Design Method of Steel Concrete Pool

Abstract

The present invention discloses a steel-concrete pool design method, comprising: S1: establishing a three-dimensional finite element model of the pool, the three-dimensional finite element model comprising concrete solid units and steel skeleton units; S2: applying load conditions to the three-dimensional finite element model, the load conditions comprising hydrostatic pressure and temperature loads; S3: running finite element analysis to obtain stress distribution data of the pool wall and calculate the stress gradient field of the stress distribution data; S4: identifying areas in the stress gradient field where the stress gradient value is greater than a preset critical gradient, the preset critical gradient being determined based on the pool wall material properties and the design safety factor; S5: in the identified areas, based on the local stress gradient value of the area, adjusting the layout spacing and cross-sectional dimensions of the steel sections in the area according to a preset proportional relationship. The present invention can help reduce material usage, reduce the risk of pool wall cracking, and achieve a synergistic improvement in structural safety and economic efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field related to civil engineering, and more particularly to a design method for a steel-concrete water tank. Background Art

[0002] The traditional design of steel-concrete reinforced concrete tanks faces significant technical bottlenecks in analyzing the structural response under three-dimensional spatial effects and multiple coupled loads, making it difficult to meet the design accuracy requirements of modern engineering. Traditional designs often use simplified planar models (such as beam elements or two-dimensional plate-shell elements), ignoring the three-dimensional stress characteristics of the tank structure. For example, three-dimensional effects such as stress concentration at the corners of rectangular tanks and the coupling of circumferential and radial stresses in circular tanks cannot be accurately simulated in simplified models, often leading to significant deviations between the actual tank wall stress and the designed value, which in turn causes cracking or localized failure. Furthermore, the interface interaction mechanism between the steel and concrete is simplified as an ideal bond in traditional models, failing to account for differences in deformation coordination between the two, resulting in systematic errors in stress distribution calculations. Load case simulation also has limitations. For example, existing technologies often only consider a single hydrostatic pressure load, which fails to reflect the actual stress state of the structure under complex service conditions.

[0003] Therefore, it is necessary to design a technical solution that can overcome the above-mentioned defects to a certain extent. Summary of the Invention

[0004] One object of the present invention is to provide a steel concrete pool design method that can help reduce material usage, reduce the risk of pool wall cracking, and achieve a synergistic improvement in structural safety and economy.

[0005] To achieve these objectives and other advantages of the present invention, according to one aspect of the present invention, a method for designing a steel-concrete water tank is provided, comprising: S1: establishing a three-dimensional finite element model of the water tank, the three-dimensional finite element model comprising concrete solid units and steel skeleton units; S2: applying load conditions to the three-dimensional finite element model, the load conditions comprising hydrostatic pressure and temperature loads; S3: running finite element analysis to obtain stress distribution data of the water tank wall, and calculating the stress gradient field of the stress distribution data; S4: identifying areas in the stress gradient field where the stress gradient value is greater than a preset critical gradient, the preset critical gradient being determined based on the material properties of the water tank wall and the design safety factor; S5: in the identified area, adjusting the arrangement spacing and cross-sectional dimensions of the steel sections in the area according to a preset proportional relationship based on the local stress gradient value of the area.

[0006] Furthermore, in S1, the concrete solid element is simulated using an eight-node hexahedral solid element, and the elastic modulus and Poisson's ratio material properties are configured; the steel skeleton element is simulated using a two-node spatial beam element, and the section geometric parameters are automatically associated based on the steel section database; in the contact area between the steel and concrete, displacement coordination is achieved by establishing displacement constraint equations between the beam element nodes and the solid element nodes; when meshing, the maximum size of the solid element in the pool wall area is controlled to not exceed 50% of the steel arrangement spacing, and at least three layers of elements are divided along the thickness direction of the pool wall.

[0007] Furthermore, the specific process of applying load conditions in S2 includes: layered application of hydrostatic pressure load: dividing the pool wall into at least 5 load application layers along the height direction, and the hydrostatic pressure value of each layer is calculated and determined according to the water depth at the centroid of the layer, and the pressure difference between adjacent layers does not exceed 15% of the maximum hydrostatic pressure; dynamic temperature load coupling simulation: establishing a temperature load spectrum including annual extreme temperature differences, in which: summer working condition: the highest temperature value of the water body is applied to the inner surface of the pool wall, and the highest temperature value of the environmental design is applied to the outer surface of the pool wall; winter working condition: the lowest temperature value of the water body is applied to the inner surface of the pool wall, and the lowest temperature value of the environmental design is applied to the outer surface of the pool wall; water level fluctuation additional load: on the basis of the hydrostatic pressure load, the water level dynamic fluctuation additional term ΔP is superimposed, and its value is based on the design water level change rate v according to the formula ΔP=0.5ρv 2 Calculation, where ρ is the water density and the fluctuation range is ±10% of the difference between the designed maximum water level and the minimum water level.

[0008] Furthermore, S3 includes: S3.1: calculation of the principal stress direction change rate, extracting the direction vector of the maximum principal stress of each finite element node, calculating the angle change of the direction vectors between adjacent nodes in the local coordinate system established on the pool wall surface, dividing the angle change by the spatial distance between the nodes to obtain the principal stress direction change rate per unit length; S3.2: calculation of the equivalent stress change rate, calculating the Mises equivalent stress value of each node, and in the global rectangular coordinate system, obtaining the difference in equivalent stress between adjacent nodes, dividing the difference by the spatial distance between the nodes to obtain the equivalent stress change rate per unit length; S3.3: dual-channel gradient fusion, assigning a first weight coefficient of 0.7 to the principal stress direction change rate, and a second weight coefficient of 0.3 to the equivalent stress change rate, taking the square values ​​of the two weighted change rates respectively and summing them, and performing a square root operation on the sum result to generate the final gradient value.

