Elastic wave velocity evaluation method, elastic wave velocity distribution evaluation method, stress estimation method, and stress distribution estimation method

Abstract

To provide an elastic wave velocity evaluation method, an elastic wave velocity distribution evaluation method, a stress estimation method and a stress distribution estimation method that reduce time and labor of installing an apparatus for a concrete structure.SOLUTION: An elastic wave velocity evaluation method is an elastic wave velocity evaluation method evaluating an elastic wave velocity in a concrete structure 1, the method comprising: a vibration detection step of installing an optical fiber 3 on the concrete structure 1 and setting a measurement point P1, a measurement point P2, and an excitation point R substantially in a straight line in a Y axis direction along an installation place of the optical fiber 3, and detecting by the optical fiber 3 respective vibrations which are generated at the measurement point P1 and the measurement point P2 by excitation at the excitation point R; and an elastic wave velocity calculation step of calculating the elastic wave velocity V1 in a region A1 between the measurement point P1 and the measurement point P2 on the basis of a difference ΔT1 between generation times of the vibrations at the measurement point P1 and the measurement point P2 detected in the vibration detection step and a distance L1 between the measurement point P1 and the measurement point P2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an elastic wave velocity evaluation method, an elastic wave velocity distribution evaluation method, a stress estimation method, and a stress distribution estimation method. [Background technology]

[0002] Conventionally, the technology of Non-Patent Document 1 below is known as a method for measuring elastic wave velocity in a concrete structure. In this method, an acceleration sensor is installed on the surface of a concrete structure, and another position on the surface of the concrete structure is struck with an iron ball. The received waveform is measured by the acceleration sensor, and an input waveform is measured by an impact accelerometer attached to the iron ball, and the time it takes for the vibration of the strike to reach the receiving position is determined by comparing the input waveform with the received waveform. The elastic wave velocity of the concrete structure is calculated based on this arrival time and the distance between the input position and the receiving position. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Satoshi Iwano and 3 others, "Estimation of compressive strength of concrete by measuring elastic wave velocity", [online], 2003, Proceedings of the Japan Concrete Institute, Vol. 25, No. 1, 2003, [Retrieved April 1, 2023], Internet<URL:https: / / data.jci-net.or.jp / data_pdf / 25 / 025-01-1267.pdf> Summary of the Invention [Problem to be solved by the invention]

[0004] However, elastic wave velocity is not necessarily uniform throughout the entire concrete structure, and depending on the application, information on elastic wave velocity at various points in the concrete structure may be required. In such cases, the measurement method of Non-Patent Document 1 requires measures such as re-installing the acceleration sensor every time the measurement target point is changed, or installing a large number of acceleration sensors on the surface of the concrete structure in advance, which is not considered to be efficient work. The present invention aims to provide an elastic wave velocity evaluation method, an elastic wave velocity distribution evaluation method, a stress estimation method, and a stress distribution estimation method that reduce the effort required to install devices on a concrete structure. [Means for solving the problem]

[0005] The gist of the present invention lies in the following [1] to [6].

[0006] [1] An elastic wave velocity evaluation method for evaluating elastic wave velocity in a concrete structure, comprising: an optical fiber installed in the concrete structure; a first measurement point, a second measurement point, and a vibration point that are set in a substantially straight line in a predetermined axial direction along an installation location of the optical fiber; a vibration detection process for detecting, by the optical fiber, vibrations that are generated at the first measurement point and the second measurement point due to vibration at the vibration point; and an elastic wave velocity calculation process for calculating the elastic wave velocity in a region between the first measurement point and the second measurement point based on a difference in occurrence time of the vibrations at the first measurement point and the second measurement point detected in the vibration detection process, and a distance between the first measurement point and the second measurement point.

[0007] [2] an elastic wave velocity distribution evaluation method for evaluating an elastic wave velocity distribution in a concrete structure, the method comprising: an optical fiber is installed in the concrete structure; a plurality of measurement points, 1 to nth measurement points (n is a natural number of 2 or more) and a vibration point are set in a substantially straight line in a predetermined axial direction along an installation location of the optical fiber; a vibration detection process for detecting, by the optical fiber, each vibration generated at the 1st to nth measurement points due to vibration at the vibration point; an elastic wave velocity calculation process for setting an area between a jth measurement point and a kth measurement point among the plurality of measurement points as a target area (j and k are natural numbers from 1 to n), and calculating the elastic wave velocity in the target area based on a difference in occurrence time between the jth measurement point and the kth measurement point detected in the vibration detection process and a distance between the jth measurement point and the kth measurement point; and an elastic wave velocity distribution acquisition process for obtaining the elastic wave velocity distribution of the concrete structure based on the elastic wave velocities in the plurality of target areas obtained by repeating the elastic wave velocity calculation process while changing the target area.

[0008] [3] A stress distribution estimation method, in which a distribution of the stress acting on the concrete structure in the predetermined axial direction is estimated based on the elastic wave velocity distribution obtained by the elastic wave velocity distribution evaluation method described in [2] and a correlation between elastic wave velocity and stress in the concrete structure obtained separately.

