A concrete structure surface prestress on-line detection device and method based on H-type orthogonal strain intelligent compensation

Abstract

The application discloses a kind of based on H type orthogonal strain intelligent compensation concrete structure surface prestress on-line detection device, comprising: strain sensing unit and strain acquisition instrument;Strain sensing unit includes transverse strain gauge and longitudinal strain gauge, longitudinal strain gauge is arranged along principal stress direction, transverse strain gauge is symmetrically separated and is arranged perpendicular to principal stress direction;Transverse strain gauge and longitudinal strain gauge constitute H type orthogonal strain gauge full-bridge measurement circuit;H type orthogonal strain gauge full-bridge measurement circuit is attached to the surface of concrete structure;Strain acquisition instrument is connected with H type orthogonal strain gauge full-bridge measurement circuit electric signal.The present application is based on H type orthogonal strain gauge structure, and Poisson's ratio is combined to establish thermal-mechanical coupling mathematical model, and temperature strain is separated;While device structure parameter is associated with stress release calibration coefficient alpha, the system error of stress release measurement is corrected, and target direction stress is obtained, which improves the accuracy and reliability of stress release measurement.

Description

Technical Field

[0001] This invention relates to the fields of civil engineering structural inspection and digital operation and maintenance and intelligent sensing technology for infrastructure, specifically to an online detection device and method for prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation. Background Technology

[0002] Prestressed concrete structures are widely used in bridges, high-rise buildings, and long-span structures due to their excellent crack resistance and load-bearing capacity. Real-time and accurate detection of effective prestress is a core technical aspect for assessing structural construction quality, monitoring service performance, and determining safety reserves and remaining life, directly determining the long-term service safety of the structure. If prestress significantly decreases during service due to factors such as relaxation, creep, or damage, the structure may fail to meet design load requirements, and may even experience cracking, excessive deflection, and ultimately failure. Therefore, the prestress level during service is a core control indicator affecting the safety performance of prestressed concrete structures. Existing methods for detecting prestress in service structures mainly rely on anchor-end tension measurement of external prestressing tendons and surface stress transfer methods of internal prestressing tendons. These methods are highly dependent on long-term manual monitoring and experience-based judgment, lacking dynamic adaptive capabilities and failing to meet the needs of large-scale, high-efficiency digital infrastructure monitoring.

[0003] Patent CN106840482A discloses a testing device and method for testing the tension stress and anchorage stress of prestressed tendons. This method collects strain through circumferential strain gauges fitted onto the prestressed tendons and calculates stress using multi-directional correction, enabling stress detection throughout the entire process from tensioning to anchorage of external prestressed tendons. However, this method is only applicable to the testing of exposed portions of external prestressed tendons. Given that internal prestressed tendons remain the primary medium for applying prestress to the structure, the anchorage tension measurement method for external prestressed tendons cannot meet the indirect testing requirements of embedded prestressed tendons in prestressed concrete structures.

[0004] Patent CN104729870A discloses a method for detecting existing prestress in concrete bridge structures. This method employs a slotted stress release method, which releases constraint stress by mechanically cutting parallel slits in the concrete. Strain gauges are used to measure strain changes before and after the cutting, and the existing prestress value at the measuring point is calculated by combining the concrete's elastic modulus and empirical coefficients for stress release efficiency. However, this method lacks an active quantitative compensation mechanism and is susceptible to the instantaneous high temperature caused by the cutting heat effect, interfering with the accurate strain measurement.

[0005] In summary, although existing methods for detecting stress transfer on concrete surfaces can achieve indirect detection, they still suffer from three major error sources: cutting heat effect, Poisson effect in non-uniform stress fields, and diurnal temperature fluctuations. These factors easily lead to large deviations in measurement results and cannot meet the high-precision detection requirements of engineering projects. Therefore, there is an urgent need for an online detection device and method for prestressed concrete surface that can be applied to environments with high temperature, direct sunlight, and significant cutting heat interference, while minimizing external interference and achieving high measurement accuracy. Summary of the Invention

[0006] To address the aforementioned technical problems and improve upon the shortcomings of existing applications, this invention is implemented through the following solution: In a first aspect, this application provides an online detection device for prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation, characterized in that the device includes: a strain sensing unit and a strain acquisition instrument; The strain sensing unit includes transverse strain gauges and longitudinal strain gauges; the longitudinal strain gauges are arranged along the principal stress direction, and the transverse strain gauges are symmetrically separated perpendicular to the principal stress direction; the transverse strain gauges and the longitudinal strain gauges form an H-shaped orthogonal strain gauge full-bridge measurement circuit; the H-shaped orthogonal strain gauge full-bridge measurement circuit is attached to the surface of the concrete structure; the spacing S between the transverse strain gauges is equal to the spacing L of the stress relief cut formed during cutting. c Satisfying 0 < S / L c The dimensionless ratio relationship is <1; the strain acquisition instrument is electrically connected to the H-type orthogonal strain gauge full-bridge measurement circuit, and is used to acquire the real strain before and after stress transfer under the same conditions in the H-type orthogonal strain gauge full-bridge measurement circuit.

[0007] Furthermore, by adopting the above-mentioned design of longitudinal and transverse strain gauges, the problem of strain component attenuation and increased measurement error caused by the strain gauge bonding direction not coinciding with the principal stress direction can be avoided.

