Measurement equipment

Abstract

To provide a measurement device with which it is possible to acquire shrinkage strain that occurs to a concrete member, using an optical fiber.SOLUTION: A measurement device 1 comprises: a cylindrical member 23A that extends so as to link two prescribed points P1, P2 on a main reinforcing bar S11 in the inside of a concrete S2; an optical fiber cable 21 which is located along the cylindrical member 23A and secured at least in part to the cylindrical member 23A; a stress suppression container 26 for accommodating the secured portion 24 of the optical fiber cable 21 and cylindrical member 23A and suppressing the propagation of stresses from the external concrete S2 to an internal concrete S3; and a shrinkage strain acquisition unit for acquiring the shrinkage strain of the internal concrete S3 of the stress suppress container 26 on the basis of the strain of the optical fiber cable 21.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a measurement device. [Background technology]

[0002] Conventionally, a Young's modulus detection device described in Patent Document 1 is known as a measuring device for measuring strain occurring in a concrete member. This Young's modulus detection device includes a storage case, an electric heater provided inside one end side of the storage case, and a strain detector provided inside the other end side of the storage case. Concrete of the same quality as the concrete surrounding the storage case is poured into the storage case. As a result, a cylindrical concrete pillar is formed inside the storage case so as to be isolated from the concrete surrounding the storage case. The strain occurring in the concrete pillar is detected by the strain detector provided inside the concrete pillar. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 60-128325 Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, attempts have been made to acquire the strain occurring in a concrete member by embedding an optical fiber in the concrete member. The optical fiber is a linear member and can measure the strain at any position on the member. However, the measured value of strain obtained is generally the total strain, which is the sum of elastic strain, creep strain, shrinkage strain, and temperature strain due to restraint and external force. In order to effectively utilize the measured data of the total strain, it is desirable to configure a measuring device that can acquire the shrinkage strain occurring in the concrete member using the optical fiber.

[0005] Therefore, an object of the present invention is to provide a measuring device that can obtain shrinkage strain occurring in a concrete member by using an optical fiber. [Means for solving the problem]

[0006] The present invention is a measuring device to be embedded in a concrete member, comprising: an optical fiber holding part that extends so as to connect two predetermined points on the same or different rebars inside the concrete member; an optical fiber that is arranged along the optical fiber holding part and has at least a portion fixed to the optical fiber holding part; a stress suppression container that houses the fixed portion of the optical fiber and the optical fiber holding part and suppresses the transmission of stress from the external concrete to the internal concrete; and a shrinkage strain acquisition part that acquires the shrinkage strain of the concrete inside the stress suppression container based on the strain of the optical fiber.

[0007] In this measuring device, the optical fiber is arranged along the optical fiber holding part, and at least a part of the optical fiber is fixed to the optical fiber holding part. This optical fiber holding part has a function of holding the optical fiber and generating a strain in the optical fiber. The optical fiber holding part is in contact with the concrete around the optical fiber holding part, and deforms together with the surrounding concrete along a direction connecting two predetermined points. Since the optical fiber in the fixed part of the optical fiber holding part is fixed to the optical fiber holding part, a strain similar to that in the optical fiber holding part is generated in the optical fiber. Furthermore, since the stress suppression container suppresses the transmission of stress from the external concrete to the internal concrete, the strain generated in the optical fiber corresponds to the shrinkage strain of the concrete. Therefore, according to this measuring device, it is possible to obtain the shrinkage strain generated in the concrete member using the optical fiber.

[0008] In one embodiment, the optical fiber may have an excess length portion that sandwiches the fixed portion between the optical fiber and the optical fiber holding part. In this case, the wiring length of the optical fiber in the excess length portion is longer than when no excess length portion is provided, so that when, for example, strains at a plurality of positions are averaged and obtained, it is possible to reduce the influence of strain of the optical fiber on the side opposite the fixed portion between the optical fiber and the optical fiber holding part as viewed from the excess length portion on strain of the optical fiber in the fixed portion.

