Evaluation Method for Fatigue Damage and Life of Bridge Structure under Multi-Factor Coupling Action

Abstract

This invention discloses a method for assessing fatigue damage and lifespan of bridge structures due to the coupling of multiple factors. The method comprises the following steps: S1, numerically reproducing the effects of complex service environments; S2, numerically analyzing bridge structural performance; S3, calculating coupled fatigue damage in vulnerable locations; and S4, predicting the remaining lifespan of bridge structures. This method can accurately assess the fatigue damage status and remaining lifespan of existing bridges due to the coupling of multiple factors, quantitatively analyzing the effects of various factors / actions and their coupling effects on fatigue damage in vulnerable locations, and providing data support and decision-making reference for bridge operation and maintenance, reinforcement and repair, and optimized design.

Description

Technical Field

[0001] The present invention belongs to the field of multi-factor disaster analysis and life assessment of bridges, and relates to a method for assessing fatigue damage and life of bridge structures under multi-factor coupling. Background Art

[0002] Bridge structures operate in a complex service environment, influenced by numerous factors, including fatigue effects from vehicle loads, wind, and temperature, as well as corrosion and wear. Under these complex load-environmental conditions, damage to long-span bridges is often caused by numerous factors and their coupled effects. The frequency and intensity of these factors and effects exhibit a high degree of randomness, varying distributions, and varying temporal phases and frequencies. The mechanisms of fatigue damage to structures under these multiple factors are unclear and complex, making structural damage and lifespan assessment difficult. However, coupled fatigue damage incidents in bridge structures are becoming increasingly prominent with increasing service life, seriously impacting bridge operation and maintenance safety. Previous studies have primarily considered bridge performance analysis and lifespan assessment under the influence of single factors, such as fatigue, corrosion, or wear. These multifactor effects are considered as generalized coefficients or by the repeated superposition of multiple single factors, leading to issues with the rationality and reliability of the results. To effectively support bridge operation and maintenance decision-making, it is necessary to develop methods that comprehensively consider the multifactorial effects of complex in-service environments and accurately assess bridge structural performance. These methods should also investigate the mechanisms of fatigue damage catastrophic under these multiple factors and analyze the influence of each factor on structural failure. In response to the above problems, the present invention establishes a method for evaluating fatigue damage and life of bridge structures under multi-factor coupling.

[0003] At present, the structural assessment methods that consider the effects of multiple factors include: Patent No. 201510225325.4 discloses a method for predicting crack propagation of structural parts based on multi-factor fusion correction, Patent No. 201510247506.7 discloses a method for predicting the remaining life of structural parts based on multi-factor fusion correction, and Patent No. 201710001052.4 discloses a method for evaluating the residual strength of structural parts based on multi-factor fusion correction. All of them consider factors that can affect the damage state of structural parts, such as fatigue life, stress concentration, stress distribution, manufacturing process, surface strength, etc. However, the effects of these factors are all considered through the influence of coefficients on stress, and the effects of various factors are not distinguished. All effects need to be converted into effects on stress; Patent No. 202111427626.7 discloses a structural safety analysis method based on the comprehensive influence of multiple factors. By setting the load magnification factor, material reduction factor, section damage factor, and support variation factor, the finite element model is adjusted to analytically analyze the influence of multiple factors on the combination of less favorable reduction factors. It does not involve a coupled fatigue model of a multi-factor competition relationship and does not involve probabilistic reliability and its dominant factor decline rate integral technology; Patent No. 201811067793.3 discloses a corrosion-fatigue-based sling steel wire remaining life assessment method and system, which is a test method and system that only considers the two factors of corrosion and fatigue, and the coupling effect is considered in a general test. Summary of the Invention

[0004] In order to realize the assessment of coupled fatigue damage and life of bridge structures under complex load-environment effects, the present invention provides a comprehensive, accurate and efficient method for assessing the coupled fatigue damage and life of vulnerable parts of bridge structures under multi-factor effects. The method can be used to analyze the fatigue damage status of bridge structures under operating conditions and predict the remaining life, providing support for maintenance decisions, reinforcement implementation and optimized design of bridges.

