STEEL BAR WITH PROJECTIONS FORMING CONCRETE FRAMEWORKS

Abstract

A steel bar with ribs to form concrete armours, which allows the concrete to be maintained on the elastic zone of its strength with a stress less than 50% of the damage stress, where such bar has a nominal diameter Dn; a distance between consecutive rib centers “L”; a rib height “h” and a rib area “A”, where such area “A” is greater than 0.12×P×L and less than 0.25×P×L. The height “h” is greater than 0.12×L and less than 0.25×L.

Description

TECHNICAL FIELD OF THE INVENTION

The current invention refers to a steel bar to form concrete armours, which has a ribbed area greater to those of the previous art. Such that, subjecting a reinforced concrete structure to a dynamic load, such reinforced concrete structure is able to resist fatigue thanks to the greater area of the ribs, allowing the concrete to be maintained on the elastic zone of its stress with strength less than 50% of the ultimate COMPRESSIVE strength.

BACKGROUND OF THE INVENTION

In reinforced concrete structures loaded to fatigue, the highest strengths on the concrete are located in the ribbed zone of the steel bars. For this reason, one of the objectives of the current invention is improving the design of the ribs, to decrease the strengths on the concrete to values less than 50% of the concrete strength. With these strengths, the reinforced concrete element is ensured to have an infinite resistance to fatigue loading cycles.

The steel bars for reinforced concrete have been optimised up to now for obtaining the necessary anchoring values in the static loads. Thus, the ribs are designed using a 100% of the concrete strength. With this design, the strength to fatigue is low and the concrete system with ribbed bars has a low duration of loading number. ASTM indicates the minimum height of the rib and the distance between them given by the Table 1 of the ASTM 615A/615M. This height and distance of the ribs have the “Relative Rib Area” between the values 0.057 and 0.087. The ASTM 615 supplement for high value bars of the “Relative Rib Area” states this value must be less than 0.10 and no greater than 0.14.

For practical effects of the slabs, columns, beams and walls design, the values used in the different concrete parameters and steel bars, subjected to static loads are standardised and a person crafted in civil engineering, using such standardised values will be able to design a resistant slab. Chilean standard of Reinforced Concrete design is based on the ACI 318 standard and the steel considered is from the Chilean standard NCh 204 and ASTM 615.

Nevertheless, facing dynamic load, i.e., loads repeating several times in a period of time, the concrete behaviour is weak and likely to collapse by fatigue.

The fatigue is the failure of a structural element by the action of such dynamic load, where the acceptable value of the dynamic load is lower than the ultimate COMPRESSIVE strength. This is, because the dynamic load is repeated “ω” times in time.

On FIG. 1, a concrete slab scheme is shown (1), which is formed by a typical mix (2) of cement and sand, plus a determined quantity of gravel (3). To form the reinforced concrete (7), steel bars are used (4), which have a surface (5) over which multiple ribs are located (6), as shown on FIG. 2. With these steel bars (4), a structure is formed surrounded by concrete (1) and therefore forming the reinforced concrete (7) shown on FIG. 3.

As seen on FIG. 3, reinforced concrete (7) is subjected to a dynamic load Fω, whose effect on concrete (1) is seen on FIGS. 4 to 7 and graphically on FIG. 8. Chart 8 shows the stress σ=F/Ah, where F is the load and Ah is the area absorbing the load on concrete. The deformation is represented by “ε”.

When the dynamic load Fω is low, less than 50% of concrete strength, the concrete (1) does not suffer damage. Because this works on the low elastic zone of its strength, always maintaining as compact material as shown on FIG. 4, being this represented by point P1 of the chart on FIG. 8.

When dynamic load increases, the concrete (1) starts suffering damage, resulting micro cracks (8), since this starts to work on the high elastic zone of its strength sensitive to fatigue micro cracks increase as shown on FIGS. 5, being this represented by point P2 of the chart on FIG. 8.

When dynamic load keeps increasing, the concrete (1) starts to suffer greater damage, as micro cracks (8) start to join resulting on cracks (9). Hence, the concrete (1) works on the maximum zone of the elastic limit of its strength as shown on FIGS. 6, being this represented by point P3 of the chart on FIG. 8.

