Analysis Of Stability And Ultimate Load-bearing Capacity Of Concrete-filled Steel Tubular X-arch Bridge

The concrete-filled steel tubular truss X-arch bridge is a complicated structure,and the rib of arch bridge is a compression-bending member under load,so the stability problem of arch bride is prominent.In this paper,the full-bridge finite element model is established to carry out the structural linear elastic buckling and nonlinear ultimate loading-bearing capacity by finite element software based on the engineering background of the Huangshan Taiping Lake Bridge,Anhui Province.The effects of live load arrangement,arch rib inclination and other factors on linear elastic stability and ultimate bearing capacity are discussed.Because the bridge has been designed and built for more than a decade and the traffic flow is increasing,the bridge inevitably became aging and even caused some diseases.This paper further discusses the influence of typical diseased bridges on the ultimate bearing capacity of the bridge,mainly discusses the influence of suspenders’ broken and partial separation of arch rib section.The main research work and conclusions of this paper are as follows:1.The analysis of the structural linear elastic buckling of the spatial finite element model of the Taiping Lake Bridge is carried out based on four load conditions,the stability safety factor and the instability mode characteristics under four load conditions were obtained.The results show that the linear elastic stability of the bridge is in accordance with the requirements of the specification,and the unstable form is the out-of-plane anti-symmetric instability of the arch rib.The effects of arch rib inclination angle,arch rib stiffness and thickness of arch rib steel pipe on linear elastic stability is also discussed.The results show that the lateral stability of arch bridge can be improved by increasing inclination angle of the arch rib,but it will reduce the in-plane stability of the arch bridge.Moreover,the effect of excessive inclination of the arch rib on improving the lateral stability of the arch bridge is not obvious;increasing the stiffness of the arch rib and the thickness of arch rib steel pipe within a certain range can increase the stability of the bridge.2.The ultimate bearing capacity analysis of the Taiping Lake Bridge based on different nonlinear factors is carried out.The results show that the geometric nonlinearity has little effect on the ultimate bearing capacity,and the material nonlinearity has a great influence on the ultimate bearing capacity,and the double nonlinearity is the most suitable control factor in the ultimate bearing capacity analysis.Through the analysis of the loading process,the invalid path of the structure is clarified,under the influence of nonlinear factors,the first part of the bridge that is unstable is also the arch rib,the final loss of the bearing capacity of the structure is because the many places of arch rib enter the plastic stage and cause structure’s damage.This paper also discusses the effects of different live load arrangements and arch rib inclination angle on the ultimate bearing capacity.The results show that the eccentric arrangement of the live load will adversely affect on the ultimate bearing capacity of the arch bridge;the increase of arch rib inclination angle will reduce the ultimate bearing capacity of the arch bridge,cross wind load will also reduce the ultimate bearing capacity of the arch bridge,the moderate inclination angle of the arch rib can suppress declining of the ultimate bearing capacity caused by cross wind load by increasing the lateral stability of the bridge.3.Assuming the damage scenarios such as the suspenders’ broken and the partial separation of arch rib section,respectively,the ultimate bearing capacity of the bridge is analyzed.The results show that the single suspender is broken in the double suspender and the single double suspender is broken has little effect on the ultimate bearing capacity,but the ultimate bearing capacity of the structure will decrease with the increase of the number of broken double suspenders;the partial separation of the arch rib section will reduce the ultimate bearing capacity of the structure,and the larger the separation ratio of the arch rib section,the earlier the arch rib enters the plastic state,the smaller the ultimate bearing capacity of the arch bridge.