A design method for large-scale concrete cave walls under gradient temperature difference

Abstract

The present invention discloses a design method for large-scale concrete cave walls under the action of gradient temperature difference. By determining basic constraint boundary conditions, a wind tunnel concrete cave wall and upper grid structure model is constructed in general finite element analysis software and traditional structural design software. Non-uniform grid division is adopted, and alternating temperature load is applied to the general software model to calculate stress. Conventional load is applied to the traditional structural design software model. The internal forces of the two are then combined to obtain the design control internal force. The reinforcement is adjusted according to the internal force and taking into account the uneven distribution of cave wall stress. The present invention can accurately analyze the internal force and stress of the structure, overcome traditional limitations, propose safe, reliable and economical design measures, ensure the performance and safety of the structure under a gradient temperature difference environment, improve the accuracy and rationality of the structural design, and effectively solve the design problem of large-scale wind tunnel concrete cave walls.

Description

Technical Field

[0001] The present invention relates to the technical field of wind tunnel construction, and in particular to a design method for a large-scale concrete tunnel wall under the action of gradient temperature difference. Background Art

[0002] The influence of temperature on structural design is reflected in the correlation between structural size and temperature. The larger the structure and the more complex the constraints, the more obvious the temperature effect. At present, domestic research on temperature effects mostly focuses on the structural response under temperature changes, solar radiation and fire. In traditional design, the temperature difference of components at different positions can be considered, such as the temperature values ​​of the concrete floor and the upper steel roof are different, but the same component at the same position can only consider one temperature value, such as Figure 1 As shown in Figure 2, for large-scale wind tunnels, there are obvious differences in temperature distribution, that is, the temperature difference of the tunnel wall in different areas along the spatial temperature is small, but at the same spatial position, such as Figure 2 As shown in the figure, the temperature difference varies greatly within a small scale along the thickness of the cave wall. Traditional design methods are difficult to accurately consider and propose safe, reliable and economical construction measures. Summary of the Invention

[0003] In view of the fact that the tunnel walls of large-scale wind tunnel structures exhibit gradient temperature differences during operation, and in order to overcome the limitations of traditional design methods, the present invention provides a design method for large-scale concrete tunnel walls under the action of gradient temperature differences, so as to accurately analyze the internal forces and stresses of the structure under the action of gradient temperature, and propose corresponding safe, reliable and economical structural design measures to ensure the performance and safety of large-scale concrete tunnel wall structures in a gradient temperature difference environment.

[0004] The present invention is achieved through the following technical solutions:

[0005] A design method for a large-scale concrete cave wall under the action of a gradient temperature difference includes the following design steps:

[0006] Step 1: After determining the accurate foundation constraint boundary conditions, construct finite element models of the wind tunnel concrete wall and the long-span grid structure connected to the upper part of the wind tunnel concrete wall in general finite element analysis software and traditional structural design software respectively;

[0007] Step 2: Meshing the established wind tunnel concrete wall model and the large-span grid structure model;

[0008] Step 3: Apply alternating temperature loads to the finite element model constructed in general finite element analysis software, and apply conventional loads to the finite element model constructed in traditional structural design software;

[0009] Step 4: Combine the temperature internal forces calculated by the general finite element analysis software with the internal forces under conventional loads calculated by the traditional structural design software to obtain the design control internal forces of the wind tunnel concrete wall, and adjust the reinforcement of the wind tunnel concrete wall according to the obtained design control internal forces.

[0010] In this scheme, by determining the foundation constraint boundary conditions, a structural model is constructed and uneven meshing is performed in general finite element analysis software and traditional structural design software respectively. By applying alternating temperature loads and calculating temperature stresses, the results are combined with traditional structural design software to determine the design control internal forces. Finally, the reinforcement design is carried out based on the internal forces and taking into account the uneven distribution of cave wall stress to ensure the performance and safety of large-scale concrete cave wall structures in a gradient temperature difference environment.

[0011] As a further solution of the design method, in step 1, when determining the foundation constraint boundary conditions, the foundation constraint stiffness is input through the equivalent stiffness method.

[0012] In this scheme, the equivalent stiffness method is used to input the foundation constraint stiffness when determining the foundation constraint boundary conditions, which plays an important role and has a significant effect. For large-scale concrete cave wall structures, the traditional column bottom foundation full constraint boundary conditions cannot accurately reflect the actual situation. The equivalent stiffness method can more realistically simulate the interaction between the foundation and the structure, taking into account the actual geological conditions and the deformation characteristics of the foundation, so that the foundation constraint boundary conditions are more in line with engineering practice.

