JPH1037127A - Cable damping device in obliquely stretched bridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the maintenance and control of an obliquely stretched bridge by connecting a section between a cable and a bridge beam through a damper made of viscoelastic rubber and a wire rope. SOLUTION: A bracket 26 is attached at a position where a line which is orthogonal to a cable C crosses a bridge beam G from a mounting position of a clamp 20 of the cable C. Next, a storage frame 24 on which viscoelastic rubber 30 and a transmission plate 22 are attached is attached to the bracket 26 by using a bracket 25 and a shaft pin 27, an eye splice 21a on one side of a wire rope 21 adjusted to predetermined length is locked in a locking metal fitting 20a of the clamp, and an eye splice 21b on the other side is locked in a locking metal fitting 22b on the storage frame 24 side. Then, when the cable C vibrates, vibration force is transmitted to the viscoelastic rubber 30 through the wire rope 21, vibration energy of the cable C is damped due to the vibration of the viscoelastic rubber 30, and the vibration of the cable C is suppressed. Consequently, it is unnecessary to replenish liquid in a damper owing to the use of the viscoelastic rubber 30 and it is possible to facilitate the maintenance and control of an obliquely stretched bridge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable damping device for suppressing cable vibration of a cable stayed bridge.

[0002]

2. Description of the Related Art Cable-stayed bridge cables often have a problem of vibration caused by wind. Known phenomena include rain vibration caused by the interaction between rain and strong wind, and vortex-induced vibration caused by Karman vortices. Although the frequency of rain vibration is not high (several times according to past observations), its frequency is less than 3Hz,
The longer the cable is, the lower the vibration frequency of the lowest-order mode becomes, so that the number of vibration modes to be damped increases. on the other hand,
Although the vortex-excited vibration does not have a large amplitude, the wind speed is 2-3.
Since it occurs at m / s or more, the frequency is very high. The generated vibration modes are observed over a wide range from the lowest order mode to the tenth or higher order mode. Since these vibrations cause fatigue of the cable anchoring portion and anxiety to pedestrians and automobile runners, measures have been taken to suppress cable vibrations.

As a means for suppressing the vibration, there is an aerodynamic measure to change the cross-sectional shape of the cable itself, but mechanical vibration suppression means is often attached to the cable. As this mechanical vibration damping means, a means for connecting cables is adopted, but this is not preferable in view of the scenery. For this reason, in recent years, a method of installing a damper that does not impair the scenery and that can predict the additional attenuation to some extent has been often adopted.

[0004] Additional damping required for damping (δ; logarithmic damping rate)
Is δ = 0.02-0.
03, it is said that δ = about 0.01 in vortex excitation.
Japanese Patent Application Laid-Open No. 6-136 discloses a method of providing this damper.
718 (Technical 1), JP-A-7-119115 (Technical 2) and JP-A-5-59703 (Technical 3).

[0005] Technique 1 is "a technique in which one end of a cylindrical member in which a cable of a cable fixing section is embedded is fixed to a bridge girder, and a solid viscoelastic body is provided between the cable and the cylindrical member.""A clamp with a flange is attached to the outer periphery of the cable near the cable fixing portion, and a high attenuation rubber is interposed between the end surface of the fixing portion and the flange." However, it is known that the magnitude of attenuation that can be added to the cable is proportional to the ratio of the cable length to the solid viscoelastic body from the cable fixing point (fixing section) and the cable length. In the technology 1 and the technology 2 in which the solid viscoelastic body is directly attached between the clamps, when a long cable exceeding 300 m is damped compared to a cable of about 100 m, the solid viscoelastic body is fixed from the cable fixing point (fixing portion). The distance to is increased. That is, the height from the bridge girder surface to the mounting position of the solid viscoelastic body is increased, and it is difficult to perform workability such as mounting of the solid viscoelastic body, inspection and maintenance. In addition, there is a problem that a vibration damping device including a solid viscoelastic body attached to a cable is easily noticeable by humans, and the landscape is deteriorated.

