JP2008020425A - Nondestructive diagnosis method and device for concrete structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine whether the vibration is caused from a hard object or a soft object to determine the quality of a concrete structure. <P>SOLUTION: The nondestructive diagnosis device is constructed of a vibration acceleration sensor 2, a central processing unit 7 performing Fourier transformation to substitute a relationship between signal intensity and the number of vibrations for a relationship between the signal intensity and the elapsed time for turning the relationship into spectra, a memory part 8 storing respective data such as sampling data, measurement data, and a spectrum of a vibration frequency, a key switch part 9 instructing processing, and a determination part determining the quality of the concrete structure based on comparison with a threshold value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a nondestructive diagnostic method for inspecting the quality of concrete without destroying a structure such as reinforced concrete or unreinforced concrete.

  There are basically two methods for examining the state of a concrete structure: a method of peeling and destroying the structure, and a non-destructive method of examining the structure in an intact state. Here, the means to be compared with the present invention will be described below as a preceding example regarding the latter non-destructive internal diagnosis.

  Measure the frequency that maximizes the amplitude when the surface of the hammering test object is struck, compare the frequency with the ideal natural frequency of the hammering test object, and index the soundness of the hammering test object There is a non-destructive inspection method for a hitting inspection object (see, for example, Patent Document 1).

  In addition, the data obtained by inspecting the concrete structure in the field according to the sound hitting method and the data of the inspection conditions are transmitted from the local concrete inspection apparatus to the simple database in the field office and stored. When a certain amount of each received data is stored, it is sent from the computer in the field office to the large computer inspection management database in the general center. The computer in the control center that received each data performs repair diagnosis from each data, creates a delamination inspection plan schedule and a repair target table, and sends it to the computer in the field office. There is an inspection device (see, for example, Patent Document 2).

  In addition, sound generating means for hitting the concrete surface to generate sound, sound collecting means for collecting the generated sound, and soundness for evaluating the soundness of the concrete based on the collected sound A soundness evaluation device for concrete including a soundness evaluation means, wherein the soundness evaluation means obtains an average value of the strength of percussion sound at an early stage among transient phenomena from occurrence of sound percussion to attenuation, There is a method and an apparatus for evaluating the soundness of concrete by comparing the obtained average value with a preset reference value (see, for example, Patent Document 3).

  Furthermore, there is a sounding device in which a microphone is arranged in a cylindrical casing corresponding to the handle portion of the sounding device, the sounding is captured, spectrum is converted via a band-pass filter, and spectrum display is performed on the display device ( For example, refer to Patent Document 4.)

JP 2002-340869 (Non-destructive inspection method, non-destructive inspection device and quality control method of hammering test object) JP2003-004711 (inspection method of concrete structure and inspection apparatus using the method) JP2003-057217 (Concrete soundness evaluation method and apparatus) JP2003-0666014 (sounding device)

  However, in the above-mentioned conventional well-known patent documents, vibration generated from a hard object or vibration generated from a soft object by separating the vibration frequencies of various striking sounds that have been emphasized during measurement by numerical analysis. There is no means for determining a threshold value on the spot by storing a large amount of pre-sampled data, processing these data at high speed, and determining a threshold value on the spot and instantaneously obtaining a pass / fail judgment result. The gist of the present invention is to solve the problems.

Means for Solving the Invention

  A stethoscope is composed of a vibration acceleration sensor, a voltage amplifier that converts the vibration detected by the vibration acceleration sensor into a voltage, and an output amplifier, and all information such as sampling data and measurement data input from the stethoscope is stored. An A / D converter necessary for numerical processing, a memory unit for recording a digitized signal, a Fourier transform for each recorded signal and determining a threshold value from the sampling data by spectrumizing the frequency, The main parts are an acceptance / rejection determination unit that determines acceptance / rejection by comparing the threshold value with measurement data, and a central processing unit that processes data at high speed according to the contents of instructions from the key switch unit and instantaneously derives a determination result. .

  In general, vibrations are a combination of high frequency waves, low frequency waves, and countless waves between them. For example, in the case of sound, our ears capture each frequency wave together, which greatly affects sound quality. ing. However, it is not possible to identify only sound waves having a specific frequency or to separate and distinguish them. Therefore, in the present invention, the synthesized vibration is decomposed into the frequency by mathematically Fourier transforming (triangular series) the vibration waveform.

  The graph of the vibration waveform shown in FIG. 2A shows a simple sine wave for explanation, and is a regular sine curve with a period of 5 indicating the signal strength in the vertical direction and the elapsed time of the signal in the horizontal direction. When this is Fourier transformed, as shown in FIG. 2 (b), the vertical direction represents the signal strength in the same manner as (a), but the horizontal direction represents the frequency (frequency) unlike (a). The graph is converted into a graph having an axis and a peak frequency at a position of period 5.