[0009] [4] A method for estimating stress acting on a concrete structure in a predetermined axial direction, comprising: an optical fiber installed in the concrete structure; a first measurement point, a second measurement point, and a reference point set along an installation location of the optical fiber; the first measurement point and the second measurement point are arranged in the predetermined axial direction; the first measurement point and the reference point are arranged in an orthogonal axial direction perpendicular to the predetermined axial direction; a vibration detection step in which vibrations generated at the first measurement point, the second measurement point, and the reference point due to excitation at a position immediately adjacent to the first measurement point are detected by the optical fiber; and a difference in occurrence time of the vibration at the first measurement point and the second measurement point detected in the vibration detection step and a time difference between the occurrence time of the vibration at the first measurement point and the second measurement point detected in the vibration detection step are detected. a predetermined axis direction elastic wave velocity calculation step of calculating an elastic wave velocity in the predetermined axis direction in a region between the first measurement point and the second measurement point based on a distance between the first measurement point and the reference point and a predetermined axis direction elastic wave velocity calculation step of calculating an elastic wave velocity in the orthogonal axis direction in a region between the first measurement point and the reference point based on a difference in occurrence time of the vibration at the first measurement point and the reference point detected in the vibration detection step and the distance between the first measurement point and the reference point; and a stress calculation step of calculating a stress acting in the predetermined axis direction in the region between the first measurement point and the second measurement point based on the elastic wave velocity in the predetermined axis direction and the elastic wave velocity in the orthogonal axis direction.

[0010] [5] A stress distribution estimation method for estimating a distribution of stress acting on the concrete structure in the predetermined axial direction by using the stress estimation method described in [1], wherein an optical fiber is installed in the concrete structure, and a plurality of measurement points, 1st to nth measurement points (n is a natural number of 2 or more) that are aligned in a substantially straight line in the predetermined axial direction, and a plurality of reference points, 1st to nth reference points, are set along an installation location of the optical fiber, the stress distribution estimation method includes: a stress estimation step of estimating the stress acting on the target region in the predetermined axial direction by the stress estimation method described in [4], using a jth reference point that is aligned in the orthogonal axial direction to the jth measurement point among the reference points, as a target region, and a stress distribution acquisition step of acquiring the distribution of stress in the concrete structure based on the stresses in the plurality of target regions obtained by repeating the stress estimation step while changing the target region.

[0011] [6] The stress distribution estimation method according to [3] or [5], wherein the concrete structure is a prestressed concrete structure in which prestress is introduced in the specified axial direction. Effect of the Invention

[0012] According to the present invention, it is possible to provide an elastic wave velocity evaluation method, an elastic wave velocity distribution evaluation method, a stress estimation method, and a stress distribution estimation method that reduce the effort required for installing equipment in a concrete structure. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram showing a schematic diagram of a concrete structure that is a target of a stress distribution estimation method according to a first embodiment; [Diagram 2] 4 is a flowchart of a stress distribution estimation method according to the first embodiment. [Diagram 3] FIG. 13 is a diagram showing signal waveforms at two measurement points. [Figure 4] FIG. 11 is a diagram illustrating a concrete structure according to a modified example. [Diagram 5]FIG. 13 is a diagram illustrating a concrete structure that is a target of the stress distribution estimation method according to the second embodiment. [Figure 6] 10 is a flowchart of a stress distribution estimation method according to a second embodiment. [Figure 7] FIG. 11 is a diagram illustrating a concrete structure according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of an elastic wave velocity evaluation method, an elastic wave velocity distribution evaluation method, a stress estimation method, and a stress distribution estimation method according to the present invention will be described in detail with reference to the drawings. During repair, reinforcement, or renewal work on a concrete structure, a temporary structural change due to cross-section chipping or the like may cause fluctuations in the stress acting on the concrete structure. Therefore, it is necessary to appropriately plan and manage the work so that the stress acting on the concrete structure during work falls within a range permitted by the design. Since the acting stress is not necessarily uniform throughout the concrete structure or within the cross-section, but differs depending on the location, it is necessary to evaluate the distribution of stress in the concrete structure.

[0015] In order to meet such demands, the stress distribution estimation method in each of the following embodiments estimates the distribution of stress acting on a concrete structure. The elastic wave velocity evaluation method, elastic wave velocity distribution evaluation method, and stress estimation method in each of the following embodiments are used for estimating the above-mentioned stress distribution.

[0016] [First embodiment] FIG. 1 is a diagram showing a concrete structure 1 which is a target of the stress distribution estimation method of this embodiment. In the following, the up-down direction in FIG. 1 is defined as the X-axis direction, and the left-right direction is defined as the Y-axis direction. The concrete structure 1 is a structure which receives an axial force in the Y-axis direction. As a specific example, the concrete structure 1 is, for example, a prestressed concrete structure, in which an axial force due to prestress is applied in the Y-axis direction. As another specific example, the Y-axis direction may be the vertical direction. In this case, the concrete structure 1 is, for example, a bridge pier, which receives a vertical axial force due to the weight of the bridge girder.

