WO2012022005A1

WO2012022005A1 - Steel bar comprising projections, used to form concrete frameworks, such that the concrete remains in the elastic range in terms of strength with a stress of less than 50% of the breaking stress, in which the bar has a diameter d and the projections are spaced apart by a distance l, have a height h and an area of less than one fourth of the perimeter multiplied by l

Info

Publication number: WO2012022005A1
Application number: PCT/CL2011/000046
Authority: WO
Inventors: Juan Pablo Covarrubias Torres
Original assignee: Juan Pablo Covarrubias Torres
Priority date: 2010-08-20
Filing date: 2011-08-18
Publication date: 2012-02-23
Also published as: WO2012022005A9; JP2013534284A; BR112013004000A2; EP2639378A4; MX2013001947A; US20130192164A1; CN103201440A; CL2010000889A1; EP2639378A1

Abstract

The invention relates to a steel bar comprising projections, which is used to form concrete frameworks and allows the concrete to remain in the elastic range thereof in terms of strength with a stress of less than 50% of the breaking stress, in which: the nominal diameter of the bar is Dn; the distance between the centers of consecutive projections is "L"; projection height is "h"; and projection area is "A," said area "A" being greater than 0.12 x P x L and less than 0.25 x P x L. The height "h" is greater than 0.12 x L and less than 0.25 x L.

Description

STEEL BAR WITH HIGHLIGHTS TO CONFORM CONCRETE ARMORS, SO THAT THE CONCRETE REMAINS IN THE ELASTIC RESISTANCE AREA WITH A VOLTAGE LESS THAN 50% OF THE BREAK TENSION, THE BAR HAS A DIAMETER D, HIGHLIGHTS A DISTANCE IN A DISTANCE L AND OF A HEIGHT H, WITH AN AREA LESS THAN A

FOURTH OF THE PERIMETER BY L.

DESCRIPTION

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a steel bar for forming concrete reinforcements, which has an area of projections, greater than those of the prior art, such that, when a reinforced concrete structure is subjected to a dynamic solicitation, said structure of reinforced concrete is able to resist fatigue, thanks to the greater area of the projections, which makes the concrete remain in the elastic zone of its resistance with a tension less than 50% of the breaking stress.

BACKGROUND OF THE INVENTION

In reinforced concrete structures applied to fatigue, the highest tensions in the concrete are in the area of the bars of the steel bars. For this reason, one of the objectives of the present invention is to improve the design of the projections so as to reduce the stresses in the concrete to values less than 50% of the concrete strength. With these stresses it is ensured that the reinforced concrete element has an infinite resistance to fatigue load cycles.

Steel bars for reinforced concrete have so far been optimized to achieve the necessary anchor values in static solicitations. This is that the projections are designed using 100% of the concrete strength. With this design, the fatigue resistance is low and the concrete system with bars with projections has a low duration of number of loads. ASTM indicates a minimum height of the shoulder and distance between them given by Table 1 of ASTM 615A 615M. This height and distance of projections has the "Relative Rib Area" between the values 0.057 and 0.087. He ASTM 615 supplement for "Reala high value bars"

This value must be at least 0.10 and not greater than 0.14.

For the practical effects of the design of slabs, pillars, beams and walls, the values used in the different parameters of concrete and steel bars, subject to static solicitations, are standardized and a person versed in the art of civil engineering, Using these standardized values you will be able to design a sturdy slab. The Chilean design standard for reinforced concrete is based on the ACI 318 standard and the steel considered is that of the Chilean standard NCh 204 and ASTM 615.

However, against dynamic loads, that is, loads that are repeated several times over a period of time, the behavior of the concrete is weak and usually collapses due to fatigue.

Fatigue is the failure of a structural element due to the action of said dynamic load, where the acceptable value of the dynamic load is lower than the breaking load. This is because the dynamic load is repeated "ω" times in time.

In figure 1, the scheme of a concrete slab (1) is shown, which is formed by a typical mixture (2) of cement and sand plus a certain amount of gravel (3). To form the reinforced concrete (7), steel bars (4) are used, which have a surface (5), on which a plurality of projections (6) are located, as shown in Figure 2. With these Steel bars (4) form a structure that is surrounded by concrete (1), thus forming reinforced concrete (7), shown in Figure 3.

As can be seen in figure 3, the reinforced concrete (7) is subjected to a dynamic load F, whose effect on the concrete (1) can be seen in figures 4 to 7, and graphically, in figure 8. The graphic 8, represents the effort σ = F / Ah, where F is the load and Ah is the area that absorbs the load in the concrete. The deformation is represented by "ε".

