Proposal for Standard Test of Modulus of Rupture of Concrete with Its Size Dependence
Proposal for Standard Test of Modulus of Rupture of Concrete with Its Size Dependence
复制标题
混凝土断裂模量及其尺寸依赖性标准测试的建议
DOI：
10.14359/10164
复制
发表时间：
2001
影响因子：
1.7
通讯作者：
D. Novák
中科院分区：
文献类型：
--
作者：
Z. Bažant;D. Novák
最近积累的关于断裂模数的测试数据以及分析研究和数值模拟清楚地表明，混凝土的弯曲强度，即断裂模数，随着梁尺寸的增加而显著降低。本文提出了一种将这种尺寸效应纳入现有试验标准的方法，并着重介绍了ASTM标准C 7894和C 293-94。该方法基于最近建立的尺寸效应公式，该公式既描述了由于梁拉伸面裂纹边界层的有限尺寸引起的截面内应力重分布引起的确定性-能量尺寸效应，也描述了由于材料局部强度的随机性引起的经典的威布尔统计尺寸效应。制定了试验程序的两种备选方案。在第一种方案中，只测试一种尺寸的梁(如现行标准中所推荐的)，并且根据所有混凝土的现有信息的平均值来近似预测尺寸对平均断裂模数的影响。在第二种选择中，测试了两个大小完全不同的梁。后者更加繁琐，但对手头混凝土的尺寸效应提供了更好的预测；它不仅允许估计断裂模数的平均值，而且还允许估计断裂模数的变异系数(特别是随着尺寸的增加而减小)。数值算例验证了该方法的可行性。
Recently accumulated test data on the modulus of rupture, as well as analytical studies and numerical simulations, clearly indicate that the flexural strength of concrete, called the modulus of rupture, significantly decreases as the beam size increases. This paper proposes a method to incorporate this size effect into the existing test standards, and focuses particularly on ASTM Standards C 7894 and C 293-94. The proposed method is based on a recently established size effect formula that describes both the deterministic-energetic size effect caused by stress redistribution within the cross section due to finite size of the boundary layer of cracking at the tensile face of beam, and the classical Weibull-type statistical size effect due to the randomness of the local strength of material. Two alternatives of the test procedure are formulated. In the first alternative, beams of only one size are tested (as is recommended in the current standard), and the size effect on the mean modulus of rupture is approximately predicted on the basis of the average of existing information for all concretes. In the second alternative, beams of two sufficiently different sizes are tested. The latter is more tedious but gives a much better prediction of size effect for the concrete at hand; it allows for the estimation of size effect on not only the mean but also the coefficient of variation of the modulus of rupture (particularly, its decrease with increasing size). Numerical examples demonstrate the feasibility of the proposed approach.