JP2824725B2 - Concrete thickness measurement method using impact sound - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the thickness of concrete in a concrete building by using impact sound.

[0002]

2. Description of the Related Art As a method for measuring the thickness of concrete in a concrete building, a method using perforation sampling has been adopted in the past, but in recent years, non-destructive inspection has become mainstream, and Japanese Patent Application Laid-Open No. 52-33755 discloses a method. Id 63-
247608, 64-65407, JP-A-3-1
Measurement methods using (ultra) sonic waves as described in JP-A Nos. 2509 and 3-13810 have been performed. These are to analyze the reflection sound or resonance frequency of the sound wave emitted by the (ultra) sound wave transmitter to measure the thickness of concrete, or to detect the presence of an internal cavity or the like.

[0003] On the other hand, Japanese Patent Publication No. 4-10987 discloses a method of analyzing the impact sound to detect the presence of voids in concrete and floating rocks such as rock.

[0004] This method is sounded the surveyed material such as concrete buildings or bedrock, and voice pickup the percussion sound, the acoustic energy of the acoustic frequency band throughout this percussion sound, the frequency band i.e. 500H _Z vicinity and comparing the only acoustic energy part of the frequency band of 2500H _Z vicinity is to determine the presence or absence of internal cracks or internal voids of the surveyed object in accordance with the magnitude of the comparison value.

[0005]

In order to measure the thickness of concrete by a non-destructive inspection method using ultrasonic waves, a conventional apparatus requires a concrete surface in order to effectively input a pulse wave into the concrete. There are restrictions such as smoothness, the need to apply a contact agent such as grease between the sensor and the concrete surface, and it may be difficult to inspect at any point. There was a drawback that the inspection required a lot of trouble.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to clarify a method and apparatus for measuring concrete thickness using an improved impact sound, which enables nondestructive inspection of concrete thickness to be performed efficiently with a simple operation. It is assumed that.

[0007]

A concrete thickness measuring method according to the present invention detects an longitudinal surface resonance frequency of an impact sound by hitting an arbitrary concrete surface whose thickness is to be measured by an impact hammer. a method for measuring the thickness of the concrete Te, a microphone that is surrounded by the hood does not have a distinct resonance characteristics in the following frequency bands 20 kHz _Z, proximity or contact with the concrete surface position the tip of the hood is close to the striking portion It is arranged in a state where it is laid, and instead of the primary air vibration sound directly generated from the impact of the impact hammer, the secondary impact sound radiated to the concrete surface through the inside of the concrete by the impact of the impact hammer is collected. Measuring the thickness of concrete by detecting the longitudinal frequency resonance frequency characteristics of the impact sound with the analyzer.
It is characterized by.

[0008]

Next, a specific configuration of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory view of concrete thickness measurement according to the method of the present invention. In the figure, reference numeral 10 denotes a hitting hammer, which hits an arbitrary concrete surface to be inspected and is generated on the hitting surface. Rather than the primary impact sound propagating in the air, the impact sound inside the concrete generated by the impact is again radiated from the concrete surface and the secondary impact sound is picked up through the sound collector 21 of the microphone 20, This is analyzed by the analyzer 22 to measure the concrete thickness.

The impact energy of the impact hammer 10 need only be a certain amount of energy, and need not be particularly constant. However, the impact hardness of the impact hammer 10 is relatively high and the impact is relatively high. It is desirable because vibration will be generated in concrete.

It is preferable that the striking portion of the striking hammer 10 has a spherical shape in order to strike at a right angle to the concrete surface, and to reduce acoustic radiation from the gripping portion of the striking hammer 10 as much as possible. It is preferable to cover with rubber or the like.

The hitting of the hitting hammer 10 may be carried out by human power or by machine.

As the microphone 20, a normal acoustic microphone can be used, but it is desirable to use a microphone having a flat frequency characteristic. Also,
Between the concrete thickness and the longitudinal resonance frequency, 60
_{cm → 3.3KH Z, 50cm → 4.0KH} Z, 40c
_{m → 5.0KH Z, 30cm → 6.7KH} Z, 20cm
Since → that there is a relationship 10.0KH _Z has been found, for example, if the measurement error of about ± 5 cm is allowed, by utilizing the microphone which resonates to the frequency portion, outstanding portion of the resonance phenomenon By reading the frequency, the thickness of the concrete can be easily measured.

