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ARTICLE: How Earthquake Resistant Buildings Work 

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ARTICLE: How Earthquake Resistant Buildings Work 

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Take a look at recent seismic activity, and you might get the impression that Earth, perhaps a bit too overcaffeinated, has a bad case of the shakes. Earthquakes rattled Chile on and off during 2010-11, beginning with a magnitude-8.8 temblor (or earthquake) that struck just off the coast near Concepcion in February 2010. Then, in March 2011, a magnitude-9.0 quake rocked Japan, triggering a tsunami that killed an estimated 29,000 people and damaged nuclear reactors [source: Amazing Planet]. And finally, in August 2011, a magnitude-5.8 quake centered near Mineral, Va., spooked residents up and down the Atlantic seaboard and damaged the Washington Monument.

While those events seem to suggest an ominous future with a shaking, quivering crust, earthquakes have always been common, as has the human resolve to survive them. Over the centuries, engineers have come to know one thing with growing certainty: Earthquakes don't kill people; buildings do. This is a gross oversimplification, of course, because tsunamis also take many lives, but not all earthquakes generate tsunamis. They do, however, cause buildings, bridges and other structures to experience sudden lateral accelerations. All of which leads to a logical question: Is it possible to keep buildings upright and intact during catastrophic earthquakes like those that shook Chile in February 2010 and Japan in March 2011?

Many engineers and architects now believe it's possible to build an earthquake-proof building -- one that would ride the waves of the most fearsome temblor and remain as good as new once the shaking had stopped. The cost of such a building, however, would be staggering. Instead, construction experts strive for something slightly less ambitious -- earthquake-resistant buildings, which are designed to prevent total collapse and preserve life, as well as construction budgets.

In recent years, the science of building earthquake-resistant structures has advanced tremendously, but it's not an entirely new subject. In fact, a few ancient buildings still stand today despite their location in active seismic zones. One of the most notable is the Hagia Sophia, a domed church (now museum) built in Istanbul, Turkey, in A.D. 537. About 20 years after it was completed, the massive dome collapsed after a quake shook the area. Engineers evaluated the situation and decided to rebuild the dome, but on a smaller scale. They also reinforced the whole church from the outside [source: PBS].

Today, the techniques are a bit different, but the basic principles are the same. Before we delve into the nuts and bolts of building earthquake-resistant structures, let's review some basics, namely, what forces are generated during an earthquake and how they affect man-made structures.

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Take a look at recent seismic activity, and you might get the impression that Earth, perhaps a bit too overcaffeinated, has a bad case of the shakes. Earthquakes rattled Chile on and off during 2010-11, beginning with a magnitude-8.8 temblor (or earthquake) that struck just off the coast near Concepcion in February 2010.

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ARTICLE: Top 5 Earthquake Resistant Buildings Around the World

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ARTICLE: Top 5 Earthquake Resistant Buildings Around the World

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Earthquakes are one of the most destructive forces of nature. Structures can suffer severe damage when an earthquake strikes. That's why, seismic loadings must be taken into account when designing structures, especially skyscrapers.

Let's roam around the world together and discover the top 5 earthquake-proof structures and learn how buildings can be designed to resist extreme seismic loadings.
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How do earthquakes happen?

As an engineer, in order to make solving a problem easier, it's important to understand what it is. So, what exactly is an earthquake and how do they happen?

Everyone knows about the existence of tectonic plates and how they influence the movement of the Earth's crust. Earthquakes happen when these tectonic plates move or collide with each other and release large amounts of energy. This is measured using the Richter scale.

The movement of these tectonic plates can generally be attributed to mantle convection, a phenomenon where warm mantle currents carry plates of lithosphere along like a conveyor belt. It may also be caused by the buoyant upwelling of the mantle at mid-ocean ridges. In this case, gravity causes the higher plate at the ridge to push away the lithosphere that lies further from the ridge. Another cause may be slab pull; it's a phenomenon where the older, colder plates sink at subduction zones. Subsequently, the cooler sinking plate pulls the rest of the warmer plate along behind it.

