This paper examines discrepancies in beam design criteria across various international codes through an experimental study focused on slender-web singly symmetric I-girders - a critical area where the design codes diverge significantly. Regardless of cross-section class, these variations stem from differing approaches to defining plateau lengths, handling inelastic lateral torsional buckling (LTB), and considering moment gradient effects. Fundamentally, the Eurocode gives importance to finite element simulations incorporating idealized boundary conditions modeled with theoretical residual stresses and initial geometric imperfections, whereas the American codes are primarily calibrated to an extensive experimental database. Some researchers have noted that experimental studies are limited to specific sections of the inelastic buckling region, particularly for slenderweb and singly symmetric girders. A few have recognized that compression flanges influence web buckling due to flexural compression in a manner inconsistent with the web classification criteria, leading to further disparities in the design equations for slender-web I-girders. For the first time, this study provides experimental validation for the influence of compression flange area on web flexural buckling behavior with simultaneous occurrence of inelastic LTB. The tested specimens in this study are subjected to uniform moment and strategically braced using an atypical detail to precisely determine effective lateral lengths, preempting inaccuracies in test data evaluations. The findings offer valuable insights into the actual behavior of such sections compared to current design code predictions.
