Seismic vulnerability and fragility of school buildings in Italy. A multiscale approach to assessment, prioritisation, and risk evaluation.

The importance of school buildings, among the built heritage of a community, is largely acknowledged. Due to past seismic events, damage or even collapse of schools have had a huge social impact. The safety of children and youth has a fundamental priority and, in addition, the unsafety of schools can aggravate social dispersion phenomena which follow an earthquake. In the aftermath of the Molise earthquake (2002), which caused the collapse of a primary school in San Giuliano di Puglia (Campobasso, Italy) and the consequent death of 27 children and a teacher, the Italian government issued a national plan for the seismic vulnerability assessment of relevant and strategic structures all over the country. The huge number of structures to be evaluated makes this operation extremely complex and, after almost twenty years, it still requires efficient and cost-effective (also in terms of execution time) tools to be effectively planned. More recently, the United Nations adopted, in March 2015, the Sendai Framework for Disaster Risk Reduction 2015-2030, which is articulated in “priorities”, providing actions to be implemented. Specifically, Priority 1 is focused on “understanding disaster risk”, while Priority 2 sets the goal of “strengthening disaster risk governance to manage disaster risk”. Both objectives require to deepen knowledge of risks and of its components (i.e., hazard, exposure and vulnerability) at various territorial scale (e.g., national or urban). This thesis presents the seismic vulnerability and fragility assessment of school buildings in Italy, to address this problem at multiple scales, at municipality level and at national level, also including investigations on case studies for refined modelling. First, a prioritisation procedure to sort school buildings part of an urban stock by their seismic vulnerability is proposed. This procedure has the aim of supporting local administrations and enterprises in charge with built stocks in decision-making for the allocation of limited funds for retrofit. The knowledge process of the building stock is comprised of on-site visual surveys and retrieval of original projects documentations. Then, the priority list is defined based on the combination of a qualitative evaluation and of a quantitative capacity/demand ratio resulting from a simplified mechanics-based model. The former results from the application of a form, counting structural and non-structural deficiencies, which is proposed in this work for masonry, reinforced concrete (r.c.), and mixed masonry-r.c. buildings, by updating an existing form. The priority-ranking procedure was applied to r.c. school buildings managed by the Municipality of Padova, in north-east Italy. Then, in the second part of the thesis, the research focuses on the fragility assessment of macro-classes of buildings, representative of the Italian school taxonomy, aimed at risk evaluation at national scale. Based on the Italian school building census, macro-classes of buildings were identified according to a limited number of parameters (i.e., the construction material, age of construction, number of stories, and plan area). Fragility curves were derived for five damage states (from slight damage to complete collapse), with reference to the European Macroseismic Scale (EMS98). For masonry schools, fragility curves were derived for 265 building types by means of a simplified mechanics-based approach, named Vulnus, which accounts for both in-plane and out-of-plane responses. Fragility assessment was also carried out for a macro-class of r.c. school buildings by selecting two representative schools from the above-mentioned urban stock managed by the Municipality of Padova. A non-linear fibre model was developed for each prototype building, taking into account its specific features, such as the presence of infills and of non-seismic joints. Non-Linear Time History Analyses (NLTHA) were carried out by applying a great number of natural and scaled ground motion records, covering a large range of seismic intensities. Fragility curves were derived by statistically processing the outcomes of NLTHA. Thus, the application of two alternative approaches for fragility estimate are provided in this work. Finally, damage maps at national scale are provided by implementing the obtained fragilities, showing the distribution of expected damage for a selected return period and for observation time windows.