Flexural behavior of cold-formed mild steel beams with web holes exposed to high temperature: analytical and experimental investigation

Cold-formed steel (CFS) sections have emerged as pivotal components in construction for sustaining small-scale loads, characterized by their distinctive feature of fabrication without the application of heat. The comprehension of CFS section responses under fire conditions or elevated temperatures stands as imperative in ensuring structural safety. In this investigation, mild steel (MS)—based CFS beams incorporating web holes of various shapes and sizes underwent prolonged heating exposure utilizing an ISO Standard fire curve to emulate real-world fire scenarios. Subsequent to the heating regimen, distinct cooling methods were implemented to restore the beams to ambient temperature. Experimental analyses were performed on beam sections without web holes, while Finite Element Method (FEM) was employed to corroborate the experimental findings. A parametric examination was conducted to study the flexural performance of beams featuring web holes of varying geometries and dimensions. Load assessments were undertaken for all sections under experimental loading conditions utilizing the direct strength method. Extensive analyses were conducted to delineate the influence of web holes, heating and cooling regimes, and failure modes. A significant decline in strength was noted after 60 min of heating. For sections heated for 60 min and cooled with air, a strength loss of 37.41% was observed compared to the unheated section, while the section cooled with water experienced a strength loss of 47.83%. The difference in stiffness between the unheated section and sections subjected to 30 min of heating was observed to be 2.64% and 4.36% for sections cooled with air and water, respectively. As the duration of heating increases, the ductility ratio also displays an upward trend. The lowest ratio is observed for the reference beam section, whereas the highest is noted for the beam section heated for 90 min and subsequently cooled with water.