Parametric study and formulation of outer-brace geometric stress concentration factors in internally ring-stiffened tubular KT-joints of offshore structures

In the present paper, results obtained from the FE analysis of 118 models, which were verified against the test data extracted from an experimental investigation, were used to study the effect of geometrical parameters on the chord-side stress concentration factors (SCFs) along the weld toe of the intersection between the outer (inclined) brace and the chord in internally ring-stiffened tubular KT-joints subjected to balanced axial loads. In this research program, geometrically parametric investigation was followed by the nonlinear regression analysis in order to establish a new set of SCF parametric equations for the fatigue design of internally ring-stiffened KT-joints. Although the tubular KT-joints are quite common in offshore structural design and despite the crucial role of SCFs in evaluating the fatigue performance of tubular joints, the SCFs in internally ring-stiffened KT-joints had not been investigated and no design equation was available to determine the SCFs for this type of joint.

▸ The chord-side SCFs in internally ring-stiffened tubular KT-joints were experimentally investigated. ▸ 118 FE models were generated for parametric SCF analysis of ring-stiffened KT-joints. ▸ Geometrical effects on the SCFs at typical positions along the outer brace weld toe were studied. ▸ A set of SCF parametric equations was established for the fatigue design.