Resistance factor calibration for fiber‐reinforced polymer‐reinforced concrete columns based on a sectional analysis model with fiber‐reinforced polymer compression contribution

This study aims to calibrate the reliability‐based resistance factor ϕ for a sectional model predicting the load‐carrying capacity of rectangular fiber‐reinforced polymer‐reinforced concrete (FRP‐RC) columns under eccentric compression. A mechanical model accounting for the compressive contribution of FRP reinforcement through a factor α f is developed based on 144 experimental specimens. The novelty lies in explicitly incorporating FRP compression effects while quantifying residual error ( M R ), and subsequently performing reliability‐based calibration using the FORM framework. Specimen‐specific optimization revealed two subgroups associated with differences in relative eccentricity and longitudinal reinforcement ratio. Separate optimization yielded α f = 0.0798 and 0.3507. The overlapping interquartile ranges ( e / h = 0.229–0.395 and ρ f = 0.701–1.397%) characterize a preliminary transition region between the two subgroups. The subgroup‐specific treatment improved predictive accuracy and yielded higher resistance factors, while α f,final = 0.0798 was conservatively retained for the transition or unclassified region pending further validation. Calibration for a target reliability index β T = 3.5 and L/D = 0.5 produced ϕ = 0.473. A parametric assessment of 12,960 design cases showed generally acceptable reliability, with lower values concentrated at low FRP reinforcement ratios and large eccentricities. The proposed framework links mechanical modeling, residual characterization, and reliability‐based design calibration for practical applications.