Device and method for monitoring a civil engineering cable

Abstract

A monitoring device (11) for monitoring damage to a civil engineering cable by detecting breaks in the prestressing wires or strands constituting the cable's metallic reinforcement; the cable comprising a sheath (4) made of metallic or plastic material; the sheath (4) being filled with a rigid injection product; the monitoring device (11) comprising: a measuring device including a strain gauge sensor (25) measuring the relative micro-deformations of the cable under the effect of wire or strand breaks; and a data acquisition unit (26) connected to the sensor (25), the data acquisition unit (26) being configured to sequentially collect a micro-voltage from the sensor (25) and to identify the break of a wire or strand of the cable. Figure 4

Description

Title of the invention: Device and method for monitoring a civil engineering cable technical field

[0001] This disclosure relates to devices and methods for monitoring civil engineering cables. In particular, this disclosure relates to monitoring damage to a civil engineering cable by detecting the breakage of wires or prestressing strands constituting the cable's metallic reinforcement. Previous technique

[0002] Civil engineering cables generally consist of a metallic reinforcement (wires and strands) protected by a sheath and an injection grout filling the interior space of the sheath. Despite these protections, the metallic reinforcement can be damaged by corrosion. Corrosion can be of endogenous origin, linked to a local absence of grout, or to a local heterogeneity in compaction or composition (abnormal cement and / or additive content). Corrosion can also be of exogenous origin, linked to the environment (for example, marine). It has been observed that the points where corrosion appears can be the sheath connection sleeves, the highest points of the cable run, or the cable bending points at the deflectors.

[0003] To assess the level of damage to a cable suspected of corrosion and to monitor it, two families of methods are currently known: (1) "non-destructive testing" methods that allow for assessing the risk of damage, such as detecting voids in conduits by infrared thermography or detecting the presence of white paste by capacitive probe, or detecting the presence of corrosion on prestressing reinforcements by magnetic probing using coils. The main drawback of all these methods is their inability to access the most sensitive areas inside deflection struts or anchorage zones; and (2) acoustic monitoring methods that allow for detecting the occurrence of new breaks on prestressing reinforcements by detecting the shock wave caused by the rupture of a wire.These methods, already in use on some structures, require the deployment of substantial equipment on site and the continuous recording of acoustic signals at high acquisition frequencies. It is sometimes difficult to distinguish the noise produced by a broken wire from ambient noise. Summary

[0004] The present disclosure proposes a monitoring device and method that do not have the drawbacks of known methods.

[0005] A device is proposed for monitoring damage to a civil engineering cable by detecting breaks in the wires or strands of prestressing constituting the metallic reinforcement of the cable; the cable comprising a sheath of metallic or plastic material; the sheath being filled with a rigid injection product; the monitoring device comprising: a measuring device including a strain gauge sensor measuring the relative micro-deformations of the cable under the effect of breaks in the wires or strands; and a data acquisition unit connected to the sensor, the data acquisition unit being configured to sequentially collect a micro-electrical voltage from the sensor and to identify the break of a wire or strand of the cable.

[0006] This device thus makes it possible to detect the breakage of a wire or strand. It does not require recording at high acquisition frequencies, which reduces the amount of data to be processed and the energy required for acquiring and storing this data. It is also not necessary to position this device at the expected location of the wire or strand breakage. Finally, the device provides reliable data that is independent of its positioning and of data analysis by an operator.

[0007] In this disclosure, a "strand" is a winding of wires around a central wire. A strand may comprise 7 wires, and the cable may comprise several strands. A strand break corresponds to the breaking of the last (unbroken) wire in the strand.

[0008] According to another aspect, the strain gauge sensor has a resolution of less than 1.107 m / m. As explained later, such a resolution makes it possible to reliably distinguish the weakest signal produced by the breakage of a single wire, and to distinguish the breakage of a wire from the breakage of a strand.

[0009] According to another aspect, the device further comprises two supports fixed to the sheath and spaced apart along the axial direction of the cable, with the measuring device positioned between the two supports. This arrangement allows the monitoring device to be adapted to existing cables. The supports can be positioned on one side of the cable and do not require access to the entire circumference of the cable. Thus, there is no constraint requiring the device to be positioned in one location rather than another.