By virtue, the concrete is no longer a compact material, resulting from the cracks (9) the concrete strength area “Ah” decreases. The material is already fatigued, therefore, a low magnitude force is enough for σ=F/Ah, and maintains in point P4 as shown on the chart of FIG. 8. In this case, cracks (9) are transformed in ruptures (10) as shown on FIG. 7.

With the objective that the concrete (1) do not work on the elastic zone with strength greater than 50% of its resistance, or on the fatigue zone on the chart (σ, ε). Therefore, it is necessary that the concrete resist well the even loads or to dynamic loads Fω, without being damaged by fatigue.

For such purpose, the current invention proposes a steel bar (10) whose multiple ribs (6) have a contact area with the concrete, greater than the bars of the state of art. In such way to decrease strengths in order to avoid the concrete (1) suffers ruptures (10) at forming the reinforced concrete (7).

Commonly, the state of art has searched to develop the adherence of the steel bars within the reinforced concrete, but does not board the fatigue problem, resulting up to date the problem previously described.

In the document ES 423821 (Wischin) published on the 16th Oct., 1976, the execution on steel rod armours for reinforced concrete is disclosed for improving the intimate joint between concrete and rod. The rod has oblique ribs of longitudinal section approximately as a sickle, arranged in at least a group over the surface of a round or polygonal rod core and go by preferably parallel between them in this group. Characterised by the bending angle of the oblique ribs respecting the rod axis and the separation of the contiguous oblique ribs in the direction of the rod axis, as well as the length of the oblique ribs are adequate one to others as the contiguous oblique ribs are so overlapped that the sum of the cross section of the rod core and of the oblique ribs is approximately equal as big in each cross section of the rod. In each case, only two oblique ribs immediately next to each other of the same group are overlapped with their border zones that go by to the rod surface. The continuous oblique ribs are overlapped in at least a quarter part, preferably and for at least a third part of their length. In this document, it is pointed that the intimate adherence strength of the rods is known, depending on the projection of the side elevation of the oblique ribs, referred to the rod core surface over the normal plane to the rod axis. According the described invention in the document ES 423821, the rod shows the same side area and therefore, the same intimate joint strength of the rods known. When the oblique ribs arranged to separations essentially smaller are relatively lower than in rods known. This document shows the flexibility and strength to the rods strength increases by decreasing the height of the oblique ribs. Therefore, the rods described in the document ES 423821 would show a better flexibility and strength to fatigue resistance than the known rods.

The document CH 651616 (BALZLI) published on the 30th Sep., 1985, discloses a reinforcement bar for reinforced concrete that has at least a longitudinal rib and multiple oblique ribs. The base of the cross section of the bar and the surrounding curve of the oblique ribs are almost circular. The transition of the longitudinal and oblique ribs on the bar surface is carry out continuously. The borders of the multiple oblique ribs are fused continuously in the longitudinal ribs of the bar surface. The reinforcement bar designed this way is distinguished by a good joint to the concrete without the deformation and fatigue strength is damaged.

The document DE 1813627 (GERHARD) published on the 25 Jun., 1970 discloses a heat laminated bar for concrete reinforcement, which has on the surface for improving adherence to concrete, ribs thread type ribs collaborating as anchoring means. Each bar is formed by two or more half or parts located parallel between them and are combined to form a complete unit of circular section with the thread ribs mounted on the exterior surface of the entire bar. The ribs can be of a unique sub-process or several sub-processes. The contact surfaces of a half or part of the bar can be rounded and the ribs can be arranged in angles respecting to such surfaces. This is to ease production of a lamination process with a thread rib distributed uniformly in all the exterior part.

The document GB 728636 (WESTFALENHUETTE) published on the 20th Apr., 1955 discloses a concrete bar made of mild steel, which is cold laminated with cross ribs while the cross section area is reduced to less than 20 per cent. The bars are then returned to 400° C. for increasing the elasticity limit. The steel may be Thomas with a maximum content of carbon of 0.5 per cent and may contain boron, copper or beryllium for improving the precipitation hardening.

