Metamaterial foundations may offer buildings better earthquake resistance

When earthquakes strike, waves pulse through the Earth’s crust and mantle, wreaking havoc on buildings above. Research over the past several decades has sought to mitigate the threat earthquakes pose to buildings by considering changes to structures themselves or ways to guide seismic waves along paths around a building, but many of these approaches do not scale well to tall structures, or they require large footprints.

A team of researchers proposes a new method to isolate buildings from seismic dangers. Their approach, described in the Journal of Applied Physics, relies on the wave-wrangling properties of metamaterials to shunt seismic energy right at a building’s foundation, effectively filtering shear waves within a particular spectral range.

The team’s test foundation comprises of four reinforced concrete plates stacked on top of each other, with a grid of nine cylindrical holes through the stack. Steel tubes are placed in the four corner holes to connect the plates, while solid steel cylinders and rubber bumpers go in the five remaining holes. The arrangement mimics an acoustic metamaterial, with each cylinder in the grid acting like a local resonator that captures and then dissipates shear waves in the stack.

By displacing the bottom plate and measuring the displacement of the others, the team found that less than half of the input energy made it to the top plate. The reduction occurred for driving frequencies between about 4.5 Hz and the simulator’s upper limit of 8 Hz, and the reduction remained even when a 1-ton test mass is added atop their model. The researchers say their proposed foundation could offer more efficient and resilient seismic protection compared to traditional seismic insulators.

Source: “Seismic isolation of buildings using composite foundations based on metamaterials,” by O. Casablanca, G. Ventura, F. Garescì, B. Azzerboni, B. Chiaia, M. Chiappini, and G. Finnocchio, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5018005 .