Geometrical effects on the local joint flexibility of two-planar tubular DK-joints in jacket substructure of offshore wind turbines under OPB loading

The local joint flexibility (LJF) of two-planar tubular DK-joints in offshore jacket structures under the out-of-plane bending (OPB) loads is studied in the present paper. Altogether, 81 finite element (FE) models were generated and analyzed by ANSYS in order to investigate the effects of DK-joint's geometrical parameters on the LJF factor (fLJF) under four types of OPB load cases. Generated FE models were validated against the existing experimental data, FE results, and parametric equations. After the parametric study of geometrical effects, the fLJF in two-planar DK- and uniplanar K-joints were compared. Results showed that the effect of multi-planarity on the fLJF values is considerable. Hence, the application of the equations already available for uniplanar K-joints to determine the fLJF in two-planar DK-joints might result in highly under-/over-predicting outputs. To suggest a solution for this issue, results of 324 analyses carried out on generated FE models were used to develop a new set of parametric formulas for the calculation of the fLJF in OPB-loaded two-planar DK-joints. Applicability of proposed formulas was assessed based on the UK DoE acceptance criteria.