A procedure for assessing and monitoring the response of critical infrastructures when subjected to natural hazards is proposed in this paper, with a particular focus on bridges and viaducts, which are very peculiar and strategic assets of transport networks. The proposed procedure is characterized by three levels of analysis (L1–L3) with increasing reliability and complexity. The first level of analysis (L1) is carried out by evaluating a Class of Attention in line with the approach that is proposed by the Italian Guidelines for the safety assessment of bridges. The second level (L2) of analysis requires the definition of a numerical model of the bridge. The third level (L3) of analysis relies on the seismic response data from a seismic monitoring network. For all the three levels of the proposed procedure, data are collected in the CIPCast Decision Support System (CIPCast-DSS), a WebGIS platform developed by ENEA to support the decision-making process related to risk prevention and the management of impacts induced by natural hazards on critical infrastructures. The real-time analysis of the data collected and processed in the CIPcast-DSS in post-disaster circumstances provides a quasi-real-time prediction of the impacted infrastructures, and the extent of damages they could have suffered before a local inspection and analysis could take place. The continuous static and dynamic monitoring in periods without seismic events enables the planning of preventive and effective maintenance interventions.

The paper presents the results of the vibration tests carried out on the pedestrian bridge accessing Civita di Bagnoregio, Italy. The structure was in bad health condition. The external beams were damaged due to deterioration exacerbated by the combined actions of rain and wind. The circular piers were also damaged with several cracks where the concrete cover was spliced and the reinforcement bars were exposed. The analysis presented in the paper focuses on the highest five piers, which seemed to show an irregular behavior during a preliminary experimental campaign. The results of the experimental campaign presented in this paper showed that the structural behavior of the bridge was qualitatively similar to the expected one. The reduced stiffness, due to the observed widespread damage state, amplified the vibrations uniformly along the structure. The Italian Guidelines for the risk and safety assessment of bridges and viaducts, issued in 2020, have been applied and tested in this study and the results are presented in the paper.