Theoretical and Numerical Simulation Analysis of the Axial Compressive Performance of Recycled Aggregate Concrete-Filled Steel Tubular Columns for Bridges

To advance the application of sustainable recycled aggregate concrete (RAC) in bridge engineering, this study introduces a novel reinforced RAC-filled circular steel tubular (RRACFCST) column, leveraging the dual confinement of an external steel tube and an internal reinforcement cage. Its primary novelty is a comprehensive analytical framework integrating a new theoretical model by using limit analysis, ferrule theory, and the twin shear unified strength theory. Then, a rigorously validated nonlinear finite element model that incorporated material nonlinearity and interface effects was used to validate the proposed theoretical model. The results demonstrate the significant performance of the steel reinforcement cage, which enhanced the axial bearing capacity by 17.86%, and an optimal recycled aggregate replacement rate of 70% yielded the bearing capacity, with 100% replacement still achieving a 13.3% higher capacity than unconfined conventional concrete, demonstrating how effective confinement can compensate for and overcome the inherent deficiencies of RCA. Conversely, larger diameter–thickness ratios would reduce the strength by 33.7%. These quantifiable findings provide critical design insights and a validated predictive tool, establishing the RRACFCST column as a promising and high-performance sustainable solution for bridge structures.