Modal identification of existing concrete half-joint bridges through free vibration tests

Vibration-based tests are widely used for the assessment of existing structures. They allow the estimation of modal parameters, a possible deviation of which may be symptomatic of the onset of damage in the structure. Specifically, in the case of bridges, free vibration testing is a rapid, low-cost method that requires the installation of a limited number of sensors on the structure. This contribution presents the results of the dynamic identification for a series of existing concrete half-joint bridges based on free vibrations recorded after the transit of heavy trucks. The bridge deck modal characteristics (frequencies, damping ratios and mode shapes) are obtained via a recently developed identification framework based on the variation mode decomposition. These experimental estimates are also analyzed and used to calibrate a finite element model of the bridge deck, based on in-situ material characterization tests. Negligible fluctuations both in frequency and mode shapes are observed between experimental and numerical findings, which suggests that the analyzed overpasses do not present any relevant damage or cracking process under the service loads.