I-1 SUSPENDED CEILING BRACING
The purpose of this example problem is to illustrate the design of suspended
ceiling bracing using Chapter 10 of this manual, and Chapter 6 of FEMA 302 (Components). Suspended
ceiling systems without adequate lateral bracing have collapsed in a number of earthquakes causing injury
to building occupants and disruption of safe egress and building function.
The problem follows the steps in Tables 4.5 and 4.6 to analyze the ceiling
bracing and anchors. Typical ceiling bracing details found in Figure 10-4 are inadequate for immediate
occupancy in high seismic zones.
The ceiling used in this example problem is suspended from a roof framing system consisting of steel joists
and metal decking. The ceiling and equipment laterally supported by the ceiling, such as light fixtures and
HVAC registers, are required to function after an earthquake.
A.1 Determine appropriate Seismic Use Group
Due to the requirement that the ceiling and associated equipment must be functional after an earthquake,
the ceiling and attachments are given a performance level of immediate occupancy (IO). The Seismic Use
Group and other performance parameters are determined from Table 4-4, as follows;
(per problem statement)
Seismic Use Group:
3/4 MCE (B)
A.2 Determine site seismicity.
The following value is assumed for this example:
SS = 1.50g
A.3 Determine site characteristics.
Soil type D is assumed for this problem
Soil type: D
A.4 Determine site coefficients.
Fa = 1.0
SMS = FaSS = 1.0(1.50)g = 1.50g
SDS = 3/4 SMS = 3/4(1.50) = 1.125g