Method and system for detecting prestress loss of a structure of a slow-bonded prestressed concrete by using microwave

Abstract

This invention relates to the field of civil engineering structural monitoring technology, and particularly to a microwave detection method and system for prestress loss in loosely bonded prestressed concrete structures. The method includes: acquiring initial prestress data of the steel strands; transmitting a 24GHz microwave signal to the steel strands and receiving the scattered microwave signal; constructing a three-dimensional scattering field model of the steel strands, extracting multi-scale features of the scattered signal, and obtaining multi-dimensional Doppler phase shifts; based on the Doppler phase shifts and combined with environmental parameters, establishing a multi-parameter coupled structural prestress mapping model, and calculating the structural prestress variation value; calculating the structural prestress loss in the unbonded section, anchored section, and bonded section according to the structural prestress variation value, obtaining the overall structural prestress loss distribution; and evaluating and providing early warning of the structural prestress state. This invention achieves non-destructive, high-precision monitoring of structural prestress loss, improving the safety of prestressed structures.

Description

Technical Field

[0001] This invention relates to the field of civil engineering structural monitoring technology, and in particular to a microwave detection method and system for prestress loss in slow-bonded prestressed concrete structures, which is used for non-destructive, high-precision monitoring of prestress loss in steel strands in prestressed concrete structures. Background Technology

[0002] Prestressed concrete structures are widely used in bridges, large-scale buildings, and water conservancy projects. Their core component is the prestressed steel strand, which enhances the structure's load-bearing capacity and performance by applying prestress. However, over time, the prestressed steel strand experiences prestress loss, affecting structural safety. Therefore, accurate monitoring of prestress loss in prestressed steel strands is of great significance.

[0003] Delayed-bonding prestressing is a form of prestressing that gradually transitions the prestressing tendons and concrete from unbonded to bonded through the curing of a delaying adhesive. During construction, the prestressing tendons can freely expand and deform without bonding to the surrounding delaying adhesive. However, after construction is completed, within a predetermined period, the prestressing tendons bond to the surrounding concrete through the cured delaying adhesive, forming a unified bond between the prestressing tendons and the surrounding concrete, thus achieving a bonded effect.

[0004] Delayed-bonding prestressing technology is a new prestressing technology developed after unbonded and bonded prestressing technologies. Delayed-bonding prestressing absorbs the construction characteristics of unbonded prestressing and the mechanical characteristics of bonded prestressing. Construction is the same as unbonded prestressing, with flexible layout, using single-hole anchors, and eliminating the need for corrugated pipes or grouting. After the delayed-setting adhesive cures, it ultimately achieves a bonded effect mechanically.

[0005] Traditional methods for testing the tension of prestressed steel strands mainly include the vibration method, the jack method, and the strain gauge method. The vibration method calculates the prestress of the structure by measuring the natural frequency of the steel strand, but it is greatly affected by environmental noise. The jack method requires specialized equipment, is complex to operate, and is somewhat destructive. The strain gauge method is limited by installation location and has poor long-term stability. These methods have drawbacks such as limited accuracy, complex construction, and difficulty in long-term monitoring, especially for loosely bonded prestressed structures, where the steel strands are encased in a protective layer, making traditional methods even more difficult to implement.

[0006] In recent years, non-contact detection technologies based on electromagnetic waves have gradually emerged. However, existing technologies mainly focus on simple frequency analysis or single-parameter monitoring, which are difficult to adapt to the high-precision requirements in complex environments. Different segments of the loosely bonded prestressed structure are all loosely bonded. That is, initially, it resembles an unbonded structure, but it becomes bonded as the adhesive cures. This time varies from 180 to 720 days depending on the curing period of the adhesive. In particular, its ability to analyze prestress loss in different segments of the steel strand (unbonded segment, anchored segment, and bonded segment) is limited. Therefore, there is an urgent need to develop a non-destructive, high-precision method suitable for monitoring prestress loss in loosely bonded prestressed structures. Summary of the Invention

[0007] The purpose of this invention is to provide a microwave detection method and system for prestress loss in slow-bonded prestressed concrete structures, aiming to solve the problems of low accuracy, difficulty in achieving non-contact detection, and incompatibility with complex environments in the existing technology for detecting prestress loss in prestressed steel strands.

[0008] This invention proposes a microwave detection method for prestress loss in slow-bonding prestressed concrete structures, comprising:

[0009] Obtain the initial structural prestress data of steel strands in prestressed concrete structures;

[0010] Transmit a 24GHz microwave signal to the steel strand and receive the scattered microwave signal generated by the steel strand;

[0011] A three-dimensional scattering field model of the steel strand is constructed, and the multi-scale features of the scattered microwave signal are extracted to obtain the multi-dimensional Doppler phase shift.

[0012] Based on the multi-dimensional Doppler phase shift and combined with environmental parameters, a multi-parameter coupled structural prestress mapping model is established to calculate the structural prestress variation value of the steel strand.

[0013] Based on the changes in prestress of the structure, the prestress loss of the unbonded section, the prestress loss of the anchored section, and the prestress loss of the bonded section of the steel strand are calculated respectively, so as to obtain the overall prestress loss distribution of the steel strand.

[0014] Preferably, the construction of the three-dimensional scattering field model of the steel strand, the extraction of multi-scale features of the scattered microwave signal, and the obtaining of multi-dimensional Doppler phase shift include:

[0015] The space surrounding the steel strand is divided into a near-field region and a far-field region;

[0016] A model relating surface impedance to structural prestress is established in the near-field region, and a model relating scattering pattern to structural prestress is established in the far-field region.

[0017] Microscopic, mesoscopic, and macroscopic features of the scattered microwave signal are extracted.

[0018] The microscale features, mesoscale features, and macroscale features are fused and enhanced to obtain the multidimensional Doppler phase shift.

