A Multi-parameter Bridge Structural Status Monitoring Method and System Based on Self-Sensing Materials

Abstract

This application provides a multi-parameter bridge structure condition monitoring method and system based on self-sensing materials. The method includes: deploying a conductive concrete layer and measuring electrode pairs in the tension zone of the bridge, and installing multiple fiber Bragg gratings; applying dual-frequency alternating excitation to acquire resistance amplitude and phase angle, while simultaneously demodulating the center wavelength of each grating; when a step increase in the resistance amplitude of the conductive concrete layer is detected and the phase angle at the low-frequency point drops more significantly than at the high-frequency point, a crack event is determined to have occurred; within the same time window of the crack event, if the change in the center wavelength of each grating does not exceed a preset range, the crack is determined to be located between two adjacent gratings. This application can dynamically coordinate the electrical response of the conductive concrete layer and the strain distribution of the fiber Bragg gratings to output a dual determination result for crack events, thereby avoiding the risk of missed crack detection caused by misjudgment of a single parameter.

Description

Technical Field

[0001] This application relates to the field of bridge structural condition monitoring technology, and more specifically, to a multi-parameter bridge structural condition monitoring method and system based on self-sensing materials. Background Technology

[0002] Bridge structural condition monitoring is evolving from manual inspection and point-based electrical measurements to multi-parameter, distributed, and online intelligent monitoring. Conductive concrete based on the piezoresistive effect combines structural load-bearing capacity with self-sensing capabilities, enabling it to detect resistance changes caused by cracks. Fiber Bragg gratings, with their advantages of anti-electromagnetic interference and quasi-distributed networking, can achieve continuous strain measurement. Deploying both in the tension zone of bridges and improving the accuracy and reliability of crack detection through multi-parameter data fusion has become an important research direction in this field.

[0003] However, existing crack monitoring methods based on conductive concrete generally rely solely on resistance amplitude for single threshold determination. In actual bridge operation, non-destructive factors such as temperature and humidity fluctuations, live load elastic strain, and concrete creep can induce gradual changes or short-term disturbances in resistance, easily triggering false alarms based on static thresholds. Furthermore, resistance amplitude is insensitive to the early initiation of microcracks; by the time a step change occurs, the crack has often expanded to a macroscopic scale, leading to delayed warnings. A single electrical parameter cannot mechanistically distinguish between environmental disturbances and actual cracks, nor can it provide spatial location information for cracks. This makes it difficult for managers to identify the real threat from a massive number of alarms, potentially leading to a loss of trust in the system due to numerous alarms or missed maintenance windows due to missed alarms. Therefore, how to dynamically coordinate the electrical response of the conductive concrete layer with the strain distribution of the fiber optic grating to output a dual determination result for crack events, thereby avoiding the risk of missed crack detection caused by single-parameter misjudgment, has become a challenge for the industry. Summary of the Invention

[0004] This application provides a multi-parameter bridge structure condition monitoring method and system based on self-sensing materials, which can dynamically coordinate the electrical response of the conductive concrete layer and the strain distribution of the fiber optic grating to output dual judgment results of crack events, thereby avoiding the risk of missed crack detection caused by misjudgment of single parameters.

[0005] In a first aspect, this application provides a multi-parameter bridge structure state monitoring method based on self-sensing materials, comprising the following steps:

[0006] A conductive concrete layer with piezoresistive effect is laid in the tension zone of the bridge concrete and a pair of measuring electrodes are pre-embedded. Multiple fiber Bragg gratings are installed at different longitudinal positions in the same tension zone.

[0007] An alternating electric excitation containing at least two frequency components is applied to the measuring electrode pair, and the resistance amplitude and phase angle of the conductive concrete layer at different frequencies are collected simultaneously.

[0008] Wavelength demodulation is performed on each fiber Bragg grating to obtain the real-time center wavelength of each grating;

[0009] A crack event is determined to have occurred when a step increase in the resistance amplitude of the conductive concrete layer is detected, and the phase angle drop amplitude at low frequency points exceeds the phase angle drop amplitude at high frequency points.

[0010] Within the same time window for determining the occurrence of a crack event, if the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed the preset fluctuation range, the crack is determined to occur between two adjacent fiber Bragg gratings.

[0011] In some embodiments, installing multiple fiber Bragg gratings at different longitudinal positions in the same tension region specifically includes:

[0012] Each fiber Bragg grating is arranged at equal intervals along the longitudinal direction of the tension zone of the bridge, and the distance between two adjacent gratings is not greater than the preset maximum blind zone width.

[0013] Each fiber Bragg grating is embedded into the concrete using a pre-embedding method and temporarily fixed before pouring;

[0014] The center wavelengths of each fiber Bragg grating are staggered according to a preset wavelength interval before installation to support wavelength division multiplexing series networking.

[0015] In some embodiments, determining that a crack event has occurred when a step increase in the resistance amplitude of the conductive concrete layer is detected, and the phase angle drop amplitude at low-frequency points exceeds the phase angle drop amplitude at high-frequency points, specifically includes:

[0016] The characteristic value of the resistance step change is determined based on the rate of change of the resistance amplitude within a preset time window;

[0017] When the resistance step change characteristic value exceeds the preset step judgment threshold, the phase angle time history corresponding to the low frequency point and the high frequency point within the same time window is extracted;

[0018] Based on the phase angle time history, the phase angle drop amplitude at the low-frequency point and the high-frequency point are calculated respectively;

[0019] The phase angle drop values ​​of low-frequency points and high-frequency points are compared. When the phase angle drop value of low-frequency points is greater than that of high-frequency points, a crack event is determined to have occurred.

[0020] In some embodiments, before determining that a crack event has occurred, the method further includes:

[0021] Extract a time history window of the resistance amplitude and a time history window of the phase angle at low frequency points for a preset time length before and after the moment when the resistance amplitude increases abruptly;

[0022] Calculate the first-order difference sequence within the time history window of the resistance amplitude and the first-order difference sequence within the time history window of the phase angle at the low frequency point, respectively.

[0023] Calculate the Pearson correlation coefficient between two first-difference sequences;

[0024] When the Pearson correlation coefficient exceeds a preset correlation threshold, the crack event is confirmed to be valid; otherwise, it is determined to be a false signal caused by environmental factors.

[0025] In some embodiments, determining that a crack occurred between two adjacent fiber Bragg gratings within the same time window for determining the occurrence of a crack event, when the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed a preset fluctuation range, specifically includes:

[0026] Extract a time history window of the resistance amplitude with a preset time length before and after the moment when the resistance amplitude increases abruptly, and calculate the first-order difference sequence within the window.

[0027] Extract the center wavelength time history of each fiber Bragg grating covering the same area within the same time window, and calculate the first-order difference sequence of the center wavelength time history of each grating respectively;

[0028] The first-order difference sequence within the resistance amplitude time history window is cross-correlated with the first-order difference sequence of the center wavelength time history of each grating one by one to obtain the cross-correlation peak value corresponding to each grating.

