Shape and Geometric Tracing of the Arches of the Late Eighteenth-Century Neuilly Bridge Over the Seine in Paris

The end of the 18th century sets a significant date for the masonry bridges construction technique evolution. Studies regarding the thickness of the pillars and shape of the arches configure innovative theories towards the traditional practice that for centuries has produced masonry bridges characterized by large pillars and round arches by modest span. The masonry bridges construction technique evolution is linked to the design experimentation of the French engineer Jean Rodolphe Perronet (1708–1794), whose program on the construction of bridges includes not only the simultaneous construction of all the arches, but also a considerable reduction of the rise-clear span ratio which, through the adoption of polycentric curves, generates very low arches and the consequent reduction of the pillars number in the water. In this sense, this contribution aims to investigate the treatise sources on the geometric tracing modalities of the semi-oval arches ‘with n centers’ of the masonry bridges by Jean Rodolphe Perronet focusing attention on the analysis of the developments and applications in the 18th-20th centuries of the rule of semi-oval arches ‘with n centers and on the geometric analysis of the project for the Neuilly bridge described by Perronet in the volume Description des Projets et de la Construction des Ponts de Neuilly, deMantes, d’Orléans, […], edites in Paris in the 1788.