Retrofitting of Structures Questions and Answers

Answer: A

A new lateral element concentrates a large moment and a large shear at its base, and the existing footing was proportioned for gravity load alone. Underpinning, new pile caps or a tie into a raft are the measures normally needed.

Answer: B

Correct answer: Fibre wrapping the columns for confinement

Wrapping adds confinement and shear capacity without adding stiffness or attracting more load, so the forces reaching the foundations are essentially unchanged. Every other option adds a stiff element that attracts lateral force and delivers it to the ground, which almost always means new or enlarged foundations.

Answer: C

Occupancy by children raises the consequence of failure well above that of an ordinary building, and many programmes set the bar higher still because schools serve as shelters. The choice belongs to the owner and is made explicitly at the outset.

Answer: D

Correct answer: rapid visual screening to rank them

With many buildings and limited resources, the first task is to decide the order of work. Screening from the outside costs a fraction of an assessment and separates the plainly dangerous from the plainly adequate, so detailed work is spent where it will change a decision.

Answer: A

Correct answer: its configuration, age and obvious deficiencies

Screening is done from the pavement in half an hour: the structural system, the number of storeys, the age and code era, the plan and vertical irregularities, and visible faults such as an open ground storey. It yields a score for ranking rather than a verdict, and a low score triggers a proper assessment.

Answer: B

Correct answer: a band at lintel and eaves level

Out-of-plane failure occurs when a wall is unrestrained at its top and free to overturn about its base. Bands at lintel and eaves level provide that restraint and tie the wall to the walls at right angles to it, so it spans horizontally as well as vertically. Plaster and crack injection restore appearance without addressing the mechanism.

Answer: C

Correct answer: checked for the additional demand it creates

Added mass raises the inertia force in proportion, so a jacket or a new wall increases the demand as well as the capacity. If the demand rises faster than the capacity in some member, the retrofit has made matters worse there - which is why the strengthened building must be reanalysed rather than merely detailed.

Answer: D

Every measure either raises what the structure can do or lowers what is asked of it, and a sound scheme usually does both. Restoration and cosmetic repair are different objectives and do not by themselves improve performance.

Answer: A

The great majority of buildings in use were designed before ductile detailing was required, or with no seismic design at all. Replacing them is not possible at that scale, so improving them is the only practical route to reducing the risk.

Answer: B

Life safety, immediate occupancy and continued operation differ greatly in cost, and the choice depends on the value and the use of the building. The engineer sets out the options and their consequences and the owner chooses.