Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKCROUND or Til~ INVrNTION
This invention relates to electrical wiring ducts for a building and
more particularly to an improved method and structure for forming electrical
wiring ducts in a concrete building floor. This application is an improvement
upon applicant's Canadian Patent No. 1,070,510, granted January 29/80.
Buildings formed from concrete are often partially constructed before
a final floor plan is selected. After the basic building structure is erected,
such buildings are subdivided into spaces such as individual offices. Utility
ducts for wiring and comfort conditioning are sometimes formed in poured
concrete floors to facilitate supplying required utilities to each space into
which the building is subsequently divided. One prior art method for forming
utility ducts in a poured concrete floor is shown in United States Patent
3,0933,933 which issued June 18, 1963 to Slingluff and in United States Patent
2,975,559 which issued March 21, 1961 to Hedgren. These patents disclose a
building floor structure having a metallic cellular subflooring which forms
parallel cells or conduits for carrying electrical cables and for air handling.
Electrical ducts also are located immediately above and perpendicular to the
cellular subflooring. These ducts are spaced across the subflooring to provide
a desired spacing for electrical service connections. Access fittings are
attached to the ducts at desired locations and the ducts are connected to the
appropriate subfloor cells. A concrete floor is then poured over the cellular
subflooring to embed the electrical ducts. Wiring for power and communications
is passed through the subflooring cells and the desired ducts for serving the
floor area wherever such service is needed. By running electrical power and
- communications wiring through different subfloor cells and through alternate
ducts, the power wiring is shielded in accordance with some building codes and
the communication wiring is isolated from the power wiring to minimize induced
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electrical noise. Ilowever, a building floor structure of this type is unneces-
sarily expensive because of the high cost Eor the cellular metallic subflooring
and of the need -Eor using separate metal channels for forming both power and
communications ducts in the floor.
SUMMARY OF TIIE INVENTION
According to the present invention, an improved method is provided
for forming wiring ducts or raceways in a prefabricated concrete floor slab.
The method provides separate raceways for electrical power wiring and communi-
cations wiring; in a preferred structure the power raceways are completely
shielded by metal.
In accordance with the present method, a prefabricated building
floor slab is poured from concrete or a similar hardenable material. In some
instances, parallel trenches are formed in the upper surface of, and spaced
interiorly from the edges of the floor slab at the time of pouring. The slab
is ultimately installed as a structural member of a building. At some point
in time after the floor slab hardens sufficiently to maintain its shape,
a metal cover plate is placed over each trench; the metal cover can be placed
either before or after the slab is installed as a structural member on suitable
building supports. In a preferred embodiment, a U-shaped metal channel
is attached to the bottom of the cover plate to extend the length of the
trench for dividing the trench into at least two and preferably three separate
raceways. Adjustment means can be provided in the sides of the U-shaped
channel to compensate for irregularities in the depth of the trench. In
other instances, a fraction of a trench extending along an upper edge of one
slab and the remainin~ fraction of the trench extending along an upper edge of
another slab form one complete trench when the two slabs are installed adjacent
to each other as structural members of a building. Grouting is then poured
into a joint formed between the slabs below the trench and, in the preferred
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cmbodiment, a cover plate having an attached ll-shaped channel is then positioned
on the trench. Preferably, anchors spaced along the bottom of the U-shaped
channel are set within the grouted joint between the two slabs. However the
trench is formed, one of the raceways, in the preferred embodiment, which is
defined by the U-shaped metal channel and the metal cover plate, is completely
shielded for varying electrical power wiring while the remaining raceways on at
]east one side of the U-shaped channel are unshielded. These channels carry
communications wiring such as telephone wires, computer input, output and control
wires, process control wires, intercom wires, etc. Access boxes are attached
to the top of the trench cover plate over one or more knockouts for providing
desired access to wires located in the raceways. Metal channels also are placed
perpendicular to and across all of the trenches for defining main power dis-
tribution ducts interconnecting the various parallel raceways. A topping or
surface layer of concrete or other hardenable material is then poured over the
prefabricated floor slab to extend flush with the top of the access boxes and the
channels forming the power distribution ducts. Electrical wiring for servicing
power and communication needs on the floor area is completed by passing wires
through the raceways between the main distribution channels and the access boxes
and finally attaching a cover plate over the main distribution channels. Through
this arrangement, power wiring for the entire system is shielded from the
communications wiring to minimize electrical noise induced into the communica-
tions wiring. Furthermore, the cost of placing a metallic cellular subflooring
in the building and separate metal ducts for defining both power and communica-
tions raceways is eliminated.
