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Roller-coaster construction

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MetalWorks Major Structures - The International Port Terminal in Yokohama, designed by Foreign Office Architects, is a bold and radical concept

When in May 1995 Alejandro Zaera-Polo and Farshid Moussavi, principals of the practice Foreign Office Architects, won a competition to design the International Port Terminal in Yokohama, Japan, it was a startling but exciting decision. That was before other 'unbuildable' architects such as Hadid and Libeskind saw major projects being realised.

The judges had evidently made a bold decision, but some will have questioned whether they made a wise one. Now this innovative project is approaching completion, with the opening planned for Novem2platform, 70m wide and projecting 420m out into Yokohama Bay, is becoming apparent.

The as-built structure differs substantially from the competition entry, but without losing its complexity. This is no surprise to the architects. Moussavi, who has written at length about the importance of not having experience, has said that 'the competition proposal was as interesting as it was naive, and needed substantial technical development to become realisable without betraying the original purpose'.

The design ditches pre-conceived notions of what a ferry terminal should look like, concentrating instead on issues such as the need to accommodate domestic and international services of varying volume and frequency with public and civic events, and the interaction of travellers with the public. As a result, the flow of cruise passengers - from car parking to customs and embarkation - is uniquely integrated with interconnecting public spaces, including a city park - a plaza - on the gently undulating roof. The park will be linked to a sequence of green spaces in the city so that it will merge seamlessly with the urban fabric. People will be able to walk from the mainland onto the terminal and into the parks and public spaces as they wish, enjoying the sense of being surrounded by sea.

The terminal superstructure is mounted on a vast concrete slab platform on piers set on the seabed; it is set back 15m from the long edges to create a boarding deck against which ships will be moored. Passengers will embark at this level via a series of moveable access decks - 'boarding fingers'.

The superstructure is a complex undulating form, changing in level and shape along the concrete platform. Essentially it consists of a pair of steel box girders with arched members spanning between them and with projecting wings cantilevered from the outer sides. The box girders are the spines of the building - functionally, mechanically and structurally. They change in shape continuously to act as ramps while supporting the two levels of folded plate floor and roof.

A car park forms the lowest level; above it are the terminal and public space, with the new plaza on the roof.

FOA approached the design of the new terminal as an 'exploration of the process of construction', of which the development of the steel structure, and particularly the folded plate roof, was a key element.

'The roof structure that we proposed in the competition was made out of a folded piece of steel, an attempt to make it consistent with the general concept of the project as a folded organisation, ' wrote Moussavi.

'This proposal was also advantageous in terms of its resistance to earthquake stresses and akin to the techniques of naval industry to which the building was affiliated. The 'cardboard' structure emerged out of what was originally a reference to the local tradition of 'origami' construction.'

'At the beginning of the design-development phase, the steel structure was clearly the most critical point of the project, as the competition proposal needed substantial technical development to become realisable without betraying the original purpose. The main problem to resolve was that of the three-dimensional complexity of the structure with a geometry which was basically axial - that of folding. We came up with a solution where the folds of the web were being woven with each other every halffold, so that we could achieve the curvature at a larger scale. This is a structural geometry that has been used, for example, by Nervi, Piano and others to make large-span shells with a kind of structural unit or cell that is repeated along the curves. But what was interesting is that the cells of the structure would become differentiated at every point of the surface, like an organic system.

One of the immediate implications of this system is that we removed the lower plate of the structure to simplify the construction, turning the folded metal plates into a crucial expressive trait of the project; the origami had finally become visible.'

As the project developed, not only the geometry changed but also the method of defining it. Moussavi explained that the project moved from ' a 'raster' space, where each point is determined by local information, to a vectorial space, where each point is determined by differentiated global orders.'

The whole process has resulted, says Moussavi, in 'a big building with very few details - this is radical'. And the design also had major implications for the construction process.

When the contractors asked for the coordinates of the points of the building, Moussavi wrote: 'To their surprise, we had to explain to them that the geometry was strictly related to the manufacturing and construction systems, and could be modified if necessary. One of them pointed out that they would have to employ the same techniques used to build roller-coasters, where the setting out utilises local references between identical templates rolled along an irregular three-dimensional geometry. 'Exactly, 'we said. 'Roller-coaster construction.'' This roller-coaster is now coming to the end of its ride. For users of the terminal, the process of design and construction by which Moussavi sets such store will be virtually irrelevant - except for the fact that it has resulted in an extraordinary building, likely to become an icon in the manner of the Sydney Opera House or Bilbao's Guggenheim.

For most architects there would be an additional satisfaction in pulling off such an achievement so early in their career, but it must seem natural to Moussavi. In the manner of The Who's infamous declaration, 'Hope I die before I get old', she has written:

'It is only experience that teaches us where our limits are and, once we have learned that, we are finished.' So the real challenge for Foreign Office Architects will, presumably, be to not learn from the experience of Yokohama and somehow, naively, manage something as original all over again.

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