Anti-cracking analysis method for mass concrete structure

Abstract

The invention relates to an anti-cracking analysis method for a mass concrete structure, and belongs to the field of concrete construction. According to the technical scheme, the mass concrete structure crack resistance analysis method comprises the following steps that S1, a mass concrete structure simulation analysis model is established with a concrete formula, the size, the construction technology and the use environment as constraint conditions, and the mass concrete structure simulation analysis model comprises a bearing platform and a main beam; s2, constructing a bearing platform heat exchange model, and calculating a temperature field; s3, constructing a stress calculation model according to the bearing platform heat exchange model and the temperature field, and calculating a stress field; and S4, according to the stress field, analyzing the early cracking possibility and crack distribution of the mass concrete structure simulation analysis model through principal tensile stress discrimination and an extended finite element method. According to the scheme, the technical problem that multi-factor coupling is insufficient in a traditional simulation method is solved, the defect that crack distribution cannot be analyzed due to the fact that the prior art only depends on a single index is overcome, and a comprehensive basis is provided for formulating targeted anti-crack measures.

Description

Technical Field

[0001] This invention relates to the field of concrete construction, and in particular to a method for analyzing the crack resistance of large-volume concrete structures. Background Technology

[0002] In bridge construction, large-volume concrete structures, such as abutments and main beams, are the core components that bear the bridge load, and their construction quality directly determines the structural safety and service life of the bridge. However, large-volume concrete structures are prone to cracking in the early stages after pouring due to a combination of factors.

[0003] Currently, although finite element simulation technology has been used in the engineering field to analyze the crack resistance of large-volume concrete structures, existing methods still have many technical limitations and cannot meet the requirements of actual engineering for analysis accuracy and comprehensiveness. Specifically, in the process of building existing simulation models, they often focus only on a single component or a single influencing factor, resulting in the model being out of touch with the actual bridge construction scenarios under different geological and soil conditions, and the simulation results have limited reference value. In addition, multiple components together constitute a stress system, and simulating them separately can easily lead to distorted results. Furthermore, the assessment of the possibility of early cracking relies solely on the principal tensile stress as a single criterion, lacking further research on the crack distribution law, making it impossible to accurately locate the crack-prone areas of the structure, resulting in a lack of targeted crack resistance measures.

[0004] In summary, existing methods for analyzing the crack resistance of large-volume concrete structures cannot comprehensively consider the coupled effects of multiple factors, making it difficult to accurately calculate the correlation between temperature and stress fields, and lacking comprehensiveness in assessing early cracking performance. Summary of the Invention

[0005] To solve the above problems, the technical solution adopted by the present invention is a crack resistance analysis method for large-volume concrete structures, comprising the following steps: S1. Establish a simulation analysis model for a large-volume concrete structure, taking concrete formula, dimensions, construction technology and usage environment as constraints. The simulation analysis model for a large-volume concrete structure includes a foundation and main beam. S2. Construct a heat exchange model for the foundation and calculate the temperature field; S3. Construct a stress calculation model based on the heat exchange model and temperature field of the foundation, and calculate the stress field; S4. Based on the stress field, the possibility of early cracking and crack distribution of the simulation analysis model of large-volume concrete structure are analyzed by using principal tensile stress discrimination and extended finite element method.

[0006] This solution addresses the technical problems of insufficient multi-factor coupling and lack of a unified multi-component model in traditional simulation methods: Step S1 uses concrete formula, dimensions, construction technology, and usage environment as constraints, while incorporating the pier cap and main beam into a unified simulation analysis model. This achieves synergistic coupling of multiple core influencing factors and solves the problem that single-component analysis cannot reflect the overall crack resistance of the structure, thus constructing an integrated analysis foundation that fits the actual engineering scenario. Step S2 constructs a heat exchange model of the pier cap and calculates the temperature field. By refining the simulation of hydration heat release, the influence of ambient temperature, and the thermal effect of cooling water pipes, it avoids the problem of insufficient temperature field accuracy caused by the simplification of calculations in existing technologies. At the same time, it provides accurate data support for subsequent stress field analysis, solving the problem of temperature field and stress from the source. The hidden danger of field disconnection; Step S3 establishes a direct correlation between "temperature change and stress response" by "inheriting the heat exchange model of the foundation and constructing a stress calculation model based on the temperature field results". At the same time, it combines the time-varying characteristics of the early tensile strength and elastic modulus of concrete to truly reflect the early stress evolution process of the structure, and completely solves the problems of fragmented analysis of temperature stress field and distortion of stress calculation in the existing technology; Step S4 adopts a dual analysis method combining principal tensile stress discrimination and extended finite element method. It scientifically determines the possibility of cracking by comparing principal tensile stress and tensile strength, and accurately locates the crack distribution area by using extended finite element method. This makes up for the shortcomings of the existing technology that only relies on a single index and cannot analyze crack distribution, and provides a comprehensive basis for the formulation of targeted crack-resistant measures.

