Characteristic parameters for stress distribution along the intersection of tubular Y,T,X and DT joints

Analysis of large-scale fatigue testing results has shown that the fatigue strength of offshore welded tubular joints is not dependent on the hot spot stress alone but is also significantly influenced by stress distributions around the intersection which are normally represented by several characteristic parameters. The through-thickness distribution for example is characterized by degree of bending. In order to represent the stress distribution along the intersection, the average stress concentration factor (SCF) concept was suggested and used in empirical stress intennsity factor (SIF) models. However, this parameter alone is not enough to characterize the stress distribution along the intersection. Furthermore, there is no parametric equation available to predict this parameter. For this reason, a new concept, stress distribution concentration factor (SDCF), has been proposed in this study to describe the spread of stress distribution along the intersection. Systematic thin shell finite element analyses have been conducted for 330 different tubular Y, T and 330 X and DT joints, typical of those used in offshore structures, subjected to different modes of loading. On the basis of these results, a set of parametric equations has been derived for the average SCF and SDCF as a function of non-dimensional joint geometric ratios a, β, γ, τ and ϑ for each mode of loading and for both the chord and brace sides of the intersection of tubular welded Y, T, X and DT joints.