A method for predicting the bearing capacity of load-bearing pipe joints reinforced with carbon fiber reinforced composite materials

Abstract

The present invention provides a method for predicting the bearing capacity of a carbon fiber reinforced composite material reinforced support pipe node, which belongs to the field of high-performance composite material applications. The method comprises: applying a first pressure to the main pipe of the pipe node through a test press, and applying a second pressure to the main pipe through a screw when the test press stops applying the first pressure; wherein, during the process of the screw providing the second pressure to the main pipe, the carbon fiber reinforced composite material is used to reinforce the pipe node to obtain the reinforced support pipe node, and a third pressure is applied to the branch pipe of the reinforced support pipe node, and a relational expression is established based on the first pressure and the second pressure; a finite element model is established based on the relational expression; a parameter analysis is performed on the finite element model, and based on the results of the parameter analysis, the target bearing capacity of the reinforced support pipe node is determined. The method provided by the present invention can accurately predict the target bearing capacity of a carbon fiber reinforced composite material reinforced support pipe node.

Description

Technical Field

[0001] The present invention belongs to the field of application of high-performance composite materials, and in particular relates to a method for predicting the bearing capacity of a carbon fiber reinforced composite reinforced load-bearing pipe node. Background Art

[0002] With the deepening development of offshore oil and gas resources, the safety and reliability of offshore jacket platforms face severe challenges. Pipe joints, as the primary load-bearing areas of offshore jacket platforms, play a decisive role in the platform's mechanical performance. However, factors such as exposure to harsh environments, material corrosion, and cracks can cause pipe joint performance degradation, further threatening platform safety. To ensure the platform's safe operation, pipe joints require reinforcement and repair. Carbon fiber reinforced composites (CFRPs), due to their high tensile strength, excellent fatigue performance, and corrosion resistance, are considered an ideal material for offshore jacket platform reinforcement. Extensive experience has demonstrated that fully impregnating CFRPs with epoxy resin and then wrapping them around the surface of the structure to be reinforced can significantly improve the structure's mechanical properties.

[0003] Currently, there are insufficient methods for predicting the mechanical properties of reinforced tubular joints. This lack of prediction methods limits the widespread application of carbon fiber reinforced composite materials in the field of tubular joint reinforcement. Therefore, when using them for tubular joint reinforcement in practical engineering projects, a method for predicting the bearing capacity of the reinforced tubular joint is essential. This method can be used to determine the quantitative relationship between the bearing capacity and the parameters of the tubular joint and the carbon fiber reinforced composite material. This can guide the reinforcement design of the tubular joint (for example, the selection of the number of carbon fiber reinforced composite material reinforcement layers) and the evaluation of the mechanical properties after reinforcement.

[0004] When reinforcing an offshore jacket platform currently in service, it is necessary to consider the adverse effects of sustained loads on the pipe joints (i.e., the main pipes continuously bearing loads) on the bearing capacity of the reinforced pipes. Traditional bearing capacity prediction formulas, such as those in the national standard "Code for Design of Steel Structures (GB50017-2017)", can only predict the bearing capacity of unreinforced pipe joints. Furthermore, traditional reinforced joint bearing capacity prediction models are based on the assumption that the structure is not bearing sustained loads, meaning that the model can only be used when the structure is unloaded, which is often difficult to achieve in actual engineering. Therefore, an effective bearing capacity assessment method for carbon fiber reinforced composite reinforced pipe joints with sustained loads is urgently needed to guide the design of pipe joint reinforcements under sustained loads. Summary of the Invention

[0005] In view of the above problems, an embodiment of the present application provides a method for predicting the bearing capacity of a carbon fiber reinforced composite material reinforced load-bearing pipe node, so as to overcome the above problems or at least partially solve the above problems.

[0006] The present application provides a method for predicting the bearing capacity of a carbon fiber reinforced composite material reinforced load-bearing pipe node, comprising:

[0007] A first pressure is applied to the main pipe of the tubular node by a test press, and when the test press stops applying the first pressure, a second pressure is applied to the main pipe by a screw; wherein, while the screw is applying the second pressure to the main pipe, the tubular node is reinforced with a carbon fiber reinforced composite material to obtain a reinforced supporting tubular node, and a third pressure is applied to the branch pipe of the reinforced supporting tubular node;

[0008] Establishing a relational expression based on the first pressure and the second pressure; wherein the relational expression represents the correlation between the first pressure and the second pressure;

[0009] Based on the relational expression, a finite element model is established; wherein the finite element model is used to simulate the mechanical behavior during the process of applying the third pressure to the branch pipe of the reinforced supporting pipe node;

[0010] Perform parameter analysis on the finite element model to determine the target bearing capacity of the reinforced load-bearing pipe node.

