JPH07102633A - Assembly type truss - Google Patents

Abstract

PURPOSE:To increase strength by forming a connection end part of a frame member constituting an assembly type truss by way of working and forming a reinforcing plate in a flat shape by way of sandwiching it. CONSTITUTION:By using an aluminum alloy and others, a hollow frame member 2 is formed. Thereafter, an end part of the frame member 2 is crushed to a certain degree by press working. Additionally, a reinforcing plate 20 consisting of carbon fiber reinforced resin and the like is inserted into the frame member 2, the end part of the frame member 2 is crushed in a flat shape, and on a connection end part 5, rigidity 4 engaged with regidity formed on a hub is formed. Consequently, even when the frame member 2 receives a load in the axial direction, it hardly bends in the in-plane direction and can increase ultimate durability of an assembly type truss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention constructs an assembled space truss structure by sequentially connecting frame members having a desired cross-section such as pipes and extruded profile members, which are structural members, by connecting members called hubs. And a structure of a frame member and a connecting portion between the frame member and the hub.

[0002]

2. Description of the Related Art An assembled truss structure has a frame member as a structural member having a flat end portion as a connecting end portion, and a plurality of connecting grooves radially formed on an outer peripheral surface of the frame member. The connection end portion of is constructed by a connection member called a hub that is press-fitted, and a high joint efficiency can be obtained without requiring a joining method such as welding in assembly, and smart and high lighting performance is exhibited, It has excellent features such as easy assembling work and a wide pillar-free space (Japanese Patent Laid-Open No. 3-247831 and US Pat.
931, 467, etc.).

FIGS. 15 (A) and 15 (B) are plan and front views of a dome structure showing an example of such an assembly type space truss structure, and FIG. 16 is an exploded view of a joint portion forming a truss mark. 17A and 17B are a front view and a plan view of the frame member. In these figures,
Reference numeral 1 is a dome-shaped truss structure, and a large number of frame members 2
And a hub 3 that connects the frame member 2. The frame member 2 is usually made of an aluminum alloy, and is crushed at both ends by pressing or the like to form a flat shape.
Further, the tip end thereof is shaped to have the unevenness 4 called a dimple, and the portion is used as the connection end portion 5. Hub 3
Is usually an aluminum alloy (eg, Al-Mg-Si alloy) extruded material or a cast forged product formed into a cylindrical body, and a bolt insertion hole 6 formed through the center and radially formed on the outer peripheral surface. A plurality of connecting grooves 8 having unevenness 7 on the inner wall surface of the groove are provided, and the connecting ends 5 of the frame members 2 are press-fitted into the connecting grooves 8 from the axial direction to connect the frame members 2 to each other. , Form truss marks. A bolt 9 is inserted through the bolt insertion hole 6, and a washer 10 and a ring 11 are fitted to the vertically projecting ends of the bolt 9,
By pressing the ring 11 against the upper and lower surfaces of the hub 3 by fastening the nut 12, the connecting end portion 5 is prevented from coming off the connecting groove 8. Then, the truss structure 1 is constructed by sequentially connecting the truss points. The bolt insertion holes 6 and the bolts 9 are for preventing the connection end portion 5 from coming off from the connecting groove 8. The bolt insertion hole 6 is not provided, and a retaining member corresponding to the ring 11 is bolted to the hub 3. You may stop.

In constructing an arbitrary three-dimensional curved surface structure in such a truss structure assembling method, that is, in order to approximately express a curve by a chord, the frame member 2
Of the frame member 2 is cut at an angle with respect to the axis of the frame member 2.
7). The truss construction method is a construction method having a high degree of freedom in designing, by determining the coin angle α by design calculation, an arbitrary three-dimensional curved surface can be configured by a triangular or quadrangular mesh pattern.