[0007] As a preferred implementation scheme for crack resistance analysis of large-volume concrete structures, in step S1, the finite element program ABAQUS is used to construct the simulation analysis model of the large-volume concrete structure; step S2 includes: establishing the heat exchange model of the foundation based on the three-dimensional eight-node hexahedral thermal conduction element DC3D8, simulating the heat release process of concrete hydration heat through the subroutine HETVAL, and running the foundation heat exchange model to obtain the numerical solution of the temperature field. The ABAQUS finite element program has powerful nonlinear analysis capabilities and a rich element library. Combined with the three-dimensional eight-node hexahedral thermal conduction element DC3D8, it can accurately restore the spatial geometric features and heat conduction path of the foundation, avoiding calculation deviations caused by simplified elements; the subroutine HETVAL can realize the dynamic simulation of the heat release process of hydration heat, which, compared with traditional fixed parameter calculations, can more realistically reflect the heat release law of concrete at different ages, ultimately controlling the error of the temperature field numerical solution to a lower range, providing higher-precision basic data for subsequent stress field calculations, and further improving the reliability of the overall crack resistance analysis.

[0008] As a preferred implementation scheme for crack resistance analysis of large-volume concrete structures, a composite exponential formula is used to calculate the early-stage hydration heat of concrete. The composite exponential formula is as follows: Q(t) = Q0 × (1 − e⁻ᵃᵗᵇ) In the formula, Q(t) is the heat of hydration generated by cement on day t of concrete pouring, in kJ / kg; Q0 is the heat of hydration generated by cement when the number of days of concrete pouring approaches infinity, in kJ / kg; t is the number of days of concrete pouring; and a and b are constants. The composite exponential formula, through the coordinated adjustment of the three parameters Q0, a, and b, can accurately fit the nonlinear variation law of the early-stage heat of hydration of concrete under different cement types and admixture ratios, overcoming the shortcomings of traditional linear formulas or single exponential formulas that cannot simultaneously consider the characteristics of "rapid heat release in the early stage" and "slow decay in the later stage." By substituting the hydration heat test data of cement in actual engineering to determine the parameters, the deviation between the calculated and measured values ​​of the early-stage heat of hydration can be reduced, thereby improving the accuracy of temperature field calculation and providing a key guarantee for the accurate calculation of thermal stress in subsequent stress analysis.

[0009] As a preferred implementation scheme for crack resistance analysis of large-volume concrete structures, in step S3, the mesh type of the foundation heat exchange model is modified to a three-dimensional eight-node hexahedral stress calculation unit C3D8. This simulates the early time-varying effects of concrete tensile strength and elastic modulus, as well as the early expansion and contraction process of concrete, and calculates the stress field of the large-volume concrete structure based on the temperature field. The three-dimensional eight-node hexahedral stress calculation unit C3D8 has excellent stress transfer and deformation simulation capabilities. Compared with other types of units, it can more accurately reproduce the stress distribution state of concrete under temperature changes and its own shrinkage. By simultaneously simulating the early time-varying effects of tensile strength and elastic modulus and the expansion and contraction process, it avoids the stress calculation distortion problems caused by using fixed mechanical parameters or ignoring shrinkage deformation in traditional methods. At the same time, the stress field is directly calculated based on the previous temperature field results, achieving seamless connection of "thermal-mechanical" coupled analysis. This ensures that the superposition calculation of temperature stress and shrinkage stress is more realistic, significantly improving the reliability of the stress field results and providing a more accurate stress basis for crack analysis.

