JP2011022029A - Distortion detecting device for concrete structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distortion detecting device which forms a strain body being not made of so-called metal and resisting corrosion, without the need to protect the strain body by using an exterior material, brings the strain body to directly come in contact with concrete, enables a distortion of the concrete to be directly transmitted by an adhesion force around the strain body, has a high quality with no fluctuation in measurement values, and can carry out a long-term measurement with a low failure frequency, and to further provide an internal temperature detecting device which has little risk of deterioration to a huge structure and can precisely measure an internal temperature of a concrete structure. <P>SOLUTION: An optical fiber having an FBG sensor is covered by a glass fiber member having a linear expansion coefficient and an elastic coefficient which are approximately equal to those of the optical fiber, thereby forming the strain body, and then a structure is constructed by casting the concrete in such the state that the strain body is internally disposed beforehand, thereby enabling the distortion arising after the construction of the concrete structure to be detected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a concrete structure distortion detection apparatus that is installed inside a concrete structure before construction and detects the internal strain and internal temperature of the concrete structure after construction.

Conventionally, various devices have been proposed as so-called buried strain gauges. That is, the buried strain gauge is installed in advance in the internal space before placing concrete and measures the amount of strain change of the hardened concrete after placing the concrete.

Thus, the conventional buried strain gauge incorporates, for example, a rod-shaped strain body made of an alloy having a strain gauge bonded thereto, and deforms the strain body caused by a change in the strain of the concrete around the strain gauge. Some of them are detected as a change in the electrical resistance value of the strain gauge adhered to the surface.
And it is mainly used for measurement when deformation converges in a relatively short period of time, such as tunnel measurement B and measurement of existing structures during close construction.

Here, the measurement of the tunnel is generally to confirm the stability and safety of the tunnel structure and to evaluate the appropriateness of the design and construction. This is performed in order to grasp the effects of members, the influence on surrounding structures, and the like.

There are two types of measurement, measurement A and measurement B, performed during tunnel construction. The measurement A is performed for daily construction management and includes the following measurements. That is, observation survey, top-end settlement measurement, inner-space displacement measurement, surface settlement measurement, and the like.
Next, the measurement B is additionally performed on the measurement A according to natural ground conditions and location conditions, and includes the following measurements. These include a ground sample test, underground displacement measurement, rock bolt axial force measurement, shotcrete stress measurement, steel support stress measurement, lining stress measurement, board bulge measurement, and AE measurement.

Next, the buried type thermometer is a device that measures the temperature inside a concrete structure. Conventionally, it is a resistance thermometer using a platinum resistor, and a thermocouple using the difference in electromotive force between two types of metals. and so on. In addition, a thermometer having a structure in which the above-described sensor is protected by a housing has been proposed in order to reduce deterioration during use due to contact with moisture or the like.

JP 2008-298568 A

  However, the conventional strain gauge is not suitable for long-term measurement for maintenance of construction structures because both the strain-generating body and the strain gauge are made of metal and easily corrode. .

In order to ease the corrosion, it is generally necessary to attach a pipe-shaped exterior material around the strain-generating body so that the strain-generating body and the strain gauge do not come into direct contact with the concrete.
Thus, by using the exterior material, the side surface of the strain body does not come into contact with the concrete. Therefore, since deformation due to adhesive force does not occur, flanges are attached to both ends of the strain-generating body to form a sensitive part, and the amount of change in the gauge distance between both flanges due to the occurrence of concrete strain is divided by the gauge distance. The strain is obtained by

However, in general, when the maximum size of coarse aggregate used in concrete is about 1/2 to 1/3 or more of the gauge distance, the ratio of aggregate to the concrete between the score distances increases, and the aggregate The strain of concrete could not be measured accurately due to its own stiffness.

Therefore, it is necessary to manufacture strain gauges with different gage distances according to the maximum size of concrete coarse aggregate to be measured. To that end, components such as strain-generating bodies, exterior materials, and tubes for adhesion insulation are required. Therefore, it is necessary to process and assemble them into dimensions that match the gauge distance of the strain gauge, which complicates the manufacturing process and causes variations in quality such as measurement accuracy and durability.

