320
Ceilings: Basic Design
When this is not the case, bracing the hangers with one diagonal member
in approximately every fifth bay in each direction will suffice. Preference
should be given to those designs which do not require diagonal bracing.
321.2
SUPPORTING FRAMEWORK
To allow use of a wide variety of short-span platform materials, an
intermediate framework is required between the platform and the hangers.
The platform may span over the framework or may be hung from it,
depending upon the nature of the material used. The latter solution is
preferred since this reduces the effective overall depth of the ceiling
structure. Provision may need to be made for penetration of the
framework by service distribution components located in this zone. The
extent of such penetrations is minimized if the direction of the main
elements of the framework (ribs, joists, etc.) is perpendicular to the
structural beams.
321.3
PLATFORM
The platform must meet many of the performance requirements stipulated
for the total ceiling assembly with regard to strength, fire resistivity,
acoustics, etc. Besides its major function of providing a working platform
both during construction and for maintenance and alterations, it must
distribute all lateral loads from the partitions to the structure, or to the
diagonal braces if it is not used as a diaphragm. Since there is no
planning grid, the partitions must be able to be fixed to any point of the
platform which should therefore be flush on the underside. Similarly, there
must be as few limitations as possible to the location of penetration for
services. Cutting and patching holes in the platform must be easy. The
platform must provide one-hour fire resistance and an acoustic flanking
path barrier if the finished ceiling does not perform these functions.
321.4
FINISHED CEILING
The finished ceiling is attached to the underside of the platform. A
finished ceiling without an exposed grid is preferred, since spaces are not
organized on the basis of a planning grid.
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