Method for identifying tensioning force of prestressed tendon under anchor based on piezoelectric sensing

Abstract

The invention provides an under-anchor prestressed tendon tensioning force identification method based on piezoelectric sensing, which is applied to a porous anchoring system adopting a post-tensioning method and comprises the following steps: flattening a contact interface of the porous anchoring system; a plurality of pairs of piezoelectric patches are uniformly arranged on the side surface of the bottom of an anchor head of the porous anchoring system to form a piezoelectric array; acquiring piezoelectric signals of each pair of piezoelectric patches in the piezoelectric array, processing the piezoelectric signals to obtain corresponding receiving coefficients, and constructing a piezoelectric monitoring index data set according to the corresponding receiving coefficients; according to a preset fitting function, the average pressure of a test interface area is calculated through the piezoelectric monitoring index data set, and an average pressure data set of the test interface area is constructed according to the average pressure; solving an influence matrix according to a mechanical method or a finite element method; and according to a relation function among the influence matrix, the prestressed tendon tensioning force data set and the average pressure data set of the test interface area, calculating the prestressed tendon tensioning force data set so as to realize identification of the tensioning force of the single prestressed tendon in the porous anchoring system.

Description

Technical Field

[0001] The invention relates to the technical field of anchoring systems, and in particular to a method for identifying the tensioning force of prestressed tendons under an anchor based on piezoelectric sensing. Background Art

[0002] Prestressed concrete structures introduce internal stress into concrete or reinforced concrete in advance, changing the size and distribution of internal stress in the bridge, so that concrete or reinforced concrete components will not crack under the use load, or will delay cracking. Prestressed concrete accounts for a large proportion of concrete structures. Because it fully utilizes the advantages of concrete, steel bars and prestressed tendons, its adaptability and spanning capacity have been significantly improved. Post-tensioning is one of the important methods for prestressed concrete structures to achieve prestressing. It has a wide range of applications, a large number of uses, and a complex construction environment. Effective identification of the prestress acting on concrete is a prerequisite for the analysis of prestressed concrete structures and is also the key to preventing structural cracking.

[0003] The prestressed anchor system has large load, small deformation and large usage, so it is difficult to test the tension of the prestressed tendons under the anchor. For porous anchor systems, which contain multiple prestressed tendons, it will be more challenging to quantitatively identify the tension of each prestressed tendon. In order to ensure that the various indicators of post-tensioned prestressed structures meet the design requirements, prestress monitoring methods are constantly emerging. Traditional available technologies rely on measuring parameters related to force levels. Such as: pressure ring method, vibration method (based on acceleration), impedance method (based on electrical impedance), acoustic elastic method (based on wave velocity), magnetoelastic method (based on magnetic permeability) and strain method (based on strain). Among them, the pressure ring method is the most commonly used method. The pressure ring is placed under the anchor to accurately obtain the tension of the entire prestressed bundle, but it is large in size and high in price. It is impossible to obtain the tension of a single prestressed tendon and is not suitable for large-scale use and long-term monitoring inside concrete. The vibration-based method is easily interfered by concrete constraints. The magnetoelastic method is mainly used for monitoring inclined cables or external prestressing, and it is costly and has many interference factors. The acoustic elastic method uses the relationship between ultrasound and the stress level of the prestressed tendons, but the velocity is not sensitive to the stress level and is easily affected by concrete. The strain method can only measure the stress change increment. When the strain history of the anchor system is unknown, it is difficult to evaluate the tension of the prestressed tendons. In addition, 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 light weight, strong processability, low economic cost and strong anti-interference ability. Piezoelectric materials are usually based on two methods in anchor system monitoring: piezoresistive impedance method and piezoelectric fluctuation method. The impedance-based method only requires the piezoelectric sheet to be attached to the structure, and the changes in the structure are sensed by sensing the changes in the impedance response of the piezoelectric sheet. The piezoresistive impedance method can effectively monitor small deformation structures. It uses high-frequency excitation, but the impedance-based method is very sensitive to small changes. Similar to the strain test method, the impedance method can only obtain the stress change increment and is easily affected by temperature and environmental factors.