In accordance with another embodiment of the present method, parallel
sets of a plurality of trenches can be formed in the upper surface of, and
spaced interiorly from the edges of, the prefabricated floor slab at the time
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of pouring. After the concrete has hardened sufficiently, a metal cover plate
is placed over the plurality of trcnches and the concrete walls, thus forming
at least two and preferably three separate wiring raceways. The slab is
ultimately installed as a structural member of a building, as previously
described, and is covered by a poured floor. Two slabs can be formed with at
least one trench and a fraction oE another trench in one slab, the fraction
extending along an upper edge of thc slab, and at least the remaining fraction
of the trench extending along an upper edge of the other slab. The slabs are
then positioned on building supports with the trench fractions abutting. The
joint is grouted, as described above, and a metal cover is placed over the
trenches, trench fractions, and concrete walls to form at least two parallel
ducts or wiring raceways.
Accordingly, it is an object of the invention to provide an improved
method for forming wiring ducts in a concrete building floor.
Another object of the invention is to provide a method for construct-
ing parallel communications and power wiring ducts in a concrete floor with
shielding for only the power wiring.
Other objects and advantages of the invention will become apparent
from the following detailed description, reference being made to the accompany-
2Q ing drawings.
BRIEF DESCRIPTION OF THE DRAWINCS
.
Figure 1 is a fragmentary, sectioned perspective view of an improved
concrete floor structure having wiring ducts formed therein in accordance with
the present invention;
Figure 2 is an enlarged fragmentary, sectioned perspective view of an
inverted cover plate for dividing a trench formed in a concrete floor slab into
three separate raceways;
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Figure 3 is an enlarged fragmentary, cross-sectional view taken along
line 3-3 of Figure l;
Figure 4 is a fragmentary, sectioned perspective view of an improved
concrete floor structure having wiring ducts formed therein in accordance with
a modified embodiment of the invention in which a portion of the floor is
constructed from prefabricated concrete slabs;
Figure 5 is an enlarged fragmentary, cross-sectional view taken along
line 5-5 of Figure 4;
Figure 6 is an enlarged fragmentary, cross-sectional view taken along
line 6-6 of Figure 4;
Figure 7 is an enlarged fragmentary, cross-sectional view of a
modified concrete floor formed in accordance with the invention;
Figure 8 is an enlarged fragmentary, cross-sectional view through
another modified concrete floor and wiring duct formed in accordance with the
present invention;
Figure 9 is an enlarged fragmentary, cross-sectional view through
still a further modified concrete floor and wiring duct structure formed in
accordance with the present invention;
Figure 10 is an enlarged fragmentary, cross-sectional view through
still another modified concrete floor and wiring duct structure where one of
the ducts is formed over a joint between two precast structural slabs in
accordance with the present invention; and
Figure 11 is an enlarged fragmentary, cross-sectional view through
still a further modified concrete floor and wiring duct structure where one of
the ducts is formed over a joint between two precast structural slabs in
accordance with the present invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to the drawings and particularly to Figure 1, a building
floor structure 10 is shown embodying the structure and constructed by the
method
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i38
of the present invention. The floor structure 10 basically comprises a concrete
floor slab 11 and a concrete surface or topr)ing layer 12. Ducts or raceways
are formed in the slab 11 and the surface layer 12 for supplying electrical
power and communications to predetermined spaced locations in the building in
which the floor structure 10 is constructed. Sufficient number of access points
to the electrical ducts are provided in the surface layer 12 for supplying power
and communications requirements over the floor area regardless of the manner in
which the floor area is subsequently subdivided.
