Load test-oriented road box culvert multi-scale finite element simulation method

Abstract

The invention provides a load test-oriented road box culvert multi-scale finite element simulation method, and relates to the technical field of structural engineering and finite element analys.The load test is simulated by establishing a three-dimensional geometric model of a box culvert to determine a key stress area, and a concrete-steel bar full-scale model is constructed; relative displacement changes of concrete and reinforcing steel bars under different loads are simulated, a material strength degradation empirical formula is established, a local fine model is constructed in a key area, a polynomial coupling degradation relation model is used for correction, then a maximum stress surface is determined, and a safety index is defined by combining a principal stress value of the maximum stress surface and the corrected material strength. And the failure probability is calculated through Monte Carlo simulation, so that the safety index is dynamically adjusted, and the load test requirement is met. According to the method, dynamic evaluation and optimization of the safety index of the road box culvert are realized by building the concrete-reinforcement model and analyzing environmental degradation.

Description

Technical Field

[0001] The present invention relates to the technical field of structural engineering and finite element analysis, and in particular to a multi-scale finite element simulation method for road box culverts oriented to load tests. Background Art

[0002] Road box culverts are important structures in civil engineering. They are usually used to cross water bodies or other obstacles under transportation facilities such as roads and railways. Their design and safety are directly related to the smoothness and safety of traffic. Finite element analysis is a powerful computational tool widely used in structural engineering to simulate the behavior of complex structures under various loads. By dividing the structure into a finite number of small units, responses such as stress, strain, and displacement can be efficiently analyzed. Due to the different specific scenarios in which road box culverts are used, their relative environments are also different, which will cause the material strength of the box culvert to change under the influence of different environmental factors. This change is often ignored in traditional global finite element analysis, and it is difficult to capture the impact of local structures on overall performance. How to apply multi-scale finite element simulation results, simulate material strength degradation, and optimize structural design to meet safety and economic requirements in the design stage is an urgent problem to be solved.

[0003] In the existing technology, traditional global finite element analysis is unable to accurately simulate the response of road box culverts under various loads and boundary conditions when faced with the complex structure of road box culverts, especially the stress distribution and deformation behavior in key areas. It is also easy to ignore the degradation of material strength in local key areas of the box culvert under the influence of different environmental factors, and fails to effectively establish a material strength degradation model, resulting in the inability to accurately evaluate the long-term performance of the structure in practical applications.

[0004] In addition, traditional finite element simulation methods lack a dynamic adjustment mechanism when evaluating safety. They often only use a single box culvert performance indicator combined with a corresponding preset threshold to determine whether a road box culvert has failed. They are unable to make timely corrections based on actual load conditions and changes in material strength, which makes the safety assessment inaccurate.

[0005] Therefore, it is necessary to provide a multi-scale finite element simulation method for road box culverts oriented to load tests to solve the above problems.

[0006] The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0007] The purpose of the present invention is to provide a multi-scale finite element simulation method for road box culverts for load testing to solve the problems raised in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solutions: A multi-scale finite element simulation method for road box culverts for load testing, including the following steps: Step 1: Based on the box culvert's dimensions and material properties, a 3D geometric model of the box culvert was constructed using CAD software. The model was then divided into grid units and simulated load tests were conducted to identify the critical areas of the box culvert. Step 2: Based on the design specifications for road box culverts and the material strength data for concrete and steel, a full-scale concrete-steel model was constructed and meshed to simulate the relative displacement changes between concrete and steel in the box culvert under different road loads. The full-scale concrete-steel model used a composite material constitutive model. Step 3: Identify environmental factors, including temperature, humidity, and chemical corrosion, and establish empirical formulas for the material strength degradation of concrete and steel under these three different environmental factors. Based on these formulas, construct a local fine model in the key areas of the box culvert. The local fine model uses a polynomial coupling degradation relationship model. Step 4: Introduce the box culvert material strength after correction by the local fine model into the full-scale model, and perform a comprehensive finite element analysis based on the full-scale model to determine the maximum stress-bearing surface in the key area of ​​the box culvert; Step 5: Set the safety threshold for the simulated load test. Define the safety index of the box culvert based on the principal stress value in the maximum load-bearing surface combined with the corrected material strength of the box culvert. Define a performance function and use the Monte Carlo simulation method to calculate the failure probability of the maximum load-bearing surface. Based on the failure probability of the maximum load-bearing surface, dynamically adjust the safety index until the load test requirements are met.

[0009] Furthermore, a three-dimensional geometric model of the box culvert is established to determine the key areas of the box culvert based on the following method: Based on the specific dimensions of the box culvert, computer-aided CAD design software was used to establish a three-dimensional geometric model of the box culvert. The specific dimensions included the length, width, height, bottom plate thickness, top plate thickness, and side wall thickness. The model was used to simulate the various components of the box culvert, including the culvert body, bottom plate, top plate, side walls, and connections. The three-dimensional geometric model of the box culvert was divided into multiple tetrahedral grid units with a side length of 10mm*10mm*10mm. The standard load required for the box culvert test was set, and load simulation experiments were performed on each tetrahedral grid of the box culvert. Obtain the eight vertex positions and displacement of each vertex of each tetrahedral grid unit under the action of standard road load, calculate the displacement difference between adjacent vertices, and thus obtain the relative displacement. Then use these relative displacements and the distance between the original vertices to calculate the local strain of each pair of adjacent vertices, integrate the strain information of all adjacent nodes into a strain matrix, and convert the strain into local stress through the constitutive relationship of the material. Finally, all local stresses are summarized to form the effective stress field of the tetrahedral grid unit, and the overall stress of the tetrahedral grid unit is obtained. , the total stress of each tetrahedral mesh element in the three-dimensional geometric model of the box culvert is With the preset stress threshold By comparison, the area connected by tetrahedral grid cells exceeding the stress threshold is marked as the critical area of ​​the box culvert.

[0010] Furthermore, a full-scale concrete-rebar model was constructed and meshed to simulate the relative displacement changes between concrete and steel in the box culvert under different loads. The method used is as follows: Material strength data for concrete and steel bars were collected separately. The full-scale concrete-steel model adopted the constitutive model of composite materials. A compression constitutive model was used for concrete to simulate the nonlinear behavior of concrete under compression loads, and a tensile softening linear model was used for steel bars to describe their tensile failure behavior. The simulated loads determined by the experiment were input into the full-scale model, and the full-scale concrete-steel model was divided into tetrahedral mesh elements. The strains of concrete and steel bars in compression and tension in each tetrahedral mesh element were obtained using finite element analysis software. The logical expression of the nonlinear constitutive model of concrete for each tetrahedral mesh element is as follows: ; in, Indicates the The stress of concrete in tetrahedral grid elements, is the maximum compressive strength of concrete, is the maximum tensile strength of concrete, The concrete is in compression The strain of a tetrahedral mesh element, The concrete is in tension The strain of a tetrahedral mesh element, is the maximum strain value that concrete can withstand under compression, is the maximum strain that concrete can withstand under tension. Indicates the material strength of concrete; The logical expression of the linear elastic constitutive law of steel bars of each tetrahedral mesh element is as follows: ; in, Indicates the The stress of the steel bar in the tetrahedral mesh element is is the elastic modulus of the steel bar, The first time a steel bar is subjected to tension or compression The strain generated by the tetrahedral mesh elements, Indicates the material strength of the steel bar; The linear constitutive logic expression for the interaction and bond properties between concrete and steel bars is used to simulate the relative displacement changes between concrete and steel bars in box culverts under different loads as follows: ; in, Indicates the The relative displacement change between concrete and steel bars in a tetrahedral grid unit is To apply loads for the simulation, 、 are the areas of concrete and steel bar bearing surfaces, is the elastic modulus of concrete, Indicates the length of the box culvert.

