Method and system for structural diagnosis of concrete railway sleepers

Abstract

TITLE: Method and system for structural diagnosis of concrete railway sleepers This structural diagnosis method comprises four steps, namely an application step, in which a mechanical stress is applied by impact to a concrete railway sleeper (2, 3) to be diagnosed, a detection step, in which a vibration generated by the mechanical stress and propagating in the diagnosed sleeper is detected on the surface of the diagnosed sleeper and is transformed into a vibrational time signal, a processing step, in which the vibrational time signal is electronically processed so as to obtain a frequency spectrum, and an analysis step, in which the frequency spectrum is compared with a reference to deduce a characterization of structural damage to the diagnosed sleeper. Figure for abstract: Figure 1

Description

Title of the invention: Method and system for structural diagnosis of concrete railway sleepers

[0001] The present invention relates to a method and system for structural diagnosis of concrete railway sleepers.

[0002] Railway sleepers are pieces laid across a railway track, on which the rails are fixed so as to maintain the gauge and the inclination of the latter, and which transmit the loads moving on the rails to a ballast on which the railway sleepers rest. We are more specifically interested here in so-called "concrete" sleepers, these sleepers can be either monobloc, in which case they are made up of a single concrete piece extending over the entire longitudinal dimension of the sleeper, or bi-bloc, in which case they are made up of two concrete end blocks, connected to each other by a central metal spacer.

[0003] Concrete railway sleepers have a long service life, which can reach several decades. However, in certain circumstances, these railway sleepers exhibit structural damage that is more marked than their expected normal wear. The causes or reasons for this situation are diverse and lead to equally varied structural consequences: without this being exhaustive, we can cite contact erosion between the underside of the sleeper and the ballast, spalling and similar damage linked to transport and / or maintenance operations, overstress cracking in service, chemical cracking following alkali-aggregate reactions, thermal shrinkage cracking during the manufacture of the sleepers, etc.In any case, it is difficult to assess non-destructively the structural damage of sleepers, typically by simple visual observation in situ, i.e. directly on the railway: in fact, the observation conditions are often poor and a large part of the sleepers is hidden by the ballast or under the rails, unless the sleeper is removed from the railway and, if necessary, examined later in a test laboratory, which is particularly tedious. Moreover, even if cracks are observable on the surface of the sleepers, it is almost impossible to reliably deduce whether the corresponding structural damage is critical for the sleeper, to the point of requiring its emergency replacement. More generally, there is a real need to be able to structurally diagnose concrete railway sleepers in situ, in order to effectively manage their maintenance in the broad sense.

[0004] The aim of the present invention is to propose a method and a system, which make it possible to structurally diagnose concrete railway sleepers of reliably, quickly and easily, if necessary directly on the railway.

[0005] To this end, the invention relates to a method for structural diagnosis of concrete railway sleepers, comprising:

[0006] - an application step, in which a mechanical stress is applied by impact on a concrete railway sleeper to be diagnosed,

[0007] - a detection step, in which a vibration generated by the stress mechanical and propagating in the diagnosed crosspiece is detected on the surface of the diagnosed crosspiece and is transformed into a vibrational time signal,

[0008] - a processing step, in which the vibrational time signal is electro-processed only so as to obtain a frequency spectrum, and

[0009] - an analysis step, in which the frequency spectrum is compared to a reference to deduce a characterization of structural damage to the diagnosed sleeper.

[0010] The invention also relates to a system for structural diagnosis of concrete railway sleepers, comprising:

[0011] - at least one impactor adapted to apply a stress by impact mechanics to a concrete railway sleeper to be diagnosed,

[0012] - at least one sensor adapted both to detect, on the surface of the diag cross-member nosticated, a vibration generated by mechanical stress and propagating in the diagnosed crosspiece, and to transform the vibration into a vibratory time signal,

[0013] - an electronic processing unit, adapted to process the time signal vi bratory so as to obtain a frequency spectrum, and

[0014] - analysis means, adapted to compare the frequency spectrum with a reference to deduce a characterization of structural damage to the diagnosed sleeper.

