Axial compressive performance of square reinforced concrete columns with hybrid CFRP ‐steel stirrup confinement

Abstract

This study proposes a novel hybrid stirrup system to enhance the axial compressive performance and ductility of square reinforced concrete (RC) columns. The system combines an inner circular strap made of a steel and carbon fiber reinforced polymer (CFRP) composite and an outer square CFRP strap. Axial compression tests were conducted to evaluate the effects of stirrup configuration and volumetric ratio of steel and CFRP. The results demonstrate that the hybrid system synergistically improves structural performance: it increases the axial compressive capacity and ultimate strain by 17.27% and 92.31%, respectively, compared to columns with conventional steel stirrups. Moreover, the ductility coefficient of the hybrid‐confined column (H3‐6) is 10.7, representing a 32.1% increase over that of the reference specimen B‐10 ( μ  = 8.1). This enhancement is attributed to a staged confinement mechanism, where the steel provides high initial stiffness and the CFRP supplies progressive post‐yield restraint, effectively mitigating the geometry‐driven confinement inefficiency inherent to square sections. A practical analytical model is developed to predict the axial capacity, showing good agreement with experimental data. The findings confirm that the proposed hybrid system is a promising solution for enhancing the strength and ductility of square RC columns in seismic and high‐load applications.