[0010] According to another aspect, the data acquisition unit is configured to identify: the breakage of a wire, when the variations in microvoltage between two successive acquisitions fall within a first predetermined range of values ​​and correspond to the micro-deformation of the cable at the device occurring when a wire in the cable breaks; and the breakage of a strand, when the variations in microvoltage between two successive acquisitions, A threshold within a second predetermined range of values ​​corresponds to the micro-deformation of the cable at the device that occurs when a strand of the cable breaks. It is indeed possible to estimate the level of micro-deformation expected when a wire breaks and that expected when a strand breaks. By detecting a threshold for variation in micro-tensions, it is therefore possible to identify when a wire or strand has broken.

[0011] According to another aspect, the first range of values ​​and the second range of values ​​are determined based on the following parameters: the re-anchoring length of a wire within its strand; and the re-anchoring length of a strand within the rigid injection-molded product. The re-anchoring length is the distance along the longitudinal direction of the cable between the broken end and the point where the wire (resp. strand) is again properly anchored within the strand (resp. rigid injection-molded product). The re-anchoring length is also the distance over which the wire (resp. strand) has completely lost its initial deformation due to a localized break. Experimentally, a re-anchoring length of 5 meters was measured for a wire, while a re-anchoring length of 8 meters was measured for a strand.

[0012] According to another aspect, the first and second ranges of values ​​are determined based on the geometry of the cable path, with or without the presence of deflectors along its path. According to another aspect, the first and second ranges of values ​​are determined based on the following parameters: the number of wires and / or strands constituting the cable's metallic armor; the cross-sectional area of ​​the metallic armor, the rigid injection molding, and the sheath; the Young's modulus of the metallic armor, the rigid injection molding, and the sheath; and the residual stress in the cable's metallic armor. The greater the number of parameters taken into account for evaluating the ranges of values, the more accurate the model will be.

[0013] According to another aspect, the first value range is included in the interval [-0.5 x 10⁶; -25 x 10⁶] and / or the second value range is included in the interval [-5 x 10⁶; -120 x 10⁶]. For various types of cables, it has been concluded that, with sufficient certainty, the first and second value ranges lie within these respective intervals. For a given cable, there is no overlap between the first and second value ranges: there can be no doubt when identifying whether a threshold belongs to one range or the other.

[0014] According to another aspect, a cover fixed to the sheath protects the measuring device. The cover can extend the reliability of the measurement by protecting the device from external elements.

[0015] According to another aspect, the gauge sensor produces signals proportional to the micro-deformations of the cable with a proportionality coefficient between 12 and 25 pV / 106. This range of values ​​allows the use of a data acquisition unit with a minimum sensitivity of 1 qV.

[0016] According to another aspect, the data acquisition unit is configured to collect between 30 and 100 values ​​per hour. Too low an acquisition frequency risks mistaking simple thermal drift for a wire or strand break, and failing to detect the signal of an actual wire or strand break. Too high an acquisition frequency leads to the acquisition of a large amount of unnecessary data.

[0017] According to another aspect, the two supports are equipped with a pre-tensioning device allowing the measuring device to be pre-tensioned. Since the measurement involves a shortening of the cable, certain sensors can advantageously be initially tensioned to continue delivering a signal (of lower voltage) as the cable shortens.

[0018] According to another aspect, at least four and preferably six screws fix each of the two supports to the sheath.

[0019] According to another aspect, each support is fixed to an adjustable clamp, itself preferably fixed to the sheath by means of several screws. This variant can be adapted when there are doubts about the local homogeneity of the rigid injection product.

[0020] According to another aspect, the data acquisition unit is configured to send a signal to a user when the number of broken wires and / or strands reaches a predetermined threshold. The data acquisition unit can count the number of broken wires and / or strands, incrementally, each time a wire or strand break is detected. The date and time of each break can also be recorded. The user can thus take appropriate action and schedule cable maintenance. The data acquisition unit can also (or alternatively) send a signal when each wire breaks.

[0021] According to another aspect, the measuring device comprises two separate attachment pieces fixed respectively to each of the two supports, and the gauge sensor forms a bridge connecting the two attachment pieces.

[0022] The invention also relates to a method for monitoring a civil engineering cable, comprising: the placement of the monitoring device according to one of the embodiments mentioned above on a portion of the cable; and the sequential acquisition of the micro-deformation of the cable with the monitoring device.

[0023] According to another aspect, the method comprises sending a signal to a user when the number of broken wires and / or strands has reached a predetermined threshold. The user can then consider a maintenance operation on the cable. The process thus improves the safety of the civil engineering structure containing this cable.

