Fatigue reliability analysis method and system based on truncation threshold probability modeling

Abstract

The present invention discloses a fatigue reliability analysis method and system based on truncation threshold probability modeling, including: establishing a fatigue limit state equation; determining the type of structural details; obtaining the stress spectrum of the structural details; determining the truncation threshold of the structural details; fitting the stress spectrum using a probability density function according to the truncation threshold; calculating the mean and standard deviation of the equivalent stress amplitude; determining the number of equivalent stress amplitude cycles; calculating the fatigue reliability index; predicting fatigue life. The fatigue reliability analysis method based on truncation threshold probability modeling proposed by the present invention can determine the reasonable value range of the truncation threshold based on the relationship between the equivalent stress amplitude and the fatigue life, fit the truncated stress spectrum using a probability density function, consider the distribution of future traffic loads in the high stress amplitude area, and obtain the probability statistical parameters of the equivalent stress amplitude, so as to achieve efficient evaluation of fatigue reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of fatigue performance evaluation, and in particular to a fatigue reliability analysis method, system, computer medium and computer based on truncation threshold probability modeling. Background Art

[0002] Fatigue cracking usually determines the safety of engineering structures. In order to improve the utilization efficiency of limited resources, accurate fatigue assessment methods need to be proposed. Over the years, a lot of research has been carried out on the establishment of SN resistance curves and fatigue life assessment theories. In general, the safety factor given by the fatigue design clause can obtain satisfactory results with its inherent safety redundancy. However, due to the uncertainties in the environment, vehicle loads, fatigue resistance design, manufacturing processes and future traffic conditions, it is extremely difficult to reliably predict the fatigue life of engineering structures based on deterministic assessment methods.

[0003] To solve this problem, reliability assessment has been gradually developed and applied in engineering. Reliability theory focuses on introducing probabilistic statistical methods to evaluate the performance of engineering operations, and is used to quantify the randomness of relevant parameters such as loading conditions, design dimensions and material properties. This method is conducive to the fatigue reliability analysis of engineering structures and gives the probability of damage to fatigue-sensitive details within a specific operating time. In order to evaluate the fatigue reliability of engineering structures, it is necessary to jointly consider the fatigue resistance and load effects of the structure. Generally, the fatigue resistance and load effects of engineering structures can be obtained from the specification SN curve and field tests under service conditions, respectively. When the fatigue detail classification meets the requirements, the specification can efficiently provide statistical parameters for resistance. However, if field tests are not carried out, it is difficult to reasonably consider the load effects. In view of the existence of these uncertain factors, field testing technology for actual engineering has gradually developed and is regarded as the best way to reliably obtain the stress state of fatigue details. However, this method still cannot solve how to reasonably quantify the measured stress spectrum and achieve accurate prediction of fatigue life, and it is difficult to reasonably consider changes in future traffic conditions. In recent years, long-term stress monitoring technology has developed rapidly, which can greatly improve the reliability of the effect, but it still cannot take into account the uncertainty of future traffic conditions. In addition, this method is costly, requires a lot of data processing time, and is inefficient. For this reason, some scholars have proposed that the traffic volume growth rate and vehicle overload rate can be appropriately considered in fatigue reliability assessment to reflect the impact of future traffic conditions on the fatigue performance of structural details. However, these parameter analyses still cannot take into account the distribution of high stress amplitudes, and the values ​​of traffic volume growth rate and vehicle overload rate are also difficult to objectively reflect the actual future traffic conditions. Summary of the invention

[0004] Purpose of the invention: In order to overcome the above shortcomings, the purpose of the present invention is to provide a fatigue reliability analysis method based on truncation threshold probability modeling, which can determine the reasonable value range of the truncation threshold based on the relationship between the equivalent stress amplitude and the fatigue life, and use the probability density function to fit the truncated stress spectrum. It can consider the distribution of future traffic loads in the high stress amplitude area, and obtain the probabilistic statistical parameters of the equivalent stress amplitude, so as to realize the efficient evaluation of fatigue reliability.

[0005] In order to solve the above technical problems, the present invention provides a fatigue reliability analysis method based on truncation threshold probability modeling, the method comprising the following steps:

[0006] Step S1: Establish fatigue limit state equation;

[0007] Step S2: Determine the type of construction details;

[0008] Step S3: Obtaining structural detail stress spectrum;

[0009] Step S4: determining a construction detail cutoff threshold;

[0010] Step S5: fitting the stress spectrum using a probability density function according to the cutoff threshold;

[0011] Step S6: Calculate the mean and standard deviation of the equivalent stress amplitude;

[0012] Step S7: determining the number of equivalent stress amplitude cycles;

[0013] Step S8: Calculate fatigue reliability index;

[0014] Step S9: predict fatigue life.