[0009] Furthermore, in S4, the method for identifying an area in the stress gradient field where the stress gradient value is greater than a preset critical gradient includes: dividing the pool wall into three functional areas according to the structural characteristics: a top exposed area extending 1.5 meters downward from the top of the pool, a bottom constrained area extending 2.0 meters upward from the bottom of the pool, and a middle stable area between the top exposed area and the bottom constrained area; configuring a risk weight coefficient for each area: assigning a weight value of 1.2 to the top exposed area, a weight value of 1.0 to the middle stable area, and a weight value of 0.8 to the bottom constrained area; performing a mesh quality assessment on each finite element unit, and when the unit aspect ratio is greater than 3 or the distortion is greater than 30 degrees, marking it as a low-quality unit and assigning a mesh correction coefficient of 0.9, and assigning a mesh correction coefficient of 1.0 to the remaining units; calculating the actual critical gradient value of the unit: actual critical gradient value = preset critical gradient × risk weight coefficient × mesh correction coefficient; when the unit stress gradient value is greater than the actual critical gradient value of the unit, including it in the identification area.

[0010] Furthermore, the preset critical gradient is determined by the following steps: calculating the material constitutive reference value G_ base , G_ base =0.28×(f_ tk / E_ c )+0.18×(f_ y / E_ s ), where f_ tk is the standard value of concrete tensile strength, E_ c is the elastic modulus of concrete, f_y is the yield strength of steel, and E_s is the elastic modulus of steel; calculate the structural geometric sensitivity coefficient λ, λ=1.0+0.15×(H / D)+0.05×|ΔT|, where H is the design water depth of the pool, D is the length of the short side of the pool, and ΔT is the change rate of the pool wall thickness; calculate the load coupling correction coefficient κ, κ=1.0+0.1×(P_ t / P_ s ), where P_ t is the maximum value of temperature load, P_ s is the maximum value of the hydrostatic pressure; determine the environmental durability coefficient γ, non-corrosive environment: γ = 1.0; weakly corrosive environment: γ = 1.15; strongly corrosive environment: γ = 1.30; calculate the preset critical gradient G, G = G_ base ×λ×κ×γ.

[0011] Furthermore, the ratio of the local stress gradient value to the preset critical gradient is divided into three levels of response zones, with a ratio of 1.0 to 1.5 as Level I response zone, 1.5 to 2.0 as Level II response zone, and greater than or equal to 2.0 as Level III response zone; in Level I response zone, the steel section spacing is reduced by 8% to 12% or the cross-sectional size is increased by 5% to 8%; in Level II response zone, the spacing is reduced by 12% to 18% and the cross-sectional size is increased by 8% to 12%; in Level III response zone, longitudinal stiffening ribs are added on the basis of reducing the spacing by 18% to 25% and increasing the cross-sectional size by 12% to 15%; when the minimum clear distance between steel sections after adjustment is less than 2.5 times the maximum particle size of coarse aggregate, the cross-sectional size increase is reduced to meet the clear distance requirements. If the cross-sectional size has reached the lower limit of the steel specification, a dense concrete cover with a steel fiber content of 25-35kg / m³ is used instead.

[0012] The present invention has at least the following beneficial effects:

[0013] The present invention reduces the stress calculation deviation caused by traditional plane models through three-dimensional finite element modeling and multi-load coupling analysis. The dynamic coupling simulation of temperature load and water level fluctuation reduces the stress response analysis error under complex working conditions. The dynamic optimization mechanism of steel sections based on the stress gradient field can quantitatively identify high-risk areas. Compared with traditional empirical layout schemes, it reduces material consumption and reduces the risk of pool wall cracking, thereby achieving a coordinated improvement in structural safety and economy.

[0014] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a flowchart of an embodiment of the present application. DETAILED DESCRIPTION

[0016] The present invention is described in further detail below so that those skilled in the art can implement the invention with reference to the description.

[0017] It should be understood that terms such as "having," "comprising," and "including" used in the embodiments of this application do not exclude the presence or addition of one or more other elements or combinations thereof. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are intended only to explain the relative positional relationships and movement of components in a specific posture. If the specific posture changes, the directional indications will also change accordingly. When an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element through an intervening element. References to "first," "second," etc. in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features designated as "first" or "second" may explicitly or implicitly include at least one of such features.

[0018] It should be noted that the technical solutions between the various embodiments of the present application can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0019] like Figure 1 As shown, an embodiment of the present application provides a steel-concrete pool design method, including: establishing a three-dimensional finite element model of the pool, the three-dimensional finite element model including concrete solid units and steel skeleton units; applying load conditions in the three-dimensional finite element model, the load conditions including hydrostatic pressure and temperature loads; running finite element analysis to obtain stress distribution data of the pool wall, and calculating the stress gradient field of the stress distribution data; identifying areas in the stress gradient field where the stress gradient value is greater than a preset critical gradient, the preset critical gradient is determined based on the material properties of the pool wall and the design safety factor; in the identified area, based on the local stress gradient value of the area, adjusting the layout spacing and cross-sectional dimensions of the steel in the area according to a preset proportional relationship.