The hub 3 connecting the frame members 2 is arranged so that its central axis is orthogonal to the truss surface. Therefore, when the truss structure has a dome shape or a spherical shape, the central axis of the hub 3 faces the center point of the sphere. Hub 3
As the connecting grooves 8 radially arranged in a cross section perpendicular to the axis of, not all the radiation angles theoretically required at each connection point of the three-dimensional curved surface structure are prepared, and the greatest common divisor is, for example, 60 °. It is provided for each. For this reason, all adjustments for forming a three-dimensional curved surface are performed by inclining the connection end portion 5 of the frame member 2 with a required angle with respect to the axis of the frame member 2, and this angle is determined by the bend angle β (see FIG. 17). ). The coin angle α and the bend angle β are calculated as a function of the curved surface shape, the mesh pattern and the length of the frame member 2. Connection end 5 of frame member 2
Is a strong axis in the direction orthogonal to the truss surface indicated by the arrow A, that is, in the out-of-plane direction, as is clear from the connection structure with the hub 3.
It is arranged so as to have a weak axis in the direction along the truss surface indicated by arrow B and in the direction orthogonal to the frame member 2, that is, in the in-plane direction. Therefore, this assembled truss structure is not a general bolt joint type truss structure having spherical pin joints at both ends of the pipe but a semi-rigid joint truss structure. This structural feature allows for fairly large single-layer dome structures for assembled trusses. Further, the above-mentioned rectangular mesh pattern is also possible due to this structural characteristic.

In the conventional assembly type truss as described above, the ultimate strength condition of the assembly type truss with the increase in load is as follows:
It is caused by more stable rotation of the hub 3 in the in-plane direction without causing local buckling called a snap-through back ring due to high rigidity in the out-of-plane direction, which is accompanied by a momentary loss of loading capacity. That is, the connection end portion 5 of the frame member 2
Has a flat shape that is long in the direction of the central axis of the hub 3, it has a large rigidity in the out-of-plane direction, but it has a low rigidity in the in-plane direction, so that a compressive or tensile load in the axial direction is applied. When received, the hub 3 rotates in the in-plane direction and the connecting end portion 5 bends. The resistance force against the rotation of the hub 3 in the in-plane direction is equal to the yield stress of the material, which is twice the section modulus based on the plate thickness of the frame member 2 because the connecting end 5 of the frame member 2 is flattened. It is specified by the yield moment multiplied by. Therefore, it is possible to increase the ultimate yield strength by increasing the yield moment.

[0007]

As described above, in the conventional assembly type truss, the rigidity of the connecting end portion 5 of the frame member 2 is large in the out-of-plane direction but small in the in-plane direction. There is a problem that the hub 3 rotates in the truss plane due to the axial compression or tensile load and the connecting end portion 5 bends, resulting in a decrease in overall strength.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to increase the rigidity of the connecting end portion of the frame member with a relatively simple structure, or It is an object of the present invention to provide a prefabricated truss in which the ultimate strength of the truss is increased by restricting the rotation of the hub in the in-plane direction and the overall strength is increased even if the same frame member is used.

[0009]

In order to achieve the above object, a first aspect of the present invention is to provide a plurality of connecting grooves into which the connecting ends of a frame member forming flat connecting ends are press-fitted. In an assembly type truss in which the frame members are sequentially connected by radially formed hubs to construct an assembly type space truss structure, a connecting end portion of the frame member is formed into a flat shape by sandwiching a reinforcing plate. It is a thing.
In a second aspect based on the first aspect, the frame member is formed of a hollow material, and a short hollow material having an outer diameter dimension equal to or smaller than the hollow inner dimension is provided at each end of the frame member. By fitting and then forming the frame member and hollow material into a flat shape,
A reinforcing plate is formed from the short hollow material. In a third aspect based on the first aspect, the frame member is made of an E-shaped or T-shaped extruded shape member, and both ends of the horizontal plate portion are bent inward so as to sandwich the reinforcing plate to form a connection end portion. Is what you are doing. According to a fourth aspect of the present invention, the frame members are sequentially connected by a hub in which a plurality of connecting grooves into which the connecting ends of the frame member forming flat connecting ends are press-fitted are radially formed. In the assembled truss for constructing the assembled space truss structure, the connection end of the frame member is formed in a flat shape and has a projection, and the projection is formed in the connecting groove of the hub of the connection end. It is provided at a position outside the fitted portion and close to or in contact with the outer peripheral surface of the hub. In a fifth aspect based on the fourth aspect, the connection end portion is formed into a flat plate shape by sandwiching the protrusion forming member, and the portion corresponding to the protrusion forming member is deformed outward to form the protrusion. It is a thing. According to a sixth aspect of the invention, in the fourth aspect of the invention, the protrusion is composed of a bolt and a nut attached to the connection end. In a seventh aspect based on the fourth aspect, the protrusion is formed of a protrusion forming member fixed to both side surfaces of the connection end. The eighth invention is the fourth invention
In the invention, the frame member has a protruding portion provided on the outer side surface, and a portion of the protruding portion inserted into the connecting groove of the hub is cut and removed to form the protruding portion. In a ninth aspect based on the fourth aspect, the connecting end portion is formed into a flat shape by sandwiching a reinforcing plate having a projection,
A portion corresponding to the protrusion is deformed outward to form a protrusion.

