METHOD FOR INSPECTING A STRUCTURAL CABLE ANCHOR DEVICE

Abstract

A method for inspecting a structural cable anchorage device in a construction structure, the anchorage device including a cover (24) enclosing a volume containing anchored ends of structural cable reinforcements (14) and a filler material (40), the method comprising: altering the temperature of at least a portion of the cover (24); measuring the temperature on an external surface (31A) of the cover (24); and analyzing the measured temperature variations to detect filler defects in the cover (24). Abstract figure: Figure 7

Description

Title of the invention: METHOD FOR INSPECTING A STRUCTURAL CABLE ANCHOR DEVICE technical field

[0001] The present disclosure falls within the field of methods for inspecting an anchoring device for a structural cable, such as a prestressing cable for a construction structure or an anchor tie rod for a reinforced wall or foundation. Previous technique

[0002] In civil engineering structures, prestressing cables are used to continuously subject the structure to stresses, generally compressive, making the structure more resistant to the stresses it faces during its useful life.

[0003] Conventionally, a prestressing cable comprises one or more reinforcements (often strands) stretched between two anchorage zones. The ends of each reinforcement are anchored in the anchorage zones using plates or blocks with holes through which the reinforcements are individually secured, for example, by means of truncated conical jaws. Similar devices can be used in the case of anchorage rods.

[0004] In an anchorage zone, the ends of the reinforcement bars are generally capped by a cover placed on or around the anchor block. A filler material with good anti-corrosion properties, such as wax, grease, polymer, resin, or cement grout, is used to fill the volume enclosed by the cover and the anchor block. The filler material is introduced into this volume through an injection orifice, for example, located on one end face of the cover. This orifice is sealed with a plug once the filling process is complete.

[0005] At least one vent is provided at a high point, for example on a side wall of the hood, to purge air during injection. Filling is considered complete when filling material begins to overflow from the vent, confirming proper filling of the hood and thus good protection of the reinforcements against corrosion.

[0006] During operation, it is sometimes necessary to check that the hood is properly filled with the filler material in order to identify potential filling defects, such as voids that may remain after hood installation or appear during its service life. Such voids increase the risk of corrosion of the reinforcement at the anchoring areas.

[0007] Currently, the hood filling level can be assessed in two ways. One possibility involves removing the hood, which allows for a complete view of its interior. Sometimes, the grout adheres quite firmly to the hood's internal surface, so it can break during removal attempts. This is often the case with cement grouts. Therefore, great care must be taken, making disassembly time-consuming and resulting in a very lengthy and costly inspection, especially for construction or civil engineering structures with numerous prestressing cables. It is also possible that removing the hood will prove impossible without causing breakage. Other types of grout may retain some fluidity, so inspection methods involving hood removal are unsatisfactory and require repeating the grouting under difficult-to-control conditions.

[0008] The second option involves removing only the plugs blocking the hood's filler openings, thus limiting the risk of breaking the hood. This option is quicker to implement than completely removing the hood, but the fill level can only be partially monitored.

[0009] It is desirable to have an inspection technique less affected by the aforementioned disadvantages. Summary

[0010] A method is proposed for inspecting an anchoring device for a structural cable of a construction structure, the anchoring device including a hood closing a volume containing anchored ends of structural cable reinforcements and a filling material, the method comprising: modifying the temperature of at least a portion of the hood; measuring the temperature on an external surface of the hood; and analyzing measured temperature variations to detect filling defects in the hood.

[0011] When the hood contains a filling defect, such as a filling void, temperature variations on the hood's external surface are detected between different points on this external surface. The method therefore makes it possible to detect the presence of filling voids in the hood using a non-destructive, rapid method that does not require dismantling the hood.

[0012] Furthermore, the method allows for simultaneous investigation of the entire hood surface, thus providing a comprehensive view of the filling quality across the entire hood. This means that the filling quality is not limited to the areas visible and accessible from the cap sealing the hood's filling opening. Therefore, a complete diagnosis of the presence or absence of filling defects, such as gaps or inconsistencies, within the hood is possible.

[0013] According to one aspect, the process further comprises obtaining an evolution temporal variations of temperature during a given measurement time.

[0014] According to one aspect, the process further comprises a conversion in a frequency domain of the temporal evolution of temperature variations.

[0015] According to one aspect, the conversion in the frequency domain of the temporal evolution of temperature variations includes obtaining an evolution of an amplitude and / or a phase of the temperature variations as a function of a frequency.

[0016] According to one aspect, the method further comprises obtaining a time evolution of the temperature at different points of at least a portion of the hood.

[0017] According to one aspect, the method further comprises the conversion in a frequency domain of the time evolution of the temperature at the different points of at least a portion of the hood.

