Experimental study on mechanical properties of high-strength fire-resistant steel at elevated temperatures

In order to study the mechanical properties of high-strength fire-resistant steel at elevated temperatures, the damage modes, stress-strain relationship curves, mechanical property parameters and thermal expansion coefficients of each grade of fire-resistant steel at 20-800 ℃ were obtained through steady-state tensile tests and thermal expansion deformation tests of domestic Q345FR, Q420FR and Q460FR fire-resistant steel at elevated temperatures, and compared with the elevated-temperature properties of ordinary structural steel and the relevant provisions of European and Chinese fire-resistant design codes. The research results show that the yield strength and tensile strength of domestic high-strength fire-resistant steel are higher than room temperature when the temperature is lower than 350-400℃. When the temperature exceeds 400℃, the yield strength and tensile strength start to drop rapidly. The formula for calculating the elastic modulus and strength of ordinary structural steel at elevated temperatures given in European code EC3 is not applicable to high-strength fire-resistant steel, and the elevated-temperature mechanical properties of fire-resistant steel in GB 51249—2017 ‘Code for fire safety of steel structures in buildings’ take values closer to the test results of Q345FR fire-resistant steel in this paper, but significantly smaller than the test results of Q420FR and Q460FR high-strength fire-resistant steel in this paper. In this paper, for Q420FR and Q460FR high-strength fire-resistant steel, the fitting formulas of elastic modulus, yield strength and tensile strength change coefficient at elevated temperatures are proposed, which can be used for fire resistance design of fire-resistant steel structures.