This paper describes the methodology and technical solutions employed to address earthquake loading challenges on the Berkut topsides, including design and operational considerations. The Berkut platform is part of the Sakhalin-I development in offshore Russia, which is located in an area of high seismicity. Offshore platforms in the region require highly specialized designs to balance the competing requirements resulting from earthquake, wave and ice loading. Design strategies used in the region to protect structures from earthquakes include a tuned mass damper to protect the drilling derrick on the Orlan platform and Friction Pendulum seismic isolation on the Lunskoye-A and Piltun-Astokhskoye-B platforms.

The Berkut structure consists of a four-shaft gravity based structure (GBS) with a topsides operating weight of approximately 50,000 tonnes. Seismic isolation devices called Friction Pendulum Bearings (FPBs) are placed between the GBS shafts and the topsides to reduce horizontal load transfer and accelerations. A performance-based design approach was developed to derive load and resistance factors providing a specified probability of non-performance (2% in 50 years with a minimum 90% level of confidence). This approach, which can be applied to a broad range of extreme environmental design criteria, enabled the seismic design for Berkut to be completed with a more consistent level of reliability than would have been achieved using traditional methods. Seismic analyses were carried out using nonlinear time history analyses of a fully coupled analytical model containing topsides, GBS and soil. This was complemented by finite element analysis for local design.

A seismic event of smaller magnitude than the design event can impact production unless Operations personnel can confirm that no safety-critical components have been compromised by earthquake loading. A custom structural monitoring system has been configured to monitor accelerations and FPB displacements; and an earthquake-response strategy has been implemented to enable Operations personnel to make prudent decisions following an event.

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