Professor Iain Stewart, a geologist from Plymouth University, explains how earthquakes happen and how they affect structures in this short clip. Knowing that waves radiate from the base of a structure throughout its whole body is essential in designing earthquake-resistant buildings.

One of the main elements of any earthquake-resistant building is base isolation. Let's take a quick look at what exactly this is.

What is base isolation?

The so-called base isolation is a technique developed by engineers to prevent - or at least minimize - the damage to buildings when exposed to earthquakes. These kinds of systems are used all over the world and are most prevalent in New Zealand, India, Japan, Italy, and the United States.

More traditional constructions, like fixed-base buildings, tend to be built directly onto the ground. While this is a sound practice for places that do not experience frequent earthquakes, it is highly advised against if not.

When an earthquake hits, the ground (and the building attached to it) moves with the quake's motion, causing massive damage to the building. To counteract this, most earthquake-proof buildings are isolated from the ground in some manner.

This usually involves using flexible bearings or pads known as base isolators. These kinds of systems move during a quake, but they move to counteract the forces generated by the movement of the building.

Base isolators work in a similar fashion to car suspension systems, which allow a vehicle to travel over rough ground by isolating the interior and absorbing the shock of uneven ground, without throwing the passengers inside around.

According to the uring an earthquake, a building can move around Science Learning Hub, "d 11 in (300 mm) or more relative to the ground. Therefore, the use of base isolation also means there must be a way for movement during an earthquake to be accommodated. This usually means a "rattle space" or "moat" has to be put in place around the building so that the building doesn't crash into something nearby. Building services such as water, sewerage, and electrical all need to be designed to accommodate this movement without being damaged."

While base isolation can be a saving grace for many medium-rise brick or stone buildings, and can reinforce concrete ones, it is not suitable for all types of structures. Base isolators tend to have a limited ability to cope with tension.

The seismic dampening widgets (Base Isolators) under the Utah State Capitol building. Source: Mike Renlund/Wikimedia Commons

This means that taller buildings have a very real risk of overturning or toppling during earthquakes if they have base isolators installed. For these kinds of buildings, other measures are required.

Base isolators are also not suitable for some sites due to other geotechnical and geographical reasons. For example, there may not be enough space to install them.

They also require hard soil, not soft soil, to operate at peak efficiency.

What are the different types of earthquakes?

A random fact about earthquakes: Did you know that there are about millions of earthquakes every single year? But don't worry, most of these are very small and virtually imperceptible.

Some of them, however, can be incredibly destructive, crumbling buildings and robbing people of their lives and livelihoods.

Earthquakes generally fall under one of a few distinct categories. These are:

Tectonic earthquakes.

Volcanic earthquakes.

Collapse earthquakes.

Explosion earthquakes.

Tectonic earthquakes occur at plate tectonic boundaries. Sometimes, friction between tectonic plates causes them to lock together and become unable to move. However, the rest of the plate carries on moving, which leads to increased pressure on the locked section. Eventually, the locked section succumbs to the pressure and shatters, the plates move rapidly, releasing energy and causing an earthquake.

Volcanic earthquakes are quakes that result whenever tectonic activity also causes volcanic activity.

Collapse earthquakes are minor earthquakes that occur whenever something like a mine or underground cavern collapses.

Explosive earthquakes are any form of an earthquake that is caused by a massive explosion, like a nuclear weapon detonation. Like collapse earthquakes, these tend to be very minor.

Earthquakes are also sometimes caused by human activity such as the injection of fluids into deep wells, the excavation of mines, and the filling of large reservoirs.

All earthquakes' relative strength is measured using the Richter Scale. According to Michigan Tech, typical ranges for various magnitudes of earthquakes include: -

If you want to learn more about what earthquakes are, Encyclopedia Britannica's entry on this subject is quite comprehensive.

What are some of the world's top earthquake-proof buildings?

And so, without further ado, here are some of the best earthquake-proof buildings from around the world. This list is far from exhaustive and is in no particular order.

1. Sabiha Gökçen International Airport is one of the world most earthquake-proof buildings

One of the major airports to serve the historical city of Istanbul, it also happens to be one of the world's most earthquake-proof buildings. Called Sabiha Gökçen, it is one of the two international airports in Istanbul, Turkey, which is located near the North Anatolian fault.

