Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02731371 2011-10-04
CONCRETE PANEL WITH FIBER REINFORCED REBAR
The present invention relates a concrete pane with fiber reinforced
reinforcing bar or "rebar" where portions of the rebar along the length are
curved or
shaped out of the straight path of the bar to form loops and to a method for
lifting the
panel.
The term "rebar" as used herein is intended to include bars and rods
which are hollow, that is tubing. The outside surface is preferably but not
necessarily of
circular cross section. The rods can be of any length.
BACKGROUND OF THE INVENTION
The use of fiber reinforced plastics (FRP) rods in construction, marine,
mining and others has been increasing for years. This is because FRP has many
benefits, such as non-(chemical or saltwater) corroding, non-metallic (or non-
magnetic)
and non-conductive, about twice to three times tensile strength and 1/4 weight
of steel
reinforcing rod, a co-efficient of thermal expansion more compatible with
concrete or
rock than steel rod. Most of the bars are often produced by pultrusion process
and
have a linear or uniform profile. Conventional pultrusion process involves
drawing a
bundle of reinforcing material (e.g., fibers or fiber filaments) from a source
thereof,
wetting the fibers and impregnating them (preferably with a thermo-settable
polymer
resin) by passing the reinforcing material through a resin bath in an open
tank, pulling
the resin-wetted and impregnated bundle through a shaping die to align the
fiber bundle
and to manipulate it into the proper cross sectional configuration, and curing
the resin in
a mold while maintaining tension on the filaments. Because the fibers progress
CA 02731371 2011-10-04
2
completely through the pultrusion process without being cut or chopped, the
resulting
products generally have exceptionally high tensile strength in the
longitudinal direction
(i.e., in the direction the fiber filaments are pulled). Exemplary pultrusion
techniques
are described in U.S, Patent No. 3,793,108 to Goldsworthy; 4,394,338 to Fuwa;
4,445,957 to Harvey; and 5,174,844 to Tong.
FRP uniform profile or linear rods offer several advantages in many
industrial applications. The rods are corrosion resistant, and have high
tensile strength
and weight reduction. In the past, threaded steel rods or bolts had been
widely used in
engineering practice. However, long-term observations in Sweden of steel bolts
grouted with mortar have shown that the quality of the grouting material was
insufficient
in 50% of the objects and more bolts have suffered from severe corrosion. In
contrast
with the steel bolts, the FRP bolts are corrosion resistant and can be
simultaneously
used in the temporary support and the final lining, and the construction costs
of single
lining tunnels with FRP rock bolts are 33% to 50% lower than of tunnels with
traditional
in-site concrete. This FRP rock bolting system is durable and as a part of the
final
lining supports a structure during its whole life span. Furthermore, due to
their
seawater corrosion resistance, the FRP bolts and anchors are also proven as
good
solutions in waterfront (e.g., on-shore or off-shore seawalls) to reinforce
the concrete
structures. In general the fibreglass rod/bolt is already an important niche,
and will be a
more important product to the mining and construction industries. The critical
needs of
these industries are for structural reinforcements that provide long-term
reliability that is
of cost-effective. The savings in repair and maintenance to these industries
will be
CA 02731371 2011-10-04
3
significant, as the composite rebar will last almost indefinitely.
The mining industry requires composite rods for mining shafts or tunnel
roof bolts. These rods are usually carried by hand and installed overhead in
mining
tunnel, so there is a benefit that the fibreglass rod is 1/4 the weight and
twice the
strength of steel rebar which are widely used currently. Fibreglass rod also
does not
damage the mining equipment. In construction industries, such as bridges,
roads,
seawall and building structures, reinforcements of the steel rebar have been
widely
used and the most of steel rebars have been corroded after a few years of
service life.
Typically, the structures with the steel rebars are often torn down after a
period of time.
Therefore, the use of the corrosion resistant composite rebars have been
increased for
construction industries in recent years.
Conventional steel rebar can of course be bent to form hooks or loops or
angled sections typically at the ends but also at other locations along the
length of the
bar. Such bends are often required for many purposes, such as for attachment
of the
bar to other components.
