JP6236413B2 - Deformation monitoring method for road bridge deck - Google Patents

Description

  The present invention relates to a road bridge deck deformation monitoring method for detecting the progress of damage such as cracks occurring in a concrete floor slab of a road bridge by utilizing vibration caused by a passing vehicle.

Conventionally, in order to ensure the safety of concrete slabs on road bridges, close visual inspection is basically performed.
However, in such concrete slabs, fatigue may occur due to fatigue caused by repeated loading of the traveling vehicle or aging of concrete and reinforcing bars, and cracks may develop inside the concrete, and these internal cracks can be grasped visually. I can't.

  In addition, the crack width of the concrete surface is small, and it is often difficult to accurately grasp the progress of the crack by visual inspection.

  Therefore, strain gauges and crack displacement meters are installed on the above concrete slabs to measure strain and crack width, to measure strain and crack width using optical fiber, and to measure AE waves (acoustic emission). Various deformation monitoring techniques have been developed, such as a technique for detecting the occurrence of damage by this method and a method for evaluating the soundness of a structure by paying attention to changes in the natural frequency of the structure.

  However, the method using a strain gauge or a crack displacement meter monitors a specific part or crack, and cannot grasp the occurrence or progress of deformation other than the part where the sensor is arranged. In addition, since the technology using optical fibers measures the displacement of the place where the optical fiber is installed, it is impossible to grasp the occurrence and progress of deformation outside the location where the sensor is located, and cracks inside the concrete will occur. However, there is a problem that progress cannot be monitored.

  In addition, the AE method can detect damage inside the concrete, but if it covers a wide area, it is necessary to place a large number of sensors, which increases costs and is susceptible to noise. When large vibrations are always generated like road bridge decks, noise countermeasures are an issue. Further, the method using the natural frequency of the structure has a problem that the progress of deformation cannot be monitored from the viewpoint of the evaluation accuracy of the natural frequency.

  On the other hand, the present inventors previously described in Patent Document 1 below as a method for monitoring the deformation of a tunnel lining to prevent the concrete pieces of a railway tunnel such as a Shinkansen or a conventional line from peeling off. The frequency characteristics of the acceleration of vibration propagating to the railway tunnel lining and the propagation speed between sensors are repeatedly measured and accumulated by the vibration generated when traveling, and the frequency characteristics of the acceleration deviating from the accumulated data are detected. Therefore, we proposed a method to monitor the progress of the deformation that occurred in the railway tunnel lining.

  In Patent Document 2 below, as a method for inspecting metal corrosion in a concrete structure in which a metal plate is integrated on a concrete surface and a reinforcing metal member is disposed inside the concrete, the method is low from the surface side of the metal plate to the inner surface side. Detects the presence of corrosion products and voids by transmitting high frequency ultrasonic waves (25kHz to 250kHz) and receiving the reflected waves, and transmits high frequency ultrasonic waves (500kHz to 2MHz) from the surface side to the inner surface side of the metal plate And the method of detecting the thickness reduction of a metal plate by receiving the reflected wave is disclosed.

JP 2011-133410 A JP 2004-163263 A

  However, if these prior arts are applied to the road bridge deck deformation monitoring method, in the invention described in Patent Document 1, the target vibration is a level exceeding 50 db in the range of 100 Hz to 1 kHz. However, in the road bridge deck, the shape of the road bridge is different depending on the type and speed of the traveling vehicle. There is a problem that it is not suitable for monitoring the deformation of concrete slabs.

  On the other hand, in the invention described in the above-mentioned Patent Document 2, it is a technique for detecting corrosion and thickness reduction of a metal plate and is based on receiving a reflected wave oscillated from an ultrasonic probe. Only the change directly above the probe can be captured. Therefore, it is not possible to apply when the location where a crack is generated is not known in advance, such as a crack generated in a concrete slab.

  In addition, fatigue cracks in road bridge decks are often generated in the vertical direction with respect to the deck, and the extension direction of such cracks is consistent with the oscillation direction of vibration from the probe. In addition to detecting the occurrence and progress of cracks, the probe cannot be applied to wide-area monitoring such as road bridge decks because it uses a probe to transmit ultrasonic waves for local flaw detection. .

  The present invention has been made in view of the above circumstances, and it is possible to continuously monitor a road bridge deck with a simple device, and it is a significant change that requires examination of countermeasures from the progress of fine deformation. It is an object of the present invention to provide a method for monitoring the deformation of a road bridge deck that makes it possible to capture the signs of the failure.

