JP7640846B2 - Steel pipe connection structure and steel pipe connection method - Google Patents

Description

The present invention relates to a steel pipe connection structure and a steel pipe connection method.

As a connection structure for steel pipes used in structures, it has been common to use flange joints formed at the ends of steel pipes, as in the example of the overhead pole described in Patent Document 1. In this case, the flanges are formed along a plane perpendicular to the axis of the steel pipes, and the steel pipes are connected by tightly fitting the flanges together and bolting them together.

JP 2014-20096 A

In the case of the overhead pole described in Patent Document 1, the flange joint mainly transmits the compressive force in the axial direction of the steel pipe. On the other hand, when a bending moment occurs in the steel pipe, for example when the steel pipe is used as a beam supported by the overhead pole, the flange joint transmits the compressive force and tensile force in the axial direction of the steel pipe. Since the tensile force is transmitted between the flanges via the bolts, in such cases it was necessary to increase the number of bolts to join the flanges.

Also, as shown in Figures 13A and 13B, in a conventional steel pipe beam-column joint 90 of an overhead line pole, the ring structures 93, 94 that transmit the load of the beam 91 to the column 92 are generally divided at a plane parallel to the flange joints 95, 96. Therefore, it is necessary to design the bolts that connect the divided ring structures 93, 94 to bear all of the bending moment transmitted from the beam 91 to the ring structures 93, 94 via the bolts of the flange joints 95, 96, which results in a wasteful structure.

The present invention aims to provide a steel pipe connection structure and a steel pipe connection method that can transmit force stably and efficiently when connecting steel pipes that generate bending moments.

[1] A steel pipe connection structure comprising a first steel pipe, a second steel pipe, and a pair of cast iron hardware divided by a plane including the axis of the first steel pipe and the axis of the second steel pipe, each of the pair of cast iron hardware including a first half pipe whose inner circumferential surface at least partially contacts the outer circumferential surface of the first steel pipe, a second half pipe whose inner circumferential surface at least partially contacts the outer circumferential surface of the second steel pipe, and a flange portion formed continuously with a side end portion of the first half pipe and a side end portion of the second half pipe, respectively, and capable of fastening the pair of cast iron hardware to each other, wherein the distance between the bottoms of the inner circumferential surfaces of the first half pipe when the flange portions of the pair of cast iron hardware are brought into close contact with each other is smaller than the outer diameter of the first steel pipe.
[2] The steel pipe connection structure described in [1], wherein the axis of the first steel pipe is perpendicular to the axis of the second steel pipe.
[3] The steel pipe connection structure described in [1], wherein the first steel pipe and the second steel pipe have a common axis, the first half pipe and the second half pipe are formed continuously with each other, and the distance between the bottoms of the inner surfaces of the second half pipe when the flange portions of the pair of cast iron metal fittings are brought into close contact with each other is smaller than the outer diameter of the second steel pipe.
[4] A steel pipe connection structure described in any one of [1] to [3], wherein the length along the axis of the first steel pipe of the section where the first half pipe and the first steel pipe are in contact is 1.0 times or more the outer diameter of the first steel pipe.
[5] The steel pipe connection structure according to any one of [1] to [4], further comprising a shear key that fits into each of a recess formed on the inner surface of the first half pipe and an opening formed on the peripheral surface of the first steel pipe.
[6] The shear key has a tapered shape in which a cross-sectional dimension decreases from the recess toward the opening, and an inner circumferential surface of the first half pipe contacts the first steel pipe via the shear key. The steel pipe connection structure described in [5].
[7] A method for connecting a first steel pipe and a second steel pipe using a first half pipe, a second half pipe, and a pair of cast iron hardware each including a flange portion formed continuously with a side end portion of the first half pipe and a side end portion of the second half pipe, respectively, the method comprising the steps of: for one of the pair of cast iron hardware, bringing the inner peripheral surface of the first half pipe at least partially into contact with the outer peripheral surface of the first steel pipe and bringing the inner peripheral surface of the second half pipe at least partially into contact with the outer peripheral surface of the second steel pipe; and, for the other of the pair of cast iron hardware, tightening the pair of cast iron hardware against each other with the flange portions, bringing the inner peripheral surface of the first half pipe at least partially into contact with the outer peripheral surface of the first steel pipe and bringing the inner peripheral surface of the second half pipe at least partially into contact with the outer peripheral surface of the second steel pipe.

