Influence of damage state threshold variability on the seismic vulnerability analysis of masonry aqueducts

The accuracy of fragility curves, a key outcome of seismic vulnerability studies, directly influences rational seismic risk assessments. In this study, analytical-based fragility curves for a masonry aqueduct were derived using tested earthquake-based Intensity Measure (IM) parameters and various threshold limit values for specific damage states, as commonly used in the literature. The Maximum Intensity Damage Ratio (MIDR) thresholds for specific damage states proposed by FEMA 356, GERMHS, and ASCE 41-13 standards were considered. Additionally, damage state thresholds were determined through a capacity curve obtained via nonlinear static analysis and empirical relationships found in the literature. The effect of damage thresholds on the Probability of Exceedance (PoE) values for a specific damage state was analyzed using the reference MIDR values determined in this study. Based on earthquake ground motion records, PoE values corresponding to different damage states were evaluated separately for each IM parameter. The results demonstrate that the damage threshold value significantly impacts the developed fragility curves. Therefore, when developing fragility curves for the seismic risk assessment of masonry structures, it is crucial to analyze and determine the appropriate threshold levels for each structure individually, rather than directly applying the threshold values used in the literature.