Research On The Force Transfer Mechanism Of Joint Section Of Steel-concrete Composite Pylons

The steel–concrete composite pylons possesses several advantages such as good force performance,high material utilization,flexible design,efficient construction,and good economy owing to its simple structure.The joint section between the steel–concrete composite pylon column and concrete pylon column or bearing platform is a crucial component in ensuring a smooth transition of tower column stiffness and effective transfer of internal force.This paper presents a study on the force performance and transmission mechanism of the steel–concrete composite pylons joint section in a cable-stayed bridge with a steel–concrete composite structure in the anchorage area of the upper pylon column.The research findings were obtained through numerical simulation and theoretical analysis,and they are summarized as follows:Firstly,the engineering cases and structural details of completed and under-construction steel pipe concrete bridge tower bond sections in China were presented.The important design parameters of the steel–concrete composite pylon joint sections were summarized,and the similarities and differences of the force transfer structures between steel–concrete composite pylon joint sections and hybrid structure bond sections were discussed.The force characteristics of the connection members used in the steel–concrete composite pylon joint sections to transfer shear forces and the design points of the joint section in the construction stage and bridge completion stage were also highlighted.Secondly,the finite element model of the full bridge rod system and the refined finite element model of the joint section were established.The section load and cable force under the maximum axial force and maximum bending moment control conditions obtained from the full bridge rod system model were applied to the finite element model of the joint section to study the force performance of the components of the joint section.Thirdly,a reasonable simplified physical model,the "strip model," was employed to analyze the stresses of each component of the model under the action of axial pressure using the finite element method,in view of the structure and stress characteristics of the bond section.The mechanism of axial force transfer from the steel wall plate to the concrete in the bond section was obtained.Fourthly,the differential equations considering the slip at the steel-mixed interface of the bonded section were established using the elastic continuous medium layer method.The force boundary conditions and displacement boundary conditions applicable to the steel–concrete composite pylon joint section were given.And the formulae for the transfer length of the bonded section under pressure and the shear force of the joint were derived,which can be used in the interface shear design of the joint section.Lastly,a sensitivity analysis was conducted on the force transfer characteristics of the steel–concrete composite pylon joint section.The law of change of force transfer length and maximum slip of the joint section with the magnitude of axial pressure load,thickness of steel wall plate,thickness of concrete,and shear stiffness of the joint was presented.