the middle’ for Portugal’s oldest
university town. The bridge’s
dislocated apex provides
not only a focus for a
formal investigation into
dynamic symmetry, but
also a layered narrative
that makes sense of its
historical setting.
Ever since the legendary École des Ponts et Chaussées was founded in 1747, its particular blend of militaristic
Rationalism has gradually squeezed out all other measures of bridge design. Not many people still think bridges so offend the natural order of things that their builders and users should propitiate the divine beings who dwell in the streams and gorges they cross. Still fewer think of bridges as ways of telling stories, despite the potential for narrative their roles as crossings contain. Instead they are means of crossing barriers through the conceptually determined most efficient use of building materials, and their higher value, if any, lies in achieving ever more spectacular engineering feats that in turn demand more conceptual Rationalism.
The possibility of breaking away from this cycle appealed to Arup’s deputy chairman Cecil Balmond in the opportunity to design a footbridge over the Mondego River in Coimbra, Portugal’s oldest university town. Aided by Antonio Adao da Fonseca, one of Europe’s leading bridge engineers and a frequent collaborator with his fellow Oportans Alvaro Siza and Eduardo Souto de Moura, Balmond set out to challenge conventional assumptions about bridges.
It is a ‘crazy design’, he confesses, ‘the first bridge that does not meet in the middle.’ Most bridge designers would make the centre of stiffness the same as the centre of symmetry, but Balmond made an initial sketch that had two subtle curves rising from each bank that just slipped past each other, as if they were young poets on the trajectory that Harold Bloom described in the Anxiety of Influence. Of course,
bridges are not poetry, and whatever their metaphorical meanings they do need some kind of central rapprochement;
otherwise they would be mere viewing platforms. But this simple sketch alone showed that bridges might follow another sort of logic to the simple linear one so favoured by the strutting peacocks of les Ponts. Splitting symmetry and stiffness releases bridges from a straitjacket. They might lunge, lurch or feint; the forces might leap out of their containment and begin to mingle with the emotions of those who cross the bridge and stories associated with the place.
These characteristics lie at the core of Balmond’s interests as a designer. His discipline is engineering, but his ambition is to create form, which he considers to be shape imbued with ideas. His principle is ‘the negotiating eye in space’, or using visual judgement as the starting point for a new visual language rooted in an understanding of form, mass and matter. Symmetry, he explains, occurs in nature ‘as an embedded series of ratios’, which makes it dynamic rather than static. He seeks to understand and reinterpret that dynamism, and use its many faces to create layered
narratives. A bridge he is designing in Philadelphia takes this to a new dimension. ‘It’s like a novel in the way it develops,’
he says, ‘with its own denouement,’ while at Coimbra there are ‘scary moments’ as pedestrians walk towards what appears to be a void.
Coimbra marks an important point in the way Balmond’s ideas have evolved. He was looking for particular visual effects, to pick up on the quality of sunlight in southern
Cecil Balmond (Arup) and Antonio Adao da Fonseca, Pedro and Inês Bridge, Coimbra, Portugal, 2006 The underside picks up reflections that can be counterintuitive.
The switch of offsets of the arch means that the strong shadow can make one side of the structure appear almost invisible, and the thin deck soar as if in surface tension.
The centre of the bridge is a place to pause and reflect, not to pass as quickly as possible.
Europe and the difference between the nearly rural west bank and more urban east bank with the old town rising above it.
Each side of the bridge seems to spring from its own bank; the dislocation at the apex prevents the domination of one direction over the other. Although each half is similar, their supporting arches are on opposite edges of the deck – for structural stability, a product of splitting symmetry and stiffness – but the visual effect is to make one half appear smooth while the other is thrown into shadow. From a distance one of the arches can almost disappear, while closer to, the surfaces of both bridge and water create a series of overlapping reflections.
Balmond’s challenge to conventional wisdom comes not so much from questioning its logic, but out of a search for different visual and experiential effects. This becomes more apparent in the balustrade. Its patterns of coloured glass at first seem to belong to a very different order to the smoothly flowing forms of the main structure. They are facetted and arresting, following a folding geometry that repeats every 12 metres (39 feet). What they do, though, is interact with the movement of pedestrians over the bridge, throwing their different colours on to the deck, bathing walkers in changing
lighting effects. The handrail itself follows a gentle zigzag, Balmond’s sketch showing the evolution of the bridge form, from the initial sketch, to two straight decks which do not quite run into each other.
Above still water the bridge appears to be mirrored.
creating any number of momentarily private stopping points to rest and take in the view, as Balmond puts it: ‘At each step something checks you.’ These little hiatuses are preparation for the large one, the point in the bridge where the two decks just touch each other long enough to allow pedestrians to move from one line to the other, rather than step into oblivion. This is where a medieval bridge would have had a chapel for its patron saint; an earlier one a shrine for offerings to the deity of the river.
Balmond postulates a different metaphysical position. His decisions are always taken in the knowledge of convention, but rather than adhere to it, in a way that is again
reminiscent of Harold Bloom, he veers away to explore different possibilities. Yet these still have to coalesce into their own contingent consistency. The integrity of the bridge, he says, ‘has to do with the condition of not meeting’. This in turn overturns the tradition of two-and-a-half centuries where form, function and expressive language have become so intertwined that it dominates our understanding of what a bridge is. So at each step Balmond has had to take ‘longer just to find the language to create and support that shift’.
Latent all the way through the bridge’s gestation and design evolution was another thread that creates a
psycho-geographical metanarrative to the particular condition of the bridge. Coimbra was where the future Pedro I of Portugal fled with his paramour Inês de Castro to escape the disapproval of his father Alfonso IV because Inês was not of ‘sang real’.
Eventually Alfonso had Inês murdered. Pedro’s response was to launch a rebellion. After Pedro became king he declared that he and Inês had married in secret and so their children were legitimate and in line to the throne. Inês’ decaying corpse was exhumed so she could take her place as his queen, and nobles could pay homage to her. He had two tombs carved for himself and Inês, placed in such a way that on Judgement Day they would arise and face each other, presumably as a prelude to being together for eternity.
Balmond was not aware of this old tale when he designed the bridge, but on seeing his creation the mayor of Coimbra named it for the thwarted lovers, who could never quite connect in life. It is hard to imagine a box girder bridge evoking such stories, and even if this affinity is pure coincidence it does show how story-telling and form-making might come from related intellectual processes. 4+
Text © 2007 John Wiley & Sons Ltd. Images: pp 118-120 © Cecil Balmond; p 121 (tl&b) © Arup; p 121(tr) © Leonardo Finotti
The deceptively simple plan belies the visual and conceptual complexity of the design and the consideration put into the two footings.
Section through the bridge showing the transference of the structure to one side and the deck cantilevering from it.
Different lighting conditions pick up different qualities in the design:
at night, the structure seems to vanish and the illuminations of the coloured handrail dominate.