JP6524460B2 - Test body, strain measurement method, contraction / expansion strain estimation method and effective prestress amount estimation method - Google Patents

Description

  The present invention relates to a test body used for estimation of contraction and expansion strain of a structure, a strain measurement method, a contraction and expansion strain estimation method, and an effective prestress amount estimation method.

  Conventionally, large-scale structures such as bridges are often manufactured using prestressed concrete. In such PC structures, it is extremely important to introduce a predetermined amount of prestress. As the amount of prestress given initially (amount of introduced prestress) is released by various factors, the long-term effective amount of effective prestress gradually decreases. Among the various factors, the main factors that affect it are shrinkage and expansion strain (for example, drying and self-shrinkage) due to cement hardening, creep strain due to the amount of applied prestress, and relaxation of PC steels, which are accurately determined. If so, it is possible to accurately grasp the long-term effective prestressing amount of actual concrete products and structures.

  Here, with respect to the creep strain amount and the relaxation amount, conventionally, the relationship with the stress is clearly determined, and an accurate value can be calculated.

JP 10-102776 A

  However, the shrinkage expansion strain is affected by various factors such as the composition of concrete, the size and shape of members, the environmental conditions, the restraint of reinforcing bars, etc., and it is not easy to precisely predict the shrinkage expansion of the actual structure.

  In the method of measuring the contraction and expansion strain so far, since the tip and the metal rod are used for the measurement unit, the measurement unit may be damaged or corroded by wind and rain outdoors. For this reason, it was difficult to obtain an accurate measurement result. In addition, since measurement can not be performed except at 20 ° C., which is also a reference, accurate measurement outdoors is difficult.

  In addition to the above, there is a method of embedding a strain sensor in the actual structure itself and measuring the contraction and expansion strain using an RFID tag. However, at the time of burying, troublesome work such as attachment of a sensor or a tag between reinforcing bars and cable wiring is required. And even if the strain sensor can be embedded in the actual structure itself, there are cases where measurement is difficult, such as the side of the bridge where the measurement point can not be reached or a roadway where a car passes.

  The present invention has been made in view of such circumstances, and it is possible to measure the contraction and expansion strain under the same environmental conditions as the actual structure, and further, the long-term effective prestress of the actual structure. It is an object of the present invention to provide a test body capable of accurately grasping the amount, a strain measurement method, a contraction / expansion strain estimation method and an effective prestress amount estimation method.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, it is a test body used to estimate the shrinkage / expansion strain of a structure, which is supported by a plurality of reinforcing bars provided to have substantially the same reinforcing bar ratio as the structure, and any of the reinforcing bars And a RFID tag that outputs a signal acquired from the strain sensor.

  Thus, a plurality of reinforcing bars provided to have substantially the same reinforcing bar ratio as the structure, a strain sensor supported by any of the reinforcing bars, and an RFID tag that outputs a signal acquired from the strain sensor , So that it is possible to form a test body as a miniature having the same configuration as the structure. Thereby, a test body can be installed in the same place as the environmental conditions of a real structure, and contraction expansion strain of a test body can be acquired.

  (2) The test body of the present invention is characterized in that it is formed in a columnar shape by at least three reinforcing bars provided parallel to the vertical direction, and the strain sensor is surrounded by the three reinforcing bars. . As described above, since the strain sensor is constituted by the at least three reinforcing bars provided parallel to the vertical direction and the strain sensor is surrounded by the three reinforcing bars, the volume necessary for embedding the strain sensor in concrete It becomes possible to make it small. In addition, since the three reinforcing bars are provided in parallel to the vertical direction, the test body can be used in a self-supporting state. Furthermore, when placing concrete, it can be easily processed and used easily.

  (3) Further, the test body of the present invention is characterized in that concrete substantially the same as the structure is cast so as to embed the reinforcing bar and the strain sensor. Thus, since concrete substantially the same as the structure is cast to embed the reinforcing bar and the strain sensor, it is possible to form a test body as a miniature having the same configuration as the structure. Become. As a result, accurate contraction and expansion strain can be measured without damage or corrosion of the measurement portion of the strain sensor due to wind and rain.

