SEISMIC VULNERABILITY OF EXISTING RC MOTORWAY BRIDGES CHARACTERIZED BY FRAMED PIERS

During last decades, the scientific community has increased its attention on the evaluation of the seismic vulnerability of the existing reinforced concrete structures, also following the damages and collapses occurred during recent strong seismic events. Among the existing structures, the motorway viaducts stand out for their strategic importance. Different types of approaches have been proposed to evaluate the seismic performance of the existing reinforced concrete bridges, especially considering the use of non-linear techniques. Among nonlinear techniques, the pushover analysis is preferably applicable in presence of structures where their dynamic behaviour is characterized by a predominant translational vibration mode, which is not the case of bridges, typically. Another approach commonly used is the non-linear time history analysis that presents different critical aspects as the correct definition of the seismic input and the modelling of strength/stiffness degradation. In recent years, some researchers have extended the use of the multi-modal pushover analysis for the evaluation of the seismic vulnerability of the reinforced concrete existing bridges. This analysis method can take into account the contribution of higher vibration modes, not neglectable in the case of multi-span and long-span viaducts with framed piers and elastomeric bearings. In this paper, the application of the multi-modal pushover analysis is proposed for the evaluation of the seismic behaviour of existing reinforced concrete viaducts located in Italy and built around the 1960’s, considering its limited computational effort. The results obtained are defined considering appropriate risk indices expressed in terms of peak ground acceleration (PGA) and related return period (RP), useful for classifying the vulnerability of the considered structures and to define their appropriate maintenance interventions.