Fitting curve method for ultrasonic detection of stress state of concrete in acoustic-elastic stage

Abstract

This invention provides a fitting curve method for ultrasonic testing of the stress state of concrete in the acoustoelastic stage, comprising: simplifying the relationship between ultrasonic longitudinal wave velocity; obtaining the structural stress of the compressed concrete; constructing a relationship curve between structural stress and ultrasonic longitudinal wave velocity; determining the acoustoelastic calculation parameters of concrete based on the initial longitudinal and transverse wave velocities of the compressed concrete in its initial stress-free state; establishing a finite element model, calculating the relationship curve, and obtaining the calculation results; and establishing a fitting curve for ultrasonic testing of the stress state in the acoustoelastic stage based on the simplified ultrasonic longitudinal wave velocity relationship, the concrete calculation parameters, and the calculation results. This invention addresses the problem that existing formulas for acoustoelastic theory have numerous parameters, making ultrasonic stress state testing of concrete difficult to apply in practice.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic nondestructive testing technology in the field of safety testing and evaluation of concrete structures, and particularly to a fitting curve method for ultrasonic testing of the stress state of concrete in the acousto-elastic stage. Background Technology

[0002] Currently, based on the average stress variation along the ultrasonic wave propagation path in an elastic medium, stress calculations for elastic media typically employ formulas from the acoustoelastic theory proposed by D.S. Hughes and J.L. Kelly. Where ρ is the density of concrete, λ and μ are Lamé constants, l, m, and n are Murnaghan's third-order elastic constants, and V L The longitudinal wave velocity is under stress. However, the above theoretical formulas have many parameters, and due to the poor homogeneity of concrete materials, even slight changes in the parameters often lead to large differences in the calculation results of the theoretical formulas. This makes it difficult to apply ultrasonic stress state detection of concrete in practice. Therefore, there is an urgent need for a fitting curve method for ultrasonic detection of the stress state of concrete in the acoustoelastic stage, in order to solve the problem that the existing formulas for acoustoelastic theory have many parameters, which makes it difficult to apply ultrasonic stress state detection of concrete in practice. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a fitting curve method for ultrasonic testing of the stress state of concrete in the acoustoelastic stage, which solves the problem that the numerous parameters in existing formulas for acoustoelastic theory make ultrasonic stress state testing of concrete difficult to apply in practice.

[0004] A fitting curve method for ultrasonic testing of the stress state of concrete in the acoustoelastic stage includes: simplifying the relationship between ultrasonic longitudinal wave velocity; obtaining the structural stress of the compressed concrete; constructing a relationship curve between structural stress and ultrasonic longitudinal wave velocity; determining the acoustoelastic calculation parameters of the concrete based on the initial longitudinal and transverse wave velocities of the compressed concrete in its initial stress-free state; establishing a finite element model, calculating the relationship curve, and obtaining the calculation results; and establishing a fitting curve for ultrasonic testing of the stress state in the acoustoelastic stage based on the simplified ultrasonic longitudinal wave velocity relationship, the concrete calculation parameters, and the calculation results.

[0005] As an embodiment of the present invention, the relationship between ultrasonic longitudinal wave velocity is simplified by: differentiating both sides of the relationship between the stress of concrete, which is considered an isotropic material, and the ultrasonic longitudinal wave velocity propagating perpendicular to the stress direction, to obtain a first formula. Among them, V L V is the propagation velocity of the longitudinal wave in the prestressed state along the direction perpendicular to the stress. L0Let V be the initial velocity of the longitudinal wave under stress-free conditions, σ be the stress value, and K be the concrete stress coefficient. Based on the relatively small variation amplitude of the ultrasonic longitudinal wave velocity, V is determined... L Approximately equal to V L0 And based on dV L Approximately equal to ΔV L Since dσ is approximately equal to Δσ, simplifying the first formula yields a linear relationship between stress and ultrasonic longitudinal wave velocity V. L = aσ + b, where a is a linear coefficient and b is a constant term.

