Ductile Detailing of RC Structures Questions and Answers

Answer: A

A slender column of small section cannot be confined effectively and buckles once its cover spalls. The larger minimum for tall columns and for those carrying long-span beams recognises that both raise the demand on the section.

Answer: B

A very elongated column behaves more like a wall in one direction and like a slender strut in the other, and confining it effectively becomes impractical. Keeping the two dimensions within a factor of two and a half of each other avoids that condition.

Answer: C

The three criteria between them cover deep members, long members and small members, and the largest governs. That length is where the plastic hinge would form if the capacity hierarchy were breached, so it is confined as a precaution even in a strong-column design.

Answer: D

The standard also states that it need not be reduced below seventy-five millimetres, which sets a practical floor for placing and compacting the concrete. Between those two figures the spacing is fixed by the member dimension and the diameter of the longitudinal bars.

Answer: A

One quarter of the minimum dimension gives \( 400/4 = 100 \) mm, and the absolute cap is also 100 mm, so both criteria agree here. Using the larger dimension would give 150 mm and would breach the requirement, which is the trap in this calculation.

Answer: B

The ends of the column are where hinging and the largest bar stresses occur, and a splice there would be the weakest point at the worst location. Confining the splices to the middle half places them where the moment is smallest.

Answer: C

A lap transfers force by bond across the concrete between two bars, and that concrete must be confined if the transfer is to survive cyclic loading. The standard also limits the proportion of bars spliced at any one section to half of them.

Answer: D

Staggering the splices means that at no section is more than half the steel relying on a lap, so the section retains continuity through the remainder. Splicing every bar at one level would concentrate the weakness into a single plane.

Answer: A

The joint transfers the full capacity of the framing beams and columns and is subjected to high shear with reversing diagonal cracking. Congestion makes the detail difficult to build, but omitting the hoops has been a repeated cause of joint failure in earthquakes.

Answer: B

The margin of forty per cent covers the overstrength the beams may actually develop through strain hardening and material variability. It is the numerical expression of the strong-column weak-beam principle and applies about each principal axis in turn.