According to the above configuration, the distance between the bottoms of the inner circumferential surfaces of the first half pipe when the flanges of the pair of cast iron hardware are brought into close contact with each other is set to be smaller than the outer diameter of the first steel pipe. Therefore, when the pair of cast iron hardware is fastened to each other, at least a part of the inner circumferential surface of the first half pipe comes into contact with the outer circumferential surface of the first steel pipe without any gaps, and the force due to the bending moment generated in the first steel pipe can be transmitted stably and efficiently by the support pressure between the first half pipe. The flanges of the pair of cast iron hardware are joined to each other by fastening means such as bolts, but in this case, the number of fastening means can be smaller than when the force due to the bending moment is directly transmitted via fastening means. In addition, there is no need to join twice to withstand the same load, as in the conventional flange joining structure, which further increases the overall efficiency.

When manufacturing a structure with a complex shape like the one in the present invention by processing and welding steel plates and steel pipes, the cost is high and it is difficult to ensure precision, but by constructing it from cast iron, it is possible to create components with high precision at a relatively low cost.

1 is a diagram showing an overhead line support structure including a steel pipe connection structure according to a first embodiment of the present invention. FIG. FIG. 2 is a perspective view of the steel pipe connection structure in the example shown in FIG. 1 . FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2. FIG. 2 is a diagram showing a steel pipe connecting process in the first embodiment of the present invention. FIG. 2 is a diagram showing a steel pipe connecting process in the first embodiment of the present invention. FIG. 11 is a diagram for explaining an example in which a shear key is used in the first embodiment of the present invention. FIG. 7 is a diagram showing an example in which the shear key in the example shown in FIG. 6 has a tapered cross section. FIG. 5 is a diagram showing a catenary support structure including a steel pipe connection structure according to a second embodiment of the present invention. FIG. 9 is a perspective view of the steel pipe connection structure in the example shown in FIG. 8 . FIG. 10 is a view showing the state in which the beam is removed and the cast iron hardware is opened in FIG. FIG. 11 is a diagram showing a steel pipe connecting process in a second embodiment of the present invention. FIG. 11 is a diagram showing a steel pipe connecting process in a second embodiment of the present invention. FIG. 13C is a diagram showing a steel pipe beam-column joint of a conventional overhead line pole, and is a view taken along line AA in FIG. 13B. FIG. 13B is a diagram showing a steel pipe beam-column joint of a conventional overhead line pole, and is a view taken along line B-B in FIG. 13A.

A preferred embodiment of the present invention will be described in detail below with reference to the attached drawings. Note that in this specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, and redundant explanations will be omitted.

(First embodiment)
1 is a diagram showing an overhead line support structure including a steel pipe connection structure according to a first embodiment of the present invention. The overhead line support structure according to this embodiment includes a beam 1 and an overhead line pole 2, both of which are made of steel pipes. The beam 1 and the overhead line pole 2 are connected using a connection structure 10 including cast iron hardware 3A, 3B, which will be described later. A suspension structure 4 for suspending an overhead line is attached to the beam 1. A bending moment is generated in the beam 1 due to its own weight and the loads of the suspension structure 4 and other equipment (not shown).

Figure 2 is a perspective view of the steel pipe connection structure in the example shown in Figure 1. In the illustrated example, the connection structure 10 includes a beam 1 (first steel pipe), an overhead pole 2 (second steel pipe), and a pair of cast iron hardware 3A, 3B. The axis X of the beam 1 is perpendicular to the axis Y of the overhead pole 2, and the cast iron hardware 3A, 3B is divided by a plane that includes both of these axes X and Y. Each of the cast iron hardware 3A, 3B includes a first half pipe 31A, 31B, a second half pipe 32A, 32B, flange portions 331A, 331B, 332A, 332B, 333A, 333B, and bolts 341A, 342A and nuts 341B, 342B that are fastening means for tightening these flange portions to each other.

Figure 3 is a cross-sectional view taken along line III-III in Figure 2. As shown in the figure, the first half-pipes 31A, 31B formed on each of the cast iron metal fittings 3A, 3B are arranged so that their inner circumferential surfaces at least partially contact the outer circumferential surface of the beam 1 (first steel pipe). The length along the axis X of the section where the first half-pipes 31A, 31B and the beam 1 contact each other is preferably 1.0 times or more the outer diameter of the beam 1. Here, the first half-pipes 31A, 31B are formed so that the distance d between the bottoms of the inner circumferential surfaces is smaller than the outer diameter D of the beam 1 when the flange portion 331A is in close contact with the flange portion 331B and the flange portion 332A is in close contact with the flange portion 332B as shown by the imaginary line in Figure 3. Here, the bottom-to-bottom distance d is the distance between the bottoms of the first half pipes 31A and 31B, i.e., the central parts when viewed in a direction perpendicular to the direction in which the half pipes extend (in the circumferential direction of the arc if the cross section of the half pipe is arc-shaped).

