The Heidrun Field: Global Structural Design and Analysis of the Heidrun TLP

Abstract The structural analysis and design of the Heidrun tension leg platform presented many technical Challenge a that had to be overcome in a fast and efficient manner to meet the demands of a very tight schedule. Some are inherent in the nature of a compliant structure such as a TLP with its complicated interaction between the structure, the mooring system and the environment and the importance of proper weight and at ability control during the different phase a of construction and operation. However, many other a were unique to the Heidrun platform. The Heidrun hull is the first large offshore structure built entirely of high strength lightweight aggregate (LWA) concrete. The topside modules form an integral component of the structural system of the platform. The interface between the steel topside modules and the concrete hull proved to be a very complex engineering task requiring very detailed analyses, tight fabrication and installation tolerances as well as testing of a number of key components. Ringing loads were included in the structural design of the platform for the first time in an offshore structure. The transportation of the large topside modules, mounted transversely on barges, and their mating to the hull was unique. The reserve capacity built into the design to provide additional safety in the critical components of the structure. The paper presents an overview of the multitude of challenges encountered during the detail design of the platform. Introduction The Heidrun TLP introduced several structural innovations not seen previously on any offshore platform. Examples of these include the concrete Module Support Beams (MSBS) as a main structural member of the platform and for supporting the topside modules, unique solutions for connecting the topside modules to the substructure, exclusive use of high strength LWA concrete in the construction of the hull, design and fabrication of very large diameter columns, and design of the platform for the structural effects of ringing. This paper gives an overview of the structural analysis and design activities required in connection with the development of the Heidrun TLP and concentrates on design aspects which are novel or required more extensive consideration due to the nature of the TLP configuration or construction method. A short description of the platform is provided followed by the most significant aspects of thehydrodynamic and structural analyses. Special analyses and some of the unique design considerations associated with the hull and topsides design are presented. For completeness brief descriptions are given of the construction sequence of the hull, the foundations and the independent design verification performed for the structural design.