Steel-concrete composite beam crack discrimination method based on bending wave structure sound intensity aggregation degree test

Abstract

The invention discloses a bending wave structure sound intensity aggregation degree test-based steel-concrete composite beam crack discrimination method, which comprises the following steps of: delimiting a plate to be tested into a series of scanning areas, setting a scanning path, and calculating the bending wave structure sound intensity aggregation degree; traversing the plate according to a scanning algorithm, and calculating the sound intensity aggregation degree of the bending wave structure of all areas; calculating the sound intensity aggregation degree of bending wave structures in all areas of the steel-concrete composite beam plate in the service period; and comparing the bending wave structure sound intensity aggregation degree frequency spectrum peak values, and if the difference value of the bending wave structure sound intensity aggregation degree frequency spectrum peak values of a certain scanning area between the two sound intensity aggregation degree frequency spectrum peak values exceeds a preset threshold value, determining that cracks exist in the scanning area of the servicing steel-concrete composite beam plate. According to the method, the characteristic that bending wave signals are easy to test is combined, the bending wave structure sound intensity testing technology and the structure sound intensity aggregation degree scanning algorithm are adopted, efficient judgment and positioning of the cracks of the steel-concrete composite beam can be achieved, and the method has great theoretical significance and engineering value for damage recognition of bridges of the type.

Description

Technical Field

[0001] The invention relates to a steel-concrete composite beam crack identification method based on bending wave structure sound intensity concentration test, belonging to the technical field of bridge damage identification. Background Art

[0002] Steel-concrete composite beam bridges have serious plate cracking problems due to fatigue loads, cyclic temperature, and environmental corrosion. Common types of cracks in this type of bridge during service include: plate cracking at the coupling boundary caused by fatigue loads, top plate cracks caused by negative bending moments, and plate splitting caused by shear connector slippage. The causes of the above damage are complex, and some cracks are typical hidden damages that cannot be effectively identified by existing methods such as manual vision and machine vision. For steel-concrete composite beam structures with complex structures and huge volumes, existing non-destructive testing methods such as acoustic emission, ultrasonic, ray, and eddy current methods have the disadvantages of low efficiency and inaccurate detection. In addition, since the structural cracks are relatively small, they have little impact on the overall stiffness of the structure. Conventional identification methods such as vibration fundamental frequency and mode are more effective in identifying overall damage, but the sensitivity to this type of local damage is low, and it is difficult to locate the damage when the number of sensors is limited.

[0003] When the vibration power flow passes through the structural crack, a bypass phenomenon will occur, and obvious vibration energy accumulation will appear at the tip of the crack. This point can be used to identify damage to the plate. Since the bridge is subjected to vertical excitation loads, the vibration energy in its top and bottom plates is mainly carried by bending waves. Bending waves are out-of-plane vibration waves, which are easy to test using sensors or high-speed cameras. However, most of the current research is theoretical research, and its calculation method is not suitable for actual measurement operations, and there is no unified judgment index. For example, patents CN202410109372.1 and CN202210364847.2 only use finite element numerical methods to calculate the structural sound intensity, and do not provide a calculation method for the structural sound intensity from a practical measurement perspective, nor do they provide judgment indicators and damage location methods. Summary of the invention

[0004] In order to overcome the defects existing in the prior art, the present invention aims to provide a method for identifying cracks in steel-concrete composite beams based on bending wave structural sound intensity concentration test. The method combines the characteristics of bending wave signals that are relatively easy to test, adopts bending wave structural sound intensity testing technology and structural sound intensity concentration scanning algorithm, and can realize efficient identification and positioning of cracks in steel-concrete composite beams, which has great theoretical significance and engineering value for damage identification of such bridges.

[0005] The present invention provides a technical solution to solve the above technical problems: a method for distinguishing cracks in steel-concrete composite beams based on bending wave structural sound intensity concentration test, comprising the following steps:

[0006] S1. Delimit the panel to be tested into a series of scanning areas and set the scanning path, and calculate the bending wave structural sound intensity concentration of the initial steel-concrete composite beam scanning area;

[0007] The scanning area size is length × width = a × b, a and b are both integer multiples of the measurement point spacing, and the area of ​​a × b is not greater than 1 / 4 of the total area of ​​the panel;

