Operational Modal Analysis as a Tool for Bridge Model Updating. Application to an Unconventional Case Study

When approaching the evaluation of an existing structure, the proper definition of its numerical model can be a difficult task. When designing new structures geometry, restrain conditions and all specific details are chosen by the designer, while in the assessment of an existing structure all these parameters are characterized by uncertainties. Therefore, visual inspections, on-site tests, and geometric surveys are of primary importance for the characterization of the actual structural behaviour and to reduce uncertainties to obtain reliable structural models. In this regard, a technique to assess the representativity of the numerical model is the Operational Modal Analysis (OMA). This technique was applied to characterize the dynamic behaviour and obtain a representative model of a bridge subjected to progressive damage due to external sources that have altered the constraint conditions, so its structural response to external actions. The area where the bridge is located is subjected to the landslide of a mountainside which causes differential movements in the foundations. Ambient vibration tests were performed to characterize the dynamic response of the structure in operational conditions and carry out OMA analysis through up-to-date methods, such as SSI covariance. The results from surveys and OMA highlighted modifications in the supports of the bridge with respect to the initial design. These outcomes were implemented into the numerical model of the bridge to closely match the experimentally obtained modal properties, therefore achieving an updated model which is suited to properly replicate the actual structural performance of the bridge.