JPH10169865A - Fitting structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide fitting structure capable of minimizing the bending crack made when the bending of a second cylindrical body and that of a third cylindrical body are maximized even though the relative swing range of the second and third cylindrical bodies is taken as much as possible by contriving to decide the molding position of a stopper section and capable of miniaturizing and lightening fittings. SOLUTION: One end side of a second cylindrical body 2(B) is liquid-tightly or air-tightly inserted into and connected to a first cylindrical body 1(A) so as to freely relatively movable in the axial direction in a fixed range, and a third cylindrical body 3(C) is airtightly or liquid-tightly and externally fitted and connected to the other end of the second cylindrical body 2(B) so as to be relatively swingable. A stopper section 8 is projectedly formed in the outer peripheral surface of the second cylindrical body 2(B) so as to restrain the abutting on the Maximum moving position to the side of the third cylindrical body 3(C) of the end section 1a of the first cylindrical body 1A. When the second cylindrical body 2(B) and the third cylindrical body 3(C) relatively move to a maximum bending angle, the end section 3a of the third cylindrical body 3(C) abuts on the outer peripheral face of the stopper 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a pipe system for a fluid transport pipe such as a water pipe buried underground, which is provided with a compressive force or a tensile force in the direction of a cylinder axis caused by an earthquake, a differential settlement, or the like. When an external force such as a shearing force or a bending moment in a direction intersecting with the cylinder axis is applied, the external force is absorbed as much as possible at the pipe connection portion, so that breakage at the fragile portion of the piping system can be suppressed. In addition, one end of the second cylindrical body is inserted and connected to the first cylindrical body in a sealed state so as to be relatively movable in the cylinder axis direction within a certain range, and is connected to the other end of the second cylindrical body. The present invention relates to a pipe joint structure in which a third cylindrical body is externally connected in a sealed state so as to be swingable relative to each other.

[0002]

2. Description of the Related Art Conventionally, as this kind of pipe joint structure,
As shown in FIG. 5, a spherical portion 52A formed on the other end of the second cylindrical body 52, a partially spherical cylindrical portion 53A formed on one end of a third cylindrical body 53, A partial spherical cylindrical portion 54A of a connecting cylinder 54 having a connecting flange 54B that can be fixedly connected via bolts 55 and nuts 56 to a connecting flange 53B protruding from the outer peripheral surface of the cylindrical portion 53A is connected to both sides in the cylinder axis direction. And the third cylindrical body 53
Connection flange 53B on the side and connection flange 5 on connection tube 54
4B is fastened by bolts 55 and nuts 56, so that the second tubular body 52 and the third tubular body 53 can be relatively slidably and slidably connected along the outer peripheral surface of the spherical tubular portion 52A. And then
The outer circumferential surface of the linear tubular portion 52B of the second tubular body 52 and an intermediate portion separated from the swing region of the end portion 54a of the connecting barrel 54 toward the first tubular body 51 side include 1 cylindrical body 5
One in which a stopper portion 57 that regulates the maximum movement position of the first cylindrical body 53 toward the side of the third cylindrical body 53 by contact with the end portion 51a of the first cylindrical body 51 is formed is proposed (eg,
See Japanese Utility Model Laid-Open No. 57-71883).

In the conventional pipe joint structure, an external force in the compression direction caused by an earthquake, uneven settlement, or the like acts to move the first tubular body 51 to the third tubular body 53 side. Even if it contracts and moves to the maximum, the end 51a of the first tubular body 51
Is restricted by the stopper portion 57 to a position outside the swing region of the end portion 54a of the connecting cylinder 54, so that the straight cylindrical portion 5 of the second cylindrical body 52
The end portion 51 of the first cylindrical body 51 whose outer diameter is larger than the outer diameter of 2B due to the presence of a sealing structure such as a sealing material.
a does not enter between the end portion 54a of the connecting cylinder 54 and the outer peripheral surface of the linear tubular portion 52B of the second tubular body 52, and the end portion 51a of the first tubular body 51 It is possible to suppress a decrease in the range of the bending swing of the second tubular body 52 and the third tubular body 53 due to the entry. However,
The stopper portion 57 is provided at an intermediate position in the cylinder axis direction of the linear tubular portion 52B of the second tubular body 52 which is largely separated from the swing region of the end portion 54a of the connecting cylinder 54 toward the first tubular body 51. As a result, the overall length of the second tubular body 52 is increased, which tends to increase the size and weight of the pipe joint structure. Moreover, when the second cylindrical body 52 and the third cylindrical body 53 relatively swing to the maximum bending angle, the end 54 of the connecting cylinder 54
Since a is strongly pressed on the outer peripheral surface of the linear tubular portion 52B of the second tubular body 52, stress concentration at this portion may cause the second tubular body 52 to be damaged such as a crack.

