A hollow anchor rod prestress detection system and detection method based on piezoelectric ceramics

Abstract

The application discloses a hollow anchor rod prestress detection system based on piezoelectric ceramics, which comprises a front-end hollow anchor rod, a first connecting piece, a to-be-detected hollow anchor rod, a second connecting piece, a rear-end hollow anchor rod, a signal amplifier, a signal processor and a computer; one end of the to-be-detected hollow anchor rod is connected with the front-end hollow anchor rod through the first connecting piece, and the other end is connected with the rear-end hollow anchor rod through the second connecting piece; the first connecting piece is connected with the signal amplifier through a shielded wire, the second connecting piece is connected with the signal processor through a shielded wire, the signal amplifier is connected with the signal processor, and the signal processor is connected with the computer; a ring-shaped piezoelectric ceramic intelligent aggregate is arranged in the first connecting piece and arranged between the front-end hollow anchor rod and the to-be-detected hollow anchor rod. The application has the advantages of simple structure, low cost, stable signal and high operation safety.

Description

Technical Field

[0001] This invention relates to the field of anchor bolt support, specifically a hollow anchor bolt prestress detection system and method based on piezoelectric ceramics. Background Technology

[0002] An anchor bolt is a slender rod that penetrates deep into the soil and rock to control its deformation. As a tension member that penetrates deep into the strata, one end of the anchor bolt is connected to the engineering structure, while the other end penetrates into the bottom layer. It is divided into a free section and an anchored section. The free section is the area that transmits the tension at the anchor bolt head to the anchor body. Its function is to apply prestress to the anchor bolt. The anchored section is the area where cement grout bonds the prestressing tendons to the soil layer. Its function is to increase the bonding friction between the anchor body and the soil layer, increase the bearing capacity of the anchor body, and transmit the tension of the free section to the depth of the soil.

[0003] In existing technologies, the prestress detection of anchor bolts is typically performed using strain gauges and fiber Bragg gratings. Since prestressed anchor bolts are often used in complex geological conditions, the devices used for prestress detection need to maintain good performance even in harsh environments. However, both strain gauge and fiber Bragg grating methods for anchor bolt prestress detection have certain drawbacks. The strain gauge method involves installing strain gauges on the anchor bolt, receiving the strain wavelength information from the anchor bolt via a detection host, preprocessing the data, and calculating the stress value at each monitoring point based on the anchor bolt's elastic modulus. Its drawbacks include: poor temperature stability of the strain gauges; large sensitivity dispersion due to crystal orientation and impurities; potential static fatigue fracture due to prolonged exposure to high stress; and susceptibility to damage during actual construction. The fiber Bragg grating (FBG) testing method calculates strain based on the relationship between tension and strain to derive the prestress value. However, its drawbacks include: the requirement for temperature compensation during strain measurement, which may not be feasible in actual construction; the need for grooving the anchor bolt when installing the FBG, which can affect the bolt's strength; and the fragility of the FBG, making it prone to breakage. Therefore, neither the strain gauge nor the FBG testing method is suitable for prestress testing of anchor bolts in harsh environments. Consequently, a testing system and method capable of performing prestress testing on anchor bolts in harsh environments are needed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a hollow anchor bolt prestress detection system and detection method based on piezoelectric ceramics.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] In a first aspect, this application provides a piezoelectric ceramic-based hollow anchor bolt prestress testing system, comprising a front-end hollow anchor bolt, a first connector, a hollow anchor bolt to be tested, a second connector, a rear-end hollow anchor bolt, a signal amplifier, a signal processor, and a computer; one end of the hollow anchor bolt to be tested is connected to the front-end hollow anchor bolt via the first connector, and the other end is connected to the rear-end hollow anchor bolt via the second connector; the first connector is connected to the signal amplifier via a shielded wire, the second connector is connected to the signal processor via a shielded wire, the signal amplifier is connected to the signal processor, and the signal processor is connected to the computer; an annular piezoelectric ceramic smart aggregate is disposed within the first connector, and the annular piezoelectric ceramic smart aggregate is disposed between the front-end hollow anchor bolt and the hollow anchor bolt to be tested; the structure of the second connector is the same as the structure of the first connector.

