Method for identifying prestressed tendon tension under anchor based on piezoelectric sensing

Abstract

The application provides a prestressed tendon tension force identification method based on piezoelectric sensing, which is applied to a porous anchoring system using the post-tensioning method, and comprises the following steps: flattening the contact interface of the porous anchoring system; arranging a plurality of pairs of piezoelectric sheets on the bottom side of the anchor head of the porous anchoring system to form a piezoelectric array; obtaining the piezoelectric signals of each pair of piezoelectric sheets in the piezoelectric array, respectively processing the piezoelectric signals to obtain corresponding receiving coefficients, and constructing a piezoelectric monitoring index dataset based on the receiving coefficients; calculating the average pressure of the test interface area based on a preset fitting function and the piezoelectric monitoring index dataset, and constructing an average pressure dataset of the test interface area; solving an influence matrix based on a mechanical method or a finite element method; and calculating a prestressed tendon tension force dataset based on a relationship function among the influence matrix, the prestressed tendon tension force dataset and the average pressure dataset of the test interface area, so that the identification of the tension force of a single prestressed tendon in the porous anchoring system is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of anchoring systems, and particularly relates to a prestressed tendon tension force identification method based on piezoelectric sensing. BACKGROUND

[0002] Prestressed concrete structures change the internal stress size and distribution law of the bridge by previously introducing internal stress in the concrete or reinforced concrete, so that the concrete or reinforced concrete member will not crack or crack will be delayed under the action of the use load. Prestressed concrete accounts for a large proportion in the concrete structure, and its adaptability and span capacity are significantly improved due to the full play of the advantages of concrete, steel and prestressed tendon materials. Post-tensioning method is one of the important methods for prestressed concrete structure to realize prestress application, and has wide application range and large quantity, and the construction environment is complex. Effective identification of the prestress applied to the concrete is the premise of prestressed concrete structure analysis and the key to prevent structure cracking.

[0003] The prestressed anchoring system has large load, small deformation and large quantity, and it is difficult to test the prestressed tendon tension force under the anchor. For a multi-hole anchoring system containing multiple prestressed tendons, it is more challenging to quantitatively identify the tension force of each prestressed tendon. In order to ensure that each index of the post-tensioned prestressed structure meets the design requirements, prestressed monitoring methods are constantly emerging, and the traditional available technologies all depend on measuring parameters related to force level. For example, pressure ring method, vibration method (based on acceleration), impedance method (based on electrical impedance), acoustic method (based on wave speed), magnetoelastic method (based on magnetic permeability) and strain method (based on strain). Among them, the pressure ring method is the most commonly used method, which can accurately obtain the tension force of the whole bundle of prestressed tendons by placing the pressure ring under the anchor, but it has large volume, high price, cannot obtain the tension force of single prestressed tendon, and is not suitable for large-scale use and long-term monitoring in the concrete. The vibration-based method is easily disturbed by the constraints of the concrete. The magnetoelastic method is mainly used for monitoring of cable-stayed cables or external prestress, and has high cost and many interference factors. The acoustic method uses the relationship between ultrasonic and prestressed tendon stress level, but the speed is not sensitive to the stress level and is easily affected by the concrete. The strain method can only measure the stress change increment, and it is difficult to evaluate the prestressed tendon tension force when the strain history of the anchoring system is unknown, and the strain measurement is easily affected by temperature and environmental factors, and is only suitable for evaluation and testing during the tensioning process.

[0004] In recent years, piezoelectric materials have been widely used in structural monitoring due to their lightweight, high machinability, low cost, and strong anti-interference properties. In anchoring system monitoring, piezoelectric materials are typically based on two methods: piezoresistive impedance and piezoelectric fluctuation. Impedance-based methods simply require attaching a piezoelectric element to the structure and sensing changes in the structure's impedance response. Piezoresistive impedance can effectively monitor structures with small deformations, using high-frequency excitation. However, impedance-based methods are highly sensitive to minute changes; similar to strain testing, they only obtain the stress increment and are easily affected by temperature and environmental factors.

