Shape optimisation of cold-formed steel framed wall studs with sheathing restraints

The optimisation of the cross sectional geometry of cold-formed steel sections has been the subject of numerous past studies. These walls consist of intermittently placed cold-formed steel studs, lined most commonly with gypsum plasterboards. Experimental evidence has shown that the restraints provided by the wall sheathing can have a significant impact on the axial compression capacity of these wall studs. However, the optimisation studies of cold-formed steel wall studs, incorporating sheathing restraints into the analysis, have been limited despite their potential for useful outcomes. A shape optimisation study was therefore conducted using two stochastic search algorithms: Simulated annealing and the Genetic algorithm. The in-plane and out-of-plane sheathing restraints to wall studs, estimated based on full-scale axial compression test results, were incorporated into the analyses. Structurally superior alternatives to four lipped channel studs currently used in the industry, made using 1.15 mm thick G500 steel, were found. The results revealed that by increasing the number of rollers used in the roll forming process to 6 or 8, significant enhancements in the structural efficiency could be obtained for the commonly used 4-roller lipped channel stud. Elimination of local buckling due to web segmentation, and distortional and minor-axis global buckling due to the provision of sheathing restraints were identified as the prime causes of strength enhancement.