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<p>Local joint flexibility (LJF) plays a key role in governing the stiffness response of offshore tubular structures when joint deformations are non-negligible. Although external ring reinforcement is a practical option for upgrading both newly fabricated and existing tubular joints, no research work is available on LJF of K-joints with external ring. This paper presents a numerical investigation of K-connections with two symmetric outer rings and subjected to axial brace loading. A three-dimensional numerical framework was constructed, explicitly incorporating weld geometry and external ring reinforcement. The modelling strategy and the procedure adopted for evaluating LJF were validated against 16 available experimental tests as well as established analytical formulations reported in the literature. A numerical database comprising 168&#xa0;K-joint configurations was generated to investigate the influence of joint and ring geometry on local joint flexibility. The results demonstrate that external ring reinforcement remains highly effective across a wide range of joint geometries, achieving reductions in local joint flexibility of 65–88% relative to the corresponding unreinforced joints. Increasing <i>β</i> significantly reduces the flexibility of reinforced joints. Also, brace angle significantly changes the stiffening efficiency of the rings. Moreover, chord slenderness has the most decisive effect on the reinforcement efficiency. Finally, a design-oriented parametric equation is proposed for estimating the reduction factor. The proposed formulation supports reliable application in stiffness-based modelling and practical design of ring-reinforced tubular K-joints.</p>

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Local joint flexibility of external ring-reinforced tubular K-joints under axial loading

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月29日

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  • Hossein Nassiraei,
  • Faraz Alidoost Master

摘要

Local joint flexibility (LJF) plays a key role in governing the stiffness response of offshore tubular structures when joint deformations are non-negligible. Although external ring reinforcement is a practical option for upgrading both newly fabricated and existing tubular joints, no research work is available on LJF of K-joints with external ring. This paper presents a numerical investigation of K-connections with two symmetric outer rings and subjected to axial brace loading. A three-dimensional numerical framework was constructed, explicitly incorporating weld geometry and external ring reinforcement. The modelling strategy and the procedure adopted for evaluating LJF were validated against 16 available experimental tests as well as established analytical formulations reported in the literature. A numerical database comprising 168 K-joint configurations was generated to investigate the influence of joint and ring geometry on local joint flexibility. The results demonstrate that external ring reinforcement remains highly effective across a wide range of joint geometries, achieving reductions in local joint flexibility of 65–88% relative to the corresponding unreinforced joints. Increasing β significantly reduces the flexibility of reinforced joints. Also, brace angle significantly changes the stiffening efficiency of the rings. Moreover, chord slenderness has the most decisive effect on the reinforcement efficiency. Finally, a design-oriented parametric equation is proposed for estimating the reduction factor. The proposed formulation supports reliable application in stiffness-based modelling and practical design of ring-reinforced tubular K-joints.