[0011] Furthermore, the empirical formulas for material strength degradation under three different environmental factors are as follows: The empirical formula for the degradation of material strength with changes in ambient humidity is: ; ; in, 、 Respectively represent the material strength of concrete and steel bars in dry state, 、 are the constants of the influence of humidity on the material strength of concrete and the material strength of steel bars, is the relative humidity, ranging from 0 to 1, where 0 represents completely dry and 1 represents saturated humidity. 、 They are the material strength of concrete and the material strength of steel bars under the influence of humidity; The empirical formula for the degradation of material strength with changes in ambient temperature is: ; ; in, 、 represents the material strength of concrete and steel bars at the reference temperature, 、 is the material strength of concrete and steel bars under the influence of temperature, is the influence coefficient of temperature on concrete, is the influence coefficient of temperature on steel bars, is the ambient temperature, is the reference temperature; The empirical formula for the degradation of material strength due to environmental chemical corrosion is: ; ; in, 、 Respectively represent the original strength of concrete and steel materials when they are not chemically corroded. is the rate of chemical attack on concrete material, is the rate of chemical attack on the steel bar, 、 are constants related to material properties and environmental conditions, representing the resistance of concrete and steel materials to corrosion, is the duration of exposure to the corrosive environment, 、 They are the material strength of concrete and the material strength of steel bars under the influence of chemical attack.

[0012] Furthermore, a local fine model is constructed, wherein the local fine model adopts a polynomial coupling degradation relationship model, and the method is as follows: Finite element software was used to construct a local fine model for the key areas of the box culvert. A polynomial coupling degradation relationship model was applied to couple the effects of humidity, temperature, and chemical corrosion to the changes in material strength to capture the nonlinear effects of environmental factors on material properties. The concrete material strength and steel material strength under the three environmental factors were used as inputs to the local fine model, and the degree of material strength degradation was used as the output of the local fine model. The polynomial fitting formula used was: ; in, Indicates the degree of degradation of material strength. It is a constant term, which is used to represent the reference value of the material strength change of the box culvert when the influence of all environmental factors is zero. It is the bias term of the model. 、 is the fitting coefficient of the local fine model, Represents the input to the model 、 , Represents the input to the model 、 , Represents the input to the model 、 , the concrete material strength and steel material strength under three environmental factors are input into the model to obtain the corresponding degradation degree of concrete material strength Degradation of steel material strength ; Collect the strength data of concrete and steel materials under different environmental conditions, and construct a matrix based on the polynomial fitting formula , define the output vector is The material strength loss caused by environmental factors in the sample test is composed of the following: ; in, yes 、 The set of fitted coefficients, is the transpose of the matrix, for The inverse of the matrix is ​​used in the least squares method to adjust the parameters so that the error between the model's predicted values ​​and the actual values ​​is minimized.

[0013] Furthermore, the box culvert material strength corrected by the local fine model is introduced into the full-scale model. The full-scale model is corrected based on the degree of degradation of the box culvert material strength. The current road load is input into the corrected model based on the full-scale model to determine the maximum load-bearing surface in the key area of ​​the box culvert. The method is based on: In the full-scale model, the input material strengths are replaced with the revised concrete and steel strengths output by the local fine model. Based on the grid element positions in the local fine model, the revised material strengths are associated with the corresponding grid elements in the full-scale model to ensure that the concrete and steel constitutive models in the key areas of the full-scale model use the revised strength characteristics. The current road load is input into the revised full-scale model to obtain the relative displacement of concrete and steel in each tetrahedral grid element in the key areas. The material strength of concrete and steel bars in the full-scale model is adjusted based on the degradation degree of the box culvert material strength obtained by fitting in the local model. The formula is: ; ; in, Indicates the modified value of concrete material strength, Indicates the corrected value of the steel bar material strength; Based on the corrected concrete and steel material strength, the corrected concrete stress and steel stress are obtained. Combined with the current road load, the concrete stress value of each tetrahedral grid element in the key area is calculated. and steel bar stress value , to obtain the relative displacement of concrete and steel bars in each tetrahedral grid element , the relative displacements of concrete and steel bars of each tetrahedral mesh unit in the key area are comprehensively sorted from large to small, and the tetrahedral mesh unit with the largest relative displacement is selected as the analysis object; The Kirchhoff-Love theory is used to describe the stress distribution of the tetrahedral mesh unit. The equation under plane stress conditions is used to analyze all the stress-bearing surfaces contained in the tetrahedral mesh unit. The equation is: ; ; ; in, Indicates Normal stress in the direction perpendicular to The force generated on the surface of the direction, Indicates Normal stress in the direction perpendicular to The force generated on the surface of the direction, 、 Respectively expressed in Strain in the direction The strain in the direction of the material and The relative deformation degree in the direction, 、 are the Poisson's ratios of concrete and steel, respectively. is Shear stress on the load-bearing surface, is The shear strain on the load-bearing surface indicates the degree of deformation of the material due to shear stress; The principal stresses of all the load-bearing surfaces in the tetrahedral mesh element with the largest relative displacement are extracted based on the following formula: ; in, express principal stresses on the load-bearing surface; All extracted The principal stresses on the load surface are sorted in descending order, and the maximum principal stress is selected. Corresponding The load-bearing surface is the maximum load-bearing surface in the key area of ​​the box culvert.