FRP rebar when formed from thermoset resin of course cannot be bent
after the bar is formed. It has up to now been a significant outstanding
problem as to
how to form such bends in rebar using a thermoset resin in an effective and
commercial
manner where the bend sections are not so compromised as to their strength as
to
severely limit the use of the bar.
SUMMARY OF THE INVENTION
It is one object of the present invention to provide a method for forming
CA 02731371 2011-10-04
4
fiber reinforced bars manufactured using a thermoset resin, where the bar
includes at
one or more section along its length a bend section.
According to a first aspect of the invention there is provided a concrete
panel comprising:
a plurality of u-shape rebar elements;
a cast concrete component in which the rebar elements are buried;
each rebar element having two straight portions and one bent portion of
180 degrees forming a loop between the two straight portions;
the loops being exposed at one edge of the concrete component for lifting
the concrete panel;
the rebar elements being formed from rovings of reinforcing fibers
arranged generally longitudinal to the body permeated by a thermoset resin
through the
rovings.
Preferably the rebar elements include a series of inner longitudinally
extending components of reinforcing fibers arranged longitudinal to the rebar
element
and providing at least one helical wrapping of at least one component wrapped
around
the inner longitudinally extending components.
Preferably said at least one helical wrapping comprises first and second
helical wrapping or wrappings in opposed direction of wrapping with the resin
being
permeated through both the inner longitudinally extending components and
through the
wrappings to form a structure integrated by the permeated resin.
Preferably the body has an outer surface portion at which the inner
CA 02731371 2011-10-04
longitudinally extending components have parts thereof between the first and
second
wrapping or wrappings exposed and bulged outwardly by tension applied by the
wrapping or wrappings during curing, the bulged parts defining components of
the outer
surface portion of the rebar element which are thus rough and exposed for
engaging a
5 material to be reinforced so as to transfer longitudinal loads between the
material to be
reinforced and the inner rovings.
According to a second aspect of the invention there is provided a method
of lifting a concrete panel comprising:
providing a plurality of u-shape rebar elements buried in a cast concrete
component;
each rebar element having two straight portions and one bent portion of
180 degrees forming a loop between the two straight portions;
the loops being exposed at one edge surface of the concrete component;
the rebar element being formed from reinforcing fibers arranged generally
longitudinal to the body permeated by a thermoset resin through the rovings;
and lifting the concrete panel using the loops.
Preferably, after lifting, the rebar elements are cut off at said one edge
surface leaving ends of the rebar elements exposed and uncovered.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side elevational view of a portion of a reinforcing bar
manufactured by a method according to the present invention.
CA 02731371 2011-10-04
6
Figure 2 is a cross sectional view along the lines 2-2 of Figure 1.
Figure 3 is a cross sectional view similar to that of Figure 2 on an
enlarged scale.
Figure 4 is a cross sectional view along the lines 4-4 of Figure 1.
Figure 5 is a schematic side elevational view of the method-of forming the
reinforcing bar of Figure 1.
Figure 6 is an isometric view of the holder and drive system of Figure 5.
Figure 7 is a side elevational view of the holderand drive system of Figure
5.
Figure 8 is side elevational view of the holder of Figure 5 removed for
curing.
Figures 9 and 10 are side elevational views of the holder of Figure 5
modified to include a reduced number of engagement bars and modified to show
an
optional method of forming additional curved sections in an opposed angular
direction.
Figure 11 is a side elevational view of a concrete panel formed using the
rebars manufactured by the holder of Figure 8.
DETAILED DESCRIPTION OF THE INVENTION
In Figure 1 is shown a reinforcing bar generally indicated at 10. This is
formed using the method described in detail hereinafter to form a straight
section 100
and a bend section 101.
The basic bar structure is formed using the method shown and described
CA 02731371 2011-10-04
7
in published US application 2008/0261042 of the present applicants, the
disclosure of
which is repeated as follows for completeness.
The bar 10 has a first section 11 extending along most of the length of
the bar together with a second section 12 which extends a part of the length
of the bar.