[0009] In one embodiment, the optical fiber holding part may include a tubular member that extends between two predetermined points on the same reinforcing bar and is inserted into the reinforcing bar via a buffer material that suppresses the transmission of force from the reinforcing bar. In this case, for example, the optical fiber can be wired along the reinforcing bar, making the wiring work of the optical fiber easier and reducing the risk of the optical fiber being broken.

[0010] In one embodiment, the optical fiber holder may include a resin rod that is spanned between two predetermined points on different reinforcing bars. In this case, it is possible to obtain shrinkage strain occurring in the concrete member located between the different reinforcing bars.

[0011] In one embodiment, the surface of the optical fiber-holding part may be provided with a recess for improving adhesion to the concrete around the optical fiber-holding part. In this case, the strain generated in the optical fiber-holding part corresponds more closely to the shrinkage strain of the concrete around the optical fiber-holding part.

[0012] In one embodiment, the stress suppressing container has a pair of end faces including a slit through which the optical fiber is inserted, a pair of side faces connecting the pair of end faces, and a lid that closes an opening defined by the end faces and the side faces, and an end of the slit on the lid side may be an opening end that reaches an edge of the side face. In this case, by attaching the stress suppressing container so that the optical fiber is inserted into the slit via the opening end of the slit, the fixed portion of the optical fiber and the optical fiber holding part can be easily accommodated. Effect of the Invention

[0013] According to the present invention, it is possible to provide a measuring device that can obtain shrinkage strain occurring in a concrete member by using an optical fiber. [Brief description of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a concrete structure in which a measuring device according to an embodiment is embedded. [Diagram 2] FIG. 2 is a partial cross-sectional view showing a main part of the measuring device of FIG. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 11 is a cross-sectional view of a concrete structure in which a measuring device according to a modified example is embedded. [Diagram 5] FIG. 5 is a cross-sectional view of the measurement device in FIG. [Figure 6] 5(a) is a side view showing the excess length portion of the measuring device of Fig. 4, (b) is a side view showing a modified example of the excess length portion, and (c) is a side view showing another modified example of the excess length portion. [Figure 7] 1A is a cross-sectional view showing a modified stress suppressing container, FIG. 1B is a cross-sectional view showing another modified stress suppressing container and a modified opening and closing mode of its lid, and FIG. 1C is a cross-sectional view showing another modified stress suppressing container and a modified opening and closing mode of its lid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of a measuring device according to the present invention will be described in detail with reference to the drawings. In the description, the same elements or elements having the same functions may be designated by the same reference numerals, and duplicated descriptions will be omitted.

[0016] Fig. 1 is a cross-sectional view showing a concrete structure (concrete member) S in which a measuring device 1 according to an embodiment is embedded. As shown in Fig. 1, the measuring device 1 measures stress acting on the concrete structure S in a state where it is embedded in the concrete structure S. The concrete structure S has, for example, a plurality of structural reinforcing bars S1 and concrete S2. As an example, the structural reinforcing bars S1 include a plurality of main reinforcing bars S11 extending in a vertical direction D1 and a distribution reinforcing bar S12 extending in a horizontal direction D2.

[0017] The main reinforcing bars S11 and the distribution reinforcing bars S12 are arranged in a lattice pattern. The measurement device 1 is arranged, for example, along one of the main reinforcing bars S11.

[0018] The measuring device 1 includes a main body 10 and a linear detection device 20 extending from the main body 10. In this embodiment, the detection device 20 includes an optical fiber cable (optical fiber) 21 and a shrinkage strain acquisition unit 22 provided at an end of the optical fiber cable 21. The optical fiber cable 21 extending from the main body 10 is arranged, for example, along a structural reinforcing bar S1 (main reinforcing bar S11 as an example).

