Method for evaluating residual mechanical performance of steel structure considering strain aging of steel material

Abstract

The application discloses a kind of steel structure residual mechanical property evaluation methods based on steel strain aging, it is related to material mechanics technical field.The application is with the mechanical property change that steel material experiences plastic damage and reflects, namely steel strain aging effect as core, engineering stress-engineering strain curve of steel material under different strain aging conditions is tested using two-stage test method, and the evolution equation of steel strain aging mechanical property index with plastic damage degree and its constitutive model are established.Based on strain aging mechanical property constitutive model, two-stage numerical simulation method is used to carry out fine numerical analysis on the residual mechanical property of steel structure with plastic damage.The technical bottleneck of traditional finite element analysis in the coupling processing of plastic damage and strain aging effect is broken through, and a reliable quantitative evaluation method is provided for the residual mechanical property evaluation of steel material after experiencing plastic damage.The application relates to steel structure residual mechanical property evaluation method and has wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of materials mechanics, and in particular to a method for evaluating the residual mechanical properties of steel structures that takes into account the strain aging of steel. Background Technology

[0002] During long-term service, steel structures are highly susceptible to typhoons, earthquakes, fires, and impact loads, leading to localized plastic damage. After a period of time, their mechanical properties change significantly due to strain aging, primarily manifested as increased yield strength and yield-to-ultimate strength ratio, significantly decreased ultimate strain and strain-hardening strain, and decreased ductility. This severely impacts the overall mechanical and ductile properties of the steel structure. Establishing a numerical analysis and evaluation system for steel structures and components considering strain-aged mechanical property changes has significant engineering practical value for the scientific assessment of damaged steel structures and the design for their reuse.

[0003] Current steel structure mechanical performance evaluation systems are primarily based on experimental and numerical analysis methods. Traditional experimental methods are mainly used to evaluate the mechanical properties of steel structures throughout their entire life cycle, but they cannot account for changes in mechanical properties caused by strain aging during service. Figure 1 The mechanical properties of strain-aged steel and steel-concrete composite beams reveal that the mechanical analysis methods established based on traditional experiments will have systematic biases in predicting the remaining load-bearing capacity of steel structures throughout their entire life cycle: they underestimate the changes in mechanical properties caused by strain aging throughout the life cycle of steel structures and overestimate the ductility reserve of strain-aged steel structures. Similarly, for steel structures in service, it is difficult to meet the conditions for conducting on-site mechanical performance tests on their important supporting components, and there is a lack of reliable basis for quantitative assessment of their remaining load-bearing capacity. Even if the local structure meets the conditions for sampling tests, its mechanical properties cannot fully characterize the true mechanical state of the component level or even the overall structure, resulting in significant uncertainty in the assessment of the remaining mechanical properties of steel structure systems with localized plastic cumulative damage.

[0004] The accuracy of traditional numerical analysis methods depends on the accuracy of steel constitutive parameters. However, after strain aging, the mechanical properties of steel undergo irreversible evolution, leading to bottlenecks in the assessment of the residual mechanical properties of partially damaged steel structures. These bottlenecks are mainly reflected in: (1) limitations in obtaining material parameters: key mechanical performance indicators of steel structures after a disaster (such as yield strength and ductility coefficient) are difficult to quantify accurately through in-situ testing; (2) limitations of steel constitutive models: existing steel constitutive models fail to fully consider the dynamic evolution characteristics of stress-strain relationships caused by strain aging; (3) significant scale effects: even if the components meet the conditions for obtaining local mechanical parameters through sampling tests, the spatial non-uniformity of strain gradient effects during plastic deformation leads to obvious regional differences in strain aging hardening, and local test data cannot accurately characterize the time-varying mechanical behavior of the overall structure. These technical defects directly result in a lack of reliable characterization methods for the evolution of mechanical properties of steel structures after a disaster. It is difficult to accurately predict the residual mechanical properties and ductility of steel structures throughout their entire life cycle using single-stage numerical analysis methods, which seriously restricts the accuracy of the assessment of the residual mechanical properties of steel structures after a disaster. Summary of the Invention

[0005] In view of this, and considering the significant technical bottlenecks of traditional numerical analysis methods in coupling plastic damage and strain aging effects, this invention innovatively provides a method for evaluating the residual mechanical properties of steel structures and components after experiencing extreme loads such as typhoons, earthquakes, fires, and impacts.

