Offshore wind turbines in seismic active areas suffer from earthquake impacts. In this study, seismic fragility analysis of a monopile offshore wind turbine considering different operational conditions was performed. A finite element model for a 5 MW monopile offshore wind turbine was developed using the OpenSees platform. The interaction between the monopile and the seabed soil was modeled as a beam-on-nonlinear-winkler-foundation (BNWF). A nonlinear time history truncated incremental dynamic analysis (TIDA) was conducted to obtain seismic responses and engineering demand parameters. Potential damage states (DSs) were defined as excessive displacement at the nacelle, rotation at the tower top, and the allowable and yield stresses at the transition piece. Fragility curves were plotted to assess the probability of exceeding different damage states. It was found that seismic responses of the wind turbine are considerably influenced by environmental wind and wave loads. Subject to earthquake motions, wind turbines in normal operation at the rated wind speed experience higher levels of probability of exceeding damage states than those in other operational conditions, i.e., in idling or operating at higher or lower wind speed conditions.

In this paper, the effects of soil–structure interaction (SSI) on the response of a girder bridge pier is evaluated by assessing the energy distributions in the barge–pier collision system. The finite-element models of two example piers of St. George Island Causeway Bridge, which have different structural and geometrical characteristics, are developed in LS-DYNA software to simulate the barge–pier collision scenarios. By comparing the energy distribution results among the barge and pier components, it is obtained that barge bow component has greater value of the internal energy contribution than pier components in the barge collision with more stiff pier. While, in the barge collision with more flexible pier, the pier components including the pier structure, piles and SSI have more internal energy contributions than the barge component. In addition, From the comparison of energy absorbed by the pier structure between the cases with and without SSI, it is found that the effect of the substructure and its relevant SSI on the response of the more flexible pier affected by the produced large deformations and relative displacements of the pier substructure, is more than that of stiff pier which displaces with semi-rigid and global deflections.