JP2006162394A - Washer for stress measurement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve furthermore measurement accuracy by reducing labor when measuring a tensile stress loaded on a steel rod, reducing cost in the whole system, and realizing easily accurate zero setting. <P>SOLUTION: This washer 2 for stress measurement is interposed between a flat plate 13 disposed so that at least the tip of a male screw part is remained and a support nut 15 screwed with the male screw part of the steel rod 12. As for the washer 2 for stress measurement, each projection part 23 capable of abutting on the support nut 15 and each projection part 24 capable of abutting on the flat plate 13 are formed beforehand on three spots approximately on the same positions on the upper surface 21 and the bottom surface 22 respectively, and strain gages 28 are stuck beforehand on the outer peripheral side surface 26 on three spots in correspondence to the positions of each projection part 23, 24. The tensile stress is measured based on a strain in the axial direction detected by the strain gages 28. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a washer for stress measurement, a stress measurement system, and a stress measurement method suitable for measuring a tensile stress applied to a steel rod having a male thread portion protruding from an end portion.

  The tensile stress applied to the PC steel bar used in the prestressed concrete (PC) structure changes over time based on friction, elastic change of the concrete, and relaxation of the PC steel bar itself. As a result, there is a possibility that after a long time has passed, there is a possibility that the installed PC steel bar will not be able to exhibit a desired tension state. Therefore, in order to avoid this, the tension applied to the PC steel bar Various methods for detecting stress in real time have been devised.

  FIG. 5 shows a measurement system 8 that measures the actual tensile stress in real time via the strain applied to the PC steel bar. In this measurement system 8, after the placed concrete 81 reaches a predetermined strength, the PC steel rod 82 inserted through a sheath or the like is tensioned by a connected jack (not shown), and the end of the PC steel rod 82 is further tightened. 83 is fixed by the fixing device 84, respectively. Thereafter, by opening a jack (not shown), it is possible to introduce so-called prestress to the concrete 81.

  At this time, on the outer peripheral side surface 82a of the PC steel rod 82, a strain gauge 86 is attached in advance, and the strain gauge 86 is connected to the switch box 87, and further this switch box 87 is connected to the strain measuring instrument 88. Keep it.

  As a result, the strain generated in the PC steel rod 82 caused by the tension described above can be detected by the strain gauge 86, and the detected strain is signaled in the switch box 87, and finally the strain measuring device 88. Will be quantified. The actual tensile stress applied to the PC steel rod 82 can be obtained from the strain obtained by the strain measuring device 88.

  By the way, in the measurement system 8 as described above, strain gauges must be attached to the outer peripheral side surface 82a for all the PC steel bars for which tensile stress is to be obtained, which increases the burden of labor and thus extends the construction period itself. There is a problem that. In addition, since the conventional measurement system 8 is based on the idea of constructing one system from the strain gauge 86, the switch box 87, and the strain measuring device 88, the cost of the entire system becomes enormous. There is also a problem that it is inconvenient to carry.

  In general, when measuring strain with a strain gauge, the voltage value from the strain gauge affixed to the PC steel rod 82 in an unloaded state is measured before the actual strain measurement. It is necessary to perform so-called zero setting in which the voltage value is set as a zero point. However, the conventional measurement system 8 has a problem in that it is difficult to accurately set the zero point in many cases when the PC steel rod 82 itself is subjected to some load at the stage of attaching the strain gauge.

  Furthermore, conventionally, the tensile stress of such a PC steel bar has been measured by a load cell. When actually measuring the tensile stress of a PC steel bar with this load cell, a load cell is provided at a location to be measured, a load applied from the PC steel bar is sensed, and this is converted into an electrical signal. By analyzing such an electrical signal with a measuring device, the tensile stress can be measured with very high resolution.

  However, such a load cell is generally expensive, and there is a problem in that the cost associated with the measurement becomes enormous if the load cell is disposed at all the locations to be measured.

