Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SEISMIC SUSPENDED CEILING SYSTEM
Field of the Invention
The present invention relates to suspended ceiling systems based upon the use
of inverted "T-bar" lattices, and more particularly to ceiling panels which,
when
installed, cannot be shaken loose from the suspension lattice.
Background
The majority of suspended or "dropped" ceiling construction in use today
employs so-called T-bar rails, having the cross-section of an inverted "T",
arranged in
a rectilinear grid and suspended from the structural ceiling by tie wires or
metal
straps. The system is essentially that described in U.S. Patent No. 2,710,679
(granted
to Bibb et at. on June 14, 1955), with minor modernizations. Rectangular
ceiling
tiles, generally either porous acoustic tile or decorative panels, are
inserted between
the T-bars at an angle, leveled, and dropped into the grid, where they rest on
the
horizontal flanges of the inverted "T". In the United States, the cell size in
the
suspension grid is typically either 24 in x 24 in or 24 in x 48 in, while in
Europe and
elsewhere the cell size in the suspension grids is 600 mm x 600 mm or 600 mm x
1200 mm. The ceiling tiles are actually about 1/4-inch (6 mm) smaller than the
nominal (i.e., cell) size, to facilitate easy installation between the
vertical stems of the
T-bars.
The popularity of this construction is due to the ease and low cost of
installation, and to the fact that the individual tiles are readily pushed up
and off of the
rails whenever access to the space above the ceiling is required, and can be
returned
to their original placement without damage. Tiles having any desired finish
and
appearance can be manufactured to fit into the standard T-bar grids, giving
decorators
and architects a wide range of design choices. Lighting fixtures and air
diffusers and
grilles, built to the same dimensions as the tiles, can be dropped into the
grid
wherever desired. Tiles and fixtures of the standard dimensions are
commercially
available from a wide range of sources.
One disadvantage of this system is that, in an earthquake, the tiles and
fixtures
can bounce up and off of the T-bar flanges, and then drop to the floor or onto
the
building's occupants, as a consequence of not being mechanically connected or
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attached to the T-bars. As tiles fall from their places, the suspended grid
becomes
flexible and prone to even greater movement and distortion, causing more tiles
to fall;
the result is often a progressive failure of the entire ceiling.
In earthquake-prone areas, seismic building codes often require splayed
(diagonal) tie wires to be installed, to limit lateral motion and distortion
of the grid
during an earthquake. Vertical posts are sometimes installed as well, to limit
vertical
motion of the grid. Such preventive measures render the grid more rigid, and
ensure
that it moves along with (and not relative to) the building, but they add to
the labor
and expense of installation, and they do not entirely prevent individual tiles
and
fixtures from separating from the T-bars. Fixing the tiles to the T-bars, for
example
by installation of retention clips, is labor-intensive, and interferes with
easy access to
the space above the ceiling. Easily accessed clips tend to be visible, and can
mar the
aesthetics of the ceiling design. Safety mechanisms that "catch" falling tiles
(e.g.,
U.S. Patent No. 5,253,463 granted to Witmyer on October 19, 1993) still permit
the
tiles to separate from the T-bars, and the grid can still suffer from the
resulting loss of
rigidity.
Tiles having a slot or kerf along the sides, into which the T-bar horizontal
flanges are fitted, are known. Kerfed tiles are intended to conceal the grid,
partially
or completely, from view from below, and by virtue of being locked to the
grid, they
also have improved seismic resistance. Tiles having four kerfed sides are
rarely
employed, because they must be slid into place as the T-bar grid is being
assembled,
and they present an installation problem when the assembly process reaches a
wall.
There are kerfed tiles designed for installation in a pre-existing grid, which
feature
some combination of breaks in the flanges and/or the upper lips of the kerfs,
that
permit the tiles to be slid into place. Tiles featuring a small upper lip
along two
adjacent kerfs, that take advantage of the 1/4-inch of leeway between tile and
grid to
enable installation, are known, but such tiles are not truly locked to the
grid. Kerfed
tiles having gaskets, that snap into place over and below the T-bar
horizontals, are
known (e.g.,U U.S. Patent Nos. 4,760, 677 granted to Nassof on August 2, 1988,
and
5,507,125 granted to McClure on April 16, 1996). Removal of kerfed tiles
without
damage, for access to the space above the ceiling, can be difficult or
impossible,
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particularly when the method of installation is not apparent to the person
attempting
the removal.
