Seismic Performance of Structures Isolated with FPS for Different Soil Conditions considering Intermediate Isolation Degrees

This study investigates the optimal properties of friction pendulum devices to seismically isolate elastic structural systems under earthquake excitations having different characteristics in terms of frequency content considering intermediate isolation degree values. A two-degree-of-freedom model is considered to describe the isolated system behavior with a velocity-dependent model for the isolators. Specifically, a non-dimensional formulation of the governing equations of motion is adopted assuming the superstructure displacements, the isolator forces and damping factors as the response parameters of interest for the performance assessment. Several seismic artificial excitations, having frequency contents properly defined to describe respectively stiff, medium and soft soil conditions, are assumed. Finally, the optimum values of the friction coefficient that minimize the superstructure displacements as a function of the structural system properties, of the intermediate isolation degree values and of the soil condition are numerically computed.