FR3121456A1 - METHOD FOR REMOVING A REINFORCEMENT FROM A STRUCTURAL CABLE AND ASSOCIATED SYSTEM - Google Patents

Abstract

The method is for removing a reinforcement from a structural cable (11) comprising several parallel reinforcements (16) stretched between two anchoring zones. It includes: installing a force-absorbing element (12) having a bearing surface (13) directed towards one of the anchoring zones (2); placing a wedging member (24) on the frame between the bearing surface and the anchoring area; install around the wedging member a containment device (20) having a surface abutting on the bearing surface of the force-absorbing element; stress the force-absorbing element in the direction of the anchoring zone (2) until the reinforcement (16) is relaxed between the bearing surface (13) and the anchoring zone; and releasing the reinforcement from the first anchoring zone. Abstract Figure: Figure 4

Description

METHOD FOR REMOVING A REINFORCEMENT FROM A STRUCTURAL CABLE AND ASSOCIATED SYSTEM

The present disclosure relates to a method for removing one or more reinforcements from a structural cable, and a system that can be used to implement the method.

In a cable structure, such as a cable-stayed bridge, each cable is stretched between two anchoring zones. In the case of a cable structure of the parallel multi-strand (MTP) type, each cable comprises a plurality of parallel strands or reinforcements. In this case, each reinforcement is stretched between the two anchoring zones independently of the other reinforcements.

Each of the reinforcements is therefore subjected to a significant tension which can prove to be problematic when one wants to dismantle one of the reinforcements to check the condition of the cable or to repair or replace it. For example, cutting the reinforcement without special precautions to ensure its controlled relaxation causes a sudden release of elastic energy stored in the reinforcement, which is dangerous for the safety of people, and risks damaging the structure.

It is known to maintain, behind at least one of the anchoring zones, an excess length of each reinforcement corresponding to its elastic elongation, making it possible to take the load under load to gradually relax the reinforcement to be dismantled. The extra length releases the tension in the reinforcement in a controlled way, by pressing on the back of the anchorage zone. However, in some cases, especially when there is insufficient space behind the anchor, this excess length is absent. There may also have been a deterioration of the excess length or of the anchoring device, preventing the resumption of tension.

It is also known to arrange around the cable a bridging device capable of taking up the tension of the latter. However, such a bridging device, in particular that described in EP 1 887 139 B1, does not allow individual treatment of each armature. It is therefore only very difficult to disassemble reinforcements in an MTP type cable.

An object of the present invention is to provide a method for working in a secure manner on a structural cable in order to relax and dismantle a reinforcement independently of the others.

Summary

To this end, a method is proposed for removing at least one reinforcement from a structural cable comprising several parallel reinforcements stretched between first and second anchoring zones. The process includes:
- installing a force-absorbing element having a support surface directed towards the first anchoring zone;
- Placing a wedging member on at least one reinforcement of the structural cable between the bearing surface and the first anchoring zone;
- Installing a confinement device around the wedging member so as to radially confine the wedging member, the confinement device having a surface in abutment on the bearing surface of the force-absorbing element;
- biasing the force-absorbing element in the direction of the first anchoring zone until the at least one reinforcement between the support surface and the first anchoring zone is relaxed; And
- releasing the at least one reinforcement from the first anchoring zone.

The method makes it possible to relax a reinforcement close to one of the anchoring zones independently of the other reinforcements, so that its use in cables of the MTP type in particular is appropriate. The transfer of force between the support surface and the first anchoring zone allows for progressive relaxation of the reinforcement.

