Proceedings of the 6 rd International Conference on Civil Structural and Transportation Engineering (ICCSTE'21) Niagara Falls, Canada – May 17-19, 2021 Paper No. XXX (The number assigned by the OpenConf System) DOI: TBA XXX-1 A Comparison Investigation into Analysis Methods to Determine the Buckling Capacity of South African Cold-Formed Steel Lipped Channel Sections Johan van Vuuren 1 , Jeffrey Mahachi 2 1 University of Johannesburg, Johannesburg, South Africa 1 johanvanvuuren026@gmail.com; 2 jmahachi@uj.ac.za Abstract - This paper presents a comparison investigation into analysis methods to determine the buckling capacity of South African cold-formed steel lipped channel sections. The research considers the evaluation of buckling capacities of five different column lengths using five different methods: 1. experimental tests; 2. the Direct Strength Method (DSM) as prescribed in SANS 10162-2; 3. Eurocode 3; 4. simplified Finite Element Analysis (FEA), i.e. only beam modelling elements; and 5. finely refined FEA, i.e. plate modelling elements. All columns have a 75 x 50 x 20 x 2.0 (h x b x c x t mm) cold-formed lipped channel cross-section. A comparison of the experimental buckling results to the aforementioned methods shows that the Eurocode 3 and DSM buckling resistance values overestimate the buckling loads by 23.8% and 12.7%, respectively. For the two Finite Element Model (FEM) buckling analyses; the simplified FEA method yields an overestimation of 76.9% and the finely refined FEA yields an overestimation of 74.8%. It is recommended that the DSM is used to calculate the buckling resistance of cold-formed lipped channels. Keywords: Buckling, thin-walled, cold-formed, Direct Strength Method, Finite Element Analysis. 1. Introduction For the design of cold-formed steel column sections, Appendix 1 of the North American Specification for the Design of Cold-Formed Steel Structural Members presents the Direct Strength Method (DSM) [1]. This method was introduced in 2004 and integrates existing code design procedures with the distinctive behaviour of structural thin-walled steel [2]. The DSM has furthmore been adopted as section 7 of SANS 10162-2: Cold-formed steel structures design code [3]. West-Russell et al. [4] assessed the inherent reliability of SANS 10162-2 codes for cold-formed lipped channel steel columns using the Direct Strength Method (DSM). In the study, it was revealed that the buckling resistance of cold-formed steel compression members exhibits a low level of reliability while considering the safety margin presented in SANS 10160-1: Basis of Structural Design codes [5]. Furthermore, it was revealed that the global buckling mode of the column members yields the lowest reliability levels. It was, therefore, recommended that different capacity reduction factors should be applied to each dominating buckling mode and that the DSM replaces the effective width method for the design of cold-formed steel columns. In a similar study by Bauer [6], it was revealed that the safety margin achieved when using the DSM, as prescribed by SANS 10162-2, to design cold-formed steel structures does not meet the reliability target prescribed by SANS 10160-1. Also, Dundu [7] conducted a study that compared experimental results with the DSM. The research investigated the buckling resistance values of short cold-formed lipped channels. It was found that the code is not conservative enough for the design of structural columns. The history of buckling failure modes for short cold-formed lipped sections (thin-walled steel) is presented by Dundu [7]. The buckling of a structural member is defined as a mode of failure, this is directly linked to the stability of a structure, and if buckling occurs then the member is unstable. The buckling modes of a lipped channel are limited to Local Buckling (LB), Distortional Buckling (DB) and Global buckling (GB). LB is defined as the plate flexural failure of the lip, flange, and web elements when the line junction of both corners does not change as illustrated in Fig. 1 (a). DB occurs at the ultimate failure by the bending of the web in either outward or inward rotational direction as illustrated in Fig. 1 (b) and (c). GB of a compression member does not involve distortion of the cross-section, instead out of plane translation (flexure) and/or rotation (torsion) about the shear centre of the entire cross-section occurs [3]. GB is associated with flexural, torsional, or flexural- torsional buckling as illustrated in Fig. 1 (d), (e) and (f) respectively.