It was designed by the engineering firm Ove Arup to have 300 base isolator systems that can withstand an earthquake of up to a maximum of 8.0 Mw ( moment magnitude). The base isolators can reduce lateral seismic loadings by 80%, which makes it one of the largest seismically isolated structures in the world.

One of the major features of the airport that makes it so earthquake-resistant is its so-called "triple friction pendulum device".

Architects Journalexplains that "the whole terminal building sits on a platform that is, to a high degree, isolated from the ground below. This enabled the team to design the terminal almost as though it were situated in a non-seismic location, and to include features such as [structures with] large spans because the platform and pendulum devices mean that violent lateral ground movements will scarcely affect it."

The airport's triple friction pendulum bearing was manufactured by Earthquake Protection Systems (EPS). They use the principle of a basic pendulum to prolong a structure's isolation during serious earthquake events.

When an earthquake hits the structure, the airport's earthquake-proofing structures move with small pendulum motions. E arthquake-induced displacements occur primarily in the bearings, so lateral loads and movements transmitted to the structure are greatly reduced.

2. The Transamerica Pyramid can really take a pounding and keep standing

The Transamerica Pyramid is an iconic 1970s structure located in the Californian city of San Francisco, which sits closely beside the San Andreas and Hayward faults. In 1989, the Loma Prieta earthquake struck the area at a magnitude of 6.9 Mw which caused the top story of the structure to sway by almost one foot (30 cm) from side to side for more than a minute, but the building stood tall and undamaged.

This earthquake resistance feat can be attributed to the 52-foot-deep steel and concrete foundation that is designed to move with seismic loadings. Vertical and horizontal loadings are supported by a unique truss system above the first level, with interior frames extending up to the 45th level. The complex combination of these structural systems makes the building resistant to torsional movements and allows the absorption of large horizontal base shear forces.

3. The Burj Khalifa is also specially designed to resist earthquakes

This skyscraper doesn't really require any introduction. The Burj Khalifa is simply one of the most iconic supertall structures in the world. It also happens to be an earthquake-proof building!

The structure is composed of mechanical floors where outrigger walls connect the perimeter columns to the interior walling. By doing this, the perimeter columns are able to support the lateral resistance of the structure. The verticality of the columns also helps with carrying the gravitational loads.

As a result, the Burj Khalifa is exceptionally stiff in both lateral and torsional directions. A complex system of base and foundation design was derived by conducting extensive seismic and geotechnical studies.

4. Taipei 101 is another of the world's best earthquake-proof buildings

Taipei 101 is perhaps one of the most mesmerizing supertall skyscrapers in the world. The exterior design ( by C.Y. Lee) was inspired by the phrase, " we climb in order to see further".

Putting aside the architecture, the mind-blowing fact about Taipei 101 is that it houses the biggest tuned mass damper (TMD) in the world! It's basically a giant metal ball that counteracts big transient loadings like wind and earthquakes to reduce the sway of the supertall tower.

The TMD is supported by hydraulic damper arms and bumper systems which function in the same way as a car's shock absorber. When large forces act upon the tower, the TMD sways in the opposite direction, bringing the entire building into equilibrium by damping out the transient forces using the ball's mass. How amazing is that?

This earthquake damper system is located between the 87th floor and the 92nd level.

5. Philippine Arena also happens to be an earthquake-resistant building

The Philippine Arena is the world's largest domed arena and is an amazing earthquake-proof structure. It is owned by the Christian group Iglesia Ni Cristo (INC) which commissioned this 55,000 seating capacity arena for their 100th anniversary three years ago on July 27, 2014.

It is also the centerpiece of the tourism enterprise zone called Ciudad De Victoria in Bulacan, Philippines. The arena was designed by Australian architecture firm Populous and the elite engineering firm Buro Happold.

The Philippine plate sits along the so-called Pacific Ring of Fire, home of the world's most notorious and active chain of earthquake fault lines. Previous earthquakes in the country have reached as much as , and have claimed thousands of lives. Seismic activities have also been responsible for volcanic eruptions and tsunamis in the region.

