Mechanical performance of stirrup-confined concrete-filled steel tubular stub columns under axial loading

• A proposal of stirrup-confined CFT columns with improved mechanical performance.
• Comparison between stirrup-confined CFT columns and CFT columns.
• Load sharing mechanism between steel tube, stirrups and concrete is clarified.
• Comprehensive parametric analysis on stirrup-confined CFT columns.
• Simplified method to predict the bearing capacity of stirrup-confined CFT columns.

This paper presents an experimental comparison between concrete-filled square steel tubular stub columns confined by internal loop or spiral stirrups, traditional square concrete-filled steel tubular stub columns (CFT), and inner stiffened square concrete-filled steel tubular stub columns. In total 11 specimens were prepared and loaded concentrically in compression to failure. From the experimental results, the superior mechanical performance of stirrup-confined CFT to stiffened CFT was first demonstrated and the effects of different configurations of confinement (such as internal stiffeners, hoops and stirrups) on the ultimate load-bearing capacity were clarified. ABAQUS was used to establish 3D finite element models for the CFT and stirrup-confined CFT stub columns under axial compression, in order to understand the contribution made by loop or spiral stirrup confinement to the improvement of overall mechanical performance. Further, a simplified approach was developed to estimate the ultimate bearing capacity of stirrup-confined CFT stub columns, with consideration of the confinement effects offered by both square steel tube and stirrups. The predicted results showed satisfactory agreement with the experimental and numerical results.