Stress concentration factors induced by out-of-plane bending loads in ring-stiffened tubular KT-joints of jacket structures

•The SCF distribution in internally ring-stiffened tubular KT-joints was experimentally investigated.•118 FE models were generated and analyzed for the parametric study of OPB-loading-induced SCFs.•Geometrical effects on the weld-toe SCFs at the saddle position under OPB loadings were studied.•A set of fatigue design formulas was proposed to determine the SCFs in OPB-loaded joints.•Significant difference exists between SCFs in axially loaded and OPB-loaded stiffened KT-joints.

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