EP0327770B1 - Method of making mechanical bar joints, bar joint making possible the method, and mechanical bar joint made by same - Google Patents

Description

The invention relates to a method for making a mechanical connection of concrete rods, to a concrete rod authorizing the implementation of said method, as well as to a mechanical connection of concrete rods thus produced. It will find its application in particular in the field of construction of building elements or concrete buildings.

To link the concrete rounds, it is common to make junctions whose role is to ensure the transmission of the tensile force; it must, moreover, be convenient in its implementation and economical. Different solutions are proposed by manufacturers to ensure the mechanical joining of concrete reinforcing bars.

First there is the overlap system. This technique has several drawbacks: in particular, it is necessary to leave a relatively long length of concrete reinforcing bar waiting, up to two meters for example, in order to be able to subsequently carry out the junction, which is annoying and difficult, even impossible to be folded due to the large diameters encountered.

Another proposed technique consists in using a mechanical connection. We know for example the conical thread system in which the ends of the concrete rods to be bonded are machined in the form of a conical thread, which allows them to be fitted and screwed inside a coupler to drown in the concrete block.

This solution suffers from numerous drawbacks; in particular, the conical thread is produced in full bar on the nominal diameter of the concrete rod. The machining of the thread locally decreases the cross section of the bar which corresponds substantially to the cross section at the bottom of the thread.

During tensile tests, breakage of the concrete reinforcing bar always occurs at its end where the thread is located. Consequently, it is undeniable that this mechanical bonding technique weakens the concrete rod which must be oversized to take account of the weakness localized at the place of the threading.

This system also does not allow the use of a simple coupling sleeve with right and left thread to ensure the junction with traction adjustment. It is necessary to use several pieces to constitute a stack and allow a length adjustment.

Finally, the tightening of the sleeve on the conical thread must be carried out with a given cut which it is necessary to monitor. This operation is not easy to do on a construction site, but it is essential for safety reasons. If the tightening torque is not reached, there is a risk of itching and a total lack of tensile strength.

From an economic point of view, this is an expensive solution since the machining of the sleeve is complex and it is in particular necessary to carry out the tapping in two stages.

Ultimately, this technique requires oversizing the diameters of concrete bars, of the order of 20%, in order to resist the forces which are concentrated at the threaded ends of the bars. Its cost is high.

Document GB-1.546.253 discloses a mechanical connection of concrete rods, in which the threaded ends of the concrete rods are assembled end to end using tapped connection sleeves.

The objective of this document is to propose to put the threads of the rounds in compression and the threads of the sleeve in tension; this is authorized by providing between the two threads of the sleeve a space less than the space formed by the two chamfers of the ends of the rounds to be bonded.

However, the method of threading proposed in this document weakens the concrete rod, as recalled above, and the circle must be oversized to take account of the weakness localized at the place of the threading.

Another mechanical connection is also used; it is the crimping of the ends of rounds to be joined. For this purpose, a sleeve is used in which the two ends of the concrete rods are threaded. Using a jack and a press, the bush is crimped onto the concrete bars.

This technique presents high risks of slipping due to crimping, which is difficult to carry out and difficult to control. This defect considerably lowers the mechanical resistance of the connection. It is often difficult on a construction site to place a press at the level of the crimping sleeve. In addition, the use of a press is expensive.

Document FR-1-1.047.189 discloses a method of fastening for wires and metal bars in which the fastener is essentially constituted by a frusto-conical pressurized head, cold stamped, this after introduction of the wire or the bar into the fasteners. The shape of the head is such that it gives the fastener the necessary support and sufficient shear strength to transfer the danger of breaking into the wire or the bar.

However, in terms of regulations regarding the use of such mechanical round to concrete, it is naturally prescribed that these must be able to withstand the ultimate breaking forces and certain countries, notably Anglo-Saxons, impose very strict slip control standards.

For example in Great Britain, the BS-81 10: par 1: 1985-3.12.8.16.2 standard stipulates that concrete reinforcing bars assembled by means of a connecting sleeve must be able to undergo a tensile test in which the circles are subjected to a force corresponding to 60 of the elastic limit and after which the permanent elongation must not exceed 0.1 mm.

