Study On The Mechanical Behavior Of The Steel-concrete Joint Section Of A Large Span Continuous Rigid Frame Rail Bridge

Long-span continuous rigid frame bridge has many advantages such as convenient construction,smooth driving,large torsional and bending stiffness,etc.As a result,the bridge was widely adopted.To achieve greater span ability,with the method of the steel-concrete bonding beam,however,the steel-concrete joint in some difficulties existed in the design and construction,such as complex structure,the internal stress distribution is not clear,the steel and concrete between the two materials key problems such as power transmission mechanism is not clear,therefore,it is necessary for the steel-concrete joint of tectonic characteristics,stress distribution,force transmission mechanism research.In this paper,on the basis of the investigation research status at home and abroad,relying on the world’s largest continuous rigid frame bridge across the tracks-the first phase of the Chongqing rail transit line 9,ka wah jialing river special bridge orbit,carried out the steel-concrete combined with reasonable structure,the overall stress state and local power transmission mechanism and the factors influencing the mechanical behavior of the theoretical and applied research,verify the rationality of the connection structure between steel members and concrete in the steel-concrete joint section,clear the stress of steel members and core concrete in steel-concrete joint section,reveal the internal force distribution principle and force transfer mechanism of the two materials in the steel-concrete joint,Finally,a method for analyzing the mechanical behavior of steel-concrete joint of continuous rigid frame bridge is developed.The main research contents of this paper are as follows:(1)On the premise of summarizing the structural form of the steel-concrete joint and the basic theoretical research of the joint,the force transfer mechanism of the structural form of the rear bearing plate in the steel-concrete joint is analyzed.The results show that,under the external load,the internal force of the main girder passes through the transition section of the steel box girder,and the internal force of the steel-concrete combination section is mainly borne by the roof plate,floor plate and bearing plate.Then the internal force is transferred to the concrete in the steel lattice room through the welded nail joints,the open-hole plate joints and the prestressed steel bars,and finally to the concrete box girder to complete the internal force transfer.The analysis provides a theoretical basis for the subsequent study of stress distribution and force transfer ratio.(2)In order to better reflect the stress state and stress transfer effect of the steel-concrete composite section,the most unfavorable load condition of the control section of the steel-concrete composite section was extracted,the local model of the steel-concrete joint section is established by using the general finite element software ANSYS.The results show that the Von-Mises stress of the bearing plate is 179.34 MPa,and the normal stress of the roof is 47.21 MPa.The other steel members are all in the yield strength of steel,the tensile strength of concrete can be improved by adding Steel Mesh in some areas at the junction of concrete and steel structure.The research on the effect of stress transfer can be divided into the transverse stress distribution and the vertical stress distribution.The finite element analysis shows that the transverse stress distribution is uniform and the transfer effect is good except the stress fluctuation at the steel-concrete interface,the vertical normal stress distribution along the bridge varies linearly in the vertical direction,which reveals the good deformation ability of the joint section and satisfies the plane section assumption.(3)In order to reveal the steel combined section as a whole and detail components of force transmission ratio and internal force distribution principle,the finite element software ANSYS for the steel combined section as a whole and the detail components are analyzed respectively,studies show that after the analysis of whole structure,300 mm cross section in the concrete bending moment accounted for 39%,61% of steel structure,as far away from the bearing plate,concrete full bending moment;After the analysis of the detailed components,the bending moment ratio of the web at the 300 mm section was up to 26%.The bending moment ratio of each plate gradually tends to 0 because it is gradually away from the pressure plate.(4)In order to analyze the influence of all kinds of external factors on the ratio of transmission force and the principle of internal force distribution in the combined section,three influencing factors including the length of the combined section,the amount of prestress loss and the change of axle weight of the train are considered from the aspects of self-structure,construction technology and the application of live load.The results show that 1.5m long section has the best transmission effect with the smallest fluctuation compared with 2.5m and 2.5m.With the increase of the prestress loss and the axle load of the train,the bending moment will be transferred from the roof and web to the shear plate and the bottom plate.In order to improve the force transmission effect of similar Bridges and optimize the mechanical behavior of structures in the future,appropriate section length,improved construction technology should be selected in the design and construction to control the prestress loss and consider the sufficient axle load of the train.The research results of this paper can provide a positive reference for the design of track continuous rigid frame bridge with steel-concrete composite beams.