JP2004325224A - Diagnostic method of corrosion thinning of anchor bolt, and device used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diagnostic method of corrosion thinning of an anchor bolt capable of diagnosing the corrosion thinning state of an exposure part of the anchor bolt in the state where a structure is remained in the present state. <P>SOLUTION: In this method for diagnosing the corrosion thinning of the anchor bolt 3 embedded into a concrete foundation 1 in the state where the exposure part 3a is exposed from the concrete foundation 1, the exposure part 3a of the anchor bolt 1 exposed from the concrete foundation 1 is struck and vibrated, and the characteristic frequency of the anchor bolt 3 at that time is measured, and the measurement result is compared with the characteristic frequency of a normal anchor bolt 3 to thereby diagnose the degree of unsoundness together with the corrosion thinned quantity of the anchor bolt 3. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for diagnosing corrosion thinning of anchor bolts and an apparatus used therefor.
[0002]
[Prior art]
In general, various steel structures such as road lighting poles and signposts, sound insulation walls, buildings, tower structures, and the like are often fixed to a concrete foundation via a base plate or the like with anchor bolts. However, this anchor bolt may be corroded with long-term use due to repeated water accumulation, drying, etc., and its cross section may be worn out (thinned), causing a problem in the safety of the structure. Has occurred. Therefore, from the viewpoint of ensuring safety, it is important to grasp the corrosion thinning state in order to clarify the replacement timing of the anchor bolt.
[0003]
Conventionally, in order to investigate corrosion thinning of anchor bolts, remove the structure and base plate, expose the anchor bolt head from the concrete foundation, and then actually measure the diameter of this outcrop. In addition, a method for directly measuring the state of corrosion thinning has been used. However, this method not only requires a large amount of work, but also may be difficult to remove depending on the structure, and may not be able to measure corrosion thinning.
[0004]
On the other hand, in order to non-destructively diagnose the corrosion state of the tensile steel material of the anchor, a method of diagnosing the corrosion state by applying a current to the tensile steel material of the anchor and measuring its natural potential has been proposed (for example, See Patent Document 1.).
[0005]
[Patent Document 1]
JP-A-11-201930 (paragraphs [0012] to [0023])
[0006]
[Problems to be solved by the invention]
However, according to the above-mentioned method, it is not possible to diagnose the corrosion thinning state of the exposed portion of the anchor bolt.
[0007]
The present invention has been made in view of such circumstances, and in a state where a structure is left as it is, a corrosion thinning state of an anchor bolt that can diagnose a corrosion thinning state of an outcrop of an anchor bolt can be diagnosed. It is an object of the present invention to provide a diagnostic method and a device used therefor.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for diagnosing corrosion thinning of anchor bolts embedded in a concrete foundation with the head exposed from the concrete foundation, and comprising: The head portion of the anchor bolt is subjected to impact vibration, the natural frequency of the anchor bolt at this time is measured, and the measurement result is compared with the natural frequency of a normal anchor bolt to reduce the corrosion of the anchor bolt. The first gist is a method of diagnosing corrosion thinning of an anchor bolt, which is used to diagnose the degree of unhealthyness along with the amount of the anchor bolt, the anchor bolt being embedded in a concrete foundation with its head exposed from the concrete foundation. A device for diagnosing corrosion thinning of concrete, comprising a vibrating device that impacts and vibrates the head of the anchor bolt exposed from a concrete foundation. Means, a measuring means for measuring the natural frequency of the anchor bolt when the anchor bolt is struck and vibrated by the vibration applying means, and a measurement result measured by the measuring means is compared with a natural frequency of a normal anchor bolt. A second aspect of the present invention is a diagnostic device for corrosion thinning of anchor bolts, comprising: a diagnosis means for diagnosing the degree of unhealthyness together with the amount of corrosion thinning of anchor bolts.
