Intermittently stiffened cold-formed steel GFRP composite lightweight built-up beams: Experimental investigation and performance assessment

Previous attempts to develop lightweight cold-formed steel (CFS) composite sections have successfully improved their buckling strengths but have been limited to unstiffened profiles only. This paper reports the results of an experimental program on the flexural behavior of newly developed CFSGFRP (Glass Fiber Reinforced Plastic) composite built-up open-section beams. In total, six large-scale specimens were tested under four-point loading with simply supported boundary conditions. To counter the inherent limitation of premature local buckling in the thin-walled CFS sections under compressive stresses, various combinations of intermittent stiffening and GFRP plank packing were adopted to improve the performance of the CFS GFRP lightweight composite beam specimens. The intermittent stiffening and GFRP plank packing were used judiciously in the compression flange and the web region of the specimens. A conventional open-section built-up beam was fabricated using two plain channels fastened through the web as a benchmark to evaluate the flexural performance of the composite beams. Furthermore, a hot-rolled steel beam with equivalent dimensions was also tested to give a broader comparison. The flexural performance of all the beams was assessed in terms of peak strength, initial stiffness, load-deformation response, failure modes and strength-to-weight parameter. The results confirmed the structural feasibility of adopting GFRP to form CFS lightweight built-up beams. The incorporation of GFRP planks significantly improved the flexural capacity by about 180% compared to the conventional CFS built-up beams. They also helped in attaining about 80% of the equivalent hot-rolled steel beam's flexural strength, resulting in highly efficient built-up beams for practical applications.