Prestressed steel strand stress measuring device and method

Abstract

The present application relates to a kind of prestressed steel strand stress measuring device and method, belong to civil engineering structure detection technical field.The prestressed steel strand (2) of the present application, measuring unit (3), first coil (4) and second coil (5);Measuring unit (3) includes mutually series-connected Hall element array (33), ammeter (32), magnetic field intensity measuring instrument (34) and DC power supply (31), first coil (4) is respectively connected with AC power supply (6), first resistance (7) series, second coil (5) is connected with second resistance (8) series;Under energized condition, the magnetic field intensity around Hall element array (33) is measured by magnetic field intensity measuring instrument (34), the current passing through Hall element array (33) is measured by ammeter (32), and then the stress of prestressed steel strand (2) is obtained.The present application can sensitively, accurately and stably nondestructively test the stress of prestressed steel strand (2), and it is convenient and fast.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering structural testing technology, and relates to a prestressed steel strand stress measurement device and method. Background Technology

[0002] Currently, the main methods for measuring stress in steel strands of prestressed concrete structural members include sonic logging, stress release, and fiber optic sensing. Sonic logging is susceptible to interference from the external environment, and the acoustic signal gradually attenuates within the concrete structure, resulting in low measurement accuracy. Stress release, a semi-non-destructive testing method involving mechanical cutting or isolation, measures the strain before and after stress release to estimate the original stress on the surface of the measuring point. However, the inhomogeneity of the concrete material leads to significant measurement errors and can cause some damage to the structure. Fiber optic sensing involves embedding Bragg grating sensors into the prestressed concrete structure; however, over time, sensor aging severely affects measurement accuracy and cannot be replaced.

[0003] In summary, there is currently no method for detecting the stress in steel strands of prestressed concrete structural members that is simultaneously sensitive, accurate, stable, and has easily replaceable testing devices. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a prestressed steel strand stress measuring device and method, which can sensitively, accurately and stably perform non-destructive testing on the stress of prestressed steel strands, and is convenient and quick.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A prestressed steel strand stress measuring device includes a steel strand and an energized coil wound on the steel strand. It also includes a measuring unit disposed in the middle of the steel strand. The measuring unit includes a Hall element array and a magnetic field strength measuring instrument and an ammeter connected in series with the Hall element array.

[0007] The steel strand generates internal current and magnetic field under the action of the energized coil. The Hall element array senses the magnetic field around the steel strand and generates a corresponding magnetic field and current in the measuring unit. The magnetic field around the Hall element array is measured by a magnetic field strength measuring instrument, and the current passing through the Hall element array is measured by an ammeter.

[0008] Optionally, the energized coil includes a first coil and a second coil, which are respectively wound around the two ends of the steel strand.

[0009] Optionally, the end of the steel strand near the first coil is further provided with an AC power supply and a first resistor connected in series with the first coil. The AC power supply is used to power the first coil.

[0010] Optionally, a second resistor connected in series with the second coil is also provided at one end of the steel strand near the second coil.

[0011] Optionally, the measuring unit is further provided with a DC power supply connected in series with the Hall element array. The DC power supply is used to power the closed circuit in which the Hall element array is located.

[0012] Optionally, the steel strands are disposed inside the prestressed concrete structural member.

[0013] Optionally, the measuring unit is disposed on the surface or inside the prestressed concrete structural member, that is, the Hall element array can be attached to the surface of the prestressed concrete structural member or embedded in the interior of the prestressed concrete structural member, so as to accurately sense and measure the magnetic field strength of the steel strand.

[0014] A method for measuring the stress of prestressed steel strands, applicable to any one of the measuring devices claimed in claims 1 to 7;

[0015] Includes the following steps:

[0016] S1 applies a known initial stress σ0 to the steel strand in the energized state, generating a magnetic field with a first magnetic field strength H1 around the Hall element array, and generating a first current I1 in the measuring unit. H1 is measured by a magnetic field strength measuring instrument, and I1 is measured by an ammeter connected in series with the Hall element array.

[0017] S2 applies an unknown stress σ to the steel strand in the energized state, generating a magnetic field with a second magnetic field strength H2 around the Hall element array, and generating a second current I2 in the measuring unit. H2 is measured by a magnetic field strength measuring instrument, and I2 is measured by an ammeter connected in series with the Hall element array.

[0018] S3 calculates the changes in magnetic field strength ΔH and current ΔI by subtracting the first magnetic field strength H1, the second magnetic field strength H2, the first current I1, and the second current I2, respectively. The calculation formulas are as follows:

[0019] ΔH=H1-H2 (1),

[0020]

[0021] Based on the changes in magnetic field strength ΔH and current ΔI described in S3, S4 obtains the unknown stress σ of the steel strand.