[0006] As an embodiment of the present invention, obtaining the structural stress of compressed concrete includes the following steps: Step 1, pre-arranging ultrasonic longitudinal wave transducers and ultrasonic transverse wave transducers for testing on both sides of the compressed concrete, and measuring the initial velocity V of the longitudinal wave under stress-free conditions. Lo initial velocity of the transverse wave V So Step 2: Only retain the ultrasonic longitudinal wave transducers arranged on both sides of the concrete and apply a vertically downward load to the compressed concrete; Step 3: Detect the average stress between the ultrasonic longitudinal wave transducers as the structural stress of the compressed concrete; wherein, the load application direction is perpendicular to the detection direction of the ultrasonic longitudinal wave transducers.

[0007] As an embodiment of the present invention, constructing the relationship curve between structural stress and ultrasonic longitudinal wave velocity includes: obtaining the structural stress of C30 concrete, C40 concrete and C50 concrete respectively, and constructing the relationship curve between structural stress and ultrasonic longitudinal wave velocity of C30 concrete, C40 concrete and C50 concrete respectively by combining the simplified ultrasonic longitudinal wave velocity relationship.

[0008] As an embodiment of the present invention, the acoustic elastic calculation parameters of concrete are determined based on the initial velocities of longitudinal and transverse waves in the initial stress-free state of compressed concrete, including: obtaining the Lamé constant calculation formula. and Where ρ is the density of concrete, V S0 Let λ and μ be the initial velocity of the transverse wave under stress-free conditions, and λ and μ be Lamé constants. The initial velocities V of the longitudinal and transverse waves in the initially stress-free state of the compressed concrete are obtained from the relationship curve. Lo V So Substituting the values ​​into the Lamé constant calculation formula, the Lamé constant is obtained and used as a parameter for calculating the acoustic elasticity of concrete.

[0009] As an embodiment of the present invention, a finite element model is established, and the relationship curves are calculated to obtain the calculation results. This includes: establishing a finite element model, using the finite element model to calculate the relationship curves between stress and ultrasonic longitudinal wave velocity of C30 concrete, C40 concrete and C50 concrete respectively, and obtaining the calculation results.

[0010] As an embodiment of the present invention, a fitting curve for ultrasonic testing of the acoustoelastic stage stress state is established based on a simplified ultrasonic longitudinal wave velocity relationship, concrete calculation parameters, and calculation results. This includes substituting relevant parameters from the concrete calculation parameters and calculation results of C30 concrete, C40 concrete, and C50 concrete into the simplified ultrasonic longitudinal wave velocity relationship to establish fitting curves for ultrasonic testing of the acoustoelastic stage stress state of C30 concrete, C40 concrete, and C50 concrete.

[0011] As an embodiment of the present invention, the load application position in step 2 is determined by the following steps: Step 21, determine the first specification of the compressed concrete; Step 22, retrieve the standard three-dimensional model of the concrete corresponding to the first specification and the optimal load application position from the preset database; Step 23, obtain the measured three-dimensional model of the compressed concrete; Step 24, calculate the three-dimensional overlap between the standard three-dimensional model and the measured three-dimensional model in each planar sub-region; Step 25, perform offset calculation on the optimal load application position based on all three-dimensional overlaps to obtain the measured optimal load application position.

[0012] As an embodiment of the present invention, the optimal load application position is offset based on all three-dimensional overlaps to obtain the measured optimal load application position, including: establishing a three-dimensional coordinate axis with the optimal load application position as the origin; obtaining the x-axis, y-axis, and z-axis three-dimensional overlaps of the planar sub-regions that are respectively in the same direction as the three axes of the three-dimensional coordinate axis; and offsetting the corresponding coordinate points of the optimal load application position based on the x-axis, y-axis, and z-axis three-dimensional overlaps and their corresponding weights to obtain the measured optimal load application position.

[0013] As an embodiment of the present invention, the three-dimensional overlap of the x-axis, y-axis, and z-axis is divided into positive x-axis three-dimensional overlap, positive y-axis three-dimensional overlap, positive z-axis three-dimensional overlap, negative x-axis three-dimensional overlap, negative y-axis three-dimensional overlap, and negative z-axis three-dimensional overlap according to the position of the corresponding planar sub-region on the three-dimensional coordinate axes; wherein, the position of the three-dimensional coordinate axes includes the positive and negative half axes of the x, y, and z axes, respectively.

