JP2519287B2 - Damping method for vortex excitation of bridge main tower - Google Patents

Description

TECHNICAL FIELD The present invention relates to a vibration damping method for vortex excitation of a bridge main tower.

(Prior Art) In the main tower of a suspension bridge or cable-stayed bridge, a cable is stretched when the main tower T is erected as shown in FIG. 8 (a) and after the main tower T is erected as shown in FIG. 8 (b). Independence until (Free Standin
In g), it is well known that wind causes vibration called vortex excitation. Furthermore, even in the case of a super-long bridge with a high tower height or a main tower with low rigidity, even after the cable a, girder b, and hanger c have been erected on the main tower T as shown in Fig. 8 (c), the bridge has been completed. , This vortex excitation may occur below the design wind speed. This vibration may cause damage such as being unable to work during erection, damage due to fatigue, etc., and may not be shared in the completed system or may be damaged due to fatigue. It is extremely important to suppress this vibration. .

As a conventional vibration control method for a main tower, a sliding block method using a structural dynamic wire rope or a weight damping method using a wire rope is also used. Further, when it is difficult to install the above-mentioned dynamic vibration damping method around the main tower, a net or seat system, a cowling system or the like is used as an aerodynamic vibration damping device.

(Problems to be Solved by the Invention) As in the prior art, it is disadvantageous in terms of space to install an additional device particularly in the bridge completion system, and the bridge must endure long-term service. In, it is very disadvantageous in terms of maintenance. Therefore,
The present invention can be applied to a erection system, an independent state and a completed system, and it is intended to provide a method capable of damping vibration without installing an additional device as in the prior art.

(Means for Solving the Problem) In the vicinity of the antinode of the vibration mode shape of the cross-shaped tower with four corners cut off, the total height is about 15 to 35.
The corner cutting amount of% was reduced by about 60% or more to make it thicker.

In addition, the amount of corner cut from the base of the tower with a cross-shaped cross section to a height of about 70% was reduced by about 60% or more, and wind resistance stability was improved.

In addition, the top of the tower is made thicker than the center to enable damping against vortex excitation in the installed system and in an independent state.

(Example) The main tower T of the bridge has a vibration mode in which the main tower T greatly vibrates not only in the erection system / independent state but also in the bridge completion system as shown in FIG. That is, the main tower bending antisymmetric vibration as shown in FIG. 9 (a) and the main tower bending symmetrical vibration as shown in FIG. 9 (b) occur. Therefore, as a result of the wind tunnel experiment on the wind speed and the amplitude when the top of the tower was restrained, the response as shown in Fig. 10 appeared. In other words, when we measured the amplitude in the approximate center of the main tower, the maximum bending occurred when the wind tunnel speed was 2 to 4 m / s, especially 3 m / s, and the maximum twist was 5 m / s. It turned out to occur.

Therefore, with the aim of stopping (suppressing) this vibration, the relationship between the combination of tower column cross sections shown in Fig. 1 and the response was investigated by a wind tunnel experiment. That is, the cross section A is used as a basic cross section, and the members B to E are attached to the four corners thereof, and the cross sectional shapes of the corners of the towers are taken to be B to E, respectively. That is, the cross section of the main tower T is gradually thickened. When any of A to E was provided over the entire height of the main tower T, the result was that the cross section A had the best wind resistance among them, as shown by the arrow a in FIG.

Furthermore, when the cross-sectional shape is partially changed in the tower height direction,
As shown in FIG. 2 (c), the basic cross section is A, and only blocks No. 5, 6, 7 are changed to cross section D from the top (corner cutting amount is A
Approximately 1/4 of the area of DT3) (arrow b in Figure 2a)
In the case of, the response value was suppressed to about 1/2 by bending vibration and about 1/3 by torsional vibration (see Fig. 2b).

Therefore, as shown in FIG. 3, in the vicinity of the antinode (the point where the displacement is the maximum) in the vibration mode shape, the corner cut amount of the cross-shaped cross section is reduced by about 60% or more in the portion of 15 to 35% of the total height (in other words, If
It was discovered that vortex excitation in the completed main tower is suppressed by shaving only 40% and thickening only that part as a tower pillar.

Although the above description is for a completed system, the present invention can also be applied to a erection system and an independent main tower. Incidentally, Fig. 5 shows the response results in the independent state, and when the shaded portion in the upper left part of the figure is attached by about 40 to 50% from the tower top, the response becomes the minimum.

(Effect) The main tower T is a structure that is tall in the vertical direction (Fig. 4). By changing the cross-sectional shape of the flow pattern near the top of the main tower T and the height in the center of the tower, the emission frequency or phase of the wake alternating vortex is changed particularly at the top and the center of the tower. As a result, due to the interference effect of the excitation force of the discharge vortex, the main tower T
The force acting on is weakened and the response value is suppressed. That is,
By controlling the discharge pattern of the wake vortex in the tower height direction by partially (or thinning) the cross section in the tower height direction, and suppressing vortex excitation, 1) the main tower of the completed system It became possible to suppress the vortex excitation of T.

2) It is aesthetically advantageous because it does not require the production of a special device that changes the cross-sectional shape in the height direction and there is no attachment of an aerodynamic countermeasure attachment. Therefore, no particular maintenance is required and no installation place is required.

3) It can be applied to erection system and independent tower.

[Brief description of drawings]

FIG. 1 is a dimension comparison diagram of tower column cross-sectional shapes. FIG. 2 (a) shows the relationship between the tower column cross-sectional shape and the maximum response value. Similarly, FIG. 2B is a graph showing the relationship between the cross section and the maximum response amplitude. FIG. 2 (c) shows the block number of the main tower, especially DT3 in FIG. 2 (a). FIG. 3 shows the vibration mode shape of the main tower of the completed system. FIG. 4 shows a conceptual diagram of vortex shedding in the wake of the main tower. Fig. 5 shows the relationship between the number of countermeasure blocks and the maximum response value from the top of the tower. FIG. 6 shows an example of a countermeasure cross-sectional shape of the main tower in the completed system. FIG. 7 shows an example of the countermeasure cross-sectional shape of the main tower in the independent state. Figure 8 is an illustration of the main tower construction stage. 9 (a) and 9 (b) show vibration modes of the main tower in the bridge completion system. Figure 10 shows a wind tunnel wind velocity-width chart showing the state of vortex-induced excitation of the main tower in the completed system.

Claims (3)

(57) [Claims] 1. A corner cutting amount of about 15 to 35% of the total height is about 60% or more in the vicinity of the antinode of the vibration mode shape of a tower column having a cross-shaped cross section by cutting the four corners. A damping method for vortex-induced vibration of a main tower of a bridge, which is characterized by reducing and thickening. 2. About 70% from the tower base of the tower with a cross-shaped cross section
2. The method for damping vibration against vortex excitation of a bridge main tower according to claim 1, wherein the amount of corner cutting is reduced by about 60% or more to the height of the bridge to improve wind resistance stability. 3. A vibration damping method for eddy excitation in an installed system / independent state, wherein the tower top is made thicker than the center.