[0020] For example, the three-dimensional finite element model can be constructed using commercial finite element software such as ANSYS, ABAQUS, or MIDASCivil. The concrete solid element uses an eight-node hexahedral solid element (such as the SOLID185 element in ANSYS). This element can accurately simulate the three-dimensional stress state of concrete. It is necessary to configure an elastic modulus for it (for example, 3×10 4 MPa, C35 concrete takes 3.15×10 4 MPa, C40 concrete takes 3.25×10 4MPa) and Poisson's ratio (typically 0.2, 0.22, or 0.24). The steel skeleton element utilizes a two-node spatial beam element (such as the B31 element in ABAQUS). The software automatically associates the cross-sectional geometry of H-beams, I-beams, or channels, including section height, flange width, and web thickness, from the software's built-in steel section database. In the contact area between the steel and concrete, the software's nodal degree of freedom coupling feature (such as the ANSYS CP command) constrains the translational degrees of freedom (UX, UY, and UZ) of the beam element nodes with those of the solid element nodes to ensure coordinated displacement. During meshing, if the steel spacing is 200mm, the maximum size of the solid element in the pool wall area is limited to 100mm (half the spacing), 90mm, or 80mm. Three layers of elements are created along the wall thickness (e.g., for a 300mm thickness), each 100mm thick. For a 350mm thickness, each layer is approximately 117mm thick to ensure accuracy. When applying load conditions, hydrostatic pressure is calculated based on the layer centroid depth (e.g., bottom pressure is 98 kPa at a water depth of 10 m). Temperature loads account for extreme conditions such as a pool water temperature of 30°C / 40°C in summer and a pool temperature of 5°C / -10°C in winter. After running the analysis, node stress data is extracted and the stress change rate between adjacent nodes is calculated, generating field data reflecting the stress distribution gradient. The preset critical gradient is calculated based on material parameters such as standard values ​​for concrete tensile strength (e.g., 2.39 MPa, 2.8 MPa, 3.0 MPa) and steel yield strength (e.g., 235 MPa, 345 MPa, 420 MPa). When adjusting steel sections, spacing can be increased or decreased by 8%-25% based on a 200 mm spacing, and cross-sectional dimensions can be adjusted by 5%-15%.

[0021] In the prior art, a two-dimensional plane beam unit model is often used, and only hydrostatic pressure loads are applied. The stress is estimated through empirical formulas, and the steel section layout is set at a fixed spacing of 200mm. The temperature effect and stress gradient distribution are not considered, resulting in the deviation of the actual stress of the pool wall from the design value by more than 30%. This embodiment uses a three-dimensional solid-beam unit coupling model to introduce temperature load and stress gradient field analysis to achieve dynamic optimization of the steel section layout. Compared with the prior art, its creativity lies in: breaking through the limitations of the plane model, quantifying the stress distribution in three-dimensional space, and verified by measured data, the stress calculation deviation can be controlled within 10%; coupling multiple load conditions to improve the authenticity of the force simulation, and reducing the cracking risks caused by the lack of working conditions compared to traditional single load analysis; the steel section adjustment mechanism based on the gradient field makes the material configuration fit the actual force requirements. In a sewage treatment pool project, the amount of steel sections in high-risk areas is reduced, and the structural safety is significantly improved.

[0022] In another embodiment, when establishing a three-dimensional finite element model of the water pool in S1, the concrete solid unit is simulated using an eight-node hexahedral solid unit, and the elastic modulus and Poisson's ratio material properties are configured; the steel skeleton unit is simulated using a two-node spatial beam unit, and the section geometric parameters are automatically associated based on the steel section database; in the contact area between the steel and the concrete, displacement coordination is achieved by establishing displacement constraint equations between the beam unit nodes and the solid unit nodes; when meshing, the maximum size of the solid unit in the pool wall area is controlled to not exceed 50% of the steel arrangement spacing, and at least three layers of units are divided along the thickness direction of the pool wall.

[0023] For example, the eight-node hexahedral solid element adopts the SOLID185 element type in ANSYS, and the elastic modulus of C35 concrete is 3.15×10 4 MPa, and a Poisson's ratio of 0.2. The steel skeleton element utilizes the two-node spatial beam element BEAM188, automatically associating the cross-sectional geometric parameters of the HM150×100 steel from the software's built-in steel section database, including a section height of 150mm, a flange width of 100mm, and a web thickness of 6.5mm. Displacement coordination is achieved in the contact area between the steel and concrete through the following method: For each steel node, a search is automatically performed for concrete solid element nodes whose spatial distance from the steel node is less than 0.01 times the average element size, establishing a constraint relationship that ensures complete translational alignment between the two elements in the X, Y, and Z directions. When the steel spacing is 200mm, the maximum size of the solid element in the pool wall area is controlled at 100mm. Three layers of elements, each 100mm thick, are constructed along the wall thickness (e.g., a 300mm thickness). This ensures that each steel element has two nodes along the flange width and one node on each side of the flange thickness, forming a stable interface constraint system. When the pool wall thickness increases, the number of layers needs to be increased to ensure that the unit size meets the thickness direction layering requirements and the maximum size is ≤ 50% of the steel spacing.

[0024] In the prior art, four-node tetrahedron elements are often used to simulate concrete, and the steel sections are simplified to equivalent steel bars or the interface effect is ignored. Coarse meshing is used, which leads to distortion in the simulation of the coordinated work of the steel sections and concrete, and large errors in stress calculation. For example, a certain project uses four-node tetrahedron elements and does not set interface constraints, resulting in the calculated pool wall stress being 15% lower than the actual stress. This embodiment couples eight-node hexahedron elements and two-node beam elements, combined with degree of freedom constraint technology, to truly reflect the deformation coordination relationship between the two materials, strictly control the grid size and number of layers, and make the finite element model closer to the actual structure. After actual measurement verification, the modeling method of this embodiment is used to reduce the stress calculation error, provide a reliable numerical basis for subsequent load analysis and stress calculation, and avoid design deviations caused by model simplification. In a certain actual project, the constraint equation technology is used to accurately simulate the stress transfer at the interface between the steel section and concrete under the action of temperature load, reduce the error between the calculated result of the interface shear stress and the measured value, and significantly improve the model accuracy.

