EP0327770A1 - Method of making mechanical bar joints, bar joint making possible the method, and mechanical bar joint made by same - Google Patents

Abstract

The mechanical coupling system, especially for cylindrical concrete components used in construction, consists of using a threaded sleeve (3) to couple the two ends (4,5) of the components (1,2), which are also threaded. Prior to fitting the components together with the sleeve, the ends of the components are reduced in diameter, for the length covering their threads, by cooling them. The ends of the components may also be pre-stressed, for the length of their threads, prior to joining, using an effort of between 70 and 95 per cent of the components' limit of elasticity.

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 rods, 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, a relatively large length of concrete reinforcing rod must be left on standby, up to two meters for example, in order to be able to subsequently join, which is inconvenient and difficult, even impossible to fold due to the diameters important encountered.

Another proposed technique consists in using a mechanical connection. For example, the conical thread system is known 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 walnut coupler 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 torque 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 absence of resistance to traction.

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.

Another mechanical connection is also used; it is the crimping of the ends of concrete reinforcing bars. 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.

However, in terms of regulations regarding the use of such mechanical connections of concrete reinforcing bars, it is naturally prescribed that they 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: part 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 circular ones 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 the 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.

According to the invention, the method of making a mechanical connection of concrete rods, which will find its application in particular in the field of construction of concrete elements or buildings, by which the connection of concrete rods is allowed, including the ends are threaded using tapped connection sleeves, is characterized in that, prior to threading, the end or ends of the concrete rods to be bonded are cold pressed.

The concrete reinforcing rod, authorizing the implementation of the method according to the invention, is characterized in that it has at least one threaded driven end.

The mechanical connection of a concrete ring, carried out by implementing the method according to the invention, in which two concrete rings are joined substantially coaxially by means of a tapped connection sleeve, is characterized in that the or the ends of the concrete rods to be bonded have a backflow at the threaded part to reinforce them.

• -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:

• FIG. 1 shows diagrammatically the connection of two concrete rods 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 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 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 threaded 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 <t> 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 section of the concrete ring at the level of the thread bottom d ₂ of the discharge end must be at least slightly greater than the current section ip 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 drawback 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 appreciably to the diameter <p of the said round in order to provide safety, 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 dismissed 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 thread 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 prestressing 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 prestressing, it is no longer necessary to use torque wrenches on site or to perform 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 précontraint la ou les extrémités 4, 5 refoulées filetées du rond à béton, ce préalablement au montage de la liaison sur site.

Thus, to carry out 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 completely traditional threading techniques,
• - Finally, we preload the end or ends 4, 5 of the threaded concrete rod, this prior to mounting the connection on site.

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

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

In the case of FIG. 4, the end 4 of the prestressing ring equipped 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 prestressed. In addition, in order to mark the preloaded 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.

Figure 5 shows a completely equivalent procedure, but reversed, 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 carry out the prestressing of the end 4.

According to the criteria of the standards to be observed, prestressing 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 preloaded threaded forced end 4 or 5.

Naturally, other implementations of the present invention, within the reach of those skilled in the art, could have been envisaged without departing from the scope thereof.

Claims (11)

1. Method for making a mechanical connection of concrete rods, which will find its application in particular in the field of construction of concrete elements or buildings, by which the connection of concrete rods (1, 2) is allowed, the ends of which are threaded (4, 5), using tapped connection sleeves (3), characterized in that, prior to threading, the end (s) (4, 5) of the concrete rods are cold pressed (1, 2) to be bonded. 2. Method according to claim 1, characterized in that the discharge is carried out over the length of the thread of said end (4, 5). 3. Method according to claim 1, characterized in that the discharge is carried out such that the section of the concrete ring (1, 2), at the level of the thread bottom of said repressed end (4, 5) is at least equal to or greater than the current section of the concrete rod (1, 2) to be connected. 4. Method according to any one of the preceding claims, characterized in that, after the threading of the said driven end (s) (4, 5), and prior to the mounting of the connection on site, the end (s) are preloaded (4, 5) threaded upsets from the concrete ring (1, 2). 5. Method according to claim 4, characterized in that one performs a prestressing with an equivalent force between 70 and 95% of the elastic limit of the concrete reinforcing bar. 6. Concrete rod, which will find its application in particular in the field of construction of concrete elements or buildings, authorizing the implementation of the method according to claim 1, characterized in that it has at least one threaded discharge end (4, 5). 7. Concrete rod according to claim 6, characterized in that the said threaded driven end (4, 5) is prestressed. 8. Concrete bar according to claim 6 or 7, characterized in that said end (4, 5) of the concrete bar (1, 2) is reinforced over a length corresponding substantially to its diameter. 9. Mechanical connection of concrete reinforcing rod, carried out by the implementation of the method according to claim 1, in which two concrete reinforcing bars (1, 2) are joined substantially coaxially by means of a threaded connecting sleeve (3 ), characterized in that the end or ends (4, 5) of the concrete rods (1, 2) to be bonded have a discharge at the level of the threaded part to reinforce them. 10. Mechanical connection of concrete reinforcing rod according to claim 9, characterized in that the discharge corresponds to a rate of increase in the diameter of the bonded part equal to or less than 30%. 11. Mechanical connection according to claim 10, characterized in that the discharge is all the more important that the diameter of the connected round is small and corresponds at least to the depth of the thread produced.

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