Design method of buried flexible pipeline joint structure under effect of ground traffic load

Abstract

The invention belongs to the technical field of pipeline engineering, and particularly relates to a buried flexible pipeline joint structure design method under the effect of ground traffic load. Aiming at the problem that the local stress concentration effect of a pipeline joint is neglected in the prior art, so that the joint is easy to lose efficacy, the invention provides the following scheme: firstly, obtaining ground traffic load parameters, a foundation stress spread angle, pipeline geometric dimension parameters and mechanical parameters of a soil body and a pipeline; according to the method, the load transmitted to the pipe top is calculated through an equivalent load formula, corresponding calculation routes are established according to the three conditions of torque release, complete transmission and partial transmission, and key parameters such as the maximum corner, the shearing force and the bending moment of the joint are accurately calculated and further used for optimization design of the joint structure. The method has the advantages that the local stress and deformation of the joint are quantified for the first time, the method is suitable for various joint types, the calculation precision and the engineering reliability are remarkably improved, and meanwhile the complex calculation process is simplified.

Description

Technical Field

[0001] The present invention belongs to the technical field of pipeline engineering, and particularly relates to a structural design method for an underground flexible pipeline joint, which is especially applicable to resisting the dynamic action of ground traffic loads. Background Art

[0002] With the acceleration of the urbanization process, the underground pipeline system, as the "lifeline" of urban infrastructure, plays an irreplaceable role in fields such as water supply, drainage, and gas transmission. However, the continuous growth of ground traffic loads (such as the increase in heavy vehicles and the intensification of traffic flow) poses a severe challenge to the mechanical properties of buried pipelines. Research shows that pipeline joints, as the core components connecting pipe segments, have a failure probability of more than 60% of pipeline system accidents, mainly due to stress concentration, fatigue damage, and sealing failure caused by traffic loads.

[0003] The influence of ground traffic loads on pipeline joints is complex, involving the nonlinear mechanical behavior of the soil-pipeline system and the load stress redistribution at the pipeline joint position. Especially the increase in heavy vehicles on modern urban roads and the continuous increase in traffic flow make pipeline joints face a more severe stress environment. Current research mainly focuses on the influence of ground traffic loads on continuous pipelines, and there is still a lack of relevant theoretical analysis methods for calculating the stress concentration effect and local deformation at the pipeline joint part. Summary of the Invention

[0004] Based on the problems summarized above, the present invention provides a structural design method for an underground flexible pipeline joint under the action of ground traffic loads. Its main feature is to simulate and calculate the flexible pipeline joint under the influence of traffic loads through a calculation method, and optimize the design of the flexible pipeline joint structure according to the calculation results. The specific technical solutions are as follows:

[0005] A structural design method for an underground flexible pipeline joint under the action of ground traffic loads includes the following steps:

[0006] S1. Obtain parameters: ground traffic load P 1 , load acting area w×l 1 , foundation stress diffusion angle θ, pipeline diameter D, pipeline burial depth h, soil spring stiffness k s , pipeline longitudinal bending stiffness EI;

[0007] S2. Calculate the equivalent load P 2 transmitted to the top of the pipeline according to the parameters obtained in step S1;

[0008] S3. Calculate the deformation, rotation angle, shear force, or bending moment of the pipeline joint when the moment acts on the pipeline joint according to the equivalent load P 2 obtained in step S2;

[0009] S4. Output the calculation results according to step S3, and optimize the structural and construction design parameters of the pipeline joint.

[0010] Specifically, in step S2, the equivalent load P 2 is calculated by formula (1):

[0011] (1);

[0012] where P 1 is the magnitude of the traffic load acting on the ground, with the unit of kN;

[0013] w is the length in the direction perpendicular to the pipeline axis, with the unit of m;

[0014] θ is the foundation stress diffusion angle;

[0015] h is the buried depth of the pipeline;

[0016] where is obtained by calculation using formula (2):

[0017] (2);

[0018] Calculate using formula (3):

[0019] (3);

[0020] D is the pipeline diameter, with the unit of m;

[0021] l 1 is the length along the pipeline axis, with the unit of m.

