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The axial compression behaviour of square steel tube (SST) columns encased with recycled aggregate concrete (RAC) and filled with RAC (RAC-encased RACFSST) columns was investigated. Using high-strength concrete, five specimens were tested under axial compression until failure. The experimental parameters included the coarse aggregate type, stirrup spacing, wall thickness of the SST and the existence of cross-tie bars in the SST. The failure mode, load–displacement curves, load–strain curves and ductility of the composite columns were obtained. The impacts of the various parameters on the mechanical performance of the RAC-encased RACFSST columns were evaluated. The failure modes of the composite columns were comparable. The inclusion of RAC enhanced the load-bearing capacity (LBC) of the column, but negatively affects its ductility and deformation capacity. Increasing the wall thickness of the SST and reducing the stirrup spacing significantly improved the axial compressive performance of the columns, as mainly reflected in the axial compressive capacity and ductility, respectively. Cross-tie bars inside the SST improved the LBC and deformation capacity. The axial bearing capacities of the columns and those in other studies were determined using existing codes. The computed results were very consistent with the experimental data.
Niu et al. (Fri,) studied this question.