GB2502893A

GB2502893A - Non-circular reinforcing bar

Info

Publication number: GB2502893A
Application number: GB201309518A
Authority: GB
Inventors: Jamie Holling; Stuart Thomas
Original assignee: CELSA Manufacturing UK Ltd
Current assignee: CELSA Manufacturing UK Ltd
Priority date: 2012-05-25
Filing date: 2013-05-28
Publication date: 2013-12-11
Also published as: GB201309518D0; GB201209223D0

Abstract

This invention relates to reinforcing bar 10. The reinforcing bar 10 is designed to be embedded within concrete in a reinforced concrete structure. The reinforcing bar comprises an elongate bar having a ribbed periphery 12, the bar having a non-circular cross-sectional shape, the cross-section having a major axis A1 and a minor axis A2, the major axis A1 being larger than the minor axis A2. The cross-sectional shape may be oval. A longitudinal portion 14 of the periphery of the reinforcing bar has may have no ribs 12. There is also provided a method of manufacturing the reinforcing bar.

Description

REINFORCING BAR AND METHOD OF MANUFACTURE

FIELD OF THE INVENTION

s This invention relates to reinforcing bar and method of manufacture, and in particular to a reinforcing bar designed to be embedded within concrete in a reinforced concrete structure.

BACKGROUND TO THE INVENTION

Reinforced concrete structures are in widespread use in the construction industry.

The reinforcing structure is typically a latticework of reinforcing bars which are temporarily connected together at the site of use or at a dedicated manufacturing is facility. The latticework of reinforcing bars is either pressed into a body of wet concrete or, more typically, the latticework is placed into the position of use and wet concrete is poured around the latticework.

Often, one or more of the reinforcing bars will project from the concrete so that the reinforced concrete structure may be tied by way of the projecting bar(s) to another part of the structure. For example, the latticework of reinforcing bars may be a pile cage designed to be embedded within an underground reinforced concrete pile. The reinforcing bars making up the cage can project from the pile so that the pile can be connected to above-ground structures such as the support of a bridge for example.

The reinforcing bars are typically made of steel, and are manufactured in predetermined lengths. The reinforcing bars are made linear, and in many applications the reinforcing bars will remain (substantially) linear in the assembled latticework and in the completed reinforced concrete structure. Often, however, it is necessary to bend a reinforcing bar so as to conform to the particular requirements of the reinforced concrete structure.

Conventional reinforcing bars have raised ribs around their periphery. The ribs are required to enhance the bond between the concrete and the reinforcing bar.

The British Standard for reinforcing bars, for example, refers to the minimum bond requirements based upon the area of the reinforcing bar which is covered by ribs.

However, the ribs increase the difficulty of accurately bending the reinforcing bars.

In particular, when bending a conventional bar there is a very small contact area between the bending former and the bar which places very high contact loading upon the former and the bar. The small contact area can cause the reinforcing H) bar to bend in an uncontrolled manner, and in particular can cause the bent reinforcing bar to deviate from the desired plane of bending. Also, if the contact area is adjacent to or includes a rib the bar can move rapidly (or "kick") relative to the bending former as the bending load is applied, again causing the reinforcing bar to deviate from the desired plane of bending. The bending of conventional is reinforcing bars is therefore an inherently unstable and unreliable process.

SUMMARY OF THE INVENTION

The present invention seeks to provide a reinforcing bar which can be bent more easily and more reliably, making the process of bending the reinforcing bar more

stable.

According to the present invention there is provided a reinforcing bar comprising an elongate bar having a ribbed periphery, the bar having a non-circular cross-sectional shape, the cross-section having a major axis and a minor axis, the major axis being larger than the minor axis.

Conventional reinforcing bars are of circular cross-section. The inventor has appreciated that by making the reinforcing bar with a larger major axis and a smaller minor axis, the bar can more readily be bent in the plane of the minor axis.

The inventor has therefore appreciated that in most reinforced concrete structures requiring bent reinforcing bars, the bars are required to bend in a single plane. By aligning the minor axis with the desired plane of bending the operator can better ensure an accurate and reliable bending operation.

The overall strength of the reinforcing bar is dependent largely upon its total cross-sectional area, and so a reinforcing bar according to the present invention can be made with the same cross-sectional area as a convention reinforcing bar of circular cross-section, and yet have a smaller minor axis about which it can be bent. The bending forces which are required can therefore also be reduced over a conventional reinforcing bar.

