Key threshold determination method for temperature control of mass concrete in construction and maintenance period

Abstract

The invention provides a method for determining a key threshold value of mass concrete temperature control in a construction period, and belongs to the technical field of constructional engineering.The method comprises the steps that a simulation analysis method is adopted, a mass bottom layer concrete model is established preferentially, and then an upper layer concrete thin-wall structure model is established on the upper surface of the mass bottom layer concrete model; the whole hydration heat process of the upper-layer concrete thin-wall structure model is simulated; a temperature time-varying load is applied to a large-volume underlying concrete model, stress and temperature distribution of an upper-layer concrete thin-wall structure model are obtained, and finally whether a temperature crack occurs or not is judged according to a stress upper limit value. And key threshold values such as a temperature change rate threshold value, an internal highest temperature threshold value and an exterior-interior temperature difference threshold value in the mass concrete temperature control process are obtained. According to the method, a simulation analysis model of the mass bottom concrete-upper concrete thin-wall structure is built, the key threshold value of model temperature control is obtained, and a design basis is provided for temperature control and cracking prevention of mass concrete in the building and maintenance period.

Description

Technical Field

[0001] The present invention belongs to the field of construction engineering technology, in particular to a temperature control technology for large-volume concrete during the construction and curing period, and more particularly to a method for determining a key threshold value for temperature control of large-volume concrete during the construction and curing period. Background Art

[0002] Controlling temperature stress and cracks caused by hydration heat in large-volume concrete has long been a technical challenge in the construction industry. During construction and maintenance, these concrete structures (such as dams, bridge foundations, and high-rise building slabs) experience a dramatic rise in internal temperature due to the massive heat generated by cement hydration reactions. This heat, coupled with rapid heat dissipation from the outside due to environmental factors, creates a significant temperature difference between the interior and exterior of the structure. If the resulting temperature stress exceeds the concrete's tensile strength, it can cause harmful cracks, seriously impacting the durability and safety of the structure.

[0003] Traditional temperature control and crack prevention methods often rely on empirical formulas or simplified models to determine temperature control thresholds (such as temperature change rate and maximum temperature limit). However, the complexity of concrete structure dimensions, material properties, environmental conditions, and layered pouring processes in actual projects makes it difficult for empirical methods to accurately predict the dynamic coupling relationship between temperature and stress fields. Although numerical simulation technology has been gradually applied to temperature control analysis, existing models often ignore the staged impact of layered construction or fail to fully consider the interaction mechanism between the "bulk bottom concrete layer and the upper thin-walled structure." For example, due to its small thickness and rapid heat dissipation, the upper thin-walled structure has a significantly different hydration heat process than the underlying bulk concrete. Existing models often use homogeneous assumptions or single-structure simulations, resulting in deviations from the actual working conditions in the temperature load application method and insufficient reliability of the threshold calculation results. Therefore, a method that can accurately simulate the layered construction process of bulk concrete and the dynamic changes in the coupled temperature and stress fields is urgently needed to scientifically determine the key temperature control thresholds and provide theoretical support for precise temperature control and crack prevention during the construction and curing period of concrete.

[0004] In response to the above problems, the present invention aims to propose a method for determining the key threshold value of temperature control of large-volume concrete during the construction and curing period. By using a simulation analysis method, a large-volume bottom concrete model is first established, and then an upper-layer concrete thin-walled structure model is established on its upper surface, and the entire hydration heat process of the upper-layer concrete thin-walled structure model is simulated; by applying a temperature-varying load to the large-volume bottom concrete model and obtaining the stress and temperature distribution of the upper-layer concrete thin-walled structure model, it is finally determined whether temperature cracks appear based on the upper stress limit value, and then key threshold values ​​such as the temperature change rate threshold, the internal maximum temperature threshold, and the inside-outside temperature difference threshold in the temperature control process of large-volume concrete are obtained. The present invention obtains the key threshold value of model temperature control by building a simulation analysis model of a large-volume bottom concrete-upper-layer concrete thin-walled structure, providing a design basis for temperature control and crack prevention of large-volume concrete during the construction and curing period.

