WO1993000528A1

WO1993000528A1 - Live cable holding device

Info

Publication number: WO1993000528A1
Application number: PCT/FR1992/000551
Authority: WO
Inventors: Brieuc Robert
Original assignee: Kley-France
Priority date: 1991-06-20
Filing date: 1992-06-18
Publication date: 1993-01-07
Also published as: FR2678036A1; FR2678036B1

Abstract

A holding device to be mounted at a given point along at least one live cable (5) to connect it to a fixed structure. The device includes two plates (1 and 2) each having at least one bore (3 or 4) with a tapered portion (6 or 7) into which a set of wedges (8 or 9) is inserted. The device further includes a set of bolts (11) and nuts (12) for tightly connecting the two plates (1 and 2) to grip the cable (5) by means of the wedges (8,9). A third plate (13) is arranged between the two plates (1 and 2) and comprises at least one bore (14) allowing the cable (5) to run freely therethrough. The sets of wedges (8 and 9) in the aligned tapering portions (6 and 7) of the plates (1 and 2) respectively engage opposite sides of the third plate (13), said third plate comprising elements for attaching it to the fixed structure.

Description

Locking device for live cable.

The present invention relates to a locking device for a live cable, intended to be installed at an intermediate point of at least one live cable to connect it to a fixed structure and comprising two plates, each having at least one bore aligned with that of the other plate for the passage of a cable, each bore having a conical part, which is flared towards the outside of the corresponding plate and which is aligned and faces the conical part of the bore of the other plate , a set of conical keys being engaged in the conical part of each bore and projecting partially outside the corresponding plate, and a set of bolts and clamping nuts to tighten the two plates towards each other to lock the cable in relation to the plates by means of the conical keys.

The present invention is applicable in particular, but not exclusively, to concrete structures in which at least one concrete element is post-stressed by at least one stretched cable of great length. Usually, the cable is anchored at both ends to the post-stressed concrete element. However, certain regulations require that the free length of the cable between two anchors does not exceed a predetermined value. Consequently, when the concrete element to be post-stressed has a length which clearly exceeds said predetermined length, it is necessary to provide at least one locking device, which is clamped on the cable at a point chosen between its two ends and which is fixed to the concrete element to be post-stressed. To this end, an can use a blocking device as defined above, one of the two plates of which is connected to the post-constrained concrete element to take up part of the forces applied to the cable. Under these conditions, as will be explained in detail below, there is a risk of slipping between the cable and the conical keys which serve to tighten the cable and to block it in relation to the two plates mentioned above.

The object of the present invention is to remedy this drawback by providing a blocking device which is safer than the blocking device defined above.

To this end, the blocking device of the present invention is characterized in that a third plate or intermediate plate is disposed between the two external plates or plates and comprises at least one bore, which is aligned with a pair of bore of the two outer plates and through which the cable passes freely :, in that the two sets of keys engaged in the aligned conical parts of the outer plates bear respectively against the opposite faces of the intermediate plate, and in that the intermediate plate comprises means for fixing it to said fixed structure.

The invention will be better understood on reading the description which follows and which is given with reference to the accompanying drawings in which:

Figure 1 shows schematically and in longitudinal section a locking device of known type.

Figure 2 is a view similar to Figure 1 showing, in its simplest form, a locking device according to the present invention.

FIG. 3 is a partial sectional view along line III-III of FIG. 2. Figure 4 shows, in longitudinal section, a clamping key used in the locking device.

Figure 5 shows, partly in longitudinal section and partly in elevation, a concrete embodiment of the locking device according to the invention.

FIG. 6 is an end view of the locking device of FIG. 3.

The known locking device shown in Figure 1 has two plates 1 and 2, each having at least one bore 3, 4. The two bores 3 and 4 are aligned and have a diameter sufficient to allow the free passage of a cable 5 through them (in the case where the locking device is intended to be installed on a cable harness, each of the two plates 1 and 2 will have a number of bores 3 or 4 equal to the number of cables). Each of the two bores 3 and 4 has a conical part 6 or 7, which flares outwards from the corresponding plate. More precisely, the two conical parts 6 and 7 are aligned and face each other in the interval between the two plates 1 and 2.

In each of the two annular spaces formed between the cable 5 and each of the two conical parts 6 and 7 there is a set of conical keys 3 or 9. Each set of keys comprises for example three keys 8 or 9, each key 8 or 9 s 'extending in the circumferential direction over a little less than 120 °. As shown in FIG. 1, each key 8 is leaned against one of the keys 9, but it is also possible to produce each pair of leaned keys 8 and 9 in the form of a single bi-conical key.

