Singularities Observed in the Calculation of the Modal Damping Ratio of a Long‐span Metal Arch Bridge

Within the recent studies that are being carried out in the structural health monitoring of bridges, it has been observed that the results of the modal damping ratio can be influenced by some ambient variables and significantly depend on the calculation method that is adopted. In this paper, the main conclusions obtained in the study of the dynamic behaviour of a real structure, the viaduct “Arcos de Alconétar”, in Spain, whose main span is a long metal arch, is reviewed. With this aim, the results obtained from the instrumentation installed during the initial months after its traffic opening are analysed.