Near-earth exposure test key index correction method considering stress difference influence

Abstract

The invention discloses a near-earth exposure test key index correction method considering stress difference influence, and belongs to the technical field of concrete structure durability testing. The correction method comprises the steps of obtaining chlorine ion content distribution data of an exposed test piece, fitting the chlorine ion influence depth in an unstressed state, obtaining service stress parameters of an actual component, calculating representative equivalent stress of the actual component, calculating a stress correction coefficient, recalculating the equivalent chlorine ion influence depth under the stress influence according to a diffusion coefficient D1, and obtaining the chlorine ion content distribution data of the exposed test piece. According to model verification, chloride ion content distribution data, obtained in a long-term exposure test, of a concrete test piece are analyzed, a chloride ion diffusion coefficient and influence depth in an unstressed state are fitted, and representative equivalent stress is calculated in combination with service stress parameters of a target engineering concrete actual component; and determining a stress correction coefficient according to different stress types so as to recalculate the equivalent chloride ion influence depth under the stress influence and realize correction of the key indexes of the near-earth exposure test.

Description

Technical Field

[0001] This invention relates to the field of concrete structure durability testing technology, and more specifically, to a method for correcting key indicators in near-ground exposure tests that takes into account the effects of stress differences. Background Technology

[0002] In chloride-corrosion environments, concrete structures are subjected to complex corrosion over long periods of time, and their durability is affected by multiple factors such as chloride corrosion and carbonation. In existing technologies, durability studies for such environments are mostly based on near-ground exposure tests, which simulate actual environmental conditions to test key indicators such as chloride ion permeability coefficient and carbonation depth. However, concrete structures may be subjected to various stress states such as compression, tension, and bending in actual service. For example, bridge piers and lock walls are subjected to dynamic multiaxial stress, combined loads of compression, tension, and bending moment. The degree of microcrack propagation varies under different stress states, resulting in significant differences in chloride ion diffusion rate and carbonation depth. Traditional near-ground exposure tests do not fully consider the impact of stress differences on test results. Test specimens are usually under no stress or single static load conditions, and the test results cannot reflect the accelerating effect of actual stress damage on durability under real stress conditions. Uncorrected test data may underestimate the chloride ion permeation rate in high-stress areas or overestimate the durability of low-stress areas. For example, the closure of microcracks in the compression zone may underestimate the permeation rate, while crack propagation in the tension zone is ignored, leading to insufficient conservatism or safety in the design scheme. Existing specifications do not provide index correction models based on stress differences, resulting in designs relying on empirical coefficients, making it difficult to balance economy and safety.

[0003] Therefore, there is an urgent need to provide a method for correcting key indicators of near-ground exposure tests that takes into account the impact of stress differences, quantify the impact of stress differences on test indicators, improve the level of refinement of durability design, and solve existing technical bottlenecks. Summary of the Invention

[0004] The purpose of this invention is to provide a method for correcting key indicators of near-ground exposure tests that takes into account the influence of force differences, thereby solving the above-mentioned technical problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for correcting key indicators in near-ground exposure tests that takes into account the effects of stress differences. The method includes the following steps: S1. Obtain chloride ion content distribution data C(t,x) of exposed specimens: Conduct long-term exposure tests on concrete specimens and obtain chloride ion content distribution data C(t,x) of exposed specimens. S2, Fitting the chloride ion influence depth x0 under stress-free conditions: Based on the chloride ion content distribution data, the chloride ion influence depth x0 under stress-free conditions is fitted in reverse. S3. Obtain the service stress parameters of the actual concrete components of the target project; S4. Calculate the representative equivalent stress σ of the actual concrete components in the target project. 等效 Calculate the equivalent stress σ based on the service stress parameters. 等效 It is used to standardize and quantify the stress level of actual concrete components in the target project; S5, Calculation of stress correction factor According to the equivalent stress σ 等效 Calculate the stress correction factor The stress correction factor Substituting the chloride ion diffusion coefficient D0, we obtain the corrected diffusion coefficient D1; S6. Recalculate the equivalent chloride ion influence depth x' under stress based on the diffusion coefficient D1; S7. Model Validation: Compare the consistency between the model's prediction results and the actual engineering data, and further optimize the model based on the validation results.

[0006] Furthermore, the method for correcting key indicators in near-ground exposure tests, considering the impact of force differences, includes the following steps: S1. Obtain chloride ion content distribution data C(t,x) of exposed specimens: In natural or artificial exposure environments, conduct long-term exposure tests on concrete specimens for an exposure time t≥1 year, and obtain chloride ion content distribution data C(t,x) of concrete specimens at different depths x after a set exposure time t. S2. Fitting the chloride ion influence depth x0 under stress-free conditions: Based on Fick's second law, curve fitting is performed on the chloride ion content distribution data C(t,x) to obtain the relationship between the chloride ion diffusion coefficient D0 and the chloride ion concentration Cs on the exposed specimen surface under stress-free conditions:

[0007] In the formula, C(t,x) represents the chloride ion content distribution data of the exposed specimen at depth x at time t, in units of %; Cs represents the chloride ion concentration on the surface of the exposed specimen, in units of %; and D0 represents the chloride ion diffusion coefficient under stress-free conditions, in units of m³. 2 / s; t is the exposure time, where t ≥ 1 year; x is the depth from the surface of the exposed specimen to its interior, in meters, where x ≤ ;erf is the error function, which is dimensionless; Set the critical chloride ion concentration C cr Based on the chloride ion content distribution data C(t,x), the corresponding chloride ion influence depth x0 is calculated using the function, satisfying the following relationship:

