Chapter 3: Recent Advances and Progress in Design Codes: Instability Problems

摘要

Cold-formed steel sections may be subject to three basic types of buckling: 1. local buckling;2. distorsional buckling; 3. global buckling. The term global buckling (or long mode buckling) embraces flexural buckling, torsional and flexural-torsional buckling and lateral-torsional buckling. The half-wave length of these modes is of the order of magnitude of the length of the member. Global buckling is characterized by rigid body movements of the whole member such that individual cross-sections rotate and translate but do not distort in shape.Local and distorsional buckling are sometimes called sectional buckling because they depend very much of the geometry of the cross-section. Local buckling is characterized by a relatively short half-wavelength of the order of magnitude of individual plate elements while the fold lines remain straight. Distorsional buckling occurs at a half-wavelength intermediate to local and global mode buckling. The half-wavelength is typically several times larger than the largest characteristic dimension of the cross-section. Distorsional buckling involves both translation and rotation at the fold lines of a member leading to a distorsion of the cross-section. Figure 1 illustrates these three modes of buckling for a member under pure compression. Each of the three generic categories of buckling is capable of mutual interaction. Empirical models for the interaction of local and global buckling are included in most design codes but there is only few fundamental knowledge of the interaction of distorsional buckling with the other modes (Davies, 1999).