Operational modal analysis in commissioning dynamic tests of different types of footbridges - Experiences and conclusions

Dynamic testing of newly constructed bridges is common practice in many European countries. Dynamic response is especially important in the case of footbridges; this is due to their low mass and stiffness compared to road and rail bridges and the specific load that these structures carry. The paper describes the use of Operational Modal Analysis (OMA) in commissioning dynamic tests of newly constructed footbridges in Poland. The subject of the described works were nine footbridges of various types and span length ranging from 30 to 60 m. As a result of conducted experiments, the method for implementing OMA in routine dynamic tests was developed. OMA has worked well in all described cases. In most of the described experiments, it was possible to identify all relevant modes with natural frequencies up to 5 Hz. The quality, unambiguity, and range of identification in each case exceeded what was possible to achieve using approach still common today - simple methods of signal processing and spectral analysis.