[0008] S3. Obtain the service stress parameters of the actual concrete components of the target project: Obtain the service stress parameters of the actual concrete components of the target project through finite element simulation and on-site monitoring, including axial force N, bending moment M, cross-sectional area A, cross-sectional moment of inertia I, and the distance y of the chloride ion detection area relative to the neutral axis. S4. Calculate the representative equivalent stress σ of the actual concrete components in the target project. 等效 The multiaxial stress is converted into an equivalent uniaxial stress, and the stress level is quantified uniformly. The equivalent stress σ 等效 The following relationship must be satisfied:

[0009] In the formula, σ 等效 The values ​​are: equivalent stress, in MPa; N / A is the average stress caused by axial force N, in MPa; My / I is the maximum normal stress caused by bending moment M, in MPa. S5, Calculation of stress correction factor : Calculate the stress correction factor for the chloride ion influence depth x0 under stress. Based on the type of force, it is divided into tensile stress zone correction factors. and the compressive stress zone correction factor The stress correction factor Substituting the chloride ion diffusion coefficient D0, we obtain the corrected diffusion coefficient D1 for the actual concrete components of the target project, which satisfies the following relationship: Tensile stress zone: Compressive stress zone: ; S6. Calculate the equivalent chloride ion influence depth x' under stress: Based on the corrected diffusion coefficient D1, recalculate the equivalent chloride ion influence depth x' of the actual concrete components of the target project, satisfying the following relationship:

[0010] S7. Model Validation: Select some existing concrete structure engineering cases in chloride-salt erosion environments, collect their long-term service data, including durability test data and actual stress data, substitute these data into the constructed modified model for validation, compare the consistency between the model prediction results and the actual engineering data, further optimize the model based on the validation results, and apply the validated modified model to near-ground exposure tests to guide concrete mix design, durability assessment and structural design optimization.

[0011] Furthermore, the test methods for the chloride ion content distribution data C(t,x) in step S1 include the grinding method, electrode method, and chemical titration method; the chloride ion concentration Cs on the surface of the exposed specimen in step S2 is obtained by directly measuring the chloride ion concentration on the surface of the exposed specimen.

[0012] Furthermore, when in the early stages of engineering design or testing, or when concrete strength parameters, elastic modulus parameters, or the state of concrete deterioration are incomplete, the stress correction coefficient mentioned in step S5 is used. The equivalent stress σ of the representative concrete components in the target project is obtained using a rapid estimation method. 等效 The ratio of the stress to the reference stress of the exposed specimen is set as the equivalent stress ratio factor λ, which satisfies the following relationship:

[0013] In the formula, σ ref The reference stress for the exposed specimen is expressed in MPa. A stress correction coefficient is established based on the equivalent force ratio factor λ. Empirical mapping relation:

[0014] In the formula, α and β are empirical fitting coefficients, determined based on existing experimental data, where α represents the proportion of diffusion increase caused by force, and β represents the degree of nonlinear enhancement. Furthermore, when the exposed specimen is not subjected to any load and only bears its own weight, the reference stress σ of the exposed specimen is calculated using the self-weight of the exposed specimen. ref It satisfies the following relationship:

[0015] In the formula, γ c The volumetric weight of the exposed specimen is expressed in kN / m³. 3 h is the height of the exposed specimen, in meters (m).

[0016] Furthermore, when the structural strength, elastic modulus, and damage information of the actual concrete components of the target project are known, the stress correction coefficient mentioned in step S5... The damage factor ω, which is related to concrete strength, is used for calculation. This damage factor ω is used to quantitatively describe the degree of permeability degradation of concrete under stress due to changes in its microstructure, such as microcracks, pore connectivity, and interface weakening. The stress correction factor is calculated using the damage factor ω. The formula satisfies the following relationship: Tensile stress zone: Compressive stress zone: ; The damage factor ω ranges from 0 to 1. When the damage factor ω = 0, it indicates that the actual concrete component of the target project has no mechanical damage and the porosity and microstructure remain unchanged. When the damage factor ω = 1, it indicates that the actual concrete component of the target project is in a state of severe damage, with microcracks penetrating and enhanced diffusion capacity.

[0017] Furthermore, the damage factor ω is calculated based on the stress intensity ratio, satisfying the following relationship: Tensile stress zone: Compressive stress zone: ; In the formula, f t f is the splitting tensile strength of concrete, expressed in MPa. c This represents the axial compressive strength of concrete, expressed in MPa.

[0018] Furthermore, the damage factor ω is calculated based on the elastic modulus degradation ratio, satisfying the following relationship:

[0019] In the formula, E0 is the initial elastic modulus of concrete, in GPa; E is the current elastic modulus of concrete, in GPa; and E / E0 is the degradation ratio of the elastic modulus of concrete, which is dimensionless.

[0020] Furthermore, the damage factor ω is calculated based on a nonlinear damage evolution model of the concrete strain state, satisfying the following relationship: Tensile stress zone:

[0021] Compressive stress zone:

[0022] In the formula, m c m is an empirical constant for concrete materials under compressive damage. t ε is the empirical constant of concrete material under tensile damage; ε is the axial strain of concrete; ε cu ε represents the peak compressive strain of concrete. cr This refers to the tensile cracking strain of concrete.

