EP0572315A1 - Improvements to devices for making intermediate anchors on prestressed cables - Google Patents

Abstract

A device for anchoring, on an intermediate element (21) of a concrete structure, a part of the useful load of a prestressed cable (4) consisting of multiple strands (5). This device comprises a plurality of parallel grooved plates (6) arranged between the various layers of strands in such a way that each strand is lodged in two opposite grooves consisting respectively of two contiguous plates, the grooves being recessed by longitudinal channels, two jaws (8, 9) integral with the intermediate element and applied respectively against the end plates of the pile consisting of the plates positioned between the strands, this pile having the general shape of a cylindrical pad of revolution, and means (11) for bringing the two jaws towards each other in such a way as to clamp the layers of strands and the plates against one another. <IMAGE>

Description

The invention relates to concrete structures which are prestressed using cables anchored at their two ends to these structures, said cables being composed of strands or multiple wires.

It relates more particularly to devices which are intended to anchor on an intermediate element constituting such a structure part of the useful force of such a cable.

Such an intermediate anchor is for example useful during the construction of a concrete structure such as the beam 1 shown diagrammatically in FIG. 1, comprising a plurality of reinforcement crosspieces 2 separated by spaces or volumes of air 3 and prestressed by prestressing cables 4, each cable successively crossing these crosspieces and these spaces, and the crossings of the crosspieces by the cables being carried out in tubes making it possible for the cables to slide relatively relative to the concrete.

In such a structure, the two ends A and B of the cable 4 are anchored on two end spans and it may be necessary to make integral with an intermediate crosspiece, such as that designated by the reference 2₁, the portion, of the cable 4, next to this cross.

Such a connection ensures a distribution of the prestress more apt to oppose the stresses in service of the structure, which improves the behavior of the latter.

Some of the devices which have been proposed to date for ensuring such intermediate anchors essentially comprise two anchor plates each perforated by a plurality of frustoconical bores suitable for each receiving one of the strands of the cable to be anchored with interposition of two tapered jaws split at opposite convergences.

• leur mise en oeuvre exige un enfilage préalable individuel de chacun des torons à l'intérieur des alésages et mors d'ancrage qui lui sont affectés, ce qui est une opération longue et fastidieuse, surtout si elle doit être répétée plusieurs fois pour chaque toron,
• le câble est fortement dilaté dans la zone d'ancrage en raison de la nécessité de placer transversalement entre les différents torons les mors et leurs logements, ce qui impose la mise en place d'organes de déviation.

These known devices have a certain number of drawbacks and in particular the following:

• their implementation requires prior individual threading of each of the strands inside the bores and anchoring jaws assigned to it, which is a long and tedious operation, especially if it must be repeated several times for each strand,
• the cable is greatly expanded in the anchoring zone due to the need to place the jaws and their housings transversely between the different strands, which requires the installation of deflection members.

To overcome these drawbacks, it has also been proposed to globally enclose the intermediate portion to be anchored of the cable between two outer shoes tightened transversely against one another using bolt-nut system, said shoes being applied longitudinally against the structure by means of jacks (document FR-A-1 062 743).

Such an anchoring is only applicable to a cable of rectangular overall section and it is difficult to ensure the necessary attachment both between the various strands juxtaposed transversely as between the peripheral strands and the shoes.

Document FR-A-1 464 818 has also proposed a device for anchoring a cable with multiple strands comprising a stack of grooved plates interposed respectively between the layers of consecutive strands, stack delimited by two end plates or clamped jaws one against the other using bolt-nut systems.

However, this device is still applicable, like the previous one, only to cables of rectangular overall section and it is in no way designed to produce intermediate anchors.

The object of the invention is, among other things, to eliminate the various drawbacks indicated above by making it possible in particular to carry out an intermediate anchoring on cables of circular or similar overall section, and in particular hexagonal.

