Seismic Fragility Assessment of a Multi‐Span Masonry Arch Bridge Using a Discontinuum Modeling Approach

This paper investigates the seismic performance of a multi-span masonry arch bridge using an advanced modeling approach based on the Distinct Element Method. Located in Italy and constructed of regular stone masonry, the bridge features three consecutive arch vaults with similar geometry. The three-dimensional structure of the bridge is modeled using the commercial software 3DEC, as an assembly of discrete blocks including all its different structural and nonstructural components, such as piers, abutments, arch vaults, backing, spandrel walls, and backfill material. Masonry is represented as an assembly of rigid blocks connected by zero-thickness interfaces, while the backfill is modeled as a continuum mesh based on plasticity theory. The bridge geometry and material properties are derived from available in-situ surveys. Sensitivity analyses on the level of detail of the model are conducted to balance numerical accuracy and computational effort. A Maxwell damping model is employed to further reduce the time window required by dynamic simulations. Multi-stripe nonlinear time-history analyses are carried out, applying 200 three-component ground-motion records. The results are presented and discussed in terms of observed damage patterns and relationships between a case-specific engineering demand parameter (EDP) and typical intensity measures. Thresholds for various performance levels (PLs), including usability preventing damage and global collapse, are defined based on a statistical correlation between the selected EDP and the damage observed in each time-history analysis. Fragility curves are then generated for each of the considered PLs. Finally, model uncertainties are explored by introducing geometric variations in bridge components, highlighting their impact on the seismic vulnerability of the structure.