Lead-rubber-bearing with negative stiffness springs (LRB-NS) for base-isolation seismic design of resilient bridges: A theoretical feasibility study

Advanced seismic isolation devices and systems have been recognized as promising measures toward resilient design of bridge structures. This paper proposes a base isolation system using lead rubber bearing with negative stiffness springs (LRB-NS), which is composed of traditional lead rubber bearing (LRB) and pre-compressed springs, installed at the bottom of bridge columns. These springs contain dual functionalities: (1) provide negative stiffness (NS) and negative restoring force during slight shakings and elongate the structural period that is determined by LRB products; and (2) offer significant restoring forces to prohibit excessive peak deformation and protect bearings from failure when subjected to strong earthquakes. Theoretical and analytical studies are first conducted to illustrate fundamental mechanics of the proposed LRB-NS device, followed by a series of parametric analyses to understand the influential factors of this device on structural behavior. Moreover, fragility analyses of typical highway bridges are conducted to demonstrate the feasibility of LRB-NS device via comparisons with non-isolated and traditional LRB systems. The results show that the LRB-NS device can be well designed to mitigate seismic demands of bridge columns, as well as highly effective to suppress the excessive deformation in bearings that often occurs in the traditional LRB system under strong excitations. The LRB-NS device can be used to facilitate the resilient seismic design of bridge structures.