Issue 51

M. Guadagnuolo et alii, Frattura ed Integrità Strutturale, 51 (2020) 398-409; DOI: 10.3221/IGF-ESIS.51.29 405 by a few simple steps, to optimize the interventions, focusing them on the story where they need: in fact, starting from the current conditions of the building, it is possible to hypothesize interventions only on some structural elements (piers or spandrel beams) of a generic story. In fact, there are interventions that affect the resistance of single piers and/or spandrels and those that modify their failure mode. This last aspect can be taken into account in the numerical model by increasing the failure coefficient Cp or Cs relative only to the involved piers or spandrels. Then, the structural analysis is performed again to recalculate the safety indices I SP and I SA . The procedure is then repeated several times until the safety indices reach an acceptable value or until it is possible to increase the strength of the structural elements or change their collapse modes. “Palazzo Petrucci Novelli” In this case, the Fig. 10 shows the increment curve of the minimum safety index I S of the building, obtained through a combination of gradual increases in the shear strength of masonry piers (shown in the figure through an increase coefficient If), of the failure coefficients of piers and the resistance of spandrel beams (Cp, Cs) at different floors of the building. It is considered that the If coefficient could not be higher than 1.50 (which corresponds to a maximum increase of 50% in resistance of the masonry piers); the failure coefficients Cp and Cs cannot, on the other hand, obviously be greater than 1.0. With the aforementioned procedure, it was possible to increase the minimum safety index I S from the initial value of 0.45 up to 0.73. The procedure starts from the weak level. In this case the ratio between the shear strength of each level and the shear strength of the entire construction highlights the distribution percentage of this force, immediately identifying the weakest level as shown in Fig. 10. The three black points represent the values of the safety index achieved by maximizing the shear strength of piers (If = 1.5) and the failure coefficients ( Cp = Cs = 1), one floor at a time. The gradually increasing curve of the seismic safety index and the points of maximum increase differ from each other in the different design choices. The points of maximum increase correspond to widespread interventions on the entire construction, maximizing the failure coefficients of all piers and spandrel beams (Cp, Cs) and of piers shear strength (If) in an entire plane. This does not consider that the value of the minimum safety index I S could be due to a specific weakness located in the construction rather than to a general stiffness lack. Figure 10 : Safety index curve of “Palazzo Petrucci Novelli”.