Base Isolation and Energy Dissipation Questions and Answers

Answer: A

Because the isolation layer is far more flexible than any storey, the deformation concentrates there and the storeys above stay nearly parallel. That is why the contents and the non-structural elements survive so much better than in a fixed-base building.

Answer: B

Exhibits, imaging equipment and services fail at accelerations well below those that threaten a structure, and isolation cuts those accelerations sharply. Savings in the frame are real but are usually secondary to keeping the contents usable.

Answer: C

Conventional strengthening means bracing, jacketing or shotcreting surfaces that are the reason the building is protected in the first place. Working at the foundation instead leaves the fabric alone, though the excavation and underpinning are demanding work.

Answer: D

Correct answer: Reducing the mass of the superstructure

Isolation does not remove any mass; the whole weight of the building still stands on the bearings. What it changes is the period, lengthening it well beyond the range where ground motion has most of its energy, so the acceleration transmitted upwards falls. Carrying the vertical load, providing horizontal flexibility, dissipating energy and re-centring are all genuine functions of a bearing.

Answer: A

Because the dampers take energy out of the response, drift and member forces both fall, and the existing members may then be adequate as they stand. It is often less disruptive than jacketing columns throughout a building in use.

Answer: B

The relative movement between two storeys is what drives the device, and a diagonal brace converts storey drift into axial movement across it. Toggle and scissor arrangements are used where the drift alone is too small to work the device.

Answer: C

Displacement-dependent devices respond to the drift itself and velocity-dependent ones to how fast it is changing, but both need relative movement across the device. A storey that does not deform gives its damper nothing to do.

Answer: D

Correct answer: A viscous fluid damper

Only the viscous damper’s force depends on how fast the structure is moving. A friction damper slips at a threshold force regardless of speed, and a metallic damper and a buckling restrained brace both dissipate through yielding, which is governed by displacement. That distinction matters in design: displacement-dependent devices add stiffness and so raise the base shear, while velocity-dependent ones do not.

Answer: A

Their force is largest as the structure passes through its neutral position, which is when the elastic force is smallest, so the two peaks do not coincide. A friction or yielding device peaks with the displacement and its force adds directly.

Answer: B

Correct answer: may leave the structure with a residual offset

A friction device has no restoring force of its own: once it has slipped it stays where it stopped, so the building can be left permanently off centre unless something else re-centres it. That is why friction dampers are usually paired with an elastic element, and why the friction pendulum builds the restoring force into the curved surface itself.