THREADED REINFORCING BAR

Description

PRIORITY

This application claims priority to and the benefit of Australian Patent Application No. 2025230832, filed Sep. 15, 2025 and Australian Patent Application No. 2024902967, filed Sep. 17, 2024, the entire contents of both of which are incorporated herein by reference.

FIELD

The present disclosure relates to a threaded reinforcing bar for use in concrete construction.

BACKGROUND

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 applicant. The thread on the reinforcing bar is quite coarse and its pitch ranges from 8 mm for a bar of 12 mm diameter to around 16.5 mm for a bar diameter of 32 mm.

Internally threaded fittings for mounting over the end of threaded reinforcing bar for example for coupling lengths of bar in series tend to be long and relatively bulky. The applicant has determined that it would be advantageous to find a way to achieve a more compact fitting without loss of load capacity performance.

The applicant has determined that it would be advantageous for there to be provided an improved reinforcing bar, reinforcing assembly, and/or reinforcing fitting.

SUMMARY

In accordance with one aspect of the present disclosure, there is provided a threaded reinforcing bar for use in concrete construction, wherein the reinforcing bar has an external thread along its length, wherein a thread profile of the external thread is such that the thread covers greater than 30% of the bar. It is to be understood that this value for how much of the bar the thread covers is along a plane through a fully developed section of the thread. Where the bar is provided with two flats—that is, two opposed flattened surfaces extending along a length of the bar—the thread would cover a smaller percentage of the surface area of the bar if it was averaged around the entire circumference.

Preferably, the thread covers greater than 30% of the bar for an entire length of the bar. More preferably, the thread covers greater than 30% of a total surface area of the bar. Even more preferably, the thread covers greater than 40% of a total surface area of the bar. Even more preferably still, the thread covers greater than 45% of a total surface area of the bar. In one form, the thread may cover greater than 48% of a total surface area of the bar.

In accordance with another aspect of the present disclosure, there is provided an assembly including a reinforcing bar as defined above, in combination with a fitting, wherein the fitting has an internal thread, the internal thread being configured for threaded engagement with the external thread of the bar.

In accordance with another aspect of the present disclosure, there is provided a threaded reinforcing bar for use in concrete construction, wherein the reinforcing bar has an external thread along its length, wherein a thread profile of the external thread is such that the thread width is greater than or equal to a threshold proportion of a pitch of the thread.

Preferably, the threshold proportion is 0.25.

In one non-limiting example, the reinforcing bar is 40 mm in diameter. It will be understood by those skilled in the art that other examples of the present disclosure could be applied to bars having other sizes such as, for example, from 12 mm diameter to 32 mm diameter, or larger diameters such as, for example, 75 mm.

In accordance with another aspect of the present disclosure, there is provided a method of reducing the length of a fitting for a reinforcing bar, including the steps of redesigning the reinforcing bar to enlarge a thread width of an external thread of the reinforcing bar such that the thread width is greater than or equal to a threshold ratio relative to a pitch of the thread, redesigning the fitting to enlarge a thread width of an internal thread of the fitting such that the internal thread of the fitting is able to threadedly receive the external thread of the reinforcing bar, and redesigning the fitting to reduce a length of the fitting without reducing load carrying capacity when compared to an original form of the fitting.

Preferably, the threshold ratio is 0.25:1 for the ratio of the thread width to thread pitch.

Preferably, the step of redesigning the fitting to reduce a length of the fitting includes reducing the length of the fitting by over 10%. More preferably, the step of redesigning the fitting to reduce a length of the fitting includes reducing the length of the fitting by over 20%. Even more preferably, the step of redesigning the fitting to reduce a length of the fitting includes reducing the length of the fitting by over 30%.

In a preferred form, the fitting is in the form of a coupler for coupling the reinforcing bar to a reinforcing item. The reinforcing item may be in the form of a second reinforcing bar.

Alternatively, the fitting may be in the form of an anchor or a nut.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present disclosure will be described, by way of non-limiting example only, with reference to the accompanying drawings.

