PSI - Issue 78

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

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5. Target reliability-based seismic action intensity The framework presented in the Sect. 2 may be applied by adopting the seismic target reliability indexes derived in Sect. 4. In this way, it is possible to highlight how the seismic action intensity on the Italian territory may be defined starting from a reliability-based approach. In order to design a new or to assess an existing construction, with a uniform seismic reliability all over the Italian territory, the seismic action spectrum should be adjusted by calculating � ̅ , � . The latter is obtained through (5) once ̅ , is chosen. Furthermore, the definition of , 1 and are necessary. In order to satisfy the reliability target, construction should be designed such that the effective fragility curve has a seismic reliability index greater than target ̅ , . To do this, the spectral acceleration, taken as reference basis (e.g. , =10% in 50 years, corresponding to =475 years), must be modified with a certain value of ( ̅ , ) , which is dependent on the site hazard characteristics due to the parameter 1 . When over-strengths are significant, for instance due to the partial factors, the ( ̅ , ) has to be reduced by 0 such to obtain ′ ( ̅ , ) . This implies that the resulting spectrum may be higher or lower than the basic reference spectrum (i.e. the site spectrum referred to , ). Fig. 5 reports the ′ ( ̅ , ) and ( ̅ , ) values obtained for all the grid points of the national territory by referring to the target reliability indexes of Fig. 2 (i.e. mean values of the , , ), where each value found is represented by its , 475 . It can be clearly observed that values of ( ̅ , ) (greed dots) are dispersed when , 475 <0.1 g, while for , 475 >0.1 g the ( ̅ , ) values decrease as the , 475 grows. Moreover, blue dots depicts the ′ ( ̅ , ) values, derived by assuming a value of 0 , for taking into account if construction over strength. One may note that the ′ ( ̅ , ) average value is equal to 1.0, demonstrating that 0 permitting of considering on average the seismic action provided with a UHA, guaranteeing at the same time also the target reliability index considered. This result is found in ULSs also for the others CCs .

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Fig. 5. ′ ( ̅ , ) based on , 475 for Italy with reference to ̅ , 2 of Fig. 2