JPH0249805A - Pneumatic oscillation preventing method - Google Patents

Abstract

PURPOSE:To prevent oscillations of a box type bridge girder and to prevent generation of air swirls at the bridge side parts by providing an opening parts at the opposed ends of the bridge girder, thereby making air circulate in the box. CONSTITUTION:Opening parts 2 are arranged at the opposed ends of a box type bridge girder 1, namely bridge beam side parts are formed in a lattice serving as the openings or merely the opening parts 2 are formed thereat. Upper and lower slant faces are provided on both the sides of the box while the opening parts 2 are positioned at the central part thereof. The wind acting from the side parts of the box 1 flows along both slant faces of the box side parts and flows in and out of the box through the opening parts. It is thus possible to prevent generation of air swirls after wind acts onto the beam and to prevent generation of oscillation in the girder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an aerodynamic vibration prevention method for preventing wind-induced vibration of a box girder bridge.

[Prior Art] Truss girders or box girders are usually used for the girders of long-span bridges where wind-induced vibration is particularly problematic. Truss girders are prone to flutter when exposed to strong winds from the sides, and box girders may experience vortex-induced vibration or flutter, so the following vibration isolation methods are generally used.

(1) Truss girder 1) As shown in FIGS. 7(a), (b), and (c), gratings 12 are provided at various locations on the floor slab 11 to allow free flow of wind in the vertical direction. Alleviates the wind pressure acting on the area.

2) As shown in FIG. 8, a closing plate 13 is installed in the center of the floor slab 11.
Or, the central railing 14 can be closed and the floor slab 11
Bridge vibration is prevented by separating the wind flow and changing its pattern.

(2) Box girder 1) As shown in Figures 9(a) and (b), flow control plates 15 are installed on both sides of the floor slab 11 to suppress the flow of wind.
(2) Prevent peeling of both side edges. In this case, the balustrade 14 is of an open type.

2) As shown in Figure 10 (a) and (b), by making the cross section of the box girder almost streamlined and preventing the creation of vortices in the wind flow, the bridge will not cause vortex-induced vibration or flutter. do it like this. In this case, the balustrade 14 is of course open type so as not to obstruct the flow of wind.

[Problems to be solved by the invention] (1) Although it is possible to suppress flutter using conventional technology for truss girders, the cross-sectional shape of truss girders not only makes it difficult to maintain sufficient strength against torsion, but also makes maintenance difficult. There are also many problems.

(2) Box girder 1) In the case of long-span bridges, box girders cannot be made very flat in order to maintain rigidity, so a certain amount of girder height is required, which causes vortex-excited vibration.

Although a flow control plate 15 is provided to prevent this vortex-excited vibration, there is a problem that this obstructs the view of passersby and spoils the scenery.

2) When using a streamlined box girder, if the girder height is reduced to create a flat streamlined shape, flutter will occur because the rigidity will be reduced. For this reason, it is preferable to ensure the girder height necessary to maintain rigidity and at the same time provide overhangs 16 on both sides of the girder as shown in FIG. 1O to rectify the aerodynamic force, but this increases manufacturing costs. Further, even with this method, flutter prevention is not completely achieved.

The present invention has been made to solve such problems, and is an aerodynamic vibration prevention method for box girder bridges that can reliably prevent vortex vibration and flutter even when box girder bridges receive strong horizontal crosswinds. The purpose is to obtain a method.

[Means for Solving the Problem] In order to achieve the above object, the aerodynamic vibration prevention method according to the present invention provides jet blowing openings on both sides of a box girder bridge, and blows jet from the sides of the bridge. To provide an aerodynamic vibration prevention method that allows wind to blow through the inside of a box girder at the same time as the outside surface of the box girder.

[Function] When wind is received from one side of the box girder, the wind flows along the outer surface of the box girder, and at the same time, the wind passes through the inside of the box girder through the openings on the side of the box girder, and the wake of the box girder. Since the air blows out inward, no vortex is formed.

[Example] FIG. 1 is a perspective view showing an embodiment of the present invention.

