Bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation

Abstract

The present invention provides a bridge structure health monitoring system based on stress amplitude and high-cycle fatigue damage accumulation, and relates to the technical field of bridge health monitoring. The present invention marks, monitors and analyzes the weld toe position of the welded component in the bridge structure, and adopts a multi-module collaborative working mode, which can not only collect the stress change data of the welded component in real time, but also provide data support for dynamic adjustment of the installation position and installation quantity of the strain acquisition equipment according to the resistance change degree and the stress amplitude spectrum analysis result, compare the measured natural frequency with the natural frequency in the undamaged state, calculate the macro damage degree prediction value, and accurately predict the macro damage degree of the welded structure.

Description

Technical Field

[0001] The present invention relates to the technical field of bridge health monitoring, and in particular to a bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation. Background Art

[0002] The health monitoring system of bridge structures has undergone a development process from simple stress measurement to complex multi-parameter monitoring. Traditional monitoring systems mainly rely on the installation of sensors such as strain gauges and accelerometers to obtain changes in physical quantities such as stress and vibration of bridge structures. However, most of these systems are limited to monitoring a single parameter and it is difficult to effectively evaluate the comprehensive health status of bridge structures, especially for the accumulation of fatigue damage in welded components. Existing technologies still have great limitations in early prediction and prevention.

[0003] In the prior art, the publication number is CN102589993B, and the name is a full-field monitoring method for fatigue damage of highway steel bridge deck welds. The method includes the following steps: Step 1: Setting of longitudinal rib strain sensors of steel bridge decks; setting longitudinal rib strain sensors along the bridge direction at the wheel load action position of each lane in the mid-span section of the steel bridge deck to monitor the longitudinal rib strain along the bridge direction caused by the passage of vehicles; Step 2: Processing of longitudinal rib strain monitoring data of steel bridge decks: taking 1 day as the calculation interval, processing the strain data obtained by the longitudinal rib strain sensor, and using the rain flow counting method to calculate the stress amplitude and cycle number of the longitudinal rib strain along the bridge direction; Step 3: Calculating the wheel load spectrum of the actual operating vehicle: Step 4: Full-field monitoring of fatigue damage of steel bridge deck welds; By arranging a small number of strain sensors on the longitudinal ribs of highway steel bridge decks, fatigue damage monitoring and evaluation of welds of different sections and types of steel bridge decks can be achieved.

[0004] Although the existing bridge structure health monitoring technology has made some progress in identifying stress concentration areas of bridges and monitoring crack expansion, it is still insufficient in accurately evaluating the high-cycle fatigue damage accumulation of welded components. Traditional methods mainly rely on the comparison of finite element simulation and historical monitoring data, lack real-time and dynamic damage accumulation monitoring methods, do not use the original monitoring data to analyze the health status of the bridge, and do not have damage detection analysis and fatigue life assessment.

[0005] In addition, the existing technology usually ignores the complex stress change characteristics of welded components under high stress amplitudes, and the influence of weld toe morphology on fatigue crack propagation. There are many weld toe positions in welded structures on bridges. If stress acquisition equipment is installed at each weld toe position, there will be great pressure on detection costs and subsequent data processing. How to set up a screening mechanism for weld toe positions? It is only necessary to install strain acquisition equipment at the position where the bridge structure is most prone to fatigue damage, and perform subsequent stress monitoring based on the screened weld toe positions, and predict the macroscopic damage degree of the welded structure, so as to realize the fatigue damage accumulation and health status evaluation of the bridge welded structure. This is the direction that needs to be improved at present.

[0006] The above information disclosed in the above Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to one of ordinary skill in the art. Summary of the invention

[0007] The object of the present invention is to provide a bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation to solve the problems raised in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solution: a bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation, specifically comprising:

[0009] Marking module: used to mark all welded components in the bridge structure to form a number set {1, 2, ..., n}, set i∈{1, 2, ..., n} to represent the number index of the i-th welded component, n is the total number of welded components, obtain the load analysis and finite element simulation data for each welded component in the bridge structure design stage, obtain the load response data corresponding to each welded component, and determine the weld toe position with the most significant stress change on each welded component based on the load response data, and the weld toe position includes the relatively set weld toes;

[0010] Weld toe morphology evaluation index generation module: used to collect weld toe morphology feature data at each determined weld toe position, analyze and process the weld toe morphology feature data to obtain a weld toe morphology evaluation index, which is used to determine the number of conductive coating strips applied on each weld toe;

[0011] Conductive coating strip setting module: used to apply at least two conductive coating strips in a point-by-point manner along the weld direction at the junction of the weld toe surface and the base material, and ensure that the conductive coating strips can deform with the stress change at the junction of the weld toe and the base material;

[0012] Benchmark data setting module: used to establish the baseline resistance value of the conductive coating strip, measure the resistance value of the conductive coating strip in an unstressed state, and record the resistance value as the benchmark data;

[0013] Comparison analysis module: used to set the current bridge to be monitored m times as an adjustment cycle, monitor the resistance value change data of the conductive coating strip on each weld toe under different stress conditions, and analyze the relative movement direction of the interface between the weld toe surface and the base material based on the resistance value change data;

[0014] Resistance change degree result generation module: used to set the resistance warning threshold corresponding to the conductive coating strip on each welding component when measuring the resistance of the conductive coating strip corresponding to the weld toe on each welding component, calculate the average measured resistance of the conductive coating strip on each welding component in the current adjustment cycle, and compare and analyze the average measured resistance with the corresponding resistance warning threshold to obtain the resistance change degree result;

[0015] Screening module: used to combine the resistance change degree results of each welded component with the relative motion direction analysis results to evaluate the health status of each welded structure. The health status includes but is not limited to the crack propagation risk and fatigue damage degree. According to the health status evaluation results, all welded components in the number set {1, 2, ..., n} are screened to obtain a screening set;

[0016] Stress amplitude generation module: used to paste strain gauges at the weld toe position determined by each welded component in the screening set, obtain stress distribution data at the weld toe position, and analyze and process the stress distribution data to obtain standard samples statistically analyzed in the frequency domain. After preprocessing the standard samples, the stress amplitude spectrum is obtained using the rain flow counting method;

[0017] Macro damage degree prediction module: used to measure the natural frequency of the selected concentrated welded components and record the corresponding strain data. The relationship between the natural frequency and the elastic modulus is used to analyze the change trend of the natural frequency. The measured natural frequency is compared with the natural frequency in the undamaged state to calculate the predicted value of the macro damage degree.

[0018] Loop module: It is used to re-execute the loop from the stress amplitude generation module to the macro damage degree prediction module in each adjustment cycle to continuously monitor and evaluate the health status of the welded structure.

[0019] Furthermore, the load analysis data includes mechanical response data of the welded components under static load, dynamic load and wind load conditions. The load analysis data is input into the finite element simulation model to simulate the mechanical behavior of the bridge structure under actual working conditions and obtain the load response data of each welded component.

[0020] Based on the load response data, determine the weld toe location where the stress change is most significant on each welded component;

[0021] The stress concentration area of ​​the welded component is screened, and the weld toe position with the largest stress amplitude is selected as the marking position.

[0022] Further, for the weld toe morphology evaluation index, the weld toe morphology evaluation index is used to determine the number of conductive coating strips applied on each weld toe, specifically including:

[0023] The weld toe morphological characteristic data include the weld width, weld height, weld angle, and weld surface roughness of the weld toe. The weld width, weld height, and weld angle are marked as W, H, and θ respectively;

[0024] Define the weld width as the distance between the two edges of the weld toe;

[0025] The weld height is defined as the vertical distance between the highest point on the weld surface and the lowest point on the weld toe;

[0026] The weld angle is defined as the angle between the weld and the parent material surface;

[0027] The weld toe shape evaluation index of the i-th welded component is defined as , the calculation formula is as follows:

[0028]

[0029] in, Determine the weld width, weld height, and weld angle of the weld toe for the i-th welded component respectively;

[0030] are the standard reference values ​​respectively; is the positive weight coefficient of each characteristic parameter;

[0031] The higher the value, the more complex the current weld toe morphology is, the stronger the stress concentration effect is, and more conductive coating strips need to be applied;

[0032] Define the number of conductive coating strips to determine the weld toe of the i-th welding component as , and establish Number of conductive coating strips The mapping relationship, The calculation formula is as follows:

[0033]

[0034] in, is the linear coefficient of the mapping relationship, and The meaning of rounding up is, .

