Experimental and numerical analysis of l-shaped column composed of recycled aggregate concrete-filled square steel tubes under eccentric compression

The eccentric compression behaviors of L-shaped columns made of recycled aggregate concrete-filled square steel tubes (L-RACFST) with various replacement ratios of recycled coarse aggregate (RCA) are introduced in this paper. The experimental study demonstrates that the overall instability failure is the final failure mode of the L-RACFST columns and that the replacement ratio of RCA has little influence on the final failure mode of the specimens. When the RCA replacement ratio exceeds 40%, the specimens frequently move right into the failure stage. Recycled aggregate concrete (RAC) inside steel tubes can increase the load-carrying capacity and stiffness, preventing them from buckling inward compared to hollow steel tubes. The load-carrying capacity of the specimens gradually decreases as the replacement ratio of the RCA rises, and the ductility and stiffness deteriorate progressively. The bearing capacity declines more quickly, and the ductility coefficient and stiffness coefficient fall more slowly when the replacement ratio of RCA is higher than 40%. The bearing capacity of the specimens decreased by 29%, the ductility coefficient by 54%, and the stiffness coefficient by 60% as the replacement ratio of RCA increased from 0% to 100%. The specimen's ultimate strength decreases as the eccentricity rises. The numerical analysis results demonstrate that in the engineering design, the specimens' ultimate strength can be increased by strengthening the steel and raising the steel ratio; however, it is not advised to increase the connection plate's width to enhance the load-carrying capacity. The connection plate's primary function is to increase the stiffness of the steel surface and prevent local buckling, which has little bearing on improving the specimens' bearing capacity. It is advised that the replacement ratio of RCA in the L-RACFST columns should be less than 40% when considered with the research findings of reference [28].