  (4) In addition, the method for measuring contraction and expansion strain according to the present invention is characterized by acquiring contraction and expansion strain data from the test body described above using an RFID tag. As described above, since data can be acquired from a strain sensor using an RFID tag, power supply and wiring are unnecessary, and measurement can be made more efficient.

  (5) Further, the method for measuring contraction and expansion strain according to the present invention is characterized in that the test body described above is placed in the same environment as the structure, and strain data is acquired from the test body. Thereby, it is possible to measure the contraction and expansion strain of the test body under the same environmental conditions as the actual structure.

  (6) Further, in the method of estimating contraction and expansion strain according to the present invention, the step of acquiring strain data from the test body described above, the acquired strain data, and the effective member thickness of the structure or the volume ratio of the structure Estimating at least the contraction and expansion strain of the structure using the surface area ratio. Thereby, the contraction and expansion strain can be estimated from a test body substantially the same as the actual structure.

  (7) Further, in the effective prestress amount estimation method of the present invention, the estimation of the effective prestress amount of the PC structure is estimated by the shrinkage / expansion strain estimation method described above from the introduced prestress amount to the PC structure It is characterized in that the contraction and expansion strain, the calculated creep strain, and the amount of relaxation are subtracted and finally calculated as a stress. Thereby, the long-term effective prestress amount of a real structure can be estimated from a test object, and tension can be grasped | ascertained.

  According to the present invention, it is possible to measure contraction and expansion strain under the same environmental conditions as an actual structure. In addition, by using the RFID strain measurement system, accurate measurement can be performed outdoors. Then, from the contraction and expansion strain measured by the test body, the contraction and expansion strain of the actual structure can be estimated, and the long-term effective prestress amount of the actual structure can be accurately grasped.

It is the perspective view which showed the outline | summary of the test body which installed the RFID distortion sensor. It is the perspective view which showed the outline | summary of the test body which installed the RFID distortion sensor. It is the perspective view which showed the outline | summary of the PC structure for verification which concerns on a present Example. It is the figure which showed the relationship between the dry material age and the contraction expansion strain which concern on a present Example. It is the figure which showed the relationship between the tendon age in the method of a present Example, and each distortion. It is the figure which showed the relationship between the tendon age in the conventional method, and each distortion. It is the figure which showed the stress change of the PC steel bar in the method of the conventional method and a present Example.

  Since it is difficult for the present inventors to measure the contraction and expansion strain of the actual structure itself, the contraction and expansion of the actual structure is realized by converting the contraction and expansion strain generated in the small sample into the contraction and expansion strain of the actual structure. Focusing on the possibility that strain can be estimated, contracting expansion strain is measured from the specimen using RFID strain measurement system, and contracting expansion strain of real structure is estimated by using the contracting expansion strain and a specific formula It has been found that it is possible to estimate the effective prestressing amount of a real structure by doing the present invention.

  That is, the present invention is a test body used to estimate the shrinkage expansion strain of a structure, and a plurality of reinforcing bars provided so as to have substantially the same reinforcing bar ratio as the structure, and any one of the above-mentioned It is characterized by comprising: a strain sensor supported by a reinforcing bar; and an RFID tag that outputs a signal acquired from the strain sensor.

  Thus, the present inventors place the test body at the same place as the environmental conditions of the actual structure, and estimate the contraction / expansion strain of the actual structure using the contraction / expansion strain obtained from the test body. , It became possible to estimate the effective prestress amount of the real structure. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Production of RFID contraction test body and PC structure for verification)
FIG. 1A and FIG. 1B are diagrams showing an outline of a test body 100, 200 in which the RFID strain sensor 1 is installed. FIG. 1A and FIG. 1B show a state in which concrete is not cast. The test body 100 shown in FIG. 1A includes at least an RFID strain sensor 1, a plurality of reinforcing bars 3 (three in the present embodiment), and an RFID tag 9. The RFID strain sensor 1 is provided so as to surround each reinforcing bar 3 and fixed by a first wire 5 so as to be disposed at the center of each reinforcing bar 3. The RFID strain sensor 1 and each reinforcing bar 3 are both provided in parallel with the vertical direction, and are configured in a columnar shape by the respective reinforcing bars 3. An RFID tag 9 connected to the RFID strain sensor 1 by a cable 11 is fixed to the second wire 7 by an RFID tag fixing belt 10. The second wire 7 is fixed to each reinforcing bar 3 by a fixing wire 6.

