Study On The Seismic Response Of Bridge With Large Number Of Spans Considering Foundation-Structure Interaction

Bridge is an important component of traffic engineering project,and its seismic behavior has an important influence on the safety operation of the line and the earthquake relief work.However,many bridges have been damaged serious under some recent earthquakes,which cause direct economic losses and affect the traffic.In the strong earthquake,in addition to the direct damage of beam and pier,a large number of multi span simply supported girder bridge are dilapidated by the collision and girder falling caused by the excessive displacement of the beam end.In seismic analysis of the relative displacement of beam end,the coupling effect between beams and piers,,the dynamic interaction of pile-soil-structure,the traveling wave effect and the seismic spectral characteristics need to be synthetically considered.In the paper,simple algorithm of the bridge with a large number of spans(the number of the span of the QingShui bridge is more than 1000)is studied and the law of the seismic response is analyzed.The major work and conclusion are as follows:(1)The transfer matrix algorithm of the seismic response on simply supported girder bridge is proposed.Based on the calculation unit and the dynamic response state vector of it,a simplified analysis model of the multi-support excitation for the long numerous spans simply supported girder bridge is established,which can consider the influences of traveling wave effect and pile-soil interaction.With the formulas presented in this paper,the transverse and the longitudinal direction displacements and internal forces of the simply supported girder bridge with any spans can be calculated.Compared with the results of the numerical calculation,the method proposed in this paper is reliable.(2)Based on the transfer matrix method derived in this paper,the effect of earthquake type and wave velocity on the maximum seismic response of simply supported girder bridge is studied under the different structural parameters and the calculation program is compiled by author.Result shows that the seismic responses are varied with the change of the structure parameters such as span length and pier high,and the change rules are approximately the same with the different site soil stiffness.The decreases of the relative displacement between the beam and the pier are limited only by increasing the stiffness of the bearing.The trends of seismic response curve decrease at firstly and then increases with the decrease of site soil stiffness.Compared with the longitudinal results,the seismic responses of transverse bridge are seriously affected by the earthquake whose components are rich in the low-frequency.(3)Study on the length of coupling effect between the girders and piers of the long numerous supported girder bridge and the relationship between it and seismic wavelength.The seismic response of long numerous supported girder bridge with different wavelengths is analyzed and the maximum seismic response of the bridge appears cycles after a certain distance.Accordingly,the maximum seismic response of the whole bridge can be estimated by calculating the seismic response of the bridge in a certain distance.As the results of this paper,the required distance is 1500m or five wavelengths.(4)Analysis of seismic response of long numerous supported girder bridge under the multi span and single span model,and the feasibility of the seismic response calculated by single span model.The results show that,compared with multi span model,the internal forces of pier bottom and the relative displacements calculated by single span model are larger and the risks of collision and girder falling would be underestimated.However,the effects of the traveling wave effect on seismic responses under the single span model are little.