Elevated temperature material properties of cold-formed advanced high strength steel channel sections

Abstract

Fire safety remains a paramount concern in the design and application of cold-formed structures, making the understanding of mechanical properties of advanced high strength steel (AHSS) at elevated temperatures essential. This paper presents a comprehensive experimental investigation into the mechanical properties of cold-formed AHSS channel sections and their virgin material at elevated temperatures. A total of 60 coupon specimens were extracted from the middle of web element, the corner-flat adjunction of web element, as well as the middle of flange element of the cold-formed AHSS channel sections. Moreover, 20 additional coupon specimens were extracted from the cold-rolled AHSS sheets, which is the virgin material. Elevated-temperature tensile coupon tests were carried out by using steady-state test method under 10 different temperatures up to 800 °C. Full range of stress-strain curves were obtained for the virgin material and three locations of the cold-formed AHSS channel sections. Key mechanical properties including elastic modulus, yield stress and ultimate strength were obtained. Differences in the mechanical properties of coupons with different thicknesses and from various cutting positions were investigated. The obtained reduction factors of the studied AHSS were compared with existing design rules, including European, American, and Australian specifications, as well as predictive models from related research work. New design curves were proposed to provide an accurate and conservative estimation of the reduction in mechanical properties at elevated temperatures, and constitutive stress-strain models were also proposed.