[0006] Embodiments of the present invention provide a method for evaluating the residual mechanical properties of steel structures considering strain aging, comprising the following steps:

[0007] S1. A two-stage test considering strain aging effects is conducted on the steel specimens. The first stage involves applying a pre-strain load to the steel specimens to simulate the load response characteristics and local plastic strain distribution of the steel structure throughout its entire life cycle. The steel specimens that have already suffered plastic damage are then subjected to aging treatment at room temperature to characterize the aging evolution process of the steel structure during the repair and reuse cycle. The second stage involves conducting quasi-static tensile tests on the steel specimens that have undergone strain aging treatment until they reach the ultimate bearing capacity state, and obtaining the engineering stress-engineering strain curves of the steel specimens after strain aging.

[0008] S2. Based on the engineering stress-engineering strain curve of steel after strain aging, extract the strain-aged mechanical property parameters of steel: yield strength f. y,SA Ultimate strength f u,SA strain hardening strain ε sh,SA Ultimate strain ε u,SA Introducing the strain aging influence factor ψi A quantitative relationship between strain aging influencing factors and pre-strain is established to obtain the evolution law of strain-aged steel mechanical properties with plastic damage level. Based on this, combined with the theoretical framework of the three-stage steel constitutive model, a strain-aged mechanical property constitutive model is established.

[0009] S3. Create a two-stage refined finite element model that considers the strain aging effect. First, create a first finite element model according to different steel structure dimensions, and apply boundary conditions according to the actual load of the target steel structure to simulate the local plastic damage distribution of the steel structure, track the equivalent plastic strain at the integration point, and record the historical maximum equivalent plastic strain at each integration point.

[0010] S4. Establish a second finite element model with the same geometry and boundary conditions as the first finite element model. Transfer the maximum plastic strain history of each integration point in the first finite element model to the second finite element model and use it as the initial state of the model. Update the steel constitutive relation in the second finite element model to a strain-aged mechanical property constitutive model. Dynamically update the material property parameters according to the plastic damage model, i.e., the equivalent plastic strain in the second model. Apply boundary conditions to simulate the residual mechanical properties of the target steel structure after strain aging.

[0011] Furthermore, the constitutive model for the evolution of time-varying mechanical properties in step S2 is as follows:

[0012]

[0013] Wherein, model parameter A i B i C i Quantitative relationship with pre-strain level

[0014] A i =a1ε pre +a2 (2)

[0015] B i =b1ε pre +b2 (3)

[0016] C i =c1ε pre +c2 (4)

[0017] Among them, A i B i C i These are model parameters; subscript i represents the pre-strain value; subscript i represents the pre-strain value; a1, a2, b1, b2, c1, c2 are correction coefficients; ε preThe pre-strain level is represented by the subscript SA, which indicates the mechanical properties of the steel after strain aging. The relationship between SA and the strain aging factor and the initial mechanical properties of the steel is as shown in equation (5):

[0018] χ SA,i =ψ i χ0 (5)

[0019] Where: χ SA,i χ0 represents the mechanical properties of the steel after standard aging; χ0 represents the initial mechanical properties of the steel; ψ is the strain aging factor, and its expression is shown in equation (6):

[0020] ψ i =χ SA,i / χ0 (6)

[0021] Furthermore, in step S1, different pre-strains are applied to the steel sample to simulate the magnitude of plastic damage to the steel structure under actual load conditions.

[0022] Furthermore, the level of pre-strain is lower than 50% of the ultimate strain of the steel.

[0023] Furthermore, the aging period set in step S1 is 7, 14, 30, 90, or 180 days, which is used to characterize the repair and reuse cycle experienced by the steel structure after plastic damage.

[0024] Furthermore, the method for obtaining the residual mechanical properties of the steel sample after catastrophic failure in step S1 is as follows: measure the cross-sectional dimensions of the steel sample after strain aging, stretch the strain-aged steel sample until it breaks, and obtain the residual stress-strain curve of the steel sample after strain aging.

