REINFORCING BAR AND METHOD FOR MANUFACTURING THE SAME

Abstract

Disclosed are an improved reinforcing bar and methods for manufacturing the same. The improved reinforcing bar is made from a high strength material, and has a circular or oval or elliptical cross section and deformation of the axis in a single plane or in multiple planes. The methods for manufacturing the improved reinforcing bar include a hot working process and a cold working process. The undulating/wavy bar with axis deformation can improve the anchorage of the bar in concrete and the bond strength without comprising any surface modifications. The amplitude and pattern of axis deformation of the bar can avoid stress concentration and its ill effects.

Claims

1-8. (canceled)

9: A method for manufacturing of an improved reinforcing bar (REBAR) for reinforced concrete constructions and reinforced concrete structures by hot working comprising steps of: making of billet for high strength bar of steel; reheating the said billet; rolling the said billet in a rolling mill and making bars of the desired size and shape; deforming the said bars using gear rollers or by any other device or means; optionally providing any heating/cooling treatment; cutting bars into desired lengths using shears cooling of said bars in a cooling bed.

10: A method for manufacturing of an improved reinforcing bar (REBAR) for reinforced concrete constructions and reinforced concrete structures by cold working comprising steps of: making of billet for high strength bar of steel; reheating the billet; rolling the said billet in a rolling mill to make bars of the desired size and shape; cutting bars into desired lengths using shears; cooling of said bars in a cooling bed; deforming the said bars using gear rollers or by any other device or means; optional annealing to relieve residual stresses.

11: The method for manufacturing of an improved bar of claim 9 wherein said rolling mill process is followed by quenching of said bar in case of thermo mechanical treatment.

12: The method of claim 9 wherein said rolling mill process is further followed by quality check of splitting tendency and other quality check.

13: The method as claimed in claim 10 wherein said process of deformation is followed by annealing the said bar to remove or reduce built-in residual stresses by a process of gradually heating and cooling.

14: The method of claim 9 wherein said rollers/gears have horizontal or vertical or inclined axes.

15: The method of claim 9 wherein said hot working temperature in case of steel is around 900 C. to 1200 C.

16: The method for manufacturing of an improved bar of claim 9 wherein said rolling mill process is followed by quenching of said bar in case of thermo mechanical treatment.

17: The method of claim 10 wherein said rolling mill process is further followed by quality check of splitting tendency and other quality check.

18: The method of claim 10 wherein said rollers/gears have horizontal or vertical or inclined axes.

19: A reinforcing bar (REBAR) for reinforced concrete constructions and reinforced concrete structures comprising: a) steel; b) a circular or oval or elliptical cross section; and c) deformation of a central longitudinal axis of the bar thereby providing the bar with a uniform wave-like formation, the bar lacking sharp bends and recesses; wherein the bar has a plain surface free from surface lugs, surface protrusions, surface indentations, and surface deformities; whereby the bar has (i) enhanced resistance to corrosion as compared to an equivalent bar having surface deformations and lacking deformation of a central longitudinal axis and (ii) enhanced resistance to slippage at a REBAR-concrete interface as compared to an equivalent plain bar lacking deformation of a central longitudinal axis.

20: The REBAR of claim 19, wherein the bar is of circular shape.

21: The REBAR of claim 19, wherein the bar has an amplitude of deformation of the central longitudinal axis in a range of 1 mm to 10 mm.

22: The REBAR of claim 19, wherein the enhanced resistance to slippage at a REBAR-concrete interface is higher compared to resistance of the equivalent plain bar lacking deformation of a central longitudinal axis.

23: The REBAR of claim 19, wherein the steel is mild steel, medium tensile steel, or high strength steel.

24: The REBAR of claim 23, wherein the steel is high strength steel.

25: Reinforced concrete comprising the REBAR of claim 19.

Description

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

[0065] FIG. 1. Illustrates some of many possible cross sections of REBARs without any surface lugs or protrusions and without any sharp or local features according to present invention.

[0066] FIG. 2. Plain round rebars, with straight line configuration, which were commonly used before the introduction of medium tensile and high strength steel REBARs with surface deformations (FIGS. 3 and 3A).

[0067] FIG. 3. Typical high strength REBARs with surface deformations but of straight line configuration, which replaced plain round bars of mild steel and medium tensile steel (FIG. 2), starting the 1960's and 1970's.

[0068] FIG. 3A. Typical cold twisted deformed (CTD) rebar with lugs and protrusions on the surface and stresses beyond yield on the entire surface.

[0069] FIG. 4. Surface view (elevation) of one end of a rebar with a deformed axis configuration, but without any surface lug or protrusion or indentation according to present invention.

[0070] FIG. 5. Surface elevation of partial lengths of some bars according to present invention.