When the dynamic load F is slight, less than 50% of the strength of the concrete, the concrete (1) does not suffer damage, because it works in the low elastic zone of its resistance, always remaining as a compact material, as can be seen in figure 4, this being represented by point P1 of the graph of figure 8.

When the dynamic load increases, the concrete (1) begins to suffer damage, generating micro-cracks (8), because it begins to work in the high elastic zone of its resistance susceptible to growth of fatigue microcracks, as seen in figures 5, being represented by

of figure 8.

When the dynamic load continues to increase, the concrete (1) begins to suffer major damage, because the micro-cracks (8) begin to join generating cracks (9), because the concrete (1), works in the area maximum of the elastic limit of its resistance, as seen in figures 6, being represented by point P3 of the graph of figure 8.

Because the concrete is no longer a compact material, product of the cracks (9), the area of resistance of the concrete "Ah" decreases, the material is already fatigued, which is enough with a force of smaller magnitude so that σ = F / Ah, remain at point P4, as shown in the graph of figure 8. In this case, the cracks (9) are transformed into breaks (10), as illustrated in figure 7.

In order that the concrete (1) does not work in the elastic zone with greater tension at 50% of its resistance, much less in the fatigue area of the graph (σ, ε), then it becomes necessary that at equal loads Or, at ugly dynamic loads, the concrete resists these loads well, without being damaged by fatigue.

For this purpose, the present invention proposes a steel bar (10), whose plurality of projections (6), has an area of contact with the concrete greater than the bars of the state of the art, in such a way to reduce tensions with in order to prevent concrete (1) from breaking (10) when forming reinforced concrete (7).

In general, in the state of the art it has been sought to improve the adhesion of the steel bars within the reinforced concrete, but they do not address the problem of fatigue, generating until now, the problem described above.

In document ES 423821 (Wischin) published on October 16, 1976, an improvement in reinforcement of reinforced concrete rod reinforcements is disclosed to improve the intimate bond between the concrete and the rod. The rod has oblique projections of approximately sickle-shaped longitudinal section, arranged in at least one group on the surface of a round or polygonal rod core and preferably running parallel to each other in this group, characterized in that the angle of inclination of the oblique projections with respect to the axis of the rod, and the separation of the adjacent oblique projections in the direction of the axis of the rod, as well as the length of the oblique projections, are suitable to each other so that the contiguous oblique projections are they overlap so much that the sum of the cross-sectional areas of the rod core and oblique projections is approximately as large in each cross section of the rod. In each case only two highlights immediately oblique neighbors of each other from the same group, it

extremes that pass to the surface of the rod. Continuous oblique projections overlap by at least a quarter, preferably and at least a third of its length. In this document it is noted that it is known that the resistance of intimate adhesion of the rods, depends on the projection of the area of elevation of the flanks of the oblique projections, referred to the surface of the rod core; on the plane normal to the axis of the rod. The rod according to the invention described in ES 423821 has the same flank area, and therefore also the same intimate bond strength as the known rods, when oblique projections arranged at essentially smaller separations are relatively lower than in the known rods. This document indicates that the flexibility and fatigue resistance of the rods increases with the height of the oblique projections decreasing. Therefore, the rods described in ES 423821 would have better flexibility and fatigue resistance than known rods.

Document CH 651616 (BALZLI) published on September 30, 1985, discloses a reinforcement bar for reinforced concrete that has at least one longitudinal projection and a plurality of oblique projections. The cross-sectional base of the bar and the envelope curve of the oblique projections are almost circular. The transition of longitudinal and oblique projections on the surface of the bar is carried out continuously. The ends of the plurality of oblique projections are fused continuously in the longitudinal projections on the surface of the bar. The reinforcement bar designed in this way is distinguished by a good union with the concrete without the deformation and resistance to fatigue being violated.

Document DE 1813627 (GERHARD) published on June 25, 1970, discloses a hot rolled bar for concrete reinforcement, which has on the surface to improve the adhesion with concrete, threads of the type that collaborate as anchoring means. Each bar is composed of two or more halves or parts, which are located parallel to each other and combine to form a complete unit of circular section, with the thread projections mounted on the outer surface of the entire bar. Highlights can be single-threaded or multi-threaded. The contact surfaces of one half or one part of the bar can be rounded, and the projections can be arranged at respective angles of said surfaces. This is to facilitate production by a lamination process, with a threaded shoulder distributed evenly throughout the outside. GB 728636 (WESTFALENHUETTE), p

from 1955, it discloses a concrete bar, made of soft steel which is cold rolled with transverse projections while the cross-sectional area is reduced to at least 20 percent. The bars are then tempered at about 400 ° C. to raise the elasticity limit. The steel may be of Thomas steel with a maximum carbon content of 0.5 percent and may contain boron, copper or beryllium, to improve precipitation hardening.