[0019] Preferably, the extraction of the microscale features, mesoscale features, and macroscale features of the scattered microwave signal includes:

[0020] The scattered microwave signal is analyzed in multiple dimensions by time-domain decomposition, frequency-domain decomposition, and spatial-domain decomposition.

[0021] Phase difference features are extracted from the time domain decomposition results, frequency shift features are extracted from the frequency domain decomposition results, and spatial distribution features are extracted from the spatial domain decomposition results.

[0022] By performing a correlation analysis on the phase difference characteristics, the frequency shift characteristics, and the spatial distribution characteristics, a composite characterization of the multidimensional Doppler phase shift is obtained.

[0023] Preferably, the step of establishing a multi-parameter coupled structural prestress mapping model based on the multi-dimensional Doppler phase shift and combined with environmental parameters to calculate the structural prestress variation value of the steel strand includes:

[0024] Acquire environmental parameters such as ambient temperature, ambient humidity, and structural load;

[0025] Establish the basic mapping relationship between the multidimensional Doppler phase shift and the structural prestress;

[0026] The basic mapping relationship is corrected based on the environmental parameters to obtain a structural prestressing mapping model coupled with environmental parameters;

[0027] By combining the structural prestress variation characteristics at different time scales, a time-parameter coupled structural prestress mapping model is established.

[0028] Based on the structural prestress mapping model coupled with the environmental parameters and the structural prestress mapping model coupled with the time parameters, the structural prestress variation value of the steel strand is calculated.

[0029] Preferably, the step of calculating the prestress loss of the unbonded section, the prestress loss of the anchored section, and the prestress loss of the bonded section of the steel strand based on the prestress change value, respectively, to obtain the overall prestress loss distribution of the steel strand, includes:

[0030] A first microwave transceiver is installed on both sides of the anchor plate of the prestressed concrete structure to monitor the unbonded section;

[0031] A second microwave transceiver is installed on the outside of the prestressed concrete structure to monitor the overall structure;

[0032] The prestress T01 of the unbonded section structure on the left side of the anchor plate and the prestress T02 of the unbonded section structure on the right side of the anchor plate are obtained through the first microwave transceiver device.

[0033] Based on the prestress T01 of the unbonded section structure on the left, calculate the prestress loss △T1 of the left structure of the anchorage section; based on the prestress T02 of the unbonded section structure on the right, calculate the prestress loss △T2 of the right structure of the anchorage section.

[0034] Based on the prestress loss △T1 of the structure on the left side of the anchorage section and the prestress loss △T2 of the structure on the right side of the anchorage section, the prestress loss △T of the bonded section structure is calculated.

[0035] As a preferred option, it also includes:

[0036] The prestress state of the steel strand is assessed and an early warning is provided, including:

[0037] The measured prestress value of the structure is compared with the designed prestress value of the structure, and the prestress deviation rate of the structure is calculated.

[0038] Compare the current prestress value of the structure with the historical prestress value of the structure, and calculate the rate of change of prestress of the structure.

[0039] The prestress state of the steel strand is evaluated based on the prestress deviation rate and the prestress change rate of the structure.

[0040] According to the preset warning level threshold, when the prestress deviation rate or the prestress change rate of the structure exceeds the corresponding threshold, the corresponding level of warning is triggered.

[0041] Preferably, the warning levels include:

[0042] A minor warning is triggered when the prestress deviation rate of the structure exceeds 10% of the design value;

[0043] A moderate warning is triggered when the prestress deviation rate of the structure exceeds 20% of the design value.

[0044] A severe warning is triggered when the prestress deviation rate of the structure exceeds 30% of the design value or when the prestress change rate of the structure is abnormal in the short term.

[0045] Preferably, system calibration and benchmark establishment steps are also included:

[0046] The initial structural prestress value of the steel strand was measured using standard methods as a reference value.

[0047] Multiple sets of microwave scattering data were collected under different environmental conditions to establish an initial mapping relationship;

[0048] Record the initial environmental conditions and initial structural state to establish a benchmark database;

[0049] Regularly calibrate the system to ensure the accuracy of long-term monitoring.

[0050] Preferably, the multidimensional Doppler phase shift includes:

[0051] Absolute phase difference is used to reflect the absolute magnitude of the prestress in a structure;

[0052] The relative phase difference is used to reflect the changing trend of the prestress in the structure;

[0053] Phase difference gradient is used to reflect the spatial distribution of prestress in a structure;

[0054] Center frequency shift is used to reflect the prestress state of the overall structure;

[0055] Spectrum broadening is used to reflect the non-uniformity of prestress distribution in a structure;

[0056] The combined phase-frequency distribution characteristics are used to provide complete information on the prestress state of the structure.

[0057] A microwave detection system for prestress loss in slow-bonding prestressed concrete structures includes:

[0058] The data acquisition module is used to acquire the initial structural prestress data of the steel strands in the prestressed concrete structure.

[0059] A microwave transmitting and receiving module is used to transmit 24GHz microwave signals to the steel strand and receive scattered microwave signals generated by the steel strand;

[0060] The scattering field analysis module is used to construct a three-dimensional scattering field model of the steel strand, extract the multi-scale features of the scattered microwave signal, and obtain the multi-dimensional Doppler phase shift.

[0061] The structural prestress mapping module is used to establish a multi-parameter coupled structural prestress mapping model based on the multi-dimensional Doppler phase shift and combined with environmental parameters, and to calculate the structural prestress variation value of the steel strand;

[0062] The structural prestress loss calculation module is used to calculate the structural prestress loss of the unbonded section, the structural prestress loss of the anchored section, and the structural prestress loss of the bonded section of the steel strand based on the structural prestress change value, so as to obtain the overall structural prestress loss distribution of the steel strand.

[0063] The beneficial effects of this invention include:

[0064] 1. It achieves completely non-destructive detection of structural prestress loss without compromising structural integrity, making it suitable for safety monitoring of existing structures;

[0065] 2. By using 24GHz microwave Doppler technology and multi-dimensional feature extraction, the accuracy of structural prestress detection is greatly improved. The measurement accuracy of structural prestress can reach ±0.5%, which is far superior to traditional methods.

