On a novel concept of locally resonant periodic foundation

In the framework of ongoing research on seismic metamaterials, this study investigates a novel locally resonant periodic foundation for the base isolation of masonry structures. The foundation consists of a periodic assembly of vertically stacked steel cells of circular shape, interconnected by circular steel-laminated elastomeric bearings. Each steel cell comprises a hollow cylinder welded to top and bottom plates and connected, through a rubber ring, to a steel ring that acts as a resonant unit oscillating in the horizontal plane. A simplified mass-spring model, formulated in dimensionless form, is used to perform elastic wave propagation analysis and predict the effectiveness of the foundation when installed at the base of a masonry structure, providing information for preliminary design. Subsequently, for proof of concept under real earthquake ground motions, a detailed 3D finite element model of a full scale benchmark masonry structure base-isolated by an array of foundations is developed. Numerical analyses of the 3D finite element model confirm the predictions of the simplified mass-spring model and demonstrate that the foundations can attenuate the effects of earthquake ground motion by inducing relevant attenuation zones in the low-frequency response of the masonry structure, with better performances than classical elastomeric isolators in most of the examined cases. Notably, the effectiveness is not limited to the low-frequency range but extends to much higher frequencies, which may be of interest for mitigating the effects of railway or road traffic.