Patent Description:
When load is applied to a concrete floor slab of a bridge due to traffic or the like, Acoustic Emission (AE) occurs due to crack propagation, friction, or the like in the floor slab. AE can be detected by installing an AE sensor on a surface of the floor slab. AE is an elastic wave generated as a fatigue crack of a material develops. Further, by installing a plurality of AE sensors, a source of location the elastic wave (hereinafter referred to as "AE source") can be located from a difference in AE arrival time between the sensors.

Generally, in a concrete floor slab of a bridge, although damage inside the floor slab such as horizontal cracks is very difficult to detect by conventional nondestructive inspection, the damage inside can be estimated by analyzing data acquired by the AE sensors. However, a large amount of time is required for installing an AE sensor in a bridge and the like and obtaining sufficient data for estimating damage thereto. Therefore, an inside of concrete cannot be evaluated efficiently in some cases. Such a problem is not limited to the concrete floor slab of a bridge but is a problem common to all the structures in which elastic waves are generated as cracks occur or develop.

Chinese patent document <CIT> discloses an automatic identification method for sound source distribution areas in tank bottom corrosion acoustic emission detection. By the method, areas where acoustic emission sources are densely distributed in a tank can be effectively identified, and the tank bottom corrosion condition is evaluated further.

United States patent document <CIT> discloses a system for monitoring a structure that includes at least one monitoring arrangement attached at a respective location to the structure, each monitoring arrangement having at least one inertial measurement unit (IMU) that measures acceleration and/or angular motion in any direction and rotation about any axis, a Global Navigation Satellite System (GNSS) receiver that determines its location, and a wireless communication system that transmits information derived from acceleration and/or angular motion measured by the IMU and a location determination by the GNSS receiver.

United States patent document <CIT> discloses a signal processing apparatus includes a receiver, a time information generator, a processor, and a communicator. The receiver receives a voltage signal from a sensor that detects an elastic wave generated from a structure. The time information generator generates time information having a bit length based on a measurement continuing time period of the structure, a propagation velocity of the elastic wave, and a position identification accuracy of a generation source of the elastic wave.

An objective of the present invention is to provide a structure evaluation system, and a structure evaluation method capable of efficiently evaluating a structure.

According to a first aspect, a structure evaluation system according to claim <NUM> is provided. According to a second aspect, a structure evaluation method according to claim <NUM> is provided.

Hereinafter, a structure evaluation system, and a structure evaluation method according to an embodiment will be described with reference to the accompanying drawings.

<FIG> is a view illustrating a system constitution of a structure evaluation system <NUM> according to an embodiment. The structure evaluation system <NUM> is used for evaluating the soundness of a structure. Although a bridge is described as an example of a structure in the embodiment, a structure is not necessarily limited to a bridge. For example, a structure may be any structure as long as an elastic wave is generated in the structure due to occurrence or development of cracks or an external impact (e.g., rain, artificial rain, etc.). Also, a bridge is not limited to a structure constructed over a river or a valley, and includes various structures provided above the ground (e.g., an elevated bridge over a highway).

The structure evaluation system <NUM> includes a plurality of acoustic emission (AE) sensors <NUM>-<NUM> to <NUM>-n (n is an integer equal to or greater than <NUM>), a signal processor <NUM>, and a structure evaluation apparatus <NUM>. The signal processor <NUM> and the structure evaluation apparatus <NUM> are connected to be able to communicate via a wire or wirelessly. Further, in the description below, the AE sensors <NUM>-<NUM> to <NUM>-n are referred to as an AE sensor <NUM> when not distinguished.

The AE sensor <NUM> is installed in a structure. For example, the AE sensor <NUM> is installed on a concrete floor slab <NUM> of a bridge. The AE sensor <NUM> has a piezoelectric element, detects an elastic wave (AE wave) generated by the structure, and converts the detected elastic wave into a voltage signal (AE source signal). The AE sensor <NUM> performs processing such as amplification and frequency limiting on the AE source signal and outputs the processing result to the signal processor <NUM>.