  In order to solve the above-mentioned problem, the invention according to claim 1 is configured to reduce the vibration acceleration of the floor slab caused by the traveling of the passing vehicle by two or more acceleration sensors installed at intervals on the floor slab of the road bridge. Measure the Fourier spectrum in the range from 0 to 4000 Hz by Fourier transform using the acceleration time history data obtained by the measurement, and then calculate the Fourier spectrum ratio between the two acceleration sensors The progress of the first deformation in the floor slab is monitored based on the change in the Fourier spectrum ratio, and the acceleration time history data obtained by the measurement is used to measure the frequency range from 0 to 20 Hz. Calculate the Fourier spectral ratio and monitor the behavior that leads to the second deformation larger than the first deformation based on the change in the Fourier spectral ratio. And it is characterized in Rukoto.

ｘ：元となる状態における２点間の上記フーリエスペクトル比の自然対数値
ｙ：ｘの状態から時間が経過した後の２点間の上記フーリエスペクトル比の自然対数値 Ｃｏｖ（ｘ、ｙ）：ｘとｙとの共分散
σ_ｘ、σ_ｙ：ｘ、ｙの標準偏差
の増加によって上記第１の変状の進展を評価することを特徴とするものである。 Further, in the invention described in claim 2, the following progress index R calculated from the Fourier spectrum ratio in the invention described in claim 1,

x: Natural logarithm of the Fourier spectrum ratio between two points in the original state y: Natural logarithm of the Fourier spectrum ratio between two points after time has elapsed from the state of x Cov (x, y): Covariance between x and y σ _x , σ _y : The progress of the first deformation is evaluated by increasing the standard deviation of x and y.

  Furthermore, in the invention according to claim 3, in the invention according to claim 2, when the progress index R exceeds a set value in a range of 0.4 to 0.6, The natural logarithm value x of the Fourier spectrum ratio between two points is set again as an initial value after exceeding the set value, and monitoring is continued.

Ｚ_０：元となる状態における２点間の上記フーリエスペクトル比の自然対数値
Ｚ_ｎ：Ｚ_０の状態から時間が経過した後の２点間の上記フーリエスペクトル比の自然対数値
Ａ：ａ＝０（Ｈｚ）〜ｂ＝２０（Ｈｚ）間のＺ_ｎの合計値
Ｂ：ａ＝０（Ｈｚ）〜ｂ＝２０（Ｈｚ）間のＺ_０の合計値
の増加によって上記第２の変状に至る挙動を監視することを特徴とするものである。 Further, in the invention according to claim 4, in the invention according to any one of claims 1 to 3, the following progress index E calculated from the Fourier spectrum ratio,

Z ₀ : Natural logarithm of the Fourier spectrum ratio between the two points in the original state Z _n : Natural logarithm of the Fourier spectrum ratio between the two points after a lapse of time from the state of Z ₀ A: a = 0 (Hz) ~b = 20 ( Hz) the total value of _{Z n} between B: a = 0 (Hz) ~b = 20 (Hz) said second Deformation by increasing the total value of _{Z 0} between the It is characterized by monitoring the reaching behavior.

  The invention according to claim 5 uses the acceleration sensor installed at the center of the floor slab as one of the two acceleration sensors in the invention according to any one of claims 1 to 4. It is characterized by this.

  Since the vibration generated in the road bridge deck by the passing vehicle differs depending on the time zone and the weight and speed of the passing vehicle, the Fourier spectrum of the measured acceleration of the vibration differs depending on the time zone. On the other hand, the potential development of crack width and length in the road bridge deck, and the development of deformation such as peeling and flaking change the boundary conditions of vibration, and therefore transfer the vibration of the object. Changes occur in the characteristics.

  And in invention of any one of Claims 1-5, in the state where deformation does not progress, it uses the Fourier spectrum ratio between two points which become a fixed relationship based on the transmission characteristic of the said vibration, and the said road Because the occurrence and progress of deformation in the bridge deck are monitored, changes in the transmission characteristics of the above vibrations caused by potential progress in crack length, progress of deformation such as peeling and flaking are constantly observed. I can grasp it.

  At this time, if the vibration wavelength is too larger than the change propagation length, it is difficult to detect a slight deformation progress by a change in vibration transfer characteristics. Since the range up to a high frequency band of 0 to 4000 Hz is taken into consideration, the progress of the potential or local fine deformation (first deformation) can be monitored.

