Assessment of Strength Equations for Overlapped Tubular K-Joints

The ISO Draft Code for offshore structures has included a formulation for the design of both gap and overlapped tubular K joints under axial loading. The formulation has been derived from a test database of 149 gap joints and 56 overlapped joints. The authors have also presented, in a series of recent articles, a strength formulation (Swansea formulation) for overlapped K joints, based on a database of joint strength generated by an extensive parametric finite element study. In this paper, the accuracy of these two formulations is assessed using the joints with equal brace inclination contained in both the test and the finite element databases. The results of the comparison show that, while the Swansea formulation can accurately back-predict the test data, the ISO formulation underpredicts the finite element data by an average of 13% and its performance is particularly poor for joints with low γ and medium to low β. With the view that the Swansea formulation may be adopted to replace that proposed by ISO for design practice, the numerical constants in the Swansea formulation were simplified and a mean bias factor was derived to convert it to the characteristic format.