Post-Peak Analysis of Reinforced Concrete Structural Members with Internal Defects

本文研究了两类含有内部缺陷的混凝土构件的峰后性能：一类是含有内部缺陷（如岩穴和裂缝）的棱柱形混凝土试件的单轴受压性能;对几种尺寸的混凝土试件进行了不同尺寸的岩穴试验。在无端部摩擦的情况下，混凝土试件最大抗压强度的降低量与缺陷在混凝土试件截面上的投影面积成正比。用DIANA软件进行了三维有限元分析，得到了与试验结果基本一致的结果。另一方面，在与端部摩擦的试样上的实验的情况下，最大抗压强度的降低被发现是更迅速的，与没有端部摩擦的情况相比。这种现象即使用三维有限元分析也无法用数值方法来表示 ...更多信息 s，其结果与不考虑端部摩擦时的分析结果相同。通过分析可知，当缺陷部分周围区域受到一定程度的约束时，可能会出现严重的失效模式。另一方面，本文对含内部缺陷的钢筋混凝土梁（120×180× 1, 400 mm）进行了点荷载试验，研究了钢筋混凝土梁的抗弯性能，并对不同边界条件下的钢筋混凝土梁的抗弯性能进行了分析。试验结果表明，与箍筋断裂相比，岩穴的存在对峰值后强度的影响更大。采用应变软化型本构模型，利用有限元程序FEAP对不同围压下的试验进行了模拟。通过分析研究得出结论，较大尺寸的岩袋，即，0.3综合目前的研究结果，如果缺陷出现在混凝土构件的预期破坏区或区域内，则应更加仔细地考虑混凝土结构构件的最大强度的降低以及峰后性能。少

In the present research, the post-peak behaviors of two types of concrete structural members with the internal defects have been investigated.The one is on the uniaxial compressive behavior of prismatic concrete specimen with internal defects, such as rock-pocket and breeding. The experiments were carried out for the several sizes of concrete specimens with the different sizes of rock-pockets. In the case of experiment on the specimen without the end friction, the reduction in maximum compressive strength is found to be proportional to the projected area of defect to the section of concrete specimen. The 3-D finite element analysis (FEM) with DIANA has given almost the same results as those of experiments. On the other hand, in the case of experiment on the specimen with the end friction, the reduction in maximum compressive strength is found to be more rapid, compared with the case without the end friction. This phenomenon could not be represented numerically even with 3-D FEM analyse … More s, which lead to the same results as those of analysis without the end friction. It has been understood from this analysis that a sever failure pattern may be occurred in the case that the surrounding area of defect portion is constrained to some extent. Therefore, a unified numerical method and modeling are required to give a rise in moderate results for any kinds of boundary conditions.The other is on the flexural behavior of RC beam with internal defects, such as rock-pocket and breaking of hoop ties, The on-point loading experiment have been done for the RC beam (120×180×1,400 mm) with defects at its center. It has been found from experimental work that the existence of rock-pocket affects much on the post-peak behavior as well as the maximum strength, compared with the existence of broken hoop tie. The finite element program FEAP has been used to simulate the experiment, by applying the strain-softening type of constitutive model under the different confining pressures. From the analytical study it has been concluded that the existence of bigger size of rock-pocket, i.e., 0.3 times the beam width, cancels the confining effect from hoop tie and core-concrete becomes almost in a plain condition.Summarizing the present research, it can be said that the reduction in maximum strength as well as the post-peak behavior of concrete structural member should be more carefully considered if the defects exist in an expected failure zone or area of concrete member. Less