Note: Descriptions are shown in the official language in which they were submitted.
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SEGMENTED COLD FORMED JOIST
Field of Invention
This invention relates generally to a joist and particularly relates to floor
and roof
joists for building construction and more particularly to methods for
producing
concentric top chord bearing cold form joists for composite concrete and non-
composite joist conditions for the construction industry.
Background of Invention
Joists are commonly used in the construction industry to span a distance and
provide a surface for a floor, roof or the like. Joists can be comprised of a
variety
of materials including wood and metal.
Metal or steel joists can be constructed in an open web configuration, which
generally consists of spaced apart upper and lower chord members which extend
longitudinally thereof and are fastened together by a zig-zag web. Such open
web joists are typically manufactured by hot-roll structural sections namely
the
upper and lower chord members and the webs. The webs typically can be
comprised of hot-rolled steel rods, which are zig-zagged and welded to the
upper
and lower chords. The webs are open in the sense that there is a space between
the rods longitudinally along the central web section that can receive
utilities such
as wires or air ducts that are installed by other trades.
Open web joists can be concentric, that is they are symmetric about the web in
cross section, or eccentric.
The joist industry has introduced various types of composite concrete non-
combustible floor and roof systems for the construction industry. Examples of
composite joists can be found in U.S. Patent Nos. 5,941,035, 4,741,138,
4,454,695, U.S. Publication No. 2002/0046534 Al and 2002/0069606 Al. A
composite joist design permits the top chord member of a joist to be designed
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with less steel in comparison with non-composite systems since the concrete
slab
when properly bonded to the upper steel joist acts as the top chord of the
floor or
roof system.
Generally speaking, for a structural joist member to be composite it must have
means to mechanically interlock with the concrete to provide sheer bonding. It
is
generally difficult and costly to design steel and concrete composite floors
using
joists because legislation exists in various jurisdictions which relate to
federal
safety laws requiring that structural members cannot have objects extending
above a structural floor member that will encumber the walking path of a
worker.
Generally speaking the details for providing sheer bond capacity between the
joist and the concrete in a composite joist are generally expensive to produce
in
the prior art.
Furthermore, camber (defined as a slight arch added to the joist) has been
introduced into the open web joist technology to offset the deflection
associated
with dead loads such that only the live load deflection of the joist needs to
be
accounted for in designs of the joist. However large machines or jigs are
needed
to impart the camber to the chords of the joist were typically the web resists
the
cambering process.
Furthermore joists are erected in a "top chord bearing condition" where they
hang
passively vertical during and after erection from its top or upper chord at
the
support ends. Alternatively joists can be" bottom chord bearing" where the
bottom
chord supports the joist.
Moreover, hot-rolled open web joists are typically coated or finished with a
primer
that can be coloured grey or red. Steel joists manufacturers typically use
large
tanks of paint into which completed welded joist assemblies are dipped to
receive
a coating of primer paint. However, the process has become more expensive
due to environmental considerations when using dipped tanks containing
volatile
solvents.
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Furthermore open web joists technology is dependent on skilled labour and in
many instances set the critical path schedule on many construction projects
during busy construction season periods when skilled labour is in highest
demand.
Joists can also be produced by cold-formed steel structural designs and have
been used in floor and roof joists in the building construction trade for some
time.
However prior art cold form steel joists are widely used for wall and floor
framing in
residential homes and non-load bearing wall framing where the span of the
joist is
not excessive. The cold form technology presently has limitation in span
lengths
for floor and roof members to be widely used.
Unless cold form materials can be used in the thin applications, the use of
these
materials is cost prohibitive since hot-rolled pre-finished steel coil
material typically
used in forming comes in at much greater cost than the hot-rolled shapes used
for
the open web industry as described above. Furthermore, cold-formed joists
presently used only provide limited span lengths and are not very cost
efficient to
provide for spans greater than 24 feet.