[0010] As a preferred implementation scheme for crack resistance analysis of large-volume concrete structures, in step S1, the concrete strength grade of the foundation is C40, the thermal conductivity λ=10.6kJ / h / m / ℃, the specific heat c=0.96kJ / kg / ℃, the density ρ=2430kg / m³, and the coefficient of linear expansion is 1.0×10⁻ 5 / ℃; the concrete strength grade of the main beam is C55, with a thermal conductivity λ=10.6kJ / h / m / ℃, specific heat c=0.96kJ / kg / ℃, density ρ=2450kg / m³, and linear expansion coefficient of 1.0×10⁻ 5 / ℃. Addressing the strength grade difference between the C40 foundation and the C55 main beam, key thermal and mechanical parameters (such as density) are clearly distinguished, avoiding the model distortion problems caused by using uniform parameters for different strength grades of concrete in traditional methods. Precise parameter values ​​accurately reflect the differences in heat conduction efficiency, mass distribution, and temperature deformation sensitivity between the two components, making the simulation model more closely match the material properties of the actual engineering structure. This improves the relevance and accuracy of temperature and stress field calculations, ensuring that subsequent crack resistance analysis can accurately match the crack resistance performance requirements of different components.

[0011] As a preferred implementation scheme for crack resistance analysis of large-volume concrete structures, the operating environment includes: for the foundation: the historical temperature of the same period of the previous year during the planned construction period, and ±5°C of that historical temperature, forming three operating environments; for the main beam: the historical temperature of the same period of the previous year during the planned construction period. Using a multi-condition environment setting of "historical temperature ±5°C" for the foundation can comprehensively cover possible temperature fluctuations during construction, avoiding the limitations of traditional single temperature parameters in dealing with extreme temperature changes, and allowing for early prediction of the foundation's crack resistance risk under different temperature conditions. The environmental parameters for the main beam are set based on the historical temperature of the planned construction period, ensuring both close alignment with the actual construction environment and considering analysis efficiency. This design makes the operating environment simulation more targeted and comprehensive, ensuring that the crack resistance analysis results can provide a more scientific basis for the construction sequence arrangement of different components and the adjustment of insulation measures, reducing engineering risks caused by environmental temperature deviations.

[0012] As a preferred implementation scheme for crack resistance analysis of large-volume concrete structures, the simulation analysis model of the foundation also includes a cooling water pipe unit. The cooling water pipe is regarded as a constant temperature source inside the concrete, and the effect of the cooling water pipe is converted into the convective heat transfer coefficient of the cooling water pipe surface.

[0013] In the formula, The inner diameter of the cooling water pipe. β is the outer diameter of the cooling water pipe; U is the cooling water flow velocity; Kp is the thermal conductivity of the cooling water pipe, which, for the cast iron pipe selected in this report, is kp = 160 kJ / (h·m·℃); α is an adjustment coefficient related to the geometric dimensions of the cooling water pipe. By treating the cooling water pipes as a constant temperature source and converting them into convective heat transfer coefficients, a quantitative simulation of the cooling effect of the cooling water pipes was achieved, overcoming the temperature field calculation deviations caused by neglecting or simplifying the cooling water pipes in traditional models. Combining the actual thermal conductivity and geometric dimension adjustment coefficients of the cast iron water pipes, the heat exchange efficiency of the cooling water pipes under different pipe diameters and water flow rates can be accurately reflected. This makes the internal temperature field distribution of the foundation more closely resemble the dynamic balance process of "hydration heat release - cooling system temperature control" during actual construction, effectively optimizing the layout and operating parameters of the cooling water pipes and improving the accuracy of foundation crack resistance control.

[0014] As a preferred implementation scheme for crack resistance analysis of large-volume concrete structures, in step S3, the early expansion and shrinkage process of concrete is simulated through the subroutine UEXPAN, and the calculation formula is as follows:

[0015] In the formula: This represents the shrinkage strain of concrete during the moisture saturation period. This represents the concrete shrinkage strain during the humidity decrease period. , To set a coefficient, when the concrete is C40, , When the concrete is C55, , E represents the elastic modulus of concrete. Let V be the volume of the hydration products. For reference volume, Here, S is the pore volume parameter of concrete, ρ is the surface area of ​​concrete, R is the density of water, T is the ambient temperature, and M is the molar mass of water. This refers to the bulk modulus of concrete. The reference modulus is RH, representing relative humidity. The subroutine UEXPAN enables refined dynamic simulation of the early expansion and shrinkage process of concrete. Compared to traditional static shrinkage coefficient calculations, it more realistically reflects the volumetric deformation patterns of concrete at different ages and under varying environmental humidity. The formula sets differentiated k_1 and k_2 coefficients for C40 and C55 concrete and incorporates multiple parameters such as elastic modulus, ambient temperature, and relative humidity. This allows for precise quantification of the shrinkage strain differences of concrete of different strength grades throughout the entire "humidity saturation-humidity reduction" stage, avoiding stress calculation errors caused by a single shrinkage parameter. This design makes the calculation of the impact of expansion and shrinkage on structural stress more accurate, providing more reliable deformation data support for subsequent crack probability assessment and crack distribution analysis.

