JPH0564299B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The disclosed technology is a method for preventing fatigue failure of concrete structures such as concrete bridge girders in which PCA steel wires are buried. It belongs to the technical field of detection technology that enables prediction and predetermined countermeasures by detecting a disconnection.

<Summary of the gist> The invention of this application is directed to a concrete structure such as a concrete bridge girder in which a tensile strength wire such as a prestressed steel wire, which is an aggregate of a plurality of wires twisted together, is embedded integrally. By non-destructively detecting the first breakage of one of the wires buried inside, fatigue fracture can be detected, regardless of the rapid progress of fatigue of the structure after the first breakage of the one wire. This invention relates to a method for predicting the failure of a concrete structure and a device directly used in the method, which enables prediction of damage to a concrete structure and taking prescribed countermeasures. A concrete structure that detects only the elastic waves propagating inside the structure using a flexible vibrator, etc. on the surface of the structure or at an internal location close to the surface, monitors and records the information, and takes appropriate measures. A method for predicting destruction, a flexible vibrator such as a piezoelectric element for the elastic wave, and a filter electrically connected to the flexible vibrator are also electrically connected to a waveform storage device, and the waveform storage device is used as a recording device. This invention relates to a concrete structure failure prediction device that is connected to a clock or the like of a time measuring device from the time when the first wire breakage occurs.

<Prior art> As is well known, various structures are constructed as buildings, but it is extremely difficult to deal with not only safety measures against sudden impact failures, but also fatigue failures due to repeated loads. is important.

For example, a concrete bridge girder on an expressway with buried PC steel wire is a typical concrete structure to which repeated loads are applied over time. It is not always possible to predict fatigue failure of PC steel wires accurately or evenly, and it is impossible to conduct non-destructive tests on the spot, and it is difficult to predict reproducibility in experiments. It is equally impossible to hold and do it accurately.

The seed PC steel wire is, for example, a stranded wire such as seven piano wires, and the whole wire does not break at once, but an unspecified one breaks due to various non-average repeated loads. When the so-called first wire breaks, a large repeated load is applied to other wires over time, causing the wires to break one after another, and finally the entire PC steel wire breaks, causing fatigue failure in the concrete structure. It is something that occurs.

The successive breakage of each strand causes fatigue on the concrete structure, but this process over time cannot be avoided from the outside because the PC steel wire is buried integrally inside the concrete structure. A potential limitation is that it is extremely difficult to detect.

Since unexpected fatigue failure of such concrete structures, such as concrete bridge girders on the expressway mentioned above, can lead to extremely serious consequences, it is important for civil engineering and construction engineers to fully predict such failures. It is important not only from an engineering perspective, but also from a social perspective.

<Problems to be Solved by the Invention> To address this, for example, by connecting electrical resistance measuring devices to both ends of the PC steel wire and measuring the electrical resistance over time, one It is possible to predict the initial breakage of a book or the breakage of one wire at a time, but the multiple wires that make up a PC steel wire have complicated mutual contact and non-contact states. Furthermore, since the filling conditions of the surrounding concrete and the contact conditions with the concrete vary,
in concrete structures where the conditions are not the same.
The method of measuring the electrical resistance of PC steel wire has the disadvantage that it cannot be predicted to sufficiently guarantee reproducibility.

In addition, measuring the break position of the initial wire breakage has the disadvantage that it is extremely cumbersome in terms of equipment, and as a result, it also has the disadvantage of increasing costs.

On the other hand, acoustically, it is also possible to attach a microphone or the like to the side of the concrete bridge girder to receive the propagation energy associated with the first break as audio energy, and perform acoustic detection and measurement using this. Although theoretically possible, there is a problem that the probability of picking up environmental noise is extremely high, and therefore it is difficult to measure the detected waveform.

In particular, it is almost impossible to attach microphones to concrete structures such as concrete bridge girders on site, and there are also certain conditions that apply to research data in laboratories etc. to fatigue fractures on site. I didn't like it because it was too different and lacked practicality.

Furthermore, for example, as seen in the invention disclosed in Japanese Patent Application Laid-open No. 50-48984, there is a technique for detecting AE position markers using a narrow band AE sensor from 10 kHz to several MHz, but this technique is not suitable for steel structures, etc. Although effective, it has the disadvantage that it cannot be applied to the broadband elastic waves of several kHz to several tens of kHz for AE of concrete structures.
In addition, for example, AE sensors for steel materials include
As disclosed in the invention disclosed in Japanese Patent No. 51-12367, there is a disadvantage that the system is extremely expensive due to the addition of a preamplifier.