The first half pipes 31A and 31B are formed with an arcuate cross section, for example, such that the cross-sectional radius of the inner surface is equal to or larger than the outer diameter of the beam 1 so that they can contact the outer surface of the beam 1. By setting the bottom-to-bottom distance d as described above, the inner surfaces of the first half pipes 31A and 31B can be brought into close contact with the outer surface of the beam 1. Specifically, when the flanges 331A, 331B, 332A, and 332B are fastened to each other using fastening means such as bolts 341A and 342A and nuts 341B and 342B, the inner surfaces of the first half pipes 31A and 31B can be brought into close contact with the outer surface of the beam 1 while leaving gaps between the flanges 331A, 331B, 332A, and 332B. This allows stable force transmission between the beam 1 and the cast iron hardware 3A and 3B by support pressure.

Referring again to FIG. 2, the second half pipes 32A, 32B formed on each of the cast iron metal fittings 3A, 3B are arranged so that their inner circumferential surfaces are at least partially in contact with the outer circumferential surface of the overhead pole 2 (second steel pipe). The second half pipes 32A, 32B may also be formed so that the distance between the bottoms of the inner circumferential surfaces when the flange portions are in close contact is smaller than the outer diameter of the overhead pole 2, similar to the first half pipes 31A, 31B described above with reference to FIG. 3.

The flanges 331A, 331B, 332A, 332B, 333A, 333B of the cast iron hardware 3A, 3B are formed continuously with the side ends of the first half pipes 31A, 31B and the side ends of the second half pipes 32A, 32B. Here, the side ends of the half pipes are the ends in a direction perpendicular to the direction in which the half pipes extend (in the circumferential direction of the arc if the cross section of the half pipe is arc-shaped). The flanges 331A, 331B and the flanges 332A, 332B are formed continuously with the side ends of the first half pipes 31A, 31B and the second half pipes 32A, 32B, respectively, and the flanges 333A, 333B are formed continuously with the side ends of the second half pipes 32A, 32B. The cast iron fittings 3A and 3B can be fastened to each other by fastening the flange portions 331A and 331B, the flange portions 332A and 332B, and the flange portions 333A and 333B to each other with fastening means such as bolts 341A and 342A and nuts 341B and 342B.

4 and 5 are diagrams showing the steel pipe connection process in the first embodiment of the present invention. First, as shown in FIG. 4, a cast iron metal fitting 3A is attached to an overhead pole 2 (second steel pipe). At this time, the outer circumferential surface of the overhead pole 2 is brought into contact with the inner circumferential surface of the second half pipe 32A formed in the cast iron metal fitting 3A. On the other hand, a recess 311 for fitting a shear key described later and a bolt hole 312 are illustrated on the inner circumferential surface of the first half pipe 31A. Next, as shown in FIG. 5, a beam 1 (first steel pipe) is attached to the cast iron metal fitting 3A. At this time, the outer circumferential surface of the beam 1 is brought into contact with the inner circumferential surface of the first half pipe 31A formed in the cast iron metal fitting 3A. After this, a cast iron metal fitting 3B is attached from the opposite side to the cast iron metal fitting 3A, and the outer circumferential surfaces of the beam 1 and the overhead pole 2 are brought into contact with the inner circumferential surfaces of the first and second half pipes 31B and 32B of the cast iron metal fitting 3B, respectively. Furthermore, the flange portions of the cast iron fittings 3A and 3B are fastened to each other using bolts 341A and 342A and nuts 341B and 342B to form a connection structure as shown in FIG. 2.

Figure 6 is a diagram for explaining an example of using a shear key in the first embodiment of the present invention. As described with reference to Figure 4, the shear key 51 is fitted into the recess 311 formed on the inner surface of the first half pipe 31A, and is also fitted into the opening 11 formed in the beam 1. The shear key 51 has a bolt hole 511, and the shear key 51 can be fixed to the cast iron hardware 3A by inserting a bolt (not shown) into the bolt hole 312 and the bolt hole 511 on the first half pipe 31A side. By fixing the shear key 51 to the first half pipe 31A and the beam 1, respectively, the axial force acting on the beam 1 can be stably transmitted through the shear key 51. For example, the bolt hole 511 of the shear key 51 can be formed at an appropriate position by on-site construction, or multiple shear keys 51 with different bolt hole 511 positions can be prepared and used separately, and the position can be adjusted between the cast iron hardware 3A and 3B in response to dimensional errors and installation errors in the axial direction of the beam 1.

