Device and method for monitoring a civil engineering cable

Abstract

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

Description

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

[0001] The present disclosure relates to the field of devices and methods for monitoring civil engineering cables. In particular, the present disclosure relates to monitoring damage to a civil engineering cable by detecting the breakage of prestressing wires or strands constituting the metal reinforcement of the cable. Prior art

[0002] Civil engineering cables are generally made up of a metal reinforcement (wires and strands), protected by a sheath and an injection grout filling the interior space of the sheath. Despite these protections, the metal reinforcement can be damaged by corrosion. Corrosion can be of endogenous origin, linked to a local absence of grout, or to local heterogeneity of compactness or composition (abnormal contents of cement and / or additives). 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 connection sleeves of the sheaths, the high points of the cable route or the inflection points of the cables 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 which make it possible to assess the risk of damage, such as the detection of filling voids in the conduits by infrared thermography or the detection of the presence of white paste by capacitive probe, or to detect the presence of corrosion on the prestressing reinforcements by magnetic auscultation using coils. The main drawback of all these methods is that they cannot access the most sensitive areas inside the deflection spacers or anchoring zones; and (2) acoustic monitoring methods which make it possible to detect the occurrence of new ruptures on the 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 on site of substantial equipment and the continuous recording of acoustic signals at high acquisition frequencies. It is sometimes difficult to distinguish the noise produced by the breakage of a wire from ambient noise. Summary.

[0004] The present disclosure provides a monitoring device and method which do not have the disadvantages of known methods.

[0005] A device is proposed for monitoring damage to a civil engineering cable by detecting breaks in the prestressing wires or strands constituting the metal reinforcement of the cable; the cable comprising a sheath made of metal or plastic material; the sheath being filled with a rigid injection product; the monitoring device comprising: a measuring device comprising a gauge sensor measuring the relative micro-deformations of the cable under the effect of breaks in the wires or strands; and an acquisition unit connected to the sensor, the acquisition unit being configured to sequentially collect an electrical micro-voltage from the sensor and to identify the breakage 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 quantity of data to be processed and the energy used to acquire and store this data. It is also not necessary to position this device at the expected location of the breakage of the wires or strands. Finally, the device makes it possible to obtain reliable data which does not depend on its positioning or on the analysis of the data by an operator.

[0007] In the present 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. The breakage of a strand corresponds to the breakage of the last wire (not yet broken) of the strand.

[0008] According to another aspect, the gauge sensor has a resolution of less than 1.107 m / m. As explained below, such 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 from each other in an axial direction of the cable, the measuring device being arranged between the two supports. This arrangement makes it possible to adapt the monitoring device to existing cables. The supports can be arranged 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 acquisition unit is configured to identify: the breakage of a wire, when the variations in electrical micro-voltage present, between two successive acquisitions, a threshold included in a first predetermined range of values ​​and corresponding to the micro-deformation of the cable at the right of the device occurring during the breakage of a wire of the cable; and the breakage of a strand, when the variations in electrical micro-voltage present, between two successive acquisitions, a threshold included in a second predetermined range of values ​​and corresponding to the micro-deformation of the cable at the right of the device occurring during the breakage of a cable strand. It is in fact possible to estimate the level of microdeformation expected when a wire breaks and that expected when a strand breaks. By detecting a threshold of 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 according to the following parameters: the re-anchoring length of a wire in its strand; and the re-anchoring length of a strand in the rigid injection product. The re-anchoring length is the distance in the longitudinal direction of the cable between the broken end and the place where the wire (resp. strand) is again properly anchored in the strand (resp. the rigid injection product). The re-anchoring length is also the distance over which the wire (resp. strand) has lost all of its initial deformation due to a localized break. By experimentation, 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 range of values ​​and the second range of values ​​are determined as a function of the geometry of the cable route, with or without the presence of deflectors on its route. According to another aspect, the first range of values ​​and the second range of values ​​are determined as a function of the following parameters: the number of wires and / or the number of strands constituting the metal reinforcement of the cable; the cross-section of the metal reinforcement, the rigid injection product and the sheath; the Young's modulus of the metal reinforcement, the rigid injection product and the sheath; and the residual stress in the metal reinforcement of the cable. The greater the number of parameters taken into account for the evaluation of the value ranges, the finer the model will be.