When the concrete floor slab 11 is poured, a plurality of parallel
trenches 13 are formed in an upper surface 14 of the slab 11. The trenches 13
may be formed by any suitable means, such as by placing wooden forms (not shown)
in the upper surface 14 for forming the trenches 13 and, after the concrete in
the floor slab 11 has at least partially hardened, removing such forms. After
the slab 11 is poured and hardened sufficiently to maintain the shape of the
trenches 13, at least some of the trenches 13 are divided into at least two
separate wiring ducts or raceways, with three raceways 15-17 shown in the
drawings. The raceways 15-17 are formed by placing a cover plate 18 over each
trench 13 to extend along the entire length of such trench. As best seen in
Figure 2, a generally U-shaped channel 19 is attached to the cover plate 18.
The U-shaped channel 19 is attached to the cover plate 18 by any suitable means,
as by spot welds 20 or by rivets, screws, bolts, etc. The channel 19 has sides
21 of a height corresponding to the depth of the trench 13 for dividing the
trench 13 into the separate ducts 15-17. It will be noted that the center duct
16 is defined by the U-shaped channels 19 and the cover plate 18 and, therefore,
is completely shielded with metal. The ducts 15 and 17 are defined by the
concrete walls of the trench 13 on two sides, by the channel sides 21 and by
the cover plate 18. Because of the shielding, the duct 16 is particularly
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suitable for carrying power wires while the ducts 15 and 17 preferably are used
for carrying communications wires such as telephone wires, local intercom wires,
process control wires, and the like. By shielding the power wires in the duct
16, electrical noise induced into the communications wires is minimized.
Groups of three knockouts 22, 23 and 24 are spaced along each of the
cover plates 18 for providing access points through the cover plate 18 into the
ducts 15-17, respectively. If, for example, the trenches 13 are located
parallel to each other with a five foot center-to-center spacing and each group
of knockouts 22-24 is placed at a five foot spacing in the cover plates 18, then
the floor structure 10 will have access points into the ducts 15-17 in a grid
pattern across the floor structure 10 with a five foot spacing. Such a spacing
would normally be sufficient for providing adequate power and communications
outlets in a building. The rectangular access boxes 25 may be attached to the
cover plate 18 at each group of knockouts 22-24. The access boxes are shown
as having a width which permits covering two adjacent ones of the knockouts, such
as the knockouts 22 and 23 for providing access to the communications and power
ducts 15 and 16 or the knockouts 23 and 24 for providing access to the power
and communications ducts 16 and 17. In a preferred embodiment, the access boxes
25 are staggered such that one box 25 on a cover plate 18 provides access to the
ducts 15 and 16 through the knockouts 22 and 23 and the next access box 25 on
the cover plate 18 provides access to the ducts 16 and 17 through the knockouts
23 and 24. However, it should be appreciated that the width of the access
boxes 25 may be such that a box 25 provides access through only one knockout
22, 23 or 24 to one duct 15, 16 or 17, or that a box 25 provides access through
all three knockouts 22-24 to the three ducts 15-17.
In addition to the access boxes 25, three channels 26-28 are posi-
tioned to extend across and rest upon the cover plates 18. The channels 26-28
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are prefer.lbly connected to eacll cover p]ate 18 to provide elcctrical ground
continuity. The channels 26 a]ld 28 are generally C-shaped while the channel 27
spaced between the channels 26 and 28 is generally U-shaped. In addition, the
channels 26-28 have the same height as the height of the access boxes 25. After
the channels 26-28 are positioned and attached to the cover plates 18, the
concrete surface or topping layer 12 is poured to form a top surface 12' which
extends flush with the tops of the access boxes 25 and the channels 26-28.
After the surface layer 12 is poured and has hardened, communications
and power wires are run through the raceways or ducts 15-17 and three main
distribution raceways 29-31 formed between the channels 26-28 and within the
channel 27. As previously indicated, the channels 26-28 extend across all of
the cover plates 18 over the trenches 13. Although not mandatory, it may be
preferable to position the channels 26-28 perpendicular to the trenches 13.