[0035] Furthermore, the method of ensuring that the conductive coating strip can deform with the stress change at the interface between the weld toe and the base material specifically includes:

[0036] Surface treatment of the interface between weld toe and base material: The surface of the interface between weld toe and base material is treated to ensure that the conductive coating strip can be firmly attached and form good insulating contact with the base material;

[0037] The conductive material is silver paste conductive paint;

[0038] Conductive coating strip coating;

[0039] An insulating layer is provided on the outside of the conductive coating strip;

[0040] The setting of resistance measurement points reserves measurement points for resistance measurement at the beginning and end of the conductive coating strip.

[0041] Further, the establishment of the baseline resistance value of the conductive coating strip, measuring the resistance value of the conductive coating strip in an unstressed state, and recording the resistance value as the baseline data, and analyzing the relative movement direction of the interface between the weld toe surface and the base material specifically include:

[0042] Under the condition that no external stress is applied, the corresponding weld toe position of the i-th weld component is The resistance of the conductive coating strip is measured and The average of the resistance measurement values ​​is used to obtain the reference resistance value of the conductive coating strip at the weld toe position corresponding to the i-th welding component. ;

[0043] Under the condition of external stress applied to the bridge, the corresponding weld toe position of the i-th welded component is The resistance of the conductive coating strip is measured and The resistance measurement values ​​are averaged to obtain the measured resistance value of the conductive coating strip on the weld toe in the i-th welding component. and ;

[0044] And calculate the measured resistance value and the reference resistance value The change in resistance is calculated by the following formula:

[0045]

[0046] in, and is the resistance change of the conductive coating strip on the weld toe in the i-th welding component, and is the measured resistance value of the conductive coating strip on the weld toe arranged oppositely in the i-th welding component;

[0047] The collected resistance value data is smoothed by moving average method to eliminate noise and abnormal values; and The positive and negative conditions determine the relative setting of the weld toe movement direction:

[0048] like Less than 0, then The resistance of the conductive coating strip on the weld toe side decreases, indicating that The weld toe on the side is squeezed;

[0049] like Less than 0, then The resistance of the conductive coating strip on the weld toe side decreases, indicating that The weld toe on the side is squeezed;

[0050] like If it is greater than 0, the resistance of the conductive coating strip on the corresponding side of the weld toe increases, indicating that The weld toe on the side is stretched;

[0051] like If it is greater than 0, the resistance of the conductive coating strip on the corresponding side of the weld toe increases, indicating that The weld toe on the side is stretched.

[0052] Furthermore, the average measured resistance is compared and analyzed with the corresponding resistance warning threshold to obtain the resistance change degree result, and according to the health status assessment result, all welding components in the number set {1, 2, ..., n} are screened to obtain a screening set, which specifically includes:

[0053] Define the set of adjustment cycle times m as {1, 2, ..., m}, and j∈{1, 2, ..., m} represents the serial index of the jth monitoring. Calculate the average measured resistance of the conductive coating strip on the i-th welding component in the current adjustment cycle. The calculation formula is as follows:

[0054]

[0055] in, is the number of welded components on the ith The average measured resistance of the side conductive coating strip during the current adjustment cycle;

[0056] is the number of welded components on the ith The average measured resistance of the side conductive coating strip during the current adjustment cycle;

[0057] and in and The maximum value is selected as the average measured resistance of the conductive coating strip at the weld toe position in the i-th welded component;

[0058] Determine the resistance warning threshold corresponding to the i-th welding component as ;

[0059] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is greater than the resistance warning threshold If the magnitude is between 1% and 5%, the resistance change is assessed as slightly abnormal, indicating the risk of early fatigue damage. When the number of screening sets is less than half of the m monitoring times, such components are included in the screening set.

[0060] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is greater than the resistance warning threshold When the amplitude is between 5% and 15%, the resistance change degree is assessed as moderately abnormal, indicating a moderate fatigue damage risk. The component is included in the screening set, but the priority is lower than that of severely abnormal components.

[0061] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is greater than the resistance warning threshold If the magnitude exceeds 15%, the resistance change is assessed as severely abnormal and the component is directly included in the screening set;

[0062] Define the filter set as {S1,S2,…,S k}, where S k is the total number of welded components in the screening set, and S r ∈{S1,S2,…,S k} indicates the S r The number index of the selected welding components is used, and the selected welding components are prioritized according to the abnormal degree of resistance change. The components with severe abnormalities are prioritized, the components with moderate abnormalities are ranked second, and the components with slight abnormalities are ranked last;

[0063] According to the above results of the resistance change degree, the health status of the i-th welding component is as follows:

[0064] For minor abnormalities, the health status assessment result is "early signs of fatigue damage", and the m monitoring times in the adjustment cycle are adjusted to m+5;

[0065] For moderate abnormality: the health status assessment result is "mid-term fatigue damage", and mid-term maintenance measures are required at this time, and the m monitoring times in the adjustment cycle are adjusted to m+8;

[0066] For serious abnormalities: if the health status assessment result is "crack extension risk", stop using the welded component immediately, conduct a thorough inspection and repair, and adjust the m monitoring times in the adjustment cycle to m+15;

[0067] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is equal to the resistance warning threshold When the difference is between 0.1% and 1%, the resistance change level is assessed as approaching warning;

[0068] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is equal to the resistance warning threshold If the difference is greater than 1%, the resistance change is assessed as normal, with no significant signs of fatigue damage;

[0069] According to the above results of the resistance change degree, the health status of the i-th welding component is as follows:

[0070] For "approaching alert", the health status assessment result is "mild fatigue", and the m monitoring times in the adjustment cycle are adjusted to m+3;

[0071] For “Normal”, the health status assessment result is “good health” and the existing monitoring cycle can be maintained without any special measures.

[0072] Furthermore, the stress distribution data is analyzed and processed to obtain a standard sample of statistics in the frequency domain. After preprocessing the standard sample, the stress amplitude spectrum is obtained using the rain flow counting method, which specifically includes:

[0073] Obtain cyclic stress amplitude series of frequency domain data;

[0074] Sort the stress sequence by size, identify the upper and lower peaks, and record the stress amplitude and number of occurrences of each cycle;

[0075] Arrange the rainflow counting results and generate stress amplitude spectrum;

[0076] applying an excitation signal to the welding component;

[0077] Synchronous record filter set S r The strain data and vibration response signals of each welded component are obtained by pre-calculating the stress amplitude spectrum;

[0078] Perform Fourier transform on the recorded vibration signal to extract the natural frequency of the welded component and define the Sth filter. r The natural frequency of a welded component is ;

[0079] The function of strain changing with time is set to , strain data will change over time and be recorded as time series data;

[0080] After obtaining the natural frequency and strain data, the relationship between the natural frequency and the elastic modulus is used to analyze the macroscopic damage of the welded components. and elastic modulus The relationship between is described by the following formula:

[0081]

[0082] in, For S r The first welded component The natural frequency, For S r constants related to the geometry and boundary conditions of a welded component, is the elastic modulus of the material, is the density of the material;

[0083] The S r The current natural frequency measured for a welded component is marked as , the natural frequency in the undamaged state is marked as ;

[0084] The macroscopic damage degree is defined as , the calculation formula is expressed as:

[0085]

[0086] in, For the damage degree, set The value range is (0,1], The closer it is to 1, the more serious the damage. is a positive constant, used to avoid The case of 0.

[0087] Furthermore, the calculation of the predicted value of the macroscopic damage degree specifically includes:

[0088] Assuming the adjustment cycle time is T, we get , and calculate the total strain accumulation value , obtained by the following integrated strain function:

[0089]

[0090] According to fatigue damage theory, the strain amplitude at each sampling moment is evaluated and introduced into the damage model. The SN curve model of the material is used to describe the fatigue damage. The expression of the SN curve is:

[0091]

[0092] Where NM is the maximum stress of the material. Fatigue life under; C and is a constant of the material;

[0093] It is S r The maximum stress of a welded component, With maximum strain is proportional to;

[0094] The strain amplitude is introduced into the damage model. Based on the rain flow counting method, the cumulative amount of fatigue damage is obtained by cycle counting. The set of strain cycle numbers is defined as {1, 2, ..., h, ..., H}, where h represents the hth cycle and H represents the total number of cycles.

