FR3119403A1 - Bridging system and implementation method - Google Patents

Abstract

Bridging system and method of implementation Bridging system intended to locally relax a structural cable before it is cut, comprising a bridging device comprising: Two collars able to be positioned around the cable, each half-collar being made with a body defining a substantially semi-cylindrical cavity, traction elements extending between the collars, means for adjusting the traction force. Each of at least two half-collars comprises, integrally therewith: longitudinal reinforcements (17) extending along said body over at least part of the length thereof, anchorages (23) extending between these longitudinal reinforcements (17) and anchorages (29, 34) located in the axial continuity of the longitudinal reinforcements (17), the transmission of the force from the traction elements to the collars (10) taking place via the said anchors (23, 29, 34). Figure for abstract: Fig.1

Description

Bridging system and implementation method

The present invention relates to the field of maintenance or repair of civil structures such as engineering structures.

The invention relates more particularly to the stress relief and removal of structural cables (concrete, metal frame or wooden frame) external to the latter, such as external prestressing cables, stay cables or bridge hangers.

Such cables are frequently made up of a bundle of reinforcements (wires, strands or bars, most often made of steel) protected by a cementitious material such as a grout, having set after injection into a cable sheath and adhering to the reinforcements.

These cables are subjected within the structure to high mechanical tension and cannot be cut without special precautions.

Patent EP1887139 describes a bridging device used to locally slacken a cable such as a guy before cutting it and laying it down. This device comprises two collars adapted to be positioned around the cable so as to ensure contact without slipping therewith. At least two traction bars (also called relay bars) connect said collars and means for adjusting the traction force passing through the bars are provided. In this patent, the way of making the collars and the connections with the bars is only briefly described.

The non-slip of each of the collars of the bridging device requires sufficient transverse tightening to mobilize friction and shear at the various interfaces between reinforcements and collars, and in particular between the reinforcements and the cementitious material surrounding them. This cementitious material is likely to be degraded, and thus to negatively affect the quality of the corresponding interface.

The patent ES2735145 describes a method and a bridging device intended for the detensioning of a structural cable. The device comprises a permanent sleeve which is put in place around the reinforcements of each of the two segments of the cable on which the device is intended to be anchored. These liners are put in place after the reinforcements have been completely exposed, and serve as permanent formwork for a filling material. Two elongated collars along the longitudinal axis of the cable are each tightened on a corresponding sleeve, after the filler material has set. Two structures of elongated shape transversely to the longitudinal axis of the cable, in the shape of a yoke, distinct from the collars, are each arranged at the end of a respective collar, to serve as axial support therefor, these structures in the form of of yoke being connected laterally by two traction bars. Each yoke-shaped structure comprises two header beams which are assembled by bolting around the cable and the two bars.

In such a device, the center distance between the cable and each traction bar is relatively large, which subjects the header beams to significant bending stresses. These forces can limit the robustness of the system insofar as an imbalance of these can lead to unstable behavior and/or expose the device to excessive mechanical stresses, which can lead to the cable slipping or breaking. Such a device is also relatively bulky and difficult to install in certain configurations of the structure to be repaired.

The invention aims to remedy the drawbacks of known bridging devices, and in particular to benefit from a bridging system that is both easy to install and offers increased security.

The invention thus relates to a bridging system intended to locally relax a structural cable before it is cut, comprising a bridging device comprising:

• Two collars to be placed on said cable, each collar being formed of two half-collars capable of being positioned around the cable, each half-collar being of elongated shape along the longitudinal axis of the cable and made with a body defining a substantially semi-cylindrical cavity ,
• traction elements extending between the collars,
• means for adjusting the tensile force passing through the traction elements,

system characterized in that each of at least two half-collars comprises, integrally therewith:

- longitudinal reinforcements extending along said body over at least part of the length thereof,
- anchorages extending between these longitudinal reinforcements,
- anchorages located in the axial continuity of the longitudinal reinforcements,

• the transmission of the force from the traction elements to the collars taking place via said anchorages.

The bridging system may include means for monitoring the force passing through the traction elements. These are more than two in number.

By "monobloc" it is necessary to understand that each half-collar forms a solid whole in one piece. Each half-collar can be manufactured from several parts welded together, or by machining a blank, or even by foundry. Preferably, the half-collars are mechanically welded and made of steel, preferably of ductile steel with an elastic limit fy greater than 300 MPa, and a breaking limit greater than 400 MPa, for example S355 steel (ductile steel with a limit elastic fy=355MPa, breaking strength 510MPa). Other more resistant grades such as S460 steel are possible, the S355 grade remaining a good compromise between mechanical strength and cost. The anchorages can thus be welded to the longitudinal reinforcements and/or to the body of the half-collar.

The substantially semi-cylindrical cavity of the body is suitable for positioning the half-collar on the cable, possibly covered with a sleeve as detailed below. The body may have a substantially semicircular shape in cross section, or be of more massive shape. The body can be made with clamps, extending along it, on its sides.

