A vertical prestressed tendon tension detection method and system using a direct current circuit

Abstract

The application discloses a vertical prestressed tendon tension detection method and system using a direct current circuit, and belongs to the technical field of tension detection, and comprises the following steps: connecting low-resistance conductors at both ends of vertical prestressed tendons to form a closed direct current circuit with a direct current resistance tester, acquiring real-time resistance values and obtaining resistance change amounts; calculating the current length and the current cross-sectional area of the prestressed tendon according to the resistance change amount and the Poisson ratio; and establishing a resistance-tension mapping model based on the elastic modulus, the current length and the current cross-sectional area, and calculating a current tension value. The application realizes nondestructive, continuous and high-precision detection of the tension of the vertical prestressed tendon through direct current resistance measurement, supports long-term automatic monitoring and loss early warning, and is low in cost and strong in environmental adaptability.

Description

Technical Field

[0001] This invention relates to the field of tension detection technology, and more specifically to a method and system for detecting the tension of vertical prestressed tendons using a DC circuit. Background Technology

[0002] Diagonal cracks in the web of bridges are a common type of defect in prestressed concrete bridges, seriously affecting the durability and load-bearing capacity of the structure. Studies have shown that the occurrence and development of diagonal cracks in the web are closely related to the tension control of the vertical prestressing tendons. Due to the short length of the vertical prestressing tendons, after tensioning and backfilling, the anchorages (wedges) will experience slight retraction, leading to a loss of prestress, and this loss is particularly significant in the vertical prestressing tendons.

[0003] Current technology primarily relies on hydraulic pressure gauge readings during tensioning to control tension. However, these gauges measure instantaneous oil pressure during tensioning and cannot reflect the actual prestress after anchoring. Once anchoring is complete, changes in the tension of the prestressing tendons cannot be effectively monitored using conventional methods. This prevents targeted secondary tensioning or remedial measures, ultimately leading to insufficient vertical prestress, causing web cracking, reducing structural service life, and even affecting the bridge's load-bearing safety.

[0004] Therefore, how to provide a method and system for detecting the tension of prestressed tendons after anchoring is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method and system for detecting the tension of vertical prestressing tendons using a DC circuit. By measuring the resistance change of the prestressing tendon in the DC circuit and combining it with material mechanical parameters, the tension change value is accurately calculated, thereby achieving non-destructive testing of the actual tension of the vertical prestressing tendon after anchoring.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, the present invention provides a method for detecting the tension of vertical prestressed tendons using a DC circuit, comprising: Low-resistance wires are connected to both ends of the vertical prestressing tendon, and the low-resistance wires are connected to a DC resistance tester to form a closed DC circuit between the vertical prestressing tendon and the DC resistance tester, thereby obtaining the real-time resistance value and the resistance change. The length and cross-sectional area of ​​the vertical prestressing tendons are calculated based on the resistance change value and Poisson's ratio. Based on the elastic modulus, length, and cross-sectional area of ​​the vertical prestressing tendons, a resistance-tension mapping model is established to calculate the current tension value.

[0007] Preferably, obtaining the current change value specifically includes: When the vertical prestressing tendon is in a stress-free state, the initial resistance value of the vertical prestressing tendon is measured and recorded by the DC resistance tester. After the vertical prestressing tendons are tensioned and anchored, the current resistance value of the vertical prestressing tendons is measured and recorded using the DC resistance tester. The resistance change is calculated based on the initial resistance value and the current resistance value.

[0008] Preferably, the length and cross-sectional area of ​​the vertical prestressing tendons are calculated based on the resistance change value, specifically including: Obtain the initial length L0 and initial cross-sectional area A0 of the vertical prestressed tendon in the stress-free state; The rate of change of resistance is obtained from the resistance change ΔR and the initial resistance value R0. Combined with Poisson's ratio, the longitudinal strain v is calculated as follows:

[0009] Calculate the current length L of the vertical prestressing tendon based on the initial length L0 and the longitudinal strain value ε:

[0010] Based on the initial cross-sectional area A0, the Poisson's ratio ν, and the longitudinal strain value ε, calculate the current cross-sectional area A of the vertical prestressing tendon: .

[0011] Preferably, based on the elastic modulus, Poisson's ratio, length, and cross-sectional area of ​​the vertical prestressing tendons, a resistance-tension mapping model is established to calculate the current tension value, including: Obtain the elastic modulus E of the vertical prestressing tendon; Based on the elastic modulus, length, and cross-sectional area, a resistance-tension mapping model is constructed to obtain the current tension value: .

