One-piece direct-buried double-pipe fixed joint for direct-buried heating pipelines and its calculation method

Abstract

The present invention relates to an integrated direct-buried double-pipe fixed joint for a direct-buried heating pipeline and a calculation method thereof. The double-pipe fixed joint is characterized in that it includes a double-pipe fixed joint body composed of an H-shaped component and supply and return pipe sections, the H-shaped component is composed of a web and two wing plates; supply and return pipe section holes are provided on the web of the H-shaped component, and the supply and return pipe sections pass through the supply and return pipe section holes respectively and are symmetrically arranged on the front and rear sides of the web; a number of ribs are symmetrically arranged on the front and rear side surfaces of the web, and the ribs surround the supply and return pipe sections and are evenly distributed and symmetrically arranged along their radial directions and connected between the supply and return pipe sections, and between the supply and return pipe sections and the wing plates and the side edges of the web; the outer side of the fixed joint body is coated with an insulation layer and a protective layer. The calculation method comprises the steps of calculating the thrust moment, calculating the wing plate size, determining the web plate size, and determining the number of ribs. Beneficial effect: a one-time formed metal structure fixed joint is used to replace a steel and concrete structure fixed pier, which is small and light, can be directly buried underground, and is simple to construct.

Description

Technical Field

[0001] The present invention relates to the technical field of fixing piers for directly buried heating pipelines, and in particular to an integrated directly buried double-pipe fixing joint for directly buried heating pipelines and a calculation method thereof. Background Art

[0002] When laying direct buried heating pipes, in order to keep the structure firm, the positioning stable and not deformed, fixed piers must be set at a certain distance. The fixed piers are generally made of reinforced concrete structure, such as Figure 1 As shown, reinforced concrete fixed pier A0 is formed by casting two parallel fixed sections B1 and B2, connecting the supply and return water supply and heating pipes, into the reinforced concrete pier body A1. These sections B1 and B2 consist of supply and return pipe sections D1 and D2, each with an annular plate C in the center of the outer sides. These sections extend across the front and rear sides of the fixed pier, respectively. These sections D1 and D2 serve as pipe connectors, their ends welded to the laid supply and return pipes.

[0003] In actual application, the fixed pier has to bear a great force from the heating pipe. This force is transferred to the concrete pier body through the fixed joint, and then transferred to the surrounding soil by the concrete pier body to bear this force.

[0004] The main drawback of reinforced concrete piers is that, because the forces acting on the heating pipes are entirely transmitted to the piers through the anchor joints and then offset by the surrounding soil, the piers are often very large. During construction, site conditions often restrict the production of piers to the required dimensions. Furthermore, during construction, while the anchor joints are prefabricated pipe fittings available on demand, concrete pouring is an on-site process, subject to individual variations due to unpredictable underground site conditions. This can impede the normal construction of conventional reinforced concrete piers. Furthermore, due to construction deadlines and other constraints, the concrete often fails to reach its curing period, directly impacting the performance and quality of the piers and ultimately affecting the strength and stability of the heating pipes.

[0005] In view of the above reasons, the applicant's prior patent CN204986035U "A fixed pier with a supply and return fixed section in one body" provides a fixed pier in which the above-mentioned supply and return fixed sections are fixedly connected as one body through an H-shaped steel connector, wherein the supply and return pipe sections both vertically pass through the web of the H-shaped steel and are fixedly connected to the web through annular plates on the outside of the supply and return pipe sections. In this way, the effect of the two pipes on the concrete is partially converted into an effect between the pipes, and the unbalanced effect of the two pipes is converted into a more balanced joint effect, which is then transmitted to the fixed pier. At this time, the force exerted by the pipes on the fixed pier has been greatly reduced, and there is no need for the concrete body to withstand such force. However, because the H-shaped steel is welded on-site and needs to be protected before being buried directly underground, it is necessary to wrap a concrete protective layer of a certain thickness on each side of the fixed section with the H-shaped steel beyond the surface of the H-shaped steel. The function of this protective layer is not only to provide protection but also to solve the instability problem of the H-shaped steel during application.

[0006] As can be seen from the above, the existing fixed piers with integrated supply and return water fixed joints use prefabricated split fixed joints with annular plates as ready-made structural components during construction. However, the H-shaped steel is temporarily connected on-site to the annular plates on the outside of the supply and return pipe sections. Therefore, this structural component is an on-site fabricated assembly. Among them, the supply and return water fixed joints are prefabricated components with a protective layer, which require secondary processing and welding of H-shaped steel, and on-site protection. In addition, the H-shaped steel material selection calculation is based on the force acting on the heating pipe, and commercially available general specifications of H-shaped steel are selected. The existing commercial H-shaped steel specifications cannot fully meet the needs. In particular, there is the problem of H-shaped steel instability during application. These problems need to be solved by composite concrete.

