JP7420123B2 - Threaded joints, steel pipes with threaded joints, structures, construction methods for structures, landslide prevention piles, construction methods for landslide prevention piles, design methods for threaded joints, manufacturing methods for threaded joints, manufacturing methods for steel pipes with threaded joints - Google Patents

Description

The present invention relates to a threaded joint used for a landslide prevention steel pipe pile (abbreviated as "landslide prevention pile") installed in a landslide zone, for example, a steel pipe with the threaded joint, a structure, a construction method of the structure, a landslide prevention pile, The present invention relates to 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 landslide prevention (hereinafter abbreviated as ``landslide prevention piles'') are installed in landslide areas, and their construction sites are often on steep slopes where it is difficult to bring in heavy machinery. For this reason, piles cannot be driven in by hammering, and piles are instead driven into holes pre-bored with an auger or the like. Incidentally, the total length of landslide prevention piles varies depending on the local situation, but generally reaches 20 to 30 meters in many cases. However, due to restrictions such as transportation, it is common practice to construct steel pipe piles of approximately 5 to 8 meters while connecting piles on site.

This pile-jointing work is carried out in an unstable environment, so there is a strong need for quick and reliable work. In addition, because it is difficult to predict on which stratum a landslide collapse will occur, landslide prevention piles must have a cross-section that exceeds the design strength at any point over almost the entire length, including the joints for joint piles. In many cases, it must have various performance characteristics.

For this reason, conventionally, connecting piles for landslide prevention piles have been performed by welding on site. However, on-site welding in such a place with a poor working environment has the following problems.
(1) Current conventional size steel pipes have thick walls, so it takes time to weld at one location.
(2) Welding quality tends to deteriorate due to the poor working environment, making it difficult to ensure joint strength.
(3) Due to poor working conditions, it is difficult to secure excellent welding technicians.
(4) Since it is difficult to ensure welding quality in on-site welding, it is difficult to use high-tensile steel.

For this reason, landslide prevention piles that are intended for on-site joint pile work are required to satisfy all of the following requirements.
(1) The joint pile work is easy and the work time is short.
(2) The quality of the joints between steel pipe piles should be ensured without being affected by the working environment or workmanship.
(3) The strength of the joint part shall 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 should not be larger than the pile body.
(5) Applicable even when the pile body is made of high-tensile steel.

As a joint for a landslide prevention pile that meets the above requirements, the pile body has a female threaded joint at the end, and a male threaded joint at the end has an outer diameter that is substantially the same as the outer diameter of the female threaded joint. The female threaded joint part and the male threaded joint part consist of a tapered threaded joint having an inclination, thread height, and thread spacing set so that screwing can be completed in a few turns. There is a structure in which the product of the section modulus and the material strength at the thread end point of the joint part is larger than the product of the section modulus and the material strength of the pile body (for example, see Patent Document 1).
Further, a landslide prevention steel pipe pile joint has been disclosed in which the male thread and the female thread are tapered threads, the thread shape is trapezoidal, and the thread is multi-threaded with two to three threads (for example, see Patent Document 2).

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

Screw joints for landslide prevention piles are required to have high resistance, but rotational joints must be performed manually at construction sites with poor footing. The basic rule for threaded joints is to screw them in until the shoulder parts touch, but because they are joined at the construction site as described above, the screws cannot be tightened completely and the shoulder parts do not touch, leaving a gap of about 2 mm. Sometimes I put it away.

In this case, it is possible to prevent gaps from forming by using a pulling tool or the like to completely join the parts, but this takes a lot of effort. Therefore, if it is assumed that a traction tool or the like is used to achieve a completely joined state, the superiority of threaded joints over general field welded joints will be diminished.

Additionally, threaded joints are generally designed so that the shoulder portion and the threaded portion resist compressive load, and the threaded portion resists tensile load. Therefore, if a compressive load due to a bending load acts on the threaded joint in an incompletely connected state in which the screw is not completely tightened, the shoulder portion will not transmit the compressive load and only the threaded portion will resist the load. As a result, the threaded portion on the compression side may come off without fully utilizing the full plastic load of the joint steel material, leading to destruction of the threaded joint.

The present invention has been made to solve this problem, and it is possible to fully utilize the total plastic load of the joint steel without causing the threaded part on the compression side to come off even in an incompletely joined state where the shoulder part does not touch. The purpose is to provide threaded joints that can be used.
In addition, steel pipes with threaded joints based on such threaded joints, structures, methods of constructing structures, landslide prevention piles, construction methods of landslide prevention piles, methods of designing threaded joints, methods of manufacturing threaded joints, threaded joints The purpose of the present invention is to provide a method for manufacturing steel pipes with attached steel pipes.

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

[2] Furthermore, in the product described in [1] above, all the threads on the male side cylinder and the female side cylinder and the pitches of the corresponding thread bottoms are the same.

[3] Furthermore, in the steel pipe with a threaded joint according to the present invention, the male side cylinder and the female side cylinder in the threaded joint described in [1] or [2] above are replaced by the following (1) to (3). It is provided in any one of the aspects.
(1) A mode in which the male side cylinder is provided at at least one end of the steel pipe. (2) A mode in which the female side cylinder is provided at at least one end of the steel pipe. (3) A mode in which the male side cylinder and the female side cylinder are provided. are provided at one end and the other end of the steel pipe.

[4] Further, a structure according to the present invention includes the threaded joint according to [1] or [2] above, and a plurality of steel pipes connected by the threaded joint.