[0019] The shrinkage strain acquisition unit 22 acquires the shrinkage strain of the concrete S3 cast inside the stress suppression container 26 described below based on the strain of the optical fiber cable 21. The shrinkage strain acquisition unit 22 includes a measuring instrument and an analyzing device. The measuring instrument inputs measuring light K1 into the optical fiber cable 21 and receives backscattered light K2 returning from each measuring position in the longitudinal direction of the optical fiber cable 21, and transmits information on the intensity, wavelength, etc. of the received backscattered light K2 to the analyzing device (not shown). Examples of the scattered light include Rayleigh scattered light and Brillouin scattered light. Examples of the measuring instrument that can be used include an OTDR (Optical Time Domain Reflectometer) that uses Rayleigh scattered light and a BOTDR (Brillouin Optical Time Domain Reflectometer) that uses Brillouin scattered light.

[0020] The analysis device is a computer including, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls the analysis device based on a control program stored in the ROM. The RAM functions as a work memory when the CPU executes the control program stored in the ROM. In the analysis device, the intensity and wavelength of the backscattered light K2 at each measurement position in the longitudinal direction of the optical fiber cable 21 are analyzed based on the principle that the intensity and wavelength of the backscattered light K2 depend on the strain applied to the optical fiber cable 21. By this analysis, the strain at each measurement position in the longitudinal direction of the optical fiber cable 21 is obtained, and as a result, the longitudinal strain distribution applied to the optical fiber cable 21 is obtained.

[0021] Fig. 2 is a partial cross-sectional view showing a main part of the measuring device of Fig. 1. In order to facilitate understanding of the figures, hatching corresponding to concrete has been omitted in figures other than Fig. 1 and Fig. 4.

[0022] 2, the measurement device 1 includes an optical fiber holding part 23 that extends to connect two predetermined points P1 and P2 on the same structural reinforcing bar (reinforcing bar) S1 inside the concrete structure S. As an example, the two points P1 and P2 here are located in a region between a pair of adjacent reinforcing bars S12 on the same structural reinforcing bar S1.

[0023] The optical fiber holding part 23 has a function of holding the optical fiber cable 21 and generating a strain in the optical fiber cable 21. The optical fiber holding part 23 is in contact with the concrete S3 around the optical fiber holding part 23, and a force from the concrete S3 along the extension direction of the optical fiber holding part 23 (i.e., the direction connecting the two points P1 and P2) is transmitted to the optical fiber holding part 23, and the optical fiber holding part 23 deforms together with the surrounding concrete S3. The optical fiber holding part 23 generates a strain similar to that of the optical fiber holding part 23 in the fixed optical fiber cable 21 via the fixed part 24 with the optical fiber cable 21. In other words, since the optical fiber cable 21 in the fixed part of the optical fiber holding part 23 is fixed to the optical fiber holding part 23, a strain similar to that of the optical fiber holding part 23 is generated in the optical fiber cable 21.

[0024] Fig. 3 is a cross-sectional view taken along line III-III in Fig. 2. As shown in Figs. 2 and 3, the optical fiber holding part 23 includes a tubular member 23A inserted into the structural reinforcing bar S1. The tubular member 23A is inserted into the structural reinforcing bar S1 via a buffer material 25. The buffer material 25 suppresses the transmission of force from the structural reinforcing bar S1 to the tubular member 23A when the tubular member 23A moves relative to the structural reinforcing bar S1. In other words, the inside of the tubular member 23A is separated from the structural reinforcing bar S1. The buffer material 25 may be, for example, grease or the like.

[0025] As an example, the cylindrical member 23A is a polyvinyl chloride pipe with a circular cross section. Other materials and shapes may be used as the cylindrical member 23A as long as they can perform the above-mentioned functions, can be attached relatively movably along the structural reinforcing bar S1, and can easily suppress the transmission of force from the structural reinforcing bar S1 to the cylindrical member 23A due to the movement.

[0026] The surface of the cylindrical member 23A may be provided with a recess (not shown) for improving adhesion to the concrete S3 around the optical fiber holding part 23. The recess may be, for example, a groove extending along a direction intersecting (for example, perpendicular) to the direction connecting the two points P1 and P2. The recess may be provided, for example, by cutting the surface of the cylindrical member 23A with a tool such as a grinder. The recess may be a groove formed in the cylindrical member 23A using a lathe or the like. In addition to or instead of the recess, a surface roughening treatment may be performed. The surface roughening treatment may be performed physically with a tool such as a sander, may be previously formed according to the shape of a resin mold, or may be a chemical treatment.

