JP2021173677A - Internal measurement system of concrete structure - Google Patents

Abstract

To provide an internal measurement system of a concrete structure capable of continuously measuring change in strain and temperature inside the concrete structure by allowing an optical fiber sensor to crawl in the concrete structure so as to draw a loop in a mesh panel and then embedding the same.SOLUTION: An optical fiber sensor 1 caused to recognize one or more portions of a strain measurement point or a temperature measurement point in advance is arranged and fixed in a stress acting direction inside a concrete structure. A measurement instrument is connected to an end of the optical fiber sensor and stress is calculated from a change value due to a frequency shift at each strain measurement point or temperature measurement point, or temperature is measured, and a stress distribution and a temperature distribution in a stress action direction are obtained. The optical fiber sensor may be provided in advance, and a block-shaped measurement unit filled with concrete may be prepared and placed inside the concrete structure.SELECTED DRAWING: Figure 2

Description

The present invention relates to an internal measurement system for a concrete structure capable of measuring strain changes, temperature changes, etc. from frequency change values inside the concrete structure using an optical fiber sensor, and measuring the distribution thereof.

Conventionally, a mold strain gauge has been the mainstream for grasping the internal stress state of a concrete structure. The mold strain gauge is also called an embedded strain gauge. A strain gauge is embedded in an internal stress point that you want to know in advance, and the static elastic modulus peculiar to the material is the average strain value generated between the flanges corresponding to the gauge point distance of the gauge. The internal stress can be grasped by multiplying by. However, the value is only measured locally, and if you want to grasp the stress distribution inside the structure, you have to bury a mold gauge in the entire area. Further, when it is desired to grasp the stress distribution in the member thickness direction inside the concrete structure, it is necessary to fix and install the mold strain gauge over many layers.

On the other hand, in recent years, using an optical fiber sensor developed for communication, it is possible to grasp changes in strain, temperature, etc. by capturing backscattered light generated by injecting pulsed light as a light source into a receiver and processing it. It has been found that it can be used for maintenance and maintenance of structures. The advantage is that it has become possible to capture changes in real time and over a long period of time. As a method for measuring strain or damage of a structure using an optical fiber sensor, for example, there are inventions described in Patent Documents 1 to 4 and Non-Patent Documents 1 and 2.

Patent Document 1 is a stress monitoring sensor that monitors the stress inside a concrete structure, and covers one or more optical fiber sensors, a steel bar holding each optical fiber sensor, and each optical fiber sensor and steel bar. A stress monitoring sensor is described in which the covering portion is provided and the material constituting the covering portion is a cement-based material or resin having a strength equal to or higher than that of concrete used for a concrete structure.

In Patent Document 2, an optical fiber sensor is arranged so that the longitudinal direction of the optical fiber is orthogonal to the surface of the concrete structure, and shear cracks occur inside the concrete when the strain measured by the optical fiber sensor increases. Describes a method for diagnosing a concrete structure, which is characterized in that it is determined that a problem has occurred.

Patent Document 3 describes a crack detection method for detecting cracks in concrete, which is based on a step of fixing an optical fiber sensor on the surface of a steel material in concrete and a change in the characteristics of a light wave propagating in the optical fiber sensor. A step of measuring the strain of a steel material and a crack detection method for detecting a crack in concrete based on the characteristics of the measured strain over time are described.

In Patent Document 4, an optical fiber is inserted into a protective tube made of synthetic resin, and a signal cable is created in which the optical fiber is fixed between the optical fiber and the protective tube at regular measurement intervals to give initial distortion to the optical fiber. Then, the signal cable is arranged on the inner wall surface of the tunnel in a plurality of grooves formed at predetermined intervals in a direction orthogonal to the tunnel axial direction and fixed by an adhesive, and the optical fiber of the signal cable and the protective tube are connected. A method of laying an optical fiber, characterized in that the fixed portion is fixed to the inner wall of the tunnel by a fixture, is described.

Non-Patent Document 1 describes an evaluation method of a bridge bearing function as a monitoring method utilizing the features of a Brillouin scattering optical fiber sensor. Further, Non-Patent Document 2 describes an experiment in which an optical fiber sensor is embedded in concrete pavement.

