Stochastic analysis of sensitivity and efficiency of base isolation system in seismic structural protection

In this research the seismic response of structures isolated at the base by means of High Damping Laminated Rubber Bearings (HDRB) is evaluated. The analysis is performed by using a stochastic approach and a Gaussian zero mean non stationary stochastic process is used in order to model the seismic acceleration acting at the base of the structure. In order to take into account of the non-linear constitutive behavior both of the base isolation device and of the structure, the hysteretic differential Bouc-Wen model (BWM) is adopted. Moreover, the stochastic linearization method in the time domain is adopted to estimate the statistical moments of the non-linear system response in the state space. After estimating the system response variance a sensitivity analysis is carried out. The final aim of the research is to asses the real capacity of base isolation devices in order to protect the structures from seismic actions, by avoiding a non-linear response with associated large plastic displacements, and, therefore, by limiting related damage phenomena in structural and non structural members. In order to achieve this objective the stochastic response of a non-linear n-dof shear-type base isolated building is analyzed. The protection level offered to the structure by the base isolators is then assessed by evaluating the reduction both of the displacement response and the hysteretic dissipated energy.