[0011] Furthermore, providing the second pressure to the main pipe through the screw comprises:

[0012] The screw rod passes through the reserved hole of the main pipe end plate, and is tightened with a nut at the end of the screw rod to connect with the main pipe end plate, so that the screw rod provides the second pressure to the main pipe; wherein the main pipe end plate is perpendicular to the end of the main pipe.

[0013] Furthermore, the angle between the branch pipe and the main pipe is 90 degrees.

[0014] Furthermore, the step of applying a first pressure to the main pipe of the pipe node by a test press is achieved by the following expression:

[0015] ;

[0016] in, is the first pressure; It is the compression amount of the main pipe when it is subjected to the first pressure applied by the test press; is the main pipe length; is the cross-sectional area of ​​the main pipe; is the elastic modulus of the main pipe.

[0017] Furthermore, the step of providing the second pressure to the main pipe through the screw is achieved by the following expression:

[0018] ;

[0019] in, is the second pressure; is the number of screws; It is the elongation of the screw or the springback deformation of the main pipe; is the screw length; is the cross-sectional area of ​​a single screw minor diameter; is the elastic modulus of the screw.

[0020] Furthermore, the step of establishing a relational expression based on the first pressure and the second pressure is achieved through the following expression:

[0021] ;

[0022] in, First pressure; is the main pipe length of the pipe node; is the cross-sectional area of ​​the main pipe; is the elastic modulus of the main tube; is the second pressure; is the number of screws; is the screw length; is the cross-sectional area of ​​a single screw minor diameter; is the elastic modulus of the screw.

[0023] Furthermore, establishing a finite element model based on the relational expression includes:

[0024] Based on the relational expression, a force boundary condition is determined; wherein the force boundary condition represents the force condition of the main pipe in the finite element model under the load state;

[0025] Obtaining geometric parameters and reinforcement parameters of the reinforced support pipe node; wherein the geometric parameters include: main pipe diameter, main pipe wall thickness, branch pipe diameter, branch pipe wall thickness, main pipe length, and branch pipe length; and the reinforcement parameters include the number of reinforcement layers of carbon fiber reinforced composite material;

[0026] Based on the geometric parameters and the reinforcement parameters, the force boundary conditions are applied to establish the finite element model.

[0027] Furthermore, the performing of parameter analysis on the finite element model to determine the target bearing capacity of the reinforced load-bearing pipe node includes:

[0028] Obtaining the bearing capacity of the pipe node when plastic failure occurs; wherein the bearing capacity is respectively associated with the diameter ratio of the branch pipe to the main pipe, the diameter-thickness ratio of the main pipe, the angle between the branch pipe and the main pipe, and the magnitude of the axial compressive stress on both sides of the main pipe;

[0029] Performing parameter analysis on the finite element model, and determining a target bearing capacity influence coefficient of the reinforced load-bearing pipe node based on the results of the parameter analysis and the bearing capacity;

[0030] Performing multivariate regression linearization processing on the target bearing capacity influence coefficient to determine the target bearing capacity.

[0031] Furthermore, the step of performing multivariate regression linearization processing on the target bearing capacity influence coefficient to determine the target bearing capacity is achieved through the following expression:

[0032] ;

[0033] in, is the target carrying capacity; is the diameter ratio of branch pipe to main pipe; is the main tube diameter-thickness ratio; is the initial load factor; is the ratio of the thickness of the carbon fiber reinforced composite material to the thickness of the main pipe; is the wall thickness of the main pipe, is the yield strength of the main steel.

[0034] Therefore, according to the method for predicting the bearing capacity of a carbon fiber reinforced composite material reinforced support pipe node provided in this embodiment, a test press is first used to apply a first pressure to the main pipe of the pipe node. When the test press stops applying the first pressure, a second pressure is provided to the main pipe through the screw to maintain the bearing state of the pipe node. In the process of the screw providing the second pressure to the main pipe, the carbon fiber reinforced composite material can also be wrapped on the pipe node to complete the reinforcement of the support pipe node, thereby obtaining the reinforced support pipe node. Then, a third pressure is applied to the branch pipe of the reinforced support pipe node. Then, based on the first pressure and the second pressure, a relational expression is established to characterize the correlation between the two to determine the magnitude of the second pressure provided by the screw to the main pipe. A finite element model is established based on the relational expression. The finite element model can simulate the mechanical behavior in the process of applying the third pressure to the branch pipe of the reinforced support pipe node. Finally, the finite element model is subjected to parameter analysis. According to the results of the parameter analysis, the target bearing capacity of the reinforced support pipe node is predicted. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0036] Figure 1This is a flowchart of the steps of a method for predicting the bearing capacity of a carbon fiber reinforced composite material reinforced load-bearing pipe node provided in an embodiment of the present application;

[0037] Figure 2 This is a schematic diagram of a manufacturing process of a reinforced carrier pipe node provided in an embodiment of the present application;

[0038] Figure 3 is a schematic diagram of a finite element model provided in an embodiment of the present application;

