JP2001182776A - Base isolation bearing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base isolation bearing which prevents large horizontal force, generated on the occurrence of an earthquake, from transmitting to architectural structures and bridge beams. SOLUTION: This base isolation bearing includes a slide bearing unit 4 composed of a plurality of low friction slide disks stocked and housed in a cylindrical reinforced rubber bearing body, and a shock-absorbing unit 5 assembled serially on the upper end of the slide bearing unit 4 and/or the bottom end of the unit 4, which has elasticity capable of easy deformation in the horizontal direction and moreover has little compression deformation with respect to vertical load and a base isolation bearing unit constituted of a shock-absorbing part 5 between the base and the upper building structure. Then by first making the shock-absorbing part 5 respond to be deformed, with respect to the horizontal force of the initial period of the earthquake, the horizontal force transmitted to the upper building structure is made to decrease, as well as makes the vibration period of the upper building structure long.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sliding bearing type seismic isolation device for preventing buildings and bridges (including elevated roads and railroad tracks) from collapsing or breaking due to an earthquake.

[0002]

2. Description of the Related Art Conventionally, especially in a wooden building, an upper end portion of an anchor bolt protruding from the upper surface of a concrete foundation is used.
The base is placed directly on the concrete foundation so as to be inserted through the through hole formed longitudinally at an appropriate position on the base, and a washer and a nut are attached to the protruding end of the anchor bolt, and the fitting is screwed into the base. The foundations were tied together to unite the two. Rigid connections are also made between buildings and foundations such as RC structures, S structures, and SRC structures, and between piers and bridge girders in bridges. However, the above structure has a problem that must be solved as described below. (1) Earthquake shocks, vibrations, etc. are transmitted to buildings and bridge girders as they are. (2) The structure is large in size, since it is only a structure that can withstand the impact of an earthquake by using many braces and bearing walls to harden it, and the buildings and bridges themselves shake in the same way as the ground vibrations. Buildings and bridges are likely to collapse or break in an earthquake.

[0003] Therefore, Japanese Patent Publication No. 62-11141,
As described in JP-B-62-11142, the friction coefficient of the sliding material is reduced so as not to transmit the horizontal vibration of the earthquake to the upper part, and the sliding bearing is constructed so that the sliding material does not deviate. A seismic device was developed. Furthermore, Japanese Patent Application No. 10-3265
As described in Japanese Patent Publication No. 74, a slip-type bearing-type seismic isolation device has been developed that uses a sliding material with extremely low frictional resistance in an elastic synthetic resin cylinder to improve the displacement restoration method and seismic isolation performance. Was done. It is also common practice to combine a sliding bearing and a rubber laminate and arrange them side by side in the same seismic isolation layer (plane).

[0004]

However, in the case of a conventional sliding bearing type seismic isolation device, when a shock such as a large earthquake is received, a friction coefficient that triggers the initial sliding is given. Because of the high initial rigidity coefficient of friction, the shearing force acts on the supporting superstructure before the seismic isolation function of the sliding bearing works, resulting in cracks at the joints, However, there was a problem such as damage. Moreover, since there is no restoring ability, there is a possibility that large deformation may remain after the earthquake. In the latter seismic isolation device consisting of a sliding bearing and a rubber laminate, the response value of the initial horizontal stiffness in the event of an earthquake shows the characteristics of the device on the higher stiffness side. In such a case, a response is made due to the characteristics of the sliding bearing, and the rubber laminate works only for the restoring action, and eventually has the same problem as the seismic isolation device described above. Also, since many devices must be installed, construction costs and the like are high, and there is a problem in practical use.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the problem that a shear force acts on an upper structure in an early stage of an earthquake based on the above-mentioned prior art. A sliding bearing portion stacked and accommodated in a cylindrical body made of: and a buffer arranged in series above and / or below the sliding bearing portion, which is easily deformable in the horizontal direction, has elasticity, and has little compressive deformation against a vertical load. The seismic isolation device is installed between the foundation and the upper structure to reduce the horizontal force transmitted to the upper structure by first responding and deforming the buffer to the initial horizontal force. Thus, the above problem is solved. Here, “easy to deform in the horizontal direction” means that the horizontal spring constant or the initial rigidity is small even for a minute displacement at the initial stage of the displacement at the time of the earthquake.
The ratio of the vertical spring constant / horizontal spring constant that can be used in the present invention is usually 50 or more. In addition, the sliding bearing has elasticity in the cylindrical body, and the cushioning part has elasticity in itself. Since the bearing and the self-restoring elastic body are integrated, the construction is simple, the construction cost is reduced, and it can be easily put into practical use.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. As shown in FIGS.
... is placed and fixed at an appropriate position on the concrete foundation B in the above.
The base C of the upper structure W is laid and fixed on 1a ..., and the seismic isolation device 1, 1a ... is interposed between the concrete foundation B and the base C. Further, a plurality of anchor bolts A, Aa... For fastening the seismic isolation devices 1, 1a.