[0008] Furthermore, the strain acquisition instrument is equipped with a data processing module.

[0009] Furthermore, the data processing module has a built-in sampling unit, an intelligent dynamic monitoring unit, and an intelligent strain extraction algorithm unit.

[0010] Furthermore, the sampling unit is used to sample the strain values ​​of the full-bridge measurement circuit of the H-type orthogonal strain gauge on the surface of the concrete structure.

[0011] Furthermore, the strain acquisition instrument is a dynamic strain acquisition instrument. Since the structural stress is released slowly during the prestressing grooving process, the strain exhibits quasi-static changes. Static strain acquisition instruments have the characteristics of high measurement accuracy, good stability, and strong anti-interference ability.

[0012] Furthermore, the sampling frequency of the strain acquisition instrument is not less than 100Hz, so as to fully record the sudden change in thermal strain at the moment of cutting and the minute fluctuations in the subsequent time sequence.

[0013] Furthermore, the overall measurement error of the strain acquisition instrument must be controlled within ±1με to meet the stringent requirement of high-precision prestress back calculation.

[0014] Furthermore, the intelligent dynamic monitoring unit is used to calculate the dispersion of the sampling in real time and make a convergence judgment; the intelligent strain extraction unit is used to automatically perform decoupled calculation of temperature strain and mechanical strain, and output stable measurement values ​​that have passed intelligent identification.

[0015] Furthermore, the data processing module is also equipped with an interface for bidirectional data synchronization with an external cloud platform, which is used to complete the uploading of local data to the cloud platform and the interaction of cloud platform control commands and configuration data.

[0016] Furthermore, the device also includes a power supply module, which is electrically connected to both the strain sensing unit and the strain acquisition instrument.

[0017] Furthermore, the transverse strain gauge and the longitudinal strain gauge are resistance strain gauges.

[0018] Preferably, there are two transverse strain gauges and two longitudinal strain gauges.

[0019] Furthermore, the resistive strain gauge is a metal foil strain gauge with a resistance of 120Ω or 350Ω and an accuracy range of ≤1με.

[0020] Furthermore, after the transverse strain gauge and longitudinal strain gauge are sanded on the concrete surface, they are glued together with adhesive and connected by wires, and then attached to the measurement points on the concrete structure surface.

[0021] Furthermore, the device also includes auxiliary measuring tools, such as calipers and rangefinders.

[0022] Furthermore, the device also includes auxiliary grooving tools, such as concrete cutters and angle grinders.

[0023] Secondly, this application provides an online detection method for prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation, the method comprising the following steps: S1. Select appropriate measurement points based on the actual working conditions of the prestressed concrete structure surface; and determine a fixed measurement time as the reference time for all subsequent measurement readings based on the environmental conditions of the test site. S2. Attach the H-type orthogonal strain gauge full-bridge measurement circuit to the measurement point on the surface of the concrete structure; zero the strain acquisition instrument according to the measurement time selected in step S1, and collect the orthogonal bidirectional strain value at the measurement point as the initial strain value; S3. 24 hours after step S2 is completed, high-frequency automatic sampling is performed by the built-in sampling unit of the strain acquisition instrument. The intelligent dynamic monitoring unit calculates the dispersion of the sampled data in real time and obtains multiple sliding windows. When the strain fluctuation values ​​within multiple consecutive sliding windows converge to the preset error threshold range, the intelligent dynamic monitoring unit automatically locks and outputs the current average strain value as the calibration strain value and triggers subsequent stress transfer commands. S4. Upon receiving the stress transfer operation command, a cutting device is used to cut both sides of the measurement point on the concrete structure surface, forming two parallel stress relief cuts; the stress relief cuts are symmetrically located on the outside of the H-shaped orthogonal strain gauge full-bridge measurement circuit; the spacing L between the stress relief cuts is... c The spacing S of the transverse strain gauges set in the H-type orthogonal strain gauge full-bridge measurement circuit satisfies 0 < S / L c Dimensionless ratios less than 1; S5. After the cutting is completed, restore the temperature of the measurement point to the temperature before the cutting operation; and at the reference time point selected in step S1, collect the orthogonal bidirectional strain value of the measurement point after cooling using a strain acquisition instrument. S6. The collected orthogonal bidirectional strain values ​​are processed by the intelligent strain extraction algorithm unit. Based on the Poisson's ratio relationship, a thermo-mechanical coupling mathematical model is established to separate the temperature strain and output the stable real mechanical strain value that has been intelligently identified. S7. The obtained real mechanical strain is synchronized to an external cloud platform and corrected by stress calibration coefficient; the corrected real mechanical strain is used to calculate the stress in the target direction based on Hooke's law and the elastic modulus of the measured material.

[0024] Furthermore, in step S3, the error refers to the difference between the measured strain value and the initial strain value.

[0025] Preferably, the error threshold is set between 3με and 10με.

[0026] Furthermore, the sliding window refers to a continuous sampling data segment set on the time axis by the built-in sampling unit of the strain acquisition instrument, which moves continuously with a fixed step size; wherein, each window contains a preset number of strain sampling points, and the window slides backward to update according to a fixed step size, forming multiple sampling data subsets that are continuous in time and partially overlap, which are used to calculate the dispersion and fluctuation values ​​of the strain data in segments.

