Design method of threaded joint and manufacturing method of threaded joint

Abstract

The threaded joint (1) of the present application is a threaded joint (1) provided at the end of a steel pipe (3) and joining the steel pipes (3) to each other, and has a pin side barrel (7) having a pin thread (5) formed by a tapered thread, a box side barrel (11) having a box thread (9) formed by a tapered thread, and the inclination angle of the stabbing flank (5a, 9a) of the thread of the pin thread (5) and the box thread (9) with respect to the right angle direction of the axis of the steel pipe is in the range of 0 degrees to +8 degrees.

Description

Technical Field

[0001] This invention relates to threaded joints, threaded steel pipes, structures, construction methods of structures, landslide suppression piles, construction methods of landslide suppression piles, design methods of threaded joints, manufacturing methods of threaded joints, and manufacturing methods of threaded steel pipes used in landslide suppression steel pipe piles (hereinafter referred to as "landslide suppression piles") located in landslide areas. Background Technology

[0002] Landslide suppression steel pipe piles (hereinafter referred to as "landslide suppression piles") are installed in landslide areas, and their construction sites are often steep slopes where heavy machinery is difficult to transport. Therefore, piles cannot be driven in by tamping; instead, they are installed in pre-drilled holes using auger drills or similar tools. Furthermore, the total length of landslide suppression piles varies depending on site conditions, typically reaching 20–30 meters. However, due to limitations in transportation, construction usually involves splicing approximately 5–8 meters of steel pipe piles on-site simultaneously.

[0003] Because this pile splicing work is carried out in an unstable environment, rapid and reliable operation is strongly required. Furthermore, since it is difficult to predict which ground surface the landslide collapse surface will occur on, landslide suppression piles often need to have cross-sectional properties exceeding the design strength at any point along almost the entire length, including the splice joint.

[0004] Therefore, in the past, the splicing of landslide suppression piles was carried out through on-site welding operations. However, on-site welding in such harsh working environments presents the following problems.

[0005] (1) Because the wall thickness of the steel pipes of the current standard size is relatively thick, welding at a single point takes a long time.

[0006] (2) Due to the poor working environment, the welding quality is prone to decline and it is not easy to ensure the joint strength.

[0007] (3) Due to poor working conditions, it is difficult to ensure the availability of excellent welding technicians.

[0008] (4) High-tensile steel is difficult to use because it is difficult to ensure welding quality in the field.

[0009] Due to these issues, landslide suppression piles based on on-site pile splicing operations must meet all of the following requirements.

[0010] (1) The pile splicing operation is easy and the operation time is short.

[0011] (2) The quality of the joints between the steel pipe piles is well ensured without affecting the working environment and skills.

[0012] (3) The strength of the joint is equal to or higher than that of the steel pipe pile body (hereinafter referred to as the pile body).

[0013] (4) The outer diameter of the joint shall not be greater than that of the pile body.

[0014] (5) It can also be used when the pile body is made of high-tensile steel.

[0015] As a joint for landslide suppression piles addressing the aforementioned requirements, there is a joint constructed as follows: a pile body having a female threaded joint at one end and a male threaded joint at one end having an outer diameter substantially the same as the outer diameter of the female threaded joint; both the female and male threaded joints are formed by tapered threaded joints; the tapered threaded joints have an inclination set to be completed by rotating several times, as well as thread height and thread spacing; the product of the section modulus and material strength at the thread endpoints of the female and male threaded joints is greater than the product of the section modulus and material strength of the pile body (see, for example, Patent Document 1). Additionally, a landslide suppression steel pipe pile joint is disclosed where the male and female threads are tapered threads, the thread tooth shape is trapezoidal, and there are multiple threads, such as 2 to 3 (see, for example, Patent Document 2).

[0016] Existing technical documents

[0017] Patent documents

[0018] Patent Document 1: Japanese Patent Application Publication No. 7-82738

[0019] Patent Document 2: Japanese Patent Application Publication No. 10-252056 Summary of the Invention

[0020] The problem that the invention aims to solve

[0021] The threaded joints of landslide suppression piles require high endurance. On the other hand, in construction sites with poor footholds, manual rotation is required for connection. Moreover, the threaded joints are basically screwed in until the shoulder contacts, but because the connection is carried out in the aforementioned construction sites, sometimes the threads cannot be fully screwed in, resulting in a gap of about 2mm where the shoulder does not contact.

[0022] In this case, although it is possible to achieve a fully engaged state without gaps by using a traction tool, it is very laborious. Therefore, if the premise is to achieve a fully engaged state using a traction tool, the superiority of threaded joints over general field welding joints is diminished.

[0023] Furthermore, threaded joints are generally designed to resist compressive loads using the shoulder and threaded portion, and tensile loads using the threaded portion. Therefore, when a compressive load based on bending load is applied to the threaded joint in an incompletely engaged state (not fully screwed in), the shoulder does not transmit the compressive load; only the threaded portion resists the load. As a result, the full plastic load capacity of the joint steel is not fully utilized, and sometimes the threaded portion on the compression side disengages, leading to joint breakage.

[0024] The present invention addresses the aforementioned issues and aims to provide a threaded joint that allows for full utilization of the fully plastic load of the joint steel without the threaded portion on the compression side disengaging, even in an incompletely engaged state where the shoulder does not contact the joint. Furthermore, another objective of the present invention is to provide, based on this threaded joint, a steel pipe with a threaded joint, a structure, a method for constructing such a structure, a landslide-suppressing pile, a method for constructing a landslide-suppressing pile, a method for designing a threaded joint, a method for manufacturing a threaded joint, and a method for manufacturing a steel pipe with a threaded joint.

[0025] Methods for solving problems

[0026] The threaded joint of the present invention is a threaded joint located at the end of a steel pipe and connecting the steel pipes to each other, comprising: a male cylindrical body having a male thread formed by a tapered thread; and a female cylindrical body having a female thread formed by a tapered thread, wherein the inclination angle of the insert tooth side of the male thread and the female thread relative to the right angle direction of the steel pipe axis is in the range of 0 degrees to +8 degrees.

