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How can we prevent walls from collapsing in earthquakes? | MIT School of Engineering

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How can we prevent walls from collapsing in earthquakes? | MIT School of Engineering

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Megan investigates

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10 Technologies That Help Buildings Resist Earthquakes | HowStuffWorks

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10 Technologies That Help Buildings Resist Earthquakes | HowStuffWorks

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Although earthquakes are among the least predictable natural hazards, losses to unprepared businesses can be substantial when they do occur. Affiliated FM, a commercial property insurer and loss prevention expert serving medium-sized companies, released actionable steps businesses can take to significantly prevent or reduce damage to their facilities from earthquakes.

"In the event of an earthquake, preparation measures can mean the difference between a business experiencing a distraction or major destruction," said Mike Lebovitz, vice president and manager of Affiliated FM. "For business owners with operations in historically active earthquake zones, it is critical for them to understand and identify the risks that earthquakes present as well as effectively address them."

Four sizable earthquakes have occurred in or off the coast of California since June 2005 and serve as a reminder of the seismic risk to businesses. According to the most recent "Progress Report for the California Earthquake Loss Reduction Plan 2002-2006" issued by the California Seismic Safety Commission in December 2003, individual business owners and corporate decision makers do not fully understand the potential economic losses resulting from earthquakes.

"Structural damage to buildings may be top of mind, but business owners should also consider shake damage to nonstructural systems, equipment and stock," said Lebovitz. "People may not realize that fires caused by damaged gas lines and the inability of broken sprinkler systems control those fires, pose the greatest threat immediately following an earthquake."

Fortunately, property damage caused by earthquakes and ensuing fires can be prevented or minimized by following a comprehensive emergency plan before and after an earthquake. To reduce the potential of business interruption, business owners should consider taking the following measures:

General Preparation:

Establish a comprehensive emergency action plan to control hazards;

Determine if secondary hazards from an earthquake exist as a result of a facility's location, such as a landslide, flooding or tsunami;

Establish and train an Emergency Response Team (ERT) covering all shifts to implement the emergency action plan, and stockpile emergency supplies that may be needed to support the ERT;

To prevent sliding of production equipment and utilities, such as boilers, generators and transformers, anchor items to the floor or to an adjacent wall; for shelved items, install restraining devices at the edges to prevent items from falling;

To prevent swinging of suspended ceilings, piping and ducts, brace items to the structure from which they are suspended;

Stock up on fire extinguishers and maintain an onsite hose with heavy water pressure.

To Prevent Fire:

Install seismic gas shutoff valves on the main service lines to each building and install automatic shutoff valves for flammable liquid and gas distribution systems;

To safeguard fire protection systems, brace sprinkler piping at regular lengths and at changes of direction, install flexibility for piping that spans joints or buildings, provide sufficient clearance of sprinkler heads and anchor water supply equipment;

To prevent overturning of materials and equipment that might result in fire, anchor items to the floor, adjacent walls or to each other in groups.

After an Earthquake Strikes:

Survey facilities for combustibles in contact with ignition sources with awareness that fire danger is greatest shortly after an earthquake;

Take inventory of damage in and around the facility and begin salvaging items as soon as possible to prevent further damage;
If sprinkler piping is damaged, empower ERT members to maintain as much fire protection in service as possible, bypass problem areas and provide alternate water supplies where possible;

Make certain that all sprinkler water supply valves are open and the water supply is freely flowing;

Check gas, water and electrical services for damage and shut off as necessary;

Repair any damaged fire protection systems immediately to prepare for aftershocks.

"With an approach to earthquake loss prevention as a long-term investment rather than a short-term expense, business owners will not only enjoy greater peace of mind, but can better ensure they will be in business for their clients and employees should Mother Nature unleash its fury," said Lebovitz.

