JP7533737B2 - Threaded joint, steel pipe with threaded joint, structure, method for constructing structure, landslide prevention pile, method for constructing landslide prevention pile, method for designing threaded joint, method for manufacturing threaded joint, method for manufacturing steel pipe with threaded joint - Google Patents

Description

The present invention relates to a threaded joint used in a steel pipe pile for preventing landslides (abbreviated as "landslide prevention pile") installed in a landslide area, a steel pipe with the threaded joint, a structure, a method for constructing a structure, a landslide prevention 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.

Steel pipe piles for preventing landslides (hereafter abbreviated to "landslide prevention piles") are installed in landslide zones, and their construction sites are often on steep slopes where it is difficult to bring in heavy machinery. For this reason, the piles cannot be driven in by hammering, and are instead driven into holes that have been pre-bored using an auger or similar tool. The total length of a landslide prevention pile varies depending on the local conditions, but generally reaches 20-30m. However, due to transportation and other restrictions, it is common to install steel pipe piles of about 5-8m in length, with piles being joined on-site.

This pile joining work is carried out in an unstable environment, so there is a strong demand for it to be done quickly and reliably. In addition, since it is difficult to predict on which stratum a landslide will occur, landslide prevention piles often must have cross-sectional performance that exceeds the design strength required at every part along almost their entire length, including the joints for the pile joining.

For this reason, conventionally, landslide prevention pile joints have been welded on-site. However, on-site welding in such a poor working environment has the following problems:
(1) Current commonly used steel pipes have a thick wall, so welding one spot takes a long time.
(2) Due to poor working conditions, welding quality is likely to deteriorate and it is not easy to ensure joint strength.
(3) Due to poor working conditions, it is difficult to secure skilled welding personnel.
(4) It is difficult to ensure welding quality in on-site welding, so high-tensile steel is difficult to use.

For this reason, landslide prevention piles that are intended to be installed in situ must meet all of the following requirements:
(1) Pile joining work is easy and takes a short time.
(2) The quality of the joints between steel pipe piles is well ensured, without being affected by the working environment or skill.
(3) The strength of the joint must be equal to or greater than that of the steel pipe pile body (hereinafter referred to as the pile body).
(4) The outer diameter of the joint must not be larger than that of the pile body.
(5) It can be applied even when the pile body is made of high-tensile steel.

As a joint for a landslide prevention pile that meets the above requirements, there is available a pile body having a female threaded joint portion at an end thereof, and a male threaded joint portion at an end thereof having an outer diameter substantially the same as that of the female threaded joint portion, wherein the female threaded joint portion and the male threaded joint portion are made of tapered threaded joints having an inclination, thread height, and thread spacing that are set so that screwing can be completed in several turns, and wherein the product of the section modulus and the material strength at the thread end points of the female threaded joint portion and the male threaded joint portion is configured to be greater than the product of the section modulus and the material strength of the pile body (for example, see Patent Document 1).
Also disclosed is a landslide prevention steel pipe pile joint in which the male and female threads are tapered threads, the thread shape is trapezoidal, and the threads are multiple threads with two to three starts (see, for example, Patent Document 2).

Japanese Patent Application Publication No. 7-82738 Japanese Patent Application Publication No. 10-252056

The screw joints of landslide prevention piles are required to have high strength, but they also need to be manually rotated at construction sites with poor footing. Furthermore, screw joints are basically screwed in until the shoulder touches the ground, but when joining at construction sites like the one described above, the screw may not be tightened completely, causing the shoulder to not touch the ground and resulting in a gap of about 2 mm.

In this case, it is possible to prevent gaps by using a towing tool or similar to achieve a complete bond, but this is extremely time-consuming. Therefore, if it is assumed that a complete bond will be achieved using a towing tool or similar, the advantages of threaded joints over typical on-site welded joints are diminished.

Furthermore, threaded joints are generally designed to resist compressive loads at the shoulder and threads, and to resist tensile loads at the threads. For this reason, when a compressive load due to a bending load acts on a threaded joint in an incomplete joint state where the threads are not completely tightened, the shoulder does not transmit the compressive load, and only the threads resist the load. As a result, the full plastic load of the joint steel cannot be fully utilized, and the threads on the compression side may come off, leading to the destruction of the threaded joint.

The present invention has been made to solve these problems, and has an object to provide a threaded joint which can fully utilize the full plastic load of the joint steel material, without the threaded portion on the compression side coming loose, even in an incompletely joined state where the shoulder portions are not touching.
Another object of the present invention is to provide a steel pipe with a threaded joint, a structure, a method for constructing a structure, a landslide prevention pile, a method for constructing a landslide prevention 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, all of which are based on such a threaded joint.

[1] The threaded joint of the present invention is a threaded joint that is located at the end of steel pipes and joins the steel pipes together, and is equipped with a male cylinder having a male thread that is a tapered thread and a female cylinder having a female thread that is a tapered thread, and the inclination angle of the stabbing flanks of the threads of the male and female threads relative to the direction perpendicular to the axis of the steel pipe is within the range of 0 degrees to +8 degrees.

[2] In addition, in the above [1], the pitch of all threads and the corresponding thread bases on the male and female cylinders are the same.

[3] Furthermore, a steel pipe with a threaded joint according to the present invention comprises the male side cylinder body and the female side cylinder body in the threaded joint described in [1] or [2] above in any one of the following (1) to (3):
(1) An embodiment in which the male side cylinder body is provided at least on one end of the steel pipe. (2) An embodiment in which the female side cylinder body is provided at least on one end of the steel pipe. (3) An embodiment in which the male side cylinder body and the female side cylinder body are provided at one end and the other end of the steel pipe.

[4] The structure according to the present invention comprises a threaded joint as described in [1] or [2] above, and a plurality of steel pipes connected by the threaded joint.

