Patent Description:
In recent years, problems related to aging of structures such as bridges constructed during the period of high economic growth have become noticeable. Because loss is immeasurable when an accident occurs in a structure, technologies for monitoring a state of a structure have been proposed. For example, a technology for detecting damage to a structure by an acoustic emission (AE) method in which an elastic wave generated due to occurrence of an internal crack or development of an internal crack is detected by a high-sensitivity sensor has been proposed. AE is an elastic wave generated due to development of fatigue crack of a material. In the AE method, an elastic wave is detected as an AE signal (voltage signal) by an AE sensor using a piezoelectric element. The AE signal is detected as an indication before breakage of the material occurs. Therefore, the frequency of occurrence of AE signals and the signal intensity are useful as an index indicating the soundness of the material. For this reason, studies are being carried out on technologies for detecting signs of deterioration of structures by the AE method.

When a load due to traffic or the like is applied on a concrete floor slab of a bridge, AE occurs due to crack propagation, friction, or the like in the floor slab. By installing an AE sensor on a surface of the floor slab, the AE generated from the floor slab can be detected. Moreover, by installing a plurality of AE sensors, a position of an AE source can be located from a difference in arrival time of AE signals between the AE sensors. A degree of damage to a target floor slab is estimated from the result of locating the position of the AE source. However, when the correspondence between the location result and the degree of damage is not sufficient, stable soundness evaluation cannot be performed in some cases. Such a problem is not limited to concrete floor slabs of a bridge but is a problem common to all structures in which elastic waves are generated as cracks occur or develop.

An objective of the present invention is to provide a structure evaluation system and a structure evaluation method capable of evaluating soundness of a structure in which elastic waves are generated.

According to a first aspect, there is provided a structure evaluation system according to claim <NUM>. According to a second aspect, there is provided a structure evaluation method according to claim <NUM>. Additional embodiments are described in the dependent claims.

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

<FIG> is a view illustrating a system constitution of a structure evaluation system <NUM>. The structure evaluation system <NUM> is used for evaluating the soundness of a structure. In the below embodiments and examples, the term evaluation refers to determining a degree of soundness of a structure, or a state of deterioration of the structure, based on a standard or standards. Although a bridge is described as an example of a structure in the embodiments and examples, the 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 of a bridge. The AE sensor <NUM> has a piezoelectric element, detects an elastic wave (an AE wave) generated from the structure, and converts the detected elastic wave into a voltage signal (an 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>. Instead of the AE sensor <NUM>, an acceleration sensor can be used. In this case, the acceleration sensor performs processing similar to the processing by the AE sensor <NUM> to generate a processed signal and output the processed signal to the signal processor <NUM>. The thickness of a concrete slab is at least <NUM>.

The signal processor <NUM> receives the AE source signal processed by the AE sensor <NUM> as an input. The signal processor <NUM> performs signal processing, such as noise removal and parameter extraction, deemed necessary on the input AE source signal to extract an AE feature amount 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 feature amount 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 a 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>, a velocity calculator <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 matching 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. The position locator <NUM> derives (calculates) an AE source density distribution (wave source distribution) by using the position location results for a certain period. The AE source density distribution represents the distribution showing the wave sources of the elastic waves generated in the structure. The position locator <NUM> outputs the derived AE source density distribution to the evaluator <NUM>.

The velocity calculator <NUM> receives the AE signal output from the signal processor <NUM> as an input. Also, the velocity calculator <NUM> pre-stores the sensor position information by matching the sensor position information to a sensor ID. The velocity calculator <NUM> derives an elastic wave propagation velocity distribution of the structure on the basis of the information such as the sensor IDs and the AE detection times included in the input AE signals and the pre-stored sensor position information. The elastic wave propagation velocity distribution represents a distribution showing the propagation velocity of the elastic waves generated in the structure. For example, the velocity calculator <NUM> derives the elastic wave propagation velocity distribution of the structure using an AE tomography analysis method. The velocity calculator <NUM> outputs the derived elastic wave propagation velocity distribution to the evaluator <NUM>. The AE tomography analysis method is a method in which elastic waves generated from a structure are detected by a plurality of AE sensors, a position of an AE source is located, and propagation velocities of an analysis model of the structure is corrected so that an error between a theoretical traveling time and a measured traveling time from the source to each sensor converges to within a tolerance range, to obtain the elastic wave propagation velocity distribution in the structure. Because a velocity of AE traveling inside decreases as a structure deteriorates, the degree of deterioration inside the structure can be evaluated from the AE velocity distribution by using the AE tomography analysis method.

