CN114059602A - Anchor cable prestressed non-destructive testing system and testing method - Google Patents
Anchor cable prestressed non-destructive testing system and testing method Download PDFInfo
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Abstract
The invention provides a nondestructive detection system and a detection method for prestress of an anchor cable. The detection method is an anchor cable prestress nondestructive detection method, hardly causes adverse effects on an original prestress structure, can solve the problems of complex operation procedure, high detection cost and the like of the existing anchor cable stress detection method, and simultaneously, because tangential excitation and vibration displacement test are carried out on an outer anchoring section of a prestress anchor cable, the detection process is convenient and fast, the detection efficiency is high, the detection cost is low, the method is applicable to anchor cables in various projects such as geotechnical engineering, bridge engineering and the like, and the application range is wide.
Description
Technical Field
The invention belongs to the field of anchor cable prestress detection engineering, and particularly relates to an anchor cable prestress nondestructive detection system and an anchor cable prestress nondestructive detection method.
Background
The prestress technology can exert the self strength and self-supporting capability of the structure, has safety and economy, and is widely applied to the engineering fields of traffic, transportation and the like. According to the regulations of the department of transportation, the prestressed technology is required to be used for beam slabs with a span of more than fifteen meters, and the prestressed anchor cable support in the slope support is also the mainstream. According to the development and statistics bulletin of the traffic and transportation industry in 2019, the business mileage of the traffic and transportation in China is increased year by year, and the use of the prestress technology can keep a good growth situation. The magnitude of the stress in the anchor cable determines the anchoring quality of the prestressed structure, which is a key factor affecting the stability and safety of the prestressed structure, and although the construction quality requirement is continuously improved, the accident of failure and damage of the engineering caused by the prestressed loss still appears endlessly, wherein the prestressed loss is a main factor affecting the failure and damage of the engineering structure. In order to ensure that the prestressed structure can normally play its role, it is necessary to detect and study the actual existing prestress of the engineering structure, so as to know the working state of the structure more truly and accurately.
The method for detecting the stress of the anchor cable in the prior art mainly comprises the following four methods:
the method comprises the following steps: and (4) carrying out reverse pulling on the prestressed anchor cable which is not anchored in the construction stage by a jack to obtain a jack reverse pulling method of the anchor cable stress. The method has the following technical problems: 1) the method belongs to a mechanical detection method, and the tensioned and anchored anchor cable needs to be pulled reversely, so that disturbance can be generated on an anchored body reinforced by the anchor cable, the anchoring effect is reduced, and only individual spot check is limited; 2) grouting and anchor sealing can be carried out on the anchor cable in the working operation stage, and the anchor cable in the operation stage cannot be measured by the detection method; 3) the jack equipment used in the reverse drawing method is difficult to flexibly use in part of complex construction environments (such as cast-in-place beams and high slopes).
The second method comprises the following steps: and in the construction stage, the straight-through pressure sensor is arranged between the anchorage device and the anchor backing plate, and the deformation amount of the pressure sensor is measured and converted in the anchor cable stretching process to obtain the prestress of the anchor cable. The method has the following technical problems: 1) the pressure sensor can only take effect if being arranged between the anchorage device and the anchor backing plate in advance, and the sensor is difficult to repair and replace once being damaged; 2) the inspection and maintenance process is complicated and difficult to replace once damaged.
The third method comprises the following steps: and the anchor cable penetrating stage is pre-embedded together with the anchor cable in advance, and the magnetic flux sensor method is based on the principle of the magnetoelastic effect of the ferromagnetic material. The method has the following technical problems: 1) the manufacturing cost is high, the anchor cable needs to be pre-embedded in advance, the installation process along with anchor cable holes is complex, and the sensor is prevented from being damaged; 2) the magnetic permeability of the ferromagnetic material is in nonlinear correlation with temperature, and is greatly influenced by the temperature; 3) the magnetic flux sensor can only monitor the prestress of the anchor cable pre-embedded in advance, and the large-range detection cost is high.
