WO2024005624A1

WO2024005624A1 - Reinforcement for reinforced concrete structures and method of its manufacture

Info

Publication number: WO2024005624A1
Application number: PCT/MD2023/000003
Authority: WO
Inventors: Nicolai BOGUSLAVSCHI
Original assignee: Boguslavschi Nicolai
Priority date: 2022-07-01
Filing date: 2023-05-12
Publication date: 2024-01-04
Also published as: MD4872C1; MD4872B1

Abstract

A reinforcement for reinforced concrete, comprising: - spiral recesses on the bar surface, - spiral longitudinal axis of the bar, - polygonal planar cross-section of the bar, where the number of polygon sides is equal to at least three, wherein each of the surfaces formed by the sides of the specified polygon is a longitudinal helical recess on the surface of the rod, with the helix pitch T determined by the relation T = (5... 20) d, where d is the diameter of an imaginary circle into which the transverse planar section of the rod is inscribed; wherein the rod is inscribed in an imaginary cylinder with a diameter D, where D is equal to (1.2... 1.6) d; wherein its planar cross-sectional area is S d = (0.35…0.45) S D , where S D is the cross-sectional area of an imaginary cylinder with a diameter D.

Description

REINFORCEMENT FOR REINFORCED CONCRETE STRUCTURES AND METHOD OF ITS MANUFACTURE

Technical field

The present invention relates to the field of building materials, in particular to reinforcement for reinforced concrete structures, both precast and monolithic, as well as to a reinforcement manufacturing method and to reinforcing concrete structures using spiral reinforcement.

General background

The strength of concrete for reinforced structures, as a rule, is not less than 300 kg/cm², which corresponds to 3 kg/mm². The tensile strength of concrete is about 0.3 kg/mm², as it is usually 10% of its compressive strength.

According to the Interstate standard GOST 34028-2016 “ROLLED REBAR FOR REINFORCED CONCRETE STRUCTURES. Specifications” the tensile strength of reinforcing steel is about 60 kg/mm², or 200 times more than that of unreinforced concrete. Therefore, when calculating the strength of building structures supporting complex loads, the strength of concrete per se is not taken into account.

Reinforced concrete is a materiai widely used in construction. It requires monolithic reinforcing structures with high tensile strength and sufficient ductility.

Trends in modern construction are increasing the number of floors of buildings in order to get more square footage from smaller plots in urban centers. Increasing a buildings height means increasing the requirements for the safety and stability of the buildings. Another modern trend is to reduce the cost of building structures. Accordingly, inventive thought focuses on solving these problems.

Prior art

Common rebar [1] is a hot-rolled steel reinforcing bar with a straight axis and ribbed surface. Ribs of various shapes add surface area to reinforce the bond between the rebar and the concrete to ensure that they work together to bear operational loads.

The disadvantage of this reinforcement is the connection between the rebar and the concrete can break under load, causing the reinforcing bar to slip relative to the concrete, which can lead to the destruction of the Structure.

To achieve the required strength, the number of reinforcing bars has to be increased, which negatively affects the cost of construction.

Reinforcement can be made out of tubular blanks with hot-rolled corrugated ribs. This manufacturing method reduces the weight of the reinforcement. However, tubular reinforcement is difficult to manufacture with a diameter of less than 20 mm. In addition, the economic effect is insignificant due to the complexity of the technology and increased energy consumption In the manufacture of such fittings.

Another type of reinforcement is rope reinforcement, which includes several metal wires twisted into bundles. Reinforcement of this design creates more efficient structure compared to rebar, but is much more expensive to manufacture.

Since the last century, multiple efforts have been made to develop spiral reinforcement, which, in terms of structural quality factor (load-bearing capacity per unit mass), can significantly exceed the currently used corrugated reinforcing bars.

None of these soiutions, due to their major shortcomings, could be implemented.

One of the existing designs of the reinforcing bar [2] is a metal rod with three to seven spiral grooves on its surface. The bottom of each groove is a convex surface; the grooves cross-sections are W or M shaped.

In this case, the depth of the grooves is much less than the diameter of the rod.

While somewhat improving the adhesion of such reinforcement to concrete, this solution has the following disadvantages:

- small volume of grooves, which does not allow full use of the strength properties of concrete;

- presence of sharp edges - stress concentrators that contribute to the destruction of concrete and its delamination from reinforcement;

- technologically challenging design complicates the manufacturing process due to the shape of the grooves.

The combination of these shortcomings makes this solution impractical.

