JPH07279122A - Cable for bridge - Google Patents

Abstract

PURPOSE:To reduce a wind load and to enhance a damping function by covering the surface of a cable used for a cable stayed bridge etc., with plastics formed by dispersing many columnar or polyprisrratic small and shallow indentations. CONSTITUTION:The surface of a cable 1 consisting of a steel wire bundle is covered with plastics 2 forming many columnar or polyprismatic small and shallow indentations 3 on its surface. The arrangement of the indentations 3 may be any of a lattice shape, a zigzag shape, or a random arrangement. Yet, the opened edges of the indentations 3 are not gentle but formed in an edge shape. No water channel is evolved on the upper surface side and the lower surface side of the cable 1 due to the interaction of wind and rain; drag coefficient is decreased; and the evolvement of rain vibration is depressed. Thus a wind load is reduced, and the design of a tower is economically done.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventional cables for cable-stayed bridges are typified by those in which a plastic jacket is used as a jacket for covering a steel wire bundle, and the cross-sectional shape is circular and the surface is finished smooth. Has been. Such a conventional cable is
It has no mechanical and aerodynamic directionality in its cross section, and is aerodynamically stable compared to other cross-sectional shapes, and few attempts have been made to improve the drag coefficient from the aspect of shape. Is the actual situation.

However, if a circular cross section cable is used,
It has been confirmed in actual bridges that vibration (hereinafter referred to as rain vibration) is generated in the cable due to the interaction between wind and rain. Conventionally, as a vibration control measure, for example, a cable such as disclosed in Japanese Unexamined Patent Publication No. 6-66344 is installed to connect a cable to each other, or a cable such as a vibration damper is provided near the cable fixing portion. A method of installing an additional device, or a method of making the cable itself have an aerodynamic damper performance by changing the surface shape of the cable, for example, a parallel protrusion shape in which a convex row extending parallel to the axial direction of the cable surface is provided. (Japanese Patent Laid-Open No. 63-197703) and the like.

[0004]

In recent years, cable-stayed bridges have become longer as well as other bridges, and along with that, the cables have become longer and thicker. The wind load on the bridge increases in a proportional manner, 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.

Further, in the conventional measures against rain vibration, in the case where the function of an aerodynamic damper is added to the cable itself by making the cross section of the cable into the shape of parallel protrusion as described above, according to the experiment, the drag coefficient is a circle of the same area. It has been confirmed that it shows about 1.2 times that of a cable having a cross section, and it becomes necessary to further cover the upper layer of the outer cover with plastic in order to secure durability. As a result, the diameter of the cable is about 15% larger than usual, so that the pressure receiving area of the wind increases, which is further disadvantageous in terms of wind load.

On the other hand, the vibration damping cable has a problem that the structure is formed by connecting the cables to each other, which impairs the aesthetic appearance. Further, since the construction at a high place is additionally required, the economical disadvantage that the construction cost and the construction period increase is unavoidable. I don't get it. In addition, with the vibration damper, as the cable length of the cable-stayed bridge becomes longer, the effect cannot be obtained unless the mounting position is located far away from the girder, which is detrimental to aesthetics. The construction period is expected to increase.

The present invention has been made in order to solve such a problem, and an object of the present invention is to significantly reduce the drag coefficient with a cable diameter similar to that of the conventional one, and at the same time to improve the rain coefficient. The purpose of this is to provide a bridge cable that can effectively suppress the occurrence of vibrations with high economic efficiency due to construction at the factory side.

[0008]

The present invention has the following constitution in order to achieve the above object. That is, the present invention comprises a steel wire bundle and a plastic jacket for covering the steel wire bundle, wherein the outer surface of the plastic jacket is
A cable for a bridge having a low drag coefficient and a vibration damping function, which is formed on a surface having a large number of small shallow depressions dispersed therein. The present invention is also a bridge cable having a low drag coefficient and a damping function, characterized in that the small and shallow depression is formed in a cylindrical shape or a polygonal prism shape.

[0009]

According to the present invention, the outer surface of the cable for bridge is formed on the outer surface of the plastic jacket with a large number of small shallow recesses dispersed therein. Therefore, in the conventional cable having a smooth circular cross section, a water channel is easily formed on both the lower surface side and the upper surface side of the cable due to the interaction of wind and rain, whereas the cable according to the present invention has a water channel on the upper surface side. Is hardly generated, and a water channel is unlikely to occur on the lower surface side, which is considered to bring about an excellent effect on the drag coefficient and rain vibration. Thus, in the present invention, by forming the outer peripheral surface of the cable into a shape having a large number of depressions, it is possible to significantly reduce the drag coefficient and suppress the occurrence of rain vibration. Further, according to the present invention, by forming the small and shallow depressions in the shape of a cylinder or a polygonal prism, the drag coefficient can be reduced and the rain vibration can be suppressed.

[0010]

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

In the bridge cable of such an embodiment, the cross-section loss of the plastic casing 2 due to the processing of the recess 3 is very small, so that it is almost unnecessary to increase the diameter for compensating for this, and therefore the windage It can be considered that the pressure receiving area is almost the same as that of the conventional circular cross-section cable having the same diameter.

