Experimental and numerical studies on mechanical behavior of stiffened concrete‐filled square steel tube columns subjected to axial compression

In this study, nine square concrete‐filled steel tubular (SCFST) columns considering longitudinal stiffeners as parameters were produced to investigate the axial compression mechanical properties of SCFST columns in the condition of constant steel consumption. This included one specimen without stiffeners, three specimens stiffened with one stiffener on each tube wall, two specimens stiffened with two stiffeners on each tube wall, two specimens stiffened with three stiffeners on each tube wall and one specimen stiffened with four stiffeners on each tube wall. Simultaneously, numerical simulations were performed under identical conditions using ABAQUS software. The results showed that the longitudinal stiffeners can act as an out‐of‐plane restriction support to delay the development of local buckling of the steel tube, which indirectly improved the constraint effect of steel tube on core concrete. First, both the number of local buckling and the ultimate displacement of the specimens grew correspondingly when the number of stiffeners increased. As the sub‐wall width‐to‐thickness ratio was increased, the steel tube became prone to local buckling. Second, the installation of stiffeners decreased the confinement effect of steel tube on the core concrete, in which the sub‐wall width‐to‐thickness ratio and the stiffener width‐to‐thickness ratio had a great influence on the ultimate bearing capacity of the specimens. Further, the experimental outcomes indicated that the bearing capacity of stiffened specimens was less than that of the unstiffened specimen. The bearing capacity of the specimens stiffened with three and four stiffeners was higher than that of the specimens stiffened with one and two stiffeners. Third, the stiffener width‐to‐thickness ratio had a considerable impact on the ductility of the specimens. The ductility of specimens stiffened with one and two stiffeners was greater than that of the specimens stiffened with three and four stiffeners. Finally, the finite element simulations were consistent with the experimental process. The confinement factor of stiffened specimens became enlarged when either the number of stiffeners in the same thickness condition increased or the thickness of steel tube wall under condition of the same number of stiffeners grew.