A numerical and analytical study on distortional buckling of doubly-symmetric steel I-beams

This study investigates the effect of web distortions in a lateral distortional buckling mode on the buckling moments of doubly-symmetric steel I-beams. Analytical buckling moment expressions applicable to both elastic and inelastic lateral distortional buckling were developed. These expressions account for the reductions in the torsional and warping rigidities of I-beams due to web distortions. Numerical results obtained from the finite element analysis showed that the buckling moments of steel I-beams with stocky flanges and slender webs are overestimated by the lateral torsional buckling solutions while the proposed distortional buckling solutions provide estimates in closer agreement with the numerical results. Finally, the lateral torsional buckling solutions in the structural steel standards were found to generally provide conservative buckling moment estimates for doubly-symmetric steel I-beams prone to web distortions.

Research highlights
► We proposed equations for estimating distortional buckling moments of I-beams.
► Proposed equations apply to both elastic and inelastic distortional buckling.
► Finite element results closely agree with the estimates from proposed equations.
► Buckling behavior is more affected by distortions with increasing web slenderness.
► Buckling behavior is more affected from distortions with increasing span length.