[5] Furthermore, the method for constructing a structure according to the present invention is the method for constructing a structure according to [4] above, in which one of the steel pipes with threaded joints to be connected is restrained from rotating, and the other is restrained from rotating. The threaded joint of the steel pipe with a threaded joint is aligned and rotationally fitted to the threaded joint of the one steel pipe with a threaded joint.

[6] Furthermore, a landslide prevention pile according to the present invention includes the threaded joint according to [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 with a threaded joint attached to the end according to [1] or [2] above, The construction shall be carried out in any one of the following manners (1) to (3).
(1) A hole drilling process in which a hole for inserting a pile into the ground is drilled over the entire required length, and the steel pipe is suspended in the drilled hole so that its head protrudes, and the steel pipe is sequentially rotated by the threaded joint. Embodiment (2) comprising the step of joining and inserting the steel pipe under its own weight, and after completing a predetermined number of joint piles, filling the gap between the circumferential surface of the steel pipe and the ground with a filler material to bring it into close contact with the ground. a hole drilling step in which a hole for inserting a pile is drilled over the entire required length; a steel pipe joining step in which the steel pipes are joined to the required length by the threaded joint; and a steel pipe joining step in which the joined steel pipes are inserted into the hole and the Embodiment comprising a step of filling the gap between the circumferential surface of the steel pipe and the ground with a filler material to bring it into close contact with the ground (3) Rotating and press-fitting the steel pipe while taking the reaction force with already installed piles or reaction members A mode comprising the steps of: penetrating into the ground with

[8] In addition, the method for designing a threaded joint according to the present invention includes a male side cylinder body having a male thread made of a tapered thread, and a female side cylinder body having a female thread made of a tapered thread, A method for designing a threaded joint for joining the steel pipes together,
The angle of inclination of the stabbing surfaces of the threads of the male thread and the female thread with respect to the direction perpendicular to the steel pipe axis is set within the range of 0 degrees to +8 degrees.

[9] Further, the design method of a threaded joint according to the present invention includes a male side cylinder body having a male thread made of a tapered thread, and a female side cylinder body having a female thread made of a tapered thread, A method for designing a threaded joint for joining the steel pipes together,
The relationship between the ratio of the applied load to the total plastic load of the steel material and the set screw vertical angle is determined in advance for each friction coefficient, and the set screw vertical angle at which the ratio is 1.0 or more at the friction coefficient set at the time of design is determined as described above. This is set as the inclination angle of the stabbing surfaces of the threads of the male side cylinder and the female side cylinder with respect to the direction perpendicular to the steel pipe axis.

[10] Further, the method for manufacturing a threaded joint according to the present invention includes a male side cylinder body having a male thread made of a tapered thread, and a female side cylinder body having a female thread made of a tapered thread, and the threaded joint has a male side cylinder body having a female thread made of a tapered thread, A method for manufacturing a threaded joint for joining the steel pipes together, the method comprising:
The stabbing surfaces of the threads of the male thread and the female thread have an inclination angle in the range of 0 degrees to +8 degrees with respect to a direction perpendicular to the axis of the steel pipe.

[11] Further, the method for manufacturing a threaded joint according to the present invention includes a male side cylinder body having a male thread made of a tapered thread, and a female side cylinder body having a female thread made of a tapered thread, A method for manufacturing a threaded joint for joining the steel pipes together, the method comprising:
The relationship between the ratio of the applied load to the total plastic load of the steel material and the setting screw vertical angle is determined in advance for each friction coefficient, and the setting screw vertical angle at which the ratio is 1.0 or more at the preset friction coefficient is determined as described above. The stabbing surfaces of the threads of the male cylinder and the female cylinder are formed at an angle of inclination with respect to a direction perpendicular to the axis of the steel pipe.

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

The threaded joint according to the present invention is located at an end of a steel pipe and joins the steel pipes together, and includes a male side cylinder body having a male thread made of a tapered thread, and a female side cylinder body having a female thread made of a tapered thread. and the inclination angle of the stabbing surfaces of the threads of the male thread and the female thread with respect to the direction perpendicular to the steel pipe axis is within the range of 0 degrees to +8 degrees, so that when a compressive load due to bending is applied to the threaded joint, Even in an incompletely joined state where the shoulder part has a gap of about 2 mm, which is not completely closed, sufficient load can be transmitted only through the threaded part on the compression side, and the threaded part on the compression side does not come off, making it possible to connect steel materials to threaded joints. The total plastic load can be fully utilized. Therefore, in the case of threaded joints used for landslide prevention piles that require manual rotational joining at construction sites with poor footing, labor-intensive closing using traction tools and strict construction management can be omitted.

FIG. 1 is an explanatory diagram of a threaded joint according to an embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating the behavior of the entire landslide prevention pile including the threaded joint in FIG. 1 when a bending load is applied to the landslide prevention pile using the threaded joint. 3 is an explanatory diagram illustrating the behavior of the threaded joint in the state shown in FIG. 2. FIG. FIG. 3 is a diagram showing the relationship between the inclination angle (setting screw vertical angle) of the stabbing surface or the loading surface with respect to the direction perpendicular to the steel pipe axis and the coefficient of friction between the stabbing surfaces or between the loading surfaces. It is an explanatory view explaining behavior of a threaded joint in a conventional example. It is an explanatory view explaining steel material total plastic load in examination of inclination angle. FIG. 3 is a diagram showing the analysis results in the study of the inclination angle (Part 1). It is a figure which shows the analysis result in the examination of an inclination angle (part 2). It is a figure which shows the analysis result in the examination of an inclination angle (part 3).