The production of each half-collar, combining a body, any clamping flanges, longitudinal reinforcements and anchorages located between them and/or axially supported on them, close to the body, in the form of a set solid one-piece, has many advantages.

First of all, the fact of making the anchorages in a single piece with the half-collars makes it possible to avoid using a structure in the form of a yoke as in the aforementioned prior art.

The presence of anchorages between the longitudinal reinforcements or in axial support on them makes it possible to reduce the eccentricity of the traction elements with respect to the axis of the cable. This reduces the induced bending forces that need to be balanced. By reducing these bending forces induced by the traction elements, thanks to the proximity of the anchorages to the longitudinal axis of the cable, the robustness of the system is improved.

Preferably, the value of the center distance between the axis of the body defining the substantially semi-cylindrical cavity (merged with the axis of the structural cable) and the axis of each traction element is thus less than or equal to 2, 5 times the outer diameter D of the cable (excluding sheath), better still less than or equal to 2 times this outer diameter, more preferably 1.5 or 1.2 times this outer diameter.

In addition, the invention makes it possible to gain in compactness and to limit the size of the device, both axially and transversely to the cable. Thus, the system according to the invention can be easily implemented on a segment of the cable located in the immediate vicinity of an element of the structure (beam, sail, slab, etc.) or in the vicinity of one or more neighboring cables, for example among a bundle of external prestressing cables in a bridge deck. In these configurations, it is advantageous to have a bridging device of limited transverse size around the axis of the cable.

In addition, the safety of the device is improved in the event of failure of a traction element, the use of three or four traction elements providing a certain redundancy to accommodate the failure of one of them.

All the half-collars are preferably identical, which simplifies their use and their manufacture.

Preferably, the bridging device comprises both anchorages extending between the reinforcements and fixed thereto, called "recovery anchorages", and anchorages coming in the axial continuity of the reinforcements, called "support anchorages ".

The support anchorages can serve as a stop, on the side of a so-called "active" end of the system, for mechanisms for tensioning the traction elements, such as jacks, while the recovery anchorages can, on the side of this same active end, serve to take up the forces when the tensioning mechanisms are released.

The anchorages can be in the form of plates welded to the longitudinal reinforcements and/or to the body of the half-collars, preferably both to the body and to the longitudinal reinforcements.

Each half-collar may comprise two pairs of longitudinal reinforcing ribs, the ribs of each pair being parallel to each other. The ribs of a first pair are for example oriented at 45° from the clamping plane of the collars, and the ribs of the second pair at 45° also from this clamping plane but at 90° from the first pair.

At least some anchors can be welded to the longitudinal reinforcing ribs, between them. These ribs can be doubled by reinforcing plates behind these anchorages, these reinforcing plates preferably extending over the facing faces of the ribs of the same pair. The anchorings forming take-up bearings can rest on these reinforcement plates, which thus contribute to taking up the axial forces.

Each half-collar may comprise a front part devoid of longitudinal reinforcements, and a rear part along which said reinforcements extend. The front part of each half-collar is directed towards the cable cut-out area. The front part may comprise only the body defining the substantially semi-cylindrical cavity and the clamping flanges, as well as transverse stiffening ribs (also called transverse stiffeners) oriented perpendicular to the longitudinal axis of the half-collar and connecting both to the corresponding flange and to the body, in particular being welded thereto. The rear part comprises the longitudinal reinforcements and the anchorages in addition to the flanges and the transverse stiffening ribs.

The longitudinal reinforcements may comprise ribs which are oriented substantially at 45° with respect to the clamping plane of the collar, as mentioned above. The flanges can then widen at the rear part, so as to leave easy access to the tightening bolts given the presence of the longitudinal reinforcements above the flanges.

The traction elements of the bridging device are preferably in the form of traction bars, also called “traction relay bars” or “relay bars”.

The anchorages can thus comprise recovery plates extending perpendicularly to the longitudinal axis of the collar and connecting to the longitudinal reinforcements, to serve as support for the recovery nuts mounted on these traction bars.

The tensile elements of the bridging device each preferably have a breaking stress fRG greater than or equal to 1000 MPa. The tensile elements are, for example, prestressing bars with a breaking stress fRG=1035MPa.

The traction bars have for example a diameter between 25 and 75mm, being for example bars with a diameter of 63.5mm, the force mobilized preferably remaining below 60% of their capacity (0.6*3167mm ² *1035 MPa i.e. 1966kN per bar of diameter equal to 63.5)

The tensioning mechanisms can be jacks having a capacity at least equal to 60% of the capacity of the traction elements.

The tension members are preferably drawbars, as noted above, and the tensioning mechanisms are preferably hollow jacks, through which the drawbars extend. The traction elements of the bridging device may comprise four traction bars, with two traction bars per half-collar, in particular traction bars having a diameter of between 50 and 75 mm.

The cylinders and the associated traction bars, in equal numbers, are preferably distributed with a substantially symmetrical arrangement around the axis of the cable.