  As shown in FIG. 1B, in the RFID contraction test body 200, the test body 100 illustrated in FIG. 1A is disposed at the center of the concrete form 13. The test bodies 100 and 200 illustrated in FIG. 1A and FIG. 1B can stand by themselves since the three reinforcing bars 3 are provided in parallel to the vertical direction. When measuring the shrinkage / expansion strain of the structure with the test body 200, since it is sufficient to cast concrete in the concrete formwork 13 shown in FIG. 1B, it can be easily processed and used easily.

  FIG. 2 is a diagram showing an outline of a verification PC structure 300 according to the present embodiment. The amount of long-term prestress in the central part of the central cross section of the verification PC structure 300 is estimated, and the accuracy of the present invention is examined.

  Next, an outline of the verification PC structure 300 and the test body 200 will be described. The configurations of the verification PC structure 300 and the RDIF contraction test body 200 described below are an example for examining the accuracy of the present invention, and the present invention is not limited to only such a configuration. .

  In the verification PC structure 300, the RFID concrete strain sensor 31 is provided at the center of the central cross section of the verification PC structure 300, and the RFID tag 33 is provided at a position where measurement is easy near the fog. 31 is used to measure the contraction and expansion strain of the verification PC structure 300.

To the outer cross section of the central portion of the verification PC structure 300 (vertical 20 cm × horizontal 40 cm) is atypical rebar D13 is present 6 (sectional area meter 760 mm ^2), D10 is present 3 (cross-sectional area meter 214 mm ²⁾ has entered The effective cross-sectional area excluding the sheath etc. is 75774 mm ² , and the rebar ratio is 0.0128.

The PC structure 300 for verification was cured in the formwork until 10 days of material age, and tension was introduced with two PC steel materials at 35 days of material age. Tension was performed using a center hole type jack, and management of tension was performed using a center hole type load cell. The height of the upper and lower PC steel bars 37 was 482.5 kN (600 N / mm ² ). This corresponds to a PC steel bar 3000μ.

  On the other hand, in the test body 200, each reinforcing bar 3 is assembled using three deformed reinforcing bars (D10) so that the reinforcing bar ratio of the PC structure for verification 300 is approximately the same (0.0126). In the concrete form 13 (diameter 15 cm × height 30 cm), concrete (water cement ratio 38%, crushed stone, crushed sand) substantially the same as that of the verification PC structure 300 was placed. Thereafter, the test body 200 is placed near the verification PC structure 300, and cured as it is in the formwork for the same 10 days as the verification PC structure 300. After 10 days of material removal, the upper and lower surfaces are epoxy resin Sealed with Thereafter, the test body 200 is placed again near the verification PC structure 300, and the same curing conditions as the verification PC structure 300 are obtained.

(Estimate of shrinkage strain of PC structure)
FIG. 3 shows the relationship between the actual value of the shrinkage / expansion strain obtained from the test body 200 and the estimated value of the shrinkage / expansion strain according to the method of this embodiment and the conventional method, and the age of the dried material.

  In this example, the shrinkage / expansion obtained from the test body 200 in which the mixing ratio of the concrete, the environmental conditions, and the axial rebar ratio, which were installed near the verification PC structure 300, was substantially the same as the verification PC structure 300. The strain is used to estimate the contraction and expansion strain of the verification PC structure 300. However, it is impossible to produce the test body 200 under the same conditions as the verification PC structure 300 only for the size and shape of the member, so the influence must be taken into consideration. For example, the degree of dryness differs depending on the age of the small specimen and the large specimen. Therefore, the drying strain also behaves differently. The final value of the shrinkage expansion strain of concrete can be regarded as substantially the same regardless of the size of the specimen, and the value representing the time-dependent change of the shrinkage expansion strain becomes larger in proportion to the square of the specimen size.

  Therefore, the contraction and expansion strain of the PC structure for verification 300 is estimated by using the equation (1) in consideration of the thickness of the effective member in the design section of the 2012 concrete standard specification.