To this end, the intermediate anchoring devices of the type in question according to the invention also comprise two shoes arranged on either side of the cable, shoes joined longitudinally, that is to say in the longitudinal direction of the cable, with the intermediate element and means for bringing the two shoes together mutually perpendicular to the longitudinal direction of the cable so as to secure them with the strands, and they are essentially characterized in that they also comprise a plurality of grooved plates arranged in parallel to each other between the different strands of strands constituting the cable so that each strand is joined contiguously in two facing grooves respectively comprised by two adjoining plates, the two shoes being applied respectively against the two end plates of the stack constituted by the various plates placed between the strands, in that the stacked set of grooved plates placed between the different strands of the cable has the general shape of a cylindrical wafer of revolution, in that the bottoms of the grooves are hollowed out by narrow longitudinal grooves so as to give the plates a certain elasticity favoring the effectiveness of their application against the strands, and in that the internal faces of the grooves suitable for receiving the strands are transversely striated so as to reduce the possibilities of relative longitudinal sliding between the strands and the plates.

• chaque sabot est solidarisé longitudinalement avec l'élément intermédiaire à l'aide d'au moins un tirant présentant un pied solidaire dudit élément et une tête filetée qui traverse le sabot et coopère avec deux écrous encadrant longitudinalement ce sabot,
• la solidarisation entre chaque pied de tirant et l'élément intermédiaire est réalisée à l'aide d'un raccord sur lequel ledit pied est monté de façon amovible,
• le rapprochement mutuel transversal des sabots est au moins maintenu par vissage de boulons transversaux,
• la pression du serrage transversal exercé sur les sabots avant le vissage de maintien des boulons transversaux est réglable,
• pour rétablir la continuité de la gaine qui délimite extérieurement le câble au niveau de la zone, de ce câble, qui est dénudée pour exécuter l'ancrage intermédiaire, on prévoit deux fourrures tubulaires entourant le câble et s'étendant chacune entre les sabots et une extrémité coupée de ladite gaine.

In preferred embodiments, use is also made of one and / or the other of the provisions following:

• each shoe is secured longitudinally with the intermediate element using at least one tie rod having a foot secured to said element and a threaded head which passes through the shoe and cooperates with two nuts longitudinally framing this shoe,
• the connection between each drawing foot and the intermediate element is carried out using a connector on which said foot is removably mounted,
• the transverse mutual approximation of the hooves is at least maintained by screwing transverse bolts,
• the pressure of the transverse tightening exerted on the shoes before the screwing to hold the transverse bolts is adjustable,
• to restore the continuity of the sheath which externally delimits the cable at the level of the zone, of this cable, which is stripped to carry out the intermediate anchoring, two tubular furring strips are provided surrounding the cable and each extending between the shoes and a cut end of said sheath.

The invention includes, apart from these main provisions, certain other provisions which are preferably used at the same time and which will be more explicitly discussed below.

In what follows, a preferred embodiment of the invention will be described with reference to the accompanying drawings in a manner which is of course not limiting.

FIG. 1, of these drawings, shows, as already indicated above, a concrete beam reinforced by a prestressing cable, an intermediate zone of this cable being anchored on an intermediate crosspiece constituting said beam, and said anchoring being executed in accordance with the invention.

Figure 2 shows partially and in more detail the intermediate cross member and the anchoring device figure 1.

FIGS. 3 and 4 show on a larger scale the same device, respectively in end view according to arrow III in FIG. 4 and in cross section according to IV-IV, FIG. 3.

Figures 5 and 6 finally show on an even larger scale, respectively in end view and in partial section along VI-VI, Figure 5, the grooved plates included by the above intermediate anchoring device.

In general, it is proposed to anchor, on an intermediate element 2₁ of a concrete structure 1, at least one intermediate zone of a prestressing cable 4 intended to be stretched between two distant points A and B of said structure, said cable being constituted by a bundle of parallel strands 5, generally twisted, having an overall hexagonal section.

For this purpose, use is made of a device which makes it possible to grasp the area to be fixed of the cable laterally, after placing this cable in the structure, but before it is tensioned, without it being in any way necessary to proceed to any individual prewiring of the strands constituting the cable in annular or tubular blocking members.

• une succession de plaques 6 d'entretoisement propres à être insérées transversalement et jointivement entre les nappes de torons 5 successives et évidées à cet effet sur leurs deux faces par des rainures 7 présentant des profils sensiblement complémentaires de ceux des torons 5,
• deux mâchoires 8 et 9 propres à encadrer transversalement la pile des plaques 6 mises en place entre les torons,
• des tirants 10 qui solidarisent longitudinalement, c'est-à-dire selon la direction longitudinale L du câble 4, les machoires avec l'élément 2₁,
• et des moyens schématisés par les flèches 11 pour rapprocher mutuellement les mâchoires l'une de l'autre de manière à solidariser entre elles par serrage les nappes de torons 5 et les plaques 6.