  Further, if the tensile stress is measured using a load cell, the stress should be uniformly applied to the pressure receiving surface. In particular, when the concrete 81 and the PC steel rod 82 in FIG. 5 described above are uneven, there is a possibility that stress is not applied evenly to the arranged load cells, and high-precision measurement cannot be realized. Further, since the pressure receiving surface of the load cell is planar, the load cell arrangement state itself is likely to be unstable when it is brought into contact with the uneven surface.

  Therefore, the present invention has been devised in view of the above-mentioned problems, and the purpose thereof is to reduce the burden of labor more when measuring the tensile stress loaded on the steel rod, To provide a stress measuring washer, a stress measuring system, and a stress measuring method capable of reducing the cost of the entire system and further improving measurement accuracy by making it possible to easily realize more accurate zero setting. is there.

  In order to solve the above-described problems, a stress measuring washer according to the present invention is a stress measuring washer for measuring a tensile stress applied to a steel rod having a male thread protruding from an end. A projection that is interposed between a flat plate disposed so as to leave at least the tip and a support nut screwed into the male thread portion of the steel rod, and that can come into contact with the support nut, and the flat plate Are formed at three positions on substantially the same position on the top and bottom surfaces, and there are three strain gauges for measuring the tensile stress corresponding to the positions of the protrusions. It is stuck on the side.

  In order to solve the above-described problem, the stress measurement system according to the present invention is a stress measurement system for measuring a tensile stress applied to a steel rod having a male thread protruding from the end, and at least the tip of the male thread. A stress measuring washer interposed between a flat plate disposed so as to leave a screw and a supporting nut screwed into the male thread portion of the steel rod, and an axial direction detected by the stress measuring washer Measuring means for measuring tensile stress based on strain, and the stress measuring washer has a protrusion that can be in contact with the supporting nut and a protrusion that can be in contact with the flat plate on the top surface and the bottom surface, respectively. Three strain gauges are formed on the side surface and are formed at three positions on the position, and further, strain gauges for detecting the strain corresponding to the positions of the respective protrusions are adhered to the three positions.

  In order to solve the above-described problems, a stress measurement method according to the present invention is a stress measurement method for measuring a tensile stress applied to a steel rod having a male thread protruding from the end, and at least the tip of the male thread is left. A stress measuring washer is interposed between the flat plate arranged in this way and a supporting nut screwed into the male threaded portion of the steel rod, and the stress measuring washer can contact the supporting nut. In addition to forming three protrusions and three protrusions corresponding to the positions of the protrusions, the protrusions and the protrusions that can come into contact with the flat plate are formed in advance on approximately the same position on the top surface and the bottom surface, respectively. The tensile stress is measured based on the axial strain detected through the strain gauge.

  In the present invention, a stress measuring washer is interposed between a flat plate disposed so as to leave at least the tip of the male screw portion and a supporting nut screwed to the male screw portion of the steel rod, and for stress measurement. In the washer, projections that can come into contact with the supporting nut and projections that can come into contact with the flat plate are formed in advance at approximately three locations on the top surface and the bottom surface, respectively. The strain gauges are pasted on the side surfaces in advance at three locations in correspondence with the positions. Then, the tensile stress is measured based on the axial strain detected through the strain gauge.

  That is, in the present invention, the tensile stress applied to the steel rod can be detected through the strain amount of the stress measuring washer to which the compressive stress is transmitted by the reaction. For this reason, since it becomes unnecessary to stick a strain gauge to the steel bar as compared with the conventional case, the burden of labor can be greatly reduced, and the construction period itself can be shortened. In particular, this stress measuring washer is inexpensive, mass-productive, lightweight, and easy to carry, so only this is placed on each steel rod, and other measuring devices are connected to the strain gauge only during measurement. It is also possible to greatly reduce the cost of the entire system. Furthermore, in the present invention, after performing so-called zero setting with high accuracy in a no-load state, this is disposed on the steel rod, so that the strain amount can be calculated with high accuracy from the obtained measurement data.

