NZ761099A - Coupler for threaded reinforcing bar - Google Patents

Abstract

Slippage is a concern in couplings for reinforcing bars. Disclosed herein is a coupler (10) for mounting to an externally threaded reinforcing bar for use in concrete construction. The coupler comprises a body having a portion with an internal thread (18,28) for engagement with a thread of the reinforcing bar. An outer flank of the thread form of the internal thread has a taper (24), which narrows towards an outer end of the coupler. The internal thread is asymmetric, whereby the outer flank of the internal thread slopes from a crest of the internal thread at a more acute angle to a longitudinal plane than an internal flank of the internal thread. This asymmetric thread causes rotation of the reinforcing bar in the coupler to wedge it in place if the end of the reinforcing bar is prevented from advancement by a stop. The stop may be provided by the end of another reinforcing bar, threaded in from the opposite end of the coupler, or an internal stop (32) inside the coupler.

Description

C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 COUPLER FOR THREADED REINFORCING BAR Field of the Invention The present invention relates to a coupler for threaded reinforcing bar as may be used in concrete construction.

Background to the Invention One form of reinforcing bar used in concrete construction incorporates a continuous coarse external thread. The thread not only acts to form a key between the bar and concrete, it also enables a range of supplementary fittings easily to be applied to the bar by engagement of a mating thread with that of the bar. One such threaded reinforcing bar is marketed under the trade mark "ReidBar" by the RamsetReid division of ITW Australia Pty Ltd, a related entity of the present applicants. As previously mentioned, the thread on the reinforcing bar is quite coarse and its pitch ranges from 8mm for a bar of 12mm diameter to around 16.5mm for a bar diameter of 32mm.

Internally threaded fittings for mounting over the end of threaded reinforcing bar for example for coupling lengths of bar in series tend, principally for cost considerations, to be of cast construction, cast iron predominantly, with the internal thread being formed during casting by a sand core. The internal thread formed in this way is not formed to the degree of accuracy which would be expected from a conventionally tapped thread and, moreover, the external thread on the bar itself is not formed to a particularly high degree of accuracy. A consequence of this is that there may not be a particularly tight engagement between the fitting and the bar and some slippage can occur between the bar and the fitting.

Slippage of a coupler on a threaded reinforcing bar can have serious consequences and relevant construction standards require that slip be limited to 0.1mm under a loading of 450 mPa using a 500 grade bar, which can be difficult to achieve as the coarse thread of C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 the reinforcing bar is typically formed to a tolerance of 0.5mm. While slippage can be avoided by filling the interior of the coupler with an epoxy cement or by mounting a lock nut on the bar to tighten against the end of the coupler, these measures add to the time and cost of installing the coupler to the bar. Other methods include machining metric threads & swaging sleeves onto the ends of the bar. These are even more time-consuming, complex and expensive due to the extra processes and equipment required. Accordingly, it is desirable to provide a coupler that can accommodate the loose tolerances of the reinforcing bar and minimise slip of the coupler along the reinforcing bar to within the required standard.

It has previously been proposed to provide a coupler manufactured using cast-iron, however due to the nature of the casting process, the internal thread was not formed with a high degree of accuracy. Moreover, the thread surface finish was rough and inconsistent and the hardness of the cast-iron was lower than the steel of the reinforcing bar. The thread profile of the coupler was changed for only the last two threads and, as such, there was minimal thread engagement. This led to the load from the bar being transferred to a small portion of these last threads, creating high stresses in this area. The result of these issues resulted in further embedment of the bar into the coupler’s threads during axial loading, creating greater slip than allowed by the construction standard.

The applicant has identified that it would be advantageous to provide a coupler which obviates or at least alleviates one or more disadvantages of existing reinforcing bar coupling systems.

