Research On Stress Mechanism Of Steel-concrete Joint Section Of Long-span Hybrid Girder Cable-stayed Bridge

The steel-concrete joint section is the transition section between the steel box girder and the concrete beam in a hybrid-beam cable-stayed bridge.Due to the changes in stiffness and cross-section at the joint section,problems such as local stress concentration and structural deformation inconsistency are likely to occur.At present,the research on the steel-concrete combined section of the hybrid-girder cable-stayed bridge is mainly focused on highway bridges,but less on railway bridges.Compared with highway bridges,railway bridges need to bear greater live loads,so the study of the force mechanism of their steel-concrete joints is of great significance.In this paper,using the method of finite element analysis,taking a large-span passenger and freight railway mixed-girder cable-stayed bridge as the research background,the force mechanism analysis of its steel-concrete joint section is carried out.The main research contents and results are as follows.(1)The CSB finite element analysis software was used to carry out finite element analysis of the entire bridge during the whole construction process,and the results of the internal force changes of the steel-concrete joint section during the entire construction phase were obtained,and the most unfavorable axial force,the most unfavorable shear force,and the most unfavorable bending force were summarized.Three load conditions of moment.And from the perspective of actual construction,the internal force change trend of the steel-concrete joint section under the synchronous construction of the tower beam and the asynchronous construction method of the tower beam is compared,and the results show that the steel-concrete joint section is changed from the asynchronous construction of the tower beam to the synchronous construction of the tower beam.The internal force changes little,and the change trend of internal force is similar.(2)The ABAQUS finite element analysis software was used to establish the local finite element model of the steel-concrete joint section,and the most unfavorable load conditions during the construction process were applied to it,and the stress and deformation laws of the steel structure and the concrete structure of the joint section were calculated and analyzed.The results show that in terms of stress,both steel structure and concrete structure have local stress concentration,but the overall stress is kept within the range allowed by the design,and the stress changes smoothly,and the overall force is relatively reasonable.In terms of deformation,the gentle deformation of the steel box girder-joint section-concrete beam proves the rationality of the design of the steel-concrete joint section of the bridge.In terms of force transmission,the bearing plate is the main force transmission member that transmits the axial force from the standard steel box girder to the concrete beam,accounting for 46.4%.(3)The structural parameters of the steel-concrete joint section were analyzed,the thickness of the bearing plate,the thickness of the top and bottom plates of the steel cell and the concrete strength were changed,and the changing trend of the force on the joint section was analyzed.The results show that the percentage of the axial force directly transferred to the concrete by the bearing plate increases with the increase of the thickness of the bearing plate,the strength of the concrete,and the thickness of the roof and floor of the steel cell.When the thickness of the bearing plate is 50-70 mm,the strength of concrete is C50-C70,and the thickness of the top and bottom plate of the steel grid is 24-28 mm,the force transmission of the steel-concrete joint section is more reasonable.