Elastic distortional buckling of doubly symmetric steel I-section beams with slender webs

• Complex finite strip method for distortional buckling of steel I-beams is proposed.
• Capability of the complex treatment is verified by comparing with other methods.
• A parametric study on the elastic distortional buckling of I-beams is carried out.
• Based on extensive parametric studies, a new design equation is developed.
• The simple formula is proposed for distortional moment of slender web I-beams.

Doubly symmetric steel I-section members with thin webs and stocky flanges have a tendency to buckle in a so-called distortional buckling mode, involving distortion of the web of the I-section in the plane of its cross-section. As this mode is more complicated than the local or global buckling, analytical expressions take empirical forms and vary in between different proposals. This paper has two main objectives. The first objective is to propose a complex finite strip method for distortional buckling analysis of I-section beams with slender webs and check the suitability for such analysis by comparing its accuracy with other methods and the second objective is to propose a simple method for predicting the distortional buckling loads of I-beams. The latter objective is superior to current methods with respect to the weight of the sections.