Rebar coupler

Abstract

A rebar coupler has an outer sleeve, an inner sleeve; and an annular void between the inner sleeve and the outer sleeve. The inner sleeve is more deformable than the outer sleeve, such that in use, when a fluid is applied into the annular void creating pressure in the annular void, the inner sleeve deforms onto and thereby grips a surface of rebars being joined by the rebar coupler.

Description

REBAR COUPLERThe present disclosure relates to rebar couplers and in particular, but not limited to, rebar couplers for connection of two co-linear rebars to create a single structurally continuous rebar.BACKGROUND

[0001] Rebar, also referred to as reinforcing bar, is typically used to reinforce concrete to improve the tensile strength of elements made of concrete when constructing buildings, factories, bridges, nuclear power plants and other structures. A variety of different materials are used to form rebar with the most common being carbon steel. Typically rebar has deformation patterns or ribs in the surface of the rebar to facilitate binding of rebar into concrete

[0002] Rebar is generally commercially available in a variety of fixed bar diameters and lengths. Thus rebar often has to be cut to particular lengths or joined to create longer lengths depending on construction requirements. Rebar is heavy and difficult to manoeuvre since the rebar is long and unwieldy.

[0003] The examples described herein are not limited to examples which solve problems mentioned in this background section.SUMMARY

[0004] Examples of preferred aspects and examples are as set out in the accompanying independent and dependent claims.

[0005] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0006] A first aspect of the disclosed technology is a rebar coupler comprising: an outer sleeve; an inner sleeve; and an annular void between the inner sleeve and the outer sleeve; wherein the inner sleeve is more deformable than the outer sleeve, such that in use, when a fluid is applied into the annular void creating pressure in the annular void, the inner sleeve deforms onto a surface of rebars being joined by the rebar coupler. The rebar coupler gives a full strength, non-slip connection of two co-linear rebars to create a single structurally continuous rebar. The rebar coupler is particularly useful for larger diameter rebar such as rebar of diameter greater than 25 millimetres because these types of rebar are especially heavy and unwieldy. The rebar coupler is able to cope well with real life tolerances between rebars because of the way the inner sleeve deforms onto the rebar surfaces. Because it is easy to insert rebar into the rebar coupler, the rebar coupler is operable in congested areas where access is poor which often happens on construction sites where cages and meshes of rebar are being constructed or installed. Also, becauseit is straightforward to apply fluid into the annular void using a flexible hose or injector mechanism the rebar coupler is easy to install in congested areas. Because the rebar coupler can be used to join ends of two rebar it is possible to move the coupling operation to a location outside of a rebar cage which facilitates construction efficiency.

[0007] Preferably the outer sleeve comprises an inlet, such that in use, the fluid is applied into the annual void via the inlet. In an example, the inlet is a hole in the outer sleeve, where the hole is sized and shaped to receive a nozzle of an injector mechanism. In another example, the inlet is at the base of a filling tube. In some cases the rebar coupler is manufactured with no inlet and end users use a drill to create the inlet or use a nozzle of an injector mechanism to create the inlet at the time of injecting the fluid.

[0008] Preferably the inner sleeve is sealed to the outer sleeve at a first end of the inner sleeve and the inner sleeve is sealed to the outer sleeve at a second end of the inner sleeve, optionally wherein a length of the outer sleeve extends beyond at least one of the first end or second end of the inner sleeve. In this way the annular void is sealed at each end of the rebar coupler so that fluid does not escape from the annular void onto the rebar. Since the annular void is sealed it is possible to increase pressure of the fluid within the annular void by applying pressure via the inlet in some cases. Wherein the outer sleeve extends beyond at least one of the first end or second end of the inner sleeve, an overlap is formed by the outer sleeve. Said overlap may be arranged to receive, for example, a threaded bar, and in such a way a bridging coupler may be formed. In some cases there is no seal between the inner sleeve and the outer sleeve created during manufacture of the rebar coupler, or a seal between the inner and outer sleeve at only one end of the rebar coupler. The fluid itself acts as a seal in some cases where the fluid hardens on contact with air at the ends of the rebar coupler, or hardens first at the ends of the rebar coupler since the fluid in that region has been dispensed longest. Fluid in regions of the annular void closer to the inlet may harden last.

[0009] Preferably the product of the thickness and strength of the outer sleeve is greater than the product of thickness and strength of the inner sleeve. In this way the outer sleeve is able to carry the forces in the rebar from one side to the other. Because the product of the thickness and strength of the outer sleeve is greater than the product of thickness and strength of the inner sleeve, the outer sleeve is able to resist high pressures applied via the fluid in the annular void without plastic deformation whilst the inner sleeve is able to sustain high deformation under the same pressure. The inner sleeve is soft enough to shape around ribs on the rebars and strong enough to act as a bridge between the outer sleeve and the rebar without bursting.

[0010] Preferably the fluid is one or more of: a fluid that sets over time to form a solid with high compression strength, a fluid that expands in volume when it sets over time to form a solid, a pozzolanic grout, a polymer micro-concrete. Where the fluid expands in volumewhen it sets to form a solid, the expansion in volume causes increase of pressure in the annular void and causes the inner sleeve to deform onto the rebar surfaces. Using a fluid that sets over time to form a solid with high compression strength facilitates joining rebars so as to form a full strength connection of two approximately co-linear rebars. A full strength connection refers to a connection between rebars which is of the same strength as a rebar manufactured as a single rebar. Further, the stiffness of said full strength connection is comparable to the stiffness of a single piece bar. In other words, under the same load, the full strength connection will deform to the same extent as a single piece bar.

