Spatial Seismic Response Analysis And Seismic Isolation Study Of Long Span Continuous Steel Truss Flexible Arch Bridge

Earthquake is a kind of natural disaster with great destructive force,sudden strong and devastating.With the continuous development of traffic and transportation,The long-span bridge structure has been widely built in railway and highway,This kind of bridge has become the lifeline of connecting transportation and national economy,and has a very important role,Therefore,it is necessary to study the seismic design of the long-span bridge.In this paper,the Yinchuan airport the Yellow River special bridge,a large span continuous steel truss flexible arch bridge,is used as the engineering background.The basic theory of seismic response analysis based on the multi-degree of freedom spatial structure system,Using ANSYS to establish the spatial finite element model,The dynamic time history analysis method is used to analyze the seismic response of bridge under the uniform input of seismic wave,traveling wave effect and multi-point input,Finally,the study on the bridge isolation design is carried out to provide some reference value for the seismic design of similar bridges.The main research contents are as follows:(1)The three-dimensional finite element model of the whole bridge is built by ANSYS.By means of lumped mass method,the dynamic characteristics of the structure are analyzed by SUBSPACE method,and the vibration mode and natural period of the bridge are obtained.The finite element analysis shows that the fundamental frequency of the bridge is 0.69097 Hz,showing the first longitudinal drift of the structure.The latter modes are shown as transverse bending of the structure,which indicates that the lateral stiffness of the bridge structure is small,which is worthy of attention in the design(2)Under the uniform input of seismic waves,the peak value of the axial force and the moment of main truss appears near the arch foot and the side pier.The peak value of the lateral displacement of the arch rib appears on the cross section of each span,and the peak value of the longitudinal displacement varies slowly along the length of the bridge,and it is zero at the fixed support pier.Lateral excitation has great influence on lateral displacement,and has little effect on longitudinal displacement.Longitudinal excitation has great influence on longitudinal displacement,and has little effect on lateral displacement.Vertical excitation has little effect on horizontal displacement.The influence of seismic wave combined input on internal force of structure is larger than that of unidirectional input.It is suggested that the seismic spatial characteristics should be fully considered in the aseismic design of long-span continuous steel truss arch bridge,and the lateral stiffness of bridge will be increased,and the structural design of arch foot and side pier should be optimized.(3)The influence of seismic wave traveling wave input and multi-point input on bridge structure is complex and changeable,and it has great influence on internal force and displacement of long-span bridge structure.The axial force of the arch foot is most unfavorable with multi-point input,and the axial force of the arch foot is 1.685 times as much as that of the same input,The outer bending moment of the beam is the most unfavorable in the traveling wave input,which is 1.267 times as much as the uniform input,The longitudinal displacement of the middle joint of the vault and main truss is the largest and multi-point input under traveling wave input.The minimum value of the maximum input and the minimum value is 2.829 times and 2.854 times that of the main truss,Therefore,the time and space of seismic waves must be considered when designing long-span bridge structures.(4)Introducing the vibration isolation support can prolong the self vibration period of the structure and effectively reduce the response of the bridge structure under the earthquake load,The maximum shock absorption rate of the axial force of the arch ribs can reach 86.25%,The maximum shock absorption rate of bending moment of pier bottom and shearing of pier top can reach 86.30% and 87.13%,The maximum displacement's shock absorption rate of top of arch rib and the middle of the vault and main truss can reach 66.40% and 66.40%.With the damping coefficient and the stiffness ratio of the bearing before and after yield,the shock absorption rate increases,and finally tends to be slow.The mechanical parameters of the isolation bearing support have the optimal value,In the design of seismic isolation bearings,the selection of the mechanical parameters of the support should be paid attention to,which makes the most effective and economical reduction of isolation effect.