Parametric study of elastic stress concentration factors in welded Y-tubular joints

Stress concentration factors (SCFs) at the brace–chord intersection govern fatigue life in welded tubular Y-joints. Efthymiou’s parametric formulae, embedded in current offshore design standards, were derived from late 1980s shell-element analyses, and their conservatism across the practical parameter space has only been partially verified, motivating an independent solid-element benchmark. This paper reports a parametric finite element study of 27 Y-tubular joints in Abaqus, using solid elements and explicit weld geometry. The diameter ratio β, thickness ratio τ and radial-stiffness parameter γ were varied within Efthymiou's validity range for β ≤ 0.60, with brace inclination and chord length parameter held fixed to 45° and 12, respectively. Three brace-end loadcases, axial, in-plane bending and out-of-plane bending were analysed, and SCFs were evaluated at the crown and saddle of both chord and brace. The numerical procedure was validated against published experimental data. Comparison with Efthymiou’s predictions showed that the formulae are not uniformly conservative. Deviations of up to 30% were observed for axial loading at the brace crown, 17% at the brace saddle and 16% at chord crown, with similar non-conservatism for out-of-plane bending at the chord saddle. The dataset provides a high-fidelity benchmark identifying where Efthymiou’s predictions remain reliable and where they may underestimate fatigue-driving stresses, supporting design practice and future code calibration.