[0013] According to another aspect, the first range of values ​​is included in the interval [-0.5.10 6 ; -25.10 6] and / or the second range of values ​​is included in the interval [-5.10 6 ; -120.10 6]. For various types of cables, it has been concluded that with sufficient certainty, the first and second ranges of values ​​are within these respective intervals. For a given cable, there is no overlap between the first and second ranges of values: there can be no doubt when identifying the belonging of a threshold to one range or another.

[0014] According to another aspect, a cover attached to the sheath protects the measuring device. The cover can make it possible to 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 microdeformations of the cable with a coefficient of proportionality between 12 and 25 qV / 106. This range of values ​​makes it possible to use an acquisition unit with a minimum sensitivity of 1 qV.

[0016] According to another aspect, the acquisition unit is configured to collect between 30 and 100 values ​​per hour. Too low an acquisition frequency presents the risk of confusing a simple thermal drift with the breakage of a wire or strand, and of not detecting the signal of an actual breakage of a wire or strand. Too high an acquisition frequency leads to acquiring a large quantity of useless data.

[0017] According to another aspect, the two supports are equipped with a pre-tensioning device allowing the pre-tensioning of the measuring device. Since the measurement relates to a shortening of the cable, certain sensors can advantageously be initially tensioned to continue to deliver a signal (of lower tension) 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 acquisition unit is configured to send a signal to a user when the number of broken wires and / or strands has reached a predetermined threshold. The acquisition unit can count the number of broken wires and / or strands, in increments, each time the breakage of a wire or strand is detected. The date and time of each breakage can also be recorded. The user can thus act accordingly and plan a maintenance operation on the cable. The 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: placing the monitoring device according to one of the embodiments mentioned above on a portion of cable; and sequentially acquiring the microdeformation of the cable with the monitoring device.

[0023] According to another aspect, the method comprises transmitting 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 method thus makes it possible to improve the safety of the civil engineering structure containing this cable.

[0024] Theoretical principle on which the present disclosure is based

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

[0026] Whatever the state of damage to the cable, the tensile force is constant over the entire length of the cable, and this for all the zones considered (type R, Ré or C). The average stresses, per zone, are inversely proportional to the resistant sections, i.e., in the previous example 0R / 0C = (133 / 132) / (133 / 133) = 133 / 132: after the breakage of the first wire, the stress in R is now equal to 133 / 132 of the stress in C. In the “R” zone, the stress has increased. In the “C” zone, the stress has decreased. When the stress in the “R” zone reaches the breaking limit, 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 has not been altered by the breakage of a wire or a strand, the change in stresses leads to a redistribution of the 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 capable of being easily measured. However, it is not necessarily judicious to install a deformation measuring device in these zones: they are small, close to cable anchors or deflectors of its route and therefore difficult to access. Also, the wire / strand breakage zones can be the site of cracks in the filling grout and therefore of weaknesses unsuitable for robust anchoring of a measuring device. It is therefore advantageous to place the device in a zone C which is not very conducive to wire / strand breakage (because it is certainly protected from corrosion).

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

[0030] Further 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 of the order of 107.

[0032] It also appears that the microdeformations in zone C are almost proportional: on the one hand, to the rate 1 / t of broken reinforcements (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 one considers a wire or a strand) and L is the length of the branch where the rupture occurs (length of the two consecutive branches which frame a deviator for a rupture at this location).

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

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

[0035] f = (nX)±a

[0036] where A; is one of the n parameters mentioned above, a; is a respective exponent for each parameter and ô is a tolerance obtained experimentally. The exponent a; corresponding to the parameters having the least impact on the microdeformation can be close to zero, thus giving no importance to the coefficient A; corresponding in the result of the expected microdeformation. Each of the exponents a; can be determined by numerical modeling and / or by successive tests by varying one of the parameters and by measuring the microdeformations at the break of a wire or a strand. It is thus possible to determine a first and a second range of values ​​in which the respective microdeformations at the break of a wire or a strand are located. The experiments mentioned here can include experiments preceding the installation of the device, and / or experiments by learning during the life of the cable. Brief description of the drawings

[0037] Other features, details and advantages will become apparent upon reading the des- detailed description below, and to the analysis of the attached drawings, on which: Fig. 1

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

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

[0040] [Fig.3] shows an example of 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 embodiments

[0045] As shown in [Fig.l], a strand 1 comprises a set of wires secured to each other. The strand 1 illustrated is of the helical type 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 a diameter denoted FC. Each peripheral wire 3 describes a general helical shape, a cross-section of which defines a diameter denoted FH. The wires 2 and 3 are metallic, preferably made of steel. The diameter FC of the central wire 2 is advantageously slightly greater 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] [Fig.2] shows a sectional view of a civil engineering cable. 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 can be made of high-density polyethylene. The injection product 5 can be a cement grout, or other rigid product. The external diameter of the sheath can be between 60 and 200 mm, and preferably it can be 110 mm for a 19-strand cable (19T15). It will be understood that the device described in the present disclosure is adaptable to smaller or larger diameters.

