A method for evaluating the stable bearing capacity of a circular steel pipe structure of an offshore platform based on CFRP reinforcement

Abstract

The application discloses a kind of based on CFRP reinforcing ocean platform round steel pipe structure stability bearing capacity evaluation method, comprising (1) obtaining CFRP pasting steel pipe parameter;(2) using equivalent section method, the equivalent slenderness ratio of reinforced composite component is calculated;(3) the stability bearing capacity of steel pipe structure after CFRP reinforcement is calculated;(4) according to actual load and stability bearing capacity is judged.The application uses equivalent section method, introduces modulus ratio parameter, combines the calculation formula of equivalent section area and equivalent section moment of inertia when CFRP hoop pasting, CFRP longitudinal pasting and CFRP hoop longitudinal alternating pasting into a kind of calculation formula, the section area of CFRP is equivalent to the section area of steel, the equivalent slenderness ratio of reinforced composite component is calculated, so as to calculate the stability bearing capacity of steel pipe structure after CFRP reinforcement, without the aid of finite element analysis for calculation, calculation process is fast, precision is high, finally realizes the direct evaluation of CFRP reinforcing ocean platform round steel pipe structure stability bearing capacity.

Description

Technical Field

[0001] This invention relates to the field of jacket reinforcement technology for offshore platforms, and in particular to a method for assessing the stability and bearing capacity of circular steel pipe structures of offshore platforms reinforced with CFRP. Background Technology

[0002] During their service life, offshore jacket platforms often experience damage such as dents and cracks in their nodes and structural members due to the complex and variable marine environment, affecting their reliability and safety. To extend the service life of these platforms and ensure safe operation, reinforcement and repair of damaged structures are necessary. Carbon fiber reinforced polymer (CFRP) is lightweight, has a high modulus of elasticity, is fire-resistant, and corrosion-resistant. Compared to traditional reinforcement methods such as grouting, clamps, and ribs, using CFRP to reinforce and repair damaged structures offers advantages such as no increase in self-weight, no residual stress, and simple and convenient construction.

[0003] Currently, carbon fiber reinforcement and repair technology has been widely applied, but research on reinforcing jacket platform members is limited. Furthermore, existing theoretical research on carbon fiber reinforcement and repair of steel structures is still immature, and there is a lack of instructive evaluation methods. To study the reinforcement effect of CFRP, a method is needed to accurately evaluate the stable bearing capacity of CFRP-reinforced circular steel pipe structures. Summary of the Invention

[0004] This invention provides a method for assessing the stability and bearing capacity of a CFRP-reinforced circular steel tube structure for offshore platforms. To provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended as a general commentary, nor is it intended to identify key / important components or describe the scope of protection of these embodiments. Its sole purpose is to present some concepts in a simple form as a prelude to the detailed description that follows.

[0005] This invention provides a method for assessing the stability bearing capacity of a CFRP-reinforced circular steel tube structure on a marine platform, the improvement of which includes:

[0006] (1) Obtain the parameters of the CFRP bonded steel pipe;

[0007] (2) The equivalent slenderness ratio of the reinforced composite member is calculated using the equivalent section method;

[0008] (3) Calculate the stable bearing capacity of the steel pipe structure after CFRP reinforcement;

[0009] (4) Make a judgment based on the actual load and stable bearing capacity.

[0010] Preferably, the steel pipe parameters in step (1) include the outer diameter of the steel pipe, the wall thickness of the steel pipe, the total length of the steel pipe, the elastic modulus of the steel pipe, and the yield strength.

[0011] Preferably, step (2) includes calculating the slenderness ratio of the composite component by calculating the equivalent cross-sectional area and equivalent cross-sectional moment of inertia of the composite component after the CFRP is pasted on the steel pipe, and obtaining the stability coefficient of the composite component from the slenderness ratio of the composite component.

