Flexural Behaviour of Composite Cold Formed Steel Beams

Abstract

The construction industry is looking out for materials and structural members that are economical and state-of-the art. Built-up thin walled Cold-Formed Steel (CFS) sections can be fabricated easily and economically than hot-rolled steel members. These cross-sections generally have thin flanges and webs. But plate buckling is a phenomenon with thin webs which can only be remedied by thickening the web, adding stiffeners or strengthening the web through other means. The provision of diagonal bars in the webs is a new way to increase the out-of- plane stiffness and shear buckling resistance of beams. Experimental and numerical investigations have been performed to investigate the structural benefits of CFS beam without vertical stiffeners in the web (PB), with Vertical stiffeners in the web (PBV), and with rebars in the Shear zone of the web (PBS), with rebars in Shear and Flexure zones of the web (PBSF) and twin inclined rebars as web (PBT).The study was carried out in three stages. In the first stage, twenty-four built- up fabricated CFS specimens with two different depth-to-thickness (d/t) ratios were tested to determine the influence of the presence or absence of diagonal rebars in shear and flexure zones. In all the twenty-four specimens, top and bottom flanges were of the same lipped configuration and dimension. The flanges were spaced apart and web was welded to the flanges to form a built- up I-beam cross section. Experiments were conducted on five types of CFS beams namely CFS beam without vertical stiffeners in web (PB), with Vertical stiffeners in the web (PBV), with rebars in the Shear zone of the web (PBS), with rebars in Shear and Flexure zones of the web (PBSF) and twin inclined rebars as web (PBT). The rebars used for the diagonals and for the twin inclined rebars as web were High Yield Strength Deformed (HYSD) reinforcing bars of Fe415 grade. The yield strength of steel used for eighteen beams was 350 N/mm2, and another six beams was 210 N/mm2.