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How Cities are Adapting to Earthquakes

How Cities are Adapting to Earthquakes

We can see hurricanes and storm cells forming, predict heavy rainfalls, and anticipate other weather patterns like droughts. But earthquakes are sudden destructive forces, and it’s that sporadic nature that makes these events so dangerous.

143 million people in the contiguous U.S. alone live within areas that are susceptible to damaging earthquakes, a group spread between major population centers and metropolitan areas like Los Angeles, Charlotte, and Nashville. Billions of people across the world are also at risk of major quakes; peoples in Japan, China, the Middle East, Indonesia, and Peru are among the most at-risk.

Fortunately, professionals have been hard at work for decades figuring out ways we can make our infrastructure more resilient against earthquakes. February is Earthquake Preparedness Month, so let’s dive into the results of those practitioners’ hard work and explore the fascinating technology behind earthquake resilience.

Going with the Flow: Base Isolation

A chicken keeps its head still as its body moves, as do a number of other avian species. If you’ve ever seen this happen, it’s probably made you wonder how.

Chickens, and other particular avian species, aren’t able to focus their vision as their heads move. So, to compensate, they’ve evolved neck and upper body muscles that stabilize their heads as they move, a behavior that maintains their vision’s focus and clarity. In nature, this is pretty advantageous and just one of many traits these species have manifested to keep themselves safe and healthy.

Researchers have applied a similar concept to buildings as a means of quake-proofing infrastructure. In the engineering world, this concept is called base isolation. It gained steam in the 1970s, but archeological evidence suggests ancient peoples from as early as the fifth century B.C. employed the practice.

Japan is one the world’s most earthquake-prone countries, and many of its buildings use this technology to keep its population safe from the abrupt and violent disasters.

So, how does base isolation work? Let’s tend to our chickens again for an answer.

When the chicken moves its body, it’s creating force. The muscles that stabilize the chicken’s head effectively dampen and eat that force, preventing the head from moving. This creates two distinct parts of the chicken: its in-motion body and its static head.

When humans and many other species walk, our heads go with the flow. The momentum of our movements cause our heads to move. Fortunately, other evolutionary adaptations help us keep our perfect vision as our entire bodies work to traverse ground.

Base isolation goes the route of the chicken. When properly constructed, the building (superstructure) is effectively split from its foundation (substructure). Only steel plates bring the two structures together. Lead-rubber bearings eat the brunt of seismic activity, allowing the  foundation to move while the building above stays relatively stable. Some researchers are already exploring more advanced ways of deploying base isolation, including using air compressors to float buildings above their foundations when seismic activity starts.

It’s gone: Shock Absorbers and Dampers

Imagine you’re at a baseball game. The pitcher misplaces their fastball right over home plate, and the batter swings. You immediately tilt your gaze up, looking for the rocket the hitter surely sent into the bleachers.

But you, and every player and other fan, see nothing. Instead, the jumbotron shows the ball dead in front of the plate, almost like it plummeted down, pulled by magnetic force. The pitcher is happy. The batter is frustrated. And the crowd is confused. It’s not what they expected or paid to see.

Could this actually happen? No, not on a baseball diamond. But maybe some wacky technology could make it a possibility in the future; a bat that absorbs the force of the baseball and transfers energy nonviolently, stopping the ball in its tracks. It would be a pitcher’s dream.

In fact, it would take some type of damper, a technology most of us benefit from today through everyday actions like driving a car.

Dampers take in vibrations, convert the movement into kinetic energy, and dissipate the energy, usually through a hydraulic fluid. Our cars’ shocks do this to keep us from feeling the tumult of uneven roads and surfaces, and engineers have slapped the idea into our shelters and structures.

There’s no one universal damper engineers use in for seismic mitigation. Viscous, metallic, and friction dampers all do the job; both viscous and friction dampers typically survive seismic events, providing longevity to the safety technology put into many buildings.

One of the most intriguing architectural dampers are tuned mass dampers, large masses with flexible attachments in tall structures that are meant to counteract the sways an earthquake normally puts on a building. After a few cycles, the large mass moves in the opposite direction the seismic energy is taking the building, counteracting the extreme one-directional force.

What We’re Made Of: Materials

There’s an even simpler approach to building earthquake resilience within our infrastructure: materials.

If construction was like cooking, materials would be the spices in the equation. They add extra flavor to the components we’ll add later, like carbs, vegetables, and proteins, to make a satisfying meal.

Food is bland without spices and herbs. Any food cooked without spices and herbs will still be nourishing, and, therefore, still a perfectly fine solution; base isolation and shock absorbers are incredible technologies that save time, money, and lives on their own, but flexible materials are the spices that can give them some extra oomph.

Concrete has long been to the taste of developers. It has a long history of being a durable and shapeable material, two factors many thought would help resist the persuasions of shifting earth.

But as our understanding of physics has dramatically improved so too have our opinions on concrete.

Many developers have turned to steel to create more resilient buildings. Steel offers greater plasticity, allowing buildings to endure more force without taking on much structural deformation.

As manufacturing and science progresses, researchers are finding even stronger metals and alloys. “Shape memory” alloys give buildings and their internals more opportunities to act like rubber bands, bracing extreme forces and reverting back to their original states.

Carbon fiber is also making a splash. These networks of polymers are being fashioned into wraps for building beams and support columns, improving the strength and ductility of the base construction.

We may not even need to turn to thing-of-tomorrow technologies to bolster our infrastructure. Mussel shells and spider silk are two viable options from the animal kingdom, boasting impressive size-to-strength ratios. Producing these materials at scale is the biggest roadblock in realizing a bio-reinforced reality.

There’s also the old reliables: wood and bamboo. Both materials offer high relative strength at a lower total weight than metals and other materials. Less weight means less weight for earthquakes to throw around, and that alone could significantly reduce damage to buildings. More importantly, it’s a viable solution for less wealthy parts of the world, where high-magnitude earthquakes have greater destructive potential.

Preparedness, not Prediction

If we can’t predict earthquakes, we should at least be prepared for their destructive energy. Engineers have worked for decades to inject more resilience into infrastructure, and much of their results are starting to pay off. We may hardly remember what a massive earthquake feels like in a few decades, and that’s not a terrible thing.

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