[0027] The optical fiber cable 21 is arranged along the optical fiber holding part 23. The optical fiber cable 21 is installed along the structural reinforcing bars S1 (main reinforcing bars S11) before the concrete S2 is poured. The optical fiber cable 21 is attached to the surface of the optical fiber holding part 23 before the concrete S3 around the optical fiber holding part 23 is poured. At least a portion of the optical fiber cable 21 is fixed to the optical fiber holding part 23. The optical fiber cable 21 is fixed to the main reinforcing bars S11 and the surface of the cylindrical member 23A with an adhesive, for example.

[0028] The stress suppression container 26 is a container that houses the fixed portion 24 of the optical fiber cable 21 and the optical fiber holding portion 23. The stress suppression container 26 suppresses the transfer of stress from the external concrete S2 to the internal concrete S3, while allowing the transfer of heat and moisture from the external concrete S2 to the internal concrete S3. The stress suppression container 26 is sometimes called a so-called stress-free container. The stress suppression container 26 is made of a hard material such as resin or metal, and may be, for example, polyvinyl chloride material.

[0029] The stress suppression container 26 has a pair of end faces 26a including a slit SL through which the optical fiber cable 21 is inserted, a pair of side faces 26b connecting the pair of end faces 26a, and a lid 26d that closes an opening 26c defined by the end faces 26a and the side faces 26b. The end of the slit SL on the lid 26d side is, for example, an opening end that reaches the edge of the side face 26b.

[0030] As an example, stress suppression container 26 may be a lidded box-shaped container having a rectangular cross section. The dimensions of stress suppression container 26 are not particularly limited, but as an example, the length in the axial direction may be about 300 mm, and the width in the direction perpendicular to the axial direction and parallel to lid 26d may be about 150 mm.

[0031] A filter 27 (e.g., felt) is attached to the inner wall surface of the stress suppression container 26 in order to suppress the transmission of stress from the external concrete S2 to the internal concrete S3. This places the external concrete S2 and the internal concrete S3 in a so-called disconnected state, suppressing the transmission of stress and strain. The inner wall surface of the stress suppression container 26 includes the inner surfaces of the stress suppression container 26, namely, the end surface 26a, the side surface 26b, the lid 26d, and the bottom surface.

[0032] The surface of the stress suppression container 26 is provided with a number of through holes (not shown) that connect the inner wall surface to the outer wall surface to allow the transfer of heat and moisture from the external concrete S2 to the internal concrete S3.

[0033] Stress suppression container 26 is attached so as to cover the periphery of fixed portion 24 between optical fiber cable 21, which is covered with tubular member 23A, and optical fiber holding part 23. After concrete S3 is filled into stress suppression container 26 through opening 26c, opening 26c is closed with lid 26d.

[0034] According to the above, the cylindrical member 23A behaves integrally with the concrete S3 inside the stress suppression container 26, and thus the axial strain can be measured by the optical fiber cable 21 installed in the cylindrical member 23A. The concrete S3 inside the stress suppression container 26 is isolated from the surrounding concrete S2 by the stress suppression container 26, and therefore shrinkage strain occurs with reduced effects of stress and strain (e.g., elastic strain, etc.) from the surrounding concrete S2, and therefore the strain measured by the optical fiber cable 21 substantially corresponds to only the shrinkage strain of the concrete S3. Therefore, the fixed portion 24, which is a partial section of the optical fiber cable 21 installed over the entire concrete structure S, can measure the shrinkage strain of the concrete S3 inside the stress suppression container 26. In addition, the concrete S3 filled inside is made of the same material and has the same material age as the external concrete S2, and therefore the shrinkage strain of the concrete S3 inside the stress suppression container 26 can be treated as the shrinkage strain occurring in the external concrete S2 (i.e., the concrete structure S).