Separate frames intended to obscure the T-bar are known (e.g., U.S. Patent
No. 4, 4980, 957 granted to Bumpus et at. on January 1, 1985), but these
frames,
which serve only an aesthetic purpose, clip to the T-bar and do not secure the
ceiling
tile. There is a need for a suspended ceiling system that remains easy to
install and
maintain, but which does not drop tiles in the event of an earthquake. Similar
needs
exist in mobile environments, such as military and passenger ships, where
ceiling
structures are sometimes subjected to unusual forces and motions.
A feature of suspended ceilings is the air space, or plenum, between the
suspended tiles and the structural ceiling above. If ductwork for both a
forced-air
supply and forced-air return is installed, the airspace is "dead", i.e.,
filled with non-
circulating air. In the absence of return air ducts, the plenum is usually
provided with
an exit duct, and the space above the tiles is an "active" plenum filled with
circulating
air. Electrical wiring installed in an active plenum can represent a fire
hazard,
because toxic gases and smoke from burning insulation and plastics are not
contained,
as they would be in a dead airspace, but are passed directly into the
building's air
circulation system. Another hazard is that a fire in a plenum space could
spread
rapidly before being detected, if combustible materials are present.
When the airspace above a dropped ceiling is used as an active plenum,
construction standards and/or local fire regulations require low-voltage
cables and
wiring either to be installed inside metal conduit, or else provided with low-
smoke/low-toxicity wire insulation which does not support combustion on its
own.
Twisted pair and coaxial cables, for telephone and data network services, are
the most
common form of wiring found above ceilings in commercial buildings.
Specialized
plenum (or plenum-rated) cable is referred to as Low Smoke Zero Halogen (LSZH
or
LSOH) cable. Plenum-rated cable is generally insulated and sheathed with
fluorocarbon polymers, which makes it significantly more costly than
equivalent non-
plenum-rated wiring, which typically has inexpensive polyethylene insulation
and
PVC sheathing.
High-voltage electrical equipment and wiring (generally, >50 volts) above a
ceiling is required to be enclosed in metal conduit or raceways, and must be
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physically isolated from low-voltage wiring. Devices and fixtures, such as
lighting
fixtures, must be enclosed in metallic boxes. Electrical outlets are permitted
inside
the plenum space (if enclosed within electrical boxes), but because the
sockets
themselves must be located on the exterior of the dropped ceiling, plug-in
connection
of fixtures is impractical. The overall result is that all fixtures and
devices installed in
a ceiling must be hard-wired, using metal conduits and junction boxes.
Meeting these construction and fire codes adds substantially to the time and
cost of installation, as the conduit and boxes represent added capital costs,
and require
a considerable amount of skilled labor to install. It is particularly
difficult and costly
to add high-voltage wiring to a previously installed system. There is a need
for
suspended ceilings that can safely be wired without the added expense of
conduit,
junction boxes, and plenum-rated wiring, and which permit the plug-in
connection of
electrical fixtures.
Summary of the Invention
The present invention provides ceiling panels that comprise an upper frame,
and a reversibly attached lower frame. The upper frame is sized and configured
to be
installed on a suspended T-bar grid in the usual manner. Once the upper frame
has
been placed on the T-bar horizontals, the lower frame is mechanically locked
to the
upper frame to complete the installation. The lower frame is sized to at least
partially
cover the T-bar horizontals, so that the two frames, when locked together, are
functionally equivalent to a kerfed tile. In a ceiling constructed from these
panels, the
T-bar flanges are trapped between the frames, and cannot separate from the
panels
when the ceiling is rocked or shaken.
When two ceiling panels of the invention are installed in adjacent cells of
the
T-bar grid, the sides of the panels, together, define a channel that is at
least large
enough to enclose and capture the T-bar horizontal flanges. In preferred
embodiments, this channel comprises additional space below the T-bar. In
alternative
embodiments, a second channel is defined. This additional space (or second
channel),
being below and outside of the plenum space, serves as a utility channel that
can carry
non-plenum-rated wiring, cabling, and fixtures. The channels between adjacent
panels
of the invention align with the channels between neighboring panels, creating
extended utility channels that run the full length and width of the ceiling.
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The present invention provides suspended ceilings that comprise a suspended
grid of inverted T-bars, upper frames fitted between the vertical stems and
resting
upon the horizontal flanges of the T-bar grid; and lower frames reversibly
attached to
the upper frames, wherein adjacent lower frames together with the adjacent
upper
frames to which they are attached define channels that partially or completely
enclose
the horizontal flanges of the T-bars upon which the upper frames are resting.
