Push-out tests of concrete-filled stainless steel SHS tubes

A total of 32 push-out tests were conducted in this paper on concrete-filled stainless steel square hollow section (SHS) tubes with different values of height-to-width ratio, width-to-thickness ratio and concrete strength. 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. Shear failure loads of bonding slip and the interface friction resistance generally decreased with more loading cycles of the repeated push-out test employed in the same direction. It can be concluded that 70% of the bonding strength at the interface was taken by the friction force of the interface elements, while the remaining 30% of the bonding strength at the interface was sustained by the chemical adhesive force and the mechanical interlock force. Furthermore, the strains at the locations close to the free end and loading end of the specimens increased with the increase of the axial load, in which the increase of the strains at the location close to the free end is much greater. On the other hand, it is demonstrated that the height-to-width ratio and the width-to-thickness ratio of the stainless steel SHS tube have insignificant influence on the shear resistance of the bonding strength of the interface elements, which generally decreased with the increase of the concrete strength. In addition, the current design rules of concrete-filled carbon steel SHS tubes were found to be inapplicable to the shear resistance of the bonding strength of concrete-filled stainless steel SHS tubes.