[0039] Figure 4 Schematic diagram of a tubular joint test and comparison of finite element load-displacement curves provided in an embodiment of the present application;

[0040] Figure 5 It is a schematic diagram comparing a bearing capacity fitting formula provided in an embodiment of the present application with finite element simulation and experimental measurement results. DETAILED DESCRIPTION

[0041] The exemplary embodiments of the present application will be described in more detail below in conjunction with the accompanying drawings in the embodiments of the present application. Although the accompanying drawings show exemplary embodiments of the present application, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0042] Reference Figure 1 , Figure 1 This is a flowchart of a method for predicting the bearing capacity of a carbon fiber reinforced composite material reinforced load-bearing pipe node provided in an embodiment of the present application. Figure 1 It can be seen that this step includes:

[0043] Step S101: Apply a first pressure to the main pipe of the pipe node through a test press, and when the test press stops applying the first pressure, apply a second pressure to the main pipe through a screw; wherein, during the process of the screw providing the second pressure to the main pipe, the pipe node is reinforced with a carbon fiber reinforced composite material to obtain a reinforced supporting pipe node, and a third pressure is applied to the branch pipe of the reinforced supporting pipe node.

[0044] In this embodiment, in order to facilitate the prediction of the bearing capacity of the reinforced load-bearing pipe node, it is necessary to make the reinforced load-bearing pipe node, referring to Figure 2 , Figure 2 This is a schematic diagram of the manufacturing process of a reinforced support pipe node provided in an embodiment of the present application, from Figure 2 (a) It can be seen that the pipe node includes a main pipe and a branch pipe, and the two ends of the main pipe are respectively provided with a main pipe end plate, and the two ends of the branch pipe are respectively provided with a branch pipe end plate. For the process of making a reinforced load-bearing pipe node, please refer to Figure 2 (b)-(e) in detail: First, the first pressure can be applied to the main tube of the tube node by a test press, that is, Figure 2 in The first pressure is the pressure directly applied by the test press to the main pipe of the pipe node. This embodiment does not limit the value of the first pressure and can be set according to actual test requirements. Secondly, in order to maintain the pipe node in a load-bearing state, after the test press applies the first pressure to the main pipe of the pipe node, the screws installed at both ends of the main pipe provide the main pipe with a second pressure, that is, Figure 2 in To ensure that after the test press is unloaded, that is, after the first pressure is stopped, the main pipe can still be in a load-bearing state through the second pressure provided by the screw. At the same time, in the process of the screw providing the second pressure to the main pipe, the fiber reinforced composite material can be wrapped around the pipe node to obtain a reinforced load-bearing pipe node, that is, Figure 2 (e) The reinforcement method of the support tube node can be to wrap or attach the carbon fiber reinforced composite material to the support tube node, thereby obtaining a reinforced support tube node. In addition, after obtaining the reinforced support tube node, Figure 2 (f) It can be seen that a third pressure needs to be applied to the branch pipe of the reinforced load-bearing pipe node, that is, Figure 2 in The third pressure can be provided by a testing press. In this embodiment, the number and size of the screws are not limited, as long as they can provide a stable second pressure to the main pipe. The pipe nodes in this embodiment are not reinforced with carbon fiber reinforced composite materials, and the reinforced supporting pipe nodes are reinforced with carbon fiber reinforced composite materials to withstand the second pressure.

[0045] Step S102: establishing a relational expression based on the first pressure and the second pressure; wherein the relational expression represents the correlation between the first pressure and the second pressure.

[0046] In this embodiment, in order to ensure that the main pipe is in a load-bearing state while being subjected to the third pressure, a second pressure is used instead of the first pressure to provide axial pressure to the main pipe. The first pressure is applied to the main pipe of the pipe node by a test press, and the second pressure is applied to the main pipe of the pipe node by a screw after the test press is unloaded. After the test press is unloaded, the screw maintains the main pipe in a load-bearing state. However, during the unloading of the test press, the main pipe in a load-bearing state on the pipe node will rebound, and the screw will elongate due to the rebound of the main pipe of the pipe node. Therefore, the first pressure and the second pressure are not equal, but there is a correlation. This correlation can be quantified by establishing a mathematical model or experimental calibration to ensure that the screw can effectively maintain the axial pressure of the main pipe after the test press is unloaded.

[0047] Step S103: establishing a finite element model based on the relational expression; wherein the finite element model is used to simulate the mechanical behavior during the process of applying the third pressure to the branch pipe of the reinforced supporting pipe node.