[0007] In implementation, this application connects the front hollow anchor rod, the hollow anchor rod under test, and the rear hollow anchor rod into a single anchor rod assembly via a first connector and a second connector. The prestress on the hollow anchor rod under test is detected using annular piezoelectric ceramic smart aggregate within the first and second connectors. During implementation, when the hollow anchor rod under test is subjected to prestress, the entire anchor rod assembly, consisting of the front hollow anchor rod, the hollow anchor rod under test, and the rear hollow anchor rod, will deform. This causes a change in its resonant frequency and the generation of a linear micro-defect, i.e., misalignment, within the anchor rod. This micro-defect affects the propagation of the stress wave, ultimately leading to a change in the piezoelectric signal. Therefore, the change in the anchor rod's prestress value can be determined by comparing the differences between the piezoelectric signals. Specifically, to better describe the scheme of this application, let's assume that the annular piezoelectric ceramic smart aggregate in the first connector is denoted as A, and the annular piezoelectric ceramic smart aggregate in the second connector is denoted as B. When performing prestress detection, firstly, when the hollow anchor rod under test is not subjected to prestress, an electrical signal is generated by a computer-controlled signal processor. After being amplified by a signal amplifier, the signal is transmitted to the annular piezoelectric ceramic smart aggregate A to generate a stress wave. The stress wave propagates along the hollow anchor rod under test to the annular piezoelectric ceramic smart aggregate B to generate an electrical signal. This electrical signal is transmitted to the signal processor via a shielded wire, and then collected by the signal processor and transmitted to the computer to obtain the piezoelectric signal of the hollow anchor rod under test when it is not subjected to prestress. When the hollow anchor rod under test is subjected to prestress, the anchor rod as a whole deforms, which affects the transmission of the stress wave. At this time, the piezoelectric signal received by the computer also changes accordingly, thereby detecting the prestress on the hollow anchor rod under test. More specifically, before the actual application of the anchor body composed of the front hollow anchor, the hollow anchor to be tested, and the rear hollow anchor, a preliminary experiment can be conducted. Different prestresses are applied to the hollow anchor to be tested, and the piezoelectric signals under different prestresses are measured. This yields the piezoelectric signal values ​​of the hollow anchor to be tested under different prestresses, allowing the solution provided in this application to better detect the prestress value of the hollow anchor to be tested during actual application. It is worth noting that the electrical signal generated by the signal processor and sent to the annular piezoelectric ceramic smart aggregate A should remain consistent during both the preliminary experiment and the actual application to ensure the accuracy of the prestress measurement during actual application.

[0008] Unlike existing technologies, the annular piezoelectric ceramic smart aggregate used in this application has better durability and a longer service life than strain gauges and fiber optic gratings, and can ensure real-time detection of prestressed anchor rods. At the same time, the annular piezoelectric ceramic smart aggregate is small in size and can be easily embedded inside the prestressed anchor rod without affecting its structural performance. Since the annular piezoelectric ceramic smart aggregate is embedded inside the prestressed anchor rod and forms a whole with it, it will not be damaged during actual construction. Therefore, the prestressed detection system provided in this application can perform detection in harsh environments without affecting the accuracy of the detection results.

[0009] Furthermore, the first connector also includes an anchor bolt connector and a pre-drilled hole for the shielded wire; the anchor bolt connector wraps around the front hollow anchor bolt and the hollow anchor bolt to be tested, and is used to fix the front hollow anchor bolt and the hollow anchor bolt to be tested; the pre-drilled hole for the shielded wire passes through the anchor bolt connector and is used to place the shielded wire. In implementation, the front hollow anchor bolt and the hollow anchor bolt to be tested are connected by the anchor bolt connector, thereby fixing the front hollow anchor bolt and the hollow anchor bolt to be tested into a whole. Since the annular piezoelectric ceramic smart aggregate is located between the front hollow anchor bolt and the hollow anchor bolt to be tested, after the front hollow anchor bolt and the hollow anchor bolt to be tested are fixed, the annular piezoelectric ceramic smart aggregate is fixed between the two. Similarly, the anchor bolt connector in the second connector fixes the hollow anchor bolt to be tested to the rear hollow anchor bolt. More specifically, the anchor bolt connector is made of internally threaded high-strength steel. Its internal thread matches the external thread of the front hollow anchor bolt, the hollow anchor bolt to be tested, and the rear hollow anchor bolt. During installation, after the anchor bolt connector securely connects the front hollow anchor bolt and the hollow anchor bolt to be tested, the shielded wire pre-drilled hole on it is placed at the annular piezoelectric ceramic smart aggregate so that the shielded wire can pass through the shielded wire pre-drilled hole and connect with the annular piezoelectric ceramic smart aggregate.

[0010] Furthermore, the inner and outer diameters of the annular piezoelectric ceramic smart aggregate are the same as those of the hollow anchor rod under test. In implementation, to better simulate the changes in the prestressed anchor rod under prestress, the inner and outer diameters of the annular piezoelectric ceramic smart aggregate are the same as those of the hollow anchor rod under test. This ensures a more stable overall anchor rod structure when the annular piezoelectric ceramic smart aggregate is embedded between the front hollow anchor rod and the hollow anchor rod under test, and between the hollow anchor rod under test and the rear hollow anchor rod, without affecting the structural performance of the anchor rod. It is worth noting that the annular piezoelectric ceramic smart aggregate located between the front hollow anchor rod and the hollow anchor rod under test, and the annular piezoelectric ceramic smart aggregate located between the hollow anchor rod under test and the rear hollow anchor rod, are two different annular piezoelectric ceramic smart aggregates.

[0011] Furthermore, the annular piezoelectric ceramic smart aggregate includes annular piezoelectric ceramic, electrode plates, and a copper shell. The inner and outer diameters of the electrode plates are the same as those of the annular piezoelectric ceramic. Two electrode plates are provided, respectively fixed to both sides of the annular piezoelectric ceramic. The copper shell wraps around the outer side of the annular piezoelectric ceramic, and the inside of the copper shell is coated with an insulating layer. In implementation of this application, two electrode plates are provided, both connected to the same shielded wire via connecting wires, and respectively disposed at both ends of the annular piezoelectric ceramic. The copper shell wraps around the outer side of the annular piezoelectric ceramic and the electrode plates to protect them. Simultaneously, a pre-drilled hole is provided in the copper shell to allow the connecting wires connected to the two electrode plates to pass through the copper shell and connect to the shielded wire.