The main distribution raceway or duct 29 between the channels 26 and 27 communi-
cates through an opening 32 in each cover plate 18 to the raceway 17. An open-
ing 33 passes through the bottom of the U-shaped channel 27 and each cover
plate 18 for communicating within the duct 30 formed by the channel 27 to each
duct 16. Similarly, the duct or raceway 31 formed between the channels 27 and
28 is connected through an opening 34 in each cover plate 18 to the duct or
raceway 15. Thus, communications wires are laid in the raceway or duct 29 and
passed through the raceway 17 for communicating through the knockouts 24 and
access boxes 25 to predetermined locations on the floor structure. Similarly,
power wires are passed through the duct 30 formed by the channel 27, through
the opening 33 and through the duct 16 for supplying power through the knockouts
23 and access boxes 25 to predetermined locations in the floor structure 10.
Communication wires may also be positioned in the duct or raceway 31 and passed
through the openings 34 and the ducts or raceways 15. After the wires are
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113~38
positioned in the ducts or racewiays 29-31 and 15-17, a cover plate 35 is
positioned over the channcls 26-28 and fastened to the channels 26 and 28 by
means of suitable fasteners 36. Ihe cover plates 35 and 18 and the channels
19 and 26-28 and the access boxes 25 are all grounded for safety. Since the
power wires in the ducts 30 and 16 are completely surrounded by the channel 27
and its cover plate 35 and the channel 19 and its cover plate 18, the power
wires are all completely shielded. The shielding protects the communications
wires from damage in the event of a short circuit in the power wires and also
reduces electrical noise which otherwise might be induced into the communi-
cations circuits.
Turning now to ~igure 3, a cross section is shown through the ducts15-17 in one trench 13 and through an access box 25. Although it may not always
be required, it will be noted that fasteners 37 are shown attaching the cover
plate 18 to the poured concrete slab 11. The fasteners 37 may be of any
suitable design, such as explosively driven nails. The primary purpose for the
fasteners 37 is to maintain the cover plate 18 centered over the trench 13
while the surface layer 12 is poured. It should be appreciated that if the cover
~plate 18 is allowed to move while pouring the surface layer 12, the concrete
or other hardenable material forming the surface layer 12 may flow into the
trench 13. After the cover plate 18 is positioned over the trench 13 to divide
the trench into the three separate raceways or ducts 15-17, the access box 25
is attached to the cover plate 18 over either the knockouts 22 and 23 or the
knockouts 23 and 24. As shown in Figure 3, the knockouts 22 and 23 are removed
leaving openings 22' and 23', respectively, through the cover plate 18 and into
the ducts 15 and 16. The access box 25 is then positioned over these openings
22' and 23'. Wires are positioned in the ducts 15-17 at any suitable time
during construction of the floor structure 10. For example, the wires may be
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run in tilC Llucts 15-17 at thc timc thc cover plate 18 is positioned over the
trcnch 13 and prior to ~ouring the surface layer 12. Or, wires may be pulled
through thc ducts 15-17 aftcr the ~loor structure 10 is completed. A telephone
wire 38 is shown excmplifying a typical wire located in the duct 15. The
telephone wire 38 passes through the cover plate opening 22' and is terminated
at a connector 39. ~hen telephone installation is completed, a serviceman
connects a mating connector 40 attached to a line 41 which connects to a tele-
phone (not shown) to the connector 39. The connectors 39 and 40 are positioned
within the access box 25 to eliminate any obstacles on the top floor surface
12'. An exemplary power wire 42 is shown in the power duct 16. The power
conductor 42 passes through the cover plate opening 23' and is terminated at a
standard power receptacle 43. An electrical appliance line cord 44 having a
standard plug 45 may subsequently be passed through an opening 46 in the access
box 25 and plugged into the receptacle 43. The opening 46 is sufficiently large
as to permit users of the building to remove the plug 45 or to plug in other
appliances.