[0005] Piezoelectric wave method is another active monitoring technology with broad application prospects. It typically requires two piezoelectric elements, one for excitation and the other for reception. Structural monitoring is achieved by capturing the differences in received signals caused by changes in the propagation medium. As the propagation mechanism of ultrasound at rough interfaces has been gradually revealed—that is, as the actual contact area increases, reflected waves gradually decrease and transmitted waves gradually increase—methods based on piezoelectric active sensing and testing rough interfaces between anchor heads and anchor plates have been developed. For example... Figure 1 As shown in Figures (a) and (b), signals are transmitted via PZT1 and received via PZT2 at different locations. By extracting the relationship between the reflected and transmitted waves and the interface contact pressure, the tension force of the entire prestressed tendon bundle can be tested. However, due to the high randomness of the rough interface between the anchor head and the anchor plate during actual testing, the test results have high specificity and lack universality. Piezoelectric smart sensors are reliable and possess various identification characteristics for the mechanical state of steel strands and their anchorage positions, which is of great significance for monitoring prestressed concrete beams. However, current methods are limited to identifying and testing the overall tension force of the entire prestressed bundle and cannot identify the tension force of a single prestressed tendon in multi-hole anchorage systems.

[0006] Defects and shortcomings of existing technology:

[0007] (1) When using piezoelectric active sensing technology to test the anchor tension of the post-tensioned anchoring system, the test data has strong characteristics due to the high randomness of the contact interface between the anchor head and the anchor plate, and the test method is not universal.

[0008] (2) Current methods are limited to identifying and testing the overall tension of the entire prestressed tendon bundle, and cannot identify the tension of a single prestressed tendon in a multi-hole anchorage system.

[0009] Therefore, a universal technical solution is needed to effectively identify the tension of a single prestressed tendon in a multi-hole anchorage system. Summary of the Invention

[0010] To solve the above technical problems, the application provides a prestressed tendon tension force identification method based on piezoelectric sensing, which is applied to a porous anchoring system using the post-tensioning method, and comprises the following specific steps:

[0011] Flattening the contact interface of the porous anchoring system;

[0012] Uniformly arranging a plurality of pairs of piezoelectric sheets matching the number of prestressed tendon holes in the anchor head of the porous anchoring system on the bottom side of the anchor head to form a piezoelectric array;

[0013] Obtaining the piezoelectric signals of each pair of piezoelectric sheets in the piezoelectric array, respectively processing to obtain the corresponding receiving coefficients, and constructing a piezoelectric monitoring index dataset with all the receiving coefficients as elements;

[0014] According to a preset fitting function, the piezoelectric monitoring index dataset is used to calculate the average pressure of the test interface area, and a test interface area average pressure dataset is constructed with all the average pressures of the test interface area as elements;

[0015] According to the mechanical method or the finite element method, the influence matrix between the prestressed tendon tension force dataset and the test interface area average pressure dataset is solved;

[0016] According to the relationship function among the influence matrix, the prestressed tendon tension force dataset and the test interface area average pressure dataset, the prestressed tendon tension force dataset is calculated through the influence matrix and the test interface area average pressure dataset.

[0017] In a possible implementation, the piezoelectric array comprises N pairs of piezoelectric sheets, and each pair of piezoelectric sheets comprises a first piezoelectric sheet for exciting signals and a second piezoelectric sheet for receiving signals;

[0018] The Mth element in the piezoelectric monitoring index dataset is obtained through the following specific steps:

[0019] The test host controls the Mth data acquisition device to issue an Mth test instruction;

[0020] The Mth data acquisition device excites an Mth test signal from the first piezoelectric sheet in the Mth pair of piezoelectric sheets through an Mth DA digital-analog channel according to the Mth test instruction;

[0021] The second piezoelectric sheet in the Mth pair of piezoelectric sheets receives the Mth test signal and transmits it to the Mth data acquisition device through an Mth AD analog-digital channel;

[0022] The Mth data acquisition device transmits the Mth test signal to the test host, and the test host performs data analysis to obtain an Mth typical characteristic value of the Mth test signal as an Mth receiving coefficient and an Mth element in the piezoelectric monitoring index data set;

[0023] Wherein, N, M are positive integers, 0

[0024] In a possible implementation, the data acquisition device adopts any one of a data acquisition card, a signal generator, and an oscilloscope.

[0025] In a possible implementation, the signal type of the test signal is a pulse signal or a sweep signal.

[0026] In a possible implementation, the test host adopts any one of a direct comparison method, a wavelet packet energy method, and a time reversal method when performing data analysis.

[0027] In a possible implementation, the Mth typical characteristic value is any one of a signal amplitude, a wavelet packet energy, and a frequency.

[0028] In a possible implementation, the piezoelectric sheet is a lead zirconate titanate piezoelectric sheet.