The two plates 1 and 2 are tightened towards one another by a set of bolts 11 and nuts 12 for tightening, the threaded rods of the bolts 11 freely passing through aligned holes provided in the plates 1 and 2 as shown in FIG. 1. When the nuts 12 are screwed onto the threaded rods of the bolts 11, the conical keys 8 and 9 sink respectively into the conical parts 6 and 7 of the bores 3 and 4 and firmly tighten the cable 5 to block it in said bores.

We will now explain the operation of the known locking device using an example. In FIG. 1, the forces applied to each of the two plates 1 and 2 are designated by P by all of the bolts 11 and nuts 12, and by F a force which it is desired to transmit to the cable 5. Usually, the force F a transmit to cable 5 is applied to one of the two plates 1 and 2, for example to plate 2 as shown in Figure 1, this plate being supported on a fixed structure or connected to it for example by the bolts 11. If the tension of the cable 5 had a value T before application of the force F, the tension of the cable takes a value T + F / 2 in the part of the cable 5 located to the right of the plate 2 and a value T - F / 2 in the part of the cable 5 located to the left of the plate 1, after application of the force F to the plate 2. To fix the ideas we will suppose for example that T = 330 t, F = 40 t and P = 100 t. It can be seen that in order to transmit the force F of 40 t to the cable 5, without the keys 8 and 9 sliding with respect to the cable 5, the total friction force between the keys 8 and 9 and the cable 5 must be generated. by the tightening force P of the bolts 11 and nuts 12, which is greater than the force F.

We know that any bolt, when the associated nut is tightened, undergoes, under the effect of the reaction forces exerted on the bolt and on the nut by the parts tightened together, an elongation whose value is substantially proportional to the clamping force. In this example, assume that when the nuts 12 are tightened to give a total tightening force of 100 t, but before the force F is applied, each of the bolts 11 undergoes an elongation Δ1. Then, when the force F is applied to the plate 2, the keys 9 sink deeper inside the conical parts 7 of the bores 4. As a result, the interval between the two plates 1 and 2 narrows and , under the effect of their internal tension, the bolts 11 shorten. It follows that the tightening force exerted by the bolts 11 and the nuts 12 decreases in proportion to the shortening of the bolts 11, that is to say in proportion to the additional depression of the keys 9 in the conical parts 7 due to the application of the force F to the plate 2. Starting from the assumptions made above, the table below indicates the values of the forces of depression of the keys in their respective conical part and the values of the total force of friction for various values of l additional depression of the keys 9 in the conical parts 7 due to the application of the force F, e being expressed as a function of the initial elongation Δ1 of the bolts 11. In the table below, Fel denotes the force of pressing the keys 8 into the conical part 6 of the bore 3 of the plate 1, Fe2 denotes the force of pressing the keys 9 into the conical part 7 of the bore 4 of the plate 2 and Ff denotes the total force the friction between the keys 3 and 9 and the cable 5, which results from the total driving force Fe1 + Fe2. F, P, e and Δ1 have the meanings already indicated above. Ff was calculated by the usual formulas by assuming that the coefficient of friction between each of the plates 1 and 2 and the respective set of keys 8 or 9 and between each set of keys 8 or 9 and the cable 5 is equal to 0.1 , and that the corner angle of the keys 8 and 9 is equal to 8 · 30. F 0 40 40 40 (tonnes) e 0 Δ1 / 2 3Δ1 / 4 Δ1

P 100 50 25 0 (tonnes)

Fe1 = P 100 50 25 0 (tonnes)

Fe2 = P + F 100 90 65 40 Ctonnes)

Fe1 + Fe2 200 140 90 40 (tonnes)

Ff

(tonnes) 152 106 68 30

From the table above, it can be seen that if the additional depression e of the keys 9 in the conical part 7 of the bore 4 is equal to half or even three quarters of the initial elongation Δ1 of the bolts it , the value of the total friction force Ff remains greater than the value of the force F to be transmitted to the cable 5, so that the latter force can be fully transmitted to the cable without it sliding between the keys. On the other hand, if the additional depression e of the keys 9 is equal to the initial elongation Δl of the bolts 11, the value of the friction force Ff becomes less than the force F. so that the cable 5 slides between the keys. The cable 5 even begins to slide for a value of e of between 3Δ1 / 4 and Δ1.

As the degree of depression of the keys 8 and 9 in the respective bores is difficult to control, it follows that with the known locking device there is a risk of cable slipping 5 between the keys 8 and 9 when a force to be transmitted to the cable 5 is applied to one of the two plates 1 and 2.