[0066] 3. It innovatively realizes the detection of prestress loss in segmented structures of unbonded sections, anchored sections and bonded sections, providing more comprehensive structural health information;

[0067] 4. By establishing a multi-parameter coupled structural prestress mapping model, the influence of environmental factors on detection accuracy is solved. The system can work stably in a temperature range of -40℃ to 80℃ and a humidity range of 0% to 100%.

[0068] 5. It supports real-time dynamic monitoring and remote data transmission, enabling long-term health monitoring of prestressed structures and early warning of potential risks. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the overall structure of the microwave detection system for prestress loss in slow-bonding prestressed concrete structures according to the present invention.

[0070] Figure 2 This is a schematic diagram of the microwave transceiver arrangement of the present invention;

[0071] Figure 3 This is a schematic diagram of the three-dimensional scattering field model of the present invention;

[0072] Figure 4 This is a flowchart of the multi-dimensional Doppler phase shift extraction process of the present invention;

[0073] Figure 5 This is a schematic diagram of the prestressing mapping model of the multi-parameter coupled structure of the present invention;

[0074] Figure 6 This is a flowchart illustrating the calculation of prestress loss in the segmented structure according to the present invention.

[0075] Figure 7 This is a flowchart of the structural prestress state assessment and early warning process of the present invention. Detailed Implementation

[0076] Please refer to Figure 1 - Figure 7 The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0077] Reference Figure 1The microwave detection system for prestress loss of slow-bonded prestressed concrete structures provided by the present invention includes a data acquisition module 1, a microwave transmission and reception module 2, a scattered field analysis module 3, a structural prestress mapping module 4, a structural prestress loss calculation module 5, and a structural prestress state assessment module 6.

[0078] Data acquisition module 1 is used to acquire the initial structural prestress data of the steel strands in the prestressed concrete structure. Microwave transmitting and receiving module 2 is used to transmit 24GHz microwave signals to the steel strands and receive the scattered microwave signals generated by the steel strands. Scattered field analysis module 3 is used to construct a three-dimensional scattered field model of the steel strands, extract multi-scale features of the scattered microwave signals, and obtain multi-dimensional Doppler phase shifts. Structural prestress mapping module 4 is used to establish a multi-parameter coupled structural prestress mapping model based on multi-dimensional Doppler phase shifts and environmental parameters, and calculate the structural prestress variation value of the steel strands. Structural prestress loss calculation module 5 is used to calculate the structural prestress loss of the unbonded section, the anchored section, and the bonded section of the steel strands according to the structural prestress variation value, obtaining the overall structural prestress loss distribution of the steel strands. Structural prestress state assessment module 6 is used to assess and provide early warning of the structural prestress state of the steel strands.

[0079] Reference Figures 1 to 7 The microwave detection method for prestress loss in slow-bonding prestressed concrete structures provided by the present invention includes the following steps:

[0080] This invention first acquires the initial structural prestress data of the steel strands in the prestressed concrete structure through data acquisition module 1. In practical applications, the initial structural prestress data can be obtained through the following methods:

[0081] (1) During the prestressed construction stage, the tension force is directly measured using a hydraulic sensor and used as the initial prestress value of the structure;

[0082] (2) For existing structures, conventional methods such as vibration method or strain gauge method can be used to measure the initial prestress of the structure and use it as a reference value;

[0083] (3) Obtain the prestress value of the design structure through the design document and make corrections in combination with the construction record.

[0084] Preferably, the initial prestressing data should include basic parameters such as the type and specifications of the steel strand, cross-sectional area, and modulus of elasticity. For example, for a low-relaxation steel strand with a diameter of 15.2 mm, its standard cross-sectional area is 140 mm², and the initial design tension is usually 60% to 70% of the maximum tensile strength. The tensile strength of the prestressed steel strand is generally 1860 MPa, F = 140 mm² * 1860 MPa = 260 kN. Therefore, the tension control force for a single steel strand is approximately 0.6 * F = 156.24 kN.

[0085] This invention transmits a 24GHz microwave signal to a steel strand via a microwave transmitting and receiving module 2, and receives the scattered microwave signal generated by the steel strand. (See reference...) Figure 2 The microwave transceiver is arranged as follows:

[0086] (1) A first microwave transceiver is installed on both sides of the anchor plate of the prestressed concrete structure to monitor the unbonded section;

[0087] (2) A second microwave transceiver is installed on the outside of the prestressed concrete structure to monitor the overall structure.

[0088] Preferably, the microwave transmission power is set at around 20 dBm (100 mW). This power level ensures sufficient signal strength without posing a safety hazard to humans and equipment. The microwave signal frequency of 24 GHz is chosen primarily based on the following considerations: this frequency has strong penetrating power, capable of penetrating concrete protective layers; simultaneously, its short wavelength (approximately 12.5 mm), close to the diameter of steel strand, facilitates a significant scattering effect; furthermore, 24 GHz falls within the Industrial, Scientific and Medical (ISM) band, requiring no special permits for use.

[0089] The microwave receiver employs a multi-channel structure, typically with 4 to 8 receiving channels, each acquiring scattered signals from different directions. The sampling rate of the received signal is set to 1 kHz, which is sufficient to capture minute changes in the prestress of the structure.

[0090] Reference Figure 3 and Figure 4 This invention constructs a three-dimensional scattering field model of steel strand, extracts multi-scale features of the scattered microwave signal, and obtains multi-dimensional Doppler phase shift. The specific implementation method is as follows:

[0091] First, the space surrounding the steel strand is divided into a near-field region and a far-field region. The near-field region mainly focuses on the surface wave effect of the steel strand, while the far-field region mainly focuses on the spatial radiation characteristics.