Joists produced by cold-forming from a single piece of sheet metal is
predominately used for bottom chord bearing conditions and these members
generally have an eccentric nature about the "Y" Axis. Other examples of cold
rolled constructions are shown in U.S. Patent Publication Nos. 2002/0020138 Al
and 2003/0084637 Al.
Moreover other manufactures have introduced "top chord bearing" single
stripped
cold-formed floor joists such as HambroTM D510 and Speed FloorTM which has
end attachments that can be welded, bolted or screwed onto a single strip cold-
formed section to provide a top chord bearing condition. However these provide
only limited load capacity due to the nature of the localised connection to
the cold-
formed joist member. Accordingly cold-forming production has generally been
applied to a single piece of sheet metal since it requires very little direct
manpower
to produce.
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Many cold-forming manufactures provide holes longitudinally along the central
web section that are sized to receive utilities for follow-up trades. Since
cold-
formed joists material can be pre-finished (i.e. the coils of galvanised steel
can be
galvanised or painted) the manufacturing process is less harmful to the worker
5 and environment than the open web production described above.
Although cold-forming provides superior surface finishes and very little
dependency on manpower to produce relative to the open web technology,
current cold-forming technology does not satisfy the requirements to optimise
material use throughout the length of the individual members of the joist. One
of
the disadvantages of continuous cold-forming from a single piece of sheet
material resides in the fact that material use along the length of the
individual
members cannot be rationalised or optimised.
Accordingly a device and method of producing the device that can combine the
beneficial attributes from each of the open web technology and cold-forming
technology is desirable. It is also increasingly desirable to manufacture
using
cold-forming methods versus open-web welded methods as a means to reduce
the need for labour shortages. Further, material optimisation is limited when
cold-forming if the section is constant in weight throughout the length.
Also both open web and cold-form structures at times require bridging systems
to
stabilize the joist about the "Y" Axis. It is common practice to weld bridging
in
open web joists while cold-forming systems have bridging structures that
commonly use screws for fastening.
Furthermore open web steel joists are traditionally assembled in a jig with a
weld
being applied at the juncture of the individual component parts; which
prevents
open web technology from using pre-finished materials as the welding process
would damage the pre-finish. Furthermore, cold-formed joists are traditionally
mechanically fastened which inherently helps prevent damage to the finished
part.
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It is an aspect of this invention to provide a joist comprised of at least one
cold-
formed elongated chord member, a segmented cold-form web, and fasteners for
securing the web to the chord member. In one embodiment of the invention the
web comprises a plurality of web members.
It is another aspect of this invention to provide a supporting surface defined
by a
plurality of joists, each of the joists comprising spaced cold-formed upper
and
lower metal chord members, a web comprising a plurality of web members
intermediate the upper and lower chord member, and fasteners to fasten the web
members to the upper and lower chords where the upper chords define a
supporting surface.
It is a further aspect of this invention to provide a composite floor system
comprising a plurality of metal joists, with the joists having, an upper chord
member formed from sheet metal to present a vertical and horizontal upper cord
extension, a lower chord member formed from sheet metal to present a
horizontal
lower chord extension, a plurality of web segments fastened together to define
a
substantially vertically disposed web, and mechanical fasteners to fasten the
web
to the spaced upper and lower chords; a concrete slab disposed on the upper
chords of the plurality of joists with the vertical extension of the upper
chord
embedded in the concrete slab to define the composite floor.
Another aspect of this invention resides in a method of producing a joist
comprising the steps of; forming upper and lower chords from sheet metal,
forming at least one web member from sheet metal, fastening the web between
the upper and lower chord with mechanical fasteners.
These and other objects and features of the invention shall now be described
in
relation to the following drawings:
Brief Description of Drawings
Fig. 1 illustrates a prior art open web steel joist (OWSJ).
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Fig. 2 illustrates a prior art cold-formed C-shaped joist.
Fig. 3 illustrates one embodiment of the invention.
Fig. 4 illustrates a segmented web.
Fig. 5 is a perspective view of the second embodiment of the invention
showing a concentric or symmetrical cold-formed joist having a segmented
web.
Fig. 6 is a side elevational view of Fig. 5.
