Stress concentration factor analysis for welded, notched tubular T-joints under combined axial, bending and dynamic loading

The finite element analysis will be used in this study to predict the location of hot-spot stresses in a welded tubular T-joint. The fillet weld has been modeled all around the joint. Using symmetry, the tubular T-joint is submitted to axial, in-plane bending (IPB) and out-of-plane bending (OPB) loadings. The finite element method analysis shows that stresses are very high on the brace member in the vicinity of the fillet weld and gradually decrease, with a quasi-stable difference, in the direction of the brace extremity. Both on the brace member and along the fillet weld (from crown to saddle), stresses are high at the crown toe, decrease in the middle and increase once again at the saddle point. From a general perspective, this stress distribution analysis reveals that hot-spot stresses (HSS) are located at the crown and saddle points. Dynamic loading greatly increases the stress concentration factor at the hot-spot stress (HSS) located on the brace member where fatigue damage is capable of appearing quickly. In the U-notch, this stress concentration factor (SCF) increases as notch width decreases. In a general way therefore, stress concentration factors decrease on the brace and chord members (in the vicinity of the weld) and increase considerably in the notch, which underscores the deleterious nature of such a defect. Consequently, these zones (HSS) require reinforcement solutions in order to ensure a sufficiently long fatigue life for offshore structures.