Is the ACI methodology related to neglecting the strain in concrete in cracked ordinary reinforced flexural members is correct? We know there is uncracked sections in between each two adjacent cracked sections certainly, why don't ACI 318 committee considered these uncracked sections?
ACI provided limiting condition which is supported by experimental work rather a step by step procedure
Dear Dr Ali
I think, in terms of flexture the design is always based on the weakest section and the weakest section is the cracked one. At the other hand, and arguably if ACI wonts to consider the uncracked section between the cracked sections, an average section will be required, this will significantly complicate the solution, but the gains are very small, since we know that the strength of concrete in tension is very small and negligible
in terms of deflection, this might be true, and the uncracked section might have a relatively considerable influence, yet currently, ACI recommends checking deflections using Branson’s model which is based on experimental investigation rather than mathematical derivation, and has limitations.
Regards
Mechanics Concrete Stress-Strain
http://athena.ecs.csus.edu/~ce113/CE113-ConcreteStressStrain.pdf
Occasionally, but not usually, when running strain compatibility models I use an average tensile strain limit of half the peak to capture a bounding condition for average curvature. One difficulty, though, is that cracking does not reflect the loading case being analyzed, but the envelope of all prior loadings/cracking capacity that the element may have been subjected to, including shrinkage, creep, and thermal, and differential shrinkage creep and thermal restraint, not something easily predicted.
Thanks Mr. Michel,
You mean that the "difficulty" is the main reason?
Yes, as the difficulty destroys the predictive value of any modeling. Could be useful for non-linear dynamic modeling of non-cyclic events, such as crash simulations or blast where the situation modeled is a one time thing of much greater amplitude than other events in the life of an element. I may get into this a bit in the future, the influence of concrete tensile capacity on bridge rail and column impacts might border on what I do.
It also may be practical for quasi static conditions to model residual tensile strength for concretes that have fiber additives that would preserve some tensile strength at cracks. I have not been involved in that as yet.
I think there is other things rather than difficulty issue. The philosophy of such methodology is somewhere not accepted by some researches and they could develop a model capable to give comprehensive study.
Thank you very much Mr. Michael.
Dear Dr. Mohammed A. Abdulrahman
Thanks for your answer, and by the way;
are these models based on experimental works? also, do researches interrelate strains developed in cracked and uncracked sections?
Thank you.
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