[0011] Preferably the rebar coupler comprises a filling tube attached to the inlet, and wherein the filling tube is configured to be closed off after fluid is applied to the annular void, such that the fluid is prevented from flowing back out of the filling tube and the fluid cures under pressure. The filling tube may be closed off by deforming the filling tube. Having a filling tube facilitates inserting the fluid into the annular void since the filling tube is easy to locate (even in congested areas of a construction site) as it protrudes from the outer sleeve. A tube of a fluid dispenser may be easily attached to the filling tube. The filling tube also provides a convenient way to seal the inlet by deforming the filling tube so as to seal the fluid within the annular void. Further, wherein said fluid expands during the curing process, by curing the fluid under pressure pre-stresses are introduced in to the system.

[0012] Preferably the rebar coupler comprises a loose spacer with a diameter similar to an internal diameter of the inner sleeve. The spacer is positioned between the ends of the rebar to fill any gap between the rebar ends and prevent the inner sleeve deforming into the gap risking failure of the inner sleeve’s fluid retention capability.

[0013] Preferably the rebar coupler comprises a circumferential bevel on one or both ends of the outer sleeve to assist movement of the rebar coupler over a rebar inserted into the inner sleeve. In some examples the bevel is machined into the end of the outer sleeve.

[0014] Preferably the inner and outer sleeves are metal and in some cases, the inner sleeve is sealed to the outer sleeve at the first and second ends of the rebar coupler by welding. Using a ductile metal inner sleeve enables it to sustain high deformation. Strain hardening ductile steel is used in some cases to give high strength after deformation. Using a metal outer sleeve enables it to resist high pressures applied by the fluid.

[0015] In some examples the coupler comprises two annular voids formed by any of: dividing the annular void between the inner sleeve and the outer sleeve into two separate annular voids both between the inner sleeve and the outer sleeve; forming an annular void between the inner sleeve and the rebar, by adding seals between the inner sleeve and the rebar at the ends of the inner sleeve. This improves versatility of the rebar coupler.

[0016] In examples, where there is an annular void between the inner sleeve and the rebar, the coupler comprises another inlet to enable another fluid to be applied between the inner sleeve and the rebar at a first pressure, wherein the first pressure is lower than the pressure in the annular void between the inner sleeve and the outer sleeve. This arrangement improves strength since there is fluid both between the inner sleeve and the rebar and between the inner and outer sleeve.

[0017] In some examples, the inner sleeve is shorter than the outer sleeve and one end of the outer sleeve, without an inner sleeve, has a thread for screwed connection to a cooperating rebar. In this way a bridging coupler capable of being connected to an existing threaded coupler is formed.

[0018] According to another aspect there is a method of joining a first rebar to a second rebar comprising: sliding a rebar coupler onto one end of the first rebar, such that the first rebar is inserted into part of the rebar coupler leaving another end of the rebar coupler empty; inserting an end of the second rebar into the other end of the rebar coupler; applying a fluid into an annular void between an inner sleeve and an outer sleeve of the rebar coupler, where the inner sleeve is more deformable than the outer sleeve; allowing pressure to build in the annular void as a result of the fluid such that the inner sleeve deforms onto the ends of the first and second rebars within the rebar coupler. The method is straightforward to perform even in congested areas of a construction site since tolerances are accommodated by having the inner sleeve deform onto the rebar surfaces. Thus even where the rebar are not precisely aligned the method is workable. The method enables a single structurally continuous rebar to be formed from two co-linear rebars by forming a full strength, non-slip connection. The connection is non-slip because the inner sleeve deforms around ribs on surfaces of the rebars. The connection is full strength because of the ability of the rebar coupler to pass forces along the rebars and because of the presence of the fluid in the annular void adding strength.

[0019] Preferably pressure is allowed to build in the annular void as a result of one or more of: increase in volume of the fluid when the fluid sets, pressure applied to the fluid through an inlet and / or filling tube in the outer sleeve, pressure applied to the fluid through an inlet and / or filling tube in the outer sleeve during solidification of the fluid, pressure applied to the fluid through an inlet and / or filling tube and closing off the filling tube once the annular void is full of fluid. Using a fluid that increases in volume as the fluid sets is an efficient and effective way of creating sustained pressure in the annular void so that the inner sleeve deforms. In this case it is not essential to seal the inlet since, after insertion is complete, the fluid sets and becomes a solid which itself seals the inlet. Where pressure is applied to the fluid through the inlet and / or filling tube it is possible to have a measurable way of recording the applied pressure so as to have a quality control record.Where pressure is applied to the fluid and that pressure is maintained by closing off the filling tube, there is an efficient sealing mechanism and a visible way to check the rebar coupler has been sealed.

[0020] In some examples the method comprises monitoring a volume of pressurised fluid being injected into the annular void and monitoring a pressure of said fluid to obtain a pressure-volume curve; comparing the pressure-volume curve with a reference pressure-volume; and stopping the injection of the fluid according to the comparison meeting a threshold. This method gives high accuracy of forming the join between the rebars. The method gives pressure volume-curves and comparison data which can be recorded for quality assurance. For example, the pressure-volume curve for a given coupler size or type is considered to be a signature. A digital program may be used to compare the signature of a given coupler with that of a large sample of the same coupler size or type and, in doing so, provide quality assurance that the coupler has been made up correctly.

