects, yes, the column moments from shortening in a prestressed structure will be larger than for an RC structure, but normally only by about 10% (depending on climate and environment) as shrinkage and temperature shortening are the same for both structures, and, as the amount of prestress is normally fairly low in building structures, creep shortening could actually be higher in the RC building. So the extra is for axial P/A. The rest occurs in RC structures and is often ignored!
RE: POST TENSIONED CIP LONG SPAN CONSTRUCTION
RE: POST TENSIONED CIP LONG SPAN CONSTRUCTION
You have lost me in the mist of the night, can you try another explanation angle.
A clear conscience is usually the sign of a bad memory
RE: POST TENSIONED CIP LONG SPAN CONSTRUCTION
When I model transfer girders in the lateral analysis program, I include an upward force (balancing force) in the model. The PCI Manual has a chart that gives you the equivalent line load that can be applied to the beam in order to simulate the effects of post-tensioning.
As Rapt said, these effects are real and you will end up with a more realistic column moment rather than something obnoxious in the case of transfer girders.
See attached.
RE: POST TENSIONED CIP LONG SPAN CONSTRUCTION
If you are interested in the ultimate load the structure can carry, you combine the positive and negative moment resistance and compare it to the simple span moment.
BA
RE: POST TENSIONED CIP LONG SPAN CONSTRUCTION
When I was a young engineer in australia I designed a few buildings with reinforced columns (by us) and PT floors that were designed by others. I took what I believed to be the conservative route and designed the columns as if the whole building was reinforced concrete.
RE: POST TENSIONED CIP LONG SPAN CONSTRUCTION