[0005] After review, no published patents involve methods for determining the critical threshold value for temperature control of large-volume concrete during the construction and curing period. The only patents related to numerical simulation of temperature control of large-volume concrete are as follows:

[0006] CN106021755B discloses a method for simulating and analyzing the temperature stress of large-volume concrete in the nuclear island raft foundation of a nuclear power plant. The method can calculate the temperature stress at any position of the nuclear island raft foundation and at any time within the simulation time, and form a temperature cloud map and a principal stress cloud map. However, the method for obtaining the key threshold value of temperature control is not mentioned.

[0007] CN116579069B discloses an intelligent design method and device for temperature control strategy of large-volume concrete structures, which can provide a "safety-quality-efficiency-cost" balanced cooling strategy for large-volume concrete structures, but does not involve the impact of lower-layer cooling on upper-layer thin-walled structures. Summary of the Invention

[0008] Based on the above-mentioned problem that the existing threshold calculation results are not reliable enough and difficult to apply to the "large-volume bottom concrete-upper thin-wall structure" mechanism, a method for determining the key threshold value for temperature control of large-volume concrete during the construction and curing period is provided, which provides a design basis for temperature control and crack prevention of large-volume concrete during the construction and curing period.

[0009] A method for determining a critical threshold value for temperature control of large-volume concrete during the construction and curing period is characterized in that it includes a method for simulating internal temperature strain of large-volume concrete during the construction and curing period, comprising the following steps:

[0010] S1: Use the 3D software Unigraphics NX to establish a geometric model of the large-volume bottom concrete layer and the upper concrete thin-walled structure. When establishing the geometric model, the model uses the large-volume bottom concrete layer and the upper concrete thin-walled structure to model together, and the height direction is taken as the z-axis in the coordinate system. The completed geometric model of the large-volume bottom concrete layer and the upper concrete thin-walled structure is saved as a file with the suffix .prt;

[0011] S2: Import the geometric model in S1 into the ABAQUS finite element software for finite element meshing. Import the file with the suffix .prt into ABAQUS / CAE through "File>Import>Geometry". In ABAQUS, first enter the "Part" module, then select the appropriate file type in the pop-up dialog box and import it. During the import process, you can set parameters such as units and scaling. After the import is complete, the geometric model of the upper concrete thin-walled structure is first divided and cut layer by layer along the layered pouring steps to facilitate the division of the finite element mesh. The specific steps include the following:

[0012] S21: To reduce the impact of irregular geometric shapes on the internal temperature simulation of the structure and reduce the amount of model calculation, the large-volume bottom concrete geometry model is established as a cylindrical structure, and the upper concrete thin-walled structure is set as a ring structure;

[0013] S22: Based on the common symmetry center of the large-volume bottom concrete geometric model and the upper concrete thin-walled structure geometric model, according to the principle of central symmetry, a section with a central angle of 15° was cut out for subsequent analysis;

[0014] S23: In order to analyze the effect of heating of large-volume bottom concrete on the upper concrete thin-wall structure, the upper concrete thin-wall structure is cut layer by layer along the height direction, and the internal steel bars of the upper concrete thin-wall structure are modeled;

[0015] S24: In order to consider that the elastic modulus of concrete cannot reach the design value in time during curing, the concrete elastic modulus reduction factor is 0.333 when assigning material properties;

[0016] S25: The force and deformation of the two end sections are set by a custom coordinate system orthogonal to the section to meet the axisymmetric requirements; in order to achieve the shrinkage value of the concrete during the curing period of 400×10 -6 The initial temperature is set by the cooling method. The initial temperature is the pouring temperature plus 40 ° C. The temperature linear expansion coefficient of concrete is defined as 1 × 10 -5 , set the concrete temperature to decrease by 40℃, and the temperature change value of the steel bar to 0℃;

[0017] S26: Mesh the massive bottom concrete, upper concrete thin-walled structure, and steel bars, using C3D8R elements for concrete and T3D2 elements for steel bars.