[0008] S2. According to the scanning algorithm, the plate is traversed to calculate the concentration of the bending wave structure sound intensity of all regions of the initial steel-concrete composite beam plate, and a spectrum diagram of the bending wave structure sound intensity concentration of the initial steel-concrete composite beam plate is drawn;

[0009] S3, calculating the bending wave structural sound intensity concentration of the scanning area of ​​the steel-concrete composite beam in service according to the scanning area and scanning path in step S1;

[0010] S4, traversing the plate according to the scanning algorithm, calculating the bending wave structure sound intensity concentration of all regions of the steel-concrete composite beam plate during service, and drawing a bending wave structure sound intensity concentration spectrum diagram of the steel-concrete composite beam plate during service;

[0011] S5. Compare the peak values ​​of the flexural wave structure sound intensity concentration spectrum of all regions of the initial steel-concrete composite beam plate with the peak values ​​of the flexural wave structure sound intensity concentration spectrum of all regions of the steel-concrete composite beam in service. If the difference in the peak values ​​of the flexural wave structure sound intensity concentration spectrum of a certain scanning area between the two exceeds a preset threshold, it is determined that cracks exist in the scanning area of ​​the steel-concrete composite beam plate in service.

[0012] A further technical solution is that the scanning area includes a plurality of target points.

[0013] A further technical solution is that the target point sets four measuring points at the same interval d / 2 at 0°, 90°, 180° and 270°; the upper limit of the ratio of the measuring point interval d to the bending wavelength λ of the plate is 0.2,

[0014] The calculation formula of the bending wavelength λ of the plate is as follows:

[0015]

[0016] Where: h is the thickness of the plate to be tested, C1 is the longitudinal wave velocity of the plate material to be tested, and f is the frequency.

[0017] A further technical solution is that the calculation process of the acoustic intensity concentration of the bending wave structure includes:

[0018] Step 1, determine the density of measuring points, and obtain vibration data of four measuring points, wherein the vibration data is vibration acceleration or vibration displacement;

[0019] Step 2, calculating the magnitude and amplitude of the bending wave structure sound intensity vector according to the vibration data of the four measuring points;

[0020] Step 3: construct frequency domain three-dimensional vector cloud diagram and streamline according to the amplitude of bending wave structure sound intensity;

[0021] Step 4: Calculate the bending wave structure sound intensity concentration in the scanning area according to the bending wave structure sound intensity amplitude.

[0022] A further technical solution is that in step 1, an acceleration sensor is placed at each measuring point to obtain vibration data, wherein the mass m of the acceleration sensor is A <1% of the structural mass m.

[0023] A further technical solution is that the specific process of step 2 includes:

[0024] Step 21, convert the vibration data into acceleration, and perform Fourier transform to obtain the real part and the imaginary part;

[0025] Step 22, differentiating the vibration acceleration data in the frequency domain;

[0026] Step 23: Calculate the magnitude and amplitude of the bending wave structural sound intensity vector at each grid point based on the measured vibration acceleration data.

[0027] The bending wave structure-borne sound intensity amplitude I at the i-th grid point is i The bending wave structure sound intensity components I in the x and y directions xi ,I yi Obtained by vector addition.

[0028] A further technical solution is that the calculation formula in step 23 is:

[0029]

[0030] Where: m is the mass per unit area of ​​the plate; d is the distance between the measuring points; D x and D y are the bending stiffness of the plate in the x and y directions respectively; G 12 , G 34 The cross spectrum of the acceleration signal in the x and y directions for each grid point.

[0031] A further technical solution is that the specific process of step 3 includes:

[0032] Step 31, performing normalization processing based on the bending wave structure sound intensity amplitude obtained in step S2;

[0033] Normalized bending wave structure-borne sound intensity I i ' is expressed as:

[0034]

[0035] Where: I max represents the maximum bending wave structure-borne sound intensity amplitude among all grid points;

[0036] Step 32, determining the spatial coordinates of the grid points according to the density of the measuring points, and drawing a three-dimensional cloud map according to the normalized bending wave structure sound intensity;

[0037] Step 33, using the grid point coordinates as the starting point and the normalized bending wave structure sound intensity as the vector length, a three-dimensional vector diagram and a streamline diagram of the bending wave structure sound intensity are drawn;

[0038] Step 34: superimpose the three-dimensional cloud map, vector map and streamline map to obtain a three-dimensional vector cloud map and streamline map of the bending wave structure sound intensity.