[0071] FIG. 6. Achieving deformed configuration of bar a schematic arrangement.

[0072] FIG. 7. A generalized process diagram for achieving (by hot working) deformed configuration of bars without any controlled cooling or thermo-mechanical treatment.

[0073] FIG. 8. A generalized process diagram for achieving (by hot working) deformed configuration of bars with optional controlled cooling (thermo-mechanical treatment).

[0074] FIG. 9. A generalized process diagram for achieving (by cold working) deformed configuration of bar which had undergone optional controlled cooling (thermo-mechanical treatment).

[0075] FIG. 10. A generalized process diagram for achieving (by cold working) deformed configuration, followed by annealing, where desired.

DETAILED DESCRIPTION OF THE INVENTION

[0076] The present invention is directed at a reinforcing bar (REBAR) of steel of any desired type and grade or of any other suitable material which is having a deformed axis but plain surface for use as reinforcing element in reinforced concrete, reinforced concrete elements, reinforced concrete structures, composite construction of steel and concrete and in any other concrete construction where reinforcing bars of steel or of any other suitable material are required to be used. The bar has a plain surface and a deformed axis for use in all concrete constructions wherever there are requirements for reinforcement and/or whichever construction requires the application of the principles of reinforced concrete design and construction. (FIGS. 4-6). According to the present invention a plain bar is provided with a deformed axis which makes the bar look undulating/wavy in perspective view. The amplitude and pattern as well as the distance between successive peaks of the said undulations may be varied such that high/increased gripping capacity, i.e., bond or resistance to pull-out is maintained without compromising in any significant way the overall linear characteristic of the bar and yet avoiding stress concentration and its ill effects, e.g., early corrosion in the case of CTD and other HSD rebars of steel. The preferred, but not limited to, range of amplitude of deformation of the axis of the REBAR is 1 to 10 mm.

[0077] The present invention is further directed at a process to manufacture the said product where a straight line bar of a desired cross section (FIG. 1) in its plastic state, e.g., hot Process working temperature of around 900 C. to 1200 C. in most cases of steel is passed through a set or more sets of toothed rollers/gears or through such other devices/tools to achieve a deformed configuration. (FIGS. 4-6).

[0078] The present invention is further directed at a process to manufacture the said product where a straight line bar of a desired cross section (FIG. 1) at less than the hot working temperature of about 900 C. to 1200 C. (in the case of steel) is made to have a deformed shape (FIGS. 4-6). In such cases, stresses, which may be locked in due to processing/bending at less-than-plastic temperature, can be released, if desired, by annealing/heat treatment.

[0079] In its Clause 5.6 Reinforcement The Indian Standard PLAIN AND REINFORCED CONCRETE CODE OF PRACTICE (Fourth Revision), IS 456:2000 permits the use of reinforcing elements thus [0080] a) mild steel and medium tensile steel bars conforming to IS 432 (Part 1) [0081] b) high strength deformed steel bars conforming to IS 1786 [0082] c) hard-drawn steel wire fabric conforming to IS 1566 [0083] d) structural steel conforming to grade A of IS 2062

[0084] Steel rebars, referred to in (a) above, are amenable to improvement according to the present invention. The present invention provides a better alternative to high strength steel rebars with surface deformations, referred to in (b) above and also referred to in other national and international codes (viz., BS 4449, ASTM A615M, ASTM A706M, EN 10080, Asian Model Code 1999, etc.), as according to the present invention there will not be early corrosion due to the effects of stress concentration and stress corrosion and yet there will be improved bond or enhanced resistance to slippage at the rebar-concrete interface. Furthermore, chances of loss of contact between rebar and surrounding concrete is minimized. The basic scheme to make rebars with a deformed axis, rather than with surface deformities, to enhance resistance to slippage is applicable also in case of rebars of any other material(s).

[0085] Other national, foreign, international codes, standards, guides, etc. permit the use of some or all of the different types of products which are identified in items (a) to (d) above as reinforcing elements, except that the products may conform to all or some or none of the standards IS 432 (Part 1), IS 1786, IS 1566 and IS 2062.

[0086] Besides other metals and materials, the present invention relates to items (a) and (b) above, except that the invention and the products are not necessarily limited to materials or products conforming to IS 432 (Part 1) or IS 1786 or to any other Indian or foreign or international code or standard or guide on REBARs for use in reinforced concrete and reinforced concrete construction.

[0087] According to the present invention, the steel (or of any other material) reinforcing bars have a circular or oval or elliptical or of any other cross section but without any sharp corners/contours or without any sharp or local features. However, instead of having a purely straight line or straight axis configuration as in prior art (FIGS. 2 and 3), rebars of the present invention, though maintaining the basic straight line orientation, have a non-straight line configuration. A rebar of many such possible configurations is shown in FIG. 4, while a surface elevation of partial lengths of a group of such bars is shown in FIG. 5.