Document GB 925939 (REIMBERT) published on May 15, 1963, discloses a reinforcement bar for concrete, which on the periphery comprises at least one shoulder, which extends longitudinally, the outer surface of which more than one important portion of its width, has a convex configuration that extends progressively away from the inscribed circle that passes through the base of the shoulder and forms an acute angle with it. The bar may be twisted around its axis to give an appearance of helical projections. Each projection includes a narrow surface that connects with the main surface of an adjacent projection, whose surface can be narrow forming acute, obtuse or right angles with the inscribed circle. Additional projections can also be considered in this bar. The reinforcement bar can be produced by extrusion to form one or more longitudinal passages arranged symmetrically with respect to the longitudinal axis of the bar, the torsion of the rear bar causes the partial or total closure of these passages.

GB 191027373 (HATTON), published on November 16, 1911, discloses an improved bar for use in reinforced concrete. The bar has longitudinal projections on the outer surface that are arranged in the form of propellers and can also have transverse projections. The bars can have any shape in their cross section.

In general, the bars of the prior art have been oriented to solve the problem of the adhesion of the bar to the concrete or the fatigue resistance of the bar itself. None of the documents mentioned above disclose steel bar projections for use in reinforced concrete, where the area of said projection is designed so that the concrete does not reach fatigue failure when subjected to dynamic loads. SUMMARY OF THE INVENTION

The present invention relates to a steel bar for forming concrete reinforcements, which has an area of projections larger than those of the prior art, such that, when a reinforced concrete structure is subjected to a dynamic solicitation, said concrete structure reinforced is able to resist fatigue, thanks to the greater area of the projections, which causes the concrete to remain in the elastic zone of least tension at 50% of its resistance to breakage.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a greater understanding of the invention, constitute part of this description and further illustrate part of the prior art and some of the preferred embodiments, to explain the principles of this invention.

Figure 1 shows a cross-sectional view of a concrete structure of the prior art.

Figure 2 shows a side view of a steel bar of the prior art.

Figure 3 shows a cross-sectional view of a reinforced concrete structure of the prior art.

Figure 4 shows a cross-sectional view of a concrete structure subjected to a first load F1, without structural damage.

Figure 5 shows a cross-sectional view of a concrete structure subjected to a second load F2, with micro-cracks.

Figure 6 shows a cross-sectional view of a concrete structure subjected to a third load F3, with cracks.

Figure 7 shows a cross-sectional view of a concrete structure subjected to a fourth load F4, with structural fatigue.

Figure 8 shows a graph (σ, ε), which exemplifies the structures shown in Figures 4 to 7.

Figure 9 shows a side view of a steel bar according to the present invention.

Figure 10 shows a cross-sectional view of a reinforced concrete structure, which uses the steel bar of the present invention. Figure 11 shows an enlarged view of an e

armed, which uses a steel bar of the prior art, where the loading area of the concrete product of the projections of said steel bar is illustrated.

Figure 12 shows an enlarged view of a reinforced concrete structure, which uses the steel bar of the present invention, where the loading area of the concrete product of the steel bar projections is illustrated.

Figure 13 shows an enlarged view of a reinforced concrete structure, which uses the steel bar of the present invention, where the area of the steel bar projections is illustrated.

Figure 14 shows a graph (σ, ε), illustrating the area in which the concrete works when using the steel bar of the present invention.

Figure 15 shows an enlarged side and front view of the bar with the projections, where the parameters defining the bar of the present invention are highlighted.

DESCRIPTION OF THE INVENTION

The present invention relates to a steel bar for forming concrete reinforcements, which has an area of projections larger than those of the prior art, such that, when a reinforced concrete structure is subjected to a dynamic solicitation, said concrete structure reinforced is able to resist fatigue, thanks to the greater area of the projections, which makes the concrete remain in the elastic zone with tensions less than 50% of its resistance to breakage.

As shown in Figures 9 and 12, the steel bar (11) of the present invention has a surface (5) on which there is a plurality of projections (12). In order that the tension in the concrete is lower, the area "A" of the shoulder (12) is greater than the area of the corresponding shoulder of the prior art.

When a structure is subjected to a load, the protrusion of the steel bar transmits that load per unit area to the concrete, generating a distribution of tension in the concrete that will depend on the area of the projection. If the area of the projection is greater, the same load per unit of area transmitted to the concrete will be less, so that the distribution of tension in the concrete will also be less.

Thus, on the basis of Figures 11 and 12, when a structure of the prior art is subjected to a load, the tension that the concrete (1) must withstand in the area (13) is much greater than the tension it must withstand the concrete (1) in the area (14), of a structure with equal load. This is because the á

steel bar (11), is larger than the corresponding area of a shoulder of a steel bar of the prior art.