[0013] As a further solution of the design method, in step one, multiple sections of cylinders without lateral constraints with a length of H and a diameter of D are established at the bottom of the wind tunnel concrete wall in the general finite element analysis software to simulate the foundation stiffness, and fixed constraints are performed at the bottom of the cylinders.

[0014] In this scheme, this design can more realistically reflect the actual stress conditions of large-scale concrete cave wall structures. By establishing these cylinders to simulate the foundation stiffness, the interaction between the foundation and the cave wall structure can be taken into account, avoiding the irrationality of the completely constrained boundary conditions in traditional design, making the calculation results more in line with engineering reality, especially for temperature stress, which is an internal stress generated by constraints. It helps to accurately analyze the internal force and stress distribution of the cave wall structure under complex effects such as temperature gradients, provide a reliable basis for structural design, improve the safety and reliability of the structure, and avoid structural design deviations and potential safety hazards caused by inaccurate foundation simulation.

[0015] As a further solution of the design method, the steps for solving the diameter D of the cylinder are as follows:

[0016] S1. First, a single pile constraint model is established, where the diameter of the single pile is set to d, wherein the total length of the single pile does not exceed 6d;

[0017] S2. Divide the single pile into not less than 10 segments with equal spacing, and apply a bidirectional spring constraint to each segment laterally;

[0018] S3. Set the length of each segment to L, and the corresponding stiffness of the bidirectional spring constraint to k = m * L * h, where m is the distance from the spring segment to the pile top;

[0019] S4. Calculate the deformation δ of the pile top under unit force F, and then calculate the cantilever column stiffness according to the formula F / (3EI / H 3 )=δ, where E is the elastic modulus and I is the section moment of inertia. The diameter D of the cylinder can then be solved according to E=π*D^4 / 64.

[0020] In this scheme, by establishing a single pile constraint model and setting a reasonable pile length range, we ensure that the model can reflect the characteristics of the actual pile foundation within the progress range that meets the project requirements, while avoiding overly complex calculations caused by excessive pile lengths. The single pile is divided into equal intervals and a bidirectional spring constraint is applied. The influence of geological conditions on the pile foundation is taken into account. The spring stiffness is determined by introducing the parameter m from the geological survey report and the distance h of the spring relative to the pile top, making the calculation more in line with the actual geological conditions. The deformation of the pile top under unit force is calculated and the bending stiffness of the cylindrical section is inversely calculated. Combined with the elastic modulus and the section moment of inertia, the cylinder diameter D is finally solved using a formula. This method provides an accurate calculation method for determining the size of the foundation simulation cylinder, which helps to more accurately simulate the interaction between the foundation and the structure in the design of large-scale concrete cave wall structures, improve the accuracy and reliability of the structural design, ensure that the structure can operate safely and stably under complex loads and temperatures, and avoid structural internal force calculation deviations and potential safety risks caused by inaccurate foundation parameters.

[0021] As a further solution of the design method, in step 1, the large-span grid structure is connected to the concrete wall of the wind tunnel via connecting supports;

[0022] Among them, the wind tunnel concrete wall in the general finite element analysis software is a solid unit, the large-span grid structure is a truss unit, the connecting support is simulated by a beam unit, and MPC-beam constraints are used between the connecting support and the wind tunnel concrete wall.

[0023] In this scheme, the concrete walls of the wind tunnel are set as solid elements, which can accurately simulate their continuous three-dimensional mechanical behavior, thereby considering their stress and strain distribution under various loads; the large-span grid structure uses truss elements, which can effectively simulate the axial force characteristics of the rod structure, consistent with the characteristics of the grid structure that mainly bears axial forces; and the connection supports are simulated through beam elements, which can better reflect the forces and deformations of the supports in different directions, such as axial force, lateral force, and rotation. MPC-beam constraints are used between the connection supports and the concrete walls of the wind tunnel. This constraint method can accurately simulate the connection relationship between the supports and the wall, ensuring the coordination of force transmission and deformation. Through this setting, the mechanical behavior of the entire structure under various loads can be more realistically reflected, providing an accurate model basis for structural analysis and design, and ensuring the safety and reliability of the structure.

