Dynamics characteristics of geometrically nonlinear isolation systems for seismic protection of equipment

Earthquakes pose risks to sensitive equipment and may result in dramatic economic loss. A widely used control strategy is to install an isolation system underneath equipment; however, excessive isolation displacements may be induced during severe earthquakes. Viscous dampers are recommended to be placed along with the isolation layer and to reduce displacements. Indeed, this combination is designed for a certain earthquake level and may be less effective in other earthquake levels. In this study, an isolation system with viscous dampers, which is installed perpendicular to the motion direction at the equilibrium position, is proposed to enhance seismic performance of important equipment through this geometrically nonlinear configuration. This configuration provides a better reduction in absolute accelerations during small-to-moderate earthquakes, while isolation displacements can be effectively mitigated during severe earthquakes. To understand the dynamic characteristics of this system, a series of investigations are carried out. The features of the effective control force are explored by the effective damping, and the phase plane analysis is conducted to understand the isolation system behavior. Then, the averaging method is employed to obtain the frequency-amplitude relationship of the proposed system, and the results inform the frequency domain behavior. The geometrically nonlinear damping is experimentally explored. Control effectiveness of the proposed system is also evaluated under seismic excitation and compared with the conventional isolation system (i.e., viscous dampers installed parallel to the isolation motion direction). As a result, the viscous damper with geometric nonlinearity can be more adaptive to different earthquake levels and thereby improves seismic isolation performance.

Automated summary

This study presents a new isolation system with viscous dampers that can effectively reduce absolute accelerations during small-to-moderate earthquakes and mitigate isolation displacements during severe earthquakes.