Offshore concrete structures are to-day designed using the best available Techniques. These include predictions of the force resultants m the structure using FE analysis with up to 1.5 million degrees of freedom, code checking of FE results using special dedicated postprocessing software, local capacity evaluations in areas where the linear FE analysis is known to be inaccurate. Further, special analyses are carried out for prediction of response from earthquake, wave induced dynamic action and geometric non-linear action. This paper addresses the finite element modelling of a large offshore structure for verification purposes, based upon the experience gained with the Draugen GBS platform for A/S Norske Shell. The paper will describe the philosophy for element selection, fineness in model, incorporation of built in stresses through the construction phases and the different load cases applied on the model. The paper further describes the post-processing of the results from the finite element analysis. This includes the accuracy of integration of stresses to obtain force resultants as basis for the general design, the accuracy of extrapolation of force resultants to critical cross-sections and the limitations in the code checking in general.
Offshore concrete structures are sometimes large, and complex in their geometric Shapes. The complexity makes it difficult to predict the force resultants with required accuracy by hand methods. More advanced approaches like the finite element method need to be used for the prediction of force resultants The use of finite element analysis also provides for incisions of many load cases and geometric refinements in the design which otherwise would have been impossible to handle. The number of load cases are considerable due to the simplicity of including more and more refinements in the analysis. With the large number of load cases and design sections, openings are made to optimize the reinforcement and prestressing reinforcement in the structure.
