钢管混凝土结构在服役阶段可能经受火灾和地震作用。进行火灾后钢管混凝土结构的抗震性能研究，对提高抗震设防区火灾后钢管混凝土结构的安全性有重要的意义。本文以带楼板的圆钢管混凝土柱-钢梁外环板式节点为研究对象，考虑受力受火全过程影响，研究节点在火灾后的抗震性能，主要工作如下： 1. 完成了火灾后考虑楼板组合作用的圆钢管混凝土柱-钢梁外环板式节点抗震性能试验研究。火灾试验中在柱顶施加恒定轴压荷载，抗震试验中保持柱顶荷载不变，在梁端施加反复荷载。试验主要参数为节点类型、柱荷载比和升温时间。得到了节点试件在火灾下的温度场分布和位移变化规律、火灾后梁端荷载-位移曲线、应变分布规律、强度和刚度退化规律以及延性和耗能能力等，比较了受火与未受火节点的破坏形态与抗震性能指标。试验结果表明，该类节点在火灾作用后仍保持较好的抗震性能。 2. 建立了火灾后钢管混凝土柱-钢梁节点抗震性能精细化分析模型。基于顺序热力耦合方法，建立了传热分析模型及后续的精细化受力分析模型。模型考虑了钢管对核心混凝土的约束、升降温全过程中材料性能的变化、反复荷载作用下混凝土的损伤，以及不同组件之间的接触关系。通过与试验结果对比，验证了模型的可靠性。 3. 开展了火灾后钢管混凝土柱-钢梁外环板式节点的工作机理分析。明晰了节点试件在火灾作用下的内力重分布变化规律和不同组件的损伤程度。揭示了火灾后节点在反复荷载作用下各组件的相互作用机制、传力路径、内力重分布、累积损伤规律和破坏形态。 4. 系统分析了钢筋混凝土楼板、梁柱线刚度比、梁柱承载力比、试件尺寸、核心区和环板性质、荷载比和升温时间比等关键参数对火灾后节点抗震性能的影响，得到了在不同升温时间比下节点核心区抗剪承载力和刚度的折减系数计算方法，提出了火灾后节点核心区剪力-剪切变形恢复力模型，为火灾后节点的抗震性能评估提供了科学依据。
Concrete-filled steel tubular (CFST) structures may be subjected to fire and earthquake during the service phase. It is of great significance to study the seismic performance of CFST structures after exposure to fire to improve the safety of CFST structures in the seismic fortification area. In this paper, the seismic performance of the CFST column-steel beam joint with external diaphragm and reinforced concrete (RC) slab after fire is studied with consideration of loading under fire. The main work is as follows: 1. Experiments are carried out on the seismic performance of the CFST column-steel beam joint after exposure to fire considering the combined effect of the concrete slab. In the fire test, a constant axial compressive load was applied on the top of the column during the fire. In the seismic test, the axial load on the top of the column was kept unchanged, and cyclic loads were applied on the beam end. The main experimental parameters are the type of the joint, the column load ratio and the heating time. The results obtained include the temperature field distribution and displacement of the joint specimen under fire, the load-displacement curve of the beam end, the strain distribution, the strength and stiffness degradation, and the ductility and energy dissipation capacity after exposure to fire. The comparisons are made between post-fire specimens and those without exposure to fire in terms of the failure mode and the seismic performance indexes. The test results show that the composite joints still maintain good seismic performance after fire. 2. A refined finite element analysis model for the seismic performance of CFST column-steel beam joints after fire is established. Based on the sequential thermo-mechanical coupling method, the heat transfer analysis model and the subsequent mechanical analysis are conducted. The model takes into account the confinement of steel tubes on the core concrete, the change of material properties during the heating and cooling process, the damage of concrete under cyclic loading, and the contact relationship between different components. By comparing with the test results, the reliability of the model is verified. 3. The working mechanism analysis is carried out on the CFST column-steel beam joint after exposure to fire. The redistribution of the internal load and the damage degree of different components of the specimen under fire are clarified. Discussions are made on the interaction between the concrete and steel tube, the load transfer mechanism, the internal load redistribution, the accumulated damage and failure modes. 4. The influence of key parameters on the seisimic performance of the composite joint after exposure to fire is analyzed, including the thickness of RC slab, the beam to column stiffness and strength ratio, the size of the joint, the properties of the external diaphragm and the panel zone, the heating time ratio, etc. The calculation method of the reduction coefficient of the shear bearing capacity and stiffness of the joint panel zone is obtained. A shear-shear deformation hysteretic relation for the panel zone of the fire-damaged joint is also proposed, which provides a scientific basis for seismic performance evaluation of joints after exposure to fire.