[0018] S3: Set the analysis type, time step, time function, initial conditions, material parameters, and ambient temperature load. The specific process is as follows:

[0019] S31: Analysis type setting: set the analysis type to static analysis mode;

[0020] S32: Time step setting, time function setting: the analysis step length is defined as needed, the initial incremental step is defined as 0.1, the maximum incremental step is defined as 0.2, and the time function is defined as a linear interpolation curve according to the time accuracy required by the calculation results;

[0021] S33: Initial condition setting: The initial temperature of the bulk bottom concrete is used as the initial condition. The initial temperature should be the temperature of the first batch of bulk bottom concrete when it is poured at the location where the bulk bottom concrete is constructed.

[0022] S34: Material parameter setting: Set the material parameters for different parts and different curing stages of large-volume bottom concrete according to the concrete grade and steel bar grade;

[0023] S35: Ambient temperature load definition: During the concrete construction and curing phase, this load is the temperature change of the concrete caused by the internal heat generated by cement hydration. To optimize the calculation process and improve efficiency, the concrete portion is defined to be gradually cooled from the initial pouring temperature to the ambient temperature. This load is applied by specifying the concrete portion in the finite element model and inputting a defined cooling function curve.

[0024] S4: Submit simulation analysis calculation. After completing the above settings, you can submit the simulation analysis calculation;

[0025] S5: Extract analysis results. After simulation analysis, the strain of any part of the large-volume bottom concrete during the pouring process and at any time within the calculation time range after the pouring is completed, as well as the strain distribution of the large-volume bottom concrete, can be extracted.

[0026] Furthermore, the method for determining the critical threshold value of temperature control of large-volume concrete during the curing period also includes a method for determining the critical threshold value of temperature control based on simulation results:

[0027] F1: Simulate the cooling effect of the large volume of bottom concrete on the upper concrete thin-walled structure. The method is as follows:

[0028] F11: Set the temperature of the bulk bottom concrete to the post-hypothermia temperature (usually the ambient temperature);

[0029] F12: In different calculation conditions, set the upper concrete thin-wall structure temperature to 10℃, 20℃, 30℃, 40℃, 50℃, etc. higher than the ambient temperature;

[0030] F13: Allow the upper concrete thin-wall structure temperature to drop to ambient temperature automatically;

[0031] F14: Observe the maximum stress between the upper concrete thin-wall structure and the bulky bottom concrete in the model, and determine the preset temperature value of the upper concrete thin-wall structure when the stress exceeds the concrete material's bearing limit. This determines the temperature difference threshold between the upper concrete thin-wall structure and the environment that would cause cracking if the bulky bottom concrete were allowed to lose temperature.

[0032] F2: Coordinated cooling simulation of a large concrete base and thin-walled upper concrete structure. The method is as follows:

[0033] F21: In different calculation conditions, set the temperature of the upper concrete thin-wall structure and the large volume bottom concrete to 10℃, 20℃, 30℃, 40℃, 50℃ higher than the ambient temperature, etc.

[0034] F22: Observe the maximum stress of the entire model and determine the corresponding model temperature drop rate when the stress exceeds the concrete material's bearing limit. This determines the cooling rate threshold that causes structural cracking while controlling the overall cooling rate of the model.

[0035] F3: Simulate the temperature difference between the inside and outside of the upper concrete thin-wall structure. The method is as follows:

[0036] F31: In different calculation conditions, the temperature difference between the inside and outside of the upper concrete thin-wall structure is set to 10℃, 20℃, 30℃, 40℃, 50℃, etc.

[0037] F32: Observe the maximum stress of the upper concrete thin-walled structure model and determine the corresponding internal and external temperature difference threshold of the upper concrete thin-walled structure model when the stress exceeds the bearing limit of the concrete material.

