ABSTRACT
Traditional design of masonry structures up to the twentieth century used empirical proportional design rules, independent of the scale. For buildings they were essentially correct: stability depends on the geometry, but not on the size, of the structure. Bridges support the pass of heavy traffic loads and the problem is non-proportional: for a given load smaller bridges are “weaker”, more sensitive to action of the passing load. However until the eighteenth century the known rules were proportional. H. Gautier (1717) proposed first a non-proportional rule, but it was too conservative. J.R. Perronet (1748) produced a non-proportional rule for arch bridge-design both simple and reliable and justified it by the comparison with more than 200 existing bridges. Perronet’s rule was in use for more than 100 years. In the present paper the use of Perronet rule and the development of arch bridge design during the eighteenth century will be studied, with a final discussion on the validity of the rules.
