PSI - Issue 78

Matteo Tatangelo et al. / Procedia Structural Integrity 78 (2026) 73–80

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4. Seismic reliability indexes This section outlines the derivation of seismic target reliability indexes, based on initial assumptions. These indexes are determined using the closed-form solution (4) to calculate the in a certain . Once a specific seismic site is selected, the slope of the seismic hazard function 1 can be computed using the FEMA (350) formulation. Subsequently, the may be estimated from the related E , t ref . To establish a specific construction performance, the dispersion of the target capacity fragility curve be assumed. By assuming from Sect. 3, one can calculate the failure probability , , using equation (4). This then allows for the estimation of the reliability index , , for each of the 10751 Italian territory grid points. Finally, a target seismic reliability index ̅ , for the entire National territory can be derived as either the mean value or a fractile of the resulting , , distribution. Note that the subscripts LS and CC denote the specific limit state and consequence class, respectively. Fig. 2 and Fig. 3 present the values of , , for the four CCs, considering both the LSLS in (Fig. 2) and CPLS (Fig. 3), sorted by , 475 . The parameters adopted for , , are = {1.0, 1.5, 2.1, 2.5} and =0.6 . In these graphs, ̅ , is calculated as the mean value of all , , values. In detail, by observing the Fig. 2 and Fig. 3 ,when , , is calculated with =1.0 , a more dispersed trend is shows highlighting a reduction for lower hazard. This aspect is less evident in the case of =2.1 and =2.5 , where the values of , , tends to stabilize around the mean value ̅ , . Anyway, it is worth to note from these figure that the reliability over all National territory is not the same from site to site and varies with strict dependence based on the seismic hazard site. For the sake of clarity, Fig. 4 summarizes the procedure for determining the seismic target reliability index of Fig. 2 and Fig. 3.

CC1

CC2

CC3

CC4

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i)

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Fig. 2. ̅ , based on =0.6, =1 and a-d) =1.0 , e-h) =2.1 , i-l) =2.5