The method four comprises the following steps: and an elastic wave detection method for detecting the prestress of the bare steel cable by using the impact elastic wave through the transverse natural frequency. The method has the following technical problems: 1) the method mainly achieves the purpose of measuring the prestress of the anchor cable by utilizing the corresponding relation between the action frequency after the steel cable is tensioned and tensioning, the middle part of the tensioned steel cable needs to be directly excited in the detection process, but the side slope anchor cable or prestressed concrete is an embedded anchor cable and cannot directly excite free vibration to the anchor cable; 2) the existing detection theory cannot meet the requirement of engineering detection precision due to the fact that the existing detection theory has more influence factors of the vibration frequency.
In summary, because the prestressed anchor cables in the side slope and the prestressed concrete are all positioned in the structure body, no embedded nondestructive testing method capable of quickly reflecting the prestress of the anchor cable is available at present.
Disclosure of Invention
The invention aims to solve the technical problems in the prior art, and aims to provide an anchor cable prestress nondestructive testing system and an anchor cable prestress nondestructive testing method so as to solve the technical problems of structural damage, complex process, high cost and the like of the existing anchor cable stress testing method.
In order to achieve the purpose, the invention adopts the following technical scheme: a prestressed nondestructive detection system of an anchor cable is characterized in that a prestressed anchor cable system carries out prestressed anchorage through the anchor cable, and an anchor backing plate for transmitting stress to an anchored body and an anchor for locking the anchor cable are sequentially arranged at the outer anchorage section of the anchor cable; the detection system comprises a detection device and a host connected with the detection device; the detection device comprises an excitation force device for applying tangential excitation force to the anchorage device and detecting the tangential excitation force, and a displacement signal collector for detecting the relative tangential displacement of the anchorage device and the anchorage backing plate; the host comprises a microprocessor, a memory and a display; the signal output ends of the exciting force device and the displacement signal collector are connected with a microprocessor, and the microprocessor is used for extracting the exciting force signal of the exciting force device and the displacement signal waveform of the displacement signal collector, simultaneously carrying out signal processing on the exciting force signal and the displacement signal and calculating a detection result; the microprocessor is connected with the memory, and the memory is used for storing working parameters and detection results of the host; the microprocessor and the memory are respectively connected with a display, and the display is used for displaying the displacement waveform, the detection result and the working parameter setting of the host.
According to the invention, tangential exciting force is applied to the anchor, and the relative tangential displacement between the anchor and the anchor backing plate is detected, so that the tangential contact rigidity between the anchor and the anchor backing plate is obtained through calculation, the detection system is an anchor cable prestress nondestructive detection system based on the tangential contact rigidity of the outer anchor head, and the problems of complex operation program, high detection cost and the like of the existing anchor cable prestress detection method can be solved; meanwhile, because the tangential excitation and the vibration displacement test are carried out on the anchorage device outside the prestressed anchor cable, the detection process is convenient and fast, and the detection cost is low.
In a preferred embodiment of the invention, the exciting force device is an exciting hammer, the exciting hammer comprises a force hammer and an acceleration sensor for measuring the acceleration of the force hammer, and the signal output end of the acceleration sensor is connected with the microprocessor.
In the technical scheme, the excitation force device is the excitation hammer with the acceleration sensor, the structure is simple, the tangential excitation force can be calculated according to the product of the mass m of the excitation hammer and the excitation acceleration, and the value of the tangential excitation force is convenient to obtain.
In a preferred embodiment of the present invention, the detection device further includes a signal processor, signal output terminals of the acceleration sensor and the displacement signal collector are respectively connected to the signal processor, an output terminal of the signal processor is connected to the microprocessor, the signal processor performs noise reduction preprocessing on data collected by the acceleration sensor and the displacement signal collector, performs a/D signal conversion, and converts continuous analog signals into discrete digital signals.
In the technical scheme, the signal processor is arranged, the signal processor performs A/D conversion on the acceleration signal acquired by the acceleration sensor and the displacement signal acquired by the displacement signal acquisition device in advance, and converts a continuous analog signal into a discrete digital signal for the microprocessor to recognize and store by the memory.
