Operational modal analysis of the Dolmsundet Bridge during construction
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This study investigates the dynamic behaviour of a cantilever bridge during construction. The investigations are carried out using operational modal analysis techniques. The Second-Order Blind Identification (SOBI) Method is implemented in MATLAB. This method is tested and compared with analytical results obtained from a shear frame with non-proportional damping properties. The accuracy is investigated for several damping ratios, and the quality of the results are considerably reduced for higher damping ratios. The method showed noteworthy improvement for longer time series durations. Modal analysis of the Dolmsundet Bridge measurements were carried out with SOBI method and compared with results from Covariance-driven Stochastic Subspace Identification. Similar modes obtained from the two methods showed little deviation in the obtained frequencies. The influence of the temporary support structure is found to be significant. Predicted values are available for two periods during construction, received from the Norwegian Public Roads Administration. The numerically predicted stage one follows the tendency found from the measurements, while the numerically predicted second building stage shows significant deviation from the observed tendency. The last mode of interest in the experimental data appears at a lower frequency than the numerically predicted mode. The damping estimates are more scattered. The predicted damping ratio appears to be non-conservative for the investigated wind loading. Modal parameters obtained from a more extensive dataset will contribute to updates of analytical models, increase knowledge and contribute to the safety during construction stage under more challenging conditions.