[0012] Furthermore, a coupling agent is applied to both the surface of the annular piezoelectric ceramic smart aggregate and both ends of the hollow anchor rod under test. In implementation, this application involves uniformly applying the coupling agent to both the surface of the annular piezoelectric ceramic smart aggregate and both ends of the hollow anchor rod under test to ensure that stress waves can propagate well at the contact surface between the annular piezoelectric ceramic smart aggregate and the hollow anchor rod under test.

[0013] Secondly, this application also provides a method for detecting the prestress of hollow anchor bolts based on piezoelectric ceramics, using the piezoelectric ceramic-based hollow anchor bolt prestress detection system described above, including the following steps:

[0014] S1: Indoors, the piezoelectric signals of the hollow anchor rod under different prestresses are acquired in advance through the detection system. Wavelet packet analysis is used to establish a curve showing the relationship between the prestress value and the degree of change of the measured piezoelectric signal.

[0015] S2: Install the hollow anchor rod to be tested into the testing system at the construction site;

[0016] S3: The piezoelectric signal of the hollow anchor rod to be tested, which has been prestressed, is detected by the detection system. Combined with the relationship curve between the prestress value and the degree of change of the measured piezoelectric signal established in step S1, the prestress value of the hollow anchor rod to be tested is obtained.

[0017] It should be noted that during the indoor experiment in step S1, the hollow anchor rod to be tested may undergo plastic deformation or even be destroyed. Therefore, the hollow anchor rod to be tested used in steps S2 and S3 is not the same as the hollow anchor rod to be tested in step S1, but is an anchor rod with the same material and size.

[0018] Furthermore, step S1 specifically includes:

[0019] S11: Determine the dimensions of the hollow anchor rod to be tested;

[0020] S12: Connect the hollow anchor rod to be tested to the detection system indoors, fix the rear hollow anchor rod with tensioning equipment, and record the piezoelectric signal when no prestress is applied;

[0021] S13: Pull out the front hollow anchor rod until the prestress on the hollow anchor rod to be tested reaches the design prestress. During this process, the piezoelectric signals corresponding to different applied prestresses are measured.

[0022] S14: Perform wavelet packet decomposition on the measured piezoelectric signal to obtain the decomposed signal;

[0023] S15: Calculate the energy of the decomposed signal, characterize the degree of change of the piezoelectric signal through statistical indicators, and establish the relationship curve between the degree of change of the piezoelectric signal and the prestress value.

[0024] Specifically, in the implementation of this application, the tensioning equipment is a horizontal pull-out apparatus, a jack equipped with a through-axis force gauge, or other equipment capable of applying prestress to the hollow anchor rod under test in real time and allowing a computer to measure the corresponding piezoelectric signal. In this application, the design prestress value is the maximum prestress value applied in the indoor experiment in step S1. It should be noted that in actual construction, the prestress value required for the hollow anchor rod under test is usually known. Therefore, in step S12, the design prestress value only needs to be greater than the required prestress value for the hollow anchor rod under test. However, when the required prestress value for the hollow anchor rod under test is unknown during actual construction, the design prestress value is the maximum prestress that the hollow anchor rod under test can withstand.

[0025] Furthermore, when applying prestress to the hollow anchor rod at the front end during pull-out, the prestress is applied in stages starting from 0 until the design prestress is reached. Each application of prestress is 10% of the design prestress, and the hollow anchor rod is left to stand after each application to allow for prestress relaxation. Specifically, in this embodiment, the purpose of applying prestress in stages is to ensure a consistent loading rhythm at different locations, improving the repeatability and accuracy of the experiment. Simultaneously, the purpose of using 10% of the design prestress for each application is to balance the smoothness of the relationship curve between the experimental time and the final piezoelectric signal change and stress value. More specifically, in actual operation, the amount of prestress applied each time can be adjusted according to actual needs, and it does not necessarily have to be 10% of the design prestress, but the amount should not be too large to avoid obtaining too little data and resulting in a less reliable final curve.

[0026] Furthermore, step S3 specifically includes:

[0027] S31: Apply prestress to the front hollow anchor rod, and measure the piezoelectric signal after the front hollow anchor rod is left to stand still to relieve the prestress relaxation.

[0028] S32: Perform wavelet packet decomposition on the piezoelectric signal measured in step S31 to obtain the decomposed signal;

[0029] S33: Calculate the energy of the decomposed signal and characterize the degree of change of the piezoelectric signal through statistical indicators;

[0030] S34: Substitute the statistical index obtained in S33 into the relationship curve between the piezoelectric signal change and the prestress value to obtain the prestress value of the hollow anchor rod to be tested.