Philippine Arena's vast stadium roof, spanning 170m, was engineered to withstand severe transient loadings such as earthquakes, winds, and typhoons. During an earthquake, the lateral loads that generate throughout the structure can reach up to 40% of its mass.

Buro Happold cleverly responded with an independent base design for the entire structure, which means that the main structural body of the arena is isolated from its base and foundation. The gap between the main structure and base foundation system is composed of lead rubber bearings (LRB) which are a flexible arrangement of materials with high energy dissipation properties.

This allows the base and foundation system to freely move with the force of the earthquake, while the top structure remains stationary. This is truly an amazing earthquake engineering feat!

That's all for now folk.

So, the next time you visit one of these structures, take a moment to appreciate not only the architectural aesthetics but also the magnificent engineering feats they have to offer.

While there's no way of defeating the awesome power of nature, our engineers can tinker with the tools at hand to at least attempt to tame her. These, and other earthquake-resistant buildings around the world, are a testament to the ingenuity of man and the skill of the engineers behind their construction.

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Top 5 Earthquake Resistant Structures Around the World

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Earthquakes are one of the most destructive forces of nature. Structures can suffer severe damage when an earthquake strikes. That's why, seismic loadings must be taken into account when designing structures, especially skyscrapers. Let's roam around the world together and discover the top 5 earthquake-proof structures and learn how buildings can be designed to resist extreme seismic loadings.

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Video: Shock absorber designed to protect buildings during earthquakes

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We are getting a first look at a new type of shock absorber designed to protect buildings during an earthquake, and it is being used right here in the Bay Area.

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High Tech Quake Survival

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Wired Science 8: High Tech Quake Survival

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How To Stop Structures from SHAKING: LEGO Saturn V Tuned Mass Damper

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ARTICLE: 5 Tips to Building an Earthquake Resistant Structure 

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ARTICLE: 5 Tips to Building an Earthquake Resistant Structure 

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Defeating Earthquakes

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Defeating Earthquakes: Ross Stein at TEDxBermuda

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How engineering earthquake proof buildings could save lives.

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Built-In Damage Prevention

On September 20, a massive 7.1 magnitude earthquake shook Mexico's capital city. Most of the approximately 230 deaths weren't from the original movement of the ground, however-in this quake, as in many others, collapsing buildings were the primary killer.

During an earthquake, the energy released by the movement of huge segments of the Earth's crust generate powerful forces that spread across hundreds of kilometers. When the base of a building shakes or lurches from the force of an earthquake, the difference between the top and bottom of the building can introduce new stress and strain onto the materials that support the structure, causing them to rupture.

Over the past few decades, new designs and materials have meant that buildings in Mexico City and elsewhere have become better engineered to withstand the forces involved during a quake, but they are far from infallible. Researchers are developing novel techniques to ensure that future structures are even better equipped to avoid collapse. In fact, they may be able to predict or even prevent earthquakes before they happen. But before we get there, we need to understand how our current structures work (and don't work).

Andrew Whittaker, a professor of civil engineering at the University of Buffalo, notes that a building during an earthquake is like a person standing on a plank supported on a roller. If someone moves the roller, the base can no longer support the upper weight, which could cause the person to fall. In general, the taller the building, the stronger the difference in forces between the bottom and the top, increasing the likelihood that the material could break.

That's why many cities in earthquake zones had restrictions on how many stories a building could have, according to Thomas Heaton, a professor of geophysics and civil engineering at the California Institute of Technology.

Of course, some materials are better at handling this changing energy than others. Wood works surprisingly well- "Wood is, in a sense, ideal in that it's extremely lightweight compared to its structural stiffness and strength," Heaton tells Futurism. Concrete is typically a brittle material, but when it's reinforced with steel rebar, it becomes much more elastic when shaken side to side. Others fare far worse: adobe clay buildings (millions of which were destroyed during the 2015 Nepal quake) and masonry (those made of brick or stone and held together by mortar).

