How Japan spent more than a century protecting its buildings from earthquakes

(CNN) — Scenes of buildings reduced to rubble have been seen around the world this week after a 7.5-magnitude earthquake struck Ishikawa Prefecture on Japan’s west coast on Monday.

The full extent of the damage remains unclear. According to authorities, at least 270 homes were destroyed in the area, but the final number is likely to be much higher. The figure does not include cities such as Suzu or Wajima, just 32 kilometers from the epicenter and home to more than 27,000 residents, where firefighters said about 200 buildings were burned, public broadcaster NHK reported.

The reports recount the personal tragedies faced by many residents in the area. However, while no two earthquakes are directly comparable, earthquakes of similar magnitude in other parts of the world, such as the 2005 magnitude 7.6 quake that collapsed more than 30,000 buildings in Kashmir, tend to cause greater damage.

In contrast, Ishikawa Prefecture likely escaped unscathed, said Robert Geller, professor emeritus of seismology at the University of Tokyo. The day after Japan’s earthquake, he told CNN that “modern architecture seems to be holding up very well,” noting that older construction homes “with heavy clay tile roofs” seemed It’s worse.

“Most of the single-family homes were damaged but not completely collapsed.”

A proverb in seismic design states that earthquakes do not kill people, they only destroy buildings. In one of the most earthquake-prone countries in the world, architects, engineers and urban planners have long tried to protect cities from the effects of major earthquakes by combining ancient wisdom, modern innovation and evolving building codes.

A building in Osaka, Japan, has been reinforced to withstand earthquakes.  (Image credit: Trevor Mogg/Alamy Stock Photo)

A building in Osaka, Japan, has been reinforced to withstand earthquakes. (Image credit: Trevor Mogg/Alamy Stock Photo)

From large “shock absorbers” that swing like a pendulum inside a skyscraper, to spring or ball bearing systems that allow a building to swing independently of its foundation, technology has advanced since the Great Kanto Earthquake destroyed much of Tokyo and Yokohama Huge progress. More than 100 years ago.

But these innovations focused above all on a simple and well-known idea: flexibility gives structures the best chance of survival. “Many buildings, especially hospitals and important critical structures, rely on these rubber (bearings) so that the building itself can function,” explains Miho Mazereeuw, associate professor of architecture and urban planning at the Massachusetts Institute of Technology (MIT), in an upcoming publication. Japan’s culture of disaster preparedness is analyzed in a new book, “Designing Before Disaster.”

“Conceptually, it comes down to the idea that you have to allow the building to move with it, rather than resist the movement of the earth.”

This principle has been used in Japan for centuries. For example, many of the country’s traditional wooden towers have survived earthquakes (and are more likely to die in fire or war), even though modern buildings have not. For example, the 55-meter-tall Toji Tower near Kyoto, built in the 17th century, survived the 1995 Great Hanshin Earthquake (also known as the Kobe Earthquake) while many nearby buildings collapsed.

A 17th-century five-story pagoda at Toji Temple in Kyoto.  (Image credit: Ivan Marchuk/Alamy Stock Photo)

A 17th-century five-story pagoda at Toji Temple in Kyoto. (Image credit: Ivan Marchuk/Alamy Stock Photo)

Japan’s traditional architecture has much in common with that of neighboring Korea and China, but differs in ways that reflect the country’s higher incidence of earthquakes.

In particular, the pagoda’s remarkable survival has long been attributed to the “shinbashira”, a central pillar made of tree trunks used by Japanese architects for at least 1,400 years.

Whether anchored in the ground, supported by beams or suspended from above, these columns bend and bend as the building’s floors move in the opposite direction from their neighbors. The resulting rocking motion (often compared to a slithering snake) helps to counteract the force of the shocks, aided by interlocking joints and loose supports and the roof’s wide eaves.

Learn from tragedy

Not all buildings in Japan today look like pagodas, but skyscrapers do.

Although the state had a strict height limit of 31 meters until the 1960s, architects have since been allowed to build taller buildings due to the dangers posed by natural disasters. According to the Council on Tall Buildings and Urban Habitat, Japan currently has more than 270 buildings over 150 meters tall, ranking fifth in the world in this ranking.

The use of a steel skeleton added flexibility to the already stiff concrete, which encouraged designers to develop large counterweights and “base isolation” systems that act as shock absorbers.