[0035] Incidentally, the optical fiber cable 21 has an excess part 28 that sandwiches the fixed part 24 between the optical fiber cable 21 and the optical fiber holding part 23. The excess part 28 is a buffer area for connecting a region including the fixed part 24 for measuring shrinkage strain with a region for measuring total strain without measuring shrinkage strain. Alternatively, the excess part 28 can be said to be a buffer area that reduces the mutual influences between the behavior of the tubular member 23A and the behavior of the structural reinforcing bar S1.

[0036] The surplus portion 28 here is disposed at both ends of the cylindrical member 23A. For example, the surplus portion 28 is formed by spirally disposing the optical fiber cable 21 on the structural reinforcing bar S1 at both ends of the cylindrical member 23A. In this portion, the wiring length of the optical fiber cable 21 is increased. As a result, the wiring length of the optical fiber cable 21 in the surplus portion 28 is longer than when the surplus portion 28 is not provided. Therefore, when strains at a plurality of positions on the optical fiber cable 21 are averaged and obtained, for example, the influence of the strain of the optical fiber cable 21 on the side opposite the fixed portion 24 between the optical fiber cable 21 and the optical fiber holding unit 23 as viewed from the surplus portion 28 on the strain of the optical fiber cable 21 at the fixed portion 24 can be reduced. In other words, the constraint due to the spatial resolution of the optical fiber cable 21 can be alleviated. The surplus portion 28 may be located near the slits SL at both ends of the stress suppression container 26.

[0037] As described above, in the measurement device 1 according to the present embodiment, the optical fiber cable 21 is arranged along the optical fiber holding part 23, and at least a part of the optical fiber cable 21 is fixed to the optical fiber holding part 23. The optical fiber holding part 23 has a function of holding the optical fiber cable 21 and generating a strain in the optical fiber cable 21. The optical fiber holding part 23 is in contact with the concrete S3 around the optical fiber holding part 23, and deforms together with the surrounding concrete S3 along the direction connecting the two predetermined points P1 and P2. Since the optical fiber cable 21 at the fixed part of the optical fiber holding part 23 is fixed to the optical fiber holding part 23, a strain similar to that of the optical fiber holding part 23 is generated in the optical fiber cable 21. In addition, since the stress suppression container 26 suppresses the transmission of stress from the external concrete S2 to the internal concrete S3, the strain generated in the optical fiber cable 21 corresponds to the shrinkage strain of the concrete S3. Therefore, according to the measurement device 1, the shrinkage strain generated in the concrete S3 can be obtained using the optical fiber cable 21.

[0038] In the measuring device 1, the optical fiber cable 21 has an excess part 28 that sandwiches the fixed part 24 between the optical fiber cable 21 and the optical fiber holding part 23. As a result, the wiring length of the optical fiber cable 21 at the excess part 28 is longer than when the excess part 28 is not provided. Therefore, when the strain at a plurality of positions is averaged and obtained, for example, it is possible to reduce the influence of the strain of the optical fiber cable 21 on the side opposite the fixed part 24 between the optical fiber cable 21 and the optical fiber holding part 23 as viewed from the excess part 28 on the strain of the optical fiber cable 21 at the fixed part 24. In other words, the influence of the total strain outside the excess part 28 is reduced on the shrinkage strain to be measured by the excess part 28. Therefore, it is expected that the measurement accuracy of the shrinkage strain is improved.

[0039] In the measurement device 1, the optical fiber holding part 23 includes a cylindrical member 23A that extends connecting two predetermined points on the same structural rebar S1 and is inserted into the structural rebar S1 via a buffer material 25 that suppresses the transmission of force from the structural rebar S1. This makes it easier to wire the optical fiber cable 21, for example, by wiring the optical fiber cable 21 along the structural rebar S1, and reduces the risk of the optical fiber cable 21 being broken.