The design of the structure, too, can concentrate or dissipate energy from an earthquake. Engineered wood, such as laminated wood, makes up the frame of the house. The beams are supported with sheer walls, which are designed to collapse under pressure from an earthquake, and are connected with metal bracings that loosen during shaking. The whole house is securely fastened to the foundation to prevent it from slipping off during a quake. Many modern skyscrapers do surprisingly well in earthquakes because the force exerted by strong winds demand that they are built to be flexible. Older structures can be retrofitted to be equipped with today's safer techniques, but that's sometimes more expensive than simply building something new.
"When I look at [structures] that people think are beautiful, open airy things full of windows, I just see crushed human bodies waiting to happen."
The structures that would do best in an earthquake would be windowless, concrete entities, the kind of thing that most architects would deem hideous. "When I look at [structures] that people think are beautiful, open airy things full of windows, I just see crushed human bodies waiting to happen," Heaton says.

Some newer, more sophisticated structures are built with a technique called base isolation. Rubbery devices are installed near the foundation of the building to absorb the energy from an earthquake, preventing it from dissipating throughout the frame. "You can think about it as something like a shock absorber in a motor vehicle scaled up to a building level," Whittaker says. Base isolation is still expensive, so it's primarily employed in buildings that are used by large numbers of people or those that would be important in an emergency, such as hospitals and airports.

Apple Park 2, the tech company's new campus, recently became the largest base-isolated structure in the world.

A Shaken City

Over the past century, engineers and architects have learned a lot about how to make structures more impervious to earthquakes.

But more knowledge is not a foolproof way to prevent damage. The most recent quake in Mexico City was an unfortunate reminder.

It's far from the first time that a quake in Mexico City has become a cautionary tale - the infamous 1985 earthquake left 10,000 people dead and 30,000 injured. Mexico is wedged between two tectonic plates, making it one of the most seismically active countries in the world. The city itself is built on an ancient lakebed and is actively sinking. Its soft soil is reminiscent of pudding, as one geologist recently told Buzzfeed, so during an earthquake it bounces more than hard rock, which has the potential to cause more buildings to collapse.

Part of the danger comes from the types of buildings that are most common there. "A lot of the buildings in Mexico City are non-ductile structures. In photos [of the destruction] you see beams, columns, and connections-they've come apart," Domniki Asimaki, professor of mechanical and civil engineering at the California Institute of Technology, tells Futurism.

Mexico has excellent engineers and fitting building codes, Whittaker notes. But most buildings in Mexico City are older, built to different specifications that may make them a hazard today. "Most modern constructions and modern codes can sustain earthquake loads pretty well. It's the older buildings, constructed under older codes or assumptions, that...were not necessarily designed for the same forces," Jason McCormick, associate professor of civil and environmental engineering at the University of Michigan, tells Futurism.

In this most recent seismic event, too many buildings still weren't ready. Mexico City simply got lucky that the quake wasn't stronger, according to the New York Times.

A Better Prepared Future

Anyone building a structure today has available the most sophisticated earthquake technology that has ever existed. But engineers are determined to make the future even better.

New materials might help buildings be better equipped for earthquakes to come. McCormick is developing polymer or metal foams, which are currently used in the aerospace industry, that could be scaled up to fit into joints between structural elements to absorb energy and prevent substantial damage. He's also working on shape memory alloys that would not only absorb energy, but also re-center a building pushed off-kilter during a quake, reducing the need for repairs. Others are working on self-healing materials - capsules in concrete that would repair a crack in a building frame or foundation that resulted during an earthquake.

Still others are developing materials that could change stiffness depending on the forces being exerted on them. Controlled by an electrical circuit and used at the joints between framing materials, these materials could soften during an earthquake so that they absorb the energy flowing into the building and prevent damage to its structure, Asimaki says. A building equipped with sensors over its base and height could function similarly to dissipate energy from an earthquake.

But there's a catch. The building industry is notoriously slow to change, Whittaker points out. Any materials created today have to be vetted by the building authorities, then worked into building codes. That means that it might take decades to see these new materials in use. That lethargy is compounded by some complacency in some of the most earthquake-prone regions. In California, for example, a strong quake hasn't happened since 1994's Northridge quake in Los Angeles or, you could even argue, since 1906, when a powerful temblor nearly decimated San Francisco. "Even in California, my generation hasn't seen a big one. My parents haven't," Asimaki says. "We don't have a memory of these things."

