Simplified calculation and analysis method for double-wall steel cofferdam

Abstract

The invention discloses a simplified calculation and analysis method for a double-wall steel cofferdam, which comprises the following steps: step S01, structure simplification: carrying out equivalent simplification treatment on a cofferdam structure according to stress characteristics of the double-wall cofferdam, including one or more of simplification of a compartment structure, simplification of an annular plate and a horizontal cross brace, simplification of a wall body panel and simplification of a bottom sealing structure; step S02, model simplification: carrying out equivalent simplification processing on the cofferdam equivalent structure, and equivalently simplifying each structure of the cofferdam equivalent structure into each model unit; and step S03, simplified model calculation: determining a simplified analysis method according to requirements, establishing a simplified unit model by utilizing finite element software, and performing automatic analysis by the software to obtain corresponding internal force, stress and deformation results. The method has the advantages that the simplified calculation method combines the advantages of a finite element analysis method and an analysis method, meanwhile, complex accurate model establishment is abandoned, and the structural calculation efficiency is improved while the structural calculation analysis accuracy is met.

Description

Technical Field

[0001] The present application relates to the design and calculation of double-walled steel cofferdam structures in the fields of bridges, buildings, etc., and specifically to a simplified calculation and analysis method for double-walled steel cofferdams. Background Art

[0002] The traditional finite element analysis method and numerical solution need to establish complex finite element analysis models or numerical solutions to ensure the accuracy of calculations and the rationality of structural design. For the increasingly complex and large steel cofferdam structures, the traditional method is suitable for calculation and analysis in the design implementation stage. For the scheme selection calculation, the efficiency is very low and a large amount of human resources are wasted.

[0003] There are two main calculation methods for double-wall steel cofferdams:

[0004] (1) Component calculation method (analytical method): This method separates the components of the double-walled steel cofferdam and treats them as single force-bearing individuals. According to the relevant mechanical formulas, the calculation is performed according to simple components such as simple beams, continuous beams and support plates. Although this method can quickly calculate structural components, it lacks overall analysis of the structure and consideration of strengthening plates, resulting in poor accuracy of structural calculations and overly conservative calculation results. It is only applicable to structures with simple structures, clear forces and regular geometric boundaries, and is almost not applicable to complex double-walled steel cofferdam structures.

[0005] (2) Finite element method (numerical analysis method): Currently, the finite element method is the mainstream solution tool for solving mechanical problems. It has rigorous mathematical logic, clear physical concepts, and is widely used. It can flexibly handle and solve various complex problems. When the calculated structural design is complex and the model is relatively large, it takes a long time to establish an accurate finite element model, especially in the scheme selection stage, and the work efficiency is low.

[0006] Now a new design method has been invented that can quickly calculate and analyze the double-walled steel cofferdam, and the results are relatively reasonable. Summary of the invention

[0007] The purpose of this application is to provide a simplified calculation and analysis method for a double-walled steel cofferdam, which solves the following problems: When the traditional steel cofferdam structure adopts a finite element model using a finite element tool, the model structure includes structures such as walls, bottom plates, hanging systems, and bottom concrete. Various loads and boundary conditions need to be considered according to different working conditions. The structure includes connections and unit couplings of plate units, beam units, and solid units. The establishment, debugging, and operation of the model take a long time and are prone to errors, resulting in increased workload.

[0008] The present application provides a simplified calculation and analysis method for a double-walled steel cofferdam. In the scheme design stage, the double-walled steel cofferdam structure can be calculated more accurately and efficiently. The method simplifies the structure equivalently based on the mechanical concept and establishes a simplified finite element model. At the same time, it combines the analytical method to analyze some structures to meet the requirements of reliable and accurate calculation of the structure.