Further, in the conventional buried type thermometer, since the so-called sensor part is made of metal, when a crack or the like occurs in the concrete structure in which the thermometer is buried and moisture enters from the outside, Due to the contact, the abnormal value of the measured value and the corrosion are easily caused by the change of the resistance value.
Moreover, although an electrical signal is used for measurement, it is difficult to transmit the electrical signal over a long distance. In other words, the distance between a thermometer and a data logger that transmits and receives electrical signals to and from the thermometer is usually about several hundreds of meters at maximum, so the application range is limited for long structures such as dams and tunnels. There is also.

Thus, the present invention was devised to solve the above-mentioned conventional problems, and it is not necessary to form a strain-generating body that is resistant to corrosion without using a so-called metal, and thus it is not necessary to protect the strain-generating body with an exterior material. Because the strain-generating body can be brought into direct contact with the concrete and the strain of the concrete can be directly transmitted to the strain-generating body by the adhesive force around the strain-generating body, it has a high quality with no variations in measured values and has a long period of less damage or failure An object of the present invention is to provide an internal temperature detection device that can measure the internal temperature of a concrete structure with a low possibility of deterioration even for a long structure and with high accuracy. It is what.

The present invention
An optical fiber provided with an FBG sensor is covered with a glass fiber member having a linear expansion coefficient and an elastic coefficient substantially equal to those of the optical fiber to form a strain generating body, and the strain generating body is installed inside in advance. , Construct concrete by placing concrete,
The strain generated after the construction of the concrete structure can be detected.
It is characterized by
Or
An FBG sensor is provided in the optical fiber, and a metal piece to be bonded to the FBG sensor is provided extending in the axial direction of the optical fiber, and the metal piece is fixed to the optical fiber on the base end side of the metal piece, The side is free, forming a temperature detection strain body, with the temperature detection strain body pre-installed inside, constructing a structure by placing concrete,
The internal temperature change that occurs after the construction of the concrete structure can be detected,
It is characterized by
Or
An optical fiber provided with an FBG sensor is covered with a glass fiber member having a linear expansion coefficient and an elastic coefficient substantially equal to those of the optical fiber to form a strain generating body, and the strain generating body is installed inside in advance. , A concrete structure distortion detection device capable of detecting the distortion generated after the concrete structure is constructed by placing concrete and building the concrete structure;
An FBG sensor is provided in the optical fiber, and a metal piece to be bonded to the FBG sensor is provided extending in the axial direction of the optical fiber, and the metal piece is fixed to the optical fiber on the base end side of the metal piece, The temperature detection strainer is formed as a free side, and the structure is constructed by placing concrete with the temperature detection strainer installed in advance, and is generated after the concrete structure is constructed. A concrete structure internal temperature detection device capable of detecting internal temperature changes;
Have
The internal temperature detection device is installed in the vicinity of the strain detection device installed in the concrete structure,
It is characterized by
Or
The concrete structure includes a structure made of an asphalt mixture.
It is characterized by
Or
The glass fiber is FRP.
It is characterized by
Or
The metal piece is a metal piece having a large coefficient of thermal expansion.
It is characterized by this.

Thus, according to the present invention, it is possible to form a strain-generating body that is resistant to corrosion without using a so-called metal, so that it is not necessary to protect the strain-generating body with an exterior material, and the strain-generating body can be brought into direct contact with the concrete. Can be transmitted directly to the strain-generating body by the adhesive force around the strain-generating body, enabling high-quality measurements with consistent measurement values and long-term measurement with little damage or failure. There is little possibility of deterioration, and there is an excellent effect that the internal temperature of the concrete structure can be accurately measured.

