A significant upgrade to the topsides facilities of the Beryl Alpha platform has recently been undertaken by Mobil North Sea Limited (MNSL). Structural reassessment of the deck structure was performed to demonstrate its continued integrity under the resultant increase in topsides loads. Previous papers [1. 2] describe how this was achieved with only minor strengthening. The reanaiysis has now been extended to incorporate an assessment of the concrete gravity base substructure, which is of the Condeep design. VTNSL's purposes for undertaking this reanaivsis were to:
reassess the structure taking into account the platform's operational history and the increased deck loads:
review the implications of extending the operational life:
investigate how the reinforced, prestressed concrete design performs against contemporary rules and codes:
provide a basis for future inspection:
provide a rapid reanalysis capability in the event of accidental damage or freak environmental loads.
Many aspects of the substructure design were evaluated, thus providing a unique opportunity to review the performance of a Condeep and its foundation after eighteen years of operation. The analysis included the development and validation of hydrodynamic and all other loads. A particular feature was the integrated use of both a simple skeletal simulation of the platform and a detailed finite element model. Extensive concrete code checking has been performed to a number of limit states using specialist software.
This paper presents the philosophy employed in, and discusses the preliminary results of, this analysis.