[0040] In the measuring device 1, a recess is provided on the surface of the optical fiber holding part 23 to improve adhesion to the concrete S3 surrounding the optical fiber holding part 23. This makes the strain generated in the optical fiber holding part 23 correspond more closely to the shrinkage strain of the concrete S3 surrounding the optical fiber holding part 23.

[0041] In the measurement device 1, the stress suppression container 26 has a pair of end faces 26a including a slit SL through which the optical fiber cable 21 is inserted, a pair of side faces 26b connecting the pair of end faces 26a, and a lid 26d closing an opening 26c defined by the end faces 26a and the side faces 26b. The end of the slit SL on the lid 26d side is an opening end that reaches the edge of the side face 26b. Thus, by attaching the stress suppression container 26 so that the optical fiber cable 21 is inserted into the slit SL via the opening end of the slit SL, the fixed portion 24 between the optical fiber cable 21 and the optical fiber holding part 23 can be easily accommodated.

[0042] In addition, when the optical fiber cable 21, which is a linear material, is used, the strain can be measured at any position on the optical fiber cable 21. Therefore, for example, by installing the optical fiber cable 21 over the entire concrete structure S, the overall strain distribution of the concrete structure S can be grasped. The measuring device 1 makes it possible to measure shrinkage strain at any section (position) of the optical fiber cable 21. Therefore, for example, it is possible to measure both total strain and shrinkage strain with a single optical fiber cable 21 that is continuously laid. This configuration is significantly simpler than a conventional configuration in which a strain detector is installed at each measurement point. In addition, by using the shrinkage strain measured by the optical fiber cable 21, it becomes possible to effectively utilize the measurement data of the total strain measured by the optical fiber cable 21.

[0043] Although an embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and may be modified within the scope of the gist described in each claim.

[0044] The arrangement direction of the measuring device 1 is not limited to the above example, and may be any direction (for example, horizontal, vertical, or other direction) with respect to the concrete structure S. In other words, the positions of the two points P1 and P2 are not limited to the above example. For example, the positions of the two points P1 and P2 do not necessarily have to be located in the area between a pair of adjacent reinforcement bars S12 on the same structural reinforcing bar S1. The positions of the two points P1 and P2 may be two predetermined points on two structural reinforcing bars S1 that are connected on the same line, not the same. In addition, the two points P1 and P2 may be two predetermined points on the same or connected on the same line, the reinforcement bars (reinforcing bars) S12.

[0045] The positions of the two predetermined points may be two predetermined points on different reinforcing bars. FIG. 4 is a cross-sectional view of a concrete structure in which a measuring device according to a modified example is embedded. FIG. 5 is a cross-sectional view of the measuring device of FIG. 4. As shown in FIG. 4 and FIG. 5, the measuring device 1 includes a rod (optical fiber holding part) 23B extending so as to connect two predetermined points P3, P4 on different reinforcing bars S12 inside the concrete structure S. As an example, the two points P3, P4 of the measuring device 1 are located in a rectangular area defined by two main reinforcing bars S11 and two reinforcing bars S12. In this case, the optical fiber cable 21 is not wired along the structural reinforcing bars S1, and is therefore wired away from the reinforcing bar cage.

[0046] Since the optical fiber cable 21 buried in the concrete S3 is a thin wire, there is a risk that the fiber may break due to impact during construction. Therefore, the optical fiber cable 21 is attached to, for example, a bar 23B. The bar 23B is preferably made of a material having elasticity (a material having a small elastic coefficient relative to the concrete S3) that does not hinder the behavior of the concrete S3 to be measured and has higher rigidity than the optical fiber cable 21. For example, an acrylic bar may be used for the bar 23B. That is, the optical fiber holding part 23 includes a resin bar 23B that is spanned so as to connect two predetermined points P3 and P4 on different reinforcing bars S12. The cross-sectional shape of the bar 23B is not particularly limited, and may be, for example, a rectangular cross section, a circular cross section, or the like. The surface of the bar 23B may be provided with a recess (not shown) that improves adhesion to the concrete S3 around the bar 23B. The material of the bar 23B may be, in addition to acrylic, for example, glass fiber or carbon fiber. By using such a configuration in which the bar 23B is used as the optical fiber holding portion 23, it is possible to obtain the shrinkage strain occurring in the concrete S3 located between the different reinforcing bars S12.