[0025] Furthermore, in step S3, boundary conditions are applied to the first finite element model according to the actual load conditions of the target steel structure, and numerical calculations are performed to record the plastic strain history of the steel structure and obtain the maximum equivalent plastic strain of the target steel structure, i.e., the maximum plastic damage.

[0026] Furthermore, both the first finite element model and the second finite element model were constructed using Abaqus finite element analysis software.

[0027] Furthermore, in step S1, the plastic damage occurring in the steel sample includes cyclic plastic damage caused by low-cycle and ultra-low-cycle fatigue.

[0028] The beneficial effects of the technical solutions provided by the embodiments of the present invention are as follows:

[0029] 1. This invention provides a method for evaluating the residual mechanical properties of steel structures considering strain aging. The method first simulates plastic damage occurring during service by applying a pre-strain load to steel samples, then loads the samples to their ultimate bearing capacity to obtain post-catastrophic residual mechanical property parameters; subsequently, it establishes a strain-aged constitutive model of the steel's mechanical properties considering plastic damage parameters. This method innovatively employs a two-stage finite element model to introduce the strain aging effect: the first finite element model simulates the load response of the target steel structure and the distribution of local plastic deformation within the steel structure throughout its entire lifespan; the second finite element model, based on historical plastic strain data, introduces a strain-aged constitutive model and dynamically updates material parameters to simulate the residual mechanical properties of the steel structure after strain aging, achieving accurate numerical analysis of the residual mechanical properties of the steel structure after a catastrophic event.

[0030] 2. This invention provides a method for evaluating the residual mechanical properties of steel structures considering strain aging. It innovatively employs restart technology to construct a two-stage numerical simulation system, solving the technical challenge of coupling plastic damage and strain aging effects in traditional finite element methods. This enables accurate evaluation of the residual load-bearing capacity of steel structures after disasters. This method is particularly suitable for evaluating the residual mechanical properties of steel structures after disasters, providing a scientific basis for the reinforcement and renovation of existing steel structures and the reuse of materials. It is of great significance for improving the accuracy of life-cycle performance evaluation of steel structures. Attached Figure Description

[0031] Figure 1 This is a diagram showing the changes in the mechanical properties of steel and components after strain aging in the background technology.

[0032] Figure 2 This is a schematic diagram of the principle of a method for evaluating the residual mechanical properties of steel structures that takes into account the strain aging of steel, according to the present invention.

[0033] Figure 3 This is a graph showing the effect of strain aging on the stress-strain curve of Q355D steel.

[0034] Figure 4 This is a schematic diagram of the mechanical properties of steel under strain.

[0035] Figure 5 This is a schematic diagram of the time-varying mechanical property evolution constitutive model TMSA for steel;

[0036] Figure 6 Evolution equation of TMSA model parameters with prestrain load level;

[0037] Figure 7 Evolution equation of the mechanical performance factor of steel under strain with pre-strain load level;

[0038] Figure 8This is a comparison chart of the constitutive model predictions and experimental results for the evolution of time-varying mechanical properties of steel considering the effects of strain aging.

[0039] Figure 9 This is a comparison chart of the load-displacement curves of the steel-concrete composite beam under experimental loading and simulation by the first finite element model.

[0040] Figure 10 This is a local plastic strain distribution diagram of a steel-concrete composite beam under 70% ultimate bearing capacity load;

[0041] Figure 11 It is a contour plot of the maximum equivalent plastic strain imported into the second finite element model;

[0042] Figure 12 This is a comparison chart of load-displacement curves from strain-aged steel-concrete composite beam tests and calculations from the second finite element model after applying 70% ultimate load. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings. The following description presents a preferred embodiment of the various possible embodiments of the present invention, intended to provide a basic understanding of the invention, but not intended to identify key or decisive elements of the invention or to limit the scope of protection sought.

[0044] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0045] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0046] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures. Also, it should be understood that, for ease of description, the dimensions of the various parts shown in the figures are not drawn to actual scale.

[0047] Please refer to Figure 2 The embodiments of the present invention provide a method for evaluating the residual mechanical properties of steel structures considering the strain aging of steel, including steps S1-S4.

