Modeling of Three-Dimensional Failure Mechanism in Reinforced Concrete Beam-Column Joints Subjected to Tri-Directional Earthquake Motions

在双向和变轴荷载作用下，抗弯矩空间框架中钢筋混凝土梁柱节点出现了复杂的应力流动。钢筋混凝土梁柱节点的破坏机理目前还没有统一的研究成果，但有人提出了节点面板混凝土压碎引起的剪切破坏或节点面板斜缝张开引起的弯曲破坏等观点。因此，通过双向荷载反向静荷载试验，研究三维梁柱节点的抗剪机理，重点研究梁柱通过梁柱节点纵向梁杆的粘结性能以及梁柱组件的形状。试验了3个半比例尺R/C三维梁柱节点试件；两个内缝四梁，一个外缝三梁。在一个内部节点中，通过焊接3块钢厚的环板，改善了沿梁杆的试件粘结，在一个节点板中增加了7mm的厚度，在另一个内部节点中，消除了沿梁杆和柱杆的试件粘结。两侧荷载控制，柱顶层位移轨迹与试件纵向呈45度倾角。所有试件均在节理剪切中破坏。在梁柱节点区域的四角处观察到严重的混凝土压碎。本研究得出的结论如下。(a)改进节点板梁柱粘结的内部节点试件抗剪强度比无节点板梁柱粘结的内部节点试件抗剪强度提高25%。(b)三梁外节点试件在达到抗剪强度后，抗剪能力明显衰减，这是由于梁不入框的梁柱节点区域内混凝土压缩损伤的进展。(c)从节点侧箍应变、柱纵筋应变等试验数据中指出，梁柱节点板的三维受力机制受节点板周围应力场差异的影响。少

Complicated stress flows develop in reinforced concrete beam-column joints in moment resisting space frames subjected to bi-lateral and varying axial loads. There is no common finding yet on failure mechanism of R/C beam-column joints, whereas some ideas are proposed such as the shear failure caused by crush in joint panel concrete or the flexural failure caused by diagonal crack opening in a joint panel. Therefore, shear resisting mechanism in three-dimensional beam-column joints was studied through static loading tests in which bi-lateral load reversals were afforded, focusing on the bond performance along longitudinal beam and column bars passing through a beam-column joint and the shape of a beam-column subassemblies. Three half-scale R/C three-dimensional beam-column joint specimens were tested ; two interior joints with four beams and one exterior joint with three beams. In one interior joint specimen bond along beam bars was improved by welding three ring plates with steel thick … More ness of 7 mm in a joint panel, and in another interior joint specimen bond along beam and column bars was eliminated within a joint panel. Bi-lateral loading was so controlled that the path of story displacement at the top of a column traced the line with 45-degree inclination to longitudinal direction of a specimen. All specimens failed in joint shear. Severe crush of concrete was observed at four corners of a beam-column joint region. Conclusions drawn by the study are indicated below.(a)Shear strength of the interior joint specimen with improved bond along beam bars in a joint panel was enhanced by 25 percent greater than that without bond along beam and column bars in a joint panel.(b)Shear capacity decayed remarkably after attaining shear strength in exterior joint specimen with three beams due to the progress of concrete compressive damage within beam-column joint region into which beams do not frame.(c)It was pointed out from test data, e.g., strain of joint lateral hoops and column longitudinal bars, that three-dimensional force-carrying mechanism in a beam-column joint panel was influenced by the difference of stress fields around a joint panel. Less