Note: Descriptions are shown in the official language in which they were submitted.
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REINFORCING
Technical Field
The present invention relates generally to reinforcing for concrete or other
cementitious
construction. In particular, the invention is directed to the coupling of
reinforcing bars
and is herein described in that context. However, it is to be appreciated that
the
invention has broader application and may be utilised in the coupling of a
reinforcing
bar to other rigid objects such as metal plates or the like.
Background of the Invention
In the construction industry, structures (such as walls, floors, slabs and
columns) of
concrete are produced by positioning reinforcing such as steel reinforcing
bars in a
region where concrete is then poured to produce the structure. The bars are
supported
in desired positions and often there is a need to join length of bars to each
other to
ensure that the reinforcing not only is correctly positioned, but is able to
transmit load
across the coupling so that the bars can accommodate a large part or even
their full axial
capacity in either tension or compression.
In the past, wire ties or wraps have been secured around overlapping ends of
adjacent
bars to hold them relative to one another prior to the concrete pour.
Axial loads are transferred from one bar to the other overlapped bar through
the
concrete encasing the two joined bars. This method uses more bar than
necessary as the
overlapped length of bar is only useful to effect the transfer of axial loads
and these
overlapping lengths can form a significant mass of reinforcing bar in a
structure.
In another arrangement, bars are formed with short externally threaded end
portions and
a sleeve with left handed and right handed internal thread portions is used to
allow
adjacent end of the bars to be connected to one another.
The formation of the external threaded portions on ends of the bars results in
those ends
being of less diameter than the remainder of the bar and thus is undesirable
since
engineering requirements may dictate that a bar having a predetermined
diameter is
used. One way to overcome this difficulty is to employ oversized bars. This
ensures
that the threaded end of the bar is still of a diameter equal to or greater
than the
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diameter dictated by the engineering requirements. However, with this
arrangement,
most of the bars are of a gauge greater than is necessary.
Ideally the properties of the coupling, such as its axial capacity and its
ductility, are at
least the same as the major portion of the bars and that only limited
longitudinal slip
will occur when the coupling is loaded. If these properties are not within
certain
tolerances, then the coupling can significantly compromise the resulting
structure. For
example, if there is excessive longitudinal slip then this can cause excessive
localised
cracking thereby heightening the risk of corrosion, and may also cause
excessive
deflection. If the coupling is not as ductile as the main part of the bar,
then this can
cause localised stress concentration which potentially could result in
catastrophic failure
of the coupling.
The use of separate coupling elements, such as the threaded sleeve mentioned
above,
may be problematic where a construction site has reinforcing bars of different
strength
as there is a danger of a potential mismatch of the sleeve to the bars.
Furthermore, the
use of a threaded arrangement requires for there to be some play between the
components to enable easy installation, which in turn may result in
unacceptable
longitudinal slip under load. Also there is an ongoing risk that the couplings
are not
adequately tightened on site which will compromise the coupling.
In the Applicant's earlier International application WO 2006/094320, a
reinforcing bar
is disclosed which includes an enlarged termination integrally formed on the
reinforcing
bar shaft. The termination is profiled to include locking formations that
enable the
termination to form part of an interlock and is disclosed as been made by
deforming an
end of the reinforcing bar. A process of forming the reinforcing with the
profiled
termination is disclosed in International application WO 2006/084321, where
the
reinforcing bar end is subjected to various forging and milling stages.
Whilst the reinforcing disclosed in these earlier applications performs well,
the
specialised equipment required to manufacture the reinforcing provides a
constraint to
distributed manufacture of the product in view of the necessary capital outlay
for that
equipment. Accordingly, alternative modes of manufacturing the reinforcing are
desirable.
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A reference herein to prior art is not an admission that the prior art forms
part of the
common general knowledge of a person of ordinary skill in the art in Australia
or
elsewhere.
