EP0166651B1 - Cable anchoring devices and their manufacturing methods - Google Patents

Abstract

The invention provides an anchorage device for a cable with multiple strands (2) comprising a block (1) in which the strands are anchored individually by radially clamping about each strand a split truncated cone shaped jaw (3) surrounding this strand and housed in a complementary housing (4) of the block. This device comprises a single thrust member (6) disposed axially opposite the different jaws (3) and a plurality of spacers (10) each interposed axially between said member (6) and a jaw (3) about the strand end (2) clamped by this jaw, said spacers (10) being identical to each other, formed from a metal or an alloy whose deformation/stress characteristic has a long plastic flow plateau and dimensioned so that at the end of the thrust the deformation of each of them has reached, but not exceeded, the plastic flow stage thereof.

Description

The invention relates to cable anchoring devices composed of multiple strands, each strand may itself be constituted by a wire or by a strand of twisted son, said cables being intended to be tensioned, in particular in order to ensure the prestressing of a concrete body or the suspension of a structure such as a bridge (guy lines).

It also covers the procedures for establishing devices of the kind in question.

It relates more particularly, among these devices, those in which the different strands of the cable are individually anchored on the same block by radial tightening around each of these strands of a split frustoconical jaw surrounding this strand and housed in a complementary recess of the block , the tightening in question being ensured at least in part by application of an axial thrust on the large base of said jaw.

With the known embodiments of the anchoring devices considered, these axial thrusts applied to the different jaws are generated individually.

Indeed, it is hardly possible to ensure, using a single thrust member, tightenings of identical intensities for the different jaws and strands of the same cable when the number of these strands is greater than three. , as is the most general case in practice, said number generally exceeding ten and possibly reaching, or even exceeding, the hundred: such a single organ cannot in fact be applied initially, that is to say before starting to really exert its thrust, as much as possible on the three jaws which project the most axially on the anchor block, jaws which define the starting plane of the tightening.

Consequently, even if the other jaws are all subsequently reached by the thrust member, their total axial clamping strokes are less than those of the first three jaws and the same is true of the resulting clamping forces.

Such a result is also observable when the thrust of the thrust member is transmitted to the different jaws by identical spacers between them interposed axially each between said member and a jaw around the end of the strand clamped by this jaw, since the spacers are made of hard steel or similar material that is not very deformable, as is the case in document FR-A-2 398 859.

The object of the invention is, above all, to remedy this drawback by making it possible to obtain, very simply from a single thrust member, tightenings of identical intensity on the different strands.

To this end, the anchoring devices according to the invention also comprise a single thrust member disposed axially opposite the different jaws and a plurality of spacers interposed axially each between said member and a jaw around the end of the strand clamped by this jaws, said spacers being identical to each other, and they are characterized in that the spacers are made of a metal or alloy whose deformation / stress characteristic has a long plastic flow bearing and are dimensioned so that at the end from the push the deformation of each of them has reached, but not exceeded, the stage of its plastic flow.

• - les entretoises sont des bagues,
• - les bagues sont des tronçons tubulaires,
• - les entretoises sont constituées en acier doux,
• - à la fin de la poussée une butée liée rigidement au bloc d'ancrage est maintenue appliquée contre l'organe de poussée, lui-même appliqué contre les entretoises, afin de l'empêcher de s'écarter dudit bloc,
• - la butée selon l'alinéa précèdent est un anneau fileté extérieurement vissé dans un manchon fileté intérieurement contenant l'organe de poussée et solidaire du bloc d'ancrage.

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

• - the spacers are rings,
• - the rings are tubular sections,
• - the spacers are made of mild steel,
• at the end of the thrust, a stop rigidly connected to the anchoring block is kept applied against the thrust member, itself applied against the spacers, in order to prevent it from moving away from said block,
• - The stop according to the preceding paragraph is an externally threaded ring screwed into an internally threaded sleeve containing the thrust member and secured to the anchoring block.

The invention may in any case be well understood with the aid of the additional description which follows as well as of the appended drawing, which supplement and drawing are in no way limiting.

Figures 1 and 2 of this drawing schematically show a device for anchoring a multi-strand cable established in accordance with the invention, respectively during its establishment and after it.

FIGS. 3 and 4 show, on a larger scale, a detail of this anchoring device, in the same situations respectively as FIGS. 1 and 2.

FIG. 5 is a graph showing a property exploited according to the invention.

It is proposed to anchor on a metal block 1 the parallel multiple strands 2, of a number greater than three, composing a cable itself intended to be tensioned in order to constitute for example a prestressing reinforcement for a concrete body or a bridge suspension strut.

In a manner known per se, the anchoring of each strand on the block is ensured with the aid of a split frustoconical jaw surrounding this strand and the narrowest portion of which is housed in the complementary flared end 4 of a hole 5 hollowed out in the block and traversed right through by the strand.

The widest end of each jaw 3 then projects axially on the face A of the block 1, where the flared ends open 4, and the ends of the strands 2 surrounded by the jaws themselves project axially on these ends the wider.

