Metabarriers with multi-mass locally resonating units for broad band Rayleigh waves attenuation

Artificial soils engineered with periodic or resonant structures, also referred as “seismic metamaterials” have been investigated for earthquake mitigation applications. In particular, an array of sub-wavelength single-mass resonators buried close the soil surface, namely the metabarrier, has been recently proposed to attenuate the ground motion induced by Rayleigh seismic waves. Here we demonstrate that the use of multi-mass resonators allows for enhanced performances of the metabarrier, in terms of amount and bandwidth of ground motion attenuation, with a smaller array of resonators. To this aim, after reviewing the single-mass metabarrier, we describe the dynamic of a multi-mass metabarrier using analytical and numerical approaches. In particular, we provide a detailed study of a metabarrier with double-mass resonators and compare its performances with those of a single-mass metabarrier with equivalent overall mass. Finally, we exploit Genetic Algorithms to design a metabarrier with multi-mass resonators with minimal mass and able to target selected frequencies. As a case study, the fundamental frequencies of two concrete-frame buildings of known dynamic properties are considered. The example shows the possibility to protect multiple buildings from Rayleigh waves with more compact metabarriers.