Civil Engineering - GATE Exam Questions - Discussion

@All.

My opinion is;

Statement 1
In under reinforcement section thre area of steel reinforcement purposely provided less than what it need to be as balanced section..then what happen NA will moves up to reduce the area of concrete in stressing to balance the section, the purpose of allow the steel to yield first before concrete fully reach it maz stess.., because ductile property of steel, so when steel yielding first it will take time and shows cracks at bottom fibers rather concrete is brittle and cause sudden failure

Statement 2:
When the load increases, then it will increase the moment when the moment increases, then we have to put more reinforcement. When we put more reinforcement than NA, it shifts downward to balance the section by increasing the stress area of concrete, which causes NA to shift downward

Under higher compression force compared to tension force.

Is the neutral axis move above or below the centroidal axis?

@Sumit Dhyani.

you are partly correct but the answer is still D because;

"Failure takes place by crushing of concrete before the steel has yielded" Although the first part of statement 1 is correct but 2nd part isn't because steel has already yielded far before the ultimate failure due to crushing of concrete.

Regarding Statement 2 it's correct because when steel yields, the bottom part of the beam starts cracking and that area becomes negligible, hence N/A keeps shifting upwards as the cracks propagate higher and higher.

Thus option D is correct.

In over reinforced section concrete fails first and neutral axis goes down as load is increased answer is B.

Yes, D is correct.

Yes, D is correct.

Option A is correct.

Yes, option C is correct.

Actually, the in under r/f section, failure is due to concrete. Ya you are confusing with the fact that steel yields earlier than crushing of concrete.

But it doesn't mean that section fails. The section gives us warning due to ductility of steel (when steel yield) and fails due to crushing of concrete.

I too agree, it is Option D.

I think option A is correct.