As shown in FIG. 1(a), the threaded joint 1 according to the present embodiment connects the steel pipes 3 to each other at the ends (in the axial direction) of the steel pipes 3, and has a taper thread. A male cylinder body 7 has a male thread 5, and a female cylinder body 11 has a female thread 9, which is a taper thread.
Each configuration will be explained in detail below.

The threaded joint 1 of the present embodiment exemplifies a landslide prevention steel pipe pile (hereinafter abbreviated as "landslide prevention pile") as an example of a structure constituted by connecting a plurality of steel pipes 3, This is applied as a means for joining the steel pipes 3. In the case of landslide prevention piles, the diameter φ of the steel pipe 3 serving as the pile body is 216 mm or more. There is no particular upper limit, but based on recent trends, the diameter φ of steel pipes is 2500 mm or less.
The state shown in FIG. 1(a) indicates a non-closing state, that is, a state in which the tip 11a of the female side cylinder 11 is not in contact with the shoulder portion 7a of the male side cylinder 7 (also referred to as not touching the shoulder). ing.

As shown in FIG. 1(a), the male side cylinder 7 and the female side cylinder 11 are screwed into ring bodies having an outer diameter substantially equal to the outer diameter of the steel pipe 3 that becomes the lower pile and the upper pile. The male cylinder 7 is attached to the lower end of the upper pile, and the female cylinder 11 is attached to the upper end of the lower pile. In the case of this embodiment, the male side cylinder or the female side cylinder is attached to the end of the steel pipe by joining by welding.

Here, the male side cylinder 7 and the female side cylinder 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 7 and the female side cylinder 11 by using the same steel type, the thickness will be required, and the overhang width with respect to the steel pipe 3 will become large. As a result, workability and load transmission performance may deteriorate. Therefore, if you do not want the thickness to be too thick, you can reduce the overhang width by selecting a steel type for the male side cylinder 7 and female side cylinder 11 that exceeds the yield strength of the steel type of the steel pipe 3. can.
For example, in general landslide prevention piles, the steel type of the steel pipe 3 is equivalent to SKK490 material (standard yield strength is 315 N/mm ² ) or SM570 material (standard yield strength is 460 N/mm ² when the plate thickness is 16 mm or less). , 450N/mm ² for plate thicknesses exceeding 16 mm and 40 mm or less, and 430 N/mm ² for plate thicknesses exceeding 40 mm and 75 mm or less) are used. Therefore, if a steel equivalent to HITEN780 material (standard yield strength is 685 N/mm ² ) is used for the male side cylinder 7 and/or the female side cylinder 11, the male side cylinder 7 and the steel type can be improved while increasing the strength. The thickness of the female side cylindrical body 11 can be reduced, and the width of the overhang relative to the steel pipe 3 can be suppressed.

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

FIG. 1(b) shows an enlarged view of the dotted circle portion in FIG. 1(a). In FIG. 1(b), the male thread 5 and female thread 9 are preferably either trapezoidal threads, square threads or buttress threads. Further, the thread of the male screw 5 includes a top portion 51 and two side surfaces 5a (stubbing surface 5a described later) and 5b (loading surface 5b described later) connected to the top portion 51. Further, the side surface 5a of the thread of the male screw 5 and the side surface 5b of the thread adjacent to one side are connected at a thread bottom 52. The side surface 5b of the male thread 5 thread and the other adjacent side surface 5a are connected at a thread bottom 52. Similarly, the female thread 9 has a thread crest 91 and two side surfaces 9b (loading surface 9b described later) and 9a (stubbing surface 9a described later) connected to the crown 91. Further, the side surface 9a of the thread of the female thread 9 and the side surface 9b of the thread adjacent to one side are connected at a thread bottom 92. The side surface 9b of the thread of the female thread 9 and the other adjacent side surface 9a are connected at a thread bottom 92.

Moreover, P shown in FIG. 1(a) indicates the pitch of the thread. The pitch P of this thread is the distance in the axial direction of the steel pipe from the end of the thread crest 51 of the male thread 5 in one thread to the starting position of the thread crest 51 of the next thread 5, or This is the distance in the axial direction of the steel pipe from the end of the thread crest 91 of the female thread 9 to the starting position of the next thread crest 91. Similarly, the pitch of the thread bottom is from the end of the thread bottom 92 corresponding to the thread crest 51 of the male thread 5 in one thread to the end of the thread bottom 92 corresponding to the thread crest 51 of the male thread 5 in the next thread. This is the distance in the axial direction of the steel pipe to the starting position. Or, the distance in the axial direction of the steel pipe from the end of the thread bottom 52 corresponding to the thread crest 91 of one female thread 9 to the starting position of the thread bottom 52 corresponding to the thread crest 91 of the next thread. be. In the case of a single thread thread, pitch means the distance the thread travels during one revolution. On the other hand, in a multi-thread thread, the distance traveled by one revolution varies depending on the number of threads of the thread, so the pitch cannot be defined as a fixed distance. Therefore, in this specification, it is defined as above.

Moreover, h shown in FIG. 1(a) indicates the screw height. Here, the thread height h is the distance from the thread top 51 of the male thread 5 to the thread bottom 52 (distance in the direction of the gradient axis orthogonal axis 23 that is orthogonal to the tapered gradient axis 21), or the thread height of the female thread 9. This is the distance from the portion 91 to the thread bottom 92 (distance in the direction of the gradient axis orthogonal axis 23 that is orthogonal to the gradient axis 21 of the taper).

