Mechanical properties of thin sheet steel after exposure to high temperatures

Abstract

There is presently very limited research work on the mechanical properties of thin sheet steel (TSS) after exposure to high temperatures (at post-fire condition). In this study, 35 coupon specimens were tested after being exposed to high temperatures. The coupon specimens were extracted from three different grades of TSS, namely, grades of G450, G500 and G550, with nominal 0.2% proof stresses (yield strengths) of 450, 500 and 550 in MPa, respectively. The TSS grades G450, G500 and G550 had nominal thicknesses of 1.90, 1.20 and 0.42 mm, respectively. The liquefied petroleum gas (LPG) furnace and the electronic furnace were used to heat the coupon specimens to four different nominal peak temperatures up to 900 °C, where the ISO-834 standard fire curve was followed by the LPG furnace. The specimens were generally soaked before being cooled to ambient temperature conditions inside the furnaces. Tensile coupon tests were conducted on the TSS, where the mechanical properties associated with the stress-strain curves were investigated, including Young's modulus, 0.2% proof stress, ultimate strength, ultimate strain and fracture strain. The residual mechanical properties at post-fire conditions were compared in terms of steel grades, the two different heating methods and the peak temperatures the specimens exposed. Furthermore, the retention factors were compared with those predicted by proposed equations in the literature. New predictive curves are proposed for the determination of the residual mechanical properties of TSS after they were exposed to elevated temperatures. It was demonstrated that the proposed predictive curves are suitable for TSS with nominal 0.2% proof stress ranged from 450 to 550 MPa, and nominal thickness up to 1.90 mm.