Modeling and Validation of a Novel Variable Stiffness System for Seismic Isolation of Acceleration-Sensitive Equipment

Seismic isolation of specific equipment, or specific floors of buildings, can be an effective protective measure for acceleration-sensitive equipment or equipment sets. However, satisfying performance requirements may be difficult due to severe horizontal absolute floor accelerations and large isolator displacements. In the present study, a novel variable stiffness isolator is proposed for seismic isolation of acceleration-sensitive equipment. It will be shown that the variable stiffness isolator can be designed to have positive stiffness at small and large displacements, and zero stiffness in between. This results in a variable restoring force that ensures stability of the system under service loading, limits excessive displacements under extreme seismic loading, and allows for zero stiffness isolation at the design level earthquake. The concept for the variable stiffness isolator will be presented along with a model for predicting its force-displacement characteristics. Then, the results of laboratory testing will be provided for validation of the variable stiffness concept. Finally, numerical simulation results will be presented to demonstrate the effectiveness of the variable stiffness isolator for seismic isolation of equipment.