JP2001081719A - Cross cable system of suspension bridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more effectively suppress generation of a flutter and increase the wind velocity generating a flutter. SOLUTION: Two main cables 1, 2 hanging a bridge dirder 4 suspended between basal chief towers cross each other at the middle position in the axial direction of a bridge. Hanger ropes 5, 6 to hang down the bridge girder 4 from the main cables 1, 2 are obliquely inclined halfway. The main cables 1, 2 are positioned on two perpendicular faces crossing each other. A position in the bridge-axial direction where two main cables cross each other is the geometrical mid-point (middle point) between the chief towers. The rigidity of the two main cables themselveas crossing each other is improved with respect to torsion on installing them and the tortional frequency is increased. Hence, a wind velocity generating a flutter is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable system for a suspension bridge, and more particularly to a cable system for a suspension bridge designed to increase the frequency of torsion and suppress the occurrence of flutter.

[0002]

2. Description of the Related Art Under conditions where the distance between main towers must be long, bridges are designed as suspension bridges. Flexible suspension bridges include rolling and pitching, as well as rotation around the bridge axis,
Twist occurs. There is a demand for a divergent vibration in which the amplitude of torsion increases as the wind speed increases, that is, suppression of flutter, which is a typical unstable vibration in aerodynamics. It is known that the occurrence of such flutter can be suppressed by increasing the torsional frequency. A system for such suppression is known from JP-A-8-49215. This known system increases the torsional frequency and improves wind resistance by connecting two main cables with a stay that faces in the horizontal direction.Furthermore, the flutter occurrence is increased by increasing the flutter speed. It is a cable system of a suspension bridge to suppress.

[0003] As shown in Fig. 4, a cross stay structure for suppressing the swing due to the torsional vibration during the installation of a steel reinforcing girder is known. This cross stay structure connects one main cable and the edge of the bridge girder on the opposite side of the cable with a supplementary cable, and is formed only when the bridge girder is erected.

[0004] Such known systems can be problematic in terms of stay reliability during storms. There is a demand for further improving the reliability of a cable system that suppresses the occurrence of flutter by increasing the wind speed at which flutter occurs. Further, it is more preferable that the torsional rigidity is already increased when only the main cable is erected, and that flutter-resistant measures are taken even when the stiffening girder is suspended directly below.

[0005]

The present invention has the technical background of suppressing the occurrence of flutter as described above, and can achieve the following objects. An object of the present invention is to provide a cross cable system for a suspension bridge that can more effectively suppress the occurrence of flutter. Another object of the present invention is to provide a cross cable system for a suspension bridge capable of effectively increasing the torsional frequency. Still another object of the present invention is to provide a cross cable system for a suspension bridge that can further improve the fluttering wind speed. Still another object of the present invention is to provide a cross cable system for a suspension bridge having a high torsional rigidity when the main cable is erected. Still another object of the present invention is to provide a cross cable system of a suspension bridge capable of increasing the fluttering wind speed from 60 m / s to 70 m / s as compared with a conventional system.

[0006]

SUMMARY OF THE INVENTION A crossover cable system for a suspension bridge according to the present invention comprises two main towers, two cables respectively bridged between the two main towers, and the two cables. In a cable system for a suspension bridge composed of a suspended bridge girder, the two cables cross each other at a midpoint in the bridge axis direction between the main towers. The hanger rope for suspending the bridge girder by the main cable is advantageously inclined at an intermediate position.

Usually, the two main cables are located on two vertical planes parallel to each other, and the height position of the support point where each one main cable is supported by the two towers is the same. is there. In such a normal case, the position in the bridge axis direction where the two main cables intersect (or intersect) is geometrically the midpoint (center point) between the main towers. If the heights of the main towers are different, or if the two main cables are not in two parallel vertical planes, the crossover position is not necessarily at the midpoint but at the midpoint.

The two main cables crossing at the center point themselves have increased rigidity with respect to torsion when only the main cable is erected, and the torsion frequency is increased. The two cross main cables (cross main cables) that form the main structural member together with the bridge girder have improved torsional rigidity as a whole bridge. In comparison with the conventional method, the flutter onset wind speed was 60 m per second in the past, but in the present invention, it was improved by about 20% compared to the conventional one, and
0 m or more. The two bodies or the two main cables are, of course, generally continuous linear bodies each having one tension between the main towers. As long as this condition is satisfied, the two main cables can be tied together by an annular fastener or the like in the intersection center point region. In addition, "two pieces" and "two pieces" represent "at least two pieces" and "at least two pieces".

