AU2004247749A1

AU2004247749A1 - A coupler

Info

Publication number: AU2004247749A1
Application number: AU2004247749A
Authority: AU
Inventors: Paul Armstrong Berry; Russel Quentin Bridge; Mark Patrick
Original assignee: Infrabuild Construction Solutions Pty Ltd; Of Western Sydney, University of; University of Western Sydney
Current assignee: Infrabuild Construction Solutions Pty Ltd; University of Western Sydney
Priority date: 2003-06-13
Filing date: 2004-06-11
Publication date: 2004-12-23
Anticipated expiration: 2024-06-11

Description

WO 2004/111363 PCT/AU2004/000780 A COUPLER The present invention relates to a coupler for mechanically splicing together reinforcing bars. 5 The present invention also relates to a coupler for mechanically connecting a reinforcing bar to a rigid object, such as an anchored steel plate, to which the coupler is welded or otherwise secured. 10 It is often important to be able to mechanically splice together reinforcing bars in the field so that the bars can develop a large part or even their full axial capacity in either tension or compression. 15 Similarly, it is often important to be able to mechanically connect reinforcing bars to rigid objects, such as anchored steel plates, in the field so that the bars can develop a large part or even their full axial 20 capacity in either tension or compression. Internally threaded couplers, swaging, and pinning are known options for mechanically splicing together reinforcing bars and for mechanically connecting 25 reinforcing bars to fixed objects. Couplers may have a fine thread or a coarse thread. 30 Coarse threaded couplers are used in situations where the ribs or deformations of hot or cold rolled reinforcing bars form the bar thread - invariably, ribs or deformations form coarse threads on bars. 35 One problem with threaded couplers is that longitudinal slip of the reinforcing bars relative to a body of a coupler of the order of 0.3-0.5 mm or more can WO 2004/111363 PCT/AU2004/000780 -2 cause serviceability problems in the final structure. For example, excessively wide cracks can form locally in concrete surrounding couplers and the cracks can be unsightly or lead to premature corrosion of steel 5 reinforcing bars. In addition, if all or a significant proportionof the main reinforcing bars in a beam or slab are coupled at.a critical section of peak bending moment, then vertical deflections of these nuts may be significantly increased if the relative longitudinal slip 10 is excessive. Longitudinal slip is more pronounced generally and therefore is more of an issue with coarse-threaded couplers than with fine-threaded couplers under service 15 load conditions. Longitudinal slip up to 1 mm or more can occur in coarse threaded couplers. A common limit for fine threaded couplers is 0.1mm. US patent 6,328,499 in the name of Reding et al 20 (assigned to Ares S.A.) discloses a coupler that includes a coupler body in the form of an internally threaded sleeve that can receive the end sections of 2 externally threaded bars and a cotter or 3 part wedge assembly that can be inserted through openings in the coupler body and 25 apply oppositely directed axial forces to the ends of the bars and pre-load the ends of the bars and thereby limit longitudinal slip between the bars and the coupler. The Reding coupler has the following 30 disadvantages: 1. The net section of the coupler body is reduced by incorporating openings in the cotter. This limits the width of the wedges, which would ideally be as wide as the 35 reinforcing bars. It also complicates the design of the cotter. The US patent explains that ordinary narrow wedges deform the ends of the bars if they slide over the bar WO 2004/111363 PCT/AU2004/000780 -3 ends, which reduces the stress that can be transmitted into the bars. 2. The gross section of the coupler body must also 5 be increased as a consequence of providing the openings. 3. The bars must always be rotated, which is not always possible, e.g. with bars with cranked ends, i.e. the coupler can be used as a turnbuckle. 