JP2936087B2 - Bridge cables - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable for a bridge having a low drag coefficient and a vibration damping function which is suitable for use in general for a bridge, in particular, a cable-stayed bridge.

[0002]

2. Description of the Related Art Cables for conventional cable-stayed bridges are typically represented by those using a plastic jacket as a jacket for covering a steel wire bundle, and have a circular cross section and a smooth surface. Have been. Such conventional cables are
It has no mechanical or aerodynamic directionality in its cross section, and its aerodynamic stability is considered to be more advantageous than other cross-sectional shapes, and few attempts have been made to improve the drag coefficient over the shape. This is the actual situation.

However, if a circular cross section cable is used,
It has been confirmed on actual bridges that vibration caused by the interaction between wind and rain (hereinafter referred to as rain vibration) is generated in the cable. Conventionally, as a vibration suppression measure, for example, a cable such as that disclosed in JP-A-6-66344, such as installing a vibration suppression cable that connects cables to each other or providing a vibration suppression damper near the cable fixing portion, is used. A method of installing an additional device, or a method of giving the performance of the cable itself as an aerodynamic damper by changing the surface shape of the cable, for example, a parallel projection shape in which a convex line array extending parallel to the axial direction is provided on the cable surface. (JP-A-63-197703).

[0004]

In recent years, cable-stayed bridges have become longer and longer like other bridges, and accordingly, the cables have become longer and thicker. The wind load has increased, especially proportionally, which is an important factor in determining the cross section of the bridge tower. Therefore, reduction of the wind load generated on the cable, that is, reduction of the drag coefficient of the cable has become a very important issue.

The conventional measures against rain vibration are such that the cable section has the parallel projection shape as described above, and the cable itself has a function as an aerodynamic damper. According to experiments, the drag coefficient is a circle having the same area. It has been confirmed that the diameter of the cable is about 1.2 times that of the cable having a cross section, and it is necessary to further cover the outer layer of the outer cover with a plastic to ensure durability. As a result, the cable has a larger diameter by about 15% than usual, so that the pressure receiving area of the wind increases, which is further disadvantageous in terms of the wind load.

[0006] On the other hand, the vibration damping cable has a problem of deteriorating its appearance due to the structure of connecting the cables, and further requires construction at a high place, thus avoiding the economic disadvantage of increasing the construction cost and construction period. I can't get it. Also, with the damper damper, as the cable stayed bridge cable becomes longer, the effect cannot be obtained unless the installation position is far away from the girder, so the aesthetic appearance is impaired. The construction period is expected to increase.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and an object of the present invention is to significantly reduce the drag coefficient with the same cable diameter as in the prior art, and at the same time, to reduce rainfall. An object of the present invention is to provide a bridge cable capable of effectively suppressing the occurrence of vibration with high economic efficiency by construction on a factory side.

[0008]

The present invention has the following configuration to achieve the above object. That is, the present invention provides a steel wire bundle and the steel flux plastic enclosure Ru putamen formed bridges cable covering, said plug <br/> stick envelope of the outer surface, a number to distribute the shallow recess small It is formed on the irregular surface having the recess, the cable diameter
Cylindrical shape or polygon with a diameter of about 10% and a depth of 1 to 3 mm
Column-shaped and divided from the center of the cable body
Are arranged in the circumferential direction at an interval of 15 °, and
Are arranged in the axial direction at the same pitch as
Rukoto such Te is bridge cable with a low drag coefficient and damping function, characterized in. The present invention also provides a small, shallow depression having a regular, staggered, or random arrangement.
A bridge cable having a low drag coefficient and a vibration damping function, characterized by being provided with:

[0009]