As shown in Figures 3, the access box 25 normally provides access to
the power duct 16 and to one of the two communication ducts 15 or 17. It may
be desirable, for example, to place only telephone wires in one of the communi-
cation ducts, duct 15 shown, and to place other communication wires in the duct
17. Furthermore, it also may be desirable to stagger the location of the access
boxes 25 such that every other access box on a cover plate 18 provides access
to the duct 15 while the remaining alternate access boxes 25 provide access to
the duct 17. As represented by the dashed lines 47, if access is subsequently
desired into the duct 17 where such access is not provided by an access box 25,
an opening above the knockout 24 may be formed through the surface layer 12.
Such an opening may be formed by any suitable means, as by drilling through the
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surface layer 12 or by providillg il l)lug in thc surfacc area 12 which is readily
removable at a later date. Of course, where access is desired into both of the
communication ducts 15 and 17, the access box 25 may be constructed sufficiently
large as to cover each of the three knockouts 22, 23 and 24.
Although l:igures 1-3 of the drawings specifically show a floor
structure 10 having three parallel ducts formed in each trench 13, it will be
appreciated that any other desired number of clucts may be formed in a floor
trench. For example, if only a single communication duct and a single power
duct are desired, the trench 13 may be formed of a width sufficient to form only
a single communication duct, duct 15 for example, and a single power duct 16.
In such event,the U-shaped channel 19 would be located near one side of the
cover plate 18 rather than centered as shown in the drawings. Where additional
ducts are desired, it will also be appreciated that more than one U-shaped
channel 19 may be attached to the bottom of the trench cover plate 18 for form-
ing the desired number of ducts in the concrete floor slab 11.
Turning now to Figure 4, a floor structure 50 is shown constructed
in accordance with a modified embodiment of the method of the present invention.
The floor structure 50 is constructed from a plurality of prefabricated floor
slabs, of which two exemplary slabs 51 and 52 are shown in transverse section.
The slabs 51 and 52 are precast at a factory in standard widths such as eight
feet or twelve feet, and in various lengths for various size structures. To
reduce the weight of the slabs 51 and 52, voids 53 are formed to extend longi-
tudinally through the slabs 51 and 52. The strength of the slabs 51 and 52 is
maintained through the use of reinforcement rods or bars 54. If desired, the
bars 54 may prestress the slabs in a known manner. Wiring ducts 55 are formed
in a trench between the abutting slabs 51 and 52 with a fraction 56 of the trench
formed in the slab 51 and the remaining fraction 57 of the trench formed in the
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slab 52. ~ groutc(l jo;nt 58 cxtends betwecll the slabs 51 and 52 and below the
trench fractions 56 and 57. /~ grouted joint 5~ is also provided hetween the
slab 51 and a next adjacent slab 60 and a grouted joint 61 is provided between
the slab 52 and a next adjacent slab 62. Irenches for use in forming wiring
ducts are formed above the grouted joints only when a desired location for
wiring ducts or raceways is above such joints. In addition to the trench defin-
ed by the trench fractions 56 and 57 ;n the abutting portions of thc slabs 51
and 52, wiring ducts or raceways 63 are formed in a trench 64 located interior
from the edges of the slab 51 and wiring ducts 65 are located in a trench 66
located interior from the edges of the slab 52. An exemplary access box 67 is
shown for providing access to the wiring ducts 55 which are located between
the slabs 51 and 52 and an exemplary access box 68 is shown for providing access
to the ducts 63 within the slab 51. The access boxes 67 and 68 are shown em-
bedded within a topping layer 69 formed from concrete or any other suitable
hardenable floor material.
Turning now to Figure 5, details are shown for the wiring ducts or
raceways 63 spaced from the edges of and extending the longitudinal length of
the floor slab 51. A generally U-shaped channel 70 divides the trench 64 into
at least two and preferably three separate wiring ducts or raceways 71, 72 and
73. The U-shaped channel 70 has upper flanges 74 which are welded, bolted or
otherwise attached to a cover plate 75 which completely covers the trench 64.
