带缺陷的钢管混凝土连接节点的失效机理和抗震性能研究

In the practical concrete filled steel tubular (CFST) joint, the existence of initial concrete imperfection may change its load transferring mechanism and failure mode, which tends to cause the unsafety of whole structural system under seismic loading. This project will provide the seismic design approach and reinforcing method for the CFST joints with initial concrete imperfection. Some key issues including the effect of concrete imperfection on the interaction between steel tube and concrete within the joint zone, the influence of concrete imperfection on failure mode of CFST joints, and the seismic design theory of CFST joints with the concrete imperfection taken into consideration will be investigated. The finite element model in different scales will be established, and the cyclic test will be performed as well. The CFST joint with concrete imperfection will be analyzed in terms of micro failure mechanism and seismic damage development under the cyclic loading condition. The effect of concrete imperfection on the load transferring mechanism, deformation, rigidity, and energy dissipated mechanism of CFST joints will be revealed, and the effect on the failure mode will be also clarified. Based on the experimental and numerical results, the maximum limit of gap ratio, the criterion for predicting failure mode, the simplified mode for predicting ultimate strength, the hysteretic model, and the joint mode will be proposed, and the reinforcing method will be provided as well. Then, a set of solutions to deal with the problem of CFST joints having concrete imperfection will be put forward. The research outcome of the project will provide the basis for the design and evaluation of practical engineering and the modification of the design codes of CFST structures.

实际钢管混凝土节点中存在的脱空缺陷会改变其传力机制和失效模式，导致结构体系存在抗震安全隐患。本项目的研究成果将提供考虑缺陷影响的钢管混凝土框架节点和桁架节点的抗震设计方法及加固对策。拟研究脱空缺陷对节点区钢管和混凝土之间相互作用的影响机理、缺陷对节点失效模式的影响规律、考虑缺陷影响的节点抗震设计理论等关键科学问题。为此，将构建基于不同尺度的非线性有限元分析模型，开展典型节点试件的滞回性能试验，分析带缺陷节点在反复荷载作用下的微观破坏机理和地震损伤演化，揭示缺陷对节点荷载传递机制、变形和刚性、耗能机制的影响机理，探明缺陷对节点失效模式的影响规律，在此基础上提出节点的最大脱空率限值、失效模式判断准则、考虑缺陷影响的承载力计算公式、恢复力模型和节点模型，并提供既有带缺陷节点的加固方法，形成钢管混凝土节点脱空问题的成套解决方案，为实际工程设计和安全评估提供依据，也为相关规范的制定或修订提供参考。

实际钢管混凝土节点中存在的脱空缺陷会改变其传力机制和失效模式，导致结构体系存在抗震安全隐患。本项目揭示了脱空缺陷对节点区钢管和混凝土之间相互作用的影响机理，探明了缺陷对节点失效模式的影响规律，提出了考虑缺陷影响的钢管混凝土框架节点和桁架节点的抗震设计方法及加固对策，具体研究工作为：开展了18个带环向脱空缺陷的钢管混凝土框架节点及加固节点试件在柱端恒定轴向压力和梁端往复侧向荷载作用下的滞回试验，考察了环向脱空缺陷对框架节点承载力、滞回曲线、延性、刚度退化和耗能等抗震性能指标的影响，研究了CFRP和钢板加固对节点性能的恢复效果。建立了带缺陷框架节点的非线性有限元分析模型，细致剖析了带缺陷节点和加固后节点的受荷全过程工作机理，结果表明环向脱空缺陷会破坏节点区钢管和混凝土之间的相互作用，影响节点的传力机制，导致节点失效模式发生改变，而采用CFRP加固核心区柱端、钢板加固节点核心区能显著提升带缺陷节点的承载力和刚度。在参数分析的基础上，提出了带缺陷框架节点承载力实用计算公式和加固构造。同时，开展了24个带球冠形缺陷的钢管混凝土T型节点和环口板加固节点在主管受拉和支管受反复轴力作用下的滞回试验、24个T型节点在支管受弯作用下的滞回试验以及24个K型节点在两支管反复拉压作用下的滞回试验，考察了缺陷对桁架节点失效模式、滞回曲线、延性、承载力、刚度和耗能的影响，验证了环口板加固效果。利用有限元模型，剖析了缺陷对钢管混凝土桁架节点工作机理的影响规律，结果表明球冠形脱空缺陷会削弱主管混凝土对钢管的支撑作用，从而导致节点局部变形增大，节点承载力和刚度随脱空率增大而降低，而采用环口板加固可实现节点抗震性能指标的完全恢复。在参数分析的基础上提出了考虑缺陷影响的钢管混凝土桁架节点承载力实用计算公式和加固构造。研究成果为实际工程设计和安全评估提供依据，也为相关规范的制定或修订提供参考。