Jim Eyre

Since the invention of the railways, methods of transport have edged ever nearer to the Roman ideal of travel in a straight line. Depending on your view, mankind has either consistently triumphed over nature or violated it – with railroads in the nineteenth century, motorways since the war, and more recently with the ultralinearity of high-speed rail travel. As the line gets straighter, more cuttings, embankments, tunnels and bridges arise. Bridges occur as incidents in transportation that overcome natural topography, while cuttings and embankments are more insidious, more damaging to the landscape, beating nature into submission.

The sheer number of structures involved in crossing an impassable natural obstacle means that the bridge becomes more a utilitarian artefact than something exceptional. Perhaps the prevalence of banality that has arisen as a result is symptomatic of the second half of the twentieth century. Dullness and repetition first appeared in the 1930s, however, in the Reichsautobahn structures, despite the heroicization of its programme – the emblematic Mang Falls, for instance, was used in a stamp design and became subject to 'bridge tourism'.

The history of bridge design can be traced from fords and primitive bridge forms, developing both in complexity and span alongside technological and material progress. With the Industrial Revolution bridge design underwent radical change but it is interesting to note how new developments at that stage still represented old forms. Abraham Darby's 30m cast-iron span at Coalbrookdale was designed to resemble an arched stone bridge.

The opposite of the compressive arch is the suspension bridge, with its tensile catenaries. There were pedestrian suspension bridges in sixth-century China – and rope bridges in Tibet even before that – but it was not until 1800 that a Pennsylvania judge, James Finley, built a suspension bridge for vehicles at Jacob's Creek; he patented a design for bridges in 1810. Although Thomas Telford is usually credited with building the first major suspension structure, the first long-span suspension bridge for vehicles was, in fact, designed by Captain Samuel Brown: the Union Bridge over the River Tweed at Horncliffe, dating from 1820. Still standing today, its 91m span is characterized by an incredible lightness and the deck is completely unstiffened.

The development of wrought iron provided new scope as regards tensile strength and in the early nineteenth century ingenuity was directed at making efficient use of this precious material. Telford's 1825 bridge over the Menai Straits used wrought-iron suspension chains. The railways required greater load capacity; however, new techniques were developed that provided the solution. The benefits of rolled and riveted steel can be seen in Stephenson's Britannia Tubular Bridge (1846–50). Engineers of vision pushed the boundaries of knowledge in structural analysis even further – sometimes with success, as in the daring long-span arches in Eiffel's 1878 Douro Bridge (with a span of 140m), and sometimes, as with Thomas Bouch's Tay Bridge in 1879, with failure.The iron bridge as a form in the 'Age of the Engineer' culminates in the Forth Bridge (1881–89), its spans a breathtaking 521m. Here the bridge becomes a defining monument of the Industrial Revolution and a destination in its own right. Critical reaction to the bridge illustrates the essential dichotomy between design philosophy and appreciation. While William Morris wrote: 'There never will be an architecture of iron, every improvement in machinery being uglier and uglier until they reach the supremest specimen of ugliness – the Forth Bridge', Alfred Waterhouse admired it, and saw it as creating its own style. The debate about the validity of so much of twentieth-century modern art and architectural endeavour was already looming.

Developments continued apace in the twentieth century: Maillart produced the first box bridges and Freyssinet increased the capabilities of reinforced concrete with prestressing techniques. Then there were long-span suspension bridges, such as the 2,220m Humber Bridge – made slender by its aerodynamic design and its high-strength cables. The poet Philip Larkin, who lived in Hull, described it as 'swallow-fall and one plane line'.

Most recently there has been the development of cable-stayed bridges which use the principles of incremental balanced cantilever construction – seen before in the railway bridge over the Firth of Forth.

The history of bridges is deceptive, however – as so much of history is deceptive – because it catalogues the triumphant and the exceptional. Since 1945 too many engineers have begun to worship the false god of economy. In the past loved ones were sacrificed or actually even built in to bridges to placate the river gods; recently the aim seems to be to achieve a design at absolutely minimal cost while issues of value to the environment are entirely forgotten. Cost is quantifiable and value is subjective.