[0024] Theoretical principle on which this disclosure is based

[0025] Corrosion of a wire results in local reductions in its cross-sectional strength. Conversely, at the damaged (corroded) point, the tensile stress increases. When this stress exceeds the steel's resistance capacity, the wire breaks abruptly. In the cable, which is made up of strands, themselves composed of wires, three distinct zones can then be distinguished: a short "R" zone where the cable's cross-sectional area has been reduced entirely by that of the broken wire (e.g., by 1 / 133rd for the first wire that breaks in a 19T15 cable); two "Re" zones of re-anchoring in which the broken wire will gradually re-anchor itself by friction / wedging within the rest of the cable; and two "C" ("current") zones where the cable has retained its full cross-sectional area.

[0026] Regardless of the degree of damage to the cable, the tensile force is constant along the entire length of the cable, and this holds true for all zones considered (type R, Ré, or C). The average stresses per zone are inversely proportional to the resisting cross-sections; that is, in the previous example, oR / oC = (133 / 132) / (133 / 133) = 133 / 132: after the first strand breaks, the stress in R is now equal to 133 / 132 of the stress in C. In zone "R", the stress has increased. In zone "C", the stress has decreased. When the stress in zone "R" reaches the breaking point, the cable breaks. This can occur in a 19T15 cable when only 6 or 7 strands have broken.

[0027] Since the total length of the cable was not altered by the breakage of a wire or strand, the change in stresses leads to a redistribution of deformations: the R and Ré zones have lengthened and the C zones have shortened.

[0028] The deformations in zones R and Ré are significant and would therefore, a priori, be physical manifestations easily measurable. However, it is not necessarily advisable to install a deformation measurement device in these zones: they are small, located near cable anchors or deflectors, and therefore difficult to access. Furthermore, the areas where wires / strands break may be the site of cracking in the grout and thus of weaknesses unsuitable for the robust anchoring of a measurement device. It is therefore advantageous to place the device in zone C, which is less prone to wire / strand breakage (because it is certainly protected from corrosion).

[0029] Tests and calculations were carried out to estimate the micro-deformations in zone C. Thus, for a 19T15 cable, a 40-meter-long branch, with a tensile stress in service estimated at 1200 MPa, wire breakage led to a micro-deformation of -3.106 to -6.106 (micro-deformations increase as wires in the same strand break) and the breaking of the last wire (and therefore of the strand) led to a micro-deformation of -35.106.

[0030] Other tests and calculations, carried out with another branch length, gave respective results of -8.106, -16.106 and -90.106.

[0031] It is therefore relevant to select a monitoring device having a resolution on the order of 107.

[0032] It also appears that the micro-deformations in zone C are almost proportional: on the one hand, to the rate 1 / t of broken reinforcement (1 / 133 for the first wire, 1 / 19 for the first strand of a 19T15); and on the other hand, to the ratio Ir / L, where Ir is the re-anchoring length of the reinforcement (the re-anchoring length is different depending on whether we consider a wire or a strand) and L is the length of the branch where the break occurs (length of the two consecutive branches that frame a deviator for a break at this point).

[0033] By varying all the parameters involved in the implementation of a cable, it is possible to assign coefficients to them and thus weight the impact of each parameter on the expected micro-deformations. It is therefore possible to obtain a predictive model. The parameters having the greatest impact on the expected micro-deformation values ​​are: the re-anchoring length of a wire in its strand; and the re-anchoring length of a strand in the rigid injection molding material. Next come: the geometry of the cable's path, with or without deviations in its path. Then: the number of wires and / or the number of strands constituting the cable's metallic reinforcement; the cross-sectional area of ​​the metallic reinforcement, the rigid injection molding material, and the sheath; the Young's modulus of the metallic reinforcement, the rigid injection molding material, and the sheath; and the residual stress in the cable's metallic reinforcement.

[0034] For example, the expected microdeformation e can be expressed as a product of coefficients with a weight respective to each parameter mentioned above: 100351 MO ±5

[0036] where A; is one of the n parameters mentioned above, a; is an exponent for each parameter, and ô is an experimentally obtained tolerance. The exponent a; corresponding to the parameters having the least impact on the microdeformation can be close to zero, thus making the corresponding coefficient A; irrelevant in the expected microdeformation result. Each of the exponents a; can be determined by numerical modeling and / or by successive tests by varying one of the parameters and measuring the microdeformations at the break of a wire or strand. It is thus possible to determine a first and a second range of values ​​representing the respective micro-deformations at the break of a wire or strand. The experiments mentioned here may include experiments prior to the installation of the device, and / or learning experiments during the cable's lifetime. Brief description of the drawings