[0017] As shown in Fig. 1, an optical fiber 3 extending linearly in the Y-axis direction is installed in a concrete structure 1 so as to be integrated with the concrete structure 1. The optical fiber 3 may be fixed to the surface of the concrete structure 1 via an adhesive or the like, or may be buried in the concrete structure 1, for example, near the surface. The optical fiber 3 is used as a sensor for sensing vibrations at each point of the concrete structure 1 by distributed acoustic sensing (DAS). One end of the optical fiber 3 is connected to a DAS measuring instrument 5 and a calculation device 7 (e.g., a computer) that performs calculations based on information input from the DAS measuring instrument 5.

[0018] DAS measurement is based on the following principle. A pulse of light is input from the DAS measuring instrument 5 to the optical fiber 3, and the light scattered from each part along the length of the optical fiber 3 returns to the DAS measuring instrument 5. The scattered light from each part of the optical fiber 3 changes depending on the strain occurring at that part, so by analyzing the change in the scattered light with the DAS measuring instrument 5, the strain at each part of the optical fiber 3 can be determined. DAS measurement is also called "distributed vibration measurement method," "distributed acoustic sensing," or "distributed vibration sensing."

[0019] Furthermore, the concrete structure 1 has a plurality of measurement points P1, P2, ..., P n(n is a natural number of 2 or more) and the vibration point R are set in a straight line in the Y-axis direction. n , and the positions of the excitation point R are known. The excitation point R is a point at which vibration for DAS measurement is applied to the concrete structure 1. In the example shown in the figure, the excitation point R is located between the measurement points P4 and P5, but the position of the excitation point R is different from that of the measurement points P1 to P5. n The measurement points P1 to P2 may be located at any position as long as they are aligned in a straight line. n All of the measurement points P1 to P n The measurement points P1 to P2 may be arranged at equal intervals. In this case, the measurement points are arranged at intervals of, for example, 20 cm. n Since the measurement points P1 to P n When strain occurs in the concrete structure 1, the measurement points P1 to P2 are detected by the optical fiber 3 according to the principle of DAS measurement. n It is possible to detect strain at every

[0020] A method for estimating stress distribution in a concrete structure 1 using the DAS measurement method will be described. Fig. 2 is a flowchart of the stress distribution estimation method of this embodiment. As shown in the figure, the stress distribution estimation method includes a vibration detection step S101, an elastic wave velocity calculation step S103, an elastic wave velocity distribution acquisition step S105, and a stress distribution acquisition step S107, which will be described next.

[0021] (Vibration detection process S101) First, the vibration point R of the concrete structure 1 is vibrated. Specifically, the vibration point R may be struck by a user with a hammer or a metal ball, or may be vibrated by an attached oscillator. Elastic waves generated by the vibration of the vibration point R propagate through the concrete structure 1 and reach each of the measurement points P1 to P n At each measurement point P1 to P n Vibration is then generated at measurement points P1 to P nThe vibrations generated at the measurement points P1 to P2 are detected by the optical fiber 3 according to the principle of DAS measurement, and are recognized as signal waveforms by the calculation device 7 via the DAS measuring device 5. n The signal waveforms representing the vibrations of the measurement points P1, P2, ..., P n Signal waveform f n ) individually.

[0022] In order to obtain an accurate signal waveform, it is preferable to set the sampling frequency of the dynamic strain at each measurement point to 10 times or more the frequency of the signal waveform. For example, since the impact elastic wave method generally uses waves with frequency components of about several tens to several hundreds of Hz for analysis, it is preferable that the DAS 5 is capable of measurement at a sampling frequency of 10 kHz or more.

[0023] (Elastic wave velocity calculation step S103) Measurement points P1~P n Among the j-th adjacent measurement points P j and the (j+1)th measurement point P (j+1) In the elastic wave velocity calculation step S101, the calculation device 7 calculates the elastic wave velocity at the measurement point P j Signal waveform f j From measurement point P j The time when the vibration occurs at T j In this case, the measurement point P j The time when the first wave reaches its peak is called the occurrence time T j Similarly, the calculation device 7 defines the measurement point P (j+1) Signal waveform f (j+1) From measurement point P (j+1) The time when the vibration occurs at T (j+1) The occurrence time T j ,T (j+1) is the elastic wave from the excitation point R to each measurement point P j ,P (j+1) And the occurrence time T j and occurrence time T (j+1) Difference ΔT j is the measurement point Pj From measurement point P (j+1) The travel time of the elastic wave from the measurement points P1 to P n Since the positions of the measurement points P j and measurement point P (j+1) Distance L between j is known. Then, the measurement point P j and measurement point P (j+1) Area A between j Elastic wave velocity V in the Y-axis direction j is the distance L j Time ΔT j Based on this knowledge, the calculation device 7 calculates the area A j Elastic wave velocity V in the Y-axis direction j is calculated using the following formula (α1) (S103a in the flow chart). V j =ΔT j / L j …Formula (α1)

[0024] The calculation device 7 calculates the area A of the object. j By repeatedly executing the above calculation process for j = 1 to (n-1) while changing (n-1) Elastic wave velocities V1, V2, …, V in the Y-axis direction (n-1) is calculated.