[0005] The present invention provides a method for evaluating fatigue damage and life of a bridge structure under multi-factor coupling, comprising the following steps:

[0006] S1. Based on the monitoring data of the bridge service environment and structure, a probability distribution model of the characterization parameters of factors / actions such as vehicles, wind, temperature, corrosion, and wear is established. The sample size is determined according to the ratio of the combined occurrence frequency and duration of each factor / action, and sampling is performed to generate the characterization parameter samples of each factor / action;

[0007] S2. Establish a finite element model of the entire bridge, including vulnerable parts, based on bridge design drawings, three-dimensional geometric models, etc.; combine the parameter samples representing each factor / action in step 1 according to the ratio of joint occurrence frequency and duration, and the action area to form a sample series; input these samples into the finite element model in sequence to perform numerical analysis of the bridge structural performance, and obtain the stress time history of the vulnerable parts of the bridge; and calculate the equivalent stress amplitude and cycle number distribution from the stress time history using the rain flow counting method;

[0008] S3. Based on the damage index under the single factor / action of fatigue, corrosion, and wear and the calculation formula for the time-varying reliability of structural performance, the reliability degradation rate of the structural performance under fatigue, corrosion, and wear in the current calculation step is calculated respectively; the factor with the largest reliability degradation rate is regarded as the dominant factor in the current calculation step, and the reliability degradation amount of the current calculation step is calculated from the reliability degradation rate of the dominant factor. That is, the reliability degradation rate under the action of each factor is determined by competition. The reliability of the current calculation step is the reliability of the previous calculation step minus the reliability degradation amount of the current calculation step, where the reliability of the first calculation step is the initial reliability;

[0009] S4. Calculate in sequence until the reliability of the previous calculation step is not less than the critical reliability, and the coupled fatigue life can be obtained; otherwise, the calculation step increases and returns to S3.

[0010] Furthermore, in the method of the present invention, the fatigue performance reliability β of the structure in S3 is F The calculation formula is as follows:

[0011]

[0012] Among them, μ lnx and σ lnx Represent the mean and standard deviation of lnx respectively, and μ x and σ x Calculated and determined, where x represents Δ, A, N(t), N0 and S in the above formula eq ; Δ is the Miner critical damage accumulation index, which can be described by the log-normal distribution function, with a mean μ Δ is 1.0, the coefficient of variation σ Δ is 0.3; A is the fatigue detail index, which is determined by the type of details of the vulnerable part according to the specification; N0 is the number of cycles; S eq is the equivalent stress amplitude, calculated by the following formula; N(t) is equal to 365×ADT×N0×t, ADT is the average daily traffic volume, and t is the time in years.

[0013]

[0014] Where m is the exponent, which is generally taken as 3; N is the equivalent stress amplitude S eq The number of cycles required for fatigue failure to occur; n iis the stress amplitude S i The actual number of cycles.

[0015] Furthermore, in the method of the present invention, the reliability of the corrosion structure performance β in S3 C The calculation formula is as follows:

[0016]

[0017] Among them, μ ac and σ ac is the mean and standard deviation of the critical corrosion damage index; a(t) is the corrosion damage index, which is determined by the following formula; μ a(t) and σ (t) are the mean and standard deviation of the corrosion damage index.

[0018]

[0019] Among them, α and β are parameters in the calculation formula of corrosion damage index, which represent the uniform corrosion rate and trend, and are related to the metal type and corrosion environment conditions. For steel corrosion, the corrosion rate increases logarithmically, and β = 0.5; α obeys the logarithmic normal distribution, and its mean and deviation coefficient are 7.91×10 -6 m / year and 0.135; t0 is the initial time; d is the dimension of the vulnerable part in the corrosion direction.

[0020] Furthermore, in the method of the present invention, the wear effect structure performance reliability β in step 3 W The calculation formula is as follows:

[0021]

[0022] Among them, μ Vc and σ Vc is the mean and standard of the critical index of wear damage; V(t) is the corrosion damage index, calculated by the following formula; μ V(t) and σ V(t) are the mean and standard deviation of the corrosion damage index.

[0023]

[0024] Among them, k is the wear depth development rate formula parameter; H is the hardness; F is the lateral force.

[0025] Furthermore, in the method of the present invention, the dominant factor of each calculation step in step three is the one with the largest decrease rate, and the reliability decrease amount and reliability of the current calculation step are calculated by the following formula.

