Dynamic Characteristics And Seismic Analysis Of Long Span Deck Concrete Filled Steel Tubular Truss Arch Bridge

Concrete-filled steel tube arch bridges have been widely used in most areas of China because of their light weight,high strength,good ductility,fatigue resistance,and impact resistance.And with the maturity of construction technology in China,the construction span of the bridge type is also increasing,so it is an urgent task to study the seismic response law and destruction mechanism.Based on relevant research at home and abroad,this paper takes the world’s largest span-type concrete-filled steel tube arch bridge-Da Xiaojing Super Bridge as the engineering background and uses the finite element software Midas/Civil to build a finite element calculation model of the bridge,and analyzes its dynamic characteristics.The effects of the changes in the stiffness of different members,the number of cross braces and the structural form of the cross braces on the dynamic characteristics of the bridge were discussed,and then the response spectrum method and time history analysis method were used to analyze the seismic response of the bridge.Finally,the influence of traveling wave effect and damping ratio on the seismic response of the bridge is considered,and the seismic response results of response spectrum method and time history analysis method are compared.The results obtained show:The fundamental frequency of the bridge model is small,the vibration mode distribution is relatively dense,the overall is flexible,and the torsion and bending resistance is strong;The change of arch rib stiffness has a great influence on the vertical vibration of this type of arch bridge.The stiffness of the cross braces has a greater influence on the lateral vibration and structural torsion of this type of bridge.The stiffness of the bridge deck mainly affects lateral vibration and torsion,but the overall impact is less than that of arch ribs and cross braces.And as the number of cross braces increases,the fundamental frequency and stiffness of the bridge continue to increase.At the same time,comparing the cross braces of various structural forms,it is found that the M-shaped cross braces are better than the X-shaped cross braces and K-shaped cross braces;The seismic action along the bridge mainly affects the longitudinal and vertical vibration of the bridge,as well as the vertical shear and transverse bending moment of the bridge.The seismic action of the transverse bridge mainly affects the transverse vibration of the bridge,as well as the transverse shear force,torque and vertical bending moment of the bridge.The seismic action of the vertical bridge has little effect on the displacement of the bridge,mainly affecting the axial force of the bridge.The maximum longitudinal displacement of the main arch ring generally occurs at the 1/4L arch rib,and the maximum lateral displacement and vertical displacement generally occur at the vault.The maximum axial force,transverse shear force and vertical bending moment of the main arch circle generally occur at the arch foot,and the maximum value of vertical shear force,transverse bending moment and torque generally occur at the arch top;The influence of the traveling wave effect on the seismic response of the structure has a great relationship with the seismic wave velocity.When the wave speed is small,the time lag effect is large,at this time,except for the vertical shear force,torque and transverse bending moment of the vault,the other responses generally showed an increasing trend,especially the structural displacement response increased more;The reduction of the structural damping ratio has little effect on the seismic response of the bridge’s 1/4L arch rib,and a greater impact on the seismic response of the arch top and arch foot;Under the action of the bridge direction,the response spectrum result is similar to the time history analysis result,under the action of the horizontal bridge direction,the response spectrum result is greater than the time history analysis result,under the action of the vertical bridge direction,the time history analysis result is greater than the response spectrum result.