Pile head spring stiffness matrix iteration method for jacket platform seismic analysis

Abstract

The invention discloses a pile head spring stiffness matrix iteration method for jacket platform seismic analysis, and the method comprises the steps: building a three-dimensional structure model of a jacket platform, simulating a seismic load in a manner of applying an acceleration field, carrying out the structural static analysis calculation, building a jacket structure analysis model copy, and judging the reasonability of a pile head spring stiffness matrix. After a reasonable pile head spring stiffness matrix is obtained, the model can be adopted to complete the subsequent structural strength check of the jacket platform under the action of the seismic load. According to the method, in the process of determining the pile head spring stiffness matrix through jacket platform earthquake analysis, designers do not need to determine the size and the application position of a concentrated point load according to experience, and the problems of calculation complexity, efficiency and the like are solved. According to the method, the seismic load is simulated by applying the acceleration field to the platform model, iterative calculation can be completed more conveniently, more accurately and more quickly, a reasonable and accurate pile head spring stiffness matrix is generated, and then seismic analysis calculation of the jacket platform is achieved.

Description

Technical Field

[0001] The invention belongs to the field of offshore fixed platform design and construction, and in particular relates to a pile head spring stiffness matrix iteration method for seismic analysis of a jacket platform. Background Art

[0002] Jacket platforms are common structures in marine engineering and are widely used in offshore oil, offshore wind power and other industries. In the process of platform design, seismic action is an important factor affecting its structural safety. Therefore, it is necessary to conduct seismic analysis on the jacket platform and verify the structural strength. Finite element software is used to model and analyze the platform structure. Generally, dynamic modal analysis is used to solve the platform's natural vibration period and vibration mode, and the seismic response of the platform structure is calculated in combination with the earthquake acceleration spectrum. In the process of dynamic modal analysis, due to the nonlinear characteristics of the pile-soil model, it cannot be directly involved in the calculation. Therefore, the pile-soil model needs to be equivalent to a linearized pile head spring stiffness matrix.

[0003] At present, the common practice is to apply concentrated point loads on the platform structure model, and use the point load as the initial assumed seismic load of the platform. The direction of the point load is usually the X direction or Y direction of the platform's overall coordinate system. The position and size of the applied concentrated point loads need to rely on the experience of the designer, and unreasonable initial seismic loads will lead to problems such as a large number of iterations and low calculation efficiency. In addition, only considering concentrated loads in a single horizontal direction may affect the accuracy of the final result. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a pile head spring stiffness matrix iteration method for seismic analysis of a jacket platform, and the technical solution adopted is: A pile head spring stiffness matrix iteration method for seismic analysis of a jacket platform is characterized by: The specific operation method is as follows: S1, establish the three-dimensional structural model of the jacket platform, including pile foundation and soil parameters, use beam unit and plate unit to simulate the main structure of the platform, model the pile foundation below the mud surface according to the structural drawings, and input it into the analysis software.

[0005] S2: The earthquake load is simulated by applying an acceleration field. Acceleration is applied in the X and Y directions of the platform at the same time. The magnitude of the acceleration is based on the earthquake acceleration spectrum of the area where the platform is located.

[0006] S3: Perform structural static analysis and calculation to obtain the overall load of the platform structure in the X and Y directions of the overall coordinate system. According to the pile-soil analysis result file, select the pile with the largest pile head axial displacement as the reference, perform pile base linearization analysis in the analysis software, and obtain the equivalent pile head spring stiffness matrix.

[0007] S4: Create a copy of the jacket structure analysis model, delete the pile foundation structure below the mud surface, use the pile head spring stiffness matrix obtained in step S3 to create a spring unit at the pile head to replace the actual pile foundation structure, carry out dynamic modal analysis of the platform structure in the analysis software, and calculate the seismic response of the platform in combination with the seismic acceleration spectrum to obtain the horizontal seismic forces in the overall X and Y directions of the platform.

[0008] S5, by comparing the horizontal seismic force in step S4 with the overall load of the platform in the X direction and the Y direction in step S3, the rationality of the pile head spring stiffness matrix is ​​judged; if the deviation is within 5%, it indicates that the pile head spring stiffness matrix generated in step S3 is reasonable; if the deviation is greater than 5%, it is necessary to return to step S2, readjust the applied acceleration, and repeat steps S3 and S4 until the seismic force deviation meets the requirements; if the horizontal seismic force in step S4 is greater than the overall load of the platform in the X direction and the Y direction in step S3, the acceleration should be increased, otherwise the acceleration should be reduced.

[0009] S6, after obtaining a reasonable pile head spring stiffness matrix, this model can be used to complete the subsequent structural strength verification of the jacket platform under seismic loads.

[0010] The invention realizes the application of seismic load in the iterative process of pile head spring stiffness matrix by applying horizontal acceleration field, simplifies the calculation operation of designers, and improves calculation efficiency. Taking into account the bidirectional acceleration load in the horizontal X direction and Y direction of the jacket platform, the seismic load condition can be simulated more accurately, making the pile head spring stiffness matrix generated by iterative calculation more reasonable, and improving the accuracy of seismic analysis of the jacket platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is an operation flow chart of the present invention. DETAILED DESCRIPTION

[0012] The present invention will be further described in conjunction with the accompanying drawings. Example

[0013] A pile head spring stiffness matrix iteration method for seismic analysis of a jacket platform is proposed. Taking a jacket platform as an example, the specific operation is as follows: S1. In the structural analysis software, a three-dimensional structural model of the jacket platform is established. The beam unit and plate unit are used to simulate the main structure of the platform. The pile foundation below the mud surface is modeled according to the structural drawings. The soil parameters are represented by the PY, TZ, and QZ curves commonly used in engineering and input into the analysis software. The SESAM software is used to perform the jacket platform structure analysis and pile-soil analysis to form a pile-soil analysis model.