Steel

[0088] According to one aspect of the invention there is provided a reinforcing bar (for use in reinforced concrete constructions and reinforced concrete structures) with plain surface and a deformed axis which has enhanced resistance to slippage inside concrete and which is not prone to early corrosion, as it would have happened in the case of HSD rebars (FIGS. 3 and 3A). Any controlled cooling/quenching (as in the thermo-mechanical treatment or TMT process) of rebar can be made following the achievement of the deformed axis (FIG. 8) in which case the bar is deformed at the final stand of Rolling Mill process (FIG. 6). In an alternative cold working process for the deforming of the bar, special cooling (as in the TMT process), if any, precedes the act of deforming the bar (FIGS. 9 and 10). Also, in the cold working process, on achieving the desired deformed shape (FIGS. 4 and 5) of the plain bar (FIG. 1), annealing/heat treatment is optionally provided for the release of any residual stress due to the manufacturing effort (FIG. 10).

Materials Other than Steel

[0089] In line with the concept of rebar of linear elements with a deformed axis but plain surface, propounded here, materials other than steel, if found otherwise suitable for use as the reinforcing element, can be manufactured as shown in FIG. 6 and made more useful as reinforcing element in the design and construction of reinforced concrete structures. These other materials may include glass fibre, carbon fibre, aramid, other high strength materials, made without or with the benefit of nanotechnology.

Deformed Configuration

[0090] According to the present invention, the pattern of deformation of the axis of the reinforcing element is unlimited, except that there will be no sharp bend, recess or protrusion which may act as a stress raiser leading to a significant enhancement of nominal stresses due to the phenomenon of stress concentration.

[0091] Though the deformed configuration can be achieved at a cold state, the best (for stress free or low residual stress condition) rolling/working (FIG. 6 or any other arrangement), i.e. causing or effecting deformation of the axis of the steel rebar, is achieved at the hot working temperature (i.e. at plastic state), which in the case of steel is around 900 C. to 1200 C.

[0092] The deformed configuration can be developed in different ways, one of which is the use of toothed rollers/gears (FIG. 6). The axes of the rollers/gears can be horizontal or vertical or inclined to suit working conditions.

[0093] The deformation of the axis of the bar or that of any other reinforcing element can be in a single plane or in multiple planes.

[0094] The bars according to the present invention, made of high strength steel or of any other steel or of any other material and yet without any surface deformations but with a deformed axis (FIGS. 4-6), can be used effectively in reinforced concrete construction as the resistance of the new bars (FIGS. 4-6) to pull out forces, compared to resistance to similar forces on plain round bars (FIG. 2) of the same size (diameter) and material but without surface deformations or without deformations of its axis, can be easily made to be 50% to 70% higher or even greater.

[0095] It is noted here that tests for resistance of HSD rebars (FIGS. 3 and 3A) to pull-out forces, as specified in IS:1786 and in IS:2770 and in similar codes of other countries are arbitrary in nature and details. Such arbitrariness in requirements for test for bond strength can be recognized when [0096] a) The tests are conducted on a single bar whereas in most of real cases rebars are in close proximity to each other and tensile forces in each bar affects the performance of its neighbouring bars in terms of their resistance to pull-out or tensile forces. [0097] b) The tests for resistance to tensile or pull-out forces are performed with rebar embedment of 5 times (Clause 4.7 and APPENDIX A of IS:1786) the diameter of the bar for rebars of different diameters and steel of different grades without any consideration of the fact that bars of the same size but of different grades of material will have different tensile forces. Furthermore, tensile forces in bars generally vary as a square of the diameter and not linearly with the diameter. [0098] c) The bond strength is determined, from tests (Clause 4.7 and APPENDIX A of IS:1786) and yet no explicit use is made of the bond strength in design.

[0099] Thus, though the rebars of the present invention are devoid of the surface modifications of the prior art bars and even if bond strength of the rebars of the present invention is not of similar nature to those of prior art it does not materially affect the working of the present rebars.

[0100] The plain bars of the present invention, with deformed axes but without any surface deformation in the form of lugs, protrusions, etc. (FIGS. 4-6), can be made of high strength steel and used as effectively as HSD rebars with surface deformations (FIG. 3), and yet giving the durability of concrete structures and other constructions with plain round bars of steel (FIG. 2) and the economy of concrete structures and other constructions with HSD rebars (FIG. 3). In other words, the rebars or reinforcing elements according to the present invention, by virtue of preservation of the surface characteristics of plain bars (FIG. 2) of the first half of the last century, have the best qualities of both plain round bars of steel and high strength rebars with surface deformations. The bars under the present invention can thus be made of the same high strength steel materials as HSD bars (FIG. 3) are made of and yet these new bars can be used much more efficiently and effectively than the conventional HSD bars as the bars according to the present invention, without the shortcomings of HSD rebars (viz., stress concentration leading to stress corrosion, gaps between rebar and concrete, greater macrocell and microcell corrosion, etc.), can endow reinforced concrete structures, reinforced concrete constructions, composite constructions and other reinforced concrete elements with the life span that plain round bars of steel could do. In addition, unlike HSD rebars there will not be any need for costly surface coating to rebars of the present invention.