[0009] The purpose of this application is achieved through the following technical solutions:

[0010] A simplified calculation and analysis method for a double-wall steel cofferdam comprises the following steps:

[0011] Step S01, structural simplification: performing equivalent simplification processing on the cofferdam structure according to the stress characteristics of the double-wall cofferdam, including one or more of simplification of the compartment structure, simplification of the ring plate and horizontal cross brace, simplification of the wall panel and simplification of the bottom cover structure;

[0012] Step S02, model simplification: performing equivalent simplification processing on the cofferdam equivalent structure, and equivalently simplifying each structure of the cofferdam equivalent structure into each model unit;

[0013] Step S03, simplified model calculation: Determine the simplified analysis method according to the requirements, use the finite element software to establish a simplified unit model, and the software automatically analyzes to obtain the corresponding internal force, stress and deformation results.

[0014] Furthermore, the force transmission path of the double-wall cofferdam structure is: the water and soil loads are transmitted to the inner and outer walls, and then the walls are coordinated by deformation to transmit the force to the compartment structure, and the compartment structure then transmits the force to the inner support.

[0015] Furthermore, in the simplification of the compartment structure, the compartment structure of the double-wall cofferdam is simplified to an I-section, an H-section or a box section according to the principle of equivalent cross-sectional characteristics; the compartment reinforcement ring plate is not considered in the design of the beam system structure, or the compartment reinforcement ring plate is considered in the cross-sectional design by the equivalent area method; the area equivalent formula is:

[0016] A=A 壁体 +A 竖肋 ;

[0017] Where A is the equivalent area of ​​the wall per unit width, A 壁体 is the wall panel area per unit width, A 竖肋 is the cross-sectional area of ​​the vertical rib within unit width;

[0018] The equivalent formula for the moment of inertia of the section is:

[0019] I=I 壁体 +I 竖肋 ;

[0020] Where I is the equivalent section inertia moment of the wall per unit width, I壁体 is the moment of inertia of the wall plate per unit width, I 竖肋 is the moment of inertia of the vertical rib section within unit width.

[0021] Furthermore, in the simplification of the ring plate and horizontal cross brace, the cross section composed of the ring plate, inner and outer walls, and horizontal cross brace is equivalent to a truss structure or a solid web structure according to the cross-sectional characteristics; the wall body and the ring plate are comprehensively considered, and the wall body with width is used as the flange plate. Both are simplified to a welded T-shaped steel section according to the cross-sectional characteristics, and the flange extension width is:

[0022] b f =15t f ε k ;

[0023] Among them, b f is the equivalent T-section flange width, t f is the flange thickness of the T-section, ε k is the steel grade correction factor; in the simplification of the ring plate and horizontal cross brace, the effect of the longitudinal secondary beam on the ring plate is not considered.

[0024] Furthermore, in the simplification of the wall panel, the structure composed of the panel wall and the panel vertical ribs is simplified to a steel plate structure of equivalent thickness according to the principle of equivalence of cross-sectional area and moment of inertia.

[0025] Furthermore, in the simplification of the bottom cover structure, the bottom cover structure is simplified into a constraint boundary with rigidity according to the elastic modulus and cross-sectional characteristics of the concrete.

[0026] Furthermore, the model analysis of the partitions and internal supports is considered: the partitions are equivalent to beam units, and the internal supports are equivalent to beam units; the structure composed of the ring plate and the horizontal cross brace is set as a virtual rod, and the structure composed of the wall and the vertical ribs is set as a virtual surface. The virtual rods and virtual surfaces are only used for load application and transfer, and the loads are directly transferred to the nodes; or no virtual rods are set, and the loads are directly transferred from the virtual surfaces to the partition beam system; the ring plates, horizontal cross braces and walls are calculated and analyzed according to the analytical method.

[0027] Furthermore, the model analysis of the partitions, internal supports, ring plates and horizontal cross braces is considered: the partitions are equivalent to beam units, and the internal supports are equivalent to beam units; the structure composed of the ring plates and vertical ribs is equivalent to T-beam section units, which form a truss structure or a solid-web structure with the horizontal supports; the structure composed of the walls and vertical ribs is set as a virtual surface, which does not bear any load and is only used for load application and transfer; the wall is calculated and analyzed according to the analytical method.

