Response variability of structures with hybrid base isolation systems

This paper investigates the effect of random parameter variation on the dynamic response of structures equipped with hybrid base isolation systems (HBIS). The considered HBIS combines high damping rubber bearings with low friction sliders modeled by a five-parameter trilinear hysteretic and a single-parameter Coulomb friction model, respectively. A shear beam type, four-degree-of-freedom model is used to simulate the superstructure. The calibration of the six-parameter mechanical model describing the HBIS is based on five initial-displacement, free vibration tests performed on two R/C residential buildings in Solarino, Sicily. The calibrated parameters values from all the experiments are used as mean values, while the standard deviation for each parameter is deduced employing best-fit optimization for each experiment separately. Monte Carlo simulation is used to compute the response variability of both the HBIS and the superstructure. It is shown that the response is highly non-stationary as its first two moments are significantly evolving with time. Moreover, a magnification of uncertainty is observed since the coefficient of variation of the response is in most cases larger than the coefficient of variation in the parameter values. The aforementioned effects can be attributed to the high level of nonlinearity in the base isolation system, as observed in the amplitude of vibration brought about by large initial displacements.