<Objective of the Invention> The object of the invention of this application is to solve the problem of detecting the initial breakage of tensile strength wires in order to deal with fatigue failure of concrete structures such as expressway concrete bridge girders where the tensile strength wires are integrally buried, based on the above-mentioned prior art. As a technical problem to be solved, one of the tensile strength wires consisting of multiple strands
It responds to and reliably detects only the specific frequency of elastic waves associated with the initial break of a book, and detects not only the break but also the break position without picking up any noise vibrations from the environment. An excellent method and method for predicting failure of concrete structures that benefits the field of safety technology application in the construction industry by enabling early detection of progress of fatigue due to repeated loads and taking prescribed measures through failure prediction. The aim is to provide a failure prediction device that can be used directly.

<Means/effects for solving the problem> In order to solve the above-mentioned problem, the structure of the invention of this application, which is summarized in the above-mentioned claims, is intended to solve the above-mentioned problem. In order to detect the first break in the strands of tensile strength wires such as PC steel wires that are integrally buried inside the concrete structure from both ends, a piezoelectric element is installed at a predetermined location on the surface or inside the surface of the concrete structure. When a broadband flexural vibrator such as the above is attached, and a suspended load is repeatedly applied to the concrete structure,
The above installed inside a concrete structure
Tension due to the loading load is applied to the tensile strength wires of stranded wires such as PC steel wires, and the breaking tension acts linearly with the fatigue that occurs in the concrete structure, and finally the highest tension among the stranded wires of the tensile strength wires is applied. The object that was hit breaks as the first break line, and the elastic wave of the ultrasonic wave generated at the time of the break propagates within the concrete structure and becomes a continuous reflected wave.The propagating wave passes through the concrete structure and causes the above-mentioned deflection. If multiple flexible vibrators are installed at different mounting locations, the arrival time of the waves will vary, and the flexible vibrators will transmit the elastic wave to the electric wave. The filter converts it into vibration and enters the filter of the fracture prediction device, and the filter removes the elastic waves of noise vibrations from the environment and the vibrations caused by concrete cracks, etc., other than the elastic waves of the first wire breakage, and detects the first wire breakage. Input only the elastic waves of
By monitoring such detection conditions, we can monitor the progress of fatigue failure in concrete structures after the first wire breakage occurs, and develop technical measures that allow us to take countermeasures before an unexpected situation occurs. This is what I learned.

<Example> Next, an example of the invention of this application will be described below with reference to the drawings.

The illustrated example is a mode of failure prediction when a concrete bridge girder of an expressway is used as a concrete structure. The target is a concrete bridge girder 2 that is prestressed by having three prestressed PC steel wires 1, 1, 1, etc. buried internally.

This example is intended for testing, and the three PC steel wires 1, 1, 1 are buried at predetermined equal intervals in the width direction, as shown in FIG. The concrete bridge girder 2 is a support with a predetermined span,
3 and 3', and repeatedly apply loading loads F and F downward from above by an appropriate actuator (not shown).

Reference numeral 5 denotes a fracture prediction device provided separately on the concrete bridge girder 2, which constitutes one aspect of the invention of this application. and a measuring section 7 electrically connected to the measuring section 6, and the detecting section 6 consists of three broadband flexible vibrators 8, which are attached and fixed to the bottom surface of the concrete bridge girder 2 via a predetermined adhesive. 8, 8 are located at the same position in the longitudinal direction along the three PC steel wires 1, 1, 1 that are integrally buried in the concrete bridge girder 2, and are provided below each PC steel wire 1 in the width direction. It is being

Each of the flexible vibrators 8 is a type of AE sensor, but is made of a piezoelectric element such as barium titanate, which is commonly commercially available, and has a frequency range of several Hz to several hundred kilohertz. It has a fundamental frequency of (AE generated by concrete destruction or PC steel wire breakage is an elastic wave of several kHz to several 10 kHz, so the flexible vibrator of the invention of this application is suitable. However, it is not applicable to AE sensors that require the narrowband preamplifier mentioned above.)
Detected vibrations can be transmitted from each connector 10 to the measuring device 7, and the piezoelectric element 9 and connector 10 are combined into a unit by a case 11 and fixed to the bottom of the concrete bridge girder 2 at the above-mentioned set interval positions. This is what is being done.

Therefore, as shown in the figure, by attaching each flexible vibrator 8 at the set position, three PC steel wires 1,
When the first wire of any one of 1 and 1 breaks for the first time, as shown in Figure 2, the elastic wave generated by the break from the first wire breaks. The ultrasonic wave propagates within the concrete bridge girder 2 directly or as a reflected wave, and due to the time lag in reaching each flexible vibrator 8, the ultrasonic wave propagates within the concrete bridge girder 2 in both the width direction as well as the length direction.
The measuring unit 7 is configured to detect whether or not the first breakage has occurred in the PC steel wire 1.

