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首页> 外文期刊>Journal of Engineering Mechanics >Fracture and Size Effect on Strength of Plain Concrete Disks under Biaxial Flexure Analyzed by Microplane Model M7
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Fracture and Size Effect on Strength of Plain Concrete Disks under Biaxial Flexure Analyzed by Microplane Model M7

机译：用M7模型分析双向弯曲下普通混凝土圆盘的断裂和尺寸效应。

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摘要

The biaxial tensile strength of concrete (and ceramics) can be easily tested by flexure of unreinforced circular disks. A recent experimental study demonstrated that, similar to plain concrete beams, the flexural strength of disks suffers from a significant size effect. However, the experiments did not suffice to determine the size effect type conclusively. The purpose of this study is to use three-dimensional stochastic finite-element analysis to determine the size effect type and shed more light on the fracture behavior.Afinite-element code using the microplane constitutive Model M7 is verified and calibrated by fitting the previously measured load-deflections curves and fracture patterns of disks of thicknesses 30, 48, and 75 mm, similar in three dimensions, and on flexure tests on four-point loaded beams. It is found that the deformability of the supports and their lifting and sliding has a large effect on the simulations, especially on the fracture pattern, and the strength and Young’s modulus of concrete must be treated as autocorrelated random fields. The calibrated model is then used to analyze the size effect over a much broader range of disk thicknesses ranging from 20 to 192 mm. The disks are shown to exhibit the typical energetic size effect of Type I, that is, the disks fail (under load control) as soon as the macrofracture initiates from the smooth bottom surface. The curve of nominal strength versus size has a positive curvature and its deterministic part terminates with a horizontal asymptote. The fact that material randomness had to be introduced to fit the fracture patterns confirms that the Type 1 size effect must terminate at very large sizes with a Weibull statistical asymptote, although the disks analyzed are not large enough to discern it.
机译：混凝土（和陶瓷）的双轴抗拉强度可以通过未加固圆盘的挠曲来轻松测试。最近的一项实验研究表明，类似于普通混凝土梁，圆盘的抗弯强度会受到明显的尺寸影响。但是，实验不足以最终确定尺寸效应的类型。这项研究的目的是使用三维随机有限元分析来确定尺寸效应类型，并更多地了解断裂行为。使用微平面本构模型M7验证并校准了有限元代码厚度，直径为30、48和75毫米的圆盘的载荷-挠度曲线和断裂模式在三个维度上相似，并且在四点载荷梁上进行了挠曲测试。结果发现，支架的可变形性及其提升和滑动对模拟，尤其是对断裂模式的影响很大，并且混凝土的强度和杨氏模量必须视为自相关的随机场。然后，将校准后的模型用于分析范围从20到192 mm的更大范围的磁盘厚度的尺寸影响。所示的圆盘表现出典型的I型能量大小效应，也就是说，一旦宏观裂缝从光滑的底面开始，圆盘就会失效（在负载控制下）。标称强度与尺寸的曲线具有正曲率，其确定性部分以水平渐近线终止。必须引入材料随机性以适应裂缝模式的事实证实，尽管分析的盘片不足以辨别它，但类型1的尺寸效应必须以威布尔统计渐近线终止于非常大的尺寸。

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