In the threaded joint 1 according to the present embodiment, the stabbing surfaces 5a and 9a of the threads of the male thread 5 formed on the male side cylinder 7 and the female thread 9 formed on the female side cylinder 11 in the direction perpendicular to the steel pipe axis. The tilt angle α is set between 0 degrees and +8 degrees.
Here, the inclination angle α will be explained.
As shown in FIG. 1(b), if the axis perpendicular to the steel pipe axis 25 is the steel pipe orthogonal axis 27, the inclination angle α is the state in which the threaded joint 1 is in cross section in the direction of the steel pipe axis (the state in FIG. 1). In this figure, the stabbing surfaces 5a and 9a of the threads of the male thread 5 and the female thread 9 form an angle with the steel pipe orthogonal axis 27 on the same cross section.
Here, although not shown, the inclination angles of the loading surfaces 5b and 9b of the threads can also be defined in the same way. In other words, if the axis perpendicular to the steel pipe axis 25 is the steel pipe orthogonal axis 27, the inclination angle of the thread loading surfaces 5b and 9b is the same as that of the threaded joint 1 in the cross section in the steel pipe axial direction (Fig. 1(a) This is the angle that the load surfaces 5b and 9b of the threads of the male thread 5 and the female thread 9 form with the orthogonal axis 27 of the steel pipe on the same cross section.

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

Figure 2 shows the behavior of the entire steel pipe pile, including threaded joint 1, when a bending load is applied to a landslide prevention pile in an unclosed state, and Figure 3 shows the behavior of threaded joint 1 in the state of Figure 2. .
First, the loading surfaces 5b, 9b and stabbing surfaces 5a, 9a of the threads will be explained using a male thread as an example.
The loading surface 5b of the thread of the male screw 5 is a surface located on the base end side of the male cylinder 7 (the side to which the steel pipe 3 is joined) among both side surfaces (flanks) of the thread of the male screw 5. Similarly, the load surface 9b of the thread of the female thread 9 is the surface on the proximal end side of the female cylinder 11 (the side to which the steel pipe 3 is joined) among both side surfaces (flanks) of the thread of the female thread 9. It is. When the threaded joint 1 receives a tensile load after the male thread 5 and the female thread 9 are rotationally fitted and connected, the load surface 5b of the thread of the male thread 5 and the load surface 9b of the thread of the female thread 9 come into contact. .

Further, the stabbing surface 5a of the thread of the male screw 5 is a surface located on the tip 11a side of the male side cylinder body 7 among both side surfaces (flanks) of the thread of the male screw 5. Similarly, the stubbing surface 9a of the thread of the female thread 9 is a surface located on the tip 11a side of the female side cylinder body 11 among both side surfaces (flanks) of the thread of the female thread 9. When the male cylindrical body 7 is rested on the female cylindrical body 11 and rotationally fitted, the stabbing surface 5a of the thread of the male screw 5 comes into contact with the stabbing surface 9a of the female screw 9. That is, to put it simply, the threaded joint 1 has a structure in which compressive force is transmitted through the stabbing surfaces 5a and 9a, and tensile force is transmitted through the loading surfaces 5b and 9b.
In addition, with respect to the inclination angle α of the stabbing surfaces 5a and 9a of the threads in the direction perpendicular to the steel pipe axis, the angle in the direction in which the width of the root widens with respect to the tops 51 and 91 of the threads is defined as a + (plus) angle, and the width narrows. The angle in the direction is expressed as a - (minus) angle.

As described above, in this embodiment, the inclination angle of the stabbing surfaces 5a, 9a of the threads with respect to the direction perpendicular to the steel pipe axis is set to 0 degrees to +8 degrees (see the partially enlarged view of FIG. 3).
By setting the screw vertical angles of the thread stabbing surfaces 5a and 9a as described above, when a bending load is applied to the threaded joint 1, the compressive force is applied to the side (in Fig. 3, the upper side is compression and the lower side is tension). ), the contact surface of the thread becomes difficult to slide out. As a result, as shown in FIG. 3, the stabbing surface 5a of the male screw 5 does not slip and come off, and a sufficient load can be transmitted.

Here, the relationship between the setting screw vertical angle of the stabbing surfaces 5a, 9a and the slippage difficulty of the screw will be explained based on FIG. 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 vertical angle of the setting screw on the stabbing surfaces 5a, 9a or loading surfaces 5b, 9b. This shows the relationship with the friction coefficient.
The vertical axis represents the vertical angle (°) of the setting screw, and the horizontal axis represents the distance between the stubbing surfaces 5a and 9a that contacted each other (sometimes referred to as "between the stubbing surfaces" for short), or the load surface 5b that contacted each other. The coefficient of friction (dimensionless quantity) between the road surface 9b and the road surface 9b (sometimes referred to as "between the road surfaces" for short) is shown.
The straight line in FIG. 4 is an equation derived from the above-mentioned Coulomb's law of friction, and shows the relationship when the setting screw vertical angle is α and the static friction coefficient is μ, which is the following equation (1).
α=tan ^-1 (μ)...(1)
Note that α is the angle of the contacting stabbing surfaces 5a, 9a or the contacting loading surfaces 5b, 9b with respect to the direction perpendicular to the steel pipe axis, and the positive and negative values are as defined above. According to equation (1), when the friction coefficient between the stabbing surfaces or between the load surfaces at a specific setting screw vertical angle α becomes smaller than the static friction coefficient μ, the stabbing surfaces or the load surfaces begin to slide against each other. In other words, if the setting screw vertical angle α is in a range equal to or less than equation (1), it will not slip.
In other words, on the stabbing surfaces 5a, 9a or the loading surfaces 5b, 9b, the hatched area in FIG. 4 where the set screw vertical angle α is equal to or less than equation (1) indicates the "range in which the screw does not slip." In addition, in the figure, a non-hatched region where the setting screw vertical angle α is higher than the equation (1) indicates the "slip range" of the screw.