[0029] In a possible implementation, the fitting function is:

[0030]

[0031] Wherein, R i is a receiving coefficient of the ith prestressed tendon, S i is an average pressure of a test interface region where the ith prestressed tendon is located, and a, b, and c are curve fitting constants.

[0032] In a possible implementation, the solution of the influence matrix includes the following specific steps:

[0033] A mechanical model or a finite element model is established among the multi-hole anchoring system, the prestressed tendon, and the anchor pad.

[0034] A unit load is applied to the first prestressed tendon, and an average pressure value of each test interface region is obtained through the mechanical model or the finite element model to obtain each influence coefficient corresponding to the first prestressed tendon.

[0035] The same method as that for obtaining each influence coefficient corresponding to the first prestressed tendon is used to cyclically apply a unit load to the remaining prestressed tendons to obtain the influence coefficients of all the prestressed tendons to form an influence matrix.

[0036] In a possible implementation, the relationship function is:

[0037] A N F=S;

[0038] Wherein, A N is the influence matrix of all prestressed tendons, F is the tension force data set of all prestressed tendins, and S is the average pressure data set of all test interface areas.

[0039] The technical scheme provided by the application has at least the following beneficial effects:

[0040] 1. By treating the contact interface between the anchor head and the anchor pad, the robustness and universality of the measured signal are improved, so that the piezoelectric active sensing technology is more universal in the test of the multi-hole post-tensioned anchoring system.

[0041] 2. The piezoelectric sheet is used as the sensing material, which greatly reduces the monitoring cost of the multi-hole post-tensioned anchoring system and can be widely used.

[0042] 3. The method can effectively identify the tension force of a single prestressed tendon in the multi-hole anchoring system and effectively monitor the actual working performance of the multi-hole anchoring system.

[0043] 4. The method does not need to know the historical state of the anchoring system during testing, and can be used for monitoring the tensioning process of the prestressed tendon, and can also be used for long-term performance monitoring of the anchoring system, and has a wider application range than the traditional method. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 It is a schematic diagram of the application scene of the existing piezoelectric wave method for testing the tension force of the whole bundle of prestressed tendons.

[0045] Figure 2 It is a flowchart of a prestressed tendon tension force identification method based on piezoelectric sensing provided by the embodiment of the application.

[0046] Figure 3 It is a structural schematic diagram of a typical multi-hole anchoring system.

[0047] Figure 4 It is a structural schematic diagram of an anchor head in a typical multi-hole anchoring system.

[0048] Figure 5 It is a structural schematic diagram of an anchor pad in a typical multi-hole anchoring system.

[0049] Figure 6 It is a structural schematic diagram of a pair of piezoelectric sheet signal emission and collection devices provided by the embodiment of the application.

[0050] Figure 7 It is a structural schematic diagram of a multi-hole anchoring system when executing the prestressed tendon tension force identification method provided by the embodiment of the application.

[0051] Figure 8 A top view of a porous anchoring system provided in an embodiment of the present application Figure 7 A top view of a porous anchoring system provided in an embodiment of the present application

[0052] Figure 9 A top view of a porous anchoring system provided in an embodiment of the present application Figure 7 A top view of a porous anchoring system provided in an embodiment of the present application

[0053] Figure 10 A top view of a porous anchoring system provided in an embodiment of the present application Figure 9 A top view of a porous anchoring system provided in an embodiment of the present application

[0054] Figure 11 A top view of a porous anchoring system provided in an embodiment of the present application Figure 9 A top view of a porous anchoring system provided in an embodiment of the present application

[0055] Figure 12 A top view of a porous anchoring system provided in an embodiment of the present application Figure 8 A top view of a porous anchoring system provided in an embodiment of the present application

[0056] Figure 13 A top view of a porous anchoring system provided in an embodiment of the present application

[0057] Figure 14 A top view of a porous anchoring system provided in an embodiment of the present application

[0058] Figure 15 A top view of a porous anchoring system provided in an embodiment of the present application

[0059] In the drawings, 11, anchor head; 12, anchor pad; 13, prestressed tendon; 14, contact interface; 15, piezoelectric sheet; 16, AD analog channel; 17, DA digital analog channel; 18, data acquisition device; 19, data transmission line; 20, test host; 21, unknown load of prestressed tendon; 22, piezoelectric sheet test pair; 141, anchor side contact surface; 142, anchor pad side contact surface; 151, first piezoelectric sheet; 152, second piezoelectric sheet. DETAILED DESCRIPTION

[0060] In order to deepen the understanding of the present application, the present application will be further described in detail below in combination with the drawings and embodiments, which are only used to explain the present application and do not constitute a limitation on the protection scope of the present application.

