Post-fire mechanical properties of high strength structural steels S460 and S690

In the recent decade, high strength steels have gained more and more popularity in the applications of building industry. The steel members made of high strength steels in building structures are sometimes inevitably exposed to fire hazards, after fire whether they are reusable or not, it needs a reliable evaluation. Post-fire mechanical properties of steels play an important role in evaluating the performance of steel structures after fire. However the post-fire mechanical properties of high strength steels have not been reported in the literature. Hence, there is an urgent need to understand the mechanical properties of high strength steels after cooling down from fire. A research project based on experimental study was carried out to investigate the deterioration of mechanical properties of high strength steels after fire. Tensile coupon tests were undertaken on two commonly used high strength steel grades S460 and S690 after cooling down from elevated temperatures up to 1000 °C. The post-fire elastic modulus, yield and ultimate strengths, ductility and stress–strain curves were obtained from this study. It is found that the post-fire mechanical properties of high strength steels are different from that of mild steels. Two separate sets of predictive equations were proposed for evaluating the mechanical properties of S460 and S690 after fire, which agree well with the test results.