[0027] Preferably, in step S3, if the strain difference exceeds the allowable error threshold, the rationality of the selection of the measurement point or the working status of the measuring device needs to be checked; after adjustment, the test benchmark is re-established, and after standing for 24 hours, the strain values ​​of the orthogonal bidirectional measurement point are collected and recorded again until the readings are stable.

[0028] Furthermore, in step S5, the cooling design for the measurement point can effectively eliminate the interference of local high-temperature thermal strain caused by cutting friction.

[0029] Preferably, localized cooling can be achieved by using cold air or fans for localized point cooling, and by using insulation cotton and foam boards to create a barrier, so that the cold air is concentrated near the measurement point and prevents external airflow turbulence from causing temperature fluctuations.

[0030] Further, in step S6, the intelligent strain extraction algorithm unit is configured as follows: (1) Based on the assumption that the temperature effect during the cutting process is isotropic, the temperature strain in the measurement direction x and the compensation direction y satisfies the following formula: Where, ε temp ε represents the strain caused by temperature during the cutting process. temp,x ε represents the strain in the x-direction caused by temperature during the cutting process. temp,y This represents the strain in the y-direction caused by temperature during the cutting process. (2) Based on the Poisson effect of mechanical strain generated by stress release in the region between mutually parallel stress release cuts, the mechanical strain satisfies the following formula: Where ν is the Poisson's ratio of the area to be measured; ε mech,x ε represents the strain in the x-direction caused by mechanical cutting. mech,y The strain in the y-direction is caused by mechanical cutting.

[0031] (3) Based on the orthogonal bidirectional strain value after cooling, which is the superposition of mechanical strain and temperature strain, the following formula is satisfied: Where, ε x The total strain is measured using strain gauges in the stress measurement direction; ε y The total strain is measured using strain gauges in the stress compensation direction; (4) By substituting the Poisson effect formula into the strain superposition formula, the mechanical strain term is eliminated, and the temperature strain is obtained separately, expressed by the following formula: (5) Substituting the temperature strain formula into the total strain superposition formula in the x-direction, the true mechanical strain after eliminating temperature interference in the x-direction is obtained, expressed by the following formula: Furthermore, due to the measured strain ε mexh,x The strain changes continuously over time due to stress redistribution and ambient temperature disturbances. Therefore, the strain acquisition instrument uses a built-in sampling unit to perform high-frequency automatic sampling. The intelligent dynamic monitoring unit calculates the dispersion of the sampled data in real time and continuously acquires the strain fluctuation values ​​within multiple sliding windows. When the strain fluctuation values ​​within multiple sliding windows converge to a preset error threshold range, the intelligent dynamic monitoring unit automatically locks and outputs the current average strain value as the true mechanical strain value after eliminating temperature interference, and triggers subsequent stress transfer commands.

[0032] Furthermore, the error threshold is set to 10με.

[0033] Furthermore, the threshold is set based on the following: when the continuous fluctuation range of the detection data is less than the system background noise of the strain acquisition instrument (i.e., ≤10με), the stress change on the concrete surface can be considered to have stabilized and reached a quasi-static equilibrium state. The automatic locking logic adopts the mean determination method based on a sliding time window.

[0034] Furthermore, the intelligent dynamic monitoring unit continuously samples at a frequency of once per second or higher, and takes the sampling data of the most recent 30 seconds as a sliding window; the intelligent dynamic monitoring unit continuously calculates the standard deviation of the data within the window. If the standard deviation remains within the preset threshold for three consecutive cycles, it automatically determines that the reading has stabilized, and calculates the arithmetic mean of the data within the window as the true mechanical strain value after eliminating temperature interference.

[0035] Furthermore, the Poisson's ratio of the cut region of the object under test ranges from 0.2 to 0.25.

[0036] Preferably, the actual Poisson's ratio should be calibrated by measuring the mix proportion data of standard concrete test blocks from the same batch before testing.

[0037] Furthermore, in step S7, the target direction stress satisfies the following formula: Where α is the stress relief calibration coefficient; E c σ represents the elastic modulus of the area to be measured; t The target stress is defined in the area where the measurement point is cut.

[0038] Furthermore, the stress relief calibration coefficient α is related to the transverse strain gauge spacing S and the stress relief slit spacing L.c dimensionless ratio S / L c The correlation is negative; the above actual ratio relationship enables precise dynamic correction of system errors, making the corrected measurement results more consistent with the real prestress state of the concrete structure, and improving the accuracy and stability of the prestress measurement results.

[0039] Furthermore, the stress relief calibration coefficient α has a value range of 0.8 ≤ α ≤ 1.0.

[0040] Preferably, the stress relief calibration coefficient α has a value range of 0.85≤α≤0.89.

[0041] More preferably, the stress relief calibration coefficient α is 0.89.

[0042] Preferably, the above detection method can achieve active identification of temperature strain by combining the collected orthogonal strain gauge readings with Poisson's ratio without using a temperature sensor.

[0043] This invention relates to an online detection device and method for prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation. It utilizes a full-bridge measurement circuit composed of H-type orthogonal strain gauges (both transverse and longitudinal) attached to measurement points. Within a selected reference time and under the same temperature environment, the strain acquisition instrument collects orthogonal bidirectional strain values ​​before and after stress transfer. An intelligent strain extraction algorithm unit automatically performs decoupling calculations of temperature strain and mechanical strain based on Poisson's ratio, establishing a thermo-mechanical coupling mathematical model and outputting the intelligently identified true mechanical strain components. Furthermore, a stress calibration coefficient corrects the systematic error in stress release measurement. Based on Hooke's law and the elastic modulus of the measured material, the stress in the target direction is calculated.