[0038] F4: Simulate the coordinated heating of a large-volume bottom concrete layer and an upper concrete thin-walled structure. The method is as follows:

[0039] F41: Set the initial temperature of the upper concrete thin-wall structure and the large volume bottom concrete to the ambient temperature;

[0040] F42: In different calculation conditions, set the temperature of the upper concrete thin-wall structure and the large volume bottom concrete to 10℃, 20℃, 30℃, 40℃, 50℃ above the ambient temperature, etc.

[0041] F43: Observe the maximum stress of the entire model and determine the internal temperature value of the model when it exceeds the bearing limit of the concrete material. This will determine the maximum cracking temperature threshold inside the model that will cause structural cracking while controlling the overall heating rate of the model.

[0042] Compared with the prior art, the advantages and positive effects of the present invention are:

[0043] (1) By modeling the large-volume bottom concrete as a cylinder and the upper thin-walled structure as a ring, and using 15° symmetrical cutting, the interference of irregular geometric shapes on the temperature field simulation is effectively reduced, while the model complexity is greatly reduced and the calculation time is shortened. The concrete elastic modulus reduction coefficient is introduced to consider the actual working conditions where the elastic modulus does not reach the design value during the curing period, avoiding the stress prediction deviation caused by the overestimation of material stiffness in traditional methods. The C3D8R unit is used to simulate concrete and the T3D2 unit is used to simulate steel bars, taking into account both calculation accuracy and efficiency, which is particularly suitable for the coupled analysis of large-volume structures and steel bars.

[0044] (2) Through four types of simulations, we systematically analyze different temperature control scenarios, including temperature loss constraint, coordinated cooling, internal and external temperature difference, and coordinated heating. For the first time, we have constructed a threshold system that covers the temperature control requirements of concrete throughout its entire life cycle. Based on step-by-step simulations with different preset temperature gradients (e.g., ±10-50°C), we accurately capture the critical point of structural stress over-limit, breaking through the static threshold limitations of traditional empirical formulas. At the same time, we consider the temperature change difference between concrete and steel bars, as well as the layered pouring and shrinkage strain (400×10 -6 ) on structural stress, solving the defect of existing technology that ignores the synergistic effect of materials.

[0045] (3) From Unigraphics NX modeling to ABAQUS finite element analysis, a standardized process is formed to support rapid adjustment of model parameters (such as initial temperature and time step) to adapt to different engineering scenarios; by defining linear interpolation curves and cooling function inputs, the complexity of hydration heat simulation is simplified and the calculation efficiency is significantly improved; by determining the threshold, the risk of cracking can be warned in advance, and maintenance measures (such as cooling rate control and insulation layer design) can be guided to reduce the rework rate of the project.

[0046] (4) Through the equivalent conversion of temperature field and strain field (ΔT = 40 ° C corresponds to 400 × 10 -6 strain), avoiding the high computational cost of traditional shrinkage models; in view of the different characteristics of large-volume and thin-walled structures, layered cutting and coordinated cooling simulation are adopted to achieve refined stress assessment of complex structures; the initial temperature and ambient temperature gradient are included in the calculation to better fit the actual construction environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0048] Figure 1 This is a flow chart of a temperature control simulation of large-volume concrete during the curing period provided in Example 1;

[0049] Figure 2 A model diagram for simulating temperature control of large-volume concrete during the curing period provided in Example 1;

[0050] Figure 3 A concrete unit diagram of an upper concrete thin-wall structure for temperature control simulation of large-volume concrete during the curing period provided in Example 1;

[0051] Figure 4A steel unit diagram of an upper concrete thin-wall structure for a temperature control simulation of large-volume concrete during the curing period provided in Example 1;

[0052] Figure 5 A concrete stress cloud diagram of an upper concrete thin-wall structure for a temperature control simulation of large-volume concrete during the curing period provided in Example 1;

[0053] Figure 6 A stress cloud diagram of the steel bars of the upper concrete thin-wall structure of a temperature control simulation of large-volume concrete during the curing period provided in Example 1;

[0054] Figure 7 A stress cloud diagram of the cross section of the junction between the upper concrete thin-wall structure and the large-volume bottom concrete layer, which simulates the constraint of the upper concrete thin-wall structure by cooling the large-volume bottom concrete layer provided in Example 2;