[0031] In summary, compared with the prior art, the present invention has the following advantages: the present invention can perform prestress detection of prestressed anchor rods in harsh environments; it is small in size and can be easily installed or embedded inside the prestressed anchor rod without affecting its structural performance; the present invention has good durability and long service life, and can ensure real-time detection; the present invention has a simple structure, low cost, stable signal, and high operational safety, and ordinary researchers and general laboratories can use this detection system and method to detect the prestress of hollow anchor rods. Attached Figure Description

[0032] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0033] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the structure of the first and second anchor bolt connectors according to an embodiment of the present invention;

[0035] Figure 3 This is a schematic diagram of the structure of the piezoelectric ceramic smart aggregate according to an embodiment of the present invention;

[0036] Figure 4 This is a curve showing the change in electrical signal (MAPD value) with the prestress value in an embodiment of the present invention.

[0037] The names corresponding to the reference numerals in the attached figures are as follows: 1. Prestressed anchor head; 2. Pad plate; 3. Grout stop plug; 4. Front hollow anchor rod; 5. Anchor hole; 6. Shielded wire; 7. First connector; 8. Hollow anchor rod to be tested; 9. Second connector; 10. Rear hollow anchor rod; 11. Third connector; 12. Anchor rod in anchoring section; 13. Resin anchoring agent; 14. Signal amplifier; 15. Signal processor; 16. Computer; 17. Anchor rod connector; 18. Shielded wire reserved hole; 19. Annular piezoelectric ceramic smart aggregate; 20. Copper shell; 21. Electrode sheet; 22. Annular piezoelectric ceramic. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0039] Example:

[0040] like Figures 1 to 3 As shown, a piezoelectric ceramic-based hollow anchor bolt prestress testing system includes a front-end hollow anchor bolt 4, a first connector 7, a hollow anchor bolt 8 to be tested, a second connector 9, a rear-end hollow anchor bolt 10, a signal amplifier 14, a signal processor 15, and a computer 16. One end of the hollow anchor bolt 8 to be tested is connected to the front-end hollow anchor bolt 4 via the first connector 7, and the other end is connected to the rear-end hollow anchor bolt 10 via the second connector 9. The first connector 7 is connected to the signal amplifier 14 via a shielded wire 6, and the second connector 9 is connected to the signal processor 15 via a shielded wire 6. The signal amplifier 14 is connected to the signal processor 15, and the signal processor 15 is connected to the computer 16. An annular piezoelectric ceramic smart aggregate 19 is disposed inside the first connector 7, and the annular piezoelectric ceramic smart aggregate 19 is disposed between the front-end hollow anchor bolt 4 and the hollow anchor bolt 8 to be tested. The structure of the second connector 9 is the same as that of the first connector 7.

[0041] In this embodiment, the front hollow anchor rod 4, the hollow anchor rod 8 to be tested, and the rear hollow anchor rod 10 are connected into a single anchor rod assembly via the first connector 7 and the second connector 9. The prestress on the hollow anchor rod 8 is detected through the annular piezoelectric ceramic smart aggregate 19 within the first connector 7 and the second connector 9. During implementation, when the hollow anchor rod 8 is subjected to prestress, the entire anchor rod assembly, consisting of the front hollow anchor rod 4, the hollow anchor rod 8 to be tested, and the rear hollow anchor rod 10, will deform. This will change its resonant frequency, and simultaneously generate a linear micro-defect, i.e., misalignment. This micro-defect will affect the propagation of the stress wave, ultimately leading to a change in the piezoelectric signal. Therefore, the change in the anchor rod prestress value can be determined by comparing the differences between the piezoelectric signals. Specifically, to better describe the scheme of this embodiment, it is assumed that the annular piezoelectric ceramic smart aggregate 19 in the first connector 7 is denoted as A, and the annular piezoelectric ceramic smart aggregate 19 in the second connector 9 is denoted as B. When performing prestress detection, firstly, when the hollow anchor rod 8 under test is not subjected to prestress, the computer 16 controls the signal processor 15 to generate an electrical signal, which is amplified by the signal amplifier 14 and transmitted to the annular piezoelectric ceramic smart aggregate 19A to generate a stress wave. The stress wave propagates along the hollow anchor rod 8 under test to the annular piezoelectric ceramic smart aggregate 19B to generate an electrical signal. This electrical signal is transmitted to the signal processor 15 through the shielded wire 6, and is collected by the signal processor 15 and transmitted to the computer 16 to obtain the piezoelectric signal of the hollow anchor rod 8 under test when it is not subjected to prestress. When the hollow anchor rod 8 under test is subjected to prestress, the anchor rod as a whole deforms, thereby affecting the transmission of the stress wave. At this time, the piezoelectric signal received by the computer 16 also changes accordingly, and thus the prestress of the hollow anchor rod 8 under test is detected. More specifically, before the overall anchor system, consisting of the front hollow anchor 4, the hollow anchor 8 to be tested, and the rear hollow anchor 10, is actually applied, a preliminary experiment can be conducted. Different prestresses are applied to the hollow anchor 8 to be tested, and the piezoelectric signals under different prestresses are measured. This yields the piezoelectric signal values ​​of the hollow anchor 8 under different prestresses, allowing the solution provided in this application to better detect the prestress value of the hollow anchor 8 during actual application. It is worth noting that the electrical signal generated by the signal processor 15 and sent to the annular piezoelectric ceramic smart aggregate 19A should remain consistent during both the preliminary experiment and the actual application to ensure the accuracy of the prestress measurement during actual application.