The invention also provides a method of constructing a suspended ceiling,
comprising the steps of suspending an inverted grid of T-bars from an existing
ceiling, installing between the vertical stems of the T-bar grid upper frames
that rest
upon the horizontal flanges of the T-bars; and reversibly attaching lower
frames to the
upper frames, wherein adjacent lower frames together with the adjacent upper
frames
to which they are attached define channels that partially or completely
enclose the
horizontal flanges of the T-bars upon which the upper frames are resting.
Brief Description of the Figures
Fig. 1 shows a top view of an exemplary upper frame of the invention.
Fig. 2 shows a side view of an exemplary upper frame of the invention.
Fig. 3 shows a cross-section of an exemplary upper frame of the invention.
Fig. 4 shows a side view of an alternative embodiment of an upper frame of
the invention.
Fig. 5 shows a top view of an exemplary lower frame of the invention.
Fig. 6 shows a side view of an exemplary lower frame of the invention.
Fig. 7 shows a cross-section of an exemplary lower frame of the invention.
Fig. 8 shows a different cross-section of an exemplary lower frame of the
invention.
Fig. 9 is a perspective drawing showing upper and lower frames of the
invention, positioned on a T-bar grid.
Fig. 10 is a perspective drawing showing a connected set of upper and lower
frames of the invention on a T-bar grid.
Fig. 11 is a perspective drawing showing a set of upper and lower frames of
the invention, assembled on a T-bar grid to form a ceiling panel of the
invention.
Fig. 12 is the perspective drawing of Fig. 10, with the T-bar grid removed for
clarity.
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Fig. 13 shows a cross-section of ceiling panels of the invention installed on
and supported by a T-bar grid.
Detailed Description of the Invention
The present invention provides ceiling panels for installation in a grid of
suspended T-bars. A panel of the invention comprises an upper frame, sized to
fit
between the verticals and rest upon the horizontals of the gridded T-bars, and
a lower
frame that is reversibly attachable to the upper frame when the upper frame is
resting
upon the horizontals of the T-bar grid. The invention is characterized by the
fact that
the lower frame, when attached to the upper frame, forms together with the
upper
frame a channel that at least partially encloses the horizontals of the T-bar
upon which
the upper frame is resting. When the horizontals on both sides of the T-bar
are thus
enclosed, the horizontals cannot escape the channels when the panels are set
in
motion by a seismic event. The panels themselves cannot be separated from the
T-
bars, and will remain suspended so long as the T-bar grid itself remains
suspended.
Various known-in-the-art means of reversibly attaching the upper and lower
frames can be employed, such as for example magnetic couplings, hook-and-loop
fabric strips or patches, spring-biased clips and snaps, and screws. In
general, the
preferred means of attachment are mechanical means which are not susceptible
to
detachment under the forces applied during an earthquake, yet are readily
reversed by
workers whenever a panel must be removed for inspection, maintenance, or
modification of the ceiling or plenum. Such attachments are referred to herein
as
"locked" or "locking" attachments. In a particularly preferred embodiment, as
illustrated in the present drawings, the ceiling panels of the invention have
the lower
frame attached to the upper frame by means of spring wire retainer clips, the
clips
being attached to one frame and engaging with and snapping into slots in the
other
frame. The frames can be separated only when the wire clips are manually
released.
Quick-release (e.g. half-turn or quarter-turn) screws are another preferred
means of
reversible attachment. Captive screws will be particularly preferred.
In other preferred embodiments, the ceiling panels of the invention may
comprise lighting fixtures or elements, and associated hardware such as
mounting
brackets, heat sinks, and diffusers. The lighting elements are preferably LED
lighting
elements affixed to either of the frames. Wiring for the LED elements may
optionally
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be affixed to either of the frames, and/or the wiring may be run between the
frames.
Electrical components are preferably located below the plane defined by the T-
bar
horizontals, where less-expensive non-plenum-rated components can be safely
installed.
In preferred embodiments, the panels define a space between one another,
below the T-bar horizontals, which serves as a utility channel. Non-plenum-
rated
wiring and cabling, such as for example telephone, Ethernet, and co-axial
cabling, can
safely be installed in the utility channel, which lies outside of the plenum.
