# Performance Evaluation of Rigid Braced Indirect Suspended Ceiling with Steel Panels
## 3 Test results
### Dynamic Characteristics  
The transfer function of the ceiling surface (A9) to the base of the shaking table (A1) for each test was examined to determine the natural frequency of each specimen. As shown in Figure 11a, the SDB-2 specimen yielded from the brace-hanger bolt connector, and the lateral stiffness was not properly achieved via the brace. On the other hand, the brace-hanger bolt connector used in the SDB-3 specimen, such as in Figure 11b, did not yield until the end of the test. In the case of Test 1 in Figure 12a, it can be observed that the amplification is significant at approximately 25 Hz, which is the natural frequency of the test frame. This analysis indicates that it has similar behavior to the ceiling-mounted frame. However, in Test 2, it gradually amplified at 3.2 Hz, which is the natural frequency of the ceiling, and during Test 8 (i.e., the final stage), the natural frequency of the ceiling was confirmed to be 3.2 Hz. The brace-hanger bolt connector first yielding from Test 2. It is believed that the dynamic characteristics, which are because of the relative displacement of the grid members that form the ceiling surface, were changed as the acceleration increased because of the decrease in the ceiling rigidity. In particular, in Test 8, most of the panels were removed; therefore, the natural frequency of the ceiling (3.2 Hz) was clearly revealed. Unlike SDB-2, SDB-3 did not yield the brace-hanger bolt connector, and it did not show a distinct natural frequency of the ceiling system in the transfer function, as shown in Figure 12b. In Figure 12b, the natural frequencies 25 Hz and 32 Hz for the test frame are significantly amplified. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Damaged Item**} & \multirow{2}{*}{**Damage State**} & \multicolumn{5}{c}{**Performance Level**} \\ \cline{3-8}  & & **I** & **II** & **III** & **IV** & **V** \\ \hline \multirow{3}{*}{\begin{tabular}{c} Panel dislodged \\ and hanging \\ \end{tabular} } & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{None} \\  & & & & & & \\ \hline \multirow{3}{*}{\begin{tabular}{c} Panel fell \\ \end{tabular} } & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{None} \\  & & & & & & \\ \hline \multirow{3}{*}{\begin{tabular}{c} Connection \\ failure \\ \end{tabular} } & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{\begin{tabular}{c} 1 or 2 \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} 3 or 4 \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} \textgreater{5} \\ \end{tabular} } \\  & & & & & \\ \hline \multirow{3}{*}{\begin{tabular}{c} System failure \\ \end{tabular} } & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{None} & \multirow{3}{*}{\begin{tabular}{c} \textless{}20\% \\ \end{tabular} } & \multirow{3}{*}{\
\begin{tabular}{c} 20–50\% \\ \end{tabular} } & \multirow{3}{*}{
\begin{tabular}{c} \textgreater{50\%} \\ \end{tabular} } \\  & & & & & \\ \hline \multicolumn{8}{c}{Performance criteria} & \textgreater{5} \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Damage state and the performance level of the T-bar type steel panel ceiling. In SDB-3, the accelerometer installation location is close to the brace installation location; thus, the natural frequency cannot be determined from the data. This is because the accelerometer is influenced by the strength of the brace. The part where the brace is installed has high rigidity; hence, it can be observed that it has the same behavior as the steel frame in the test data. However, considering that the relative displacement occurred between the installed brace part and the uninstalled part because of the low stiffness on the ceiling surface, the natural frequency was determined from the test video. The test video indicated that the relative displacement of the ceiling surface was larger after the panel left the seat.