ABSTRACT Cold‐formed steel (CFS) beams are made by cold‐working steel sheets or strips to produce precise profiles and dimensions, and they are well‐known for their material efficiency, cost‐effectiveness, and versatility in modern engineered structures, such as modular and prefabricated systems. CFS sections are often used in the construction of industrial facilities, residential buildings, and low‐ to mid‐rise commercial structures due to their high strength‐to‐weight ratio, which allows for minimal material utilization while maintaining structural performance and resilience. Despite these benefits, multiple buckling modes govern the structural behavior of CFS components. Therefore, limiting such buckling deformations in thin‐walled sections is critical for achieving superior efficiency and adaptability in construction practice. This work discusses a test program designed to restrict local buckling deformations in CFS built‐up I‐sections with rectangular compression flanges using a variety of sustainable lightweight fillers. For the first time, bamboo poles, repurposed steel tubes, and timber blocks were utilized as lightweight fillers to prevent local buckling in the compression zone. These fillers were chosen with sustainability in consideration, as all three are either renewable, repurposed, or have a reduced environmental footprint, making them ideal for eco‐friendly and adaptable construction applications. The performance output in the form of peak load, type and magnitude of buckling failure, stiffness, moment capacity, capacity‐to‐weight ratio, and test moment‐to‐yield/plastic moment ratios were evaluated to determine the effectiveness of the various composite stiffening techniques used. Further, the theoretical strengths were also quantified and compared with the test strengths. The test findings suggested that all of the sustainable composite stiffening techniques successfully enhanced the flexural performance of CFS built‐up beams with rectangular compression flanges, although to varying degrees. These findings contribute to expanding the limited dataset available on such lightweight built‐up beams and highlight their potential for construction efficiency, adaptability to evolving functional needs, and long‐term sustainability in modern structural systems.
Dar et al. (2026) studied this question.