[0014] Furthermore, a load test safety threshold is set, and the safety index of the box culvert is defined based on the principal stress value in the maximum load-bearing surface combined with the modified material strength of the box culvert. The failure probability of the maximum load-bearing surface is introduced to dynamically adjust the safety index until the load test requirements are met. The method is based on: The safety index indicates the safety of the structure under load. It is defined based on the ratio of the modified value of the box culvert's material strength to the principal stress value on the maximum load-bearing surface. The formula is: ; ; in, represents the safety index of the box culvert, is the principal stress value of the maximum stress surface, is the material strength correction value of the box culvert, 、 are the influence coefficients of the degradation degree of concrete material strength and the degradation degree of steel material strength, respectively, and ; The failure probability is calculated based on Monte Carlo simulation to dynamically adjust the safety index to meet the preset load test safety threshold conditions. The performance function is set to describe the safety status of the road box culvert system. The formula is: ; in, is a performance function used to describe the safety status of the road box culvert system. Indicates the maximum stress of the box culvert under stress state, It represents the simulated road load. When the performance function of the road box culvert safety system is less than zero, the system is considered to be failed. A large number of samples are taken from a certain random variable distribution, and the performance function is calculated for each group of random variable samples. The number of times the performance function is less than zero is recorded as , the formula for calculating the failure probability is: ; in, represents the failure probability of the maximum stress-bearing surface of the road box culvert, is the number of times the performance function is less than zero, is the total number of simulations; The safety index is dynamically adjusted by introducing the failure probability to meet the preset load test safety threshold. The formula is: ; in, It is a safety index that is dynamically adjusted after considering the failure probability; Will and the preset safety index threshold For comparison, if There is no need to adjust the safety index; if The safety index is dynamically adjusted until Meet the preset safety index threshold conditions.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention effectively overcomes the limitations of traditional global finite element analysis in complex road box culvert structures by establishing a multi-scale finite element simulation method. By leveraging a three-dimensional geometric model and meticulous meshing, it can more accurately simulate the response of box culverts under various loads and boundary conditions, particularly the stress distribution and deformation behavior in key areas. Furthermore, by incorporating comprehensive considerations of the interaction between concrete and steel and the degradation of local material strength, it addresses the problem of traditional methods neglecting the degradation of material strength in key local areas under the influence of different environmental factors, thereby improving the accuracy of long-term structural performance assessments. Secondly, the present invention also uses the Monte Carlo simulation method to calculate the failure probability of the maximum stress-bearing surface of the box culvert, and dynamically adjusts the safety index of the road box culvert by combining the failure probability with the principal stress of the maximum stress-bearing surface and the corrected material strength. This solves the problem of underestimation or over-conservatism of the safety of the road box culvert structure by traditional methods, making the safety assessment more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the overall method flow of the present invention; Figure 2 Schematic diagram of safety index fitting analysis in the present invention DETAILED DESCRIPTION

[0017] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0018] It should be noted that, unless otherwise defined, the technical or scientific terms used in the present invention should have the usual meanings understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative position relationships. When the absolute position of the object being described changes, the relative position relationship may also change accordingly.

[0019] Example: See also Figures 1 to 2 The present invention provides a multi-scale finite element simulation method for road box culverts for load testing, the specific steps of which include: Step 1: Based on the box culvert's dimensions and material properties, a 3D geometric model of the box culvert was constructed using CAD software. The model was then divided into grid units and simulated load tests were conducted to identify the critical areas of the box culvert. Step 2: Based on the design specifications for road box culverts and the material strength data for concrete and steel, a full-scale concrete-steel model was constructed and meshed to simulate the relative displacement changes between concrete and steel in the box culvert under different road loads. The full-scale concrete-steel model used a composite material constitutive model. Step 3: Identify environmental factors, including temperature, humidity, and chemical corrosion, and establish empirical formulas for the material strength degradation of concrete and steel under these three different environmental factors. Based on these formulas, construct a local fine model in the key areas of the box culvert. The local fine model uses a polynomial coupling degradation relationship model. Step 4: Introduce the box culvert material strength after correction by the local fine model into the full-scale model, and perform a comprehensive finite element analysis based on the full-scale model to determine the maximum stress-bearing surface in the key area of ​​the box culvert; Step 5: Set the safety threshold for the simulated load test. Define the safety index of the box culvert based on the principal stress value in the maximum load-bearing surface combined with the corrected material strength of the box culvert. Define a performance function and use the Monte Carlo simulation method to calculate the failure probability of the maximum load-bearing surface. Based on the failure probability of the maximum load-bearing surface, dynamically adjust the safety index until the load test requirements are met.

[0020] It should be noted that by creating a detailed model through computer-aided design software and dividing it into tetrahedral mesh elements, the response of each component under different loads can be accurately simulated. Through load simulation experiments, the overall stress of each mesh element is obtained, which helps to identify the weakest links and potential structural risks. The reason for choosing tetrahedral mesh elements to divide the model is that tetrahedral elements generally exhibit good numerical stability in finite element analysis, especially when dealing with nonlinear material behavior, contact problems or large deformation problems. In addition, tetrahedral elements can reduce the numerical locking phenomenon caused by the element shape, which will lead to error aggregation in the calculation.

[0021] To construct a 3D geometric model of a box culvert, we must first determine the relevant parameters of the box culvert, such as length, width, height, bottom plate thickness, top plate thickness, and side wall thickness, according to the design requirements, and determine the material properties of the concrete and steel bars, including compressive strength, tensile strength, elastic modulus, and Poisson's ratio. Then, we create a rectangular block in the CAD software as the basic model of the box culvert, stretch and scale it according to the specific dimensions of the box culvert, and draw the bottom plate, top plate, side walls, and joints of the box culvert to ensure that the connections between the various parts of the model are complete and seamless, and meet the actual design specifications.

[0022] Therefore, it is necessary to establish a three-dimensional geometric model of the box culvert and determine the key areas of the box culvert. The method is based on: Based on the specific dimensions of the box culvert, computer-aided CAD design software was used to establish a three-dimensional geometric model of the box culvert. The specific dimensions included the length, width, height, bottom plate thickness, top plate thickness, and side wall thickness. The model was used to simulate the various components of the box culvert, including the culvert body, bottom plate, top plate, side walls, and connections. The three-dimensional geometric model of the box culvert was divided into multiple tetrahedral grid units with a side length of 10mm*10mm*10mm. The standard load required for the box culvert test was set, and load simulation experiments were performed on each tetrahedral grid of the box culvert. Obtain the eight vertex positions and displacement of each vertex of each tetrahedral grid unit under the action of standard road load, calculate the displacement difference between adjacent vertices, and thus obtain the relative displacement. Then use these relative displacements and the distance between the original vertices to calculate the local strain of each pair of adjacent vertices, integrate the strain information of all adjacent nodes into a strain matrix, and convert the strain into local stress through the constitutive relationship of the material. Finally, all local stresses are summarized to form the effective stress field of the tetrahedral grid unit, and the overall stress of the tetrahedral grid unit is obtained. , the total stress of each tetrahedral mesh element in the three-dimensional geometric model of the box culvert is With the preset stress threshold In contrast, the area connected by tetrahedral grid units that exceed the stress threshold is marked as the critical area of ​​the box culvert; in the above description, the standard load applied to the model in the test refers to the corresponding load standard table in the "Code for Loads on Building Structures" based on the specific use scenario of the box culvert, and the load standard value of the test design is determined by referring to the corresponding load standard table in the code.

[0023] It should be noted that the reason for establishing a full-scale concrete-steel model is that it can simulate the changes in the relative displacement between the concrete and steel bars inside the box culvert under different loads, and can reflect the real changes in the strength of the box culvert material under different environments. It is necessary to use different constitutive models to describe the behavior of concrete and steel bars respectively, because these two materials have significant differences in mechanical properties. Concrete mainly bears compressive loads and exhibits nonlinear behavior. Therefore, a nonlinear constitutive model adapted to its compressive characteristics is used to simulate its response under load. The steel bars mainly bear tensile loads, and their behavior is usually linear. Therefore, it is reasonable to use a linear elastic constitutive model to describe their tensile and compressive behaviors.