[0024] As a further solution of the design method, in the step 2, the wind tunnel concrete wall is meshed by a non-uniform meshing method, the meshing characteristic size on the wall surface is not greater than 200 mm, and the meshing characteristic size on the remaining basic parts of the wind tunnel concrete wall (1) is not less than 500 mm.

[0025] In this scheme, the grid division characteristic size is controlled to no more than 200mm at the cave wall surface. This is because the cave wall is the key part of the structure that directly bears various complex loads, especially the temperature gradient. The smaller grid size can more accurately capture the stress and deformation of the cave wall under different working conditions, accurately simulate the impact of the gradient temperature difference caused by temperature changes on the cave wall, and ensure more accurate analysis of the mechanical behavior of key areas. In the remaining foundation of the wind tunnel concrete cave wall, the grid division characteristic size is set to no less than 500mm. On the one hand, considering that the stress and deformation of the foundation part are not the most critical focus in this design compared to the cave wall, the larger grid size can reduce the amount of calculation and improve the calculation efficiency while ensuring the overall calculation accuracy. On the other hand, through this uneven grid division method, different parts of the structure can be analyzed more targeted with limited computing resources, realizing efficient and accurate design of large-scale concrete cave wall structures.

[0026] As a further solution of the design method, in step three, the alternating temperature load is input by defining a mapping field in a general finite element analysis software.

[0027] In this scheme, inputting alternating temperature loads by defining mapping fields in general finite element analysis software can accurately describe complex temperature load distribution patterns, and effectively input alternating temperature loads generated in actual projects due to wind tunnel equipment operation and other reasons into the structural analysis model. The mapping field can flexibly adjust the numerical information of temperature at different positions according to actual conditions, and realize the application of alternating temperatures of different sizes at different positions of the tunnel wall, thereby more realistically simulating the temperature changes faced by large-scale concrete tunnel walls in actual working environments, which helps to accurately analyze the stress distribution, deformation of the tunnel wall under the action of alternating temperature loads and the impact on the overall performance of the structure, providing a reliable basis for subsequent structural design and optimization, and ensuring that the wind tunnel concrete tunnel wall structure can operate safely and stably in complex temperature environments.

[0028] As a further solution of this design method, when inputting the alternating temperature load, a combination of local coordinates, geometric element segmentation and loading predefined fields is used to apply alternating temperatures of different magnitudes to different locations of the wind tunnel concrete wall, and the temperature stress is calculated based on the static general solver combined with the material thermodynamic parameters.

[0029] In this solution, the use of local coordinates can more conveniently determine points at different locations on the cave wall, accurately describe the complex geometric shape of the cave wall, and make the application of temperature loads more accurately correspond to specific locations of the actual structure. Geometric element decomposition further subdivides the cave wall, which can more finely control the temperature application in different areas. Taking into account the differences in characteristics of different parts of the cave wall, it is possible to apply alternating temperatures of different sizes to different locations, thereby more realistically simulating the actual temperature distribution. Loading predefined fields ensures that temperature loads defined by mapping fields and other methods are accurately loaded to the corresponding areas of the model. Based on the static general solver combined with the thermodynamic parameters of the material to calculate temperature stress, it can fully consider the mechanical properties of the material under temperature changes, such as thermal expansion coefficient, specific heat capacity, thermal conductivity, etc., and accurately calculate the stress distribution of the structure under alternating temperature, providing a reliable basis for the structural design and safety assessment of large-scale concrete cave walls, ensuring the stability and reliability of the structure in complex temperature environments.

[0030] As a further solution of the design method, in step 4, based on the obtained design control internal force, when the temperature inside the wind tunnel concrete wall is mainly increased, the concrete outside the wind tunnel concrete wall will be subjected to large tensile stress and the concrete inside the wind tunnel concrete wall will be subjected to large compressive stress. Therefore, the internal reinforcement of the wind tunnel concrete wall is designed to be asymmetrical.

[0031] Among them, the number of steel bars required for the outer reinforcement is greater than the number of steel bars for the inner reinforcement.