[0005] Piezoelectric wave method is another active monitoring technology with broad application prospects. Piezoelectric wave method usually requires two piezoelectric plates, one for exciting signals and the other for receiving signals. The structure is monitored by capturing the difference between the received signals caused by the changes in the propagation medium. As the propagation mechanism of ultrasonic waves at rough interfaces is gradually revealed, that is, as the actual contact area increases, the reflected wave gradually decreases and the transmitted wave gradually increases, the test method based on piezoelectric active sensing and the rough interface between the anchor head and the anchor pad has been developed. Figure 1 As shown in Figures (a) and (b), the signal is transmitted by PZT1, and received by PZT2 at different positions. By extracting the relationship between the reflected wave and the transmitted wave and the interface contact pressure, it can be used to test the tension of the entire bundle of prestressed tendons. Since the rough interface between the anchor head and the anchor pad has a high degree of randomness during the actual test, the test results have a high degree of characteristics and are not universal. The piezoelectric intelligent sensor has reliable performance and has a variety of identification characteristics for the mechanical state of the steel strand and the anchor position of the steel strand. It is of great significance for the monitoring of prestressed concrete beams, but the current method is limited to the identification and testing of the overall tension of the entire prestressed bundle, and cannot identify the tension of a single prestressed tendon in a porous anchoring system.

[0006] Defects and shortcomings of the existing technology:

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

[0008] (2) The current method is limited to the identification and testing of the overall tension force of the entire prestressed tendon, and is unable to identify the tension force of a single prestressed tendon in a porous anchor system.

[0009] Therefore, a universal technical solution is needed that can well identify the tension of a single prestressed tendon in a porous anchoring system. Summary of the invention

[0010] In order to solve the above technical problems, the present invention provides a method for identifying the tension force of prestressed tendons under anchors based on piezoelectric sensing, which is applied to a porous anchoring system using a post-tensioning method, and includes the following specific steps:

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

[0012] A plurality of pairs of piezoelectric sheets whose number matches the number of prestressed tendon holes on the anchor head are evenly arranged on the bottom side of the anchor head of the porous anchoring system to form a piezoelectric array;

[0013] Acquire the piezoelectric signals of each pair of piezoelectric sheets in the piezoelectric array, process them respectively to obtain corresponding reception coefficients, and construct a piezoelectric monitoring indicator data set using all the reception coefficients as elements;

[0014] According to a preset fitting function, the average pressure of the test interface area is calculated through the piezoelectric monitoring index data set, and the average pressure of the test interface area is constructed using all the average pressures of the test interface area as elements.

[0015] Solve the influence matrix between the prestressed tendon tensioning force data set and the average pressure data set of the test interface area according to a mechanical method or a finite element method;

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

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

[0018] The Mth element in the piezoelectric monitoring indicator data set is obtained by the following specific steps:

[0019] Controlling the test host to send the Mth test instruction to the Mth data acquisition device;

[0020] The Mth data acquisition device excites the Mth test signal from the first piezoelectric sheet in the Mth pair of piezoelectric sheets through the Mth DA digital-to-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 the Mth AD analog-to-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 the Mth typical eigenvalue of the Mth test signal and use it as the Mth receiving coefficient and the Mth element in the piezoelectric monitoring index data set;

[0023] Among them, N and M are positive integers, 0<M≤N.

[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 manner, the test signal is of a pulse signal or a swept frequency signal.

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

[0027] In a possible implementation, the Mth typical eigenvalue is any one of signal amplitude, wavelet packet energy, and 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] Among them, R i is the acceptance coefficient of the i-th prestressed tendon, S i is the average pressure in the test interface area where the ith prestressed tendon is located, and a, b, and c are curve fitting constants.