As can be seen from FIG. 4, if the friction coefficient between the stabbing surfaces or between the load surfaces is the same, the smaller the setting screw vertical angle α, that is, the smaller the inclination angle of the stabbing surfaces 5a and 9a with respect to the direction perpendicular to the steel pipe axis, the more the stabbing It can be seen that the surfaces 5a and 9a become less slippery.
According to the inventor's study shown in [Study of inclination angle] below, by setting the inclination angle of the stabbing surfaces 5a and 9a with respect to the direction perpendicular to the steel pipe axis to 0 degrees to +8 degrees, the total plastic load of the steel material is achieved. It was found that no slippage occurred until Based on this knowledge, the present invention sets the vertical angle of the setting screw to 0 degrees to +8 degrees.

FIG. 5 shows that the angle of the stabbing surfaces 15a and 17a (corresponding to the screw insertion surfaces 13 and 23 in Patent Document 2) in the threaded joint 13 described in Patent Document 2 is an inclination angle of +20 degrees to the direction perpendicular to the steel pipe axis. It shows the behavior when the bending load shown in FIG. 2 is applied to the conventional threaded joint 13 at +45 degrees.
In the threaded joint 13 of Patent Document 2, when a bending load is applied, a force exceeding the frictional force of the threaded portion acts on the threaded portion on the upper side of the figure where compressive force is applied, and as shown in FIG. Slipping occurs on the stabbing surface 15a of the screw, causing the screw to come off.

As described above, in the threaded joint 1 of the present embodiment, the inclination angle of the stabbing surfaces 5a, 9a with respect to the direction perpendicular to the steel pipe axis (setting screw vertical angle) is set to 0 degrees to +8 degrees. As a result, when a compressive load due to bending of the steel pipe 3 is applied to the joint, even if the threaded joint 1 is in an incompletely joined state where the shoulder portion 7a has a gap of about 2 mm, the compression side Sufficient load transmission is possible with just the threaded part. As a result, the entire plastic load of the joint steel material can be fully utilized without the threaded portion on the compression side coming off.
Therefore, it is particularly suitable for the threaded joint 1 used in landslide prevention piles. The reason for this is that threaded joints 1 used for landslide prevention piles are often manually joined by rotation at construction sites with poor footing, and in that case, labor-intensive closing using traction tools and strict construction management are omitted. This is because it is possible.

The following three methods can be considered as specific construction methods when the threaded joint 1 of this embodiment is applied to a landslide prevention pile.
(a) A hole drilling process in which a hole for inserting a pile into the ground is drilled over the entire required length, and a steel pipe to which the threaded joint 1 of the present invention is attached is hung in the drilled hole so that its head protrudes. After the specified number of joint piles are completed, filler material (e.g., grout, mortar, etc.) is filled into the gap between the steel pipe circumferential surface and the ground, and the ground is ground. Closely contact.
(b) A hole drilling process in which a hole for inserting a pile into the ground is excavated over the entire required length, and a steel pipe joining process in which the required length of steel pipes to which the threaded joint 1 of the present invention is attached is joined by the threaded joint 1. Then, the joined steel pipes are inserted into the holes using a crane or the like, and a filler (e.g., grout, mortar, etc.) is filled into the gap between the steel pipe circumferential surface and the ground, and the pipes are brought into close contact with the ground.
(c) The step of penetrating the steel pipe fitted with the threaded joint 1 of the present invention into the ground by rotational press-fitting while taking the reaction force with the already constructed pile or reaction member, and the step of inserting the steel pipe into the ground that has penetrated into the ground. A method comprising a step of rotatably joining steel pipes to which the threaded joint 1 of the present invention is attached, and a step of penetrating the rotatably joined steel pipes into the ground by rotary press-fitting.

Of course, the present invention can also be used for piles or steel pipes other than landslide prevention piles. More specifically, it can be used for support piles, friction piles, steel pipe sheet piles, diagonal piles, or steel pipes that are part of structures. Even when used in these applications, the effect already explained, that is, when compressive load due to bending of the steel pipe 3 acts on the joint, an incomplete joint that is not completely closed, such as a gap of about 2 mm in the shoulder portion 7a, may occur. Even with the threaded joint 1 in this state, it is possible to obtain the effect that sufficient load can be transmitted only by the threaded portion on the compression side.