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Although earthquakes are among the least predictable natural hazards, losses to unprepared businesses can be substantial when they do occur. Affiliated FM, a commercial property insurer and loss prevention expert serving medium-sized companies, released actionable steps businesses can take to significantly prevent or

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A Tested, Inexpensive Way to Protect Buildings from Earthquakes — NOVA Next | PBS

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A Tested, Inexpensive Way to Protect Buildings from Earthquakes — NOVA Next | PBS

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In 1985, construction workers in the southern California city of Rancho Cucamonga put the finishing touches on an unremarkable looking yet revolutionary building. Foothill Communities Law and Justice Center is a four-story courthouse located just 12 miles from the San Andreas fault, the crack in the Earth's crust responsible for the devastating 7.9 magnitude quake that struck southern California in 1857 and the infamous 1906 earthquake in San Francisco. Geologists think the fault is due for a "big one" with a magnitude that could top 8.0. If and when that comes, the Foothill Communities Law and Justice Center will be prepared, not because it's anchored in stone, but because sits atop its foundations on pads of rubber.

For decades, engineers have been using rubber in buildings and structures. Since the 1950s, it has been installed in highway bridges to cope with thermal expansion and in buildings to quell vibrations from trains and highways, though it wasn't until the early 1980s that the compound was finally used to isolate buildings from earthquakes. Where rubber bearings have been installed, they have been a huge success-and if used more widely, they have the potential to save countless lives and prevent billions of dollars in damage.

Despite that, many buildings still lack the protection that comes with proper seismic engineering. In developing countries, the problem is particularly acute. Take the magnitude 7.0 earthquake which struck Haiti in 2010 and killed more than 100,000 people, many of whom perished when buildings collapsed. Vulnerable structures also plague developed countries like the United States. A recent investigation by the Los Angeles Times discovered that more than 1,000 older concrete buildings in the city could collapse in the next major earthquake.

There are many ways to make a building resilient against earthquakes. In wood structures, extra strappings can be nailed to key parts of the frame. Steel-reinforced concrete is another option, with the strengths and weaknesses of each compound offsetting the other, though even that may not be enough to prevent damage in a large quake. Some buildings use dampers similar to shock-absorbers in a car. The most effective, though, may be base isolation, where the building is separated from the ground using dampers or bearings.

To isolate the base, engineers can turn to a variety of different bearings and dampers. Rubber bearings, like those installed in the Foothill Communities Law and Justice Center, are among the most promising. Like other bearings, they decouple the building from an earthquake's horizontal motions, literally providing a buffer between the building and the earthquake. The system doesn't absorb the earthquake's energy, but rather deflects it through the dynamics of the system. The earthquake's higher frequencies-and their destructive energy-aren't transmitted to the rest of the structure. Buildings built on rubber bearings will still shake during an earthquake, but they'll glide on their base rather than wobble dangerously.

With so many options available, what makes rubber bearings so appealing? For one, they're effective. The way they're constructed-thin sheets of natural rubber are bonded to thin steel plates-gives them high stiffness in the vertical direction while being very flexible in the horizontal direction. In other words, they are stiff enough to support a building, but pliant enough to deflect the energy of an earthquake. But perhaps more importantly, they're affordable, which could bring life-saving seismic safety to poorer, vulnerable countries.

Quelling Vibrations, Large and Small

The idea of reinforcing rubber blocks by thin steel plates was invented by French engineer Eugene Freyssinet. He recognized that the vertical capacity of a rubber pad was inversely proportional to its thickness, but its horizontal flexibility was directly proportional to the thickness. In other words, a thin piece of rubber could be stiff in one direction but flexible in another. Freyssinet is known for another engineering innovation, the development of prestressed concrete, and for the discovery of creep, or deformation, in concrete. Both of these are important parts of bridge engineering today, and it's possible that he invented the reinforced rubber pad to deal with two challenges of bridge building-supporting the heavy prestressed deck while allowing it to shrink as a result of creep and the prestress load.

Freyssinet's bearings have been used extensively throughout the world, though most of their use in buildings is to damp unwanted vibrations, like those from an underground train, a practice which originated in the United Kingdom in the 1960s. Since then, many projects in the U.K. have used natural rubber isolators, including low-cost public housing and a number of hospitals, where vibrations can disrupt precision diagnostic equipment.

In that same vein, the Benaroya Concert Hall in Seattle, completed in 1999, and the Walt Disney Concert Hall in Los Angeles, completed in 2003, both use rubber bearings to minimize vibrations. The Benaroya Concert Hall sits atop a train tunnel, while the Disney Concert Hall is built directly above a loading dock for the building next door. Bearings in both buildings work well to isolate vibrations, but they weren't designed to mitigate earthquakes. Instead, Benaroya and Disney have duplicate systems, though they certainly don't have to. My colleagues and I used the shake table at the Earthquake Engineering Research Center of the University of California, Berkeley to show that it was possible to design for both.

