Local joint flexibility of two-planar tubular DK-joints in OWTs subjected to axial loading: Parametric study of geometrical effects and design formulation

Tubular DK-joint is one of the most common joint types in jacket substructure of offshore wind turbines (OWTs). Results of a parametric investigation carried out on the local joint flexibility (LJF) of two-planar tubular DK-joints under axial loading are presented and discussed in this paper. A total of 162 finite element (FE) analyses were conducted on 81 FE models under two types of axial loading in order to study the effect of the geometrical properties of the DK-joint on the LJF factor (fLJF). Developed FE models were validated based on the available experimental data, FE results, and parametric equations. The weld profile effects were also studied. The fLJF in two-planar DK- and uniplanar K-joints were compared. Results showed that the multi-planarity effect on the LJF is considerable and consequently the application of the equations already available for uniplanar K-joints to calculate the fLJF in two-planar DK-joints can result in highly over-predicting results. To tackle this problem, FE results were used to derive a set of parametric formulas for the prediction of the fLJF in axially loaded two-planar DK-joints and the developed formulas were checked according to the UK DoE acceptance criteria.