DEVICE FOR DETECTING WIRE BREAK(S) IN AT LEAST ONE CABLE OF A CIVIL ENGINEERING STRUCTURE

Abstract

This wire break detection device (20) in at least one cable (10) of a civil engineering structure comprises: – a set of acoustic sensors (14a) intended to be fixed on a cable (10) or on anchor points (11, 12) of the cable (10) so as to receive an acoustic wave when a wire or strand of the cable (10) breaks; the acoustic sensors (14a) being capable of capturing this acoustic wave; and – an analysis unit (17) capable of receiving detection information of said acoustic wave by the acoustic sensors (14a) and of locating a wire break in the cable (10) according to the locations of the acoustic sensors (14a) which detected the acoustic wave.The acoustic sensors (14a) are grouped into clusters (16a), each cluster (16a) comprising a monitoring unit (15) equipped with: – a signal acquisition card for the signals from the acoustic sensors (14a); – a memory (18) for recording and time-stamping the signals from the acoustic sensors (14a) for a predetermined period before and after exceeding an acoustic vibration threshold; and – means for transmitting the recorded signals to the analysis unit (17); the analysis unit (17) being capable of receiving all the signals recorded by the different monitoring units (15) of the same cable (10) and of characterizing and locating a wire break based on the shape of the signals. Figure for the abbreviation: Fig 1.

Description

Title of the invention: DEVICE FOR DETECTING WIRE BREAK(S) IN AT LEAST ONE CABLE OF A CIVIL ENGINEERING STRUCTURE Scope of the invention

[0001] The invention belongs to the field of civil engineering structures, typically engineering works incorporating one or more cables, such as suspension bridges, cable-stayed bridges and internal or external prestressed structures, cable structures of stadium roofs or large facilities receiving the public: concert hall, gymnasium, etc.

[0002] More specifically, the invention aims at monitoring such structures to detect the breakage of a wire in at least one cable in order to anticipate a need for intervention on the cable and improve the safety of the associated engineering structure.

[0003] The invention relates more specifically to the acoustic monitoring of at least one cable, for example with the CASC method, an acronym in the technical field considered to designate "Acoustic Control for Cable Monitoring".

[0004] The invention relates more specifically to the acoustic instrumentation of at least one cable. Prior state of the art

[0005] Cable monitoring has relied since the 1970s on the development of methods detecting the acoustic wave of the rupture, the historical example in France being the development of the CASC system, acronym for "Acoustic Control for Cable Monitoring" - in the 1970s by the Central Laboratory of Bridges and Roads (LCPC).

[0006] The CASC method enables the detection and localization of breaks in the wires used in structural cables. This method utilizes the energy and acoustic waves generated by the wires when they break. More specifically, this method is based on the observation that a break in a wire under tension releases energy, generating an acoustic wave that propagates along the cable at a specific speed. Thus, by using an array of acoustic sensors placed on the cable under tension, it is possible to detect the propagation of the acoustic wave at several positions along the cable on either side of the wire break point, and to locate the source of the acoustic wave—that is, the wire break point—by triangulation.

[0007] It follows that, in order to obtain effective triangulation, it is necessary to precisely detect the times of propagation of the acoustic wave for different positions. However, the propagation of sound in a live cable of an engineering structure takes place typically at a very high speed, approximately 5000 meters per second.

[0008] It is therefore necessary to implement a system enabling very precise detection of the times of passage of the acoustic wave in order to obtain an effective triangulation of the breaking point of the wire.

[0009] To this end, document EP 0 988 539 proposes using a network of acoustic sensors fixed to one or more cables of an engineering structure and connected to a central analysis unit by means of an electrical detection network. More specifically, each sensor is configured to detect when an acoustic vibration threshold is exceeded and to close a switch in the electrical detection network when such an exceedance is detected.

[0010] In the electrical detection network, each sensor is associated with a resistor of a specific value, such that closing the switch associated with a sensor changes the voltage on the electrical detection network according to the value of the resistance associated with the sensor. Thus, the analysis unit can measure the voltage on the electrical detection network and determine which switch is closed by the change in voltage on the electrical detection network.

[0011] This implementation theoretically makes it very easy to detect which switch is closed at each measurement time increment of the analysis unit. By knowing the position of the sensors associated with these switches, it is therefore possible to model the propagation of the acoustic wave and obtain an effective triangulation of the wire's breaking point.

