A method for monitoring a cable of a cable-stayed bridge by using a sheath outside acoustic emission

Abstract

The present application relates to a kind of cable-stayed bridge cable multi-source damage signal's sheath outer acoustic emission monitoring method, effectively solve the problem that acoustic emission sensor cannot be accurately installed when being used for bridge cable damage monitoring, the technical solution includes: the sound wave transmission coefficient of cable sheath and the law of cable hoop attenuation are obtained by acoustic emission test and the law of cable hoop attenuation is constructed according to the law of cable hoop attenuation, so as to obtain the accurate monitoring range of acoustic emission sensor according to cable hoop attenuation model;The present scheme can propose corresponding acoustic emission sensor arrangement mode for different damage signals of cable, with the advantages of refinement, quantification, easy to be widely popularized and the like, provide a new idea for acoustic emission monitoring method of other civil engineering structures.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for structures, specifically to a method for monitoring the external acoustic emission of multi-source damage signals from the sheath of cables in cable-stayed bridges. Background Technology

[0002] Cables are one of the most important load-bearing components of cable-stayed bridges. During the actual operation of cable-stayed bridges, due to environmental factors and traffic loads, cables are prone to corrosion, fatigue, and other damage. The deterioration of cable damage can lead to extremely serious safety accidents. Therefore, it is particularly important to monitor the health of cables to avoid safety accidents. Acoustic emission is a passive non-destructive testing technology. Acoustic emission systems collect the elastic waves released by damaged materials and convert them into electrical signals to monitor the health of the materials. Acoustic emission technology is widely used in cable health monitoring due to its low cost and ability to achieve real-time monitoring. In the process of acoustic emission monitoring of cable damage, the damage signal generally needs to pass through the sheath to be collected by the sensor. The acoustic emission transmission coefficient of the HDPE sheath affects the acquisition of the damage signal. Regarding the acoustic emission transmission coefficient, current research mainly focuses on composite materials or interface structures such as cement mortar, porous media, solid-liquid-solid coupling interfaces, mechanical equipment with stiffening ribs, and asphalt pavement. Currently, the acoustic emission monitoring of cable damage does not consider the attenuation of the acoustic emission signal by the sheath, which may result in the loss of the damage signal and thus fail to accurately achieve the safety warning of the cable. Blindly deploying acoustic emission sensors can lead to high costs or difficulty in acquiring material damage signals. How to achieve accurate monitoring with the fewest possible sensors is a problem worthy of research. Currently, acoustic emission sensor deployment methods are mainly based on two aspects: 1. Arrange sensors based on the attenuation characteristics of the materials; 2. Place the sensors in areas of the structure that are susceptible to damage; Existing research only gives vague values ​​for the spacing of acoustic emission sensors based on two factors: material attenuation characteristics and the need to place acoustic emission sensors in areas where the material is susceptible to damage. It does not provide precise values ​​for the monitoring range of acoustic emission sensors, nor does it propose corresponding acoustic emission sensor placement schemes based on different types of material damage (cables generally have damage such as fracture, corrosion, and fatigue, and existing sensor placement methods are all based on a certain type of damage). In view of the above, this application provides a method for monitoring the acoustic emission from the outer sheath of multi-source damage signals of cable-stayed bridge cables to solve the above problems. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, this invention provides a method for monitoring the acoustic emission of multi-source damage signals of cable-stayed bridge cables from the outer sheath. Based on the acoustic wave transmission coefficient of the cable sheath and the circumferential attenuation law of the cable, a circumferential attenuation model of the cable is constructed. Based on the circumferential attenuation model of the cable, the accurate monitoring range of the acoustic emission sensor is obtained (the damage signal that the acoustic emission sensor farthest from the cable damage location can collect is at least the signal of the cable crack propagation stage).

[0004] A method for monitoring the external acoustic emission of multi-source damage signals from the cable sheath of a cable-stayed bridge, characterized by comprising the following steps: S1: Simultaneously, acoustic emission sensors are deployed on the cable wires and sheaths, and the acoustic transmission coefficients of sheaths with different thicknesses are obtained through acoustic emission tests. S2: Arrange acoustic emission sensors at equal intervals along the circumferential direction of the cable sheath, and obtain the circumferential attenuation law of the cable through acoustic emission tests; S3: Construct a cable circumferential attenuation model using the cable circumferential attenuation law obtained in step S2; S4: Select two suitable acoustic emission signals based on the characteristics of acoustic emission signals of cable damage, namely the acoustic emission signals at the initiation time of cable crack propagation and the time of failure. S5: Substitute the two acoustic emission signals selected in S4 into the attenuation model to obtain the accurate monitoring range of the acoustic emission sensor.