The bar is generally formed in continuous construction so that the first and
second
sections are repeated alternately. The length of the second section generally
will
comprise only a short portion relative to the length of the main section 1 so
that for
example the main section may be 12 feet long and the second section only 6"
long.
The reinforcing bar is formed solely from a resin material 14 which is
permeated through to sections of reinforcing fibers including longitudinal
reinforcing
fibers 15 and wrapping reinforcing fiber 16, 17.
The longitudinal reinforcing fibers 15 constitute the main volume of the
structure so that typically the fiber content may be constituted as
longitudinal fibers 90
to 97% and wrapping fibers 3 to 10 %, where the resin content can be of the
order of 20
to 30 % by weight.
The structure in the area of the portion 11 is formed without any
compression of any of the fibers by a pultrusion process. Thus neither the
inner core
formed by the longitudinal fibers 15 nor the outer wrapping 16 and 17 pass
through a
die structure so that they are free to take up their positions as determined
by the
tensions in the material when formed.
The resin may be a two part resin which sets without heat but more
preferably is a thermosetting resin which is heated by any one of a number of
available
CA 02731371 2011-10-04
8
heating techniques such as microwave heating, forced air heating, infra-red
heating,
RF-heating, or induction heating where at least one metal fiber is included in
the
structure to absorb the electromagnetic energy. Thus the heat is applied to
the
structure to effect curing of the resin without contact by the heating device
on the
structure. In this way the fibers in the first section 11 are free to take up
their position
depending upon their tension and they take up a position within the resin so
that the
resin extends both through the longitudinal fibers and the wrapping fibers.
In order to obtain this situation where the resin 14 extends outwardly to
the outer surface 18 and permeates through all of the fibers, the longitudinal
fibers and
the wrapping fibers are both preferably wetted preferably using a bath or
dipping
process so that the fibers are fully enveloped with the resin prior to entry
into the
forming system generally described above and shown in more detail in the above
US
patent of the present inventor.
The wetting of the fibers ensures that the resin permeates through the
whole structure of the outside surface 18.
The absence of any compression by the provision of any form of die
through which the core of longitudinal fibers passes ensures that the wrapping
fibers 16
and 17 apply pressure onto those parts of the longitudinal fibers which are
contacted by
the wrapping fibers squeezing those longitudinal fibers inwardly and causing
bulging of
the longitudinal fibers in the sections 19. Thus between each wrapped strip of
fibers
there is a portion of the longitudinal fibers which is squeezed and bulged
outwardly so
that it projects to a position which is preferably slightly proud of the
outside surface of
CA 02731371 2011-10-04
9
the wrapping fibers.
The wrapping fibers are of course spaced in the longitudinal direction by a
helical wrapping action so that the width of the wrapping fibers is less than
the width of
the bulged intermediate sections 19.
Typically the wrapping fibers in each direction can be spaced of the order
of 1 to 3 to the inch. However a wider or lesser spacing may be used provided
the
longitudinal fiber are properly controlled and provided there is enough space
to ensure
bulging between the wraps.
The wrapping fibers may be wrapped as a single roving in a single start
wrapping process or as multiple rovings applied in a multi-start wrapping
process. In
such a multi start process the number of rovings side by side may be in the
range 3 to
10. The number of rovings or the thickness of the roving at the wrapping
position may
vary depending on the diameter of the core.
The wrapping action occurs in both directions so that the wrapping fibers
overlap one another as they cross as shown for example at 20. In this way the
bulged
sections are generally diamond shape in front elevation and are squeezed at
the top
and bottom by the wrapping action of the wrapping fibers. Thus the bulging
sections 19
are individual and separated by the wrapping fibers and yet the longitudinal
fibers are
properly contained and held into the structure by the wrapping at top and
bottom of the
bulging sections.
The provision of the wrapping or wrappings symmetrically in both
directions tends to contain and locate the inner longitudinal rovings and
maintain them
CA 02731371 2011-10-04
in the longitudinal direction even when tension is applied. Thus the full
strength of the
longitudinal fibers in the longitudinal direction is maintained and is not
reduced or
compromised by any tendency of the longitudinal fibers to twist. Any such
twisting of
the longitudinal fibers can significantly reduce strength by applying loads
sequentially to
5 different fibers leading to sequential failure. In addition the wrappings in
opposite
directions accommodate torque applied to the rod in both directions.