[0014] The beneficial effects of this invention are as follows:

[0015] This invention provides a fitting curve method for ultrasonic testing of the stress state of concrete in the acoustoelastic stage, which solves the problem that the numerous parameters in existing formulas for acoustoelastic theory make ultrasonic stress state testing of concrete difficult to apply in practice.

[0016] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0019] Figure 1 This is a flowchart of a method for fitting curves of ultrasonic testing of the stress state of concrete in the acoustoelastic stage according to an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of the ultrasonic stress detection mode of a concrete structure in a fitting curve method for ultrasonic detection of the stress state of concrete in the acoustoelastic stage according to an embodiment of the present invention.

[0021] Figure 3 This is a curve showing the relationship between structural stress and ultrasonic longitudinal wave velocity in a fitting curve method for ultrasonic detection of the stress state of concrete in the acoustic elastic stage according to an embodiment of the present invention.

[0022] Figure 4 This is the result of the calculation of ultrasonic longitudinal wave velocity and structural stress in the finite element model of a fitting curve method for ultrasonic detection of the stress state of concrete in the acoustoelastic stage in an embodiment of the present invention. Detailed Implementation

[0023] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0024] Please see Figure 1 This invention provides a method for fitting curves of ultrasonic testing of the stress state of concrete in the acoustoelastic stage, comprising: S101, simplifying the relationship between ultrasonic longitudinal wave velocity; S102, obtaining the structural stress of the compressed concrete; S103, constructing a relationship curve between structural stress and ultrasonic longitudinal wave velocity; S104, determining the acoustoelastic calculation parameters of concrete based on the initial longitudinal and transverse wave velocities of the compressed concrete in its initial stress-free state; S105, establishing a finite element model, calculating the relationship curve, and obtaining the calculation results; S106, establishing a fitting curve for ultrasonic testing of the stress state in the acoustoelastic stage based on the simplified ultrasonic longitudinal wave velocity relationship, concrete calculation parameters, and calculation results.

[0025] The working principle of the above technical solution is as follows: This method treats concrete as an isotropic material and utilizes the relationship between stress and the longitudinal wave velocity of ultrasonic waves propagating perpendicular to the stress direction using simplified parameters.

[0026]

[0027] Through experimental testing and simulation, the relationship between ultrasonic wave velocity and stress in concrete during the acoustoelastic stage is presented, providing a fitting curve method for ultrasonic testing of concrete stress.

[0028] Specifically: S1, a simplified method based on theoretical foundation; S2, ultrasonic testing mode for concrete structure stress; S3, measured concrete structure stress and ultrasonic wave velocity; S4, using measured initial velocities of longitudinal and transverse waves under stress-free conditions to deduce acoustoelastic calculation parameters of concrete; S5, establishing a finite element model to simulate the propagation of ultrasonic waves in concrete; S6, establishing a fitting curve for ultrasonic testing of concrete stress state in the acoustoelastic stage.

[0029] The beneficial effects of the above technical solution are as follows: the above solution can solve the problem that the existing formulas for acoustoelasticity theory have many parameters, which makes it difficult to apply ultrasonic stress state detection of concrete in practice.

[0030] In one embodiment, simplifying the relationship between ultrasonic longitudinal wave velocity includes: differentiating both sides of the relationship between the stress of concrete, which is considered an isotropic material, and the ultrasonic longitudinal wave velocity propagating perpendicular to the stress direction, to obtain a first formula. Among them, V L V is the propagation velocity of the longitudinal wave in the prestressed state along the direction perpendicular to the stress. L0 Let V be the initial velocity of the longitudinal wave under stress-free conditions, σ be the stress value, and K be the concrete stress coefficient. Based on the relatively small variation amplitude of the ultrasonic longitudinal wave velocity, V is determined... L Approximately equal to V L0 And based on dV L Approximately equal to ΔV L Since dσ is approximately equal to Δσ, simplifying the first formula yields a linear relationship between stress and ultrasonic longitudinal wave velocity V. L = aσ + b, where a is a linear coefficient and b is a constant term;

[0031] The working principle of the above technical solution is as follows: Taking the derivative of both sides of the aforementioned relationship between stress and the longitudinal wave velocity of ultrasound propagating perpendicular to the stress direction (1), we obtain...

