\r范圣刚^{1, 2}，刘 平²，石 可²，肖韩杰²，钱 峰²，方 超\r²\r
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AuthorsHTML:\r范圣刚^{1, 2}，刘 平²，石 可²，肖韩杰²，钱 峰²，方 超\r²\r
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AuthorsListE:\rFan Shenggang^{1, 2}，Liu Ping²，Shi Ke²，Xiao Hanjie²，Qian Feng²，Fang Chao\r²\r
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AuthorsHTMLE:\rFan Shenggang^{1, 2}，Liu Ping²，Shi Ke²，Xiao Hanjie²，Qian Feng²，Fang Chao\r²\r
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Unit:\r1. 东南大学混凝土及预应力混凝土结构教育部重点实验室，南京210096；
2. 东南大学土木工程学院，南京210096\r
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Unit_EngLish:\r1. Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education，Southeast University，Nanjing 210096，China；
2. School of Civil Engineering，Southeast University，Nanjing 210096，China\r
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Abstract_Chinese:\r高强钢具有强度高、韧性好、可焊性优良等优点，其在土木工程中的应用越来越广泛．高强钢在火灾下的力学性能是钢结构抗火设计的重要影响因素．为获取高温下与高温后Q550D 高强钢材料的力学性能，基于稳态试验方法，对Q550D 高强钢开展了拉伸试验，考察了不同冷却方式(自然冷却与浸水冷却)与过火温度对Q550D 高强钢力学性能的影响，获取了不同温度工况下Q550D 高强钢的应力-应变曲线和高温下与高温后各项力学性能参数指标(弹性模量、屈服强度、抗拉强度和极限伸长率)的折减系数，并将试验结果与已有规范和文献结果进行了对比分析．结果表明：高温下Q550D 高强钢的弹性模量、屈服强度、抗拉强度随着试验温度的升高而逐渐下降，其折减系数均低于各国规范的取值；当温度超过400℃时，高温下Q550D 高强钢的弹性模量、屈服强度和抗拉强度下降明显，当温度超过700℃时，3 个力学性能指标均接近于零；不同冷却方式与过火温度对Q550D 高强钢的弹性模量影响不大；当温度低于600℃时，高温冷却后Q550D 高强钢的屈服强度和抗拉强度的折减并不明显，当温度超过600℃时，屈服强度和抗拉强度显著下降，且自然冷却方式下的下降程度更大；高强钢与普通钢高温冷却后的屈服强度与抗拉强度存在较大差别．\r
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Abstract_English:\rHigh-strength steels are widely used in civil engineering because of their high strength，good toughness，and excellent weldability. Their mechanical properties in fire are critical influence factors on the fire resistance design of steel structures. To investigate mechanical properties of Q550D high-strength steel at elevated temperatures and after cooling from elevated temperatures，tensile tests based on steady-state test technique were conducted，including steady-state method and post-fire tensile tests. Influences of different cooling conditions(natural cooling and water cooling)and various temperatures on the mechanical properties of Q550D high-strength steel were investigated. Stress-strain curves and reduction factors of mechanical performance indexes(elastic modulus，yield strength，tensile strength and elongation)at different temperatures were obtained. Test results were compared with those of similar studies and design standards of various countries. The results showed that with the increase of test temperatures，elastic modulus，yield strength and tensile strength of Q550D high-strength steel gradually decreased at elevated temperatures and the reduction factors were lower than the values in design standards. When the heating temperature exceeded 400℃，the elastic modulus，yield strength and tensile strength of Q550D high strength steel significantly decreased at elevated temperature，and when the heating temperature exceeded 700℃，these three mechanical properties were close to zero. Different cooling methods and various temperatures had little influence on the elastic modulus of Q550D high-strength steel. When the heating temperature was under 600℃，the reduction of yield strength and tensile strength of Q550D high-strength steel was not obvious after cooling from elevated temperatures，whereas，when the temperature was over 600℃，there was a significant reduction in yield strength and tensile strength. The yield strength and tensile strength of naturally cooled specimens decreased more than those cooled in water. Large differences existed between both yield strengths and tensile strengths of high-strength steels and ordinary structural steels after cooling from elevated temperatures.\r
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Keyword_Chinese:高强钢；力学性能；稳态试验；高温冷却；折减系数\r

Keywords_English:high-strength steel；mechanical property；steady-state test；cooling from elevated temperature；reduction factor\r


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