Nevertheless, throughout this period there is a well-documented and discernible thread of excellence in bridge design – with architects having no more than a peripheral role:

Christian Menn's Ganter Bridge, for example, is perhaps the defining bridge monument of the twentieth century – an absolute triumph of man over natural topography. It contains all the ingredients: concrete, a combination of tensile and compressive elements, curvature, visual movement, elegance and proportion, economy and efficiency, all in a spectacular mountain setting and without an architect in sight.

Since the 1980s architect/engineers (and there are only a few) such as Santiago Calatrava have promoted bridges as urban sculpture, acquiring for them the status of civic icons (his Alamillo Bridge of 1987–92, built for Expo '92 Seville, for example). The architectonic possibilities are fully explored and structural expression overcomes the dogma of minimizing material at all costs. The practice of adding weight for the sake of appearance is, in strict engineering terms, anathema and for this Calatrava makes himself unpopular in certain engineering quarters. Indeed, when conscious decisions are made to deviate from purist solutions, they should be made after careful consideration of the step's worth – and mindful of this alleged sin. I believe that there are value judgements to be made, and the designer should be given sufficient latitude to determine the disposition of mass for any given form. The real sin is making a structure ungainly simply because it is cheaper to design it that way, and justifying it on the basis that an ill-fitting component makes it cheap to build.

In the 1990s a number of architects were quick to see the latent potential in bridge design in the United Kingdom. Architects with an interest in structure, materials and the tectonic rather than exclusively the narrative could readily and successfully adapt, working on a collaborative basis with engineers who possessed the innovative vision but who recognized the conceptual skills on offer.

The common and insidious misconception held particularly by many civil engineers is that architects just come along and 'prettify' a structure once the engineer has determined the form and details. Certainly, nothing could be further from the truth on the bridge projects with which WilkinsonEyre has been involved. If a bridge turns out 'pretty', it is felt that the client's money has been wasted, with no consideration given to any genuine civic, urban value that may have been contributed by architectural and sculptural intervention. This nonsensical view has its roots in ignorance; and it is ignorance which equally informs the sense of bewilderment that anyone other than an architect can make a contribution to buildings. (The reality, of course, is that there are as few innovative engineers as there are creative architects.)

There are numerous books on bridges and it is possible to sense a common theme in even the most erudite that, broadly speaking, the architect has been a disruptive influence, essentially undermining the confidence of the designers. The feeling, really, is that there is hardly a place for the architect in 'structural art'.

The architect's role, however, has always been to attempt to civilize what at the time would have been perceived as brutal structures. With hindsight, of course, it is possible to see that many of these bridges were either not brutal at all or else that the raw power of their construction (on such a large scale) merely transcended normal perceptions of beauty and aesthetics. This argument can still hold true today, for some structures are so big and ugly that they are – perversely – beautiful. This beauty, however, comes from a different set of parameters; and the fact that there is progressively less and less for the architect to do, as the bridge gets bigger, is proof of that.

It is, however, the architect's contribution now that I find interesting. The era of twentieth-century functionalist design, ranging between the extremes of the reductionist 'no design' approach to more expressionistic styles, has, in fact, been most instructive. Architects now not only know how to use all the elements of construction, they tend also to adopt a broader palette when making architecture – including form, space and the subjective in their designs.

WilkinsonEyre's architectural approach grew out of the rigour of 1970s' modernism, with an obvious interest in context, utility, structure, construction, form, proportion and lightness. Arguably this way of thinking is much more relevant to bridge design than the rather divergent agendas of previous generations' architects. And just as the architecture is more engineered, so the bridges are more 'architected'. WilkinsonEyre, by working collaboratively with engineers, manages to fill a gap in their armoury, and brings more to the design as well. It is through just this type of collaboration and standard-raising that cultural vision and civil engineering will associate again.

It seems worth stressing that when WilkinsonEyre is involved in a bridge project, more often than not the raw concept comes from that quarter. To do this requires not only a degree of ingenuity, which architects generally possess, but also some knowledge – albeit modest – of general engineering principles. Some sort of intuitive understanding of what feels as if it might work is also essential – not just the bridge's capacity to stand up but whether it will be intelligible as a structure in its own right, with a legible flow of forces and a spatial sequence that seems rooted in its context.