[0025] Note that the further away from the excitation point R the measurement point is, the smaller the elastic wave that reaches it, but here it is assumed that the elastic wave from the excitation point R reaches even the farthest measurement point with a sufficient magnitude. Here, a sufficiently large elastic wave means an elastic wave with an amplitude sufficiently large compared to the noise W, as shown in FIG. 3. The noise W is vibration that is constantly occurring in the concrete structure 1 for reasons other than the excitation of the excitation point R. Suppose that the measurement points P1 to P n If all the elastic waves reaching the measurement points P1 to P2 are not large enough, the vibration detection step S101 and the elastic wave velocity calculation step S103 may be performed multiple times while moving the excitation point R. nThe measurement is performed with a magnitude such that the elastic waves reaching the DAS are within a range that can be measured by the DAS measuring instrument 5.

[0026] (Elastic wave velocity distribution acquisition step S105) As described above, the regions A1 to A (n-1) Elastic wave velocities V1 to V (n-1) That is, in the calculation device 7, the measurement points P1 to P n In the region where the elastic wave velocity in the Y-axis direction of the concrete structure 1 is arranged, a distribution in the Y-axis direction of the elastic wave velocity in the Y-axis direction of the concrete structure 1 is acquired.

[0027] (Stress distribution acquisition process S107) There is a linear correlation between the elastic wave velocity V in the concrete structure in the Y-axis direction and the stress σ in the Y-axis direction acting on the concrete structure, as expressed by the following formula (α2). This correlation is stored in the computing device 7 in advance. V=aσ+b …Formula (α2) The calculation device 7 calculates each elastic wave velocity V of the elastic wave velocity distribution obtained in the elastic wave velocity distribution acquisition step S105 by the formula (α2). j Let σ be the stress j By converting each A1, A2, …, A (n-1) Stresses σ1, σ2, …, σ acting in the Y-axis direction (n-1) That is, the distribution in the Y-axis direction of the stress acting on the concrete structure 1 in the Y-axis direction is obtained. Note that the a-values ​​and b-values ​​in the above formula (α2) vary depending on the type of concrete. Therefore, a test including core sampling of the concrete structure 1 is carried out in advance to obtain the a-values ​​and b-values, and the formula (α2) for the a-values ​​and b-values ​​corresponding to the concrete structure 1 is stored in the calculation device 7 in advance.

[0028] The information on the stress distribution thus obtained may be visualized, for example, by expressing it in a contour diagram, and displayed on a display monitor or the like provided in the computing device 7 to be presented to the user.

[0029] In the elastic wave velocity calculation step S103, adjacent measurement points Pj and measurement point P (j+1) Area A between j Elastic wave velocity V at j However, the present invention is not limited to this. For example, in the elastic wave velocity calculation step S103, the measurement points P j and measurement point P k The elastic wave velocity V in the region between the measurement points P1 to P2 may be repeatedly calculated. In this case, in the elastic wave velocity distribution acquisition step S105, the elastic wave velocity V in the region between the measurement points P1 to P2 may be calculated based on the calculated elastic wave velocities V in the randomly selected region. n The distribution of the elastic wave velocity in the region where the measurement points P are arranged may be obtained. j and measurement point P k The positional relationship between is not limited to being random, and may have some regularity other than being adjacent to each other (k=j+1).

[0030] In addition, measurement points P1 to P n The excitation points R are arranged in a substantially straight line on the concrete structure 1, and the measurement points P1 to P n As long as the measurement points P1 to P2 are located along the optical fiber 3, the optical fiber 3 does not have to be straight. For example, as shown in FIG. 4, the optical fiber 3 may extend in a zigzag pattern while being regularly bent. n are arranged in a straight line in the Y-axis direction at a pitch corresponding to the repeat pitch of the shape of the optical fiber 3, and are positioned along the optical fiber 3. n The excitation point R may be located away from the optical fiber 3 as long as it is located in a position that is approximately in line with the optical fiber 3. With this configuration, the linear distance between the measurement points can be made shorter compared to the optical path length of the optical fiber 3 between the measurement points. Therefore, the measurement points P1 to P2 on the concrete structure 1 are spaced apart from each other at intervals shorter than the minimum measurement point interval that can be set by the DAS measuring instrument 5. n Therefore, it is possible to obtain a more detailed elastic wave velocity distribution and stress distribution.

[0031] Alternatively, n may be 2. In this case, in the vibration detection step S101, the vibrations generated at the measurement points P1 and P2 due to the excitation of the excitation point R are detected by the optical fiber 3. In the elastic wave velocity calculation step S103, the elastic wave velocity V1 in the region A1 between the measurement points P1 and P2 is calculated by the formula (α1) based on the difference ΔT1 in the occurrence time of the vibrations at the measurement points P1 and P2 detected in the vibration detection step S101 and the distance L1 between the measurement points P1 and P2. In this case, in the elastic wave velocity distribution acquisition step S105, strictly speaking, only the elastic wave velocity V1 is obtained, not the distribution of the elastic wave velocity. In addition, in the stress distribution acquisition step S107, strictly speaking, only the stress σ1 is obtained, not the distribution of the stress. In this case, the elastic wave velocity distribution acquiring step S105 and the stress distribution acquiring step S107 may be omitted, and the arithmetic device 7 may present the elastic wave velocity V1 obtained in the elastic wave velocity calculating step S103 to the user.

