Time-dependent seismic fragility curves for aging jacket-type offshore platforms subjected to earthquake ground motions

Abstract

This paper assesses the seismic vulnerability of a recently designed jacket-type offshore platform through development of fragility curves and presents the formulation of time-dependent seismic fragility curves to capture the effects of ageing and deterioration on the seismic vulnerability of the representative platform. Among the various ageing processes, the corrosion deterioration of the structure is taken into account by applying a time-dependent model of corrosion deterioration of the tubular elements in the splash zone. Incremental dynamic analysis is performed on the initial uncorroded and corroded platforms considering soil–pile–structure interaction. A full probabilistic analysis is then performed to develop time-dependent seismic fragility curves for the immediate occupancy and collapse prevention limit states. Finally, a time variant cubic model is proposed to develop fragility curves at any point in time during platform’s service life, without need to perform a complete time-consuming fragility analyses. Results show substantial increase in probability of failure of the platform throughout its lifetime due to corrosion deterioration. The results also indicate that the time-dependent fragility curves can be used in offshore platforms to assess the seismic vulnerability of the structure and demonstrate the influence of various factors affecting the seismic vulnerability of the platform during its lifetime.