RANDOM VIBRATION AND OPTIMIZATION OF DESIGN OF ASEISMIC BASE ISOLATION SYSTEMS (EARTHQUAKES, PROBABILISTIC, STRUCTURES)

Mitigation of the effects of earthquakes on structures may be accomplished by two methods: the traditional method which relies on the strength and ductility of the elements comprising the building structure and the alternative new method of base isolation. In this method, the structure is mounted on horizontally flexible reinforced rubber bearings which isolate the structure from horizontal seismic motions while special dampers provide additional energy absorption capacity to limit displacements and inhibit structural resonances.; This thesis studies the random vibration and optimization of design of the prominent base isolation systems. Random vibration is important both in optimization studies and risk assessment. Herein only the former is considered.; The overall conclusion of this investigation is that base isolation is very effective. The effectiveness appears to be primarily affected by the fundamental frequency of the structure if conventionally founded and by the frequency content of the stochastic seismic excitation. Most effective are systems which use special dampers of hysteretic nature.