[0021] In various examples the method comprises adding a spacer between the ends of the rebars in the rebar coupler, wherein the spacer prevents deformation of the inner sleeve into the gap between the two rebars and promotes integrity of the inner sleeve. The spacer may, for example, be metal or grout. Wherein the spacer is a grout spacer, said grout is allowed to cure prior to the fluid being injected.

[0022] In some examples, low pressure seals are applied at each end of the inner sleeve, creating a second annular void between the rebar and the inner sleeve (as opposed to between the inner sleeve and the outer sleeve as for the first annular void). The second annular void is filled with grout, optionally rapid setting grout. Once set, a high pressure fluid is applied between the inner and outer sleeves, creating a prestress in the system. The high pressure fluid may also be grout. A setting time may be required between the application of the grout in the second annular void and the application of the high pressure fluid in the first annular void. Said setting time may be at least 24 hours. To fill the second annular void, between the rebar and the inner sleeve, there is another inlet or filling tube. The seal or weld between the inner sleeve and the outer sleeve is moved in board (towards the centre of the coupler) a little, and an inlet or filling tube located between an outer sleeve to rebar seal and the outer sleeve to inner sleeve seal. In a variant (such as that of FIG. 8B below) where there are two separate annular voids, both between the outer sleeve and the inner sleeve, the additional inlet or filling tube is in a centre of the coupler so that it does not pass through the two separate annular voids (giving three filling tubes in total).

[0023] It will also be apparent to anyone of ordinary skill in the art, that some of the preferred features indicated above as preferable in the context of one of the aspects of the disclosed technology indicated may replace one or more preferred features of otherones of the preferred aspects of the disclosed technology. Such apparent combinations are not explicitly listed above under each such possible additional aspect for the sake of conciseness.

[0024] Other examples will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the disclosed technology.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1A is a perspective view of a rebar coupler;

[0026] FIG. 1B shows a rebar coupler with a first rebar inserted and with a second rebar being inserted;

[0027] FIG. 2A shows a rebar coupler with a first rebar inserted and with a spacer and a second rebar being inserted;

[0028] FIG. 2B shows a first and second rebar joined using a rebar coupler;

[0029] FIG. 2C is a cross section through the arrangement of FIG. 2B along a longitudinal axis of the rebar coupler;

[0030] FIG. 3 is a cross section of a rebar coupler which illustrates an example of sealing both ends of the rebar coupler;

[0031] FIG. 4A is a cross section through a first and second rebar and a rebar coupler, where the first rebar is inserted into the rebar coupler;

[0032] FIG. 4B is a cross section through a first and second rebar which are inserted into a rebar coupler and before a fluid is applied;

[0033] FIG. 4G shows the arrangement of FIG. 3B after fluid is applied into an annular void of the rebar coupler;

[0034] FIG. 5A is a perspective view of a rebar coupler with half of the rebar coupler cut away along a longitudinal axis of the rebar coupler;

[0035] FIG. 5B is a cross section through a rebar coupler along a longitudinal axis of the rebar coupler;

[0036] FIG. 6A is a perspective view of a rebar coupler joining a first and a second rebar, shown in cross section along a longitudinal axis of the coupler, and where a fluid has not been applied in an annular void of the rebar coupler;

[0037] FIG. 6B is a perspective view of the arrangement of FIG. 5A and where a fluid has been applied in the annular void of the rebar coupler;

[0038] FIG. 7A is an elevation view of a rebar coupler joining a first and a second rebar, shown in cross section along a longitudinal axis of the coupler, and where a fluid has not been applied in an annular void of the rebar coupler;

[0039] FIG. 7B is the arrangement of FIG. 6A and where a fluid has been applied in the annular void of the rebar coupler;

[0040] FIG. 8A is cross section, along a longitudinal axis of a rebar coupler, joining a first and a second rebar;

[0041] FIG. 8B is cross section, along a longitudinal axis of a rebar coupler that has two filling tubes, and a second rebar coupler;

[0042] FIG. 8C is a cross section, along a longitudinal axis of a rebar coupler that has two filling tubes;

[0043] FIG. 9A is a cross section, along a longitudinal axis of a rebar coupler that has two filling tubes;

[0044] FIG. 9B is a cross section, along a longitudinal axis of a rebar coupler that has three filling tubes;

[0045] FIG. 10A is perspective view of a rebar coupler joining a first and a second rebar;

[0046] FIG. 10B is an elevation of a rebar coupler joining a first and a second rebar;

[0047] FIG. 11 is a flow diagram of a method of joining a first and a second rebar using a rebar coupler.

[0048] The accompanying drawings illustrate various examples. The skilled person will appreciate that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the drawings represent one example of the boundaries. It may be that in some examples, one element may be designed as multiple elements or that multiple elements may be designed as one element. Common reference numerals are used throughout the figures, where appropriate, to indicate similar features.DETAILED DESCRIPTION

[0049] The following description is made for the purpose of illustrating the general principles of the present technology and is not meant to limit the inventive concepts claimed herein. As will be apparent to anyone of ordinary skill in the art, one or more or all of the particular features described herein in the context of one embodiment are also present in some other embodiment(s) and / or can be used in combination with other described features in various possible combinations and permutations in some other embodiment(s).