The bulging sections 19 are thus presented on the outside surface 18 for
engagement with material within which the bar is embedded. Thus if the
material to be
reinforced is concrete, the concrete sets around the reinforcing bar and
engages the
10 bulging sections 19. Longitudinal loads from the concrete to the
reinforcing bar are
therefore transferred to the bulging sections 19 and not only to the wrapping
section 16
and 17. The wrapping sections because of their angle to the longitudinal
direction have
less ability to accommodate longitudinal tension than do the longitudinal
fibers which
are longitudinal and continuous. Thus transferring the loads in the
longitudinal direction
to the bulged sections 19 ensures that the loads are transferred into the
longitudinal
fibers and avoid transference to elements which can be moved longitudinally or
stripped
from the outside surface 18. The bulge sections 19 cannot of course move
longitudinally since they are part of longitudinal fibers.
Yet the outside surface thus can be free from additional bonded projecting
elements such as grit or sand which is commonly applied to the outside surface
of such
reinforcing bars.
The fact that the resin is permeated throughout both the longitudinal fibers
CA 02731371 2011-10-04
- -- ----------
11
and the wrapping fibers to the outside surface 18 ensures that the wrapping
fibers are
bonded effectively into the structure.
The second section 12 is formed periodically along the bar as it is formed
by clamping the portion of the bar within a clamping die. The clamping die may
move
with the structure as it moves forwardly or the movement could be halted while
the
clamping action occurs and the curing occurs in the clamped position.
Generally the
formation of the clamped section occurs before the remainder of the bar moves
into the
heating section to complete the curing action. The clamping die has an inside
surface
which is shaped to a polygonal shape such as square and squeezes both the
wrapping
fibers and the longitudinal fibers to form them into the required outer shape
22 as
shown in Figure 4. The clamping action squeezes the fibers together and may
reduce
the cross sectional area due to squeezing of the resin from the structure. The
longitudinal fibers extend through the clamp section and also the wrapping
fibers
extend through the clamp section as shown in Figure 4. Thus the wrapping
fibers in
both directions of wrap are clamped into the structure at the polygonal second
section
12.
As an alternative to the polygonal shape, any other non-circular shape
may be used such as a compressed flat shape.
As a further alternative the rough rebar may be formed with a hole
through the fibers to provide a connection for an anchor.
The second section 12 is thus shaped so that the bar can be grasped by a
chuck or other clamping element so that the bar can be rotated around its axis
during
CA 02731371 2011-10-04
12
insulation of the bar in particular circumstances, The wrapping of the fibers
16 and 17
ensures that rotation at the second section 12 is transmitted into torque
throughout the
length of the bar by those wrapped section 16 and 17.
In one example of use of an arrangement of this type, the bar can be
inserted into a drilled hole in rock in a mining situation and the drilled
hole filled with a
suitable resin. The stirring action in the resin caused by the rotation of the
bargrasping
the second section 12 and rotating the first section 11 causes the resin to be
spread
through the hole around the periphery in an effective stirring action caused
by the
bulged sections 19. Thus the bar can be bonded into place within the drilled
hole to act
as reinforcement for mining structures at for example the roof area of a mine.
In another alternative use of reinforcing bars of this type, a drill tip can
be
attached at one section 12 and the bar grasped at another section 12 allowing
the bar
to be rotated with the drill tip causing a drilling action driving the bar
directly into a
drilled hole while the bar causes the drilling of the hole. The bar can then
remain in
place and the drill tip selected be of a sufficiently disposable type so that
it can be
discarded within the hole.
Again the direct connection between the polygonal section 12 and the
main portion of the bar caused by the presence of the wrapping fibers 16 and
17 within
the resin allows the transfer of loads between the polygonal section and the
main
section 11.
