Vulnerability of existing infrastructures: the Morandi bridge and SHM possible prospects

European Union’s economic growth and social development passes through the correct operation of transport infrastructures, which comprises physical networks, terminals and intermodal nodes, information system, as well as refueling and electrical supply networks. The safe operation of the Europe’s aging transport infrastructure during their entire life cycle is insured by an effective and proactive maintenance. Among the physical network, bridges are structures that facilitate transport, creating connection between countries and regions. Lack of maintenance and material degradation are identified as causes of several bridge failures. After the collapse of the Polcevera Viaduct in Genova, Italy, on August 14th, 2018, the state of the European bridges has been questioned. The first part of this work is focused on the study of the collapse of the Morandi bridge in Genoa. From the free-available literature data, a numerical model of the structure has been prepared. However, the refined numerical approach and the collected design conditions allow a reasonable heuristic study to be carried out, to outline potential structural behaviors and responses to external perturbation ns. The analysis identified two critical aspects that may have affected the structural response. Both are related to the time variable that has likely affected both the operating conditions of the bridge and its loading capacity. The traffic load at the time of the structural design (60's) has certainly undergone a preponderant evolution, linked both to the evolution of transports in general (increasing in loading and traffic volume) and to the port development of the city of Genoa. At the same time, it makes sense to consider how the structural materials employed in different technologies (reinforced and prestressed concrete, prestressed stays) may have been subject to the degradation of their characteristics. Indeed, the effect of atmospheric agents and the proximity to the marine environment may have influenced the resistant capacity of the bridge. Furthermore, the cyclic load of traffic may have induced fatigue effects. Besides, structural solutions for stays (e.g. saddles) and the essentially static determinate scheme may have also affected the response. Structural Health Monitoring (SHM) is identified as a key point for the bridge maintenance and for the prevention of dramatic collapse. Indeed, reinforced concrete elements in bridge structures are subjected during their service life to different loading conditions that may affect their durability and efficiency, in particular, reinforced concrete elements can develop cracking conditions due to tensile stresses. However, such cracking conditions can develop and propagate leading to the exposure of the steel reinforcement bars to the aggression of external agents such as chlorides. Being able to monitor the development and evolution of cracking can be crucial and the second part of this research is aimed at this purpose. In particular, laboratory tests have been performed on reinforced concrete beams monitored by two nondestructive systems: distributed fiber optics sensors (FOS) and digital image correlation (DIC) to monitor the state of cracking and its propagation within the thickness. The main objectives of the research can be summarized as follows: (i) Deformation development from concrete casting, (ii) Crack detection and localization with distributed FOS and DIC, (iii) Crack opening quantification.