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

[0033] Establish a mechanical model or finite element model between the porous anchor system, prestressed tendons, and anchor pads;

[0034] Applying a unit load to the first prestressed tendon, obtaining an average pressure value of each test interface area through the mechanical model or the finite element model, and obtaining each influence coefficient corresponding to the first prestressed tendon;

[0035] The same method as that used to obtain the influence coefficients corresponding to the first prestressed tendon is used to cyclically apply unit loads to the remaining prestressed tendons to obtain the influence coefficients of all prestressed tendons and form an influence matrix.

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

[0037] A N F = S;

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

[0039] The technical solution provided by the present invention has at least the following beneficial effects:

[0040] 1. By processing the contact interface between the anchor head and the anchor pad, the robustness and versatility of the measured signal are improved, making the piezoelectric active sensing technology more versatile in the testing of porous post-tensioning anchoring systems;

[0041] 2. Using piezoelectric sheets as sensing materials can significantly reduce the monitoring cost of porous post-tensioning anchoring systems and can be widely promoted and used;

[0042] 3. This method can effectively identify the tension of a single prestressed tendon in a porous anchor system and effectively monitor the actual working performance of the porous anchor system;

[0043] 4. When testing this method, there is no need to predict the historical status of the anchor system. It can be used to monitor the prestressed tendon tensioning process and can also be used for long-term performance monitoring of the anchor system. Its application range is wider than that of traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of the application scenario of the existing piezoelectric wave method for testing the tension of a whole bundle of prestressed tendons;

[0045] Figure 2 A flow chart of a method for identifying the tension force of prestressed tendons under anchors based on piezoelectric sensing provided by an embodiment of the present invention;

[0046] Figure 3 It is a schematic diagram of the structure of a typical porous anchoring system;

[0047] Figure 4 It is a schematic diagram of the structure of the anchor head in a typical porous anchoring system;

[0048] Figure 5 It is a schematic diagram of the structure of the anchor plate in a typical porous anchoring system;

[0049] Figure 6 A schematic diagram of the structure of a pair of piezoelectric sheet signal transmission and collection devices provided in an embodiment of the present invention;

[0050] Figure 7 A schematic structural diagram of a porous anchoring system when performing a method for identifying the tension force of prestressed tendons under an anchor provided by an embodiment of the present invention;

[0051] Figure 8 The embodiment of the present invention provides Figure 7 Top view of the medium porous anchoring system;

[0052] Fig. 9 The embodiment of the present invention provides Figure 7 Side view of the medium porous anchor system;

[0053] Fig.10 The embodiment of the present invention provides Fig. 9 Sectional view along AA direction;

[0054] Fig.11 The embodiment of the present invention provides Fig. 9 Cross-sectional view along the BB direction;

[0055] Fig.12 The embodiment of the present invention provides Figure 8 Schematic diagram of the corresponding contact interface test area;

[0056] Fig.13 Schematic diagram of the excitation sweep signal of PZT1 in a typical piezoelectric piece test pair;

[0057] Fig.14 Schematic diagram of the received signal of PZT2 in the piezoelectric piece test;

[0058] Fig.15 It is a schematic diagram of the curve of the piezoelectric piece test centering acceptance coefficient changing with the contact pressure;

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

[0060] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments are only used to explain the present invention and do not limit the protection scope of the present invention.

[0061] Please refer to Figures 2 to 15 The present invention provides a method for identifying the tension force of prestressed tendons under anchors based on piezoelectric sensing, which is applied to a porous anchoring system using a post-tensioning method, and includes the following specific steps:

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

[0063] In order to realize the identification of the tension force of the prestressed tendons under the anchor of the post-tensioning porous anchor system, the present invention takes the contact interface 14 between the anchor head 11 and the anchor pad 12 as the test interface (such as Figures 3 to 5 As shown in FIG. 1 , the prestressed tendon 13 passes through the anchor head 11 and extends to the other side of the anchor pad 12.

