Structural Performance and Compression Resistances of Thin-Walled Square CFST Columns with Steel Lining Tubes

This paper proposes an innovative thin-walled square concrete-filled steel tubular (CFST) column with a circular/octagonal steel lining tube, in which the outer steel tube and the lining tube are fabricated independently of each other and then connected by slot welds. The advantages of a simplified manufacturing process, an insensitivity to local buckling, and good confinement could be expected in this composite column. Twelve short columns were tested to failure under compression, and various key parameters including nominal width-to-thickness ratios of steel tubes, stiffener types, yield strengths of steel tubes, and lining tubes were considered. The test results indicated that the proposed steel lining tubes were able to improve the axial behavior of these thin-walled square CFST short columns in various ways, including a more uniformly spaced buckling pattern with smaller intervals, larger axial stiffness, higher section resistances, and enhanced confinement and ductility. The octagonal lining tubes were more effective than the circular ones in terms of buckling constraints while the circular lining tubes were superior in terms of confining enhancement. A finite-element parametric analysis was also carried out to assess the axial resistances of these thin-walled square CFST columns with lining tubes. A simplified model was developed incorporating both the postlocal buckling of the square steel tubes and the confinement of the lining tubes.