First, the final value of shrinkage strain ε ′ _{sh, inf} is calculated using the shrinkage strain of the obtained test body 200 as the shrinkage strain of the member. Final value of shrinkage strain ε ' _{sh, inf} of specimen 200: material age of specimen 200 measured at 11, 24, 49, 88, 115 days of drying material age, shrinkage / expansion strain, daily average relative by JMA The average value of the humidity and the effective member thickness (150 mm) were substituted into the equation (1), and 351 μ was calculated by the least squares method.

  Next, the contraction / expansion strain of the verification PC structure 300 according to the present invention is estimated as the contraction strain of the member using the calculated final value of the contraction strain. The estimation of the contraction and expansion strain of the verification PC structure 300 is performed by setting the effective member thickness to the half power of the cross-sectional area (283 mm), and using the same value as the test body 200 for the final value of the contraction strain. It calculated similarly using Formula (1).

Next, the shrinkage expansion strain of the PC structure is estimated using a conventional method. In the conventional method, ε ' _{sh, inf} and β of the formula (1) change with time of contraction and expansion strain under the environment of temperature 20 ° C. and relative humidity 60% 7 days after curing in water of 100 × 100 × 400 mm specimen Regress using equation (2) which is a curve.

この場合、実際の現場でＰＣ構造物に打設されたコンクリートと同一のコンクリートで作製した１００×１００×４００ｍｍ供試体を水中養生し、その後２０℃、相対湿度６０％の環境下で保存しながら収縮膨張ひずみの測定を行なわなければならない。１００×１００×４００ｍｍ供試体の収縮膨張ひずみによらない場合は、ε’_{ｓｈ，ｉｎｆ}およびβは、式（３）より求める。ここでの従来法は、式（３）より求めた。

In this case, a 100 × 100 × 400 mm specimen made of the same concrete as the concrete placed on the PC structure at the actual site is cured in water and then stored at 20 ° C. and 60% relative humidity. Measurement of contraction and expansion strain must be made. If it does not depend on the contraction and expansion strain of a 100 × 100 × 400 mm specimen, ε ′ _{sh, inf} and β are obtained from equation (3). The conventional method here was obtained from equation (3).

In addition, in the Japan Society of Civil Engineering Design Standard Design Edition p105, the estimated value ε ' _sh of the test value of shrinkage of the conventional method is a measured value according to JIS A 1129 using various aggregates actually used in the whole country. It is stated that it is clear that the variation is about ± 50% at the maximum for each test value. Therefore, it is difficult to estimate the shrinkage / expansion strain of the actual structure in which the reinforcing bar is inserted by the test value according to the conventional method.

  As shown in FIG. 3, it can be seen that there is a gap between the estimated value of the shrinkage / expansion strain of the PC structure according to the method of the present embodiment and the estimate of the shrinkage / expansion strain of the PC structure according to the conventional method.

(Estimated amount of effective prestress)
Next, a method of estimating the effective prestress amount will be described. As the actual phenomenon of the PC structure, shrinkage strain, creep strain and relaxation of PC steel gradually occur after the introduction of tension force, so the amount of effective prestress decreases with the age of material. In calculating the shrinkage strain, creep strain, and relaxation that are factors of reduction, strictly, the prestressing force at the material age is applied to the concrete, and it is considered that the prestressing force changes with the material age There is a need to.

  The amount of effective prestress can be estimated by subtracting the shrinkage strain, creep strain and relaxation of PC steel from the amount of introduced prestress. And it is already known that creep strain and relaxation can be calculated by a formula.

  The calculation of creep strain and relaxation will be described. Here, contraction and expansion strain, creep strain and relaxation are calculated on a daily basis. The amount of effective prestress at the material age was converted to the amount of strain of the PC steel rod, and calculated for each step on a day. The creep strain was calculated according to the formula of the concrete standard specification.

  In addition, about compressive strength and Young's modulus of concrete, early strength cement was used and it was made constant because 35 years of tending material age has passed considerably, but strength development is late and tension strength is achieved at early age. It is also considered effective to change these as a coefficient of time, if introduced.

In addition, the relaxation rate (%) of PC steel bars is shown in the test report
Relaxation rate (%) = 0.3185 log _e (t) + 2.0122
Here, t: period (day)
And the reduction in tension due to relaxation was treated as the amount of strain reduction (relaxation equivalent strain) of the PC steel rod.