[0064] The method for identifying the tensioning force of the prestressed tendons under the anchor in the present invention is implemented based on the piezoelectric wave method. According to experiments, the test interface has a great influence on the measured signal. In order to improve the robustness and versatility of the measured signal, the test interface needs to be processed. Before the prestressed tendons 13 are tensioned, the two sides of the contact interface 14 of the porous anchoring system (i.e., the anchor side contact surface 141 on the side of the anchor head 11 and the anchor pad side contact surface 142 on the side of the anchor pad 12) are first planed or milled. When processing the anchor side contact surface 141 and the anchor pad side contact surface 142, specific methods include but are not limited to knurling and etching (such as Fig.10 and Fig.11 As shown), and the two contact surfaces are quenched to improve the hardness of the contact surfaces, so that the contact interface 14 is flat and has uniform roughness.

[0065] S200: evenly arranging a number of pairs of piezoelectric sheets 15 whose number matches the number of prestressed tendon holes on the anchor head 11 on the bottom side of the porous anchoring system to form a piezoelectric array.

[0066] In this embodiment, Figures 6 to 8 , every two piezoelectric sheets 15 form a piezoelectric sheet test pair 22, and the number of piezoelectric sheet test pairs 22 is the same as the number of holes on the anchor head 11 for inserting the prestressed tendons 13. The process of the method for identifying the tension force of the prestressed tendons under the anchor can be understood as the process of testing the tension force of each prestressed tendon 13. The test adopts the piezoelectric active sensing mode. Before the test, the number of unknown tension forces of the N prestressed tendons 13 during the test can be determined according to the number of holes N in the anchoring system, and an unknown prestressed tendon tension force data set F = {F1, F2, F3, …, F N}, where F i F1 to F N Any value in represents the tension force of the i-th prestressed tendon 13. Figure 7 , the prestressed tendon 13 is subjected to the unknown prestressed tendon load 21 in the direction of the arrow, and there will be a corresponding unknown tensile force. It should be pointed out that when arranging the piezoelectric array, it is necessary to evenly arrange the corresponding piezoelectric sheet test pairs 22 on the side of the anchor head 11 close to the test interface according to the number of holes in the porous anchoring system and the position of the prestressed tendon 13. The piezoelectric sheet 15 can be glued to the surface of the anchor head 11 with glue, and the glue includes but is not limited to epoxy resin glue, 502 glue, and casting glue. During the pasting process, the pasting position is first leveled and polished. The pasting position of each piezoelectric sheet 15 should be accurate, and the thickness of the pasting glue layer should be uniform.

[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 be of various specifications, and a lead zirconate titanate piezoelectric sheet is preferred.

[0069] S300: Acquire the piezoelectric signals of each pair of piezoelectric sheets 15 in the piezoelectric array, process them respectively to obtain corresponding receiving coefficients, and construct a piezoelectric monitoring indicator data set using all the receiving coefficients as elements.

[0070] In this embodiment, the typical characteristic values ​​of the piezoelectric signals of each pair of piezoelectric sheets 15 in the piezoelectric array can be obtained pair by pair, and the typical characteristic values ​​are used as the corresponding receiving coefficients. All the receiving coefficients finally obtained are used as the indicators for piezoelectric monitoring to form a piezoelectric monitoring indicator data set 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 a signal and a second piezoelectric sheet 152 for receiving a signal.

[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 be 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 indicator data set is obtained by the following specific steps:

[0074] Control the test host 20 to send the Mth test instruction to the Mth data acquisition device 18;

[0075] The Mth data acquisition device 18 excites the Mth test signal from the first piezoelectric sheet 151 in the Mth pair of piezoelectric sheets 15 through the Mth DA digital-to-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-to-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 inversion focusing signal through a signal processing method, obtains the Mth typical eigenvalue of the Mth test signal and serves as the Mth receiving coefficient and the Mth element in the piezoelectric monitoring index data set;

[0078] Among them, N and M are positive integers, 0<M≤N.