Summary of the Invention
In a first aspect, the present invention provides a termination for
reinforcing, the
termination having a body extending in a longitudinal direction between
opposite first
and second ends, and a lateral engagement face formed on the body, in use the
first end
is joined to an end of a reinforcing bar, and the engagement face incorporates
locking
formations thereon arranged to interfit with a complementary shaped
termination to
form an interlock arranged to accommodate loading applied in the longitudinal
direction.
In one form, the termination is formed as a metal casting.
In accordance with this aspect of the invention, the termination is made
separately,
preferably by a casting process, and then joined to the reinforcing bar. This
has the
advantage in that it can reduce the cost of equipment required to manufacture
the
reinforcing. Further, by permanently bonding the termination to a reinforcing
bar, the
resultant reinforcing can be of an integral form and can have the same
attendant
advantages as reinforcing formed by deforming an end of the reinforcing bar.
In yet a further aspect there is provided reinforcing comprising a reinforcing
bar
extending along a portion of the length of the reinforcing, and a termination
according
to the above form extending along an end portion of the reinforcing, the
termination
being permanently bonded to the reinforcing bar.
In the context of the specification, the term "permanently" means that the
components
joined by bonding can not be separated without causing destruction of the
connection
and/or the components.
In one form, the first end of the termination is permanently bonded to an end
of the
reinforcing bar so that the termination and the reinforcing bar are joined in
end to end
relation.
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In a particular form, the termination is enlarged as compared to the bar.
In one form, a reference axis of the termination that extends between the
first and
second ends is aligned with an axis of the reinforcing bar. The alignment of
these axes
reduces eccentric loading on the termination so as to maintain axial loading
at the
interlock on tensioning of the reinforcing bar. In another form, the
termination may be
arranged to be offset to the bar axis if required.
In the context of the specification, "axial loading" means loading that is
applied in the
direction that the termination extends so that the interlock is in tension or
compression.
Further, the term "interlock" means an arrangement where components are
connected
together in a manner that prevents separation under load in at least one
direction, even if
the components are free to separate under load in another direction.
In one form, the termination is fused to the shaft to form the permanent
connection. In
one form, a forging operation is used to bond the termination to the
reinforcing bar. In
one form, the bond is formed by welding.
In a particular form, the termination is friction welded to the shaft.
Friction welding
involves a process where two components are forced together (under a friction
or forge
force) and are heated by mechanical friction of one component rubbing against
the
other (typically by rotating one component whilst holding the other component
stationary). The heating by mechanical friction continues for sufficient time
until the
material softens and some shortening (upset) of the components occur under the
friction
force. The rotation driving force is then discontinued but the friction force
is
maintained or increased to fuse the materials together. Technically, because
no melt
occurs, friction welding is not actually a welding process in the traditional
sense, but a
forging technique.
An advantage of friction welding is that because of the direct heat input at
the weld
surface, it gives rise to relatively small heat affected zones. Also as there
is no melting,
no solidification defects occur. The resulting joints are of forge quality,
with a
complete butt joint weld through the contact area.
In accordance with this aspect of the invention, reinforcing is provided
which, by virtue
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of the termination, allows direct connection of a reinforcing bar with another
object,
such as another reinforcing bar, having a complementary shaped termination.
The
advantage of this arrangement is that the integrity of the coupling is
enhanced as it does
not require the use of other components to transmit axial load across the
interlock.
Further, by making the terminations of appropriate size and shape, it is
possible for the
coupling to meet desired requirements for ductility and axial capacity. Also
longitudinal slip under load can be maintained to acceptable levels.
In one form, the termination has the same material properties as the
reinforcing bar and
is enlarged as compared to the bar shaft so that the interlock exhibits
adequate
performance characteristics (e.g. strength under axial load and ductility).
In another form, to ensure adequate performance characteristics of the
interlock, the
termination is made from a different material to the reinforcing bar shaft or
from the
same material as the shaft but with its material properties altered. In these
latter
arrangements, the termination may be the same size as the bar shaft, or
smaller, or may
be enlarged as in the earlier arrangement.