[0032] Here, in the above method, 1N / mm 2 This section explains the sampling frequency required to estimate the difference in stress of about 10 N / mm. The difference in stress that can be detected by this method depends on the distance between the measurement points and the sampling frequency. For example, in previous measurements, the elastic wave velocity in concrete is about 4000 m / s in a stress-free state, and 10 N / mm 2 When a stress of about 1N / mm is applied, the elastic wave velocity is about 4150m / s. 2 In order to measure a difference in stress of about 15 m / s, it is necessary to measure a difference in elastic wave velocity of about 15 m / s. If the distance L between the measurement points when calculating the elastic wave velocity is 1 m, the difference in the time it takes for vibration to arrive at the two measurement points is 1 / 4000 s in a stress-free state and 1 N / mm 2 When applied, it is 1 / 4015s. In other words, 1N / mm 2 In order to measure the difference in vibration arrival time difference due to the difference in minutes, a sampling frequency of about 1070 kHz is required to realize measurements at intervals of 1 / 4000-1 / 4015 = about 1 / 1070000 s. 2The sampling frequency required to estimate the difference in stress is inversely proportional to the distance L between the measurement points when calculating the elastic wave velocity, but when measuring the distribution of stress in a structure, taking into account the size of a typical structure, it is thought that a distance between measurement points of approximately 3 m or less is desirable, and in the case of a distance of 3 m, a sampling frequency of approximately 357 kHz or more is required.

[0033] The effects of this embodiment will be described. One form of the elastic wave velocity evaluation method of this embodiment in which n=2 includes the vibration detection step S101 and the elastic wave velocity calculation step S103 described above, and obtains the elastic wave velocity V1 in the Y-axis direction of the target area of ​​the concrete structure 1. According to this elastic wave velocity evaluation method, even when the target area on the concrete structure 1 is changed, it is sufficient to move the measurement point along the installation location of the optical fiber 3. Therefore, when the target area is changed, measures such as re-installing the device are not required, and the effort of installing the device on the concrete structure 1 can be reduced. Furthermore, the target area can be relatively freely selected along the installation location of the optical fiber 3 without installing any additional device on the concrete structure 1.

[0034] The elastic wave velocity distribution evaluation method of the present embodiment includes the vibration detection step S101, the elastic wave velocity calculation step S103, and the elastic wave velocity distribution acquisition step S105. n According to this elastic wave velocity distribution evaluation method, the optical fiber 3 extending in the Y-axis direction is arranged at each of the measurement points P1 to P n Assume that an acceleration sensor or the like for detecting vibration is placed at each of the measurement points P1 to P n In contrast, the elastic wave velocity distribution evaluation method of the present embodiment requires only installing the optical fiber 3 in the concrete structure 1, which reduces the effort required for installing a device in the concrete structure.

[0035] The stress distribution estimation method of the present embodiment includes the vibration detection step S101, the elastic wave velocity calculation step S103, the elastic wave velocity distribution acquisition step S105, and the stress distribution acquisition step S107. n The stress distribution estimation method obtains the distribution in the Y-axis direction of the stress in the Y-axis direction acting on the concrete structure 1 in the region where the elastic wave velocity distribution is arranged. According to this stress distribution estimation method, the stress distribution can be obtained based on the above elastic wave velocity distribution, for example, by formula (α2). Since the above elastic wave velocity distribution evaluation method is used in this way, the same effects as those of the above elastic wave velocity distribution evaluation method are obtained.

[0036] Furthermore, even after the above-mentioned stress distribution estimation method is carried out in repair, reinforcement, or renewal work on the concrete structure 1, the optical fiber 3 may be left in the concrete structure 1. Then, a strain measuring instrument (not shown) for measuring static strain of the optical fiber 3 is connected to the end of the optical fiber 3 instead of the DAS measuring instrument 5. As such a strain measuring instrument, for example, an OTDR (Optical Time Domain Reflectometer) or a BOTDR (Brillouin Optical Time Domain Reflectometer) can be used.

[0037] This makes it possible to continuously measure the change in strain distribution of the concrete structure 1 during repair, reinforcement, or renewal work, as well as after the work is completed and after it is in service. Furthermore, the change in stress distribution can be grasped by multiplying the obtained change in strain distribution by the elastic modulus of concrete. In this way, since it is possible to grasp the stress distribution of the concrete structure 1 and measure the subsequent change, it is possible to rationalize the construction planning and management of reconstruction, repair, and reinforcement work of the concrete structure 1 based on the results. Moreover, since it is possible to measure the change after construction, it can also be used for structural performance evaluation in maintenance management.

[0038] Second Embodiment 5 is a diagram showing a concrete structure 1 in this embodiment. In this embodiment, the installation state of the optical fiber 3 is different from that in the first embodiment. In this embodiment, the optical fiber 3 is installed so as to turn back and forth at one end side of the concrete structure 1. On the concrete structure 1, two linear portions of the optical fiber 3 extend parallel to each other in the Y-axis direction.