The signal processor <NUM> receives the AE source signal processed by the AE sensor <NUM> as an input. The signal processor <NUM> performs necessary signal processing such as noise removal and parameter extraction on the input AE source signal to extract an AE parameters including information on the elastic wave. The information on the elastic wave is, for example, information such as an amplitude, an energy, a rise time, a duration, a frequency, and a zero-crossing count number of the AE source signal. The signal processor <NUM> outputs information based on the extracted AE parameters to the structure evaluation apparatus <NUM> as an AE signal. The AE signal output from the signal processor <NUM> includes information such as a sensor ID, an AE detection time, an AE source signal amplitude, an energy, a rise time, and a frequency.

Here, the amplitude of the AE source signal is, for example, a value of the maximum amplitude among elastic waves. The energy is, for example, a value obtained by time integration of squared amplitude at each time point. The definition of energy is not limited to the above example, and may be, for example, one approximated by using an envelope curve of a waveform. The rise time is, for example, a time T1 until an elastic wave rises above a preset predetermined value from zero. The duration is, for example, an amount of time from the start of the rise of an elastic wave until the amplitude becomes smaller than a preset value. The frequency is a frequency of an elastic wave. The zero-crossing count number is, for example, the number of times that an elastic wave crosses a reference line passing a zero value.

The structure evaluation apparatus <NUM> includes a central processing unit (CPU), a memory, an auxiliary storage device or the like connected via a bus, and executes an evaluation program. By executing the evaluation program, the structure evaluation apparatus <NUM> functions as an apparatus including a position locator <NUM>, an evaluator <NUM>, and a display <NUM>. Further, all or some of the functions of the structure evaluation apparatus <NUM> may be realized by using hardware such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable gate array (FPGA), or the like. Also, the evaluation program may be recorded in a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a read-only memory (ROM), a compact disc (CD)-ROM or the like, or a storage device such as a hard disk embedded in a computer system. Also, the evaluation program may be transmitted and received via an electric communication line.

The position locator <NUM> receives an AE signal output from the signal processor <NUM> as an input. Also, the position locator <NUM> pre-stores information on an installation position of the AE sensor <NUM> in the structure (hereinafter referred to as "sensor position information") by associating the information to a sensor ID. The information on the installation position is, for example, latitude and longitude, or a distance in the horizontal direction and the vertical direction from a specific position on the structure, and the like. The position locator <NUM> locates a position of an AE source on the basis of the information such as the sensor ID and the AE detection time included in the input AE signal and the pre-stored sensor position information. For example, the position locator <NUM> uses a plurality of AE signals caused by an impact on the structure to locate the position of the AE source. Here, the impact on the structure is an impact generated due to colliding of numerous micro-objects. The numerous micro-objects are objects generated by weather phenomena such as raindrops, hail and snow pellets. Also, the position locator <NUM> derives a source distribution by using the position location results. The source distribution represents the distribution of AE sources generated from the structure. The position locator <NUM> outputs the derived source distribution to the evaluator <NUM>.

The evaluator <NUM> receives the source distribution output from the position locator <NUM> as an input. The evaluator <NUM> evaluates the soundness of the structure on the basis of the input source distribution. Specifically, on the basis of the source distribution, the evaluator <NUM> evaluates a region in which the density of the AE sources is less than a first threshold value as a region in which deterioration of the structure is occurring. The evaluator <NUM> makes the display <NUM> display the evaluation result. The first threshold value may be set in advance or may be appropriately set.

The display <NUM> is an image display device such as a liquid crystal display or an organic electro luminescence (EL) display. The display <NUM> displays the evaluation result according to the control of the evaluator <NUM>. The display <NUM> may be an interface for connecting the image display device to the structure evaluation apparatus <NUM>. In this case, the display <NUM> generates a video signal for displaying the evaluation result, and outputs the video signal to the image display device connected to the display <NUM>.