The radial tightening of each jaw around the strand which it surrounds is ensured by a wedge effect by biasing this jaw upon axial insertion into his accommodation.

In the usual embodiments, this axial stress is generated by the very tension of the strand due to the friction which exists between this strand and the internal face of the jaw.

In the present case, the tension of the cable can contribute to the axial stress of the jaw, but it is not the main cause of it and this tension can even be zero during the establishment of the anchoring according to the present invention, the cable not energized until a later phase.

Such a measure makes it possible to dissociate the solidity of the anchorage and the tension of the cable, which is precious in cases where said tension can be greatly reduced, or even canceled, during the actual service of the cable such a situation occurs for example. when receiving a shock from a suspension bridge shroud, shock for example caused by an earthquake, a tornado or the loss of control of a heavy vehicle.

Here the stress of each jaw in the axial insertion is obtained by exerting an axial thrust on this jaw and the invention makes it possible to ensure the thrusts corresponding to the different jaws using a single thrust member 6, even if the number of these jaws is greater than three, which is the most general case, the only one considered here.

In view of the inevitable differences which exist between the dimensions of the strands 2, jaws 3 and housings 4, the heights corresponding to the respective axial projections of the different jaws 3 on the face A are different.

If therefore the thrust member 6 was applied directly to these different jaws 3, it could not reach the maximum, among these jaws, before starting to truly exert its thrust, only the three jaws projecting the most on side A.

The axial strokes then imposed on these three jaws by the member 6 would be longer than those imposed on the other jaws, the intensities of the tightening operations carried out on the different strands would therefore not be identical with each other and the overall tension exerted on the cable composed of these strands during its service could not be distributed uniformly between these strands, so that some of them would risk being overly stressed at the tension while others, on the contrary, would be exploited below their capacity.

To remedy this drawback, the properties presented by certain metals or alloys, such as mild steel, aluminum or copper alloys, are exploited here to have a long plastic flow stage 7 (fig. 5) in the curve which represents their deformation in compression d (deformation expressed in percentages of shortening) as a function of the stress c applied to them.

In other words, if said stress c is gradually increased, the deformation d is first of all very small and proportional to the stress (portion 8 of the curve). Then from the moment when the stress c reaches a given threshold E, or elastic limit, the deformation d increases very quickly for insignificant increases in the stress c (level 7) and this until reaching a new threshold E ′, or plastic flow limit, beyond which it is again necessary to substantially increase the stress c in order to increase the deformation d (portion 9 of the curve).

This property is exploited according to the invention by interposing between the thrust member 6 and the different jaws 3 of the spacers 10 made of such a metal or alloy, these spacers being chosen so that at the end of the thrust exerted by organ 6, the deformation of each of them has reached, but not exceeded, the stage of plastic flow.

• - le raccourcissement de l'entretoise placée contre le mors faisant initialement le plus saillie sur la face A soit inférieur à celui correspondant à la limite plastique E',
• - et que le raccourcissement de l'entretoise placée contre le mors faisant initialement le moins saillie sur la face A soit supérieur à celui correspondant à la limite élastique E.

This result assumes that at the end of the push:

• - the shortening of the spacer placed against the jaw initially making the most projection on the face A is less than that corresponding to the plastic limit E ',
• - And that the shortening of the spacer placed against the jaw initially making the least projection on the face A is greater than that corresponding to the elastic limit E.

It is therefore certain that the axial thrust forces p applied respectively to the different jaws 3 are practically identical to each other and that, consequently, all the strands 2 are anchored in the block 1 with the same clamping force.

Each of these thrusts p is indeed equal to the difference between the thrust P exerted by the member 6 on each spacer 10 and the portion E, of this thrust P, necessary to partially crush said spacer: or each of the two values P and E is the same for all spacers.

In the preferred embodiment, each spacer 10 is constituted by a ring and preferably by a tube section and its plastic deformation has the effect of inflating it radially as visible in FIGS. 2 and 4.

It should be noted that each axial thrust force p exerted on a jaw 3 is strictly independent of the tension force exerted on the corresponding strand 2 and the resistance of this strand.

In particular, this pushing force p can be chosen to be greater than the maximum value of the tensioning force capable of being exerted during service on the strand 2, the corresponding spacer 10 then being of course dimensioned accordingly: one is then sure that the anchoring of the strand will be ensured regardless of the extent of the fluctuations in the tension exerted on this strand during service, even if this tension is canceled.

It is advisable to maintain the thrust member 6 in its end-of-thrust position in order to oppose the elastic return of the deformations generated in the spacers 10 by said thrust and to preserve the high value and the identity of the forces. anchoring carried out between the different strands 2 and the block 1.

To this end, this member 6 is advantageously housed, which is preferably constituted by a thick plate, pierced right through or partially with holes 12 to allow passage at the ends of the strands 2 so that these ends do not come to abut against this plate -, inside a sleeve 11 internally threaded integral with the block 1 and said member 6 is locked in this position using a ring 13 (fig. 2, externally threaded, bearing axially on this member and screwed into the sleeve 11.