The present invention has been made in view of the above circumstances, and a main problem thereof is to make the outer diameter of the stopper portion smaller than the outer diameter of the end portion of the second cylindrical body. By focusing on the possible points, the position of the stopper portion is devised so that the relative swing range between the second cylindrical body and the third cylindrical body is as large as possible, but the two cylindrical bodies are maximized. It is an object of the present invention to provide a pipe joint structure that can suppress breakage when bent to the utmost, and can also achieve a reduction in size and weight of the pipe joint structure at the same time.

[0004]

According to a first aspect of the present invention, in the pipe joint structure according to the first aspect, an end portion of the first cylindrical body is provided on an outer peripheral surface of the second cylindrical body. A stopper portion for restricting the maximum movement position of the third cylindrical body toward the outside of the swing region at the end of the third cylindrical body is formed so as to protrude, and the second cylindrical body and the third cylindrical body are formed. Is configured so that the end portion of the third cylindrical body contacts the outer peripheral surface of the stopper portion when the relative swing of the third cylindrical member reaches the maximum bending angle. According to the above-mentioned characteristic configuration, even if an external force in the compression direction caused by an earthquake, uneven settlement, or the like acts, the end of the first cylindrical body contracts and moves to the third cylindrical body side to the maximum. The maximum movement position of the end of the first cylindrical body is restricted by the stopper to a position outside the swing region of the end of the third cylindrical body. The end of the first cylindrical body, whose outer diameter has become larger due to the presence of a sealing structure such as a sealing material than the outer diameter of the end, is connected to the inner peripheral surface of the end of the third cylindrical body and the second cylindrical body. It does not enter between the outer peripheral surface of the cylindrical body. In addition, when an external force such as a shearing force or a bending moment caused by an earthquake, uneven settlement, or the like acts, the second cylindrical body and the third cylindrical body relatively swing to a maximum bending angle. Since the end of the cylindrical body abuts on the outer circumferential surface of the stopper having a high mechanical strength and formed on the outer circumferential surface of the second cylindrical body, external force can be reliably received by the stopper. . Further, while the relative movement range between the first tubular body and the second tubular body is configured to be the same as the conventional movable range, the stopper is close to the end of the third tubular body, The overall length of the second cylindrical body can be reduced. However, the outer diameter of the stopper portion can be configured to be smaller than the outer diameter of the end portion of the first tubular body to which a sealing structure such as a sealing material is added. The end of the third tubular body and the second
The relative swing range between the second cylindrical body and the third cylindrical body can be increased as compared with a case where the cylindrical body enters between the outer peripheral surface of the cylindrical body and the cylindrical body. Therefore, by devising the formation position of the stopper portion as described above, while maximizing the relative swing range between the second cylindrical body and the third cylindrical body, these two cylindrical bodies are maximized. Breakage when bent can be suppressed, and the size and weight of the pipe joint structure can be reduced at the same time.

[0005] The characteristic feature of the pipe joint structure according to claim 2 of the present invention is that when the second cylindrical body and the third cylindrical body relatively swing to a maximum bending angle, the end of the third cylindrical body is bent. And the outer peripheral surface of the stopper portion is configured to abut along the cylinder axis direction. According to the above-mentioned characteristic configuration, when the second cylindrical body and the third cylindrical body relatively swing to the maximum bending angle and the end of the third cylindrical body is pressed against the outer peripheral surface of the stopper portion. Since the pressing force can be dispersed and supported in the cylinder axis direction, the durability of the pipe joint structure can be improved.