[0050] Rebar coupler function is more than just strength. Rebar couplers also need to be as stiff as a continuous bar. In particular, rebar couplers should not extend inelastically by more than about 0.1mm when subject to load-unload cycles. This can be a challenge to achieve. In threaded connections either the rebar coupler is made to exacting tolerances (which is expensive and error prone), or threads are pre-loaded to reduce slip.

[0051] In general, a single, isolated rebar can be connected to another rebar using a rebar coupler. However, for large structures, it is desirable to make rebar arrays (2D) or cages (3D) off site and join them together once they have been transported and placed in-situ. This results in the connection of multiple rebars that are parts of large and adjacent assemblies. The inventors have recognized the following challenges:

[0052] rebars are to align axially so they can be joined but this is difficult to achieve in practice;

[0053] rebars cannot easily be rotated or moved axially and therefore a rebar coupler is to be able to cope with this as far as possible;

[0054] in large rebar cages multiple layers of rebar greatly restrict access to the lower layers and so it is difficult to make rebar connections to rebar in the lower layers;

[0055] the spacing of rebars often prevents the use of large diameter rebar couplers.

[0056] One approach is to use a bridging coupler comprising a female coupler, a bridging stud assembly and a male coupler as well as a bridging nut, bridging stud and lock nut. This type of bridging coupler is complex as it involves several separate components. Access for satisfactory tightening of these types of bridging coupler remains a challenge. With multiple precision components, the bridging coupler is relatively expensive.

[0057] Another challenge of rebar connection is that the rebar often need loading into a special tool to put a connection feature on the end. For large structures rebars can be heavy; consider a 12 metre length of rebar with diameter 40 millimetres which weighs over 120 kilograms. Adding additional movement activities into the rebar process is not trivial and increases cost.

[0058] The inventors have developed a one piece rebar coupler which is simple to use and results in full strength, non-slip connections. The rebar coupler is suitable for use with large diameter rebar such as rebar diameters over 25 millimetres but this is not essential. Rebars of diameter of less than 25 millimetres may be preferable in some instances. For example, wherein an automated manufacturing method is employed smaller diameter variants may be more economic. The rebar coupler is compact thus saving space which is beneficial where rebar are to be placed close together, such as for creating structures with very high levels of reinforcement. The rebar coupler is cylindrical and comprises an outer sleeve and an inner sleeve. Between the outer and inner sleeve is an annular void which receives fluid. Pressure is created using the fluid and causes the inner sleeve to deform around surfaces of rebar within the rebar coupler.

[0059] FIG. 1A is a perspective view of a rebar coupler 100 showing the generally cylindrical form of the rebar coupler 100 as well as showing an outer sleeve 106, an inner sleeve 104 and a seal 102. The seal 102 is circumferential in that it seals a circumference of the inner sleeve to the outer sleeve, at one end of the inner sleeve. A similar circumferential seal is present at the other end of the inner sleeve in some examples. The rebar coupler 100 has an inlet 108 which is a hole in the outer sleeve 106 through which fluid can enter an annular void between the outer sleeve 106 and the inner sleeve 102. A filling tube 110 is attached to the inlet 108 in some examples. The filling tube protrudes from the outer sleeve 106. In the example of FIG. 1A the inlet 108 and filling tube 110 are approximately at a mid-point of the longitudinal axis of the rebar coupler since thisfacilitates even distribution of fluid within the annular void as explained in more detail later in the document. In other examples there is more than one inlet 108 and more than one filling tube.

[0060] FIG. 1 B shows a rebar coupler 100 such as that of FIG. 1A with a first rebar 112 inserted and with a second rebar 114 being inserted. In FIG. 1 B the first rebar 112 is inserted part way into the rebar coupler so that the first rebar is within part of the inner sleeve of the rebar coupler. The second rebar 114 is about to be inserted into the other end of the inner sleeve of the rebar coupler. As shown in FIG. 1 B the first rebar 112 and the second rebar 114 are ribbed. In various examples, the inner sleeve internal diameter is chosen to pass over the largest standard rebar. This typically has a diameter 15% larger than the nominal diameter of the rebar, thus a 32bar has an inner sleeve diameter of about 37mm and a 40mm rebar an inner sleeve diameter of about 46mm.

[0061] FIG. 2A shows a rebar coupler (such as that of the earlier figures) with a first rebar 112 inserted and with a spacer 200 and a second rebar 114 being inserted. The first rebar 112 is inserted into a first end of an inner sleeve of the rebar coupler and is almost protruding from the second end of the inner sleeve. A spacer 200 which is a metal disc of generally the same diameter as the first rebar 112 is being inserted into the inner sleeve such that it abuts the first rebar 112. The second rebar is being offered up to the inner sleeve. The second rebar has no special preparation other than to remove burrs that may block the rebar coupler being slid over. The second rebar is inserted into the second end of the inner sleeve so as to push the spacer 200 onto the end of the first rebar 112.