[0032] In this scheme, when the concrete on the outer side of the wind tunnel concrete wall is subjected to large tensile stress and the concrete on the inner side is subjected to large compressive stress, the asymmetric reinforcement design can fully consider the actual stress conditions of the wall under the action of temperature stress. Since the tensile stress on the outer side is large, more steel bars can be configured to effectively bear the tensile force on the outer side, improve the tensile resistance of the outer side of the wall, and prevent the concrete from cracking and damage due to excessive tension. Since the compressive stress on the inner side is large, the number of steel bars required can be appropriately reduced. While meeting the compressive resistance requirements on the inner side, unnecessary waste of steel bars is avoided, and the economy of the structural design is achieved. In addition, this asymmetric reinforcement design can enable the wind tunnel concrete wall to better adapt to the stress requirements at different positions under the action of complex temperature gradients, ensuring the overall stability and safety of the structure.

[0033] As a further solution of the design method, in step 4, based on the obtained design control internal force, when the temperature inside the wind tunnel concrete wall is mainly increased, the concrete outside the wind tunnel concrete wall will be subjected to large tensile stress and the concrete inside the wind tunnel concrete wall will be subjected to large compressive stress, and the reinforcement outside the wind tunnel concrete wall is in the form of additional steel plates;

[0034] Wherein, the steel plate is only attached to the outer side of the wind tunnel concrete wall.

[0035] In this solution, when the concrete on the outside of the wind tunnel concrete wall is subject to high tensile stress and the concrete on the inside is subject to high compressive stress, the reinforcement form of adding steel plates only on the outside of the wall can effectively enhance the tensile capacity of the outside of the wall based on the specific stress distribution characteristics. Since the tensile stress on the outside is large, the additional steel plates can provide higher strength and rigidity, taking on most of the tensile force and preventing the concrete on the outside of the wall from cracking and damage due to excessive tension. At the same time, adding steel plates only on the outside can avoid unnecessary intervention in the internal structure while meeting the structural force requirements, reducing construction complexity and cost. Therefore, this form of reinforcement can be targeted according to the actual stress conditions, improving the overall performance and safety of the wind tunnel concrete wall under complex temperature stress.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] 1. After determining the foundation constraint boundary conditions, the present invention constructs a structural model and performs non-uniform meshing in general finite element analysis software and traditional structural design software. Alternating temperature loads are applied and temperature stresses are calculated. The results are combined with traditional structural design software to determine the design control internal forces. Finally, reinforcement design is performed based on the internal forces and taking into account the non-uniform distribution of cave wall stress, ensuring the performance and safety of large-scale concrete cave wall structures in gradient temperature environments.

[0038] 2. Based on the stress distribution characteristics of the tunnel wall, the present invention adopts an asymmetric reinforcement design or adds steel plates to the outer side of the tunnel wall. This reinforcement design specifically enhances the tensile capacity of the structure, while avoiding unnecessary waste of steel bars, thereby improving the economy and safety of the structure.

[0039] 3. By defining a mapping field in the software and combining multiple methods to accurately apply alternating temperature loads, the present invention accurately calculates temperature stress based on a static general solver and material thermodynamic parameters. This allows for more precise simulation of the stress distribution of the cave wall under actual temperature, providing a more accurate basis for structural design. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0041] Figure 1 It is the temperature difference diagram of the cave wall in different areas along the spatial temperature;

[0042] Figure 2 is the temperature distribution curve along the thickness direction of the cave wall;

[0043] Figure 3 It is a design flow chart of the present invention;

[0044] Figure 4 This is a schematic diagram of the temperature distribution inside and outside the cave wall of the present invention;

[0045] Figure 5 This is a schematic diagram of the enlarged structure of a certain section of the cave;

[0046] Figure 6 The top plate temperature effect diagram of cave segment-1 and cave segment-3;

[0047] Figure 7 This is a schematic diagram of a three-dimensional model of a wind tunnel concrete wall according to the present invention;

[0048] Figure 8 This is a schematic diagram of the local mesh division of the wind tunnel concrete wall;

[0049] Figure 9 This is a schematic diagram of the mesh division of the foundation part of the wind tunnel concrete wall;

[0050] Figure 10 This is a temperature gradient distribution curve of the sidewall and roof of cave section 3 when operating at low temperature;

[0051] Figure 11 This is the temperature distribution cloud diagram of the side wall and roof of cave segment 3;

[0052] Figure 12is the stress distribution diagram of the cave wall under the alternating temperature field;