[0028] Furthermore, the model analysis of partitions, internal supports, ring plates, horizontal cross braces and walls is considered: the partitions are equivalent to beam units, and the internal supports are equivalent to beam units; the structure composed of ring plates and vertical ribs is equivalent to T-beam section units, which form a truss structure or a solid-web structure with the horizontal supports; the walls and vertical ribs are equivalent to plate units.

[0029] Furthermore, for structures without modeling, less favorable working conditions were analyzed using analytical methods based on loads and design boundary conditions combined with mechanical formulas;

[0030] Calculation and analysis by wall plate unit analytical method: If the design plate is supported on two sides, it is analyzed as a continuous beam; if the design plate is supported on three or four sides, the internal force and deflection values ​​of the plate are calculated by looking up the table in the relevant manual. When the internal force and deflection of the plate unit are known, the stress value per unit width of the plate is calculated by the mechanical formula:

[0031]

[0032] Among them, σ x is the stress in the x direction, σ y is the stress in the y direction, σ z is the stress in z direction, z is the distance from the upper and lower plate surfaces to the center of the plate thickness, t is the plate thickness, M x is the bending moment in the x direction, M y is the bending moment in the y direction, M z is the bending moment in the z direction.

[0033] The beneficial effects of the present application are as follows: the simplified calculation method combines the advantages of the finite element analysis method and the analytical method, while also abandoning the complex and precise model establishment, thereby improving the efficiency of the structural calculation while satisfying the accuracy of the structural calculation analysis.

[0034] The aforementioned main scheme of the present application and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection in the present application; and in the present application, (non-conflicting options) can also be freely combined with each other and with other options. After understanding the scheme of the present application, those skilled in the art can understand that there are many combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present application, and they are not exhaustively listed here. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a simplified schematic diagram of the compartment structure of the present application.

[0036] Figure 2 It is a simplified schematic diagram (top view) of the ring plate and horizontal cross brace of the present application.

[0037] Figure 3 It is a simplified schematic diagram (side view) of the ring plate and horizontal cross brace of the present application.

[0038] Figure 4 It is a simplified schematic diagram of the wall panel of the present application.

[0039] In the figure: 101-partition wall, 102-partition web, 103-partition vertical rib, 104-partition reinforcing ring plate, 111-first partition equivalent wall, 112-second partition equivalent wall, 113-partition equivalent web; 201-structural wall, 202-structural vertical rib, 203-structural ring plate, 204-horizontal diagonal brace, 205-reinforcing diagonal brace, 211-structural equivalent wall; 301-panel wall, 302-panel vertical rib, 311-panel equivalent wall. DETAILED DESCRIPTION

[0040] The following non-limiting examples are provided to illustrate the present application.

[0041] Example 1

[0042] The main structures of double-wall steel cofferdam are side walls, bottom plates, internal supports, hanging systems and auxiliary structures.

[0043] Side wall: mainly composed of inner and outer wall panels, longitudinal secondary beams (vertical ribs), horizontal ring plates, horizontal cross braces, bulkheads and box beams. The inner and outer wall panels directly bear the water and soil loads; the longitudinal secondary beams, horizontal ring plates and horizontal cross braces are mainly used to strengthen the rigidity of the inner and outer wall panels, making the wall panels a force-bearing whole; bulkheads are the reinforcement components of the side walls, used to enhance the bearing capacity of the side walls, transfer the lateral pressure to the inner supports, and install the hanging system.

[0044] Bottom plate: It is welded from steel plate and steel, with piles reserved on the bottom plate and steel casings through holes. It is mainly composed of panels, bottom plate main beams and bottom plate secondary beams. Internal support: It includes steel pipe support, steel internal support, connection support, etc.; it is the same as the internal support structure of single-wall steel hanging box. Hanging system: It includes cantilever beams, hangers, shelving beams, tension and compression rods, etc.; it is the same as the hanging system structure of single-wall steel hanging box. Auxiliary system: It includes connecting vessels, sealing hoop, safety facilities, ladder railings, etc.; it is the same as single-wall steel hanging box.

