Near-fault Seismic Response Analysis Of Long-span Bridges Considering Displacement Input

With the rapid development of China's high-speed railway,the proportion of bridges to passenger dedicated lines is gradually increasing,and the probability of train crossing bridges increases when the earthquake strikes.In recent years,large-span cable-stayed bridges have been rapidly developed and widely used in China,and their seismic performance has been widely concerned by the engineering community.Based on the theory of Train-Track-Bridge dynamic interaction and the latest research results of seismic engineering,this paper makes some analysis,research and Discussion on seismic response under uniform and non-uniform excitation.The main contents of this paper are as follows:(1)Taking multi-degree-of-freedom frame structure as an example,El-centro wave is selected as the excitation source of seismic wave,and the influence of traveling wave effect on structure is discussed.The results show that the traveling wave effect does have an important influence on the dynamic response of long-span structures,which is mainly reflected in the time-history curves of displacement,velocity and acceleration.The trend of the figures is basically the same,but the values of the corresponding positions vary greatly.(2)The full bridge model of Yujiang double-track super-large bridge is established by ANSYS finite element software.According to the mechanism of acceleration method and large stiffness method,the model constraints are modified,and the modal analysis of both models is carried out.The 500 order modes are extracted by Block Lanczos method.The results show that the higher order modes still play an important role in the long-span bridges,but only a small number of low order modes are selected to calculate,which has a great influence on the error of the calculation results.Therefore,it is necessary to introduce the equivalent mass and cumulative mass fraction of the modes for the seismic design of long-span structures.(3)Taking El-centro wave as seismic excitation source,considering the influence of different shear wave velocities on the structure of cable-stayed bridge,the displacement and internal force responses of key parts of bridge structure under 14 working conditions are analyzed and calculated.The results show that the change of shear wave velocity will change the stress of the whole bridge structure,and the effect of traveling wave effect on the displacement of bridge structure becomes more obvious with the decrease of shear wave velocity.(4)Based on the full-bridge model of long-span cable-stayed bridge,the dynamic response of train-bridge system is analyzed under different vehicle speeds without seismic action,and the influence of train speed on train operation safety is studied,and the safe and reliable train operation speed is determined to be 350 km/h.The near-fault seismic motion is the main excitation source,and the track excitation of bridge structure is considered,and the non-linear time history analysis method is adopted.The traveling wave effect,the ratio of vertical to horizontal peak acceleration V/H and the ratio of horizontal peak acceleration to horizontal peak acceleration PGV/PGA are analyzed.With the increase of V/H ratio,the dynamic response of key parts of bridge structure decreases in varying degrees.In addition,with the increase of PGV/PGA,the dynamic response of key parts of bridge structure increases in varying degrees.