## 5 Validation Experiments  
### Experimental Objectives  
Damage detection and localization are of major interests in SHM. Three tasks are pursued herein: (1) global damage detection, (2) local damage detection, and (3) local damage pattern recognition. In Task 1, the global health condition of the whole structure was assumed to be independent of the damage location. In other words, the occurrence of any damage in the structure denoted a damaged state (a binary classification problem). For this purpose, all signals were mixed together with labels of either \"undamaged\" (UD) or \"damaged\" (D) ignoring the floor information. This can be considered as one idealization of the structure as two independent single-degree-of-freedom (SDOF) systems, one in the X direction and one in the Y direction, Figure 7.  
In Task 2, a more fine-grained detection was conducted to locate the damage based on the floor level. Considering only the X direction and the rigid diaphragm assumption [34; 35], the steel structure can be idealized as an MDOF system with one translational \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Hazard** & \multicolumn{2}{c}{**Record**} & \multicolumn{2}{c}{**PGA (g)**} & \multicolumn{2}{c}{**Fundamental**} & \multicolumn{1}{c}{**Damage Pattern**} \\ \cline{2-7}
**Level** & **No.** & **Name** & **X** & **Y** & **Period (sec)** & \\ \hline \multirow{2}{*}{B-FOE 1} & EQ1 & El Centro-X 2 & 0.035 & 0.03 & 1.36 & AL \\  & EQ2 & El Centro-Y & 0.03 & 0.035 & 1.36 & AL \\ \hline \multirow{2}{*}{FOE} & EQ3 & SHW2-X 3 & 0.035 & 0.03 & 0.56 & UD \\  & EQ4 & Kobe-X 4 & 0.035 & 0.03 & 0.56 & UD \\  & EQ5 & Kobe-Y & 0.03 & 0.035 & 0.56 & UD \\ \hline \multirow{2}{*}{DBE} & EQ6 & El Centro-X & 0.1 & 0.085 & 0.56 & UD \\  & EQ7 & El Centro-Y & 0.085 & 0.1 & 0.56 & UD \\  & EQ8 & SHW2-X & 0.1 & - & 0.56 & UD \\  & EQ9 & Kobe-Y & 0.085 & 0.1 & 0.67 & UD in floors 1 \& 2; AL in floor 3 \\ \hline \multirow{4}{*}{MCE} & EQ10 & El Centro-X & 0.22 & 0.187 & 0.74 & PL in floors 1 \& 2; AL in floor 3 \\  & EQ11 & El Centro-X & 0.187 & 0.22 & 0.81 & PL in floors 1 \& 2; AL in floor 3 \\ \cline{1-1}  & EQ12 & SHW2-X & 0.22 & - & 1.13 & PL in floors 1 \& 2; AL in floor 3 \\ \cline{1-1}  & EQ13 & SHW2-Y & - & 0.22 & 1.13 & PL in floors 1 \& 2; AL in floor 3 \\ \cline{1-1}  & EQ14 & Kobe-X & 0.22 & 0.187 & 1.36 & AL in all floors \\ \cline{1-1}  & EQ15 & Kobe-Y & 0.187 & 0.22 & 1.36 & AL in all floors \\ \hline \multirow{2}{*}{A-DBE 5} & EQ16 & El Centro-X & 0.1 & 0.085 & 0.56 & UD \\  & EQ17 & El Centro-Y & 0.085 & 0.1 & 0.56 & UD \\ \hline \hline \end{tabular}  
* The FOE level earthquake input before brace installation. 2 El Centro record from the 1940 California Imperial Valley earthquake.
* Shanghai artificial accelerogram [33]. 4 JMA Kobe record from the 1995 Kobe earthquake. 5 Aftershock at the DBE level applied after re-tightening/replacing all loosened braces.  
\end{table} 
Table 1: Structural information and damage patterns recorded under earthquake loading (UD: undamaged, PL: partial braces loosened, and AL: all braces loosened). Figure 6: Loosening of the braces. DOF for each floor, Figure 7, and the detection accuracy was restricted to the floor level. Only signals collected from the same floor were mixed along with their damage state, and the damage detection was performed floor by floor. In other words, sensors in different locations of one floor shared the same label. Therefore, this task is three pairs of a binary classification problem. In Task 3, the development of damage in the test steel frame was further investigated. As mentioned above, three different patterns based on the floor level were assigned: UD, PL, and AL, which is a three-class classification problem. The design of the test frame had a single brace in each of the two exterior bays (Y-direction) of floor 3, Figure 4a, and the section area of each of these braces on floor 3 was smaller than that used on the other floors, which led to its fragility under earthquake excitation.