[0018] According to one aspect, the conversion in the frequency domain of the time evolution of the temperature includes obtaining an evolution of an amplitude and / or a phase of the absolute temperatures at the different points of at least a portion of the hood.

[0019] According to one aspect, the change in temperature of at least one portion of the hood is obtained by heating said at least one portion of the hood.

[0020] According to one aspect, the heating is carried out from at least one coil arranged around the external surface of the hood.

[0021] According to one aspect, at least a portion of the hood is heated by induction, preferably at a power between 100 W and 15000 W.

[0022] According to one aspect, at least a portion of the hood is heated by pulse, by a modulated signal or by a pseudo-random binary signal.

[0023] According to one aspect, heating at least a portion of the hood includes a temperature rise of said portion of between 1°C and 50°C relative to an initial temperature of said portion.

[0024] According to one aspect, at least a portion of the hood is heated for a time interval of between 1 second and 600 seconds.

[0025] According to one aspect, the change in temperature of at least one portion of the hood is obtained by cooling said at least one portion of the hood.

[0026] According to one aspect, the temperature of the external surface of the hood is measured by infrared thermography, for example from a thermal camera.

[0027] According to one aspect, the temperature on the external surface of the hood is measured for a measurement time of between 1 second and 3600 seconds.

[0028] According to one aspect, the construction work comprises several structural cables, each having at least one anchoring device, each anchoring device including a respective cover closing a respective volume containing anchored reinforcement ends and a filling material, in which the modification steps of the temperature are repeated from one hood to another, and in which the temperature variations analyzed include variations between temperatures measured from one hood to another. Brief description of the drawings

[0029] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the accompanying drawings, on which:

[0030] [Fig-1] shows a schematic longitudinal cross-sectional view of one end of a prestressing cable with its anchoring device.

[0031] [Fig.2] shows a schematic longitudinal sectional view of the front part of the anchoring device of [Fig.1], with a hood and a heating device used for implementing the method according to this disclosure.

[0032] [Fig.3] shows a schematic cross-sectional view of the part of the anchoring device covered by the hood according to a first example.

[0033] [Fig.4] shows an example of a thermogram of the surface of the hood of the [Fig.3] subjected to the process according to this disclosure.

[0034] [Fig.5A] shows a diagram illustrating a time evolution of the surface temperature in two elementary points of the hood of the [Fig.3] subjected to the process according to the present disclosure.

[0035] [Fig.5B] shows a diagram illustrating a temporal evolution of the temperature difference between the two elementary points analyzed on [Fig.5A].

[0036] [Fig.6A] shows a diagram illustrating an evolution of the amplitude of absolute temperatures in the two elementary points analyzed on [Fig.5A] as a function of frequency.

[0037] [Fig.6B] shows a diagram illustrating an evolution of the phase of the absolute temperatures in the two elementary points analyzed on the [Fig.5A] as a function of frequency.

[0038] [Fig.7] shows a schematic cross-sectional view of the part of the anchoring device of [Fig.1] covered by the hood according to a second example.

[0039] [Fig.8] shows an example of a thermogram of the surface of the hood of the [Fig.7] subjected to the process according to this disclosure.

[0040] [Fig.9A] shows a diagram illustrating a time evolution of the temperature in two elementary points of the hood of the [Fig.7] subjected to the process according to the present disclosure.

[0041] [Fig.9B] shows a diagram illustrating a temporal evolution of the temperature difference between the two elementary points analyzed on [Fig.9A].

[0042] [Fig. 1OA] shows a diagram illustrating an evolution of the amplitude of the absolute temperatures in the two elementary points analyzed on [Fig. 9A] in function of frequency.

[0043] [Fig.1OB] shows a diagram illustrating an evolution of a phase of the absolute temperatures in the two elementary points analyzed on [Fig.9A] as a function of frequency.

[0044] [Fig. 11 A] shows a diagram illustrating two temperature evolution curves Temperature depending on the time.

[0045] [Fig. 1 IB] shows a diagram illustrating two curves representing the evolution of a temporal evolution of the temperature difference at elementary points of a hood comprising filling voids at different depths

[0046] [Fig. 12] shows a graph representing a maximum depth of detection of a filling void as a function of the size of this filling void depending on whether the process according to the present disclosure is implemented with a time-domain analysis or a frequency-domain analysis. Description of the implementation methods

[0047] The invention is illustrated below in the non-limiting case of a structural cable consisting of a prestressing cable. Figure 1 shows one end of such a prestressing cable 10 and an anchoring device 12 for this cable 10.

[0048] The cable 10 comprises parallel metallic reinforcements 14, collectively housed within a sheath 16 of the prestressing cable. The space between the sheath 16 and each reinforcement 14 may be filled with a corrosion-preventing substance, for example, petroleum wax, grease, or cement grout. The reinforcements 14 consist, for example, of metallic strands, each of which may be contained within an individual sheath of a polymer material, such as high-density polyethylene (HDPE), or a metallic sheath. They may also consist of bare strands or another type of metallic reinforcement.

