The Italian bridge asset is dated, and the functionality of many bridges is jeopardised by degradation due to ageing and environmental effects, as well as by increasing traffic loads. An adequate operational monitoring and maintenance program is essential for ensuring the safety condition of these critical structures. Administrations in charge and policymakers must clearly understand the actual condition of the infrastructure asset in order to optimise maintenance and retrofit planning. For this purpose, visual inspections might fail to reflect the current condition accurately; thus, additional experimental investigation campaigns are desirable. In the knowledge process for existing bridges, valuable information can be obtained through appropriate experimental tests, such as material testing and dynamic identification. Moreover, the potential of on-site test results in updating structural modelling has been demonstrated, successfully improving the performance assessment of bridges. However, sensitivity-based Finite Element model updating requires a deep knowledge of the examined structure to determine which parameters mainly affect the dynamic response.

In this framework, the contribution of this paper consists in a typological analysis and model updating of an existing RC tied-arch bridge dating back to the 1930s. The structural condition was assessed by an on-site investigation campaign, including a geometric survey, material testing, and ambient vibration test (AVT). For the latter, three algorithms for operational modal analysis were performed to extract the bridge's modal parameters and then compare outcomes. Lastly, results from experimental tests were used to update a 3D finite element model, and the overall structural safety of the bridge was evaluated.