Center and Characteristic Seismic Reliability as new indexes for accounting uncertainties in seismic reliability analysis

Seismic reliability analysis is a powerful tool to assess structural safety against ground shaking actions induced by earthquake occurrences. The classic approach for computing seismic reliability of a structural system requires a seismic hazard curve and a fragility function and leads to the estimation of the failure probability of the investigated damage state. However, resulting failure probability is strongly related to the preliminary assumptions in both hazard and fragility analyses, and slight changes in the input model parameters may cause relevant variability of seismic reliability estimates. The present work formalizes a general approach to be followed when dealing with seismic reliability assessment of structural systems, aimed at taking into account the whole uncertainties of the input parameters within hazard and fragility models. In the proposed approach, probability of failure becomes in turn a random variable and therefore new indexes are introduced, namely Expected Failure Rate, Failure Rate Dispersion, Characteristic Failure Rate, Center of Seismic Reliability and Characteristic Seismic Reliability. Lastly, such approach is applied to a case study, where seismic reliability of an existing open-spandrel reinforced concrete arch bridge is analyzed, and results are discussed highlighting some relevant issues.