[5] The method for constructing a structure according to the present invention is the method for constructing a structure according to the above [4], in which, while restricting the rotation of one of the threaded joint-equipped steel pipes to be connected, the threaded joint of the other threaded joint-equipped steel pipe is aligned with the threaded joint of the one threaded joint-equipped steel pipe and rotationally fitted.

[6] The landslide prevention pile according to the present invention comprises a threaded joint as described in [1] or [2] above and a plurality of steel pipes connected by the threaded joint.

[7] Furthermore, the method for constructing a landslide prevention pile according to the present invention is a method for constructing a landslide prevention pile using a steel pipe having the threaded joint described in [1] or [2] above attached to its end, and is constructed in any one of the following forms (1) to (3):
(1) A hole drilling step of drilling a hole for inserting a pile into the ground over the entire length of the required length, and a step of hanging the drilled hole so that the head of the steel pipe protrudes, sequentially rotating and joining the steel pipe with the screw joint, and inserting it under its own weight. After a predetermined number of joint piles are completed, a gap between the circumferential surface of the steel pipe and the ground is filled with a filler material to adhere to the ground. (2) A hole drilling step of drilling a hole for inserting a pile into the ground over the entire length of the required length, a steel pipe joining step of joining the steel pipe to the required length with the screw joint, and a step of inserting the joined steel pipe into the hole, filling the gap between the circumferential surface of the steel pipe and the ground with a filler material to adhere to the ground. (3) A step of penetrating the steel pipe into the ground by rotary press-in while taking a reaction force from an already constructed pile or a reaction member, a step of rotary joining the steel pipe to the head of the steel pipe that has penetrated into the ground, and a step of penetrating the rotary-joined steel pipe into the ground by rotary press-in.

[8] A method for designing a threaded joint according to the present invention is a method for designing a threaded joint that has a male cylinder having a male thread formed of a tapered thread and a female cylinder having a female thread formed of a tapered thread, and is located at the end of a steel pipe and joins the steel pipes,
The inclination angle of the stabbing flanks of the threads of the male and female threads relative to the direction perpendicular to the axis of the steel pipe is set within the range of 0 degrees to +8 degrees.

[9] A method for designing a threaded joint according to the present invention is a method for designing a threaded joint that has a male cylinder having a male thread formed of a tapered thread and a female cylinder having a female thread formed of a tapered thread, and is located at the end of a steel pipe and joins the steel pipes,
The relationship between the ratio of the applied load to the steel full plastic load and the set vertical thread angle is determined in advance for each friction coefficient, and the set vertical thread angle at which the ratio is 1.0 or more for the friction coefficient set during design is set as the inclination angle of the stabbing flanks of the threads on the male side cylinder and the female side cylinder with respect to the direction perpendicular to the steel pipe axis.

[10] Also, a method for manufacturing a threaded joint according to the present invention is a method for manufacturing a threaded joint having a male side cylinder body having a male thread formed of a tapered thread and a female side cylinder body having a female thread formed of a tapered thread, which is located at the end of a steel pipe and joins the steel pipes together,
The inclination angle of the stabbing flanks of the threads of the male and female threads relative to the direction perpendicular to the axis of the steel pipe is formed within the range of 0 degrees to +8 degrees.

[11] Also, a method for manufacturing a threaded joint according to the present invention is a method for manufacturing a threaded joint having a male side cylinder body having a male thread formed of a tapered thread and a female side cylinder body having a female thread formed of a tapered thread, which is located at the end of a steel pipe and joins the steel pipes,
The relationship between the ratio of the applied load to the steel full plastic load and the set vertical thread angle is determined in advance for each friction coefficient, and the set vertical thread angle at which the ratio is 1.0 or more for a preset friction coefficient is formed as the inclination angle of the stabbing flanks of the threads of the male side cylinder and the female side cylinder with respect to the direction perpendicular to the steel pipe axis.

[12] Furthermore, the method for manufacturing a steel pipe with a threaded joint according to the present invention comprises attaching the male side cylinder body and the female side cylinder body in the threaded joint described in [1] or [2] above in any one of the following (1) to (3):
(1) An embodiment in which the male side cylinder body is attached to at least one end of the steel pipe. (2) An embodiment in which the female side cylinder body is attached to at least one end of the steel pipe. (3) An embodiment in which the male side cylinder body and the female side cylinder body are attached to one end and the other end of the steel pipe.

The threaded joint according to the present invention is located at the end of steel pipes and connects the steel pipes together. It comprises a male cylinder having a male thread made of a tapered thread, and a female cylinder having a female thread made of a tapered thread. The inclination angle of the stabbing surface of the threads of the male and female threads relative to the direction perpendicular to the steel pipe axis is within the range of 0 degrees to +8 degrees. Therefore, when a compressive load due to bending acts on the threaded joint, even in an incomplete joint state where the shoulder part has a gap of about 2 mm and the joint is not completely closed, sufficient load can be transmitted only by the threaded part on the compression side, and the full plastic load of the threaded joint steel material can be fully utilized without the threaded part on the compression side coming loose. Therefore, in threaded joints used for landslide prevention piles that require manual rotary joining at construction sites with poor footing, labor-intensive closing with a towing tool and strict construction management can be omitted.

FIG. 1 is an explanatory diagram of a threaded joint according to one embodiment of the present invention. 2 is an explanatory diagram illustrating the behavior of the entire landslide prevention pile including the threaded joint of FIG. 1 when a bending load acts on the landslide prevention pile. FIG. FIG. 3 is an explanatory diagram illustrating the behavior of the threaded joint in the state shown in FIG. 2 . FIG. 1 is a diagram showing the relationship between the inclination angle (set thread vertical angle) of a stabbing flank or a load flank with respect to a direction perpendicular to the steel pipe axis and the friction coefficient between stabbing flanks or load flanks. FIG. 11 is an explanatory diagram illustrating the behavior of a threaded joint in a conventional example. FIG. 11 is an explanatory diagram for explaining a full plastic load of a steel material in considering an inclination angle. FIG. 13 is a diagram showing the analysis results in the study of the inclination angle (part 1). FIG. 13 is a diagram showing the analysis results in the study of the inclination angle (part 2). FIG. 11 is a diagram showing the analysis results in the study of the inclination angle (part 3).

