JP6550015B2 - Failure detection method of tendon in prestressed concrete structure - Google Patents

Description

  The present invention relates to the above tension in a prestressed concrete structure (hereinafter referred to as a PC structure) in which a concrete structure is prestressed by an unbond method or an outer cable method by a tendon such as a PC steel rod or PC steel material. The present invention relates to a method for detecting breakage of a material.

  With regard to the breakage of the tendon in the PC structure such as a road bridge or a railway bridge, it is important to detect the breakage of the tendon in advance to predict the collapse of the PC structure. Therefore, as a conventional tendon monitoring system, for example, as described in Patent Document 1, in order to distinguish between a signal due to breakage of the tendon and a signal due to noise, the energy of the leading portion of the signal is A ratio to the total energy is determined, and a signal whose ratio is larger than a threshold is judged as a noise signal which is a signal with large attenuation, and a signal smaller than the threshold is judged as a signal due to breakage of a tendon which is a signal whose attenuation is small. The method of doing is known.

JP, 2005-291735, A

  However, in the conventional PC structure, for example, in the post tension type PC structure, deterioration caused by adhesion of a tendon or poor filling of a PC grout material (bond method) for the purpose of rust prevention is Breaking of the tendon has occurred.

  Therefore, many unbonded type and outer cable type PC structures that do not require the filling of the grout material are designed and adopted. Even in such a PC structure, it is important to detect breakage of the tendon accurately. The method for detecting breakage of a tendon in a prestressed concrete structure according to the present invention is proposed to solve such a problem.

The gist of the method for detecting breakage of a tendon in a prestressed concrete structure according to the present invention for achieving the object by solving the above problems is a tendon in a prestressed concrete structure provided with a prestress by an unbonded method or an outer cable method. Was measured by the sensor in a method of measuring an elastic wave with a sensor provided in the structure, and distinguishing and detecting a noise signal and a signal due to a break of the tendon according to the characteristics of the elastic wave. A desired noise determination threshold is set in the frequency band of the elastic wave, and a break of the tension material is observed and detected in real time depending on whether the set noise determination threshold and the frequency band of the detected signal are small or large. It is.

A signal in a band smaller than the set noise judgment threshold is judged as a noise signal, a signal in a band larger than the noise judgment threshold is judged as a signal due to breakage of the tension material, and the breakage of the tension material is detected. is there.

The set threshold for noise determination is a frequency of 500 Hz.

  The second aspect of the present invention is to provide a second determination means based on an attenuation time, which determines whether the attenuation time of the elastic wave exceeds a desired attenuation threshold.

  The breaking position of the tendon is determined from the difference in propagation time to the sensor of the elastic wave signal exceeding the noise determination threshold value.

  A broadband elastic wave sensor is provided in the vicinity of the fixing portion of the tendon to detect a signal due to breakage of the tendon.

  According to the method for detecting breakage of a tendon in a PC structure according to the present invention, a noise signal and a signal due to breakage of the tendon can be reliably discriminated and detected. Thus, the collapse of the PC structure can be reliably predicted in advance. In addition, using a band pass fitter, running noises from vehicles etc. can be reliably eliminated, and signal data from broken tendons can be acquired and stored, so a large amount of data can be stored as in the prior art. The inconvenience of saving is eliminated.

  Furthermore, by providing a broadband elastic wave sensor at the anchorage portion of the tendon, it is possible to construct an efficient and economical tensor break detection system. In addition, since the detection method according to the present invention can be implemented compactly using a commercially available device, the cost can be reduced.