[0037] Other features, details and advantages will become apparent from reading the detailed description below and from analyzing the accompanying drawings, in which: Fig. 1

[0038] [Fig.1] shows a strand of a civil engineering cable. Fig. 2

[0039] [Fig.2] illustrates a cross-sectional view of a cable. Fig. 3

[0040] [Fig.3] shows an example of an arrangement of an external prestressing cable. Fig. 4

[0041] [Fig.4] represents a monitoring device. Fig. 5

[0042] [Fig.5] shows an example of a measurement timing diagram. Fig. 6

[0043] [Fig.6] represents a variant of a monitoring device. Fig. 7

[0044] [Fig.7] represents a variant of a monitoring device. Description of the implementation methods

[0045] As shown in [Fig. 1], a strand 1 comprises a set of wires joined together. The illustrated strand 1 is helical, comprising a central wire 2 and six peripheral wires 3 distributed around the central wire 2. The central wire 2 has a general shape of a right circular cylinder with diameter FC. Each peripheral wire 3 describes a general helical shape, the cross-section of which defines a diameter FH. The wires 2 and 3 are metallic, preferably steel. Advantageously, the diameter FC of the central wire 2 is slightly larger than the diameter FH of each peripheral wire 3. The strand extends in a longitudinal direction z=L which coincides with a longitudinal axis of the central wire 2.

[0046] Figure 2 shows a cross-sectional view of a civil engineering cable. The cable 6 comprises a plurality of strands 1, surrounded by a sheath 4. An injection or filling product 5 fills the interior space of the sheath 4. The sheath 4 may be made of high-density polyethylene. The injection product 5 may be a cement grout or other rigid product. The outer diameter of the sheath may be between 60 and 200 mm, and preferably it may be 110 mm for a 19-strand cable (19T15). It will be understood that the device described in this disclosure is adaptable to smaller or larger diameters.

[0047] Figure 3 illustrates an example of the arrangement of a cable 6. In this example, the cable 6 is an external prestressing cable for a bridge deck. The cable 6 is anchored at both ends by an anchorage 7. The cable 6's path may include one or more deflectors 8, one or more pier crossbeams 9, and one or more end crossbeams 10. Between any two of these elements, the branches of the path are substantially straight.

[0048] It is understood that the examples in Figures 1 to 3 are given only as examples and are not limiting with respect to this disclosure.

[0049] Figure 4 illustrates an example of a monitoring device 11. The monitoring device 11 comprises two supports 12 spaced apart along the axial (or longitudinal) direction Z. The supports may be of identical design. Each support 12 may be made of metallic material, for example, possibly stainless steel. Each support 12 may be formed from a welded assembly. Each support 12 may include two lateral elements 13, 14 which may bear stably on the sheath 4. A base 15 may join the lateral elements 13, 14. Screws 16 or other equivalent fasteners may secure the base 15 to the sheath 4 in order to secure each support 12 to the sheath 4. The screws 16 may consist of 4 or 6 self-drilling screws. These penetrate the sheath 4 and optionally the injection product (5 on [Fig.2]).

[0050] Each support 12 may include a central plate 17 arranged between the lateral elements 13, 14. The central plate 17 may be in contact with the base 15.

[0051] A fastener 18 can be connected to the central plate 17, for example, by means of a pre-tensioning screw 19. Each fastener 18 can comprise a body 20 from which extend two parallel tabs 21 separated from each other by a slot 22. The slot 22 can have an axial length of between 20 and 50 mm. The slot 22 can receive one end of a shim 23. A fastening means (pin, screw, pre-tensioned bolt, etc.) 24 allows the shim 23 to be attached to the fastener 18. The distance between the two fastening means 24 (more precisely between their central axes) can be between 100 and 200 mm, preferably this distance can be 140 mm.

[0052] Thus, the deformations of the cable at the device 11 are reflected in deformations of the shim 23.

[0053] A gauge sensor 25 can be arranged on the shim 23, preferably on a central portion of the shim 23, which has a smaller cross-section than its ends that are received in the slots 22. The gauge sensor 25 is connected to a data acquisition unit 26 via a wired or wireless connection. The data acquisition unit 26 includes suitable computing resources (memory, processor, etc.) for collecting and processing / analyzing the data from the strain gauge sensor. The data acquisition unit 26 may include means of communication with a third-party system (remote server). Thus, the data acquisition unit 26 can communicate each wire break to a user, and / or the number of broken wires and / or strands, and / or provide a signal when the number of broken wires and / or strands has reached a critical threshold. The data acquisition unit 26 may consist of a housing located near the supports 12.