The document GB 925939 (REIMBERT) published on the 15th May, 1963 discloses a reinforcement bar for the concrete, which in the periphery comprehends at least one rib extending lengthways. The exterior surface of which more than one important portion of its width has a convex configuration extending progressively moving away from the registered circle, which goes through the rib base and forms an acute angle with this. The bar can be twisted around the axis for giving an appearance of helicoidal ribs. Each rib includes a narrow surface, connecting to the main surface of an adjacent rib, whose surface may be narrow forming acute, thick or straight angles with the registered circle. Additional projections can also be considered on this bar. The reinforcement bar may be produced by extrusion conforming one or more longitudinal passages arranged symmetrically respecting the longitudinal axis of the bar, the rear bar torque provokes the partial or total close of these passages.

The document GB 191027373 (HATTON), published on the 16th Nov., 1911 disclosures an improved bar for use on the reinforced concrete. The bar has on the exterior surface longitudinal ribs arranged in form of helix and besides may have cross ribs. The bars may have any form in its cross section.

Generally, the bars of the previous art have been oriented to solve the problem of the adherence of the bar to concrete or the strength to fatigue of the same bar. None of the documents previously mentioned disclose ribs of steel bars to be used on the reinforced concrete, where the area of such rib is designed for the concrete not to get the damage by fatigue when is subject to dynamic loads.

BACKGROUND OF THE INVENTION

The current invention refers to a steel bar for conforming concrete armours, which has a major area of ribs to the previous of the art, being subjected to a reinforced concrete structure to a dynamic load, such structure of reinforced concrete is able to resist the fatigue, thanks to the major area of the ribs, making the concrete to be maintained on the elastic zone of stress less than 50% of its strength to damage.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings attached are included to provide a greater comprehension of the invention, constituting part of this description and besides illustrate part of the previous art and some preferred executions for explaining the principles of this invention.

FIG. 1 shows the cross section view of a concrete structure of the previous art.

FIG. 2 shows a side view of a steel bar of the previous art.

FIG. 3 shows a cross section view of a reinforced concrete structure of the previous art.

FIG. 4 shows a cross section view of a concrete structure subjected to a first load F1, without having structural damage.

FIG. 5 shows a cross section view of a concrete structure subjected to a second load F2, with micro cracks.

FIG. 6 shows a cross section view of a concrete structure subjected to a third load F3, with cracks.

FIG. 7 shows a cross section view of a concrete structure subjected to a fourth load F4, with structural fatigue.

FIG. 8 shows a chart (σ, ε), which illustrate the structures shown on FIGS. 4 to 7.

FIG. 9 shows a cross section view of a steel bar according the current invention.

FIG. 10 shows a cross section of a reinforced concrete structure, using a steel bar of the current invention.

FIG. 11 shows an extended view of a reinforced concrete structure using a steel bar of the previous art, where the concrete load zone of the concrete resulting from the ribs of such steel bar is illustrated.

FIG. 12 shows an extended view of a reinforced concrete structure using the steel bar of the current invention, where the concrete load zone resulting from the ribs of the steel bar is illustrated.

FIG. 13 shows an extended view of the reinforced concrete structure using the steel bar of the current invention, where the ribs area of the steel bar is illustrated.

FIG. 14 shows a chart (σ, ε) illustrating the zone where the concrete works by using the steel bar of the current invention.

FIG. 15 shows a side extended view and front view of the ribs, where the parameters defining the bar of the current invention are highlighted.

DESCRIPTION OF THE INVENTION

The current invention refers to a steel bar to form concrete armours, which has ribs greater than those of the previous art, such that, being subjected to a reinforced concrete structure to a dynamic load, such reinforced concrete structure is able to resist the fatigue, thanks to the ribs greater, making the concrete to be maintained on the elastic zone with stresses less than 50% of its damage strength.

As shown on FIGS. 9 and 12, the steel bar (11) of the current invention has a surface (5) over which exists multiple ribs (12). With the objective of the stress on the concrete to be less, the “A” area of the rib (12) is greater than the corresponding area to the rib of the previous art.

When a structure is subjected to a load, the steel bar rib transmits that load per unit of the concrete area, creating a stress distribution on the concrete, which will depend of the rib area. If the rib are is greater, the same load per area unit transmitted to the concrete is less and the stress distribution on the concrete will be less as well.

