Operational modal analysis of two similar multi-span bridges

This paper presents the dynamic characterization of two similar multi-span viaducts, supporting the two carriageways of A4 highway between Padova and Trieste. The bridges are characterized by 7 spans of different lengths, steel-concrete composite girders and slightly curvilinear planimetric shapes. The main differences between the East and West carriageways are primarily related to the length of the second span; nevertheless, the resulting dynamic behaviour is quite different. With the aim of Structural Health Monitoring (SHM), each viaduct was equipped with a continuous dynamic monitoring system consisting of 42 accelerometers, enabling real-time vibration measurements. During the first days of monitoring, many key vibration modes were identified within the 0-8 Hz frequency range. The comparison of the identified modal parameters highlights the impact of span arrangement on mode shapes, revealing significant variations despite the structural similarities. These findings contribute to a better understanding of the dynamic behaviour of multi-span continuous viaducts and provide the reference parameters for the SHM of the two structures.