A prestressed steel strand damage broken wire acoustic emission waveguide rod wave induction cross section positioning method

Abstract

The application relates to a prestressed steel strand damage acoustic emission waveguide rod wave-directing double-sensor cross-section positioning method, which uses a waveguide rod to connect prestressed steel strands in different channels in series, expands a one-dimensional linear positioning method to three-dimensional space, and directly monitors the damage conditions of the prestressed steel strands in different channels in a bridge by using only two acoustic emission sensors, compared with the prior art, the prestressed steel strands in different channels in the bridge can be directly monitored, and the prestressed steel strands damaged in the box girder can be determined more simply and accurately.

Description

Technical Field

[0001] This invention relates to the field of acoustic emission monitoring technology, specifically to a method for locating the cross-section of a prestressed steel strand damaged wire broken acoustic emission waveguide rod using dual waveguide sensors. Background Technology

[0002] Currently, bridge collapses caused by damage to prestressed steel strands occur frequently. It is difficult to afford to deploy high-cost health monitoring equipment in the numerous small- and medium-span post-tensioned prestressed bridges. Existing three-dimensional spatial positioning methods cannot directly monitor the damage status of prestressed steel strands inside the bridge (the bridge has multiple prestressed ducts, and each prestressed steel strand is installed in the duct). This greatly hinders the development and application of three-dimensional spatial positioning methods in the health monitoring of small- and medium-span bridges. Therefore, there is an urgent need for a low-cost, simple, and accurate spatial positioning method for prestressed steel strand damage and broken wires.

[0003] Based on this, in order to address the problem of damage monitoring and location of steel strands in post-tensioned prestressed bridges, this invention proposes a cross-sectional location method using a waveguide rod with dual sensors to locate the damaged wires in prestressed steel strands. This method uses waveguide rod wave-inducing technology to directly locate the damaged position of the prestressed steel strands inside the bridge. Summary of the Invention

[0004] To address the above issues and overcome the shortcomings of existing technologies, this invention proposes a method for locating the cross-section of prestressed steel strands damaged by acoustic emission waveguides and dual sensors. This invention uses waveguides to connect prestressed steel strands in different ducts, extending the one-dimensional linear positioning method to three-dimensional space. Only two acoustic emission sensors are needed to directly monitor the damage status of prestressed steel strands in different ducts inside the bridge.

[0005] A method for locating the cross-section of a prestressed steel strand damaged and broken acoustic emission waveguide rod using a dual-sensor approach, characterized by the following steps:

[0006] S1: Based on the actual position of the steel strands in the post-tensioned prestressed bridge, select a waveguide rod of appropriate length to connect the prestressed steel strands located at different duct positions in the bridge.

[0007] S2: Fix two acoustic emission sensors at the beginning and end of the waveguide rod to obtain acoustic emission signals when the prestressed steel strands in different channels are damaged and broken.

[0008] S3: Calculate the arrival time difference of the acoustic emission signals collected by the two acoustic emission sensors. The sign of the arrival time difference is used to determine whether the steel strands in the left or right duct of the post-tensioned prestressed bridge are damaged. The magnitude of the arrival time difference is compared to determine whether the steel strands in the top or bottom duct of the post-tensioned prestressed bridge are damaged.

[0009] The beneficial effects of the above technical solution are as follows:

[0010] (1) The invention uses waveguide rods to connect the prestressed steel strands in the prestressed ducts at different locations in the bridge, extending the one-dimensional linear positioning method to three-dimensional space. Based only on the arrival time and amplitude of the damage signals collected by two acoustic emission sensors, the damage status of the prestressed steel strands in the prestressed ducts at different locations in the bridge can be directly monitored, thus minimizing the monitoring cost.

[0011] (2) The maximum amplitude of the acoustic emission signal generated by the damage of the prestressed steel strand is greater than the amplitude of the ambient noise (the ambient noise is much smaller than the maximum amplitude of the acoustic emission signal generated by the damage of the steel strand), and the determination of the maximum amplitude is not affected by the threshold setting. Therefore, in practical engineering applications, it is recommended to use the arrival time difference of the maximum amplitude of the acoustic emission signal to identify and locate the damage location of the steel strand, so as to ensure the safety of the bridge. Attached Figure Description

[0012] Figure 1 This is a schematic diagram showing the installation position relationship of the acoustic emission sensor, waveguide rod, and prestressed steel strands in the duct of the present invention;

[0013] Figure 2 This is a schematic diagram of the anchor structure of the present invention;

[0014] Figure 3 This is a diagram illustrating the lateral positioning results based on the arrival time difference of the maximum amplitude when the steel strand S1 of the present invention is damaged.