According to a third aspect of the present invention, a characteristic feature of the pipe joint structure is that the pipe joint is relatively slidably contacted with the spherical cylindrical portion formed at the other end of the second cylindrical body along the outer peripheral surface of the spherical cylindrical portion. A third cylindrical body provided with a swingable partial spherical cylindrical portion is externally fitted from one side in the axial direction of the cylindrical shaft, and an outer peripheral surface of the spherical cylindrical portion of the second cylindrical body and the third cylindrical shape A sliding guide member, which is in sliding contact with the outer peripheral surface of the spherical cylindrical portion of the second cylindrical body, is fitted into the gap formed between the inner peripheral surface of the partial spherical cylindrical portion of the body from the other side in the cylinder axis direction. And the second tubular body and the third tubular body are connected so as to be relatively slidable and swingable. According to the above-mentioned characteristic configuration, when the second cylindrical body and the third cylindrical body are detachably connected to each other so as to be slidable and slidable relative to each other, the sliding contact guide member is connected to the spherical cylinder of the second cylindrical body. Since it is fitted in the gap formed between the outer peripheral surface of the portion and the inner peripheral surface of the partially spherical cylindrical portion of the third cylindrical body from the axial direction of the cylindrical shaft, the connecting flange is formed as in the conventional pipe joint structure. The connecting components such as the bolts and nuts do not protrude outward in the radial direction, so that the pipe joint structure can be made compact and the outer shape can be simplified. Moreover, by employing such a retaining connection means, the opening diameter of the gap formed between the inner peripheral surface of the end of the third cylindrical body and the outer peripheral surface of the second cylindrical body is reduced. The outer diameter of the end of the first cylindrical body may be larger than the outer diameter of the first cylindrical body. In this case, however, the stopper can prevent the end of the first cylindrical body from entering, so that the first cylindrical body can be prevented from entering. The described effects can be reliably exerted.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] The pipe joint structure for fluid transport (for example, for tap water) shown in FIGS. 1 and 2 is a pipe-shaped first joint pipe 1 made of cast iron serving as a first cylindrical body A at both ends. And one end of the second joint pipe 2 made of cast iron as the second cylindrical body B is inserted and connected in a sealed state so as to be relatively movable in the cylinder axis X direction (tube axis direction) within a certain range. At the same time, a third joint pipe 3 made of cast iron as a third cylindrical body C is externally fitted to the other end side of each of the second joint pipes 2 in a sealed manner so as to be relatively swingable. One joint pipe 1, two second joint pipes 2, and both third joint pipes 3 are connected for communication.

As shown in FIGS. 1 to 3, each of the portions of the outer peripheral surface of the straight pipe portion 2B of the two second joint pipes 2 inserted into the first joint pipe 1 has the first joint pipe. Forming an annular mounting groove 5 having a length in the cylinder axis X direction smaller than that of the annular regulating groove 4 formed in an intermediate portion of the inner peripheral surface of the joint pipe 1 in the cylinder axis X direction;
A radial expansion deformation that restricts the first joint pipe 1 from coming out from one end of the second joint pipe 2 by surface contact of each of the mounting grooves 5 with the end face 4 a of the regulating groove 4 in the direction of the cylinder axis X. A possible stainless steel C-shaped locking member 6 is detachably fitted to the first joint pipe 1 so as to be relatively movable in a state where one end of the second joint pipe 2 is prevented from coming off. Is inserted and connected. The distance between the outer peripheral surface of the straight pipe portion 2B of the second joint pipe 2 and the inner peripheral surface 4b of the regulating groove 4 in the cylinder radial direction (diameter direction) allows the insertion and removal of the locking member 6. The interval is set. In other words, an annular space is formed between the outer peripheral surface of the straight pipe portion 2B of the second joint pipe 2 and the inner peripheral surface 4b of the regulating groove 4 so as to allow insertion and removal of the locking member 6. It is. Further, as shown in FIG. 3, an external force (tensile force) in the pull-out direction caused by an earthquake, uneven settlement, or the like acts on the pipe joint structure, and the first joint pipe 1 has an open end side (second end).
Each of the locking members 6 fitted in the mounting grooves 5 of the second joint pipes 2 is positioned from the cylinder axis X direction with respect to each end face 4a of the restriction groove 4 located on the side of the insertion of the joint pipe 2). When you have an interview,
A diameter-enlargement restricting portion 7 is provided for preventing the locking member 6 from coming out of the mounting groove 5 outward in the cylinder radial direction.