[0023] Furthermore, step S5 also includes a dynamic correction method that considers the depth x0 of the influence of tensile-compressive cyclic loading on chloride ions, the specific steps of which are as follows: S10. Obtain the time history data of tensile-compressive cyclic stress during the service life of the actual concrete components of the target project through a dynamic strain monitoring system, and use the rainflow counting method to statistically analyze the stress amplitude Δσ. i and its corresponding number of iterations n i Calculate the equivalent symmetrical cyclic stress ratio R:

[0024] S20. Calculate the cumulative damage degree D based on the improved Miner criterion. fat Introducing a stress amplitude weighting factor γ i :

[0025] In the formula, A, τ1, and τ2 are material fatigue parameters, which are calibrated through a three-point bending fatigue test; For fatigue life; γ i Determined based on stress level classification:

[0026] Where f t It refers to the tensile strength of concrete; S30. Establish a dynamic correction model for the diffusion coefficient, and correlate cyclic damage with the stress correction coefficient. coupling:

[0027] In the formula, D is the cyclic stress correction factor, η is the cyclic-diffusion coupling factor, calibrated through electromigration acceleration tests; cr This is the critical damage threshold; S40. Define cyclic stress correction factors for the tension and compression zones of bending members respectively. : Tensile stress zone:

[0028] Compressive stress zone:

[0029] S50, adjust the cyclic stress correction coefficient Substituting into the diffusion equation, we obtain the corrected time-varying diffusion coefficient D1' for the actual concrete components of the target project. Tensile stress zone: Compressive stress zone: ; S60. Considering the unsteady-state Fick's second law regarding the diffusion coefficient changing with time, the equivalent chloride ion influence depth x' under tensile-compressive cyclic stress is calculated using the equivalent time integration method, satisfying the following relationship:

[0030] In the formula, C is the equivalent diffusion coefficient, representing the average value of the time-varying diffusion coefficient D1' over the time interval [0, t]. cr This represents the critical chloride ion concentration.

[0031] In summary, compared with the prior art, the beneficial effects of the present invention are: This invention considers the impact of the complex stress states experienced by concrete structures in actual service on durability test results. It uses Fick's second law to fit the chloride ion diffusion depth of stress-free specimens, making the data from near-ground exposure tests closer to reality. This allows for more accurate prediction of the initiation time of steel corrosion, guiding the optimization of concrete mix proportions and the design of protective layer thickness. Through mechanical-diffusion multiphysics coupling modeling, it achieves a leap from "static stress-free" to "dynamic multiaxial" concrete durability testing. This provides a solution for improving the scientific design and service safety of concrete structures under corrosive environments. It solves the problems of inaccurate test results, conservative design schemes, or insufficient safety caused by neglecting stress differences in traditional test methods, and provides a more accurate and reliable basis for the durability assessment and design of concrete structures. In addition, the cumulative effect of tensile and compressive cyclic loads on concrete damage was considered, and a dynamic correction model for the diffusion coefficient was established. This model can correct the chloride ion influence depth in real time based on the tensile and compressive cyclic stress time history data of concrete components during service, more accurately reflecting the durability changes of concrete under long-term complex stress and environmental effects, and further improving the accuracy of chloride ion diffusion depth prediction. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the method for correcting key indicators in near-ground exposure tests that takes into account the effects of stress differences, as described in this invention. Detailed Implementation

[0033] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments given herein are for illustration and explanation only and are not intended to limit the present invention.

[0034] This invention provides a method for correcting key indicators in near-ground exposure tests that takes into account the effects of stress differences. The method includes the following steps: S1. Obtain chloride ion content distribution data C(t,x) of exposed specimens: Conduct long-term exposure tests on concrete specimens and obtain chloride ion content distribution data C(t,x) of exposed specimens. S2, Fitting the chloride ion influence depth x0 under stress-free conditions: Based on the chloride ion content distribution data, the chloride ion influence depth x0 under stress-free conditions is fitted in reverse. S3. Obtain the service stress parameters of the actual concrete components of the target project; S4. Calculate the representative equivalent stress σ of the actual concrete components in the target project. 等效 Calculate the equivalent stress σ based on the service stress parameters. 等效 It is used to standardize and quantify the stress level of actual concrete components in the target project; S5, Calculation of stress correction factor According to the equivalent stress σ等效 Calculate the stress correction factor Stress correction factor Substituting the chloride ion diffusion coefficient D0, we obtain the corrected diffusion coefficient D1; S6. Recalculate the equivalent chloride ion influence depth x' under stress based on the diffusion coefficient D1; S7. Model Validation: Compare the consistency between the model's prediction results and the actual engineering data, and further optimize the model based on the validation results.

[0035] Furthermore, the method for correcting key indicators in near-ground exposure tests considering the influence of force differences is characterized by: S1. Obtain chloride ion content distribution data C(t,x) of exposed specimens: In natural or artificial exposure environments, conduct long-term exposure tests on concrete specimens for an exposure time t≥1 year, and obtain chloride ion content distribution data C(t,x) of concrete specimens at different depths x after a set exposure time t. The chloride ion content distribution of concrete specimens after time t under standard exposure conditions is collected, and samples are taken along the depth of grinding and measurement. The surface chloride ion concentration Cs and the content C(t,x) curves at different depths x are recorded. If long-term multi-stage data of the specimens are available, parameters such as the time function of C(t,x) and the age decay coefficient can be established.