[0053] Figure 13 This is a schematic diagram of the structure of the present invention in which asymmetric steel bars are arranged on the inner and outer sides of the cave wall;

[0054] Figure 14 This is a schematic diagram of the structure of adding a steel plate to the outside of the cave wall in the present invention;

[0055] Figure 15 This is a simplified diagram of the stiffness calculation of the simulated pile of the present invention;

[0056] Figure 16 This is a simplified calculation diagram of the equivalent cantilever column of the present invention;

[0057] Figure 17 This is a simplified diagram of the actual structure of the simulated pile;

[0058] Figure 18 Schematic diagram of the bottom constraint of a traditionally designed cylinder;

[0059] Figure 19 A schematic diagram of the bottom constraint of the cylinder designed for the present invention;

[0060] Figure 20 This is a diagram showing the horizontal stress distribution on the outer side of the concrete wall of the wind tunnel according to the present invention;

[0061] Figure 21 for Figure 20 Cross-sectional view of the middle AA region;

[0062] Figure 22 for Figure 20 Cross-sectional view of the middle BB;

[0063] Figure 23 for Figure 20 Cross-sectional view of CC;

[0064] Figure 24 for Figure 20 Cross-sectional view of the middle DD;

[0065] Markings and corresponding parts names in the accompanying drawings:

[0066] 1- wind tunnel concrete wall, 2- cylinder, 3- spring constraint, 4- long-span grid structure, 5- connection support, 6- outer reinforcement, 7- inner reinforcement, 8- steel plate. DETAILED DESCRIPTION

[0067] 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 in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0068] Example

[0069] This embodiment provides a design method for large-scale concrete cave walls under the action of gradient temperature difference, such as Figure 4 As shown in the figure, when the wind tunnel is working, the airflow heats up rapidly, causing the inner wall concrete structure to form a gradient temperature field with high temperature inside and low temperature outside. This temperature field will cause the structure to produce large temperature stress. After the wind tunnel stops working, the air temperature inside the tunnel gradually drops to the ambient temperature until the next work, when the tunnel wall produces a gradient temperature field again. In the process of the structure returning to the ambient temperature, the stress on the tunnel wall is also released. Therefore, the focus of the analysis of the alternating temperature field is the impact of the temperature field generated by the wind tunnel operation on the structure.

[0070] Therefore, in order to avoid excessive temperature effects caused by super-long structures, the wind tunnel body is usually divided into several structural monomers through structural seams. When two monomers have similar structural layout, geometric dimensions and temperature effects, the component responses obtained by analyzing the structure are basically the same; in this embodiment, Figure 5 As shown in the figure, the tunnel segment-1 (hereinafter referred to as DT-1) and tunnel segment-3 (hereinafter referred to as DT-3) with similar geometric dimensions are selected for analysis. Figure 6 The results show that the temperature effects between the two sections are similar, which proves that when the two sections have similar structural arrangements and geometric dimensions, the analysis results are also similar under similar temperature effects. Therefore, this embodiment 1 only needs to be described in detail using DT-3 as an example.

[0071] like Figure 3-Figure 19 As shown, the design of DT-3 includes the following steps:

[0072] Step 1: After determining the accurate foundation constraint boundary conditions, construct finite element models of the wind tunnel concrete wall and the long-span grid structure connected to the upper part of the wind tunnel concrete wall in general finite element analysis software and traditional structural design software respectively;

[0073] Specifically, first, the finite element models of the wind tunnel concrete wall 1 and the large-span grid structure 4 connected to the upper part of the wind tunnel concrete wall 1 are established in the general structural finite element analysis software ABAQUS and the traditional structural design software MIDAS, as shown in Figure 2. Figure 9As shown, the large-span grid structure 4 is connected to the wind tunnel concrete wall 1 through the connecting support 5. Since the constructed model must be able to truly reflect the actual situation of the large-scale wind tunnel concrete wall 1 and the upper large-span grid structure 4, in this embodiment, the wind tunnel concrete wall 1 constructed in ABAQUS is a solid unit C3D8R, the large-span grid structure 4 is a truss unit T3D2, the connecting support 5 is simulated by the beam unit B31, and the MPC-beam constraint is adopted between the connecting support 5 and the wind tunnel concrete wall 1. This constraint method can accurately simulate the connection relationship between the support and the wall, ensuring the force transmission and deformation coordination.

