Behavior of manufactured sand and recycled coarse aggregate concrete‐filled steel tubular stub columns with circular section

Abstract Accelerated urbanization has intensified environmental concerns due to excessive natural resource consumption and construction waste generation. Circular concrete‐filled steel tube (CFST) columns incorporating manufactured sand recycled coarse aggregate (MS‐RCA) concrete have emerged as an innovative composite element offering notable environmental and economic benefits. To advance the use of MS‐RCA concrete in CFST structures, this paper presents experimental investigations into the behavior of 72 circular CFST stub columns constructed with MS‐RCA concrete. The effects of aggregate type, steel tube thickness, and stone powder content on structural response are examined. The results show that the failure modes of CFST columns with MS‐RCA concrete are characterized by local buckling and shear failure, similar to those of circular CFST columns with natural aggregate concrete. CFST columns with MS‐RCA have about 5.6% higher ultimate axial strength than those filled with natural sand‐RCA concrete. The inclusion of MS significantly enhances the ductility of CFST columns by an average of 34.6%, 25.4%, and 28.6% for steel tube thicknesses of 3.0, 3.5, and 4.0 mm, respectively. Moreover, for high‐strength concrete, the ultimate strength of columns filled with pebble MS‐RCA concrete is higher than that of those filled with limestone MS‐RCA concrete. Existing codes for CFST columns are evaluated and found to be highly conservative. Therefore, a new formula is proposed for CFST columns filled with MS‐RCA concrete and validated by experimental data. These findings confirm the viability of CFST columns with MS‐RCA concrete and highlight their potential to advance sustainable civil infrastructure.