Assessment of equivalent geometric imperfections for shear buckling design of hybrid I-girders

This study investigates the influence of imperfections on the shear buckling resistance of steel welded I-section girders, with the objective of improving the reliability of the numerical model-based shear buckling resistance calculation method of EN 1993-1-14. A geometrically and materially nonlinear analysis with imperfections (GMNIA) is employed to evaluate shear buckling capacity using various imperfection magnitudes, combined with residual stresses. To support practical design applications, equivalent geometric imperfections are calibrated to align with the shear buckling resistance curve of EN 1993-1-5 as well as with various imperfection–residual stress combinations. A reliability-based analysis is conducted to determine partial safety factors associated with each equivalent imperfection, taking into account material overstrength, parameter variability, and basic variable dependencies. Refined reliability assessment methods are employed in the analysis and compared based on the resulting equivalent imperfections. The results highlight the limitations of commonly used imperfection assumptions, such as h w /1000, and demonstrate the effectiveness of refined, slenderness-dependent imperfections. Based on the current findings, the study provides recommendations for selecting appropriate equivalent imperfection magnitudes that comply with Eurocode safety provisions while improving the reliability of shear buckling predictions.