[0029] When the cross-correlation peak of any grating exceeds the preset cross-correlation threshold, it is determined that the crack occurs at the location of the grating, and the crack width is determined according to the center wavelength step amplitude of the grating.

[0030] When the cross-correlation peak of all gratings does not exceed the preset cross-correlation threshold, it is determined that the crack occurs between two adjacent fiber Bragg gratings, and the longitudinal position of the crack between the two is determined according to the difference in the center wavelength offset of the two adjacent fiber Bragg gratings before and after the resistance step.

[0031] In some embodiments, the low frequency point is an excitation frequency not higher than 100 Hz, and the high frequency point is an excitation frequency not lower than 1 kHz.

[0032] In some embodiments, after determining that the crack occurs between two adjacent fiber Bragg gratings, the method further includes:

[0033] Extract the difference in the center wavelength offset between two adjacent fiber Bragg gratings before and after the crack event;

[0034] When the offset difference is not zero, the offset distance of the crack relative to the midpoint of the two adjacent gratings is determined according to the ratio of the offset difference to the spacing between the two adjacent gratings.

[0035] Secondly, this application provides a multi-parameter bridge structure condition monitoring system based on self-sensing materials, the system comprising:

[0036] The pre-embedded module is used to lay a conductive concrete layer with piezoresistive effect in the tension zone of bridge concrete and pre-embed a pair of measuring electrodes, and to install multiple fiber Bragg gratings at different longitudinal positions in the same tension zone.

[0037] The processing module is used to apply alternating electrical excitation containing at least two frequency components to the measuring electrode pair and simultaneously acquire the resistance amplitude and phase angle of the conductive concrete layer at different frequencies.

[0038] The processing module is also used to perform wavelength demodulation on each fiber Bragg grating to obtain the real-time center wavelength of each grating.

[0039] The determination module is used to determine that a crack event has occurred when a step increase in the resistance amplitude of the conductive concrete layer is detected and the phase angle drop amplitude at the low frequency point exceeds the phase angle drop amplitude at the high frequency point.

[0040] The determination module is also used to determine that the crack occurred between two adjacent fiber Bragg gratings when the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed the preset fluctuation range within the same time window when determining the occurrence of the crack event.

[0041] Thirdly, this application provides a computer device, the computer device including a memory and a processor, the memory storing code, and the processor being configured to acquire the code and execute the above-described multi-parameter bridge structure state monitoring method based on self-sensing materials.

[0042] Fourthly, this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method for monitoring the state of a multi-parameter bridge structure based on self-sensing materials.

[0043] The technical solutions provided by the embodiments disclosed in this application have the following beneficial effects:

[0044] This application achieves complementary results in two aspects: crack identification anti-interference capability and location spatial continuity through the synergistic operation of multi-frequency impedance spectroscopy of conductive concrete and fiber optic grating wavelength demodulation. In crack identification, the high sensitivity of ion conduction paths to crack physical truncation under low-frequency electric fields, contrasted with the relative insensitivity of electron conduction paths to micro-cracks under high-frequency electric fields, creates a frequency asymmetry characteristic where the amplitude of the low-frequency phase angle drop exceeds that of the high-frequency field. This characteristic directly corresponds to the differential damage caused by the crack to the two conduction mechanisms, constituting a specific criterion for crack identification. Non-damaging factors such as temperature and humidity changes and live load elastic deformation cannot produce this frequency-selective response. The criterion itself possesses physical anti-interference capabilities, suppressing the false alarm problem of the single resistance threshold method from the source. In crack location, ... The continuous electrical sensing of the conductive concrete layer is logically coupled with the discrete strain measurement of the fiber optic grating array. When the electrical criteria confirm that a crack has occurred and the change in the center wavelength of each grating does not exceed the preset fluctuation range, it can be inferred that the crack is located within the strain sampling interval of two adjacent gratings. By using the ratio of the difference in the center wavelength offset of the two gratings to the grating spacing, the specific offset position of the crack in the blind zone can be determined. This processing method transforms the monitoring blind zone between point sensors into a quantifiable positioning range, making up for the inherent deficiency of discrete fiber optic sensing networks in spatial continuity. The electrical channel provides event triggering and anti-interference confirmation, while the optical channel provides position calibration. The two functions complement each other, enabling the system to simultaneously obtain the ability to resist false alarms throughout the entire area and the ability to accurately locate the point. Attached Figure Description

[0045] Figure 1 This is a schematic diagram illustrating an application scenario of a multi-parameter bridge structure condition monitoring method based on self-sensing materials, according to some embodiments of this application.

[0046] Figure 2 This is an exemplary flowchart of a multi-parameter bridge structure condition monitoring method based on self-sensing materials, according to some embodiments of this application.

[0047] Figure 3 This is a schematic diagram of a multi-parameter bridge structure condition monitoring system based on self-sensing materials, according to some embodiments of this application.

[0048] Figure 4 This is a schematic diagram of the structure of a computer device for implementing a multi-parameter bridge structure condition monitoring method based on self-sensing materials, according to some embodiments of this application. Detailed Implementation

[0049] To better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] refer to Figure 1This figure is a schematic diagram of an application scenario for a multi-parameter bridge structure condition monitoring method based on self-sensing materials, according to some embodiments of this application. The figure includes three main components: a data acquisition terminal, a server, and a data storage device. The data acquisition terminal applies alternating electrical excitation containing at least two frequency components to measuring electrodes embedded in the conductive concrete layer within the tension zone of the bridge concrete. It simultaneously acquires the resistance amplitude and phase angle of the conductive concrete layer at different frequencies and performs wavelength demodulation on multiple fiber Bragg gratings installed at different longitudinal positions within the same tension zone to obtain the real-time center wavelength of each grating. The data is then transmitted to the server via a communication network. The server calculates the rate of change of the resistance amplitude within a preset sliding time window based on the received data and compares the sudden drop in phase angle between low-frequency and high-frequency points. The system determines a crack event when the resistance amplitude increases abruptly and the phase angle at low-frequency points drops more sharply than at high-frequency points. Within the same time window, it checks whether the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed a preset fluctuation range. If it does not, the crack is determined to occur between two adjacent fiber Bragg gratings. Simultaneously, it extracts the difference in center wavelength offset between two adjacent gratings and determines the longitudinal offset position of the crack in the blind zone based on the ratio of this difference to the grating spacing, generating crack event alarms and location information. The data storage device stores the original time history data of resistance amplitude, phase angle, and grating center wavelength uploaded by the acquisition terminal, as well as the crack determination results, location information, and event logs generated by the server, providing a data foundation for long-term trend analysis and historical retrospective of the bridge structure's health status.

