This study experimentally investigates the axial compressive behavior of 10 square high-strength fully recycled aggregate concrete-filled steel tube (HSFRACFT) columns, focusing on the effects of concrete strength and length-to-width ratio on failure modes, load-displacement responses, and load-bearing capacity. The results indicate that both stub and slender columns experience brittle failure. Poor ductility and composite effect were observed for the present test which has a confinement factor of 0.31≤ ξ ≤ 0.42. A numerical parametric study was carried out to examine the effects of concrete strength, steel yield strength, and width-to-thickness ratio on the axial behavior of square HSFRACFT columns. Results showed that increasing the confinement factor enhances the ductility but hardly improves overall composite strength. It is recommended to incorporate additional confinement measures, such as internal spiral stirrups or tie rods, in the practical application of square HSFRACFT columns. Finally, an axial load-bearing capacity model of HSFRACFT columns was developed and validated based on experimental data.
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