Lateral Torsional Buckling Behaviour of Steel Beams - On the Influence of the Structural System

This paper analyses the lateral torsional buckling (LTB) behaviour of cantilever and two-span steel beams. The structural behaviour in terms of load-deflection curves, plasticisation of the cross section, ultimate capacities and failure modes of these beams is compared to the corresponding behaviour of simple beams, which are often considered as a basis for developing simplified models for design purposes. The results of the numerical study show that the ultimate capacity of steel beams is strongly affected by the yield-zone development and limited by four different failure criteria, namely the cross section failure, the eigenvalue-failure of the partially plastic system, the rotation limit and the eigenvalue-failure of the elastic system. Different ranges of slenderness are crucial for each failure criteria and these ranges vary for the different structural systems.