Mechanical properties and constitutive model of Q460 steel during the fire-cooling stage

Abstract

The mechanical properties of steel under fire-induced elevated temperatures is fundamental and crucial for structural fire-resistance design and analysis. Mechanical properties of high-strength steel (HSS) during the fire-heating and post-fire stages have been extensively investigated, while those during the fire-cooling stage were rarely studied. This study investigated the mechanical properties of HSS Q460 during the fire-cooling stage by steady-state tensile experiments Results show that the mechanical performance of HSS Q460 at the fire-cooling stage is not only related to the test temperature (Tt) but also the peak heating temperature (Tp) before cooling for tests. The strength of HSS Q460 at identical Tt shows an overall download trend with the increase of Tp. The mechanical properties of HSS Q460 at the fire-cooling are similar to those at the fire-heating stage when Tp is not greater than a certain value. This value is 600 °C for Young’s modulus and yield strength f0.2, and 400 °C for yield strength f1.0, f2.0 and ultimate strength. When Tp exceeds certain values, the Young’s modulus and strengths at the fire-cooling stage are less than those at the fire-heating stage. Moreover, the mechanical properties of HSS Q460 were compared with those of HSS Q690, indicating that the degradation rules of mechanical properties of HSSs Q460 and Q690 differ during the fire-cooling stage. Besides, formulas were proposed to calculate the mechanical properties and stress–strain relationship of the HSS Q460 during the fire-cooling stage.