[0032]

[0033] Because the wave velocity changes very little, therefore V L ≈V L0

[0034]

[0035] And because of dV L ≈ΔV L Equation (1) can be simplified to a linear relationship between stress and wave velocity: dσ≈Δσ

[0036] V L =aσ+b (4)

[0037] Where: V L V is the propagation velocity of the longitudinal wave in the prestressed state along the direction perpendicular to the stress. L0 σ is the initial velocity of the longitudinal wave under stress-free conditions; K is the stress value; a is the concrete stress coefficient; b is the linearity coefficient;

[0038] The beneficial effects of the above technical solution are as follows: the above solution simplifies the theoretical basis, helps to reduce the formula parameters involved in the calculation, and improves the detection accuracy.

[0039] In one embodiment, obtaining the structural stress of compressed concrete includes the following steps:

[0040] Step 1: First, ultrasonic longitudinal wave transducers and ultrasonic transverse wave transducers are pre-positioned on both sides of the compressed concrete for testing, and the initial velocity V of the longitudinal wave under stress-free conditions is measured. Lo initial velocity of the transverse wave V So Step 2: Only retain the ultrasonic longitudinal wave transducers arranged on both sides of the concrete and apply a vertically downward load to the compressed concrete; Step 3: Detect the average stress between the ultrasonic longitudinal wave transducers as the structural stress of the compressed concrete; wherein, the load application direction is perpendicular to the detection direction of the ultrasonic longitudinal wave transducers.

[0041] The working principle and beneficial effects of the above technical solution are as follows: Figure 2 As shown, the test uses an ultrasonic longitudinal wave transducer with the load applied vertically downwards. The transducers are arranged opposite each other, perpendicular to the load application direction, and the average stress between the ultrasonic transducers is measured. This test method is beneficial to improving the accuracy of stress detection.

[0042] In one embodiment, constructing the relationship curve between structural stress and ultrasonic longitudinal wave velocity includes: obtaining the structural stress of C30 concrete, C40 concrete and C50 concrete respectively, and constructing the relationship curve between structural stress and ultrasonic longitudinal wave velocity of C30 concrete, C40 concrete and C50 concrete respectively by combining the simplified ultrasonic longitudinal wave velocity relationship.

[0043] The working principle and beneficial effects of the above technical solution are as follows: Figure 3As shown, C30, C40, and C50 concrete test blocks were subjected to graded loading, and the stress-longitudinal wave velocity relationship curves were measured. The above technical solution is beneficial for providing data support for subsequent calculations.

[0044] In one embodiment, determining the acoustoelastic calculation parameters of concrete based on the initial velocities of longitudinal and transverse waves in the initial stress-free state of the compressed concrete includes: obtaining the Lamé constant calculation formula. and Where ρ is the density of concrete, V S0 Let λ and μ be the initial velocity of the transverse wave under stress-free conditions, and λ and μ be Lamé constants. The initial velocities V of the longitudinal and transverse waves in the initially stress-free state of the compressed concrete are obtained from the relationship curve. Lo V So Substituting into the Lamé constant calculation formula, the Lamé constant is calculated and used as a parameter for calculating the acoustic elasticity of concrete.

[0045] The working principle and beneficial effects of the above technical solution are as follows: Concrete calculation parameters are derived by using the measured relationship between stress and longitudinal wave velocity; Figure 3 It is known that the test results for concrete are closest to a simple linear relationship within the compressive strength range of 50% to 70%. Outside this range, the ultrasonic wave velocity and stress exhibit a nonlinear relationship. Within the acoustoelastic range, concrete calculation parameters can be derived using partial test data, including but not limited to using test data within 50% of the compressive strength. The Lamé constant calculation formula can be used to deduce these parameters. and Where ρ is the density of concrete, V S0 Let λ and μ be the initial velocity of the transverse wave under stress-free conditions, and λ and μ be Lamé constants. The initial velocities V of the longitudinal and transverse waves in the initially stress-free state of the compressed concrete are obtained from the relationship curve. Lo V So Substituting the values ​​into the Lamé constant calculation formula, the Lamé constant is calculated and used as a parameter for calculating the acoustic elasticity of concrete. This method provides data support for subsequent calculations. In a specific embodiment, the calculation results of the Lamé constant (concrete parameter) are shown in Table 1.