[0061] Please refer to Figures 2 to 15 The present application provides a prestressed tendon tension identification method based on piezoelectric sensing, which is applied to a porous anchoring system using post-tensioning method, and includes the following specific steps:

[0062] S100: flattening the contact interface 14 of the porous anchoring system.

[0063] To identify the tension force of the prestressed tendons under the anchor in a post-tensioned multi-hole anchoring system, this invention uses the contact interface 14 between the anchor head 11 and the anchor plate 12 as the test interface (e.g., Figures 3 to 5 As shown, the prestressed tendon 13 passes through the anchor head 11 and extends to the other side of the anchor plate 12.

[0064] The anchorage prestressing tendon tension identification method in this invention is based on the piezoelectric fluctuation method. Experiments show that the test interface has a significant impact on the measured signal. To improve the robustness and versatility of the measured signal, the test interface needs to be processed. Before tensioning the prestressing tendon 13, both sides of the contact interface 14 of the porous anchoring system (i.e., the anchorage side contact surface 141 on the anchor head 11 side and the anchor plate side contact surface 142 on the anchor plate 12 side) are first planed or milled. Specific methods for processing the anchorage side contact surface 141 and the anchor plate side contact surface 142 include, but are not limited to, knurling and etching (e.g., ...). Figure 10 and Figure 11 As shown in the figure, the two contact surfaces are quenched to increase the hardness of the contact surfaces, so that the contact interface 14 is flat and has uniform roughness.

[0065] S200: A number of pairs of piezoelectric plates 15, whose number matches the number of holes in the prestressing tendons on the anchor head 11, are evenly arranged on the bottom side of the anchor head 11 of the multi-hole anchoring system to form a piezoelectric array.

[0066] In this embodiment, as Figures 6 to 8 Two piezoelectric elements 15 form a piezoelectric element test pair 22, and the number of piezoelectric element test pairs 22 is the same as the number of holes on the anchor head 11 used for threading the prestressing tendons 13. The process of identifying the tension force of the prestressing tendons under the anchor can be understood as the process of testing the tension force of each prestressing tendon 13. The test adopts the piezoelectric active sensing mode. Before the test, the number of unknown tension forces of N prestressing tendons 13 during the test can be determined according to the number of holes N in the anchoring system, and an unknown prestressing tendon tension force dataset F = {F1, F2, F3, ..., F...} can be established. N}, where F i For F1 to F N Any value in the formula represents the tension force of the i-th prestressed tendon 13. For example... Figure 7 The prestressing tendon 13, subjected to the unknown load 21 in the direction of the arrow, will experience a corresponding unknown tension. It should be noted that when arranging the piezoelectric array, the corresponding piezoelectric test pairs 22 should be evenly arranged on the side of the anchor head 11 near the test interface, according to the number of holes in the multi-hole anchoring system and the position of the prestressing tendon 13. The piezoelectric pieces 15 can be glued to the surface of the anchor head 11 using adhesives including but not limited to epoxy resin, 502 glue, and casting adhesive. During the gluing process, the gluing area should first be flattened and sanded. The gluing position of each piezoelectric piece 15 should be accurate, and the adhesive layer should be of uniform thickness.

[0067] In a possible implementation, the piezoelectric sheet 15 is a lead zirconate titanate piezoelectric sheet.

[0068] In this embodiment, the piezoelectric sheet 15 can adopt various specifications, and preferably a lead zirconate titanate piezoelectric sheet.

[0069] S300: Obtain the piezoelectric signal of each pair of piezoelectric sheets 15 in the piezoelectric array, respectively process to obtain the corresponding receiving coefficient, and construct the piezoelectric monitoring index dataset with all the receiving coefficients as elements.

[0070] In this embodiment, the typical eigenvalue of the piezoelectric signal of each pair of piezoelectric sheets 15 in the piezoelectric array can be obtained pair by pair, and the typical eigenvalue is taken as the corresponding receiving coefficient. All the receiving coefficients obtained finally are taken as the index for piezoelectric monitoring to form the piezoelectric monitoring index dataset R. R = {R1, R2, R3, …, R N} T , R N represents the Nth receiving coefficient.

