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

在本研究中，研究了两种具有内部缺陷的混凝土构件的峰后性能。一是研究含岩洞、裂缝等内部缺陷的柱形混凝土试件的单轴压缩特性。对不同尺寸的混凝土试件和不同尺寸的岩洞进行了试验。在无端部摩擦的试件上进行试验时，发现最大抗压强度的降低与缺陷在试件截面上的投影面积成正比。利用DIANA进行的三维有限元分析结果与实验结果基本一致。另一方面，在有端部摩擦的情况下，与没有端部摩擦的情况相比，最大抗压强度的降低速度更快。这一现象即使采用三维有限元分析也无法在数值上表示，其结果与不考虑端部摩擦的分析结果相同。从分析中可以理解，当缺陷部分的周围区域受到一定程度的约束时，可能会发生严重的失效模式。因此，需要统一的数值方法和建模，以提高各种边界条件下的温和结果。二是研究了含岩袋和环箍断裂等内部缺陷的RC梁的抗弯性能。对中心存在缺陷的RC梁（120×180×1,400 mm）进行了点加载试验。通过试验研究发现，岩穴的存在对峰后性能和最大强度的影响要大于环箍断裂的存在。采用有限元程序FEAP，采用不同围压下的应变软化型本构模型对试验进行了模拟。分析研究表明，较大的岩穴尺寸（0.3倍梁宽）的存在，抵消了箍箍的围合作用，使核心混凝土几乎处于平直状态。综上所述，当缺陷存在于混凝土构件的预期破坏区域或区域时，应更加认真地考虑混凝土构件的最大强度降低和峰后行为。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