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目的:钢框架焊接梁柱节点在地震作用下往往容易产生脆性裂纹,裂纹的发展和损伤累积将导致节点延性降低,发生脆性断裂。本文旨在探究节点在地震往复荷载作用下的损伤性能,分析其主要影响因素,提出有效的损伤评估模型,为后续节点损伤数值模拟提供基础,为钢框架的抗震设计提供参考。创新点:1.通过足尺节点试验,分析加载幅值、加载历程和荷载峰值对节点损伤性能的影响;2.基于试验结果,标定并验证3种经验损伤演化模型,提出基于疲劳断裂力学的节点损伤评估模型。方法:1.通过对9个足尺梁柱节点试件开展往复加载试验,包括5种变幅加载制度及4种常幅加载制度,分析加载幅值、加载历程和荷载峰值对节点损伤性能的影响;2.基于试验结果,根据节点损伤特点,在能量模型基础上,推导并拟合适用于节点循环加载的双参数损伤演化方程,并与其他模型进行比较,以验证其准确性;3.结合疲劳和延性断裂理论,依据损伤机理,定义“有效塑性应变”量化损伤过程,并以疲劳裂纹发展公式为基础,推导适用于计算在极低周循环荷载下节点损伤过程的损伤演化方程。结论:1.加载跨幅对节点性能影响较小;加载历程的影响与历程中峰值位移循环次数密切相关;突发性的强峰值对节点造成的损伤最大。2.节点损伤过程为幂函数形式;通过比较表明,在能量模型基础上推导出的适用于节点循环加载的双参数损伤演化方程,相对于单参数线性模型,能够更准确模拟节点在极低周循环下的损伤过程。3.基于疲劳断裂力学理论的损伤演化方程物理意义明确,能够描述节点循环损伤试验中所表现出的加速损伤及“损伤拐点”特征。
OBJECTIVE: The joints of welded steel beam and column joints tend to be prone to brittle cracks under the earthquake. The development of cracks and the accumulation of damage will lead to the ductility reduction and brittle fracture of joints. The purpose of this paper is to study the damage performance of joints under earthquake reciprocating loads. The main influencing factors are analyzed and an effective damage assessment model is proposed to provide the foundation for numerical simulation of subsequent joint damage. It provides a reference for the seismic design of steel frames. The innovation points: 1. Through the full-scale node test, the influence of load amplitude, load history and load peak on the damage performance of the joints is analyzed.2. Based on the test results, three kinds of empirical damage evolution models are calibrated and verified, and the fatigue damage mechanics Nodal damage assessment model. Through the reciprocating loading test of nine full-scale beam-column joint specimens, including five kinds of luffing loading system and four kinds of normal loading system, the effects of loading amplitude, loading history and load peak on the damage performance of joints Based on the experimental results, according to the damage characteristics of nodes, the two-parameter damage evolution equations suitable for cyclic loading of nodes are deduced and fitted on the basis of energy model and compared with other models to verify its accuracy.3. According to the theory of fatigue and ductile fracture, according to the mechanism of damage, the process of quantitative damage is defined as “effective plastic strain”, and the damage evolution equation suitable for calculating the damage process of joints under extremely low cyclic loading is derived based on the fatigue crack growth formula . The effect of loading history is closely related to the number of peak displacement cycles in the process. The sudden strong peaks cause the most damage to the nodes. The damage process of nodal point is in the form of exponential function. The comparison shows that the two-parameter damage evolution equation derived from energy model based on energy model is more accurate than the one-parameter linear model, Cyclic damage process. The damage evolution equations based on the theory of fatigue fracture mechanics have clear physical meaning and can describe the accelerated damage and the “inflection point of injury” features in the cyclic damage test.