Numerical Investigation of Cold Formed Steel Plain Channel Stub Columns Subjected to Concentric and Eccentric Compressive Loading

Abstract: Cold-formed steel members are susceptible to local, distortional, global, and interactive buckling modes. The Plain channel section comprises stiffened and unstiffened elements concerning local buckling and does not undergo distortional buckling. Local buckling deformation of the section results in an effective shift in centroid, which further reduces its capacity for pin-supported stub columns compared to fixed-supported stub columns. Plain channels are used mainly as wall studs and are subject to axial compression with bending moments. These conditions require a complete understanding of elements subject to varying compressive stress distribution in local and post-local buckling behaviour. The inter-element interaction can result in the lowest ultimate strength if both stiffened and unstiffened elements undergo simultaneous local buckling. This simultaneous local buckling is demonstrated through the cross-section aspect ratio (web-to-flange ratio), which is generally omitted in the design. Cold-formed steel sections fall under slender sections, which will undergo local buckling before yielding and cannot be designed as per IS:800-2007. The Effective Width Method accounts the local buckling of the cross-section in the design through the various effective widths corresponding to compressive stress distribution in the elements. IS:801-1975 details the design guidelines fo r cold-formed steel members. EWM involves a tedious iterative design procedure and does not account for the inter-element interaction leading to a conservative design. Implementing the EWM is simple for the plain channel but complicated for the crosssections having more elements. The Direct Strength Method, which includes the inter-element interactions and accounts for the gross-section properties without iteration, is simple and effective for any cross-section shape. This study examines the influence of the aspect ratio of the plain channel subject to uniaxial eccentric loading through a systematic numerical analysis and compares the results with DSM predictions. The results are summarized, and essential conclusions on the limitations of DSM are discussed.