## 3 Results
### Blake-Table Data  
The performance of DSFs for data-driven identification of nonlinearity/damage is further assessed on actual vibration-based monitoring data that has been recorded during shake-table tests performed by [PERSON] et al. [90] with a four-story mixed reinforced-concrete unreinforced-masonry building on the EUcentre shake table in Pavia. The building specimen has been tested with the Montenegro earthquake, and scaled to increasing amplitudes. The last test has led to failure (unstable building) and is therefore discarded, as SHM is not required for flagging collapsed buildings. Structural damage accumulated during the first eight earthquake, as reported in Table 3, and EMS-98 damage grades (DGs), ranging from 1 to 3, have been attributed based on visual inspection of the specimen. The building has been excited with uni-directional WN signals after each earthquake (except after Test # 7). More details about the test protocol and the building geometry can be found in [90]. \begin{table}
\begin{tabular}{l c c l} \hline
**Test \#** & **PGA [g]** & **D.G.** & **Damage Description** \\ \hline
1 & 0.05 & 1 & Single hairline crack one URM wall of first floor. \\
2 & 0.1 & 1 & Haircracks in one wall of first two floors and in the construction joint between wall and foundation \\
3 & 0.2 & 1 & Cracks in all masonry walls of first two floors \\  & & & Several diagonal cracks over the entire wall height of one wall of the 1 st floor with negligible residual crack width. \\
4 & 0.3 & 2 & Many flexural cracks in the concrete slab of the first floor; masonry spandrels and concrete wall remained undamaged. \\
5 & 0.4 & 2 & Same as previous. \\  & & & Significant increase in damage to the structure. All masonry walls with diagonal cracks at all floors. First and second floor walls present residual cracks of 0.8 mm. \\
7 & 0.4 & 2 & This test, with a smaller amplitude than the previous EQK6, was intended to simulate a possible aftershock but led only to very minor additional dam-age to the structure. \\
8 & 0.7 & 3 & Walls started concentrating in one diagonal crack. Diagonal cracks passed through bricks. \\ \hline \end{tabular}
\end{table} 
Table 3: Description of the eight earthquake sequences and the evolution of damage observed by [PERSON] et al. [90]. Figure 15: Influence of measurement noise, expressed as the signal-to-noise ratio, on the DSF values derived from AVs. The DSFs are derived from recorded accelerations, with one sensor per floor considered for the analysis. However, the base shear is also recorded by the table, and the top displacement has been measured [90]. While displacements and, above all, reaction forces are challenging to measure in a large population of existing buildings, these quantities are used to validate the capacity of DSFs to detect nonlinearity by computing the peak roof drift ratio and the hysteretic work dissipated by the structure. The residual damage is mostly characterized by the damage description and the EMS-98 DG (see Table 3). The results for five DSFs, which have been found to perform well on the simulated case study, are represented in Figure 16. The DSFs are calculated with respect to two different references: the WN excitation corresponding to the healthy reference state, recorded prior to the first earthquake test, and the WN excitation performed prior to the respective earthquake (labeled \(WN-1\) in Figure 16). Only for Test #7, no pre-earthquake WN data were available, and therefore, the equivalent data prior to test #6 have been used. While deriving DSFs with respect to the healthy reference state corresponds to tracking the absolute damage of the structure, using the WN before the earthquake provides an estimate of the additional damage that is sustained by the structure. Generally, the values of the DSFs are in good agreement with the nonlinearity indicators (hysteretic work on the left of Figure 16) and peak roof drift ratio on the right of Figure 16) and the damage description (see Table 3).