Incorporating the shear and transverse extension effects in the global and distortional buckling modes

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Cold-Formed Steel Research Consortium (CFSRC) Colloquium
The traditional global (G), distortional (D), and local (L) mode classes of thin-walled members are conventionally defined according to the characteristics of deformation shape, and the shear and transverse extension strains are separated to form the Shear and Transverse extension mode class (ST), which are not considered in the G, D, and L classes. This paper proposes a new set of basic mode definitions based on the orthogonal completeness principle and the force characteristics, which are more compatible with the complexity of the stress-strain relationships. In contrast to the current generalized beam theory (GBT) and constrained finite strip method (cFSM), the proposed G, D, and L classes span the entire deformation space of the thin-walled member, and are strictly orthogonal to each other with respect to the stiffness of the member. The GD mode class is proposed at first as the deformation of thin-walled members subjected to cross-section mid-line direction uniformly distributed forces, through which the corresponding shear and transverse extension effects are introduced in the G and D modes. The D class is further defined based on an additional force characteristic. Finally, the G and L classes are derived based on orthogonal conditions. Buckling mode decomposition and identification according to the proposed mode classes are realized based on finite strip models of thin-wall members. The numerical example shows that the effects from shear and transverse extension deformations can be reasonably accommodated in the resulting global and distortional buckling modes of the proposed method.