10 4. As described in the US patent, the ends of the bars must be positioned within a quarter of a turn of the cotter so that the cotter applies sufficient stress. This would be a tedious operation and difficult to repeat 15 reliably on site. 5. Two openings are provided at 90 degrees to each other to improve access, but this is still not guaranteed on a building site, depending on the situation, e.g. when 20 splicing closely-spaced bars in a column access is restricted to the outside of the column cage. 6. The US patent discloses that the cotter is hammered in. Access for this operation can be limited on 25 site. The cotter could also be pressed in, but again, access can be difficult, particularly for the end anchorage. The above reference to and discussion of the 30 Reding US patent is not to be taken as an admission that the coupler disclosed in the US patent is part of the common general knowledge in Australia or elsewhere. An object of the present invention is to provide 35 an alternative coupler to that disclosed in the Reding US patent that limits relative longitudinal slip between reinforcing bars (particularly coarse-threaded bars) and WO 2004/111363 PCT/AU2004/000780 -4 is not subject to at least some of the above-described disadvantages of the Reding coupler. According to the present invention there is 5 provided a coupler for a reinforcing bar having an external thread, the coupler including (a) an insert having an externally threaded shank and (b) a body having an internally threaded bore extending through the body, the body being adapted to receive the shank of the insert 10 via one end of the bore and to receive an end section of the reinforcing bar via an opposite end of the bore, whereby in use relative rotation of the insert and the body moves the ends of the shank and the reinforcing bar within the body axially into contact and applies an axial 15 force to the end of the reinforcing bar and thereby pre loads the reinforcing bar. With the above-described arrangement the pre-load applied to the reinforcing bar is applied via the insert, 20 and the friction interface between the bar and the shank has a low polar second moment of area, with the result that the required tightening torques are moderate and can be applied with standard spanners. 25 The present invention is based on the realisation that applying a direct axial force to the end of the reinforcing bar by means of the shank of the insert is an effective way of generating significant levels of pre-load on the bar and coupler threads that are necessary to 30 minimise longitudinal slip of the reinforcing bar relative to the body when the bar is loaded under service conditions in hardened concrete. In particular, the applicant has shown that it is 35 possible to generate significantly higher levels of pre load to a reinforcing bar by applying a direct axial force to an end of a reinforcing bar located in a coupler than WO 2004/111363 PCT/AU2004/000780 -5 can be achieved with known pre-loading methods, such as by rotating a reinforcing bar into a coupler against a reaction surface located in the coupler or by turning a locknut to pull a reinforcing bar from a coupler end. 5 The present invention avoids the disadvantage of known pre-loading methods, such as methods involving the use of locknuts, of inducing high torsional stresses in a reinforcing bar and thereby reducing the strength of the 10 bar or causing torsional failure of the bar. One known option for avoiding this disadvantage is to put a bar in tension first by using a specifically-designed hydraulic jack to grip the bar on each side of a coupler, thereafter engaging locknuts with the coupler ends, and then 15 releasing the force in the bar. However, this option of inducing large pre-loading is less practical than the present invention. Preferably the axial force i.e, the pre-loading 20 force, is at least equivalent to 200 MPa. More preferably the axial force is at least equivalent 300 MPa. 25 The amounts of 200-300 MPa are a significant proportion of the maximum tensile stresses that the reinforcing bars are likely to experience in normal service conditions. 