[0095] The total cumulative damage is obtained by linear accumulation, and the calculation formula is as follows:

[0096]

[0097] In this formula, is the total accumulated damage, Pl is the fatigue index of the material, is the maximum allowable strain of the material, is the strain amplitude per cycle;

[0098] The damage obtained by the change of natural frequency The cumulative damage corrected based on strain data Combined, the calibrated damage prediction model is obtained:

[0099]

[0100] in, It is S r The predicted damage value of a welded component; u1 is the weight coefficient, which represents the relative influence of natural frequency change and strain accumulation damage, and the value range of u1 is (0,1);

[0101] when The closer it is to 1, the more r The more severe the damage prediction of a welded component is, The closer it is to 0, the more r The less damage is predicted for each welded component;

[0102] set up The judgment threshold is Q1, 0.38≤Q1≤0.69; and the reference value of Q1 is set to 0.52, the Q1 approach interval is set to [Q1-0.1, Q1+0.1], and adjustments are made based on the health status assessment obtained from the resistance change results;

[0103] when When it is greater than Q1+0.1, the predicted damage level is severe abnormality;

[0104] at this time Approaching 1 means that the damage degree of the welded component approaches 100%, that is, close to the critical state, and represents a higher risk of crack extension;

[0105] The health status assessment result is "crack extension risk", which means that the welded component needs to be stopped from use immediately and thoroughly inspected and repaired. To avoid further damage, the number of monitoring times in the next monitoring cycle is adjusted from m+15 to m+18 to ensure continuous monitoring until the repair is completed;

[0106] when When the threshold Q1 is approached, the predicted damage level is moderately abnormal, indicating that the welded component has suffered obvious fatigue damage but has not yet reached a critical state;

[0107] If the health status assessment result is "mid-term fatigue damage", mid-term maintenance measures are taken, specifically local reinforcement or more detailed inspections. The number of monitoring times in the next monitoring cycle is adjusted from m+8 to m+11, with a higher frequency of monitoring to ensure timely handling of any potential deterioration;

[0108] when When it is less than Q1-0.1, the predicted damage level is slightly abnormal; When it approaches 0, it means that the damage degree of the welded component is relatively light, and only shows signs of early fatigue damage;

[0109] The health status assessment result is "early signs of fatigue injury". The existing monitoring plan will be maintained, and the number of monitoring times in the next monitoring cycle will be adjusted from m+5 to m+7 to increase the monitoring frequency and closely monitor the development of injuries.

[0110] Compared with the prior art, the beneficial effects of the present invention are: by marking, monitoring and analyzing the weld toe position of the welded components in the bridge structure, and adopting a multi-module collaborative working mode, not only can the stress change data of the welded components be collected in real time, but also the installation position and the number of the strain acquisition equipment can be dynamically adjusted according to the resistance change degree and the stress amplitude spectrum analysis results, and according to the resistance change degree results, data support can be provided for dynamic adjustment, and the health status of the welded components can be dynamically evaluated and predicted;

[0111] Comparing the measured natural frequency with the natural frequency in the undamaged state and calculating the predicted value of the macro damage degree can accurately predict the macro damage degree of the welded structure, detect potential fatigue damage earlier, provide accurate damage accumulation assessment, and effectively improve the safety and durability of the bridge structure;

[0112] Through this system, bridge management departments can carry out repairs and reinforcements earlier and more accurately, extend the service life of bridges, reduce the risk of sudden accidents, and provide reliable guarantees for the safe operation of bridges. BRIEF DESCRIPTION OF THE DRAWINGS

[0113] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0114] Figure 1 It is a schematic diagram of the overall system flow of the present invention.

[0115] Figure 2 This is a flow chart of the bridge fatigue life assessment system of the present invention.

[0116] Figure 3 It is a schematic diagram of the relatively arranged weld toes of the present invention. DETAILED DESCRIPTION

[0117] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0118] See the picture as shown Figure 1 , Figure 2 and Figure 3 , the present invention provides a technical solution:

[0119] Figure 3 1 represents the base material, 2 represents the oppositely arranged weld toe, and 3 represents the conductive coating strip;

[0120] The bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation includes:

[0121] Marking module: used to mark all welded components in the bridge structure to form a number set {1, 2, ..., n}, set i∈{1, 2, ..., n} to represent the number index of the i-th welded component, n is the total number of welded components, obtain the load analysis and finite element simulation data for each welded component in the bridge structure design stage, obtain the load response data corresponding to each welded component, and determine the weld toe position with the most significant stress change on each welded component based on the load response data, and the weld toe position includes the relatively set weld toes;

[0122] Weld toe morphology evaluation index generation module: used to collect weld toe morphology feature data at each determined weld toe position, analyze and process the weld toe morphology feature data to obtain a weld toe morphology evaluation index, which is used to determine the number of conductive coating strips applied on each weld toe;

[0123] Conductive coating strip setting module: used to apply at least two conductive coating strips in a point-by-point manner along the weld direction at the junction of the weld toe surface and the base material, and ensure that the conductive coating strips can deform with the stress change at the junction of the weld toe and the base material;

[0124] Benchmark data setting module: used to establish the baseline resistance value of the conductive coating strip, measure the resistance value of the conductive coating strip in an unstressed state, and record the resistance value as the benchmark data;

[0125] Comparison analysis module: used to set the current bridge to be monitored m times as an adjustment cycle, monitor the resistance value change data of the conductive coating strip on each weld toe under different stress conditions, and analyze the relative movement direction of the interface between the weld toe surface and the base material based on the resistance value change data;

[0126] Resistance change degree result generation module: used to set the resistance warning threshold corresponding to the conductive coating strip on each welding component when measuring the resistance of the conductive coating strip corresponding to the weld toe on each welding component, calculate the average measured resistance of the conductive coating strip on each welding component in the current adjustment cycle, and compare and analyze the average measured resistance with the corresponding resistance warning threshold to obtain the resistance change degree result;

[0127] Screening module: used to combine the resistance change degree results of each welded component with the relative motion direction analysis results to evaluate the health status of each welded structure. The health status includes but is not limited to the crack propagation risk and fatigue damage degree. According to the health status evaluation results, all welded components in the number set {1, 2, ..., n} are screened to obtain a screening set;

[0128] Stress amplitude generation module: used to paste strain gauges at the weld toe position determined by each welded component in the screening set, obtain stress distribution data at the weld toe position, and analyze and process the stress distribution data to obtain standard samples statistically analyzed in the frequency domain. After preprocessing the standard samples, the stress amplitude spectrum is obtained using the rain flow counting method;

[0129] Macro damage degree prediction module: used to measure the natural frequency of the selected concentrated welded components and record the corresponding strain data. The relationship between the natural frequency and the elastic modulus is used to analyze the change trend of the natural frequency. The measured natural frequency is compared with the natural frequency in the undamaged state to calculate the predicted value of the macro damage degree.

[0130] Loop module: It is used to re-execute the loop from the stress amplitude generation module to the macro damage degree prediction module in each adjustment cycle to continuously monitor and evaluate the health status of the welded structure.

[0131] Further explanation: for the number set {1, 2, …, n}, to ensure the uniqueness and traceability of the number, each number is clearly marked in the design drawings and models of the bridge structure, and corresponds one-to-one with the actual component position. In this way, the marking module can accurately locate each welded component to ensure the accuracy of subsequent steps;

[0132] The load analysis data includes the mechanical response data of the welded components under static load, dynamic load and wind load conditions. The mechanical response data is obtained by the finite element analysis (FEA) method and will not be described in detail.