[0039] A further technical solution is that the calculation formula in step 4 is:

[0040]

[0041] Where: Max.I j is the maximum bending wave structure-borne sound intensity amplitude of the jth scanning area, Ave.I plate A is the average bending wave structure sound intensity amplitude of all grid points of the panel to be tested; j is the concentration of the bending wave structure acoustic intensity in the jth scanning area.

[0042] A further technical solution is that the specific process of the scanning algorithm traversing the plate includes:

[0043] A. Determine the appropriate step size k and translate the scanning area;

[0044] Wherein, the step length k is an integer multiple of the measurement point spacing d, and k<5d;

[0045] B. According to the scanning path, the scanning area is translated by a distance k, and the bending wave structure sound intensity concentration A of the scanning area is calculated. j+1 ;

[0046] C. Repeat step B until the entire panel to be tested is traversed to obtain the bending wave structure sound intensity concentration of each scanning area.

[0047] The present invention has the following beneficial effects: the present invention draws a spectrum diagram of the sound intensity concentration of the bending wave structure in each area, and by comparing its single-frequency pulse peak value, it can realize the discrimination of cracks in the steel-concrete composite beam, which has great theoretical significance and engineering value for the vibration wave transmission analysis and crack identification of thin-walled bridge damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1This is a schematic diagram of the steel-concrete composite beam structure according to an embodiment of the present invention;

[0049] Figure 2 This is a schematic diagram of acceleration measurement points according to an embodiment of the present invention;

[0050] Figure 3 Schematic diagram of the scanning algorithm of the acoustic intensity concentration of the bending wave structure according to an embodiment of the present invention;

[0051] Figure 4 This is a vector cloud diagram of the sound intensity of the bending wave structure of the concrete slab according to the embodiment of the present invention;

[0052] Figure 5 This is a spectrum diagram of the acoustic intensity concentration of the bending wave structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0054] Before describing the specific embodiments of the present invention, some key terms need to be explained to make the scheme of the present invention clearer and more complete:

[0055] Steel-concrete composite box girder: A box structure composed of an upper concrete slab 01 and a lower steel beam 02 that jointly bears the upper load of the bridge. Its plates can all be regarded as thin-walled plates.

[0056] Lower steel beam 02: A steel trough structure composed of a flange plate 021, a web plate 022, a diaphragm 023, and a bottom plate 024.

[0057] Structural sound intensity: mathematically defined as the product of stress and velocity response at any point, it represents the magnitude of the power flow through the unit cross-section of the structure. It is composed of longitudinal wave, shear wave, bending wave, and torsional wave components.

[0058] Bending wave structure-borne sound intensity: a component of the structure-borne sound intensity that dominates the top and bottom plates of steel-concrete composite beams.

[0059] Measuring point 03: The test point of vibration acceleration, used to differentially calculate the original data of bending wave structural sound intensity. There are 4 target points 04, namely 031, 032, 033, and 034.

[0060] Target point 04: The point where the bending wave structure-borne acoustic intensity is to be obtained.

[0061] Scanning area 05: an area where the plate is further divided according to the estimated crack size, including several target points 04, and is the minimum area for determining whether there are cracks.

[0062] Maximum bending wave structure-borne sound intensity point 06: the target point with the maximum bending wave structure-borne sound intensity amplitude in the scanning area.

[0063] Scanning path 07: ensure that the scanning area 05 can traverse the translation route of the entire panel.

[0064] In this embodiment, Figure 2 As shown in the figure, the flexural wave structural sound intensity of the top plate of a steel-concrete composite box girder was tested using the differential acceleration sensor, and the three-dimensional visualization of its flexural wave energy transfer was realized. The concentration of structural sound intensity in the damaged and undamaged states was compared based on the scanning algorithm. Specifically, a single-box single-chamber steel-concrete composite box girder model was investigated, which consists of an upper concrete slab and a lower steel beam, with a total size of 3180 (length) × 1150 (width) × 680 (height) mm, a concrete slab thickness of 60 mm, and a steel beam slab thickness of 6 to 10 mm. A vibrator was used to apply sinusoidal excitation at the center of the top plate.

