Structural size optimization of single and built-up cold-formed steel beam-column members

The use of cold-formed steel (CFS) elements in residential and industrial buildings is widely gaining popularity due to their ability to provide cost-effective and sustainable solutions. A high degree of flexibility in the manufacturing of various cross-sectional shapes provides a unique opportunity to further improve the load-carrying capacity of these elements through an optimization process, leading to more efficient and economical structural systems. This paper aims to offer a practical methodology for the optimum design of CFS beam-column members with different lengths and thicknesses, subject to various combinations of axial compression and bending moment, but with constant material use. The optimization process is carried out using a genetic algorithm and aims to maximize the resistances of CFS members, determined according to the European design guidelines (Eurocode 3). Six initial prototype cross sections, including both single and built-up channel sections, are selected and their relative dimensions and edge stiffener configurations are allowed to vary during the optimization process. To ensure practically relevant solutions Eurocode 3 slenderness constraints, as well as a range of practical manufacturing and construction limitations, are imposed on the cross sections. Standard commercially available single and back-to-back lipped channel sections are taken as the starting points of the optimization and used to benchmark the efficiency of the optimized sections. Significant gains in capacity (of up to 156% in the present study) can be obtained compared to the initial cross sections, while the optimization results also offer further insights on the material efficiency achievable with various cross-sectional shapes in combined loading scenarios ranging from pure bending to pure compression.