Jacket structures are widely used in oil or gas production facilities and wind turbines. The bracing members of jacket structures must be designed to withstand intense and repeated stresses, such as those caused by wind and wave forces. The continual exposure to fluctuating stresses and the harsh marine environment can lead to material deterioration, resulting in stress concentrations at tubular joints that may induce fatigue cracks. This study aims to investigate the fatigue life due to differences in the brace position and crack initiation during cyclic loading. The study employs 3D fatigue finite element (FE) analysis based on cyclic hysteresis elastoplastic constitutive theory and continuum damage mechanics. Initially, to reproduce the welding members, a 3D non-steady heat conduction analysis was conducted to calculate the temperature history. Subsequently, residual stresses and welding deformation were calculated using thermal elastoplastic analysis. Finally, a 3D fatigue FE analysis was conducted to calculate fatigue life and predict the crack initiation position due to differences in brace positions. The S-N curves obtained from the 3D fatigue FEM were compared with the S-N curves recommended by Eurocode 3 and IIW. The FEM data was compared with the hotspot stress method (HSS).

导管架结构广泛应用于石油或天然气生产设施和风力涡轮机。导管架结构的支撑构件必须设计成能够承受强烈和重复的应力，例如由风和波浪力引起的应力。持续暴露于波动应力和恶劣的海洋环境中可能会导致材料劣化，导致管接头处应力集中，从而可能引发疲劳裂纹。本研究旨在研究循环加载期间支撑位置和裂纹萌生差异导致的疲劳寿命。该研究采用基于循环磁滞弹塑性本构理论和连续介质损伤力学的 3D 疲劳有限元 (FE) 分析。最初，为了重现焊接构件，进行了 3D 非稳态热传导分析来计算温度历史。随后，使用热弹塑性分析计算残余应力和焊接变形。最后，进行 3D 疲劳有限元分析来计算疲劳寿命并预测由于支撑位置差异而产生的裂纹萌生位置。将 3D 疲劳 FEM 获得的 SN 曲线与 Eurocode 3 和 IIW 推荐的 SN 曲线进行了比较。将 FEM 数据与热点应力法 (HSS) 进行比较。