Nonlinear Seismic Response Analysis Of Long-span Continuous Isolated Bridges Under Strong Earthquakes

As an important transportation hub and lifeline engineering,the seismic performance of long-span bridges has always been the focus of attention in the field of bridge engineering.As one of the effective aseismic techniques,isolation technology has been gradually applied in the field of bridge engineering.The seismic response of isolated bridges is different from that of traditional non-isolated bridges because of their special isolation devices.The seismic behavior of isolated bridges under strong earthquakes has been a focus of attention.Based on this background,the friction pendulum isolation bearing is applied to long-span continuous isolation bridge,the seismic isolation effect,seismic performance and failure mode of the isolated bridge were studied under rare and extremely rare earthquakes,the effects of horizontal component,dimension and traveling wave of ground motion on seismic response of isolated and non-isolated bridges were researched under the strong earthquakes,the performance of these two kinds of structures was compared.The main research work of this paper is as follows:(1)The nonlinear finite element model of the whole bridge was established by Midas Civil software considering the nonlinear characteristics of the piers.The nonlinear time-history analysis method is used to verify the seismic isolation effect of isolated bridge.In this paper,the difference of bridge isolation effect is stueied under the fortification,rare andextremely rare earthquakes,and the influence of material nonlinearity on bridge isolation effect is revealed.The results show that the seismic isolation bridges have good seismic isolation effects under the ground motion of different intensities.Considering the material nonlinearity,the seismic isolation effect of bridges under rare earthquakes is the best,which is higher than that of fortification and extremely rare earthquakes.However,without considering the material nonlinearity,the seismic isolation effect of the bridge increases with the increase of the seismic intensity,which is obviously higher than that of the material nonlinearity.(2)The damage criterion of bridge is studied,and the curvature ductility ratio of bridge piers and the allowable displacement of bearing limit are determined as the damage index of bridge.The seismic performance of isolated and non-isolated bridges under rare and extremely rare earthquakes was quantitatively evaluated,and the differences of failure modes of the structures under earthquake action were analyzed.The results show that the seismic performance of isolated bridges under strong earthquakes is obviously higher than that of non-isolated bridges.The piers of non-isolated Bridges are damaged before the basin bearing,while the bearing of the isolated bridge is usually damaged before the piers,and the failure mode of these two kinds of bridges are under earthquake.(3)Considering the effects of two vertical horizontal components of ground motion and ground motion dimension on the seismic response of bridge structures,the most unfavorable input mode of ground motion is abtained by comparing the results of various nonlinear time-history analyses.Compared with unidirectional earthquake,the damage of nonisolated bridge piers is more serious than of the isolated bridge piers under bi-directional earthquake.But the isolation bearing displacement will significantly increase considering bidirectional seismic coupling effects.However,the vertical ground motion only has a certain effect on the axial force of bridge piers,but has little effect on the failure of non-isolated and isolated bridges.(4)Considering the material nonlinearity,the traveling wave excitation is carried out on the bridge structure,and the influence law of the traveling wave effect of ground motionon the seismic response of isolated and non-isolated Bridges is further studied.The results show that structural members at different locations of non-isolated and isolated bridges are affected by traveling wave effects to different degrees.Compared with the non-isolated bridge,the isolated bridge is relatively less affected by the traveling wave effect,the side piers of the isolated bridge is more affected by the traveling wave effect than the intermediate piers,and the traveling wave effect is beneficial to the intermediate pier.(5)In this paper,the difference of traveling wave effect between isolated and non-isolated bridge structures with or without material nonlinearity is studied.The results show that when material nonlinearity is taken into account,the bending moment of pier bottom of non-isolated bridge is less affected by traveling wave effect.Moreover,the deformation of the structure under earthquake will be underestimated without considering the material nonlinearity.However,the influence degree of the traveling wave effect on the isolated bridge is smaller than that without considering the material nonlinearity.