  Diverting, and controlling, elastic vibrations impacting upon infrastructure
is a major challenge for seismic hazard mitigation, and for the reduction of
machine noise and vehicle vibration in the urban environment. Seismic
metamaterials (SMs), with their inherent ability to manipulate wave
propagation, provide a key route for overcoming the technological hurdles
involved in this challenge. Engineering the structure of the SM serves as a
basis to tune and enhance its functionality, and inspired by split rings,
swiss-rolls, notch-shaped and labyrinthine designs of elementary cells in
electromagnetic and mechanical metamaterials, we investigate altering the
structure geometries of SMs with the aim of creating large bandgaps
\textcolor{black}{in a subwavelength regime}. We show that square stiff
inclusions, perform better in comparison to circular ones, whilst keeping the
same filling fraction. En route to enhancing the bandgap, we have also studied
the performance of SMs with different constituent materials; we find that steel
columns, as inclusions, show large bandgaps, however, the columns are too large
for steel to be a feasible material in practical or financial terms.
Non-reinforced concrete would be preferable for industry level scaling up of
the technology because, concrete is cost-effective, easy to cast directly at
the construction site and easy to provide arbitrary geometry of the structure.
As a part of this study, we show that concrete columns can also be designed to
exhibit bandgaps if we cast them within a soft soil coating surrounding the
protected area for various civil structures like a bridge, building, oil
pipelines etc.
