320
Ceiling
321
BASIC DESIGN (Figures 320-1 and 320-2)
The ceiling subsystem consists essentially of a continuous walk-on
platform suspended by hangers from the structural beams, with a finished
ceiling applied to or suspended from the underside. The platform is hung
a sufficient distance below the structural slab so that a horizontally
accessible service zone is created above it. Except for two-hour fire
barriers, and certain smoke barriers, all partitions stop at the ceiling-
platform which is one-hour fire resistive. The height of the platform above
the floor is constant in each major segment of the hospital. (The rationale
leading to this basic design is discussed in Section 722.)
Ideally, the platform, the supporting framework and the finished ceiling
would be one thin sandwich. However, no single material or product is
presently available which answers all the design and performance
requirements; the ceiling subsystem must therefore be regarded as an
assembly of at least four different components, the basic characteristics of
which are described below.
321.1
HANGERS
Compared with hanger spacings of conventional ceilings, the steel
hangers are widely spaced. They are approximately 1/2"-3/4" in diameter
and are attached along the centerline of the bottom of the structural
beams. The recommended spacing is such that each supports a
maximum of approximately fifty to sixty square feet of platform. The
hangers are likely to be used to delineate the secondary subzones in the
service zone above the ceiling so the spacing should be coordinated with
these subzones. (See Section 224.2.)
Hangers may be attached to steel beams by means of welded studs, and
to concrete beams by means of continuous or individual inserts cast into
the beams. Hangers are attached to the horizontal supporting framework
of the platform via adjustment devices for leveling purposes.
For most combinations of materials and details likely to be selected for the
ceiling-platform-framework assembly, sufficient diaphragm action can be
developed to transfer all partition lateral loads to the structure and to
support the ceiling under seismic loading.
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