[0039] Furthermore, the concrete structure 1 has a plurality of measurement points P1, P2, ..., P2 along one of the two linear portions of the optical fiber 3. n (n is a natural number of 2 or more) are set in a substantially straight line in the Y-axis direction. In addition, a plurality of reference points Q1, Q2, ..., Q3 are set along the other of the two straight line portions of the optical fiber 3. n are set in a straight line in the Y-axis direction. n and reference points Q1 to Q n The positions of the reference point Q1 and the measurement point P1 are known. Similarly, the reference point Q2 is aligned with the measurement point P2, the reference point Q3 is aligned with the measurement point P3, ..., the reference point Q n is the measurement point P n The measurement points P1 to P n and each reference point Q1 to Q n When strain occurs in the concrete structure 1, the measurement points P1 to P2 are detected by the optical fiber 3 according to the principle of DAS measurement. n and reference points Q1 to Q n It is possible to detect strain at every

[0040] In this embodiment, a method for estimating stress distribution in a concrete structure 1 using the DAS measurement method will be described. Fig. 6 is a flowchart of the stress distribution estimation method of this embodiment. As shown in the figure, the stress distribution estimation method includes a vibration detection step S201, a Y-direction elastic wave velocity calculation step S203, an X-direction elastic wave velocity calculation step S205, a stress calculation step S207, and a stress distribution acquisition step S209, which will be described next.

[0041] (Vibration detection process S201) Measurement points P1~P n Among the j-th adjacent measurement points P j and the (j+1)th measurement point P (j+1) In the vibration detection process S201, a measurement point P j An excitation point R is set in the immediate vicinity of the concrete structure 1. Then, this excitation point R is excited. Specifically, the user may strike the excitation point R with a hammer or a metal ball, or the excitation point R may be excited by an attached oscillator. Elastic waves generated by the excitation of this excitation point R propagate through the concrete structure 1 and reach each of the measurement points P1 to P n and each reference point Q1 to Q n At each measurement point P1 to P n and each reference point Q1 to Q n This generates vibrations.

[0042] Among these vibrations, the measurement point P j , measurement point P (j+1) , and reference point Q j The vibrations occurring at the measurement points P are detected by the optical fiber 3 according to the principle of DAS measurement, and are recognized as signal waveforms by the arithmetic unit 7 via the DAS measuring instrument 5. j Signal waveform f j and measurement point P (j+1) Signal waveform f (j+1) and reference point Q j Signal waveform of g j and are recognized separately.

[0043] (Y-direction elastic wave velocity calculation step S203) Next, the calculation device 7 calculates the signal waveform f j and signal waveform f (j+1) Based on this, the measurement point P j and measurement point P (j+1) Area A between j Elastic wave velocity Vy in the Y-axis direction j That is, the signal waveform f j Measurement point P obtained from jThe time when the vibration occurs at T j and the signal waveform f (j+1) Measurement point P obtained from (j+1) The time when the vibration occurs at T (j+1) The difference between and is ΔTy j And the measurement point P j and measurement point P (j+1) Let Ly be the distance (known) between j Then, the calculation device 7 calculates the area A j Elastic wave velocity Vy in the Y-axis direction j is calculated using the formula (β1) below. Vy j =ΔTy j / Ly j …Formula (β1)

[0044] (X-direction elastic wave velocity calculation step S205) Next, the calculation device 7 calculates the signal waveform f j and signal waveform g j Based on this, the measurement point P j and reference point Q j Area B between j Elastic wave velocity Vx in the X-axis direction j That is, the measurement point P j and reference point Q j The difference in the occurrence time of vibration between and is ΔTx j And the measurement point P j and reference point Q j Let Lx be the distance (known) between j Then, the calculation device 7 calculates the area B j Elastic wave velocity Vx in the X-axis direction j is calculated using the formula (β2) below. Vx j =ΔTx j / Lx j …Formula (β2)

[0045] (Stress calculation process S207) Next, the calculation device 7 calculates the elastic wave velocity Vy j and the elastic wave velocity in the X-axis direction Vx j Based on this, the area A of the concrete structure 1 jThe stress σ acting in the Y-axis direction on j Specifically, previous research has shown that in cases where stress acts mainly in only one direction on a concrete member and the stress in the perpendicular direction is negligibly small compared to the stress in this direction, then when the stress acting on the concrete member is σ, the elastic wave velocity in the direction of that stress σ is Vs, and the elastic wave velocity in the direction perpendicular to that stress σ is Vv, then σ and (Vs-Vv) / Vv are proportional. Therefore, from this relationship, it is possible to estimate stress σ from the elastic wave velocities Vs and Vv.

[0046] Based on the above findings, the calculation device 7 calculates the area A of the concrete structure 1. j The stress σ acting in the Y-axis direction on j The estimated value is calculated using the formula (β3) below. σ j =c (Vy j -Vx j ) / Vy j …Formula (β3) Here, c is a predetermined constant.

