JPS5944443B2 - suspension bridge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The wind speed that causes the swinging and vertical and torsional movements of the girder of a suspension bridge depends on the strength of the excitation force and the natural frequency of each type of structure.

Vertical motion is not a major problem, but torsional and related motions are catastrophic.

The effect of the wind acting on the side of the bridge girder is to apply a push-up blade to the bridge girder.
Acts on a location at a distance of /4.

This eccentric push-up blade tends to cause rocking of the girder about the centerline.

The conventional method to overcome this disadvantage is to increase the torsional frequency of the suspended bridge girder by increasing the structural stiffness, but this method is expensive, especially for spans over 1000 m. .

The purpose of this invention is to reduce the size of the push-up blade and to move the area where the push-up blade acts closer to the center line.

Accordingly, the invention provides that the bridge girder is constituted by spaced apart beams extending transversely to the suspension cables and slats supported on the beams and extending parallel to said cables;
The purpose of the present invention is to provide a suspension bridge in which the slats allow upward flow of air through or between them.

According to this device, the torsional stiffness of the suspended bridge girder can be reduced by adjusting the force that hinders the stability of the suspension bridge, and furthermore, the material and construction costs can be reduced due to the reduction in dead weight.

The slats are made up of a number of thin girder units that allow air to pass through small openings placed close to the slats.
or arranged to flow through slots formed between the slats.

Air flow can be adjusted by selecting the optimal ratio between open and closed bridge sections, which is generally about 1-2.

Preferably, the slats are provided separated by slots and the lower surface of the slats is aerodynamically shaped so that the slots narrow upwardly.

As will be explained later, it is also advantageous to form the slots in such a way that the air flows upwardly through the slots in a direction obliquely from the vertical towards the centerline of the bridge.

The slats serve to support the wheels of road vehicles crossing the bridge in suitable lanes.

Slats with flat upper surfaces are bent or trapezoidally shaped on the lower surface to form the desired aerodynamic shape.

If desired, the slats may be concrete slabs with wider longitudinal passages at the bottom than at the top to allow air to flow upwardly through them.

Alternatively, slots may not be provided in lanes located on either side of the centerline.

Embodiments of the invention will now be described in more detail with reference to the accompanying drawings, by way of example.

Like numerals indicate like parts in the drawings.

The bridge girder 10 shown in FIG. 1 consists of spaced beams 11 which are suspended by the suspension cables 12 of the suspension bridge and support spaced apart slats 13 on their upper surfaces, said slats 13 They are separated by slots 14 which extend parallel to the cables 12 and allow air to flow upwardly through the bridge 10.

Both beams 11 and slats 13 can be constructed of concrete or steel.

The spacing between beams 110 is, for example, 6.096 to 18.288 m.
(20 to 60 ft, ), and the width at the top of the slot 14 is 15.24 crrL (6 in, ).

Cable 12 may be of conventional design or may be arranged as described in British Patent No. 911,350.

The slats 13 serve to support the wheels of road vehicles crossing the bridge, and are trapezoidal on the underside so that the slots 1
4 forms an upwardly narrowing passage which allows air to flow upwardly through the girder 10.

The bridge girder 10 shown in FIG. It is almost the same as the bridge girder in the figure.

When the wind acts on the left side of the bridge girder 10, the push-up blade usually acts at a location 16 of one quarter of the chord of the bridge girder 10 from the side where the wind acts, as shown in FIG.

By shifting the area where this push-up blade acts toward the center line of the bridge girder 10 to reduce the tendency of the bridge girder 10 to swing, air can pass through the slot 14 vertically as shown in FIG. This is possible by forming the slot 14 so that it flows upwardly in a direction inclined from the line towards the center line of the girder 10.

The slats 13 shown in FIG. 3 have flat undersides, but the undersides of the slats 13 encourage air to flow upwardly toward the slots 14, as shown in FIG. It is also possible to configure the structure so that the air flows in an oblique direction from the vertical towards the center line.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the girder of a suspension bridge, FIG. 2 is a cross-sectional view showing deformation of the girder, and FIGS. 3 and 4 are schematic diagrams showing the deformed arrangement of the slats. 10: Bridge girder, 11: Beam, 12: Suspension cable, 13
Nisrat, 14: Groove.

Claims (1)

[Claims] 1. A bridge girder consisting of spaced apart beams extending transversely to the suspension cables and slats supported on the beams and extending parallel to said cables, inclined relative to the vertical towards the center line of the girder. 1. A suspension bridge characterized in that the bridge girder has slots between the slats forming an upwardly narrowing sloping passage to allow air to flow upwardly through the bridge girder.