[0015] One of the ideas underlying the invention is to seek to provide a characterization of structural damage to a concrete railway sleeper, from a simple non-destructive impact, applied to the sleeper to be diagnosed, in particular in situ, that is to say directly on the railway track where the sleeper is used, which is particularly simple and practical to implement. The characterization of structural damage is dimensionless, in the sense that it does not quantify a geometric dimension or a dimensional parameter of the diagnosed sleeper, but this characterization of structural damage associates with the diagnosed sleeper a structural state among several states.Thus, the characterization of structural damage provides advantageous information on, with a controlled margin of error, (i) the presence of at least one structural defect relating to one or more given types of defect and / or (ii) structural wear that is different, and therefore potentially more severe, from wear. nominal structural. To do this, the invention provides that the vibration generated in the sleeper by the aforementioned impact is detected on the surface of the sleeper and transformed into a vibrational time signal, in practice by means of one or more ad hoc sensors. This signal is then processed, in particular by an ad hoc electronic processing unit, to move from the time domain to a frequency domain, in the form of a frequency spectrum, advantageously provided in situ. The analysis of the frequency spectrum then makes it possible to determine the characterization of structural damage to the diagnosed sleeper, by comparison with a predetermined reference which is for example obtained from a reference sleeper, typically new or considered healthy, or from the prior statistical processing of a homogeneous population of sleepers.This analysis of the frequency spectrum can either be carried out partially by a human operator, in particular to whom the frequency spectrum and the aforementioned reference are displayed on screen, advantageously in situ, or carried out entirely by ad hoc computer means, where appropriate partially remote, as explained in detail below. In all cases, the corresponding analysis means are particularly practical and make it possible to control the reliability of the diagnosis provided, that is to say the characterization of structural damage which is deduced by or thanks to these analysis means.

[0016] According to advantageous optional characteristics of the method and / or the structural diagnostic system in accordance with the invention, taken in isolation or in all technically possible combinations:

[0017] - the application step, the detection step and the processing step, as well as at least part of the analysis stage is implemented on railway tracks.

[0018] - in the analysis step, the frequency spectrum and a reference spectrum constituting said reference are displayed to a human operator who deduces, by visual observation, the characterization of structural damage to the diagnosed sleeper.

[0019] - in the analysis step, (i) the frequency spectrum is compared by computer to a reference spectrum constituting said reference, by calculating a distance score which is representative of a mathematical distance between the frequency spectrum and the reference spectrum, and (ii) the characterization of structural damage is determined from the calculated distance score.

[0020] - in the analysis step, (i) the frequency spectrum is compared by computer to several reference spectra constituting said reference, by calculating distance scores which are respectively representative of mathematical distances between the frequency spectrum and the reference spectra, and (ii) the characterization of structural damage is determined from the calculated distance scores.

[0021] - in the application step, the mechanical stress is applied to the cross member at diagnose by an impact having an energy of less than 3 joules, preferably in- less than 1 joule.

[0022] - in the processing step, the vibrational time signal is processed so as to extract a significant part, before applying a band-pass filter to this significant part and then a mathematical transformation on a frequency domain to obtain the frequency spectrum.

[0023] - the bandpass filter has a low cutoff frequency substantially equal to 3,000 Hz, preferably 3,500 Hz, and a high cut-off frequency substantially equal to 20,000 Hz, preferably 15,500 Hz.

[0024] - the impactor(s), the sensor(s) and the electronic processing unit, as well that at least part of the analysis means form a portable hardware set, usable by a human operator on the railway.

[0025] The invention will be better understood on reading the description which follows, given solely by way of example and made with reference to the drawings in which: - [Fig.l] [Fig.l] is a schematic perspective view of two concrete railway sleepers and of a structural diagnostic system for such sleepers; - [Fig.2] [Fig.2] is a flowchart of a structural diagnostic process, implemented implemented by the structural diagnostic system of [Fig.l]; - [Fig.3] [Fig.3] is a schematic section of part of the system of structural diagnosis of [Fig.l], used on a sleeper, this section being schematically associated with signals produced by the structural diagnosis system; - [Fig.4] [Fig.4] includes inserts a) and b) corresponding respectively to frequency spectrum diagrams implemented in the structural diagnostic method, as well as an insert c) corresponding to a diagram of a distance score, also implemented in the structural diagnostic method; and - [Fig.5] [Fig.5] includes two inserts a) and b) which correspond respectively to diagrams including a representation space, implemented in the structural diagnosis process.