[0024] Therefore, it is necessary to construct a full-scale concrete-steel model and perform grid unit division to simulate the relative displacement changes between concrete and steel bars in the box culvert under different loads. The method is based on: Material strength data for concrete and steel bars were collected separately. The full-scale concrete-steel model adopted the constitutive model of composite materials. A compression constitutive model was used for concrete to simulate the nonlinear behavior of concrete under compression loads, and a tensile softening linear model was used for steel bars to describe their tensile failure behavior. The simulated loads determined by the experiment were input into the full-scale model, and the full-scale concrete-steel model was divided into tetrahedral mesh elements. The strains of concrete and steel bars in compression and tension in each tetrahedral mesh element were obtained using finite element analysis software. The logical expression of the nonlinear constitutive model of concrete for each tetrahedral mesh element is as follows: ; in, Indicates the The stress of concrete in tetrahedral grid elements, is the maximum compressive strength of concrete, is the maximum tensile strength of concrete, The concrete is in compression The strain of a tetrahedral mesh element, The concrete is in tension The strain of a tetrahedral mesh element, is the maximum strain value that concrete can withstand under compression, is the maximum strain that concrete can withstand under tension. represents the material strength of concrete; in the above formula, It is the expression of concrete in compression state. When concrete is subjected to compression load, the stress is equal to the maximum compressive strength of concrete. is the limit, and increases with the increase of strain, but the increase gradually decreases, showing the characteristics of nonlinear softening, which is consistent with the material strength characteristics of concrete; It is the expression of concrete under tension. When concrete is subjected to tensile load, the stress of concrete gradually increases with the increase of strain, reflecting the brittle characteristics of concrete under tension.

[0025] The logical expression of the linear elastic constitutive law of steel bars of each tetrahedral mesh element is as follows: ; in, Indicates the The stress of the steel bar in the tetrahedral mesh element is is the elastic modulus of the steel bar, The first time a steel bar is subjected to tension or compression The strain generated by the tetrahedral mesh elements, Represents the material strength of the steel bar; in the above expression, in this expression, the relationship between stress and strain is linear, which means that when the load applied to the steel bar increases, the stress of the steel bar will also increase linearly, and when the load applied to the steel bar increases, the corresponding strain of the steel bar will also increase, resulting in the stress of the steel bar also increasing.

[0026] The linear constitutive logic expression for the interaction and bond properties between concrete and steel bars is used to simulate the relative displacement changes between concrete and steel bars in box culverts under different loads as follows: ; in, Indicates the The relative displacement change between concrete and steel bars in a tetrahedral grid unit is is the road load, 、 are the areas of concrete and steel bar bearing surfaces, is the elastic modulus of concrete, represents the length of the box culvert; in the above formula, and Represents the total force of concrete and steel under the applied load and self-stress respectively. These two combined stresses affect the relative movement between concrete and steel. In the denominator of each part and The influence of the cross-sectional area and material strength of concrete and steel bars is taken into account. A larger area and higher material strength means that the deformation of the material is relatively small, which makes the relative displacement change between concrete and steel bars smaller. The above relationship can simulate the relative displacement change between concrete and steel bars in the box culvert under different loads, thereby determining the simulated load used in the final test.

[0027] It should be noted that establishing empirical formulas for the material strength degradation of box culverts under different environmental factors can more accurately predict the durability and safety of the structure in different humidity, temperature and chemical corrosion environments, thereby ensuring the long-term reliability of the structure and reducing maintenance and replacement costs. Especially for common environmental factors such as groundwater level changes, temperature fluctuations and chemical corrosion, these formulas can help designers optimize material selection and structural design, and improve the service life of box culverts.

[0028] Among these three empirical degradation formulas, concrete and steel strength are equally applicable. This is because the two work together in the structure, jointly bearing loads and affecting overall performance. Concrete strength degradation is affected by ambient humidity and temperature, and steel, as a reinforcing material, has strength characteristics that are also closely related to ambient humidity and temperature. For example, under the influence of humidity, the relative humidity of concrete and steel is different due to the strong water absorption capacity of concrete. Similarly, under the influence of temperature, the base temperatures of concrete and steel are also different due to the different thermal conductivity of the two materials. Under the influence of chemical erosion, steel corrosion may lead to a decrease in strength, affecting the performance of the overall structure. The chemical erosion rate of concrete is different from that of steel. These environmental factors that lead to material strength degradation will reduce the bonding strength between concrete and steel, resulting in a decrease in the bonding performance between the two, thereby affecting the load-bearing capacity of the overall structure. Therefore, considering the degradation characteristics of the strength of concrete and steel is crucial for evaluating the overall performance of box culverts. Therefore, the three empirical degradation formulas are still applicable to the degradation characteristics of the strength of concrete and steel.

[0029] The reason why the material strength of the overall box culvert is used to establish the degradation empirical formula is that the three environmental factors do not act solely on concrete or steel bars. In the use scenario of road box culverts, these three environmental factors often interact with each other, so the material strength of the box culvert must be constructed as a whole to characterize it. This overall construction method can more accurately reflect the performance of the box culvert in the actual use environment.

[0030] Therefore, it is necessary to establish empirical formulas for material strength degradation under three different environmental factors, as follows: The empirical formula for the degradation of material strength with changes in ambient humidity is: ; ; in, 、 Respectively represent the material strength of concrete and steel bars in dry state, 、 are the constants of the influence of humidity on the material strength of concrete and the material strength of steel bars, is the relative humidity, ranging from 0 to 1, where 0 represents completely dry and 1 represents saturated humidity. 、 are the material strength of concrete and the material strength of steel bars under the influence of humidity; in the above formula, as the relative humidity of the environment Continuously increasing, 、 It will become smaller and smaller, indicating that with the increase of humidity, the material strength of concrete and steel bars will gradually decrease, and the bonding performance between concrete and steel bars will be reduced. This means that when bearing loads, the synergistic effect of concrete and steel bars will be weakened, and the material strength of the overall box culvert will also become smaller.

[0031] The empirical formula for the degradation of material strength with changes in ambient temperature is: ; ; in, 、 represents the material strength of concrete and steel bars at the reference temperature, 、 is the material strength of concrete and steel bars under the influence of temperature, is the influence coefficient of temperature on concrete, is the influence coefficient of temperature on steel bars, is the ambient temperature, is the reference temperature; in the above formula, when the ambient temperature When the temperature rises, the moisture in the concrete will evaporate, which will affect the hydration reaction of the concrete, resulting in a decrease in the material strength of the concrete. The material strength of the steel bar is affected by temperature mainly due to the change in its material properties. The increase in temperature will cause the yield strength and tensile strength of the steel bar to decrease, thereby reducing the material strength of the steel bar.

