PSI - Issue 78

Matjaž Dolšek et al. / Procedia Structural Integrity 78 (2026) 1569 – 1576

1573

flood event catalogue, expressed in terms of spatially-distributed water depths, forms the basis for scenario-based loss estimation in later stages of BORIS2. This approach allows for a more realistic and spatially consistent representation of flooding impacts at regional scale, ensuring compatibility with both hazard- and consequence-driven analyses. In BORIS2, compound scenarios simulate the sequential occurrence of an earthquake and a flood within a short time window, focusing on their combined impact on exposure, vulnerability, and emergency response. These scenarios can be used to test the resilience of local EMS under credible, low-probability high-impact conditions. Thus, the two risks (earthquake and fluvial flood) are assumed independent while occurring in the same short time window for the compound scenario. 3.3. Scenario-based loss estimations for the affected area In STEP 3, the focus is on understanding the impacts of a hazard scenario (flood, earthquake or compound) selected from the ones obtained in STEP2. This is achieved through two complementary consequence analyses: (1) the calculation of expected losses for the population and residential buildings; and (2) the estimation of expected damage and operability of EMS units. Note that, when dealing with compound scenarios, the interaction between hazards in BORIS2 is simplified to avoid double counting impacts. The first can be addressed using the exposure and vulnerability models already introduced, along with the hazard model selected from STEP2. The principal output is the calculation of the expected losses for population/residential buildings and the refinement of the definition of the most affected areas (scenario-based hotspot). The consequence analysis on EMS units requires additional inputs: the identification, geolocation and classification of EMS units by type; the extension of the exposure model to include vulnerability data of these elements in a building by-building form; and the definition of hazard-specific fragility models and consequence functions that link physical damage to operational capacity. In terms of seismic risk, the operability assessment is performed firstly by the selection of a specific fragility model for EMS units for which BORIS2 methodology allows quite a flexibility. In fact, since no harmonized approach exists for developing vulnerability and consequence models for EMS units internationally, four main approaches were proposed based on data availability and territorial context: (i) Application of fragility curves specifically developed for the selected EMS unit within the specific territorial context and already available from previous studies, such as Cattari et al. (2024), Shooraki et al. (2024), Praticò et al. (2022); (ii) Application of fragility curves developed for residential buildings adjusted with factors calculated to represent the relationship between the seismic response of a generical residential building and corresponding EMS units based on existing studies; (iii) Assessing parametric fragility curves for EMS units using a parametric pushover curve and fragility model (Fazarinc et al. 2024 , Dolšek et al. 2024); (iv) Assessing fragility curves on basis of mechanical-analytical approaches. The selection among these approaches depends largely on the availability of existing models, along with the level of information available. Once the probability of attaining each damage level (EMS-98, Grünthal, 1998) is calculated for each EMS unit, consequence functions can be applied to translate physical damage into the probability of it remaining functional following the specific event scenario. In BORIS2, these functions are derived from post-earthquake usability data observed in school buildings after the 2009 L’Aquila eart hquake (Di Ludovico et al., 2023), emphasizing the critical role of non-structural damage in determining inoperability. Although specifically obtained for school buildings, the resulting consequence functions (Cattari et al., 2024) can also be applied to other types of strategic buildings, lacking specifically tailored ones. The output informs the estimation of available emergency capacity in STEP 4. Typically, for flood scenarios, fragility and consequence functions are integrated into depth – damage or depth – functionality curves. In BORIS2, literature-based models specifically tailored for critical infrastructures were examined to estimate their flood-related vulnerability. In particular, the curves proposed in FEMA (2013) provide detailed depth-damage curves for a variety of essential facilities, including hospitals, schools, fire and police stations, and different types of shelters. Other works, such as Huizinga et al. (2017), Kok et al. (2004), De Bruijn et al. (2015), Batica et al. (2018), and Grant et al. (2024), apply the same approach to link water depth to expected damage or functionality loss, often specifying critical thresholds beyond which facilities are assumed nonfunctional.