[0010]

In the first invention, the reinforcing plate increases the thickness of the connecting end portion. Therefore, the strength and rigidity of the connection end portion is increased, and the frame member is unlikely to bend in the in-plane direction even when a load is applied in the axial direction. In the fourth aspect of the invention, the protrusion contacts the outer peripheral surface of the hub to prevent the hub from rotating in the in-plane direction. In the ninth invention, the reinforcing plate reinforces the connection end portion and increases strength and rigidity. Further, the protrusion prevents the rotation of the hub in the in-plane direction from being restricted.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 1 is a perspective view of an essential part of a frame member used in the assembled truss according to the first invention. In addition,
In the figure, the same components as those of the conventional components shown in FIGS. 15 to 17 are designated by the same reference numerals, and the description thereof will be omitted. In this figure, in this embodiment, a reinforcing plate 20 is provided on the connecting end 5 of the frame member 2 to increase the thickness T of the connecting end 5. The reinforcing plate 20 is inserted into the frame member 2 when the end portion of the frame member 2 is flattened by pressing or the like to form the connection end portion 5, and is inserted into the frame member 2 at a time when the end portion is pressed in this state. It is pinched by crushing. The connection end portion 5 is provided with the unevenness 4 that engages with the unevenness formed on the hub 3. Reinforcing plate 20
Although the material and plate thickness of CFRP are not specified, CFRP
It is very effective to use a composite material such as (carbon fiber reinforced resin). A part of the reinforcing plate 20 protrudes from the frame member 2 for holding the reinforcing plate 20 during press working. If grooves are formed in the reinforcing plate 20 in a direction orthogonal to the axis of the frame member 2, the reinforcing plate 2 after crushing will be processed.
0 and the frame member 2 are completely adhered to each other, and the strength is further improved.

2 (A) and 2 (B) are a perspective view of an essential part showing a state before crushing and a perspective view after crushing showing a modified example of the above embodiment. In this embodiment, as shown in (A), a short hollow member 20 having an outer diameter dimension equal to or slightly smaller than an inner diameter dimension of the frame member 2 at the end portion of the frame member 2 when the end portion of the frame member 2 is crushed. 'Is fitted in advance, and then the ends of the frame member 2 and the hollow member 20' are crushed to make them flat as shown in (B), whereby the short hollow member 20 'is used as a reinforcing plate. It is the one that is used. According to this example, in the case of the embodiment shown in FIG. 1, if the reinforcing plate 20 is not inserted during the end working, a gap is formed at the upper and lower ends of the reinforcing plate 20. Absent. Further, since the plate thickness of the end portion of the frame member 2 is increased by the thickness of two short hollow members 20 ', the strength is further increased. Further, the processing is also easy because the short hollow member 20 'is set in the hollow portion of the frame member 2 so as not to loosen so much that it can be easily fitted and fixed.

FIG. 3 is a perspective view of a main part showing another embodiment in which a frame member 2 having a D-shaped cross section is used as a structural member, and FIG. 4 is a front view of the main part. In this embodiment, two frame members 2 are extruded and composed of upper and lower horizontal plate portions 21A and 21B facing each other vertically and a vertical plate portion 21C connecting the centers of the upper and lower horizontal plate portions 21A and 21B. The reinforcing plates 20 (20A, 20B) are brought into close contact with both end portions of the vertical plate portion 21C, and the end portions 21 of the upper and lower horizontal plate portions 21A, 21B.
0a and 210b are bent inward by press working or the like and pressed against the reinforcing plates 20A and 20B to be flattened to form the connection end portion 5. In this case, although the two reinforcing plates 21A and 21B are used in this embodiment, the number of the reinforcing plates may be one, and in this case, the upper and lower horizontal plate parts 21A are in close contact with either one of the vertical plate parts 21C. , 21B are bent by pressing or the like, and the bent end on the side where the reinforcing plate 20 is provided is pressed against the reinforcing plate 20,
The bent end portion on the side opposite to the reinforcing plate side may be pressed against the vertical plate portion 21C. Then, the unevenness 4 is formed on the connection end portion 5. Further, if the reinforcing plate 20 is bonded to the joint between the reinforcing plate 20 and the frame member 2 or if irregularities are formed in the joint, the joint strength of both members increases and the in-plane strength of the connection end 5 also increases. .

