Comparative assessment of code-based capacity models for RC elements with stirrups under uniaxial and biaxial shear

In common practice, the shear capacity of slender reinforced concrete (RC) beams and columns with stirrups is evaluated using code-based expressions, which are usually derived from a truss-type resisting mechanism. The wide range of alternative provisions highlights the absence of a unified mechanical theory for force transfer in cracked RC members, resulting in various empirical formulations and corrective coefficients calibrated against experimental data. In this context, the present paper offers a comprehensive and up-to-date comparative assessment of thirteen shear strength models adopted in international codes, including the latest second-generation Eurocodes 2 and 8. All uniaxial shear capacity models are categorized into three groups according to their formulation: empirical-additive models, equilibrium-based variable-angle truss models (VATMs), and compatibility-enhanced VATMs. The present comparative assessment also encompasses biaxial shear capacity models, including empirical approaches based on the interaction domain as well as four mechanically based formulations. The predictive accuracy of these shear capacity models is assessed using homogeneous, carefully selected experimental databases. Additionally, the sensitivity of the models’ performance to key input parameters is examined. This study is the first to conduct a large comparative assessment involving the second-generation Eurocode shear capacity models and to include biaxial shear models, thereby offering a broad and sound foundation for future design practice as well as for code development and revision. The results indicate that a code-compliant, equilibrium-based VATM, enhanced with machine-learning-calibrated coefficients, provides a robust and accurate yet practical formulation for diverse shear loading scenarios, outperforming other models without requiring iterative procedures.