As shown in FIG. 1(a), a threaded joint 1 according to this embodiment is located at the (axial) end of steel pipes 3 and joins steel pipes 3 together, and comprises a male cylinder body 7 having a male thread 5 consisting of a taper thread, and a female cylinder body 11 having a female thread 9 consisting of a taper thread.
Each component will be described in detail below.

The threaded joint 1 of this embodiment is applied as a means for connecting steel pipes 3 to a steel pipe pile for preventing landslides (hereinafter, abbreviated as "landslide prevention pile"), which is an example of a structure formed by connecting a plurality of steel pipes 3. In the case of a landslide prevention pile, the diameter φ of the steel pipe 3 that forms the pile body is 216 mm or more. There is no particular upper limit, but in light of recent trends, the diameter φ of the steel pipe is 2500 mm or less.
The state shown in FIG. 1(a) is the non-closed state, i.e., the state in which the tip 11a of the female cylinder body 11 is not in contact with the shoulder portion 7a of the male cylinder body 7 (also referred to as no shoulder touch).

As shown in FIG. 1(a), the male cylinder 7 and the female cylinder 11 are threaded into rings having an outer diameter substantially equal to the outer diameter of the steel pipe 3 that serves as the lower and upper piles, with the male cylinder 7 attached to the lower end of the upper pile and the female cylinder 11 attached to the upper end of the lower pile. In this embodiment, the male cylinder or female cylinder is attached to the end of the steel pipe by welding.

Here, the male side cylinder body 7 and the female side cylinder body 11 may be made of the same steel type as the steel pipe 3. However, if it is desired to increase the strength of the male side cylinder body 7 and the female side cylinder body 11 using the same steel type, a thickness is required, and the overhang width relative to the steel pipe 3 becomes large. As a result, workability and load transmission performance may be reduced. Therefore, if it is not desired to increase the thickness too much, the overhang width can be reduced by selecting a steel type for the male side cylinder body 7 and the female side cylinder body 11 that exceeds the yield strength of the steel type of the steel pipe 3.
For example, in a typical landslide prevention pile, a steel type equivalent to SKK490 material (standard yield strength of 315 N/ ^mm2 ) or SM570 material (standard yield strength of 460 N/ ^mm2 for plate thickness of 16 mm or less, 450 N/ ^mm2 for plate thickness of 16 mm to 40 mm, and 430 N/ ^mm2 for plate thickness of 40 mm to 75 mm) is used for the steel pipe 3. Therefore, if a steel type equivalent to HITEN780 material (standard yield strength of 685 N/ ^mm2 ) is used for the male side cylinder 7 and/or the female side cylinder 11, the thicknesses of the male side cylinder 7 and the female side cylinder 11 can be reduced while increasing the strength, and the overhang width relative to the steel pipe 3 can be reduced.

The male thread 5 formed on the male cylinder 7 and the female thread 9 formed on the female cylinder 11 are both tapered threads. The male thread 5 and the female thread 9 are joined by rotating the male cylinder 7 and the female cylinder 11 in a direction that brings them closer together. In FIG. 1(a), the male cylinder 7 is on the upper side and the female cylinder 11 is on the lower side, but the top and bottom may be reversed. The shoulder portion 7a mentioned above is stepped so that the end of the tapered thread of the male cylinder 7 can come into contact with the tip 11a of the female cylinder 11.

An enlarged view of the dotted circle in FIG. 1(a) is shown in FIG. 1(b). In FIG. 1(b), the male thread 5 and the female thread 9 are preferably either trapezoidal threads, square threads, or buttress threads. The thread of the male thread 5 has a crest 51 and two side faces 5a (the stabbing face 5a described below), 5b (the load face 5b described below) connected thereto. Furthermore, the side face 5a of the thread of the male thread 5 and the side face 5b of one adjacent thread are connected by a thread root 52. The side face 5b of the thread of the male thread 5 and the side face 5a of the other adjacent thread are connected by a thread root 52. Similarly, the female thread 9 has a crest 91 and two side faces 9b (the load face 9b described below), 9a (the stabbing face 9a described below) connected thereto. Furthermore, the side 9a of the thread of the female thread 9 and the side 9b of the thread of one adjacent thread are connected by a thread root 92. The side 9b of the thread of the female thread 9 and the side 9a of the other adjacent thread are connected by a thread root 92.

Also, P shown in FIG. 1(a) indicates the pitch of the thread. The pitch P of the thread is the distance in the axial direction of the steel pipe from the end of the thread crest 51 of a male thread 5 in a certain thread to the start position of the thread crest 51 of the next male thread 5 in a certain thread, or the distance in the axial direction of the steel pipe from the end of the thread crest 91 of a female thread 9 in a certain thread to the start position of the thread crest 91 of the next thread. Similarly, the pitch of the thread root is the distance in the axial direction of the steel pipe from the end of the thread root 92 corresponding to the thread crest 51 of a male thread 5 in a certain thread to the start position of the thread root 92 corresponding to the thread crest 51 of the next male thread 5 in a certain thread. Or, it is the distance in the axial direction of the steel pipe from the end of the thread root 52 corresponding to the thread crest 91 of a female thread 9 in a certain thread to the start position of the thread root 52 corresponding to the thread crest 91 of the next thread. In the case of a single thread thread, the pitch means the distance the thread advances in one rotation. In contrast, in the case of multiple-start threads, the distance traveled per revolution varies depending on the number of threads in the thread, so the pitch cannot be defined as a fixed distance. For this reason, the above definition is used in this specification.