[0012] Furthermore, step (2) includes the compressive stiffness and flexural stiffness of the CFRP-reinforced composite member, which can be expressed as:

[0013] E s A eq =E s A s +E cfrp A cfrp (1)

[0014] E s I eq =E s I s +E cfrp I cfrp (2)

[0015] From equations (1) and (2), the equivalent cross-sectional area and equivalent moment of inertia of the composite component can be obtained as follows:

[0016]

[0017]

[0018] In the formula, E s A represents the elastic modulus of the steel pipe. eq A is the equivalent cross-sectional area of ​​the composite component; s E represents the cross-sectional area of ​​the steel pipe. cfrp The elastic modulus of CFRP;

[0019] Orthogonality should be discussed specifically for different pasting methods; A cfrp I is the cross-sectional area of ​​the CFRP. eq I is the equivalent moment of inertia of the composite component; s I is the moment of inertia of the steel pipe section; cfrp The moment of inertia of the CFRP section;

[0020] When CFRP is circumferentially bonded, E in equations (3) and (4) cfrp It refers to the elastic modulus E in the non-principal fiber directions. s,cfrp ;

[0021] When CFRP is pasted vertically, E in equations (3) and (4)cfrp It refers to the elastic modulus E in the principal direction of the fiber. p,cfrp Define two modulus ratios α s and α p as follows:

[0022]

[0023] When CFRP is pasted alternately in circumferential and longitudinal directions:

[0024] A eq =A s +(α p n L +α s n H )πD s t cfrp (6)

[0025]

[0026] In the formula, n H D represents the number of CFRP layers bonded circumferentially. s t is the outer diameter of the steel pipe; cfrp n is the thickness of a single layer of CFRP; L This refers to the number of CFRP layers pasted vertically.

[0027] Equations (6) and (7) are the expressions for the equivalent cross-sectional area and equivalent moment of inertia of the composite component; these two equations can summarize the CFRP all-circumferential bonding (i.e., n L =0), CFRP full vertical pasting (i.e., n H =0) and three cases of alternating CFRP circumferential and vertical pasting.

[0028] The slenderness ratio of the composite member can be calculated based on its equivalent cross-sectional area and equivalent moment of inertia.

[0029]

[0030] In the formula, λ c L0 represents the corrected slenderness ratio of the composite component; L0 represents the effective calculated length of the reinforced steel pipe.

[0031] Preferably, step (3) includes a method for calculating the stability bearing capacity of an unreinforced circular steel pipe, which can be used to obtain the stability bearing capacity of the CFRP-reinforced circular steel pipe.

[0032] Furthermore, step (3)

[0033] Stable bearing capacity N of CFRP-reinforced composite member c The following formula can be obtained:

[0034]

[0035] In the formula, N c For the stable bearing capacity of composite components; f y The yield stress of the steel pipe; The stability coefficient of the composite component.

[0036] Where, when λ c When the calculated value is not an integer, the stability coefficient of the composite component is calculated using the formula, and the regularized slenderness ratio of the composite component is also calculated.

[0037] Then we have:

[0038] When λ n >0.215

[0039]

[0040] When λ n When ≤0.215

[0041]

[0042] In the formula, α1, α2 and α3 are adopted according to Table D.0.5, which are the cross-section classifications specified in Table 7.2.1 of the standard.

[0043] Furthermore,

[0044] Calculate the regularized slenderness ratio of the composite member according to formula (D.0.5-2) in Appendix D of GB 50017-2017 "Standard for Design of Steel Structures";

[0045] According to λ c The table header in Appendix D of the "Code for Design of Steel Structures" is λ. c / ε k , ε k This is the steel grade correction factor, which is the square root of the ratio of 235 to the yield strength value in the steel grade.

[0046] Furthermore, based on the orthogonal anisotropy of carbon fiber cloth, the stress situation under different bonding directions is analyzed. CFRP must restrict the compressive deformation of the steel pipe while also restricting the lateral bending deformation of the steel pipe. When bonded along the circumferential direction, the carbon fiber cloth bears the compressive load in the non-major fiber direction, while when bending deformation occurs, the non-major fiber direction restricts the bending deformation of the steel pipe. When bonded along the longitudinal direction, the carbon fiber cloth bears the compressive load in the major fiber direction, while also restricting the bending deformation of the steel pipe.

[0047] Furthermore, step (4) includes the following: when the actual load on the round steel pipe is greater than the stable bearing capacity, the round steel pipe will become unstable and fail; otherwise, the steel pipe structure will be stable.

[0048] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0049] This invention proposes a method for calculating the stable bearing capacity of CFRP-reinforced steel pipe structures based on the equivalent section method. This method can be used to accurately calculate the stable bearing capacity of steel pipe structures, thereby determining whether the steel pipe structure is prone to instability. Furthermore, the finite element model calculation for CFRP reinforcement is time-consuming, while the formula-based calculation of the stable bearing capacity is faster and yields more accurate results.

