# Perspectives on the Structural Health Monitoring of Bridges by Synthetic Aperture Radar
## 3 Analyses of Structural Integrity of Bridges from SAR
### Study Case 5  
\"Morandi\" was one of the world's longest reinforced concrete bridges when it opened in September 1967. The 1960s were Italy's economic explosion years. For the first time, many Italians could have a car, but the most of country's roads needed to be renovated. The \"Morandi\" Bridge was the fulcrum of a brand-new motorway network connecting heavy traffic from the East to the West of Italy. This was the beginning of the Italian industrial era, for the first time, after World-War Two. The \"Morandi\" Bridge was very different in other ways with respect also to the \"Bisantis\" bridge. The deck was entirely made of reinforced concrete, and it had only four cables per tower, instead of the usual dozens. Crucially, the cables were covered in pre-compressed concrete, specifically designed to resist traction. As a result, \"Morandi\" Bridge was stronger and lighter, with minimal use of steel, than any other bridge of its era and boasted a clean, distinct design that quickly became a symbol of Italian engineering, tangible proof of the country?s technical abilities. On 14 August 2018, the city of Genoa was surrounded by a strong summer storm. At 11.30 a.m., the rain was so heavy that visibility had fallen dramatically. During those severe weather conditions, the third supporting tower and 200 m section of the the \"Morandi\" Bridge, collapsed. The disaster killed 43 people and left 600 people homeless. Case Study 5 presents an extended survey of the collapsed bridge. To this end, we resort to the satellite data before the break-down, consisting of a time series of interferometric SAR data observed by the COSMO-SkyMed satellite system. For this case study, we perform the modal analysis, carried out on various points of the bridge and also the bridge axes. Figure 25a is a schematic representation of the \"Morandi\" bridge. Pylons 9, 10, and 11 are the largest constituting the main deck arches of the \"Morandi\" Bridge, while the collapsed pylon is number 9. Figure 26a shows in perspective the \"Morandi\" bridge where the collapsed pylon (number 9). Point (a) depicts the stall attack which, by falling, probably caused the whole pylon to collapse. Figure 27a,b shows the vibration profile of the \"Morandi\" bridge. The processed SLC SAR image was acquired before the collapse, on 21 January 2016 and 5 July 2018, respectively. By observing the vibration energy, one can observe interesting energy accumulations in proximity of the pylon 9 stays. Figure 28 depicts the particular of the figure inserted within the red square A of Figure 27. The red spots indicated by the yellow arrows (accumulation points (a)), represent the broken stay indicated in Figure 26a. The frequency analysis is performed on pixel P1 and P2, points belonging to the broken stay. Figure 28 shows the exact position of the measurement points. Figure 29a represents the trend in time of the oscillations observed on point P2, while, Figure 30a,b represent the spectrum in the linear and logarithmic scales, respectively. Looking at the figures, it is possible to observe the presence of a very energetic resonant peak polarized on about 10 Hz and another, of similar strenght, on about 780 Hz. The P2 point has a very different trend. Being the stall attack, the oscillations in the time domain have very high amplitude (Figure 29b). The spectra, in linear and logarithmic scale, represented in Figure 31a,b respectively, have a very particular trend, presenting a maximum at about 210 Hz. Figure 25: “Morandi” bridge: (**a**) Schematic representation, (**b**) Optical representation. Figure 28: Vibration map of the “Morandi” bridge (details). 5 July 2018  
Figure 26: (**a**) Optical representation of the “Morandi” bridge, (**b**) SAR-SLC in magnitude of the “Morandi” bridge. Figure 27: Vibration maps of the “Morandi” bridge: (**a**) 21 January 2016, (**b**) 5 July 2018. Figure 32 shows the \"Morandi\" bridge before the collapse. The vibration energy along the red line positioned longitudinally on the bridge roadway is computed.