A study on a MR damping system with lumped mass for a two-span bridge to diminish its earthquake-induced longitudinal vibration

This paper examines the effectiveness of a MR damping system with lumped mass for a longitudinal vibration control of two-span bridge, preventing spans from pounding each other and mitigating its seismic responses when earthquake-induced load is inflicted. The MR damping system with lumped mass proposed in this study it was constituted by three components: a MR damper (30 kN) which connected two spans of a bridge and two spans themselves made different mass and stiffness. Its function was designed to impose an effective check on relative displacement and pounding. In order to prove its effectiveness, a two-span bridge (8.3 m long) was constructed with a MR damper installed beneath the two spans. First, a mathematical model of the bridge was derived; also, a model of the MR damper was verified through a separate test on its performance. Next, shaking table tests were carried out by inflicting 150% of El-centro earthquake and 60% of Kobe earthquake to see how effective the system would be in mitigating seismic responses. All the tests were done under various conditions (un-control, passive off, passive on, Lyapunov control, and Clipped-optional control) in order to closely examine and analyze under which condition mitigation could be maximized and how mitigation could be effected. As a result of the tests, it was found that the MR damping system with lumped mass was effective in preventing two spans from pounding each other and its active performance decreased the relative displacement of the bridge structure. Therefore, it was proven to be effective in attenuating the seismic responses of two-span bridge in longitudinal direction.