Reliability and obsolescence of existing structures: evaluation of the seismic vulnerability of Scuola Rossini building

The continued use of existing structures is of great importance because the built environment is a huge economic and political asset, growing larger every year. The assessment of existing structures is now a major engineering task. The structural engineer is increasingly called upon to devise ways for extending the life of structures whilst observing tight cost constraints, so obsolescence analysis is fundamental in the process of life extending. It is fundamental to establish principles for the assessment of existing structures, since it is a process based on an approach which is obviously different from designing new structure. Moreover, the process of assessment requires knowledge beyond the scope of design codes. Engineers may apply specific methods for assessment in order to save structures and to reduce a client's expenditure. The ultimate goal is to limit the interventions to the minimum needed and to consider the various solutions, such as refurbishment, adaptive reuse or demolition; those goals are clearly in agreement with the principles of sustainable development. Moreover, it is worth noticing that demolition is not the only possible solution. This document is intended as an example of principals and procedures for the obsolescence analysis and the assessment of aging structure. Various concepts are introduced and studied in this research: useful life, physical life and target life, which are compared each other. Moreover, various practical examples are carried on, dealing with the case study. The aim of this research, that was developed in collaboration with OTH – Ostbayerische Technische Hochschule of Regensburg and with a meeting at the Klokner Institute - Czech Technical University of Prague, is based on the study and applications of the ISO 13822 (Bases for design of structures), ISO 2394 (General principles on reliability for structures) and on the analysis of Eurocode 8 (Seismic design of buildings). The basis for reliability assessment is contained in the performance requirements for safety and serviceability of ISO 2394. This Standard enables the possibility to regulate, verify and document the adequate safe performance of structures, and also to consider them in a broader sense as part of societal systems; it provides approaches at three levels, namely: risk informed, reliability based and semi-probabilistic approach. The methodical basis for this edition of the ISO 2394 is described in JCSS (2008), JCSS (2001) and EN 1990 (2007). The building of Scuola Rossini (Firenze) is an adequate case study, since it is an aging and obsolete building; it was subjected to the earthquake of 1919, whose epicentre was in Mugello, and to a flood in 1966. The mentioned structure is affected by several decay phenomena that occurred during the years, because of ordinary and extraordinary causes. The goal of the surveys which were conducted on the structure is to understand how and why the deterioration phenomena were originated. Furthermore, the case study is a significant example since its structure is a mixture between masonry and reinforced concrete frames. Since masonry structures constitute a huge part of the buildings heritage, their assessment is an important engineering task nowadays, and it requires the application of sophisticated analysis methods, based on national building codes and on International Standards. Since the masonry behaves according to a set of specific macro-elements, namely of rigid-bodies, the structural analysis mainly concerns the identification of these macro-elements and the related failure mechanisms activated by specific actions, such as earthquakes. Seismic and kinematic analysis were done on the building. Dealing with seismic and seismic vulnerability too, this research was focused on the seismicity of Firenze: the European requirements are analysed together with the Italian ones; the attenuation laws depending on intensity and acceleration are studied too, and a practical example is provided. The seismic and kinematic analysis bring to a complete picture of the case study, and the seismic risk indexes are provided and discussed too. The study is organized in accordance with a step-by-step procedure, such as the flow chart of the ISO 13822 suggests: in the first step the preliminary assessment was performed, considering the available documentation and results from inspection and check; the following step concerns a more detailed appraisal, in which the structural analysis is carried out