[0015] Using the above technical solution:

[0016] The selection of the truncation threshold has an important impact on the performance evaluation of fatigue details. The truncation threshold under the existing technical solutions is taken as 1 / 4 times the normal amplitude fatigue limit value or directly taken as 5MPa according to the specifications. If the value is too large, the fatigue life will be overestimated, and vice versa, it will cause excessive calculation. The method proposed in the present invention is based on the relationship between the equivalent stress amplitude and the fatigue life, and can determine the upper and lower limits of the truncation threshold, which can improve the accuracy and efficiency of fatigue life prediction.

[0017] For fatigue assessment under stress monitoring, the existing method calculates the equivalent stress amplitude of fatigue details based on the measured stress time history. This method cannot consider the distribution of future traffic loads in high stress amplitudes, which will cause overestimation or underestimation of fatigue life. The method proposed in this technology uses a probability density function to fit the measured stress spectrum, and then predicts the equivalent stress amplitude based on the fitted probability density function. This method can consider the distribution of future traffic loads in high stress amplitude areas, which can improve the accuracy of fatigue life prediction.

[0018] For the calculation of statistical parameters of equivalent stress amplitude under stress monitoring, the existing method is based on long-term (at least one month) monitoring data, calculates the equivalent stress amplitude of each day, and then solves the statistical parameters, which is extremely labor-intensive and costly. The method proposed in this technology is based on different truncation thresholds. It can obtain the fitting probability density function of the corresponding truncated stress spectrum based on the stress spectrum of one day or one week, thereby obtaining multiple equivalent stress amplitudes, based on which the probability statistical parameters of the equivalent stress amplitude can be calculated, and the corresponding number of stress amplitude actions can be obtained according to the Miner linear cumulative damage criterion, providing a method for calculating the probability statistical parameters of the action effect based on the truncation threshold for fatigue reliability analysis.

[0019] As a preferred embodiment of the present invention, the method for establishing the fatigue limit state equation is:

[0020] The limit state function represented by two random variables, structural fatigue resistance and action effect, is:

[0021] g(X)=RS

[0022] Among them, R represents the fatigue resistance of the structure, S represents the structural effect, and X is a random variable.

[0023] As a preferred embodiment of the present invention, the method for determining the type of construction details is:

[0024] According to the fatigue design specification, the structural detail level is determined, and the value of the fatigue detail constant A, the cumulative damage critical value Δ, and the corresponding probability statistics of each parameter are obtained, including the mean μ and the coefficient of variation δ s .

[0025] As a preferred embodiment of the present invention, the method for obtaining the structural detail stress spectrum is:

[0026] Based on the on-site stress monitoring data, the rainflow counting method is used to obtain the stress spectrum of the structural details under random loads, and the stress amplitude below the preset value is set to be ignored in the rainflow counting method.

[0027] As a preferred embodiment of the present invention, the method for determining the construction detail cutoff threshold is:

[0028] According to the preset cutoff threshold, the equivalent stress amplitude ΔS is calculated eq And the corresponding stress amplitude cycles:

[0029]

[0030] Among them, ΔS i and n i are the structural detail stress amplitude and the number of cycles respectively; m is the material constant.

[0031] As a preferred embodiment of the present invention, the method for calculating the mean and standard deviation of the equivalent stress amplitude is:

[0032] According to the probability density function f(x) fitted at different cutoff thresholds, the equivalent stress amplitude over the entire life span is calculated.

[0033]

[0034] Where x is the stress amplitude variable;

[0035] Based on the calculated equivalent stress amplitude, the mean and standard deviation of the equivalent stress amplitude are calculated.

[0036] As a preferred embodiment of the present invention, the method for determining the number of equivalent stress amplitude cycles is:

[0037] According to Miner's linear cumulative damage criterion, the corresponding number of cycles was calculated based on the average value of the equivalent stress amplitude.

[0038] As a preferred embodiment of the present invention, the method for calculating the fatigue reliability index is:

[0039] After determining the probability and statistical parameters of all random variables, the fatigue reliability index β is calculated:

[0040] β=Φ -1 (1-P f )=-Φ -1 (P f )

[0041] Among them, Φ -1 is the inverse function of the standard normal distribution, P f is the failure probability of a structure or system.