Closest to the claimed solution is spiral reinforcing bar [3] which has a straight central axis, with a pitch of turns ranging from 1 to 10 diameters of an imaginary cylinder into which the specified rod fits, the planar cross section of which includes a central part around the central axis of the rod and at least two petals connected to the central part and separated by gaps, while the material of the rod section is redistributed, as far as possible, to the periphery of its section;

This solution has the following serious drawbacks:

- almost complete absence of tensile elongation, which does not allow the use of such reinforcement in reinforced concrete structures, especially in seismic regions

- impossibility of ribs forming on the sides of the petals due to the difference in linear velocities along the height of the tapered sections of the rolls. This leads to a deterioration in the adhesion of reinforcement to concrete, and, as a result, to a decrease in the strength of the reinforced concrete structure;

- slippage of the conical sections of the rolls relative to the formed profile reduces the service life of the rolls, increases energy consumption and requires the mandatory application of lubricant, which then must be removed from the finished profile;

- uneven hardening of the metal, which inevitably occurs during its cold rolling between rolls with a triangular cross-sectional profile.

- overhardened area of the rebar adjacent to the central part of the rod, which causes it to become excessively brittle, leading to its destruction when loads are applied. Therefore it is impossible to fully use the strength properties of the reinforcement;

- due to the same increased fragility of the reinforcement, it is extremely difficult, up to complete impossibility, to bend the rods in the manufacture of reinforcing cages.

These shortcomings make the usage of this type of rebar in reinforced concrete structures inexpedient The purpose of the invention.

The objectives of the present invention are:

1. Development of steel reinforcement for reinforced concrete, which allows full use of the strength properties of both the reinforcement itself and the concrete that is part of the structure, when this structure carries tensile and bending loads.

2. Development of a production method for such reinforcement, as well as recommendations for the creation of reinforced concrete building products using fittings according to the present invention.

Proposed technical solution.

The aforementioned goals are achieved by the following technical solutions:

- the reinforcing bar is made polyhelical due to the fact that its central longitudinal axis has a spiral shape;

- the planar cross-section of the reinforcing bar is made in the shape of a polygon with the number of sides equal to or greater than 3. and each of the surfaces formed along the length of the bar by the sides of the specified polygon is a longitudinal spiral recess on the surface of the bar;

- the cross-sectional area of the reinforcing bar according to the invention is (70±5)% less than the cross-sectional area of a standard rebar similar in number, while ensuring the strength class of the reinforcing bar according to the invention in the range (800 ... 1100) N/mm²;

- the surfaces of the spiral recesses are textured;

- edges between them are rounded.

- a polyhelical reinforcing bar is made from rod billets by rolling, for example, on a single-stand longitudinal-helical rolling mill, including an appropriate number of forming rolls deployed to an imaginary rectilinear axis of the formed bar at an angle α = (17 ... 40)°;

- rolling is carried out cold or hot, followed by thermal hardening;

The following presentation is based on the example of a reinforcing bar, the planar cross section of which is a polygon with the minimum possible number of sides, in this case, a triangle, and provides a general understanding of the essence of the invention. It is not intended to be an all-inclusive overview of all possible variations and is intended neither to identify key or critical elements of all variations nor to limit the scope of any one or variations of the invention, it is only intended to present a description of the invention in a simplified form.

The invention is illustrated in the following figures: Fig.1 - side view of a polyhelical reinforcing bar. Fig. 2: end view of a polyhelical reinforcing bar.

The cross planar section of the specified rod is inscribed in an imaginary circle with a diameter d, which determines the number of reinforcement

The specified rod is inscribed in an imaginary cylinder with a diameter D, which determines the height of the wave of the longitudinal axis of the rod, which determines the size of the plastic deformation region of the rod before its destruction when a tensile load is perceived. Wherein

D = (1.2...1.6) d (1)

The step T of the helix of the proposed reinforcing bar is determined by the ratio

T= ( 5...20) d (2)

The cross planar section of the specified rod is a polygon with the number of sides N ≥ 3 (3)

The planar cross-sectional area of the rod is described by the relation = (0.35...0.45) S_D, (4) where S_D is the area of an imaginary circle with a diameter D. Each of these spiral surfaces is textured with a system of linear, mesh or dotted protrusions. The shaping can also be chaotic, formed, for example, by shot blasting the rolls. In any case, the height of said protrusions k is k = (0.03 ... 0,05) d (5)

All reinforcing bar edges are rounded with a radius R equal to

R≥ 0.5mm (6)

Not all obvious variations are shown in this description. The language or terms of this description are descriptive and not restrictive.

No term in the specification or claims should be given an unusual or special meaning unless it is expressly given as such.

Comparative evaluation of the strength characteristics of reinforcement samples according to the present invention and according to GOST 34028-2016 (test results).

Polyhelical reinforcing bars according to the present invention were rolled from a billet, which is a Ø8 bar made of steel 25G2S, so that their planar section is inscribed in an imaginary Ø8 circle, and the entire rod is inscribed in an imaginary Ø12 cylinder. The mass of such a rod was 0.232 kg/m,

Its strength characteristics were compared with those of reinforcing bar No. 8 according to GOST 34028-2016, made of the same steel, the mass of which was 0.395 kg/m., that is, 1.7 times more than that of the bar according to the present invention.

