Add to ORKGThe paper presents the analytical and experimental modal analysis of an existing reinforced concrete arch bridge, built in the fifties across the Volturno river on "Domitiana" state road. First the modal properties of different 3D finite element models of the bridge were determined with/without reference to some structural strengthening carried out in the seventies. Then ambient vibration tests under traffic excitation are designed and developed in order to identify the bridge modal properties and calibrate its theoretical model. Finally starting from results obtained by that model, the structural response under different load conditions (traffic and seismic loads) was carried out in order to evaluate the real bridge behaviour and the struc...