[0065] A method for distinguishing cracks in a steel-concrete composite beam based on a bending wave structure sound intensity concentration test of the present invention specifically comprises the following steps:

[0066] S1. Delimit the panel to be tested into a series of scanning areas and set the scanning path, and calculate the bending wave structural sound intensity concentration of the initial steel-concrete composite beam scanning area;

[0067] In this embodiment, assuming that the estimated crack length is 0.4 mm, the scanning area 05 size of 0.6×0.4 m is selected, the horizontal and vertical dimensions are 6 times and 4 times the test grid size respectively, and the area of ​​the scanning area 05 is much smaller than 1 / 4 of the total area of ​​the plate;

[0068] The scanning area 05 includes 10 target points 04, and the target points 04 are provided with 4 measuring points at the same interval d / 2 at 0°, 90°, 180°, and 270°;

[0069] In this embodiment, the frequency is 20-2000 Hz, and the bending wavelength λ of the concrete slab at 2000 Hz is determined to be 0.46 mm, and the calculation formula is as follows:

[0070]

[0071] Where: h is the thickness of the plate to be tested, C1 is the longitudinal wave velocity of the plate material to be tested, and f is the frequency;

[0072] Therefore, the target point spacing is determined to be 0.1 m, and the spacing is 0.1 m. At this time, the ratio of the test grid to the bending wavelength of the plate is 0.19 < 0.2, and the measurement point spacing d = 0.2 m.

[0073] The specific calculation process of the acoustic intensity concentration of the bending wave structure is as follows:

[0074] Step 1, determine the density of measuring points, and place an acceleration sensor at each measuring point to obtain vibration data to obtain vibration data of four measuring points;

[0075] like Figure 3 As shown, the mass of the acceleration sensor is m A About 50g, much less than 1% of the structure's mass;

[0076] Step 2, calculating the magnitude and amplitude of the bending wave structure sound intensity vector according to the vibration data of the four measuring points;

[0077] Step 21, convert the vibration data into acceleration, and perform Fourier transform to obtain the real part and the imaginary part;

[0078] Step 22: cyclically select the measuring point 03 corresponding to each target point 04, perform differential on the acceleration signal, and calculate the cross-spectrum G of the acceleration signal of each target point 04 in the x and y directions. 12 , G 34 ;

[0079] The cross spectrum G of the acceleration signal in the x and y directions of each grid point 12 , G 34 It is expressed as:

[0080]

[0081] Where: is the complex conjugate of the acceleration of the measuring points 031 and 033 at the frequency ω, A2(ω) and A4(ω) are the complex acceleration of the measuring points 032 and 034 at the frequency ω, G 12 The positive direction is 032 pointing to 031, G 34 The positive direction is 034 pointing to 033;

[0082] Step 23, calculating the magnitude and amplitude of the bending wave structure sound intensity vector of each target point 04;

[0083] The bending wave structure-borne sound intensity amplitude I at the i-th grid point is i The bending wave structure sound intensity components I in the x and y directions xi ,I yi Obtained by vector addition;

[0084]

[0085] Where: m is the mass per unit area of ​​the plate; d is the distance between the measuring points; D x and D y are the bending stiffness of the plate in the x and y directions respectively; G 12 , G34 The cross spectrum of acceleration signals in the x and y directions for each grid point;

[0086] Step 3: construct frequency domain three-dimensional vector cloud diagram and streamline according to the amplitude of bending wave structure sound intensity;

[0087] Step 31: Based on the result obtained in step S2, normalization processing is performed to normalize the amplitude of the global maximum structure-borne sound intensity vector to 1;

[0088] Normalized bending wave structure-borne sound intensity I i ' is expressed as:

[0089]

[0090] Where: I max represents the maximum bending wave structure-borne sound intensity amplitude among all grid points;

[0091] Step 32: Visualize the structural sound intensity of the steel-concrete composite beam by using Tecplot software to draw a three-dimensional cloud map according to the geometric position of the target point 04 and its corresponding bending wave structural sound intensity vector;

[0092] Step 33, take the coordinates of target point 04 as the starting point of the vector and calculate I x and I y As the vector length, draw the three-dimensional vector diagram of the bending wave structure sound intensity;

[0093] Step 34, superimposing the three-dimensional cloud map, vector map and streamline map to obtain a three-dimensional vector cloud map and streamline map of bending wave structure sound intensity;

[0094] Step 4, calculating the bending wave structure sound intensity concentration of the scanning area according to the bending wave structure sound intensity amplitude;