[0071] In a possible implementation, the piezoelectric array includes N pairs of piezoelectric sheets 15, such as Figure 6 Each pair of piezoelectric sheets 15 includes a first piezoelectric sheet 151 for exciting signals and a second piezoelectric sheet 152 for receiving signals.

[0072] The process of arranging the piezoelectric array can be understood as the process of building a piezoelectric signal transmission and collection system. In specific implementation, the piezoelectric sheet 15 can adopt a PZT-5h piezoelectric sheet with a diameter of 8 mm and a thickness of 1 mm.

[0073] The Mth element in the piezoelectric monitoring index dataset is obtained through the following specific steps:

[0074] The control test host 20 sends an Mth test instruction to the Mth data acquisition device 18;

[0075] The Mth data acquisition device 18 excites an Mth test signal by the first piezoelectric sheet 151 in the Mth pair of piezoelectric sheets 15 through the Mth DA digital-analog channel 17 according to the Mth test instruction;

[0076] The second piezoelectric sheet 152 in the Mth pair of piezoelectric sheets 15 receives the Mth test signal and transmits it to the Mth data acquisition device 18 through the Mth AD analog-digital channel 16;

[0077] The Mth data acquisition device 18 transmits the Mth test signal to the test host 20, and the test host 20 performs data analysis, extracts the amplitude of the received signal, the frequency of the received signal, the wavelet packet energy of the received signal, or the peak value of the inverted focused signal through a signal processing method, obtains the Mth typical characteristic value of the Mth test signal, and takes it as the Mth received coefficient and the Mth element in the piezoelectric monitoring index data set.

[0078] Wherein, N, M are positive integers, 0 < M ≤ N.

[0079] In this embodiment, the DA digital-analog channel 17 can be understood as a DA digital-analog signal transmission channel, and the AD analog-digital channel 16 can be understood as an AD analog-digital signal receiving channel. M takes values from 1 to N respectively, and the typical characteristic values of the piezoelectric signals, i.e. test signals, are obtained pair by pair, and the final N typical characteristic values form a piezoelectric monitoring index data set R.

[0080] In a specific embodiment, as Figures 7 to 12 N = 4, the piezoelectric sheet 15 adopts a lead zirconate titanate piezoelectric sheet, and two lead zirconate titanate piezoelectric sheets are required to form a piezoelectric sheet test pair 22. In the four piezoelectric sheet test pairs 22, the first piezoelectric sheet 151 is used to excite signals, and the second piezoelectric sheet 152 is used to receive signals. The distance between the first piezoelectric sheet 151 and the second piezoelectric sheet 152 in the same piezoelectric sheet test pair 22 is about 2-3 cm. During the test, M takes values from 1 to 4 respectively, and the test host 20 compiles a test program, and the data acquisition device 18, including but not limited to a data acquisition card, a signal generator and an oscilloscope, is instructed by the data transmission line 19. Then, the data acquisition device 18 transmits the test signal to the first piezoelectric sheet 151 through the DA digital-analog channel 17, and the signal type is not limited to pulse signal and sweep signal. The data acquisition device 18 receives the test signal from the second piezoelectric sheet 152 through the AD analog-digital channel 16 by setting the trigger of the data acquisition device 18, and then transmits the received signal back to the test host 20 through the data transmission line 19, and the test host 20 performs data analysis. Through different methods including but not limited to direct comparison method, wavelet packet energy method, and time reversal method, the typical characteristic values of the signal are obtained, including but not limited to signal amplitude, wavelet packet energy, and frequency. Finally, through the analysis of the characteristic signal, the appropriate value, i.e. the typical characteristic value, is selected as the characteristic index for monitoring. The piezoelectric monitoring index data set is finally represented as R = {R1, R2, R3, …, R4} T R i represents the i-th received coefficient, i.e. the i-th characteristic index, i is an integer from 1 to 4.

[0081] In a specific implementation, the data acquisition device 18 can adopt a NI USB-6366 data acquisition card, and the piezoelectric sheet 15 is connected with the data acquisition device 18 through a BNC coaxial cable. The test host 20 can adopt a notebook computer, the data acquisition device 18 is connected with the test host 20 through a USB data line for communication, and a control program is compiled through LabVIEW. During testing, the test host 20 (i.e. the notebook computer) sends a sweep signal of 0-1 MHz (for example Figure 13 ), a digital-to-analog conversion is performed through an AO interface of the NI USB-6366 (i.e. the data acquisition device 18), a voltage excitation signal is transmitted to the first piezoelectric sheet 151 (i.e. PZT1), a signal of the second piezoelectric sheet 152 (i.e. PZT2) is received through an AI interface of the NI USB-6366, an analog-to-digital conversion is performed through the NI USB-6366, and data is transmitted to the notebook computer for display and processing. When the prestress is subjected to a load, a typical signal received by the second piezoelectric sheet 152 is as shown in Figure 14 .