[0042] As a preferred embodiment of the present invention, the method for predicting fatigue life is:

[0043] Select the target reliability index according to the design specifications and the importance of the project, and calculate the time when the reliability index in the previous step reaches the target value.

[0044] The present invention also provides a fatigue reliability analysis system based on truncation threshold probability modeling, comprising:

[0045] Equation building module, used to build fatigue limit state equation;

[0046] A detail determination module, used to determine the type of construction details;

[0047] Stress spectrum acquisition module, used to obtain structural detail stress spectrum;

[0048] A threshold determination module, used to determine a construction detail cutoff threshold;

[0049] A stress spectrum fitting module, used to fit the stress spectrum using a probability density function according to the cutoff threshold;

[0050] The first calculation module is used to calculate the mean and standard deviation of the equivalent stress amplitude;

[0051] A cycle determination module, used to determine the number of equivalent stress amplitude cycles;

[0052] The second calculation module is used to calculate the fatigue reliability index;

[0053] Fatigue prediction module, used to predict fatigue life.

[0054] The above technical solution of the present invention has the following advantages compared with the prior art:

[0055] 1. Based on the relationship between equivalent stress amplitude and fatigue life, the upper and lower limits of the cutoff threshold can be determined, which can improve the accuracy and efficiency of fatigue life prediction.

[0056] 2. The measured stress spectrum is fitted with a probability density function, and then the equivalent stress amplitude is predicted based on the fitted probability density function. This can take into account the distribution of future traffic loads in the high stress amplitude area and improve the accuracy of fatigue life prediction;

[0057] 3. Based on different truncation thresholds, the fitting probability density function of the corresponding truncated stress spectrum can be obtained based on the stress spectrum of one day or one week, so as to obtain multiple equivalent stress amplitudes. Based on this, the probability statistical parameters of the equivalent stress amplitude can be calculated, and the corresponding number of stress amplitude actions can be obtained according to the Miner linear cumulative damage criterion. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0059] Figure 1 It is a flow chart of the fatigue reliability analysis method based on truncation threshold probability modeling.

[0060] Figure 2 It is a schematic diagram of the cutoff threshold and the number of cycles.

[0061] Figure 3 It is a schematic diagram of the cutoff threshold and fatigue life.

[0062] Figure 4 It is a schematic diagram of the stress history of structural details.

[0063] Figure 5 It is a schematic diagram of the stress spectrum of structural details.

[0064] Figure 6 It is a schematic diagram of the cutoff threshold and the SN curve.

[0065] Figure 7 is a schematic diagram of the fitted probability density function.

[0066] Figure 8 It is a schematic diagram showing the change of reliability index with operation time.

[0067] Fig. 9 It is a connection diagram of the fatigue reliability analysis system based on truncation threshold probability modeling.

[0068] Explanation of the reference numerals in the specification: 100, equation building module, 101, detail determination module, 102, stress spectrum acquisition module, 103, threshold determination module, 104, stress spectrum fitting module, 105, first calculation module, 106, cycle determination module, 107, second calculation module, 108, fatigue prediction module. DETAILED DESCRIPTION

[0069] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0070] In order to improve the evaluation efficiency of fatigue reliability of engineering structures, in the fatigue reliability analysis method based on truncation threshold probability modeling proposed in the present invention, the calculation method of probability statistical parameters of action effects is mainly optimized and improved. By selecting different truncation thresholds, the stress spectrum is fitted using probability density functions, and the equivalent stress amplitude is calculated accordingly. This method can take into account the distribution of future traffic loads in high stress amplitude areas and improve the accuracy of fatigue reliability evaluation. The present invention is of great significance for fatigue reliability analysis of key major projects such as bridge engineering, industrial plants, and mechanical engineering under random loads.

[0071] In some embodiments, a fatigue reliability analysis method based on truncation threshold probability modeling is involved, which can maximize the fatigue reliability assessment accuracy, improve the assessment efficiency, and reduce the cost. Figure 1 As shown, the specific method includes the following steps:

[0072] Step S1: Establish the fatigue limit state equation. The reliability of a structural component or system is related to the probability of a specific limit state. The limit state function represented by two random variables, structural fatigue resistance and action effect, is shown in the following equation (1):

[0073] g(X)=RS (1)

[0074] Among them, R represents the fatigue resistance of the structure, S represents the structural effect, and X is a random variable.