[0048] In this embodiment, since the relational expression associates the first pressure applied by the test press and the second pressure applied by the screw, reflecting the mechanical relationship between the first pressure and the second pressure, this relationship can be incorporated into the finite element model to facilitate setting accurate force boundary conditions so that the finite element model can be used to simulate the mechanical behavior of the reinforced support pipe node. In order to determine the bearing capacity of the reinforced support pipe node, Figure 2 (f) It can be seen that a third pressure can be applied to the branch pipe of the reinforced load-bearing pipe node. The third pressure can be provided by a test press or other equipment that can provide the third pressure. The third pressure can be a continuously changing force. In the process of applying the third pressure to the branch pipe of the reinforced load-bearing pipe node, a relationship curve between the third pressure and the displacement of the branch pipe end plate can be obtained. The peak value of the curve is the test value of the bearing capacity. The finite element model can be used to simulate the mechanical behavior of the process, and the finite element model can be verified by comparing the relationship curve and the bearing capacity.

[0049] Step S104: performing parameter analysis on the finite element model to determine the target bearing capacity of the reinforced load-bearing pipe node.

[0050] In this embodiment, parameter analysis can be performed on the verified finite element model. Specifically, the parameter analysis is performed by changing the values ​​of different parameters in the finite element model, running the finite element model, and finally determining the target bearing capacity of the reinforced load-bearing pipe node based on the results of the numerical analysis of different parameters.

[0051] Therefore, according to the method for predicting the bearing capacity of a carbon fiber reinforced composite material reinforced support pipe node provided in this embodiment, a test press is first used to apply a first pressure to the main pipe of the pipe node. When the test press stops applying the first pressure, a second pressure is provided to the main pipe through the screw to maintain the bearing state of the pipe node. In the process of the screw providing the second pressure to the main pipe, the carbon fiber reinforced composite material can also be wrapped on the pipe node to complete the reinforcement of the support pipe node, thereby obtaining the reinforced support pipe node, and then, a third pressure is applied to the branch pipe of the reinforced support pipe node. Then, based on the first pressure and the second pressure, a relational expression characterizing the correlation between the two is established to determine the magnitude of the second pressure provided by the screw to the main pipe, and a finite element model is established based on the relational expression to simulate the mechanical behavior in the process of applying the third pressure to the branch pipe of the reinforced support pipe node. Finally, the finite element model is subjected to parameter analysis, and the target bearing capacity of the reinforced support pipe node is accurately predicted based on the results of the parameter analysis.

[0052] In a specific embodiment, providing the second pressure to the main pipe by means of a screw comprises: passing the screw through a reserved hole of an end plate of the main pipe, and tightening the end of the screw with a nut to connect it to the end plate of the main pipe, so that the screw provides the second pressure to the main pipe; wherein the end plate of the main pipe is perpendicular to the end of the main pipe.

[0053] In this embodiment, the second pressure provided by the screw to the main pipe is specifically achieved by the following method: Figure 2 ,from Figure 2 As shown in (a) and (d), the main pipe end plates are installed at both ends of the main pipe. Screws pass through the reserved holes in the main pipe end plates and are tightened with nuts at the ends of the screws to connect to the main pipe end plates. When the test press is unloaded, the pressure applied by the screws continues to increase. After the test press is completely unloaded, the pressure applied by the screws on the main pipe reaches the second pressure, which is the sum of the loads applied by all screws to the main pipe of the tubular joint.

[0054] For example, the following will be combined with Figure 2 , the process of establishing the relational expression in this embodiment is described in detail:

[0055] When the test press applies the first pressure to the main pipe of the tubular node, compression deformation will occur on the main pipe. If the tubular node is an X-type node, the steps of applying the first pressure to the main pipe of the tubular node by the test press are implemented by formula (1):

[0056] Formula (1);

[0057] in, is the first pressure; It is the compression amount of the main pipe when it is subjected to the first pressure applied by the test press; is the main pipe length; is the cross-sectional area of ​​the main pipe; is the elastic modulus of the main pipe.

[0058] In addition, since the unloading of the test press requires the screw to provide pre-axial pressure for the main tube in the pipe node, as the pressure applied by the test press decreases, the main tube of the pipe node will rebound. When the test press value decreases to 0, the rebound deformation of the main tube of the pipe node is The screw is in a relaxed state when the test press provides the first pressure to the main pipe. When the test press is unloaded, the screw will be extended by the rebound of the main pipe of the pipe node. The elongation of the screw is equal to the rebound deformation of the main pipe of the pipe node. .

[0059] Therefore, the step of providing the second pressure to the main pipe through the screw can be achieved by formula (2):

[0060] Formula (2);

[0061] in, is the second pressure; is the number of screws; The elongation of the screw and the rebound deformation of the main pipe; is the screw length; is the cross-sectional area of ​​a single screw minor diameter; is the elastic modulus of the screw.

[0062] The final compression deformation of the main tube of the X-type tubular node is , the final axial pressure it receives is the second pressure provided by the screw on the X-type tube node, and formula (3) can be obtained as follows:

[0063] Formula (3);

[0064] in, It is the compression amount of the main pipe when it is subjected to the first pressure applied by the test press; The elongation of the screw and the rebound deformation of the main pipe; is the screw length; is the cross-sectional area of ​​a single screw minor diameter; is the elastic modulus of the screw; is the main pipe length; is the cross-sectional area of ​​the main pipe; is the elastic modulus of the main pipe.

