Temperature compensation high-frequency resonance type in-service steel strand prestress loss real-time monitoring method
By setting the excitation coil and induction coil inside the steel strand to form a resonant transformer, and setting the temperature-compensated inductor at the unforced end, using the hysteresis and expansion theory, the real-time accuracy problem of in-service prestressed steel strand monitoring in the prior art is solved, and a rapid and accurate analysis of the stress conditions of the steel strand is achieved.
Patent Information
- Application Number
- CN202311523245.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-14
- Publication Date
- 2025-07-11
AI Technical Summary
It is difficult for the prior art to achieve real-time and accurate monitoring of in-service prestressed steel strands, especially after tensile service, optical fibers, strain gauges, anti-tensioning method and magnetic resonance methods have problems such as fragility, fatigue, and temperature influence, resulting in inaccurate monitoring data.
The temperature-compensated high-frequency resonance method is adopted, and an excitation coil and an induction coil are arranged inside the steel strand to form a resonant transformer, and a temperature-compensated inductor is set at the unforced end. Through the sinusoidal excitation signal and temperature compensation, the magnetic permeability change of the steel strand is calculated using the hysteresis expansion and contraction theory to obtain the stress condition.
Real-time and accurate monitoring of in-service structures is achieved, magnetic loss and temperature drift problems are overcome, and the reliability and accuracy of monitoring data are ensured.
Smart Images
Figure CN120293358A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of prestress monitoring of steel strands, and particularly relates to a real-time monitoring method for prestress loss of in-service steel strands by means of temperature-compensated high-frequency resonance. Background Art
[0002] Prestress is the compressive stress pre-applied to a structure during construction in order to improve its service performance. During the service period of the structure, the pre-applied compressive stress can offset all or part of the tensile stress caused by the load, avoiding structural failure. The real-time prestress of prestressed steel strands is a difficulty and key point in structural detection. Only by obtaining the real-time stress value of the steel strands in the in-service prestressed structure can the health and safety of the structure be well monitored and evaluated.
[0003] Currently, there are mainly four methods for real-time prestress monitoring of prestressed steel strands after tensioning and service. One method is to implant optical fibers into the prestressed steel strands when casting a reinforced prestressed beam. Since prestressed steel strands are generally composed of multiple wires such as 5 or 7 wires twisted together, and the center lines of multiple steel strands are straight, the straight center line is replaced by an optical fiber, and the stress change value is obtained by using the stress-induced deformation of the optical fiber. However, there is a certain elongation in length during the application and removal of prestress. Optical fibers are brittle and not easy to stretch, so there are great difficulties in processing and monitoring. At the same time, the prestress obtained is only the stress on the center line and cannot completely replace the stress on the other 4 or 6 wires. Another method is to measure the stress under the anchor. When tensioning the prestressed steel strands, strain gauges are installed behind the anchor, and the stress change is monitored in real time after the steel bars are tensioned. However, strain gauges have disadvantages such as fatigue damage and temperature influence, and cannot work in a long-term servo mode. At the same time, the data monitored is only the prestress at the joint, and the stress changes caused by factors such as prestressed tendons and corrugated pipes cannot be monitored, resulting in low accuracy of the monitored data. The third method is to obtain the stress value by the reverse tension method. By applying a reverse force at the tip of the prestressed steel bar until the anchor head becomes loose, the tension at this time is used to replace the force on the original prestressed steel strand. Obviously, it is very difficult to calibrate and judge the loosening of the anchor head. The reverse tension force is not exactly equal to the force during the prestress work, and at the same time, it is very difficult to monitor the in-service structure in real time. The fourth method is to introduce the magnetostrictive principle into the concrete steel strands, establish a magnetic resonance coil circuit on the steel strands, and monitor the prestress of the steel strands by using the change in the induced electromotive force of the secondary coil in the magnetic resonance sensor caused by the change in the prestress of the steel strands. However, this method has serious eddy current and hysteresis losses, and the test results cannot separate these losses. At the same time, this method has an output temperature drift problem caused by the change in the magnetic permeability of the steel strands with temperature, which restricts its practical application. Therefore, how to achieve accurate monitoring of in-service structures in real time has become an urgent problem to be solved at present. Summary of the Invention
[0004] In view of the deficiencies of the above-mentioned existing technologies, the present invention provides a real-time monitoring method for the prestress loss of in-service steel strands by temperature-compensated high-frequency resonance. The resonance overcomes all losses such as magnetic loss and eddy current, and at the same time solves the temperature drift problem caused by temperature changes, and can achieve accurate monitoring of real-time in-service structures.