Figure 7 shows an example in which the shear key in the example shown in Figure 6 has a tapered cross section, and is a cross-sectional view taken along line VII-VII in Figure 6 when the shear key is fitted. In this case, the shear key 51 is positioned so that its cross-sectional dimensions decrease from the recess 311 toward the opening 11. When the cast iron fittings 3A, 3B are tightened against each other, the tapered shape of the shear key 51 is inserted into the opening 11, so that the shear key 51 and the beam 1 come into contact with no gaps. In this case, the inner surface of the first half pipe 31A contacts the beam 1 via the shear key 51, not directly.

In the first embodiment of the present invention described above, the cast iron hardware 3A, 3B are divided on a plane including both the axis X of the beam 1 (first steel pipe) and the axis Y of the overhead pole (second steel pipe), and are fastened to each other at the flange portion. By dividing the cast iron hardware 3A, 3B on a plane including the axis of each steel pipe, the force due to the bending moment acting on the steel pipe is not directly applied to the fastening means such as bolts that fasten the flange portions of the cast iron hardware 3A, 3B, so that the number of fastening means can be reduced. The force due to the bending moment is transmitted by support pressure to the first half pipe 31A, 31B that contacts the beam 1, and is further transmitted through the inside of the cast iron hardware 3A, 3B and transmitted by support pressure to the overhead pole 2 that contacts the second half pipe 32A, 32B. Such transmission of force by support pressure is more stable and efficient than, for example, via fastening means such as bolts. Cast iron hardware 3A and 3B have a complex shape that includes two half pipes and a flange, so it is advantageous to mold them as a single piece by casting. Cast iron also has the advantage of being highly corrosion resistant and resistant to fatigue because it has no welds.

For example, when steel pipes are connected to each other using a flange joint formed along a plane perpendicular to the axis of the steel pipe, it is difficult to adjust the position to accommodate dimensional errors and installation errors in the axial direction of the steel pipe. However, when the steel pipe is clamped between half pipes divided along a plane including the axis of the steel pipe as in this embodiment, the position can be adjusted in the axial direction of the steel pipe. As described above, even when a shear key is used, the position of the steel pipe can be adjusted in the axial direction by adjusting only the bolt hole position of the shear key. This simplifies the process of adjusting the position between the steel pipe column and the beam in the case of a flange joint, even when constructing an overhead line support structure such as that shown in Figure 1 within a limited working time.

Second Embodiment
8 is a diagram showing an overhead line support structure including a steel pipe connection structure according to a second embodiment of the present invention. The overhead line support structure according to this embodiment includes beams 1A, 1B and an overhead line pole 2, which are made of steel pipes, as in the first embodiment described above. Each of the beams 1A, 1B and the overhead line pole 2 may be connected to each other using a connection structure 10 including cast iron metal fittings 3A, 3B, as in the first embodiment described above, but this example is not limited to this. On the other hand, in this embodiment, since the interval between the overhead line poles 2 is wide, the two beams 1A, 1B are connected to each other using a connection structure 20 including cast iron metal fittings 6A, 6B, which will be described later. A bending moment is also generated in the beams 1A, 1B due to their own weight and the load of the suspension structure 4 and other equipment not shown.

Figure 9 is a perspective view of the steel pipe connection structure in the example shown in Figure 8. In the illustrated example, the connection structure 20 includes a beam 1A (first steel pipe), a beam 1B (second steel pipe), and a pair of cast iron fittings 6A, 6B. The beams 1A, 1B have a common axis X, and the cast iron fittings 6A, 6B are divided by a plane including this axis X. Also referring to FIG. 10, which shows the cast iron hardware 6A, 6B opened with the beams 1A, 1B removed, each of the cast iron hardware 6A, 6B includes a first half pipe 61A, 61B (the first half pipe 61A is shown in FIG. 10), a second half pipe 62A, 62B, flange portions 631A, 631B, 632A, 632B, and bolts 641A, 642A and nuts 641B, 642B, which are fastening means for fastening these flange portions to each other.

