【作者】 苏捷；

【导师】 方志；

【作者基本信息】 湖南大学 ， 土木工程， 2013， 博士

【摘要】 混凝土的力学性能与其几何尺寸密切相关，为准确描述不同混凝土力学性能上的差异，系统研究混凝土的尺寸效应显得尤为必要。目前，国内外在混凝土受压变形性能尺寸效应、骨料组分和配筋情况对混凝土力学性能尺寸效应的影响等方面的研究较少。此外，在对混凝土力学性能进行数值模拟时，通常将硬化水泥砂浆基体的力学性能假定为一常数进行分析，忽略其自身的尺寸效应，该假定的有效性尚未得到试验证实。受各种因素的限制，尺寸效应的试验研究往往只能在一个较小的尺度范围内进行，采用数值模拟的方法可有效解决试验研究的不足之处，为尺寸效应的研究提供另外一种研究手段。采用试验研究与数值分析相结合的方法，对混凝土的受压与弯拉性能尺寸效应进行了较系统研究。主要研究内容如下：1.对162个立方体试件的抗压强度尺寸效应进行了试验研究，结果表明：混凝土抗压强度具有尺寸效应，边长150mm和200mm试件的抗压强度约为边长100mm试件的94%和88%；混凝土、砂浆和净浆抗压强度的尺寸效应依次减弱，砂浆与净浆的尺寸效应仅为混凝土的1/3和30%左右；混凝土抗压强度的尺寸效应随着强度等级的提高而增强，C60混凝土的尺寸效应约为C20混凝土的1.8倍。2.对216个棱柱体试件单轴受压性能尺寸效应进行了试验研究，结果表明：混凝土单轴受压性能具有较明显的尺寸效应，边长200mm试件的峰值应力、应变及极限应变分别为100mm试件的85%、104%和110%。边长150mm试件的峰值应力、应变及极限应变分别为100mm试件的92%、102%与105%；强度等级越高，尺寸效应越明显，C20混凝土的尺寸效应仅为C60混凝土的1/2；尺寸效应受骨料组分影响较大，混凝土的尺寸效应分别约为砂浆和净浆的2.7倍和2.8倍；配筋混凝土的尺寸效应明显弱于混凝土试件，对于配筋率约1%时的钢筋混凝土，其内混凝土的尺寸效应约为未配筋混凝土的28%左右。3.对162个棱柱体试件弯拉性能试验研究结果表明：弯拉强度具有尺寸效应，边长70mm和100mm混凝土试件的弯拉强度分别为150mm试件的1.15倍和1.1倍；混凝土弯拉强度的尺寸效应强于砂浆和净浆，砂浆和净浆的尺寸效应分别为混凝土的30%和24%；强度等级对弯拉强度尺寸效应影响较大，C60混凝土弯拉强度的尺寸效应约为C20混凝土的2倍。4.对统计尺寸效应理论、基于能量释放准则的尺寸效应理论及基于裂纹分形特征的尺寸效应理论进行了比较分析，基于试验数据，给出了各尺寸效应率中相关参数的建议值，提出了不同强度等级混凝土立方体抗压强度、轴心抗压强度以及弯拉强度尺寸效应率中各参数的计算公式。定义临界尺寸和临界强度为：当试件几何尺寸大于某一尺寸后，抗压和抗拉强度的变化率分别小于0.01和0.001，则该尺寸为临界尺寸，相应的强度为临界强度。混凝土各力学性能参数的临界尺寸均随强度等级的提高而增大，C40和C60混凝土的临界尺寸分别约为C20混凝土的1.7倍和2.1倍。5.编写了随机骨料的投放程序，建立了二维与三维混凝土随机骨料模型。基于试验数据和随机骨料模型，得到了各强度等级混凝土中粘结界面层的力学性能参数，建立了粘结界面层力学性能与混凝土宏观力学性能间的关系。6.采用均质弹脆性、非均质弹脆性和均质弹塑性模型对混凝土的单轴受压性能进行了数值模拟，得到了破坏过程和宏观应力-应变全曲线，结果表明：非均质弹脆性模型得到的上升段和均质弹塑性模型得到的全曲线与试验结果吻合较好。7.采用随机骨料模型分析了混凝土的受压和受拉性能，研究了各力学性能参数的尺寸效应，提出了相应的尺寸效应率，得到了临界尺寸和临界强度。结果表明：临界尺寸随强度等级的提高而增大，C40与C60混凝土的临界尺寸分别约为C20混凝土的1.8倍和2.4倍；配筋混凝土中混凝土强度的临界尺寸明显低于未配筋混凝土，临界强度高于未配筋混凝土，当配筋率为1%时，其临界尺寸和临界强度分别为未配筋混凝土的45%和1.3倍左右。更多还原

