Stochastic energy measures for hybrid base isolation systems

Two R/C residential buildings were retrofitted by using a hybrid base isolation system in Solarino, Sicily, in 2004 and subsequently five free vibration tests were carried out in one of these buildings. The hybrid base isolation system combined high damping rubber bearings with low friction teflon sliders. For numerical modeling purposes, a single-degree-of-freedom system was developed with a new trilinear hysteretic model for the simulation of the high damping rubber bearing response, coupled with a Coulomb friction model for the simulation of the low friction slider response. Five sets of data were obtained from initial-displacement, free vibration tests and were subsequently used for the calibration of this six parameter model. Following up on the numerical model development, the present study employs Monte-Carlo simulations in order to investigate the effect of variations in the values of the six-parameter model on the response of the hybrid base isolation system. The calibrated parameters' values from the experiments are used as mean values, while the standard deviation for each parameter is deduced from the identification tests employing best-fit optimization for each experiment separately. The results of the Monte-Carlo simulations show a non-stationary effect in the response, which can be traced by the time evolution of the standard deviation of various energy measures computed at different time instants. The high level of nonlinearity in the base isolation system response due to large initial displacements helps explain the previously described effects.