JP7655830B2 - Measurement equipment - Google Patents

Description

The present invention relates to a measuring device.

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 of the storage case, and a strain detector provided inside the other end 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, 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.

Japanese Unexamined Patent Publication No. 128325/1983

Meanwhile, attempts have been made to obtain the strain occurring in concrete members by embedding optical fibers in the members. Optical fibers are linear components that can measure strain at any position on the member. However, the measured strain value obtained is generally the total strain, which is the sum of elastic strain due to restraint and external forces, creep strain, shrinkage strain, and temperature strain. To effectively utilize the measured data of total strain, it is desirable to configure a measuring device that can obtain the shrinkage strain occurring in concrete members using the optical fiber.

The present invention aims to provide a measuring device that can obtain shrinkage strain occurring in concrete members using optical fibers.

The present invention is a measuring device that is embedded in a concrete member, and includes an optical fiber holding section that extends 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 section and at least a portion of which is fixed to the optical fiber holding section, a stress suppression container that contains the fixed portion of the optical fiber and the optical fiber holding section and suppresses the transmission of stress from the external concrete to the internal concrete, and a shrinkage strain acquisition section that acquires the shrinkage strain of the concrete inside the stress suppression container based on the strain of the optical fiber.

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 the function of holding the optical fiber and generating strain in the optical fiber. The optical fiber holding part is in contact with the concrete surrounding the optical fiber holding part, and deforms together with the surrounding concrete along the 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. In addition, 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.

In one embodiment, the optical fiber may have an excess length 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 is longer than when no excess length is provided. Therefore, when, for example, strains at multiple positions are averaged to obtain the strain, the influence of the 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 on the strain of the optical fiber in the fixed portion can be reduced.

In one embodiment, the optical fiber holding portion may include a tubular member that extends between two predetermined points on the same rebar and is inserted into the rebar via a buffer material that suppresses the transmission of force from the rebar. In this case, for example, wiring the optical fiber along the rebar makes wiring the optical fiber easier and reduces the risk of the optical fiber breaking.

In one embodiment, the optical fiber holding unit may include a resin rod that is stretched across two specific points on different reinforcing bars. In this case, it is possible to obtain the shrinkage strain that occurs in the concrete member located between the different reinforcing bars.

In one embodiment, the surface of the optical fiber holding part may be provided with a recess that improves adhesion to the concrete surrounding 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 surrounding the optical fiber holding part.

In one embodiment, 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 that closes an opening defined by the end faces and the side faces, and the end of the slit on the lid side may be an opening end that reaches the edge of the side face. In this case, the fixing portion between the optical fiber and the optical fiber holding part can be easily accommodated by attaching the stress suppression container so that the optical fiber is inserted into the slit through the opening end of the slit.

The present invention provides a measuring device that can obtain shrinkage strain occurring in concrete members using optical fibers.

1 is a cross-sectional view of a concrete structure in which a measuring device according to an embodiment is embedded. FIG. 2 is a partial cross-sectional view showing a main part of the measuring device of FIG. 1 . FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2 . FIG. 11 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 measurement device of FIG. 4 . 5A is a side view showing an excess portion of the measuring device of FIG 4, (b) is a side view showing a modified example of the excess portion, and (c) is a side view showing another modified example of the excess portion. 1A is a cross-sectional view showing a modified example of a stress suppressing container, FIG. 1B is a cross-sectional view showing another modified example of the stress suppressing container and a modified opening and closing mode of its lid, and FIG. 1C is a cross-sectional view showing another modified example of the stress suppressing container and a modified opening and closing mode of its lid.

Below, an embodiment of the measuring device according to the present invention will be described in detail with reference to the drawings. In the description, the same reference numerals may be used for the same elements or elements having the same functions, and duplicate descriptions will be omitted.

Figure 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 Figure 1, the measuring device 1 measures the stress acting on the concrete structure S while embedded in the concrete structure S. The concrete structure S has, for example, multiple structural rebars S1 and concrete S2. As an example, the structural rebars S1 include multiple main rebars S11 extending in the vertical direction D1 and distribution rebars S12 extending in the horizontal direction D2.

The main reinforcing bars S11 and the distribution reinforcing bars S12 are arranged in a grid pattern. The measuring device 1 is arranged, for example, along one of the main reinforcing bars S11.

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

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 analysis device. The measuring instrument inputs measurement light K1 into the optical fiber cable 21 and receives backscattered light K2 returning from each measurement 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 analysis 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.

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. This analysis obtains the strain at each measurement position in the longitudinal direction of the optical fiber cable 21, and as a result, the longitudinal strain distribution applied to the optical fiber cable 21 is obtained.

Figure 2 is a partial cross-sectional view showing the main parts of the measuring device in Figure 1. Note that, to make the figures easier to understand, hatching corresponding to concrete has been omitted in figures other than Figures 1 and 4.