Here, a threaded joint for oil country tubular goods, in which a tapered threaded joint is generally used, will be explained. Oil country tubular goods have a small maximum diameter of 240mm, so they can be rotated and joined with less torque. In addition, there is a high demand for sealing performance for the purpose of transporting the contents inside the pipe without leaking. As a result, it is used with the screw fully tightened, that is, with the tip 11a of the female cylinder 11 in contact with the shoulder portion 7a of the male cylinder 7 (also referred to as shoulder touching). Therefore, when a bending load is applied to the connected oil country tubular goods, compressive force can be transmitted through the shoulder portion. Furthermore, since it is not a structural member that is subjected to any external load, high strength is not required. Considering the above circumstances and from the viewpoint of improving sealing performance, the angle of inclination of the stabbing surface with respect to the direction perpendicular to the axis of the steel pipe is set to +30° to +60° so that the shaft rotates with a small torque. On the other hand, threaded joints used as structural members have a maximum diameter of approximately 2,500 mm, so they require a very large torque to rotate, making joining difficult. Furthermore, since it is a structural member, high strength is required of the thread, and it is desirable that the angle of inclination of the stabbing surface with respect to the direction perpendicular to the axis of the steel pipe be large. Furthermore, sealing properties as good as oil country tubular goods are not required. Therefore, when conventional taper threaded joints (particularly oil country tubing technology) are applied as they are to structural components, the tip 11a of the female side cylinder 11 does not completely contact the shoulder portion 7a of the male side cylinder 7. Requires use under closed conditions.
In other words, the very remarkable effect of the threaded joint according to the present invention is that it is a threaded joint that ensures the strength of the thread as a structural member and that the threaded part on the compression side does not come off even in the non-clamped state. be.

In addition, in Patent Document 2, if the screw insertion surface angle (setting screw vertical angle) is smaller than +20 degrees, the cutting resistance during thread cutting increases, so the amount of cutting in one pass must be reduced, and the machining It is stated that efficiency decreases.
However, by applying the present invention, the load transmission efficiency of the threaded portion increases, and the number and height of threads can be reduced, so the reduction in the amount of cutting in one pass does not become a major problem.
Additionally, Patent Document 2 states that during joint pile work, it becomes difficult to center the upper and lower piles, and the screw fastening performance decreases, but the target structure is If the outer diameters are the same, alignment will not be a major problem because the position can be confirmed in four directions.

Although the present invention is directed to tapered threads, it is applicable not only to single thread threads but also to multi thread threads.

In addition, it is preferable that all the threads in the male side cylinder 7 and the female side cylinder 11 and the pitches of the corresponding thread bottoms are set to be the same.
By setting in this way, when a load is applied to the threaded joint 1, all the screw threads are evenly abutted in the axial direction and the load can be transmitted.

In addition, in order to construct a landslide prevention pile as a structure having a threaded joint 1, for example, with the rotation of one of the threaded joint steel pipes to be connected being restrained, the threaded joint 1 of the other threaded joint steel pipe, What is necessary is just to align with the threaded joint 1 of said one steel pipe with a threaded joint, and to rotationally fit it.

Further, in order to design the threaded joint 1, the following design method is used.
1. A method for designing a threaded joint for joining steel pipes together at an end of a steel pipe, the threaded joint having a male cylinder having a male thread made of a tapered thread, and a female cylinder body having a female thread made of a tapered thread. ,
A method for designing a threaded joint, in which the inclination angle of the stabbing surfaces of the threads of the male thread and the female thread with respect to the direction perpendicular to the axis of the steel pipe is set within the range of 0 degrees to +8 degrees.

Moreover, in order to manufacture the threaded joint 1, the following manufacturing method is used.
A method for manufacturing a threaded joint for joining steel pipes together at an end of a steel pipe, the threaded joint having a male cylinder having a male thread made of a tapered thread, and a female cylinder body having a female thread made of a tapered thread. ,
A method for manufacturing a threaded joint, wherein the stubbing surfaces of the threads of the male thread and the female thread are inclined at an angle of inclination to a direction perpendicular to the axis of the steel pipe within a range of 0 degrees to +8 degrees.

In addition, in order to manufacture a steel pipe with a threaded joint including the male side cylinder body 7 and the 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 are attached to one end of the steel pipe. and the other end.

[Study of inclination angle]
In the present invention, as described above, the optimum range of the inclination angle of the thread stabbing surfaces 5a, 9a with respect to the direction perpendicular to the steel pipe axis is 0 degrees to +8 degrees, but this is based on the FEM analysis results. This FEM analysis will be explained below.
The analysis model is a three-dimensional four-point bending (see Figure 2) 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 distance between loading points of 1200 mm. In this model, the threaded joint 1 is placed in the center of the uniform bending section when the female side cylinder 11 attached to the other steel pipe 3 is joined, and the strength against the bending load is confirmed.

Further, in order to consider the non-closing state, the initial arrangement of the male side cylinder 7 and the female side cylinder 11 was such that the gap between the shoulder portion 7a and the tip 11a of the female side cylinder 11 was 2 mm. Furthermore, in order to take the contact state into consideration, the male side cylinder 7 and the female side cylinder 11 are given contact conditions that enable contact determination, and the stubbing surfaces 5a and 9a and the loading surfaces 5b and 9b, which are the contact parts, are set as follows. The coefficients of friction between the stabbing surfaces and between the loading surfaces were used. It is a contact analysis elastic-plastic model that takes into account the elastic-plastic behavior of steel materials.

The coefficient of friction between the stabbing surfaces and between the loading surfaces used in the analysis was set to 0.1, which is the general coefficient of friction between steel materials under sliding conditions (for example, under conditions where lubricant is applied).