In a preferred embodiment of the invention, the contact between the anchor and the anchor pad is a rough contact under the stress of the anchor cable, and the contact surface material of the anchor and the anchor pad is still in an elastic contact range under the stress of the anchor cable.
In a preferred embodiment of the invention, the displacement signal collector measures the relative tangential displacement between the anchor and the anchor backing plate in real time after the exciting hammer applies tangential exciting force, the displacement signal collector is arranged at the lower edge of the outer surface of the anchor in a magnetic attraction mode, is close to but not in direct contact with the anchor backing plate, and the exciting hammer applies tangential exciting force at the upper edge of the outer surface of the anchor.
In the technical scheme, the displacement signal collector is arranged at the lower edge of the outer surface of the anchorage device, and the vibration exciting hammer applies tangential exciting force on the opposite side of the displacement signal collector, so that the displacement signal detected by the displacement signal collector is more accurate.
In order to achieve the purpose, the invention also adopts the following technical scheme: an anchor cable prestress nondestructive testing method comprises the following steps:
parameter acquisition: the memory obtains the material parameters of the contact surface between the anchor and the anchor pad
σ and μ, wherein
Is the composite shear modulus between the contact surfaces of the anchorage device and the anchor backing plate,
is the equivalent elastic modulus between the contact surfaces of the anchorage device and the anchor backing plate, sigma is the equivalent surface roughness between the contact surfaces of the anchorage device and the anchor backing plate, and mu is the friction coefficient between the contact surfaces of the anchorage device and the anchor backing plate;
data acquisition: applying tangential exciting force F capable of making anchor implement slide relatively to anchor backing plate on the anchor implement close to anchor backing plate interface by means of exciting force deviceτSimultaneously, detecting the relative tangential displacement X of the anchorage device and the anchor backing plate by a displacement signal collector;
and (4) stress output: the microprocessor calculates the anchor cable prestress F according to the following formula (1) and formula (2)nAnd the output is carried out,
in the formula, KτThe tangential contact rigidity between the anchorage device and the anchor backing plate is called tangential contact rigidity for short.
In another preferred embodiment of the invention, the parameter isThe method comprises the following steps: modulus of equivalent elasticity
According to the formula
Is calculated to obtain wherein E1、ν1Respectively, modulus of elasticity and Poisson's ratio of anchor material, E2、ν2Respectively the elastic modulus and the Poisson ratio of the anchor backing plate material; and/or composite shear modulus
According to the formula
Is calculated to obtain wherein G1、ν1Shear modulus and Poisson's ratio, G, of anchor material2、ν2Respectively the shear modulus and the Poisson ratio of the anchor backing plate material; and/or the equivalent surface roughness sigma is the root mean square value of the roughness of the contact surface of the anchorage device and the anchor backing plate; and/or the coefficient of friction mu is the maximum static coefficient of friction.
In another preferred embodiment of the present invention, in the data collecting step, the exciting force device is an exciting hammer, the exciting hammer comprises a force hammer and an acceleration sensor for measuring acceleration of the force hammer, and the tangential exciting force FτAccording to formula FτAnd ma, wherein m is the mass of the vibration hammer, and alpha is the vibration acceleration and the maximum acceleration of the force hammer measured by the acceleration sensor.
In another preferred embodiment of the present invention, in the stress outputting step, the anchor cable is prestressed FnUsing formula (4)
And (6) calculating.
In the technical scheme, the formula (4) is obtained by simplifying the formula of the technical anchor cable prestress, so that the calculation of the anchor cable prestress is simpler and quicker.
In the inventionIn another preferred embodiment, formula (1) is simplified to obtain formula (5)
Before the detection test, K is determined according to formula (5)τ-FnThe relation curve is input into a memory, and in the test process, when the microprocessor receives an exciting force signal transmitted by an exciting force device and a displacement signal transmitted by a displacement signal collector, the tangential contact rigidity K is calculated by using a formula (2)τSubsequently at Kτ-FnFinding the tangential contact stiffness K from the relationshipτCorresponding anchor cable prestress Fn。
In the above technical scheme, for the anchorage device and the anchorage backing plate which adopt the same material and have the same processing requirement, the material parameters are used
σ and μ are the same. According to the formula (5), K is set in advanceτ-FnThe relationship curve is input into a memory, and the tangential contact rigidity K is calculated according to the formula (2) in the detection processτCan be at Kτ-FnFinding the tangential contact stiffness K from the relationshipτCorresponding anchor cable prestress FnAnd the detection efficiency is improved.
