A ground motion model for seismic vulnerability assessment of prototype industrial plants

Relationships between seismic action, system response and relevant damage levels in industrial plants require a solid background both in experimental data, due to the high level of nonlinearity, and in knowledge of seismic input due to large uncertainty. Besides, risk and fragility analyses depend on the adoption of a huge number of seismic records usually not available in a site-specific analysis. In order to manage these issues and to gain knowledge on the definition of damage levels, limit states and performance for major-hazard industrial plant components, we present a possible approach and discuss results of an experimental campaign based on a real prototype industrial steel structure. The investigation of the seismic behaviour of the reference structure has been carried on through shaking table tests, focusing in particular on the structural or process-related interactions that can lead to serious secondary damages as leakage in piping systems or connections with tanks and cabinets. This has been possible thanks to the adoption of a ground motion model (GMM) able to generate a suite of synthetic time-histories records for specified site characteristic and earthquake scenarios. In fact, model parameters can be identified by matching the statistics of a target-recorded accelerogram to the ones of the model in terms of faulting mechanism, earthquake magnitude, source-to-site distance and site shear-wave velocity. Hence, the stochastic model, based both on these matched parameters and on filtered white-noise process, generates the ensemble of synthetic ground motions capable to capture the main features of real earthquake ground motions, including intensity, duration, spectral content and peak values. Finally, by means of the combination of a high-fidelity and a low-fidelity FE model as well as the stochastic input generated by a GMM, a seismic vulnerability assessment of both industrial components and the global structure can be carried out.