[0047] (Stress distribution acquisition process S209) The calculation device 7 calculates the area A of the object. j While changing the vibration detection step S201, the Y-direction elastic wave velocity calculation step S203, the X-direction elastic wave velocity calculation step S205, and the stress estimation step S211 including the stress calculation step S207 are repeatedly executed for j=1 to (n-1), thereby obtaining the vibration detection step S201, the Y-direction elastic wave velocity calculation step S203, the X-direction elastic wave velocity calculation step S205, and the stress estimation step S211 including the stress calculation step S207. (n-1) Stresses σ1, σ2, …, σ acting in the Y-axis direction (n-1) In this way, the areas A1 to A (n-1) For each stress σ1, σ2, …, σ (n-1) That is, in the calculation device 7, the measurement points P1 to P nIn the region where the stress distribution in the Y-axis direction acting on the concrete structure 1 is arranged, the distribution in the Y-axis direction of the stress in the Y-axis direction acting on the concrete structure 1 is acquired. The information on the stress distribution thus obtained may be visualized, for example, by expressing it in a contour diagram, and displayed on a display monitor or the like provided in the computing device 7 to be presented to the user.

[0048] In the above-mentioned vibration detection process S201 to stress calculation process S207, adjacent measurement points P j and measurement point P (j+1) Area A between j Elastic wave velocity V at j However, the present invention is not limited to this. For example, in the vibration detection process S201 to the stress calculation process S207, the measurement points P j and measurement point P k In this case, in the stress distribution acquisition step S209, the stress in the region between the measurement points P1 to P2 may be calculated repeatedly based on the stress in the randomly calculated region. n The distribution of stress in the region where the measurement points P are arranged may be obtained. j and measurement point P k The positional relationship between is not limited to being random, and may have some regularity other than being adjacent to each other (k=j+1).

[0049] Also, for example, the optical fiber 3 may be installed as shown in FIG. 7, and the measurement points and the reference points may be arranged. In this embodiment, the optical fiber 3 extends in a zigzag manner while repeatedly and regularly bending the Y-axis direction and the X-axis direction. A plurality of measurement points Py are arranged along the Y-axis direction of the optical fiber 3, and a plurality of measurement points Px are arranged along the X-axis direction of the optical fiber 3. According to this configuration, by setting the excitation point R immediately adjacent to the intersection between the Y-axis direction of the optical fiber 3 and the X-axis direction of the optical fiber 3, the elastic wave velocity in the Y-axis direction is obtained based on each signal waveform obtained at the plurality of measurement points Py, and at the same time, the elastic wave velocity in the X-axis direction is obtained based on each signal waveform obtained at the plurality of measurement points Px. Then, based on the above-mentioned obtained elastic wave velocity in the Y-axis direction and the elastic wave velocity in the X-axis direction, the stress in the Y-axis direction or the X-axis direction acting near the excitation point R can be obtained in accordance with the above-mentioned stress calculation step S207.

[0050] Alternatively, n may be 2. In this case, in the vibration detection step S201, the optical fiber 3 detects the vibrations generated at the measurement point P1, the measurement point P2, and the reference point Q1 due to the excitation of the excitation point R set immediately adjacent to the measurement point P1. In the Y-direction elastic wave velocity calculation step S203, the elastic wave velocity Vy1 in the Y-axis direction in the region A1 between the measurement point P1 and the measurement point P2 is calculated, and in the X-direction elastic wave velocity calculation step S205, the elastic wave velocity Vx1 in the X-axis direction in the region B1 between the measurement point P1 and the reference point Q1 is calculated. In the stress calculation step S207, the stress σ1 in the Y-axis direction acting on the region A1 is calculated based on the elastic wave velocity Vy1 and the elastic wave velocity Vx1. In the stress distribution acquisition step S209, strictly speaking, only the stress σ1 is obtained, not the distribution of the stress. In this case, the stress distribution acquisition step S209 may be omitted, and the arithmetic device 7 may present the stress σ1 obtained in the stress calculation step S207 to the user.

[0051] The effects of the present embodiment will be described. The stress estimation method of the present embodiment includes the vibration detection step S201, the Y-direction elastic wave velocity calculation step S203, the X-direction elastic wave velocity calculation step S205, and the stress calculation step S207, and obtains the stress in the Y-axis direction acting on the target area of ​​the concrete structure 1. According to this stress estimation method, even if the correlation between the elastic wave velocity and the stress in the concrete structure 1, such as the above-mentioned formula (α2), is unknown, the stress can be estimated. Therefore, it is not necessary to carry out a test including core sampling of the concrete structure 1 in advance. Note that the formula (β3) used in the stress calculation step S207 of the present embodiment does not change much depending on the type of concrete, and there is little need to determine it for each concrete structure 1.

[0052] The stress distribution estimation method of the present embodiment includes the vibration detection step S201, the Y-direction elastic wave velocity calculation step S203, the X-direction elastic wave velocity calculation step S205, the stress calculation step S207, and the stress distribution acquisition step S209, and obtains the distribution in the Y-direction of the stress in the Y-direction acting on the concrete structure 1. The stress distribution estimation method uses the above-mentioned stress estimation method, and therefore provides the same effects as the above-mentioned stress estimation method.

[0053] The present invention can be embodied in various forms, including the above-described embodiment, with various modifications and improvements based on the knowledge of those skilled in the art. In addition, the following modified examples can be constructed by utilizing the technical matters described in the above-described embodiment. The configurations of each embodiment may be used in appropriate combination. [Explanation of symbols]

[0054] 1...concrete structure, 3...optical fiber, P1...measurement point (first measurement point), P2...measurement point (second measurement point), P1 to P n …Measuring points, Q1~Q n...reference point, R...excitation point, S101...vibration detection process, S103...elastic wave velocity calculation process, S105...elastic wave velocity distribution acquisition process, S107...stress distribution acquisition process, S201...vibration detection process, S203...Y-direction elastic wave velocity calculation process (specific axial direction elastic wave velocity calculation process), S205...X-direction elastic wave velocity calculation process (orthogonal axial direction elastic wave velocity calculation process), S207...stress calculation process, S209...stress distribution acquisition process, S211 stress estimation process.