Once the first break occurs in the PC steel wire, the measurement unit 7 detects only the elastic waves of the trigger operation and eliminates elastic wave vibrations caused by surrounding environmental vibrations, cracks in concrete, etc. A high-pass or band-pass filter 12 serving as a filter is electrically connected to each flexible vibrator 8, and the filter 12 is further connected to a waveform storage device 13 to which the trigger operation is continuously applied. The waveform storage device 13 is electrically connected in parallel to a storage device 14 and a clock 15 of the time measuring device, so as to record the time at which the trigger operation occurs.

Therefore, only the elastic waves from the initial disconnection are input to the waveform storage device 13.

The clock 15 of this time measurement device can also be used as a counter for recording the number of times the load F4 is repeatedly placed on the rack.

In the recording device 14, as shown in FIGS. 3 and 4, a recording paper 16 is wound around a drum (not shown).
is fed out and runs at a constant speed, and a recording pen (not shown) records the waveforms of the detected elastic waves (time t on the horizontal axis and voltage on the vertical axis) from the three flexible vibrators 8, 8, 8. has been done.

Depending on the design, there may be an arbitrary (first disconnection)
The recording device 14 may be designed to operate when the first triggering ultrasonic wave from the PC steel wire 1 is generated to store the elastic waves of successive triggering operations.

In the above-mentioned configuration, when the repeated loading load F4 is repeatedly applied to the concrete bridge girder 2 from above by a predetermined actuator (the repeated application status of the loading load is of course recorded by another recording and measuring device). (measured and recorded), an initial break occurs in one of the strands of PC steel wires 1, 1, 1 at a predetermined timing due to an increase in the loading load F4, and the elasticity due to ultrasonic waves at the time of the breakage occurs. As shown in FIG. 2, the wave propagates within the concrete bridge girder, and the direct wave and reflected wave propagate within the concrete bridge girder 2 and reach the piezoelectric element 9 of each flexible vibrator 8. Received.

In this case, the acoustic waves from the PC steel wire 1 differ in sound pressure from the elastic waves caused by cracks in concrete, etc., and only the elastic waves caused by the initial break are input into the waveform storage device 13 by the filter 12.

At this time, since there is no trigger vibration before the first wire breakage occurs, no vibration occurs in the recording paper 16 of the recording device 14, as shown in FIG. 3.

Therefore, when the first breakage of one of the strands of the PC steel wire 1 occurs, in this embodiment, the time difference is determined according to the reception of the trigger vibration of the three flexible vibrators 8, 8, 8. Each of the signals is immediately converted into an elastic wave, converted into an electric signal, and transmitted through a filter 12 to a waveform storage device 13.

The filter 12 removes noise vibrations and disturbance vibrations from other measuring devices and peripheral equipment for the concrete bridge girder 2, as well as elastic wave vibrations caused by cracks in the concrete, etc., and stores them in the waveform storage device 13. When the set voltage (voltage caused by the elastic wave from the first disconnection set in advance) is exceeded, the signal is temporarily stored.

Then, the received elastic wave signal is transmitted to a recording device 14.
As shown in Figure 4, the continuous waveform of the trigger signal from the occurrence of trigger vibration is accurately recorded. As shown in FIG. 4, time differences t, t', and t'' are generated and recorded according to the difference in the propagation of the elastic waves to each of the flexible vibrators 8, 8, and 8.

In addition, as described above, the time difference between the signals input to the waveform storage device 13 is stored by the clock of the time measurement device 15, and it is possible to determine which strand of the PC steel wire 1 caused the first breakage according to the time difference. It can be calculated immediately by a computer (not shown),
The location of the break can be determined.

Thus, the fracture position can be determined not only in the longitudinal direction but also in the lateral direction by recording the reception record of the first trigger action elastic wave detected and measured.

Therefore, when the state of the detected elastic wave changes from the state shown in FIG. It is possible to immediately detect the first breakage of the stranded PC steel wire 1 buried inside where it cannot be visually observed, and thereby it is possible to non-destructively predict fatigue failure of the concrete bridge girder 2.

It goes without saying that the embodiments of the invention of this application are not limited to the above-mentioned embodiments. For example, in the above-mentioned embodiments, the flexible vibrators are arranged in the horizontal direction, but they may also be arranged in the vertical direction, or is horizontal, and
Various embodiments can be adopted in which the first breaks of a plurality of PC steel wires can be detected and measured three-dimensionally by arranging them in a two-dimensional matrix in the longitudinal direction.

