Base Isolation and Energy Dissipation Questions and Answers

Answer: C

Damping does reduce the displacement, but beyond a point it couples the superstructure back into the response and raises the floor accelerations that isolation was installed to reduce. The quantity is therefore optimised rather than maximised.

Answer: D

The reduced force still has to travel from every floor down to the bearings, so frames or walls are needed as usual. What changes is the magnitude of that force and the expectation that the members stay elastic while carrying it.

Answer: A

Retrofit is one of the main applications, because a damped brace can often be added in a bay without touching the rest of the structure. Reducing demand is frequently less disruptive than jacketing columns throughout an occupied building.

Answer: B

The trade is at the heart of the technique: the structure feels less but moves more, and the movement has to be accommodated in the moat and the services. Forgetting the second half of the trade is what produces isolation systems that fail in service.

Answer: C

Correct answer: To reduce the mass of the superstructure

Isolation changes nothing about the mass - the same building stands on the bearings. The three genuine reasons are all here: keeping a critical facility functional rather than merely standing, strengthening a historic building without touching its visible fabric, and protecting acceleration-sensitive contents, which conventional ductile design does nothing for because it accepts damage as the price of survival.

Answer: D

Bearings, the moat, flexible services and a lifetime of inspection all cost money that an ordinary building cannot justify. Codes cover the technique, the analysis is well established, and the bearings carry vertical load perfectly well.

Answer: A

Dampers occupy a few bays and need no moat, no flexible services and no underpinning, which is why they dominate retrofit work. Isolation gives the greater reduction in acceleration where it can be afforded and where the site suits.

Answer: B

Matching the site period invites the largest demand the site can deliver, which is the opposite of what isolation is meant to achieve. A different isolated period, more damping, or a different strategy altogether would be needed there.

Answer: C

Without it the building would drift progressively under successive cycles and end the earthquake off centre. Rubber provides it elastically, a curved sliding surface provides it through gravity, and a flat slider provides none at all.

Answer: D

Correct answer: the building may be left permanently off centre

A residual offset leaves the superstructure displaced relative to the ground, so the moat clearance in one direction is used up, the services crossing the plane are strained, and the capacity available for the next earthquake is reduced. The bearings still carry the vertical load and the period is essentially unchanged; the problem is the lost travel, which is why re-centring capability is specified.