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  • The ground began to shake,

  • 32 million people here in Tokyo brace themselves for the worst.

  • 8.9 magnitude, now we know that's a big number.

  • It was the fifth largest earthquake in history.

  • But the real damage comes

  • from the ferocious tsunami that was unleashed.

  • In some areas,

  • the waves reached 40 meters in height-

  • Sweeping up everything in its path

  • including cars and ships

  • unable to withstand the strength

  • and the power of the surging water.

  • Japan is located

  • in the Pacific earthquake belt.

  • This means the country is struck

  • by some of the strongest earthquakes

  • and tsunamis in the world.

  • In the past decade, about 30 tropical storms

  • have also hit the country each year.

  • These natural disasters kill on average 100 to 200 people

  • per year and take a huge toll on the country's economy.

  • But learning from painful experience,

  • Japan has built one of the world's best

  • natural disaster response systems,

  • which includes regular disaster preparedness drills

  • and early warning alerts.

  • Japanese engineers and architects

  • have also pushed the boundaries of technology and design

  • to create resilient, disaster-proof buildings.

  • This is Tokyo Skytree.

  • At 634 meters, it's the world's tallest tower.

  • Designed for broadcasting and observation,

  • the base of Skytree occupies a relatively small plot of land

  • that isn't ideal for such a tall structure.

  • Atsuo Konishi and his colleagues

  • designed a steel truss tower,

  • so instead of fighting against the wind,

  • it can simply pass through the gaps between the trusses.

  • To stabilize the tower,

  • the team used a traditional Japanese design

  • called Shinbashira that dates back over 1000 years.

  • This is the flexible central pillar of a Japanese pagoda,

  • which stabilizes the tiered wooden structure

  • during an earthquake or typhoon.

  • In a similar way to a tree trunk supporting its branches.

  • A Shinbashira has been found at the center

  • of the world's oldest wooden structure,

  • made from a tree felled in 594 AD.

  • For Skytree, the team designed a 375-meter-tall

  • concrete core column

  • connected to the tower's steel outer frame

  • by a series of flexible oil dampers,

  • devices that control unwanted vibrations.

  • The swaying of the core column and outer frame

  • in opposite directions reduce the vibration

  • of the entire tower by up to 50% during an earthquake

  • and 30% during strong winds.

  • The core column is set

  • on six seismic isolators made of rubber,

  • these absorb unwanted movement

  • and work together with the oil dampers at various heights.

  • The top part of Skytree is a broadcasting antenna.

  • To ensure high quality,

  • the antenna needs to stay as stable as possible.

  • So two tuned mass damper systems were installed

  • to reduce unwanted vibrations.

  • One is at an altitude of 625 meters and weighs 25 tons,

  • and the other is at an altitude of 620 meters

  • and weighs 40 tons.

  • When the tower shakes,

  • these two dampers act together as reverse pendulums,

  • reducing vibrations caused by wind or an earthquake.

  • When Skytree was designed in the late 2000s,

  • architects and engineers flew weather balloons

  • to collect data on wind speeds

  • and build models which they tested in a wind tunnel.

  • But for some building designs,

  • this expensive and time-consuming process

  • has been replaced by faster and cheaper software

  • powered by artificial intelligence.

  • After a decade of research,

  • architectural engineering company Takenaka

  • has developed a typhoon

  • simulation software called Kazamidori.

  • For a 3 kilometer square urban area,

  • it usually takes three months to build a model,

  • conduct a wind tunnel test and get the results,

  • but with Takenaka's software,

  • the entire process can happen in just two or three days

  • and its engineers are trying to reduce that down

  • to half a day.

  • Japanese architects are also experimenting

  • with unconventional building material for highrises.

  • Skyscrapers are usually built from concrete or steel

  • because they're strong and cost-effective.

  • But building from wood is more environmentally-friendly.

  • Compared with the production of steel and concrete,

  • production of timber consumes less energy

  • and releases less carbon dioxide.

  • New trees can also be planted to absorb emissions.

  • But building tall structures with wood

  • offers up its own engineering and financial challenges.

  • That didn't stop Japanese construction company Maeda

  • from trying though.

  • Maeda is going to construct a 13-story wood

  • and steel hybrid office building

  • in Tokyo's Shibuya district.

  • To make the building earthquake-proof,

  • designers came up with a hybrid lattice structure

  • that will support the walls

  • and create a more user-friendly experience.

  • These designs and technologies

  • have helped high-rise buildings

  • to withstand typhoons and earthquakes.

  • And now many low-rise buildings in Japan

  • are starting to adopt them as well.

  • Some vulnerabilities still exist,

  • like older buildings constructed

  • before regulations were tightened in 1981.

  • With natural disasters becoming more and more frequent,

  • these innovative designs and technologies

  • could be key to protecting the economy and lives

  • both in Japan and around the world.

The ground began to shake,

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How Japan Is Building Disaster-Proof Skyscrapers

  • 7 1
    joey joey に公開 2021 年 04 月 26 日
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