Circular concrete filled double skin steel tubular (CFDST) has broader application aspects in engineering practice due to its superior confinement and elegant architectural appearance compared with square CFDST. However, there is still lack of an effective and reliable assembled method to connect the circular CFDST column to the beam. This paper focused on the theoretical and structural behavior on the assembled joint between circular CFDST column and composite beam. A sophisticated theoretical model was proposed to evaluate the initial rotational stiffness and moment capacity of the assembled joint. This theoretical model firstly accounted for the curved end plate in bending considering the clamping forces of blind bolts. Furthermore, a simplified arch model was developed to assess the circular steel tube in compression and the stiffness coefficients related to the circular CFDST column determined by the load transfer mechanism were also involved in the theoretical model. Subsequently, an experimental investigation on such kind of joint was conducted as a basis to verify the developed numerical model, indicating the numerical model could well replicate the typical failure modes and hysteresis curves. Parametric analyses based on the validated numerical model were performed to identify the effects of various parameters on the typical assembled joint. The theoretical model was verified to be capable of predicting the initial stiffness and moment capacity of assembled composite joint to circular CFDST column by comparing with the numerically observed results. The theoretical and analytical results performed in this paper would be beneficial for the application of the assembled beam to column joint in CFDST structures.

中文翻译：

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圆形CFDST柱与组合梁组合节点的理论模型和结构性能

与方形CFDST相比，圆形混凝土填充双壁钢管（CFDST）具有优越的封闭性和优雅的建筑外观，在工程实践中具有更广泛的应用领域。但是，仍然缺乏有效且可靠的组装方法来将圆形CFDST柱连接到梁。本文重点研究圆形CFDST柱与组合梁组合节点的理论和结构性能。提出了一种复杂的理论模型来评估组装接头的初始旋转刚度和力矩能力。该理论模型首先考虑了弯曲螺栓的弯曲端板，考虑了盲板螺栓的夹紧力。此外，建立了简化的拱形模型以评估圆形钢管的压缩情况，并且理论模型还涉及到由荷载传递机制确定的圆形CFDST圆柱相关的刚度系数。随后，对这种接头进行了实验研究，以验证所开发的数值模型，表明该数值模型可以很好地复制典型的破坏模式和磁滞曲线。基于已验证的数值模型进行了参数分析，以识别各种参数对典型组装接头的影响。通过与数值观察结果进行比较，验证了该理论模型能够预测组装到圆形CFDST柱上的复合节点的初始刚度和弯矩承载力。