So instead of clamoring for better technology or insisting their residences are better engineered for impending threats, residents in these areas might be satisfied with the bare minimum of earthquake preparedness. That's especially true for stronger quakes. "I'm confident that we do know how to build structures that can go through the most severe earthquake shaking, but we're not currently doing that," Heaton says. "Things have been too quiet. People are too busy making money to really invest in what's necessary based on things that we've learned in last 20 to 30 years."

In the next few decades, researchers may be able to achieve an engineering feat they've worked towards for years: predicting earthquakes. Though we already have early warning systems in places like California and Japan, these give people at most a minute to find a safe place. Future systems could work better, giving people even more time. To truly understand the nature of earthquakes and the chaotic forces involved in them, seismologists need even more data, from satellite data of incremental ground movements to information gathered from sensors deep in the earth-expensive experiments that are too resource-intensive for any single research team, Asimaki notes.

In the next century, cities will be designed to take the dangers of earthquakes into account, Asimaki suspects. Electricity, phone lines, traffic lights, and transportation will automatically shut off before an earthquake hits. That could prevent them from causing further damage, as ruptured electrical and gas lines are some of the biggest reasons that fires plague cities after earthquakes.

Even further into the future, it's possible that we could diffuse an earthquake's energy before it ruptures destructively. We could cause a smaller, controlled quake using liquid pressure, the way we are already doing by accident during the fracking process and which NASA has proposed doing to neutralize the enormous volcano under Yellowstone. "That's definitely far away. But that's something that's not impossible," Asimaki says.

As for the most recent quake in Mexico, engineers and seismologists will learn from it. Figuring out just what those lessons are will take time. And yet it's surprising that earthquakes are still so mysterious to us. "One of the world's greatest unsolved physics problems is how earthquakes work in the first place," Heaton says. With every new quake, even the destructive ones, humans inch closer to understanding them.

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How engineering earthquake-proof buildings could save lives

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On September 20, a massive 7.1 magnitude earthquake shook Mexico's capital city. Most of the approximately 230 deaths weren't from the original movement of the ground, however-in this quake, as in many others, collapsing buildings were the primary killer.

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ARTICLE: The Science Behind Earthquake Proof Buildings

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ARTICLE: The Science Behind Earthquake Proof Buildings

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Chicago, IL - Ever since humans began engineering buildings, the Earth has been knocking them down. Before starting any major construction project, engineers must evaluate the building site's seismic activity and propose an appropriate design. Although poorly-built structures can sometimes resist vertical loads, horizontal loads cause the worst damage, often collapsing buildings on the first shake.

To earthquake-proof buildings, engineers must ensure that the structures and their foundations are resistant to potential horizontal loads by employing a number of key design features:

Diaphragms

Diaphragms are the primary component of a building's horizontal structure, including the floors and the roof. To earthquake-proof a building, diaphragms must be placed on their own deck and strengthened horizontally to share forces with vertical structures.

Trusses

Trusses strengthen the diaphragm where the deck is weakest. Simply put, they are diagonal structures that are inserted into the rectangular areas of the frame.

Cross-Bracing

Engineers incorporate a variety of columns, braces, and beams to transfer seismic forces back to the ground. Cross braces incorporate two diagonal sections in an X-shape to build wall trusses.

Shear Walls

To help resistance swaying forces, engineers use vertical walls, known as shear walls, to stiffen the structural frame of the building. These can be used in place of braced frames or in addition to them.

Moment-Resisting Frames

Since shear walls limit a building's flexibility, some designers choose moment-resisting frames to allow positive movement. Although columns and beams can bend, joints and connectors stay rigid. These features also give building designers more flexibility to create exterior walls, ceilings, and arrange building contents.

A Light Roof

As a general rule, the roofs of earthquake safe structures must be as light as possible. Many builders prefer profiled steel cladding on light-gauge steel Zed purlins or a double-skin with insulation and spacers.