The first half-pipes 61A and 61B formed on the cast iron metal fittings 6A and 6B are arranged so that their inner circumferential surfaces at least partially contact the beam 1A (first steel pipe). The second half-pipes 62A and 62B are arranged so that their inner circumferential surfaces at least partially contact the beam 1B (second steel pipe). As described above, the axis X of the beams 1A and 1B is common, so the first half-pipe 61A and the second half-pipe 62A, and the first half-pipe 61B and the second half-pipe 62B are formed continuously. Here, as described above with reference to FIG. 3 for the first embodiment, when the flange portion 631A is brought into close contact with the flange portion 631B between the cast iron metal fittings 6A and 6B, and the flange portion 632A is brought into close contact with the flange portion 632B, the distance between the bottoms of the inner circumferential surfaces of the first half-pipes 61A and 61B becomes smaller than the outer diameter of the beam 1A. Similarly, when the flanges are tightly attached between the cast iron fittings 6A and 6B, the distance between the bottoms of the inner circumferential surfaces of the second half pipes 62A and 62B is smaller than the outer diameter of the beam 1B. Note that, for example, when the outer diameters of the beams 1A and 1B are different, a step may be formed between the inner circumferential surfaces of the first half pipes 61A and 61B and the second half pipes 62A and 62B, which are formed continuously.

Figure 10 also shows shear keys 51, 52 that fit into recesses formed on the inner circumferential surfaces of the first and second half pipes 61A and 62A, respectively. These shear keys 51, 52 also fit into openings formed in the beams 1A and 1B, respectively. The configuration in which the bolt hole positions of the shear keys 51, 52 are used to adjust the position between the cast iron hardware 6A, 6B in response to axial dimensional errors and installation errors of the beams 1A, 1B can be adopted in this embodiment as in the first embodiment. Also, the configuration in which the shear keys 51, 52 have a tapered cross section to contact the beams 1A, 1B without any gaps can be adopted as in the first embodiment.

11 and 12 are diagrams showing the steel pipe connection process in the second embodiment of the present invention. As shown in FIG. 11, first, a cast iron metal fitting 6A is attached to a beam 1A (first steel pipe). At this time, the outer peripheral surface of the beam 1A is brought into contact with the inner peripheral surface of the first half-split pipe 61A formed in the cast iron metal fitting 6A, and the shear key 51 is fitted into the opening formed in the beam 1A. Next, as shown in FIG. 12, a beam 1B (second steel pipe) is attached to the cast iron metal fitting 6A. At this time, the outer peripheral surface of the beam 1B is brought into contact with the inner peripheral surface of the second half-split pipe 62A formed in the cast iron metal fitting 6A, and the shear key 52 (not shown in FIG. 12) is fitted into the opening formed in the beam 1B. Note that although the end faces of the beams 1A and 1B are illustrated as being in contact with each other, there may be a gap between the end faces of the beams 1A and 1B. It is preferable that the length along the axis X of the section where the first half-pipes 61A, 61B and the beam 1A contact each other is 1.0 times or more the outer diameter of the beam 1A. Similarly, it is preferable that the length along the axis X of the section where the second half-pipes 62A, 62B and the beam 1B contact each other is 1.0 times or more the outer diameter of the beam 1B.

After this, cast iron hardware 6B is attached from the opposite side to cast iron hardware 6A, and the outer peripheral surfaces of beams 1A and 1B are brought into contact with the inner peripheral surfaces of the first and second half pipes 61B and 62B of cast iron hardware 6B, respectively. Furthermore, the flange portions of cast iron hardware 6A and 6B are fastened to each other using bolts 641A and 642A and nuts 641B and 642B, forming a connection structure as shown in FIG. 9.

For example, by providing a hinge (not shown) between flange portion 631A and flange portion 631B, cast iron hardware 6A, 6B can be held connected to each other before being tightened to each other, as shown in Figures 10 to 12. Workability is further improved by eliminating the need to store and transport cast iron hardware 6A, 6B separately. A similar hinge can also be provided in the first embodiment above, for example, between flange portions 333A, 333B of cast iron hardware 3A, 3B.

In the second embodiment of the present invention as described above, the cast iron hardware 6A, 6B is divided on a plane including the common axis X of the beam 1A (first steel pipe) and the beam 1B (second steel pipe) and is fastened to each other at the flange portion. By dividing the cast iron hardware 6A, 6B on a plane including the axis of each steel pipe, the force due to the bending moment acting on the steel pipe is not directly applied to the fastening means such as bolts that fasten the flange portion of the cast iron hardware 6A, 6B, so that the number of fastening means can be reduced. The force due to the bending moment is transmitted by support pressure from each of the beams 1A, 1B to the first half pipe 61A, 61B and the second half pipe 62A, 62B, respectively. Such transmission of force by support pressure is more stable and efficient than, for example, via a fastening means such as a bolt. The advantages of forming the cast iron hardware 6A, 6B by casting are also obtained in the same way as in the first embodiment.

