Local joint flexibility of two-planar tubular DY-joints in jacket-type substructures of offshore wind turbines: parametric study of geometrical effects and design formulation

The present paper discusses the results of a parametric study conducted on the local joint flexibility (LJF) of two-planar tubular DY-joints in jacket-type substructures of offshore wind turbines. A set of finite element (FE) analyses were carried out on 81 FE models subjected to two types of axial loading to study the effects of geometrical characteristics of two-planar DY-joint on the LJF factor (fLJF). The fLJF values in two-planar DY- and uniplanar Y-joints were compared. Results showed that the multi-planarity effect on the LJF is significant and consequently the application of equations already available for uniplanar Y-joints to calculate the fLJF in two-planar DY-joints may result in highly over- or under-predicting results. To tackle this problem, FE results were used to develop a new parametric equation for the prediction of the fLJF in axially loaded two-planar DY-joints and the derived equation was checked against the UK DoE acceptance criteria.