In addition, h in FIG. 1(a) indicates the thread height. Here, the thread height h is the distance from the thread crest 51 to the thread root 52 of the male thread 5 (the distance in the direction of the gradient axis orthogonal axis 23 perpendicular to the gradient axis 21 of the taper) or the distance from the thread crest 91 to the thread root 92 of the female thread 9 (the distance in the direction of the gradient axis orthogonal axis 23 perpendicular to the gradient axis 21 of the taper).

In the threaded joint 1 of this embodiment, the inclination angle α of the stabbing flanks 5a, 9a of the threads of the male thread 5 formed on the male side cylinder body 7 and the female thread 9 formed on the female side cylinder body 11 with respect to the direction perpendicular to the steel pipe axis is set to be between 0 degrees and +8 degrees.
Here, the inclination angle α will be described.
As shown in Figure 1 (b), if the axis perpendicular to the steel pipe axis 25 is defined as the steel pipe orthogonal axis 27, the inclination angle α is the angle formed by the stabbing flanks 5a, 9a of the threads of the male thread 5 and the female thread 9 with the steel pipe orthogonal axis 27 on the cross section in the axial direction of the steel pipe when the threaded joint 1 is shown on the cross section (the state in Figure 1).
Although not shown, the inclination angle of the thread load surfaces 5b, 9b can also be defined in a similar manner. In other words, if the axis perpendicular to the steel pipe axis 25 is defined as the steel pipe orthogonal axis 27, the inclination angle of the thread load surfaces 5b, 9b is the angle that the thread load surfaces 5b, 9b of the male thread 5 and female thread 9 make with the steel pipe orthogonal axis 27 on the cross section of the threaded joint 1 in the axial direction of the steel pipe (as shown in FIG. 1(a)).

The reason for setting the inclination angle α of the stabbing flanks 5a, 9a of the threads relative to the direction perpendicular to the steel pipe axis in this manner will be explained below with reference to Figs. 2 to 4.
In this specification, the inclination angle α set on the stabbing flanks 5a, 9a and the loading flanks 5b, 9b of the threads with respect to the direction perpendicular to the steel pipe axis 66 may be referred to as the set thread vertical angle.

FIG. 2 shows the behavior of the entire steel pipe pile including the threaded joint 1 when a bending load acts on the landslide prevention pile in an open state, and FIG. 3 shows the behavior of the threaded joint 1 in the state shown in FIG. 2.
First, the load flanks 5b, 9b and the stabbing flanks 5a, 9a of the threads will be described using a male thread as an example.
The loaded surface 5b of the thread of the male thread 5 is the surface on the base end side of the male cylinder 7 (the side to which the steel pipe 3 is joined) of both side surfaces (flanks) of the thread of the male thread 5. Similarly, the loaded surface 9b of the thread of the female thread 9 is the surface on the base end side of the female cylinder 11 (the side to which the steel pipe 3 is joined) of both side surfaces (flanks) of the thread of the female thread 9. After the male thread 5 and the female thread 9 are connected by rotational engagement, when the threaded joint 1 is subjected to a tensile load, the loaded surface 5b of the thread of the male thread 5 and the loaded surface 9b of the thread of the female thread 9 come into contact with each other.

Furthermore, the stabbing flank 5a of the thread of the male thread 5 is the surface on the tip 11a side of the male cylinder body 7, among both side surfaces (flanks) of the thread of the male thread 5. Similarly, the stabbing flank 9a of the thread of the female thread 9 is the surface on the tip 11a side of the female cylinder body 11, among both side surfaces (flanks) of the thread of the female thread 9. When the male cylinder body 7 is placed on the female cylinder body 11 and rotated and fitted, the stabbing flank 5a of the thread of the male thread 5 comes into contact with the stabbing flank 9a of the female thread 9. In other words, simply put, the threaded joint 1 is structured so that the stabbing flanks 5a, 9a transmit compressive forces, and the load flanks 5b, 9b transmit tensile forces.
With respect to the inclination angle α of the stabbing flanks 5a, 9a of the threads with respect to the direction perpendicular to the steel pipe axis, the angle in the direction in which the width of the root widens relative to the crest 51, 91 of the thread is represented as a + (plus) angle, and the angle in the direction in which it narrows is represented as a - (minus) angle.

As described above, in this embodiment, the inclination angle of the stabbing flanks 5a, 9a of the threads with respect to the direction perpendicular to the axis of the steel pipe is set to 0 degrees to +8 degrees (see the partially enlarged view of FIG. 3).
By setting the set thread vertical angles of the stabbing flanks 5a, 9a of the threads as described above, the contact surfaces of the threads are less likely to slip on the side where a compressive force acts (in Figure 3, the upper side is compression and the lower side is tension) when a bending load acts on the threaded joint 1. This results in a state where the stabbing flank 5a of the male thread 5 does not slip off and sufficient load transmission is possible, as shown in Figure 3.

Here, the relationship between the set thread vertical angle of the stabbing flanks 5a, 9a and the difficulty of thread slipping will be explained with reference to Figure 4. Figure 4 shows Coulomb's law of friction (F=μN: F is frictional force, μ is the coefficient of friction between solids, and N is normal force) and the relationship between the set thread vertical angle of the stabbing flanks 5a, 9a or the loading flanks 5b, 9b and the coefficient of friction.
The vertical axis indicates the set thread vertical angle (°), and the horizontal axis indicates the friction coefficient (dimensionless quantity) between the stabbing flanks 5a and 9a in contact (sometimes referred to as "between stabbing flanks") or between the road flanks 5b and 9b in contact (sometimes referred to as "between road flanks")
The straight line in FIG. 4 is an equation derived from Coulomb's law of friction and shows the relationship when the set screw vertical angle is α and the static friction coefficient is μ, which is given by the following equation (1).
α=tan ^-1 (μ)...(1)
Here, α is the angle of the contacting stabbing flanks 5a, 9a or the contacting load flanks 5b, 9b with respect to the direction perpendicular to the steel pipe axis, and positive and negative are as defined above. According to formula (1), when the friction coefficient between the stabbing flanks or the load flanks at a specific set vertical thread angle α becomes smaller than the static friction coefficient μ, the stabbing flanks or the load flanks start to slip. In other words, they do not start to slip under conditions in the region where the set vertical thread angle α is equal to or less than formula (1).
In other words, on the stabbing flanks 5a, 9a or the loading flanks 5b, 9b, the hatched areas in Fig. 4 where the set vertical thread angle α is equal to or less than formula (1) indicate the "non-slip range" of the thread. Also, the non-hatched areas in the figure where the set vertical thread angle α is greater than formula (1) indicate the "slip range" of the thread.

