Negative stiffness enhanced TMD for seismic response mitigation of bridges isolated with friction pendulum system (FPS)

Abstract

Traditional seismic isolators, such as the friction pendulum system (FPS), exhibit high isolation efficiency during slight-to-moderate earthquakes, but their ability to constrain isolation deformations under severe earthquakes remains limited. The negative stiffness enhanced tuned mass dampers (NS-TMDs), which exist in two configurations (NS-TMD I and NS-TMD II), have been successfully employed to improve the seismic performance of isolated bridges. However, previous studies have focused primarily on the control performance of NS-TMDs in simplified linear systems, without considering structural nonlinearities. To address this gap, this paper explores the effectiveness of using NS-TMDs for the seismic protection of bridges isolated with a FPS, and proposes a stability-based optimization strategy for NS-TMDs. In particular, the working mechanism and mechanical model of NS-TMDs are first introduced. The control devices are integrated into a FPS-isolated single-degree-of-freedom (SDOF) system. For this system, the nonlinear equilibrium equations are formulated, and a stochastic linearization analysis is performed. Subsequently, a stability-based optimization strategy is proposed for NS-TMDs and their control performance under stationary excitation is examined. Finally, a comprehensive analysis on the control effectiveness of NS-TMDs in the FPS-isolated bridge under non-stationary excitation is conducted. The results show that the optimized NS-TMDs could enhance the isolation efficiency of FPS while effectively constraining isolation deformation within a limited range under both far-field and near-fault earthquakes. In addition, NS-TMD I demonstrates greater effectiveness in reducing deck acceleration than deck displacement, whereas NS-TMD II exhibits the opposite trend. Overall, NS-TMDs provide an effective vibration control solution for improving the seismic performance of FPS-isolated bridges.