[0022] Specifically, in step S3, according to different situations of the moment acting on the pipeline joint, the corresponding calculation routes are established, including:

[0023] If it is a moment release pipeline joint, calculate the maximum total rotation angle and the maximum shear force ;

[0024] If it is a moment fully transmitted pipeline joint, calculate the maximum bending moment and the maximum shear force ;

[0025] If it is a moment partially transmitted pipeline joint, based on the relationship between the bending moment of the moment partially transmitted pipeline joint and its total rotation angle , calculate the bending moment of the pipeline joint.

[0026] Furthermore, when it is a moment release pipeline joint, it includes:

[0027] (a) Under the condition of a = l 2 / 2, calculate the maximum total rotation angle through the rotation angle formula ;

[0028] (b) Under the conditions of a = l 2 , b = 0, calculate the maximum shear force through the shear force formula:

[0029] ;

[0030] where a and b are the lengths of the pipelines on both sides of the pipeline joint affected by the load, and a + b = l 2 ;

[0031] is the soil spring stiffness, with the unit of kN / m 2 .

[0032] Further, under the action of ground traffic load, the deflection deformation of the socket end of the pipeline joint downward can be calculated by the following formula (4):

[0033] (4);

[0034] In the formula,

[0035] (5);

[0036] (6);

[0037] (7);

[0038] (8);

[0039] (9);

[0040] In the formula, EI is the longitudinal bending stiffness of the pipeline, with the unit of kN•m 2 ;

[0041] By taking the derivative of formula (4), the rotation angle β of the socket end of the pipeline joint can be obtained:

[0042] (10);

[0043] When a = / 2, the rotation angle of the socket end of the pipeline joint is equal to the rotation angle of the spigot end of the pipeline joint. At this time, the total rotation angle of the pipeline joint reaches the maximum value. According to formula (10), it can be obtained:

[0044] (11).

[0045] Furthermore, the method for calculating the maximum shear force of the pipe joint is as follows:

[0046] When a = , and b = 0, the shear force at the pipe joint reaches the maximum. At this time, the downward deflection deformation of the socket end of the pipe joint , according to formula (4), formula (12) can be obtained:

[0047] (12);

[0048] Meanwhile, the shear force of the pipe joint and the downward deflection deformation of the socket end of the pipe joint have the relationship as shown in formula (13):

[0049] (13);

[0050] Substitute formula (12) into formula (13) to obtain the maximum shear force of the pipe joint :

[0051] (14).

[0052] Furthermore, for a pipe joint with complete moment transfer, it includes:

[0053] (a) Under the condition of a = b = l 2 / 2, based on the principle of moment superposition, calculate the maximum moment through formula

[0054] ;

[0055] (b) Under the condition of a = l 2 , and b = 0, calculate the maximum shear force under extreme loads through the shear force formula

[0056] ;

[0057] where a and b are the pipe lengths on both sides of the pipe joint affected by the load, and a + b = l 2 .

[0058] Furthermore, the load transmitted to the top of the pipe is P 2 , and the bending moment at the pipe joint can be calculated by the following formula (15):

[0059] (15);

[0060] When a = b = / 2, the bending moment at the pipe joint reaches the maximum value. According to formula (15), it can be obtained:

[0061] (16).

[0062] Further, the shear force at the pipe joint is calculated by the following formula (17):

[0063] (17);

[0064] When a = l 2 , b = 0, the shear force at the pipe joint reaches the maximum value. According to formula (17), we can get:

[0065] (18).

[0066] Further, when the moment part is transferred to the pipe joint, the relationship between the moment part transferred to the pipe joint moment and its total joint rotation angle is expressed as formula (19):

[0067] (19);

[0068] In the formula, r is the rotational stiffness of the pipe joint;

[0069] At the same time, the pipe joint moment can also be calculated by the following formula (20):

[0070] (20);

[0071] Substituting formula (19) into formula (20), we can get

[0072] (21);

[0073] For the moment at the pipe joint where the moment is completely transferred , it can be calculated by the following formula (22):

[0074] (22);

[0075] Substituting formula (21) and formula (22) into formula (19), we can get:

[0076] (21).

