混凝土材料强度率无关性研究

发布时间：2018-09-04 19:52

【摘要】：混凝土材料强度的动力特性是一由来已久而又持续受到广泛关注的热点问题，对该问题的认识正确与否将直接影响混凝土结构工程动力设计的安全度。本文分别从分子动力学材料数值试验、连续介质动力学理论以及有限元数值模拟三个角度对混凝土强度动力试验展开研究，逐步细化和深化对于混凝土材料强度率无关性的认识。论文获得的主要研究成果如下： 1.分析并明确了传统混凝土强度动力试验处理和分析方法的两个不足之处。第一，动力试验的一维应力假定并不严格成立，在缺乏必要的试验数据信息过滤和甄别的前提下，试验测得的名义强度并不能代表材料强度的真实性能。第二，理想均质材料的分子动力学数值试验结果表明，名义强度率相关性的主要来源并不是材料的非均匀性，而是材料自身惯性约束效应及其引起的动态应力多轴性。 2.基于连续介质动力学建立了适用于混凝土强度动力试验惯性效应分析的理论模型。在承受动力荷载时，混凝土试件自身的轴向和径向惯性约束效应，会在试件两端面引起附加的轴向应力，从而使得试验实测的名义强度高于材料强度。动态压缩时，径向惯性效应引起的径向惯性围压与混凝土抗压强度围压敏感性发生耦合作用，随应变率的增加而进一步大幅度提高名义强度测量值。 3.利用有限元方法分别对混凝土抗拉和抗压强度动力试验进行了仿真模拟，具体分析总结了不同试验条件对试验结果的影响规律，并在此基础上对前人试验结果进行了信息过滤以提炼真实的材料性能，以此对混凝土材料强度率无关性做出了综合论证。模拟结果表明，试验测得的名义强度包含尺寸效应、端部约束效应、单纯惯性效应、径向惯性围压耦合效应、试件端面摩擦以及粘性阻尼等多种试验条件的综合影响。虽然材料强度并不改变，但随着应变率的提高，混凝土试件受惯性效应及其它试验条件的综合作用，，导致其内部应力应变状态逐渐发生过渡和转变，而最终反映表达出与前人试验结果一致的名义强度率相关性规律。 4.以印度Koyna大坝的地震破坏为工程实例，研究了混凝土材料强度率无关性对大坝抗震设计分析的重要影响。使用混凝土强度静力值得到的大坝地震破坏模式，比按照规范要求提高后的动力值更接近真实情况；因此应使用混凝土强度静力值用于抗震设计，大坝工程量的少量增加会换来切实可靠的抗震安全保障。
[Abstract]:The dynamic characteristics of concrete strength is a hot issue which has been paid more and more attention for a long time. Whether the understanding of this problem is correct or not will directly affect the safety degree of the dynamic design of concrete structure engineering. In this paper, the strength dynamic test of concrete is studied from three aspects: molecular dynamics material numerical test, continuum medium dynamics theory and finite element numerical simulation. Gradually refine and deepen the understanding of concrete strength rate independent. The main research results are as follows: 1. Two shortcomings of the traditional concrete strength dynamic test treatment and analysis method are analyzed and defined. First, the one-dimensional stress assumption of dynamic test is not strictly established, and the nominal strength can not represent the true properties of material strength without the necessary information filtering and screening of test data. Secondly, the results of molecular dynamics numerical experiments of ideal homogenized materials show that the main source of the correlation of nominal strength rate is not the heterogeneity of the materials. It is the material itself inertial confinement effect and its dynamic stress multiaxiality. 2. Based on continuum dynamics, a theoretical model for the analysis of inertia effect in concrete strength dynamic test is established. Under dynamic load the axial and radial inertial confinement effect of concrete specimen itself will cause additional axial stress at both ends of the specimen thus making the nominal strength measured by the test higher than the strength of the material. Under dynamic compression, the radial inertial confining pressure caused by radial inertia effect is coupled with the confining pressure sensitivity of concrete compressive strength, and the nominal strength measurement value is further greatly increased with the increase of strain rate. The dynamic test of concrete tensile strength and compressive strength is simulated by finite element method, and the influence of different test conditions on the test results is analyzed and summarized in detail. On the basis of this, the information filter is carried out to extract the real material properties of the former experimental results, and the irrelevance of the strength rate of the concrete material is proved synthetically. The simulation results show that the nominal strength measured by the test includes the effects of dimension effect, end restraint effect, simple inertial effect, radial inertial confining pressure coupling effect, end surface friction and viscous damping. Although the strength of the material does not change, with the increase of strain rate, the concrete specimen is subjected to the combined action of inertia effect and other test conditions, which leads to the gradual transition and transformation of the internal stress-strain state. And the final reflection expresses the correlation law of nominal intensity rate consistent with the results of previous experiments. 4. 4. Taking the earthquake damage of the Koyna dam in India as an engineering example, the important influence of the strength ratio of concrete material on the seismic design analysis of the dam is studied. The seismic failure mode of dam with concrete strength and static force is closer to the real situation than the dynamic value after increasing according to the code; therefore, the static value of concrete strength should be used in seismic design. A small increase in the volume of dam construction will result in reliable seismic safety.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU528

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