Issue 51

M. Guadagnuolo et alii, Frattura ed Integrità Strutturale, 51 (2020) 398-409; DOI: 10.3221/IGF-ESIS.51.29 406 On the contrary it is possible to minimize interventions and consequent costs gradually increasing the shear strength and the specific failure coefficients (where necessary). Essentially with a view to achieving the same improvement result but optimizing choices and costs. Following the latter approach (hypothesis of targeted and optimized interventions), the maximum increase in the minimum safety index is obtained by increasing the shear strength by 50% at the third and second floors and only 20% on the first floor. The failure coefficients of piers and spandrel beams (assumed equal in both the x and y directions) are increased up to the unity for the third and second floor while they remained unchanged at the first floor. By maximizing all the values of shear strength (If = 1.5) and failure coefficients (Cp = Cs = 1) at every level of the constructions, the safety index curve rises rapidly to reach the same value of 0.73. In such a case, there would therefore be a waste in terms of costs, uselessly strengthening the first floor too, where instead it is sufficient to increase by only 20% the pier shear strength without changing the failure modes of piers and spandrels. The aforementioned analyses highlight that both design choices allow to improve the seismic capacity of the building, increasing the minimum safety index I S from 0.45 to 0.73. However, in the case of optimized interventions, the strengthening would be lower, less expensive and really located on the structural parts affected by structural deficiencies, while in the other case (widespread interventions) there would be unjustifiable and expensive interventions at a global level on the whole building. “Palazzo Ducale” In this case, as pointed out in Fig. 11, the building analysis returns an initial safety index of 0.25, which being lower than 1 shows a significant incapability to cope with a seismic event, a more critical condition than the previously studied case. Also, for this second building, a double analysis is carried out based on two different design choices: the first with a gradual increase in resistance and failure coefficients and a second one based on the simultaneous maximization of all increases. Figure 11 : Safety index curve of “Palazzo Ducale”.