EP1156158B1 - Shock absorbing device - Google Patents

Abstract

The shock absorber for a cable car traction cable (c ) has metal discs (2,3) which are stacked and shaped to allow the passage of two runs (6,7) of the cable to form a loop. The loop is held in the stack of discs by a cross pin (13) which is slidably mounted at the end of the stack. A weld bead (4) connects the discs.

Description

The present invention relates to a shock-absorbing device for a tensile-stressed cable, comprising an envelope capable of housing a cable portion, the shape of the envelope being chosen so that at least a portion of the forces generated by a traction on said cable is transmitted to the envelope by said cable portion, the envelope being able to undergo plastic deformation when said portion of the forces exceeds a predetermined value.

The invention also relates to a protection screen against falling rocks.

Protective screens in sloping terrain to protect downstream areas from falling rocks are often made of wire rope nets. These nets are composed of either diagonal mesh with crossings fixed by flanges, all connected to a border cable, or rings connected to a border cable by sleeves. The interception structure of large stones can also be formed of continuous cables, held parallel to each other by guide tubes and lined with a wire net, designed to retain small stones.

The protective screens are on the one hand anchored to the ground by means of junction cables, and on the other hand are connected to posts, fixed or articulated. The base of the posts is mounted on a foundation implanted in the ground and each post is held in position by upstream and side stay cables, attached to the upper part of the post.

In order to increase the energy absorption capacity of the barrier beyond the limits of elastic deformation of the net during shocks due to falling large stones, shock absorption devices, commonly called brake blocks, are mounted on the guys, as well as on the junction cables, possibly the edge cables.

A type of brake block commonly used consists of a cable ring, interposed between two cable sections of the stay cables, forming a braking loop with the aid of a bit with two flanges, tightened to a predetermined tightening torque. , constituting a friction block. The perimeter of the braking loop is often of the order of 1.5 m. The bit, or a similar friction plate, can also be directly attached to a portion of cable shaped guy loop. Such brake blocks are described for example in US 5,435,524. A major disadvantage of this shock absorbing device results from the fact that the braking is a function of the clamping of the friction plate. Overtightening prevents the brake block from operating, too low a clamp makes it work too easily, with low absorption of friction energy. Even if the flanges are locked with a predetermined tightening torque, for example using a torque wrench, this can at best guarantee a first operation under the prescribed conditions. When a first movement of the cable a few centimeters in the friction block has occurred, subsequent actuations are no longer predictable. In addition, the system is very sensitive to atmospheric influences: rust or humidity modify the cable / block interaction.

To overcome this defect, other friction devices, independent of the clamping force have been proposed, wherein the cable passes over pads or friction pulleys, inside a housing. Documents EP-531574, CH-684704, FR-2605653 and FR-2576047 describe such devices. These devices are more expensive to make than the friction loops described above.

Another important disadvantage, common to all friction devices described above, lies in the fact that the energy absorption is only through the friction phenomenon. This phenomenon can not induce the absorption of very large amounts of energy in a very short time.

To overcome this drawback, shock absorption devices based on the principle of plastic deformation have been proposed. EP-877122 discloses an energy dissipation loop for carrying cables comprising one or more fusible cable sections connected in parallel by pairs of sleeves on the carrier cable. The fuse cable (s) break before the carrier cable suffers damage. This device becomes expensive and difficult to implement when the number of fusible sections per dissipation loop exceeds 3 or 4. Each section breaking before the next section is requested, the impact of a large stone generates a succession of pulsed shocks that can cause the assembly to break.

EP-494046 discloses an absorption device of the defined input type. In this device, the cable capable of undergoing sudden pulls passes inside a tube shaped in one or more helical turns; the two ends of this tube, which overlap, are connected by a flange. A pull on the cable causes deformation of the tube, elastic or plastic depending on the intensity of traction, accompanied by a reduction of the diameter of the propeller. This device allows a reproducible energy absorption in case of shocks of low or medium intensity. However, in case of major shocks, the evolution of the plastic deformation of the tube is difficult to predict. It can be located at a point of a turn of the tube, and cause the bend or rupture of the tube at this point, while the rest of the turn is barely deformed. In this case, the cable itself will be bent and permanently damaged at this point. This risk increases in the event of repeated shocks: slight plastic deformation of a zone of the turn will induce a strong localized plastic deformation of the same zone during the next shocks. Such weakened areas may be poorly visible and may be beyond the control of periodic site inspections.