30 The external thread of the shank of the insert may be a thread cut into the shank. Such threads are generally regarded as being "fine" threads. Typically, the fine thread has a pitch of 2-3mm. 35 The external thread of the reinforcing bar may be ribs or deformations on the bar. Such threads are generally regarded as being "coarse" threads. Typically, WO 2004/111363 PCT/AU2004/000780 -6 the coarse thread has a pitch of 10mm. Preferably the reinforcing bar has a coarse external thread and the shank of the insert has a 5 relatively fine thread. With this arrangement, the bore of the body has a complementary coarse thread in one section of the bore extending from one end of the body and a complementary 10 relatively fine thread in another section of the bore extending from the other end of the body. The transition between the coarse and fine threaded sections forms a stop for axial movement of the reinforcing bar and the shank of the insert in the body. 15 Preferably the external diameter of the shank of the insert is less than the internal diameter of the coarse-threaded section of the body so that the coarse threaded section does not interfere with axial movement of 20 the insert shank in situations in which the insert shank extends into this section of the body. Preferably the shank of the insert includes a formation that includes a series of angled faces that 25 enable the insert to be gripped by a spanner. The coupler is suitable for use in two applications in particular. It is noted that these are not the only two applications of the coupler. 30 In one application the coupler mechanically connects reinforcing bars to fixed objects, such as anchored steel plates. 35 In the other application, which is not the only other possible application, the coupler mechanically splices together two reinforcing bars. In this WO 2004/111363 PCT/AU2004/000780 -7 application, preferably the coupler includes two separate bodies, with each body having an internally threaded bore extending through the body, and the insert includes a central element and two externally threaded shanks 5 extending in opposite directions from the central element, with each body being adapted to receive one of the shanks of the insert via one end of the bore and to receive an end section of one of the reinforcing bars via an opposite end of the bore, whereby relative rotation of the insert 10 and the bodies moves the ends of each pair of the shanks and the reinforcing bars axially into contact and applies oppositely directed axial forces to the ends of the reinforcing bars and thereby pre-loads the reinforcing bars. 15 Preferably each body includes a coarse thread in one section of the bore extending from one end of the body and a relatively fine thread in another section of the bore extending from the other end of the body. 20 Preferably the shanks of the insert have the same thread as the fine-threaded section of the bodies. The threads on each shank of the insert may be 25 the same hand or opposite hands when the insert is viewed from a side of the insert. When the threads of the shanks of the insert are opposite hands when viewed in side elevation, the insert 30 can function as a turnbuckle. Specifically, with the bodies assembled onto the ends of coaxially aligned reinforcing bars, and the insert positioned so that each shank of the insert is engaged with one of the bar/body assemblies, rotation of the insert about its lengthwise 35 extending axis pulls the bar/body assemblies toward each other without requiring rotation of the bars about their lengthwise extending axes and facilitates applying a WO 2004/111363 PCT/AU2004/000780 -8 required pre-load to each bar. Preferably the central element of the insert is formed as a nut that has angled faces so that the nut can 5 be gripped by a spanner. Preferably the reinforcing bars have a diameter of at least 10 mm. 10 Preferably the yield stress of the reinforcing bars is at least 400 MPa. More preferably the yield stress of the reinforcing bars is at least 500 MPa. 15 The present invention is described further by way of example with reference to the accompanying drawings, of which; 20 Figure 1 is a diagrammatic cross-section of one embodiment of a coupler in accordance with the present invention for mechanically splicing together two reinforcing bars in end-to-end relationship; 25 Figure 2 is a free body diagram that illustrates the force transfer on one side of the coupler shown in Figure 1; and Figures 3 to 5 are diagrammatic cross-sections of 30 other embodiments of the coupler in accordance with the present invention for mechanically connecting a reinforcing bar to a rigid object. The coupler shown in Figure 1 is suitable for 35 mechanically connecting two externally threaded reinforcing bars 17.