[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:
[0006] The real-time monitoring method for the prestress loss of in-service steel strands by temperature-compensated high-frequency resonance includes the following steps:
[0007] S1. Set two coils on the corrugated pipe inside the steel strand. One of them is used as the excitation coil, and the other is used as the induction coil. The two coils and the steel strand inside the corrugated pipe together form a resonant transformer;
[0008] S2. Wind and set a temperature-compensated inductor on the unloaded end of the steel strand in the form of a transmission line transformer. The double-wire winding eliminates the influence of the residual magnetic field left by the excitation coil and the induction coil on the steel strand, and electrically connects the temperature-compensated inductor to the induction coil; the temperature-compensated inductor is used for temperature compensation during stress monitoring work;
[0009] S3. Input a sinusoidal excitation signal with a resonant frequency to the excitation coil;
[0010] S4. Obtain the output voltage, which is the voltage obtained after the current flows through the temperature-compensated inductor after the induced voltage forms a current in the induction coil;
[0011] S5. Calculate the change in the magnetic permeability of the steel strand by calculating the change in the output voltage obtained in S4; and then based on the magnetostriction theory, obtain the stress condition of the steel strand through the change in the magnetic permeability of the steel strand.
[0012] Compared with the existing technologies, the present invention has the following beneficial effects:
[0013] 1. This method makes full use of the magnetic material characteristics of the steel strand. Since the steel strand is a magnetic material, according to the magnetostriction theory, when the steel strand is subjected to tensile force, its magnetic permeability will change, and measuring the change in magnetic permeability can obtain the magnitude of the force. Similarly, since the steel strand is a magnetic material, following the B-H principle of magnetic materials and combining the electromagnetic induction principle, the change in the magnetic permeability of the steel strand can be obtained based on the obtained output voltage. Through such a setting, the magnetic material characteristics of the steel strand are fully utilized, and the stress condition of the steel strand can be monitored in real time conveniently and quickly.
[0014] 2. Since the steel strand is a magnetic material, its magnetic permeability changes with temperature, resulting in zero drift of the system. To overcome the error caused by the zero drift of the system, a temperature compensation inductor is set at a place where the steel strand is not stressed in this method to offset the zero drift caused by temperature changes. At the same time, to overcome the residual magnetic interference leaked by the excitation coil and the induction coil through the steel strand, a transmission line transformer model with double wires wound in series is set up. Such a setting can ensure the accuracy of calculating the change in the magnetic permeability of the steel strand based on the change in the output voltage.
[0015] In summary, the present invention can achieve accurate monitoring of in-service structures in real time.
[0016] Preferably, in S2, the temperature compensation inductor is a transmission line transformer wound in a double-wire parallel manner, including coil L1 and coil L2.
[0017] Preferably, in S2, the connection method between the temperature compensation inductor and the induction coil is that one end of the induction coil is electrically connected to one end of L1 and L2 of the temperature compensation inductor respectively, and the other end of the induction coil is electrically connected to the other end of L1 and L2 of the temperature compensation inductor respectively.
[0018] In this way, it is possible to overcome the fact that there is a certain magnetic field at the end of the steel strand due to the magnetic field generated by excitation on the same steel strand.
[0019] Preferably, the number of turns of the excitation coil is equal to that of the induction coil; the number of turns of coil L1 and coil L2 of the temperature compensation inductor is equal, and the number of turns of coil L1 is twice that of the induction coil.
[0020] In this way, it can be ensured that when the resonant transformer works, the inductance of the transformer is equal to the inductance of the temperature compensation inductor, so that the output voltage is equal to the induced voltage. During subsequent processing and analysis, the output voltage can be directly used as the induced voltage of the induction coil for processing and analysis.