Summary of the Invention In accordance with the present invention, there is provided a coupler for mounting to externally threaded reinforcing bar for use in concrete construction, the fitting comprising a body having a portion with an internal thread for engagement with the thread of the reinforcing bar, wherein a thread form of the internal thread has a taper which narrows toward an outer end of the fitting such that the thread of the reinforcing bar is C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 wedged into engagement with the taper as the thread of the reinforcing bar is driven outwardly relative to the internal thread of the fitting.

Preferably, the thread of the reinforcing bar is wedged into an interference fit engagement with the taper as the threaded reinforcing bar is moved outwardly relative to the fitting.

Preferably, each turn of the internal thread has said taper which narrows toward an outer end of the fitting such that each turn of the thread of the reinforcing bar within the fitting is wedged simultaneously as the threaded reinforcing bar is moved outwardly relative to the fitting.

In a preferred form, there is provided a coupler for coupling two threaded reinforcing bars in end to end relation, the coupler having respective internal threads extending inwardly from opposite ends and separated at their inner ends by an internal stop, the thread form of each internal thread having a taper which narrows toward an outer end of the internal thread.

Preferably, one end portion of the fitting has a first internal thread, a thread form of the first internal thread having a taper which narrows toward a first end of the fitting such that the thread of a first reinforcing bar is wedged into engagement with the taper as the first reinforcing bar is moved outwardly relative to the fitting, and wherein an opposite end portion of the fitting has a second internal thread, a thread form of the second internal thread having a taper which narrows toward a second end of the fitting, the second end of the fitting being opposite to the first end of the fitting, such that the thread of a second reinforcing bar is wedged into engagement with the taper as the second threaded reinforcing bar is moved outwardly relative to the fitting.

Preferably, for each threaded reinforcing bar, the thread of the reinforcing bar is driven outwardly relative to the internal thread of the fitting when the reinforcing bar is rotated in a first rotational direction such that an end of the reinforcing bar is driven into C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 abutment with said stop, and the reinforcing bar is subsequently rotated further in said first rotational direction while in contact with said stop.

More preferably, for each threaded reinforcing bar, the thread of the reinforcing bar is driven outwardly relative to the internal thread of the fitting when the reinforcing bar is rotated in a first rotational direction such that an end of the reinforcing bar is driven into abutment with said stop, and the reinforcing bar is subsequently rotated through one eighth of a turn in said first rotational direction while in contact with said stop.

Preferably, the stop is in a central portion of the fitting.

In a preferred form, there is provided a coupler for coupling two threaded reinforcing bars in end to end relation, the coupler having respective internal threads extending inwardly from opposite ends, wherein the fitting is arranged such that when the two threaded reinforcing bars are rotationally driven inwardly of the fitting to be in direct end-to-end abutment within the fitting, further relative rotation of the threaded reinforcing bars in abutment causes the threads of reinforcing bars to become wedged into engagement with the tapers of the respective internal threads.

Preferably, the interference fit engagement is continuous along the length of the thread of the reinforcing bar inside the internal thread.

Preferably, the internal thread is asymmetric whereby an outer flank of the internal thread slopes from a crest of the thread at a more acute angle to a longitudinal plane than an inner flank of the internal thread.

In a preferred form, an outer surface of the fitting is provided with opposed flat surfaces to facilitate with engagement by a tool for rotating the fitting relative to the reinforcing bar. More preferably, an outer surface of the fitting is formed in a hexagonal shape to facilitate with engagement by a tool for rotating the fitting relative to the reinforcing bar.

C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 Preferably, the fitting is formed of a material having a greater hardness than the reinforcing bar.

It is preferred that the taper provides a void for accommodating material displaced during tightening.

Brief Description of the Drawings Preferred embodiments of the invention will be described, by way of non-limiting example only, with reference to the accompanying drawings in which: Figure 1 is a cutaway view of a coupler in accordance with an example of the present invention; Figure 2 is a cutaway view of the coupler shown joining ends of adjacent threaded reinforcing bars; Figure 3 is a detailed view of a central portion of the cutaway view of Figure 2; Figure 4 is a perspective view of the coupler of Figure 1, shown coupling two reinforcing bars; and Figure 5 is a side view of the coupler.

