OPTIMUM DAMPING IN A NONLINEAR BASE-ISOLATION SYSTEM

Optimum isolation damping for minimum acceleration of a base-isolated structure subjected to earthquake ground excitation is investigated. T he stochastic model of the El-Centro 1940 earthquake, which preserves the non-stationary evolution of amplitude and frequency content of gro und motion, is used as an earthquake excitation. The base isolated str ucture consists of a linear flexible shear type multi-storey building supported on a base isolation system. The resilient-friction base isol ator (R-FBI) is considered as an isolation system. The non-stationary stochastic response of the system is obtained by the time dependent eq uivalent linearization technique as the force-deformation behaviour of the R-FBI system is non-linear. The optimum damping of the R-FBI syst em is obtained under important parametric variations: i.e., the coeffi cient of friction of the R-FBI system, the period and damping of the s uperstructure; the effective period of base isolation. The criterion s elected for optimality is the minimization of the top floor root mean square (r.m.s.) acceleration. It is shown that the above parameters ha ve significant effects on optimum isolation damping. (C) 1996 Academic Press Limited