[0051] refer to Figure 2 The figure is an exemplary flowchart of a multi-parameter bridge structure condition monitoring method based on self-sensing materials, according to some embodiments of this application. This multi-parameter bridge structure condition monitoring method based on self-sensing materials mainly includes the following steps:

[0052] In step 101, a conductive concrete layer with piezoresistive effect is laid in the tension zone of the bridge concrete and a pair of measuring electrodes are pre-embedded, and multiple fiber Bragg gratings are installed at different longitudinal positions in the same tension zone.

[0053] In some embodiments, a conductive concrete layer with piezoresistive effect is laid in the tension zone of bridge concrete. Specifically, short-cut carbon fibers with a length of 6 mm to 12 mm and a diameter of 7 micrometers to 10 micrometers are first mixed with ordinary silicate cement, fine aggregate, coarse aggregate, water, and a high-efficiency water-reducing agent. The mixture is dry-mixed for 3 minutes, then wet-mixed for 5 minutes to obtain an uncured mixture. This uncured mixture is used to form a three-dimensional continuous conductive network after hardening, which is the conductive concrete material. Then, before pouring this mixture, two measuring electrodes are fixed to the reinforcing steel skeleton in the tension zone of the bridge. Each measuring electrode uses a stainless steel mesh with a mesh diameter of 2 mm to 5 mm and a planar dimension of 100 mm x 100 mm. The two stainless steel meshes are arranged parallel to each other along the thickness direction of the layer to be poured, and the vertical distance between the two stainless steel meshes is set to [specify the distance]. The thickness of the layer is 0.6 to 1.0 times that of the stainless steel mesh, and multiple strands of copper core flexible wire are welded from the edge of each stainless steel mesh as electrode leads. The two parallel stainless steel meshes with leads constitute a measuring electrode pair, which is used to apply dual-frequency alternating electric excitation and synchronously acquire the resistance amplitude and phase angle. Finally, the uncured mixture is poured into the template where the measuring electrode pair is located, with a pouring thickness of 20 mm to 50 mm. After vibration, the mixture is kept away from the stainless steel mesh and covered with plastic film for moist curing for no less than 7 days to allow the mixture to harden and form a solid with a stable conductive network. This solid is the conductive concrete layer, which is used to indicate crack events by a step increase in resistance amplitude and a sudden drop in phase angle when cracks occur in the tension zone of the bridge. In the above manner, the hardened carbon fiber reinforced concrete solid serves as the conductive concrete layer with piezoresistive effect.

[0054] In some embodiments, the pre-embedded measurement electrode pair can be achieved by the following steps:

[0055] Stainless steel mesh is used as the electrode substrate and is fixed to the steel reinforcement frame before the conductive concrete layer is poured.

[0056] The electrode pairs are arranged parallel to the thickness of the concrete layer, and the electrode spacing is set to a preset ratio of the concrete layer thickness.

[0057] Electrode leads are led out from the side of the concrete layer and sealed for connecting to the external excitation and acquisition unit.

[0058] It should be noted that the preset ratio in this application specifically refers to the ratio of the vertical distance between the two stainless steel meshes in the electrode pair to the thickness of the conductive concrete layer. The value of this ratio ranges from 0.6 to 1.0. When the ratio is 0.6, the two electrodes are relatively close, and the excitation electric field is concentrated in the central region of the conductive concrete layer, which is suitable for detecting through cracks. When the ratio is 1.0, the two electrodes are located near the two surfaces of the conductive concrete layer, and the excitation electric field covers the entire layer thickness, which is suitable for detecting surface and internal cracks. In practical applications, the preset ratio can be selected as 0.8 according to the crack sensitivity depth in the tension zone of the bridge.

[0059] In practice, before pouring the conductive concrete layer, stainless steel mesh with a mesh diameter of 2 to 5 mm and a plane size of 100 mm by 100 mm is selected as the electrode substrate. A rubber insulating pad with a thickness of 1 to 2 mm is inserted between the stainless steel mesh and the steel reinforcement frame, and it is fixed to the steel reinforcement frame with insulating nylon binding tape to ensure that there is no electrical connection and that the plane of the mesh is parallel to the surface of the tension zone of the bridge. Take two electrode substrates fixed as described above and place them parallel to each other along the thickness direction of the conductive concrete layer. One of them is arranged 5 mm to 10 mm away from the tension surface, and the other is arranged 5 mm to 10 mm away from the back side. The vertical distance between the two electrode substrates is set to 0.6 to 1.0 times the layer thickness. This distance is the electrode spacing. These two parallel electrode substrates with fixed positions and spacing are used as a measuring electrode pair. This measuring electrode pair is a paired electrode structure used to apply a uniform alternating electric field in the thickness direction of the conductive concrete layer and synchronously acquire the resistance amplitude and phase angle signals. Weld multiple strands of copper core flexible wires from the edge of each electrode substrate as electrode leads. Lead the leads along the steel reinforcement skeleton to the outside of the template. Fill the junction of the template and the leads with epoxy resin sealant. After curing, put heat shrink tubing or wrap insulating tape around the end of the lead outside the template and prefabricate the terminals. The electrode leads are flexible conductive paths used to transmit electrical excitation and response signals and have the functions of preventing grout leakage and preventing mechanical damage.

[0060] In some embodiments, installing multiple fiber Bragg gratings at different longitudinal positions in the same tension region can be achieved using the following steps:

[0061] Each fiber Bragg grating is arranged at equal intervals along the longitudinal direction of the tension zone of the bridge, and the distance between two adjacent gratings is not greater than the preset maximum blind zone width.

[0062] Each fiber Bragg grating is embedded into the concrete using a pre-embedding method and temporarily fixed before pouring;

[0063] The center wavelengths of each fiber Bragg grating are staggered according to a preset wavelength interval before installation to support wavelength division multiplexing series networking.

[0064] In practice, the required number of fiber Bragg gratings is calculated based on the longitudinal length of the bridge's tension zone and the preset maximum blind zone width. The preset maximum blind zone width ranges from 1 to 2 meters. The installation positions of each grating are marked along the longitudinal direction of the tension zone at equal intervals not exceeding this blind zone width. The distance between two adjacent gratings is this fixed length. This distance is a positioning parameter used to limit the longitudinal distribution density of the fiber Bragg gratings and ensure that cracks within the blind zone can be located. At each marked position, the fiber Bragg grating sensor, pre-encapsulated in a capillary tube or carbon fiber rod, is axially adjusted to align with the longitudinal direction of the tension zone. Insulating nylon cable ties are used to bind both ends of the sensor to the nearby reinforcing steel frame, ensuring it is tightly attached to the steel and remains flat. To ensure that the grating does not shift, bend, or directly impact the concrete during the pouring process, this method of implantation and temporary fixation is called the pre-embedding method. This pre-embedding method is an installation method used to ensure that the grating and concrete deform together without being damaged. Before installation, the fixed wavelength interval of 2 to 4 nanometers is determined according to the total number of gratings and the effective wavelength range of the wavelength demodulator. The center wavelengths of each grating connected in series on the same optical fiber are staggered according to this interval, such as 1528 nanometers, 1532 nanometers, 1536 nanometers, etc., to ensure that the reflection spectra do not overlap. This staggering setting is called the center wavelength staggering setting. This center wavelength staggering setting is used to distinguish the reflection spectra of each grating on a single optical fiber to support the wavelength allocation scheme of wavelength division multiplexing series networking.

