Reducing the sweep of a prestressed box beam.
Reducing the sweep of a prestressed box beam.
(OP)
A prestressed beam on one of my projects has a sweep of 1.5 inches which is more than the 1 inch tolerance. The prestressed beam fabricator is planning on reducing the sweep by post tensioning the beam. Has anyone used post tensioning to reduce sweep in prestressed beams using this technique, and if so did it work?






RE: Reducing the sweep of a prestressed box beam.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Reducing the sweep of a prestressed box beam.
RE: Reducing the sweep of a prestressed box beam.
KootK, yes this is for a bridge. Its actually the fascia beam of the bridge. I am researching on how I can tackle this problem using AASHTO LRFD. My starting point is a transverse post tensioning calculations that I did on one of my projects, very similar to example one of this link: http://www.fhwa.dot.gov/bridge/prefab/if09010/appa...
Thank you again for your help!
RE: Reducing the sweep of a prestressed box beam.
If you were to go ahead you should make sure the deck is cast shortly after the post-tensioning to reduce the chance for unwanted twisting.
RE: Reducing the sweep of a prestressed box beam.
1.show that the force required to take out the excess deflection does not exceed the allowable cracking capacity of the beam.
2. Design calculations showing that the transverse tendon anchor plates and surrounding concrete are not overstressed.
Any good examples or instructions that can guide me would be helpful.
RE: Reducing the sweep of a prestressed box beam.
RE: Reducing the sweep of a prestressed box beam.
RE: Reducing the sweep of a prestressed box beam.
Using LRFD the allowable concrete strength is 0.6 x fc' with fc' = 10 ksi, so I get an allowable concrete strength of 6 Ksi. Now the force applied is 21 kips, also keep in mind that this force was applied only at the middle duct, which means it will be distributed on the diaphragm of the beam which has an area of 518 in2 (14" x 37"). 21,000 lbs / 518 in2 = 40.5 psi. That's what I get.
is that all I have to do, to check that concrete will not crush at the ends? am I missing any thing?
RE: Reducing the sweep of a prestressed box beam.
RE: Reducing the sweep of a prestressed box beam.
RE: Reducing the sweep of a prestressed box beam.
I would investigate first what caused the sweep. Is this pre or pos tensioned, it pre, it could have been an imbalance on the stressing force among the strands.....
Cheers