Effect of holes and stiffeners on the behavior of Eccentric loaded cold-formed steel built-up channel columns - numerical investigation

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Cold-formed steel members often need to be opened in the web due to the passage of the building system pipeline. In general stiffeners of the web maybe strengthen their structural performance. In the field of cold-formed steel structures, such as multi-layer houses, wall frames and portal frames, the use of built-up cold-formed steel channel sections are becoming increasingly popular. Such members are often under the combined effects of compression and bending. Limited research has been done on the subject. In this paper, the back-to-back built-up cold-formed steel beam-columns are studied to understand the influence of stiffeners and openings on the ultimate bearing capacity and failure mode. First, this paper presents the results of experimental tests performed on back-to-back built-up cold-formed steel channel sections under axis and eccentric compression. Detailed observations on different failure modes and column strengths were made through varying the location of stiffeners and holes, length and cross section of columns, the magnitude and direction of eccentricity. Then, a non-linear finite element model was developed which includes material non-linearity, geometric imperfections and explicit modeling of web fasteners. A comprehensive parametric study consisting of 222 models has been carried out covering a wide range of eccentricity and web fasteners for the considered back-to-back built-up columns. Finally, based results of numerical research, the ultimate capacities were used to assess the performance of the current technical specifications of cold-formed thin-walled steel structures, North American codes, AS/NZS and China specification. As the test cannot be done during the epidemic, the correctness of the formula needs to be verified by subsequent tests.