A steel-concrete structure vibration energy flow field closed-loop reconstruction and damage grading test method based on DIC dynamic full-field response

Abstract

This invention discloses a closed-loop reconstruction and damage grading test method for vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response, belonging to the field of civil engineering structural health monitoring and damage identification technology. This method acquires the full-field displacement, velocity, and strain response during the vibration process of a reinforced concrete structure using digital image correlation (DIC) technology. Combined with dynamic load information, a vibration energy flow calculation model is established to calculate the characteristics of structural vibration energy transfer, accumulation, and dissipation, reconstructing a continuous spatiotemporal vibration energy flow field. By comparing the energy flow fields in the undamaged and damaged states, damage characteristics such as energy flow density, propagation path, and energy gradient changes are extracted. Closed-loop iterative correction is used to optimize and reconstruct the energy flow field, further completing damage localization and grade evaluation. This invention enables dynamic visualization of the vibration energy flow field and quantitative damage grading of reinforced concrete structures, and can be used for health monitoring and safety assessment of bridges, buildings, and large reinforced concrete structures.

Description

Technical Field

[0001] This invention relates to the field of civil engineering structural testing and health monitoring technology, specifically to a digital image correlation (DIC) vibration test method for reconstructing the vibration energy flow field of damaged reinforced concrete structures. Background Technology

[0002] Reinforced concrete structures, due to their high load-bearing capacity, excellent overall performance, and strong durability, are widely used in bridge engineering, building construction, underground engineering, and large-scale infrastructure. During long-term service, they are susceptible to damage from factors such as vehicle loads, wind loads, seismic action, fatigue accumulation, and environmental erosion, leading to cracks, steel corrosion, interface debonding, concrete spalling, and localized stiffness degradation. As this damage continues to expand, it will cause a decline in the structure's dynamic performance and load-bearing capacity, and in severe cases, even endanger structural safety. Therefore, conducting damage detection and health monitoring of reinforced concrete structures is of great significance for ensuring the safe operation of engineering structures and extending their service life.

[0003] Currently, damage detection in reinforced concrete structures mainly employs ultrasonic testing, acoustic emission testing, fiber optic sensing, and dynamic testing methods based on acceleration, displacement, and strain sensors. Among these, ultrasonic testing and acoustic emission testing primarily target localized areas, limiting their detection range. While fiber optic sensing technology offers high accuracy, its sensor deployment is complex and costly. Traditional dynamic testing methods typically rely on a limited number of sensors to acquire response data from discrete measurement points, making it difficult to comprehensively reflect the dynamic response characteristics of the structure within continuous space during vibration, thus limiting their applicability in complex reinforced concrete structures.

[0004] In recent years, Digital Image Correlation (DIC) technology, as a non-contact full-field optical measurement technique, has been widely used in structural deformation measurement and crack monitoring, as it can acquire full-field displacement and strain information of structural surfaces. However, existing DIC technology is mainly used for full-field displacement or strain measurement, and its research focuses on kinematic response analysis. There is relatively little research on the laws of vibration energy transfer and damage evolution, and the application value of full-field dynamic response data in structural damage identification has not yet been fully explored.

[0005] On the other hand, vibration energy flow analysis can reflect the energy input, propagation, and dissipation laws during structural vibration from the perspective of energy transfer, and is highly sensitive to changes in local structural stiffness and damage. Most existing methods for constructing vibration energy flow fields rely on finite element models or a small amount of discrete measurement data for calculation. Their reconstruction accuracy is greatly affected by model parameters, boundary conditions, and the arrangement of measurement points, making it difficult to accurately reflect the true energy flow distribution throughout the entire vibration process of complex reinforced concrete structures. Furthermore, existing technologies generally lack closed-loop correction mechanisms for energy flow fields based on dynamic full-field response data, making it difficult to effectively reduce the impact of model errors and environmental noise. They also lack damage grading and evaluation methods that incorporate energy flow evolution characteristics, resulting in insufficient damage identification accuracy and quantitative evaluation capabilities.

