Bond-slip behaviour of concrete-filled stainless steel circular hollow section tubes

This paper presents the repeated push-out tests on concrete-filled stainless steel circular hollow section (CHS) tubes with different values of height-to-diameter ratio, diameter-to-thickness ratio and concrete strengths. The bond-slip behaviour of all specimens and the strain distribution on the exterior of stainless steel tubes along the longitudinal height direction were carefully investigated. It was found that the shear failure loads of bonding slip decreased successively with more loading cycles of the repeated push-out test employed in the same direction. Hence, the mechanical interlock force and friction force of the interface elements gradually decreased. Furthermore, the bond-slip failure of the interface elements between the inner concrete and outer stainless steel tube of the specimens consists of the adhesive stage, the sliding stage and the friction resistant stage. It can be generally concluded that 70% of the shear resistance of the bonding strength is taken by the interface friction force, while the remaining 30% of the shear resistance of the bonding strength is sustained by the chemical adhesive force and the mechanical interlock force. On the other hand, it was demonstrated that the height-to-diameter ratio (H/D) and the diameter-to-thickness ratio (D/t) of the stainless steel tube as well as the concrete strength (C) have insignificant influence on the shear resistance of the bonding strength of the interface elements. It was also shown from the comparison that the current design rules of concrete-filled carbon steel CHS tubes are inapplicable to the shear resistance of the bonding strength of concrete-filled stainless steel CHS tubes.