EP1231331B1 - Reinforcing bar with ribs and reinforced concrete - Google Patents

Abstract

Reinforcing steel comprises ribs (2) having a rib head width (b) greater than 0.2 times, preferably smaller than 0.5 times, especially 0.3-0.4 times, particularly 0.32-0.37 times the nominal diameter. Preferred Features: The angle ( beta ) of the rib to the longitudinal axis of the reinforcing steel is 25-55, preferably 35-45, especially 37-42 degrees , and is identical for all ribs. The reinforcing steel is rod-like and made by hot rolling.

Description

The present invention relates to a rod-shaped reinforcing steel with ribs. The present invention finds application wherever reinforcing bars are used to produce reinforced concrete. The present invention is used in particular in the production of reinforced concrete, in particular here in the production of welded steel mesh and reinforcing steel, preferably in rings application.

A rod-shaped reinforcing steel according to the preamble of claim 1 is known from FR-A-0399910.

In reinforcing mats, several reinforcing bars are cross-stacked and welded at their points of contact. Usually, cold-rolled reinforcing steel is used for this reinforcing steel. Furthermore, reinforcing steel is often wound on spools, so-called "rings", and transported on to the customer. For further processing of this reinforcing steel, this is fed to a straightening or bending and cutting machine, or for example a mat machine, to produce welded meshes. The reinforcing steel is straightened in so-called roller straightening sets or alternatively in rotor straightening sets. For a higher quality rebar, hot rolled reinforcing steel is increasingly being used. The rib geometries prescribed in the corresponding reinforcing steel standards result in relatively pronounced ribs. Thus, the directed rods tend when they are fed via a rod magazine for further processing, as often customary, when singulating or pulling out of the magazine to hook each other. Furthermore, one obtains the crosswise overlapping for welding z. Part unfavorably small contact surfaces. Due to the above-mentioned disadvantages with hot-rolled reinforcing steel, it has hitherto scarcely been used for the production of reinforcing mats. In the case of prior art reinforcing steels, for example reinforcing steel according to DIN 488, the angle of inclination β of the ribs present on the surface is usually about 60 °. This geometric arrangement of the ribs affects the bonding behavior of the reinforcing steel in the reinforced concrete.

The use of reinforcing bars without ribs is not possible in most applications, as the ribs play an important role in composite behavior, as these ribs direct the forces from the concrete into the reinforcing steel.

FIGS. 1a to 1d show prior art reinforcing bars as described in DIN 488 or in building inspectorate approvals. The reinforcing steel 1 has in the present embodiment, four rows of (in the drawing from top to bottom) ribs 2. The rib inclination angle β between the longitudinal direction of the considered rib and the direction of the longitudinal axis A of the reinforcing steel is approximately 60 ° in the case of prior art reinforcing bars. The distance between two ribs 2 in the longitudinal direction (rib distance) is c, the rib head width of a rib 2 transverse to the longitudinal direction of the considered rib is denoted by b. In each case between two adjacent ribs 2 is a sink 8. Fig. 1d shows a section through the reinforcing steel 1 along the section line D shown in Fig. 1b.

2a in FIG. 1c is the rib head surface, 2b designates the rib flank (on the other side of the fin head surface 2a is also a rib flank not visible in the drawing), and 8 is the sink between two adjacent ribs 2. In FIG the projection of a reinforcing steel in the longitudinal direction. The approximately circular contour is created by the backdrops appearing one behind the other and thus the circumferential contour forming ribs 2. The sectional contour 4 itself appears rather irregular. However, it quite regularly arises in the production of reinforcing steel. Here, the approximately square basic shape 5 with optionally rounded edges and the ribs 2 are rolled by rolling into the raw material. This can be hot rolling or cold rolling. The overall structure in cross-sectional area can thus be thought of as ribs 2, which rest on a basic body with a square cross section (reference numeral 5). The actual cross-sectional contour 4 results depending on where the cross section intersects the respective ribs. The above applies to reinforcing bars with four rows of ribs. The rows of ribs are formed by webs 6 extending in the longitudinal direction of the material (fin row spacing or rolling gap) and, depending on the basic shape (eg round, square, hexagonal, etc.) and the rib penetration depth, e.g. T. separated by further webs 7 ..

In Fig. 2a, the composite behavior of concrete steel is outlined in concrete. The composite behavior indicates with which force F the reinforcing steel has to be pulled so that there is a displacement Δ1 of the reinforcing steel in the concrete. As a characteristic curve, the bond stress is displayed via the pull-out path. As can be seen from Fig. 2a, the composite voltage reaches a maximum. With further displacement of the reinforcing steel in the concrete, the force decreases again, since the composite of the reinforcing steel is weakened by shearing the concrete base between the ribs.

