Double-cavities steel-concrete composite short-columns with recycled concrete: Mechanical behavior and load-bearing capacity

• A novel double-cavities steel–concrete column with recycled concrete is proposed. • Axial and eccentric tests reveal effects of cavity design and load eccentricity. • Double-cavity confinement enhances strength, stiffness, and ductility. • A simplified bearing capacity formula shows <10% deviation from tests. • Offers a sustainable solution for recycling waste concrete in green buildings. To address the increasing environmental pressure from construction waste and improve the mechanical performance of recycled aggregate concrete (RAC), this study proposes a novel Double-cavities Rectangular Steel-Concrete Composite Column (DRSCRC). This structure utilizes an internal steel web to enhance the confinement of the core RAC. A total of 6 short column specimens were tested under axial and eccentric compression to investigate the effects of the coarse aggregate replacement ratio ( r =0%, 50%, 100%), eccentricity ratio ( e =0, 0.31, 0.5), and loading direction. The experimental results demonstrate that the double-cavity configuration effectively delays local buckling. Quantitatively, while the ultimate load-bearing capacity decreased by 9.94% and 15.26% as r increased to 50% and 100% respectively, the ductility coefficient notably improved by 15.58% at 100% replacement ratio. Furthermore, the bearing capacity was significantly sensitive to eccentricity, dropping by 36.1% at an eccentricity ratio of 0.5. Based on the superposition theory, a simplified bearing capacity formula was derived. Based on the experimental and simulation results, a theoretical formula for calculating the ultimate bearing capacity was proposed, with error margins controlled within 10%. This research confirms that DRSCRC provides a feasible, high-ductility solution for the structural utilization of waste concrete.