  Hereinafter, as a best mode for carrying out the present invention, a stress measurement system for measuring a tensile stress applied to a steel rod will be described in detail with reference to the drawings.

  For example, as shown in FIG. 1, the stress measurement system 1 includes a steel rod 12 embedded in a cast concrete 11 and having only an end projecting from the concrete 11, and an end of the steel rod 12. The protruding male screw portion 14, the flat plate 13 disposed so as to leave at least the tip of the male screw portion 14, the supporting nut 15 screwed into the male screw portion 14 of the steel rod 12, and the male screw portion 14 are inserted. A stress measuring washer 2 interposed between the flat plate 13 and the supporting nut 15; and a switch box 3 connected to the stress measuring washer 2; A data logger 4 electrically connected to the data logger 4 and a personal computer (PC) 5 connected to the data logger 4 via a GP-IB interface. It is.

  The steel bar 12 is embedded in various structures such as bridges and slabs, for example, and is held in the concrete 11 in a state of being strained at least in the direction A in the drawing. The structure made of concrete 11 in which the steel rod 12 is embedded is embodied as so-called prestressed concrete (PC). In such a case, for example, after the cast concrete 81 has reached a predetermined strength, the steel rod 12 inserted through the sheath or the like is tensioned by a jack (not shown), and the end of the steel rod 12 is fixed to the flat plate 13 or the like. To fix. Thereafter, by opening a jack (not shown), a tensile stress is applied to the steel rod 12, and as a result, prestress can be introduced into the concrete 11.

  The flat plate 13 is composed of a steel plate or the like having a flat surface extending in a direction substantially perpendicular to the axial direction of the steel rod 12, and is fixed to the steel rod 12. For example, the flat plate 13 may have a female screw portion (not shown) at the center, and the male screw portion 14 is screwed to the female screw portion (not shown) so as to be fixed to the steel rod 12. Also good.

  The supporting nut 15 is formed such that a female screw portion that can be screwed with the male screw portion 14 penetrates the center. After the stress measuring washer 2 is inserted into the male threaded portion 14, the supporting nut 15 is fastened to fix the steel rod 12 loaded with tensile stress in a stable state. It is possible to firmly attach the stress measuring washer 2 for measuring. The supporting nut 15 may be directly screwed onto the flat plate 13 without using the stress measuring washer 2. Further, a plain washer 9 may be interposed between the supporting nut 15 and the stress measuring washer 2 and / or between the stress measuring washer 2 and the flat plate 13.

  The switch box 3 is connected to a strain gauge described later in the stress measuring washer 2. The fixed resistor mounted in the switch box 3 forms a so-called Wheatstone bridge with the strain gauge, takes out a resistance change caused by the strain of the strain gauge as a voltage change, and transmits this to the data logger 4. .

  The data logger 4 detects a change in voltage transmitted from the switch box 3. The voltage value detected by the data logger 4 is transmitted to the PC 5 via the GP-IB interface.

  The PC 5 plays a role as a so-called central control device for controlling the entire stress measurement system 1 and transmits a necessary information signal in response to a request from each component via the GP-IB interface. Further, the PC 5 is connected to a user interface such as a keyboard and a mouse for inputting desired information, and the user can input various conditions necessary for measurement via these. The PC 5 calculates the amount of strain in the axial direction of the steel rod 12 based on the voltage value transmitted from the data logger 4 and calculates the tensile stress applied to the steel rod 12 at the present time. The PC 5 stores the calculated data in its own memory and displays them to the user via various display means such as a display if necessary.

  Next, the configuration of the stress measuring washer 2 will be described in detail with reference to FIGS. 2 is a perspective view of the stress measuring washer 2, FIG. 3 (a) is a top view of the stress measuring washer 2, and FIG. 3 (b) is a side view thereof.