In one form, the locking formations are profiled so that the interlock is
arranged to
accommodate substantially all of the axial load. In one embodiment, a
retaining device
may be utilised to retain the terminations in engagement, but this device is
not
necessarily designed to be placed under load on axial loading of the
reinforcing. In a
particular form, the locking formations are shaped so that the reaction force
at the
interlock under axial loading does not induce separation of the terminations.
According to a second aspect, there is provided a coupling for interconnecting
first and
second reinforcing bars, the coupling comprising:
first and second terminations connected to or integrally formed with the first
and second reinforcing bars respectively, at least one of the terminations and
reinforcing bars being in the form of reinforcing according to any form
described
above, each termination including an engagement face incorporating locking
formations
thereon, the engagement faces of the terminations being in opposing abutting
relation
with the locking formations interfitting to form an interlock; and
a retaining device disposed around the interlock to retain the engagement
faces
in the opposing abutting relation to one another.
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In a particular embodiment, the termination is shaped to form an interlock
with a
complementary termination of identical shape. As such, the first and second
terminations are the same. Such an arrangement is beneficial in that it does
not require
the terminations to be handed thereby making it easier to install onsite.
In a particular form of termination, the locking formations comprise one or
more
upstands extending transversely across the engagement face and one or more
recesses.
In use, the one or more upstands and recesses interfit with one or more
upstands and
recesses disposed on the complementary shaped termination to form the
interlock.
In a particular embodiment, each upstand includes at least one side wall.
Furthermore,
the at least one recess is defined at least in part by one side walls of an
adjacent
upstand.
In a particular form, the side wall(s) incorporate bearing surfaces which are
arranged to
interengage in formation of the interlock.
In a particular form, a plurality of upstands are stepped downwardly along the
engagement face towards the second end of the termination. This arrangement
enables
the loading to be distributed more evenly across the termination. In one
embodiment,
the upstands are of different size so as to facilitate correct location of the
upstands into
corresponding recesses of the other termination.
In one embodiment, in use, the coupling is able to accommodate axial loading
which is
at least equal to the axial capacity of the shafts of the reinforcing bars and
exhibits
increased ductility as compared to the bar shafts. In some situations, the
coupling may
be advantageously used to connect reinforcing that has different shaft
diameters. This
is commonly desirable in construction where the loading conditions change
across the
structure. Using the coupling of at least one embodiment of the present
invention, this
can be achieved by providing reinforcing having a termination which is
typically
oversized (or undersized)for that bar shaft but which is in complementary
shape to
reinforcing of the larger (or smaller) bar diameter.
In one form the bearing surfaces extend generally normal to the direction of
axial
loading. With this arrangement the reaction forces applied in the coupling are
contained within the terminations and there is no significant vector force
that will load a
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surrounding retaining device under normal elastic loading conditions.
Furthermore, by
having the bearing surfaces generally normal to the direction of axial
loading, the
longitudinal slip within the coupling may be contained to acceptable limits
without
requiring the fit between the retaining device and the terminations being of a
very tight
tolerance to inhibit lateral movement of the interlocks. In this arrangement
any lateral
movement between the terminations (say for example that which may be possible
due
to the gap between the retaining device and the interlocked terminations) will
not
translate to a longitudinal displacement. Alternatively, the tight tolerance
between the
retaining device and the terminations may be provided through post forming of
the
retaining devices (e.g. when a sleeve is used, by forcing that sleeve over a
mandrel) or
by the use of packing, such as shims or the like in between the interlocking
terminations
and the retaining device. In this latter form, the slope of the bearing
surfaces is not as
critical.
In a particular form, the bearing surfaces extend at an angle of within 10 to
a plane
perpendicular to a reference axis (being in the direction of axial loading)
and more
preferably within an angle of 5 to the perpendicular.