In other countries, these standards are even more stringent. For example in the United States, the applied force corresponds to 80% of the elastic resistance. Similar tests are also applied in the nuclear field.

These tests, when carried out on site, are difficult to implement and require the use of torque wrenches on site, which increases the cost of the connection made.

Furthermore, if the machining of the various elements has not been carried out with precision, it may be that during the test, the mechanical connection does not meet the criteria of these standards. It is then necessary to start the connection again, which is not without importance on the cost price. However, manufacturing with high precision requires manpower and special attention such that the solution is not economical.

The main object of the present invention is to present a method of making a mechanical connection of concrete rods, to a concrete rod authorizing the implementation of said method as well as to a mechanical connection of concrete rods thus produced which offer the advantages of high job security, easy implementation and competitive cost, while overcoming the drawbacks of known systems.

In terms of safety of use, thanks to the present invention, the tensile tests which have been carried out show that the rupture always occurs in full bar and no longer at the level of the mechanical connection as is traditionally encountered. Consequently, the mechanical connection of the present invention does not constitute a zone of weakness.

In addition, ease of implementation is provided by the use of a threaded connecting sleeve. This technique allows in particular an adjustment of the positioning of the concrete bars and the clamping material is limited, which is particularly well suited for use on site.

Economically, the technique of the present invention requires limited machining and the use of conventional non-binding means.

One of the aims of the present invention is to propose a method for producing a mechanical connection of concrete rods, to a concrete rod authorizing the implementation of said method, as well as to a mechanical connection of concrete rods thus produced, which make it possible to comply with the very severe deformation criteria imposed by certain standards or regulations imposing tests up to 80% of the elastic resistance.

One of the aims of the present invention is to propose a method for producing a mechanical connection of concrete rods which makes it possible to produce mechanical connections in which all the threaded concrete rods are tested, which is fundamental in terms of quality control and which provides an important guarantee for the structure.

Until now, known techniques would certainly allow mechanical connections to be made, but only the parts tested were authentic. The present invention shows a significant advance towards 100% reliability by the fact that all the concrete reinforcing bars are tested.

Other objects and advantages of the present invention will be explained in the following description which is however only given for information and which is not intended to limit it.

• - préalablement au filetage, on refoule à froid la ou les extrémités des ronds à béton à liaisonner, afin de réaliser une zone renforcée de diamètre "di " supérieur à la dite section nominale "$",
• - on réalise le filetage sur la dite zone renforcée tel que le diamètre à fond de filet "d₂" soit égal ou supérieur à la dite section nominale "$".

According to the invention, the process for producing a mechanical connection of concrete reinforcing bars, which will find its application in particular in the field of construction of concrete elements or buildings, by which the connection of concrete reinforcing bars, nominal section "$" and the ends of which are threaded, using tapped connection sleeves, is characterized by the fact that:

• - prior to threading, the cold end (s) of the concrete rods to be bonded are cold-pressed, in order to produce a reinforced zone of diameter "di" greater than the said nominal section "$",
• - The threading is carried out on the said reinforced zone such that the diameter at the bottom of the thread "d ₂ " is equal to or greater than the said nominal section "$".

The concrete reinforcing rod, authorizing the implementation of the method according to the invention, having a nominal section "$", is characterized in that it has at least one threaded repressed end, said threaded repressed end having a reinforced section of diameter "di" greater than said nominal section "$", and a bottom diameter "d ₂ " equal to or greater than said nominal section "Φ".

In addition, the mechanical connection of concrete rod obtained by implementing the method of the present invention, comprising at least one connecting sleeve having at least one internal thread, as well as a concrete rod to be bonded having a nominal section. "Φ" and at least one end to be bonded, is characterized in that the said end to be bonded has at least one zone reinforced by cold delivery, carrying a threaded part and corresponding to said tapping, said reinforced zone having a section of diameter "di" greater than the said nominal section "$", the said threaded portion having a diameter at the bottom of the thread "d ₂ ", and being provided on the said reinforced zone such that the diameter "d ₂ " is equal to or greater than the nominal section "4 >".

