Seismic design of cold-formed steel beams based on flexural capacity-ductility - Energy dissipation

In the past decade, cold-formed steel (CFS) has been widely used in building structures due to its excellent structural performance. In particular, due to its remarkable light weight, CFS is ideally suited as a major component of buildings in seismic zones. However, CFS has an inherent characteristic of a large width-to-thickness ratio, which does provide high flexural stiffness, but at the same time weakens the seismic capacity of the member to some extent. Specifically, under seismic loading, members with large width-to-thickness ratios are more prone to local buckling, thus unable to fully consume seismic wave energy. Apparently, the direct application of CFS to buildings in seismic zones is challenging due to the lack of design specifications. Accordingly, for the safety of CFS buildings in seismic zones, the maximum width-to-thickness ratio of CFS members must be specified to ensure that their energy dissipation capacity, bearing capacity, and ductility are adequate. Therefore, in this study, the effect of the web width-to-thickness ratio and flange width-to-thickness ratio of CFS beams on flexural capacity, ductility, and energy dissipation capacity under monotonic and seismic loads is investigated, and a design metric of width-to-thickness ratio threshold (Tw/t) is proposed. Under seismic loading, for CFS members of different cross-section types, when the width-to-thickness ratio is within the specified range of Tw/t, it shall be regarded as fulfilling the requirements of bearing capacity, ductility and energy dissipation capacity. To introduce Tw/t in detail, in this study, a numerical model of the CFS beam is first constructed and its accuracy is verified by comparison with experiments and other studies; Then, the effects of prototype, wall thickness, and section size on bearing capacity, ductility, and energy dissipation capacity under monotonic and seismic loading are analyzed, respectively; Subsequently, the damage modes of CFS beams are discussed and a buckling energy dissipation factor is proposed as an indicator of the energy dissipation capacity of CFS members; Finally, based on the above analyses, the Tw/t of each prototypical CFS beam is determined. The results show that all CFS members with a width-to-thickness ratio within Tw/t can fulfill the seismic design requirements in terms of flexural capacity, ductility and energy dissipation.