【摘要】：混凝土材料強度的動力特性是一由來已久而又持續(xù)受到廣泛關(guān)注的熱點問題，對該問題的認(rèn)識正確與否將直接影響混凝土結(jié)構(gòu)工程動力設(shè)計的安全度。本文分別從分子動力學(xué)材料數(shù)值試驗、連續(xù)介質(zhì)動力學(xué)理論以及有限元數(shù)值模擬三個角度對混凝土強度動力試驗展開研究，逐步細(xì)化和深化對于混凝土材料強度率無關(guān)性的認(rèn)識。論文獲得的主要研究成果如下： 1.分析并明確了傳統(tǒng)混凝土強度動力試驗處理和分析方法的兩個不足之處。第一，動力試驗的一維應(yīng)力假定并不嚴(yán)格成立，在缺乏必要的試驗數(shù)據(jù)信息過濾和甄別的前提下，試驗測得的名義強度并不能代表材料強度的真實性能。第二，理想均質(zhì)材料的分子動力學(xué)數(shù)值試驗結(jié)果表明，名義強度率相關(guān)性的主要來源并不是材料的非均勻性，而是材料自身慣性約束效應(yīng)及其引起的動態(tài)應(yīng)力多軸性。 2.基于連續(xù)介質(zhì)動力學(xué)建立了適用于混凝土強度動力試驗慣性效應(yīng)分析的理論模型。在承受動力荷載時，混凝土試件自身的軸向和徑向慣性約束效應(yīng)，會在試件兩端面引起附加的軸向應(yīng)力，從而使得試驗實測的名義強度高于材料強度。動態(tài)壓縮時，徑向慣性效應(yīng)引起的徑向慣性圍壓與混凝土抗壓強度圍壓敏感性發(fā)生耦合作用，隨應(yīng)變率的增加而進(jìn)一步大幅度提高名義強度測量值。 3.利用有限元方法分別對混凝土抗拉和抗壓強度動力試驗進(jìn)行了仿真模擬，具體分析總結(jié)了不同試驗條件對試驗結(jié)果的影響規(guī)律，并在此基礎(chǔ)上對前人試驗結(jié)果進(jìn)行了信息過濾以提煉真實的材料性能，以此對混凝土材料強度率無關(guān)性做出了綜合論證。模擬結(jié)果表明，試驗測得的名義強度包含尺寸效應(yīng)、端部約束效應(yīng)、單純慣性效應(yīng)、徑向慣性圍壓耦合效應(yīng)、試件端面摩擦以及粘性阻尼等多種試驗條件的綜合影響。雖然材料強度并不改變，但隨著應(yīng)變率的提高，混凝土試件受慣性效應(yīng)及其它試驗條件的綜合作用，，導(dǎo)致其內(nèi)部應(yīng)力應(yīng)變狀態(tài)逐漸發(fā)生過渡和轉(zhuǎn)變，而最終反映表達(dá)出與前人試驗結(jié)果一致的名義強度率相關(guān)性規(guī)律。 4.以印度Koyna大壩的地震破壞為工程實例，研究了混凝土材料強度率無關(guān)性對大壩抗震設(shè)計分析的重要影響。使用混凝土強度靜力值得到的大壩地震破壞模式，比按照規(guī)范要求提高后的動力值更接近真實情況；因此應(yīng)使用混凝土強度靜力值用于抗震設(shè)計，大壩工程量的少量增加會換來切實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.
【學(xué)位授予單位】：清華大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TU528

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