[0005] The beneficial effects of the above technical solution are as follows: (1) In this scheme, the monitoring range of the acoustic emission sensor is quantitatively solved and the position of the acoustic emission sensor is arranged according to the monitoring method of this scheme, so as to ensure that the damage signal collected by the acoustic emission sensor at the farthest distance from the cable damage location is at least the signal of the cable crack propagation stage, thereby satisfying the effect of early (timely) warning, and thus achieving accurate monitoring effect with the least number of sensors. (2) This scheme proposes a corresponding sensor arrangement method based on different damage signals of the cable, which has the advantages of being refined, quantitative and easy to be widely promoted, and provides a new idea for acoustic emission monitoring methods of other civil engineering structures. Attached Figure Description

[0006] Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 This is a schematic diagram showing the arrangement of the acoustic emission sensors in the cable sheath transmission experiment of the present invention; Figure 3 This is a schematic diagram showing the arrangement of the acoustic emission sensors in the cable circumferential attenuation test of the present invention; Figure 4 This is a schematic diagram of the cable circumferential attenuation model of the present invention. Implementation

[0007] 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.

[0008] This solution provides a method for monitoring the external acoustic emission of multi-source damage signals from the cable sheath of a cable-stayed bridge, as detailed below: S1: As Figure 2 As shown in the diagram, one of the outermost steel wires of the cable is pulled out. Acoustic emission sensors (acoustic emission sensor a and acoustic emission sensor b, respectively) are placed on the pulled-out steel wire and on the cable sheath. The sound wave transmission coefficient of the cable sheath with different thicknesses is obtained through acoustic emission tests. The specific process is as follows: Cable sheath (such as) Figure 3 As shown, the product of the acoustic transmission coefficient of the inner and outer layers (which are made of the same material) and the damage source signal (the cable wire damage signal collected by acoustic emission sensor a) is the cable wire damage signal collected by acoustic emission sensor b. By combining the damage source signal collected by acoustic emission sensor a and the cable wire damage signal collected by acoustic emission sensor b, the acoustic transmission coefficient of the sheath can be obtained. It is found that the acoustic emission coefficient of the cable sheath decreases linearly with the thickness of the sheath (the thicker the sheath, the smaller its acoustic transmission coefficient, and vice versa). The acoustic emission test in this step is a lead-breaking test. Using a broken lead signal to simulate a damage signal is a common testing method, mainly because the broken lead signal has the following advantages: 1. Simulation Realism: The lead breakage signal can better simulate the characteristics and properties of actual damage signals, making the test results more realistic and reliable; 2. Stability: The lead breakage signal can be precisely controlled and adjusted, making the testing process more stable and reducing testing errors and uncertainties; 3. Economical and practical: Compared with the generation and acquisition of actual damage signals, using lead breakage signals is relatively simple and low-cost, and can meet general testing needs. 4. Repeatability: The lead-broken signal can be reused multiple times, allowing for repeated verification and comparison of the test results, ensuring consistency and reliability of the test results; The study of material degradation generally uses a lead breakage test. Typically, an HB pencil with a diameter of 0.5 mm is selected, with the lead extending 2.5 mm out. The pencil is held at a 30° angle to the plane, and the lead is broken at the breakage point to simulate damage signals. The acoustic emission test mainly measures the attenuation of acoustic emission signals by the sheath. Since the outermost steel wire of the cable is most susceptible to damage, the outermost steel wire is randomly selected as the lead break point. This steel wire is pulled out to a certain distance and a sensor is placed on it. There is also more than one sensor on the sheath outside this steel wire. The pencil is at a 30° angle to the steel wire. The lead is broken three times in succession on the steel wire to simulate the damage signal. The sensor placed on the steel wire collects the incident wave signal, and the sensor on the sheath collects the transmitted wave signal. The ratio of the intensity of the transmitted wave signal to the intensity of the incident wave signal is the transmission coefficient.

[0009] S2: As Figure 3 As shown, five acoustic emission sensors are arranged at equal intervals along the circumferential direction of the cable. The angle between sensor 1 and sensor 5 is 180° (this is because the cross-section of the cable is 360°, and the elastic wave generated by the damage signal expands outward in a spherical shape. The symmetrical arrangement of the sensors can realize the monitoring of the entire cross-section, so the angle between the first and last sensors is 180°). The attenuation law of the cable in the circumferential direction can then be obtained (by breaking the lead three times in a row on the steel wire corresponding to Sensor 1, the attenuation law of the cable in the circumferential direction can be obtained by analyzing the signal amplitude collected by the five sensors).

[0010] S3: As Figure 4 As shown, a circumferential attenuation model is constructed based on the circumferential attenuation law of the cable. Specifically, the circumferential attenuation model is obtained by fitting the values ​​collected by several sensors arranged in a circumferential direction using an e-exponential function.