Therefore, over the base of FIGS. 11 and 12, when a structure of the previous art is subjected to a load, the stress must bear the concrete (1) on the zone (13), being much greater than the stress the concrete must bear (1) on the zone (14) from a structure with the same load. This is because the “A” area of the rib in the steel bar (11) is greater than the corresponding area of a steel bar rib of the previous art.

Upon the above exposed, in order the concrete will not suffer from fatigue, the “A” area must be such that the GA stress of the concrete must be comprehended on the elastic zone below 50% of its damage stress.

In this way, we have the “A” are of the rib (12) steel bar (11) of the current invention must be calculated, so the concrete would work in the elastic zone below the range σA1-σA2 and εA1-εA2. According the shown on the chart of the FIG. 14, where σA2 is the stress equal to 50% of the concrete damage stress GR.

To define the bar of the current invention, ACI 408-3 standard parameters will be used. This standard is based on the studies performed by Clark (1946, 1949), who found a relation of improved performance for the bars, given by the area parameter relative to the Rr rib:

$\begin{array}{cc}\mathrm{Rr}=\frac{\mathrm{Rib}\mathrm{area}\mathrm{projected}\mathrm{normally}\mathrm{to}\mathrm{the}\mathrm{bar}\mathrm{axis}}{\begin{array}{c}\mathrm{Nominal}\mathrm{perimeter}\mathrm{of}\mathrm{the}\mathrm{bar}\times \\ \mathrm{consecutive}\mathrm{between}\mathrm{centers}\mathrm{ribs}\mathrm{distance}\end{array}}& \left(1\right)\end{array}$

Where;

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

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

3) The ribs are located in a β angle of 45° to 65° respecting to the bar axis. The ribs must not cross. The use of X patterns and diamond patterns for ribs is not allowed;

4) The spacing of the ribs is at least 0.44 of the nominal diameter “Dn” of the reinforcement bar;

5) The average width of the rib must be less or equal than a third of the average distance “L” between the ribs.

6) The size of the bar must not be greater than N° 11 of the following table:

TABLE 1
Designation Numbers of Deformed Bars. Nominal Weight [Masses],
Nominal Dimensions and Deformation Requirements.
	Nominal	Deformation Requirements,
	DimensionsB	in [mm]
	Nominal		Cross-				Maximum Opening
Designation	Weight, lb/ft		sectional		Maximum	Minimum	(Segment of
Number of	[Nominal	Diameter in	Area in 2	Perimeter, in	Average	Average	12.5% of the
the BarA	Mass, kg/m]	[mm]	[mm2]	[mm]	Spacing	Height	Nominal Perimeter)
3 [10]	0.376 [0.560]	0.375 [9.5]	0.11 [71]	1.178 [29.9]	0.262 [6.7]	0.015 [0.38]	0.143 [3.6]
4 [13]	0.668 [0.994]	0.500 [12.7]	0.20 [129]	1.571 [39.9]	0.350 [8.9]	0.020 [0.51]	0.191 [4.9]
5 [16]	1.043 [1.552]	0.625 [15.9]	0.31 [199]	1.963 [49.9]	0.437 [11.1]	0.028 [0.71]	0.239 [6.1]
6 [19]	1.502 [2.235]	0.750 [19.1]	0.44 [284]	2.356 [59.8]	0.525 [13.3]	0.038 [0.97]	0.286 [7.3]
7 [22]	2.044 [3.042]	0.875 [22.2]	0.60 [387]	2.749 [69.8]	0.612 [15.5]	0.044 [1.12]	0.334 [8.5]
8 [25]	2.670 [3.973]	1.000 [25.4]	0.79 [510]	3.142 [79.8]	0.700 [17.8]	0.050 [1.27]	0.383 [9.7]
9 [29]	3.400 [5.060]	1.128 [28.7]	1.00 [645]	3.544 [90.0]	0.790 [20.1]	0.056 [1.42]	0.431 [10.9]
10 [32]	4.303 [6.404]	1.270 [32.3]	1.27 [819]	3.990 [101.3]	0.889 [22.6]	0.064 [1.63]	0.487 [12.4]
11 [36]	5.313 [7.907]	1.410 [35.8]	1.56 [1006]	4.430 [112.5]	0.987 [25.1]	0.071 [1.80]	0.540 [13.7]
14 [43]	7.65 [11.38]	1.693 [43.0]	2.25 [1452]	5.32 [135.1]	1.185 [30.1]	0.085 [2.16]	0.648 [16.5]
18 [57]	13.60 [20.24]	2.257 [57.3]	4.00 [2581]	7.09 [180.1]	1.58 [40.1]	0.102 [2.59]	0.864 [21.9]
AThe bar numbers are based on an inch octave included on the nominal diameter of the bars [bar numbers approximately the millimeters number of the bar nominal diameter]
BThe nominal dimensions of a deformed bar are equivalent to those of a smooth bar which has the same weight [mass] by feet [meter] as the deformed bar.

