Assessment of Similar Reinforced Concrete Arch Bridges by Operational Modal Analysis and Model Updating

Results of the multidisciplinary activities carried out on the different spans of a historic RC arch bridge are presented in the paper. The bridge, completed in May 1917, crosses the Adda river between the small towns of Brivio and Cisano Bergamasco (about 50 km North-East of Milan) and represents a crucial node for the regional vehicular traffic. The investigation program included: (i) documentary research in the archives of Brivio town hall and National Roadway Authority (ANAS), (ii) visual inspection and geometric survey of the arches intrados, (iii) ambient vibration tests, (iv) mechanical characterization of the concrete materials, (v) finite element modeling of each span and vibration-based model tuning. The present paper, after a concise summary of the multidisciplinary investigation carried out on the different spans of the bridge, is mainly focused on structural modeling and vibration-based model updating. In order to take advantage of the similarity of the different tied arches, a simple system identification technique was used to update the models. The application of this technique provided optimal models that accurately fit the identified modal parameters of each span; in addition, the identified structural parameters are in good agreement with the available characterization of the materials.