[0042] Unlike existing technologies, the annular piezoelectric ceramic smart aggregate 19 used in this embodiment has better durability and a longer service life than strain gauges and fiber optic gratings, and can ensure real-time detection of prestressed anchor rods. At the same time, the annular piezoelectric ceramic smart aggregate 19 has a small volume, which can be easily embedded into the prestressed anchor rod without affecting its structural performance. Since the annular piezoelectric ceramic smart aggregate 19 is embedded in the prestressed anchor rod and forms a whole with it, it will not be damaged during actual construction. Therefore, the prestress detection system provided in this embodiment can perform detection in harsh environments without affecting the accuracy of the detection results.

[0043] like Figure 2 As shown, the first connector 7 also includes an anchor bolt connector 17 and a shielded wire pre-drilled hole 18; the anchor bolt connector 17 wraps around the front hollow anchor bolt 4 and the hollow anchor bolt 8 to be tested, and is used to fix the front hollow anchor bolt 4 and the hollow anchor bolt 8 to be tested; the shielded wire pre-drilled hole 18 penetrates the anchor bolt connector 17 and is used to place the shielded wire 6. In this embodiment, the front hollow anchor bolt 4 and the hollow anchor bolt 8 to be tested are connected by the anchor bolt connector 17, so that the front hollow anchor bolt 4 and the hollow anchor bolt 8 to be tested are fixed to form a whole. Since the annular piezoelectric ceramic smart aggregate 19 is located between the front hollow anchor bolt 4 and the hollow anchor bolt 8 to be tested, after the front hollow anchor bolt 4 and the hollow anchor bolt 8 to be tested are fixed, the annular piezoelectric ceramic smart aggregate 19 is fixed between the two. Similarly, the anchor bolt connector 17 in the second connector 9 fixes the hollow anchor bolt 8 to be tested and the rear hollow anchor bolt 10. More specifically, the anchor bolt connector 17 is made of internally threaded high-strength steel, and its internal thread matches the external thread of the front hollow anchor bolt 4, the hollow anchor bolt 8 to be tested, and the rear hollow anchor bolt 10. During installation, after the anchor bolt connector 17 securely connects the front hollow anchor bolt 4 and the hollow anchor bolt 8 to be tested, the shielded wire reserved hole 18 provided on it is placed at the annular piezoelectric ceramic smart aggregate 19 so that the shielded wire 6 can pass through the shielded wire reserved hole 18 and connect with the annular piezoelectric ceramic smart aggregate 19.

[0044] Furthermore, the inner and outer diameters of the annular piezoelectric ceramic smart aggregate 19 are the same as those of the hollow anchor rod 8 under test. In this embodiment, to better simulate the changes in the prestressed anchor rod under prestress, the inner and outer diameters of the annular piezoelectric ceramic smart aggregate 19 are the same as those of the hollow anchor rod 8 under test. This ensures that the overall anchor rod structure formed when the annular piezoelectric ceramic smart aggregate 19 is embedded between the front hollow anchor rod 4 and the hollow anchor rod 8 under test, and between the hollow anchor rod 8 under test and the rear hollow anchor rod 10, is more stable without affecting the structural performance of the anchor rod. It is worth noting that the annular piezoelectric ceramic smart aggregate 19 located between the front hollow anchor rod 4 and the hollow anchor rod 8 under test, and the annular piezoelectric ceramic smart aggregate 19 located between the hollow anchor rod 8 under test and the rear hollow anchor rod 10, are two different annular piezoelectric ceramic smart aggregates 19.

[0045] like Figure 3 As shown, the annular piezoelectric ceramic smart aggregate 19 includes annular piezoelectric ceramic 22, electrode plates 21, and a copper shell 20. The inner and outer diameters of the electrode plates 21 are the same as those of the annular piezoelectric ceramic 22. Two electrode plates 21 are provided, respectively fixed to both sides of the annular piezoelectric ceramic 22. The copper shell 20 is wrapped around the outside of the annular piezoelectric ceramic 22, and the inside of the copper shell 20 is coated with an insulating layer. In this embodiment, two electrode plates 21 are provided, both connected to the same shielded wire 6 via connecting wires, and respectively located at both ends of the annular piezoelectric ceramic 22. The copper shell 20 is wrapped around the outside of the annular piezoelectric ceramic 22 and the electrode plates 21 to protect them. At the same time, a reserved hole is provided in the copper shell 20 to allow the connecting wires connected to the two electrode plates 21 to pass through the copper shell 20 and connect to the shielded wire 6.

[0046] Furthermore, a coupling agent is applied to both the surface of the annular piezoelectric ceramic smart aggregate 19 and both ends of the hollow anchor rod 8 under test. In this embodiment, the coupling agent is evenly applied to both the surface of the annular piezoelectric ceramic smart aggregate 19 and both ends of the hollow anchor rod 8 under test to ensure that the stress wave can propagate well at the contact surface between the annular piezoelectric ceramic smart aggregate 19 and the hollow anchor rod 8 under test.