[0065] It should be noted that in this application, multiple fiber Bragg gratings are connected in series to form a quasi-distributed strain measurement array via wavelength division multiplexing.

[0066] In step 102, an alternating electrical excitation containing at least two frequency components is applied to the measuring electrode pair, and the resistance amplitude and phase angle of the conductive concrete layer at different frequencies are collected simultaneously.

[0067] In some embodiments, applying alternating electrical excitation containing at least two frequency components to the measuring electrode pair can be achieved as follows: a signal generator generates a low-frequency sine wave signal with a frequency not higher than 100 Hz and a high-frequency sine wave signal with a frequency not lower than 1 kHz, respectively. These two signals are superimposed by an adder to form a composite signal, which is then amplified by a power amplifier to a voltage amplitude of 1 to 5 volts. This amplified composite signal is applied between the two stainless steel meshes of the measuring electrode pair via electrode leads. This composite signal is the alternating electrical excitation. This alternating electrical excitation is a dual-frequency electrical excitation signal used to simultaneously generate low-frequency and high-frequency electric field responses in the conductive concrete layer to obtain the characteristics of resistance amplitude and phase angle changes at different frequencies.

[0068] In some embodiments, the synchronous acquisition of the resistance amplitude and phase angle of the conductive concrete layer at different frequencies can be achieved in the following manner: while applying alternating electric excitation, the voltage response signal at both ends of the conductive concrete layer is acquired through two stainless steel meshes of the measuring electrode pair. The voltage response signal is amplified and filtered and then sent to the analog-to-digital converter for synchronous sampling. The sampling frequency is not less than 10 times the high-frequency excitation frequency. The low-frequency component and the high-frequency component are extracted from the sampled digital signal, and the resistance amplitude and phase angle under the low-frequency component and the resistance amplitude and phase angle under the high-frequency component are calculated.

[0069] It should be noted that the low-frequency point in this application is an excitation frequency not higher than 100 Hz, and the high-frequency point is an excitation frequency not lower than 1 kHz. As a preferred embodiment, the excitation frequency of the low-frequency point can be set to 50 Hz and the excitation frequency of the high-frequency point can be set to 2 kHz. The reason for this setting is that 50 Hz is at the end of the low-frequency band, which is sensitive to the interface polarization effect in the conductive concrete layer and has a strong ability to resist power frequency harmonic interference; 2 kHz has entered the bulk resistance-dominated frequency band, and the phase angle is less affected by cracks, which makes it easy to reliably identify crack events by the difference in the sudden drop amplitude of the phase angle between the two frequencies.

[0070] In step 103, wavelength demodulation is performed on each fiber Bragg grating to obtain the real-time center wavelength of each grating.

[0071] In some embodiments, wavelength demodulation of each fiber Bragg grating to obtain the real-time center wavelength of each grating can be achieved by the following steps:

[0072] Injecting optical signals into a fiber Bragg grating string using a frequency-sweeping laser;

[0073] The echo signals reflected from each grating are received, and the reflection spectrum is obtained after photoelectric conversion and analog-to-digital acquisition.

[0074] The reflection spectrum is processed by peak finding, and the peak wavelength of each grating reflection peak is extracted as the real-time center wavelength of the grating.

[0075] It should be noted that the reflection spectrum in this application refers to the digital sequence of the reflected light power distribution of each fiber Bragg grating with wavelength; the real-time center wavelength refers to the peak wavelength corresponding to each reflection peak in the reflection spectrum, which is used to characterize the current strain state at the location of the grating.

[0076] In practice, the output port of the swept laser is first connected to the input port of the fiber Bragg grating string. The swept laser is then activated, continuously varying its output wavelength from the starting wavelength to the ending wavelength within its operating wavelength range. During this wavelength variation, the swept laser continuously injects a beam of light into the fiber Bragg grating string. This beam serves as the optical signal, exciting each grating to produce wavelength-selective reflection. Then, when the optical signal propagates to each fiber Bragg grating, the grating reflects only a narrowband light component matching its center wavelength. The narrowband light components reflected by each fiber Bragg grating return along the same fiber. This returning beam is guided to a photodetector via a fiber coupler. The photodetector then converts the received optical signal... The signal is converted to an analog electrical signal and then sent to an analog-to-digital converter for digital sampling to obtain a series of discrete digital quantities. These digital quantities are arranged in wavelength order to form a reflection spectrum. Finally, the reflection spectrum is input into a digital signal processor. First, the reflection spectrum is smoothed and filtered to eliminate noise interference. Then, a peak detection algorithm is used to traverse the entire reflection spectrum to find each local maximum point. For each local maximum point, several sampling points are extracted with that point as the center. The centroid method or Gaussian curve fitting method is used to calculate the precise wavelength position of the peak. This precise wavelength position is taken as the peak wavelength of the reflection peak of the corresponding fiber Bragg grating. This peak wavelength is the real-time center wavelength of the grating.

[0077] In step 104, when a step increase in the resistance amplitude of the conductive concrete layer is detected, and the phase angle drop amplitude at the low frequency point exceeds the phase angle drop amplitude at the high frequency point, a crack event is determined to have occurred.

[0078] In some embodiments, when a step increase in the resistance amplitude of the conductive concrete layer is detected, and the phase angle drop amplitude at low frequency points exceeds the phase angle drop amplitude at high frequency points, the determination of a crack event can be achieved by the following steps:

[0079] The characteristic value of the resistance step change is determined based on the rate of change of the resistance amplitude within a preset time window;

[0080] When the resistance step change characteristic value exceeds the preset step judgment threshold, the phase angle time history corresponding to the low frequency point and the high frequency point within the same time window is extracted;

[0081] Based on the phase angle time history, the phase angle drop amplitude at the low-frequency point and the high-frequency point are calculated respectively;

[0082] The phase angle drop values ​​of low-frequency points and high-frequency points are compared. When the phase angle drop value of low-frequency points is greater than that of high-frequency points, a crack event is determined to have occurred.

[0083] It should be noted that the resistance step change characteristic value in this application is a dimensionless index used to quantify the degree of sudden jump in resistance amplitude within a short period of time; the phase angle drop amplitude is an index that measures the magnitude of the phase angle drop in the conductive concrete layer caused by the crack event.

