Seismic Response Of Bridges Isolated By Combining With Buckling Restrained Braces And Lead Rubber Bearings

The seismic isolation design is an important way to reduce earthquake damage for bridges.In this paper,a bidirectional seismic isolation system with BRBs in the transverse direction of double-column bents and LRB in longitudinal direction of bridge is proposed.The BRBs between the double-column piers will yield first and consume energy to protect the piers and control damage by ”Fuse";the relative displacement reaction between the main beam and the piers in the LRB of the longitudinal direction of the bridge consumes seismic energy,which is the same as the conventional isolation design of the bridge.The structural models are established by Midas-civil software,including LRB isolated only in longitudinal direction of bridges,LRB isolated in both longitudinal and transverse directions of bridges,and BRBs together with LRB isolated only in longitudinal direction of bridges.The reaction of bridge pier was calculated by nonlinear time-history analysis,such as displacement drift ratios,residual displacement ratios and curvature ductility of pier bottom section.The deformation reaction of LRBs and BRBs reaction characteristics are also evaluated.Depend on the case analysis and comparison,the initial recognitions obtained as follows:(1)The bidirectional seismic isolation of bridges of by combing BRBs and LRBs has an obvious damping effect.Compared to the bridge which used LRB only in longitudinal direction,it can effectively reduce the plastic deformation of the piers and play a role in protecting the piers.In lateral direction of bridges,the maximum lateral displacement drift ratios,residual displacement ratios and the maximum curvature ductility coefficients of the columns are all significantly reduced.Compared to the bridge which used LRB isolated in both longitudinal and transverse directions,it overcomes the weaknesses of the transverse bridge expansion joints and stopper to reserve sufficient clearance or deformation capacity.(2)In the near-fault ground motions,the isolation bridge of BRBs with LRBs compared with isolation bridge of LRB only longitudinal,the maximum lateral displacement drift ratios are reduced by more than 30% to 40%.And it will not affect the LRBs longitudinal deformation.The isolation bridge of BRBs with LRBs compared with isolation bridge of LRB isolated in both longitudinal and transverse directions,the two bridges damping effect is similar.Compared with the bridge of increasing the piers strength,which use of HRB500 more high-strength steel,setting BRB to reduce the effect of seismic damage to the bridge is better.(3)From the BRB maximum axial nominal strain and hysteresis curve can be seen,setting BRB dampers,including herringbone braces and single braces,have good energy dissipation.BRBs can protect reinforced concrete piers in the far-fault or near-fault ground motions.Relatively speaking,BRB dampers should give priority to the use of herringbone brace.