[0047] Next, a modified example of the slack portion 28 in Fig. 2 will be described. Fig. 6(a) is a side view showing the slack portion of the measuring device in Fig. 4. In the example of Fig. 6(a), as an alternative to the optical fiber cable 21 being spirally arranged on the rod 23B at both ends of the stress suppression container 26, a partition wall 26e is added inside the end face 26a of the stress suppression container 26 to form a double bottom shape, and the optical fiber cable 21 is in a slack state in the space between the end face 26a and the partition wall 26e (slack portion). The space between the end face 26a and the partition wall 26e may be hollow, or may be filled with a buffer material such as a filter 27.

[0048] FIG. 6(b) is a side view showing a modified example of the surplus portion. In the example of FIG. 6(b), instead of providing a surplus portion that increases the length of the optical fiber cable 21, a section 28A in which the optical fiber cable 21 is not attached to the bar 23B may be provided. The section 28A includes the boundary between the inside and the outside of the stress suppression container 26. Furthermore, in the section 28A, the surface of the optical fiber cable 21 may be provided with a lubricating film or coating such as grease. Alternatively, in the section 28A, a cylindrical member through which the optical fiber cable 21 is inserted may be disposed so as to cover the optical fiber cable 21. In this way, by bonding the optical fiber cable 21 only to the section 28A and / or covering the surface of the optical fiber cable 21, it is possible to cut the edge so that the strain generated in the concrete S2 outside the stress suppression container 26 is unlikely to act on the concrete S3 inside the stress suppression container 26. The surface of the bar 23B may also be provided with a similar coating or the like.

[0049] FIG. 6(c) is a side view showing another modified example of the excess length portion. In the example of FIG. 6(c), a section 28B is provided on the surface of the bar 23B where no recess is formed to improve adhesion with the concrete S3 around the bar 23B. Recesses are formed on the surface of the bar 23B in other sections. Section 28B includes the boundary between the inside and outside of the stress suppression container 26. In this way, by reducing the adhesion with the concrete S3 around the bar 23B only in section 28B, it is possible to cut off the edge so that the strain generated in the concrete S2 outside the stress suppression container 26 is less likely to act on the concrete S3 inside the stress suppression container 26. Particularly in the example of FIG. 6(c), in the section where the recess is formed outside the stress suppression container 26, the sum of the elastic strain, creep strain, shrinkage strain, and temperature strain due to restraint and external force can be measured using the same optical fiber cable 21. It becomes possible to extract the elastic strain and creep strain due to restraint and external forces by subtracting from the measured value the shrinkage strain of concrete S3 measured by optical fiber cable 21 inside stress suppression container 26 and the temperature strain evaluated from the temperature that can also be detected by optical fiber cable 21. As a result, it is expected that the measured data will be effectively utilized in analyses focusing on elastic strain and creep strain.

[0050] Next, modified examples of the stress suppression container 26 will be described. The stress suppression container 26 may be a lidded container having a cross section other than a rectangular shape. FIG. 7(a) is a cross-sectional view showing a modified stress suppression container. FIG. 7(b) is a cross-sectional view showing another modified stress suppression container and a modified opening and closing mode of its lid. FIG. 7(c) is a cross-sectional view showing another modified stress suppression container and a modified opening and closing mode of its lid. In the example of FIG. 7(a), the cross-sectional shape of the stress suppression container 26 is U-shaped. In the examples of FIGS. 7(b) and (c), the cross-sectional shape of the stress suppression container 26 is semicircular. The lid 26d may be configured to slide to close the opening 26c as in the example of FIG. 7(b), or may be configured to close the opening 26c by using one end of the lid 26d as a hinge or the like as a branch to be freely opened and closed as in the example of FIG. 7(c). The lid 26d may also be simply fitted in and fixed to close the opening 26c.