[0027] It is permissible that all the threads and their corresponding thread roots in the male-side cylinder and the female-side cylinder have the same pitch.

[0028] The threaded steel pipe of the present invention comprises a male-side cylinder and a female-side cylinder in the threaded joint of the present invention in any of the following ways (1) to (3).

[0029] (1) The method of setting the male side cylinder at at least one end of the steel pipe;

[0030] (2) The method of setting the female side cylinder at at least one end of the steel pipe;

[0031] (3) The method of setting the male side cylinder and the female side cylinder at one end and the other end of the steel pipe.

[0032] The structure of the present invention includes the threaded connector of the present invention and a plurality of steel pipes connected by the threaded connector.

[0033] The construction method of the structure of the present invention is a construction method of the structure of the present invention, wherein, under the state of rotational constraint of one of the threaded joint steel pipes that will be connected, the threaded joint of the other threaded joint steel pipe is rotated and fitted onto the threaded joint of the threaded joint steel pipe located on one of the threaded joint steel pipes.

[0034] The landslide suppression pile of the present invention comprises the threaded joint of the present invention and a plurality of steel pipes connected by the threaded joint. The construction method of the landslide suppression pile of the present invention is a construction method of a landslide suppression pile using a steel pipe with a threaded joint of the present invention installed at the end, wherein the landslide suppression pile is constructed in any of the following (1) to (3) manner. Method (1) includes: a hole excavation process for digging holes for inserting piles into the foundation along the entire length of the required length; a process of lowering the steel pipe into the excavated hole with the head of the steel pipe protruding, sequentially rotating and engaging the threaded joints and inserting them by their own weight, and filling the gap between the circumference of the steel pipe and the foundation with filling material to seal it to the foundation. Method (2) includes: a hole excavation process for excavating a hole for inserting a pile into the foundation along the entire length of the required length; a steel pipe joining process for joining the steel pipe to the required length using the threaded joint; and a process for inserting the joined steel pipe into the hole and filling the gap between the circumference of the steel pipe and the foundation with a filling material to seal it to the foundation.

[0035] Method (3) includes: a process of inserting the steel pipe into the ground by rotating and pressing it in while using the already constructed piles or reaction components to receive the reaction force; a process of rotating and joining the steel pipe to the head of the steel pipe inserted into the ground; and a process of inserting the rotated and joined steel pipe into the ground by rotating and pressing it in. The design method of the threaded joint of the first aspect of the present invention is as follows: the threaded joint is located at the end of a steel pipe and joins the steel pipes together; the threaded joint has a male side cylinder and a female side cylinder; the male side cylinder has a male thread formed by a tapered thread; and the female side cylinder has a female thread formed by a tapered thread. In the design method, the inclination angle of the insert tooth side of the thread teeth in the male thread and the female thread relative to the right angle direction of the steel pipe axis is set within the range of 0 degrees to +8 degrees.

[0036] The second aspect of the present invention provides a threaded joint design method, wherein the threaded joint is located at the end of a steel pipe and joins the steel pipes together. The threaded joint has a male side cylinder and a female side cylinder. The male side cylinder has a male thread formed by a tapered thread, and the female side cylinder has a female thread formed by a tapered thread. In the design method, the relationship between the ratio of the load to the fully plastic load of the steel and the set vertical angle of the thread is calculated in advance according to the friction coefficient. The set vertical angle of the thread, where the ratio is 1.0 or more under the friction coefficient set during design, is set as the inclination angle of the insert tooth side of the thread teeth in the male side cylinder and the female side cylinder relative to the right angle direction of the steel pipe axis.

[0037] The first embodiment of the present invention is a method for manufacturing a threaded joint, wherein the threaded joint is located at the end of a steel pipe and joins the steel pipes together, the threaded joint has a male side cylinder and a female side cylinder, the male side cylinder has a male thread formed by a tapered thread, and the female side cylinder has a female thread formed by a tapered thread, wherein in the manufacturing method, the inclination angle of the insert tooth side of the thread teeth in the male thread and the female thread relative to the right angle direction of the steel pipe axis is set in the range of 0 degrees to +8 degrees.

[0038] The second aspect of the present invention provides a method for manufacturing a threaded joint, wherein the threaded joint is located at the end of a steel pipe and joins the steel pipes together. The threaded joint has a male side cylinder and a female side cylinder. The male side cylinder has a male thread formed by a tapered thread, and the female side cylinder has a female thread formed by a tapered thread. In the manufacturing method, the relationship between the ratio of the load to the fully plastic load of the steel and the set vertical angle of the thread is calculated in advance according to the friction coefficient. The set vertical angle of the thread, where the ratio is 1.0 or more under the pre-set friction coefficient, is set as the inclination angle of the insert tooth side of the thread teeth in the male side cylinder and the female side cylinder relative to the right angle direction of the steel pipe axis.

[0039] The male-side cylinder and the female-side cylinder can be installed in any of the following ways (1) to (3).

[0040] (1) The method of setting the male side cylinder at at least one end of the steel pipe;

[0041] (2) The method of setting the female side cylinder at at least one end of the steel pipe;

[0042] (3) The method of setting the male side cylinder and the female side cylinder at one end and the other end of the steel pipe.

[0043] The effects of the invention

[0044] According to the present invention, even in an incompletely engaged state where the shoulder gap is approximately 2 mm and the threaded joint is not fully tightened, the load can be adequately transferred using only the threaded portion on the compression side when subjected to compressive loads due to bending. This allows full utilization of the plastic load-bearing capacity of the threaded joint steel without the threaded portion on the compression side coming loose. Therefore, in threaded joints used in landslide suppression piles where manual rotational engagement is required at construction sites with poor footing, the need for labor-intensive traction tools for full tightening and strict construction management can be eliminated. Attached Figure Description

[0045] Figure 1 This is an explanatory diagram of a threaded connector according to an embodiment of the present invention.