[0032] The empirical formula for the degradation of material strength due to environmental chemical corrosion is: ; ; in, 、 Respectively represent the original strength of concrete and steel materials when they are not chemically corroded. is the rate of chemical attack on concrete material, is the rate of chemical attack on the steel bar, 、 are constants related to material properties and environmental conditions, representing the resistance of concrete and steel materials to corrosion, is the duration of exposure to the corrosive environment, 、 They are the material strength of concrete and the material strength of steel bars under the influence of chemical corrosion. In the above formula, as the chemical corrosion rate increases or time passes, concrete is exposed to certain chemicals, such as sulfuric acid and chlorides, which will affect the hydration reaction of the concrete, thereby reducing the strength of the concrete material and its curing ability. Chemical corrosion of steel bars mainly occurs through some chemicals, such as acids and salts. These substances will undergo redox reactions with the metal on the surface of the steel bars, making the thermal expansion characteristics of the rusted layer different from those of the uncorroded part, resulting in uneven stress distribution when the temperature changes, reducing the strength of the steel bar material, and increasing the risk of structural damage.

[0033] It should be noted that when establishing the empirical formula for the degradation of material strength due to environmental chemical erosion, the reason why a logarithmic function is used to describe it is because chemical erosion is usually a complex process, and its rate changes with time and environmental conditions. The logarithmic function can effectively describe this nonlinear degradation characteristic. As time goes by, the erosion rate will show a "saturation" phenomenon. This characteristic emphasizes the importance of the inherent properties of the material itself in resisting external chemical erosion.

[0034] It should be noted that the local fine model is particularly suitable for capturing the nonlinear influence of environmental factors on material properties. Compared with the full-scale model, the local fine model can describe the behavior of the material under specific conditions in more detail, thereby improving the accuracy of strength degradation prediction. The polynomial coupling degradation relationship model can more fully reflect the actual performance of the material in a complex environment by considering the interaction of different environmental factors.

[0035] In box culvert structures, certain areas may be more susceptible to environmental impacts, such as the bottom, base, joints, and connections. Material strength variations in these critical areas are crucial to overall structural safety. Building a detailed local model allows for focused detail in these critical areas, enabling more accurate stress distribution and strength degradation analysis through finite element analysis, providing more targeted recommendations for structural design and maintenance.

[0036] Constructing a local fine model is used to improve the reliability of the model. The full-scale model is usually a macroscopic analysis of the entire structure and cannot fully consider the complex local environmental effects. The local fine model subdivides the area and applies polynomial coupling degradation relationships to more realistically reflect the actual use conditions of the material, thereby improving the reliability and predictive ability of the model.

[0037] Therefore, it is necessary to construct a local fine model, which adopts a polynomial coupling degradation relationship model based on the following method: Finite element software was used to construct a local fine model for the key areas of the box culvert. A polynomial coupling degradation relationship model was applied to couple the effects of humidity, temperature, and chemical corrosion to the changes in material strength to capture the nonlinear effects of environmental factors on material properties. The concrete material strength and steel material strength under the three environmental factors were used as inputs to the local fine model, and the degree of material strength degradation was used as the output of the local fine model. The polynomial fitting formula used was: ; in, Indicates the degree of degradation of material strength. It is a constant term, which is used to represent the reference value of the material strength change of the box culvert when the influence of all environmental factors is zero. It is the bias term of the model. 、 is the fitting coefficient of the local fine model, Represents the input to the model 、 , Represents the input to the model 、 , Represents the input to the model 、 , the concrete material strength and steel material strength under three environmental factors are input into the model to obtain the corresponding degradation degree of concrete material strength Degradation of steel material strength ; Collect the strength data of concrete and steel materials under different environmental conditions, and construct a matrix based on the polynomial fitting formula , define the output vector is The material strength loss caused by environmental factors in the sample test is composed of the following: ; in, yes 、 The set of fitted coefficients, is the transpose of the matrix, for The inverse of the matrix is ​​used in the least squares method to adjust the parameters so that the error between the model's predicted value and the actual value is minimized; It should be noted that the constructed matrix With the output vector The formula is as follows: ; ; Among them, the matrix The first column of constant 1 is used to represent the bias term of the model. 、 、 Indicates the Input features in samples 、 、 Value, input feature 、 、 Respectively represent the strength of concrete and steel under humidity conditions, the strength of concrete and steel under temperature conditions, and the strength of concrete and steel under chemical corrosion conditions. Indicates the The material strength of concrete and steel bars in the samples under the interaction of humidity and temperature, Indicates the The material strength of concrete and steel in the samples under the interaction of temperature and chemical attack, Indicates the The material strength of concrete and steel in the samples under the interaction of humidity and chemical attack, Indicates the The material strength of concrete and steel in the samples under the combined influence of humidity, temperature and chemical attack, Indicates the The test sample, A road box culvert.

[0038] It should be noted that by fitting the above-mentioned local fine model, not only the material strength of concrete and steel bars under different environments can be obtained, but also the relevant environmental constants in the above-mentioned three degradation empirical formulas can be obtained.

[0039] It should be noted that by introducing the material strength corrected by the local fine model into the full-scale model, the performance of the material under actual use conditions can be more accurately reflected, thereby improving the analysis accuracy of the full-scale model. In particular, in the strength assessment of critical areas, after applying the corrected concrete and steel strength in the full-scale model, the concrete and steel stress values ​​of each tetrahedral mesh element can be accurately calculated.

[0040] The Kirchhoff-Love theory is used to describe the relationship between stress and strain because it is specifically designed to describe the behavior of thin shell and plate structures. It can effectively handle complex stress states such as bending and shear that occur in structures. This theory is particularly suitable for analyzing structures such as box culverts, as they are typically thin-walled structures and are subject to various types of loads during use. Secondly, the theory can be used to extract principal stresses using simple formulas and sort them according to their relative magnitude. This process is crucial for identifying critical load-bearing surfaces, allowing for quick identification of areas requiring the most attention and helping engineers make more informed decisions during design and maintenance.

[0041] Therefore, it is necessary to introduce the box culvert material strength after correction by the local fine model into the full-scale model, and correct the full-scale model based on the degree of degradation of the box culvert material strength. Based on the full-scale model, the current road load is input into the corrected model to determine the maximum load-bearing surface in the key area of ​​the box culvert. The method is based on: In the full-scale model, the input material strengths are replaced with the revised concrete and steel strengths output by the local fine model. Based on the grid element positions in the local fine model, the revised material strengths are associated with the corresponding grid elements in the full-scale model to ensure that the concrete and steel constitutive models in the key areas of the full-scale model use the revised strength characteristics. The current road load is input into the revised full-scale model to obtain the relative displacement of concrete and steel in each tetrahedral grid element in the key areas. The material strength of concrete and steel bars in the full-scale model is adjusted based on the degradation degree of the box culvert material strength obtained by fitting in the local model. The formula is: ; ; in, Indicates the modified value of concrete material strength, Indicates the correction value of the strength of the steel bar material; in the above formula, as the strength of the box culvert material deteriorates The increase means that the correction range of the concrete material strength and the steel material strength is also greater, which means that the material strength of the overall box culvert is reduced and the actual bearing capacity is reduced.