[0009]
That is, the method for diagnosing corrosion thinning of an anchor bolt according to the present invention is such that the head portion of an anchor bolt exposed from a concrete foundation is struck and vibrated, and the natural frequency of the anchor bolt at this time is measured. Is compared with the natural frequency of a normal anchor bolt, whereby the degree of unhealthyness is diagnosed together with the amount of corrosion thinning of the anchor bolt (the diameter of the corroded anchor bolt). Therefore, in the method of the present invention, it is not necessary to remove the structure, the base plate, and the like, and to check whether or not the anchor bolt is actually corroded and reduced in thickness. It can be diagnosed whether or not the bolt is corrosion-reduced. For this reason, even when it is difficult to remove the structure, the corrosion thinning state can be measured. In addition, the head of the anchor bolt is hit and vibrated by a hammer or the like, and the natural frequency of the anchor bolt at this time can be measured by a sound collecting microphone, an acceleration pickup, or the like. On the other hand, according to the apparatus for diagnosing corrosion thinning of an anchor bolt of the present invention, the diagnostic method of the present invention exhibiting the above-described excellent effects can be easily realized.
[0010]
In the above diagnosis, the natural frequency of a normal anchor bolt embedded in a concrete foundation with the head exposed from the concrete foundation was solved by bending vibration of the beam fixed to the elastic body. It can be obtained from a calculation formula. In this case, as the Young's modulus, the elastic modulus (spring constant) of concrete, and the like, a measured value of a local normal anchor bolt or a known value can be adopted. Similarly, the natural frequency of the anchor bolt in which the diameter of the predetermined portion is formed small (the wall thickness is reduced by processing or the like) can also be obtained by a theoretical calculation formula. Further, these theoretical calculated values can be verified by measured values measured by experiments using a normal anchor bolt and an anchor bolt having a predetermined portion with a small diameter. Further, the measurement result of the present invention may be compared with only the measurement value actually measured by the above experiment.
[0011]
Further, the natural frequency of the anchor bolt is obtained by calculating the diameter d of the anchor bolt and the length (outcrop length) L of the head portion of the anchor bolt exposed from the concrete foundation (the ratio of the outcrop length L to the diameter d: L / D is called an aspect ratio) (see FIG. 3). And, as shown in FIG. 4, the diameter d of the corrosion-thinned portion of the corrosion-thinned anchor bolt is smaller than that of a normal anchor bolt (that is, the aspect ratio is large), and the corrosion-thinned bolt has a reduced aspect ratio. The natural frequency of the thinned anchor bolt is lower than that of a normal anchor bolt.
[0012]
Therefore, it is possible to diagnose the degree of unhealthyness together with the corrosion thinning amount of the anchor bolt in consideration of the following. That is, in the case of the anchor bolt having the same outcrop length L and the same diameter d, the lower natural frequency is measured for the anchor bolt having the reduced corrosion thickness (see FIG. 5). In addition, when the diameter d is the same and the outcrop length L is different, it can be compared with a theoretical calculation value or a measurement value actually measured by an experiment at each outcrop length L. Further, by comparing the natural frequency (theoretical calculation value or a measurement value actually measured by an experiment) of the anchor bolt having a predetermined portion with a small diameter with the measurement value measured by the present invention, the anchor bolt having a reduced corrosion thickness is obtained. (That is, the amount of corrosion loss) can also be determined. For the description of the reference numerals in FIGS. 3 to 5, refer to an embodiment described later.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
FIG. 1 shows an embodiment of a method for diagnosing corrosion thinning of an anchor bolt according to the present invention. In the drawing, 1 is a concrete base, 2 is a flat plate-shaped structural base plate disposed on the upper surface of the concrete base 1, and a plurality of bolt insertion holes 2a (only two are shown in FIG. 1). ) Are drilled. Reference numeral 3 denotes an anchor bolt embedded in the concrete foundation 1 (see FIG. 3), and an exposed portion of the concrete foundation 1 (a portion of the anchor bolt 3 exposed from the concrete foundation 1) 3a is a base plate. 2 and is exposed through each bolt insertion hole 2a. Reference numeral 4 denotes a structure such as a lighting column welded and fixed to the upper surface of the base plate 2. A plurality of leg plates 4 a welded and fixed to the outer peripheral surface of the lower end portion are welded and fixed to the upper surface of the base plate 2. I have. In use, the nuts 8 and 9 (see FIG. 2) are engaged with the screw portions 3b formed on the exposed portions 3a of the anchor bolts 3 so that the structure 4 is attached to the concrete base 1 by the base plate. It is fixed by an anchor bolt 3 through 2.