[0012] In real-world situations, this implementation nevertheless presents a problem with the efficient transmission of information from the sensors to the analysis unit. Indeed, the switching time varies from one switch to another, and obtaining a clear signal at the analysis unit requires high-performance coaxial cables between the sensors and the analysis unit to limit the appearance of spurious signals that could cause a change in voltage and therefore incorrect detection of the closed switch.

[0013] It follows that the implementation time for such a solution on an engineering structure, such as a bridge, typically requires a day's work to properly install and fix all the sensors and cables necessary for the efficient transmission of information.

[0014] Furthermore, the solution in document EP 0 988 539 also presents risks of incorrect detection due to the characterization of a break based solely on crossing an acoustic vibration threshold. Indeed, an acoustic wave can be transmitted in a cable through mechanical friction, during strong winds, during a bridge accident, or when an object collides with the cable, without these events causing a break in a strand of the cable. With the solution of the document EP 0 988 539, these events can generate the issuance of a false alert and a rupture search phase can be initiated unnecessarily.

[0015] The technical problem of the invention is therefore to obtain a wire break detection device in at least one cable of a civil engineering structure with effective detection and easy to install on an engineering structure. Description of the invention

[0016] The invention consists of deploying a modular architecture of sensors, grouped into clusters, each cluster having its own supervisor managing local acquisition and storage before transmission, notably digitally, i.e., wirelessly, to the analysis unit. This architecture provides the system with great flexibility in its implementation and evolution, since the addition of clusters is unlimited. This architecture also allows for substantial savings in components, particularly cabling.

[0017] To address this technical problem, the invention proposes to capture, record, and analyze all signals emitted by acoustic sensors following the exceeding of an acoustic vibration threshold, for a predetermined duration. The analysis unit can thus compare the shape of the signals captured by different acoustic sensors within the same time range with signals expected for a wire break event. Therefore, the analysis unit can distinguish a wire break from another event causing cable vibration, thereby limiting the risk of false detection.

[0018] This solution involves transmitting a large amount of information to the analysis unit. To achieve this, the invention proposes forming clusters of acoustic sensors, each sensor cluster comprising a supervisory unit equipped with a signal acquisition card for the signals from the sensors and a memory for recording and time-stamping the signals in order to transmit them to the analysis unit.

[0019] Thus, the analysis unit can subsequently retrieve the time-stamped signals to search for events analogous to a break in a wire of a cable in the set of signals captured by the different clusters without it being necessary to carry out this analysis in real time.

[0020] In addition, the analysis unit now obtains precise information on the shape of the signals from the sensors to characterize whether or not a wire in a cable has broken.

[0021] The invention therefore abandons the principle of a centralized architecture. This abandonment, however, encounters two obstacles: - Synchronization of the different clusters: by relinquishing timestamping to the central unit, which combines the roles of supervisor and analysis unit, it is necessary to perform very precise synchronization of the different clusters in order to locate the events with the required accuracy, at least equal to that of previous systems; - the size of each cluster component, particularly the module acting as the supervisor. Indeed, in common situations such as cable-stayed bridges, the cluster has no attachment point other than the cable itself. However, implementing a standard-sized enclosure (several tens of centimeters for the largest dimension) would be completely unacceptable for this type of structure: wind resistance, alteration of the cable's dynamic behavior that could lead to unwanted vibrations. It is therefore essential that integrating the supervisor function into each cluster does not generate a significant increase in size compared to a conventional sensor, such as an accelerometer. The conventional supervisory components used in previous systems do not meet this size requirement.

[0022] In order to address this problem, the invention provides: - that the signals from the sensors constituting a cluster are synchronized by a multi-channel analog-to-digital conversion card, - that with regard to synchronization between clusters: a synchronization procedure by superimposing two successive clusters is planned, instead of synchronization at the global system level. This pairing is achieved by overlapping sensors between two clusters; - that with regard to size, a miniaturized solution combining the sensor function and the supervisor function on one element of the cluster is preferred.