[0012] Preferably, the method further includes: A time-varying resistance monitoring sequence was established, and the prestress loss time history was fitted using an exponential decay model:

[0013] Where ΔR0 is the change in resistance at the instant the anchoring is completed, ΔR ∞ The resistance change after long-term stabilization is given by β, where β is the attenuation coefficient. Based on the attenuation coefficient β obtained from the fitting and the long-term stable resistance change ΔR... ∞ The resistance change at future moments is predicted and substituted into the resistance-tension mapping model to calculate the predicted tension value. When the predicted tension value is lower than the preset value, a tension loss warning message is output.

[0014] On the other hand, the present invention provides a vertical prestressing tendon tension detection system utilizing a DC circuit, comprising: Low-resistance wires are used to connect vertical prestressing tendons to a DC resistance tester to form a closed DC circuit. A DC resistance tester is used to measure resistance values. The initial parameter acquisition module is used to acquire the initial length L0, initial cross-sectional area A0, elastic modulus E, and Poisson's ratio v of the vertical prestressing tendon; The resistance change calculation module is used to calculate the resistance change value and the resistance change rate based on the initial resistance value and the current resistance value measured by the DC resistance tester. The geometric parameter calculation module is used to calculate the current length L and current cross-sectional area A of the vertical prestressing tendon based on the resistance change rate, the Poisson's ratio v, the initial length L0 and the initial cross-sectional area A0. The tension mapping model module is used to establish a resistance-tension mapping model and calculate the current tension value based on the elastic modulus E, the current length L, the current cross-sectional area A, and the rate of change of resistance. The output module is used to output the current tension value.

[0015] Preferably, the system further includes: The tension prediction module is used to establish a time-varying resistance monitoring sequence, fit the prestress loss time history with an exponential decay model, predict the resistance change at future moments, and substitute it into the resistance-tension mapping model to calculate the predicted tension value. The early warning module is used to output tension loss early warning information when the predicted tension value is lower than the preset value.

[0016] As can be seen from the above technical solution, compared with the prior art, this invention discloses a method and system for detecting the tension of vertical prestressed tendons using a DC circuit. By constructing a closed DC circuit at both ends of the prestressed tendon, the change in resistance value after anchoring is directly measured. Combined with a resistance-tension mapping model established by the Poisson effect, the actual tension value of the prestressed tendon is calculated. This method does not require disassembling the anchorage or damaging the structure, achieving non-destructive testing of the prestress after anchoring. Testing can be completed with only low-resistance wires and a DC resistance tester, eliminating the need for strain gauges, sensors, or large testing equipment. On-site operation only requires connecting the wires and reading the resistance value; a single person can quickly complete the testing of multiple vertical prestressed tendons, significantly reducing testing costs and time. Furthermore, this invention establishes a time-varying resistance monitoring sequence, uses an exponential decay model to fit the prestress loss time history, and predicts the tension value at future moments using the obtained decay coefficient and long-term stable resistance change. An early warning is issued when the predicted tension is lower than a preset value. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the process provided by the present invention.

[0019] Figure 2 This is a schematic diagram of the structure provided by the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention discloses a method for detecting the tension of vertical prestressed tendons using a DC circuit, such as... Figure 1 As shown, it includes: Low-resistance wires are connected to both ends of the vertical prestressing tendon, and the low-resistance wires are connected to a DC resistance tester to form a closed DC circuit between the vertical prestressing tendon and the DC resistance tester, thereby obtaining the real-time resistance value and the resistance change.

[0022] The low-resistance conductors employ a four-wire Kelvin connection method, where each end is connected to two independent conductors: one for applying a constant DC current (I+, I-), and the other for measuring the voltage drop (V+, V-), thus completely eliminating the influence of conductor resistance and contact resistance on the measurement results. The connection points are soldered or brazed and wrapped with waterproof insulating tape to prevent corrosion that could cause fluctuations in contact resistance.

[0023] The DC resistance tester uses a high-precision micro-ohmmeter or a digital low-resistance tester with a resolution of no less than 0.1 μΩ and a measurement range covering 0.1 mΩ to 100 Ω. The output constant DC current ranges from 1 A to 10 A (selected based on the cross-sectional area of ​​the prestressing tendon, with a current density not exceeding 5 A / mm²). 2 To avoid the Joule heating effect, the pulsed DC reverse method is used to eliminate the thermoelectric potential and contact potential, that is, the forward and reverse currents are applied alternately, and the resistance is calculated by taking the average of the two voltages.

