BEHAVIOR OFSLIDING ISOLATORS WITHVARIABLE FRICTIONUNDER NEAR-FAULTEARTHQUAKES

One of the ways to make FPS adaptable is to make its friction coefficient variable.For a sliding isolator with variable friction (SIVF), the sliding surface may have a constant radius, but the friction coefficient of the isolator is assumed to be a function of the isolator displacement which results in adaptive damping that varies along the isolator displacement.Variable Friction Pendulum System (VFPS) is a kind of SIVF isolator whichis very similar to FPS except that the friction coefficient of FPS is considered to be constant whereas the friction coefficient of VFPS is variedin the form of a curve. However, suchavariation of coefficient of friction is difficult and impractical to be achieved in the real world.The present studyintroduces an alternative isolator, namely, Modified Variable Friction Pendulum System (M-VFPS) with a very simple and practical variation of coefficient of friction. To compare the responses of the two isolators, an idealized 2-DOF shear building with an isolation system modeled by a nonlinear friction element and a variable spring element is simulated by using a general mathematical model. Moreover, a set of seven near-fault earthquake excitations are considered for evaluation purposes with two main aspects governing effectiveness of isolator: (1) base displacement and (2) super-structural acceleration. The results indicate that the seismic behavior of M-VFPS is close to that of VFPS and, thus, it can be considered as an alternative. In addition, in comparison to a conventional FPS isolator, both M-VFPS and VFPS show better behavior in reduction of base displacement while they are not so successful in controlling of the acceleration transmitted to the superstructure.