[0075] Step S2: Determine the type of structural detail. According to the fatigue design specification, determine the structural detail level, obtain the value of the fatigue detail constant A, the cumulative damage threshold Δ, and the corresponding probability statistics of each parameter, such as the mean μ and the coefficient of variation δ s .

[0076] Step S3: Obtaining the stress spectrum of the structural details. Based on the on-site stress monitoring data, the rain flow counting method can be used to obtain the stress spectrum of the structural details under random loads. Since too small a stress amplitude has almost no contribution to the entire fatigue damage, the rain flow counting method can be set to ignore stress amplitudes below a certain value, such as 5MPa.

[0077] Step S4: Determine the structural detail cutoff threshold. For each predetermined cutoff threshold, the equivalent stress amplitude ΔS can be calculated according to the Miner linear cumulative damage criterion of the following formula (2): eq and the corresponding stress amplitude cycles.

[0078]

[0079] Among them, ΔS i and n i are the structural detail stress amplitude and the number of cycles respectively; m is the material constant;

[0080] Then, the scattered points consisting of multiple groups of equivalent stress amplitudes and the corresponding stress amplitude cycle numbers are plotted in a double logarithmic coordinate system, and the corresponding Figure 2 The SN curve shown in the figure shows the positional relationship between the scatter points and the SN curve. For the points where the scatter point trend is parallel to the slope of the SN curve, it means that the cutoff threshold value of the scatter point has no effect on the fatigue life assessment of the structural details, and thus can be used as the cutoff threshold value. At the same time, the scatter points formed by the cutoff threshold and the fatigue life can also be plotted in a Cartesian rectangular coordinate system, and the range of the cutoff threshold value when the fatigue life does not change can also be obtained, such as Figure 3 shown.

[0081] Step S5: Fitting the stress spectrum based on the probability density function. According to the adopted cutoff threshold, the probability density function can be used to fit the stress spectrum, such as the log-normal distribution can be used for fitting under the action of random traffic flow.

[0082] Step S6: Estimate the mean and standard deviation of the equivalent stress amplitude. According to the probability density function f(x) fitted under different cutoff thresholds, the equivalent stress amplitude over the entire life span can be calculated according to formula (3):

[0083]

[0084] Where x is the stress amplitude variable;

[0085] Furthermore, based on multiple groups of equivalent stress amplitude data, the mean and standard deviation of the equivalent stress amplitude can be obtained.

[0086] Step S7: Determine the number of cycles of the equivalent stress amplitude. According to the Miner linear cumulative damage criterion, the corresponding number of cycles is calculated based on the average value of the equivalent stress amplitude.

[0087] Step S8: Calculate the fatigue reliability index. After determining the probability statistical parameters of all random variables, the fatigue reliability index can be calculated using formula (4):

[0088] β=Φ -1 (1-P f )=-Φ -1 (P f ) (4)

[0089] Among them, Φ -1 is the inverse function of the standard normal distribution, P f is the failure probability of the structure or system;

[0090] Among them, P f It can be calculated using formula (5):

[0091] P f=P[g(X)<0] (5)

[0092] Step S9: predict fatigue life. Select a target reliability index according to the design specification and the importance of the project, and calculate the time when the reliability index in the previous step reaches the target value, which is the fatigue life.

[0093] For example, in this embodiment, for an orthotropic steel-ultra-high performance concrete (UHPC) composite bridge deck project, stress monitoring of arc-shaped cutout fatigue structure details under random traffic flow was carried out, and its one-week (7-day) stress time history and stress spectrum were respectively Figure 4 and Figure 5 According to the AASHTO fatigue design provisions, by selecting different cutoff thresholds (i.e. 5MPa to 55MPa, with an interval of 5MPa), the corresponding equivalent stress amplitude and cycle number scatter points can be obtained and plotted in a double logarithmic coordinate system, as shown in Figure 6 As shown in Figure 2, it can be seen that when the cutoff threshold of the scattered points is lower than 20 MPa, its development trend is consistent with the SN curve. Therefore, the reasonable cutoff threshold of the structural details can be taken as 5 MPa to 20 MPa.

[0094] Since the stress spectrum of the fatigue structure details of the bridge under the action of random traffic conforms to the log-normal distribution, according to the four cut-off threshold values ​​(5MPa, 10MPa, 15MPa and 20MPa), the log-normal distribution function can be used to fit the four stress spectra respectively, and the fitting curves are shown in Figure 2. Figure 7 According to formula (3), the four equivalent stress amplitudes are calculated to be 29.7MPa, 32.5MPa, 34.2MPa and 35.5MPa, respectively, with a mean and standard deviation of 33.0MPa and 2.17, respectively, and the corresponding average daily cycle number is 477.