Depending on the particular characteristics of the process, which can be used separately or in combination:
- the containment device is configured to withstand a tensile force greater than 20% of a maximum load prescribed for the at least one reinforcement, preferably up to 60% of the maximum load;
- the containment device is configured to withstand a tension greater than 50 kN in the at least one armature, preferably up to 180 kN;
- the containment device is configured to withstand a tensile force intensity greater than 350 MPa in the at least one reinforcement, preferably up to 1200 MPa;
- at least one traction element is placed between the force-absorbing element and a part secured to the first anchoring zone, and the traction element is actuated to urge the force-absorbing element in the direction of the first anchoring zone;
- the wedging member is a frustoconical jaw, while the containment device comprises a female element having a frustoconical housing having a shape complementary to the jaw;
- the female element has a first slot to allow the at least one armature to pass when the female element is put in place, the containment device further comprising an external element having a housing into which the element is inserted female and a second slot to let the at least one armature pass when the outer element is put in place;
- The interface between the female element and the external element is cylindrical;
- the installation of the containment device comprises a rotation between the external element and the female element to bring the first and second slots into different angular positions around the at least one armature;
- The rotation is performed so as to orient the first and second slots diametrically opposite around the at least one armature;
- the female element comprises at least two half-elements assembled around the at least one armature;
- the force-absorbing element comprises two beams engaged on either side of the at least one reinforcement from a first side of the structural cable, the two beams being joined on a second side of the structural cable opposite the first side, the support surface being shared between the two beams once they are joined together.
- At least one of the two beams is engaged between the at least one reinforcement and one or more other reinforcements of the structural cable.
- the stressing of the force-absorbing element in the direction of the first anchoring zone comprises actuating at least one traction element disposed between a part integral with the first anchoring zone and a part of the two beams projecting from the section of the structural cable.

According to another aspect of the invention, there is proposed a system for relieving at least one reinforcement of a structural cable. The system comprises a force-absorbing element, at least one wedging member and a containment device adapted to the implementation of the method presented above.

Depending on the particular characteristics of the system, can be used separately or in combination:
- the wedging member comprises a frustoconical jaw, while the containment device comprises a female element having a housing of complementary shape to receive the frustoconical jaw;
- the containment device further comprises an outer element disposed around the female element, the outer element being rotatable around a longitudinal direction of the female element;
- the female element and the outer element each have a longitudinal slot for insertion around the at least one armature;
- the female element comprises at least two half-elements interconnected;
- The force-absorbing element comprises two beams to be engaged laterally on either side of the at least one reinforcement.

Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the appended drawings, in which:

Fig. 1

is a schematic side view of an example of a cable structure.

Fig. 2

is a schematic view of a cross-section of an example cable of the structure of the .

Fig. 3

is a basic diagram of the dismantling of a cable reinforcement from the according to one embodiment of the method according to the invention, the armature being in a first position.

Fig. 4

is a diagram similar to that of , with the armature in a second position.

Fig. 5

is a schematic cross-sectional view of an armor of the cable of the , a wedging member placed on this frame and a containment device according to a first embodiment of the present invention.

Fig. 6

is a diagrammatic view in longitudinal section of the containment device, the wedging device and the reinforcement of the in a first position.

Fig. 7

is a schematic view in longitudinal section of the containment device and the frame of the in a second position.

Fig. 8

is a schematic view similar to that of the after introduction of the containment device.

Fig. 9

is a view analogous to that of once the installation of the containment device has been completed.

Fig. 10

is a view analogous to that of in the example of another embodiment of the method.

Fig. 11

is a perspective diagram of a containment device according to another embodiment.

Fig. 12

is a front view of a half-element of the containment device of the .

Description of embodiments

A cable structure 1 comprises at least one cable 11 stretched between a first anchoring zone 2 and a second anchoring zone 3. The structure 1 is for example a cable-stayed bridge comprising a deck 4, where the first zone is located. anchor 2, and one or more pylons 5 comprising the second anchor zone 3. On the , a single pylon 5 and a single cable 11 are shown, but this is not limiting.

The cable 11 comprises several reinforcements 16, preferably arranged parallel to each other. In the non-limiting description which follows, the reinforcements 16 are strands with 7 wires having a substantially circular cross-section S1. The diameter of each strand 16 is for example of the order of 15.7 mm, with a resistant section of the order of 150 mm².

The strength class of a 16 reinforcement, which corresponds to a rounded value of the maximum stress that it supports before rupture, is for example 1860 MPa or 1960 MPa.

The product between the maximum stress supported by a reinforcement 16 and the resistant section defines a maximum load (or breaking force) supported by the reinforcement. Thus, for a reinforcement 16 with a resistant section substantially equal to 150 mm², the maximum load is approximately 279 kN when the resistance class is 1860 MPa, and approximately 294 kN when the resistance class is 1960 MPa.

