JP4912673B2 - Tensile force detection method for tendons - Google Patents

Description

  The present invention relates to a tension detecting method for a tension material that detects a tension force acting on the tension material based on a result of magnetostriction measurement performed by pressing a magnetostrictive sensor against the tension material.

  Traditionally, it was most standard to measure the tension of a tendon using a load cell, but it takes a lot of money to install the load cell on all tendons. It is common to install in a few percent of the total.

  However, if there is a change in the measurement value of the load cell after the tension material is installed or if there is a concern about the tension tension being lowered, the tension force is measured even for the tension material without the load cell installed. It is necessary to grasp the tension that is acting on.

  In particular, the tension material installed before the Showa era is a standard equivalent to a so-called temporary anchor when viewed from the current product standards, and the wire breaks due to corrosion over time and the installation environment including the ground. It has been pointed out that

  Therefore, with regard to the tension members installed before the Showa era, the total number of tensions was measured over a certain period of time, and the overall soundness of the tension members was evaluated. It is desirable to go.

  Therefore, at present, the tension force is measured by performing a lift-off test using a jack for the tension material in which the load cell is not installed.

In addition, the correlation between tension and magnetostriction value was obtained in advance using a test piece of the same quality as the tension material, and the magnetostriction measurement was performed by pressing the magnetostriction sensor against the tension material actually installed. A method is also known in which the magnetostriction value is compared with the correlation between the tension force obtained from the test piece and the magnetostriction value, and the tension force acting on the tension material is estimated (for example, see Patent Document 1).
JP 2002-173935 A

  However, in the method of measuring the tension force by the above-described lift-off test, since the apparatus is large and takes time and cost, there is a problem that it is not practical to test all the tension materials. there were.

  In addition, in the method of estimating the tension force by comparing the correlation between the tension force and magnetostriction value obtained by the test piece and the measured magnetostriction value, in order to improve the magnetostriction sensitivity and obtain the accurate tension force In addition, it is necessary to install a tension member using a predetermined fixing member or the like that has been subjected to treatment for reducing the influence of the anisotropy of the tissue and the residual stress in advance, and to set the predetermined fixing member as a measurement target.

  Therefore, a predetermined fixing member is required from the beginning of the tension member installation, and there is a problem that it is difficult to apply to existing tension members already installed.

  Then, this invention makes it the subject to provide the tension | tensile_strength tension | tensile_strength detection method of the tension | tensile_strength material which can detect the tension | tensile_strength which has acted on the existing tension | tensile_strength already installed easily and cheaply.

In order to solve the above-mentioned problem, the invention described in claim 1 performs magnetostriction measurement by pressing a magnetostrictive sensor against an exposed portion of a tension material embedded in the ground, and the tension based on the measured magnetostriction value. In the tension material detecting method for detecting the tension force acting on the material, the tension material is a long material that penetrates the structure, and is fixed to the upper end of the material. A fixing member that applies tension to the tension member; and an anchor plate that is disposed between the fixing member and the structure and receives the fixing force of the fixing member, and is set for each fixed site. At the same time, tension of various load levels is applied to a predetermined number of tension bodies , and at the same time, the magnetostriction sensor is pressed against the anchor plate to perform magnetostriction measurement, and the correlation between the tension force and the measured magnetostriction value is obtained. After finding the approximate expression shown, Performed magnetostrictive measurement by pressing the magnetostrictive sensor to the anchor plate of another tendon, by substituting the measured magnetostrictive value to the approximate expression, the determination of the tension acting on the other tendons It is a feature.
Further, the invention according to claim 2 is the method for detecting tension of tension material according to claim 1, wherein tension of various load levels is applied to a predetermined number of tension bodies set for each fixed site. When the magnetostriction measurement is performed by the magnetostriction sensor at the same time as applying, the magnetostriction measurement is performed by pressing the magnetostriction sensor against the fixing member in addition to the anchor plate, and the magnetostriction measured using the tension force and the anchor plate as a measurement object. After obtaining an approximate expression indicating a correlation with a value and an approximate expression indicating a correlation between a tension force and a magnetostriction value measured using the fixing member as a measurement target, The magnetostriction sensor is pressed against the anchor plate or the fixing member to perform magnetostriction measurement. The magnetostriction value measured using the anchor plate as a measurement target is obtained by measuring the tension force and the anchor plate. Substituting into the approximate expression indicating the correlation with the magnetostriction value measured as the target, the magnetostriction value measured with the fixing member as the measurement target is the magnetostriction value measured with the tension force and the fixing member as the measurement target. This is characterized by substituting into an approximate expression indicating the correlation between the two, and obtaining a tension force acting on another tension material.

