Probabilistic seismic analysis of offshore platforms incorporating uncertainty in soil–pile–structure interactions

• An existing fixed platform constructed in the Persian Gulf is simulated in OPENSEES software.
• Comprehensive Interaction Incremental Dynamic Analyses are performed to address aleatory and epistemic uncertainties simultaneously with a reasonable number of simulations.
• Statistical data is represented by employing the results and their summarizations as a good indication of the level of shaking needed in different limit states.
• The results can be combined with the site hazard curve to generate mean annual frequencies of exceedance in various levels.

In this paper a novel methodology is presented to incorporate uncertainties associated with seismic loads, characterization of structural model parameters, and description of soil properties in the probabilistic assessment of seismic-related damage of existing jacket type offshore platforms located in seismic active areas.The main objective of this methodology is to facilitate the probabilistic analysis of soil–pile–structure interactions (SPSI) by implementing a Comprehensive Interaction Incremental Dynamic Analysis (Comprehensive Interaction IDA) method that involves the convolution of uncertainties associated with three separate elements: structure, piles and supporting soil. This quantitative seismic analysis procedure consists of: a) selecting an appropriate suite of strong ground motion records and performing a Comprehensive Interaction IDA on a nonlinear model of an existing fixed platform; b) summarizing the Comprehensive Interaction IDA results into various percentile performance bounds; and c) integrating the results with respect to hazard intensity–recurrence relations into a probabilistic seismic format. To address and propagate these uncertainties, the Latin Hypercube Sampling technique in conjunction with the Simulated Annealing optimization is applied to evaluate their effects on the structural responses with a relatively small number of simulations. The proposed methodology with the ability of incorporating uncertainties in existing platforms can be effectively used to evaluate the structural integrity in other industries.