[0015] Figure 4 This is a diagram illustrating the lateral positioning results based on the arrival time difference of the maximum amplitude when the steel strand S2 of the present invention is damaged;

[0016] Figure 5 This is a diagram illustrating the lateral positioning results based on the arrival time difference of the maximum amplitude when the steel strand S3 of the present invention is damaged;

[0017] Figure 6 This is a diagram illustrating the lateral positioning results based on the arrival time difference of the maximum amplitude when the steel strand S4 of the present invention is damaged.

[0018] Figure 7 This is a schematic diagram of the longitudinal propagation attenuation model of acoustic emission signal amplitude when damage occurs in the prestressed duct of the present invention.

[0019] Figure 8 This is a flowchart illustrating the longitudinal damage localization process of the prestressed steel strands according to the present invention. Detailed Implementation

[0020] The foregoing and other technical contents, features and effects of the present invention will be clearly presented in the following detailed description of the embodiments with reference to the accompanying drawings. The structural contents mentioned in the following embodiments are all based on the accompanying drawings.

[0021] Existing box girders typically have multiple prestressed ducts inside, with prestressed steel strands (in conjunction with anchorages) placed within these ducts. Grouting is used to fill the prestressed ducts. This scheme is described using an example of a box girder with four prestressed ducts (each containing a prestressed steel strand). Two acoustic emission sensors (Sensor-1 and Sensor-2) are fixedly installed at the beginning and end of a waveguide rod (preferably made of metal), as shown in the attached diagram. Figure 1 As shown, the four prestressed steel strands are S1, S2, S3, and S4. d1 is the distance from the acoustic emission sensors (Sensor-1 and Sensor-2) to the bend of the waveguide rod, d2 is the distance between the bends of the waveguide rod, and d3 is the distance between steel strands S3 and S4. During the test, steel strands were inserted into different prestressed ducts and anchors were installed at both ends of the steel strands (the anchors at both ends are located outside the two ends of the box girder, i.e., in an exposed state). The anchors corresponding to several prestressed ducts at one end face of the box girder are connected by waveguide rods, and the waveguide rods are also exposed outside the box girder.

[0022] A method for locating the cross-section of a prestressed steel strand damaged and broken acoustic emission waveguide rod using a dual-sensor approach includes the following steps:

[0023] S1: Based on the actual position of the steel strands in the post-tensioned prestressed bridge (i.e., the position of the prestressing ducts in the bridge), select a waveguide rod of appropriate length to connect the prestressed steel strands in the bridge (each prestressed steel strand in the duct includes several steel strands, and several steel strands cooperate with anchors to form a steel strand, and fix the waveguide rod to the anchor in each prestressing duct). Specifically, the connection between the waveguide rod and the anchor at different positions can be by welding or gluing, etc., and finally realize the connection of the steel strands in different ducts in the bridge through the waveguide rod.

[0024] S2: Attach the two acoustic emission sensors to the two ends of the waveguide rod respectively (as shown in the attached image). Figure 1As shown), the acoustic emission sensors and waveguide rod are coated with Vaseline (used as a coupling agent). The two acoustic emission sensors are connected to an acoustic emission data acquisition device via a preamplifier. When the steel strands in different prestressed ducts are damaged, the excited mechanical vibration is transmitted to the existing steel strands, and then to the waveguide rod in contact with them (causing vibration on the surface of the waveguide rod). The two acoustic emission sensors attached to the two ends of the waveguide rod convert the transient displacement into an electrical signal, which is amplified by the preamplifier and transmitted to the acoustic emission data acquisition device to finally obtain the acoustic emission signal when the prestressed steel strand is damaged.

[0025] S3: The arrival time of the acoustic emission signals collected by two acoustic emission sensors (simulating damage signals by striking the steel strands at the other end of the hollow slab of the post-tensioned prestressed bridge) is calculated. The sign of the arrival time difference determines whether the steel strands (steel strands S1, S4) in the ducts on the left or right side of the post-tensioned prestressed bridge have been damaged. The magnitude of the arrival time difference is compared to determine whether the steel strands in the ducts at the top (steel strands S1, S2) or bottom (steel strands S4, S3) of the post-tensioned prestressed bridge have been damaged. The arrival time difference of the acoustic emission signals when the prestressed steel strands in different ducts are damaged and broken has different value ranges. The specific steps include:

[0026] S3-1: Set the time for the acoustic emission wave (steel strand damage source) to travel to Sensor-1 and Sensor-2 to T1 and T2 respectively. When the prestressed steel strand S1 is damaged, the time difference between the arrival of the acoustic emission signal is ΔT1:

[0027]

[0028] Similarly, when steel strands S2, S3, and S4 are damaged, the arrival time differences of the acoustic emission signals are ΔT2, ΔT3, and ΔT4, respectively.