The evaluator <NUM> receives the AE source density distribution output from the position locator <NUM> and the elastic wave propagation velocity distribution output from the velocity calculator <NUM> as inputs. The evaluator <NUM> evaluates the soundness of the structure on the basis of the input AE source density distribution and elastic wave propagation velocity distribution. The evaluator <NUM> makes the display <NUM> display the evaluation result.

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 an evaluation result in accordance with 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 an image signal for displaying the evaluation result and outputs the image signal to the image display device connected thereto.

<FIG> shows the AE source density distribution, and <FIG> shows the elastic wave propagation velocity distribution. The AE source density distribution and the elastic wave propagation velocity distribution are distributions obtained on the basis of the same region of the same structure. <FIG> illustrates a result of using fifteen AE sensors <NUM> on a floor slab of a structure of a certain road. In <FIG>, the horizontal axis and the vertical axis represent the length (mm) in the horizontal direction from a specific position on the structure to be evaluated and the length (mm) in the vertical direction from the specific position on the structure to be evaluated. Further, in <FIG>, the horizontal axis and the vertical axis represent the horizontal length (m) and the vertical length (m) from a specific position on the structure to be evaluated.

In <FIG>, a region is shown more darkly as the number of wave sources becomes larger (as the wave sources become more densely arranged), and a region is shown more lightly as the number of wave sources becomes smaller (as the wave sources becomes more sparsely arranged). For example, a region <NUM> in <FIG> represents a region in which the number of wave sources is larger than in other regions. Further, in <FIG>, a region is shown more darkly as the propagation velocity becomes higher, and a region is shown more lightly as the propagation velocity becomes lower. The AE source density distribution and the elastic wave propagation velocity distribution shown in <FIG> are input to the evaluator <NUM>.

Hereinafter, with reference to <FIG> and <FIG>, specific processing of the evaluator <NUM> will be described.

On the basis of a reference value related to the density of the wave sources (hereinafter referred to as "density reference value"), the evaluator <NUM> segments the input AE source density distribution into two regions, including a region in which the wave sources are sparsely arranged and a region in which the wave sources are densely arranged. Specifically, the evaluator <NUM> segments the AE source density distribution by binarizing the AE source density distribution on the basis of the density reference value. For example, the density reference value is set as <NUM>. The evaluator <NUM> segments the AE source density distribution by binarizing a region having a density higher than the density reference value as a region in which the wave sources are densely arranged and a region having a density lower than the density reference value as region in which the wave sources are sparsely arranged. The density reference value is not necessarily limited to the above value and may be appropriately changed.

Further, on the basis of a reference value related to the propagation velocity of the elastic wave (hereinafter referred to as "propagation velocity reference value"), the evaluator <NUM> segments the input elastic wave propagation velocity distribution into two regions, including a region in which the propagation velocity is high and a region in which the propagation velocity is low. Specifically, the evaluator <NUM> segments the elastic wave propagation velocity distribution by binarizing the elastic wave propagation velocity distribution on the basis of the propagation velocity reference value. For example, the propagation velocity reference value is set as <NUM>/s. The evaluator <NUM> segments the elastic wave propagation velocity distribution by binarizing a region having a propagation velocity higher than the propagation velocity reference value as a region in which the propagation velocity is high and a region having a propagation velocity lower than the propagation velocity reference value as a region in which the propagation velocity is low. The propagation velocity reference value is not necessarily limited to the above value and may be appropriately changed.