According to a third aspect of the present invention, in the tension tension detecting method of the tension material according to the first or second aspect, the magnetostriction measurement is performed by pressing against a plurality of measurement points that are symmetrically spaced across the central axis of the tension material. The magnetostriction value is obtained by averaging the measurement values measured at each measurement point.

According to a fourth aspect of the present invention, in the tension material tension detecting method according to any one of the first to third aspects, the approximate expression is obtained by a method of least squares.

According to the first and second aspects of the present invention, the tension force and magnetostriction value are determined based on the measurement result of magnetostriction measurement performed simultaneously with applying tension force of various load levels to a predetermined number of tension members set in advance. Therefore, it is only necessary to substitute the result obtained by performing magnetostriction measurement for the other tendons into the approximate expression indicating the correlation.

  Thereby, it is possible to detect the tension of the existing tension material by performing magnetostriction measurement in the state where the existing tension material is already installed, and the tension force can be easily and inexpensively obtained. .

  In addition, since an approximate expression indicating the correlation between the tension force and the magnetostriction value is obtained using a part of the tension material actually installed at a certain site, the predetermined number obtained for each of the predetermined number of tension materials By statistically processing the results showing the correlation between the tension force and magnetostriction value, the anisotropy and residual stress of the individual tendons at this site, the eccentricity of the tendons, etc. It is possible to grasp the variation in the measured magnetostriction value.

  That is, it is possible to grasp the degree of error included in the approximate expression by performing statistical processing when determining the approximate expression.

According to the invention of claim 3 , in addition to the effect of claim 1 or 2 , it is possible to eliminate errors caused by eccentricity of the tension material, variation of the measured magnetostriction value due to the difference in measurement position, etc. It is possible to improve the measurement accuracy.

According to the invention of claim 4 , in addition to the effect of any one of claims 1 to 3, it is possible to easily obtain a highly accurate approximate expression that is closer to actuality when the approximate expression is obtained.

  Next, the best mode for carrying out the tension detecting method for tension materials according to the present invention will be described with reference to the drawings.

  In FIG. 1, reference numeral 1 denotes a ground anchor (tension material) constructed to fix the ground collapse prevention structure 2 to the ground 3.

  The ground anchor 1 is a long tension member 5 that penetrates the structure 2 and a nut 8 that is a fixing member that applies tension to the tension member 5 by fixing to the upper end of the tension member 5. And an anchor plate 7 disposed between the nut 8 and the structure 2 to receive the fixing force of the nut 8.

  The ground anchor 1 includes a step of excavating an anchor hole 4 in the ground 3, a step of inserting a tension body 5 into the anchor hole 4, and a fixing material 6 is injected into the anchor hole 4 so that the lower end portion of the tension body 5 is grounded. A step of fixing inside, a step of temporarily attaching the nut 8 to the upper end of the tension body 5 via the anchor plate 7, a step of applying tension to the tension body 5 using a hydraulic jack (not shown), and tightening the nut 8 It is constructed through a process of fixing the tension body 5 and the like.

  And the tension | tensile_strength force provided to the tension body 5 acts as a pressing force on the structure 2 via the nut 8 and the anchor plate 7, and the structure 2 is fixed to the ground 3 by this pressing force. .

  Here, the tension body 5 is composed of a PC steel strand formed by a plurality of cables, a tension portion 9 formed by a rod-shaped shaft member, and a fixing member integrally connected to one end of the tension portion 9. 10 and a screw-shaped condominium part 11 integrally connected to the other end of the tension part 9. And most of this tension body 5 is embed | buried under the ground 3, and the edge part of the apartment part 11 is exposed from the ground 3. FIG.