As can be seen from FIG. 4, if the coefficient of friction between the stabbing flanks or between the loading flanks is the same, the smaller the set thread vertical angle α, i.e., the smaller the inclination angle of the stabbing flanks 5a, 9a with respect to the direction perpendicular to the steel pipe axis, the more difficult it becomes for the stabbing flanks 5a, 9a to slip.
The inventors' study, which will be described later in [Study of Inclination Angle], has found that by setting the inclination angle of the stabbing flanks 5a, 9a with respect to the direction perpendicular to the steel pipe axis to 0 degrees to +8 degrees, slippage does not occur up to the full plastic load of the steel material. Based on this knowledge, the present invention sets the set thread vertical angle to 0 degrees to +8 degrees.

FIG. 5 shows the behavior of a conventional threaded joint 13 described in Patent Document 2 in which the angles of the stabbing flanks 15a, 17a (which correspond to the thread stabbing flanks 13, 23 in Patent Document 2) with respect to the direction perpendicular to the steel pipe axis are +20 degrees to +45 degrees, when the bending load shown in FIG. 2 is applied to the threaded joint 13.
In the threaded joint 13 of Patent Document 2, when a bending load is applied, a compressive force acts on the threaded portion at the upper side in the figure, and a force that exceeds the frictional force of the threaded portion acts on the threaded portion, causing slippage on the stabbing surface 15a of the male thread 15, as shown in Figure 5, and causing the thread to come off.

As described above, in the threaded joint 1 of this embodiment, the inclination angle (set thread vertical angle) of the stabbing flanks 5a, 9a with respect to the direction perpendicular to the steel pipe axis is set to 0 degrees to +8 degrees. As a result, when a compressive load due to bending of the steel pipe 3 acts on the joint, even in a threaded joint 1 that is in an incomplete joint state where it is not completely closed such that the gap in the shoulder portion 7a is about 2 mm, sufficient load can be transmitted by the compression side threads alone. As a result, the full plastic load of the joint steel material can be fully utilized without the threads on the compression side coming loose.
Therefore, it is particularly suitable for the threaded joint 1 used in landslide prevention piles. The reason is that the threaded joint 1 used in landslide prevention piles is often rotary joined by hand at construction sites with poor footing, and in such cases, labor-intensive tightening using a towing tool and strict construction management can be omitted.

The following three specific construction methods are considered when the threaded joint 1 of this embodiment is applied to a landslide prevention pile.
(a) A hole drilling process in which holes for inserting piles into the ground are drilled over the entire length required, and a steel pipe having a threaded joint 1 of the present invention attached thereto is hung in the drilled hole so that the head thereof protrudes, and the steel pipe is sequentially rotationally joined using the threaded joint 1 and inserted under its own weight. After the required number of pile joints have been completed, a filler material (e.g., grout, mortar, etc.) is filled into the gap between the outer surface of the steel pipe and the ground to adhere it to the ground.
(b) a hole excavation process in which a hole for inserting a pile into the ground is excavated over the entire length of the required length; a steel pipe joining process in which a steel pipe equipped with the threaded joint 1 of the present invention is joined to the required length using the threaded joint 1; and the joined steel pipe is inserted into the hole using a crane or the like, and the gap between the circumference of the steel pipe and the ground is filled with a filler material (e.g., grout, mortar, etc.) to adhere it to the ground.
(c) A method comprising the steps of penetrating a steel pipe having a threaded joint 1 of the present invention attached thereto into the ground by rotary pressing while a reaction force is taken up by an already constructed pile or a reaction member, rotary joining the steel pipe having a threaded joint 1 of the present invention attached thereto to the head of the pile that has penetrated into the ground, and rotary pressing the rotary joined steel pipe into the ground.

Of course, the present invention can also be used for piles or steel pipes other than landslide prevention piles. More specifically, it can also be used for support piles, friction piles, steel pipe sheet piles, inclined piles, or steel pipes that are part of a structure. Even when used for these purposes, the effect already described can be obtained, that is, when a compressive load due to bending of the steel pipe 3 acts on the joint, even if the threaded joint 1 is in an incomplete joint state that is not completely closed, such as when the gap in the shoulder portion 7a is about 2 mm, sufficient load transmission can be achieved using only the threaded portion on the compression side.

