Analysis of an Isolation System with Vertical Spring-viscous Dampers in Horizontal and Vertical Ground Motion

Abstract

This paper proposes a new vibration isolation mounting system, with spherical balls and vertical spring dampers, that provides seismic protection from horizontal and vertical ground excitation. To characterize the system, nonlinear governing equations are derived by considering the kinematics and interaction forces of the structures, and the dynamic characteristics of the design parameters are investigated by numerical analysis. The condition of contact stability for sustaining continuous friction of the isolation device is discussed, along with the design parameters. The vibration transfer characteristics are analyzed for the displacement transfer ratio obtained for the design parameters satisfying the sustainable contact condition, when the base is harmonically excited. The results confirm that the relative motion occurrence satisfies the conditional expression, and a jump in which the transfer ratio suddenly increases at a specific frequency is identified. Finally, design variables that are suitable for the horizontal and vertical acceleration of the El Centro earthquake are set, and a simulation confirms the vibration reduction effect in both the horizontal and vertical motions.