Degree of bending (DoB) in offshore tubular KT-joints under the axial, in-plane bending (IPB), and out-of-plane bending (OPB) loads

Through-the-thickness stress distribution characterized by the degree of bending (DoB) has a major effect on the fatigue behavior of tubular joints commonly found in steel offshore structures. The determination of DoB values is essential for improving the accuracy of fatigue life estimation using the stress-life (S-N) method and particularly for predicting the fatigue crack growth based on the fracture mechanics (FM) approach. In the present research, data extracted from 648 finite element (FE) analyses carried out on 81 tubular KT-joint models was used to study the effects of geometrical parameters on the DoB values in KT joints subjected to eight different types of loading including two types of axial loading, three types of in-plane bending (IPB) moment loading, and three types of out-of-plane bending (OPB) moment loading. Generated FE models were validated using experimental data, previous FE results, and available parametric equations. Geometrically parametric investigation was followed by a set of nonlinear regression analyses to develop 21 parametric design formulas for the calculation of the DoB in tubular KT-joints under the axial, IPB, and OPB loadings.