Advanced line-finite-element for lateral-torsional buckling of beams with torsion and warping restraints

Steel beams are susceptible to lateral-torsional buckling (LTB) failure when subjected to bending. Considering the effect of semi-rigid connections, the partial end restraints in torsion and warping can significantly influence the buckling behavior of members. However, these restraints are not properly simulated in the traditional line-finite-element method (LFEM), which may lead to an error in the estimation of member buckling capacity. To fill this gap, this research introduces an improved end-spring model into the formulation of an advanced co-rotational (CR)-LFEM, where the partial restraints in axial, bending, torsion, and warping degree of freedom (DOF) can be considered. A parametric study on the LTB behavior of steel beams is conducted using the modified CR-LFEM, where a series of elastic buckling analyses are conducted. The results show that the stiffness of partial torsion and warping restraints have a significant influence on the LTB capacity. The influence of various cross-section shapes and member slenderness ratios on the LTB behavior is also discussed. Finally, design recommendations are provided for classifying connection stiffness in torsion and warping DOF, offering guidelines for practitioners. In addition, the improved CR-LFEM with end-springs proposed in this study has been implemented into the educational software MSASect2.