The ceiling weight, WP, will include all light fixtures
prevent the stair from imposing an unwanted
and other equipment laterally supported by the
constraint on the frame.
For purposes of determining the lateral
force, a ceiling weight of not less than 4 pounds per
(7) Cantilever parapets, ornamentation, and
appendages shall be designed with ap and Rp equal to
square foot (0.2kPa) will be used. The support of the
ceiling systems will be by positive means, such as
2.5 in accordance with Table 10-1.
wire or an approved seismic clip system. Typical
details of suspended acoustical tile ceilings are
(8) Storage racks.
shown in Figure 10-4.
(a) Storage racks supported at grade will be
(5) Window Frames. Window frames will be
treated as non-building structures in accordance with
Chapter 14 of FEMA 302. The weight, W, will be
designed to accommodate deflections of the structure
without imposing a load on the glass. Because glass
equal to the weight of the rack plus its contents.
is a brittle material, a considerable hazard of falling
glass may be present. It is particularly serious if the
1. Rigid racks. Racks having periods of
glass is above and adjacent to a public way. This
vibration less than 0.06 second will be governed by
hazard can be eliminated by proper isolation between
Section 14.2.2 of FEMA 302.
glass and its enclosing frame. It is obvious that the
magnitude of isolation required depends upon the
2. Flexible Rack. Racks having a period
drift and the size of the individual pane or enclosing
of vibration greater than 0.06 second will be
frame; thus, a pane of glass in a full-story-height
governed by Section 14.3 of FEMA 302.
frame should have an isolation or movement
capability as great as the maximum possible drift (
Storage racks supported by other
structures will be governed by Section 14.1.2 of
displacement in Table 6-1).
The actual isolation
clearance will depend on the geometry and
Alternative Designs. Where an accepted
deformation characteristics of enclosing frame,
frame support, and structural system. Special care
national standard or approved test data provide the
will be exercised in the field to see that such
basis for earthquake resistance of a particular type of
isolation is actually obtained.
architectural element or rack, such standards of data
may be accepted as a basis for design.
Stairways tend to act like
approved standards or test data define acceptance
struts; therefore, the rigidity of the stairway, relative
criteria in terms of allowable stresses as opposed to
to the structure, will be considered. In some cases,
strength, the design seismic forces shall be obtained
the stairway will be isolated in order to prevent
from FEMA 302 and reduced by a factor of 1.4 for
damage to the stair by the building frame, or to
use with allowable stresses. Allowable stress