Each of the seismic isolation devices 1, 1a... Is formed of a plurality of slide disks 2, 2a... Made of an elastic material such as synthetic resin or rubber (hereinafter referred to as an elastic synthetic resin). The sliding support portion 4 is formed in the cylindrical body 3 by being stacked and housed in the cylindrical outer shell 3a, and the buffer portion 5 is disposed above and / or below the sliding support portion 4. Specifically, as shown in FIGS. 1 to 3, a concrete foundation B is provided on the upper and lower portions of a cylindrical body 3 made of a rubber material having excellent weather resistance.
And fixing plates 6, 6a to the base C are fixedly provided, and a buffer 5 is provided between the upper and / or lower fixing plates 6, 6a and the uppermost and / or lowermost slide disks 2, 2a,. Have been. The cylindrical body 3 is horizontally deformed by a low reaction force,
It is desirable to form the elastic member so as to have elasticity that automatically restores after unloading.

As shown in FIG. 3, the slide disks 2, 2a,... Are made of a hard material having substantially the same diameter as the inner diameter of the cylindrical body 3 and having extremely small frictional resistance on the front and back surfaces. Specifically, a metal plate is processed with low friction resin, such as by baking fluorine resin (such as ethylene tetrafluoride resin) on a stainless steel plate or by using polyamide (nylon) resin, polyacetal resin, or polyethylene resin as the material. And a synthetic resin plate or a low-friction resin processed therewith, or a low-friction material previously formed into a plate shape is fixed.

In addition, circular recesses 8 and 8a are provided at the centers of the sliding contact surfaces 7 and 7a of the adjacent slide disks 2, 2a.
An accommodation space is formed by the circular recesses 8 and 8a, and a stopper disk 9 thicker than the depth of the lower circular recess 8a is accommodated in the accommodation space. Also, each slide disk 2, 2a ...
The upper and lower outer peripheral edges are provided with chamfered portions 10 and 10a. or,
Plate-shaped sliders 11 and 11a having outer peripheral portions protruding from the stopper disk 9 on both front and back surfaces of the stopper disk 9
And escape grooves 12 and 12a into which the outer peripheral portions of the sliders 11 and 11a are inserted into the inner peripheral surfaces of the concave portions 8 and 8a.
Has been established.

