Mechanical properties of cold-formed steel tubular sections at elevated temperatures

Cold-formed steel tubular sections have been increasingly used as structural components in modern structures due to the many advantages they possess over conventional hot-rolled sections. Lack of knowledge on the structural fire performance of cold-formed steel tubular sections has raised concerns with respect to fire safety designs. Hence the knowledge of elevated temperature mechanical property deterioration characteristics of these sections is essential. Although design standards and past research studies provide empirical equations to predict these mechanical property deterioration characteristics, a detailed experimental investigation of cold-formed steel tubular sections to determine their elevated temperature mechanical properties is scarce. Therefore, an experimental investigation was carried out to determine the mechanical properties of cold-formed SHS, RHS and CHS at elevated temperatures. Tensile coupon tests were performed at temperatures ranging from 20 °C to 800 °C under steady state conditions to determine the reduced values of yield strength, stress at 2% strain, elastic modulus, and ultimate strength with increasing temperatures. Experimental results were then compared with those obtained from the current design standards and past research studies, which lead to a conclusion that the available reduction factors are either unsafe or more conservative. Therefore, suitable equations were proposed to determine the mechanical property reduction factors at elevated temperatures. This paper presents the details of this experimental investigation of cold-formed steel tubular columns and the results, which include the developed equations and a stress-strain model for elevated temperatures.