[0026] In [Fig.l] is shown a structural diagnostic system 1 for non-destructively controlling the concrete structure of concrete railway sleepers, such as sleepers 2 and 3 shown in [Fig.l] as examples.

[0027] The sleeper 2 is a so-called monobloc sleeper and comprises a concrete body 2.1 extending continuously from one to the other of two ends of the sleeper 2, opposite one another in a longitudinal direction of the sleeper 2. The concrete body 2.1 includes two end portions 2.2 and 2.3, which are opposite one another in the longitudinal direction of the sleeper 2, as well as an intermediate portion 2.4, which connects the end portions 2.2 and 2.3 to one another and which is possibly thinned with respect to the end parts 2.2 and 2.3. The sleeper 2 is provided, on each of its end parts 2.2 and 2.3, with arrangements 2.5 dedicated to the fixing of a railway rail, not shown in the figures. The sleeper 2 optionally comprises a reinforcement of metal wires, embedded in the concrete body 2.1.

[0028] The sleeper 3 is a so-called two-block sleeper and comprises two concrete blocks 3.1 and 3.2, which form two end parts of the sleeper 3, opposite one another in a longitudinal direction of the sleeper 3, and which are connected to one another by a metal spacer 3.3. In a similar manner to the sleeper 2, the sleeper 3 is provided, on each of its concrete blocks 3.1 and 3.2, with arrangements 3.4 dedicated to the fixing of a railway rail.

[0029] The specificities of the sleeper 2 and the sleeper 3 are not limiting since their structure is mainly, but not necessarily exclusively, made of concrete, like the concrete body 2.1 for the sleeper 2 and the concrete blocks 3.1 and 3.2 for the sleeper 3. Thus, the concrete of these sleepers 2 and 3 is for example reinforced, prestressed or post-stressed.

[0030] In all cases, in a usual manner in the field and without this being shown in [Fig. 1], the sleeper 2 and the sleeper 3 are used indifferently in a railway which comprises both a support, typically a ballast, on which rests a group of sleepers, such as sleepers 2 and 3, distributed regularly in a longitudinal direction of the railway, and rails, which extend in length in the longitudinal direction of the railway and which are fixed to the sleepers, at the level of dedicated arrangements of the latter, such as arrangements 2.5 for sleeper 2 and arrangements 3.4 for sleeper 3.

[0031] Whatever the specificities of sleepers 2 and 3, their concrete structure necessarily evolves over time, undergoing structural damage. This structural damage results from wear, which can be described as normal, of sleepers 2 and 3, linked in particular to the stresses that the sleepers transmit between the ballast and railway equipment rolling on the rails of the railway. As mentioned in the introductory part of this document, under certain conditions of use and / or due to certain manufacturing conditions of sleepers 2 and 3, the structural damage to these sleepers is likely to be greater than normal wear. In particular, cracks or other structural defects are likely to appear and substantially and rapidly degrade the structural damage.If such structural defects appear in the concrete structure of sleepers 2 and 3, the lifespan of these sleepers may be less than that of the same sleepers but exempt from such structural defects.

[0032] In order to characterize the actual structural damage of concrete railway sleepers, such as sleepers 2 and 3, while these sleepers are used in a track railway, it is proposed to implement a structural diagnostic method, which will be described in detail below. In the following, this structural diagnostic method is applied for example to sleeper 2 but it is understood that this structural diagnostic method is equally applicable to sleeper 3. An embodiment of this structural diagnostic method is illustrated schematically in [Fig.2] and is advantageously implemented by the structural diagnostic system 1, suitably controlled by a human operator.