[0082] In the embodiment, the wavelet packet energy of the signal received by the PZT2 is taken as a signal characteristic value. The wavelet packet energy value of the signal received by the PZT2 when there is no prestressed tendon load is taken as W0, and the wavelet packet energy value of the signal received by the PZT2 when there is a prestressed tendon load is taken as W i , i is an integer in 1 to N, and the ratio of the wavelet packet energy value W i under different loads to the wavelet packet energy value W0 when there is no load is taken as a receiving coefficient, which is taken as a monitoring index in the embodiment. With the increase of the prestressed tendon load, the contact pressure of the contact interface 14 between the anchor head 11 and the anchor backing plate 12 increases, the actual contact area gradually increases, the reflected wave gradually decreases, and the transmitted wave gradually increases. The arrangement mode of the piezoelectric sheet 15 in Figure 7 is mainly affected by the reflected wave, and with the increase of the prestressed tendon load, the wavelet packet energy value of the signal received by the PZT2 gradually decreases, that is, the receiving coefficient also decreases with the increase of the prestressed tendon load.

[0083] In a possible implementation, the data acquisition device 18 adopts any one of a data acquisition card, a signal generator and an oscilloscope.

[0084] In a possible implementation, the signal type of the test signal is a pulse signal or a sweep signal.

[0085] In a possible implementation, the test host 20 adopts any one of a direct comparison method, a wavelet packet energy method and a time reversal method when performing data analysis.

[0086] In a possible implementation, the Mth typical characteristic value is any one of a signal amplitude, a wavelet packet energy and a frequency.

[0087] S400: According to the preset fitting function, the average pressure of the test interface region is calculated through the piezoelectric monitoring index data set, and all the average pressures of the test interface region are taken as elements to construct an average pressure data set of the test interface region.

[0088] In this embodiment, the porous anchoring system is pre-stressed by a whole bundle to perform a staged loading from a no-load state to a full-load state. Through at least three independent loading tests, a function relationship between the signal receiving coefficient and the corresponding average pressure of the test interface region, i.e., a fitting characteristic signal R i , is established. i The function relationship curve of R i with respect to the corresponding average pressure S i of the test interface region is obtained according to at least three independent tests. Figure 15 ) is fitted.

[0089] The fitting function can be expressed as R i = f(S i ), where R i is the i-th characteristic signal, i.e., the receiving coefficient, S i is the i-th corresponding average pressure of the test interface region, and i is an integer in 1 to N. The inverse function can be expressed as S i = g(R i ).

[0090] In a specific implementation, the test interface can be divided into N corresponding regions according to the number of piezoelectric sheet test pairs 22. When the pre-stressed tendon is loaded, the average pressures of the regions form a test interface region average pressure data set S = {S1, S2, S3, …, S N} T . For example, Figure 12 when there are four piezoelectric sheet test pairs 22, the test interface is divided into four corresponding regions. When the pre-stressed tendon is loaded, the average pressures of the four regions form a test interface region average pressure data set S = {S1, S2, S3, …, S4} T . For a four-hole anchoring system, there are four unknown pre-stressed tendon tension forces, i.e., F = {F1, F2, F3, …, F4} T .

[0091] In one possible implementation, through three uniform step-by-step loading and step-by-step unloading tests, the receiving coefficient under different pre-stressed tendon loads is obtained. Taking the pre-stressed tendon load as the independent variable and the receiving coefficient as the dependent variable, the fitting function form and fitting parameters are obtained through the method of juxtaposed fitting and repeated iteration when the goodness of fit R 2 reaches 0.95 or above. In the embodiment, the fitting function form is:

[0092]

[0093] wherein R i is the receiving coefficient of the i-th prestressed tendon 13, i.e., a characteristic signal, S i is the average pressure of the test interface region where the i-th prestressed tendon 13 is located, and a, b, c are curve fitting constants. In an embodiment, a = 0.131, b = 1.373, and c = 1.083.

