Nonlinear Dynamic Soil-Pile-Structure-Interaction Analysis of Offshore Platform for Ductility Level Earthquake under Soil Liquefaction Conditions

Abstract eng:
This paper presents the rigorous methodology and structural analysis procedures required for nonlinear dynamic soil-pile-structure-interaction analysis of offshore platforms under ductility level earthquakes with emphasis on the soil liquefaction conditions. The nonlinear inelastic soil properties including the cyclic strain rate, gapping, and the hysteretic energy dissipation are considered. The non-linear beam-column element and non-linear strut element, which were calibrated with numerous test results for offshore structures, are modeled and presented. Three sets of representative ground motion time histories, which characterize the likely envelop of ground intensity, frequency content, phasing and duration expected at the site, are considered in the analysis. The comparison of the evolutionary power spectral density of the earthquake ground motion accelerations is outlined for soil liquefaction and non-liquefaction conditions in terms of the intensity and frequency content of the ground motion accelerations. The impact of the soil liquefaction conditions on the structural response and especially for the pile foundation system design, are illustrated using a recently successfully designed platform in the seismic active area offshore Trinidad. API and ISO seismic design requirements are briefly discussed. The most critical structural components of the pile-jacket connections design are demonstrated by the nonlinear finite element analysis with the large deformation of the platform and the material plasticity of the steel considered.

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