According to the present invention, the outer surface of the bridge cable is formed on the outer surface of the plastic jacket with an uneven surface having a large number of small and shallow depressions dispersed therein. Therefore, in the conventional cable having a smooth circular cross section, a waterway is easily formed on both the lower surface side and the upper surface side of the cable due to the interaction between wind and rain, whereas the cable according to the present invention has a waterway on the upper surface side. It is considered that water is hardly generated on the lower surface side, and this has excellent effects on the drag coefficient and the rain vibration. Accordingly, the present invention provides a cable having an outer peripheral surface of about 10% of the cable diameter.
Small shallow depressions with a depth of 1 to 3 mm in diameter at predetermined intervals
By having a shape having a large number in the circumferential direction and the axial direction, it is possible to significantly reduce the drag coefficient and suppress the occurrence of rain vibration. The invention further a shallow recess small, mouth edge it is a smooth
By forming it into a cylindrical shape or a polygonal pillar shape having an edge shape, a more excellent effect can be obtained by reducing the drag coefficient and suppressing the rain vibration.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 are a partial external view and a cross-sectional view taken along line AA of a bridge cable according to an embodiment of the present invention. FIG. 3 is an enlarged view of FIG. 2, and FIG. 3 is an enlarged view showing a part of FIG. In the cable 1, a steel wire bundle and a plastic jacket 2 covering the steel wire bundle form a main body indicated by hatching. The plastic jacket 2 has a large number of small shallow depressions 3 dispersed on its outer surface. The depression 3 has, for example, a columnar shape, and is formed in an edge shape instead of a gentle edge. The cable 1 specifically has a diameter of φ100 to φ2.
In the case of a 00mm body, the division angle is 15 °
At intervals (24 divisions, see FIG. 3), diameter φ10-20mm
(Approximately 10% of the cable diameter), the recesses 3 having a depth of 1 to 3 mm are arranged and provided, and the recesses 3 are also arranged in the longitudinal direction (axial direction) at the same pitch as the circumferential division angle of 15 °. It is provided in an array. The depressions 3 are not limited to the regular lattice arrangement shown in the drawing, but may be a staggered lattice arrangement or a random arrangement.

In the bridge cable of this embodiment, since the cross-section of the plastic jacket 2 due to the processing of the recess 3 is very small, it is not necessary to increase the diameter to compensate for this. The pressure receiving area is considered to be almost the same as that of a conventional cable having a circular cross section of the same diameter.

In order to clarify that the cable according to the present invention has a low drag coefficient and is excellent in the vibration damping function, the following "Table 1" showing a comparison relationship between cable design conditions and experimental results is shown. As described above, various experiments were repeated on each of the examples A and B of the cable according to the present invention while comparing with the conventional circular cross-section cable C having the same diameter, and the following results were obtained. The experimental conditions in this case are:
Each of the examples A and B of the cable according to the present invention has the same diameter of 100 mm, and “A” has 24 dimples 3 each having a diameter of 10 mm and a depth of 1 mm equally divided around the circumference, "B" is one in which 24 dents 3 having a diameter of 10 mm and a depth of 3 mm are equally divided around the circumference and arranged. On the other hand, the conventional cable C is a cable having a diameter of 100 mm and a circular cross section with a smooth surface.

The following graphs showing the results of static tests on the aerodynamic characteristics of bridge cables include the relationship between drag coefficient (CD, vertical axis) and the number of Reynolds nozzles (Re, horizontal axis) corresponding to wind speed, rain vibration. The relationship between (2A / D, vertical axis) and wind speed (V / fD, horizontal axis) and the relationship between aerodynamic damping (δ _a , vertical axis) and wind speed (V / fD, horizontal axis) are shown. . Incidentally, Re number, CD number and formula for the aerodynamic damping [delta] _a is below the "number 1", "Number 2"
And “Equation 3”. In this case, the aerodynamic damping is an index that can confirm that the cable is aerodynamically unstable by reducing this value as the wind speed increases even if no vibration occurs in the cable.

[0014]

[Table 1]

[0015]

Rey nozzle number (Re); Re = V × h (θ) / μ where V: wind speed (m / s) h (θ): height of projected figure viewed from wind direction for each wind direction angle ( m) μ: Kinematic viscosity coefficient (= 1.46 × 10 ^-5 m / s)

[0016]

[Number 2] ● drag coefficient (CD); CD = PD ( θ) / {1/2 × ρ × V 2 × A (θ)} However, PD (θ): drag of each wind direction angle (kg) ρ: Air density (= 0.125kg · s / m ⁴ ) V: Wind speed (m / s) A (θ): Projected area viewed from the wind direction at each wind direction angle

[0017]

[Equation 3] aerodynamic damping δ _a ; δ _a = δ _total -δ _s where δ _total : logarithmic decay rate when the test sample is forcibly shaken under the set wind speed δ _s : logarithmic decay rate in no wind

For each of these examples, first, the drag coefficient (C
D) was measured. In each of Examples A and B of the present invention, the relationship between the drag coefficient (CD) and the number of Reynolds nozzles (Re) is shown in FIG. 5 and FIG. So that
When the Re number is in the range of 10 ⁴ to 10 ⁵ , it shows a remarkably low drag coefficient value. Also, as is apparent from FIGS. 5 and 6 (b) in which measured values of the drag coefficient when the wind is applied while changing the angle in the circumferential direction (angle of attack, horizontal axis) are shown,
The drag coefficient value hardly changes even when the wind is applied by changing the angle of attack. Therefore, each of the examples A and B of the present invention has a very aerodynamically stable shape despite the provision of the depression 3. I can say.

In contrast to Examples A and B of the present invention, Conventional Example C always shows a high drag coefficient when the Re number is in the range of 10 ⁴ to 10 ⁵ , as is clear from FIG. You can see that.

