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.

Curved surface sliders are generally preferred for the seismic isolation of buildings because of their technical features, such as the fact that the value of the vibration period is theoretically independent of the mass. Given the experimental evidence that indicates that the isolated system did not work under low seismic actions, in this paper, the influence of the static friction on the global behavior of some structures is studied in detail. By adopting a suitable model of friction, the onset of motion is analyzed with reference to simple isolation systems in which the influence of the friction values and its variability among the isolation devices are analyzed. The results pointed out that the behavior of curved surface sliders is not independent of the vertical load and highlights the importance of a suitable choice of the design friction, which must be different for devices with different vertical loads.

The behavior of a reinforced concrete building, seismically isolated with high damping rubber bearing (HDRB) and sliding devices (SD), observed during the most important events of the seismic sequence that struck central Italy from August 2016 to January 2017, is analyzed. Due to the epicenter distances, all the events had light effects at the site, thus the isolation system was not always put into action. A previous very low energy earthquake and the ambient vibration analysis are used for comparison. The study of the isolation system response is first carried out and the variability of the resonance frequencies with the input energy at the site is pointed out. These frequencies are quite close to those of the superstructure considered as fixed base. Small cracks were observed after the sequence in some partition walls of the building. The analysis of the superstructure was performed by means of a finite element model, assuming a non-linear model for the isolators, based on previous experimental data. The importance of a suitable decoupling between the superstructure and the ground and the contribution of the sliding devices under low energy earthquake is pointed out.

The great diffusion of masonry arch bridges, sometimes of historical interest, requires the development of simple but effective methodologies for a preliminary but reliable evaluation of their static and seismic capacity. In this paper, the behaviour under longitudinal seismic actions is analysed by using the mechanism method. The masonry is supposed to have no tension strength but a rigid–perfect plastic behaviour with finite strength in compression. The arch is subject to permanent loads and to a horizontal acceleration acting in the longitudinal direction, which causes a horizontal inertial loading acting on the arch. Three hypotheses about the effects of the inertial actions of the backfill are considered, which correspond to three different real behaviours. A comprehensive numerical investigation is performed, which allows us to point out the influence of the geometrical and mechanical parameters on the seismic capacity of a masonry arch bridge. The results are given by means of diagrams that can be easily used for a preliminary seismic check of a masonry arch bridge.