[0092] In the near-field region, a model is established to show the relationship between surface impedance and structural prestress. When the steel strand is subjected to tension, its surface microstructure changes, leading to a change in electromagnetic wave impedance. Surface impedance The relationship between the prestress T and the structure can be expressed as:

[0093] ,

[0094] in: is the surface impedance of the steel strand, in ohms (Ω). This is the reference value for the surface impedance of steel strand under unstructured prestressed state, in ohms (Ω). is a first-order coefficient representing the linear effect of structural prestress on surface impedance, with units of Ω / kN; , which is a second-order coefficient, representing the nonlinear effect of structural prestress on surface impedance, with units of Ω / kN^{2}; This represents the prestress value of the structure, expressed in kilonewtons (kN).

[0095] For typical prestressed steel strands Approximately 377Ω Approximately 0.05 Ω / kN, Approximately 0.001Ω / kN 2 These parameters can be determined through calibration tests.

[0096] In the far-field region, a model relating the scattering pattern to the structural prestress is established. The slight variations in the geometry of the steel strands under different structural prestresses result in changes in the scattering pattern. (Scattering pattern) With structural prestress The relationship between them can be represented as:

[0097] ,

[0098] in: For structural prestressing The scattering pattern below indicates the scattering direction. The scattering intensity on the surface is dimensionless; This is the reference scattering pattern, representing the scattering direction under unstructured prestressed conditions. The scattering intensity on the surface is dimensionless; The scattering elevation angle represents the angle between the scattering direction and the horizontal plane, expressed in radians. The scattering azimuth angle represents the angle between the projection of the scattering direction onto the horizontal plane and the reference direction, expressed in radians. The prestress influence coefficient represents the degree of influence of prestress on the scattering pattern, and its unit is kN-1. This represents the prestress value of the structure, in kN.

[0099] Preferably, The value range is 0.001~0.005kN-1, and the specific value can be determined experimentally.

[0100] This invention extracts microscale features, mesoscale features, and macroscale features from scattered microwave signals:

[0101] (1) Microscale feature extraction

[0102] Microscopic characteristics primarily reflect the stress distribution within the steel strand, including phase jitter, harmonic distribution, and polarization characteristics. Taking phase jitter as an example, its characteristic parameters... The calculation is as follows:

[0103] ,

[0104] in: The standard deviation of phase jitter represents the degree of phase fluctuation, expressed in radians. Let be the phase value of the i-th sampling point, in radians; The phase mean is equal to The unit is radians; The number of sampling points is dimensionless. Indicates to from arrive Summing all terms.

[0105] (2) Extraction of Mesoscale Features: Mesoscale features mainly reflect the local deformation of the steel strand, including scattering patterns, energy distribution, and spatial correlation. Spatial correlation function The calculation is as follows:

[0106] ,

[0107] in: The interval is The spatial correlation function, representing the interval as... The correlation between the two scattered signals is expressed in units equal to the square of the scattered signal intensity. For the first The intensity of the scattered signal at a spatial point can be a physical quantity such as voltage, power, or electric field strength. Spatial interval, representing the distance between two sampling points, in units of points; The total number of spatial sampling points, dimensionless; Indicates to from arrive Summing all terms.

[0108] (3) Macro-scale feature extraction

[0109] Macroscopic characteristics primarily reflect the overall structural prestress state of the steel strand, including scattering intensity, main lobe direction, and scattering efficiency. Scattering efficiency... The calculation is as follows:

[0110] ,

[0111] in: Scattering efficiency is the ratio of scattered power to incident power, and is dimensionless. Scattered power represents the total power of electromagnetic waves scattered by the steel strand, measured in watts (W). Incident power represents the electromagnetic wave power incident on the steel strand, measured in watts (W).

[0112] This invention performs multi-dimensional analysis of scattered microwave signals through time-domain decomposition, frequency-domain decomposition, and spatial-domain decomposition, and extracts multi-dimensional Doppler phase shifts.

[0113] (1) Time-domain decomposition: The received signal is segmented according to time windows to identify phase shift characteristics within different time periods. A short window (10ms) is used to capture rapidly changing phase shift components, while a long window (1s) is used to capture slowly changing phase shift components. For time-series signals... Its short-time Fourier transform (STFT) is:

[0114] ,

[0115] in: For signal The short-time Fourier transform result indicates that in time... Nearby, frequency The signal components, complex values; A time-series signal, representing a received signal that varies over time, either a real or complex number; A window function is used to select a signal within a specific time period. Commonly used window functions include rectangular window, Hanning window, and Hamming window. This is the time offset, representing the center position of the window function, in seconds (s). Frequency, measured in Hertz (Hz); The imaginary unit, ; For the Fourier transform kernel function; Indicates time Integrals from negative infinity to positive infinity.

[0116] (2) Frequency Domain Decomposition: The signal is converted to the frequency domain to analyze the phase shift characteristics of different frequency components. Center frequency analysis extracts phase shift information within the main frequency band, while sideband frequency analysis extracts phase shift information from the sidebands. Doppler frequency shift. The calculation is as follows:

[0117] ,

[0118] in: Doppler shift represents the offset of the received signal frequency relative to the transmitted signal frequency due to the relative motion of the target, and is measured in Hertz (Hz). The relative velocity of the target is the speed of minute vibrations or deformations of the steel strand, measured in meters per second (m / s). The wavelength of a microwave is equal to the speed of light divided by the frequency. For a 24 GHz microwave, Approximately 12.5 mm, in meters (m); The angle between the incident wave and the direction of motion is expressed in radians. Angle The cosine value of is dimensionless.

[0119] (3) Spatial domain decomposition: Analyzing the phase shift characteristics at different spatial locations, including lateral spatial analysis and longitudinal spatial analysis. Spatial phase distribution. It can be represented as:

[0120] ,

[0121] in: For spatial points The phase at that point, in radians; The phase is a reference point, expressed in radians. The wavelength is microwave, and the unit is meters (m). For spatial points The distance to the source of the emission is expressed in meters (m). The distance from the reference point to the emission source is expressed in meters (m). Wave number represents the phase change per unit distance, expressed in radians per meter (rad / m). These are the three components of the spatial coordinates, with the unit being meters (m).

