Behaviour of round-ended recycled aggregate concrete-filled stainless steel tubular stub column under axial compression

Recycled aggregate concrete-filled stainless steel tubular (RACFSST) columns combine aesthetic superiority with enhanced corrosion resistance, offering a sustainable alternative for coastal bridge piers. Axial compression tests were conducted on 14 specimens, evaluating stainless steel grades (Austenitic 304 vs. Duplex 2205) and aspect ratios ( B/D = 1.44–1.92). Results revealed that round-ended RACFSST columns demonstrated a 129.6 %-higher axial compressive resistance compared to stainless steel tubular (SST) counterparts. A finite element model was implemented to study parametric effects and mechanisms of this column. Mechanistic analysis revealed that the round-ended RACFSST column exhibits higher load-carrying capacity, ductility, and confining stress than the column made with a carbon steel tube. Parametric analysis indicated that axial compressive resistances increase with higher concrete strength, SST yield strength, and steel ratio, but decrease with larger aspect ratio. Existing design methods underestimated the load-carrying capacity of round-ended RACFSST stub columns. New predictive methods were developed for axial compressive resistance, axial compressive stiffness, and peak strain.