Abstract
The jacket structure is one of the most important offshore structures. It’s a relatively stiff structure because its base is fixed to the foundation. Due to the fixidity at the bottom its natural period of vibration is much small in comparison to other floating structures. A jacket structure is framed structure that is generally made of tubular members and each member is connected rigidly. Under a huge load of platform and ocean waves, the member’s connection/joint undergoes rotation and deformation. Due to rotational and deformational responses at joints, the nonlinearity develops, and depending on structure properties and load it can be significant enough to affect the responses of the overall jacket structure. In this study, the joint of the jacket structure is remodeled using an analytical technique available in the literature, and the effect of the angle between the members is considered one of the factors for the nonlinearity in its flexibility matrix. The present study shows that considering the changing angle between the members shows a higher degree of nonlinearity in the flexibility matrix. Further, the same joint is modeled in Abaqus software for understanding the analytical results obtained previously. Further, buckling of the tubular member at the joint level due to external load is also considered in Abaqus for obtaining the relationship between load and displacement. This helps in obtaining the nonlinear stiffness matrix in the concerned degrees of freedom under the consideration of varying angles between members and buckling at the joint level of the tubular member. Further, the obtained nonlinear stiffness matrix is utilized to do the dynamic analysis of the joint in its concerned degree of freedom. Study shows that the nonlinear effect of joint is considerable enough and its effect is visible on dynamic response.
