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.
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.