It is a schematic explanatory drawing explaining the structure of the strain body by this invention. It is a schematic sectional drawing explaining the structure of the strain body by this invention. It is a schematic explanatory drawing (the 1) explaining the structure of the strain sensing element for temperature detection by this invention. It is a schematic explanatory drawing (the 2) explaining the structure of the strain sensing element for temperature detection by this invention. It is a schematic explanatory drawing of the application example (the 1) which used the distortion detection apparatus and internal temperature detection apparatus of the concrete structure by this invention as a set. It is a schematic explanatory drawing of the application example (the 2) which used the distortion detection apparatus and the internal temperature detection apparatus of the concrete structure by this invention as a set. It is a schematic explanatory drawing of the application example (the 3) which used the distortion detection apparatus and internal temperature detection apparatus of the concrete structure by this invention as a set. (A), (b) of this figure is schematic explanatory drawing of the application example (the 4) which used the distortion detection apparatus and internal temperature detection apparatus of the concrete structure by this invention as a set.

  The present invention will be described below with reference to embodiments shown in the drawings.

  FIG. 1 shows an embodiment of a strain body 1 formed according to the present invention. As the strain body 1, an optical fiber 3 in which a so-called FBG sensor 2 is formed in the axial direction is used.

  The portion of the optical fiber 3 formed in the axial direction of the FBG sensor 2 is covered with a glass fiber 4 having substantially the same linear expansion coefficient and elastic coefficient as the optical fiber 3 to form the strain body 1. The One specific example is shown in FIG. FIG. 2 is a cross-sectional view of the strain body 3, in which the FBG sensor 2 is covered with the optical fiber 3 formed in the axial direction sandwiched in a substantially central portion.

  For example, the glass fiber member formed in a thin sheet shape is arranged in the vertical direction so that the FBG sensor 2 is sandwiched between the optical fibers 3 formed in the axial direction, and then the sheet-like glass fiber member is arranged in the vertical direction. They are laminated to form a substantially square cross section.

Here, as a glass fiber 4 having a linear expansion coefficient and an elastic coefficient substantially equal to those of the optical fiber 3, for example, fiber reinforced plastic, that is, FRP can be given as a specific example.
By the way, the FBG sensor 2 is a high-sensitivity sensor formed in a range of about 10 mm, and detects a strain generated in the FBG sensor 2 as a change in natural wavelength.

Here, the optical fiber 3 to be used has a small diameter of 0.125 mm, for example, and is made of the same material as the glass fiber member used for the FRP described above. There is no significant change in the elastic modulus.
Therefore, the FBG sensor 2 can accurately detect the strain generated by the axial deformation.

In addition, when it embeds in the concrete 5, in order to increase the adhesive force of this strain body 1 and the concrete 5, as can be understood from FIG. By attaching it, it is conceivable to further increase the adhesion with the concrete 5. Therefore, when the projections 6 and 6 are provided in this way, the projections 6 and 6 can be sufficiently used for strain measurement of an asphalt mixture or the like which is not as solid as the concrete 5.

Next, FIGS. 3 and 4 show a temperature detecting strain generating body 7 according to the present invention.
As can be understood from these figures, the temperature detecting strain generating body 7 uses an optical fiber 3 in which a so-called FBG sensor 2 is formed in the axial direction.
A metal piece 8 bonded to the FBG sensor 2 is provided extending in the axial direction of the optical fiber 2.

Further, the optical fiber 2 is fixed on the proximal end side 14 of the metal piece 8 having a substantially flat bar shape, and the optical fiber 2 is not fixed on the distal end side 13 of the metal piece 8 and is in a free state.
Therefore, when the metal piece 8 expands or contracts or expands in response to a change in temperature, the change appears directly on the FBG sensor 2 as strain detection.

That is, the FBG sensor 2 is a sensor element formed in a part in the axial direction on the optical fiber 3, and detects distortion generated in the axial direction of the optical fiber 3 as a wavelength change amount of the optical signal.
Therefore, if the metal piece 8 and the FBG sensor 2 are bonded together, the FBG sensor 2 can detect the strain corresponding to the expansion / contraction associated with the temperature change of the metal piece 8.