The effort required to ensure said retention in place is very low compared to that required to exert the thrust P above.

All of the elements 1, 3, 6, 10, 11 and 13 form a one-piece anchoring head in which the different strands 2 are all anchored securely with identical resistances to tearing: it is this head which will then be anchored itself in the portions of structures to be fitted, which is why it has all the appropriate ranges 14.

• - celles où l'on établirait un pré-ancrage entre chaque brin 2 et le bloc 1, en sollicitant axialement chaque mors 3 à l'enfoncement dans son logement 4 par l'exercice d'une tension préalable sur le brin correspondant, les ancrages assurés par poussée axiale sur les différents mors conformément à la présente invention n'étant plus alors que des compléments d'ancrage exécutés notamment à des fins de sécurité, la pièce de butée 13 ci-dessus devenant alors inutile puisqu'il n'y a plus alors de risque de retour en arrière des mors en fin de serrage,
• - celles où le bloc dans lequel sont ancrés les différents brins 2 du câble ne serait pas constitué par un élément unique mais par plusieurs éléments superposés conformément aux enseignements du brevet FR-A-2 495 720 (8 025 757) de la demanderesse.

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

• - those where a pre-anchoring would be established between each strand 2 and the block 1, by axially urging each jaw 3 to be pushed into its housing 4 by the exercise of a prior tension on the corresponding strand, the anchors ensured by axial thrust on the different jaws in accordance with the present invention then being no more than additional anchoring executed in particular for security purposes, the abutment piece 13 above then becoming useless since there is no more then the risk of the jaws going backwards at the end of tightening,
• - those where the block in which the different strands 2 of the cable are anchored would not be constituted by a single element but by several superimposed elements in accordance with the teachings of patent FR-A-2,495,720 (8,025,757) to the applicant.

Claims (10)

1. Device for anchoring a cable with multiple strands (2) comprising a block (1) in which these strands are anchored individually by radially clamping about each strand a split truncated cone shaped jaw (3) surrounding this strand and housed in a complementary recess (4) of the block, a single thrust member (6) disposed axially opposite the different jaws (3) and a plurality of spacers (10) each interposed axially between said member (6) and a jaw (3) about the strand portion (2) clamped by this jaw, said spacers (10) being identical to each other, characterized in that the spacers (10) are formed from a metal or an alloy whose deformation/stress characteristic has a long plastic flow plateau and are dimensioned so that at the end of the thrust, deformation of each of them has reached, but not exceeded, the plastic flow stage thereof.

2. Anchorage device according to claim 1, characterized in that the spacers (10) are rings.

3. Anchorage device according to claim 2, characterized in that the rings (10) are tubular sections.

4. Device according to claim 1, characterized in that the spacers (10) are formed from soft steel.

5. Anchorage device according to any one of the preceding claims, characterized in that a stop (13) rigidly connected to the anchorage block (1) is held against the thrust member (6) itself applied against the spacers (10), so as to prevent it from moving away from said block.

6. Device according to claim 5, characterized in that the stop (13) is an externally threaded ring screwed into an internally threaded sleeve (11) containing the thrust member (6) and integral with the anchorage block (1).

7. Process for forming an anchoraqe device for a cable with multiple strands (2) according to any one of the preceding claims, device comprising a block (1) in which these strands are anchored individually by radially clamping about each strand a split truncated cone shaped jaw (3) surrounding this strand and housed in a complementary recess (4) of the block, a single thrust member (6) disposed axially opposite the different jaws (3) and a plurality of spacers (10) each interposed axially between said member (6) and a jaw (3) about the strand portion (2) clamped by this jaw, characterized by the succession of the following steps:

- the corresponding metal spacer (10) is placed axially opposite each jaw (3), about the strand portion (12) projecting from this jaw, said spacers being identical to each other, formed from a metal or an alloy whose deformation /stress characteristic has a long plastic flow plateau,

- then the thrust member (6) is placed axially opposite the whole of the spacers (10),

- and finally the anchorage thrust (P) is applied to the member (6), said spacers being dimensioned so that at the end of the thrust, deformation of each of them has reached, but not exceeded, the plastic flow stage thereof.

8. Process according to claim 7, characterized in that, after the anchorage thrust (P) has been exerted on the member (6), this latter is locked in its end of travel position.

9. Process according to any one of the claims 7 and 8, characterized in that the anchorage thrust (P) is given a value such that the axial thrust (p) exerted on each jaw (3) is greater than the maximum tension likely to be exerted on the corresponding strand (2) during service.

10. Process according to any one of the claims 7 to 9, characterized in that, before the thrust (P) has been exerted on the spacers (10), pre- anchorage is provided between each strand (2) and the block (1) by axially urging each jaw (3) to penetrate into its housing (4) by exerting a previous tension on the corresponding strand.

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