Fig. 7 is a cross sectional view along the line 7-7 of Fig. 5.
Fig. 8 illustrates a side-view of a plurality of joists having bridging
members.
Fig. 9 is a side view of a plurality of joists having crossed bridging
members.
Fig. 10 is a perspective view of the symmetrical or concentric cold-formed
joist to be used in a composite joist.
Fig. 11 is a side elevational view of Fig. 10.
Fig. 12 is a cross sectional view along the lines 12-12 of Fig. 10.
Fig. 13 is a side elevational view of a composite floor system having a
plurality of joists.
Fig. 14 is a perspective view showing a top chord bearing condition of the
joist.
Fig. 15 illustrates a perspective top chord extension condition.
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Fig. 16 is a cross sectional view through line 16-16 of Fig. 6.
Fig. 17 is a cross sectional view along the line 17-17 of Fig. 6.
Fig. 18 is a partial side elevational view of a segmented web.
Fig. 19 is a partial top view of Fig. 18.
Fig. 20 is a top expanded view of region 20-20 shown in Fig. 18.
Fig. 21 is a partial side elevational view of the reinforcing member.
Fig. 22 is a partial view of Fig 21.
Fig. 23 is a partial top plan view of the reinforcing member.
Fig. 24 is a cross-sectional view another embodiment of the joist.
Fig. 25 is a cross-sectional view of another embodiment of the invention.
Fig. 26 is a cross sectional view of another embodiment of the invention.
Fig. 27 is a cross-sectional view of another embodiment of the invention.
Fig. 28 is a schematic view of a roll forming machine.
Fig. 29 is a partial perspective view of a reinforced chord.
Fig. 30 is a side elevational view of another embodiment of the invention.
Fig. 31 is a partial enlarged view of Fig 30.
Fig. 32 is a side elevational view of applications of the invention.
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Fig .33 is a chart showing man hours per ton vs joist span.
Fig. 34 is a chart showing percentage weight evaluation vs joist span.
Fig. 35 is another embodiment of the invention.
Fig. 36a is a top plan view of the flap 82.
Fig. 36b is a perspective view of a further reinforced flap.
Fig. 37 is a top plan view of a further reinforcing member.
Fig. 38 is another embodiment of the invention.
Fig. 39 is an end view of Fig. 38.
DETAILED DESCRIPTION OF THE INVENTION
In the description that follows, like parts are marked throughout the
specification
and the drawings with the same respective reference numbers. The drawings are
not necessary to scale and in some instances proportions may have been
exaggerated in order to more clearly depict certain features of the invention.
Fig. 1 illustrates a prior art open web joist construction 2 consisting of an
upper
chord assembly 4 spaced from a lower chord assembly 6. The chords are joined
together by a zig zag web 8 which is generally connected to the upper and
lower
chord assembly 6 by a number of means including welding or the like.
Fig. 2 illustrates a prior art cold formed joist construction 10 having a web
portion
12 having a plurality of holes 14 disposed there through for receiving utility
such
as wire or the like.
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Fig. 3 illustrates one embodiment of the invention which comprises an
assembled
joist 20 having a first or upper chord member 22 spaced from a second or lower
chord member 24. A web member 26 is also disclosed. The web member 26 is
fastened to the upper and lower chord members 22 and 24 by fastening means
5 28 . The fastening means can comprise of a variety of fastening means such
as
bolts and nuts (not shown), welding, rivets 30 or spot clinch 32 (Fig. 7).
The upper chord member 22 can be produced from a sheet of sheet metal. The
sheet metal can be formed in a concentric fashion shown in Fig. 7 where the
10 upper and lower chord members 22 and 24 are symmetrically disposed about
web 26 or in an eccentric fashion shown in Fig. 25.
In one embodiment the upper chord member 22 is formed or bent to present a
substantially flat upper load bearing surface 34 which is formed as shown in
Fig.
