Post-fire residual material properties of cold-formed steel elliptical hollow sections

An experimental programme to investigate the residual material properties of fire exposed cold-formed steel elliptical hollow sections has been presented in this study. The test specimens were made of cold-formed steel elliptical hollow sections (CFSEHS) of the mild steel grade. The CFSEHS members were heated inside a gas furnace by generally following the ISO-834 standard fire (1999, [1]) curve. A total of 4 sets (set-1, 2, 3 and 4) of fire exposures with peak temperatures of 300 °C, 550 °C, 750 °C and 900 °C was carefully selected for this investigation. The identical sets of CFSEHS members were exposed to these fire exposure temperatures followed by their natural cooling inside the gas furnace. Upon complete cooling, 36 longitudinal tensile coupon specimens were fabricated from the flattest and curviest portions of ISO-834 standard fire exposed CFSEHS members. Subsequently, residual material properties and corresponding residual factors were determined from the static post-fire stress-strain curves. It is worth mentioning that no investigation is available on the post-fire material behaviour of CFSEHS members. Therefore, using the test results of this study, empirical equations are proposed to predict the post-fire residual material properties of CFSEHS members