EP0306887B1 - Hot rolled concrete reinforcing rod, particularly a concrete ribbed bar - Google Patents

Abstract

In a hot rolled concrete reinforcing rod (1), the ribs (3) of which are arranged along a helix and form parts of a thread for the screwing on of an anchoring or connecting member provided with a counter- thread, a rib shape and rib arrangement improved with respect to the dynamic stressability of the thread connection are proposed. <IMAGE>

Description

The invention relates to a hot-rolled concrete reinforcement bar, in particular a concrete ribbed bar according to the preamble of claim 1.

Concrete reinforcement bars of this type are described for example in concrete and reinforced concrete construction 2/1973, pages 25 to 35.

In the case of screwable concrete reinforcement bars, the ribs are assigned a double task. On the one hand, they must ensure a sufficient bond in the concrete and, on the other hand, in their function as parts of a thread, they must be able to transmit the required forces into an anchoring or connecting body into which one end of the concrete reinforcement bar is screwed.

In view of these two functions, the concrete reinforcement bars known as GEWI steel (trademark), which are described in the above-mentioned magazine, have become established in practice.

These concrete reinforcement bars have, based on the bar diameter, relatively wide ribs at a relatively short distance. The ratio of the base width to the height of the rib is approximately 3.7 and the rib spacing, measured in the longitudinal direction of the reinforcing steel, is 0.5 in relation to the nominal diameter. This corresponds to an angle of inclination α of the ribs with respect to the longitudinal axis of the concrete reinforcement bar of approximately 81.5 °.

Because of this rib shape and arrangement of ribs, short threaded connections are possible, and because of the relatively large inclination angle α of the ribs with respect to the longitudinal axis of the concrete reinforcing bar, a self-locking of the threaded connection is ensured.

The object of the invention is to provide a concrete reinforcement bar of the type mentioned in the preamble of claim 1, which is characterized by improved dynamic strength. The notch effect caused by the thread ribs is to be reduced and the fatigue strength in the area of the threaded connection is to be increased.

The object is achieved by a concrete reinforcement bar with the features according to claims 1, 3 or 4.

Advantageous embodiments of the invention can be found in the remaining claims.

Thereafter, the ribs are made much slimmer and have a smaller angle of inclination α with respect to the longitudinal axis of the reinforcing steel than in the case of the known screwable concrete reinforcing bar. These measures not only reduce the notch effect and thus increase the dynamic strength of the threaded connection, but also the degree of filling during hot rolling and thus the manufacturability of the concrete reinforcement bar.

In order to prevent the limit of self-locking for the threaded connection from being exceeded by the smaller angle of inclination α of the ribs relative to the longitudinal axis of the concrete reinforcement bar, measures are provided to prevent the To increase the coefficient of friction of the rib flanks of the concrete reinforcing bar used for the threaded connection. Such measures are mentioned in claims 1, 3 and 4. They can be implemented individually or in combination.

By changing the rib shape and rib arrangement according to the invention, that is to say by reducing the ratio b / h and the angle of inclination α, the shear area per unit length that is decisive for the load-bearing behavior of the threaded connection is also reduced, so that the length of the anchoring or connecting body is normally increased must if the same forces are to be transmitted.

An extension of the anchoring or connecting body, which is undesirable in particular with regard to the accumulating rolling tolerances in the fin spacings, can be avoided, that is to say with the same length, despite the reduced shear area in the thread area, the same or greater forces can be transmitted if the shear strength of the concrete reinforcement bar is enlarged in the rib area. According to a further development of the invention, this is done by using a concrete reinforcement bar which has increased strength in the edge and rib area compared to the core. Such concrete reinforcement bars have become known, for example, under the trade name Tempcore steels (registered as a trademark). Such steels are produced in such a way that they are so intensely cooled in the edge zone by a water cooling section when they emerge from the last rolling stand of a hot rolling mill that there is a hardness structure in this zone and that the hardened edge zone after the rod emerges from the water cooling section through the Heat content of the core zone is left on. Steels of this type and methods of making the same are general known, so that a detailed description is unnecessary. Not only do they have increased strength compared to the core, they also have a higher coefficient of friction on their surface and thus in the rib area compared to other hot-rolled concrete reinforcement bars. In view of this property, they are therefore particularly suitable for the concrete reinforcement bar according to this invention.

