JPS6044441B2 - Flutter prevention bridge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to prevention of flutter in a bridge that is relatively long in the spanning direction.

Bridges such as those mentioned above, such as suspension bridges, generally have a suspension bridge stiffening girder with a truss structure suspended by hanger ropes from a main cable stretched between main towers erected on both sides of a river, bay, etc. Although it is covered with deck plates, the main part of the bridge generally has a cross section as shown in Figure 1.

When the wind blows in the X direction in the figure, flutter (vibration) is likely to occur.

To explain this using a diagram, flutter vibration occurs when wind O2 blows in the direction perpendicular to the bridge axis (X direction) on the suspension bridge stiffening girder 01. In response to this vibration, the current Ξ prism 03, the partition plate 04
Alternatively, a method of suppressing vibration by attaching a rectifier plate 05 and changing the flow around the floor plate 06 has been considered.
Generally speaking, suspension bridges, due to their public nature, require the installation of not only railways and roads, but also communication cables, water pipes, power cables, electrical cables, and various other public additions.

Therefore, in addition to the above public additives, installing an aerodynamic damper such as an Ξ prism, a partition plate, or a rectifying plate solely for the purpose of preventing flutter has the following disadvantages.

(1) Dead weight increases.

(2) There is a lot of waste in the design.

(3) Not aesthetically pleasing.

The present invention attempts to propose a bridge that eliminates the above-mentioned problems, and its structure consists of a floor plate whose cross section is approximately horizontal, which is bridged along the direction of traffic, and a bridge below the floor plate. A duct with a cross section approximately inverted trapezoidal, which is bridged at an appropriate height, approximately parallel to the floorboard, and with its windward side projecting to the windward side from the side of the floorboard. The present invention is a flutter-preventing bridge characterized by the above-mentioned structure J, so that the wind blown from the side hits the slope of the inverted trapezoidal part of the duct, and the main flow is guided downward, so that the wind blows in from the side and hits the slope of the inverted trapezoidal part of the duct. Almost parallel flow enters between the duct and the duct, which prevents flutter from occurring, and the duct can also be used as a storage duct for public additives, so it has the following advantages over the conventional method.

(b) No dead weight loss occurs.

(b) Less waste in design.

(c) Aesthetics are improved.

Next, one embodiment of the present invention will be described with reference to the drawings.

In Fig. 2, reference numeral 1 denotes a suspension bridge stiffening girder, and a floor plate 2 for traffic is placed on the upper surface of the girder 1, forming a road. Reference numeral 3 denotes a duct, which is composed of a fairing 4 and a duct body 5, which will be described later, and whose cross section has an inverted trapezoidal shape, and whose windward side 7, which will be described later, protrudes from the side 6 of the floor plate 2 to the windward side X as shown in the figure. There is.

4 is a triangular fairing attached to both sides of the duct body 5, which will be described later, to form the duct 3 into an inverted trapezoid. 5 is a triangular fairing that forms the duct 3 together with the fairing 4, and public additives such as communication cables are stored therein. Duct body with rectangular cross section,
6 is the windward side of the floorboard 2, 7 directly corresponds to the long side of the fairing 4, the duct 3 is the side corresponding to the oblique side of the inverted trapezoid, and the arrow X indicates the direction of the wind. The floor plate 2 and duct 3 on the left side of Figure 2 are shown to be upwind.

Therefore, for the right side, the opposite side is upwind. Next, the effects of the above embodiment will be explained.

In general, flutters are more likely to occur when the wind blowing on a bridge is upward wind C rather than downhill wind A or horizontal wind B for bridge 1'' whose cross section is shown in Figure 3. For example, duct 3 for wind direction
As shown in Fig. 4 as duct 3A, this is the most suitable storage duct. When the cross-sectional shape is rectangular, which is a general shape, the relationship between the flow of the wind blowing against the floor plate 2 and the duct 3A is as shown in FIG. In other words, the wind blowing in the direction However, if the duct 3A has an inverted trapezoidal shape like the duct 3 of this embodiment, the wind blowing in the direction of X as shown in FIG. The wind on the upper side hits the duct 3 and bends downward due to the side part 7, and the wind on the upper side is almost influenced by the duct 3 and flows between the duct 3 and the floor plate 2 as a parallel wind in the direction b. Since the atrium will pass through the floor board 2, flutter will hardly occur on the floor board 2. In Fig. 6, 1 is a part of the suspension bridge stiffening, 8 is the railing of the floor board 2, and 9 is the top of the duct 3. Fig. 7 is a graph showing the experimental results of the above embodiment, and shows the duct 3 of this embodiment which forms an inverted trapezoid, and
A simple rectangular duct 3A as shown in Figures 4 and 5
Shows wind tunnel test data.

In the figure, the horizontal axis is the angle of attack α, and the vertical axis is the wind speed at the limit of flutter occurrence. The A curve shows the flutter wind speed limit for the duct 3A, and the B curve shows the flutter wind speed limit for the duct 3 according to the embodiment of the present invention. Note that the angle of attack α here is an angle measured from the horizontal line in the direction of the arrow shown as 1 angle of attack α in FIG. As can be seen from the figure, in the case of duct 3A, the wind speed around the angle of attack of 3 degrees is about 65rrL.
While flutter occurs at wind speeds above Is, in the case of the duct 3 of the example, flutter does not occur at least at wind speeds below 907 TLIS, which indicates a remarkable effect. In the above embodiment, only one side of the symmetrical cross section of the bridge has been described, but it goes without saying that the same explanation can be applied to the other symmetrical side. Duct 3
Although shown in FIG. 2, it is made up of a fairing 4 and a duct body 5, but it may of course be made to have an inverted trapezoidal cross-sectional shape from the beginning.
As specifically explained above with respect to the embodiment, the present invention is characterized in that the wind blown from the side hits the slope of the inverted trapezoidal part of the duct, and the main flow is guided downward, and there is almost no space between the floorboard and the duct. The duct has the above-mentioned advantages (a) to (c) compared to the conventional example, since flutters do not occur due to parallel flow and the duct can be used as a storage duct for public additives.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a general example for explaining the case where wind blows from the side on a bridge using a cross section of a bridge, Fig. 2 is a cross section schematically showing an embodiment of the present invention, and Fig. 3 The figure is a cross-sectional view for explaining various cases of the direction of the wind blowing from the side on the bridge, and Figure 4 is a normal duct used in contrast to explain the effect of the duct 3 of one embodiment of the present invention. Fig. 5 is a cross-sectional view of a bridge to explain the undesirable effects caused by the duct shown in Fig. 4 (however, only one side of the symmetrical cross-section is shown); Fig. 6 5 is a cross-sectional view for explaining the preferable effect of an embodiment of the present invention, and FIG. 7 shows the normal example shown in FIG. 5 using a normal duct, and FIG. FIG. 8 is a graph showing the results of a comparative experiment to find the flutter wind speed limit with respect to an embodiment of the present invention shown in FIG. 2...floorboard, 3...duct, 6,7.
·····side.

Claims (1)

[Claims] 1. A floor plate whose cross section is substantially horizontal, which is spanned along the traffic direction of the bridge, and which is located approximately parallel to the floor plate at an appropriate height below the same floor plate, and whose side facing upwind is said floor plate. A flutter-preventing bridge characterized by comprising a duct extending upwind from the side of the bridge and having a cross section substantially in the form of an inverted trapezoid.