[0026]

[0027] β(t)=β(t)i-1 -Δβ i (4)

[0028] Among them, Δβ i is the reliability decrease of the current calculation step; Δt is the time increment in years; β(t) i and β(t) i-1 is the reliability of the current calculation step and the previous calculation step.

[0029] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the program is executed by a processor, the steps of the method for evaluating fatigue damage and life of a bridge structure under multi-factor coupling effects of the present invention are implemented.

[0030] The present invention is used to accurately evaluate the fatigue damage and remaining life of bridge structures under multi-factor coupling effects under in-service load environments, providing a basis for damage analysis and detection, maintenance and reinforcement decisions of bridge structures.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. The existing technology focuses on the effect of single factors and does not give enough consideration to the joint effect of multiple factors. The accuracy of the evaluation results needs to be improved. The "A method for evaluating fatigue damage and life of bridge structures under the coupling effect of multiple factors" in this application takes into account the coupling effect of multiple factors, and considers the influence of complex in-service environmental factors in a relatively comprehensive and reasonable manner. The evaluation results are reasonable and reliable.

[0033] 2. When considering the effects of multiple factors, the existing technology often uses general coefficients or repeatedly superimposes multiple single factors, which makes it impossible to quantitatively analyze the influence of each factor. There is a problem of repeated calculation, and the rationality of the method needs to be improved. The "A method for evaluating fatigue damage and life of bridge structures under the coupling of multiple factors" in this application adopts a coupled fatigue damage model that calculates the reliability reduction amount by the reliability reduction rate of the dominant factor in each calculation step and obtains the reliability by accumulating between calculation steps. It realizes the quantitative analysis of each factor and the reasonable calculation of its coupling effect, and the calculation accuracy.

[0034] 3. The present invention adopts the reliability degradation rate as an indicator to determine the dominant factor and its transformation, avoiding the problem of different differentiation of damage characterization quantities of different factors, and realizing unified consideration of damage determination of different factors, with strong adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Flowchart for reproducing vehicle, wind, temperature, corrosion and wear values for monitoring complex service environments;

[0036] Figure 2 This is a finite element model of the bridge structure and an example diagram of vulnerable parts;

[0037] Figure 3 is the equivalent stress amplitude;

[0038] Figure 4 is the number of cycles;

[0039] Figure 5 This is the reliability degradation rate diagram for fatigue, wear and corrosion damage;

[0040] Figure 6 A flow chart of the method for evaluating fatigue damage and life of bridge structures under multi-factor coupling effects;

[0041] Figure 7 It is a diagram showing the competition of reliability degradation rate, time-varying reliability and life assessment of various factors. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the embodiments and the accompanying drawings, with bolted channel steel nodes being taken as an example of vulnerable parts.

[0043] like Figure 1-7 As shown, a method for evaluating fatigue damage and life of a bridge structure under multi-factor coupling effects includes the following steps:

[0044] S1. Based on the monitoring data of the bridge service environment structure, a probability distribution model of the parameters of vehicle, wind, temperature, corrosion, wear and other factors / actions is established. The sample size is determined according to the ratio of the combined occurrence frequency and duration of each factor / action, and sampling is performed to generate samples of the parameters of each factor / action, such as Figure 1 shown.

[0045] The probability distribution model for vehicle action parameters includes the axle weight probability distribution function, wheelbase probability distribution function, and vehicle model lane distribution ratio, which are established by analyzing vehicle monitoring data such as mobile weighing systems and monitoring videos. Wind action parameters include hourly average wind speed and wind direction angle distribution ratio, which are statistically established from measured wind load data. Temperature action parameters include daily average temperature and temperature gradient, which are statistically established from monitored temperature data. Corrosion action parameters include parameters α and β for the corrosion damage index calculation formula, which are statistically established from corrosion test measurement data; α follows a log-normal distribution, with a mean and coefficient of variation of 7.91×10 -6 m / year and 0.135, β = 0.5. Wear characterization parameters include the wear depth development rate formula parameter k, hardness H, and lateral force F, which are statistically established based on wear test measurement data; k follows a normal distribution with a mean of 7×10 -4 , the coefficient of variation is 0.1.