The strands 16 can be sheathed individually and/or collectively. On the example of the , the strands 16 are housed in a collective sheath 17.

Each strand 16 is anchored individually in the anchoring zones 2, 3, and is therefore tensioned independently of the other strands, so that a specific tension is applied to each individual strand 16. The tension can therefore be the same or different between the strands 16 of the cable 11. In the permanent state of the structure 1, the tension is typically equalized between all the strands 16 of the same cable 11.

The tension applied to an armature 16 is less than the maximum load supported by this armature 16. Advantageously, the tension in each armature 16 is between 20% and 50% of its maximum load.

Furthermore, a tensile force intensity in each armature 16 corresponds to the ratio between the tension in the armature 16 on its resistant section.

Individual anchoring also allows individual dismantling of each strand 16. However, when one of the strands 16 is relaxed and dismantled, care must be taken that the tensile force in the other strands remains below an allowable limit. This limit is for example equal to 60% of the maximum load of a strand. When the tension force exceeds this limit, the relaxation of the last strands of the cable 11 can be broken down into two or more stages.

A method is now described for removing at least one reinforcement 16 independently of the others.

The method uses a force-absorbing element 12 installed close to one of the two anchoring zones, for example the anchoring zone 2 located on the deck of the cable-stayed bridge of the . The force-absorbing element 12 is inserted laterally between the strands 16 and movable in translation along the cable 11.

The force-absorbing element 12 comprises a surface 13, called the bearing surface, directed towards the anchoring zone 2.

The force-absorbing element 12 comprises, for example, two substantially parallel beams engaged on either side of the strand to be removed 16, from one side of the structural cable. One of the beams, or both if the strand to be removed is not located on the periphery of the cable 11, is engaged laterally between the strand in question 16 and other strands of the structural cable. If the strands are too close to each other, it is possible to separate them a little so that the lateral engagement of the beams of the force-absorbing element 12 can be carried out. This spacing is facilitated if the force-absorbing element 12 is placed sufficiently far from the anchoring zone (for example at a distance of one meter or more). The two beams are joined on the side of the cable 11 which is opposite the side from which they were engaged. Once the two beams have been joined together and maintained using an appropriate fixing, for example with a collar or bolts, their faces directed towards the anchoring zone 2 together constitute the bearing surface 13 indicated on figures 3 and 4.

As a variant, the force-absorbing element 12 can be a beam or a plate, preferably perforated for the passage of a strand 16 and open to allow lateral engagement around this strand.

Advantageously, the length of the force-absorbing element 12 is greater than the width of the cable 11, so that it protrudes on either side of the section of the cable.

As shown in Figures 3 and 4, one or more traction elements 14 are interposed between the force-absorbing element 12 and the anchoring zone 2, or more generally a part of the structure integral with the zone of anchor 2 (for example a part of the deck of the bridge in the example illustrated by the ).

In the example considered below with reference to Figures 3 and 4, the traction element 14 comprises two hoists 15. Other traction elements 14, such as strong pulls or traction bars equipped with cylinders, can of course be employed.

The hoists 15 are connected on one side to the two beams of the force-absorbing element 12, in the parts of these beams which protrude from the section of the structural cable, and on the other side to the part of the structure attached to the anchoring zone 2.

A wedging member 24, visible in Figures 5 to 10, is installed on the strand to be removed 16. This wedging member 24 is placed between the bearing surface 13 of the force-absorbing element 12 and the zone anchor 2.

In the example shown, the wedging member 24 is, in a conventional manner, a frustoconical jaw comprising three sectors or wedges which are arranged radially around the strand 16. This jaw 24 provides radial clamping of the strand 16, so as to show a significant friction between the strand 16 and the jaws 24. Any device allowing the radial clamping of the armature 16, other than a jaw, is possible. The jaw 24 has a central cylindrical channel whose wall is provided with teeth which cause an indentation on the periphery of the strand 16, thus reinforcing the friction which opposes the sliding of the jaw along the strand. If the cable is made up of individually sheathed strands, the steel of the strand should be stripped before installing the jaw 24.

