Cold-formed steel portal frame moment-resisting joints: behaviour, capacity and design

The work presented in this paper investigates the strength of moment-resisiting apex brackets of cold-formed steel portal frames. The results of two previously reported full-scale portal frame tests, where the frames failed through buckling of the apex bracket, were used to validate a finite element model that included material nonlinearity, geometric imperfections, and bolt bearing behaviour. From portal frame test results as well as the finite element results, the importance of appropriate detailing for the apex brackets for strength is demonstrated. A simplified finite element model of the apex bracket is then presented, again validated against previously reported experimental tests. The effects of geometrical parameters of the brackets, bolt-group configuration, and yield stress of brackets were investigated through a parametric study comprising 648 models. From the results of this parametric study, design equations are proposed that can be used by practicing engineers to predict the strength of apex brackets used for cold-formed steel portal frames.