The object of the present invention is to provide shock absorption devices for tensile stressed cables that do not have the aforementioned drawbacks. In particular, an object of the present invention is to provide a shock absorbing device whose effectiveness is independent of human factors, such as more or less careful tightening during assembly. It is also an object of the invention to provide an absorption device whose operation is independent of meteorological factors. It is another object of the invention to provide a shock absorbing device which, after implementing only a part of its energy absorption capacity, still retains a certain remaining functionality. Finally, it is an object of the invention to provide a shock absorbing device whose operating state is easy to control during inspections.

These objects are achieved by means of a shock absorber device of the defined input type, in which the envelope consists of a plurality of separate fusible elements, arranged so that the part of the forces transmitted by the portion of cable housed in the envelope, generating the plastic deformation of the envelope, is exerted sequentially on fusible elements adjacent to this envelope, and which comprises a retaining means for retaining a portion of the cable inside the remaining part of the envelope as long as there is at least one unbroken envelope element.

The term "fuse element" designates, within the meaning of the present invention, an element likely to undergo a plastic deformation under the effect of a mechanical stress, then a break, when the mechanical stresses exceed a certain intensity. According to the invention, the fusible elements absorb the energy of an impact first by plastic deformation and then by rupture. Because the fusible elements plastically deform and then break sequentially, when the device has suffered a shock sufficient to deform and possibly break only a first part of the fusible elements, a second part of the elements remains functionally intact. Thanks to the retaining means, which holds a portion of cable inside the remaining portion of the envelope, this remaining portion can still absorb a shock corresponding to the number of elements remaining intact. At the end of the process of deformation and rupture of the envelope, the cable is completely released and works according to its own characteristics.

Preferably, the envelope of the shock absorbing device is capable of housing the cable portion, which transmits to it the traction forces exerted on the cable, shaped loop or loop, and has at least one opening through which two strands of the cable extending the shaped portion in loop or loop can pass. In this way, in case of traction on the cable, the fuse element bordering the opening first undergoes deformation. Then the deformation, followed by the break, propagates from element to element.

According to a preferred embodiment of the invention, the fuse elements are stackable rings, the dimensions of which are such that they pass in their opening the aforementioned cable portion shaped loop, and the envelope consists of a stack of these stackable rings secured to each other by a stack maintaining means.

These rings can be discs of various shapes. The rings of the stack can be circular. They can also have an elliptical shape. The shape of rings may vary depending on their position in the stack; in particular, the rings of the central portion of the stack may be circular while the rings at one end, or both, may have an elliptical shape to spare the cable. The rings may have the same rigidity throughout the stack, the stiffness may also vary along the stack, either by the choice of the dimensions of the rings or by a choice of the nature of the materials. In particular, the rings intended to break last may be more resistant to promote the passage of the behavior of the cable assembly + absorber device to the mechanical behavior of the cable alone.

In particular, these rings may be metal washers welded together by means of at least one weld that maintains their stack. It is also possible to house the stack of rings in a common sheath, such as a molded plastic tube or threaded on the rings, or the like.

Preferably, the dimensions of the rings, in particular the thickness, and the nature of the material of the rings are chosen so that, under the effect of a pull on the cable, an element of the envelope begins to deform before the previous element solicited before him, is totally broken. This choice of material and dimensions avoids the appearance of pulsed forces or shocks, or at least decreases their amplitude.

Any part capable of holding and blocking a portion of cable engaged inside the envelope may serve as a retaining means. A particularly simple retaining means to achieve is constituted by an axis whose length is greater than the largest inner dimension of the rings. This axis is slid inside the top of the loop or loop protruding from the end of the stack opposite to that from which the two strands come out. A such axis may be of generally cylindrical shape and have two recesses shaped so as to come into contact and fit against two portions of the surface of the ring constituting one end of the stack.

To avoid the sliding of the axis out of this position, in particular because under the effect of wind or traction, the stay or cable ballots, the axis may have fixing means for securing it to the cable and / or the ring constituting the end of the device through which the handle or the cable loop exceeds. This ring may have recesses or bores or corresponding pins.

• la figure 1 est une vue en perspective d'un dispositif d'absorption de chocs avec un câble engagé dans l'enveloppe;
• la figure 2 est une vue en coupe d'une rondelle, selon son axe,
• la figure 3 est une vue en perspective d'un axe d'extrémité du dispositif,
• la figure 4 montre l'axe de la figure 3 engagé sur l'empilement,
• les figures 5, 6, 7 et 8 sont des photos montrant un dispositif d'absorption de chocs respectivement avant le début d'un essai de traction, après le début de l'essai, en cours d'essai et vers la fin de l'essai.
• la figure 9 montre 3 diagrammes Allongement du câble/Force de traction.

