Structural Evaluation of Steel–Concrete Joint with UHPC Grout in Single Cable–Plane Hybrid Cable-Stayed Bridges

In order to investigate the mechanical behavior of the steel–concrete joint with ultrahigh performance concrete (UHPC) grout in single cable–plane hybrid cable-stayed bridges, a model test with a scale of 1:3 for a hybrid girder consisting of a flat steel box girder, a prestressed concrete (PC) box girder, and a steel–concrete joint connecting the steel and prestressed concrete girders was conducted. Structural responses of large-scale specimens under combined actions of axial compression, bending, and twisting moments are presented and discussed. Experimental results indicated that steel–concrete joints with UHPC grout exhibited favorable combined behavior and adequate strength. Under a maximum applied load that is twice as much the design load, the system components, including surface plates/slabs, UHPC, perforated webs, and perforated rebars, behaved within the elastic range. Stresses generated at the steel–concrete joint were mainly determined by axial and flexure forces. The influence of torsion on joint behavior was insignificant. It was also shown that approximately 65% of the overall force transferred through the steel–concrete joint was in the form of compression effects between the bearing steel plate and UHPC, and that the remaining 35% force was dispersed via shear connectors. Furthermore, finite-element (FE) models were developed and calibrated with the experimental results. The numerical results indicated that load transferred via the bearing plate compression effect gradually increased with the steel cell height. The outcomes of this study provide a reference for future application of the steel–concrete joint with UHPC in hybrid girder bridges.