Concrete reinforcement bars made from such steels with the shape and arrangement of the ribs according to the invention are also distinguished by improved ductility. The ductility of a concrete reinforcement bar is determined by the uniform expansion, the ratio of tensile strength to yield strength and the bond. In the case of concrete reinforcement bars according to the invention, a uniform expansion ≧ 6%, a ratio of tensile strength to yield strength of ≧ 1.1 and a sufficient, soft or mild bond supported by the surface roughness of the bar can be achieved.

By reducing the angle of inclination α of the ribs with respect to the longitudinal axis of the reinforcing steel and reducing the ratio h / d _s , that is to say the rib height based on the rod diameter, the related rib surface is also reduced. This can be counteracted by extending the ribs so that they each extend almost over half the full circumference of the rod and / or that the ribs are arranged along a two-start helix. These two measures also have an effect in terms of increasing the shear area per unit length, that is to say the resilience of the threaded connection. The reduction in the related rib area can also be counteracted by the fact that additional ribs or between the ribs Incisions are arranged. At least the additional ribs, which have a position lying outside the helical line of the thread or are widened, must have a rib height which is reduced to such an extent that the screwing on of the associated anchoring or connecting body is not hindered by them. The diameter of the cylindrical envelope of the additional ribs must therefore be smaller than the inside diameter of the thread of the anchoring or connecting body to be screwed onto the concrete reinforcement bar.

As the position of the additional ribs or incisions that increase the related rib area and thus the bond are not determined by the helix of the thread, they can also be used to identify the concrete reinforcement bar, i.e. the additional ribs or incisions can be used because they can function as Do not interfere with the thread of the thread ribs, if necessary, be arranged in connection with the thread ribs in the manner desired for marking with regard to the type of steel or supplying plant.

• Fig. 1 einen Abschnitt eines schraubbaren Betonbewehrungsstabes in einer Draufsicht;
• Fig. 2 den Schnitt II-II von Fig. 1;
• Fig. 3 in einer vergrößerten Darstellung den Schnitt III-III von Fig. 1; und
• Fig. 4 einen Abschnitt aus einem Betonbewehrungsstab mit Zusatzrippen und Einschnitten in einer Seitenansicht.

The invention is explained in more detail by two exemplary embodiments with reference to four figures. Show it

• Figure 1 shows a section of a screwable concrete reinforcement bar in a plan view.
• Fig. 2 shows the section II-II of Fig. 1;
• Fig. 3 is an enlarged view of section III-III of Fig. 1; and
• Fig. 4 shows a section of a concrete reinforcement bar with additional ribs and incisions in a side view.

The hot-rolled concrete reinforcement bar 1 shown in Figures 1 to 3 has a circular core cross-section 2, shown hatched in Fig. 2, and two mutually opposite rows of ribs 3 and 4 arranged along a helical line, the parts of a thread for screwing one with a counter thread provided anchoring or connecting body. The ribs 3 and 4 formed in the same way are also referred to below as threaded ribs. As shown in FIG. 2, they extend at full height almost over half the rod circumference.

b =

Fußbreite der Rippe

d_s =

Nenndurchmesser des Betonstahls

h =

Rippenhöhe

R =

Ausrundungsradius am Rippenfuß in mm

α =

Neigungswinkel der Rippe gegenüber der Längsachse 5 des Betonstahls in Altgrad

β =

Neigungswinkel der Rippenflanke in Altgrad

C =

Abstand der Rippen, gemessen in Längsrichtung des Betonbewehrungsstabes.