As shown in FIG. 3, each of the two diameter-enlarging restricting portions 7 is provided with the restricting groove 4 close to the outer peripheral surface 6a of the locking member 6 which is in contact with one end surface 4a of the restricting groove 4. Inner peripheral surface 4b
And the outer peripheral surface 6a and the diameter expansion regulating surface 7a of the locking member 6 are configured to be parallel or substantially parallel to the cylinder axis X. I have. Further, both end surfaces 6c of the locking member 6 on both sides in the cylinder axis X direction, and both end surfaces 4 of the regulating groove 4 in the cylinder axis X direction.
a are each formed on a deviated flat surface along a direction orthogonal or substantially orthogonal to the cylinder axis X, and are respectively formed on the two enlarged diameter regulating surfaces 7a of the inner peripheral surface 4b of the regulating groove 4. A continuous boundary surface portion 4c is formed on the tapered surface.

As shown in FIGS. 1 to 4, a spherical tube portion 2A as a spherical cylindrical portion having a partially spherical outer peripheral surface 2a formed on the other end side of the second joint pipes 2 is provided. Spherical tube part 2
A partial spherical tube portion 3A as a partial spherical cylindrical portion provided with a partial spherical inner peripheral surface 3b and a circular inner peripheral surface 3c that can freely slide and swing along the outer peripheral surface of A. The third joint pipe 3 provided is externally fitted from the outside of the other end of the second joint pipe 2 in the cylinder axis X direction, and the outer peripheral surface 2a of the spherical pipe portion 2A of the second joint pipe 2 In the gap formed between the partially spherical tube portion 3A of the three-joint tube 3 and the inner circumferential surface 3c of the partial spherical tube portion 3A,
A spherical sliding contact surface 13a slidingly contacting the outer peripheral surface 2a of the spherical tube portion 2A of the second joint tube 2 slidingly contacting the outer peripheral surface 2a of the spherical tube portion 2A of the joint tube 2, and a partial spherical tube of the third joint tube 3 A circumferential sliding surface 13b slidingly contacting the circumferential inner surface 3c of the portion 3A
The sliding contact guide member 13 made of cast iron having the following is fitted from the first joint pipe 1 side in the cylinder axis X direction, and furthermore, the inner circumferential surface of the partial spherical pipe part 3A of the third joint pipe 3 is formed. Diameter-reducing deformable stainless steel C for preventing the slide-out guide member 13 from coming out of contact with the holding groove 3d formed on the peripheral surface 3c.
The second joint pipe 2 and the third joint pipe 3 are relatively positioned by detachably fitting a U-shaped stopper member 14 to prevent the sliding contact guide member 13 from moving out of the gap. It is connected so that it can slide and swing freely.

Further, as shown in FIGS. 2 and 4, external force in the compression direction caused by an earthquake, uneven settlement, etc. is applied to each of the outer peripheral surfaces of the straight pipe portions 2B of the second joint pipes 2. When acting on the structure, the end portion 1a of the first joint tube 1 comes into surface contact with the end portion 1a of the first joint tube 1 from the direction of the cylinder axis X, and the maximum movement position of the end portion 1a of the first joint tube 1 toward the third joint tube 3 is determined. A stopper portion 8 for restricting the end of the third joint pipe 3 on the side of the first joint pipe 1 on the side of the swinging region 3a.
Are formed integrally with each other, and the end face 4a of the regulating groove 4 is formed.
Surface contact between the first joint pipe 1 and one of the second joint pipes 2 by surface contact between the first joint pipe 1 and the stopper part 8 and surface contact between the end 1a of the first joint pipe 1 and the stopper part 8. The relative movement range in the X direction is regulated so as to be within a certain range. The stopper portion 8 is formed of an annular ridge integrally formed on the outer peripheral surface of the straight pipe portion 2B of the second joint pipe 2 along the circumferential direction thereof. The outer diameter of the outer peripheral surface of the stopper portion 8 is configured to be smaller than the maximum outer diameter of the end portion 1 a of the first joint pipe 1.