Old buildings can be retrofit to take advantage of base isolation. In California, Oakland City Hall and San Francisco City Hall, both of which were badly damaged in the 1989 Loma Prieta earthquake, now float above their foundations on dampers. The Los Angeles City Hall, which was damaged in the 1994 Northridge earthquake, was retrofitted with high-damping natural rubber bearings four years later. At 454 feet, is now the tallest seismically isolated building in the country.

Keeping the Structure Separate

Outside of the United States, Base isolation has been very actively pursued in Japan, one of the most earthquake-prone countries in the world. There, the first base-isolated building was completed in 1986, and one of the largest base-isolated buildings in the world is the West Japan Postal Computer Center in Sanda, Kobe Prefecture. This six-story, 500,000-square-foot structure is supported on 120 elastomeric isolators with a number of additional steel and lead dampers. During the infamous 1995 Kobe earthquake, the building-which was just 19 miles from the epicenter-experienced severe ground motion. Fortunately, the postal center wasn't damaged. The same couldn't be said of an adjacent fixed-based structure.

After the Kobe earthquake, more buildings in Japan were constructed using base isolation, including apartments and condominiums, which are normally constructed using traditional methods. Today, about 100 base isolated buildings are built in Japan each year, not including single family homes.

Now, Japanese engineers are taking the concept of isolation a step further with "ground isolation." In Sagamihara City outside Tokyo, they have built 21 separate buildings -six to 14 stories tall-on top of a three-acre concrete slab. The slab then sits on 150 isolation devices, including many very large rubber bearings, and all of the buildings move in sync. Ground isolation shows great promise and could bring base isolation to even more high-rise complexes.

Safer Structures for Everyone

Currently, most buildings that are base-isolated are large structures which house sensitive or expensive equipment, but there is increasing interest in using it in public housing, schools, and hospitals, especially in developing countries. A number of base-isolated demonstration projects have already been completed in a variety of countries, from Italy to Chile and Indonesia. Often, these buildings sit right next to identical, fixed-base structures, allowing engineers like myself to compare their behaviors during earthquakes. Time and again, we have seen base-isolated buildings emerge from an earthquake relatively unscathed compared with their neighbors.

My colleagues and I have high hopes that inexpensive base isolation technology, including natural rubber bearings, will be used around the world. One demonstration project is in Indonesia, where workers on a tea plantation in the southern part of West Java now live in a four-story, reinforced-concrete, base-isolated building. It contains eight low-cost apartment units and is supported by 16 high-damping natural rubber bearings.

Apart from base isolation, the building isn't substantially different from others in Java, which makes it less expensive to construct and more likely that it will be accepted by local building officials. The isolation bearings, which are inexpensive to manufacture, are located at ground level and are connected to the rest of the building using an innovative, cost-effective, and easy-to-install technique.

Rubber bearings like these are could dramatically change the way buildings in earthquake zones are designed and built. They allow historic buildings to be easily retrofit without losing their charm. They have the potential to expand earthquake engineering to inexpensive structures like condominiums and single-family homes, which today must rely on less sophisticated measures. And perhaps most significantly, rubber bearings could bring much needed safety and security to make buildings in earthquake-prone developing countries, preventing costly property damage and saving countless lives.

# data[].attributes.attachment_link.title
A Tested, Inexpensive Way to Protect Buildings from Earthquakes - NOVA Next | PBS

# data[].attributes.attachment_link.description
In 1985, construction workers in the southern California city of Rancho Cucamonga put the finishing touches on an unremarkable looking yet revolutionary building. Foothill Communities Law and Justice Center is a four-story courthouse located just 12 miles from the San Andreas fault, the crack in the Earth's crust responsible for the devastating 7.9 magnitude quake that struck southern California in 1857 and the infamous 1906 earthquake in San Francisco.