JP-A-2019-109164 Japanese Unexamined Patent Publication No. 2019-066388 Japanese Unexamined Patent Publication No. 2016-188850 Japanese Unexamined Patent Publication No. 2001-0597797

Mayuko Nishio, Keita Mizuno, Hiroshi Katsuchi, Hitoshi Yamada "Basic Study on Bridge Bearing Monitoring Using Distributed Optical Fiber Sensors", Proceedings of Structural Engineering, March 2014, p.484-492 Kenichi Soga, "Putting" nerves "in sensorized infrastructure", Nikkei Construction, September 23, 2019, p.46-47

The mold strain gauge is one of the stress sensors that utilizes the fact that the resistance wire expands and contracts due to strain and appears as a change in the resistance value, like a normal strain gauge, and is a measurement method in the normal range of electrical resistance. , It is not suitable for long-term measurement. In addition, since it is the average value of the strain generated between the flanges, multiple installations are required when pursuing its certainty, and for large structures, a method of lengthening the distance between the flanges of the mold gauge and It is considered that it will be necessary to take measures such as arranging a plurality of pieces in the depth direction in a discrete manner.

In the first place, it is very difficult to measure the pressure inside the structure as a measurement technology, and it can be said that there has never been a method.

In the invention described in Patent Document 1, an optical fiber sensor is held by a steel bar, and a stress monitoring sensor in which the steel bar is coated with a cement-based material or resin is installed in a concrete structure. In this configuration, the optical fiber sensor is a steel bar. And the stress and damage status of the covering part will be monitored, and accurate data cannot be obtained as the stress inside the concrete structure.

In the invention described in Patent Document 2, the optical fiber sensor is attached as a shear reinforcing bar so as to be in close contact with the reinforcing bar to be arranged, and is arranged so as to be orthogonal to the surface of the concrete structure, so that the strain is increased. This is to determine the shear cracks inside the concrete structure, and it is not possible to obtain the bearing stress and stress distribution of the concrete structure.

The invention described in Patent Document 3 measures the strain of a steel material using an optical fiber sensor to detect cracks in concrete, and similarly to Patent Document 2, obtains bearing stress and stress distribution of a concrete structure. It is not something that can be done.

Further, conventionally, a method of providing an optical fiber in a structure long in the longitudinal direction such as a mountain tunnel and measuring the strain in the longitudinal direction, or a method in which an optical fiber is inserted in a protective tube as described in Patent Document 4 is used. A method of laying an optical fiber fixed to the inner wall of a tunnel is shown, but it is used in a plane and does not collect strain data inside the structure.

The present invention has been made to solve the above problems, and by laying an optical fiber sensor inside a concrete structure in a loop on a mesh panel and then burying it, the inside of the concrete structure is embedded. It provides an internal measurement system for a concrete structure capable of continuously measuring a stress distribution or a temperature distribution.

The present invention is a measurement system for monitoring the internal stress or temperature of a concrete structure using an optical fiber sensor, the optical fiber sensor having one or a plurality of strain measurement points or temperature measurement points recognized in advance. By arranging and fixing it inside the concrete structure and connecting a measuring instrument to the end of the optical fiber sensor, the distribution was obtained from the frequency change value at each strain measuring point or temperature measuring point. It is a feature.

The distributed optical fiber sensor connected to the measuring instrument can inject pulsed light as a light source at one end and obtain the distribution of the position and strain difference according to the spatial resolution to the other end, and this space. The resolution corresponds to the gauge length of the conventional strain gauge, and the shorter the spatial resolution, the more detailed strain difference distribution can be obtained.

Further, by arranging the optical fiber sensor inside the concrete structure, the temperature distribution can be grasped. Especially in mass concrete, temperature cracks are likely to occur, so it can be effectively used for maintenance of structures.

Not only one of these stress distributions and temperature distributions can be measured, but both can be measured at the same time, and measurement targets other than stress and temperature that can be measured by a distributed optical fiber sensor can be measured at the same time. You can also.