[0062] FIG. 2B shows a first and second rebar joined using a rebar coupler such as that of the earlier figures. A mark 202 is applied to the first rebar 112 at a specified distance from one of its ends. A mark 202 is applied to the second rebar 114 at the same specified distance from one of its ends. The mark 202 may be a paint mark. When the first and second rebars are inserted into the rebar coupler inner sleeve, the marks 202 are used to indicate when to stop inserting. The specified distance may be about half the length of the rebar coupler. In some examples a gap is left between the edge of the mark and an end of the inner sleeve. The rebar between the mark and the inner sleeve may be locally shaded. The rebar coupler is rotated about its longitudinal axis so that orientation of the filler tube is easy to connect to.

[0063] FIG. 2C is a cross section through the arrangement of FIG. 2B along a longitudinal axis of the rebar coupler. A first rebar 112 is inserted into an inner sleeve 104 of the rebar coupler and ribs of the first rebar are visible. The first rebar 112 is inserted approximately halfway into the inner sleeve 104 and a spacer 200 is placed at the end of the first rebar 112 within the inner sleeve 104. A second rebar 114 is inserted into the other end of the inner sleeve 104. A seal 102 is visible sealing the inner sleeve 104 to the outer sleeve 106 at the end of the inner sleeve near the second rebar 114. The other end of the innersleeve is not sealed to the outer sleeve. Fluid 204 is present between the inner sleeve 104 and the outer sleeve. Pressure of the fluid has caused the inner sleeve to deform against the surface of the first rebar 112 and the surface of the second rebar 114 thereby forming a non-slip connection between the first and second rebars. Curing of the fluid under pressure leaves compressive stresses in the fluid and, in doing so, imparts tensile capacity to the fluid. Once cured in this way, the fluid behaves similarly to an isotropic material of a tensile strength equivalent to the compressive stress created in the fluid. In other words, creating a pre-stress of, for example, 70MPa in the fluid via the described curing process, causes the cured fluid to behave similarly to an isotropic material having a tensile strength of 70MPa.

[0064] The inner sleeve material is selected for it’s ability to sustain high deformation. It is preferably soft enough to shape around the rebar ribs, yet strong enough to act as a bridge between the outer sleeve and the rebar without bursting. Note that most of the highly ductile steels strain harden, providing significant strength. The inner sleeve thickness is preferably as thin as it is possible to make it whilst reliably retaining the fluid under pressure.

[0065] Where rebars have a gap between their ends, the inner sleeve may have a tendency to deform into it. This risks failure of the inner sleeve’s fluid retention capability. A disk the diameter of the rebar is inserted into the gap. The disk thickness is selected so that any gaps are less than about 4mm.

[0066] The outer sleeve may have as small a diameter as practical. A nominal upper bound limit which generally keeps the rebar coupler compact enough not to create clash issues and to keep fire cover in check is about 1.75x the nominal bar diameter.

[0067] The outer sleeve acts to resist the high pressures applied via the fluid. The elastic expansion of the outer sleeve caused by the fluid pressure is locked in such that the fluid is always under prestress. This increases the effective strength of the fluid.

[0068] The outer sleeve material is a high strength steel in some cases. Depending on the manufacturing route, the outer sleeve may have a smooth internal surface. In order to enhance the transfer of force between the fluid and the outer sleeve, it is possible to increase the surface roughness by machining a fine thread to the inside surface of the sleeve. Other mechanical roughening options may be available.

[0069] The inside diameter of the inner sleeve may be increased in order to accommodate poor alignment tolerances. If it is increased, then the thickness of the inner sleeve may need to be increased so it is strong enough to bridge the annular void gap.

[0070] FIG. 3 is a cross section of a rebar coupler 100 which illustrates an example of sealing both ends of the rebar coupler 100. The rebar is absent so that the centre of the rebar coupler is empty. The outer sleeve 106 is visible as well as inner sleeve 104 and an annular void 400 between the inner sleeve 104 and outer sleeve 106 is very narrow inthis example and is just visible in FIG. 3. In this example, each end of the inner sleeve 104 extends beyond a respective end of an outer sleeve 106. The protruding ends of the inner sleeve 104 are each bent to form a cone that flares away from the rebar coupler. In the cross-sectional view this is shown as an acute angle formed between each end of the inner sleeve 104 and the respective end of the outer sleeve 106. In such a way, a V- shaped gap is formed between the inner sleeve 104 and the outer sleeve 106 at each end of the rebar coupler 100. A weld or seal 116 is applied to each V-shaped gap. As described above, fluid is applied via a filling tube 110 to an annular void 400 between the inner and outer sleeves. In combination, the welds 116 or seals prevent the fluid from exiting the annular void 400 at the ends of the rebar coupler. In such a way, pressure is built up between the inner and outer sleeve, causing the inner sleeve 104 to deform. This example of welding or sealing the ends of the rebar coupler can be applied to any of the rebar couplers described herein. In particular, the inner sleeve 104 described in relation to this example can be two inner sleeves arranged side by side wherein one end of each inner sleeve extends beyond an end of the outer sleeve.

[0071] A process of joining two rebar using a rebar coupler according to an example is now given with reference to FIGs. 4A to43C.

[0072] FIG. 4A is a cross section through a first and second rebar and a rebar coupler, where the first rebar 112 is inserted into the rebar coupler. The rebar coupler has an inner sleeve 104 and an outer sleeve 106 as well as a filling tube 110 in this example. The first rebar 112 is inserted into the inner sleeve until it begins to protrude from the other end of the inner sleeve. Gap 300 is present between the ends of the first and second rebars. The second rebar 114 has a mark 202 spaced from its end by a distance approximately half the length of the rebar coupler. The mark 202 helps centralisation of the rebar coupler.

