Effect of earthquake directional uncertainty on the seismic response of jacket-type offshore platform

In the seismic risk assessment of structures, two main random variables are involved, namely the vulnerability of the structure and the seismic action. The aim of the study presented here is to analyze the seismic behavior of the jacket-type offshore platforms as an expensive and vital structure. Furthermore, the influence of the incidence angle of the seismic action is also investigated by using twelve ground motions, rotating the direction of both orthogonal components by 22.5° (from 0° to 180°). Three damage states have been used in result interpretation. The variability of structural response to the direction of seismic input becomes larger as the level of inelastic behavior increases. In the present study, the critical directions were determined and the vulnerability of jacket type offshore structure was examined by fragility curve based on methodology suggested by Pacific Earthquake Engineering Research Center (PEER) for three damage limit states by both multicomponent incremental dynamic analysis (MIDA) and directional multicomponent incremental dynamic analysis (DMIDA). Finally, it is found that structural behavior in the collapse zone is sensitive to directional uncertainty can change the results by up to 10%.