Engineering architecture

Architectural Review, The, Feb, 2007 by Jurg Conzett

The cliches are tiresome but as usual contain some truth: engineers and architects struggle to work really creatively together. They are, after all, distinct disciplines with separate bodies of knowledge, but also involve different ways of seeing, and often have different values. Yet to achieve a successful building or structure, something uplifting, architect and engineer must be able to understand each other, respecting their differences while working towards the same goals. For the architect this means an engineer with an architectural sensibility, one who does not think he is an architect but who can be a true design partner. To this end, Steven Spier looks at the work and careers of Werner Sobek and Jurg Conzett.

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While the staggering engineering achievements of the nineteenth and early twentieth centuries can be readily appreciated, the typical examples chosen for the historiography of modern architecture are monumental and heroic, singled out for their technical advance or bravura. But the development of a modern infrastructure was mostly through works more well-done than heroic, and these played an important part in the development of landscape and cultural identity. That the modernisation of a motorway or railway line should address technical, cultural and visual aspects of its own history as well as basic technical requirements is an approach exemplified by Swiss engineering firm Conzett, Bronzini, Gartmann (CBG) in their work for the Rhatische Bahn.

The red railway carriages of Rhatische Bahn connect every major valley in the Graubunden, Switzerland's most south-easterly canton, passing through spectacular Alpine scenery. But beyond being an important piece of traffic engineering, the rail network has played a crucial role in the invention of the Alps as a tourist destination. This may have started in the English Romantic era but by the late nineteenth century, Switzerland was creating an infrastructure of hotels and railways capable of accommodating more than the hardy solitary poet or gentleman. Today tourism is the Graubunden's most important industry and the Rhatische Bahn's network is a vital part of this. Designed as a single, coherent work of art and for technical, economic and architectural reasons built largely in stone, it remains, remarkably, more or less unchanged. However, after a hundred years it needs major structural renovation. But how to upgrade the crumbling stone bridges in a way that acknowledges their cultural importance?

The existing, picturesque Farbtobel Viaduct, which dates from 1913, forms part of a rail line linking Chur, the canton's capital, with the resort of Arosa to the south-east. Six stone arches, each spanning around 8m, carry tracks in a tight curve 20m above the valley floor. The steep walls of the valley are slowly but steadily eroding, however, and so the existing viaduct is no longer structurally sound. The most obvious and pragmatic solution was to replace the stone bridge entirely, and there was some precedent for steel and concrete bridges. But the stone bridge is not just of archaeological interest. It can be seen from the train itself on its approach and from the nearby village and so is an integral part of the landscape. Saving the old bridge or constructing a new one out of stone was impractical, but CBG proposed retaining the bridge visually by building a new one along its inner curve. A parallel bridge had the further advantage of not disrupting existing train traffic.

Completed in 2005, the new Farbtobel Viaduct spans the valley in three steps of 20, 25 and 20m respectively. These symmetrically frame the existing stone bridge. Structurally, the new viaduct is a prestressed concrete beam sitting on pivot connections carried in turn by two thin, round columns. The connections are also a structural response to the considerable ground movement. The delicacy of the thin horizontal surface, the round columns and their connections might seem incongruous in this crumbling landscape. But they not only maximise transparency, they also formally act as foil to the stone bridge. The square base rises prominently out of the ground to make their connection to the columns possible during construction. It also helps protect them from damage in the event of a landslide.

A common problem of bridges, roads and tunnels in mountain terrain is that they are often just too narrow. This was the case with the existing stone Valember Bridge, in the Engadin, which needed to be twice as wide. Normal practice would have been to widen it on both sides or even replace it, but here the geometry of the approaching road with its retaining walls precluded the former strategy. Because of the bridge's cultural significance, CBG decided not to replace it. Careful inspection and testing proved it to be structurally sound so it could be reused. Half of the road surface actually sits on the old bridge while the other half sits on elegant prefabricated, cylindrical columns. They are placed on either side of the bridge and frame the arched opening. The road surface is raised so that it does not obstruct the arch. The slender columns and thin road surface--the edge of the bridge is detailed to be as abstract as possible, to show one line instead of a separate beam and kerb--maximise transparency and contrast with the massive stone structure of the original bridge.