PSI - Issue 78

S. Cattari et al. / Procedia Structural Integrity 78 (2026) 1577–1584 Author name / Structural Integrity Procedia 00 (2025) 000–000

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of the structural units feature unidirectional frames. These latter cases correspond to buildings constructed prior to the 1980s. The URM buildings are mostly constructed using rubble stone masonry or soft tuff stone; in some cases, portions of the structure are made of solid brick masonry. An important factor for assessing the seismic behavior of URM buildings is the presence of construction details aimed at preventing the activation of out-of-plane failure mechanisms and ensuring the box-like behavior of the structure. Within the analysed sample, only one case study is entirely lacking such construction details, while the majority (58%) is equipped with systematic reinforced concrete ring beams or steel tie rods. The intermediate floors are mostly made of clay hollow block and concrete slab systems (50%) or composed of steel joists and hollow clay tiles (25%); the remaining cases feature mixed floor types, sometimes with masonry vaults at the ground floor level. The fact that most of the schools are characterized by rigid or semi-rigid diaphragms is consistent with findings from national-scale dataset (Cattari et al. 2024).

a)

b)

Fig. 3. Photos of selected school buildings in RC (a) and in URM (b) from the analysed sample

Fig. 4. Distribution of the sample in terms of construction age and number of storeys for URM and RC structural units

4. Preliminary key findings emerged from the collected data The collected data, even preliminary, reveal clear trends. Table 1 presents the findings from the analysis of available data on the interventions carried out on both URM and RC buildings. For URM structures, the interventions targeting vertical load-bearing walls and the overall structural system have been classified into the following main categories: • Interventions aimed at improving masonry quality and ensuring monolithic behavior (to prevent disaggregation phenomena in the potential activation of out-of-plane responses), such as grout injections; • Interventions intended to enhance the mechanical performance of load-bearing elements (distinguished between masonry piers and spandrels), such as the application of reinforced plaster; • Interventions designed to inhibit out-of-plane failure mechanisms, such as the installation of steel tie-rods; • Interventions aimed at ensuring box-like behavior of the building, by improving the connection quality between orthogonal walls, such as reinforced corner stitching.