Here, we will explain threaded joints for oil well pipes, which generally use taper thread joints. In the case of oil well pipes, the maximum diameter is small at 240 mm, so they can be rotated and joined with little torque. In addition, there is a high demand for sealing properties in order to transport the contents inside the pipe without leakage. As a result, they are used in a state where the threads are fully tightened, that is, in a state where the tip 11a of the female side cylinder 11 is in contact with the shoulder portion 7a of the male side cylinder 7 (also called shoulder touch). Therefore, when a bending load acts on the connected oil well pipes, the compression force can be transmitted by the shoulder portion. Furthermore, since it is not a structural member that is subjected to any load from the outside, high strength is not required. For the above reasons and from the viewpoint of improving sealing properties, the inclination angle of the stabbing surface relative to the direction perpendicular to the steel pipe axis is set to +30° to +60° so that it can be rotated with a small torque. On the other hand, in the case of threaded joints used as structural members, the maximum diameter is expected to be about 2500 mm, so a very large torque is required to rotate them, and joining is difficult. In addition, because it is a structural member, the threads are required to have high strength, and it is desirable for the inclination angle of the stabbing surface to the direction perpendicular to the steel pipe axis to be large. Furthermore, the same sealing performance as that of oil country tubular goods is not required. Therefore, if conventional tapered thread joints (particularly oil country tubular goods technology) are applied as they are to structural member applications, they must be used in an unfastened state in which the tip 11a of the female side cylinder 11 is not in complete contact with the shoulder portion 7a of the male side cylinder 7.
In other words, a threaded joint according to the present invention has a very significant effect in that it is a threaded joint which ensures the strength of the threads as a structural member while preventing the threaded portion on the compression side from coming loose even in an untightened state.

In addition, Patent Document 2 describes that if the thread stabbing flank angle (set thread vertical angle) is made smaller than +20 degrees, the cutting resistance during thread cutting increases, so that the cutting amount in one pass must be reduced, resulting in a decrease in processing efficiency.
However, by applying the present invention, the load transmission efficiency of the threaded portion is increased, making it possible to reduce the number of threads and the thread height, so that the reduction in the amount of cutting in one pass does not become a major problem.
Patent Document 2 also states that it becomes difficult to align the upper and lower piles during pile joining work, which reduces the ability to tighten the screws; however, if 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 aligning the piles does not pose a major problem.

This invention is intended for tapered threads, but it can be applied to tapered threads that are not only single-start threads but also multiple-start threads in the same way.

It is preferable that the pitches of all the threads and the corresponding thread bases of the male cylinder body 7 and the female cylinder body 11 are set to be the same.
By setting it in this manner, when a load acts on the threaded joint 1, all of the threads come into uniform contact in the axial direction, enabling the load to be transmitted.

To construct a structure having a threaded joint 1, such as a landslide prevention pile, the threaded joint 1 of the other threaded joint steel pipe is aligned with the threaded joint 1 of the threaded joint steel pipe to be connected and rotated to fit together while restricting the rotation of one of the threaded joint steel pipes.

Moreover, the threaded joint 1 is designed according to the following design method.
A method for designing a threaded joint having a male cylinder having a male thread formed of a tapered thread and a female cylinder having a female thread formed of a tapered thread, the threaded joint being located at an end of a steel pipe and joining the steel pipes, comprising:
A method for designing a threaded joint, in which the inclination angle of the stabbing flanks of the threads of the male and female threads relative to the direction perpendicular to the steel pipe axis is set within the range of 0 degrees to +8 degrees.

The threaded joint 1 is manufactured by the following manufacturing method.
A method for manufacturing a threaded joint having a male cylinder having a male thread formed of a tapered thread and a female cylinder having a female thread formed of a tapered thread, the threaded joint being located at an end of a steel pipe and joining the steel pipes together, comprising:
A method for manufacturing a threaded joint, in which the inclination angle of the stabbing flanks of the threads of the male and female threads relative to the direction perpendicular to the steel pipe axis is formed within the range of 0 degrees to +8 degrees.

To manufacture a steel pipe with a threaded joint having a male side cylinder body 7 and a female side cylinder body 11 in the threaded joint 1, the male side cylinder body and the female side cylinder body in the threaded joint according to the present invention can be attached to one end and the other end of the steel pipe.

[Consideration of the inclination angle]
As described above, in the present invention, the optimum range of the inclination angle of the stabbing flanks 5a, 9a of the threads with respect to the direction perpendicular to the steel pipe axis is set to 0 degrees to +8 degrees. This is based on the results of FEM analysis, and this FEM analysis will be explained below.
The analytical model is a three-dimensional four-point bending model (see Figure 2) with a steel pipe outer diameter of 508 mm, a plate thickness of 23 mm, a cylinder outer diameter of 508 mm, and a distance between load points of 1200 mm. In this model, a male side cylinder 7 attached to a steel pipe 3 and a female side cylinder 11 attached to the other steel pipe 3 are joined, and a threaded joint 1 is placed in the center of the equal bending section, and the strength against bending load is confirmed.

To take into account the non-closed state, the initial positioning of the male cylinder 7 and female cylinder 11 was set to a state in which the gap between the shoulder portion 7a and the tip 11a of the female cylinder 11 was 2 mm. To further take into account the contact state, contact conditions were given to the male cylinder 7 and female cylinder 11 that enable contact determination, and the friction coefficients between the stabbing surfaces and the loading surfaces set below were used for the contacting areas, stabbing surfaces 5a and 9a, and loading surfaces 5b and 9b. This is an elastic-plastic contact analysis model that takes into account the elastic-plastic behavior of steel.

The coefficient of friction between the stabbing surfaces and the load surfaces used in the analysis was set to 0.1, which is the typical coefficient of friction between steel materials under sliding conditions (e.g., when lubricated).

The set screw vertical angle of the load surfaces 5b and 9b was 0 degrees.
Generally, it is said that the load transmission force is high when the set vertical screw angle of the load surface is 0 degrees. When the set vertical screw angle is negative, the shape is generally called a hook screw, which can suppress slippage of the screw part, but the width of the base of the screw thread (the width of the base of the sides 5a, 9a and 5b, 9b of the screw thread) becomes small, so the rigidity of the screw part decreases and it becomes easy to deform. For this reason, it is difficult to apply it to structural members that require high strength (especially landslide prevention piles, landslide prevention walls, retaining walls, steel pipe piles for foundations, steel pipe sheet piles, and steel pipe columns). On the other hand, when it is positive, the shape is generally called a trapezoidal screw, which has high rigidity of the screw part and is difficult to deform, but the screw part is easy to slip.