[0042] Based on the corrected concrete and steel material strengths, the corrected concrete stress and steel stress are obtained. Combined with the road loads applied in the full-scale model, the concrete stress value of each tetrahedral grid element in the critical area is calculated. and steel bar stress value , to obtain the relative displacement of concrete and steel bars in each tetrahedral grid element , the relative displacements of concrete and steel bars of each tetrahedral mesh unit in the key area are comprehensively sorted from large to small, and the tetrahedral mesh unit with the largest relative displacement is selected as the analysis object; The Kirchhoff-Love theory is used to describe the stress distribution of the tetrahedral mesh unit. The equation under plane stress conditions is used to analyze all the stress-bearing surfaces contained in the tetrahedral mesh unit. The equation is: ; ; ; in, Indicates Normal stress in the direction perpendicular to The force generated on the area in the direction, Indicates Normal stress in the direction perpendicular to The force generated on the area in the direction, 、 Respectively expressed in Strain in the direction The strain in the direction of the material and The relative deformation degree in the direction, 、 are the Poisson's ratios of concrete and steel, respectively. is Shear stress on the load-bearing surface, is The shear strain on the load-bearing surface indicates the degree of deformation of the material due to shear stress; The principal stresses of all the load-bearing surfaces in the tetrahedral mesh element with the largest relative displacement are extracted based on the following formula: ; in, express principal stresses on the load-bearing surface; All extracted The principal stresses on the load surface are sorted in descending order, and the maximum principal stress is selected. Corresponding The load-bearing surface is the maximum load-bearing surface in the key area of ​​the box culvert.

[0043] It should be noted that the safety threshold is defined by combining the principal stress value in the maximum load-bearing surface with the corrected material strength to define the safety index of the box culvert, thereby ensuring that under the actual load, the structure can effectively bear the load without failure. By dynamically introducing the failure probability of the maximum load-bearing surface and adjusting the safety index accordingly, the safety status of the structure can be monitored and evaluated in real time to ensure that it is always within an acceptable safety range.

[0044] The reason why Monte Carlo simulation is used to calculate the failure probability to dynamically adjust the safety index is that this method can effectively handle complex random variables and uncertainties. In engineering structures, many factors such as material strength, load changes and environmental impacts are uncertain. Traditional deterministic analysis methods are often unable to comprehensively evaluate the impact of these factors on structural safety. Monte Carlo simulation can systematically consider various possible situations through a large number of random sampling, thereby providing a statistical estimate of the failure probability. In addition, Monte Carlo simulation can generate a large amount of sample data, so that under different load conditions, the performance of the performance function can be accurately evaluated. The performance function established is an important tool for evaluating the safety status of the structure under specific load conditions. In the safety analysis of road box culverts, the design of the performance function can clearly evaluate the changes in the safety of the box culvert when the load changes, especially when using Monte Carlo simulation. A large number of sampling calculations can help obtain the failure probability and then dynamically adjust the safety index.

[0045] Therefore, it is necessary to set a load test safety threshold. The safety index of the box culvert is defined based on the principal stress value in the maximum load-bearing surface combined with the corrected material strength. The failure probability of the maximum load-bearing surface is introduced to dynamically adjust the safety index until the load test requirements are met. The method is based on: The safety index indicates the safety of the structure under load. It is defined based on the ratio of the modified value of the box culvert's material strength to the principal stress value on the maximum load-bearing surface. The formula is: ; ; in, represents the safety index of the box culvert, is the principal stress value of the maximum stress surface, is the material strength correction value of the box culvert, 、 are the influence coefficients of the degradation degree of concrete material strength and the degradation degree of steel material strength, respectively, and ; In the above formula, is the material strength correction value of the box culvert, which is determined by the degree of degradation of the concrete material strength. Degradation of steel material strength jointly decided, The larger the safety index of the box culvert is, the The higher it is, the better the box culvert material's actual strength remains relative to its degradation, indicating that the box culvert has sufficient bearing capacity and can better cope with external loads. The smaller the box culvert, the safety index The higher the It represents the highest principal stress that the box culvert can bear under the maximum stress state. When this stress value decreases, it means that the internal stress level experienced by the box culvert when bearing external loads is reduced, thereby relatively reducing the stress state of the material. The reason why the influence coefficient is set to This is because concrete mainly bears compressive loads, and its compressive strength is usually high, but its tensile strength is relatively low. During use, concrete is easily affected by environmental factors such as humidity, temperature changes, and chemical erosion, which can lead to a decrease in strength. For example, long-term immersion in water or dry environment may cause cracks and strength degradation in concrete. Therefore, the strength degradation of concrete has a relatively greater impact on the safety of the overall structure, so a larger impact coefficient is given. Steel bars are mainly used to provide tensile and bending resistance. Their strength is relatively stable under normal use conditions. Although steel bars are also affected by factors such as corrosion and fatigue, their strength degradation is usually not as obvious as concrete. Therefore, in safety assessments, steel bars contribute relatively little to structural safety and are assigned a smaller impact coefficient. .

[0046] As shown in the table below, twenty groups of materials with strength ranges between The road box culvert was subjected to a road simulation load test. After selecting the simulated load, the simulated load was applied to 20 different groups of road box culverts, and the principal stress of the corresponding maximum load-bearing surface was obtained. The data showed that there is an obvious positive correlation between material strength and the principal stress of the maximum load-bearing surface. As the material strength increases, the principal stress of the maximum load-bearing surface also increases. For example, when the material strength is 30 When the principal stress is 30 , and the material strength reaches 200 When the principal stress increases to 105 ,This trend shows that stronger materials are better able to resist deformation and ,damage when subjected to loads. The safety index ranges from 1 to 1.90. As the strength of the material increases, the ,safety index shows an overall upward trend; When the material strength is 30 When the safety index is 1, it means that the material strength is just balanced with the applied load and is within the safety boundary. As the material strength increases, the safety index gradually increases, especially when the material strength reaches 185. and 200 When , the safety index reaches 1.85 and 1.90 respectively, showing that there is a lot of room for bearing capacity under these materials; By analyzing the simulated load test results, the following conclusions can be drawn: 1. There is a linear positive correlation between material strength and the principal stress of the maximum load-bearing surface; 2. With the increase of material strength, the safety index shows a significant increase, which enhances the structural safety of the box culvert; 3. When selecting materials, the safety index, material cost and actual application environment should be comprehensively considered to ensure the safety and economy of the road box culvert.

[0047] Table 1-Safety index analysis table under simulated load test

[0048] The safety index is dynamically adjusted based on the Monte Carlo simulation to calculate the failure probability so that it meets the preset load test safety threshold conditions. The performance function is set to describe the safety status of the road box culvert system. The formula is: ; in, is a performance function used to describe the safety status of the road box culvert system. Indicates the maximum stress of the box culvert under stress state, It represents the simulated road load. When the performance function of the road box culvert safety system is less than zero, the system is considered to be failed. A large number of samples are taken from a certain random variable distribution, and the performance function is calculated for each group of random variable samples. The number of times the performance function is less than zero is recorded as , the formula for calculating the failure probability is: ; in, represents the failure probability of the maximum stress-bearing surface of the road box culvert, is the number of times the performance function is less than zero, is the total number of simulations; The safety index is dynamically adjusted by introducing the failure probability to meet the preset load test safety threshold. The formula is: ; in, is the safety index after dynamic adjustment considering the failure probability; in the above formula, Safety Index As the failure probability changes, when the failure probability When increasing, The value of will decrease, resulting in the dynamically adjusted This mechanism can reflect that the safety index of the structure should be reduced accordingly under higher failure risks.