In a particular embodiment the surrounding sleeve has a section modulus which
is able
to provide resistance to shear loading greater than the loading capacity of
the
reinforcing bar shaft. In this way, the couplings may be used when loaded as a
shear
connector.
In yet a further aspect, the present invention provides a method of forming
reinforcing
comprising the steps of providing a termination according to any form
described
above; and bonding the termination onto an end of a reinforcing bar so as to
make the
termination integral with the reinforcing bar.
In one form, the termination is fused to the reinforcing bar.
In one form, the termination is joined to the reinforcing bar by forging. In
one form, the
termination is welded to the reinforcing bar.
In a particular form, the termination is friction welded to the reinforcing
bar.
Accordingly, reinforcing is provided which incorporates a profiled termination
bonded
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on an end of a reinforcing shaft. The termination may be made as a cast
component
thereby enabling it to be made to a requisite high standard under controlled
conditions.
The termination can be joined to standard reinforcing bar by a friction
welding process
using relatively inexpensive equipment and with only minimal if any pre-
treatment of
the reinforcing bar. The resultant reinforcing is of integral form and each
stage of the
process (i.e. casting and joining) can be adequately controlled so that a
coupling
utilising the reinforcing can provide the required properties of strength,
ductility and
longitudinal slip. Also, by making the termination separately from the
reinforcing bar,
the reinforcing can be produced without requiring the specialised equipment
necessary
to produce the termination by deforming the reinforcing bar end thereby
reducing a
constraint to manufacture of the product.
Description of the Drawings
It is convenient to hereinafter describe an embodiment of the present
invention with
reference to the accompanying drawings. It is to be appreciated however that
the
particularity of the drawings and the related description is to be understood
as not
limiting the preceding broad description of the invention.
In the drawings:
Fig. 1 is a partial perspective view of reinforcing showing a termination of
the
reinforcing on a reinforcing bar end;
Fig. 2 is a plan view of the reinforcing of Fig. 1;
Fig. 3 is a sectional elevation of the reinforcing along section lines III -
III of
Fig. 2;
Fig. 4 is a detailed view to an enlarged scale of the locking formations on
the
termination of the reinforcing of Fig. 1;
Fig. 5 is an exploded view showing the components of a coupling of reinforcing
of Fig. 1;
Fig. 6 is a sectional view of the coupling of Fig. 5;
Fig. 7 is a sectional view of a variation of the coupling of Fig. 5 when
installed
as a shear connector;
Fig. 8 is a perspective view of a variation of the reinforcing of Fig. 1 with
a
different engagement face profile;
Fig. 9 is a side view of yet a further variation of the termination of Fig. 1;
Fig.10 is a perspective view of a cast termination and reinforcing bar;
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Fig. 11 is a perspective view of reinforcing formed by the bonding of the cast
termination and reinforcing bar of Fig.10; and
Fig. 12 is a schematic view of friction welding machine used to join the
termination and reinforcing bar of Fig 10.
Detailed Description of the Drawings
Turning firstly to Figs. 1 to 3, a partial view of a reinforcing bar 10 is
shown. The bar
10, which is typically made from steel, incorporates a shaft 11 which extends
along the
majority of the length of the bar 10. Whilst only a small portion of the shaft
11 is
shown, it is to be appreciated that this shaft may extend for many metres.
These bars
are made in continuous lengths and are cut to size depending on the
requirements of a
particular job. Furthermore, for convenience, the shaft 11 as shown is plain.
Again, it
is to be appreciated that the shaft may include ribbing, and such bar is
commonly
referred to as deformed bar.
The reinforcing bar 10 further includes a termination 12 which extends along
an end
portion of the bar to the terminal end 13 of the reinforcing bar 10. In the
illustrated
form, the termination 12 is integrally formed with the shaft 11 and is
enlarged as
compared to that shaft (i.e. it extends radially outwardly from a central axis
CL of the
reinforcing bar a greater distance than the shaft). A transition zone 14 is
present
between the shaft 11 and the enlarged termination 12.