[0050] This invention employs the equivalent section method, introducing a modulus ratio parameter. It combines the calculation formulas for the equivalent cross-sectional area and equivalent moment of inertia of CFRP in circumferential bonding, longitudinal bonding, and alternating circumferential and longitudinal bonding into a single formula. The cross-sectional area of ​​CFRP is equated to that of steel, and the equivalent slenderness ratio of the reinforced composite component is calculated. This allows for the calculation of the stable bearing capacity of the CFRP-reinforced steel pipe structure without the need for finite element analysis. The calculation process is fast and highly accurate, ultimately enabling direct assessment of the stable bearing capacity of CFRP-reinforced circular steel pipe structures on offshore platforms.

[0051] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0052] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0053] Figure 1 This is a schematic diagram illustrating a method for assessing the stability bearing capacity of a CFRP-reinforced circular steel tube structure for offshore platforms, according to an exemplary embodiment.

[0054] Figure 2 This is a schematic diagram of a reinforced circular steel pipe according to an exemplary embodiment;

[0055] Figure 3 This is a schematic diagram of carbon fiber circumferential winding according to an exemplary embodiment;

[0056] In the diagram, 1 represents the main direction of the CFRP fabric fibers, and 2 represents the axial direction of the steel pipe.

[0057] Figure 4 This is a schematic diagram of longitudinal winding of carbon fiber according to an exemplary embodiment;

[0058] In the diagram, 1 represents the main direction of the CFRP fabric fibers, and 2 represents the axial direction of the steel pipe.

[0059] Figure 5 This is a schematic diagram illustrating alternating winding of carbon fibers according to an exemplary embodiment;

[0060] Figure 6 This is a schematic diagram of the process for evaluating the stability bearing capacity of a circular steel pipe structure for a CFRP-reinforced offshore platform, as shown in Example 2. Detailed Implementation

[0061] The following description and accompanying drawings fully illustrate specific embodiments of the invention to enable those skilled in the art to practice them. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. The scope of embodiments of the invention encompasses the entire scope of the claims and all available equivalents thereof. Throughout this document, each embodiment may be referred to individually or collectively with the term "invention," which is merely for convenience and, if more than one invention is disclosed, is not intended to automatically limit the scope of application to any single invention or inventive concept. Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without requiring or implying any actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed. The various embodiments in this document are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the structures, products, etc., disclosed in the embodiments, since they correspond to the disclosed parts, the descriptions are relatively simple; relevant details can be found in the method section.

[0062] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0063] like Figure 1 As shown, this invention provides a method for calculating the stability bearing capacity of a CFRP-reinforced circular steel pipe structure for offshore platforms. The method employs the equivalent section method, calculating the equivalent cross-sectional area and equivalent moment of inertia of the composite member after CFRP bonding based on structural parameters. This allows for the calculation of the slenderness ratio of the composite member. Based on Appendix D of GB 50017-2017 "Code for Design of Steel Structures" and the stability coefficient calculation formula, the stability coefficient of the composite member can be obtained from its slenderness ratio. Finally, based on the calculation method for the stability bearing capacity of an unreinforced circular steel pipe, the stability bearing capacity of the CFRP-reinforced circular steel pipe can be obtained. When the actual load on the circular steel pipe exceeds the stability bearing capacity, the circular steel pipe will fail; conversely, the steel pipe structure will not fail.

[0064] Example 1:

[0065] (1) Obtaining CFRP bonded steel pipe parameters

[0066] The parameters of a steel pipe include its outer diameter, wall thickness, total length, elastic modulus, and yield strength.

[0067] like Figures 2-5 As shown, Figure 2 Model for CFRP-reinforced round steel pipe Figures 3-5 This is a schematic diagram of the CFRP winding direction. Since the tensile strength of CFRP is much greater than that of round steel pipe, the final state of the round steel pipe is defined as yielding.

[0068] (2) The equivalent slenderness ratio of the reinforced composite member was calculated using the equivalent section method.

[0069] By calculating the equivalent cross-sectional area and equivalent moment of inertia of the composite member with CFRP bonded steel pipe section, the slenderness ratio of the composite member is obtained, and the stability coefficient of the composite member is obtained from the slenderness ratio.

