Parametric Evaluation of Stress Concentration Factor (SCF) at Brace – Chord Intersection of a Ring Stiffened Tubular Joint

Abstract

Tubular joints are common in offshore framed structures such as jackets. These joints are subjected to fatigue due to cyclic loads from waves. Stress concentration factor plays a major role in the estimation of fatigue life. Studies have been carried out in the past on stress concentration factors for these joints. However, literature on ring stiffened joints is limited. In the present study, numerical simulations have been carried out on ring stiffened tubular joints, especially the T joints, subjected to axial tension load using finite element method in linear analysis using ABAQUS software. A solid type 20-node quadratic brick element (C3D20R) has been used in the study. Stresses in hotspot locations at brace/chord intersection, ring/chord intersection and ring inner edge are examined. The numerical model has been validated using published experimental data and Lloyd’s register recommendations. Further parametric study has been carried out with 20 models, which includes geometric parameters of ring stiffener such as width of stiffener, thickness of stiffener and spacing between the ring stiffeners. The results of parametric study show a significant reduction of SCF at saddle location by placing ring stiffeners in unstiffened T joint. A set of new parametric equations are developed to calculate SCF for ring stiffened T joint at saddle location for axial tensile load.