楼板对RC空间框架结构抗连续倒塌性能影响试验研究

为研究楼板对RC空间框架结构抗连续倒塌性能的影响作用，文章以汶川地震中完全倒塌的漩口中学教学楼为原型结构，设计3个单层2×2跨1/3缩尺模型，包括2个带楼板子结构和1个纯框架子结构，通过拟静力加载试验研究RC框架结构在拆除中柱状态下的连续倒塌破坏过程。试验结果表明：纯框架子结构首先进入梁机制阶段，框架梁内产生轴向压力，产生“压拱效应”，在梁端部截面抗弯承载力丧失后，进入悬链线机制阶段，依靠梁内部钢筋拉结力抵抗上部荷载。对比分析带楼板子结构与纯框架子结构试验结果，由于楼板的“薄膜效应”使梁机制峰值承载力提高了145%，悬链线机制峰值承载力提高了75%，楼板显著提高了梁机制和悬链线机制的抗连续倒塌能力。增加板厚增加梁板的“压拱效应”，极大提高梁机制承载力，然而大变形下梁板开始不协同作用，板发生冲切破坏，降低了悬链线阶段承载力和延性。

Experimental study on the effect of floor slab on the progressive collapse resistance of RC spatial frame structure

To study the effect of floor slab on the progressive collapse of reinforced concrete (RC) spatial frame, three one-story two-by-two bays 1/3 scaled models with the Xuankou middle school building collapsed in Wenchuan earthquake taken as the prototype structure were constructed. Among them, two models incorporate floor slab sub-structures and one is a pure framed sub-structure. The progressive collapse procedure of RC frame after removing the middle columns under the quasi-static loading can be experimentally studied. The experimental results show that the pure framed sub-structure may first exhibit the beam mechanism, with the occurrence of the “compressive arch” due to the axial compressive forces in the frame beams. Once the flexural capacity in the beam ends is lost, and the pure framed sub-structure goes into the stage of catenary mechanism with the tensile force of steel in beams to resist the loads from upper structure. Based on the comparison of experimental results between floor slab sub-structure and pure framed sub-structure, it is found that the peak capacities of beam mechanism and catenary mechanism are increased by 145% and 75%, respectively, due to the “membrane effect”, indicating that the slabs can significantly enhance the progressive collapse capacity of beam mechanism and catenary mechanism. Increasing the slab thickness increases the “compressive arch’’ of beams and slabs, and hence significantly enhances the capacity of beam mechanism. However, beams and slabs fail to work together under large deformation, leading to the punch failure of slabs and the decrease of the capacity and ductility of catenary mechanism.