JPH05248122A - Reduction of wind pressure against aerial line support structure - Google Patents

Abstract

PURPOSE:To reduce the load of wind pressure, by providing a cover in which a number of smooth peaks and troughs are formed in the longitudinal direction of the outer periphery or a steamline-shaped cover and attaching them at the outer periphery of the constituting members of a steel tower. CONSTITUTION:A number of longitudinal lines having round peaks and troughs are formed on the outer periphery of a cylindrical cover 15 made of plastics or metal like aluminum. Next, the outer face of angle-shaped steel members of a steel tower is coated with the covers 15 which are fixed by fasteners 23 like bands. The peeling off point of an air stream is forced to stick again and shift backward by means of the faces of peaks and troughs against a strong wind and constrict the vortex area at the back stream side to lessen the drag coefficient. Moreover, the cover is formed to have a streamline-shaped secsion or peak and trough lines on the surface thereof with an elliptic secsion. And these may be attached on the steel pipes of the tower to be freely rotatable to reduce the drag coefficient by making parallel with wind direction. In this way, the load of wind pressure can be reduced and collapsing accidents can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing the wind pressure of structures such as steel towers and steel structures that support overhead transmission and distribution lines.

[0002]

2. Description of the Related Art Steel towers or steel structures for supporting or suspending overhead transmission lines are designed to withstand wind pressure loads such as typhoons, but in rare cases collapse due to wind pressure. May occur. Recently, in September 1991, Typhoon No. 19, which crossed the Kyushu and Shikoku regions, caused a continuous collapse of more than 10 towers of 500,000 volt overhead transmission lines.

In order to prevent such a collapse accident due to the wind pressure of the overhead line supporting structure, it is conceivable to increase the strength of the structure itself in the case of a new construction, but for that purpose, a significant cost increase is achieved. It is inevitable. In addition, it is extremely difficult as a practical matter to increase the strength of existing steel towers and steel structures.

[0004]

In view of the above problems, the present invention has a limit in the approach from the viewpoint of improving the strength of the structure, and therefore reduces the wind pressure load of the structure. It was made from a point of view.

Angle members (shaped steel) and steel pipes are generally used as constituent members of the overhead wire support structure. It is well known that the drag coefficient C _D when the angle member is placed at right angles to the wind flow is 1.45 to 1.9 regardless of the Reynolds number Re.

On the other hand, when the steel pipe (cylindrical) is placed at right angles to the flow of wind, the drag coefficient C _D increases with Re when the Reynolds number Re exceeds 2 × 10 ^5, as shown in FIG. 6a. It rapidly decreases, and Re becomes an extremely small value of about 0.3 to 0.4 in the range of 4 × 10 ⁵ to 10 × 10 ⁵ . However, at a wind speed of 42 m / sec, which is considered as the maximum wind speed when designing a tower or steel structure for overhead lines, the drag coefficient decreases as described above, and the diameter of the cylinder that can be assumed to have a low wind pressure is about 1
A cylinder with a diameter of 40 to 150 mm or more and a diameter of less than 40 mm has a drag coefficient of around 1.0.

Therefore, the present invention intends to reduce the drag coefficient of the constituent members and the wind pressure load by covering the outer periphery of the angle member and the steel pipe which are the constituent members of the overhead wire support structure with a suitable cover. is there.

That is, the first solution according to the present invention is
On the outer periphery of the member constituting the overhead wire support structure such as a steel tower or steel structure, having a large number of peaks extending in the longitudinal direction on the outer peripheral surface, and a valley sandwiched between those peaks, It is characterized in that a cylindrical cover in which each crest is a rounded outer convex curved surface and each valley is a rounded outer concave curved surface is attached. It is desirable that the crests on the outer peripheral surface of the cylindrical cover be formed at equal intervals in the circumferential direction, but there is no problem even if the intervals of the crests are somewhat uneven.