[0021] Preferably, in S3, the frequency of the sinusoidal excitation signal is the resonant frequency of the resonant transformer.
[0022] To ensure the feasibility of the method, it is necessary to ensure the intensity of the output signal (i.e., the output voltage). According to analysis, the intensity of the output voltage is not only related to the amplitude of the input magnetic field intensity H, but also related to the input frequency. Increasing the frequency can increase the intensity of the output signal, but when the frequency increases, the magnetic loss of the steel strand and the eddy current loss of the transformer will increase, making the test signal smaller. To overcome the above problems, the inventor established a distributed parameter model for the transformer for analysis and found that when the frequency of the sinusoidal excitation signal is the resonant frequency of the resonant transformer, the effect is very good. Such a setting can ensure the intensity of the output signal to a certain extent, thus ensuring the effectiveness of subsequent analysis.
[0023] Preferably, in S1, when setting the coil, the number of turns of the excitation coil and the induction coil is set in combination with the resonance frequency of the resonance transformer.
[0024] With such a setting, the amplitude of H can be increased by increasing the number of coil turns. Moreover, due to losses such as resonance frequency and resistance, the number of coil turns cannot be increased indefinitely. Therefore, the number of turns of the excitation coil and the induction coil is set in combination with the resonance frequency of the resonance transformer. In this way, while enhancing the intensity of the output signal, the effectiveness of the output signal can be ensured.
[0025] Preferably, in S5, the change in the permeability of the steel strand is calculated by the following formula:
[0026] ΔV 感应 (t) = -N 感应 [A 钢绞线 Δμ 钢绞线 (t)ωBsin(ωt)];
[0027] In the formula, ΔV 感应 is the change value of the voltage of the induction coil, Δμ 钢绞线 is the change in the permeability of the steel strand, N 感应 is the number of turns of the induction coil, A 钢绞线 is the cross-sectional area of the steel strand, ω is the resonance frequency, and B is the amplitude of the resonance excitation voltage.
[0028] This formula is obtained by combining the electromagnetic induction law with the analysis of the circuit structure in this method. The change in the permeability of the steel strand can be quickly and accurately obtained through the change value of the voltage of the induction coil, thereby ensuring the accuracy and efficiency of the analysis of the stress condition of the steel strand.
[0029] Preferably, in S5, the stress condition of the steel strand is calculated by the following formula:
[0030]
[0031] In the formula, ΔF is the change in cable force, E is the elastic modulus of the material, A is the cross-sectional area of the steel strand. θ0 is the angle between the magnetic field and the easy magnetization axis, λ s is the axial deformation constant, M s is the saturation magnetization intensity, k u is the uniaxial magnetic anisotropy constant, and H is the magnetic field strength.
[0032] This formula is obtained by comprehensively analyzing and processing the Joule effect, Hooke's law of material mechanics, and the magnetization theory of ferromagnetic materials. The stress condition of the steel strand can be accurately and quickly obtained through the change in the permeability of the steel strand. Brief Description of the Drawings
[0033] To make the objectives, technical solutions, and advantages of the invention more clear, the following further detailed description of the present invention will be provided in conjunction with the accompanying drawings, where:
[0034] Figure 1 is the flow chart of the present invention;
[0035] Figure 2 is the schematic diagram of the coil structure in the embodiment;
[0036] Figure 3 is the schematic diagram of the magnetic hysteresis loop and the change curve of magnetic permeability of the steel strand in the embodiment;
[0037] Figure 4 is the schematic diagram of the equivalent circuit model in the embodiment;
[0038] Figure 5 is the schematic diagram of the winding structure of the temperature-compensated inductor in the embodiment;
[0039] Figure 6 is the schematic diagram of the equivalent calculation model of the circuit in the embodiment;
[0040] Figure 7 is the schematic diagram of the cross-section of the excitation and induction coils wound on the outer wall of the corrugated pipe in the embodiment. Specific Embodiments
[0041] The following is a further detailed description through specific embodiments:
[0042] Embodiment:
[0043] As Figure 1 shown, an in-situ real-time monitoring method for prestress loss of temperature-compensated high-frequency resonant steel strands is disclosed in this embodiment, including the following steps:
[0044] S1. Two coils are arranged on the corrugated pipe inside the steel strand, one of which is used as the excitation coil and the other as the induction coil. The two coils and the steel strand inside the corrugated pipe together form a resonant transformer.