[0049] As shown in [Fig. 1], one end 18 of each reinforcement 14 protrudes from the sheath 16. This end 18 is received and anchored in the anchoring device 12, as will be detailed. If the reinforcement is a sheathed strand, its individual sheath is removed near the anchoring to allow the reinforcement to be anchored at its bare end 18.

[0050] The anchoring device 12 includes an anchoring trumpet 20, an anchoring plate 22 and a cover 24. In the non-limiting example of [Fig.1], the trumpet 20 and the plate 22 can form a single piece called a trumpet.

[0051] The anchor plate 22 comprises cavities 26, each cavity 26 being shaped to partially receive the bare end 18 of a respective reinforcement 14. A clamping member 28, such as a frustoconical jaw (also called a wedge), can be positioned radially around each reinforcement 14. The frustoconical jaw 28 holds each reinforcement 14 in position within its respective cavity 26, so that each armature 14 is put under tension to a desired stress value.

[0052] The hood 24 is generally made of a metallic material, such as steel, with ferromagnetic properties.

[0053] The hood 24 has a substantially cylindrical shape comprising a side wall 30, a bottom wall 32, and an open end 34 located opposite the bottom wall 32. The bottom wall 32 advantageously includes an opening 33 which is closed by a removable plug 35. The hood 24 has a thickness e between an external surface 31A and an internal surface 31B of the hood 24.

[0054] As can be seen from [Fig. 1], the cover 24 covers the plate 22 in the longitudinal extension of the trumpet. In particular, the open end 34 of the cover 24 is connected, directly or indirectly, to one end of the trumpet, for example by screws 36.

[0055] The cover 24 closes a volume 38 comprising a filling material 40 which protects the bare end 18 of each reinforcement 14 from corrosion. The volume 38 is delimited in particular by the internal surface 31B against which the filling material 40 comes into contact.

[0056] The filling material 40 can be introduced into the hood 24 through the orifice 33 before sealing it with the plug 35. The filling material 40 can be a wax, a grease, a polymer, a resin or a cement grout, among others.

[0057] The hood 24 may also include at least one vent 42. This vent 42 allows for the purging of air, or even a small volume of filling material 40, in order to validate proper filling of the hood 24 during its installation.

[0058] A method for inspecting an anchoring device 12 similar or identical to that described previously will now be described. As will be detailed below, this method makes it possible to detect filling defects, in particular filling voids, in the anchoring device 12. By "filling void" is meant a portion of the volume 38 closed by the cover 24 in which there is a lack of filling material 40. Although the following refers mainly to filling voids, other defects that the method according to the invention can detect include, for example, the presence of filling heterogeneities.

[0059] According to a first example of implementing the method, it includes a step of modifying the temperature of at least a portion of the cover 24 of an anchoring device 12. In the example described below, this portion of the cover 24 is heated, which is relatively easy to achieve, particularly by induction, but alternatively it could be cooled. Therefore, in what follows, all the terms "heat," "heated," and their equivalents could be replaced by "cool," "cooled," etc. According to a non-limiting example, up to 4 cm of the cover's thickness can be heated.

[0060] The heated portion of the hood 24 comprises a number of elementary points. Each elementary point corresponds to a specific position on the hood 24, in particular in its side wall 30 or its bottom wall 32. If all the elementary points of the hood 24 are grouped together, the complete shape of the hood 24 is obtained.

[0061] To heat the hood 24, a heating device 44 can be arranged outside the hood 24, around the portion to be heated. According to the non-limiting example schematically illustrated in [Fig. 2], the heating device 44 covers the entire hood 24, in particular its side walls 30 and bottom wall 32.

[0062] In what follows, the heated portion of the hood 24 is considered to correspond to its entire external surface 31 A. However, the entire exposition is applicable to the case where this external surface 31 A is partially heated (that is to say, the heated portion of the hood 24 does not include the entire external surface 31 A).

[0063] The heating device 44 is, for example, an inductor for heating the hood 24 by induction. Induction heating is created by an alternating current of a given frequency and allows for a rapid, efficient, homogeneous, and reproducible temperature rise in the heated area. Moreover, induction heating allows for heating a precise area of ​​the hood 24. It does not damage the hood.

[0064] Preferably, the inductor 44 includes a housing shaped to receive the hood 24 and is adapted to each type of hood. The inductor 44 includes a coil 46 arranged around the outer surface 31A of the hood 24 when the latter is received in the inductor housing. The coil 46 and the outer surface 31A are advantageously separated from each other. To heat the outer surface 31A, an alternating current creating an electromagnetic field flows through the coil 46. The energy created by this electromagnetic field can then create, by Joule heating, a thermal excitation that dissipates in the material of the hood 24 as heat. Furthermore, induction heating also has the advantage of being flameless, which increases the safety of the process.

