全过程火灾作用下钢管混凝土单边螺栓连接节点的工作机理研究

This project aims to study the structural performance of a new type of concrete filled steel tube (CFST) column to steel beam joints with blind-bolted connections subjected to a full-range fire, which is a coupled loading and fire process, including ambient temperature loading, heating and cooling with constant loads and post-fire loading stages. Blind-bolted connections can be used to connect steel beams to CFST columns from the outside of steel tubes, and satisfy the requirement of modern assembly structures. It is expected that the blind-bolted connections will be widely used in high-rise buildings in the nearly future. Therefore, it is necessary to investigate the structural performance of CFST column to steel beam joints with blind-bolted connections under full-range fire, which will benefit both the theoretical backgrounds and engineering application in terms of improving the fire safety of this type of joint. A finite element analysis (FEA) model is established to study the working mechanism of CFST column to restrained steel beam joints with blind-bolted connections under full-range fire. Fire resistance and post-fire tests are conducted on the joint specimens with different parameters, such as beam load ratio and beam boundary conditions. Based on the theoretical analysis and experimental study, the temperature field distribution, deformation development and failure modes of this type of joint subjected to full-range fire are investigated, and the structural response of this type of joint during the entire loading and fire process is studied. Systematical parametric study is conducted to investigate the influence of main parameters including column load ratio, beam load ratio, heating time ratio, material properties and geometric dimension on the structural performance of the composite joint under full-range fire. Finally, simplified equations for predicting the fire resistance, post-fire residual strength and stiffness of the CFST column to steel beam joint with blind-bolted connections are proposed on the basis of the parametric study.

本项目以新型的钢管混凝土柱-钢梁单边螺栓连接节点为研究对象，对其在全过程火灾（包括常温下加载、火灾升、降温阶段持荷和火灾后加载）作用下的工作机理展开研究。单边螺栓连接是一种可以在钢管外侧将钢梁和钢管连接的构造措施，符合现代装配式结构要求，在高层建筑中应用前景广泛。因此，深入进行本课题研究对于提高该类节点的火安全性具有重要的理论和工程应用价值。本课题拟通过建立有限元模型，对考虑梁端约束作用的该类节点在全过程火灾下的工作机理展开理论分析。进行节点在不同参数（如梁荷载比和梁端约束条件等）下的耐火极限和火灾后力学性能试验研究。通过理论分析和试验研究，明晰该类节点的温度分布、变形发展和破坏模态等变化规律，研究该类节点在全过程火灾作用下的结构反应。在系统分析柱荷载比、梁荷载比、升温时间比、材料强度和几何尺寸等主要参数对该类节点性能影响规律的基础上，提出其耐火极限、火灾后剩余承载力和刚度的实用计算方法。

钢管混凝土柱-钢梁单边螺栓连接节点具有安装便利和可靠性高等优点，日益受到工程技术人员和研究者的关注。本项目以考虑梁端约束作用的钢管混凝土柱-钢梁单边螺栓连接节点为研究对象，对其在全过程火灾（包括常温下加载、升、降温阶段持荷和火灾后加载）作用下的力学性能展开试验研究和理论分析，所完成的主要工作如下：.1.进行考虑梁端约束作用的钢管混凝土柱-钢梁单边螺栓连接双跨子节点的耐火极限试验研究。获得中柱节点在外荷载和火灾共同作用下的温度发展、梁柱变形和耐火极限等试验数据，研究整体结构中钢管混凝土柱-钢梁单边螺栓连接节点的典型破坏形态。.2.进行梁端受轴向约束作用的钢管混凝土柱-钢梁单边螺栓连接T字形子节点的耐火极限和全过程火灾后试验研究。获得该类节点在常温加载、升、降温阶段持荷和火灾后加载过程中的节点变形发展、约束梁温度内力变化，耐火极限和火灾后剩余承载力等试验数据，明确整体结构中梁的温度内力对单边螺栓连接节点工作性能的影响规律。.3.建立考虑梁端约束作用的钢管混凝土柱-钢梁单边螺栓连接节点的耐火性能有限元分析模型。模型综合考虑不同温度阶段钢材和混凝土的材性变化、高温所致的钢材高温蠕变和混凝土高温徐变等因素对节点工作性能的影响，利用试验数据对模型进行验证，试验和模拟结果吻合良好。基于建立的有限元模型，深入分析该类节点的火灾下（后）工作机理，对节点梁内力变化、单边螺栓应力分布和节点弯矩-转角关系等进行研究，为进一步开展考虑梁端约束作用的单边螺栓连接节点的抗火设计和火灾后评估研究提供参考。