7 to present lower load bearing wings or extensions 36 and 38. The upper load
bearing surface 34 is in contact with the lower load bearing extensions 36 and
38
so as to produce a rigid and structurally solid member which is fastened
together
by the spot clinch 32. The spot clinch process is conducted in the manner well
known to those persons skilled in the art and generally consists of a
mechanism
which pushes material by a plunger (not shown) to present a mushroomed head
40 as shown so as to secure the members together.
The upper load bearing surface 34 and lower load bearing extensions 36 and 38
are disposed symmetrically about the web 26 which defines "Y" axis as shown in
Fig. 7. Accordingly, the upper load bearing surface 34 in concert with the
lower
load bearing extension 36 on one side of the axis 27 defines a horizontal
extension 42 while the upper load bearing surface 22 to the right of the Y
axis 27
in concert with the lower load bearing extension 38 defines a horizontal
extension
44 disposed to the right side of the axis 27. The lower load bearing
extensions 36
and 38 are bent to form to spaced apart web receiving tabs 46 and 48 as shown.
The upper portion 50 of the web 26 includes a plurality of holes 52 which are
adapted to receive the fastening means 28. Fig, 7 shows a fastening means 28
comprising a rivet 30.
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The spot clinches 32 in combination with the cold-formed chords connect the
two
folded portions 34 and 36 and 38 and 44 to reduce the width to thickness ratio
of
the section to avoid local buckling. The spot clinch 32 in combination with
the
cold work forming increases the yield strength of the steel part.
As shown in Fig. 7 the lower chord 24 is similarly constructed by forming
sheet
metal to present a lower chord surface 54 bent so as to present lower chord
extensions 56 and 58 symmetrically disposed about axis 27. The lower chord 54
in combination with the lower chord extension 56 and 58 define lower chord
horizontal extensions 60 and 62 symmetrically disposed about the web 26. The
lower chord extensions 56 and 58 present two spaced apart web receiving tabs
64 and 66 which are adapted to receive the lower portion 68 of the web 26.
The web 26 can include a plurality of utility holes 72 which provide an access
for
utilities such as electrical wires, air ducts or the like. The holes 72 as
shown are
circular although any configuration can be produced including square holes or
the
like. Furthermore, the holes 72 can include a lip 74 as shown in Fig. 16. The
holes 72 lighten the total weight of the joist 20 while the lip 74 adds
rigidity to the
web structure 26 particularly in the "Y" axis.
The web 26 also includes a plurality of stiffening means 80 to stiffen the
rigidity of
the web member 26.
The stiffening means 80 comprises a first stiffening means 82 and a second
stiffening means 84. The first stiffening means 82 generally consists of the
ends
of the web 26 being bent to form a stiffening tab 82 which is disposed at
approximately a 90 degree angle from the web 26. The second stiffening means
84 generally consists of a hollow rib structure 86 as best illustrated in Fig.
21.
The hollow rib structure 86 can be produced by a variety of means and in one
example is produced by a punch (not shown) which pushes the web material 26
to present the stiffening structure 84 The stiffening structure has two spaced
side
walls 88 and 90 as well as upper and lower walls 92 and 94 and stiffening
front
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wall 96. The stiffening front wall 96 has stiffening holes 98 which are
adapted to
receive bridging members 100 in a manner to be more fully particularized
herein.
Furthermore, the web 26 can comprise of a plurality of web segments 104, 106
and 108 as shown in Fig. 4. Although only three segments are shown in Fig. 4
any number of segments can be used. Each of the web segments 104, 106 and
108 are adapted to be fastened to one another. In particular, the web segments
104, 106, 108 include a first stiffening means 82 which comprise of sheet
metal
flaps which are bent at substantially 90 degrees from the web material 26. The
first stiffening flaps 82 include a plurality of holes 110 which are adapted
to
receive fasteners such as rivets, nuts and bolts, or spot clinches to secure
the
plurality of web segments 104, 106, and 108 together to form a web 26. The web
segments 104, 106, and 108 also include second stiffening means 84.
The web segments can either all have the same thickness or can have different
selected thickness. For example the web segments can be thicker at the ends of
the joist than segments in the middle of the joist since the load-bearing load
is
greater at the ends than in the middle.
