AbstractThe objective of this paper is to to ascertain the reliable mechanical properties of cold-formed Q345 steel at elevated temperatures while considerting the effects of tensile strain rate and specimen width. This paper presents an experimental study on the mechanical properties of cold-formed Q345 steel at temperatures ranging from 20°C to 800°C tested with two specimen widths and three tensile–strain rates, namely 0.06/min, 0.6/min, and 1.2/min. Tensile specimens were fabricated from a steel plate with a nominal thickness of 2.5 mm and tensile tests were carried out to determine the stress–strain relationship, yield strength, tensile strength, and elastic modulus. The test results showed that the tensile–strain rate has a maximum influence of 9% on yield and tensile strength at 600°C and the specimen width has a maximum influence of 14% on yield and tensile strength at 400°C. The maximum influence of the tensile–strain rate and specimen width on the elastic modulus is 18% and 12% respectively at 500°C. The necking phenomenon is less noticeable at temperatures below 300°C but is clearly observed at temperatures above 300°C. The comparison of the test results with predictions obtained from design standards (EC3, AISC, and AS4100) indicates a good agreement on the yield and tensile strength, but the magnitudes of elastic modulus obtained from the test are considerably higher than those obtained from the design standards. Based on averaged values of the test results associated with different tensile–strain rates and specimen widths, predictive equations were proposed to determine the mechanical properties of cold-formed Q345 steel at elevated temperatures.