[0045] S2. A temperature-compensated inductor is arranged at the unloaded end of the steel strand, and the temperature-compensated inductor is connected to the induction coil and a resistor to form a test output circuit; the temperature-compensated inductor is used for temperature compensation when the resonant transformer detects stress.
[0046] During specific implementation, the temperature-compensated inductor is a transmission line transformer wound in a double-wire parallel winding manner, including coil L1 and coil L2. The connection method between the temperature-compensated inductor and the induction coil is that one end of the induction coil is electrically connected to one end of L1 and L2 of the temperature-compensated inductor respectively, and the other end of the induction coil is electrically connected to the other ends of L1 and L2 of the temperature-compensated inductor through a resistor respectively.
[0047] The present invention proposes a real-time monitoring method for the prestress of high-frequency resonant steel strands using the basic principle of magnetostriction. In order to solve the temperature drift problem and overcome the residual magnetism leaked from the excitation coil and the induction coil along the steel strand, a transmission line transformer with double-wound wires is arranged in the non-stressed section of the steel bar for temperature compensation. As Figure 2 shown, two coils are installed on the corrugated pipe inside the steel strand, one as the excitation coil and the other as the induction coil. The voltage induced by the induction coil passes through the temperature compensation inductor of the transmission line transformer type externally connected to the non-stressed end to achieve temperature drift voltage compensation caused by temperature for the material. Figure 2 The temperature compensation coil with double-wound wires in it is the temperature compensation inductor set in S2.
[0048] S3. Input a sinusoidal excitation signal to the excitation coil. During specific implementation, the frequency of the sinusoidal excitation signal is the resonance frequency of the resonance transformer.
[0049] According to the magnetostriction theory, when the steel strand is subjected to tensile force, its magnetic permeability will change. Measuring the change in magnetic permeability can obtain the magnitude of the force. Since the steel strand is a magnetic material and completely follows the B-H principle of magnetic materials, according to Figure 3 the magnetic hysteresis loop (B~H) of the steel strand shown, the relationship between B and H is non-linear during the action process, and the magnetic permeability has different values at different points. However, the test system has a given μ value for the change in magnetic permeability. According to Figure 3 shown, to implement the test using the B-H method, H needs to be set to the maximum value of the magnetic permeability change, that is, the point marked in the figure. At the same time, the magnetic hysteresis loop has a certain area, representing the magnetic loss of the system. Although the test system realizes the solution of the magnetic permeability change Δμ by finding B according to the given H, in order to directly display the change in magnetic permeability, the test reading is directly realized by the output V method. The test method uses a sleeve-type transformer (i.e., the resonance transformer set in S1) to achieve the correlation between the output amplitude and the magnetic permeability under the excitation action. Since the output (i.e., the induced voltage of the induction coil) is related to the magnetic permeability and H as:
[0050] or Vin=-NAHωcos(ωt);
[0051] In the formula, Vin represents the induced voltage, N represents the number of turns of the coil, Φ(t) represents the magnetic flux, A represents the area of the induction coil, H(t) represents the magnetic field strength, and ω represents the frequency.