# data[].attributes.headline
10 Technologies That Help Buildings Resist Earthquakes | HowStuffWorks

# data[].attributes.subject
10 Technologies That Help Buildings Resist Earthquakes | HowStuffWorks

# data[].attributes.attachment_link.readable_text
In 1985, construction workers in the southern California city of Rancho Cucamonga put the finishing touches on an unremarkable looking yet revolutionary building. Foothill Communities Law and Justice Center is a four-story courthouse located just 12 miles from the San Andreas fault, the crack in the Earth's crust responsible for the devastating 7.9 magnitude quake that struck southern California in 1857 and the infamous 1906 earthquake in San Francisco. Geologists think the fault is due for a "big one" with a magnitude that could top 8.0. If and when that comes, the Foothill Communities Law and Justice Center will be prepared, not because it's anchored in stone, but because sits atop its foundations on pads of rubber.

For decades, engineers have been using rubber in buildings and structures. Since the 1950s, it has been installed in highway bridges to cope with thermal expansion and in buildings to quell vibrations from trains and highways, though it wasn't until the early 1980s that the compound was finally used to isolate buildings from earthquakes. Where rubber bearings have been installed, they have been a huge success-and if used more widely, they have the potential to save countless lives and prevent billions of dollars in damage.

Despite that, many buildings still lack the protection that comes with proper seismic engineering. In developing countries, the problem is particularly acute. Take the magnitude 7.0 earthquake which struck Haiti in 2010 and killed more than 100,000 people, many of whom perished when buildings collapsed. Vulnerable structures also plague developed countries like the United States. A recent investigation by the Los Angeles Times discovered that more than 1,000 older concrete buildings in the city could collapse in the next major earthquake.

There are many ways to make a building resilient against earthquakes. In wood structures, extra strappings can be nailed to key parts of the frame. Steel-reinforced concrete is another option, with the strengths and weaknesses of each compound offsetting the other, though even that may not be enough to prevent damage in a large quake. Some buildings use dampers similar to shock-absorbers in a car. The most effective, though, may be base isolation, where the building is separated from the ground using dampers or bearings.

To isolate the base, engineers can turn to a variety of different bearings and dampers. Rubber bearings, like those installed in the Foothill Communities Law and Justice Center, are among the most promising. Like other bearings, they decouple the building from an earthquake's horizontal motions, literally providing a buffer between the building and the earthquake. The system doesn't absorb the earthquake's energy, but rather deflects it through the dynamics of the system. The earthquake's higher frequencies-and their destructive energy-aren't transmitted to the rest of the structure. Buildings built on rubber bearings will still shake during an earthquake, but they'll glide on their base rather than wobble dangerously.

With so many options available, what makes rubber bearings so appealing? For one, they're effective. The way they're constructed-thin sheets of natural rubber are bonded to thin steel plates-gives them high stiffness in the vertical direction while being very flexible in the horizontal direction. In other words, they are stiff enough to support a building, but pliant enough to deflect the energy of an earthquake. But perhaps more importantly, they're affordable, which could bring life-saving seismic safety to poorer, vulnerable countries.

Quelling Vibrations, Large and Small

The idea of reinforcing rubber blocks by thin steel plates was invented by French engineer Eugene Freyssinet. He recognized that the vertical capacity of a rubber pad was inversely proportional to its thickness, but its horizontal flexibility was directly proportional to the thickness. In other words, a thin piece of rubber could be stiff in one direction but flexible in another. Freyssinet is known for another engineering innovation, the development of prestressed concrete, and for the discovery of creep, or deformation, in concrete. Both of these are important parts of bridge engineering today, and it's possible that he invented the reinforced rubber pad to deal with two challenges of bridge building-supporting the heavy prestressed deck while allowing it to shrink as a result of creep and the prestress load.

Freyssinet's bearings have been used extensively throughout the world, though most of their use in buildings is to damp unwanted vibrations, like those from an underground train, a practice which originated in the United Kingdom in the 1960s. Since then, many projects in the U.K. have used natural rubber isolators, including low-cost public housing and a number of hospitals, where vibrations can disrupt precision diagnostic equipment.

