Development of a two-phased nonlinear mass damper for displacement mitigation in base-isolated structures

This paper developed a two-phased arc nonlinear energy sink (2PA NES) for displacement mitigation in base isolated structures. The 2PA NES is a type of nonlinear mass damper that can produce nonlinear restoring force through the auxiliary mass moving on a track. The track is designed in two phases that provide softening restoring force for the 2PA NES. In the base-isolated structures, the 2PA NES is attached to the top story as the building roof without restriction of the location and space. The 2PA NES can be precisely tuned to match the hysteretic behavior of the isolated structures. Restoring force of the 2PA NES and equations of motion of the 2PA NES-base-isolated system were derived first. Subsequently, the design philosophy of the 2PA NESs was proposed and applied in an eight-story base-isolated structure. The displacement mitigation capacity of the 2PA NES was then computationally investigated under a suite of pulse-type seismic excitations. Analysis results showed that the 2PA NES was more effective than a comparable tuned mass damper (TMD) in reducing the base displacement. In addition, the stroke of the 2PA NES was smaller than that of the TMD and the supplement of the 2PA NES had a slight effect on the response of the superstructure. With little installation limitation and high control effectiveness, the 2PA NES provides a promising solution for displacement mitigation in base-isolated structures.