Claims

1. An elastic wave velocity evaluation method for evaluating an elastic wave velocity in a concrete structure, comprising: an optical fiber is installed in the concrete structure, and a first measurement point, a second measurement point, and a vibration point are set along a predetermined axial direction along a location where the optical fiber is installed, so as to be substantially aligned in a straight line; a vibration detection step of detecting, by the optical fiber, vibrations generated at the first measurement point and the second measurement point due to excitation at the excitation point; an elastic wave velocity calculation step of calculating the elastic wave velocity in a region between the first measurement point and the second measurement point based on a difference in occurrence time of the vibration at the first measurement point and the second measurement point detected in the vibration detection step and a distance between the first measurement point and the second measurement point; The elastic wave velocity evaluation method includes:

2. An elastic wave velocity distribution evaluation method for evaluating an elastic wave velocity distribution in a concrete structure, comprising: An optical fiber is installed in the concrete structure, and a plurality of measurement points, 1st to nth measurement points (n is a natural number of 2 or more), and a vibration point are set along a predetermined axial direction in a substantially straight line along the installation location of the optical fiber, a vibration detection step of detecting, by the optical fiber, vibrations generated at the first to n-th measurement points due to excitation at the excitation point; an elastic wave velocity calculation process in which an area between a j-th measurement point and a k-th measurement point among the plurality of measurement points is set as a target area (j and k are natural numbers from 1 to n), and the elastic wave velocity in the target area is calculated based on a difference in occurrence time of the vibration at the j-th measurement point and the k-th measurement point detected in the vibration detection process and a distance between the j-th measurement point and the k-th measurement point; an elastic wave velocity distribution acquisition process in which the elastic wave velocity distribution of the concrete structure is obtained based on the elastic wave velocities in the plurality of target areas obtained by repeating the elastic wave velocity calculation process while changing the target area; and The elastic wave velocity distribution evaluation method includes:

3. 3. A stress distribution estimation method, in which a distribution of the stress acting on the concrete structure in the specified axial direction is estimated based on the elastic wave velocity distribution obtained by the elastic wave velocity distribution evaluation method described in claim 2 and a correlation between elastic wave velocity and stress in the concrete structure obtained separately.

4. A method for estimating a stress acting on a concrete structure in a predetermined axial direction, comprising: An optical fiber is installed in the concrete structure, and a first measurement point, a second measurement point, and a reference point are set along a location where the optical fiber is installed; the first measurement point and the second measurement point are aligned in the predetermined axis direction, and the first measurement point and the reference point are aligned in an orthogonal axis direction perpendicular to the predetermined axis direction, a vibration detection step of detecting, by the optical fiber, vibrations generated at the first measurement point, the second measurement point, and the reference point due to excitation at a position immediately adjacent to the first measurement point; a predetermined axis direction elastic wave velocity calculation step of calculating an elastic wave velocity in the predetermined axis direction in a region between the first measurement point and the second measurement point based on a difference in occurrence time of the vibration at the first measurement point and the second measurement point detected in the vibration detection step and a distance between the first measurement point and the second measurement point; an orthogonal axis direction elastic wave velocity calculation process for calculating an elastic wave velocity in the orthogonal axis direction in a region between the first measurement point and the reference point based on a difference in occurrence time of the vibration at the first measurement point and the reference point detected in the vibration detection process and a distance between the first measurement point and the reference point; a stress calculation step of calculating a stress acting in the predetermined axis direction in a region between the first measurement point and the second measurement point based on the elastic wave velocity in the predetermined axis direction and the elastic wave velocity in the orthogonal axis direction; A stress estimation method comprising:

5. A stress distribution estimation method for estimating a distribution of stress acting on the concrete structure in the predetermined axial direction by using the stress estimation method according to claim 4, An optical fiber is installed in the concrete structure, and first to n-th measurement points (n is a natural number of 2 or more) which are a plurality of measurement points and are aligned in a substantially straight line in the predetermined axial direction, and first to n-th reference points which are a plurality of reference points are set along an installation location of the optical fiber, a stress estimating step of estimating a stress acting on the target region in the predetermined axis direction by the stress estimation method according to claim 4, using a j-th reference point arranged in the orthogonal axis direction with respect to the j-th measurement point among the reference points, the j-th reference point being a region between a j-th measurement point and a k-th measurement point (j and k are natural numbers from 1 to n) among the plurality of measurement points as a target region; a stress distribution acquisition process for acquiring a distribution of the stress in the concrete structure based on the stresses in each of the plurality of target regions acquired by repeating the stress estimation process while changing the target region; A stress distribution estimation method comprising:

6. 6. The stress distribution estimating method according to claim 3, wherein the concrete structure is a prestressed concrete structure in which prestress is introduced in the predetermined axial direction.

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