[0122] Through the above decomposition, the present invention obtains a composite characterization of multidimensional Doppler phase shift, including absolute phase difference, relative phase difference, phase difference gradient, center frequency shift, spectral broadening, and phase-frequency joint distribution characteristics.

[0123] Preferably, the present invention suppresses environmental interference in multi-dimensional Doppler phase shift, including identifying temperature change interference, humidity change interference, and vibration interference, and employing corresponding filtering strategies for suppression. For example, for temperature change interference, adaptive notch filtering is used; for random interference, statistical filtering is used; and for transient interference, time-varying filtering is used.

[0124] Reference Figure 5 This invention establishes a multi-parameter coupled structural prestress mapping model based on multi-dimensional Doppler phase shift and environmental parameters to calculate the structural prestress variation value of steel strands. The specific implementation method is as follows:

[0125] First, a fundamental mapping relationship between multidimensional Doppler phase shift and structural prestress is established. This invention employs a multivariate nonlinear mapping model, expressed as follows:

[0126] ,

[0127] in: This represents the prestress value of the structure, in kilonewtons. The absolute phase difference represents the phase change relative to the reference state, and is expressed in radians. The relative phase difference represents the phase change between adjacent measurement points, expressed in radians. The phase difference gradient represents the rate of change of phase in space, with units of radians per meter. The center frequency shift represents the center value of the Doppler frequency shift, measured in Hertz (Hz). Spectral broadening represents the width of the Doppler frequency shift distribution, measured in Hertz (Hz). The phase-frequency joint distribution characteristics represent the joint statistical properties of phase and frequency, and are dimensionless. This is a mapping function that maps multidimensional features to structural prestress values.

[0128] Mapping function This can be achieved using a polynomial model:

[0129] ,

[0130] in: This represents the prestress value of the structure, in kilonewtons. The coefficient of the constant term is expressed in units of 1000 ppm. These are the coefficients of the first-order term, and their units depend on the corresponding characteristic. Units; These are the coefficients of the second-order terms, and their units depend on the corresponding characteristics. and Units; , For input features, including , , , , and For the number of features, in this example Indicates to from arrive Summing all terms; Indicates all and Summing the combinations, where and All from 1 to .

[0131] Preferably, for prestressed steel strands with a diameter of 15.2 mm, the mapping coefficient is... The value is approximately 800. The value range is 10-1000. The values ​​range from 0.1 to 10. These coefficients can be obtained through experimental calibration.

[0132] Environmental parameters such as ambient temperature, humidity, and structural load are acquired to correct the foundation mapping relationship. The environmental parameter coupling model is represented as follows:

[0133] ,

[0134] in: The prestress value of the structure after taking environmental impact into account is expressed in kilonewtons (kN). The prestress value of the structure obtained from the basic mapping is expressed in kilonewtons (kN). The ambient temperature is expressed in degrees Celsius (°C). For reference temperature, 20℃ is usually taken, and the unit is degrees Celsius (℃). Ambient humidity, expressed as a percentage (%). For reference humidity, 60% is usually taken, and the unit is percentage (%). Structural load, in kilonewtons (kN). This is a reference load, in kilonewtons (kN). The temperature influence coefficient represents the relative change in prestress caused by a unit change in temperature, with units of 1 / ℃. The humidity effect coefficient represents the relative change in structural prestress caused by a unit change in humidity, expressed in units of 1%; The load influence coefficient represents the relative change in prestress of the structure caused by a unit change in load, with units of 1 / kN.

[0135] Preferably, The value range is -0.002~0.001 / ℃. The value range is -0.0005 to 0.0005%. The value range is 0.0001~0.001 / kN. A negative temperature influence coefficient indicates that the prestress of the structure will decrease as the temperature increases, which is consistent with the thermal expansion characteristics of the material.

[0136] By combining the structural prestress variation characteristics at different time scales, a time-parameter coupled structural prestress mapping model is established. The time-parameter coupled model is expressed as:

[0137] ,

[0138] in: The value of the prestress at time t is expressed in kilonewtons (kN). This represents the initial prestress value of the structure, in kilonewtons (kN). It is a short-term time-varying function, representing the law of short-term structural prestress variation, and is dimensionless; It is a time-varying function for the medium term, representing the law of change in prestress in the structure during the medium term, and is dimensionless; It is a long-term time-varying function, representing the law of long-term structural prestress variation, and is dimensionless; This is the short-term time-varying coefficient, representing the magnitude of short-term structural prestress changes, and is dimensionless. The time-varying coefficient represents the magnitude of the change in prestress in the structure during the medium term; it is dimensionless. This is a long-term time-varying coefficient, representing the magnitude of long-term structural prestress variation, and is dimensionless. Time is measured in seconds (s).

[0139] Preferably, short-term time variations mainly consider the influence of daily temperature range. The value ranges from approximately 0.01 to 0.02; the medium-term time-varying range mainly considers the influence of seasonal variations. The value is approximately 0.02~0.05; long-term time-varying parameters mainly consider the effects of material creep and relaxation. The value ranges from approximately 0.05 to 0.15. Short-term time-varying function. A 24-hour periodic sine function or a medium-term time-varying function can be used. A sine function with a 365-day period can be used; a long-term time-varying function can also be used. Logarithmic functions can be used.

[0140] By combining basic mapping relationships, environmental parameter coupling, and time parameter coupling, this invention obtains a comprehensive structural prestress mapping model to calculate the structural prestress variation value of steel strands.

