The present invention relates to an interface inspection method and apparatus for a composite structure, and more particularly, to an interface inspection method and apparatus for inspecting an interface condition of a composite structure.
Generally, in relation to composite structures such as bridges, a method of construction is known which disposes reinforcement bars in a frame of a bottom steel plate provided with steel side plates and rigidly connected with an upper part of a main girder, pours concrete in the frame, and thereby constructs a composite slab. When the frame is filled with concrete, there are cases in which voids are produced in an interface between the bottom steel plate and concrete. If air does not come out of the voids completely and voids are left after the concrete hardens, there is fear that strength and durability of the composite structure may be reduced. Thus, there is demand for a method of inspecting a condition of the interface between the bottom steel plate and concrete before the placed concrete hardens.
Thus, a method is known for inspecting a concrete-filled condition of such a composite structure by inputting an electrical signal which changes continuously in a predetermined frequency range to a piezoelectric loudspeaker and detecting changes in position and magnitude of a peak voltage in frequency-voltage characteristics of the piezoelectric loudspeaker (see Patent Document 1).
However, the method disclosed in Patent Document 1 provides only local information because small piezoelectric sensors are used, allowing a filling condition of concrete to be grasped only at places where piezoelectric sensors are placed. Also, if one attempts to apply the method to a large composite structure such as a bridge, a large number of piezoelectric sensors are needed in order to obtain information about interface conditions of the entire composite structure, resulting in complicated construction conditions due to an increased number of cables as well as in increased inspection costs. This is not desirable.
Also, when the inspection of filling condition is finished, there is troublesome after-treatment carried out to cut off the cables of the piezoelectric sensors extending outside from the interface between the bottom steel plate and concrete and bury the cables in the concrete and the like. Furthermore, the piezoelectric sensors used for inspection are thrown away and cannot be reused for inspection of other composite structures.
Also, once the concrete hardens, forming voids in the interface between the bottom steel plate and concrete, there is concern that water such as rain water will intrude the voids, corroding reinforcement members such as reinforcement bars and studs which reinforce the bottom steel plate and concrete. Once reinforcement members corrode, there is fear that the strength of the composite structure may be reduced. Thus, there is also demand for an inspection technique for identifying the presence or absence of trapped water in the voids formed in the interface of the composite structure between the bottom steel plate and concrete.
The present invention has been made in view of the above problems and has an object to provide an interface inspection method and apparatus capable of easily inspecting an interface condition in a desired part of a composite structure.
In order to achieve the above object, an aspect of the present invention is directed to providing an interface inspection method comprising the steps of: transmitting ultrasound to a composite structure to be inspected, via an ultrasound generating unit adapted to generate ultrasound of a frequency suitable for a member making up the composite structure and acquiring a signal waveform by receiving a reflected wave from the composite structure using a receiving unit; performing signal processing on the acquired signal waveform and acquiring signal amplitude versus frequency characteristics; and determining an interface condition of the composite structure based on an amplitude in a frequency band unique to the composite structure as observed on the signal waveform subjected to signal processing.
In the above-described step of performing signal processing, frequency analysis may be performed on the acquired signal waveform.
Alternatively, in the step of performing signal processing described above, the acquired signal waveform may be processed by a bandpass filter to pass specific frequency components of the signal waveform.
The interface condition described above may be a filling condition of fresh concrete in an interface of the composite structure made up of a steel plate and the fresh concrete.
Alternatively, the interface condition described above may be a condition of trapped water in an interface of the composite structure made up of a steel plate and hardened concrete.
An aspect of the present invention is directed to providing an interface inspection apparatus comprising: an ultrasound generating unit configured to apply ultrasound to a composite structure to be inspected, the ultrasound having a frequency suitable for a member making up the composite structure; a receiving unit configured to receive a reflected wave from the composite structure and acquiring a signal waveform; a signal processing unit configured to perform signal processing on the signal waveform received by the receiving unit and acquiring signal amplitude versus frequency characteristics; and a determination unit configured to determine an interface condition of the composite structure based on an amplitude in a frequency band unique to the composite structure as observed on the signal waveform subjected to signal processing.
According to the present invention, the interface inspection method and apparatus applies ultrasound of a frequency suitable for the composite structure, performs signal processing by receiving a reflected wave from the composite structure, and determines the interface condition of the composite structure based on an amplitude in the frequency band unique to the composite structure. Consequently, the interface condition in a desired location of the composite structure can be inspected easily based on the amplitude in the frequency band unique to the composite structure, making it possible to grasp the interface conditions of the entire composite structure by inspecting the composite structure as a whole.
