B. Steck, E. Robbe & N. Humbert


4.4. Analysis of the evolution of mode shapes with time Although the modal shapes remain sufficiently stable during the year of measurement to enable the modal identification described in paragraph 4.2, second-order shape variations can be observed. The following figure illustrates these variations in the modal shape of the third mode, calculated daily over a four- month period between July 2023 and October 2023. A localized variation is observed on the right bank, specifically at sensors 758 and 875. These variations are likely associated with localized stiffness changes, potentially corresponding to partial openings of certain joints between cantilever blocks. This information could be used within the framework of a numerical model of the arch, providing insights into a non-linear behaviour linked to joint openings.


Figure 13. Variation of the mode shapes for the third normal mode every day between July 2023 and October 2023. The mode shapes belonging to each month is represented with a different colour


4.5. Potential effect of the reservoir on the dam An interesting observation can be made by looking at the data of the vertical component: another peak can be observed during the whole year, with a frequency between the fourth and the fifth mode. The following figure displays in orange the stable poles excluded from detection by the “low damping” filtering process described in Section 4.2. The pole that persists throughout the year is visible and highlighted with a grey line.


152 | Dam Engineering | Vol XXXIII Issue 3


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