A method and system for detecting the final tightening torque of in-service bolts

Abstract

This invention relates to the field of engineering testing technology, and in particular to a method and system for detecting the final tightening torque of in-service bolts. The method includes: acquiring design data related to steel structure bridges and calculating the target final tightening torque of the bolts based on the design data; tightening the bolt sample to the target final tightening torque, recording the final tightening torque value and the scale indicated by the bolt end face pointer as reference data; gradually loosening the bolt according to a preset angle increment, recording the torque value at each increment angle, and establishing an angle torque mathematical model; calculating the actual torque value of the current bolt by using the number of exposed threads of the in-service bolt and the scale indicated by the bolt end face pointer, combined with the angle torque mathematical model; and determining whether the in-service bolt is loose based on the actual torque value and assessing its degree of loosening. This invention effectively solves the problem that the detection of the final tightening torque of in-service bolts relies on manual experience and cannot be quantitatively evaluated, achieving accurate judgment and safety assessment of bolt loosening status.

Description

Technical Field

[0001] This invention relates to the field of engineering testing technology, and in particular to a method and system for detecting the final tightening torque of in-service bolts. Background Technology

[0002] Steel structure bridges are widely used in modern transportation construction due to their advantages such as lightweight, high strength, compressive strength, and tensile strength. The long-term use of bridges requires ensuring that their connections do not loosen or fail during operation. Bolted connections are one of the main connection methods for steel structure bridges, and the torque value of the bolts is crucial to the stability of the bridge structure. Currently, bolt tightening during the construction phase of steel structure bridges typically involves three stages: initial tightening, secondary tightening, and final tightening. The final tightening torque is calculated according to relevant standards, and tightening is performed using the torque method.

[0003] However, as steel bridges age, bolt loosening can threaten their safety. Detection of bolt loosening during operation typically relies on manual observation and experience, which carries high safety risks and uncertainties. Furthermore, it cannot quantify the degree of bolt loosening. Existing detection methods largely depend on visual inspection and manual experience, making it difficult to accurately determine the impact of bolt loosening on bridge structural stability. In complex or hazardous inspection environments, traditional manual inspection methods have significant limitations. Summary of the Invention

[0004] This invention provides a method for detecting the final tightening torque of in-service bolts, which can effectively solve the problems in the background art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for detecting the final tightening torque of in-service bolts, the method comprising:

[0007] Obtain design data related to steel structure bridges, and calculate the target final tightening torque of bolts based on the design data;

[0008] Tighten the bolt sample to the target final tightening torque, and record the final tightening torque value and the scale indicated by the pointer on the bolt end face as reference data;

[0009] Loosen the bolts gradually according to the preset angle increments, record the torque value at each increment angle, and use linear regression analysis to analyze the relationship between angle and torque to establish an angle-torque mathematical model.

[0010] During routine maintenance, the actual torque value of the bolt is calculated by using the number of exposed threads on the bolt and the scale indicated by the pointer on the bolt end face, combined with the angular torque mathematical model.

[0011] Based on the actual torque value, determine whether the in-service bolt is loose, assess the degree of loosening, and obtain the final tightening torque detection result.

[0012] Furthermore, the bolts are gradually loosened in preset angle increments, and the torque value at each increment angle is recorded. A linear regression analysis of the relationship between angle and torque is then used to establish a mathematical model of angle and torque, including:

[0013] Loosen the bolts gradually according to the preset angle increments, and record the corresponding torque value at each angle;

[0014] Linear regression analysis was performed on the recorded angle and the torque value. The relationship between the angle and the torque was fitted using the least squares method. The regression equation was calculated, and the mathematical model of the angle and torque was obtained.

[0015] Furthermore, a mathematical model for angular torque is established, including:

[0016] Slowly rotate the nut with fine-tuning steps until the predetermined incremental angle is reached;

[0017] After maintaining a stationary position at the incremental angle for a set duration, record the torque reading;

[0018] After each recording is completed, the re-tightening operation is started simultaneously to re-tighten the nut to the initial torque state;

[0019] A linear relationship is fitted to the torque readings at multiple incremental angles to generate the mathematical model of the angle torque.

[0020] Furthermore, the slope of the linear relationship fitting is used to characterize the decay rate of the bolt's axial preload. When the slope is lower than the preset critical slope, it is determined that the bolt has yield deformation.

