Text: Anne Isopp
Anne Isopp: Since the inauguration of the Simone de Beauvoir Bridge in Paris, your name has been associated with bridges. Have bridges always interested you?
Dietmar Feichtinger: I didn't choose to build bridges as such. It's more a result of my interest in construction. You can already see that in my early designs. When I entered bridge design competitions the jurors probably noticed that my projects have an underlying constructional approach.
AI: With bridges – more so than with buildings – I always think that design and construction have to be one. When does the engineer come into play?
DF: In the building of bridges there are many constructional possibilities. Many bridges are logical in terms of construction, fully exploit the potential of materials and are economically justifiable, yet absolutely uninteresting from the point of view of design. Unfortunately this applies to most bridges. They have no added value. The fact is the creative will is what determines the appearance of a bridge. The bridge in Weil am Rhein, for example, is an arched structure that spans 235 metres. The engineers' first reaction to my design was: 'That is the wrong kind of construction.' All the other competition participants had gone for a suspension bridge. But I wanted to bridge the gap between France and Germany symbolically. I found an arched bridge much more powerful as a gesture indicating connection. In the course of development, the design idea also turned into a very good arched bridge in engineering terms… Wolfgang Strobl, the head engineer, often had to oppose the conventional engineering solutions put forward by his own office. The engineer plays an important part when it comes to achievability. Collaborating on an unusual or new kind of construction presupposes a high degree of willingness and understanding on the engineer's part.
With the bridge across the Seine, it was not the usual matter of linking two points, but four points: the upper and the lower walls of the quay on each side. At some point I found the following solution: two superimposed arches, one upright and one inverted. The two arches cross each other. The paths across the bridge follow the arch geometry. I made one path more dominant, that is, wider, and the other narrower. If you take the upper path you are very high above the river and can overlook the urban space; if you walk below, you are protected and relatively close to the water.
Only after I had developed this idea in structural terms did I get together with the engineers. First, there has to be an approach that is strongly associated with the place. These bridges are site-specific and non-transferable. The engineers' reaction to my design was that the arch could not function as such, because of the modest rise, which is limited by walkability. They were especially keen to deploy the stress ribbon. A stressed ribbon bridge can cope with a relatively low rise, but has the disadvantage that the anchorage blocks on the riverbanks have to be enormous. I assumed that you could do both, that you could superimpose the two arches and profit from both structures. And that is how the project developed in the end. The design intent provided the source and motivation for the project.
In another project of mine, at Mont Saint-Michel, the theme of lightness and blending into the landscape is even more important. Here we have a two-kilometre link between the mainland and Mont Saint-Michel, a rocky island topped by a monastery off the coast of Normandy. Feasibility studies called for spans of between 35 and 100 metres. It bothered me from the start that this was referred to as a bridge. Long spans that are clearly legible make the breadth of a space measurable and become narrow. I therefore conceived more of a boardwalk across the tidal flats, and proposed placing pairs of extremely slender supports every twelve metres. Because of the large number of supports, the structure is read as an integral whole. It has the additional advantage that you can make the bridge's deck thin – a horizontal line in the bay. The immensity of the landscape is thus underscored.
AI: You have built not only bridges but also remarkable works of architecture. What roles do construction and materials play in your buildings?
DF: How could you not be interested in materials and structure as soon as you start thinking about a building? No project of mine is mere image. To me construction and material are very powerful design elements. What matters to me is the legibility of a building's structure. It begins with the visible network of conduits, which tells us about the inner life of a building and determines the design. And as for materials, steel is a building material predestined for a constructional approach of this kind. Steel is well suited to negotiating long spans with relatively low structures, compared to concrete and wood. The school in Taufkirchen was all about openness, transparency and relating to the surroundings. The supports are therefore made of steel and very delicate. To me a project is successful if it expresses coherence between place, content, construction and material.
AI: The school building in Taufkirchen, however, is not purely a steel structure but a hybrid one of steel and wood. Why is that?
DF: Even though steel is a building material very much predestined for my kind of constructional thinking, I don't have any constructional principles. Hybrid structures have many positive qualities; you can extract the best from each material. In Taufkirchen, wood was the material that suggested itself. The site is near the River Pram and is very closely related to the natural landscape. Decisions about spatial organization and floor plans brought steel into play. There is a three-part gym, half of which is underground. Above it is a two-storey classroom wing. We covered the gym with the help of a steel structure, almost like a bridge, which is over 40 metres across. The load-bearing ceilings are made of 20-centimetre-thick solid wood panels, their undersides left exposed. There are no suspended ceilings. The logic of the project develops from this approach.
AI: Yet your buildings do not seem fragile, either…
DF: When I am grappling with structure, I often think of insects. If you look at an insect, it has an extremely efficient structure, optimized for the conditions in which it lives. Just think of the feelers, the legs and the eyes. The design of an insect is actually the outcome of these abilities. Concepts such as lightness, openness, transparency, which I also use in connection with my architecture, correspond to this approach. The footbridge in Weil am Rhein or the one in Paris are meant to touch down very lightly on the riverbank, like an insect that stretches out its legs and finds its footing.