[0036] S2. Fitting the chloride ion influence depth x0 under stress-free conditions: Based on Fick's second law, curve fitting is performed on the chloride ion content distribution data C(t,x) to obtain the relationship between the chloride ion diffusion coefficient D0 and the chloride ion concentration Cs on the exposed specimen surface under stress-free conditions:

[0037] In the formula, C(t,x) represents the chloride ion content distribution data of the exposed specimen at depth x at time t, in units of %; Cs represents the chloride ion concentration on the surface of the exposed specimen, in units of %; and D0 represents the chloride ion diffusion coefficient under stress-free conditions, in units of m³. 2 / s; t is the exposure time, where t ≥ 1 year; x is the depth from the surface of the exposed specimen to its interior, in meters, where x ≤ To avoid data truncation leading to fitting bias; erf is the error function, dimensionless, representing the cumulative distribution of chloride ions along the depth; Set the critical chloride ion concentration C cr Based on the chloride ion content distribution data C(t,x), the corresponding chloride ion influence depth x0 is calculated using the function, satisfying the following relationship:

[0038] The diffusion of chloride ions in concrete follows Fick's second law, but the stress state of concrete components in actual engineering will change the distribution of microcracks and affect the diffusion path. Therefore, it is necessary to obtain the baseline data of stress-free specimens first.

[0039] S3. Obtain the service stress parameters of the actual concrete components of the target project: Obtain the service stress parameters of the actual concrete components of the target project through finite element simulation and on-site monitoring, including axial force N, bending moment M, cross-sectional area A, cross-sectional moment of inertia I, and the distance y of the chloride ion detection area relative to the neutral axis. For the mechanical performance evaluation of actual concrete structural members of the target project, the analysis should be based on the differences in member type. For bending beam members, the distribution of tension and compression zones of the section needs to be clearly defined, and the maximum tensile and compressive stress values ​​should be quantitatively determined. For compression column members, the axial compression ratio parameter should be calculated to evaluate their compressive bearing characteristics. For tension members, the tensile stress distribution characteristics of key sections need to be determined. When a member is under a combined stress state, the region should be divided according to the stress distribution characteristics. For example, for bending members, mechanical models of tension and compression zones should be established separately, and corresponding stress analysis systems should be established for each region.

[0040] S4. Calculate the representative equivalent stress σ of the actual concrete components in the target project. 等效 Converting multiaxial stress into equivalent uniaxial stress, standardizing and quantifying the stress level, and equivalent stress σ 等效 The following relationship must be satisfied:

[0041] In the formula, σ 等效 The values ​​are: equivalent stress, in MPa; N / A is the average stress caused by axial force N, in MPa; My / I is the maximum normal stress caused by bending moment M, in MPa. N / A represents the uniform axial stress of the component, and My / I represents the maximum normal stress at the upper or lower edge of the section of the bending component. The sum of the two represents the total stress at the location most sensitive to chloride ion migration.

[0042] Traditional near-ground exposure tests only consider stress-free or single static load conditions, neglecting the influence of multiaxial stresses (such as combined tensile, compressive, and bending loads) on chloride ion diffusion in actual engineering projects. For example, bridge piers bear both axial compression and bending moment during service. Traditional methods, based solely on stress-free specimen data, may underestimate the chloride ion intrusion rate on the tension side. This invention establishes an equivalent stress model to convert complex multiaxial stresses into equivalent uniaxial stresses. The equivalent stress model and zonal corrections quantify the stress level. Simultaneously, the chloride ion diffusion coefficient is dynamically corrected by combining damage factors, thereby reflecting the accelerating or inhibiting effect of microstructural changes such as microcracks and pore connectivity on the permeation path, making the predicted chloride ion influence depth closer to the actual monitoring value.

[0043] S5, Calculation of stress correction factor : Calculate the stress correction factor for the chloride ion influence depth x0 under stress. Based on the type of force, it is divided into tensile stress zone correction factors. and the compressive stress zone correction factor Stress correction factor Substituting the chloride ion diffusion coefficient D0, we obtain the corrected diffusion coefficient D1 for the actual concrete components of the target project, which satisfies the following relationship: Tensile stress zone: ; Compressive stress zone: ; Under pure compressive stress, if the stress level is below the cracking threshold of concrete, the concrete pores may be compressed, the chloride ion diffusion path is restricted, and the diffusion rate may be slightly lower than in the stress-free state. At this time, there are basically no new cracks inside the component, and chloride ions mainly diffuse through the existing pores, with little or no change in permeability. However, when the compressive stress approaches the concrete strength or causes compressive cracking damage, microcracks and interface failure will occur inside, which will increase the permeability of the concrete. Compressive damage will increase the chloride ion influence depth x0, but the increase is relatively small compared to the case of tensile cracking. Under pure tensile stress, concrete is prone to tensile cracking. Even if the tensile stress does not reach the fracture stress, repeated or long-term tensile stress will promote the appearance and development of micro-cracks, greatly increasing the pore connectivity. Chloride ions can penetrate into the concrete interior more quickly through cracks. Therefore, the chloride ion diffusion coefficient of concrete in the tension zone is significantly higher than that in the stress-free state. When tensile stress is present, the time required for steel corrosion is greatly shortened, resulting in a multiple increase in the chloride ion erosion rate, a significant increase in the corresponding chloride content, and an increase in the chloride ion influence depth x0. Under bending conditions, when a component is subjected to bending, one side of the cross-section is under tension and the other under compression. The chloride ion intrusion characteristics are asymmetrical. Bending cracks easily form on the side of tensile stress, and chloride ions can rapidly enter along these cracks. On the side of compressive stress, if crushing damage does not occur, chloride ion diffusion is relatively slow. Therefore, the chloride ion penetration behavior of bending components can be viewed in zones: the tensile zone is similar to the tensile state with accelerated erosion, while the compressive zone is similar to the compressive state with suppressed or normal diffusion. When environmental chloride salts enter from the tensile zone, the chloride ion content will be significantly higher than when there is no bending; conversely, erosion from the compressive zone is slightly slower. Therefore, under bending or other combined stresses, the chloride ion migration characteristics of the tensile and compressive zones should be considered separately. If necessary, the bending effect can be equivalent to the superposition of tensile and compressive stresses for correction.