In other words, the reason why the set vertical thread angle of the loaded surfaces 5b, 9b is 0 degrees is that if the set vertical thread angle of the loaded surfaces 5b, 9b were +10 degrees, for example, it would be a condition in which the joint would tend to come off on the tension side, but by setting the set vertical thread angle of the loaded surfaces 5b, 9b to 0 degrees, the tensile load transmission force of the threaded joint 1 as a structure is the highest, and it is a condition in which the joint is relatively more likely to come off on the compression side.

By specifying the set vertical thread angle of the stabbing flanks 5 a, 9 a that can prevent backout of the threaded portion on the compression side under such conditions and can exert a full plastic load on the steel, it is possible to specify the set vertical thread angle of the stabbing flanks 5 a, 9 a that can suppress backout of the threads on the compression side regardless of the set vertical thread angle of the load flanks 5 b, 9 b.
The total plastic load of the steel material is a value calculated based on the plastic section modulus and the yield stress of the steel material when a hypothetical steel pipe 19 is assumed to be equivalent to a cross section (see the area surrounded by a dashed square in FIG. 6) at the center of the thread bottom on the root side of the male thread 5, which is the weak point of the joint, as shown in FIG. 6.

In this study, the set vertical thread angle of the load faces 5b, 9b was 0 degrees with respect to the direction perpendicular to the steel pipe axis 66, and five cases were performed in which the set vertical thread angles of the stabbing faces 5a, 9a were 0 degrees, +5 degrees, +6 degrees, +8 degrees, and +10 degrees.
As with the set vertical thread angle of the load flank, when the set vertical thread angle of the stabbing flank is negative, a shape generally known as a hook thread can be used to suppress slippage of the threaded portion. However, as the base width of the thread becomes smaller, the rigidity of the threaded portion decreases and it becomes prone to deformation, making it difficult to apply to structural members that require high strength. Therefore, it was excluded from the study.

FIG. 7 shows the analysis results when the set thread vertical angle of the loading flanks 5b, 9b is 0 degree and the set thread vertical angle of the stabbing flanks 5a, 9a is 0 degree.
The vertical axis in Figure 7 is the load ratio (applied load/steel full plastic load) which has been made dimensionless by dividing the load found by the analysis by the steel full plastic load, and the horizontal axis is the displacement (mm) at the center of the span.

From FIG. 7, it can be seen that when the set thread vertical angle of the stabbing flanks 5a and 9a is 0 degrees, the load ratio decreases when it exceeds 1.12.
When the set vertical thread angle of a is 0 degrees, it shows that the threaded portion will not come off under the full plastic load of the steel, and it is clear that the full plastic load of the steel can be exerted. Here, the maximum value just before the load ratio decreases (the part marked with an inverted black triangle ▼ in Figure 7) is called the maximum load ratio. From Figure 7, the maximum load ratio when the set vertical thread angle is 0 degrees is 1.12.

A similar analysis was also performed when the set vertical thread angles of the stabbing flanks 5a, 9a were +5 degrees, +6 degrees, +8 degrees, and +10 degrees, obtaining analysis results similar to those in Figure 7 and determining the maximum load ratio for each set vertical thread angle. The results of the maximum load ratio for each set vertical thread angle, including the case where the set vertical thread angle of the stabbing flanks 5a, 9a is 0 degree, are summarized in the graph of Figure 8.
The vertical axis of FIG. 8 is the load ratio (applied load/steel full plastic load) as in FIG. 7, and the horizontal axis is the set screw vertical angle (°).

The graph in Figure 8 shows a dotted line that represents the result of a regression analysis of the analysis results. From the results of this regression analysis, it can be seen that if the set screw vertical angle is 8 degrees or less, the load ratio (applied load/steel full plastic load) is 1 or more, meaning that the threaded portion on the compression side will not come off and the steel full plastic load can be utilized. On the other hand, if it is more than 8 degrees, the steel load ratio will be less than 1, and the threaded portion on the compression side will come off before the steel full plastic load is reached, meaning that the steel full plastic load cannot be utilized.

The above analysis results demonstrate that the set screw vertical angle specified in this invention is appropriate to be 8 degrees or less.

The above study was conducted assuming a friction coefficient of 0.1 between the stabbing flanks and the road flanks. The friction coefficient between the steel materials that make up the joint is approximately 0.45, and when lubricant is applied and the friction coefficient slides, it becomes 0.1 to 0.2. Therefore, 0.1 was used as the most severe condition.
Therefore, the above results apply to general threaded joints.

However, as shown in Figure 4, the set thread vertical angle at which slippage begins to occur decreases as the coefficient of friction between the stabbing flanks or between the loaded flanks decreases. For this reason, just to be sure, the inventors performed an analysis for five cases in which the coefficient of friction between the stabbing flanks and between the loaded flanks was set to 0.06, with the set thread vertical angle of the loaded flanks 5b, 9b being 0 degrees, and the set thread vertical angles of the stabbing flanks 5a, 9a being 0 degrees, +3 degrees, +4 degrees, +8 degrees, and +10 degrees.
The analysis results are shown in Figure 9. Figure 9 also shows the case where the friction coefficient between the stabbing flanks and the road flanks is set to 0.1.

The graph in Figure 9 shows that when the coefficient of friction between the stabbing faces and the load faces is set to 0.06, the set vertical thread angle must be set to 3 degrees or less in order to utilize the full plastic load of the steel without the thread on the compression side coming loose.