[0007] Application practice shows that the disadvantage of this on-site secondary composite structure is that the on-site connection of H-shaped steel makes the construction complicated, time-consuming and labor-intensive. The size specifications of commercially available H-shaped steel cannot meet the application needs, especially the subsequent application of the H-shaped steel protective layer and the need to overcome the instability problem, all of which require combined concrete. As a result, after the improvement, it is still a mixed structure of steel and concrete. Although the amount and volume of concrete are greatly reduced, there are still problems such as volume occupation, maintenance period, environmental adaptation, construction quality and efficiency brought about by concrete construction.

[0008] How to improve the existing reinforced concrete fixed pier structure, remove the concrete, avoid adding secondary processed structural parts and eliminate the disadvantages of instability, so as to develop a new type of integrated fixed section, replace the steel and concrete mixed fixed pier with a single metal structure fixed section formed in one step, so as to achieve a small and light weight, simple construction, labor-saving, time-saving and labor-saving effect while ensuring quality has become a concern of the industry. Summary of the Invention

[0009] The main purpose of the present invention is to address the above-mentioned problems and provide an integrated direct-buried double-pipe fixed joint for direct-buried heating pipelines and a calculation method thereof. Through scientific calculation, the double-pipe fixed joint structure is reasonably set to achieve a small and light weight, avoid secondary processing, and be directly buried, thereby achieving the effect of simple construction, saving labor, time, and effort, and ensuring quality, thereby ensuring the firmness and stability of the direct-buried heating pipelines.

[0010] The technical solution adopted by the present invention to solve its technical problem is:

[0011] The invention relates to an integrated direct-buried double-pipe fixed joint for a direct-buried heating pipeline, characterized in that it includes a double-pipe fixed joint body consisting of an H-shaped component and supply and return pipe sections, the H-shaped component being composed of a web and two wing plates symmetrically connected at the top and bottom edges thereof, and the dimensions of the web and the two wing plates being calculated according to usage requirements; on the web of the H-shaped component, supply and return pipe section holes are centrally symmetrically arranged along its horizontal centerline, the supply and return pipe sections respectively pass through the supply and return pipe section holes perpendicular to the web and are symmetrically arranged at the front and rear sides of the web, the supply and return pipe sections being fixed to the web with their pipe walls respectively closely adhering to the hole walls of the supply and return pipe section holes; a plurality of ribs are symmetrically arranged on the front and rear side surfaces of the web, the plurality of ribs respectively surrounding the supply and return pipe sections and symmetrically arranged along their radial directions and connected between the supply and return pipe sections and between the supply and return pipe sections and the wing plates and side edges of the web on the same side; and an insulation layer and a protective layer are sequentially coated on the outside of the fixed joint body from the inside to the outside.

[0012] The thickness of the web is the same as that of the wing, and the height of the rib is the same as the overhanging width of the wing; the number of ribs is set as follows: when the pipe diameter is ≤DN150, 4 8mm thick ribs are set on both sides of the web; when the pipe diameter is in the range of DN200-600, 8 8mm thick ribs are set on both sides of the web; when the pipe diameter is in the range of DN700-1000, 12 20mm thick ribs are set on both sides of the web; when the pipe diameter is in the range of DN1200-1400, 16 25mm thick ribs are set on both sides of the web.

[0013] The double-tube fixed section body is an integral steel casting.

[0014] The heat-insulating layer is a polyurethane foam plastic layer with a thickness of 50-60 mm; the protective layer is a high-density polyethylene layer with a thickness of 6-8 mm.

[0015] A method for calculating the main body of the double-tube fixed joint of the direct-buried double-tube fixed joint is characterized by comprising the following steps:

[0016] (1) Calculate the moment generated by the thrust on the return pipe caused by the water supply pipe at the web of the double-pipe fixed joint body;

[0017] (1.1) Determine the reasonable center distance of the supply and return water pipes according to different pipe diameters;

[0018] (1.2). Calculate the torque;

[0019] M=T*d;

[0020] Where: M is the torque, (KNm);

[0021] T is the thrust of the double-tube fixed joint of the water supply pipe, (KN);

[0022] d is the center distance between the supply and return pipes, (m);

[0023] (2) Calculate the wing plate size;

[0024] (2.1) Determine the net section modulus of the flange that can withstand the above moment M strength in accordance with the following sections and clauses ① to ④ of the Standard for Design of Steel Structures GB50017-2017:

[0025] ① Calculation formula in Section 6.1.1;

[0026] ② Table 3.5.1 “Plate width-to-thickness ratio grades and limits”;

[0027] ③ Clause 6.1.2 on the plastic development coefficient of the section;

[0028] ④ Table 4.4.1 “Design strength indexes of steel materials”;

[0029] ① Calculation formula in Section 6.1.1:

[0030]

[0031] Where:

[0032] M x 、M y ——Design value of bending moment about x-axis and y-axis at the same cross section (N*mm);

[0033] W nx 、W ny ——Net section modulus about x-axis and y-axis (mm 3 );

[0034] γ x , γ y ——Plastic development coefficient of the section about the principal axes x and y;

[0035] f——Design value of steel bending strength (N / mm 2 );

[0036] The supply and return pipes connected to the main body of the double-pipe fixed joint are laid along the X-axis, and the vertical pipe laying direction is the Y-axis;

[0037] Here, for the double-tube fixed section body: M y =M;M x =0;

[0038] ② In Table 3.5.1 “Plate width-to-thickness ratio grades and limits”, the plate width-to-thickness ratio is divided into 5 grades S1 to S5;

[0039] ③ Clause 6.1.2 stipulates that “γ x , γ y The value shall be taken as follows: When the width-to-thickness ratio of the plate is S4 or S5, the cross-section plastic development coefficient shall be taken as 1.