The cylinders have for example a minimum capacity of 1966kN, and are for example cylinders with a capacity of 2300kN, offering a certain margin of safety.

The difference between the outer and inner diameters of such cylinders is for example greater than or equal to 180mm, with for example an outer diameter of 270mm and an inner diameter of 73mm.

The installation of the bridging device requires a preliminary stage of preparation of the segment of the cable where the cut-out zone is located, this segment having to be made suitable for receiving the bridging device, that is to say suitable for the transverse tightening of the collars in order to resist the tangent (sliding) forces induced by them when tensioning the device.

Except in special cases (the one where the cable sheath would participate in the permanent tensile stress in the cable), the first step consists in cutting and removing the outer sheath of the cable (steel sheath, HDPE or other) on the segment concerned.

The preparation of the section of the cable then consists in reconstituting sections and surfaces, in particular around the reinforcements and the solid protective material integrating the bundle, capable of anchoring the two collars of the device by transverse tightening. The reconstruction of these sections is carried out by pouring or injecting a filling material compatible with the protective material of the reinforcements, for example a cementitious grout or a hardening polymer resin.

This casting or injection can be carried out in each collar of the device, before tightening, thanks in particular to the presence of at least one orifice provided for this purpose, for example thanks to the presence of at least one injection orifice and at least one vent on each half-collar, preferably opening onto the inner surface of the body defining the substantially semi-cylindrical cavity. Alternatively, casting or injection is carried out in a permanent sleeve serving as permanent formwork or in a removable tubular formwork, the cable segment thus prepared being able to receive a collar of the device. The half-collars can each be devoid of an orifice for injecting a wedging material and/or a vent, opening onto the interior surface of the body.

Thus, in a first example of implementation of the invention, the system comprises wedges to provide a space between the cable and each half-collar, and at least one of the half-collars preferably comprises at least one orifice injection of a wedging material around the cable in this space. The collars can be prepositioned on the cable, and the wedging material injected in this configuration.

In a second example of implementation of the invention, the system comprises a sleeve adapted to be put in place around the cable before the collars are laid, each collar being configured to be tightened on the underlying sleeve, the force of traction exerted by the collar being transmitted to the cable via this lining. The system may include shims to provide a space between the cable and the liner for the purpose of injecting into this space, around the cable, a wedging material, the liner acting as a permanent formwork for the material gap. The liner may comprise two substantially semi-cylindrical half-shells, and longitudinal seals at the junction between the half-shells. Each half-shell may have an outer surface and/or a rough inner surface, preferably being metallic. The roughness of the outer and/or inner surface of the liner improves the transmission of forces without the collars slipping on the liner. The roughness of the inner surface can be improved if necessary with weld beads.

In a third example of implementation of the invention, the bridging system comprises a removable formwork configured to be put in place around the cable in order to inject a wedging material around it, each collar being adapted to be placed on the cable where the wedging material was injected, after removal of the removable formwork. The latter may comprise sectors, in particular three in number, and between them longitudinal joints. In the last two cases, it is not normally necessary to inject a wedging material between the collars and the liner or the stripped section, but such injection is not excluded to further improve the absorption of forces.

Another subject of the invention is a method for locally taking up the tension of a structural cable with a view to its severing, using the bridging system according to the invention, comprising the steps consisting in:
- Prepare the surface of the cable, in particular by removing its sheath, removing the spalls and bush-hammering it, then:
To)
- put the collars in place around the cable,
- inject a wedging material into the spaces formed between the collars and the cable, or
b)
- set up a sleeve around the cable at the level of each segment of the latter intended to receive a clamp,
- injecting a wedging material into a space formed between the sleeve and the cable,
- place each collar around the corresponding sleeve, or
vs)
- set up a removable formwork around the cable at the level of each segment of the latter intended to receive a clamp,
- inject a wedging material into a space formed between the cable and the formwork,
- remove the formwork,
- set up each collar on the corresponding portion thus stripped,

then tension the traction elements extending between the clamps to take up the tension of the cable.

The reconstruction of the sections and surfaces suitable for receiving the collars of the device may require increased precautions which justify the use of a permanent lining (steps b) above) or a removable formwork (steps c) above) for the preparation of these segments. In addition, the use of a permanent lining or a removable formwork can save time by carrying out this preparatory work outside the critical path for implementing the device.

The wedging material, especially when it is a cement grout, can reach a minimum compressive strength fck of at least 40MPa at 2 days, and can reach 100MPa and more at 28 days.

Another subject of the invention is a process for cutting a structural cable, comprising the steps consisting of:

• Locally relax the cable by implementing the above relaxation process,
• cut the cable in the slack area.

The invention is applicable to any type of cable, in particular steel: closed, helical or bundle of parallel reinforcement cables (wires, strands, bars).

Another subject of the invention, according to another of its aspects, independently or in combination with the foregoing, is a bridging device intended to locally relax a structural cable before it is cut, comprising:

• Two collars to be placed on said cable, each collar being formed of two half-collars able to be placed around the cable, each half-collar comprising a body (also called "jaw") of elongated shape along the longitudinal axis of the cable and made in one piece with anchors,
• at least two traction elements connecting the collars, the transmission of the force from the traction elements to the collars taking place via said anchorages.

