Roman masonry stairways. Geometry, construction and stability

This article focuses on the study of the so-called “Roman Masonry Stairways” which represent a rather common typology in historical buildings particularly in the Neapolitan area. The vaulted system of the numerous examples of Neapolitan open staircases consists of the use of the main elements of structural support, such as arches and vaults, underlining the close dialectical relationship between form and structure. Therefore, the analysis of the vaulted space is carried out in relation to functional requirements, materials and construction techniques within the articulation of the architectural figure [1]. This research proposes an interpretation of the static behavior of this type of staircase through simplifications that facilitate its analysis. In this paper reference is made to the case study of the stairway of Palazzo Persico in Naples, whose structural analysis is carried out in the theoretical framework of the Limit Analysis as applied by Heyman to masonries [2]. The main objective of the investigation is to demonstrate the static equilibrium of this structure and to understand its mechanical behavior. Before dealing with the analysis, the structural process was defined from different points of view, by interlocking formal, material and spatial aspects. The formal definition concerns its geometric configuration, while the material and spatial one concerns the elements that compose it and the relationship existing between them. Specifically, the staircase in issue is characterized by a cantilevered structural system with a planimetric scheme consisting of a 45° rotated square. Its vertices are rounded off by arches of circumference along the sides of which are placed the flights. The flights are cantilevered from the walls and connected by small vaults constituting the landings, as common for these masonry vaulted staircases. The aim of the work is to obtain an equilibrium solution that, being compatible with the loads, does not violate the limit condition of the material [3]. In other words, a solution for which there is no traction and where the compressive stresses are contained within the masonry. The structural analysis was performed taking into account the principles of limit analysis and by applying the Safe Theorem. Ultimately a static graphic analysis has been conducted.