Study On Seismic Behavior Of Steel Truss Cable-stayed Bridge With High And Low Pylons Of Double Layer Four-line Railway

Railway communication plays an important role in China's comprehensive communication system.In recent years,with the construction of high-speed railway network,long-span cable-stayed bridges are increasingly used in railways.Seismic calculation and analysis is an important part in bridge design and Seismic design determines the ability of bridges to resist earthquakes.In the seismic code of highway or railway engineering,there is a perfect calculation theory and method for seismic design of reinforced concrete bridges with small span,but only the main points and principles for the long span bridges.In this paper,based on steel truss girder cable-stayed bridge for high and low pylons,the appropriate supporting system is studied and influencing factors of seismic action are analyzed.Finally,the seismic reduction and isolation measures for high level earthquakes are explored and the seismic checking calculation for the three seismic levels is carried out.The main content includes the following aspects:(1)Based on the supporting project of a Yangtze river bridge on the east ring line of chongqing,the seismic conceptual design method of the railway cable-stayed bridge is analyzed from the aspects of seismic type selection of the overall structure and seismic support system.The finite element software Midas /civil was used to establish the whole strut element model,the geometric non-linear and optimization of the cable force of the completed state are analyzed.(2)The structural system of railway cable-stayed bridge(supporting system,rigid frame system,semi-floating system)and its influence are discussed.The internal force and displacement responses of the three structural systems of railway cable-stayed bridges are analyzed considering the earthquake loads and the braking force loads,and the differences of the natural frequencies and modes of the three structures are compared.The results show that the rigid frame system is disadvantageous to earthquake resistance,the internal force and displacement of members are reduced under supporting system,and the semi-floating system is disadvantageous to the control of seismic displacement.(3)According to the characteristics of steel truss girder cable-stayed bridge of double deck four-line railway,the responses of main tower,main girder and bearing under the action of earthquake are analyzed by considering many factors,such as nonuniform excitation,influence of traveling wave effect,arrangement of spatial cable plane and non-equal high tower,etc.The results show that the non-uniform excitation and traveling wave effect have a great influence on the seismic response of long-span bridges,the cable-plane layout has an influence on the lateral seismic response,and the seismic internal force and displacement of high and low towers vary greatly.(4)Based on the dependent engineering,the sensitivity of the parameters of liquid viscous damper is analyzed,and the ideal parameters of viscous damper are put forward.The results show that the viscous damper can effectively reduce the internal force and displacement of the components,and the lock up device can partially reduce the internal force and displacement of the components.Three seismic levels were used to calculate the seismic resistance of the supporting project,the main tower and the auxiliary piers were in the elastic range in the case of low-level earthquakes,the steel ball bearings meet the bearing capacity requirements in the case of design earthquakes,and the tower remained basically elastic in the case of high-level earthquakes.