43 pages (496 KB PDF)

Lateral-torsional buckling is a limit state where beam deformation includes in-plane deformation, out-of-plane deformation and twisting. The load causing lateral instability is called the elastic lateral-torsional buckling load and is influenced by many factors such as loading and support conditions, member cross-section, and unbraced length. In the 2001 and earlier versions of the National Design Specification®(NDS®) for Wood Construction the limit state of lateral torsional buckling is addressed using an effective length format whereby unbraced lengths are adjusted to account for load and support conditions that influence the lateral-torsional buckling load. Another common format uses an equivalent moment factor to account for these conditions. This report describes the basis of the current effective length approach used in the NDS and summarizes the equivalent uniform moment factor approach; provides a comparison between the two approaches; and proposes modification to NDS design provisions.