<FIG> is a view illustrating a state of propagation of an elastic wave due to rainfall. As illustrated in <FIG>, when a raindrop <NUM> collides with a road surface <NUM>, an elastic wave <NUM> is generated from the collision position. The elastic wave <NUM> propagates through the interior of the floor slab and also to a lower surface thereof. The elastic wave <NUM> that maintains a sufficient amplitude until reaching the AE sensor <NUM> installed at the lower surface is detected by the AE sensor <NUM>. As in the case of the elastic wave <NUM> due to damage, the position locator <NUM> can identify an approximate collision position of the raindrop <NUM> by locating a position with respect to the elastic wave <NUM> generated by rain. In this way, an impact caused by collision of a micro-object is an impact applied to a surface (the road surface <NUM> in <FIG>) opposite to the surface at which the AE sensor <NUM> is installed.

However, when a large horizontal crack <NUM> is present inside the floor slab, the elastic wave <NUM> generated by the raindrop <NUM> colliding with the road surface <NUM> is blocked by the crack, or bypasses or is attenuated by the crack. Therefore, it is difficult for the elastic wave <NUM> having a sufficient amplitude to reach the AE sensor <NUM> located directly below the crack. Consequently, when the position locator <NUM> locates positions of the AE sources on the lower surface of the floor slab having the large horizontal crack <NUM>, the number of located AE sources is reduced. Collision of the raindrops <NUM> against the road surface <NUM> due to rainfall occurs randomly and evenly with respect to the entire region. Therefore, the elastic wave <NUM> is detected on the lower surface of the floor slab without large damage, and AE sources are evenly located all over a region when the position location of the AE sources is performed. On the other hand, when the inside of the floor slab has large damage, it is assumed that the density of the AE sources directly below the damaged portion is reduced. The structure evaluation apparatus <NUM> in the embodiment evaluates the soundness of the structure on the basis of such assumption.

<FIG> is a view illustrating a trend of the number of occurrences of elastic waves during a certain measurement period. In <FIG>, the horizontal axis represents the time (hours) during the measurement period, and the vertical axis represents the number of hits. The number of hits is the number of detected elastic waves. The number of hits represents the number of detected elastic waves every <NUM> minutes, for example. In <FIG>, the number of hits from <NUM> hours to <NUM> hours in the measurement period is the number of detected elastic waves in the normal state. With respect to the number of hits during the measurement period from <NUM> hours to <NUM> hours, a period in which a large number of elastic waves <NUM> are observed as compared with the number of occurrences of elastic waves at the normal time (measurement period from <NUM> hours to <NUM> hours) is present (reference numeral <NUM> in <FIG>). At this time, rainfall with strong wind is observed. In the event of heavy rain such as guerrilla heavy rain, a large amount of elastic waves are generated in such a short time. Since the AE sensor <NUM> is a very sensitive piezoelectric sensor, the AE sensor <NUM> also detects elastic waves generated due to factors not caused by damage to the floor slab, such as an impact on the structure due to rain. Thus, rainfall or the like may become a noise source for detection of damage using the AE sensor <NUM>.

On the other hand, the position locator <NUM> in the structure evaluation apparatus <NUM> derives the source distribution by using AE signals within a predetermined period including a time at which a large amount of elastic waves are detected (hereinafter referred to as "target time") as illustrated in <FIG> as the plurality of AE signals caused by the impact on the structure. Whether a large amount of elastic waves is detected is determined on the basis of whether the number of elastic waves detected at a certain time is a second threshold value or larger. When the number of elastic waves detected at a certain time is the second threshold value or larger, it is determined that a large amount of elastic waves have been detected. On the other hand, when the number of elastic waves detected at a certain time is less than the second threshold value, it is determined that a large amount of elastic waves have not been detected. The second threshold value may be set in advance or may be appropriately set. Further, the predetermined period may be a predetermined period of time before and after a target time (for example, <NUM> minutes before and after the target time), or may be a period before the target time or a period after the target time when the target time is included in the predetermined period.