[0014] S2, a horizontal acceleration field is applied to the jacket model to simulate the seismic load. Referring to the seismic acceleration spectrum of the platform, an acceleration of 0.14g is applied in the X direction of the platform and an acceleration of 0.14g is applied in the Y direction of the platform.

[0015] S3, based on the load in step S2, perform a structural static analysis of the jacket platform to obtain the overall load of the platform in the horizontal X and Y directions, where the X-direction load Fsx is 14.637 MN and the Y-direction load Fsy is 14.637 MN. Check the pile-soil analysis result file, select the pile with the largest axial displacement of the pile head, perform a pile-base linearization analysis in the analysis software, and obtain the equivalent pile head spring stiffness matrix. The process of the jacket platform structural static analysis includes the pile-soil analysis, and generates the pile-soil analysis result file.

[0016] S4, establish a copy of the jacket structure analysis model, delete the pile foundation structure below the mud surface, and use the pile head spring stiffness matrix obtained in step S3 to establish a spring unit at the pile head to replace the actual pile foundation structure. Carry out dynamic modal analysis of the platform structure in the analysis software, and calculate the seismic response of the platform in combination with the earthquake acceleration spectrum, and output the overall horizontal seismic force of the platform from the result file, where the seismic force Fdx in the horizontal X direction is 16.252 MN, and the seismic force Fdy in the horizontal Y direction is 15.570 MN.

[0017] S5, compare the horizontal seismic force in S4 with the overall load of the platform in the X and Y directions in S3 to determine the rationality of the pile head spring stiffness matrix. In this case, Fsx = 14.637 MN, Fdx = 16.252 MN, the deviation between the two is about 11%; Fsy = 14.637 MN, Fdy = 15.570 MN, the deviation between the two is about 6%. The load deviation in both directions is greater than 5%, which does not meet the calculation requirements.

[0018] Therefore, it is necessary to return to step S2 and readjust the applied acceleration value. Since the horizontal seismic force of S4 is greater than the overall load of the platform in S3, it indicates that the currently applied acceleration value is too small, so the acceleration value is increased to 0.15g, and steps S3 and S4 are repeated.

[0019] After calculation and readjustment of the acceleration value, Fsx=15.682 MN, Fdx=16.195 MN, the deviation between the two is about 3.3%; Fsy=15.682 MN, Fdy=15.511 MN, the deviation between the two is about 1.1%. The load deviation in both directions is less than 5%, which meets the calculation requirements.

[0020] S6. After the calculation and comparison in the above steps, it is proved that the pile head spring stiffness matrix in the model is reasonable and reliable. The jacket platform model including the pile head spring stiffness matrix can be used to carry out the subsequent structural strength verification work under the action of seismic load.

[0021] In this embodiment, the horizontal accelerations in the X and Y directions are applied with the same value, which is only one implementation mode. For jacket platforms with different structural characteristics, different horizontal acceleration values ​​in the X and Y directions may also be applied.

Claims

1. A pile head spring stiffness matrix iteration method for seismic analysis of a jacket platform, characterized in that: The specific operation method is as follows: S1: Establish a three-dimensional structural model of the jacket platform, including pile foundation and soil parameters, use beam units and plate units to simulate the main structure of the platform, model the pile foundation below the mud surface according to the structural drawings, and input it into the analysis software; S2: The earthquake load is simulated by applying an acceleration field. Acceleration is applied in the X and Y directions of the platform at the same time. The magnitude of the acceleration is based on the earthquake acceleration spectrum of the area where the platform is located. S3: Perform structural static analysis and calculation to obtain the overall load of the platform structure in the X and Y directions of the overall coordinate system. According to the pile-soil analysis result file, select the pile with the largest pile head axial displacement as a reference, perform pile base linearization analysis in the analysis software, and obtain the equivalent pile head spring stiffness matrix; S4: Create a copy of the jacket structure analysis model, delete the pile foundation structure below the mud surface, use the pile head spring stiffness matrix obtained in step S3 to create a spring unit at the pile head to replace the actual pile foundation structure, perform dynamic modal analysis of the platform structure in the analysis software, and calculate the seismic response of the platform in combination with the seismic acceleration spectrum to obtain the horizontal seismic forces in the overall X and Y directions of the platform; S5: By comparing the horizontal seismic force in the X and Y directions in step S4 with the overall load of the platform in the X and Y directions in step S3, the rationality of the pile head spring stiffness matrix is ​​judged; if the deviation is within 5%, it indicates that the pile head spring stiffness matrix generated in step S3 is reasonable; if the deviation is greater than 5%, it is necessary to return to step S2, readjust the applied acceleration, and repeat steps S3 and S4 until the seismic force deviation meets the requirements; if the horizontal seismic force in step S4 is greater than the overall load of the platform in the X and Y directions in step S3, the acceleration should be increased, otherwise the acceleration should be reduced; S6: After obtaining a reasonable pile head spring stiffness matrix, this model can be used to complete the subsequent structural strength verification of the jacket platform under seismic loads.

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