Stress concentration due to in-plane bending (IPB) loads in ring-stiffened tubular KT-joints of offshore structures: Parametric study and design formulation

• The SCF distribution in internally ring-stiffened tubular KT-joints was experimentally studied.
• 118 FE models were generated and analyzed for the parametric study of SCFs due to IPB loadings.
• Geometrical effects on the SCFs at the crown, toe, and heel positions under IPB loads were studied.
• A set of parametric equations was developed for the SCF calculation in IPB-loaded stiffened KT-joints.
• Significant difference exists between SCFs in axially loaded and IPB-loaded stiffened joints.

Although tubular KT-joints are commonly found in offshore jacket structures and despite the crucial role of stress concentration factors (SCFs) in the evaluation of the tubular joint's fatigue performance, the SCFs in internally ring-stiffened KT-joints subjected to in-plane bending (IPB) loads have not been investigated so far and no design equation is available to determine the SCFs for IPB-loaded joints of this type. In the present research, data extracted from the finite element analysis of 118 models, which were verified using test results obtained from an experimental investigation, were used to study the effect of geometrical parameters on the weld-toe SCFs of central and outer braces in internally ring-stiffened tubular KT-joints subjected to four different types of IPB loads. Parametric study was followed by a set of the nonlinear regression analyses to develop SCF parametric equations for the fatigue analysis of ring-stiffened KT-joints under IPB loadings.