The above defines the ribs and geometry for the bars of the state of art. However, for the concrete to be maintained on the elastic zone with stresses less than 50% of its strength to fatigue damage, the bars of the current invention have an Rr, which is in a range of between 0.12 and 0.25.

On FIG. 15, the parameters that define the bar of the current invention are shown clearly. Therefore, we have that “P” is the corresponding perimeter to the nominal diameter of the bar, “L” is the distance between the centers of the consecutive ribs; Dn is the nominal diameter of the bar; h is the height of the bar rib; and “A” is the rib area of the bar.

According the parameters of the bar shown on FIG. 15, the value of Rr, is then as:

$\begin{array}{cc}\mathrm{Rr}=\frac{A}{P\times L}& \left(2\right)\end{array}$

With the above, the ribs area of the bar of the current invention is:

A=Rr×P×L   (3)

If the nominal perimeter is:

P=Dn×Tr   (4)

Then, the rib area of the current invention is comprehended between:

0.12×P×L<A<0.25×P×L;   (5)

otherwise

0.12×Dn×π×L<A<0.25×Dn×π×L   (6)

Taking into account that the “A” area, shaded on FIG. 15, is equal to:

A=Dn×π×h   (7)

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

$\begin{array}{cc}\mathrm{Rr}=\frac{\mathrm{Dn}\times \pi \times h}{\mathrm{Dn}\times \pi \times L}& \left(8\right)\end{array}$

Then, the rib height “h” of the current invention is comprehended between:

0.12×L<h<0.25×L   (9)

Therefore, the distance “L” between the ribs defining the bar area of the current invention is fixed by the Rr and h values, preferring the given value for the maximum average spacing of the Table 1 of ASTM 615.

Likewise, according to the publication Materials Research: “Analysis of the relative rib area of reinforcing bars pull out tests” (Gomes Barbosa et al.), October/December 2008, states the conclusions that: “The bar with a spacing of 70% of the diameter with a height equal to 9% of the diameter, developed a greater stress to adherence, according the results obtained in this research.”

Therefore, is also applicable to the distance “L” between ribs defining the ribs area of the bar of the current invention. Such distance would be about 70% of the nominal diameter Dn of the bar.

It is important to point out that both the Table 1 of ASTM 615 and the publication of Gomes Barbosa et al. Defining the distance “L” between ribs, such distance “L” is already known in the previous art and only is considered in this request as help to define with greater accuracy the ribs area of the bar, which is the object issue of the current invention.

Claims

1. A steel bar to form concrete armours, which allow the concrete to be maintained on the elastic zone with a stress less than 50% of the damage stress, where such bar has a nominal diameter Dn; a distance between centers of consecutive ribs “L”; a rib height “h” and a rib area “A”, CHARACTERISED because such area “A” is greater than 0.12×P×L and less than 0.25×P×L.

2. A steel bar with ribs to form concrete armours, according to claim 1, CHARACTERISED because such area “A” is greater than 0.12×Dn×Tr×L and less than 0.25×Dn×Tr×L.

3. A steel bar with ribs to form concrete armours, according to claim 1, CHARACTERISED because such height “h” is greater than 0.12×L and less than 0.25×L.

4. A steel bar with ribs to form concrete armours, according claim 1, CHARACTERISED because the distance “L” between ribs is fixed by the values of Rr and h, preferring the given value for the maximum average spacing of the Table 1 of ASTM 615.

5. A steel bar with ribs to form concrete armours, according claim 1, CHARACTERISED because the distance “L” is about 70% of the nominal diameter Dn of such bar.