[0045] A simplified calculation and analysis method for a double-wall steel cofferdam comprises the following steps:

[0046] Step S01, structural simplification: The force transmission path of the double-wall cofferdam structure is: the water and soil loads are transmitted to the inner and outer walls, and then the walls transmit the force to the compartment structure through deformation coordination, and the compartment structure then transmits the force to the inner support. According to the force characteristics of the double-wall cofferdam, the cofferdam structure is equivalently simplified, including simplification of the compartment structure, simplification of the ring plate and horizontal cross brace, simplification of the wall panel and simplification of the bottom cover structure.

[0047] In the simplification of the compartment structure, the compartment structure of the double-wall cofferdam is simplified to an I-section, an H-section or a box section according to the equivalent principle of cross-sectional characteristics (area, centroid, centroidal axis moment of inertia). The compartment reinforcement ring plate is mainly used to improve the shear and torsion resistance of the compartment and the local stability of the box beam wall, and has little effect on the bending stiffness of the box beam. The compartment reinforcement ring plate is not considered in the design of the beam system structure, or the compartment reinforcement ring plate is considered in the cross-sectional design by the equivalent area method.

[0048] The area equivalent formula is:

[0049] A=A 壁体 +A 竖肋 ;

[0050] Where A is the equivalent area of ​​the wall per unit width, A 壁体 is the wall panel area per unit width, A 竖肋 is the cross-sectional area of ​​the vertical rib per unit width.

[0051] The equivalent formula for the moment of inertia of the section is:

[0052] I=I 壁体 +I 竖肋 ;

[0053] Where I is the equivalent section inertia moment of the wall per unit width, I 壁体 is the moment of inertia of the wall plate per unit width, I 竖肋 is the moment of inertia of the vertical rib section within unit width.

[0054] refer to Figure 1 As shown, the compartment structure includes a compartment wall 101, a compartment web 102, a compartment vertical rib 103 and a compartment reinforcement ring plate 104. The compartment walls 101 are connected to the compartment web 102 to form a compartment. A plurality of compartment vertical ribs 103 are arranged at intervals on the compartment wall 101 and the compartment web 102. The compartment reinforcement ring plate 104 located in the compartment is arranged on the compartment wall 101 and the compartment web 102. In the simplification of the compartment structure, the compartment wall 101 and the compartment vertical rib 103 are firstly equivalent to the first compartment equivalent wall 111, and then the first compartment equivalent wall 111 and the compartment vertical rib 103 are equivalent to the second compartment equivalent wall 112, the compartment web 102 and the compartment vertical rib 103 are equivalent to the compartment equivalent web 113, and the compartment equivalent web 113 is connected between the second compartment equivalent wall 112.

[0055] In the simplification of the ring plate and horizontal cross brace, the cross section composed of the ring plate, inner and outer walls, and horizontal cross brace is equivalent to a truss structure or a solid web structure according to the cross-sectional characteristics (area, centroid, centroid axis moment of inertia). The wall and the ring plate are considered comprehensively, and the wall with width is used as the flange plate. Both are simplified to a welded T-shaped steel section according to the cross-sectional characteristics, and the flange extension width is:

[0056] b f =15t f ε k ;

[0057] Among them, b f is the equivalent T-section flange width, t f is the flange thickness of the T-section, ε k is the steel grade correction factor. The role of the longitudinal secondary beam of the wall is to strengthen the wall, and the role of the longitudinal secondary beam on the ring plate is not considered.