For this reason, when designing a threaded joint 1 when the friction coefficient between the stabbing flanks is special, it is more preferable to design taking into consideration the friction coefficient between the stabbing flanks, and the design method in this case is as follows.
A method for designing a threaded joint having a male cylinder body (7) having a male thread (5) made of a tapered thread and a female cylinder body (11) having a female thread (9) made of a tapered thread, the threaded joint being located at an end of steel pipes (3) and used to join steel pipes (3), comprising:
A threaded joint design method in which the relationship between the ratio of the applied load to the steel full plastic load and the set thread vertical angle is determined in advance for each coefficient of friction between the stabbing flanks, and the set thread vertical angle at which the ratio is 1.0 or greater for the coefficient of friction between the stabbing flanks set during design is set as the inclination angle of the stabbing flanks (5a, 9a) of the threads of the male cylinder (7) and female cylinder (11) with respect to the direction perpendicular to the steel pipe axis.

Furthermore, when manufacturing a threaded joint 1 in a case where the friction coefficient between the stabbing flanks is special, it is more preferable to form the threaded joint taking into account the friction coefficient between the stabbing flanks, and the manufacturing method in this case is as follows.
A method for manufacturing a threaded joint having a male cylinder having a male thread formed of a tapered thread and a female cylinder having a female thread formed of a tapered thread, the threaded joint being located at an end of a steel pipe and joining the steel pipes together, comprising:
A method for manufacturing a threaded joint in which the relationship between the ratio of the applied load to the steel full plastic load, and a set thread vertical angle is determined in advance for each coefficient of friction between stabbing flanks, and a set thread vertical angle at which the ratio is 1.0 or greater for a predetermined coefficient of friction between the stabbing flanks is formed as the inclination angle of the stabbing flanks of the threads of the male side cylinder body and the female side cylinder body with respect to the direction perpendicular to the steel pipe axis.

According to the present invention, it is possible to provide a threaded joint that can fully utilize the full plastic load of the joint steel material without the threaded portion on the compression side coming loose, even in an incomplete joint state where the shoulder portions are not touching. In addition, according to the present invention, it is possible to provide a steel pipe with a threaded joint, a structure, a method for constructing a structure, a landslide prevention pile, a method for constructing a landslide prevention 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, all of which are based on such a threaded joint.

Reference Signs List 1 Threaded joint 3 Steel pipe 5 Male thread 5a Stabbing flank 5b Load flank 51 Crest 52 Thread root 7 Male tubular body 7a Shoulder 9 Female thread 9a Stabbing flank 9b Load flank 91 Crest 92 Thread root 11 Female tubular body 11a Tip 13 Threaded joint (Patent Document 2)
15 Male thread 15a Stabbing surface 15b Load surface 17 Female thread 17a Stabbing surface 17b Load surface 19 Virtual steel pipe 21 Taper gradient axis 23 Gradient axis perpendicular axis 25 Steel pipe axis 27 Steel pipe perpendicular axis P Thread pitch h Thread height α Inclination angle, set thread vertical angle (with respect to the stabbing surface or with respect to the load surface)

Claims (5)

A steel pipe with a threaded joint, which is attached to an end of a steel pipe constituting a landslide prevention pile, a landslide prevention wall, an earth retaining wall, a steel pipe pile for foundations, a steel pipe sheet pile, and a steel pipe column, the end of which is provided with a male side cylindrical body having a male thread formed of a tapered thread and a female side cylindrical body having a female thread formed of a tapered thread,
The threaded joint is formed of a steel type having a higher strength than the steel pipe, and the inclination angle of the stabbing flanks of the threads of the male thread and the female thread with respect to the direction perpendicular to the steel pipe axis is within a range of 0 degrees to +3 degrees,
A steel pipe with a threaded joint comprising the male side cylinder body and the female side cylinder body in any one of the following aspects (1) to (3).
(1) An embodiment in which the male side cylinder body is provided at least on one end of the steel pipe. (2) An embodiment in which the female side cylinder body is provided at least on one end of the steel pipe. (3) An embodiment in which the male side cylinder body and the female side cylinder body are provided at one end and the other end of the steel pipe. 2. A steel pipe with a threaded joint as set forth in claim 1, wherein the pitches of all the threads and the corresponding thread roots in said male side cylinder body and said female side cylinder body are the same. A landslide prevention pile, a landslide prevention wall, a retaining wall, a steel pipe pile for foundations, a steel pipe sheet pile, or a steel pipe column comprising a plurality of steel pipes with threaded joints according to claim 1 or 2 . A method for constructing a landslide prevention pile, a landslide prevention wall, an earth retaining wall, a steel pipe pile for foundations, a steel pipe sheet pile, or a steel pipe column according to claim 3, in which, while restricting the rotation of one of the threaded joint-equipped steel pipes to be connected, the threaded joint of the other threaded joint-equipped steel pipe is aligned with the threaded joint of the one threaded joint-equipped steel pipe and rotated to fit it. A method for constructing a landslide prevention pile using the steel pipe with threaded joint according to claim 1 or 2, the method being carried out in any one of the following modes (1) to (3).
(1) A method including a hole drilling step of drilling holes for inserting piles into the ground over the entire length of the required length, and a step of hanging the steel pipe with the threaded joint so that the head of the steel pipe protrudes from the drilled hole, rotating the steel pipe with the threaded joint in sequence and inserting it under its own weight, and after a predetermined number of joint piles are completed, filling the gap between the circumferential surface of the steel pipe and the ground with a filler material to make it adhere to the ground. (2) A method including a hole drilling step of drilling holes for inserting piles into the ground over the entire length of the required length, and a step of joining the steel pipe with the threaded joint to the required length using the threaded joint. A pipe joining step, and a step of inserting the joined threaded joint steel pipe into a hole and filling a gap between the circumferential surface of the threaded joint steel pipe and the ground with a filler material to adhere it to the ground. (3) A step of penetrating the threaded joint steel pipe into the ground by rotary press-in while taking a reaction force from an already installed pile or reaction member, a step of rotary joining a front threaded joint steel pipe to the head of the threaded joint steel pipe penetrated into the ground, and a step of rotary pressing in the rotary-joined threaded joint steel pipe into the ground.

Images