Further, the vertical angle of the setting screws of the load surfaces 5b and 9b was set to 0 degrees.
Generally, it is said that the load transmission force is high when the vertical angle of the setting screw on the load surface is 0 degrees. When the vertical angle of the setting screw is negative, it is generally called a hook screw shape, which can suppress the slippage of the thread part, but the width of the root of the screw thread (the width of the root of the screw thread sides 5a, 9a and the sides 5b, 9b) As the width (width) becomes smaller, the rigidity of the threaded part decreases, making it more likely to deform. Therefore, it is difficult to apply it to structural members that require high strength (especially landslide prevention piles, landslide prevention walls, earth retaining walls, foundation steel pipe piles, steel pipe sheet piles, and steel pipe columns). On the other hand, in the case of a positive thread, the shape is generally called a trapezoidal thread, and the threaded part has high rigidity and is difficult to deform, but the threaded part is likely to slip.

In other words, the reason why the vertical angle of the setting screws on the load surfaces 5b and 9b was set to 0 degrees is that if the vertical angle of the setting screws on the load surfaces 5b and 9b were +10 degrees, it would be easy to come off on the tension side. This is because by setting the vertical angle of the setting screws 5b and 9b to 0 degrees, the tensile load transmission force is the highest in the threaded joint 1 as a structure, and the conditions are such that it is relatively easy to come off on the compression side.

By specifying the vertical angle of the setting screw on the stubbing surfaces 5a and 9a that can exert the full plastic load on the steel material without causing the threaded part on the compression side to come off under such conditions, the vertical angle of the setting screw on the loading surfaces 5b and 9b can be adjusted. It is possible to define a set screw vertical angle of the stabbing surfaces 5a, 9a that can suppress screw dislodgement on the compression side regardless of the compression side.
As shown in Figure 6, the steel total plastic load is equivalent to the cross section at the center of the bottom of the male thread 5, which is the weak point of the joint (see the area surrounded by the broken line square in Figure 6). This is a value calculated based on the plastic section modulus and steel yield stress assuming a virtual steel pipe 19.

In this study, the vertical angle of the setting screws on the loading surfaces 5b and 9b is 0 degrees with respect to the direction 66 perpendicular to the steel pipe axis, and the vertical angles of the setting screws on the stabbing surfaces 5a and 9a are 0 degrees, +5 degrees, +6 degrees, +8 degrees. It was conducted in 5 cases at 10°C and +10°C.
Note that, similarly to the case of the vertical angle of the setting screw on the loading surface, when the vertical angle of the setting screw on the stabbing surface is negative, slippage of the threaded portion can be suppressed by a shape generally called a hook screw. However, since the width of the base of the screw thread becomes smaller, the rigidity of the threaded part decreases and it becomes easily deformed, making it difficult to apply it to structural members that require high yield strength. Therefore, it was excluded from consideration.

FIG. 7 shows the analysis results when the vertical angle of the setting screws on the loading surfaces 5b, 9b is 0 degrees, and the vertical angle of the setting screws on the stabbing surfaces 5a, 9a is 0 degrees.
The vertical axis in Figure 7 is the load ratio (load load/total plastic load of the steel material), which is made dimensionless by dividing the load determined by analysis by the total plastic load of the steel material, and the horizontal axis is the displacement at the center of the span (mm). It is.

From FIG. 7, it can be seen that when the vertical angle of the setting screw of the stabbing surfaces 5a, 9a is 0 degrees, the load ratio decreases when it exceeds 1.12. That is, the stabbing surfaces 5a, 9
When the vertical angle of the set screw in a is 0 degrees, it is shown that the threaded part does not come off under the full plastic load of the steel material, and it can be seen that the full plastic load of the steel material can be exerted. Here, the maximum value immediately before the load ratio decreases (inverted black triangle mark ▼ in FIG. 7) is referred to as the maximum load ratio. From Figure 7, the maximum load ratio is 1.12 when the vertical angle of the setting screw is 0 degrees.

A similar analysis was carried out for the cases where the setting screw vertical angles of the stabbing surfaces 5a and 9a were +5 degrees, +6 degrees, +8 degrees, and +10 degrees, and the same analysis results as in Fig. 7 were obtained. The maximum load ratio for each vertical angle was determined. The graph of FIG. 8 summarizes the results of the maximum load ratio for each set screw vertical angle, including the case where the set screw vertical angle of the stabbing surfaces 5a and 9a is 0 degrees.
The vertical axis in FIG. 8 is the same load ratio (load load/total plastic load of steel material) as the vertical axis in FIG. 7, and the horizontal axis is the setting screw vertical angle (°).

The graph of FIG. 8 is marked with a dotted line, which is the result of regression analysis of the analysis results. From the results of this regression analysis, if the vertical angle of the set screw is 8 degrees or less, the load ratio (load load/total plastic load of the steel material) is greater than 1, which means that the thread on the compression side will not come off and the full plastic load of the steel material will be utilized. I can read that it can be done. On the other hand, if it exceeds 8 degrees, the steel load ratio will be less than 1, and the threaded part on the compression side will come off before the steel's total plastic load is reached, indicating that the steel's total plastic load cannot be utilized.

From the above analysis results, it has been demonstrated that 8 degrees or less is appropriate as the setting screw vertical angle defined in the present invention.

The above study assumes that the coefficient of friction between the stabbing surfaces and between the loading surfaces is 0.1. This is because the coefficient of friction between the steel materials that form the joint is approximately 0.45, and under conditions where the joint is coated with lubricating oil and slips, it becomes 0.1 to 0.2, so 0.1 is used as the most severe condition.
Therefore, the above results are valid for general threaded joints.