[0065] The inductor 44 can be configured to heat the external surface 31A by pulse, by a modulated signal, or by a pseudo-random binary signal. A control unit for the inductor 44 can be provided to select the heating method.

[0066] In the case of pulse heating (also known as the "flash method"), the electromagnetic field circulating in the coil 46 is applied for a certain time, during which electromagnetic waves at multiple frequencies are generated. The excitation frequency of the electromagnetic field circulating in the coil 46 changes during the application of the electromagnetic field, for example, in the form of a square wave, a triangle wave, etc. The shape of the induction excitation generated during heating therefore has a time and an excitation signal shape that can generate a wide band of excitation frequencies, making it possible to detect any type of defect. the inside of the hood 24, and not just the empty spaces.

[0067] In the case of signal-modulated heating, the electromagnetic field circulating in the coil 46 is generated by a signal that varies sinusoidally over several cycles. This sinusoidal signal generates a single excitation frequency, which makes it possible to detect only one type of defect inside the hood 24 at a targeted depth. In this case, the excitation frequency of the sinusoidal signal has a value that allows the detection of voids in the hood 24.

[0068] In the case of pseudo-random binary signal heating, the electromagnetic field circulating in the coil 46 is applied at low power levels during time intervals of random duration. This induces a limited increase in the temperature of the external surface 31A while generating broad frequency bands. It is therefore possible to detect any type of defect inside the cover 24, and not just voids.

[0069] The inductor 44 can be activated so as to cause a temperature rise in the heated portion of the hood 24 of between 1°C and 50°C relative to its initial temperature, preferably between 10°C and 30°C. By a non-limiting example, the temperature increase of the external surface 31A is approximately equal to 20°C.

[0070] If the duration and / or intensity of the heating produced by the inductor 44 is varied, the maximum depth of fault detection or the surface area of ​​the heated portion can be modified.

[0071] According to a non-limiting example, the inductor 44 heats the hood 24 for a time interval of between 1 second and 600 seconds, preferably between 10 seconds and 120 seconds. According to another non-limiting example, the hood 24 is heated by the inductor for 60 seconds. The temperature increase is therefore achieved rapidly.

[0072] Furthermore, the inductor 44 can operate at a power level between 100 W and 15,000 W. As a non-limiting example, the power of the heating source is approximately 3,500 W. When heating is pulsed, this power can be between 1,000 W and 16,000 W. When heating is modulated, the heating power can be between 1,000 W and 8,000 W. When heating is achieved using a pseudo-random binary signal, the heating power can be between 100 W and 1,000 W. Preferably, the power of the inductor 44's source remains constant throughout the temperature change step of the surface 31A of the hood 24.

[0073] It is noted that to obtain the same value of temperature rise, the heating time required will be shorter the higher the operating power of the inductor 44.

[0074] When the hood 24 is heated, heat propagates through its thickness e, primarily by conduction, and reaches its inner surface 31B. This heat then dissipates into the filling material 40. The presence of one or more voids inside the hood 24 leads to heterogeneity in the heat diffusion within the filling material 24. In particular, heat diffuses by conduction more readily through the filling material than through the voids. This results in a local accumulation of heat along the thickness of the hood in areas of the outer surface 31A aligned with the void(s), i.e., those that are extensions of the voids. Also, as will be detailed later, when the inside of the hood 24 includes voids, the temperature distribution on the external surface 31A is heterogeneous, the areas of this surface 31A aligned with the void(s) having a higher temperature than the rest of the external surface 31A.

[0075] After changing the temperature of the external surface 31A of the hood 24, the process continues by measuring and / or recording, using radiometric video, the surface temperatures at all elementary points of the heated portion for a given measurement time. For this step, the heating device 44 is removed from the hood 24. The temperature of the hood 24 also decreases gradually during the measurement until it reaches equilibrium with the external environment. The recording therefore takes place during the cooling phase of the hood.

[0076] This measurement is, for example, performed by infrared thermography. For this purpose, at least one thermal camera capable of obtaining thermal images of the heated surface of the hood 24 is used. By way of non-limiting example, four infrared cameras can be distributed around the external surface 31A to take thermal images of it.

[0077] Advantageously, each camera is placed at a distance from the hood 24, for example at a distance between 50 cm and 150 cm.

[0078] The measurement time can be between 1 second and 3600 seconds, preferably between 180 seconds and 1500 seconds. According to a non-limiting example, the measurement time is 300 seconds.

