PSI - Issue 58

Dipendra Gautam et al. / Procedia Structural Integrity 58 (2024) 102–108 D. Gautam et al. / Structural Integrity Procedia 00 (2019) 000–000

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Acceleration (g)

Fig. 2. Example of detrended signal used for system identification.

Fig. 3. PSD plots for: (a) 2019 measurement; (b) 2023 measurement. Blue and red lines correspond to X and Y directions, respectively.

Table 1 highlights that the modal frequencies along the Y direction have significantly reduced in 2023. It is also interesting to note that the governing vibration mode of the building has changed from X to Y between 2019 and 2023. The table highlights that there is no significant reduction in the first mode frequency along the X direction between 2019 and 2023, but the changes are more prominent in the higher mode frequencies. On the other hand, the reduction in the first mode frequency along the Y direction is ~44%. Since the Y direction adheres to the long wall side that sustained more damage than the short wall direction (X). Due to the lack of repair and strengthening, the damage extent should have propagated not only due to environmental actions but also due to the hundreds of seismic events that struck the building after May 2019. Although not visible morphologically, the connection region between the main building and the extension could have also played a role in such grave reduction along the Y direction since the extension is a continued construction from the Y direction wall and any separation could easily alter the stiffness of the long direction walls. To further highlight the changes due to the likely damage aggravation, the MAC matrix is plotted as shown in Fig. 6. All the MAC values in Fig. 6 are found to be less than 0.85, which is often considered a threshold to characterize damage. The MAC values are found between 0.33 to 0.79, highlighting a very weak correlation between the mode shapes. This evidence also confirms the damage aggravation in the building.