[0074] Since in structural design, the foundation constraint boundary conditions have an important influence on the mechanical properties of the entire structure, usually Figure 18 As shown in the figure, for large-scale concrete cave wall structures, the traditional column base fully constrained boundary conditions cannot accurately reflect the actual situation. Figure 19 As shown, the equivalent stiffness method is used to constrain the boundary conditions;

[0075] Therefore, after the above model is constructed, Figure 7 As shown in the figure, a cylinder 2 with a specific length H and diameter D without lateral constraints is built at the bottom of the wind tunnel concrete wall 1 to simulate the foundation stiffness, and a fixed constraint is placed at the bottom of the column to simulate the connection between the foundation and the foundation and to limit the movement of the column bottom in space. The relevant principles are as follows Figure 15-17 shown.

[0076] At the same time, under the premise of specifying the total height H of cylinder 2, only by accurately determining the cross-sectional dimensions of cylinder 2 can the simulated foundation stiffness be consistent with the actual situation, thereby more realistically reflecting the interaction between the foundation and the structure. Therefore, determining the cross-sectional dimensions of cylinder 2 is a key step. This requires solving by establishing a single pile constraint model, such as Figures 15-19 As shown, assuming that the pile diameter is d, the pile length is simplified in the model. Regardless of the actual total length of the pile, it is only necessary to consider that the total length does not exceed 6d. Then the pile is divided into no less than 10 segments with equal spacing. A bidirectional spring constraint 3 is applied to each segment laterally. For each segment of spring constraint 3, its stiffness is calculated as follows: Given that the length of each segment is L, the relevant parameters m (related to the geological conditions) and the distance h of the spring segment relative to the pile bottom are obtained according to the geological survey report. The stiffness of the spring constraint 3 is calculated according to the formula k=m*L*h. Then, by applying a unit force F in the single pile constraint model, the pile top deformation δ is calculated, and the cantilever column stiffness calculation formula F / (3EI / H 3 )=δ to inversely calculate the column section bending stiffness, where E is the elastic modulus and I is the section moment of inertia. For cylinder 2, according to the formula E=π*D^4 / 64 (where D is the cylinder diameter to be determined), the cylinder diameter D is further solved using the calculated bending stiffness.

[0077] After the above finite element model construction and constraint conditions are completed, step 2 is entered: meshing the established wind tunnel concrete wall 1 model and the large-span grid structure 4 model;

[0078] Specifically, considering the different stress characteristics and importance of different parts of the tunnel wall structure, the wind tunnel concrete wall 1 is meshed using the non-uniform meshing method, such as Figure 8 As shown in the figure, the characteristic size of the grid division on the cave wall is no more than 200 mm. The side wall and the top plate are the key analysis areas, and the grid can be appropriately encrypted to 50-100 mm. Figure 9 As shown, the characteristic size of the grid division in the remaining basic parts of the wind tunnel concrete wall 1 is not less than 500 mm. Taking into account the calculation efficiency and the analysis and application of the results, the role of steel bars and steel frames is not considered in the analysis model, and only the elasticity of concrete is considered, while the plasticity of steel structures is considered.

[0079] After the meshing of the finite element model is completed, proceed to step three: apply alternating temperature loads to the finite element model constructed in the general finite element analysis software, and apply conventional loads to the finite element model constructed in the traditional structural design software;

[0080] Specifically, conventional loads are applied to the finite element model constructed in traditional structural design software in MIDAS software. The conventional loads include dead load, live load, earthquake action, long-term ambient temperature action and wind load.

[0081] In ABAQUS, alternating temperature loads are input by defining a mapped field. A mapped field is a tool that accurately describes load distribution and allows complex temperature load distribution patterns to be input into the model. To more accurately apply alternating temperatures of varying magnitudes to different locations on the cave wall, a combination of local coordinates, geometric element segmentation, and predefined field loading is required. Local coordinates are used to determine the locations of points on the cave wall within the model. By defining appropriate local coordinates, temperature loads can be conveniently applied to specific locations on the cave wall. Geometric element segmentation further subdivides the geometric model of the cave wall into smaller geometric elements (such as triangles or quadrilaterals), allowing for more precise control over the application of temperature loads to different elements. Predefined field loading applies the temperature loads defined by the mapped field to the corresponding areas of the model. By combining these three methods, alternating temperature loads of varying magnitudes can be applied to different locations on the cave wall, making the temperature load distribution more consistent with actual conditions.

