Effect of Shear and Distortion Deformations on Lateral Buckling Resistance of Box Elements in the Framework of Eurocode 3

This paper treats the distortional and shear deformation effects on the elastic lateral torsional buckling of thin-walled box beam elements, under combined bending and axial forces. For the purpose, a nonlinear kinematic model based on higher order theory is used applicable to both short and long thin-walled box beams. Because in the kinematic model of the higher order theory integrates additional flexibility terms related to shear, distortion and warping effects, it accurately predicts the lateral torsional buckling of the straight box beams. Ritz’s method is adopted as solution strategy in order to obtain the nonlinear governing equilibrium equations, then the buckling loads are computed by solving the eigenvalue problem basing on the singularity of the tangential stiffness matrix. Owing to flexural–torsional and distortional couplings, new matrices are obtained in both geometric and initial stress parts of the tangent stiffness matrix. The proposed method with the new stiffness terms, is efficient and accurate in lateral torsional buckling predictions, when compared with the commercial FEM code ABAQUS results. Based on the existing European guidelines EC3, an extensive numerical investigation is performed to demonstrate the effects of both shear and distortional deformations on the moment carrying capacity. The convenience of the model is outlined and the limit of models developed without shear and distortion deformation effects on lateral buckling loads evaluation is discussed.