Local joint flexibility of multi-planar tubular TT-joints: Study of geometrical effects and the formulation for offshore design practice

Abstract

Results of a parametric investigation carried out on the local joint flexibility (LJF) of multi-planar tubular TT-joints, also called two-planar DT-joints, are presented and discussed in this paper. A set of finite element (FE) analyses were conducted on 81 FE models subjected to two types of axial loading in order to study the effects of geometrical properties of the DT-joint on the LJF factor (fLJF). Developed FE models were validated using available experimental data and parametric equations. Results indicated that the increase of the γ leads to the increase of the fLJF; while the increase of the β and/or the τ leads to the decrease of the fLJF. In joints with bigger values of the γ, the increase of the β results in more drastic decrease of the fLJF. The amount of the fLJF change due to the increase of the parameter τ is much smaller compared to the other geometrical parameters. The fLJF values in two-planar DT- and uniplanar T-joints were compared. Results showed that the multi-planarity effect on the LJF is considerable and consequently the application of the equations already available for uniplanar T-joints to calculate the fLJF in two-planar DT-joints may result in highly over- or under-predicting results. To tackle this problem, FE results were used to derive a new parametric equation for the prediction of the fLJF in axially loaded two-planar DT-joints and the developed formula was checked against the UK DoE acceptance criteria.