[0046] Table 1 Calculation results of concrete parameters

[0047]

[0048] In one embodiment, establishing a finite element model and calculating the relationship curves to obtain calculation results includes: establishing a finite element model and using the finite element model to calculate the relationship curves between stress and ultrasonic longitudinal wave velocity of C30 concrete, C40 concrete and C50 concrete respectively, and obtaining calculation results.

[0049] The working principle and beneficial effects of the above technical solution are as follows: Figure 4As shown, a finite element model is established to simulate the propagation of ultrasonic waves in concrete. Based on the ultrasonic longitudinal wave velocity and structural stress information, the finite element model is established. The relationship curves between stress and ultrasonic longitudinal wave velocity of C30 concrete, C40 concrete and C50 concrete are calculated using the finite element model, and the calculation results are obtained. The above scheme is beneficial to provide data support for subsequent calculations.

[0050] In one embodiment, a fitting curve for ultrasonic testing of the acoustoelastic stage stress state is established based on a simplified ultrasonic longitudinal wave velocity relationship, concrete calculation parameters, and calculation results. This includes substituting relevant parameters from the concrete calculation parameters and calculation results of C30 concrete, C40 concrete, and C50 concrete into the simplified ultrasonic longitudinal wave velocity relationship to establish fitting curves for ultrasonic testing of the acoustoelastic stage stress state of C30 concrete, C40 concrete, and C50 concrete.

[0051] The working principle and beneficial effects of the above technical solution are as follows: Based on the results of the aforementioned steps, a fitting curve for ultrasonic testing of the stress state in the acoustoelastic stage (concrete in this paper at 50% compressive strength) is established. In a specific embodiment, the fitting curve for ultrasonic testing of the stress state is shown in Table 2:

[0052] Table 2 Fitting curves of ultrasonic testing under stress state

[0053]

[0054] The above scheme provides a fitting curve method for ultrasonic testing of concrete stress detection.

[0055] In one embodiment, the load application location in step 2 is determined by the following steps: Step 21, determine the first specification of the compressed concrete; Step 22, retrieve the standard three-dimensional model of the concrete corresponding to the first specification and the optimal load application location from the preset database; Step 23, obtain the measured three-dimensional model of the compressed concrete; Step 24, calculate the three-dimensional overlap between the standard three-dimensional model and the measured three-dimensional model in each planar sub-region; Step 25, perform offset calculations on the optimal load application location based on all three-dimensional overlaps to obtain the measured optimal load application location;

[0056] The working principle of the above technical solution is as follows: Step 21: Determine the first specification of the compressive concrete; wherein, the first specification includes C100, C70, C50, C40, C30, C20, etc.; Step 22: Retrieve the standard three-dimensional model and the optimal load application position of the concrete corresponding to the first specification from the preset database; wherein, the preset database stores all standard three-dimensional models corresponding to the specification to be used, and the standard three-dimensional model is preferably formed by merging several standard specifications based on analysis; Step 23: Obtain the measured three-dimensional model of the compressive concrete; due to differences in preparation conditions, there may be certain differences between the measured three-dimensional model and the standard three-dimensional model of the compressive concrete; Step 24: Calculate the three-dimensional overlap between the standard three-dimensional model and the measured three-dimensional model in each planar sub-region; wherein, the calculation method preferably adopts a three-dimensional model overlap calculation method; Step 25: Perform offset calculation on the optimal load application position based on all three-dimensional overlaps to obtain the measured optimal load application position; furthermore, the optimal load application position can also be calculated by combining the specification information of the load;

[0057] The beneficial effects of the above technical solution are as follows: compared with the method of measuring the position of each load application by human eyes, this solution can more accurately and automatically identify the optimal position of load application, providing more accurate data support for stress detection.

[0058] In one embodiment, the optimal load application position is offset based on all three-dimensional overlaps to obtain the measured optimal load application position. This includes: establishing a three-dimensional coordinate axis with the optimal load application position as the origin; obtaining the x-axis, y-axis, and z-axis three-dimensional overlaps of a planar sub-region that are in the same direction as the three axes of the three-dimensional coordinate axis; and offsetting the corresponding coordinate points of the optimal load application position based on the x-axis, y-axis, and z-axis three-dimensional overlaps and their corresponding weights to obtain the measured optimal load application position.