[0016] As a preferred implementation scheme for crack resistance analysis of large-volume concrete structures, in step S2, the heat exchange model of the foundation considers the heat exchange between concrete and air: the thermal emissivity of concrete is taken as 0.92; the convective heat transfer coefficient β of concrete to air is calculated based on surface roughness and wind speed. The formula for the convective heat transfer coefficient of rough surface is β=19.8×(1+0.33F), and the formula for the convective heat transfer coefficient of smooth surface is β=17.4×(1+0.33F), where F is the wind force level and v is the wind speed. By setting a specific value for the thermal emissivity of concrete and differentiating the calculation formula of the convective heat transfer coefficient according to surface roughness, the accurate quantification of the heat exchange process between concrete and air is achieved. Traditional methods often use a fixed convective heat transfer coefficient, which cannot reflect the influence of surface condition and wind speed on heat exchange efficiency. However, this scheme correlates wind force level with wind speed, which can dynamically adapt to wind field conditions under different construction environments, making the heat exchange calculation of the foundation surface more realistic. Accurate heat exchange simulation can effectively improve the reliability of the boundary conditions of the temperature field of the foundation, avoid distortion of the internal temperature gradient caused by deviations in surface heat dissipation calculations, and further ensure the overall accuracy of temperature field calculations.

[0017] As a preferred implementation scheme for crack resistance analysis of large-volume concrete structures, in step S3, the formula for calculating the elastic modulus of concrete is:

[0018] In the formula: This is the elastic modulus of concrete at an age of t, in MPa. The modulus of elasticity of concrete under standard curing conditions for 28 days is 34,500 MPa for C40 concrete and 36,000 MPa for C55 concrete. The coefficient is set to 0.09. The correction factor for admixtures is 0.98 when 30% fly ash is added. The formula for calculating tensile strength is:

[0019] In the formula, The tensile strength of concrete at age t, in MPa; The standard value for tensile strength of concrete is 2.39 MPa for C40 concrete and 2.74 MPa for C55 concrete; R is a coefficient, taken as 0.3.

[0020] The elastic modulus calculation formula incorporates an admixture correction coefficient β, accurately reflecting the impact of fly ash content on the mechanical properties of concrete. The tensile strength calculation formula uses an exponential function to fit the early strength growth pattern. Both formulas set differentiated standard parameters for C40 and C55 concrete, overcoming the distortion of mechanical parameters caused by traditional methods that ignore the influence of admixtures or use uniform time-varying formulas. The elastic modulus and tensile strength calculated using these formulas can dynamically match the early mechanical property evolution of concrete from pouring to curing, making the matching of "material strength - structural stress" in stress field calculations more accurate, significantly improving the reliability of stress calculation results, and providing a more scientific strength basis for crack analysis.

[0021] As can be seen from the above technical solutions, the advantages of this invention are as follows: This solution improves the accuracy and practicality of crack resistance analysis of large-volume concrete structures from multiple dimensions. Specifically, it uses the ABAQUS finite element program with three-dimensional eight-node hexahedral elements and dedicated subroutines, combined with mechanical parameter formulas such as composite exponential formulas and admixture correction coefficients, to accurately reproduce the nonlinear changes in the heat of hydration of concrete, the time-varying laws of early mechanical properties, and the dynamic process of expansion and contraction. Furthermore, by distinguishing the thermal and mechanical parameters of C40 foundations and C55 concrete, it achieves precise matching of the characteristics of components with different strength grades. Simultaneously, it adopts differentiated settings for the foundation's "historical temperature ±5℃" multi-condition and the main beam's historical temperature, taking into account the service environment. By combining the constant temperature source conversion of cooling water pipes with the correlation calculation of surface roughness and wind speed in the heat exchange between concrete and air, this method comprehensively covers actual influencing factors such as temperature fluctuations, cooling system effects, and wind field conditions during construction. It effectively avoids calculation deviations caused by parameter standardization, environment simplification, and process simplification in traditional methods. Finally, through seamless connection of "thermal-mechanical" coupling and multi-parameter collaborative optimization, the calculation errors of temperature field and stress field are significantly reduced, and the crack probability judgment and crack distribution analysis are more in line with engineering practice. This not only provides a scientific basis for the construction sequence arrangement of different components, the adjustment of insulation measures, and the optimization of cooling water pipes, but also allows for the early prediction of crack resistance risks, significantly improving the reliability and engineering guidance value of the overall crack resistance analysis. Attached Figure Description

[0022] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart illustrating a specific embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the specific embodiments. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this patent, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this patent.

