Effect of stressed-skin action on optimal design of a cold-formed steel portal framing system

Cold-formed steel portal frames can be a viable alternative to conventional hot-rolled steel portal frames. They are commonly used for low-rise commercial, light industrial and agricultural buildings. In this paper, the effect of semi-rigid joints and stressed-skin action are taken into account in the optimal design of cold-formed steel portal frames. A frame idealization is presented, the results of which are verified against full-scale. A real-coded niching genetic algorithm (RC-NGA) is then applied to search for the minimum cost for a building of span of 6 m, height-to-eaves of 3 m and length of 9 m, with a frame spacing of 3 m. It was shown that if stressed-skin action and joints effects are taken into account, that the wind load cases are no longer critical and that the serviceability limit state controls for the gravity load case with the apex deflection binding. It was also shown that frame costs are reduced by approximately 65%, when compared against a design that does not consider stressed-skin action, and 50% when compared against a design based on rigid joints.