  And the exposed part of the apartment part 11 is inserted in the insertion hole 7a of the anchor plate 7, and the anchor plate 7 is mounted in the structure 2. FIG. A nut 8 is screwed to the apartment portion 11 protruding from the anchor plate 7.

  At this time, as shown in FIG. 2A, stress in a direction to be drawn toward the lower end side of the tension body 5 acts on the anchor plate 7. That is, the anchor plate 7 is subjected to a tensile stress whose main stress direction is the direction toward the center of the insertion hole 7a indicated by the arrow in FIG.

  At this time, the magnitude of the tensile stress acting on the anchor plate 7 is proportional to the magnitude of the tension force of the tension body 5.

  Further, the tension force of the tension body 5 transmitted from the thread formed in the condominium part 11 to the thread groove of the nut 8 and the reaction force from the anchor plate 7 act on the nut 8. That is, the compressive stress which makes the axial direction (up-down direction) of the tension body 5 shown by the arrow in FIG.

  At this time, the magnitude of the compressive stress acting on the nut 8 is proportional to the magnitude of the tension force of the tension body 5.

  Moreover, since the tension | tensile_strength transmitted to the nut 8 is transmitted as a shearing force via the thread of the apartment part 12, the magnitude | size of the tension | tensile_strength transmitted by the position of the height direction of the nut 8 changes. . This tension force becomes maximum at the lower end (on the anchor plate 7 side) of the nut 8 and becomes minimum (zero) at the upper end.

  In the embodiment of the present invention, the measurement object in the magnetostriction measurement is the anchor plate 7 or the nut 8.

  3A and 3B, the measurement surface of the anchor plate 7 is an upper surface 7b spaced from the side surface 8a of the nut 8 by a predetermined distance, and the measurement position is a nut formed in a hexagonal shape in plan view. The six points (S1 to S6) are located opposite to the flat portion of the side surface 8a. Here, each measurement point S1-S6 is spaced apart symmetrically across the central axis O of the tension body 5.

  And it is set as the result of the magnetostriction measurement in the anchor plate 7 by averaging the measured value measured in each measurement point S1-S6. Thereby, the error by the position shift of the central axis O of the tension body 5, the dispersion | variation in the tension principal stress which is acting on the anchor plate 7, etc. can be suppressed.

  When the magnetostriction of the anchor plate 7 is measured, the magnetostrictive sensor is pressed so as to measure the tensile stress acting on the anchor plate 7.

  On the other hand, the measurement surface of the nut 8 is a side surface 8a as shown in FIGS. 3A and 3B, and the measurement position is substantially the center of the flat portion of the side surface 8a of the nut 8 formed in a hexagonal shape in plan view. There are 6 points (S7 to S12) located in the center in the lateral direction and in the height direction at a constant height from the anchor plate 7. Here, the measurement points S7 to S12 are symmetrically separated with the central axis O of the tension body 5 interposed therebetween.

  And it is set as the result of the magnetostriction measurement in the nut 8 by averaging the measured value measured in each measurement point S7-S12. Thereby, the error by the position shift of the central axis O of the tension body 5, the variation accompanying a measurement, etc. can be suppressed.

  When the magnetostriction of the nut 8 is measured, the magnetostrictive sensor is pressed so as to measure the compressive principal stress acting on the nut 8.

  Next, the tension | tensile_strength detection method of the tension material of this invention is demonstrated.

  In order to measure the tension force acting on the ground anchor 1 which is an existing tension material already installed, first, a predetermined number of ground anchors are selected from among a large number of ground anchors 1 installed at a certain site. Select 1. Hereinafter, the selected ground anchor 1 is referred to as a sample anchor SP.

  Here, the “certain site” indicates a group of ground anchors 1 in which the tension body 5, the anchor plate 7, the nut 8, and the like used in the ground anchor 1 are manufactured under substantially the same manufacturing conditions.

  Further, the “predetermined number” may be, for example, a fixed number arbitrarily set regardless of the total number of ground anchors 1 installed at a fixed site, or a predetermined ratio of the total number of ground anchors 1 (For example, about 5%). In consideration of workability and accuracy, a minimum of about 5 and a maximum of about 10 are desirable.