Compared with the prior art, the invention has the following beneficial effects:
1) the detection method uses the vibration generated by the exciting hammer to measure the tangential contact rigidity between the anchorage device and the anchor backing plate, is nondestructive detection, and hardly causes adverse effect on the original prestressed structure;
2) the vibration excitation and the vibration response of the detection system are both in the outer anchoring section of the anchor cable, the detection system is convenient to operate, the prestress under the anchor cable can be quickly detected, and the detection efficiency is high;
3) the detection system has low cost and is beneficial to popularization and use;
4) the detection system and the detection method have higher detection accuracy rate and meet the requirement of detection errors at the present stage;
5) the tangential exciting force is applied to enable the displacement between the anchorage device and the anchor backing plate to occur, received displacement signals are gradually reduced after the tangential exciting force is applied to be instantly increased, the signals are clear and reliable, and the detection precision is high;
6) the detection method takes the tangential contact rigidity between the anchorage device of the external anchoring section of the prestressed anchor cable and the anchor pad as a measurement object, is applicable to anchor cables in various projects such as geotechnical engineering, bridge engineering and the like, and has wide application range;
7) the method is not influenced by the engineering stage, and can be used in the engineering construction stage and the engineering operation stage;
8) the tangential exciting force signal source and the displacement signal collector share the signal input and output interface, so that the number of connecting wires during detection is reduced, and the field operation and the rapid detection during the detection are facilitated;
9) the invention is provided with the microprocessor, can rapidly and automatically process and calculate the detection data, and obtains the detection result.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic view of the construction of an anchor cable, an anchor device and an anchor backing plate according to the present invention;
FIG. 2 is a schematic side view of an anchor cable being tested by the anchor cable pre-stress nondestructive testing system of the present invention;
FIG. 3 is a schematic front view of an anchor cable being tested by the anchor cable pre-stress nondestructive testing system of the present invention;
FIG. 4 is a schematic view of a detection device according to the present invention;
FIG. 5 is a schematic diagram of a host of the detecting device of the present invention;
FIG. 6 is a schematic view of an anchor cable pre-stress nondestructive testing system of the present invention;
fig. 7 is a detection flow chart of the anchor cable prestress nondestructive detection method of the present invention.
Reference numerals in the drawings of the specification include: the device comprises a prestressed anchor cable system 1, an anchor cable 11, an anchorage 12, an anchor backing plate 13, a detection device 2, an excitation hammer 21, a displacement signal collector 22, a signal processor 23, a detection device host 3, a display 31, a microprocessor 32, a memory 33, a keyboard 34, a USB interface 35, a power supply 4 and a charging circuit 5.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "vertical", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, should not be construed as limiting the present invention.
In the description of the present invention, unless otherwise specified and limited, it is to be noted that the terms "mounted," "connected," and "connected" are to be interpreted broadly, and may be, for example, a mechanical connection or an electrical connection, a communication between two elements, a direct connection, or an indirect connection via an intermediate medium, and specific meanings of the terms may be understood by those skilled in the art according to specific situations.
Example one
In the embodiment, a nondestructive testing system for prestress of an anchor cable (hereinafter referred to as a testing system) is provided, as shown in fig. 1, a prestressed anchor cable system 1 performs prestressed anchoring through an anchor cable 11, and an anchor backing plate 13 for transmitting stress to an anchored body and an anchor 12 for locking the anchor cable are sequentially arranged at an outer anchoring section (located at the outer side of the anchored body) of the anchor cable 11. The contact between the anchorage device 12 and the anchorage backing plate 13 is rough contact under the stress action of the anchor cable 11, and the contact surface materials of the anchorage device 12 and the anchorage backing plate are still in an elastic contact range under the stress action of the anchor cable 11. Wherein the anchor backing plate 13 is a flat steel backing plate, the anchor cable 11 is a single-strand steel strand or a multi-strand steel strand, and three strands are arranged as shown in fig. 3.
