Influence of web distortion and onset of yield on doubly symmetric built-up I-girders subjected to high moment gradient

Recent studies have shown the AISC 360 Specification overpredicts the strength of certain built-up I-girders. The largest overpredictions occur for thin-unstiffened web members subjected to large moment gradient. The current study analytically investigates the combined effects of web distortion, web shear, web buckling and postbuckling, and onset of flexural yielding on built-up I girders. The findings show that AISC 360 overpredicts the member strengths due to: (1) unaccounted for web shear effects and (2) direct scaling of the uniform bending strength curve by the moment gradient factor. Based on these findings, potential paths toward AISC 360 Specification improvements are discussed.