In that same vein, the Benaroya Concert Hall in Seattle, completed in 1999, and the Walt Disney Concert Hall in Los Angeles, completed in 2003, both use rubber bearings to minimize vibrations. The Benaroya Concert Hall sits atop a train tunnel, while the Disney Concert Hall is built directly above a loading dock for the building next door. Bearings in both buildings work well to isolate vibrations, but they weren't designed to mitigate earthquakes. Instead, Benaroya and Disney have duplicate systems, though they certainly don't have to. My colleagues and I used the shake table at the Earthquake Engineering Research Center of the University of California, Berkeley to show that it was possible to design for both.

Old buildings can be retrofit to take advantage of base isolation. In California, Oakland City Hall and San Francisco City Hall, both of which were badly damaged in the 1989 Loma Prieta earthquake, now float above their foundations on dampers. The Los Angeles City Hall, which was damaged in the 1994 Northridge earthquake, was retrofitted with high-damping natural rubber bearings four years later. At 454 feet, is now the tallest seismically isolated building in the country.

Keeping the Structure Separate

Outside of the United States, Base isolation has been very actively pursued in Japan, one of the most earthquake-prone countries in the world. There, the first base-isolated building was completed in 1986, and one of the largest base-isolated buildings in the world is the West Japan Postal Computer Center in Sanda, Kobe Prefecture. This six-story, 500,000-square-foot structure is supported on 120 elastomeric isolators with a number of additional steel and lead dampers. During the infamous 1995 Kobe earthquake, the building-which was just 19 miles from the epicenter-experienced severe ground motion. Fortunately, the postal center wasn't damaged. The same couldn't be said of an adjacent fixed-based structure.

After the Kobe earthquake, more buildings in Japan were constructed using base isolation, including apartments and condominiums, which are normally constructed using traditional methods. Today, about 100 base isolated buildings are built in Japan each year, not including single family homes.

Now, Japanese engineers are taking the concept of isolation a step further with "ground isolation." In Sagamihara City outside Tokyo, they have built 21 separate buildings -six to 14 stories tall-on top of a three-acre concrete slab. The slab then sits on 150 isolation devices, including many very large rubber bearings, and all of the buildings move in sync. Ground isolation shows great promise and could bring base isolation to even more high-rise complexes.

Safer Structures for Everyone

Currently, most buildings that are base-isolated are large structures which house sensitive or expensive equipment, but there is increasing interest in using it in public housing, schools, and hospitals, especially in developing countries. A number of base-isolated demonstration projects have already been completed in a variety of countries, from Italy to Chile and Indonesia. Often, these buildings sit right next to identical, fixed-base structures, allowing engineers like myself to compare their behaviors during earthquakes. Time and again, we have seen base-isolated buildings emerge from an earthquake relatively unscathed compared with their neighbors.

My colleagues and I have high hopes that inexpensive base isolation technology, including natural rubber bearings, will be used around the world. One demonstration project is in Indonesia, where workers on a tea plantation in the southern part of West Java now live in a four-story, reinforced-concrete, base-isolated building. It contains eight low-cost apartment units and is supported by 16 high-damping natural rubber bearings.

Apart from base isolation, the building isn't substantially different from others in Java, which makes it less expensive to construct and more likely that it will be accepted by local building officials. The isolation bearings, which are inexpensive to manufacture, are located at ground level and are connected to the rest of the building using an innovative, cost-effective, and easy-to-install technique.

Rubber bearings like these are could dramatically change the way buildings in earthquake zones are designed and built. They allow historic buildings to be easily retrofit without losing their charm. They have the potential to expand earthquake engineering to inexpensive structures like condominiums and single-family homes, which today must rely on less sophisticated measures. And perhaps most significantly, rubber bearings could bring much needed safety and security to make buildings in earthquake-prone developing countries, preventing costly property damage and saving countless lives.

# data[].attributes.attachment_link.title
A Tested, Inexpensive Way to Protect Buildings from Earthquakes - NOVA Next | PBS

# data[].attributes.attachment_link.description
In 1985, construction workers in the southern California city of Rancho Cucamonga put the finishing touches on an unremarkable looking yet revolutionary building. Foothill Communities Law and Justice Center is a four-story courthouse located just 12 miles from the San Andreas fault, the crack in the Earth's crust responsible for the devastating 7.9 magnitude quake that struck southern California in 1857 and the infamous 1906 earthquake in San Francisco.