  Next, a magnetostriction sensor is pressed against a predetermined number of sample anchors SP and a magnetostrictive sensor is pressed at the same time to perform magnetostriction measurement.

  In order to apply tension to the sample anchor SP, first, a hydraulic jack or the like (not shown) is connected to the condominium part 11. Then, after the tension body 5 is pulled with a predetermined tension with a hydraulic jack or the like, the nut 8 is screwed into the apartment portion 11. As a result, the sample anchor SP is in a state (tension fixing state) where a tension force of a predetermined load level is applied.

  And in this tension fixed state, magnetostriction measurement is performed at measurement points S1 to S12 shown in FIG. Since this magnetostriction measurement method is well known, detailed description thereof is omitted.

  The magnetostriction value measured at each measurement point is obtained by averaging the magnetostriction values obtained in S1 to S6 for the anchor plate 7. Depending on the influence of residual stress, etc., some of the measured magnetostriction values may be rejected.

  Moreover, about the nut 8, it calculates | requires by averaging the magnetostriction value obtained by S7-S12. Depending on the influence of residual stress, etc., some of the measured magnetostriction values may be rejected.

  In this way, by averaging the results obtained at a plurality of measurement points, errors caused by eccentricity of the tension body 5 and variations in the reaction force acting on the anchor plate 7 are eliminated, and the measured magnetostriction value Accuracy can be improved.

  Thus, the relationship between the predetermined tension force and the magnetostriction value in each of the anchor plate 7 and the nut 8 when the tension force of the predetermined load level is acting (when the tension is fixed at the predetermined load level) is obtained. It is done.

  Next, the load level of the tension force applied to the sample anchor SP is changed from the above case, and the magnetostriction measurement of the anchor plate 7 and the nut 8 is performed again in a state where the tension force of the changed load level is applied. .

  Then, according to the same procedure as described above, predetermined tension in each of the anchor plate 7 and the nut 8 when a tension force of a load level different from the above is applied (when the tension is fixed at a load level different from the above). Find the relationship between force and magnetostriction.

  The above is repeated by applying a plurality of stages of load level tension, and the relationship between the tension in each of the anchor plate 7 and the nut 8 and the magnetostriction value is obtained.

  Further, a tension of various load levels is applied to all of the predetermined number of sample anchors SP, and at the same time, a magnetostriction sensor is pressed against the anchor plate 7 and the nut 8 to perform magnetostriction measurement.

  These results are plotted in a scatter diagram of tension and magnetostriction values as shown in FIG. 4, and an approximate expression indicating the correlation between the tension and magnetostriction is statistically obtained.

  Here, the approximate expressions to be obtained are different approximate expressions for the anchor plate 7 and the nut 8. That is, an approximate expression with the anchor plate 7 as a measurement target and an approximate expression with the nut 8 as a measurement target are obtained.

This approximate expression is, for example, Expression (1). In Equation (1), x represents a magnetostriction value. Here, K ₁ , K ₂ , C, and D are constants.

Tension ^{_{= K 1 x 2 -K 2 x}} + C (± D) ··· (1)
Further, a graph showing the correlation between the tension force and the magnetostriction value obtained from this approximate expression is as shown in FIG.

  In FIG. 4, a line A indicated by a solid line indicates an approximate expression obtained by the method of least squares, a line B indicated by a one-dot chain line positioned above the solid line A indicates, for example, a 90% confidence range upper limit, A line C indicated by an alternate long and short dash line located below the solid line A indicates, for example, a 90% confidence range lower limit.

  Thus, the ground anchor 1 actually installed at a certain site is selected as a sample, and the correlation between the tension force and the magnetostriction value obtained in the selected ampoule anchor SP is statistically processed. Is used to find an approximate expression.

  As a result, an approximate expression capable of grasping the degree of variation due to the anisotropy of the tissue such as the anchor plate 7 or the residual stress can be obtained.

  Subsequently, a magnetostriction sensor is pressed against the ground anchor 1 other than the sample anchor SP to perform magnetostriction measurement. Hereinafter, the ground anchor 1 other than the sample anchor SP is referred to as an investigation target anchor TA.

