JP2010181277A - Method of measuring axial force of tensioning material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring the axial force of a tensioning material and capable of accurately measuring a maximum load received by the tensioning material in the past and accurately measuring an axial force acting on the tensional material at present. <P>SOLUTION: The axial force measuring method includes both the step of bringing magnetostrictive sensors into contact with a plurality of sections to be measured in the side of a nut 3 and aligned in an axial direction and measuring an output voltage of a magnetostrictive sensor in each section to be measured and the step of estimating a maximum load received by a cable 1 after the cable 1 is embedded on the basis of the shape of a curve made of output voltages of the magnetostrictive sensors at the plurality of sections to be measured and estimating a load received by the cable 1 at present on the basis of the shape of the curve made of the output voltages of the magnetostrictive sensors at the plurality of sections to be measured and at least one output voltage among the output voltages of the magnetostrictive sensors at the plurality of sections to be measured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for measuring the axial force of a tendon, and more particularly, to a method for measuring the axial force of a tendon that is buried in the ground and fixed by a nut.

  For example, tension materials embedded in the ground, such as anchors used in power plants using underground cavities, are conventionally known. In order to use the structure safely and in the long term, it is necessary to establish a maintenance method.

  In JP-A-2007-155475 (Patent Document 1), a magnetostriction sensor is pressed against an exposed portion of a ground anchor (tension material) embedded in the ground to perform magnetostriction measurement, and based on the measured magnetostriction value. It has been shown to detect tension forces acting on ground anchors.

JP 2007-155475 A

  In Patent Document 1, a correlation between a detection voltage by a magnetostriction method and a tension load is obtained in advance, and the voltage of an existing ground anchor is determined based on the voltage output by on-site magnetostriction measurement and the information on the correlation. It is supposed to detect tension.

  However, depending on the behavior of the surrounding rock mass, this tension may decrease after the tension of the ground anchor increases. When a part of the exposed portion is plastically deformed when the tension is maximized, the strain does not completely return even if the load is reduced thereafter. For this reason, even if the output voltage of the magnetostriction measurement is the same between the state in which the tension force is increasing and the state in which the tension force is decreased after the tension force is increased until the measurement location is plastically deformed, Tension (axial force) is different.

  Such a situation is not taken into consideration in the tension detection method described in Patent Document 1, and the current axial force cannot always be accurately measured with this method. Further, when the axial force decreases after the axial force increases until a part of the nut is plastically deformed, the maximum load received in the past cannot be detected.

  The present invention has been made in view of the above problems, and one object of the present invention is to provide an axial force of a tendon that can accurately measure the maximum load that the tendon has received in the past. It is to provide a measurement method. Another object of the present invention is to provide a method for measuring the axial force of a tendon capable of measuring an accurate axial force currently acting on the tendon.

  The method for measuring the axial force of a tendon according to the present invention is a method for measuring the axial force of a tendon that is buried in the ground and fixed by a nut.

  In one aspect, the above axial force measurement method includes a step of contacting the magnetostrictive sensor with a plurality of measurement locations arranged in the axial direction on the side surface of the nut and measuring the output voltage of the magnetostriction sensor at each measurement location; And estimating a maximum load received by the tendon after the tendon is embedded based on the shape of the curve formed by the output voltage of the magnetostrictive sensor at the measurement location.

  In one embodiment, in the axial force measurement method, the step of estimating the maximum load includes estimating the maximum load based on a position where the output voltage of the magnetostrictive sensor has a peak at a plurality of measurement locations.

  In one embodiment, in the axial force measurement method, when the output voltage of the magnetostrictive sensor at a plurality of measurement points increases from the upper side of the nut toward the ground side and then decreases, the magnetostrictive sensor at the plurality of measurement points. It is detected that the maximum load is relatively high as compared with the case where the output voltage increases substantially monotonically from the upper side of the nut toward the ground side. In the present specification, “the upper side of the nut” means the opposite side of the underground side.

