Retrofitting of Structures Questions and Answers

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Flexural strength comes from the longitudinal bars developing tension and compression across the critical section at the joint. A jacket stopping at the floor has nowhere to anchor those bars, so it adds confinement and shear capacity but very little flexural strength - which is why continuity through the slab is the difficult and essential detail.

Answer: B

Injection restores continuity and keeps water away from the reinforcement, which is worth doing, but a member deficient in steel or confinement remains deficient afterwards. Repair and strengthening are different operations.

Answer: C

Full compliance is frequently impossible without rebuilding, so the standards accept less in recognition of the remaining life and the cost. Essential facilities and buildings undergoing major alteration are generally held to a higher standard.

Answer: D

Correct answer: Anchoring parapets, cladding and heavy contents

These measures cost very little, need no analysis of the structure and remove a large fraction of the casualties, since falling non-structural elements injure many more people than collapsing frames do. They are the first thing done in any programme, and often the only thing done for the majority of buildings.

Answer: A

Drift is a stiffness problem, and it is corrected by stiffening the structure or by damping the response rather than by adding capacity that is already sufficient. Diagnosing which quantity is deficient is what the assessment is for.

Answer: B

Where drift is already acceptable, the deficiency is in what the members can carry, and jacketing, wrapping or added elements answer it. Reducing mass also helps, since it lowers demand, and is worth considering alongside.

Answer: C

Steel jackets or fibre wraps at the ends of columns raise the rotation capacity without adding appreciable strength or stiffness, so the rest of the design is undisturbed. It is the cheapest of the structural measures where it is the right one to use.

Answer: D

Correct answer: strength, stiffness and ductility

A building may be deficient in any of the three, and the remedy differs for each: shear walls for strength, bracing for stiffness, jacketing and confinement for ductility. Reducing the demand - by removing mass or isolating the base - is the fourth approach, addressing the other side of the comparison.

Answer: A

Correct answer: works but consumes usable floor space

A new internal frame is effective and can be tied readily to the existing floors, but it stands where the occupants would otherwise be and it needs new foundations beneath it. That loss of space is what drives owners towards an external solution where appearance permits.

Answer: B

Chemical anchors, dowels and shear keys are what let the added element take its share, and a connection that slips leaves the new work as an ornament. Pull-out testing of a sample of anchors is standard practice for that reason.