A containment device 20 is engaged around the strand 16 and the jaw 24. This containment device 20 comprises a housing 23 adapted to receive the strand 16. More specifically, the housing 23 has a shape complementary to that of the jaw, adapted to receive the jaw 24 so as to confine it radially.

Advantageously, the confinement device 20 is configured to withstand a tension in the strand greater than 50 kN. In some cases, it supports a tension in the strand greater than 150 kN, which can go up to 180 kN. A tensile force intensity supported by the confinement device can be between 350 MPa and 1200 MPa in the strand. It can also be considered that the configuration of the confinement device 20 allows it to withstand a tension in the strand of between 20% and 60% of the maximum load supported by the strand. The confinement device 20 is therefore configured to withstand at least the tension prevailing in the strand 16.

The confinement device 20 is installed around the jaw 24 by being brought around the jaw 24 from a relative movement of the confinement device 20 and the jaw 24. The tension in the strand 16 can thus be supported by the confinement device 20.

The force-absorbing element 12 is then urged to rest on the containment device 20. In this case, the force-absorbing element 12 is urged in the direction of the anchoring zone 2 by means of hoists 15.

As shown in Figures 3 and 4, the rear surface of the containment device 20 comes into abutment on the support surface 13. Thus, when the hoists 15 are actuated, the tension of the strand 16 is transferred to the recovery element of the force 12 via the jaws 24 and the containment device 20. It is thus possible, by controlling the traction applied by the hoists 15, to perform a progressive relaxation of the strand 16 between the force-absorbing element 12 and anchor area 2.

The actuation of the hoists 15 stresses the force take-up element 12 in the direction of the anchoring zone 2. It is carried out until the tension accumulated in the hoists balances the tension in the strand 16. From this way, the tension prevailing in the segment of the strand 16 located between the jaws 24 and the anchoring zone 2 is canceled, as schematized on the . The tension prevailing in the other segment of the strand 16, between the force-absorbing element 12 and the anchoring zone 3 increases slightly when the hoists apply a traction corresponding to the initial tension in the strand 16.

Once the strand 16 has been relaxed, the strand 16 can be released from the anchoring zone 2 and from the anchoring zone 3. The relaxed strand can be cut in its segment between the jaws 24 and the anchoring zone 2 before to be freed from its anchorages.

It is noted that the containment device 20 being configured to withstand a tension of between 20% and 60% of the maximum load supported by the reinforcement 16, the method described above can be applied to reinforcements stretched at a significantly high tension. with regard to their breaking force.

The containment device 20 is described below, with reference to Figures 5 to 12.

Figures 5 to 10 show a first embodiment of the containment device 20. In this embodiment, the containment device 20 comprises two coaxial pots respectively forming an internal female element 21 and an external element 22.

The pot 21 has an elongated shape of length L1 in the longitudinal direction A (Figs. 6-7). The cross section of pot 21 can be constant or variable over this length L1. In the example of Figures 5-10, this cross-section is circular in shape. The female element formed by the pot 21 is crossed over its entire length L1 by the housing 23 intended to receive the strand 16 and the jaws 24 in the longitudinal direction A, as illustrated in Figures 6 to 10.

The pot 21 comprises a slot 25 allowing lateral engagement of the strand 16 in the housing 23. This slot 25 extends over the entire length L1 and has a width W1 slightly greater than the diameter of the strand 16, so as to allow the strand to pass 16 when the pot 21 is put in place.

In some cases, the pot 21 can be associated with a removable part 26, visible on the , allowing the closing of the slot 25 once the armature 16 has been engaged in the housing 23.

The other pot 22 forming the external element of the containment device 20 has an elongated shape of length L2 in the longitudinal direction A. In the example shown, the external element 22 has a substantially cylindrical shape, without this being limiting.

The outer pot 22 is arranged around the inner pot 21. In particular, the outer element 22 comprises a housing 27 of complementary section to the outer section of the pot 21. The interface between the two pots 21, 22 is for example cylindrical.

