JPH0769136B2 - Strain gauge - Google Patents

Description

[Detailed Description of the Invention] (Industrial field of application) The present invention relates to a strain gauge of a reinforcing bar type incorporated in a concrete pile for measuring strain in the pile.

(Prior art) Reinforcing bar type strain gauges measure concrete strain as reinforcing bar strain by transmitting it to the reinforcing bar and it is necessary to have a waterproof effect and easy handling. The target shape is, for example, as shown in FIGS. 5 and 6. In the figure, reference numeral 1 denotes a rod-shaped main body composed of a sensitive portion 3 to which a strain gauge 2 is attached, and connecting portions 4 having large diameters at both end portions of the sensitive portion 3. A coating material 5 is provided around the sensing unit 3 so that the sensing unit 3 is held liquid-tight. The strain gauge 2 is connected to one end of a cable 6 that transmits a signal from the strain gauge 2, and the other end of the cable 6 is led to the outside of the coating material 5 and connected to a measuring device (not shown). The connecting portion 4 is provided with a screwing portion 8 for connecting the mounting leg 7 at the axial center portion.

The diameter of the sensing unit 3 is made the same as the diameter of the mounting leg 7.
This is because it is necessary to directly and uniformly transmit the strain transmitted from the mounting leg 7 to the sensing unit 3 without performing cross-section correction. In addition, since the strain gauge 2 is a portion that generates an electrical signal, waterproofing is an absolutely necessary condition, and in order to satisfy this condition, the strain gauge 2 is coated around the sensitive portion 3 formed by pasting. Material 5 is provided. In a strain gauge attached to a high-temperature / high-pressure treatment such as an autoclave curing pile, a heat-resistant material is used for the coating material 5, and the cable 6 is coated with Teflon.

(Problems to be Solved by the Invention) In the above-described conventional strain gauge, the connecting portion 4 is necessarily larger than the sensing portion 3 because the mounting leg 7 is screwed and connected to the connecting portion 4. It has a diameter and the bar body 1 has a step. By extending the cable along the stepped portion from the waterproof portion, the extraction portion of the cable is stabilized and at the same time, the waterproof effect is improved.

However, in this conventional device, since the rod-shaped body has the stepped portion, the distribution of strain transmitted to the sensing portion 3 is disturbed,
It affects the output characteristics of strain, and causes the difference between the measured strain value and the actual strain value.

Further, when the Teflon coating is used for the cable 6, the cable 6 easily forms a passage for moisture to the strain gauge 2 because the Teflon material has poor adhesiveness to other materials. It was extremely difficult to ensure waterproofness. Therefore, as a method for leading out a cable with improved waterproofness and high waterproofness, a method in which a hole having a sealing mechanism is provided and the cable is led out through this hole is adopted. In this case, usually, the portion where the cable is led out from the sensing unit is formed directly on the main body by providing the rod-shaped main body with a large diameter portion. However, in such a cable deriving method, the cross-sectional area of the cable deriving portion increases or decreases, so that there is a problem in that the output characteristics of strain due to the concrete burying state are affected as described above.

(Means for Solving the Problem) The present invention is a sensing unit formed by attaching a strain gauge to an intermediate portion of a metal rod, and a cable whose one end is connected to the strain gauge and which transmits a signal from the strain gauge, A strain gauge consisting of a waterproof protection part covering the sensing part and a cable lead-out part provided with a hole having a sealing mechanism for guiding the cable to the outside from the waterproof sensing part inside the waterproof protection part. The waterproof protection portion is made of a circular pipe, and the inner peripheral surface of the circular pipe is welded to a metal rod on the opposite side of the cable lead-out portion with the O-ring provided in the cable lead-out portion and the sensing portion sandwiched therebetween. The O-ring provided on the reinforced portion is closely sealed and the cable lead-out portion is externally fitted in the vicinity of the sensing portion.
Further, the strain gauge was constructed such that its one end side peripheral portion was fixed to the outer periphery of the facing metal rod by welding.

(Operation) The strain generated in the concrete pile is transmitted to a metal rod of a specified length, appears as a strain in the sensing section, is detected as an electrical signal by the strain gauge, and is measured by the cable connected to the strain gauge. Transmitted to the vessel. This cable is guided to the outside from a waterproof sensing unit and a cable outlet. The cable lead-out part is welded to the outer periphery of the opposing metal rod at the one end side peripheral part, so it is mechanically separated from the metal rod, and it cannot practically become a strain transmission path, and it occurs in the concrete pile. The applied strain transmits the entire amount of the strain to the sensing section and acts on the strain gauge.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. In the figure, 11 is a concrete pile main body, inside which a strain gauge 12 according to the present invention is provided. The strain gauge 12 is a sensing unit 15 in which a strain gauge 14 is attached to an intermediate portion of a metal rod 13, and a cable 16 having one end connected to the strain gauge 14 and transmitting a signal from the strain gauge 14, A waterproof protection part 21 covering the sensing part 15 and a cable 16 from the waterproof sensing part 15 inside the waterproof protection part 21 to the outside.
And a cable lead-out portion 17 provided with a hole 19 having a sealing mechanism for guiding.