[0079] During this time of measuring and recording the temperature evolution, several thermal images are obtained. In particular, the image acquisition frequency of the camera is, for example, between 0.1 Hz and 100 Hz, preferably between 9 Hz and 60 Hz.

[0080] Infrared thermography thus makes it possible to visualize the spatial and temporal mapping of temperatures on the heated surface of the hood 24 using thermograms obtained from thermal images taken by each camera or from video-radiometric data (thermal film). These thermograms represent the thermal signature of the heated surface of the hood 24.

[0081] Figures 4 and 8 show examples of thermograms represented in greyscale, in which darker areas correspond to areas of higher temperature, and lighter areas correspond to areas of lower temperature.

[0082] Figure 4 shows an example of a thermogram obtained for a hood 24 that is heated over its entire external surface 31A and is completely filled with filler material 40, like that of Figure 3. A homogeneous temperature distribution is then observed over the entire hood 24. A homogeneous temperature distribution over the entire external surface 31A would also be observed if the hood 24 were completely empty, but with equal heating power, time, and excitation pattern, higher temperatures would be measured in the latter case.

[0083] Figure 8 shows an example of a thermogram obtained for a hood 24 that is heated over its entire external surface 31A and is half-filled with filler material 40 (Fig. 7). In particular, the area within the dashed curve corresponds to the area not filled with filler material 40. A heterogeneous temperature distribution is then observed over the entire hood 24, with higher temperatures on the part of the hood that is in direct contact with, or closer to, the area containing filler voids.

[0084] Furthermore, by measuring the temperature evolution on all elementary points of the heated portion, graphs can be obtained representing the curves of the evolution of the absolute temperature T as a function of time t on one or more chosen elementary points of the heated surface of the hood 24. Preferably, the chosen elementary points correspond to points on the heated surface of the hood 24 which are located at similar distances from the center of the hood 24.

[0085] Figure 5A shows the temperature evolution curves T as a function of time t for a hood that is completely filled, such as that of Figure 3. In particular, Figure 5A includes a first curve C1-1 and a second curve C2-1 representing the temperature evolution T as a function of time t at, respectively, a first elementary point P1 and a second elementary point P2 of the heated surface of the hood 24 of Figure 3. Since points P1 and P2 are located on areas of the hood that have similar temperatures according to the thermogram of Figure 4, the temperature evolutions at points P1 and P2 are also similar.

[0086] Figure 9A represents the temperature evolution curves T as a function of time t for a hood that is only half filled, like that of Figure 7. In particular, this Figure 9A comprises a first curve D1-1 and a second curve D2-1 representing the temperature evolution T as a function of time t at, respectively, a first elementary point P1' and a second elementary point P2' of the heated surface of the hood 24 of Figure 7. As points P1' and P2' are located on areas of the hood which have very different temperatures according to the thermogram of [Fig.8], the temperature evolutions on points PI' and P2' are also dissimilar.

[0087] The method then includes analyzing the temperature variations AT (also referred to hereafter as the temperature difference AT) measured to detect filling defects in the hood 24, in particular filling voids. Specifically, this step includes detecting a temperature difference AT existing during the measurement time between the first elementary point PI, PI' and the second elementary point P2, P2' of the hood 24. To this end, curves representing the time evolution of the temperature difference AT between the selected elementary points during the measurement time can be obtained.

[0088] Figure 5B shows the evolution over time t of the temperature difference AT between points P1 and P2 of the hood in Figure 3. As clearly visible in Figure 5B, the temperature difference between the two elementary points P1 and P2 is small, with absolute values ​​of the temperature difference AT between 0°C and 1°C. This confirms that the interior of the hood 24 is homogeneously filled by the filling material 40. It should be noted that similar temperature differences would be obtained if the hood 24 were completely empty.

[0089] Figure 9B represents the evolution over time t of the temperature difference AT between points PI' and P2' of the hood in Figure 7. As clearly visible in Figure 9B, the temperature difference between the two elementary points PI' and P2' is large, with absolute values ​​of the AT difference that can exceed 1°C. This confirms that the filling of the hood 24 by the filling material is heterogeneous, with empty areas.

[0090] More generally, when a filling void is present in the hood 24, the temperature evolution at two points can have the shape shown in the curves of [Fig. 1 IA]. The curve of the temperature difference AT as a function of time t corresponding to the curves of [Fig. 11 A] is shown in [Fig. 1 IB] with the curve EL. The shape of the curve shows an increasing portion, followed by a peak, then a decreasing portion. The deeper the filling void inside the hood 24, the lower the peak of the curve of the temperature difference AT as a function of time t is on the y-axis and shifted to the right on the x-axis. Indeed, the deeper the void, the greater the heat dissipated in the filling material 40, and the longer it takes for the thermal waves created during the heating of the hood 24 to reach this void. In this case, the curve El of the [Fig.[1 IB] is representative of a shallower filling void than curve E2, given that the peak of curve E1 is higher on the ordinate axis and further to the left on the x-axis than the peak of curve E2. Also, . It is only possible to obtain information about the depth of the filling vacuum from the curve representing the temperature difference AT as a function of time t.

