Quantitative detection method for corrosion of steel bar in simply supported beam

Abstract

The invention discloses a quantitative detection method for corrosion of a steel bar in a simply supported beam, which comprises the following steps: a) acquiring a magnetic signal of the steel bar in the simply supported beam; b) establishing a quantitative diagnosis index which reflects the fluctuation amplitude of the magnetic signal and has correlation with the corrosion depth of the corrosion area; and c) obtaining the corrosion depth of the corrosion area according to the correlation between the quantitative diagnosis index and the corrosion depth. According to the method, on the premise that the magnetic signal of the steel bar in the simply supported beam is detected and the position and the corrosion area of the corroded steel bar are obtained, the quantitative diagnosis index which reflects the fluctuation amplitude of the magnetic signal and has correlation with the corrosion depth of the corrosion area is established, and the corrosion depth of the corrosion area is quantitatively analyzed through the correlation. Therefore, the corrosion condition of the load-bearing steel bar can be better evaluated, and a basis is provided for follow-up management and maintenance of simply supported beams.

Description

Technical Field

[0001] The invention relates to the technical field of steel bar corrosion detection, and in particular to a quantitative detection method for steel bar corrosion inside a simply supported beam. Background Art

[0002] The corrosion of steel bars inside a simply supported beam bridge is a hidden disease, which seriously affects the safety and durability of the simply supported beam bridge, and brings huge safety hazards and life crisis to the normal operation of the bridge. The main load-bearing structure of a simply supported beam bridge 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 bar 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 simply supported 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 simply supported beam bridge, the efficiency and accuracy of the evaluation of the bearing capacity, and brings great inconvenience to the management and maintenance of the simply supported beam bridge.

[0004] Based on the above problems in the prior art, the inventors have proposed a method and a detection device that can qualitatively detect the position and rusted area of ​​the corroded steel bars inside a simply supported beam. However, there is currently a lack of methods for quantitatively analyzing the corrosion conditions of the rusted areas. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a quantitative detection method for steel bar corrosion inside a simply supported beam, so as to solve the problem that the prior art lacks a quantitative analysis method for the corrosion condition of the steel bar corrosion area inside a simply supported beam.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: a quantitative detection method for steel bar corrosion inside a simply supported beam comprises the following steps:

[0007] a) Collect the magnetic signals of the steel bars inside the simply supported beam;

[0008] b) establishing a quantitative diagnostic index that reflects the fluctuation amplitude of the magnetic signal and is correlated with the corrosion depth of the corroded area;

[0009] c) obtaining the corrosion depth of the corroded area according to the correlation between the quantitative diagnostic index and the corrosion depth.

[0010] As an optimization, step a includes the following steps,

[0011] a1) a scanning track is arranged parallel to the length direction of the simply supported beam, and a preset lifting height is provided between the scanning track and the simply supported beam;

[0012] a2) 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;

[0013] a3) 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.

[0014] As an optimization, in step a3, when the curve has left-right symmetrical peaks or troughs, it is judged that the longitudinal reinforcement along the scanning direction in the simply supported 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 simply supported 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 simply supported 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 shape change, it is judged that the steel bars inside the simply supported beam are not corroded.

[0015] As an optimization, in step a3, the curve of the change of the magnetic signal with the position signal is obtained by establishing a theoretical model of the magnetic field of the steel skeleton in the simply supported beam;

[0016] 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 simply supported beam as force bars and two frame bars located at the bottom of the simply supported 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.

[0017] 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,

[0018]

[0019] The magnetic field intensity along the X-axis direction generated by another longitudinal rib at this point is,

[0020]

[0021] The magnetic field at any point p(x, y, z) 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:

[0022] H px =H 1x +H 2x (3)

[0023] In formula (1) and formula (2), b is the 1 / 2 defect 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.

