Mechanical properties of an innovative steel-concrete joint for high-speed railway long-span hybrid girder cable-stayed bridges

This study investigates the mechanical properties of an innovative steel-concrete joint (SCJ) in a four-line long-span high-speed railway hybrid girder cable-stayed bridge with a main span of 672 m. Tests were conducted on a partial 3:8 scale model, supported by nonlinear finite element analysis (FEA), and the results of both were used to derive and validate mathematical formulae for bearing plate force transfer. The results revealed an uneven transverse distribution of stress in the SCJ, with a larger stress observed in the edge box. The non-uniformity coefficient lambda i is defined as the ratio of the absolute maximum stress to the transverse cross-sectional average at a given location, and lambda i,max of steel and concrete in the SCJ were 1.59 and 1.68, respectively. Drastic stress changes appeared in the bearing plate in the longitudinal direction. The maximum measured slip was relatively small, indicating that the steel and concrete in the SCJ functioned cooperatively. Concrete cracks observed in physical tests were mainly distributed in the edge box of the steel and concrete segments, revealing the superior force performance of the SCJ compared to the steel and concrete segments. The deformations of the SCJ changed elastically with an increasing load and satisfied Chinese standards. The bearing plate transferred approximately 59.92% of the axial force and dominated the force transfer. Formulae for the force transfer of the bearing plate were derived based on the stress characteristics of the innovative SCJ, revealing that, rather than its thickness, the bearing plate mainly relied on welds connecting the top and bottom plates and ribs to transfer force. Parameter analysis of the weld sizes of the bearing plate based on the derived formulae and FEA indicated that a reasonable thickness of the bearing plate is 38-60 mm, based on the matched weld sizes. The SCJ structure, the formulae for bearing plate force transfer, and the optimal bearing plate thickness can serve as valuable references during the initial design phase of SCJs.