[0095] For a bridge project, when it is in operation for y years, its fatigue limit state equation can be expressed by equation (6):

[0096]

[0097] Where N c is the number of critical stress amplitude actions for fatigue failure of the structural detail; N is the number of stress amplitude actions experienced by the structural detail; e is the correction factor for sensor error during the test. It can be calculated according to formula (3), where the material-related constant m is taken as 3.

[0098] Fatigue failure probability P of structural details under random traffic flow F It can be calculated using formula (7):

[0099] PF =P[g(X)<0]=Φ(-β) (7)

[0100] For the bridge project of this embodiment, it can be assumed that all random variables A, e, Δ and ΔS eq All obey the log-normal distribution, so the reliability index can be expressed by formula (8):

[0101] β=ln(N c / N) / σ lnN (8)

[0102] Among them, σ lnN It can be calculated using formula (9):

[0103]

[0104] Among them, σ lnN represents the coefficient of variation of each random variable.

[0105] If all random variables obey the log-normal distribution, the fatigue reliability index β can be calculated using formula (10):

[0106]

[0107] Among them, λ y , y They represent the statistical parameters of the logarithm of the random variable ln(y), namely the mean and standard deviation.

[0108] In this embodiment, the mean and coefficient of variation of fatigue constant A are 82.0×10 12 and 0.45; the mean and coefficient of variation of the critical damage Δ are 1.0 and 0.3 respectively; the mean and coefficient of variation of the experimental test error e are 1.0 and 0.03 respectively.

[0109] According to formula (10), the fatigue reliability analysis of the structural details is carried out, such as Figure 8 As shown, the relationship between the reliability index of the structural details and the operation time is given. The target reliability index is 3.72, and its guarantee rate and failure probability are 99.99% and 0.01% respectively. For this embodiment, due to the use of the UHPC rigid structural layer and the 16mm thicker diaphragm in the steel bridge deck, the fatigue reliability index of the structural details is significantly greater than the target reliability index during the design life cycle of the bridge, the fatigue life exceeds 100 years, and the fatigue performance is excellent, indicating that the fatigue reliability analysis results are consistent with the design concept of the engineering structure. It can be seen that the technical solution proposed in the present invention can efficiently carry out fatigue reliability analysis of structural details based on shorter stress time history data.

[0110] Since the action effect has an important influence on the fatigue reliability analysis of structural details, the coupling effect of multiple loads can be considered in the actual engineering evaluation, and the equivalent stress amplitude generated by random loads can be calculated using the method proposed in this technical solution to improve the accuracy and efficiency of fatigue reliability analysis.

[0111] In some embodiments, reference Fig. 9 As shown, the present invention also provides a fatigue reliability analysis system based on truncation threshold probability modeling, comprising:

[0112] Equation building module, used to build fatigue limit state equation;

[0113] A detail determination module, used to determine the type of construction details;

[0114] Stress spectrum acquisition module, used to obtain structural detail stress spectrum;

[0115] A threshold determination module, used to determine a construction detail cutoff threshold;

[0116] A stress spectrum fitting module, used to fit the stress spectrum using a probability density function according to the cutoff threshold;

[0117] The first calculation module is used to calculate the mean and standard deviation of the equivalent stress amplitude;

[0118] A cycle determination module, used to determine the number of equivalent stress amplitude cycles;

[0119] The second calculation module is used to calculate the fatigue reliability index;

[0120] Fatigue prediction module, used to predict fatigue life.

[0121] In some embodiments, the present invention further provides a computer medium having a computer program stored thereon, and the computer program is executed by a processor to implement the fatigue reliability analysis method based on truncation threshold probability modeling.

[0122] In some embodiments, the present invention also provides a computer, comprising the computer medium described above.