[0046] S2. According to the bridge design drawings, 3D geometric models, etc., a finite element model of the entire bridge including vulnerable parts is established, such as Figure 2As shown in the figure, the main beams are modeled using Joe elements, the main towers using 6-DOF beam elements, and the cables using 3-DOF rod elements, which are tension-only and not compression-sensitive. Material properties are assigned to the corresponding elements as specified. For vulnerable locations, bolted channel joints are used as an example. Based on their local structural geometry, these locations are refined locally or using sub-modeling techniques to create a refined local finite element model.

[0047] The sample of each factor / action characterization parameter in step 1 is combined into a sample series according to the ratio of joint occurrence frequency and duration and action area; the sample series is sequentially input into the finite element model for numerical analysis of bridge structural performance to obtain the stress time history of the vulnerable parts of the bridge; the equivalent stress amplitude and cycle number distribution are calculated from the stress time history using the rain flow counting method, and the probability distribution function of the equivalent stress amplitude and cycle number is obtained by regression analysis fitting, such as Figure 3 and 4 shown.

[0048] S3. Calculate the reliability degradation rate of the structural performance under fatigue action in step i, such as Figure 5 As shown in Figure 2, the calculation formula for the time-varying reliability of the structural performance under fatigue damage is as follows:

[0049]

[0050] Among them, μ lnx and σ lnx Represent the mean and standard deviation of lnx respectively, and μ x and σ x Calculated and determined, where x represents Δ, A, N(t), N0 and S in the above formula eq ; Δ is the Miner critical damage accumulation index, which can be described by the log-normal distribution function, with a mean μ Δ is 1.0, the coefficient of variation σ Δ is 0.3; A is the fatigue detail index, which is determined by the type of details of the vulnerable part according to the specification; N0 is the number of cycles; S eq is the equivalent stress amplitude; N(t) is equal to 365×ADT×N0×t, ADT is the average daily traffic volume, t is the time in years, and m is the exponent, which can generally be taken as 3.

[0051] Calculate the reliability degradation rate of the structural performance under corrosion in step i, as Figure 5 As shown in Figure 2, the calculation formula for the time-varying reliability of the structural performance under corrosion damage is as follows:

[0052]

[0053] Among them, μ ac and σ ac is the mean and standard deviation of the critical corrosion damage index; a(t) is the corrosion damage index, which is determined by the following formula; μ a(t)and σ (t) are the mean and standard deviation of the corrosion damage index.

[0054]

[0055] Where t0 is the initial time; d is the corrosion direction dimension of the vulnerable part.

[0056] Calculate the reliability degradation rate of the structural performance under wear in step i, as Figure 5 As shown in Figure 2, the calculation formula for the time-varying reliability of the structural performance under wear damage is as follows:

[0057]

[0058] Among them, μ Vc and σ Vc is the mean and standard of the critical index of wear damage; V(t) is the corrosion damage index, calculated by the following formula; μ V(t) and σ V(t) are the mean and standard deviation of the corrosion damage index.

[0059]

[0060] The factor with the largest reliability decline rate is the dominant factor in step i. The reliability decline amount Δβ in step i is calculated based on the reliability decline rate of the dominant factor in step i. i , that is, the reliability degradation rate under the action of various factors is determined by competition, and the reliability of step i β i Using the i-1 step reliability β i-1 Subtract the reliability drop Δβ of step i i , where the first step reliability is the initial reliability β0 = 12.0. The specific calculation formula is as follows:

[0061]

[0062] β(t)=β(t) i-1 -Δβ i (4)

[0063] Among them, Δβ i is the reliability decrease of the current calculation step; Δt is the time increment in years; β(t) i and β(t) i-1 is the reliability of the current calculation step and the previous calculation step.

[0064] S4, calculate in sequence until the reliability of the previous calculation step is not less than the critical reliability β th , the coupled fatigue life can be obtained; otherwise, the calculation step increases and returns to S3. Critical reliability β th It can be set to 0, indicating complete damage and needing repair or replacement.

[0065] The process of the above-mentioned bridge structure multi-factor coupling fatigue damage and life assessment method is as follows: Figure 6 According to the above process, the time-varying reliability of the structural performance under fatigue, corrosion and wear and the residual life of coupled fatigue damage are calculated as follows: Figure 7 As shown in the figure, the dominant factors will change during service, the structural performance reliability will continue to decline over time, and the remaining life of the bolted channel steel node due to fatigue damage caused by multi-factor coupling is about 24.8 years.

