JPH09125412A - Construction of vibration isolation of bridge pier foundation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rigid bridge pier to secure a stable driving of vehicle usually or in a small scale earthquake and prevent the bridge pier from collapsing in a more violent earthquake than a specified extent and further, make the structure stable. SOLUTION: This construction is provided with the first footing 11 integrally constructed together with the bridge pier 17 and formed to have the upper face 11a, the lower face 11c, and the side faces 11b and the second footing 12 formed to surround the upper face, the lower face and the side faces of the first footing and contact the ground. Vibration isolation devices 13a, 13b attenuating the horizontal vibrations are arranged between the upper and lower faces of the first footing and the second footing. And a weak layer 14 which is broken by a larger external force than a specified strength is provided between the side faces and the bridge pier of the first footing and the second footing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base isolation structure for a pier foundation.

[0002]

2. Description of the Related Art As a prior art of a seismic isolation structure for a bridge, Japanese Patent Laid-Open No. 5-247911 proposes a seismic isolation device provided on a pier foundation. As shown in FIG. 4, this seismic isolation device is formed by supporting the lower end of the bridge pier 53 on the footing 55 through the laminated rubber 56 and installing a damper 57 between the lower end of the pier 53 and the footing 55. And
When horizontal vibration occurs in the ground 54, this horizontal vibration is attenuated by the damper 57 and the laminated rubber 56 and transmitted to the pier 53.

[0003]

However, in the above-described seismic isolation structure, the laminated rubber 56 is provided in an unconstrained state so that it can always damp horizontal vibrations, and even if a small earthquake occurs, It deforms and tries to absorb the seismic force. Therefore, structures such as bridge piers and bridge girders are shaken even with a small earthquake, and there is a risk that the original function of the bridge, namely, the stable running function of the traffic vehicle, may be lost. In addition, there is a problem in that the structure becomes unstable in a substantially unrestrained state between the pier and the footing.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a rigid pier for ensuring stable running of a vehicle at all times and at the time of occurrence of a small-scale earthquake, and to provide a rigid pier having a predetermined strength or more. The aim is to provide a base isolation structure for the pier foundation, which is free from collapse of the pier during an earthquake and structurally stable.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned object, and its gist is to provide a pier footing integrally formed with a pier and having upper and lower surfaces and side surfaces. Footing portion and a second footing portion formed so as to contact the ground by surrounding the lower surface and the side surface of the first footing portion, the lower surface of the first footing portion and the second footing portion A seismic isolation device for damping horizontal vibrations is arranged between the first footing portion and the second footing portion, and a weak layer portion is provided between the second footing portion and the side surface of the first footing portion to be destroyed by an external force of a predetermined strength or more. It is characterized by the seismic isolation structure of the pier foundation.

Another gist of the present invention is that a pier footing is
A first footing portion formed integrally with the pier and having upper and lower surfaces and side surfaces, and a second footing portion formed so as to surround the upper surface, lower surface and side surfaces of the first footing portion and contact the ground. And a seismic isolation device for damping horizontal vibrations is arranged between the upper and lower surfaces of the first footing portion and the second footing portion, and the side surface of the first footing portion and the pier And a weak layer portion that is destroyed by an external force of a predetermined strength or more is provided between the second footing portion and the second footing portion.

In the seismic isolation structure of the pier foundation of the present invention, the weak layer portion is destroyed by an external force having a predetermined strength or more, for example, horizontal vibration due to seismic motion having a seismic intensity of about 6 or more, and is not broken by an external force having a predetermined strength or less. Any structure may be used. In such a weak layer portion, a steel plate is fixed to the side surface of the first footing portion, another steel plate is fixed to the inner surface of the second footing portion facing the steel plate, and a plurality of steel plates are provided between the facing steel sheets. It may be formed by welding a reinforcing bar. In addition, in addition to this, the weak layer portion is formed by placing a material having a compressive strength lower than that of the concrete of the first and second footing portions between the steel plates facing each other, and applying an external force of a predetermined value or more. It can be formed to break.