• - la figure 1 schématise la liaison de deux ronds à béton selon une mise en oeuvre de la présente invention.
• - la figure 2 illustre une liaison mécanique de ronds à béton fixes,
• - la figure 3 illustre un troisième exemple de liaison mécanique de ronds à béton au niveau d'un point d'ancrage,
• - la figure 4 montre schématiquement un dispositif de précontrainte des ronds à béton selon la présente invention,
• - la figure 5 montre schématiquement une variante d'exécution du dispositif de précontrainte de la figure 4.

The invention will be better understood on reading the following description accompanied by attached drawings, among which:

• - Figure 1 shows schematically the connection of two concrete bars according to an implementation of the present invention.
• FIG. 2 illustrates a mechanical connection of fixed concrete rods,
• FIG. 3 illustrates a third example of mechanical connection of concrete rods at an anchor point,
• FIG. 4 schematically shows a prestressing device for concrete reinforcing bars according to the present invention,
• FIG. 5 schematically shows an alternative embodiment of the prestressing device of FIG. 4.

The present invention relates to a method of making a mechanical connection of concrete rods, to a concrete rod authorizing the implementation of said method, as well as to a mechanical connection of concrete rods thus produced which will find their applications in particular in field of construction of concrete elements, buildings or buildings.

In this area, tie rods are used which pass right through the concrete elements and which are placed under tension to generate a compressive force in the concrete. The adjustment of the tensile force and the choice of the location of the tie rods must be carefully determined by preliminary calculations.

In practice, the tie rods are formed by a combination of concrete bars placed end to end. The junction used to secure the concrete reinforcing bars must be able to withstand the tensile force, be easily installed and also be economical.

Currently, several solutions such as overlapping or crimping are proposed, but they impose serious imperatives for its implementation and have many drawbacks.

The mechanical connection of the present invention allows the fixing of two concrete rods 1 and 2, end to end, substantially coaxially as illustrated in FIG. 1. A tapped sleeve 3 for connection is used to receive the ends threaded 4 and 5 respectively of concrete bars 1 and 2.

With regard to threads and threads, two solutions can be envisaged, namely: use of ends of bars having the same right or left thread, in this case, it is necessary to obtain tightening by rotation of the bar 1 or 2; or then use of threaded ends 4 and 5 having a reverse thread pitch, right and left, the same for the tap sleeve 3, in which case the tightening is obtained by rotation of the coupling sleeve 3. The implementation of the present invention does not create any limitation at this level.

However, if a simple thread is made at the end of the concrete rods 1 and 2, the tensile tests show that the breaking of the bars always occurs at the place of the thread of one of them. This phenomenon can be explained by the fact that the cross-section of the bar is reduced at this location. Indeed, the threading practiced on the surface of the concrete round begins the section and this being less, it creates a weakness.

With the mechanical connection of the present invention, the end of the concrete reinforcing bar is reinforced, so that it is more resistant than the central part of the bar.

Thus, in the event of traction, the rupture occurs in the central part of the bar and no longer at the junction. The choice of the section of the concrete reinforcing bar can be made according to the resistance to be obtained in the central part of the bar and no longer in the weakened part of the connection as is traditionally encountered. For equal strength, the concrete bars used in the context of the present invention will be of smaller cross section, which makes it possible to achieve substantial savings.

According to the main characteristic of the present invention, the reinforcement of the end of the concrete rod to be bonded is obtained, prior to threading, by a cold discharge.

We must emphasize the limited nature of the operation, contrary to custom in the field. The traditional technique of cold delivery means that one obtains dimensional modifications of the workpiece greater than 30%. For example, a diameter of 40 mm cold pressed using traditional techniques leads to a diameter of around 55 mm. However, such a deformation of the material does not provide the expected results and there is a loss of strength. This is located mainly at the level of the diameter change zone. Tensile tests show that failure occurs at this level.