FIG. 1 shows an example of a geometry of an existing threaded reinforcement bar within a threaded nut.

FIG. 2 shows a geometry of an existing thread profile of an externally threaded reinforcing bar, within an internally threaded fitting.

FIG. 3 shows a threaded reinforcing bar within an internally threaded fitting, in accordance with an example embodiment of the present disclosure.

FIG. 4 shows an example of an existing reinforcing bar on which an external thread covers about 30% of the bar.

FIG. 5 shows an example of a reinforcing bar in accordance with an example embodiment of the present disclosure, on which an external thread covers approximately 48% of the bar.

FIG. 6 shows a table listing bar values with corresponding descriptions for ribs or indentations on reinforcement bar according to standards in Australia and New Zealand.

FIG. 7 shows a diagrammatic view of a reinforcing bar, depicting dimensions listed in the table in FIG. 6.

FIG. 8 shows a cross-sectional view of a thread profile taken through line A-A in FIG. 7.

FIG. 9 shows top and side views of a reinforcing bar having Grade 250N ribs.

FIG. 10 shows a side view of a reinforcing bar having Grade 500E ribs.

FIG. 11 shows examples of externally threaded reinforcing bars having Grade 500E ribs.

FIG. 12 shows a graph depicting cross-sectional area of a moving section for three different thread profiles.

FIG. 13 shows a graph depicting thread width versus core and cross-sectional area.

FIG. 14a and FIG. 14b show two example thread profiles to illustrate that a wider thread profile will increase the amount of thread in any given cross-section, reducing the impact of the flat sections.

FIGS. 15a to 15d show four example couplers.

FIGS. 16a to 16c show three examples of headed anchors.

FIGS. 17a to 17d show four examples of couplers having a variety of lengths.

FIG. 18 shows an example of a headed anchor.

FIG. 19 shows a graph depicting the ratio between the growth of the minimum area (in % of area) versus the growth of maximum area (in % of area).

FIG. 20 cross-sectional area of moving section for reinforcing bars having four different thread widths.

DETAILED DESCRIPTION

While the systems, devices, and methods described herein may be embodied in various forms, the drawings show, and the specification describes certain exemplary and non-limiting embodiments. Not all components shown in the drawings and described in the specification may be required, and certain implementations may include additional, different, or fewer components. Variations in the arrangement and type of the components; the shapes, sizes, and materials of the components; and the manners of connections of the components may be made without departing from the spirit or scope of the claims. Unless otherwise indicated, any directions referred to in the specification reflect the orientations of the components shown in the corresponding drawings and do not limit the scope of the present disclosure. Further, terms that refer to mounting methods, such as mounted, connected, etc., are not intended to be limited to direct mounting methods but should be interpreted broadly to include indirect and operably mounted, connected, and like mounting methods. This specification is intended to be taken as a whole and interpreted in accordance with the principles of the present disclosure and as understood by one of ordinary skill in the art.

In FIGS. 1 to 20, there is shown a threaded reinforcing bar 10 with a body and an optimised external thread 12 that enables a fitting such as a coupler to be shortened in length, significantly adding to convenience and utility, without compromising load-bearing performance. The reinforcing bar 10 of the example shown, enabling the shortened coupler, may also be advantageous in terms of other factors such as cost and environmental impact.

With reference to FIGS. 1 and 2, the applicant has identified that it would be beneficial to update the thread profile of reinforcing bars to reduce the size/length of components used in a reinforcing bar system. Advantageously, the applicant has determined that it may be possible to achieve a 20 to 30% reduction in thread length for mating components.

The geometry of reinforcement bar in Australia and New Zealand is controlled by AS/NZS 4671:2019 which specifies acceptable geometries for ribs on reinforcement bar. If both bar and nut (outer and inner thread) are made of materials with the same strength, then a balanced thread (one where the strength of the outer and inner thread are equal) would have the same thread material width on both inner and outer threads. This is, for example, the case on a standard metric thread as shown in FIG. 1 which depicts a reinforcing bar 10 within an internally threaded nut 14.