It is a basic schematic block diagram of the fracture detection method of the tendon in the PC structure concerning the present invention. It is a longitudinal cross-sectional view of the Example which provided AE sensor in nine places in the PC structure (bridge girder) in the fracture detection method of the tendon in the prestressed concrete structure of the same invention. They are the cross-sectional view (A) along the XX line, and the cross-sectional view (B) along the YY line of the Example which provided AE sensor in said PC structure (bridge girder). A diagram showing an example in which an elastic wave due to vehicle running noise is propagated to an AE sensor provided at nine places with respect to a PC structure (bridge) on a monitor screen of a waveform storage device and detected through a low pass filter (100 Hz). is there. It is explanatory drawing which shows the example of traveling vehicle noise by which the elastic wave input into said nine AE sensors is displayed on a monitor screen through 100 Hz-5 kHz band pass filters (a)-(f). It is explanatory drawing which shows the relationship between the setting conditions of a band pass filter, and a vehicle driving | running | working noise in the attachment position of AE sensor in an upper floor slab (A-1, B-1, C-1 in FIG. 2). It is explanatory drawing which shows the relationship between the setting conditions of a band pass filter, and a vehicle driving | running | working noise in the lower floor slab (A-2, B-2, C-2 in FIG. 2) of the attachment position of AE sensor. The attachment position of the AE sensor is an explanatory view showing the relationship between the setting condition of the band pass filter and the vehicle running noise in the fixing portion (D-1, D-1, D-1 in FIG. 2) of the outer cable. is there. It is a figure of an analysis table showing analysis of existence of noise concerning each band pass filter of an elastic wave by run noise of vehicles 5. FIG. It is a flowchart figure which shows the judgment procedure of the breakage detection method of the tendon in the prestressed concrete structure concerning the present invention. It is a comparison figure (A), (B) which shows the difference of the attenuation time of an elastic wave in the fracture | rupture of a tension material, and a driving | running | working noise, and a figure (C) which shows the high-pass function of a filter.

  The method for detecting breakage of a tendon in a PC structure according to the present invention, for example, a PC structure which is a bridge girder such as a concrete building, a road bridge or a railway bridge, is an elasticity detected by a broadband sensor provided in the PC structure. The wave is determined by differentiating an elastic wave due to breakage of the tendon and an elastic wave due to running noise, using the frequency as a threshold for noise determination.

  In the present invention, as shown in FIGS. 1 to 3A and 3B, in the sensor 3 provided in the PC structure 1, breakage of the tendon 2 in the PC structure 1 causes the individual to be deformed or broken. It is a method of measuring the elastic wave 4 generated at the time of separation, and distinguishing and detecting the noise signal by the traveling of the vehicle 5 and the signal by the breakage of the tendon 2 based on the characteristic of the elastic wave 4.

  The tendon 2 is a PC steel rod or PC steel using an unbonded type or an outer cable type. By eliminating the need for PC grout of PC steel material, the grout filling failure is eliminated. The tendon 2 of the PC structure 1 of the road bridge shown in FIGS. 2 to 3A and 3B is an outer cable type tendon.

  The sensor 3 is, for example, a wide band type elastic wave sensor having constant sensitivity in a wide frequency range, AE (Acoustic Emission) sensors 3a to 3i, and uses a flexible vibrator. The wide band of the AE sensors 3a to 3i is several Hz to several hundreds kHz. According to the method of detecting the elastic wave 4 by the AE sensors 3a to 3i, the progress of breakage of the tendon 2 can be observed in real time, and a plurality of AE sensors 3a to 3i can be used to position fractures or defects. There is an advantage.

  As shown in FIGS. 1 to 3A and 3B, the AE sensors 3a to 3i are upper floor plates (A-1, B-1, C-1) and lower floor plates of the PC structure 1 ( A-2, B-2, C-2), fixing portion (D-1) of the outer cable, middle portion (D-2), and deflection portion (D-3) are provided at nine locations.

The outputs (voltages) of the elastic waves 4 due to the running noise of the vehicle 5 of the AE sensors 3a to 3i correspond to the mounting positions of each ch and the sensor 3 sequentially from the top as shown in FIG. 4-A. ,
ch1 ... A-1 (AE sensor 3a),
ch2 ... A-2 (AE sensor 3b),
ch3 ... B-1 (AE sensor 3c),
ch4 ... B-2 (AE sensor 3d),
ch5 ... C-1 (AE sensor 3e),
ch6 ... C-2 (AE sensor 3f),
ch7 ... D-1 (AE sensor 3g),
ch8 ... D-2 (AE sensor 3h),
ch9... D-3 (AE sensor 3i). In addition, the elastic wave 4 of FIG. 4-A passes through the low-pass filter of 100 Hz, and is the enlarged view which expanded (a) low-pass filter 100 Hz in FIG. 4-B for description.