[0058] refer to Figure 2 and Figure 3 As shown, the ring plate and horizontal cross brace specifically include a structural wall 201, a structural vertical rib 202, a structural ring plate 203, a horizontal diagonal brace 204 and a reinforcing diagonal brace 205. A plurality of structural vertical ribs 202 are arranged on the inner side of the structural wall 201, and a plurality of layers of structural ring plates 203 are arranged at the same time. Horizontal diagonal braces 204 and reinforcing diagonal braces 205 are arranged between the structural walls 201. In the simplification of the ring plate and horizontal cross brace, the cross section composed of the structural wall 201, the structural ring plate 203 and the horizontal diagonal brace 204 is equivalent to a truss structure according to the cross-sectional stiffness and area, and the effect of the structural vertical rib 202 on the annular member is not considered. The structural wall 201 and the structural wall 201 are both simplified to a structural equivalent wall 211 of a welded T-shaped steel cross section according to the cross-sectional characteristics.

[0059] In the simplification of wall panels, the structure composed of panel walls and panel vertical ribs is simplified to a steel plate structure of equivalent thickness according to the principle of equivalent cross-sectional area and moment of inertia. Figure 4 As shown, the wall panel structure includes a panel wall 301 and panel vertical ribs 302 . A plurality of panel vertical ribs 302 are arranged on the inner side of the panel wall 301 . The thickness of the two are simplified according to the cross-sectional equivalent principle, and they are equivalent to a panel equivalent wall 311 .

[0060] In the simplification of the bottom structure, the bottom structure is simplified into a constraint boundary with rigidity according to the elastic modulus and cross-sectional characteristics of concrete.

[0061] Step S02, model simplification: perform equivalent simplification processing on the cofferdam equivalent structure, simplify each structure of the cofferdam equivalent structure into each model unit, and select different model analysis methods according to different structures under consideration.

[0062] Model analysis considering bulkheads and internal supports: It is mainly used to calculate the main structures such as bulkheads and internal supports. Bulkheads are equivalent to beam units, and internal supports are equivalent to beam units; the structure composed of ring plates and horizontal cross braces is set as virtual rods, and the structure composed of walls and vertical ribs is set as virtual surfaces. Virtual rods and virtual surfaces are only used for load application and transmission, and the loads are directly transferred to the nodes; or virtual rods are not set, and the loads are directly transferred from the virtual surfaces to the bulkhead beam system. The ring plates, horizontal cross braces and walls are calculated and analyzed according to the analytical method.

[0063] Model analysis considering partitions, internal supports, ring plates and horizontal cross braces: used to calculate structures such as partitions, internal support ring plates and horizontal cross braces. The partitions are equivalent to beam units, and the internal supports are equivalent to beam units; the structure composed of ring plates and vertical ribs is equivalent to T-beam section units, and forms a truss structure or a solid-web structure with horizontal supports. The structure composed of walls and vertical ribs is set as a virtual surface, which does not bear loads, but is only used for load application and transfer. The wall is calculated and analyzed according to the analytical method.

[0064] Model analysis considering compartments, internal supports, ring plates, horizontal cross braces and walls: the compartments are equivalent to units, and the internal supports are equivalent to beam units. The structure composed of ring plates and vertical ribs is equivalent to T-beam cross-section units, which form a truss structure or a solid-web structure with horizontal supports. The walls and vertical ribs are equivalent to plate units.

[0065] Step S03, simplified model calculation: According to the model simplification method, the main structure (partition, internal support, ring plate, horizontal cross brace, etc.) uses finite element analysis software to calculate its simplified structure. The steps are: determine the simplified analysis method according to the needs, use finite element software to establish a simplified unit model, and the software automatically analyzes to obtain the corresponding internal force, stress and deformation results.

[0066] For structures without established models, such as wall panels, the analytical method is used to analyze the less favorable working conditions based on the load and design boundary conditions combined with mechanical formulas.