[0006] Therefore, it is necessary to propose a closed-loop reconstruction and damage grading test method for vibration energy flow field of steel-concrete structures based on DIC dynamic full-field response, so as to realize the acquisition of dynamic full-field response of steel-concrete structure vibration throughout the entire process, high-precision reconstruction and closed-loop correction of vibration energy flow field, and establish a damage location and grading evaluation method based on vibration energy flow characteristics, thereby improving the accuracy, reliability and engineering application value of health monitoring and damage identification of steel-concrete structures. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a closed-loop reconstruction and damage grading test method for the vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response. This method acquires dynamic full-field response data of the entire vibration process of the reinforced concrete structure using Digital Image Correlation (DIC) technology, constructs the structural vibration energy flow field using vibration energy flow theory, and establishes a closed-loop reconstruction mechanism based on dynamic response feedback to achieve high-precision reconstruction of the vibration energy flow field of the reinforced concrete structure. Simultaneously, a damage identification and damage level evaluation method is constructed based on the spatiotemporal evolution characteristics of the vibration energy flow field, enabling accurate identification of damage locations and quantitative evaluation of damage severity in the reinforced concrete structure. This improves the accuracy and reliability of health monitoring, damage detection, and safety status assessment of reinforced concrete structures.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A closed-loop reconstruction and damage grading test method for vibration energy flow field of steel-concrete structures based on DIC dynamic full-field response is proposed. First, a vibration test system is established according to the structural form, geometric dimensions, material parameters and boundary conditions of the steel-concrete structure under test. Random speckle patterns are prepared in the structural measurement area. The installation, calibration and synchronous control of the digital image correlation measurement system, dynamic excitation system and data acquisition system are completed to construct a test platform that meets the requirements of dynamic full-field response measurement.

[0010] During structural vibration testing, dynamic loads are applied to the reinforced concrete structure using methods such as impact excitation, electromagnetic excitation, hydraulic servo excitation, or frequency sweep excitation. A high-speed industrial camera continuously acquires a sequence of speckle images throughout the entire vibration process, simultaneously obtaining excitation load, acceleration, strain, and other dynamic response data. Digital image correlation algorithms are used to perform correlation matching calculations on the continuous speckle images to obtain the full-field displacement information of the structural surface. Furthermore, the velocity field, acceleration field, and strain field are calculated to establish a dynamic full-field response database for the entire vibration process of the reinforced concrete structure.

[0011] Based on the obtained dynamic full-field response data, a vibration energy flow calculation model is established by combining the material parameters of the steel-concrete structure, the structural dynamic characteristics, and the energy conservation relationship. By calculating the vibration energy density, energy flow density, energy propagation direction, energy gradient, and local energy dissipation characteristics at each moment during the structural vibration process through the coupling relationship between the stress field, strain field, and velocity field, a vibration energy flow field with temporal and spatial continuity is constructed, realizing a dynamic and visual representation of the vibration energy propagation process of the steel-concrete structure.

[0012] A benchmark vibration energy flow field for the steel-concrete structure under non-destructive conditions was further established. Spatial registration and feature matching were performed between the vibration energy flow field of the structure under test and the benchmark vibration energy flow field to extract damage-sensitive characteristic parameters such as the rate of change of energy flux density, the rate of change of energy gradient, the offset of energy propagation direction, the local energy dissipation rate, the change of energy propagation path, and the degree of energy accumulation. Based on these parameters, a vibration energy flow field error feedback model was established. Dynamic full-field response data was used as feedback constraints to iteratively correct the vibration energy flow field, and the vibration energy flow calculation model was updated in real time. When two consecutive reconstruction results meet the preset convergence conditions, the closed-loop reconstruction of the vibration energy flow field of the steel-concrete structure is completed.

[0013] After completing the closed-loop reconstruction of the vibration energy flow field, a comprehensive damage evaluation index is constructed based on the spatial distribution characteristics, temporal evolution law, and energy propagation anomaly characteristics of the vibration energy flow field. The index is then used to conduct a fusion analysis of vibration energy flow density changes, local energy dissipation degree, energy accumulation characteristics, propagation direction shift, and propagation path changes to determine the location and scope of structural damage. A damage level evaluation model is established in conjunction with the comprehensive damage evaluation index to achieve quantitative classification of reinforced concrete structures from undamaged to severely damaged states, providing a basis for service status evaluation, maintenance decisions, and life prediction of reinforced concrete structures.

[0014] Furthermore, to improve the accuracy of vibration energy flow field reconstruction, this invention establishes a dynamic response-energy flow field bidirectional feedback mechanism. The DIC dynamic full-field response is used as a model correction constraint, and the vibration energy flow field calculation results are used as the basis for response prediction. Through error feedback, the structural dynamic parameters, boundary constraint parameters, and energy propagation parameters are continuously corrected, so that the vibration energy flow field is consistent with the actual dynamic response of the structure. This reduces the impact of model parameter errors, environmental noise, and measurement errors on the reconstruction results, and improves the reconstruction accuracy and stability of vibration energy flow field of complex steel-concrete structures.

