Geometrical effects on the degree of bending (DoB) of multi-planar tubular KK-joints in jacket substructure of offshore wind turbines

Abstract

The degree of bending (DoB) characterizes the member through-the-thickness stress distribution which has a profound effect on the fatigue behavior of tubular joints commonly found in steel offshore structures and the determination of DoB values is essential for improving the accuracy of fatigue life estimation. Multi-planar joints are an intrinsic feature of offshore tubular structures and the multi-planarity might have a considerable effect on the DoB values at the brace-to-chord intersection. Nevertheless, for multi-planar joints which cover the majority of practical applications, much fewer investigations have been reported on the DoB due to the complexity and high cost involved. In the present research, data extracted from the stress analysis of 243 finite element (FE) models, verified based on available parametric equations, was used to study the effects of geometrical parameters on the DoB values in multi-planar tubular KK-joints which are among the most common joint types in jacket substructure of offshore wind turbines (OWTs). Parametric FE study was followed by a set of nonlinear regression analyses to develop three new DoB parametric equations for the fatigue analysis and design of axially loaded multi-planar KK-joints.