Accurate positioning method and detection device for corrosion of steel bars in concrete beam

Abstract

The invention discloses an accurate positioning method and detection device for corrosion of steel bars in a concrete beam, and the method comprises the following steps: a) arranging a scanning track in parallel along the length direction of the concrete beam, and having a preset lift-off height between the scanning track and the concrete beam; b) moving the magnetic sensor along the scanning track, and collecting a position signal of the magnetic sensor and a magnetic signal of a corresponding position in the moving process; and c) drawing a magnetic curve of a plurality of magnetic signals which are acquired when the magnetic sensor moves along the scanning tracks with different lift-off heights and change along with the position signals, and judging the direction and the corrosion area of the corrosion reinforcing steel bar in the concrete beam according to the shape and the fluctuation characteristic of the magnetic curve. According to the method and the device, the direction and the corrosion area of the corroded steel bar are judged through different magnetic curve shapes and fluctuation characteristics, the direction and the corrosion area of the corroded steel bar in the concrete beam can be accurately positioned, and accurate information is provided for subsequent maintenance.

Description

Technical Field

[0001] The present invention relates to the technical field of steel bar corrosion detection, and in particular to a precise positioning method and a detection device for steel bar corrosion inside a concrete beam. Background Art

[0002] The corrosion of steel bars inside concrete beam bridges is a hidden disease, which seriously affects the safety and durability of concrete beam bridges, and brings huge safety hazards and life crisis to the normal operation of bridges. The main load-bearing structure of concrete beam bridges is the main beam, which has a criss-cross steel mesh structure inside. The longitudinal bars, stirrups, and the coupled corrosion of the two may occur inside the main beam. The corrosion of the longitudinal bars affects the bending bearing capacity of the beam bridge, and the corrosion of the stirrups affects the shear bearing capacity of the beam bridge. The coupled corrosion of the two affects the bending and shear bearing capacity of the beam bridge at the same time. The degree of influence of steel corrosion in different orientations on the bearing capacity of the beam bridge is different. Therefore, a non-destructive testing method is proposed to accurately detect the orientation and corrosion area of ​​the corroded steel bars inside the concrete beam bridge, which is an important basis for rapid assessment of bearing capacity and subsequent precise management and maintenance.

[0003] At present, the commonly used methods for steel bar corrosion detection are mainly visual inspection and half-cell potential method. The visual inspection method is a damage detection method, which is simple and intuitive, but it is harmful to the bridge itself, and the preparation work before detection is complicated. The half-cell potential method is a non-destructive detection method. During the measurement, the concrete surface needs to be treated to a certain extent to make it conductive, and the half-cell is placed on each measuring point in turn to fully contact the concrete surface. The measured potential value is used to determine the corrosion state of the steel bar. This method belongs to the contact detection method, the detection speed is slow, and the evaluation of the corrosion state is at a vague qualitative level. In summary, the traditional method has the significant defects of low detection efficiency and inability to accurately locate the position of the corroded steel bar, which affects the technical status of the concrete beam bridge, the efficiency and accuracy of the evaluation of the bearing capacity, and brings great inconvenience to the management and maintenance of the concrete beam bridge. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a method and a detection device for accurately locating the corrosion of steel bars inside a concrete beam, so as to solve the problems of low detection efficiency and inability to accurately locate the position of the corroded steel bars in the prior art.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: a method for accurately locating the corrosion of steel bars inside a concrete beam, comprising the following steps:

[0006] a) a scanning track is arranged parallel to the length direction of the concrete beam, and a preset lifting height is provided between the scanning track and the concrete beam;

[0007] b) moving the magnetic sensor along the scanning track, and collecting the position signal of the magnetic sensor and the magnetic signal of the corresponding position during the movement;

[0008] c) Draw a magnetic curve of the change of multiple magnetic signals collected by the magnetic sensor along the scanning track with different lifting heights along with the position signal, and judge the position and rusted area of ​​the corroded steel bars in the concrete beam according to the shape and fluctuation characteristics of the magnetic curve.

