Ductile Detailing of RC Structures Questions and Answers

Answer: C

Each member type has its own dimensional floor, set by what the detailing physically needs. The two ratios are easy to confuse: three tenths applies to a beam's width against its depth, and four tenths to a column's two cross-sectional dimensions.

Answer: D

The two reinforcement ratios differ by a factor of ten and are frequently transposed, so it helps to remember that a beam may carry two and a half per cent while a wall needs a quarter of one per cent. The capacity factor is dimensionless and applies to moment capacities at a joint.

Answer: A

Cracking comes first and is harmless, beam yielding is the intended mechanism, column hinging is undesirable and is pushed well back by the capacity factor, and joint failure should never be reached at all. Capacity design is the ordering of exactly that sequence.

Answer: B

The hinge is where the curvature, the bar compression and the concrete strain are all greatest, so close spacing is required exactly there and may be relaxed away from it. The reason states the purpose of the requirement and therefore explains it.

Answer: C

A lap is the weakest point along a bar, so it is placed where the demand upon it is least, which in a column means the middle of its height. The reason identifies why the ends are unsuitable and is thus the explanation for the requirement rather than merely a true statement beside it.

Answer: D

Correct answer: A is false but R is true

The reason is correct and it is what condemns the assertion. Under cyclic loading the cover spalls, and a 90-degree hook then has nothing to bear against and opens out, releasing the confinement at the moment it is required. Confining hoops must therefore have 135-degree hooks with an extension of at least ten bar diameters, anchored into the core where the concrete survives.

Answer: A

A soft storey or a floating column concentrates demand somewhere no amount of detailing can comfortably provide for. Detailing makes a sound configuration perform well; it cannot rescue one that channels the whole drift into a few members.

Answer: B

The joint transfers the full capacity of the members framing into it and cracks diagonally in both directions under reversal. Continuing the column hoops through it at close spacing is a requirement, and its omission has caused many failures.

Answer: C

The hook detail is what keeps the hoop closed after the cover spalls, and no compensating measure restores that function. Rebending or replacing the cages is the only remedy, and it is far cheaper before the concrete is placed.

Answer: D

Just above floor level is at the end of the column, inside the confining length and where hinging would occur, which is the worst place for a lap. Convenience of construction does not displace the requirement, and the change costs little to avoid.