[0051] In the above embodiment and modified example, the extra length portion 28, the section 28A, or the section 28B is provided, but these are not essential.

[0052] In the above embodiment and modified example, the optical fiber holding part extending to connect two predetermined points on the reinforcing bar is parallel to the reinforcing bar, but is not limited to this. The optical fiber holding part may extend in a direction that is not parallel to either the main reinforcing bar S11 or the distribution reinforcing bar S12 but is twisted in a direction that is not parallel to either the main reinforcing bar S11 or the distribution reinforcing bar S12.

[0053] In the above embodiment and modified example, the cylindrical member 23A and the rod 23B are exemplified as the optical fiber holding part, but the optical fiber holding part is not limited to these. Anything having the function of the optical fiber holding part described above may be used.

[0054] The surface of the optical fiber holding portion does not necessarily need to be provided with a recess for improving adhesion to the concrete surrounding the optical fiber holding portion.

[0055] In the stress suppression container, the end of the slit on the lid side does not necessarily have to be an opening end that reaches the edge of the side surface. It may reach another edge, or it may not reach any edge. The stress suppression container is not limited to a configuration having a pair of end faces including a slit, a pair of side faces connecting the pair of end faces, and a lid that closes the opening defined by the end faces and side faces. The stress suppression container may be, for example, a container divided into two in the axial direction, or various containers may be used as long as they have the functions of the stress suppression container described above. [Explanation of symbols]

[0056] 1...measuring device, 21...optical fiber cable (optical fiber), 22...shrinkage strain acquisition section, 23...optical fiber holding section, 23A...cylindrical member (optical fiber holding section), 23B...rod (optical fiber holding section), 24...fixing section, 25...buffer material, 26...stress suppression container, 26a...end face, 26b...side face, 26c...opening, 26d...lid section, 28...excess length, S...concrete structure (concrete member), S2, S3...concrete (concrete member), SL...slit.

Claims

1. A measuring device embedded in a concrete member, an optical fiber holding portion extending so as to connect two predetermined points on the same or different reinforcing bars inside the concrete member; an optical fiber arranged along the optical fiber holding part and at least a portion of the optical fiber fixed to the optical fiber holding part; a stress suppression container that accommodates a fixed portion of the optical fiber and the optical fiber holding part and suppresses the transmission of stress from the external concrete to the internal concrete; a shrinkage strain acquisition unit that acquires a shrinkage strain of the concrete inside the stress suppression container based on the strain of the optical fiber, The optical fiber holding portion of the measuring device includes a tubular member extending between two specified points on the same reinforcing bar and inserted into the reinforcing bar via a cushioning material that suppresses the transmission of force from the reinforcing bar.

2. A measuring device to be embedded in a concrete member, an optical fiber holding portion extending so as to connect two predetermined points on the same or different reinforcing bars inside the concrete member; an optical fiber arranged along the optical fiber holding part and at least a portion of the optical fiber fixed to the optical fiber holding part; a stress suppression container that accommodates a fixed portion of the optical fiber and the optical fiber holding part and suppresses the transmission of stress from the external concrete to the internal concrete; a shrinkage strain acquisition unit that acquires a shrinkage strain of the concrete inside the stress suppression container based on the strain of the optical fiber, the stress suppression container has a pair of end faces including a slit through which the optical fiber is inserted, a pair of side faces connecting the pair of end faces, and a lid portion closing an opening defined by the end faces and the side faces, A measuring device, wherein the end of the slit on the lid side is an open end that reaches the edge of the side surface.

3. The measuring device according to claim 1 , wherein the optical fiber has an excess length that sandwiches a fixed portion between the optical fiber and the optical fiber holder.

4. 4. The measuring device according to claim 1, wherein the optical fiber holding unit includes a resin rod that is bridged so as to connect two predetermined points on different reinforcing bars.

5. 5. The measuring device according to claim 1, wherein a surface of the optical fiber holding part is provided with a recess for improving adhesion to the concrete around the optical fiber holding part.

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