Study On The Ultimate Bearing Capacity Of Long-span Half-through Steel Box Truss Arch Bridge

Taking a long-span half-through steel box truss arch bridge with the main span of 519 m as engineering background,the elastic stability,ultimate bearing capacity,and failure mechanism of the long-span half-through steel box truss arch bridge is studied in the paper.The main research contents and conclusions are as follows:1 The analysis of elastic stability on background project is curried under different load case to study the stability safety coefficient and instability mode.The results show that the most common instability mode of long-span half-through steel box truss arch bridge is out-plane toppling and out-plane antisymmetric bending-torsion instability.The juncture between arch ring and floor system is the weak area of stability.2 The influence from structure parameters on long-span half-through steel box truss arch bridge is discussed in the paper.The results show that diamond-shaped and Kshaped longitudinal bracing is the most suitable to improve stability.The oblique than the vertical hanger can improve the stability of inner surface,but reduce that of outer surface.The axial rigidity and out-plane flexural rigidity of the arch rib has a significant influence on in-plane stability and out-plane stability respectively.3 Based on the plastic zone theory and push-over function of midas/civil,the numerical model to solve the ultimate bearing capacity of long-span half-through steel box truss arch bridge is builded.In which the material nonlinear effect is considered through the elastic-plastic relation between force and deformation of cross section.The complete analysis considering geometric nonlinearity and material nonlinearity on background project is curried.The load-displacement curve and the gradual development situation of the plasticity of components is obtained.It shows that there experiences three stages in the whole failure process for long-span half-through steel box truss arch bridge,such as elastic stage,plastic zone extension stage,failure stage,4 Through analyzing the gradual development situation of the plasticity of components and the final distribution location of plastic zone,the results show that there are 4 plastic zones in the arch rib until limit state.And the plastic zones appear in the upper and bottom chords alternatively.The structure would be destroyed when the 4 plastic zones develop fully and the structure changes into geometrically variable system finally.5 The influence on the ultimate bearing capacity of long-span half-through steel box truss arch bridge from typical influencing factors is discussed in the paper.The results show that the material strength and the material nonlinearity has a significant influence on the ultimate bearing capacity.Comparied with out-plane geometric initial defect,the in-plane geometric initial defect affect the ultimate bearing capacity significantly.The construction planning influence the initial yield load coefficient only,and it has slightly influence on ultimate bearing capacity.The temperature and wind load has slightly influence on ultimate bearing capacity.