[0021] Further, calculate the actual torque value of the current bolt, including:

[0022] Measure and record the current number of exposed threads and the current pointer scale position of the in-service bolts;

[0023] The angle offset is determined based on the offset of the current pointer scale position relative to the initial pointer scale position;

[0024] Substitute the angular offset into the angular torque mathematical model to output the actual torque value.

[0025] Furthermore, the mathematical model for angular torsion includes an ambient temperature correction term, which compensates for the relationship between angle and torque by introducing a temperature coefficient.

[0026] Furthermore, the scale interval between the pointer on the bolt end face and the scale on the nut end face is 7.5°.

[0027] Furthermore, abnormal data processing is performed before calculating the actual torque value of the in-service bolts, including:

[0028] Statistical analysis was performed on the raw angle-torque measurement data to remove outliers exceeding the preset standard deviation range;

[0029] The remaining data after removing the outliers are smoothed and weighted averaged, and the angle torque mathematical model is updated based on the corrected data.

[0030] A final tightening torque detection system for in-service bolts, the system comprising:

[0031] The target torque calculation module acquires design data related to the steel structure bridge and calculates the target final tightening torque of the bolts based on the design data.

[0032] The reference data acquisition module applies the final tightening torque to the bolt sample to the target final tightening torque, records the final tightening torque value and the scale indicated by the pointer on the bolt end face, as reference data;

[0033] The mathematical model building module gradually loosens the bolts according to preset angle increments, records the torque value at each increment angle, and uses linear regression analysis to analyze the relationship between angle and torque to establish an angle-torque mathematical model.

[0034] The actual torque calculation module calculates the actual torque value of the bolt during regular maintenance by using the number of exposed threads on the bolt and the scale pointed to by the pointer on the bolt end face, combined with the angular torque mathematical model.

[0035] The detection result acquisition module determines whether the in-service bolt is loose based on the actual torque value, assesses the degree of loosening, and obtains the final tightening torque detection result.

[0036] Furthermore, the mathematical model construction module includes:

[0037] The torque value recording unit gradually loosens the bolts according to preset angle increments and records the corresponding torque value at each angle;

[0038] The linear regression analysis unit performs linear regression analysis on the recorded angle and the torque value, uses the least squares method to fit the relationship between the angle and the torque, calculates the regression equation, and obtains the mathematical model of the angle and torque.

[0039] The technical solution of this invention can achieve the following technical effects:

[0040] It effectively solves the problem that the final tightening torque detection of in-service bolts relies on manual experience and cannot be quantitatively evaluated, and realizes accurate judgment and safety assessment of bolt loosening status.

[0041] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a flowchart illustrating the method for detecting the final tightening torque of bolts in service.

[0044] Figure 2 A flowchart illustrating the process of recording torque values ​​at each incremental angle and establishing an angular torque mathematical model;

[0045] Figure 3 A flowchart illustrating the process of establishing a mathematical model for angle torque;

[0046] Figure 4 A flowchart illustrating the process of calculating the actual torque value of the current bolt;

[0047] Figure 5 This is a schematic diagram showing the relationship between the bolt end face pointer and the nut end face;

[0048] Figure 6 This is a flowchart illustrating the process of handling abnormal data. Detailed Implementation

[0049] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0051] Example 1:

[0052] like Figure 1As shown, this application provides a method for detecting the final tightening torque of in-service bolts, the method comprising:

[0053] S1: Obtain design data related to steel structure bridges and calculate the target final tightening torque of bolts based on the design data;

[0054] Specifically, operators calculate the target final tightening torque based on the bolt preload, torque coefficient, and nominal bolt diameter provided in the design documents. During the calculation process, to ensure accuracy, the results need to be corrected based on actual site conditions. For example, when the friction surface has been sandblasted or has a thick coating, the torque coefficient may be slightly higher. Operators can adjust this by referring to existing construction experience or relevant test data to obtain a more realistic target final tightening torque. In actual testing, to improve the comparability of calculation results for different testing locations, bolts of the same type, specification, and friction surface treatment are usually grouped together. Each group uses a uniform torque coefficient to calculate the target final tightening torque. After calculation, operators record the final tightening torque value and use it as a reference value for sample tightening and subsequent angle-torque model establishment.