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Building for the Big One
What do San Francisco, Tokyo, and Istanbul have in common? They are the three most densely populated cities on the planet where seismologists expect major earthquakes. While the events that will inevitably shake these cities may be similar, the tolls they will take on the cities' populations and infrastructures will be very different. Why? The answer lies in how their buildings and bridges are designed.

Most of the damage we associate with earthquakes involves human-built structures: people trapped by collapsed buildings or cut off from vital water or energy supplies. How a quake will affect the people of a city has a lot to do with how the city, its residents, and nearby governments have engineered structures and pipelines.

It might seem obvious to say that earthquakes do most of their damage by shaking the ground. But groundshaking is actually a complex phenomenon. Engineering the seismic safety of a structure involves the same considerations as any real estate venture-design, construction, and location, location, location.

When the ground beneath a building shakes, it makes the building sway as the energy of a quake's waves moves through it. You might think that a skyscraper would be more dangerous than a smaller office building, but in fact, the opposite is often true. Here's why:

The taller a structure, the more flexible it is. The more flexible it is, the less energy is required to keep it from toppling or collapsing when the earth's shaking makes it sway. You can feel this same phenomenon while you're riding a bus or subway. It requires less effort to remain standing if you flex your body and flow with the bumps and jolts than if you stiffly try to defy them.

Because shorter buildings are stiffer than taller ones, a three-story apartment house is considered more vulnerable to earthquake damage than a 30-story skyscraper. When planning the seismic safety of a building, structural engineers must design the support elements of shorter buildings to withstand greater forces than those of taller buildings.

Of course, the materials a building is constructed from also determine its strength, and again, flexibility is important. Wood and steel have more give than stucco, unreinforced concrete, or masonry, and they are favored materials for building in fault zones. Skyscrapers everywhere must be reinforced to withstand strong forces from high winds, but in quake zones, there are additional considerations. Engineers must design in structures that can absorb the energy of the waves throughout the height of the building. Floors and walls can be constructed to transfer the shaking energy downward through the building and back to the ground. The joints between supportive parts of a building can be reinforced to tolerate being bent or misshapen by earthquake forces.

Perhaps the most visually recognizable seismic safety feature of tall buildings is the truss. The TransAmerica pyramid in San Francisco is famous for its architecture: a wide base that narrows as it goes up increases the building's stability. A network of diagonal trusses at its base supports the building against both horizontal and vertical forces.

In addition to strengthening a building against earthquake shocks, engineers can actually reduce the force a building is subjected to. They install what are called base isolators, which isolate the base of the building from the earth's movements. Most are one of two forms. Some are like giant hockey pucks that squish and deform as the building rocks atop them, absorbing some of the energy of the shaking. Others are sets of two horizontal surfaces, plates made frictionless so that they will slide past each other. The building sits on the top plates, the bottom plates rest on the ground. When the earth lurches, only the bottom plates move, sliding back and forth under the top plates.

Location, location, location
Sometimes the characteristics of a particular earthquake and the ground a structure is on coincide in just the right (or wrong) way, and the quake is particularly devastating. Occasionally, a seismic wave hitting a building will have a frequency that just matches that structure's natural sway. In physics terms, the building has the same resonant frequency as the wave. When this happens, multiple waves at the resonant frequency pass through the structure, their effects amplifying each other. This makes for a very destructive force.

The impact of resonance was very apparent after a large quake in Mexico City in 1985. Mid-range buildings of 10-14 stories were in resonance with the seismic waves, causing those buildings to sufer more damage than shorter or taller ones.

As quake waves pass through the earth, they are filtered in different ways by different kinds of soils. Mexico City sits on a mud plain, which happened to allow waves of a particularly devastating frequency to strike the buildings. Surprisingly, Mexico City is quite far from the epicenter of the 1985 quake. But because of this resonance phenomenon, the city suffered much more damage than some other towns closer to the fault.

So, the ground below a structure can be as important a safety consideration as its construction. Bedrock absorbs more wave energy than sandy soils or landfill, so buildings on solid rock will be much less affected than those built on softer soils. And if softer soils have water in them, they can become a little like quicksand during an earthquake. When seismic waves pass through saturated soil, they give it a strong squeeze. The soil loses its strength and behaves like a liquid, a process called liquefaction. Buildings on top of liquefied soil sink, and often
topple.