For example, when an aluminum alloy 5052 is used for the metal piece 8, its linear expansion coefficient is 22 to 24 μ / ° C., whereas the FBG sensor 2 itself has thermo-optical characteristics of 10 μ / ° C., so the FBG sensor 2 is 1 Strain of 32 to 34μ per degree will be detected. Since the FBG sensor 2 has a strain resolution of about 0.8 μm, the temperature has a resolution of about 0.02 ° C. If the FBG sensor 2 is used, it can be a highly sensitive thermometer. The linear expansion coefficient changes slightly from 22μ / ° C to 24μ / ° C as the temperature increases. For example, by calibrating using a quadratic polynomial, distortion and temperature change obtained from the amount of change in wavelength The relationship between the quantities is strictly calibrated, and the variation in measured values can be further reduced.

Next, the use state of the present invention will be described.
The concrete structure strain detection device 11 and the internal temperature detection device 12 according to the present invention can be used alone, or the concrete structure strain detection device 11 and the internal temperature detection device 12 according to the present invention are used as a set. You can also
Here, an application example in which the strain detection device 11 and the internal temperature detection device 12 for a concrete structure according to the present invention are used as a set will be described.

FIG. 5 shows a first application example in which the strain detection device 11 and the internal temperature detection device 12 of the concrete structure according to the present invention are used as a set, and these devices 11 and 12 are set in the lining concrete 10 of the tunnel 9. This is an example.
For example, there is a case where it is necessary to monitor the long-term soundness of a structure in which an applied load changes after use in an underground structure such as a defective ground section of a tunnel 9 or a box culvert.

That is, if the applied load changes in the tunnel 9 after use due to fluctuations in the natural ground or close construction, the strain in the lining concrete 10 changes due to the influence.
Moreover, the effective repair time of the tunnel 9 etc. can be grasped by measuring the strain generated in the circumferential direction of the tunnel 9.

Furthermore, by installing the internal temperature detection device 12 corresponding to the same position as the strain detection device 11, the internal temperature of the lining concrete 10 can be measured, and by observing the variation of the strain with respect to the temperature change, the observation For example, it can be estimated whether the strain variation is due to a seasonal temperature change or an applied load change. Therefore, it can be said that it is significant to install the internal temperature detection device 12 so as to correspond to the same position as the strain detection device 11.
Here, reference numeral 15 denotes an optical measuring device, and reference numeral 16 denotes a control personal computer.

Next, FIG. 6 shows a second application example in which the strain detection device 11 and the internal temperature detection device 12 of the concrete structure according to the present invention are used as a set. Is used for the long-term health monitoring of the structure where the bridge acts, here the bridge 17.

For example, the bridge 17 deteriorates when it receives a load repeatedly due to the passage of an automobile. As the deterioration progresses, the static deflection increases. The increase in the static deflection changes the internal strain of the concrete 5.

Thus, by measuring the strain inside the concrete 5 in the bridge 17 over a long period of time, for example, an effective repair time can be grasped.
Furthermore, by measuring the temperature inside the concrete 5 in the bridge 17, it can be estimated whether the observed strain fluctuation of the bridge 17 is due to seasonal temperature change or deterioration.

  Next, FIG. 7 shows a third application example in which the strain detection device 11 and the internal temperature detection device 12 of the concrete structure according to the present invention are used as a set, and these devices 11 and 12 are used for the long term of the dam dam body concrete 18. Used for health monitoring.

That is, a partial crack may occur in the dam body due to the temperature stress of the dam body concrete 18, and it is necessary to grasp the behavior thereof. And when grasping | ascertaining a temperature stress, it is necessary to grasp | ascertain the temperature inside the concrete 5 instead of external temperature. Therefore, the installation of the apparatus according to the present invention is effective. Moreover, it is necessary to grasp the temperature change and the stress change in the levee once a year after the completion of the dam.

Next, FIG. 8 shows a fourth application example in which the strain detection device 11 and the internal temperature detection device 12 of the concrete structure according to the present invention are used as a set, and these devices 11 and 12 are connected to the side wall 20 of the underground tank 19. This is used for long-term health monitoring of the bottom plate 21.

The period of use of the underground tank 19 is generally said to be 50 years. Here, for example, the LNG entering the underground tank 19 is low in temperature, and it is considered that the concrete 5 constituting the underground tank 19 is constantly subjected to great stress. Therefore, the soundness of the underground tank situation can be effectively measured by measuring the strain and temperature in the concrete 5 for a long time with the apparatus according to the present invention.