[0059] The working principle of the above technical solution is as follows: A three-dimensional coordinate axis is established with the optimal load application position as the origin; then, the three-dimensional overlap of the x-axis with the x-axis, the y-axis with the y-axis, and the z-axis with the z-axis of the planar sub-regions in the same direction as the x-axis are obtained; based on standard compressive concrete, the three-dimensional model is divided into 6 faces, with each coordinate axis corresponding to two faces; then, based on the x-axis, y-axis, and z-axis three-dimensional overlap and their corresponding weights, the corresponding coordinate points of the optimal load application position are offset to obtain the measured optimal load application position. The calculation method is preferred. Where (x, y, z) are the coordinates of the optimal position for load application; (x0, y0, z0) are the coordinates of the optimal position for load application; α x α y and α z These represent the three-dimensional overlap along the x-axis, y-axis, and z-axis, respectively; β x ,β y and β z These are the corresponding weights for the three-dimensional overlap along the x-axis, y-axis, and z-axis, respectively.

[0060] The beneficial effects of the above technical solution are as follows: By using the above solution, the offset calculation of the corresponding coordinate point of the optimal load application position is performed on the overlap of the three-dimensional model in various directional planes, and each coordinate point is analyzed separately, which is beneficial to improving the detection accuracy of the optimal load application position in actual measurement.

[0061] In one embodiment, the three-dimensional overlap of the x-axis, y-axis, and z-axis is divided into positive x-axis, positive y-axis, positive z-axis, negative x-axis, negative y-axis, and negative z-axis overlap based on the position of the corresponding planar sub-region on the three-dimensional coordinate axes; wherein the position of the three-dimensional coordinate axes includes the positive and negative half axes of the x, y, and z axes, respectively.

[0062] The working principle and beneficial effects of the above technical solution are as follows: By using the positive and negative half-axis of the x, y, and z axes in a three-dimensional coordinate system, the three-dimensional overlap of the x-axis, y-axis, and z-axis is distinguished as positive or negative, i.e. Where, α -x α -y and α -z These represent the three-dimensional overlap along the negative x-axis, negative y-axis, and negative z-axis, respectively; α +x α +y and α +z These are the three-dimensional overlap along the positive x-axis, the positive y-axis, and the positive z-axis, respectively. The above scheme can effectively adjust the overall variation trend of the optimal position of the measured load application caused by the changes in each plane, and improve the detection accuracy of the optimal position of the measured load application.