As shown in FIG. 2, the measurement device 1 is equipped with an optical fiber holding unit 23 that extends to connect two predetermined points P1 and P2 on the same structural rebar (reinforcing bar) S1 inside the concrete structure S. As an example, the two points P1 and P2 here are located in the area between a pair of adjacent reinforcing bars S12 on the same structural reinforcing bar S1.

The optical fiber holding part 23 has the function of holding the optical fiber cable 21 and generating 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 is transmitted 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), 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.

Figure 3 is a cross-sectional view taken along line III-III in Figure 2. As shown in Figures 2 and 3, the optical fiber holding portion 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 prevents the force from being transmitted 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 so-called disconnected from the structural reinforcing bar S1. The buffer material 25 may be, for example, grease or the like.

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, are attached so as to be relatively movable 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.

The surface of the cylindrical member 23A may be provided with a recess (not shown) that improves adhesion to the concrete S3 surrounding the optical fiber holding portion 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 formed in advance according to the shape of the resin mold, or may be a chemical treatment.

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 bar S1 (main reinforcing bar 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, for example, with an adhesive to the main reinforcing bar S11 and the surface of the tubular member 23A.

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 transmission of stress from the external concrete S2 to the internal concrete S3, while allowing the transmission of heat and moisture from the external concrete S2 to the internal concrete S3. The stress suppression container 26 is sometimes called a 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.

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 an opening end that reaches, for example, the edge of the side face 26b.

The stress suppression container 26 may be, for example, a box-shaped container with a rectangular cross section and a lid. The dimensions of the stress suppression container 26 are not particularly limited, but for example, the axial length may be about 300 mm, and the width in the direction perpendicular to the axial direction and parallel to the lid portion 26d may be about 150 mm.

A filter 27 (e.g., felt) is attached to the inner wall surface of the stress suppression container 26 to suppress the transmission of stress from the external concrete S2 to the internal concrete S3. This creates a so-called disconnect between the external concrete S2 and the internal concrete S3, suppressing the transmission of stress and strain. The inner wall surface of the stress suppression container 26 includes the inner surfaces of the end surface 26a, side surface 26b, lid 26d, and bottom surface of the stress suppression container 26.

The surface of the stress suppression vessel 26 is provided with numerous through holes (not shown) that connect the inner and outer wall surfaces to allow the transfer of heat and moisture from the external concrete S2 to the internal concrete S3.

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

According to the above, the cylindrical member 23A behaves integrally with the concrete S3 inside the stress suppression container 26, and the axial strain can be measured by the optical fiber cable 21 installed in the cylindrical member 23A. Since the concrete S3 inside the stress suppression container 26 is separated from the surrounding concrete S2 by the stress suppression container 26, shrinkage strain occurs with reduced influence of stress and strain (e.g. elastic strain, etc.) from the surrounding concrete S2, and 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 part 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, since the concrete S3 filled inside is made of the same material and has the same material age as the external concrete S2, 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).

Incidentally, the optical fiber cable 21 has an excess length 28 that sandwiches the fixed portion 24 between the optical fiber cable 21 and the optical fiber holding portion 23. The excess length 28 is a buffer region that connects the region including the fixed portion 24 for measuring shrinkage strain with the region in which shrinkage strain is not measured but total strain is measured. Alternatively, the excess length 28 can be said to be a buffer region that mitigates the mutual influence of the behavior of the tubular member 23A and the behavior of the structural reinforcing bar S1.

The surplus portion 28 here is arranged at both ends of the cylindrical member 23A. For example, the optical fiber cable 21 is arranged in a spiral shape on the structural reinforcing bar S1 at both ends of the cylindrical member 23A as the surplus portion 28. 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 the strain at multiple positions on the optical fiber cable 21 is averaged and obtained, for example, the influence of the strain of the optical fiber cable 21 on the side opposite the fixed portion 24 of the optical fiber cable 21 and the optical fiber holding portion 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 near the slit SL at both ends of the stress suppression container 26.

As described above, in the measuring device 1 according to this 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. This 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 this measuring device 1, the shrinkage strain generated in the concrete S3 can be obtained using the optical fiber cable 21.

In the measuring device 1, the optical fiber cable 21 has an excess portion 28 that sandwiches the fixed portion 24 between the optical fiber cable 21 and the optical fiber holding portion 23. As a result, the wiring length of the optical fiber cable 21 at the excess portion 28 is longer than when the excess portion 28 is not provided. Therefore, when averaging and obtaining strains at multiple positions, 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 portion 23 as viewed from the excess portion 28 on the strain of the optical fiber cable 21 at the fixed portion 24 can be reduced. In other words, the influence of the total strain outside the excess portion 28 is reduced for the measured shrinkage strain due to the excess portion 28. Therefore, the measurement accuracy of the shrinkage strain is expected to be improved.

In the measuring device 1, the optical fiber holding section 23 includes a tubular member 23A that extends between 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 breaking.

In the measuring device 1, the surface of the optical fiber holding part 23 is provided with a recess that improves adhesion to the concrete S3 surrounding the optical fiber holding part 23. This makes the strain generated in the optical fiber holding part 23 more responsive to the shrinkage strain of the concrete S3 surrounding the optical fiber holding part 23.