[0023] Thus, the invention relates to a wire break detection device in at least one cable of a civil engineering structure, comprising: - a set of acoustic sensors intended to be fixed to a cable or to cable anchor points so as to receive an acoustic wave when a wire of the cable breaks, said acoustic sensors being capable of capturing this acoustic wave; and - an analysis unit capable of receiving detection information for said acoustic wave from the acoustic sensors and of locating a break in a cable wire based on the locations of the acoustic sensors that detected the acoustic wave.

[0024] The invention is characterized in that the acoustic sensors are grouped into clusters, each cluster comprising a monitoring unit equipped with: - a signal acquisition card for the signals from the acoustic sensors; - a memory capable of recording and time-stamping signals from acoustic sensors for a predetermined period before and after an acoustic vibration threshold is exceeded; and - means of transmitting the recorded signals to the analysis unit.

[0025] According to the invention, the analysis unit is capable of receiving all recorded signals by the different monitoring units of the same cable and to characterize and locate a break in a wire based on the shape of the signals.

[0026] For the purposes of the invention, a "cluster" is a group of a small number of objects, and in this case, a small number of acoustic sensors. For example, a cluster according to the invention may comprise up to eight acoustic sensors, one of which may be integrated into the monitoring unit.

[0027] The cluster is preferably small to limit the complexity of installing the cables connecting the acoustic sensors to the monitoring unit. Typically, the maximum length between the acoustic sensors in a cluster can be 200 meters.

[0028] Grouping a small number of acoustic sensors with a monitoring unit simplifies the installation of the acoustic sensors. It is no longer necessary to run coaxial cables between each acoustic sensor and the analysis unit, since the monitoring unit is now used to transmit signals to the analysis unit, for example, using wireless communication.

[0029] Analysis of the aggregated signals from several clusters by the analysis unit makes it possible to obtain particularly effective detection of a wire break in at least one cable of a civil engineering structure. Experimentally, it was possible to triangulate the position of a wire break with an average detection accuracy of 20 centimeters.

[0030] To achieve this, the acquisition card of the supervisory unit preferably has a sampling frequency of at least 50 kHz, allowing for particularly efficient detection and localization to within 20 centimeters.

[0031] Furthermore, the monitoring unit preferably includes a watchdog. This watchdog allows the system to be monitored for proper operation and, if necessary, to be sequentially restarted so that the monitoring unit is always able to record signals emitted by the acoustic sensors.

[0032] As regards the transmission means of the supervisory unit, they are preferably made up of wireless communication means, for example a 4G modem router. Thus, it is not necessary to run data cables between the supervisory unit and the analysis unit.

[0033] The acoustic sensors and the monitoring unit are electrically powered. Furthermore, in the event of a failure of this power supply, such as resulting from a temporary interruption, a battery can be integrated into the monitoring unit and the acoustic sensors.

[0034] The acoustic sensors may consist of passive components or be powered by the supervisory unit.

[0035] For example, acoustic sensors consist of MEMS type sensors for microscopic electromechanical systems or "Micro Electro Mechanical System" in the Anglo-Saxon literature.

[0036] Preferably, to obtain relevant signals, the acoustic sensors incorporate an acoustic accelerometer capable of detecting accelerations up to plus or minus 100 g, i.e. about 1000 m / s2, with a bandwidth between 100 Hz and 30 kHz.

[0037] In addition to the acoustic accelerometer, the sensors can also perform other measurements to obtain information on the stresses experienced by the structure at the level of the various cables. These additional measurements can also be transmitted to the analysis unit and used in conjunction with overall measurements, such as meteorological or seismic readings. To this end, at least one acoustic sensor incorporates a temperature and / or humidity sensor.

[0038] The monitoring unit and acoustic sensors can be attached by any means. For example, the monitoring unit and acoustic sensors can be glued, screwed, or bolted to the cables or to the cable anchor points. Preferably, the monitoring unit and acoustic sensors incorporate a magnetic support for attaching them to the cable. These magnetic supports can be mounted directly onto the cover of the monitoring unit or the acoustic sensors, or attached to the cover with clamps.

[0039] By using magnetic mounts, clusters less than 200 meters long, and wireless communication between the monitoring unit and the analysis unit, the wire break detection device of the invention can be installed very quickly on an entire civil engineering structure. Typically, it is now possible to place all the acoustic sensors in 30 minutes, whereas existing solutions require at least a day of installation, particularly for attaching the connecting cables of all the acoustic sensors to the analysis unit.

