Application of Probability-Based Seismic Assessment to the Bridges of Catania (Italy)

In this study, the seismic assessment of some typical bridges dating back to the 60ies and 70ies, belonging to the highway system of the city of Catania, in southeastern Sicily (South Italy), is presented. An assessment method is proposed, based on the probabilistic description of the bridge exceeding predefined Performance Levels (PL). Three PLs have been defined, through a simple damage function, in terms of requested/available ductility ratio, that are to be checked for, depending on the bridge importance. Uncertain quantities influencing the bridge response are treated as random, with mean and variance evaluated from both on-site testing and materials data at the time of construction. The bridge response (yield force, ductility, etc.), obtained with numerical models, is therefore random. The probability of exceeding each PL, as function of the peak ground acceleration (PGA), gives raise to a fragility curve. Thus, a target fragility curve is introduced, defined as the fragility curve pertaining to the same bridge, built at the same site, with same typology and materials, but correctly designed. By comparing the actual exceeding probability of the bridge, under a scenario PGA, with the target one, the bridge can be assessed. The simplicity of the method should be regarded as a positive feature when dealing with a large number of bridges, as is the case of studies at the territorial level, and when a rapid screening of the damage scenario after an earthquake is to be carried out.