A Study On Longitudinal Seismic Responses Of LRB Isolated Continuous Girder Bridge Subjected To Near-fault Ground Motions

The Lead Rubber Bearings(LRB) have been used widely because of it’s good isolation effect. However the near-fault ground motions have several characteristics such as rupture directivity effect, hanging wall effect and velocity pulse effect, which may influence the isolation effect of the LRB isolated bridge. It has important practical significance to study the seismic behaviors of the LRB isolated continuous girder bridges subjected to near-fault ground motions. The main contents are as follows:(1)Based on related status reading of literatures home and abroad, the current related research status on near-fault ground motions, seismic isolation technology, effect of rail restraints and restrainer devices are summarized.(2)A scheme of seismic response reduction was proposed, in which LRB isolation bearings installed at main piers to reduce the longitudinal internal force of the fixed pier. To study the vibration-suppressing effect of LRB isolation bearings, a dynamic analytical model was established by OpenSees software. The results show that the LRB isolation bearings can reduce fixed piers’ internal force remarkably and maximum amplitude is reduced to 76.12%.(3)The research demonstrate that the characteristics of the near-fault ground motions include rupture directivity effect, hanging wall effect and velocity pulse effect, can amplifies the longitudinal seismic responses of LRB isolated continuous girder bridge differently, in which the effect of velocity pulse is largest, rupture directivity effect is larger and hanging wall effect is the smallest.(4)A model of rail-bridge to study the impact of railway on the longitudinal seismic response of LRB isolated continuous girder bridge was established. And two load cases, the vertical live load and non-live load is analyzed. The results indicate that the rails can reduce the seismic response of LRB isolated bridge and maximum amplitude is reduced to 25.50%. In addition, the vibration reduction of rails on vertical live load is bigger than non-live load.(5)Although the isolation effect of the LRB isolated bridge is higher, the displacement of girder is larger. The best way to reduce the displacement of girder is installing the viscous damper in the pier-girder connections of side pier. The principle of choose proper viscous dampers parameter is given. The results show that the girder displacement decrease significantly, the internal force of main piers decrease slightly and the side pier work in the elastic status all the time.