The World's Biggest Earthquake-Proof Buildings

U.S. Bank Tower in Los Angeles - This 1,018-foot building was designed to withstand a 8.3 magnitude earthquake

The Burj Khalifa in Dubai - This 2,717-foot building can withstand earthquakes between 5.5 and 7.0 on the Richter scale

Yokohama Landmark Tower in Japan - This 972-foot building sits on rollers, has an active mass damper system, and is made from flexible materials

Taipei 101 in Taiwan - This 1,671-foot building houses a 730-ton steel ball inside to counteract swaying from seismic tremors

Transamerica Pyramid in San Francisco - This 853-foot high building sits atop a 52-foot steel and concrete foundation, which helped it survive a 7.1 magnitude quake in 1989

Engineers around the world continue to test new design theories to produce buildings that can withstand the worst natural disasters. Researchers at Stanford and Northeastern University recently tested a new system on a 26-foot tall with the world's largest earthquake simulator in Japan. Instead of structural elements, steel fuses absorbed the shock of an 7+ magnitude earthquake and cables pulled the building back into place when the shaking stopped. These are the types of buildings that will solidify the next step in environmentally-sustainable construction. As one of the participating San Francisco engineers, Jim Malley, put it, "our sustainable design is the ability not to have to tear buildings down after earthquakes, but to use them for hundreds of years."

*Photo credit: Shustov, Brad Wilkins via WikiMedia Commons

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The Science Behind Earthquake-Proof Buildings

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Chicago, IL - Ever since humans began engineering buildings, the Earth has been knocking them down. Before starting any major construction project, engineers must evaluate the building site's seismic activity and propose an appropriate design. Although poorly-built structures can sometimes resist vertical loads, horizontal loads cause the worst damage, often collapsing buildings on the first shake.

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VIDEO: TedEd: Why do Building fall in Earthquakes? 

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VIDEO: TedEd: Why do Building fall in Earthquakes? 

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Why do buildings fall in earthquakes? - Vicki V. May

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Throughout history, earthquakes have taken many lives and destroyed property in all parts of the world. While the smallest quakes are often not felt by humans, the largest ones have destroyed entire cities, causing billions of dollars worth of damage.

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ARTICLE: 10 Technologies that Help Building Resist Earthquakes 

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ARTICLE: 10 Technologies that Help Building Resist Earthquakes 

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The Bronze Age saw the rise of several successful civilizations, including a few that managed to build impressive cities with ordered grids and sophisticated plumbing. Now, scientists think that tectonic activity may have contributed to the demise of some of these ancient cultures. For example, research conducted at the city of Megiddo (now part of present-day Israel) suggests that a massive earthquake may have devastated the city, leading to the sandwich-like layers found in excavations. And a series of earthquakes may have brought down the Harappan civilization (in what's now Pakistan), which disappeared suddenly in 1900 B.C.E.

We're just as susceptible today to the aftereffects of powerful earthquakes. When exposed to the sudden lateral forces produced by seismic waves, even modern buildings and bridges can fail completely and collapse, crushing the people in, on and around them. If anything, the problem has become worse as more people live in urban environments and as structures have grown. Luckily, over the last few decades, architects and engineers have devised a number of clever technologies to ensure that houses, multidwelling units and skyscrapers bend but don't break. As a result, the building's inhabitants can walk out unharmed and start picking up the pieces.

On the next few pages, we've assembled 10 of these temblor-thwarting technologies. Some have been around for several years. Others, like the first item in our countdown, are relatively new ideas that are still being tested.

Engineers and seismologists have favored base isolation for years as a means to protect buildings during an earthquake. As its name suggests, this concept relies on separating the substructure of a building from its superstructure. One such system involves floating a building above its foundation on lead-rubber bearings, which contain a solid lead core wrapped in alternating layers of rubber and steel. Steel plates attach the bearings to the building and its foundation and then, when an earthquake hits, allow the foundation to move without moving the structure above it.

