Prediction of degree of bending in tubular X and DT joints

Analysis of the large scale fatigue testing results of offshore welded tubular joints showed that the fatigue life is not dependent on the hot spot stress alone, but is also significantly influenced by the through thickness stress distribution which can be characterised by degree of bending (DoB). Accurate prediction of DoB data in tubular joints is crucial for improving the accuracy of fatigue life prediction using stress-life (S–N) curve and particularly for predicting fatigue crack growth using the fracture mechanics method. However, there is no set of DoB parametric equations available for tubular X and DT joints. For this reason, comprehensive thin shell finite element (FE) analyses were carried out for 330 tubular X and DT joints typical of those used in offshore structures, under six different modes of loading. The results of these FE analyses were used to derive a set of parametric equations to predict the DoBs at the critical positions on both brace and chord toes in tubular X and DT-joints under each mode of loading