[0077] Where M j1 is the moment at the pipe joint where the moment is completely transferred, M j2 is the moment at the pipe joint where the moment is partially transferred, α 1 is the total joint rotation angle at the pipe joint where the moment is completely transferred, and α 2 is the total joint rotation angle at the pipe joint where the moment is partially transferred.

[0078] Further, the load acting area w×l 1 is determined according to the vehicle wheelbase and wheel pressure distribution.

[0079] Compared with the prior art, the present invention has the following beneficial effects:

[0080] 1. The prior art mostly focuses on the influence of ground traffic loads on continuous pipelines. However, the present invention, by establishing classified mechanical models (moment release, complete transfer, partial transfer), combines the soil spring stiffness and the longitudinal bending stiffness of the pipeline, and for the first time systematically quantifies the stress concentration effect, angular deformation, shear force and bending moment at the pipeline joint, filling the gap in the analysis of the local mechanical behavior of pipeline joints in the prior art.

[0081] 2. For the three cases of moment release, complete transfer and partial transfer, the present invention respectively provides corresponding calculation formulas and models, which can be flexibly adapted to the requirements of different engineering scenarios, and solves the problem of insufficient calculation accuracy caused by ignoring the differences in joint types in the existing methods.

[0082] 3. By quantifying the deformation and stress changes at the joint under traffic loads, the present invention can provide theoretical support for the structural health and safety design of pipeline joints, reduce the risks of water leakage, air leakage or fracture caused by joint failure, and ensure the safe operation of the urban lifeline system.

[0083] 4. Through the formulaic parameter transfer and model matching, the present invention transforms the complex soil-pipeline interaction problem into a programmable calculation step, greatly reducing the time cost of traditional empirical analysis or finite element simulation, and providing an efficient tool for engineering design and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] The following further specifically describes the present invention in conjunction with the drawings and specific embodiments, and the above and / or other advantages of the present invention will become clearer.

[0085] Figure 1 is a flowchart of a design method for a buried flexible pipeline joint structure under ground traffic loads according to the present invention;

[0086] Figure 2 is a three-dimensional schematic diagram of a flexible pipeline joint affected by ground traffic loads;

[0087] Figure 3 is a plan schematic diagram of a flexible pipeline joint affected by ground traffic loads. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0088] The present invention can be better understood according to the following embodiments.

[0089] The following embodiments further explain and illustrate the technical solutions of the present invention. It is specifically pointed out that each specific implementation manner is a concretization and explanation of the technical solution, and should not be regarded as a limitation on the protection scope of the present invention. Those of ordinary skill in the art still have the right to modify the technical solutions of these embodiments and perform equivalent replacements on some or all of the technical features, and these modifications or replacements do not change the essence of the corresponding technical solutions and do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0090] As shown in the Figure 1 accompanying drawings, a design method for buried flexible pipe joint structures under ground traffic loads according to this embodiment includes the following steps:

[0091] S1: Obtain parameters: ground traffic load P 1 , load acting area w×l 1 , foundation stress diffusion angle θ, pipe diameter D, pipe burial depth h, soil spring stiffness k s , longitudinal bending stiffness EI of the pipe;

[0092] S2: Calculate the equivalent load P 2 transmitted to the top of the pipe;

[0093] S3: According to different situations where the moment acts on the pipe joint, establish corresponding calculation routes to calculate the deformation, rotation angle, shear force or bending moment of the joint;

[0094] S4: Output the calculation results and optimize the structural and construction design parameters of the pipe joint.

[0095] Among them, the specific calculation routes for S2 and S3 are as follows:

[0096] As shown in the Figure 2 and Figure 3 accompanying drawings, the magnitude of the traffic load acting on the ground is P 1 (kN), and the acting area is w (m)×l 1 (m), where w is the length in the direction perpendicular to the pipe axis, and l 1 is the length in the direction along the pipe axis. The foundation stress diffusion angle is θ, the pipe diameter is D (m), and the burial depth is h (m).

