Steel Interchange

Lateral Bracing for Cantilevers

Answer

This is correct. Section 6.3.1 in Appendix 6 of the AISC Specification requires that cantilever bracing must be attached near the tension flange.

The center of rotation for a cantilevered beam is located at a point below the bottom flange. Accordingly, an unbraced cantilevered end will undergo greater rotational displacement at the top flange than at the bottom flange. Bracing the bottom flange will move the center of rotation upward, but the top flange will still have the tendency to rotate out of plane. Therefore, in the case of cantilever beams, the best way to restrain the out-of-plane displacements associated with lateral-torsional buckling is to brace the top flange.

Heath Mitchell, P.E.