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。按尺寸归一化的荷载（如用单位面积力表示的强度）和按尺寸归一化的变形往往随尺寸的增大而减小。本文研究了尺寸对混凝土和钢筋混凝土构件强度和变形的影响，并通过试验和数值分析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。得到了尺寸效应对强度的影响机理：—较弱的部分往往出现在元素较多的体系中，从而降低了强度。-体系层内变形的不均匀性降低了强度。对于单配筋梁，其变形能力随有效深度的增加而减小，从而认识到尺寸效应。在峰值荷载后，曲率的局部化变得显著。结果表明，拉伸软化图是处理各种混凝土受弯破坏行为的有效方法。提出了确定拉伸软化图的测试方法。4)指出超高强度混凝土对无腹板钢筋混凝土梁抗剪强度的尺寸效应显著。测量了混凝土梁受弯时受拉面上微裂缝引起的应变分布。应变分布的形状在很大程度上取决于量规长度。用分形方法可以很好地解释这种现象。

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.