||Base isolation has been popular by implemented in civil engineering. However, conventional isolation system possessing linear restoring force may be invalid under a near-fault earthquake which possesses low-frequency content and may induce resonance. Therefore, the eccentric rolling isolation system (ERIS) possessing nonlinear restoring is proposed. The base, which can be mounted on a structure or equipment, is eccentrically pinned on a circular isolator; and friction damping, which can be tuned by bolts, is considered.
In passive case, the ERIS performs as good as conventional linear isolation system under far-field earthquake. Subjected to near-fault earthquake, the ERIS shows better reduction in acceleration than the corresponding linear one. The ERIS also reduced the amplification under resonant sinusoidal excitation due to nonlinearity. However, the passive isolation case under non-design earthquake may not perform as well as itself subjected to design earthquake. Thus, semi-active control is considered to improve the performances of ERIS. Several switch control laws with low and high gain are investigated. The gain mode is switched by appropriate switch logic. When the system is subjected to a small earthquake, the low gain mode is taken to make sure that the system is effective. When the system is subjected to a large earthquake, the high gain mode is taken to reduce the base displacement and provide more energy dissipation. Moreover, the continuous type switch control law can mitigate the chatter and jerk which may occur for some discontinuous switch control law.