[0009] As an optimization, in step c, when the curve has left-right symmetrical peaks or troughs, it is judged that the longitudinal reinforcement along the scanning direction in the concrete beam has been corroded, and the area between the intersection points of the curves at different lift-off heights is the corroded area; when the curve reverses up and down to form peaks and troughs, it is judged that the stirrups perpendicular to the scanning direction in the concrete beam have been corroded, and the area between the peaks and troughs is the corroded area; when the curve shows a curve feature of left-right symmetrical peaks or troughs coupled with peaks and troughs formed by up and down reversal, it is judged that the longitudinal reinforcement and stirrups at that position in the concrete beam have been coupled corroded, and the area between the intersection points of the curves at different lift-off heights is the coupled corroded area; when the curve does not have a sudden change in shape, it is judged that the steel bars inside the concrete beam are not corroded.

[0010] As an optimization, in step c, the magnetic curve of the magnetic signal changing with the position signal is obtained by establishing a theoretical model of the magnetic field of the steel skeleton in the concrete beam;

[0011] The steel skeleton in the model includes four longitudinal steel bars distributed in a rectangular shape and stirrups wound around the outside of the four longitudinal steel bars. The longitudinal steel bars include two longitudinal bars located at the upper part of the concrete beam as force-bearing bars and two frame bars located at the bottom of the concrete beam. The spatial coordinates are established, with the scanning direction along the bottom of the beam as the X-axis, the X-axis is located between the two longitudinal bars and has the same distance with the two longitudinal bars, the Y-axis is perpendicular to the X-axis, passes through the contact points between the two longitudinal bars and the stirrups and is parallel to the direction of the stirrups at the bottom of the beam, and the Z-axis intersects the X-axis and the Y-axis and is perpendicular to the XY plane.

[0012] When the longitudinal reinforcement is corroded, it is assumed that the cross section of the longitudinal reinforcement is uniformly reduced in the radial direction, thereby forming two opposite annular defective sections in the corroded area, where equal and opposite surface magnetic charges are distributed on the annular defective sections on both sides; the corroded area is simplified to the XZ plane to form four linear defective sections distributed on both sides of the residual steel bar, so that the surface magnetic charge is simplified to the line magnetic charge, and it is assumed that the line magnetic charge on the defective section is uniformly distributed, then the magnetic field intensity along the X-axis direction generated by the four defective sections of one longitudinal reinforcement at a certain point p(x, y, z) in space is,

[0013]

[0014] The magnetic field intensity along the X-axis direction generated by another longitudinal rib at this point is,

[0015]

[0016] Then the magnetic field at any point p in the final space is the vector sum of the magnetic field strengths generated by the defective sections of the two longitudinal bars, as shown in the following formula:

[0017] H px =H 1x +H 2x (3)

[0018] In formula (1) and formula (2), b is the 1 / 2 corrosion width of the longitudinal reinforcement corrosion area, l is the 1 / 2 length of the stirrup at the bottom of the beam, h is the 1 / 2 corrosion depth of the longitudinal reinforcement corrosion area, D is the longitudinal reinforcement diameter, ρ s is the magnetic charge density at the defect section, η is the Z-axis coordinate of any point on the defect section, μ 0 is the magnetic permeability of vacuum.

[0019] As an optimization, when the stirrups at the bottom of the beam are corroded, it is assumed that the cross section of the stirrups is uniformly reduced in the radial direction, thereby forming two opposite annular defective sections in the corroded area, where equal and opposite surface magnetic charges are distributed on the annular defective sections on both sides; the corroded area is simplified to the YZ plane to form four linear defective sections distributed on both sides of the residual steel bars, so that the surface magnetic charge is simplified to the line magnetic charge, and it is assumed that the line magnetic charge on the defective section is uniformly distributed. Then, the magnetic field intensity along the X-axis direction generated by the four defective sections of the stirrups at the spatial point p (x, y, z) is,

[0020]

[0021] Among them, l is 1 / 2 length of the stirrup at the bottom of the beam, which is also 1 / 2 corrosion width of the stirrup corrosion area, h′ is 1 / 2 corrosion depth of the stirrup corrosion area, and d is stirrup diameter.