[0040] Here, for the double-tube fixed section body: γ y Take 1;

[0041] ④ According to the application convention, the plate thickness used in the main body of the double-tube fixed joint is within the range of 16 to 40 mm. Based on this, the material and bending strength design value f of the plate are determined according to Table 4.4.1;

[0042] Therefore, the combined cross-section W of the two wing plates can be calculated from My, γy and f. ny The net section modulus of:

[0043] W ny ≥M y / (γ y *f);

[0044] (2.2) Derive the wing plate calculation formula;

[0045] (2.2.1) Determine the net section modulus W of the combined two rectangles whose area is by*t. ny :According to the material mechanics formula, the moment of inertia of the rectangular section I y1 =t*by 3 / 12, we get the moment of inertia I of the combined section of two rectangles with an area of by*t y =2*t*by 3 / 12;

[0046] (2.2.2) According to the formula definition provided in Section 6.1.1 of the "Standard for Design of Steel Structures" GB50017-2017: W nx 、W ny The net section modulus about the x-axis and y-axis. Section modulus is the moment of resistance of the section. From the mechanics of materials, it is the ratio of the moment of inertia of the section about its centroid to the distance from the farthest point on the section to the centroid. Therefore, the combined section modulus W of two rectangles with an area of by*t is y =I y / by / 2=2tby 2 / 6; then derive: W y=2tby 2 / 6; Since there is no opening or other weakening in the cross section, its net section modulus is equal to the section modulus, that is, W ny =W y ;

[0047] Where: W ny is the rectangular net section modulus;

[0048] W y is the rectangular section modulus;

[0049] t is the wing thickness (mm);

[0050] by is the wing width (mm);

[0051] (2.3) Calculate and determine the wing plate size:

[0052] (2.3.1) First, set the value of the wing plate thickness t and calculate the value of the wing plate width by;

[0053] (2.3.2) Set the web thickness t f The value of web thickness t f The setting value of = the setting value of the wing plate thickness t;

[0054] (2.3.3) Calculate the value of the wing panel extension width b;

[0055] (2.3.4) Calculate the value of the wing length L0;

[0056] Wing length L0=d+2R+2d1

[0057] Where: d is the center distance between the supply and return pipes;

[0058] R is the radius of the supply and return pipes;

[0059] d1 is the length of the rib connection section where the outer wing plates of the supply and return pipes extend;

[0060] (2.3.5) Calculate the ratio of the wing panel's overhang width (b) to its thickness (t) (S = b / t). If the S value is within the range of S4-S5, the requirement is met and the wing panel thickness and overhang width are determined. Otherwise, recalculate.

[0061] Add the margin to the determined value of the wing plate thickness as the applicable value of the wing plate thickness;

[0062] (3) Determine the web size: the web thickness is the same as the wing thickness, the web height is 100-120mm larger than the outer diameter of the supply and return pipes, and the web length is the same as the wing length;

[0063] (4) Set ribs on the web and determine the appropriate number of ribs.

[0064] The beneficial effects of the present invention are as follows: compared with the prior art, (1) the integrated direct-buried double-tube fixed joint provided has a double-tube fixed joint body composed of an H-shaped component and supply and return pipe sections, and the H-shaped component is composed of a web and two wing plates, and the size values of the web and the two wing plates are calculated according to the use requirements, rather than the existing commercially available steel products, so that the size is accurate and meets the performance requirements. Furthermore, ribs are added to the web, connecting between the supply and return pipe sections, between the supply and return pipe sections and the two wing plates, and between the side edges of the web on the same side. Thus, concrete is not required, further solving the problem of instability. The main body of the double-tube fixed joint is an integral steel casting and the outer insulation layer and protective layer are completed at one time. This prefabricated part is directly used as a finished pipe fitting in the on-site direct-buried pipeline installation construction, omitting on-site welding and concrete coating operations, and also removing the concrete structure. This makes it possible to achieve the performance indicators of the original concrete fixed pier by using a small and light double-tube fixed section, overcome environmental restrictions, expand the scope of application, bury it directly underground, simplify the construction process, save labor, time and effort, ensure construction quality and improve construction efficiency.