[0046] Figure 2 This indicates that the bending load is applied to the device. Figure 1 A diagram illustrating the overall movement of a threaded joint in a landslide suppression pile.

[0047] Figure 3 This is an explanation Figure 2 A diagram illustrating the behavior of a threaded joint in a certain state.

[0048] Figure 4 It is a graph showing the relationship between the inclination angle (setting the thread vertical angle) of the insert tooth side or the bearing tooth side relative to the right angle direction of the steel pipe axis and the friction coefficient between the insert tooth side or the bearing tooth side.

[0049] Figure 5 This is an explanatory diagram illustrating the operation of a threaded joint in an existing example.

[0050] Figure 6 This is an explanatory diagram illustrating the fully plastic load on steel in a study of tilt angles.

[0051] Figure 7 This is a diagram (one of) showing the analytical results in the study of tilt angle.

[0052] Figure 8 This is a diagram (second one) showing the analytical results in the study of tilt angle.

[0053] Figure 9 This is a diagram (third one) showing the analytical results in the study of tilt angle. Detailed Implementation

[0054] like Figure 1As shown in (a), the threaded joint 1 of this embodiment joins the steel pipes 3 together at their (axial) ends, and includes a male cylindrical body 7 and a female cylindrical body 11. The male cylindrical body 7 has a male thread 5 formed by a tapered thread, and the female cylindrical body 11 has a female thread 9 formed by a tapered thread. The structure will be described in detail below.

[0055] As an example of a landslide suppression steel pipe pile (hereinafter referred to as "landslide suppression pile"), which is a structure constructed by connecting multiple steel pipes 3, the threaded joint 1 in this embodiment is used as the connecting part of the steel pipes 3. In the case of the landslide suppression pile, the diameter of the steel pipe 3 that becomes the pile body is... The diameter should be 216mm or larger. There is no specific upper limit, but based on recent trends, the diameter of the steel pipe... It is below 2500mm. Figure 1 (a) shows the state of not being fully screwed in, that is, the front end 11a of the female cylinder 11 is not in contact with the shoulder 7a of the male cylinder 7 (also known as no shoulder contact).

[0056] like Figure 1 As shown in (a), the male-side cylinder 7 and the female-side cylinder 11 are components formed by threading an annulus having an outer diameter substantially equal to that of the steel pipe 3. The male-side cylinder 7 is installed at the lower end of the upper pile, and the female-side cylinder 11 is installed at the upper end of the lower pile. The steel pipe 3 serves as both the lower and upper piles. In this embodiment, the installation of the male-side cylinder or the female-side cylinder at the end of the steel pipe is performed by welding.

[0057] Here, the positive-side cylinder 7 and the negative-side cylinder 11 can be made of the same steel grade as the steel pipe 3. However, when using the same steel grade and wanting to improve the strength of the positive-side cylinder 7 and the negative-side cylinder 11, thickness becomes necessary, resulting in a larger protrusion width relative to the steel pipe 3. As a result, this can sometimes reduce workability and load transfer performance. Therefore, if it is not desired to excessively increase the thickness, the protrusion width can be reduced by selecting a steel grade with a yield strength exceeding that of the steel pipe 3 for the positive-side cylinder 7 and the negative-side cylinder 11. For example, in a typical landslide suppression pile, a steel grade equivalent to SKK490 material (rated yield strength of 315 N / mm²) can be used as the steel grade for the steel pipe 3. 2 Or equivalent to SM570 material (rated yield strength of 460 N / mm² when plate thickness is below 16 mm). 2 The rated yield strength is 450 N / mm² when the plate thickness is greater than 16 mm and less than 40 mm. 2 The rated yield strength is 430 N / mm² when the plate thickness is greater than 40 mm and less than 75 mm. 2Therefore, if the steel grade of the male side cylinder 7 and / or the steel grade of the female side cylinder 11 are equivalent to HITEN 780 material (rated yield strength of 685 N / mm²), then... 2 The steel grade can improve strength while reducing the thickness of the male side cylinder 7 and the female side cylinder 11, and can suppress the protruding width relative to the steel pipe 3.

[0058] The male thread 5 formed on the male side of the cylindrical body 7 and the female thread 9 formed on the female side of the cylindrical body 11 are both tapered threads. The male thread 5 and the female thread 9 are engaged by rotation in a direction that brings the male side of the cylindrical body 7 and the female side of the cylindrical body 11 closer together. Figure 1 In (a), the male side cylinder 7 is designated as the upper side and the female side cylinder 11 as the lower side, but the upper and lower sides can also be reversed. The shoulder 7a is stepped in such a way that the front end 11a of the female side cylinder 11 can contact the end of the tapered thread of the male side cylinder 7.

[0059] exist Figure 1 (b) shows Figure 1 An enlarged view of the dashed circle in (a). Figure 1 In (b), the male thread 5 and the female thread 9 are preferably any one of a trapezoidal thread, a square thread, or a buttress thread. Furthermore, the male thread 5 has a top 51 and two connected sides 5a (hereinafter referred to as the insert tooth side 5a) and 5b (hereinafter referred to as the bearing tooth side 5b). The side 5a of the male thread 5 and the side 5b of one adjacent thread are connected by a thread root 52. The side 5b of the male thread 5 is connected to the other adjacent side 5a by a thread root 52. Similarly, the female thread 9 has a top 91 and two connected sides 9b (hereinafter referred to as the bearing tooth side 9b) and 9a (hereinafter referred to as the insert tooth side 9a). The side 9a of the female thread 9 and the side 9b of one adjacent thread are connected by a thread root 92. The side 9b of the female thread 9 is connected to the adjacent side 9a of the other by the thread root 92.