[0029]

[0030]

[0031]

[0032] In the formula, d1 is the distance from the acoustic emission sensor to the bend of the waveguide rod; d2 is the distance between the bends of the waveguide rod; d3 is the distance between steel strands S3 and S4; V is the propagation speed of the acoustic emission wave in the plane of the waveguide rod (which needs to be measured). Since the sound wave first passes through the anchor to the waveguide rod from the steel strand, and the signal propagates in two directions on the waveguide rod to the acoustic emission sensors arranged at both ends, the entire path is only different on the waveguide rod. Therefore, it is only necessary to measure the propagation speed of the sound wave on the waveguide rod (it is not necessary to know the propagation speed of the sound wave on the anchor).

[0033] Take the arithmetic mean ΔT of the arrival time differences ΔT1 and ΔT4. 14 To determine the boundary point where damage occurs in tendons S1 or S4:

[0034]

[0035] Similarly, take the arithmetic mean ΔT of the arrival time differences ΔT2 and ΔT3. 23 To determine the boundary point where damage occurs in tendon S2 or S3:

[0036]

[0037] Wherein, ΔT is calculated from the time difference between the acoustic emission signals received by the two acoustic emission sensors. 14 and ΔT 23 All of these are calculated using the relationship between d and v through a formula, which is the theoretical value of this method (d and v are the theoretical values ​​of material properties, which is a criterion for this method. The time difference between the acoustic emission signals received by the two acoustic emission sensors in the field is used to achieve the core of this invention, namely, to locate the steel strand damage).

[0038] In this scheme, the time difference ΔT is uniformly calculated as the difference between the arrival time of the amplitude of sensor-2 and the arrival time of the amplitude of sensor-1. 14 ΔT represents the time threshold for damage to the two steel strands S1 and S4 on the left. 23 The time boundary value for damage to the two steel strands S2 and S3 on the right is ΔT. The projection of the damage onto the plane of the waveguide rod reaches the two sensors at different distances, and therefore at different times. When S1 is damaged, the distance difference between the two acoustic emission sensors is larger, so it is ΔT. 14 <ΔT; S4 is damaged, and the distance difference to the two acoustic emission sensors is large, so it is ΔT. 14 >ΔT>0;

[0039] The waveguide rod is an axisymmetric figure. Separated from the axis of symmetry, the time differences on the left and right sides are exactly opposite, so ΔT 23 =-ΔT 14 Similarly, if S2 is damaged, the distance difference between the two acoustic emission sensors is large, so it is ΔT. 23 =-ΔT 14 >ΔT; S3 is damaged, and the distance difference to the two acoustic emission sensors is large, so it is ΔT. 23 =-ΔT 14 <ΔT<0;

[0040] Therefore, when the arrival time difference of the acoustic emission signals received by the two sensors satisfies ΔT 14If ΔT < -ΔT, it is determined that the prestressed steel strand S1 has been damaged; similarly, if ΔT < -ΔT, it is determined that the prestressed steel strand S1 has been damaged. 14 When -ΔT occurs, it is determined that the steel strand S2 is damaged; when -ΔT 14 When 0 < ΔT < 0, the steel strand S3 is considered damaged; when 0 < ΔT < ΔT 14 At that time, it was determined that steel strand S4 was damaged;

[0041] The dividing point is an arithmetic mean used as a criterion for judging the location of damage, introduced in this invention to improve the tolerance of the method in actual monitoring. Since ΔT1, ΔT2, ΔT3 and ΔT4 are theoretical calculation results, but actual bridges are affected by various environmental factors such as temperature and climate, which may affect the acquisition of acoustic emission signals. The introduction of this arithmetic mean, i.e. "dividing point", is to improve the applicability of the method in actual engineering.