As shown in FIG. 2 and FIG. 4, when an external force such as a shearing force or a bending moment in a direction intersecting with the cylinder axis X due to the earthquake or uneven settlement acts on the pipe joint structure, Outer peripheral surface 2a of spherical tube portion 2A of second joint tube 2
And the spherical inner peripheral surface 3 of the partially spherical pipe portion 3A of the third joint pipe 3
b along the spherical surface, and the relative sliding along the spherical surface between the outer peripheral surface 2a of the spherical tube portion 2A of the second joint pipe 2 and the spherical sliding contact surface 13a of the sliding contact guide member 13. In addition, the second joint pipe 2 and the third joint pipe 3 are relatively slidably contacted and rocked to bend, thereby suppressing damage to the pipe joint structure. Further, when the second joint pipe 2 and the third joint pipe 3 relatively slide and swing along the spherical surface to the maximum bending angle, the first joint pipe 1 and the third joint pipe 3 do not interfere with each other. In the state, the third joint pipe 3
The inner peripheral corner 3e of the opening of the end 3a is configured to contact the outer peripheral surface of the stopper portion 8. For more information,
As shown in FIG. 4, when the second joint pipe 2 and the third joint pipe 3 relatively slide and swing along the spherical surface to the maximum bending angle, the end 1a of the first joint pipe 1 and the third joint pipe 3 Joint tube 3 and end 3a
The inner peripheral edge corner 3e of the opening and the outer peripheral surface of the stopper portion 8 are configured to contact along the cylinder axis X direction without contact. That is, the stopper portion 8 is formed on the outer peripheral surface of the straight pipe portion 2B of the second joint pipe 2 at a position intersecting with the swing locus of the opening inner peripheral corner 3e of the end 3a of the third joint pipe 3. In a state in which the second joint pipe 2 and the third joint pipe 3 are relatively slidably contacted and swung up to the maximum bending angle, the inner peripheral edge corner portion 3 e is attached to the outer peripheral surface of the stopper portion 8 by the cylindrical shaft core. It is formed on a tapered surface along the X direction.

As shown in FIGS. 1 to 4, a straight pipe portion 2B of the second joint pipe 2 is provided near each end of the inner peripheral surface of the first joint pipe 1 in the direction of the cylinder axis X. An annular seal holding groove 10 for holding a first elastic seal material 9 made of synthetic rubber (for example, styrene-butadiene rubber), which is an example of a sealing structure for sealing the outer peripheral surface of the third seal member, is formed. A synthetic structure which is an example of a sealing structure for sealing between the inner peripheral surfaces 3b and 3c of the partial spherical tube portion 3A of the joint tube 3 and the outer peripheral surface 2a of the spherical tube portion 2A of the second joint tube 2. Second elastic sealing material 11 made of rubber (for example, styrene-butadiene rubber)
An annular seal holding groove 12 is formed, and each of the ends of the straight pipe portions 3B of the third joint pipes 3 is provided with a fluid transport pipe (for example, a water pipe) and a gate valve device. A plurality of connection through holes 3f for fixing and connecting the fluid piping devices P with bolts and nuts are integrally formed with a connection flange 3C.

Therefore, in the pipe joint structure constructed as described above, an external force in the compression direction due to an earthquake, differential settlement, or the like acts, and the end 1a of the first joint pipe 1 is moved to the third joint pipe 3 side. End of the first joint pipe 1
The maximum movement position of the second joint pipe 2 is restricted by the stopper portion 8 at a position outside the swing region of the end 3a of the third joint pipe 3, so that the outer diameter of the end of the second joint pipe 2 The end 1 of the first joint pipe 1 whose outer diameter is increased by the presence of the first elastic sealing material 9 which is an example of a sealing structure
a does not enter between the inner peripheral surface of the end 3 a of the third joint pipe 3 and the outer peripheral surface of the second joint pipe 2. In addition, when an external force such as a shearing force or a bending moment caused by an earthquake, uneven settlement, or the like acts, the second joint pipe 2 and the third joint pipe 3 relatively swing to a maximum bending angle. An opening inner peripheral edge corner portion 3e of the end portion 3a of the joint pipe 3 protrudes from the outer peripheral surface of the second joint pipe 2 on the outer peripheral surface of the stopper portion 8 having high mechanical strength along the cylinder axis X direction. In other words, the inner wall edge 3e of the opening at the end 3a of the third joint pipe 3 has the wall thickness of the pipe wall of the outer peripheral surface of the straight pipe section 2B of the second joint pipe 2. Since the outer peripheral surface of the thickest stopper portion 8 is contacted along the cylinder axis X direction, this stopper portion 8
Thus, the external force can be reliably received as the press-contact force from the end 3a of the third joint pipe 3 and can be dispersed and supported.

