Stress Concentrations Analyses Of Tubular Joints In The Offshore Structure

Tubular joint of offshore structure is a weak link, for most of the fracture of structure frequently starts in the welded tubular joints by its fatigue failure, Therefore it is important to to understand the stress concentration in the fatigue life of the welded tubular joints.This paper is starting from the numerical analysis , selecting three typical multiplanar joints based on engineering example, using finite element software to study the stress concentration of the joints. The shell element finite is mainly used to simulate the tubular wall, while the three-dimensional solid element is mainly used to simulate the welding seam, and entities between the deferent units will use the appropriate connection. Boundary conditions and loads is also based on the engineering examples, which is mainly under the independent of the three basic load circumstances. The data of stress concentration factors(SCF) obtained from numerical analysis is compared with the experimental data calculated by the socalids, and the error betweens them is within 5%. Then the text calculate the SCF of the joints after changing the geometric parametersα,β,γ,τ,θ,ξ, from which we can obtain some characteristics and commonalities of the geometric parameters that influencing the SCF.The text is using APDL to calculate 3575 joints'stress concentration factor, using Visual Basic to fit all numerical results by non-linear least squares, from that we can obtain the parameters formula of the SCF, which is proved by the Fatigue Guidance Review Panel. The formula can be used to calculate related tubular joints stress concentration factor.In addition, the text is comparing three joints'SCF in the same geometric parameters and the same loading, we can see that the SCF is more sensitive to the axial load and out-plane bending load, so the structure should be designed to minimize the axial load and out-plane bending load.