SEISMIC RESPONSE OF HEAVILY DAMPED BASE-ISOLATION SYSTEMS

The development of an efficient energy-dissipating mechanism that work s in conjunction with laminated elastomeric bearings in order to reduc e the lateral deformation of the isolation system has always been a go al of base isolation research. Theoretically, this deformation will be reduced to the minimum if damping augmentation of the isolation syste m can reach a critical value. However, augmenting the isolation dampin g may cause some unwanted side effects. The purpose of this paper is t o study the influence of isolation damping on the seismic response of heavily damped base-isolated buildings. The base isolation system is a ssumed to be linearly viscoelastic and is analysed using the complex m ode method. Solutions derived by using perturbation techniques for a t wo-degree-of-freedom system and the computer simulation for a multiple -degree-of-freedom system reveal that augmenting the isolation damping can reduce efficiently the deformation of the isolation system, but a t the price of increasing the high-frequency vibration in the superstr ucture. When the damping ratio of the isolation system is beyond some level, increasing the isolation damping will enlarge the extreme value s of the base and superstructural accelerations. It is also found that approximate solutions derived from the use of classical damping and c lassical modes of vibration in the seismic analysis of heavily damped base isolation systems can be substantially in error.