A petal–cylindrical seismic metamaterial occupying low-frequency wide bandgaps in horizontally stratified soils

Earthquake prevention is of fundamental interest in seismic research area. Seismic metamaterials proved very useful for this purpose, but because they are mainly based on resonant structures, the working frequency bandwidth of these metamaterials is narrow. This work aims to increase the bandwidth by improving cylindrical resonant structure. Two types of cylindrical structures with four petals attached to the four sides of hollow and solid cylinders are proposed. Their bandgap properties have been investigated by using the finite element method. Particularly, considering more realistic site conditions for seismic surface wave propagation, we explored the properties of the proposed structures for horizontally stratified soils, besides homogeneous soil. The results show that a low-frequency wide bandgap is provided in case of homogeneous soil. Excitedly, in case of a stratified substrate, an additional bandgap is obtained in lower frequency region. Moreover, to confirm the feasibility of the proposed structures, the transmission coefficients for the finite unit cells are calculated for both homogeneous and horizontally stratified soils along with the different directions. The finding substantiates that the finite system for stratified soils can effectively attenuate seismic surface waves within the two low-frequency bandgaps occupying the relative bandwidths of 154% and 81%.