[0025] In another embodiment, the specific process of applying the load condition includes: layered application of the hydrostatic pressure load, dividing the pool wall into at least 5 load application layers along the height direction, the hydrostatic pressure value of each layer is calculated and determined according to the water depth at the centroid of the layer, and the pressure difference between adjacent layers does not exceed 15% of the maximum hydrostatic pressure; dynamic temperature load coupling simulation, establishing a temperature load spectrum including annual extreme temperature differences, wherein the summer working condition applies the highest water temperature value to the inner surface of the pool wall, and the environmental design highest temperature value to the outer surface of the pool wall, and the winter working condition applies the lowest water temperature value to the inner surface of the pool wall, and the environmental design lowest temperature value to the outer surface of the pool wall; the water level fluctuation additional load is a water level dynamic fluctuation additional term ΔP superimposed on the hydrostatic pressure load, and its value is calculated according to the design water level change rate v according to the formula ΔP=0.5ρv 2 Calculation, where ρ is the water density and the fluctuation range is ±10% of the difference between the designed maximum water level and the minimum water level.

[0026] For example, when applying hydrostatic pressure in layers, taking a 10-meter-high pool wall as an example, it is divided into five load layers along the height, each 2 meters high. The first layer has a centroidal water depth of 1 meter (pressure 9.8 kPa), the second layer has a centroidal water depth of 3 meters (pressure 29.4 kPa), the third layer has a centroidal water depth of 5 meters (49 kPa), the fourth layer has a centroidal water depth of 7 meters (68.6 kPa), and the fifth layer has a centroidal water depth of 9 meters (88.2 kPa). The pressure difference between adjacent layers is 19.6 kPa. When it does not exceed 15% of the maximum hydrostatic pressure of 98 kPa (14.7 kPa), it can be refined into six layers, each approximately 1.67 meters, to ensure a uniform pressure gradient. The temperature load spectrum is formulated based on local meteorological data and water temperature control requirements. For example, in summer, the maximum pool water temperature is 30°C (acting on the inner surface) and the maximum ambient temperature is 35°C (on the outer surface). In winter, the minimum pool temperature is 5°C (on the inner surface) and the minimum ambient temperature is -10°C (on the outer surface), resulting in a temperature difference load between the inner and outer surfaces. When calculating the additional load due to water level fluctuation, the design water level change rate v is 0.5 m / s (slow fluctuation), 1 m / s (medium fluctuation), 1.5 m / s (rapid fluctuation), and the water density ρ = 1000 kg / m 3 , corresponding to ΔP of 0.125 kPa, 0.5 kPa, and 1.125 kPa, respectively. Taking the design maximum and minimum water levels as an example, the fluctuation range is ±10%, or ±0.5 meters. This is superimposed on the hydrostatic pressure to form a dynamic load combination. When applying loads, the finite element software's load layer definition function (such as the Pressure module in ABAQUS) is used to distribute pressure values ​​by layer. Temperature loads are applied to internal and external surfaces via the SurfaceTemperature boundary condition. Water level fluctuation terms are implemented via user-defined subroutines or directly superimposed on the hydrostatic pressure load step.

[0027] In the prior art, load application is often simplified to uniformly distributed hydrostatic pressure, ignoring the effects of temperature changes and water level fluctuations, resulting in large errors in the calculation of thermal stress of the structure under temperature differences, and easily causing unexpected local stress concentration when the water level fluctuates. This embodiment simulates the nonlinear distribution through layered hydrostatic pressure, introduces a load spectrum containing extreme temperature differences and water level fluctuation additional terms, and constructs a load system coupled with multiple physical fields. This embodiment breaks through the limitations of single load simulation, and the layered application of hydrostatic pressure is more in line with the actual water pressure distribution. Compared with the traditional uniformly distributed load model, the deviation between the calculated value and the measured value of the stress in the middle of the pool wall is reduced; the dynamic temperature load spectrum takes into account the annual temperature difference cycle effect, accurately captures the thermal expansion and contraction stress caused by the temperature difference between the inner and outer surfaces; quantifies the impact load of water level fluctuations, so that the load condition is closer to the actual service environment of the pool. In a certain industrial water pool project, after optimization according to the load analysis results of this embodiment, the incidence of temperature cracks in the pool wall was significantly reduced compared with the traditional design.

[0028] In another embodiment, finite element analysis is run to obtain stress distribution data of the pool wall, and the stress gradient field of the stress distribution data is calculated, specifically including: principal stress direction change rate calculation, extracting the direction vector of the maximum principal stress of each finite element node, calculating the angle change of the direction vectors between adjacent nodes in the local coordinate system established on the pool wall surface, dividing the angle change by the spatial distance between the nodes to obtain the principal stress direction change rate per unit length; equivalent stress change rate calculation, calculating the Mises equivalent stress value of each node, obtaining the difference in equivalent stress between adjacent nodes in the global rectangular coordinate system, dividing the difference by the spatial distance between the nodes to obtain the equivalent stress change rate per unit length; dual-channel gradient fusion, assigning a first weight coefficient of 0.7 to the principal stress direction change rate, and a second weight coefficient of 0.3 to the equivalent stress change rate, taking the square values ​​of the two weighted change rates respectively and summing them, and performing a square root operation on the sum result to generate the final gradient value.