[0065] (2) This invention also provides a calculation method based on the "Steel Structure Design Standard" GB50017-2017, scientifically calculating the dimensions of the two wings and web of the double-pipe fixing joint body and appropriately selecting the ribs. This ensures the performance and quality of the concrete-free, one-piece, direct-buried double-pipe fixing joint provided by the present invention, and ensures the firmness and stability of the heating pipeline. Application practice has demonstrated that the use of this double-pipe fixing joint ensures the smooth and safe operation of the heating pipeline network, meeting normal operating standards. This pipe fitting has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 This is a schematic diagram of the existing concrete fixing pier structure for directly buried heating pipelines;

[0067] Figure 2 This is the appearance diagram of the integrated direct-buried double-pipe fixed joint provided by the present invention;

[0068] Figure 3 yes Figure 2 Schematic diagram of the three-dimensional structure of the main body of the middle double-tube fixed section

[0069] Figure 4 yes Figure 2 Schematic diagram of the main structure of the double-tube fixed section

[0070] Figure 5 It is a schematic diagram of the structural dimensions of the H-shaped member cross section;

[0071] Figure 6 This is a schematic diagram of the force analysis of an integrated direct-buried double-pipe fixed joint;

[0072] Figure 7 This is a simplified diagram of the pipeline arrangement of the present invention applied in a heating pipeline.

[0073] In the picture:

[0074] A0 reinforced concrete fixed pier, A1 pier body, B1 water supply fixed joint, B2 return water fixed joint, C annular plate, D1 water supply pipe section, D2 return water pipe section, E integrated direct buried double pipe fixed joint, F double pipe fixed joint body, G water supply pipe, H return water pipe;

[0075] by wing plate width, b wing plate extension width, d supply and return pipe center distance, d1 supply and return pipe outer wing plate extension rib connection section length, h web plate height, h1 rib plate height; t wing plate thickness, tf web plate thickness; L0 wing plate length, L1-L2 distance between double pipe fixed sections, L3 web plate length;

[0076] 11 water supply pipe section, 12 return pipe section, 2H-type component, 21 wing plate, 22 web plate, 3 rib plate, 4 insulation layer, 5 protective layer, 6 compensator.

[0077] The present invention is described in detail below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0078] Figures 2 to 6 An integrated direct-buried double-pipe fixed joint E for a direct-buried heating pipeline is shown, which is characterized in that it includes a double-pipe fixed joint body F composed of an H-shaped component 2 and supply and return pipe sections 11 and 12. The H-shaped component is composed of a web 22 and two wing plates 21 symmetrically connected at the top and bottom edges and perpendicularly connected, and the dimensions of the web and the two wing plates are calculated according to the requirements of use; on the web 22 of the H-shaped component, supply and return pipe section holes are symmetrically arranged along its horizontal center line, and the supply and return pipe sections 11 and 12 respectively pass through the supply and return pipe section holes perpendicular to the web and are symmetrically arranged on both sides of the web. The supply and return pipe sections 11 and 12 are fixed to the web 22 with their pipe walls tightly attached to the hole walls of the supply and return pipe section holes.

[0079] A number of ribs 3 are symmetrically arranged on the front and rear side surfaces of the web 22. The ribs are respectively arranged around the supply and return pipe sections 11 and 12 and are evenly distributed and symmetrically arranged along their radial directions and connected between the supply and return pipe sections, and between the supply and return pipe sections and the wing plates 21 and side edges of the web 22 on the same side; the outer side of the fixed node body F is sequentially coated with an insulation layer 4 and a protective layer 5 from the inside to the outside.

[0080] Another feature of the present invention is that the thickness of the web 22 is the same as the thickness t of the wing, and the height h1 of the ribs 3 is the same as the overhanging width b of the wing. The number of ribs is set as follows: when the pipe diameter is ≤ DN150, four 8mm thick ribs are set on each side of the web; when the pipe diameter is between DN200 and DN600, eight 8mm thick ribs are set on each side of the web; when the pipe diameter is between DN700 and DN1000, twelve 20mm thick ribs are set on each side of the web; and when the pipe diameter is between DN1200 and DN1400, sixteen 25mm thick ribs are set on each side of the web.

[0081] The present invention is also characterized in that the double-tube fixed joint body E is an integral steel casting, which is integrally cast during processing.

[0082] The present invention is also characterized in that the heat-insulating layer 4 is a polyurethane foam plastic layer with a thickness of 50-60 mm; and the protective layer 4 is a high-density polyethylene layer with a thickness of 6-8 mm.

[0083] Working principle of the present invention

[0084] Hereinafter, the integrated direct-buried double-pipe fixed joint will be referred to as the "double-pipe fixed joint".

