Not only did the building have to go up fast; it also had to be high quality. Sound like an impossible task? Construction manager Bovis Lend Lease and structural frame subcontractor O'Rourke took on this challenge and managed to meet it by using a new fast-build system of construction.
Viv Jones, contracts manager for O'Rourke, says it originally used the system on office buildings for BAA. "We used this post-tension slab and precast column system on a job for BAA at Stansted," he says. "It went up very quickly, there was minimal need for on-site labour and everyone was happy with the result. Peter Rogers at Stanhope heard about this and asked us to get involved at Chiswick." The system uses post-tensioned concrete slabs and precast concrete columns around a structural steel frame for stability. "With this system we can create a good quality building quickly, without the need for people on site to be sawing away at timber for hours," says Jones.
The structural steel frame goes up first to act as temporary access. This means there is no need to erect temporary staircases. The post-tension slab, which Jones describes as "very light and elegant", is then poured. "So not only is it easier to install, but it also makes the building more attractive," he says.
Precast column
Another feature of the fast-build system is the precast column, which sits straight on top of the piling, so there is no need for a pile cap. "It also means there is also no need to pour vertical concrete on site," says Neale Brydon, project director for Bovis at Chiswick. The column has to be attractive as it is exposed on the inside of the building.
"We encourage use of prefabrication," says Simon Jenner, project executive for Stanhope at Chiswick, "because you can control the processes and quality of the product to a greater degree. You are limited with what you can do on site, and using a more factory-biased process speeds up installation." "The edge beams were also precast," says Brydon. "Not only did this save time, but it ensured that the process was very accurate. It didn't encroach onto the cladding, which it can have a tendency to do if you pour it on site."
Phase one
Phase one of the project was completed at the end of last year, in just 10 and a half months, on programme and budget. The frame for building one was completed in just 11 weeks. And Jones recognises that although the process is fast at present, with the possibility of 11 buildings to construct at Chiswick over the next four years, there is still room to improve. "We have learnt from building phase one (three buildings) and have applied that knowledge to fine tune phase two, started this January," he says.
"For example, in phase one we built the structure then fitted the lift motor, which effectively forms the waterproofing for the core of the building. In phase two, we have built the lift motor into the structure, so only that has to be waterproofed before the fit-out trades can move in. That has shaved about two weeks off the project, which is a significant amount of time in a programme of 40 weeks." And especially handy given the torrential rain that has been falling in Britain for the last six months.
"We have also fitted a handrail to the structural steel, which made it easier for the glazing and dry lining contractors to do their job," Jones adds.
Design process
Although the system contributed hugely to the success of the project, so did the atmosphere of partnership that characterised the project team, says Jones. "What has really made a difference on this contract," he comments, "is that we sat down with the developer and construction manager at the concept stage.
"A lot of buildability issues were sorted out then, so problems were avoided further on into the process. It was recognised that we can contribute to the design process, which can improve the quality and safety of the construction." Brydon agrees about the importance of that initial collaboration. "It was a team effort," he says. "Stanhope, ourselves, O'Rourke and the engineer Ove Arup all sat down and decided how we could meet the schedule. We did have some problems with the steel structure on site, but the rest of the process was very smooth. O'Rourke had expertise in this area and knew this system would be very quick, and it was. On phase one we were laying a floor every week and a half." So it seems that the old choice between quantity and quality has become obsolete. Using the O'Rourke system, you can now enjoy both.
Source
Construction Manager
