Study on the bonding performance of ultra-high-performance concrete with stainless steel circular tubes

To investigate the interfacial bonding performance of ultra-high-performance concrete (UHPC) confined by stainless steel circular tubes, twelve stainless steel circular tube UHPC short column specimens were designed and fabricated, followed by repeated push-out tests. The load-slip curves of the specimens were obtained, and the components of the bonding force between the steel tube and concrete, as well as the effects of slenderness ratio and width-to-thickness ratio of the steel tube on the bond strength, were analyzed. The entire degradation process of bonding performance was divided into four stages: crack initiation, crack propagation, crack penetration, and complete slip. Temperature was found to influence the shape of the bond stress-slip curve. In the first push-out test, the bond stress-slip curve under low temperatures exhibited a higher peak and a more pronounced ascending trend in the stable phase compared to that under normal temperatures. In multiple push-out tests, the decrease in the bond stress-slip curves of the first and subsequent push-out tests at low temperatures was more significant than that at normal temperatures. Low temperatures significantly increased the ultimate bond strength of the stainless steel circular tube UHPC. A formula for calculating the ultimate bond strength of the stainless steel circular tube UHPC was proposed, based on the UHPC steel fiber content, geometric parameters of the stainless steel tube, and temperature. ABAQUS was used to simulate the entire experimental process, and the results were compared and validated against the bond stress-slip curves from the push-out tests.