Geometrically parametric study of central brace SCFs in offshore three-planar tubular KT-joints

In the present paper, a set of geometrically parametric FE stress analyses is carried out for right-angle three-planar tubular KT-joints under three different axial loading conditions. Three-planar KT-joints are one of the most important joint types in the six-legged offshore jacket-type structures since they connect the bracing members to the main legs of the jacket template. The analysis results are used to present general remarks on the effect of geometrical characteristics on the stress concentration factors (SCFs) at different saddle positions on the central braces. Based on the results of FE analyses which are verified against the experimental data, a complete set of SCF databases is developed. Afterwards, through nonlinear regression analysis, a new set of SCF design equations is established for the fatigue design of three-planar KT-joints under three different axial load cases. An assessment study of these equations is conducted against the experimental data and the acceptance criteria proposed by the UK Department of Energy (DoE).

► 81 FE models were generated for the stress analysis of 3-planar tubular KT-joints. ► Effects of geometrical parameters on saddle SCFs at central braces were studied. ► A set of fatigue design equations was established to calculate the SCFs. ► Significant difference exists between SCFs in 3-planar and 2-planar KT-joints. ► SCF values in 3-planar and uni-planar KT-joints are remarkably different.