[0024] 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,

[0025]

[0026] Among them, l is 1 / 2 length of the stirrup at the bottom of the beam, which is also 1 / 2 defect width of the stirrup corroded area, h′ is 1 / 2 corrosion depth of the stirrup corroded area, and d is stirrup diameter.

[0027] As an optimization, when coupled corrosion occurs, the magnetic field intensity generated by multi-directional steel bar coupled corrosion at any point p(x,y,z) in space is,

[0028]

[0029] In the formula, H ix is the magnetic field intensity generated by the corroded areas of the longitudinal reinforcement and stirrups at point p (x, y, z).

[0030] 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:

[0031] B=μ0μ r H (6)

[0032] μ0 is the vacuum magnetic permeability, which is a constant, μ r is the relative magnetic permeability of air, μ r ≈1.

[0033] As an optimization, in step b, the quantitative diagnostic index is:

[0034]

[0035] In the formula, I x It is based on the magnetic induction curve B of the magnetic induction intensity B x The quantitative diagnostic index established, x m 、x n is the position coordinate corresponding to the edge of the rusted area, where x m >x n , m and n are the serial numbers of the measuring points corresponding to the edge of the rusted area, is B at the i measuring point x magnetic signal.

[0036] As an optimization, in step c, a correlation model between the quantitative diagnostic index and the corrosion depth is first established, wherein for the corrosion of the longitudinal reinforcement, a model M1 is established, and for the corrosion of the stirrups, a model M2 is established. For the coupled corrosion of the longitudinal reinforcement and the stirrups, the quantitative diagnostic index is corrected by the importance coefficient reflecting the importance of the longitudinal reinforcement and the stirrups, and the corrected quantitative diagnostic index is substituted into the model M1 and the model M2, respectively, to obtain the corrosion depths of the longitudinal reinforcement and the stirrups under coupled corrosion, respectively;

[0037] The importance coefficient is determined by the following method:

[0038] Assuming that the distance between any part of the simply supported beam and the support is x, the importance coefficients of the longitudinal reinforcement and stirrups in any section of the simply supported beam are defined as follows:

[0039]

[0040]

[0041] Where L is the length of the simply supported beam, λ1 is the importance coefficient of the longitudinal reinforcement, and λ2 is the importance coefficient of the stirrups.

[0042] As an optimization, the model M1 is:

[0043]

[0044] The model M2 is:

[0045]

[0046] Compared with the prior art, the present invention has the following advantages: the present invention establishes a quantitative diagnostic index that reflects the fluctuation amplitude of the magnetic signal and has a correlation with the corrosion depth of the corroded area on the premise of detecting the magnetic signal of the steel bars inside the simply supported beam and obtaining the corrosion orientation and the corrosion area, and quantitatively analyzes the corrosion depth of the corroded area through the correlation, thereby better evaluating the corrosion condition of the stressed steel bars and providing a basis for the subsequent maintenance of the simply supported beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 : Schematic diagram of corrosion of longitudinal reinforcement inside a simply supported beam;

[0048] Figure 2 : Schematic diagram of internal stirrup corrosion in simply supported beams;

[0049] Figure 3 : Schematic diagram of the process of using the detection device to detect the simply supported beam;

[0050] Figure 4 :Working parameters of theoretical magnetic field of steel bars inside simply supported beams

[0051] Figure 5 : Theoretical magnetic field curve of longitudinal reinforcement corrosion;

[0052] Figure 6 : Theoretical magnetic field curve of stirrup corrosion;

[0053] Figure 7 : Theoretical magnetic field curve of multi-directional steel bar coupled corrosion;

[0054] Figure 8 : Magnetic curve of longitudinal reinforcement corrosion during actual detection;

[0055] Fig. 9 : Magnetic curve of stirrup corrosion in actual detection;

[0056] Fig.10 : Magnetic curve diagram of multi-directional steel bar coupled corrosion in actual detection;

[0057] Fig.11 : Magnetic curves of longitudinal reinforcement at different corrosion depths;

[0058] Fig.12 : Magnetic curves of stirrups at different corrosion depths;