[0024] Furthermore, to improve measurement accuracy, this embodiment of the invention installs a high-precision temperature sensor on the surface of the prestressed tendon while simultaneously measuring the ambient temperature. A temperature-resistance correction model is established:

[0025] Where, α T The temperature coefficient of resistance of the prestressing tendon material (α for steel strand) T (≈0.0065 / ℃), where T is the reference temperature during stress-free calibration (e.g., 20℃). Temperature data is acquired in real time, and online temperature compensation is performed on the resistance value to eliminate pseudo-resistance changes caused by temperature drift.

[0026] The length and cross-sectional area of ​​the vertical prestressing tendons are calculated based on the resistance change value and Poisson's ratio. Based on the elastic modulus, length, and cross-sectional area of ​​the vertical prestressing tendons, a resistance-tension mapping model is established to calculate the current tension value.

[0027] Furthermore, the change in current is obtained, specifically including: When the vertical prestressing tendons are in a stress-free state, the initial resistance value of the vertical prestressing tendons is measured and recorded using the DC resistance tester. The stress-free state should be achieved under conditions where the prestressing tendons are freely suspended, not subjected to any axial force, and the ambient temperature is stable. If these conditions cannot be met on-site, a comparative sample bar method can be used. Under the same environmental conditions, the resistance of a standard sample bar of the same material and cross-section, without stress, can be measured as a reference value.

[0028] After the vertical prestressing tendons are tensioned and anchored, the current resistance value of the vertical prestressing tendons is measured and recorded using the DC resistance tester. For structures already in service, if there is no initial stress-free resistance record, a partial unloading method can be used: a clamping device is temporarily installed on the exposed section of the prestressing tendon and the stress in that section is completely unloaded, and its resistance is measured as an approximate value of R0. The influence of residual stress is then corrected using finite element analysis.

[0029] The resistance change is calculated based on the initial resistance value and the current resistance value.

[0030] Preferably, the length and cross-sectional area of ​​the vertical prestressing tendons are calculated based on the resistance change value, specifically including: Obtain the initial length L0 and initial cross-sectional area A0 of the vertical prestressed tendon in the stress-free state; The rate of change of resistance is obtained from the resistance change ΔR and the initial resistance value R0. Combined with Poisson's ratio, the longitudinal strain v is calculated as follows:

[0031] Calculate the current length L of the vertical prestressing tendon based on the initial length L0 and the longitudinal strain value ε:

[0032] Based on the initial cross-sectional area A0, the Poisson's ratio ν, and the longitudinal strain value ε, calculate the current cross-sectional area A of the vertical prestressing tendon: .

[0033] Preferably, based on the elastic modulus, Poisson's ratio, length, and cross-sectional area of ​​the vertical prestressing tendons, a resistance-tension mapping model is established to calculate the current tension value, including: Obtain the elastic modulus E of the vertical prestressing tendon; Based on the elastic modulus, length, and cross-sectional area, a resistance-tension mapping model is constructed to obtain the current tension value: .

[0034] Preferably, the method further includes: A time-varying resistance monitoring sequence was established, and the prestress loss time history was fitted using an exponential decay model:

[0035] Where ΔR0 is the change in resistance at the instant the anchoring is completed, ΔR ∞ The resistance change after long-term stabilization is given by β, where β is the attenuation coefficient. Based on the attenuation coefficient β obtained from the fitting and the long-term stable resistance change ΔR... ∞The resistance change at future moments is predicted and substituted into the resistance-tension mapping model to calculate the predicted tension value. When the predicted tension value is lower than the preset value, a tension loss warning message is output.

[0036] On the other hand, the present invention provides a vertical prestressing tendon tension detection system utilizing a DC circuit, such as... Figure 2 As shown, it includes: Low-resistance wires are used to connect vertical prestressing tendons to a DC resistance tester to form a closed DC circuit. A DC resistance tester is used to measure resistance values. The initial parameter acquisition module is used to acquire the initial length L0, initial cross-sectional area A0, elastic modulus E, and Poisson's ratio v of the vertical prestressing tendon; The resistance change calculation module is used to calculate the resistance change value and the resistance change rate based on the initial resistance value and the current resistance value measured by the DC resistance tester. The geometric parameter calculation module is used to calculate the current length L and current cross-sectional area A of the vertical prestressing tendon based on the resistance change rate, the Poisson's ratio v, the initial length L0 and the initial cross-sectional area A0. The tension mapping model module is used to establish a resistance-tension mapping model and calculate the current tension value based on the elastic modulus E, the current length L, the current cross-sectional area A, and the rate of change of resistance. The output module is used to output the current tension value.

[0037] Preferably, the system further includes: The tension prediction module is used to establish a time-varying resistance monitoring sequence, fit the prestress loss time history with an exponential decay model, predict the resistance change at future moments, and substitute it into the resistance-tension mapping model to calculate the predicted tension value. The early warning module is used to output tension loss early warning information when the predicted tension value is lower than the preset value.

