混凝土双轴压缩强度尺寸效应机理

为了研究混凝土双轴强度尺寸效应产生的机理,考虑混凝土尺寸效应及其宏观力学非线性源于其材料组成的非均质性,结合混凝土细观结构形式,从细观角度将混凝土看作由骨料颗粒、砂浆基质和界面过渡区组成的三相复合材料,建立了尺寸分别为150 mm×150 mm、300 mm×300 mm和600 mm×600 mm的数值混凝土试件.首先通过对150 mm×150 mm方形混凝土试件进行单轴压缩力学特性模拟,采用反演法确定了界面过渡区的力学参数,进而对双轴压缩加载下混凝土的破坏行为及其尺寸效应进行了分析.研究结果表明:1)损伤破坏形式随试件尺寸发生变化,试件最终破坏消耗的断裂能不同是导致混凝土双轴压缩强度产生尺寸效应的主要原因;2)混凝土单、双轴压缩强度均存在明显的尺寸效应行为,并且Bazant尺寸效应律能够较好地描述混凝土在单、双轴压缩加载下的强度尺寸效应.

Mechanism of Size Effect of Concrete Under Biaxial Compression

The size effect and macroscopic nonlinearity of concrete are caused by its inherent heterogeneity. Considering the mesoscopic heterogeneity, concrete was regarded as a tril-phase composite material consisting of aggregate, mortar matrix and the interfacial transition zone ( ITZ) at meso-scale. Numerical concrete specimens sized by 150 mm × 150 mm, 300 mm × 300 mm and 600 mm × 600 mm were set up. First, several uniaxial compressive tests of square concrete specimens were conducted and the mechanical parameters of the ITZs were fixed by an inversion method. Then the failure behavior and the size effect of concrete under biaxial compression were analyzed. Some conclusions can be drawn as, 1) damage failure evolves with dimension of the specimen, and difference of the fracture energy dissipated per unit is the main reason of the presence of size effect in concrete subjected to bi-axial compression. 2) an obvious size effect can be observed on the uniaxial/biaxial compressive strength of concrete and the simulation results of present work follow closely the size effect law ( SEL) proposed by Ba(z)ant.