The real estate company behind Japan’s new tallest building, which opened in Tokyo’s Azabutaiyama development district last July, said its earthquake-resistant design features, including large shock absorbers, “will allow businesses to continue operating in the event of a strong earthquake.” Tohoku region, Japan, 2011 A record-breaking magnitude 9.1 earthquake occurred, shaking the entire country.

But in many places in Japan that don’t have skyscrapers, like Wajima, anti-seismic efforts focus more on protecting everyday buildings: homes, schools, libraries and shops. In this sense, Japan’s success is not only a technical issue, but also a political issue.

On the one hand, Japanese architecture schools have ensured that—perhaps because of the country’s history of natural disasters—students are trained in design and engineering, Mazereeuw explains. Climate risks faced by cities.

After the Great Kanto Earthquake of 1923, Tokyo was in ruins.  (Photo credit: Hulton Deutsch/Corbis/Getty Images)

After the Great Kanto Earthquake of 1923, Tokyo was in ruins. (Photo credit: Hulton Deutsch/Corbis/Getty Images)

“Unlike most countries, Japanese architecture schools combine architecture with structural engineering; in the U.S. they teach structural engineering courses, but those courses are very superficial,” he said, adding that in Japan the two disciplines “always is unified.”

Over the years, Japanese authorities have also tried to learn lessons from every major earthquake the country has suffered, with researchers conducting detailed studies and updating building regulations accordingly.

This process dates back to at least the 19th century, Mazereeuw said, explaining how the widespread destruction of new European-style masonry buildings in the 1891 Mino-Owari earthquake and the 1923 Great Kanto earthquake led to the creation of new urban planning laws and urban architecture .

The piecemeal evolution of building regulations continued throughout the 20th century. But the introduction of a code called the “New Amendment to Earthquake-Resistant Building Standards” in 1981 – a direct response to the Miyagi earthquake three years earlier – marked a before and after.

The new standards put forward stricter requirements for the load-bearing capacity of new buildings and required greater “story drift” (how many floors can be moved relative to each other), etc. The new standards have proven to be so effective that they are designed according to the pre-designed Homes built to the -1981 standards (called “kyu-taishin” or “earthquake resistance”) may be harder to sell and more expensive to insure.

The first real test of this rule came in 1995, when the Great Hanshin Earthquake caused widespread damage in southern Hyogo Prefecture. The results are overwhelming: 97% of collapsed buildings were built before 1981, according to the Global Foundation for Disaster Reduction and Recovery.

Innovation and preparation

The 1995 earthquake sparked a nationwide movement to adapt older buildings to 1981 standards, a process encouraged by municipalities through subsidies. In the decades since, innovation has continued, with Japanese architects often at the forefront of earthquake-resistant design.

For example, Kengo Kuma, one of Japan’s most renowned architects, collaborated with textile company Komatsu Matere in 2016 to develop a curtain composed of thousands of woven carbon fiber rods that anchored the company’s headquarters to the ground like a tent. superior. photo above). Most recently, he co-designed a kindergarten building in southern Kochi Prefecture that features a seismic checkerboard wall system.

Elsewhere, prominent Japanese architects such as Shigeru Ban and Toyo Ito have pioneered the use of cross-laminated timber (CLT), a new type of wood that proponents believe could change the way skyscrapers are built.

Earthquake-resistant columns used in the design of an old wooden house in Miyama, Kyoto Prefecture.  (Image credit: Eric Lafforgue/Art for All of Us/Corbis/Getty Images)

Earthquake-resistant columns used in the design of an old wooden house in Miyama, Kyoto Prefecture. (Image credit: Eric Lafforgue/Art for All of Us/Corbis/Getty Images)

Advanced computer models also allow designers to simulate seismic conditions and build accordingly. However, the limits of most disaster-resistant buildings are never tested.

“There are a lot of high-rise buildings, and we put a lot of effort into making them safe, but most of these designs are based on computer simulations,” said Geller of the University of Tokyo. “We may not know whether these simulations are accurate until a big earthquake occurs. If one of these skyscrapers collapses, it could cause a lot of damage.”

So a question that has long vexed Japanese engineers and seismologists remains: What would happen if a major earthquake directly shook a city like Tokyo, which authorities in the Japanese capital have warned has a 70% chance of happening within the next 30 years. %?

“Tokyo is probably quite safe,” he added. “But we won’t know for sure until the next big earthquake actually happens.”

CNN’s Eric Cheung and Saki Toi contributed to this report.

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