Uncertainties reduction on modal parameters estimation in existing bridges using ambient and free-vibration tests

The correct estimation of modal parameters has an important role in ensuring the structural reliability of existing bridges. Operational modal analysis provides rather accurate extraction of natural frequency and mode shape but the corresponding damping estimates are subjected to higher uncertainties. This paper reports the results of ambient and free-vibration tests performed on four different typologies of road and railway bridges: steel trusses, multi-girder reinforced concrete, masonry and reinforced concrete arch bridges. In one case data acquired by a continuous structural health monitoring (SHM) system over a period of one year are available. In another case the passage of trains is exploited to perform free decays. Several frequency and time domain identification techniques are used to process AVT, whereas measured free decays are analyzed by the logarithmic decrement method applied to the autocorrelation functions of the signals. Outcomes are compared, evaluating the quality of modal damping estimates and results accuracy.