Flexural Strength for General Lateral–Torsional Buckling

The lateral–torsional buckling behavior of general prismatic and tapered steel members with doubly and singly symmetric sections are investigated based on the general forms of differential equilibrium equations for minor-axis bending and torsion. Fundamental lateral–torsional buckling moments are derived for general tapered steel members that are in forms similar to those for prismatic members. The factor accounting for the effects of level loading application is derived and incorporated into the moment diagram modification factor that is generalized for the prismatic and tapered steel members. American Institute of Steel Construction-type equations for calculating the inelastic lateral–torsional capacity are proposed by using straight-line transition, and limiting unbraced member lengths are explicitly derived. The analytical procedure presented can give reasonable results with consistent accuracy for general design consideration and follows the same philosophy as for prismatic doubly symmetric wide-flange design rules. The proposed procedure is user friendly for structural design.