In a preferred embodiment, as shown in fig. 2 and 3, the detection system comprises a detection device 2 and a host 3 connected to the detection device.
As can be seen from fig. 4, the detecting device 2 includes an exciting force device for applying a tangential exciting force to the anchor 12 and detecting the tangential exciting force, a displacement signal collector 22 for detecting the relative tangential displacement between the anchor 12 and the anchor pad 13, and a signal processor 23.
The exciting force device is an exciting hammer 21, the exciting hammer 21 comprises a force hammer and an acceleration sensor for measuring the acceleration of the force hammer, and the exciting hammer 21 is used as a radial exciting force applying device.
The displacement signal collector 22 is a device for measuring the relative tangential displacement between the anchorage device 12 and the anchor backing plate 13 in real time after the exciting hammer 21 applies a tangential exciting force, and the displacement signal collector 22 is arranged on the outer surface of the anchorage device 12 in a magnetic attraction mode, is close to the outer surface of the anchorage device 12 and is not in direct contact with the anchor backing plate 13. Preferably, the displacement signal collector 22 is arranged on the opposite side of the vibration exciter 21, such as shown in fig. 2 and 3, the displacement signal collector 22 is mounted on the lower edge of the outer surface of the anchor 12, and the vibration exciter 21 applies a tangential exciting force on the upper edge of the outer surface of the anchor 12 to excite the anchor 12.
The signal output ends of the acceleration sensor and the displacement signal collector 22 are respectively connected with the signal processor 23, and the signal processor 23 performs noise reduction preprocessing, such as filtering, smoothing, zero line adjustment and other preprocessing, on the data collected by the acceleration sensor and the displacement signal collector 22, and then performs a/D signal conversion, and converts continuous analog signals into discrete digital signals.
As shown in fig. 5 and 6, the detection device host 3 includes a microprocessor 32, a memory 33, and a display 31. The output end of the signal processor 23 is connected to the microprocessor 32, and the microprocessor 32 is configured to extract an excitation force signal (which may be obtained by converting an acceleration signal in the following manner) of the excitation hammer 21 and a displacement signal waveform of the displacement signal collector 22, perform signal processing on the excitation force signal and the displacement signal, and calculate a detection result. The microprocessor 32 is connected to a memory 33, and the memory 33 is used for storing the operation parameters of the host 3 and the detection result. The microprocessor 32 and the memory 33 are respectively connected with the display 31, and the display 31 is used for displaying the exciting force, the displacement waveform, the detection result and the working parameter setting of the host 3.
The microprocessor 32 is further connected with a keyboard 34 and a USB interface 35, wherein the keyboard 34 is used for setting the operating parameters of the host 3, and the USB interface 35 is used for importing and exporting the detection result. It should be noted that the display 31 may also be a touch screen display, so that the parameters of the host 3 can be directly set on the display 31.
The detection system further comprises a power source 4 for supplying electrical energy and a charging circuit 5 for charging the power source 4, both of which are prior art and will not be described in detail herein.
Example two
The embodiment provides a detection method using the anchor cable prestress nondestructive detection system of the first embodiment. As shown in fig. 7, the detection method includes four steps of parameter acquisition, data acquisition, signal processing and stress output, and specifically includes the following steps:
parameter acquisition: the memory of the host machine 3 acquires the material parameters of the contact surface between the anchorage device 12 and the anchorage plate 13
σ and μ, wherein
Is the composite shear modulus between the contact surfaces of the anchorage device and the anchor backing plate,
is equivalent elastic modulus between the contact surfaces of the anchor and the anchor backing plate, and sigma is the contact surface between the anchor and the anchor backing plateMu is the friction coefficient between the contact surface of the anchorage device and the anchor backing plate. For anchors and anchor backing plates of different materials and different hole numbers, the material parameters of the contact surfaces of the anchors and the anchor backing plates
σ, μ are different.