The breaking force for rebar No. 8 according to GOST 34028-2016 was 32.44 KN, and for rebar No. 8 according to the present invention - 28.25 KN, which is confirmed by "Raport de incercari No. 67 din 08.02.2022." (Research report No. 67 dated 08.02.2022).

The same samples were molded into a parallelepiped with a cross section of 60 x 60 mm from fine-grained concrete of class B25 (M300). The resistance of concrete to axial tension and tension in bending was not standardized.

According to the test results, samples with polyhelical reinforcement showed a strength of 33.0 KN (Raport de incercari No. 270 din 10.05.2022), slightly higher than that of samples with reinforcement according to GOST 34028-2016 (5).

Thus, the sample in concrete showed an increase in tensile strength compared to reinforcement as such 33.0 : 28.25= 1.16.

In other words, fine-grained concrete M300, not very strong under tensile toads without dispersed reinforcement, increased the resistance of the reinforcement as such by 16%.

It should be expected that dispersion-reinforced concrete with a higher tensile strength would increase this difference even more significantly.

The same tests showed that the elongation of polyhelical reinforcement samples as such was 1 and 2%, and in the same samples molded into concrete - about 3%.

This confirms the assumption underlying the present invention, that the replacement of reinforcement according to GOST 34028-2016 with polyhelical reinforcement will provide synergy - a phenomenon when the total effect of the influence of two or more factors exceeds the sum of the influence of individual factors. In other words, the tensile resistance of concrete becomes in this case so effective that it must be taken into account when calculating the reinforced concrete structure for tensile and/or bending strength.

It should be remembered that at present, when calculating reinforced concrete structures for tensile and bending loads, the strength of concrete is not taken into account due to its negligible influence.

The bend test of the reinforcement sample around the mandrel, the radius of which was equal to 3d, showed the complete absence of visible cracks, which is illustrated by the photograph below (Photo 1):

Photo 1

Thus, the test results confirmed the full compliance of the tested samples of polyheiical rebar No. 8 with the requirements of the standard.

A 70% increase in finished rebar footage with the same steel consumption was also confirmed.

Method for manufacturing a polyheiical reinforcing bar

The reinforcing bar described above is made from rod billets, for example, on a single-stand longitudinal-helical rolling mill, including an appropriate number of forming rolls turned at an angle a to the imaginary axis of the formed bar, equal to α = (17...40)°. (7)

The gap between the forming rolls determines the shape and dimensions of the polygon that forms the cross section of the reinforcing bar.

The turn angle of the mill rolls relative to the axis of the rolled rebar determines the pitch of the helix. During cold rolling, in order to improve the conditions for gripping the billet by the forming rolls of the mill, the lead end of the billet is heated by, for instance, induction heating with industrial or high frequency currents, to a temperature of C, in the range

C = (400...600) °C (8) in which the steel becomes significantly more ductile, in the section L, with a length

L = (10...30) mm (9)

It is also possible to increase the billet surface gripped by mill rolls by machining or plastic deformation of its lead-in end.

This method of production provides the strength class of reinforcement according to the invention in the range (800 ... 1000) N/mm² This means the yield strength of the reinforcement exceeds the yield strength of the hot-rolled billet from which it is made by (60 ... 80)%.

In the manufacture of patentable rebar at metallurgical plants, It can be hot-rolled, also from rod billets, with subsequent heat strengthening.

It is also possible to produce polyhelical rebar from a continuous billet by making the end stand of a small section mill rotating.

Comparative tests of concreted samples of polyhelical and standard reinforcement have shown that failures during joint work under ultimate tensile loads occur in different ways, that is, the claimed reinforcement and standard reinforcement work jointly with concrete in completely different ways.

For samples with standard reinforcement, with increasing load, the weakest of the concrete protrusions located in one of the gaps between the longitudinal and inclined protrusions on the reinforcing bar is cut off. After that, the process of cutting off these discrete protrusions of concrete acquires an avalanche-like character. With further elongation of the reinforcement, a transverse crack appears in the concrete, along which the reinforcement breaks. In parallel, cracks in the concrete develop, located randomly, pieces of concrete are separated from the product and collapse down.

For samples with poiyhelical reinforcement according to the present invention, the influence of the heterogeneity of the concrete matrix ceases to play such a significant role due to the absence of discrete areas of its contact with the reinforcement. in addition, not only individual thin layers of concrete working in shear are involved in the work, but much larger volumes of concrete working in tension.