WO 2004/111363 PCT/AU2004/000780 -9 The coupler includes a body in the form of two sleeves 3 having internally-threaded bores 5 and an insert 9 having a central nut 11 and two axially-aligned externally threaded shanks 13. 5 Each sleeve 3 of the body has a first threaded section extending from one end of the bore that has the same thread as the thread of the reinforcing bars 17 and a second threaded section extending from the other end of 10 the bore that has the same thread as the thread of the shanks 13 of the insert 9. Typically, the reinforcing bars 17 have a thread that is relatively coarse compared to that of the shanks 13 of the insert 9. 15 The central nut 11 of the insert 9 has a series of angled faces that enable the nut 11 to be gripped by a spanner. In use, two reinforcing bars 17 are mechanically 20 spliced together as shown in Figure 1 by firstly rotating each bar 17 into the bore 5 of one of the sleeves 3 to the maximum extent possible until the end of the bar reaches the end of the coarse internal thread of the sleeve 3. Thereafter, one of the shanks 13 of the insert 9 is 25 rotated into one of the bar/sleeve assemblies until the end of the shank contacts the end of the bar 17 in the assembly and is tightened against the end of the bar 17 until the required pre-load is applied. The required tightening of the shank 13 against the end of the bar 17 30' can be achieved without difficulty by means of standard spanners. Thereafter, the other shank 13 of the insert is engaged with the other bar/sleeve assembly so that the required pre-load is applied to the bar 17 of that assembly. 35 Subsequently, in service, when the reinforcing bars/coupler have been cast in concrete and are loaded in WO 2004/111363 PCT/AU2004/000780 - 10 tension, the pre-load of the bars 17 reduces the amount of longitudinal slip between the bars 17 and the open ends of the coupler. 5 More particularly, the amount of longitudinal slip between the bars 17 and the coupler is an inverse relationship with the amount of pre-load applied to the bar 17. 10 With the above-described coupler, the stress is applied to a much greater portion of the ends of the reinforcing bars 17, particularly in situations in which the ends of the bars are cut square. (The bars can be cut in a factory or on site.) In this way, the insert 9 can 15 rotate relative to the end of a bar and achieve the necessary bearing pressure without requiring a complicated mechanism like the cotter of the Reding coupler. The internal force equilibrium of the coupler 20 shown in Figure 1 is explained in Figure 2. With reference to Figure 2, the fine-threaded insert 7 applies a compressive force to the end of the reinforcing bar 17 to deform the coarse threads of the bar 25 and the coupler. An equal and opposite tensile force develops in the coupler body. The diameter of the insert shank is less than that of the bar, but nevertheless the average contact stress on the end of the bar needed to overcome the slip problem is much less than that using the 30 cotter of the Reding coupler. The principle of a coupler having a fine-threaded insert and a dual-threaded body as described above in relation to Figures 1 and 2 can be extended into a wide 35 range of practical cases as shown, by way of example, in Figures 3 to 5.

