Mechanical-Analytical Soil-Dependent Fragility Curves of Existing RC Frames with Column-Driven Failures

In seismic risk estimation, among the different types of fragility curves used (judgement-based, mechanical, empirical/observational, hybrid), the mechanical ones have the twofold advantage of allowing a better control over the basic parameters and of representing a validation test of the consistency of empirical/observational ones. In this study, fragility curves of RC frames with column-driven failures are obtained from a simplified analytical pushover method implemented in a simple spreadsheet, thus allowing the user to perform a large number of analyses. More importantly, the proposed method introduces the concept that Limit States at the structural level are obtained consequent to the attainment of the same Limit States at the local level, in the columns’ sections. This avoids using additional criteria, such as interstorey drift thresholds. This simple analytical model allows for rapid development of fragility curves, for any Limit State, of different building typologies identified by a set of global quantities (number of storeys, story heights, number of spans and span lengths) and by a set of local quantities (element sizes, reinforcement, and material properties). It also allows for a straightforward treatment of the influence of the soil class on the fragility curves parameters, which is another critical issue addressed in this work that helps when interpreting some literature results using empirical/observational methods.