Friction Pendulum bearings (FPBs) are seismic isolation devices that reduce the lateral accelerations of the supported structure in an earthquake. This paper describes the application of probabilistic methods to establish criteria for qualification testing of reduced-size prototype bearings. The methodology is used to determine demands to impose during testing (displacements, velocities, etc.) that are representative of desired performance standards (probabilities of exceedence). Previous test programs used in the offshore and onshore industry have used deterministic analysis based on lower bound and upper bound properties to establish demands for the test program. These follow from the deterministic analysis approach used in the global structural design. These methods establish maximum demands to target in the test, but do not give information on their actual probabilities of exceedence. Use of the methodology described in this paper allows engineers to test the FPBs at levels having probabilities of exceedence aligned with other major platform components, ensuring that the test conditions are not excessively conservative or unconservative. Rather, the test conditions comply with a specified probability of non performance of 2% in 50 years achieved with a particular level of confidence (90% generally and 99% for more critical parameters). The performance-based (response-based) approach described in this paper can be applied to a broad range of seismically isolated platforms. These methods were originally developed for onshore seismic design of buildings. Hence, the underlying probabilistic framework is general and can be applied to structural design and qualification testing of other components. Introduction Friction Pendulum Bearings (FPBs) are specialized devices that will be used to isolate the topsides of the Arkutun-Dagi platform from earthquakes. The Arkutun-Dagi platform is part of the Sakhalin-I development which is located in an area of high seismicity. Offshore platforms located in the region require highly specialized design to balance the competing requirements of the harsh demands from earthquake, wave and ice loading. Structural design strategies that have been 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.

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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.

Bow-ties are increasingly used in multiple industries to effectively manage risks during operation. Benefits of bow-ties include clear communication, operator ownership, relationship between safeguards for various threats and consequences, and the visibility of safeguard health during operations. In oil and gas, the main application of bow-ties has been to manage high consequence risks pertaining to process safety, i.e. loss of primary containment of hazardous substances. Unlike onshore facilities, escape from hazards can be inhibited by limited egress and evacuation options can be compromised as part of the events themselves, which heightens the potential number of fatalities in an offshore process safety event. Additionally, while the root cause of a good proportion of incidents originates from process safety hazards, many significant events have originated from offshore and marine structure hazards as well. Since offshore structural and marine failures are not always driven by loss of primary containment, the use of bow-ties in offshore structures and marine is less established. This paper introduces the use of bow-ties and associated principles as tools to manage all offshore risks, both process-safety and structural or marine related. It evaluates the application of bow-ties for a range of high consequence risk scenarios specific to fixed and floating offshore platforms, and provides simplified bow-ties for a range of different types of assets. Though it represents a less conventional approach than those commonly employed for offshore failure scenarios, use of bow-ties can support effective management of these risks, especially those requiring proactive management of safeguards, particularly ice feature overload, offshore collisions, multi-line mooring failures, and loss of floating stability.

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