The joist shown in Fig. 5 can include angled end members 140 to secure the
ends of the lower chord 24 and upper chord 22. Furthermore rigidifying members
150 may be added so as to present one end 152 fastened to the lower chord 24
and another end 154 fastened to the stiffening tab 82 as shown in Fig. 7.
A plurality of joists 20 partially shown at Figs. 8 and 9 can define a
supporting
surface 160 to support a platform 162 such as a roof floor or the like. Each
of the
joists 20 comprises of spaced cold-formed upper and lower chord members 22
and 24 and a web 26 intermediately upper and lower chord members 22 and 24.
Fasteners 28 are utilised to fasten the web to the upper and lower chords;
where
the upper chords 22 define the supporting surface.
A plurality of bridging members 1700 may be used to connect adjacent joists 20
together as shown so as to stiffen the joist 20 in the "Y" axis. Parallel
bridges 170
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may be used as shown in Fig. 8 along with criss-crossed bridges 172 that are
appropriately fastened at 174 as shown in Fig. 9.
The bridge members 170 can comprise of L-shaped sheet metal. Bridging
member 170 can be made from sheet material which is bent to produce a first
surface 172 and a second surface 174. The second surface 174 is slotted at 176
as shown and the width W of surface 174 is less than the depth D of the hole
98
to permit the end 178 of the bridging member 170 to be inserted into the hole
98
and then rotated so as to lock the edges of the slot 176 against the
reinforcement
face 96 adjacent the hole 98. Criss-crossed bridging members 172 may then be
added and fastened as shown in Fig. 9.
Figs. 12 and 13 illustrate another embodiment of the invention defining a
composite floor. In particular, the upper chord 22 can be formed so as to
present
horizontal extensions 190 symmetrically disposed about the central web 26 and
presents spaced apart vertical extensions 192 and 201 adapted to receive the
top
portion 50 of the web 26 to define a vertical extension 194. A rivet 196 may
be
utilized to fasten the upper chord 22 to the web 26 as shown.
A deck 198 is adapted to rest on the top surface of the horizontal upper chord
extensions 190 as shown in Figs. 12 and 13. A wire mesh 205 is added.
Thereafter concrete 206 can be poured onto the deck 198 so as to produce a
floor or ceiling. Since the vertical extensions 194 are embedded into the
concrete
200, a very solid composite floor system is produced. The vertical extension
194
can also include a generally horizontal concrete engaging extension 202 which
runs along the length of the chord 22. Since the horizontal concrete engaging
extension 202 runs along the length L of the chord 22, the possibility of
snagging
a worker's foot or pant trouser is minimized thereby adding to the safety
feature
of the joist prior to pouring of the concrete 206 over the deck 198.
The shear bond between the extensions 194 and 202 and the concrete is
increased by using rivets spot clinches 32 or the like to increase the surface
area
of contact.
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Fig. 24 illustrates another embodiment of the invention which includes an
upper
cold-formed chord 22 fastened to a web 26 by fasteners 30. In the embodiment
shown on Fig. 25, the bottom chord 24 is formed so as to present one
horizontal
extension 250 which is doubled upon itself and hole clinched; while the other
horizontal extension 252 presents a single section of sheet metal.
A further embodiment of the invention is shown in Fig. 25 where the lower
chord
member 24 is a bent extension of the web 26.
Fig. 26 illustrates another embodiment of the invention where the upper chord
22
has a single layer of sheet metal which is bent to produce the horizontal
extensions 42 and 44 spaced apart to accommodate the end 50 of web 26 so as
to define an upper vertical extension 194 having a horizontal concrete
engaging
extension 202. The horizontal concrete engaging extension 202 can include a
plurality of hole clinches to further strengthen the bond between the concrete
and
the upper chord 22 and thereby increase the shear strength of the composite.
Fig. 27 illustrates a further embodiment of the invention whereby the lower
chord
24 is a bent extension of the bottom of the web 26.
