10.17: Mechanical properties of high strength Q690 steel at elevated temperatures

Abstract

ABSTRACTHigh strength steels have been used extensively as primary load bearing structural members in many applications in the building industry. Therefore, fire safety design of structures using such steels has become more important. Deterioration of mechanical properties and creep deformation are considered the most important factors affecting the behaviour of steel structures in fires. A research project based on experimental studies was, therefore, undertaken to investigate the deterioration of mechanical properties and creep of high strength Q690 steel with nominal yield strength of 690MPa. Tensile coupon tests were undertaken to determine the mechanical properties of this steel at temperatures ranging from 20 to 900°C. Test results showed that the currently available reduction factors are not applicable to fire safety design of high strength Q690 steels. Therefore, new predictive equations for the mechanical properties of yield strength and elasticity modulus were developed at elevated temperatures. Creep test were also carried out to quantity the creep deformation of Q690 steel at temperatures ranging from 450 to 900°C. Results from creep tests are utilized to develop relations for expressing creep as a function of temperature and stress. These relations, which are based on Fields & Fields model, can be utilized to account for creep effect in modelling the response of Q690 steel structures exposed to fire.