[0085] A heating pipeline typically consists of two pipes: a supply pipe and a return pipe. Water is transported from the heat source through the supply pipe to the heat user. After dissipating heat in the heat user, the water temperature drops and returns to the heat source through the return pipe. The water in the supply pipe is hot, and due to thermal expansion and contraction, thrust is first generated at the double-pipe fixed joint E during operation. Since the web 22 is directly connected to the pipe, this thrust is transmitted to the web. At this time, the return pipe is at room temperature and has no hot water. This creates a moment at the web, with the return pipe as the point of action and the distance d between the center of the supply and return pipes as the lever arm. The double-pipe fixed joint itself withstands the thrust of thermal expansion and contraction. This thrust is transmitted to the web, but the web alone is insufficient to withstand the torque. Therefore, wings 21 are provided at its top and bottom edges to withstand the torque, thus achieving thermal force balance. The dimensions of the wings and web are determined through calculations and operational state analysis. They are scientifically accurate and meet the requirements for withstanding pipeline thrust. In particular, ribs are evenly and symmetrically arranged along the radial direction around the supply and return pipe sections. The ribs are welded to the pipe wall, web and wing plates on three sides, which not only strengthens the pipeline at the double-pipe fixed joint but also solves the instability of the plate.

[0086] Early designs involved casting two discrete anchoring sections with annular outer edges within reinforced concrete, with the concrete supporting the thrust of the two anchoring sections. More recently, anchoring piers with H-shaped steel connectors have eliminated the need for concrete to support the thrust. However, to address instability and protection, concrete must still be combined, creating a hybrid steel-concrete structure. This still presents challenges such as the volume occupied by concrete construction, environmental restrictions, and maintenance time.

[0087] The present invention, through structural improvements, provides a one-piece, direct-buried double-pipe anchor. Targeted to different heating pipelines, the dimensions and number of the anchor body F are determined through scientific calculations. This includes selecting the appropriate sized wing plates 21, web plates 22, and ribs 3, along with the appropriate number of ribs. This transforms the thrust of the water supply pipes into interactions within the double-pipe anchor, completely eliminating the need for concrete and replacing traditional reinforced concrete anchor piers with the double-pipe anchor. The double-pipe anchor is specifically cast as a single piece, with a single, integrated outer insulation and protective coating, eliminating the need for secondary processing. During construction, it can be directly buried underground, making it convenient, shortening the construction period, saving investment, and ensuring construction quality.

[0088] The present invention provides a method for calculating the double-tube fixed section body F of the double-tube fixed section E. The calculation steps are described in detail below with reference to specific embodiments.

[0089] like Figure 7 The figure shows a section of directly buried heating pipeline in Tianjin, with nodes ① to ⑤. Nodes ①, ③, and ⑤ are double-pipe fixed joints E, and nodes ② and ④ are compensators 6. The buried depth is 1.5 m, the pipe diameter is DN600, and the center-to-center distance d is 1 m. The distance between each double-pipe fixed joint is L1 = L2 = 70 m. The supply and return water temperatures are 130 / 70°C, and the pressure is 1.6 MPa. In the figure, G represents the supply pipe, and H represents the return pipe. In this heating pipeline, the fixed joints are subjected to a thrust force T of 400 kN.

[0090] At this time, the construction unit proposed the ordering conditions of node ③ fixed joint to the manufacturer, namely: the technical indicators of the double-pipe fixed joint are: "DN600, PN16, T=400KN", DN600 represents the pipe with a nominal diameter of 600mm; PN16 represents the design pressure of 1.6 MPa, which controls the pipe wall thickness; T=400KN means that the fixed joint can withstand a thrust of 400KN.

[0091] The thrust calculation adopts conventional algorithm and is based on the Technical Specifications for Directly Buried Hot Water Pipelines for Urban Heating.

[0092] Calculated according to CJJ / T81-2013.

[0093] For the above project, the fixed joint adopts the double-tube fixed joint provided by the present invention, and the thrust T is the thrust borne by the water supply pipe at the web position of the double-tube fixed joint body F.

[0094] For this heating pipeline, the specific steps for calculating the double-pipe fixed joint body of the double-pipe fixed joint are as follows:

[0095] (1) Calculate the moment generated by the thrust on the return pipe caused by the water supply pipe at the web of the double-pipe fixed joint body;

[0096] (1.1) Determine the reasonable center distance d of the supply and return water pipes according to different pipe diameters;

[0097] The center distance d = 1m provided by the construction company for the supply and return pipes. The outer diameter of the directly buried DN600 pipe, including the insulation and protective layer, is 760mm. The double-pipe fixed joint uses 2m-long supply and return pipe sections 11 and 12. During construction, the ends of the supply and return pipe sections will need to be welded to the supply and return pipes. Therefore, the value of d should take into account the welding space. A clear distance of approximately 200mm is ideal. A larger value will increase the torque. Therefore, the d = 1m provided by the construction company is appropriate.

[0098] (1.2). Calculate the torque;

[0099] M=T*d;

[0100] Where: M is the torque (KNm);

[0101] T is the thrust of the double-tube fixed joint of the water supply pipe, (KN);

[0102] d is the center distance between the supply and return pipes, (m);

[0103] See also Figures 5-6 , the pipeline is laid along the X-axis. O1 is the axis of the water supply pipe; O2 is the axis of the return pipe; T is the thrust of the double-pipe fixed joint of the water supply channel, that is, the thrust of the water supply pipe at the web position. In this example, T = 400KN, and the torque M generated is B =400KNM.