<FIG> shows a region segmentation result of the AE source density distribution, and <FIG> shows a region segmentation result of the elastic wave propagation velocity distribution. Hereinafter, the view shown in <FIG> is described as a binarized AE source density distribution, and the view shown in <FIG> is described as a binarized elastic wave propagation velocity distribution.

Then, the evaluator <NUM> evaluates the soundness of the structure using the binarized AE source density distribution and the binarized elastic wave propagation velocity distribution. Specifically, the evaluator <NUM> superimposes the binarized AE source density distribution and the binarized elastic wave propagation velocity distribution to evaluate the soundness of the structure as four phases according to the result of segmentation of the superimposed region. Here, a specific example of the four phases for evaluation may include Sound, Intermediate deterioration I, Intermediate deterioration II and Limit deterioration. Sound, Intermediate deterioration I, Intermediate deterioration II, and Limit deterioration represent a progress of deterioration of a structure in that order. In other words, Sound indicates that the deterioration of the structure has not progressed most, and a phase approaching Limit deterioration indicates that the deterioration of the structure has progressed. Based on the following evaluation conditions, the evaluator <NUM> evaluates to which of Sound, Intermediate deterioration I, Intermediate deterioration II, and Limit deterioration each region (each of the superimposed regions) of the structure corresponds.

Sound: "sparse" region in the binarized AE source density distribution and "high" region in the binarized elastic wave propagation velocity distribution.

Intermediate deterioration I: "dense" region in the binarized AE source density distribution and "high" region in the binarized elastic wave propagation velocity distribution.

Intermediate deterioration II: "dense" region in the binarized AE source density distribution and "low" region in the binarized elastic wave propagation velocity distribution.

Limit deterioration: "sparse" region in the binarized AE source density distribution and "low" region in the binarized elastic wave propagation velocity distribution.

As described above, when the superimposed region is a region in which the wave sources are sparsely arranged and a region in which the propagation velocity is high, the evaluator <NUM> evaluates the region as a region in a Sound phase. When the superimposed region is a region in which the wave sources are densely arranged and a region in which the propagation velocity is high, the evaluator <NUM> evaluates the region as a region in an Intermediate deterioration I phase. Further, when the superimposed region is a region in which the wave sources are densely arranged and the propagation velocity is low, the evaluator <NUM> evaluates that region as a region in an Intermediate deterioration II phase. Further, when the superimposed region is a region in which the wave sources are sparsely arranged and the propagation velocity is low, the evaluator <NUM> evaluates the region as a region in a Limit deterioration phase.

As described above, by evaluating to which of Sound, Intermediate deterioration I, Intermediate deterioration II, and Limit deterioration each of the superimposed regions corresponds, the evaluator <NUM> derives an evaluation result distribution in which an evaluation result of each of the regions is shown. For example, in the evaluation result distribution, the evaluator <NUM> indicates a region in a Sound phase as "<NUM>", a region in an Intermediate deterioration I phase as "<NUM>", a region in an Intermediate deterioration II phase as "<NUM>", and a region in a Limit deterioration phase as "<NUM>. " The evaluator <NUM> makes the display <NUM> display the derived evaluation result distribution.

<FIG> is a view illustrating an example of the evaluation result distribution. An operator or a manager can easily find out which region of a structure is deteriorating with the evaluation result distribution displayed as illustrated in <FIG>.

<FIG> is a view illustrating a verification result of the validity of the evaluation result. <FIG> shows results of collecting and checking the inside of a floor slab of the structure shown in <FIG>. <FIG> shows a core sample collected from a portion of a circle <NUM> in the region "<NUM>" indicating a Limit deterioration phase in <FIG>. As illustrated in <FIG>, it can be seen that deterioration inside the core sample has progressed to an extent that the core may be separated due to horizontal cracks. On the other hand, <FIG> shows a core sample collected from a portion of a circle <NUM> in the region "<NUM>" indicating a Sound phase in <FIG>. As illustrated in <FIG>, cracks are not seen with visual observation inside the core sample. Thus, the effectiveness of the evaluation method with the structure evaluation apparatus <NUM> is confirmed. The length of a core sample as shown in <FIG> is about <NUM>. The structure evaluation apparatus <NUM> can evaluate the state of deterioration of the structure at at least a depth of <NUM>.