[0055] S2: Tighten the bolt sample to the target final tightening torque, record the final tightening torque value and the scale indicated by the pointer on the bolt end face as reference data;

[0056] Specifically, in practice, the testing personnel select standard sample bolts that match the bolt specifications, strength grade, and friction surface treatment method in the structure being tested for the final tightening torque calibration test. The bolt samples are installed in a clean and dry environment to ensure that the bolt holes, washers, and friction surfaces are free from obvious contamination or oil stains, in order to reduce the interference of external factors on the tightening results. To ensure measurement accuracy, it is preferable to use a calibrated torque wrench or electric torque loading device for tightening. During the tightening process, the load is applied in stages according to the pre-calculated target final tightening torque value. In the initial stage, a pre-torque of approximately 50% of the target torque is applied to ensure that the contact surfaces of the bolt and nut are fully engaged. In the intermediate stage, the torque is gradually increased to induce elastic deformation of the bolt and form a stable friction force. In the final stage, the bolt is slowly tightened to the target final tightening torque to prevent slippage of the friction surface or a sudden increase in thread stress due to rapid loading. After reaching the target final tightening torque, the inspector immediately reads and records the value displayed on the torque wrench as the final tightening torque value. At the same time, they observe the position of the pointer on the bolt end face relative to the scale on the nut end face and record the scale line number or angle value corresponding to the pointer. To facilitate subsequent comparison, the scale lines on the nut are usually numbered in a clockwise direction, and the position of the pointer is recorded as the initial scale. To prevent errors from manual recording, the inspector can make a mark near the nut scale or use a digital camera to take a picture of the pointer and scale position after tightening is completed for subsequent calibration.

[0057] S3: Loosen the bolts step by step according to the preset angle increment, record the torque value at each increment angle, and use linear regression analysis to analyze the relationship between angle and torque to establish an angle-torque mathematical model;

[0058] Specifically, by controlling the reverse rotation of the bolt and recording the relationship between angle and torque in stages, a mathematical model is established to quantitatively describe the stress variation of the bolt. During the loosening process, the bolt torque and rotation angle exhibit a measurable regular change, reflecting the attenuation characteristics of the bolt's axial preload. By gradually loosening the bolt and recording the torque values ​​at each incremental angle, a series of data points reflecting the bolt's mechanical response can be obtained. Subsequently, linear regression analysis is used to fit these data to obtain a mathematical relationship model between angle and torque. The establishment of this model allows inspectors to calculate the current torque value based solely on the angle changes of the in-service bolt without needing to reload or disassemble the bolt in the future, thus achieving non-destructive testing.

[0059] S4: During regular maintenance, the actual torque value of the bolt is calculated by using the number of exposed threads on the bolt and the scale indicated by the pointer on the bolt end face, combined with the angle torque mathematical model.

[0060] Specifically, in practice, inspectors regularly check key connection nodes according to the bridge maintenance plan. Each bolt at each inspection point is equipped with an end face pointer and a nut scale structure to reflect the relative rotational changes of the bolt during long-term service. Inspectors first confirm the pointer position and the corresponding scale line number of the scale with the naked eye or a magnifying glass, and then record the scale value as the current reading. At the same time, they use vernier calipers or a steel ruler to measure the number of exposed threads of the bolt to assess whether the bolt has axial displacement or loosening tendency.

[0061] S5: Based on the actual torque value, determine whether the bolts in service are loose and assess their degree of loosening to obtain the final tightening torque test result.

[0062] Specifically, based on the calculated actual torque value, the stress state of the bolt can be analyzed to determine whether it has loosened. After completing the torque calculation, the inspector compares the result with the target final tightening torque determined in the design phase. The difference between the two reflects the maintenance status of the bolt preload. If the calculated result is close to the target value, it indicates that the bolt connection is stable. If it is significantly lower, it indicates that the bolt may have loosened or the preload may have decreased, requiring further evaluation or maintenance measures. To improve the reliability of the judgment, a comprehensive analysis can be conducted by combining the inspection time, environmental conditions, installation location, and inspection results of other bolts in the same area to judge the overall tightness consistency and structural safety of the connection node. This method can achieve a quantitative assessment of the bolt loosening state without damaging the connection, improving the accuracy of in-service inspection and engineering practicality.

