OPTIMAL FRICTION COEFFICIENTS FOR ISOLATED STRUCTURES DEPENDING ON THE SOIL CONDITION

This study aims at evaluating the optimal properties of friction pendulum bearings to be employed for the seismic protection of elastic isolated structural systems under earth-quake excitations with different characteristics in terms of frequency content. A two-degree-of-freedom model is considered to describe the isolated system behavior while accounting for the superstructure flexibility and a non-dimensional formulation of the governing equations of motion is employed to relate the characteristic parameters describing the isolator and struc-ture properties to the response parameters of interest for the performance assessment. Seis-mic excitations are modelled as time-modulated filtered Gaussian white noise random processes of different intensity within the power spectral density method. The filter parame-ters control the frequency content of the random excitations and are calibrated to describe stiff, medium and soft soil conditions, respectively. Finally, multi-variate regression expres-sions are obtained for the optimum values of the friction coefficient that minimize the super-structure displacements relative to the base mass as a function of the structural system properties, of the seismic input intensity and of the soil condition