The drag coefficient C _D when the cylindrical cover as described above is placed at right angles to the wind flow is as shown in FIG. 7B (when the number of peaks is N = 12) and c (when N = 16). Case), d (N =
24) and e (in the case of N = 30), the drag coefficient is significantly smaller than that of the cylinder a having a smooth surface. This has been confirmed experimentally, but the phenomenon can be explained as follows.

That is, in the case of a cylinder with a smooth surface, Re
In the region of <1 × 10 ⁵ , the drag coefficient C _D becomes large because the separation point P of the wind flow occurs on the windward side of the cylinder 1 and the large wake region on the leeward side of the cylinder 1 as shown in FIG. However, in the case of a cylinder having smooth ridges and valleys on the surface like the above-mentioned cylindrical cover, the flow separated at point P due to the presence of unevenness on the surface as shown in FIG. It is considered that a phenomenon such as redeposition occurs at point Q, the wake region becomes smaller, and the drag coefficient becomes smaller.

When the cylindrical cover as described above is attached to the outer periphery of the constituent member of the overhead wire supporting structure, the diameter of the wind receiving surface increases, but the Reynolds number is the same as the diameter of the air receiving surface under the same wind speed. Increase in proportion. Therefore, it is possible to reduce the wind pressure of the overhead wire support structure by attaching a cylindrical cover whose drag coefficient becomes small at the maximum wind speed that should be considered in design.

A second means for solving the problems according to the present invention is to provide an outer periphery of a member constituting an overhead wire supporting structure such as a steel tower or a steel structure,
It is characterized in that a tubular cover having a streamlined or elliptical cross section is rotatably attached such that its long axis direction becomes parallel to the wind direction when the wind blows.

When a tubular cover having a streamline or elliptical cross section is placed at right angles to the wind flow, the drag coefficient C _D is much smaller than that of the cylinder a, as shown by m and n in FIG. .. This is because the separation point of the wind flow moves rearward compared to the case of the cylinder, and the wake region becomes smaller. Therefore, it is possible to reduce the wind pressure of the overhead wire support structure by rotatably attaching the cylindrical cover as described above to the outer periphery of the constituent member of the overhead wire support structure according to the wind direction.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 and 2 show an embodiment of the present invention. In this example, the angle member that is a constituent member of the steel tower 11 is used.
A cylindrical cover 15 is attached to the outer circumference of 13.
The cylindrical cover 15 is made of plastic or aluminum, and on its outer peripheral surface, a large number of crests 17 extending in the longitudinal direction at equal intervals in the circumferential direction and valleys sandwiched between the crests 17. And a part 19 are formed. Each crest 17 has a rounded outer convex curved surface, and each valley 19 has a rounded outer concave curved surface.

A vertical slit 21 is formed at one location in the circumferential direction of the cylindrical cover 15, and the cylindrical cover 15 is covered with the angle member 13 by opening the vertical split 21 and tightening a band or the like. It is fixed to the angle member 13 by the member 23. It is desirable that the vertical dividing portion 21 be located inside the steel tower 11. When such a cylindrical cover 15 is attached, the drag coefficient is lowered and the wind pressure can be reduced as shown in FIGS.

In the above-described embodiment, the cylindrical cover having a large number of peaks and valleys extending in the longitudinal direction is used as the cylindrical cover, but the cylindrical cover has a large number of irregularities formed on the surface. It is also conceivable to use a thing or one whose surface is roughened.

3 and 4 show another embodiment of the present invention. In this embodiment, a tubular cover 27 having a streamline cross section is rotatably attached to the outer circumference of a steel pipe 25 which is a component of the steel tower 11. The tubular cover 27 has a vertical split portion 21 formed in a portion corresponding to the rear fin, and by opening this portion and covering the steel pipe 25 and tightening the screw 29, the steel pipe
Attached to 25. Further, stoppers 31 that prevent the tubular cover 25 from moving in the longitudinal direction are fixed to portions of the steel pipe 25 located at both ends of the tubular cover 25.