[0067] Calculation and analysis by wall plate unit analytical method: If the design plate is supported on two sides, it is analyzed as a continuous beam; if the design plate is supported on three or four sides, the internal force and deflection values ​​of the plate are calculated by looking up the table in the relevant manual. When the internal force and deflection of the plate unit are known, the stress value per unit width of the plate is calculated by the mechanical formula:

[0068]

[0069] Among them, σ x is the stress in the x direction, σ y is the stress in the y direction, σ z is the stress in z direction, z is the distance from the upper and lower plate surfaces to the center of the plate thickness, t is the plate thickness, M x is the bending moment in the x direction, My is the bending moment in the y direction, M z is the bending moment in the z direction.

[0070] Step S04, comparison of simplified model calculation results: Taking a double-wall cofferdam with a height of 9.6m as an example, considering the water head H = 9.6m, the structure is calculated and compared according to the above method. After calculation and analysis, the overall deformation error between the simplified model and the refined model is about 6% to 10%, which is very small.

[0071] When the simplified equivalent model is used, the stress at the connection between the ring plate equivalent beam unit and the compartment is relatively large, and the stress of the unit calculated by the simplified model and the refined model is close at the non-connection point position (between compartments). Therefore, when calculating the simplified model, the peak elimination effect of the compartment should be considered according to the compartment size.

[0072] When using a simplified equivalent model, the position where the horizontal cross brace is directly connected to the compartment structure will cause an increase in the axial force of the rod due to the sudden change in stiffness. The axial force of the horizontal support rod connected to the compartment beam unit is relatively large, and the axial force of the horizontal cross brace rod at the non-connection point position (between compartments) is close. Therefore, the calculated internal force of the horizontal cross brace analyzed by the simplified model is relatively safe and feasible.

[0073] When a simplified equivalent model is used, the error in calculating the wall plate stress is within 10%. Generally, the stress of the entire simplified model is larger, and the structural calculation results are relatively safe and feasible.

[0074] The aforementioned basic examples and their further selected examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed for protection in this application. In the scheme of this application, each selected example can be arbitrarily combined with any other basic examples and selected examples.

[0075] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A simplified calculation and analysis method for double-walled steel cofferdam, characterized in that: The steps include: Step S01, structural simplification: performing equivalent simplification processing on the cofferdam structure according to the stress characteristics of the double-wall cofferdam, including one or more of simplification of the compartment structure, simplification of the ring plate and horizontal cross brace, simplification of the wall panel and simplification of the bottom cover structure; Step S02, model simplification: performing equivalent simplification processing on the cofferdam equivalent structure, and equivalently simplifying each structure of the cofferdam equivalent structure into each model unit; Step S03, simplified model calculation: Determine the simplified analysis method according to the requirements, use the finite element software to establish a simplified unit model, and the software automatically analyzes to obtain the corresponding internal force, stress and deformation results.

2. The simplified calculation and analysis method for double-walled steel cofferdam according to claim 1 is characterized in that: The force transmission path of the double-wall cofferdam structure is as follows: the water and soil loads are transmitted to the inner and outer walls, and then the walls are coordinated through deformation to transmit the force to the compartment structure, and the compartment structure then transmits the force to the inner support.

3. The simplified calculation and analysis method for double-walled steel cofferdam according to claim 1 is characterized in that: In the simplification of the compartment structure, the compartment structure of the double-wall cofferdam is simplified into an I-section, H-section or box section according to the principle of equivalent cross-sectional characteristics; the compartment reinforcement ring plate is not considered in the design of the beam system structure, or the compartment reinforcement ring plate is considered in the cross-sectional design by the equivalent area method; The area equivalent formula is: A=A 壁体 +A 竖肋 ; Where A is the equivalent area of ​​the wall per unit width, A 壁体 is the wall panel area per unit width, A 竖肋 is the cross-sectional area of ​​the vertical rib within unit width; The equivalent formula for the moment of inertia of the section is: I=I 壁体 +I 竖肋 ; Where I is the equivalent section inertia moment of the wall per unit width, I 壁体 is the moment of inertia of the wall plate per unit width, I 竖肋 is the moment of inertia of the vertical rib section within unit width.

