Large-scale metamaterials can attenuate the energy and amplitude of harmful low-frequency vibrations associated with seismic shocks.
This is the conclusion of a European study published in the New Journal of Physics that proposes the use of metamaterials in regions threatened by earthquakes.
The metamaterials in question are artificial structures that exhibit extraordinary vibrational properties and the study, carried out by a team using detailed computer simulations, shows that large-scale metamaterials can attenuate the energy and amplitude of the low-frequency vibrations that earthquakes deliver.
Many large, modern structures including bridges and office blocks are protected against earthquakes through vibration isolation strategies that can be difficult to implement retrospectively, especially in historical buildings, and only apply locally.
Shielding vulnerable structures using large-scale metamaterials – which inhibit the propagation of incoming seismic waves through interference effects – could help to protect a much wider area without any direct modification to existing buildings in the region.
One of the simplest and most effective seismic shields proposed by the team involves digging 2-3 rows of equally spaced cross-shaped cavities in the ground.
“The exact dimensions will depend on the soil type and the frequency range of the shield,” said Marco Miniaci of the Universities of Torino and Le Havre. “For sandy conditions and low-frequency seismic excitations, the width, spacing and depth of the cavities, which should be lined with concrete to prevent the surrounding soil from collapsing, could reach 10m.”
To extend the performance of the protective structure, the group proposes adding a number of smaller cylindrical cavities measuring 2m in diameter. There are other tweaks that can be applied too. By scaling down the size of the array, the shield’s properties could be redirected towards similar problems occurring at higher frequency ranges. Scenarios include vibration prevention in the vicinity of high-speed train networks or heavy tramways. Blast protection could be another potential application.
“The next steps should involve experimental tests using scaled models in specialized geotechnical seismic and vibration labs,” said Miniaci. “This would provide further validation of the proposed structures and help to build on earlier work in the field.”
Other researchers contributing to the project include Anastasiia Krushynska and Federico Bosia of the University of Torino, and Nicola Pugno of the University of Trento, FBK Trento and Queen Mary University of London.
How many projects – let alone existing buildings – would have sufficient space outside the structure perimeter for this? Also, how does it affect landscaping?
For centuries (and built by architects : derivation arch- technician, who were in essence leaders of groups of stone masons who would never have seen an equation in their lives!) the largest buildings were palaces and churches. Presumably when and if these fell down 9and the often did by failure or ‘quake’ those in ‘power’ would simply demand that such be replaced. Those of the lower ‘orders’ lived in flimsy single storey dwellings: which were easily replaced and had little ‘raised’ load that might become a subsequent threat to inhabitants in a quake. But we now build ‘solid’ (mostly stone?) many storied structures in areas we know are ‘suspect’. Why? Surely this is just asking for the slightest jar or judder to bring it down. Perhaps we have to expect ‘slight’ movement (and design foundations for just that eventuality) and accept that the occasional ‘crack’ in a structure is a sign of its success in reacting to a ‘quake’. Surely better than the whole thing tumbling down, entrapping and killing the occupants because of that ‘raised’ load.
A life time ago, along with three other fellow students, I recall driving to Greece. Passing along the ‘autoput’ on our way home in what was then Yugoslavia, I recall near Skopje that there were a series of massive ‘bumps’ perhaps two metres high, both at the side of the roadway and indeed in it. We watched these with interest:
We had a meal in Skopje, then carried on with our journey. On our arrival home, a few days later the first picture we saw in the newspapers was the very building -our restaurant was in its base- lying in the ‘square’ : completely destroyed by the Skopje Quake. Was there a sense, from the greatly disturbed ground variations we had seen, that something epic was about to occur? That was (and is) as close to a quake that I have ever been: and I hope it stays that way!