Tricky Ways to Pull Down a Skyscraper

But here in Tokyo, a cheek-by-jowl city with many outdated high-rises and tough recycling and environmental restrictions, Japanese companies are perfecting what might be called stealth demolition.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.”

Aside from the cap, though, the Taisei system is similar to other methods in that the structure is taken apart from the top down. 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.

“There are many ways to renovate,” said Tsuyoshi Seike, an associate professor at the Institute of Environmental Studies at the University of Tokyo. “But with buildings in the middle of Tokyo, they think it’s better to demolish.” About a dozen high-rises have been torn down so far, Dr. Seike said.