JP7700530B2 - Bridges and bridge construction methods - Google Patents

Description

The present invention relates to a bridge equipped with seismic isolation bearings and a method for constructing such a bridge.

Conventionally, bridges support their bridge girders (main girders) via multiple bearings on multiple piers (abutments) spaced apart in the bridge axis direction. In order to prevent earthquake forces from being transmitted to the bridge deck, seismic isolation bearings are sometimes used (see, for example, Patent Document 1). The bearing device described in this document is equipped with a mechanism that generates a horizontal force between the superstructure and substructure in the opposite direction to the inertial force of the superstructure.

JP 2011-226123 A

Rubber bearings are sometimes used as seismic isolation bearings. In this case, the thickness of the rubber layer needs to be increased to reduce horizontal rigidity, and the height of the rubber bearings needs to be increased to a certain extent. Therefore, when changing a bridge that previously used steel bearings (metal bearings) for fixed and movable bearings to rubber bearings, the height of the bridge deck may need to increase.

The bridge that solves the above problem is a bridge that includes a main girder that supports the deck, a pier that supports the main girder, and a seismic isolation bearing that connects the pier and the main girder, and the seismic isolation bearing has a protruding portion that protrudes at a position higher than the lower portion of the main girder, and includes a plurality of support members that are arranged around the main girder on the pier, and a tension member that is arranged between the plurality of support members and connects the lower portion of the main girder and the protruding portion while keeping them apart.

A bridge construction method that solves the above problem is a bridge construction method that includes a main girder that supports a deck, a pier that supports the main girder, and a seismic isolation bearing that connects the pier and the main girder, in which multiple support members with protruding parts that protrude higher than the lower part of the main girder are constructed around the main girder on the pier, and the lower part of the main girder, which is arranged between the multiple support members, is connected to the protruding parts by tension members while being spaced apart.

The present invention makes it possible to reduce the height from the bridge pier to the deck of a bridge.

FIG. 2 is a front view of an earthquake-resistant bridge according to an embodiment. FIG. 2 is a perspective view of an earthquake-resistant bridge according to an embodiment. FIG. 2 is a front view of a bridge before an earthquake-resistant structure is constructed in an embodiment. FIG. 2 is a front view of a bridge provided with mounting members and support members in an embodiment. FIG. 2 is a front view of a bridge provided with a tension member according to an embodiment. FIG. 13 is a front view of an earthquake-resistant bridge in the first modified example. FIG. 13 is a front view of an earthquake-resistant bridge in a second modified example. FIG. 13 is a right side view of an earthquake-resistant bridge in the third modified example. FIG. 13 is a right side view of an earthquake-resistant bridge in the fourth modified example.

Below, an embodiment of a bridge and a bridge construction method will be described with reference to Figures 1 to 5. Here, the bridge of this embodiment will be described as a simple girder bridge in which girders (main girders) are supported by adjacent piers (abutments). The bridge construction method of this embodiment assumes seismic reinforcement renovation work in which conventional metal bearings are replaced with seismic isolation bearings.

Figure 1 is a front cross-sectional view of bridge 10 after repair work, as viewed from the bridge axis direction, Figure 2 is a perspective view of bridge 10, and Figures 3 to 5 are side cross-sectional views of bridge 10, as viewed from the bridge axis direction.
As shown in Fig. 2, a bridge 10 of this embodiment includes a plurality of piers (abutments) 11, main girders 15, and a deck slab 16. The piers 11 are arranged in a line at a distance from each other in the bridge axis direction.

As shown in FIG. 1, seismic isolation bearings are provided on the pier 11 to support multiple (three in this case) main girders 15. The seismic isolation bearings are composed of multiple support members 21, tension members 26, and mounting members 25 provided on the main girders 15.

Multiple support members 21 are fixed so as to surround each main girder 15. Each support member 21 is arranged on both sides of the main girder 15 perpendicular to the bridge axis. Each support member 21 is made of, for example, reinforced concrete, and has an overhang 21a and a main body 21b. The main body 21b supports the overhang 21a and is fixed onto the pier 11.

