Elastic flange local buckling of I-shaped beams considering effect of web restraint

•The test data for elastic FLB strength of I beams in the AISC Specification found to be inconsistent.•More rational and theoretical measure for web restraint effect on elastic FLB of I beams proposed.•More accurate but still practical formula for elastic FLB proposed using variational approach.

The 2010 AISC flexural strength of I-shaped beams with slender flange was proposed based on Johnson (1985)’s experimental plate bucking coefficient (kc). However, our close examination revealed that most of I-beam specimens tested by Johnson to derive kc had section configuration of slender web and noncompact flange, indicating the inappropriateness of the test database itself and probable underestimation of web restraint effect in the AISC codification. In this paper, the effect of web slenderness on the elastic flange local buckling is analytically investigated using the mixed variational approach, and more accurate but still practical formula is proposed.