[0123] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0124] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A fatigue reliability analysis method based on truncation threshold probability modeling, characterized in that: The following steps are involved: Step S1: Establish fatigue limit state equation; Step S2: Determine the type of construction details; Step S3: Obtaining structural detail stress spectrum; Step S4: determining a construction detail cutoff threshold; Step S5: fitting the stress spectrum using a probability density function according to the cutoff threshold; Step S6: Calculate the mean and standard deviation of the equivalent stress amplitude; Step S7: determining the number of equivalent stress amplitude cycles; Step S8: Calculate fatigue reliability index; Step S9: predicting fatigue life; Among them, the method for determining the construction detail cutoff threshold is: According to the preset cutoff threshold, the equivalent stress amplitude ΔS is calculated eq And the corresponding stress amplitude cycles: In the formula, ΔS i and n i are the structural detail stress amplitude and the number of cycles respectively; m is the material constant; Then, the scatter points consisting of multiple groups of equivalent stress amplitudes and the corresponding stress amplitude cycle numbers are plotted in a double logarithmic coordinate system, and the corresponding SN curve is plotted to observe the positional relationship between the scatter points and the SN curve. For the points where the scatter point trend is parallel to the slope of the SN curve, it means that the truncation threshold value of the scatter point has no effect on the fatigue life assessment of the structural details, and is used as the value of the truncation threshold. At the same time, the scatter points consisting of the truncation threshold and the fatigue life are plotted in a Cartesian rectangular coordinate system, and the range of the truncation threshold value when the fatigue life does not change can also be obtained. Among them, the probability density function is used to fit the measured stress spectrum, and then the equivalent stress amplitude is predicted based on the fitted probability density function. This can take into account the distribution of future traffic loads in the high stress amplitude area and improve the accuracy of fatigue life prediction.

2. A fatigue reliability analysis method based on truncation threshold probability modeling according to claim 1, characterized in that: The method to establish the fatigue limit state equation is: The limit state function represented by two random variables, structural fatigue resistance and action effect, is: g(X)=RS Where R represents the fatigue resistance of the structure, S represents the structural effect, and X is a random variable.

3. The fatigue reliability analysis method based on truncation threshold probability modeling according to claim 1 is characterized in that: The method to determine the type of construction detail is: According to the fatigue design specification, the structural detail level is determined, and the value of the fatigue detail constant A, the cumulative damage critical value Δ, and the corresponding probability statistics of each parameter are obtained, including the mean μ and the coefficient of variation δ s .

4. The fatigue reliability analysis method based on truncation threshold probability modeling according to claim 1 is characterized in that: The method to obtain the structural detail stress spectrum is: Based on the on-site stress monitoring data, the rainflow counting method is used to obtain the stress spectrum of the structural details under random loads, and the stress amplitude below the preset value is set to be ignored in the rainflow counting method.

5. The fatigue reliability analysis method based on truncation threshold probability modeling according to claim 1 is characterized in that: The method for calculating the mean and standard deviation of the equivalent stress amplitude is: According to the probability density function f(x) fitted at different cutoff thresholds, the equivalent stress amplitude over the entire life span is calculated. Where x is the stress amplitude variable; Based on the calculated equivalent stress amplitude, the mean and standard deviation of the equivalent stress amplitude are calculated.

6. The fatigue reliability analysis method based on truncation threshold probability modeling according to claim 1 is characterized in that: The method for determining the number of equivalent stress amplitude cycles is: According to Miner's linear cumulative damage criterion, the corresponding number of cycles was calculated based on the average value of the equivalent stress amplitude.

7. The fatigue reliability analysis method based on truncation threshold probability modeling according to claim 1 is characterized in that: The method for calculating fatigue reliability index is: After determining the probability and statistical parameters of all random variables, the fatigue reliability index β is calculated: β=Φ -1 (1-P f )=-Φ -1 (P f ) In the formula, Φ -1 is the inverse function of the standard normal distribution, P f is the failure probability of a structure or system.

8. The fatigue reliability analysis method based on truncation threshold probability modeling according to claim 1 is characterized in that: The method to predict fatigue life is: Select the target reliability index according to the design specifications and the importance of the project, and calculate the time when the reliability index in the previous step reaches the target value.

9. A fatigue reliability analysis system based on truncation threshold probability modeling using the fatigue reliability analysis method according to any one of claims 1 to 8, characterized in that: include: Equation building module, used to build fatigue limit state equation; A detail determination module, used to determine the type of construction details; Stress spectrum acquisition module, used to obtain structural detail stress spectrum; A threshold determination module, used to determine a construction detail cutoff threshold; A stress spectrum fitting module, used to fit the stress spectrum using a probability density function according to the cutoff threshold; The first calculation module is used to calculate the mean and standard deviation of the equivalent stress amplitude; A cycle determination module, used to determine the number of equivalent stress amplitude cycles; The second calculation module is used to calculate the fatigue reliability index; Fatigue prediction module, used to predict fatigue life.

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