[0033] As illustrated in [Fig. 2], the structural diagnostic method comprises four main steps which follow one another, namely an application step 101, a detection step 102, a processing step 103 and an analysis step 104. Before describing in detail each of these four steps in succession, it will be noted that the application step 101, the detection step 102 and the processing step 103, as well as at least part of the analysis step 104 are advantageously implemented in situ, that is to say directly on the railway, in particular while the concrete sleepers of the latter are left as they are, in other words maintained in an operational situation within the railway.

[0034] In the application step 101, a mechanical stress is applied by impact to a concrete railway sleeper to be diagnosed, here the sleeper 2, so as to, as schematically illustrated in [Fig. 3], generate a vibration V in the sleeper 2, more precisely in the concrete structure of the latter, here the concrete body 2.1. Once generated by the mechanical impact stress, the vibration V propagates in the sleeper 2, in particular through the concrete structure of the latter, here the concrete body 2.1, while being reflected by the external surfaces of the sleeper 2, as well as by internal defects or, more generally, internal structural heterogeneities, such as cracks, like that illustrated in [Fig. 3] under the reference F, but also such as voids, segregation interfaces, etc.

[0035] In practice, the impact which mechanically stresses the sleeper 2 to generate the vibration V there during the application step 101 is of sufficiently low intensity so as not to damage the sleeper 2, or even to move the latter relative to the support on which the sleeper rests, typically the ballast when the application step 101 is implemented on a railway. In addition, the intensity of this impact is dimensioned so that the vibration V resulting therefrom in the concrete structure of the sleeper 2 has a wavelength appropriate to the structural damage that the structural diagnostic method aims to characterize. For this purpose, this impact has an energy advantageously less than 3 joules, preferably less than 1 joule.

[0036] For the purposes of implementing the application step 101, the structural diagnostic system 1 comprises an impactor 10 which is schematically visible in Figures 1 and 3. The impactor 10 is adapted to apply by impact the stress aforementioned mechanical to a crosspiece to be diagnosed, here to the crosspiece 2. As a non-limiting example, the impactor 10 comprises an electromagnet which controls the movement of an impact weight. Of course, other embodiments are conceivable for the impactor 10 provided that it allows mechanical stress to be applied by impact to the crosspiece 2 to generate the vibration V in the latter.

[0037] In the detection step 102, the vibration V is detected on the surface of the diagnosed crosspiece, here the crosspiece 2, and is transformed into a vibrational time signal, as illustrated schematically in [Fig. 3] in which this vibrational time signal is referenced SV. The vibrational time signal SV is thus representative of the evolution, over time, of surface movements of the concrete body 2.1, induced by the vibration V.

[0038] For the purposes of implementing the detection step 102, the structural diagnostic system 1 comprises a sensor 20 shown schematically in FIGS. 1 and 3. The sensor 20 is adapted to detect the vibration V and to transform the latter into the vibrational time signal SV. By way of non-limiting example, the sensor 20 comprises a contact microphone, with a piezoelectric transducer. Of course, other embodiments are conceivable for the sensor 20 provided that the latter emits a vibrational time signal, such as the signal SV, obtained by detection and transformation of the vibration V by this sensor.

[0039] In the embodiment envisaged in the figures, the impactor 10 and the sensor 20 are advantageously integrated into a portable tool 30 of the structural diagnostic system 1. This portable tool 30 can be controlled manually by the operator using the structural diagnostic system 1, in particular in situ. This portable tool 30 comprises, for example, a housing 31, in which the impactor 10 and the sensor 20 are arranged and which is capable of being applied against the cross-member 2 so as to bring the impactor 10 and the sensor 20 into contact with the latter, as illustrated schematically in [Fig. 3]. The portable tool 30 here also comprises a handle 32, which extends from the housing 31 and which allows the operator to control and manipulate the portable tool 30 in a practical manner. In particular, the handle 32 is provided with a manual trigger 33, the actuation of which by the operator controls the impactor 10.In practice, the shape and dimensions of the handle 32 are not limiting.