  In another aspect, the axial force measuring method includes a step of contacting the magnetostrictive sensor with a plurality of measurement locations arranged in the axial direction on the side surface of the nut and measuring the output voltage of the magnetostriction sensor at each measurement location; Estimating a current load applied to the tendon material based on the shape of a curve composed of the output voltage of the magnetostrictive sensor at the measurement location and at least one output voltage among the output voltages of the magnetostriction sensor at the plurality of measurement locations; Is provided.

  In one embodiment, in the above axial force measurement method, the step of estimating the current load includes the position where the output voltage of the magnetostrictive sensor at the plurality of measurement points shows a peak, and the output voltage of the magnetostrictive sensor at the plurality of measurement points. Estimating a current load based on at least one of the output voltages.

  In one embodiment, in the axial force measurement method, the current load is estimated based on the output voltage of the magnetostrictive sensor at the measurement location closest to the axial center of the nut among the plurality of measurement locations.

  According to the present invention, as one effect, it is possible to provide an axial force measurement method for a tendon that can accurately measure the maximum load that the tendon has received in the past. Further, as another effect, it is possible to provide an axial force measuring method for a tendon that can measure an accurate axial force that currently acts on the tendon.

It is the schematic of the underground anchor which concerns on one embodiment of this invention. It is a figure (the 1) which shows the measurement result by the magnetostriction sensor in the state which made axial force act on a nut. It is a figure (the 2) which shows the measurement result by the magnetostriction sensor in the state which made axial force act on a nut. It is FIG. (The 3) which shows the measurement result by the magnetostriction sensor in the state which made axial force act on a nut. It is FIG. (4) which shows the measurement result by the magnetostriction sensor in the state which made axial force act on a nut. It is a figure (the 5) which shows the measurement result by the magnetostriction sensor in the state which made axial force act on a nut. It is a figure (the 6) which shows the measurement result by the magnetostriction sensor in the state which made axial force act on a nut. It is a figure which shows the measurement location by the magnetostriction sensor in the axial force measuring method of the tendon material which concerns on one embodiment of this invention. It is a figure (the 1) which shows the measurement result by the magnetostriction sensor in each position of the nut in each load state in a laboratory experiment. It is FIG. (2) which shows the measurement result by the magnetostriction sensor in each position of the nut in each load state in a laboratory experiment. It is a figure (the 3) which shows the measurement result by the magnetostriction sensor in each position of the nut in each load state in a laboratory experiment. It is FIG. (4) which shows the measurement result by the magnetostriction sensor in each position of the nut in each load state in a laboratory experiment. It is FIG. (5) which shows the measurement result by the magnetostriction sensor in each position of the nut in each load state in a laboratory experiment. It is FIG. (6) which shows the measurement result by the magnetostriction sensor in each position of the nut in each load state in a laboratory experiment. It is a figure (the 1) which shows the measurement result by the magnetostriction sensor in each position of the nut by field measurement. It is a figure (the 2) which shows the measurement result by the magnetostriction sensor in each position of the nut by field measurement. It is the figure (the 3) which shows the measurement result by the magnetostriction sensor in each position of the nut by field measurement. It is a figure (the 4) which shows the measurement result by the magnetostriction sensor in each position of the nut by field measurement. It is FIG. (5) which shows the measurement result by the magnetostriction sensor in each position of the nut by field measurement. It is a figure (the 6) which shows the measurement result by the magnetostriction sensor in each position of the nut by field measurement. It is a figure (the 7) which shows the measurement result by the magnetostriction sensor in each position of the nut by field measurement. It is a figure which shows collectively the measurement result shown in FIGS. It is a figure which shows typically the characteristic of the voltage distribution in a nut side surface. It is a flowchart (the 1) which shows the axial force measuring method of the tension material which concerns on one embodiment of this invention. It is a flowchart (the 2) which shows the axial force measuring method of the tension material which concerns on one embodiment of this invention. It is a flowchart (the 3) which shows the axial force measuring method of the tension material which concerns on one embodiment of this invention.

  Embodiments of the present invention will be described below. Note that the same or corresponding portions are denoted by the same reference numerals, and the description thereof may not be repeated.