  The stress measuring washer 2 is a ring-shaped jig in which a hole portion 25 for allowing the male screw portion 14 to be inserted is formed in the center portion, and an upper surface 21 and a bottom surface 22 are formed integrally with each other, A peripheral side surface 26 is formed around the periphery.

  On the upper surface 21, projections 23a, 23b, and 23c that can come into contact with the supporting nut 15 are formed at three locations. Further, the bottom surface 22 is formed with projections 24a, 24b, and 24c that can come into contact with the flat plate 13 at three locations. The protrusion 23 a formed on the upper surface 21 is formed at substantially the same position as the protrusion 24 a formed on the bottom surface 22. Similarly, the protrusion 23 b formed on the upper surface 21 is formed at substantially the same position as the protrusion 24 b formed on the bottom surface 22. Further, the protrusion 23 c formed on the upper surface 21 is formed at substantially the same position as the protrusion 24 c formed on the bottom surface 22. That is, the protrusions 23a, 23b, and 23c and the protrusions 24a, 24b, and 24c are disposed at positions that overlap each other in the top view of FIG.

  The protrusions 23 and 24 are formed on the top surface 21 and the bottom surface 22 so that the center lines are spaced at approximately 120 ° intervals. The minimum width Wa of the protrusions 23 and 24 is 5 mm, and the minimum value of the thickness h is 1 mm. The arithmetic average roughness on the contact surface of the protrusion 23 is 0.4a or more and 1.6a or less. The protrusions 23 and 24 may be made of a material different from the upper surface 21 and the bottom surface, or may be made of the same material. When the protrusions 23 and 24 are made of a material different from that of the upper surface 21 and the like, the protrusions 23 and 24 may be manufactured by pasting the material constituting the protrusions 23 and 24 on the upper surface 21 and the bottom surface 22 later. Good. Further, when the protrusions 23 and 24 are made of the same material as that of the upper surface 21 etc., only the protrusions 23 and 24 are cut so as to protrude from the upper surfaces 21 and 22. Also good. Incidentally, in the following embodiment, the case where the protrusions 23 and 24, the upper surface 21 and the like are formed of S45C will be described as an example.

  In the stress measuring washer 2, strain gauges 28 are attached to the outer peripheral side surface 26 at least at three locations. That is, a strain gauge 28a is attached to the outer peripheral side surface 26 in a region from the projection 23a to the projection 24a, and a strain gauge 28b is attached to a region from the projection 23b to the projection 24b. A strain gauge 28c is attached to a region from the protrusion 23c to the protrusion 24c. The strain gauge 28 is distorted in accordance with the compression of the outer peripheral side surface 26, and its resistance can be changed.

  The thickness of the outer peripheral side surface 26 may be reduced to any size within a range where the strain gauge 28 can be attached, or may be set to be as thin as about 15 mm. Thereby, the structure itself of the washer 2 for stress measurement can be finished more compactly, and it becomes possible to improve lightness and ease of carrying.

  Next, a method for measuring the tensile stress actually applied to the steel rod 12 in the stress measurement system 1 to which the present invention is applied will be described in detail.

  First, a voltage value from the strain gauge 28 in a no-load state is measured for the stress measuring washer 2, and so-called zero setting is performed in which the voltage value is set as a zero point.

  Next, the hole portion 25 in the stress measuring washer 2 is inserted into the male screw portion 14 to be fitted. Next, the supporting nut 15 is screwed into the male screw portion 14 in which the stress measuring washer 2 is fitted, thereby fastening it. As a result, the protrusions 23a, 23b, and 23c are in contact with the support nut 15, and the protrusions 24a, 24b, and 24c are in contact with the flat plate 13, respectively. In other words, in the present invention, the protrusions 23 and 24 are formed on the top surface 21 and the bottom surface 22 at three locations so that the center lines thereof are spaced at an interval of about 120 °, so that these support nuts 15 are formed. And the flat plate 13 can be brought into contact with each other steadily.