This device includes:

• a succession of bracing plates 6 suitable for being inserted transversely and contiguously between the layers of successive strands 5 and hollowed out for this purpose on their two faces by grooves 7 having profiles substantially complementary to those of the strands 5,
• two jaws 8 and 9 suitable for transversely framing the stack of plates 6 placed between the strands,
• tie rods 10 which join longitudinally, that is to say in the longitudinal direction L of the cable 4, jaws with element 2₁,
• and means shown diagrammatically by the arrows 11 for bringing the jaws mutually closer to one another so as to secure the strand plies 5 and the plates 6 to one another by tightening.

As can be seen in FIGS. 3 to 5, all of the grooved plates 6 placed between the strands of strands 5 form a sort of cylindrical wafer of revolution and the edge of this wafer is trapped axially and radially in an annular groove 12 of exactly complementary profile hollowed out in jaws 8 and 9.

The feet of the tie rods 10 are secured to the element 2₁.

This fastening of the feet of the tie rods 10 with the element 2₁ can be achieved by direct embedding of the ends of these feet in this element.

It can also be obtained by connecting said feet to roots embedded in the element 2₁ by means of connection pieces R on which these feet can be assembled in an easily removable manner.

As for the heads of the tie rods 10, they are threaded, pass through the jaws 8 and 9 and are secured to the latter by screwing each of these heads with two nuts 13 and 14 enclosing said jaws between them (FIG. 4).

To reduce the possibility of sliding between the bottoms of the grooves 7 and the strands 5 housed in these grooves, transverse ridges 15 are practiced in these bottoms (FIG. 6).

To ensure proper application of the grooved plates 6 against the strands 5, there are also hollowed out in the bottoms of the grooves 7 narrow longitudinal grooves 16, which gives said plates a certain flexibility allowing a good adaptation to tolerances. diametral strands.

To simplify the drawings, FIGS. 3 and 5 show only a few of the grooves 16, but such grooves are preferably hollowed out at the bottom of all the grooves 7.

It is also to simplify the drawings that have been shown in Figures 3 and 5 that a few strands 5 broken down into their constituent son, here seven in number, the other strands being shown schematically by simple circles.

The transverse approximation of the jaws 8 and 9 is preferably carried out using an appropriate jack (not shown) and the finally obtained tight state of all of the strand plies 5 and of the plates 6 is then easily preserved by screwing of appropriate bolts 17 passing through smooth bores 18 of the jaw 8 into threaded bores 19 of the jaw 9, the pressure of the jack being released only after such a screwing.

It should be noted that, due to the shape of a cylindrical "wafer" of revolution given to the stacking of the plates 6 with interposition of strands 5, the clamping of the jaws 8 and 9 results in the exercise of oblique forces on the sides of said plates 6, these forces being oriented radially with respect to the axis of the wafer, which effectively urges the closing of the narrow grooves 16 hollowed out in the bottoms of the grooves 7.

This measure ensures a very firm connection between the strands 4 and the grooved plates 6.

Said grooved plates 6 are advantageously constituted by steel molded in lost wax, the surface of said plates preferably being hardened by a thermochemical treatment.

FIG. 2 also shows furs or tubular sections 20 which serve to restore the continuity of the seal between, on the one hand, the ends cut from the sheath 21 enveloping the strands 5 and, on the other hand, the jaws 8 and 9, after execution of the intermediate anchoring on the element 2₁.

To carry out such an intermediate anchoring, the procedure is as follows.

Initially the cable 4 with multiple strands 5 is put in place in the structure 1, including its two ends A and B, the element 2₁ being traversed with the possibility of sliding of the sheath 21 which externally delimits the cable in a tube of guide, for example metallic.

A small length of the cable is then released by cutting its sheath 21 in correspondence.

Then the plates 6 are introduced transversely between the stripped portions of the strands 5 which are not yet stretched.

After having completed the "pancake" formed by the various plates 6, the jaws 8 and 9 are put in place, on the one hand, by covering the pancake laterally with these jaws and, on the other hand, by introducing longitudinally into them here the tie rods 10.

The longitudinal positioning of the jaws on the tie rods is then completed by tightening the nuts 13 and 14.