Preferably, the cross-sectional shape of the reinforcing bar is oval.

Desirably, a longitudinal portion of the periphery of the reinforcing bar has no ribs, and is ideally formed to be substantially planar. By arranging this longitudinal is portion to be aligned with the minor axis of the cross-section it can be arranged that the bending former engages the longitudinal portion. This reduces the likelihood that the bending former will engage a rib, and thereby reduces the likelihood of unwanted and uncontrolled movement of the bar during the bending operation. Also, the bending former can engage the substantially planar portion whereby the contact area is significantly increased, thereby reducing the contact loading upon the bar and the former.

Preferably, the ratio of the major axis to the minor axis is between approximately 7:5 and approximately 11:10, and is ideally approximately 6:5. One suitable reinforcing bar has a major axis of nominally 30 mm (approx.) and a minor axis of nominally 25 mm (approx.).

Preferably also, the longitudinal portion which is free of ribs is between approximately 6 mm and approximately 10 mm wide, and is ideally approximately 8 mm wide.

Desirably, ribs are located on approximately 75% of the surface of the reinforcing bar. The ribs are preferably formed by pressing or deforming the surface of the bar inwardly, so that the ribs are left upstanding between the pressed-in-areas.

The longitudinal portions can therefore be aligned with the periphery of the ribs, rather than the ribs being upstanding from the periphery of the cross-section. This helps to ensure that the ribs do not cause any point loading with the bending former. Alternatively stated, if the ribs engage the bending former they do so in addition to the longitudinal portion, not instead of the longitudinal portion.

In addition, the form of the ribs is preferably made visually significantly different to the form of the ribs of conventional reinforcing bars so that reinforcing bars made H) according to the present invention can be readily identified, both at the manufacturing facility and on site. This is a particularly desirable feature, as many different types of reinforcing bars will often be provided to a construction site, and the designer of the reinforced concrete structures will wish to ensure that the operator uses the correct reinforcing bar in each reinforced concrete structure.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which: Fig.1 shows a perspective view of a part of a reinforcing bar according to the present invention; Fig.2 shows a top view of the reinforcing bar; Fig.3 shows a side view of the reinforcing bar; and Fig.4 shows a cross-sectional view through the reinforcing bar.

DETAILED DESCRIPTION

The reinforcing bar 10 comprises an elongate bar of steel. The particular grade of steel will be determined by the required characteristics of the reinforced concrete structure. Whilst standard grades of steel can be used, the inventor envisages adding ferroalloys to the steel composition during casting, and varying the cooling s procedure during rolling, in order to increase the tensile strength of the steel used in the present reinforcing bar to around 600N/mm2 (compared to the standard conventional reinforcing bar having a tensile strength of 500 N/mm2).

The periphery or surface of the reinforcing bar 10 carries a number of ribs 12, the H) ribs 12 being angled relative to the longitudinal axis L-L of the bar 10, whereby the ribs extend in both the longitudinal and circumferential direction, in known fashion.

Importantly, the ribs 12 do not extend around the complete periphery of the reinforcing bar. A longitudinal portion or strip 14 is provided between the ribs, the is longitudinal portion being aligned with the longitudinal axis L-L. As better seen in Fig.4 the longitudinal portion is planar, so that there are two flat portions 14 of the surface joining the curved (ribbed) regions 20.

The longitudinal portions 14 are ideally parallel to the major axis A1 of the bar 10.

In addition, in this embodiment there are two further longitudinal portions 16 which are devoid of ribs, the further longitudinal portions 16 being substantially parallel to the minor axis A2 of the bar 10. The width w of the two further longitudinal portions 16 is less than the width W of the two longitudinal portions 14. The periphery of the ribbed portions 20 of the bar 10 is curved, and in this embodiment comprises a quarter of a circle. In this embodiment it is therefore the difference between the width W and the width w which provides the difference between the length of the major axis A1 and the minor axis A2.

It will be understood that in other embodiments the curvature of the ribbed portions need not be part-circular. It will also be understood that in other embodiments there are no further longitudinal portions, i.e. the ribs cross the major axis A1.

In yet other embodiments the longitudinal portions (14) and/or the further longitudinal portions (16) may be curved slightly rather than being planar. If the longitudinal portion (14) is curved, it is desired that the curvature be significantly s less than the curvature of the ribbed portions 20, so that the longitudinal portions are substantially planar.

