Engineering architecture.

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.

For CBG such design solutions start by understanding the importance of an architectural language in defining the Swiss landscape. Sometimes the beauty of engineering lies not in the singular or expressive solution but in one that is outwardly modest yet elegant. This kind of beauty should not be confused with a reductive or minimal aesthetic; rather it is perhaps best described as taking on architectural considerations.

The careers of CBG's principals also reflect this. Jurg Conzett is the best-known partner and the oldest, having graduated from the ETH-Zurich in 1980; Gianfranco Bronzini and Patrik Gartmann from polytechnics in 1989 and 1994 respectively. After graduating as an engineer Conzett worked for six years in Peter Zumthor's atelier. In recognition of his architectural sensibility, Conzett has been awarded honorary membership of the Swiss Institute of Architects and of the Royal British Institute of Architects (RIBA). Gartmann has degrees in both architecture and civil engineering and was an assistant lecturer for two years in the architecture department at the ETH Zurich. Conzett is perhaps best known for his work in timber, and he was lecturer for timber engineering at the Polytechnic in Chur for 17 years. One of his most famous designs is the Traversiner Footbridge in Viamala, completed in 1996. A space-truss system with panelled side rails acting as stiffening girders, it had to be light enough to be brought to its mountain site by helicopter. Sadly it was destroyed by a rockfall three years later. Part of the infrastructure for the Viamala Ecomuseum, the bridge again demonstrates CBG's appreciation of the cultural and visual importance of the built environment.

The Viamala is the longest gorge and the most direct route through the Alps between Lake Constance and Milan. It has thus been an important passage between southern and northern Europe since at least Roman times but was only made passable again by foot in 1996. With the destruction of the first Traversiner Bridge, the route through the gorge was cut. The initial response was to reconstruct the bridge in the same spot but eventually it became clear that this would only leave it vulnerable again. The safest option seemed to be to move the crossing across the ravine down the valley but at the cost of tackling a more difficult site. For here the north side of the valley is a steep vertical rockface that would have required an ambitious and expensive suspension bridge spanning 100m. Gradually CBG developed the idea of shortening the span by making an angled walkway, which resulted in a stair spanning around 57m.

The combination of existing geology and 22m drop between the two sides of the ravine meant the almost 100m-long suspension cable could be fastened to low pillars and anchored with a counterweight on the south side. On the north side it was slung around a boulder. The suspension cables are not arranged conventionally but as two crossed diagonals. This creates a diamond truss system that is much stiffer and so more comfortable to traverse than a standard swaying bridge. The pillars anchor the cables at their highest point, which simplifies post-tensioning and also creates a gateway to the crossing. Because the walkway itself is narrower than the substructure, where horizontal forces are taken up through cross-bracing, users cannot peer directly downward. The thinness of the handrails, however, allows you to see along the length of the ravine. Structural members are made of larch glulam beams, with stair treads and railings of weather-resistant heartwood of fir felled locally. The bridge is part of a tourist trail and so, as with the Rhatische Bahn, the engineering also defines how the natural and cultural landscape is perceived. However in the case of the Traversiner Footbridge, while more technically innovative and singular, it is not merely expressive, but a thing of joy which takes its place within a stunning natural and cultural landscape.

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Werner Sobek

While the title architectural engineer has not quite caught on to describe a profession, it does describe Werner Sobek, whose education and career as an engineer have always intersected with architecture. Sobek places great emphasis on the efficient use of resources, be it by minimising material and energy expenditure or maximising durability, reliability, recyclability and environmental compatibility. In the first two of the three projects described here, Sobek operates freely, as an engineer/designer. In the third, however, his role is that of a more conventional collaborator.

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A papal visit is normally a major occasion, but the visit to Bavaria in 2006 of newly elected Pope Benedict XVI, himself Bavarian, was especially highly anticipated. Sobek was commissioned to design a temporary altar at the New Munich Trade Fair Centre where the Pope was to celebrate mass before more than 250 000 people.

While the entire structure had to be temporary, which meant it was used for only a few hours and had to be demountable, it was much more than just an altar and a roof. The 12 x 14.5m plinth was a steel structure clad in wood, like a normal stage. The abstract, massive looking base not only had to accommodate 300 bishops plus 90 other celebrants but also cope with needs of the flesh. In addition to the stage-like front where mass was celebrated, it had temporal functions such as a small kitchen, lavatories, a sacristy for the Pope and another one for the bishops. There was also space for security guards, medical personnel and an ambulance.