<FIG> is a sequence diagram illustrating the process flow of the structure evaluation system <NUM>. In <FIG>, each of the AE sensors <NUM> and the signal processor <NUM> is a sensor unit.

Each of the AE sensors <NUM> detects an elastic wave (an AE wave) generated by a structure (Step S101). The AE sensor <NUM> converts the detected elastic wave into a voltage signal (an AE source signal), performs processing such as amplification and frequency limiting on the AE source signal, and outputs the result to the signal processor <NUM>. The signal processor <NUM> performs signal processing, such as noise removal and parameter extraction, deemed necessary on the input AE source signal (Step S102). The signal processor <NUM> outputs information based on an AE feature amount extracted by performing signal processing to the structure evaluation apparatus <NUM> as an AE signal (Step S <NUM>). The process from Step S101 to Step S103 is executed for a predetermined period.

The position locator <NUM> locates a position of the AE source on the basis of the AE signal output from the signal processor <NUM> and the pre-stored sensor position information (Step S104). The position locator <NUM> executes the process of Step S104 for a predetermined period. Then, the position locator <NUM> derives the AE source density distribution using the position location results for the predetermined period (Step S105). The position locator <NUM> outputs the derived AE source density distribution to the evaluator <NUM>.

Based on the AE signals output from the signal processor <NUM>, the velocity calculator <NUM> derives the elastic wave propagation velocity distribution of the structure (Step S106). For example, the velocity calculator <NUM> may derive the elastic wave propagation velocity distribution using the AE signals for a predetermined period, or may derive the elastic wave propagation velocity distribution using AE signals for a period shorter than the predetermined period. The velocity calculator <NUM> outputs the derived elastic wave propagation velocity distribution to the evaluator <NUM>. Step S105 and Step S106 may be performed in any order.

The evaluator <NUM> derives the binarized AE source density distribution and the binarized elastic wave propagation velocity distribution by binarizing each of the AE source density distribution output from the position locator <NUM> and the elastic wave propagation velocity distribution output from the velocity calculator <NUM> (Step S107). Using the derived binarized AE source density distribution and binarized elastic wave propagation velocity distribution, the evaluator <NUM> derives the evaluation result distribution by evaluating each region of the structure on the basis of the evaluation conditions (Step S108). The evaluator <NUM> makes the display <NUM> display the derived evaluation result distribution. The display <NUM> displays the evaluation result distribution according to control of the evaluator <NUM> (Step S109).

<FIG> is a view illustrating a basic concept of soundness evaluation in accordance with an example useful for understanding the invention, using the structure evaluation apparatus <NUM> of <FIG>. As illustrated in <FIG>, in the structure evaluation apparatus <NUM>, the high and low level of the elastic wave propagation velocity and the degree of the AE source density each are on two-dimensional evaluation axes which are divided into <NUM> quadrants. Then, the structure evaluation apparatus <NUM> distinguishes the four quadrants as Sound, Intermediate deterioration I, Intermediate deterioration II, and Limit deterioration on the basis of the evaluation conditions.

<FIG> shows evaluation based only on AE source location, and <FIG> shows evaluation based only on the propagation velocity. As illustrated in <FIG>, in the evaluation based only on AE source location, the probability that the structure has deteriorated becomes higher as AE sources become more densely arranged. Further, as illustrated in <FIG>, in the evaluation based only on the propagation velocity, the probability that the structure has deteriorated becomes higher as the propagation velocity becomes lower.

