板柱节点冲切破坏后受力性能试验研究

Experimental research on post-punching behavior of slab-column connections

完成12个钢筋混凝土板柱节点试件冲切破坏试验,通过改变剪跨比、纵筋配筋率和整体性钢筋布置方式,以期得到能够提高冲切破坏后承载力、避免连续倒塌的构造措施。试验结果表明,纵筋配筋率对承载力影响并不明显,纵筋较早发生锚固失效,对冲切破坏后承载力的贡献非常有限。整体性钢筋能够有效提高残余承载力和冲切破坏后承载力,剪跨比越大效果越明显。在大挠度情况下,整体性钢筋成为冲切锥体和剩余板的唯一连接,依靠整体性钢筋轴力的竖向分量和大挠度形成的力矩来抵抗外部竖向荷载的作用,试件破坏由整体性钢筋断裂或锚固失效控制,通过布置足量的整体性钢筋、提高混凝土强度以及增大钢筋保护层厚度等措施,可进一步提高冲切破坏后承载力。采用规范公式对试件冲切承载力和冲切破坏后承载力进行预测并与试验结果对比表明,预测值相比试验值偏差较大。最后给出了冲切破坏后承载力的建议计算式和构造措施,为我国相关规范的编写提供参考。

Post-punching behavior of 12 slab-column connections with various longitudinal reinforcement ratios, shear- span ratios and the integrity reinforcement layout was studied and compared. Some solutions could be adopted to enhance the post-punching behavior of fiat slabs and to avoid progressive collapse. The test results show that the post- punching bearing capacity provided by the longitudinal reinforcement is insignificant because of the anchorage invalidation at early stage. On the contrary, integrity reinforcements could carry loads by developing the vertical component of the tensile stress and moment accompanied by a significant deflection which plays a major role in the post-punching process as they are the only remaining link between the punching cone and the rest of the slab. The effect is significant as the shear-span ratio is increased. The resistance is governed either by the breakout of the concrete or the fracture of the integrity reinforcement. It is essential to provide sufficient integrity reinforcement, increase the strength of concrete and cover thickness to improve the post-punching bearing capacity. The test results on the punching and post-punching bearing capacity were compared with the predictions of the formulas proposed by codes of GB 50010--2010 and ACI 318-95, which had a relatively large errors. At last, the suggested formula and structural measures were proposed which could give some suggestions for the compilation of Chinese codes