Define Types of Seismic Isolation Bearing - Rubber Bearings?

Seismic isolation is obtained by two types of isolation bearings.

a) Rubber bearings

b) Friction pendulum bearings

Rubber bearings are composed of a lead case and natural or synthesized rubber with embedded layers of steel plates.

Figure: Rubber Bearing

The force-displacement behaviour of this bearing is elastic under service load and inelastic during an earthquake when the lead case deforms beyond its elastic limits. In fact, the bearing distribute the inertial forces from the deck level to all supporting substructures on the basis of their relative stiffness. Rubber bearings are meant to shift the vibrational period of the structure so as to avoid resonance with the excitations. These are usually combined with high damping material to prevent the isolated structures from over-displacing.