[0044] S6. Calculate the equivalent chloride ion influence depth x' under stress: Based on the corrected diffusion coefficient D1, recalculate the equivalent chloride ion influence depth x' of the actual concrete components of the target project, satisfying the following relationship:

[0045] S7. Model Validation: Select some existing concrete structure engineering cases in chloride-salt erosion environments, collect their long-term service data, including durability test data and actual stress data, substitute these data into the constructed modified model for validation, compare the consistency between the model prediction results and the actual engineering data, further optimize the model based on the validation results, and apply the validated modified model to near-ground exposure tests to guide concrete mix design, durability assessment and structural design optimization.

[0046] Furthermore, the test methods for the chloride ion content distribution data C(t,x) in step S1 include the grinding method, electrode method, and chemical titration method; the chloride ion concentration Cs on the exposed specimen surface in step S2 is obtained by directly measuring the chloride ion concentration on the exposed specimen surface.

[0047] Furthermore, when in the early stages of engineering design or the experimental stage, or when concrete strength parameters, elastic modulus parameters are incomplete, or the state of concrete deterioration is unknown, the stress correction factor in step S5... The equivalent stress σ of the representative concrete components in the target project is obtained using a rapid estimation method. 等效 The ratio of the stress to the reference stress of the exposed specimen is set as the equivalent stress ratio factor λ, which satisfies the following relationship:

[0048] In the formula, σ ref The reference stress for the exposed specimen is expressed in MPa. Stress correction coefficient is established based on the equivalent force ratio factor λ. Empirical mapping relation:

[0049] In the formula, α and β are empirical fitting coefficients, determined based on existing experimental data, where α represents the proportion of diffusion increase caused by force, and β represents the degree of nonlinear enhancement. stress correction factor Substituting the chloride ion diffusion coefficient D0, we obtain the corrected diffusion coefficient D1 for the actual concrete components of the target project, which satisfies the following relationship:

[0050] The empirical fitting coefficients α and β are determined as follows: S100. Establishing the prior interval for parameters: Based on the porosity-crack evolution theory caused by stress, the prior interval is set as follows: in, , C, n, and δ are the material crack permeability coefficient, diffusion index, and crack activation index, respectively, all determined by experiments or literature. S200, Collect two sets of calibration points: Obtain at least two sets of stress-diffusion coefficient comparison data (λ1, ), (λ2, ),in , Here are the diffusion correction factors for the specimen under loading conditions, i = 1, 2; S300, Solve for the empirical fitting coefficients α and β:

[0051]

[0052] S400, Prior Interval Verification: If α and β exceed the prior interval range given in S100, then take α = min(max(α, αmin), αmax); β = min(max(β, βmin), βmax); S500, Update empirical fitting coefficients α, β: After obtaining new field monitoring data (λ) i , After i=1, 2....n, a variant of Kalman filtering is used to perform recursive calculation. The empirical fitting coefficients α and β are treated as random variables and the post-calibrated mean is updated with the least negative logarithmic posterior function to complete the online adaptive correction of the empirical fitting coefficients α and β.

[0053] Furthermore, when the exposed specimen is not subjected to any load and only bears its own weight, the reference stress σ of the exposed specimen is calculated using its own weight. ref It satisfies the following relationship:

[0054] In the formula, γ c The volumetric weight of the exposed specimen is expressed in kN / m³. 3 h represents the height of the exposed specimen, in meters (m).

[0055] Furthermore, when the structural strength, elastic modulus, and damage information of the actual concrete components of the target project are known, the stress correction factor in step S5... The damage factor ω, which is related to concrete strength, is used for calculation. The damage factor ω is used to quantitatively describe the degree of degradation of the permeability of concrete under stress due to changes in the microstructure caused by microcracks, pore connectivity, and interface weakening. The stress correction factor is calculated using the damage factor ω. The formula satisfies the following relationship: Tensile stress zone: ; Compressive stress zone: ; The damage factor ω ranges from 0 to 1. When the damage factor ω = 0, it indicates that the actual concrete component of the target project has no mechanical damage, and the porosity and microstructure remain unchanged. When the damage factor ω = 1, it indicates that the actual concrete component of the target project is in a state of severe damage, with microcracks penetrating and enhanced diffusion capacity.

