Bombproof. Engineers, Architects and Theories on Vaulted Structures in a mid-18th Century Military Construction Site

Abstract

The construction of the new Citadel in Alessandria, since the 1730s, sparked several debates among the different actors involved in the project. Among the themes that were discussed, there are issues that are now considered crucial to the development of construction science in the 18th Century: from foundation systems to the form of vaulted structures.
This essay considers the complex debate that developed on the best form to assign to the “bombproof” vaults of the buildings to be erected inside the fortified perimeter. In 1756, engineers, architects and State administrators met in a “congress” to discuss whether semi-circular or elliptical designs were to be preferred: while on the one hand this meeting highlighted a situation of
crisis, on the other hand it became a favourable occasion of improvement, and promotion of a truly scientific approach to construction.
The need to counteract the effects of the concentrated force due to the bomb impact on the vault extrados introduced a new and never before considered factor, in a debate on vault design which was by then widespread. In respect to the theories (notably De La Hire’s) then considered as “state of the art”, the problem was approached by considering the newest theoretical developments
in balistics. The problem is analyzed by a close reading of the expertises, leading to more general observations on the relationship between science, technology and the architectural professions in the 18th Century.