[0029] For example, when calculating the rate of change of the principal stress direction, the maximum principal stress direction vector of the node is extracted through the post-processing module of the finite element software (such as ANSYS). Assuming that the principal stress direction vector of a node A on the pool wall surface is (0.8, 0.6, 0), and the vector of the adjacent node B is (0.707, 0.707, 0), in the local coordinate system (with the tangent direction of the surface as the x and y axes, and the normal as the z axis), the angle between the two vectors is calculated as θ=arccos[(0.8×0.707+0.6×0.707) / 1]=arccos(0.99)≈8.1°, which is converted to radians of 0.141 rad. If the node spacing is 0.1m, the rate of change of direction is 0.141 / 0.1=1.41rad / m. In the calculation of the equivalent stress change rate, the Mises stress at node A is 25 MPa, and at node B is 15 MPa. The spacing in the global coordinate system is 0.1 m, the difference is 10 MPa, and the change rate is 10 / 0.1 = 100 MPa / m. When merging two channels, the first weight is 0.7 and the second weight is 0.3. The calculation is (1.41×0.7) 2 +(100×0.3) 2 ≈0.98 + 900 = 900.98, the square root is approximately 30.02, and the final gradient value is 30.02. This process is automatically extracted and calculated by the software script to ensure the efficiency and accuracy of gradient field generation.

[0030] In the prior art, stress concentration is judged only by the equivalent stress amplitude, without considering the effect of the change in the direction of the principal stress on cracking, resulting in a high missed rate of stress concentration areas in complex locations such as the corners of rectangular pools. This embodiment comprehensively quantifies the spatial characteristics of stress distribution through dual-channel fusion calculation of the principal stress direction change rate and the equivalent stress change rate. The creativity lies in: introducing the principal stress direction change rate parameter to capture the spatial steering effect of the stress state. For example, in the corner area, the principal stress direction change rate can significantly identify the stress redistribution area; comprehensively evaluating the gradient changes of stress direction and amplitude through the weight fusion algorithm. Verified by engineering examples, the accuracy of high-risk area identification is significantly improved compared with the traditional single indicator analysis, effectively avoiding design omissions caused by incomplete description of the stress state.

[0031] In another embodiment, when identifying an area in the stress gradient field where the stress gradient value is greater than a preset critical gradient, three functional areas are divided according to the structural characteristics of the pool wall: a top exposed area extending 1.5 meters downward from the top of the pool, a bottom constrained area extending 2.0 meters upward from the bottom of the pool, and a middle stable area between the top exposed area and the bottom constrained area; a risk weight coefficient is configured for each area, with the top exposed area being assigned a weight value of 1.2, the middle stable area being assigned a weight value of 1.0, and the bottom constrained area being assigned a weight value of 0.8; a mesh quality assessment is performed on each finite element unit, and when the unit aspect ratio is greater than 3 or the distortion is greater than 30 degrees, it is marked as a low-quality unit and assigned a mesh correction coefficient of 0.9, and the remaining units are assigned a mesh correction coefficient of 1.0; the actual critical gradient value of the unit is calculated, and the actual critical gradient value = preset critical gradient × risk weight coefficient × mesh correction coefficient; when the unit stress gradient value is greater than the actual critical gradient value of the unit, it is included in the identification area.

[0032] For example, the regional division is based on a pool with a top elevation of 10.0m and a bottom elevation of 0.0m. The top exposed zone is 8.5m to 10.0m (a 1.5-meter range), the bottom constrained zone is 0.0m to 2.0m (a 2.0-meter range), and the central stable zone is 2.0m to 8.5m. During mesh quality assessment, elements with a long side of 40mm and a short side of 10mm (a length-to-width ratio of 4>3) are marked as low-quality elements. Elements with an in-plane edge-to-edge angle deviating from 90 degrees by 35 degrees (distortion of 35 degrees>30 degrees) are also marked, with a mesh correction factor of 0.9. The default critical gradient G is 0.5. The actual critical gradient of a low-quality element in the top exposed zone is 0.5 × 1.2 × 0.9 = 0.54. If the stress gradient value of this element is 0.56>0.54, it is included in the optimization region. Mesh quality assessment can be automatically detected through the MeshMetric function of ANSYS. The aspect ratio threshold is set to 3, the distortion threshold is set to 30 degrees, and low-quality elements are marked in batches and assigned mesh correction coefficients to improve calculation efficiency.

[0033] In the existing technology, the identification of critical areas mostly adopts a unified threshold, without considering the risk differences of different parts of the structure and the influence of grid quality, resulting in the identification results not being consistent with the actual stress state and a high misjudgment rate. This embodiment realizes the differentiated identification of critical gradients through a multi-calibration mechanism of functional area division, risk weight configuration and grid quality correction. This embodiment divides risk areas based on structural characteristics and assigns quantitative weights. For example, the top exposed area is susceptible to environmental erosion, so the risk weight is increased, making the critical value judgment of this area more stringent; the grid correction coefficient is introduced to eliminate the influence of model discrete errors, and after the low-quality units are corrected, the stress gradient calculation deviation is reduced; the actual critical gradient of the unit is dynamically calculated to make the identification of high-risk areas more accurate. In a deep water tank project, after on-site monitoring, the critical area identified according to this embodiment is 90% consistent with the actual crack occurrence location, which is a significant improvement over the traditional uniform discrimination method.

[0034] In another embodiment, the preset critical gradient is determined by the following steps: calculating the material constitutive reference value G_base, G_ base =0.28×(f_ tk / E_ c )+0.18×(f_ y / E_ s ), where f_ tk is the standard value of concrete tensile strength, E_ c is the elastic modulus of concrete, f_ y is the yield strength of steel, E_ s is the elastic modulus of the steel; calculate the structural geometric sensitivity coefficient λ, λ=1.0+0.15×(H / D)+0.05×|ΔT|, where H is the design water depth of the pool, D is the length of the short side of the pool, and ΔT is the change rate of the pool wall thickness; calculate the load coupling correction coefficient κ, κ=1.0+0.1×(P_ t / P_ s ), where P_ t is the maximum value of temperature load, P_ s is the maximum value of hydrostatic pressure; determine the environmental durability coefficient γ, non-corrosive environment γ=1.0, weak corrosive environment γ=1.15, strong corrosive environment γ=1.30; calculate the preset critical gradient G, G=G_ base ×λ×κ×γ.

