Stochastic seismic response of structures isolated by rolling rods

The stochastic response to earthquake motion of flexible multi-storey shear type buildings isolated by rolling rods with a recentering device is investigated. The re-centering device in the form of a spring or cantilever beam attached to the base of the structure reduces the rolling base displacement and returns the system to its original position after the earthquake. The stochastic model of the El-Centro 1940 earthquake which preserves the non-stationary evolution of amplitude and frequency content is considered as an earthquake excitation. The non-stationary response of the isolated structural system is obtained using a time-dependent equivalent linearization technique since the force-deformation behavior of the rolling rods is highly non-linear. The responses of the isolated structure are compared with the corresponding fixed base system in order to investigate the effectiveness of the rolling rods. The effectiveness of rolling rods in isolating the structure is investigated under important parametric variations. The parameters included are: the time period of the superstructure (as a fixed base), the period of isolation and the friction coefficient of the rolling rods. It is shown that the rolling rods are quite effective in reducing the stochastic response of the structure against earthquake excitation. The presence of the re-centering device significantly reduces the relative base displacement without transmitting additional accelerations into the superstructure. In addition, there exists an optimum value of the friction coefficient of the rolling rods for which the acceleration response of the superstructure attains the minimum value. The effects of system parameters on the variation of optimum friction coefficient of the rolling rods are also investigated. (C) 2000 Elsevier Science Ltd. All rights reserved.