[0056] Under combined stress conditions, a zonal correction strategy should be implemented based on the stress distribution characteristics. For non-uniform stress regions, such as stress concentration areas and gradual transition areas, tensor decomposition is needed to determine the principal stress directions and proportional relationships in each region, and stress correction coefficients should be calculated separately for different regions. When the structure exhibits a uniform triaxial stress state, the three principal stress components can be integrated into an equivalent stress correction coefficient using the principle of energy equivalence.

[0057] Furthermore, the damage factor ω is calculated based on the stress intensity ratio, satisfying the following relationship: Tensile stress zone: ; Compressive stress zone: ; In the formula, f t f is the splitting tensile strength of concrete, expressed in MPa. c This represents the axial compressive strength of concrete, expressed in MPa.

[0058] When a concrete member is in service and has not yet developed observable cracks, and its stress magnitude is known, the damage factor ω can be calculated based on the stress level. This is suitable for rapid assessment, indicating that the material's entry into the damage stage is mainly determined by the ratio of stress to its ultimate strength. The larger the ratio, the more microcracks appear, and ω approaches 1 when σ≥f t or f c When the value is ω, it is considered as the limit damage, and ω = 1.

[0059] Furthermore, the damage factor ω is calculated based on the elastic modulus degradation ratio, satisfying the following relationship:

[0060] In the formula, E0 is the initial elastic modulus of concrete, in GPa; E is the current elastic modulus of concrete, in GPa; and E / E0 is the degradation ratio of the elastic modulus of concrete, which is dimensionless.

[0061] When non-destructive testing data, such as ultrasonic velocity and resilient modulus, are available on-site, or when structural simulation can predict material stiffness degradation, the damage factor ω can be calculated based on the elastic modulus attenuation. This is applicable to existing structures and indicates that material damage leads to a decrease in structural stiffness. The lower the elastic modulus, the looser the concrete structure and the more developed the microcracks. When E=E0, it indicates that the structure is undamaged, i.e., ω=0; when E=0, it indicates that the structure has completely failed, i.e., ω=1. The elastic modulus of concrete can be obtained through non-destructive testing, numerical simulation, or experimental estimation. Non-destructive testing includes using ultrasonic velocity detection and resilient modulus conversion technology. Numerical simulation mainly calculates residual stiffness based on stress-strain curves. Experimental estimation obtains the E / E0 ratio through load tests.

[0062] Furthermore, the damage factor ω is calculated based on the nonlinear damage evolution model of the concrete strain state, satisfying the following relationship: Tensile stress zone:

[0063] Compressive stress zone:

[0064] In the formula, m c is an empirical constant for concrete material under compressive damage, taken as 3.45 in the absence of experimental data; m t ε is the empirical constant for concrete under tensile damage, taken as 1.46 in the absence of experimental data; ε is the axial strain of concrete; ε cu ε represents the peak compressive strain of concrete. cr This refers to the tensile cracking strain of concrete.

[0065] Furthermore, step S5 also includes a dynamic correction method that considers the depth x0 of the influence of tensile-compressive cyclic loading on chloride ions, the specific steps of which are as follows: S10. Obtain the time history data of tensile-compressive cyclic stress during the service life of the actual concrete components of the target project through a dynamic strain monitoring system, and use the rainflow counting method to statistically analyze the stress amplitude Δσ. i and its corresponding number of iterations n i Calculate the equivalent symmetrical cyclic stress ratio R:

[0066] S20. Calculate the cumulative damage degree D based on the improved Miner criterion. fat Introducing a stress amplitude weighting factor γ i :

[0067] In the formula, A, τ1, and τ2 are material fatigue parameters, which are calibrated through a three-point bending fatigue test; For fatigue life; γ i Determined based on stress level classification:

[0068] Where f t It refers to the tensile strength of concrete; S30. Establish a dynamic correction model for the diffusion coefficient, and correlate cyclic damage with the stress correction coefficient. coupling:

[0069] In the formula, D is the cyclic stress correction factor, η is the cyclic-diffusion coupling factor, calibrated through electromigration acceleration tests; cr This is the critical damage threshold; S40. Define cyclic stress correction factors for the tension and compression zones of bending members respectively. : Tensile stress zone:

[0070] Compressive stress zone:

[0071] S50, Adjust the cyclic stress correction factor Substituting into the diffusion equation, we obtain the corrected time-varying diffusion coefficient D1' for the actual concrete components of the target project. Tensile stress zone: Compressive stress zone: ; S60. Considering the unsteady-state Fick's second law regarding the diffusion coefficient changing with time, the equivalent chloride ion influence depth x' under tensile-compressive cyclic stress is calculated using the equivalent time integration method, satisfying the following relationship: ; In the formula C is the equivalent diffusion coefficient, representing the average value of the time-varying diffusion coefficient D1' over the time interval [0, t]. cr This represents the critical chloride ion concentration.

[0072] This invention addresses tension-compression ring loads, such as the wet-dry cycle stress of concrete structures in tidal zones. It introduces the rainflow counting method to statistically analyze the stress amplitude and the number of cycles, combines it with the improved Miner criterion to calculate the cumulative damage, and further uses a cycle-diffusion coupling model to dynamically correct the diffusion coefficient. In particular, for the problem that fatigue damage to offshore wharf pile foundations under wave loads gradually increases the chloride ion diffusion rate, this invention can predict corrosion risk in advance and guide the optimization of maintenance cycles.

