Abstract
The aging and progressive deterioration of prestressed concrete bridges in the Czech Republic highlight the need for advanced monitoring methods of key structural parameters. This study combines numerical modelling and operational modal analysis of bridge structures composed of precast prestressed beams with transverse connections. A numerical model was developed in Midas Civil with several damage variants and validated using measurements on a real bridge with simulated weakening. The results show that partial loss of prestressing caused only a minor reduction of the first natural frequency, while higher modes were more strongly affected and proved more sensitive to local stiffness changes. These findings confirm that higher and asymmetric modes are more suitable for detecting early stages of degradation. Incorporating the transverse stiffness of girder connections into the model significantly improved agreement with experimental data. It is further assumed that reducing the stiffness of the joints may lead to more significant changes in amplitudes within certain frequency bands, which could be verified through harmonic analysis.