In the figure, 1 is a box girder with sloped surfaces on both sides to form a cross section close to a streamlined shape, 2 is an opening on both sides of the box girder 1,
3 is a lattice structure installed in the opening 2, 4 is an open railing, and 5 is the upper part of the box girder 1, which becomes the floor slab.

Next, this effect will be explained. FIGS. 4(a) and 4(b) are diagrams explaining the detailed principle of the present invention, where (a) schematically shows the flow of wind in the box girder according to the present invention and (b) in the conventional box girder. It is something that Conventional box girder 6 shown in Figure 4(b)
In this case, when the wind flow 10 is received from the side, the wind flow 10 is separated from the rear corner 6a of the box girder 6, a vortex 10a is formed in the wake, and vortex excitation vibration is generated in the box girder 6. On the other hand, in the case of the box girder 1 according to the present invention shown in FIG. A flow tab of air is generated which enters the box girder 1 from the upstream side opening 2 of the box girder 1, passes through the inside of the box girder, and blows out in a jet form from the downstream side opening 2. This can prevent the vortex 10a from being generated in the wake of the wind.

FIG. 2 is a perspective view showing another embodiment according to the present invention, in which openings 2a are arranged at regular intervals on both sides of a box girder 1 formed integrally, and other symbols indicate first Shows the same thing as the figure. The effect of this embodiment is exactly the same as described above.

FIG. 3 is a perspective view showing still another embodiment, in which a box-shaped girder 1a is provided at the bottom of the floor slab 5, and openings 2a are provided on both sides of the box-shaped girder 1a, and other symbols are shown in FIG. 1. indicates the same thing as. The effect of this embodiment is also exactly the same as described above.

Next, FIG. 5 is a diagram showing the results of a wind tunnel experiment of the present invention, and FIGS. 6(a) and (b) are sectional views of the models used in the experiment. In Figure 5, the vertical axis is the torsional amplitude, the horizontal axis is the actual bridge equivalent wind speed (i+/s), and the white circle A is the result of a wind tunnel experiment on the conventional box girder model 6p shown in Figure 6 (a). The plot points showing , and the black circles B are the plot points showing the results of wind tunnel experiments on the box girder model 1p according to the present invention shown in Fig. 6(b). Compared to the conventional box girder model 6p, the box girder model 1p according to the invention hardly twists even when subjected to actual bridge equivalent wind speeds of 0 to 50 m/s, and it can be seen that it has an extremely large anti-vibration effect. .

[Effects of the Invention] As explained above, the present invention provides openings on both sides of the box girder to allow air to flow freely through the box girder, thereby reducing the wake of wind against the box girder bridge. As a result, it was possible to reliably prevent vortex-induced vibrations from occurring in the box girder bridge.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing one embodiment of the present invention, and FIG.
3 are perspective views of other embodiments, and FIG. 4 is an explanatory view showing the principle, where (a) shows the present invention and (b) shows the conventional example. Figure 5 is a line diagram of the wind tunnel experiment results, and Figure 6 is a cross-sectional view of the model used in the wind tunnel experiment, where (a) is a conventional box girder model, (b)
) are models of the box girder of the present invention, Figures 7(a) and (b)
, (c) is a cross-sectional view of a conventional truss girder bridge, Fig. 8 is a partially detailed view of the cross section of the central part of a truss girder bridge, and Fig. 9 (a) is a cross-sectional view of a conventional truss girder bridge.
) and (b) are cross-sectional views of a conventional box girder bridge, and FIGS. 10(a) and (b) are cross-sectional views of a conventional streamline box girder bridge. 1: Box girder, 2: Opening, 3: Lattice structure, 4: Railing, 5
: Floor slab, 6: Conventional box girder, 6a; Back corner, 10: Wind flow, 10a: Vortex.

Claims (1)

[Claims] An aerodynamic vibration prevention method in which openings are provided on both sides of a box girder bridge so that the wind blowing from the sides of the bridge blows through the inside of the box girder at the same time as the outside of the box girder, and blows into the wake of the wind.