# Performance Evaluation of Rigid Braced Indirect Suspended Ceiling with Steel Panels
## 4 Summary and Conclusions  
The suspended ceiling system with nonadhesive ceiling panels with an applied steel panel can directly lead to personal injury to the inhabitants and damage to important property if the panel is removed during an earthquake. In addition, the ceiling installed on the evacuation route can lead to secondary damage by blocking the evacuation path, which requires seismic design. In this study, a seismic ceiling system that is based on a rigid brace that is suitable for the Korean situation is proposed for the ceiling system. This ceiling system consists of steel panels to which the indirect suspended ceiling mainly used in Korea was applied, and the seismic performance was evaluated by the shaking table test. The main conclusions from this study are as follows. Figure 19: Main T-bar–cross T-bar connection used in the specimens. (**a**) Connection failure of the main T-bar–cross T-bar joint, SDB-2, and the (**b**) main T-bar–cross T-bar connector, SDB-3. All the specimens to which the brace was applied to were evaluated as level I at 0.864 g, which is the level of the 100% artificial seismic wave. The confirmed performance at level I satisfies the life safety level that is required by KDS 41 17 00, but the ceiling installation area for the experiment that was conducted in this study is small, which is different from the actual ceiling behavior. It was determined that problems such as buckling of the member itself, which did not occur in the experiment, will appear in the actual ceiling belonging to a large space. This problem requires an analytical follow-up study because large-scale experiments on ceiling systems are limited. * Based on the experimental results, the damage caused to the ceiling grid members and the panels was analyzed. It was confirmed that the factors that caused the dislodged panel and the hanging state, which is a damage state that can occur because of the anti-falling clip that is used in the experiment, and the factor that causes the panel falling state appeared in order. This is because the damage state in the previous stage directly affects the damage state at the later stage. In addition, further research, such as product development, may be conducted based on these results at a later time. The anti-falling clip that was used in this experiment was developed from these results. * When comparing the results of SDB-2 and USD, it can be observed that SDB-2 with a brace has a lower performance level. In SDB-2, the relative displacement between the member at the point where the brace was installed and the point where the brace was not installed increased, and the panel was first removed. As a result, it was determined that the increase in the relative displacement between the grid members in the ceiling surface is more fatal to the falling panel than the impact load that is applied to the end of the ceiling with the installed brace. In other words, when installing the brace, the diaphragm behavior on the ceiling surface is more important than the occurrence of the impact at the end, and this point should be considered when installing the brace. * In the case of SDB-3, the displacement of the ceiling surface itself was reduced by securing the rigidity of the brace-hanger bolt connection and the brace reinforcement. In addition, the relative displacement between the members was reduced by more than half. This was obtained by adjusting the brace installation interval and the additional application of a T-bar connector, which shows a better performance than USD and SDB-2. To increase the lateral force resistance level, SDB-3 requires a large amount of jointed hardware and screw bolts for the mechanical connection, which can be evaluated as having a lower workability than USD or SDB-2. When applying a brace, there are many points to consider, such as the brace installation spacing, the diaphragm behavior of the ceiling surface, and the mechanical jointing. All of these can be considered to obtain advantages when installing a rigid brace.