[0052] The intensity of the output signal is related not only to the input H but also to the input frequency. Increasing the frequency can increase the intensity of the output signal. However, as the frequency increases, the magnetic loss of the steel strand and the eddy current loss of the transformer will increase, resulting in a smaller test signal. To overcome the above problems, the inventor established a distributed parameter model for the transformer, and the equivalent circuit of the model is as follows Figure 4 as shown
[0053] In view of this, the frequency of the input excitation is selected at the system resonance frequency, and the amplitude of H is solved by increasing the number of turns of the coil. Due to resonance frequency and resistance losses, the number of turns of the coil cannot be increased without limit. Therefore, in the specific implementation, in S1, when setting the coil, the number of turns of the excitation coil and the induction coil is set in combination with the resonance frequency of the resonance transformer. It should be noted that the specific calculation method for setting the number of turns of the excitation coil and the induction coil in combination with the resonance frequency of the resonance transformer is common knowledge in the art, and the specific content of this calculation process is not the innovation point of the present invention. Therefore, the specific calculation process will not be elaborated here
[0054] S4. Obtain the output voltage, which is the voltage obtained after the current flows through the temperature compensation inductor after the induced voltage forms a current in the induction coil
[0055] At the same time, since the steel strand is a magnetic material, its magnetic permeability will change with temperature, resulting in system zero drift. To overcome the error caused by system zero drift, a temperature compensation inductor is wound in a double-wire parallel winding manner at a place where the steel strand is not stressed to offset the zero drift caused by temperature change. The winding method is as Figure 5 shown. The double-wire parallel winding and the connection according to the figure are mainly to overcome the magnetic field existing at the end of the steel strand due to the magnetic field generated by the excitation on the same steel strand
[0056] The equivalent calculation model of the circuit in this method is as Figure 6 shown, and the way to achieve temperature compensation is: when the induced voltage is Vg, the output voltage is the voltage result obtained after the current formed by the induced voltage in the induction coil flows through the double-wire parallel wound temperature compensation reference inductor, that is
[0057]
[0058] In the formula, Vout is the actual output voltage, L 温补电感 is the inductance of the temperature compensation inductor, L 变压器 is the equivalent inductance of the excitation coil and the induction coil at resonance, Vg is the resonance induced voltage, ΔL 温度引起温补电感增加量 is the change in the inductance of the temperature compensation inductor (i.e., the temperature compensation inductor) caused by temperature change, ΔL 温度引起的变压器电感增加量 is the change in the inductance of the resonance transformer caused by temperature change
[0059] Since at the same location, when ensuring that the number of turns of the temperature-compensating inductor is twice that of the transformer inductor during winding, and the temperature-compensating inductor is connected in the way of a transmission-line transformer, with the head and tail connected, from a microscopic perspective, the two coils are in series. The induced electromotive force generated by the excitation leaking from the steel bar and the induced magnetic field cancels each other out, and no external influence effect is generated. Macroscopically, on the output side, working lines are led out from both ends of the two inductors (in parallel), and the external inductance is 1 / 2 of the actual inductance (see Figure 6 the connection method of the temperature-compensating inductor in). When ensuring that the length of the transmission-line winding is twice that of the transformer, since it is wound on the same medium, it can ensure that L 温补电感 and L 变压器 have the same inductance. Macroscopically, the equivalent inductances are the same. The change in the permeability of the steel strand caused by temperature in this area results in an increase of ΔL in the macroscopic inductance L 温补电感 and L 变压器 . Since the two inductors are equivalent macroscopically, the increase amount of ΔL is the same, so the ratio in equation (1) remains 1, making Vg independent of temperature and achieving temperature compensation.
[0060] Therefore, when setting up the coils, the number of turns of the excitation coil and the induction coil are equal; the number of turns of the coils L1 and L2 of the temperature-compensating inductor are equal, and the number of turns of coil L1 is twice that of the induction coil, ensuring that L 变压器 and L 温补电感 are equal. Since all the devices are in the same position and affected by temperature, the inductance of the secondary side of the transformer increases by a ΔL due to the increase in permeability, and the temperature-compensation inductor also increases by ΔL. The ratio between the two does not change and is not affected by temperature changes.
[0061] In this way, when the resonant transformer is working, the inductance of the transformer can be ensured to be equal to that of the temperature-compensating inductor, so that the output voltage is equal to the induced voltage. During subsequent processing and analysis, the output voltage can be directly used as the induced voltage of the induction coil for processing and analysis.
[0062] The cross-sections of the excitation and induction coils wound on the outer wall of the corrugated pipe are as Figure 7 shown. The induced voltage is generated by the excitation voltage exciting a magnetic field, and through the change of magnetic flux generated by the magnetic field in the secondary side of the transformer, an induced voltage is obtained at both ends of the induction coil.
[0063] S5. By calculating the change in the output voltage obtained in S4, the change in the permeability of the steel strand is obtained; then based on the magnetostriction theory, the stress condition of the steel strand is obtained through the change in the permeability of the steel strand.
