Analysis of 3D scale and size effects in numerical concrete
Analysis of 3D scale and size effects in numerical concrete
复制标题
DOI：
10.3929/ethz-a-006015699
复制
发表时间：
2010
期刊：
影响因子：
--
通讯作者：
Hau-Kit Man
中科院分区：
文献类型：
--
作者：
Hau-Kit Man
准脆性材料（如混凝土、冰和岩石）的尺寸效应，在文献中通常被称为岩土材料，在过去的三十年中一直是一个讨论的问题。通过实验和数值模拟对尺寸效应进行了研究。通常研究的是不同尺寸（体积）试样的力学性能。最常见的是，对标本进行二维缩放。在数值研究中，研究了三点弯曲作用下的断裂实验。在这里，混凝土棱镜在所有三个维度上都是缩放的。数值模型采用了三维梁格模型，该模型较好地模拟了混凝土的断裂试验。样品采用包含混凝土非均质性的规则晶格进行建模。骨料含量Pk和骨料几何形状可以变化。骨料的形状可以是理想的球形、碎状或椭圆形。为了建立理想的球形骨料分布，使用了计算机程序。对于非球形骨料，采用了第4章中描述的不同方法：通过x射线断层扫描直接扫描含有高密度骨料（如大理石）的小型真实混凝土棱镜，并将所得3D图像实现到3D晶格中。如果没有庞大的计算设备和并行求解器，就无法进行三维模型裂缝模拟和尺寸效应研究。即使在进行模拟时使用最先进的计算设备，从最小到最大的样品的尺寸范围也被限制在1:8。还存在其他约束：试样尺寸较小，某些尺寸的试样尺寸与最大骨料直径之比D/dmax较小（D/dmax < 3）。尺寸效应分析的数值结果在第五章到第七章给出。根据混合物中使用的骨料形状不同，断裂行为也不同。无论骨料含量和形状如何，尺寸对抗弯强度的影响都是存在的。然而，计算出的斜率
Size effect on strength of quasi-brittle materials like concrete, ice and rock, in the literature often referred as geomaterials, has been an issue of discussion over the last three decades. Size effect investigations have been carried out either by experiments or through numerical simulations. Usually mechanical properties of specimens of different sizes (volumes) are investigated. Most commonly, specimens are scaled two-dimensionally. In a numerical study, fracture experiments were investigated subjected to 3point bending. Here, concrete prisms are scaled in all three dimensions. As numerical model a 3D beam lattice model was used, which has proven to be quite suitable for simulating fracture experiments of concrete. Samples are modeled with regular lattices with inclusion of the concrete heterogeneity. The aggregate content Pk and the aggregate geometry can vary. The aggregates shapes can be either ideal spherical, crushed or oval shaped. For building an ideal spherical aggregate distribution, a computer program is used. In case of non-spherical aggregates, a different approach, which is described in Chapter 4, is adopted: Small real concrete prisms containing aggregates with high density (like marble) are scanned directly by means of X-ray tomography and the resulting 3D images are implemented into the 3D lattice. Without the availability of huge computing facilities and parallel solvers, fracture simulation with 3D models and size effect investigation can not be done. Even with state-of-the-art computing facilities at the time the simulations were conducted, the size range from the smallest to the largest specimen was limited to 1:8. There were also other constraints: specimen sizes are rather small and the ratio of the specimen size and largest aggregate diameter D/dmax is for some sizes small (with D/dmax < 3). Numerical results of the size effect analyses are presented in Chapters 5 to 7. Dependent which aggregate shapes are used in the mixture, the fracture behaviour differs. Regardless of aggregate content and shape, size effect on bending strength can be found in all cases. However, the calculated slopes in