It is only through the altruism of clients who recognize that infrastructure can make civic gestures that the firm has had the opportunity to express their concern for architectural space and the potential to modulate the urban fabric using as a vehicle that most symbolic of engineering structures: the bridge. One such client is the London Docklands Development Corporation who, in the mid-1990s, nearing the end of its remit, embarked upon a series of competitions – for bridge designs – and enlisted architect/engineer teams.

WilkinsonEyre was fortunate to participate in the 1994 competition to design an opening bridge at South Quay near Canary Wharf – and to win the commission. The rather complex requisites of the brief, including a navigable opening span and the potential for shortening and relocation to a different alignment in the future, were turned to advantage and addressed in a single constructional idea. Employing the diagonal and a swinging configuration, the bridge takes the form of an 's'-shaped deck with canted masts and stay cables, its curvilinearity acting in contrast to the austere urban grain of its context. Perceived movement across the bridge is accelerated by the psycho-kinetic form. Despite the proximity of Canary Wharf Tower, which stands as a regional visual landmark, WilkinsonEyre's bridge at South Quay carves out its own place, modulating the urban fabric on a more humane level.

This was a happy introduction to the genre of the bridge. It was followed by further competition wins in Manchester, Bedford, Maidstone and – perhaps most significantly – by a commission to span the Tyne [between Gateshead and Newcastle] – a river defined by its bridges.

An enduring quality of many bridges is their sense of arrested movement. What can imply more movement than the graduated curves of an arch or a suspension catenary? The form of the structure is obviously important in this regard but the sense that all the various elements are juxtaposed in a dynamic counterpoise – where balance is only just maintained, somewhere close to the limits – is crucial too. The new architecture is also concerned with the careful composition of surfaces and lines which can bring a gracefulness to the bridge structure.

At the barest minimum a bridge engages with the space defined by the area of its deck. While the bridge's relationship with the sky above is indeterminate, the space below the structure is easily defined; the two spaces are not always related, however. I regard the space above and below the bridge as being continuations of the landscape in both directions and in my mind the spaces over and below the bridge are also connected. When there is a structure above deck level these interconnected spaces are easier to read, and there are overt visual clues to the bridge's spanning capacity for all to see. When the structure of the bridge reaches out beyond the conventional confines of the vertical plane that define the edges of the deck the bridge moves into a new dimension. Suddenly a dynamism has evolved and the architect gets a real gut feeling that the structure is engaging with its surroundings, and the space above the deck opens out. Geometrical devices, such as the twisting of a plane of cables into the third dimension, can enhance the feeling of movement in space. In open landscape such structures can become at one with nature, while in an urban context the excitement of the forms is potentially magnetic and other-worldly.

As ubiquitous as the bridge itself is the symbolism of the bridge. Today 'architecture' is used as often to describe the construction of a political agreement or a piece of software design as it is to discuss the built environment. In the same way, 'bridge' metaphorically spans any divide. More than the word, however, the power of the bridge as a symbol of regeneration has few peers.

In a machine age interwoven with information technology and media power, bridge structures stand as potent symbols of how mankind has tamed nature. Images of bridges appear constantly in advertising – usually for cars or cigarettes. Deployed as powerful symbols of technological triumphs, they also represent an acceptable face of modernity, their daring structures provide good, dramatic, attractive imagery. The subtext: 'If you can fly in the face of nature with such daring structures you can fly in the face of nature by smoking or driving too fast.'

The power of a well-designed bridge lies not just in its symbolic strength but also in the quality of its imagery. The scale of the image, presented in settings that make it highly visible, using structures that contrast sharply with all the other usual constructions in the environment, ensures that the bridge as a typology is pregnant with possibility. Beautifully designed and well rooted in its setting, a structure can provoke more than pure admiration; a bridge can become an icon. The Golden Gate Bridge is the definitive icon for San Francisco just as the opera house – harbour bridge image stands for Sydney.

'Landmark' is a word increasingly used by those who commission buildings and bridges; it reflects their aspirations for the project. The word means different things to different people, however: for some a landmark has iconic status, while literally, a landmark is something big that stands out from its surroundings, and on another level it is no more than qualitative recognition. While I realize it is an obvious watering-down of the word, I would like to promote the latter usage because – obviously – not every new structure can be a landmark statement.

