Maintenance interventions period of existing RC motorway viaducts located in moderate/high seismicity zones

Considering the recent collapses which have affected several existing reinforced concrete (RC) motorway bridges, the correct maintenance interventions planning of these strategic infrastructures has acquired increasing importance to maintain a suitable safety level even in case of seismic loads. One of the most important problems which influences the structural performance of existing RC motorway bridges is the presence of corrosion which may affect the bearing-capacity members. In particular, the corrosion of steel reinforcement of the piers due to the carbonation phenomenon is strictly related to the seismic performance of these structures as the viaducts of the Italian motorway networks realized around the 1970s. In this paper, the evaluation of the seismic vulnerability of three existing RC motorway bridges has been developed using non-linear time history analysis. Three corrosion scenarios (slight, moderate and high) have been analysed. The effects of the carbonation, expressed in terms of piers steel rebars area reduction, have been considered as a function of the age of the viaduct. Risk indices calculated as the ratio of the peak ground acceleration leading to collapse of the first structural element and the design peak ground acceleration, are useful to optimize the scheduling of the motorway networks maintenance interventions.