Multi-Level Design of Tubular Joints

Abstract

In offshore jacket design, it has long been recognized that an accurate global structural model requires implementation of the effects of local joint flexibility (LJF). However, there is still no general method for implementing these effects accurately and efficiently without complicating the application of loads. The literature describes several techniques for determining LJFs using parametric formulas and implementing these in global models of a jacket structure. These techniques are simple but associated with uncertainties and a risk of compromising the accuracy of the global model. Alternative methods, such as the use of superelements, provide very accurate results but complicate the consistent application of external loads as well as postprocessing. This paper introduces a new methodology which is called the Correction Matrix Methodology. This allows the effects of LJF from detailed three-dimensional (3D) finite-element (FE) shell or solid models to be incorporated in a global beam FE model via a simple correction matrix. The effectiveness of the methodology is improved by using interpolation between a limited number of correction matrices. The new methodology provides exact results when correction matrices associated with the actual geometry are applied. When using the interpolation procedure, the methodology provides accurate results and computational efficiency when the database has been established. The Correction Matrix Methodology is a significant improvement of the conventional methods for modelling LJF and is currently being implemented in a general form for arbitrary joints in Rambolls Offshore Structural Analysis Program (ROSAP).