Mechanical properties of CFSST with steel reinforcement cage under biaxial eccentric compression

To study the biaxial eccentric compression mechanical properties of high-strength concrete-filled square steel tube (CFSST) columns (high-strength materials are used for both steel tube and concrete) with steel reinforcement cage, twelve high-strength CFSST columns with the same cross-sectional dimensions were designed and fabricated with the form of the steel reinforcement cage, eccentricity, and the steel tube width-to-thickness ratio as the main parameters. The constraint enhancement mechanism of the concrete by the steel reinforcement cage and the effect of different parameters on the biaxial eccentric ultimate bearing capacity of column specimens was further analyzed by combining with ABAQUS simulation. The results show that the bearing capacity of the specimens decreases sharply with the increase of eccentricity and steel tube width-to-thickness ratio; the steel reinforcement cage can improve the bearing capacity and ductility of the specimen but has little effect on the stiffness; the arrangement of double orthogonal horizontal steel reinforcement can enhance the constraint effect of the steel tube in the middle of the cross-section edge length on the concrete of the specimens within a certain height range and weaken the constraint effect of the corner within the same height range; the enhancement effect of the steel reinforcement cage on the biaxial eccentric ultimate bearing capacity of the column specimens gradually decreases with the increase of eccentricity; when the eccentricity is constant, the effect of the steel reinforcement cage on the improvement of the biaxial eccentric ultimate bearing capacity of the column specimens with different width-to-thickness ratios is basically the same. •The mechanical properties of concrete filled steel tube column columns with built-in reinforcement cages were investigated.•The effects of eccentricity and steel tube width-thickness ratio on the load capacity of the columns were studied.•The effects of the built-in steel bar cage on the bearing capacity, ductility, and stiffness of the member were studied.•The restraint enhancement mechanism of the concrete by the built-in steel bar cage was explained.