[0015] Furthermore, this invention establishes a damage grading method based on the evolution law of vibration energy flow. It uses the degree of energy flow anomaly, energy dissipation change rate, energy accumulation index, propagation path deviation degree, and comprehensive damage index as evaluation criteria to form a quantitative evaluation standard applicable to different damage stages of steel-concrete structures. This realizes the transformation of structural damage from qualitative identification to quantitative evaluation and improves the engineering applicability and comparability of health monitoring results for steel-concrete structures.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. This invention utilizes digital image correlation technology to obtain dynamic full-field response information of the entire vibration process of steel-concrete structures. Compared with traditional discrete measurement point testing methods, it can obtain displacement field, velocity field and strain field in continuous space, providing high-density and high-precision basic data for vibration energy flow field reconstruction.

[0018] 2. This invention establishes the vibration energy flow field of steel-concrete structures based on dynamic full-field response, and reflects the energy transfer law inside the structure through energy propagation direction, energy flow density and local energy dissipation characteristics, so as to realize the spatiotemporal continuous visualization of the vibration process and improve the ability to analyze the vibration characteristics of complex steel-concrete structures.

[0019] 3. This invention establishes a closed-loop reconstruction method for vibration energy flow field under dynamic response feedback constraints. Through iterative correction between dynamic response information and vibration energy flow field, the adaptive updating of the vibration energy flow field calculation model is achieved, which improves the reconstruction accuracy of vibration energy flow field and reduces the impact of model error, boundary condition changes and environmental noise on the detection results.

[0020] 4. This invention establishes a comprehensive damage evaluation method based on the evolution characteristics of vibration energy flow. By integrating the characteristics of energy flow density change, propagation path offset, local energy dissipation and energy accumulation, it realizes the identification of damage location and quantitative classification of damage degree in steel-concrete structures, thereby improving the accuracy, stability and evaluation consistency of structural damage detection.

[0021] 5. This invention does not require the extensive deployment of contact sensors on the structural surface. It features non-contact, full-field measurement, wide applicability, and ease of engineering implementation. It can be applied to health monitoring, dynamic performance testing, damage detection, and safety status assessment of large-scale engineering structures such as bridges, buildings, underground engineering, hydraulic structures, and steel-concrete composite structures. Attached Figure Description

[0022] Figure 1 The overall flowchart of the test method for closed-loop reconstruction of vibration energy flow field and damage grading of steel-concrete structures based on DIC dynamic full-field response in this invention;

[0023] Figure 2 Schematic diagram of the experimental system of this invention;

[0024] Figure 3 Flowchart of closed-loop reconstruction of vibration energy flow field in this invention;

[0025] Figure 4 This invention provides a flowchart for damage grading evaluation. Detailed Implementation

[0026] The present invention will now be clearly and completely described in conjunction with the technical solutions in the embodiments thereof. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] In the description of this invention, the terms "installation," "setting," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a signal connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] Example 1: Closed-loop reconstruction and damage grading test of vibration energy flow field in a simply supported reinforced concrete beam

[0029] This embodiment uses a reinforced concrete simply supported beam as the test object to explain in detail the implementation process of the method of the present invention.

[0030] 1. Experimental model establishment and speckle preparation

[0031] In this embodiment, the selected reinforced concrete simply supported beam has a total length of 3000mm, a cross-sectional dimension of 150mm × 250mm, a concrete strength grade of C30, and uses four 18mm diameter HRB400 grade steel bars for longitudinal reinforcement. The stirrups are 8mm diameter HPB300 grade steel bars spaced 150mm apart. The beam is simply supported at both ends, with one end being a fixed hinge support and the other end being a rolling hinge support. The loading point is at the mid-span.

[0032] White primer was sprayed onto the measurement area (mid-span region, 1800mm in length) on the beam surface. After the primer dried, random speckle patterns were created using matte black paint. The speckle size was controlled to be 3-5 pixels, with a speckle coverage of approximately 50%. After the speckle preparation was completed, reflective markers were affixed to the side of the measurement area for spatial calibration and image stitching registration of the DIC system.

[0033] 2. DIC Measurement System Setup and Synchronization Control

[0034] This embodiment employs a binocular stereo DIC measurement system, comprising two high-speed industrial cameras (2448×2048 pixels resolution, maximum frame rate 500fps), equipped with 50mm fixed-focus lenses. The optical axis angle between the two cameras is approximately 25°, and the working distance is 1200mm. An LED array light source is used for supplemental lighting to ensure sufficient and uniform illumination in the speckle image.