According to the invention, the end is reinforced over the length of the thread by a cold discharge which provides an increase in diameters, equal to or less than 30%, and in particular between 10 and 30%.

This value makes it possible both to obtain an increase in resistance due to the increase in cross-section and also a slight increase in internal stress so as not to weaken the concrete reinforcing bar at the level of the change in diameter.

Table 1 below indicates, by way of example, values of delivery diameter di to be obtained before threading as a function of the nominal diameter 4) of the bar used, giving good results in use.

The values indicated show that the cold discharge can be in percentage the smaller the larger the bar diameter. The cross section of the concrete ring at the level of the thread d ₂ of the discharge end must be at least slightly greater than the current cross section φ of the concrete round to be connected.

The delivery operation of the present invention should preferably be carried out cold. Indeed, a hot discharge has the disadvantage of weakening the transition zone due to uncontrolled cooling. Generally, hyper-quenching occurs which weakens the metal. The hot process must also be implemented off site because it requires ovens which must be supplied with energy often not available on site.

Concrete rounds, being generally made of steels with a high carbon and manganese content, are therefore very sensitive to thermal shock and cold delivery is therefore recommended.

The length of the thread produced at the end of the concrete rounds must correspond substantially to the diameter φ of said round to provide security, since thread lengths of 0.7 times the diameter are sufficient to resist traction. However, it could be higher.

The mechanical connection of the present invention may also be implemented in the case of fixed concrete rods, which cannot be moved aside as illustrated in FIG. 2. In this case, one of the bars 1 has a thread 4 of double length made around a repressed end, and the sleeve 3 initially placed around the thread 4 will be rotated to cover the threads of the concrete rods 2. The threads 4 and 5 will have the same direction.

It is also necessary that the implementation of the mechanical connection of the present invention can also be carried out at the level of anchor points for concrete rods 1 as illustrated in FIG. 3. In this case, the threaded end 4 of the concrete ring receives beforehand a backflow made cold to reinforce it, and this end is fixed to an anchoring sleeve 6 integral with the concrete block 7.

Furthermore, to resist the tensile tests imposed by certain safety standards, the end 4 and / or 5 of the concrete reinforcing bar 1 and / or 2, reinforced by a backflow, is prestressed.

This constraint makes it possible to cancel all the displacements and elongations of the concrete reinforcing bars and in particular of their ends during the safety tests implemented.

In addition, thanks to this constraint, it is no longer necessary to use torque wrenches on site or to make threads with very high mechanical precision.

• - préalablement au filetage, on refoule à froid la ou les extrémités 4, 5 des ronds à béton 1, 2 à liaisonner,
• - ensuite, on réalise le filetage de la ou les extrémités refoulées 4, 5, selon des techniques de filetage tout à fait traditionnelles,
• - enfin, on contraint mécaniquement par compression la ou les extrémités 4, 5 refoulées filetées du rond à béton, ce préalablement au montage de la liaison sur site.

Thus, to make the mechanical connections of concrete bars according to the present invention, the procedure is as follows:

• - before threading, cold end (s) 4, 5 of the concrete rods 1, 2 to be bonded,
• - then, the threaded end (s) 4, 5 are threaded, according to quite traditional threading techniques,
• - Finally, the forced end or ends 4, 5 are forced mechanically by compression of the concrete ring, this prior to mounting the connection on site.

To carry out this constraint, FIGS. 4 and 5 illustrate by way of example two devices that can be used.

To constrain the threaded driven end 4 of the concrete ring 1 for example, a threaded support sleeve 11 is placed on it then the concrete ring thus equipped is immobilized and the end considered 4 is subjected to action a cylinder 6 or the like.

In the case of FIG. 4, the end 4 of the constraining ring fitted with its support sleeve 11 is inserted between a support plate 7 and the end 8 of the jack.

When the jack 6 is actuated, the sleeve 11 is then blocked on the support plate 7 and the jack acts directly on the end to be constrained. In addition, in order to mark the constrained end, the end 8 of the jack can be equipped with a punch which makes an indelible mark at the level of the driven end 4.