[0044] Compared with the prior art, the beneficial effects of the present invention include: 1. This invention provides an online detection device and method for prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation. It solves the problem that traditional prestress detection methods cannot simultaneously eliminate measurement errors caused by temperature changes, cutting heat effects, and the Poisson effect of non-uniform stress fields, further improving the accuracy and reliability of stress release measurement. Simultaneously, it is suitable for high-precision and high-robust detection of prestress values ​​in concrete structures under various scenarios.

[0045] 2. This invention provides an online detection device for prestress on the surface of concrete structures based on H-shaped orthogonal strain intelligent compensation. By arranging transverse and longitudinal strain gauges in an H-shape orthogonal separation, it effectively avoids the stress concentration distortion zone at the end of the stress release cut, overcomes the problem that existing measurement structures cannot collect transverse deformation in certain areas, strengthens the offsetting effect of Poisson's ratio relationship, and accurately restores the true strain at the measurement point.

[0046] 3. This invention provides an online detection device for prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation. Based on Saint-Venant's principle, the device designs the transverse strain gauge spacing S and the stress release slit spacing L. c Satisfying 0 < S / L c The reasonable range of <1 avoids the problem of exponential attenuation of released strain due to the distance of the stress sensing unit from the stress release source. This ensures that the strain acquisition is always in a smooth and representative region of the stress field, guaranteeing the stability and reliability of the measurement data and solving the problems of large deviation and poor repeatability of traditional methods.

[0047] 4. This invention provides a method for online detection of prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation. This method actively separates temperature and strain, and correlates the device's structural parameters with a stress release calibration coefficient α. The stress release calibration coefficient α is then compared with the S / L ratio. c The negative correlation pattern design improves the accuracy of systematic error correction in stress release measurement, making the entire testing process simpler and more convenient to operate.

[0048] 5. This invention provides a method for online detection of prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation. By fixing the reference measurement time and static calibration, and combining the mean value judgment method of the sliding time window, the method effectively eliminates the periodic fluctuation error caused by the diurnal temperature difference in the prior art, ensuring the stability and accuracy of long-term measurement and improving the reliability of the detection data.

[0049] 6. This invention provides a method for online detection of prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation. It can highly meet the development needs of intelligent operation and maintenance and online monitoring of major infrastructure. Through the built-in data processing mechanism, it realizes intelligent convergence judgment of multi-frequency sampling, breaking through the limitation of traditional methods that require long-term manual fixed-point monitoring. Furthermore, by automatically stripping the coupling interference of temperature and mechanical strain online, it provides high-precision underlying data support for the digital assessment of the service status of structures and the full life cycle health monitoring. Attached Figure Description

[0050] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a schematic diagram of the actual stress release zone slot arrangement in the full-bridge measurement circuit of the H-type orthogonal strain gauge; (the arrows indicate the directions along the stress compensation direction y and the stress measurement direction x, respectively). Figure 2 A schematic diagram of the H-type orthogonal strain gauge full-bridge measurement circuit layout; Figure 3A schematic diagram of the stress distribution in the stress relief cut; (a) mesh generation of the cutting area; (b) stress field distribution in the cutting area after stress relief. Figure 4 A schematic diagram of the 24-hour variation curve of strain; The attached figures are labeled as follows: 1-H-type orthogonal strain gauge full-bridge measurement circuit, 101-longitudinal strain gauge, 102-transverse strain gauge, 2-strain acquisition instrument, 3-stress relief cut, 4-concrete structure surface, and measurement points include measurement point A, measurement point B, measurement point C and measurement point D. Detailed Implementation

[0051] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0053] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0054] This invention provides an online detection device for prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation, comprising: a strain sensing unit and a strain acquisition instrument 2; (e.g.) Figure 1 (As shown) The strain sensing unit includes two transverse strain gauges 102 and two longitudinal strain gauges 101. The longitudinal strain gauges 101 are arranged along the principal stress direction, while the transverse strain gauges 102 are symmetrically separated perpendicular to the principal stress direction. The transverse strain gauges 102 and the longitudinal strain gauges 101 form an H-type orthogonal strain gauge full-bridge measurement circuit 1. The H-type orthogonal strain gauge full-bridge measurement circuit 1 is attached to the surface 4 of the concrete structure. The spacing S between the transverse strain gauges 102 is equal to the spacing L of the stress-relieving cut 3 formed during cutting. c Satisfying 0 < S / L c The dimensionless ratio relationship is <1; the strain acquisition instrument 2 is electrically connected to the H-type orthogonal strain gauge full-bridge measurement circuit 1 to acquire the real strain before and after stress transfer under the same conditions in the H-type orthogonal strain gauge full-bridge measurement circuit.

