Axial compression behavior of high-strength recycled concrete filled steel tubular composite columns

To study the difference of the axial compressive performance of recycled concrete composite columns and ordinary concrete composite columns, the experiments of two high-strength ordinary concrete-filled steel tube reinforced concrete columns (CFSTRCC) and three high-strength recycled CFSTRCC were conducted under axial loading. The concrete type, cross-sectional shape of the steel tube and whether the cross-shaped tie bars were set or not in the square steel tube were chosen to be the main parameters. The experimental results show that the damage development process and failure modes of recycled concrete specimens are similar to those of normal concrete specimens. The bearing capacity and energy dissipation capacity of recycled concrete specimens are higher than those of the ordinary concrete specimens. However, it has serious spalling of concrete and poor ductility. When the set cross-shaped tie bars were installed in the square steel tube, the ductility has been significantly improved, and the bearing capacity and energy consumption have also been significantly increased due to the tie bar enhancing the restraint of the square steel tube to the core concrete. Meanwhile, the peak load corresponds to a larger peak strain, so the materials are more fully utilized. Under the condition of the steel tube equal cross-sectional area and close material strength, CFSTRCC with circular steel tube has higher bearing capacity, better deformation ability and stronger energy dissipation capacity than CFSTRCC with square steel tube. According to the relevant domestic and foreign regulations, the ultimate bearing capacity of 26 recycled CFSTRCC from this paper and other references were calculated. The results show that the calculation results for the axial compression bearing capacity of CFSTRCC are in well agreement with the experiment results.