[0011] S4: Among numerous acoustic emission signal characteristics, the acoustic emission signals corresponding to the propagation initiation time and failure time of the cable damage crack are selected as suitable acoustic emission signals, with intensities y2 and y2, respectively. 1， Furthermore, by substituting this value into the constructed cable circumferential attenuation model, the obtained distance difference represents the precise monitoring range of the acoustic emission sensor. The specific derivation process is as follows: In the attenuation model, the horizontal and vertical axes represent the propagation distance and intensity of the acoustic emission signal, respectively (the acoustic emission signal intensity y2 at the moment of crack propagation and the acoustic emission signal intensity y1 at the moment of crack failure). The distance difference refers to the difference in the propagation distance of the acoustic emission signal. In the attenuation model, the intensity of the acoustic emission signal decreases exponentially with the propagation distance. Different acoustic emission signal intensities correspond to different propagation distances in the same attenuation model. That is, first obtain the acoustic emission signal intensity on the vertical axis and substitute it into the attenuation model. Each acoustic emission signal intensity corresponds to a horizontal axis (propagation distance). x The two acoustic emission signal intensities correspond to two horizontal axes. x 2- x 1 represents the acoustic emission signal strength. y 1 decay toy The distance corresponding to 2 is defined as the sensor's monitoring range; The monitoring range of the acoustic emission sensor here refers to the maximum distance between the damage source and the sensor. That is, the damage signal that the acoustic emission sensor at the farthest point from the cable damage location can collect is at least the signal of the cable crack propagation stage, so as to meet the effect of early (timely) warning and achieve accurate monitoring effect with the least number of sensors. Since a cable typically goes through stages such as crack initiation, crack propagation, and failure from the initial damage to its final fracture, the acoustic emission signals corresponding to the crack propagation initiation moment and the failure moment are chosen as appropriate acoustic emission signals because: 1. The acoustic emission signal intensity is low before the crack propagation stage, making it difficult to collect; the acoustic emission signal intensity is high during the crack propagation stage and at the moment of failure, making it easy to collect. 2. The crack propagation stage and the moment of failure of the cable mean that the damage is already very large. Generally, the entry of the cable into the crack propagation stage is used as a safety warning signal (that is, the cable should be alerted when it reaches the crack propagation stage). In other words, the core idea of ​​choosing the signals of these two stages to solve the sensor monitoring range is: the signal collected by the sensor farthest from the cable failure location is at least the signal of the cable crack propagation stage. This farthest distance is the monitoring range of the acoustic emission sensor. In this step, cable damage includes three types of damage: wire breakage, corrosion, and fatigue (the acoustic emission signal intensity corresponding to the failure time and crack propagation time of the three types of damage is different). The acoustic emission signals corresponding to the propagation initiation time and failure time of the fracture damage crack in the cable wire were respectively substituted into the circumferential attenuation model of the cable. The acoustic emission signals corresponding to the propagation initiation time and failure time of corrosion damage cracks in the cable wire were incorporated into the circumferential attenuation model of the cable. The acoustic emission signals corresponding to the propagation initiation time and failure time of fatigue damage cracks in the cable wire were incorporated into the circumferential attenuation model of the cable. Furthermore, the difference obtained represents the precise monitoring range of the acoustic emission sensor based on different damage signals (wire breakage, corrosion, fatigue), such as... Figure 4 The x-axis (distance) in the data. x 2- x 1.

[0012] 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 monitoring the external acoustic emission of multi-source damage signals of cables in cable-stayed bridges, characterized in that, Includes the following steps: S1: Simultaneously, acoustic emission sensors are placed on the cable wire and sheath, and the acoustic transmission coefficient of sheaths with different thicknesses is obtained through acoustic emission tests. S2: Arrange acoustic emission sensors at equal intervals along the circumferential direction of the cable sheath, and obtain the circumferential attenuation law of the cable through acoustic emission tests; S3: Construct a cable circumferential attenuation model using the cable circumferential attenuation law obtained in step S2. Specifically, constructing the circumferential attenuation model based on the cable circumferential attenuation law in step S3 includes: fitting the values ​​collected by several sensors arranged in a circumferential direction to the e-exponential function to obtain the circumferential attenuation model. S4: Select two suitable acoustic emission signals based on the characteristics of acoustic emission signals of cable damage, namely the acoustic emission signals at the initiation time of cable crack propagation and the time of failure. S5: Substitute the two acoustic emission signals selected in S4 into the attenuation model to obtain the precise monitoring range of the acoustic emission sensor. In S5, the acoustic emission signals at the start time and failure time of the cable crack are substituted into the constructed cable circumferential attenuation model, and the distance difference obtained is the precise monitoring range of the acoustic emission sensor according to different damage signals.

2. The method for monitoring the external acoustic emission of multi-source damage signals of cable-stayed bridge cables according to claim 1, characterized in that, In step S1, one of the outermost steel wires of the cable is extracted, and acoustic emission sensors are arranged on the extracted steel wire and the sheath of the cable. The acoustic transmission coefficient of the cable sheath is obtained through acoustic emission test.

3. The method for monitoring the external acoustic emission of multi-source damage signals of cable-stayed bridge cables according to claim 1, characterized in that, In S2, several acoustic emission sensors are arranged at equal intervals along the circumferential direction of the cable, and the included angle between the two acoustic emission sensors at the beginning and end of the cable is 180°.

4. The method for monitoring the external acoustic emission of multi-source damage signals of cable-stayed bridge cables according to claim 1, characterized in that, The damage signal of the cable wire collected by the acoustic emission sensor arranged on the cable sheath in S1 is the product of the damage source signal and the acoustic wave transmission coefficient of the cable sheath.

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