[0022] As an optimization, when coupled corrosion occurs, the magnetic field intensity generated at any point p in space under multi-directional steel bar coupled corrosion is,

[0023]

[0024] In the formula, H ix is the magnetic field intensity generated by the corroded area of ​​longitudinal reinforcement and stirrups at point p.

[0025] As an optimization, the data collected by the magnetic sensor is the magnetic induction intensity B. The magnetic field intensity H in the theoretical model has the following relationship with the magnetic induction intensity B:

[0026] B=μ 0 μ r H (6)

[0027] μ 0 is the vacuum permeability, a constant, μr is the relative magnetic permeability of air, μ r ≈1.

[0028] Based on the above method, the present invention also provides a precise positioning detection device for steel bar corrosion inside a concrete beam, which is used to implement the method described, including multiple scanning tracks arranged in parallel along the length direction of the concrete beam, the multiple scanning tracks are located in the same plane and have different lift-off heights with the concrete beam, and a magnetic sensor and an automatic drawing module are slidably installed on the scanning track, and the magnetic sensor is connected to the automatic drawing module, wherein the automatic drawing module is used to draw a magnetic curve of multiple magnetic signals collected by the magnetic sensor moving along the scanning track with different lift-off heights as the position signal changes.

[0029] Compared with the prior art, the present invention has the following advantages: the present invention first sets a scanning detection path according to the design drawings, the path is set along the longitudinal steel bar direction, and multiple lifting heights are set, and then a detection device is used to scan and obtain the magnetic signals of the steel bars inside the beam body, and the magnetic signals are plotted into a curve. The position and rusted area of ​​the corroded steel bars are determined by different magnetic curve shapes and fluctuation characteristics. This method and device can accurately locate the position and rusted area of ​​the corroded steel bars inside the concrete beam, and provide accurate information for subsequent maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 : Schematic diagram of corrosion of longitudinal reinforcement inside concrete beam;

[0031] Figure 2 : Schematic diagram of the corrosion of stirrups inside concrete beams;

[0032] Figure 3 : Schematic diagram of the process of testing concrete beams using a testing device;

[0033] Figure 4 :Working parameters of theoretical magnetic field of steel bars inside concrete beams

[0034] Figure 5 : Theoretical magnetic field curve of longitudinal reinforcement corrosion;

[0035] Figure 6 : Theoretical magnetic field curve of stirrup corrosion;

[0036] Figure 7 : Theoretical magnetic field curve of multi-directional steel bar coupled corrosion;

[0037] Figure 8 : Magnetic curve of longitudinal reinforcement corrosion during actual detection;

[0038] Fig. 9 : Magnetic curve diagram of stirrup corrosion in actual detection;

[0039] Fig.10 : Magnetic curve diagram of multi-directional steel bar coupled corrosion in actual detection;

[0040] In the figure, 1 is longitudinal reinforcement, 2 is stirrup reinforcement, 3 is vertical reinforcement, 4 is scanning track, and 5 is magnetic sensor. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] Example: See Figure 1-Figure 10 A method for accurately locating steel bar corrosion inside a concrete beam comprises the following steps:

[0045] a) A scanning track 4 is arranged parallel to the length direction of the concrete beam, and there is a preset lift-off height (the distance between the magnetic sensor and the steel bar surface) between the scanning track 4 and the concrete beam. The lift-off height should be as small as possible to ensure the accuracy of the magnetic signal.

[0046] b) Move the magnetic sensor 5 along the scanning track 4, and collect the position signal of the magnetic sensor 5 and the magnetic signal of the corresponding position during the movement. Specifically, set the spatial coordinate system and driving parameters, use the driving device to drive the magnetic sensor to move on the track, and automatically collect the spatial coordinates and magnetic signals of different positions during the movement.