[0073] FIG. 4B is a cross section through the first and second rebar which are inserted into the rebar coupler and before a fluid is applied. If there is a gap of more than about 4 millimetres between the first and second rebar ends a spacer is used. The spacer 200 fills gap 300 between the first and second rebar. Marks 200 on the first and second rebar are visible and generally align with ends of the inner sleeve.

[0074] FIG. 4G shows the arrangement of FIG. 4B after fluid 204 is applied into an annular void of the rebar coupler, between the inner sleeve 104 and the outer sleeve 106. The fluid enters through the filling tube in this example. In an example the filling tube is connected to a source of fluid. The annular void is filled with fluid under high pressure. Pressure is applied up to the capacity of the outer sleeve. In some examples the fluid cures under pressure. In an example a pump is used to pump fluid into the annular void via the filling tube and inlet. The pump may be a standard 700bar high pressure pump. . When the filling operation is complete, the filling tube is sealed. The pump is then disconnected and attached to the next rebar coupler. The pressure and volume of fluiddelivered by the pump is monitored. The pressure-volume curve produced is an indication of satisfactory filling and acts an a quality assurance measure. To give the reader an idea of the level of pressure used please consider the pressure on the tyre of a motor vehicle which is typically around 2bar; thus 700bar is hundreds of multiples of the amount of pressure in a domestic vehicle tyre. By way of further example, a pressure of 700bar is equivalent to the pressure at the deepest point of the Indian Ocean (around 7450m).

[0075] FIG. 5A is a perspective view of a rebar coupler with half of the rebar coupler cut away along a longitudinal axis of the rebar coupler. Outer sleeve 106 is visible as well as inner sleeve 104.

[0076] FIG. 5B is a cross section through a rebar coupler (such as that of FIG. 4A) along a longitudinal axis of the rebar coupler. In this example filling tube 110 is visible as well as outer sleeve 106, annular void 400 (which is between the inner sleeve and the outer sleeve), and seal 102 is also shown.

[0077] FIG. 6A is a perspective view of a rebar coupler joining a first and a second rebar, shown in cross section along a longitudinal axis of the coupler, and where a fluid has not been applied in an annular void of the rebar coupler. FIG. 6A shows outer sleeve 106, inner sleeve 104 and spacer 200. There is a gap between the rebar surfaces and the inner sleeve 104.

[0078] FIG. 6B is a perspective view of the arrangement of FIG. 6A and where a fluid has been applied in the annular void of the rebar coupler. In this case there is no gap between the rebar surfaces and the inner sleeve 106 since pressure in the annular void caused by the fluid has led to deformation of the inner sleeve around the rebar surfaces.

[0079] FIG. 7A is an elevation view of a rebar coupler joining a first and a second rebar 112, 114, shown in cross section along a longitudinal axis of the coupler, and where a fluid has not been applied in an annular void 400 of the rebar coupler. Outer sleeve 106 and inner sleeve 104 of the rebar coupler are visible as well as filling tube 110 and seal 102.

[0080] FIG. 7B is the arrangement of FIG. 7A and where a fluid 204 has been applied in the annular void of the rebar coupler. In the example of FIG. 7A the inner sleeve 104 has deformed around the surfaces of the rebar 112, 114.

[0081] FIG. 8A is cross section, along a longitudinal axis of a rebar coupler, joining dissimilar bars; in this case a threaded bar 710 and second rebar 114. In this example there is a gap 300 between the end of the threaded bar 710 within the inner sleeve and the end of the second rebar 114 within the inner sleeve. Fluid 204 has been applied between the outer sleeve 106 and the inner sleeve so the inner sleeve deforms against the surfaces of the threaded bar 710 and the second rebar 114. FIG. 8A demonstrates the versatility of the rebar coupler in being able to join dissimilar bars such as rebar and threaded bar. The rebar coupler will grip a range of bar types. Due to the prestress in the fluid, the rebar coupler has the capability of gripping a plain bar via friction. With a frictioncoefficient between inner sleeve and rebar of 0.5, a connector lapping 3x diameter on a 32diameter rebar will hold approximately 270kN, a bar tensile stress of 336MPa. If the rebar is threaded, e.g., for attachment to an adjacent coupler, then there will be a mechanical interlock. It can be seen that, subject to testing, the rebar coupler offers a wide range of possibilities for connecting to bars of different types. This includes connection to Basalt reinforcement, or with an appropriate collet system, connection to cable systems.

[0082] FIG. 8B is cross section, along a longitudinal axis of a rebar coupler that has two annular voids and optionally two inlets with filling tubes 110, 702, and is used together with a threaded coupler 708. The rebar coupler receives one end of a threaded bar 710 and a first one of the filling tubes 702 and annular voids is used to apply fluid to a first inner sleeve of the rebar coupler. The first inner sleeve deforms against the end of the threaded bar 710. The other end of the threaded bar is threaded into a threaded coupler 708 which itself has another threaded bar 700 in its other end. The rebar coupler receives another rebar (referred to as second rebar 114 in the examples herein) and gap 300 exists between the end of the second rebar 114 and an end of the threaded bar 710. Fluid is applied into filling tube 110 to make a second inner sleeve of the rebar coupler deform onto the second rebar surface. In the example of FIG. 8B this deformation has not yet happened. FIG. 8B demonstrates versatility of the rebar coupler by separating the inner sleeve into more than one inner sleeve. Separating the inner sleeve into more than one inner sleeve enables independent control of deformation of the inner sleeves. Rebar couplers may be needed to connect at each end at different times. A two annular void solution provides this capability as illustrated in FIG. 8B. Each end operates as described with reference to FIG. 1A. The body length may be adjusted to suit the applications. Subject to the chosen weld method between inner and outer sleeve, it may be possible to make the rebar coupler in two halves. These can be welded together to create a single part.