[0055] Figure 8 A concrete stress cloud diagram of an upper layer of thin-walled concrete structure simulating the constraint of an upper layer of thin-walled concrete structure by cooling a large volume of bottom layer of concrete provided in Example 2;

[0056] Figure 9 A stress cloud diagram of the steel bars of the upper concrete thin-walled structure provided in Example 2, simulating the constraint of the upper concrete thin-walled structure by cooling of a large volume of bottom concrete;

[0057] Figure 10 The overall stress cloud diagram of the upper concrete thin-wall structure provided in Example 3 for the collaborative cooling simulation of a large-volume bottom concrete and an upper concrete thin-wall structure;

[0058] Figure 11 The stress cloud diagram of the entire upper concrete thin-wall structure (the temperature difference between the inner and outer walls changes from uniform to linearly distributed -5°C to 15°C) simulated by the temperature difference between the inner and outer walls of the upper concrete thin-wall structure provided in Example 4;

[0059] Figure 12 The stress cloud diagram of the entire upper concrete thin-walled structure (the temperature difference between the inner and outer walls changes from a uniform temperature to a sudden change at the center of the thickness, with a bidirectional linear distribution of -5°C to 0°C to -5°C) simulated by the temperature difference between the inner and outer walls of the upper concrete thin-walled structure provided in Example 4;

[0060] Figure 13 The stress cloud diagram of the large-volume bottom concrete layer provided in Example 5 for the coordinated heating simulation of the large-volume bottom concrete layer and the upper concrete thin-wall structure;

[0061] In the above figures, 1. Large volume bottom concrete; 2. First layer of upper concrete thin-walled structure; 3. Second layer of upper concrete thin-walled structure; 4. Third layer of upper concrete thin-walled structure; 5. Fourth layer of upper concrete thin-walled structure; 6. Fifth layer of upper concrete thin-walled structure. DETAILED DESCRIPTION

[0062] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other in the absence of conflict.

[0063] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0064] Example 1: This example aims to implement a temperature control simulation process for large-volume concrete during the curing period. Figures 1 to 6 , the simulation needs to be carried out according to the following steps to ensure the correctness of the simulation:

[0065] 1. Use the 3D software Unigraphics NX to establish a geometric model of the massive bottom concrete layer and the upper concrete thin-walled structure. When establishing the geometric model, the model is modeled using the massive bottom concrete layer and the upper concrete thin-walled structure, and the height direction is taken as the z-axis in the coordinate system. The completed geometric model of the massive bottom concrete layer and the upper concrete thin-walled structure is saved as a file with the suffix .prt;

[0066] 2. Import the geometric model in S1 into the ABAQUS finite element software for finite element mesh division. Import the file with the suffix .prt into ABAQUS / CAE through "File>Import>Geometry". In ABAQUS, first enter the "Part" module, then select the appropriate file type in the pop-up dialog box and import it. During the import process, you can set parameters such as units and scaling. After the import is complete, first divide and cut the geometric model of the upper concrete thin-wall structure layer by layer along the layered pouring steps to facilitate the division of the finite element mesh;

[0067] 3. In order to reduce the impact of irregular geometric shapes on the internal temperature simulation of the structure and reduce the amount of model calculation, the geometric model of the large-volume bottom concrete is established as a cylindrical structure, and the upper concrete thin-walled structure is set as a ring structure. According to the common symmetry center of the geometric model of the large-volume bottom concrete and the upper concrete thin-walled structure, a section with a central angle of 15° is cut out for subsequent analysis according to the principle of central symmetry. In order to analyze the impact of the heating of the large-volume bottom concrete on the upper concrete thin-walled structure, the upper concrete thin-walled structure is layered and cut along the height direction, and the internal steel bars of the upper concrete thin-walled structure are modeled. In order to consider that the elastic modulus of concrete cannot reach the design value in time during the curing period, the concrete elastic modulus reduction coefficient of 0.333 is used when assigning material properties. The force and deformation of the cross-sections at both ends are set by a custom coordinate system orthogonal to the cross-section to meet the axisymmetric requirements. In particular, in order to achieve the shrinkage value of concrete during the curing period of 400×10 -6 The initial temperature is set by the cooling method. The initial temperature is the pouring temperature plus 40 ° C. The temperature linear expansion coefficient of concrete is defined as 1 × 10 -5 , set the concrete temperature to drop by 40℃, and the temperature change value of the steel bar to 0℃; mesh the large volume bottom concrete, upper concrete thin-wall structure and steel bar, using C3D8R unit for concrete and T3D2 unit for steel bar;