Other properties and advantages of the invention will become apparent to those skilled in the art from the following description of a preferred embodiment, with reference to the drawing, in which:

• Figure 1 is a perspective view of a shock absorbing device with a cable engaged in the envelope;
• FIG. 2 is a sectional view of a washer, along its axis,
• FIG. 3 is a perspective view of an end axis of the device,
• FIG. 4 shows the axis of FIG. 3 engaged on the stack,
• FIGS. 5, 6, 7 and 8 are photos showing a shock absorbing device respectively before the start of a tensile test, after the start of the test, during the test and towards the end of the test. 'trial.
• Figure 9 shows 3 diagrams Cable elongation / Traction force.

FIG. 1 shows the envelope (1) of a shock absorbing device consisting of a stack of metal washers 2, 3. The washers 2 situated in the middle of the stack are circular in shape, whereas the washers or end discs 3 are slightly elliptical in shape. The washers are welded together by two welding beads, one of which, 4, is visible in Figure 1, the second being substantially diametrically opposite. These weld seams are sufficient to ensure the maintenance of the stack, while ensuring a mechanical connection between the relatively small washers, so that they, under the effect of deformation forces, present their own mechanical behavior. A portion of a twisted metallic cable C is shaped so as to form a loop, whose top 5, protrudes from the lower end of the stack, while the two strands 6 and 7 extend the handle towards the two. cable ends, both stand out from the upper end of the stack. The axis 13 disposed across the last washer blocks the top 5 of the loop relative to the stack and prevents the cable from escaping. The ends of the axis 13, which rest on the last washer, are thinned and soldered by 2 points to this washer.

Another embodiment of this axis is visible in FIG. 3. This axis, 12, of generally cylindrical shape, has two plates 8 and 9, to limit the deformation of the end washer and rests on the last washer by these two plates 8 and 9 as shown in Figure 4. This axis is also traversed by two holes 10 and 11. These holes can ensure, by the use of means not shown, such as knotted son, maintaining the position of the axis 12 in contact with the top of the loop formed by the cable, even if the brake is violently shaken a storm or by a violent pull on one end of the cable. The diameter of the shaft 12 is approximately half the outer diameter of the washers.

FIG. 2 shows a section of a washer, illustrating its geometrical parameters, namely the length of the washer L in the direction of its axis, the thickness of the washer E and the outside diameter of the washer D. The rigidity of a washer is proportional to its thickness E, and the rigidity of the absorption device depends mainly on the thickness E of the washers, for a given material. The rigidity of the device is also proportional to the modulus of elasticity of the material. Steel 37-2 has proved to be an advantageous material, neither too rigid, which would lead to an immediate rupture under the effect of a stress without prior plastic deformation, nor too soft, which would result in a quasi deformation and destruction. simultaneous too many washers.

The length L of the washers is important with regard to the overall operation of the device. If the washers are long, successive shocks appear when the washers break one after the other. If the washers are short, they tend to pass over each other during the deformation phenomenon. For steel washers 37-2, the length of the washers is preferably between 5 and 12 mm. The best results are obtained with a length of 7 mm, regardless of the thickness E of the washer. On the other hand, the force necessary for the operation of the device, that is to say the deformation and the successive breaking of the washers, is not very dependent on the length L of the washers.

Example 1: Sequence of the destruction process of a shock absorber

The test is carried out on a stack of 65 washers 7 mm long, 70 mm in diameter and 5 mm thick. The picture in Figure 5 shows the intact device at the beginning of the test. Both strands of cable are slightly stretched. The pulling force plate the axis located at the top of the photo, surrounded by the top of the handle formed by the cable, against the top washer. As can be seen in the photo, the washers close to the axis are oval, the major axis being located in the median plane of the top of the loop of the cable. When the pulling force on both strands of the cable increases, the first washers of the bottom begin to deform. The picture in Figure 6 shows the beginning of the destruction of the device: washer 1 is already broken, washers 2 and 3 are strongly deformed, washers 4 and 5 begin to deform, the other washers are still in their initial state. Photo 7 shows the device in the middle phase of the test: in the bottom of the photo we see many broken washers, the three washers of the bottom of the remaining part of the device are being deformed. The washers above are not yet deformed. The picture in Figure 8 shows a near-end phase of the test, that is, the last four pucks just before breaking.

Example 2: Influence of the thickness of the washers on the absorbed energy

FIG. 9 shows three A / F diagrams, elongation of the cable / tensile force applied, for three stacks of Ac 37-2 washers of the same overall length, 750 mm, having the same outside diameter, 70 mm, each washer having a length individual 7 mm. The thickness of each washer is respectively 6 mm, 5 mm and 4 mm. These tests show that the breaking force remains substantially constant, without significant pulsations, during the sequential failure of the device. The breaking force increases with the thickness: The average forces are respectively 120, 85 and 55 kN for respective thicknesses of 6, 5 and 4 mm. The absorbed energy is respectively 180 Kj, 127 Kj and 82 Kj. The tests also show that the elongation of the cable during the operation is substantially due to the disappearance of the looped portion, without significant plastic elongation of the cable itself.