However, as shown in FIG. 4, as the coefficient of friction between the stabbing surfaces or between the loading surfaces becomes smaller, the vertical angle of the setting screw at which it begins to slide becomes smaller. For this reason, the inventor set the vertical angle of the setting screws on the loading surfaces 5b and 9b to 0 degrees and the vertical angle of the setting screws on the stabbing surfaces 5a and 9a when the friction coefficient between the stabbing surfaces and between the loading surfaces is set to 0.06. We analyzed five cases with angles of 0 degrees, +3 degrees, +4 degrees, +8 degrees, and +10 degrees.
The analysis results are shown in Figure 9. FIG. 9 also shows a case where the friction coefficient between the stabbing surfaces and between the load surfaces described above is set to 0.1.

From the graph in Figure 9, when the coefficient of friction between the stabbing surfaces and between the loading surfaces is set to 0.06, in order to take advantage of the full plastic load of the steel material without the threaded part on the compression side coming off, it is necessary to It can be seen that the angle should be set to 3 degrees or less.

Therefore, in order to design the threaded joint 1 when the friction coefficient between the stabbing surfaces is special, it is more preferable to design the threaded joint 1 by considering the friction coefficient between the stabbing surfaces.In this case, the design method is as follows. The design method is as follows.
A threaded joint that is located at the end of a steel pipe 3 and joins the steel pipes 3 together, and has a male side cylinder body 7 having a male thread 5 made of a tapered thread, and a female side cylinder body 11 having a female thread 9 made of a tapered thread. A design method,
The relationship between the ratio of the applied load to the total plastic load of the steel material and the set screw vertical angle is determined in advance for each friction coefficient between the stabbing surfaces, and the ratio is 1.0 or more for the friction coefficient between the stabbing surfaces set during design. A method for designing a threaded joint in which the vertical angle of the setting screw is set as the inclination angle of the stabbing surfaces 5a and 9a of the threads in the male cylinder 7 and the female cylinder 11 with respect to the direction perpendicular to the steel pipe axis.

In addition, when the friction coefficient between the stabbing surfaces is special, in order to manufacture the threaded joint 1, it is more preferable to form the threaded joint by considering the friction coefficient between the stabbing surfaces, and in this case, the manufacturing method is as follows: , the manufacturing method is as follows.
A method for manufacturing a threaded joint for joining steel pipes together at an end of a steel pipe, the threaded joint having a male cylinder having a male thread made of a tapered thread, and a female cylinder body having a female thread made of a tapered thread. ,
The relationship between the ratio of the applied load to the total plastic load of the steel material and the set screw vertical angle is determined in advance for each friction coefficient between the stabbing surfaces, and the ratio is 1.0 or more for the preset friction coefficient between the stabbing surfaces. A method for manufacturing a threaded joint, in which the setting screw vertical angle is formed as an inclination angle of stabbing surfaces of threads in the male side cylinder and the female side cylinder with respect to a 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 entire plastic load of the joint steel without causing the threaded portion on the compression side to come off even in an incompletely joined state in which the shoulder portion does not touch. Further, according to the present invention, a steel pipe with a threaded joint, a structure, a method of constructing a structure, a landslide prevention pile, a construction method of a landslide prevention pile, a design method of a threaded joint, a threaded joint and a method for manufacturing a steel pipe with a threaded joint.

1 Threaded joint 3 Steel pipe 5 Male thread 5a Stubbing surface 5b Loading surface 51 Top 52 Threaded bottom 7 Male cylinder 7a Shoulder part 9 Female thread 9a Stubbing surface 9b Loading surface 91 Top 92 Threaded bottom 11 Female cylinder 11a Tip 13 Threaded joint ( Patent document 2)
15 Male thread 15a Stubbing surface 15b Load surface 17 Female thread 17a Stubbing surface 17b Load surface 19 Virtual steel pipe 21 Taper gradient axis 23 Gradient axis orthogonal axis 25 Steel pipe axis 27 Steel pipe orthogonal axis P Thread pitch h Thread height α Inclination angle, setting Thread vertical angle (relative to stabbing surface or relative to loading surface)

Claims (2)

1. A method for designing a threaded joint for joining steel pipes together at an end of a steel pipe, the threaded joint having a male cylinder having a male thread made of a tapered thread, and a female cylinder body having a female thread made of a tapered thread. ,
The relationship between the ratio of the applied load to the total plastic load of the steel material and the set screw vertical angle is determined in advance for each friction coefficient, and the set screw vertical angle at which the ratio is 1.0 or more at the friction coefficient set at the time of design is determined as described above. A method for designing a threaded joint in which the stabbing surfaces of the threads of the male side cylinder and the female side cylinder are set as an inclination angle with respect to a direction perpendicular to the axis of the steel pipe. A method for manufacturing a threaded joint for joining steel pipes together at an end of a steel pipe, the threaded joint having a male cylinder having a male thread made of a tapered thread, and a female cylinder body having a female thread made of a tapered thread. ,
The relationship between the ratio of the applied load to the total plastic load of the steel material and the setting screw vertical angle is determined in advance for each friction coefficient, and the setting screw vertical angle at which the ratio is 1.0 or more at the preset friction coefficient is determined as described above. A method for manufacturing a threaded joint, in which the stabbing surfaces of the threads of the male side cylinder and the female side cylinder are formed at an angle of inclination with respect to a direction perpendicular to the axis of the steel pipe.

Images