[0104] (2) Calculate the wing plate size;

[0105] (2.1) Determine the net section modulus of the flange that can withstand the above moment M strength in accordance with the following sections and clauses ① to ④ of the "Standard for Design of Steel Structures" GB50017-2017:

[0106] ① Calculation formula in Section 6.1.1,

[0107] ② Table 3.5.1 “Plate width-to-thickness ratio grades and limits”;

[0108] ③ Clause 6.1.2 on the plastic development coefficient of the section;

[0109] ④ Table 4.4.1 “Design strength indexes of steel materials”;

[0110] ① Calculation formula in Section 6.1.1:

[0111]

[0112] Where:

[0113] M x 、M y——Design value of bending moment about x-axis and y-axis at the same section, (N*mm);

[0114] W nx 、W ny ——Net section modulus about x-axis and y-axis, (mm 3 );

[0115] γ x , γ y ——Plastic development coefficient of the section about the principal axes x and y;

[0116] f——design value of steel bending strength, (N / mm 2 );

[0117] The supply and return pipes connected to the main body of the double-pipe fixed joint are laid along the X-axis, and the vertical pipe laying direction is the Y-axis;

[0118] Here, for the double-tube fixed section body: M y =M;M x =0;

[0119] ② In Table 3.5.1 “Plate width-to-thickness ratio grades and limits”, the plate width-to-thickness ratio is divided into 5 grades S1 to S5. The higher the grade, the greater the plate width-to-thickness ratio and the wider the plate.

[0120] ③ Clause 6.1.2 stipulates that “γ x , γ y The value shall be taken as follows: When the width-to-thickness ratio of the plate is S4 or S5, the cross-section plastic development coefficient shall be taken as 1. ";

[0121] Here, for the double-tube fixed section body: γ y Take 1;

[0122] ④ According to the application convention, the thickness of the plate used for the main body of the double-tube fixed joint is within the range of 16 to 40 mm;

[0123] Application practice shows that the fixed joints of direct-buried heating pipes generally bear greater thrust, and steel with a thickness of less than 16 mm is not suitable for fixed joints; while the properties of steel with a thickness greater than 40 mm will change, which is an unconventional application. Therefore, the thickness of the plate used for the fixed joint is in the range of 16 to 40 mm.

[0124] Based on this, determine the material and bending strength design value f of the steel according to Table 4.4.1,

[0125] In this example: For plates with a thickness between 16 and 40 mm, the material selected is Q235B.

[0126] f=205N / mm 2 ;

[0127] Therefore, My , γ y and f to calculate the combined cross-section W of the two wing plates ny The net section modulus of

[0128] W ny ≥M y / (γ y *f)=400*10 6 / (1*205)=1951cm 3 .

[0129] (2.2) Derive the wing plate calculation formula

[0130] (2.2.1) Determine the net section modulus W of the combined two rectangles whose area is by*t. ny :

[0131] See also Figure 5 According to the material mechanics formula, the moment of inertia of the rectangular section I y1 =t*by 3 / 12, we get the moment of inertia I of the combined section of two rectangles with an area of by*t y =2*t*by 3 / 12;

[0132] (2.2.2) According to the formula definition provided in Section 6.1.1 of the "Standard for Design of Steel Structures" GB50017-2017: W nx 、W ny The net section modulus about the x-axis and y-axis. Section modulus is the moment of resistance of the section. From the mechanics of materials, it is the ratio of the moment of inertia of the section about its centroid to the distance from the farthest point on the section to the centroid. Therefore, the combined section modulus W of two rectangles with an area of by*t is y =I y / by / 2=2tby 2 / 6; then derive: W y =2tby 2 / 6; Since there is no opening or other weakening in the cross section, its net section modulus is equal to the section modulus,

[0133] That is W ny =W y ;

[0134] Where: W ny is the rectangular net section modulus;

[0135] W y is the rectangular section modulus;

[0136] t is the wing thickness (mm);

[0137] by is the wing width (mm);

[0138] (2.3) Calculate and determine the wing plate size;

[0139] (2.3.1) First, set the value of the wing plate thickness t and calculate the value of the wing plate width by;

[0140] By W ny =2tby 2 / 6=1951cm 3 ,

[0141] Use Q235B steel plate with wing plate thickness t=20mm,

[0142] Then by=54cm, that is, the wing width ≥54cm, take by=600mm;

[0143] (2.3.2) Set the web thickness t f The value of web thickness t f The setting value of = the setting value of the wing plate thickness t;