[0060] in addition, Figure 1(a) shows P as the thread pitch. This thread pitch P is the distance along the steel pipe axis from the end of the thread tip 51 of a male thread 5 to the beginning of the thread tip 51 of the next male thread 5, or from the end of the thread tip 91 of a female thread 9 to the beginning of the thread tip 91 of the next thread. Similarly, the thread root pitch is the distance along the steel pipe axis from the end of the thread root 92 corresponding to the thread tip 51 of a male thread 5 to the beginning of the thread root 92 corresponding to the thread tip 51 of the next male thread 5, or from the end of the thread root 52 corresponding to the thread tip 91 of a female thread 9 to the beginning of the thread root 52 corresponding to the thread tip 91 of the next thread. In the case of a single thread, the pitch refers to the distance the thread advances in one revolution. In contrast, with multiple threads, the distance traveled per revolution varies depending on the number of threads, making it impossible to define a fixed pitch. Therefore, this specification defines the pitch as described above.

[0061] in addition, Figure 1 (a) shows the thread height h. Here, the thread height h is the distance from the top 51 of the male thread 5 to the bottom 52 of the thread (the distance in the direction of the orthogonal axis 23 of the gradient axis orthogonal to the tapered gradient axis 21) or the distance from the top 91 of the female thread 9 to the bottom 92 of the thread (the distance in the direction of the orthogonal axis 23 of the gradient axis orthogonal to the tapered gradient axis 21).

[0062] In the threaded connector 1 of this embodiment, the inclination angle α of the insertion tooth sides 5a and 9a of the male thread 5 formed in the male side cylinder 7 and the female thread 9 formed in the female side cylinder 11 relative to the right angle direction of the steel pipe axis is set to 0 degrees to +8 degrees. Here, the inclination angle α will be explained. Figure 1 As shown in (b), if the axis orthogonal to the steel pipe axis 25 is set as the steel pipe orthogonal axis 27, then the tilt angle α is the state of the section where the threaded joint 1 is set as the steel pipe axis direction. Figure 1 In state (a), the angle formed by the insertion tooth sides 5a and 9a of the male thread 5 and the female thread 9 with the orthogonal axis 27 of the steel pipe located on the same cross section. Here, although not illustrated, the inclination angle of the bearing tooth sides 5b and 9b of the thread can also be defined in the same way. That is, if the axis orthogonal to the steel pipe axis 25 is set as the orthogonal axis 27 of the steel pipe, then the inclination angle of the bearing tooth sides 5b and 9b of the thread is in the state where the threaded joint 1 is set as the cross section in the direction of the steel pipe axis ( Figure 1 (a) Under the condition of the male thread 5 and the female thread 9, the angle formed by the bearing tooth sides 5b and 9b of the thread teeth with the orthogonal axis 27 of the steel pipe located on the same cross section.

[0063] The following is based on Figures 2-4 This explains the reason for setting the inclination angle α of the insert tooth sides 5a and 9a of the threaded teeth relative to the right angle direction of the steel pipe axis. Furthermore, in this specification, the inclination angle α set relative to the right angle direction 66 of the steel pipe axis on the insert tooth sides 5a and 9a and the bearing tooth sides 5b and 9b of the threaded teeth is sometimes referred to as the setting thread vertical angle.

[0064] Figure 2 This illustrates the behavior of a steel pipe pile, including threaded joint 1, under bending load when a landslide suppression pile is not fully screwed in. Figure 3 Show Figure 2 The operation of the threaded joint 1 in the specified state. First, taking the male thread as an example, the bearing tooth sides 5b and 9b and the insertion tooth sides 5a and 9a of the thread are explained. The bearing tooth side 5b of the male thread 5 is the face of the male thread 5 located at the base end of the male cylinder 7 (the side for joining the steel pipe 3) of the two sides (tooth side surfaces, flanks) of the male thread 5. Similarly, the bearing tooth side 9b of the female thread 9 is the face of the female thread 9 located at the base end of the female cylinder 11 (the side for joining the steel pipe 3) of the two sides (tooth side surfaces, flanks) of the female thread 9. After the male thread 5 and the female thread 9 are rotated and connected, when the threaded joint 1 is subjected to tensile load, the bearing tooth side 5b of the male thread 5 contacts the bearing tooth side 9b of the female thread 9.

[0065] Furthermore, the insertion tooth side 5a of the male thread 5 is the side of the male cylinder 7 located at the front end 11a of the male thread 5. Similarly, the insertion tooth side 9a of the female thread 9 is the side of the female cylinder 11 located at the front end 11a of the female thread 9. When the male cylinder 7 is placed on the female cylinder 11 and rotated to engage, the insertion tooth side 5a of the male thread 5 contacts the insertion tooth side 9a of the female thread 9. In other words, simply put, the threaded joint 1 is a structure that transmits compressive force on the insertion tooth sides 5a and 9a and tensile force on the bearing tooth sides 5b and 9b. It should be noted that for the inclination angle α of the insertion tooth sides 5a and 9a of the thread with respect to the right angle direction of the steel pipe axis, the angle of the width of the base relative to the direction in which the thread tooth widens 51 and 91 is set as a + (positive) angle, and the angle of the direction in which the thread tooth narrows is recorded as a - (negative) angle.

[0066] As described above, in this embodiment, the inclination angle of the insert tooth sides 5a and 9a of the threaded tooth relative to the right angle direction of the steel pipe axis is set to 0 degrees to +8 degrees (refer to...). Figure 3(Partial enlarged view). By setting the thread vertical angle of the insert tooth sides 5a and 9a of the thread as described above, when bending load is applied in the threaded joint 1, on the side where compressive force is applied (in... Figure 3 (The upper part is under compression, and the lower part is under tension), making it difficult for the thread teeth to slip out of the contact surface. Therefore, as... Figure 3 As shown, this is a state in which sufficient load transfer can be achieved without the insertion tooth side 5a of the male thread 5 slipping off.