It should be noted that the optical fiber sensor cannot take in scattered light if the wire is broken even in one place. For example, it is advisable to use a plurality of sensors as spare optical fiber sensors, to reinforce them with wires, and to take measures such as coating by embossing.

In the internal measurement system of the concrete structure of the present invention, it is preferable that the optical fiber sensor is repeatedly reciprocated in the bearing stress action direction from the upper part to the lower part inside the concrete structure.

Further, the present invention is a measurement system for monitoring the internal stress or temperature of a concrete structure using an optical fiber sensor, and the optical fiber sensor having one or a plurality of strain measurement points or temperature measurement points recognized in advance. By creating a block-shaped measuring unit that is arranged and filled with concrete and installing the measuring unit in the concrete structure, the optical fiber sensor built in the measuring unit can be used to reduce the internal stress of the concrete structure. It is arranged in the direction of action, and a measuring instrument is connected to the end of the optical fiber sensor so that the distribution can be measured from the frequency change value at each strain measuring point or temperature measuring point in the measuring unit. Is to be.

If a block-shaped measurement unit in which the optical fiber sensor is arranged is created in advance, the work of arranging the optical fiber sensor on site becomes unnecessary, and the measurement unit only needs to be arranged inside the structure, and the construction on site can be performed. It is easy and the construction time can be shortened. Further, the measuring unit may be arranged only in the portion where the strain and the temperature are to be measured.

In the measurement system for a concrete structure of the present invention, the measurement units are arranged side by side, and the optical fiber sensors of the adjacent measurement units are connected to each other to form the concrete structure, so that the measurement units are built into the measurement unit. The optical fiber sensor is arranged in the bearing stress action direction inside the concrete structure, and by connecting a measuring device to the end of the optical fiber sensor, the distribution at each strain measurement point or temperature measurement point can be measured. It can also be.

By connecting the optical fiber sensors of adjacent measurement units, it is possible to grasp the stress state and temperature inside the structure over a wide range even in a large concrete structure.

For precast concrete products, if a measurement unit is similarly embedded in advance and the optical fiber terminals from each product are connected at the site, the stress status and temperature inside the structure can be easily grasped.

In the measurement system for concrete structures of the present invention, an optical fiber sensor is arranged in the stress direction to be grasped inside the structure, and the internal stress can be grasped by the difference in the strain distribution. Unlike strain gauges, it is possible to continuously and semi-permanently monitor the inside of concrete structures. It is also possible to grasp the temperature distribution inside the structure.

By unitizing the optical fiber sensor as a precast product in advance instead of installing it on site, the on-site construction can be done by connecting the optical fiber sensor or replacing the unit, and the work can be done easily. Further, in the structure, a unit provided with an optical fiber sensor may be arranged at a portion where data is to be measured.

A loading experiment situation diagram of an example in which the measurement system of the concrete structure according to the present invention is used for a synthetic steel pipe column is shown, (a) is a front view, and (b) is a plan view. (a) is a vertical cross-sectional view showing a state in which an optical fiber sensor is laid on a mesh panel in a repeating loop inside the foundation concrete of the loading experiment shown in FIG. 1, and (b) is a mesh before placing the foundation concrete. It is a top view which showed the arrangement state of a panel. In the embodiment of FIG. 1, the result of the strain distribution inside the foundation concrete is shown, (a) is a plan view showing the positions of the strain measurement point and the strain mold gauge, and (b) to (d) are the centers. In the graph showing the relationship between the distance from and the generated strain, (b) is the strain measurement points of the strain mold gauges M5 and M6 and the optical fiber sensor, and (c) is the strain measurement points of the strain mold gauges M1 to 4 and the optical fiber sensor. , (D) are the results of the strain measuring points of the strain mold gauges M7 and M8 and the optical fiber sensor. It is a graph which showed the generated strain in the foundation concrete in the embodiment of FIG. 1 by the depth distribution. In the measurement system of the concrete structure according to the present invention, it is a graph which showed the bearing stress distribution of an arbitrary cross section inside a foundation concrete, (a) is the bearing stress action direction (depth) of -200mm, (b). Is −300 mm, and (c) is −400 mm.

Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the embodiments shown below.

