Base Isolation and Energy Dissipation Questions and Answers

Answer: C

The steel shims restrain the rubber from bulging under vertical load, which makes the bearing stiff vertically, while the rubber remains free to shear horizontally. This combination of properties in one component is what makes the laminated bearing so widely used.

Answer: D

The lead core yields at a low stress and reforms its grain structure afterwards, so it can absorb energy cycle after cycle without degrading. It also provides the initial stiffness that resists wind and small tremors before the isolation engages.

Answer: A

The first branch comes from the lead core and the rubber acting together, and the second from the rubber alone once the lead has yielded. Analysis usually replaces the two branches with an effective stiffness and an effective damping at the design displacement.

Answer: B

Fillers added to the compound give the rubber a fat hysteresis loop, so the bearing damps without any separate device. The properties depend on temperature and on the strain history, which is why such bearings are tested extensively before acceptance.

Answer: C

Because the slider rides up a concave surface, gravity pulls it back towards the centre, and the radius of that surface fixes the isolated period. Friction between the slider and the surface provides the damping at the same time.

Answer: D

The pendulum relation \( T = 2\pi\sqrt{R/g} \) involves the radius alone, so the period is independent of the mass carried. That independence is a considerable practical advantage, since it means the period does not change as the building's loading does.

Answer: A

Correct answer: 2.0 s

\[ T = 2\pi\sqrt{\frac{R}{g}} = 2\pi\sqrt{\frac{1.0}{9.81}} = 2\pi \times 0.319 = 2.0\ \mathrm{s}. \] The remarkable feature of the friction pendulum is that the mass cancels out entirely, exactly as it does for a simple pendulum: the period depends on the radius of the sliding surface alone, so the isolated period does not change as the building is loaded or altered.

Answer: B

Friction dissipates a great deal of energy, but nothing pulls the building back to its starting position, so residual displacement accumulates. Practical systems therefore pair sliders with a recentring element, or use a curved surface that recentres by itself.

Answer: C

Every gravity load path passes through the isolation plane, and any appreciable vertical softness would produce rocking and unacceptable settlement. Vertical isolation is generally not attempted, which is why vertical ground motion reaches the superstructure largely undiminished.

Answer: D

It is read from the spectrum at the isolated period, allowing for the effective damping of the system, and it governs the size of the bearings and of the surrounding gap. Values of two to four hundred millimetres are common for a building on a strong-motion site.