The enlarged termination 12 in the embodiment shown in Figs. 1 to 3 is
typically
formed by deforming an end of the bar. In this arrangement, prior to
formation, the
whole of the bar 10 has a diameter corresponding to the diameter of the shaft
11.
The termination 12 includes a lateral engagement face 15 which extends along a
length
of the bar 10 and projects outwardly therefrom. This engagement face 15 is
profiled to
.30 include locking formations which enables the bar 10 to be coupled to
another bar or
other object to form an interlock as will be discussed in more detail below.
The locking
formations in the illustrated form comprise a plurality of spaced apart
upstands 16, 17,
18 and 19 and a plurality of recesses 20, 21, 22 and 23. The majority of these
recesses
21, 22 and 23 extend between adjacent ones of the upstands (16, 17, 18 and
19). A
proximal one of the recesses 20 extends between a hub portion 24 of the
termination
and its adjacent upstand 16.
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As best illustrated in Figs. 2 and 3, the termination is configured as a part
cylinder
having a diameter which is greater than the axis of the shaft 11. Furthermore,
the
engagement face 15 is formed effectively as a "cut out" from that cylindrical
termination. However, it is to be appreciated that whist the engagement face
15 may be
considered as a cut out portion, it is not limited to such a method of
manufacturing as
the termination maybe formed into its final shape by a forging operation,
casting
operation or the like without the need for any substantial removal of
material. Co-
pending International application filed by the Applicant and entitled "A
Method and
Apparatus for Forming Metal Reinforcing" discloses processes for the
manufacture of
the reinforcing bar 10 using a forging operation, and the contents of this
application are
herein incorporated by cross reference. Reinforcing 70 using a cast
termination 71 is
disclosed in more detail below with reference to Figs. 10 to 12.
As best illustrated in Fig. 3, each of the upstands (16, 17, 18 and 19)
include opposite
side walls 25 which are interconnected by bridging portions 26. Furthermore
the hub
portion 24 of the termination 12 includes a side wall 27. With this
arrangement, the
walls 25, 27 also act as the side walls for the recesses. Base portions 28
interconnect
these adjacent side walls to form the base of the respective recesses (20, 21,
22, 23).
The side walls 25 in the illustrated form are linear and extend across the
entire engaging
face 15. Further, the bridging portions 26 and the bases 28 are also formed as
flat
surfaces. As best illustrated in the enlarged view of Fig. 4, each of the side
walls 25 is
formed from three components. The first component is a bearing surface 29
which is
disposed in a mid region of the side wall and which is normal to the
centreline (CL) of
the bar 10. A first transition region 30 is formed above the bearing surface
29 and
forms the intersection between that bearing surface 29 and the bridging
surface 26. A
lower transition region 31 extends from the bearing surface 29 to the base
portion 28.
Both the upper and the lower transition regions (30 and 31) incorporate a
radius with
the radius of the top transition region 30 being smaller than the radius of
the lower
transition region 31.
The upstands and recesses of the engagement face 15 are shaped so that the
termination
12 will form an interlock with a termination of the same shape.
The end upstand 19 adjacent the terminal end 13 of the bar 10 is wider than
the other
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upstands. Further, the innermost recess 20 is also wider so as to be able to
receive an
upstand of the shape of the end upstand 19. This arrangement is provided so as
to
facilitate proper mating of the terminations in forming the interlock.
Finally, as best illustrated in Fig. 3, the upstands are arranged to step
downwardly
towards the terminal end 13. With this arrangement, the bearing faces 29 of
the various
upstands are not axially aligned but rather are at different radial spacings
from the
centreline CL. This is advantageous as it enables a more even distribution of
stress
through the termination when it is coupled to another termination.
