Since 1971 about twenty offshore concrete structures have been designed and built for North Sea operation. The design of such platform structures is based on several requirements related to function, safety and economy. These requirements, together with large water depths and harsh environmental conditions, normally lead to complex structures. A high utilization of the materials and a high level of accuracy are generally also required. In order to satisfy all these demands, advanced linear elastic finite element analyses (FEA), using solid elements, and a corresponding automatic postprocessing, i.e. conversion of FEA stress results into sectional forces for the design, have proved to be necessary. This paper presents an overview of the current practice for structural analysis, postprocessing and design of offshore concrete structures. Itis stated that an efficient and flexible postprocessing and design computer program must be available for the engineer. However, to avoid an undesirable "black box" design work and to secure a satisfactory accuracy of the design results, It must be possible to trace and verify the intermediate as well as the final results through the use of suitable printouts and graphical presentations.
The objective of the present paper is to give an overall description of the structural finite element analysis (FEA), postprocessing, i.e. the conversion of stress results into sectional design forces, and design of offshore concrete structures. For the FEA, focus is put on the adequacy of different element modelling alternatives. With respect to the subsequent postprocessing and design. The techniques of combining separate load cases to design combinations form an important part of the postprocessing work, see Chp 4. Great emphasis is put on the design calculation process itself, with special focus on the need for having an accurate, efficient and flexible system, without reducing the overview and detail verification possibility (Quality Control) of the design calculations and the final results.
