PSI - Issue 44

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Andrea Natale et al. / Procedia Structural Integrity 44 (2023) 1768–1775 Andrea Natale et al./ Structural Integrity Procedia 00 (2022) 000–000

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compressive strength also affects the shear strength of columns and, in turn, the collapse of the building. However, in this case study, the column shear strength is more sensitive to the transverse reinforcement ratio rather than concrete compressive strength (see Fig.7a) resulting in a decrease in the EALs, by increasing the amount of transverse reinforcement. The result in terms of EALs for the As-Built configuration are reported in Fig.7a. The EALs for the building in the base isolated configuration is reported in Fig. 7b. In this case both the concrete strength and the transversal reinforcement ratio have no effect on the EALs, this is justified by the higher reduction of the drift and shear demand on the columns due to the base isolation. The PBT of the base isolated configuration, as reported di Fig.8, has the same trend of the EALs of the as-built configuration. Indeed, the PBT is here calculated as the cost of the intervention over the savings (reduction in the EALs) related to the retrofit solution. The latter are computed as the difference between the EALs in the as-built configuration and that of the retrofit solution. In this case, because the concrete compressive strength has no significant effects on the cost of intervention and on the EALs of the base isolated configuration, the variability of is the PBT is directly related to the variability of the EALs of the building in the as-built configuration. It is worth mentioning that the cost of base isolation system is taken from the financial documents developed for design purposed, while the cost of the local strengthening interventions (that may change with according to the used variables) are calculated by the proposed methodology.

PBT - Base Isolation

10 15 20 25 30 35 40 45 50 PBT [years]

Mean EALs As/s=0.09425 As/s=0.1131 As/s=0.14137 As/s=0.16755 As/s=0.20106 As/s=0.25133

0 5

Fig.8. PBT for the base isolation as retrofit solution

The PBT has a mean value equal to 33 years with a negligible variability regards the fcm, in fact the minimum value is equal to 32 years and the maximum equal to 33 years. Instead, it is possible to observe a variability for the different range of A sw /s, where the minimum value is equal to 28 years and the maximum equal to 45 years, respectively corresponding to the lowest and highest value of Asw/s considered. This suggest that a worst seismic performance provide a minor value of PBT, thus a higher convenience. As regard the others retrofit solutions considered, the FRP and the Rebuilt, the mean value of the PBT are respectively, 24 years and 72 years. The base isolation has PBT near to that of FRP, with a value, a little bit higher, but it is worth mentioning that the FRP shows a variability with A sw /s between 19 years and 40 years, this suggests that there is a range where the base isolation could be more convenient than the FRP. The rebuilt show the highest value of PBT due to its high cost. 6. Conclusion In this study a novel methodology is proposed to have preliminary estimation of the economic convenience in the use of base isolation as seismic retrofit solution for existing RC buildings. The procedure has been implemented in a Matlab routine relying on some simplified assumptions for the structural analysis and on the full development of the PBEE framework for the seismic loss-assessment. It allows to have a first estimation of the PBT knowing the main properties of the building (i.e. geometry, position of columns, seismic input). The structural analysis on a MDOFs system is main EDPs in term of acceleration, drift and shear actions are calculated. Damage and loss analyses are performed to assess the influence of structural and non-structural components and to define the loss curve and the