In the base isolation structure of the pier foundation of the present invention, the provision of the first footing portion integrally with the pier means, for example,
The first footing portion and the bridge pier are constructed by integrally casting reinforcing bars and / or steel-framed concrete, or the first footing section is constructed by reinforcing bars and / or steel-framed concrete, and steel pipes and / or steel pipes are constructed. The pier constructed with concrete may be fixed integrally with anchor bolts or the like.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a sectional view of a base isolation structure of a pier foundation of the present invention, and FIG. 2 is an enlarged sectional view of a weak layer portion in FIG. In FIG. 1, the pier footing 1 is formed so as to include a first footing portion 11 and a second footing portion 12. That is, the first footing portion 11
Is formed integrally with the bridge pier 17 by reinforced steel frame concrete or the like, and is formed into a three-dimensional shape having the upper surface 11a, the lower surface 11c and the side surface 11b, while the second footing portion 12 is the first footing portion 11 Is formed so as to maintain a predetermined length of clearance between the upper surface 11a, the lower surface 11c and the side surface 11b of the pier 17 and the lower end surface of the pier 17, and the lower surface is supported by the pile head of the foundation pile 16. To form. Seismic isolation devices such as laminated rubbers 13a and 13b are sandwiched between the upper surface 11a and the lower surface 11c of the first footing portion 11 thus formed and the inner surface of the second footing portion 12, respectively. Also, the weak layer portion 14 is provided in the clearance between the side surface 11b of the first footing portion 11 and the inner surface of the second footing portion 12.
Further, a weak layer portion 14 ′ is also provided in the clearance between the lower end surface of the pier 17 and the inner surface of the second footing portion 12. The weak layer portions 14 and 14 'are formed so as to be destroyed by an external force having a predetermined strength or more, for example, horizontal vibration caused by a seismic motion having a seismic intensity of 6 or more.

Since the weak layer portions 14 and 14 'can be formed with the same structure, only the weak layer portion 14 will be described in more detail below. As shown in FIG. 2, the weak layer portion 14 includes a steel plate 14c fixed to the side surface 11b of the first footing portion 11 and a steel plate 14a fixed to the inner surface of the second footing portion 12 facing the steel plate 14c. And a plurality of reinforcing bars 14b welded and fixed between the steel plates 14a and 14c, and by appropriately adjusting the strength, diameter and number of the reinforcing bars 14b to be used, the weak layer portion 14
Can have a desired breaking strength. In such a weak layer portion 14, due to an earthquake or the like, the second footing portion 12 is
When horizontal vibration is transmitted from the
b receives a compressive force from the steel plates 14a and 14c, the horizontal vibration reaches a predetermined strength or more, and the compressive force is applied to all the reinforcing bars 1.
When the sum of the compressive strength of 4b is exceeded, the reinforcing bar 14b buckles and breaks.

In the pier footing 1 having the above structure, the vertical load of the first footing portion 11 is supported by the second footing portion 12 via the laminated rubber 13b on the lower surface 11c thereof, and the first footing portion 11 is also supported. When the bending stress to rotate is applied from the pier 17, the second footing portion 12 arranged on the upper surface 11a via the laminated rubber 13a acts to restrain the rotation, and further the pier footing 1 is attached. When horizontal vibration is applied,
The first footing portion 11 and the second footing portion 12 are restrained by the weak layer portions 14 and 14 'so as not to vibrate at different cycles.

In the seismic isolation structure of the present invention, as shown in FIG. 1, the first footing portion 11 and the second footing portion 11 are used to inspect and maintain the laminated rubbers 13a and 13b for damage and the like. Hole 15 that communicates with the clearance with the portion 12
May be formed in the second footing portion 12.

When horizontal vibration occurs in the ground provided with the pier foundation as described above due to an earthquake or the like, this vibration is transmitted from the ground to the second footing portion 12. When the horizontal vibration is less than the predetermined strength, the weak layer portions 14 and 14 'are not destroyed and the vibration is transmitted from the second footing portion 12 to the lower end portions of the first footing portion 11 and the pier 17. To be done. Therefore, the laminated rubber 1
Since horizontal force does not act on 3a and 13b and deformation does not occur, the first footing portion 11 and the second footing portion 12 can maintain a rigid structure, and this rigid structure allows the horizontal structure to be maintained. It is possible to counter directional vibration.

On the other hand, when a horizontal vibration of a predetermined strength or more is generated, the weak layer portions 14 and 14 'are destroyed, and the first footing portion 11 has the second footing portion 12 through only the laminated rubbers 13a and 13b. The laminated rubbers 13a and 13b can be deformed in the horizontal direction. Therefore, when the horizontal vibration is transmitted to the second footing portion 12, the laminated rubbers 13a and 13b are deformed to damp the vibration and are transmitted to the first footing portion 11 and the pier 17, so that the pier footing 1 is soft. The structure makes it possible to prevent the pier 17 from collapsing.

