# Performance Evaluation of Rigid Braced Indirect Suspended Ceiling with Steel Panels
## 1 Introduction  
In Korea, the Gyeongju earthquake of 2016 and the Pohang earthquake of 2017 resulted in substantial damage to nonstructural elements such as exterior walls, suspended ceilings, and partition walls. As a result, the interest in seismic design of nonstructural elements has recently increased. Even if a building does not collapse owing to the damage to structural materials in the event of an earthquake, damage to the nonstructural elements may lead to casualties or property damage. When considering the nonstructural elements, the suspended ceiling system can directly lead to casualties inside the building because of failure of finishing or collapse of the ceiling frame. This can lead to additional damage, such as by blocking evacuation paths and damaging the various facilities. Figure 1 shows a suspended ceiling with steel panel damage at Pohang Station during the Pohang earthquake. The KDS 41 17 00 [1] is a Korean building seismic design standard that was revised in early 2019. This standard mandates the use of ceiling bracing systems if a ceiling system with non-adhesive panels belongs to the seismic design category D, has certified perimeter clips, or the ceiling area exceeds 250 m\({}^{2}\). This is the same as the ASCE7 in the United States, which includes two seismic designs on the ceiling. If the perimeter clips are used, walls are needed to hold the clips, and if the brace is used, brace members and other members to connect them are needed. A ceiling system with non-adhesive ceiling panels is different from one with attached ceiling panels. A ceiling system with attached ceiling panels is placed in or is inserted into the grid member, which is fixed with screws or nails to the ceiling grid. The KDS 41 17 00 ceiling standards in are similar to those in theASCE7-16 [2]; however, the details of seismic design category (SDC) C are not provided, and the ceiling area to which the ceiling bracing system is applied to has been eased. The ASTM E580/E580M [3] in the United States requires braces at intervals of 1.8-3.6 m for ceiling installation areas not less than 1000 ft2. In particular, when considering rigid braces, the relative displacement is less than 6 mm. The details of the gap between the sprinklers are specified, but there is no information on the end separation distance when installing the brace. For spacing with sprinklers, it is deemed that the end separation distance should not be less than 25 mm, and the end molding must have a width of at least 50 mm. In the United States and Japan, seismic designs of ceilings are typically used, but the concepts of applying and installing braces are different. This is because the typical ceiling systems are different in the United States and Japan. In 2013, the report in Japan, \"Determining a Safe Structural Method for Specific Ceilings and Specific Ceiling Structural Strengths\" Notice No. 771, was published by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT). According to this report, when the ceiling installation area is more than 200 m2, the brace should be placed in the shape of a V by calculating the required brace number, with the end clearance being at least 60 mm. The V shape indicates a rigid brace; the width of the molding is not given. As specified in the recommendations for seismic design and construction of nonstructural elements [4] from the Architectural Institute of Japan (AIJ), one V brace member should be within 30 m2 in each direction. This is determined to be a regulatory design method through experimentation, but the installation spacing of the brace and end clearance are not specified; thus, it is considered to be difficult to apply in practice. Table 1 provides a brief summary of the contents of the ceiling system that are related to the brace installation in KDS 41 17 00, ASCE7-16, and MLIT Notice No. 771. The installation of a ceiling system with non-adhesive ceiling panels that is presented in ASCE7-16 is described in detail in ASTM E580/E580M.