The appeal of the design comes partly from the graceful form of the tension fabric structure, a five-pointed sail that swoops upwards towards the audience and the sky. But its impact also derives from an engineer's understanding of the highly metaphoric nature of programme. A heavy-looking plinth steps up from the earth, with the Pope sitting at its zenith. Above him, like the canopy traditionally carried by cardinals, floats heaven over earth. The refined, delicate detailing helps sustain this metaphor, and is especially noticeable where the canopy connects to the columns without any apparent mechanical fasteners or puncturing of the fabric.

Born in 1953, Sobek studied engineering and architecture and received his PhD in engineering from the University of Stuttgart, where he now has two professorships. In 1994 he succeeded to the chair held by Frei Otto. Although it is unusual for an engineer to assume a chair occupied by an architect, Sobek's method of applying the traditional methods and means of civil engineering--analysis, knowledge of construction and of material technology--with the elemental architectural values of form and design was similar to Otto's Institute for Lightweight Structures.

In 2000, Sobek was also named successor to the professor of engineering Jorg Schlaich, the latest in a long line of eminent civil engineering professors at the university that includes Emil Morsch and Fritz Leonhardt. Sobek formerly brought the disciplines of architecture and civil engineering together in 2001 by forming, with Professor Balthasar Novak, the Institute for Lightweight Structure and Conceptual Design, which currently has about 60 members. Alongside this remarkable academic career is the firm Werner Sobek Engineering and Design with approximately 100 employees and offices in Frankfurt, Khartoum, New York and Stuttgart.

Although slightly more mundane than the papal commission, H16, a single-family house outside Stuttgart completed in 2006, indulges in some of the same poetry of heaven and earth. Set on a steep site defined by a stone retaining wall, the house consists of two boxes. The lower box is earthbound. It appears heavy, almost opaque and concrete (though it has a steel skeleton). Appropriately, it contains all the private, quotidian functions of a house that require a sense of enclosure--bedrooms, lavatories and so on. But a stairway leads upwards, from the earthbound to the ethereal, from within the landscape to literally above it. Dramatically cantilevered above the hermetic box is a fully transparent living space.

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Technically, the house is zero energy, zero emission and is also recyclable. It has photovoltaics for electricity and employs a geothermal air exchange for warmth. It is thus significantly automated, with an integrated climate system to control environmental conditions. Yet though the glass box is triple-glazed with solar resistant glass, human beings have other human needs. So within this brave new world there is also a fireplace.

Most of Sobek's work, however, is done with architects and his collaborators over the years include Hans Hollein, Christoph Ingenhoven, Helmut Jahn, Kengo Kuma, Dominique Perrault and SOM. But what he always insists on is that he and his firm are involved from the very beginning of a project so that they can work and engage with the architect as a critical partner.

With HG Merz in Berlin, Sobek worked on an enclosure for the ruins of the crematorium at Sachsenhausen concentration camp. The ruins consist only of low-level walls and foundations but are, of course, an immensely important memorial. Some basic architectural concepts were agreed at the outset. First, the enclosure should not have obvious tectonic details, ie, it should be abstract; second, as the ground is sacred, any enclosure should not touch it, even though the span is enormous.

The response from Sobek was an advance on a vacuum-fastening technique he had developed earlier at a much smaller scale for an exhibition stand. At Sachsenhausen, the primary structure is a steel lattice fabricated from standard rectangular box sections. The secondary structure consists of a skin of gratings and perforated metal sheeting, over which is stretched a translucent membrane of fibreglass with a PTFE (Teflon-like) coating. It is sealed air-tight along its edges and affixed to the structure through a continuous vacuum created by a small pump. Because the coating on the fabric is anti-adhesive it stays clean and white. The entire structure is recyclable.

As with all of Sobek's work, the considerable innovation in the engineering itself is not the point. Rather, the engineering serves the larger programme. Here, the white, atectonic walls do not compete with the tactility and recognisable materiality of the crematorium's remains. The luminescence of the walls and roof bathes the ruins in a soft, reverential light. And lurking behind the skin you can make out the grids of the structure, like a neutral, rational field. Animated by a delicate luminosity, Sobek's calm, dignified composition allows us to comprehend even more clearly the barbarity of what happened in this place.

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