In order to clarify that the cable according to the present invention has a low drag coefficient and an excellent vibration damping function, the following Table 1 shows a contrasting relationship between cable design conditions and experimental results. As described above, various experiments were repeated for each of the cables A and B according to the present invention in comparison 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 recesses 3 having a diameter of 10 mm and a depth of 1 mm, which are equally divided into the circumference. "B" has 24 depressions 3 with a diameter of 10 mm and a depth of 3 mm, which are equally divided on the circumference. On the other hand, the conventional cable C is a circular cross section cable having the same diameter of 100 mm and a smooth surface.

The following graphs showing the static test results concerning the aerodynamic characteristics of the cable for bridge show the relationship between the drag coefficient (CD, vertical axis) and the Reynolds number corresponding to the wind speed (Re, horizontal axis), and the rain vibration. The relationship between (2 A / 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. . The formulas for obtaining the Re number, the CD number, and the aerodynamic damping δ _a are shown in the following "Equation 1" and "Equation 2".
And as shown in “Equation 3”. In this case, aerodynamic damping is an index that can confirm that the cable is aerodynamically unstable because its value decreases as the wind speed increases, even if vibration does not occur.

[0014]

[Table 1]

[0015]

[Equation 1] Rey Nozzle number (Re); Re = V × h (θ) / μ where V: wind speed (m / s) h (θ): height of the projected figure from the wind direction for each wind direction angle ( m) μ: Dynamic 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 for each wind direction angle

[0017]

[Equation 3] ● Aerodynamic damping δ _a ; δ _a = δ _total − δ _s where δ _{total is} the logarithmic decay rate when the sample is forcibly shaken under the set wind speed δ _s : The logarithmic decay rate when there is no wind

For each of these examples, first the drag coefficient (C
D) was measured, but in each of the examples A and B of the present invention, it corresponds to each of (a) in FIG. 5 and FIG. 6, which is a relational diagram between the drag coefficient (CD) and the Reynolds number (Re). So that
The Re coefficient shows a remarkably low drag coefficient value in the range of 10 ⁴ to 10 ⁵ . Further, as is clear from each (b) of FIG. 5 and FIG. 6, in which the 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,
Even if the angle of attack is changed and wind is applied, the drag coefficient value hardly changes. Therefore, each of the examples A and B of the present invention has a very aerodynamically stable shape despite having the depression 3. Can say

In contrast to the examples A and B of the present invention as described above, as is apparent from FIG. 11, the conventional example C always exhibits a high drag coefficient value in the Re number range of 10 ⁴ to 10 ⁵ . I understand.

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 a cable-stayed bridge cable.
The result of the vibration characteristic experiment under the influence of wind and rain of the cable in Conventional Example C at 7 ° is shown. In this figure, the vertical axis represents vibration: 2 A / D, and the horizontal axis represents wind speed: V / fD (where D is diameter, A is vibration amplitude, V is wind speed), and (a) is rainfall: 0 liters / min, (b) is the rainfall:
1.6 l / min, (c) Rainfall: 3 l / min,
(D) is the case of rainfall: 6, l / min. In addition,
The horizontal declination (α) and the rising angle (β) are as shown in the cable model posture (normal posture) diagram of FIG. 13.
As shown in FIG. 12, the amount of rainfall in the circular cross section cable:
It can be seen that rain vibration occurs under most wind speed conditions except at 6 liters / min.

In contrast to the above-mentioned conventional example C, FIGS. 7 and 8 show the experimental results under the same conditions as the comparative example shown in FIG. 12 for two examples A and B in each example of the present invention. Figures 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 a very excellent effect of suppressing rain vibration is exerted.

Further, FIG. 9 and FIG. 10 show the relationship between the wind speed: V / fD (horizontal axis) and the aerodynamic damping: δ _a (vertical axis) for the two examples A and B of the present invention. The rainfall is shown as a parameter in the graph, but as is clear from these figures, it can be confirmed that the aerodynamic damping is tending to increase with increasing wind speed under any rainfall condition, so it is very stable aerodynamically. .

[0023]

As described above, according to the present invention, since the outer surface of the plastic jacket of the cable for a bridge is formed as a surface having a large number of small shallow depressions dispersed therein, the drag force is reduced. The reduction of the coefficient, that is, the wind load can be significantly reduced as compared with the conventional circular cross-section cable with the same diameter, and it is very effective especially for the economical design of the tower of the cable-stayed bridge. In addition to this, the present invention can suppress the generation of cable vibration (rain vibration) due to the interaction between wind and rain, and since the aerodynamic damping increases as the wind speed increases, it is extremely aerodynamic. The special effect of being stable is exhibited. The present invention further comprises a small shallow depression,
By forming it in the shape of a cylinder or a polygonal prism, the effect of reducing the drag coefficient and suppressing the rain vibration is further enhanced.

[Brief description of 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 the line AA of FIG.

FIG. 3 is an enlarged view of FIG.

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

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 drag coefficient in the 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 the 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 the second embodiment B of the present invention.

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

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

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

[Explanation of symbols]

 1 ... Cable, 2 ... Plastic jacket, 3 ... Dimple,

Claims (2)

[Claims] 1. A low characterized in that it comprises a steel wire bundle and a plastic jacket for covering the steel wire bundle, and the outer surface of the plastic jacket is formed on a surface having a large number of small shallow recesses dispersed therein. Bridge cable with drag coefficient and damping function. 2. The cable having a low drag coefficient and a vibration damping function according to claim 1, wherein the small shallow depression is formed in a cylindrical shape or a polygonal prism shape.