The arrangement described herein has been found to be significantly
advantageous in that it provides an improved embedment strength which is a
factor
CA 02731371 2011-10-04
13
used in calculating parameters for reinforcing bars in concrete. Thus the
shape of the
outer surface (wrappings in both directions, bulging of the longitudinal
strands) provides
a higher degree of attachment with the adhering material (concrete or epoxy
resin).
This higher mechanical bond translates into a high embedment strength.
The arrangement described herein has been found to be significantly
advantageous in that it provides an improved control of crack width.
Measurement of
crack width is another factor used in calculating parameters for reinforcing
bars in
concrete with the intention of maintaining a low crack width factor. When
designing for
crack control reinforcement, the nature of this product and its high embedment
strength
will allow for a smaller bond dependant co-efficient to be used (for example,
sand
coated bars use 0.8, and a smooth pultruded bar would be higher). A lower bond
dependant co-efficient translates into smaller crack widths, or less
reinforcement
required for the same crack width.
In Figures 5 to 8 is shown the method for manufacturing the rebar having
the straight portion 100 and the bend portion 101. This method includes a
conventional
system 20 for forming an elongate body 23 from rovings of reinforcing fibers
arranged
generally longitudinal to the body which is fed forwardly along its length
from a supply
assembly 21. The body 23 is wetted with a unset curable resin permeated
through the
rovings in a bath 22. The body 23 is fed forwardly by a drive and guide system
23A
and is fed from this system at a predetermined speed either by being driven
forwardly
or more generally by controlling the feed from the supply 21 to ensure
constant supply
in order to try to maintain a predetermined tension, bearing in mind that the
speed may
CA 02731371 2011-10-04
14
be varied depending on various factors.
The body 23 is fed from the former 22 to a holder or reel 24 for receiving
a length of the elongate body mounted on a drive system 25 for rotation about
an axis.
The holder comprises generally a reel 26 with a plurality of bars 27 arranged
at spaced
positions around the axis of the reel.
Thus the holder comprises a hub 28 including a plurality of transverse
rails 30 extending outwardly for supporting the bars 27 at positions spaced
outwardly or
the axis of the hub. The rails 30 support a plurality of the engagement
members or
bars 27 at spaced positions around the axis 31A with each bar parallel to the
axis.
Each bar 27 is generally cylindrical with an outer surface 33 for receiving
the rebar body 23 to be wrapped around the reel. Each bar 27 has on its outer
surface
a series of axially spaced grooves 34 with each groove 34 having a radius of
curvature
and a width arranged to match the outer periphery of the rebar body 23. Thus
as the
reel is rotated about its axis, the rebar body is laid into each groove 34 in
turn along the
bars 27 with the grooves holding the rebar body at a specific position on the
bar 27 and
spaced from the next wrapping of the rebar body. Thus there is no contact
between
each wrap and the next. In order to maintain the rebar body confined into a
generally
cylindrical shape, at least one wrapping of at least one component is wrapped
around
the inner rovings.
This wrapping can be part of the structure in that it is intended to remain
in place after the roving is complete and is in use. In the alternative the
wrapping can
be provided for the purpose of maintaining the integrity of the structure
during the
CA 02731371 2011-10-04
winding around the bars for the bending process. In this case, the wrapping
may have
no structural contribution in the finished rebar and is used merely to keep
the bundle
together, or even the material can be removed and discarded as a sacrificial
material
after curing is complete. In some cases particles can be adhesively attached
to the
5 exterior surface of the rebar when complete for added bonding to the
material in which
the rebar is embedded.
Where the wrapping is structural, it is typically helical. However
longitudinally extending wrapping materials can be used. That is the material
can
either wind around the bar or be simply clad over it.
10 The bars 27 have a radius of curvature around the bar arranged to
receive and to form a respective bent portion of the body. Thus in the figures
where the
bars 27 are shown as cylindrical, the radius of curvature of the cylinder
matches the
intended curvature of the required bent portion to be formed. It will be
appreciated that
the bar 27 only contacts the rebar body over a portion of the periphery of its
outer
15 surface 33 which will be roughly 90 degrees in the arrangement using four
bars as
shown in Figure 6, This portion of the surface 33 must match the shape of the
bent
portion to be formed. The remaining part of the bar around the remaining 270
degrees
can be of any shape since it has no contact with the rebar body 23.