As described above, when the plate thickness of the connecting end portion 5 of the frame member 2 is increased by the reinforcing plate 20, the strength and rigidity of the connecting end portion 5 is increased, and the frame member 2 receives the compressive or tensile load in the axial direction. In this case, the resistance against rotation of the hub in the in-plane direction can be increased. Therefore, the connecting end portion 5 does not bend in the in-plane direction (arrow direction),
The ultimate strength of the assembled truss can be increased.

Further, as shown in FIG. 3, the frame member 2
When the H is extruded, the exterior material 24 such as glass for covering the truss can be attached more easily than the frame member 2 including the pipe in FIG. That is, as shown in FIG. 3, in the D-shaped frame member 2, the upper horizontal plate portion 21
Since the upper surface of A forms a flat surface, a screw mounting portion 26 is provided at the center of the upper surface, and a pair of cushioning member mounting portions 27 are provided at both sides of the screw mounting portion 26 so as to project. A cushioning member 28 made of rubber or the like is fitted and fixed in the cushioning member mounting portion 27, and the cushioning member 28 supports the edge portion of the glass 24, and is screwed and fixed to the screw mounting portion 26 (not shown). Then, the exterior material 24 such as glass may be pressed against the cushioning member 28, whereby the frame member 2 can also serve as a holding member for the exterior material 24. The screw mounting portion 26 and the pair of cushioning member mounting portions 27 are easily formed at the same time when the frame member 2 is extruded. It is cut and removed when the portion 5 is processed and formed.

FIG. 5 is a view showing an embodiment in which the reinforcing plate 20 is sandwiched in the flattening process of the connecting end portion 5 using the frame member 2 made of a T-shaped extruded shape member as in the above embodiment. is there. The same components as those in the above embodiment are designated by the same reference numerals and the description thereof will be omitted. Even with such a configuration, the same effect as that of the above embodiment can be obtained.

FIG. 6 is a perspective view of a connecting end portion of a frame member used in the assembled truss according to the fourth invention, and FIG. 7 is a sectional view. In this embodiment, when the hub 3 starts to rotate in the in-plane direction, the rotation is prevented and prevented by the protrusion 30 provided on the connection end 5. When forming the protrusion 30, the protrusion forming member 31 such as a hard ball is inserted into the end of the frame member 2 in advance, and in this state, the end is crushed into a flat shape to form the connection end 5. A portion of the connection end portion 5 corresponding to the protrusion forming member 31 is deformed outward to form the protrusion 30. And this protrusion 30
Is formed at a position outside the portion of the connecting end 5 that is press-fitted into the coupling groove 8 of the hub 3 and is in contact with or close to the outer peripheral surface of the hub 3.

FIGS. 8A and 8B are perspective views showing examples of the protrusion forming member. (A) shows an example in which a plurality of protrusions 33 are provided on both sides of a plate 32 having an appropriate plate thickness at appropriate intervals in the longitudinal direction, and (B) shows an example in which the protrusions 33 are provided over the entire length in the longitudinal direction. . In this case, the plate 32 is not always necessary, and hard balls or the like may be simply used as the protrusion forming member and sandwiched by the connecting end portions 5.

FIG. 9 is a sectional view showing still another example of the protrusion forming member. This embodiment shows an example in which a plurality of protrusions 33 or a plurality of protrusions 33 are continuously provided on a plate 32 having substantially the same length as the connecting end portion 5. In such a configuration, the plate 32 increases the strength and rigidity of the connection end portion 5, and the protrusion 33
However, since the corresponding plate portion of the connection end portion 5 is deformed to the outside to form the protrusion portion 30 to prevent the rotation of the hub in the in-plane direction from being restricted, it is possible to further increase the ultimate yield strength of the assembled truss. Have.

