Lead rubber bearings were developed as base isolators in the 1970s. They consist of three basic components ¨C a lead plug, rubber and steel, which are generally placed in layers.
The rubber provides flexibility through its ability to move but return to its original position. At the end of an earthquake, if a building hasn¡¯t returned to its original position, the rubber bearings will slowly bring it back. This might take months, but it will return to its original position.
Lead was chosen because of its plastic property ¨C while it maydeform with the movement of the earthquake, it will revert to its original shape, and it is capable of deforming many times without losing strength. During an earthquake, the kinetic energy of the earthquake is absorbed into heat energy as the lead is deformed.
Using layers of steel with the rubber means the bearing can move in a horizontal direction but is stiff in a vertical direction.
Another method for controlling seismic damage in buildings is the installation of seismic dampers. In this case, the dampening is provided by a lead-based device that looks very similar to a car damper (shock absorber).
Ground movement forces the lead to pass through a narrow gap. When the direction of movement changes, the flow of lead is reversed. The principle is still the same as the lead rubber bearing, with kinetic energy being converted into heat energy, thereby preventing the building absorbing the kinetic energy.