  The magnetostriction measurement of the survey target anchor TA is performed in the same manner as the sample anchor SP described above.

  Here, the magnetostriction value at the anchor TA to be investigated is also the average of the magnetostriction values measured at the measurement points S1 to S6 for the anchor plate 7, and the magnetostriction value measured at the measurement points S7 to S12 for the nut 8. The average of

  Thereby, the error which arises by the eccentricity of the tension body 5, the variation accompanying the measurement of the anchor plate 7, etc. can be excluded, and the precision of the measured magnetostriction value can be improved.

  Then, the magnetostriction value measured at the survey target anchor TA is substituted into the approximate expression, and the tension force acting on the survey target anchor TA is calculated.

  The approximate expression to be substituted when calculating the tension force may be an approximate expression with the anchor plate 7 as a measurement target or an approximate expression with the nut 8 as a measurement target. It is desirable to use an approximate expression that has a smaller (smaller) variation in the correlation between the tension and magnetostriction value obtained in the sample anchor SP.

  Further, when using an approximate expression with the anchor plate 7 as the measurement target, the measurement target in the survey target anchor TA is the anchor plate 7 and when using an approximate expression with the nut 8 as the measurement target, the survey target. A measurement object in the anchor TA is a nut 8.

  As described above, the tension of various load levels was applied to a predetermined number of sample anchors SP set for each fixed site, and at the same time, the magnetostriction sensor was pressed to measure the magnetostriction, and the tension was measured. An approximate expression indicating a correlation with the magnetostriction value is obtained. Thereafter, the magnetostriction measurement is performed on the survey target anchor TA at this site, and the magnetostriction value measured at the survey target anchor TA is substituted into the approximate expression obtained in advance to obtain the tension force acting on the survey target anchor TA. .

  By substituting the result of the magnetostriction measurement performed on the survey target anchor TA, which is an existing tension material already installed, into the approximate expression obtained based on the measured magnetostriction value of the magnetostriction measurement performed on the sample anchor SP, It becomes possible to detect the tension of the survey target anchor TA.

  Therefore, by performing magnetostriction measurement in the state where the investigation target anchor TA is used as it is, the tension force acting on the investigation target anchor TA can be easily and inexpensively obtained.

  Moreover, since the approximate expression which shows correlation with a tension | tensile_strength and a magnetostriction value is calculated | required using the sample anchor SP which is a part of tension material actually installed in the fixed site, each of predetermined number of sample anchor SP is obtained. By statistically processing the results showing the correlation between the predetermined number of tensions and magnetostriction values obtained with respect to the anisotropy and residual stress of the tissue possessed by each ground anchor 1 at this site The variation in the measured magnetostriction value can be grasped.

  That is, it is possible to grasp the degree of error included in the approximate expression by performing statistical processing when determining the approximate expression.

  Further, in the tension detecting method of the ground anchor 1 described above, the magnetostrictive sensor is pressed against a plurality of measurement points S1 to S6 and S7 to S12 that are symmetrically separated with the central axis O of the tension body 5 interposed therebetween to perform magnetostriction measurement. The magnetostriction value is obtained by averaging the measurement values measured at each measurement point.

  As a result, it is possible to eliminate errors in the measured magnetostriction value caused by the eccentricity of the tension body 5 and variations in tension due to the displacement of the measurement position where the magnetostrictive sensor is pressed, thereby improving the measurement accuracy of the magnetostriction value. It becomes possible.

  And in the tension | tensile_strength detection method of the above-mentioned ground anchor 1, the approximate expression which calculates | requires the correlation of tension | tensile_strength and a magnetostriction value is calculated | required by the least square method.

  As a result, when obtaining an approximate expression, it is possible to easily obtain a highly accurate approximate expression that is closer to the actual. In the above-described embodiment, an approximate expression using a quadratic expression is used. However, the present invention is not limited to this and may be arbitrarily set such as a cubic expression or a quartic expression.

  As mentioned above, although embodiment concerning this invention has been explained in full detail with drawing, a concrete structure is not restricted to the above-mentioned embodiment. Design changes and the like within the scope not departing from the gist of the present invention are included in the present invention.