[0064] During specific implementation, the change in the permeability of the steel strand is calculated through the following formula:
[0065] ΔV 感应 (t) = -N感应 [A 钢绞线 Δμ 钢绞线 (t)ωBsin(ωt)];
[0066] Wherein, ΔV 感应 is the voltage change value of the induction coil, and Δμ 钢绞线 is the change in the permeability of the steel strand, N 感应 is the number of turns of the induction coil, A 钢绞线 is the area of the steel strand, ω is the resonance frequency, and B is the excitation amplitude.
[0067] This formula is obtained by combining the electromagnetic induction law with the analysis of the circuit structure in this method. The change in the permeability of the steel strand can be quickly and accurately obtained through the voltage change value of the induction coil, thereby ensuring the accuracy and efficiency of the analysis of the stress condition of the steel strand. The analysis and derivation process is as follows:
[0068] According to the Joule effect, there is the following formula:
[0069]
[0070] Wherein, ε is the axial strain, λ s is the axial deformation constant, M s is the saturation magnetization intensity, K u is the uniaxial magnetic anisotropy constant, θ0 is the angle between the magnetic field and the easy magnetization axis, and ΔM is the change in magnetization intensity.
[0071] From Hooke's law (elastic law) in material mechanics, there is:
[0072]
[0073] Wherein, F is the cable force, E is the elastic modulus of the material, A is the cross-sectional area of the cable, and σ is the stress.
[0074] In the case of constant magnetic field strength, according to the magnetization theory of ferromagnetic materials, there is:
[0075] M = kH = (μ - μ0)H (4);
[0076] Wherein, M is the magnetization intensity, k is the magnetic susceptibility, μ is the permeability, μ0 is the vacuum permeability, and H is the magnetic field strength.
[0077] Substituting the above formulas (3) and (4) into (2), there is:
[0078]
[0079] After that, the stress condition of the steel strand is calculated through the following formula:
[0080]
[0081] Wherein, ΔF is the cable force change, E is the elastic modulus of the material, A is the cross-sectional area of the steel strand. θ0 is the angle between the magnetic field and the easy magnetization axis, and λ is the permeability change of the steel strand s is the axial deformation constant, M s is the saturation magnetization intensity, k u is the uniaxial magnetic anisotropy constant, and H is the magnetic field strength.
[0082] This formula is obtained by comprehensive analysis and processing of the Joule effect, Hooke's law of material mechanics, and the magnetization theory of ferromagnetic materials. The stress condition of the steel strand can be accurately and quickly obtained through the permeability change of the steel strand. The analysis and derivation process is as follows:
[0083] According to the electromagnetic induction law, there is
[0084]
[0085] Wherein, V 感应 (t) is the induced voltage, N 感应 is the number of turns of the induction coil, and φ(t) is the magnetic flux of the induction coil;
[0086]
[0087] Wherein, A 钢绞线 is the area of the steel strand, μ 钢绞线 is the permeability, H(t) is the magnetic field, A 灌浆液 is the area of the grouting liquid, μ 灌浆液 is the permeability of the grouting liquid, μ0 is the permeability in vacuum, A 波纹管 is the area of the corrugated pipe.
[0088] Based on the fact that H is proportional to the excitation current (voltage), and the input voltage is vin = Bcos(ωt). Considering the input signal as a stable signal, the induced voltage output changes with the tension as follows:
[0089] V 感应 (t) = -N 感应 [A 钢绞线 μ 钢绞线 (t)ωBsin(ωt) + A 灌浆液 μ 灌浆液 ωBsin(ωt) + μ0A 波纹管 ωBsin(ωt)] (8)
[0090] Wherein, ω is the frequency.
[0091] When μ increases by a Δμ due to the force, the amplitude of V induced(t) changes,
[0092] ΔV 感应(t) = -N 感应 [A 钢绞线 Δμ 钢绞线 (t)ωBsin(ωt)] (9)
[0093] Combining formula (5), it can be obtained that the force causes the terminal voltage (rms value) to change. Measuring this change can obtain the change in force.
