Mixed structure buildings of the early XX century: pathologies and causes

Materials naturally undergo physical and performance decay, which becomes pathological, whenever the development is abrupt and rapid and the extent is substantial, due to inner defects and outer disturbing factors, rather than inherent ageing. Design and construction defects, as well as missing and poor maintenance, might be responsible for speeding up the physiological decay and, thus, requiring repair and refurbishment measures. As far as the mixed structure buildings of the early XX century are concerned, a preliminary analysis points out that construction systems were characterized by several techniques and solutions, which were developed in a very short time. In fact, at that time, an overall transformation occurred following the Industrial Revolution. As a consequence, in the building sector, traditional materials and components were progressively combined and/or replaced with modern ones. Owing to the increase of scientific studies and industrial patents about products and processes, the new technological solutions showed increasing complexity and variety. Moreover, they were developed, regardless the traditional analysis of the whole building. As a result, the connections among different sub-systems were neglected, leading to potential critical points. The analysis of more than 110 housing buildings in Puglia and Basilicata Regions (South Italy), dating back to 1900-1940, was carried out. First, it comprised the research on technical handbooks of that period [Breymann, G.A., 1885; Koniger O., 1902; Levi, C., 1907; Donghi, 1906]; the historical, technical and typological classification of buildings and; the identification of construction materials and structural technologies (at building and component scale). Then, it focused on all the mixed structure typologies (including some sub-typologies), in terms of definition of possible critical points for decay development and possible pathological alterations, connected with obsolescence processes [De Tommasi G. and Fatiguso F., 2008]. Specifically, physical obsolescence was mainly analysed from the observation of decay and deterioration in materials and components, as well as pathology patterns. Such an obsolescence seemed the result of a very peculiar occurrence, namely the combination of traditional and innovative materials, generally showing poor compatibility and the unawareness of actual performances of new systems by the early XX century designers and builders. It was observed that physiological and pathological ageing simultaneously occur and affect each other, causing reduced service life and functionality of building components and sub-systems. As a result, they are not always easy to differentiate. The present contribution is going to discuss the results of the above mentioned analysis, with specific reference to slabs and staircases, where mixed structure solutions were thoroughly applied.