The following sizes, shown in FIGS. 1 to 3, serve to identify the shape of the rib and the arrangement of the ribs:

b =

Rib foot width

d _s =

Nominal diameter of the reinforcing steel

h =

Rib height

R =

Rounding radius on the fin base in mm

α =

Angle of inclination of the rib relative to the longitudinal axis 5 of the reinforcing steel in degrees

β =

Tilt angle of the rib flank in degrees

C =

Distance of the ribs, measured in the longitudinal direction of the concrete reinforcement bar.

The shear area per unit length that determines the load-bearing capacity of the threaded connection is determined by the base width b, the length and the distance C or the angle of inclination α of the ribs. Compared to known threaded rods, the base width b of the rib is reduced. The resulting reduction in the shear area is partly due to an increase in the length of the ribs and also by increasing the strength of the concrete reinforcement bar in the area of Edge zone, i.e. in the rib area, compensated. The increased strength in the area of the ribs is achieved in that the hot-rolled steel is so intensively cooled by a water cooling section as it emerges from the last rolling stand in the edge zone that there is a hardness structure in this zone and that the hardened edge zone emerges after the steel emerges the water cooling section is started by the heat content of the core zone. A concrete reinforcement bar produced in this way is also characterized by an increased coefficient of friction due to the scale formation in the edge and rib area, which is desirable with regard to self-locking of the thread.

Due to the rib shape and rib arrangement specified in patent claims 1, 3 and 4, the reinforcing steel according to the invention is characterized by an increased dynamic load capacity, so that it can also be used with the usual anchoring or connecting bodies for dynamically stressed components.

The concrete reinforcement bar shown in Fig. 4 differs from the concrete reinforcement bar shown in Figures 1 to 3 in that 3 additional ribs 6 are arranged between the threaded ribs and 4 incisions 7 between the threaded ribs. These measures serve to improve the bond between the concrete reinforcing bar and the concrete . They may be necessary if, with a reduced angle of inclination α of the threaded ribs, that is to say with an increased pitch of the thread, the distance C between the threaded ribs exceeds a certain dimension and the related rib surface thus becomes too small. If it is not possible or undesirable to change to a two or more thread and arrange the additional ribs along the additional helical lines of such a thread, if so as in the case shown Additional ribs 6 have a position lying outside of such a helical line, they must have a rib height that is so far reduced compared to the threaded ribs 3 or 4 that the screwing of the associated anchoring or connecting body is not hindered by the additional ribs. The diameter D of the cylindrical envelope of the additional ribs 6 must therefore be smaller than the inside diameter of the thread of the anchoring or connecting body to be screwed onto the concrete reinforcement bar. Instead of additional ribs, projections with a shape that differs from a rib shape, such as knobs, can also be provided.

In addition to additional ribs 6, the concrete reinforcement bar according to FIG. 4 also shows impressions or incisions 7 for the purpose of illustrating two basic options. Only additional ribs or only incisions can be provided at any point between threaded ribs 3 and / or 4. This also creates the possibility of identifying the screwable concrete reinforcement bar with regard to the type of steel or delivery plant by the arrangement of the ribs or cuts. The rib arrangement shown in FIG. 4 characterizes the steel grade Fe B 500 in accordance with Euronorm 80-85.

Example:

C =

0,19 Gewichtsprozente

Mn =

1,04 Gewichtsprozente

Si =

0,24 Gewichtsprozente

Cu ≦

0,20 Gewichtsprozente

P =

0,015 Gewichtsprozente

S =

0,01 Gewichtsprozente.

A hot-rolled concrete ribbed rod BSt 500/550 S with a nominal diameter of d _s = 28 mm was produced according to the Tempcore process (registered trademark) from a steel which had the following composition:

C =

0.19 percent by weight

Mn =

1.04 percent by weight

Si =

0.24 percent by weight

Cu ≦

0.20 percent by weight

P =

0.015 percent by weight

S =

0.01 percent by weight.

b =

4,5 mm

d_s =

28 mm

h =

1,65 mm

R =

1,8 mm

α =

76 Grad

β =

45 Grad

C =

11 mm

h/d_s =

0,059

b/h =

2,7

C/d_s =

0,4.

