Parametric investigation of geometric effects on the degree of bending in three-planar tubular Y-joints for offshore wind turbines

This research presents a comprehensive investigation of axially loaded three-planar tubular Y-joints, focusing on the degree of bending (DoB) and its implications for fatigue design in offshore structures. DoB is a fundamental parameter characterizing through-thickness stress distributions in tubular joints and reflects the combined influence of bending and membrane stresses. It is critical for assessing fatigue crack propagation and stress intensity factors (SIF) at weld toes, particularly in jacket-type offshore wind turbine (OWT) substructures. The present study evaluates how principal geometric parameters affect the DoB, using a parametric investigation on 243 finite element (FE) simulations. Based on a comprehensive FE analysis method, two parametric equations were derived to estimate the DoB for such complex joints, addressing the limitations of existing formulas. The new methodology offers engineers a useful tool for assessing and optimizing joint geometry, thereby enhancing fatigue resistance and reducing reliance on expensive reinforcements needed in critical zones of structures. The results are especially applicable in cases of substructures of OWTs and jacket-type platforms, where assessment of multi-planar joints is highly essential.