An embodiment of the present invention will be described below with reference to the drawings.
As shown in
The transmitter probe 11 is connected to the pulser/receiver 14 adapted to transmit and receive ultrasound of a predetermined frequency and transmits the ultrasound of the frequency transmitted from the pulser/receiver 14 to the bottom steel plate 2. The pulser/receiver 14 inputs ultrasound of a frequency, which is set in a range of 20 kHz to 1 MHz, to the transmitter probe 11.
The receiver probe 12 is connected to the pulser/receiver 14 and receives a reflected wave reflected off the bottom steel plate 2. As shown in
Note that as the contact medium 13 used to efficiently transmit ultrasound, a medium capable of transmitting ultrasound, such as a gel sheet made, for example, of a soft elastomer, may be used instead of the glycerin paste. When a gel sheet is used as the contact medium 13, the gel sheet has such hardness that the gel sheet will be deformable when pressed by the transmitter probe 11 and receiver probe 12, and preferably has, for example, Asker hardness of C30 or less. Also, regarding thickness of the gel sheet, even if the gel sheet get deformed and becomes thin by being pressed by the transmitter probe 11 and receiver probe 12, preferably the thinned part has a predetermined thickness. Furthermore, since elastomers have stable characteristics against changes in ambient temperature, the gel sheet provides a stable state of contact especially during the hot days of summer and during the cold days of winter regardless of the season of the year. Also, when a gel sheet is used as the contact medium 13, it only remains to remove the gel sheet and no special after-treatment is required. Also, preferably the gel sheet has a size substantially equal to the area of contact surfaces of the transmitter probe 11 and receiver probe 12 placed in contact with a contact surface 2a of the bottom steel plate 2 via the gel sheet.
As shown in
The reflected wave received by the receiver probe 12 is converted into an electrical signal by the pulser/receiver 14. The reflected wave converted to the electrical signal is converted into a digital signal by the A/D converter 16 and subjected to signal processing by the arithmetic unit 18. Specifically, the arithmetic unit 18 includes a signal processing unit (a signal processing unit) 20 and determination unit (a determination unit) 22, of which, the signal processing unit 20 performs frequency analysis of the reflected wave and displays analysis results on the monitor 24. The determination unit 22 determines the condition of the interface 8 between the bottom steel plate 2 and concrete 4 in the composite slab 6 based on the reflected wave subjected to the analysis process by the signal processing unit 20. Note that although not illustrated, the arithmetic unit 18 may include a notification unit and may give a notice using the notification unit according to determination results produced by the determination unit 22. Also, although not illustrated, the arithmetic unit 18 includes memories such as a ROM and RAM, and a threshold and the like described later are set in the memories.
Description will be given below of an interface inspection method for inspecting the interface 8 of the composite slab 6 using the interface inspection apparatus 10 configured as described above.
In step S1, ultrasonic flaw detection of the composite slab 6 is performed. Specifically, the transmitter probe 11 and receiver probe 12 are placed at desired locations on a lateral surface of the bottom steel plate 2, and the ultrasound is transmitted to the bottom steel plate 2 from the transmitter probe 11, and a reflected wave from the bottom steel plate 2 is received by the receiver probe 12. The frequency of the ultrasound used in this step is selected appropriately according to the thickness of the bottom steel plate 2.
An example of waveforms obtained as a result of flaw detection in this step is shown in
In step S2, frequency analysis is performed on the reflected wave acquired in step S1 above. Specifically, the Fast Fourier Transform (hereinafter referred to as FFT) of a signal waveform of the reflected wave obtained in step S1 above is performed and a graph of frequency-amplitude characteristics is created. It can be confirmed from the graph that when there is any void in the interface 8 between the bottom steel plate 2 and concrete 4, amplitudes in a frequency band unique to the bottom steel plate 2 are larger than when there is no void. This is because if low-frequency ultrasound (frequency: 20 kHz to 1 MHz) is incident upon the interface 8 between the bottom steel plate 2 and concrete 4 when there is any void in the interface 8, the ultrasound propagates mainly as a Lamb wave (plate wave) by repeating multiple reflections, mode conversion, and interference in the bottom steel plate 2 without escaping into the concrete 4 and consequently components of the reflected wave are detected as the frequency of the ultrasound incident upon the bottom steel plate 2 and frequency components due to the interval of multiple reflection echoes of a longitudinal wave given by Eq. (1) below, i.e., the frequency band unique to the bottom steel plate 2. The frequency band unique to the bottom steel plate 2 is found from Eq. (1) below.
