Experimental and Numerical Investigation of Moment Capacity of Cold-Formed Steel Built-Up Box Beam with Self-Drilling Screw Connection

The structural behavior of Cold-Formed Steel (CFS) built-up beam sections have been extensively investigated by numerous researchers. Most existing studies focus primarily on the use of screws solely to assemble two channel profiles into built-up sections. This study proposes the use of self-drilling screws for connecting two separated segments of CFS built-up box beam. These box beams are assembled from two channel sections C 75×35×0.75 placed face-to-face. Their flexural strength is investigated by two methods: experiment, and Finite Element Analysis (FEA). The experiment comprises by means of four-point flexural test at simple beam with lateral restraint at support. This study involves a two-stage experimental test, where at the first stage three beams are tested without any connection, and the second stage employs beam with a specific connection, namely Cf connection at the beam’s mid-span. This connection is un-spliced self-drilling screw connection. FEA models have been developed and compared to the experimental results. It is shown that the FEA models can accurately predict the behaviour of CFS built-up box beams without and with Cf connections. The experimental and numerical results were compared with the design strength predicted by Direct Strength Method (DSM) for CFS structures, only for the beams without Cf connection. Beam specimens without Cf connection experienced failure due to local buckling at the upper flanges under the applied loads. At the beam with screw connections, local buckling predominantly occurred at the web area near the connection zone. Those local modes are also shown by the FEA models.