The present invention avoids this risk by providing an additional plate 13 (Figure 2), which has at least one hole 14 for the passage of the cable 5 and which is disposed between the two plates 1 and 2, practically without contact with those -this, that is to say without substantial forces directed parallel to the axis of the cable 5 can be transmitted from the plate 13 to the plate 1 or to the plate

2. The bolts pass freely through smooth holes provided in plate 13 and aligned with the smooth holes provided in plates 1 and 2 for these same bolts. The thickest part of the keys

3, outside the conical part 6 of the bore 3, is supported on one of the two circular edges of the hole 14, on one side of the plate 13, while the thickest part of the keys 9 is supported on the circular edge opposite the hole 14, on the other side of the plate 13. For the rest, the locking device of the present invention, shown in FIG. 2, is similar to that of FIG. 1.

With the locking device of the present invention, the force F to be transmitted to the cable 5 is applied not to one of the two plates i and 2, but to the plate 13. Under these conditions, the force F is applied to the 'one of the two sets of keys, for example to the keys 8, which transmit this force directly to the cable 5, by friction, without sinking further into the conical part 6 of the bore 3. In fact, the plate 1 does not being supported on any fixed structure, the force F therefore does not cause an additional depression of the keys 8 in the conical part 6 of the bore 3. Consequently, the bolts 11 do not tend to shorten and the initial force of tightening, adjusted by the bolts 12, is fully maintained, so that there is no risk of the cable 5 slipping between the keys 8 to 9.

Preferably, the radius r1 (FIG. 3) of the internal cylindrical surface of each key 8 or 9 is slightly smaller (1 to 3 tenths of a mm) than the external radius r2 of the cable 5 in the stretched state, so that that, before complete tightening, the keys 8 or 9 are in contact with the cable 5 along two generators spaced therefrom as shown in FIG. 3. Likewise, for any cross section of the conical part 6 or 7 of bore 3 or 4, the outside radius R1 of the section of any of the keys 8 or 9 is slightly smaller (1 to 3 tenths of a mm) than the inside radius R2 of the section of the conical part 6 or 7 of bore 3 or 4, so that, before complete tightening, each key 8 or 9 is in contact with the conical part 6 or 7 only along a generatrix of its conical surface as is also shown in the figure 3. In this figure, the difference between the radii r1 and r2 and the difference between the rays R1 and R2 have been deliberately exaggerated only for the purpose of illustration of what has just been described.

In addition, each of the keys 8 and 9 has a corner angle a (Figure 4) which, preferably, is not less than 8 · 30 for a steel cable 5 and keys 8 and 9 in steel. Under these conditions, the tightening of the cable 5 by the keys 8 and 9 is reversible, that is to say that it is possible to make the keys 8 and 9 stop tightening the cable 5 by loosening the nuts. 12 and the locking device can be removed if desired. It will also be noted that the internal cylindrical surface 15 of the keys 8 and 9 is smooth as appears in particular in FIG. 4. This thus avoids damaging the cable 5 when the keys 8 and 9 are tightened thereon. With the locking device of the present invention, the keys 8 and 9, when tightened on the cable 5, do not slip relative to the latter, their smooth internal cylindrical surface 15.

The blocking device which has been described above is intended to block a single cable or strand 5. In practice, blocking devices of this kind are generally designed to block several cables or cable strands at a time. Figures 5 and 6 show, by way of example, a blocking device according to the invention for blocking nineteen cables or strands of cables at a time. The elements of the blocking device of FIGS. 5 and 6, which are identical or which play the same role as those of the blocking device of FIG. 2, are designated by the same reference numbers and will therefore not be described again in detail. .

As shown in Figure 6, the plate 1 has nineteen bores 3, through which the nineteen cables or strands 5 pass, respectively. Each bore 3 has a conical part similar to the conical part 6 of FIG. 2, and each conical part contains a set of clamping keys 8, for example three keys 8. Similarly, the plate 13 has nineteen holes 14, of which the axes are respectively aligned with those of the bores 3, and the plate 2 also has nineteen bores 4, whose axes are respectively aligned with those of the holes 14 of the plate 13. Each bore 4 has a conical part similar to the conical part 7 of FIG. 2 and each conical part contains a set of tightening keys 9, for example three keys 9 for tightening one of the nineteen cables 5.

As shown in FIG. 5, the intermediate plate 13 can advantageously include, in each of its two opposite faces, a recess 16 with a flat bottom, the outline of which, for example circular, corresponds to the outside outline of the plates 1 and 2.

