Considering Cumulative Damage in URM Buildings for Clustered Seismicity Risk Assessment

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Abstract
Unreinforced masonry (URM) buildings are highly susceptible to cumulative damage, as demonstrated by the damage observations collected during and after numerous earthquake sequences. However, most previous numerical studies assessing cumulative damage in URM buildings have failed to fully capture the extent of the phenomenon observed in real events. This article aims to address this gap by applying a newly developed methodology for modeling the accumulation of damage in URM buildings in risk assessment case studies. This methodology quantifies the cumulative damage using an energy‐ and displacement‐based damage index (DI) within a component‐based framework. The methodology is validated using data from the URM school building in Visso that sustained severe, progressive damage during the 2016 Central Italy earthquake sequence. Additionally, this DI is employed to develop hazard‐consistent, damage‐state‐dependent fragility curves for five case‐study URM buildings through consecutive nonlinear dynamic analyses. The fragility analysis results align with real‐world observations, indicating a significant reduction in structural capacity due to cumulative damage. These set of fragility curves are then utilized in a risk assessment exercise. The last part of this study compares the impact on risk estimates when incorporating damage accumulation and earthquake sequences using the proposed methodology versus the conventional approach, which assumes only independent mainshocks affecting buildings in their intact state. The results reveal that the conventional approach underestimates the average annual losses for these five URM buildings in Central Italy by 45%–85%. Although the level of underestimation may vary for other URM buildings in other regions, it is undeniable that the conventional approach consistently underestimates the risk for URM structures by a significant margin.

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