This device may have any of the characteristics of the system defined above. In particular, the value of the center distance between the axis of the structural cable and the axis of each traction element can thus be less than or equal to 2.5 times the outer diameter D of the cable (excluding sheath), better still less than or equal to 2 times this outside diameter, even better still 1.5 or 1.2 times this outside diameter.

Similarly, this device can be implemented by following steps a), b) or c) of cable preparation, defined above.

The invention may be better understood on reading the detailed description which follows, non-limiting examples of implementation thereof, and on examining the appended drawing, in which:

There is a schematic side view of an example of a bridging device according to the invention,

there partially and schematically represents, in perspective, the so-called "active" part of the device of the ,

there represents in isolation a half-collar of the bridging device of the (that of the so-called active end),

there represents in isolation in cross section a cable to be cut, after removal of spalls and bush hammering,

there is a view analogous to illustrating the positioning of the wedges on the cable,

there is a cross section of the bridging device in place on the cable, according to a first example of implementation of the invention,

there is a section illustrating the installation of a jacket on the cable, in accordance with a second example of implementation of the invention,

there is a view analogous to after closing the sleeve and injecting a wedging material therein,

there is a view analogous to , in this second example of implementation of the invention,

there is a section illustrating the use of a removable formwork to pour the wedging material, according to a third example of implementation of the invention,

there illustrates the removal of the formwork from the ,

there is a view analogous to , illustrating the use of the bridging device in this third example of implementation of the invention, and

there illustrates the cable cutout.

detailed description

There is shown in Figures 1 and 2 a bridging device 1 according to the invention, intended to be mounted on a cable of structure C, such as an external prestressing cable or a stay, to relax it locally before its sectioning and its removal.

The cable C comprises, as visible on the , reinforcements T embedded in a cementitious material B, and its external diameter (without the sheath) is equal to D.

The device 1 comprises two collars 10 (also called "jaw collars") each composed of two half-collars 11 (also called "half-shells"), one of which is shown separately in .

Each half-collar 11 comprises, as seen in this figure, a body 14 defining a substantially semi-cylindrical cavity (this body also being called a "jaw"), this body 14 being elongated along the longitudinal axis of the cable. In the example considered, the body 14 has a substantially semi-circular shape in cross section, and it is bordered laterally over substantially its entire length on its opposite sides by two respective flanges 12 extending parallel to the clamping plane of the collars 10.

The flanges 12 of the two half-collars 11 are assembled by means of a succession of bolt/nut assemblies 13, the tightenings of which ensure the tightening of the collar 10 on the cable.

Each half-collar 11 has at the rear, as seen in the , longitudinal reinforcements 17, in the form of a set of two pairs of ribs attached to the body 14.

As seen more particularly on the , the ribs 17 of each pair are parallel to each other and located on either side of a median plane R oriented radially, substantially at 45° to the clamping plane of the collar 10. The half-collar 11 thus has a symmetry with respect to a median plane perpendicular to the clamping plane of the collar.

It is also seen in Figures 1 and 2 in particular that each half-collar 11 comprises a set of transverse stiffeners 33, connecting perpendicularly to the flanges 12 and to the body 14 between the holes intended for the bolts 13.

The flanges 12 widen on the rear part of the half-collar 11, to maintain the axis of the passage holes of the bolts 13 out of the ribs 17, when the half-collar is observed in top view, perpendicular to the clamping plane .

As can be seen on the in particular, the collars 10 define between them an intermediate zone A allowing access to the cable C in order to cut it.

A connection system 20 connects the collars 10 and makes it possible to adjust their spacing, and thus to take up the tension of the cable C.

This connection system 20 comprises a set of traction elements 21, preferably consisting of bars, for example four in number as shown, arranged all around the cable C. These bars 21 can be protected by sleeves 22, for example in HDPE, at least in zone A intended for cutting the armor of cable C.

These bars 21 each have a threaded end 21a engaged through an anchor consisting of a retaining plate 29, the latter bearing axially on the reinforcements 17 of the collar 10 located on the "passive" side of the device, i.e. say the necklace 10 right on the .

So-called “passive” nuts 28 are engaged on each of the ends 21a and each come to rest on the corresponding retaining plate 29.

The opposite end 21b of each bar 21 is engaged through an anchor constituting a take-up bearing 23, fixed relative to the collar 10 located on the side of the so-called "active" end of the bridging device 1, that is to say the left collar on the , as well as through a drive plate 30. The take-up bearing 23 is formed by a plate located between two reinforcing ribs 17 and fixed to the latter, being preferably welded both to the ribs 17 and to the body 14.

The ribs 17 are doubled by plates 15, located behind the bearings 23, to absorb part of the axial forces induced by the bearings 23.

The drive plate 30 can be moved in the axial direction by a cylinder 31, the body of which is fixed with respect to the collar 10 and the piston rod 32 movable with the plate 30.