Example 3

Table 1 summarizes test results from two different steels and washers of different sizes. The table illustrates the influence of the thickness and the length of the washers on the behavior of the device being destroyed.

All the tests show that there is a good correlation between the dimensions of the washers and the operating force of the device.

The tests also show that the cable is very weak after a first operation of the energy absorbing device; it remains functional and usable. Once the device has worked, the cable remains tight and it still has all its own strength to ensure the function for which it was planned.

It follows from the above description that this shock absorbing device is extremely simple to perform and very effective in dissipating a large amount of energy. A judicious choice of dimensions makes it suitable for a wide variety of uses.

If the device is mounted on a rockfall protection screen stay, the device can absorb the kinetic energy of stones falling into the net and the cable continues to retain all of the masses.

During inspection inspections, it is easy to see if the device has worked, because it is easy to observe the breakage of the washers. The change of the cable is not necessary after a first operation of the cable if a majority of undestroyed washers remain. <u> Table 1 </ u> material Outside diameter Thickness (E) Length (L) Strength obtained Remarks Ac 37-2 (welded) 70 mm 5 mm 7mm 83 kN Very constant strength, very good result Ac 37-2 (welded) 70 mm 5 mm 5 mm 78 kN Constant force, but the washers overlap Ac 37-2 (welded) 70 mm 5 mm 10 mm 85 kN Pulsed force with shock Ac 35 seamless tube 70 mm 6 mm 10 mm 120 kN Slightly pulsed force Ac 35 seamless tube 70 mm 5 mm 13 mm 70 kN Pulsed force with big shocks Ac 35 seamless tube 60 mm 4 mm 10 mm 50 kN Pulsed force with shocks Ac 35 seamless tube 60 mm 3 mm 5 mm Pucks overlap

Claims (14)

1. Shock-absorbing device for a cable that is subjected to traction stress, comprising a casing which is able to house a cable portion, the shape of the casing being selected such that at least part of the forces generated by traction on said cable is transmitted to the casing by said cable portion, the casing being able to undergo plastic deformation when said part of the forces exceeds a predetermined value, characterised in that the casing (1) consists of a plurality of separate fusible elements (2, 3) which are arranged such that the part of the forces transmitted by the cable portion housed in the casing, and giving rise to said plastic deformation, is exerted sequentially on neighbouring fusible elements, and in that the device comprises a retaining means (12, 13) for retaining a portion of the cable inside the remaining part of the casing for as long as at least one fusible element of the casing remains unbroken.
2. Device according to claim 1, characterised in that the casing (1) is capable of housing said cable portion shaped into a loop and has at least one opening through which the two strands (6, 7) extending the loop-shaped cable portion can pass.
3. Device according to claim 1 or 2, characterised in that the fusible elements (2, 3) are stackable rings, the dimensions of which allow the passage of said loop-shaped cable portion, and in that the casing (1) consists of a stack of said stackable rings, secured together by a stack-holding means (4).
4. Device according to claim 3, characterised in that said rings are washers (2, 3) which are welded together by at least one weld bead (4).
5. Device according to claim 3, characterised in that said rings are kept in a stack by means of a sheath.
6. Device according to one of claims 3 to 5, characterised in that the dimensions of the rings and the nature of the materials forming said rings are selected such that, during deformation of the casing (1), an element starts to deform before the previous element subjected to stress before it is broken.
7. Device according to claim 6, characterised in that said washers are made of steel 37-2 and have a length (2) of between 5 and 12 mm, in particular a length of approximately 7 mm.
8. Device according to one of claims 3 to 7, characterised in that the rings (2) of the central part of the stack are circular, and in that the rings (3) of at least an end part of said stack are elliptical.
9. Device according to one of claims 3 to 8, characterised in that the rigidity of the rings varies as a function of their position in the stack.
10. Device according to one of claims 3 to 9, characterised in that said retaining means is a pin (12, 13), the length of which is greater than the largest inner dimension of the rings.
11. Device according to one of claims 3 to 9, characterised in that said retaining means is a cylindrical pin (12) which has two depressions (8, 9) shaped so as to fit against two portions of the surface of the ring constituting one of the ends of the stack.
12. Device according to claim 11, characterised in that the pin (12) has fixing means (10, 11) which make it possible to fix it to the cable.
13. Device according to one of claims 10 to 12, characterised in that the pin (12) is fixed, in particular by welding, to the last ring.
14. Screen for protecting against falling stones, characterised in that it comprises at least one shock-absorbing device according to any one of claims 1 to 13.

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