Next, a seismic isolation structure of the pier foundation different from that shown in FIG. 1 will be described with reference to FIG. The pier footing 20 of FIG. 3 differs from the pier footing 1 of FIG. 1 in that
The second footing portion 22 is formed so as to maintain a predetermined length of clearance between the lower surface 21c and the side surface 21b of the first footing portion 21, and the laminated rubber 23 is sandwiched in this clearance to form the weak layer portion. 24 is the point formed. That is, the laminated rubber corresponding to the laminated rubber 13a of FIG. 1 is not provided on the upper surface of the first footing portion 21, and the second footing portion 22 is formed above the laminated rubber 13a of FIG. A portion corresponding to the second footing portion 12 is not formed, and the lower surface of the pier 27 has a weak layer portion 1 shown in FIG.
The pier footing 20 of FIG. 3 differs from the pier footing 1 of FIG. 1 in that it does not form a portion corresponding to 4 ′.

A structure other than the above-mentioned differences, that is, the pier 2
7, the first footing portion 21, the laminated rubber 23 and the weak layer portion 24 can be formed similarly to the seismic isolation structure of FIG.
Further, as in the case of FIG. 1, in order to maintain and manage the laminated rubber 23, a hole communicating with the clearance between the lower surface 21c of the first footing portion 21 and the second footing portion 22 from the ground may be formed.

When the ground vibrates in the horizontal direction due to an earthquake or the like, the pier footing 20 shown in FIG. 3 has the same action and effect as the pier footing 1. That is,
When the vibration in the horizontal direction is equal to or less than the predetermined strength, the weak layer portion 24 is not broken and the second footing portion 22, the first footing portion 21 and the pier 27 are integrally restrained as a rigid structure, and the laminated rubber 23 is restrained. Does not deform due to no horizontal force.
Therefore, this rigid structure can resist horizontal vibrations.

On the other hand, when the horizontal vibration reaches or exceeds a predetermined strength, the weak layer portion 14 is broken and the laminated rubber 23 can be deformed in the horizontal direction. Therefore, the second footing portion 2
When the horizontal vibration is transmitted to 2, the laminated rubber 23 is deformed to damp the vibration, and the pier footing 20 has a flexible structure to prevent the pier 27 from collapsing.

[0019]

According to the seismic isolation structure for a pier foundation of the present invention, a seismic isolation device for damping horizontal vibration between the first and second footing portions and a weak layer portion that is destroyed by an external force of a predetermined strength or more. Since it is provided, the weak layer portion integrally connects the first and second footing portions to maintain a rigid structure at all times and at the time of an earthquake with a predetermined strength or less, and the rigid structure resists external force and the vehicle It is possible to secure stable running of the vehicle. In addition, during an earthquake with a certain strength or more, the weak layer that rigidly connects the first and second footing parts is destroyed, and the seismic isolation device that is interposed between the first and second footing parts moves horizontally. It acts to damp vibrations, which can prevent the pier from collapsing.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a base isolation structure for a pier foundation of the present invention.

FIG. 2 is an enlarged sectional view of a weak layer portion in FIG.

FIG. 3 is a schematic sectional view of a base isolation structure for a pier foundation different from that in FIG.

FIG. 4 is a schematic view showing a conventional example.

[Explanation of symbols]

 1,20 Bridge pier footing 11,21 First footing portion 11a First footing portion upper surface 11b, 21b First footing portion side surface 11c, 21c First footing portion lower surface 12,22 Second footing portion 13a, 13b, 23 Laminated rubber (seismic isolation device) 14, 14 ', 24 Weak layer 17, 27 Pier

Claims (2)

[Claims] 1. A first footing portion having a pier footing integrally formed with the pier and having an upper surface, a lower surface and a side surface, and a ground surrounding the upper surface, the lower surface and the side surface of the first footing portion. A second footing portion formed so as to be in contact with the second footing portion, and a seismic isolation device for damping horizontal vibrations is arranged between the upper and lower surfaces of the first footing portion and the second footing portion. A base isolation structure of a pier foundation, characterized in that a weak layer portion that is destroyed by an external force of a predetermined strength or more is provided between the side surface and the pier of the first footing portion and the second footing portion. 2. A pier footing is provided integrally with the pier and has a first footing portion formed so as to have an upper surface, a lower surface and a side surface, and surrounds the lower surface and the side surface of the first footing portion to contact the ground. A second footing portion formed on the first footing portion, and a seismic isolation device for damping horizontal vibrations is arranged between the lower surface of the first footing portion and the second footing portion. A base isolation structure for a pier foundation, wherein a weak layer portion that is destroyed by an external force of a predetermined strength or more is provided between the side surface of the portion and the second footing portion.