柱截面形状对板柱节点受冲切性能影响的试验研究

Experimental study of the effects of cross-sectional shape of column on punching shear performance of slab-column connection

我国《混凝土结构设计规范》(GB 50010—2010)的板柱节点受冲切承载力计算公式考虑了柱截面形状的影响,但相关的试验研究十分有限,机理尚不明确。为研究柱截面形状及纵筋配筋率对板柱节点受冲切性能的影响,完成了10个轴心荷载作用下的板柱节点冲切破坏试验。试验变量为柱截面形状(包括圆形、六边形、方形和矩形截面)以及纵筋配筋率。通过试验获取了荷载-挠度曲线、破坏形态、钢筋和混凝土的应变分布。采用专门设计制作的应变测杆,得到了板柱节点内部裂缝发展过程。结合试验结果和已有试验数据进行分析,结果表明:柱截面形状对受冲切承载力的不利影响的根本原因是冲切截面计算周长与板截面有效高度的比值增大导致的应力集中现象;现行《混凝土结构设计规范》(GB 50010—2010)假定的冲切锥面倾角以及圆柱板柱节点的受冲切承载力计算方法存在不合理之处;板内斜裂缝首先在靠近柱头的中上部区域形成,冲切破坏呈现剪切劈裂的特点。

In the code for design of concrete structures of China, the influences of cross-sectional shape of column were considered in the calculation formula of punching shear, but relevant experimental studies were very limited and the mechanism was also unclear. In order to investigate the influences of cross-sectional shape of column and longitudinal reinforcement ratio on the punching shear behavior of slab-column loading. In the experiments, the cross-sectional shape of column connection, 10 specimens were tested under the axial （including circle, hexagon, square, and rectangle） and the longitudinal reinforcement ratio were defined as variables. The load-deflection curves, the failure mode and the strain distributions in concrete and steel were obtained through the tests. Based on the specially designed strain measuring rod, the formation and development of internal shear crack can be observed. In combination with the test results and the existing experimental data, it is found that the adverse effect of the cross-sectional shape of column on the punching shear capacity was basically attributed to the stress concentration due to the increase of the ratio ttm/ho ; there are some unreasonable considerations for the assumed angle of the punching shear conical surface and the calculation of the slab-column connection of circular column; on the other hand, the internal shear crack was firstly formed at the upper and middle part nearing the column top, and the shear fracturing characteristics can be observed in the punching shear failure.