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 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 an opening end that reaches the edge of the side face 26b. As a result, by attaching the stress suppression container 26 so that the optical fiber cable 21 is inserted into the slit SL through the opening end of the slit SL, the fixed portion 24 between the optical fiber cable 21 and the optical fiber holding portion 23 can be easily accommodated.

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. For example, if the optical fiber cable 21 is installed 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 wired. This configuration is significantly simpler than the conventional configuration in which strain detectors are installed at each measurement point. In addition, by using the shrinkage strain measured by the optical fiber cable 21, it is possible to effectively utilize the measurement data of the total strain measured by the optical fiber cable 21.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and may be modified without departing from the spirit of the invention as set forth in the claims.

The arrangement direction of the measuring device 1 is not limited to the above example, and may be any direction (e.g., horizontal, vertical, or other direction) relative 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 reinforcing bars S12 on the same structural reinforcing bar S1. The positions of the two points P1 and P2 may be two specified points on two structural reinforcing bars S1 that are not the same but are connected on the same straight line. In addition, the two points P1 and P2 may be two specified points on the same or connected on the same straight line reinforcing bars (reinforcing bars) S12.

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 FIGS. 4 and 5, the measuring device 1 is provided with a rod (optical fiber holding part) 23B that extends 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 in this case 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, so it is wired away from the reinforcing bar cage.

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 the impact of construction. Therefore, the optical fiber cable 21 is attached to, for example, a rod 23B. The rod 23B is preferably made of a material that has elasticity to such an extent that it does not hinder the behavior of the concrete S3 being measured (a material with a small elastic coefficient compared to the concrete S3) and is more rigid than the optical fiber cable 21. For example, an acrylic rod may be used for the rod 23B. That is, the optical fiber holding part 23 includes a resin rod 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 rod 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 rod 23B may be provided with a recess (not shown) that improves adhesion to the concrete S3 around the rod 23B. The material of the rod 23B may be, in addition to acrylic, for example, glass fiber or carbon fiber. By using such a rod 23B as the optical fiber holding part 23, it is possible to obtain the shrinkage strain that occurs in the concrete S3 located between different reinforcing bars S12.

Next, a modified example of the excess length portion 28 in FIG. 2 will be described. FIG. 6(a) is a side view showing the excess length 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 arranged spirally 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 (excess length 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.

6(b) is a side view showing a modified example of the excess part. In the example of FIG. 6(b), instead of providing an excess part 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 rod 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, a lubricating film or coating such as grease may be applied to the surface of the optical fiber cable 21. Alternatively, in the section 28A, a cylindrical member through which the optical fiber cable 21 is inserted may be arranged 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. Note that a similar coating or the like may also be provided on the surface of the rod 23B.

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 provided 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. In particular, in the example of FIG. 6(c), in the section where a 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. By subtracting from the measured value the shrinkage strain of concrete S3 measured by the optical fiber cable 21 inside the stress suppression container 26 and the temperature strain evaluated by the temperature that can be detected by the optical fiber cable 21, it becomes possible to extract the elastic strain and creep strain due to restraint and external forces. As a result, it is expected that the measured data can be effectively utilized, such as in analyses focusing on elastic strain and creep strain.

Next, modified examples of the stress suppression container 26 will be described. The stress suppression container 26 may be a covered container with a cross section other than rectangular. FIG. 7(a) is a cross-sectional view showing a modified example of the stress suppression container. FIG. 7(b) is a cross-sectional view showing another modified example of the stress suppression container and the opening and closing manner of the lid. FIG. 7(c) is a cross-sectional view showing another modified example of the stress suppression container and the opening and closing manner of the 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 FIG. 7(b) and (c), the cross-sectional shape of the stress suppression container 26 is semicircular. In addition, 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 opening and closing one end of the lid 26d with a hinge or the like as a branch. In addition, the lid 26d may be simply fitted in and fixed to close the opening 26c.

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

In the above embodiment and modified example, the optical fiber holding part extending to connect two specific points on the reinforcing bar is parallel to the reinforcing bar, but this 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.

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 that has the function of the optical fiber holding part described above may be used.

The surface of the optical fiber holding part does not need to have a recess that improves adhesion to the concrete surrounding the optical fiber holding part.

In a 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 other edges, or it may not reach any edges. A 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 that is divided into two in the axial direction, and various other containers can be used as long as they have the functions of the stress suppression container described above.

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

Claims (5)

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 houses a fixed portion of the optical fiber and the optical fiber holding portion 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 . 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 houses a fixed portion of the optical fiber and the optical fiber holding unit 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. 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. The measurement device according to any one of claims 1 to 3, wherein the optical fiber holding section includes a resin rod that is stretched across two predetermined points on different reinforcing bars. The measurement device according to any one of claims 1 to 4, wherein the surface of the optical fiber holding part is provided with a recess that improves adhesion to the concrete surrounding the optical fiber holding part.

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