Fuzzy Control For Seismic Protection Of Semiactive Base-Isolated Ststems Subjected To Near-Fault Earthquakes

Base isolation has been demonstrated to be an effective technique that is used in seismic protection of crucial civil engineering structures. Although the supplement of dampers reduces the isolated system’s damage against strong earthquake excitations, it brings about large damping forces and causes significant magnifications of superstructural responses. Semi-active control is an intelligent control algorithm, which can regulate the output power of dampers according to current stage of structural responses. Therefore, semi-active control has better adaptability than traditional passive control. Near-field earthquake has become a hot research topic because its distinct seismic model and destruction patterns that are different from far-field earthquake. The near-field earthquakes and base-isolated structures are studied in this paper, moreover, a developed fuzzy logic control which is designed for seismic protection of base-isolated buildings using piezoelectric friction damper against Chi-chi near-field earthquakes of different ground sites is investigated. The primary innovative contents include:In order to investigate the distinctive characteristics of near-field earthquakes, several near-field seismic records of different ground sites are selected from database, and elastic design spectrum for near-field earthquake is proposed to generate artificial earthquakes of different ground sites. The study shows that near-field earthquake possesses obvious pulses with peak velocity due to forward effect and slip effect. The characteristic periods and dynamic coefficient of near-field earthquake are larger than far-fault earthquakes, the softer the site condition, the greater the characteristic period and the dynamic coefficient.A new type fuzzy control strategy, which is designed for seismic protection of a base-isolated building with piezoelectric friction damper, is presented in this study. The controller adopts a hierarchic fuzzy control algorithm. The sub-level fuzzy controller is designed to determine the command voltage of the piezoelectric friction damper by the input of the acceleration and displacement of base floor. According to the current level of the seismic acceleration, the high-level fuzzy controller governs a sub-level fuzzy controller by altering its input quantization factors and scaling factor in real-time. The genetic algorithm is used to optimize the parameters of fuzzy controller.The efficiency of the proposed multi-level fuzzy controller is also investigated through numerical simulations of a base-isolated structure by MATLAB software. For comparison purpose, the optimal controller and passive controller are conducted with the proposed hierarchic fuzzy control method. Numerical results show that the developed fuzzy logic controller not only can successfully mitigate the displacement of base floor and the superstructure acceleration response, but also has favorably adaptability subjected to different intensity ground motions. The problem of poor adaptability of traditional fuzzy control is successfully resolved.