Data acquisition: referring to FIGS. 2 and 3, the top of the anchor 12 near the anchor pad 13 interface is excited by the exciter 21, which applies a tangential exciting force F that causes the anchor 12 to slide downward relative to the anchor pad 13τ(i.e. the striking force of the hammer 21 on the anchor 12); simultaneously, the displacement signal collector 22 detects the tangential exciting force FτUnder the action of the force, the anchor 12 and the anchor backing plate 13 are in relative tangential displacement X.
As shown in fig. 3, under the application of tangential excitation force FτIn the process, the vibration exciting direction is carried out along the central line direction of the anchorage 12, and the vibration propagation direction is consistent with the vibration exciting direction and is vertical to the axial direction of the steel strand. Before the displacement signal collector 22 is installed, attention should be paid to removing impurities on the outer surface of the anchor 12, and preferably, the displacement signal collector 22 is installed at a position between anchor cable bundles, so that the influence of the vibration of the anchor cable 11 on signal receiving is reduced.
In the data acquisition process, the knocking force of the vibration hammer 21 needs to be reasonably controlled, so that the vibration of the anchorage 12 has stronger vibration waveform and cannot have excessive noise influence, and the step can be adjusted by combining the amplification factor of the amplifier and the knocking force. When the displacement signal collector 22 receives the signal, resistance signals within a certain range are set, and the signals at the receiving end cannot be received when the signals are too large or too small.
Signal processing: the signals collected by the acceleration sensor and the displacement signal collector 22 are a/D converted in advance by the signal processor 23, and the continuous analog signals are converted into discrete digital signals for the microprocessor 32 in the host 3 to recognize and store in the memory 33.
And (4) stress output: the microprocessor 32 calculates the anchor cable prestress F according to the following formula (1) and formula (2)nAnd the output is carried out,
in the formula, KτThe tangential contact stiffness between the anchorage 12 and the anchor backing plate 13 is referred to as tangential contact stiffness for short.
The anchor 12 and the anchor backing plate 13 form a contact and signal transmission system, an excitation force is applied to the top of the anchor 12 (the top is an excitation end), and meanwhile, a displacement signal of the anchor 12 relative to the anchor backing plate 13 is detected and received on the opposite side of the excitation end of the anchor 12; calculating the tangential contact rigidity K between the anchor cable and the anchor pad plate according to the existing tangential contact rigidity formula (2)τThen calculating the anchor prestress F of the anchor cable according to the formula (1)n。
In order to prevent detection errors caused by inconsistent magnitude of tangential exciting force, multiple detections are preferably performed, at least 10 effective detection results are reserved, and the final prestress under the anchor is obtained after the average value is obtained.
The real contact interface of the anchorage device 12 and the anchor backing plate 13 is a random rough surface, the real contact interface can be simplified into the contact between hemispherical microprotrusions with exponentially distributed heights according to a classical GW statistical contact model, the contact stress of the two hemispherical microprotrusions and the microslip contact displacement under the action of tangential force are calculated through a Boussinesq solution and a Hertz contact theory, finally the load and the displacement borne by the contact surface are converted into the sum of the load and the displacement borne by all the microprotrusions by utilizing the GW statistical contact model, and the K is solved by combining the statistical rule that the microprotrusions are exponentially distributed in terms of heightsτAnd FnAnd FτThereby establishing an anchor-contact theoretical formula
Namely, equation (1).
In the step of collecting the parameters, the parameters are collected,
sigma and mu are material parameters, which can be obtained by calibration or field measurement, and are as follows:
modulus of equivalent elasticity
According to the formula
Is calculated to obtain wherein E1、ν1Respectively, modulus of elasticity and Poisson's ratio of anchor material, E2、ν2Respectively, the elastic modulus and the poisson ratio of the anchor backing plate material. In general, the materials of the anchorage device and the anchor backing plate (both are called as outer anchor head for short) in the engineering are the same, and at the moment, a formula can be used
Calculating the composite modulus of elasticity of the contact surface
Wherein E and ν are the shear elastic modulus and Poisson's ratio of the outer anchor head material.
