Experimental studies on mechanical properties of Q890D steel in the entire fire process

Mechanical properties of steel at elevated temperatures induced by fire are essential for structural fire-resistance design and analysis. Currently, the mechanical properties of high-strength steel have been widely examined in the heating and post-fire stages, whereas little study has been conducted on the fire-cooling stage. This study experimentally investigates the mechanical properties of high-strength steel Q890D throughout the entire process of fire, including fire-cooling stage. It was found that mechanical properties of Q890D steel in the fire-heating stage are solely determined by the current test temperature (Tt), while those in the fire-cooling stage are also affected by the prior peak heating temperature (Tp). When Tp is below 600 °C, mechanical properties in fire-cooling stage at the same Tt are close to those in the heating stage. However, after Tp exceeds 700 °C, the discrepancies between them magnify and become significant, which might be related to changes in the microstructure of the steel during heating and cooling processes. Based on test results, formulas were proposed to predict the mechanical properties of Q890 steel during the entire process of fire. •Mechanical properties of Q890D HSS during the entire fire process were studied.•A cooling stage influence coefficient (λ) was introduced.•Formulas were proposed for mechanical property parameters of Q890D HSS during the entire fire process.•The presented work enables more reliable structural analysis of steel structures during the cooling stage of fire.