Stress Concentration Factor For Some Simple Joints

The maximum stress is very important in estimating the fatigue life of offshore platforms by an S-N approach. We can calculate the maximum stress by stress concentration factor(SCF). Therefore, SCF is crucial for the safety of offshore platforms. The existing empirical formulas, such as Kuang formula and NORSOK formula, are suitable only to simple tubular joints including K, X, Y and TX etc joints. SCF for complex spatial tubular joints has not been referred in the existing empirical formulas. Instead, SCF for complex tubular joints is usually considered by the method for simple tubular joints. Comparing to the results for simple TK joint with the same dimensions, it's shown in this paper that SCF for DTK, TK-K, TK-T and K-T tubular joints is frequently higher. The existing empirical SCF formulas for simple tubular joints are not suitable for these tubular joints, therefore, it is essential to establish SCF parametric equations for these joints.Based on simple tubular joints, thin-shell element analyses have been conducted for thousands of DTK, TK-K, TK-T and K-T joints frequently used in offshore structures. These joints are subjected to three kinds of loadings, including axial load, in-plane moment and out-plane moment. By use of nonlinear least squares fitter, the above results are then used to derive a new set of parametric equations, in terms of several non-dimensional geometric ratiosγ,ξ,β,τandθ. These parametric equations of SCF could be used directly to calculate the maximum stress around the interface between brace and chord of DTK, TK-K, TK-T and K- T tubular joints.Further in the paper, separate analyses have been conducted for the influence ofξ,β,τandθon brace and chord SCFs in these joints subjecting to the three kinds of loading and on the difference of SCFs in these joints and SCFs for TK joint from empirical formulas. The results are given through both tables and figures.The SCF results for these joints given in this paper could act as a good reference for both further academic studies on SCF of other complex joints and engineering designing works...