PSI - Issue 44

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Elena Speranza et al. / Procedia Structural Integrity 44 (2023) 1784–1791 Elena Speranza et al../ Structural Integrity Procedia 00 (2022) 000–000

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Keywords: seismic risk; seismic prevention; critical buildings; seismic vulnerability; statistical analysis

1. Introduction Over the last years, from 1968 (the year associated with the seismic event that occurred in Belice, Sicily) to 2016 (Central Italy seismic sequence), the impact of strong earthquakes, which struck the Italian peninsula, is impressive: losses in terms of human lives amount to almost 5,000 victims while consequences on the Italian public expenditure are likewise shocking. According to recent actualizations updated to 2019, costs afforded by the State to cover emergency services, recovery and temporary shelters, assistance to the population, damage repair, and structural upgrading of several assets such as residential, infrastructural, lifelines, cultural heritage and so on, are impressive: more than two hundred billion euros were spent by the Italian Government over this temporal span, while this amount, turned into annual expenditure entails an average annual cost of around four billion euros (Dolce et al 2021). The above picture is the result of the combination of the high magnitudes registered for the seismic events in this temporal term, the high vulnerabilities of the assets and, the concentration of human lives, all features governing the risk and its associated losses in terms of direct and indirect costs [Borzi et al., (2021), Di Ludovico et al., (2017a,b), Di Ludovico et al., (2021), Guidoboni e Valensise (2011), INRA (2018)]. In fact, the high seismic risk depends not only on the frequency and the magnitude of the earthquakes that periodically strike the national territory to a large extent on the high vulnerability of the building stock. This is due to the presence of a high number of buildings built before the first seismic classification of the municipalities in which they are located and therefore built without seismic provisions. Improvement of the seismic prevention policies is the only effective strategy that can be pursued to reduce the seismic risk. However, this is not an easy task, since seismic prevention is a combination of structural and non structural activities that should interoperate under a unitary view, according to definitions of the Civil Protection Code (Decree-Law n.1 of 2/1/2018, article 2). Coherently with this broader approach to the problem, the Italian National Seismic Prevention Plan (NSPP), issued in Italy in 2009, is grounded on a multi-purpose view. Optimizing potential benefits and human life safeguard are pursued through the combination of structural prevention measures, such as seismic vulnerability reduction programs, and of non-structural measures, such as knowledge increase on local seismic hazard and emergency planning. In 2009, the NSPP, funded by Decree Law 39/2009 turned into Law 77/2009, granted a former endowment of 965 million euros distributed over 7 years (from 2010 to 2016). In 2018, the Plan was further increased by additional funds, according to Law 145/2018 which allocated 50 million euros per year, from 2019 onwards. The reduction of the expected human losses was settled as a priority objective of the NSPP and, considering the available resources, interventions granted were concentrated on the most dangerous areas of the country [Dolce et al. (2021)]. Across a combination of non-structural and structural prevention, the main targets of the Plan were devoted to increasing territory knowledge to support urban and emergency planning and reducing the vulnerability of private/public buildings and infrastructures. Over the first 7 years, the initial endowment of 965 million euros was dedicated to three main measures: (i) Seismic Micro-zonation studies (SM) and Limit Condition for Emergency analyses (LCE); (ii) Interventions of vulnerability reduction on public buildings or infrastructures with either a strategic task in the emergency phase or critical importance for the consequence of their collapse; (iii) Interventions of vulnerability reduction on private buildings. While the coordination and monitoring of the Plan at a national level is in charge of the ICPD, Regions are responsible for its execution at a local level, including scheduling and prioritization of studies and interventions through a strict interaction with the territory. For structural interventions, priorities mainly rely on the seismic structural safety assessment of the building (or infrastructure) in the original configuration. In 2021, some statistical analyses were carried out by the authors on a sample of around 1,000 structural interventions on public strategic and relevant buildings, with a focus on intervention costs, seismic safety indices, and marginal costs of retrofit interventions (Dolce et al., 2021). The paper, after a short overview of the measures adopted by the NSPP over the first 7 year-program, presents updated elaborations on a sample of 1,207 structural interventions, ranging from local strengthening or seismic upgrading as far as demolition and reconstruction. Definition of unitary costs and of the increment in seismic safety