[0040] In the processing step 103, the vibrational time signal SV is electronically processed so as to obtain a frequency spectrum, illustrated schematically in [Fig. 3] under the reference SF. The frequency spectrum SF is thus representative of a spectral amplitude as a function of the frequency, typically quantified in hertz, of symbol Hz. According to an efficient and effective embodiment, during the processing step 103, the vibrational time signal SV is, at least in part, mathematically transformed on a frequency domain to have the frequency spectrum SF: the corresponding mathematical transformation is for example a Fourier transformation, in particular a fast Fourier transformation. In addition, what is subjected to the aforementioned mathematical transformation is advantageously only a part of the vibrational time signal SV, namely a filtered part, which is obtained by applying a band-pass filter to the vibrational time signal, in particular to only a significant part of this signal, extracted from the vibrational time signal using for example a threshold value applied to the amplitude of this signal. According to a preferred dimensioning which results in remarkable performances for the structural diagnosis method, the aforementioned band-pass filter has a low cut-off frequency equal to 3,000 Hz, preferably 3,500 Hz, and a high cut-off frequency equal to 20,000 Hz, preferably 15,500 Hz.

[0041] In practice, it will be noted that the absolute values ​​of the amplitude of the frequency spectrum SF, obtained at the end of the processing step 103, are not of interest for the structural diagnosis method, in the sense that these absolute values ​​are not intended to be used in this method. On the other hand, the variation of this amplitude of the frequency spectrum SF as a function of the frequency is of interest, in particular to identify one or more peaks therein, as mentioned again later.

[0042] For the purposes of implementing the processing step 103, the structural diagnostic system 1 comprises an electronic processing unit 40 which is shown schematically in FIGS. 1 and 3. The electronic processing unit 40 is adapted to process the vibrational time signal SV so as to obtain the frequency spectrum SF. The electronic processing unit 40 is advantageously adapted to successively extract a significant part of the vibrational time signal SV and apply the aforementioned bandpass filter, then the aforementioned mathematical transformation. In all cases, the embodiment of the electronic processing unit 40 is not limiting.In practice, the electronic processing unit 40 can comprise an assembly of analog electronic components, dedicated to the processing operations implemented by this electronic processing unit 40, as well as comprise a set of digital electronics, typically including a microprocessor or the like, programmed to implement the aforementioned processing operations.

[0043] In the embodiment envisaged in the figures, the electronic processing unit 40 is advantageously integrated into portable computer equipment 50, such as a tablet or a laptop or even a specific terminal. The advantage of this portable computer equipment 50 will appear a little later.

[0044] In the analysis step 104, the frequency spectrum SF is compared to a reference to deduce a characterization of structural damage to the diagnosed crossmember, here crossmember 2. Various embodiments are possible for this analysis step 104, in particular according to the nature of the aforementioned reference, as well as according to the way in which the frequency spectrum SF is compared to this reference. Before explaining this aspect of the structural diagnosis method in more detail, it will be noted that, for the purposes of implementing the analysis step 104, the structural diagnosis system 1 comprises analysis means 60 illustrated schematically in [Fig.l]. These analysis means 60 are adapted to determine the characterization of structural damage to the diagnosed crossmember, by comparing the frequency spectrum SF supplied to the analysis means 60 by the processing unit 40 to the aforementioned reference. Various embodiments for the analysis means 60 will be described in more detail below, being associated with the different embodiments of the analysis step 104, explained later.This being the case, in all cases, at least part of the analysis means 60 is advantageously computer-based, being able to process the frequency spectrum SF provided by the electronic processing unit 40. In particular, this computer-based part of the analysis means 60 includes: .

[0045] - a computer processing unit 61, which is integrated into the equipment in portable computing unit 50 and which, where appropriate, shares all or part of the digital electronics assembly of the electronic processing unit 40, and / or

[0046] - a remote computer equipment 62, such as a computer or a server, which is at even to read a transportable data medium from the portable computing equipment 50 or which is in wireless communication with this portable computing equipment 50.

[0047] In the embodiment envisaged in [Fig.l], the impactor 10, the sensor 20 and the electronic processing unit 40, as well as the computer processing unit 61 of the analysis means 60 form a portable hardware assembly, which can be used by an operator on the railway and which, here, brings together the portable tool 30 and the portable computer equipment 50.