Testing, testing. . . .
How can engineers know for sure that their designs will withstand quakes? The short answer is that they have to see the building through a temblor. Quakes in Los Angeles, California, and Kobe, Japan, saw the collapse of buildings and freeways that were built to strict seismic standards. In recent years, though, researchers have developed shake tables that can subject full-scale buildings to quakelike forces. In 2005, engineers at the University of California, San Diego tested a seven-story, 275-ton building to see whether it could withstand tremors like the ones delivered by the 1994 Northridge quake that hit Los Angeles. They can use the same shake table to test models of other new building designs.

Seismic strengthening tricks are great for new buildings, but most structures in earthquake zones were built before seismic engineering was developed. What about the beloved Golden Gate Bridge, designed by engineers using slide rules? And critical freeway overpasses vital to a city's traffic flow? For that, we have the after-the-fact fixes of retrofitting.

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Building for the Big One What do San Francisco, Tokyo, and Istanbul have in common? They are the three most densely populated cities on the planet where seismologists expect major earthquakes. While the events that will inevitably shake these cities may be similar, the tolls they will take on the cities' populations and infrastructures will be very different.

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How Do You Make a Building Invisible to an Earthquake? | Science | Smithsonian

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How Do You Make a Building Invisible to an Earthquake? | Science | Smithsonian

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Engineer William Parnell may have found a way to save at-risk cities from destruction

Smithsonian Magazine |

An inventive mathematician has a new idea for protecting buildings from earthquake damage: hide them.

William Parnell, of the University of Manchester in England, suggests wrapping a building's base, or at least key components, in specialized rubber that diverts certain temblor shock waves, leaving the building virtually untouched by them.

Parnell's "elastodynamic cloak," which engineers have just started testing, builds on a familiar concept: Waves headed directly for an object can be diffracted or bent so they miss it entirely. In the best-known example, scientists make objects appear invisible by encasing them within substances that have been engineered to alter the trajectory of light. When light waves pass through the cloak, they are channeled like water flowing around a rock. To an observer downstream, it appears that the light moved along a straight line, as if the object was not there.

Earthquakes are generated when two sections of the earth's crust suddenly slip against each other along a fault line, releasing energy that ripples through the surrounding rock as seismic waves. Among the most destructive are Love waves (named after British mathematician A.E.H. Love), which move the ground side to side in a zigzagging fashion.

According to Parnell's mathematical model, it's possible to channel seismic waves around an object by placing it at the precise center of an underground rubber cloak. Parnell calculates that if rubber is "pre-stressed"-stretched in a specific manner-it can mimic the capabilities of light-cloaking materials.

To be sure, engineers already lay rubber shock absorbers under some buildings to protect against earthquakes. But Parnell's cloak should prevent the structure from feeling Love waves at all. And, additional calculations indicate the cloak could potentially lessen the impact of other types of seismic waves-such as P waves, which alternately compress and stretch rock as they move through the ground.

While it may not be practical to surround whole buildings with rubber rings, cloaks could be placed around pilings or important electrical components. "Earthquake damage is not necessarily just caused by buildings falling down, but also by fires caused by electrical problems," Parnell says.

The earthquake cloak will be put to the test by engineers Biswajit Banerjee and Emilio Calius at Industrial Research Limited in New Zealand. They plan to create a pre-stressed region around a hole in a circular slab of rubber-like silicon. Then they'll measure whether vibrations are diverted around the hole.

Even if successful, Calius says, it will be many years before engineers could conceivably construct a building-size cloak. Still, if stressed rubber proves its worth, it might lend itself to other applications, such as soundproofing buildings from outside street noise. "Beyond invisibility," says Calius, "cloaking technology has profound implications for everyday life."

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How Do You Make a Building Invisible to an Earthquake?

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Smithsonian Magazine | An inventive mathematician has a new idea for protecting buildings from earthquake damage: hide them. William Parnell, of the University of Manchester in England, suggests wrapping a building's base, or at least key components, in specialized rubber that diverts certain temblor shock waves, leaving the building virtually untouched by them.