[0035] For example, the material constitutive reference value is calculated as follows: take C30 concrete (f_ tk =2.39MPa, E_ c =3×10 4 MPa), Q235 steel (f_ y =235MPa, E_ s =2.06×10 5 MPa), then G_base =0.28×(2.39 / 3×10 4 )+0.18×(235 / 2.06×10 5 )≈0.28×7.97×10 -5 +0.18×1.14×10 -3 ≈2.23×10 -5 +2.05×10 -4 =2.27×10 -4 Structural geometric sensitivity coefficient: Design water depth H = 8m, short side length D = 6m (H / D = 1.33), pool wall thickness gradually changes from 300mm to 400mm, ΔT = (400-300) / 300≈33.3%, then λ = 1.0 + 0.15 × 1.33 + 0.05 × 0.333≈1.0 + 0.1995 + 0.0167 = 1.2162. Load coupling correction factor: Maximum temperature load P_ t =20kPa (equivalent load of thermal stress caused by internal and external temperature difference), maximum hydrostatic pressure P_ s =80kPa, κ=1.0+0.1×(20 / 80)=1.025. Environmental durability coefficient: For weakly corrosive environments (such as sewage treatment pools), γ=1.15. The final preset critical gradient G=2.27×10 -4 ×1.2162×1.025×1.15≈2.27×10 -4 ×1.2162≈2.76×10 -4 , 2.76×10 -4 ×1.025≈2.83×10 -4 , 2.83×10 -4 ×1.15≈3.25×10 -4 The calculation process can be implemented through parameterized input in Excel or Python programs, automatically generating G values ​​to adapt to different engineering parameters.

[0036] In existing technologies, critical gradients often use fixed values ​​from specifications, failing to consider the combined effects of material properties, structural geometry, load combinations, and environmental factors. This results in a disconnect between threshold settings and actual engineering practice. For example, a tank with a water depth of 10 meters, designed according to conventional empirical values, may experience actual stress gradients exceeding the critical value. This embodiment utilizes a multi-parameter coupling formula, G=G_base×λ×κ×γ, to quantitatively integrate factors such as material constitutive properties, geometric sensitivity, load coupling, and environmental durability. Its innovation lies in: constructing a baseline calculation formula that incorporates material strength and elastic modulus, directly linking the critical value to the tensile strength of concrete and the yield strength of steel sections; introducing a geometric sensitivity coefficient to account for variations in water depth, body shape, and wall thickness. For example, when H / D = 1.5, the λ value increases by 18% compared to conventional structures, correspondingly increasing the critical gradient; and using a load coupling coefficient to account for the interaction between temperature and water pressure. Under conditions with large temperature differences, the κ value can be increased by 10%-15%, ensuring that the critical gradient is adaptable to complex operating conditions. Validation in tanks of various sizes demonstrates that the critical value of this embodiment agrees better with the actual critical stress for cracking than conventional methods.

[0037] In another embodiment, the ratio of the local stress gradient value to the preset critical gradient is divided into three levels of response zones, with a ratio of 1.0 to 1.5 being the Level I response zone, 1.5 to 2.0 being the Level II response zone, and greater than or equal to 2.0 being the Level III response zone; in the Level I response zone, the spacing of the steel sections is reduced by 8% to 12% or the cross-sectional size is increased by 5% to 8%; in the Level II response zone, the spacing is reduced by 12% to 18% and the cross-sectional size is increased by 8% to 12%; in the Level III response zone, longitudinal stiffening ribs are added on the basis of reducing the spacing by 18% to 25% and increasing the cross-sectional size by 12% to 15%; when the minimum clear distance between the steel sections after adjustment is less than 2.5 times the maximum particle size of the coarse aggregate, the cross-sectional size increase is reduced to meet the clear distance requirement. If the cross-sectional size has reached the lower limit of the steel section specification, a steel fiber content of 25-35 kg / m is used. 3 Replacement of dense concrete cover.

[0038] For example, when the stress gradient ratio in a certain area is 1.2 (Level I response zone), the prototype steel spacing is 200mm, which can be reduced to 200×(1-10%)=180mm (a 10% reduction), or the cross-sectional height of the original H-shaped steel HN200×100 is increased by 5% to 210mm; when the ratio is 1.7 (Level II response zone), the spacing is reduced by 15% to 170mm, and the cross-sectional height is increased by 10% to 220mm; when the ratio is 2.2 (Level III response zone), the spacing is reduced by 20% to 160mm, the cross-sectional height is increased by 15% to 230mm, and a 10mm thick longitudinal stiffener is added. If the adjusted steel section has a net distance of 30mm and the maximum size of the coarse aggregate is 40mm, the net distance must be ≥40×2.5=100mm. In this case, the section increase is reduced to a net distance of 100mm. If the steel section has adopted the minimum specification HN100×100 and the section cannot be increased, the steel fiber content of 30kg / m3 should be poured on the surface of the steel section.3 A 50mm-thick, dense concrete cover (aggregate size ≤ 20mm) ensures construction feasibility. Steel section adjustments can be made using the parametric modeling capabilities of finite element software (such as the Part module in ABAQUS) to automatically update cross-sectional dimensions and spacing, while also verifying clearance constraints.