f=v/(2×t) (1)
where f is the frequency band unique to the bottom steel plate 2, v is the sound velocity of the ultrasound propagating through the bottom steel plate 2, and t is the plate thickness of the bottom steel plate 2. An example of frequency analysis results in this step is shown in
In step S3, it is determined whether or not the magnitude of the amplitude in the specific frequency band according to the frequency analysis results obtained in step S2 above is smaller than a preset threshold. The threshold is a value at or above which it is determined that the interface 8 contains a void in excess of a tolerance. When the determination result is true (Yes), the arithmetic unit 18 goes to step S4. On the other hand, when the determination result is false (No), the arithmetic unit 18 goes to step S5. The specific frequency band used to determine the filled condition in this step is a unique frequency band which depends on the thickness of the bottom steel plate 2 to be inspected.
In step S4, since the amplitude in the specific frequency band according to the frequency analysis results obtained in step S2 above is smaller than the threshold, meaning that no void exists in the interface 8 between the bottom steel plate 2 and concrete 4 or that the size of the void existing in the interface 8 is within the tolerance, the flowchart is terminated by determining that the filled condition of the interface 8 is sufficient.
On the other hand, in step S5, since the amplitude in the specific frequency band according to the frequency analysis results obtained in step S2 above is equal to or larger than the threshold, it is determined that the size of the void existing in the interface 8 between the bottom steel plate 2 and concrete 4 exceeds the tolerance, and the flowchart is terminated by determining that the filled condition of the interface 8 is insufficient.
The reason why the filled condition of the interface 8 can be identified by carrying out steps S1 to S5 described above is as follows. That is, when fresh concrete exists on the bottom steel plate 2, part of a reflected component of the longitudinal wave passes into the fresh concrete. On the other hand, when no fresh concrete exists on the bottom steel plate 2, the reflected component of the longitudinal wave repeats multiple reflections in the bottom steel plate 2. Thus, by noting the reflected component of the frequency found from Eq. (1) above, it is possible to ascertain and identify a filled/unfilled state on the bottom steel plate 2 with fresh concrete 4 by carrying out each of the steps described above.
In this way, according to the present embodiment, ultrasonic flaw detection of the composite slab 6 is performed by placing the ultrasound probes 11 and 12 at desired locations on the bottom steel plate 2, the magnitude of the amplitude in a specific frequency band is compared with a threshold by performing frequency analysis of a received waveform, and the filled condition of the interface 8 with concrete 4 is determined. Consequently, since a desired part of the interface 8 can be inspected, the filled condition of the entire interface 8 can be grasped by inspecting the entire composite slab 6. Also, since frequency-amplitude characteristics can be obtained by performing frequency analysis on a received signal obtained by ultrasonic flaw detection, the condition of the interface 8 can be grasped easily by checking the magnitude of the amplitude in a specific frequency band.
Furthermore, if glycerin paste is used as a contact medium in a process after the end of interface inspection, it only remains to remove the glycerin paste applied to the respective abutment points at which the transmitter probe 11 and receiver probe 12 abut the bottom steel plate 2. Thus, the filled condition of the interface 8 can be inspected efficiently. The interface inspection method of the present invention uses ultrasonic probes, which can be used repeatedly for interface inspection of other composite slabs, making it possible to reduce inspection cost.
<Variation>
A variation of the interface inspection method according to the embodiment will be described below. The variation differs from the embodiment in that the void formed in the interface between the bottom steel plate and hardened concrete is inspected for trapped water using the interface inspection method described above. The rest of the configuration is in common with the embodiment, and thus description thereof will be omitted.
In step S13, it is determined whether or not the magnitude of the amplitude in the specific frequency band according to the frequency analysis results obtained in step S12 is smaller than a preset threshold. The threshold is a value at or above which it is determined that the interface 8 contains trapped water. When the determination result is true (Yes), the arithmetic unit 18 goes to step S14. When the determination result is false (No), the arithmetic unit 18 goes to step S15. The specific frequency band used to determine the condition of trapped water in this step is a unique frequency band which depends on the thickness of the bottom steel plate 2 to be inspected.
In step S14, since the amplitude in the specific frequency band according to the frequency analysis results obtained in step S12 above is smaller than the threshold, the flowchart is terminated by determining that there is a void in the interface 8 between the bottom steel plate 2 and hardened concrete and that water is trapped in the void.