[0009]

FIG. 1 is a perspective view showing an embodiment of a cross cable system for a suspension bridge according to the present invention. The suspension cross cable system includes two main towers, not shown in FIG. 1, namely, a front main tower F and a rear main tower R. Here, the front and the rear are defined with respect to the bridge axis direction. One direction of a line connecting the two main towers is referred to as a bridge axis direction D (see FIG. 2).

As shown in FIG. 1, the crossover cable system of the suspension bridge further includes two main cables, one main cable 1 and the other main cable 2, which respectively form catenary lines. Height of the front main tower F and the rear main tower R (the height of the support point that supports the main cable)
Are assumed to be equal. As shown in FIG. 2, a support point between the rear main tower R and the other main cable 2 is indicated by a point X, and a support point between the rear main tower R and the one main cable 1 is indicated by a point. The support point between the front main tower F and the one-side main cable 1 is indicated by a point Z, and the support point between the front main tower F and the other-side main cable 2 is indicated by a point W. Is shown. Although the shape of the two main cables is a catenary, those lines projected and drawn on the plan view of FIG. 2 are hereinafter referred to as straight lines or line segments as straight line parts with respect to FIG.

In FIG. 2, one side main cable 1 has a line segment Y
Z, and the other main cable 2 matches the line segment XW. It is assumed that the quadrilateral XYWZ is a rectangle. One vertical plane including the line segment XW and one vertical plane including the line segment YZ intersect. Therefore, the line segment XW and the line segment YZ intersect at the midpoint P of the center line in the longitudinal direction.

However, the one-side main cable 1 and the other-side main cable 2 do not actually intersect at one point, but as shown in FIG. If the distance between the main towers is sufficiently long and the width between the two support points on the same main tower is sufficiently narrow, the two main cables substantially intersect at one point. In this specification, including the claims, "intersection" and "crossover" are used interchangeably.

Both ends Y and Z of the one-side main cable 1 are supported by a rear main tower R and a front main tower F, respectively, and both ends X and W of the other main cable 2 are respectively supported by a rear main tower. R, supported by the front main tower F, and both main towers R,
The structure composed of F and the two main cables 1 and 2 has a structure in which four apex members are connected by diagonal beams, and only this structure has improved torsional rigidity as compared with a conventional suspension bridge.

The main cable 1 on the one side and the main cable 2 on the other side have their respective end points Y, Z, X, W extended to the connection point of the earth-side fixed structure, as in the prior art. It is. One side main cable 1,
The other main cable 2 is a continuous linear body such as a monofilament having one tension each. This means that one main cable 1 and the other main cable 2
Means that they are substantially independent, in other words,
It means that it crosses three-dimensionally. However, this does not mean that the one-side main cable 1 and the other-side main cable 2 are tied together by a ring-shaped fastener in the vicinity of the middle point P, that is, at the intersection area.

FIG. 1 shows a hanger cable and a bridge girder 4 in the midpoint region among a large number of hanger cables. The hanger cable includes a first hanger cable 5 and a second hanger cable 6. The bridge girder 4 is suspended from one main cable 1 and the other main cable 2 by a first hanger cable 5 and a second hanger cable 6. The upper end of each first hanger cable 5 is connected to the other main cable 2, and the upper end of each second hanger cable 6 is connected to the one main cable 1.

The first hanger cable 5 is divided into a group of front first hanger cables 5 and a group of rear first hanger cables 5 at the middle point. The second hanger cable 6 is divided into a group of the front second hanger cable 6 and a group of the rear second hanger cable 6 with the middle point as a boundary. All hanger cables 5, 6 are on respective vertical planes orthogonal to the bridge axis. The lower end points of all the hanger cables 5, 6 are connected to both side edges of the bridge girder 4. All hanger cables 5, 6 are joined to the edge on the side where their length is minimized.

In the first hanger cable 5 whose upper end point is connected to the other main cable 2, the edge of the bridge girder 4 to which the lower end points are connected is switched on the left and right sides with the middle point as a boundary. The second end where the upper end point is connected to the one-side main cable 1
In the hanger cable 6, the edge of the bridge girder 4 to which the lower end points are connected is switched on the left and right sides with the middle point as a boundary.