[0047] Based on the aforementioned piezoelectric ceramic-based hollow anchor bolt prestress detection system, this embodiment also provides a piezoelectric ceramic-based hollow anchor bolt prestress detection method, comprising the following steps:

[0048] S1: In the indoor environment, the piezoelectric signals of the hollow anchor rod 8 under different prestresses are acquired in advance through the detection system. By wavelet packet analysis, a relationship curve between the prestress value and the degree of change of the measured piezoelectric signal is established.

[0049] S2: Install the hollow anchor rod 8 to be tested into the testing system at the construction site;

[0050] S3: The piezoelectric signal of the hollow anchor rod 8 under test, which has been prestressed, is detected by the detection system. Combined with the relationship curve between the prestress value and the degree of change of the measured piezoelectric signal established in step S1, the prestress value of the hollow anchor rod 8 under test is obtained.

[0051] It should be noted that during the indoor experiment in step S1, the hollow anchor rod 8 to be tested may undergo plastic deformation or even be destroyed. Therefore, the hollow anchor rod 8 to be tested used in steps S2 and S3 is not the same as the hollow anchor rod 8 to be tested in step S1, but is an anchor rod with the same material and size.

[0052] Furthermore, step S1 specifically includes:

[0053] S11: Determine the dimensions of the hollow anchor rod 8 to be tested;

[0054] S12: Indoors, connect the hollow anchor rod 8 to the detection system, fix the rear hollow anchor rod 10 with tensioning equipment, and record the piezoelectric signal when no prestress is applied.

[0055] S13: Pull out the front hollow anchor rod 4 until the prestress on the hollow anchor rod 8 to be tested reaches the design prestress. During this process, the piezoelectric signals corresponding to different applied prestresses are measured.

[0056] S14: Perform wavelet packet decomposition on the measured piezoelectric signal to obtain the decomposed signal;

[0057] S15: Calculate the energy of the decomposed signal, characterize the degree of change of the piezoelectric signal through statistical indicators, and establish the relationship curve between the degree of change of the piezoelectric signal and the prestress value.

[0058] Specifically, in this embodiment, the tensioning equipment is a horizontal pull-out apparatus, a jack equipped with a through-axis force gauge, or other equipment capable of applying prestress to the hollow anchor rod 8 under test in real time and allowing the computer 16 to measure the corresponding piezoelectric signal. In this embodiment, the designed prestress value is the maximum prestress value applied in the indoor experiment in step S1. It should be noted that in actual construction, the required prestress value for the hollow anchor rod 8 under test is usually known. Therefore, in step S12, the designed prestress value only needs to be greater than the required prestress value for the hollow anchor rod 8 under test. However, when the required prestress value for the hollow anchor rod 8 under test is unknown during actual construction, the designed prestress value is the maximum prestress that the hollow anchor rod 8 under test can withstand.

[0059] Furthermore, when applying prestress to the hollow anchor rod 4 at the front end during pull-out, the prestress is applied in stages starting from 0 until the design prestress is reached. Each application of prestress is 10% of the design prestress, and the hollow anchor rod 4 is left to stand after each application to allow for prestress relaxation. Specifically, in this embodiment, the purpose of applying prestress in stages is to ensure a consistent loading rhythm at different locations, improving the repeatability and accuracy of the experiment. Simultaneously, the purpose of using 10% of the design prestress for each application is to balance the smoothness of the relationship curve between the experimental time and the final piezoelectric signal change and stress value. More specifically, in actual operation, the amount of prestress applied each time can be adjusted according to actual needs, and it does not necessarily have to be 10% of the design prestress, but the amount should not be too large to avoid obtaining too little data and resulting in a less reliable final curve.

[0060] Furthermore, step S3 specifically includes:

[0061] S31: Apply prestress to the front hollow anchor rod 4, and measure the piezoelectric signal after allowing the front hollow anchor rod 4 to relax the prestress.

[0062] S32: Perform wavelet packet decomposition on the piezoelectric signal measured in step S31 to obtain the decomposed signal;

[0063] S33: Calculate the energy of the decomposed signal and characterize the degree of change of the piezoelectric signal through statistical indicators;

[0064] S34: Substitute the statistical index obtained in S33 into the relationship curve between the piezoelectric signal change and the prestress value to obtain the prestress value of the hollow anchor rod 8 to be tested.

[0065] To better illustrate this detection method, a more specific embodiment is provided below to explain the detection system and method.

[0066] S11: Determine the dimensions of the hollow anchor rod 8 to be tested: the front hollow anchor rod 4 is 1m long, the hollow anchor rod 8 to be tested is 0.5m long, and the rear hollow anchor rod 10 is 1m long. In this embodiment, the front hollow anchor rod 4, the hollow anchor rod 8 to be tested, and the rear hollow anchor rod 10 are all hollow high-strength threaded steel with an inner diameter of 15mm, an outer diameter of 25mm, and a thread pitch of 5mm. The matching first connector 7 and second connector 9 are internally threaded high-strength steel with a length of 100mm and a thickness of 5mm. To match the hollow anchor rod 8 to be tested, the selected annular piezoelectric ceramic smart aggregate 19 has an inner diameter of 15mm, an outer diameter of 25mm, and a thickness of 3mm.