[0015]
Numeral 11 denotes a corrosion thinning measuring device, which is a test hammer 12 which strikes the outer peripheral surface of the upper end edge of the exposed portion 3a of the anchor bolt 3 to apply impact vibration to the exposed portion 3a (the hitting portion 12a of the test hammer 12 is made of iron or plastic. ), A condenser microphone 13 that records a sound (that is, a vibration sound of the exposed part 3a) emitted when the test hammer 12 gives a striking vibration, and converts the recorded sound pressure signal into an electric signal. An FFT (Fast Fourier Transform) analyzer (not shown) that converts an electric signal input from the microphone 13 into a vibration waveform and a vibration spectrum, and an anchor bolt 3 based on the vibration waveform and the vibration spectrum input from the FFT analyzer. The natural frequency is determined, and the diameter d and the outcrop length L of the anchor bolt 3 previously input. From the theoretical calculation value of the normal anchor bolt 3 calculated from the above or the theoretical calculation value of the anchor bolt 3 in which the diameter of the predetermined portion is formed to be thin, the measured corrosion thinning amount of the anchor bolt 3 is measured and numerically or graphed. And a computing device (not shown) such as a personal computer (PC). In the figure, reference numeral 13a denotes a sound collecting port of the condenser microphone 13.
[0016]
Using the above-described corrosion thinning measuring device 11, for example, diagnosis of corrosion thinning can be performed as follows. First, the nuts 8 and 9 (see FIG. 2) are removed from the exposed portion 3a of the anchor bolt 3 (see FIG. 1). Next, the diameter d of the anchor bolt 3 is measured (or checked by a construction design document or the like) and input to the arithmetic unit. Further, the length of the anchor bolt 3 exposed from the base plate 2 and the thickness of the base plate 2 were measured (see FIG. 4), and the length of the exposed head 3a of the anchor bolt 3 exposed from the upper surface of the concrete foundation 1 (exposure length L ) Is calculated and input to the arithmetic unit. In addition, the sound collecting port 13a of the condenser microphone 13 is positioned near the outer peripheral surface of the upper end edge of the exposed portion 3a of the anchor bolt 3. Next, the outer peripheral surface of the upper end edge of the exposed part 3a of the anchor bolt 3 is hit with the test hammer 12 to give a vibration to the exposed part 3a. At this time, the striking vibration sound generated by the exposed portion 3a is recorded by the condenser microphone 13, and the recorded sound pressure signal is converted into an electric signal and input to the FFT analyzer. In this FFT analyzer, the electric signal input from the condenser microphone 13 is converted into a vibration waveform and a vibration spectrum, and then input to a calculation device. A graph is displayed on the screen of the provided display unit.
[0017]
In the display section, four types (A to D) of natural frequencies determined from the input outcrop length L and diameter d (A zone: a safety zone in which no or little corrosion thinning is considered) , B zone: a zone in which corrosion thinning is slightly reduced but it is considered that replacement is not required yet. C zone: a danger zone in which corrosion thinning is in progress and need to be replaced. D zone: corrosion reduction. A zone where the meat is large and a very dangerous zone is displayed, so that it is possible to see at a glance which zone the determined natural frequency belongs to (see FIG. 6. In FIG. 6, the Fourier transform is used). The resulting spectrum waveform is displayed on the upper side, and the TIME waveform of the sound pressure data is displayed on the lower side, and the determined natural frequency is in the C zone.) In this manner, diagnosis and determination of corrosion thinning of the anchor bolt 3 can be performed mechanically (independent of human judgment).