  In addition, as a result of verification at the time of the wheel load running test of the floor slab by the inventors, which will be described later, by paying attention to the Fourier spectrum ratio in the range up to a relatively low frequency of 0 to 20 Hz obtained by the above measurement, We obtained knowledge that the signs can be grasped in advance before the plate has undergone significant changes (second change) that require countermeasures.

  Therefore, in addition to being able to constantly monitor the occurrence and progress of the first deformation in the road bridge deck, by further monitoring the change in the Fourier spectrum ratio in the range from 0 to 20 Hz, further The progress of the second deformation can be monitored, so that the sign can be detected in advance before a significant deformation occurs on the floor slab that requires countermeasures to be examined.

  In addition, since traffic vibrations on road bridge decks are constantly generated, acceleration sensors and control devices are installed, and automatic measurement and calculation processes are performed. Accumulation and monitoring can be performed, and as a result, it is possible to grasp the precursors from the progress of minute changes to the significant changes that require examination of countermeasures.

  Further, when monitoring the progress of the first deformation and the second deformation based on the change of the Fourier spectrum ratio, the progress index R and the progress index E as in the invention of claim 2 or 4 are set. If used, it is possible to grasp the change of the vibration transfer characteristic, that is, the progress of the first and second deformations with high accuracy.

  At this time, the progress index R can grasp the progress of fine deformation, but has a tendency to decrease in accuracy when it becomes a large numerical value. Then, after exceeding a preset value in the range of 0.4 to 0.6, the natural logarithm value (initial value) x of the Fourier spectrum ratio between the two points in the original state is set again for monitoring. It is preferable to continue.

  Further, according to the invention described in claim 5, as one of the two acceleration sensors for measuring the vibration acceleration for calculating the Fourier spectrum ratio, it is installed at the center portion of the floor slab in which a larger acceleration is generated. Therefore, it is possible to further improve the accuracy of deformation detection.

It is a perspective view which shows the road bridge deck targeted by one Embodiment of this invention. It is a perspective view from the bottom face side which shows arrangement | positioning of the acceleration sensor etc. of FIG. It is a flowchart of the said one embodiment. It is a graph which shows the change of the progress parameter | index R at the time of measuring the vibration acceleration of the day of an actual concrete floor slab in the Example of this invention. It is a graph which shows the relationship between the frequency | count of loading and the change of the progress parameter | index R in the wheel load running test done using the test body which imitated the said floor slab. It is a graph which shows the change of the progress parameter | index R when the progress parameter | index R of FIG. 5 is updated to the initial value sequentially. It is a graph which shows the change of the progress parameter | index E at the time of measuring the vibration acceleration of the day of an actual concrete floor slab. It is a graph which shows the relationship between the frequency | count of loading and the change of the progress parameter | index E in the wheel load running test done using the test body which simulated the said floor slab.

Hereinafter, based on FIGS. 1-3, one Embodiment of the deformation | transformation monitoring method of the road bridge deck according to this invention is described.
In this deformation monitoring method, as shown in FIG. 1 and FIG. 2, a plurality of (3 in the figure) spaced in the traveling direction of the vehicle on the lower surface of the concrete slab 2 installed between the beams 1 of the road bridge. The acceleration sensor 3 is installed in each of the locations P _{1 to} P ₃ . At this time, the three acceleration sensors 3 are installed on the lower surface of the concrete floor slab 2 at both ends P ₁ and P ₃ and the center P ₂ in the traveling direction.

  Further, on the lower surface of the concrete slab 2, a progress index R and a progress index E, which will be described later, are automatically calculated at predetermined time intervals based on detection signals from these acceleration sensors 3, and the resulting data Is installed.

  The acceleration sensor 3 measures the acceleration of vibration generated by the vehicle traveling on the concrete floor slab 2 as shown in FIG. At this time, acceleration in a frequency range of 0 to 4000 Hz is measured for several minutes (about 1 to 3 minutes) at a sampling interval of 12 kHz or more, for example, and stored in the control device 4 as time history data.

Next, the control device 4 calculates a Fourier spectrum by Fourier transform using time history data of acceleration ranging from 0 to 4000 Hz, and further calculates a Fourier spectrum ratio between the two acceleration sensors 3 for smoothing. Turn into. At this time, as one of the acceleration sensor 3, used those placed in the center portion P ₂ of the slab 2. Then, the progress index R is calculated from the obtained Fourier spectrum ratio by the following equation (1).

