Cyclic Performance of Simplified Cold-Formed Steel Friction-Slip Moment Connections with Flat-Flange Beams and Oversized Holes

Previous work by the authors demonstrated that cold-formed steel (CFS) moment-resisting bolted connections incorporating a friction-slip mechanism can effectively delay local buckling and yielding in thin-walled CFS beams with thicknesses between 2 and 6 mm, compared with conventional slip-resistant connections. However, those configurations relied on segmental-flange beams and slotted bolt holes, leading to increased fabrication complexity and construction challenges. To address these limitations, the present study introduces flat-flange beam configurations combined with oversized bolt holes while maintaining the friction-slip energy-dissipation mechanism. The proposed connections are designed to undergo controlled slip before the initiation of local buckling in the CFS beam or bolt shear failure. Finite element (FE) modelling is developed to simulate the cyclic behaviour of the system and is validated against experimental results. Three full-scale cyclic tests are conducted on flat-flange beam-to-column connections with oversized holes, and their performance is compared with previously investigated segmental-flange configurations and slotted-hole systems. The cyclic response is evaluated in terms of strength, stiffness, hysteretic behaviour, energy dissipation and rotational capacity. Although the segmental-flange connections with slotted holes achieve higher peak moment capacity and cumulative energy dissipation, by up to approximately 30% and 50%, respectively, the flat-flange specimens exhibit stable hysteretic behaviour, adequate ductility and rotation capacities exceeding 0.04 rad, consistent with the rotational demand used in AISC 341 qualification of Special Moment Frame connections. The use of oversized holes and a continuous flat flange simplifies fabrication by eliminating segmental flange assemblies, specialised slotted-hole machining and the associated alignment requirements.