Hold on to your hard hats. A Japanese contractor has developed the technology to add a storey to a building every three days. How? Using robots, of course.
Large construction sites in Japan have more in common with a well-oiled machine than with a muddy mass of diggers and cranes. In a country where construction has become a byword for technology, precision and efficiency, contractor Obayashi has become the leading exponent of high-tech building. The company鈥檚 latest efforts have resulted in an impressive three-day construction time for each of the 27 storeys on a tower. That might even make the Guinness Book of Records.

Built in Osaka, Japan鈥檚 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 鈥渃ultural, information and business centre for the 21st century鈥�, and has a host of ambitious building projects to prove it.

Speed was of the essence on Obayashi鈥檚 tower of flats. Chihiro Tsuji, an engineer in the company鈥檚 building construction engineering department in Osaka, who oversaw the project, says: 鈥淭he client wanted a turn-around as quick as possible to cash in on the current boom in demand for housing.鈥�

But speed had to be achieved alongside quality.

鈥淲e 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,鈥� 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. 鈥淣ormally, 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,鈥� 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. 鈥淔rom design to construction, everything was co-ordinated for precision and speed,鈥� 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.

鈥淭his method will certainly become the norm in the construction of high-rise collective housing in Japan,鈥� says Tsuji. 鈥淚t may be applicable also in the UK, as the goal is to maximise the use of factory products and reduce reliance on site labour.鈥�

How the latest technologies combined to build a storey in three days

Day 1 Morning: All precast components and scaffolding to support the floor slabs are delivered from the warehouse to site. The components are lifted by automated crane to the top of the building. The larger components are hung from a delivery girder (see pictures above). Preassembled cages of reinforcement bars for each column are fitted into place and hollow precast concrete column units dropped over them. Afternoon: Precast floor beams are craned into position. Reinforcing bars projecting from the beams and columns are connected by threaded steel sleeves. Steel staircases are installed and scaffolding erected for the floor slabs. Day 2 Precast floor slabs spanning entire structural bays are craned into position, along with precast balconies. Reinforcing mesh and trunking for cabling are laid on top of the slabs and formwork is erected around the joints between columns and beams. Day 3 Trunking within the floor slabs is completed. After inspection, the structural erection process is completed by pouring insitu concrete into the columns, the joints between them and the beams, and the topping to the floor slabs.

Say hello to Ninja

In Japan, robots have muscled in on construction sites in the same way that they have come to dominate car factories. One of contractor Obayashi鈥檚 revolutionary concepts involves robotisation of the entire construction system. Known as the fully automatic building construction system, it is protected by six patents. The heart of the system is the 鈥渟uper construction floor鈥�, an automated factory. Inside it, overhead cranes cover the entire floor. An individual crane has its own robots, each with its own task of assembly, welding, inspection, exterior panel installation and internal component placement. Robots and cranes are computer-controlled to ensure precision and accuracy in placement and assembly. Self-propelled conveyor cars and elevators carry components and materials to the assembly site. Other companies leading the way in reducing labour needs are Fujita Corporation and Kawasaki Heavy Industries, which have jointly developed a fully automated welding robot system for cages of reinforcing bars for columns. Conventional robots for welding steel cages require the operator to remove waste slag and clean nozzles by hand after each application. The new robot system automates the entire series of welding processes, from sensing and reading out the co-ordinates of the welding parts to the removal of slag and other waste by-products. The new robot system cuts labour by a half.