Three sides of the duct 71 are defined by the U-shaped channel 70 and the fourth
side is defined by the metal cover plate 63. As a consequence, the duct 71 is
completely shielded to prevent passage of electromagnetic radiation from wires
within the duct 71. The ducts 72 and 73 are located on opposite sides of the
U-shaped channel 70 and are defined on two sides by the slab 51, on a third side
by the U-shaped channel 70 and on a fourth side by the cover plate 75. Thus,
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tlle ducts 72 alld 73 arc not sh-iclclccl. Ilectrical power wiring about which sub-
stantial electromagnetic fields may be established is preferably located within
the duct 71 while control and communication wiring is located within the ducts
72 and 73. In the event that only two ducts are required, one of the two ducts
72 and 73 may be eliminated either by shortening the size of the trench 64 or by
moving the channel 70 to one side of the trench 64. On the other hand, if
additional ducts are required, more than one U-shaped channel 70 may be attached
to the cover plate 75.
The U-shaped channel 70 is provided with two spaced parallel sides
76 and 77 and a flat bottom 78. The sides 76 and 77 extend below the bottom 78
to define lower fins or projections 79 on each side of the channel 70. The
projections extend below the cover plate 75 and below the bottom a distance
greater than the depth of the trench 64. The cover plate 75 and attached U-
shaped channel 70 are positioned over the trench 64 after the slab 51 is formed
and the concrete has solidified only sufficiently to maintain its shape. When
the cover plate 75 is positioned over the trench 64, sufficient downward force
is applied to force the projections 79 into the concrete at the bottom of the
trench 64. By deforming the concrete with the projection 79, the two ducts 72
and 73 are completely isolated, despite minor variations in the depth of the
trench 64 along the length of the slab 51. If desired, the cover plate 75 can
be anchored to the slab 51 with fasteners similar to the fasteners 37 in Figure
3 to retain the cover plate 75 in place during shipment and installation of the
slab 51. Thus, the slab 51 with the attached cover plate 75 and the U-shaped
channel 70 dividing the trench 64 into the three separate ducts 71-73 are
prefabricated in a factory.
I During construction of a building from the slab 51, the slab 51 is
positioned on suitable supports which may be concrete walls or columns or steel
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bcams. One or more o ~ thc acccs.s cove-rs 68 arc positioned over the trench 64
and attached to the cover ~late 75 to provicle access ;nto thc ducts 71-73,
as required. In the embodiment shown in Figure 5, thc access box 68 is
positioned over thc ducts 71 and 73. Thc access box 68 has an interior open-
ing 80 which communicates through a hole 81 in the cover plate 75 leading into
the duct 71 and through a hole 82 in the covcr plate 75 leading into the duct
73. The holes 81 and 82 may be formed, for example, by removing knockouts or
by any other conventional method. The final step in constructing the floor
structure 50 is to pour the topping layer 69 over the slab 51 and flush with a
removable cover 83 attached to the top of the access box 68.
Turning now to Figure 6, a cross sectional view is shown through
the wiring ducts 55 and the access box 67 from Figure 4. The ducts 55 are de-
fined by a U-shaped channel 86 and an attached cover plate 87 which enclose and
separate the trench fractions 56 and 57. The ducts 55 include a completely
shielded duct 88 formed by the U-shaped channel 86 and the cover plate 87, and
unshielded duct 89 formed by the trench fraction 56 in the slab 51, one side of
the U-shaped channel 86 and the cover plate 87 and an unshielded duct 90 formed
by the trench fraction 57 in the slab 52, the duct 86 and the cover plate 87.