[0091] The curves of the evolution of temperature T and temperature difference AT as a function of time, such as those in Figures 5A, 5B, 9A, and 9B, are derived from image and signal processing in the time domain. In some cases, these temperature and temperature difference evolutions as a function of time may be subjected to image and signal processing in the frequency domain. This frequency domain processing makes it possible to confirm the conclusions regarding the presence or absence of filling gaps reached during the time domain processing.

[0092] In the frequency domain, from the series of thermograms recorded previously, the Fourier transform of the temperature evolution as a function of time can be calculated for each selected elementary point. In practice, the calculation can be performed using the Fast Fourier Transform algorithm. The result of the transformation is a complex spectrum composed of the amplitude and phase of the signal, both functions of the frequency. The amplitude corresponds in particular to the power P of heat dissipated at each elementary point. The lower the power P, the more the hood 24 is filled with filler material 40, i.e., the fewer filler voids it contains.

[0093] [Fig.6A] includes a Cl-2 curve and a C2-2 curve. The Cl-2 curve shows the evolution of the power P for the first point PI of the fully filled hood 24 of [Fig.3] as a function of the frequency of the absolute temperatures in this first point PI, while the C2-2 curve shows the evolution of the power P for the second point P2 of this hood 24 as a function of the frequency of the absolute temperatures in this second point P2.

[0094] The [Fig.6B] includes a Cl-3 curve and a C2-3 curve showing the evolution of phase 0 for, respectively, point PI and point P2 of the fully filled hood 24 of the [Fig.3] as a function of the frequency of absolute temperatures in the corresponding point PI or point P2.

[0095] The curves Cl-2 and Cl-3 are obtained by applying the Fourier transform to the temperature evolution as a function of time at point PI (i.e., by converting the time evolution of the temperature at point PI into the frequency domain). The curves C2-2 and C2-3 are obtained by applying the Fourier transform to the temperature evolution as a function of time at point P2 (i.e., by converting the time evolution of the temperature at point P2 into the frequency domain).

[0096] Since the Cl-2 and C2-2 curves of [Fig. 6A] are almost identical to each other, and the Since the Cl-3 and C2-3 curves in [Fig. 0B] are also almost identical, it is possible to confirm that the hood 24 in [Fig. 3] is completely filled with filler material 40. By "identical," we mean here that the temperature difference and phase shift are negligible. (The amplitude would be greater for a completely empty hood—there would be no temperature difference and no phase shift.)

[0097] The [Fig.1OA] includes a Dl-2 curve and a D2-2 curve. The Dl-2 curve shows the evolution of the power P or DSP (Power Spectral Density) for the first point PI' of the hood 24 half filled in [Fig.7] as a function of the frequency of the absolute temperatures in this first point PI', while the D2-2 curve shows the evolution of the power P or DSP (Power Spectral Density) for the second point P2' of this hood 24 as a function of the frequency of the absolute temperatures in this second point P2'.

[0098] The [Fig.1OB] includes a D1-3 curve and a D2-3 curve showing the evolution of the phases 0 of the temperatures for, respectively, the point PI' and the point P2' of the hood 24 of the [Fig.7] as a function of the frequency of the absolute temperatures in the corresponding point PI' or point P2'.

[0099] The curves Dl-2 and Dl-3 are obtained by applying the Fourier transform to the temperature evolution as a function of time at point PI' (i.e., by converting the time evolution of the temperature at point PI' into the frequency domain). The curves D2-2 and D2-3 are obtained by applying the Fourier transform to the temperature evolution as a function of time at point P2' (i.e., by converting the time evolution of the temperature at point P2' into the frequency domain).

[0100] The curves Dl-2 and D2-2 of [Fig. 1OA], and the curves Dl-3 and D2-3 of [Fig. 1OB] are clearly different from each other, which allows us to deduce the existence of at least one void filled with filler material. In particular, the power P or DSP (Power Spectral Density) associated with point PI' is lower than that associated with point P2' ([Fig. 1OA]). As previously stated, the lower the power P or DSP (Power Spectral Density), the more the hood 24 is filled with filler material 40. In this case, as can be seen from [Fig. 7], point PI' corresponds to an elementary point of the hood 24 that is closer to the part of the hood 24 filled with filler material 40 than to the empty area of ​​the hood 24, which is closer to point P2'. The result concerning the presence of voids in hood 24 obtained in the time domain is therefore confirmed.