[0133] The load analysis data is input into the finite element simulation model to simulate the mechanical behavior of the bridge structure under actual working conditions and obtain the load response data of each welded component; the load response data includes the stress-strain distribution diagram of the welded component at different time steps. The specific steps are as follows:

[0134] Finite element meshing: Meshing the bridge structure, ensuring that the mesh density is fine enough, especially at the weld toe, to capture subtle changes in stress concentration areas;

[0135] Apply boundary conditions: According to the design conditions of the actual bridge structure, apply boundary conditions and external loads, including gravity, vehicle loads, and wind force, to ensure that the simulation results are consistent with the actual situation;

[0136] Run simulation: Use simulation software (such as ANSYS, ABAQUS) to run load case simulation and generate stress-strain response data of each welded component under time history;

[0137] Based on the load response data, the weld toe location where the stress change is most significant on each welded component is determined as follows:

[0138] Calculate the maximum stress amplitude Δσ of each welded component during the entire load cycle, that is:

[0139]

[0140] in, and They represent the maximum and minimum stress values ​​of the ith welded component during the load cycle;

[0141] Screen the stress concentration area of ​​the welded component and select the weld toe position with the largest stress amplitude as the marking position; this step identifies the stress concentration area and determines the position where the stress changes significantly by analyzing the stress distribution on the surface of the welded component;

[0142] Explanation for the relatively set weld toes: On each welded component, the welded section between the welded component and the bridge structure is regarded as the base material, and the junction between the weld surface and the base material is called the weld toe. There are at least two weld points between the welded component and the bridge structure, and they are relatively set. Therefore, the weld between the welded component and the bridge structure is relatively set to ensure that the positions of the weld toes on both sides are identified and recorded; the reason for this step is that the weld toe position is often the most likely location for fatigue cracks, and there is a difference in the stress distribution of the weld toes on both sides, so they need to be marked separately;

[0143] After identifying the weld toe locations where stress changes are most significant, the marking module uses these locations as key monitoring areas and generates a complete database containing welding component numbers, load response data, stress concentration areas and marking locations; this database will be used for subsequent structural health monitoring and fatigue life assessment.

[0144] Further description, it is used to collect weld toe morphological feature data at each determined weld toe position, analyze and process the weld toe morphological feature data, and obtain a weld toe morphological evaluation index, which is used to determine the number of conductive coating strips applied on each weld toe, specifically including:

[0145] The weld toe morphological feature data include the weld width, weld height, weld angle, and weld surface roughness of the weld toe. The weld width, weld height, and weld angle are marked as W, H, and θ respectively, and the weld toe is scanned using 3D laser scanning technology to generate a high-precision 3D morphological model of the weld toe.

[0146] Weld width: refers to the width of the weld at the weld toe, that is, the horizontal distance from the weld edge to the edge of the parent material; changes in width affect the strength and fatigue performance of the welded joint;

[0147] Weld height: refers to the vertical distance from the weld surface to the lowest point of the weld toe; weld height affects the strength and stress distribution of the weld joint;

[0148] Weld angle: refers to the angle between the weld surface and the parent material surface; changes in weld angle will affect stress concentration and the propagation direction of fatigue cracks;

[0149] The specific steps are as follows:

[0150] Equipment calibration: Before data collection, the 3D laser scanning equipment is calibrated to ensure the accuracy of the scanned data; the calibration parameters include the resolution and focal length of the laser scan;

[0151] Scanning operation: Aim the laser scanner at the weld toe position and perform a full-scale scan to obtain complete 3D morphological data of the weld toe; these data will be used for subsequent morphological analysis;

[0152] Data storage: The weld toe 3D data obtained by scanning is stored in the database in the form of point cloud as the basic data for subsequent analysis;

[0153] The collected three-dimensional morphological data of weld toe are analyzed and processed to extract the key morphological features of weld toe. The feature extraction process includes:

[0154] De-noising and correcting point cloud data to eliminate noise and deviations generated during the scanning process, including median filtering and point cloud registration;

[0155] Define the weld width as the distance between the two edges of the weld toe;

[0156] The weld height is defined as the vertical distance between the highest point on the weld surface and the lowest point on the weld toe;

[0157] The weld angle is defined as the angle between the weld and the parent material surface;

[0158] Based on the extracted weld toe morphological feature data, the weld toe morphological evaluation index for the i-th welded component is defined as , the calculation formula is as follows:

[0159]

[0160] in, Determine the weld width, weld height, and weld angle of the weld toe for the i-th welding component respectively; since the weld toe position includes relatively set weld toes, it is sufficient to select any one of the weld toes for calculation; are the standard reference values ​​respectively; is the positive weight coefficient of each characteristic parameter, which is preset according to the degree of influence on the weld toe morphology. In this embodiment, ;

[0161] The higher the value, the more complex the current weld toe morphology is, the stronger the stress concentration effect is, and more conductive coating strips need to be applied;

[0162] According to actual application requirements and experimental data, the number of conductive coating strips for the weld toe of the i-th welding component is defined as , and establish Number of conductive coating strips The mapping relationship, The calculation formula is as follows:

[0163]

[0164] in, is the linear coefficient of the mapping relationship, and The meaning of rounding up is, According to the expert group through actual testing and experience, in this embodiment, .

[0165] Further description, at least two conductive coating strips are applied in a point-by-point manner along the weld direction at the interface between the weld toe surface and the base material, and the conductive coating strips are ensured to deform with the stress change at the interface between the weld toe and the base material, specifically including:

[0166] 1.1) Surface treatment at the interface between weld toe and base material;

[0167] The surface at the junction of the weld toe and the base material is treated to ensure that the conductive coating can be firmly attached and form good insulating contact with the base material. The surface treatment includes the following steps:

[0168] Cleaning: Use degreaser or other surface cleaner to remove surface oil, oxide layer and other impurities to ensure surface cleanliness;

[0169] Grinding: Lightly grind the weld toe surface with fine-grit sandpaper to remove any minor surface irregularities and increase the roughness of the coating surface to improve the adhesion of the conductive coating strip;

[0170] Surface pretreatment: Use surfactant to pretreat the polished surface to further enhance the adhesion between the conductive coating strip and the weld toe surface, and ensure whether the interface between the base material and the weld is coated with insulating paint. If the measurement shows that there is no insulation effect, apply insulating paint to the interface between the base material and the weld in advance, or set up flexible materials that can transfer the stress of the weld toe to the conductive coating strip that is subsequently applied. Flexible materials include polyurethane elastomers and polyester elastomers.

[0171] 1.2) Choose silver paste conductive paint as the conductive material;

[0172] When selecting conductive strip material, the material's conductivity, flexibility, and compatibility with the weld toe surface should be considered:

[0173] Silver paste conductive paint: It has excellent conductivity and flexibility, and can adapt to the slight deformation at the junction of the weld toe and the base material; the particle size of silver paste conductive paint is controlled between 10 nanometers and 1 micron to ensure that it can be evenly coated and maintain conductivity during deformation;

[0174] The reason for choosing silver paste conductive paint is its high conductivity and adaptability to deformation, which enables the coated strip to stably reflect the strain during stress changes;

[0175] At the junction of the determined weld toe surface and the base material, apply the conductive coating strip in a point-by-point manner along the weld direction; the specific operation steps are as follows.

[0176] 1.3) Conductive coating strip coating;

[0177] Material preparation: Get a certain amount of silver paste conductive paint and make sure all the paint comes from the same batch to reduce the difference between materials;

[0178] Coating mold production: Make standardized coating molds. The shape and size of the molds should meet the design requirements of the conductive coating strips. The mold specifications should include length, width and thickness to ensure uniformity of coating.

[0179] Apply test strips: Use the prepared mold to apply multiple test strips on the weld toe surface. The size of each test strip needs to be consistent. When applying, ensure that the thickness of the coating is between 10 microns and 50 microns to ensure the stability of the conductive performance;

[0180] Positioning and marking: According to the number of conductive coating strips , use precision positioning tools to mark the coating position of the conductive coating strip along the weld direction at the junction of the weld toe and the base material; the coating interval of the point-break method should be uniform, and the recommended interval is 3 mm to 5 mm to ensure sufficient strain sensitivity between the coating strips;

[0181] Applying conductive coating strips: Use micro-coating equipment to apply silver paste conductive paint on the marked positions according to the predetermined dot-break intervals; the coating thickness is selected from a quantitative value between 10 microns and 50 microns to ensure the consistency of the specifications of each conductive coating strip, while ensuring the sensitivity and stability of the conductive coating strip;

[0182] Curing after coating: After the conductive coating is applied, it needs to be cured. The curing method is heating curing or natural curing. The appropriate curing conditions are selected according to the material properties. The recommended temperature is 80°C to 120°C and the curing time is 30 minutes to 1 hour.