The metal rod 13 has a predetermined length that is easy to handle, and both ends of the metal rod 13 can be connected to metal rods for extension (not shown). In the vicinity of one end of the sensitive portion 15 to which the strain gauge 14 at the middle portion of the metal rod 13 is attached, the cable lead-out portion 17
Is fitted. The cable lead-out portion 17 is provided with an O-ring portion 18 in close contact with the outer periphery of the end surface portion on the inner side of the sensing portion 15, and a hole 19 is bored through between both end surfaces in the axial direction. It is set up. A seal mechanism 20 is provided inside the hole 19 so that the cable 16 passing therethrough is hermetically sealed near the outlet. One end of the cable 16 is connected to the strain gauge 14, and the other end is led out to the outside through a hole 19 and connected to a strain measuring device (not shown).

The waterproof protection part 21 is for waterproof protection of the sensing part 15, and is formed of, for example, a tubular metal, the O-ring parts 18 and 23 are closely attached to the inner peripheral surface, and the inside of the waterproof protection part 21 is It is kept liquid tight. Reference numeral 22 denotes a reinforcement portion externally fitted to the metal rod 13 near the other end on the opposite side of the sensing portion 15 provided with the cable lead-out portion 17, and the O-ring portion 23 is closely attached to the outer peripheral surface of the reinforcement portion 22. Is provided.

The outer peripheral edge portion of the cable lead-out portion 17 facing the metal rod 13 is fixed to the metal rod 13 by welding (shown by A in FIG. 2). Further, the reinforcing portion 22 is also fixed to the metal rod 13 by welding at the peripheral edge portion of the outer end surface on the side opposite to the sensing portion 15 (shown by B in FIG. 2).

Fig. 4 shows the state where the strain gauge 12 is actually set in the concrete pile body 11.
The strain gauge 12 was pre-assembled to the reinforcing bar of the reinforcing bar basket during the manufacturing of and was molded from concrete.

Next, the measurement of strain will be described. As shown in Fig. 4, when the concrete pile 11 receives a compressive force in the arrow direction,
Strain is generated in the concrete pile 11 due to the compressive force, and this strain is transmitted to the metal rod 13. That is, strain is generated in the sensitive portion 15 located in the middle portion of the metal rod 13. The strain gauge 14 detects this strain, and an electrical signal corresponding to this strain is guided to the cable 16 and read by a predetermined strain measuring instrument. When the strain of the sensing unit 15 occurs, the strain distribution from the metal rod 13 to the sensing unit 15 passes through the large diameter portion of the cable derivation unit 17 and the reinforcement unit 22 in the middle, but these cable derivation unit 17 and the reinforcement Since both of the parts 22 are opposed to the metal rod 13 and are welded only to the peripheral part on the one end side, uniform strain transmission is carried out without being affected by the change in cross-sectional area.

In addition, in the above-described embodiment, the waterproof protection portion is configured as a metal tubular case, but the waterproof protection portion may be formed of a coating material or the like without departing from the gist of the present invention. Also, although the peripheral portion of the end surface of the cable lead-out portion on the side of the sensing portion was welded to the metal rod, it is sufficient to weld either the inner or outer end peripheral portion of the cable lead-out portion to the metal rod, or by soldering or brazing. Of course, it may be such.

(Effect of the Invention) According to the present invention, since the strain gauge is protected by the circular pipe sealed by the O-ring provided in the cable lead-out portion and the O-ring provided in the reinforcing portion, the sealing can be surely performed. Moreover, the assembly can be done easily and the cost can be reduced.
Even if a cable with a Teflon coating for high temperature and high pressure resistance (for autoclave piles, etc.) is used, it is waterproof by leading it out of the sensing section through a hole with a sealing mechanism provided in the cable outlet section. And mounting strength are significantly increased. Furthermore, by setting the diameters of the metal rod and the sensitive portion to be the same, even if the cable lead-out portion and the reinforcing portion having a large diameter are provided, the strain value can be obtained in a stable state without being affected by these. That is, according to the present invention, the cable is pulled out by the cable lead-out portion, so that the cable and the cable lead-out portion are tightly and firmly made, but the cable lead-out portion is substantially welded to the metal rod by welding only the one end side peripheral portion. Strain distribution is a separated state,
There is no room for unnecessary elements to get into the distortion of the sensing section, and extremely reliable data can be obtained.

[Brief description of drawings]

1 to 4 show an embodiment of the present invention. FIG. 1 is a front view, FIG. 2 is an explanatory view with a case removed, and FIG. 3 is a perspective view of a cable lead-out portion. FIG. 4 is a longitudinal sectional view showing a setting state of the strain gauge, FIGS. 5 and 6 show a conventional example, FIG. 5 is a front view, and FIG.
The figure is an illustration of a state in which the coating material is removed. 13 …… Metal rod, 14 …… Strain gauge 15 …… Sensor, 16 …… Cable 17 …… Cable outlet, 19 …… Hole 20 …… Seal mechanism, 21 …… Waterproof protection

Claims (1)

[Claims] 1. A sensing unit having a strain gauge attached to an intermediate portion of a metal rod, a cable having one end connected to the strain gauge and transmitting a signal from the strain gauge, and a waterproof protection covering the sensing unit. And a cable lead-out portion provided with a hole having a sealing mechanism for guiding the cable from the waterproof sensing section inside the waterproof protection section to the outside, the strain gauge comprising: Is a circular pipe, and the inner peripheral surface of the circular pipe is provided on the reinforcing portion welded to the metal rod on the opposite side of the cable guiding part with the O-ring provided on the cable guiding part sandwiching the sensing part. It is characterized in that it is in close contact with the O-ring and is sealed, the cable lead-out portion is externally fitted in the vicinity of the sensing portion, and the end side peripheral edge portion is fixed to the outer circumference of the facing metal rod by welding. Strain gauge.