  Further, as a result of fitting and fixing the support nut 15, as shown in FIG. 4, the reaction force f 1 against the tensile stress applied to the steel rod 12 is applied to the flat plate 13 with respect to the stress measuring washer 2. And a compressive force f2 accompanying tightening from the support nut 15 is further applied. That is, the force f1 is transmitted to the stress measuring washer 2 through the protrusion 24 abutting against the flat plate 13, and the compression force f2 is transmitted through the protrusion 23 abutting against the support nut 15. It is transmitted to the washer 2 for stress measurement. For this reason, force is applied to the stress measuring washer 2 from both the flat plate 13 and the supporting nut 1 via the projections 23 and 24. When a force is applied from both through the protrusions 23 and 24, the stress measuring washer 2 is distorted in the direction in which the force is applied.

  Incidentally, the amount of strain based on strain is more accurately reflected in the region from the projection 23a to the projection 24a, the region from the projection 23b to the projection 24b, and the region from the projection 23c to the projection 24c. become. For this reason, in the stress measurement system 1 to which the present invention is applied, the strain in the axial direction applied to the stress measuring washer 2 can be detected more accurately by attaching a strain gauge 28 to the region. It becomes possible.

  The resistance change due to the distortion of the strain gauge 28 is detected as a voltage change via the switch box 3 and the data logger 4, and the detected voltage value is transmitted to the PC 5 and analyzed. The actual amount of distortion can be calculated from the detected voltage value, and the forces f1 and f2 applied to the stress measuring washer 2 via the protrusions 23 and 24 can be similarly obtained. It becomes. Actually, the PC 5 measures the forces f1 and f2 based on a value obtained by averaging the strain amounts calculated from the strain gauges 28a, 28b, and 28c. If relatively large irregularities are formed on the flat plate 13 or the supporting nut 15 or if the flat plate 13 or the supporting nut 15 is inclined in one direction, the output from each strain gauge 28 may vary. It becomes possible to remove the influence by making it.

  Note that the force f1 applied to the stress measuring washer 2 is only caused by the reaction of the tensile stress applied to the steel rod 12, so that the tensile stress itself can be obtained if the force f1 is known. Become.

  That is, in the stress measurement system 1 to which the present invention is applied, the tensile stress applied to the steel rod 12 can be detected through the strain amount of the stress measuring washer 2 to which the compressive stress is transmitted by the reaction. For this reason, since it becomes unnecessary to stick a strain gauge to the steel rod 12 as compared with the prior art, the burden of labor can be greatly reduced, and the construction period itself can be shortened. In particular, since the stress measuring washer 2 can be manufactured in a large amount at a factory, it is possible to further shorten the construction period in the field.

  Moreover, in this stress measurement system 1, you may make it detect distortion amount by a fixed time interval under control by PC5. Further, such an operation may be executed continuously for several months, or may be executed continuously for several years. The tensile stress in the steel bar 12 can be detected in real time for changes over time in units of months or years, and it is always detected whether or not the steel bar 12 itself exhibits a desired tension state. It is also possible to do. Incidentally, the stress measuring washer 2 is useful even in that it can be removed from the steel rod 12 without any problem even after the measurement is completed, and it can be omitted. .

  In the stress measurement system 1, the stress measurement washer 2 is a main component. Since this stress measuring washer 2 is inexpensive, mass-productive, lightweight and easy to carry, only this is disposed on each steel rod 12, and the configuration of the switch box 3, data logger 4, and PC 5 is used only during measurement. May be connected. That is, in the stress measurement system 1, by sharing the configuration of the switch box 3, the data logger 4, and the PC 5 between the stress measurement washers 2, it is possible to greatly reduce the cost of the entire system.

  Further, in this stress measurement system 1, since so-called zero setting in the stress measurement washer 2 is accurately executed in a no-load state, and this is disposed on the steel rod 2, the strain amount is obtained from the obtained measurement data with high accuracy. Can be calculated.