[0025] like Figure 1 As shown, a crack resistance analysis method for large-volume concrete structures includes the following steps: S1. Using concrete formulation, dimensions, construction technology, and service environment as constraints, a simulation analysis model of a large-volume concrete structure is established using the finite element program ABAQUS. This simulation analysis model includes the foundation cap and main beams. The concrete of the foundation is grade C40, with a thermal conductivity λ = 10.6 kJ / h / m / ℃, specific heat c = 0.96 kJ / kg / ℃, density ρ = 2430 kg / m³, and coefficient of linear expansion of 1.0 × 10⁻⁻⁻⁶. 5 / ℃; the concrete strength grade of the main beam is C55, with a thermal conductivity λ=10.6kJ / h / m / ℃, specific heat c=0.96kJ / kg / ℃, density ρ=2450kg / m³, and linear expansion coefficient of 1.0×10⁻ 5 / ℃; The usage environment includes: Foundation: The historical temperature of the same period of the previous year during the construction planning period, plus or minus 5°C of that historical temperature, form three usage environments; Main beam: Historical temperature of the same period of the previous year during the planned construction period.

[0026] S2. Construct a heat exchange model for the foundation and calculate the temperature field: A heat exchange model for the foundation was established based on a three-dimensional eight-node hexahedral heat conduction element (DC3D8). The heat release process of concrete hydration heat was simulated using the subroutine HETVAL. The numerical solution of the temperature field was obtained by running the heat exchange model of the foundation. The simulated numerical solution of the temperature field was compared with the measured temperature to ensure the correctness of the model. Among them, a composite exponential formula was used to calculate the early hydration heat generation of concrete. The composite exponential formula is as follows: Q(t) = Q0 × (1 − e⁻ᵃᵗᵇ) In the formula, Q(t) is the heat of hydration of cement on day t of concrete pouring, in kJ / kg; Q0 is the heat of hydration of cement when the number of days of concrete pouring approaches infinity, in kJ / kg; t is the number of days of concrete pouring; a and b are constants. The simulation analysis model of the foundation also includes a cooling water pipe unit. The cooling water pipe is regarded as a constant temperature source inside the concrete, and the effect of the cooling water pipe is converted into the convective heat transfer coefficient of the cooling water pipe surface.

[0027] In the formula, The inner diameter of the cooling water pipe. β is the outer diameter of the cooling water pipe; U is the cooling water flow velocity; Kp is the thermal conductivity of the cooling water pipe, which, for the cast iron pipe selected in this report, is kp = 160 kJ / (h·m·℃); α is an adjustment coefficient related to the geometric dimensions of the cooling water pipe. ; The heat exchange model of the foundation considers the heat exchange between concrete and air: the thermal emissivity of concrete is taken as 0.92; the convective heat transfer coefficient β of concrete to air is calculated based on surface roughness and wind speed. The formula for the convective heat transfer coefficient of rough surface is β=19.8×(1+0.33F), and the formula for the convective heat transfer coefficient of smooth surface is β=17.4×(1+0.33F), where F is the wind force level and v is the wind speed.

[0028] S3. Construct a stress calculation model based on the foundation heat exchange model and temperature field, calculate the stress field, modify the mesh type of the foundation heat exchange model to a three-dimensional eight-node hexahedral stress calculation element C3D8, simulate the early time-varying effects of concrete tensile strength and elastic modulus and the early expansion and contraction process of concrete, and calculate the stress field of the large-volume concrete structure based on the temperature field: The formula for calculating the elastic modulus of concrete is:

[0029] In the formula: This is the elastic modulus of concrete at an age of t, in MPa. The modulus of elasticity of concrete under standard curing conditions for 28 days is 34,500 MPa for C40 concrete and 36,000 MPa for C55 concrete. The coefficient is set to 0.09. The correction factor for admixtures is 0.98 when 30% fly ash is added. The formula for calculating tensile strength is:

[0030] In the formula, The tensile strength of concrete at age t, in MPa; The standard value for tensile strength of concrete is 2.39 MPa for C40 concrete and 2.74 MPa for C55 concrete; R is a coefficient, taken as 0.3.