[0073] It should be understood that the above embodiments are one or more embodiments of the present invention. There are many other embodiments and variations based on the present invention. Any variations and modifications made by those skilled in the art without making pioneering innovations are within the protection scope of the present invention.

Claims

1. A method for correcting key indicators in near-ground exposure tests considering the influence of stress differences, characterized in that... Includes the following steps: S1. Obtain chloride ion content distribution data C(t,x) of exposed specimens: Conduct long-term exposure tests on concrete specimens and obtain chloride ion content distribution data C(t,x) of exposed specimens. S2, Fitting the chloride ion influence depth x0 under stress-free conditions: Based on the chloride ion content distribution data, the chloride ion influence depth x0 under stress-free conditions is fitted in reverse. S3. Obtain the service stress parameters of the actual concrete components of the target project; S4. Calculate the representative equivalent stress σ of the actual concrete components in the target project. 等效 Calculate the equivalent stress σ based on the service stress parameters. 等效 It is used to standardize and quantify the stress level of actual concrete components in the target project; S5, Calculation of stress correction factor According to the equivalent stress σ 等效 Calculate the stress correction factor The stress correction factor Substituting the chloride ion diffusion coefficient D0, we obtain the corrected diffusion coefficient D1; S6. Recalculate the equivalent chloride ion influence depth x' under stress based on the diffusion coefficient D1; S7. Model Validation: Compare the consistency between the model's prediction results and the actual engineering data, and further optimize the model based on the validation results.

2. The method for correcting key indicators of near-ground exposure tests considering the influence of force differences according to claim 1, characterized in that: S1. Obtain chloride ion content distribution data C(t,x) of exposed specimens: In natural or artificial exposure environments, conduct long-term exposure tests on concrete specimens for an exposure time t≥1 year, and obtain chloride ion content distribution data C(t,x) of concrete specimens at different depths x after a set exposure time t. S2. Fitting the chloride ion influence depth x0 under stress-free conditions: Based on Fick's second law, curve fitting is performed on the chloride ion content distribution data C(t,x) to obtain the relationship between the chloride ion diffusion coefficient D0 and the chloride ion concentration Cs on the exposed specimen surface under stress-free conditions: In the formula, C(t,x) represents the chloride ion content distribution data of the exposed specimen at depth x at time t, in percentage terms (%). Cs represents the chloride ion concentration on the surface of the exposed specimen, in %; D0 represents the chloride ion diffusion coefficient under stress-free conditions, in m³. 2 / s; t represents the exposure time, where t ≥ 1 year; x represents the depth from the surface of the exposed specimen to its interior, in meters, where x ≤ ;erf is the error function, which is dimensionless; Set the critical chloride ion concentration C cr Based on the chloride ion content distribution data C(t,x), the corresponding chloride ion influence depth x0 is calculated using the function, satisfying the following relationship: ； S3. Obtain the service stress parameters of the actual concrete components of the target project: Obtain the service stress parameters of the actual concrete components of the target project through finite element simulation and on-site monitoring, including axial force N, bending moment M, cross-sectional area A, cross-sectional moment of inertia I, and the distance y of the chloride ion detection area relative to the neutral axis. S4. Calculate the representative equivalent stress σ of the actual concrete components in the target project. 等效 The multiaxial stress is converted into an equivalent uniaxial stress, and the stress level is quantified uniformly. The equivalent stress σ 等效 The following relationship must be satisfied: In the formula, σ 等效 N is the equivalent stress, in MPa; N / A is the average stress caused by axial force N, in MPa. My / I is the maximum normal stress caused by the bending moment M, in MPa; S5, Calculation of stress correction factor : Calculate the stress correction factor for the chloride ion influence depth x0 under stress. Based on the type of force, it is divided into tensile stress zone correction factors. and the compressive stress zone correction factor The stress correction factor Substituting the chloride ion diffusion coefficient D0, we obtain the corrected diffusion coefficient D1 for the actual concrete components of the target project, which satisfies the following relationship: Tensile stress zone: Compressive stress zone: ; S6. Calculate the equivalent chloride ion influence depth x' under stress: Based on the corrected diffusion coefficient D1, recalculate the equivalent chloride ion influence depth x' of the actual concrete components of the target project, satisfying the following relationship: ； S7. Model Validation: Select some existing concrete structure engineering cases in chloride-salt erosion environments, collect their long-term service data, including durability test data and actual stress data, substitute these data into the constructed modified model for validation, compare the consistency between the model prediction results and the actual engineering data, further optimize the model based on the validation results, and apply the validated modified model to near-ground exposure tests to guide concrete mix design, durability assessment and structural design optimization.

3. The method for correcting key indicators of near-ground exposure tests considering the influence of force differences according to claim 2, characterized in that: The test methods for the chloride ion content distribution data C(t,x) in step S1 include the grinding method, electrode method, and chemical titration method; the chloride ion concentration Cs on the surface of the exposed specimen in step S2 is obtained by directly measuring the chloride ion concentration on the surface of the exposed specimen.

