Finite locally resonant metafoundations for the protection of slender storage tanks against vertical ground accelerations

Inspired by recent findings in the field of Metamaterials, finite lattice locally resonant metafoundations represent an innovative solution for the seismic protection of storage tanks. One of the advantages with respect to traditional rubber bearings is the possibility of protecting the structure against the vertical component of ground accelerations, which has a significant influence on the hydrodynamic pressure of tanks. In this respect, we propose feasible configurations for a finite lattice metafoundation formed by steel columns, concrete slabs and concrete resonators, which allow for the protection of a slender tank against earthquakes with a significant vertical component. Based on the acceleration response variance of the liquid mass involved in the breathing mode, we develop an optimization procedure in frequency domain, which is adopted to design resonators stiffness and damping ratio. Time history analyses validate the efficacy of the proposed systems and show that staggering the columns at the second level of the outer frame allows for a higher attenuation of base pressure; it can decrease by 22.7% and 23.3% for OBE and SSE earthquakes, respectively. Eventually, we investigate the relationships between seismic signals frequency content and dynamic properties of coupled foundation-tank systems.