Identification of modal parameters using response only measurements on the two identical single span road bridges is presented. The main advantage of output – only measurements is that it is not necessary to have information about excitation applied to the investigated structure. This technique is known as Operational modal analysis (OMA) as it uses ambient excitation, in this case heavy trucks passing over the bridge multiple times. Furthermore, 3D finite element numerical model of the bridge superstructure was constructed, and results were compared to the measured ones. Overview of modal parameters (natural frequencies, modal shapes and damping ratios) determined on two identical road bridges using Operational modal analysis and their comparison to the results calculated within numerical model are given. Experimentally determined modal parameters can be used for damage detection and assessment of health condition of the structure as damage, i.e. and structural deterioration causes changes in these parameters. Finally, the aim was to validate a cost effective and time saving procedure of modal parameter determination.

operational modal analysis, modal parameters, road bridges, natural frequency, modal shapes