FIG. 10 shows a bolt 35 as a protrusion forming member.
FIG. 6 is a cross-sectional view of a connection end portion showing an example in which a protrusion 30 is formed by using a nut 36 and a nut 36. Head 3 of bolt 35
5A is not limited to a hexagon, but may be a quadrangle,
Any one of the side surfaces may be opposed to the outer peripheral surface of the hub 3. Further, the method of attaching the protrusion forming member may be by adhesion.

FIG. 11 is a sectional view showing still another example of the protrusion forming member. In this embodiment, a flat plate-shaped projection forming member 37 (37A, 37A, 37A,
37B) is fastened and fixed by bolts 35 and nuts 36, and the hub-side end surface of the projection forming member 37 is brought into contact with or close to the outer peripheral surface of the hub 3 to form the projection 30. In addition, the method of attaching the protrusion forming member 37 may be adhesion.

FIG. 12 is a sectional view of a frame member showing still another example of the protrusion forming member, and FIG. 13 is a perspective view of the connecting end portion. In this embodiment, a plurality of ridges 40 each having an appropriate plate thickness are integrally provided on the outer peripheral surface of the frame member 2 over the entire length, and the end portions of the frame member 2 are formed into a flat shape or before or before the processing. The ridge portion of the hub that is press-fitted into the connecting groove is cut and removed, and the cut end portion that abuts the outer peripheral surface of the hub is used as the protrusion portion 30. Then, the protrusion 40 of the connection end 5 is cut and removed, and the unevenness 4 is formed on the surface of the portion to be inserted into the connecting groove of the hub.

As shown in FIGS. 6 to 13, when the protrusion 30 is provided on the base side of the connection end 5 and brought into contact with or close to the outer peripheral surface of the hub 3, the protrusion 30 moves in the in-plane direction of the hub 3. In order to prevent the rotation from being restricted, the ultimate yield strength of the assembled truss can be increased as in the case where the strength and bending rigidity of the connecting end 5 are increased by the reinforcing plate.

FIG. 14 is a view showing an experiment in which a compressive load in the axial direction is applied to the frame member 2. The frame member 2 has an outer diameter 66 with the hubs 3 attached to both ends.
A pipe having a thickness of 3 mm, a plate thickness of 3 mm, and a length of 1.3 m was used, and the projection 30 was provided on the outer surface of the connection end 5 by adhesively fixing the projection forming member. The bend angle β of the connection end portion 5 is 0 °. In the conventional frame member that does not include the protrusion 30, the hub 3 rotates in the in-plane direction and loses the loading capacity in about 2.0 to 2.5 tons, but the frame according to the present invention including the protrusion 30 is included. In the member 2, the in-plane rotation of the hub 3 did not occur even with a compressive load of 4.0 tons. Judging from the output of the strain gauge attached to the connection end portion 5, bending strain occurs in the connection end portion 5 immediately after loading, but the presence of the slight protrusions 30 causes strain in the subsequent load increasing process. It was found that the increase was effectively suppressed.

[0025]

As described above, in the assembled truss according to the present invention, since the reinforcing plate is sandwiched between the connecting ends of the frame member to increase the plate thickness of the connecting ends, the strength and rigidity are increased.
Even if the frame member receives a load in the axial direction, it is difficult to bend in the in-plane direction, and the ultimate yield strength of the assembled truss can be increased. Further, according to the present invention, since the protrusion is provided at the connecting end of the frame member and the protrusion is brought into contact with or brought close to the outer peripheral surface of the hub, when the frame member receives an axial compressive load, the hub is exposed to the surface. It is possible to prevent rotation inward. Therefore, the connection end portion is not bent, and the ultimate strength of the assembled truss can be increased. further,
Since the present invention is configured such that the reinforcing plate is sandwiched between the connection ends and the protrusions are provided, the reinforcing plates reinforce the connection ends, and the protrusions prevent rotation of the hub in the in-plane direction. The ultimate strength of the assembled truss can be increased.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part showing an embodiment of a frame member used in an assembled truss according to the present invention.