[0083] FIG. 8C is a cross section, along a longitudinal axis of a rebar coupler that has two filling tubes and where the inner sleeve is divided into two inner sleeves by adding circumferential seals. In this example there are two annular voids, each shown filled with fluid. The use of two annular voids removes the need for a spacer between the rebar being joined. Having two annular voids (or two inner sleeves) is generally more tolerance tolerant since the amount of deformation of one of the inner sleeves may be different from the amount of deformation of the other inner sleeve. .

[0084] FIG. 9A is a cross section, along a longitudinal axis of a rebar coupler that has two filling tubes 110, 702. FIG. 9A shows a rebar coupler with two annular voids which has been manufactured by welding together (at welds 804) two rebar couplers that have only one annular void each. The arrangement can be extended by welding more rebar couplers together in series. A gap 300 between the rebar exists.

[0085] With a two cavity solution a third inlet and / or filling tube can be used to fill any voids between the inner sleeve and the rebar. In some two cavity solution examples, fluid is applied via the third inlet between the inner sleeve and the rebar at a first pressure, and fluid is applied to the two annular voids (between the inner and outer sleeves) at a second, higher, pressure.

[0086] FIG. 9B is a cross section, along a longitudinal axis of a rebar coupler that has three filling tubes. FIG. 9B shows an example of a two cavity solution. An option to increase strength in the case of a rebar coupler with two annular voids (i.e. a two cavity solution), is to inject a second fluid 802 into the gap 300 between the rebars (rather than using a spacer). This is achieved using a third filling tube 800 as indicated in FIG. 9B.

[0087] FIG. 10A is perspective view of a rebar coupler 100 joining a first rebar 112 and a second rebar 114 and where the rebar coupler 100 has a filling tube 110.

[0088] FIG. 10B is an elevation of a rebar coupler 100 such as that of FIG. 10A joining a first rebar 112 and a second rebar 114.

[0089] FIG. 11 is a flow diagram of a method of joining a first and a second rebar using a rebar coupler.

[0090] Marks are optionally painted 1000 on ends of the rebar, spaced a specified distance from each rebar end.

[0091] A rebar coupler is slid 1002 partly onto the end of a first rebar.

[0092] Optionally a spacer or grout is inserted into an inner sleeve of the rebar coupler and abutting an end of the first rebar within the inner sleeve.

[0093] An end of a second rebar is inserted 1006 into the inner sleeve of the rebar coupler.

[0094] Optionally the outside diameter of the outer sleeve is measured diametrically before filling begins. The measurement increases in proportion to the hoop stress in the outer sleeve. In this manner the pressure in the rebar coupler can be confirmed at a later time. For accurate hoop stress estimating in a steel sleeve the measurement accuracy should be circa + / - 2microns. This is achievable with a good quality micrometer.

[0095] Fluid is applied 1008 into an annular void between an inner sleeve and an outer sleeve of the rebar coupler. The fluid is applied under pressure and / or creates pressure within the annular void. Optionally a measurement device is used to monitor a pressurevolume curve of the fluid. In some examples the fluid has a pozzolanic or polymer (e.g. epoxy) base. The fluid may have fillers. In some cases the fluid has generally zero shrinkage, or even an expansion characteristic on curing.

[0096] When fluid is pumped into the annular void, any air in the annular void may be trapped. Assuming manufacturing results in an average 0.2mm annular void, the volume of air trapped is approximately 8cc (40mm diameter). At 700bar, heat will be generated due to compression. The large surface area of the annular void will result in near instant cooling. This gives isothermal compression such that the volume will reduce by the ratioof the pressure (approximate). The net volume of the air reduces to 11 ,4mm3. Most of this will be pushed ahead of the fluid into a weld area of the rebar coupler. This zone is discounted in design, hence annular void air has no impact on strength.

[0097] The fluid is pressurised indirectly in some examples. Fluid is placed inside a flexible bag inside a pressure vessel. The bag is connected to pipes or tubes connecting with the filler tube on the rebar coupler. A pressure vessel is filled with oil and closed. Any air is removed. An oil cavity in the pressure vessel is connected to a high pressure oil supply. Applying pressure to the oil will transfer this pressure to the fluid which will flow through the tubing and into the connector.

[0098] The volume of fluid placed for each rebar coupler is relatively small. With minimum sensible grout mixing volumes being say 1 litre, the fluid is to remain fully pumpable for a period of circa 1 hour. Excessive cure time is undesirable since the rebar coupler has a degree of vulnerability to movement until the fluid has hardened.

[0099] An option to allow the fluid to have a long working time is to fill the annular void with an accelerator. The shearing action of the fluid as it flows mixes the accelerator into the fluid. With this process the fluid may be prepared off-site and supplied as a flowable paste. This process is well suited to polymer fluids.

