Buckling behaviour of back‐to‐back cold‐formed steel channels under bending: An experimental study

Abstract Cold‐formed steel profiles are increasingly in demand in the construction market because of their speed of assembly and low material consumption. Thus, it is necessary to investigate their behaviour in depth, since in recent years they have been used as the main structural components of buildings. The paper presents an experimental program where several types of built‐up section configurations were tested made of lipped or plain channels, such as simple built‐up back‐to‐back and back‐to‐back with spacers cross‐sections and two types of discrete connections, i.e. bolts and spot welding. The static scheme of the beams used the 4‐point bending setup so that the central area is subject only to the bending moment. The length between the loading points was monitored to capture the behaviour of the beams from local to distortional and interactive local‐global buckling. A total of thirty beams subjected to pure bending with built‐up sections were tested. Additionally, out‐of‐plane displacements were restricted at the loading points to control the failure area. Before the tests were performed, the sectional dimensions and imperfections of the elements were measured, as this represents a critical issue in the behaviour of thin‐walled cold‐formed steel elements. A 3D laser scanner was used to determine the initial imperfections. The records allowed measurement of the initial imperfections in relation to the nominal cross‐section. Force‐displacement curves of the tests highlight the good performance of spot‐welds to reach similar resistance as for the bolted elements. The gapped built‐up elements showed a higher resisting force when compared to the direct contact back‐to back elements prone to global buckling.