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May 31, 2013 6:42 pm
One of the world’s largest cities is in trouble. Teetering on the crunch point of four tectonic plates, Tokyo’s 13m inhabitants live in daily anticipation of a colossal earthquake, which experts predict could strike any day. Despite this, developers continue to build ever-taller towers – but can the view from the penthouse really be worth the risk?
The last strong seismic tremor to hit Tokyo, the 1923 Great Kanto earthquake, killed 143,000 people and destroyed 695,000 homes. In January 2012, Tokyo University seismologists calculated that there was a 70 per cent likelihood of a tremor of seven or higher on the “moment magnitude” scale occurring directly beneath Tokyo within the next four years.
This scale is the global standard (and an updated version of the Richter scale), measuring the magnitude of energy released at a quake’s epicentre. Japan prefers to measure the intensity of ground motion using the Shindo scale of one to seven. So, the 2011 Tohoku quake was a level nine in magnitude at its epicentre, but the vibrations in Tokyo, 230 miles away, were a mere Shindo level five. Skyscrapers shook but survived.
“There have been no really big earthquakes with the epicentre underneath high-rise buildings,” says Professor Hiroshi Kawase of Kyoto University’s Disaster Prevention Research Institute. “So their safety has not been proven.”
Since 1981, all new buildings in Japan have been built to withstand an earthquake of Shindo level six. However, the construction code does not cover level-seven earthquakes – the highest on the scale. “The problem is that the law was based on the principle of rigid construction,” says Kawase, “so all buildings in Japan have been built as rigid structures. We now know that deformability is much better, but it is not a legal requirement.”
Tokyo’s most upmarket skyscrapers are given added flexibility. The apartment block at Midtown, where two-bedroom flats are let for Y1.6m ($15,800) per month, sits on rubber pads. This is a system known as base isolation, where the building is separated from the ground by a layer of rubber, ballbearings – or even air.
Mori, developer of the vast Roppongi Hills mixed-use complex, has taken a different approach with its flagship Mori Tower office building, installing 192 hydraulic oil dampers (shock absorbers) and braces made of flexible steel. These are positioned all the way up the 238m building.
The dampers are very expensive, says Yukihiro Namba, a Mori spokesman, but blue-chip office tenants are prepared to pay: “foreign companies do not like earthquakes”. A range of apartments is available to rent in the Roppongi Hills development, starting from Y830,000 per month for a two-bed, 93 sq metre apartment.
Another building with dampers fitted is the Tokyo Twin Parks development in Shimbashi. Here, a three-bedroom penthouse on the 47th floor is on the market for Y420m through Japan Sotheby’s International Realty.
Mori’s most recent mixed-use tower, Ark Hills Sengokuyama, uses “sticky wall” technology in the cavities between each floor. During a swaying motion, steel plates attached to the upper wall of the floor cavity move through a viscous fluid in a container attached to the lower wall, creating a resisting force. Here, a five-bed, 415 sq metre apartment is on the market through Japan Sotheby’s International Realty for Y820m.
Mitsubishi Estate, which owns the Marunouchi business district, says that buyers at its new Parkhouse Harumi Towers apartment building in Tokyo’s Bayside area, where flats are for sale from Y32m, are so concerned about seismic safety that its sales office has installed an earthquake simulation room to demonstrate the base isolation system. “For 70 per cent of our buyers, our technology was a major factor in their decision to purchase,” says Masato Kameda of Mitsubishi Estate.
Japan is considered to be the world leader in anti-seismic building technologies, with even more research institutes than San Francisco. Japanese knowhow is in high demand in China, where Bridgestone, the Tokyo-based tyre company, exports a growing number of base isolation systems.
New technology is also in development. Professor Yoshikazu Araki, an architectural engineer at Kyoto University, is working with alloys of copper and iron that can pull a twisted building back into position. “By using super-elastic alloys, it’s possible to recover a building’s original shape and to use it immediately after an earthquake,” he says. The technology is currently being tested at Nasa, and Araki hopes that construction companies will be using it within five years.
Meanwhile, Kawase is developing a damping system that he says can be inserted into every floor of a tower block. Layers of concrete blocks are bolted together loosely and topped by steel plates. During an earthquake, these blocks and plates grind, creating friction, to expend seismic energy.
The technique is based on work that Kawase has already done reinforcing the traditional wooden houses in which most Japanese people still live. Here, he has replaced the glue used to attach braces to walls with looser screws. “The connection between the braces is loose enough to allow them to move with an earthquake,” he says.
There is another, odder, way to protect wooden houses: levitation. A company called Air Danshin, based just outside Tokyo, has invented a system which, when a tremor is detected, forces compressed air between two layers of concrete foundations. The gap then inflates like an airbag, lifting the house by 2cm, before sinking back to the ground as the air is released.
In the 2011 quake, “all our houses survived without damage, while their neighbours suffered damages”, says Masatake Honda, a spokesman for Air Danshin, which has installed basement airbags in 150 Japanese homes.
Riccardo Tossani, founder of Tokyo-based Riccardo Tossani Architecture, says the most advanced Japanese buildings now consist of an exoskeleton fitted with hydraulic dampers. “The façade moves and absorbs energy using these pistons,” he says. “Instead of causing cracks, seismic energy is converted into heat, which then dissipates.” Indestructibility, he believes, is now a given: “The challenge now is to minimise cosmetic damage. It’s not about saving lives any more, it’s about saving cost.”
Yukihiro Namba agrees: “If there was a big earthquake underneath Tokyo, you could keep working at your desk at Roppongi Hills.”
According to Kawase, the prohibitive cost means that the level of technology seen at Roppongi Hills is rare. Modern skyscrapers with base isolation often do not have enough dampers, he says. “Base isolation theory relies on one layer in the basement absorbing all the energy, but if the ground motion is very strong, the rubber can break, and the floors collide.”
As for older concrete tower blocks, these “will start to crack” in a strong quake. “They might not collapse, but deformation is inevitable,” he says. “You may not lose your life, but it’s quite probable that you would not be able to live in your home.”
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