[0063] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A fitting curve method for ultrasonic testing of stress state of concrete in the acoustic-elastic stage, characterized in that, include: The relationship between ultrasonic longitudinal wave velocity and the stress of concrete (considered as an isotropic material) and the ultrasonic longitudinal wave velocity propagating perpendicular to the stress direction is simplified to obtain the first formula. Among them, V L V is the propagation velocity of the longitudinal wave in the prestressed state along the direction perpendicular to the stress. L0 Let V be the initial velocity of the longitudinal wave under stress-free conditions, σ be the stress value, and K be the concrete stress coefficient. Based on the relatively small variation amplitude of the ultrasonic longitudinal wave velocity, V is determined... L Approximately equal to V L0 And based on dV L Approximately equal to ΔV L Since dσ is approximately equal to Δσ, simplifying the first formula yields a linear relationship between stress and ultrasonic longitudinal wave velocity V. L = aσ + b, where a is a linear coefficient and b is a constant term; Obtaining the structural stress of compressed concrete includes the following steps: Step 1, pre-arranging ultrasonic longitudinal wave transducers and ultrasonic transverse wave transducers on both sides of the compressed concrete for measurement, and measuring the initial longitudinal wave velocity V under stress-free conditions. L0 initial velocity of the transverse wave V S0 Step 2: Only retain the ultrasonic longitudinal wave transducers arranged on both sides of the concrete, and apply a vertically downward load to the compressed concrete. The load application position in Step 2 is determined through the following steps: Step 21: Determine the first specification of the compressed concrete; Step 22: Retrieve the standard 3D model of the concrete corresponding to the first specification and the optimal load application position from the preset database; Step 23: Obtain the measured 3D model of the compressed concrete; Step 24: Calculate the 3D overlap between the standard 3D model and the measured 3D model in each planar sub-region; Step 25: Calculate the offset of the optimal load application position based on all 3D overlaps to obtain the measured optimal load application position; Step 3: Detect the average stress between the ultrasonic longitudinal wave transducers as the structural stress of the compressed concrete; wherein the load application direction is perpendicular to the detection direction of the ultrasonic longitudinal wave transducers. The process involves offsetting the optimal load application position based on all three-dimensional overlap values ​​to obtain the measured optimal load application position. This includes: establishing a three-dimensional coordinate axis with the optimal load application position as the origin; obtaining the x-axis, y-axis, and z-axis three-dimensional overlap values ​​of the planar sub-regions that are in the same direction as the three axes of the three-dimensional coordinate axis; offsetting the corresponding coordinate points of the optimal load application position based on the x-axis, y-axis, and z-axis three-dimensional overlap values ​​and their corresponding weights to obtain the measured optimal load application position; and calculating the offsetting of the corresponding coordinate points of the optimal load application position based on the x-axis, y-axis, and z-axis three-dimensional overlap values ​​and their corresponding weights. Where (x, y, z) are the coordinates of the optimal position for load application; (x0, y0, z0) are the coordinates of the optimal position for load application; α x α y and α z These represent the three-dimensional overlap along the x-axis, y-axis, and z-axis, respectively; β x ,β y and β z These are the corresponding weights for the three-dimensional overlap along the x-axis, y-axis, and z-axis, respectively. The relationship curve between structural stress and ultrasonic longitudinal wave velocity was constructed. Specifically, the structural stress of C30 concrete, C40 concrete and C50 concrete were obtained respectively. Combined with the simplified relationship of ultrasonic longitudinal wave velocity, the relationship curve between structural stress and ultrasonic longitudinal wave velocity of C30 concrete, C40 concrete and C50 concrete was constructed respectively. Based on the initial velocities of longitudinal and transverse waves in the initial stress-free state of compressed concrete, the acoustoelastic calculation parameters of the concrete are determined. This determination includes obtaining the Lamé constant calculation formula. and Where ρ is the density of the compressive concrete, and V S0 Let λ and μ be the initial velocity of the transverse wave under stress-free conditions, and λ and μ be Lamé constants. The initial velocities V of the longitudinal and transverse waves in the initially stress-free state of the compressed concrete are obtained from the relationship curve. L0 V S0 Substituting into the Lamé constant calculation formula, the Lamé constant is calculated and used as a parameter for calculating the acoustic elasticity of concrete. Based on the measured data of pressure and ultrasonic velocity of concrete within 50% of its compressive strength, a finite element model was established, the relationship curves were calculated, and the calculation results were obtained. Specifically, the finite element model was established, and the relationship curves between stress and ultrasonic longitudinal wave velocity of C30 concrete, C40 concrete, and C50 concrete were calculated using the finite element model, respectively, and the calculation results were obtained. Based on the simplified ultrasonic longitudinal wave velocity relationship, concrete calculation parameters, and calculation results, a fitting curve for ultrasonic testing of the acoustoelastic stage stress state is established. Specifically, by substituting the relevant parameters from the concrete calculation parameters and calculation results of C30, C40, and C50 concrete into the simplified ultrasonic longitudinal wave velocity relationship, fitting curves for ultrasonic testing of the acoustoelastic stage stress state of C30, C40, and C50 concrete are obtained. The three-dimensional overlap of the x-axis, y-axis, and z-axis is divided into positive x-axis, positive y-axis, positive z-axis, negative x-axis, negative y-axis, and negative z-axis based on the position of the corresponding planar sub-region on the three-dimensional coordinate axes. The position of the three-dimensional coordinate axes includes the positive and negative half axes of the x, y, and z axes, respectively. Distinguish between positive and negative values ​​for the x-axis, y-axis, and z-axis 3D overlap, which is... Where, α -x α -y and α -z These represent the three-dimensional overlap along the negative x-axis, negative y-axis, and negative z-axis, respectively; α +x α +y and α +z These represent the three-dimensional overlap along the positive x-axis, the three-dimensional overlap along the positive y-axis, and the three-dimensional overlap along the positive z-axis, respectively.

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