[0082] Step 4: Combine the internal forces generated by temperature stress calculated by ABAQUS software with the internal forces under conventional loads calculated by traditional structural design software to obtain the design control internal forces of the wind tunnel concrete wall, and adjust the reinforcement of the wind tunnel concrete wall according to the obtained design control internal forces.

[0083] In this embodiment, the temperature stress process calculated by ABAQUS software is as follows:

[0084] First, the temperature field data "280MW fan input power, initial ambient temperature -3℃, corresponding index requirements: under all working conditions, continuous operation for 10 minutes, air flow temperature not higher than 60℃" is input into ABAQUS software, and the following is obtained: Figure 10 and Figure 11 The results are shown in Figure 1. The top plate temperature rises to a maximum of 26°C with a penetration depth of 63mm, and the side wall temperature rises to a maximum of 36°C with a penetration depth of 170mm. Since the upper surface of the bottom plate is usually provided with an insulation layer separated from the main structure, the temperature effect caused by wind tunnel operation will not directly affect the bottom plate, so no temperature effect is applied. The calculation results are as follows: Figure 12 From the stress distribution diagram shown, we can see that the inner concrete is under compression and the outer concrete is under tension. The overall stress distribution characteristics of the component are completely different from the overall temperature rise. Therefore, the horizontal stress of the side wall is divided into four reinforcement areas, namely the half rib wall spacing area on the left and right sides of the side wall, the large face value and stress concentration value in the upper 3 / 4 of the middle area of ​​the side wall, and the lower 1 / 3 of the middle area of ​​the side wall. The results are as follows Figure 20-24 As shown in the figure, based on the obtained stress cloud diagram of the horizontal section of the side wall, the following calculation table for the horizontal reinforcement of the side wall is obtained:

[0085] Calculation table for horizontal reinforcement of side walls

[0086]

[0087] The above reinforcement results are combined with the reinforcement results calculated by traditional structural design software. This embodiment uses the BB section of the middle side wall of DT-3 as an example. The specific reinforcement method is as follows:

[0088] The reinforcement after considering various factors in traditional design, such as ultimate bearing capacity state, elasticity in moderate earthquake, unyielding in large earthquake, ultimate bearing capacity state considering fatigue stiffness reduction, serviceability limit state and fatigue design, is as follows: horizontal reinforcement of side wall can be d14@200(1)(outer wall)+d12@200(1)(inner wall)+d14@200(1)(inner wall), and vertical reinforcement is d14@200(1)(outer wall)+d12@300(1)(inner wall)+d14@200(1)(inner wall), where d12@200(1)(inner) and d12@300(1)(inner) are structural reinforcements not included in the calculation results. Inner wall refers to the side of the cavity wall that is in direct contact with the test airflow, and outer wall refers to the side of the cavity wall that is in contact with the atmospheric environment.

[0089] The additional steel reinforcement under the combined effect of the above airflow alternating temperature and ambient temperature is d22@100, and the actual reinforcement area is 3800mm 2 >3333mm 2 (The required reinforcement area is calculated using the BB section.) The final reinforcement is: d14@200 + d22@100 on the outside of the hole wall, d12@200 on the inside of the hole wall, and d14@200 on the inside of the hole wall.

[0090] In summary, based on the combined internal force results and the stress distribution characteristics of the tunnel wall, the reinforcement is adjusted. If asymmetric reinforcement or additional steel plates are required, the appropriate amount of external and internal reinforcement is determined to meet the combined internal force requirements while maintaining economy and safety. The adjusted reinforcement scheme is then combined with the reinforcement scheme in traditional structural design software to obtain the final reinforcement design.

[0091] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A design method for large-scale concrete cave walls under the action of gradient temperature difference, characterized in that: The design steps include: Step 1: After determining accurate foundation constraint boundary conditions, construct finite element models of the wind tunnel concrete wall (1) and the large-span grid structure (4) connected to the upper part of the wind tunnel concrete wall (1) in general finite element analysis software and traditional structural design software respectively; Step 2: Meshing the established wind tunnel concrete wall (1) model and the large-span grid structure (4) model; Step 3: Apply alternating temperature loads to the finite element model constructed in general finite element analysis software, and apply conventional loads to the finite element model constructed in traditional structural design software; Step 4: Combining the temperature internal force calculated by the general finite element analysis software with the internal force under the conventional load calculated by the traditional structural design software to obtain the design control internal force of the wind tunnel concrete wall (1), and adjusting the reinforcement of the wind tunnel concrete wall (1) according to the obtained design control internal force.