Composite shear modulus
According to the formula
Is calculated to obtain wherein G1、ν1Shear modulus and Poisson's ratio, G, of anchor material2、ν2Respectively, the shear modulus and the poisson ratio of the anchor pad material. In general, the anchor and the anchor backing plate are made of the same material in engineering, and a formula can be used in the process
Calculating the composite shear modulus of a contact surface
Wherein G and ν are the shear modulus and Poisson's ratio of the outer anchor head material.
The equivalent surface roughness sigma is the root mean square value of the roughness of the contact surface of the anchorage device and the anchorage backing plate, the reference specification GB/T1031-.
The friction coefficient mu is the maximum static friction coefficient, can be measured on site by referring to the specification GB/T1031-2009, and the value can also be selected by referring to the surface roughness parameter of the related material in the tribology principle.
In the step of data acquisition, the tangential exciting force FτAccording to formula FτAnd ma, wherein m is the mass of the exciting hammer (the sum of the mass of the exciting hammer and the mass of the acceleration sensor), and alpha is the exciting acceleration and is the maximum acceleration of the exciting hammer measured by the acceleration sensor. The measuring method of the relative tangential displacement x comprises the following steps: after the excitation hammer 21 applies tangential excitation force to the anchorage device 12, the displacement signal collector 22 arranged on the anchorage device 12 measures the relative tangential displacement between the anchorage device 12 and the anchorage backing plate 13 in real time.
In the stress output step, the formula (1) and the formula (2) are combined to obtain the formula (3)
The size of the knocking force of the exciting hammer 21 on the anchorage device 12 is less than 100N, namely the tangential exciting force FτLess than 100N, and has a large difference of several hundred kN orders of magnitude compared with the pre-stress of the anchor cable, so that the formula (3)
The ratio of (A) is extremely small and can be ignored, the formula (3) is simplified, and the formula (4) can be used in the actual calculation process
Calculating anchor cable prestress Fn。
In a similar manner, in the formula (1)
The ratio of (A) is extremely small and can be ignored, the formula (1) is simplified to obtain the formula (5)
Before the detection test, K is determined according to formula (5)τ-FnThe relationship curve of (2) is input into the memory 33 of the host 3; during the test, the microprocessor 32 receives the acceleration signal (which can be converted into tangential exciting force F) transmitted by the vibration exciter 21τSignal) and displacement signal transmitted by the displacement signal collector 22, the tangential contact stiffness K is calculated by using the formula (2)τSubsequently at Kτ-FnFinding the tangential contact stiffness K from the relationshipτCorresponding anchor cable prestress FnThis is the pre-stress level of the cable bolt.
The basic principle of the invention for detecting the prestress of the anchor cable is as follows: the prestressed anchor cable has the working mechanism that stress is exerted in advance by stretching the high-strength anchor cable, the anchor cable is limited to retract by clamping and meshing the clamping pieces in the working stage, and the stress is transmitted to the anchor backing plate 13 in a surface pressing mode through the anchor 12, so that the prestress can be exerted on an anchored body through the anchor backing plate 13. According to the force transfer characteristic of the prestressed anchor cable in the external anchoring section, the material parameters and properties of the contact surface between the anchorage device and the anchor backing plate can be changed along with the change of the tensile force, namely the contact tangential rigidity K between the anchorage device and the anchor backing plateτTo reflect the magnitude of the tensile force (i.e., anchor cable pre-stress).
In practice, the prestressed anchor cable systems 1 with different anchor cable hole numbers have different contact surface material parameters, the tangential contact stiffness and the prestress have a corresponding relation under the action of the prestress of the anchor cable, and the independent contact systems formed by the anchors and the anchor backing plates with different anchoring types are respectively subjected to excitation detection according to the detection method in the invention, so that the anchoring prestress values of the anchor cables with different types in the construction operation stage can be obtained, and the actual anchoring effect of the anchor cable can be directly mastered.
In the description herein, reference to the description of the terms "preferred embodiment," "one embodiment," "some embodiments," "an example," "a specific example" or "some examples" or the like means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
Claims (10)
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