[0065] According to formula (3), the springback deformation of the main tube of the tube node can be deduced as follows: After the first pressure is applied by the test press, the compression deformation of the tube node The relationship is formula (4), as follows:

[0066] Formula (4);

[0067] in, It is the compression amount of the main pipe when it is subjected to the first pressure applied by the test press; is the elongation of the screw and the main pipe Rebound deformation; is the screw length; is the cross-sectional area of ​​a single screw minor diameter; is the elastic modulus of the screw; is the main pipe length; is the cross-sectional area of ​​the main pipe; is the elastic modulus of the main pipe.

[0068] In a specific embodiment, the second pressure borne by the main pipe of the pipe node is established by combining formula (1), formula (2) and formula (4). With the first pressure The relationship is formula (5):

[0069] Formula (5);

[0070] in, is the first pressure; is the main pipe length of the pipe node; is the cross-sectional area of ​​the main pipe; is the elastic modulus of the main tube; is the second pressure; is the number of screws; is the screw length; is the cross-sectional area of ​​a single screw minor diameter; is the elastic modulus of the screw.

[0071] In a specific embodiment, the angle between the branch pipe and the main pipe is 90 degrees.

[0072] In this embodiment, a branch pipe is provided on the pipe node, and the branch pipe can be connected to the main pipe by welding, and the angle between the branch pipe and the main pipe is 90°, so the pipe node can be an X-type node.

[0073] In a specific embodiment, the establishment of a finite element model based on the relational expression includes: determining a force boundary condition based on the relational expression; wherein the force boundary condition characterizes the stress condition of the main pipe loading state in the finite element model; obtaining the geometric parameters and reinforcement parameters of the reinforced supporting pipe node; wherein the geometric parameters include: main pipe diameter, main pipe wall thickness, branch pipe diameter, branch pipe wall thickness, main pipe length and branch pipe length, and the reinforcement parameters include the number of reinforcement layers of carbon fiber reinforced composite materials; based on the geometric parameters and the reinforcement parameters, the force boundary condition is applied to establish the finite element model.

[0074] In this embodiment, a third pressure is applied to the branch pipe of the reinforced load-bearing pipe node, and the force boundary condition is determined based on the relational expression. Since the force boundary condition represents the stress condition of the main pipe in the finite element model, the stress condition of the main pipe in the load-bearing state can be reflected by the initial load rate of the main pipe, the main pipe loading boundary condition in the finite element model can be determined by referring to Figure 3 , Figure 3 This is a schematic diagram of a finite element model provided in an embodiment of the present application, Figure 3As can be seen in the finite element model, a reference point is set for each of the upper and lower branch end plates. This reference point is bound to the branch end plate, completely fixing the reference point of the lower branch end plate to restrict displacement and rotation in all directions. The upper end plate of the pipe node serves as the loading end, releasing displacement of the upper end plate reference point in the Z-axis direction. Furthermore, a relational expression is used to express the correlation between the first pressure applied by the test press and the second pressure applied by the screw. This correlation allows us to determine the magnitude of the second pressure provided by the screw, i.e., the load borne by the main pipe. The geometric parameters and reinforcement parameters of the reinforced loaded pipe node are then obtained. The geometric parameters include: main pipe diameter, main pipe wall thickness, branch pipe diameter, branch pipe wall thickness, main pipe length, and branch pipe length. The reinforcement parameters include the number of carbon fiber reinforced composite material reinforcement layers. Obtaining geometric parameters such as main pipe diameter, wall thickness, and length, as well as parameters such as the number of carbon fiber reinforced composite material reinforcement layers, can restore the actual size and reinforcement design of the pipe node, ensuring that the geometric shape, size, and number of reinforcement layers of the finite element model are consistent with the pipe node in actual engineering, thereby improving the accuracy of the finite element model simulation.

[0075] Since the force boundary condition represents the stress situation of the main pipe in the finite element model, the force boundary condition can be applied based on the geometric parameters and reinforcement parameters to establish the finite element model.

[0076] The finite element model established above is verified in the following way. First, the established finite element model is run, and then the load-displacement curve of the finite element model simulation tube node is obtained. Figure 4 , Figure 4 : is a schematic diagram of a tubular joint test and a comparison of finite element load-displacement curves provided in an embodiment of the present application. Figure 4 middle is the ultimate load calculated by the finite element model, is the ultimate load obtained from direct test of tubular joints, Figure 4 As can be seen from the finite element simulation curve and the experimental curve before the specimen reaches its bearing capacity, the finite element results are slightly greater than the experimental results after the specimen reaches its bearing capacity. However, the load-displacement curves derived from both the finite element results and the experimental results show a decreasing trend, indicating that the finite element model accurately captures the key mechanical behavior of the reinforced load-bearing pipe joint: the carbon fiber reinforced composite material in the intersection region loses its ability to resist load after fracture. Therefore, the bearing capacity of the reinforced load-bearing pipe joint simulated by the finite element model decreases slowly. Therefore, the above comparison of load-displacement curves and bearing capacity shows that the finite element model established in this embodiment can relatively accurately simulate the mechanical behavior of the reinforced load-bearing pipe joint when the branch pipe is subjected to the third pressure.