  It is to be noted that it was confirmed that the influence of the friction was not directly affected by the fact that the PC steel rod directly arranged this time was not filled with grout, and that the amount of decrease during fixing was hardly caused by the behavior of strain.

The strain change amount (introductory prestress amount) of PC steel rod by tension force introduction is 3000μ (= σ _pt / E _p ), and from that, it is calculated by equation (4), contraction expansion strain estimated by equation (1) Due to the effects of creep strain and relaxation of PC steel rods, it is decided that the strain of PC steel rods will decrease with concrete.

Therefore, it is possible to estimate that the amount of strain reduction of the PC steel rod is a value obtained by combining the estimated value of the shrinkage expansion strain, the estimated value of the creep strain, and the strain equivalent to relaxation. In other words,
Estimated amount of strain reduction of PC steel bar = Shrinkage strain estimated value + creep strain estimated value + relaxation equivalent strain amount. And the amount of effective prestress can be calculated | required by subtracting the reduction amount of distortion of PC steel rod from the amount of introduction prestress. In other words,
The amount of effective prestress = the amount of introduced prestress−can be estimated by the amount of reduction in strain of the PC steel rod.

  FIG. 4 and FIG. 5 show the relationship between the tendon age and each strain estimated by the method of the present embodiment described above and the conventional method. In each of FIGS. 4 and 5, actual measurement values of contraction and expansion strain obtained from the RFID concrete strain sensor 31 embedded in the verification PC structure 300 are also illustrated.

  From FIG. 4, the estimated amount of decrease of the PC steel rod estimated by the method of the present embodiment and the actual measurement value obtained from the RFID concrete strain sensor 31 of the PC structure 300 for verification almost coincided. On the other hand, it can be seen that there is a difference between the contraction strain calculated by the conventional method and the actual measurement value obtained from the RFID concrete strain sensor 31 of the verification PC structure 300. Therefore, it can be understood that the contraction strain can be accurately estimated by the method of the present embodiment.

FIG. 6 is a view showing a stress change of the PC steel bar from the time of introduction of tension in the present examination. The effective prestressing amount of PC steel was 510.7 N / mm ² . In the case of using the specimen in the conventional method, it was found that 503.6N / mm ^2, and the error of the minute corresponding to the strain amount difference component of the specimen of the present invention (7.1N / mm ²⁾ occurs (Since 3000 μ is 600 N / mm ² , strain reduction 450 μ corresponds to 90 N / mm ² min).

  As described above, according to the present embodiment, the contraction and expansion strain can be measured under the same environmental conditions as the actual structure, and accurate measurement can be performed outdoors as well by using the RFID strain measurement system. It becomes possible. Then, from the contraction and expansion strain measured by the test body 200, the contraction and expansion strain of the actual structure can be estimated, and the long-term effective prestress amount of the actual structure can be accurately grasped.

1 RFID strain sensor, strain sensor 3 Rebar 5 First wire 6 Fixing wire 7 Second wire 9 REID tag 10 RFID tag fixing belt 11 Cable 13 Formwork for concrete 31 RFID concrete strain sensor 33 RFID tag 35 Cable 37 PC steel bar 100, 200 RFID shrinkage test body (test body)
300 PC structure for verification

Claims (1)

An effective prestress amount estimation method for estimating an effective prestress amount of a PC structure, comprising:
The estimation of the effective prestressing amount of the PC structure is performed by subtracting the contraction / expansion strain estimated by the contraction / expansion strain estimation method, the calculated creep strain, and the relaxation amount from the introduced prestressing amount to the PC structure, and finally Calculated as stress,
The method for estimating the contraction and expansion strain includes the steps of acquiring strain data from a test body installed under the same environment as the PC structure, the acquired strain data, and an effective member thickness of the PC structure or the PC structure Estimating the shrinkage / expansion strain of the PC structure using the volume ratio / surface area ratio of the object;
The test body includes a plurality of reinforcing bars provided to have substantially the same reinforcing bar ratio as the PC structure, a strain sensor supported by any of the reinforcing bars, and a signal acquired from the strain sensor A method of estimating an effective prestress amount, comprising: an RFID tag to be acquired; and substantially the same concrete as the PC structure is cast so as to embed the reinforcing bar and the strain sensor.

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