Technique 3 has been proposed to solve such a problem. This vibration damping device will be described with reference to FIG. A two-part clamp 1 is fixed to the cable C with a tightening bolt 2. On the other hand, the cylindrical member 5, the lid 6, the spring receiving cylinder 7, the spring 8 housed in the cylindrical member 5, and one end are fixed to the center of the bottom of the cylindrical body 7 on the bridge girder G, and the other end is the lid A connecting rod 4 penetrating through 6 and a damper 10 made of a viscous fluid injected into the cylindrical member 5 are mounted so that the connecting rod 4 stands upright. Reference numeral 9 denotes an orifice opened in the bottom plate of the cylinder 7.
A minute gap g is provided between the outer peripheral wall of the cylindrical body 7 and the inner wall of the cylindrical member 5. The clamping bolt 2 of the clamp 1 and the connecting rod 4 are connected by a wire rope 3. 3a is an ice price formed on the upper end of the wire rope 3. The spring 8 has a function of returning the cylinder body 7 with a biasing force with respect to the displacement of the cylinder body 7, and applies a predetermined tension to the wire rope 3. When vibration occurs in the cable C due to the action of wind, rain, or the like, the vibration displacement is transmitted to the cylinder 7 of the damper 10 via the wire rope 3. Since the cylindrical member 5 is immovable, viscous shear resistance of the viscous fluid is generated between the outer peripheral wall of the cylindrical member 7 and the inner peripheral wall of the cylindrical member 5, and a resistance force acts in a direction in which the movement of the cylindrical member 7 is stopped.
This resistance attenuates the swing of the cable C interlocked via the wire rope 3 and the clamp 1. With the above configuration, the point of action of the resistance of the damper is
Since the damper body having a large volume is attached to the bridge girder G, inspection and maintenance are easy, and the landscape is not spoiled.

[0007]

However, the technology 3
The vibration damping device has a complicated structure for accommodating the spring receiving cylinder 7 and the spring 8 in the cylindrical member 5 and causing the viscous fluid to viscous shear resistance in the spring receiving cylinder 7. Further, since the viscous fluid is used, there is a possibility that a liquid leak may occur when the damper is replaced and used, and in such a case, there is a problem that the surroundings are contaminated or the liquid must be replenished.

An object of the present invention is to provide a cable damping device for a cable-stayed bridge which has a simple structure, is easy to maintain, and does not impair the scenery.

[0009]

According to the present invention, the above object is achieved by the following apparatus.

A first device is a vibration damping device provided between a cable and a bridge girder in a cable-stayed bridge, wherein the cable and the bridge girder are connected via a damper made of viscoelastic rubber and a wire rope. A cable damping device for a cable stayed bridge.

The second device is the same as the first device,
The cable damping device for a cable-stayed bridge according to claim 1, wherein the viscoelastic rubber of the damper undergoes shear deformation.

A third device according to claim 1, wherein in the first device or the second device, the cable and the bridge girder are connected with the wire rope being tensioned in advance. Cable damper for cable-stayed bridge.

[Operation] First device: When a cable vibrates, a vibration force is transmitted to the viscoelastic rubber via a wire rope, and vibration is generated in the viscoelastic rubber. The vibration energy of the cable is attenuated by the vibration of the viscoelastic rubber, and the vibration of the cable is suppressed.

Since the viscoelastic rubber is a member having both a vibration damping function and a spring function, after the vibration is suppressed, the viscoelastic rubber can return to the position before the occurrence of the vibration by the spring function. In addition, if the damper is installed near the bridge girder or connected to the bridge girder, the scenery is not impaired.

Second device: The mounting structure of the viscoelastic rubber is as follows:
It is desirable that the cable be capable of quickly absorbing the vibration energy when the cable vibrates. If the damper is attached to the bridge girder so that the viscoelastic rubber is sheared, high energy loss can be obtained.

Third device: Since the wire rope does not transmit the compressive force, when the vibration direction of the cable is the compression direction of the wire rope, the viscoelastic rubber does not attenuate the vibration energy. If a damper is attached with tension applied to the wire rope in advance, the wire rope will not loosen even if the cable vibrates, so even if the vibration direction of the cable is the compression direction of the wire rope, it will vibrate into the viscoelastic rubber. Can be transmitted. Therefore, the amount of energy attenuation per cycle of cable vibration is increased as compared with a case where tension is not applied to the wire rope in advance, and vibration of the cable can be suppressed more quickly.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing an attached state of the device of the present invention, and FIG. 2 is a view taken along the line AA of FIG.

C is a cable for a cable stayed bridge, and G is a bridge girder.
Reference numeral 20 denotes a split clamp, and one clamp piece is provided with a locking member 20a such as a wire rope. The clamp 20 is firmly attached to the middle of the cable C with a fastening bolt (not shown). 21 is a wire rope, 30
Is a viscoelastic rubber, 22 is a transmission plate for embedding the lower part in the center of the viscoelastic rubber 30 and being vulcanized and joined, and for transmitting a vibration force to the viscoelastic rubber 30. Reference numeral 22a denotes a locking bracket mounting plate mounted on the upper end of the transmission plate 22;
Reference numeral 2b denotes a locking metal attached to the upper surface of the locking metal mounting plate 22a. The outer end surface of the viscoelastic rubber 30 is
4 is vulcanized to the side plates 24b, 24b. The storage frame 24 has a bottom plate 24a. A bracket 25 is formed at the center of the lower surface of the bottom plate 24a. In addition, bridge girder G
A bracket 26 that engages with the bracket 25 is provided above. These brackets 25 and 26
Since the housing frame 24 is connected by the shaft pin 27,
It is possible to swing around the shaft pin 27 as a fulcrum. The storage frame 24 is attached so that the transmission plate 22 is parallel to a plane perpendicular to the stretched cable C so that the vibration force acts on the viscoelastic rubber 30 as a shearing force.
This is desirable because a high attenuation rate can be obtained.