[0055] The strain acquisition instrument 2 is equipped with a data processing module (not shown in the figure); the data processing module has a built-in sampling unit, an intelligent dynamic monitoring unit, and an intelligent strain extraction algorithm unit; the sampling unit is used to sample the strain values ​​of the full-bridge measurement circuit of the H-type orthogonal strain gauge on the surface of the concrete structure; the intelligent dynamic monitoring unit is used to calculate the dispersion of the sampling in real time and perform convergence judgment; the intelligent strain extraction unit is used to automatically perform decoupled calculation of temperature strain and mechanical strain; the data processing module is also equipped with an interface for bidirectional data synchronous transmission with an external cloud platform; The device also includes a power supply module, which is electrically connected to both the strain sensing unit and the strain acquisition instrument.

[0056] The slotting method refers to a non-destructive testing method in which shallow slots are mechanically cut into the surface of a prestressed concrete structure under non-uniform stress field, thereby partially cutting off the stress transmission path inside the concrete. This releases the original prestress in the vicinity of the cut and causes strain redistribution. The effective stress of the prestress inside the structure is then calculated by measuring the strain change of the structural surface before and after slotting.

[0057] Time sequence refers to selecting a fixed time each day as a unified measurement reference time. All subsequent tests are completed at this fixed time point, and the measurement results at this time serve as a unified time sequence reference for subsequent comparative analysis, trend judgment, and prestress change calculation. This eliminates the interference of external factors that change over time, such as diurnal temperature variations, solar radiation, and fluctuations in ambient temperature and humidity, on the measurement results, ensuring that monitoring data from each batch are acquired under similar environmental conditions. The reference time can be set to any time point each day, such as 3:00, 5:00, 7:00, 8:00, 9:00, 12:00, 14:00, 18:00, 20:00, and 22:00.

[0058] To address the systematic errors caused by temperature effects, Poisson's effect, and non-uniform stress fields in existing concrete structure stress measurements, this invention proposes a corresponding online prestress detection method for concrete structure surfaces, based on the aforementioned online prestress detection device. This method uses stress calibration coefficients to correct errors in the thermo-mechanical coupling mathematical model, thereby improving the accuracy and reliability of the measurement. The specific detection steps are as follows: (e.g.) Figure 2-3 (As shown) S1. Select appropriate measurement points based on the actual working conditions of the prestressed concrete structure surface 4; the measurement points include measurement point A, measurement point B, measurement point C and measurement point D; determine a fixed measurement time as the reference time for all subsequent measurement readings based on the environmental conditions of the test site (e.g., 9:00 AM every day). S2. Attach the H-type orthogonal strain gauge full-bridge measurement circuit 1 to the measurement point on the surface 4 of the concrete structure; ensure that the arrangement of the transverse strain gauges and the longitudinal strain gauges meets the requirements: the longitudinal strain gauges are arranged along the principal stress direction, and the transverse strain gauges are symmetrically separated perpendicular to the principal stress direction; zero the strain acquisition instrument 2 according to the reference time selected in step S1 (9 o'clock every day), and collect the orthogonal bidirectional strain values ​​at the measurement point as the initial strain values. S3. 24 hours after step S2 is completed, high-frequency automatic sampling is performed by the built-in sampling unit of the strain acquisition instrument. The intelligent dynamic monitoring unit calculates the dispersion of the sampled data in real time and obtains multiple sliding windows. When the strain fluctuation values ​​within multiple consecutive sliding windows converge to the preset error threshold range, the intelligent dynamic monitoring unit automatically locks and outputs the current average strain value as the calibration strain value and triggers subsequent stress transfer commands. Preferably, if the strain difference exceeds the allowable error threshold, the rationality of the selection of the measurement point or the working status of the measurement device should be checked, and the test benchmark should be re-established after adjustment. After standing still for 24 hours again, the strain values ​​of the orthogonal bidirectional measurement point should be collected and recorded until the readings are stable. S4. Upon receiving the stress transfer operation command, a cutting device is used to cut both sides of the measurement point on the concrete structure surface, forming two parallel stress relief cuts; the stress relief cuts are symmetrically located on the outside of the H-type orthogonal strain gauge full-bridge measurement circuit; the spacing L of the stress relief cuts... c The spacing S of the transverse strain gauges set in the H-type orthogonal strain gauge full-bridge measurement circuit satisfies 0 < S / L c Dimensionless ratios less than 1; S5. After the cutting is completed, restore the temperature of the measurement point to the temperature before the cutting operation; and at the reference time selected in step S1 (9:00 a.m. every day), collect the orthogonal bidirectional strain value of the measurement point after cooling using a strain acquisition instrument; at this time, the collected strain value is the superposition of mechanical strain and temperature strain. S6. The acquired orthogonal bidirectional strain values ​​are processed by the intelligent strain extraction algorithm unit. Based on the Poisson's ratio, a thermo-mechanical coupling mathematical model is established to separate temperature strain and output stable, true mechanical strain values ​​identified by intelligent analysis. The intelligent strain extraction algorithm unit is configured as follows: (1) Based on the assumption that the temperature effect during the cutting process is isotropic, the temperature strain in the measurement direction x and the compensation direction y satisfies the following formula: Where, ε temp ε represents the strain caused by temperature during the cutting process. temp,x ε represents the strain in the x-direction caused by temperature during the cutting process. temp,y This represents the strain in the y-direction caused by temperature during the cutting process. (2) The Poisson effect of mechanical strain generated by stress release in the parallel stress release slit region, the mechanical strain satisfies the following formula: ν represents the Poisson's ratio of the area to be measured, ranging from 0.2 to 0.25; ε mech,x ε represents the strain in the x-direction caused by mechanical cutting. mech,y The strain in the y-direction caused by mechanical cutting; (3) Based on the orthogonal bidirectional strain value after cooling, which is the superposition of mechanical strain and temperature strain, the following formula is satisfied: Where, ε x The total strain is measured using strain gauges in the stress measurement direction; ε y The total strain is measured using strain gauges in the stress compensation direction; (4) Substituting the Poisson effect formula into the strain superposition formula, eliminating the mechanical strain term, and separating the temperature strain, the following formula is used to express it: (5) Substituting the temperature strain formula into the total strain superposition formula in the x-direction, the true mechanical strain after eliminating temperature interference in the x-direction is obtained, expressed by the following formula: Due to the measured strain ε mexh,xThe strain changes continuously over time due to stress redistribution and ambient temperature disturbances. Therefore, the strain acquisition instrument uses a built-in sampling unit to perform high-frequency automatic sampling. The intelligent dynamic monitoring unit calculates the dispersion of the sampled data in real time and continuously acquires the strain fluctuation values ​​within multiple sliding windows. When the strain fluctuation values ​​within multiple sliding windows converge to a preset error threshold range, the intelligent dynamic monitoring unit automatically locks and outputs the current average strain value as the true mechanical strain value after eliminating temperature interference, and triggers subsequent stress transfer commands.