[0183] 1.4) Setting an insulating layer on the outside of the conductive coating strip;

[0184] After the conductive coating strip is coated and cured, an insulating layer is set on its periphery; the function of the insulating layer is to protect the conductive coating strip from the influence of the external environment and avoid the error of resistance measurement caused by external contact or moisture. The specific steps are as follows:

[0185] Insulation material selection: Select insulation materials with high resistivity and good weather resistance, such as polyimide film or epoxy resin coating; the thickness of the insulation layer should be between 50 microns and 100 microns to ensure the insulation effect without excessively affecting the flexibility of the structure;

[0186] Insulation coating: Spray or dip the insulating material evenly on the surface of the conductive coating strip; ensure that the coating covers the entire conductive coating strip area, but reserve the beginning and end of the conductive coating strip for contact points for subsequent resistance measurement;

[0187] Insulation layer curing: After the insulation layer is coated, it is cured; the curing conditions should be selected according to the characteristics of the insulation material. The recommended temperature is 60°C to 90°C and the curing time is 1 hour to 2 hours.

[0188] 1.5) Setting of resistance measurement points: reserve measurement points for resistance measurement at the beginning and end of the conductive coating strip; the measurement points should be set at both ends of the weld and ensure a stable connection with the measuring equipment. The specific operation steps are as follows:

[0189] Measuring point marking: When applying the conductive coating strip, leave 5 mm areas at both ends without insulating layer coating to facilitate subsequent connection of electrodes for resistance measurement;

[0190] Electrode connection: Use conductive adhesive to fix the measuring electrode to the reserved measuring point; use copper or gold-plated electrodes as electrode materials to ensure low resistance connection and stable resistance measurement;

[0191] Connection test: After the electrode connection is completed, a preliminary resistance measurement test is performed to ensure the stability and reliability of the connection between the conductive coating strip and the measuring equipment.

[0192] Further description, for establishing the baseline resistance value of the conductive coating strip, measuring the resistance value of the conductive coating strip in an unstressed state and recording the resistance value as the baseline data specifically includes:

[0193] Use a high-precision digital multimeter or other resistance measuring device to connect its two ends to the beginning and end of the conductive coating strip, making sure the connection points are clean and firm to avoid the influence of contact resistance;

[0194] Under the condition that no external stress is applied, the corresponding weld toe position of the i-th welded component is The resistance of the conductive coating strip is measured and The average of the resistance measurement values ​​is used to obtain the reference resistance value of the conductive coating strip at the weld toe position corresponding to the i-th welding component. .

[0195] The measured resistance value is recorded in the database and marked as the reference resistance data.

[0196] Further explanation: Analyze the relative movement direction of the interface between the weld toe surface and the base material, including:

[0197] Under the condition of external stress applied to the bridge, the corresponding weld toe position of the i-th welded component is The resistance of the conductive coating strip is measured and The resistance measurement values ​​are averaged to obtain the measured resistance value of the conductive coating strip on the weld toe in the i-th welding component. and ;

[0198] And calculate the measured resistance value and the reference resistance value The change in resistance is calculated by the following formula:

[0199]

[0200] in, and is the resistance change of the conductive coating strip on the weld toe in the i-th welding component, and is the measured resistance value of the conductive coating strip on the weld toe arranged oppositely in the i-th welding component;

[0201] The collected resistance value data is smoothed by moving average method to eliminate noise and abnormal values; and The positive and negative conditions determine the relative setting of the weld toe movement direction:

[0202] like Less than 0, then The resistance of the conductive coating strip on the weld toe side is reduced, indicating that The weld toe on the side is squeezed;

[0203] like Less than 0, then The resistance of the conductive coating strip on the weld toe side is reduced, indicating that The weld toe on the side is squeezed;

[0204] like If it is greater than 0, the resistance of the conductive coating strip on the corresponding side of the weld toe increases, indicating that The weld toe on the side is stretched;

[0205] like If it is greater than 0, the resistance of the conductive coating strip on the corresponding side of the weld toe increases, indicating that The weld toe on the side is stretched.

[0206] This judgment is based on the fact that when the conductive coating strip is compressed, the conductive path will be compressed, thereby reducing the resistance, while when it is pulled, the conductive path will be stretched and the resistance will increase.

[0207] Further explanation: the average measured resistance is compared and analyzed with the corresponding resistance warning threshold to obtain the resistance change degree result, and according to the health status assessment result, all welding components in the number set {1, 2, ..., n} are screened to obtain the screening set, which specifically includes:

[0208] Define the set of adjustment cycle times m as {1, 2, ..., m}, and j∈{1, 2, ..., m} represents the serial index of the jth monitoring. Calculate the average measured resistance of the conductive coating strip on the i-th welding component in the current adjustment cycle. The calculation formula is as follows:

[0209]

[0210] in, is the number of welded components on the ith The average measured resistance of the side conductive coating strip during the current adjustment cycle;

[0211] is the number of welded components on the ith The average measured resistance of the side conductive coating strip during the current adjustment cycle;

[0212] and in and The maximum value is selected as the average measured resistance of the conductive coating strip at the weld toe position in the i-th welded component;

[0213] According to the finite element simulation model in the marking module, the load response data of the i-th welding component before load failure is determined, and the resistance change data of the conductive coating strip on the weld toe set relatively in the i-th welding component is imported into the finite element simulation model for simulation, and combined with the expert group to make adjustments through experimental data, the resistance warning threshold corresponding to the i-th welding component is determined to be ; The specific steps are as follows:

[0214] The resistance change data of the conductive coating strips on the relatively set weld toes in the i-th welding component are imported into the finite element simulation model for simulation:

[0215] Finite element software is used to simulate the change in resistance under different load conditions, and the extracted load response data is combined with the resistance change model to calculate the resistance change value of each welded component under the applied load;

[0216] After obtaining the resistance change simulation data, it needs to be verified and adjusted by the expert group:

[0217] Experimental data collection: Collect the real resistance change data obtained from relevant laboratory or field tests and compare them with the simulation results; ensure that these experimental data can cover the real behavior of the material and the influence of environmental factors;

[0218] Model adjustment and optimization: Based on the feedback from the expert group and experimental data, adjust the material parameters, load conditions and resistance change model in the finite element model to ensure that the simulation results can more accurately reflect the actual situation;

[0219] Repeated iteration: In multiple iterations, the model is optimized and adjusted by constantly comparing the simulation results with the actual measured values ​​until the error between the simulation results and the experimental data is within an acceptable range;

[0220] After finite element simulation and experimental verification, the resistance warning threshold of the i-th welding component is finally determined. :

[0221] If the resistance change trend of the welded component is found to be inconsistent with expectations during subsequent monitoring, feedback will be given to the expert group for re-evaluation and adjustment;

[0222] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is greater than the resistance warning threshold If the magnitude is between 1% and 5%, the resistance change is assessed as slightly abnormal, indicating the risk of early fatigue damage. When the number of screening sets is less than half of the m monitoring times, such components are included in the screening set.

[0223] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is greater than the resistance warning threshold When the amplitude is between 5% and 15%, the resistance change degree is assessed as moderately abnormal, indicating a moderate fatigue damage risk. The component is included in the screening set, but the priority is lower than that of severely abnormal components.

[0224] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is greater than the resistance warning threshold If the magnitude exceeds 15%, the resistance change is assessed as a serious anomaly and the component is directly included in the screening set. Immediate measures are required at this time, as early signs of crack extension or structural failure have appeared.

[0225] Define the filter set as {S1,S2,…,S k}, where S k is the total number of welded components in the screening set, and S r ∈{S1,S2,…,S k} indicates the S r The number index of the selected welding components is used, and the selected welding components are prioritized according to the abnormal degree of resistance change. The components with severe abnormalities are prioritized, the components with moderate abnormalities are ranked second, and the components with slight abnormalities are ranked last;

[0226] According to the above results of the resistance change degree, the health status of the i-th welding component is as follows:

[0227] For minor abnormalities, the health status assessment result is "early signs of fatigue damage", and the m monitoring times in the adjustment cycle are adjusted to m+5;

[0228] For moderate abnormality: the health status assessment result is "mid-term fatigue damage", and mid-term maintenance measures are required at this time, adjusting the m monitoring times in the adjustment cycle to m+8, and performing reinforcement or more detailed inspections;

[0229] For serious abnormalities: if the health status assessment result is "crack extension risk", stop using the welded component immediately, conduct a thorough inspection and repair, and adjust the m monitoring times in the adjustment cycle to m+15;

[0230] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is equal to the resistance warning threshold When the difference is between 0.1% and 1%, the resistance change level is assessed as approaching warning;

[0231] If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is equal to the resistance warning threshold If the difference is greater than 1%, the resistance change is assessed as normal, with no significant signs of fatigue damage;

[0232] According to the above results of the resistance change degree, the health status of the i-th welding component is as follows:

[0233] For "approaching alert", the health status assessment result is "mild fatigue", and the m monitoring times in the adjustment cycle are adjusted to m+3 to ensure that potential problems can be discovered in time in the future;

[0234] For “Normal”, the health status assessment result is “good health” and the existing monitoring cycle can be maintained without any special measures.