FIG. 2b shows the expansion behavior of reinforcing steel. The reinforcing steel expands in a first linear range, the elastic range, in proportion to the applied force F up to a yield strength F _s . Subsequently, the reinforcing steel deforms plastically. This deformation is not reversible. Furthermore, a fatigue test is shown in which the reinforcing steel is subjected to a periodically changing force which is less than F _s . Although the applied force is so small that it does not yet come to a plastic deformation, such a load can lead to a fatigue fracture of the reinforcing steel.

These mechanical / dynamic properties (fatigue properties) can be improved. The initiated static and dynamic forces can then be safely and permanently absorbed.

An object of the present invention is to provide a reinforcing steel which can be used in mat machines or straightening and ironing machines, without causing problems during processing on the machine.

This object is achieved with the features of claim 1.

The rib inclination angle β to the longitudinal axis of the reinforcing steel may be 25 to 55 °, preferably 35 to 45 °, more preferably 37 to 42 °. This small rib inclination angle β relative to the reinforcing steel axis has several advantages: Studies have shown that in a Such a low rib inclination angle substantially improved fatigue properties can be achieved, ie a fatigue fracture of the reinforcing steel occurs less often or only after a longer time than in conventional reinforcing steel with a greater rib inclination angle. There are less pronounced edges in the longitudinal direction of the reinforcing steel in the reinforcing bar according to the invention with reduced rib inclination angle. As a result, in the reinforcing steel and in the concrete lower stress levels or notch stresses that usually occur at such edges. Due to the inclination results in the direction of the longitudinal axis a smaller pitch than a rib with the same height, but a larger rib inclination angle. This voltage overshoots or the notch effect of the reinforcing steel according to the invention can be reduced. Furthermore, the area distribution on the sheathing of the reinforcing steel in the direction of the longitudinal axis is more uniform than in a ribbed reinforcing steel with a steeper rib inclination angle.

In a preferred embodiment, the rib inclination angle is substantially the same for all ribs of the reinforcing steel. This achieves the above advantages over the entire length of the reinforcing steel.

The rib head width b of the ribs is greater than 0.2 times, preferably less than 0.5 times the nominal diameter, and more preferably 0.3 to 0.4 times the nominal diameter. This results in an improved rib filling in the rolling process, which leads to a lower ovality or uniform roundness of the outer diameter of the reinforcing steel. As a result, the reinforcing steel can be better processed. In the case of possibly round reinforcing steels, i. with the least possible ovality, the steel rests more uniformly on the roll. If the rod is guided, for example, between two opposing rollers, then the play between the rollers with rods that are as round as possible does not depend on the position of the rod. A rotation of the preferably rod-shaped reinforcing steel about its own longitudinal axis does not change this game if the rod is round and not oval. In addition, the force parameters are then more uniform.

Furthermore, this also results in a more uniform surface distribution on the envelope in the bar direction. This is advantageous for the welding of the reinforcing bars to welded mesh, since the welding surfaces of two superimposed Reinforcing steel bars are larger than conventional reinforcing bars with a larger rib inclination angle and a narrower rib.

The ratio of the rib width in the longitudinal direction b 'to the rib distance c in the direction of the reinforcing steel axis may be greater than 0.35, preferably greater than 0.4, more preferably greater than 0.45. This also leads to a more uniform distribution on the enveloping in bar direction, which has the above advantages. This ratio of the rib width in the longitudinal direction to the rib spacing is also suitable for use in high-strength concrete or for use in self-compacting concrete (SVB, slump according to ASTM at least 60 cm, preferably at least 65 cm, more preferably at least 70 cm).

The reinforcing steel is produced by hot rolling.

Furthermore, the preferably rod-shaped, but often also supplied as a coil reinforcing steel may have a plurality of rows of ribs, preferably 4. However, it may also be provided 2, 3 or 6 rows of ribs.

The fin coverage is greater than 50%, preferably greater than 55%.

The minimum value of the related rib area is preferably in the range between 30% below and 30% above the minimum value prescribed in DIN 488. This is especially true for reinforcing bars with a nominal diameter greater than or equal to 4 mm.

Fig. 1a bis 1d

eine Seitenansicht, eine um die Längsachse um 90° gedrehte Seitenansicht, eine perspektivische Ansicht sowie einen Schnitt an der Linie D von Fig. 1b eines Betonstahls nach dem Stand der Technik,

Fig. 2a

schematisch das Verbundverhalten von Betonstahl in Beton und Fig. 2b eine Dehnungskurve für Betonstahl,

Fig. 3a und 3b

zwei um 90° um die Längsachse gedrehte Ansichten eines erfindungsgemäßen Betonstahls, und

Fig. 4

eine Skizze zur Ermittlung des Rippenbedeckungsgrades.