[0063] This invention effectively solves the problem that the final tightening torque detection of in-service bolts relies on manual experience and cannot be quantitatively evaluated, and realizes accurate judgment and safety assessment of bolt loosening status.

[0064] As a preferred embodiment of the above, such as Figure 2 As shown, in step S3, the bolts are gradually loosened according to preset angle increments, the torque value at each increment angle is recorded, and the relationship between angle and torque is analyzed using linear regression to establish a mathematical model of angle and torque, including:

[0065] S31: Loosen the bolts gradually according to the preset angle increments, and record the corresponding torque value at each angle;

[0066] S32: Perform linear regression analysis on the recorded angle and torque values, use the least squares method to fit the relationship between angle and torque, calculate the regression equation, and obtain the angle and torque mathematical model.

[0067] Specifically, the bolt is first loosened gradually according to a preset angle increment, and the corresponding torque value is recorded at each increment. Before testing, it should be ensured that the bolt sample is securely fixed, the contact surface is clean and dry, and there is no lubricant residue to avoid changes in friction conditions affecting the results. The tester uses a calibrated torque loading device to rotate the nut in the opposite direction at a stable tightening rate. After each predetermined angle increment, the tightening is paused and held for several seconds to allow the stress release to stabilize. The torque value at this time is then read and recorded. To improve measurement accuracy, the measurement can be repeated two to three times at the same angle position and the average value is taken. If there is a significant deviation, the reading is repeated. The loosening test continues until the bolt torque drops to a low proportion of the initial torque or there are obvious signs of free slippage to prevent data distortion caused by entering an unloaded state. Subsequently, linear regression analysis is performed on the collected angle and torque data. The relationship between angle and torque is fitted using the least squares method to obtain the regression equation. During the analysis, the tester should check the data distribution characteristics. If individual outliers are found, residual analysis can be used to determine whether to remove them. If the slope changes significantly in different angle intervals, a piecewise regression method can also be used to establish a multi-interval model. The slope and intercept of the equation can be obtained through regression calculation. After fitting and verification, the final angle-torque mathematical model can be used for back calculation of the torque of in-service bolts, providing a quantitative basis for non-destructive testing during the structural operation phase.

[0068] As a preferred embodiment of the above, such as Figure 3 As shown, a mathematical model for angular torque is established, including:

[0069] A10: Slowly rotate the nut with fine-tuning steps until the predetermined incremental angle is reached;

[0070] A20: After holding the position at the incremental angle for the set duration, record the torque reading;

[0071] A30: After each recording is completed, start the re-tightening operation simultaneously to re-tighten the nut to the initial torque state;

[0072] A40: Perform linear relationship fitting on torque readings at multiple incremental angles to generate an angle torque mathematical model.

[0073] Specifically, the nut is slowly rotated with a fine-tuning step to evenly loosen it within a small angle range until the predetermined incremental angle is reached. The fine-tuning step is preferably set between 2° and 5° to ensure high angular resolution and continuous measurability of torque changes. After rotating to the target angle, the inspector remains stationary at that position for a set duration, typically several seconds to ten seconds, to eliminate reading fluctuations caused by instantaneous elastic-plastic recovery. Once the torque wrench or sensor reading stabilizes, the torque value at that angle is recorded. To reduce the influence of instrument drift or operational inertia, the torque measurement at each angle position can be repeated two to three times and the average value is taken. After recording, the inspector immediately initiates a re-tightening operation, returning the nut to its initial torque state. This re-tightening process helps maintain consistent stress on the sample and prevents permanent deformation or friction caused by the previous loosening. Changes in state affect subsequent test data. The above steps are repeated sequentially until all incremental angle measurements are completed. During this process, the tightening rate should be kept constant and external vibration interference should be avoided. After collecting torque readings at multiple incremental angles, the testing personnel perform fitting analysis on all data. By performing linear regression on the relationship between angle and torque, a regression equation that conforms to the least squares criterion is obtained. If the fitting residuals are evenly distributed and the coefficient of determination is high, it indicates that the model has good linear correlation and can be directly used as an angle-torque mathematical model. If local deviations occur, piecewise linear fitting or curve correction methods can be used to improve the fitting accuracy. The final angle-torque mathematical model is used to describe the torque change law of the bolt during the loosening stage, providing a reliable mathematical basis for calculating the actual torque of the bolt from the angle offset in subsequent in-service testing.

