What about Lateral Torsional Buckling (LTB) of our structures?

 

What about Lateral Torsional Buckling (LTB) of our structures?

Lateral Torsional Buckling (LTB) is the deformation experienced by a beam with generally unrenstrained ends.

Causes: The applied loads away from its longitudinal axis. It then undergoes both lateral displacement and bending.

Steel beams with "unrestrained" ends are beams whose compression flange is free to move (or shift) in the lateral direction and also to bend. If we are referring to a simply supported beam, then its compression flange is, of course, the upper flange. As this flange deforms laterally, the flange in tension tends to hold the beam in a straight configuration and thus generates "restoring" forces due to the lateral bending of the beam.

However, these forces alone are not sufficient to hold the beam in a straight configuration. The resistance of the beam to LTB is therefore determined by both the restoring forces and the lateral component of the tensile forces in the tensioned flange of the beam.

Design Provisions: The desired restraint can be fully achieved by the composite action of a concrete deck. Partial restraint can be achieved by the use of intermediate beams.  Sufficiently sized and appropriately placed bracing may also be used.