Study of the UHPC–NC Interfacial Bonding Properties of Steel Tubes with Internally Welded Reinforcement Rings

Ultra-high-performance concrete (UHPC) has the advantages of high strength, excellent durability performance, etc., and its compressive strength is several times that of normal concrete (NC). Due to the role of materials such as steel fibers, the tensile strength of UHPC is higher than that of NC. For steel-tube concrete columns in corrosive seawater environments, UHPC–NC columns with welded ring reinforcement inside the steel tube are proposed to strengthen the interfacial bonding performance, and the effects of seawater corrosion of steel-tube concrete are studied. Eight steel-tube UHPC–NC specimens were designed for push-out tests. The steel tubes were internally constructed with glossy unconstructed and reinforcing rings, with the core concrete with UHPC used below and the C40 plain concrete used above. By examining push-out load, slip displacements, and steel-tube wall strains, this study analyzed the influence of different factors on the bond behavior and failure mechanism of bond-slip in shear-resistant reinforcing ring connectors. The push-out simulation of the steel-tube concrete was carried out using ABAQUS 2021 software, and the simulation results were compared with the experimental results, which showed good agreement. The results show that the bond strength of the steel tube–concrete column interface can be significantly improved by using the construction measures of internally welded reinforcement rings; for specimens with the same percentage of core concrete UHPC and C40 thickness, the bond strength of the two rings was significantly improved by approximately 33% over that of the one-ring reinforcement ring; corrosive environments will degrade the bond strength of the steel tube–concrete column interface.