[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limiting the technical solutions. Those of ordinary skill in the art should understand that any modifications or equivalent replacements made to the technical solutions of the present invention without departing from the purpose and scope of the present technical solution shall be covered by the scope of the claims of the present invention.
Claims
1. A real-time monitoring method for prestress loss of in-service steel stranded wires based on warm-compensation high-frequency resonance, characterized in that, It includes the following steps: S1. Set two coils on the corrugated pipe inside the concrete to wrap the steel strand. One of them serves as the exciting coil and the other as the induction coil. The two coils and the steel strand inside the corrugated pipe together form a resonant transformer; S2. Wind and set a temperature compensation inductor on the non-loaded end of the steel strand in the way of a transmission line transformer. The double-wire parallel winding eliminates the influence of the residual magnetic field left by the exciting coil and the induction coil on the steel strand, and electrically connect the temperature compensation inductor to the induction coil; the temperature compensation inductor is used to perform temperature compensation when the resonant transformer works; S3. Input a resonant sine exciting signal to the exciting coil; S4. Obtain the output voltage, which is the voltage obtained after the current flows through the temperature compensation inductor after the induced voltage forms a current in the induction coil; S5. Calculate the change in the magnetic permeability of the steel strand by calculating the change in the output voltage obtained in S4; then, based on the magnetostrictive theory, obtain the stress condition of the steel strand through the change in the magnetic permeability of the steel strand.
2. The real-time monitoring method for prestress loss of in-service steel stranded wires by temperature-compensated high-frequency resonance type according to claim 1, characterized in that: In S2, the temperature compensation inductor is a transmission line transformer wound in a double-wire parallel winding manner, including coil L1 and coil L2.
3. The real-time monitoring method for prestress loss of in-service steel strand by temperature-compensated high-frequency resonance as claimed in claim 2, wherein: In S2, the connection mode between the temperature compensation inductor and the induction coil is that one end of the induction coil is electrically connected to one end of L1 and L2 of the temperature compensation inductor respectively, and the other end of the induction coil is electrically connected to the other ends of L1 and L2 of the temperature compensation inductor through a resistor respectively.
4. The real-time monitoring method for prestress loss of in-service steel strand by temperature-compensated high-frequency resonance type according to claim 3, characterized in that: The number of turns of the exciting coil is equal to that of the induction coil; the number of turns of coil L1 and coil L2 of the temperature compensation inductor is equal, and the number of turns of coil L1 is twice that of the induction coil.
5. The real-time monitoring method for prestress loss of in-service steel strand by temperature-compensated high-frequency resonance as claimed in claim 4, wherein: In S3, the frequency of the sine exciting signal is the resonant frequency of the resonant transformer.
6. The real-time monitoring method for prestress loss of in-service steel strand by temperature-compensated high-frequency resonance type according to claim 5, wherein: In S1, when setting the coils, set the number of turns of the exciting coil and the induction coil in combination with the resonant frequency of the resonant transformer.
7. The real-time monitoring method for prestress loss of in-service steel strand by temperature-compensated high-frequency resonance as claimed in claim 6, wherein: In S5, calculate the change in the magnetic permeability of the steel strand through the following formula: ΔV 感应 (T) = -N 感应 [A 钢绞线 Δμ 钢绞线 (t)ωBsin(wt)]; Where, ΔV 感应 is the voltage change value of the induction coil, Δμ 钢绞线 is the permeability change of the steel strand, N 感应 is the number of turns of the induction coil, A 钢绞线 is the cross-sectional area of the steel strand, ω is the resonance frequency, and B is the amplitude of the resonance excitation voltage.
8. The real-time monitoring method for prestress loss of in-service steel strand by temperature compensation high-frequency resonance as claimed in claim 7, wherein: In S5, calculate the stress condition of the steel strand through the following formula: Where, ΔF is the cable force change, E is the elastic modulus of the material, A is the cross-sectional area of the steel strand, θ0 is the angle between the magnetic field and the easy magnetization axis, and Δμ 钢绞线 is the permeability change of the steel strand, and λ s is the axial deformation constant, M s is the saturation magnetization intensity, k u is the uniaxial magnetic anisotropy constant, and H is the magnetic field intensity.