[0101] As indicated, to obtain the curves 6A, 6B, 10A, 10B, a conversion is performed in the frequency domain of the time evolution of the temperature at the first elementary point P1, P1', and of the time evolution of the temperature at the second elementary point P2, P2'. Alternatively or complementaryly, it It is possible to perform a frequency domain conversion of the time evolution of the temperature difference. In such a case, one obtains an evolution of the amplitude and / or phase difference from the temperature difference as a function of frequency. Applying frequency analysis to the time evolution of the temperature difference between two elementary points, instead of the time evolution of the temperature at each chosen elementary point, improves the thermal contrast and phase shift of the results obtained, since the scale used is more discretized in the case of the time evolution of the temperature difference.

[0102] Image and signal processing in the time domain or in the frequency domain as described above can be implemented, for example, by a computer. Image processing software and signal processing software can be used to process images and signals in the time domain and / or in the frequency domain.

[0103] It should be noted that, generally speaking, when frequency processing is applied, the results obtained for power P or DSP (Power Spectral Density) are more sensitive to emissivity and heating uniformity. Phase shift results have the advantage of being less affected by heating non-uniformity and surface emissivity variations encountered in on-site applications.

[0104] The larger the filling void in the injected volume, the greater the depth at which it can be detected. In [Fig. 12], the points within the reference line 50 correspond to the maximum depth at which a filling void can be detected by time-domain analysis as a function of the void size. The points within the reference line 60 correspond to the maximum depth at which a filling void can be detected by frequency-domain analysis as a function of the void size. It follows that, in addition to confirming the results obtained by time-domain image and signal processing, frequency-domain processing improves the detection of filling voids at greater depths than when only time-domain processing is used.All points located above line 60 correspond to depths at which the vacuum is undetectable by either temporal analysis or temporal analysis.

[0105] The following definition allows us to estimate the depth z at which a filling void detected in the hood 24 is located:

[0106] in which, C corresponds to the specific heat of the filling material 40, a corresponds to the diffusivity of this material 40 and fb corresponds to the frequency of vacuum detection.

[0107] Alternatively, to determine the depth of the defect, it is possible to introduce an endoscope through plug 35 or one of the vents.

[0108] This first example of implementation of the method disclosed in this text therefore makes it possible to detect the filling voids present in a hood 24 from the application of the different steps described above to the hood 24 of a single anchoring device 12.

[0109] In a second example of implementing this method, the cover of a first anchoring device and the cover of a second anchoring device are involved. The first and second anchoring devices are similar or identical to the anchoring device 12 described previously.

[0110] For the sake of brevity, only the differences between this second embodiment and the first embodiment described above are detailed below. The remaining process features explained for the first embodiment are applicable to this second embodiment.

[0111] In this second embodiment, the process includes modifying the temperature of a portion of the hoods 24 of each of the first and second anchoring devices 12. In what follows, it is assumed that the two hoods 24 are structurally (i.e., in geometry and material) identical to each other, but as will be detailed later they could be structurally different.

[0112] As explained previously, the temperature of each hood 24 can be changed by heating, for example as detailed above, or by cooling. Advantageously, an identical stress for changing the temperature is applied to the hoods 24 of the first and second anchoring devices. Therefore, the temperature evolution on the heated portion is identical between the two hoods 24 only if the filling of both hoods 24 is identical. When the filling of the two hoods 24 is different, the temperature evolution on the heated portion differs between the two hoods 24. In particular, as indicated previously, the areas of the heated portion of each hood 24 aligned with the void(s) have a higher temperature than the rest of the heated portion of the respective hood.

[0113] After changing the temperature of the hood 24 of the first and second anchoring devices 12, the temperature evolution is measured over a given measurement time at all elementary points of the heated portion of each hood 24. This measurement can be carried out in the manner described above for the embodiment where only one hood is involved in the process. This yields thermograms representing the thermal signature of each of the hoods 24.

[0114] If the temperature distribution differs between the thermograms of the two hoods 24, voids exist in at least one of them. By "differences" we mean that the temperature of one hood deviates from the temperature of the other hood by more than 1°C. Furthermore, if the temperature distribution is heterogeneous on the same hood 24, voids exist on that hood, as explained above with reference to the first embodiment example.

[0115] By measuring the temperature evolution on each of the hoods, graphs can be obtained representing the curves of the evolution of the absolute temperature T as a function of time t at a first elementary point located on one of the hoods 24 and a second elementary point located on the other hood 24. Advantageously, the first and second elementary points are located at the same position on their respective hoods, although this is not a limitation. Subsequently, it is possible to apply to these chosen elementary points of the two hoods 24 the time and / or frequency processing as explained above with reference to the first embodiment example with a single hood.