On the other hand, FIG. 12 shows a horizontal deflection angle (α) of 48 ° and a rising angle (β) of 2 which are one of the wind direction conditions in which rain vibration is most likely to occur in the case of a cable-stayed bridge cable.
The result of the vibration characteristic experiment by the influence of wind and rain on the cable in the conventional example C at 7 ° is shown. In this figure, the vertical axis represents vibration: 2A / D, and the horizontal axis represents wind speed: V / fD (where D is diameter, A is amplitude of vibration, V is wind speed), and (a) is rainfall: 0 liter / min, (b) rainfall:
1.6 liter / min, (c) rainfall: 3 liter / min,
(D) is the case of rainfall: 6, liter / min. In addition,
The horizontal deflection angle (α) and the rising angle (β) are as shown in the cable model posture (normal posture) diagram of FIG.
As shown in FIG. 12, the rainfall in the circular section cable is:
Except for the case of 6, liter / min, it can be seen that rain vibration occurs under most wind speed conditions.

7 and 8 show the results of experiments under the same conditions as those of the comparative example shown in FIG. 12 for the two examples A and B in each example of the present invention, in contrast to the conventional example C described above. 7 and 8
As is clear from the above, it is proved that the cable according to the present invention does not vibrate at all under any conditions of wind and rain, and that a very excellent rain vibration suppressing effect is exhibited.

9 and 10 show the relationship between the wind speed: V / fD (horizontal axis) and the aerodynamic damping: δ _a (vertical axis) for two examples A and B in the respective examples of the present invention. The graph is shown with rainfall as a parameter.As is clear from both figures, under all rainfall conditions, aerodynamic damping tends to increase with increasing wind speed, so it can be confirmed that the aerodynamics are very stable. .

[0023]

As described above, according to the present invention, the outer surface of the plastic jacket in the bridge cable is provided with a predetermined surface.
Diameter dimension, circumferentially and small shallow recess having a depth
By adopting a configuration in which a large number of uneven surfaces dispersed in the axial direction are formed, the drag coefficient is reduced, that is, the wind load can be significantly reduced as compared with the conventional circular cable having the same diameter, It is very effective especially for the economic design of the cable stayed bridge tower. In addition to this, the present invention can suppress the occurrence of cable vibration (rain vibration) due to the interaction between wind and rain, and since aerodynamic damping increases with an increase in wind speed, it is very aerodynamic. A special effect of stabilization is achieved. In the present invention, furthermore, by forming the small shallow depression into a cylindrical or polygonal column shape having an edge shape rather than a smooth edge, a further effect is exhibited for reduction of the drag coefficient and suppression of rain vibration. Things.

[Brief description of the drawings]

FIG. 1 is a partially omitted external view of a bridge cable according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along line AA of FIG.

FIG. 3 is an enlarged view of FIG. 2;

FIG. 4 is an enlarged view showing a part of FIG. 3;

FIG. 5 is a graph showing a measurement result of a drag coefficient in the first embodiment A of the present invention.

FIG. 6 is a graph showing measurement results of a drag coefficient according to a second embodiment B of the present invention.

FIG. 7 is a graph showing rain vibration in the first embodiment A of the present invention.

FIG. 8 is a graph showing rain vibration in a second embodiment B of the present invention.

FIG. 9 is a graph showing aerodynamic damping in the first embodiment A of the present invention.

FIG. 10 is a graph showing aerodynamic damping in a second embodiment B of the present invention.

FIG. 11 is a graph showing a drag coefficient of Conventional Example C which is a comparative example.

FIG. 12 is a graph showing a rain vibration of Conventional Example C which is a comparative example.

FIG. 13 is a model posture (normal posture) of the cable stayed bridge cable.

[Explanation of symbols]

 1 ... cable, 2 ... plastic jacket, 3 ... hollow,

Claims (2)

(57) [Claims] 1. A steel wire bundles and plastic enclosure color formation Ru bridges cable covering the steel wire bundles, the positive <br/> tick jacket of the outer surface has numerous distributed depressions shallow small It is formed on an uneven surface, and the depression is approximately
Cylindrical or polygonal pillar with 10% diameter and 1-3mm depth
The shape and the dividing angle with respect to the center of the cable body
Are arranged in the circumferential direction at intervals of 15 °, and
Arranged in the axial direction at the same pitch as the spacing
Low drag coefficient and bridges cable having a damping function, characterized in that Rukoto. 2. Small and shallow depressions are arranged in a regular lattice pattern, staggered.
The bridge cable having a low drag coefficient and a vibration damping function according to claim 1, which is provided in a lattice arrangement or a random arrangement .