[0049] Will and the preset safety index threshold For comparison, if There is no need to adjust the safety index; if The safety index is dynamically adjusted until Meet the preset safety index threshold conditions.

[0050] from Figure 2 The safety index fitting analysis diagram shows that when the box culvert material strength correction value X1 increases from approximately 30 to 200, the safety index value increases significantly. When X1 reaches 200, the safety index exceeds 1.9, indicating that the increase in material strength directly leads to a significant increase in the safety index, thereby enhancing the box culvert's bearing capacity. The figure shows that when the maximum load-bearing surface principal stress value X2 is low, for example, around 50, the safety index value is between 4 and 5. However, as X2 increases to near 120, the safety index gradually decreases from around 5.35 to a lower level. This shows that when the maximum load-bearing surface principal stress value increases, the safety index tends to decrease, indicating that under high stress conditions, the structure faces a greater risk of failure. The entire surface of the graph presents a parabolic shape, reflecting the balance between material strength and stress. The safety index is optimal when the material strength is maximized and the stress is minimized.

[0051] The above formulas are all dimensionless and numerical calculations. The formulas are obtained by collecting a large amount of data and performing software simulation to obtain the most recent real situation. The preset parameters in the formulas are set by technicians in this field according to actual conditions.

[0052] The above embodiments can be implemented in whole or in part by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented in whole or in part in the form of a computer program product. Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed by hardware or software depends on the specific application and design constraints of the technical solution.

[0053] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, and may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment as needed.

[0054] The above is only a specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be covered by the scope of protection of the present application.

Claims

1. A multi-scale finite element simulation method for road box culverts for load testing, characterized by: The specific steps include: Step 1: Based on the box culvert's dimensions and material properties, a 3D geometric model of the box culvert was constructed using CAD software. The model was then divided into grid units and simulated load tests were conducted to identify the critical areas of the box culvert. Step 2: Based on the design specifications for road box culverts and the material strength data for concrete and steel, a full-scale concrete-steel model was constructed and meshed to simulate the relative displacement changes between concrete and steel in the box culvert under different road loads. The full-scale concrete-steel model used a composite material constitutive model. Step 3: Identify environmental factors, including temperature, humidity, and chemical corrosion, and establish empirical formulas for the material strength degradation of concrete and steel under these three different environmental factors. Based on these formulas, construct a local fine model in the key areas of the box culvert. The local fine model uses a polynomial coupling degradation relationship model. Step 4: Introduce the box culvert material strength after correction by the local fine model into the full-scale model, and perform a comprehensive finite element analysis based on the full-scale model to determine the maximum stress-bearing surface in the key area of ​​the box culvert; Step 5: Set the safety threshold for the simulated load test. Define the safety index of the box culvert based on the principal stress value in the maximum load-bearing surface combined with the corrected material strength of the box culvert. Define a performance function and use the Monte Carlo simulation method to calculate the failure probability of the maximum load-bearing surface. Based on the failure probability of the maximum load-bearing surface, dynamically adjust the safety index until the load test requirements are met.

2. The multi-scale finite element simulation method for road box culverts for load testing according to claim 1 is characterized in that: The three-dimensional geometric model of the box culvert is established and the key areas of the box culvert are determined based on the following method: Based on the specific dimensions of the box culvert, computer-aided CAD design software was used to establish a three-dimensional geometric model of the box culvert. The specific dimensions included the length, width, height, bottom plate thickness, top plate thickness, and side wall thickness. The model was used to simulate the various components of the box culvert, including the culvert body, bottom plate, top plate, side walls, and connections. The three-dimensional geometric model of the box culvert was divided into multiple tetrahedral grid units with a side length of 10mm*10mm*10mm. The standard load required for the box culvert test was set, and load simulation experiments were performed on each tetrahedral grid of the box culvert. Obtain the eight vertex positions and displacement of each vertex of each tetrahedral grid unit under the action of standard road load, calculate the displacement difference between adjacent vertices, and thus obtain the relative displacement. Then use these relative displacements and the distance between the original vertices to calculate the local strain of each pair of adjacent vertices, integrate the strain information of all adjacent nodes into a strain matrix, and convert the strain into local stress through the constitutive relationship of the material. Finally, all local stresses are summarized to form the effective stress field of the tetrahedral grid unit, and the overall stress of the tetrahedral grid unit is obtained. , the total stress of each tetrahedral mesh element in the three-dimensional geometric model of the box culvert is With the preset stress threshold By comparison, the area connected by tetrahedral grid cells exceeding the stress threshold is marked as the critical area of ​​the box culvert.

3. The multi-scale finite element simulation method for road box culverts for load testing according to claim 1 is characterized in that: A full-scale concrete-rebar model was constructed and meshed to simulate the relative displacement between concrete and steel in the box culvert under different loads. The method used is as follows: Material strength data for concrete and steel bars were collected separately. The full-scale concrete-steel model adopted the constitutive model of composite materials. A compression constitutive model was used for concrete to simulate the nonlinear behavior of concrete under compression loads, and a tensile softening linear model was used for steel bars to describe their tensile failure behavior. The simulated loads determined by the experiment were input into the full-scale model, and the full-scale concrete-steel model was divided into tetrahedral mesh elements. The strains of concrete and steel bars in compression and tension in each tetrahedral mesh element were obtained using finite element analysis software. The logical expression of the nonlinear constitutive model of concrete for each tetrahedral mesh element is as follows: ； in, Indicates the The stress of concrete in tetrahedral grid elements, is the maximum compressive strength of concrete, is the maximum tensile strength of concrete, The concrete is in compression The strain of a tetrahedral mesh element, The concrete is in tension The strain of a tetrahedral mesh element, is the maximum strain value that concrete can withstand under compression, is the maximum strain that concrete can withstand under tension. Indicates the material strength of concrete; The logical expression of the linear elastic constitutive law of steel bars of each tetrahedral mesh element is as follows: ； in, Indicates the The stress of the steel bar in the tetrahedral mesh element is is the elastic modulus of the steel bar, The first time a steel bar is subjected to tension or compression The strain generated by the tetrahedral mesh elements, Indicates the material strength of the steel bar; The linear constitutive logic expression for the interaction and bond properties between concrete and steel bars is used to simulate the relative displacement changes between concrete and steel bars in box culverts under different loads as follows: ； in, Indicates the The relative displacement change between concrete and steel bars in a tetrahedral grid unit is To apply loads for the simulation, 、 are the areas of concrete and steel bar bearing surfaces, is the elastic modulus of concrete, Indicates the length of the box culvert.