[0235] Further explanation: the stress distribution data is analyzed and processed to obtain the statistical standard samples in the frequency domain. After preprocessing the standard samples, the stress amplitude spectrum is obtained using the rain flow counting method, and the macro damage degree prediction value is calculated, which specifically includes:

[0236] 2.1) Set up a data acquisition system to ensure that the output signal of the strain gauge can be transmitted to a computer or data recording device in real time, and use a suitable device such as an NI data acquisition card for signal conversion;

[0237] During the acquisition process, define the sampling frequency , the sampling frequency is specifically selected as 200 Hz to meet the requirements of stress amplitude analysis;

[0238] 2.2) In the collected data, the noise is first removed and the signal is smoothed using a digital filter; the filter is selected to set the cutoff frequency to ;

[0239] After data denoising, linearization is performed to ensure the rationality of the data, remove outliers, and ensure that the data is clear and meets the usage standards;

[0240] 2.3) After the strain data is processed, it enters the stress analysis stage. The stress calculation formula is:

[0241]

[0242] in, is stress, is the elastic modulus of the material, For strain, is Poisson's ratio, in this embodiment The value is 0.3;

[0243] 2.3) Using the above formula, calculate the stress value based on the output voltage of the strain gauge and the physical properties of the material; this calculation should be performed automatically after data processing to ensure real-time feedback;

[0244] 2.4) Perform frequency domain analysis on the collected stress data to obtain more comprehensive stress amplitude information;

[0245] 2.5) Perform fast Fourier transform (FFT) on the preprocessed stress data;

[0246] 2.6) Perform statistical analysis on the frequency domain signal to extract the characteristics of stress amplitude, which are mean and variance, for subsequent rain flow counting method application; according to the statistical characteristics, establish a standard sample set and record the stress amplitude data under normal working conditions;

[0247] 2.7) After obtaining the frequency domain data of stress amplitude, the stress amplitude spectrum is extracted using the rain flow counting method, which effectively identifies the number of cycles of fatigue load;

[0248] Implement the rain flow counting method through programming or software tools. The specific steps are as follows:

[0249] 2.71) Obtain cyclic stress amplitude series of frequency domain data;

[0250] 2.72) Sort the stress sequence by size, identify the upper and lower peaks, and record the stress amplitude and number of occurrences of each cycle;

[0251] 2.8) Organize the rainflow counting results and generate stress amplitude spectrum, which will be used for subsequent fatigue damage prediction and health assessment; visualize the stress amplitude spectrum to ensure that the data is easy to understand and further analyze;

[0252] Before measuring the natural frequency of the welded components in the screening set, an excitation signal is applied to the welded components to induce their vibration mode; specifically, an impact hammer or an electromagnetic exciter is used. These two methods can generate a wide spectrum of excitation signals covering multiple frequency ranges, thereby effectively exciting the natural vibration mode of the welded components;

[0253] 3.1) Use a high-precision accelerometer (a triaxial accelerometer in this embodiment) to install it at the frequency monitoring part of the welded component. The frequency monitoring part is the area where the strain gauge is pasted at the weld toe position, which is used to synchronously record the S-th frequency of the screening concentration. r The strain data and vibration response signals of each welded component are obtained by pre-calculating the stress amplitude spectrum;

[0254] 3.2) Perform Fourier transform on the recorded vibration signal to extract the natural frequency of the welded component and define the screened S r The natural frequency of a welded component is ;

[0255] 3.3) While applying the excitation signal, start the strain gauge and collect data, ensuring that the strain gauge acquisition frequency is higher than the highest frequency of the excitation signal to capture the complete strain change;

[0256] 3.4) Assume that the function of strain changing with time is , strain data will change over time and be recorded as time series data;

[0257] With discrete time points The corresponding strain value To represent the strain data during the entire measurement period:

[0258]

[0259] in, is the sampling time, and One-to-one correspondence with the set of adjustment cycle times {1, 2, ..., m}, indicating that each sampling moment corresponds to the number of single acquisitions in the adjustment cycle. is the strain value at each moment, and the maximum value in the strain data is determined as ;

[0260] According to the collected strain time series data, select polynomial fitting or Fourier series for function fitting to generate a continuous function of strain changing with time , this function is used to describe the strain response of the welded component at different time points;

[0261] The polynomial fitting formula is as follows:

[0262]

[0263] The Fourier series formula is as follows:

[0264]

[0265] in, is the fitting parameter, is the amplitude of the Fourier series, f is the frequency, is the phase angle, Represents the number of frequency components in the Fourier series, each Corresponding to a frequency component, represents the total number of frequency components in the Fourier series;

[0266] 3.5) After obtaining the natural frequency and strain data, the relationship between the natural frequency and elastic modulus is used to analyze the macroscopic damage of the welded component. and elastic modulus The relationship between is described by the following formula:

[0267]

[0268] in, For S r The first welded component The natural frequency, For S r constants related to the geometry and boundary conditions of a welded component, is the elastic modulus of the material, is the density of the material, Determined by a panel of experts using experimental data;

[0269] 3.6) The S r The current natural frequency measured for a welded component is marked as , the natural frequency in the undamaged state is marked as , to compare, and Compare and calculate to get the change of natural frequency :

[0270]

[0271] in, It is S r The natural frequency of a welded component in an intact state, It is S r The natural frequency of each welded component measured at the current time;

[0272] 3.7) According to the mining fatigue theory and cumulative damage model, the macroscopic damage degree is defined as , the calculation formula is expressed as:

[0273]

[0274] in, is the degree of damage, with the S r The cumulative damage of each welded component will increase, which will lead to gradually decreases, so The ratio is always less than or equal to 1, setting The value range is (0,1], The closer it is to 1, the more serious the damage. is a positive constant, used to avoid When is 0, in this embodiment, ;

[0275] Combined strain data , further calibrate the damage model to correct the damage prediction value to improve the prediction accuracy, including:

[0276] Assuming the adjustment cycle time is T, we get , and calculate the total strain accumulation value , obtained by the following integrated strain function:

[0277]

[0278] According to fatigue damage theory, the strain amplitude at each sampling moment is evaluated and introduced into the damage model. The SN curve (stress-life curve) model of the material is used to describe fatigue damage. The expression of the SN curve is:

[0279]

[0280] Where NM is the maximum stress of the material. Fatigue life under

[0281] C and is a constant of the material, determined by the expert group through experimental data;

[0282] It is S r The maximum stress of a welded component, With maximum strain is proportional to;

[0283] The strain amplitude is introduced into the damage model. Based on the rain flow counting method, the cumulative amount of fatigue damage is obtained by cycle counting. The set of strain cycle times is defined as {1, 2, …, h, …, H}, where h represents the hth cycle, H represents the total number of cycles, and each strain cycle corresponds to the damage of a welded component:

[0284]

[0285] in, is the strain amplitude per cycle; is the maximum allowable strain of the material; Pl is the fatigue index of the material;

[0286] The total cumulative damage is obtained by linear accumulation, and the calculation formula is as follows:

[0287]

[0288] In this formula, is the cumulative total damage;

[0289] The damage obtained by the change of natural frequency The cumulative damage corrected based on strain data Combined, the calibrated damage prediction model is obtained:

[0290]

[0291] in, It is S r The predicted damage value of a welded component; u1 is a weight coefficient, which characterizes the relative influence of natural frequency change and strain accumulation damage, and the value range of u1 is (0,1); the specific determination of u1 is determined by the expert group through experimental data and will not be elaborated on;

[0292] when The closer it is to 1, the more r The more serious the damage prediction of a welded component is, the closer it is to 0, indicating that the Sth r The less damage is predicted for each welded component;

[0293] set up The judgment threshold is Q1, 0.38≤Q1≤0.69; the reference value of Q1 is set to 0.52, and the Q1 approximate interval is set to [Q1-0.1, Q1+0.1]. The specific value of Q1 is determined by the expert group through experimental data; and it is adjusted based on the health status assessment obtained from the resistance change results;