As shown in Figures 6 and 7, one end 28 of the housing 27 is open to allow engagement of the outer pot 22 around the inner pot 21, while its opposite end may be partially closed by a wall 29. The wall 29 comprises an opening 30 to allow the strand to be relaxed 16 to pass. Thus, the pot 21 is introduced into the housing 27 by the end 28 and is kept there in contact with the wall 29. The wall 29 and the bearing surface 13 of the force-absorbing element 12 bear on each other when the hoists 29 are actuated to relax the strand 16.

The length L3 of the housing 27 may be equal to or greater than the length L1 of the pot 21, which allows the latter to be fully introduced into the housing 27.

The pot 22 includes a slot 31 allowing lateral engagement of the strand 16 in the housing 27 and extending over the length L2. The width W2 of the slot 31 is sufficient to allow the strand 16 to pass when the pot 22 is put in place.

The pots 21, 22 of the containment device 20 can be put in place together or separately around the strand 16. If they are put in place together, their slots 25, 31 are oriented angularly in the same way, to make it possible to engage the strand 16 laterally, as shown in . Then, the pots 21, 22 are rotated relative to each other around the longitudinal direction A so that the slots 25, 31 are brought into different angular positions around the strand 16, preferably diametrically opposite positions. as illustrated in Figures 9 and 10. That the slots 25, 31 have different angular positions allows the containment device 20 to have better resistance to the force which tends to open the pots 21, 22 under the effect of the tension prevailing in the strand 16.

Figures 11 and 12 show another embodiment of the confinement device 20, comprising a female element 21 produced by assembling two half-elements 32. The half-elements 32 can have similar shapes that are symmetrical with respect to their joint plane, without this being limiting.

The half-elements 32 are for example connected by means of tightening bolts 34. On the example of the , four clamping bolts 34 are provided. These bolts 34 make it possible to maintain a face 35, called the connection face, of a half-element 32 in contact with the connection face 35 of the other half-element 32, the interface between the connection faces 35 constituting the parting plane of the half-elements 32.

Each bolt 34 passes through the two half-elements 32 perpendicular to the connection faces 35 through a respective bore 36.

As seen on the , the face 35 of each half-element 32 comprises a bore 33 having a tapered longitudinal section. When the two half-elements 32 are assembled, the bores 33 of each connection face 35 face each other, so as to form the housing 23 as described above.

The confinement device 20 according to this second embodiment also makes it possible to confine the jaw 24 radially. The half-elements 32 are brought together laterally towards the armature 16 until the connection faces 35 come into contact. The clamping bolts 34 are then installed in order to hold the two half-elements 32 in position relative to each other, which will block the jaws 24 gripping the strand 16.

Pins or shear pins can, optionally, be arranged in addition to the tightening bolts 34 in order to further secure the connection between the half-elements 32 against a risk of relative sliding between them.

As indicated above, the confinement device 20 according to the two embodiments presented above is capable of withstanding a tensile force intensity in the strand of between 350 MPa and 1200 MPa, and a tension in the higher strand 50 kN, even greater than 150 kN, up to 180 kN. In particular, the containment device 20 is configured to support a tension in the frame of between 20% and 60% of the maximum load supported by the frame 16.

Since the containment device 20 can be installed individually around a strand 16, the method described above can be applied for the dismantling of a strand from an MTP type cable. A special case is when the entire MTP cable needs to be removed; in this case, the strands can be removed one by one, or small group by small group. Another use case is when it is requested to extract one or a few strands from an MTP cable for the purpose of inspecting the condition of the cable.

The process also has the advantage of limiting the footprint of the replacement site and limiting the impact on safety when the structure is kept in service during the dismantling of the strand or cable to which it belongs.

The embodiments described above are a simple illustration of the present invention. Various modifications can be made to them without departing from the scope of the invention which emerges from the appended claims.