FIG. 5 shows a completely equivalent, but inverted procedure, in which a threaded support sleeve 11 and a support plate 7 are used. But, in this case, it is the body of the concrete rod 1 which is blocked by any clamp device, shown schematically at 9 in the figure, and the jack acts on the support plate 7, in the direction of the arrows 10, action which is reflected on the threaded support sleeve 11 for realize the constraint of the end 4.

According to the criteria of the standards to be observed, a mechanical compressive stress is carried out with an equivalent force of between 70 and 95% of the elastic limit of the concrete reinforcing bar.

This method of producing a concrete reinforcing bar therefore makes it possible to obtain a concrete reinforcing bar 1 or 2 having a forced threaded forced end 4 or 5.

Naturally, other implementations of the present invention, within the reach of ordinary skill in the art, could have been envisaged without departing from the scope thereof, as defined by the claims.

Claims (11)

1. Process for producing mechanical connections for concrete reinforcing rods which will find an application, in particular, in the field of concrete element or building construction, permitting the connection of concrete reinforcing rods (1, 2) having a nominal cross-section "Φ" and the ends of which are threaded (4, 5), using internally threaded connecting sleeves (3), characterized by the fact that:

- prior to threading, the end or ends (4, 5) of the concrete reinforcing rods (1, 2) to be connected undergo cold upsetting, in order to produce a reinforced area having a diameter "d, " greater than the said nominal cross-section "Φ",

- the threading is carried out on the said reinforced area such that the diameter "d₂" at thread bottom is equal to or greater than the said nominal cross-section "Φ".

2. Process according to claim 1, characterized by the fact that the upsetting is carried out over the length of threaded portion of the said end (4, 5).

3. Process according to claim 1, characterized by the fact that upsetting is carried out corresponding to an increase in the diameter of the connected portion equal to or less than 30%.

4. Process according to any one of the preceding claims, characterized by the fact that, following the threading of the upset end or ends (4, 5) and prior to effecting the connection on site, the threaded upset end or ends (4, 5) is/are subjected to mechanical compression.

5. Process according to claim 4, characterized by the fact that mechanical compression is carried out with an equivalent force of between 70 and 95% of the elastic limit of the concrete reinforcing rod.

6. Concrete reinforcing rod which will find an application, in particular, in the concrete element or building construction field, permitting implementation of the process according to claim 1, having a nominal cross-section "4)", characterized by the fact that it has at least one threaded upset end (4, 5), the said threaded upset end having a reinforced cross-section with a diameter "d, greater than the said nominal cross-section "Φ" and a diameter "d₂" at thread bottom equal to or greater than the said nominal cross-section "Φ".

7. Concrete reinforcing rod according to claim 6, characterized by the fact that the said threaded upset end (4, 5) is mechanically compressed.

8. Concrete reinforcing rod according to claim 6 or 7, characterized by the fact that the said end (4, 5) of the concrete reinforcing rod (1, 2) is reinforced over a length corresponding substantially to its diameter "Φ",

9. Mechanical connection for a concrete reinforcing rod which will find an application in the concrete element or building construction field, obtained by implementing the process according to claim 1, including at least one connecting sleeve (3) having at least one internally threaded portion, as well as a concrete reinforcing rod (1, 2) for connection having a nominal cross-section "Φ" and at least one end for connection,
characterized by the fact that the said end for connection has at least one area reinforced by cold upsetting, bearing a threaded portion and corresponding to the said internally threaded portion, the said reinforced area having a cross-section with a diameter "d, " greater than the said nominal cross-section "Φ", the said threaded portion having a diameter "d₂" at thread bottom and being provided over the said reinforced area such that the diameter "d₂" is equal to or greater than the nominal cross-section "$".

10. Mechanical connection for a concrete reinforcing rod according to claim 9, characterized by the fact that the upsetting corresponds to an increase in the diameter of the connected portion equal to or less than 30%.

11. Mechanical connection according to claim 10, characterized by the fact that the extent of upsetting is all the greater the smaller the diameter of the connected reinforcing rod and corresponds at least to the depth of the threading produced.

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