JP4498962B2 - Method for measuring internal strain of concrete structure and concrete structure - Google Patents

Description

  The present invention relates to a method for measuring internal strain of a concrete structure that calculates the internal stress state of the concrete structure and evaluates the safety of the concrete structure, and the concrete structure.

Conventionally, in measuring the internal strain of a concrete structure (see Non-Patent Document 1 below), a uniaxial strain gauge is provided on the reinforcing bar, and measurement is performed on a uniaxial strain field.
Japan Society of Civil Engineers: Standard Specification for Concrete [Structural Performance Review], 2002.2.3

However, it has been difficult to accurately measure the complex internal stress generated in a concrete structure with the above-described conventional gauge for a uniaxial strain field.
The present invention provides in view of the above situation, and measuring the strain state of the internal 2 Jikujo of the concrete structure, measuring methods and concrete structure of the internal strain concrete structure for measuring the stress state of the interior of the concrete structure The purpose is to do.

In order to achieve the above object, the present invention provides
[1] In the method of the concrete structure inside strain, without affecting the performance of concrete structures, and a member having rigidity to withstand pouring pressure of the concrete after casting, x-axis, y-axis and A cross-shaped member having an x-axis and a y-axis corresponding to the x-axis and the y-axis of the three-axis strain gauge so that the strain in the two-axis field of the xy axis can be measured. the shaft portion subjected to means to secure the adhesion and fixing performance of the concrete structure, x-axis in the center of the cross-shaped member, Paste the triaxial strain gauge consisting of y-axis and the xy axes, the three axes A plurality of the cross-shaped members to which strain gauges are affixed are arranged in a row in the y-axis direction, and the plurality of the arranged members are arranged at a predetermined interval in the x-axis direction . in embedded, said Using measurements from axial strain gauges and measuring the stress state of the interior of the concrete structure.

[2] In the method of internal strain concrete structure of [1] Symbol placement, spacing means for ensuring the adhesion and fixing performance of the concrete of the member is formed by sandwiching the triaxial strain gauge x It is characterized in that both the axial direction and the y-axis direction are set at equal intervals and smaller than an assumed crack interval.
[ 3 ] The method for measuring internal strain of a concrete structure according to [1] above, wherein the method is used for health monitoring of underground concrete structures such as concrete piles that cannot be visually inspected.

[4] In the method of internal strain concrete structure according to [1] and performs Health monitoring from a remote location an output from the triaxial strain gauge was collected from a remote location.
[5] without adversely affecting the performance of the concrete structure, and have a rigidity to withstand pouring pressure of the concrete after casting, can measure the strain of 2 Jikujo the x-axis, y-axis and xy axes Yo triaxial strain the x-axis and y-axis of the gauge and the member which is formed in a cross shape having an x-axis and y-axis is made to correspond, x-axis is pasted at the center portion of the cross-shaped member of the member, y-axis and a triaxial strain gauge composed of an xy axis, the member is provided with means for ensuring adhesion and fixing performance with the concrete on the x axis portion and the y axis portion, and the triaxial strain gauge is attached to the member. the members of the cross-shaped plurality continuously arranged so as to line up in a row in the y-axis direction, I embed the concrete structure by arranging a plurality taking a predetermined interval the continuously provided with members in the x axis direction the concrete structure Measure the stress state inside an object A measuring device.

[ 6 ] The concrete structure according to [ 5 ], wherein the member is a plastic plate.
[ 7 ] The concrete structure according to [ 5 ], wherein the member is an acrylic plate.
[8] In the above-mentioned [5] Concrete structure wherein the means to ensure the adhesion and fixing performance of the concrete, characterized in that the cut edge formed in the member.

In [9] above [5] Concrete structure wherein the means to ensure the adhesion and fixing performance of the concrete and wherein the at-out cut unplug formed in said member.
In [10] above [5] Concrete structure wherein the means to ensure the adhesion and fixing performance of the concrete is characterized by a decorated with roughening treatment on the surface of the member.

According to the present invention, since the strain in the biaxial field can be measured , the internal stress state with respect to the concrete structure having a complicated stress state can be reliably measured .
In addition, health monitoring of underground concrete structures such as concrete piles that cannot be visually inspected, and output from triaxial strain gauges from remote locations can be used for health monitoring of concrete structures from remote locations. Is possible.

