Study On Seismic Response Analysis Of Multi-span Long-span Seismic Isolated Continuous Beam Bridge

In recent years,the world is in an active period of earthquakes.As a lifeline project of earthquake relief,bridges will cause huge economic losses,casualties and serious disasters once damaged.With the vigorous development of infrastructure construction in China,the continuous girder bridge is widely used in practical engineering construction due to its advantages of convenient construction,reasonable force and smooth running,and is developing towards the direction of asymmetry and long-span.However,in order to reduce the effects of concrete shrinkage and creep and temperature effects,multi-span continuous girder bridges usually have only one fixed pier in one connection.When the longitudinal ground motion is applied,the horizontal seismic load is mainly borne by the fixed pier,which will cause the seismic response of the fixed pier to be too large,and it is difficult to meet the design requirements.At present,many scholars are committed to the research on seismic resistance of multi-span long-span continuous beam bridges,and have achieved a lot of research results,but there are still some problems to be solved.In this paper,the Haizi Lake Bridge(A 15-span asymmetric multi-span continuous girder bridge)is used as the engineering background to carry out research on earthquake resistance.The main work is as follows:(1)Read the relevant literature,summarize the commonly used bridge seismic design theory and seismic response analysis methods,and determine the suitable seismic measures and seismic response analysis methods for this bridge.(2)Based on MIDAS/Civil,the finite element model of the whole bridge is established.Considering the pile-soil-structure interaction,the multi-Ritz vector method is used to calculate the natural vibration characteristics of the structure.It is found that the natural vibration period of multi-span continuous girder bridges is much larger than that of similar ordinary continuous girder bridges.The first several modes of vibration are mainly the longitudinal translation of the whole bridge and the vertical bending vibration of the main girder.(3)Considering the influence of multi-directional earthquake,the dynamic time history analysis of multi-span continuous girder bridges with common bearings is carried out as a comparison of the results of seismic isolation structures.The results show that the response of the fixed pier is very large when there is longitudinal seismic action of the bridge,so the seismic isolation design must be carried out.(4)The design parameters of friction pendulum are calculated by parameter analysis.On this basis,the dynamic time history analysis of multi-span continuous girder bridge with friction pendulum is carried out.The results show that under the influence of friction pendulum,there are obvious differences between the structural response and the non-isolation structure,which are roughly as follows: horizontal two-way < three-way < horizontal one-way < horizontal one-way and vertical combination.(5)Taking the internal force of the pier bottom and the displacement of the pier top as the research object,the decreasing amplitude ratio is defined to evaluate the effect of friction pendulum isolation bearing.The results show that the response of the fixed pier decreases obviously after the friction pendulum bearing is installed,and the piers are loaded together,and the deformation is uniform.Within the allowable working range of the friction pendulum,with the increase of PGA,the vibration reduction and isolation effect of the friction pendulum is more obvious.(6)Based on the magnitude of apparent wave velocity and the direction of traveling wave action,the non-uniform excitation of multi-span continuous girder bridge with friction pendulum is analyzed by using the large mass method,and compared with the uniform excitation.The results show that the response of the control section is the largest when the apparent wave velocity is v=600m/s,and the closer to the calculation result of uniform excitation with the increase of the apparent wave velocity;In addition,the direction of traveling wave action will have a significant impact on the structural response,and the response of the side will increase significantly when the local vibration is input along one side.