[0074] As a preferred embodiment of the above, the slope of the linear relationship fitting is used to characterize the decay rate of the bolt's axial preload. When the slope is lower than the preset critical slope, it is determined that the bolt has yield deformation.

[0075] Specifically, during the testing process, the angle-torque curve of the bolt in the loosening stage usually shows a linear decreasing trend. The larger the slope, the faster the torque decreases and the more obvious the preload decay. By analyzing the fitted slope of different bolt samples, the deformation characteristics and material state of the bolt during the force release process can be intuitively reflected. In practice, the testers obtain the regression equation based on the linear regression analysis results and calculate its slope value. If the slope remains within the normal range, it indicates that the bolt is still in the elastic working stage and the force release is stable. If the slope decreases significantly, it indicates that the bolt has a large strain in the early stage of loosening, the axial stiffness decreases, and plastic deformation or local yielding may occur. By comparing with the pre-established critical slope, it can be determined whether the bolt exceeds the safe deformation range. The critical slope can be determined based on the bolt material properties, diameter specifications, and test statistical results, representing the boundary before the bolt enters the yielding stage.

[0076] As a preferred embodiment of the above, such as Figure 4 As shown, the calculation of the actual torque value of the current bolt includes:

[0077] B10: Measure and record the current number of exposed threads and the current pointer scale position of the bolts in service;

[0078] B20: Determine the angle offset based on the offset of the current pointer scale position relative to the initial pointer scale position;

[0079] B30: Substitute the angular offset into the angular torque mathematical model to output the actual torque value.

[0080] Specifically, the inspection personnel first conduct on-site measurements of the target bolt. Before measurement, dust, oil, and rust should be removed from the bolt ends to ensure the scale and pointer are clearly visible. Then, using tools such as vernier calipers, steel rulers, or thread gauges, the number of exposed threads is read and recorded in the inspection table. Changes in the number of exposed threads reflect whether the bolt has undergone axial displacement during long-term service. Simultaneously, photographs of the bolt end face are taken and stored for later verification. When reading the scale position, the inspection personnel observe the mark number pointed to by the pointer from a vertical direction on the bolt end face. If the ambient light is insufficient, an auxiliary light source or magnifying glass can be used to ensure accurate readings. Confirmation is then obtained. Subsequently, the inspectors compare the current scale position with the initial scale position when the bolt is finally tightened to determine the angular offset. The magnitude and direction of the offset angle reflect the rotation trend of the bolt during service: clockwise offset indicates loosening, while counterclockwise offset may be caused by temperature changes or stress reversal effects. The angular offset is usually calculated in scale intervals. After obtaining the angular offset, the value is substituted into the previously established angle torque mathematical model for calculation. This model is fitted from loosening test data and describes the near-linear relationship between torque and angle, which can be used to back-calculate the current torque value.

[0081] As a preferred embodiment of the above, the angle torsion mathematical model further includes an ambient temperature correction term, which compensates for the relationship between angle and torque by introducing a temperature coefficient.

[0082] Specifically, the angle-torque mathematical model further incorporates an ambient temperature correction term to compensate for the impact of temperature changes on bolt material properties and friction characteristics. During long-term service, the bolt's elastic modulus, thread friction coefficient, and contact surface friction conditions all change with ambient temperature. Without correction, the calculated torque value may not match the actual preload. In practice, before on-site testing, inspectors obtain the real-time temperature of the bolt and its surrounding environment using temperature sensors or infrared thermometers and compare it with the standard temperature used when establishing the model. Based on the material characteristic curve and friction coefficient temperature sensitivity data, a temperature correction coefficient is determined. This coefficient reflects the proportional deviation of torque change for each increase or decrease in temperature. During correction, the temperature correction coefficient is introduced into the angle-torque relationship expression to adjust the calculated torque value, ensuring it reflects the bolt's true stress state at the current temperature. This method effectively eliminates the influence of ambient temperature changes on the torque back-calculation results, improving the stability and accuracy of bolt torque testing in service.

[0083] As a preferred embodiment of the above, such as Figure 5 As shown, the interval between the pointer on the bolt end face and the scale on the nut end face is 7.5°.