As shown, at least the periphery of the sound collecting portion 21 of the microphone 20 is surrounded by a hood 23 so that sound radiated from the concrete surface can be efficiently collected.

When the hood 23 is used, resonance may occur at a specific frequency, which may hinder measurement. Possible causes of the resonance include the internal volume of the hood 23, the diameter of the hood 23, reflection on the inner wall of the hood, the distance from the concrete surface to the sound collection unit 21 of the microphone 20, and the like.

[0016] According to an experiment, when the thickness of the concrete to be measured assuming than about 10 cm, the range of the sound to be measured is not more than about 20 kHz _Z, adverse effect on the measurement result even resonance occurs in more frequency bands Turned out not to give. Therefore, although it is sufficient to manufacture the hood so as not to have a distinct resonance characteristics in the frequency region below 20 kHz _Z, which is possible by changing the item - as described above. For example, it is possible to adopt a method of (a) providing irregularities on the inner wall surface of the hood in order to diffusely reflect an incident acoustic wave, and (b) bringing the sound collection unit 21 of the microphone 20 closer to a concrete surface. However, the present invention is not limited to this.

The hood 23 is preferably made of rubber or plastic having fine irregularities formed on the inner wall surface, and is preferably made of a soft material at least in a portion in contact with the concrete surface.

The shape of the hood 23 is not limited to a bell-shaped one as shown, but may be a pyramid or any other shape.

[0019] As food 23, the purpose of integrity assessment of the concrete is required to be no resonance in the range of 0～0.3KH _Z, it is intended for the purpose of thickness measurements of concrete 3～10KH _Z range is required that no resonance, as described below, in embodiments having both concrete integrity evaluation function, it is required that no resonance in the range of 0~0.3KH _Z.

The analyzer 22 may basically be any FFT analyzer that can read the frequency distribution. In the case where the above-described numerical value of the relationship between the concrete thickness and the longitudinal wave resonance frequency is used, it is also possible to configure a simple dedicated measuring instrument using a bandpass filter.

[0021] In soundness evaluation of concrete using the striking sound, has set the use frequency range of impact sound to 0~3KH _Z, a thickness measurement according to the present invention, 20cm~ the thickness range of concrete 3 to 1 in case of 60cm
It is set to 0KH _Z. Therefore, by adding a function corresponding to a frequency of 0 to 3 KHz to an apparatus for implementing the method of the present invention, it is possible to use the apparatus for soundness evaluation of concrete. Incidentally, the vertical resonant frequency in concrete 90cm thick has confirmed that a 2.1KH _Z, adding concrete integrity evaluation function,
This also increases the measurable range of concrete thickness measurement.

[0022]

According to the present invention, the concrete thickness measurement technique based on the longitudinal wave resonance method, which has been conventionally measured by an ultrasonic sensor, can be changed to a method using an acoustic microphone. It is possible to use an acoustic microphone instead of an expensive sensor, so that it is possible to use an inexpensive device.It is possible to incorporate it into a concrete soundness inspection system by the impact sound of a hammer. In addition to the soundness of concrete, the concrete thickness can be measured, and the concrete soundness inspection system can be upgraded.

[Brief description of the drawings]

FIG. 1 is an illustration of concrete thickness measurement by the method of the present invention.

[Explanation of symbols]

 Reference Signs List 10-hitting hammer 20-microphone 21-microphone sound collecting part 22-analyzer 23-hood

Claims (1)

(57) [Claims] The method according to claim 1 Any concrete surface to be measured thickness was struck by the striking hammer, a method for measuring the thickness of the concrete by detecting the longitudinal resonant frequency of the struck sound, 20 kHz _Z frequencies below A microphone surrounded by a hood that does not have a distinct resonance characteristic in the band, the tip of the hood is arranged in a state in which the tip of the hood is close to or in contact with the concrete surface at a position close to the hitting portion,
Rather than the primary air vibration sound directly generated from the impact of the impact hammer, the impact sound of the impact hammer collects the secondary impact sound radiated through the inside of the concrete and radiated to the concrete surface. A concrete thickness measuring method using a striking sound, wherein a concrete thickness is measured by detecting a longitudinal resonance frequency characteristic of a sound.