[0048] A first embodiment of the analysis step 104 is illustrated by each of the inserts a) and b) of [Fig. 4]. In this first embodiment, the reference used in the analysis step 104 consists of a predetermined reference spectrum SR, which is represented in dotted lines on the inserts a) and b) of [Fig. 4] and which is for example stored in an ad hoc memory of the analysis means 60. In practice, this reference spectrum SR is for example acquired either by prior implementation of the application 101, detection 102 and processing 103 steps on a reference sleeper, typically a sleeper for which it is known that the structural damage corresponds to normal wear, or by prior statistical processing of results obtained by implementing the application 101, detection 102 and processing 103 steps on a population of sleepers considered to be homogeneous.

[0049] Furthermore, in the first embodiment of the analysis step 104, the spectrum of reference spectrum SR and the frequency spectrum SF, as resulting from the application 101, detection 102 and processing 103 steps applied to a sleeper to be diagnosed, such as sleeper 2, are displayed, typically on a screen of the analysis means 60, here a screen 51 integrated into the portable computer equipment 50, so that, by direct visual observation, the operator assesses the comparison between the reference spectrum SR and the frequency spectrum SF and deduces therefrom the structural damage characteristic for the diagnosed sleeper. Thus, this deduction is carried out by the operator in situ, that is to say directly on the railway. In practice, the respective displays of the reference spectrum SR and the frequency spectrum SF on the screen 51 are advantageously simultaneous and superimposed: as corresponding schematic illustrations, the frequency spectrum associated with a first sleeper to be diagnosed is represented in solid lines on the insert a) of [Fig.4], labeled El, and the frequency spectrum associated with a second crosspiece to be diagnosed is represented in solid lines on insert b) of [Fig.4], labeled E2, while on these two inserts, the reference spectrum SR is represented in dotted lines.

[0050] In practice, the characterization of structural damage is for example to determine, by the operator, that the structural damage of the diagnosed sleeper is either normal, that is to say similar to that of the reference sleeper, as in the case illustrated in insert a) of [Fig. 4], or abnormal, that is to say substantially different from that of the reference sleeper, as in the case illustrated in insert b) of [Fig. 4]. On a railway, the operator can thus quickly determine, among all the sleepers of a railway, those whose structural damage is abnormal.

[0051] A second embodiment of the analysis step 104 is illustrated by the inserts a), b) and c) of [Fig.4].

[0052] Here again, the reference used in the analysis step 104 consists of a reference spectrum, here the reference spectrum SR described above for the first embodiment.

[0053] Furthermore, in this second embodiment, the frequency spectrum SF, as resulting from the application 101, detection 102 and processing 103 steps, is compared by computer to the reference spectrum SR, by calculating a distance score which is representative of a mathematical distance between the reference spectrum SR and the frequency spectrum SF. The specificities of the calculation of this distance score are not limiting, it being emphasized that various calculation formulas are known in the art, such as the so-called DTW formulas which is the acronym for the English expression in "Dynamic Time Warping", the so-called DTW formulas relying on the difference between respective peaks of the reference spectrum and the frequency spectrum analyzed, as schematically illustrated by the double-headed arrows, schematically drawn on insert b) of [Fig.4].

[0054] In all cases, for each diagnosed sleeper, an associated distance score is calculated and then the structural damage characteristic is determined from this calculated distance score. As a schematic illustration, distance scores calculated respectively for the frequency spectrum labeled El on insert a) of [Fig.4] and for the frequency spectrum labeled E2 on insert b) of [Fig.4] are, on insert c) of [Fig.4], plotted on a distance score axis D whose zero origin corresponds to the distance score, necessarily zero, for the reference spectrum SR. It is understood that it is thus possible to assess to what extent the structural damage of a diagnosed sleeper is more or less distant from the structural damage of the reference sleeper and therefore, for example, to classify the diagnosed sleepers along a railway into two or more categories.