It will be seen from Fig.4 in particular that the periphery of the reinforcing bar 10 (including the ribs) is substantially continuous, i.e. the periphery of the ribs io continues into the longitudinal portions 14 and 16. This is a feature of the method of forming the ribs 12 by inwardly deforming parts 22 of the reinforcing bar 10.

The resulting cross-section means that the reinforcing bar can readily be loaded into a bending former, and there are no ribs upstanding beyond the longitudinal portions 14 which can foul the bending former and cause unwanted or is uncontrolled movement when the bending force is applied.

The reinforcing bar 10 is designed to be bent in the plane of the minor axis A2, i.e. the bending force is applied in a direction parallel to the minor axis. The oval shape of the cross-section makes the reinforcing bar easier to bend in the plane of the minor axis than in the plane of the major axis (and in the planes of the intermediate axes). It will be understood that the fact that the reinforcing bar is harder to bend in the planes of the major axis and the intermediate axes is not a disadvantage in practice because the reinforcing bar will typically be required to bend in only one plane.

It will be appreciated that the reinforcing bar 10 can readily be distinguished from conventional reinforcing bar, primarily by the form of the ribs 12. Thus, the operator is not required to identify the reinforcing bar by virtue only of the shape of its cross-section.

In one embodiment of the present invention the major axis A1 is approximately 30 mm and the minor axis A2 is approximately 25 mm. The width W of the longitudinal portions 14 is approximately 8 mm and the width w of the longitudinal portions 16 is approximately 3 mm. The radius of curvature of the periphery of the ribbed portions 20 is approximately 11 mm. This reinforcing bar has a ratio of the major axis to the minor axis of approximately 6:5. Clearly, the invention could be utilised with reinforcing bars having different dimensions, for example the above dimensions could simply be scaled up or down, or individual dimensions could be adjusted to suit a particular application.

These dimensions are nominal, and it will be appreciated that manufacturing tolerances will cause the actual dimensions to vary between different reinforcing H) bars, and also perhaps along the length of a single reinforcing bar. A suitable manufacturing tolerance for the major axis A1 and the minor axis A2 is approximately 1 mm, for example. It is desired, however, that the width W of the longitudinal portion be relatively tightly controlled, and have a small manufacturing tolerance, as variations in the width W will significantly affect the contact loading is between the bar and the bending former.

Claims

CLAIMS1. A reinforcing bar comprising an elongate bar having a ribbed periphery, the bar having a non-circular cross-sectional shape, the cross-section having a major axis and a minor axis, the major axis being larger than the minor axis.
2. The reinforcing bar according to claim 1 in which the cross-sectional shape is oval.
3. The reinforcing bar according to claim 1 or claim 2 in which a longitudinal portion of the periphery of the reinforcing bar has no ribs
4. The reinforcing bar according to claim 3 in which the longitudinal portion is formed to be substantially planar.
5. The reinforcing bar according to claim 3 or claim 4 in which the longitudinal portion is between approximately 6 mm and approximately 10mm wide.
6. The reinforcing bar according to claim 5 in which the longitudinal portion is approximately 8 mm wide.
7. The reinforcing bar according to any one of claims 1-6 in which ribs occupy approximately 75% of the surface area of the reinforcing bar.
8. The reinforcing bar according to any one of claims 1-7 in which the ratio of the major axis to the minor axis is between approximately 7:5 and approximately 11:10.
9. The reinforcing bar according to claim 8 in which the ratio of the major axis to the minor axis is approximately 6:5.
10. A method of manufacturing a reinforcing bar comprising the steps of: {i} providing an elongate steel bar having a predetermined material composition; {ii} passing the bar through a set of rollers configured to deform the surface of the bar, selected parts of the surface of the bar being depressed and other parts of the surface of the bar not being depressed so as to form a plurality of depressions and a plurality of ribs between the depressions, the cross section of the bar being non-circular and having a major axis and a minor axis, the major axis being larger than the minor axis.
11. The method according to claim 10 in which the non-circular cross-sectional shape is created by the rolling operation.
12. The method according to claim 10 or claim 11 in which the other parts of the is surface of the bar which are not depressed includes at least one longitudinal portion.
13. The method according to claim 12 in which the periphery of the longitudinal portion(s) coincides with the periphery of the ribs.