[0077] In a specific embodiment, the parameter analysis of the finite element model is performed to determine the target bearing capacity of the reinforced load-bearing pipe node, including: obtaining the bearing capacity of the pipe node when plastic failure occurs; wherein the bearing capacity is respectively associated with the diameter ratio of the branch pipe to the main pipe, the diameter-thickness ratio of the main pipe, the angle between the branch pipe and the main pipe, and the magnitude of the axial compressive stress on both sides of the main pipe; the parameter analysis of the finite element model is performed, and based on the results of the parameter analysis and the bearing capacity, the target bearing capacity influence coefficient of the reinforced load-bearing pipe node is determined; the target bearing capacity influence coefficient is subjected to multivariate regression linearization processing to determine the target bearing capacity.

[0078] In this embodiment, the bearing capacity of the tubular joint when plastic failure occurs can be obtained according to the Code for Design of Steel Structures. For details, see formula (6):

[0079] Formula (6);

[0080] in, is the influencing parameter of the main pipe axial stress, When the pipe joint is under tension on both sides or one side, take , is the main pipe wall thickness; The design values ​​of tensile, compressive and flexural strength of the main steel; The angle between the main and branch pipe axes is less than a right angle; is the bearing capacity of the tubular joint when plastic failure occurs; is the yield strength of the main steel; It is the smaller absolute value of the axial compressive stress of the main pipe on both sides of the tubular node.

[0081] From formula (6), it can be seen that the bearing capacity is related to the diameter ratio of the branch pipe to the main pipe, the diameter-thickness ratio of the main pipe, the angle between the branch pipe and the main pipe, and the magnitude of the axial compressive stress on both sides of the main pipe. Without considering the influence of the angle between the branch pipe and the main pipe, the bearing capacity of the X-type pipe node reinforced with carbon fiber reinforced composite material under the axial force of the main pipe when the main pipe undergoes plastic failure is given in combination with the standard formula, as shown in formula (7).

[0082] Formula (7);

[0083] in, is the bearing capacity influence coefficient of the pipe joint, and its value is related to the geometric parameters of the X-type pipe joint (the ratio of the diameter of the branch pipe to the main pipe). , main body diameter-thickness ratio ), carbon fiber reinforced composite material reinforcement parameters (number of carbon fiber reinforced composite material reinforcement layers ) and initial stress state (initial load rate ) is related. Use the main pipe wall thickness Number of reinforcement layers for carbon fiber reinforced composite materials Normalized by the ratio of the thickness of the carbon fiber reinforced composite material to the thickness of the main tube ( ), which represents the influence of the number of carbon fiber reinforced composite material reinforcement layers on the bearing capacity of the tubular joint.

[0084] It should be noted here that the yield strength of the main steel can be used in formula (7) Design values ​​of tensile, compressive and flexural strength of alternative main steel materials This is because the design value of steel strength is less than the steel yield strength. In order to improve the accuracy of the bearing capacity prediction formula, the steel yield strength is used to calculate the bearing capacity of the pipe node, which is closer to the measured bearing capacity.

[0085] In addition, it is necessary to perform parameter analysis on the finite element model. The parameter analysis process of the finite element model is as follows:

[0086] First, the influence of different parameter ranges on the bearing capacity of the pipe joint is determined. The initial load rate parameter , we can consider the influence of the initial axial force applied to the main pipe on the bearing capacity of the pipe node, so the initial load rate is expressed as the axial stress generated by the initial axial force on the main pipe and steel yield strength The ratio between , where The second pressure Cross-sectional area of ​​main pipe The ratio of . The range considered is 0-80%.

[0087] Pipe node geometric parameters: The influence of the pipe node geometric dimensions on the bearing capacity of the pipe node can be considered, and the ratio of the branch pipe to the main pipe diameter can be used to calculate the geometric parameters of the pipe node. Ratio of main tube diameter to thickness Indicates that the diameter ratio of the branch pipe to the main pipe is , the consideration range is 0.4-0.8, the main tube diameter thickness ratio , the range is 10-20. Main pipe diameter , considering the range of 0-300. is the reinforcement parameter of carbon fiber reinforced composite materials, which can consider the influence of different layers of carbon fiber reinforced composite materials on the bearing capacity of the load-bearing pipe node, and the consideration range is 0-20.

