Stress Concentration Factor For KK Joints

The maximum stress is very important in estimating the fatigue life of offshore T-joints by an S-N approach. Therefore, stress concentration factor (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 K joint with the same dimensions, it's shown in this paper that SCF for KK tubular joints is frequently higher, The existing empirical SCF formulas for simple tubular joints are not suitable for complex tubular joints, therefore, it is essential to establish SCF parametric equations for complex KK-joints.Based on former research on simple tubular joints, thin-shell element analyses have been conducted for thousands of KK joint frequently used in offshore structures. These KK joints are subjected to three kinds of loadings, including axial load, in-plane moment and out-plane moment. By use of regression analysis, the above results are then used to derive a new set of parametric equations, in terms of several non-dimensional geometric ratiosα,γ,ξ,β,τandθ. These parametric equations could be used directly to calculate the maximum stress around the interface between brace and chord of KK tubular joints.Further in these paper, separate analyses has been conducted for the influence ofα,γ,ξ,β,τandθon brace and chord SCFs in KK joint subjecting to the three kinds of loading and on the difference of SCFs in KK joint and SCFs for K joint from empirical formulas. The results are given through both tables and figures.The SCF results for KK joint 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.