The ducts 88-90 are formed during the construction of a building including the
floor structure 50. Initially, the slabs 51 and 52 are positioned on a suitable
support structure (not shown). The grouted joint 58 is then formed by filling
a groove 91 extending between the slabs 51 and 52 and below the trench fractions
56 and 57 with a suitable concretious grouting material. Before such grouting
material within the joint 58 has hardened, the cover plate 87 is positioned
over the trench fractions 56 and 57 with the U-shaped channel 86 abutting the
grouted joint 58. Preferably, a plurality of studs 92 having irregular surfaces
or a plurality of other suitable anchors are attached to the bottom of the
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U-shaped channel 86 at prcdctermincd spacings along its length. The studs or
other suitable anchors 92 are pressed into thc grouted joint 58 to securely
anchor in place the cover plate 87 and attached U-shaped channel 86. The grout-
ed joint 58 is also deformed suCficiently by the U-shaped channel 86 to assure
that the ducts 89 and 90 are completely isolated from each other. After the
U-shaped channel 86 and cover plate 87 are positioned over the trench fractions
56 and 57 and the grouted joint 58, the floor structure 50 is completed in a
manner similar to that described for Figures 1-3. The access box 67 and other
access boxes, as needed, are attached to the cover plate 87 either over the
channels 88 and 90 or over the channels 88 and 89 or over all three channels
88-90, as required and at any desired location. The topping layer 69 is then
applied to complete the floor. The topping layer 69 is of a thickness suffi-
cient to extend flush with a removable cover 93 for the access box 67. After
the floor structure 50 is completed, the space above the floor structure 50 may
be divided into rooms, as desired. A typical partition 95 is shown in dashed
lines in Figure 6 located adjacent the access box cover 93. At the same time
the building is partitioned into rooms, or if necessary at a subsequent date,
suitable electrical power wiring, control wiring, communication wiring and the
like is run through the ducts 88-90 to supply the needs of the space above the
floor structure 50.
In the embodiment shown in Figure 5, projections 79 at the bottom of
the U-shaped channel 70 were forced into the slab 51 before the concretious
material forming the slab 51 had completely hardened. The function of the pro-
jections 79 was to assure that the ducts 72 and 73 were completely isolated by
the U-shaped channel 70.
Turning now to Figure 7, a different method is shown for assuring
that two ducts 97 and 98 spaced on either side of a U-shaped channel 99 are
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complctely isolatcd, dcspite variations ;n thc depth along the length of a
trench 100 in which the U-shaped channel 99 is located. The U-shaped channel
99 includes two upper side flanges 101 and 102 which are welded or otherwise
attached to a cover plate 103. ~ lower U-shaped channel member 104 is posi-
tioned between the flanges 101 and 102. The U-shaped member 104 includes sides
105 and 106 which are firmly held between the flanges 101 and 102, respectively,
by spring tension. When the U-shaped channel 99 and cover plate 103 are
positioned within the trench 100, the U-shaped channel 104 is forced upwardly
between the flanges 101 and 102 as a bottom 107 of the channel 104 contacts
the trench 100. Through this method, the lower U-shaped member 104 contacts
the trench 100 to completely isolate the ducts 97 and 98, despite variations
in the depth of the trench 100 along its length.
Turning to Figure 8, still another structure and method are shown
for compensating for variations in the depth of a trench 110 when a floor
structure is constructed in accordance with the present invention. In this
embodiment, a U-shaped channel 111 is not attached to a cover plate 112, as in
the previously described embodiments. The trench llQ is formed within a con-
crete slab 113 having an upper surface 114. The U-shaped channel 111 includes
a lower U-shaped member 115 having spaced sides 116 and 117. Bolts 118 pass
through vertical slots within a flange 119 and attach such flange 119 to the
side 116. Similarly, others of the bolts 118 pass through vertical slots in a
flange 120 and attached such flange 120 to the side 117. The bolts 118 are
threaded into the sides 116 and 117 and are sufficiently short as not to project
appreciably into the duct 122. During construction of ducts 121-123 in the
trench 110, the U-shaped channel 111 is positioned in the center of the trench
110. A workman then positions a straightedge on the upper surfaces 114 of the
slab 113 to span the trench 110 and to extend over the flanges 119 and 120 of
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the iJ-sha~ed charlnel 111. The f]an~es 119 and 12() are then moved into contact
with such straightedge so they arc flush with the upper surfaces 114. The
cover plate 112 is then positioned over thc trench 110 and the U-shaped channel
111, access boxes are installed as necessary, and a topping layer 124 is applied
to complete the floor structure. Seals 125 are located between the flanges
119 and 120 and the cover plate 112. The seals 125 may consist of resilient
members formed from a suitable synthetic resinous material or they may consist
of a suitable adhesive which bonds the flanges 119 and 120 to the cover plate
112.