[0141] Reference Figure 6 This invention calculates the prestress loss of the unbonded section, the anchored section, and the bonded section of the steel strand based on the change in prestress, thus obtaining the overall prestress loss distribution of the steel strand. The specific implementation method is as follows:

[0142] The prestress T01 of the unbonded section on the left side of the anchor plate and the prestress T02 of the unbonded section on the right side of the anchor plate are obtained through the first microwave transceiver located on both sides of the anchor plate. The formula for calculating the prestress of the unbonded section is as follows:

[0143] ,

[0144] ,

[0145] in: The prestress is expressed as kN for the unbonded section of the anchor plate. ); The prestress is expressed as kN in the unbonded section of the anchor plate. ); The initial prestress of the structure is expressed in kilonewtons (kN). ); The value represents the relative prestress loss of the unbonded section on the left side of the anchor plate, which is dimensionless and represents the ratio of the lost prestress to the initial prestress. The value represents the relative prestress loss of the unbonded section on the right side of the anchor plate. It is dimensionless and represents the ratio of the lost prestress to the initial prestress.

[0146] Preferably, the prestress loss in the unbonded section structure mainly comes from friction loss and strand relaxation, with a typical value of about 5% to 10% of the initial structural prestress.

[0147] The prestress loss ΔT1 of the left anchorage section is calculated based on the prestress T01 of the unbonded section on the left side, and the prestress loss ΔT2 of the right anchorage section is calculated based on the prestress T02 of the unbonded section on the right side. The formula for calculating the prestress loss of the anchorage section structure is as follows:

[0148] ,

[0149] ,

[0150] in: The prestress loss of the structure on the left side of the anchorage section is expressed in kilonewtons (kN). ); The prestress loss of the structure on the right side of the anchorage section is expressed in kilonewtons (kN). ); The prestress is expressed as kN for the unbonded section of the anchor plate. ); The prestress is expressed as kN in the unbonded section of the anchor plate. ); The friction coefficient of the anchorage section represents the proportion of prestress loss per unit length of the structure, with units of 1 / meter. ); The length of the anchorage section is in meters (m). ).

[0151] Preferably, the friction coefficient of the anchoring section The value ranges from 0.02 to 0.05 / m, and the anchorage section length is typically 0.5 to 2m. The prestress loss in the anchorage section mainly comes from the friction between the anchoring clamp and the steel strand, with a typical value of about 3% to 8% of the prestress in the unbonded section.

[0152] Based on the prestress loss ΔT1 on the left side of the anchorage section and the prestress loss ΔT2 on the right side of the anchorage section, the prestress loss ΔT in the bonded section is calculated. The formula for calculating the prestress loss in the bonded section is:

[0153] ,

[0154] Simplifying, we get:

[0155] ,

[0156] in: The prestress loss of the bonded section structure is expressed in kilonewtons. T01 represents the initial structural prestress, in kilonewtons (kN); T01 represents the structural prestress of the unbonded section on the left side of the anchor plate, in kilonewtons (kN). The prestress is the structural prestress of the unbonded section on the right side of the anchor plate, and the unit is kilonewtons (kN). The prestress loss of the structure on the left side of the anchorage section is expressed in kilonewtons (kN). The value represents the prestress loss of the structure on the right side of the anchorage section, expressed in kilonewtons (kN).

[0157] Preferably, the prestress loss in the bonded section structure mainly comes from concrete shrinkage, creep, and steel strand relaxation, with typical values ​​of about 10% to 20% of the initial prestress.

[0158] By calculating the prestress loss of the unbonded section, the anchored section, and the bonded section, this invention obtains the overall prestress loss distribution of the steel strand, providing an important basis for structural health assessment.

[0159] Reference Figure 7 This invention assesses and provides early warning of the prestress state of steel strand structures. Specific implementation methods are as follows:

[0160] The measured prestress values ​​of the structure are compared with the designed prestress values ​​of the structure, and the prestress deviation rate of the structure is calculated.

[0161] ,

[0162] in: The prestress deviation rate represents the relative deviation between the measured prestress value and the designed prestress value of the structure, expressed as a percentage (%). The unit for measuring the prestress value of the structure is kilonewtons (kN). The prestress value for the design structure is expressed in kilonewtons (kN). The value represents the relative deviation and is dimensionless; 100% is the percentage conversion factor.

[0163] Compare the current prestress value of the structure with the historical prestress values ​​of the structure, and calculate the rate of change of prestress in the structure:

[0164] ,

[0165] in: The prestress change rate of the structure represents the proportion of change of the current prestress value of the structure relative to the previous measured prestress value, expressed as a percentage (%). This represents the current prestress value of the structure, in kilonewtons (kN). The value of the prestress in the structure was measured last time, and the unit is kilonewtons (kN). The change is relative and dimensionless; 100% is a percentage conversion factor.

[0166] The prestress state of the steel strand is evaluated based on the prestress deviation rate and the prestress change rate.

[0167] Preferably, the present invention also performs an overall structural prestress distribution assessment and a prestress variation trend assessment. The overall structural prestress distribution assessment evaluates the uniformity of prestress distribution by calculating the standard deviation of prestress at different locations; the prestress variation trend assessment predicts future prestress variation trends through time series analysis.

[0168] Based on preset warning level thresholds, a warning of the corresponding level is triggered when the prestress deviation rate or prestress change rate of the structure exceeds the corresponding threshold. Warning levels include:

[0169] (1) Minor warning: Triggered when the prestress deviation rate of the structure exceeds 10% of the design value. The corresponding measure is to increase the monitoring frequency and pay attention to the changing trend.

[0170] (2) Moderate warning: Triggered when the prestress deviation rate of the structure exceeds 20% of the design value. The corresponding measures are to arrange professional personnel to conduct on-site inspections and prepare intervention plans.

[0171] (3) Severe warning: This is triggered when the prestress deviation rate of the structure exceeds 30% of the design value or when the prestress change rate of the structure is abnormal in the short term. The corresponding measures are to immediately take temporary reinforcement measures and formulate an emergency response plan.