[0059] Fig.13 : Magnetic curves of multi-directional steel bar coupled corrosion at different corrosion depths;

[0060] Fig.14 : Correlation between Ix and corrosion depth K under corrosion state of longitudinal reinforcement;

[0061] Fig.15 : Correlation between Ix and corrosion depth K' of stirrups under corrosion state;

[0062] Fig.16 : Flow chart of quantitative detection method;

[0063] In the figure, 1 is longitudinal reinforcement, 2 is stirrup reinforcement, 3 is frame reinforcement, 4 is scanning track, and 5 is magnetic sensor. DETAILED DESCRIPTION

[0064] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0065] 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.

[0066] 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.

[0067] Example: See Figure 1-Figure 10 A method for accurately locating the corrosion of steel bars inside a simply supported beam comprises the following steps:

[0068] a) Collect the magnetic signals of the steel bars inside the simply supported beam.

[0069] Specifically, the magnetic signal acquisition adopts the following method:

[0070] a1) A scanning track 4 is arranged parallel to the length direction of the simply supported 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 simply supported beam. The lift-off height should be as small as possible to ensure the accuracy of the magnetic signal.

[0071] a2) 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.

[0072] a3) 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, take the scanning path as the X-axis and the collected magnetic signal Bx along the scanning direction as the Y-axis, use the automated drawing module to output the Bx magnetic curve graph at different lift-off heights, and accurately locate the position and rusted area of ​​the corroded steel bars inside the main beam based on the Bx magnetic curve graph: determine the position and rusted area of ​​the corroded steel bars through different magnetic curve shapes and fluctuation characteristics. Specifically, when the curve has left-right symmetrical peaks or troughs, it is judged that the longitudinal reinforcement 1 along the scanning direction in the simply supported beam has been corroded. The area between the intersection points of the curves at different lift-off heights The curve is the corroded area; when the curve has crests and troughs formed by up and down reversal, it is judged that the stirrup 2 perpendicular to the scanning direction in the simply supported beam has been corroded, and the area between the crests and troughs is the corroded 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 simply supported 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 simply supported beam are not corroded.

[0073] 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.

[0074] 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 simply supported beam. When the longitudinal reinforcement inside the simply supported 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.

[0075] 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 simply supported beam as force bars and two frame bars 3 located at the bottom of the simply supported 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;

[0076] 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,

[0077]

[0078] The magnetic field intensity along the X-axis direction generated by another longitudinal rib at this point is,

[0079]

[0080] 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:

[0081] H px =H 1x +H 2x (3)

[0082] In formula (1) and formula (2), b is the 1 / 2 defect 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.

[0083] 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,

[0084]

[0085] Among them, l is 1 / 2 length of the stirrup at the bottom of the beam, which is also 1 / 2 defect width of the stirrup corroded area, h′ is 1 / 2 corrosion depth of the stirrup corroded area, and d is stirrup diameter.

[0086] 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.

[0087]

[0088] In the formula, H ix is the magnetic field intensity generated by the corroded area of ​​longitudinal reinforcement and stirrups at point p.

[0089] 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 / 2πμ0),ρ s / 2πμ0 is usually regarded as a constant, so H x 'With H x With a consistent trend, 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 7 As shown, this curve is the magnetic field curve of the theoretical model.

[0090] 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:

[0091] B=μ0μ r H (6)

[0092] μ0 is the vacuum magnetic permeability, which is 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 As shown in the magnetic curve diagram of the actual detection, the position and rusted area of ​​the corroded steel bars can be accurately located by performing magnetic detection on the simply supported beam.

[0093] The detection device for detecting magnetic signals in the present invention includes a plurality of scanning tracks arranged in parallel along the length direction of a simply supported beam, the plurality of scanning tracks are located in the same plane and have different lift-off heights with the simply supported beam, and a magnetic sensor and an automatic drawing module are slidably installed on the scanning tracks, the magnetic sensor being connected to the automatic drawing module, wherein the automatic drawing module is used to draw curves of changes in a plurality of magnetic signals collected by the magnetic sensor moving along scanning tracks with different lift-off heights along with position signals.