[0084] Specifically, this design was determined after comprehensively considering bolt specifications, angular resolution, processing feasibility, and on-site reading conditions. The 7.5° interval ensures that the resolution of angular changes meets the torque back-calculation accuracy requirements, while avoiding visual recognition difficulties or processing error accumulation caused by overly dense scales. Compared to the 5° subdivision scheme, this spacing achieves a balance between processing cost and on-site readability; compared to 10° or larger scale divisions, it significantly improves the sensitivity and repeatability of angle measurement. Structurally, the scale is evenly distributed on the outer ring of the nut end face, with each division corresponding to a 7.5° rotation angle. The entire ring is divided into 48 scales, and the pointer is fixed at the center of the bolt end face. The nut rotation angle can be indicated by screwing the bolt.

[0085] As a preferred embodiment of the above, such as Figure 6 As shown, abnormal data processing is performed before calculating the actual torque value of in-service bolts, including:

[0086] C10: Perform statistical analysis on the raw angle-torque measurement data and remove outliers that exceed the preset standard deviation range;

[0087] C20: Smooth and weighted average the remaining data after removing outliers, and update the angle torque mathematical model based on the corrected data.

[0088] Specifically, firstly, the collected raw angle-torque measurement data are statistically analyzed. The overall distribution characteristics of the data are determined by calculating the mean and standard deviation. Based on preset thresholds, inspectors identify and remove outlier data points that deviate from the main trend. These outliers typically originate from factors such as reading delays during operation, equipment vibration, sudden frictional changes, or local material inhomogeneity. Failure to remove them will significantly impact the model's fitting accuracy. After removing outliers, the remaining data undergoes consistency verification to confirm that the data distribution conforms to the basic assumption of a linear relationship. Subsequently, the filtered data is smoothed and weighted. Smoothing can employ moving averages or weighted moving averages to reduce the impact of measurement noise and local fluctuations. Weighting coefficients can be set based on the data's temporal order or measurement stability, giving higher weight to data points close to the standard torque range to highlight their representativeness. Based on this, the linear regression equation between angle and torque is recalculated using the corrected data, updating the angle-torque mathematical model. This process effectively reduces the impact of occasional errors on the model fitting results, improves the stability of the slope and intercept parameters, and enhances the model's reliability and repeatability when used for subsequent actual torque back-calculation.

[0089] Example 2:

[0090] Based on the same inventive concept as the in-service bolt final tightening torque detection method in the foregoing embodiments, the present invention also provides an in-service bolt final tightening torque detection system, comprising:

[0091] The target torque calculation module acquires design data related to steel structure bridges and calculates the target final tightening torque of bolts based on the design data.

[0092] The reference data acquisition module applies the final tightening torque to the bolt sample to the target final tightening torque, records the final tightening torque value and the scale indicated by the pointer on the bolt end face, and uses it as reference data.

[0093] The mathematical model building module gradually loosens the bolts according to preset angle increments, records the torque value at each increment angle, and uses linear regression analysis to analyze the relationship between angle and torque to establish an angle-torque mathematical model.

[0094] The actual torque calculation module calculates the actual torque value of the bolt during regular maintenance by using the number of exposed threads on the bolt and the scale pointed to by the pointer on the bolt end face, combined with the angular torque mathematical model.

[0095] The test result acquisition module determines whether the bolts in service are loose based on the actual torque value, assesses the degree of loosening, and obtains the final tightening torque test result.

[0096] The detection system described above in this invention can effectively realize the final tightening torque detection method for in-service bolts, and the technical effects it can achieve are as described in the above embodiments, which will not be repeated here.

[0097] As a preferred embodiment of the above, the mathematical model construction module includes:

[0098] The torque value recording unit gradually loosens the bolts according to preset angle increments and records the corresponding torque value at each angle;

[0099] The linear regression analysis unit performs linear regression analysis on the recorded angle and torque values, uses the least squares method to fit the relationship between angle and torque, calculates the regression equation, and obtains the angle and torque mathematical model.

[0100] Similarly, the above-mentioned optimization schemes for the system can also achieve the optimization effects corresponding to the methods in Embodiment 1, which will not be repeated here.

[0101] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely exemplary illustrations of the application as defined herein, and are to be considered as covering any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Thus, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.

