PSI - Issue 78

Michele Morici et al. / Procedia Structural Integrity 78 (2026) 1673–1680

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highlighted by vertical lines of red dots, corresponding to well-defined peaks that stand out distinctly from the surrounding spectral content. The analysis for the permanent monitoring system (Figure 3a) reveals stable modes at 3.367 Hz, 4.122 Hz, and 4.476 Hz, while the validation monitoring system (Figure 3b) identifies modes at 3.392 Hz, 4.190 Hz, and 4.523 Hz. The results confirm close agreement between the two monitoring setups.

a)

b)

c)

Figure 3. Validation Monitoring System: (a) sensors placement at roof level; stabilization diagrams obtained using the SSI-UPCX estimator for the (b) permanent and (c) validation monitoring systems, focusing on the 0 – 5 Hz range.

The results (Table 3) show good agreement between the permanent and validation monitoring systems, with consistent identification of the first three modes: a roto-translational mode in the Y direction, a translational mode in the X direction, and a torsional mode. The mode shapes (Figure 4) are highly similar. Interestingly, the first mode in the structure is a predominantly translational motion along the Y axis, but it presents a torsional component. This coupling may result from irregularities introduced by architectural layouts and voids (see Figure 1b), asymmetric distribution of stiffness and mass. The second mode is a clean translational mode along the X-axis while the third mode is purely torsional. It is important to note that the analyzed OMA derives exclusively from the second acquisition chain (accelerometers A1, A2, and A3 in Figure 2) of the permanent monitoring system, as the first chain experienced technical issues. Consequently, the dynamic behavior discussed herein pertains solely to the uppermost level of the ChIP building (roof, Level 2), while the lower storeys (Level 0 and Level 1) are not considered in this analysis. Figure 5 shows the results of OMA identifications performed every 3 hours on the ChIP building using the permanent monitoring system and the SSI-UPCX estimator, from May 9, 2024, to July 12, 2025, illustrating the evolution of the natural frequencies for the first three vibration modes (F1 in red, F2 in green, and F3 in blue) with average values around 3.392 Hz, 4.159 Hz, and 4.450 Hz, respectively. The data reveals a stable and consistent trend over time, with only minor fluctuations likely caused by measurement noise or temporary environmental effects, and no significant changes observed. Table 3. First three natural frequencies identified for the ChIP building using the permanent and the validation monitoring system and SSI-UPCX Permanent Monitoring System Validation Monitoring System Frequency Type Damping Complexity Frequency Type Damping Complexity 3.367Hz Rototranslational Y 0.003 % 0.164 % 3.392 Hz Rototranslational Y 0.003 % 0.019 % 4.122Hz Translational X 0.005 % 1.164 % 4.190 Hz Translational X 0.006 % 3.538 % 4.476Hz Torsional 0.005 % 0.084 % 4.523 Hz Torsional 0.009 % 0.197 %