[0047] c) Draw magnetic curves of the changes in the position signals of the multiple magnetic signals collected when the magnetic sensor moves along the scanning track at different lift-off heights, and judge the position and rusted area of ​​the corroded steel bars in the concrete beam based on the shape and fluctuation characteristics of the magnetic curve. After the scan is completed, the scanning path is used as the X-axis, and the magnetic signal Bx collected along the scanning direction is used as the Y-axis. The Bx magnetic curve graph at different lift-off heights is output using an automated drawing module. The position and rusted area of ​​the corroded steel bars inside the main beam are accurately located based on the Bx magnetic curve graph: the position and rusted area of ​​the corroded steel bars are determined by different magnetic curve shapes and fluctuation characteristics. Specifically, when the curve has left-right symmetrical peaks or troughs, it is determined that the longitudinal reinforcement 1 along the scanning direction in the concrete beam has been corroded. The area between the intersection points of the curves at different lift-off heights is Corrosion area; when the curve shows crests and troughs formed by up and down reversal, it is judged that the stirrup 2 perpendicular to the scanning direction in the concrete beam has been corroded, and the area between the crests and troughs is the corrosion area; when the curve shows the curve characteristics of left-right symmetrical crests or troughs coupled with crests and troughs formed by up and down reversal, it is judged that the longitudinal reinforcement and stirrups at this position in the concrete beam have been coupled corroded, and the area between the intersection points of the curves at different lift-off heights is the coupled corrosion area; when the curve does not show a sudden change in shape, it is judged that the steel bars inside the concrete beam are not corroded.

[0048] The principle of the present invention is that as a ferromagnetic component, the steel bar itself has a magnetic field. The directions of the external magnetic field and the internal magnetic field of the steel bar are opposite. When the steel bar rusts, the cross-sectional area of ​​the rusted position decreases, and the internal magnetic field "leaks out". The spatial magnetic field in the rusted area undergoes a mutation compared with the non-corroded area. The different distribution directions of the steel bars will also lead to differences in the magnetic field distribution. The inventors have further established a theoretical model of the magnetic field for steel bars corroded in different directions.

[0049] Specifically, the curve of the change of magnetic signal with position signal is obtained by establishing a theoretical model of magnetic field of steel skeleton in concrete beam. When the longitudinal reinforcement inside the concrete beam is corroded, it can be approximately considered that the cross section of the longitudinal reinforcement is uniformly reduced, and defects are generated after the longitudinal reinforcement is corroded, and magnetic charge is generated on the defective section, thereby generating a magnetic field in space.

[0050] The steel skeleton in the model includes four longitudinal steel bars distributed in a rectangular shape and stirrups wound around the outside of the four longitudinal steel bars, wherein the longitudinal steel bars include two longitudinal bars 1 located at the upper part of the concrete beam as force-bearing bars and two frame bars 3 located at the bottom of the concrete beam; a spatial coordinate is established, with the scanning direction along the bottom of the beam as the X-axis, the X-axis is located between the two longitudinal bars and has the same distance with the two longitudinal bars, the Y-axis is perpendicular to the X-axis, passes through the contact points between the two longitudinal bars and the stirrups and is parallel to the direction of the stirrups at the bottom of the beam, and the Z-axis intersects the X-axis and the Y-axis and is perpendicular to the XY plane;

[0051] When the longitudinal reinforcement 1 is corroded, it is assumed that the cross section of the longitudinal reinforcement 1 is uniformly reduced in the radial direction, thereby forming two opposite annular defective sections in the corroded area, where equal and opposite surface magnetic charges are distributed on the annular defective sections on both sides; the corroded area is simplified to the XZ plane to form four linear defective sections distributed on both sides of the residual steel bar, so that the surface magnetic charge is simplified to the line magnetic charge, and it is assumed that the line magnetic charge on the defective section is uniformly distributed, then the magnetic field intensity along the X-axis direction generated by the four defective sections of one longitudinal reinforcement at a certain point p(x, y, z) in space is,

