Experimental study of bond behavior between concrete-filled steel tube and UHPC-encased

Abstract

This paper examines the bond behavior between steel and ultra-high-performance concrete (UHPC) in members made of UHPC-encased concrete-filled steel tubes (CFST). For the push-out test, a total of ten UHPC-encased CFST specimens, eight normal concrete-encased CFST specimens, and two CFST specimens were designed. The specimen parameters considered for variation include steel fiber content, thickness of the steel tube, anchorage length, thickness of outer concrete, and concrete type. Through experimental observation and measured data, the force failure process and crack development pattern of the specimens were observed, and load-slip curves were obtained for the loading end and the free end. A comprehensive analysis was conducted to examine the influence and mechanism of different parameters on the bonding performance of the specimens. Furthermore, an equation was derived to calculate the bonding strength at the interface between the steel tube and the outer concrete. The findings reveal that both UHPC-encased CFST and normal concrete-encased CFST specimens exhibited bond-anchorage failure, with the load-slip curve exhibiting a sudden change at the peak value, indicating a high degree of brittleness. The bond strength between steel and outer UHPC was found to be twice that between steel and core UHPC, and 1.4 times that between steel and outer normal concrete. Increasing the steel fiber content and the thickness of outer concrete within a certain range effectively improved the bonding performance of the specimens. The thickness of the steel tube did not have a significant effect on the bonding performance of UHPC specimens. Additionally, when the anchorage length reached a certain value, further increases did not significantly enhance the bond strength. Moreover, the influence range of the steel tube's anchorage length and outer UHPC on the bonding performance was smaller compared to outer normal concrete.