<FIG> is a view illustrating an example of a source distribution derived using an AE signal within a predetermined period. In <FIG>, the horizontal axis and the vertical axis represent the length (mm) in the horizontal direction and the length (mm) in the vertical direction from the specific position on the structure to be evaluated. In <FIG>, a result of locating AE sources using AE signals during about ten minutes during rainfall in <FIG> (e.g., about ten minutes including the time (reference numeral <NUM>) at which a great number of elastic waves <NUM> are observed in the measurement period from <NUM> hours to <NUM> hours) is shown. The + mark in the figure indicates an installation position of the AE sensor <NUM>. While the AE sources are distributed throughout the region of the structure to be evaluated, hardly any of the AE sources are located in a central region <NUM>. The evaluator <NUM> evaluates a region in which the density of the AE sources is less than the first threshold value (the region <NUM> in <FIG>) as a region in which deterioration of the structure is occurring. Any region may be a target for evaluation of the evaluator <NUM>. For example, the evaluator <NUM> may perform evaluation for each region surrounded by four AE sensors <NUM>, may perform evaluation for each region surrounded by four or more AE sensors <NUM>, may perform evaluation for each region surrounded by three AE sensors <NUM>, or may perform evaluation for each region having a designated range.

<FIG> is a flowchart illustrating a flow of an evaluation process of the structure evaluation apparatus <NUM>. The process in <FIG> is executed when the number of detected elastic waves is the second threshold value or larger. Further, it is assumed that an AE signal output from the signal processor <NUM> is accumulated in a buffer (not illustrated).

The position locator <NUM> acquires an AE signal within a predetermined period from the buffer (not illustrated) (Step S101). That is, the position locator <NUM> obtains an AE signal within a predetermined period including the target time from the buffer (not illustrated). The position locator <NUM> locates positions of the AE sources by using a plurality of acquired AE signals (Step S102). Then, the position locator <NUM> derives the source distribution on the basis of the position location results (Step S103).

The position locator <NUM> outputs the generated source distribution to the evaluator <NUM>. Using the source distribution output from the position locator <NUM>, the evaluator <NUM> determines whether a region in which the density of the AE sources is less than the first threshold is present (Step S104). When a region in which the density of the AE sources is less than the first threshold value is present (YES to Step S104), the evaluator <NUM> evaluates the region in which the density is less than the first threshold value as a region in which deterioration of the structure is occurring (Step S105).

On the other hand, when a region in which the density of the AE sources is less than the first threshold value does not exist (NO to Step S104), the evaluator <NUM> evaluates that a region in which deterioration of the structure is occurring is not present (Step S106). The evaluator <NUM> makes the display <NUM> display the evaluation result. For example, the evaluator <NUM> displays the evaluation result by displaying a region in which deterioration is occurring in the source distribution in a form different from that of other regions. The form different from that of other regions may include coloring the region in which deterioration is occurring, surrounding the region in which deterioration is occurring by a circle, or marking the region in which deterioration is occurring using a letter. The display <NUM> displays the evaluation result according to the control of the evaluator <NUM>.

According to the structure evaluation system <NUM> configured as described above, a structure can be efficiently evaluated. Hereinafter, the effect thereof will be described in detail.

By using the AE signal due to the impact on the structure, the structure evaluation apparatus <NUM> derives a source distribution including a large amount of AE sources. Then, on the basis of the source distribution, the structure evaluation apparatus <NUM> evaluates a region in which the density of the AE sources is less than the first threshold value as a region in which the deterioration of the structure is occurring. In this way, by using data which is conventionally a source of noise, a structure can be efficiently evaluated.

Also, the structure evaluation apparatus <NUM> derives the source distribution by using the AE signal within a predetermined period including the target time as the AE signal caused by the impact on the structure. Conventionally, several tens of hours of measurement is required to perform the evaluation. In comparison with this, according to the method using the structure evaluation apparatus <NUM>, the required time is significantly shortened by using only the AE signal within the predetermined period including the target time, and the evaluation can be performed efficiently.

Hereinafter, a modified example of the structure evaluation apparatus <NUM> will be described.

A part or all of the functional units of the structure evaluation apparatus <NUM> may be provided in separate housings. For example, the structure evaluation apparatus <NUM> may include only the evaluator <NUM>, and the position locator <NUM> and the display <NUM> may be provided in separate housings. In this case, the evaluator <NUM> acquires the source distribution from another housing and evaluates the soundness of the structure using the acquired source distribution. Then, the evaluator <NUM> outputs the evaluation result to the display <NUM> provided in another housing.

By the above constitution, by using an existing device for deriving the source distribution, the manufacturing cost of the structure evaluation apparatus <NUM> can be suppressed.