In the buffer section 5, an intermediate flange plate 15 having the same diameter as the slide disks 2, 2a, and one or a plurality of buffer bodies 16 fixed on the intermediate flange plate 15 are provided. The upper part of the buffer 16 is fixed to the lower surface of the upper fixed plate 3a. In addition, in the cushioning member 16, vibration-proof rubber,
As shown in FIGS. 1 to 3, the shape and the number are formed by high damping rubber or the like, and a plurality of cushioning bodies 16 are formed in a cylindrical shape and regularly arranged on the intermediate flange plate 15. As shown in FIG. 7, a plurality of shock absorbers 16 are formed in a ring shape having different diameters and are arranged concentrically on the intermediate flange plate 15, or as shown in FIG. It is formed in a spiral shape and arranged at the center on the intermediate flange plate 15.
In addition, the buffer 16 is formed of a material that has a property of being deformed in response to a horizontal load, that is, not deforming in response to a vertical load, that is, a compressive load, or being deformed only slightly, specifically, It is formed by alternately laminating a metal plate such as a thin steel plate, a hard plate 18 made of ceramic or the like, and a soft plate 19 made of an elastic material such as rubber.
As shown in FIG. 6, in the cushioning body 16, flanges 31 and 31a vertically arranged in a rubber cylindrical body 30 are arranged at predetermined intervals between the flanges 31 and 31a. A plurality of hard plates 18, 18a... Are embedded and integrated. Also, flange 3
1, 31a and hard plates 18, 18a ... between and adjacent hard plates 18, 18a
A rubber material forming the cylindrical body 30 is interposed between the cylindrical members 30 and the outer peripheral portions of the flanges 31 and 31a and the hard plates 18, 18a are surrounded by the rubber material forming the cylindrical body 30. The flanges 31, 31a and the hard plates 18, 18a are buried, and the upper surface of the upper flange 31 and the lower surface of the lower flange 31a are flush with the upper and lower surfaces of the cylindrical body 30. Further, in the case of the seismic isolation device 1, 1a, etc. in which a plurality of shock absorbers 16 are formed in a cylindrical shape and are regularly arranged on the intermediate flange plate 15, the number of the shock absorbers 16 is about 1 to 10. , Preferably 3 to 8, more preferably 4 to 6. Also, the size of the buffer body 16, the number of laminations of the hard plates 18, 18a ... and the soft plates 19, 19a ...
The materials of the soft plates 19, 19a... Are designed under optimal conditions because they differ depending on the superstructure W, the allowable deformation required during an earthquake, the allowable response acceleration, the allowable shear coefficient of the superstructure W, and the like. The buffer 16 is used.

As shown in FIGS. 1 to 3, the fixing plates 6, 6a are made of metal, and anchor bolts A,
.. Are formed in the upper fixing plate 6a, and joint bolts J, described later, are formed in the upper fixing plate 6a. In addition, metal flanges 22 and 22a are fixed to the upper and lower outer peripheral portions of the cylindrical body 3, and fixing plates 6 and 6a for closing the opening of the cylindrical body 3 are fixed to upper and lower portions of the flanges 22 and 22a. Set up
It is desirable in the manufacturing process to stack the slide disks 2, 2a,. Specifically, bolt rods 23, 23a... Are fixedly mounted on the fixing plates 6, 6a.
The bolt holes 23, 23a are formed in the insertion holes 24, 24a in the bolt holes 23, 23a.
Nuts 25, 25a are screwed into the protruding end portions of the flange portions 22, 22.
Fixing plates 6 and 6a are fixed to a. Further, the outer peripheral shape of the fixing plates 6 and 6a is made the same shape and size as the flange portions 22 and 22a, and the insertion holes 20 and 20
a ... and the insertion holes 21, 21a are fixed to the fixing plates 6, 6a and the flange portions 22, 22a.
Is formed so as to penetrate through.

The seismic isolation devices 1, 1a,...
In this embodiment, the sliding bearing 4 and the cushioning part 5 are formed integrally, but the present invention is not limited to such a form. As shown in FIGS. Then, an intermediate structure C may be interposed between the slide bearing 4 and the buffer 5, and the upper structure W may be constructed thereon.

The concrete foundation B on which the seismic isolation devices 1, 1a... Are installed has a flat shape without beams in the drawing.
Without limiting to such a form, a general continuous footing basis,
It may be a solid basis or the like.

Next, the operation of mounting the seismic isolation device according to the present invention will be described. First, the anchor bolts A, Aa... Are inserted into the insertion holes 20, 20a... Of the fixed plate 6 below the seismic isolation devices 1, 1a. Seismic isolation device 1 at a predetermined position on concrete foundation B,
After fixing 1a ..., the base C is placed on the seismic isolation device 1, 1a ...
And the joint bolts J and Ja having the base C penetrated from above are inserted into the insertion holes 21 and 21a of the fixed plate 6a above the respective seismic isolation devices 1, 1a. , N1a, and the base C is fixed on the seismic isolation devices 1, 1a..., And the seismic isolation devices 1, 1a. I do. Alternatively, after fixing one of the sliding bearing portion 4 and the buffer portion 5 in each of the seismic isolation devices 1, 1a... To a predetermined position on the concrete foundation B, an intermediate structure C is laid thereon, and the intermediate structure C After fixing the other of the sliding bearing part 4 and the buffer part 5 at a predetermined position on the intermediate structure C, the base C is fixed thereon, and FIG.
As shown in FIG. 2, seismic isolation devices 1, 1a... Are interposed between the concrete foundation B and the base C.

