Abstract Summary
The Brivio bridge, completed in 1917, consists of three reinforced concrete (RC) tied arches spanning 44.0 m each. The bridge crosses the Adda river on the route between Lecco and Bergamo and still represents a crucial node for the vehicular traffic of the region network. Hence, in the context of a research promoted by the Lombardy Region, the bridge has been equipped with a dynamic monitoring system, consisting of 8 seismometers per span. The response to operational excitations is collected at a sampling frequency of 100 Hz, with datasets of 3600s being created every hour for automated processing. The paper describes the dynamic monitoring system installed in the bridge and selected results obtained during the first two years of continuous monitoring. Several vibration modes are identified for each span, with the temperature significantly affecting the natural frequencies, whereas no remarkable changes of mode shapes are detected so far. The possible onset of structural changes is identified by through structural pattern recognition driven by both the changes in mode shapes and the cleansed natural frequencies. It is further noticed that two adjacent spans of the bridge exhibit a common mode, whose presence is determined by the interaction between the main girders of the two spans.
