Optimal ground motion intensity measure selection for probabilistic seismic demand modeling of fixed pile-founded offshore platforms

The safety and serviceability of fixed pile-founded offshore platforms during and after an earthquake will ensure their continuous operation and prevent irreparable economic and environmental loss in a seismically prone area. The probabilistic seismic demand model is a performance-based earthquake engineering design method for offshore platforms. The level of uncertainty in PSDMs depends on the selected seismic intensity measures (IMs), although these models are traditionally conditioned with a single IM. The optimal IM selection used in the present study has not yet been investigated for offshore platforms. Because of the geometrical uncertainties of these types of structure, they were examined using 3D models of five braced configurations of fixed pile-founded offshore platforms by considering the soil-pile-structure interaction (SPSI). Twenty-seven optimal IMs were chosen with regard to their effectiveness, efficiency, practicality, proficiency, sufficiency, relative sufficiency, and hazard computability assessments. Probabilistic seismic demand analysis was performed and each model was subjected to 80 unscaled ground motions. The optimal velocity-related IMs performed well, especially those for the Housner intensity (HI) and velocity spectrum intensity (VSI) for predicting a fixed pile-founded offshore platforms response measured in terms of drift ratio and differential settlement. On the other hand, peak ground velocity (PGV) and HI for the ductility demand parameter present optimal pairs. These most informative IMs were able to provide improved probabilistic seismic demand models (PSDMs) and accurate fragility analysis of the structures.