[0094] On this basis, in order to quantitatively analyze the corrosion depth of the rusted area, further,

[0095] b) establishing a quantitative diagnostic index that reflects the fluctuation amplitude of the magnetic signal and is correlated with the corrosion depth of the corroded area.

[0096] Specifically, the spatial magnetic field is closely related to the steel bar diameter (D for longitudinal bars and d for stirrups), the position of the magnetic sensor (x, y, z), the corrosion width (b), and the corrosion depth (K = 2h and K' = 2h'). When the other magnetic field influencing parameters are fixed (x = -50cm~50cm, y = 1cm, z = 3cm, b = 10cm, D = 1.2cm, l = 5cm, d = 0.8cm), the magnetic field curve of the spatial magnetic field changing with the 1 / 2 corrosion depth (h for longitudinal bars and h' for stirrups) is as follows: Figure 11-13 shown.

[0097] It can be seen that when the other magnetic field influencing parameters are fixed, whether it is the longitudinal reinforcement, stirrup or multi-directional steel coupled corrosion, although the Hx' curve shape is different, it also has a common evolution trend with the increase of corrosion depth: the greater the steel corrosion depth, the greater the corresponding magnetic field fluctuation amplitude, and the magnetic field fluctuation amplitude can be used to describe the corrosion defect depth. Since the detection device collects the magnetic induction intensity signal, and the change law of the magnetic induction intensity Bx is consistent with that of Hx', it is feasible to use the Bx signal to quantitatively diagnose the corrosion depth of the steel bar.

[0098] Based on this, quantitative diagnostic indicators are first established, which are:

[0099]

[0100] In the formula, I x It is based on the magnetic induction curve B of the magnetic induction intensity B x The quantitative diagnostic index established, x m 、x n is the position coordinate corresponding to the edge of the rusted area, where x m >x n , m and n are the serial numbers of the measuring points corresponding to the edge of the rusted area, is B at the i measuring point xMagnetic signal. It can be seen from formula (7) that the quantitative diagnostic index reflects the average fluctuation amplitude of the magnetic field in the corrosion area. The larger the average fluctuation amplitude of the magnetic field, the greater the corrosion depth in the area.

[0101] c) obtaining the corrosion depth of the corroded area according to the correlation between the quantitative diagnostic index and the corrosion depth.

[0102] Specifically, in actual engineering, a simply supported beam is usually designed in a standardized manner, and the diameter of the internal steel bars (D for the longitudinal bars and d for the stirrups) is a fixed value. If the position of the magnetic sensor (x, y, z) remains unchanged during each detection, only the corrosion width and corrosion depth are variables in the magnetic field theoretical model, and the two are important parameters that affect the spatial magnetic field. Since the fluctuation range of the magnetic field reflects the corrosion width of the steel bar, and the fluctuation amplitude of the magnetic field reflects the corrosion depth of the steel bar, the corrosion depth of the steel bar can be obtained by the quantitative diagnostic index proposed by the present invention on the premise of locating the orientation and corrosion area of ​​the corroded steel bar.

[0103] In this embodiment, the longitudinal reinforcement and stirrups inside the beam are corroded by the power-on method, and then the spatial magnetic signal is collected by the magnetic sensor to calculate the quantitative diagnostic index Ix corresponding to different corrosion depths, and the correlation between the two is obtained as follows: Figure 14-15 As shown, the test data is linearly fitted to obtain the correlation models M1 and M2 between the quantitative diagnostic index and the corrosion depth, wherein the model M1 is:

[0104]

[0105] The model M2 is:

[0106]

[0107] For unidirectional reinforcement corrosion (i.e., only longitudinal reinforcement corrosion or stirrup corrosion exists somewhere inside the simply supported beam), the quantitative diagnostic index I is calculated. X , substituting the index into model M1 or M2, the corrosion depth of the corresponding longitudinal reinforcement or stirrup can be finally obtained.