[Other Embodiments] In the above-described first embodiment, the stopper portion 8 is formed integrally with the outer peripheral surface of the second cylindrical body B, but is formed separately from the second cylindrical body B. The stopper portion 8 may be fixed to a predetermined position on the outer peripheral surface of the second cylindrical body B. In this case, the material of the stopper 8 is not limited to cast iron, but may be stainless steel, hard synthetic resin, or synthetic rubber. In the above-described first embodiment, the stopper portion 8 is formed of an annular ridge, but is not limited to this shape. For example, the stopper portion 8 may be intermittently arranged along the circumferential direction of the second cylindrical body B. It may be composed of a formed projection group. In the above-described first embodiment, a pipe joint structure including a combination of five cylindrical bodies including one first cylindrical body A, two second cylindrical bodies B, and two third cylindrical bodies C will be described. But
On the other end side, a first cylindrical body A provided with a connecting portion integrally connectable to another cylindrical body and one second cylindrical body B and one third cylindrical body C The technology of the present invention can also be applied to a pipe joint structure including a combination of three cylindrical bodies.

[Brief description of the drawings]

FIG. 1 is an overall longitudinal sectional view showing a first embodiment of a pipe joint structure of the present invention.

FIG. 2 is an overall longitudinal sectional view when an external force in a compression direction and an external force in a direction intersecting a cylinder axis are received;

FIG. 3 is an enlarged cross-sectional view of a main part when subjected to an external force in a pull-out direction.

FIG. 4 is an enlarged cross-sectional view of a main part when receiving an external force in a compression direction and an external force in a direction intersecting with a cylinder axis;

FIG. 5 is a longitudinal sectional view showing a conventional pipe joint structure.

[Explanation of symbols]

 A first cylindrical body (first joint pipe) B second cylindrical body (second joint pipe) C third cylindrical body (third joint pipe) X cylindrical shaft core 1a end surface 2A spherical cylindrical portion 2a outer peripheral surface 3A Partially spherical cylindrical part 3a End part 3c Inner peripheral surface 8 Stopper part 13 Sliding guide member

Claims (3)

[Claims] An end of a second cylindrical body is inserted and connected to a first cylindrical body in a sealed state so as to be relatively movable in a direction of a cylindrical axis within a predetermined range, and the other end of the second cylindrical body is connected to the first cylindrical body. A pipe joint structure in which a third cylindrical body is externally connected in a sealed state so as to be relatively swingable on an end side, and an end of the first cylindrical body is provided on an outer peripheral surface of the second cylindrical body. A stopper portion for restricting the maximum movement position of the portion toward the third cylindrical body outside the swing region at the end of the third cylindrical body, and protrudingly forming the stopper portion;
A pipe joint configured such that when the second cylindrical body and the third cylindrical body relatively swing to a maximum bending angle, an end of the third cylindrical body comes into contact with an outer peripheral surface of a stopper portion. Construction. 2. When the second cylindrical body and the third cylindrical body relatively swing to a maximum bending angle, an end of the third cylindrical body and an outer peripheral surface of the stopper are aligned with a cylindrical shaft center. The pipe joint structure according to claim 1, wherein the pipe joint structure is configured to abut in a direction. A third spherical cylindrical portion formed on the other end side of the second cylindrical body and having a partial spherical cylindrical portion which is slidably and slidably movable along an outer peripheral surface of the spherical cylindrical portion. The cylindrical body is externally fitted from one side in the axial direction of the cylindrical shaft, and between the outer peripheral surface of the spherical cylindrical portion of the second cylindrical body and the inner peripheral surface of the partial spherical cylindrical portion of the third cylindrical body. A sliding contact member that slides on the outer peripheral surface of the spherical cylindrical portion of the second cylindrical body is fitted into the gap formed from the second cylindrical body and the third cylindrical body with the third cylindrical body. 2. The tubular body is connected so as to be able to slide and swing relative to each other.
Or the pipe joint structure according to 2.