The invention will be explained in more detail with reference to the accompanying schematic drawings using an exemplary embodiment. Hereby show:

Fig. 1a to 1d

a side view, a rotated about the longitudinal axis by 90 ° side view, a perspective view and a section on the line D of Fig. 1b of a reinforcing steel according to the prior art,

Fig. 2a

schematically the composite behavior of reinforcing steel in concrete and Fig. 2b a strain curve for reinforcing steel,

Fig. 3a and 3b

two rotated by 90 ° about the longitudinal axis views of a reinforcing steel according to the invention, and

Fig. 4

a sketch to determine the degree of rib coverage.

In the figures, the same reference numerals generally designate the same components or features.

In Fig. 3, an inventive reinforcing steel is shown. The rib inclination angle β is between 25 ° and 55 ° and preferably about 40 ° +/- 5%. The rib head width b is greater than 0.2 times, and preferably less than 0.5 times the diameter. The diameter is the nominal diameter (i.e., the diameter of a monoblock rod of uniform cross section).

The fin head width b is larger than in the case of reinforcing steel according to the prior art. The ratio of the rib width in the longitudinal direction b 'to the rib spacing c is greater than 0.35, which is not the case with prior art reinforcing steel. There, this ratio is less than 0.35. In the illustrated embodiment, the rebar according to the invention is shown with four rows of ribs. It may as well be another number of rows of ribs are used. The rows of ribs preferably extend in the longitudinal direction of the reinforcing steel. In Fig. 3b, two of them are indicated by the reference numerals 9 and 10. The rows of ribs are each bounded by webs 6 and optionally 7.

The combination of the larger rib width in the longitudinal direction b 'and the smaller rib inclination angle β leads, especially in combination, to a better rib filling and thus to a lower ovality. This results in the largest possible and evenly distributed in rod longitudinal direction surface on the envelope. These geometric properties improve the processing options on the processing machines, a hooking of the reinforcing steel in the machine is prevented. Likewise, a larger welding surface is available, whereby the connection of two welded reinforcing bars is improved.

wobei $F_R=\underset{n=1}{\overset{x}{{\displaystyle \mathrm{\Sigma }}}}\left(h_{s\left(n\right)}\cdot \mathit{\Delta l}\right)$

die Längsschnittfläche einer Rippe in deren Achse

h_S

die mittlere Höhe eines beliebigen Schrärippenabschnitts der Länge Δl der in x Abschnitte unterteilten Schrägrippe

β

die Neigung der Rippen zur Stabachse hin

d_S

der Nenndurchmesser des Stabes in mm

c_S

der Mittenabstand der Schrärippen in mm

k

die Anzahl der Schrägrippen am Umfang

m

die Anzahl der Schrägrippen je Reihe

i

die Anzahl der Längsrippen

h_l

die Höhe der Längsrippen

(n), (n, l)

Laufvariablen sind.

The related rib area f _{R is} calculated according to the formula $$f_R=\frac{1}{\mathrm{\Pi }\cdot d_s}\underset{n=1}{\overset{k}{{\displaystyle \mathrm{\Sigma }}}}\frac{\frac{1}{m}\underset{l=1}{\overset{m}{{\displaystyle \mathrm{\Sigma }}}}{F}_{R(n.l)\cdot }{\mathrm{sin\beta }}_{\left(n.l\right)}}{c_{s\left(n\right)}}.$$

in which $F_R=\underset{n=1}{\overset{x}{{\displaystyle \mathrm{\Sigma }}}}\left(H_{s\left(n\right)}\cdot \mathit{.DELTA.l}\right)$

the longitudinal sectional area of a rib in its axis

h _S

The average height of any Schrarippenabschnitts the length .DELTA.l of the divided into x sections Schrägrippe

β

the inclination of the ribs towards the rod axis

d _S

the nominal diameter of the bar in mm

c _p

the center distance of the Schrärippen in mm

k

the number of helical ribs on the circumference

m

the number of helical ribs per row

i

the number of longitudinal ribs

h _l

the height of the longitudinal ribs

(n), (n, l )

Running variables are.

It is a measure of how much rib cross-sectional area is relatively present on the reinforcing steel. A priori, a high related rib area is desired because then a good bond between reinforcing steel and the surrounding concrete can be expected. Under certain conditions and in particular in connection With high-strength concretes (strength greater than 55 N / mm ² ), a comparatively small rib area can produce the same or even better results. According to the invention, reinforcing steels with a related rib area f _R less than 130% of the minimum value provided for in DIN 488 appear to be advantageous. Preferably, the referenced fin area is less than 115%, more preferably less than 100%.