<FIG> is a view illustrating an example of an evaluation result when it is assumed that the two conventional evaluation methods shown in <FIG> and <FIG> are combined. As illustrated in <FIG>, when the two conventional evaluation methods are simply combined, a linear change is expected in which a region in which the elastic wave propagation velocity is higher than a certain reference and the AE source density distribution is sparse (a region in which the wave sources are sparsely arranged) is in a Sound phase, and a region in which the elastic wave propagation velocity is lower than the certain reference and the AE source density distribution is dense (the wave sources are densely arranged) has deteriorated and reached a Limit deterioration phase. This is not always a correct evaluation index because it has been experimentally confirmed that a structure in the Limit deterioration state may still have a sparse AE source density distribution and a structure which has deteriorated to some extent may still have an elastic wave propagation velocity that is substantially the same as that in the Sound state. On the other hand, the basic concept of soundness evaluation by the structure evaluation apparatus <NUM> illustrated in <FIG> may be considered as a correct evaluation index, as can also be seen from the verification result of the validity of the evaluation result illustrated in <FIG>.

According to the structure evaluation system <NUM> configured as described above, the soundness of a structure that generates an elastic wave can be evaluated. Hereinafter, an effect thereof will be described in detail.

The structure evaluation apparatus <NUM> evaluates the soundness of the structure on the basis of the evaluation conditions using the AE source density distribution obtained from the elastic wave detected by each of the plurality of AE sensors <NUM> and the elastic wave propagation velocity distribution. As described above, the structure evaluation apparatus <NUM> according to the embodiment can evaluate a deterioration level for each region of the structure by combining the AE source density distribution and the elastic wave propagation velocity distribution. Therefore, the soundness of the structure generating elastic waves can be evaluated. Also, the structure evaluation apparatus <NUM> can evaluate with higher accuracy by using a plurality of pieces of information instead of one piece of information obtained from elastic waves.

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

Part or all of 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>, the velocity calculator <NUM>, and the display <NUM> may be provided in separate housings. In this case, the evaluator <NUM> acquires the AE source density distribution and the elastic wave propagation velocity distribution from another housing, and evaluates the soundness of the structure by using the acquired AE source density distribution and elastic wave propagation velocity 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 AE source density distribution and the elastic wave propagation velocity distribution, the manufacturing cost of the structure evaluation apparatus <NUM> can be minimized.

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 processor s <NUM> and have a plurality of sensor units by the signal processor s <NUM> being connected to the AE sensors <NUM>, respectively.

The constitution in which the velocity calculator <NUM> derives the elastic wave propagation velocity distribution has been shown above. The velocity calculator <NUM> may be configured to derive a velocity in a region having a density equal to or greater than a predetermined threshold in the AE source density distribution shown in <FIG> or a velocity in a region having a density less than the predetermined threshold value. In this case, the evaluator <NUM> evaluates the soundness of the structure using the AE source density distribution derived by the position locator <NUM> and the velocity derived by the velocity calculator <NUM>.

Further, the evaluator <NUM> may operate as an output control unit. The output control unit controls an output unit such that it 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 such that it transmits the evaluation result to another device. Further, when the output unit is a printing unit, the output control unit controls the printing unit such that it 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 position locator <NUM> may derive the AE source density distribution using only the AE information generated from a wave source in which an amplitude of a first arrival wave of the AE is a predetermined threshold or higher. For example, the position locator <NUM> may derive the AE source density distribution using only AE information generated from a wave source in which an amplitude of a first arrival wave of the AE is <NUM> dB or more. This will be described in detail with reference to <FIG> shows an AE source density distribution derived using the AE information generated from a wave source in which an amplitude of a first arrival wave of AE is <NUM> dB or higher, and <FIG> shows an AE source density distribution derived using the AE information generated from a wave source in which an amplitude of a first arrival wave of AE is <NUM> dB or higher. In consideration of the validity verification result of <FIG>, more accurate evaluation can be performed by using only AE information generated from a wave source having a predetermined amplitude or higher as illustrated in <FIG>. Therefore, with such a constitution, it is possible to make a contribution to effective deterioration diagnosis. Also, the first arrival wave refers to an elastic wave that reaches the AE sensor first when a certain elastic wave generation event (referred to as an event) that has occurred in the structure is detected by a plurality of AE sensors.