[0042] S4: Take the acoustic emission signal amplitudes collected by the two acoustic emission sensors, substitute the damage signal amplitudes collected by the acoustic emission sensors into the propagation attenuation model, and deduce the longitudinal position of the acoustic emission source (the damage source of the steel strand is generated when the acoustic emission wave propagates on the prestressed steel strand. The signal amplitude collected by the acoustic emission sensor attenuates exponentially with the increase of the propagation distance. The longitudinal position of the damage source can be deduced from the collected acoustic emission signal amplitudes). The specific steps include:

[0043] S4-1: Conduct lead breakage test; randomly select a prestressed steel strand in one of the channels, and break the lead 3 times at distances of 0m, 1m, 2m, 3m, 4m and 5m from the waveguide rod on the steel strand, and collect the lead breakage signal at different longitudinal positions on the steel strand in all prestressed channels.

[0044] S4-2: Extract the amplitude of the lead-breaking signal; extract the amplitude of the three lead-breaking signals and calculate the mean and standard deviation (a commonly used number in the field of acoustic emission technology). The "mean" is because the three identical tests were performed and averaged to represent a single point amplitude, while the "standard deviation" represents the degree of dispersion of the three test results (as an indicator to verify the degree of dispersion of the test).

[0045] S4-3: Establish a propagation attenuation model; fit the amplitude of the broken lead signal collected by the two acoustic emission sensors to establish a propagation attenuation model between the two acoustic emission sensors and the steel strand, such as... Figure 7 The figure shows the longitudinal propagation attenuation model of the acoustic emission signal amplitude, where y is the amplitude of the acquired acoustic emission signal, e indicates that the signal amplitude attenuation model is an e-exponential function, x is the distance from the acoustic emission source, and R... 2 This indicates the degree of fit between the fitted function and the measured data points;

[0046] S4-4: Conduct a longitudinal positioning test; select any prestressed steel strand in a duct, break the lead on it to simulate the steel strand damage signal, and collect the acoustic emission signal of the simulated damage source.

[0047] S4-5: Extract the amplitude of the damage signal; extract the amplitude of the simulated damage signal collected by the two acoustic emission sensors;

[0048] S4-6: Obtain the longitudinal positioning result; substitute the amplitude of the acoustic emission signal collected by the two acoustic emission sensors into the propagation attenuation model of the steel strand in the corresponding channel to deduce the damage location, and take the average value of the two acoustic emission sensors as the longitudinal position of the final acoustic emission damage source.

[0049] As shown in Table 1, the location results obtained by the above propagation attenuation model after the lead was broken three times at distances of 0m, 1m, 2m, 3m, 4m and 5m from the waveguide rod on the steel bundle are shown in Table 1.

[0050]

[0051] Table 1

[0052] As shown in Table 1, the error range is small and the relative positioning accuracy is high. The positioning accuracy of the longitudinal positioning method proposed in this scheme can meet the requirements of practical engineering applications.

[0053] This invention uses waveguide rods to connect prestressed steel strands in different ducts, extending the one-dimensional linear positioning method to three-dimensional space. It can directly monitor the damage status of prestressed steel strands in different ducts inside the bridge using only two acoustic emission sensors. Compared with the prior art, this invention can directly monitor the damage status of prestressed steel strands inside the bridge and can more easily and accurately determine the prestressed steel strands that have been damaged in the solid beam.

[0054] The maximum amplitude of the acoustic emission signal generated by damage to the prestressed steel strands is greater than the amplitude of the ambient noise (the maximum amplitude of the acoustic emission signal from ambient noise is generally below 40 dB, which is a generally accepted convention in the field of acoustic emission monitoring; the maximum amplitude of the acoustic emission signal collected by this invention is much greater than 40 dB, therefore it is concluded that the maximum amplitude of the acoustic emission signal generated by damage to the prestressed steel strands is greater than the amplitude of the ambient noise). Figure 3-6 The figures shown represent the lateral positioning results based on the time difference of arrival of the maximum amplitude when steel strands S1, S2, S3, and S4 are damaged, respectively. T... M1 T M2 These represent the arrival time of the maximum amplitude of the acoustic emission signal;

[0055] Furthermore, the determination of the maximum amplitude is not affected by the threshold setting (because there are non-target signals such as environmental noise and mechanical noise during acoustic emission monitoring, so the collected acoustic emission signals need to be denoised. A common denoising method is to set an amplitude threshold to eliminate signals smaller than the set threshold. Since the maximum amplitude of the acoustic emission signal is generally much larger than the set threshold, "the determination of the maximum amplitude is not affected by the threshold setting").