Next, the operation of the seismic isolation device according to the present invention will be described. By fixing the fixing plates 6 and 6a having the bolt insertion holes 20, 20a..., 21, 21a at both ends on both upper and lower surfaces of the cylindrical body 3, the bolt insertion holes 20, 20a.
The anchor bolts A, Aa on the concrete foundation B side
Through the bolt holes 2 of the upper fixing plate 6a.
1, 21a, joint bolt J which penetrated base C,
By inserting Ja respectively, the seismic isolation devices 1, 1a,... Can be installed, and the installation work is simplified.

Since the upper structure W on the concrete foundation B is constructed on the seismic isolation devices 1, 1a,.
The upper structure W and the concrete foundation B are separated, the transmission of vibration due to the earthquake to the upper structure W is suppressed, and the entire upper structure W is shaken at a long cycle by the seismic isolation devices 1, 1a,. At the same time, vibration caused by the earthquake is transmitted to the upper structure W while being attenuated. Specifically, first, as shown in FIG.
, The horizontal force applied to the upper structure W side is reduced. That is, since the buffer 16 is deformed to absorb the horizontal force, the horizontal force acting on the upper structure W is reduced. Next, when the slide disks 2, 2a... Slide sequentially, the seismic isolation devices 1, 1a... Deform, and when all the slide disks 2, 2a. The horizontal force acting on the upper structure W when returning is absorbed. Also, the buffer portion 5 itself has a restoring function and is attached to the slide disks 2, 2a,... Via the intermediate flange plate 15, so that a stable friction coefficient can be obtained in design. Since the seismic isolation devices 1, 1a,... Have a cylindrical shape, no matter which direction the roll comes from, they are similarly deformed in accordance with the direction, and the cylindrical body 3 is easily deformed in the horizontal direction. .., And the interior thereof is constituted by the slide disks 2, 2a,..., The horizontal rigidity of the seismic isolation devices 1, 1a,. Since the cylindrical body 3 and the buffer 5 have a self-restoring function, the deformation of the seismic isolation devices 1, 1a,... After the earthquake becomes extremely small, and is almost restored to the original state. Also, the slide disks 2, 2a... And the shock absorber 16 prevent the upper structure W from being compressed and deformed in the vertical direction at the time of deformation, and the seismic isolation devices 1, 1a. Therefore, in the seismic isolation device 1, 1a,... According to the present invention, in order to reduce a large horizontal force acting on the upper structure W at the time of an earthquake and to exhibit a safer and higher seismic isolation function, the sliding type is used. The number of load-bearing walls required for the structure to provide the bearing can be reduced, and an economical structural design becomes possible.

The slide disks 2, 2a,... Slide on the stopper disk 9 with the peripheral surface of one adjacent circular recess 8 abutting against the stopper disk 9, and the stopper disk 9 slides on the other circular recess 8a. The slide between them stops upon contact with the peripheral surface. Then, the above-described slide disk 2 which is sequentially adjacent,
2a... And finally, as shown in FIG. The inclination deformation angle of the seismic isolation devices 1, 1a,... Is not limited to the above-mentioned approximately 45 degrees because it varies depending on the number, diameter, thickness, and maximum sliding amount of the slide disks 2, 2a. It is desirable to set.

[0018]