[0144] The "plate width-to-thickness ratio" in Table 3.5.1 above corresponds to the ratio of the flange's overhanging width b to its thickness t, so the web thickness also needs to be determined. For DN600, PN16 direct-buried heating pipes, the pipe wall thickness is generally 8mm. According to the principle of equal strength, the web thickness can be 8mm. However, this is quite different from the flange thickness of 20mm. In addition, the thinner the plate, the more likely it is to become unstable. In particular, since the structure of the present invention has no concrete constraints, it is necessary to consider the plate size and instability in an integrated manner. Here, a 20mm thick steel plate is selected for the web. That is, the web thickness t f =20mm

[0145] (2.3.3) Calculate the value of the wing panel extension width b;

[0146] See also Figure 5 , b=(by-t f ) / 2=(600-20) / 2=290mm;

[0147] (2.3.4) Calculate the value of the wing length L0;

[0148] Wing length L0=d+2R+2d1

[0149] Where: d is the center distance between the supply and return pipes;

[0150] R is the radius of the supply and return pipes;

[0151] d1 is the length of the rib connection section where the outer wing plates of the supply and return pipes extend;

[0152] Depend on Figure 6As can be seen, the wing plate is unloaded outside the pipes and only needs to meet structural requirements. This means a 100mm-long ribbed connection section extending outside the supply and return pipes is sufficient. The wing plate length L0 = 1000 + 2*630 / 2 + 2*100 = 1830mm.

[0153] (2.3.5) Calculate the ratio of the wing panel's overhang width (b) to its thickness (t) (S = b / t). If the S value is within the range of S4-S5, the requirement is met and the wing panel thickness and overhang width are determined. Otherwise, recalculate.

[0154] In this example, the wing panel overhang width b = 290 mm, and S = b / t = 290 / 20 = 14.5. This corresponds to the S4 grade requirement in Table 3.5.1 above. This gives the wing panel thickness of 20 mm and the wing panel overhang width of 290 mm.

[0155] In actual application, to improve structural safety, a 2mm margin is added to the determined wing panel thickness of 20mm as the applicable wing panel thickness. In this example, the applicable wing panel thickness is 22mm.

[0156] (3) Determine the web size: the web thickness is the same as the wing thickness, the web height is 100-120mm larger than the outer diameter of the supply and return pipes, and the web length is the same as the wing length;

[0157] For DN600, PN16 direct buried heating pipe, the pipe specification is φ630*8. In this example, according to the principle of equal strength, the web thickness t f The value is the same as the determined value of the wing plate thickness, which is 20mm. The web height value is 120mm larger than the outer diameter of the supply and return pipes, which is 630mm. The web height h = 750mm and the web length L3 = 1830mm are obtained.

[0158] (4) Install ribs on the web and determine the appropriate number of ribs;

[0159] In the above calculations, the web thickness of 20mm is close to the recommended wing plate thickness of 22mm, but it differs significantly from the pipe wall thickness of 8mm, resulting in unequal strength. Therefore, ribs are evenly and symmetrically distributed radially around the supply and return pipe sections. The ribs are welded to the pipe wall, web, and wing plates on three sides, strengthening the pipe at the double-pipe anchoring joint and preventing plate instability. In this example, for a DN600 direct-buried heating pipe with a pipe diameter ranging from DN200 to DN600, eight 8mm thick ribs are installed on either side of the web.

[0160] Thus, the calculation is completed.

[0161] In this embodiment, the above method is used to calculate: the web thickness t f= 20mm, web height h = 750mm, flange thickness t = 20mm, flange thickness application value is 22mm, flange width by = 600mm, flange overhang width b = 290mm, web length L3 = flange length L0 = 1830mm. Eight 8mm thick ribs are provided on both sides of the web, with rib height h1 = flange overhang width b = 290mm.

[0162] In this embodiment, the polyurethane foam insulation layer covering the outer side of the double-tube fixed joint body has a thickness of 54 mm; the high-density polyethylene protective layer has a thickness of 8 mm.

[0163] Application practice has proven that the integrated direct-buried double-pipe fixing joint provided by this invention significantly reduces its volume compared to existing concrete-bonded fixing piers, overcoming environmental limitations, expanding its application scope, and ensuring construction quality. Direct burial simplifies the construction process, saving labor, time, and effort, improving construction efficiency, and ensuring stable and safe operation of the heating pipe network, meeting normal operating standards. This pipe fitting has broad application prospects.

[0164] The above description is only a preferred embodiment of the present invention and does not constitute any formal limitation on the structure of the present invention. Any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. An integrated direct buried double pipe fixing joint for direct buried heating pipes, characterized in that The invention comprises a double-pipe fixed section body consisting of an H-shaped member and supply and return pipe sections. The H-shaped member is composed of a web and two wing plates symmetrically connected at the top and bottom edges of the web and perpendicularly connected. The sizes of the wing plates and the web are determined by calculation and implementation status analysis. On the web of the H-shaped member, supply and return pipe section holes are symmetrically arranged along its horizontal center line. The supply and return pipe sections are respectively perpendicular to the web and pass through the supply and return pipe section holes and are symmetrically arranged at the front and rear sides of the web. The supply and return pipe sections are fixed to the web in a manner that their pipe walls are tightly attached to the hole walls of the supply and return pipe section holes respectively. A number of ribs are symmetrically arranged on the front and rear side surfaces of the plate, and the ribs are respectively arranged around the supply and return pipe sections and symmetrically distributed along their radial directions and connected between the supply and return pipe sections, as well as between the supply and return pipe sections and the wing plates and web side edges on the same side of each other; the ribs are welded around the pipe walls, web plates and wing plates of the supply and return pipe sections on three sides to strengthen the supply and return pipe sections at the double-tube fixed joint and convert the thrust of the supply and return pipes into mutual action inside the double-tube fixed joint; the outer side of the main body of the double-tube fixed joint is coated with an insulation layer and a protective layer from the inside to the outside.