[0056] Therefore, in practical engineering applications, it is recommended to use the time difference of arrival of the maximum amplitude of the acoustic emission signal to identify and locate the damage location of the prestressed steel strand (the maximum amplitude of the acoustic emission signal generated by the damage of the prestressed steel strand is greater than the amplitude of the ambient noise, and the determination of the maximum amplitude is not affected by the threshold setting, so the time difference of arrival of the maximum amplitude of the acoustic emission signal is used for location. The time difference of arrival of the first wave and other parameters can also be used for location, but it is easily affected by the ambient noise, which makes the location results inaccurate) to ensure bridge safety.

[0057] The above description is only for illustrating the present invention and should be understood as not being limited to the above embodiments. Various modifications that conform to the spirit of the present invention are within the protection scope of the present invention.

Claims

1. A method for locating the cross-section of a prestressed steel strand damaged and broken acoustic emission waveguide rod using a dual-sensor approach, characterized in that... Includes the following steps: S1: Based on the actual position of the steel strands in the post-tensioned prestressed bridge, select a waveguide rod of appropriate length to connect the prestressed steel strands located at different duct positions in the bridge. S2: Fix two acoustic emission sensors at the beginning and end of the waveguide rod to obtain acoustic emission signals when the prestressed steel strands in different channels are damaged and broken. S3: Calculate the arrival time difference of the acoustic emission signals collected by the two acoustic emission sensors. The sign of the arrival time difference determines whether damage has occurred to the steel strands in the left or right ducts of the post-tensioned prestressed bridge. The magnitude of the arrival time difference is compared to determine whether damage has occurred to the steel strands in the top or bottom ducts of the beam in the post-tensioned prestressed bridge. Specifically, this includes: Let T1 and T2 be the times when the acoustic emission wave from the steel strand damage source reaches acoustic emission sensor one and acoustic emission sensor two, respectively. When damage occurs in prestressed steel strand one, the time difference between the arrival of the acoustic emission signal and ΔT1 is: Similarly, when strands two, three, and four are damaged, the arrival time differences of the acoustic emission signals are ΔT2, ΔT3, and ΔT4, respectively. In the formula, d1 is the distance from the acoustic emission sensor to the bend of the waveguide rod; d2 is the distance between the bends of the waveguide rod; d3 is the distance between steel strand three and steel strand four; V is the propagation speed of the acoustic emission wave in the plane of the waveguide rod; Take the arithmetic mean ΔT of the arrival time differences ΔT1 and ΔT4. 14 To determine the boundary point where damage occurs in strand one or strand four: Similarly, take the arithmetic mean ΔT of the arrival time differences ΔT2 and ΔT3. 23 To determine the dividing point between damage to strand two or three: The waveguide rod is an axisymmetric figure. Separated from the axis of symmetry, the time differences on the left and right sides are exactly opposite, so ΔT 23 =-ΔT 14 Similarly, if the second steel strand is damaged, the distance difference between the two acoustic emission sensors will be large, so it is ΔT. 23 = -ΔT 14 >ΔT; Damage to the steel strand resulted in a significant difference in the distances reaching the two acoustic emission sensors, hence ΔT. 23 = -ΔT 14 <ΔT<0; Therefore, when the arrival time difference of the acoustic emission signals received by the two sensors satisfies ΔT 14 If the value is less than ΔT, it is determined that the prestressed steel strand has been damaged. Similarly, when ΔT < -ΔT 14 At that time, it was determined that the second steel strand was damaged; when -ΔT 14 When ΔT < 0, the steel strand is considered damaged; when 0 < ΔT < ΔT 14 At that time, it was determined that the fourth steel strand was damaged.

2. The method for locating the cross-section of a prestressed steel strand damaged wire broken acoustic emission waveguide rod using a dual-sensor approach according to claim 1, characterized in that, The steel strand is fitted with an anchor, and in S1, the waveguide rod is fixedly connected to the anchor by welding or gluing.

3. The method for locating the cross-section of a prestressed steel strand damaged wire broken acoustic emission waveguide rod using a dual-sensor approach according to claim 1, characterized in that, Vaseline is applied to the location where the acoustic emission sensor and the waveguide rod are attached in S2.

4. The method for locating the cross-section of a prestressed steel strand damaged wire broken acoustic emission waveguide rod using a dual-sensor approach according to claim 1, characterized in that, In S2, the acoustic emission sensor is connected to the acoustic emission acquisition device via a preamplifier.

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