4. The multi-scale finite element simulation method for road box culverts for load testing according to claim 3 is characterized in that: The empirical formulas for material strength degradation under three different environmental factors are as follows: The empirical formula for the degradation of material strength with changes in ambient humidity is: ； ； in, 、 Respectively represent the material strength of concrete and steel bars in dry state, 、 are the constants of the influence of humidity on the material strength of concrete and the material strength of steel bars, is the relative humidity, ranging from 0 to 1, where 0 represents completely dry and 1 represents saturated humidity. 、 They are the material strength of concrete and the material strength of steel bars under the influence of humidity; The empirical formula for the degradation of material strength with changes in ambient temperature is: ； ； in, 、 represents the material strength of concrete and steel bars at the reference temperature, 、 is the material strength of concrete and steel bars under the influence of temperature, is the influence coefficient of temperature on concrete, is the influence coefficient of temperature on steel bars, is the ambient temperature, is the reference temperature; The empirical formula for the degradation of material strength due to environmental chemical corrosion is: ； ； in, 、 Respectively represent the original strength of concrete and steel materials when they are not chemically corroded. is the rate of chemical attack on concrete material, is the rate of chemical attack on the steel bar, 、 are constants related to material properties and environmental conditions, representing the resistance of concrete and steel materials to corrosion, is the duration of exposure to the corrosive environment, 、 They are the material strength of concrete and the material strength of steel bars under the influence of chemical attack.

5. The multi-scale finite element simulation method for road box culverts for load testing according to claim 4 is characterized in that: A local fine model is constructed, wherein the local fine model adopts a polynomial coupling degradation relationship model, and the method is based on: Finite element software was used to construct a local fine model for the key areas of the box culvert. A polynomial coupling degradation relationship model was applied to couple the effects of humidity, temperature, and chemical corrosion to the changes in material strength to capture the nonlinear effects of environmental factors on material properties. The concrete material strength and steel material strength under the three environmental factors were used as inputs to the local fine model, and the degree of material strength degradation was used as the output of the local fine model. The polynomial fitting formula used was: ； in, Indicates the degree of degradation of material strength. It is a constant term, which is used to represent the reference value of the material strength change of the box culvert when the influence of all environmental factors is zero. It is the bias term of the model. 、 is the fitting coefficient of the local fine model, Represents the input to the model 、 , Represents the input into the model 、 , Represents the input to the model 、 , the concrete material strength and steel material strength under three environmental factors are input into the model to obtain the corresponding degradation degree of concrete material strength Degradation of steel material strength ; Collect the strength data of concrete and steel materials under different environmental conditions, and construct a matrix based on the polynomial fitting formula , define the output vector is The material strength loss caused by environmental factors in the sample test is composed of the following: ； in, yes 、 The set of fitted coefficients, is the transpose of the matrix, for The inverse of the matrix is ​​used in the least squares method to adjust the parameters so that the error between the model's predicted values ​​and the actual values ​​is minimized.

6. The multi-scale finite element simulation method for road box culverts for load testing according to claim 5 is characterized in that: The box culvert material strength corrected by the local fine model is introduced into the full-scale model. The full-scale model is corrected based on the degree of degradation of the box culvert material strength. The current road load is input into the corrected model based on the full-scale model to determine the maximum load-bearing surface in the key area of ​​the box culvert. The method is based on: In the full-scale model, the input material strengths are replaced with the revised concrete and steel strengths output by the local fine model. Based on the grid element positions in the local fine model, the revised material strengths are associated with the corresponding grid elements in the full-scale model to ensure that the concrete and steel constitutive models in the key areas of the full-scale model use the revised strength characteristics. The current road load is input into the revised full-scale model to obtain the relative displacement of concrete and steel in each tetrahedral grid element in the key areas. The material strength of concrete and steel bars in the full-scale model is adjusted based on the degradation degree of the box culvert material strength obtained by fitting in the local model. The formula is: ； ； in, Indicates the modified value of concrete material strength, Indicates the corrected value of the steel bar material strength; Based on the corrected concrete and steel material strength, the corrected concrete stress and steel stress are obtained. Combined with the current road load, the concrete stress value of each tetrahedral grid element in the key area is calculated. and steel bar stress value , to obtain the relative displacement of concrete and steel bars in each tetrahedral grid element , the relative displacements of concrete and steel bars of each tetrahedral mesh unit in the key area are comprehensively sorted from large to small, and the tetrahedral mesh unit with the largest relative displacement is selected as the analysis object; The Kirchhoff-Love theory is used to describe the stress distribution of the tetrahedral mesh unit. The equation under plane stress conditions is used to analyze all the stress-bearing surfaces contained in the tetrahedral mesh unit. The equation is: ； ； ； in, Indicates Normal stress in the direction perpendicular to The force generated on the surface of the direction, Indicates Normal stress in the direction perpendicular to The force generated on the surface of the direction, 、 Respectively expressed in Strain in the direction The strain in the direction of the material and The relative deformation degree in the direction, 、 are the Poisson's ratios of concrete and steel, respectively. is Shear stress on the load-bearing surface, is The shear strain on the load-bearing surface indicates the degree of deformation of the material due to shear stress; The principal stresses of all the load-bearing surfaces in the tetrahedral mesh element with the largest relative displacement are extracted based on the following formula: ； in, express principal stresses on the load-bearing surface; All extracted The principal stresses on the load surface are sorted in descending order, and the maximum principal stress is selected. Corresponding The load-bearing surface is the maximum load-bearing surface in the key area of ​​the box culvert.

7. The multi-scale finite element simulation method for road box culverts for load testing according to claim 6 is characterized in that: The safety threshold of the load test is set. The safety index of the box culvert is defined based on the principal stress value in the maximum load-bearing surface combined with the material strength of the modified box culvert. The failure probability of the maximum load-bearing surface is introduced to dynamically adjust the safety index until the load test requirements are met. The method is based on: The safety index indicates the safety of the structure under load. It is defined based on the ratio of the modified value of the box culvert's material strength to the principal stress value on the maximum load-bearing surface. The formula is: ； ； in, represents the safety index of the box culvert, is the principal stress value of the maximum stress surface, is the material strength correction value of the box culvert, 、 are the influence coefficients of the degradation degree of concrete material strength and the degradation degree of steel material strength, respectively, and ; The failure probability is calculated based on Monte Carlo simulation to dynamically adjust the safety index to meet the preset load test safety threshold conditions. The performance function is set to describe the safety status of the road box culvert system. The formula is: ； in, is a performance function used to describe the safety status of the road box culvert system. Indicates the maximum stress of the box culvert under stress state, It represents the simulated road load. When the performance function of the road box culvert safety system is less than zero, the system is considered to be failed. A large number of samples are taken from a certain random variable distribution, and the performance function is calculated for each group of random variable samples. The number of times the performance function is less than zero is recorded as , the formula for calculating the failure probability is: ； in, represents the failure probability of the maximum stress-bearing surface of the road box culvert, is the number of times the performance function is less than zero, is the total number of simulations; The safety index is dynamically adjusted by introducing the failure probability to meet the preset load test safety threshold. The formula is: ； in, It is a safety index that is dynamically adjusted after considering the failure probability; Will and the preset safety index threshold For comparison, if There is no need to adjust the safety index; if The safety index is dynamically adjusted until Meet the preset safety index threshold conditions.

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