Dynamic Characteristics of Two Similar Steel-Concrete Composite Bridges

Operational Modal Analysis (OMA) aims to identify the modal parameters—natural frequencies, mode shapes, and damping ratios—of existing structures under ambient excitation. These parameters are essential for applications such as vibration control, finite element model validation, damage detection, and Structural Health Monitoring (SHM). While the application of OMA to bridges is increasing, limited attention has been given to multi-span continuous viaducts. This paper investigates the dynamic characteristics of two similar steel-concrete composite viaducts, each consisting of 7 spans and exhibiting a slightly curvilinear planimetric layout. The deck widths range from approximately 18 m (West track) to 20 m (East track), with overall lengths of 276 m and 272 m, respectively. The span configurations differ primarily in the length of the second span. Both viaducts are instrumented with 42 accelerometers for continuous dynamic monitoring. During the initial monitoring period, several vibration modes were identified in the frequency range 0–8 Hz. Selected results on the extracted modal parameters are presented in the paper, emphasizing the effects of geometric span configurations on the observed mode shapes.