  Note that in the embodiments described below, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified. In the following embodiments, each component is not necessarily essential for the present invention unless otherwise specified.

  The method for measuring the axial force of a tendon according to the present embodiment is applied to, for example, measuring the axial force of an underground anchor. The underground anchor is used, for example, in a power generation facility using an underground cavity, and is inserted into the rock from the wall surface of the underground power station cavity.

  FIG. 1 is a schematic view of an underground anchor according to the present embodiment. As shown in FIG. 1, the underground anchor includes a cable 1 as a “tension material” on which an axial force acts, an anchor plate 2, and a nut 3. One end of the cable 1 is fixed to the rock in the fixing unit 4. The other end of the cable 1 is inserted into the anchor plate 2, and a nut 3 is screwed to the other end. The other end of the cable 1, the anchor plate 2, and the nut 3 are exposed from the rock.

  The cable 1 is introduced with an axial tensile force (axial force). At this time, the nut 3 receives a force toward the right side in FIG. 1 from the cable 1 in a screwed relationship, and receives a force toward the left side in FIG. 1 from the anchor plate 2 as the reaction force. As a result, compressive stress acts on the nut 3. Here, when the axial force of the cable 1 increases, the compressive stress of the nut 3 also increases correspondingly. The axial force measurement method according to the present embodiment uses this property to measure the axial force of the existing cable 1 embedded in the rock. In other words, the axial force measurement method according to the present embodiment uses the magnetostrictive stress measurement method (magnetostriction method) after obtaining the correlation between the axial force of the cable 1 and the compressive stress generated in the nut 3 in advance. The stress of the nut 3 is measured and the current axial force and the like of the cable 1 are estimated based on the measurement result and the correlation. The inventor of the present application previously measured the residual stress of the nut 3 and compared with the anchor plate 2 or the like, the ratio of variation for each product is relatively low, and the measurement target for estimating the axial force of the cable 1 is as follows. It is confirmed that it is suitable.

  In the magnetostriction method, the probe around which the detection coil is wound is brought into contact with the nut 3, a magnetizing current is passed, and the magnetic potential changes due to the magnetic anisotropy induced by the stress. The generated voltage is detected and the detected voltage is converted to obtain the stress. However, since the magnetostriction method itself is a generally well-known method, a detailed description of the method and the apparatus used therefor is not provided. Omitted.

  Next, an example of how to obtain the correlation between the axial force of the cable 1 and the compressive stress generated in the nut 3 will be described.

  The inventor of the present application changes the magnitude of the compressive load acting on the nut from the cable and the anchor plate in the laboratory in order, and for each of the magnitudes of load, in the plural (here, six) side faces of the nut. Magnetostriction measurement was performed at a predetermined measurement location (here, the center of the side surface). Here, as shown in Table 1, magnetostriction measurement was performed by giving three different patterns of load fluctuations to six nuts A to F of the same type. 2-7 is a figure which shows this measurement result.

  2 to 7 show the measurement results of the nuts A to F, respectively. In FIGS. 2 to 7, “Face 1” to “Face 6” are the respective measurement results on the six side surfaces of the nut. “Ave” indicates the average of the measurement results in the six aspects.

  As shown in FIGS. 2 to 7, the above measurement result is almost stable when looking at the “Ave” curve of each nut, although there is a slight backlash due to variations due to manual work and variations in characteristics of each nut. It can be seen that the measured results are obtained.

  Moreover, as shown in FIGS. 2-7, when the load which acts on a nut is increased, the voltage measured by a magnetostriction sensor will also change according to it (it decreases here), but when reducing a load after that, The voltage measured by the magnetostrictive sensor is not completely restored. That is, the curves shown in FIGS. 2 to 7 show a state in which the load increases (referred to as “loading state” in the present specification) and a state in which the increased load decreases (in the present specification, “unloading”). The load (kN) -voltage (V) curves have different shapes. 2 to 7 are curves in the loaded state, and curves located in the lower left side in FIGS. 2 to 7 are curves in the unloaded state.

