Structural Health Monitoring of Arch Dam from Dynamic Measurements

This paper presents the system identification of the Fei-Tsui arch dam using the recorded seismic data and ambient vibration data. The modal properties of the dam under different reservoir water level are identified using the recorded seismic data from 84 earthquake events. Considering the spatial variability of input excitation, both multi-input and single-input system models are employed in the input/output subspace identification. The regression curves between the natural frequencies and the reservoir water level are developed from the statistical analysis of identification results. In order to compare the current behavior of the dam to the past, an ambient vibration experiment is performed and the output-only stochastic subspace identification method is used to identify the current modal properties of the dam. Finally, a safety evaluation is made by pointing the current identification result on the developed regression curve. Further more, the comparison between different identification algorithms in this study is made. From the stability diagram of the identification the output-only stochastic subspace identification (using ambient data) provides more clear system characteristics than the input/output subspace identification (using seismic data). Discussion on the single-input model and the multi-input model for subspace identification is also made in this study.