API-RP2EQ (2021) has recommended annual probabilities of failure for Jacket-Type Offshore Platforms (JTOPs) against earthquake events and has specified that catastrophic failure modes that can lead to environmental damage or loss of structural integrity shall not occur during an Abnormal Level Earthquake (ALE). In this study some structural and non-structural limit states are proposed for the seismic evaluation of JTOPs and a comprehensive methodology is used for evaluating the probabilities of reaching relevant limit states, considering the nonlinear dynamic behavior of JTOPs, soil-pile interaction, pipeline risers, and relevant uncertainties. Incremental Dynamic Analysis (IDA) has been carried out on finite element models of platforms, and record-to- record and epistemic uncertainties have been considered in deriving fragility curves. Results show that the slope-based limit states derived from nonlinear static pushover curves provide a fairly good estimate of the target annual probability of structural failure. They also show that a non-structural limit state associated with containment leakage of pipeline risers should also be considered in the analysis. The research provides valuable insights into probabilistic performance-based seismic assessment of steel jacket-type offshore platforms and indicates that the reserve strength coefficients recommended in the relevant standard may be too conservative.

来源平台：OCEAN ENGINEERING