  Further, when the elastic wave 4 of the running noise of the vehicle 5 in the AE sensors 3a to 3i is passed through a band pass filter, for example, the elasticity in the case of a low pass filter 100 Hz, a high pass filter 300 Hz, 500 Hz, 2 kHz, 3 kHz, 5 kHz The appearance of the waveform relating to the wave 4 is shown in FIG.

  Looking at the elastic wave 4 of the traveling noise by the vehicle 5 of FIG. 4-B, the noise component due to the traveling of the vehicle 5 mainly exists at a frequency of 500 Hz or less. These are shown in FIGS. 5 (A) to 5 (C) and 6 in the analysis of the running noise by the band pass filter. In FIGS. 5A to 5C, the vertical axis is the AE maximum voltage (mVp-p), and the horizontal axis is the filter set frequency.

  As shown in FIG. 6, the band pass filters applied to the elastic wave 4 due to the running noise of the vehicle 5 are compared. For example, in the low pass filter (100 Hz), the noise level of the ch1 to ch6 is excessive, which is unsuitable as a monitor. Also, in the high pass filter (2 kHz to 5 kHz), the noise level is almost absent, which is also unsuitable as a monitor. In such a case, it can be seen that the frequency "500 Hz" of the high pass filter is an appropriate frequency for judging the presence or absence of the traveling noise.

  Therefore, a desired threshold (hereinafter referred to as a noise determination threshold) is set in the frequency band of the elastic wave 4 measured by the sensor 3 and the signal by the running noise of the vehicle or the tension according to the threshold of the frequency Whether the signal is due to the breakage of the material 2 is detected. The noise determination threshold is, for example, a frequency of “500 Hz”.

  When the threshold for noise determination related to the frequency is determined, as shown in FIG. 1, an AE sensor (wide band type: several Hz to several hundreds kHz) 3a to 3i is provided by attaching to a suitable place on the PC structure 1; High-pass filter (High-pass function: several Hz to several 10 kHz, Performance: about 24 dB / OCT: See Fig. 8 (C)) 6 and waveform recorder 7 (specification: memory recorder, measurement range: 5mV to 20V / div, sampling Constructs an AE measurement system consisting of the minimum necessary combination of 1 μs / s or more, isolation between channels, trigger function, FFT (Fast Fourier Transform) frequency analysis), and detects elastic wave 4 due to breakage of tension material 2 Do.

  As shown in FIG. 7, the method for detecting breakage of a tendon in a PC structure according to the present invention will be described with reference to a flowchart. AE sensor provided on PC structure 1 in the first step (hereinafter referred to as ST) 1 At 3, nine elastic waves 4 are detected. Note that one of the nine AE sensors (3a to 3i) does not always measure the elastic wave 4 in the real mode but to measure it efficiently. When it exceeds, it is preferable to start a trigger and to automatically record the elastic wave 4 by the waveform recording device 7.

  Next, at ST2, the elastic wave 4 passes through the high pass filter 6 and reaches the waveform recording device 7 at ST3. The waveform recording device 7 converts the analog signal of the elastic wave 4 input into a digital signal, and transmits the digital signal to a control device (not shown) of a personal computer, and the detection program incorporated in the control device is converted to data. It is transmitted as

  In ST4, in the detection program, for example, the signal according to the threshold of the presence or absence of the signal set for each channel by screening data concerning the maximum voltage amplitude of the elastic wave 4 or the average value of the maximum voltage amplitude. The data is converted to "0" for no and "1" for signal.

  At the positions of the AE sensors 3a to 3i, which are data for the presence or absence of the signal, at each of the nine channels, the number of points where the position becomes 1 at 100 Hz to 500 Hz under the filter setting conditions is large If the number of places where the position is “0” is large, this is because the component of the elastic wave 4 is the running noise of the vehicle 5 in ST 4 and there is no running noise signal at frequencies above 500 Hz, “No” It is determined that the process returns to ST1.

  The data relating to the presence or absence of the signal in the elastic wave 4 becomes "0" at 100 Hz to 500 Hz under the filter setting conditions at the positions of the nine AE sensors 3a to 3i corresponding to the respective channels, contrary to the above. If the number of positions is large, and the number of positions becoming “1” at 1 kHz or more is large, the component of the elastic wave 4 is due to breakage of the tension material 2 in ST 4 and this is for noise determination Since it exists in "a frequency of 500 Hz or more" related to the threshold value, it is judged "Yes" and it goes to ST5.