While the resin remains unset, the body is wrapped around the holder
such that the fed length of the body is wrapped from one engagement member to
a
next engagement member such that bent portions of the body are wrapped partly
around each engagement member and straight portions of the body extend between
CA 02731371 2011-10-04
16
each engagement member and the next. Thus each engagement member has
angularly extending axially separated surface portions which are shaped to
mold the
bent portions to a required bent shape. The drive system 25 provides both
rotation of
the reel by driving the hub 28 around the axis 31A but also provides relative
movement
between the rebar body 23 as it is fed forwardly and the holder 24 so as to
wrap the
body 23 around the bars 27 of the holder at the stepped positions along the
bars 27
defined by the grooves 34.
As shown in Figure 8, the holder when filled, that is each of the grooves
34 has been engaged by a portion of the rebar body, the resin in the rebar
body is
cured on the holder while the body 23 remains wrapped on the holder. That is
the
wrapping is stopped when the holder is filled by side by side portions of the
body
arranged along the engagement members and the resin is cured after the
wrapping is
stopped and the holder removed and placed in a suitable oven 50 or other
heating
system.
It will be appreciated that each bar 27 is spaced from the next by a
distance so as to define a required length between each bent portion and the
next. For
this reason the position of the bars 27 along the rails 30 is adjustable for
example by
defining a guide track and locking system which allows the bars to slide
inwardly while
being set at the required position parallel to the axis 31A.
The drive system 25 includes towers 251 and 252 for supporting
respective ends of the hub 28, or the hub may be cantilevered from one tower.
The
hub is driven by a drive train 253 mounted on a base frame 254 The relative
CA 02731371 2011-10-04
17
movement between the rebar body 23 and the holder 24 is obtained by guiding
the
rebar body 23 at a fixed feed position defined by the drive and guide system
23A and
by indexing the holder 24 along the axis 31A. The indexing movement is
obtained, as
shown in Figure 6, by moving the frame 254 carrying the hub 28 along an outer
support
frame 257 by an indexing motor 258 including a suitable drive system which may
be a
worm, chain or rack or other mechanical drive system. The indexing movement
across
the frame 257 can be constant or can be stepped as required, bearing in mind
that the
rebar body is laid into grooves and thus held and guided by those grooves to
be
properly positioned on the holder at the axially spaced locations defined by
the grooves.
The holder is thus driven around the axis with constant torque for applying
constant
tension to the rebar body 23. In order to obtain constant linear wind-up
speed, the
angular velocity of the hub 28 and therefore the bars 27 around the axis must
change
at different angular positions around the axis as the radial position of the
winding
location on the respective bar changes inwardly and outwardly of the axis.
When filled, the holder can be simply removed from the drive system by
removing the hub from the towers and moving away the holder to the oven 50
(Figure
8). The holder can then be replaced by a second empty holder of a set of
holders of a
suitable number to allow continuous production where the filled holders are in
curing
while another empty holder is in winding.
The holders can be of various diameters allowing various locations of the
bars 27. For example a reel can have a diameter as much as 25 feet with many
different locations of the bars being possible to provide many different
numbers and
CA 02731371 2011-10-04
18
locations of the bars for different angles of wrap for the bent portions and
different
lengths of straight portions. Typically the rebar body is bent at a radius of
curvature
which is matched to the diameter of the rebar body so that the outside surface
33 of the
bars 27 is typically always the same diameter regardless of the angle of wrap.
This
diameter of the surface of the bar is of course matched to the width of the
grooves for
the diameter of rebar being formed. Different reels are therefore provided for
different
diameter rebar such as 0.5 inch, 1.0 inch or 1.5 inch and that reel can carry
out all
required shapes for the dedicated rebar diameter to which it is designed.
In Figure 8, the holder is arranged such that the number of engagement
members is changed. That is two of the bars 27 are removed leaving only two
bars
allowing a wrapping around each bar of 180 degrees.