Now some Japanese engineers have taken base isolation to a new level. Their system actually levitates a building on a cushion of air. Here's how it works: Sensors on the building detect the telltale seismic activity of an earthquake. The network of sensors communicates with an air compressor, which, within a half second of being alerted, forces air between the building and its foundation. The cushion of air lifts the structure up to 1.18 inches (3 centimeters) off the ground, isolating it from the forces that could tear it apart. When the earthquake subsides, the compressor turns off, and the building settles back down to its foundation. The only thing missing is the theme song from the "Greatest American Hero."

Damping can take many forms. Another solution, especially for skyscrapers, involves suspending an enormous mass near the top of the structure. Steel cables support the mass, while viscous fluid dampers lie between the mass and the building it's trying to protect. When seismic activity causes the building to sway, the pendulum moves in the opposite direction, dissipating the energy.

Engineers refer to such systems as tuned mass dampers because each pendulum is tuned precisely to a structure's natural vibrational frequency. If ground motion causes a building to oscillate at its resonance frequency, the building will vibrate with a large amount of energy and will likely experience damage. The job of a tuned mass damper is to counteract resonance and to minimize the dynamic response of the structure.

Taipei 101, which refers to the number of floors in the 1,667-foot-high (508-meter-high) skyscraper, uses a tuned mass damper to minimize the vibrational effects associated with earthquakes and strong winds. At the heart of the system is a 730-ton (660-metric-ton), gold-colored ball suspended by eight steel cables. It's the largest and heaviest tuned mass damper in the world.

In the world of electricity, a fuse provides protection by failing if the current in a circuit exceeds a certain level. This breaks the flow of electricity and prevents overheating and fires. After the incident, you simply replace the fuse and restore the system to normal.

Researchers from Stanford University and the University of Illinois have been experimenting with a similar concept in the quest to build an earthquake-resistant building. They call their idea a controlled rocking system because the steel frames that make up the structure are elastic and allowed to rock on top of the foundation. But that by itself wouldn't be an ideal solution.

In addition to the steel frames, the researchers introduced vertical cables that anchor the top of each frame to the foundation and limit the rocking motion. Not only that, the cables have a self-centering ability, which means they can pull the entire structure upright when the shaking stops. The final components are the replaceable steel fuses placed between two frames or at the bases of columns. The metal teeth of the fuses absorb seismic energy as the building rocks. If they "blow" during an earthquake, they can be replaced relatively quickly and cost-effectively to restore the building to its original, ribbon-cutting form.

In many modern high-rise buildings, engineers use core-wall construction to increase seismic performance at lower cost. In this design, a reinforced concrete core runs through the heart of the structure, surrounding the elevator banks. For extremely tall buildings, the core wall can be quite substantial -- at least 30 feet in each plan direction and 18 to 30 inches thick.

While core-wall construction helps buildings stand up to earthquakes, it's not a perfect technology. Researchers have found that fixed-base buildings with core-walls can still experience significant inelastic deformations, large shear forces and damaging floor accelerations. One solution, as we've already discussed, involves base isolation -- floating the building on lead- rubber bearings. This design reduces floor accelerations and shear forces but doesn't prevent deformation at the base of the core-wall.

A better solution for structures in earthquake zones calls for a rocking-core wall combined with base isolation. A rocking core-wall rocks at the ground level to prevent the concrete in the wall from being permanently deformed. To accomplish this, engineers reinforce the lower two levels of the building with steel and incorporate post-tensioning along the entire height. In post-tensioning systems, steel tendons are threaded through the core wall. The tendons act like rubber bands, which can be tightly stretched by hydraulic jacks to increase the tensile strength of the core-wall.

Author's Note: 10 Technologies That Help Buildings Resist Earthquakes

When the 2011 Virginia earthquake struck, I was about 55 miles (89 kilometers) from the epicenter. It produced a locomotive-like rumbling and moved the earth in an unsettling way that's hard to describe. In the small towns of Louisa and Mineral, near my mother's house, a couple of structures collapsed, and many more experienced significant damage. While the quake itself was frightening, what was more disturbing was our collective sense that, being so far from the Ring of Fire and the constant threat of tectonic activity, we were somehow insulated from these kinds of events. Makes me wonder if the building codes in Virginia have been updated to incorporate some of these earthquake-resistant technologies.

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