[0108] If the diagnosis result is multi-directional reinforcement coupled corrosion (i.e., coupled corrosion of longitudinal reinforcement and stirrups exists somewhere inside the simply supported beam), the quantitative diagnostic index I calculated at this time is X It is the sum of the results of corrosion of longitudinal reinforcement and stirrups. It is impossible to obtain the quantitative diagnostic indicators corresponding to longitudinal reinforcement and stirrups respectively based on this superposition result. The corrosion depth of the two should be further diagnosed in combination with the stress characteristics of simply supported beams and the importance of the two types of steel bars at different positions.

[0109] Since the steel bars in different positions in a simply supported beam bridge play different roles, the longitudinal bars are bending resistant and the stirrups are shear resistant, the stress characteristics of different parts of the beam bridge are different, and the importance of the two types of steel bars is also different. Assuming that the importance coefficients of the longitudinal bars and stirrups in different parts are λ1 and λ2, at any part of the beam bridge, λ1+λ2=1, the internal force borne in the span of the simply supported beam is mainly bending moment, and the longitudinal bars play a greater role here, and their importance is higher. The internal force borne at the support is mainly shear force, and the stirrups are more important here. Assuming that the distance between any part and the support is x, then at any section of the beam, the importance coefficients of the longitudinal bars and stirrups are defined as:

[0110]

[0111]

[0112] Where L is the length of the simply supported beam, λ1 is the importance coefficient of the longitudinal reinforcement, and λ2 is the importance coefficient of the stirrups.

[0113] λ1 and λ2 reflect the importance of longitudinal reinforcement and stirrups. The larger the importance coefficient, the more important the steel bar is on the corresponding section, and the more unfavorable the consequences of corrosion of the steel bar are. A larger allocation coefficient should be considered when allocating quantitative diagnostic indicators. This allocation takes into account the most unfavorable situation. The importance coefficient determines the allocation ratio of diagnostic indicators for steel bars in various directions. After determining the quantitative diagnostic indicators of longitudinal reinforcement and stirrups, quantitative diagnosis can be performed on them. The specific steps are as follows:

[0114] (1) Calculate the quantitative diagnostic index I of multi-directional steel bar coupled corrosion using formula (7): X This index is the result of coupled corrosion of longitudinal reinforcement and stirrups, and is the superposition of the two quantitative indicators.

[0115] (2) According to the corrosion position of the simply supported beam, the distance x between the center of the corrosion area and the beam support is determined, and then the importance coefficients λ1 and λ2 of the longitudinal reinforcement and stirrups at the corrosion position are calculated by equations (8) and (9).

[0116] (3) The total quantitative index is allocated according to the importance coefficient, and the quantitative diagnostic index of the longitudinal reinforcement in the corroded part is obtained as λ1I X , the quantitative diagnostic index of stirrups is λ2I X .

[0117] (4) The quantitative diagnostic index λ1I of the longitudinal reinforcement is X , quantitative diagnostic index of stirrups λ2I X Substituting into the corresponding quantitative diagnostic models M1 and M2, the corrosion depths K and K' of the longitudinal reinforcement and stirrups under the multi-directional steel bar coupled corrosion state can be predicted.

[0118] 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 orientation and corrosion area of ​​the corroded steel bars are determined by different magnetic curve shapes and fluctuation characteristics. On this basis, quantitative diagnostic indicators are proposed, and a correlation model between the quantitative diagnostic indicators and the corrosion depth is established. The corrosion depth of the steel bars can be obtained from the indicators, providing accurate information for subsequent maintenance.