Turning now to Figs. 5 and 6, a coupling 50 is disclosed which is formed from
interconnection of the termination 12 of one reinforcing bar with an identical
termination of another like bar. For convenience in the following description
of the
coupling 50 one reinforcing bar is designated using superscript I whereas the
other
reinforcing bar includes superscript II with associated features given like
designations.
The coupling 50 is formed by interconnecting the terminations 121 and 1211 to
form an
interlock 51. With the upstands of one termination interfitting within
corresponding
recesses of the other termination. The interlock extends along an axis
(designated A-A)
which, in the illustrated form, is coaxial with the central axis of the
respective
reinforcing bars 101 and 1011. Furthermore, once the terminations 121 and 1211
are
interconnected along their engagement faces 151 and 1511 the exterior surface
of the
termination forms a complete cylinder (which in the illustrated form is a
circular
cylinder) having a diameter which is greater than the diameter of the
respective shafts
111 and 1111.
The coupling 50 also includes a retaining device 52 which is arranged to
prevent
separation of the terminations. In the illustrated form, the retaining device
51 is in the
form of a sleeve, typically a metal sleeve having an internal bore which is
just slightly
larger than the exterior diameter of the cylinder formed by the interconnected
terminations. In this way the sleeve can slide over the lapping terminations
and is
typically retained in place by a wire tie or the like.
In use, the reinforcing bars 101 and 101, are arranged to be embedded in
concrete so as to
accommodate load induced in the resulting structure. Typically there are two
types of
loading conditions. The first is axial loading which extends primarily in the
direction of
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the bars axis CL. This axial loading may be in tension or in compression. The
other
loading condition is shear where the loading is in a direction normal to the
centreline
CL. The coupling 50 is arranged to accommodate loading in both these
conditions as
will be discussed in more detail below.
Under axial load, the reinforcing bars 101 and 101, may be biased apart (under
tension)
or biased together, with tensile loading being the predominant condition. This
axial
loading is accommodated by the coupling 50 through interengagement of the
upstands
in the two terminations 12, and 1211. In particular, the upstands are arranged
to engage
along their bearing surfaces 291, 2911 formed in the side walls. These form
the regions
of contact of the upstands under axial loading and in particular there are no
points of
contact between the transition regions 30, 31 because of the smaller radius of
the top
transition region 30 as compared to the lower transition region 31. Because
the bearing
surfaces 291, 2911 are disposed normal to the direction of loading there is no
vector force
developed to load the surrounding sleeve 51. As such, this axial loading is
fully
contained within the terminations.
To accommodate the shear load, the retaining device 51 has a section modulus
which is
sufficient to accommodate the design shear loading. With this arrangement, it
is not
necessary to orientate the reinforcing bars so that shear is accommodated by
the
interlock.
Fig. 7 illustrates a shear coupling 60 which is a variation of the coupling
50. As the
shear coupling includes the components of the coupling 50 described above for
2.5 convenience like features have been given like reference numerals.
Furthermore for
ease of description, superscript is used to distinguish between the two
reinforcing bars
provided in the coupling 60.
The shear connector 60 is utilised to interconnect reinforcement from a wall
100
through to a slab 101. To form this connection, the wall 100 is constructed
first and
incorporates reinforcing bars 101. Instead of extending solely in the plane of
the wall
100, the reinforcing bars 10, are turned so as to extend to a face 102 of the
wall 100.
The wall 100 is cast with recesses 103 that project in from the face 102 so as
to expose
the terminations 121 and make those terminations accessible from the face 102
of the
wall 100. In this way these terminations 121 are ready to receive the
reinforcing bars
10i1 in the set up of the reinforcing for the slab 101.
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In the illustrated form, the terminations 121121, are of a shorter length
having only three
upstands rather than the four upstands in the earlier embodiment. With this
arrangement, the terminations 12, do not protrude form the face 102 of the
wall 100.