[0059] The error threshold is set to 10με.

[0060] The threshold is set based on the mean judgment method of sliding time window: when the continuous fluctuation range of the detection data is less than the system background noise of the strain acquisition instrument (i.e. ≤10με), the stress change on the concrete surface can be considered to have stabilized and reached a quasi-static equilibrium state.

[0061] The intelligent dynamic monitoring unit continuously samples at a frequency of once per second or higher, and takes the sampling data of the most recent 30 seconds as a sliding window. The intelligent dynamic monitoring unit continuously calculates the standard deviation of the data within the window. If the standard deviation remains within the preset threshold for three consecutive cycles, it automatically determines that the reading has stabilized and calculates the arithmetic mean of the data within the window as the true mechanical strain value after eliminating temperature interference.

[0062] S7. The obtained real mechanical strain is synchronized to an external cloud platform and corrected using a stress calibration coefficient. The corrected real mechanical strain is then used to calculate the stress in the target direction based on Hooke's law and the elastic modulus of the measured material. The stress calibration coefficient α is related to the transverse strain gauge spacing S and the stress relief slit spacing L. c dimensionless ratio S / L c The stress in the target direction is negatively correlated; the stress in the target direction is expressed by the following formula: Where α is the stress relief calibration coefficient, with a value range of 0.8 ≤ α ≤ 1.0; E c σ represents the elastic modulus of the area to be measured; t The target stress is defined in the area where the measurement point is cut.

[0063] To better understand the technical solution of the present invention, the following specific implementations are used to verify the effectiveness and necessity of the H-type orthogonal strain gauge arrangement and online design.

[0064] Example 1: Verification of Surface Prestressing in Concrete Structures Based on H-Type Orthogonal Strain Intelligent Compensation According to Saint-Venant's Principle in structural mechanics, the stress release field caused by the kerf is highly localized. As the H-spacing of the orthogonal strain gauges increases infinitely, the strain gauges become increasingly farther from the stress release source, and the released strain decays exponentially, eventually approaching zero. However, the H-spacing of the orthogonal strain gauges does not increase infinitely; the resulting error exhibits a U-shaped curve of "first decreasing and then rapidly increasing." If the H-spacing of the orthogonal strain gauges increases infinitely, it will inevitably lead to measurement failure, but the resulting error will not decrease infinitely as the measurement approaches failure.

[0065] This embodiment is based on the finite element simulation of stress release of solid elements on the surface of concrete structures. It uses the arrangement rules of the H-type orthogonal strain gauge full-bridge measurement circuit of this invention as its core (longitudinal strain gauges are symmetrically separated along the principal stress direction, and transverse strain gauges are symmetrically separated perpendicular to the principal stress direction). The results are verified by comparing the strain field data with those of traditional cross-shaped strain gauge arrangements. Simultaneously, the stress release calibration coefficient α in the detection method of this invention is calibrated; the formula for α is α = σ / σ. c (σ is the applied stress, σ) c (For calculating stress), the specific results are shown in Table 1: Table 1. Strain data results for the two arrangement points. Note: Condition C is the traditional cross-shaped strain gauge arrangement; Conditions H10~H80 are the H-shaped orthogonal strain gauge arrangements that meet the requirements of the device of this invention, with the transverse strain gauge spacing ranging from 10mm to 80mm, and satisfying the condition that 0 < S / L in the device. c Dimensionless ratio requirement <1.

[0066] In a non-uniform stress field, the transverse stress distribution between parallel cuts exhibits significant non-uniform characteristics (e.g., Figure 3 The local stress concentration and gradient changes shown in a-3b are analyzed below, along with the simulation data and the calibration results of α: 1) The traditional cross-shaped layout can only collect local strain at the center of the measuring point. This strain cannot represent the average lateral deformation of the entire measuring point area. At this time, the Poisson's ratio relationship is directly applied for mechanical strain separation. Its calibration coefficient α=0.89 and the relative error reaches 12.59%. That is, the measured value deviates greatly from the true value of the concrete surface stress, which is difficult to meet the high precision requirements of prestress detection.