[0088] For details, please refer to Table 1, which shows the specific values ​​of the research parameters, as shown below:

[0089] Table 1 - Specific values ​​of research parameters

[0090] ;

[0091] In the process of parameter analysis of the reinforced load-bearing pipe node, it is assumed that the angle between the main pipe and the branch pipe is 90°; the basic parameters of the specimen are as follows: main pipe diameter =114mm, main pipe length =1400mm, tensile elastic modulus of carbon fiber reinforced composite materials =238000MPa, carbon fiber reinforced composite fiber tensile strength =2549MPa, thickness of single-layer carbon fiber reinforced composite material =0.167mm, carbon fiber reinforced composite material reinforcement layers =4, CFRP reinforcement length of main pipe =500mm and the length of the branch pipe reinforced with carbon fiber reinforced composite material =140mm. In addition, considering the influencing factors of the main pipe diameter size of the pipe node, the parameter analysis of the large-size main pipe diameter model was carried out, and the large-size pipe node main pipe diameter used in the calculation was 300mm.

[0092] Diameter ratio of branch pipe to main pipe Ratio of main tube diameter to thickness The change is made by changing the branch pipe diameter and main pipe wall thickness In addition, this embodiment does not consider the wall thickness ratio of the branch pipe to the main pipe. The influence of such parameter changes on the bearing capacity of pipe joints, the wall thickness ratio of branch pipe to main pipe, The change of the wall thickness ratio of the branch pipe to the main pipe may cause the failure of the component to occur earlier than the failure of the pipe node. When the branch pipe is smaller, it will fail first. The bearing capacity obtained by this failure mode is not the bearing capacity considered in the design of the pipe joint. The real bearing capacity of the pipe joint is the radial bearing capacity of the main pipe when the main pipe plastically fails under the axial pressure of the branch pipe under the condition of certain geometric dimensions. Therefore, in the parameter analysis, the wall thickness ratio of the branch pipe to the main pipe is set to Both are 1, that is, the wall thickness of the branch pipe is designed to be equal to the wall thickness of the main pipe, ensuring that the branch pipe will not fail before the main pipe.

[0093] According to the above parameter analysis results, the diameter ratio of branch pipe to main pipe is , main body diameter-thickness ratio , initial load factor and the ratio of carbon fiber reinforced composite material thickness to main pipe thickness The four dimensionless parameters are the key parameters that affect the bearing capacity of X-type tubular joints reinforced with carbon fiber reinforced composite materials under the action of main pipe axial force. Therefore, the expression of the influence coefficient of the bearing capacity of the tubular joint can be written as formula (8).

[0094] Formula (8);

[0095] In addition, the linearization method of multiple regression is used to transform formula (8) into a linear form, and the logarithm of both sides of formula (8) is taken to obtain formula (9), as follows:

[0096] Formula (9);

[0097] Finally, based on the results of parameter analysis and combined with the multivariate linear regression analysis method, the multivariate regression linearization processing of the target bearing capacity influence coefficient is realized through formula (9), and the result is: The value of , where are all fitting constants. The steps to determine the target bearing capacity are:

[0098] Formula (10);

[0099] in, is the target carrying capacity; is the diameter ratio of branch pipe to main pipe; is the main tube diameter-thickness ratio; is the initial load factor; is the ratio of the thickness of the carbon fiber reinforced composite material to the thickness of the main pipe; is the wall thickness of the main pipe, is the yield strength of the main steel.

[0100] In order to verify the accuracy of the fitting formula for the bearing capacity of tubular joints, the finite element parameter analysis results and the experimental measured values ​​of the X-type tubular joints reinforced with carbon fiber reinforced composite materials under axial force in the experimental study were compared with the calculation results of formula (10). The comparison results are shown in Figure 10. Figure 5 . Figure 5 This is a schematic diagram showing the comparison between a load-bearing capacity fitting formula provided in the embodiment of the present application and the finite element simulation and test results. The horizontal axis represents the finite element model calculation results in parameter analysis and the test measured values. N uc,η , the vertical axis is the prediction result of the fitting formula of formula (10) N cX,η . N cX,η / N uc,η The mean value is 1.0014 and the standard deviation is 0.0516. Figure 5 It can be seen that the error between the bearing capacity results of the tubular joints predicted by the fitting formula and the bearing capacity results of the finite element simulation in the parameter analysis and the experimental measurement is within 10%. The above results show that the formula (10) proposed in this embodiment can more accurately predict the target bearing capacity of the reinforced load-bearing tubular joints.

[0101] In addition, the parameter range of formula (10) proposed in this embodiment is: 、 、 and .

