Seismic Response Characteristics Of Long-span Railway Cable-stayed Bridge With Twin Towers And Double Decks

The railway construction in China has entered a new historical phase of development during the past few years.The long-span railway cable-stayed bridge has become an important choice to stride over wide rivers and grand valleys.At the same time,China suffers extremely serious earthquake disasters.For long-span bridges,the influence of traveling wave effect has attracted extensive attention.Existing researchs are concentrated on highway cable-stayed bridges.Studies on the railway cable-stayed bridges,especially which considering the effect of tracks,are blank.Therefore,with the emergence of such bridges,it is of great significance to systematically analyze the influence of traveling wave effect on the seismic response of long-span railway cable-stayed bridges.In this paper,the new Baishatuo Yangtze River Bridge of Chongqing-guizhou new railway line,was taken as a sample.This bridge,which adopts steel truss girder with double decks and bears six-line railways,is the world’s first railway cable-stayed bridge with the largest span and heaviest load.The finite element model of long-span railway cable-stayed bridge with twin towers and double decks was established based on the OpenSEES software.When the orbital constraint is considered or not,only the influence of longitudinal traveling wave effect on seismic response of long-span cable-stayed bridge was discussed.Meanwhile,the influence of transverse traveling wave effect on traffic safety was analyzed quantitatively.The main research work in this paper is as follows:(1)Detailed simulations of cables,tracks,steel truss girder,supports,towers and piers,pile foundations and pile-soil interaction were carried out.A comparison group of finite element models of cable-stayed bridges with or without orbital constraint was established and compared with the natural vibration periods given in the literature.The result shows that,to a certain extent,the period of natural vibration of the structure is reduced by the orbital constraint and the overall stiffness of the cable-stayed bridge is improved under the orbital constraint.(2)Seven strong motion records matching the response spectrum were selected from the PEER seismic database.The finite element model of cable-stayed bridge was excited by displacement input method,and only the influence of longitudinal traveling wave effect on seismic response of long-span cable-stayed bridge was analyzed by taking apparent wave velocity and phase difference as indexes.The results show that,under the influence of traveling wave effect,the seismic response of the bridge towers was reduced and the relative displacement between pier and beam was increased.When the phase difference of ground motion acting under the two towers changes,the moment at the bottom of the towers,the displacement at the top of the towers and the relative displacement between pier and beam show periodic changes.(3)Moment and displacement of towers,axial force of chords and relative displacement between pier and girder were taken as analysis indexs.Only the influence of longitudinal traveling wave effect on structural response,considering the orbital constraint,was compared and analyzed.The research shows that,when the orbital constraint greatly reduces the seismic response of the structure,under the influence of traveling wave effect,the displacement of the part above the upper beam and the moment of the part below the lower beam are reduced,and the dynamic response of other components is magnified.(4)The transverse displacement and the turning angle of tracks were taken as the index.Only the influence of the transverse traveling wave effect on the traffic safety on the bridge was assessed quantitatively.The research shows that,under the action of rare earthquake,the deformation of the track structure on the bridge does not exceed the specified limit of the standard,and it would not pose a threat to traffic safety.The transverse displacement of the track is reduced and the horizontal turning angle of the track at the corresponding position in the mid-span of the cable-stayed bridge is reduced and turning angles of other positions were increased by traveling wave effect.