高强度耐火钢高温下力学性能试验研究

为研究高强耐火钢在高温下的力学性能，通过国产Q345FR、Q420FR、Q460FR耐火钢的高温下稳态拉伸试验和热膨胀变形试验，得到了20~800℃下各等级耐火钢的破坏模式、应力-应变关系曲线、力学性能参数及热膨胀系数，并与普通结构钢高温性能以及欧洲、中国的抗火设计规范的相关规定进行了对比。研究结果表明：在温度低于350~400℃时，国产高强耐火钢屈服强度、抗拉强度高于常温的，当温度超过400℃后，屈服强度、抗拉强度开始快速下降；欧洲规范EC3中给出的高温下普通结构钢的弹性模量、强度计算公式不适用于高强度耐火钢；温度低于450℃时，耐火钢试验值与GB 51249—2017《建筑钢结构防火技术规范》中普通钢取值更吻合；温度高于450℃时，耐火钢试验值与规范GB 51249—2017中耐火钢取值更吻合。针对Q345FR、Q420FR、Q460FR高强耐火钢，提出了高温下弹性模量、屈服强度、抗拉强度变化系数拟合公式，可用于耐火钢结构抗火设计。

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.