The viscoelastic rubber 30 is required to have a high vibration damping function and a high spring function (elasticity).
Specifically, in addition to natural rubber, SBR (styrene butadiene rubber), NBR (acrylonitrile butadiene rubber), silicone rubber, butyl rubber and the like are used.

Next, a method of mounting the vibration damping device of the present invention will be described. First, the mounting position of the damper and the required spring constant of the viscoelastic rubber that satisfy various conditions such as additional damping determined by the design are determined by performing a complex eigenvalue analysis on the analysis model of the cable and the damper. Next, the clamp 20 is attached to the clamp attachment position of the cable C determined based on these factors. The bracket 26 is mounted at a position where a line orthogonal to the cable C intersects the bridge girder G from the mounting position of the clamp 20. The storage frame 24 to which the viscoelastic rubber 30 and the transmission plate 22 are attached is attached to the bracket 26 by the bracket 25 and the shaft pin 27. One of the ice prices 21a of the wire rope 21 adjusted to a predetermined length is locked by the locking metal fitting 20a of the clamp, and the other ice price 21b is locked by the locking metal fitting 22b on the storage frame side.

In the above-described wire rope attaching method, if the wire rope 21 is attached while applying tension to the wire rope 21 using a general-purpose chain block or the like, the clamp 20
Can be connected by a pre-tension wire rope to the locking bracket 22b on the storage frame side. If a turnbuckle (not shown) is attached to one end or the middle of the wire rope 21, the clamp 20 and the storage bracket 22b can be connected. The frame-side locking fittings 22b can be easily connected with a pretension wire rope.

[0022]

An example of the pretension required for the wire rope 21 and the physical properties of the viscoelastic rubber 30 in the apparatus of the present invention will be described below.

Cable length; 450 m Tension acting on the cable; 500 tf Unit weight of the cable; 0.1 tf / m, the primary natural frequency of this cable is about 0.
25 Hz. To set the logarithmic decrement δ of the viscoelastic rubber 30 to 0.02 up to the 10th-order frequency 3 Hz, the mounting position of the clamp 20 is 11.7 m from the fixing unit. The required spring constant of the viscoelastic rubber 30 at this time is 4
0 tf / m. Since the displacement of the viscoelastic rubber 30 at the time of cable vibration is at most 1-2 cm, the pre-tension required for the wire rope 21 may be 1 tf. At this time, the displacement of the viscoelastic rubber 30 is 2.5 cm. Thus, during one cycle of cable vibration, viscoelastic rubber 30
Works to attenuate the vibration at all times, and can quickly attenuate the vibration of the cable.

[0024]

The present invention uses a viscoelastic rubber as the damper, and the damper body is installed on the bridge girder. Therefore, when the damper is replaced and used, it is necessary to contaminate the surroundings due to liquid leakage or to replenish the liquid. Absent. The structure is simple,
The effect that maintenance is easy and the scenery is not spoiled is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an attached state of the device of the present invention.

FIG. 2 is a view as viewed in the direction of arrows AA in FIG. 1;

FIG. 3 is a schematic diagram showing an attached state of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 20 Clamp 20a Locking metal 21 Wire rope 21a, 21b Ice price 22 Transmission plate 22a Locking metal mounting plate 22b Locking metal 24 Storage frame 25, 26 Bracket 27 Axis pin 30 Viscoelastic rubber C Cable G Bridge girder

Claims (3)

[Claims] 1. A vibration damping device provided between a cable and a bridge girder in a cable-stayed bridge, wherein the cable and the bridge girder are connected via a damper made of viscoelastic rubber and a wire rope. Cable damping device for a cable-stayed bridge. 2. The cable damping device for a cable-stayed bridge according to claim 1, wherein the viscoelastic rubber of the damper undergoes shear deformation. 3. The cable damping device for a cable-stayed bridge according to claim 1, wherein the cable and the bridge girder are connected with each other with tension applied to the wire rope in advance.