[0084] It should also be noted that the principle behind the above judgment is that, under normal environmental factors such as pressure or temperature changes, the resistance amplitude and phase angle of the conductive concrete layer typically exhibit a slow drift, with the phase angle change trends at low and high frequencies being similar. However, when cracks appear in the tension zone, the conductive network undergoes irreversible fracture, causing a sudden step increase in resistance amplitude. Simultaneously, the cracks cause a drastic change in the interfacial polarization characteristics within the conductive concrete. Since low-frequency excitation signals are more sensitive to interfacial polarization effects, their sudden phase angle drop is significantly greater than that of high-frequency excitation signals, which primarily reflect bulk resistance characteristics. Based on this physical mechanism, crack events can be effectively distinguished from conventional environmental interference by comparing the sudden drop differences in the phase angles of the two frequencies. The advantages of this judgment method are: firstly, it avoids the shortcomings of single resistance parameters being easily affected by factors such as temperature, humidity, and load fluctuations, significantly reducing the false alarm rate; secondly, the dual-frequency comparison strategy does not require a complex temperature compensation model, the algorithm is simple and reliable, and it can identify micro-cracks with a width of only 0.05 mm in real time during bridge structural condition monitoring, providing early warning for bridge maintenance.

[0085] In practice, the characteristic value of a step change in resistance can be determined based on the rate of change of the resistance amplitude within a preset time window in the following way: a fixed-length time window is extracted with the current moment as the endpoint. The length of the time window is preset to 0.5 seconds. The rate of change of the resistance amplitude with time is calculated within the time window. That is, the resistance amplitude at the end of the window is subtracted from the resistance amplitude at the beginning of the window and then divided by the window duration. The absolute value of this rate of change is taken as the characteristic value of a step change in resistance.

[0086] In specific implementation, when the resistance step change characteristic value exceeds the preset step judgment threshold, the extraction of the phase angle time history corresponding to the low-frequency point and the high-frequency point within the same time window can be achieved in the following way: Under the condition that the bridge is undamaged and the environment is stable, continuously collect resistance amplitude data for no less than 10 seconds, calculate the standard deviation of the data sequence as the noise level, take three times the standard deviation as the preset step judgment threshold, and then compare the calculated resistance step change characteristic value with the preset step judgment threshold. When the resistance step change characteristic value exceeds the threshold, it is determined that the resistance has increased stepwise, and the moment with the largest absolute value of the rate of change within the time window is taken as the moment when the resistance step occurs. Extract a time window of 1 second before and after the moment when the step occurs, and extract the phase angle numerical sequence corresponding to the low-frequency point and the phase angle numerical sequence corresponding to the high-frequency point from the synchronously collected data. These two numerical sequences are the phase angle time history, which is a discrete sequence used to characterize the phase angle of the low-frequency point and the high-frequency point over time.

[0087] In specific implementation, the phase angle drop amplitude values ​​for low-frequency and high-frequency points can be calculated based on the phase angle time history as follows: Based on the determined resistance step occurrence time and the extracted low-frequency point phase angle time history, the average value of all phase angle values ​​within 0.2 seconds before the step occurrence time is taken as the reference value, and the minimum value of all phase angle values ​​within 0.5 seconds after the step occurrence time is taken as the valley value. The low-frequency point phase angle drop amplitude value is obtained by subtracting the valley value from the reference value. Similarly, based on the high-frequency point phase angle time history, the high-frequency point phase angle drop amplitude value is obtained using the same calculation method. This phase angle drop amplitude value is used to measure the degree of phase angle drop caused by the crack event. The calculated low-frequency phase angle drop amplitude and high-frequency phase angle drop amplitude are respectively used as the low-frequency point phase angle drop amplitude value and the high-frequency point phase angle drop amplitude value.

[0088] In practice, the phase angle drop amplitude of the low-frequency point is compared with that of the high-frequency point. When the phase angle drop amplitude of the low-frequency point is greater than that of the high-frequency point, the occurrence of a crack event can be determined as follows: The phase angle drop amplitude of the low-frequency point is compared with that of the high-frequency point. When the phase angle drop amplitude of the low-frequency point is greater than that of the high-frequency point, a crack event is determined to have occurred. Conversely, if the phase angle drop amplitude of the low-frequency point is not greater than that of the high-frequency point, it is not determined to be a crack event. This crack event is a damage event that characterizes the irreversible rupture of the conductive network inside the conductive concrete layer due to crack formation in the tensile zone of the bridge concrete.

[0089] In some embodiments, before determining that a crack event has occurred, the method further includes:

[0090] Extract a time history window of the resistance amplitude and a time history window of the phase angle at low frequency points for a preset time length before and after the moment when the resistance amplitude increases abruptly;

[0091] Calculate the first-order difference sequence within the time history window of the resistance amplitude and the first-order difference sequence within the time history window of the phase angle at the low frequency point, respectively.

[0092] Calculate the Pearson correlation coefficient between two first-difference sequences;

[0093] When the Pearson correlation coefficient exceeds a preset correlation threshold, the crack event is confirmed to be valid; otherwise, it is determined to be a false signal caused by environmental factors.

[0094] It should be noted that the principle of using the above steps for false signal verification in this embodiment is as follows: When a real crack event occurs, the step change in resistance amplitude and the sudden drop in phase angle at low frequency points are both caused by the breakage of the same conductive network and the abrupt change in interface polarization characteristics. The changes of the two are highly synchronized in time, and the waveforms of their first-order difference sequences are similar. Therefore, the Pearson correlation coefficient is close to 1. However, when environmental factors such as slow temperature drift or humidity changes cause changes in resistance amplitude, the phase angle at low frequency points may respond with lag or change at different rates. The correlation between the first-order difference sequences of the two is significantly reduced. Based on this physical mechanism, by comparing the Pearson correlation coefficient with a preset threshold, the real crack event with good synchronicity and the environmental interference signal with significant asynchronicity can be effectively distinguished.

[0095] It should also be noted that the first-order difference sequence in this application refers to the temporal arrangement of the differences between adjacent data points within a time window, used to highlight the instantaneous changes in the signal.

[0096] In specific implementation, the time history window of resistance amplitude and the time history window of low-frequency point phase angle, which are preset time lengths before and after the moment when the resistance amplitude increases abruptly, can be implemented in the following way: Continuously collect resistance amplitude data at a sampling frequency of not less than 100Hz. When the resistance step change characteristic value exceeds the preset step judgment threshold, the moment with the largest absolute value of the rate of change is determined as the moment when the resistance amplitude increases abruptly. Based on this moment, a time length of 1 second is extracted both forward and backward. Since the sampling frequency is 100Hz, each time history window contains 201 data points. The extracted continuous data sequence of resistance amplitude is used as the resistance amplitude time history window. Simultaneously, a continuous data sequence completely corresponding to the above time window is extracted from the synchronously collected low-frequency point phase angle data and used as the low-frequency point phase angle time history window. This resistance amplitude time history window provides a time series segment of the complete change process of the resistance amplitude before and after the crack event, and this low-frequency point phase angle time history window provides a time series segment of the change process of the low-frequency point phase angle within the same time window as the resistance amplitude.