[0094] Due to the pre-smoothing treatment of the contact interface 14 between the anchor head 11 and the anchor pad 12, the fitting function has strong universality, and each piezoelectric sheet test 22 can be used. Through the inverse function of the fitting function, S i can be calculated, and the inverse function is as follows:

[0095]

[0096] S500: According to the mechanical method or the finite element method, an influence matrix between the prestressed tendon tension force data set and the average pressure data set of the test interface region is solved.

[0097] In a possible implementation, the solving of the influence matrix includes the following specific steps:

[0098] A mechanical model or a finite element model between the multi-hole anchoring system, the prestressed tendon 13, and the anchor pad 12 is established;

[0099] A unit load is applied to the first prestressed tendon 13, and the average pressure values of each test interface region are obtained through the mechanical model or the finite element model, and each influence coefficient corresponding to the first prestressed tendon 13 is obtained;

[0100] The same method as obtaining each influence coefficient corresponding to the first prestressed tendon 13 is used to cyclically apply a unit load to the remaining prestressed tendons 13, so as to obtain the influence coefficients of all the prestressed tendons 13, and the influence matrix is formed.

[0101] In this embodiment, according to the mechanical method or the finite element method, an influence matrix A N between the prestressed tendon tension force data set F and the average pressure data set S of the test interface region is solved, A N is an N x N positive definite matrix, which can be expressed in the following form:

[0102]

[0103] wherein a ij represents the influence coefficient of the unit tension force of the j-th prestressed tendon in the average pressure of the i-th test interface region, a ij is any number in a 11 to a NN .

[0104] In the specific implementation, assuming N=4, the influence matrix A4 can be solved according to the finite element method, a three-dimensional numerical finite element model of the corresponding anchoring system is established, a 1t load (i.e., F1) is applied at the No. 1 prestressed tendon 13, and the vertical pressure of the test interface in four areas is extracted according to the analysis results of the three-dimensional numerical finite element model, i.e., the measured a 11 , a 21 , a 31 , a 41 coefficient. Similarly, a 1t load (i.e., F2) is applied at the No. 2 prestressed tendon 13, and the vertical pressure of the test interface in four areas is calculated, i.e., the measured a 12 , a 22 , a 32 , a 42 coefficient. A 1t load (i.e., F3) is applied at the No. 3 prestressed tendon 13, and the vertical pressure of the test interface in four areas is calculated, i.e., the measured a 13 , a 23 , a 33 , a 43 coefficient. A 1t load (i.e., F4) is applied at the No. 4 prestressed tendon 13, and the vertical pressure of the test interface in four areas is calculated, i.e., the measured a 14 , a 24 , a 34 , a 44 coefficient. In this way, through the cyclic calculation at different steel strands, the influence matrix A4 can be finally obtained. According to the analysis, the influence matrix of a typical four-hole anchoring system is as follows:

[0105]

[0106] S600: According to the relationship function between the influence matrix, the prestressed tendon tension force data set, and the test interface area average pressure data set, the prestressed tendon tension force data set is calculated by the influence matrix and the test interface area average pressure data set.

[0107] In one possible implementation, since the multi-hole anchoring system is a linear system under the action of the prestressed tendon load in the working state, the relationship between the prestressed tendon load and the test interface area average pressure can be represented by a linear equation set, and the relationship function is:

[0108] A N F=S;

[0109] wherein A N is the influence matrix of all prestressed tendons 13, F is the tension force data set of all prestressed tendons 13, and S is the average pressure data set of all test interface areas.

[0110] In the embodiment, the average pressure data set S of the interface area and the relationship function are used to solve the linear equation set F of the tension data set of all the prestressed tendons 13, so that the tension of each prestressed tendon of the porous anchorage system is identified by the piezoelectric active sensing technology.

[0111] In the specific implementation, assuming N=4, the wavelet packet energy value of the signal received by PZT2 when there is no prestressed tendon load is W0=562V 2 When the wavelet packet energy W1=91.6, W2=160.2, W3=95.5, and W4=89.9 is measured by the four pairs of piezoelectric sheets in the test pair 22, the received coefficient values R1=0.163, R2=0.285, R3=0.170, and R4=0.160 are obtained according to the definition of the received coefficient. T According to the fitting function and its inverse function, the average pressure data set S={8.9, 4.99, 7.89, 10.24} of all the test interface areas can be calculated. T Thus, the influence matrix A N and the average pressure data set S of all the test interface areas are used to obtain the tension of each prestressed tendon, i.e., the tension data set F={14.79, 2.98, 12.24, 16.24} of all the prestressed tendons 13. T Therefore, the tension of each prestressed tendon in the porous anchorage system is identified.