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

[0080] In a specific embodiment, Figures 7 to 12 , N=4, the piezoelectric sheet 15 adopts a lead zirconate titanate piezoelectric sheet, and the test requires two lead zirconate titanate piezoelectric sheets 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 the signal, and the second piezoelectric sheet 152 is used to receive the signal. In the same piezoelectric sheet test pair 22, the distance between the first piezoelectric sheet 151 and the second piezoelectric sheet 152 is about 2-3cm. During the test, M takes values ​​from 1 to 4 respectively, and the test program is compiled through the test host 20. The data transmission line 19 sends instructions to the data acquisition device 18. The data acquisition device 18 includes but is not limited to a data acquisition card, a signal generator and an oscilloscope. Then, the data acquisition device 18 transmits a test signal to the first piezoelectric sheet 151 through the DA digital-to-analog channel 17. The signal type is not limited to a pulse signal and a swept frequency signal. By setting a trigger on the data acquisition device 18, the data acquisition device 18 receives the test signal from the second piezoelectric piece 152 through the AD analog-to-digital channel 16, 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 inversion method, the typical characteristic values ​​of the signal including but not limited to signal amplitude, wavelet packet energy, and frequency are obtained. Finally, through the analysis of the characteristic signal, the appropriate value, that is, the typical characteristic value, is selected as the characteristic indicator for monitoring. The piezoelectric monitoring indicator data set is finally expressed as R = {R1, R2, R3, ..., R4} T , R i represents the i-th reception coefficient, i.e., the i-th characteristic index, where i is an integer from 1 to 4.

[0081] In the specific implementation, the data acquisition device 18 can be a NI USB-6366 data acquisition card, and the piezoelectric sheet 15 and the data acquisition device 18 are connected by a BNC coaxial cable. The test host 20 can be a laptop computer, and the data acquisition device 18 and the test host 20 are connected and communicated by a USB data cable, and the control program is compiled by LabVIEW. During the test, the laptop computer, i.e., the test host 20, sends out a 0-1MHz sweep frequency signal (such as Fig.13 ), the AO interface of the NI USB-6366, i.e., the data acquisition device 18, performs digital-to-analog conversion, and transmits the voltage excitation signal to the first piezoelectric piece 151, i.e., PZT1. The signal of the second piezoelectric piece 152, i.e., PZT2, is received through the AI ​​interface of the NI USB-6366, and the NI USB-6366 performs analog-to-digital conversion, and transmits the data to the laptop computer for display and processing. When the prestress is subjected to a load, the typical signal received by the second piezoelectric piece 152 is as follows: Fig.14 shown.

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

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

[0084] In a possible implementation manner, the test signal is of a pulse signal or a swept frequency signal.

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

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

[0087] S400: Calculate the average pressure of the test interface area according to the preset fitting function through the piezoelectric monitoring index data set, and construct the average pressure data set of the test interface area with all the average pressures of the test interface area as elements.

[0088] In this embodiment, the porous anchor system is subjected to graded loading of the entire prestressed bundle from a no-load state to a full-load state, and at least three independent loading tests are performed to establish a functional relationship between the signal receiving coefficient and the average pressure of the corresponding test interface area, that is, a fitting characteristic signal R i The average pressure S of the corresponding test interface area i The functional relationship curve is based on at least three independent test tests (such as Fig.15 ).

