Axial behavior and stability of built-up cold-formed steel columns with and without concrete infill: Experimental and numerical investigation

In recent years, cold-formed steel (CFS) built-up sections have gained a lot of attention in construction. This is mainly because of their structural efficiency and the design advantages they offer. They provide better load-bearing strength and show greater resistance to elastic instability. This study looks at both experimental and numerical analysis of built-up CFS columns. The columns were formed by joining two C-sections in different ways: back-to-back, face-to-face, and box arrangements. Each type was tested with different slenderness ratios. For the experiments, the back-to-back and box sections were connected using two rows of rivets. The face-to-face sections, on the other hand, were joined by welding. In order to improve axial strength and overall stability, all column samples were filled with ordinary concrete, conforming to class C25/30. The numerical modeling was done in ABAQUS to study the mechanical behavior of the columns. This helped in understanding how different joining methods affect their axial compression performance. Analytical checks were also carried out using Eurocode 3 for hollow sections and Eurocode 4 for concrete-filled sections. The role of concrete confinement was examined as well, following American Concrete Institute (ACI) guidelines, for both face-to-face and box-shaped columns. The numerical results matched closely with the experimental findings, with variations of less than 5%. The study identified key failure modes such as local buckling and distortional buckling. It highlighted how section shape, type of connection, and concrete infill all play a major role in improving the strength of built-up CFS columns.