Limited research exists on the behavior of square CFDST slender columns, especially under the consideration of the relation global buckling and confinement effect. This study evaluates square concrete-filled double-skin steel tubular (CFDST) columns using nonlinear finite element analysis (FEA) to simulate structural behavior under axial and eccentric loads until failure. Parametric analyses of extensive specimens of square CFDST pin-ended columns evaluate various parameters, providing design insights for engineering applications. The study was conducted over a wide range of slenderness ratios. Four concrete varieties with compressive strengths were tested: normal concrete (NC), engineered cementitious composites (ECCs), high-strength concrete (HSC), and ultra-high-strength concrete (UHSC). Parametric variables included inner to outer steel tube thickness ratios, hollow ratios with a wide range, inner tube steel grades, and load eccentricities. An increasing slenderness ratio reduced the axial capacity, causing failure to change from yielding to buckling. By increasing the inner thickness, the capacity increased for intermediate columns compared to very long (i.e., slender) columns. The ideal hollow ratio is () for short columns compared to () for slender columns. UHSC improved short columns. Concrete’s performance was impacted by eccentric loading, which decreased the capacity, particularly in long columns. Designers should take into consideration the diminished efficacy of material strength enhancements under eccentric loading and prioritize stability in long, slender columns. The design formula was modified to enhance the strength estimates of square CFDST columns.
Nawar et al. (Sat,) studied this question.