  FIG. 3A shows the same graph as FIG. 2A, except that the difference is a vibration waveform when two sine waves of period 5 and period 10 are combined. Although it is a repetitive waveform, it is not a sine wave but a distorted waveform.

Therefore, when the Fourier transform is performed on FIG. 3A as in FIG. 2B, a frequency graph showing the peak of the frequency at the positions of period 5 and period 10 is obtained as shown in FIG. 3B. .
However, the vibration that occurs when an actual concrete structure is consulted on site is not a composite waveform of such a simple vibration, and a large number of vibrations with different periods are complicatedly overlapped.

The invention's effect

  The relationship between signal strength and temporal change can be transformed into the relationship between signal strength and frequency by Fourier transform, and high frequency vibration and low frequency vibration are separated on the graph and discriminated. It is possible to characterize and treat high frequency vibrations from hard objects and low frequency vibrations from soft objects (low density materials).

  Therefore, numerical analysis of the vibration frequency when the impact sound obtained by striking a concrete structure is detected by an acceleration sensor, and the spectrum can be clearly clarified, and these numerical values can be clearly identified. Processing can be performed quickly by a central processing unit incorporating many functions, and these inspections are carried out by bringing a small, portable device to the inspection site and the results are obtained instantaneously.

  The result of this device should not change at all, regardless of the person performing the inspection. It is stable without being affected by the magnitude of the blow. In addition, it has many functions necessary for inspection and can be easily brought to the inspection site, and results can be obtained instantaneously.

  A sensor 2 installed in the vibration acceleration sensor 1 is brought into contact with the surface of the object to be measured (concrete structure), and a separately prepared impact hammer (particularly any shape, but in practice a small ball is attached to the tip of the rod) The sensor 2 hits a plurality of locations (usually 5 locations) around the contact portion of the sensor 2 with the detection sensor 2. This signal includes not only the impact vibration when the hammer strikes the object to be measured, but also the primary reflection vibration, secondary reflection vibration and other vibrations resulting from this, and it appears as one waveform. Appears as

  However, the vibration wave (waveform) detected by the sensor 2 of the vibration acceleration sensor 1 is converted into a voltage by the charge amplifier 3, and the voltage is weak as it is, so that it is transmitted by the amplifier 4 to prevent it from being attenuated during transmission. Amplifies even easier.

  Next, since all signals received via the cable are analog signals, they are converted into digital signals suitable for various numerical processing by the A / D converter 6 in the concrete diagnostic device 5, and then sent to the sensor 2. All the information such as sampling data and measurement data obtained in this way is stored in the memory unit 8 of the central processing unit 7, and the relation between the vibration strength and time of the data stored in the memory unit 8 is further stored in the central processing unit 7. The frequency is converted into spectrum by Fourier transform.

  In addition, a threshold value that is a criterion for pass / fail judgment is set from the sampling data stored in the memory unit 8, and the pass / fail judgment unit 11 of the central processing unit 7 sends the threshold value and measurement data from the key switch 9. The concrete structure is judged to be accepted or rejected by processing according to the instructions, and the display 10 is checked for confirmation. At the same time, the pass / fail judgment result is identified in the three ranks of normal / abnormal / caution in the pass / fail display section 12 and displayed with color lamps, respectively. ing.

  In the figure, reference numeral 13 denotes a device for relay connection to an external display device 14 through an interface. FIG. 4 shows a Fourier transform of the vibration waveform of the measurement data, and FIG. 5 shows a state where the vibration frequency is spectrumized.

Block diagram showing the configuration of the apparatus of the present invention 5 period sine wave and waveform graph after Fourier transform Distorted wave consisting of 5 and 10 sine waves and waveform graph after Fourier transform Waveform after Fourier transform of measurement data Graph of frequency spectrum

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vibration acceleration sensor 2 Sensor 7 Central processing unit 8 Memory part 9 Key switch part 11 Pass / fail judgment part 12 Pass / fail display part

Claims (2)

By performing a Fourier transform on the relationship between the signal strength and the elapsed time of the signal, it is converted into a spectrum by replacing it with the relationship between the signal strength and the frequency, and the threshold value is set based on the sampling data detected by the sensor. Nondestructive diagnosis method for concrete structure characterized in that quality of concrete structure is judged by comparing with data A vibration acceleration sensor, a central processing unit that performs a Fourier transform on the relationship between the signal strength and the elapsed time of the signal, and replaces it with the relationship between the signal strength and the vibration frequency, and the sampling data, measurement data, spectrum Memory part that stores data such as vibration frequency, key switch part that instructs the central processing unit to perform numerical processing, and pass / fail judgment that compares the measured data with a threshold value to determine the quality of the concrete structure Non-destructive diagnostic device for concrete structures characterized by comprising

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