[0018]
As described above, in this embodiment, the nuts 8 and 9 are removed from the exposed portions 3a of the anchor bolts 3 that are exposed from the concrete foundation 1, and the exposed portions 3a are hit with the test hammer 12 to be hit and vibrate. By measuring the impact vibration sound at this time with the condenser microphone 13, the corrosion thinning state of the anchor bolt 3 can be diagnosed mechanically. Therefore, there is no need to remove the structure 4 and the base plate 2 from the concrete foundation 1. In addition, the exposed portion 3a of the anchor bolt 3 is struck and vibrated by the test hammer 12, and the striking vibration sound at this time is measured by the condenser microphone 13, so that the operation can be performed in a short time with a small device.
[0019]
FIG. 7 shows another embodiment of the method for diagnosing corrosion thinning of an anchor bolt according to the present invention. In this embodiment, the natural frequency of the exposed head 3a when the test head hammer 12 applies a striking vibration to the exposed head 3a of the anchor bolt 3 is measured by the acceleration pickup 15 provided on the upper end surface of the exposed head 3a. Then, the measurement result is input to an FFT analyzer via a charge amplifier (not shown). Other parts are the same as those of the above-described embodiment, and the same parts are denoted by the same reference numerals. In this embodiment, the same operation and effect as those of the above embodiment can be obtained.
[0020]
Note that, in the above embodiment, instead of the theoretical calculation value of the normal anchor bolt 3 and the theoretical calculation value of the anchor bolt 3 in which the diameter of the predetermined portion is formed to be small, measured values measured by experiments (that is, measured by experiments) are used. The normal frequency of the normal anchor bolt 3 and the natural frequency of the anchor bolt 3 having a predetermined portion with a small diameter may be used.
[0021]
【The invention's effect】
That is, according to the method for diagnosing corrosion thinning of an anchor bolt of the present invention, it is not necessary to remove a structure, a base plate, or the like, and to check whether the anchor bolt is actually thinned by corrosion. In the state where the anchor bolt is left as it is, the degree of unhealthyness can be diagnosed together with the corrosion thinning amount of the anchor bolt. Therefore, even when it is difficult to remove the structure, the corrosion thinning state can be measured. In addition, the head of the anchor bolt is hit and vibrated by a hammer or the like, and the natural frequency of the anchor bolt at this time can be measured by a sound collecting microphone, an acceleration pickup, or the like. On the other hand, according to the apparatus for diagnosing corrosion thinning of an anchor bolt of the present invention, the diagnostic method of the present invention exhibiting the above-described excellent effects can be easily realized.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing one embodiment of a method for diagnosing corrosion thinning of an anchor bolt according to the present invention.
FIG. 2 is an explanatory diagram of the diagnostic method.
FIG. 3 is a sectional view showing a normal anchor bolt.
FIG. 4 is a cross-sectional view showing an anchor bolt with reduced corrosion.
FIG. 5 is an explanatory diagram of the diagnostic method.
FIG. 6 is an explanatory diagram of a waveform displayed on a display unit.
FIG. 7 is an explanatory view showing another embodiment of the method for diagnosing corrosion thinning of an anchor bolt according to the present invention.
[Explanation of symbols]
1 Concrete foundation 3 Anchor bolt 3a Open head

Claims (3)

A method for diagnosing corrosion thinning of an anchor bolt embedded in a concrete foundation with the head exposed from the concrete foundation, wherein the head of the anchor bolt exposed from the concrete foundation is hit with vibration. Then, measure the natural frequency of the anchor bolt at this time, compare this measurement result with the natural frequency of a normal anchor bolt, and diagnose the degree of unhealthyness together with the corrosion thinning amount of the anchor bolt. A method of diagnosing corrosion thinning of an anchor bolt, characterized in that: A device for diagnosing corrosion thinning of anchor bolts embedded in a concrete foundation with the head exposed from the concrete foundation, and impact vibration of the anchor bolt head exposed from the concrete foundation A vibration imparting means for causing the anchor bolt to be struck and vibrated by the vibration imparting means, and a measuring means for measuring a natural frequency of the anchor bolt; Diagnostic means for diagnosing the amount of corrosion thinning of the anchor bolt and the degree of unhealthyness in comparison with the method for diagnosing corrosion thinning of the anchor bolt. The diagnostic device for corrosion thinning of an anchor bolt according to claim 2, wherein the vibration imparting means is a hammer.

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