[0095] Calculate the maximum bending wave structure-borne sound intensity amplitude in the first scanning area 05 as Max.I1, wherein Max.I1 is obtained by comparing the bending wave structure-borne sound intensity of all target points 04 in the scanning area 05;

[0096] The bending wave structure sound intensity concentration A1 of the scanning area 05 (j=1) is calculated, and its expression is:

[0097]

[0098] Where: Max.I1 represents the maximum bending wave structure-borne sound intensity amplitude of the first scanning area, Ave.I plate It represents the average bending wave structure-borne sound intensity amplitude of all grid points of the panel to be tested;

[0099] S2. According to the scanning algorithm, the plate is traversed to calculate the concentration of the bending wave structure sound intensity of all regions of the initial steel-concrete composite beam plate, and a spectrum diagram of the bending wave structure sound intensity concentration of the initial steel-concrete composite beam plate is drawn;

[0100] The specific process of the scanning algorithm traversing the plate is as follows:

[0101] A. In this embodiment, the step length k is determined to be 0.1 m, which is 1 times the grid size;

[0102] B. Figure 3 As shown, the scanning area 05 is translated by 0.1 m along the scanning path 07, and the bending wave structure sound intensity concentration A2 of the scanning area 05 is recalculated;

[0103] C. After completing the previous step, continue to translate the scanning area 05 by 0.1 m along the scanning path 07, calculate the bending wave structure sound intensity concentration A3 of the scanning area 05, repeat this process until the entire plate is traversed, and obtain the bending wave structure sound intensity concentration of each scanning area 05;

[0104] S3, according to the scanning area and scanning path in step S1, the bending wave structural sound intensity concentration of the scanning area of ​​the steel-concrete composite beam in service period is calculated (using the same calculation steps as step S1);

[0105] S4, traversing the plate according to the scanning algorithm (using the same traversal steps as step S2), calculating the bending wave structure sound intensity concentration of all regions of the steel-concrete composite beam plate during service, and drawing a bending wave structure sound intensity concentration spectrum of the steel-concrete composite beam plate during service;

[0106] S5. Compare the peak values ​​of the flexural wave structure sound intensity concentration spectrum of all areas of the initial steel-concrete composite beam-slab with the peak values ​​of the flexural wave structure sound intensity concentration spectrum of all areas of the steel-concrete composite beam in service. If the difference in the peak values ​​of the flexural wave structure sound intensity concentration spectrum of a certain scanning area between the two exceeds a preset threshold (the difference between the two is 20 dB), it is determined that cracks exist in the scanning area of ​​the steel-concrete composite beam-slab in service.

[0107] According to the concentration of structural sound intensity in each scanning area, a spectrum curve of the concentration of bending wave structural sound intensity in the crack area is drawn. The black solid line and dotted line in the figure represent the concentration of bending wave structural sound intensity before and after damage, respectively. Figure 5 The frequency spectrum graphs of three scanning areas where cracks exist are given;

[0108] Obtain the single frequency peak of the bending wave structure sound intensity concentration spectrum in each scanning area, by Figure 5It can be seen that the bending wave structural sound intensity concentration of the scanning area 05 where the three cracks 081, 082, and 083 exist all shows an obvious peak at 190 Hz, and its amplitude is generally more than 20 dB higher than other frequencies. It can be highly suspected that cracks appear there. The coordinates of the three scanning areas are recorded to complete the crack identification of the steel-concrete composite beam based on the bending wave structural sound intensity concentration test.

[0109] In this embodiment, combined with Figure 4 and Figure 5 The flexural wave structural sound intensity vector cloud map and spectrum curve were obtained by using flexural wave measurement and scanning algorithm, revealing the flexural wave transmission characteristics of the steel-concrete composite beam concrete slab with cracks; generally, the flexural wave structural sound intensity will be significantly concentrated in the crack area, which appears as a significant single-frequency peak on the spectrum curve, and accurate identification of the crack area can be achieved through this point.

[0110] In this embodiment, the bending wave structure sound intensity test method adopted is an acceleration sensor, and the method of obtaining the original data for bending wave structure sound intensity calculation by using a laser vibrometer, a high-speed camera, etc. should also be included in the protection scope of the present invention.