In summary, according to the present invention, a plurality of slide disks 2, 2a... Having a low coefficient of friction are accommodated in a cylindrical body 3 made of an elastic material, so that the cylindrical outer shell 3a and the slide disks 2, 2a. Are separate, there is no connection between them,
With the deformation of the cylindrical body 3, the upper structure W can be vibrated in a long cycle. The effect of the cylindrical body 3 is that firstly, the individual slide disks 2, 2a... Are given an equal amount of slip, and secondly, the restoring force is applied to the entire seismic isolation device 1, 1a. Return to the position, in particular, to provide a restoring force to the slide disks 2, 2a... Which do not have a restoring function, and thirdly, to improve weather resistance by covering the inside, and to drop the slide disks 2, 2a. Is to prevent Also, above the sliding bearing 4 and / or
Alternatively, the buffer section 5 having elasticity by making it easy to deform in the horizontal direction and having a small compressive deformation with respect to a vertical load is arranged in series, so that the horizontal force at the time of the initial stage of the earthquake is absorbed by the buffer section 5, and then slide. Since the disks 2, 2a,... Are sequentially slid and the subsequent horizontal force is absorbed, the action of the shearing force on the upper structure W can be suppressed as much as possible. The horizontal rigidity of the shock absorber 5 is designed so as not to be shaken by a wind load during a typhoon, but is set to be as low as possible, and the initial rigidity of the seismic isolation device 1, 1a. The response to the structure W becomes soft. The cylindrical body 3 is easy to deform once it starts to be displaced in the horizontal direction, and the frictional resistance between the slide disks 2, 2a,.
Although the horizontal rigidity of the seismic isolation devices 1, 1a... Can be reduced, the compressive deformation of the upper structure W becomes very large because the load of the upper structure W acts on the seismic isolation devices 1, 1a. Since the sliding bearing portion 4 in which the disks 2, 2a... Are stacked and accommodated in the vertical direction and the buffer portion 5 with little compressive deformation against vertical load are arranged in series in the vertical direction, the seismic isolation device 1 by the weight of the upper structure W is used. , 1a... And the horizontal rigidity of the seismic isolation devices 1, 1a. Therefore, the seismic isolation device 1 according to the present invention,
In 1a ..., since the concrete base B and the base C are not directly connected, the deformation of the seismic isolation device 1, 1a ... between the fixing plates 6, 6a is not hindered. The seismic function can be made to function efficiently, and the entire upper structure W is shaken at a long cycle during a strong earthquake, preventing the collapse of furniture inside the upper structure W, the destruction and collapse of the upper structure W You can do it. In addition, the self-restoring ability of the sliding bearing part 4 and the cushioning part 5 minimizes deformation after an earthquake, and can be used as long as the seismic isolation devices 1, 1a ... are not damaged. Can be done.

The uppermost slide disks 2, 2a... And / or the lowermost slide disks 2, 2a.
Since the intermediate flange plate 15 is interposed therebetween and the buffer portion 5 is fixed to the intermediate flange plate 15, the slide bearing portion 4 and the buffer portion 5 can be integrated, so that the efficiency of the installation work is improved. Therefore, it is possible to provide a seismic isolation device which can realize a low construction cost and can be easily put into practical use.

Although it is unpredictable in which direction the earthquake will roll, the plurality of shock absorbers 16 may be formed in a columnar shape and arranged regularly, or the plurality of shock absorbers 16 may have different diameters. Or a concentric arrangement, or one buffer 16 is formed in a spiral shape, so that in the buffer section 5 having such a buffer 16, any direction from which the roll can be made. Even if it acts, it can be similarly deformed, so that the seismic isolation function can be prevented from deteriorating due to the direction of roll. Further, the buffer body 16 is formed of a thin hard plate 18, 18a... And a soft plate 19, 19a.
Are alternately laminated, so that the buffer 16 can have both ease of deformation for a horizontal load and difficulty of deformation for a vertical load (compression load).

Also, a pair of adjacent slide disks 2,
Concave portions 8 and 8a are opposed to the sliding contact surfaces 7 and 7a in 2a... A stopper disk 9 that is thicker than the concave portion 8a and smaller than the concave portion 8a is placed in the lower concave portion 8a. It is possible to regulate the slide amount of 2, 2a ...
The sum of the slide amounts of all the slide disks 2, 2a ... can be used as the horizontal deformation amount of the seismic isolation device 1, 1a ...
Therefore, when the seismic isolation device 1, 1a,.
Can prevent vertical buckling due to the load.
In addition, since the recesses 8 and 8a and the stopper disk 9 are formed in a circular shape, the sliding amount of the slide disks 2, 2a... or,
Even if the slide between the pair of adjacent slide disks 2, 2a... Is stopped by the stopper disk 9, there is a possibility that the upper slide disks 2, 2a. The sliders 11 and 11a whose outer peripheral portions protrude from the stopper disk 9 are fixed on both front and back surfaces of the stopper disk 9, and the sliders 11 and 11a are provided on the inner peripheral surface of the concave portions 8 and 8a. Since the escape grooves 12 and 12a are provided around the outer periphery of the stopper disk 9a, the stopper disk 9
The outer peripheral portion of the upper slider 30 is inserted into the clearance groove 12 of the concave portion 8 of the upper slide disk 2, 2a. Is big.