  Thus, the correlation between the axial force (kN) of the cable and the output voltage (V) of the magnetostrictive sensor differs depending on whether the cable is in the loaded state or unloaded state. Therefore, even if the output voltage of the magnetostrictive sensor is the same, the axial force of the cable to be estimated differs between when the cable is in the loaded state and when it is in the unloaded state. On the other hand, even if the current axial force of the cable is the same, the output voltage of the magnetostrictive sensor differs between when the cable is in the loaded state and when it is in the unloaded state. Further, as described later, the second and subsequent loading states following the unloading state tend to be different from the first loading state. Therefore, the current load cannot always be accurately estimated from the output voltage of the magnetostrictive sensor without grasping the cable load history.

  The above phenomenon is considered to be due to plastic deformation of a part of the nut when the load acting on the nut increases to a certain value or more. In the plastically deformed portion, even if the load decreases thereafter, the strain does not completely return to the original state. Therefore, the load (kN) -voltage (V) curve in the unloaded state is the load (kN)-in the loaded state. The shape is different from the voltage (V) curve.

In addition, this inventor calculated | required an example of the load (kN) -voltage (V) in the 1st loading state based on the measurement result shown in FIGS. 2-7, and some other measurement results. . In this example, the load (kN) is “y” and the voltage (V) is “x”.
y = 892.33x ⁴ + 1603.1x ³ + 223.88x ² -1215.8x + 137.57 (1)
It becomes. The curve in the unloading state can also be obtained from the measurement results shown in FIGS. 2 to 7 as in the loading state.

  Next, measurement points by the magnetostrictive sensor in the cable axial force measurement method according to the present embodiment will be described with reference to FIG. The axial force measurement method according to the present embodiment is characterized in that magnetostriction measurement is performed at a plurality of measurement points provided in the axial direction of the nut 3, as shown in FIG. As shown in FIG. 8, in this embodiment, magnetostriction measurement is performed at five measurement locations “1” to “5”. In FIG. 8, the measurement point “3” is located at the center of the side surface of the nut 3, and the measurement points “2” and “4” are shifted in the axial direction by 5 mm from the measurement point “3”. The measurement points “1” and “5” are in positions shifted in the axial direction by 5 mm from the measurement points “2” and “4”, respectively. As a result, five measurement locations that are 5 mm apart in the axial direction of the nut 3 are set.

  In the example of FIG. 8, the lower side in FIG. 8 is the side close to the anchor plate (underground side). That is, in the example of FIG. 8, the measurement location “1” is the measurement location farthest from the rock, and the measurement location “5” is the measurement location closest to the rock.

  The inventor of the present application measures the plurality of (here, five) measurements on the nut for each magnitude of load while sequentially changing the magnitude of the compressive load acting on the nut from the cable and anchor plate in the laboratory. Magnetostriction measurement was performed at the location. Here, as shown in Table 2, magnetostriction measurement was performed by giving three different patterns of load fluctuations to six nuts G to L of the same type. 9-14 is a figure which shows this measurement result.

  9 to 14 show the measurement results of the nuts G to L, respectively. In FIGS. 9 to 14, “Load” and “Unload” indicate the loaded state and the unloaded state, respectively. “0 kN”, “294 kN”,..., “980 kN” indicate the magnitude of the load acting on the nut, respectively. “1st” and “2nd” It shows that it is the loading state / unloading state of the 2nd time and the 2nd time.

  As can be seen from the measurement results shown in FIGS. 9 to 14, when the load is not so large in the first loading state (specifically, in the case of “(1st) Load-294 kN”), “1” to “ The voltage tends to decrease substantially monotonously (that is, the stress increases substantially monotonically) toward the measurement location of “5”. However, when the load increases more than a certain value (specifically, in the case of “(1st) Load-686 kN”, etc.), a peak value is generated in the voltage distribution, and plasticity occurs around the measurement point “5” close to the anchor plate. It can be seen that deformation has occurred. This tendency is maintained even when the load is further increased (specifically, in the case of “(1st) Load-784kN”, etc.), and after unloading once, the state is again loaded and the load is so large. It is maintained even when there is not (specifically, in the case of “2ndLoad-294 kN” shown in FIGS. 11 to 14).

