JPH0765292B2 - Aerodynamic vibration prevention structure for box girder bridge - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an aerodynamic vibration preventing structure for a box girder bridge that prevents vibration due to wind.

[Prior Art] Usually, truss girders or box girders are used for girders of long-span bridges in which vibration due to wind is a problem. Truss girders are prone to flutter when exposed to strong winds from the side, and box girders may cause vortex excitation or flutter. Therefore, the following vibration isolation structures are generally used.

(1) Truss girder 1) As shown in Figs. 7 (a), (b), (c), floor slab
Gratings 12 are provided at various points on 11 to make the air flow in the vertical direction free and to reduce the wind pressure acting on the floor slab 11.

2) As shown in Fig. 8, a bridge 13 is provided at the center of the floor slab 11, or the central railing 14 is used as a closed type to separate the wind flow along the floor slab 11 and change the pattern of the bridge. To prevent vibration.

(2) Box girder 1) As shown in FIGS. 9 (a) and 9 (b), the flow restricting plates 15 are installed on both sides of the floor slab 11 to suppress the flow of wind and to prevent the air from flowing in the both ends of the floor slab 11. Prevent peeling. In this case, the balustrade 14 is open type.

2) As shown in Figs. 10 (a) and 10 (b), the cross section of the box girder is made to be almost streamlined so that no vortex is created in the wind flow, so that the bridge does not cause vortex excitation or flutter. To do so. In this case, of course, the balustrade 14 is an open type so as not to obstruct the flow of wind.

[Problems to be Solved by the Invention] (1) Truss girder Although flutter can be suppressed by conventional techniques, not only is the truss girder inherently difficult to maintain sufficient strength due to twisting, etc. However, there are many problems.

(2) Box girders 1) Box girders cannot be flattened to maintain rigidity in the case of long span bridges, so a certain amount of girder height is required and vortex excitation occurs. Although the flow restricting plate 15 is provided to prevent the vortex excitation, there is a problem that this obstructs the view of passersby and damages the scenery.

2) In the case of a streamlined box girder, if the girder height is reduced to a flat streamlined shape, flutter occurs because the rigidity is reduced. Therefore, at the same time as securing the girder height necessary for maintaining rigidity, it is preferable to provide the overhanging portions 16 on both sides of the girder to rectify the aerodynamic force as shown in FIG. 10, but this increases the manufacturing cost. Also, even in this case, the flutter prevention is not perfect.

The present invention has been made to solve such a problem, and particularly in a box girder bridge, it is possible to reliably prevent vortex excitation and flutter even when a strong horizontal cross wind is applied, and prevent aerodynamic vibration of the box girder bridge. The purpose is to obtain the structure.

[Means for Solving the Problems] In the aerodynamic vibration preventing structure for a box girder bridge according to the present invention, the main girder is provided with inclined portions on both side edges of the main girder for guiding cross wind in a direction along the main girder. A plurality of blow-throughs are provided on both side surfaces of the air passage to allow wind to pass from one of the both side surfaces to the other.

[Operation] In the structure for preventing aerodynamic vibration of the box girder bridge configured as described above, when a cross wind is received from one side of the main girder, the cross wind flows in a streamline shape along the sloped portion, so The width becomes smaller and the vortex generating force in the wake becomes smaller. Further, a part of the cross wind passes through the blow-through and prevents this wind from blowing into the wake and forming a vortex in the wake.

[Embodiment] FIG. 1 is a perspective view showing an embodiment of the present invention. In the figure, 1 is a box girder having inclined surfaces on both sides to form a cross-section close to a streamline, 2 is openings on both sides of the box girder, 3 is a lattice structure provided in the opening 2, and 4 is It is an open type on the balustrade, and 5 is a floor slab above the box girder 1.