<FIG> is a view illustrating another example of the basic concept shown in <FIG>. In the example shown in <FIG>, in addition to the distinguishing in <FIG>, An "Initial" phase corresponding to the initial phase immediately after a structure is constructed or repaired is added. This represents a situation in which a large amount of wave sources are observed when a load is applied for the first time in the initial state after a structure is constructed or manufactured. This does not indicate that deterioration of the structure starts immediately, but indicates a response of the structure to the first load experienced by the structure. Then, the occurrence of AE decreases with respect to the past load. Therefore, the Initial phase is positioned as the preliminary phase of the Sound phase in <FIG>, and it can be shown that, after the Initial phase, a shift toward the Sound phase occurs with a decreasing number of wave sources. For example, the example shown in <FIG> is a phase to be taken into consideration when soundness is evaluated immediately after a structure is constructed or repaired.

The evaluator <NUM> may be configured to derive an evaluation result distribution showing only a region of limit deterioration, so that the display <NUM> displays the evaluation result distribution as derived. For example, the evaluator <NUM> superimposes a binarized AE source density distribution and a binarized elastic wave propagation velocity distribution. The evaluator <NUM> retrieves, in the superimposed region, a region of the limit deterioration under the evaluation conditions and a region in which the evaluation conditions are satisfied. The evaluator <NUM> allocates a predetermined pattern such as a pattern of "<NUM>" and colored as shown in <FIG> to the region satisfying the evaluation condition in the region of limit deterioration without allocating the predetermined pattern to other region not satisfying the evaluation condition in the region of limit deterioration, so as to derive the evaluation result distribution showing only a region of limit deterioration satisfying the evaluation condition in. The evaluator <NUM> supplies the evaluation result distribution derived to the display <NUM> so that the display <NUM> displays the evaluation result distribution as derived.

In the examples as described above, the evaluator <NUM> uses the binarized AE source density distribution as two dimensional data and the binarized elastic wave propagation velocity distribution as two dimensional data, to derive the evaluation result distribution as two dimensional data and allow the display <NUM> to display the evaluation result distribution. The evaluator <NUM> uses the binarized AE source density distribution as three dimensional data and the binarized elastic wave propagation velocity distribution as three dimensional data, to derive the evaluation result distribution as three dimensional data and allow the display <NUM> to display the evaluation result distribution as three dimensional data. The three dimensional binarized AE source density distribution and the three dimensional binarized elastic wave propagation velocity distribution can be obtained by extending the two dimensions to the three dimensions in the deriving process by the position locator <NUM> and the velocity calculator <NUM>.

In the examples described above, the evaluator <NUM> is configured to segment the region of the AE source density distribution into two regions, for example, wave source sparse region and wave source dense region, based on a density reference value and also segment a region of the elastic wave propagation velocity distribution into two regions, for example, high propagation velocity region (fast region) and low propagation velocity region (slow region) based on the propagation velocity reference value. According to the invention, the evaluator <NUM> is configured to use as thresholds a first region having a predetermined range including the density reference value and a second region having a predetermined range including the propagation velocity reference value so as to segment the region of the AE source density distribution into three regions, for example, a source-sparse region, a source-dense region, and the other region different from the source-sparse region and the source-dense region, and segment the region of the elastic wave propagation velocity distribution into three regions, for example, a high propagation velocity region (fast region), a low propagation velocity region (slow region), and the other region different from the high propagation velocity region (fast region) and the low propagation velocity region (slow region). For example, the first region may be ranged from <NUM> to <NUM>. The second region may be from <NUM>/s to <NUM>/s. In some cases, the first and second regions may be previously set. In other cases, the first and second regions may be set by a user.