The protruding portion 21a is a portion that protrudes horizontally from the upper portion of the main body portion 21b toward the main girder 15. The protruding portion 21a is arranged so as to overlap the end of the mounting member 25 when viewed from above.

Tension members 26 are provided to connect the end of each overhang 21a to the mounting member 25 of the main girder 15. Each main girder 15 is suspended by two tension members 26 at the same pier 11. In this embodiment, each tension member 26 is arranged to extend vertically. The upper end of the tension member 26 is pin-joined to the overhang 21a of the support member 21, and the lower end is pin-joined to the mounting member 25 of the main girder 15. Typically, the natural period of a bridge 10 is set in the range of just over 1 second to about 2 seconds. When these natural periods are set, the suspension length of the tension members 26 is set in the range of about 30 cm to 1 m.

The multiple main girders 15 are spaced apart in a direction perpendicular to the bridge axis. Each main girder 15 is arranged with a gap between it and the top surface of the pier 11. The main girder 15 has an I-shaped cross section and includes an upper flange portion 15a, a lower flange portion 15b, and a web portion 15w that connects these.

The mounting members 25 attached to the main girder 15 are provided at the lower part of the main girder 15, above the lower flange portion 15b. Each mounting member 25 is fixed to the web portion 15w at a height corresponding to the hanging length of the tension member 26. Each mounting member 25 is a plate member protruding in both horizontal directions from the web portion 15w. The ends of each mounting member 25 protrude outward beyond the ends of the lower flange portion 15b.
In addition, a deck slab 16 is fixed to the upper surface of the upper flange portion 15a of each main girder 15.

(Bridge Construction Method)
Next, the above-mentioned bridge construction method will be described with reference to Figures 1 and 3 to 5. Here, the case where the conventional metal bearings are replaced with seismic isolation bearings will be described.

Figure 3 shows a bridge 30 that uses conventional metal bearings 31. This bridge 30 has multiple piers 11 spaced apart in the bridge axis direction. Multiple metal bearings 31 are arranged on top of each pier 11, spaced apart in the direction perpendicular to the bridge axis. A main girder 15 is fixed on top of each metal bearing 31. The multiple main girders 15 then fix and support the deck slab 16 placed on top of them.

First, as shown in Fig. 4, the mounting members 25 are welded to the lower part of the main girder 15. Note that holes for passing the tension members 26 through are formed in advance at the ends of each mounting member 25.
Then, a support member 21 is constructed on each pier 11 of the conventional bridge 30 described above. This support member 21 is constructed of cast-in-place reinforced concrete. In this case, a hole is provided in the protruding portion 21a of the support member 21 for passing the tension member 26 through. This hole is provided directly above the hole in the tension member 26. Note that the support member 21, which is made of a precast reinforced concrete member or a material other than concrete, may be fixed to the pier 11 with an anchor or the like.

Next, as shown in FIG. 5, the tension member 26 is passed through the hole in the support member 21 and the hole in the mounting member 25 of the main girder 15. Then, the lower end of the tension member 26 is pin-joined while protruding downward from the mounting member 25, and the upper end of the tension member 26 is pin-joined while protruding above the overhanging portion 21a of the support member 21.

Then, as shown in Figure 1, the metal support 31 that was placed under the main girder 15 is removed. As a result, the main girder 15 is suspended and supported by the pier 11 with which the support member 21 is integrated via the tension member 26.

(effect)
In the bridge 10 of this embodiment, the main girder 15 supporting the deck 16 is suspended from the support member 21 of the pier 11 via the tension member 26. Therefore, seismic isolation is achieved by the pendulum without disposing a support between the pier 11 and the main girder 15.