[0067] Here, based on Figure 4 This section explains the relationship between the set vertical angle of the thread on the insert tooth sides 5a and 9a and the difficulty of thread sliding. Figure 4 This diagram illustrates the relationship between Coulomb's law of friction (F=µN: F is the frictional force, µ is the coefficient of friction between solids, and N is the perpendicular force), the set vertical angle of the insert tooth flanks 5a and 9a, or the bearing tooth flanks 5b and 9b, and the coefficient of friction. The vertical axis shows the set vertical angle of the thread (°), and the horizontal axis shows the coefficient of friction (dimensionless) between the contacting insert tooth flanks 5a and 9a (sometimes simply referred to as "between insert tooth flanks") or between the contacting bearing tooth flanks 5b and 9b (sometimes simply referred to as "between bearing tooth flanks"). Figure 4 The straight line in the equation is a formula derived from the above Coulomb's law of friction, showing the relationship when the vertical angle of the thread is set to α and the static friction coefficient is set to µ, which becomes the following equation (1).

[0068] α=tan -1 (µ)...(1)

[0069] It should be noted that α is the angle between the contacting insert tooth surfaces 5a, 9a or the contacting bearing tooth surfaces 5b, 9b and the perpendicular direction relative to the steel pipe axis, and its sign is as defined above. According to equation (1), when the coefficient of friction between the insert tooth surfaces or the bearing tooth surfaces under a specific set thread vertical angle α is less than the static friction coefficient µ, the insert tooth surfaces or the bearing tooth surfaces will slide off each other. That is, if the set thread vertical angle α is in the region below equation (1), then they will not slide off. In other words, on the insert tooth surfaces 5a, 9a or the bearing tooth surfaces 5b, 9b, Figure 4 In the figure, the area below the vertical angle α of the thread, defined by equation (1), represents the "non-slipping range" of the thread. In addition, the area above the vertical angle α of the thread, defined by equation (1), without additional shaded lines, represents the "slipping range" of the thread.

[0070] from Figure 4It is known that if the coefficient of friction between the insert tooth surfaces or the bearing tooth surfaces is the same, then the smaller the vertical angle α of the thread is set, that is, the smaller the inclination angle of the insert tooth surfaces 5a and 9a relative to the right angle of the steel pipe axis, the more difficult it is for the insert tooth surfaces 5a and 9a to slip. Moreover, as shown in the inventor's research in the [study on inclination angle] described later, it is known that by setting the inclination angle of the insert tooth surfaces 5a and 9a relative to the right angle of the steel pipe axis to 0 degrees to +8 degrees, slippage will not occur until the full plastic load of the steel is reached. Based on this insight, the present invention sets the vertical angle of the thread to 0 degrees to +8 degrees.

[0071] Figure 5 Show Figure 2 The bending load shown is applied to the insertion tooth surfaces 15a and 17a (corresponding to threaded insertion surfaces 13 and 23 in Patent Document 2) of the threaded joint 13 described in Patent Document 2 at an angle of inclination of +20 degrees to +45 degrees relative to the right angle of the steel pipe axis, as in a conventional threaded joint 13. In the threaded joint 13 of Patent Document 2, the threaded portion on the upper side of the diagram, where the compressive force acts when the bending load is applied, acts by a force exceeding the frictional force of the threaded portion, thereby... Figure 5 As shown, the thread slips on the insert tooth side 15a of the male thread 15, causing the thread to come off.

[0072] As described above, in the threaded joint 1 of this embodiment, the inclination angle (setting the thread vertical angle) of the insert tooth sides 5a and 9a relative to the right angle direction of the steel pipe axis is set to 0 degrees to +8 degrees. Therefore, even in a partially engaged state where the gap at the shoulder 7a is about 2 mm and not fully tightened, the threaded joint 1 can still transfer sufficient load using only the threaded portion on the compression side when the compressive load of the joint steel is applied to the joint. As a result, the fully plastic load of the joint steel can be fully utilized without the threaded portion on the compression side coming loose. Therefore, it is particularly suitable for threaded joint 1 used in landslide suppression piles. The reason is that in threaded joint 1 used in landslide suppression piles, manual rotational engagement is often performed at construction sites with poor footing. In such cases, the need for labor-intensive traction tools for full tightening and strict construction management can be eliminated.

[0073] The following three methods can be considered as specific construction methods when applying the threaded joint 1 of this embodiment to landslide suppression piles.

[0074] (a) includes: a hole excavation process for digging holes for inserting piles into the foundation along the entire length of the required length; a process for lowering the steel pipe into the excavated hole with the head of the steel pipe fitted with the threaded joint 1 of the present invention protruding, sequentially rotating and inserting the steel pipe by its own weight, and after completing the splicing of a specified number of piles, filling the gap between the circumference of the steel pipe and the foundation with a filling material (e.g., mortar, cement, etc.) to seal it to the foundation.

[0075] (b) includes: a hole excavation process for digging holes for inserting piles into the foundation along the entire length of the required length; a steel pipe jointing process for joining steel pipes with the threaded joint 1 of the present invention installed to the required length using a threaded joint 1; and a process for inserting the joined steel pipes into the holes using a crane or the like and filling the gap between the steel pipe circumference and the foundation with a filling material (e.g., mortar, cement, etc.) to seal them to the foundation.

[0076] (c) includes: a process of inserting a steel pipe with the threaded joint 1 of the present invention into the ground by rotating and pressing it in while receiving the reaction force using a pile or reaction member that has already been constructed; a process of rotating and joining the steel pipe with the threaded joint 1 of the present invention to the head of the pile inserted into the ground; and a process of inserting the rotated and joined steel pipe into the ground by rotating and pressing it in.

[0077] Of course, this invention can also be used for piles or steel pipes other than landslide suppression piles. More specifically, it can also be used for support piles, friction piles, sheet piles, inclined piles, or steel pipes that are part of a structure. When used in these applications, the effects already described can be obtained, namely, even if the threaded joint 1 is in an incompletely engaged state with a shoulder 7a gap of about 2 mm and is not fully screwed in, sufficient load can be transferred using only the threaded portion on the compression side when the compressive load caused by the bending of the steel pipe 3 is applied to the joint.