Since the cylindrical cover 27 is attached so as to be rotatable around the steel pipe 25, when the wind blows, the long axis direction becomes parallel to the wind direction, and the wind pressure is always the smallest. Such a streamlined tubular cover 27
When attached, the drag coefficient is lowered as shown by m in FIG. 6, and the wind pressure can be reduced.

FIG. 5 shows still another embodiment of the present invention.
In this embodiment, a tubular cover 33 having an elliptical cross section is rotatably attached to the outer circumference of a steel pipe 25 which is an individual component of a steel tower. The elliptical cylindrical cover 33 may have a smooth surface without irregularities, but the elliptical cylindrical cover 33 has the same ridges 17 and valleys 19 as the cylindrical cover of FIG. , The wind pressure is lower. Other configurations are the same as those of the embodiment shown in FIGS. 3 and 4.

The cylindrical cover 15 and the streamline cylindrical cover
27 or the elliptic cylindrical cover 33 does not necessarily have to be attached to all parts of the steel tower, and it is particularly effective to attach it to a member constituting the upper part of the steel tower, arm, or the like that is greatly affected by wind pressure. In addition, the cylindrical cover 15 and the streamline cylindrical cover 27
Alternatively, if a water-repellent resin coating, for example, a fluororesin coating such as a tetrafluoroethylene resin is provided on the surface of the elliptical cylindrical cover 33, the drag coefficient is further reduced and the wind pressure load can be reduced.

[0021]

As described above, according to the present invention, a cylindrical cover having smooth peaks and troughs on the surface is attached to the outer periphery of the constituent members of the overhead wire supporting structure, or the streamline shape is provided. Alternatively, by rotatably attaching the elliptical cylindrical cover, it is possible to reduce the wind pressure load on the overhead wire support structure, which is effective in preventing a collapse accident due to the wind pressure on the overhead wire support structure.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a wind pressure reducing method for a steel tower according to the present invention.

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

FIG. 3 is a front view showing another embodiment of the present invention.

FIG. 4 is a sectional view taken along line BB of FIG.

FIG. 5 is a sectional view showing still another embodiment of the present invention.

FIG. 6 is a graph showing the relationship between Reynolds number and drag coefficient.

FIG. 7 is a graph showing the relationship between the Reynolds number and the drag coefficient when a mountain portion and a valley portion are provided on the surface of a cylinder.

FIG. 8 is an explanatory view showing a state when wind is blown on the cylinder.

FIG. 9 is an explanatory diagram showing a state in which wind blows on a cylinder having peaks and valleys on the surface.

[Explanation of symbols]

11: Steel tower 13: Angle material 15: Cylindrical cover 17: Mountain part 19: Valley part 21: Vertically divided part 23: Tightening member 25: Steel pipe 27: Streamline cylindrical cover 31: Stopper 33: Elliptical cylindrical cover

Claims (4)

[Claims] 1. A plurality of crests extending in the longitudinal direction on the outer peripheral surface and a trough sandwiched between the crests are provided on the outer circumference of a member constituting an overhead line supporting structure such as a steel tower or a steel structure. The wind pressure of the overhead wire support structure, characterized in that each of the crests has a rounded outer convex curved surface, and a cylindrical cover in which each valley has a rounded outer concave curved surface is attached. Reduction method. 2. A cylindrical cover having a streamline or elliptical cross section is provided on the outer periphery of a member constituting an overhead line supporting structure such as a steel tower or a steel structure, and when the wind blows, the major axis direction is parallel to the wind direction. The method for reducing the wind pressure of an overhead wire support structure is characterized in that it is rotatably attached. 3. The wind pressure reducing method according to claim 2, wherein the tubular cover is sandwiched between a plurality of crests extending in the longitudinal direction on the outer circumferential surface at equal intervals in the circumferential direction and extending in the longitudinal direction. Characterized in that each crest has a rounded outer convex curved surface, and each trough has a rounded outer concave curved surface. 4. The wind pressure reducing method according to claim 1, wherein the cylindrical cover or the cylindrical cover comprises:
It is made of metal or plastic and has a water-repellent resin coating on its outer surface.