[Brief description of the drawings]

FIG. 1 is a plan view of a seismic isolation device.

FIG. 2 is a front view of FIG.

FIG. 3 is a sectional view taken along line XX of FIG.

FIG. 4 is a sectional view showing an initial deformation state of the seismic isolation device of FIG.

FIG. 5 is a sectional view showing a maximum deformation state of the seismic isolation device of FIG. 1;

FIG. 6 is a plan view and a central longitudinal sectional view of a buffer in a stacked state.

FIG. 7 is a horizontal sectional view of the seismic isolation device in which a plurality of shock absorbers are formed in a modified ring shape.

FIG. 8 is a horizontal sectional view of the seismic isolation device in which one buffer is formed in a spiral shape.

FIG. 9 is an enlarged front view of a main part showing an installed state of the seismic isolation device.

FIG. 10 is an enlarged sectional view taken along the line YY of FIG. 9;

FIG. 11 is an enlarged front view of a main part showing an installed state of a seismic isolation device in which a slide bearing and a buffer are separately provided.

12 is an enlarged vertical sectional view taken along the line ZZ of FIG. 11;

[Explanation of symbols]

 2, 2a ... Slide disk 3 Cylindrical body 3a Cylindrical body skin 4 Sliding bearing part 5 Buffer part 7, 7a Sliding surface 8, 8a recess 9 Stopper disk 11, 11a Slider 12, 12a Relief groove 15 Intermediate flange plate 16 Buffer body 18 , 18a… hard plate

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) E04B 1/36 E04B 1/36 D E04H 9/02 331 E04H 9/02 331E F16F 7/08 F16F 7/08 (72) Inventor Teruo Sasaki 380-10 Uohashi, Amida-cho, Takasago-shi, Hyogo (72) Inventor Fumiyoshi Sugimoto 1-3-7 Sorimachi, Kanagawa-ku, Yokohama-shi

Claims (9)

[Claims] 1. A sliding bearing in which a plurality of slide disks having a low coefficient of friction are stacked and accommodated in a cylindrical body made of an elastic material, and arranged in series above and / or below the sliding bearing, and are arranged in a horizontal direction. A sliding bearing type seismic isolation device characterized by comprising a buffer portion which is easily deformable, has elasticity, and has little compressive deformation against a vertical load. 2. An intermediate flange plate is interposed between the uppermost slide disk and / or the lowermost slide disk and the buffer, and the buffer is fixed to the intermediate flange plate. The sliding bearing type seismic isolation device described. 3. The sliding bearing type seismic isolation device according to claim 1, wherein the buffer portion is constituted by one or a plurality of buffer bodies. 4. A sliding bearing type seismic isolation device according to claim 3, wherein the cushioning member is formed by interposing a rubber material between a plurality of thin metal plates arranged vertically. 5. A sliding bearing type seismic isolation device according to claim 1, wherein the cylindrical outer shell is made of rubber. 6. The sliding bearing type seismic isolation device according to claim 1, wherein the slide disk is formed on a metal plate by surface processing with a fluorine resin or surface fixing of a fluorine resin material. 7. A sliding disk according to claim 7, wherein a concave portion is provided on a sliding contact surface of a pair of adjacent slide disks, and a stopper disk having a thickness larger than the depth of the concave portion and smaller than the concave portion is placed in the lower concave portion. The sliding bearing type seismic isolation device according to any one of claims 1 to 6. 8. A plate-like slider having an outer peripheral portion protruding from the stopper disk is fixedly provided on both front and back surfaces of the stopper disk, and an escape groove into which the outer peripheral portion of the slider is inserted into the inner peripheral surface of the concave portion. 8. The sliding bearing type seismic isolation device according to claim 7, wherein a peripheral member is provided. 9. The sliding bearing type seismic isolation device according to claim 7, wherein the concave portion and the stopper disk are formed in a circular shape.