【作者】 朱劲松；

【导师】 宋玉普；

【作者基本信息】 大连理工大学 ， 结构工程， 2003， 博士

【摘要】 许多混凝土结构工程，如高等级刚性混凝土路面与机场道面、桥梁、轨枕、吊车梁、海洋平台和核反应堆压力容器、安全壳和重型机械基础等，除受静载作用外，还受到诸如车辆、核动力、风浪、水流冲击与机械振动等重复荷载作用，疲劳破坏是它们的主要破坏形式之一。这些结构内部混凝土常常处于多轴复杂应力状态下工作，但是混凝土在复杂应力状态下的疲劳力学性能研究却远未深入，混凝土多轴疲劳试验资料与疲劳破坏预测理论研究资料的匮乏是这些结构的合理设计与准确分析的障碍。本文结合国家科学基金项目：混凝土多轴变幅疲劳破坏准则(50078010)开展的试验与理论研究工作包括以下几方面内容： (1) 改造MTS单轴液压伺服疲劳试验系统，实现了定侧压下棱柱体(立方体)混凝土试件的拉、压疲劳加载，首先对这方面内容进行了介绍；然后对有关混凝土多轴疲劳试验中确定试件初始强度的方法、试验中注意问题、疲劳损伤测量技术等进行了分析研究。 (2) 进行了定侧压下混凝土双轴等幅与变幅抗压疲劳试验，分析了定侧压下混凝土双轴疲劳破坏的机理；建立了相应的S-N关系，提出了综合考虑侧压应力水平与应力比的统一疲劳破坏准则；得到了混凝土在定侧压作用下单级等幅和多级变幅抗压疲劳的变形发展规律，包括纵横向应变、第二阶段应变率、疲劳变形模量等随循环次数的发展规律和混凝土超声波速三阶段的衰减规律，并给出了相应的经验公式。 (3) 分别选用最大疲劳应变、残余塑性应变、疲劳变形模量及横向超声波速表示的损伤参量研究了混凝土疲劳损伤累积规律，并提出一个表征混凝土损伤本质的平均损伤变量，得到了损伤累积方程。对常用的不同应力水平下的损伤等效原理进行了修正；讨论了Miner准则和Corten-Dolan损伤公式的适用性与精度问题。 (4) 进行了定侧压下变截面棱柱体混凝土试件的等幅拉-压疲劳试验，得到了考虑侧压水平的混凝土拉-压疲劳方程和疲劳强度包络线，并研究了混凝土在这种疲劳工况下的破坏形态与变形性能，包括循环应力-应变特性、应变发展规律与疲劳变形模量衰减规律，给出了相应的经验公式。 (5) 在对变截面的棱柱体混凝土试件进行定侧压下轴心拉-压单级等幅和多级高-低、低-高变幅疲劳试验的基础上，总结了实测等幅与变幅疲劳应变与变形模量的衰减规律，基于疲劳变形模量定义了损伤变量，建立了损伤演变方程，并给出了利用该模型进行疲劳损伤分析和剩余寿命预测的方法。 (6) 对混凝土疲劳破坏随机预测模型及其应用进行了研究，包括以下内容：(a) 以少数高应力水平下混凝土疲劳试验结果为基础，建立了疲劳强度预测的灰色GM(1，1)模型，用以预测混凝土的(条件)疲劳强度；(b) 从疲劳过程中强度衰减的本质出发，提出了估算多级复杂应力下混凝土疲劳剩余寿命估算模型，并给出了由混凝土S-N曲线确定模型参数的简化方法；(c) 采用神经网络技术描述了混凝土累积疲劳损伤与材料性能、应力参数间复杂的非线性映射关系，运用系统仿真的原理构造了混凝土随机疲劳损伤及寿命预测的智能化仿真系统。这几方面的研究都与文献记载的试验结果进行了比较，证明了方法的可行性与先进性。 (7) 总结了混凝土边界面模型发展的历史及其基本概念，分析了混凝土边界面模型构建的一般方法。然后通过数值程序研究了常用的边界面模型对疲劳荷载作用下混凝土大连理工大学博士学位论文性能描述的能力，为改进模型奠定了基础。更多还原

【Abstract】 Fatigue is the process of progressive, localized and permanent material damage, which often leads to sudden failures with little or no plastic deformation or causes severe damage in such civil engineering structures as continuously reinforced concrete pavements, concrete bridges, concrete crane beams, concrete sleepers, concrete offshore platforms, safety hulls of nuclear power plants, foundations of rotating machinery etc.. These structures may be subjected to fatigue loading caused by vehicle, crane, nuclear power, wind, wave and vibration. Concrete in such structures works in the complex states of multi-axial stresses, whereas, the mechanism of fatigue failure is still not clearly understood in these stress states. Literature on the experiments and the theories of failure prediction of concrete under multi-axial cyclic loadings is extremely scarce, which is the drawback on the design and analysis of these structures. The thesis is an important part of the project of National Natural Science Foundation-Failure criterion of concrete under multi-axial variable-amplitude fatigue loading (No. 50078010), the contents of which are summarized as follows:(1) The testing facility composing with the uni-axial MTS closed-loop system and the lateral loading frames is applied to conduct the experimental program to cubic specimens (and prism specimens) under fatigue load with constant confined pressure. In the first part of this thesis the experiment system is stated, and some key experiment techniques such as the methods to determine the initial strength, technique to measure the fatigue damage are studied.(2) An experimental research program is carried out with the aim of investigating the deformation characteristics of normal strength concrete under biaxial multistage cyclic compression with constant confined stress. A fatigue equation is gained by modifying the classical Aas-Jakobsen’s S-N equation for taking into account the effect of the confined stress on fatigue strength of plain concrete. The deformation characteristics including the development of longitudinal and transverse strains, the secondary creep rate, under the states of constant-amplitude and variable-amplitude cyclic compressive loads, and deformation modulus of concrete in terms of cyclic number, are gained from the analysis of experiment results. In addition, An ultrasonic pulse velocity method is used to measure the damage growth during cyclic loading of concrete, and whose results imply the progress of failure of concrete under biaxial cyclic compressive loads with constant confined stress. The analysis of the microcosmic destructive mechanism of concrete under the present stress states is conducted, too.(3) A study on the cumulative fatigue damage of plain concrete due to biaxial compression is conducted basing on the experiment results of concrete specimens subjected to constant and variable amplitude cyclic loading with constant confined pressure. The applicability and precision of Miner’s rule and Corten-Dolan formula are discussed. In addition, the longitudinal maximum strains, residual strains, deformation modulus of concrete and the ultrasonic pulse velocity are used to define the damage, which induces different lawsthe cumulative fatigue damage following. An average damage variable is proposed in present study for taking into account all of factors mentioned above, and the law of cumulative damage and its evolution were obtained. In this part, the equivalent cumulative damage theory is modified to predict the residual fatigue life of concrete under variable amplitude cyclic loading.(4) The fatigue tests of concrete on biaxial tension-compression under constant -amplitude cyclic loading with constant confined stress are described in this part of the thesis. The relationship of S-N and the fatigue strength envelopes of concrete under tension-compression loads with constant confinement are obtained firstly, basing on the analysis of the results of present experiments and fatigue te更多还原