FIG. 1 shows an embodiment of a concrete structure measurement system according to the present invention in which an optical fiber sensor 1 is arranged inside a foundation concrete 13 in a loading experiment of a synthetic steel pipe column 11, and FIG. 1A is a front view. , (B) is a plan view. The steel pipe column 11 provided on the foundation concrete 13 has a diameter of 500 mm, and an anchor bar 12 is provided inside the steel pipe column 11.

Pulsed light is incident on the optical fiber sensor 1, and Rayleigh waves are collected as backscattered light with a spatial resolution of 20 mm. The optical fiber sensor 1 was placed inside the foundation concrete 13 after being laid in a loop on the mesh streaks in advance, and the foundation concrete 13 was placed. A measuring device is connected to the end of the optical fiber sensor 1 to aggregate the data at each strain measurement point.

FIG. 2 shows a state in which the optical fiber sensor 1 was crawled so as to draw a loop in which the optical fiber sensor 1 was repeatedly reciprocated on the mesh panel 2 in the loading experiment of FIG. As a method of positioning the optical fiber sensor 1 inside the concrete structure, as shown in FIG. 2A, for example, a mesh panel 3 is used, and the optical fiber sensor 1 is laid on the fixed mesh panel 3. It is advisable to create an optical fiber sensor unit in which the optical fiber sensor 1 is laid on the mesh panel 3. In addition, any method may be used as long as the position of the optical fiber sensor 1 does not shift when placing concrete.

After crawl on a net-like object while being careful not to break the optical fiber sensor 1 and attach it with an adhesive or the like, the optical fiber sensor 1 is made to recognize the position information, and the strain measurement point or the temperature measurement point is placed on the optical fiber sensor 1. To set. As a method for this, for example, strain is forcibly generated by cooling or warming the position of interest, and the position information is confirmed.

Further, as shown in FIGS. 2 to 3, in order to confirm the consistency of the strain measurement values of the strain measurement points 1b set on the optical fiber sensor 1, mold strain gauges M1 to M8 are also installed, and the optical fiber sensor 1 is installed. In addition to measuring the strain with, the strain was also measured with a mold strain gauge.

FIG. 2B shows a plan view showing the arrangement state of the optical fiber sensor 1 embedded inside the foundation concrete 13 in the loading experiment of FIG. 1. The optical fiber sensor 1 fixed to the mesh panel 2 reciprocates left and right to draw a loop. Inside the foundation concrete 13, a plurality of layers of mesh panels 2 to which the optical fiber sensor 1 is fixed are provided in the bearing stress acting direction (depth direction) so that the stress distribution or temperature distribution in the bearing stress acting direction can be obtained. do.

FIGS. 3 and 4 show the results of the strain distribution inside the foundation concrete 13 in the loading experiment of the synthetic steel pipe column carried out to confirm the validity of the measurement system of the present invention. FIG. 3A shows the positions of the strain measuring point 1b and the strain mold gauges M1 to 8. 3 (b) to 3 (d) are graphs showing the relationship between the distance from the center and the generated strain at the strain measurement points 1b and the strain mold gauges M1 to 8, and FIG. 3 (b) shows the strain mold gauge M5. M6 and each measurement point of the optical fiber sensor, (c) is the result of each measurement point of the strain mold gauges M1 to 4 and the optical fiber sensor, and (d) is the result of each measurement point of the strain mold gauges M7, M8 and the optical fiber sensor.

From the graph of FIG. 3B, the values of the generated strain in the strain mold gauges M5 and M6 and the generated strain at the strain measurement point are substantially the same. Similarly, in the graphs of FIGS. 3 (c) and 3 (d), it can be seen that the values of the generated strain in the strain mold gauges M1 to 4 and M7 and M8 and the values of the generated strain at the strain measurement point are almost the same. From the above, the validity of the measurement system of the present invention could be confirmed.

FIG. 4 shows the generated strain inside the foundation concrete 13 in the embodiment of FIG. 1 in terms of depth distribution. Further, in this graph as well, in order to confirm the validity of the measurement system of the present invention, the values of the mold strain gauges M1 to 4 are also shown. By plotting the generated strain at each strain measurement point as shown in FIG. 4, the strain distribution in the bearing stress acting direction (depth direction) can be grasped.