[0022] Optionally, in step S4, the formula for calculating the unknown stress σ of the steel strand (2) is formula (3):

[0023]

[0024] Where λ s M is the magnetostriction constant. s K is the saturation magnetization. H V is the Hall coefficient, θ is the angle between the magnetic field and the easy magnetization axis, and V is the magnetization coefficient. H K represents the DC power supply voltage, d represents the thickness of the Hall element conductor, and K represents the voltage of the DC power supply. μ is the anisotropy constant of uniaxial magnetic anisotropy.

[0025] Optionally, in step S4, the known initial stress σ0 is in the range of 0 to 1800 MPa.

[0026] The beneficial effects of this invention are as follows:

[0027] Based on the relationship between stress and magnetic field in the Villari effect, this invention innovatively derives the relationship between stress, magnetic field, and current in prestressed steel strands under magnetic field conditions; and for the first time, it applies Hall element arrays to measure the stress value of steel strands in prestressed concrete structural members.

[0028] The device of this invention can monitor the stress value of steel strands in prestressed concrete structural members for a long time. The measuring device has low maintenance cost and a wide range of applications. It can be placed on the surface of existing prestressed concrete structural members or embedded in them. Even small changes in external stress (10MPa level) will cause changes in the measuring magnetic field. Therefore, the measuring device has high sensitivity and accuracy. External non-magnetic field environmental factors do not affect the measurement results, and the device has strong stability.

[0029] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0031] Figure 1 This is a schematic diagram of a prestressed steel strand stress measuring device.

[0032] Figure label:

[0033] 1 Prestressed concrete structural member, 2 Steel strand, 3 Measuring unit, 31 DC power supply, 32 Ammeter, 33 Hall element array, 34 Magnetic field strength measuring instrument, 4 First coil, 5 Second coil, 6 AC power supply, 7 First resistor, 8 Second resistor. Detailed Implementation

[0034] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0035] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0036] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0037] Please see Figure 1 A prestressed steel strand stress measuring device includes a prestressed concrete structural member 1 and a steel strand 2 disposed inside the prestressed concrete structural member 1, with both ends of the steel strand 2 protruding from the cross-section of the prestressed concrete structural member 1. The device also includes a first coil 4 and a second coil 5 wound around the steel strand 2 protruding from the ends of the prestressed concrete structural member 1, and a measuring unit 3 disposed on the surface or inside the prestressed concrete structural member 1.

[0038] The measuring unit 3 includes a Hall element array 33, a magnetic field strength measuring instrument 34 connected in series with the Hall element array 33, an ammeter 32, and a DC power supply 31.

[0039] The steel strand 2 is also provided with an AC power supply 6 and a first resistor 7 connected in series with the first coil 4 at one end. The AC power supply 6 is used to supply power to the first coil 4.

[0040] The steel strand 2 is also provided with a second resistor 8 connected in series with the second coil 5 at one end near the second coil 5.

[0041] When the AC power supply 6 and the DC power supply 31 are turned on, the steel strand 2 wound by the first coil 4 and the second coil 5 will generate a magnetic field that passes through the Hall element array 33. The magnetic field strength measuring instrument 34 can measure the magnetic field strength around the Hall element array 33, and the ammeter 32 can measure the current passing through the Hall element array 33. Then, the stress of the steel strand 2 can be obtained by the prestressed steel strand stress measurement method of the present invention.

[0042] A method for measuring the stress of prestressed steel strands, applied to the aforementioned prestressed steel strand stress measuring device, comprises the following steps:

[0043] When AC power supply 6 and DC power supply 31 are in the open state, the steel strand 2 is subjected to a known initial stress σ0 (within the range of 0-1800MPa). The steel strand 2, which is wound by the first coil 4 and the second coil 5, will generate a magnetic field passing through the Hall element array 33. The first magnetic field strength H1 around the Hall element array 33 for calibration is measured by the magnetic field strength measuring instrument 34.

[0044] Under the action of an unknown stress σ, the second magnetic field strength H2 around the Hall element array 33 is measured by the magnetic field strength measuring instrument 34;

[0045] S3 calculates the change in magnetic field strength ΔH based on the first magnetic field strength H1 and the second magnetic field strength H2:

[0046] ΔH=H1-H2(1);

[0047] Under the same known initial stress σ0 as in step S1, the first current I1 used for calibration in the series circuit of Hall element array 33 is measured by ammeter 32 in steel strand 2 of S4.

[0048] Under the same unknown stress σ as in S2, the second current I2 in the series circuit of Hall element array 33 is measured by ammeter 32;

[0049] S6 calculates the current change ΔI based on the first current I1 in step S4 and the second current I2 in step S5:

[0050] ΔI=I1-I2 (2);

[0051] S7 obtains the stress magnitude σ of the steel strand 2 based on the changes in magnetic field strength ΔH and current ΔI:

[0052]

[0053] Where λ s M is the magnetostriction constant. s K is the saturation magnetization. H V is the Hall coefficient, θ is the angle between the magnetic field and the easy magnetization axis, and V is the magnetization coefficient. H K represents the DC power supply voltage, d represents the thickness of the Hall element conductor, and K represents the voltage of the DC power supply. μ is the anisotropy constant of uniaxial magnetic anisotropy.