Next, this action will be described. FIGS. 4 (a) and 4 (b) are principle diagrams for explaining the operation of the present invention. FIG. 4 (a) is a box girder according to the present invention, and FIG. It is a thing. In the case of the conventional box girder 6 shown in FIG. 4 (b), when the wind flow 10 is received from the side surface, the rear corner 6a of the box girder 6 is received.
The wind flow 10 separates from the above to form a vortex 10a in the wake, and vortex excitation occurs 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. 4 (a), the wind flow 10 includes the wind flowing along the outer surface of the box girder 1 facing from the upstream side to the downstream side as well as the box girder. A wind flow 10b that enters the box girder 1 through the upstream side opening 2 and passes through the box girder and is jetted out in the form of a jet from the downstream side opening 2 is generated. This creates a vortex in the wake of the wind 1
It is possible to prevent the occurrence of 0a. That is,
The box girder 1 according to the present invention is provided with inclined portions on both sides of the box girder, thereby reducing the width of the dead water region of the wake to reduce the vortex generation force, and passing the inside of the box girder 1 to the wake. The generation of the vortex is surely prevented by blowing the generated wind.

FIG. 2 is a perspective view showing another embodiment according to the present invention, in which the openings 2a are arranged at regular intervals on both sides of the box girder 1 which is integrally formed. The same as the figure is shown. The operation of this embodiment is exactly the same as that described above.

FIG. 3 is a perspective view showing still another embodiment, in which a box-shaped girder 1a is provided in the lower part of the floor slab 5 and openings 2a are provided on both sides thereof, and other symbols are shown in FIG. Shows the same thing as.
The operation according to this embodiment is exactly the same as that described above.

Next, FIG. 5 is a diagram showing the results of the wind tunnel experiment of the present invention, and FIGS. 6 (a) and 6 (b) are cross-sectional views of the model used in the experiment. In Fig. 5, the vertical axis is the torsional amplitude, the horizontal axis is the actual bridge converted wind speed (m / s), and the white circle A is the result when the conventional box girder model 6p shown in Fig. 6 (a) was subjected to the wind tunnel test. The black circle B is the plot point showing the result of the wind tunnel experiment of the box girder model 1p according to the present invention shown in FIG. 6 (b). As is clear from FIG. 5, the box girder model according to the present invention
Compared to the conventional box girder model 6p, 1p is 0-50m /
Even if it receives s, it hardly turns out to be twisted, and it can be seen that the vibration damping effect is extremely large.

[Effects of the Invention] As described above, in the present invention, the vortex generating force of the wake is reduced by flowing the side wind in the streamline shape along the inclined portion, and the wind that has passed through the stairwell is diverted in the wake. Since the vortex is prevented from being generated by being blown out to the vortex, it is possible to reliably prevent the vortex excitation due to the wake.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing an embodiment of the present invention, and FIG.
FIG. 3 and FIG. 3 are perspective views of other embodiments, and FIG. 4 is an explanatory view showing the principle, (a) showing the present invention, and (b) showing the conventional example. Fig. 5 is a diagram of the wind tunnel test results, Fig. 6 is a cross-sectional view of the model used in the wind tunnel experiment, (a) is a conventional box girder model,
(B) is a model of the box girder of the present invention, FIGS. 7 (a), (b),
(C) is a cross-sectional view of a conventional truss girder bridge, FIG. 8 is a partial detailed view of a cross-section of the central portion of the truss girder bridge, FIG. 9 (a),
(B) is a cross-sectional view of a conventional box girder bridge, FIG. 10 (a),
(B) is sectional drawing of the conventional streamlined box girder bridge. 1: Box girder, 2: Opening part, 3: Lattice structure, 4: Handrail, 5: Floor slab, 6:
Conventional box girder, 6a: rear corner, 10: wind flow, 10a: vortex.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naohiro Maeda 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (56) Reference JP-A-61-225406 (JP, A) JP Sho 32-2336 (JP, B1) Japanese Patent Sho Sho 33-680 (JP, B1)

Claims (1)

[Claims] 1. A main girder is provided with inclined portions on both side edges thereof for guiding a cross wind in a direction along the main girder, and a plurality of blow-throughs are provided on both side surfaces of the main girder to allow wind to pass from one of the both side surfaces to the other. An aerodynamic vibration prevention structure for box girder bridges, which is characterized by the provision of