Earthquake In Japan: Stricter rules proved their worth
Friday 20 January 1995
There are three main types of "earthquake proof" building structures, all used in Japan over the past decade. The first has a heavy concrete weight on the top of a building that, activated by computer-controlled dampers, is shifted across the roof to counteract the force of the earthquake; however, a power cut could stop this sophisticated system working. The second employs shock absorbers, normally a sandwich rubber composition that acts as a form of suspension; this is suitable for buildings up to 15 storeys.
The third method, represented by Foster's Century Tower in Tokyo, is the eccentrically braced frame. "This", says Ed Booth of the engineers Ove Arup and Partners, "has steel braces providing stiffness for moderate earthquake motions, but a sacrificial ductile shear link between braces designed to yield in an intense earthquake, absorbing seismic energy and acting as a fuse which prevents the braces from buckling."
"But, earthquake engineering", adds Mr Booth, "is still a relatively new field. During this century more than 1.5million people have lost their lives as a result of earthquakes and the vast majority of this toll because of buildings that have collapsed through unsuitable design."
"I telephoned my parents in Kobe", says "Mog" Morishima, a Japanese architect working in London, "and they tell me that many of the new buildings on Port Island, a major land reclamation project in the Eighties, have survived. These include the Port OpiaHotel, the tallest building in the area. This is where you can find many new fashionable buildings designed by architects like Tadao Ando and Frank Gehry; it seems that new methods of construction and the new building regulations established in 1971 andrevised in 1980 have saved many buildings and, so, many lives."
Those regulations came into force as a result of an earthquake, measuring 7.7 on the Richter scale, that ripped through Hokkaido, Japan's north island, in 1968. Violent and unpredictable earthquakes have been an integral part of human settlement in Japan; traditionally, buildings, were not expected to last for long.
The city of Osaka was also hit by the massive earthquake that ripped through Japan on Tuesday; significantly - and thankfully - the magnificent new Kansai International Airport constructed on artificial island in the Bay of Osaka and opened last year hasalso emerged unscathed from the disaster.
What is certain is that buildings dating from before the Seventies and Eighties have fared badly. The mass reconstruction of Japan after the Second World War led to a rash of second-rate building. It is these buildings that suffered worst this week in the Kobe, Osaka and Kyoto regions. The cost of rebuilding has been estimated at £85bn.
Japan's construction standards are the world's most demanding. "When we designed the Century Tower in Tokyo in the late Eighties", says David Nelson of Sir Norman Foster and Partners, "the engineering calculations filled what I can only describe as a setof Encylopedia Britannica.
"The main structural frame of the office tower was 25 to 30 per cent bigger than it would have been outside a seismic zone, window panes had to move 80mm without dropping from their frames and we devised, with Ove Arup and Partners, what's called an eccentrically braced frame that allows the building to flex considerably before becoming dangerous. I would say that the Japanese employ building regulations that are both appropriate and stringent. You can never truly predict the power and behaviour of natural forces, while every society has to balance the cost of profitability of construction with safety and endurance."
As the Kobe Institute, Kansai International Airport and other new buildings have proved this week, appropriate structural design for seismic areas is slowly on the way, if too late for the thousands who lost homes, health and lives on Tuesday.
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