Design approach of cold-formed steel portal frames

Abstract

A structural arrangement of a portal frame that is easy to fabricate and assemble is developed. The rafter and column members are formed from single cold-formed channel sections, which are bolted, back-to-back at the eaves and apex joints, and connected to the foundation through angle irons. Variables in the frames include the span, width of the channel flanges and the strength of the channels. The design of the frame members follows the traditional approach of applying the effective width method to control local buckling, followed by an assessment of cross-sectional and buckling requirements. However, the yield and overall buckling requirements are modified by a factor of 0.8 to account for stress concentrations, shear lag and bearing deformations in the connections. All deflections of the frames considered are found to be within the limits provided in the literature and by the two codes of practice. It is proposed that the frames of the structure should be provided in a kit form and erected in “meccano” fashion