Issue 48

M. L. Puppio et alii, Frattura ed Integrità Strutturale, 48 (2019) 706-739; DOI: 10.3221/IGF-ESIS.48.66 709 Figure 4: Schematic plan of the building with the indication of the structural units [19]. Figure 5: School main entrance [19]. The Structural Units SU1 and SU2 have two storeys (ground floor and first floor) with classrooms and laboratories; on the mezzanine floor there are the administration offices. In the SU3 there is a gym and a storage area for sports equipment. Only the structural unit containing the gym was examined; this was the subject of a seismic retrofitting in November 2016. Built in the late 1960s, the structure is characterized by poor quality of materials; moreover, the shape of the plan of the unit is much longer in one direction and this leads to important torsional deformations. It is possible to highlight some critical points that determine the seismic vulnerability of the building:  Asymmetry in plan with an irregular arrangement of the infills which are formed by two layers: full blocks outside and perforated blocks inside;  Columns with reduced section compared to the beams;  Presence of ribbon windows;  Beam-column knots with brittle behaviour. A chevron bracing system has been included as a consolidation intervention (Fig. 6 and Fig. 7). Figure 6: First typology of inverted V-bracing [20]. Figure 7: Northwest side view [20] . For the diagonals and columns, circular hollow steel profiles are used. This solution has undoubted advantages:  Preservation of the existing resistant structure;  Reduced work inside the structure;  Uninterrupted school use;  Restricted construction times;