PSI - Issue 78

Marco Faggella et al. / Procedia Structural Integrity 78 (2026) 2141–2146

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and regulatory uncertainty demands a shift toward multi-risk frameworks that account for the interaction between structural vulnerability and operational or environmental pressures. This work introduces a time-adaptive reliability method grounded in NTC18-compliant PSHA, intended to incorporate seismic risk dynamically into broader decision-making under uncertainty. The approach allows for comparative risk analysis across different failure modes — such as earthquake-induced collapse and functional loss due to precautionary or emergency decisions — by quantifying the probability of adverse outcomes over variable time horizons. We apply this framework to the Camastra Dam in Southern Italy, a strategic yet vulnerable water infrastructure subjected to cascading risks: outdated pre-code non-seismic design, partial hydraulic outlet failure, regulatory restrictions, and extended drought. This case highlights the need for decision models that balance seismic safety with the continuity of essential services under compound risk scenarios. 2. PSHA Multi-risk Reliability The multi-risk approach compares the different risks on the same probability plot, based on the following steps: 1) Probabilistic Multi-Risk Poisson Time-to-Failure Model; 2) PSHA-based Earthquake Risk Model; 3) Storage Loss Reliability Model; 4) Risk Comparison and Time-adaptive Reliability. The probabilistic multi-risk analysis is based on the approach by Cheng et al. 1993, which assumes exceedance probabilities of different risks on a two-ways logarithmic plot. Poisson probabilities express the likelihood of a given risk parameter occurring at least once in a reference time interval of years, according to equation (1) = 1 − − ( ) (1) This model is implemented in the Italian NTC18-C seismic code which provides seismic hazard levels at a given site in terms of discrete values of PGA and corresponding λ (Faggella et al. 2013). It is particularly suited to match and compare seismic risks with hydraulic risks, as in Cheng et al. 1993, assuming that risks can be expressed by a Poisson rule. Seismic vulnerability can be visualized on a PSHA plot, reducing the performance in terms of PGA by a certain percentage with respect to the NTC18 code mandated compliance probabilities of exceedance (81% at SLO, 63% at SLD, 10% at SLV, 5% at SLC) and the respective return periods. 3. Earthquake Vulnerability and Risk Model The framework is described through the case example of the Camastra Dam in Southern Italy (Faggella and Barbosa, 2025). Vulnerability is accounted for lowering the performance PGA. With reference to SLC, the 5% PoE threshold PGA performance (New Design) is brought down to a 30% PGA lower value, thus providing an Upper Bound seismic risk scenario. Extensive and detailed seismic analyses of the Camastra Dam have been presented in Sica and Pagano (2009) in a number of works, addressing seismic performance, hazard, and geotechnical response modelling of the embankment volume. The nonlinear dynamic time history performance under strong motions with PGA higher than 0.18g consistent with seismic faults was presented in terms of top permanent settlements, with a critical point from above 520 m height. These analyses point out a very good overall seismic performance of the embankment with respect to: Permanent Crest Settlements, Liquefaction Factor, and Core Fracturing (pre-earthquake) safety factor. To streamline the seismic vulnerability assessment process, a further key vulnerability identifiable at the Camastra Dam concerns the auxiliary facilities and the access Fontanelle viaduct, which, upon visual inspection, exhibits significant structural degradation. A conservative assumption aimed at maximizing the seismic risk estimate suggests a potential 50% reduction of resistance and a 30% reduction in their seismic performance relative to the Collapse Limit State (SLC). Thus, this can be approximated as a 30% decrease in the Peak Ground Acceleration (PGA) threshold required to induce structural failure (0.3 x 0.3215 g ≈ 0.1g PGA). Regarding the auxiliary facilities, it must be noted that Spillways, Dissipators and Access Wells checked fine against earthquake actions. Instead, vulnerabilities were found with respect to SLV in a range from 0.60 down to 0.36 times the reference code