As earthquakes tend to cause ultra-low cycle fatigue failure of spatial grid structures in composite members and joints, this study sets out to test six groups of specimen comprising steel pipes and bolt sphere joints and analyzes the influence of joints and loading systems on failure modes, hysteretic behavior, skeleton curves, stiffness degradation, energy dissipation capacity, and the formation and development of plastic hinges. Results showed that the instability of the specimen in compressive loading led to the occurrence of denting and the formation of plastic hinges. Cracks originated in dented area, and ultra-low cycle fatigue fractures occurred in a dozen cycles. Plastic hinge was located in the middle area of the pipe, and the energy dissipation capacity was limited owing to the confined plastic hinge length. As the joint bending stiffness increased, so did the length of the plastic hinge, the degree of the dent, and the cumulative damage. Early fractures and a reduction in total energy consumption also occurred. Furthermore, a function related to the cumulative damage and macroscopic deformation that can evaluate the damage of the members in spatial grid structures was also established.

中文翻译：

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空间网格结构复合构件超低周疲劳行为试验研究

由于地震容易引起复合构件和节点中空间网格结构的超低周疲劳破坏，本研究开始对钢管和螺栓球节等六组试件进行试验，分析节点和加载系统对破坏模式的影响。 、滞后行为、骨架曲线、刚度退化、能量耗散能力以及塑性铰的形成和发展。结果表明，试样在压缩载荷下的不稳定性导致了凹痕的发生和塑性铰的形成。裂纹起源于凹陷区域，十几个循环发生超低周疲劳断裂。塑性铰位于管道的中间区域，由于塑性铰长度受限，能量耗散能力受到限制。随着接头弯曲刚度的增加，塑性铰的长度、凹痕的程度和累积损伤也随之增加。还发生了早期骨折和总能量消耗的减少。此外，还建立了与累积损伤和宏观变形相关的函数，用于评估空间网格结构中构件的损伤。