FIG. 5 is a graph showing the bearing stress distribution of an arbitrary cross section inside the foundation concrete 13 in the measurement system of the concrete structure according to the present invention, and FIG. 5A is a graph in which the bearing stress acting direction (depth) is −. 200 mm, (b) is -300 mm, and (c) is -400 mm.

That is, the bearing stress can be calculated from the strain generated at each strain measurement point to obtain the stress distribution in the bearing stress acting direction. In FIG. 6, the bearing stress in a specific direction in the horizontal cross section for each depth direction can be obtained. It is a graph of the distribution.

From the above, it was confirmed that it is possible to grasp the distribution of the bearing pressure on an arbitrary cross section over a long period of time within the measurement focus area shown in FIG.

The foundation concrete 13 described with reference to FIG. 1 can also be used as a measuring unit. If a block-shaped measuring unit is created by arranging the optical fiber sensor 1 as a precast concrete product in advance, the optical fiber sensor 1 can be placed by simply installing the measuring unit at the site inside the structure where the measurement is desired. can do. The size of the measuring unit is, for example, about 4 tons if it is 1.3 m square or less, and it is considered that on-site construction is easy without any transportation problem.

If the measuring unit is created as a precast concrete product, the measuring system of the present invention can be constructed only by connecting the measuring units to each other, and the attachment / detachment can be done only at the damaged part, which is expected to save labor for maintenance. ..

In the case of large structures such as dams and nuclear facilities, if a block with an optical fiber sensor embedded is installed in advance along with the aggregate of prepacked concrete, even in a facility where people cannot easily enter after construction. It is possible to measure the internal stress and temperature of concrete semi-permanently. In that case, a wireless sensor system may be used.

Further, in the embodiment of FIG. 1, the distribution of the bearing stress shown in FIG. 5 is shown from the values from the generated strain at each measurement point shown in FIGS. 3 and 4, but the temperature is measured at each measurement point. It is also possible to show the temperature distribution inside the concrete structure.

1: Optical fiber sensor 1a: Optical fiber sensor unit end 1b: Strain measurement point (temperature measurement point) of optical fiber sensor
2: Mesh panel 3: Mold strain gauge 11: Synthetic steel pipe column 12: Anchor bar 13: Foundation concrete 14: Load meter 15: Loading plate M1-8: Mold strain gauge

Claims (4)

A measurement system for monitoring the internal stress or temperature of a concrete structure using an optical fiber sensor.
The optical fiber sensor having one or a plurality of strain measurement points or temperature measurement points recognized in advance is arranged and fixed inside the concrete structure.
By connecting a measuring instrument to the end of the optical fiber sensor,
An internal measurement system for a concrete structure, characterized in that the distribution is obtained from the frequency change value at each strain measurement point or temperature measurement point. In the internal measurement system for a concrete structure according to claim 1,
An internal measurement system for a concrete structure, characterized in that the optical fiber sensor is repeatedly reciprocated in the direction of action of internal stress from one end to the other end inside the concrete structure. A measurement system for monitoring the internal stress or temperature of a concrete structure using an optical fiber sensor.
The optical fiber sensor that recognizes one or more strain measurement points or temperature measurement points in advance is arranged to create a block-shaped measurement unit filled with concrete.
By installing the measuring unit on the concrete structure,
The optical fiber sensor built in the measuring unit is arranged in the direction of action of internal stress of the concrete structure.
Connect a measuring instrument to the end of the optical fiber sensor,
An internal measurement system for a concrete structure, characterized in that the distribution can be measured from the frequency change value at each strain measurement point or temperature measurement point in the measurement unit. In the measurement system for concrete structures according to claim 3,
By arranging the measuring units in parallel and connecting the optical fiber sensors of the adjacent measuring units to each other to form the concrete structure,
The optical fiber sensor built in the measuring unit is arranged in the stress acting direction inside the concrete structure.
By connecting a measuring instrument to the end of the optical fiber sensor,
An internal measurement system for concrete structures, characterized in that the distribution at each strain measurement point or temperature measurement point can be measured.

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