Post-fire mechanical response of Q960E ultra-high-strength structural steel

Abstract

The ultra-high-strength steel (UHSS) has gained significant attention in recent years owing to its prominent benefits in structural performance, economics and environmental aspect. The fire resistance of steel structures is always of great concern as the mechanical properties of steel are sensitive to high temperatures which could threaten the safety of the steel structures, and so do UHSS structures. The post-fire mechanical performance of steel is crucial for evaluating the residual capacity of the structure. Therefore, it is also necessary to evaluate the post-fire mechanical properties of UHSS. In this study, tensile tests were carried out to investigate the post-fire mechanical properties of Q960E UHSS with two types of cooling techniques, i.e. cooling in air or cooling in water. The residual elastic modulus, yield stress, tensile strength, tensile strain, rupture stress, and percentage reduction of area of Q960E UHSS subjected to various temperature levels were obtained from the post-fire stress-strain curves. The influence of the cooling techniques and temperature level on the post-fire mechanical properties of Q960E UHSS were discussed, and some empirical predictive equations were proposed for evaluating the post-fire mechanical properties. Finally, a novel stress-strain model was also proposed to predict the post-fire response of Q960E UHSS. The proposed model showed good consistency with laboratory experimental results. Therefore, it is concluded that the model can provide accurate predictions for the plastic strain-true stress curve for various types of steels.