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27 June 2008
By Ellis Woodman
Zaha Hadid’s bridge over the River Ebro for the Zaragoza Expo is another creative triumph, but will it achieve its legacy role once the expo is over, wonders Ellis Woodman
The Spanish city of Zaragoza lies just about midway between Madrid and Barcelona, an hour and a half’s train ride from each. Earlier this month after travelling north from the capital and arriving close to midnight, I headed for the shower. On turning the tap, however, I had second thoughts. The water that emerged was an alarming shade of chocolate brown.
The next morning as I walked down to the Ebro, the river that winds through the middle of the city, it soon became apparent why. Ordinarily Zaragoza’s climate verges on the desert-like, with average annual rainfall of just 310mm. This year, the region has experienced its wettest spring since 1930. Having burst its banks, the river was consuming everything in its path under a raging torrent of muddy water.
The timing could not have been worse. The reason I and a 100 other journalists were in town was that Expo Zaragoza 2008 was about to open its doors.The 25ha site is caught in a wide meander of the river, and one of its outdoor stages even projects out into the water. In the end, judicious sandbagging ensured that the only major casualty was the opening ceremony. Yet as the waters rose, the organisers must surely have begun to fear they had been singled out as the butt of some cosmic joke: the exhibition on which they had just spent €700 million takes as its theme the subject of water and sustainable development.
The exhibits were still being installed during my visit, but there was enough visible to get a handle on the general tone: an uneasy straddling between the school room and the theme park. Gormleyesque sculpture, French circus troops, MDF architecture and inspirational super-graphics were the order of the day — anyone who survived a visit to the Millennium Dome will know the drill.
These doubts were compounded by the suspicion that there must be better ways of promoting sustainability than by staging a gargantuan exhibition — there are 140 pavilions — which ends up in a skip after three months. In fairness, the project has been undertaken with a legacy plan in place. After September, a number of the larger structures will be adapted to office space and the whole site will be redesignated as a business park.
At least one element of Expo 2008 will also continue to function as a public resource: the 260m-long pedestrian bridge that has been built across the Ebro to a design by Zaha Hadid. In its current incarnation the bridge forms the site’s principal entrance, while after September it promises to play a critical role in unlocking the regeneration of Zaragoza’s north bank. Particularly significant in this regard is the fact that it has a very direct relationship with the city’s main railway station — a really splendid work by Carlos Ferrater — which stands half a kilometre to the south.
No doubt this basic infrastructure requirement could have been satisfied for a fraction of the €34 million expended on Hadid’s bridge. However, her project has additional functions to perform: it doubles as an exhibition pavilion in its own right, hosting a display devoted to best practice in water management across the world. As such, it represents the long delayed realisation of an idea that Hadid has rehearsed across a series of unbuilt projects — the habitable bridge.
Two designs to which that theme is particularly key are her 1977 AA graduation scheme for a Malevich-inspired hotel intended to sit on London’s Hungerford Bridge, and the winning entry in the Royal Academy’s 1996 competition for a habitable crossing over the Thames, conceived for a site just a couple of hundred metres downriver from the earlier project.
Hadid’s architecture had developed significantly in the interim, the neoconstructivist agglomerations of the early work having been exchanged for the language of quasi-organic forms that dominates her current production. Nonetheless, a clear conceptual thread exists between the two schemes: both were much concerned with cultivating spatial relationships — coincidences — between the diverse programmes distributed along their length.
“The bridge entirely wrong-foots one’s sense of perspective”
That impulse is also clearly present in the Zaragoza project, but Hadid had a rather less appetising set of ingredients to work with on this occasion. The bridge’s programme is a far simpler than those of the earlier schemes, while the urban situation into which it has been inserted is at present all but non-existent.
What it has principally in its favour is a wonderful landscape setting, to which the bridge proves responsive in a number of ways. For one thing, it curves in plan, gently resolving the divergent geometries of the north and south banks. In order to keep it above flood level, it extends far beyond the river’s edge on both sides. Massive embankments serve to anchor — both structurally and visually — either end in the ground.
The structure is not, however, a single span. A third point of support is provided by a small island two thirds of the way along the bridge’s length. The island’s eccentric location invests the structure with an asymmetry that Hadid — if not her engineer — has clearly relished.
