Compressive Behavior of Square Mixed Recycled Concrete‐Filled Double‐Skin Steel Tubular Short Columns

ABSTRACT The structural utilization of waste sintered bricks is currently restricted by the inherent defects of recycled brick aggregates, such as low strength and high variability. To address this issue, this study proposes a novel mixed recycled concrete‐filled double‐skin steel tube (MRCFDST) column with a square‐in‐square section, which utilizes a dual‐confinement mechanism to enhance the performance of brick‐aggregate concrete. A comprehensive investigation involving axial and eccentric compression tests on six specimens, along with finite element analysis (FEA), was conducted to evaluate the effects of the recycled aggregate replacement rate ( r ), load eccentricity ( e ), and sectional form. Experimental results indicate that the dual confinement effectively mitigates the brittleness of brick aggregates, ensuring a ductile failure mode dominated by the local buckling of steel tubes even at a 100% replacement rate. While the ultimate bearing capacity decreased by 14.1% and 34.2% as r increased from 0% to 100% and e increased from 0 to 40 mm, respectively, the hollow sandwich configuration exhibited an 11.2% higher bearing capacity compared to the solid section equivalent. Furthermore, a validated FEA model was developed, achieving high prediction accuracy with an average experimental‐to‐calculated ratio of 0.978. Based on the parametric analysis, a practical calculation method for the bearing capacity of MRCFDST accounts for the confinement factor is proposed. This study demonstrates that the proposed double‐skin configuration effectively “upgrades” low‐quality recycled materials for load‐bearing structural applications.