Lateral torsional buckling occurs when an applied load causes both lateral displacement and twisting of a member. This failure is usually seen when a load is applied to an unconstrained, steel I-beam, with the two flanges acting differently, one under compression and the other tension. ‘Unconstrained’ in this case simply means the flange under compression is free to move laterally and also twist [a]. The buckling will be seen in the compression flange of a simply supported beam.

The best way to prevent this type of buckling from occurring is to restrain the flange under compression, which prevents it from rotating along its axis. Some beams have restraints such as walls or braced elements periodically along their lengths, as well as on the ends [b].

This failure can also occur in a cantilever beam, in which case the bottom flange needs to be more restrained than the top flange [b].

The location of the applied load is a major concern. If the load is applied above the shear center of a section it is considered a destabilizing load, and the beam will be more susceptible to lateral torsional buckling. Therefore loads applied at or below the shear center is a stabilizing load, with little risk of the buckling occurring [a].