  The stress measurement system 1 to which the present invention is applied is not limited to the above-described embodiment. For example, when the unevenness formed on the flat plate 13 or the support nut 15 is very large, or when the inclination angle is large, any of the protrusions 23 and 24 may not be able to contact them. In some cases, the forces f1 and f2 cannot be transmitted through the protrusions 23 and 24. In such a case, the heights of the protrusions 23 and 24 may be set high in advance so that all the protrusions 23 and 24 can come into contact with the flat plate 13 and the support nut 15. Of course.

In the embodiment described above, the case where the strain gauge 28 is formed on the outer peripheral side surface of the stress measuring washer 2 has been described as an example. However, the present invention is not limited to such a case, and the hole 25 is formed. It may be formed on the inner peripheral side surface. That is, the strain gauge 28 may be formed on the side surface of the stress measuring washer 2.

It is a block diagram of the stress measurement system to which this invention is applied. It is a perspective view of the washer for stress measurement to which the present invention is applied. It is a side view of the washer for stress measurement to which the present invention is applied. It is a figure for demonstrating operation | movement of the stress measurement system to which this invention is applied. It is a figure for demonstrating per prior art.

Explanation of symbols

1 Stress Measurement System 2 Stress Washer 3 Switch Box 4 Data Logger 5 PC
DESCRIPTION OF SYMBOLS 11 Concrete 12 Steel bar 13 Flat plate 14 Male thread part 15 Supporting nut 21 Upper surface 22 Bottom surface 23,24 Projection part 25 Hole part 26 Outer peripheral side surface 28 Strain gauge

Claims (6)

In the stress measuring washer for measuring the tensile stress applied to the steel rod with the male thread protruding from the end,
It is interposed between a flat plate arranged so as to leave at least the tip of the male screw part and a supporting nut screwed into the male screw part of the steel rod,
Protrusions that can come into contact with the supporting nut, and projections that can come into contact with the flat plate are formed at approximately three positions on substantially the same position on the top and bottom surfaces, respectively.
Furthermore, a strain gauge for measuring the tensile stress corresponding to the position of each projection is attached to the side surface at three locations. The stress measuring washer according to claim 1, wherein the protrusions are formed on the top surface and the bottom surface so that the center lines thereof are spaced at approximately 120 ° intervals. 3. The stress measuring washer according to claim 1, wherein the contact surface of the protrusion has an arithmetic average roughness of 0.4 a or more and 1.6 a or less. The washer for stress measurement according to any one of claims 1 to 3, wherein the protrusion has a height of 1.0 mm or more. In the stress measurement system for measuring the tensile stress applied to the steel rod with the male thread protruding from the end,
A stress measuring washer interposed between a flat plate disposed so as to leave at least the tip of the male screw portion and a supporting nut screwed into the male screw portion of the steel rod;
Measuring means for measuring the tensile stress based on the axial strain detected by the stress measuring washer,
The stress measuring washer has protrusions that can come into contact with the support nut and protrusions that can come into contact with the flat plate at substantially three positions on the top surface and the bottom surface, respectively. A stress measurement system characterized in that strain gauges for detecting the strain corresponding to the positions of the protrusions are stuck on the side surface at three locations. In the stress measurement method for measuring the tensile stress applied to the steel rod with the male thread protruding from the end,
A stress measuring washer is interposed between a flat plate disposed so as to leave at least the tip of the male screw portion and a support nut screwed into the male screw portion of the steel rod;
The stress measuring washer is previously formed with projections that can come into contact with the supporting nut and projections that can come into contact with the flat plate at approximately three positions on the top surface and the bottom surface. In addition, a strain gauge is attached in advance on the side surface over three locations corresponding to the position of each of the protrusions,
A method for measuring stress, comprising: measuring the tensile stress based on an axial strain detected through the strain gauge.

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