[0068] 4. Set the analysis type, time step, time function, initial condition, material parameters, and ambient temperature load, including: setting the analysis type to static analysis mode; defining the analysis step length as needed, the initial incremental step to 0.1, the maximum incremental step to 0.2, and the time function to a linear interpolation curve based on the time accuracy required by the calculation results; the initial temperature of the bulk base concrete is used as the initial condition, and the initial temperature should be the temperature of the first batch of bulk base concrete at the location where the bulk base concrete is constructed; setting the material parameters of different parts and different curing stages of the bulk base concrete according to the concrete grade and steel bar number; during the concrete construction and curing stage, the load is the concrete temperature change caused by the internal heat generated by cement hydration heat inside the concrete. In order to optimize the calculation process and improve the calculation efficiency, the concrete part is defined to be gradually cooled from the initial pouring temperature to the ambient temperature. The application method is to specify the concrete part in the finite element model and input it by defining the cooling function curve;

[0069] 4. Submit simulation analysis calculation. After completing the above settings, you can submit simulation analysis calculation;

[0070] 5. Extract analysis results. After simulation analysis, the strain of any part of the large-volume bottom concrete during the pouring process and at any time within the calculation time range after the pouring is completed, as well as the strain distribution of the large-volume bottom concrete, can be extracted.

[0071] Example 2: This example aims to simulate the cooling of a large volume of bottom concrete layer to constrain the upper concrete thin-wall structure. Figures 7-9 , the simulation needs to be carried out according to the following steps to ensure the correctness of the simulation:

[0072] 1. Set the temperature of the bulk bottom concrete to the post-hypothermia temperature (usually the ambient temperature);

[0073] 2. In different calculation conditions, the temperature of the upper concrete thin-wall structure is set to 10℃, 20℃, 30℃, 40℃, 50℃, etc. higher than the ambient temperature;

[0074] 3. Allow the upper concrete thin-wall structure temperature to drop to ambient temperature;

[0075] 4. Observe the maximum stress between the upper thin-walled concrete structure and the bulky bottom concrete layer in the model, and determine the preset temperature value of the upper thin-walled concrete structure when the concrete material exceeds its limit. This will determine the threshold temperature difference between the upper thin-walled concrete structure and the surrounding environment that would cause structural cracking if the bulky bottom concrete layer were allowed to lose temperature.

[0076] Example 3: This example aims to implement a large volume bottom concrete and upper concrete thin wall structure coordinated cooling simulation, please refer to Figure 10 , the simulation needs to be carried out according to the following steps to ensure the correctness of the simulation:

[0077] 1. In different calculation conditions, the temperature of the upper concrete thin-wall structure and the large volume bottom concrete is set to be 10℃, 20℃, 30℃, 40℃, 50℃, etc. higher than the ambient temperature;

[0078] 2. Observe the maximum stress of the entire model and determine the corresponding model temperature drop rate when it exceeds the concrete material's tolerance limit. This will determine the cooling rate threshold that causes structural cracking while controlling the overall cooling rate of the model.