In the processing of reinforced concrete results from the improved geometry less noise, especially in Rollenrichtanlagen and roller guides and a lesser influence on mechanical, dynamic and geometric properties by the processing machines used. This means that the processing of hot-rolled steel is thereby significantly improved.

With a reinforcing steel as described above, a reinforced concrete can be produced. The reinforced concrete then has a concrete and the reinforcing steel described above. The concrete preferably has a strength greater than 55 N / mm ² .

Fig. 4 shows a sketch for determining the degree of rib coverage, where c is the rib distance, b is the rib head width and 1 is the rib length. The degree of rib coverage is, as can be clearly said, the proportion of the hatched area A on the envelope in relation to the total envelope of the reinforcing steel, with the areas of bars 6 and possibly 7 being included.

mit

• b = Rippenkopfbreite,
• l' = Länge der Rippen in Rippenrichtung innerhalb einer Schrittweite c,
• e = Stegbreite (Rippenreihenabstand),
• c = Rippenabstand in Längsrichtung,
• d = Nenndurchmeser.

The fin coverage is a relative measure of the area occupied by rib heads 2a and lands 6, 7 on the envelope of a rebar. The rib coverage RBG is preferably calculated according to the following formula:

With

• b = rib head width,
• l '= length of the ribs in rib direction within a step size c,
• e = web width (rib row spacing),
• c = rib distance in the longitudinal direction,
• d = nominal diameter.

The summation takes place over the circumference.

The required rib coverage has the advantage that the smoothness and the Richtbarkeit the reinforced concrete improve. Also, the risk of entanglement during processing is lower, and the weldability is better due to the larger contact surfaces.

Typical diameter rod-shaped material of the reinforcing steel are a minimum of 4 mm, a maximum of 65 mm, preferably a minimum of 6 mm, a maximum of 32 mm. Typical lengths of rod-shaped material are a minimum of 2 m, a maximum of 30 m, preferably a minimum of 6 m, a maximum of 24 m. Typical diameters of rings of reinforcing steel are a minimum of 0.5 m, a maximum of 2 m, preferably a minimum of 0.7 m, a maximum of 1.8 m. The reinforcing steel may also be mat-shaped. Here then rods that are formed as above, connected to each other in a grid, preferably welded. The reinforcing steel may also be used as a prefabricated reinforcement, e.g. B. be designed as a lattice girder, reinforcing cage or reinforcing bar or rod in fixed length.

Claims (7)

1. Rod-like concrete reinforcing steel, applicable also as coil, comprising ribs (2) and ligaments (6), the ribs (2) having a rib inclination angle (β) with respect to the longitudinal axis of the concrete reinforcing steel (1) and the ligaments extending in longitudinal direction of the concrete reinforcing steel (1), wherein the width b of the rib heads of the ribs (2) is larger than 0,2 times the nominal diameter of the concrete reinforcing steel (1), characterized in that
   the concrete reinforcing steel is made by hot rolling and that the rib covering degree on the enveloping surface is larger than 50 %, the rib covering degree being the relative measure for the area covered by the rib heads (2a) of the ribs (2) and by the ligaments (6) on the enveloping surface, wherein the enveloping surface has circular cross-section with the nominal diameter of the concrete reinforcing steel as diameter of the circle.
2. Concrete reinforcing steel (1) of claim 1, characterized in that the rib inclination angle (β) with respect to the longitudinal axis of the concrete reinforcing steel is between 25 ° and 55 °, preferably between 35 ° and 45 °, further preferably between 37 ° and 42 °.
3. Concrete reinforcing steel (1) of claim 1, characterized in that the rib inclination angle is substantially the same for all ribs (2).
4. Concrete reinforcing steel (1) according to one of the preceding claims, characterized in that the ratio of rib width in longitudinal direction b' and rib distance c in direction of the concrete reinforcing steel axis (A) is larger than 0,35.
5. Concrete reinforcing steel (1) according to one of the preceding claims, characterized in that it comprises a plurality of, preferably four, rows of ribs.
6. Concrete reinforcing steel (1) according to one of the preceding claims, characterized in that the rib covering degree is larger than 55 %.
7. Concrete reinforcing steel (1) according to one of the preceding claims, characterized in that the related rib area f_R is smaller than 130 % of the value prescribed in DIN 488, preferably smaller than 115 %, further preferably smaller than 100 %.

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