[0054] For the above formula (3), the derivation process is as follows:

[0055] S1 has formula (4) based on the Villari effect:

[0056]

[0057] Where Δσ represents the change in stress and ΔM represents the change in magnetic flux;

[0058] S2 is derived from the magnetization theory of ferromagnetic materials by formula (5):

[0059] ΔM=ΔμH (5),

[0060] Where Δμ represents the rate of change of magnetic permeability;

[0061] S3 is also defined by the permeability, as shown in formula (6):

[0062]

[0063] Where ΔB represents the change in magnetic flux density;

[0064] S4 combines formulas (4), (5), and (6) to obtain formula (7):

[0065]

[0066] S5 also has formula (8):

[0067]

[0068] S6 combines formulas (7) and (8) to obtain formula (3):

[0069]

[0070] Where λ s M is the magnetostriction constant. s K is the saturation magnetization. HV is the Hall coefficient, θ is the angle between the magnetic field and the easy magnetization axis, and V is the magnetization coefficient. H K represents the DC power supply voltage, d represents the thickness of the Hall element conductor, and K represents the voltage of the DC power supply. μ is the anisotropy constant of uniaxial magnetic anisotropy.

[0071] The Villari effect, also known as magnetoelasticity, is the phenomenon where the magnetic properties of ferromagnetic materials change under mechanical stress (strain). It is the opposite of magnetostriction and is therefore also called inverse magnetostriction, or sometimes piezomagnetism. Because it was discovered by Villari in 1865, it is called the Villari effect.

[0072] Based on the relationship between stress and magnetic field in the Villari effect, this invention innovatively derives the relationship between stress, magnetic field and current in prestressed steel strands under magnetic field conditions; and for the first time, it uses Hall element array 33 to measure the stress value of steel strand 2 in prestressed concrete structural member 1.

[0073] The device of the present invention can monitor the stress value of the steel strand 2 in the prestressed concrete structural member 1 for a long time. The measuring device has low maintenance cost, is easy to replace, and has a wide range of applications. The Hall element array 33 can be arranged on the surface of the existing prestressed concrete structural member 1 or embedded in the prestressed concrete structural member 1. Even small changes in external stress (10MPa level) will cause changes in the measuring magnetic field. Therefore, the measuring sensitivity and accuracy of this device are high. External non-magnetic field environmental factors do not affect the measurement results, and the device has strong stability.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for measuring the stress of prestressed steel strands, characterized in that: The device is applied to a measuring device, which includes a steel strand (2) and an energized coil wound on the steel strand (2), characterized in that it further includes a measuring unit (3) disposed in the middle part of the steel strand (2), the measuring unit (3) including a Hall element array (33), and a magnetic field strength measuring instrument (34) and an ammeter (32) connected in series with the Hall element array (33). The energized coil includes a first coil (4) and a second coil (5), which are respectively wound around the two ends of the steel strand (2); The steel strand (2) is also provided with an AC power supply (6) and a first resistor (7) connected in series with the first coil (4) at one end; the steel strand (2) is also provided with a second resistor (8) connected in series with the second coil (5) at one end; The measuring unit (3) is also equipped with a DC power supply (31) connected in series with the Hall element array (33). Includes the following steps: S1 applies a known initial stress to the steel strand (2) under energized conditions. A first magnetic field strength is generated around the Hall element array (33). The magnetic field generates a first current within the measuring unit (3). ; S2 applies an unknown stress to the steel strand (2) under energized conditions. A second magnetic field strength is generated around the Hall element array (33). The magnetic field generates a second current within the measuring unit (3). ; S3 Based on the first magnetic field strength Second magnetic field strength and the first current Second current The change in magnetic field strength is obtained by subtracting the values ​​of each. and change in current The calculation formula is as follows: （1）， （2）； S4 Based on the change in magnetic field strength described in S3 and change in current The unknown stress of the steel strand (2) is obtained. The unknown stress of the steel strand (2) The calculation formula is formula (3): （3）， in It is the magnetostriction constant. The saturation magnetization is Hall coefficient, The angle between the magnetic field and the easy magnetization axis. This is the DC power supply voltage. For the thickness of the Hall element conductor, is the anisotropy constant of uniaxial magnetic anisotropy.

2. The method for measuring the stress of prestressed steel strands according to claim 1, characterized in that: The steel strand (2) is installed inside the prestressed concrete structural member (1).

3. The method for measuring the stress of prestressed steel strands according to claim 1, characterized in that: The measuring unit (3) is set on the surface or inside the prestressed concrete structural member (1).

4. The method for measuring the stress of prestressed steel strands according to claim 1, characterized in that: In step S4, the known initial stress The magnitude is in the range of 0~1800MPa.

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