2A and 2B are a perspective view of a main part before crushing and a perspective view after crushing showing another embodiment of the present invention.

FIG. 3 is a perspective view of an essential part showing another embodiment in which a frame member having a D-shaped cross section is used as a structural member.

FIG. 4 is a front view of a main part.

FIG. 5 is a perspective view of essential parts showing an embodiment using a frame member made of a T-shaped extruded shape member.

FIG. 6 is a perspective view showing another embodiment of the connecting end portion of the frame member used in the assembled truss according to the present invention.

FIG. 7 is a sectional view.

8A and 8B are perspective views each showing an example of a protrusion forming member.

FIG. 9 is a cross-sectional view showing still another example of the protrusion forming member.

FIG. 10 is a cross-sectional view of a connection end showing an example in which a protrusion is formed by using a bolt and a nut as a protrusion forming member.

FIG. 11 is a cross-sectional view showing still another example of the protrusion forming member.

FIG. 12 is a cross-sectional view of a frame member showing still another example of the protrusion forming member.

FIG. 13 is a perspective view of a connection end portion.

FIG. 14 is a view showing an experiment in which an axial compressive load is applied to a frame member.

15A and 15B are a plan view and a front view of a dome-shaped structure showing an example of an assembled truss structure.

FIG. 16 is an exploded perspective view of a joint portion forming a truss mark.

17A and 17B are a front view and a plan view of a frame member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Dome type truss structure 2 Frame member 3 Hub 5 Connection end part 8 Connection groove 20 Reinforcing plate 20 'Hollow material 30 Projection part 31 Projection part formation member 33 Projection 35 Bolt 36 Nut 37 Projection part formation member 40 Projection part

Front page continuation (72) Inventor Yoshihiro Takeda 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka

Claims (9)

[Claims] 1. A frame member, which has flattened ends at both ends, is assembled by sequentially connecting the frame members by a hub radially formed with a plurality of connecting grooves into which the connecting ends are press-fitted. An assembling truss for constructing a three-dimensional space truss structure, wherein the connecting end of the frame member is formed into a flat shape by sandwiching a reinforcing plate. 2. The assembled truss according to claim 1, wherein
The frame member is formed of a hollow material, and short hollow members having an outer diameter dimension equal to or smaller than the inner dimension of the hollow member are fitted into both ends of the frame member, and then the frame member and the hollow member are flattened. An assembly type truss, characterized in that a reinforcing plate is formed from the short hollow material by processing and forming. 3. The assembled truss according to claim 1, wherein
The frame member is made of a D-shaped or T-shaped extruded shape,
An assembling truss, wherein both ends of the horizontal plate portion are bent inward so as to sandwich the reinforcing plate to form a connecting end portion. 4. The frame member is sequentially connected and assembled by a hub having a plurality of connecting grooves radially formed with a plurality of connecting grooves into which the connecting ends of the frame member forming flat connecting ends are press-fitted. In an assembled truss for constructing a three-dimensional space truss structure, the connecting end of the frame member is formed in a flat shape and has a protrusion, and the protrusion fits in a connecting groove of the hub of the connecting end. An assembling truss, which is provided at a position outside of a mating portion and close to or in contact with the outer peripheral surface of the hub. 5. The assembled truss according to claim 4,
The assembly type truss is characterized in that the connection end portion is formed into a flat plate shape by sandwiching the protrusion forming member, and the portion corresponding to the protrusion forming member is deformed outward to form the protrusion. 6. The assembled truss according to claim 4,
The assembly type truss, wherein the protrusion is composed of a bolt and a nut attached to the connection end. 7. The assembled truss according to claim 4,
The assembly type truss, wherein the projection is formed of a projection forming member fixed to the outer surface of the connection end. 8. The assembled truss according to claim 4,
The frame member has a protruding portion provided on the outer side surface, and the protruding portion is formed by cutting and removing the portion of the protruding portion that is inserted into the connecting groove of the hub. . 9. The assembled truss according to claim 4,
The assembly type truss is characterized in that the connecting end portion is formed into a flat shape by sandwiching a reinforcing plate having a protrusion, and a portion corresponding to the protrusion is deformed outward to form a protrusion portion.