With reference to FIG. 2, the current ReidBar reinforcing bar 10 has an external thread 12 with a thread profile which is much narrower than a gap between the threads, which means that with equal material strengths for bar and nut, the bar thread strength will be much below the nut thread strength. The section in FIG. 2 shows the current ReidBar thread profile (RB32—32 mm diameter) and its interaction with an external thread. Note how narrow the threads are compared to the pitch (the distance between the threads).

Turning to FIG. 3, the applicant has identified that if the external thread 12 on the ReidBar reinforcing bar 10 is made wider then the strength is increased, however AS/NZS 4671:2019 sets limits for the rib (thread) width so it is not possible to make the ultimate thread. However, it is possible to move the thread geometry to the limit of what is allowed in the standard—this will result in a thread as shown in FIG. 3.

As can be seen, each thread profile is wider than the previous design. Also, unlike earlier, the thread profile on the ReidBar reinforcing bar 10 shown in FIG. 3 is wider than the thread profile in the nut 14—the reason for this is that the nut 14 material properties are better than the bar 10, so less material is required in the nut 14.

Accordingly, one aspect of the present disclosure provides a threaded reinforcing bar 10 for use in concrete construction, wherein the reinforcing bar 10 has a body having an external thread 12 along its length. A thread profile of the external thread 12 is such that the thread 12 covers greater than 30% of the bar 10.

The optimised thread 12 may cover greater than 30% of the bar 10 for an entire length of the bar 10. In preferred forms, the thread 12 may cover greater than 30% of a total surface area of the bar 10, greater than 40% of a total surface area of the bar 10, or even greater than 45% of a total surface area of the bar 10. In the existing reinforcing bar 10 shown in FIG. 4, the thread 12 covers about 30% of the bar 10. In the example according to the present disclosure shown in FIG. 5, the thread 12 may cover greater than 48% of a total surface area of the bar 10.

Accordingly, another aspect of the present disclosure provides an assembly 16 (see FIG. 3) including a reinforcing bar 10 as defined above, in combination with a fitting 18, wherein the fitting 18 has an internal thread 20, the internal thread 20 being configured for threaded engagement with the external thread 12 of the bar 10.

The applicant has also determined a lower limit of thread crest width which is acceptable according to an example of the present disclosure and where the benefit of the optimised thread profile becomes clear.

Accordingly, in another aspect there is provided a threaded reinforcing bar 10 for use in concrete construction, wherein the reinforcing bar 10 has a body having an external thread 12 along its length, wherein a thread profile of the external thread 12 is such that the thread width 22 (see FIG. 8) is greater than or equal to a threshold proportion of a pitch 24 of the thread 12.

In one example, the threshold proportion is 0.25, such that the dimension of the thread width 22 is 0.25 times the dimension of the pitch 24. In one form, the reinforcing bar is 40 mm in diameter.

Another aspect of the present disclosure provides a method of reducing the length of a fitting 18 for a reinforcing bar 10, including a step of redesigning the reinforcing bar 10 to enlarge a thread width 22 of an external thread 12 of the reinforcing bar 10 such that the thread width 22 is greater than or equal to a threshold ratio relative to a pitch 24 of the thread 12. The method also includes a step of redesigning the fitting 18 to enlarge a thread width of an internal thread 20 of the fitting such that the internal thread 20 of the fitting 18 is able to threadedly receive the external thread 12 of the reinforcing bar 10. The method also includes the step of redesigning the fitting 18 to reduce a length of the fitting 18 without reducing load carrying capacity when compared to an original form of the fitting 18.

The applicant has determined that the threshold ratio may be 0.25:1 for the ratio of the thread width 22 to thread pitch 24.

The step of redesigning the fitting 18 to reduce a length of the fitting 18 includes reducing the length of the fitting 18 by over 10%. In preferred forms, the step of redesigning the fitting 18 to reduce a length of the fitting 18 may include reducing the length of the fitting 18 by over 20%, or even by over 30%.