By the way, as described above, the strain generating body 1 used in the strain detection apparatus 11 of the present invention is composed of the optical fiber 3 including the FBG sensor 2 and the glass fiber 4 such as FRP covering these, and uses metal. Not. Therefore, it is resistant to corrosion.

Further, for example, it is not necessary to protect the strain body 1 with an exterior material such as a metal, and the concrete 5 is of a type that directly contacts the strain body 1. Therefore, since the strain of the concrete 5 is quickly transmitted to the strain generating body 1 by the adhesion force around the strain generating body 1, it is not particularly necessary to attach a projection 6 such as a flange.

Further, for example, the production of the strain detection device 11 for a concrete structure according to the maximum size of the coarse concrete aggregate is merely a change in the size of the strain generating body 1, and therefore the number of constituent members of the device 11 is small. Becomes simple and the cause of failure is reduced.

Next, the concrete structure internal temperature detection device 12 according to the present invention is capable of measuring the temperature inside the concrete structure with high accuracy and with little possibility of deterioration even for a long structure of the concrete 5. .

Therefore, regardless of whether these devices are used alone or in combination, it is possible to provide a high-quality detection device with little possibility of breakage or failure, little variation in detection values, and long-term measurement. Is possible.

DESCRIPTION OF SYMBOLS 1 Strain body 2 FBG sensor 3 Optical fiber 4 Glass fiber 5 Concrete 6 Protrusion 7 Temperature detection strain body 8 Metal piece 9 Tunnel 10 Covering concrete 11 Strain detection device 12 Internal temperature detection device 13 The front end side 14 of a metal piece Base end side 15 of metal piece Optical measuring device 16 Control PC 17 Bridge 18 Dam dam concrete 19 Underground tank 20 Side wall 21 Bottom plate

Claims (6)

An optical fiber provided with an FBG sensor is covered with a glass fiber member having a linear expansion coefficient and an elastic coefficient substantially equal to those of the optical fiber to form a strain generating body, and the strain generating body is installed inside in advance. , Construct concrete by placing concrete,
The strain generated after the construction of the concrete structure can be detected.
A strain detection apparatus for a concrete structure characterized by the above.
An FBG sensor is provided in the optical fiber, and a metal piece to be bonded to the FBG sensor is provided extending in the axial direction of the optical fiber, and the metal piece is fixed to the optical fiber on the base end side of the metal piece, The side is free, forming a temperature detection strain body, with the temperature detection strain body pre-installed inside, constructing a structure by placing concrete,
The internal temperature change that occurs after the construction of the concrete structure can be detected,
A device for detecting the internal temperature of a concrete structure.
An optical fiber provided with an FBG sensor is covered with a glass fiber member having a linear expansion coefficient and an elastic coefficient substantially equal to those of the optical fiber to form a strain generating body, and the strain generating body is installed inside in advance. , A concrete structure distortion detection device capable of detecting the distortion generated after the concrete structure is constructed by placing concrete and building the concrete structure;
An FBG sensor is provided in the optical fiber, and a metal piece to be bonded to the FBG sensor is provided extending in the axial direction of the optical fiber, and the metal piece is fixed to the optical fiber on the base end side of the metal piece, The temperature detection strainer is formed as a free side, and the structure is constructed by placing concrete with the temperature detection strainer installed in advance, and is generated after the concrete structure is constructed. A concrete structure internal temperature detection device capable of detecting internal temperature changes;
Have
The internal temperature detection device is installed in the vicinity of the strain detection device installed in the concrete structure,
A strain detection apparatus for a concrete structure characterized by the above.
The concrete structure includes a structure made of an asphalt mixture.
The detection apparatus according to claim 1, 2, or 3.
The glass fiber is FRP.
The detection apparatus according to claim 1, 3 or 4.
The metal piece is a metal piece having a large coefficient of thermal expansion.
The detection apparatus according to claim 2, 3, or 4.

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