[0097] In practice, the Pearson correlation coefficient between two first-order difference sequences can be calculated as follows: Arrange the data sequence within the resistance amplitude time history window obtained in the first step in chronological order, and calculate the difference between the previous data and the next data in turn. For a sequence containing 201 data points, a total of 200 differences are obtained. The sequence formed by arranging these 200 differences in their original order is used as the first-order difference sequence of the resistance amplitude time history window. Similarly, calculate the difference between the previous data and the next data in the low-frequency point phase angle time history window in the same way, and obtain a sequence of 200 differences, which is used as the first-order difference sequence of the low-frequency point phase angle time history window. This first-order difference sequence is a differential feature sequence used to highlight the location and amplitude of abrupt changes in the signal and suppress slow drift components.

[0098] In practice, the Pearson correlation coefficient of two first-order difference sequences can be calculated as follows: Since the two first-order difference sequences obtained in the second step each contain 200 differences and are of equal length, these two first-order difference sequences are regarded as two numerical vectors. The covariance and standard deviation of the two vectors are calculated respectively. The covariance is divided by the product of the two standard deviations, and the quotient is the Pearson correlation coefficient. The Pearson correlation coefficient is a dimensionless index used to quantify the degree of linear correlation between the first-order difference sequence of resistance amplitude and the first-order difference sequence of phase angle at low frequency points. Its value ranges from -1 to 1.

[0099] In specific implementation, when the Pearson correlation coefficient exceeds a preset correlation threshold, the crack event is confirmed as valid; otherwise, it is determined to be a false signal caused by environmental factors. This can be achieved by comparing the calculated Pearson correlation coefficient with the preset correlation threshold, which is determined based on the lower limit of the statistical distribution of the correlation between two first-order difference sequences under a real crack event and is set to 0.7. When the Pearson correlation coefficient is greater than 0.7, the detected resistance step event is confirmed as a valid crack event caused by a crack. When the Pearson correlation coefficient is not greater than 0.7, the resistance step event is determined to be a false signal caused by changes in environmental factors such as temperature drift or humidity. This valid crack event is used to characterize a real crack damage event that has been double-verified and can proceed to the subsequent positioning steps.

[0100] In step 105, within the same time window when the crack event is determined to have occurred, if the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed the preset fluctuation range, it is determined that the crack occurred between two adjacent fiber Bragg gratings.

[0101] It should be noted that the preset fluctuation range in this application refers to the limit value of the normal drift of the center wavelength of each fiber Bragg grating caused by environmental vibration and slow temperature change. This range is determined based on the standard deviation of continuous monitoring data under crack-free conditions, and is usually taken as ±5 picometers. When the absolute value of the change in the center wavelength of a certain grating is greater than 5 picometers, it is considered that the grating has sensed the local strain concentration caused by the crack. When the absolute value of the change in the center wavelength of all gratings does not exceed 5 picometers, it indicates that the crack has not directly passed through the cross section of any grating and may be located in the blind zone between two adjacent gratings.

[0102] In some embodiments, determining that a crack occurred between two adjacent fiber Bragg gratings within the same time window for determining the occurrence of a crack event, when the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed a preset fluctuation range, specifically includes:

[0103] Extract a time history window of the resistance amplitude with a preset time length before and after the moment when the resistance amplitude increases abruptly, and calculate the first-order difference sequence within the window.

[0104] Extract the center wavelength time history of each fiber Bragg grating covering the same area within the same time window, and calculate the first-order difference sequence of the center wavelength time history of each grating respectively;

[0105] The first-order difference sequence within the resistance amplitude time history window is cross-correlated with the first-order difference sequence of the center wavelength time history of each grating one by one to obtain the cross-correlation peak value corresponding to each grating.

[0106] When the cross-correlation peak of any grating exceeds the preset cross-correlation threshold, it is determined that the crack occurs at the location of the grating, and the crack width is determined according to the center wavelength step amplitude of the grating.

[0107] When the cross-correlation peak of all gratings does not exceed the preset cross-correlation threshold, it is determined that the crack occurs between two adjacent fiber Bragg gratings, and the longitudinal position of the crack between the two is determined according to the difference in the center wavelength offset of the two adjacent fiber Bragg gratings before and after the resistance step.

[0108] The cross-correlation peak value in this application is an indicator used to quantify the degree of temporal synchronization and waveform similarity between the change in resistance amplitude and the change in fiber Bragg grating wavelength.

[0109] In a preferred embodiment, the above determination process first checks the change in center wavelength of each fiber Bragg grating before and after the occurrence of the crack event: the average center wavelength of each grating within 0.5 seconds before the resistance step occurs is calculated as the initial value, and the average center wavelength within 1 second after the resistance step occurs is calculated as the final value. The change in center wavelength is obtained by subtracting the initial value from the final value. If the absolute value of the change in center wavelength of all gratings does not exceed the preset fluctuation range of ±5 picometers, the crack is directly determined to occur between two adjacent gratings. If the absolute value of the change in center wavelength of any grating exceeds ±5 picometers, the crack is further located precisely through cross-correlation calculation.

[0110] In practice, firstly, taking the determined moment of the step increase in resistance amplitude as the center, a preset time length, such as 1 second, is extracted forward and backward to form a resistance amplitude time history window. The resistance amplitude data sequence within the window is calculated sequentially by subtracting the previous data from the next data in chronological order. All differences are arranged in the original order to obtain the first-order difference sequence of the resistance amplitude time history window.

[0111] Secondly, within the same time window, the data sequence of the center wavelength of each fiber Bragg grating covering the same area is extracted from the synchronously acquired data. The difference between the previous and subsequent data is calculated for the wavelength data sequence of each grating in the same way to obtain the first-order difference sequence of each grating. The first-order difference sequences of all gratings are summarized as the first-order difference sequence of the center wavelength time history of each grating. This first-order difference sequence of the center wavelength time history of each grating is a set of characteristic sequences used to cross-correlate with the resistance amplitude difference sequence to identify the crack location.

[0112] Then, the first-order difference sequence of the calculated resistance amplitude time history window is cross-correlated with the first-order difference sequence of each grating. That is, for each grating, the sum of the products of its first-order difference sequence and the resistance amplitude difference sequence is calculated according to different time offsets to obtain a set of cross-correlation function values. The maximum value of the set of cross-correlation function values ​​is taken as the cross-correlation peak value corresponding to the grating. The cross-correlation peak value is a dimensionless index used to quantify the waveform similarity and synchronization between the resistance amplitude difference sequence and the wavelength difference sequence of a single grating.