[0070] The compressive stiffness and flexural stiffness of the CFRP-reinforced composite member can be expressed as:

[0071] E s A eq =E s A s +E cfrp A cfrp (1)

[0072] E s I eq =E s I s +E cfrp I cfrp (2)

[0073] From equations (1) and (2), the equivalent cross-sectional area and equivalent moment of inertia of the composite component can be obtained as follows:

[0074]

[0075]

[0076] In the formula, E s A represents the elastic modulus of the steel pipe. eq A is the equivalent cross-sectional area of ​​the composite component; s E represents the cross-sectional area of ​​the steel pipe. cfrp The elastic modulus of CFRP;

[0077] The orthogonality should be discussed specifically when considering different pasting methods; Acfrp I is the cross-sectional area of ​​the CFRP. eq I is the equivalent moment of inertia of the composite component; s I is the moment of inertia of the steel pipe section; cfrp The moment of inertia of the CFRP section;

[0078] Considering the orthotropic nature of carbon fiber reinforced polymer (CFRP), it is necessary to analyze the stress conditions under different bonding directions. CFRP must restrict both the compressive deformation and lateral bending deformation of the steel pipe. When bonded circumferentially, the CFRP bears compressive loads in the non-major fiber directions, and when bending deformation occurs, the non-major fiber directions also restrict the bending deformation of the steel pipe. When bonded longitudinally, the CFRP bears compressive loads in the major fiber directions, while also restricting the bending deformation of the steel pipe.

[0079] When CFRP is circumferentially bonded, E in equations (3) and (4) cfrp It refers to the elastic modulus E in the non-principal fiber directions. s,cfrp ;

[0080] When CFRP is pasted vertically, E in equations (3) and (4) cfrp It refers to the elastic modulus E in the principal direction of the fiber. p,cfrp Define two modulus ratios α s and α p as follows:

[0081]

[0082] When CFRP is pasted alternately in circumferential and longitudinal directions:

[0083] A eq =A s +(α p n L +α s n H )πD s t cfrp (6)

[0084]

[0085] In the formula, n H D represents the number of CFRP layers bonded circumferentially. s t is the outer diameter of the steel pipe; cfrp n is the thickness of a single layer of CFRP; L This represents the number of CFRP layers pasted vertically.

[0086] Equations (6) and (7) are the expressions for the equivalent cross-sectional area and equivalent moment of inertia of the composite component. These two equations can summarize the CFRP all-circumferential bonding (i.e., n L =0), CFRP full vertical pasting (i.e., n H=0) and three cases of alternating CFRP circumferential and vertical pasting.

[0087] The slenderness ratio of the composite member can be calculated based on its equivalent cross-sectional area and equivalent moment of inertia.

[0088]

[0089] In the formula, λ c L0 represents the corrected slenderness ratio of the composite component; L0 represents the effective calculated length of the reinforced steel pipe.

[0090] (3) Calculate the stable bearing capacity of the steel pipe structure after CFRP reinforcement.

[0091] The stability bearing capacity of a CFRP-reinforced round steel pipe can be obtained by calculating the stability bearing capacity of an unreinforced round steel pipe.

[0092] Step (3) includes

[0093] Stable bearing capacity N of CFRP-reinforced composite member c The following formula can be obtained:

[0094]

[0095] In the formula, N c For the stable bearing capacity of composite components; f y The yield stress of the steel pipe; Let λ be the stability coefficient of the composite component. c The table header in Appendix D of the "Code for Design of Steel Structures" is λ. c / ε k , ε k This is the steel grade correction factor, which is the square root of the ratio of 235 to the yield strength value in the steel grade.

[0096] Where, when λ c When the calculated value is not an integer, the stability coefficient of the composite member is calculated using the formula, and the regularized slenderness ratio of the composite member is calculated according to formula (D.0.5-2) in Appendix D of GB50017-2017 "Standard for Design of Steel Structures".

[0097] Then we have:

[0098] When λ n >0.215

[0099]

[0100] When λ n When ≤0.215

[0101]

[0102] In the formula, α1, α2 and α3 are adopted according to Table D.0.5, which are the cross-section classifications specified in Table 7.2.1 of the standard.

[0103] (4) Judgment based on actual load and stable bearing capacity

[0104] This includes situations where the actual load on the round steel pipe exceeds its stable bearing capacity, causing instability and failure; conversely, the steel pipe structure remains stable when the actual load exceeds the stable bearing capacity.

