Retrofitting of Structures Questions and Answers

Answer: C

A jacket that stops at each floor adds confinement but no flexural capacity, because its longitudinal steel cannot develop force across the joint. Coring through the slab to pass the bars is laborious and is where the cost of the method lies.

Answer: D

A steel shell acts in hoop tension in place of the missing ties, letting the core sustain much larger strain. Because it adds little flexural capacity, it improves ductility without disturbing the capacity hierarchy at the joints.

Answer: A

Hoop-wise fibres restrain the lateral expansion of the concrete and so raise its strain capacity, which is the deficiency in an unconfined column. Longitudinal fibres are added only where flexural strengthening is deliberately wanted.

Answer: B

The wrap is a few millimetres thick, so the column dimensions and the building's mass are essentially unchanged and the work is quick. Fire protection and surface preparation are both real requirements and add to the cost.

Answer: C

Filling and bonding the crack restores the section's continuity and keeps water and air away from the reinforcement. It is a repair rather than a strengthening measure, and it does nothing about a deficiency of steel or confinement.

Answer: D

Correct answer: can be applied to irregular surfaces without formwork

Existing buildings are irregular, and formwork against an old wall or an odd-shaped column is slow and expensive. Shotcrete is sprayed onto the prepared surface and the reinforcement behind it, following whatever shape is there. Its strength is comparable with placed concrete rather than superior.

Answer: A

Beams arrive on up to four faces and the slab covers the top, so there is very little surface to work on. Steel collars, fibre wrapping around the accessible faces and haunches added beneath the beams are the measures normally available.

Answer: B

The splints reinforce the corners and jambs where cracking begins, and the bandages tie the walls together into a box that can act as a unit. Both are applied on the surface, which suits buildings whose walls cannot be opened up.

Answer: C

Correct answer: tie the walls together so that they act as a box

An unreinforced masonry building fails when its walls separate at the corners and each is left to resist out-of-plane shaking alone. A continuous band at lintel and eaves level ties them into a closed box, so the walls parallel to the shaking support those perpendicular to it. It is the single most effective measure for such buildings.

Answer: D

The mesh gives the panel tensile strength in both directions, and the mortar bonds it to the masonry so that the two act together. Anchorage of the mesh through the wall is what decides whether the overlay stays attached.