Predictive tools for seismic fragility and damage probability maps of bridges with reinforced concrete circular piers

This paper presents a comprehensive numerical investigation into the seismic fragility of circular reinforced concrete bridge piers, which represent a widely adopted structural typology due to their structural isotropy and hydraulic efficiency. Despite their prevalence, there is a lack of tailored fragility functions that systematically account for the specific geometric and mechanical parameters governing their seismic response. To address this gap, a parametric study was conducted on a wide range of pier configurations, varying the height-to-diameter ratio, the normalized axial load, the longitudinal reinforcement ratio, and the transverse reinforcement volumetric ratio. Nonlinear time-history analyses were performed using multiple stripe analysis to derive fragility curves for five distinct damage states, ranging from initial yielding to collapse, including both ductile and brittle failure mechanisms. The role of the parameters on the seismic response is studied by systematically addressing the sensitivity of fragility parameters to the investigated input variables. Furthermore, simplified prediction tools are proposed, including multivariate regression models and artificial neural networks, to estimate fragility parameters without the need for computationally expensive nonlinear analyses. Finally, the applicability of these tools in the framework of the post-earthquake emergency management is demonstrated.