[0097] (1) When the pipe joint is a moment-releasing pipe joint:

[0098] ① Calculate the maximum total rotation angle of the pipe joint

[0099] The load P 2 transmitted to the top of the pipe is:

[0100] (1);

[0101] In the formula,

[0102] (2);

[0103] (3);

[0104] Under the action of ground traffic load, the downward flexural deformation of the socket end of the pipe joint can be calculated by the following formula:

[0105] (4);

[0106] In the formula,

[0107] (5);

[0108] (6);

[0109] (7);

[0110] (8);

[0111] (9);

[0112] In the formula, k s is the soil spring stiffness (kN / m 2 ), and EI is the longitudinal flexural stiffness of the pipe (kN•m 2 ).

[0113] Taking the derivative of formula (4), the rotation angle β of the socket end of the pipe joint can be obtained:

[0114] (10);

[0115] When a = / 2, the rotation angle of the socket end of the pipe joint is equal to the rotation angle of the spigot end of the pipe joint. At this time, the total rotation angle a 1 of the pipe joint reaches the maximum value. According to formula (10), it can be obtained that

[0116] (11);

[0117] ② Calculate the maximum pipe joint shear force

[0118] When a = l 2 , b = 0, the shear force at the pipe joint reaches the maximum. At this time, the downward flexural deformation of the socket end of the pipe joint. According to formula (4), it can be obtained that

[0119] (12);

[0120] Meanwhile, the shear force V of the pipe joint j1 and the downward deflection of the socket end of the pipe joint have the following relationship

[0121] (13);

[0122] Substituting formula (12) into formula (13) gives the maximum shear force V of the pipe joint j1max ,

[0123] (14);

[0124] (2) When the pipe joint is a moment fully transmitted pipe joint

[0125] ① Calculate the maximum bending moment of the pipe joint

[0126] The load transmitted to the top of the pipe is P 2 , and the bending moment at the pipe joint can be calculated by the following formula

[0127] (15);

[0128] When a = b = l 2 / 2, the bending moment at the pipe joint reaches the maximum value. According to formula (15),

[0129] (16);

[0130] ② Calculate the maximum shear force of the pipe joint

[0131] The shear force at the pipe joint can be calculated by the following formula

[0132] (17);

[0133] When a = l 2 , b = 0, the shear force at the pipe joint reaches the maximum value. According to formula (17),

[0134] (18);

[0135] (3) When the pipe joint is a moment partially transmitted pipe joint

[0136] The relationship between the bending moment M of the moment partially transmitted pipe joint j2 and its total joint rotation angle α 2 can be expressed as

[0137] (19);

[0138] where r is the rotational stiffness of the pipe joint

[0139] Meanwhile, the bending moment M of the pipe joint j2 can also be calculated by the following formula

[0140] (20);

[0141] Substituting formula (19) into formula (20), we can get

[0142] (21);

[0143] For the bending moment M at the pipe joint with complete moment transfer j1 , it can be calculated by the following formula

[0144] (22);

[0145] Substituting formula (21) and formula (22) into formula (19), we can get

[0146] (23).

[0147] Substituting the measured data of flexible pipes in a certain section into the above calculation route, specifically as follows:

[0148] The diameter D of the corrugated steel pipe is 0.94 m, the burial depth h is 0.61 m, and the longitudinal flexural rigidity EI is 700 kN•m 2 , and the soil spring stiffness k s is 23500 kN / m 2 , the traffic load P acting on the ground 1 is 186.9 kN, and the acting area is w (m) × l 1 (m) = 0.51m × 0.25 m, and the foundation stress diffusion angle is 33°.