  For example, in the above-described embodiment, the magnetostrictive sensor is pressed against the plurality of measurement points S1 to S12 to perform magnetostriction measurement. However, the number and positions of the measurement points are not limited to those described above, and accuracy, workability, etc. It is possible to change appropriately considering the above.

  Further, even if the magnetostrictive sensor is pressed so as to measure the main stress direction acting on the anchor plate 7 or the nut 8, it is pressed so as to measure the stress acting in the direction orthogonal to the direction in which the main stress acts. Or any case.

  Furthermore, in the above-described embodiment, the tension material imparts a tension force by tightening the nut 8. However, the present invention is not limited to this, and the tension body is sandwiched between the fixing member and the tension body. It may be of a wedge fixing system that fixes and applies tension.

  Even in this case, for the anchor plate, the correlation between the tension force and the magnetostriction value can be obtained according to the above-described method.

  Further, the fixing member in this case becomes an anchor disk instead of the nut 8, and the correlation between the tension force and the magnetostriction value may be obtained by using the anchor disk as a measurement target.

It is explanatory drawing which shows the whole structure of a ground anchor. (A) is explanatory drawing which shows the exposed part of a ground anchor, and sectional drawing which showed the outline of the stress which acts, (b) shows explanatory drawing which shows the exposed part of a ground anchor, and the outline of the stress which acts FIG. (A) is a top view which shows the measuring point of an anchor plate and a nut, (b) is a perspective view which shows the measuring point of an anchor plate and a nut. It is a graph which shows an example of the correlation with tension force and the output value of a magnetostriction sensor.

Explanation of symbols

1 Ground anchor

Claims (4)

Magnetostriction measurement is performed by pressing a magnetostrictive sensor against an exposed portion of the tendon embeded in the ground, and the tension force acting on the tendon is detected based on the measured magnetostriction value. In the method
The tendon is a long and penetrating body that penetrates the structure, a fixing member that fixes to the upper end of the tension body and applies tension to the tension body, the fixing member, and the structure And an anchor plate that receives the fixing force of the fixing member.
For a predetermined number of tension bodies set for each fixed site, tension force of various load levels was applied, and at the same time, the magnetostriction sensor was pressed against the anchor plate to measure magnetostriction, and the tension force was measured. After obtaining an approximate expression showing the correlation with the magnetostriction value,
The magnetostrictive sensor is pressed against the anchor plate of the other tension material at this site to measure the magnetostriction, and the measured magnetostriction value is substituted into the approximate expression to obtain the tension force acting on the other tension material. A method for detecting a tension force of a tendon, characterized in that it is obtained. When a predetermined number of tension bodies set for each fixed site are applied with tension of various load levels and simultaneously when magnetostriction measurement is performed by the magnetostriction sensor, the magnetostriction is applied to the fixing member in addition to the anchor plate. Measure the magnetostriction by pressing the sensor,
An approximate expression showing a correlation between a tension force and a magnetostriction value measured using the anchor plate as a measurement object, and an approximate expression showing a correlation between a tension force and a magnetostriction value measured using the fixing member as a measurement object; After asking
Measuring the magnetostriction by pressing the magnetostrictive sensor against the anchor plate or the fixing member of the other tension material at this site,
The magnetostriction value measured using the anchor plate as a measurement object is substituted into an approximate expression indicating the correlation between the tension force and the magnetostriction value measured using the anchor plate as a measurement object,
The magnetostriction value measured using the fixing member as a measurement target is substituted into an approximate expression indicating the correlation between the tension and the magnetostriction value measured using the fixing member as a measurement target.
The tension force detecting method for a tension material according to claim 1, wherein a tension force acting on another tension material is obtained . 2. The magnetostriction measurement is performed by pressing a plurality of measurement points that are symmetrically spaced across the central axis of the tendon, and the magnetostriction value is obtained by averaging the measurement values measured at each measurement point. The tension | tensile_strength detection method of the tension material of 1 or 2. The tension force detecting method according to any one of claims 1 to 3, wherein the approximate expression is obtained by a least square method.

Images