Wednesday, February 28, 2024

Japan is inspired by creative ideas to build earthquake-resistant homes

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For more than a century, Japan has been able to build earthquake-resistant homes on this island known for its severe earthquakes. Last week, after a 7.5-magnitude earthquake hit Ishikawa Prefecture on Japan's west coast, scenes of buildings reduced to rubble were broadcast around the world.

According to Robert Keller, a professor of seismology at the University of Tokyo, Ishikawa could have easily escaped. Keller spoke about the Japan earthquake: “The design of modern buildings works very well,” noting that “the old houses with heavy clay tile roofs were the worst,” even though most of the single-family homes were damaged, “it didn't completely collapse.”

Anti-earthquake architects say, “Earthquakes don't kill people, it's the buildings that collapse on them that kill them.” In one of the world's most earthquake-prone countries, architects and urban planners have long tried to disaster-proof cities and towns against major tremors through ancient wisdom, modern innovations and ever-evolving building codes.

Since the Great Kanto earthquake that destroyed large parts of Tokyo and Yokohama 100 years ago, building technology in Japan has grown dramatically, starting with applications of large-scale so-called “dumpers” that swing like pendulums. In skyscrapers, structures have springs or ball bearings that allow the buildings to swing independently of their foundations. These findings often focus on a simple and long-understood idea: flexibility gives building structures a greater chance of survival.

“A lot of buildings, especially hospitals and critical structures, rest on these rubber bearings so that the building itself can shake,” says Miho Maserio, an associate professor of architecture and urbanism at the Massachusetts Institute of Technology. He adds: “In theory, it all comes back to the idea that the building can move with the movement of the ground, rather than resisting it.”

This principle has been used in Japan for centuries. For example, many traditional wooden temples in the country have survived earthquakes, even in the absence of modern structures. Take, for example, the 180-foot-tall (55-meter) Toji Temple built in the 17th century near Kyoto. The temple survived the Great Hanshin Earthquake of 1995, also known as the Gobi Earthquake, when other buildings collapsed. close to him. In particular, the remarkable survival rate of the temples is due to the long shinbashira, central columns made of tree trunks used by Japanese architects for at least 1,400 years.

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Whether anchored to the ground, resting on a beam, or suspended from above, these columns bend and flex as the building's individual floors move in opposite directions. The resulting movement, compared to a sliding snake, helps resist the force of vibration, aided by interlocking joints, loose arches and wide roof cornices.

Learning from tragedy

Buildings in Japan today do not resemble Buddhist temples, but skyscrapers certainly do. Although the country imposed a height limit of 31 meters until the 1960s due to risks from natural disasters, architects were allowed to build taller. Today, Japan has 270 buildings taller than 150 meters, the fifth-tallest in the world, according to data from the Council on Buildings and Urban Habitat.

Using steel frames to add flexibility to the more rigid concrete, tall designers went bolder by creating “base isolation” systems such as large counterweights and rubber bearings that acted as shock absorbers.

The real estate firm behind Japan's tallest new building, which opened in Tokyo's Asabutai Hills project last July, says its earthquake-resistant design features, including a wide range of dampers, will encourage companies to continue their operations even during a major seismic event. It was almost as powerful as the 9.1-magnitude Tohoku earthquake in 2011.

Building regulations gradually evolved throughout the twentieth century, but a law introduced in 1981 called the Shin Taishin, or New Standard Revision for Earthquake-Resistant Buildings, was a direct response to the Miyagi Sea earthquake three years earlier.

The new standards have proven more effective by setting higher requirements for the load-bearing capacity of new buildings, requiring more “floor clearance” (the amount of floors relative to each other), among other things. Some pre-1981 standards (known as “Q-tashin” or “pre-seismic resistance”) may be more difficult to sell and more expensive to insure.

The first real test of Shin Taishin's law came in 1995 when the Great Hanshin Earthquake in the southern part of Hyogo Prefecture caused widespread destruction. The results were stark: 97% of the collapsed buildings were built before 1981, according to the Global Facility for Disaster Reduction and Recovery.

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Innovation and Productivity

A 1995 earthquake spurred a national campaign to retrofit older buildings to 1981 standards, which city officials encouraged through grants. Innovation continued in the decades that followed, with Japanese architects often at the forefront of seismic design.

For example, Kengo Kuma, one of the country's best-known architects, teamed up with textile company Komatsu Material in 2016 to create a screen of thousands of braided carbon fiber wires that stabilizes the company's headquarters (the company is located 85 miles from the epicenter of last week's earthquake) on a tent-like floor. Most recently, he was involved in the design of a kindergarten building in South Cochin Prefecture, which features a checkerboard-style earthquake-resistant wall structure.

Elsewhere, major Japanese architects such as Shigeru Ban and Toyo Ito were distinguished by their use of cross-timbering, a new type of engineered wood whose inventors believed it could change the way tall buildings were constructed. Despite plans for a 1,148-foot cross-timber tower in Tokyo proposed by Japan's Sumitomo Forestry, the first full-scale earthquake simulation test with an engineered timber tower was conducted last spring at the University of California, San Diego. That may not be possible due to Japan's strict building codes.

“You have a lot of tall buildings, and a lot of effort has gone into designing them to be safe, but those designs are mostly based on computer simulations,” says Robert Keller. He adds: We won't know whether these simulations are accurate or not until a major earthquake occurs. If one of these tall buildings collapses, there will be massive damage.

A question that has long vexed engineers and seismologists in Japan: What if a major earthquake struck a city like Tokyo directly, something officials in the Japanese capital have warned has a 70 percent chance of occurring in the next 30 years. . Tokyo is probably reasonably safe, but there's no way to know for sure until the next big quake, many engineers and seismologists say.

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• Since the Great Kanto earthquake that destroyed large parts of Tokyo and Yokohama 100 years ago, building technology in Japan has evolved dramatically, swinging like a pendulum with large-scale “dumpers.” Inside skyscrapers.

• The remarkable survival rate of the temples has long been attributed to the “shinbashira,” central columns made of tree trunks used by Japanese architects for at least 1,400 years.

extinguishers

“Dampers” are a type of seismic damping system and are used in high-rise buildings to resist earthquake loads. They were approved and used in the 1950s for facilities in the World Trade Building in the United States, and their use became widespread in the 1980s. They were used to reinforce existing facilities.

“Dumpers” are similar to a car's shock absorbers to reduce the severity of collisions when hitting bumps. Damper consists of a liquid with a specific viscosity coefficient, which is placed in critical buildings and bridges to absorb the shocks that affect the building during earthquakes and reduce the effect of vibration waves on the building. “Dumpers” are very expensive, and a special task force is required to design and implement this technology in the building. Their location is determined by the structural engineer according to the design, and there must be coordination with the architect.

Earthquake building codes

Japan is a seismically active country, and has some of the strictest seismic building standards in the world. Although building codes are regularly updated, a major change took place in the Building Standards Act in 1981. Buildings built according to pre-1981 standards are called Q-Taishin and buildings built according to the new standards are called Shin-Taishin. This is a very important distinction for many Japanese looking to buy an apartment. The recent 9.0 Tohoku earthquake has put seismic building codes at the forefront of many buyers' minds.

Rolf Colon
Rolf Colon
"Creator. Award-winning problem solver. Music evangelist. Incurable introvert."

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