[0048] S1. A two-stage test considering strain aging effects is conducted on the steel specimens. The first stage involves applying a pre-strain load to the steel specimens to simulate the load response characteristics and local plastic strain distribution of the steel structure throughout its entire life cycle. The steel specimens that have already suffered plastic damage are then subjected to aging treatment at room temperature for the target period to characterize the aging evolution process of the steel structure during the repair and reuse cycle. The second stage involves conducting a quasi-static tensile test on the aging treated steel specimens until the ultimate bearing capacity is reached, and obtaining the engineering stress-engineering strain curves of the steel specimens after strain aging.

[0049] In the first stage, pre-strain loads are applied to steel specimens and aged to the target period to simulate the plastic damage that occurs in steel during service. By varying the level of pre-strain load applied to the steel specimens, the degree of plastic damage to the steel structure after a disaster is simulated.

[0050] In this embodiment, standard tensile specimens and test loading regimes were prepared according to GB / T 228.1-2021 "Metallic materials, tensile testing—Part 1: Test at room temperature," and the standard tensile specimens were used as steel samples. Two-stage monotonic tensile mechanical property tests were conducted based on the plastic damage level and aging period parameters. The specimen cross-sectional diameter was measured, a 50mm extensometer was selected, and the MTS tensile-torsional fatigue testing loading system was used for the test loading.

[0051] Considering that the strain hardening phenomenon and ductility of steel disappear when the pre-strain level exceeds 0.5 times the ultimate strain, the steel can only be designed in the elastic stage at this point. The pre-strain level should not exceed half of the steel's ultimate strain; a pre-strain level of 0.1ε is generally chosen. u ,0.2ε u ,0.3ε u ,0.4ε u 0.5ε u , where ε u This represents the ultimate strain of the steel. As in this embodiment, the target pre-strain value ε is applied to the standard tensile specimen. pre The target prestrain values ​​are selected as 2%, 3%, 4%, 6%, and 8% prestrain levels.

[0052] After loading the standard tensile specimen to the target pre-strain level, the test loading is paused, and the load is unloaded at a uniform rate according to the test loading rate until the load is 0. The standard tensile specimen is then removed, and the standard tensile specimen with plastic damage is aged at room temperature for the set period.

[0053] refer to Figure 3The diagram showing the effect of strain aging on the stress-strain curve of Q355D steel reveals significant differences in the engineering stress-strain curve and parameters of steel without strain aging compared to those with strain aging. The mechanical property characteristics of strain-aged steel, such as yield strength, ultimate strength, strain hardening strain, and ultimate strain, exhibit regular changes with the pre-strain parameter. Compared to the aging period parameter, the mechanical property parameters of strain-aged steel are more sensitive to the pre-strain level. When the aging period exceeds 90 days, ignoring the effect of aging time has a relatively small impact on the assessment of mechanical properties. Considering that the evolution of steel mechanical properties over time mainly occurs before 90 days, and the effect of strain aging on mechanical properties after 90 days can be ignored, the aging period is generally set to 7, 14, 30, 90, or 180 days.

[0054] During the first stage of the test loading process, the initial plastic damage of the steel specimen is not limited to the strain aging effect caused by tensile plastic damage, but also includes cyclic plastic damage caused by low-cycle and ultra-low-cycle fatigue.

[0055] During the second stage of the test loading process, after the standard tensile specimen has been aged to the set period, the cross-sectional dimensions of the strain-aged steel specimen are measured. The strain-aged steel specimen is then stretched until fracture to obtain the engineering stress-engineering strain test parameters of the strain-aged steel. For example... Figure 4 As shown, the mechanical properties of strain-induced biomechanical stress mainly include yield strength, ultimate strength, strain hardening strain, and ultimate strain.

[0056] S2. Based on the engineering stress-engineering strain curve of steel after strain aging, extract the strain-aged mechanical property parameters of steel: yield strength f. y,SA Ultimate strength f u,SA strain hardening strain ε sh,SA Ultimate strain ε u,SA Introducing the strain aging influence factor ψ i A quantitative relationship between the strain aging influencing factor and the pre-strain is established to obtain the evolution law of the mechanical properties of strain-aged steel with the level of plastic damage. Based on this, combined with the theoretical framework of the three-stage steel constitutive model, a strain-aged mechanical property constitutive model considering the strain aging effect of steel is established.