[0052]

[0053] The magnetic field intensity along the X-axis direction generated by another longitudinal rib at this point is,

[0054]

[0055] Then the magnetic field at any point p in the final space is the vector sum of the magnetic field strengths generated by the defective sections of the two longitudinal bars, as shown in the following formula:

[0056] H px =H 1x +H 2x (3)

[0057] In formula (1) and formula (2), b is the 1 / 2 corrosion width of the longitudinal reinforcement corrosion area, l is the 1 / 2 length of the stirrup at the bottom of the beam, h is the 1 / 2 corrosion depth of the longitudinal reinforcement corrosion area, D is the longitudinal reinforcement diameter, ρ s is the magnetic charge density at the defect section, η is the Z-axis coordinate of any point on the defect section, μ 0 is the magnetic permeability of vacuum.

[0058] When stirrup 2 is corroded, it is assumed that the cross section of stirrup 2 is uniformly reduced in the radial direction, thereby forming two opposite annular defective sections in the corroded area. Since the length of stirrup 2 at the bottom is relatively small, it is assumed here that stirrup 2 is corroded along the entire length of the bottom edge, and magnetic charges are generated on the corroded defective sections, generating a micro-magnetic field in space. Among them, equal and opposite surface magnetic charges are distributed on the annular defective sections on both sides; the corroded area is simplified to the YZ plane to form four linear defective sections distributed on both sides of the residual steel bars, so that the surface magnetic charges are simplified to linear magnetic charges, and it is assumed that the linear magnetic charges on the defective sections are uniformly distributed, then the magnetic field intensity along the X-axis direction generated by the four defective sections of the stirrup at the spatial point p (x, y, z) is,

[0059]

[0060] Among them, l is 1 / 2 length of the stirrup at the bottom of the beam, which is also 1 / 2 corrosion width of the stirrup corrosion area, h′ is 1 / 2 corrosion depth of the stirrup corrosion area, and d is stirrup diameter.

[0061] When coupled corrosion occurs, that is, multi-directional steel bars at the same position are all corroded, the magnetic response problem under coupled corrosion of multi-directional steel bars is involved. Assuming that the cross-section of the steel bars is uniformly reduced after corrosion, when multi-directional steel bars are all corroded, taking the corrosion of a single stirrup and two longitudinal bars as an example, after the corrosion of the longitudinal bars and stirrups, opposite positive and negative magnetic charges are generated on their defective end faces respectively. The three-dimensional distribution of surface magnetic charges is simplified to the linear magnetic charge distribution in the XZ and YZ planes. The magnetic field intensity generated at any point p in space under coupled corrosion of multi-directional steel bars should be the superposition of the magnetic fields of unidirectional steel bar corrosion.

[0062]

[0063] In the formula, H ix is the magnetic field intensity generated by the corroded area of ​​longitudinal reinforcement and stirrups at point p.

[0064] By analyzing the above model, it can be seen from equations (1) to (5) that the position coordinates of a certain point p (x, y, z) in space, the diameters of the longitudinal reinforcement and stirrups, and the defect size are important parameters that affect the spatial magnetic field. Under the premise of determining the influencing parameters, the magnetic field intensity at any point can be calculated. Let H x '=H x / (ρ s / 2πμ 0 ), ρ s / 2πμ 0 It is usually regarded as a constant, so H x 'With H x With a consistent trend of change, the model parameter values ​​are set as Figure 3 As shown, calculate and plot the H corresponding to different corrosion states x The distribution curve is as follows Figure 5-Figure 7As shown, this is the magnetic curve diagram of the theoretical model.