[0031] The early expansion and shrinkage process of concrete is simulated using the subroutine UEXPAN, and the calculation formula is as follows:

[0032] In the formula: This represents the shrinkage strain of concrete during the moisture saturation period. This represents the concrete shrinkage strain during the humidity decrease period. , To set a coefficient, when the concrete is C40, , When the concrete is C55, , E represents the elastic modulus of concrete. Let V be the volume of the hydration products. For reference volume, Here, S is the pore volume parameter of concrete, ρ is the surface area of ​​concrete, R is the density of water, T is the ambient temperature, and M is the molar mass of water. This refers to the bulk modulus of concrete. The reference modulus is RH, which represents relative humidity.

[0033] S4. Based on the stress field, the possibility of early cracking and crack distribution of the simulation analysis model of large-volume concrete structure are analyzed by using principal tensile stress discrimination and extended finite element method.

[0034] As can be seen from the above embodiments, the beneficial effects of the present invention are as follows: This solution employs the ABAQUS finite element program, combined with three-dimensional eight-node hexahedral elements and dedicated subroutines, and introduces mechanical parameter formulas based on composite exponential formulas and admixture correction coefficients. This combination not only accurately reproduces the nonlinear variation characteristics of concrete hydration heat, the evolution of early mechanical properties over time, and the dynamic process of expansion and contraction, but also achieves precise adaptation of the characteristics of components with different strength grades by distinguishing the differences in thermal and mechanical parameters between C40 foundations and C55 concrete. In terms of environmental conditions and boundary conditions, differentiated designs are implemented for the component's usage scenarios: multi-condition simulation with "historical air temperature ±5℃" is used for foundations, while separate settings are applied to the main beams based on historical air temperatures; simultaneously, a constant temperature source conversion method for cooling water pipes is incorporated, along with concrete-air heat exchange calculations relating surface roughness and wind speed. Through these measures, the actual influencing factors such as temperature fluctuations, the effect of the cooling system, and the wind field environment during construction are comprehensively covered, effectively avoiding calculation deviations caused by parameter standardization, singular environmental conditions, and simplified physical processes in traditional analysis methods. By leveraging seamless integration of thermo-mechanical coupling and multi-parameter collaborative optimization, the calculation errors of temperature and stress fields are significantly reduced, making crack probability assessment and crack distribution analysis more consistent with actual engineering conditions. This solution not only provides scientific support for the planning of construction sequence for different components, adjustment of insulation measures, and optimization of cooling water pipe layout, but also allows for the early prediction of crack resistance risks, thereby significantly enhancing the reliability of overall crack resistance analysis and increasing its guiding significance for practical engineering projects.

[0035] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for crack resistance analysis of large-volume concrete structures, characterized in that, Includes the following steps: S1. Establish a simulation analysis model for a large-volume concrete structure, taking concrete formula, dimensions, construction technology and usage environment as constraints. The simulation analysis model for a large-volume concrete structure includes a foundation and main beam. S2. Construct a heat exchange model for the foundation and calculate the temperature field; S3. Construct a stress calculation model based on the heat exchange model and temperature field of the foundation, and calculate the stress field; S4. Based on the stress field, the possibility of early cracking and crack distribution of the simulation analysis model of large-volume concrete structure are analyzed by using principal tensile stress discrimination and extended finite element method.

2. The method for crack resistance analysis of large-volume concrete structures according to claim 1, characterized in that, In step S1, the finite element program ABAQUS is selected to construct the simulation analysis model of the large-volume concrete structure. Step S2 includes: establishing the foundation heat exchange model based on the three-dimensional eight-node hexahedral heat conduction unit DC3D8, simulating the heat release process of concrete hydration heat through the subroutine HETVAL, and running the foundation heat exchange model to obtain the numerical solution of the temperature field.

