Size Effect on Strength and Deformation of Concrete Members and Its Mechanism

混凝土构件的承载能力并不总是与其尺寸成正比。用尺寸标准化的载荷（例如，用每单位面积的力表示的强度）以及用尺寸标准化的变形通常倾向于随着尺寸减小。本文通过试验和数值分析，研究了混凝土和钢筋混凝土构件强度和变形的尺寸效应，探讨了尺寸效应的机理.研究了局部（单元）破坏行为与整体（系统）破坏行为之间的关系。得出了强度的尺寸效应的以下机理：-较弱的部分，往往出现在系统中的大量元素，降低强度。层间变形的不均匀性降低了系统的强度.在单筋梁的情况下，变形能力随着有效深度的增加而减小，因此尺寸效应是公认的。在峰值载荷之后，曲率的局部化变得显著.试验结果表明，用拉伸软化曲线可以较好地反映混凝土的弯曲破坏特性。提出了确定抗拉软化曲线的试验方法。4）指出了采用超高强混凝土时，无腹筋钢筋混凝土梁抗剪强度的尺寸效应显著。通过对混凝土受弯构件受拉面上微裂纹引起的应变分布的测量，发现应变分布的形状与标距有很大关系。这一现象可以通过分形方法得到很好的解释。

The load carrying capacity of concrete members is not always proportional to their size. The load normalized with the size (for example, the strength expressed with the force per unit area) as well as the deformation normalized with the size often tend to decrease with the size. In this investigation, the size effects on strength and deformation of concrete and reiforced concrete members are investigated and the mechanism of size effects is discussed through experiments and numerical analyzes.1. The relationship between the failure behavior of the portion (element) and that of the whole (system) is investigated. The following mechanisms of the size effect on strength are derived :-Weaker portions, which tend to appear in the system of a larger number of elements, decreases the strength.-Unevenness of deformation in the layr of the system decreases the strength.2. In case of singly reinforced beams, the deformation capacity decreases with the increase in the effective depth and hence the size effect is recognized. the localization of the curvature becomes remarkable after the peak load.3. It is shown that the tension softening diagrams are effective to deal with the flexural failure behavior of various kinds of concrete. The testing method to determine tension softening diagrams is proposed.4) It is pointed out that the size effect on the shear strength of RC beams without web reinforcement is remarkable when super-high strength concrete is used.5. The strain distribution due to micro-cracks is measured on tension surface of concrete beams in bending.The shape of strain distributions highly depends on the gauge length. This phenomena can be well explained through the fractal approach.