Design of Cantilever Steel Beams: Refined Approach

A new set of effective-length factors is presented for designing doubly symmetric I-shaped built-in cantilever beams against lateral-torsional buckling when subject to different loading and restraint conditions at the cantilever tip. This refined approach rectifies inherent problems of current solutions caused by overlooking the restraint conditions as well as the limitations that existed in their original derivation. Because of these problems, the effective-length factors currently available may result in either overly conservative or unconservative designs, depending on the type of problem involved. Also, an interaction buckling design model is suggested for overhanging beams, in which the load is applied only at the cantilever tip. This design model takes into account the ratio of the length of the cantilever span to that of the back span, a significant parameter that has not generally been considered. Finally, a design procedure is given for determining the elastic critical moments of crane-trolley beams. These analyses are based on a finite-element model that correlated well with the results of 31 full-scale tests.