Shear Failure Mechanism of Reinforced Concrete Columns and Beam-Column Joints under Tri-lateral Excitations and Prevention Design Method

通过对三维梁柱组合试件的试验，研究了柱或梁柱节点的剪切破坏对钢筋混凝土框架结构在变轴向荷载和双向荷载作用下抗震性能的影响。两个试件从中层钢筋混凝土框架的底层拆除了大约半个缩尺的模型，在平面图的拐角位置有两根纵梁和横梁垂直的柱。一个试件按柱剪力破坏，另一个按梁柱节点剪力破坏。在全跨梁的中心放置钢制的力传感器，以测量对梁的轴力和剪力。在对安装在钢筋混凝土梁试件中心的力传感器进行的补充试验中，验证了该力传感器不会阻碍梁在反复荷载作用下的滞回行为。双向剪力和变轴向LOA…在R/C组合试验中，每个柱顶同时施加从受压到拉伸的更多d。这两个试件的破坏方式都是假定的，即一个是在柱的中部受剪，另一个是在梁柱节点板上受剪。在柱破坏试件中，剪切裂缝首先出现在外柱上。然而，由于双向剪切荷载的作用，内柱的剪切破坏变得非常明显，为了研究单侧荷载和双向荷载作用下受剪性能的差异，进行了两个与三维组合试件尺寸和配筋相同的孤立柱的单侧和轴向加载试验。试验是通过在柱的顶部和底部提供反对称弯矩来进行的。通过试验，内柱的轴压荷载保持恒定，而外柱的轴向荷载从拉到压变化。两根单向往复荷载作用下的孤立柱均发生剪力破坏。多条斜向剪切裂缝均匀分布在柱体的整个表面。相反，在三维组合试件中，剪切裂缝集中在柱的中部区域。内柱和外柱在双向荷载作用下的抗剪强度分别是相应的单侧荷载作用下的0.78倍和0.86倍。较少

Objective of the study is to investigate the influence of shear failure in columns or beam-column joints on earthquake resistant performance of a R/C frame building subjected to varying axial and bi-lateral loads by testing three-dimensional beam-column subassemblage specimens. Two specimens were approximately half a scale model removed from first story in middle-rise R/C frame, and had two columns with orthogonal beams in longitudinal and transverse direction at comer position of a plan view. One specimen was designed to fail by column shear and the other by beam-column joint shear. Force transducer made from steel was placed at the center of full-span beam to measure both axial force and shear force induced to the beam. In supplementary test to calibrate the force transducer incorporated in the center of R/C beam specimen, it was verified that the force transducer did not hamper hysteretic behavior of a beam under reversed cyclic loading. Bi-lateral shear forces and varying axial loa … More d from compression to tension were applied simultaneously at each column top in R/C subassemblage test. Both specimens failed in supposed manner, i.e., one by shear at the middle portion of columns and the other by shear in beam-column joint panels. In column failure specimen, shear cracks occurred in the exterior column at first. However, shear failure in the interior column became remarkable due to bi-lateral shear loading.Two isolated columns with the same dimension and steel arrangement as the three-dimensional subassemblage specimen were tested under uni-lateral and axial loading to investigate the difference of shear performance caused by uni-lateral or bi-lateral loading. Tests were carried out by providing anti-symmetric bending moments at the top and bottom of a column. Compressive axial load to interior column was kept constant through testing whereas varying axial load was applied to exterior column from tension to compression. Two isolated columns subjected to uni-lateral load reversals failed in shear. Many diagonal shear cracks occurred uniformly in entire surface of a column. On the contrary, shear cracks concentrated in the middle region of columns in the three-dimensional subassemblage specimen. Shear strength of interior and exterior columns subjected to bi-lateral loading was 0.78 times and 0.86 times smaller respectively than that of corresponding isolated columns subjected to uni-lateral loading. Less