[0057] The residual mechanical property parameters, including yield strength, ultimate strength, strain hardening strain, and ultimate strain, are extracted from the residual stress-strain curve of the steel specimen after strain aging. Based on the mechanical property parameters of the unstrain-aged steel, the mechanical property parameters of the strain-aged steel are normalized.

[0058] Establish a constitutive model of steel's mechanical properties under strain: Using regression analysis, a constitutive model of steel's mechanical properties under strain considering different damage levels is established.

[0059] Considering the significant changes in strain hardening strain and strain hardening modulus of steel after strain aging, parameter A is introduced into the classic three-stage steel constitutive model. i B i and C i This is used to characterize the evolution of strain hardening characteristics in the stress-strain curve of steel after strain aging. Regression analysis is employed to establish the model parameters A. i B i and C i The relationship between the strain and plastic damage level was investigated, and a time-varying mechanical property evolution constitutive model (TMSA) for steel that takes into account the effects of strain aging was determined.

[0060] The specific constitutive model for the evolution of mechanical properties of steel over strain time, TMSA, is as follows:

[0061]

[0062] Wherein, model parameter A i B i C i Quantitative relationship with pre-strain level

[0063] A i =a1ε pre +a2 (2)

[0064] B i =b1ε pre +b2 (3)

[0065] C i =c1ε pre +c2 (4)

[0066] Among them, A i B i C i These are model parameters; the subscript i represents the pre-strain value; a1, a2, b1, b2, c1, and c2 are correction coefficients; ε pre The pre-strain level is represented by the subscript SA, which indicates the mechanical properties of the steel after strain aging. The relationship between SA and the strain aging factor and the initial mechanical properties of the steel is as shown in equation (5):

[0067] χ SA,i =ψ i χ0 (5)

[0068] Where: χ SA,i This indicates the mechanical properties of steel after strain aging, such as the yield strength f of steel after strain aging. y,SA Ultimate strength f u,SA , strain hardening strain εsh,SA Ultimate strain ε u,SA ; χ0 represents the initial mechanical properties of the steel, i.e., the case where the pre-strain value i = 0 in the above formula; ψ i The strain aging factor is expressed as shown in equation (6):

[0069] ψ i =χ SA,i / χ0 (6)

[0070] The strain-time mechanical property constitutive model TMSA proposed in this invention only requires input of basic mechanical property indices of unaged steel, such as yield strength f. y,0 Elastic modulus E, ultimate strength f u,0 and prestrain level ε pre This allows for accurate prediction of the residual mechanical properties and constitutive model parameters A of steel after strain aging. i B i and C i Based on the experimental results, the constitutive model parameters A were obtained using regression analysis. i B i and C i With the evolution equation of prestrain as follows Figure 6 As shown, the evolution equation of the strain aging factor with pre-strain load is determined using the least squares method, as follows: Figure 7 As shown, according to equations (5) to (6), the evolution law of the mechanical properties of the strain time with the pre-strain level is determined by the initial basic mechanical property parameters of the steel and the strain aging factor, and then the steel constitutive model TMSA considering the plastic damage level is determined. Figure 8 The comparison between the strain-age stress-strain curve predicted by TMSA and the experimental curve shows that the TMSA model prediction results are in good agreement with the experimental curve, indicating that the strain-age mechanical performance constitutive model proposed in this invention can accurately predict the engineering stress-engineering strain curve of steel after strain aging.

[0071] This embodiment lists the nominal yield strength f. y The strain-time biomechanical property constitutive model (TMSA) for ordinary strength steel with a strength ≤460MPa is shown in the table below:

[0072] Table 1. Parameter Expressions of the TMSA Mechanical Constitutive Model

[0073]

[0074] S3. Create a two-stage refined finite element model that considers the strain aging effect. First, create a first finite element model based on different steel structure dimensions, and apply boundary conditions according to the actual load conditions of the target steel structure to simulate the local plastic damage distribution of the steel structure, track the equivalent plastic strain at the integration point, and record the historical maximum equivalent plastic strain at each integration point.