  At ST5, it is determined whether the attenuation time of the waveform of the elastic wave 4 is long or short. In this case, as shown in FIGS. 8A and 8B, the damping time of the elastic wave 4 is long (for example, about 10 ms) in the damping time of the waveform in the tension material breakage, and the noise during running of the vehicle is Uses a known judging means that the decay time of the waveform is short (for example, about 1 ms).

  The elastic wave 4 due to the tension material breakage shown in FIG. 8A is considered to be in the range of 3 to 90 kHz in which the dominant frequency exceeding the setting voltage amplitude appropriately set. This ST5 is a step as a second determination means for confirming that the elastic wave 4 is a signal due to breakage of the tendon 2 just in case.

  Therefore, in ST5, the numerical value of the attenuation time of the waveform of the elastic wave 4 is compared with the set threshold value for attenuation (for example, 5 ms), and if it is shorter, it becomes "No" and returns to ST1. "Yes" and go to ST6.

  At ST6, it is determined that the waveform of the elastic wave 4 is a signal due to breakage of the tension material 2 and whether to go to the position evaluation of the fractured part of ST6a or alarm means (means such as known sound, light blink, vibration, warning image display etc. Go to ST7 to notify in). The alarm means is transmitted from the local AE measurement system with the PC structure 1 to a plurality of management offices etc. that remotely monitor the PC structure 1 by, for example, a network line such as the Internet. An alarm signal may be simultaneously transmitted to share crisis management information between the local and remote locations.

  In the step ST6a, the difference between the time when the elastic wave 4 firstly propagates to the AE sensor among the plurality of AE sensors (3a to 3i) and the time when the elastic wave 4 propagates to AE sensors in other places, The cut tendon 2 of the plurality of tendons 2 and the broken position thereof are obtained by a known method.

  As notified by the alarming means at ST7, at ST8, replacement work of the tendon 2 in the PC structure 1 and the like are performed. Then, the detection process of the elastic wave 4 ends.

  Thus, depending on whether the component of the elastic wave 4 generated in the PC structure 1 is less than or equal to 500 Hz, which is the frequency of the threshold for noise determination, whether it is a noise component due to traveling of the vehicle 5 or tension The breakage of the tendon 2 is detected by judging whether the component is the breakage of the material 2 or not. In addition, when the said determination method is processed by an automatic program etc., it does not specifically limit, also when using a manual. Moreover, unless it is contrary to the meaning of this invention, it does not restrict to said one Example, and includes all the well-known means.

  In the method of detecting breakage of a tendon in a PC structure according to the present invention, the presence or absence of breakage of the tendon can be determined with certainty depending on where in the frequency band the waveform component of the elastic wave is present. It can be widely applied to the safety management of tendons in bridges and other PC structures.

1 PC structure,
2 tendons,
3 sensors, 3a to 3i AE sensors,
4 elastic waves,
5 vehicles,
6 high pass filter,
7 Waveform recorder.

Claims (3)

Breaking of the tendon in the prestressed prestressed concrete structure by the unbond method or outer cable method is measured for the elastic wave by the sensor provided on the structure, and the characteristics of the elastic wave determine the noise signal and the tendon In the method of distinguishing and detecting the signal due to breakage,
A desired noise determination threshold is set in the frequency band of the elastic wave measured by the sensor,
Observing and detecting breakage of a tendon in real time depending on whether the set threshold for noise determination and the frequency band of the detected signal is small or large ;
Method of detecting breakage of tendon in prestressed concrete structure characterized by A signal of a band smaller than the set noise judgment threshold is judged as a noise signal, a signal of a band larger than the noise judgment threshold is judged as a signal due to breakage of the tension material, and breakage of the tension material is detected.
A method for detecting breakage of a tendon in a prestressed concrete structure according to claim 1, characterized in that: The set threshold for noise determination may have a frequency of 500 Hz,
A method for detecting breakage of a tendon in a prestressed concrete structure according to claim 1, characterized in that:

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