[0040] The invention thus makes it possible to obtain a wire break detection device in at least one cable of an engineering structure with effective and easy-to-install detection. Brief description of the figures

[0041] The manner in which the invention can be implemented and the advantages arising therefrom will be more apparent from the following example of implementation, given by way of illustration and not limitation, in support of the attached figures.

[0042] Figure 1 is a schematic representation of a wire break detection device in at least one cable of a civil engineering structure according to a first mode of realization of the invention;

[0043] Figure 2 is a schematic representation of a wire break detection device in at least one cable of a civil engineering structure according to a second embodiment of the invention; and

[0044] The [Fig.3] is a flowchart of the detection steps carried out on the supervisory unit and the analysis unit of the [Fig.1]. Detailed description of the invention

[0045] As mentioned above, [Fig. 1] is a schematic representation of a civil engineering structure, in this case a partially shown box girder bridge. In a box girder bridge, at least one prestressing cable extends through several adjacent box girders. [Fig. 1] more specifically illustrates a box girder 13 within which a prestressing cable 10 extends. At the lateral ends of the box girder 13, two anchor points 11 and 12 allow the cable 10 to be fixed by embedding the concrete structure of the box girder 13 around the cable 10.

[0046] To detect a break in at least one wire in this cable 10, the invention proposes using a detection device 20 comprising acoustic sensors 14a and a monitoring unit 15, integrated into the housing 13, as well as a remote analysis unit 17. For example, the analysis unit 17 can be located in a control room near the bridge. Alternatively, the analysis unit 17 can be decentralized and accessible via the Internet.

[0047] With regard to the elements integrated into the box 13, in the embodiment of [Fig.1], three acoustic sensors 14a are directly fixed on the cable 10. In the embodiment of [Fig.2], three acoustic sensors 14a are directly fixed on the cable 10 and two acoustic sensors 14b are fixed on the anchor points 1112.

[0048] These acoustic sensors 14a-14b enable the detection of the propagation of an acoustic wave resulting from the breaking of a wire in the cable 10. To this end, each of these acoustic sensors can consist of a MEMS-type accelerometer with a detection capacity for accelerations up to ±100 g and a bandwidth between 100 Hz and 30 kHz, for example, a bandwidth of 23 kHz. These acoustic sensors 14a-14b can also perform other measurements, such as a voltage-measuring accelerometer, a temperature sensor, or a humidity sensor.

[0049] These various elements are conventionally integrated into a housing designed to protect the electromechanical components from moisture. To attach this housing to the cable 10 or to the anchor points 11 and 12, it is possible to fix the housing by gluing, screwing, or any other mechanical means of fastening. Furthermore, it is It is also possible to use a housing with magnetic support means so as to fix the acoustic sensors 14a-14b by magnetization onto the cable 10.

[0050] The data from these acoustic sensors 14a-14b are transmitted by a wire to the monitoring unit 15 also integrated in the housing 13. In the example of [Fig.1], this monitoring unit 15 integrates an acoustic sensor 14a fixed on the cable 10. Thus, the monitoring unit 15 can be fixed via the acoustic sensor 14a on the cable 10.

[0051] This monitoring unit 15 includes a signal acquisition card for the acoustic sensors 14a-14b and a memory 18, for example an SD card or RAM or ROM memory. The acquisition card preferably corresponds to an electronic board integrating a processor or a microcontroller. This processor or microcontroller is configured to analyze the signals from the acoustic sensors 14a-14b and to detect whether a signal exceeds a threshold acoustic vibration value. If so, the monitoring unit 15 records the signal captured by the acoustic sensor 14a-14b in the memory 18. Preferably, this acquisition card has a sampling frequency greater than 50 kHz, for example 57 kHz at 24 bits.

[0052] Typically, the memory records the signals from the acoustic sensors after the threshold has been exceeded. However, advantageously, it can save a few tens of milliseconds of signal before the threshold is exceeded, in order to reliably record the acoustic wavefront. Indeed, this wavefront provides important information for characterizing the wave.

[0053] Furthermore, this supervisory unit 15 also includes means for transmitting signals recorded in memory 18 to the analysis unit 17. These transmission means 19 can be integrated on the acquisition card.

