论文标题:侧压下混凝土静态受拉与受拉疲劳性能研究
Study on Static and Fatigue Behaviors in Tension for Concrete under Lateral Pressures
论文作者 杨健辉
论文导师 宋玉普,论文学位 博士,论文专业 结构工程
论文单位 大连理工大学,点击次数 82,论文页数 135页File Size5944k
2003-04-01论文网 http://www.lw23.com/lunwen_980694782/ 混凝土;疲劳;损伤;单轴/二轴/三轴应力;受拉;强度;变形;异常值;EM算法
concrete,fatigue,damage,uniaxial/biaxial/triaxial stress,tension,strength,deformation,singular value,EM algorithm
混凝土作为现代建筑结构最为重要的工程材料，并以其抗压性能高于抗拉性能为其显著特点。现今的研究文献不但对混凝土受压性能方面的试验研究较多，而且对所取得的试验成果也得到较为一致的认可。然而有关混凝土在多向侧压下的静态受拉行为研究则相对较少，而关于受拉疲劳方面的研究则几乎处于空白状态。 本文是基于国家自然科学基金项目《混凝土多轴变幅疲劳破坏准则》(50078010)中的一部分作为研究内容。本文主要研究内容为单、双向侧压下的混凝土静态受拉与等幅及变幅受拉疲劳，同时也对单轴静态受拉与受拉疲劳文献成果进行了总结，从而全面揭示了混凝土在多侧压下的静态受拉与受拉疲劳特性，为相关研究与应用奠定了基础。 本文具体研究了如下内容： 1)对混凝土分别在无侧压及单、双向侧压下进行了静态受拉试验，然后对极限抗拉强度进行了比较；对静态受拉峰值应力所对应的应变(峰值应变)与疲劳极限总应变也进行了比较；同时也比较了不同侧压作用下的受拉疲劳寿命、疲劳变形模量比； 2)总结了混凝土受拉试验所主要采用的试件形状与规格，对采用不同形状的混凝土试件所得到的抗压和抗拉(抗折、劈拉)强度关系进行了定性和定量归纳总结。对混凝土单轴受拉疲劳和三分点弯拉疲劳也进行了总结比较； 3)对混凝土进行了单、双向侧压下的受拉等幅疲劳试验。得到了疲劳方程和应力应变曲线，应变及疲劳变形模量比与循环次数关系曲线(呈现三阶段规律)，并通过定义的数学变换ε_t和e_(tm)，分别将三阶段曲线转换为直线，通过这种线性关系可以方便确定应变及疲劳变形模量比随循环次数变化的趋势； 4)对混凝土进行了单、双向侧压下受拉变幅疲劳试验，得到了变幅疲劳寿命。采用了疲劳变形模量比作为损伤变量，这种损伤模型不但形式简单，而且对疲劳寿命的预测结果也较为准确； 5)对混凝土疲劳寿命这一类特殊问题的方程拟合方法，建立了搜索计算最优疲劳方程的计算流程，并通过该计算流程找到了最优疲劳方程。而通过EM算法对疲劳寿命异常值进行了合理调整，并对调整后的疲劳寿命建立了最优疲劳方程。EM算法不但可以对异常疲劳寿命进行合理调整，而且还可以对新的应力水平下的疲劳寿命进行合理预测。
Concrete is one of the most importance engineering materials for modem building structures, it is main specialty that compressive capability is better than tensile one. Though the studies on concrete compression is much more than tension, and these test results are gained universal recognition in compression, studies on tension is not only fewer on static but also few on tensile fatigue under multilateral pressures.This paper bases on a part of the project of National Natural Science Foundation "Failure criterion of concrete under multiaxial variable-amplitude fatigue loading"(50078010) for study contents. The main study contents are static and const- and variable- amplitude fatigue in tension under no-, one- and two-lateral pressure respectively in the paper, at the same time, history studies on uniaxial static and fatigue in tension are summarized, so this paper systematically studies both static and fatigue behaviors in tension for concrete under multilateral pressures, and establish a foundation for relative studies and applications.Main study contents in the paper are as follows:1) This paper tests static axial tension for concrete under no-, one- and two-lateral pressure respectively, compares ultimate tensile strengths under different lateral pressures, and compares static strain when tensile stress is maximum (named peak strain) and ultimate fatigue strain (that is total fatigue strain), fatigue life and fatigue deformation modulus ratio are also compared under different lateral pressures;2) This paper summarizes main shape and specification of specimens used for axial tensile tests for concrete, and also summarizes quantitative and qualitative relations between compressive strength and tensile strength (including resistance to breaking and splitting tensile strength) by adopted difference specimens shapes for concrete tensile tests, the behaviors of uniaxial tensile fatigue and flexural tensile fatigue under three-point loading in the end;3) This paper tests constant-amplitude fatigue in tension for concrete under, one- and two-lateral pressure, founds fatigue equations, and draws stress-strain curves. The test makes clear that strains, deformation modulus ratios of concrete fatigue present three-stage curves which are transformed into linear ones by defined two mathematic changes ? t and etm, this linear relation can easily estimate the changing trends of fatigue strains and deformation modulus ratios and the number of cycles.4) This paper carries out variable-amplitude fatigue tests in tension for concrete under one- and two-lateral pressures, and takes deformation modulus ratio of concrete fatigue as damage variable. This damage model not only is simple in style, but also predicting result of concrete fatigue life is better.5) This paper founds a computation flow on how to search out the best fitting equation of concrete fatigue for the special question, and obtains the best fatigue equation by using it, at the same time, this paper adjusts singular values of test data by using of EM algorithm which can forecast concrete fatigue life under the stress levels having not been tested too.
|