3. The method for crack resistance analysis of large-volume concrete structures according to claim 2, characterized in that, The early-stage hydration heat generation of concrete is calculated using a composite index formula, which is: Q(t) = Q0 × (1 − e⁻ᵃᵗᵇ) In the formula, Q(t) is the heat of hydration of cement on day t of concrete pouring, in kJ / kg; Q0 is the heat of hydration of cement when the number of days of concrete pouring approaches infinity, in kJ / kg; t is the number of days of concrete pouring; a and b are constants.

4. The method for crack resistance analysis of large-volume concrete structures according to claim 2, characterized in that, In step S3, the mesh type of the foundation heat exchange model is modified to a three-dimensional eight-node hexahedral stress calculation unit C3D8 to simulate the early time-varying effects of concrete tensile strength and elastic modulus and the early expansion and contraction process of concrete, and the stress field of the large-volume concrete structure is calculated based on the temperature field.

5. The method for crack resistance analysis of large-volume concrete structures according to claim 1, characterized in that, In step S1, the concrete strength grade of the foundation is C40, with a thermal conductivity λ = 10.6 kJ / h / m / ℃, specific heat c = 0.96 kJ / kg / ℃, density ρ = 2430 kg / m³, and linear expansion coefficient of 1.0 × 10⁻⁻⁻⁶. 5 / ℃; the concrete strength grade of the main beam is C55, with a thermal conductivity λ=10.6kJ / h / m / ℃, specific heat c=0.96kJ / kg / ℃, density ρ=2450kg / m³, and linear expansion coefficient of 1.0×10⁻ 5 / ℃.

6. The method for crack resistance analysis of large-volume concrete structures according to claim 1, characterized in that, The usage environment includes: Foundation: The historical temperature of the same period of the previous year during the construction planning period, plus or minus 5°C of that historical temperature, form three usage environments; Main beam: Historical temperature of the same period of the previous year during the planned construction period.

7. The method for crack resistance analysis of large-volume concrete structures according to claim 1, characterized in that, The simulation analysis model of the foundation also includes a cooling water pipe unit. The cooling water pipe is regarded as a constant temperature source inside the concrete, and the effect of the cooling water pipe is converted into the convective heat transfer coefficient of the cooling water pipe surface. In the formula, The inner diameter of the cooling water pipe. β is the outer diameter of the cooling water pipe; U is the cooling water flow velocity; Kp is the thermal conductivity of the cooling water pipe, which, for the cast iron pipe selected in this report, is kp = 160 kJ / (h·m·℃); α is an adjustment coefficient related to the geometric dimensions of the cooling water pipe. .

8. The method for crack resistance analysis of large-volume concrete structures according to claim 4, characterized in that, In step S3, the early expansion and shrinkage process of concrete is simulated using the subroutine UEXPAN. The calculation formula is as follows: In the formula: This represents the shrinkage strain of concrete during the moisture saturation period. This represents the concrete shrinkage strain during the humidity decrease period. , To set a coefficient, when the concrete is C40, , When the concrete is C55, , E represents the elastic modulus of concrete. Let V be the volume of the hydration products. For reference volume, Here, S is the pore volume parameter of concrete, ρ is the surface area of ​​concrete, R is the density of water, T is the ambient temperature, and M is the molar mass of water. This refers to the bulk modulus of concrete. The reference modulus is RH, which represents relative humidity.

9. The method for crack resistance analysis of large-volume concrete structures according to claim 1, characterized in that, In step S2, the heat exchange model of the foundation considers the heat exchange between concrete and air: the thermal emissivity of concrete is taken as 0.92; the convective heat transfer coefficient β of concrete to air is calculated based on surface roughness and wind speed. The formula for the convective heat transfer coefficient of rough surface is β=19.8×(1+0.33F), and the formula for the convective heat transfer coefficient of smooth surface is β=17.4×(1+0.33F), where F is the wind force level and v is the wind speed.

10. The method for crack resistance analysis of large-volume concrete structures according to claim 4, characterized in that, In step S3, the formula for calculating the elastic modulus of concrete is: In the formula: This is the elastic modulus of concrete at an age of t, in MPa. The modulus of elasticity of concrete under standard curing conditions for 28 days is 34,500 MPa for C40 concrete and 36,000 MPa for C55 concrete. The coefficient is set to 0.

09. The correction factor for admixtures is 0.98 when 30% fly ash is added. The formula for calculating tensile strength is: In the formula, The tensile strength of concrete at age t, in MPa; The standard value for tensile strength of concrete is 2.39 MPa for C40 concrete and 2.74 MPa for C55 concrete; R is a coefficient, taken as 0.3.

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