Art differentiates itself from science by being in essence unmeasurable: as Louis Kahn pointed out, a great building must begin with the unmeasurable, must go through measurable means when it is being designed and built, but must, in the end, be unmeasurable. While a bridge cannot be sculpture in the purest sense because of its inherent functionality, which is measurable, and because it is an engineering structure, it can nevertheless possess extraordinary sculptural qualities, drawing it closer to art than science.

Innovation is an imperative. I believe, however, that technological advance is less often the result of direct scientific discovery than part of a creative process – thinking out new ways of doing things. Working in bridge design, however, this effort – and the identification of any achievement – is always very focused, because one is operating in a language which essentially has only three basic forms: the truss or beam, the arch and the suspension or cable stay. All bridge proposals are variations on a theme working within these parameters of basic type.

Opening bridges provide the opportunity to create an entirely integrated design – one that actually speaks of its method of opening. The act of opening is something to celebrate. The structure is transformed as the bridge opens: this can either be a surprise and a revelation, or a clear expression explicit in the structural form. Our bridge over the River Tyne for Gateshead Metropolitan Borough Council belongs to the former category; the whole bridge is mobilized in an unexpected manner to change like the opening of an eyelid. The static is imbued with a sense of movement and then real movement becomes a spectacle.

The contrasts that can be experienced in architecture, whether they be contrasts of form, weight, texture, space or setting, are hugely enjoyable. And everyone's perspective on every structure built is influenced by comparison and contrast, within and without: there is no such thing as a truly stand-alone building. By their very nature, bridges are relatively unusual structures so the contextual contrast is emphatic. And the inherent contrast created by the apparent lightness of bridges is well established and much enjoyed. Historically, however, it was the introduction of iron in the Industrial Revolution that fostered an altogether new design aesthetic though, initially at least, it was combined with contrasting masonry elements. Interestingly, it is with these great compressive elements that architects have in the past been involved, as if it were too risky to delegate to the engineers. Since then technological progress has marched on ceaselessly, creating ever lighter structures and pushing further and further into engineering territory. I sense now that there might be room for bridge structures which contain both light and heavy elements, the contrast between them accentuating the quality of each as it does in architecture.

'Form follows function' is an old mantra widely known beyond the limits of the design profession: it is a paradox, however, that in structural terms the reverse is also true. The structural function of a form follows the determined geometry of that form. The form is in the hands of the designer; he/she effectively selects a geometry which sets the framework for controlling the forces and the forces flow where they need to. Material is then added to or taken away from a given form or geometry – to respond to the flow of forces. The geometry used with bridges is always clear cut but the sophistication of the spaces created by those bridges are dependent on quite subtle interventions, none of them scientific in any sense – except in the ways they have been worked out.

Just like an aeroplane's wings, which must deflect or else their stiffness would cause them to fail in the face of shock loads, buildings – and bridges too – must never be without elasticity. This, in a sense, can be construed as a passive form of responsivity. Technological progress and analytical capacity are now so advanced that architects can design structures that are responsive in an interactive way with loads or encounters with other forces. WilkinsonEyre explored the expressive potential of an interactive bridge structure at the Science Museum in London; light, sound and graphic imagery were activated by changing loads. The firm is now looking forward to designing adaptive structures that can respond to loads, environment or even location.

Intuitive thinking is of paramount importance in the creative process; knowledge and intellect are important because they can put us further in touch with how and why we feel we like something or believe it is right for what we are trying to achieve. The most powerful positive sensation that a structure – or bridge, in particular – can provoke is a sense of wonder. This combines admiration with a 'wow factor' – usually having caught sight of something outside the normal range of experience. Although, in the art world, immediacy is not always regarded as an attribute, in the world of engineering structures that exhibit a clarity of thought and execution have a very direct appeal. The daring and defiant bridges that span long distances or that seem to challenge our sense of the possible are a constant source of great wonder.

Jim Eyre

This essay originally appeared in the practice monograph 'Bridging Art and Science' (Booth –Clibborn Editions, 2001).