IN THE heart of Tokyo an iconic skyscraper, the Grand Prince Hotel Akasaka, is being demolished. But there are no explosives or wrecking balls in sight. Instead, all that can be seen is the roof slowly sinking as the aluminium-clad building shrinks beneath it.
The demolition is being carried out by the Taisei Corporation, which has developed what it claims is a cleaner and more environmentally friendly way to tear down high-rises. Called the Taisei Ecological Reproduction System, it works from the top down, breaking a building apart floor by floor. The once 140-metre tall hotel is now missing its top 30 metres. By May it will have vanished.
The levels being diantled are sealed within an enclosure that wraps around the building (see time-lapse photo), while huge jacks slowly lower the original roof down as floors are removed. Fully enclosing the demolition area reduces the volume of dust particles emitted from the site by a factor of 100 compared with conventional methods, says Taisei's Hideki Ichihara.
Before demolition begins, all non-structural elements of the building are removed by hand. Workers then take out beams and concrete flooring, which are carried to ground level by a crane system that generates electricity as the pieces are lowered. By recycling building materials and getting rid of heavy machinery that runs on fossils fuels, Ichihara says, the process reduces carbon dioxide emissions by as much as 85 per cent.
In Japan alone there are 797 skyscrapers over 100 metres tall, around 150 of which will be between 30 and 40 years old in the next decade, says Ichihara. This has historically been the age when such buildings are earmarked for demolition, but conventional methods are not suitable for such tall skyscrapers. This has prompted Taisei and its compes Kajima and Takenaka Corporations to develop new demolition systems. Kajima's "cut and down" method diantles floors from the ground up, while Takenaka's approach is almost identical to Taisei's.
Whether the country's current crop of high-rises should have such a short life span is a matter of debate. After Tokyo was shaken by earthquakes in March 2011, the prominent billionaire property developer Akira Mori called for the country to stop building skyscrapers over 100 metres high. Instead he suggested lower, wider-based structures should be built.
No such restrictions have yet been imposed. Takuro Yoshida, a professor at Kogakuin University in Tokyo, argues that newer engineering techniques could keep buildings safely standing for longer periods. "The idea that buildings are rebuilt on a 30- to 40-year cycle is itself about 20 years old," he says, adding that the ecological benefits of keeping a building in service outweigh even the most efficient means of demolition.