As configured above, the evaluator <NUM> is configured to segment the region of the AE source density distribution into the wave source dense region which is higher in source-density than the maximum value of the first region, the wave source sparse which is lower in source-density than the minimum value of the first region, and the other region ranged in source-density between the maximum value and the minimum value of the first region. The evaluator <NUM> is configured to segment the region of the elastic wave propagation velocity distribution into the high propagation velocity region which is higher in propagation velocity than the maximum value of the second region, the low propagation velocity region which is lower in propagation velocity than the minimum value of the second region, and the other region ranged in propagation velocity between the maximum value and the minimum value of the second region. The basic concepts of the evaluation as configured above is as shown in <FIG>.

<FIG> is a view illustrating the basic concept of the soundness evaluation by the structure evaluation apparatus <NUM> in case that regions of a predetermined ranges including the reference values are used as thresholds. As shown in <FIG>, a first region <NUM> having a predetermined range including a reference value and a second region <NUM> having a predetermined range including a reference value are used as thresholds, wherein it is possible to evaluate that it does not belong to any of the four evaluations. If however regions having predetermined ranges including the reference values are not used as thresholds, it is possible to evaluate the sound region to be the limit deterioration due to a slight variation of the value as shown in <FIG>. In contrast, however, as described above, using the regions having the predetermined ranges including the reference values as the thresholds will reduce the possibility of evaluating the sound region to be the limit deterioration.

The evaluator <NUM> may use any one of the first region <NUM> and the second region <NUM> as the threshold to evaluate the state of deterioration.

In the examples described above, the evaluator <NUM> is configured to make the evaluations in such a method as shown in <FIG>, but not limited to this method. The evaluator <NUM> may be configured to make the evaluations in such a method as mentioned below. For example, evaluator <NUM> may be configured to make the evaluations in such a method as shown in <FIG> until a predetermined condition or conditions are satisfied, and then make the evaluation in such a method as shown in <FIG> once the predetermined condition or conditions are satisfied. The predetermined condition is that the frequency of occurrence of the elastic waves (the number of detection of the elastic waves) exceeds a predetermined first threshold, or that the propagation velocity rapidly drops. The rapid drop of the propagation velocity is such that a difference between a propagation velocity calculated at a time t-<NUM> by the velocity calculator <NUM> and a propagation velocity calculated at a time t by the velocity calculator <NUM> exceeds the second threshold. The evaluation based on the predetermined condition will be described with reference to Fig S. 13A and 13B. <FIG> is the view illustrating the basic concept of the soundness evaluation by the structure evaluation apparatus <NUM> in case that the regions having the predetermined ranges including the reference values are used as the thresholds, according to the invention. As shown in <FIG>, using the first region <NUM> having the predetermined range including the reference value and the second region <NUM> having the predetermined range including the reference value as the thresholds will make it possible to evaluate that it does not belong to any of the four evaluations. If however regions having predetermined ranges including the reference values are not used as thresholds, it is possible to evaluate the sound region to be the limit deterioration due to a slight variation of the value as shown in <FIG>. In contrast, however, as described above, using the regions having the predetermined ranges including the reference values as the thresholds will reduce the possibility of evaluating the sound region to be the limit deterioration.

<FIG> is a view illustrating an evaluation method used in a case that the predetermined condition is that the frequency of occurrence of the elastic waves (the number of detections of the elastic waves) exceeds the predetermined first threshold. In <FIG>, the horizontal axis represents time T, the vertical axis represents the frequency of occurrence of the elastic waves. In <FIG>, the time t1 represents a time at which the frequency of occurrence of the elastic waves (the number of detections of the elastic waves) exceeds the predetermined first threshold. As shown in <FIG>, the frequency of occurrence of the elastic waves generally increases as the deterioration of the structure increases and exceeds the first threshold, and further the frequency of occurrence of the elastic waves increases from the first threshold and then reaches a peak before the frequency of occurrence of the elastic waves decreases. The structure has such a property as described. Thus, the evaluator <NUM> makes the evaluation in such a method as shown in <FIG> until the frequency of occurrence of the elastic waves reaches the first threshold, and then makes the evaluation in such a method as shown in <FIG> after the frequency of occurrence of the elastic waves exceeds the first threshold. For example, the evaluator <NUM> the evaluation in such a method as shown in <FIG> until the time t1, and then makes the evaluation in such a method as shown in <FIG> after the time t1.