[0101] There are no restrictions or limits to the lengths of bars according to the present invention. Similarly, there are neither any lower nor any upper limit to bar sizes (diameter) or sizes of other reinforcing elements under the present invention. Thus, besides bars of all the sizes from 4 mm to 50 mm, as identified in Clause 5.1 of IS:1786, bars of other intermediate sizes as well as bars less than 4 mm and bars above 50 mm are amenable to and permissible according to the present invention.

[0102] Similarly, the present invention covers, besides steel rebars, rebars of other metals and materials.

[0103] According to the present invention, there is no limitation on the extent of deformation of the axis from its original straight line (FIGS. 4-6), except that sharp contours are preferably avoided. Also, the axis can be deformed in a single plane or in multiple planes. However, the overall straight line orientation is maintained. There is also no upper or lower limits on the distance between two successive crests or valleys (created by the deformed shape of the rebar) as long as these reside within the workability and resistance to slippage of the bar.

[0104] Tests have shown that an amplitude or deviation of even 2-3 millimeters from the straight axis can raise the resistance of plain round bars of steel to pull out forces by 50%-70% (Table 1). It should be possible to increase the resistance further with proper selection of the pattern and extent of deformation. For the purpose of the present invention and in due consideration of field conditions it is proposed that the deformation/departure of the axis of the bar from its normal straight line be made to be 1 mm to 10 mm.

[0105] Though steel rod (of any desired/permissible metallurgical composition, of any and all practical grades, strengths, ductility, malleability and/or any other property of intent and interest) for use in reinforced concrete structures is at the focus of this invention, the basic features of this invention cover rods, bars, plates of steel or any other material (including composites) and shape where the objective will be the avoidance of the ill effects of stress concentration and yet the achievement of high resistance to slippage or bond failure of the reinforcing elements (e.g., rebar) in a matrix of another material (e.g., concrete, mortar) or materials.

[0106] Both hot working (during plastic state of material) and cold working is possible according to the present invention.

[0107] As illustrated in FIGS. 7 and 8 the process steps involved in case of hot working for achieving deformed configuration of bars with/without any controlled cooling or thermo-mechanical treatment (optional) are: [0108] making of billet for high strength bar of steel, reheating the said billet, rolling the said billet in a rolling mill and making bars of the desired size and shape, deforming the said bars using gear rollers or by any other device or means, optionally providing any heating/cooling treatment as in the case of thermo mechanical treatment, cutting bars into desired lengths using shears and cooling of said bars in a cooling bed.

[0109] As illustrated in FIGS. 9 and 10 the process steps in case of cold working for achieving deformed configuration of bars with controlled cooling or thermo-mechanical treatment followed by annealing (optional) are: [0110] making of billet for high strength bar of steel, reheating the billet, rolling the said billet in a rolling mill to make bars of the desired size and shape, optionally providing any heating/cooling treatment as in the case of thermo mechanical treatment, cutting bars into desired lengths using shears, cooling of said bars in a cooling bed, deforming the said bars using gear rollers or by any other device or means, optional annealing to relieve residual stresses.

[0111] Further in case of both hot and cold working to achieve deformed configuration of bars splitting tendency and other quality checks are performed in the above mentioned processes which is optional.

[0112] As a result of the present invention, providing any post-treatment is not essential when the deformation process involves hot working at a stage when the material will be in its plastic state. However, there is no bar to any post-treatment. Should it be so desired, stress relieving by annealing (in the case of cold working) or any other post treatment (e.g. controlled cooling as in thermo-mechanical treatment) can be provided.

TABLE-US-00001 TABLE 1 RESISTANCE TO PULL-OUT FORCES Amplitude of surface Shape (cross % of Resis- Material lug or Amplitude of section) of tance to pull used axis deformation Bar out forces Plain Medium Round 100% round strength surface + bar of straight Mild axis. steel Deformed High 0.5 mm- Round 180% surface + strength 2.0 mm straight bar of axis. steel Present High 1-10 mm* Round 150%- invention strength 170%* (plain bar of surface + steel deformed axis. Note: *Figures indicate values for and from specific tests. Amplitude and plane of deformation can be changed and resistance to pull-out forces enhanced.