Stress concentration factor analysis for notched welded tubular T-joints

In this study, the finite element method (FEM) is applied on a welded tubular T-joint, in order to analyse stress distribution in the vicinity of the weld fillet. The weld has been modelled all around the joint. A notch is to be simulated in the weld element, all around the joint as well. Using symmetry, the tubular T-joint is submitted to three loading cases: axial loading, in-plane bending (IPB), and out-of-plane bending (OPB). The stress distribution analysis, conducted using the (ARSEM, API, RP2A) code, has enabled locating the peak hot-spot stresses. The finite element method analysis shows that stresses are very high on the brace member, in the vicinity of the weld, and decrease gradually, with a quasi-stable difference, in the direction of the brace extremity. Both on the brace member and along the weld (from crown to saddle), the stresses are high at the crown toe, decrease in the middle and increase once again at the saddle point. Consequently, these zones are susceptible to fatigue damage and require reinforcement solutions in order to ensure sufficiently-long fatigue life for tubular T-joints. For the V-notch, the stress intensity factor at the notch is the parameter selected when processing crack-related problems. Stress distribution from the notch bottom towards the load-bearing segment indicates that the stress intensity factor rises as the radius increases at the notch bottom. The stress concentration factor is higher in the bottom of the notched weld at the load-bearing segment, which in most instances causes crack problems with an increase in stress intensity factor; this finding explains the harmful character of such defects and reveals the extent to which the presence of a notch in a weld fillet lowers the resistance of offshore structures to fatigue cracks.