[0038] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0039] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting the tension of vertical prestressed tendons using a DC circuit, characterized in that, include: Low-resistance wires are connected to both ends of the vertical prestressing tendon, and the low-resistance wires are connected to a DC resistance tester to form a closed DC circuit between the vertical prestressing tendon and the DC resistance tester, thereby obtaining the real-time resistance value and the resistance change. The length and cross-sectional area of ​​the vertical prestressing tendons are calculated based on the resistance change value and Poisson's ratio. Based on the elastic modulus, length, and cross-sectional area of ​​the vertical prestressing tendons, a resistance-tension mapping model is established to calculate the current tension value.

2. The method for detecting the tension of vertical prestressed tendons using a DC circuit according to claim 1, characterized in that, Obtaining current change values ​​specifically includes: When the vertical prestressing tendon is in a stress-free state, the initial resistance value of the vertical prestressing tendon is measured and recorded by the DC resistance tester. After the vertical prestressing tendons are tensioned and anchored, the current resistance value of the vertical prestressing tendons is measured and recorded using the DC resistance tester. The resistance change is calculated based on the initial resistance value and the current resistance value.

3. The method for detecting the tension of vertical prestressed tendons using a DC circuit according to claim 2, characterized in that, The length and cross-sectional area of ​​the vertical prestressing tendons are calculated based on the resistance change value, specifically including: Obtain the initial length L0 and initial cross-sectional area A0 of the vertical prestressed tendon in the stress-free state; The rate of change of resistance is obtained from the resistance change ΔR and the initial resistance value R0. Combined with Poisson's ratio, the longitudinal strain v is calculated as follows: Calculate the current length L of the vertical prestressing tendon based on the initial length L0 and the longitudinal strain value ε: Based on the initial cross-sectional area A0, the Poisson's ratio ν, and the longitudinal strain value ε, calculate the current cross-sectional area A of the vertical prestressing tendon: 。 4. The method for detecting the tension of vertical prestressed tendons using a DC circuit according to claim 1, characterized in that, Based on the elastic modulus, Poisson's ratio, length, and cross-sectional area of ​​the vertical prestressing tendons, a resistance-tension mapping model is established to calculate the current tension value, including: Obtain the elastic modulus E of the vertical prestressing tendon; Based on the elastic modulus, length, and cross-sectional area, a resistance-tension mapping model is constructed to obtain the current tension value: 。 5. The method for detecting the tension of vertical prestressed tendons using a DC circuit according to claim 1, characterized in that, The method further includes: A time-varying resistance monitoring sequence was established, and the prestress loss time history was fitted using an exponential decay model: Where ΔR0 is the instantaneous change in resistance upon completion of anchoring, ΔR ∞ The resistance change after long-term stabilization is given by β, where β is the attenuation coefficient. Based on the attenuation coefficient β obtained from the fitting and the long-term stable resistance change ΔR... ∞ The resistance change at future moments is predicted and substituted into the resistance-tension mapping model to calculate the predicted tension value. When the predicted tension value is lower than the preset value, a tension loss warning message is output.

6. A vertical prestressing tendon tension detection system utilizing a DC circuit, characterized in that, include: Low-resistance wires are used to connect vertical prestressing tendons to a DC resistance tester to form a closed DC circuit. A DC resistance tester is used to measure resistance values. The initial parameter acquisition module is used to acquire the initial length L0, initial cross-sectional area A0, elastic modulus E, and Poisson's ratio v of the vertical prestressing tendon; The resistance change calculation module is used to calculate the resistance change value and the resistance change rate based on the initial resistance value and the current resistance value measured by the DC resistance tester. The geometric parameter calculation module is used to calculate the current length L and current cross-sectional area A of the vertical prestressing tendon based on the resistance change rate, the Poisson's ratio v, the initial length L0 and the initial cross-sectional area A0. The tension mapping model module is used to establish a resistance-tension mapping model and calculate the current tension value based on the elastic modulus E, the current length L, the current cross-sectional area A, and the rate of change of resistance. The output module is used to output the current tension value.

7. A vertical prestressing tendon tension detection system utilizing a DC circuit according to claim 1, characterized in that, The system also includes: The tension prediction module is used to establish a time-varying resistance monitoring sequence, fit the prestress loss time history with an exponential decay model, predict the resistance change at future moments, and substitute it into the resistance-tension mapping model to calculate the predicted tension value. The early warning module is used to output tension loss early warning information when the predicted tension value is lower than the preset value.

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