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

[0090] In specific implementation, the test interface can be divided into N corresponding areas according to the number of piezoelectric sheet test pairs 22. When the prestressed tendon load acts, the average pressure of each area is combined into a test interface area average pressure data set S = {S1, S2, S3, ..., S N} T .like Fig.12 When there are four pairs of piezoelectric test pairs 22, the test interface is divided into four corresponding regions. When the prestressed tendon load acts, the average pressure of the four regions constitutes the test interface region average pressure data set S = {S1, S2, S3, ..., S4} T For the four-hole anchor system, there are four unknown prestressed tendon tension forces, which can be obtained as F = {F1, F2, F3, ..., F4} T .

[0091] In one possible implementation, three uniform step-by-step loading and step-by-step unloading tests are performed to obtain the acceptance coefficient under different prestressed tendon loads. The prestressed tendon load is used as the variable and the acceptance coefficient is used as the dependent variable. The goodness of fit R is obtained through repeated iterations by the juxtaposition fitting method. 2 The function form and fitting parameters reaching above 0.95, the fitting function form described in the embodiment is:

[0092]

[0093] Among them, R i is the receiving coefficient of the i-th prestressed tendon 13, i.e., the 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, and c are curve fitting constants. In one embodiment, a=0.131, b=1.373, and c=1.083.

[0094] Since the contact interface 14 between the anchor head 11 and the anchor pad 12 is flattened in advance, the above fitting function has strong universality and can be used by all piezoelectric sheet test pairs 22. The inverse function of the above fitting function can be used to calculate S i , the inverse function is as follows:

[0095]

[0096] S500: Solve the influence matrix between the prestressed tendon tensioning force data set and the average pressure data set of the test interface area according to a mechanical method or a finite element method.

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

[0098] Establishing a mechanical model or a finite element model among the porous anchoring system, the prestressed tendons 13, and the anchor pad 12;

[0099] Applying a unit load 13 to the first prestressed tendon, obtaining an average pressure value of each test interface area through the mechanical model or the finite element model, and obtaining each influence coefficient corresponding to the first prestressed tendon 13;

[0100] The same method as that used to obtain the influence coefficients corresponding to the first prestressed tendon 13 is used to cyclically apply unit loads to the remaining prestressed tendons 13, thereby obtaining the influence coefficients of all prestressed tendons 13 to form an influence matrix.

[0101] In this embodiment, the influence matrix A between the prestressed tendon tension data set F and the average pressure data set S of the test interface area is solved according to the mechanical method or the finite element method. N , A N is an N×N positive definite matrix and can be expressed as follows:

[0102]

[0103] Among them, a ij represents the influence coefficient of the average pressure of the j-th prestressed tendon unit tension on the i-th test interface area, a ij for a 11 to a NN Any number in .

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

[0105]

[0106] S600: Calculate the prestressed tendon tensioning force dataset through the influence matrix and the test interface area average pressure dataset according to the relationship function among the influence matrix, the prestressed tendon tensioning force dataset and the test interface area average pressure dataset.

[0107] In a possible implementation, since the porous anchor 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 average pressure in the test interface area can be expressed by a linear equation group, and the relationship function is:

[0108] A N F = S;

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

[0110] In this embodiment, for a porous anchoring system that bears a load, the linear equation group F, i.e., the tension data set of all prestressed tendons 13, can be solved by testing the average pressure data set S of the interface area and the relationship function, thereby realizing the identification of the tension force of each prestressed tendon in the porous anchoring system through piezoelectric active sensing technology.

[0111] In the specific implementation, assuming N = 4, first, when there is no prestressed tendon load, the wavelet packet energy value of the PZT2 receiving signal is W0 = 562V 2 When the wavelet packet energy W1=91.6, W2=160.2, W3=95.5, W4=89.9 is measured for the 4 pairs of piezoelectric test pairs 22, then according to the definition of the receiving coefficient, the values ​​of the receiving coefficient are R1=0.163, R2=0.285, R3=0.170, R4=0.160, R={0.163, 0.285, 0.170, 0.160} 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 test interface areas can be calculated. T So far, through the influence matrix A N And the average pressure data set S of all test interface areas, the tension of each prestressed tendon, that is, the tension data set F of all prestressed tendons 13 can be obtained = {14.79, 2.98, 12.24, 16.24} T , so as to complete the identification of the tension force of a single prestressed tendon in the porous anchor system.