[0294] when When it is greater than Q1+0.1, the predicted damage level is severe abnormality;

[0295] at this time Approaching 1 means that the damage degree of the welded component approaches 100%, that is, close to the critical state, and represents a higher risk of crack extension;

[0296] The health status assessment result is "crack extension risk", which means that the welded component needs to be stopped from use immediately and thoroughly inspected and repaired. To avoid further damage, the number of monitoring times in the next monitoring cycle is adjusted from m+15 to m+18 to ensure continuous monitoring until the repair is completed;

[0297] when When the threshold Q1 is close to the interval, the predicted damage level is moderately abnormal, indicating that the welded component has suffered obvious fatigue damage but has not yet reached a critical state;

[0298] If the health status assessment result is "mid-term fatigue damage", mid-term maintenance measures are taken, specifically local reinforcement or more detailed inspections. The number of monitoring times in the next monitoring cycle is adjusted from m+8 to m+11, with a higher frequency of monitoring to ensure timely handling of any potential deterioration;

[0299] when When it is less than Q1-0.1, the predicted damage level is slightly abnormal; When it approaches 0, it means that the damage degree of the welded component is relatively light, and only shows signs of early fatigue damage;

[0300] The health status assessment result is "early signs of fatigue injury". The existing monitoring plan is maintained, and the number of monitoring times in the next monitoring cycle is adjusted from m+5 to m+7 to slightly increase the monitoring frequency and closely monitor the development of injuries.

[0301] The above formulas are all dimensionless and numerical calculations. The formula is a formula for the most recent real situation obtained by collecting a large amount of data and performing software simulation. The preset parameters in the formula are set by technicians in this field according to actual conditions.

[0302] The above embodiments may be implemented in whole or in part by software, hardware, firmware or any other combination thereof. When implemented by software, the above embodiments may be implemented in whole or in part in the form of a computer program product. Those skilled in the art may appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein may be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed by hardware or software methods depends on the specific application and design constraints of the technical solution.

[0303] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, and may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0304] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation, characterized in that: Specifically include: Marking module: used to mark all welded components in the bridge structure to form a number set {1, 2, ..., n}, set i∈{1, 2, ..., n} to represent the number index of the i-th welded component, n is the total number of welded components, obtain the load analysis and finite element simulation data for each welded component in the bridge structure design stage, obtain the load response data corresponding to each welded component, and determine the weld toe position with the most significant stress change on each welded component based on the load response data, and the weld toe position includes the relatively set weld toes; Weld toe morphology evaluation index generation module: used to collect weld toe morphology feature data at each determined weld toe position, analyze and process the weld toe morphology feature data to obtain a weld toe morphology evaluation index, which is used to determine the number of conductive coating strips applied on each weld toe; Conductive coating strip setting module: used to apply at least two conductive coating strips in a point-by-point manner along the weld direction at the junction of the weld toe surface and the base material, and ensure that the conductive coating strips can deform with the stress change at the junction of the weld toe and the base material; Benchmark data setting module: used to establish the baseline resistance value of the conductive coating strip, measure the resistance value of the conductive coating strip in an unstressed state, and record the resistance value as the benchmark data; Comparison analysis module: used to set the current bridge to be monitored m times as an adjustment cycle, monitor the resistance value change data of the conductive coating strip on each weld toe under different stress conditions, and analyze the relative movement direction of the interface between the weld toe surface and the base material based on the resistance value change data; Resistance change degree result generation module: used to set the resistance warning threshold corresponding to the conductive coating strip on each welding component when measuring the resistance of the conductive coating strip corresponding to the weld toe on each welding component, calculate the average measured resistance of the conductive coating strip on each welding component in the current adjustment cycle, and compare and analyze the average measured resistance with the corresponding resistance warning threshold to obtain the resistance change degree result; Screening module: used to combine the resistance change degree results of each welded component with the relative motion direction analysis results to evaluate the health status of each welded structure. The health status includes but is not limited to the crack propagation risk and fatigue damage degree. According to the health status evaluation results, all welded components in the number set {1, 2, ..., n} are screened to obtain a screening set; Stress amplitude generation module: used to paste strain gauges at the weld toe position determined by each welded component in the screening set, obtain stress distribution data at the weld toe position, and analyze and process the stress distribution data to obtain standard samples statistically analyzed in the frequency domain. After preprocessing the standard samples, the stress amplitude spectrum is obtained using the rain flow counting method; Macro damage degree prediction module: used to measure the natural frequency of the selected concentrated welded components and record the corresponding strain data. The relationship between the natural frequency and the elastic modulus is used to analyze the change trend of the natural frequency. The measured natural frequency is compared with the natural frequency in the undamaged state to calculate the predicted value of the macro damage degree. Loop module: It is used to re-execute the loop from the stress amplitude generation module to the macro damage degree prediction module in each adjustment cycle to continuously monitor and evaluate the health status of the welded structure.

2. The bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation according to claim 1 is characterized in that: The load analysis data includes the mechanical response data of the welded components under static load, dynamic load and wind load conditions. The load analysis data is input into the finite element simulation model to simulate the mechanical behavior of the bridge structure under actual working conditions and obtain the load response data of each welded component. Based on the load response data, determine the weld toe location where the stress change is most significant on each welded component; The stress concentration area of ​​the welded component is screened, and the weld toe position with the largest stress amplitude is selected as the marking position.

3. The bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation according to claim 2 is characterized in that: The weld toe morphology evaluation index is used to determine the number of conductive coating strips applied on each weld toe, specifically including: The weld toe morphological characteristic data include the weld width, weld height, weld angle, and weld surface roughness of the weld toe. The weld width, weld height, and weld angle are marked as W, H, and θ respectively; Define the weld width as the distance between the two edges of the weld toe; The weld height is defined as the vertical distance between the highest point on the weld surface and the lowest point on the weld toe; The weld angle is defined as the angle between the weld and the parent material surface; The weld toe shape evaluation index of the i-th welded component is defined as , the calculation formula is as follows: ； in, Determine the weld width, weld height, and weld angle of the weld toe for the i-th welded component respectively; are the standard reference values ​​respectively; is the positive weight coefficient of each characteristic parameter; The higher the value, the more complex the current weld toe morphology is, the stronger the stress concentration effect is, and more conductive coating strips need to be applied; Define the number of conductive coating strips to determine the weld toe of the i-th welding component as , and establish Number of conductive coating strips The mapping relationship, The calculation formula is as follows: ； in, is the linear coefficient of the mapping relationship, and The meaning of rounding up is, .

4. The bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation according to claim 3 is characterized in that: The method of ensuring that the conductive coating strip can deform with the stress change at the interface between the weld toe and the base material specifically includes: Surface treatment of the interface between weld toe and base material: The surface of the interface between weld toe and base material is treated to ensure that the conductive coating strip can be firmly attached and form good insulating contact with the base material; The conductive material is silver paste conductive paint; Conductive coating strip coating; An insulating layer is provided on the outside of the conductive coating strip; The setting of resistance measurement points reserves measurement points for resistance measurement at the beginning and end of the conductive coating strip.

5. The bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation according to claim 4 is characterized in that: The method of establishing a baseline resistance value of the conductive coating strip, measuring the resistance value of the conductive coating strip in an unstressed state, and recording the resistance value as the reference data, and analyzing the relative movement direction of the interface between the weld toe surface and the base material, specifically includes: Under the condition that no external stress is applied, the corresponding weld toe position of the i-th welded component is The resistance of the conductive coating strip is measured and The average of the resistance measurement values ​​is used to obtain the reference resistance value of the conductive coating strip at the weld toe position corresponding to the i-th welding component. ; Under the condition of external stress applied to the bridge, the corresponding weld toe position of the i-th welded component is The resistance of the conductive coating strip is measured and The resistance measurement values ​​are averaged to obtain the measured resistance value of the conductive coating strip on the weld toe in the i-th welding component. and ; And calculate the measured resistance value and the reference resistance value The change in resistance is calculated by the following formula: ； in, and is the resistance change of the conductive coating strip on the weld toe in the i-th welding component, and is the measured resistance value of the conductive coating strip on the weld toe arranged oppositely in the i-th welding component; The collected resistance value data is smoothed by moving average method to eliminate noise and abnormal values; and The positive and negative conditions determine the relative setting of the weld toe movement direction: like Less than 0, then The resistance of the conductive coating strip on the weld toe side decreases, indicating that The weld toe on the side is squeezed; like Less than 0, then The resistance of the conductive coating strip on the weld toe side decreases, indicating that The weld toe on the side is squeezed; like If it is greater than 0, the resistance of the conductive coating strip on the corresponding side of the weld toe increases, indicating that The weld toe on the side is stretched; like If it is greater than 0, the resistance of the conductive coating strip on the corresponding side of the weld toe increases, indicating that The weld toe on the side is stretched.