The signal processor <NUM> may be provided in the structure evaluation apparatus <NUM>. In this case, the signal processor <NUM> acquires an AE source signal processed by the AE sensor <NUM> directly from the AE sensor <NUM> or via a relay device (not illustrated).

In <FIG>, although a single signal processor <NUM> is connected to the plurality of AE sensors <NUM>-<NUM> to <NUM>-n, the structure evaluation system <NUM> may include a plurality of signal processors <NUM> and have a plurality of sensor units by the signal processors <NUM> being connected to the AE sensors <NUM>, respectively.

The evaluator <NUM> may be configured to derive the source distribution by using the AE signal at the target time as the AE signal caused by an impact on the structure.

Further, the evaluator <NUM> may operate as an output control unit. The output control unit controls an output unit and outputs the evaluation result. Here, the output unit includes the display <NUM>, a communication unit, and a printing unit. When the output unit is a communication unit, the output control unit controls the communication unit and transmits the evaluation result to another device. Further, when the output unit is a printing unit, the output control unit controls the printing unit and prints the evaluation result. The structure evaluation apparatus <NUM> may include some or all of the display <NUM>, the communication unit, and the printing unit as the output unit and execute the above operations.

The evaluator <NUM> may display the source distribution as a contour map on the display <NUM>.

A factor causing increase in the number of generated elastic waves is not necessarily limited to the above example (weather phenomenon). For example, the measurement timing can be controlled by using a source of elastic waves generated due to an impact generated by artificial actions such as scattering or spraying chemicals, hitting multiple times using a device, and the like. Therefore, diagnosis can be performed more efficiently. In this case, because the timing at which elastic waves are generated is known in advance, the structure evaluation system <NUM> is at rest at normal times, and a trigger for notifying the activation timing may be input from outside in accordance with the timing of generating elastic waves. In this way, operation is possible with reduced power consumption.

To decrease the power required for the measurement, for example, only some of the AE sensors <NUM> may be activated at normal times, and other AE sensors <NUM> may be activated when a sharp increase in the number of generated elastic waves is detected. The processing in this case will be described with reference to <FIG> and <FIG>.

<FIG> and <FIG> are sequence diagrams illustrating a processing flow of the structure evaluation system <NUM>. In <FIG> and <FIG>, it is assumed that the AE sensor <NUM>-<NUM> is operating at the start of the processing and the AE sensor <NUM>-<NUM> is at rest. Being at rest does not mean that all functions of the apparatus are paused, but means that only functions related to activation are operating.

The AE sensor <NUM>-<NUM> detects an elastic wave (an AE wave) generated by the structure (Step S201). The AE sensor <NUM>-<NUM> converts the detected elastic wave into a voltage signal (an AE source signal), performs processing, such as amplification, frequency limiting, and the like, on the AE source signal, and outputs the processing result to the signal processor <NUM> (Step S202). The signal processor <NUM> performs necessary signal processing such as noise removal and parameter extraction on the input AE source signal (Step S203). The signal processor <NUM> outputs information based on the AE parameters extracted by performing signal processing to the structure evaluation apparatus <NUM> as an AE signal (Step S204). The processing from Step S201 to Step S204 is repeatedly executed. The AE signal output from the signal processor <NUM> is accumulated in the buffer (not illustrated).

It is assumed that the position locator <NUM> has detected a sharp increase in the number of generated elastic waves (Step S206). For example, the position locator <NUM> detects that a sharp increase in the number of generated elastic waves has occurred when a difference between the number of elastic waves generated at the current time and the number of elastic waves generated at an immediately preceding time exceeds a third threshold value. The third threshold value may be set in advance or may be appropriately set. Then, the position locator <NUM> notifies the signal processor <NUM> that a sharp increase in the number of generated elastic waves has been detected (Step S206). Upon receiving the notification from the position locator <NUM>, the signal processor <NUM> transmits an activation signal to the AE sensor <NUM>-<NUM> that is at rest (Step S207). The activation signal refers to a signal for instructing execution of activation processing.