The cylinders 31 are preferably hydraulic cylinders, hollow and crossed axially by the bars 21, and allow the tensioning, the adjustment and the tensioning of the tension bars 21, as will be detailed later.

The body of each jack 31 is arranged to bear on an anchoring of the corresponding half-collar 11, consisting of a plate 34. The latter rests axially on a pair of corresponding ribs 17 of the half-collar 11, preferably being welded against their ends. .

The cylinders 31 are preferably the same number as the bars 21, in this case four in the example considered, and are distributed with a substantially symmetrical arrangement around the longitudinal axis of the cable C.

A nut 26, called "tool nut", is mounted on the so-called "active" end 21b of each bar 21, and can rest on the corresponding drive plate 30.

Another nut 27, called "return nut", is also mounted on bar 21 and can rest on bearing 23. The distance between support plate 34 and return bearing 23 provides sufficient axial travel for the corresponding bar 21 to carry out resumptions, in tension or detension, of the bars 21. Preferably, this distance is close to the useful stroke of the cylinders 31. Load transfers are thus possible between tool nuts 26 and recovery nut 27 to provide a stroke total tension, adjustment or relaxation, multiple of that of jacks 31.

The device 1 allows monitoring of the tensile force transiting in the bars 21.

Each cylinder 31 is to do this equipped with a pressure sensor as well as a displacement sensor of its piston rod. Furthermore, each of the bars 21 can be provided with a sensor such as a strain gauge giving access to the elongation of the latter.

In addition, a displacement sensor, for example optical based on the use of one or more LASER distance meters, or the like, can be arranged between the two collars 10 or placed so as to be able to observe them, preferably on the side opposite to the one provided for the cable cutting tool. This sensor makes it possible to measure the distance between the two collars 10, in the axial direction.

Alternatively or in addition, each of the collars 10 can be provided with at least one collar displacement sensor relative to the cable segment where it is anchored, such as a mechanical comparator, intended to detect any slipping of this collar.

The cylinders 31 preferably have pistons of equal areas, and are preferably connected to the same hydraulic circuit and controlled at equal pressure.

Cable preparation

Before using the bridging device 1 according to the invention, the cable C is prepared by removing its outer sheath over segments of sufficient length to allow the placement of the two collars 10 on either side of the zone A spared for its cutting.

The cutting of this sheath is carried out with the appropriate precautions so as not to damage the T reinforcements of the cable. Circumferential cuts are preferably made at the ends of the segment concerned, followed by a longitudinal cut to open and remove the sheath segment.

On the cable segments from which the sheath has been removed and intended for tightening the collars 10, the cementitious material is struck with a hammer to remove any spalling then bush-hammered by means of a manual or mechanical bush-hammer according to the required intensity, to give a sufficient roughness to the cementitious material, as shown in . This operation makes it possible to eliminate any areas of friable material (fragile elements easily separated from the mass of cementitious material enveloping the reinforcements) and to ensure better adhesion with the wedging material injected around the cable.

There are three ways to use the bridging device according to the invention.

The first corresponds to the , and consists in using the collars 10 themselves as formwork for the injection of the wedging material. The second, illustrated in Figures 6 to 8, relies on the use of a liner 80, which is left in place under the collars, and the third, illustrated in Figures 9 to 11, relies on the use of a removable formwork 90.

In all cases, in zone A provided for the cutting of the cable, the cementitious material B is kept as it is in order to avoid damaging the reinforcements T before cutting.

First example of implementation

Coming back to the , according to the first example of implementation of the invention, the four half-collars 11 are positioned on either side of the zone A provided for the cutout. The collars 10 are held in position with appropriate supports in the lower part, supplemented by wedges 70, visible in Figures 5 and 6. These wedges allow each collar 10 to be substantially centered around the cable C, this centering being desirable for the good distribution of forces in the bridging device 1.

These wedges 70 are preferably made beforehand with the same material as that which will be injected between the collars and the cementitious material B of the cable. Gaskets 50, preferably flexible, are interposed between the flanges 12 of the collars, as can be seen in the notably. Each gasket 50 extends inside collar 10 as far as cable C. The material of gasket 50 is for example an elastomer or a compressible material such as polystyrene or plywood.

Rigid wedges 51 can be arranged between the flanges 12, along their outer edge, to adjust the spacing between the flanges 12 before the injection of the wedging material P. Clips 52 can enclose the flanges 12 on their outer edge , to hold them fixedly in the absence of the bolts 13 or tightening of the latter.

The flexible seals 50 are interposed between the half-collars 11, and the rigid wedges 51 are added locally and temporarily in order to maintain the distance between the half-collars 11, if necessary.

The half-collars 11 are thus kept separated by an appropriate distance before tightening, which is for example 5 to 10 mm for a cable diameter C close to 100 mm.

