Axial compression behavior of square concrete-filled steel tubular columns reinforced with CFRP-ECC hybrid composite

Concrete-Filled Steel Tube (CFST) columns often encounter challenges such as insufficient compressive capacity, susceptibility to local buckling, and limited ductility. To mitigate these issues, a combined reinforcement approach using Carbon Fiber Reinforced Polymer (CFRP) and Engineered Cementitious Composites (ECC), termed Composite Enhanced Steel-Confined (CESC), is proposed. This paper investigates the axial compressive behavior of CESC through numerical simulation. A refined finite element model is developed and validated against experimental load–displacement curves, failure modes, and ultimate capacities. Based on this validation, a parametric study is conducted to examine the effects of CFRP mesh size, steel tube width-to-thickness ratio, and core concrete strength on the axial compression performance of CESC. Results show that reducing the CFRP mesh size from 40 to 10 mm enhances ultimate capacity by 42.1% and effectively suppresses local buckling. Increasing the width-to-thickness ratio from 31.5 to 80.4 improves bearing capacity by 54.1% and the ductility coefficient by approximately 30%. Raising concrete strength from C30 to C70 increases capacity by 48.8%, though ductility improvement remains limited. Furthermore, multiple linear regression is employed to develop a predictive model for bearing capacity, and a modified theoretical formula is proposed for practical design of CESC columns.