On LTB predictions using equivalent geometric imperfection modeling

The critical moment analytical expressions used in engineering design are based on the thin-walled beam model of warping torsion and the linear eigenvalue analysis (LEA) while the analytical formulation of the buckling curve equation follows the Ayrton-Perry model with the Maquoi-Rondal initial imperfection parameter. Using the equivalent geometric imperfection concept for the resistance prediction, the Maquoi-Rondal initial imperfection amplitude for lateral-torsional buckling is usually related to the equivalent minor axis bow amplitude or the twist rotation amplitude for the lowest eigenmode imperfection profile. Such concept is also used in this paper for the evaluation of the buckling resistance of beams in bi-axial bending. Recent investigations based on the so-called GMNA+ large displacements analysis have shown that the LTB critical moment evaluated with use of LEA needs to be modified in order to account for the fact that H-section slender beams may fail by developing large inelastic twist rotations, the effect that is not included in the elastic linear buckling theory. In the present study, the influence of critical moment predictions on the LTB resistance evaluation is dealt with and the analytical formulation is proposed. Comparisons of the buckling curve formulations are presented.