2. The method for designing a large-scale concrete cave wall under the action of a gradient temperature difference according to claim 1, characterized in that: In the step 1, when determining the foundation constraint boundary conditions, the foundation constraint stiffness is input through the equivalent stiffness method.

3. The method for designing a large-scale concrete cave wall under the action of a gradient temperature difference according to claim 1 is characterized in that: In the step 1, multiple sections of cylinders (2) without lateral constraints with a length of H and a diameter of D are established at the bottom of the wind tunnel concrete wall (1) in the general finite element analysis software to simulate the foundation stiffness, and fixed constraints are performed at the bottom of the cylinders (2).

4. The method for designing a large-scale concrete cave wall under the action of a gradient temperature difference according to claim 3 is characterized in that: The steps for solving the diameter D of the cylinder (2) are as follows: S1. First, a single pile constraint model corresponding to a real project is established in finite element software, and the diameter of the single pile is set to d, wherein the total length of the single pile does not exceed 6d; S2. Divide the single pile into not less than 10 segments at equal intervals, and apply a bidirectional spring constraint (3) to each segment laterally; S3. Set the length of each segment to L, and the corresponding stiffness of the bidirectional spring constraint to k = m * L * h, where m is the distance from the spring segment to the pile top; S4. Calculate the deformation δ of the pile top under unit force F, and then calculate the cantilever column stiffness according to the formula F / (3EI / H 3 )=δ to inversely calculate the bending stiffness of the cylinder (2) section, where H is the specified length of the cylinder (2), E is the elastic modulus, I is the section inertia moment, and then according to E=π*D 4 / 64 can be used to solve the diameter D of the cylinder (2).

5. The method for designing a large-scale concrete cave wall under the action of a gradient temperature difference according to claim 1, characterized in that: In the step 1, the large-span grid structure (4) is connected to the wind tunnel concrete wall (1) via a connecting support (5); The wind tunnel concrete wall (1) in the general finite element analysis software is a solid unit, the large-span grid structure (4) is a truss unit, the connecting support (5) is simulated by a beam unit, and an MPC-beam constraint is adopted between the connecting support (5) and the wind tunnel concrete wall (1).

6. The method for designing a large-scale concrete cave wall under the action of a gradient temperature difference according to claim 1, characterized in that: In the second step, the wind tunnel concrete wall (1) is meshed by a non-uniform meshing method, with the meshing characteristic size on the wall surface being no greater than 200 mm, and the meshing characteristic size on the remaining basic parts of the wind tunnel concrete wall (1) being no less than 500 mm.

7. The method for designing a large-scale concrete cave wall under the action of a gradient temperature difference according to claim 1, characterized in that: In the step three, the alternating temperature load is input by defining a mapping field in a general finite element analysis software.

8. The method for designing a large-scale concrete cave wall under the action of a gradient temperature difference according to claim 7, characterized in that: When inputting the alternating temperature load, a combination of local coordinates, geometric element segmentation and loading predefined fields is used to apply alternating temperatures of different magnitudes to different positions of the wind tunnel concrete wall (1), and temperature stress is calculated based on a static general solver combined with material thermodynamic parameters.

9. A method for designing a large-scale concrete cave wall under the action of a gradient temperature difference according to any one of claims 1 to 8, characterized in that: In the step 4, according to the obtained design control internal force, when the temperature of the inner side of the wind tunnel concrete wall (1) is mainly increased, the internal reinforcement of the wind tunnel concrete wall (1) is an asymmetric reinforcement design; The number of steel bars required for the outer steel bars (6) is greater than the number of steel bars required for the inner steel bars (7).

10. A method for designing a large-scale concrete cave wall under the action of a gradient temperature difference according to any one of claims 1 to 8, characterized in that: In the step 4, according to the obtained design control internal force, when the temperature of the inner side of the wind tunnel concrete wall (1) is mainly increased, the internal reinforcement of the wind tunnel concrete wall (1) is in the form of additional steel plates (8); The steel plate (8) is only attached to the outer side of the wind tunnel concrete wall (1).

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