[0112] The above embodiment should not limit the present application in any way, and any technical solution obtained by equivalent replacement or equivalent conversion falls within the protection scope of the present application.

Claims

1. A method for identifying the tension force of prestressed tendons under anchors based on piezoelectric sensing, applied to multi-hole anchorage systems using post-tensioning, characterized in that... The specific steps include the following: The contact interface of the porous anchoring system is smoothed. A piezoelectric array is formed by uniformly arranging a number of pairs of piezoelectric plates on the bottom side of the anchor head of the multi-hole anchoring system, the number of which matches the number of holes in the prestressing tendons on the anchor head. The piezoelectric signals of each pair of piezoelectric elements in the piezoelectric array are obtained, processed to obtain the corresponding receiving coefficients, and a piezoelectric monitoring index dataset is constructed using all the receiving coefficients as elements. According to the preset fitting function, the average pressure of the test interface area is calculated through the piezoelectric monitoring index dataset, and the average pressure of the test interface area is constructed using all the average pressures of the test interface area as elements. Based on mechanical or finite element methods, solve the influence matrix between the prestressed tendon tension force dataset and the average pressure dataset of the test interface region; Based on the relationship function between the influence matrix, the prestressed tendon tension force dataset, and the average pressure dataset of the test interface region, the prestressed tendon tension force dataset is calculated using the influence matrix and the average pressure dataset of the test interface region. The fitting function is: ； Among them, R i S is the acceptance factor for the i-th prestressed tendon. i is the average pressure in the test interface area where the i-th prestressing tendon is located, and a, b, and c are curve fitting constants; The relational function is: A N F=S; Among them, A N Let F be the influence matrix for all prestressed tendons, F be the tension force dataset for all prestressed tendons, and S be the average pressure dataset for all test interface regions.

2. The method for identifying the tension force of prestressed tendons under anchors according to claim 1, characterized in that, The piezoelectric array includes N pairs of piezoelectric elements, each pair of piezoelectric elements including a first piezoelectric element for exciting a signal and a second piezoelectric element for receiving a signal; The Mth element in the piezoelectric monitoring index dataset is obtained through the following specific steps: The control test host sends the Mth test command to the Mth data acquisition device; The Mth data acquisition device, according to the Mth test command, excites the Mth test signal from the first piezoelectric element in the Mth pair of piezoelectric elements through the Mth DA digital-to-analog channel; The second piezoelectric element in the Mth pair of piezoelectric elements receives the Mth test signal and transmits it to the Mth data acquisition device through the Mth AD analog-to-digital channel; The Mth data acquisition device transmits the Mth test signal to the test host, and the test host performs data analysis to obtain the Mth typical feature value of the Mth test signal, which is used as the Mth receiving coefficient and the Mth element in the piezoelectric monitoring index data set. Where N and M are positive integers, and 0 < M ≤ N.

3. The method for identifying the tension force of prestressed tendons under anchors according to claim 2, characterized in that, The data acquisition device can be any one of a data acquisition card, a signal generator, and an oscilloscope.

4. The method for identifying the tension force of prestressed tendons under anchors according to claim 2, characterized in that, The test signal is either a pulse signal or a frequency sweep signal.

5. The method for identifying the tension force of prestressed tendons under anchors according to claim 2, characterized in that, The test host uses one of the following methods for data analysis: direct comparison, wavelet packet energy, or time inversion.

6. The method for identifying the tension force of prestressed tendons under anchors according to claim 2, characterized in that, The Mth typical feature value is any one of the following: signal amplitude, wavelet packet energy, and frequency.

7. The method for identifying the tension force of prestressed tendons under anchors according to claim 1, characterized in that, The piezoelectric element is a lead zirconate titanate piezoelectric element.

8. The method for identifying the tension force of prestressed tendons under anchors according to claim 1, characterized in that, Solving the influence matrix includes the following specific steps: Establish a mechanical model or finite element model of the porous anchorage system, prestressed tendons, and anchor plates; A unit load is applied to the first prestressing tendon, and the average pressure value of each test interface region is obtained through the mechanical model or the finite element model, thereby obtaining the influence coefficients corresponding to the first prestressing tendon. Using the same method as for obtaining the influence coefficients corresponding to the first prestressing tendon, unit loads are applied cyclically to the remaining prestressing tendons to obtain the influence coefficients of all prestressing tendons, forming an influence matrix.

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