Section moment capacity design rules for rivet fastened rectangular hollow flange channel beams

The rivet fastened Rectangular Hollow Flange Channel Beam (RHFCB) is a new type of cold-formed steel section, made of two torsionally rigid rectangular hollow flanges, connected to a web via intermittent rivet fastening. The hollow flanges and the absence of free edges in the RHFCB contribute to improved structural performance. The structural behaviour of the RHFCB is unique compared to other conventional cold-formed steel sections and its moment capacity reduces with increasing rivet spacing. The current cold-formed steel design standards do not provide a calculation method to include the effects of intermittent fastening. In this research an extensive parametric study was conducted using validated finite element models to investigate the section moment capacity of RHFCBs. This paper presents the findings from the parametric study and proposes new design equations for the section moment capacity of RHFCBs in the Direct Strength Method format. The parametric study considers various slenderness regions, section dimensions and rivet spacing. In the new design equations, a reduction factor parameter is included to calculate the section moment capacity of RHFCBs at any rivet spacing up to 200 mm. Optimum rivet spacing was also recommended for RHFCBs.