Negative stiffness enhanced tuned mass damper (NS-TMD) for seismic induced response mitigation of isolated bridges

Abstract

Seismic isolators have been extensively utilized in the field of structural vibration control due to their superior control effectiveness in reducing absolute acceleration responses. However, this effectiveness comes with a compromise on large isolation deformation, which may result in various issues, such as pounding and/or unseating damages of bridge decks. To address these issues, a negative stiffness enhanced tuned mass damper (NS-TMD) was proposed, aiming to minimize absolute acceleration while simultaneously limiting isolation deformation, and its control effectiveness has been demonstrated. However, the previous studies primarily focused on single-objective optimization without considering NS-TMD stroke, and the conventional negative stiffness (NS) devices, e.g., the pre-compressed helical springs with revolute joints, could not be well compatible with NS-TMD due to limited operating range. To this end, this study proposes a novel NS-TMD, which consists of a TMD with a curved-type mass block and an NS element based on a cam-roller-spring (CRS) mechanism. The working mechanism of the novel NS-TMD is first introduced, and its mechanical model is formulated. This novel system is then applied to a typical isolated bridge to illustrate its control effectiveness. Equilibrium equations and state space formulations of the system are derived. Subsequently, parametric analysis on NS-TMD is performed, followed by the proposal of a multi-objective optimization strategy to simultaneously minimize the relative displacement of the bridge deck and the stroke of NS-TMD. Finally, the control performance of NS-TMD is systematically evaluated. Numerical results show that the optimized NS-TMD not only reduces the deck displacement of the bridge system (with a maximum reduction ratio of 49.50 %) but also decreases its absolute acceleration. Furthermore, NS-TMD can achieve superior control performance in terms of the deck displacement, while limiting the stroke within a reasonable range. In summary, NS-TMD is a highly efficient alternative to conventional TMDs in terms of control effectiveness and feasibility.