Although several different methods have been described for adjusting
or compensating for variations in the depth of a trench when such trench is
divided into a plurality of ducts it will be appreciated that other methods
may also be used without departing from the invention. For example, the U-
shaped channel member may fit within a recess in the bottom of the trench
formed in the concrete floor slab. Before positioning the U-shaped channel
member within the recess, a suitable hardenable material such as a synthetic
resinous material or a concretious material may be positioned within the recess
to bond the U-shaped channel member to the floor slab and also to isolate ducts
formed on either side of the U-shaped member.
Turning to Figure 9, another method is shown for producing at least
two ducts which are completely isolated when a floor is constructed in accor-
dance with the present invention. A plurality of trenches 126 can be formed in
the upper surface 127 of a precast structural slab 128. The center one of the
trenches 126 is separated from the adjacent ones by concrete walls 129 and 130.
After the concrete has hardened sufficiently, a cover plate 131 is placed over
the trenches 126 and the concrete walls 129 and 130, thus converting the three
trenches into three wiring ducts or raceways. The cover plate 131 extends
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1~34~3~
alorlg tilc cnt;re lengths o-f the trenchcs. The slah l28, either before or
after installation of the cover plate 131, is installed as one of the required
structural members of a building floor, as previously described, and the several
members arc covered by a poured floor 132.
Referring to Figure 10, three trenchcs 133 separated by concrete
walls 134 and 135 are shown, one of the trenches 133 and the wall 134 being a
part of a precast structural slab 136 and a second of the trenches 133 and the
wall 135 being a part of a second structural slab 137. A fraction of the center
one of the trenches 133 is in the upper surface 138 of the slab 136, while the
remaining fraction thereof is in the upper surface 139 of the slab 137. The
center one of the trenches 133 is formed during the construction of a building
when slabs 136 and 137 are positioned on a suitable support structure (not shown).
A grouted joint 140 is then formed by filling a groove 141 extending between the
slabs 136 and 137 and below the center one of the trenches 133 with a suitable
concretious grouting material. A cover plate 142 is placed over the trenches
133 and concrete walls 134 and 135, thus converting the three trenches into
three wiring ducts or raceways. The slabs are then covered by a poured floor
143 as previously described.
Referring to Figure 11, the center and right ones of trenches 144,
two concrete walls 145 and 146, and a fraction of a left trench 144 are formed
in the upper surface 147 of a slab 148. The remaining fraction of the left
one of the trenches 144 is formed in the upper surface 149 of a slab 150. The
left one of the trenches 144 is formed in the same manner as the center one
of the trenches 133 in Figure 10.
The trenches in precast slabs can be formed in any appropriate manner,
for example, by placing suitable forms in a casting bed, preferably after con-
crete has been cast in the bed to a depth which corresponds with the bottoms
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~3'~ 8
of the trenches, and then casting additiona] concrete around the forms to pro-
duce the completed slab with the desired number of trenches. Casting beds
used for producing precast structural concrete members usua]ly consists of an
elongate form having the length and width of the desired precast slab, e.g.,
a length of, perhaps, 40 feet and a width of 6 feet. Concrete is cast into the
form from a mixing hopper which rides on rai.ls, one mounted on each side of
the form and is moved lengthwise of the form as casting progresses. The trench
can also be formed in a precast slab by a contoured roller carried by the
mixing hopper, and extending across the top of the form in which the slab is
cast. The roller can have at least one radially enlarged portion to form at
least one trench in the slab, and the remainder thereof can be flush with the
upper surface of the slab, as ultimately formed. It is often advantageous to
use a plurality of rollers progressively differing in contour so that the forma-
tion of each trench is commenced by the first roller, continued by the second
and completed by the last, which shapes the entire upper surface of the cast
slab to the desired contour.
It will be apparent that various changes and modifications can be
made from the specific details of the invention as described herein and shown
in the attached drawings without departing from the spirit and scope thereof
as defined in the appended claims.
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