[0067] 2) When using the H-type orthogonal strain gauge arrangement of this invention, two transverse strain gauges are symmetrically separated and arranged in a region where the stress field is relatively smooth and more representative. Data comparison results show that the H-type orthogonal strain gauge arrangement can effectively average and comprehensively cancel out this non-uniform transverse strain distribution. Under the same stress release condition, when the strain data collected by the H-type orthogonal strain gauge arrangement is substituted into the target stress calculation formula for back-calculation, compared with the measurement results of the traditional cross-type arrangement (condition C) with a relative error of 17.71% and a calibration coefficient of 0.85, the measurement accuracy is significantly improved with the increase of the spacing when using the H-type orthogonal strain gauge arrangement of this invention. Specifically, when the transverse strain gauge spacing is within the range of 0 < S / L as claimed in the claims... c When the value is less than 1, the relative error steadily decreased from 17.71% to 12.59%, and the calibration coefficient α was optimized from 0.85 to 0.89.

[0068] 3) Taking the H80 working condition as an example, shifting the transverse compensation strain gauges to both sides (e.g., an 80mm spacing, i.e., a 40mm deviation on one side) can effectively avoid the stress redistribution distortion zone at the cut end, obtaining purer material Poisson transverse deformation data. Compared to the traditional working condition C, its relative error absolute value is reduced by 5.22% (the error is reduced by approximately 29.5%), and the stress calibration coefficient is also closer to the theoretical value of 1. This fully demonstrates that the arrangement of H-shaped orthogonal strain gauges can effectively reduce the distortion interference caused by stress concentration at the cut end.

[0069] In summary, the strain data results fully demonstrate that the H-shaped orthogonal strain gauge arrangement scheme can effectively avoid the stress redistribution distortion zone at the cut end, obtain purer Poisson transverse deformation data, solve the technical problems of large measurement deviation and poor repeatability of traditional methods under non-uniform stress fields, and improve the robustness of the detection method under complex engineering conditions.

[0070] Example 2: Online Detection and Verification of Prestress on Concrete Structure Surface Based on H-type Orthogonal Strain Compensation All-weather strain monitoring was conducted on the sidewall of a box girder. The strain at the measurement points exhibited periodic fluctuations with the passage of time, with each fluctuation cycle lasting approximately 24 hours (i.e., one 24-hour period). The monitoring results are as follows: Figure 4 As shown, the results indicate that: The difference between the peak and trough of the strain measurement results during day and night can be as large as nearly 40 microstrains. Substituting this strain deviation into the target stress calculation formula, the deviation of the obtained stress measurement results can be as large as 1~2MPa.

[0071] Therefore, this invention introduces time-series features into in-situ stress measurement of structures based on the stress release method. These features distinguish mechanical strain from spurious strain signals generated by temperature strain, cutting thermal interference, etc., effectively improving the anti-interference capability and measurement accuracy of in-situ stress detection in complex field environments.

[0072] This invention provides an online detection device and method for prestressed concrete surface based on H-type orthogonal strain intelligent compensation, suitable for environments with significant high temperatures, direct sunlight, and cutting thermal interference. Its core principle addresses the unique stress distribution between parallel cuts by setting up an assembly of H-type orthogonal strain gauges on the concrete surface. Combined with time-series control, and based on Poisson's ratio, temperature strain is eliminated. The actual mechanical strain value is corrected using a stress calibration coefficient α. Based on Hooke's law and the elastic modulus of the measured material, the stress in the actual target direction is calculated. This improves the accuracy of identifying the prestressed values ​​of embedded prestressed tendons in prestressed concrete structures, providing a more accurate, efficient, and reliable technical means for detecting stress transfer on the surface of prestressed concrete within the structure.

[0073] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An online detection device for prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation, characterized in that, The device includes: a strain sensing unit and a strain acquisition instrument; The strain sensing unit includes transverse strain gauges and longitudinal strain gauges; the longitudinal strain gauges are arranged along the principal stress direction, and the transverse strain gauges are symmetrically separated perpendicular to the principal stress direction; the longitudinal strain gauges and the transverse strain gauges form an H-shaped orthogonal strain gauge full-bridge measurement circuit; the H-shaped orthogonal strain gauge full-bridge measurement circuit is attached to the surface of the concrete structure; the spacing S between the transverse strain gauges is equal to the spacing L of the stress relief cut formed during cutting. c Satisfying 0 < S / L c The dimensionless ratio relationship is <1; the strain acquisition instrument is electrically connected to the H-type orthogonal strain gauge full-bridge measurement circuit, and is used to acquire the real strain before and after stress transfer under the same conditions in the H-type orthogonal strain gauge full-bridge measurement circuit.

2. The online detection device for prestress on the surface of concrete structures according to claim 1, characterized in that, The strain acquisition instrument is equipped with a data processing module; the data processing module has a built-in sampling unit, an intelligent dynamic monitoring unit, and an intelligent strain extraction algorithm unit; the sampling unit is used to sample the strain values ​​of the full-bridge measurement circuit of the H-type orthogonal strain gauge on the surface of the concrete structure; the intelligent dynamic monitoring unit is used to calculate the dispersion of the sampling in real time and perform convergence judgment; the intelligent strain extraction unit is used to automatically perform decoupled calculation of temperature strain and mechanical strain and output stable measurement values ​​that have passed intelligent identification.