As stated above, in order for the concrete not to suffer fatigue, the area "A" must be such that, the tension OA of the concrete must be comprised in the elastic zone under 50% of its breaking stress.

Thus, the area "A" of the projection (12) of the steel bar (11) of the present invention must be calculated so that the concrete works in the elastic zone under the range OAI - OA2 and CAÍ - £ A2, according to what is shown in the graph of figure 14, where OA2 is the tension equal to 50% of the breaking stress of the OR concrete.

To define the bar of the present invention, the parameters of the ACI 408-3 standard will be used. This standard is based on studies conducted by Clark (1946, 1949), who found an improved performance ratio for the bars, given by the relative area parameter of the Rr highlight:

Where:

1) The relative area of the shoulder is between the values 0.057 and 0.087 for normal bars according to ASTM 615;

2) The relative area of the projection is at least 0.10 but not greater than 0.14 for bars with relative area of high projection;

3) The projections are at an angle β of 45 ° to 65 ° with respect to the axis of the bar. The highlights should not intersect. The use of X-patterns and diamond patterns for highlights is not allowed;

4) The spacing of the projections is at least 0.44 of the nominal diameter "Dn" of the reinforcement bar;

5) The average width of the projection must be less than or equal to one third of the average distance "L" between the projections.

6) The size of the bar must not exceed N ° 11, from the following table:

The above defines the highlights and geometry for the state of the art bars. However, for the concrete to remain in the elastic zone with stresses less than 50% of its resistance to fatigue breakage, the bars of the present invention have an Rr that is in a range between 0.12 and 0.25 .

In Fig. 15, the parameters defining the bar of the present invention are clearly shown. Thus we have that "P" is the perimeter corresponding to the nominal diameter of the bar, "L" is the distance between centers of the consecutive projections; Dn is the nominal diameter of the bar; h is the height of the bar protrusion; and "A" is the area of the bar protrusion.

According to the parameters of the bar shown in Figure 15, the value of Rr then remains as:

With the foregoing, the area of the bar projections of the present invention is:

A = Rr x P x L (3) If the nominal perimeter is:

P = Dn x π (4) Then, the area of the projection of the present invention is comprised between:

0.12 x P x L <A <0.25 x P x L; or ( ⁵ )

0.12 χ Dn χ π χ L <A <0.25 χ Dη χ π χ L (6) Taking into account that the area "A", shown in Figure 15, is equal to:

Replacing (7) and (4) in equation (2), you have:

Then, the height "h" of the shoulder of the present invention is comprised between:

Therefore, the distance "L" between projections that define the area of the bar of the present invention, is set by the values of Rr and h, preferring the value given for the maximum average spacing of Table 1 of ASTM 615.

Also, according to Materials Research: "Analysis of the relative rib area of reinforcing bars pulí out tests" (Gomes Barbosa et al.), October / December 2008, it is stated in the conclusions that: "The bar with a spacing of 70 % of the diameter and a height equal to 9% of the diameter developed a greater tension of adhesion, according to the results obtained in this investigation. "

Therefore, it is also applicable to the distance "L" between projections, which defines the area of projections of the bar of the present invention, is that said distance is about 70% of the nominal diameter Dn of the bar.

It is important to note that both Table 1 of ASTM 615 and the publication of Gomes Barbosa et al., Which define the distance "L" between projections, said distance "L" is already known in the prior art, and is only considered in this request as an aid to define more accurately, the area of projections of the bar that is the subject matter of the present invention.

Claims

1. - A steel bar with protrusions to form concrete reinforcements, which allows the concrete to remain in the elastic zone of its resistance with a tension less than 50% of the breaking stress, where said bar has a nominal diameter Dn; a distance between centers of consecutive projections "L"; a height of the projection "h", and an area of projection "A", CHARACTERIZED because said area "A" is greater than O, 12 x P x L and less than 0.25 x P x L.

2. - A steel bar with projections for forming concrete reinforcements, according to claim 1, CHARACTERIZED because said area "A" is greater than 0.12 χ Dη χ π χ L and less than 0.25 x Dn x π x L.

3. - A steel bar with projections for forming concrete reinforcements, according to claim 1 or 2, CHARACTERIZED because said height "h" is greater than 0.12 x L and less than 0.25 x L.

4. - A steel bar with projections for forming concrete reinforcements, according to any of claims 1 to 3, CHARACTERIZED because the distance "L" between projections is fixed by the values of Rr and h, preferring the value given for the average spacing maximum of Table 1 of ASTM 615.

5. - A steel bar with projections for forming concrete reinforcements, according to any of claims 1 to 4, CHARACTERIZED because the distance "L" is about 70% of the nominal diameter Dn of said bar.