[0055] In practice, the calculation of the distance score of each diagnosed sleeper is advantageously carried out by an ad hoc computer program of the computer part of the analysis means 60. This amounts to saying that the analysis means 60 are configured to compare by computer the frequency spectrum of the diagnosed sleeper with a reference spectrum, by calculating a corresponding distance score, and to determine the characterization of structural damage for the diagnosed sleeper from the calculated distance score, it being noted that this determination can also be carried out by computer and / or by a human operator.

[0056] A third embodiment of the analysis step 104 is illustrated by inserts a) and b) of [Fig.5].

[0057] In this third embodiment, the reference used in the analysis step 104 consists of several reference spectra, which are individually similar to the reference spectrum SR described above in the first and second embodiments, but which are distinguished from each other by corresponding to frequency spectra respectively representative of predetermined structural damage states, which are different from each other. By way of schematic illustration, in insert a) of [Fig. 5], four structural damage states, respectively different from each other, are considered, being respectively associated with reference spectra labeled SR1, SR2, SR3 and SR4. Of course, the number of reference spectra, here equal to four, is only a non-limiting example.These four reference spectra are illustrated here in a representation space which is here two-dimensional, being defined by two orthonormal axes, namely a first distance score axis DI and a second distance score axis D2, whose respective distance score calculations are different from each other. Thus, we understand that, here, the representation space is reduced along two main axes of variation. More generally, and as re-mentioned a little later, we understand, through this example, . that it is possible to use other dimension reduction techniques than that illustrated in [Fig.5], and this, if necessary, by providing a number of dimensions other than two as in the example illustrated in [Fig.5].

[0058] Furthermore, in the third embodiment of the analysis step 104, the distance scores associated with the diagnosed sleeper are calculated for each diagnosed sleeper respectively along the distance score axes DI and D2, which makes it possible to assess the “position” of the diagnosed sleeper in the aforementioned representation space, as illustrated schematically in insert b) of [Fig. 5]. From this “position”, a characterization of structural damage for the diagnosed sleeper can be determined, for example by classifying the diagnosed sleepers along a railway track into various categories according to the respective “positions” of these sleepers in the representation space.

[0059] Here again, in practice, the calculation of the distance score of each diagnosed sleeper is advantageously carried out by an ad hoc computer program of the computer part of the analysis means 60. This amounts to saying that the analysis means 60 are configured to compare by computer the frequency spectrum of each diagnosed sleeper with several reference spectra, by calculating a corresponding distance score, and to determine, in particular by computer, the characterization of structural damage for the diagnosed sleeper from the calculated distance score.

[0060] Other embodiments of the analysis step 104. By way of non-exhaustive examples:

[0061] - division into groups of the measurements carried out in order to define groups of res similarity with respect to the distance between the frequency spectra, using Machine Learning techniques such as k-means partitioning; and / or

[0062] - representation of the position of the measurements along reduced axes using nonlinear dimension reduction techniques, in order to evaluate the positions of measurements relative to each other in a reduced-dimensional and more easily interpretable representation, such as a one-dimensional, two-dimensional or three-dimensional representation.

[0063] Regardless of the embodiment of the analysis step 104, it is understood that the structural diagnosis method results in determining a characterization of structural damage for each of the diagnosed sleepers. This characterization of structural damage associates with the diagnosed sleeper a structural state among several states, predetermined and / or classified a posteriori. Thus, the characterization of structural damage provides information, with a controlled margin of error, in particular on:

[0064] - the presence of at least one structural defect falling within one or more types of given defect, such as the crack F mentioned above, and / or

[0065] - structural wear more marked than nominal structural wear.

[0066] Also, whatever the embodiment of the analysis step 104, the implementation of this analysis step 104 potentially involves the operator for the deduction of this characterization of structural damage, in which case the analysis means 60 provide the operator, by computer processing, with the necessary assessment information, for example in the form of at least one comparative display, as in the first embodiment detailed above. Alternatively, the implementation of the analysis step 104 is entirely computer-based, which may require significant computing power, in particular made available by the remote computer equipment 52.

