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Robert Maillart’s Salginatobel Bridge, built in Switzerland in 1930, epitomizes a tradition of bridge design in which an efficient flow of forces, low construction cost, and rich aesthetic significance are embodied in a single structure. This bridge defies the commonly accepted belief that it is necessary to spend more money to make bridges elegant, i.e., that beauty is something that has to be added to a minimum-cost skeleton of functionality. Rather, in the design of this bridge, Maillart responded to the challenge of minimizing cost by creating an entirely new structural system, which created economic value far in excess of what would have been gained had he merely attempted to refine material quantities in a conventional structural system. This technical innovation in turn gave Maillart new opportunities for visual expression which he, as a gifted designer, used to create Salginatobel’s bold visible form. In Maillart’s bridges, therefore, technological innovation provides the crucial link between an economic imperative and aesthetic significance.41371
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Maillart is not the only engineer to have designed bridges that link economy and aesthetic significance through engineering innovation. He is part of what David P. Billington (2003) refers to as a “grand tradition” of structural design, which includes engineers such as Thomas Telford, Gustave Eiffel, and Othmar Ammann (Billington 1983). In the work of all of these engineers, we recognize bold, unique visible forms that were created under challenging economic conditions, and significant technological advances relative to their contemporaries. It is significant that all of the designers within this tradition are engineers, for if we accept that technological innovation is the link between the need to minimize cost and new opportunities for aesthetic expression, then it follows that only those people who understand the technical aspects of bridges can follow the creative process thus defined. 论文网
The visual impact of the Salginatobel Bridge is strong enough to ensure that the bridge’s aesthetic significance would be broadly recognized, regardless of how much it cost. The fact that it would never have been built had it not been the lowest cost option, however, enriches its significance and transforms it from a merely beautiful bridge into a vivid symbol of the strength of the human creative spirit. The fact that it was designed without any intervention from architects or other creative consultants makes it particularly relevant to all civil engineers.
Notwithstanding the compelling nature of Salginatobel, it is difficult to find its successors among bridges built in recent years. Although many bridges from the past decade have been recognized for particular aesthetic merit, they share little in common with the work of Maillart. In these bridges, instead of economy, we find extravagance. Instead of clean and efficient load paths, we find flows of forces that are indirect and inefficient. Instead of design leadership by engineers, we find architects playing key roles in defining the primary characteristics of the structural system.
The Esplanade Riel Bridge, completed in 2003 in Winnipeg, is an example of such a bridge. Given the presence of a restaurant housed in a semicircular platform at the tower, there is little doubt that the architect on the project, Gaboury Préfontaine Perry, would have played an important role in defining the main features of the bridge with engineerWardrop Associates. The inclined tower, which is arguably the most distinctive visible feature of the structure, must resist significant bending moments under dead load. This indirect load path required reinforcement that was significantly greater than what would have been needed had the tower been plumb and concentric with the girder.
The bridge cost 21.5 million dollars to build (Welch 2003), which corresponds to approximately $12,000 per square metre of deck. In comparison, a vehicular bridge (the piers of which are visible in the figure) built adjacent to the Esplanade Riel Bridge and completed in 2002 cost approximately $5500 per square metre (O’Brien 2001). Assuming that a pedestrian bridge could have been built at a similar unit cost, the premium that was paid for the Esplanade Riel Bridge compared to a low cost option was approximately 12 million dollars. On this basis, we can reasonably conclude that the design of the Esplanade Riel Bridge was not significantly influenced by the discipline of economy.