The joints 50 also make it possible to prevent the wedging material from creating a rigid joint, that is to say a hard point, between the half-collars 11 of each set, and the wedging material P, after setting and hardening, does not constitute a tube which, by vault effect (circumferential pressure) would prevent adequate tightening, that is to say the application of a transverse tightening force on the reinforcements T and the cementitious material B by the bolts 13 tightened on the joint plane of the collars.

Once the half-collars 11 are in place, the bolts 13 can be tightened slightly.

Then, the drawbars 21 and their nuts can be installed, then the correct alignment of the collars and the drawbars can be checked. Additional rigid wedging can be applied if necessary. The device 1 comprises annular formwork cheeks (not shown), to axially close the space between the collars 10 and the cable C, and create a substantially closed volume where the wedging material P can be injected. These flanges are, for example, annular flanges held on the collars by screwing or any other suitable fastening means.

Each half-collar 11 has at least one orifice 18 used for injection or venting, as will be specified later. This orifice can be equipped, if necessary, with a quick or threaded coupling, allowing the connection of a pipe connected to a pump to deliver the cushioning material under pressure.

The annular formwork cheeks placed at each of the ends of the half-collars 11 make it possible to obtain a tight closure of the volume defined between the half-collars 11 and the cable C.

The wedging material P can be injected via the orifices 18 in fluid form into the volume delimited by each half-collar 11 and the cable C. Thanks to its fluidity, the injected wedging material P can fill the volume optimally and s interfere, if necessary, in any cracks in the cementitious material B of the cable C.

Depending on the nature of the cable C, the wedging material P can be either a cementitious mortar or a polymer resin, setting as it solidifies to achieve a resistance adapted to the transverse tightening of the collar 10 and to the tangent forces induced by the bridging.

When the material P has begun to set and has sufficient hold, the flexible seals 50 and any wedges 51 present in the thickness of this seal 50 can be removed. Any surplus P material present in this thickness is removed before hardening.

Second example of implementation work

In this second mode of implementation of the invention, the element or elements arranged between the half-collars to form sealed volumes for the injection of the wedging material are left in place, and crushed during the tightening of the collars.

On the , there is illustrated the installation of a permanent lining 80 on the cable, to produce a formwork used for the injection of the wedging material.

This lining 80 comprises, for example, two metal half-shells 81, the outer and inner surfaces of which are rough, and longitudinal seals 82 making it possible to ensure sealing at their junction, once the lining is in place, as illustrated in .

Once the wedging material has hardened, each collar 10 can be installed leaving the liner 80 in place, as shown in , the tightening of the cable C being effected through the lining 80.

In this case, it is not necessary to provide the half-collars with orifices 18 used for injection or venting, even if they have been shown in this figure, nor with the above-mentioned shuttering cheeks.

Third example of implementation

We will now describe with reference to Figures 10 to 12 the third example of implementation of the invention, where a removable formwork 90 is used to pour the wedging material on each segment of the cable to receive a collar 10, this formwork being removed before the collars 10 are put in place.

In the example considered, this formwork 90 comprises, as illustrated in three sectors 91 which each make a little less than 120° of angular extension and longitudinal seals 92 which are arranged between the sectors 91.

Once the wedging material P has hardened, the sectors 91 can be removed, as illustrated in , then the installation of the collars 10 around the cable whose outer surface has been reconstituted, as illustrated in the . The relatively limited angular extent of each sector 91 facilitates the removal of the formwork without damaging the reconstituted surface.

In this case, it is not necessary to provide the half-collars with orifices 18 used for injection or venting, even if they have been shown in this figure, nor with the above-mentioned shuttering cheeks.

In the three examples above, the steps of clamp tightening, tension relief and cutting can be performed as described below.

Tightening of collars

Test specimens taken during the injection of the wedging material P make it possible to evaluate its rise in resistance to guarantee a minimum value in compression (for example 40 MPa for a cementitious wedging material), before tightening the bolts 13 of the collars.

The bolts 13 are tightened successively, in an order favorable to a good distribution of the forces and such as to limit the losses induced by the non-simultaneity of the tightenings. For example, at least two successive passes are carried out according to a so-called “staggered” pattern, alternating the two ends of the collar and the two sides. The tightening is preferably carried out by means of a hydraulic wrench whose tightening force or torque is calibrated according to the calculation note of the collar. The tensioning of the bolts can alternatively be carried out by means of hollow hydraulic cylinders.

The tightening force FT of the half-collars, required for non-slip under a TC force, is preferably between 1.25xTC and 1.75xTC, taking into account the safety, friction and shape coefficients taken into account in the verification clamping regulations.

For example, to take up a sliding force FS=TC=7226kN, a clamping force of FT=1.69xTC=12206kN is required, for example. For class 10.9 M30 HR bolts (fu=1000MPa, fy=900MPa), tensioned at FT1=70%*1000MPa*561mm ² =392700N, we obtain 393kN of tightening force per bolt. The minimum transverse tightening FT then corresponds, for example, to 2 symmetrical rows (diametrically opposed) of 16 HR M30-10.9 bolts (2*16*392.6kN=12563kN) thus tightened.