Each of the two plates 1 and 2 is partially engaged in one of the two recesses 16 of the plate

13. An annular seal 17 is preferably interposed between the intermediate plate 13 and each of the two outer plates 1 and 2, in the region of the outer edge thereof, as shown in Figure 5. Thus, the spaces between the plate 13 and each of the two plates 1 and 2 and the conical holes in which the keys 8 and 9 are located are protected against the ingress of dust and moisture. The two seals 17 must be made of an easily compressible or deformable material so that, in service, they transmit practically no force from plate 1 or 2 to plate 13, or vice versa, in a direction parallel to the axes of the cables. 5.

To allow the fixing of the plate 13 to a fixed structure, for example a concrete structure, the plate 13 is for example made integral with a plate

18, perpendicular to the plate 13, the assembly of the two plates 13 and 18 being stiffened by reinforcing gussets, for example four gussets. The plates 13 and 18 and the gussets 19 can for example be fixed to each other by welding or they can be made in one piece by molding. As shown in Figures 5 and 6, the plate 18 has a number of holes 21, for example four holes for screws or fixing studs 22 (shown only schematically in Figure 6) for fixing the device blocking on the fixed structure 23.

It goes without saying that the embodiment of the present invention which has been described above was given by way of purely indicative example and in no way limiting, and that many modifications can be easily made by those skilled in the art without departing from the scope of the invention. Thus, in particular, the fixing of the intermediate plate 13 to a fixed structure can be carried out in a manner different from that shown in FIGS. 5 and 6. For example, the plate 13 could have larger dimensions than those shown in FIGS. 5 and 6 and the holes for the passage of the fixing screws could be formed directly in the plate 13 radially outside the plates 1 and 2. In the latter case, the fixed support structure must then have an opening for cable passage 5.

In addition, although FIGS. 2 and 3 show the invention applied to a single cable, the invention is also applicable in particular to stranded cables or cables with parallel strands. Thus the number of keys arranged in the same conical hole can be adapted to the external profile of the cable seen in cross section. For example, in the embodiment of FIG. 2, for a cable composed of 19 strands (1 + 6 + 12), it is possible to make sets of 12 keys 8 or 9 corresponding to the transverse profile of the 12 strands of the outer layer of the cable.

Claims

1.- Locking device for live cable, intended to be installed at an intermediate point of at least one live cable (5) to connect it to a fixed structure (23), and comprising two plates (1 and 2) each having at least one bore (3) aligned with that (4) of the other plate for the passage of the cable, each bore having a conical part (6 or 7) which is flared towards the outside of the corresponding plate (1 or 2) and which is aligned and faces the conical part of the bore of the other plate, a set of conical keys (8 or 9) being engaged in the conical part (6 or 7) of each bore (3 or 4) and partially projecting outside the corresponding plate (1 or 2), and a set of bolts (11) and clamping nuts (12) to tighten the two plates (1 and 2) one towards the other to block the cable (5) relative to the plates by means of the conical keys (8 and 9), characterized in that a third pl aque or intermediate plate (13) is disposed between the two plates to the outer plates (1 and 2) and comprises at least one bore (14), which is aligned with a pair of bores (3,4) of the two outer plates and through which the cable (5) passes freely, in that the two sets of keys (8 and 9) engaged in the aligned conical parts (6 and 7) of the outer plates (1 and 2) bear respectively against the opposite faces of the intermediate plate (13), and in that the intermediate plate includes means (18-22) allowing its attachment to said fixed structure (23).

2. A locking device according to claim 1, characterized in that the intermediate plate (13) comprises in each of its two opposite faces a recess (16) whose contour corresponds to the external contour of the external plates (1 and 2), and in that each of the outer plates is partially engaged in one of the recesses (16) of the intermediate plate (13).

3. A locking device according to claim 1 or 2, characterized in that an annular seal (17) is interposed between the intermediate plate (13) and each of the outer plates (1 and 2).

4. A locking device according to any one of claims 1 to 3, characterized in that each conical key has a corner angle (and) which is not less than 8 · 30 for a steel cable and keys made of steel, so that the locking device is reversible.

5. A locking device according to any one of claims 1 to 4, characterized in that each of the conical keys (8 and 9) has an inner cylindrical surface (15), the radius of which is smaller, by a few tenths of millimeter, that the outer radius of the cable (5) in the stretched state, and an outer conical surface, of which any section perpendicular to the axis of the cone has a smaller radius, of a few tenths of a millimeter, than the inner radius of the corresponding section of the conical part (6 or 7) of the bore (3 or 4) in which the conical key is located.

6. A locking device according to any one of claims 1 to 5, characterized in that the keys (8 and 9) have an inner cylindrical surface (15) which is smooth.