Built in Osaka, Japan’s second city, the tower is a housing scheme that has tapped into the latest IT, uses factory-assembled components for its frame and has brought automated cranes and other plant on site to put it all together. The result is a high-quality apartment block built in super-quick time that the contractor says cost the same to build as a standard block using conventional techniques.
It is no coincidence that Japan is home to this scheme. With the highest building costs in the world and a tightening labour market, the country has been at the forefront of high-tech construction for some time. In the past, the pursuit of speed resulted in shoddy, short-lived buildings, but there is now a demand for high-quality, durable buildings.
Osaka seems the perfect Japanese city for a project that uses factory production and all the latest mechanical technologies and computerised controls. It is busily reinventing itself as a “cultural, information and business centre for the 21st century”, and has a host of ambitious building projects to prove it.
Speed was of the essence on Obayashi’s tower of flats. Chihiro Tsuji, an engineer in the company’s building construction engineering department in Osaka, who oversaw the project, says: “The client wanted a turn-around as quick as possible to cash in on the current boom in demand for housing.”
But speed had to be achieved alongside quality.
“We found that prefabricated components and materials increased precision and quality, as only assembly work is performed on site. This enables us to offer high-quality, durable buildings in super-quick time,” he says.
The speedy result was down to a combination of the latest technologies both on and off site. Prefabrication is the norm in Japan, as is the use of reinforced concrete for high-rises, but, on this project, Obayashi pushed the limits of what can be done with the factory precasting of structural columns and beams. “Normally, the construction of each floor of a building takes six to 14 days because reinforcement bars and formwork are assembled at the site and then the wet concrete mix is poured in. Using the factory-made components for the building frame enabled us to finish some floors in just three days, once the team had got the hang of the new techniques,” says Tsuji.
The IT was also sophisticated, which allowed the construction and assembly process to be automated. The prefabricated components were stored in a warehouse near the site. Once on site, they were conveyed to their position in the assembly by self-propelled stacker cranes. The cranes were preprogrammed to retrieve the right parts at the right time and stack them on conveyor cars.
Tsuji likens the automated assembly system to that of a sophisticated manufacturing system for computer production. “From design to construction, everything was co-ordinated for precision and speed,” he says.
As well as being used to automate site activity, IT played a central role in the project from the start. Design, estimates and execution were all guided by computer-aided technology. The same computer system also managed the just-in-time delivery as well as the erection of the precast and pre-assembled components. Bar codes attached to each component at the factory indicated its specification and exact final position in the building.
“This method will certainly become the norm in the construction of high-rise collective housing in Japan,” says Tsuji. “It may be applicable also in the UK, as the goal is to maximise the use of factory products and reduce reliance on site labour.”