THE STOCHASTIC RESPONSE OF ASYMMETRIC BASE-ISOLATED BUILDINGS

The coupled lateral-torsional stochastic response of an asymmetric one -storey base isolated building to earthquake excitation is presented. The stochastic model of the 1940 El-Centro earthquake, which preserves the non-stationary evolution of the amplitude and frequency content o f the ground acceleration, is used as earthquake excitation. The base isolator consists of an array of elastomeric bearings between the base of the structure and its foundation. The root mean square (r.m.s.) re sponse of the system is obtained under different parametric variations in order to investigate the effects of superstructure and isolator ec centricities on the stochastic response of a base isolated building. T he system parameters include the eccentricity of the superstructure, t he uncoupled torsional to lateral frequencies ratio of the superstruct ure, the eccentricity of the isolator, and the uncoupled torsional to lateral base isolation frequencies ratio of the isolator. It is shown that these parameters have considerable influence on the response of a base isolated structure and the effectiveness of base isolation in re ducing the seismic forces in the superstructure.