The concrete ribbed rod had an almost circular core cross section and two opposite rows of ribs with an approximately trapezoidal cross section. The ribs were arranged along the helical lines of a two-start thread. The rib shape and rib arrangement were further characterized by the following parameters as defined above:

b =

4.5 mm

d _s =

28 mm

h =

1.65 mm

R =

1.8 mm

α =

76 degrees

β =

45 degrees

C =

11 mm

h / d _s =

0.059

b / h =

2.7

C / d _s =

0.4.

The ribs extended in full almost over half the circumference of the bar, namely over 170 degrees.

R_e =

568 N/mm²

R_m =

666 N/mm²

A₅ =

21,4%.

The following mechanical characteristics of the ribbed bars were determined by test tests according to DIN 488:

R _e =

568 N / mm²

R _m =

666 N / mm²

A₅ =

21.4%.

• die Schwingbreite 2σ_A  =  250 N/mm² und
• die maximale Spannung σ₀  =  325 N/mm².

In addition, fatigue tests were carried out in accordance with DIN 488 on a straight rod:

• the vibration range 2σ _A = 250 N / mm² and
• the maximum tension σ₀ = 325 N / mm².

No breakage occurred even after a load cycle of 3.5 million.

Tensile tests with threaded sockets (connecting body of the adjacent ends of two threaded rods), the one length of 2 · 47 = 94 mm resulted in a load-bearing capacity of the socket connection that was 1.2 times the yield strength of the concrete reinforcement bars.

Both the fatigue tests and the load tests of the socket connection gave 10 to 20% better values than those of the threaded connections described in "Concrete and reinforced concrete construction", 2/1973, pages 25 to 35.

Claims (17)

1. A hot-rolled concrete reinforcing bar (1), in particular a ribbed concrete reinforcing bar, of circular or almost circular core cross-section (2) and with two mutually opposite rows of ribs (3, 4) of substantially trapezoidal cross-section, which are arranged along a helical line and which form portions of a thread for screwing on an anchoring or connecting body provided with a co-operating thread, and which with the definitions:

b =   base width of the rib

d_s =   nominal diameter of the concrete reinforcing steel member

h =   rib height

R =   fillet radius at the rib base in mm

α =   angle of inclination of the rib relative to the longitudinal axis of the concrete reinforcing steel member in degrees of angle, and

β =   angle of inclination of the rib flank in degrees of angle have a rib form and rib arrangement which satisfies the following conditions:

$$\text{40° < β < 60°}$$

$$\text{1.0 < R < 3.0}$$

characterised in that $${\text{0.04 ≦ h/d}}_{\text{s}}\text{ ≦ 0.06}$$

$$\text{1.5 ≦ b/h ≦ 3.3}$$

$$\text{60° < α < 80°}$$

and by increasing the surface roughness of the incisions provided for the ribs (3, 4) in the rib rolls the coefficient of friction of the concrete reinforcing bar is increased in the rib region.

2. A concrete reinforcing bar according to claim 1 characterised in that the surface roughness is increased by sand blasting of the rolling passage of the rib rolls.

3. A hot-rolled concrete reinforcing bar (1), in particular a ribbed concrete reinforcing bar, of circular or almost circular core cross-section (2) and with two mutually opposite rows of ribs (3, 4) of substantially trapezoidal cross-section, which are arranged along a helical line and which form portions of a thread for screwing on an anchoring or connecting body provided with a co-operating thread, and which with the definitions:

b =   base width of the rib

d_s =   nominal diameter of the concrete reinforcing steel member

h =   rib height

R =   fillet radius at the rib base in mm

α =   angle of inclination of the rib relative to the longitudinal axis of the concrete reinforcing steel member in degrees of angle, and

β =   angle of inclination of the rib flank in degrees of angle have a rib form and rib arrangement which satisfies the following conditions:

$$\text{40° < β < 60°}$$

$$\text{1.0 < R < 3.0}$$

characterised in that: $${\text{0.04 ≦ h/d}}_{\text{s}}\text{ ≦ 0.06}$$

$$\text{1.5 ≦ b/h ≦ 3.3}$$

$$\text{60° < α < 80°}$$

and by scale formation by means of a quenching and tempering treatment from the rolling heat the coefficient of friction of the concrete reinforcing bar is increased in the rib region in comparison with the rolled state.

