字幕表 動画を再生する 英語字幕をプリント 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.