Detailed Description With reference to Figures 1 to 5, there is shown a coupler 10 according to a preferred embodiment of the present invention. The coupler 10 is configured for joining ends of sections of threaded reinforcing bar 12, 14 in end-to-end relation. Advantageously, the coupler 10 is convenient to use in that it does not require modification of the C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 reinforcing bars 12, 14, while providing a secure join with distributed forces and meeting or exceeding slip requirements.

More specifically, as shown in Figures 1 and 2, there is shown a coupler 10 for mounting to externally threaded reinforcing bar 12 for use in concrete construction, the fitting 16 comprising a body having a portion with an internal thread 18 for engagement with the thread 20 of the reinforcing bar 12, wherein a thread form 22 of the internal thread 18 has a taper 24 (see Figure 3) which narrows toward an outer end 26 of the fitting 16 such that the thread 20 of the reinforcing bar 12 is wedged into engagement with the taper 24 as the thread 20 of the reinforcing bar 12 is driven outwardly relative to the internal thread 18 of the fitting 16.

As can be seen best in Figure 2 and Figure 3, the thread 20 of the reinforcing bar 12 is wedged into an interference fit engagement with the taper 24 as the thread 20 of the reinforcing bar 12 is driven outwardly relative to the internal thread 18 of the fitting 16.

Each turn of the internal thread 18 has said taper 24 which narrows toward the outer end 26 of the fitting 16 such that each turn of the thread 20 of the reinforcing bar 12 within the fitting 16 is wedged simultaneously as the thread 20 of the reinforcing bar 12 is driven outwardly relative to the internal thread 18 of the fitting 16.

In the preferred embodiment shown in the drawings, with particular reference to Figure 2, the coupler 10 is for coupling two threaded reinforcing bars 12, 14 in end-to-end relation, the coupler 10 having respective internal threads 18, 28 extending inwardly from opposite ends 26, 30 and separated at their inner ends by an internal stop 32. The thread form 22, 34 of each internal thread 18, 28 has a taper 24 which narrows toward an outer end 26, 30 of the respective internal thread 18, 28.

One end portion 36 of the fitting 16 has a first internal thread 18, a thread form 22 of the first internal thread 18 having a taper 24 which narrows toward a first end 26 of the fitting 16 such that the thread 20 of a first reinforcing bar 12 is wedged into engagement C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 with the taper 24 as the thread 20 of the first reinforcing bar 12 is moved outwardly relative to the internal thread 18 of the fitting 16. An opposite end portion 38 of the fitting 16 has a second internal thread 28, a thread form 34 of the second internal thread 28 having a taper 24 which narrows toward a second end 30 of the fitting 16, the second end 30 of the fitting 16 being opposite to the first end 26 of the fitting 16. The thread 40 of a second reinforcing bar 14 is wedged into engagement with the taper 24 as the thread 40 of the second threaded reinforcing bar 14 is moved outwardly relative to the internal thread 28 of the fitting 16.

For each threaded reinforcing bar 12, 14, the thread 20, 40 of the reinforcing bar 12, 14 is driven outwardly relative to the internal thread 18, 28 of the fitting 16 when the reinforcing bar 12, 14 is rotated in a first rotational direction (for example, clockwise when viewed from an outer end of the respective bar 12, 14) such that a forward end 42, 44 of the reinforcing bar 12, 14 is driven into abutment with said stop 32 (see Figure 2), and the reinforcing bar 12, 14 is subsequently rotated further in said first rotational direction while in contact with said stop 32.

In one example, the coupler 10 may be arranged such that said subsequent rotation to cause the interference fit is a rotation of the bar 12, 14 relative to the coupler 10 through one eighth of a turn in said first rotational direction while in contact with said stop 32. The stop 32 may be in a central portion of the fitting 16.

