Material properties of cold-formed high strength steel at elevated temperatures

This paper presents the material properties of cold-formed high strength steel at elevated temperatures. Material properties at elevated temperatures have a crucial role in fire resistance design of steel structures. The fire resistances of steel structures in the existing international standards are mainly based on experimental data of hot-rolled mild steel. However, investigation of high strength steel at elevated temperatures is limited. Therefore, a test program has been carried out to investigate the material properties of cold-formed high strength steel at elevated temperatures. The coupon specimens were extracted from cold-formed high strength steel square and rectangular hollow sections with nominal yield stresses of 700 and 900 MPa at ambient temperature. The coupon tests were carried out through both steady and transient state test methods for temperatures up to 1000 degrees C. Material properties including thermal elongation, elastic modulus, yield stress, ultimate strength, ultimate strain and fracture strain were obtained from the tests. The test results were compared with the design values in the European, American, Australian and British standards. The comparison results revealed the necessity of proposing specified design rules for material properties of cold-formed high strength steel at elevated temperatures. New design curves to determine the deterioration of material properties of cold-formed high strength steel at elevated temperatures are proposed. It is shown that the proposed design curves are suitable for high strength steel materials with nominal yield stresses ranged from 690 to 960 MPa at ambient temperature.