[0149] (1) When the pipe joint is a moment release pipe joint:

[0150] ① Calculate the maximum total pipe joint rotation angle

[0151] According to formula (2), we can get

[0152]

[0153] According to formula (3), we can get

[0154]

[0155] According to formula (1), we can get

[0156] =

[0157] According to formula (9), it can be obtained that

[0158]

[0159] According to formula (11), the total maximum rotation angle of the pipeline joint can be obtained

[0160]

[0161] ② Calculate the maximum shear force of the pipeline joint

[0162] According to formula (14), it can be obtained that

[0163]

[0164] (2) When the pipeline joint is a moment fully transmitted pipeline joint:

[0165] ① Calculate the maximum bending moment of the pipeline joint

[0166] According to formula (16), it can be obtained that

[0167]

[0168] ② Calculate the maximum shear force of the pipeline joint

[0169] According to formula (18), it can be obtained that

[0170]

[0171] (3) When the pipeline joint is a moment partially transmitted pipeline joint:

[0172] The rotational stiffness of the moment partially transmitted pipeline joint is 500 kN•m / rad. According to formula (21), the maximum bending moment of the pipeline joint can be obtained:

[0173]

[0174] In order to verify that the values calculated by the calculation route are within an acceptable error range, the same parameters of flexible pipelines in the same section are measured actually. The test methods refer to [1] "Technical Specification for Buried Socket and Spigot Flexible Joint Steel Pipe Pipelines" (T / CECS 492-2017); [2] "Technical Specification for Buried Plastic Drainage Pipelines" (CECS 164:2004); [3] Gao Yifan. "Research on the Ultimate Bearing Capacity of Composite Flexible Pipes under Combined Bending and External Pressure Loads" [D]. Zhejiang University, 2023.

[0175] The test comparison results are as follows:

[0176] Table 1 Comparison between the test measured values and the calculated values of the present invention

[0177]

[0178] As can be seen from the table, the errors between the calculated values and the experimentally measured values are all less than 5%, indicating that this calculation method is reliable and effective when calculating the influence of ground traffic loads on underground pipeline joints.

[0179] In S4, based on the calculated numerical results, evaluate whether the current flexible pipeline joint structure can withstand the corresponding influence. If it exceeds the tolerable threshold, optimize the structural and construction design parameters of the pipeline joint. Specifically, it includes:

[0180] (1) Improve the pipe grade or increase the wall thickness to enhance the self - resistance of the pipeline;

[0181] (2) Install a pipe sleeve at the pipeline joint position or set a flexible material buffer layer around the pipeline to reduce the influence of ground traffic loads.

[0182] The present invention provides an idea and method for the structural design of buried flexible pipeline joints under the action of ground traffic loads. There are many methods and ways to specifically implement this technical solution. The above - mentioned is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. Each component not clearly defined in this embodiment can be realized by existing technologies.

Claims

1. A method for designing a buried flexible pipe joint structure under ground traffic load, characterized in that: The steps include: S1. Obtain parameters: ground traffic load P1, load action area w×l1, foundation stress diffusion angle θ, pipeline diameter D, pipeline burial depth h, soil spring stiffness k s , pipeline longitudinal bending stiffness EI; S2, calculating the equivalent load P2 transmitted to the top of the pipeline according to the parameters obtained in step S1; S3, according to the equivalent load P2 in step S2, calculating the deformation, rotation angle, shear force or bending moment of the pipe joint when the moment acts on the pipe joint; S4. According to the calculation results output in step S3, the structure and construction design parameters of the pipe joint are optimized.

2. A method for designing a buried flexible pipe joint structure under ground traffic loads as claimed in claim 1, characterized in that: In step S2, the equivalent load P2 is calculated by formula (1): （1）； Where P1 is the traffic load acting on the ground, in kN; w is the length in the direction perpendicular to the pipeline axis, in meters; θ is the foundation stress diffusion angle; h is the buried depth of the pipeline; in, Calculated by formula (2): （2）； Calculated by formula (3): （3）； D is the pipe diameter, in m; l1 is the length along the pipeline axis, in meters.