According to this embodiment, the following effects can be obtained.
(1) In this embodiment, the main girder 15 is suspended from the support member 21 fixed on the pier 11 via the tension member 26. As a result, the bridge 10 is suspended within the height of the main girder 15 from the top surface of the pier 11, so the height from the top surface of the pier 11 to the deck 16 can be reduced. In this case, the natural period is determined by the suspension length, not by the weight supported by the tension member 26. Therefore, the desired seismic isolation can be achieved by appropriately setting the suspension length. In addition, due to the characteristics of the pendulum, a restoring force acts to always return to the origin after an earthquake, so no residual displacement remains.

(2) In this embodiment, the support member 21 and tension member 26 that constitute the seismic isolation structure are provided in the space above the pier 11. This allows the seismic isolation structure to be realized without any part of the seismic isolation structure protruding in the bridge axis direction of the pier 11.

(3) In this embodiment, since it is sufficient that the main girder 15 can be raised above the top surface of the pier 11, the support members 21 and tension members 26 can be installed with the conventional metal bearings 31 still attached, and after these installations are completed, the metal bearings 31 can be removed and the main girder 15 can be suspended. Therefore, the height from the top surface of the pier 11 of the bridge 10 to the deck 16 can be made the same as that of the bridge 30 with the conventional metal bearings 31. Also, there is no need to jack up the main girder 15 to install a new seismic isolation bearing in place of the conventional metal bearings 31.

(4) In this embodiment, each tension member 26 extends vertically. This allows the tension members 26 to maintain the same length regardless of the direction of vibration, so that the vibration of the main girder 15 can be absorbed in a balanced manner.

(5) In this embodiment, the main girder 15 is provided with an attachment member 25 to which the tension member 26 is pin-joined. By changing the installation height of the attachment member 25, the length of the tension member 26 can be changed, so that an appropriate natural period can be achieved.

This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction.
In the above embodiment, the mounting member 25 to which the lower end of the tension member 26 is pin-joined is provided at the lower part of the main girder 15. The structure in which the tension member 26 for suspending the main girder 15 is provided at the lower part of the main girder 15 is not limited to this.

For example, as shown in FIG. 6, a bridge 41 may be constructed in which the lower end of the tension member 36 is directly pin-joined to the lower flange portion 15b of the main girder 15. This allows the lower flange portion to be used as is without providing the mounting member 25.

- In the above embodiment, in order to arrange the tension member 26 in the vertical direction, the hole in the protruding portion 21a of the support member 21 is provided directly above the hole in the tension member 26. In this case, the lower flange portion 15b does not need to be directly below the protruding portion 21a of the support member 21. For example, as shown in FIG. 6, the tension member 36 may be arranged at an angle.

- In the above embodiment, the protruding portion 21a of the support member 21 is provided at a position lower than the upper flange portion 15a of the main girder 15. The protruding portion 21a is not limited to a position below the upper flange portion 15a, so long as it is provided protruding from multiple support members arranged on the pier in order to connect the upper portions of the tension members. For example, if the tension members are to be made longer than the main girder in accordance with the natural period, the protruding portion may be arranged at a position higher than the deck slab, and the tension members may be suspended from this protruding portion.

In the above embodiment, the main girder 15 is suspended by the tension members 26 and is supported by seismic isolation bearings that can swing in the bridge axis direction and in the direction perpendicular to the bridge axis.
The main girder 15 may be configured to be able to swing only in the bridge axis direction, without swinging in the direction perpendicular to the bridge axis.
For example, a bridge 42 shown in FIG. 7 may be used. In this bridge 42, the mounting member 35 provided on the main girder 15 is arranged with a small gap between the surface of the main girder 15 side of the main body 21b of the support member 21. As a result, when the main girder 15 tries to sway in the direction perpendicular to the bridge axis, the mounting member 35 abuts against the support member 21, suppressing the displacement in the direction perpendicular to the bridge axis. Furthermore, a part of the support member 21 may be brought into contact with the lower flange portion 15b of the main girder 15, or another member fixed to the support member 21 may be brought into contact with a part of the main girder 15. Furthermore, instead of abutting against the main body 21b, the mounting member 35 may be made to have a length that is separated from the main body 21b by an allowable range amount that suppresses the displacement. Also, a structure may be used that limits the amount of displacement not only in the direction perpendicular to the bridge axis but also in the direction of the bridge axis.