  Further, comparing the results shown in FIGS. 9 and 10 with the results shown in FIGS. 11 to 14, the shape of “Unload-0kN” in FIGS. 9 and 10 is “1stUnload−” shown in FIGS. 11 to 14. The tendency does not necessarily match the shape of “0 kN”, but the tendency matches well with the shape of “2ndUnload-0 kN” shown in FIGS. In the examples of FIGS. 9 and 10, the maximum load is 980 kN, whereas in the examples of FIGS. 11 to 14, the maximum load of the first load is 686 kN or 784 kN, and the maximum load of the second load is 980 kN. From this result, it is understood that the tendency of the shape of the voltage distribution curve in the unloaded state is determined by the magnitude of the maximum load received in the past regardless of the number of times of loading / unloading.

  In this way, by providing a plurality of measurement points in the axial direction and analyzing the distribution curve of the output voltage from the magnetostrictive sensor, it is possible to know the load history (especially the maximum load received so far) acting on the cable. it can. As a result, the output voltage of the magnetostrictive sensor (here, the measurement result of “3” located in the center of the side surface of the nut) and the load (kN) −voltage calculated from the experimental results shown in FIGS. It is possible to estimate the axial force of the cable based on the correlation of V).

  The inventor of the present application performed magnetostriction measurement at the plurality of (here, five) measurement points on the nuts provided on the plurality (here, seven) of anchors by on-site measurement.

  15 to 21 show the measurement results of the anchors “A” to “K”, respectively. In FIGS. 15 to 21, “Face 1” to “Face 6” are the six side faces of the nut. Each measurement result is indicated, and “Ave” indicates an average of the measurement results in the six aspects. Further, FIG. 22 is a diagram comprehensively showing the measurement results (“Ave” curves) shown in FIGS.

  With reference to FIGS. 15 to 17 (see also FIG. 22), for anchors “A” to “C”, the absolute value of the output voltage is greatly reduced at the measurement point “5”. On the other hand, the load increases, and it can be seen that a part of the nut is plastically deformed on the anchor plate side.

  18 and 19 (see also FIG. 22), the anchors “e” and “o” are compared with the anchors “a” to “c” (FIGS. 15 to 17). The amount of decrease in the absolute value of the output voltage at the measurement point of “5” is small. Compared with the anchors “A” to “C”, the increase in load from construction is much larger for the anchors “E” and “O”. I understand that there is no.

  Referring to FIG. 20 (refer to FIG. 22 as well), the absolute value of the output voltage of the anchor “K” is low overall, but the absolute value of the output voltage is decreased at the measurement point “5”. Therefore, it is considered that the load is slightly increased compared to the time of construction.

  Referring to FIG. 21 (refer to FIG. 22 together), regarding the anchor “ki”, the voltage value variation on the six surfaces of the nut is large, but the average value of the six surfaces is the entire axial direction of the nut. Since it shows a low absolute value, it is thought that the load was consistently low from the time of construction. In FIG. 21, the large variation in voltage value on the six surfaces of the nut is considered to be due to boundary conditions such as the axial direction of the cable and the anchor plate not being provided at right angles. It is possible to reduce measurement errors due to such boundary conditions by performing measurement on six surfaces.

  As described above, it can be seen that the anchors “a” to “ki” are placed in different states, but in any case, the axial force of the cable can be estimated by the above-described equation (1). This is considered to be in the range. Table 3 shows estimated loads obtained by substituting the output voltage at the measurement point “3” of the anchors “A” to “K” into x in the expression (1). In addition, in order to examine the validity of this estimated load, the inventor of the present application obtained the lift-off loads of the anchors “D”, “O”, and “K” in the field, and the results are also shown in Table 3. The lift-off load is a load when the anchor cable is pulled using a jack at the site and the nut starts to move away from the anchor plate, and corresponds to an actual load currently acting on the cable.

  Referring to Table 3, in any of the anchors “D”, “O”, and “K”, the estimated load described above and the actually measured lift-off load agree well. Thereby, the validity of the axial force estimation method is shown.

