Cold-Formed Steel Portal Frame

Abstract

Cold-formed steel portal frames are a popular form of construction for low-rise commercial, light industrial and agricultural single-storey buildings of spans of up to 30 m. Such buildings typically use cold-formed steel channel-sections for the columns and rafters, with joints formed through back-to-back gusset plates bolted to the webs of the channel-sections. This chapter investigates effects of frame topography on the frame weight and cost per metre length of building. An optimisation technique that uses a real-coded genetic algorithm is applied to search for the optimum topography of steel portal frame for a building, to minimise the cost of the main frame of such buildings. The key decision variables considered in this algorithm consist of both the spacing and pitch of the frame as continuous variables, as well as the discrete section sizes. A routine taking the structural analysis and frame design for cold-formed steel sections is embedded into the genetic algorithm. The real-coded genetic algorithm handles effectively the mixture of design variables, with high robustness and consistency in achieving the optimum solution. All wind load combinations according to Australian code are considered in this research. Also, frames with knee braces are included for which the optimisation achieved even larger savings in cost.