高强钢高温下和高温后力学性能指标的标准值研究

高强钢高温下和高温后的力学性能是进行高强钢结构抗火设计和火灾后评估的重要基础。我国GB 51249—2017《建筑钢结构防火技术规范》和欧洲规范EC3中针对普通低碳钢提出了高温下屈服强度和弹性模量计算公式，但其不适用于高强钢。国内外学者对高温下和高温后高强钢力学性能已开展了一系列试验研究，但由于钢材强度等级、试验设备、加热速率和加载制度等影响，导致试验结果离散性较大，不能应用于实际工程中。同时不同学者提出的力学性能指标计算式各不相同，均不具有普遍适用性。采用数理统计中t分布与置信区间的方法对高强钢高温下和高温后力学性能试验数据进行统计分析，得到不同温度下力学性能指标具有95%保证率的标准值，拟合出高强钢高温下和高温后力学性能指标的计算式，并与GB 51249—2017和欧洲规范EC3预测结果进行对比。结果表明：自然冷却和浸水冷却条件下，高强钢高温后屈服强度发生明显下降的转折点分别是600℃和 500℃；高温下高强钢的屈服强度折减系数低于普通结构钢；高强钢弹性模量折减系数在作用温度小于600℃时低于普通结构钢的，而在温度大于600℃时高于普通结构钢的。

Study on nominal values of mechanical properties of high strength steel at elevated temperature and after fire exposure

The mechanical properties of high-strength steel at elevated temperature and after high temperature are important basis for fire resistance design and post-fire evaluation of high-strength steel structures. The calculation equations of mechanical properties at elevated temperature proposed by the current code GB 51249—2017 ‘Code for fire safety of steel structures in buildings’and Eurocode EC3 are not applicable to high-strength steel. A series of experimental studies on mechanical properties of high-strength steels at elevated temperature and after fire exposure have been studied world-widely. Due to the influences of steel strength grade, test equipment, heating rate, and loading system, the test results are discrete and cannot be applied to actual engineering. At the same time, the predictive equations of mechanical properties proposed by different scholars are different, which are not universally applicable.The test data of mechanical properties of high-strength steels at elevated temperature and after fire exposure were analyzed by means of t distribution and confidence interval, and the nominal values of 95% guarantee rate of mechanical properties at different temperatures were obtained. The equations for calculating the mechanical properties of high-strength structural steels at elevated temperature and after fire exposure were fitted and compared with those predicted by GB 51249—2017 and Eurocode EC3. The results show that the turning points at which the strength of the steel decreases significantly after air and water cooling conditions are 600 ℃ and 500 ℃, respectively. The yield strength reduction factor of high strength steels at high temperature is lower than that of mild structural steel, the elastic modulus reduction factor is lower than that of common mild steel under 600 ℃ but higher than that of mild steel beyond 600 ℃.