[0105] Example 2

[0106] like Figure 6 As shown, taking the calculation of the stable bearing capacity of a long circular steel tube column reinforced with carbon fiber reinforced composite (CFRP) as an example, the basic parameters of the long circular steel tube column are: outer diameter D of the steel tube. s =180mm, steel pipe wall thickness t s =5mm, total length L = 1500mm. Elastic modulus E of the steel pipe. s =190GPa, yield strength f y =310MPa.

[0107] The carbon fiber fabric reinforcement consists of 6 layers, with a reinforcement pattern of 90° / 0° / 90° / 0° / 90° / 0°, i.e., n layers of circumferential carbon fiber fabric. H =3, n is the number of longitudinal carbon fiber layers. L =3. Basic parameters of carbon fiber cloth: single layer thickness t cfrp =0.167mm, Elastic modulus E in the fiber direction of carbon fiber cloth p,cfrp =238 GPa, elastic modulus E of carbon fiber cloth perpendicular to the fiber direction s,cfrp =2400MPa.

[0108] The steps of the calculation method for the stability bearing capacity of the circular steel tube structure of the offshore platform based on CFRP reinforcement according to the present invention are as follows:

[0109] (a) Elastic modulus E in the fiber direction of carbon fiber cloth p,cfrp The elastic modulus E of carbon fiber cloth perpendicular to the fiber direction s,cfrp Calculate the ratio α of the two moduli s and α p as follows

[0110]

[0111] The ratio of fiber orientation modulus to steel pipe modulus α p The modulus perpendicular to the fiber direction is 1.253, and the ratio of the modulus to the modulus of the steel pipe is α. s It is 0.0126;

[0112] (b) Calculate the cross-sectional area of ​​the steel pipe based on its basic parameters. and moment of inertia of cross section

[0113]

[0114] (c) Calculate the equivalent cross-sectional area A of the composite component eq and equivalent cross section moment of inertia I eq as follows

[0115] A eq =A s +(α p n L +α s n H )πD s t cfrp =3107.4mm 2

[0116]

[0117] (d) Calculate the slenderness ratio of the composite component

[0118] (e) This example uses rolled steel pipe with a circular cross-section. According to GB 50017-2017 "Standard for Design of Steel Structures", the cross-section is a type a cross-section. Therefore, according to λ... c Select the stability coefficient of the composite component according to Appendix D.0.1

[0119] (f) Calculate the header of Table D.0.1 in Appendix D.0.1 of GB 50017-2017 "Standard for Design of Steel Structures". The stability coefficient for 27 in the table is 0.968, and the stability coefficient for 28 is 0.966.

[0120] (g) Calculate the stability coefficient of the composite member more accurately, and calculate the regularized slenderness ratio of the composite member according to formula (D.0.5-2) in Appendix D of GB 50017-2017 "Standard for Design of Steel Structures". λ n If the value is greater than 0.215, then we have Where α2 = 0.986 and α3 = 0.152, their values ​​are adopted according to Table D.0.5 based on the section classification specified in Table 7.2.1 of the standard;

[0121] (h) The stable bearing capacity of the composite component is

[0122] (i) The formula results are compared with the experimental test results as follows, and the error is within the allowable range.

[0123] φ180*5 SJ-1C 3H3L 998 930 1.07

[0124] It should be understood that the present invention is not limited to the processes and structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for assessing the stability and bearing capacity of a circular steel tube structure on a CFRP-reinforced offshore platform, characterized in that, include: (1) Obtain the parameters of the CFRP bonded steel pipe; (2) The equivalent slenderness ratio of the reinforced composite member is calculated by using the equivalent section method, including: calculating the equivalent cross-sectional area and equivalent moment of inertia of the composite member with the steel pipe section after CFRP bonding, and obtaining the slenderness ratio of the composite member from the slenderness ratio of the composite member. The compressive stiffness and flexural stiffness of the CFRP-reinforced composite member can be expressed as: From equations (1) and (2), the equivalent cross-sectional area and equivalent moment of inertia of the composite component can be obtained as follows: wherein E s is the elastic modulus of the steel tube; A eq is the equivalent cross-sectional area of the composite member; A s is the cross-sectional area of the steel tube; E cfrp is the elastic modulus of the CFRP; Wherein, the orthotropic should be discussed in different pasting ways; A cfrp CFRP sectional area; I eq Equivalent moment of inertia of composite member; I s Moment of inertia of steel tube section; I cfrp Moment of inertia of CFRP section; When CFRP is circumferentially bonded, E in equations (3) and (4) cfrp It refers to the elastic modulus E in the non-principal fiber directions. s,cfrp ; When CFRP is pasted vertically, E in equations (3) and (4) cfrp It refers to the elastic modulus E in the principal direction of the fiber. p,cfrp Define two modulus ratios α s and α p as follows: When CFRP is pasted alternately in circumferential and longitudinal directions: In the formula, n H D represents the number of CFRP layers bonded circumferentially. s t is the outer diameter of the steel pipe; cfrp n is the thickness of a single layer of CFRP; L This refers to the number of CFRP layers pasted vertically. Equations (6) and (7) are expressions for the equivalent cross-sectional area and equivalent moment of inertia of the composite component; these two equations summarize the CFRP full-circumferential bonding, i.e., n L =0, CFRP full vertical pasting, i.e., n H =0 and three cases of alternating CFRP circumferential and vertical pasting; Based on the equivalent cross-sectional area and equivalent moment of inertia of the composite member, the slenderness ratio of the composite member can be calculated: In the formula, λ c L0 represents the corrected slenderness ratio of the composite component; L0 represents the effective calculated length of the reinforced steel pipe. (3) Calculate the stable bearing capacity of the steel pipe structure after CFRP reinforcement; (4) Make a judgment based on the actual load and stable bearing capacity.