  FIG. 23 is a diagram schematically illustrating the characteristics of the voltage distribution on the side surface of the nut. With reference to FIG. 23, the above-described contents will be described generally.

  In FIG. 23, a curve A shows a typical voltage distribution when the cable has never received a large load, and an area A0 shows a voltage distribution region when the cable has never received a large load. Is shown. Similarly, curve B shows the voltage distribution when the load acting on the cable is increased (when in a loaded state) as compared to curve A. Similarly, the curve C shows the voltage distribution at the stage where the load acting on the cable reaches a certain value (for example, 588 kN) or more and plasticization has started locally from the bottom of the nut (portion close to the anchor plate). Point C0 indicates the peak point of the voltage distribution that appears after local plasticization has started. Similarly, curve D shows the voltage distribution at the stage where the load acting on the cable further increases and the peak of voltage distribution (point D0) shifts to the left (upper side of nut) compared to curve C. It is. Similarly, a curve E shows a voltage distribution when a large load is received in the past and then unloaded. The curve E is characterized in that the peak of voltage distribution (point E0) is located at the upper part of the nut, and the voltage at the lower part of the nut is large.

  As shown in FIG. 23, when the load acting on the cable is relatively small (curve B), the voltage distribution is a so-called triangular distribution. When the load exceeds a certain value, plasticization starts from the bottom of the nut, and a peak appears in the voltage distribution (curve C). Thereafter, when the load increases, the peak position moves to the upper side of the nut, and the absolute value of the voltage at the lower side becomes smaller (curve D). When unloaded from that state, the peak position slightly moves to the upper side of the nut, while the voltage at the lower side is greatly shifted to the positive side (curve E).

  Thus, in the present embodiment, the maximum load is estimated based on the position where the output voltage of the magnetostrictive sensor shows a peak.

  In the present embodiment, when the output voltage of the magnetostrictive sensor at a plurality of measurement points increases from the upper side of the nut toward the ground side and then decreases (in the case of C, D, and E in FIG. 23), a plurality of Compared with the case where the output voltage of the magnetostrictive sensor at the measurement point increases substantially monotonically from the upper side of the nut toward the ground side (in the case of B in FIG. 23), the maximum load received by the cable in the past is relatively Detecting high.

  Further, in the present embodiment, one of the positions (C0, D0, E0 in FIG. 23) at which the output voltage of the magnetostrictive sensor at the plurality of measurement points shows a peak and the output voltage of the magnetostrictive sensor at the plurality of measurement points. The current load is estimated based on the voltage (the output voltage at “3” in FIG. 8).

  As described in detail above, the inventors have studied and found that there is a correlation between the characteristics of the output voltage distribution of the magnetostrictive sensor and the current load received by the cable and the maximum load received in the past. It has also been found that a more detailed study can be performed on anchors for which lift-off load is not required. By using this axial force measurement method, it is possible to measure a large number of anchors. By comprehensively analyzing the results, the behavior of the surrounding rock mass can be understood in more detail, and safety management of the entire underground cavity can be performed. Can help.

  The above contents are summarized as follows. That is, the axial force measurement method according to the present embodiment is a method for measuring the axial force of the cable 1 (tension material) embedded in the ground and fixed by the nut 3. As one example, FIG. As shown in FIG. 25, the maximum load received in the past is estimated (S12). As another example, as shown in FIG. 25, the current axial force is estimated (S22). As an example, as shown in FIG. 26, both the maximum load received in the past and the current axial force are estimated (S32).

  That is, in the example shown in FIG. 24, the magnetostrictive sensor is brought into contact with a plurality of measurement locations (for example, 5 locations shown in FIG. 8) arranged in the axial direction on the side surface of the nut 3, and the output voltage of the magnetostriction sensor at each measurement location is obtained. Based on the measurement step (S11) and the shape of the curve formed of the output voltage of the magnetostrictive sensor at a plurality of measurement locations (for example, the shape of the curve shown in FIGS. 15 to 21), the cable 1 receives the cable 1 after being embedded. Estimating the maximum load (S12).