4. The method for correcting key indicators of near-ground exposure tests considering the influence of force differences according to claim 2, characterized in that: When the stress correction coefficient mentioned in step S5 is used in the early stages of engineering design or the experimental stage, or when concrete strength parameters, elastic modulus parameters are incomplete, or the state of concrete deterioration is unknown. The equivalent stress σ of the representative concrete components in the target project is obtained using a rapid estimation method. 等效 The ratio of the stress to the reference stress of the exposed specimen is set as the equivalent stress ratio factor λ, which satisfies the following relationship: In the formula, σ ref The reference stress for the exposed specimen is expressed in MPa. A stress correction coefficient is established based on the equivalent force ratio factor λ. Empirical mapping relation: In the formula, α and β are empirical fitting coefficients determined based on existing experimental data, where α represents the proportion of diffusion increase caused by force and β represents the degree of nonlinear enhancement.

5. The method for correcting key indicators of near-ground exposure tests considering the influence of force differences according to claim 4, characterized in that: When the exposed specimen is not subjected to any load and only bears its own weight, the reference stress σ of the exposed specimen is calculated using the self-weight of the exposed specimen. ref It satisfies the following relationship: In the formula, γ c The volumetric weight of the exposed specimen is expressed in kN / m³. 3 h is the height of the exposed specimen, in meters (m).

6. The method for correcting key indicators of near-ground exposure tests considering the influence of force differences according to claim 2, characterized in that: When the structural strength, elastic modulus, and damage information of the actual concrete components of the target project are known, the stress correction coefficient mentioned in step S5 The damage factor ω, which is related to concrete strength, is used for calculation. This damage factor ω is used to quantitatively describe the degree of permeability degradation of concrete under stress due to changes in its microstructure, such as microcracks, pore connectivity, and interface weakening. The stress correction factor is calculated using the damage factor ω. The formula satisfies the following relationship: Tensile stress zone: Compressive stress zone: ; The damage factor ω ranges from 0 to 1. When the damage factor ω = 0, it indicates that the actual concrete component of the target project has no mechanical damage and the porosity and microstructure remain unchanged. When the damage factor ω = 1, it indicates that the actual concrete component of the target project is in a state of severe damage, with microcracks penetrating and enhanced diffusion capacity.

7. The method for correcting key indicators of near-ground exposure tests considering the influence of force differences according to claim 6, characterized in that: The damage factor ω is calculated based on the stress intensity ratio and satisfies the following relationship: Tensile stress zone: Compressive stress zone: ; In the formula, f t f is the splitting tensile strength of concrete, expressed in MPa. c This represents the axial compressive strength of concrete, expressed in MPa.

8. The method for correcting key indicators of near-ground exposure tests considering the influence of force differences according to claim 6, characterized in that: The damage factor ω is calculated based on the elastic modulus degradation ratio, satisfying the following relationship: In the formula, E0 is the initial elastic modulus of concrete, in GPa; E is the current elastic modulus of concrete, in GPa; and E / E0 is the degradation ratio of the elastic modulus of concrete, which is dimensionless.

9. The method for correcting key indicators of near-ground exposure tests considering the influence of force differences according to claim 6, characterized in that: The damage factor ω is calculated based on a nonlinear damage evolution model of concrete strain state, satisfying the following relationship: Tensile stress zone: ； Compressive stress zone: In the formula, m c m is an empirical constant for concrete materials under compressive damage. t ε is the empirical constant of concrete material under tensile damage; ε is the axial strain of concrete; ε cu ε represents the peak compressive strain of concrete. cr This refers to the tensile cracking strain of concrete.

10. The method for correcting key indicators of near-ground exposure tests considering the influence of force differences according to claim 2, characterized in that... Step S5 also includes a dynamic correction method that considers the depth x0 of the influence of tensile-compressive cyclic loading on chloride ions, the specific steps of which are as follows: S10. Obtain the time history data of tensile-compressive cyclic stress during the service life of the actual concrete components of the target project through a dynamic strain monitoring system, and use the rainflow counting method to statistically analyze the stress amplitude Δσ. i and its corresponding number of iterations n i Calculate the equivalent symmetrical cyclic stress ratio R: S20. Calculate the cumulative damage degree D based on the improved Miner criterion. fat Introducing a stress amplitude weighting factor γ i : In the formula, A, τ1, and τ2 are material fatigue parameters, which are calibrated through a three-point bending fatigue test; For fatigue life; γ i Determined based on stress level classification: Where f t It refers to the tensile strength of concrete; S30. Establish a dynamic correction model for the diffusion coefficient, and correlate cyclic damage with the stress correction coefficient. coupling: In the formula, D is the cyclic stress correction factor, and η is the cyclic-diffusion coupling factor, calibrated through electromigration acceleration tests; cr This is the critical damage threshold; S40. Define cyclic stress correction factors for the tension and compression zones of bending members respectively. : Tensile stress zone: Compressive stress zone: ； S50, adjust the cyclic stress correction coefficient Substituting into the diffusion equation, we obtain the corrected time-varying diffusion coefficient D1' for the actual concrete components of the target project. Tensile stress zone: Compressive stress zone: ; S60. Considering the unsteady-state Fick's second law regarding the diffusion coefficient changing with time, the equivalent chloride ion influence depth x' under tensile-compressive cyclic stress is calculated using the equivalent time integration method, satisfying the following relationship: In the formula, C is the equivalent diffusion coefficient, representing the average value of the time-varying diffusion coefficient D1' over the time interval [0, t]. cr This represents the critical chloride ion concentration.

Images