基于细观模拟的混凝土动态压缩强度尺寸效应研究

在混凝土静态破坏尺寸效应方面开展的研究已经较为完善，而在动态破坏尺寸效应方面的研究还远没有形成一个统一的认知。混凝土尺寸效应根源于内部组成的非均质性，从细观角度出发，考虑材料非均质及细观组分的应变率效应，将混凝土看作由骨料、砂浆及界面过渡区组成的三相复合材料，建立了混凝土动态破坏行为研究的细观数值分析方法，对不同应变率（1×10-5 s-1~2×102 s-1）及不同尺寸方形混凝土试件单轴压缩破坏行为进行模拟与分析。数值结果表明:混凝土动态与静态加载下压缩强度尺寸效应规律存在明显差异，在动态压缩强度尺寸效应规律中，存在一个临界应变率（约为1 s-1），即:低于临界应变率时，应变率增大时，压缩强度随试件尺寸增大而减小，且尺寸效应逐渐被削弱；达到临界应变率时，混凝土动态压缩强度与尺寸无关，尺寸效应被完全抑制；高于临界应变率时，应变率增大时，压缩强度随试件尺寸增大而增大，尺寸效应逐渐增强。最后对混凝土动态强度尺寸效应的产生机理进行了分析与讨论。

RESERCH ON SIZE EFFECT OF DYNAMIC COMPRESSIVE STRENGTH OF CONCRETE BASED ON MESO-SCALE SIMULATION

The static size effect of concretes has been relatively well addressed, while studies on the dynamic size effect of concretes have not yet generated a unified understanding. The size effect of concrete can be attributed to the inner heterogeneities. Herein the study, a meso-scale simulation method was built to study the dynamic failure and size effect of concrete. Considering the material heterogeneity and strain rate effects of meso-components, concrete was simulated as a three-phase composite composed of aggregate, mortar matrix and interface transition zone at meso-scale. The square concrete specimens with different sizes were built and the dynamic compressive failure and the size effect of concrete under the strain rates from 10-5 s-1 to 200 s-1 were investigated using the meso-scale simulation method. There are obvious differences between static size effect and dynamic size effect in the compressive strength of concrete. There exists a critical strain rate (the critical strain rate is s-1 approximately). When the applied strain rate is less than the critical strain rate, the size effect on the dynamic compressive strength is weakened or suppressed as the strain rate increases. The dynamic compressive strength would be independent of the structural size of the specimen when the applied strain rate reaches the critical strain rate. When the applied strain rate is more than the critical strain rate, the size effect on the dynamic compressive strength is strengthened as the strain rate increases. Finally, based on the simulation results, the mechanism of concrete dynamic size effect was analyzed and discussed.