In the embodiment described above, the shear key has an oval shape, but this is to reduce stress concentration at the end and increase the shear cross-sectional area of the shear key while reducing the cross-sectional loss of the steel pipe. Since the shape of the shear key is determined by design, in other embodiments it is not limited to an oval, and can be various shapes such as a circle, an ellipse, or a rounded rectangle.

The above describes in detail preferred embodiments of the present invention with reference to the attached drawings, but the present invention is not limited to these examples. It is clear that a person skilled in the art of the technical field to which the present invention pertains can come up with various modified or revised examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

1, 1A, 1B...beam, 2...overhead pole, 3A, 3B...cast iron hardware, 4...suspension structure, 6A, 6B...cast iron hardware, 10, 20...connection structure, 11...opening, 31A, 31B...first half pipe, 32A, 32B...second half pipe, 51, 52...sear key, 511...bolt hole, 61A, 61B...first half pipe, 62A, 62B...second half pipe, 311...recess, 312...bolt hole, 331A, 331B, 332A, 332B, 333A, 333B...flange portion, 341A, 342A...bolt, 341B, 342B...nut, 631A, 631B, 632A, 632B...flange portion.

Claims (6)

A first steel pipe, a second steel pipe, and a pair of cast iron metal parts separated by a plane including an axis of the first steel pipe and an axis of the second steel pipe,
Each of the pair of cast iron metal parts is
a first half pipe, the inner circumferential surface of which at least partially contacts the outer circumferential surface of the first steel pipe;
A second half pipe, the inner circumferential surface of which at least partially contacts the outer circumferential surface of the second steel pipe;
a flange portion formed continuously with a side end portion of the first half pipe and a side end portion of the second half pipe, the flange portion being capable of fastening the pair of cast iron fittings to each other;
When the flange portions of the pair of cast iron metal fittings are brought into close contact with each other, the distance between the bottoms of the inner peripheral surfaces of the first half pipe is smaller than the outer diameter of the first steel pipe,
The steel pipe connection structure further includes a shear key that fits into each of a recess formed in an inner peripheral surface of the first half pipe and an opening formed in the peripheral surface of the first steel pipe . The steel pipe connection structure according to claim 1, wherein the axis of the first steel pipe is perpendicular to the axis of the second steel pipe. the first steel pipe and the second steel pipe have a common axis;
the first half-tube and the second half-tube are formed contiguous with one another;
The steel pipe connection structure described in claim 1, wherein the distance between the bottoms of the inner surfaces of the second half pipe when the flange portions of the pair of cast iron metal fittings are brought into close contact with each other is smaller than the outer diameter of the second steel pipe. The steel pipe connection structure according to any one of claims 1 to 3, wherein the length along the axis of the first steel pipe of the section where the first half pipe and the first steel pipe are in contact is 1.0 times or more the outer diameter of the first steel pipe. The shear key has a tapered shape in which a cross-sectional dimension decreases from the recess toward the hole,
The steel pipe connection structure according to claim 1 , wherein an inner circumferential surface of the first half pipe contacts the first steel pipe via the shear key. A method for connecting a first steel pipe and a second steel pipe using a pair of cast iron fittings each including a first half pipe, a second half pipe, and a flange portion formed continuously with a side end portion of the first half pipe and a side end portion of the second half pipe, respectively, comprising:
For one of the pair of cast iron fittings, at least partially contacting an inner peripheral surface of the first half pipe with an outer peripheral surface of the first steel pipe, and at least partially contacting an inner peripheral surface of the second half pipe with an outer peripheral surface of the second steel pipe;
A step of fitting a shear key into each of a recess formed on an inner peripheral surface of the first half pipe and an opening formed on a peripheral surface of the first steel pipe;
and a step of tightening the pair of cast iron fittings against each other at the flange portions, thereby bringing the inner circumferential surface of the first half pipe into at least partial contact with the outer circumferential surface of the first steel pipe and bringing the inner circumferential surface of the second half pipe into at least partial contact with the outer circumferential surface of the second steel pipe for the other of the pair of cast iron fittings.

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