The fitting 18 may be in the form of a coupler 26 for coupling the reinforcing bar 10 to a reinforcing item. The reinforcing item may be in the form of a second reinforcing bar 10.

Alternatively, the fitting 18 may be in the form of an anchor 28 or a nut 14.

The applicant has identified an opportunity for a 40 mm bar, which may be particularly suitable for the New Zealand market and has used the opportunity to optimize the bar design with the knowledge gained about threaded joints over the past years.

AS/NZS 4671:2019 “Steel for the reinforcement of concrete” defines limits on the geometry of ribs and indentations. As long as the bar design falls inside these limits a change in thread geometry compared to the current ReidBar reinforcing bar should not result in increased qualification or approval requirements.

On a very basic level, the strength of the thread on the ReidBar is proportional to the amount of material in the thread. On the current ReidBar reinforcing bars, current RB32 is shown in FIG. 4, the thread 12 covers about 30% of the bar 10. If bar 10 and nut 14 have same material strength, the optimal ratio (considering thread strength only) is 50%. If the nut material is stronger than the bar material, then the optimal ratio is >50%.

FIG. 5 shows a bar 10 with a thread coverage of 48%. Compared to the current thread profile, this will increase thread load carrying capacity by 53%, thereby shortening required nut length significantly, for example by around 37%.

The current coupler 26 (RB 32) used in the New Zealand market has a 102 mm thread, which could be reduced to 64 mm by using the present disclosure. The applicant has determined that, with no other changes, this will reduce the overall length of the coupler from 242 mm to 166 mm—a 30% reduction.

The increased thread width might increase material use, although the wider threads increase the stress area (the effective cross-sectional area) of the bar 10, reducing the required core diameter. So, the overall change in required material is quite limited and is evaluated in further detail below.

Standard AS/NZS 4671:2019 defines the geometry requirements for ribs or indentations on reinforcement bar for sale in Australia and New Zealand. The main values considered are captured in the table shown in FIG. 6, with FIG. 7 and FIG. 8 illustrating the dimensions listed in the table.

When looking at the bar geometry the main design drivers, without knowledge of production limitations, are:

Optimize material use—least weight per metre bar.

Optimise thread strength—shortest possible nut lengths.

Reduce tolerance sensitivity—minimise strength impact of geometry changes on bar and/or nut.

With regard to material use, AS/NZS 4671:2019 section 7.3.1 specifies the required relationship between the bar nominal diameter and the mass, i.e. the bar mass must be within ±4.5% of a solid round bar with the nominal diameter and a material density of 7850 kg/m3. However, section 3.2 defines the term “assigned diameter” as the “diameter of a bar used for designating a product” and mentions that “In some cases the assigned and nominal diameters may be the same”, suggesting that a bar can be assigned a diameter which differs from its nominal diameter.

From a bar tensile strength to material viewpoint, the most efficient bar geometry is a (round) bar with no protrusions or indentations. In some cases, most easily exemplified by the Grade 250N ribs, the rib geometry is such that only the bar core diameter supports loads in between the ribs, see FIG. 9. In this case only the core caries load and all material used to form the ribs is ‘lost’ from the carrying capacity of the bar.

In other layouts, where the rib geometry is such that the ribs geometry overlap in the longitudinal direction, the ribs will add to the stressed cross section of the bar and, as such, only a proportion of the material formed into the ribs is ‘lost.’ This is only really the case for threaded bar, for example Grade 500 E, where the ribs on each side of the bar are offset by half a pitch—see FIG. 10.

The location with the reduced size identification rib will have slightly lower strength, however from discussion with structural engineers, the direction is that this can be ignored due to: 1. The large distance between such identification ribs, 2. The low likelihood that their position will line up with max stress planes when installed and, 3. The low likelihood that this rib will line up across adjacent reinforcement in a structure. As such, the strength of the bar will be evaluated based on the full thread profile.

