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TFI Daily News

World News for World Changers

Jun 20

Tricky Ways to Pull Down a Skyscraper

By Henry Fountain, NY Times, June 17, 2013

TOKYO—There are many ways to demolish a building, and some of them are spectacular: blowing it up from the inside so it collapses on itself, or smashing it to bits with a two-ton wrecking ball.

But here in Tokyo, a cheek-by-jowl city with many outdated high-rises and tough recycling and environmental restrictions, Japanese companies are perfecting what might be called stealth demolition. Some tall buildings are dismantled from the top down, the work hidden by a moving scaffold, others from the bottom up, the entire structure being slowly jacked down.

At times the techniques seem to defy gravity, or at least common sense, for although the buildings appear intact, they slowly shrink. The methods, which make for a cleaner and quieter work site, may eventually find favor in New York and other cities as aging skyscrapers become obsolete and the best solution is to take them down and rebuild.

The latest Tokyo high-rise to get the stealth treatment is the Akasaka Prince Hotel, a 40-story tower with a distinctive saw-toothed facade overlooking one of the city’s bustling commercial districts. Since last fall, its steel and concrete innards have been torn apart, floor by floor, starting near the top, by hydraulic shears and other heavy equipment. The building has been shrinking by about two floors every 10 days; this month it will be gone, to be replaced by two new towers.

Hideki Ichihara, a manager with Taisei Corporation, which developed the system being used to tear down the hotel, said the technique had environmental benefits and allowed for more efficient separation of metal, concrete and other recyclable materials. Another advantage is visual: The vanishing building looks normal for as long as possible. “We want people not to really see the demolition work,” he said.

Mr. Ichihara was speaking in the bowels of the hotel on a late winter day while, about 250 feet above, workers were demolishing two floors, removing the exterior aluminum and glass, cutting up the steel beams and pulverizing the concrete slabs. But none of the work was visible to passers-by—the top four floors were shrouded in a scaffold that hung from the intact roof and was covered in panels that mimicked the facade.

When the two floors are gone, the roof and scaffold cap slowly descends, thanks to computer-controlled jacks on each of 15 temporary columns. Then the columns are lowered into new positions, and the workers start taking apart the next two floors.

The cap helps keep noise and dust down compared with more conventional methods of demolishing tall buildings, which involve erecting a scaffold all the way up and around the structure but leaving the top exposed. “All the work is inside the covered area,” Mr. Ichihara said. “The noise level is 20 decibels lower than the conventional way, and there’s 90 percent less dust leaving the area.”

Another Japanese company, Kajima Corporation, has developed a bottom-up approach, cutting a building’s steel columns at ground level and jacking the entire structure down as each floor is removed. Since all the demolition work is done on or near the ground, there is no need to place heavy equipment, or workers, at the top of the building.

"The idea is to keep the building as intact as possible," said Ryo Mizutani, an official with Kajima, which in January finished demolishing a 24-story office tower, the Resona Maruha building, near the Imperial Gardens. Huge hydraulic jacks supported the building’s 40 columns, and workers cut 30 inches from each column, over and over, to allow the structure to be slowly lowered.

The Resona Maruha building was completed in 1978, the Akasaka Prince tower in 1982. Ordinarily, a building that is 30 or 40 years old should have many years of life left, if properly maintained. The Empire State Building, for example, is 82 and doing just fine after major renovation work.

But the Tokyo buildings fell victim to the vagaries of commercial real estate here, where high property values, changing design standards and other factors have conspired to create a bull market for demolition.

The boom in Japan’s economy in the 1970s spawned scores of dull, cookie-cutter office towers in Tokyo. Now many of those buildings are obsolete, with relatively low ceilings (height standards were increased in 1990) that have become even more cramped by having to accommodate the infrastructure of information technology.

Tokyo’s situation may be unique, but New York and other cities may eventually face the need to demolish some high-rises. A recent study by Terrapin Bright Green, a New York consulting firm, suggested that many office towers in Manhattan needed to be overhauled or demolished. These structures were built from the late 1950s to the early ’70s and have low ceilings, tight column spacing that limits floor layouts, and inefficient heating and cooling systems.

Bill Browning, a partner in Terrapin, said that some of these buildings, built in an era of cheap energy, had facades of single-glazed glass, and the structures could not support the weight of additional insulating glass to make them more energy-efficient. Other buildings might be able to be renovated, but it would take decades for the investment to pay for itself.

In those cases, Mr. Browning said, it might make better economic sense to take the building down and build a new tower that would have more space at higher rents and use the same energy, or less.

While there are probably several hundred buildings that are outdated, Mr. Browning said, only a handful might actually be demolished. “I think we’ll see a few around Midtown and a few in Lower Manhattan,” he said.

It is unclear whether demolition contractors in the United States will adopt any of the Japanese methods; even in Tokyo many buildings are demolished in more conventional ways. (With the new techniques, setting up the project can be more expensive, but the demolition often takes less time than with conventional methods.)

Bill Moore, a past president of the National Demolition Association and marketing director of Brandenburg Industrial Services, a demolition company, said that an Italian contractor had tried to interest American companies in a top-cap system that is similar to Taisei’s, to little effect. “Our environmental regulations are not that strict,” Mr. Moore said, and dust can be effectively contained by spraying with water.

One thing is clear, Mr. Moore said: Implosion by use of precisely placed explosives would not be used, nor would a wrecking ball. Both methods are largely forbidden in New York because of safety and environmental concerns, although this month officials allowed the first implosion in more than a decade, of an old Coast Guard apartment building on largely isolated Governors Island.

Implosion is also outlawed in Tokyo, which is even more densely packed than New York. But the main impetus there for the new demolition techniques, said Dr. Seike of the University of Tokyo, was a recycling law that took effect in 2002.

In addition to valuable metals like steel, aluminum and copper, the law required that wood and concrete waste be recycled, even if the demolition contractors had to pay to do so. “People started to take recycling seriously,” Dr. Seike said. “And things have changed quite drastically with demolition.”

For greater efficiency, recyclable materials need to be separated at the site, he said. By creating controlled work environments, both Japanese methods allow for on-site separation.

At the Akasaka Prince, Mr. Ichihara said, the sorting starts at the top, and the concrete and steel are brought down by separate cranes. With the Kajima bottom-up method, Mr. Mizutani said, all of the debris is created on the ground level, allowing for efficient sorting.

But the Kajima method has one major disadvantage: In earthquake-prone Tokyo, a building that is cut loose from its foundation could easily topple when the ground shakes. The company’s solution is to build temporary concrete structures, about three stories high, within parts of the building’s steel frame. Locking devices that would activate quickly in an earthquake would tie the frame to the concrete structures, presumably keeping the building stable.