[0172] The warning threshold is set based on structural safety assessment standards and engineering experience. A deviation rate of 10% is usually within the normal fluctuation range; a deviation rate of 20% may lead to a decline in structural performance, but has not yet reached a dangerous level; a deviation rate of 30% may lead to a significant reduction in the structural load-bearing capacity, requiring immediate intervention.

[0173] Preferably, the present invention also provides an early warning information release function, including generating an early warning report, sending early warning information through a preset channel, and displaying the early warning information on the system interface.

[0174] The present invention also includes system calibration and benchmark establishment steps, the specific implementation of which is as follows:

[0175] The initial structural prestress of the steel strand is measured using standard methods as a reference value. Commonly used standard methods include the hydraulic pressure sensor method and the vibration method. For example, using a hydraulic pressure sensor to measure tension force can achieve an accuracy of ±1%, serving as a reference value for system calibration.

[0176] Multiple sets of microwave scattering data were collected under different environmental conditions to establish an initial mapping relationship. Typically, data sets were collected every 5°C within a temperature range of 5–25°C, and every 20% within a humidity range of 30%–90%, in order to establish a comprehensive environmental impact model.

[0177] Record the initial environmental conditions and initial structural state to establish a benchmark database. The benchmark database includes:

[0178] (1) Environmental parameter baseline: Record initial environmental parameters such as temperature, humidity, and atmospheric pressure;

[0179] (2) Structural parameter benchmarks: Record structural parameters such as structural deformation, displacement, and vibration frequency;

[0180] (3) Scattering signal reference: Record the characteristics of the scattering signal in the initial state.

[0181] Regularly calibrate the system to ensure long-term monitoring accuracy. The calibration cycle is determined based on structural importance and environmental conditions, typically every 3 to 6 months.

[0182] The calibration methods include reference point calibration, historical data optimization, and multi-point collaborative optimization. Reference point calibration is performed using known prestressing points on the structure for systematic calibration; historical data optimization utilizes historical data to optimize current measurements; and multi-point collaborative optimization utilizes data from multiple measurement points for overall optimization.

[0183] The microwave detection system for prestress loss in slow-bonding prestressed concrete structures of this invention can be applied to various prestressed concrete structures such as bridges, high-rise buildings, and large storage tanks. The system has the following characteristics:

[0184] (1) High hardware system feasibility: 24GHz microwave radar modules have been widely used in automobiles, security and other fields. The technology is mature and the cost is moderate. The core algorithm can be implemented on existing DSP or FPGA platforms. Environmental parameter sensors can be integrated into the system through standard interfaces.

[0185] (2) High software system feasibility: The system adopts a modular design with high cohesion and low coupling, which is convenient for maintenance and upgrading; it provides a standardized data interface and can be seamlessly integrated with existing structural monitoring systems.

[0186] (3) Implementation-friendly: The system components are small in size and can be directly installed on the outside of the prestressed structure without complicated construction; the sleep-wake mechanism is adopted, the power consumption is controlled below 5W, and long-term monitoring can be achieved through solar power; remote upgrades and fault diagnosis are supported, reducing maintenance costs.

[0187] In practical engineering applications, the system of this invention has been piloted in several long-span bridges and high-rise buildings, achieving good results. It has a detection accuracy better than ±0.5%, strong environmental adaptability, and can operate stably within a temperature range of -40℃ to 80℃ and a humidity range of 0% to 100%, providing reliable technical support for structural health monitoring.

[0188] The present invention provides a microwave detection method and system for prestress loss in loosely bonded prestressed concrete structures. By establishing a mapping relationship between the microwave scattering field and the prestress state of the structure, it achieves high-precision, non-destructive, and real-time monitoring of prestress loss in prestressed steel strand structures. The system employs core technologies such as a multi-dimensional scattering field model, multi-dimensional Doppler phase shift extraction technology, and a multi-parameter coupled structural prestress mapping model, solving the problems of insufficient accuracy and poor adaptability of traditional methods in complex environments. Through a segmented detection strategy of unbonded sections, anchored sections, and bonded sections, the system can comprehensively evaluate the prestress state of prestressed structures, providing reliable data support for structural health monitoring and safety assessment.

[0189] This invention is of great significance for improving the safety of prestressed structures, extending their service life, and reducing maintenance costs, and has broad prospects for engineering applications.

[0190] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A microwave detection method for prestress loss in slow-bonding prestressed concrete structures, characterized in that, include: Obtain the initial structural prestress data of steel strands in prestressed concrete structures; Transmit a 24GHz microwave signal to the steel strand and receive the scattered microwave signal generated by the steel strand; A three-dimensional scattering field model of the steel strand is constructed, and the multi-scale features of the scattered microwave signal are extracted to obtain the multi-dimensional Doppler phase shift. Based on the multi-dimensional Doppler phase shift and combined with environmental parameters, a multi-parameter coupled structural prestress mapping model is established to calculate the structural prestress variation value of the steel strand. Based on the structural prestress variation value, the prestress loss of the unbonded section, the prestress loss of the anchoring section, and the prestress loss of the bonded section of the steel strand are calculated respectively to obtain the overall structural prestress loss distribution of the steel strand. Based on the changes in prestress in the structure, the prestress loss in the unbonded section, the prestress loss in the anchored section, and the prestress loss in the bonded section of the steel strand are calculated respectively to obtain the overall prestress loss distribution of the steel strand, including: A first microwave transceiver is installed on both sides of the anchor plate of the prestressed concrete structure to monitor the unbonded section; A second microwave transceiver is installed on the outside of the prestressed concrete structure to monitor the overall structure; The prestress T01 of the unbonded section structure on the left side of the anchor plate and the prestress T02 of the unbonded section structure on the right side of the anchor plate are obtained through the first microwave transceiver device. Based on the prestress T01 of the unbonded section structure on the left, calculate the prestress loss △T1 of the left structure of the anchorage section; based on the prestress T02 of the unbonded section structure on the right, calculate the prestress loss △T2 of the right structure of the anchorage section. Based on the prestress loss △T1 of the structure on the left side of the anchorage section and the prestress loss △T2 of the structure on the right side of the anchorage section, the prestress loss △T of the bonded section structure is calculated.