Alternatively, in another example not shown, the stop 32 may be omitted such that the bars 12, 14 abut in direct end-to-end contact. That is, the fitting 16 may be arranged such that when the two threaded reinforcing bars 12, 14 are rotationally driven inwardly of the fitting 16 to be in direct end-to-end abutment within the fitting 16, further relative rotation of the threaded reinforcing bars 12, 14 in abutment causes the threads 20, 40 of the reinforcing bars 12, 14 to become wedged into engagement with the tapers 24 of the respective internal threads 18, 28.

The coupler 10 may be arranged such that the interference fit engagement is C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 continuous along the length of the thread 20, 40 of the reinforcing bar 12, 14 inside the internal thread 18, 28. The internal thread 18, 28 may be asymmetric (see detail of Figure 3) whereby an outer flank 46 of the internal thread 18, 28 slopes from a crest 48 of the thread 18, 28 at a more acute angle to a longitudinal plane than an inner flank 50 of the internal thread 18, 28.

With reference to Figures 4 and 5, an outer surface of the fitting 16 may be provided with opposed flat surfaces 52 to facilitate with engagement by a tool (not shown) for rotating the fitting 16 relative to the reinforcing bar 12, 14. In the particular example shown, the outer surface of the fitting 16 is formed in a hexagonal shape 54 to facilitate with engagement by a tool (for example, a spanner or a wrench) for rotating the fitting 16 relative to the reinforcing bar 12, 14.

The fitting 16 may be formed of a material having a greater hardness than the reinforcing bar. Also, the taper 24 may provide a void 56 for accommodating material displaced during tightening.

Although the invention has been described with reference to a coupler for coupling two lengths of threaded reinforcing bar in end-to-end relation, it will be understood that the invention is applicable to a wide variety of internally threaded couplers for mounting on the end of the bar. By way of non-limiting example, the coupler may alternatively be in the form of a tubular insert internally threaded at one end portion as described above for engagement over the threaded reinforcing bar, and internally threaded at its other end portion with a standard thread for receiving a standard bolt or standard threaded bar, or it may be in the form of a grouter in which the other end portion of the fitting is of hollow construction which permits anchoring therein of bar by means of a cement composition.

Accordingly, the present design relates to a coupler for mounting to externally threaded reinforcing bar for use in concrete construction, the fitting comprising a body having a portion with an internal thread for engagement with the thread of the reinforcing bar. The coupler has a body in which ends of adjacent sections of reinforcing bars can be C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 received. The body has an internal thread formed therein and an internal stop or stand against which ends of the adjacent sections of reinforcing bar can abut. The coupler is formed with hexagonal formations to permit gripping by a spanner or wrench. The coupler is formed by a process of extrusion of high tensile steel with the internal threads being formed by machining. This tensile steel has a higher Ultimate Tensile Stress & Hardness rating than the reinforcement bar.

To minimise slippage of the bar and the fitting, the internal thread profile of the coupler is asymmetrical and does not match the thread profile of the corresponding reinforcing bar. The outer flank, i.e. the flank further from the stand, has a more acute angle than the inner flank and the flanks on the reinforcing bar.

When the bar is engaged in the coupler and tightened against the coupler’s stand, the crest of the thread of the bar will engage with this acute outer flank, creating frictional engagement between the outer flank of the coupler and the crest adjacent to the outer flank of the bar. This contact will be more like a line contact rather than a face contact. When this frictional engagement occurs, and the assembly is tightened further by torque, the crest will be pushed further into this ramp locking it in place and/or some material will be removed from the crest of the thread of the bar, increasing surface contact and/or allow for other threads along the bar to frictionally engage with the coupler’s outer flanks. This will prevent slippage or at least minimise slippage to within the required standard. With the contact initially being more like a line contact, this allows for a lower tightening torque to achieve these results.

