Degree of bending (DoB) in jack-up unit tubular KK-joints under the axial, in-plane bending (IPB), and out-of-plane bending (OPB) loads

The determination of degree of bending (DoB) is critical to improve the accuracy of estimating fatigue life using stress life (S-N) method. Based on the truss structure of jack-up unit, the numerical model of tubular KK-joints including rack plate (thickness is 180mm) is established. In the present research, the data extracted from 378 FE analyses on 108 tubular KK-joints models were used to study the effect of geometric parameters on DoB values of KK-joints under six different types of axial loading, IPB and OPB loadings. The geometric parameters affecting the DoB of tubular KK-joints are analyzed by multiple nonlinear regression analysis, and 21 parameter design formulas are obtained to calculate the DoB values of tubular KK-joints under axial loadings, IPB and OPB loadings. The established geometric parameter equation can effectively evaluate the fatigue characteristics of truss legs with rack plate of jackup unit.