This can be seen from the nature of the destruction of concrete when the ultimate loads are reached during research (Photo 2)

Based on this, recommendations for using poiyhelical rebar in reinforced concrete building structures were developed, aimed at increasing the resistance of concrete to tensile and bending loads, including:

- the project should include requirements for the strength properties of concrete not only in compression, but also in tension and bending;

- the preferred use of fiber-reinforced concrete;

- in the manufacture of flat meshes, it is necessary to use the poiyhelical rebar of the correct size, both in the longitudinal and transverse directions, choosing the size of rebar by calculating loads in each of the directions:

- in spatial frames, transverse rods or rings must also be made of poiyhelical reinforcement;

- in the structures of frames for molded products (columns, crossbars, supports for power supply networks, etc.), instead of annular transverse products, it is preferable to use a spiral of the appropriate shape, also made of polyhelical reinforcement;

- in the manufacture of frames, in all cases it is preferable to replace welding with ligatures, since cold-strengthened polyhelical rebar loses strength significantly more when heated than hot-rolled smooth or corrugated rebar.

Advantages of the polyhelical reinforcing bar and technical result

As we have demonstrated, implementation of polyhelical rebar allows for a more effective use of the strength properties of both the concrete and rebar itself due to cold hardening of the billet material, which makes it possible to increase its yield strength by an average of 70%. The increased effectiveness is due to:

- a patented reinforcement geometry, which significantly increases the volume of concrete that takes tensile loads;

- replacement of discrete sections of concrete at the points of contact with reinforcement by continuous volumetric contact;

- measures to improve the perception of tensile loads by concrete due to changes in the structures of the frames and in the formulation of the concrete used.

As a result, the proposed reinforcing bar provides a higher strength of the reinforced concrete structure than a 70% heavier standard reinforcing bar of the same size.

Thus, the proposed polyhelical reinforcing bar makes it possible to almost halve the cost of reinforcing of reinforced concrete structures. Accordingly, logistics costs are reduced.

Considering that the annual global consumption of rebar is about 2 billion tons, the total replacement of standard rebar with polyhelical rebar will almost halve the carbon footprint of its production and transportation, dramatically improving the industry’s sustainability.

A very important advantage of the patented reinforcement is that, in the event of the destruction of a reinforced concrete structure, for example, during an earthquake or explosion, its use significantly reduces the risk of death or injury to people by falling pieces of concrete, since its adhesion to the reinforcement is continuous, and not limited to discrete sections, as with standard fittings, In other words, the destroyed concrete part of the structure remains hanging on the reinforcement, and does not fail from it

1. INTERSTATE STANDARD GOST 34028-2016 RELATED REINFORCEMENT

FOR REINFORCED CONCRETE STRUCTURES. Specifications

2.CN201321682

3. EA 031981

Claims

1. A reinforcement for reinforced concrete, comprising:

- spiral recesses on the bar surface,

- spiral longitudinal axis of the bar,

- polygonal planar cross-section of the bar, where the number of polygon sides is equal to at least three, wherein each of the surfaces formed by the sides of the specified polygon is a longitudinal helical recess on the surface of the rod, with the helix pitch T determined by the relation T = (5 ... 20) d, where d is the diameter of an imaginary circle into which the transverse planar section of the rod is inscribed;

2. A reinforcement as in claim 1, wherein the rod is inscribed in an imaginary cylinder with a diameter D, where D Is equal to (1.2... 1.6) d.

3. A reinforcement as in claims 1 and 2, wherein its planar cross-sectional area is S_d = (0.35...0,45) S_D, where SD _is the cross-sectional area of an imaginary cylinder with a diameter D.

4. A reinforcement as in claims 1 , 2, and 3, wherein the ribs formed by the joints of the indicated spiral recesses are rounded with a radius R ≥ 0.5 mm.

5. A reinforcement as in claims 1 , 2, 3, and 4, wherein the surfaces of the spiral recesses are made textured, for example, linear, dotted, mesh corrugation, or chaotic irregularities, with the height k of the irregularities in any of their shapes is determined by the ratio k = (0.03...0.05) d.

6. Method of manufacturing of a rebar as in claims 1 , 2, 3, 4, and 5, wherein rebar is produced from rod billets, for example, on a single-stand longitudinal-helical rolling mill, including an appropriate number of forming rolls deployed to an imaginary rectilinear axis of the formed rod at an angle α = ( 17...40)°.

7. Method of manufacturing reinforcement as in ciaim 6, characterized by that the roiling is cold.

8. Method for manufacturing of a rebar as in claims 6 and 7, wherein before the billet is captured by the forming rolls, its lead-in end is heated to (400...600) °C by, for example, induction heating with industrial or high frequency currents, in the area (10...30) mm.

9. Method for manufacturing of rebar as in claims 6, 7, and 8, wherein the rolling is carried out on a multi-stand mill in the form of an endless billet, which is cooled until it enters the end stand, which is made rotating.

10. Method for manufacturing of rebar as in claim 9, wherein the hot rolling is carried out with subsequent heat strengthening of the reinforcing bar.