[0075] The target steel structure is an in-service steel structure that requires residual mechanical performance evaluation. In this embodiment, the target steel structure is selected as a steel-concrete composite beam. Based on the actual geometric dimensions, boundary conditions, and initial mechanical properties of the steel-concrete composite beam, a first finite element model is established using Abaqus finite element analysis software.

[0076] A comparison of the load-displacement curves obtained from the four-point bending test loading of a steel-concrete composite beam and the two-stage finite element simulation method based on the steel constitutive model (TMSA) considering strain aging effects is shown below. Figure 9 As shown, the two match well, indicating that the established first finite element model is accurate and meets the accuracy requirements. Figure 10 The local plastic strain distribution diagram of the steel-concrete composite beam shown indicates that at 70% ultimate bearing capacity F... u Under load, the steel exhibits localized plastic damage with a non-uniform distribution.

[0077] In the first finite element model, boundary conditions were applied according to the actual loading conditions of the steel-concrete composite beam. The USDFLD subroutine-1 was used to track the equivalent plastic strain (PEEQ) at the integration points in real time, and the historical maximum equivalent plastic strain (PEEQ value) at each integration point was recorded. The load response and local plastic damage distribution of the target steel structure under extreme working conditions were obtained.

[0078] S4. Establish a second finite element model with the same geometry and boundary conditions as the first finite element model. Transfer the maximum plastic strain history of each integration point in the first finite element model to the second finite element model and use it as the initial state of the model. Update the steel constitutive relation in the second finite element model to a strain-aged mechanical property constitutive model. Dynamically update the material property parameters according to the plastic damage model, i.e., the equivalent plastic strain in the second model. Apply boundary conditions to simulate the residual mechanical properties of the target steel structure after strain aging.

[0079] The second finite element model was also established using Abaqus finite element analysis software, and its dimensions, initial boundary conditions, mesh, and element numbering were consistent with the first finite element model. Utilizing the ABAQUS two-stage restart-user-defined field variable coupling technique, the maximum plastic strain history from the first finite element model of the steel-concrete composite beam was transferred to the second finite element model, as follows: Figure 11As shown, based on the established steel strain-time mechanical property evolution constitutive model TMSA, the mechanical property parameters of the steel after strain aging are dynamically updated according to the maximum equivalent plastic strain PEEQ value through the USDFLD subroutine-2. By applying load to the second finite element model of the steel-concrete composite beam, the residual mechanical properties of the steel-concrete composite beam after strain aging are simulated, thus realizing the complete chain of numerical analysis from pre-strain history inheritance to dynamic correction of strain aging effect to secondary response analysis of structure.

[0080] A comparison of the strain-aging load-displacement curves output from the second finite element model of the steel-concrete composite beam with the strain-aging test curves of the steel-concrete composite beam is shown below. Figure 12 As shown, the two-stage finite element numerical analysis method based on the TMSA constitutive model can accurately characterize the influence of strain aging on the ultimate bearing capacity and deformation performance of steel-concrete composite beams. This demonstrates that the numerical analysis method for residual mechanical properties of steel structures considering strain aging proposed in this invention can accurately characterize the residual mechanical properties and deformation performance of steel structures after a catastrophic event.

