Automatic erection

The use of canopies is gaining popularity among Japanese building contractors. The principle is that a temporary steel roof, the canopy, is constructed over a building site and jacked up metre by metre as the building beneath it takes shape. It allows work to continue in the seasonal hard rains that are a feature of certain climates, and also protects workers and materials from intense sunlight. The theory is that it speeds construction and improves workmanship.

Last year Shimizu completed construction of a new headquarters building for the Singapore Housing Development Board (HDB) using a canopy, which was supported by the masts of Potain tower cranes. The HDB was sufficiently impressed to sanction a similar method to be used by another Japanese contractor, Penta-Ocean, on a high-rise housing project. This one, however, goes one step further.

Penta-Ocean has used a canopy system before, when it built the Nihonbashi-hamacho F Tower in Tokyo from 1994 to 1996. This was a steel framed office building. As with the Shimizu project, beneath the canopy ran a gantry crane that was programmed to place materials when and where they were needed. Penta-Ocean called its system on this project FACES - Future Automated Construction Efficient System. Researchers from Penta-Ocean's own Institute of Technology, which devised the system, monitored the results and found that construction costs were only slightly below what they would otherwise have been, but that quality control was significantly improved.

On Toa Payou Redevelopment Contract 30 in Singapore, which is now only at the groundworks stage, a variant of FACES is being used, called Automated Building Construction System.

It still uses tower crane masts to support the canopy - in this case, three Peiner SN 630s and a Peiner SN 1000 that were previously used in the construciton of Hong Kong's Tsing Ma bridge. The cranes were procured via Continental Equipment in Hong Kong and Roger Poon in Singapore.

The key difference at Toa Payou is that PLC controlled tower cranes will be used beneath the canopy for materials handling instead of a gantry crane. The tower cranes to be used are two Liebherr 180 EC-B10 cranes (10t maximum lift capacity), which are flat-top to enable the hook height to get as close to the canopy as possible. They will be protected by an ABB anti-collision system.

The cranes are connected to a central server and the location of the storage bays from which the cranes will pick precast concrete panels is programmed in. On each concrete panel is a unique barcode that determines when it should be lifted and where in the structure it should be placed. As each panel is attached to the hook, an operative scans the barcode, which tells the crane where to take the load. The crane then takes the load automatically to where it needs to go. Once the load is unhooked, the crane returns automatically to the storage bay. The computer not only controls the material management system but also the strokes of the hydraulic pressure jacks in each of the four masts, to raise the canopy.

The benefit of automating crane operations, according to Sanno, is that it saves time. There is not so much difference between automation and a human operator in the morning, says Sanno, but in the afternoon and evening the difference becomes apparent, especially as the building gets higher and the operator's view of the storage bay becomes blocked. In fact, a skilled operator, Sanno concedes, may even be quicker than automation in early stages.

The results at Tao Payou will be easy to measure. Penta-Ocean is putting up four buildings on the site, only one of which is using the automation system. Phase one, the buildings using traditional methods, began on site in October 2001. The automated building starts in the middle of this year. Completion for phase one is scheduled for October 2004. No handover date has been set for the automated building, but Sanno hopes to finish it earlier, despite starting later.

The whole operation is not yet entirely automated, however. With each pick the crane will automatically stop the hook one metre above the load. At this point the crane operator takes over. Similarly, the automation process only takes the load to one metre above its final position. Again the operator has to do the fine positioning. This is because the deflection of the crane cannot yet be accurately predicted.

Tanaka and the research institute guys are working on this problem, however, so that in the near future crane operations on buildings can be totally automated, just as they are already in certain shipyards. Says Sanno: 'I think that it is possible to eliminate the operator completely in future.'