Claims (23)

Method for removing at least one reinforcement (16) from a structural cable (11) comprising several parallel reinforcements stretched between first and second anchoring zones (2, 3), the method comprising:
- installing a force-absorbing element (12) having a support surface (13) directed towards the first anchoring zone (2);
- placing a wedging member (24) on at least one reinforcement (16) of the structural cable (11) between the support surface (13) and the first anchoring zone (2);
- installing a confinement device (20) around the wedging member (24) so as to radially confine the wedging member (24), the confinement device (20) having a surface in abutment on the surface of support (13) of the force-absorbing element (12);
- urging the force-absorbing element (12) in the direction of the first anchoring zone (2) until the at least one reinforcement (16) between the bearing surface (13) and the first anchor area (2);
- releasing the at least one armature (16) from the first anchoring zone (2). A method according to claim 1, wherein the containment device (20) is configured to withstand a tensile stress greater than 20% of a prescribed maximum load for the at least one armature (16). A method according to claim 2, wherein the containment device (20) is configured to withstand a tensile stress of up to 60% of the maximum load prescribed for the at least one reinforcement (16). A method according to any preceding claim, wherein the containment device (20) is configured to withstand a tension greater than 50kN in the at least one armature (16). A method according to claim 4, wherein the containment device (20) is configured to withstand a tension of up to 180 kN in the at least one armature (16). Method according to any one of the preceding claims, in which the containment device (20) is configured to withstand a tensile stress intensity greater than 350 MPa in the at least one reinforcement (16). Method according to claim 6, in which the containment device (20) is configured to withstand a tensile stress intensity of up to 1200 MPa in the at least one reinforcement (16). Method according to any one of the preceding claims, further comprising placing at least one traction element (14) between the force-absorbing element (12) and a part integral with the first anchoring zone (2), and actuating the traction element (14) to urge the force-absorbing element (12) in the direction of the first anchoring zone (2). Method according to any one of the preceding claims, in which the wedging member (24) comprises a frustoconical jaw, and in which the confinement device (20) comprises a female element (21) having a frustoconical housing (23) having a shape complementary to that of the bit. Method according to claim 9, in which the female element (21) has a first slot (25) to allow the at least one armature (16) to pass when the female element (21) is put in place, the containment device (20) further comprising an outer element (22) having a housing (27) into which the female element (21) is inserted and a second slot (31) to allow passage of the at least one reinforcement (16 ) during the establishment of the outer element (22). A method according to claim 10, wherein the interface between the female element (21) and the outer element (22) is cylindrical. A method according to claim 10 or claim 11, wherein installing the containment device (20) includes rotation between the outer member (22) and the female member (21) to bring the first and second slots (25 , 31) in different angular positions around the at least one frame (16). A method as claimed in claim 12, wherein the rotation is effected so as to orient the first and second slots (25, 31) diametrically opposite around the at least one armature (16). Method according to claim 9, in which the female element (21) comprises at least two half-elements (32) assembled around the at least one armature (16). Method according to any one of the preceding claims, in which the force-absorbing element (12) comprises two beams engaged on either side of the at least one reinforcement (16) from a first side of the structure (11), the two beams being joined on a second side of the structural cable opposite the first side, the support surface (13) being shared between the two beams once they are joined. Method according to claim 15, in which at least one of the two beams is engaged between the at least one reinforcement (16) and one or more other reinforcements of the structural cable. Method according to Claim 15 or Claim 16, in which the biasing of the force-absorbing element (12) in the direction of the first anchoring zone (2) comprises actuating at least one traction element (15) disposed between a part integral with the first anchoring zone and a part of the two beams protruding from the section of the structural cable. System for relieving at least one reinforcement (16) of a structural cable (11), the system comprising a force-absorbing element (12), at least one wedging member (24) and a confinement device (20) suitable for implementing the method according to any one of the preceding claims. System according to Claim 18, in which the wedging member (24) comprises a tapered jaw, and in which the confinement device (20) comprises a female element (21) having a housing (23) of complementary shape to receive the tapered jaw. System according to Claim 19, in which the containment device (20) further comprises an outer element (22) arranged around the female element (21), the outer element (22) being movable in rotation around a longitudinal direction (A) of the female element (21). A system according to claim 20, wherein the female element (21) and the outer element (22) each have a longitudinal slot for insertion around the at least one armature (16). System according to claim 19, in which the female element (21) comprises at least two half-elements (32) connected together. System according to any one of Claims 18 to 22, in which the force-absorbing element (12) comprises two beams to be engaged laterally on either side of the at least one reinforcement (16).