Experimental Study of Confinement Effects in Concrete-Filled Double Skin Tubular Columns under Axial Loading

Abstract

This study investigates the performance of hybrid concrete-filled double skin tubular (CFDST) columns, specifically configurations with inner and outer steel tubes (SCFDST) and inner steel tubes with fiber reinforced polymer (FRP) outer tubes (FCFDST). By utilizing concrete-filled steel tubes (CFT), which enhance stiffness and compressive strength, the research examines short and slender columns with varying diameter-to-thickness ratios (D/t). An analytical approach employs nonlinear post-buckling finite element analysis using ABAQUS, supported by experimental tests on ten specimens: five short columns (two SCFDST, two FCFDST, and one reinforced concrete) and slender columns with a slenderness ratio of 12.5. Results reveal that both steel and FRP effectively confine the concrete, significantly boosting strength. SCFDST short columns fail through local buckling of the outer tube, while FCFDST columns rupture at the outer tube. Slender columns experience global buckling, with load-carrying capacities reduced by 23% for SCFDST and 28% for FCFDST compared to short columns. This research provides important insights into the behavior of hybrid CFDST columns, offering implications for future structural applications..