Study on interface bond behavior of high strength concrete filled square steel tube after high temperatures

In order to reveal the bond-slip behavior of high strength concrete filled square steel tube (HSCFST) experiencing high temperatures, a total of 17 high strength concrete filled square steel tube specimens were designed for push out test and the load-slip curves of the whole process and parameters of feature points were obtained from the experiments. The parameters of concrete strength, temperature and bond length were considered to research their influences on bond strength of HSCFST. Based on test mechanism analysis, the bond-slip constitutive formula of HSCFST experiencing high temperatures was put forward. Test results show that the shape of load-slip curves at the loading ends and free ends are similar. The bond strength of HSCFST is proportional to the anchoring length, and increases first and then decreases partly with the increase of the constant temperature. The bond damage of specimens with lower constant temperature develops earlier and faster than the specimens with higher constant temperature. The energy dissipation capacity of the bonding interface is generally enhanced with the increase of concrete strength, but is roughly a downward trend with increasing temperature. The strain and stress of square steel tube presents exponential distribution, and decreases from free end to load end.