Evaluation of <scp>ACI CODE</scp> 440.11‐22 design provisions for <scp>GFRP</scp> ‐ <scp>RC</scp> columns: Constitutive models and practical interaction diagrams

Abstract With the release of ACI CODE‐440.11‐22, which introduces design provisions for GFRP‐Reinforced Concrete (RC) columns, it is important to evaluate the limitations of the adopted approach and provide practical design tools. This study develops and validates an analytical cross‐sectional model—based on equilibrium and strain compatibility—against theoretical and experimental data, to generate axial load–bending moment (N–M) interaction diagrams for short GFRP‐RC columns in accordance with the new code. The model uses the equivalent rectangular stress block for concrete in compression and incorporates key design parameters, including GFRP bar properties and strength reduction factors. To assess the conservatism of the code approach, the study compares interaction diagrams generated using the code's stress block with those developed using nonlinear concrete constitutive models. Results show that the code‐based diagrams are more conservative, and a scaling factor of 1.1 is suggested to better match actual behavior. As the ACI code neglects the compressive contribution of GFRP bars, their tensile strength affects only the tension side of the interaction diagram. Moreover, variations in the bar's elastic modulus influence the diagram from the balance point on the tension side up to the point where all bars are in compression and thus excluded from the analysis.