One can theoretically estimate the tensile force prevailing in the cable to be relaxed by considering the total section of the reinforcements (for example cable 19T15 or 19×150mm²), the class of resistance of these (for example strand in high limit steel elastic frg=1860 MPa) and the tensioning level specified during the installation of the tendon (generally 70% to 80% of frg for the T15-1860MPa reinforcements of a prestressing tendon).

Only a theoretical value of the force prevailing in the cable C to be relaxed is known beforehand. However, knowledge of a force value sufficiently close to the real value is required to guarantee the safety of the cable cutting and tensioning operation. Indeed, a significant difference between the actual value and the theoretical setpoint applied to the bridging device can lead to rapid (even sudden) variations in tension in the traction bars 21 of the device during the cutting of the reinforcements T. In the case the more unfavourable, a tensile force value that is too largely underestimated can induce, when cutting the reinforcements, a sudden variation in tension in the traction bars and potentially slippage of a collar of the device.

Preferably, a preliminary test of non-slip of the collars 10 is carried out, to validate a sufficient level of security of the device 1 before cutting and tensioning of the cable. For this purpose, the traction bars 21 are tensioned at a force value greater, for example, by 5% to 30% than that estimated.

The cylinders 31 allow for example to work in a pressure range limited to 700 bars. The test phase can be carried out in successive stages with pressure increments of 100 bars or less, taking into account the final pressure to be reached.

For each level, the effort is maintained for a sufficient time to observe the non-slip, for example 15 minutes for the first level then 5 minutes for the following ones. These observations are aided by the simultaneous monitoring of the total force prevailing in the traction bars 21 on the one hand, given by the pressure in the jacks 31, and of the relative displacement of the two collars 10 on the other hand. The maximum effort can be maintained for a longer period, between 30 minutes and an hour for example, to validate the test.

Once the behavior of the clamps 10 has been tested, the tensile force in the bars 21 is reduced to the estimated value in the cable C.

Cable cutting

The cementitious material B and the reinforcements T of the cable C are cut using any means that does not risk damaging the traction bars 21.

A means of mechanical cutting is preferred over cutting by heating (oxyacetylene torch) likely to further expose the tensile bars. For example, a diamond wire saw W is used as illustrated in the .

A follow-up of the total force prevailing in the bars 21 is carried out during the cutting of the reinforcements T of the cable. The relative movement of the two collars 10 is followed synchronously.

A significant variation of this force after cutting a first or two first reinforcements T can give rise to a correction to be made on the tension of the traction bars 21: an increase in the tension in these bars indicates that the tension force prevailing in cable C has been undervalued and vice versa. The tension correction to be made is assessed by relating the tension variation observed in the bars to the relative proportion of cut reinforcements, also taking into account the compared stiffnesses of the tension bars and the cable reinforcements.

The monitoring of the force in the bars 21 and that of the relative displacement of the two collars 10 continues throughout the reinforcement cutting operation. Once the cut is complete, the transfer of the tension force from the cable to the bars is complete.

The progressive relaxation of the traction bars 21 then allows the relaxation and removal of the cable.

For steel reinforcements whose modulus of elasticity is close to 200GPa and whose resistance class is 1860MPa, the typical elongation of the reinforcements is close to 7mm/m.

Taking into account the free length of the cable, the total elastic elongation to be compensated can represent several times the stroke of the cylinders. The recovery nuts 27 and the associated recovery bearings 23 allow the required number of recovery operations to be carried out. Each recovery is carried out with a loading of the bars 21 on the tool nuts 26 and the recovery nuts 27 in an alternating manner.

In variants not shown, the bars are replaced by other traction relay elements such as cables (or strands) or chains.

Hydraulic cylinders can be replaced by torque wrenches or by hoists associated with chains, when the required capacities are adapted to these means.

Claims (31)

Bridging system intended to locally relax a structural cable (C) before it is cut, comprising a bridging device (1) comprising:

• Two collars (10) to be placed on said cable, each collar (10) being formed of two half-collars (11) capable of being positioned around the cable, each half-collar (11) being of elongated shape along the longitudinal axis of the cable and produced with a body (14) defining a substantially semi-cylindrical cavity,
• traction elements (21) extending between the collars (10),
• means (31, 26, 27) for adjusting the tensile force passing through the traction elements (21),

system characterized in that each of at least two half-collars (11) comprises, integrally therewith:

• longitudinal reinforcements (17) extending along said body (14) over at least part of the length thereof,
• anchorages (23) extending between these longitudinal reinforcements (17) and
• anchorages (29, 34) located in the axial continuity of the longitudinal reinforcements (17),

the transmission of the force from the traction elements (21) to the collars (10) taking placeviasaid anchors (23, 29, 34). System according to claim 1, the value of the center distance (E) between the axis of the body (14) and the axis of each traction element (21) being less than or equal to 2.5 times the outside diameter (D) of the cable without sheath. System according to claim 1, the value of the center distance (E) between the axis of the body (14) and the axis of each traction element (21) being less than or equal to 2 times the external diameter of the cable , more preferably at 1.5 or 1.2 times the outer diameter of the cable. System according to one of Claims 1 to 3, each half-collar (11) comprising two pairs of longitudinal reinforcing ribs (17), the ribs of each pair being parallel to each other, the ribs of each pair preferably being oriented 45° in relation to the clamping plane of the collar (10). System according to claim 4, comprising anchorages (23) welded to the longitudinal reinforcing ribs (17), between the latter, preferably consisting of plates (23) welded to the body (14) and to the ribs (17). System according to one of Claims 4 and 5, the anchorages (34) comprising end plates (34) serving as a support for cylinders (31) for tensioning the traction elements, these end plates ( 34) being located in the extension of the ribs (17). A system according to any preceding claim, the bridging device traction elements comprising traction bars (21). System according to claim 7, the traction elements (21) each having a breaking stress at fRG greater than or equal to 1000 MPa. System according to one of Claims 7 and 8, the traction elements of the bridging device comprising four traction bars (21), with two traction bars (21) per half-collar (11), in particular traction bars having a diameter between 50 and 75mm. System according to one of Claims 4 and 5 on the one hand, and one of Claims 7 to 9 on the other hand, the anchorages comprising recovery plates (23) extending perpendicularly to the longitudinal axis of the collar and fixed to the longitudinal reinforcements (17), to serve as a support for the recovery nuts (27) mounted on the traction bars (21). System according to claim 10, comprising backing plates (15) extending against the ribs (17) of a pair of ribs and between these, the take-up plates (23) extending in contact with these plates dubbing (15). System according to any one of the preceding claims, comprising wedges (70) to create a space between the cable and each half-collar, and at least one of the half-collars comprising at least one injection orifice (18) cushioning material (P) around the cable in this space. A system according to any one of claims 1 to 12, including a liner (80) adapted to be placed around the cable inside each collar, each collar being configured to be tightened on the underlying liner, the tensile force exerted by the collar being transmitted to the cable via this lining. System according to claim 13, comprising wedges (70) to provide a space between the cable and the liner (80) for the purpose of injecting into this space, around the cable, a wedging material. System according to one of Claims 13 and 14, the liner (80) comprising two substantially semi-cylindrical half-shells (81), and longitudinal seals (82) at the junction between them. System according to claim 15, each half-shell of the liner (80) having a rough outer surface, preferably being metallic. System according to any one of Claims 1 to 12, comprising a removable formwork (90) configured to be placed around the cable in order to inject around the latter a wedging material (P), each collar being adapted to be placed on the cable where the wedging material was injected, after removal of the removable formwork. System according to claim 17, the removable formwork (90) comprising sectors (91), in particular three in number, and between these longitudinal joints (92). System according to any one of the preceding claims, each half-collar (11) being made of steel. System according to claim 19, each half-collar being made of ductile steel with an elastic limit fy greater than 300 MPa, preferably S355 steel. System according to any one of the preceding claims, without attachment to claim 12, each half-collar (11) being produced without an injection orifice (18) and/or without a vent (18), opening onto the interior surface of the body (14). System according to any one of the preceding claims, the means for adjusting the tractive effort comprising hollow cylinders (31). System according to claim 22, the difference between the outer and inner diameters of the cylinders (31) being greater than or equal to 180mm. System according to claims 22 or 23, the cylinders (31) having a capacity at least equal to 60% of the capacity of the traction elements (21). System according to any one of the preceding claims, each half-collar (11) comprising clamping flanges (12) on the sides of the body (14). Method for locally taking up the tension of a structural cable in view
its severing, using the system (1) according to any one of the preceding claims, comprising the steps consisting in:
- Prepare the surface of the cable, in particular by removing its sheath, removing the spalls and bush-hammering it, then:
To)
- fit the clamps (10) around the cable (C),
- inject a wedging material (P) into the spaces formed between the clamps and the cable, or
b)
- set up a sleeve (80) around the cable (C) at the level of each segment of the latter intended to receive a clamp,
- injecting a wedging material (P) into a space formed between the sleeve and the cable,
- place each collar around the corresponding sleeve, or
vs)
- setting up a removable formwork (90) around the cable at the level of each segment of the latter intended to receive a clamp,
- inject a wedging material into a space formed between the cable and the formwork,
- remove the formwork (90),
- set up each collar on the corresponding portion thus stripped,

then tensioning the traction elements (21) extending between the collars (10) to take up the tension of the cable. Method according to claim 26, comprising the steps defined under a). Method according to claim 26, comprising the steps defined under b). Method according to claim 26, comprising the steps defined under c). Process according to one of Claims 26 to 29, the wedging material (P) being a cement grout reaching a minimum compressive strength fck of at least 40 MPa at 2 days, and preferably at least 100 MPa at 28 days. Process for cutting a structural cable, comprising the steps consisting in:

• locally slackening the cable by implementing the method according to any one of claims 26 to 30,
  - cut the cable (C) in the slack area.