Method of measuring strain inside the concrete structure of the present invention does not affect the performance of the concrete structure, and a member having rigidity to withstand pouring pressure of the concrete after casting, x-axis, y-axis and A cross-shaped member having an x-axis and a y-axis corresponding to the x-axis and the y-axis of the three-axis strain gauge so that the strain in the two-axis field of the xy axis can be measured. the shaft portion subjected to means to secure the adhesion and fixing performance of the concrete structure, x-axis in the center of the cross-shaped member, Paste the triaxial strain gauge consisting of y-axis and the xy axes, the three axes A plurality of the cross-shaped members to which strain gauges are affixed are arranged in a row in the y-axis direction, and the plurality of the arranged members are arranged at a predetermined interval in the x-axis direction . the embedding, the triaxial Measuring the stress state of the interior of the concrete structure by using the measurements from Zumi gauge.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a diagram showing an element shape of an acrylic plate having a triaxial strain gauge showing an embodiment of the present invention, and FIG. 2 is a diagram showing an arrangement of the acrylic plate in the concrete structure.
As shown in FIG. 1, a triaxial strain gauge 2 is attached to the center of an acrylic plate 1 'processed into a cross shape, and this is used as an element to form a cross shape continuously as shown in FIG. By embedding the long acrylic plate 1 in the concrete structure 11, the strain state of the biaxial field inside the concrete structure 11 is measured. In order to cope with the distortion of the biaxial field, the acrylic plate 1 ′ processed into a cross shape was provided with notches 1A in the x-axis direction and the y- axis direction to ensure the fixing performance. Further, the interval between the cutouts 1A with the triaxial strain gauge 2 interposed therebetween must be set to be equal in both the x- axis direction and the y- axis direction and smaller than the assumed crack interval. In the present invention, an acrylic plate or the like having a low rigidity is used as a material to eliminate the influence on the performance of the concrete structure 11. Reference numeral 3 denotes an axial reinforcing bar.

Moreover, it can replace with the said Example and can comprise as follows.
(1) strain gauge attaching member is not limited to the acrylic plate described above, without adversely affecting the performance of the concrete structure, and a member having a rigidity to withstand pouring pressure of the concrete after casting If it is. For example, a plastic plate may be used.
(2) The strain gauge attaching member described above has been to provide a notch, but the invention is not limited thereto, and Ru can be ensured adhesion and fixing performance of the concrete in the x-axis and y-axis directions If it is. For example, provided a cut-out, such as circular member, it may be a roughening treatment was applied to the surface of the member.

Specific examples will be described below.
Reinforced concrete (hereinafter referred to as RC) such as piles and columns that receive shearing force The design of a circular cross-section member is performed by converting the cross-section into an equal square and applying the strength formula derived from the beam member experiment (above Non-patent document 1). However, since the boundary conditions such as piles and pillars are generally close to fixing both ends, the shear strength of the member may be underestimated. Therefore, in the present invention, paying attention to the shear span ratio, the proof stress of the circular cross-section member subjected to the antisymmetric bending load and the mechanism of fracture were considered by measuring the strain inside the concrete.

Therefore, the experiment was performed as follows.
In addition, the validity of the measurement results was verified using an experimental specimen (concrete structure).
FIG. 3 is a view showing a concrete structure as a specimen, and FIGS. 4 and 5 show the angle of the maximum principal strain calculated from strain values obtained from the triaxial gauge of the present invention. In this experiment, it was confirmed that the magnitude and direction of the main strain were appropriate.

  Here, three specimens having different shear span ratios without shear reinforcing bars were used for the shape and specifications of the specimens. The specimen shape is as shown in FIG. 3, and the specifications are shown in Table 1.

この表１において、ａは剪断スパン（ｍｍ）、Ｄは直径（ｍｍ）、ｄは設計上の有効高さ（ｍｍ）、ａ／ｄはせん断スパン比、ｆ_C ′はコンクリートの圧縮強度（Ｎ／ｍｍ² ）、Ｅ_C はコンクリートの弾性係数（ｋＮ／ｍｍ² ）、Ｐ_t は引張鉄筋比、ｆ_y は軸方向鉄筋の降伏強度（Ｎ／ｍｍ² ）である。

In Table 1, a is the shear span (mm), D is the diameter (mm), d is the effective design height (mm), a / d is the shear span ratio, and f _C ′ is the compressive strength of the concrete (N / Mm ² ), E _C is the elastic modulus (kN / mm ² ) of concrete, P _t is the tensile reinforcement ratio, and f _y is the yield strength (N / mm ² ) of the axial reinforcement.

