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。按大小规格化的载荷(例如，用单位面积的力表示的强度)以及按大小规格化的变形通常会随着大小的增加而减小。通过试验和数值分析，研究了尺寸效应对混凝土和钢筋混凝土构件强度和变形的影响，并探讨了尺寸效应的机理。研究了局部(单元)和整体(系统)的破坏行为之间的关系。得出了尺寸效应对强度影响的以下机理：-较弱的部分往往出现在较多元素的系统中，降低强度。-系统层中变形的不均匀降低强度。对于单筋梁，其变形能力随着有效深度的增加而减小，因此考虑了尺寸效应。峰值荷载后，弯曲度局部化现象明显。结果表明，拉伸软化图能较好地反映各种混凝土的抗弯破坏行为。提出了确定张拉软化图的试验方法。4)指出采用超高强混凝土时，无腹筋钢筋混凝土梁的抗剪强度受尺寸影响较大。在受弯混凝土梁的拉伸面上测量了由于微裂缝引起的应变分布，应变分布的形状高度依赖于应变片的长度。这种现象可以用分形学的方法很好地解释。

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.