[0078] This section describes threaded connectors for oil well tubing that generally use tapered threaded fittings. In the case of oil well tubing, since the maximum diameter is as small as 240 mm, it is possible to rotate and engage it with relatively low torque. Furthermore, due to the purpose of leak-free delivery of the tubing contents, a high level of sealing is required. Therefore, it is used in the state where the thread is fully tightened, i.e., the front end 11a of the female cylindrical body 11 contacts the shoulder 7a of the male cylindrical body 7 (also known as shoulder contact). Thus, when bending loads are applied to the connected oil well tubing, the shoulder can transmit compressive force. Moreover, since it is not a structural member that applies certain loads from the outside, high strength is not required. From the above perspective and the viewpoint of improving sealing, in order to rotate with low torque, the inclination angle of the insert tooth side relative to the right angle direction of the steel pipe axis is set to +30° to +60°. On the other hand, in threaded connectors used as structural members, since the expected maximum diameter is around 2500 mm, a very large torque is required to rotate it, making engagement more difficult. Furthermore, since it is a structural component, the thread teeth also require high strength, and it is preferable that the inclination angle of the insert tooth side relative to the right angle direction of the steel pipe axis is large. Moreover, the level of sealing performance required for oil well pipes is not required. Therefore, when applying conventional tapered threaded joints (especially oil well pipe technology) directly to structural component applications, it is required to use them in a non-fully tightened state where the front end 11a of the female cylinder 11 does not fully contact the shoulder 7a of the male cylinder 7. In other words, the threaded joint of the present invention is a very significant effect of ensuring the strength of the thread teeth as a structural component while preventing the threaded portion on the compression side from disengaging even in a non-fully tightened state.

[0079] It should be noted that Patent Document 2 describes the following: When the thread insertion face angle (setting the thread vertical angle) is smaller than +20 degrees, the cutting resistance during thread cutting increases, necessitating a reduction in the amount of material cut per pass, thus decreasing processing efficiency. However, by applying this invention, the load transfer efficiency of the threaded portion increases, allowing for a reduction in the number of thread teeth and thread height, making the reduction in the amount of material cut per pass less of a problem. Furthermore, Patent Document 2 also describes that axial alignment of the upper and lower piles becomes difficult during pile splicing operations, leading to a decrease in thread tightness. However, when the outer diameters of the upper and lower piles of the target structure are the same, their positions can be confirmed in four directions, so axial alignment is not a major issue.

[0080] This invention focuses on tapered threads, but it can be applied not only to a single thread but also to multiple threads.

[0081] It should be noted that it is preferable to set all the threads and their corresponding thread roots in the male side cylinder 7 and the female side cylinder 11 to be the same. By setting them in this way, when a load is applied to the threaded joint 1, all the threads will abut evenly in the axial direction, thus enabling load transfer.

[0082] It should be noted that, as a structure with threaded joint 1, for example when constructing a landslide suppression pile, while constraining the rotation of one of the threaded joint steel pipes that is the object of connection, the threaded joint 1 of the other threaded joint steel pipe can be rotated and fitted onto the threaded joint 1 of the threaded joint steel pipe located on one side.

[0083] In addition, the following design method is used when designing threaded connector 1. The threaded connector is located at the end of a steel pipe and joins the steel pipes together. The threaded connector has a male cylindrical body and a female cylindrical body. The male cylindrical body has a male thread formed by a tapered thread, and the female cylindrical body has a female thread formed by a tapered thread. In this design method, the inclination angle of the insert tooth side of the male and female threads relative to the right angle direction of the steel pipe axis is set within the range of 0 degrees to +8 degrees.

[0084] In addition, the following manufacturing method is used when manufacturing threaded connector 1. The manufacturing method of the threaded connector is as follows: the threaded connector is located at the end of a steel pipe and joins the steel pipes together. The threaded connector has a male cylindrical body and a female cylindrical body. The male cylindrical body has a male thread formed by a tapered thread, and the female cylindrical body has a female thread formed by a tapered thread. In the manufacturing method, the inclination angle of the insert tooth side of the male and female threads relative to the right angle direction of the steel pipe axis is set within the range of 0 degrees to +8 degrees.

[0085] In addition, when manufacturing a steel pipe with a threaded joint, which includes a male side cylinder 7 and a female side cylinder 11 in the threaded joint 1, the male side cylinder and the female side cylinder in the threaded joint of the present invention can be installed at one end and the other end of the steel pipe.

[0086] [Study on the angle of inclination]

[0087] In this invention, as described above, the optimal range of the inclination angles of the insert tooth sides 5a and 9a relative to the right angle direction of the steel pipe axis is set to 0 degrees to +8 degrees, which is based on the FEM analysis results. The FEM analysis is explained below. The analytical model is a three-dimensional four-point bending model with a steel pipe outer diameter of 508 mm, a plate thickness of 23 mm, a cylinder outer diameter of 508 mm, and a load point spacing of 1200 mm (refer to...). Figure 2The model is as follows: with the male side cylinder 7 installed on the steel pipe 3 and the female side cylinder 11 installed on the other side of the steel pipe 3 joined together, a threaded joint 1 is arranged in the center of the equal bending interval, and the endurance caused by the bending load is confirmed.

[0088] Furthermore, to account for the non-fully screwed-in state, the initial configuration of the male side cylinder 7 and the female side cylinder 11 is set such that the gap between the shoulder 7a and the front end 11a of the female side cylinder 11 is 2mm. To further consider the contact state, contact conditions capable of contact determination are provided to the male side cylinder 7 and the female side cylinder 11. The friction coefficients between the insert tooth surfaces 5a and 9a and the bearing tooth surfaces 5b and 9b, which become the contact parts, are set as follows. This forms a contact analytical elastoplastic model that takes into account the elastoplastic behavior of the steel.

[0089] The coefficient of friction between the insert tooth lateral surface and the bearing tooth lateral surface used in the analysis is set to 0.1, which is the general coefficient of friction between steels under sliding conditions (e.g., under conditions where lubricating oil is applied).