[0067] S12: Apply KMD-398A ultrasonic transducer adhesive evenly to the surface of the annular piezoelectric ceramic smart aggregate 19, and apply KMD-398A ultrasonic transducer adhesive evenly to both ends of the hollow anchor rod 8 to be tested. Connect the front hollow anchor rod 4 to the hollow anchor rod 8 to be tested via the first connector 7, and connect the rear hollow anchor rod 10 to the hollow anchor rod 8 to be tested via the second connector 9. Record the piezoelectric signal when no prestress is applied.

[0068] S13: Prestress was applied to the front hollow anchor rod in four stages using a horizontal pull-out apparatus, with each stage being 5 kN, up to a total of 50 kN. After each stage of prestress was applied, the rod was allowed to stand still for 5 minutes to allow the prestress to relax, and then the piezoelectric signals under each stage of prestress were measured.

[0069] Specifically, the annular piezoelectric ceramic smart aggregate 19 in the first connector 7 is used as the signal transmitter, denoted as SA1, and the annular piezoelectric ceramic smart aggregate 19 in the second connector 9 is used as the signal receiver, denoted as SA2. The specific method for measuring the piezoelectric signal corresponding to the applied prestress is as follows: When measuring the piezoelectric signal without applied prestress: The signal processor 15 is controlled by LabVIEW software on a computer to generate a sweep frequency excitation signal. After being amplified by the signal amplifier 14, a stress wave is generated via SA1. The stress wave propagates along the hollow anchor rod 8 to be tested to SA2, generating an electrical signal. This signal is collected by the signal processor 15 and transmitted to the computer 16 to obtain the piezoelectric signal corresponding to the absence of applied prestress. The sweep frequency excitation signal has a starting frequency of 100Hz, an ending frequency of 200,000Hz, 400,000 sampling points, a period of 1s, and an amplitude of 5V. When measuring the piezoelectric signal when prestress is applied: the starting frequency, ending frequency, number of sampling points, period, and amplitude of the generated sweep excitation signal are the same as when measuring the piezoelectric signal when no prestress is applied. After applying prestress and allowing it to stand still for 5 minutes, the piezoelectric signal when prestress is applied is measured.

[0070] In this embodiment, there are ten levels of prestress applied, and ten sets of piezoelectric signals can be collected. In addition to the piezoelectric signals when no prestress is applied, a total of eleven sets of piezoelectric signals are collected.

[0071] S14: Using MATLAB software, wavelet packet decomposition was performed on the eleven received piezoelectric signals. Each piezoelectric signal underwent three-level wavelet packet decomposition, resulting in eight decomposed signals for each piezoelectric signal.

[0072] S15: The energy values ​​of each decomposed signal are calculated, and after nonlinear fitting, the curve of the piezoelectric signal change (MAPD value) versus the prestress value is plotted, as shown below. Figure 4 As shown.

[0073] Specifically, after performing wavelet packet decomposition on the measured piezoelectric signal, the energy of the decomposed signal is calculated as follows:

[0074]

[0075] In the formula, E j L represents the energy of the decomposed signal in band j; js represents each sampling point of the decomposed signal in band j; m represents the number of sampling points.

[0076] Therefore, the degree of change in the piezoelectric signal can be further characterized by the statistical indicator MAPD (absolute proportional deviation).

[0077]

[0078] In the formula: N represents the number of decomposed signals; E i,j E represents the signal energy in band j under prestress (kN); r,j The signal energy represents the signal energy of band j in the initial state (without prestress).

[0079] Substituting the energy values ​​of each decomposed signal under different prestress states into the above formula, we obtain the energy values ​​of each decomposed signal under different prestress states. After nonlinear fitting, we plot the curve of the piezoelectric signal variation (MAPD value) as a function of the prestress value, as shown below. Figure 4 As shown.

[0080] S2: At the construction site, such as Figure 1 The connection detection system is shown. In this embodiment, the front hollow anchor rod 4 is equipped with a prestressed anchor head 1, a pad 2, and a grout stop plug 3. The rear hollow anchor rod 10 is connected to the anchoring section anchor rod 12 via a third connector 11, which has a reserved grouting hole. The anchoring section anchor rod 12 is surrounded by a resin anchoring agent 13 to tightly bond the anchoring section anchor rod 12 to the wall of the anchor hole 5. Specifically, the material and structure of the third connector 11 are the same as those of the anchor rod connector 17, the only difference being that the third connector 11 does not have a reserved hole 18 for shielded wires.

[0081] S31: After the anchoring is stable, apply a prestress of 50KN to the front hollow anchor rod 4. After the application is completed, let it stand for 5 minutes to relax the prestress and then measure the piezoelectric signal.

[0082] S32: Perform wavelet packet decomposition on the piezoelectric signal measured in step S31 to obtain the decomposed signal;

[0083] S33: Calculate the energy of the decomposed signal and characterize the degree of change of the piezoelectric signal through statistical indicators;

[0084] S34: Substitute the statistical indicators obtained from S33 into... Figure 4 The curve showing the relationship between the degree of change of the piezoelectric signal and the prestress value yields the actual prestress value applied to the hollow anchor rod 8 under test.

[0085] In this embodiment, the detection system and method can continuously monitor changes in the hollow anchor bolt, thereby preventing accidents from occurring.