2. The integrated direct buried double pipe fixing joint for direct buried heating pipe according to claim 1 is characterized in that The thickness of the web is the same as that of the wing, and the height of the rib is the same as the overhanging width of the wing; the number of ribs is set as follows: when the pipe diameter is ≤DN150, 4 ribs with a thickness of 8 mm are set on both sides of the web; when the pipe diameter is in the range of DN200-600, 8 ribs with a thickness of 8 mm are set on both sides of the web; when the pipe diameter is in the range of DN700-1000, 12 ribs with a thickness of 20 mm are set on both sides of the web; when the pipe diameter is in the range of DN1200-1400, 16 ribs with a thickness of 25 mm are set on both sides of the web.

3. The integrated direct-buried double-pipe fixing joint for direct-buried heating pipes according to claim 1 or 2 is characterized in that The double-tube fixed section body is an integral steel casting.

4. The integrated direct-buried double-pipe fixing joint for direct-buried heating pipes according to claim 3 is characterized in that The heat-insulating layer is a polyurethane foam plastic layer with a thickness of 50-60 mm; the protective layer is a high-density polyethylene layer with a thickness of 6-8 mm.

5. A method for calculating the main body of a double-tube fixed joint of a direct-buried double-tube fixed joint as claimed in claim 4, characterized in that The steps include: (1) Calculate the moment on the return pipe caused by the thrust on the supply pipe at the web of the double-pipe fixed joint. (1.1) Determine the reasonable center distance of the supply and return pipes according to different pipe diameters; (1.2) Calculate the torque; M=T*d; Where: M is the moment; T is the thrust of the double-tube fixed joint of the water supply pipe; d is the center distance between the supply and return pipes; (2) Calculate the wing plate dimensions; (2.1) According to the "Steel Structure Design Standard" GB50017-2017, calculate the net section modulus of the flange that can withstand the above moment M strength: The calculation formula is: ； Where: M x 、 M y —Design values of bending moments about the x-axis and y-axis at the same cross section; W nx 、W ny ——net section modulus about the x-axis and y-axis; γ x , γ y ——Plastic development coefficient of the section about the principal axes x and y; f — design value of steel’s bending strength; The supply and return pipes connected to the main body of the double-pipe fixed joint are laid along the X-axis, and the vertical pipe laying direction is the y-axis; y =M;M x =0; Select the section plastic development coefficient 1 corresponding to the plate width-to-thickness ratio of S4 or S5; γ y Take 1; Determine the material and bending strength design value f of the plate; Combined cross section W of the two wing plates ny The net section modulus of: W ny ≥M y / (c) y * f ); (2.2) Derive the wing plate calculation formula; (2.2.1). The moment of inertia I of the combined cross section of two rectangles with area by*t y =2*t*by 3 / 12; (2.2.2). The combined section modulus W of two rectangular sections with area by*t is y =I y / by / 2=2tby 2 / 6; then derive: W y =2tby 2 / 6; where W ny =W y ; Where: W ny is the rectangular net section modulus; W y is the rectangular section modulus; t is the thickness of the wing plate; by is the wing width; (2.3) Calculate and determine the wing plate size: (2.3.1) First, set the value of the wing plate thickness t and calculate the value of the wing plate width by; (2.3.2) Set the web thickness t f The value of web thickness t f The setting value of = the setting value of the wing plate thickness t; (2.3.3) Calculate the value of the wing panel extension width b; (2.3.4) Calculate the value of the wing length L0; Wing length L0=d+2R+2d1 Where: d is the center distance between the supply and return pipes; R is the radius of the supply and return pipes; d1 is the length of the rib connection section where the outer wing plates of the supply and return pipes extend; (2.3.5) Calculate the ratio of the wing panel's overhang width (b) to its thickness (t) (S = b / t). If the S value is within the range of S4-S5, the requirement is met and the wing panel thickness and overhang width are determined. Otherwise, recalculate. Add the margin to the determined value of the wing plate thickness as the applicable value of the wing plate thickness; (3) Determine the web plate dimensions: the web plate thickness should be the same as the wing plate thickness, the web plate height should be 100-120 mm greater than the outer diameter of the supply and return pipes, and the web plate length should be the same as the wing plate length. (4) Install ribs on the web and determine the appropriate number of ribs.

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