[0066] The above embodiments are only preferred implementations of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and equivalent substitutions can be made without departing from the principles of the present invention. These technical solutions after improvements and equivalent substitutions to the claims of the present invention all fall within the scope of protection of the present invention.

Claims

1. A method for evaluating fatigue damage and life of bridge structures under multi-factor coupling, characterized in that: The method comprises the following steps: S1. Numerical reproduction of complex service environment effects; S2. Numerical analysis of bridge structure performance; S3. Calculation of coupled fatigue damage at vulnerable parts; S4. Prediction of remaining life of bridge structure; Among them, the specific steps of S3 are: according to the damage index under the single factor / action of fatigue, corrosion, and wear and the calculation formula of the time-varying reliability of structural performance, respectively calculate the reliability degradation rate of the structural performance under fatigue, corrosion, and wear in the current calculation step; the factor with the largest reliability degradation rate is taken as the dominant factor of the current calculation step, and the reliability degradation amount of the current calculation step is calculated from the reliability degradation rate of the dominant factor, that is, the reliability degradation rate under the action of each factor is competitively determined, and the reliability of the current calculation step is the reliability of the previous calculation step minus the reliability degradation amount of the current calculation step, where the reliability of the first calculation step is the initial reliability; Structural performance reliability β under fatigue conditions in S3 F The calculation formula is as follows: Among them, μ lnx and σ lnx Represent the mean and standard deviation of lnx, respectively, where x represents Δ, A, N(t), N0 and S in the above formula eq ; Δ is the Miner critical damage accumulation index; A is the fatigue detail index; N0 is the number of cycles; S eq is the equivalent stress amplitude; N(t) is equal to 365×ADT×N0×t, ADT is the average daily traffic volume, and t is the time in years; Structural performance reliability β under corrosion in S3 C The calculation formula is as follows: Among them, μ ac and σ ac is the mean and standard deviation of the critical corrosion damage index; a(t) is the corrosion damage index; μ a(t) and σ (t) are the mean and standard deviation of the corrosion damage index; Structural performance reliability β under wear in S3 W The calculation formula is as follows: Among them, μ Vc and σ Vc is the mean and standard of the critical index of wear damage; V(t) is the corrosion damage index; μ V(t) and σ V(t) are the mean and standard deviation of the corrosion damage index; The dominant factor of each calculation step in S3 is the one with the largest decrease rate. The reliability decrease and reliability of the current calculation step are calculated by the following formula: β(t) i =β(t) i-1 -Db i (4) Among them, Δβ i is the reliability decrease of the current calculation step; Δt is the time increment in years; β(t) i and β(t) i-1 is the reliability of the current calculation step and the previous calculation step.

2. The method for evaluating fatigue damage and life of a bridge structure under multi-factor coupling according to claim 1 is characterized in that: The specific steps of S1 are: based on the monitoring data of the bridge service environment structure, a probability distribution model of the factor / action characterization parameters is established, the sample size is determined according to the ratio of the joint occurrence frequency and duration of each factor / action, and sampling is performed to generate samples of the factor / action characterization parameters.

3. The method for evaluating fatigue damage and life of a bridge structure under multi-factor coupling according to claim 1 is characterized in that: The specific steps of S2 are: establishing a finite element model of the entire bridge including the vulnerable parts; combining the sample of each factor / action characterization parameter in S1 according to the ratio of joint occurrence frequency and duration and action area to form a sample series; The finite element model is sequentially input into the numerical analysis of the bridge structure performance to obtain the stress time history of the vulnerable parts of the bridge; the rain flow counting method is used to calculate the equivalent stress amplitude and cycle number distribution from the stress time history.

4. The method for evaluating fatigue damage and life of a bridge structure under multi-factor coupling according to claim 1 is characterized in that: The specific steps of S4 are: calculate in sequence until the reliability of the previous calculation step is not less than the critical reliability, and then the coupled fatigue life can be obtained; otherwise, the calculation step increases and returns to S3.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method for evaluating fatigue damage and life of a bridge structure under multi-factor coupling effects as claimed in any one of claims 1 to 4 are implemented.

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