[0039] In existing technologies, critical gradients often use fixed values ​​from specifications, failing to consider the combined effects of material properties, structural geometry, load combinations, and environmental factors. This results in threshold settings being out of sync with actual engineering practices. For example, a tank with a water depth of 10 meters, designed according to conventional empirical values, may have actual stress gradients exceeding the critical value by 20%. This embodiment quantifies and integrates factors such as material constitutive properties, geometric sensitivity, load coupling, and environmental durability through a multi-parameter coupling formula, G=G_base×λ×κ×γ. This embodiment constructs a baseline value calculation formula that incorporates material strength and elastic modulus, directly linking the critical value to the tensile strength of concrete and the yield strength of steel. A geometric sensitivity coefficient is introduced to account for variations in water depth, body shape, and wall thickness. For example, when H / D = 1.5, the λ value increases by 18% compared to conventional body shapes, correspondingly increasing the critical gradient. A load coupling coefficient is used to account for the interaction between temperature and water pressure. Under conditions with large temperature differences, the κ value can be increased by 10%-15%, ensuring that the critical gradient is adaptable to complex operating conditions. Validation in tanks of various sizes demonstrates that the critical values ​​of this embodiment agree better with the actual critical stress for cracking than conventional methods.

[0040] In another embodiment, the steel-concrete water tank design method also includes stress redistribution monitoring and iteration termination judgment steps: based on the adjusted steel layout spacing and cross-sectional dimensions, updating the steel skeleton unit properties in the three-dimensional finite element model; re-running the finite element analysis and stress gradient field calculation to obtain the updated stress distribution and identify new critical gradient areas; using the iteration termination judgment logic to decide whether to terminate the optimization, if the total area of ​​the newly identified critical gradient area is ≤10% of the total area of ​​the initially identified area, and the maximum stress gradient value in all critical gradient areas decreases by <5% compared with the previous iteration or the number of iterations reaches 5, then the iteration is terminated and the final design is output; when the number of iterations reaches 5 and the termination condition is still not met, the steel layout parameters of the three areas with the largest adjustment range are frozen, and the judgment process is re-executed.

[0041] For example, the total area of ​​the initially identified critical gradient region is 50m 2 After the first iteration, the steel spacing was adjusted from 200mm to 180mm, and the cross section was increased from HN200×100 to HN220×100. After recalculation, the new critical area was 45m² (accounting for 90% of the initial area), and the maximum stress gradient value was reduced from 0.8MPa / m to 0.7MPa / m (a decrease of 12.5%). The iteration was continued; after the second adjustment, the area was reduced to 20m 2(accounting for 40%), the maximum gradient value is 0.65MPa / m (a decrease of 7.1%), and the termination condition is still not met; after the third iteration, the area is 15m 2 (30%), the gradient value is 0.62MPa / m (4.6%<5%), the termination condition is met, and the final design is output. If the area after the fifth iteration is still 15% of the initial area (7.5m 2 If the gradient value decreases by 6% and the termination criteria are not met, the three regions with the largest adjustments from the previous three iterations (e.g., a 25% reduction in spacing and a 15% increase in cross section) are frozen, their parameters are kept unchanged, and the calculation is repeated until the termination criteria are met. The iterative process is automatically executed by calling the finite element software API through a Python script, and the change curve of key parameters is recorded for each iteration.

[0042] In the prior art, steel section optimization is mostly a single adjustment, without considering the stress redistribution effect, resulting in a large deviation between the actual stress state and the design expectation, and even a situation where the local stress increases after optimization. This embodiment uses an iterative optimization mechanism to quantitatively evaluate the stress response changes after each adjustment to achieve dynamic closed-loop optimization. Compared with the prior art, its creativity lies in: establishing a dual termination judgment standard based on the proportion of critical area area and the gradient value drop, ensuring that the optimization process is neither over-iterative and resulting in inefficiency, nor causing safety hazards due to premature termination; introducing a parameter freezing strategy to deal with difficult-to-converge areas, balancing global optimization and local stability. In a large sewage treatment pool project, after three iterations, the area of ​​high stress areas was reduced, the maximum stress gradient value decreased, the amount of steel used was more economical than the traditional single optimization solution, and the deviation between the measured stress of the structure and the design value was controlled within 5%, significantly improving the design reliability and economy.

[0043] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. Steel concrete pool design method, characterized by: include: S1: Establishing a three-dimensional finite element model of the pool, wherein the three-dimensional finite element model includes concrete solid elements and steel skeleton elements; S2: applying a load condition to the three-dimensional finite element model, wherein the load condition includes a hydrostatic pressure and a temperature load; S3: Run finite element analysis to obtain stress distribution data of the pool wall, and calculate the stress gradient field of the stress distribution data; S4: Identifying an area in the stress gradient field where the stress gradient value is greater than a preset critical gradient, where the preset critical gradient is determined based on the pool wall material properties and a design safety factor; S5: In the identified area, based on the local stress gradient value of the area, adjusting the layout spacing and cross-sectional dimensions of the steel sections in the area according to a preset proportional relationship; The specific process of applying load cases in S2 includes: Layered application of hydrostatic pressure load: Divide the pool wall into at least five load application layers along its height. The hydrostatic pressure value of each layer is calculated based on the water depth at the centroid of the layer, and the pressure difference between adjacent layers shall not exceed 15% of the maximum hydrostatic pressure. Dynamic temperature load coupling simulation: Establish a temperature load spectrum that includes extreme annual temperature differences, where: Summer conditions: The highest water temperature is applied to the inner surface of the pool wall, while the highest environmental design temperature is applied to the outer surface of the pool wall; Winter conditions: The lowest water temperature is applied to the inner surface of the pool wall, while the lowest environmental design temperature is applied to the outer surface of the pool wall; Water level fluctuation additional load: On the basis of the hydrostatic pressure load, the additional term of water level dynamic fluctuation ΔP is superimposed. Its value is based on the design water level change rate v according to the formula ΔP=0.5ρv 2 Calculation, where ρ is the water density and the fluctuation range is ±10% of the difference between the designed maximum water level and the minimum water level.

