Distribution of weld toe stress concentration factors on the central brace in two-planar CHS DKT-connections of steel offshore structures

Two major issues can be noted regarding the research efforts expended so far on the calculation of stress concentration factors (SCFs) in tubular joints: (1) majority of these research works focused on the values of the SCF at certain positions such as the saddle and the crown, and they have ignored the hot-spot stress at other locations along the weld toe; (2) significant effort has been devoted to the study of SCFs in various uni-planar tubular joints. Nevertheless, for multi-planar joints, which cover the majority of practical applications, very few investigations have been reported due to the complexity and high cost involved. In this paper, the effects of geometrical parameters on the SCF distribution along the weld toe of two-planar tubular DKT-joints under the axial loads are investigated. In order to study the multi-planar effect, SCF distribution in multi-planar joints is compared with the distribution in a uni-planar joint with the same geometrical properties. Based on the multi-planar DKT-joint FE models, which are verified against experimental results and the predictions of Lloyd's Register (LR) equations, a complete set of SCF database is constructed. The FE models cover a wide range of geometrical parameters. Through nonlinear regression analysis, a new set of SCF parametric equations is established for the accurate and reliable fatigue design of multi-planar DKT-joints under axial loads. An assessment study of these equations is conducted against the experimental data and the acceptance criteria recommended by the UK DoE.

► Stress distribution along the central brace weld toe of two-planar DKT-joints is investigated.
► Effects of geometrical characteristics on the chord-side SCFs are studied.
► Highly remarkable differences exist among two-planar and uni-planar SCFs.
► For fatigue design purposes, parametric equations are proposed to calculate SCFs.