Here, footings 12 and 13 are provided above and below the concrete structure 11 in order to apply an antisymmetric bending load (see FIG. 3). In addition, although the high-strength reinforcing bar is used as the axial rebar 3, from the viewpoint of avoiding the adhesion failure, the specimen of the specimen is subjected to shear failure even if the axial rebar 3 is assumed to be a normal strength reinforcing bar of about SD390. Designed.
Next, a loading method and measurement items will be described.

In this experiment, an antisymmetric bending load was applied by applying horizontal force to the upper footing 12 of FIG. 3 by displacement control. The main measurement items of this experiment are the load at the loading point, displacement, crack properties, and strain inside the concrete.
Hereinafter, the strain measurement inside concrete will be described in detail.
In discussing the shear strength of RC members with different boundary conditions and the mechanism leading to failure, the strain inside the concrete is very important information. In addition, analytical methods such as the finite element method greatly affect the stress state after that due to the modeling of the crack surface or concrete after cracking. Is difficult.

(Measuring method)
The RC member that shears and breaks is a biaxial strain field, and the direction of the main strain changes with the occurrence of cracks. Therefore, it is difficult to grasp the strain with the conventional measurement method. In the present invention, as shown in FIG. 1 and FIG. 2 described above, the triaxial strain gauge 2 is attached to an acrylic plate 1 ′ processed into a shape corresponding to a biaxial strain field and embedded in a concrete structure 11. The strain was measured (see FIG. 1). In addition, the acrylic plate 1 'used in this experiment has a thickness of 10 mm and an elastic modulus of 3.1 kN / mm ² , and since the area ratio and the rigidity ratio with respect to the specimen are sufficiently small, there is no influence on the proof stress. Conceivable. With the triaxial strain gauge 2 affixed to the acrylic plate 1 ', the maximum principal strain, minimum principal strain, and principal strain angle inside the concrete can be calculated in the present invention.

(Measurement position)
The acrylic plate 1 was arranged inside the axial reinforcing bar in parallel with the loading direction. The arrangement of the acrylic plate 1 of the specimen I is as shown in FIG. Similarly, the specimen II and specimen III were arranged so as to be at the end (S point, N point) and the member axis (C point, E point) when viewed from the side. In addition, the triaxial strain gauge 2 was arranged at intervals of 100 mm or 150 mm from the lower end to the upper end of the specimen so that the strain distribution of the entire specimen could be grasped.

(Verification of measurement results)
Here, the measured value of the triaxial strain gauge 2 attached to the acrylic plate 1 is verified. The maximum principal strain calculated from the measured value of the N point of the specimen III having the largest shear span ratio and the angle of the principal strain are shown in FIG. 4 and FIG. 5 as verification examples. Here, the horizontal axis represents the maximum principal strain (FIG. 4) or the principal strain angle (FIG. 5), and the vertical axis represents the member height. Since loading is performed in the N point direction from the S point in FIG. 2, the upper side of the N point is tensile and the lower side is compressed. Further, as shown in FIG. 6, the angle of the main strain is determined such that the horizontal direction is the maximum main strain orthogonal direction, that is, the crack direction is clockwise.

  In the specimen III having a large shear span ratio, bending cracks occurred at a position of 300 mm from the upper end at 81 kN. From FIG. 4, it can be seen that the maximum principal strain at a position 300 mm from the upper end exceeds the strain at the time of tensile strength of the concrete (hereinafter, the limit tensile strain) of about 100 μm from 74 kN to 104 kN. Also, the main strain angle was 0 degree at the upper end, that is, the crack direction was horizontal, and the lower end was 90 degrees, that is, the crack direction was vertical, which was consistent with the assumed crack property. Thus, it was confirmed that the strain inside the concrete can be measured with high accuracy by the triaxial strain gauge.

  Furthermore, even for an actual concrete structure, the safety against fracture can be quantitatively determined by applying it to a structure having a complicated stress state. For example, by placing it on an underground structure such as a pillar member, beam member, or pile that cannot be visually inspected with a low shear span ratio, the safety of the structure after receiving a large external force such as an earthquake Evaluation becomes possible. In addition, for prestressed concrete structures, it is possible to find defects such as poor fixing by evaluating parts with complicated stresses such as fixing parts and deflecting parts, and measuring distortion of general parts.

Moreover, as an experimental specimen, the structure may be a reinforced concrete structure, an unreinforced concrete structure, a prestressed concrete structure, a composite structure, or the like.
The arrangement of the gauge is preferably equal to or less than the assumed crack interval, but may not necessarily be equal to or less than the assumed crack interval. Arrange so that the measurement direction and gauge attachment surface are parallel.
Furthermore, the method for measuring the internal strain of the concrete structure of the present invention is as follows:
(1) Health monitoring of underground concrete structures such as concrete piles that cannot be visually inspected.