If the bar mass is kept constant, then the bar core area (largest fitting circular section) will decrease as the thread is made wider, however the lowest cross-sectional area of any section through the bar increases slightly. The graph in FIG. 13 shows the change in core area (vertical axis) and cross-sectional area as a function of thread width (horizontal axis)—note: the first data point also has a different thread height).

Because the thread cannot be extended all the way around the bar, due to the rolling process, the two flats on the side of the bar results in a ‘gap’ in the thread. A wider thread profile will increase the amount of thread in any given cross section, thereby reducing the impact of the flat sections.

FIG. 14a and FIG. 14b attempt to illustrate this (note: thread geometry is for illustration only).

With regard to FIG. 12, this graph shows the change in cross sectional area along the length of the bar. The graph shows 3 different bars including: (1) a current reinforcing bar product (bottom line in legend box); (2) a reinforcing bar with a taller and (slightly) wider thread profile having a crest width giving a ratio of pitch of 0.165 (top line in legend box); and (3) a reinforcing bar with an even larger crest width giving a ratio of pitch of 0.235, (middle line in legend box), the latter having a thread which the applicant has determined as the largest possible inside the limits in AS/NZS 4671:2019. From the graph it can be seen that when the thread width is increased the ‘max’ cross sectional area drops, however the minimum increases. The cross-sectional area is only reduced by ˜0.1% when the crest width is increased from 0.165 (ratio of pitch) to 0.235 (ratio of pitch).

Analytically it is difficult to estimate what the strength change of the bar is as the thread geometry changes: Some load will be carried through the thread profile, however not as efficiently as through the core—so adding a thread will reduce strength, however how will the stress change with thread width. A simple finite element analysis (FEA) comparison was conducted by the applicant.

An FEA was run on three different variants of the 32 mm bar: Current, 0.165 ratio of pitch thread width and 0.235 ratio of pitch thread width. The core areas are reduced by 4.3% and 6.7% respectively compared to the current bar, however the cross-sectional area increases slightly.

The FEA suggests that the stresses in the core only change very little with the different thread geometries. However, the max stress around the corner between core and thread does increase as the thread gets larger and therefore supports more load. Also, because the threads are closer to each other, the stress does not fall as low between the two threads.

Overall, it appears that changing the thread profile inside the limits of AS/NZS 4671:2019, will have no significant/measurable impact on the bar strength. As a result, if manufacturing capability allows, it is most likely feasible to optimise the thread to achieve the shortest possible coupler.

The above work has all been done with a 45° thread flank angle—a steeper angle will reduce the width at the root of the thread (since AS/NZS 4671:2019 defines max crest width), which will negatively impact the load carrying capacity of the thread, though hit will reduce sensitivity to radial tolerances of bar and coupler. In other words, on a design with an angled thread flank, and therefore strength variation resulting from radial tolerances, the min strength will be the same as the strength achieved with a thread profile with 90° thread flanks. So, there is no strength benefit from increasing the thread flank angle beyond the minimum 45° required angle.

The increased thread width on the bar 10 results in the advantage that the coupler length can be reduced.

The length calculated is the minimum length to bring contact pressure and shear load below bar yield. The cuts in the thread, due to the flat sides, are ‘averaged,’ so if the length is short compared to the pitch, then cut position of the bar could become significant.

The contact pressure on the thread, surface to surface, is the limiting factor in the design. For the current configuration, the coupler must be 108 mm long to ensure a contact pressure below yield—the actual coupler is 105 mm long, which fits the theory well.

With the revised design the length can be reduced to 69 mm, a reduction of 36%.

The length required to bring the thread shear load below yield is much shorter, the reason for this is the very coarse pitch and low height of the thread profile. Reducing the pitch and making each thread narrower would balance these two lengths, however this is not allowed within AS/NZS 4671:2019.

Turning to FIGS. 15a to 15d, FIG. 15a shows the current RB32 coupler 26, FIG. 15b shows the RB32 coupler 26 with optimised outside diameter (OD), FIG. 15c shows the RB32 coupler 26 for optimised thread and with optimised outside diameter (OD), and FIG. 15d shows the RB32 coupler 26 machined through and plugged.

