# Performance Evaluation of Rigid Braced Indirect Suspended Ceiling with Steel Panels
## 3 Test results
### Relative Displacement between the Test Frame and Ceiling System  
Figure 14 shows the displacement of the ceiling and the test frame, and their relative displacement of SDB-2 and SDB-3 in Test 8 (2.16 g). Depending on the specimen, the maximum ceiling displacement shown in the graph may vary. This is because the maximum displacement of the ceiling system can be measured differently depending on the location and the number of braces installed, as shown in Figure 15. The relative displacement of the graph is the value that is obtained by subtracting the maximum displacement of the ceiling from the displacement of the test frame. Figure 11: Brace–hanger bolt connection, Test 8 (2.16 g), (a) yield of the SDB-2 connection and (b) SDB-3. Figure 12: Natural frequency confirmed by the transfer function in Test 1 and Test 8: (a) A1 to A9, SDB-2, y-direction; (b) A1 to A9, SDB-3, y-direction. Figure 14: Relative displacement between the test frame and the ceiling systems: (**a**) SDB-2, Test 8 (2.16 g); (**b**) SDB-3, Test 8 (2.16 g). Figure 13: Natural frequency confirmed by the transfer function, Un-Seismic Designed ceiling (USD). (**a**) Transfer function (base to ceiling) and (**b**) the natural frequency estimated by using the transfer function below a frequency of 10 Hz. In the final stage, the maximum relative displacement of SDB-2 was 59.67 mm, and for SDB-3 it was 19.83 mm. As demonstrated from the graph, it was confirmed that SDB-3 shows more integrated behavior with the test frame than the SDB-2 specimen. Because of this characteristic, the panel falling rate was low. The panel falling rates are listed in Table 5. The causes of the panel loss for the ceiling system can be divided into (1) a panel loss due to the occurrence of the impact load at the end, and (2) the panel loss is because of the relative displacement between the grid members on the ceiling surface. The first factor in the USD panel loss that was conducted in the previous study was the occurrence of the impact loads at the ends owing to the short clearance distances. In contrast, the brace-applied ceiling system in this study was expected to be lost by the relative displacement between the grid members on the ceiling surface before the impact load occurred. This is because SDB-2 has a clearance distance of 60 mm, and SDB-3 has a clearance distance of 25 mm, which is larger than the USD. In Table 5, the level of acceleration at which the panel became dislodged and was hanging for each test subject can be checked. The lowest level of the damage state that was identified in this study is the dislodged and hanging panel; however, the damage state that affects the life safety level is because of a panel falling. However, a panel being dislodging and hanging can be observed as a factor that directly affects the ceiling system, such as the relative displacement between the grid members of the ceiling system. To confirm this effect, the relative displacement of the frame and ceiling was checked to determine whether the impact load was applied to the acceleration level that is caused by panel dislodging and hanging. Table 6 shows the maximum displacement of the test frame, the maximum displacement of the ceiling, and the maximum relative displacement of the frame and ceiling in the x-direction. As shown in Table 6, the point where the panel became dislodged and was hanging indicated panel failure, and the point where the impact load occurred was identified using the test video. It was predicted that the impact load would occur when the displacement of SDB-2 (60 mm) or of SDB-3 (25 mm) was smaller than the frame-ceiling relative displacement; however, it showed a different pattern from the actual experiment. In addition, the impact load occurred after the panel failure, which means that panel failure occurred owing to the relative displacement between the grid members in the ceiling. Figure 15: Maximum ceiling displacement of each specimen: (**a**) location of the maximum displacement of SDB-2, and (**b**) the location of the maximum displacement of SDB-3.