[0065] The data collected by the magnetic sensor is the magnetic induction intensity B. The magnetic field intensity H in the theoretical model has the following relationship with the magnetic induction intensity B:

[0066] B=μ 0 μ r H (6)

[0067] μ 0 is the vacuum permeability, a constant, μ r is the relative magnetic permeability of air, μ r ≈1. It can be seen that the magnetic induction intensity B detected by the sensor has a similar variation law to the theoretically calculated magnetic field intensity H, such as Figure 8-Figure 10 The magnetic signal curve in the actual detection is shown in Figure 5-Figure 7 The characteristics of the medium magnetic field theoretical curve are similar, which proves that the method proposed in the present invention can accurately locate the position and corrosion area of ​​the corroded steel bars.

[0068] Based on the above method, the present invention also provides a precise positioning detection device for steel bar corrosion inside a concrete beam, which is used to implement the method described, including multiple scanning tracks arranged in parallel along the length direction of the concrete beam, the multiple scanning tracks are located in the same plane and have different lift-off heights with the concrete beam, and a magnetic sensor and an automatic drawing module are slidably installed on the scanning track, and the magnetic sensor is connected to the automatic drawing module, wherein the automatic drawing module is used to draw a curve of changes in multiple magnetic signals collected by the magnetic sensor moving along the scanning track with different lift-off heights along with the position signal.

[0069] In summary, the present invention first sets a scanning detection path according to the design drawings. The path is set along the longitudinal direction of the steel bars and multiple lifting heights are set. Then, a detection device is used to scan and obtain the magnetic signals of the steel bars inside the beam body. The magnetic signals are plotted into a curve. The position and the corroded area of ​​the corroded steel bars are determined by the different shapes and fluctuation characteristics of the magnetic curves. This method and device can accurately locate the position and the corroded area of ​​the corroded steel bars inside the concrete beam, and provide accurate information for subsequent maintenance.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A method for accurately locating steel bar corrosion inside a concrete beam, characterized in that: The following steps are included: a) a scanning track is arranged parallel to the length direction of the concrete beam, and a preset lifting height is provided between the scanning track and the concrete beam; b) moving the magnetic sensor along the scanning track, and collecting the position signal of the magnetic sensor and the magnetic signal of the corresponding position during the movement; c) Draw a magnetic curve of the change of multiple magnetic signals collected by the magnetic sensor along the scanning track with different lifting heights along with the position signal, and judge the position and rusted area of ​​the corroded steel bars in the concrete beam according to the shape and fluctuation characteristics of the magnetic curve.

2. The method for accurately locating steel bar corrosion inside a concrete beam according to claim 1, characterized in that: In step c, when the curve has left-right symmetrical peaks or troughs, it is judged that the longitudinal reinforcement along the scanning direction in the concrete beam has been corroded, and the area between the intersection points of the curves at different lift-off heights is the corroded area; when the curve reverses up and down to form peaks and troughs, it is judged that the stirrups perpendicular to the scanning direction in the concrete beam have been corroded, and the area between the peaks and troughs is the corroded area; when the curve shows a curve feature of left-right symmetrical peaks or troughs coupled with peaks and troughs formed by up and down reversal, it is judged that the longitudinal reinforcement and stirrups at this position in the concrete beam have been coupled corroded, and the area between the intersection points of the curves at different lift-off heights is the coupled corroded area; when the curve does not have a sudden change in shape, it is judged that the steel bars inside the concrete beam are not corroded.

