Ultimate moment capacity of prestressed beam
Ultimate moment capacity of prestressed beam
(OP)
HELLO!
Recently, I've dealt with a 243-meter-long prestressed bridge using RM bridge.
After analysis, I found that the ultimate moment capacity after 30 years is greater than the capacity after 28 days.
Does it make sense?
It is consistent with what I expected(after 30 years, the steel relaxation causes the lower initial stress in tendon. Hence the stress state of tendon becomes far away from rupture point, As shown in the picture).
I told many engineers this result, they have another opinion but i didn't get it.(may be i don't think i am wrong)
Hope anyone can help me!Thanks!
Recently, I've dealt with a 243-meter-long prestressed bridge using RM bridge.
After analysis, I found that the ultimate moment capacity after 30 years is greater than the capacity after 28 days.
Does it make sense?
It is consistent with what I expected(after 30 years, the steel relaxation causes the lower initial stress in tendon. Hence the stress state of tendon becomes far away from rupture point, As shown in the picture).
I told many engineers this result, they have another opinion but i didn't get it.(may be i don't think i am wrong)
Hope anyone can help me!Thanks!






RE: Ultimate moment capacity of prestressed beam
so if you design with a certain value of pre-stress, when does your design assumption become invalid ?
another day in paradise, or is paradise one day closer ?
RE: Ultimate moment capacity of prestressed beam
Design assumption becomes invalid? because these calculation procedures are only approximations, i think they are always valid.
if it is possible, i want to explain that phenomenon by simple intuitive concepts.
RE: Ultimate moment capacity of prestressed beam
another day in paradise, or is paradise one day closer ?
RE: Ultimate moment capacity of prestressed beam
Relaxation of the steel over time does not alter the ultimate strength of the steel. Prestressing steel does not gain strength over time.
BA
RE: Ultimate moment capacity of prestressed beam
http://mucc.mahidol.ac.th/~egpcp/Handout406/40610%...
it said there is no prestress in ultimate state
RE: Ultimate moment capacity of prestressed beam
* At ultimate of prestressed concrete beam, the stress in steel is
somewhere between yield strength fpy and ultimate strength fpu
* Stress is lower for unbonded tendon because stress is distributed
throughout the length of the beam instead of just one section as in the
case of bonded tendon
* At ultimate, the effect of prestressing is lost and the section behaves just like an RC beam
If you prestress a steel bar with tensile force T, then start applying tension to the prestressed bar, the prestressing force will be lost when the applied force equals or exceeds T.
In the case of prestressed concrete, the stress in the steel at factored load fps is given by the expression in the article. Its value does not change as a result of loss of prestress over time.
BA
RE: Ultimate moment capacity of prestressed beam
RE: Ultimate moment capacity of prestressed beam
RE the loss of prestress at ultimate, logically when the strain in the concrete at the level of the prestress reaches the pre-strain in the prestress steel, the steel will no longer be "prestressed" compared to the concrete around it, but it has no effect on the design. It is a meaningless statement!
RE: Ultimate moment capacity of prestressed beam
It will effect serviceability states, but not ultimate.
RE: Ultimate moment capacity of prestressed beam