[0054] The assembly of supports 12, fasteners 18, and measuring device 23, 25, as well as optionally the data acquisition unit, can be covered. For example, a metal cover with a generally parallelepiped shape (not shown) can be positioned to cover the system. The cover may have curved edges conforming to the shape of the sheath 4, and seals may be arranged to prevent water from entering the internal gap of the cover. The cover may be removable and / or may include an access panel for inspection or maintenance of the device. For example, depending on the sensor used, it may be advantageous to retension the shim with the pre-tensioning screws during the cable's service life. The cover may have dimensions close to or smaller than 5x5x30 cm³.If the data acquisition unit is not housed within the cover, a cable can exit the cover through a designated opening to connect to the nearby data acquisition unit. A single data acquisition unit can collect signals from more than one sensor.

[0055] The strain gauge sensor 25 may include strain gauges mounted in a Wheatstone bridge configuration. The strain gauge sensor 25 delivers a microvoltage proportional to the relative strain (in "106") to the acquisition unit 26.

[0056] Since the aim is to measure a shortening, it may be necessary to initially apply a tensile force to the swaging, a force that will be progressively released with each break in a wire or strand. The pre-tensioning screws 19 are used for this purpose. In practice, the measurement range can extend over the interval [-250 x 10⁶, +100 x 10⁶]. This range allows, depending on the type of cable being monitored, for up to 15 individual broken wires, or 2 complete strands, to be detected without needing to reapply pre-tensioning.

[0057] It is understood that [Fig. 4] is only one example of mounting the measuring device 11. The supports 12, the fasteners 18, and the shim 23 may have different shapes and designs. Other examples are shown in Figures 6 and 7, discussed below.

[0058] Figure 5 illustrates an example of measuring micro-deformation variations over time using a monitoring device. The x-axis represents time, and the breakage of two strands is observed, indicated by 14 successive intervals corresponding to 14 successive wire breaks. The 7th and 14th intervals, corresponding to the breakage of the last wire in a strand (and therefore to the breakage of the entire strand), are of a different order of magnitude than the other intervals. The monitoring device is thus capable, by comparing the micro-deformation intervals to predetermined ranges of values, of identifying (and counting) wire and strand breaks.

[0059] Figure 6 illustrates a variant of the monitoring device in which, instead of the flashing extending from one attachment to the other, the measuring device 23, 25 can extend from one support 12 to the other support 12. In this example, the base 15 can cantilever over the lateral elements 13. A strain gauge sensor 25 is directly attached (by welding or screws, for example) to the base 15. The strain gauge sensor can be one with a measuring amplitude of + / - 500 N / 10⁶ and a strain stiffness of 0.25 N / 10⁶. The center-to-center distance between the two sensor attachments to the base 15 can be approximately 50 mm. The entire device can thus have an axial length of about 15 cm.

[0060] In another embodiment illustrated in [Fig. 7], the cable deformation is measured using a small-diameter tie rod 23' (for example, between 2 and 4 mm) which, subjected to a deformation imposed by the cable, compresses a load cell 25 equipped with strain gauges. The signals from the load cell (in N) 25 are transmitted to the data acquisition unit and converted into micro-deformations using Hooke's Law. The tie rod 23' is tensioned between two supports 12, only one of which is shown in [Fig. 7]. The tie rod 23' is held against the load cell by means of a support piece 28 which receives one end of the tie rod 23' by means of a clamping cone 30. A centering washer 29 can be interposed between the support piece 28 and the load cell 25.

[0061] List of reference signs

[0062] 1: Toron 2: central wire 3: Peripheral wire 4: sheath 5: Injection product 6: cable 7: anchoring 8: diverter 9: spacer on battery 10: end spacer 11: monitoring device 12: support 13, 14: lateral element 15: base 16: screw 17: central plate 18: attachment 19: Pre-tensioning screw 20: body of the fastener 18 21: tab of the attachment 18 22: Slot for fastener 18 23: flashy 23': shooting 24: element for attaching the sash 23 to the fastener 18 25: Gauge sensor 26: central purchasing office 28: support piece 29: Centering washer 30: clamping cone Z: axial or longitudinal direction of the cable 6