[0035] Camera calibration was performed using a checkerboard calibration board, measuring 500mm × 400mm with a grid spacing of 20mm. Twenty calibration images were acquired at different positions and orientations. The camera's intrinsic parameters (focal length, principal point coordinates, distortion coefficients) and extrinsic parameters (rotation matrix, translation vector) were obtained using the Zhang Zhengyou calibration method. The calibration reprojection error was controlled within 0.05 pixels.

[0036] In terms of synchronization control, the data acquisition controller is used as the clock source to output a synchronization trigger signal to two high-speed cameras, the exciter controller and the dynamic signal acquisition instrument, ensuring that the synchronization error of the sampling start time of all channels is less than 1μs.

[0037] 3. Dynamic load application and data acquisition

[0038] In this embodiment, an electromagnetic vibrator (rated excitation force 500N, frequency range 5~2000Hz) is used as the excitation device. The vibrator is connected to the mid-span of the beam through a force sensor. The frequency sweeping excitation method is adopted, with a frequency sweeping range of 10~200Hz, a frequency sweeping rate of 1oct / min, and an excitation amplitude of 50N.

[0039] The acquisition parameters were set as follows: the high-speed camera sampling frequency was 500fps, the acquisition time was 10s, and a total of 5000 frames of speckle image sequence were obtained; the force sensor sampling frequency was 2kHz; accelerometers (sensitivity 100mV / g) were placed at the mid-span, 1 / 4-span and support positions of the beam to synchronously acquire acceleration response data.

[0040] 4. Calculation of full-field response data

[0041] Commercial DIC analysis software was used to analyze the speckle image sequence. A frame of the beam before surface deformation was selected as the reference image. The calculation sub-region size was set to 31×31 pixels, the step size was 5 pixels, and the calculation area was 1800mm×200mm, resulting in approximately 360×40=14400 calculation points.

[0042] For each frame of the deformed image, sub-region matching is performed using the zero-mean normalized least square distance (ZNSSD) correlation function, and the displacement field is iteratively solved using the inverse combined Gauss-Newton (IC-GN) algorithm, with the iteration convergence threshold set to 0.001 pixels. Finally, the full-field displacement data u(x,y,t) and v(x,y,t) at each time step are obtained.

[0043] The displacement time history is time-differenterated using the central difference method to obtain the velocity and acceleration fields:

[0044] ,

[0045] in, The time interval is 0.002 s. The strain field is calculated using the displacement gradient method:

[0046] , ,

[0047] 5. Vibrational energy flow field reconstruction

[0048] Based on the constitutive relation of linear elastic materials, the stress field is calculated from the strain field:

[0049] , ,

[0050] Where E is the elastic modulus of concrete (taken as 30 GPa). The value is Poisson's ratio (taken as 0.2).

[0051] The vibration energy flux density vector is calculated using the following formula:

[0052] ,

[0053] Vibration energy density is calculated as follows:

[0054]

[0055] Where ρ is the density of concrete (taken as 2400 kg / m³).

[0056] Through the above calculations, the energy flow density vector at each spatial point at each time can be obtained, and then the energy propagation path and energy flow field distribution map can be drawn.

[0057] 6. Establishment of reference energy flow field and extraction of damage features

[0058] The above experimental steps were performed on a reinforced concrete simply supported beam under undamaged conditions to obtain undamaged reference energy flow field data. Then, a crack with a width of 0.3 mm and a depth of 30 mm was prefabricated at the bottom of the mid-span of the beam to simulate slight damage, and the above experiment was repeated.

[0059] Spatially register the energy flow fields of the damaged state and the reference state, and calculate the following damage sensitivity parameters:

[0060] Change in energy flux density: Δq(x,y,t) = |q_damage(x,y,t) - q_benchmark(x,y,t)|

[0061] Energy gradient change rate: obtained by calculation of the spatial gradient of the energy flux density field.

[0062] Propagation path offset: Calculates the angular deviation of the principal direction of energy propagation.

[0063] Local energy dissipation rate: calculated from the divergence of energy flux density.

[0064] 7. Closed-loop iterative correction

[0065] An energy flow field error feedback model is established, using the deviation between the excitation force measured by the force sensor and the excitation force inverted by the energy flow field, and the deviation between the displacement field measured by DIC and the displacement field predicted by the energy flow field as feedback quantities, to iteratively correct the material damping parameters and boundary constraint stiffness parameters.