2. The method for evaluating the stability bearing capacity of a CFRP-reinforced circular steel pipe structure for offshore platforms according to claim 1, characterized in that, The parameters of the steel pipe in step (1) include the outer diameter of the steel pipe, the wall thickness of the steel pipe, the total length of the steel pipe, the elastic modulus of the steel pipe, and the yield strength.

3. The method for evaluating the stability bearing capacity of a CFRP-reinforced circular steel pipe structure for offshore platforms according to claim 1, characterized in that, Step (3) includes a method for calculating the stability bearing capacity of an unreinforced circular steel pipe, which can be used to obtain the stability bearing capacity of a CFRP-reinforced circular steel pipe.

4. The method for evaluating the stability bearing capacity of a CFRP-reinforced circular steel pipe structure for offshore platforms according to claim 3, characterized in that, Step (3) includes determining the stable bearing capacity N of the CFRP-reinforced composite component. c It can be obtained from the following formula: In the formula, N c For the stable bearing capacity of composite components; f y φ is the yield stress of the steel pipe. c Let λ be the stability coefficient of the composite component, where λ is the stability coefficient of the composite component. c When the calculated value is not an integer, the stability coefficient of the composite component is calculated using the formula, and the regularized slenderness ratio of the composite component is also calculated. Then we have: When λn > 0.215 When λn≤0.215 In the formula, α1, α2 and α3 are the cross-section classifications specified in Table 7.2.1 of GB 50017-2017 "Standard for Design of Steel Structures" and are adopted according to Table D.0.

5.

5. The method for evaluating the stability bearing capacity of a CFRP-reinforced circular steel pipe structure for offshore platforms according to claim 4, characterized in that, Calculate the regularized slenderness ratio of the composite member according to formula (D.0.5-2) in Appendix D of GB 50017-2017 "Standard for Design of Steel Structures"; According to λc, it can be found in Appendix D of GB 50017-2017 "Standard for Design of Steel Structures", and the appendix table header is λ. c / ε k , ε k This is the steel grade correction factor, which is the square root of the ratio of 235 to the yield strength value in the steel grade.

6. The method for evaluating the stability bearing capacity of a CFRP-reinforced circular steel pipe structure for offshore platforms according to claim 1, characterized in that, Based on the orthogonal anisotropy of carbon fiber cloth, the stress situation when its bonding direction is different is analyzed. CFRP must not only restrict the compressive deformation of the steel pipe, but also restrict the lateral bending deformation of the steel pipe. When bonded in the circumferential direction, the carbon fiber cloth bears the compressive load in the non-major fiber direction, while when bending deformation occurs, the non-major fiber direction restricts the bending deformation of the steel pipe. When bonded longitudinally, the carbon fiber cloth bears the compressive load in the main fiber direction, while also limiting the bending deformation of the steel pipe.

7. The method for evaluating the stability bearing capacity of a CFRP-reinforced offshore platform circular steel pipe structure according to claim 3, characterized in that, Step (4) includes the following: when the actual load on the round steel pipe is greater than the stable bearing capacity, the round steel pipe will become unstable and fail; otherwise, the steel pipe structure will be stable.

Images