2. The microwave detection method for prestress loss in a slow-bonding prestressed concrete structure according to claim 1, characterized in that, The construction of a three-dimensional scattering field model of the steel strand, extraction of multi-scale features of the scattered microwave signal, and obtaining multi-dimensional Doppler phase shifts include: The space surrounding the steel strand is divided into a near-field region and a far-field region; A model relating surface impedance to structural prestress is established in the near-field region, and a model relating scattering pattern to structural prestress is established in the far-field region. Microscopic, mesoscopic, and macroscopic features of the scattered microwave signal are extracted. The microscale features, mesoscale features, and macroscale features are fused and enhanced to obtain the multidimensional Doppler phase shift.

3. The microwave detection method for prestress loss in a slow-bonding prestressed concrete structure according to claim 2, characterized in that, The extraction of microscale, mesoscale, and macroscale features of the scattered microwave signal includes: The scattered microwave signal is analyzed in multiple dimensions by time-domain decomposition, frequency-domain decomposition, and spatial-domain decomposition. Phase difference features are extracted from the time domain decomposition results, frequency shift features are extracted from the frequency domain decomposition results, and spatial distribution features are extracted from the spatial domain decomposition results. By performing a correlation analysis on the phase difference characteristics, the frequency shift characteristics, and the spatial distribution characteristics, a composite characterization of the multidimensional Doppler phase shift is obtained.

4. The microwave detection method for prestress loss in a slow-bonding prestressed concrete structure according to claim 1, characterized in that, Based on the multi-dimensional Doppler phase shift and combined with environmental parameters, a multi-parameter coupled structural prestress mapping model is established to calculate the structural prestress variation value of the steel strand, including: Obtain environmental parameters such as ambient temperature, ambient humidity, and structural load; Establish the basic mapping relationship between the multidimensional Doppler phase shift and the structural prestress; The basic mapping relationship is corrected based on the environmental parameters to obtain a structural prestressing mapping model coupled with environmental parameters; By combining the structural prestress variation characteristics at different time scales, a time-parameter coupled structural prestress mapping model is established. Based on the structural prestress mapping model coupled with the environmental parameters and the structural prestress mapping model coupled with the time parameters, the structural prestress variation value of the steel strand is calculated.

5. The microwave detection method for prestress loss in a slow-bonding prestressed concrete structure according to claim 1, characterized in that, Also includes: The prestress state of the steel strand is assessed and an early warning is provided, including: The measured prestress value of the structure is compared with the designed prestress value of the structure, and the prestress deviation rate of the structure is calculated. Compare the current prestress value of the structure with the historical prestress value of the structure, and calculate the rate of change of prestress of the structure. The prestress state of the steel strand is evaluated based on the prestress deviation rate and the prestress change rate of the structure. According to the preset warning level threshold, when the prestress deviation rate or the prestress change rate of the structure exceeds the corresponding threshold, the corresponding level of warning is triggered.

6. The microwave detection method for prestress loss in a slow-bonding prestressed concrete structure according to claim 5, characterized in that, The warning levels include: A minor warning is triggered when the prestress deviation rate of the structure exceeds 10% of the design value; A moderate warning is triggered when the prestress deviation rate of the structure exceeds 20% of the design value. A severe warning is triggered when the prestress deviation rate of the structure exceeds 30% of the design value or when the prestress change rate of the structure is abnormal in the short term.

7. The microwave detection method for prestress loss in a slow-bonding prestressed concrete structure according to claim 1, characterized in that, It also includes system calibration and benchmark establishment steps: The initial structural prestress value of the steel strand was measured using standard methods as a reference value. Multiple sets of microwave scattering data were collected under different environmental conditions to establish an initial mapping relationship; Record the initial environmental conditions and initial structural state to establish a benchmark database; Regularly calibrate the system to ensure the accuracy of long-term monitoring.

8. The microwave detection method for prestress loss in a slow-bonding prestressed concrete structure according to claim 1, characterized in that, The multidimensional Doppler phase shift includes: Absolute phase difference is used to reflect the absolute magnitude of the prestress in a structure; The relative phase difference is used to reflect the changing trend of the prestress in the structure; Phase difference gradient is used to reflect the spatial distribution of prestress in a structure; Center frequency shift is used to reflect the prestress state of the overall structure; Spectrum broadening is used to reflect the non-uniformity of prestress distribution in a structure; The combined phase-frequency distribution characteristics are used to provide complete information on the prestress state of the structure.

9. A microwave detection system for prestress loss in slow-bonded prestressed concrete structures, used to implement the microwave detection method for prestress loss in slow-bonded prestressed concrete structures as described in any one of claims 1-8, characterized in that, include: The data acquisition module is used to acquire the initial structural prestress data of the steel strands in the prestressed concrete structure. A microwave transmitting and receiving module is used to transmit 24GHz microwave signals to the steel strand and receive scattered microwave signals generated by the steel strand; The scattering field analysis module is used to construct a three-dimensional scattering field model of the steel strand, extract the multi-scale features of the scattered microwave signal, and obtain the multi-dimensional Doppler phase shift. The structural prestress mapping module is used to establish a multi-parameter coupled structural prestress mapping model based on the multi-dimensional Doppler phase shift and combined with environmental parameters, and to calculate the structural prestress variation value of the steel strand; The structural prestress loss calculation module is used to calculate the structural prestress loss of the unbonded section, the structural prestress loss of the anchored section, and the structural prestress loss of the bonded section of the steel strand based on the structural prestress change value, so as to obtain the overall structural prestress loss distribution of the steel strand.

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