[0100] The figures show a short filling tube. The use of longer tubing will permit the attachment point for the fluid filling operation to be moved to an accessible location. Whilst the tubing is quite stiff, at circa 6mm diameter it can be bent and manipulated as required.

[0101] As a result of the pressure of the fluid in the annular void, the inner sleeve deforms 1010 onto the rebar surfaces.

[0102] The fluid cures 1012 over time in some cases. In some cases an inlet through which the fluid was applied to the annular void is sealed 1014 so the fluid remains under pressure within the annular void.

[0103] The inlet is sealed 1012 by the solidification of the fluid or by a filling tube extending from the inlet being bent or flattened over the inlet.

[0104] The steps of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. The arrows between boxes in the figures show one example sequence of method steps but are not intended to exclude other sequences or the performance of multiple steps in parallel. Additionally, individual blocks may be deleted from any of the methods without departing from the spirit and scope of the subject matter described herein. Aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples without losing the effect sought. Where elements of the figures are shown connected by arrows, it will be appreciated that these arrows show just one example flow of communications (including data and control messages) between elements. The flow between elements may be in either direction or in both directions.

[0105] Where the description has explicitly disclosed in isolation some individual features, any apparent combination of two or more such features is considered also to be disclosed, to the extent that such features or combinations are apparent and capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

CLAIMS1. A rebar coupler comprising: an outer sleeve; an inner sleeve; and an annular void between the inner sleeve and the outer sleeve; wherein the inner sleeve is more deformable than the outer sleeve, such that in use, when a fluid is applied into the annular void creating pressure in the annular void, the inner sleeve deforms onto a surface of rebars being joined by the rebar coupler.

2. The rebar coupler of claim 1 wherein the outer sleeve comprises an inlet, such that in use, the fluid is applied into the annual void via the inlet.

3. The rebar coupler of claim 1 or claim 2 wherein the inner sleeve is sealed to the outer sleeve at a first end of the inner sleeve and the inner sleeve is sealed to the outer sleeve at a second end of the inner sleeve, optionally wherein a length of the outer sleeve extends beyond at least one of the first end or the second end of the inner sleeve.

4. The rebar coupler of any preceding claim wherein the product of the thickness and strength of the outer sleeve is greater than the product of thickness and strength of the inner sleeve.

5. The rebar coupler of any preceding claim wherein the fluid is one or more of: a fluid that sets over time to form a solid with high compression strength, a fluid that expands in volume when it sets over time to form a solid, a pozzolanic grout, a polymer micro-concrete.

6. The rebar coupler of any of claims 2 to 5, comprising a filling tube attached to the inlet, and wherein the filling tube is configured to be closed off after the fluid is applied to the annual void, such that the fluid is prevented from flowing back out of the filling tube and the fluid cures under pressure.

7. The rebar coupler of any preceding claim comprising a loose spacer with a diameter similar to an internal diameter of the inner sleeve.

8. The rebar coupler of any preceding claim wherein the inner and outer sleeves are metal and wherein the inner sleeve is sealed to the outer sleeve at the first and second ends of the rebar coupler by welding.

9. The rebar coupler of any preceding claim comprising two annular voids formed by any of: dividing the annular void between the inner sleeve and the outer sleeve into two separate annular voids both between the inner sleeve and the outer sleeve; forming an annular void between the inner sleeve and the rebar, by adding seals between the inner sleeve and the rebar at the ends of the inner sleeve.

10. The rebar coupler of claim 9 wherein, in the case where there is an annular void between the inner sleeve and the rebar, the coupler comprises another inlet to enable another fluid to be applied between the inner sleeve and the rebar at a first pressure, wherein the first pressure is lower than the pressure in the annular void between the inner sleeve and the outer sleeve.

11. The rebar coupler of any preceding claim where the inner sleeve is shorter than the outer sleeve and where one end of the outer sleeve, without an inner sleeve, has a thread for screwed connection to a cooperating rebar.

12. A method of joining a first rebar to a second rebar comprising: sliding a rebar coupler onto one end of the first rebar, such that the first rebar is inserted into part of the rebar coupler leaving another end of the rebar coupler empty; inserting an end of the second rebar into the other end of the rebar coupler; applying a fluid into an annular void between an inner sleeve and an outer sleeve of the rebar coupler, where the inner sleeve is more deformable than the outer sleeve; allowing pressure to build in the annular void as a result of the fluid such that the inner sleeve deforms onto the ends of the first and second rebars within the rebar coupler.

13. The method of claim 12 wherein pressure is allowed to build in the annular void as a result of one or more of: increase in volume of the fluid when the fluid sets, pressure applied to the fluid through an inlet and / or filling tube in the outer sleeve, pressure applied to the fluid through an inlet and / or filling tube in the outer sleeve during solidification of the fluid, pressure applied to the fluid through an inlet and / or filling tube and closing off the filling tube once the annular void is full of fluid.

14. The method of claim 12 or 13 comprising monitoring a volume of pressurised fluid being injected into the annular void and monitoring a pressure of said fluid to obtain a pressure-volume curve; comparing the pressure-volume curve with a reference pressure-volume; and stopping the injection of the fluid according to the comparison meeting a threshold.

15. The method of any of claims 12 to 14 comprising adding a spacer between the ends of the rebars in the rebar coupler, wherein the spacer is metal or grout.

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