This paper proposes a new fuzzy logic controller, which is designed for seismic protection of base-isolated structures utilizing piezoelectric friction damper against near-fault earthquakes for different ground sites. According to the elastic design spectrum that Eurocode 8 recommends, one 5% damped elastic design spectrum for Chi-Chi earthquake is proposed to generate artificial earthquakes of different ground sites. The proposed controller employs a hierarchic fuzzy control algorithm, in which a supervisory fuzzy controller governs a sublevel fuzzy controller by altering its input normalization factors according to current level of ground motion. In order to simultaneously reduce the base displacement and superstructure responses of the base-isolated structure during seismic excitations, genetic algorithm is employed to optimize the supervisory fuzzy controller and the preload of piezoelectric friction damper. The efficiency of the proposed controller is also compared with passive controller and a linear quadratic Gauss optimal controller. Numerical results show that the proposed fuzzy logic controller has favorable performance in mitigating the responses of the base-isolated structure.

Based on the shortcoming of the passive friction damper that the friction force cannot be adjusted during working, a new type of piezoelectric variable friction damper that the friction force can be adjusted by piezoelectric actuator was developed. The energy dissipation capacity of the damper under cyclic loading was investigated by Material Testing System. The energy dissipation performance of the damper was also analyzed by the preload, loading frequency and displacement amplitude. The experimental results indicate that the proposed piezoelectric variable friction damper has both stable hysteretic performance and good energy dissipation capacity. The energy performance of the damper varies with preload and excitation amplitude. The excitation frequency has little effect on the energy dissipation of the proposed piezoelectric variable friction damper.