疲劳荷载与冻融循环作用后混凝土动态特性试验研究

发布时间：2018-08-26 20:26

【摘要】：寒区的隧道、大坝及桥梁等混凝土结构会经历荷载历史与冻融循环作用,同时动力荷载作用对这些结构的安全性和稳定性有着重要的影响。本文开展了180个混凝土棱柱体试件分别经历疲劳荷载、冻融循环、先疲劳后冻融以及先冻融后疲劳等四种模式作用后的单轴动态抗压试验,系统研究了疲劳荷载和冻融循环单一因素作用、疲劳与冻融双重因素作用对混凝土动态力学性能的影响,同时分析了疲劳与冻融不同作用次序下混凝土的微观形貌和损伤演化机理。主要成果如下:(1)研究了单因素作用后混凝土动态特性,包括疲劳荷载、冻融循环作用后混凝土动态特性。首先,开展了受疲劳混凝土单轴动态抗压试验,研究了疲劳次数和应变率对混凝土强度和变形性能的影响。结果表明抗压强度和峰值应变均随疲劳次数增加呈先增后减的趋势;随着应变率的增加,抗压强度增大,而峰值应变减小。其次,开展了受冻融混凝土单轴动态抗压试验,分析了混凝土抗压强度、峰值应变与冻融次数、应变率的关系,提出考虑应变率和冻融次数影响的混凝土应力-应变曲线模型,结果表明抗压强度随应变率的增大均明显增加,而峰值应变呈减小的趋势;随着冻融次数的增加,抗压强度均有所降低,降低幅度最大达7.46%,而峰值应变逐渐增大。(2)研究了疲劳与冻融双重因素作用后混凝土动态特性,包括先疲劳后冻融以及先冻融后疲劳作用下混凝土动态特性。首先,开展了先疲劳后冻融作用模式下混凝土动态抗压特性试验,探讨了疲劳次数以及冻融次数对混凝土动态力学性能的影响规律。结果表明先疲劳后冻融作用下混凝土的强度损失大于在疲劳单一作用下的损失,强度随疲劳次数、冻融次数的增加均呈减小的趋势,随应变率的增大均明显增大,相比未经损伤的混凝土静态强度,强度降低最大可达10MPa。其次,开展了先冻融后疲劳作用模式下混凝土动态抗压特性试验研究,基于试验结果,分析了冻融次数、疲劳次数和应变率对混凝土抗压强度、峰值应变和应力-应变曲线的影响,结果表明先冻融后疲劳作用下的混凝土具有明显率效应,较少的疲劳荷载次数对混凝土的冻融损伤具有缓解作用。(3)探讨了疲劳与冻融作用的先后次序对混凝土动态特性的影响,引入叠加效应变量Kc对疲劳与冻融损伤叠加效应进行表征,结果表明先疲劳后冻融作用模式下,疲劳荷载与冻融循环联合作用均为正效应,先疲劳后冻融作用模式导致强度的损失大于同一应变率下先冻融后疲劳作用模式。采用扫描电子显微镜对混凝土损伤后的微观形貌进行观察分析,从微观角度揭示了疲劳与冻融不同次序作用下混凝土损伤劣化的机理。
[Abstract]:Concrete structures such as tunnels, dams and bridges in cold regions will undergo load history and freeze-thaw cycles, and dynamic loads will have an important impact on the safety and stability of these structures. In this paper, the uniaxial dynamic compression tests of 180 concrete prisms subjected to fatigue loading, freeze-thaw cycle, first fatigue, freeze-thaw and first freeze-thaw after fatigue were carried out respectively. The effects of fatigue load and freeze-thaw cycle on the dynamic mechanical properties of concrete are systematically studied. At the same time, the microstructure and damage evolution mechanism of concrete under different action order of fatigue and freeze-thaw are analyzed. The main results are as follows: (1) the dynamic characteristics of concrete after single factor action, including fatigue load and freeze-thaw cycle, are studied. First, the uniaxial dynamic compressive tests of fatigue concrete are carried out, and the effects of fatigue times and strain rates on the strength and deformation properties of concrete are studied. The results show that the compressive strength and peak strain increase first and then decrease with the increase of fatigue times, and increase with the increase of strain rate, while the peak strain decreases with the increase of strain rate. Secondly, the uniaxial dynamic compression test of freeze-thawed concrete is carried out, and the relationship between compressive strength, peak strain and freeze-thaw times, strain rate is analyzed, and the stress-strain curve model of concrete considering the influence of strain rate and freeze-thaw number is put forward. The results show that the compressive strength increases obviously with the increase of strain rate, while the peak strain decreases, and the compressive strength decreases with the increase of freeze-thaw times. The maximum reduction range is 7.46, while the peak strain increases gradually. (2) the dynamic characteristics of concrete after fatigue and freeze-thaw are studied, including first fatigue and freeze-thaw after fatigue. Firstly, the dynamic compressive properties of concrete under the mode of first fatigue and freeze-thaw are tested, and the effects of fatigue times and freeze-thaw times on the dynamic mechanical properties of concrete are discussed. The results show that the strength loss of concrete under first fatigue and freeze-thaw is larger than that under single fatigue, and the strength decreases with the increase of fatigue times and freeze-thaw times, and increases obviously with the increase of strain rate. Compared with the static strength of undamaged concrete, the maximum reduction of strength can be up to 10 MPA. Secondly, the dynamic compressive behavior of concrete under the mode of freeze-thaw and fatigue is studied. Based on the test results, the influence of freeze-thaw times, fatigue times and strain rate on the compressive strength of concrete is analyzed. The effect of peak strain and stress-strain curve shows that concrete under freeze-thaw and fatigue has obvious rate effect. Less fatigue loads can alleviate the freeze-thaw damage of concrete. (3) the influence of the order of fatigue and freeze-thaw action on the dynamic characteristics of concrete is discussed. The superposition effect variable Kc is introduced to characterize the superposition effect of fatigue and freeze-thaw damage. The results show that the combined effect of fatigue load and freeze-thaw cycle is positive under the mode of first fatigue and freeze-thaw. The strength loss caused by the first fatigue and then freeze-thaw action mode is greater than that under the same strain rate. The microstructure of concrete after damage was observed and analyzed by scanning electron microscope (SEM), and the mechanism of damage deterioration of concrete under different order of fatigue and freeze-thaw was revealed from the microcosmic point of view.
【学位授予单位】：烟台大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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