With reference to FIGS. 16a to 16c, FIG. 16a shows the current RB32 anchor 28, FIG. 16b shows the RB32 anchor 28 with optimised outside diameter (OD) around bar (flange size unchanged), and FIG. 16c shows the RB32 anchor 28 with revised thread.

The above estimates of the impact from changing the thread profile have been evaluated on the current RB32 ReidBar 10, coupler 26 and headed anchor 28. The main notable outcomes are:

• • A. The strength of the thread can be increased by 57% compared to the current profile.
  • B. The stress in the bar, at a given load, will change by <4.6% with unchanged bar mass per metre.
  • C. The coupler changes, for the same strength, are (baseline is current coupler with optimised OD):
    • (i) Length reduction of 26% from 242 mm to 178 mm
    • (ii) Mass reduction of 28% from 1.82 kg to 1.30 kg (61% improvement from current coupler which weighs 3.38 kg).
  • D. The anchor changes, for same strength, are (baseline is current anchor with optimised shank OD):
    • (i) Length reduction of 26% from 95 mm to 70 mm.
    • (ii) Mass reduction of 16% from 1.24 kg to 1.04 kg (35% improvement from current anchor which weighs 2.34 kg).

The improvements gained from optimizing the thread size should be similar across other bar sizes, however the mass gains for couplers and anchors might vary depending on how optimised the current components are.

The applicant has determined that geometry variation of the ReidBar reinforcing bar 10 will impact the strength of the threaded interface between bar 10 and coupler 26. With the current rigid coupler design, the coupler must clear the largest possible bar geometry, which reduces carrying area on the smallest possible bar geometry.

With reference to FIGS. 17a to 17d, FIG. 17a shows a current RB32 coupler 26, FIG. 17b shows a coupler 26 with pockets at the end of the internal thread with 100% load to surface yield, FIG. 17c shows a coupler 26 with pockets at the end of the internal thread with 60% load to surface yield, and FIG. 17d shows a coupler 26 with no pocket at the end of the internal thread with 60% load to surface yield.

FIG. 18 shows an example RB40 headed anchor 28.

Accordingly, as will be appreciated from the above, the applicant has made investigations to determine a minimum thread width which achieves optimal advantages. To achieve this, the applicant looked into when the thread widening became very beneficial, and it was found to occur gradually across a range. The applicant examined cross sections through the reinforcing bar 10 at the location with the smallest cross-sectional area and largest cross-sectional area with different thread widths.

The growth of the minimum area (in percentage of area) is much quicker than in maximum area, meaning that the ratio between the two areas moves towards 1:1 as the thread width is increased. The graph in FIG. 19 shows the ratio between the two. The graph includes a linear trend line for reference.

It is demonstrated above that having a wider thread is of benefit, however there is no exact point where there is a sudden improvement. The applicant has determined that, on an actual product the limit is set by process control capabilities, i.e. the thread width would be set as close to the maximum as possible while ensuring conformance with the design standard.

Finally, with reference to FIG. 20, the applicant investigated cross-sectional areas along the length of reinforcing bars with different thread widths. The graph in FIG. 20 shows this cross-sectional analysis across a range of thread widths (similar to the graph in FIG. 12) with the thread widths expressed as Wc, being a ratio of pitch as per relevant standards. The transition from a deep bottom to a flat bottom is relatively smooth, and the applicant considers that the advantages of the present disclosure become particularly active at a ratio of 0.25, as depicted by the bottom line shown in the legend box. The four lines shown in the legend box have progressively larger Wc values from top to bottom.

While various embodiments of the present disclosure 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 present disclosure. Thus, the present disclosure should not be limited by any of the above described exemplary embodiments.

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.

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.

LIST OF NUMBERED FEATURES

• • Reinforcing bar 10
  • External thread 12
  • Nut 14
  • Assembly 16
  • Fitting 18
  • Internal thread 20
  • Thread width 22
  • Pitch 24
  • Coupler 26
  • Anchor 28