WO 2004/111363 PCT/AU2004/000780 - 11 The embodiments shown in Figures 3 to 5 are based on illustrations in the Reidbar design manual RB DM2002, appropriately modified for the purpose of illustrating the present invention. 5 Figures 3 to 5 explain several important design features of the coupler of the present invention, namely: (a) when the coupler is already attached to a 10 coarse-threaded bar 17 in concrete, it should be of a design that can resist the torque that is applied to it when the fine-threaded insert is tightened, which will normally occur when the concrete is "green"; and 15 (b) during this tightening operation, although rotation of the embedded coupler sleeve 3 should be prevented, the body should be able to break the adhesion bond with the concrete and slide relatively freely toward the insert 9 so that longitudinal slip between the body 20 and the deformations on the reinforcing bar 17 can occur as part of the normal pre-loading operation to prevent slip under service loads. In the arrangement shown in Figure 3 the 25 objective is to connect a reinforcing bar 17b to a reinforcing bar 17a that is embedded in concrete 25. Figure 3 illustrates a pair of parallel reinforcing bars 17a that was embedded in the concrete 25 30 in a "previous" pour. A coupler sleeve 3 of the coupler shown in Figure 1 (identified by the numeral 3a in Figure 3) is engaged with the end of the lower bar 17a and is also embedded in 35 the concrete 25. The coupler sleeve 3a is positioned in the concrete 25 so that the bore of the sleeve 3a can be accessed from the exposed face 91 of the concrete 25 at WO 2004/111363 PCT/AU2004/000780 - 12 that time. Prior to pouring the concrete for the "current" pour the lower reinforcing bar 17b is connected to the 5 lower bar 17a by means of the coupler shown in Figure 1. Specifically, one of the shanks 13 of the insert 9 is wound into the bore of the sleeve 3a and the insert is tightened to provide a required pre-load to the bar 10 17a. The action of tightening the insert 9 brings the end of the shank 13 into contact with the end of the bar 17a within the coupler sleeve 3a, and further tightening of the insert thrusts the shank 13 against the end of the bar 17a and has the result of moving the sleeve 3a within the 15 concrete 25 towards the insert 9. Consequently, it is important that the coupler sleeve 3a be formed to minimise interference to the necessary longitudinal movement of the sleeve 3a. 20 Thereafter, the other coupler sleeve 3b of the coupler is wound onto the reinforcing bar 17b and the bar/sleeve assembly is wound onto the other shank 13 of the insert 9 and is tightened to provide a required pre load. 25 It is noted that in situations in which the threads of the shanks 13 of the insert 9 are opposite hands the insert can act as a turnbuckle and the bar/sleeve assembly that includes the reinforcing bar 17b 30 can be engaged with the insert 9 by rotating the insert 9 rather that the bar/sleeve assembly. In the arrangement shown in Figure 4 the objective is to secure a reinforcing bar 17 to a precast 35 panel 29. An anchor 31 for the reinforcing bar 17 is WO 2004/111363 PCT/AU2004/000780 - 13 embedded in the precast panel 29. The anchor 31 has an internally fine threaded bore. The insert 9 and one of the coupler sleeves 3 of 5 the coupler shown in Figure 1 connect the reinforcing bar 17 to the anchor 31. Specifically, one shank 13 of the insert 9 is wound into the anchor 31. Thereafter, the coupler sleeve 10 3 is wound onto the reinforcing bar 17 and the bar/sleeve assembly is wound onto the other shank 13 of the insert 9 and tightened to provide a required pre-load. Again, it is noted that in situations in which 15 the threads of the shanks 13 of the insert 9 are opposite hands the insert can act as a turnbuckle and the bar/sleeve assembly that includes the reinforcing bar 17 can be engaged with the.insert 9 by rotating the insert 9 rather that the bar/sleeve assembly. 20 In the arrangement shown in Figure 5 the objective is to anchor a series of reinforcing bars 17b that form part of vertical column starters 51 to a reinforced concrete base 53. 25 Figure 5 illustrates three parallel vertically extending reinforcing bars 17a embedded in the concrete base 53. 30 A coupler sleeve 3 of the coupler shown in Figure 1 is wound onto the end of each bar 17a and is also embedded in the concrete base 53. The coupler sleeves 3a are positioned in the concrete base 53 so that the bores of the sleeves 3 can be accessed from the exposed top face 35 55 of the concrete base 53. The reinforcing bars 17b are connected to the WO 2004/111363 PCT/AU2004/000780 - 14 bars 17a by means of the coupler shown in Figure 1 - and as illustrated on the left hand side of Figure 5. Specifically, one of the shanks 13 of each of three inserts 9 are wound into the bores of the sleeves 3a 5 and the inserts are tightened to provide a required pre load to the bars 17a. The action of tightening the inserts 9 brings the ends of each of the shanks 13 into contact with the ends of each of the bars 17a within the coupler sleeves 3a and further tightening of the inserts thrusts 10 the shanks 13 against the ends of the bars 17a and has the result of moving the sleeves 3a within the concrete base 53 towards the inserts 9. Consequently, it is important that the coupler sleeves 3a be formed to minimise interference to the necessary movement of the sleeves 3a. 15 Thereafter, the other coupler sleeves 3b of the coupler are wound onto the reinforcing bars 17b and the bar/sleeve assembly are wound onto the other shanks 13 of the inserts 9 and are tightened to provide a required pre 20 load. Again, it is noted that in situations in which the threads of the shanks 13 of the inserts 9 are opposite hands the inserts can act as turnbuckle and the bar/sleeve 25 assemblies that include the reinforcing bars 17b can be engaged with the inserts 9 by rotating the inserts 9 rather that the bar/sleeve assemblies. The above-described coupler is an effective 30 option for a wide range of applications. Many modifications may be made to the preferred embodiment of the present invention as described above without departing from the spirit and scope of the present 35 invention. By way of example, the present invention is not WO 2004/111363 PCT/AU2004/000780 - 15 limited to couplers that receive one or two reinforcing bars as shown in the Figures and also extends to couplers that can receive in excess of two bars. In such couplers the bars need not be in the same plane.