[0067] Finally, various arrangements and variants to the structural diagnostic method, as well as to the structural diagnostic system 1, described so far, are conceivable. For example: - the vibration V is detectable and measurable by several sensors of the structural diagnostic system, such as sensor 20, these different sensors being able to be distributed on the cross member to be diagnosed; - the vibration V can be generated by several impactors of the structural diagnostic system, such as the impactor 10, then being, if necessary, detected by a single sensor, such as the sensor 20, these different impactors being able to be distributed over the cross member to be diagnosed; and / or - rather than the entire analysis step 104 being implemented in situ, i.e. on the railway, part of this analysis step 104 can be implemented at a distance from the railway, for example in an office.

Claims

Claims

1. Method for structural diagnosis of concrete railway sleepers (2, 3), comprising: - an application step (101), in which a mechanical stress is applied by impact to a concrete railway sleeper (2, 3) to be diagnosed, - a detection step (102), in which a vibration (V) generated by the mechanical stress and propagating in the diagnosed sleeper is detected on the surface of the diagnosed sleeper and is transformed into a vibrational time signal (SV), - a processing step (103), in which the vibrational time signal (SV) is electronically processed so as to obtain a frequency spectrum (SF), and - an analysis step (104), in which the frequency spectrum (SF) is compared with a reference (SR; SR1, SR2, SR3, SR4) to deduce therefrom a characterization of structural damage to the diagnosed sleeper.

2. The method of claim 1, wherein the applying step (101), the detecting step (102) and the processing step (103), and at least part of the analyzing step (104) are performed on a railway.

3. Method according to one of claims 1 or 2, in which, in the analysis step (104), the frequency spectrum (SF) and a reference spectrum (SR) constituting said reference are displayed to a human operator who deduces therefrom, by visual observation, the characterization of structural damage to the diagnosed crossmember.

4. Method according to any one of the preceding claims, in which, in the analysis step (104): - the frequency spectrum (SF) is compared computationally to a reference spectrum (SR) constituting said reference, by calculating a distance score which is representative of a mathematical distance between the frequency spectrum and the reference spectrum, and - the characterization of structural damage is determined from the calculated distance score.

5. Method according to any one of the preceding claims, in which, in the analysis step (104): - the frequency spectrum (SF) is compared by computer to several reference spectra (SRI, SR2, SR3, SR4) constituting said reference, by calculating distance scores which are respectively representative of mathematical distances between the frequency spectrum and the reference spectra, and - the characterization of structural damage is determined from the calculated distance scores.

6. Method according to any one of the preceding claims, wherein, in the applying step (101), the mechanical stress is applied to the cross member to be diagnosed (2, 3) by an impact having an energy of less than 3 joules, preferably less than 1 joule.

7. Method according to any one of the preceding claims, in which, in the processing step (103), the vibrational time signal (SV) is processed so as to extract a significant part therefrom, before applying to this significant part a band-pass filter then a mathematical transformation on a frequency domain to obtain the frequency spectrum (SF).

8. A method according to claim 7, wherein the bandpass filter has a low cut-off frequency substantially equal to 3,000 Hz, preferably 3,500 Hz, and a high cut-off frequency substantially equal to 20,000 Hz, preferably 15,500 Hz.

9. Structural diagnostic system (1) for concrete railway sleepers (2, 3), comprising: - at least one impactor (10) adapted to apply by impact a mechanical stress to a concrete railway sleeper (2, 3) to be diagnosed, - at least one sensor (20) adapted both to detect, on the surface of the diagnosed sleeper, a vibration (V) generated by the mechanical stress and propagating in the diagnosed sleeper, and to transform the vibration (V) into a vibrational time signal (VS), - an electronic processing unit (40), adapted to process the vibrational time signal (SV) so as to obtain a frequency spectrum (SF), and - analysis means (60), adapted to compare the frequency spectrum (SF) with a reference (SR; SRI, SR2, SR3, SR4) to deduce therefrom a characterization of structural damage to the diagnosed crossmember.

10. System according to claim 9, in which the impactor(s) (10), the sensor(s) (20) and the electronic processing unit (40), as well as at least a part (61) of the analysis means (60) form a portable hardware assembly, usable by a human operator on the railway.

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