[0047] [Fig.3] illustrates an example of arrangement of a cable 6. In this example, the cable 6 is an external prestressing cable of a bridge deck. The cable 6 is anchored at its two ends by an anchor 7. The route of the cable 6 may include one or more deflectors 8, one or more pier spacers 9, and one or more end braces 10. Between two of these elements, the branches of the layout are substantially straight.

[0048] It is understood that the examples of Figures 1 to 3 are given only by way of illustration and are not limiting with regard to the present disclosure.

[0049] [Fig. 4] illustrates an example of a monitoring device 11. The monitoring device 11 comprises two supports 12 spaced apart from each other in the axial direction Z (or longitudinal). 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 of a mechanically welded assembly. Each support 12 may comprise two lateral elements 13, 14 which may be in stable support on the sheath 4. A base 15 may join the lateral elements 13, 14. Screw elements 16 or other equivalent fixing means may accomplish the fixing of the base 15 to the sheath 4 in order to secure each support 12 to the sheath 4. The screw elements 16 may consist of 4 or 6 self-drilling screws. These penetrate into the sheath 4 and optionally into the injection product (5 in [Fig.2]).

[0050] Each support 12 may comprise 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 may be connected to the central plate 17 for example by means of a pre-tensioning screw 19. Each fastener 18 may comprise a body 20 from which extend two parallel tabs 21 separated from each other by a slot 22. The slot 22 may have an axial length of between 20 and 50 mm. The slot 22 may receive one end of a shim 23. A fixing means (pin, screw, pre-stressed bolt, etc.) 24 makes it possible to attach the shim 23 to the fastener 18. The distance between the two fixing means 24 (more precisely between their central axes) may be between 100 and 200 mm, preferably this distance may be 140 mm.

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

[0053] On the foil 23 can be arranged a gauge sensor 25, preferably on a central portion of the foil 23, of smaller section than its ends which are received in the slots 22. The gauge sensor 25 is connected to an acquisition center 26 by means of a wired or wireless connection. The acquisition center 26 comprises suitable computer means (memory, processor, etc.) for collecting the data coming from the gauge sensor and processing / analyzing them. The acquisition center 26 can comprise means of communication with a third-party system (remote server). Thus, the acquisition center 26 can communicate to a user each wire break, and / or the number of wires and / or strands broken and / or provide a signal when the number of broken wires and / or strands has reached a critical threshold. The acquisition unit 26 may be formed of a box arranged in the vicinity of the supports 12.

[0054] The assembly of supports 12, fasteners 18 and measuring device 23, 25, as well as possibly the acquisition unit, can be covered. For example, a metal cover of generally parallelepiped shape (not shown) can be positioned to cover the system. The cover can have curved edges matching the shape of the sheath 4 and seals can be arranged to prevent water from penetrating into the internal space of the cover. The cover can be removable and / or can include a hatch for inspection or maintenance of the device. For example, depending on the sensor used, it may be advantageous to re-tension the foil with the pre-tensioning screws during the life of the cable. The cover can be of a dimension close to or less than 5x5x30 cm3.If the acquisition unit is not contained in the cover, a cable can escape from the cover through a hole provided for this purpose, to reach the acquisition unit, located nearby. The same acquisition unit can collect the signals provided by more than one sensor.

[0055] The gauge sensor 25 may comprise gauges mounted in a Wheatstone Bridge. The gauge sensor 25 delivers a micro-voltage proportional to the relative deformation (in “106”) to the acquisition unit 26.

[0056] Since it is a question of being able to measure a shortening, it may be necessary to initially generate a tensile force on the foil, a force which will be released progressively at each wire or strand break. The pre-tensioning screws 19 are used for this purpose. In practice, the measuring range may extend over the interval [-250.106, +100.106]. This range makes it possible, depending on the type of cable monitored, to reach up to 15 broken individual wires, or 2 complete strands without needing to apply pre-tensioning again.

[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 foil 23 may have different shapes and designs. Other examples are shown in Figures 6 and 7 discussed below.