Here, x is a natural logarithm value (initial value) of the Fourier spectrum ratio between the two points in the original state, and y is the Fourier spectrum ratio between the two points after a lapse of time from the state of x. The natural logarithm value, Cov (x, y) is the covariance between x and y, and σ _x and σ _y are the standard deviations of x and y, respectively.

  Then, the progress of the minute deformation (first deformation) is monitored by the calculated progress index R. Incidentally, when the progress index R increases with time, it is assumed that fine deformation has progressed. At this point, it can be determined whether or not monitoring is necessary.

  And if the said progress parameter | index R increases and becomes a big numerical value, the precision of the said progress parameter | index R will fall. Therefore, the upper limit value of the progressive index R is set to a value in the range of 0.4 to 0.6 (for example, 0.5) in advance, and when the set value is exceeded, the above formula (1) The natural logarithm value x of the Fourier spectrum ratio between two points in the original state is set again as the initial value after exceeding the set value, the progress index R is calculated, and the progress of the deformation is continuously monitored. To do.

  In parallel with this, data of a sampling interval of about 100 to 200 Hz is created using the above-described time history data of acceleration ranging from 0 to 4000 Hz. Similarly, after calculating and smoothing the Fourier spectrum ratio between the two points, the progress index E for evaluating the significant deterioration progress (second deformation) of the floor slab 2 by the following equation (2). Is calculated.

Here, Z ₀ is the natural logarithmic value of the Fourier spectrum ratio between the two points in the original state, and Z _n is the natural value of the Fourier spectrum ratio between the two points after a lapse of time from the Z ₀ state. logarithm, a is, a = 0 (Hz) ~b = 20 (Hz) the total value of _{Z n} between, B is, a = 0 (Hz) ~b = 20 (Hz) total value of _{Z 0} between It is.

  Then, when the obtained progress index E increases, it is determined that the deterioration of the floor slab 2 has progressed remarkably, and detailed countermeasures are examined.

  As described above, according to the above-described road bridge deck deformation monitoring method, a plurality of acceleration sensors 3 installed on the road bridge deck 2 generate 0 to 4000 Hz generated by a vehicle traveling on the floor deck 2. By measuring the vibration acceleration in the range up to a high frequency, calculating the Fourier spectrum ratio between two points from the Fourier spectrum of the acceleration, calculating the progress index R, and monitoring the increase in the progress index R, the road bridge Since the occurrence and progress of deformation in the floor slab 2 are judged, the first minute deformation such as the potential or local progress of the crack length, peeling or flaking is always grasped with high accuracy. be able to.

  Furthermore, in addition to being able to constantly monitor the occurrence and progress of the above-mentioned fine first deformation in the road bridge deck 2, the progress index E is determined from the Fourier spectrum ratio in the range from 0 to 20 Hz. Since the calculation of the progress index E can also grasp the second deformation that leads to significant deformation that requires significant countermeasures due to significant deformation of the floor slab, By monitoring the second deformation, the sign can be detected in advance before the floor slab 2 undergoes a significant deformation that requires examination of countermeasures.

  In addition, since traffic vibrations are constantly generated in the road bridge deck 2, the acceleration bridge 3 and the control device 4 are installed to automatically perform measurement and calculation processing, thereby allowing the road bridge deck to be obtained with a simple device. 2 can be accumulated and monitored, and as a result, it is possible to grasp the precursors from the progress of fine deformation to the significant deformation that requires examination of countermeasures.

The acceleration of traffic vibration was measured on the concrete slab of a real bridge. The target floor slab was 20m wide x 35m long, and two acceleration sensors were installed at 15m intervals on the bottom of the floor slab.
The deformation progress index R was calculated using the above equation (1) for the vibration acceleration measured by the acceleration sensor up to a high frequency band (0 to 4,000 Hz). The vibration acceleration was measured 15 times a day.

  Since each of the 15 measurements is a short time, it is considered that there is no progress of deformation in the floor slab during this period. FIG. 4 shows this result, and the value of the deformation progress index R is less than 0.1, and it was confirmed that when the floor slab is not deformed, it stably shows a small value. .

Next, a wheel load running test was carried out using a specimen simulating a concrete slab. The dimensions of the specimen were 2.8m x 4.5m, and two accelerometers were installed at 1.8m intervals.
Here, the wheel load running test is a test in which a vertical load is loaded by reciprocating a wheel load (iron wheel) on a specimen. In this test, the vertical load was increased stepwise from 157 kN to 353 kN. The maximum wheel load speed is 25 reciprocations / minute (50 times / minute).