[0054] As illustrated in [Fig. 3], the monitoring unit 15 implements a first step 30 in which the acquisition card retrieves the signals from the acoustic sensors 14a-14b. In a second step 31, when the monitoring unit 15 detects that one of the signals from the acoustic sensors 14a-14b is greater than the acoustic vibration threshold value, the signal is recorded in the memory 18. This threshold value can be set according to each cable during the installation of the device 20.

[0055] The recording is associated with a timestamp of the signal from the acoustic sensor 14a-14b and is carried out for a predetermined duration, for example, for two seconds after the detection of the exceeding of the acoustic vibration threshold. This recording duration can also be set according to each cable during the installation of the device 20.

[0056] During this phase of recording and time-stamping the signals, a watchdog 34. Check that the system is working correctly.

[0057] When all the signals from the acoustic sensors 14a-14b have been captured after the occurrence of an event in which at least one signal exceeded the acoustic emission threshold, the supervisory unit 15 continues to perform the first step 30 of signal acquisition.

[0058] Furthermore, the signals captured and recorded in memory 18 are transmitted periodically, for example hourly, to the analysis unit 17 via the transmission means 19. In this transmission step 33, the watchdog 34 continuously performs its function of verifying the correct operation of the system. The transmission of information via the transmission means 19 can be carried out wirelessly, for example using a 4G modem router.

[0059] The elements integrated into the caisson 13 form a cluster 16a ([Fig.1]) or 16b ( [Fig.2]) so that the civil engineering structure is instrumented by a set of juxtaposed and independent clusters 16a-16b.

[0060] These clusters 16a-16b are independent insofar as no data transfer is necessary between two supervisory units 15, even if the clusters 16a-16b can be powered by the same electrical network. Thus, each supervisory unit 15 communicates independently with the analysis unit 17.

[0061] The acoustic sensors 14a-14b of these different clusters 16a-16b can be placed at a distance D2 between two acoustic sensors 14a-14b of between 10 and 30 meters, for example 20 meters. Preferably, the maximum length of the clusters 16a-16b is less than a distance DI of 200 meters, in order to limit the constraints of attenuation and electromagnetic interference in the signals transmitted between the acoustic sensors 14a-14b and the monitoring unit 15. Preferably, each cluster 16a-16b comprises up to eight acoustic sensors 14a-14b. Furthermore, acoustic sensors 14a-14b of a first cluster 16a-16b can be redundant with acoustic sensors 14a-14b of a second cluster 16a-16b.

[0062] The analysis unit 17 includes means 21 for receiving signals transmitted by the various monitoring units of the different clusters 16a-16b. When these signals are received by the analysis unit 17, it records them in a first event memory 23, and an analysis element 22 checks whether the shape of the captured signals is analogous to a break in a wire. To do this, this analysis element 22 preferentially uses a database 24 containing expected signal shapes for different events in order to compare the captured signals with these expected signals for different events. These expected signals for different events can be modeled numerically or captured experimentally for each cable during the installation of the device 20 or upstream of this installation.

[0063] It is thus possible to characterize whether the signals captured reveal an event of wire breakage, rather than an impact on the bridge, mechanical friction or the presence of a violent wind likely to generate vibrations in the cable 10.

[0064] Furthermore, the analysis unit 17 can also integrate means of transmitting an alert 25 when a wire break is detected and located.

[0065] More specifically, as illustrated in [Fig.3], the analysis unit 17 can implement a first step 40 in which the signals are retrieved and stored in the memory 23, followed by a second step 41 in which the shape of the signals is analyzed to look for whether the signals of the same time period correspond to a wire break.

[0066] To do this, when the signals are stored in memory 23, the analysis unit 22 can search for all signals whose timestamp falls within a predetermined window, for example, a three-second window. All of these signals are then associated and processed to verify that their shape corresponds to an expected event, such as a broken wire.

[0067] The analysis unit 22 can thus detect several types of events depending on the shape of the signals.

[0068] Furthermore, when the analysis unit 22 detects a wire break event, it also searches for the location of the break in the cable 10. To do this, the analysis unit 22 preferentially isolates the wavefront of each signal, that is, the first moments of exceeding the acoustic vibration threshold, in order to determine the precise timestamp of this wavefront. By knowing the position of the acoustic sensor 14a-14b associated with this wavefront, it is possible to model the propagation of the acoustic wave inside the cable 10 and to locate the break point based on this detected propagation.