Furthermore, although the above-mentioned embodiments are for testing and experimentation, measurements may be taken by attaching the apparatus of the invention of this application at predetermined intervals to concrete bridge girders of expressways that are actually constructed, or Of course, it is also possible to attach and detect predetermined locations at different times over time, and it can also be applied to concrete structures with buried tensile strength lines other than expressway concrete bridge girders. Of course.

<Effects of the Invention> As described above, according to the invention of this application, fatigue failure of concrete structures in which tensile strength wires such as prestressed steel wires are integrally buried, such as concrete bridge girders of expressways, is basically minimized in a non-destructive manner. This has the advantage of being able to detect and measure early, predicting fatigue failure before it becomes fatal, and taking appropriate repairs.

Since it is a non-destructive inspection, it also has the advantage that it does not cause any damage to the concrete structure itself, such as concrete bridge girders, and can be inspected and measured while maintaining normal usage conditions. be done.

In addition, by detecting the elastic waves propagating inside the structure when the first break of the tensile strength wires, such as twisted wires of tensile strength wires, which are integrally buried inside the structure, elastic waves of a specific frequency can be detected. In order to be able to detect only
Because noise vibrations from the environment, disturbance vibrations, and elastic vibrations caused by cracks in concrete can be removed and detected without the influence of these, the inspection and measurement can be performed with great accuracy. Ru.

In addition, the flexible vibrator can be easily attached to a predetermined outer surface of the structure by adhesive or other means using a commercially available piezoelectric element, which has the excellent effect of making preliminary work easier. It also has the advantage that the detection device can be installed relatively easily.

In this device, since the flexible vibrator is electrically connected to the filter, it is possible to remove external vibrations, etc. as described above, and only the elastic waves caused by the initial disconnection can be input. Furthermore, since a recording device is provided, the inspection and measurement can be visually observed, which also has the effect that the data can be used for other inspection and measurement, and that accurate measures can be taken.

In addition, since the waveform storage device is electrically connected to the time measurement device, it is possible to detect only specific trigger vibrations in which only waveforms exceeding a predetermined voltage are stored, thereby increasing the accuracy of measurement. This has the excellent effect of maintaining the fatigue fracture, and the time measurement device allows us to know where the first breakage occurred, and therefore, it is possible to determine the location where fatigue failure occurs or where it is predicted to occur in the entire structure. Since it is possible to detect this, there is also the effect that modal measures can be taken accurately.

[Brief explanation of the drawing]

The drawings are explanatory diagrams of one embodiment of the invention of this application, in which Fig. 1 is a vertical cross-sectional side view of a portion where the initial breakage of fatigue fracture is detected, Fig. 2 is a cross-sectional image of the same, and Fig. 3 is a diagram showing the occurrence of the initial breakage of fatigue fracture. FIG. 4 is a plan view of the recording state in a state where there is no wire breakage, and FIG. 4 is a plan view of the trigger waveform generated due to the initial disconnection. DESCRIPTION OF SYMBOLS 1... Tensile force line, 2... Structure, 8... Flexible vibrator, 12... Filter, 13... Waveform storage device, 14... Recording device, 15... Time measuring device.

Claims (1)

[Scope of Claims] 1. A method for predicting fatigue failure of a concrete structure in which a tensile strength wire consisting of a plurality of wire aggregates is buried by detecting the occurrence of the first breakage of the wire. A concrete structure failure prediction method characterized by detecting and monitoring and recording only the elastic waves propagated within the structure due to the initial breakage of the strands at the surface of the concrete structure. 2. The method for predicting failure of a concrete structure according to claim 1, wherein the detection of the elastic wave is performed by a flexible vibrator. 3. The concrete structure failure prediction method according to claim 1, wherein the elastic waves are detected at a plurality of positions on the surface of the concrete structure. 4. The method for predicting failure of a concrete structure according to claim 3, wherein the position of the first break of the wire is detected by detecting the elastic waves. 5. In a device that is directly used in a method for predicting fatigue failure of a concrete structure in which a tensile strength wire consisting of a plurality of wire aggregates is buried by detecting the first breakage of the wire, the above tensile strength wire is A flexible vibrator attached to the surface of the buried concrete structure is electrically connected to a filter, and the filter is electrically connected to a waveform recording device that is connected to a recording device and a time measuring device. A concrete structure failure prediction device characterized by: 6. The concrete structure failure prediction device according to claim 5, wherein the filter is a high-pass filter. 7. The concrete structure failure prediction device according to claim 5, wherein the flexible vibrator comprises a piezoelectric element.