As the internal thread within the coupler is machined from steel, the thread has a better surface finish and a higher hardness than the reinforcement bar. This minimises slippage due to embedment, which is common in other embodiments of couplers i.e. cast- iron couplers.

Another feature of the coupler’s thread profile is that due to ramping effect of the bar’s threads being pulled into the acute angled flanks, the bar centralises within the C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 coupler and minimises lateral movement of the bar. This minimises the assembly loosening due to vibration and/or dynamic load. Therefore, the coupler does not require extra locking devices.

The advantages of this coupler include that the coupler is easier to use, saves time, and reduces cost for the customer but still meets the slip performance criteria as set out by the relevant construction standards.

By utilizing the deformed rib on the bar to thread the connection, the bar ends do not have to be processed i.e. enlarged ends by cold working and/or threads machined by a customer. Therefore, the coupler does not require any specialist equipment for processing.

This makes the coupler cheaper, quicker and simpler for the customer.

As the deformed rib runs the full length of the bar, the customer can use the entire length of the bar. Waste is reduced and makes the system more adaptable than alternative options which do not use the coarse thread of the reinforcement bar.

The wedge of the female thread wears the crest of the threaded bar until sufficient surface area contacts between the female and male thread form. This creates mating load bearing surfaces and improves performance by reducing slip.

By mating on the outer rib of the male thread with the wedge-like flank, this centres the bar within the fitting and limits lateral movement. This improves performance by reducing slip.

Advantageously, the present coupler requires less torque than existing coarse thread couplers, resulting in the present coupler being easier and quicker to assemble for the customer.

The design eliminates the need for other locking devices e.g. lock nuts. This also facilitates the coupler being cheaper, quicker and simpler for the customer.

C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/01/2019 Free spinning of the bar until the bar hits the end stop enables the coupler to be assembled with the reinforcing bars easily by hand.

To be finally tightened, it just requires the use of a standard pipe wrench to apply the tightening torque. The coupler does not require any specialist tools reducing cost, time and complexity.

The embodiment has been described by way of example only and modifications are possible within the scope of the invention disclosed.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

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Claims (5)

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A coupler for mounting to externally threaded reinforcing bar for use in concrete construction, the fitting comprising a body having a portion with an internal thread for engagement with the thread of the reinforcing bar, wherein a thread form of the internal thread has a taper which narrows toward an outer end of the fitting such that the thread of the reinforcing bar is wedged into engagement with the taper as the thread of the reinforcing bar is driven outwardly relative to the internal thread of the fitting.

2. A coupler as claimed in claim 1, wherein the thread of the reinforcing bar is wedged into an interference fit engagement with the taper as the threaded reinforcing bar is moved outwardly relative to the fitting.

3. A coupler as claimed in claim 1 or claim 2, wherein each turn of the internal thread has said taper which narrows toward an outer end of the fitting such that each turn of the thread of the reinforcing bar within the fitting is wedged simultaneously as the threaded reinforcing bar is moved outwardly relative to the fitting.

4. A coupler according to any one of claims 1 to 3 for coupling two threaded reinforcing bars in end to end relation, the coupler having respective internal threads extending inwardly from opposite ends and separated at their inner ends by an internal stop, the thread form of each internal thread having a taper which narrows toward an outer end of the internal thread.

5. A coupler as claimed in claim 4, wherein one end portion of the fitting has a first internal thread, a thread form of the first internal thread having a taper which narrows toward a first end of the fitting such that the thread of a first reinforcing bar is wedged into engagement with the taper as the first reinforcing bar is moved outwardly relative to the fitting, and wherein an opposite end portion of the fitting has a second internal thread, a thread form of the second internal thread having a taper which narrows toward a second end of the fitting, the second end of the fitting being opposite to the first end of the fitting, C:\Interwoven\NRPortbl\DCC\EJL\18144378_1.docx-24/