[0069] When the analysis unit 22 has identified a break in one or more wires and located the point of break, a step 42 preferentially requires an operator to confirm the presence of this break by manual analysis of the signals or by on-site or visual inspection, for example by means of cameras installed on the bridge or by the use of other analysis devices, such as modal accelerometers used by intentionally vibrating the cable 10.

[0070] When human analysis has concluded that there is indeed a break at the detected location, an alert can be transmitted to a bridge operator, in step 43, in order to carry out any necessary renovation work.

[0071] Furthermore, the signals for which a break is confirmed can be stored in database 24, which incorporates expected signal patterns for different events. This database 24 can be shared between several engineering structures with cables and similar structures.

[0072] Thus, the invention makes it possible to obtain a wire break detection device 20 that is simple and quick to implement since the clusters 16a-16b are easier to deploy than the solutions of the prior art.

[0073] In real test, the invention enabled high repeatability of wire break detection measurements with a location exhibiting a particularly low standard deviation of 20 centimeters.

[0074] Furthermore, by efficiently dimensioning the protective housings of the acoustic sensors 14a-14b and the supervisory unit 15, it is also possible to obtain the clusters 16a-16b which are particularly robust and resistant in the event of a cable 10 breaking, so that they can be reused even after such a break.

Claims

Demands

1. A wire break detection device (20) in at least one cable (10) of a civil engineering structure, comprising: - an array of acoustic sensors (14a-14b) intended to be fixed to a cable (10) or to anchor points (11, 12) of the cable (10) so as to receive an acoustic wave upon a break in a wire or strand of the cable (10); the acoustic sensors (14a-14b) being capable of capturing this acoustic wave; and - an analysis unit (17) capable of receiving detection information of said acoustic wave by the acoustic sensors (14a-14b) and of locating a break in a wire of the cable (10) according to the locations of the acoustic sensors (14a-14b) which detected the acoustic wave; characterized in that the acoustic sensors (14a-14b) are grouped by cluster (16a-16b), each cluster (16a-16b) comprising a supervisory unit (15) equipped with: - a card for acquiring signals from the acoustic sensors (14a-14b);- a memory (18) allowing the recording and time-stamping of signals from acoustic sensors (14a-14b) for a predetermined duration before and after exceeding an acoustic vibration threshold; and - means for transmitting (19) the recorded signals to the analysis unit (17); the analysis unit (17) being capable of receiving all signals recorded by the different monitoring units (15) of the same cable (10) and of characterizing and locating the break in a wire according to the shape of the signals.

2. Wire break detection device according to claim 1, wherein the acquisition card of the supervisory unit (15) has a sampling frequency of at least 50 kHz.

3. Wire break detection device according to claim 1 or 2, wherein the supervisory unit (15) includes a watchdog (34).

4. Wire break detection device according to any one of claims 1 to 3, wherein the transmission means (19) of the supervisory unit (15) are made up of wireless communication means, including a 4G modem router.

5. Wire break detection device according to any one of claims 1 to 4, wherein each cluster (16a-16b) comprises up to eight acoustic sensors (14a-14b), one acoustic sensor (14a-14b) being able to be integrated into the supervisory unit (15).

6. Wire break detection device according to any one of claims 1 to 5, wherein the acoustic sensors (14a-14b) of a cluster (16a-16b) are separated by a maximum length (Dl) of 200 meters.

7. Wire break detection device according to any one of claims 1 to 6, wherein at least one acoustic sensor (14a-14b) incorporates an acoustic accelerometer capable of detecting accelerations up to plus or minus 100 g with a bandwidth between 100 Hz and 30 kHz.

8. Wire break detection device according to any one of claims 1 to 7, wherein at least one acoustic sensor (14a-14b) incorporates a temperature and / or humidity sensor.

9. Wire break detection device according to any one of claims 1 to 8, wherein the monitoring unit (15) and at least one acoustic sensor (14a-14b) incorporate a magnetic support for fixing the monitoring unit (15) and the acoustic sensor (14a-14b) to the cable (10).

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