Restoring-force model for reinforced concrete members failing in shear or bond after yielding

本研究的第一个目标是建立钢筋混凝土构件在弯曲屈服后发生剪切破坏的恢复力模型。对20根钢筋混凝土柱进行了恒定轴压试验。试验参数包括混凝土强度、纵向配筋量和剪切配筋量以及尺寸。其中一些尺寸与实际列相似，而另一些尺寸约为实际列的一半。其中大部分在循环非弹性载荷反转后发生剪切破坏。将钢丝埋入试件中，测量核心混凝土中的平均横向应变。在某些情况下，核心混凝土的应变比横向钢筋的应变大几十倍。在一些试件的最大挠度处，注入了环氧树脂。树脂硬化后，将样品卸载。然后，对每个试件进行CT扫描，获得裂纹的三维图像。计算结果与核心混凝土的应变实测值相吻合。本研究的第二个目的是建立钢筋混凝土粘结劈裂破坏模型。试件参数包括钢筋直径、肋骨形状、保护层厚度以及是否有约束钢筋。试验结果表明，尺寸效应主要是由脆性劈裂裂缝引起的，而不是由钢筋肋前混凝土的局部压碎引起的。基于这一发现，我们提出了对于小盖子和短拼接长度的拼接产生大尺寸效应的公式，这些拼接预计会发生脆性破坏。所提出的方程与本研究中给出的实验结果和文献中报道的大部分实验数据都是一致的。

The first objective of this study is to establish a restoring-force model for reinforced concrete members failing in shear after flexural yielding. Twenty specimens of reinforced concrete columns are tested under constant axial load. Test parameters were concrete strengths, amount of longitudinal and shear reinforcement, and the dimensions. Some of them had dimensions similar to actual columns, while the others had dimensions about a half of actual columns. Most of them failed in shear after cyclic inelastic load reversals. Piano wires were embedded in the specimens so that average transverse strains in the core concrete were measured. In some cases, core concrete strain was larger than several ten times of the strain in the transverse reinforcement. At the maximum deflection of some of the specimens, epoxy resin was injected. After the resin hardened, the specimens were unloaded. Then, CT scanning was conducted to obtain three-dimensional image of the cracks in each specimen. The results agreed with the measured strains in the core concrete. Such findings were utilized to propose a restoring-force model for reinforced concrete members failing in shear after flexural yielding.The second objective of this study is to establish a model for bond splitting failure in reinforced concrete. The specimen parameters include bar diameter, rib shape, cover thickness, and the presence/absence of confining reinforcement. The experimental results show that the size-effect is mainly attributable to brittle splitting cracks, and not to local crushing of concrete in front of the bar ribs. Based on this finding, we proposed equations that yield a large size effect for splices with small cover and short splice length, where brittle failure is expected. The proposed equations agree with both the experimental results presented in this study and the bulk of the experimental data reported in the literature.