This paper presents an experimental investigations to study the hysteretic behavior of circular hollow section (CHS) X-connections which widely applied in various tubular structures. Cyclic in-plane bending moment (IPBM) loading patterns and geometric parameter of brace-to-chord diameter ratio (β) were varied in testing four connection specimens, to evaluate the influence of load patterns on the hysteretic behavior of the connections. Test results shown that regardless of load patterns and connection details, all specimens showed plump and no pinching effect for the hysteresis curve before cracking occurred, all specimens shared similar final failure modes (the chord wall near the intersection teared) and similar energy dissipation modes (mainly rely on the plastic deformation of the chord wall near the intersection). However, the influence of loading patterns on the hysteretic behavior of the X-connections with varied β is different. For the CHS X-connections with large β, it developed higher flexural strength, better ductility and more energy dissipation performance under synchronized down and up IPBM (SDUI) loading pattern than that under take turns to align clockwise and counterclockwise IBPM (TCCI) loading pattern; while for the X-connections with small β, it is opposite. This experimental observation result was further affirmed by a simplified analytical model and FE analysis results. The test results also indicated that regardless of the load patterns, increasing β trend to significantly improve the strength, ductility ratio and energy dissipation behavior of CHS X-connections under cyclic IPBM, and the current specification trend to give conservative prediction on the in-plane flexural strength of the X-connections.

本文提出了一项实验研究，以研究广泛应用于各种管状结构的圆形空心截面 (CHS) X 连接的滞后行为。循环平面弯矩 (IPBM) 加载模式和支撑弦直径比 ( β ) 的几何参数在测试四个连接样本时发生变化，以评估加载模式对连接的滞后行为的影响。试验结果表明，无论荷载模式和连接细节如何，所有试件在开裂前的滞后曲线均表现出丰满且无夹挤效应，所有试件具有相似的最终破坏模式（交叉点附近的弦墙撕裂）和相似的能量耗散模式（主要依靠交叉点附近弦墙的塑性变形）。然而，加载模式对具有不同β的 X 连接的滞后行为的影响是不同的。对于具有大β的CHS X连接，在同步上下IPBM（SDUI）加载模式下比在顺时针和逆时针轮流对齐IBPM（TCCI）加载模式下具有更高的抗弯强度，更好的延展性和更好的能量耗散性能; 而对于β较小的 X 连接，则相反。简化的分析模型和有限元分析结果进一步证实了这一实验观察结果。测试结果还表明，无论负载模式如何，增加β趋势显着提高循环 IPBM 下 CHS X 连接的强度、延性比和能量耗散行为，并且当前规范趋势对 X 连接的平面内抗弯强度给出保守预测。