  In the example shown in FIG. 25, the magnetostrictive sensor is brought into contact with a plurality of measurement points (for example, five points shown in FIG. 8) arranged in the axial direction on the side surface of the nut 3, and the output voltage of the magnetostrictive sensor at each measurement point is obtained. Of the measuring step (S21), the shape of the curve composed of the output voltages of the magnetostrictive sensor at a plurality of measurement locations (for example, the shape of the curve shown in FIGS. 15 to 21), and the output voltage of the magnetostriction sensor at the plurality of measurement locations Estimating the current load received by the cable 1 based on one output voltage (for example, the output voltage at “3” shown in FIG. 8).

  In the example shown in FIG. 26, the magnetostrictive sensor is brought into contact with a plurality of measurement locations (for example, 5 locations shown in FIG. 8) arranged in the axial direction on the side surface of the nut 3, and the output voltage of the magnetostriction sensor at each measurement location is obtained. Based on the measurement step (S31) and the shape of the curve composed of the output voltage of the magnetostrictive sensor at a plurality of measurement locations (for example, the shape of the curve shown in FIGS. 15 to 21), the cable 1 receives after the cable 1 is embedded. The maximum load is estimated, and the shape of the curve composed of the output voltages of the magnetostrictive sensor at a plurality of measurement locations (for example, the shape of the curve shown in FIGS. 15 to 21) and the output voltage of the magnetostriction sensor at the plurality of measurement locations A step (S32) of estimating a current load received by the cable 1 based on one output voltage (for example, the output voltage at “3” shown in FIG. 8). Obtain.

  Note that the output voltage of the magnetostrictive sensor referred to when estimating the current load received by the cable is not necessarily one, and the current load is estimated based on the output voltage of the magnetostrictive sensor at two or more measurement locations. May be.

  Although the embodiments of the present invention have been described above, the embodiments disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 cable, 2 anchor plate, 3 nut, 4 fixing part.

Claims (6)

A method for measuring the axial force of a tendon material embedded in the ground and fixed by a nut,
Measuring the output voltage of the magnetostrictive sensor at each of the measurement locations by bringing a magnetostriction sensor into contact with the plurality of measurement locations arranged in the axial direction on the side surface of the nut;
An axial force measurement of the tendon material, comprising: estimating a maximum load received by the tendon material after the tendon material is embedded based on a shape of a curve composed of an output voltage of the magnetostrictive sensor at the plurality of measurement locations. Method.   The tension material shaft according to claim 1, wherein the step of estimating the maximum load includes estimating the maximum load based on a position where an output voltage of the magnetostrictive sensor at the plurality of measurement points shows a peak. Force measurement method.   When the output voltage of the magnetostrictive sensor at the plurality of measurement points decreases after increasing from the upper side of the nut toward the ground side, the output voltage of the magnetostrictive sensor at the plurality of measurement points is increased above the nut. The method for measuring an axial force of a tendon according to claim 2, wherein the maximum load is detected to be relatively high as compared with a case where the maximum load increases substantially monotonously from the ground toward the ground. A method for measuring the axial force of a tendon material embedded in the ground and fixed by a nut,
Measuring the output voltage of the magnetostrictive sensor at each of the measurement locations by bringing a magnetostriction sensor into contact with the plurality of measurement locations arranged in the axial direction on the side surface of the nut;
Based on the shape of the curve composed of the output voltage of the magnetostrictive sensor at the plurality of measurement locations and at least one output voltage among the output voltages of the magnetostriction sensor at the plurality of measurement locations, A method for measuring an axial force of a tendon, comprising a step of estimating a load.   The step of estimating the current load includes a position at which the output voltage of the magnetostrictive sensor at the plurality of measurement points shows a peak, and at least one output voltage among output voltages of the magnetostrictive sensor at the plurality of measurement points. The method for measuring an axial force of a tendon according to claim 4, comprising estimating the current load based on the current load.   The method for measuring an axial force of a tendon according to claim 5, wherein the current load is estimated based on an output voltage of the magnetostrictive sensor at a measurement location closest to an axial center of the nut among the plurality of measurement locations. .

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