[0102] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0103] The embodiments of the present invention are described with reference to the flowcharts and / or block diagrams of the methods and apparatuses according to the embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as the combination of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing terminal device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0104] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing terminal device to operate in a specific manner, so that the instructions stored in the computer readable memory produce a manufactured product including an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0105] These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device so that a series of operating steps are executed on the computer or other programmable terminal device to produce a computer-implemented process, thereby providing instructions for executing on the computer or other programmable terminal device to implement the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0106] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0107] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "includes," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or terminal device. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of additional identical elements in the process, method, article, or terminal device that includes the element.

[0108] The above is a detailed introduction to the method for predicting the bearing capacity of carbon fiber reinforced composite material reinforced load-bearing pipe nodes provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for general technical personnel in this field, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for predicting the bearing capacity of carbon fiber reinforced composite material reinforced load-bearing pipe nodes, characterized in that: include: A first pressure is applied to the main pipe of the tubular node by a test press, and when the test press stops applying the first pressure, a second pressure is applied to the main pipe by a screw; wherein, while the screw is applying the second pressure to the main pipe, the tubular node is reinforced with a carbon fiber reinforced composite material to obtain a reinforced supporting tubular node, and a third pressure is applied to the branch pipe of the reinforced supporting tubular node; Establishing a relational expression based on the first pressure and the second pressure; wherein the relational expression represents the correlation between the first pressure and the second pressure; A finite element model is established based on the relational expression; wherein the finite element model is used to simulate the mechanical behavior during the process of applying the third pressure to the branch pipe of the reinforced load-bearing pipe node; wherein, establishing the finite element model based on the relational expression includes: determining a force boundary condition based on the relational expression; wherein the force boundary condition represents the force condition of the main pipe in the finite element model in the load-bearing state; Obtaining geometric parameters and reinforcement parameters of the reinforced support pipe node; wherein the geometric parameters include: main pipe diameter, main pipe wall thickness, branch pipe diameter, branch pipe wall thickness, main pipe length, and branch pipe length; and the reinforcement parameters include the number of reinforcement layers of carbon fiber reinforced composite material; Applying the force boundary conditions based on the geometric parameters and the reinforcement parameters to establish the finite element model; Performing parameter analysis on the finite element model to determine the target bearing capacity of the reinforced load-bearing pipe node; wherein performing parameter analysis on the finite element model to determine the target bearing capacity of the reinforced load-bearing pipe node includes: Obtaining the bearing capacity of the pipe node when plastic failure occurs; wherein the bearing capacity is respectively associated with the diameter ratio of the branch pipe to the main pipe, the diameter-thickness ratio of the main pipe, the angle between the branch pipe and the main pipe, and the magnitude of the axial compressive stress on both sides of the main pipe; Performing parameter analysis on the finite element model, and determining a target bearing capacity influence coefficient of the reinforced load-bearing pipe node based on the results of the parameter analysis and the bearing capacity; Performing multivariate regression linearization processing on the target bearing capacity influence coefficient to determine the target bearing capacity.

2. The prediction method according to claim 1, characterized in that Providing the second pressure to the main pipe through the screw comprises: The screw rod passes through the reserved hole of the main pipe end plate, and is tightened with a nut at the end of the screw rod to connect with the main pipe end plate, so that the screw rod provides the second pressure to the main pipe; wherein the main pipe end plate is perpendicular to the end of the main pipe.

3. The prediction method according to claim 1, wherein: The included angle between the branch pipe and the main pipe is 90 degrees.

4. The method according to claim 1, wherein The step of applying the first pressure to the main pipe of the tubular joint by the test press is realized by the following expression: ； in, is the first pressure; It is the compression amount of the main pipe when it is subjected to the first pressure applied by the test press; is the main pipe length; is the cross-sectional area of ​​the main pipe; is the elastic modulus of the main pipe.

5. The method according to claim 1, wherein The step of providing the second pressure to the main pipe through the screw is achieved by the following expression: ； in, is the second pressure; is the number of screws; It is the elongation of the screw or the springback deformation of the main pipe; is the screw length; is the cross-sectional area of ​​a single screw minor diameter; is the elastic modulus of the screw.

6. The method according to claim 1, characterized in that The step of establishing a relational expression based on the first pressure and the second pressure is achieved through the following expression: ； in, is the first pressure; is the main pipe length; is the cross-sectional area of ​​the main pipe; is the elastic modulus of the main tube; is the second pressure; is the number of screws; is the screw length; is the cross-sectional area of ​​a single screw minor diameter; is the elastic modulus of the screw.

7. The method according to claim 1, characterized in that The step of performing multivariate regression linearization processing on the target bearing capacity influence coefficient to determine the target bearing capacity is achieved through the following expression: ； Among them, N cX,η is the target carrying capacity; is the diameter ratio of branch pipe to main pipe; is the main tube diameter-thickness ratio; is the initial load factor; is the ratio of the thickness of the carbon fiber reinforced composite material to the thickness of the main pipe; is the wall thickness of the main pipe, is the yield strength of the main steel.

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