(2) Moreover, the health monitoring of the concrete structure from a remote place can be performed by collecting the output from the triaxial strain gauge from a remote place.
That is, underground concrete structures such as concrete piles that cannot be visually inspected are damaged after accidental earthquakes, storms and floods, etc. (specifically, the damage index that gives the relationship between main strain and damage level) (Evaluation) can be used as a means for speeding up, and it can contribute to the realization of early restoration of concrete structures by taking measures such as replacement and reinforcement based on the determination.

  In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.

  The method for measuring internal strain of a concrete structure and the concrete structure of the present invention can be used for measuring internal strain of a concrete structure having a complicated stress state.

It is a figure which shows the element shape of the acrylic board which has a triaxial strain gauge which shows the Example of this invention. It is a figure which shows arrangement | positioning of the acrylic board to the concrete structure which shows the Example of this invention. It is a figure which shows the concrete structure which is a test body. It is a figure which shows the example of a measurement of maximum distortion. It is a figure which shows the example of a measurement of the angle of main distortion. It is a figure which shows the angle of the main distortion.

DESCRIPTION OF SYMBOLS 1 Long acrylic board in which cross shape was formed continuously 1 'Acrylic board processed into cross shape 2 Triaxial strain gauge 3 Axial rebar 11 Concrete structure 12, 13 Footing

Claims (10)

Without affecting the performance of the concrete structure, and a member having rigidity to withstand pouring pressure of the concrete after casting, so that it can measure the distortion of the 2 Jikujo the x-axis, y-axis and xy axis 3 Formed in a cross shape having an x-axis and a y-axis corresponding to the x-axis and y-axis of the axial strain gauge , and adhesion / fixing performance with the concrete structure on the x-axis portion and the y-axis portion of the cross-shaped member The triaxial strain gauge comprising the x-axis, y-axis and xy-axis is attached to the center of the cross-shaped member , and the cross-shaped member to which the triaxial strain gauge is attached is attached. A plurality of connected members are arranged in a line in the y-axis direction, and a plurality of the arranged members are arranged at predetermined intervals in the x-axis direction and embedded in the concrete structure, and measured values from the triaxial strain gauge are obtained. the concrete structure in using Concrete structure internal strain measurement method and measuring the state of stress. In the method of internal strain concrete structure according to claim 1 Symbol placement, spacing means for ensuring the adhesion and fixing performance of the concrete of the member is formed, x-axis direction across the triaxial strain gauge, y A method for measuring internal strain of a concrete structure, characterized in that it is set at equal intervals in the axial direction and smaller than an assumed crack interval. The method for measuring internal strain of a concrete structure according to claim 1, wherein the internal strain is used for health monitoring of an underground concrete structure such as a concrete pile that cannot be visually inspected. In claim 1 the measuring method of the concrete structure inside strain, wherein said triaxial strain output from the gauge was collected remotely internal strain of the concrete structure and performing Health monitoring from a remote location Measuring method. Without adversely affecting the performance of the concrete structure, and have a rigidity to withstand pouring pressure of the concrete after casting, strain triaxial as capable of measuring the strain of 2 Jikujo the x-axis, y-axis and xy axes a member formed into a cross shape having an x-axis and y-axis in correspondence with the x-axis and y-axis of the gauge, 3 consisting of the x-axis is pasted to the central portion in the cross-shaped, y-axis and xy axis of the member An axial strain gauge, and the member is provided with means for ensuring adhesion and fixing performance to the concrete at the x-axis portion and the y-axis portion, and the cross-shaped member to which the triaxial strain gauge is attached is provided. plurality continuously arranged so as to line up in a row in the y-axis direction,該連set the member taking a predetermined interval in the x-axis direction plural side by side stress state of the interior of the concrete structure I embed the concrete structure Equipped with a measuring device that can measure Concrete structure characterized by Rukoto. 6. The concrete structure according to claim 5 , wherein the member is a plastic plate. 6. The concrete structure according to claim 5 , wherein the member is an acrylic plate. In claim 5 concrete structure according, concrete structure, characterized in that means for securing the adhesion and fixing performance of the concrete is cut edge formed in the member. In claim 5 concrete structure according, concrete structure, characterized in that means for securing the adhesion and fixing performance of the concrete is-out cut unplug formed in said member. In claim 5 concrete structure according, concrete structure, characterized by means for securing the adhesion and fixing performance of the concrete is a roughening treatment to be applied to the surface of the member.

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