The basic module from which the whole structure has been derived is a triangular steel frame. It is repeated at 3.6m intervals along the bridge’s length, and adjusted in height and width with each iteration. What emerges through this procedure is an arched truss which is then lined out to become a spatial enclosure.
The bridge comprises four such trusses. Two are laid end to end, forming the public route. The other two are rammed in from either side and serve as exhibition halls. The plan that results is trident-like, the handle bearing on the south bank, the forks pointing north.
Early on in the project’s development, the design team considered the possibility of an engineering solution based on a series of shell structures. This was ultimately rejected because the architect felt that such a monolithic structure would give the project the presence of a piece of heavy engineering. What Hadid wanted was a finer, more building-like scale. The bridge’s external image is very largely, therefore, a matter of cladding.
The lower level has been faced in premoulded steel panels, giving it a sinuous, aerofoil profile. Above, we are presented with a skin of mosaic-like glass-reinforced concrete panels. Comprising a series of interlocking triangles, this treatment is built up of ten different cutting patterns, each of which is assigned a distinct tone, graduating from black to white.
On first sight, the impression is dazzling, entirely wrong-footing one’s sense of perspective, so that the surface appears more heavily profiled than it truly is. Having assumed that it could only have been generated parametrically, I was surprised when, drawing closer, its systematic and charmingly low-tech nature became apparent.
Many panels are also omitted, casting a rich pattern of light and shadow on the bridge’s floor. The lighting requirements of the exhibition — the demand was essentially for a black-box environment — limited the number of these perforations, but the plan is to introduce more once the bridge passes into legacy mode.
“The structure is the realisation of an idea Hadid has rehearsed across a series of unbuilt projects — the habitable bridge”
More substantial openings have been introduced at the junction of the glass-reinforced concrete panels and moulded steel cladding. The interplay between this horizon line, the ridge and the bridge’s underside forms the primary motive for the elevations: a simple idea, but one handled here with fantastic dynamism and invention.
If the bridge’s interior proves somewhat less happy, that is not altogether the architect’s fault. A continuous lining of moulded plasterboard extends down the length of the space, faced in several layers of resin to give a white plastic finish. The subcontractor was also responsible for the linings of Gehry’s Bilbao Guggenheim, and the craftsmanship on show at Zaragoza is every bit as impressive.
The exhibition halls are entirely lined out, but at high level, large expanses of wall along the public route have been left unlined. This is the one point where the building’s construction is legible: we can see the triangular frames, a grid of secondary steelwork laid on the diagonal, and finally the underside of the GRC panels.
The difficulties that have arisen are related to the realisation of the Expo programme. Hadid had hoped to design the exhibition, but the commission was handed to a firm of US specialists. What it has done is fine enough, but one regrets that the opportunity to give the building and its contents a common expression has been lost.
Far more problematically, it was decided that the smaller of the two exhibition halls would stand empty, serving merely as overflow space on days when visitor numbers are particularly high. As a result, there is little sense of the programmatic juxtaposition that characterised Hadid’s earlier habitable bridge projects.
After the Expo closes, the plan is for the structure to retain its use as an exhibition venue, although what form those exhibitions might take remains unclear. The absence of vertical walls and the very particular nature of the daylighting will certainly limit the choices.
However, an issue which will surely pose a far greater threat to the building’s future is its urban dislocation. Given that it lies in such an undeveloped part of the city, it is hard to imagine how it will find the density of activity that its scale demands for some time to come.
To be blunt, without careful stewardship, one can see it very quickly becoming a target of vandalism and anti-social activity. As ever with Hadid’s work, the project presents a challenge to the world. And not for the first time, I fear it is one the world may prove incapable of meeting.
Project team
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Client Expoagua 2008,
Architect Zaha Hadid Architects,
Engineer Arup,
Lighting Bartenback Lichtlabor,
General contractor UTE Dragados – URSSA
Photos by Fernando Guerra

Exit to the Expo site

The bridge forms the entance to the Expo site from the south.

The GRC cladding uses 10 different cutting patterns, each assigned a different colour.

Upper floor site plan

Cross-sections along bridge part 2

Cross-sections along bridge part 1