Experimental investigation on mechanical performance and bearing capacity calculation of spiral stirrup-reinforced concrete-filled square steel tubular columns under eccentric compression

In order to investigate the mechanical performance of square steel tubular and spiral stirrup confined concrete columns under eccentric loading, eighteen specimens were prepared for eccentric loading test, including seventeen square steel tubular and spiral stirrup confined concrete columns and one conventional concrete-filled square steel tubular column. Six parameters were considered including the spacing of spiral stirrup, radius of spiral stirrup to side length of square steel tubular ratio, slenderness ratio, eccentricity ratio, longitudinal steel ratio and thickness of steel tube. The failure process and modes were observed and the load-deformation and load-strain curves were obtained, on the basis of which the influence of various parameters on the performance of specimens was discussed. The results show that square steel tubular and spiral stirrup confined concrete columns exhibit similar failure mode with conventional concrete-filled steel tubular columns. Spiral stirrups play an important role mainly in the elasto-plastic and descending stages, which can also improve the bearing capacity and ductility of the specimens, as well as delay the local buckling of steel tube. Meanwhile, the strengths of different materials can be fully utilized, and the deformation properties of the specimen decreases with the spacing of spiral stirrup. The eccentricity ratio and the thickness of steel tube have a significant effect on the bearing capacity, while the influence of other parameters is relatively small. Finally, two calculation formulas of the bearing capacity under eccentric loading were proposed, which both agreed well with the test results. © 2020, Editorial Office of Journal of Building Structures. All right reserved.