3. The online detection device for prestress on the surface of concrete structures according to claim 2, characterized in that, The data processing module is also equipped with an interface for bidirectional data synchronization with an external cloud platform.

4. The online detection device for prestress on the surface of concrete structures according to claim 3, characterized in that, The device also includes a power supply module, which is electrically connected to the strain sensing unit and the strain acquisition instrument.

5. A method for online detection of prestress on the surface of concrete structures based on H-type orthogonal strain intelligent compensation, based on the online detection device for prestress on the surface of concrete structures according to any one of claims 1-4, characterized in that, The method includes the following steps: S1. Select appropriate measurement points based on the actual working conditions of the prestressed concrete structure surface; and determine a fixed measurement time as the reference time for all subsequent measurement readings based on the environmental conditions of the test site. S2. Attach the H-type orthogonal strain gauge full-bridge measurement circuit to the measurement point on the surface of the concrete structure; zero the strain acquisition instrument according to the measurement time selected in step S1, and collect the orthogonal bidirectional strain value at the measurement point as the initial strain value; S3. 24 hours after step S2 is completed, high-frequency automatic sampling is performed by the sampling unit built into the strain acquisition instrument; the intelligent dynamic monitoring unit calculates the dispersion of the sampled data in real time and obtains multiple sliding windows; when the strain fluctuation values ​​in multiple consecutive sliding windows converge to the preset error threshold range, the intelligent dynamic monitoring unit automatically locks and outputs the current average strain value as the calibration strain value, and triggers subsequent stress transfer commands. S4. Upon receiving the stress transfer operation command, a cutting device is used to cut both sides of the measurement point on the concrete structure surface, forming two parallel stress relief cuts; the stress relief cuts are symmetrically located on the outside of the H-shaped orthogonal strain gauge full-bridge measurement circuit; the spacing L between the stress relief cuts is... c The spacing S of the transverse strain gauges set in the H-type orthogonal strain gauge full-bridge measurement circuit satisfies 0 < S / L c Dimensionless ratios less than 1; S5. After the cutting is completed, restore the temperature of the measurement point to the temperature before the cutting operation; at the reference time point selected in step S1, collect the orthogonal bidirectional strain value of the measurement point after cooling using a strain acquisition instrument. S6. The collected orthogonal bidirectional strain values ​​are processed by the intelligent strain extraction algorithm unit. Based on the Poisson's ratio relationship, a thermo-mechanical coupling mathematical model is established to separate the temperature strain and output the stable real mechanical strain value that has been intelligently identified. S7. The obtained real mechanical strain is synchronized to an external cloud platform and corrected by stress calibration coefficient; the corrected real mechanical strain value is used to calculate the stress in the target direction based on Hooke's law and the elastic modulus of the material being measured.

6. The online detection method for prestress on the surface of concrete structures according to claim 5, characterized in that, In step S6, the intelligent strain extraction algorithm unit is configured as follows: (1) Based on the assumption that the temperature effect during the cutting process is isotropic, the temperature strain in the measurement direction (x) and the compensation direction (y) satisfies the following formula: Where, ε temp ε represents the strain caused by temperature during the cutting process. temp,x ε represents the strain in the x-direction caused by temperature during the cutting process. temp,y This represents the strain in the y-direction caused by temperature during the cutting process. (2) Based on the Poisson effect of mechanical strain generated by stress release in the region between mutually parallel stress release cuts, the mechanical strain satisfies the following formula: Where ν is the Poisson's ratio of the area to be measured; ε mech,x ε represents the strain in the x-direction caused by mechanical cutting. mech,y The strain in the y-direction caused by mechanical cutting; (3) Based on the orthogonal bidirectional strain value after cooling, which is the superposition of mechanical strain and temperature strain, the following formula is satisfied: Where, ε x The total strain is measured using strain gauges in the stress measurement direction; ε y The total strain is measured using strain gauges in the stress compensation direction; (4) By substituting the Poisson effect formula into the strain superposition formula, the mechanical strain term is eliminated, and the temperature strain is obtained separately, expressed by the following formula: (5) Substituting the temperature strain formula into the total strain superposition formula in the x-direction, the true mechanical strain after eliminating temperature interference in the x-direction is obtained, expressed by the following formula: 。 7. The online detection method for prestress on the surface of concrete structures according to claim 6, characterized in that, The Poisson's ratio of the cut region of the object under test ranges from 0.2 to 0.

25.

8. The online detection method for prestress on the surface of concrete structures according to claim 4, characterized in that, In step S7, the target direction stress satisfies the following formula: Where α is the stress relief calibration coefficient; E c σ represents the elastic modulus of the area to be measured; t The target stress is defined in the area to be measured.

9. The online detection method for prestress on the surface of concrete structures according to claim 8, characterized in that, The stress relief calibration coefficient α is related to the transverse strain gauge spacing S and the stress relief slit spacing L. c dimensionless ratio S / L c It shows a negative correlation.

10. The online detection method for prestress on the surface of concrete structures according to claim 9, characterized in that, The stress relief calibration coefficient α has a value range of 0.8 ≤ α ≤ 1.0.

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