Other
devices which can be installed along with their wiring include wireless
routers and
repeaters, smoke detectors, fire alarms, security cameras, and the like.
The upper and lower frames can be manufactured from any material
customarily employed in the manufacture of ceiling tiles and panels.
Preferable
materials are fiberglass composites and rigid polymer foams, which can be
formed in
molds and then further shaped, if necessary, by machining. Rigid, closed-cell
polyurethane foams are particularly preferred. Polyurethane foams are produced
by
reacting a di- or polyisocyanate with isocyanate-reactive diols or polyols,
generally in
the presence of one or more blowing agents, catalysts, surfactants and other
additives.
In general, any binary "A/B" polyurethane foam system that produces a rigid
foam can be employed, and there are numerous commercially-available systems
that
are suitable. Preferably the cured foam is a closed-cell foam having a density
of
between 2 and 8 lbs/cubic foot. By way of example, a flame-resistant binary
"A/B"
pourable urethane foam precursor can be prepared according to US Patent No.
7,141,613 (granted to Albach et al. on Nov. 28, 2006). Preferred isocyanate
precursors include 4,4' diphenylmethane diisocyanate, polymethylene polyphenyl
isocyanate, and mixtures thereof. Preferred polyol components include
polyalkylene
ether polyols and alkoxylated and non-alkoxylated Mannich polyols. To confer
fire-
retardant properties, any polyurethane-compatible flame retardant known in the
art
may be employed, such as for example tris(1-chloro-2-propyl)phosphate. As a
blowing agent, water is preferred, but it may be supplemented with known
blowing
agents such as hydrocarbons, hydrofluorocarbons, or alkyl formates. Rigid
"architectural" polyurethane foams that meet or exceed building construction
and fire
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standards are well-known to those of skill in the art, and these will be
especially
preferred in the present invention.
Turning to the drawings, Figures 1, 2 and 3 show a top view, side view and
cross-section, respectively, of an exemplary upper frame 1. In the interest of
clarity in
the drawings, the embodiment that is illustrated in Figs. 1-3 has an open
upper frame,
but it can be closed off with any type of decorative panel 2, as shown in the
alternative embodiment of Fig. 4, so as to form a coffered ceiling when
installed on
the T-bar flanges. The decorative panel may be co-formed with, and integral
with, the
upper frame, or it may be formed separately, from any material known in the
art to be
suitable for use in the construction of suspended ceilings, and attached to
the upper
frame by routine means, including but not limited to adhesives, staples,
screws, clips,
and the like. Acoustic tile, or metal or plastic sheeting shaped or sculpted
for
aesthetic appeal, are particularly contemplated. The decorative panel 2 may be
fitted
with conventional lighting or ventilation fixtures, as is known in the art.
Acoustic
and/or thermal insulating materials (not shown) may be attached to the upper
surface
of the decorative panel. In the embodiment shown, which is adapted for the use
of
wire clips to attach the lower frame as disclosed further below, L-shaped
slots 3 are
formed into or cut through the upper frame near each corner. An optional cut-
out 6a
is shown; these cutouts are discussed below in connection with Figure 6.
Figures 5, 6, 7 and 8 show a top view, side view and two cross-sections,
respectively, of an exemplary lower frame 4. In the embodiment shown, wire
form
spring clips 5 are attached to the lower frame, and these serve as the means
of
reversibly attaching the lower frame to the upper frame. Suitable wire forms
can be
manufactured from any resilient metal wire known in the art to be suitable for
wire
spring clips, such as for example the 0.03-inch diameter piano wire used in
this
particular embodiment. An optional cut-out 6b is shown; these cutouts are
preferably
present on all four sides of the lower frame. The cutouts 6b align with the
cutouts 6a
in the upper frame, and together form an aperture 6 (Figure 13) that allows
indirect
lighting to be directed upwards from lighting elements (not shown) installed
within
the utility channel. The lighting elements are preferably LED lamps with their
associated wiring, and they are preferably installed on a circuit board that
is attached
to the lower frame. Such circuit boards can advantageously be pre-installed on
the
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lower frame, so that lighting is installed at the same time the ceiling is
installed. The
installer of ceiling panels corresponding to this embodiment needs only to
plug the
LED wiring into an outlet connected to a power supply cable running within the
utility channel 8 (Figure 13), to effect a complete and code-compliant
installation of
the ceiling's lighting.