Upon receiving the activation signal from the signal processor <NUM>, the AE sensor <NUM>-<NUM> executes the activation processing (Step S208). As a result, the AE sensor <NUM>-<NUM> is operated from the state at rest. The AE sensor <NUM>-<NUM> detects an elastic wave (AE wave) generated by the structure (Step S209). The AE sensor <NUM>-<NUM> converts the detected elastic wave into a voltage signal (AE source signal), performs processing such as amplification and frequency limiting, on the AE source signal, and outputs the processing result to the signal processor <NUM> (Step S210). The signal processor <NUM> performs necessary signal processing such as noise removal and parameter extraction on the input AE source signal (Step S211). The signal processor <NUM> outputs information based on the AE parameters extracted by performing signal processing to the structure evaluation apparatus <NUM> as an AE signal (Step S212). The processing from Step S209 to Step S212 is repeatedly executed. The AE signal output from the signal processor <NUM> is stored in the buffer (not illustrated).

The AE sensor <NUM>-<NUM> detects an elastic wave (an AE wave) generated by the structure (Step S213). The AE sensor <NUM>-<NUM> converts the detected elastic wave into a voltage signal (an AE source signal), performs processing, such as amplification, frequency limiting, and the like, on the AE source signal, and outputs the processing result to the signal processor <NUM> (Step S214). The signal processor <NUM> performs necessary signal processing such as noise removal and parameter extraction on the input AE source signal (Step S215). The signal processor <NUM> outputs information based on the AE parameters extracted by performing signal processing to the structure evaluation apparatus <NUM> as an AE signal (Step S216). The processing from Step S213 to Step S216 is repeatedly executed. The AE signal output from the signal processor <NUM> is accumulated in the buffer (not illustrated).

The position locator <NUM> acquires an AE signal within a predetermined period including the target time from the buffer (not illustrated). Using the acquired AE signal, the position locator <NUM> locates positions of the AE sources (Step S217). Then, the position locator <NUM> derives the source distribution on the basis of the position location results (Step S218). The position locator <NUM> outputs the derived source distribution to the evaluator <NUM>. The evaluator <NUM> performs evaluation using the source distribution output from the position locator <NUM> (Step S <NUM>). The evaluation method is the same as the above-mentioned method and will thus be omitted. The evaluator <NUM> makes the display <NUM> display the evaluation result. The display <NUM> displays the evaluation result according to the control of the evaluator <NUM> (Step S220).

By the above constitution, it is not always necessary for all the AE sensors <NUM> to be in operation. Thus, power consumption can be reduced.

Further, when some or all of the AE sensors <NUM> are at rest, the AE sensor <NUM> may be activated when a micro-object is detected by a device such as a rain gauge, a camera, and a microphone. Also, for example, the AE sensor <NUM> may be activated at a time when an event due to an impact on a structure is expected based on weather information such as rainfall, temperature and humidity levels near a measurement region.

According to at least one of the embodiments described above, a structure can be evaluated efficiently by having the plurality of AE sensors <NUM> configured to detect elastic waves generated from a structure, the signal processor <NUM> configured to perform signal processing on the elastic waves detected by the AE sensors <NUM> to output an AE signal, a position locator <NUM> configured to derive a source distribution by using an AE signal caused by an impact on the structure, and the evaluator <NUM> configured to evaluate a state of deterioration of a predetermined region of the structure from a density of AE sources obtained on the basis of the source distribution.

Claim 1:
A structure evaluation system (<NUM>) comprising:
a plurality of AE sensors (<NUM>) configured to detect elastic waves generated from a structure;
a position locator (<NUM>) configured to derive a source distribution of the elastic waves generated from the structure caused by an impact on the structure; and
an evaluator configured to evaluate a state of deterioration of a predetermined region of the structure from a density of sources of the elastic waves obtained on the basis of the source distribution,
wherein the position locator (<NUM>) is configured to derive the source distribution by using a signal obtained from the elastic waves at a time at which the number of detected elastic waves is a second threshold value or larger or a signal obtained from the elastic waves within a predetermined period including the time;
wherein the evaluator (<NUM>) is configured to evaluate a region in which the density of sources of the elastic waves is less than a first threshold value as a region in which deterioration of the structure is occurring.