Numerical Study of CFRP-Strengthened Square RC Columns under Axial Compression with Initial Geometric Imperfections

Reinforced concrete (RC) columns are the enablers of modern cities; their numerical modeling requires precise treatment of initial geometric imperfections and confinement effects to represent their structural behavior realistically. This study describes a finite element analysis (FEA) framework developed in Abaqus/CAE to investigate the axial behavior of full-scale short and slender square RC columns with and without interior transverse reinforcement (ties). The models include external confinement with carbon fiber–reinforced polymer (CFRP) jacketing, and different global and local imperfection cases were considered to assess their effects on strength and ductility. Calibration against code provisions was achieved by comparing the numerical results with an interaction diagram derived in accordance with ACI 318-25 and ACI PRC-440.2-23 design requirements. The study showed that as the imperfection amplitude increases, the strength and ductility of short, slender RC columns decrease, irrespective of confinement. For short columns subjected to axial compression, one can achieve good correlation with code-based nominal axial load predictions without considering explicit imperfections, provided no strength reduction factor is included, and accidental eccentricities are ignored. In contrast, for slender columns, imperfections are key in inducing slenderness effects, particularly in global imperfection cases with pinned-end boundary conditions.