[0116] This second embodiment is particularly advantageous for determining whether a hood is completely filled with filler material 40 or completely empty. Indeed, when the process described here is applied to a single hood and the temperature is uniform over its entire surface, it is only possible to conclude that it is completely empty or completely filled with filler material if it is compared to a control hood for which the fill level is known. If, for example, the control hood is completely filled, and the temperature distribution is the same as for the analyzed hood, it is possible to conclude that the analyzed hood is completely filled. Conversely, if the temperature on the external surface 31A of the analyzed hood is higher than that of the completely filled control hood, it can be concluded that the analyzed hood is completely empty.

[0117] As previously stated, advantageously, the two hoods are identical, particularly in shape, size, thickness, material, etc. This situation is typically encountered when the same structure has been built with multiple prestressing cables equipped with anchoring devices and hoods of the same model. It is then convenient to compare thermograms obtained from one hood to the other. However, it is also possible that there may be some structural difference between the two hoods. In such a case, to compare the temperature evolution of the two hoods, it is possible to establish relationships between the two hoods that take these differences into account when analyzing the various curves of temperature evolution, temperature difference, power, and / or phase shift associated with the chosen elementary points of each hood 24.

[0118] It should be noted that the process described below also makes it possible to detach the material from the hood.

[0119] The embodiments described above are merely an illustration of the present invention. Various modifications may be made to them without departing from the scope of the invention as set forth in the appended claims. For example, as a complement to or alternative to the thermal imaging camera, surface temperature measurements at all elementary points of the heated portion may be taken using thermocouple temperature probes. These may be arranged on the external surface 31A of the cover 12, without this being a limitation.

Claims

Demands

1. Method for inspecting an anchoring device (12) of a structural cable (10) of a construction structure, the anchoring device (12) including a hood (24) closing a volume containing anchored ends (18) of reinforcements (14) of the structural cable (10) and a filling material (40), the method comprising: - modifying the temperature of at least a portion of the hood (24); - measuring the temperature (T) on an external surface (31 A) of the hood (24); and - analyzing temperature variations (AT) measured to detect filling defects in the hood (24).

2. A method according to claim 1, further comprising obtaining a time evolution of temperature variations (AT) during a given measurement time.

3. Method according to claim 2, further comprising a conversion in a frequency domain of the time evolution of temperature variations (AT).

4. A method according to claim 3, wherein the conversion in the frequency domain of the time evolution of the temperature variations (AT) comprises obtaining an evolution of an amplitude (P) and / or a phase (0) of the temperature variations (AT) as a function of a frequency (f).

5. A method according to any one of the preceding claims, further comprising obtaining a time evolution of the temperature (T) at different points (PI, PI', P2, P2') of at least a portion of the hood (24).

6. Method according to claim 5, further comprising conversion in a frequency domain of the time evolution of the temperature (T) at the different points of at least a portion of the hood (24).

7. A method according to claim 6, wherein the conversion in the frequency domain of the time evolution of the temperature (T) comprises obtaining an evolution of an amplitude (P) and / or a phase (0) of the absolute temperatures at different points of at least a portion of the hood (24).

8. A method according to any one of the preceding claims, wherein the change in temperature (T) of at least one portion of the hood (24) is obtained by heating said at least one portion of the hood (24).

9. Method according to claim 8, wherein the heating is carried out from at least one coil (46) arranged around the external surface (31 A) of the hood (24).

10. A method according to any one of claims 8 or 9, wherein at least a portion of the hood (24) is heated by induction, preferably at a power between 100 W and 15000 W.

11. A method according to any one of claims 8 to 10, wherein at least a portion of the hood (24) is heated by pulse, by a modulated signal or by a pseudo-random binary signal.

12. A method according to any one of claims 8 to 11, wherein the heating of at least a portion of the hood (24) comprises a temperature rise of said portion of between 1°C and 50°C relative to an initial temperature of said portion.

13. A method according to any one of claims 8 to 12, wherein at least a portion of the hood (24) is heated for a time interval of between 1 second and 600 seconds.

14. A method according to any one of claims 1 to 7, wherein the change in temperature (T) of at least one portion of the hood (24) is obtained by cooling said at least one portion of the hood (24).

15. A method according to any one of the preceding claims, wherein the temperature of the external surface of the hood (12) is measured by infrared thermography, for example from a thermal camera.

16. A method according to any one of the preceding claims, wherein the temperature (T) on the external surface of the hood (24) is measured for a measurement time of between 1 second and 3600 seconds.

17. A method according to any one of the preceding claims, wherein the construction work comprises several structural cables (10) each having at least one anchoring device (10), each anchoring device (10) including a respective hood (24) closing a respective volume containing anchored ends (18) of reinforcements (14) and a filling material (40), wherein the temperature modification steps (T) are repeated from one hood (24) to another, and wherein the temperature variations (AT) analyzed include variations between temperatures measured from one hood (24) to another.

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