On the other hand, in step S15, since the amplitude in the specific frequency band according to the frequency analysis results obtained in step S12 above is equal to or larger than the threshold, the flowchart is terminated by determining that although there is the void in the interface 8 between the bottom steel plate 2 and hardened concrete, water is not trapped in the void.
If water is trapped in the void formed in the interface 8 between the bottom steel plate 2 and hardened concrete, part of a reflected component of the longitudinal wave expressed by Eq. (1) described above passes into the trapped water. On the other hand, when there is no trapped water, the reflected component of the longitudinal wave repeats multiple reflections in the bottom steel plate 2. Thus, by noting the reflected component of the frequency found from Eq. (1) described above, it is possible to ascertain and identify the presence or absence of trapped water in the void formed in the interface 8 between the bottom steel plate 2 and hardened concrete by carrying out steps S11 to S15 described above. In this way, since the trapped water inspection method according to the present variation is based on the same principle as the interface inspection method according to the embodiment described above, the interface inspection method according to the embodiment described above can be applied to the trapped water inspection method according to the present variation.
The present invention will be described below by citing examples, but the present invention is not limited to the following examples.
Using the interface inspection apparatus 10 according to the present invention, the interface inspection method described above was performed to inspect the filled condition of the interface 8 of the composite slab 6 filled with fresh concrete.
A schematic diagram of the interface inspection method performed in this example is shown in
Results are shown in
As shown in
On the other hand, as shown in
In
Thus,
Using the interface inspection apparatus 10 according to the present invention, the above-described interface inspection method according to the present invention was performed to inspect the filled condition of the interface 8 of the composite slab 6 filled with concrete. Note that this example differed from example 1 above in that the object to be inspected was a composite slab 6 made up of the bottom steel plate 2 and hardened concrete 4′, but the rest of the configuration and the inspection conditions were the same as example 1 described above.
Survey results are shown in
Using the interface inspection apparatus 10 according to the present invention, trapped water inspection of the interface 8 of a composite slab 6′ filled with concrete was performed by the trapped water inspection method according to the above-described variation of the present variation.
A schematic diagram of the trapped water inspection method performed in this example is shown in
Results are shown in
As shown in
When water is trapped in the simulated void 9 the ultrasound multiply reflected off the bottom steel plate 2 escapes into the water and consequently no notable amplitude is observed as with
Using the interface inspection apparatus 10 according to the present invention, the interface inspection method described in the above embodiment was performed to inspect the filled condition of the interface 8 of the composite slab 6 filled with fresh concrete 4.
A schematic diagram of the interface inspection method performed in this example is shown in
Results are shown in
As shown in
This concludes the description of the embodiment and examples, but the present invention is not limited to the embodiment and examples described above.
For example, although in the embodiment, an FFT-based frequency analysis is performed on the reflected wave received by the receiver probe 12, a bandpass filter (regardless of whether the bandpass filter is analog or digital) or wavelet transform may be applied instead of frequency analysis, where the bandpass filter passes only a specific frequency of a received signal waveform and the wavelet transform is a type of frequency analysis. The wavelet transform, in particular, is preferable because even after a received signal obtained by ultrasonic flaw detection is converted, time axis information remains in addition to frequency-amplitude characteristics, making it possible to use an analysis method for a sum, product, or the like of any desired components.
Furthermore, although in the embodiment, description has been given of how to determine the filled condition of the interface 8 using the interface inspection method, when it is determined in step S3 above that the filled condition of the interface 8 is insufficient, the concrete 4 may be compacted by installing a vibrator or the like at a flaw detection location on the bottom steel plate 2 and then the filled condition of the interface 8 may be inspected again using the interface inspection method described above. This allows a desired location of the interface 8 to be inspected easily. Also, since the condition of the interface 8 can be grasped before the concrete 4 hardens, eliminating the need to make repairs by making a hole in the steel plate after the concrete 4 hardens and filling concrete or the like into the void, it is possible to improve working efficiency.
Besides, in the examples described above, the interface inspection method of the present invention has been applied to check the interface 8 of fresh concrete 4, interface 8 of hardened concrete 4′, and for trapped water in interface 8, this is not restrictive and the interface inspection method can be applied to check, for example, separation of laminated fiber-glass reinforced plastic layers. Also in cast molding which involves pouring rubber into a mold to cause the rubber to cure, the method can be applied to check the filled condition of an interface between rubber and mold, for example, to check for any cavity produced when the rubber is stagnant.
Number | Date | Country | Kind |
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2012-259955 | Nov 2012 | JP | national |
Number | Date | Country | |
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Parent | PCT/JP2013/072117 | Aug 2013 | US |
Child | 14617293 | US |