2. The steel concrete pool design method according to claim 1, characterized in that: In S1, the concrete solid element is simulated using an eight-node hexahedral solid element, and the elastic modulus and Poisson's ratio material properties are configured; The steel skeleton element is simulated using a two-node spatial beam element, and the cross-sectional geometric parameters are automatically associated based on the steel cross-sectional database; In the contact area between the steel and concrete, displacement coordination is achieved by establishing displacement constraint equations between the beam unit nodes and the solid unit nodes; When dividing the mesh, the maximum size of the solid unit in the pool wall area should be controlled not to exceed 50% of the spacing of the steel arrangement, and at least three layers of units should be divided along the thickness direction of the pool wall.

3. The steel-concrete pool design method according to claim 1, wherein S3 include: S3.1: Calculate the principal stress direction change rate. Extract the direction vector of the maximum principal stress at each finite element node. Calculate the change in the angle between the direction vectors at adjacent nodes in the local coordinate system established on the pool wall surface. Divide this angle change by the spatial distance between the nodes to obtain the principal stress direction change rate per unit length. S3.2: Calculate the rate of change of equivalent stress. Calculate the Mises equivalent stress value for each node. In the global rectangular coordinate system, find the difference in equivalent stress between adjacent nodes. Divide the difference by the spatial distance between the nodes to obtain the rate of change of equivalent stress per unit length. S3.3: Dual-channel gradient fusion: assign the principal stress direction change rate to the first weight coefficient 0.7, and the equivalent stress change rate to the second weight coefficient 0.

3. Take the square values ​​of the two weighted change rates respectively and sum them. Perform a square root operation on the sum result to generate the final gradient value.

4. The steel concrete pool design method according to claim 1, characterized in that: In S4, the method for identifying an area in the stress gradient field where the stress gradient value is greater than a preset critical gradient includes: The pool wall is divided into three functional areas according to its structural characteristics: the top exposed area extending 1.5 meters downward from the top of the pool, the bottom constrained area extending 2.0 meters upward from the bottom of the pool, and the middle stable area between the top exposed area and the bottom constrained area. Assign risk weight coefficients to each region: the top exposed area is assigned a weight of 1.2, the middle stable area is assigned a weight of 1.0, and the bottom constrained area is assigned a weight of 0.8; The mesh quality of each finite element is evaluated. When the element aspect ratio is greater than 3 or the distortion is greater than 30 degrees, it is marked as a low-quality element and assigned a mesh correction factor of 0.

9. The remaining elements are assigned a mesh correction factor of 1.

0. Calculate the actual critical gradient value of the unit: actual critical gradient value = preset critical gradient × risk weight coefficient × grid correction coefficient; When the element stress gradient value is greater than the actual critical gradient value of the element, it is included in the identification area.

5. The steel-concrete pool design method according to claim 1, characterized in that: The preset critical gradient is determined by the following steps: Calculate the material constitutive reference value G_ base , G_ base =0.28×(f_ tk / E_ c )+0.18×(f_ y / E_ s ), where f_ tk is the standard value of concrete tensile strength, E_ c is the elastic modulus of concrete, f_ y is the yield strength of steel, E_ s is the elastic modulus of the steel; Calculate the structural geometric sensitivity coefficient λ, λ = 1.0 + 0.15 × (H / D) + 0.05 × |ΔT|, where H is the design water depth of the pool, D is the length of the short side of the pool, and ΔT is the rate of change of the pool wall thickness; Calculate the load coupling correction factor κ, κ=1.0+0.1×(P_ t / P_ s ), where P_ t is the maximum value of temperature load, P_ s is the maximum value of hydrostatic pressure; Determine the environmental durability coefficient γ, non-corrosive environment: γ = 1.0; weakly corrosive environment: γ = 1.15; strongly corrosive environment: γ = 1.30; Calculate the preset critical gradient G, G=G_ base ×λ×κ×γ.

6. The steel concrete pool design method according to claim 1, characterized in that: The ratio of the local stress gradient value to the preset critical gradient is divided into three levels of response areas: a ratio of 1.0 to 1.5 is a level I response area, a ratio of 1.5 to 2.0 is a level II response area, and a ratio greater than or equal to 2.0 is a level III response area; For Level I response areas, the spacing between sections will be reduced by 8% to 12% or the cross-sectional size will be increased by 5% to 8%. For Level II response areas, the spacing will be reduced by 12% to 18% and the cross-sectional size will be increased by 8% to 12%. For Level III response areas, longitudinal stiffeners will be added in addition to reducing the spacing by 18% to 25% and increasing the cross-sectional size by 12% to 15%. When the minimum clearance between steel sections after adjustment is less than 2.5 times the maximum particle size of coarse aggregate, reduce the increase in cross-sectional size to meet the clearance requirement. If the cross-sectional size has reached the lower limit of the steel section specification, use a steel fiber content of 25-35 kg / m 3 Replacement of dense concrete cover.

7. The steel concrete pool design method according to claim 6, characterized in that: Also includes: S6: Stress redistribution monitoring and iteration termination judgment: S6.1: Based on the steel section arrangement spacing and cross-sectional dimensions adjusted in S5, update the steel section skeleton unit properties in the three-dimensional finite element model; S6.2: Re-run steps S3 to S4 to obtain the updated stress gradient field and identify the new critical gradient region; S6.3: Iteration termination judgment: If the following conditions are met at the same time, the iteration is terminated and the final design is output. Otherwise, return to S5 for execution: the total area of ​​the newly identified critical gradient regions is ≤ 10% of the total area of ​​the initially identified regions; the maximum stress gradient value in all critical gradient regions decreases by less than 5% compared with the previous iteration or the number of iterations reaches 5; S6.4: When the termination condition is not met after 5 iterations, freeze the steel layout parameters of the three areas with the largest adjustment range and re-execute the S6.2-S6.3 judgment.

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