Reliability-based design model for compressive strength of axially loaded FRP-confined concrete columns

Numerous models predict the compressive strength of FRP-confined concrete, yet most rely on narrow calibration datasets, overlook key parameter interactions (e.g., non-circularity, partial confinement), and lack explicit reliability-based design frameworks, limiting their safe implementation in practice. This study develops a reliability-based Load and Resistance Factor Design (LRFD) framework for axially loaded FRP-confined concrete columns. A unified probabilistic approach is introduced to incorporate uncertainties in material properties, geometric tolerances, and confinement configurations. Using a database of 2117 tests, existing models were evaluated, and the most accurate one—previously developed by the authors—was selected. This model captures the effects of confinement stiffness, cross-sectional shape, confining system type, and size. To enable practical design, reliability-based calibration was performed for both the global resistance factor ( ϕ ) and partial resistance factor ( γ R ), ensuring compliance with Eurocode 0 target reliability levels. Variable formulations for ϕ and γ R were also proposed to reflect the influence of confinement level and unconfined concrete strength. Benchmarking against ACI 440.2 and fib Bulletin 90 demonstrates that the proposed design model achieves higher material utilization with minimal increases in unsafe predictions. Approximately 70% of specimens fall within the appropriate safety range, greatly outperforming ACI 440.2 (2.3%) and fib Bulletin 90 (47%).