【Abstract】 The mechanical properties of concrete closely relate to its geometric dimension.In order to accurately describe the differences of damage process and mechanicalproperties, the research on size effect is particularly necessary. The research on thesize effect of compression behavior and aggregate composition is still insufficient.Furthermore, the mechanical properties of mortar are generally assumed as a constant.The effectiveness of this assumption has not yet been confirmed by test results. Thenumerical analysis on size effect can effectively solve the limitation of theexperimental investigation and also provide another research method for the study.A series of experimental and numerical analysis research were conducted in thispaper. The following conclusions can be made:1.162concrete cubic specimens were tested in order to investigate the size effecton compressive strength. Test results indicate that the larger the size, the lower theconcrete compressive strength. The concrete compressive strengths with dimension of150mm and200mm are94%and88%of100mm specimens. The size effect ofconcrete is stronger than the mortar and cement. The size effect of mortar and cementare33%and30%of concrete. With the raise of strength level, the size effect comesmore obvious. The size effect in C60concrete is1.8times of C20concrete.2.216uniaxial compression specimens were experimented in order to obtain thesize effect on axial compressive behavior. The experiment result shows that the sizeeffect exists in each kind of specimens. The peak stress, strain at peak stress,ultramate strain of specimens with dimension200mm are85%,104%and110%ofspecimens with dimension100mm respectively. These mechanical paramters of150mm specimens are92%,102%and105%of100mm specimens. The higher thestrength level, the more dramatical the size effect. The size effect of C20concrete is50%of C60concrete. The size effect in concrete is much stronger than the mortar andcement. The size effect on compressive behavior of concrete are about2.7and2.8times of the mortar and cement respectively. Reinforcement can reduces the sizeeffect dramatically. The size effect on compressive behavior of reinforced concrete isabout28percent of concrete.3. The test result of162flexural tensile specimens proves that: the flexuraltensile strength increased with the decrease of specimen size. The flexural tensile strength of concrete specimens with dimension of70mm and100mm are anbout1.15and1.1times of150mm concrete specimens. The extent of size effect for the threeaggregate composition is concrete, mortar, cement, respectively. The size effect ofmortar and cement are30%and24%of concrete. The size effect on flexural tensilestrength of C60specimens is2times stronger than the C20specimens.4. Based on the fully understanding of the size effect theories, the parameters ofsize effect laws were suggested. Also, the computational formulas of size effect wereproposed in this paper. The higher the compressive strength, the larger the critiacl size.The critical size of C40ad C60concrete are1.7and2.1times of C20concrete.5. The two dimensional and three dimensional concrete random aggregate launchprogramm were compiled. Based on the test result and the random aggregate model,the mechanical properties of bonding interface were obtained by a series of numericalanalysis. Also, the relationship between the bonding interface and concre mechanicalbehavior were built in this paper.6. Mesoscopic numerical models of homogeneous and heterogeneous concretematerial are established in combination with elastic brittle constitutive and bothelastic brittle and plastic constitutive model for concrete mesoscopic elements. Thedestruction process and macroscopic stree-strain curves were acquired by numericalanalyze.7. A series of numerical analysis were performed on the size effect of concretecompressive and tensile behavior. Based on the analysis result, the critical dimensionsof size effect on several mechanical parameters were obtained. Furthermore, the sizeeffect law of various concrete mechanical properties were proposed in this paper.更多还原