Degree of bending (DoB) in tubular K-joints of offshore structures subjected to in-plane bending (IPB) loads: Study of geometrical effects and parametric formulation

The fatigue life of tubular joints in offshore structures is not only dependent on the value of hot-spot stress (HSS), but is also significantly influenced by the through-the-thickness stress distribution characterized by the degree of bending (DoB). The determination of DoB values in a tubular joint is essential for improving the accuracy of fatigue life estimation using the stress-life (S-N) method and particularly for predicting the fatigue crack growth using the fracture mechanics (FM) approach. Although the tubular K-joints are commonly found in offshore jacket structures, the DoB in K-joints subjected to in-plane bending (IPB) loads have not been investigated so far and no design equation is available to calculate the DoB for IPB-loaded joints of this type. In the present research, comprehensive finite element (FE) analyses were carried out on 81 generated models of tubular K-joints. Results of FE models were verified against experimental data and parametric equations. Data extracted from FE analyses was used to investigate the effects of geometrical parameters on the DoB values in K-joints subjected to two types of IPB loadings. Parametric study was followed by a set of nonlinear regression analyses to develop DoB parametric equations for the fatigue analysis of IPB-loaded K-joints.