  Fig. 5 shows the progress index based on the frequency characteristics of the vibration acceleration for the number of repeated loads on the slab in the above test, the displacement of the center of the slab and the high frequency band (0 to 4,000Hz). This shows the relationship of R. In the figure, the horizontal axis represents the number of repeated loadings.

  The index value at the start of loading is zero, and as shown in FIG. 5, the test progresses from there, cracking of the floor slab occurs, the center displacement of the slab increases, and the progress index R It can be seen that the value increases.

  Further, in FIG. 5, the value of the progress index R is in spite of the progress of cracking of the slab when the loading frequency is between 50,000 times and 100,000 times and between 200,000 times and 250,000 times. As is clear from the decrease, the accuracy decreases when the progress index R becomes a large numerical value.

  FIG. 6 shows a reference state (here, the number of times of loading) when calculating the progress index R in the wheel load running test of the specimen simulating the concrete floor slab described above in order to prevent such a decrease in accuracy. The case where it changed is shown.

  As shown in FIG. 6, when the progress index R exceeds 0.4 to 0.5, the progress index increases as the deformation progresses by setting the state of the index as the current state again. This shows that the progress of deformation can be monitored continuously with high accuracy.

  Next, with regard to the deformation progress index E for the range up to the low frequency band (0 to 20 Hz), the acceleration of traffic vibration is measured on the concrete floor slab of the actual bridge, and the deformation does not change The stability was confirmed. FIG. 7 shows the result of calculating the deformability progress index E by the above equation (2).

  Since the transformation progress index E is the ratio of A to B with the total value B of the Fourier spectrum ratio Z of the first measurement as the initial value, E is 1.0 when there is no change in the frequency characteristics. In FIG. 7, the progress index E is around 1.0, and it can be seen that if there is no change in the state of the floor slab, it becomes a substantially constant value.

  Next, FIG. 8 shows a change in the value of the progress index E based on the frequency characteristics of vibration acceleration in a low frequency band (0 to 20 Hz) in a wheel load running test of a specimen simulating a concrete floor slab. Is. The index value for the low frequency band indicates that the sign that the specimen is approaching the final state can be detected.

2 Concrete slab 3 Acceleration sensor 4 Control device

Claims (5)

Measure the vibration acceleration of the floor slab caused by the running of the passing vehicle with two or more acceleration sensors installed at intervals on the floor slab of the road bridge,
Using the acceleration time history data obtained by the above measurement, a Fourier spectrum in a range from 0 to 4000 Hz by Fourier transform is calculated, and then a Fourier spectrum ratio between the two acceleration sensors is calculated. Monitoring the progress of the first deformation in the floor slab based on the change in spectral ratio;
The Fourier spectrum ratio in the range from 0 to 20 Hz is calculated using the acceleration time history data obtained by the measurement, and a larger number than the first deformation is calculated based on the change in the Fourier spectrum ratio. 2. A method for monitoring the deformation of a road bridge deck characterized by monitoring the behavior leading to the deformation of 2. The following progress index R calculated from the Fourier spectrum ratio:

x: Natural logarithm of the Fourier spectrum ratio between two points in the original state (initial value)
y: natural logarithm of the Fourier spectrum ratio between two points after time has elapsed from the state of x Cov (x, y): covariance between x and y σ _x , σ _y : standard deviation of x, y 2. The method for monitoring a deformation of a road bridge deck according to claim 1, wherein the progress of the first deformation is evaluated by an increase in the number of the road bridges.   When the progress index R exceeds a set value in the range of 0.4 to 0.6, the natural logarithmic value x of the Fourier spectrum ratio between two points in the original state exceeds the set value. 3. The road bridge deck deformation monitoring method according to claim 2, wherein the monitoring is continued after being set again as an initial value. The following progress index E calculated from the Fourier spectrum ratio,

Z ₀ : Natural logarithm of the Fourier spectrum ratio between the two points in the original state Z _n : Natural logarithm of the Fourier spectrum ratio between the two points after a lapse of time from the state of Z ₀ A: a = 0 (Hz) ~b = 20 ( Hz) the total value of _{Z n} between B: a = 0 (Hz) ~b = 20 (Hz) said second Deformation by increasing the total value of _{Z 0} between the 4. The method for monitoring deformation of a road bridge deck according to any one of claims 1 to 3, characterized in that:   5. The road bridge slab deformation monitoring method according to claim 1, wherein an acceleration sensor installed at the center of the floor slab is used as one of the two acceleration sensors. .

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