【作者】 资伟；

【导师】 余志武；

【作者基本信息】 中南大学 ， 结构工程， 2012， 博士

【摘要】 本文以经历不同受热温度和受热时间的混凝土试块和梁为研究对象,采用理论分析和实验研究相结合的方法,对混凝土试块和梁的力学性能以及耐久性能进行了分析与探讨,主要内容包括：(1)完成了33组高温后混凝土试块的剩余抗压强度试验,并测定了不同受热温度和受热时间后混凝土的烧失率,系统研究了高温后混凝土剩余抗压强度与受热温度、受热时间的耦合关系以及高温后混凝土的质量变化规律,分别提出了基于受热温度、受热时间和基于烧失率的混凝土剩余抗压强度计算公式；修正了现有检测混凝土强度的超声法、回弹法和超声回弹综合法,得到了能应用于火灾后混凝土强度检测的强度回归公式。(2)完成了高温后混凝土耐久性能试验,主要包括碳化试验和氯离子侵蚀试验两部分。碳化试验完成了33组高温后混凝土烧损层深度的测定和快速碳化试验,研究了烧损层深度与受热温度和受热时间之间的关系,提出了混凝土剩余抗压强度与烧损深度之间函数关系,对比常温下混凝土试块碳化深度,得到了高温后混凝土碳化高温影响系数k’ca与受热温度和受热时间的计算公式。氯离子侵蚀试验完成了33组高温后混凝土RCM试验,测定了混凝土在规定电压和通电时间后氯离子渗透深度,并推导出高温后混凝土氯离子扩散系数,对比常温下混凝土试块氯离子扩散系数,提出了高温后混凝土氯离子扩散高温影响系数kd’与受热温度和受热时间的计算公式。(3)完成了10根经历不同受热温度、受热时间的钢筋混凝土梁的抗弯承载力试验,探讨了高温后钢筋混凝土梁的受弯破坏机理和裂缝扩展形态等试验规律。在热传导理论基础上,简化了钢筋混凝土梁内部温度场的计算过程,提出了一种高温后钢筋混凝土梁剩余抗弯承载力的简化计算方法。基于混凝土梁抗弯承载力试验结果,提出了小火、中火和大火三级火灾分类标准,分析了不同大小火灾对混凝土抗压强度、碳化高温影响系数kca’和氯离子扩散高温影响系数kcl’的影响,并给出了不同大小火灾后混凝土结构加固的维修建议。(4)完成了11根高温后钢筋混凝土梁通电快速锈蚀后的抗弯承载力试验,分析了抗弯试验过程中梁的荷载与挠度的关系和梁截面应力沿截面高度方向的分布等变形规律。根据试验结果,提出了高温后锈蚀钢筋屈服强度降低系数ky,建立了高温后锈蚀钢筋混凝土梁剩余抗弯承载力计算模型,并与试验值进行了对比分析。(5)引入了可靠度理论,在已有混凝土碳化深度模型和氯离子扩散模型的基础上,分别以碳化深度达到钢筋表面和钢筋表面氯离子浓度达到临界浓度而开始锈蚀作为混凝土结构耐久性失效极限,得到了基于可靠度理论的高温后混凝土碳化耐久性剩余寿命和氯离子侵蚀耐久性剩余寿命的预测模型,并分析了不同大小火灾对混凝土耐久性寿命的影响。更多还原

【Abstract】 This paper presents theoretical analyses and experimental research deeply on the mechanical properties and durability of the concrete specimens and beams, which were subjected to different heating temperature and time. The main contents are listed as follows:(1)33groups of post-fire concrete residual compressive strength test were completed, and the burn-off ratio of concrete was measured. The concrete quality change regulation and coupled relationship between concrete residual compressive strength and heating temperature and time had been studied systematically. The formulae had been proposed based on heating temperature, time and concrete burn-off ratio respectively. Ultrasonic Method, Rebound Method and Ultrasonic-rebound Combined Method had been amended which could be used in the concrete strength detection after fire, and its precision was enough for the practical engineering requirement.(2) The durability experiment of concrete after high temperature had been completed, which included carbonation test and chloride penetration test.In the carbonation test, the measurement on concrete burning depth and33groups of concrete rapid carbonation test had been completed. The relationship between burning depth and heating temperature and time had been researched, and the calculation formula of concrete residual compressive strength and burning depth was obtained. In comparison with the carbonation depth of natural state concrete, the formula of high temperature coefficient of carbonation k’ca had been obtained.In the chloride penetration test,33groups of RCM test on post-fire concrete had been finished. The chloride diffusion coefficient was deduced by the measurement of chloride penetration depth after RCM test. Compared with the chloride diffusion coefficient of natural state concrete, the computational formula of high temperature coefficient of chloride diffusion k’cl had been proposed.(3) Bearing capacity experiment of10reinforced concrete simple support beams after fire damage had been finished. The test law such as failure mechanism and fracture development had been discussed. Based on the theory of heat conduction, the temperature field in concrete member had been simplified for calculation and the simple method had been put forward to calculate the flexural capacity of reinforced concrete beam after fire. The fire classification standard had been established based on the experiment results. According to the influence of concrete compressive strength, k’ca and k’cl by different fire, the suggestion for concrete structure repair and reinforcement had been presented.(4) Bearing capacity experiment of11post-fire concrete beams after accelerated corrosion had been completed, and the failure characteristics, fracture shapes and the stress distribution in section had been analyzed. According to the experiment results, the yield strength reduction coefficient ky of post-fire concrete after corrosion had been introduced, and the bearing capacity calculation model for corroded reinforced concrete beam after fire had been established in comparison with the experiment results.(5) The reliability theory was introduced, and the concrete durability failure limit was determined respectively, which were that the carbonation depth reached on the surface of steel in concrete and chloride concentration on steel surface had arrived to the critical concentration. Based on the reliability theory and existing model of concrete carbonation and chloride diffusion, the carbonation and chloride penetration residual durability life forecasting model of post-fire concrete had been established respectively. The influence of concrete durability life after different fire had been analyzed.更多还原