The Olla bridge is a multi-span masonry arch bridge dating back to the second half of the 19 th century. The bridge is 117 m long and includes five arches of different spans. Since no original drawings or blueprints of the bridge were found in the archives, the missing information on the geometry of the structure were retrieved through a geomatic survey, whereas the unknown structural details were assumed according to historical handbooks and similar projects. In addition, limited material

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... es were taken to solve typical uncertainties such as the effective thickness of arches. Subsequently, ambient vibration tests were performed, and different output-only techniques were applied to the acquired time series with the two-fold objective of identifying the dynamic characteristics of the bridge and roughly verifying the invariance of the modal parameters. Finally, all the available information were summarised in a Finite Element model, that -after the updating of uncertain parameters -turned out to be capable of reproducing the identified dynamic characteristics of the structure with a high level of accuracy.