Claims

1. A method for detecting the final tightening torque of in-service bolts, characterized in that, The method includes: Obtain design data related to steel structure bridges, and calculate the target final tightening torque of bolts based on the design data; Tighten the bolt sample to the target final tightening torque, and record the final tightening torque value and the scale indicated by the pointer on the bolt end face as reference data; Loosen the bolts gradually in preset angle increments, record the torque value at each increment angle, and use linear regression analysis to analyze the relationship between angle and torque to establish an angle-torque mathematical model. The establishment of the angle-torque mathematical model includes: Slowly rotate the nut with fine-tuning steps until the predetermined incremental angle is reached; After maintaining a stationary position at the incremental angle for a set duration, record the torque reading; After each recording is completed, the re-tightening operation is started simultaneously to re-tighten the nut to the initial torque state; Linear relationship fitting is performed on torque readings at multiple incremental angles to generate the angle torque mathematical model. The slope of the linear relationship fitting is used to characterize the decay rate of the bolt axial preload. When the slope is lower than the preset critical slope, it is determined that the bolt has yield deformation. During routine maintenance, the actual torque value of the bolt is calculated by using the number of exposed threads on the bolt and the scale indicated by the pointer on the bolt end face, combined with the angular torque mathematical model. The calculation of the actual torque value of the bolt includes: Measure and record the current number of exposed threads and the current pointer scale position of the in-service bolts; The angle offset is determined based on the offset of the current pointer scale position relative to the initial pointer scale position; Substitute the angular offset into the angular torque mathematical model to output the actual torque value; Based on the actual torque value, determine whether the in-service bolt is loose, assess the degree of loosening, and obtain the final tightening torque detection result.

2. The method for detecting the final tightening torque of in-service bolts according to claim 1, characterized in that, Loosen the bolts gradually in preset angle increments, record the torque value at each increment angle, and use linear regression analysis to analyze the relationship between angle and torque to establish an angle-torque mathematical model, including: Loosen the bolts gradually according to the preset angle increments, and record the corresponding torque value at each angle; Linear regression analysis was performed on the recorded angle and the torque value. The relationship between the angle and the torque was fitted using the least squares method. The regression equation was calculated, and the mathematical model of the angle and torque was obtained.

3. The method for detecting the final tightening torque of in-service bolts according to claim 1, characterized in that, The mathematical model for angular torsion further includes an ambient temperature correction term, which compensates for the relationship between angle and torque by introducing a temperature coefficient.

4. The method for detecting the final tightening torque of in-service bolts according to claim 1, characterized in that, The interval between the pointer on the bolt end face and the scale on the nut end face is 7.5°.

5. The method for detecting the final tightening torque of in-service bolts according to claim 1, characterized in that, Anomaly processing is performed before calculating the actual torque value of the in-service bolts, including: Statistical analysis was performed on the raw angle-torque measurement data to remove outliers exceeding the preset standard deviation range; The remaining data after removing the outliers are smoothed and weighted averaged, and the angle torque mathematical model is updated based on the corrected data.

6. A final tightening torque detection system for in-service bolts, employing the final tightening torque detection method for in-service bolts as described in any one of claims 1-5, characterized in that, The system includes: The target torque calculation module acquires design data related to the steel structure bridge and calculates the target final tightening torque of the bolts based on the design data. The reference data acquisition module applies the final tightening torque to the bolt sample to the target final tightening torque, records the final tightening torque value and the scale indicated by the pointer on the bolt end face, as reference data; The mathematical model building module gradually loosens the bolts according to preset angle increments, records the torque value at each increment angle, and uses linear regression analysis to analyze the relationship between angle and torque to establish an angle-torque mathematical model. The actual torque calculation module calculates the actual torque value of the bolt during periodic maintenance by using the number of exposed threads on the bolt and the scale pointed to by the pointer on the bolt end face, combined with the angular torque mathematical model. The detection result acquisition module determines whether the in-service bolt is loose based on the actual torque value, assesses the degree of loosening, and obtains the final tightening torque detection result.

7. The in-service bolt final tightening torque detection system according to claim 6, characterized in that, The mathematical model construction module includes: The torque value recording unit gradually loosens the bolts according to preset angle increments and records the corresponding torque value at each angle; The linear regression analysis unit performs linear regression analysis on the recorded angle and the torque value, uses the least squares method to fit the relationship between the angle and the torque, calculates the regression equation, and obtains the mathematical model of the angle and torque.

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