[0079] Example 4: This example aims to simulate the temperature difference between the inside and outside of an upper concrete thin-walled structure. Figures 11-12 , the simulation needs to be carried out according to the following steps to ensure the correctness of the simulation:

[0080] 1. In different calculation conditions, the temperature difference between the inside and outside of the upper concrete thin-wall structure is set to 10°C, 20°C, 30°C, 40°C, 50°C, etc.;

[0081] 2. Observe the maximum stress of the upper concrete thin-walled structure model and determine the corresponding temperature difference threshold between the inside and outside of the upper concrete thin-walled structure model when the stress exceeds the bearing limit of the concrete material.

[0082] Example 5: This example aims to simulate the coordinated heating of a large volume bottom concrete and an upper concrete thin-wall structure. Figure 13 , the simulation needs to be carried out according to the following steps to ensure the correctness of the simulation:

[0083] 1. Set the initial temperature of the upper concrete thin-wall structure and the large volume bottom concrete to the ambient temperature;

[0084] 2. In different calculation conditions, the temperature of the upper concrete thin-wall structure and the large volume bottom concrete is set to 10℃, 20℃, 30℃, 40℃, 50℃, etc. higher than the ambient temperature;

[0085] 3. Observe the maximum stress of the entire model and determine the internal temperature value of the model when it exceeds the bearing limit of the concrete material. Calculate the maximum cracking temperature threshold inside the model that causes structural cracking while controlling the overall heating rate of the model.

Claims

1. A method for determining the critical threshold value of temperature control of large-volume concrete during the curing period, characterized in that: The method includes a simulation method of internal temperature strain of large volume concrete during the curing period, including the following steps: S1: Use the 3D software Unigraphics NX to establish a geometric model of the large-volume bottom concrete layer and the upper concrete thin-walled structure. When establishing the geometric model, the model uses the large-volume bottom concrete layer and the upper concrete thin-walled structure to model together, and the height direction is taken as the z-axis in the coordinate system. The completed geometric model of the large-volume bottom concrete layer and the upper concrete thin-walled structure is saved as a file with the suffix .prt; S2: Import the geometric model from S1 into the ABAQUS finite element software for finite element meshing. Import the file with the .prt suffix into ABAQUS / CAE via "File>Import>Geometry". In ABAQUS, first enter the "Part" module, then select the appropriate file type in the dialog box that pops up and import it. During the import process, you can set parameters such as units and scaling. After importing, first divide and cut the geometric model of the upper concrete thin-wall structure layer by layer along the layered pouring steps to facilitate finite element meshing. This includes the following steps: S21: To reduce the impact of irregular geometric shapes on the internal temperature simulation of the structure and reduce the amount of model calculation, the large-volume bottom concrete geometry model is established as a cylindrical structure, and the upper concrete thin-walled structure is set as a ring structure; S22: Based on the common symmetry center of the large-volume bottom concrete geometric model and the upper concrete thin-walled structure geometric model, according to the principle of central symmetry, a section with a central angle of 15° was cut out for subsequent analysis; S23: In order to analyze the effect of heating of large-volume bottom concrete on the upper concrete thin-wall structure, the upper concrete thin-wall structure is cut layer by layer along the height direction, and the internal steel bars of the upper concrete thin-wall structure are modeled; S24: In order to consider that the elastic modulus of concrete cannot reach the design value in time during curing, the concrete elastic modulus reduction factor is 0.333 when assigning material properties; S25: The force and deformation of the two end sections are set by a custom coordinate system orthogonal to the section to meet the axisymmetric requirements; in order to achieve the shrinkage value of the concrete during the curing period of 400×10 -6 The initial temperature is set by the cooling method. The initial temperature is the pouring temperature plus 40 ° C. The temperature linear expansion coefficient of concrete is defined as 1 × 10 -5 , set the concrete temperature to decrease by 40℃, and the temperature change value of the steel bar to 0℃; S26: Mesh the massive bottom concrete, upper concrete thin-walled structure, and steel bars, using C3D8R elements for concrete and T3D2 elements for steel bars. S3: Set the analysis type, time step, time function, initial conditions, material parameters, and ambient temperature load. The specific process is as follows: S31: Analysis type setting: Set the analysis type to static analysis mode, S32: Time step setting, time function setting: the analysis step length is defined as needed, the initial increment step is defined as 0.1, the maximum increment step is defined as 0.2, and the time function is defined as a linear interpolation curve according to the time accuracy required by the calculation results. S33: Initial condition setting: The initial temperature of the bulk bottom concrete is used as the initial condition. The initial temperature should be the temperature of the first batch of bulk bottom concrete when it is poured at the location where the bulk bottom concrete is constructed. S34: Material parameter setting: Set the material parameters of different parts and different curing stages of large-volume bottom concrete according to the concrete grade and steel bar grade. S35: Ambient temperature load definition: During the concrete construction and curing phase, this load is the temperature change of the concrete caused by the internal heat generated by cement hydration. To optimize the calculation process and improve efficiency, the concrete portion is defined to be gradually cooled from the initial pouring temperature to the ambient temperature. This load is applied by specifying the concrete portion in the finite element model and inputting a defined cooling function curve. S4: Submit simulation analysis calculation. After completing the above settings, you can submit the simulation analysis calculation; S5: Extract analysis results. After simulation analysis, the strain of any part of the large-volume bottom concrete during the pouring process and at any time within the calculation time range after the pouring is completed, as well as the strain distribution of the large-volume bottom concrete, can be extracted.