Turning now to Figures 9-11, the installation and in situ assembly of a
ceiling
panel, according to one embodiment of the invention, is illustrated in
perspective
views. Initially, as shown in Figure 9, upper frame 1 is installed on a T-bar
grid 7 in
the usual manner, so that it rests on the upper surfaces of the T-bar flanges.
The
upper frame is penetrated by four L-shaped slots 3. Lower frame 4 is shown
with four
wire form spring clips 5 attached near each corner. The wire spring clips
stand
vertically, and feature a first horizontal segment at the upper end, and a
second
horizontal segment at right angles to the first, located near the mid-point of
the wire.
Viewed end-on, the first and second horizontal segments project an L shape,
which is
dimensioned and oriented so as to align with the L-shaped slots 3 in upper
frame 1.
The precise location of the slots 3 in the upper frame 1, and the precise
location of the
wire spring clips 5 on the lower frame 4, are not critical, so long as they
align when
the frames are brought together. For maximum stability of the installed
panels, an
arrangement close to the corners is preferred. For ease of installation, a
symmetric
arrangement of the slots and wires is preferred.
To install the panel into the T-bar grid, the first horizontal segment of each
of
the wire spring clips 5 is inserted into a parallel limb of each of the
complimentary L-
shaped slots 3. The lower frame 4 is then moved upwards, until the first
horizontal
segments of the wire spring clips pass through upper frame 1 and emerge from
the
slots 3. The wire spring clips are preferably biased so that each first
horizontal
segment, upon emerging from its corresponding slot, is displaced away from the
slot.
The arrangement is now as shown in Figure 10, where the lower frame 4 is shown
hanging from the upper frame 1 by the four wire spring clips 5. In this
configuration,
the installation of additional features such as wiring and electrical
components, and
the making of electrical connections, may be carried out.
To complete the assembly and installation of the panel, the lower frame is
pressed further upwards, until the second horizontal segments of the spring
wire clips
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emerge from slots 3. The wire spring is inwardly biased, in a direction
parallel to
the side of the frame, so that the second horizontal segment, upon clearing
the slot 3,
is displaced away from the slot. The lower frame now hangs from the upper
frame as
shown in Figure 11, with its weight borne by the four second horizontal
segments. In
this configuration, the four wire spring clips are locked into the positions
shown by
the biasing force of the wire spring itself. In this locked configuration, the
two frames
are in contact, or nearly so, so that the locked-together frames act as a
rigid unit that
cannot be displaced from the T-bar.
In preferred embodiments, the distance between the frames in the
configuration of Fig. 10 is large enough to permit placement of the upper
frame onto
the T-bar grid, after the lower frame has been connected via the wire clips as
shown in
Figure 12. This mode of installation consists of simply placing the upper
frame of the
assembly shown in Figure 12 onto the T-bar grid, arriving at the arrangement
shown
in Figure 10. After making any necessary electrical connections, the two
frames are
pressed together, as described above, until the wire clips snap into place.
The frames may be separated, and the panel uninstalled, by manually
displacing the wire spring clips 5 so that the second horizontal segments drop
back
into their corresponding slots, and then allowing the lower frame to drop
down,
returning the frames to the configuration shown in Figure 10. Reversal of the
installation is straightforward from this point, and the upper frame may be
removed
from the grid, and then re-installed at a later time without damage.
Figure 13 shows a cross section of ceiling panels of the invention,
essentially
along the lines of Figures 3 and 7, which have been assembled from upper
frames 1
and lower frames 4 as described above, and suspended from T-bars 7. The wire
clips
5 are omitted from this view. In this embodiment, the sides of adjacent panels
together define a utility channel 8 directly below the T-bar. In an
alternative
embodiment (not shown), the sides of adjacent panels define a utility channel
separate
from the channel enclosing the T-bar 7. As can be seen from Figure 13, the
utility
channel 8 lies below the T-bar grid and is not within the plenum space above
the
ceiling. This location outside of the plenum makes possible the installation
of non-
plenum-rated wire and cable, and simple plug connectors for lighting fixtures,
without
the need for metal conduit, raceways, and junction boxes. The cut-outs 6a and
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(see Figures 3 and 6) align to define aperture 6, which can be used to admit
light from
lighting elements mounted within utility channel 8.
The drawings and descriptions provided with this specification are intended to
be illustrative, and are not intended to convey limitations on the scope of
the
invention. Modifications and alterations will be obvious to those of skill in
the art,
and such modifications and alterations are intended to be within the scope of
the
invention.
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