Mechanical properties of high-strength Q690 steel at elevated temperature

High-strength steels are finding wide applications in steel-framed buildings. Therefore, fire resistance design of high-strength steel structures has gained more attention in recent years. Rapid reduction in mechanical properties, together with high creep deformations, are the most significant factors influencing the fire behavior of high-strength steel structures. A comprehensive experimental investigation was carried out to evaluate temperature-dependent mechanical properties and creep deformation of high-strength Q690 steel with nominal yield strength of 690 MPa. Standard tensile tests were conducted to obtain the mechanical properties of Q690 steel at temperatures ranging from 20 to 900°C. Test data on strength and elastic modulus properties show that the reduction factors developed for carbon (mild) steel are not applicable to high-strength Q690 steels. Therefore, new reduction factors for temperature-dependent yield strength and elastic modulus, as well as the stress-strain relationship, were developed. Creep tests were also carried out to quantify the creep deformation of Q690 steel at temperatures ranging from 450 to 900°C. Data from creep tests are used to develop relations for expressing creep as a function of temperature and stress. These relations, which are based on the Fields and Fields model, can be used to account for creep effects in modeling the response of Q690 steel structures exposed to fire.