4. A hot-rolled concrete reinforcing bar (1), in particular a ribbed concrete reinforcing bar, of circular or almost circular core cross-section (2) and with two mutually opposite rows of ribs (3, 4) of substantially trapezoidal cross-section, which are arranged along a helical line and which form portions of a thread for screwing on an anchoring or connecting body provided with a co-operating thread, and which with the definitions:

b =   base width of the rib

d_s =   nominal diameter of the concrete reinforcing steel member

h =   rib height

R =   fillet radius at the rib base in mm

α =   angle of inclination of the rib relative to the longitudinal axis of the concrete reinforcing steel member in degrees of angle, and

β =   angle of inclination of the rib flank in degrees of angle have a rib form and rib arrangement which satisfies the following conditions:

$$\text{4.0° < β < 60°}$$

$$\text{1.0 < R < 3.0}$$

characterised in that: $${\text{0.04 ≦ h/d}}_{\text{s}}\text{ ≦ 0.06}$$

$$\text{1.5 ≦ b/h ≦ 3.3}$$

$$\text{60° < α < 80°}$$

and by mechanical and/or chemical treatment the coefficient of friction of the concrete reinforcing bar is increased in the rib region in comparison with the rolled state.

5. A concrete reinforcing bar according to claim 4 characterised in that the coefficient of friction is increased by sand blasting.

6. A concrete reinforcing bar according to claim 4 or claim 5 characterised in that the coefficient of friction is increased by a corrosion treatment.

7. A concrete reinforcing bar according to one of claims 1 to 6 characterised in that in the rib region it has a coefficient of friction which ensures self-locking.

8. A concrete reinforcing bar according to one of claims 1 to 7 characterised in that in the edge and rib region it is of a strength which is increased in comparison with the core.

9. A concrete reinforcing bar according to one of claims 1 to 8 characterised in that the ribs (3, 4) are arranged along a two-flight helical line.

10. A concrete reinforcing bar according to one of claims 1 to 9 characterised in that the spacing C of the ribs (3, 4) as measured in the longitudinal direction of the reinforcing bar satisfies the condition: $${\text{0.38 ≦ C/d}}_{\text{s}}\text{ ≦ 0.60.}$$

11. A concrete reinforcing bar according to one of claims 1 to 10 characterised in that the ribs (3, 4) each extend at their full height approximately over half the bar periphery.

12. A concrete reinforcing bar according to one of claims 1 to 11 characterised in that it has uniform elongation A_g  ≧  6%.

13. A concrete reinforcing bar according to one of claims 1 to 12 characterised in that disposed between the ribs (3) are projections or additional ribs (6) of which at least those which are in a position disposed outside the single-flight or multi-flight helical line or which are of increased width are of a rib height which is reduced to such an extent that screwing on of the associated anchoring or connecting body is not obstructed by the additional ribs.

14. A concrete reinforcing bar according to one of claims 1 to 13 characterised in that impressions or incisions (7) are disposed between the ribs (3, 6).

15. A concrete reinforcing bar according to one of claims 1 to 14 characterised in that b/h of the ribs satisfies the condition 2.0  ≦  b/h  ≦  3.0.

16. A concrete reinforcing bar according to claim 8 in conjunction with claim 3 characterised in that the steel comprises a content of: $$\text{0.10 ≦ C ≦ 0.27}$$

$$\text{0.40 ≦ Mn ≦ 1.40}$$

$$\text{Cu ≦ 0.80.}$$

17. A method of making a concrete reinforcing bar according to one of claims 1 to 16 characterised in that after leaving the last roll stand of a hot rolling installation it is intensively cooled in the edge zone by a water cooling line in such a way that in that zone martensite and/or bainite formation occurs and after the bar issues from the water cooling line the hardened edge zone is tempered by the heat content of the core zone.

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