Elevated temperature mechanical properties of cold-rolled steel sheets and cold-formed steel sections

Cold-formed steel (CFS) is increasingly used in building construction in many countries due to its lightweight and fast and easy construction characteristics. However, its fire resistance is not well understood, which may restrict its applications. For fire design purposes, a good knowledge of the elevated temperature mechanical properties of CFS is essential. Although several useful studies have been conducted on the mechanical properties of CFS, the elevated temperature reduction factors vary significantly among them while no predictive equation is available to calculate the proportional limit stress of CFS at elevated temperatures. Moreover, they also show significant variations between the elevated temperature reduction factors of cold-rolled steel sheets and CFS sections. In this research, low and high strength cold-rolled steel sheets and high strength CFS lipped channel sections and floor decks were tested in the temperature range of 20–700 °C under isothermal conditions to determine the reductions in their mechanical properties. Predictive equations given in AS/NZS 4600 for yield strength and Young's modulus were verified, and new predictive equations for ultimate strength, stress at 2% total strain, 0.05% proof stress and proportional limit stress were proposed. Finally, a two-stage stress-strain model was proposed to accurately predict the stress-strain curves of CFS at ambient and elevated temperatures.