[0066] The iterative convergence condition is set as follows: the root mean square error of the energy flux density across the entire field changes by less than 0.5% in two consecutive iterations, and the overlap rate of the damaged areas is greater than 95%. In this embodiment, the convergence condition is met after 4 iterations, and the closed-loop reconstruction of the energy flux field is completed.

[0067] 8. Damage localization and grading assessment

[0068] Damage characteristic parameters of the energy flow field after closed-loop reconstruction are extracted, and a comprehensive damage evaluation index is calculated. In this embodiment, the abnormal energy flow area is mainly concentrated in the mid-span region (within 1400~1600mm from the left support), which coincides with the location of the precast crack.

[0069] Based on the comprehensive damage index value, the crack damage in this embodiment is assessed as "minor damage". The specific grading criteria are as follows: comprehensive damage index D < 0.10 is no damage, 0.10 ≤ D < 0.30 is minor damage, 0.30 ≤ D < 0.55 is moderate damage, 0.55 ≤ D < 0.80 is severe damage, and D ≥ 0.80 is serious damage.

[0070] Example 2: Vibration Energy Flow Field Reconstruction and Damage Grading Test of Reinforced Concrete Frame Joints

[0071] This embodiment uses a reinforced concrete frame beam-column joint as the test object to verify the applicability of the method of the present invention in complex reinforced concrete structures.

[0072] The test model was a T-shaped node, consisting of a column (400mm×400mm cross-section, 3000mm height) and a beam (250mm×500mm cross-section, 1500mm cantilever length), with concrete strength grade C40. The column was fixed at the bottom, and an axial pressure of 500kN was applied to the top of the column to simulate the upper load. The free end of the beam served as the loading point, and a hydraulic servo actuator was used to apply cyclic loads at a frequency of 1Hz, with the amplitude controlled by displacement (±10mm, ±20mm, ±30mm increments).

[0073] A binocular stereo DIC system consisting of four high-speed cameras was used, with the cameras focused on two measurement areas: the core area of ​​the node and the root of the beam. The overall displacement field was obtained through image stitching technology. The total measurement area was 1200mm × 1200mm, and the speckle size was controlled to be 2-4 pixels.

[0074] The experiment was divided into two stages: the first stage was a non-destructive test to establish the reference energy flow field; the second stage was a damage test after pre-setting local buckling of the steel bars and crushing damage of the concrete in the core area of ​​the node.

[0075] When calculating the energy flow field, the stress concentration effect in the nodal region is considered. A non-uniform meshing strategy is adopted. The calculation point density is increased in the core area of ​​the nodal region (within 200mm of the beam-column interface) by 3 pixels, while a sparser mesh is used in other areas by 8 pixels.

[0076] The experimental results show that, under damaged conditions, energy streamlines exhibit significant flow around and convergence in the core area of ​​the node. The peak value of the energy flux density change rate occurs at the beam root, 100-150 mm from the column edge, consistent with the measured crack propagation area. After closed-loop iterative correction (5 iterations), the damage location accuracy reaches ±20 mm, and the damage level is evaluated as "moderate damage," consistent with the actual damage degree.

[0077] The theoretical basis of this invention lies in the fact that structural damage is essentially a change in local stiffness and damping characteristics, which directly affects the propagation path and dissipation characteristics of vibration energy within the structure. The full-field dynamic response data provided by DIC technology can capture subtle changes in the energy flow field, while the closed-loop iterative mechanism uses the response data to continuously correct the computational model, gradually converging the reconstructed energy flow field results to the true physical field. Numerical simulations and experimental verification results demonstrate that the above method exhibits good convergence and robustness.