In Figures 9 and 10 is shown a method for bending the rebar body 23 at
second bend positions 40 in an inverse direction to form second bent portions
41
having angles curved in opposite directions to the bent portions formed by the
bars 27.
Thus, as shown in Figure 9, the rebar body 23 is wrapped around the bars
of the reel 26 firstly in the same manner as described above. When this
wrapping is
complete and the reel ready to be removed, or after the reel has been removed,
the
second bent portions are formed by inserting second engagement members or bars
42
onto the reel and by moving them inwardly toward the axis 31A at positions
between
the bars 27. Thus in Figures 9 and 10 there are shown four bars 27 at
equiangular
spacing and four bars 42 also at equiangular spacing located directly between
the bars
27. However the number and angular spacings of the bars 27 and 42 can be
varied as
CA 02731371 2011-10-04
19
required. The original wrapping takes place with the bars 42 removed. The bars
42 are
then applied onto the reel and the inward movement M1 of the bars 42 as shown
in
Figure 10 pulls the rebar body 23 inwardly and thus requires inward movement
of the
bars 27A and 27B toward the axis 31A in movement M2 to accommodate this
movement to release lengths of the body 23 to engage the second bars 42. The
inward
movement of the bars 27 can be controlled automatically using springs 42A to
accommodate this movement. In this way, various different designs of bent
rebar can
be formed with bends at different locations and spacings, bends of different
angles of
wrap, and bends of different directions depending on the requirements of
customer.
After the curing is complete in the oven 50, the wrapped lengths
extending around the bars 27 are cut at required positions on the bars
depending on
the shape required. Thus in one example, the body 23 is cut at one bent
portion on
one side of the bar 27 to form a series of lengths of the body 23 each having
one
straight portion extending from the bar to the next bar and one bent portion
wrapped
around the bar. In this way a series of required rebar portions are formed by
cutting
along the length of each bar 27.
in another example, the body 23 is cut to form a u-shape rebar with two
straight portions and one bent portion of 180 degrees between the two straight
portions.
This is obtained by using only two bars 27 on the reel and by cutting at a
positions
equidistantly spaced between the bars 27.
However these are only examples and many different shapes and
arrangements can be designed and formed using this system.
CA 02731371 2011-10-04
In particular, the u-shape rebar 55 is shown in Figure 11 where the base
of the U is shown at 50 and the legs are shown at 51 and 52. This u-shape
rebar 55 is
cast in a concrete panel 53 with the straight portions 51 and 52 within the
panel and the
bent portion at the U 50 exposed at one edge 54 of the panel to form a lifting
loop. The
5 loops 50 thus form a row of lifting loops at the edge 54 which can be
engaged by the
bars 56 of a lifting system to simultaneously lift all loops to lift and carry
the panel into a
required position. The loops are then cut simply off after the panel is lifted
into a
required location.
As explained previously and shown in Figure 1, the step of forming the
10 reinforcing bar includes providing a series of inner rovings of reinforcing
fibers arranged
longitudinal to the bar, providing a first helical wrapping or wrappings of at
least one
roving wrapped around the inner rovings in a first direction of wrapping, and
providing a
second helical wrapping or wrappings of at least one roving wrapped around the
inner
rovings in a second opposed direction of wrapping with the resin being
permeated
15 through both the inner rovings and through the wrappings to form a
structure integrated
by the permeated resin.
The bar thus has an outer surface portion which extends along at least
most of the length of the bar and at the outer surface portion, the inner
rovings have
parts thereof between the first and second wrapping or wrappings exposed and
bulged
20 outwardly by tension applied by the wrapping or wrappings during curing,
the bulged
parts defining components of the outer surface portion of the bar which are
thus rough
and exposed for engaging a material to be reinforced so as to transfer
longitudinal
CA 02731371 2011-10-04
21
loads between the material to be reinforced and the inner rovings.
While the inner components are preferably or typically rovings, other
material can be used or various types known to person skilled in the art. The
inner
components are preferably but not necessarily wrapped in one or both
directions.
Again the wrappings are preferably or typically rovings, but other material
such as mat
or thread can be used or various types known to person skilled in the art.
