Why should steel fail(yield) first before the concrete in RC beam?
Why should steel fail(yield) first before the concrete in RC beam?
(OP)
1. Could someone kindly explain why steel should yield first before concrete fails?
2. Let's say on the tension side of a beam, how would the steel fails first before the concrete knowing that the steel is basically the one that support the tensile stress? Isn't it that the concrete would crack/crash first before the tension rebars yield?
2. Let's say on the tension side of a beam, how would the steel fails first before the concrete knowing that the steel is basically the one that support the tensile stress? Isn't it that the concrete would crack/crash first before the tension rebars yield?






RE: Why should steel fail(yield) first before the concrete in RC beam?
RE: Why should steel fail(yield) first before the concrete in RC beam?
RE: Why should steel fail(yield) first before the concrete in RC beam?
RE: Why should steel fail(yield) first before the concrete in RC beam?
RE: Why should steel fail(yield) first before the concrete in RC beam?
RE: Why should steel fail(yield) first before the concrete in RC beam?
The steel should not yield before the concrete cracks in tension; if it does there is a possibility that the beam will develop sufficient momentum to cause immediate failure.
So the sequence is:
- Concrete in tension cracks; transfer of stress to the steel with large increase in steel strain, but still within the elastic range.
- Steel starts to yield, large increase in deformations, loads are transferred elsewhere.
- Either steel rupture or concrete crushing; sudden failure.
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: Why should steel fail(yield) first before the concrete in RC beam?
Because you can get a ductile failure (desired) as opposed to a brittle failure (not desired).
RE: Why should steel fail(yield) first before the concrete in RC beam?
RE: Why should steel fail(yield) first before the concrete in RC beam?
RE: Why should steel fail(yield) first before the concrete in RC beam?
RE: Why should steel fail(yield) first before the concrete in RC beam?
I hope the OP is a student, because a practicing structural engineer who does not understand the basis for designing for yield of reinforcement has no business designing concrete. This would be like designing steel without understanding LTB. The entire code is developed around this concept. Phi factors for compression failure are significantly lower to prevent the design of members subject to compression failure without substantial margins.
RE: Why should steel fail(yield) first before the concrete in RC beam?
What I said was misleading. At the point where the concrete cracks the strain in the steel will be much less than the yield strain, but after cracking the steel strain increases until the moment provide by the steel tension is equal to the moment previously supplied by the now cracked concrete. What I meant to say was that the moment capacity of the section ignoring concrete in tension should be greater than the cracking moment, so that after the concrete has cracked the steel is still well below its yield stress.
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/