In setting up the reinforcing for the slab 101, the reinforcing bars 101, can
simply be
connected to the reinforcing bars 101 by forming an interlock 61 through
interconnection of the termination 1211 with the terminations 121. The sleeves
62 are
then disposed over the interlocks to retain the terminations in engagement.
Moreover
the sleeves 62 have a section modulus which is sufficient to accommodate the
design
shear loading at the couplings 60.
Once the reinforcing has been connected, the concrete can then be poured to
form the
sleeve. In casting the concrete the recesses 103 are fully filled so as to
ensure there is
adequate cover over the reinforcing.
Figs. 8 and 9 show further variations on the profile of the terminations 12
disclosed
above. Again as these terminations include many of the features described
above like
features have been given like reference numerals.
In the embodiment of Fig. 18, the upstands 16, 17 and 18 of the terminations
12 are of
more complex design being arcuate rather than linear as in the earlier
embodiments.
Fig. 9 illustrates yet a further variation on the profile of the termination
12. In this
embodiment, the upstands are more undulating than in the earlier embodiments.
In the
embodiments of both Figs. 8 and 9, the bearing surfaces formed in the side
wall
inclined from perpendicular to the direction of axial loading. This is
particularly the
case for the embodiment of Fig. 9. As such, in these embodiments, under axial
loading
there will be a transfer of force to the retaining device, although a majority
of the load
can be taken through the bar. Further, because of the shape of these upstands,
it maybe
necessary to have a very tight tolerance between the terminations and the
retaining
device to minimise lateral slip. This tolerance can be formed by post forming
of the
retaining device or by the use of packing as described above.
Figs. 10 to 12 show a further variation where reinforcing 70 is formed from
two
separate components; namely an end component (or termination) 71 and a length
of
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conventional reinforcing bar 75 (shown as deformed bar). The termination 71 is
profiled to include the lateral engagement face 15 and locking formations
(16,17,18,19,20,21,22,23) of the reinforcing bar 10 and for convenience like
features
have been given like reference numerals. The termination 71 is formed separate
to the
bar, and in a particular form is cast as a single piece. However, it is to be
appreciated
that the process of making the termination is not limited to casting and it
may be formed
by other material working techniques such as forging, milling, pressing and
like or by a
combination of those processes.
The termination includes a first and second end (72, and 73), with the first
end 72 being
in use joined to an end 76 of the reinforcing bar 75. In the illustrated form,
the diameter
of the first end 72 is generally the same size as the diameter of the bar 75
so that when
joined there is a consistent connection bond 78 between those components in
the
reinforcing 70(as shown in Fig. 11). This connection bond 78 in the
illustrated form is
substantially perpendicular to the axis of the reinforcing bar CL. As such the
bond is
perpendicular to the principal loading condition (axial) of the reinforcing.
In forming the reinforcing 71, the join 78 between the termination and the
reinforcing
bar is made permanent. This has the advantage of making the reinforcing a
fully
integral unit that obviates the need for any manual assembly of components on
site.
This both provides for ease of installation and obviates the problem of
incorrect fitting
of separate couplings. It also allows the join to be made in an environment
where the
properties of the join can be controlled to ensure they are satisfactory.
Furthermore,
bonding of the components, rather than using a mechanical connection such as a
collar
swaged onto both components, minimise the components used in the connection,
and
allows for better control of the join to ensure that the requirements of
strength under
axial load and ductility are met.
In a particular form, the termination and bar are connected by a friction
welding process
where the two components are forced together (under a friction or forge force)
and are
heated by mechanical friction of one component rubbing against the other (in
the
illustrated form of Fig.12 by rotating one component whilst holding the other
component stationary). In particular, the bar 75 is held in a non rotating
chuck 121 of a
friction welding machine 120, whilst the termination 71 is attached to a
rotating chuck
122. The components 71, 75 are aligned so that the axis CL of the bar 75
aligns with a
reference axis RA of the termination 71. The component ends 72, 76 are brought
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together by relative movement of the chucks 121 and 122 and the chuck 122 is
rotated
to cause the termination end 72 to rub against the bar end 76 causing the
components to
heat. The heating by mechanical friction continues for sufficient time until
the metal
softens and some shortening (upset) of the components occur under the friction
force.
