Toward Structural Mechanics Through Wooden Bridges in France (1716-1841)

One of the distinctive elements of the École des Ponts et Chaussées is that it has always created an open-minded attitude to new and interesting activities outside France. In the early 19th century, great interest was directed towards new wooden bridges structural typologies that flourished in the United States. France is drawn by the rationalization of design as a consequence of the need for standardization of the American world leading to the definition of simple, versatile, repeatable patterns. In turn the basis of structural mechanics has been developed by the French experience. The result is the beginning of a new approach to design based on structural mechanics that needs to be further developed, investigated and examined. The earliest French application of Navier’s bending theory is permitted by the simplicity of the structural layout proposed and patented by Ithiel Town. Furthermore, the first applications of A synopsis of the wooden bridges carried out in the second part of the eighteenth century would be hard to construct, as it would necessarily result much fragmented and incomplete. In that period, a sign of the need for renewing the criteria and rules of design may be perceived in the Traité des ponts by Henri Gautier. The state of knowledge at that time is well testified by the Encyclopédie of Diderot and D’Alembert, which had a primary role in characterizing the culture at that time. An extended research at the Fonds Ancien of the École des Ponts et Chaussées has led to identify a particularly significant manuscript, dated 1793, in which the beginning of a new approach to design is clearly evident. The very meaningful story of the Concours de pont within the Concours d’architecture at the École des Ponts et Chaussées is thus addressed. The cultural institutions of the period played a key role in generating and disseminating knowledge in a variety of forms. The Académie Royale des Sciences, intrigued by the accomplishments of the wooden bridges designed by the Grubenmann brothers created the opportunity to obtain a copy of the drawings and drew up a report of the bridge of Schaffhausen. Finally, some works by Karl Friedrick von Wiebeking are presented in this chapter. The first decades of the nineteenth century are characterized by the publication of numerous French engineering and architecture treatises. These treatises are important for the formalization of the solution of structural mechanics problems: in particular the tests of resistance in bending. It is a difficult path, bounded with Galileo’s theories, with the mathematical and theoretical apparatus and with experimental tests as well. The proper solution to the problem is marked also by intuitions, errors and false ideas but, above all, by a huge experimental research in order to find the rules related to the strength of materials, which the design can be based on. The attention was focused on the works by Pierre Simon Girard, Jean-Baptiste Rondelet, Jean Henri Hassenfratz, Emiland Marie Gauthey, Joseph Mathieu Sganzin, Claude Louis Navier, preceded by a brief introduction to the works by Antoine Parent and George Louis Leclerc Comte de Buffon, to which constant reference is made. In this study reference is made to wood, whose mechanical characteristics let the observation on the mechanical behavior in bending possible. Navier’s bending theory to practice are relative to testing procedures mainly related to existing structures and not to the design of new ones. This is not surprising considering that the typical deductive logic of the scientific procedure leads directly to the formulation of criteria for existing structures and, only at a later stage, is adapted to design needs. During this time span, most of the considered wooden bridge structural typologies are temporary structures, sometimes built for the rapid restoration of damaged or demolished masonry structures.