[0113] Next, the calculated cross-correlation peak value of each grating is compared with a preset cross-correlation threshold value of 0.6. When the cross-correlation peak value of any grating exceeds 0.6, it is determined that the crack occurs at the location of that grating. At this time, the crack width is determined according to the center wavelength step amplitude value of the grating. Specifically, the crack width is equal to the center wavelength step amplitude value divided by the strain sensitivity coefficient and then divided by the conversion coefficient between strain and crack width. The strain sensitivity coefficient is 1.2 picometers per microstrain for ordinary single-mode optical fiber. The conversion coefficient is pre-calibrated according to the grating packaging form and the elastic modulus of concrete, and is usually in the range of 0.5 to 0.8.

[0114] Finally, when the cross-correlation peak values ​​of all gratings do not exceed the preset cross-correlation threshold (i.e., none are greater than 0.6), it is determined that the crack does not penetrate any installed gratings, but is located between two adjacent fiber Bragg gratings. At this point, the offset of the center wavelength of each of the two adjacent gratings before and after the resistance step is extracted, the difference between the two offsets is calculated, and the longitudinal position of the crack between them is determined according to the following formula: Let the distance between the two adjacent gratings be... The wavelength shift of the first grating is The wavelength shift of the second grating is Then the distance of the crack relative to the first grating is The offset distance of the crack relative to the midpoint of the two gratings is The fact that the crack occurred between two adjacent fiber Bragg gratings is a location determination result used to indicate that the crack is located in the monitoring blind zone between the two gratings and cannot be directly detected by either grating.

[0115] In some embodiments, after determining that the crack occurs between two adjacent fiber Bragg gratings, the method further includes:

[0116] Extract the difference in the center wavelength offset between two adjacent fiber Bragg gratings before and after the crack event;

[0117] When the offset difference is not zero, the offset distance of the crack relative to the midpoint of the two adjacent gratings is determined according to the ratio of the offset difference to the spacing between the two adjacent gratings.

[0118] In specific implementation, firstly, the difference in center wavelength offset between two adjacent fiber Bragg gratings before and after the crack event is extracted. These two gratings are designated as the first grating and the second grating, respectively. The average center wavelength of the first grating is extracted from the stable period before the crack event as its initial center wavelength, and the average center wavelength of the first grating is extracted from the stable period after the crack event as its final center wavelength. The center wavelength offset of the first grating is obtained by subtracting the initial center wavelength from the final center wavelength. The center wavelength offset of the second grating is obtained using the same method. Then, the center wavelength offset difference is obtained by subtracting the center wavelength offset of the second grating from the center wavelength offset of the first grating. When this center wavelength offset difference is not equal to... At zero, the offset distance of the crack relative to the midpoint of the two gratings is determined according to the ratio of the difference to the spacing between the two adjacent gratings. Specifically, the straight-line distance between the first grating and the second grating is measured as the spacing between the two adjacent gratings. Half of this spacing is calculated as the half spacing. Then, the product of the difference in center wavelength offset and the half spacing is calculated. Finally, the product is divided by the aforementioned spacing between the two adjacent gratings. The result is the offset distance of the crack relative to the midpoint of the two adjacent gratings. The sign of this offset distance is determined by the sign of the difference in center wavelength offset. Its absolute value indicates the distance of the offset. A positive sign indicates that the crack is biased towards the first grating, and a negative sign indicates that the crack is biased towards the second grating. This achieves precise positioning of the crack located between adjacent fiber Bragg gratings.

[0119] In summary, this application achieves reliable identification of crack events by comparing the dual-frequency electrical excitation and phase angle of the conductive concrete layer, and realizes accurate determination of crack location through cross-correlation analysis of the fiber Bragg grating array. In particular, it can locate blind zone cracks between adjacent gratings that are difficult to detect by traditional methods. It has beneficial effects such as low false alarm rate, high positioning accuracy, and strong environmental adaptability, and is suitable for long-term health monitoring of various bridge concrete structures.

[0120] On the other hand, in some embodiments, this application provides a multi-parameter bridge structure condition monitoring system based on self-sensing materials, referencing... Figure 3 The figure is a schematic diagram of a multi-parameter bridge structure condition monitoring system based on self-sensing materials according to some embodiments of this application. The multi-parameter bridge structure condition monitoring system based on self-sensing materials includes: a pre-embedded module 301, a processing module 302, and a judgment module 303, which are described as follows: Pre-embedded module 301, in this application, the pre-embedded module 301 is mainly used to lay a conductive concrete layer with piezoresistive effect in the tension zone of bridge concrete and pre-embed a pair of measuring electrodes, and install multiple fiber Bragg gratings at different longitudinal positions in the same tension zone;

[0121] Processing module 302, in this application, is used to apply alternating electric excitation containing at least two frequency components to the measuring electrode pair, and simultaneously acquire the resistance amplitude and phase angle of the conductive concrete layer at different frequencies;

[0122] In this application, the processing module 302 is also used to perform wavelength demodulation on each fiber Bragg grating to obtain the real-time center wavelength of each grating.

[0123] The determination module 303 in this application is mainly used to determine that a crack event has occurred when the resistance amplitude of the conductive concrete layer increases abruptly and the phase angle drop amplitude at the low frequency point exceeds the phase angle drop amplitude at the high frequency point.

[0124] In this application, the determination module 303 is also used to determine that the crack occurred between two adjacent fiber Bragg gratings when the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed the preset fluctuation range within the same time window when determining the occurrence of the crack event.

[0125] In addition, this application also provides a computer device, which includes a memory and a processor. The memory stores code, and the processor is configured to acquire the code and execute the above-described multi-parameter bridge structure state monitoring method based on self-sensing materials.

[0126] In some embodiments, reference Figure 4 The figure is a schematic diagram of a computer device for implementing a multi-parameter bridge structure condition monitoring method based on self-sensing materials, according to some embodiments of this application. The multi-parameter bridge structure condition monitoring method based on self-sensing materials in the above embodiments can... Figure 4 The computer device shown is used to implement this, and the computer device 400 includes at least one processor 401, a communication bus 402, a memory 403, and at least one communication interface 404.

[0127] Processor 401 can be a general-purpose central processing unit (CPU) or an application-specific integrated circuit (ASIC).

[0128] The communication bus 402 can be used to transmit information between the aforementioned components.

[0129] The memory 403 may be a read-only memory (ROM) or other type of static storage device capable of storing static information and instructions, random access memory (RAM) or other type of dynamic storage device capable of storing information and instructions, or electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disks or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but not limited thereto. The memory 403 may exist independently and be connected to the processor 401 via the communication bus 402. The memory 403 may also be integrated with the processor 401.

[0130] The memory 403 stores program code for executing the scheme of this application, and its execution is controlled by the processor 401. The processor 401 executes the program code stored in the memory 403. The program code may include one or more software modules. The multi-parameter bridge structure state monitoring method based on self-sensing materials in the above embodiments can be implemented by the processor 401 and one or more software modules in the program code in the memory 403.

[0131] Communication interface 404 uses any transceiver-like device to communicate with other devices or communication networks, such as Ethernet, radio access network (RAN), wireless local area networks (WLAN), etc.