The rotation driving force on the chuck 122 is then discontinued but the
friction force is
maintained or increased to fuse the termination to the bar end 76.
Technically, because
no melt occurs, friction welding is not actually a welding process in the
traditional
sense, but a forging technique. The resulting join is of forge quality and is
a complete
butt joint weld through the contact area. The friction welding machine
requires no
special installation requirements, there are no gases generated that need to
be exhausted,
and the process is easily automated for high production rates. A further
advantage is
that the ends to be joined do not need to be specially prepared thereby
minimising pre-
treatment of the components 71, 75.
A coupling arrangement using the reinforcing bars 10 or reinforcing 70 as
described
above has substantial practical benefit. As each termination is permanently
joined to
the bar shaft, the strength of the termination can be properly matched to the
strength of
the bar, particularly where the termination is formed from the same material
as the bar
shaft. A major problem with prior art couplers that use separate components is
the fact
that the reinforcing bar may vary in strength (e.g. nominally 500MPa/bar may
have an
allowed top strength of 650Mpa). This means that couplers may be mismatched
with
extremely strong bars so the couplers need to be made to accommodate this
possible
mismatch. This can have attendant problems as it may reduce the ductility
properties of
the coupler itself by providing a coupler of higher strength than required.
The integral
nature of the termination to the shaft obviates this mismatch and allows for
ductility and
strength to the joint to be correctly matched to the bar shaft.
Typically by incorporating an enlarged end with the profiled engagement face
and
having the material of the termination the same as the shaft, the strength at
the coupling
is greater than the bar being joined. In one form, the coupling has a strength
of
approximately 110% of the strength of the bar although as will be appreciated
this could
be varied by varying the dimensions of the various components in the
termination.
Even with this increased strength, the coupling exhibits greater ductility
than the bar
shaft and tests conducted by the inventor has shown this to be the case.
Without being
bound by theory, this ductility increase has shown to be found as under
plastic
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deformation the upstands tend to collapse which allows elongation along the
coupling.
Also, the normal bearing faces limit the longitudinal slip of the coupling
under load.
Again tests conducted by the inventor have indicated that there is slip of
less than
0.lmm under prescribed loading test conditions (typically under 300Mpa of
axial
loading). A feature of having the bearing faces normal to the direction of
axial loading
is that the slip is not dependent on the fit between the sleeve 51 and the
coupled
terminations. With this arrangement, the sleeve does not need to be
manufactured to a
precise tolerance.
Further, the coupling has a relatively thin profile which is advantageous as
it may allow
thinner concrete sections to be used in some circumstances whilst still
allowing
adequate concrete cover to provide over the reinforcing.
Finally, an advantage of the coupling is that it is easy to assemble onsite
and easy to
ascertain onsite whether the coupling has been properly installed. If the
terminations
have not been properly connected together, then it may not be possible to
locate the
sleeve over the coupled terminations and/or it is clearly visible as part of a
termination
projects beyond the sleeve length.
The option of preforming the terminations and then subsequently joining those
terminations to reinforcing bars, enables the resultant reinforcing to be made
without
the need for highly specialised equipment, thereby providing flexibility in
the
manufacture of the product and in particular allows for distributed
manufacturing which
can reduce transporting and handling costs, and if desired on site
manufacture.
In the claims which follow and in the preceding description of the invention,
except
where the context requires otherwise due to express language or necessary
implication,
the word "comprise" or variations such as "comprises" or "comprising" is used
in an
inclusive sense, i.e. to specify the presence of the stated features but not
to preclude the
presence or addition of further features in various embodiments of the
invention.
Variations and modifications may be made to the parts previously described
without
departing from the spirit or ambit of the invention.