2. The method for determining the critical threshold value of temperature control of large-volume concrete during the curing period according to claim 1 is characterized in that: It also includes a method for determining the critical threshold of temperature control based on simulation results: F1: Simulate the cooling effect of the large volume of bottom concrete on the upper concrete thin-walled structure. The method is as follows: F11: Set the temperature of the bulk bottom concrete to the post-hypothermia temperature (usually the ambient temperature); F12: In different calculation conditions, set the upper concrete thin-wall structure temperature to 10℃, 20℃, 30℃, 40℃, 50℃, etc. higher than the ambient temperature; F13: Allow the upper concrete thin-wall structure temperature to drop to ambient temperature automatically; F14: Observe the maximum stress between the upper concrete thin-wall structure and the bulky bottom concrete in the model, and determine the preset temperature value of the upper concrete thin-wall structure when the stress exceeds the concrete material's bearing limit. This determines the temperature difference threshold between the upper concrete thin-wall structure and the environment that would cause cracking if the bulky bottom concrete were allowed to lose temperature. F2: Coordinated cooling simulation of a large concrete base and thin-walled upper concrete structure, as follows: F21: In different calculation conditions, set the temperature of the upper concrete thin-wall structure and the large volume bottom concrete to 10℃, 20℃, 30℃, 40℃, 50℃ higher than the ambient temperature, etc. F22: Observe the maximum stress of the entire model and determine the corresponding model temperature drop rate when the stress exceeds the concrete material's bearing limit. This determines the cooling rate threshold that causes structural cracking while controlling the overall cooling rate of the model. F3: Simulate the temperature difference between the inside and outside of the upper concrete thin-wall structure. The method is as follows: F31: In different calculation conditions, the temperature difference between the inside and outside of the upper concrete thin-wall structure is set to 10℃, 20℃, 30℃, 40℃, 50℃, etc. F32: Observe the maximum stress of the upper concrete thin-walled structure model and determine the corresponding internal and external temperature difference threshold of the upper concrete thin-walled structure model when the stress exceeds the bearing limit of the concrete material. F4: Simulate the coordinated heating of a large-volume bottom concrete layer and an upper concrete thin-walled structure. The method is as follows: F41: Set the initial temperature of the upper concrete thin-wall structure and the large volume bottom concrete to the ambient temperature; F42: In different calculation conditions, set the temperature of the upper concrete thin-wall structure and the large volume bottom concrete to 10℃, 20℃, 30℃, 40℃, 50℃ above the ambient temperature, etc. F43: Observe the maximum stress of the entire model and determine the internal temperature value of the model when it exceeds the bearing limit of the concrete material. This will determine the maximum cracking temperature threshold inside the model that will cause structural cracking while controlling the overall heating rate of the model.

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