混凝土板柱子结构抗连续倒塌试验研究

节点脆性冲剪破坏易导致板柱结构体系的连续倒塌。对1个横、纵向均为2跨的混凝土板柱子结构进行连续倒塌静力加载试验，试件制作时移除底部中柱以模拟初始失效，试验中首先对中柱柱头施加向下的集中力使其节点发生初始冲剪破坏，其后对楼板施加均布荷载直至发生后继连续倒塌破坏，分析了试件不同变形阶段的受力机理并对承载力进行了评估。结果表明：子结构的中柱节点冲剪破坏具有一定延性，但板内张拉力导致冲剪承载力比中国规范计算值低50%；初始加载时边中柱和角柱分别承担82%和18%的荷载，随着变形增大，边中柱节点逐步损伤，边中柱承担荷载下降、角柱承担荷载上升，结构倒塌时边中柱和角柱分别承担51%和49%的荷载；小变形下试件通过楼板面外受弯能力和面内受压薄膜效应承载，在中柱节点发生冲剪破坏的时刻，受压薄膜效应提供的承载力贡献为12%；大变形下试件通过节点区的残余受弯能力和面内受拉薄膜效应承载，当节点发生严重损伤后，荷载由板底整体钢筋的受拉薄膜效应承担。

Experimental study on a flat plate substructure against progressive collapse

Punching shear failure of slab-column joints tends to trigger the progressive collapse of a flat plate structural system. A static progressive collapse test was conducted on a 2×2 bay flat plate substructure with a missing interior column. At first, a downward concentrated force was applied on the central removed column till the initial punching shear failure occurred. Subsequently, a downward uniformly distributed load was alternatively imposed on the slab, and the load was maintained until the progressive collapse of the substructure. The collapse mechanism and collapse-resisting resistance of the substructure under different deformation stages were analyzed and evaluated. Results show that the punching shear failure of the slab-column joint within a substructure exhibits a certain level of ductility. But the tensile force of the membrane action developed in the slab results in a 50% decrease of the punching capacity of the joint compared to that calculated by the Chinese code. In the initial stage, 82% and 18% of the applied load are resisted by the middle edge and corner columns, respectively. Then the slab-column joints at the middle edge columns are gradually damaged as the deformation increased, which lead to a decrease and an increase of the loads carried by the middle edge and corner columns, respectively. At the end of the test, 51% and 49% of the applied load are resisted by the middle edge and corner columns when the substructure collapsed. At small deformation, the substructure resists the load via out-of-plane bending capacity and in-plane compressive membrane action. The compressive membrane action contributes to 12% of the collapse resistance when the joint of the central column damaged in punching shear. At large deformation, both the residual flexural capacity of the remaining joints and the tensile membrane action contribute to the collapse resistance. When the slab-column joints are severely damaged, only the integrity reinforcement at the bottom of the slab effectively provides the collapse resistance in the form of tensile membrane action.