Claims

Demands

1. A monitoring device (11) for damage to a civil engineering cable (6) by detecting breaks in the prestressing wires (2, 3) or strands (1) constituting the metallic reinforcement (1, 2, 3) of the cable (6); the cable (6) comprising a sheath (4) of metallic or plastic material; the sheath (4) being filled with a rigid injection product (5); the monitoring device (11) comprising: - two supports (12) adapted to be fixed on the sheath (4) at a distance from each other along an axial direction (Z) of the cable (6); - a measuring device (23, 23', 25) disposed between the two supports (12) and comprising a strain gauge sensor (25) measuring the relative micro-deformations of the cable (6) under the effect of breaks in the wires or strands (1);and - a data acquisition unit (26) connected to the sensor (25), the data acquisition unit (26) being configured to sequentially collect a micro-voltage from the sensor (25) and to identify the breakage of a wire or strand (1) of the cable (6).;

2. Device (11) according to claim 1, wherein the gauge sensor (25) has a resolution of less than 1.107 mm / m.

3. Device (11) according to any one of claims 1 or 2, wherein the acquisition unit (26) is configured to identify: - the breakage of a wire (2, 3), when the variations in electrical microvoltage have, between two successive acquisitions, a threshold within a first predetermined range of values ​​and corresponding to the microdeformation of the cable (6) at the device occurring during the breakage of a wire (2, 3) of the cable (6); and - the breakage of a strand (1), when the variations in electrical microvoltage have, between two successive acquisitions, a threshold within a second predetermined range of values ​​and corresponding to the microdeformation of the cable (6) at the device occurring during the breakage of a strand (1) of the cable (6).

4. Device (11) according to claim 3, wherein the first range of values ​​and the second range of values ​​are determined as a function of the following parameters: the re-anchoring length (Ir) of a wire (2, 3) in its strand (1); and the re-anchoring length (Ir) of a strand (1) in the rigid injection product (5).

5. Device (11) according to claim 3 or 4, wherein the first range of values ​​and the second range of values ​​are determined according to the geometry of the cable path (6), with or without the presence of deviators (8) on its path.

6. Device (11) according to any one of claims 3 to 5, wherein the first range of values ​​and the second range of values ​​are determined as a function of the following parameters: the number of wires (2, 3) and / or the number of strands (1) constituting the metallic armor of the cable (6); the cross-section of the metallic armor (1, 2, 3), of the rigid injection product (5) and of the sheath (4); the Young's modulus of the metallic armor (1, 2, 3), of the rigid injection product (5) and of the sheath (4); and the residual stress in the metallic armor (1; 2; 3) of the cable (6).

7. Device (11) according to any one of claims 3 to 6, wherein the first range of value is included in the interval [-0.5.10 6 ; -25.106] and / or the second range of value is included in the interval [-5.106 ;-120.106].

8. Device (11) according to any one of claims 1 to 7, wherein a cover fixed on the sheath (4) protects the measuring device.

9. Device (11) according to any one of claims 1 to 8, wherein the gauge sensor (25) produces signals proportional to the micro-deformations of the cable with a proportionality coefficient between 12 and 25 qV / 106.

10. Device (11) according to any one of claims 1 to 9, wherein the acquisition unit (26) is configured to collect between 30 and 100 values ​​per hour.

11. Device (11) according to any one of claims 1 to 10 in combination with claim 3, wherein the two supports (12) are equipped with a pre-tensioning device (19) allowing the pre-tensioning of the measuring device (23, 23', 25).

12. Device (11) according to any one of claims 1 to 11 in combination with claim 3, wherein at least four and Preferably six screws (16) fix each of the two supports (12) onto the sheath (4).

13. Device (11) according to any one of claims 1 to 11 in combination with claim 3, wherein each support is fixed to an adjustable clamp, itself preferably fixed to the sheath (4) by means of several screws (16).

14. Device (11) according to any one of claims 1 to 13, wherein the acquisition unit (26) is configured to send a signal to a user when the number of broken wires (2, 3) and / or strands (1) has reached a predetermined threshold.

15. Device (11) according to any one of claims 1 to 14 in combination with claim 3, wherein the measuring device comprises two separate attachment pieces fixed respectively to each of the two supports, and the gauge sensor forms a bridge connecting the two attachment pieces.

16. Method for monitoring a civil engineering cable (6), comprising: - placing the monitoring device (11) according to one of the preceding claims on a portion of cable (6); and - sequentially acquiring the micro-deformation of the cable (6) with the monitoring device (11).

17. A method according to claim 16, further comprising the transmission of a signal to a user when the number of broken wires (2, 3) and / or strands (1) has reached a predetermined threshold.

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