Fig. 29 illustrates that a chord member can include a cold-formed reinforcing
section 300 which consists of sheet metal that is formed so as to present a
lower
chord reinforcing section 302 and an upper chord reinforcing section 304
adapted
to embrace a portion of one of the chords 22 and 24 as shown. Alternatively,
the
reinforcing section 300 may extend along the full length of the chord member
22
and 24 as desired. The reinforcing portion 300 may be utilized to as to
increase
the strength of the chord member 22 and 24 as a desired position. Generally
speaking, the ends of the chord members 22 and 24 may be reinforced as this is
where the maximum load bearing stress occurs.
The chord members 22 and 24 extend longitudinally along a Length thereof
which presents a first portion 310 having a first thickness FT and a second
portion 320 having a second thickness ST.
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Fig. 14 illustrates that the ends 300 of the upper chord 22 can include
support
shoes 302. The support shoes can be comprised of sheet metal which
are bent to present horizontal support shoe member 304 and a vertical support
shoe member 306 having a plurality of holes 308 aligned with holes presented
at
5 the ends 300 of upper chord member 22 so as to fasten the support shoe 302
thereto. The support shoe 302 can be utilized when the joist 20 is supported
by
the ends 300 of the upper chord member 22. Reinforcing gussets 310 can be
formed so as to add strength to the structure.
10 Fig. 15 illustrates a top chord extension condition whereby a support shoe
302 is
spaced from the end 300 of the upper chord member 22 so as to present an
extension 312 that can be utilized in a variety of conditions including that
of
manufacturing and eave structure.
15 Alternatively the joist 20 can be supported along the bottom chord 24 as
shown in
Fig. 30 in a bottom chord bearing condition. Fig. 30 illustrates a cold form
composite joist 20 supported along the bottom chord 24.
In particular the ends 400 of the joist are disposed within the lower stud
wall 402
and upper stud wall 404 as shown. The lower stud wall 402 includes a stud wall
track 406 which is generally a flat piece of sheet metal 408 bent at its ends
so as
to present a solid surface to the joist. The upper stud wall 402 includes a
similar
stud wall track 406. The stud wall 402 and 404 also includes a floor joist
track
412 adjacent the end 400 of joist 20.
The cross-section of the joist 20 seen in Fig. 30 can have any number of cross
sections as described in the context of the composite joist including that
shown
in Figure 12. The composite joist is constructed in the manner previously
described. An erection clip 414 can be utilized so as to locate the joist 20
prior to
pouring the concrete to produce the composite joist. In particular the
erection clip
414 comprises a general J-shaped clip in cross-section which is secured to the
bottom of the stud wall track 406 and extension 202. Once the concrete is
poured the composite cold formed steel joist is supported by the bottom chord
24
at the ends 400 of the joist 20.
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Fig. 35 illustrates another embodiment of the invention utilizing concentric
cold-
formed joists which are bottom chord supporting in a residential home.
In particular the joist 20 rests on a foundation 402 having a support 410. The
end
400 of the joist 20 includes a reinforced flap 82 which is further
particularized in
Fig. 36a and 36b. In particular the flap 82 is cut along cut lines 600, 602
and 604
so as to present portions 620 and 622. In particular portions 620 and 622 are
folded along fold lines 606 and 608. Thereafter portions 620 and 622 are
further
folded along fold lines 621 and 623 so as to present wing portions 624 and 626
which are adapted to contact the lower surface of upper chord member 22 and
lower surface of lower chord member 24 as best shown in Fig. 35. Fastening
means may be utilized to fasten the reinforcing wings 624 and 626 to upper and
lower chord members 22 and 24 so as to further rigidify and strengthen the
joist
20.
Wooden or metal backing plates 412 are also utilized as shown in Fig. 35.
Wooden pieces 414 may also be utilized as shown. The upper chord 22
produces a support surface for supporting plywood 416 or the like.
