Study on Shear Resistance Mechanisms of RC Beam-Column Joints and Development of Seismic Design Method

最近，ACI建筑规范和新西兰规范对钢筋混凝土梁柱节点进行了抗震规定。开发合理的梁柱节点设计方法在日本也已成为人们关注的问题。在ACI和新西兰规范中，对通过节理的梁杆发展长度和节理剪应力限制的规定是非常重要的，但这些规定并没有建立在充分的试验数据和合理的理论基础上。针对试验结果，讨论了梁杆粘结状态与节理剪应力水平的相互关系。对8个半比例尺内梁柱节点进行了试验。改进粘结型采用小尺寸低强度棒材，粘结劣化型采用大尺寸高强度棒材。节理剪应力水平在ACT规范的限制值范围内变化。在节理少量侧剪配筋的第一个试验系列中，侧剪配筋屈服，节理剪切裂缝张开显著。节理破坏发生在梁屈服后。层间剪切-层间漂移滞回线表现出与梁杆粘结情况无关的挤压效应。在第2组试验中，对节理进行加筋，使其侧向加筋能够承受一半的剪力，有效地抑制了节理剪切裂缝的张开，有效地防止了节理剪切破坏。改良粘结型试样的滞回线呈粗纺锤形，而粘结劣化型试样的滞回线呈捏缩效应。根据这些试验结果，研究了梁杆粘结状态对其抗剪机理的影响。最后给出了节点剪应力的限制条件和梁杆粘结指标的限制条件。

The aseismatic provision for reinforced concrete beam-column joints has been made recently in ACI Building Code and New Zealand Code. The development of the rational design method for the beam-column joint has become a matter of concern also in Japan. In the ACI and New Zealand codes, the provisions for the development length of beam bars passing through a joint and the limitation to the joint shear stress are very important, but they are not based on the sufficient test data and the rational theory. In this study, the interrelation between the bond situation of beam bars and the joint shear stress level were discussed for the experimental results.Eight half-scale interior beam-column joints were tested. Small-size low-strength bars were used in the improved bond type, and large-size high-strength bars were used in the bond deterioration type. The joint shear stress level was varied in the region of the restricted value in ACT Code.In the first test series with a small amount of lateral shear reinforcement in a joint, the lateral reinforcing bars yielded and the opening of joint shear cracks was remarkable. The joint shear failure occurred after beam yielding. The story shear-story drift hysteresis loop showed the pinching effect independently of the bond situation of beam bars. In the second test series in which a joint was reinforced so that half of the entire shear could be resisted by the lateral reinforcement, the opening of the joint shear cracks was restrained and the joint shear failure was prevented effectively. The hysteresis loop was fat spindle-shaped in the improved bond type, but the bond deterioration type specimens showed a pinching effect.From these experimental results, the effect of the bond situation of beam bars on the shear resistance mechanisms was investigated. Finally the limitation to the joint shear stress and the restriction of beam bar bond index were presented.