[0090] Furthermore, the vertical angle of the thread on the bearing tooth sides 5b and 9b is set to 0 degrees. Generally, the load transfer force is higher when the vertical angle of the thread on the bearing tooth sides is 0 degrees. When the vertical angle of the thread is set to negative, it is generally called a hook thread shape. Although it can suppress slippage of the thread, the rigidity of the thread part decreases and it is prone to deformation because the root width of the thread teeth (the root width of the thread teeth on sides 5a, 9a and 5b, 9b) becomes smaller. Therefore, it is difficult to apply to structural components requiring high strength (especially landslide suppression piles, landslide suppression walls, retaining walls, foundation steel pipe piles, steel pipe sheet piles and steel pipe columns). On the other hand, when the vertical angle of the thread is set to positive, it is generally called a trapezoidal thread shape. Although the rigidity of the thread part is higher and it is not easy to deform, the thread part is prone to slippage.

[0091] That is, the vertical angle of the thread on the bearing tooth sides 5b and 9b is set to 0 degrees because if the vertical angle of the thread on the bearing tooth sides 5b and 9b is +10 degrees, it becomes a condition that is easy to fall off on the tensile side. By setting the vertical angle of the thread on the bearing tooth sides 5b and 9b to 0 degrees, the tensile load transmission force is the highest in the threaded joint 1 as a structure, and it is relatively easy to fall off on the compression side.

[0092] By specifying the vertical angle of the insert tooth flanks 5a and 9a that prevents thread slippage on the compression side under these conditions and allows for the full plastic load-bearing capacity of the steel, the vertical angle of the insert tooth flanks 5a and 9a that suppresses thread slippage on the compression side can be specified independently of the vertical angle of the load-bearing tooth flanks 5b. It should be noted that, as... Figure 6 As shown, the full plastic load of the steel is a value calculated based on the plastic section modulus and yield stress of the steel under the assumption of a hypothetical steel pipe 19. The hypothetical steel pipe 19 is the cross-section at the center of the root of the male thread 5, which will become the weak point of the joint (refer to...). Figure 6 It is equivalent to the part enclosed by a square with a dotted line.

[0093] In this study, the vertical angle of the thread on the bearing tooth sides 5b and 9b relative to the right angle 66 of the steel pipe axis was set to 0 degrees. Five examples were implemented with the vertical angles of the thread on the insert tooth sides 5a and 9a set to 0 degrees, +5 degrees, +6 degrees, +8 degrees, and +10 degrees. It should be noted that, similar to the case of the vertical angle of the thread on the bearing tooth sides, when the vertical angle of the thread on the insert tooth sides is negative, it is generally called a hook thread shape, which can suppress slippage of the threaded portion. However, because the root width of the thread teeth becomes smaller, the rigidity of the threaded portion decreases and it is prone to deformation, making it difficult to apply to structural components requiring high strength. Therefore, it was excluded from this study.

[0094] exist Figure 7 The diagram shows the analytical results when the vertical angle of the set threads on the bearing tooth sides 5b and 9b is 0 degrees and the vertical angle of the set threads on the insert tooth sides 5a and 9a is 0 degrees. Figure 7 The vertical axis is the load ratio (load / steel full plastic load) obtained by dividing the load obtained analytically by the full plastic load of the steel, and the horizontal axis is the displacement (mm) of the center of the support.

[0095] from Figure 7 It can be seen that when the vertical angle of the thread on the insert tooth sides 5a and 9a is set to 0 degrees, the load ratio decreases above 1.12. That is, it can be concluded that when the vertical angle of the thread on the insert tooth sides 5a and 9a is set to 0 degrees, it indicates that the threaded portion will not disengage under the full plastic load of the steel, and the full plastic load of the steel can be utilized. Here, the maximum value before the load ratio is about to decrease is... Figure 7 The position of the black inverted triangle mark in the diagram is called the maximum load ratio. According to... Figure 7 The maximum load ratio is 1.12 when the vertical angle of the thread is set to 0 degrees.

[0096] The same analysis is applied to cases where the vertical angle of the thread is set to +5 degrees, +6 degrees, +8 degrees, and +10 degrees for the insert tooth sides 5a and 9a, respectively, yielding the same result as... Figure 7 Using the same analytical results, the maximum load ratio for each set thread vertical angle was calculated. This included cases where the set thread vertical angle for insert tooth sides 5a and 9a was 0 degrees. The results of the maximum load ratio for each set thread vertical angle were then summarized. Figure 8 As shown in the chart. Figure 8 The vertical axis is the same as Figure 7 The vertical axis represents the same load ratio (load weight / steel full plastic load), and the horizontal axis represents the set thread vertical angle (°).

[0097] exist Figure 8 The chart is marked with dashed lines, which represent the results of regression analysis of the analytical results. According to this regression analysis, if the vertical angle of the thread is set to below 8 degrees, the load ratio (load weight / steel's full plastic load) is above 1, meaning that the steel's full plastic load can be utilized without the threaded portion on the compression side detaching. On the other hand, it can be seen that when the angle exceeds 8 degrees, the steel load ratio is less than 1, and the threaded portion on the compression side detaches before reaching the steel's full plastic load, thus the steel's full plastic load cannot be utilized.

[0098] Based on the above analysis results, it is confirmed that setting the vertical angle of the thread below 8 degrees is appropriate as specified in this invention.

[0099] The above study assumes a friction coefficient of 0.1 between the insert tooth surfaces and the bearing tooth surfaces. This is because the friction coefficient between the steels forming the joint is approximately 0.45, decreasing to 0.1–0.2 under conditions of lubrication and sliding. 0.1 was used as the most stringent condition. Therefore, the above result is appropriate for general threaded joints.

[0100] However, as Figure 4 As shown, as the coefficient of friction between the insert tooth lateral surfaces or the bearing tooth lateral surfaces decreases, the vertical angle of the sliding thread decreases. Therefore, for the sake of caution, the inventors analyzed five examples where the coefficient of friction between the insert tooth lateral surfaces and the bearing tooth lateral surfaces was set to 0.06, and the vertical angle of the thread on the bearing tooth lateral surfaces 5b and 9b was set to 0 degrees, while the vertical angle of the thread on the insert tooth lateral surfaces 5a and 9a was set to 0 degrees, +3 degrees, +4 degrees, +8 degrees, and +10 degrees. Figure 9 The parsing results are shown in [the image / table]. Figure 9 The text also describes the case where the friction coefficient between the lateral surfaces of the inserted teeth and the lateral surfaces of the bearing teeth is set to 0.1.