3. The method for accurately locating steel bar corrosion inside a concrete beam according to claim 2, characterized in that: In step c, a magnetic curve of the magnetic signal changing with the position signal is obtained by establishing a theoretical model of the magnetic field of the steel skeleton in the concrete beam; The steel skeleton in the model includes four longitudinal steel bars distributed in a rectangular shape and stirrups wound around the outside of the four longitudinal steel bars. The longitudinal steel bars include two longitudinal bars located at the upper part of the concrete beam as force-bearing bars and two frame bars located at the bottom of the concrete beam. The spatial coordinates are established, with the scanning direction along the bottom of the beam as the X-axis, the X-axis is located between the two longitudinal bars and has the same distance with the two longitudinal bars, the Y-axis is perpendicular to the X-axis, passes through the contact points between the two longitudinal bars and the stirrups and is parallel to the direction of the stirrups at the bottom of the beam, and the Z-axis intersects the X-axis and the Y-axis and is perpendicular to the XY plane. When the longitudinal reinforcement is corroded, it is assumed that the cross section of the longitudinal reinforcement is uniformly reduced in the radial direction, thereby forming two opposite annular defective sections in the corroded area, where equal and opposite surface magnetic charges are distributed on the annular defective sections on both sides; the corroded area is simplified to the XZ plane to form four linear defective sections distributed on both sides of the residual steel bar, so that the surface magnetic charge is simplified to the line magnetic charge, and it is assumed that the line magnetic charge on the defective section is uniformly distributed, then the magnetic field intensity along the X-axis direction generated by the four defective sections of one longitudinal reinforcement at a certain point p(x, y, z) in space is, The magnetic field intensity along the X-axis direction generated by another longitudinal rib at this point is, Then the magnetic field at any point p in the final space is the vector sum of the magnetic field strengths generated by the defective sections of the two longitudinal bars, as shown in the following formula: H px =H 1x +H 2x (3) In formula (1) and formula (2), b is the 1 / 2 corrosion width of the longitudinal reinforcement corrosion area, l is the 1 / 2 length of the stirrup at the bottom of the beam, h is the 1 / 2 corrosion depth of the longitudinal reinforcement corrosion area, D is the longitudinal reinforcement diameter, ρ s is the magnetic charge density at the defect section, η is the Z-axis coordinate of any point on the defect section, and μ0 is the vacuum permeability.

4. The method for accurately locating steel bar corrosion inside a concrete beam according to claim 3, characterized in that: When the stirrups at the bottom of the beam are corroded, it is assumed that the cross section of the stirrups is uniformly reduced in the radial direction, thereby forming two opposite annular defective sections in the corroded area, where equal and opposite surface magnetic charges are distributed on the annular defective sections on both sides; the corroded area is simplified to the YZ plane to form four linear defective sections distributed on both sides of the residual steel bars, so that the surface magnetic charge is simplified to the line magnetic charge, and it is assumed that the line magnetic charge on the defective section is uniformly distributed, then the magnetic field intensity along the X-axis direction generated by the four defective sections of the stirrups at the spatial point p (x, y, z) is, Among them, l is 1 / 2 length of the stirrup at the bottom of the beam, which is also 1 / 2 corrosion width of the stirrup corrosion area, h′ is 1 / 2 corrosion depth of the stirrup corrosion area, and d is stirrup diameter.

5. The method for accurately locating steel bar corrosion inside a concrete beam according to claim 4, characterized in that: When coupled corrosion occurs, the magnetic field intensity generated at any point p in space under multi-directional steel bar coupled corrosion is: In the formula, H ix is the magnetic field intensity generated by the corroded area of ​​longitudinal reinforcement and stirrups at point p.

6. The method for accurately locating steel bar corrosion inside a concrete beam according to claim 5, characterized in that: The data collected by the magnetic sensor is the magnetic induction intensity B. The magnetic field intensity H in the theoretical model has the following relationship with the magnetic induction intensity B: B = μ0μ r H (6)μ0 is the vacuum magnetic permeability, which is a constant, μ r is the relative magnetic permeability of air, μ r ≈1.

7. A precise positioning detection device for steel bar corrosion inside a concrete beam, used to implement the method described in claims 1-6, characterized in that: It includes multiple scanning tracks arranged in parallel along the length direction of the concrete beam, the multiple scanning tracks are located in the same plane and have different lift-off heights with the concrete beam, and magnetic sensors and automatic drawing modules are slidably installed on the scanning tracks. The magnetic sensors are connected to the automatic drawing module, wherein the automatic drawing module is used to draw magnetic curves of multiple magnetic signals collected by the magnetic sensors moving along the scanning tracks with different lift-off heights as the position signals change.

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