6. The bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation according to claim 5 is characterized in that: The average measured resistance is compared and analyzed with the corresponding resistance warning threshold to obtain the resistance change degree result, and according to the health status assessment result, all welding components in the number set {1, 2, ..., n} are screened to obtain the screening set, which specifically includes: Define the set of adjustment cycle times m as {1, 2, ..., m}, and j∈{1, 2, ..., m} represents the serial index of the jth monitoring. Calculate the average measured resistance of the conductive coating strip on the i-th welding component in the current adjustment cycle. The calculation formula is as follows: ； in, is the number of welded components on the ith The average measured resistance of the side conductive coating strip during the current adjustment cycle; is the number of welded components on the ith The average measured resistance of the side conductive coating strip during the current adjustment cycle; and in and The maximum value is selected as the average measured resistance of the conductive coating strip at the weld toe position in the i-th welded component; Determine the resistance warning threshold corresponding to the i-th welding component as ; If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is greater than the resistance warning threshold If the magnitude is between 1% and 5%, the resistance change is assessed as slightly abnormal, indicating the risk of early fatigue damage. When the number of screening sets is less than half of the m monitoring times, such components are included in the screening set. If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is greater than the resistance warning threshold When the amplitude is between 5% and 15%, the resistance change degree is assessed as moderately abnormal, indicating a moderate fatigue damage risk. The component is included in the screening set, but the priority is lower than that of severely abnormal components. If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is greater than the resistance warning threshold If the magnitude exceeds 15%, the resistance change is assessed as severely abnormal and the component is directly included in the screening set; Define the filter set as {S1,S2,…,S k }, where S k is the total number of welded components in the screening set, and S r ∈{S1,S2,…,S k } indicates the S r The number index of the selected welding components is used, and the selected welding components are prioritized according to the abnormal degree of resistance change. The components with severe abnormalities are prioritized, the components with moderate abnormalities are ranked second, and the components with slight abnormalities are ranked last; According to the above results of the resistance change degree, the health status of the i-th welding component is as follows: For minor abnormalities, the health status assessment result is an early sign of fatigue damage, and the m monitoring times in the adjustment cycle are adjusted to m+5; For moderate abnormality: the health status assessment result is mid-term fatigue damage, and mid-term maintenance measures are required at this time, and the m monitoring times in the adjustment cycle are adjusted to m+8; For serious abnormalities: If the health status assessment result is a risk of crack propagation, stop using the welded component immediately, conduct a thorough inspection and repair, and adjust the m monitoring times in the adjustment cycle to m+15; If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is equal to the resistance warning threshold When the difference is between 0.1% and 1%, the resistance change level is assessed as approaching warning; If the average measured resistance of the conductive coating strip at the weld toe position in the i-th weld component is equal to the resistance warning threshold If the difference is greater than 1%, the resistance change is assessed as normal, with no significant signs of fatigue damage; According to the above results of the resistance change degree, the health status of the i-th welding component is as follows: For the approaching alert, the health status assessment result is mild fatigue, and the m monitoring times in the adjustment cycle are adjusted to m+3; For normal, the health status assessment result is good health, and the existing monitoring cycle can be maintained without special measures.

7. The bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation according to claim 6 is characterized in that: The stress distribution data is analyzed and processed to obtain the standard samples in the frequency domain. After preprocessing the standard samples, the stress amplitude spectrum is obtained using the rain flow counting method, which includes: Obtain cyclic stress amplitude series of frequency domain data; Sort the stress sequence by size, identify the upper and lower peaks, and record the stress amplitude and number of occurrences of each cycle; Arrange the rainflow counting results and generate stress amplitude spectrum; applying an excitation signal to the welding component; Synchronous record filter set S r The strain data and vibration response signals of each welded component are obtained by pre-calculating the stress amplitude spectrum; Perform Fourier transform on the recorded vibration signal to extract the natural frequency of the welded component and define the Sth filter. r The natural frequency of a welded component is ; The function of strain changing with time is set to , strain data will change over time and be recorded as time series data; After obtaining the natural frequency and strain data, the relationship between the natural frequency and elastic modulus is used to analyze the macroscopic damage of the welded components. and elastic modulus The relationship between is described by the following formula: ； in, For S r The first welded component The natural frequency, For S r constants related to the geometry and boundary conditions of a welded component, is the elastic modulus of the material, is the density of the material; The S r The current natural frequency measured for a welded component is marked as , the natural frequency in the undamaged state is marked as ; The macroscopic damage degree is defined as , the calculation formula is expressed as: ； in, For the damage degree, set The value range is (0,1], The closer it is to 1, the more serious the damage. is a positive constant, used to avoid The case of 0.

8. The bridge structure health monitoring system based on stress amplitude and high cycle fatigue damage accumulation according to claim 7 is characterized in that: The calculation of the predicted value of the macroscopic damage degree specifically includes: Assuming the adjustment cycle time is T, we get , and calculate the total strain accumulation value , obtained by the following integrated strain function: ； According to fatigue damage theory, the strain amplitude at each sampling moment is evaluated and introduced into the damage model. The SN curve model of the material is used to describe fatigue damage. The expression of the SN curve is: ； Where NM is the maximum stress of the material. Fatigue life under; C and is a constant of the material; It is S r The maximum stress of a welded component, With maximum strain is proportional to; The strain amplitude is introduced into the damage model. Based on the rain flow counting method, the cumulative amount of fatigue damage is obtained by cycle counting. The set of strain cycle numbers is defined as {1, 2, ..., h, ..., H}, where h represents the hth cycle and H represents the total number of cycles. The total cumulative damage is obtained by linear accumulation, and the calculation formula is as follows: ； In this formula, is the total accumulated damage, Pl is the fatigue index of the material, is the maximum allowable strain of the material, is the strain amplitude per cycle; The damage obtained by the change of natural frequency The cumulative damage corrected based on strain data Combined, the calibrated damage prediction model is obtained: ； in, It is S r The predicted damage value of a welded component; u1 is the weight coefficient, which represents the relative influence of natural frequency change and strain accumulation damage, and the value range of u1 is (0,1); when The closer it is to 1, the more r The more severe the damage prediction of a welded component is, The closer it is to 0, the more r The less damage is predicted for each welded component; set up The judgment threshold is Q1, 0.38≤Q1≤0.69; and the reference value of Q1 is set to 0.52, the Q1 approach interval is set to [Q1-0.1, Q1+0.1], and adjustments are made based on the health status assessment obtained from the resistance change results; when When it is greater than Q1+0.1, the predicted damage level is severe abnormality; at this time Approaching 1 means that the damage degree of the welded component approaches 100%, that is, close to the critical state, and represents a higher risk of crack extension; The health status assessment result is a risk of crack expansion. The welded component needs to be stopped immediately and thoroughly inspected and repaired. To avoid further damage, the number of monitoring times in the next monitoring cycle is adjusted from m+15 to m+18 to ensure continuous monitoring until the repair is completed. when When the threshold Q1 is approached, the predicted damage level is moderately abnormal, indicating that the welded component has suffered obvious fatigue damage but has not yet reached a critical state; If the health status assessment result is mid-term fatigue damage, mid-term maintenance measures are taken, specifically local reinforcement or more detailed inspections. The number of monitoring times in the next monitoring cycle is adjusted from m+8 to m+11, with a higher frequency of monitoring to ensure timely handling of any potential deterioration; when When it is less than Q1-0.1, the predicted damage level is slightly abnormal; When it approaches 0, it means that the damage degree of the welded component is relatively light, and only shows signs of early fatigue damage; The health status assessment results are early signs of fatigue damage. The existing monitoring plan will be maintained and the number of monitoring times in the next monitoring cycle will be adjusted from m+5 to m+7 to increase the monitoring frequency.

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