[0112] The above embodiments should not limit the present invention in any way, and any technical solutions obtained by equivalent replacement or equivalent conversion shall fall within the protection scope of the present invention.

Claims

1. A method for identifying the tension force of prestressed tendons under anchors based on piezoelectric sensing, applied to a porous anchoring system using post-tensioning method, characterized in that: The specific steps include: Flattening the contact interface of the porous anchoring system; A plurality of pairs of piezoelectric sheets whose number matches the number of prestressed tendon holes on the anchor head are evenly arranged on the bottom side of the anchor head of the porous anchoring system to form a piezoelectric array; Acquire the piezoelectric signals of each pair of piezoelectric sheets in the piezoelectric array, process them respectively to obtain corresponding reception coefficients, and construct a piezoelectric monitoring indicator data set using all the reception coefficients as elements; According to a preset fitting function, the average pressure of the test interface area is calculated through the piezoelectric monitoring index data set, and the average pressure of the test interface area is constructed using all the average pressures of the test interface area as elements. Solve the influence matrix between the prestressed tendon tensioning force data set and the average pressure data set of the test interface area according to a mechanical method or a finite element method; According to the relationship function among the influence matrix, the prestressed tendon tensioning force data set, and the test interface area average pressure data set, the prestressed tendon tensioning force data set is calculated through the influence matrix and the test interface area average pressure data set.

2. The method for identifying the tension force of prestressed tendons under anchorage according to claim 1, characterized in that: The piezoelectric array includes N pairs of piezoelectric sheets, each pair of piezoelectric sheets includes a first piezoelectric sheet for exciting a signal and a second piezoelectric sheet for receiving a signal; The Mth element in the piezoelectric monitoring indicator data set is obtained by the following specific steps: Controlling the test host to send the Mth test instruction to the Mth data acquisition device; The Mth data acquisition device excites the Mth test signal from the first piezoelectric sheet in the Mth pair of piezoelectric sheets through the Mth DA digital-to-analog channel according to the Mth test instruction; 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 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 eigenvalue of the Mth test signal and use it as the Mth receiving coefficient and the Mth element in the piezoelectric monitoring index data set; Among them, N and M are positive integers, 0<M≤N.

3. The method for identifying the tension force of prestressed tendons under anchorage according to claim 2, characterized in that: The data acquisition device adopts 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 anchorage according to claim 2, characterized in that: The signal type of the test signal is a pulse signal or a swept frequency signal.

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

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

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

8. The method for identifying the tension force of prestressed tendons under anchorage according to claim 1, characterized in that: The fitting function is: Among them, R i is the acceptance coefficient of the i-th prestressed tendon, S i is the average pressure in the test interface area where the ith prestressed tendon is located, and a, b, and c are curve fitting constants.

9. The method for identifying the tension force of prestressed tendons under anchorage according to claim 1, characterized in that: The solution of the influence matrix includes the following specific steps: Establish a mechanical model or finite element model between the porous anchor system, prestressed tendons, and anchor pads; Applying a unit load to the first prestressed tendon, obtaining an average pressure value of each test interface area through the mechanical model or the finite element model, and obtaining each influence coefficient corresponding to the first prestressed tendon; The same method as that used to obtain the influence coefficients corresponding to the first prestressed tendon is used to cyclically apply unit loads to the remaining prestressed tendons to obtain the influence coefficients of all prestressed tendons and form an influence matrix.

10. The method for identifying the tension force of prestressed tendons under anchorage according to claim 1, characterized in that: The relationship function is: A N F=S; Among them, A N is the influence matrix of all prestressed tendons, F is the tension data set of all prestressed tendons, and S is the average pressure data set of all test interface areas.

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