[0081] Where there is no conflict, the embodiments and features described above can be combined with each other. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for evaluating the residual mechanical properties of steel structures considering strain aging, characterized in that, Includes the following steps: S1. A two-stage test considering strain aging effects is conducted on the steel specimens. The first stage involves applying a pre-strain load to the steel specimens to simulate the load response characteristics and local plastic strain distribution of the steel structure throughout its entire life cycle. The steel specimens that have already suffered plastic damage are then subjected to aging treatment at room temperature to characterize the aging evolution process of the steel structure during the repair and reuse cycle. The second stage involves conducting quasi-static tensile tests on the steel specimens that have undergone strain aging treatment until they reach the ultimate bearing capacity state, and obtaining the engineering stress-engineering strain curves of the steel specimens after strain aging. S2. Based on the engineering stress-engineering strain curve of steel after strain aging, extract the strain-aged mechanical property parameters of steel: yield strength f. y,SA Ultimate strength f u,SA strain hardening strain ε sh,SA Ultimate strain ε u,SA Introducing the strain aging influence factor ψ i A quantitative relationship between strain aging influencing factors and pre-strain is established to obtain the evolution law of strain-aged steel mechanical properties with plastic damage level. Based on this, combined with the theoretical framework of the three-stage steel constitutive model, a strain-aged mechanical property constitutive model is established. S3. Create a two-stage refined finite element model that considers the strain aging effect. Create the first finite element model according to the geometric dimensions of the steel structure, and apply boundary conditions according to the actual load of the target steel structure to simulate the local plastic damage distribution of the steel structure, track the equivalent plastic strain at the integration point, and record the historical maximum equivalent plastic strain at each integration point. S4. Establish a second finite element model with the same geometry and boundary conditions as the first finite element model. Transfer the maximum plastic strain history of each integration point in the first finite element model to the second finite element model and use it as the initial state of the model. Update the steel constitutive relation in the second finite element model to a strain-aged mechanical property constitutive model. Dynamically update the material property parameters according to the plastic damage model, i.e., the equivalent plastic strain in the second model. Apply boundary conditions to simulate the residual mechanical properties of the target steel structure after strain aging.

2. The method for evaluating the residual mechanical properties of steel structures considering strain aging as described in claim 1, characterized in that: The strain-time biomechanical performance constitutive model in step S2 is as follows: Wherein, model parameter A i B i C i Quantitative relationship with pre-strain level A i =a1ε pre +a2 (2) B i =b1ε pre +b2 (3) C i =c1ε pre +c2 (4) Among them, A i B i C i These are model parameters; the subscript i represents the pre-strain value; a1, a2, b1, b2, c1, and c2 are correction coefficients; ε pre The pre-strain level is represented by the subscript SA, which indicates the mechanical properties of the steel after strain aging. The relationship between SA and the strain aging factor and the initial mechanical properties of the steel is as shown in equation (5): x SA,i =ψ i x0 (5) Where: χ SA,i χ0 represents the mechanical properties of the steel after aging; χ0 represents the initial mechanical properties of the steel; ψ i The strain aging factor is expressed as shown in equation (6): ψ i =x SA,i / x0 (6).

3. The method for evaluating the residual mechanical properties of steel structures considering strain aging as described in claim 1, characterized in that: In step S1, different pre-strain loads are applied to the steel samples to simulate the degree of plastic damage to the steel structure under actual load conditions.

4. The method for evaluating the residual mechanical properties of steel structures considering strain aging as described in claim 3, characterized in that: The level of pre-strain is less than 50% of the ultimate strain of the steel.

5. The method for evaluating the residual mechanical properties of steel structures considering strain aging as described in claim 1, characterized in that: The aging period set in step S1 is 7, 14, 30, 90, and 180 days, which are used to characterize the repair and reuse cycle of steel structures after plastic damage.

6. The method for evaluating the residual mechanical properties of steel structures considering strain aging as described in claim 1, characterized in that: The method for obtaining the residual mechanical properties of the steel sample after the catastrophic event in step S1 is as follows: measure the cross-sectional dimensions of the steel sample after strain aging, stretch the strain-aged steel sample until it breaks, and obtain the residual engineering stress-engineering strain curve of the steel sample after strain aging.

7. The method for evaluating the residual mechanical properties of steel structures considering strain aging as described in claim 1, characterized in that: In step S3, boundary conditions are applied to the first finite element model according to the actual load conditions of the target steel structure, and numerical calculations are performed to record the plastic strain history of the steel structure and obtain the maximum equivalent plastic strain of the target steel structure, i.e., the maximum plastic damage.

8. The method for evaluating the residual mechanical properties of steel structures considering strain aging as described in claim 1, characterized in that: Both the first and second finite element models were constructed using Abaqus finite element analysis software.

9. The method for evaluating the residual mechanical properties of steel structures considering strain aging as described in claim 1, characterized in that: In step S1, the plastic damage occurring in the steel sample includes cyclic plastic damage caused by low-cycle and ultra-low-cycle fatigue.

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