- The bridge 10 in the above embodiment is provided with a seismic isolation bearing by suspending the main girder 15 using tension members 26 provided on the support members 21. Furthermore, vibration dampers may be provided to attenuate the shaking that occurs in the bridge.

For example, as in the bridge 46 shown in Figure 8, a fixed member M1 is provided below the main girder 15. Then, a vibration damper D1 is provided between the pier 11 and the fixed member M1. The location where the vibration damper is attached can be determined arbitrarily.

- The bridge 10 in the above embodiment has been described as a simple girder bridge with a simple girder spanning two adjacent piers (abutments) in the bridge axis direction. The bridge configuration is not limited to this, and may be, for example, a continuous bridge with seamless bridge girders (main girders) spanning three or more piers (including abutments) arranged in the bridge axis direction.

As shown in Figure 9, in the case of a multi-span continuous bridge 47, a vibration damper D2 is provided between the pier 12 supporting the continuous girder at the center and the fixed member M2 provided below the main girder 15. Here, the vibration damper is not limited to one, and multiple dampers may be provided side by side in the bridge axis direction.

The bridge 10 in the above embodiment was constructed by seismic reinforcement renovation work to replace the conventional bridge 30 using metal bearings 31 with seismic isolation bearings. The configuration of the bridge 10 is not limited to seismic reinforcement renovation work, and can also be used as the structure of a newly constructed bridge 10.

Next, the technical ideas that can be understood from the above embodiment and other examples will be described below.
(a) A bridge as described in any one of claims 1 to 3, further comprising a vibration control device for stopping the vibration of the main girder.
(b) A bridge according to any one of claims 1 to 3 or (a) above, further comprising a displacement limiting member for limiting the displacement of the main girder.

D1, D2... vibration damper, M1, M2... fixing member, 10, 30, 41, 42, 46... bridge, 11, 12... pier, 15... main girder, 15a... upper flange portion, 15b... lower flange portion, 15w... web portion, 16... deck, 21... support member, 21a... extension portion, 21b... main body portion, 25, 35... mounting member, 26, 36... tension member, 31... metal bearing, 47... multi-span continuous bridge.

Claims (3)

A bridge comprising a main girder supporting a deck, a pier supporting the main girder, and a seismic isolation bearing connecting the pier and the main girder,
The main girder includes a lower flange portion and a mounting member provided on a web portion above the lower flange portion and protruding in a horizontal direction,
The seismic isolation bearing is
A plurality of support members each having a protruding portion protruding at a position higher than the lower portion of the main girder and arranged around the main girder on the pier;
a tension member that connects the lower part of the main girder and the overhanging portion in a spaced-apart state and is disposed between the plurality of support members ;
A bridge, characterized in that the overhanging portion and the mounting member are connected by the tension member . 2. The bridge according to claim 1 , wherein the mounting member protrudes horizontally beyond an end of the lower flange portion. A method for constructing a bridge having a main girder supporting a deck, a pier supporting the main girder, and a seismic isolation bearing connecting the pier and the main girder, comprising:
The main girder includes a lower flange portion, an upper flange portion, and a web portion connecting the lower flange portion and the upper flange portion,
A mounting member protruding horizontally is provided on a web portion above the lower flange portion of the main girder placed on an existing support,
After constructing a plurality of support members having protruding portions protruding at a position higher than the lower portion of the main girder around the main girder on the pier,
The mounting member of the main girder disposed between the plurality of support members and the overhanging portion are connected by a tension member in a spaced-apart state ;
and then removing the existing bearing .