Optimization of cold-formed steel members considering reduced stiffness and strength due to cross-sectional instabilities

The objective of this paper is to provide the development of an optimization scheme that produces a family of optimized cold-formed steel lipped channel sections that are subjected to cross-sectional instabilities such as local and distortional buckling. Similar research was done in the past to optimize cold-formed steel sections using only a strength constraint for a broad set of axial (P) and bending (M) demands. In this new study, optimization algorithms further take into account not only those strength demands (i.e., P-M) but also the stiffness constraint for serviceability. A stiffness constraint characterized by effective moment of inertia (Ieff) due to cross-section stabilities is imbedded in the optimization algorithms. A two-level optimization framework is utilized: the first level focuses on member optimization of the P-M (Axial-Moment) demand space as derived from current commercially available lipped channel sections in the United States; while the second level focuses on the selection of a new family of optimal lipped channel sections that have the same efficiency in covering the design space but utilize a minimal family size. The results of the study show this family size is significantly smaller than currently commercially available sections (i.e., 108 sections), but can still achieve the same and/or improved performance in terms of both strength and stiffness demands. The developed family of sections demonstrates that optimization techniques have a great potential for improvement of the cold-formed steel production industry.

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