[0078] It should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention. Those skilled in the art can also make several modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A closed-loop reconstruction and damage grading test method for vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response, characterized in that, Includes the following steps: S1. Establish a vibration test model for the steel-concrete structure. Determine the test object based on the structural form, geometric dimensions, material parameters and boundary constraints of the steel-concrete structure to be tested. Set up a digital image correlation (DIC) measurement area on the surface of the structure. At the same time, complete the installation and calibration of the excitation device and auxiliary sensors. S2. Random speckle pattern is prepared in the measurement area, and a DIC measurement system consisting of a high-speed industrial camera, light source, synchronous trigger and image acquisition equipment is built. A unified clock synchronization mechanism is established between the image acquisition system, vibration excitation system and data acquisition system. S3. Apply dynamic loads to the steel-concrete structure using impact excitation, electromagnetic excitation, hydraulic excitation or servo excitation, and simultaneously acquire speckle image sequences, excitation load signals and dynamic response signals of the entire structural vibration process. S4. Calculate the full-field displacement field of the steel-concrete structure during the entire vibration process using digital image correlation algorithms, and obtain the velocity field, acceleration field and strain field based on the displacement time history to form dynamic full-field response data of the steel-concrete structure. S5. Based on the mechanical parameters of the steel-concrete structure material, dynamic full-field response data and vibration excitation parameters, establish a vibration energy flow calculation model, calculate the vibration energy density, energy flow density, energy propagation direction and energy dissipation parameters of the structure at each moment, and reconstruct the vibration energy flow field of the steel-concrete structure. S6. Establish the vibration energy flow field of the steel-concrete structure in a non-destructive state as the reference energy flow field. Perform registration analysis between the vibration energy flow field of the structure to be tested and the reference energy flow field to obtain damage-sensitive parameters such as energy flow density change, energy gradient change rate, propagation path offset and local energy dissipation rate. S7. Construct an energy flow field error feedback model based on damage-sensitive parameters, perform closed-loop iterative correction on the vibration energy flow field, continuously update the vibration energy flow calculation model, and complete the closed-loop reconstruction of the vibration energy flow field of the steel-concrete structure when the results of two consecutive iterations meet the preset convergence conditions. S8. Extract damage characteristic parameters from the vibration energy flow field after closed-loop reconstruction, establish a damage level evaluation model, identify the damage location of the steel-concrete structure based on the distribution of abnormal energy flow areas, degree of energy accumulation, changes in propagation direction, and local energy dissipation characteristics, and complete the damage level classification.

2. The method for closed-loop reconstruction and damage grading test of vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response as described in claim 1, characterized in that, The random speckle pattern described in step S2 uses a black and white high-contrast speckle pattern with a speckle size of 2 to 5 pixels and a speckle coverage of 40% to 60% to ensure the accuracy of digital image correlation calculations.

3. The method for closed-loop reconstruction and damage grading test of vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response as described in claim 1, characterized in that, The dynamic load mentioned in step S3 includes one or more of sinusoidal excitation, frequency sweep excitation, random excitation, and transient impact excitation.

4. The method for closed-loop reconstruction and damage grading test of vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response as described in claim 1, characterized in that, In step S4, the subpixel digital image correlation algorithm is used to calculate the full-field displacement data, and the velocity field and acceleration field are obtained by using the time difference method. The strain field is calculated by using the displacement gradient.

5. The method for closed-loop reconstruction and damage grading test of vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response as described in claim 1, characterized in that, In step S5, the vibration energy flow calculation model is established based on material density, elastic modulus, Poisson's ratio, damping parameters and dynamic response data, and the structural vibration energy flow density vector, energy propagation direction and local energy dissipation parameters are calculated.

6. The method for closed-loop reconstruction and damage grading test of vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response as described in claim 1, characterized in that, In step S6, an energy flow field registration algorithm is used to spatially register the energy flow fields of the baseline state and the damaged state, and to calculate the energy flow density difference, energy gradient change rate, propagation path offset, and energy dissipation rate.

7. The method for closed-loop reconstruction and damage grading test of vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response as described in claim 1, characterized in that, The closed-loop iterative correction in step S7 includes four processes: error calculation, parameter correction, model update, and convergence determination. The convergence determination is based on the energy flux density error, propagation direction error, and damage region overlap rate between two consecutive iterations.

8. The method for closed-loop reconstruction and damage grading test of vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response as described in claim 1, characterized in that, In step S8, a comprehensive damage evaluation index is established. Based on the energy flux density change rate, energy accumulation index, local dissipation rate and propagation direction deflection angle, the damage level is classified into five levels: no damage, minor damage, moderate damage, severe damage and serious damage.

9. The method for closed-loop reconstruction and damage grading test of vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response as described in claim 1, characterized in that, It also includes an adaptive optimization step for test parameters, which automatically adjusts the excitation frequency, excitation amplitude, image sampling frequency and exposure time based on the results of the first test, and repeats the vibration test to improve the accuracy of vibration energy flow field reconstruction and damage identification.

10. A method for closed-loop reconstruction and damage grading test of vibration energy flow field of reinforced concrete structures based on DIC dynamic full-field response, as described in any one of claims 1 to 9, characterized in that, The steel-concrete structure includes reinforced concrete beams, reinforced concrete columns, reinforced concrete frames, steel-concrete composite beams, steel-concrete composite columns, bridge structures, building structures, and other steel-concrete composite engineering structures.

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