<FIG> is a view illustrating an evaluation method used in a case that the predetermined condition is that the propagation velocity is rapidly dropped. In <FIG>, the horizontal axis represents time T and the left vertical axis represents the propagation velocity. As shown in <FIG>, the propagation velocity of the elastic waves generally decreases as the deterioration of the structure increases. The structure has such a property as described. Thus, the evaluator <NUM> makes the evaluation in such a method as shown in <FIG> until the propagation velocity of the elastic waves drops to the second threshold, and then makes the evaluation in such a method as shown in <FIG> after the propagation velocity of the elastic waves dropped to the second threshold. For example, in <FIG>, the evaluator <NUM> the evaluation in such a method as shown in <FIG> until the time t1, and then makes the evaluation in such a method as shown in <FIG> after the time t1.

The evaluation method as shown in <FIG> uses the above-described evaluation condition. The evaluation method as shown in <FIG> is that the evaluator <NUM> evaluates the state of deterioration to be the limit deterioration as the propagation velocity of the elastic wave is below the reference value and as the AE source density distribution or wave source density is dense, and evaluates the state of deterioration to be soundness as the propagation velocity of the elastic wave is above the reference value and as the AE source density distribution or wave source density is sparse. In each of <FIG> and <FIG>, the limit deterioration refers to a state of relative maximum deterioration degree. The maximum deterioration degree in <FIG> is greater than the maximum deterioration degree in <FIG>. As described above, the methods of evaluation are switched under the condition for making a highly sensitive evaluation of a change of the state of deterioration of the structure in a state that the deterioration of the structure has not yet progressed significantly.

According to at least one of the embodiments and examples described above, the soundness of a structure that generates elastic waves is evaluated by having the plurality of AE sensors <NUM> configured to detect elastic waves generated from a structure, a position locator <NUM> configured to derive a wave source distribution on the basis of the elastic waves, the velocity calculator <NUM> configured to derive a propagation velocity based on the elastic waves, and the evaluator <NUM> configured to evaluate the soundness of the structure on the basis of the wave source distribution and the propagation velocity.

Claim 1:
A structure evaluation system (<NUM>) comprising:
a plurality of sensors (<NUM>-<NUM>,...,<NUM>-n) configured to detect elastic waves generated from a structure;
a position locator (<NUM>) configured to derive a wave source distribution of the elastic waves generated from the structure, on the basis of the detection time of the elastic waves output from the plurality of sensors and information on an installation position of the plurality of sensors;
a velocity calculator (<NUM>) configured to derive a propagation velocity distribution indicating a distribution of the propagation velocity of the elastic waves generated from the structure, by using tomography analysis on the basis of the detection time of the elastic waves output from the plurality of sensors and information on an installation position of the plurality of sensors; and
an evaluator (<NUM>) configured to: segment the wave source distribution into two regions including a source-sparse region in which the wave sources are sparsely arranged based on a first reference value and a source-dense region in which the wave sources are densely arranged, and a predetermined range (<NUM>) including said first reference value;
segment the propagation velocity distribution into two regions including a fast region in which the propagation velocity is high based on a second reference value and a slow region in which the propagation velocity is low, and a predetermined range (<NUM>) including said second reference value, superimpose the segmented wave source distribution and the segmented propagation velocity distribution; evaluate each region of the structure as belonging to one of the four phases resulting from superimposing said two regions of the segmented wave source distribution and said two regions of the segmented propagation velocity distribution, or not belonging to any of said four phases;
derive an evaluation result distribution indicating to which phase each of the regions of the structures corresponds; and output the derived evaluation result distribution.