[0119] 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 quantitative detection method for steel bar corrosion inside a simply supported beam, characterized in that: The following steps are included: a) Collect the magnetic signals of the steel bars inside the simply supported beam; b) establishing a quantitative diagnostic index that reflects the fluctuation amplitude of the magnetic signal and is correlated with the corrosion depth of the corroded area; c) obtaining the corrosion depth of the corroded area according to the correlation between the quantitative diagnostic index and the corrosion depth.

2. The quantitative detection method for steel bar corrosion in a simply supported beam according to claim 1, characterized in that: Step a comprises the following steps, a1) a scanning track is arranged parallel to the length direction of the simply supported beam, and a preset lifting height is provided between the scanning track and the simply supported beam; a2) 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; a3) 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.

3. The quantitative detection method for steel bar corrosion inside a simply supported beam according to claim 2, characterized in that: In step a3, when the curve has left-right symmetrical peaks or troughs, it is judged that the longitudinal reinforcement along the scanning direction in the simply supported 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 simply supported 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 simply supported 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 shape change, it is judged that the steel bars inside the simply supported beam are not corroded.

4. The quantitative detection method for steel bar corrosion inside a simply supported beam according to claim 3, characterized in that: In step a3, the curve of the change of the magnetic signal with the position signal is obtained by establishing a theoretical model of the magnetic field of the steel skeleton in the simply supported 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 simply supported beam as force bars and two frame bars located at the bottom of the simply supported 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, The magnetic field at any point p(x, y, z) 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: px =H 1x +H 2x (3) In formula (1) and formula (2), b is the 1 / 2 defect 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.

5. A quantitative detection method for steel bar corrosion inside a simply supported beam according to claim 4, 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 defect width of the stirrup corroded area, h′ is 1 / 2 corrosion depth of the stirrup corroded area, and d is stirrup diameter.

6. A quantitative detection method for steel bar corrosion inside a simply supported beam according to claim 5, characterized in that: When coupled corrosion occurs, the magnetic field intensity generated by multi-directional steel bar coupled corrosion at any point p(x,y,z) in space is: In the formula, H ix is the magnetic field intensity generated by the corroded areas of the longitudinal reinforcement and stirrups at point p (x, y, z).

7. A quantitative detection method for steel bar corrosion inside a simply supported beam according to claim 6, 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.

8. A quantitative detection method for steel bar corrosion inside a simply supported beam according to claim 7, characterized in that: In step b, the quantitative diagnostic index is: In the formula, I x It is based on the magnetic induction curve B of the magnetic induction intensity B x The quantitative diagnostic index established, x m 、x n is the position coordinate corresponding to the edge of the rusted area, where x m >x n , m, n are the measuring point numbers corresponding to the edge of the rusted area, B x(i) is B at the i measuring point x magnetic signal.

9. A quantitative detection method for steel bar corrosion inside a simply supported beam according to claim 8, characterized in that: In step c, first, a correlation model between the quantitative diagnostic index and the corrosion depth is established, wherein for the corrosion of the longitudinal reinforcement, a model M1 is established, and for the corrosion of the stirrups, a model M2 is established. For the coupled corrosion of the longitudinal reinforcement and the stirrups, the quantitative diagnostic index is corrected by the importance coefficient reflecting the importance of the longitudinal reinforcement and the stirrups, and the corrected quantitative diagnostic index is substituted into the model M1 and the model M2, respectively, to obtain the corrosion depths of the longitudinal reinforcement and the stirrups under the coupled corrosion, respectively; The importance coefficient is determined by the following method: Assuming that the distance between any part of the simply supported beam and the support is x, the importance coefficients of the longitudinal reinforcement and stirrups in any section of the simply supported beam are defined as follows: Where L is the length of the simply supported beam, λ1 is the importance coefficient of the longitudinal reinforcement, and λ2 is the importance coefficient of the stirrups.

10. A quantitative detection method for steel bar corrosion inside a simply supported beam according to claim 9, characterized in that: The model M1 is: The model M2 is: Among them, the corrosion depth of the longitudinal reinforcement is K=2h, and the corrosion depth of the stirrups is K'=2h'.

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