Composite structures are increasingly being utilized in modern construction. This computational analysis focuses on the structural performance of composite beams formed by thin-walled, cold-formed steel channel sections strengthened with concrete. The primary objective of this research was to enhance the strength and stability of composite cold-formed steel beams. In this study, back-to-back C-channel sections and concrete slabs with various stiffener configurations were analyzed. The key parameters considered include stiffener spacing, type, and thickness. Additionally, different beam cross-sections, such as C-channel and sigma sections, were investigated. A finite element analysis was conducted using the ABAQUS program, incorporating both geometric and material nonlinearities. The developed models were validated against experimental results from previous research and existing design guidelines. Three beam specimens were examined in this study to assess their structural behavior under static loading conditions. A novel aspect of this research is the investigation of composite cold-formed steel beams under a combination of ultra-high-performance concrete (UHPC) and negative moment effects. The load–deflection behavior of all beam specimens was analyzed, considering variations in cross-sectional dimensions and span lengths. Additionally, the study highlights key material properties, including the maximum compressive strength of concrete, the yield strength of cold-formed steel channels, and the cross-sectional area of the steel components for each beam specimen. This research provides valuable insights for structural engineers, contributing to the optimization of composite cold-formed steel beam design for enhanced performance in practical applications.

Slender welded steel I-girders rely on web post-buckling strength, but their failure mode depends on the interaction of web shear buckling, flange local buckling, and lateral-torsional buckling. This study examines the effect of a longitudinal stiffener, consisting of plates welded to both sides of the web at one-fifth of the web depth from the compression flange. Four full-scale girders with [[EQUATION]] of 115 and 154 and [[EQUATION]] of 1.83 and 1.38 were tested under four-point bending, including two stiffened specimens. The stiffener increased maximum load by 31% and 48% and shifted failure from flange local buckling in the central panel to shear buckling in the end panels. A validated nonlinear shell finite element model was then used in a 120-model parametric study of laterally unbraced girders with [[EQUATION]] to 300, [[EQUATION]] to 20, and [[EQUATION]] to 3. The results were summarized in a failure-mode map and stiffener-benefit chart. A capacity-envelope model combining sub-panel shear buckling, effective-section bending, and lateral-torsional buckling identified the governing mode in 86% of the models. Calibrated reduction relations predicted finite element strengths with a mean ratio of 1.02 and coefficient of variation of 0.19. Measured capacities exceeded AISC 360, Eurocode 3 Part 1-5, and Egyptian code predictions by 24% to 56%, mainly because of the near-fixed web-to-flange junction and the neglect of stiffener effects in flexural and lateral-torsional checks.