4. The simplified calculation and analysis method for double-walled steel cofferdam according to claim 1 is characterized in that: In the simplification of the ring plate and horizontal cross brace, the cross section composed of the ring plate, inner and outer walls, and horizontal cross brace is equivalent to a truss structure or a solid web structure according to the cross-sectional characteristics; the wall and the ring plate are comprehensively considered, and the wall with width is used as the flange plate. Both are simplified to a welded T-shaped steel section according to the cross-sectional characteristics, and the flange extension width is: b f =15t f e k ; Among them, b f is the equivalent T-section flange width, t f is the flange thickness of the T-section, ε k is the steel grade correction factor; In the simplification of the ring plate and horizontal cross brace, the effect of the longitudinal secondary beam on the ring plate is not considered.

5. The simplified calculation and analysis method for double-walled steel cofferdam according to claim 1 is characterized in that: In the simplification of the wall panel, the structure composed of the panel wall and the panel vertical ribs is simplified to a steel plate structure of equivalent thickness according to the principle of equivalent cross-sectional area and moment of inertia.

6. The simplified calculation and analysis method for double-walled steel cofferdam according to claim 1 is characterized in that: In the simplification of the bottom structure, the bottom structure is simplified into a constraint boundary with rigidity according to the elastic modulus and cross-sectional characteristics of concrete.

7. The simplified calculation and analysis method for double-walled steel cofferdam according to claim 1 is characterized in that: Model analysis considering partitions and internal supports: the partitions are equivalent to beam units, and the internal supports are equivalent to beam units; the structure composed of the ring plate and horizontal cross braces is set as a virtual member, and the structure composed of the wall and vertical ribs is set as a virtual surface. The virtual members and virtual surfaces are only used for load application and transfer, and the loads are directly transferred to the nodes; or no virtual members are set, and the loads are directly transferred from the virtual surfaces to the partition beam system; the ring plates, horizontal cross braces and walls are calculated and analyzed according to the analytical method.

8. The simplified calculation and analysis method for double-walled steel cofferdam according to claim 1 is characterized in that: Model analysis considering partitions, internal supports, ring plates and horizontal cross braces: the partitions are equivalent to beam units, and the internal supports are equivalent to beam units; the structure composed of ring plates and vertical ribs is equivalent to T-beam section units, which form a truss structure or a solid-web structure with horizontal supports; the structure composed of walls and vertical ribs is set as a virtual surface, which does not bear loads but is only used for load application and transfer; the wall is calculated and analyzed according to the analytical method.

9. The simplified calculation and analysis method for double-walled steel cofferdam according to claim 1 is characterized in that: Model analysis considering partitions, internal supports, ring plates, horizontal cross braces and walls: the partitions are equivalent to beam units, and the internal supports are equivalent to beam units; the structure composed of ring plates and vertical ribs is equivalent to T-beam section units, which form a truss structure or a solid-web structure with the horizontal supports; the walls and vertical ribs are equivalent to plate units.

10. The simplified calculation and analysis method for double-walled steel cofferdam according to claim 1 is characterized in that: For structures without modeling, the less favorable working conditions are analyzed by analytical method according to load and design boundary conditions combined with mechanical formulas; Calculation and analysis by wall plate unit analytical method: If the design plate is supported on two sides, it is analyzed as a continuous beam; if the design plate is supported on three or four sides, the internal force and deflection values ​​of the plate are calculated by looking up the table in the relevant manual. When the internal force and deflection of the plate unit are known, the stress value per unit width of the plate is calculated by the mechanical formula: Among them, σ x is the stress in the x direction, σ y is the stress in the y direction, σ z is the stress in z direction, z is the distance from the upper and lower plate surfaces to the center of the plate thickness, t is the plate thickness, M x is the bending moment in the x direction, M y is the bending moment in the y direction, M z is the bending moment in the z direction.

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