18 February 2009

Bridge criticism 11: The French Connection

The last three posts in this series have covered the views on "good bridge design" of Santiago Calatrava, Fritz Leonhardt, and Christian Menn, all of them amongst the great bridge designers of the last century.

Unusually forthright views were presented by French engineer Michel Virlogeux in a 1996 paper, "Bridges and the structural art" (available online). Virlogeux worked on the Pont de Normandie (pictured right, image courtesy of Francoise Roche on flickr), and is probably best known for designing the Millau Viaduct.

I've previously discussed David Billington's ideas on bridge design, which suggest that for a bridge to be "good", it must be elegant, efficient and economic. Like Leonhardt and Menn, Billington is opposed to extravagance, and to bridges which pay little heed to a structural optimum.

Virlogeux does not agree:

"Of course, David Billington is strongly influenced by the American philosophy of life, based on the individuals and on economy ... Economy has been too much the unique goal of narrow-minded engineers, resulting in some poor, ugly and repetitive structures which discredited the profession ... Engineers used to live in their narrow professional world, sure of a legitimacy based on rationality and competence. They have not been able to feel the evolution of our Society and the growing power of politicians and media, and of the lobbies which are able to influence them."
While advocating that engineers adopt a wider view, this is not to detract from "good" structural engineering, but to ensure that structural engineers have a greater voice in design:

"Structural engineers failed in having access to those who take the decisions, and it is not surprising that the result is often poor as regards structural projects in the recent years. The most striking is that design competitions have been organized for some bridge projects - when bridges are the essence of engineering art - which were only open to architects or in which engineers had only a limited role and no responsibility. Resulting in some clear disasters."
In essence, Virlogeux still adheres to the engineering party line, that structures should be efficient and never dishonest. Writing about Marc Mimram's Solférino Footbridge (pictured right, image courtesy of Etienne Cazin on flickr), he comments that:

"fantasy governed the detailed design, a fantasy which had not been tempered by the rationality of a serious engineer; the arches, for an example, are made of inclined I-shaped beams with totally irrational details. There is no web - for transparency - just a series of diaphragms, and the members are transversely curved, [which] obliged these beams [to be] made from cast steel elements ... back to the 19th Century and to enormous costs."
Virlogeux's prescriptions for a successful bridge design are that it be:
  • structurally efficient, and sometimes innovative
  • expressive of the state-of-the art in construction methods
  • built with perfection and elegance as a goal
  • built by the most eminent builders
  • in agreement with its surroundings
As may be obvious, Virlogeux is refreshing in his willingness to criticise his fellow engineers. From the same paper, there comes this example:

"We take an example from the World Exhibition in Sevilla to evidence such a difference, with the two major bridges built on this occasion: the Alamillo Bridge, which can be considered an attractive sculpture, but which is a total nonsense structurally, and the Barqueta Bridge [image courtesy of Guillermo Vale on flickr] designed by Juan Jose Arenas, a real structure which shows the natural flow of forces, and which is elegant and efficient in the same time."
So, it turns out, that while Virlogeux does not think engineers should be slaves to economy, there is nonetheless a moral imperative to avoid structural inefficiency:

"These monstrous errors must be systematically denounced to avoid their repetition, and to convince that excellence in bridge design can only come from a rational structural organization. Unfortunately, even some good architects who used to work efficiently with engineers are going in the wrong direction when they are given the responsibility of design. What is wrong? - too much searching for originality, aiming at producing a surprise more than trying to develop a pure structural design which is not, by essence, in their real competence.

"Modesty must be considered again a quality!"
This sense of anger seems to drive many bridge engineers commenting on bridge aesthetics in the last couple of decades. It is not entirely directed at the increasingly key role of architects in landmark bridge design, but also at clients and the wider society for promoting that focus. Hardly anyone wins a bridge design competition with a simple, efficient bridge of a form that has been used many times before. The anger is also provoked by a sense of loss, as bridge engineers are simply not used to having their controlling role in design usurped by others.

Ultimately, however, these debates are not about the interests of architects or engineers, but about whether bridge design serves the wider public well. The public do not care if a bridge design is structurally inefficient - but they do care if it is ugly, or if it requires far more of their money than an alternative. Virlogeux's focus on the principles of good structural design is only helpful where it serves these demands.

So, from all of this, is there any useful guidance as to how we can evaluate good bridge design, how we can criticise poor design? The expressed philosophies of the four designers I've highlighted are all subtly different, but all fundamentally derived from modernism and a belief that efficiency or economy is a moral rather than a purely commercial requirement. Personally, I think there should be room for idiosyncrasy, eccentricity, bravado, and even humour from time time - so long as there is accountability, and people understand both what they are paying for, and what the alternatives really are. This isn't the case as often as it should be.

Calatrava seems to have paid little heed to the Vitruvian ideals that he espoused twenty-five years ago, and his willingness to ignore prevailing wisdom remains admirable however ridiculous some of the resulting structures have been. There's room in this world both for Calatrava's flamboyant structure-as-sculpture, and for the elegant exploitation of structural behaviour that characterises many other bridge designers. I think the challenge is to make the public, and the clients who spend their money, really understand the choices that are available, and the real consequences of those choices in cost and risk. That will require better procurement processes, more visible structural engineers, and undoubtedly more public criticism of bridge design, both good and bad.

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