Further reinforcing members 700 may be utilized which comprises an elongated
section of sheet metal having web contacting portions 702 and rigidifying
portions
704 extending generally perpendicular to the web contacting portions 702. The
ends of the rigidifying portions 704 are are bent at 706 and 708 and adapted
to
contact the upper chord 22 and lower chord 24 respectively. Furthermore
fastening means may be utilized to fasten the rigidifying section 700 to web
26
and upper and lower chords 22 and 24.
Moreover Fig. 38 illustrates another embodiment of a load bearing bottom chord
utilizing the rigidifying structure 700 shown in Fig. 37.
Fig. 28 generally illustrates the method of producing the cold-formed joist.
The
upper chord 22 can be produced from unrolling a roll of sheet metal 112 along
path 114 to a roll forming machine 116 such as sold by Samco machinery located
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in Toronto, Canada. The roll forming machine 116 can include a station to
flatten
and cut a selected length of the upper chord member 22. Similarly, the lower
chord member 24 can be produced by unrolling a roll of sheet metal 118 and
flattening same along a path 120 to a roll forming machine 116 and cut to the
desired length. Furthermore, the web 26 can also be produced by unwinding a
roll of sheet metal 122 and flattening same at flattening station 123. A shear
125
can be used so as to shear the web member 26 to its desired length.
Thereafter,
the web 26 approaches stiffening section 128 so as to produce the first and
second stiffening means 82 and 84 as described.
The shear 125 can be used to produce the plurality of segmented webs 104, 106
and 108. Each web segment 104, 106, 108 can have the left hand and right hand
stiffening flaps 82 produced by stiffening station 130 and 132. An appropriate
punch 133 is used to produce in the second stiffening means 84 as described
above in a drawing operation.
The sheet metal at stations 112, 118 and 122 can be galvanized or painted as
desired prior to the forming process. Furthermore the roll forming machine 116
includes punches to punch the appropriate holes 52 in the upper and lower
chord
members 22 and 24 so as to accommodate the appropriate fastening means 28.
Alternatively the roll forming machine 116 can include apparatus to spot
clinch 32
the members together.
Accordingly the joist fabricated herein can be coated with a variety of paint
colours which are painted prior to fabrication so as to produce a variety of
joists
having different colours and avoiding the dip painting characteristic of open
web
joist construction.
The invention as described herein presents a number of advantages over the
prior art. For example, many of the prior art joists included a cambering of
the
upper and lower chords 22 and 24 so as to present a slight arch to increase
load
bearing capabilities of the joist. Such prior art cambering techniques
required
working against the web during the cambering process. Applicant's invention on
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the other hand presents an advantage since the upper and lower chord members
22 and 24 can be cambered separately. Once the upper and lower chord
members 22 and 24 are cambered they can be attached to the web 26 as
described. Since the web 26 is not part of the upper and lower chord members
22
and 24 during the cambering process there is less resistance to the cambering.
Furthermore, the composite joist as described herein exhibits excellent
resistance
to shear forces due to the presence of fastening means 30 and particularly
when
utilizing spot clinches.
The support structures described herein can be utilized either as floor joists
500
or roof joists 502 as shown in Fig. 32 whether for office, multi-residential,
retail or
warehouse facilities.
Furthermore Fig. 33 illustrates an example of a comparison between the number
of man hours per ton to produce prior art composite open web steel joist
(composite OWSJ), a prior art open web steel joist (OWSJ) and applicants
concentric or symmetrically disposed cold formed joist (CCFJ) and a prior art
C-
shaped joist represented by Fig. 2. Savings can be experienced using the
invention described herein.
Furthermore, Fig. 34 illustrates a comparison of a prior art OWSJ, prior art
composite OWSJ, and a prior art C-shaped joist vs. the invention described
herein between applicants concentric cold formed joist and segmented
concentric cold formed joist in connection with performance as a percentage of
weight of valuation.
Although the preferred embodiment as well as the operation and use have been
specifically described in relation to the drawings, it should be understood
that
variations in the preferred embodiment could be achieved by a person skilled
in
the art without departing from the spirit of the invention as claimed herein.