[0086] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A prestress detection system for hollow anchor bolts based on piezoelectric ceramics, characterized in that, The system includes a front hollow anchor rod (4), a first connector (7), a hollow anchor rod to be tested (8), a second connector (9), a rear hollow anchor rod (10), a signal amplifier (14), a signal processor (15), and a computer (16). One end of the hollow anchor rod to be tested (8) is connected to the front hollow anchor rod (4) via the first connector (7), and the other end is connected to the rear hollow anchor rod (10) via the second connector (9). The first connector (7) is connected to the signal amplifier (14) via a shielded wire (6). The second connector (9) is connected to the signal processor (15) via a shielded wire (6), the signal amplifier (14) is connected to the signal processor (15), and the signal processor (15) is connected to the computer (16); the first connector (7) is provided with an annular piezoelectric ceramic smart aggregate (19), which is located between the front hollow anchor rod (4) and the hollow anchor rod to be tested (8); the structure of the second connector (9) is the same as that of the first connector (7); The first connector (7) further includes an anchor bolt connector (17) and a shielded wire reserved hole (18); the anchor bolt connector (17) is wrapped around the front hollow anchor bolt (4) and the hollow anchor bolt to be tested (8) to fix the front hollow anchor bolt (4) and the hollow anchor bolt to be tested (8); the shielded wire reserved hole (18) passes through the anchor bolt connector (17) and is used to place the shielded wire (6); The inner and outer diameters of the annular piezoelectric ceramic smart aggregate (19) are the same as the inner and outer diameters of the hollow anchor rod (8) to be tested.

2. The hollow anchor bolt prestress detection system based on piezoelectric ceramics according to claim 1, characterized in that, The annular piezoelectric ceramic smart aggregate (19) includes an annular piezoelectric ceramic (22), electrode plates (21), and a copper shell (20); the inner and outer diameters of the electrode plates (21) are the same as the inner and outer diameters of the annular piezoelectric ceramic (22), and two electrode plates (21) are provided, which are respectively fixed on both sides of the annular piezoelectric ceramic (22). The copper shell (20) is wrapped around the outer side of the annular piezoelectric ceramic (22), and the inside of the copper shell (20) is coated with an insulating layer.

3. The hollow anchor bolt prestress detection system based on piezoelectric ceramics according to claim 1, characterized in that, The surface of the annular piezoelectric ceramic smart aggregate (19) and both ends of the hollow anchor rod (8) to be tested are coated with coupling agent.

4. A method for detecting prestress in hollow anchor bolts based on piezoelectric ceramics, characterized in that, The hollow anchor bolt prestress detection system based on piezoelectric ceramics as described in any one of claims 1 to 3 includes the following steps: S1: In the indoor environment, the piezoelectric signals of the hollow anchor rod (8) under different prestresses are obtained in advance by the detection system. By wavelet packet analysis, the relationship curve between the prestress value and the degree of change of the measured piezoelectric signal is established. S2: Install the hollow anchor rod (8) to be tested into the testing system at the construction site; S3: The piezoelectric signal of the hollow anchor rod (8) under test that has been prestressed is detected by the detection system. The prestress value of the hollow anchor rod (8) under test is obtained by combining the relationship curve between the prestress value and the degree of change of the measured piezoelectric signal established in step S1.

5. The method for detecting prestress in hollow anchor bolts based on piezoelectric ceramics according to claim 4, characterized in that, Step S1 specifically involves: S11: Determine the dimensions of the hollow anchor rod (8) to be tested; S12: Indoors, connect the hollow anchor rod (8) to be tested to the detection system, fix the rear hollow anchor rod (10) by tensioning equipment, and record the piezoelectric signal when no prestress is applied; S13: Pull out the front hollow anchor rod (4) until the prestress of the hollow anchor rod (8) to be tested reaches the design prestress. During this process, the piezoelectric signals corresponding to different prestresses are measured. S14: Perform wavelet packet decomposition on the measured piezoelectric signal to obtain the decomposed signal; S15: Calculate the energy of the decomposed signal, characterize the degree of change of the piezoelectric signal through statistical indicators, and establish the relationship curve between the degree of change of the piezoelectric signal and the prestress value.

6. The method for detecting prestress in hollow anchor bolts based on piezoelectric ceramics according to claim 5, characterized in that, When applying prestress to the front hollow anchor rod (4) during the pulling process, the prestress is applied in stages starting from 0 until the design prestress is reached. The amount of pressure applied each time is 10% of the design prestress. After each pressure application, the front hollow anchor rod (4) is left to stand still to relieve the prestress relaxation.

7. The method for detecting prestress in hollow anchor bolts based on piezoelectric ceramics according to claim 5, characterized in that, Step S3 specifically involves: S31: Apply prestress to the front hollow anchor rod (4), and measure the piezoelectric signal after the front hollow anchor rod (4) is left to relax the prestress. S32: Perform wavelet packet decomposition on the piezoelectric signal measured in step S31 to obtain the decomposed signal; S33: Calculate the energy of the decomposed signal and characterize the degree of change of the piezoelectric signal through statistical indicators; S34: Substitute the statistical index obtained in S33 into the relationship curve between the piezoelectric signal change and the prestress value to obtain the prestress value of the hollow anchor rod (8) to be tested.

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