During said positioning of the jaws, the transverse position of the latter already corresponds to a contiguous transverse application, that is to say with contact, but without clamping, between the various rigid elements intended to be clamped transversely the against each other: it is therefore not necessary to provide a possibility of transverse displacement of the jaws relative to the tie rods, the slight flexibility of these tie rods being quite sufficient to absorb by itself the very small mutual transverse displacements of the jaws due to subsequent tightening.

The cable 4 is then tensioned between the extreme anchoring devices A and B.

Then, this tension being maintained, the intermediate anchoring device C is tightened (FIG. 1), that is to say the mutual approximation of the jaws in the manner indicated above, by successively involving the pressure d 'a jack, then tightening the bolts 17 and finally the release of the jack.

The desired intermediate anchoring between the stripped portion of the cable 4 and the 2₁ element is then achieved.

Then restoring the continuity of the seal which was previously produced by the sheath 21 around said stripped portion by sliding the furs 20 and sealing the ends of these furs respectively on the sheath 21 and on the jaws 8 and 9, after what we can proceed to the injection of a protective wax or similar product inside the sheath 21 thus completed again.

It is important to note that the intermediate anchoring device described above makes it possible to modulate the intermediate anchoring force applied at any intermediate point C of the cable 4 between the extreme limits 0 and 100% of the tension applied to this cable between its ends A and B.

It suffices for this purpose to adjust the pressure of the transverse clamping exerted on the jaws 8 and 9 by the jack, which pressure is applied directly to the plates 6, without using any conical wedging system of the kind of those usually provided, of which the 'Efficiency depends, on the one hand, on the coefficients of friction of the surfaces in mutual contact and, on the other hand, on manufacturing tolerances.

Of course, it is possible to make such intermediate anchors at several distinct points on the same cable.

As it goes without saying, and as it results from elsewhere already from the above, the invention is in no way limited to those of its modes of application and embodiments which have been more especially envisaged; on the contrary, it embraces all its variants.

Claims (6)

Device for anchoring to an intermediate element (2₁) of a concrete structure (1) part of the useful force of a prestressing cable (4) composed of multiple strands (5), comprising two shoes (8,9 ) arranged on either side of the cable, shoes joined longitudinally, that is to say in the longitudinal direction of the cable, with the intermediate element (2₁), and means (11) for bringing the two shoes together perpendicular to the longitudinal direction of the cable so as to secure them with the strands, characterized in that it comprises a plurality of grooved plates (6) arranged parallel to each other between the different layers of strands constituting the cable so that each strand (5) is housed contiguously in two facing grooves (7) respectively comprised by two contiguous plates, the two shoes (8, 9) being applied respectively against the two end plates of the stack co nstituted by the different plates placed between the strands, in that the stacked assembly of grooved plates (6) placed between the different strands (5) of the cable (4) has the general shape of a cylindrical wafer of revolution, in that the bottoms of the grooves (7) are hollowed out by narrow longitudinal grooves (16) so as to give the plates (6) a certain elasticity favoring the effectiveness of their application against the strands, and in that the inner faces of the grooves (7) suitable for receiving the strands (5) are transversely striated (at 15) so as to reduce the possibilities of relative longitudinal sliding between the strands and the plates. Device according to any one of the preceding claims, characterized in that each shoe (8, 9) is secured longitudinally with the element intermediate (2₁) using at least one tie (10) having a foot integral with said element and a threaded head which passes through the shoe and cooperates with two nuts (13,14) framing this shoe longitudinally. Device according to claim 2, characterized in that the connection between each tie-rod (10) and the intermediate element (2₁) is carried out by means of a connector (R) on which said leg is removably mounted . Device according to any one of the preceding claims, characterized in that the transverse mutual approximation of the shoes is at least maintained by screwing transverse bolts (17). Device according to claim 4, characterized in that the pressure of the transverse tightening exerted on the shoes (8, 9) before the screwing to hold the transverse bolts (17) is adjustable. Device according to any one of the preceding claims, characterized in that, in order to restore the continuity of the sheath (21) which externally delimits the cable (4) at the level of the area, of this cable, which is stripped to carry out the intermediate anchor, it comprises two tubular furs (20) surrounding the cable and each extending between the shoes (8, 9) and a cut end of said sheath.

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