Claims

1. A coupler for a reinforcing bar having an external thread, the coupler including (a) an insert 5 having an externally threaded shank and (b) a body having an internally threaded bore extending through the body, the body being adapted to receive the shank of the insert via one end of the bore and to receive an end section of the reinforcing bar via an opposite end of the bore, 10 whereby in use relative rotation of the insert and the body moves the ends of the shank and the reinforcing bar axially into contact and applies an axial force to the end of the reinforcing bar and thereby pre-loads the reinforcing bar. 15

2. The coupler defined in claim 1 wherein the axial force i.e, the pre-loading force, is at least equivalent to 200 MPa. 20

3. The coupler defined in claim 2 wherein the axial force is at least equivalent 300 MPa.

4. The coupler defined in any one of the preceding claims wherein the axial force is a significant proportion 25 of the maximum tensile stresses that the reinforcing bars are likely to experience in normal service conditions.

5. The coupler defined in any one of the preceding claims wherein the external thread of the shank of the 30 insert is a fine thread cut into the shank.

6. The coupler defined in any one of the preceding claims wherein the external thread of the reinforcing bar has a coarse thread in the form of ribs or deformations on 35 the bar.

7. The coupler defined in any one of the preceding WO 2004/111363 PCT/AU2004/000780 - 17 claims wherein the reinforcing bar has a coarse external thread and the shank of the insert has a relatively fine thread. 5

8. The coupler defined in claim 7 wherein the bore of the body has a coarse internal thread in one section of the bore extending from one end of the body that is complementary to the coarse external thread of the reinforcing bar and a relatively fine thread in another 10 section of the bore extending from the other end of the body that is complementary to the relatively fine thread of the shank of the insert.

9. The coupler defined in claim 7 wherein the 15 transition between the coarse and fine threaded sections forms a stop for axial movement of the reinforcing bar and the shank of the insert in the body.

10. The coupler defined in claim 7 or claim 8 wherein 20 the external diameter of the shank of the insert is less than the internal diameter of the coarse-threaded section of the body so that the coarse-threaded section does not interfere with axial movement of the insert shank in situations in which the insert shank extends into this 25 section of the body.

11. A coupler for coupling together two reinforcing bars, each reinforcing bar having an external thread, the coupler including two separate bodies, each body having an 30 internally threaded bore extending through the body, and an insert including a central element and two externally threaded shanks extending in opposite directions from the central element, each body being adapted to receive one of the shanks of the insert via one end of the bore and to 35 receive an end section of one of the reinforcing bars via an opposite end of the bore, whereby relative rotation of the insert and the bodies moves the ends of each pair of WO 2004/111363 PCT/AU2004/000780 - 18 the shanks and the reinforcing bars axially into contact and applies oppositely directed axial forces to the ends of the reinforcing bars and thereby pre-loads the reinforcing bars. 5

12. The coupler defined in claim 11 wherein each body includes a coarse thread in one section of the bore extending from one end of the body and a relatively fine thread in another section of the bore extending from the 10 other end of the body.

13. The coupler defined in claim 12 wherein the shanks of the insert have the same thread as the fine threaded section of the bodies. 15

14. The coupler defined in claim 13 wherein the threads on each shank of the insert are the same hand when the insert is viewed from a side of the insert. 20

15. The coupler defined in claim 13 wherein the threads on each shank of the insert are opposite hands when the insert is viewed from a side of the insert whereby, with the bodies assembled onto the ends of coaxially aligned reinforcing bars, and the insert 25 positioned so that each shank of the insert is engaged with one of the bar/body assemblies, rotation of the insert about its lengthwise extending axis pulls the bar/body assemblies toward each other without requiring rotation of the bars about their lengthwise extending axes 30 and facilitates applying a required pre-load to each bar.

16. The coupler defined in any one of the preceding claims wherein the reinforcing bars have a diameter of at least 10 nm. 35

17. The coupler defined in any one of the preceding claims wherein the yield stress of the reinforcing bars is WO 2004/111363 PCT/AU2004/000780 - 19 at least 400 MPa.

18. The coupler defined in claim 17 wherein the yield stress of the reinforcing bars is at least 500 MPa. 5