3. A method for designing a buried flexible pipe joint structure under ground traffic loads as claimed in claim 2, characterized in that: In step S3, according to different situations of the moment-acting pipe joints, establishing corresponding calculation routes includes: If it is a torque release pipe joint, calculate the maximum total rotation angle and maximum shear force ; If it is a pipe joint that fully transfers moment, calculate the maximum bending moment and maximum shear force ; If it is a moment-transfer pipe joint, based on the moment-transfer pipe joint bending moment Total rotation angle of its joint Calculate the bending moment of pipe joints .

4. A method for designing a buried flexible pipe joint structure under ground traffic loads as claimed in claim 3, characterized in that: If it is a torque release pipe joint, it includes: (a) Under the condition of a=l2 / 2, the angle formula Calculate the maximum total rotation angle; (b) Under the conditions of a=l2, b=0, according to the shear force formula: Calculate the maximum shear force; Where a and b are the lengths of the pipes on both sides of the pipe joint affected by the load, and a+b=l2; is the soil spring stiffness, unit kN / m 2 .

5. A method for designing a buried flexible pipe joint structure under ground traffic loads as claimed in claim 4, characterized in that: Under the action of ground traffic load, the downward deflection of the pipe joint socket end can be calculated using the following formula (4): （4）； In the formula, （5）； （6）； （7）； （8）； （9）； Where EI is the longitudinal bending stiffness of the pipeline, unit: kN•m 2 ; By taking the derivative of formula (4), we can obtain the rotation angle β of the pipe joint socket end: （10）； When a = / 2, the angle of the pipe joint socket end is equal to the angle of the pipe joint spigot end. At this time, the total angle of the pipe joint To reach the maximum value, according to formula (10) we get: （11）。 6. A method for designing a buried flexible pipe joint structure under ground traffic loads as claimed in claim 5, characterized in that: The method for calculating the maximum pipe joint shear force is as follows: When a = When b=0, the shear force at the pipe joint reaches the maximum, and the downward deflection of the pipe joint socket end , according to formula (4), we can get formula (12): (12）； At the same time, the shear force of the pipe joint Downward deflection of the pipe joint socket end As shown in formula (13): （13）； Substituting formula (12) into formula (13) yields the maximum pipe joint shear force: : (14）。 7. A method for designing a buried flexible pipe joint structure under ground traffic loads as claimed in claim 3, characterized in that: If it is a pipe joint that fully transmits torque, it includes: (a) Under the condition of a=b=l2 / 2, based on the principle of moment superposition, the formula is: Calculate the maximum bending moment; (b) Under the conditions of a=l2, b=0, according to the shear force formula: Calculate the maximum shear force under extreme loads; Where a and b are the lengths of the pipes on both sides of the pipe joint affected by the load, and a+b=l2.

8. A method for designing a buried flexible pipe joint structure under ground traffic loads as claimed in claim 7, characterized in that: The load transferred to the top of the pipeline is P2, and the bending moment at the pipeline joint can be calculated using the following formula (15): （15）； when a = b= / 2, the bending moment at the pipe joint reaches the maximum value. According to formula (15), we can get: （16）。 9. A method for designing a buried flexible pipe joint structure under ground traffic loads as claimed in claim 8, characterized in that: The shear force at the pipe joint is calculated by the following formula (17): （17）； When a = l2, b = 0, the shear force at the pipe joint reaches the maximum value. According to formula (17), we can get: （18）。 10. A method for designing a buried flexible pipe joint structure under ground traffic loads as claimed in claim 3, characterized in that: When the moment part is transferred to the pipe joint, the moment part is transferred to the pipe joint bending moment Total rotation angle of its joint The relationship is expressed as formula (19): （19）； Where r is the angular stiffness of the pipe joint; At the same time, the pipe joint bending moment It can also be calculated by the following formula (20): （20）； Substituting formula (19) into formula (20), we can obtain: （21）； For complete moment transfer of bending moments at pipe joints , can be calculated using the following formula (22): （22）； Substituting formula (21) and formula (22) into formula (19), we can obtain: （21） 。

Images