Responses of Two-Degree-of-Freedom Sliding Base Systems Subjected to Harmonic Ground Motions

Responses of two-degree-of-freedom sliding base systems subjected to harmonic ground motions were studied. This study continues the previous work on this topic and focuses on explaining the inherent mechanism of the sliding base system and derivation of the theoretical solutions for important responses. Unlike fixed base structures, several resonant frequencies were observed after sliding occurred. These resonances are induced by the changing of the vibration center at the moment when the relative displacement is located farthest from the new vibration center. In general, the maximum pseudo-acceleration decreases as the mass ratio increases. For the sliding-sliding case, the maximum pseudo-acceleration reaches an upper limit, which is independent of the amplitude of the ground acceleration. Explicit expressions were derived for this upper limit. The amplitude of the sliding displacement is a suitable response quantity to represent the extent of sliding. As the ground acceleration increases, the sliding displacement amplitude tends toward the vibration amplitude of the ground displacement. (C) 2016 American Society of Civil Engineers.