[0058] [Fig.5] represents an example of measurement of microdeformation variations measured by a monitoring device over time. The x-axis represents time and we observe the breakage of 2 strands, which can be seen by 14 successive steps corresponding to 14 successive wire breakages. We observe that the 7th and 14th steps, which correspond to the breakage of the last wire of a strand (and therefore to the breakage of a strand) are of a different order of magnitude from the other steps. The monitoring device is therefore capable, by comparing the microdeformation steps to predetermined value ranges, of identifying (and counting) the wire and strand breaks.

[0059] [Fig.6] illustrates a variant of the monitoring device in which, instead of the foil which extends 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 extend cantilevered from the lateral elements 13. A gauge sensor 25 is directly fixed (by welding or screw elements for example) to the base 15. The strain gauge sensor can be a sensor whose measurement amplitude is + / - 500 106 and the deformation stiffness 0.25 N / 106. The center distance between the two attachments of the sensor to the base 15 can be approximately 50 mm. The entire device can thus have an axial length of approximately fifteen centimeters.

[0060] In another variant illustrated in [Fig.7], the deformation of the cable is measured using a tie rod 23' of small diameter (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 communicated to the acquisition unit and transformed 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 in abutment 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: anchor 8: deflector 9: spacer on pile 10: end spacer 11: monitoring device 12: support 13, 14: side element 15: base 16: screws 17: central plate 18: attachment 19: pre-tensioning screw 20: body of the attachment 18 21: tab of the attachment 18 22: clip slot 18 23: flashy 23': shooting 24: element for fixing the foil 23 to the fastener 18 25: gauge sensor 26: acquisition center 28: support piece 29: centering washer 30: clamping cone Z: axial or longitudinal direction of the cable 6

Claims

Claims

1. Device (11) for monitoring damage to a civil engineering cable (6) by detecting breaks in the prestressing wires (2, 3) or strands (1) constituting the metal reinforcement (1, 2, 3) of the cable (6); the cable (6) comprising a sheath (4) made of metal or plastic material; the sheath (4) being filled with a rigid injection product (5); the monitoring device (11) comprising: - a measuring device (23, 23', 25) comprising a gauge sensor (25) measuring the relative microdeformations of the cable (6) under the effect of breaks in the wires or strands (1); and - an acquisition unit (26) connected to the sensor (25), the acquisition unit (26) being configured to sequentially collect an electrical 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 m / m.

3. Device (11) according to claims 1 and 2, further comprising two supports (12) fixed on the sheath (4) and spaced apart from each other in an axial direction (Z) of the cable (6), the measuring device (23, 23', 25) being arranged between the two supports (12).

4. Device (11) according to one of claims 1 to 3, in which 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 included in a first predetermined range of values and corresponding to the microdeformation of the cable (6) at the right of 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 included in a second predetermined range of values and corresponding to the microdeformation of the cable (6) at the right of the device occurring during the breakage of a strand (1) of the cable (6).

5. Device (11) according to claim 4, 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).

6. Device (11) according to claim 4 or 5, wherein the first range of values and the second range of values are determined as a function of the geometry of the route of the cable (6), with or without the presence of deflectors (8) on its route.

7. Device (11) according to one of claims 4 to 6, 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 metal reinforcement of the cable (6); the cross-section of the metal reinforcement (1, 2, 3), of the rigid injection product (5) and of the sheath (4); the Young's modulus of the metal reinforcement (1, 2, 3), of the rigid injection product (5) and of the sheath (4); and the residual stress in the metal reinforcement (1; 2; 3) of the cable (6).

8. Device (11) according to one of claims 4 to 7, wherein the first value range is included in the interval [-0.5.106; -25.106] and / or the second value range is included in the interval [-5.106; -120.106].

9. Device (11) according to one of claims 1 to 8, in which a cover fixed on the sheath (4) protects the measuring device.

10. Device (11) according to one of claims 1 to 9, in which the gauge sensor (25) produces signals proportional to the microdeformations of the cable with a coefficient of proportionality between 12 and 25 qV / 106.

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

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

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

14. Device (11) according to one of claims 1 to 12 in combination with claim 3, in which each support is fixed to an adjustable clamping collar, itself preferably fixed to the sheath (4) by means of several screws (16).

15. Device (11) according to one of claims 1 to 14, in which 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.

16. Device (11) according to one of claims 1 to 15 in combination with claim 3, in which 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.

17. 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 - sequential acquisition of the microdeformation of the cable (6) with the monitoring device (11).

18. A method according to claim 17, further comprising transmitting 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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