[0132] In a specific implementation, as one example, a computer device may include multiple processors, each of which may be a single-core (single-CPU) processor or a multi-core (multi-CPU) processor. Here, a processor may refer to one or more devices, circuits, and / or processing cores used to process data (e.g., computer program instructions).

[0133] The aforementioned computer device can be a general-purpose computer device or a special-purpose computer device. In specific implementations, the computer device can be a desktop computer, a portable computer, a network server, a handheld digital assistant (PDA), a mobile phone, a tablet computer, a wireless terminal device, a communication device, or an embedded device. This application does not limit the type of computer device.

[0134] In addition, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described multi-parameter bridge structure state monitoring method based on self-sensing materials.

[0135] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0136] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A multi-parameter bridge structural condition monitoring method based on self-sensing materials, characterized in that, The method includes the following steps: A conductive concrete layer with piezoresistive effect is laid in the tension zone of the bridge concrete and a pair of measuring electrodes are pre-embedded. Multiple fiber Bragg gratings are installed at different longitudinal positions in the same tension zone. An alternating electric excitation containing at least two frequency components is applied to the measuring electrode pair, and the resistance amplitude and phase angle of the conductive concrete layer at different frequencies are collected simultaneously. Wavelength demodulation is performed on each fiber Bragg grating to obtain the real-time center wavelength of each grating; A crack event is determined to have occurred when a step increase in the resistance amplitude of the conductive concrete layer is detected, and the phase angle drop amplitude at low frequency points exceeds the phase angle drop amplitude at high frequency points. The determination of whether a crack event has occurred also includes: Extract a time history window of the resistance amplitude and a time history window of the phase angle at low frequency points for a preset time length before and after the moment when the resistance amplitude increases abruptly; Calculate the first-order difference sequence within the time history window of the resistance amplitude and the first-order difference sequence within the time history window of the phase angle at the low frequency point, respectively. Calculate the Pearson correlation coefficient between two first-difference sequences; When the Pearson correlation coefficient exceeds the preset correlation threshold, the crack event is confirmed to be valid; otherwise, it is determined to be a false signal caused by environmental factors. Within the same time window for determining the occurrence of a crack event, if the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed the preset fluctuation range, the crack is determined to occur between two adjacent fiber Bragg gratings.

2. The method as described in claim 1, characterized in that, The installation of multiple fiber Bragg gratings at different longitudinal positions in the same tension region specifically includes: Each fiber Bragg grating is arranged at equal intervals along the longitudinal direction of the tension zone of the bridge, and the distance between two adjacent gratings is not greater than the preset maximum blind zone width. Each fiber Bragg grating is embedded into the concrete using a pre-embedding method and temporarily fixed before pouring; The center wavelengths of each fiber Bragg grating are staggered according to a preset wavelength interval before installation to support wavelength division multiplexing series networking.

3. The method as described in claim 1, characterized in that, When a step increase in the resistance amplitude of the conductive concrete layer is detected, and the phase angle drop amplitude at low frequency points exceeds the phase angle drop amplitude at high frequency points, the determination of a crack event specifically includes: The characteristic value of the resistance step change is determined based on the rate of change of the resistance amplitude within a preset time window; When the resistance step change characteristic value exceeds the preset step judgment threshold, the phase angle time history corresponding to the low frequency point and the high frequency point within the same time window is extracted; Based on the phase angle time history, the phase angle drop amplitude at the low-frequency point and the high-frequency point are calculated respectively; The phase angle drop values ​​of low-frequency points and high-frequency points are compared. When the phase angle drop value of low-frequency points is greater than that of high-frequency points, a crack event is determined to have occurred.

4. The method according to claim 1, characterized in that, Within the same time window for determining the occurrence of a crack event, if the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed a preset fluctuation range, the crack is determined to occur between two adjacent fiber Bragg gratings. Specifically, this includes: Extract a time history window of the resistance amplitude with a preset time length before and after the moment when the resistance amplitude increases abruptly, and calculate the first-order difference sequence within the window. Extract the center wavelength time history of each fiber Bragg grating covering the same area within the same time window, and calculate the first-order difference sequence of the center wavelength time history of each grating respectively; The first-order difference sequence within the resistance amplitude time history window is cross-correlated with the first-order difference sequence of the center wavelength time history of each grating one by one to obtain the cross-correlation peak value corresponding to each grating. When the cross-correlation peak of any grating exceeds the preset cross-correlation threshold, it is determined that the crack occurs at the location of the grating, and the crack width is determined according to the center wavelength step amplitude of the grating. When the cross-correlation peak of all gratings does not exceed the preset cross-correlation threshold, it is determined that the crack occurs between two adjacent fiber Bragg gratings, and the longitudinal position of the crack between the two is determined according to the difference in the center wavelength offset of the two adjacent fiber Bragg gratings before and after the resistance step.

5. The method as described in claim 1, characterized in that, The low-frequency point is an excitation frequency not higher than 100 Hz, and the high-frequency point is an excitation frequency not lower than 1 kHz.

6. The method as described in claim 1, characterized in that, After determining that the crack occurred between two adjacent fiber Bragg gratings, the following steps are also included: Extract the difference in the center wavelength offset between two adjacent fiber Bragg gratings before and after the crack event; When the offset difference is not zero, the offset distance of the crack relative to the midpoint of the two adjacent gratings is determined according to the ratio of the offset difference to the spacing between the two adjacent gratings.

7. A multi-parameter bridge structural condition monitoring system based on self-sensing materials, which uses the method described in any one of claims 1 to 6 to monitor the bridge structural condition, characterized in that... The system includes: The pre-embedded module is used to lay a conductive concrete layer with piezoresistive effect in the tension zone of bridge concrete and pre-embed a pair of measuring electrodes, and to install multiple fiber Bragg gratings at different longitudinal positions in the same tension zone. The processing module is used to apply alternating electrical excitation containing at least two frequency components to the measuring electrode pair and simultaneously acquire the resistance amplitude and phase angle of the conductive concrete layer at different frequencies. The processing module is also used to perform wavelength demodulation on each fiber Bragg grating to obtain the real-time center wavelength of each grating. The determination module is used to determine that a crack event has occurred when a step increase in the resistance amplitude of the conductive concrete layer is detected and the phase angle drop amplitude at the low frequency point exceeds the phase angle drop amplitude at the high frequency point. The determination module is also used to determine that the crack occurred between two adjacent fiber Bragg gratings when the change in the center wavelength of each fiber Bragg grating covering the same area does not exceed the preset fluctuation range within the same time window when determining the occurrence of the crack event.

8. A computer device comprising a memory and a processor, the memory storing code, characterized in that, The processor is configured to acquire the code and execute the multi-parameter bridge structure state monitoring method based on self-sensing materials as described in any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the multi-parameter bridge structure status monitoring method based on self-sensing materials as described in any one of claims 1 to 6.

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