Anchorage Performance of Hooked Bars in Reinfored Concrete Members

在前期研究中，作者将中间层梁柱外节点90 °弯钩钢筋锚固破坏分为三种模式：侧劈破坏、局部受压破坏和斜拔破坏（作者新命名）。本研究的目的是阐明所有破坏模式的锚固性能，特别是90度钩形梁钢筋在外部梁柱节点中的拔出破坏模式。本报告的第一部分估计了在中间层节点的锚固性能，并提出了一些锚固强度评估的63个测试样本的基础上。对斜拔破坏的评论是：（1）在轴向应力比小于1/3的范围内，随着柱轴向应力的增加，强度急剧增加;（2）由于水平截面上出现了梯形的破坏裂缝线，在保护层厚度较大的情况下，侧缝钢筋对强度降低的影响。通过24个膝关节试件的试验研究，探讨了顶层节点的锚固性能。结论如下：（2）影响锚固强度的主要因素有弯后尾长、尾筋与柱筋、尾筋与梁端的水平距离、节点侧筋率和混凝土强度，（3）提出了锚固强度和变形能力的评估公式。第三部分对某中间层梁柱外节点进行了钢筋混凝土构件非线性有限元模拟。采用离散的裂纹单元和柱杆在裂纹单元上的销钉作用，对具有拔出破坏的试件进行了较好的模拟。

In the previous study, the authors classified the anchorage failure of 90-degree hooked bars in exterior beam-column joints at an intermediate story into three modes : a side split failure, a local compression failure and a raking-out failure (named by the authors newly.) The purpose of this study is to clarify anchorage performances for all failure modes, especially for the raking-out failure mode of 90-degree hooked beam bars in exterior beam-column joints.The part one of this report estimates anchorage behavior of the joints at an intermediate floor and proposed some anchorage strength evaluations on the basis of 63 test specimens. The remarks on the rakig-out failure are (1) the strength increased severely according to increase of column axial stress in range of the axial stress ratio less than about one third, (2) since the failure crack lines with a trapezoidal shape in horizontal cross section appeared, the effect of lateral joint reinforcement on the strength reduced in case of large thickness of cover concrete.The part two of this report says the anchorage behavior of joints at a top floor on the basis of 24 knee joint specimens. The conclusions are follows : (1) the anchorage mechanism depends on stress transmission from tail portion of hooks to adjacent column bars, (2) main influence factors on the anchorage strength sre tail length after bent portion, horizontal distances between tail and column bars and between tail bars and beam end, lateral reinforcement ratio in joint and concrete strength, and (3) evaluation formulas on anchorage strength and deformability were proposed.In the part three, the exterior beam-column joints at an intermediate floor were simulated by a non-linear finite element method for reinforced concrete members. The good simulation for the specimen with raking-out failure was obtained by using discrete crack elements and dowel action of column bars at the crack elements.