[0101] according to Figure 9As can be seen from the chart, when the coefficient of friction between the insert tooth lateral surface and the bearing tooth lateral surface is set to 0.06, in order to utilize the full plastic load of the steel and prevent the threaded part on the compression side from dislodging, the vertical angle of the thread should be set to 3 degrees or less.

[0102] Therefore, when designing a threaded joint 1 under the condition that the friction coefficient between the insert tooth surfaces is relatively special, it is more preferable to consider the friction coefficient between the insert tooth surfaces in the design. As a design method in this case, the following design method is adopted. In the following threaded joint design method, the threaded joint is located at the end of the steel pipe 3 and connects the steel pipes 3 to each other. The threaded joint has a male side cylinder 7 and a female side cylinder 11. The male side cylinder 7 has a male thread 5 formed by a tapered thread, and the female side cylinder 11 has a female thread 9 formed by a tapered thread. In the design method, the relationship between the ratio of the load to the fully plastic load of the steel and the set vertical angle of the thread is calculated in advance according to the friction coefficient between the insert tooth surfaces. The set vertical angle of the thread with a friction coefficient between the insert tooth surfaces set at the time of design that is 1.0 or more is set as the inclination angle of the insert tooth surfaces 5a and 9a of the thread teeth in the male side cylinder 7 and the female side cylinder 11 relative to the right angle direction of the steel pipe axis.

[0103] Furthermore, when manufacturing a threaded joint 1 under the condition that the friction coefficient between the insert tooth lateral surfaces is particularly special, it is more preferable to consider the friction coefficient between the insert tooth lateral surfaces when forming the threaded joint. As a manufacturing method in this case, the following manufacturing method is adopted. In the following manufacturing method for a threaded joint, the threaded joint is located at the end of a steel pipe and the steel pipes are joined together. The threaded joint has a male side cylinder and a female side cylinder. The male side cylinder has a male thread formed by a tapered thread, and the female side cylinder has a female thread formed by a tapered thread. In this manufacturing method, the relationship between the ratio of the load to the fully plastic load of the steel and the set vertical angle of the thread is calculated in advance according to the friction coefficient between the insert tooth lateral surfaces. The set vertical angle of the thread, which is 1.0 or more under the pre-set friction coefficient between the insert tooth lateral surfaces, is set as the inclination angle of the insert tooth lateral surface of the thread in the male side cylinder and the female side cylinder relative to the right angle of the steel pipe axis.

[0104] Industrial availability

[0105] According to the present invention, a threaded joint can be provided that, even in an incompletely engaged state where the shoulder does not contact, the fully plastic load of the joint steel can be fully utilized without the threaded portion on the compression side disengaging. Furthermore, according to the present invention, a steel pipe with a threaded joint, a structure, a method for constructing the structure, a landslide suppression pile, a method for constructing the landslide suppression pile, a method for designing a threaded joint, a method for manufacturing a threaded joint, and a method for manufacturing a steel pipe with a threaded joint can be provided based on this threaded joint.

[0106] Explanation of reference numerals in the attached figures

[0107] 1. Threaded connector

[0108] 3 steel pipes

[0109] 5 Male thread

[0110] 5a Insertion of the tooth lateral surface

[0111] 5b Bearing tooth lateral surface

[0112] 51 Top

[0113] 52 Threaded Bottom

[0114] 7. Yang side cylinder

[0115] 7a Shoulder

[0116] 9. Female thread

[0117] 9a Insertion of the tooth side

[0118] 9b Bearing tooth lateral surface

[0119] 91 Top

[0120] 92 threaded bottom

[0121] 11. Internal cylindrical body

[0122] 11a Frontend

[0123] 13 Threaded connector (Patent Document 2)

[0124] 15 Male thread

[0125] 15a Insertion tooth lateral surface

[0126] 15b Bearing tooth lateral surface

[0127] 17. Female thread

[0128] 17a Insertion tooth lateral surface

[0129] 17b Bearing tooth lateral surface

[0130] 19 Imaginary steel pipe

[0131] 21. Conical gradient axis

[0132] 23. Gradient axis orthogonal axis

[0133] 25 steel pipe shaft

[0134] 27. Orthogonal axis of steel pipe

[0135] P is the pitch of the thread.

[0136] h thread height

[0137] α Inclination angle, setting the thread vertical angle (relative to the insert tooth side or relative to the bearing tooth side).

Claims

1. A design method for a threaded joint, wherein the threaded joint is located at the end of a steel pipe and joins the steel pipes together, the threaded joint having a male cylindrical body and a female cylindrical body, the male cylindrical body having a male thread formed by a tapered thread, and the female cylindrical body having a female thread formed by a tapered thread. In the design method, the relationship between the ratio of the load to the fully plastic load of the steel and the set vertical angle of the thread is calculated in advance according to the friction coefficient. The set vertical angle of the thread with the ratio of 1.0 or more under the friction coefficient set during the design is set as the inclination angle of the insert tooth side of the thread in the male side cylinder and the female side cylinder relative to the right angle direction of the steel pipe axis.

2. A method for manufacturing a threaded joint, wherein the threaded joint is located at the end of a steel pipe and joins the steel pipes together, the threaded joint having a male cylindrical body and a female cylindrical body, the male cylindrical body having a male thread formed by a tapered thread, and the female cylindrical body having a female thread formed by a tapered thread. In the manufacturing method, the relationship between the ratio of the load to the fully plastic load of the steel and the set vertical angle of the thread is calculated in advance according to the friction coefficient. The set vertical angle of the thread, where the ratio is 1.0 or more under the pre-set friction coefficient, is formed as the inclination angle of the insert tooth side of the thread in the male side cylinder and the female side cylinder relative to the right angle direction of the steel pipe axis.

Images