High damping natural rubber seismic isolators

Laminated high damping rubber bearings provide a simple means of isolating structures from horizontal earthquake ground motions. The key properties of the rubber compounds are dynamic shear modulus and damping. The effect of strain amplitude, repeated cycling and temperature on these properties is given. The need to prevent changes in modulus associated with low temperature crystallization of rubber is discussed. Assessment of the long term stability of rubber properties from both accelerated ageing tests and measurements on bearings removed after prolonged service is considered. A model for the behaviour of high damping rubber is presented, and used to show how the response of a structure to ground acceleration depends upon the level of damping.