Research On The Seismic Behavior Of Suspension Bridge With Separated Girder And Tower

There has been a new type of suspension bridge structure in recent years the main girder of which is supported over the massif,not the main tower to adapt to canyon terrains in mountainous regions and make the bridge compatible and harmonious with the local terrain and environment reducing massif excavation.As a result of separating girder and tower,the length of girder is less than the distance between two main tower centers,meanwhile,the layout of cable system is altered accordingly leading to the change in some extent of the mechanical characteristics of bridge structure compared with conventional suspension bridges.There were few related structural theories about this kind of bridge before Aizhai Bridge in Hunan,Xiangxi which is the first formally built suspension bridge with separated girder and tower at home and abroad.In recent years,some detailed researches have been carried out on suspension bridge with separated girder and tower,including its structural property and seismic vulnerability etc.But there are some contents about this bridge type which deserve further analysis and supplement.The dynamic and seismic characteristics of suspension bridges with separated gieder and tower may be affected by the following three factors: the change in boundary conditions,the ratio of distance between end hangers to main span of bridge,the ground anchor wires.In this paper,the influence law of the above three factors on the seismic behavior of structures is studied on the basis of Aizhai Bridge,so as to provide some mentality for similar engineering proposal in the future.The main research contents are as follows.Firstly,the history,tendency and structure analysis theories of suspension bridge is introduced and the fundamental theories of structural seismic analysis and the finite element analysis method of suspension bridge vibration are summarized.Static structural analysis,dynamic analysis,initial equilibrium state analysis and finite element analysis are mainly elaborated to make theoretical preparations for modeling analysis.Afterwards,nine spatial finite element models of suspension bridges with different structure settings are established and their modal analysis and comparison are carried out.The influence of above three factors on the dynamic performance of suspension bridge is discussed by summarizing the differences of vibration characteristics between the three sets of models.The results also provide a reference for the dynamic time-history analysis of the bridge models.Finally,based on analysis settings including LMM,damping,earthquake wave and plastic hinge obtained by theoretical analysis and calculation,elastic and elastoplastic dynamic time-history analysis of the modals are executed respectively in longitudinal and transverse directions.The displacement and internal force response of different models are compared in order to obtain preliminary conclusions about the influence of the above three factors on the seismic performance of the suspension bridge with separated girder and tower.