[0111] The above description is not intended to limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test, characterized in that: The following steps are involved: S1. Delimit the panel to be tested into a series of scanning areas and set the scanning path, and calculate the bending wave structural sound intensity concentration of the initial steel-concrete composite beam scanning area; S2. According to the scanning algorithm, the plate is traversed to calculate the concentration of the bending wave structure sound intensity of all regions of the initial steel-concrete composite beam plate, and a spectrum diagram of the bending wave structure sound intensity concentration of the initial steel-concrete composite beam plate is drawn; S3, calculating the bending wave structural sound intensity concentration of the scanning area of ​​the steel-concrete composite beam in service according to the scanning area and scanning path in step S1; S4, traversing the plate according to the scanning algorithm, calculating the bending wave structure sound intensity concentration of all regions of the steel-concrete composite beam plate during service, and drawing a bending wave structure sound intensity concentration spectrum diagram of the steel-concrete composite beam plate during service; S5. Compare the peak values ​​of the flexural wave structure sound intensity concentration spectrum of all regions of the initial steel-concrete composite beam plate with the peak values ​​of the flexural wave structure sound intensity concentration spectrum of all regions of the steel-concrete composite beam in service. If the difference in the peak values ​​of the flexural wave structure sound intensity concentration spectrum of a certain scanning area between the two exceeds a preset threshold, it is determined that cracks exist in the scanning area of ​​the steel-concrete composite beam plate in service.

2. The method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test according to claim 1 is characterized in that: The scanning area includes a plurality of target points.

3. The method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test according to claim 2 is characterized in that: The target points are arranged with four measuring points at the same intervals of 0°, 90°, 180° and 270°.

4. The method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test according to claim 3 is characterized in that: The calculation process of the bending wave structure sound intensity concentration includes: Step 1: Determine the density of measuring points and obtain vibration data of four measuring points; Step 2, calculating the size and amplitude of the bending wave structure sound intensity vector according to the vibration data of the four measuring points; Step 3: construct frequency domain three-dimensional vector cloud diagram and streamline according to the amplitude of bending wave structure sound intensity; Step 4: Calculate the bending wave structure sound intensity concentration in the scanning area according to the bending wave structure sound intensity amplitude.

5. The method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test according to claim 4 is characterized in that: In step 1, an acceleration sensor is placed at each measuring point to obtain vibration data.

6. The method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test according to claim 4 is characterized in that: The specific process of step 2 includes: Step 21, convert the vibration data into acceleration, and perform Fourier transform to obtain the real part and the imaginary part; Step 22, differentiating the vibration acceleration data in the frequency domain; Step 23: Calculate the size and amplitude of the bending wave structural sound intensity vector at each grid point based on the measured vibration acceleration data.

7. The method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test according to claim 4 is characterized in that: The calculation formula of step 23 is: Where: m is the mass per unit area of ​​the plate; d is the distance between the measuring points; D x and D y are the bending stiffness of the plate in the x and y directions respectively; G 12 , G 34 The cross spectrum of the acceleration signal in the x and y directions for each grid point.

8. The method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test according to claim 4 is characterized in that: The specific process of step 3 includes: Step 31, performing normalization processing based on the bending wave structure sound intensity amplitude obtained in step S2; Step 32, determining the spatial coordinates of the grid points according to the density of the measuring points, and drawing a three-dimensional cloud map according to the normalized bending wave structure sound intensity; Step 33, using the grid point coordinates as the starting point and the normalized bending wave structure sound intensity as the vector length, a three-dimensional vector diagram and a streamline diagram of the bending wave structure sound intensity are drawn; Step 34: superimpose the three-dimensional cloud map, vector map and streamline map to obtain a three-dimensional vector cloud map and streamline map of bending wave structure sound intensity.

9. The method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test according to claim 4 is characterized in that: The calculation formula in step 4 is: Where: Max.I j is the maximum bending wave structure-borne sound intensity amplitude of the jth scanning area, Ave.I plate A is the average bending wave structure sound intensity amplitude of all grid points of the panel to be tested; j is the concentration of the bending wave structure acoustic intensity in the jth scanning area.

10. The method for identifying cracks in steel-concrete composite beams based on bending wave structural acoustic intensity concentration test according to claim 1, characterized in that: The specific process of the scanning algorithm traversing the plate includes: A. Determine the appropriate step size k and translate the scanning area; B. According to the scanning path, the scanning area is translated by a distance k, and the bending wave structure sound intensity concentration A of the scanning area is calculated. j+1 ; C. Repeat step B until the entire panel to be tested is traversed to obtain the bending wave structure sound intensity concentration of each scanning area.

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