钢框架-组合楼板结构抗连续倒塌的三维整体效应研究

In "911" event, the World Trade Centre progressively collapsed. After that, progressive collapse research work about high-rise buildings has become one of the hottest topics in the field of building structures. However, limited research works about the three-dimensional behaviour of frame-floor structures against progressive collapse can be found, especially for steel frame-composite floor structures. Therefore, further research works about the three-dimensional behaviour and the theoretical calculation method of frame-floor structures against progressive collapse are needed. This project will focus on the three-dimensional effect of steel frame-composite floor structures under a middle-column-removal scenario. The research work will be conducted through "experimental tests--finite element simulation and parametric study--theoretical model establishment". A new experimental test method about the three-dimensional effect of building structures under displacement-controlled uniform loading against progressive collapse will be proposed. And the pseudo-static responses of three-dimensional structures, which can consider dynamic effect, will be obtained by using energy theory. The three-dimensional behaviour and the alternate load path of steel frame-composite floor structures will be studied. Catenary action of steel frame and tensile membrane action of composite floor will also be investigated. In addition, a theoretical calculation method considering three-dimensional effect of steel frame-composite floor structures against progressive collapse will be proposed. This project can provide the theoretical basement for drafting the related structure design codes and for the structural behaviour improvement of composite steel building structures against progressive collapse in our country.

“911”事件世贸大厦发生连续倒塌后，多高层建筑结构的抗连续倒塌研究已成为近期建筑结构研究的热点，但是现阶段抗连续倒塌研究中，框架-楼板三维整体结构体系研究成果有限，尤其是钢-混凝土组合结构体系，考虑三维整体效应的抗连续倒塌力学性能与计算方法研究有待进一步深入。申请人拟以钢框架-组合楼板结构体系在中间柱失效后的三维整体效应研究为切入点，以“试验研究—有限元模拟及影响参数分析—理论计算模型探索”的研究方法为手段，探索一种位移控制均布荷载下抗连续倒塌的三维整体效应试验方法，并运用能量原理获得考虑动力效应的伪静态三维结构响应，揭示三维整体效应的力学性能和传力路径，阐明三维整体效应中钢框架悬链线效应与组合楼板受拉薄膜效应等传力机制，提出一种考虑三维整体效应的钢框架-组合楼板结构抗连续倒塌理论计算方法。项目研究成果可为提高我国多高层钢-混凝土组合结构建筑抗连续倒塌性能和编制相关设计规范提供理论依据。

常规设计中，设计人员一般只考虑常规荷载下的结构承载力和安全性，结构遭受偶然荷载时的抗连续倒塌承载力设计理论还有待完善。 “911”事件中世贸大厦的连续倒塌掀起多高层建筑结构的抗连续倒塌研究的热潮。课题组完成了4个钢框架-组合楼板结构构件在中柱失效工况下的1/3缩尺模型实验研究，研究参数包括楼板长宽比、组合作用强弱和楼板边界条件，主梁与柱采用平齐式端板节点，其余节点采用腹板双角钢节点。实验结果表明，楼板长宽比为1:1的构件承载比长宽比为1:1.5的高，但是变形能力弱；组合作用强弱不影响最大承载力，较弱的组合作用会增加结构延性，有利于大变形阶段荷载的增长；楼板边界条件强，利于梁悬链线效应和楼板受拉薄膜效应的形成。此外，通过深入分析实验数据，课题组明确了三维楼板结构的传力机理。在中柱失效工况下，试件的整个破坏过程大致可以分为三个阶段。第一阶段主要是双跨主梁的受压拱作用和双跨主梁的抗弯作用抵抗竖向荷载。主梁节点破坏以后进入第二阶段，此时原本双跨主梁上承担的部分荷载将传递给双跨次梁承担，双跨次梁抗弯及悬链线机制开始发挥较大作用。第三阶段结构已经产生很大变形，楼板形成了较强的受拉膜效应，未破坏的部分次梁也形成了悬链线效应，二者共同抵抗外荷载。然后，课题组进行了端板节点、双角钢节点的组件实验和抗剪栓钉推出实验，基于组件实验建立了钢框架-组合楼板结构的有限与模型，验证了实验结论，还得出增加压型钢板厚度能提高结构抗倒塌承载力；增加抗剪栓钉数量能小幅度地提高结构抗倒塌承载力；提高节点延性能大幅提高结构抗倒塌承载力；增强节点承载力对结构抗倒塌承载力没有太大影响。通过有限元非线性动力分析得出，DOD中有关组合平面框架抗连续倒塌承载力动力放大系数的规定偏不安全。最后，课题组在实验研究和有限元分析的基础上，提出了易于工程实践使用的钢框架组合楼板结构抗连续倒塌承载力的双折线理论模型，与实验结果和有限元分析结果吻合良好。