The first hanger cable 5 and the second hanger cable 6 are almost vertical in a region near the main tower, and the inclination angle (angle with respect to the vertical line) becomes maximum near the midpoint. The maximum inclination angle is designed to be small enough not to impede traffic on the bridge girder 4.

The cross cable system of a suspension bridge in which a bridge girder is suspended on a cross cable structure having an increased torsional rigidity can increase the torsional rigidity of the suspension bridge itself.
The increased torsional stiffness increases the torsional frequency of the suspension bridge. It is actually confirmed by a known theory that the improvement of the torsional frequency increases the wind speed at which flutter occurs. FIG. 3 shows the result of the three-dimensional flutter analysis of the present invention in comparison with the conventional art. It is an analysis result when it is assumed that a bridge girder is a flat plate and its cross-sectional shape is rectangular.

The left column shows a conventional cable system, which is a conventional cable system, and a cross cable system according to the present invention. The right column shows the flutter onset wind speed. The fluttering wind speed of the conventional system is 60.8m
/ S, the fluttering wind speed of the system of the present invention is 74.1 m / s, indicating an improvement of 20% or more.

[0021]

The cross cable system for a suspension bridge according to the present invention can more effectively improve the wind speed at which flutter occurs, and can ensure high reliability especially in the event of a storm. Furthermore, there is an effective anti-flutter effect even when the stiffening girder is suspended directly below.

[Brief description of the drawings]

FIG. 1 is an oblique projection view showing an embodiment of a cross cable system for a suspension bridge according to the present invention.

FIG. 2 is a plan view showing a geometrical positional relationship between a cross-main cable and both main towers.

FIG. 3 is a table showing a result of a three-dimensional flutter analysis.

FIG. 4 is an oblique projection view showing a main cable system of a known suspension bridge.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... One side main cable 2 ... The other side main cable 4 ... Bridge girder 5 ... 1st hanger cable 6 ... 2nd hanger cable P ... Middle point F ... Front main tower R ... Rear main tower X, Y, Z, W … Support point

 ──────────────────────────────────────────────────続 き Continued on the front page (71) Applicant 000000099 Ishikawajima-Harima Heavy Industries, Ltd. 2-2-1 Otemachi, Chiyoda-ku, Tokyo (71) Applicant 000000974 Kawasaki Heavy Industries, Ltd. 3-chome, Higashikawasaki-cho, Chuo-ku, Kobe-shi, Hyogo 1-1-1 (71) Applicant 000200367 Kawada Industries Co., Ltd. 1-3-11 Takinogawa, Kita-ku, Tokyo (71) Applicant 000002107 Sumitomo Heavy Industries, Ltd. 5-9-1-11 Kita-Shinagawa, Shinagawa-ku, Tokyo ( 71) Applicant 000004123 Nippon Kokan Co., Ltd. 1-2-1, Marunouchi, Chiyoda-ku, Tokyo (71) Applicant 000005119 Hitachi Zosen Corporation 1-89, Minami Kohoku, Suminoe-ku, Osaka-shi, Osaka (71) Applicant 000005902 Mitsui Engineering & Shipbuilding Co., Ltd. 5-6-1, Tsukiji, Chuo-ku, Tokyo (71) Applicant 000006208 Mitsubishi Heavy Industries, Ltd. Chiyoda-ku, Tokyo 2-5-1, Nouchi (72) Inventor Hirofumi Sato, Asahi Ichibanchi, Tsukuba, Ibaraki Pref., Japan Civil Engineering Research Institute (72) Inventor Shinsuke 5-717-1, Fukahori-cho, Nagasaki, Nagasaki Pref. Heavy Industry Co., Ltd., Nagasaki Research Institute (72) Inventor Akihiro Honda 5-717-1, Fukabori-cho, Nagasaki City, Nagasaki Prefecture Sanishi Heavy Industries Co., Ltd.Nagasaki Research Center (72) Inventor Ichiro Masuda 4--6 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture No.22 Mitsubishi Heavy Industries, Ltd. Hiroshima Works F-term (reference) 2D059 AA05 AA41 AA47 BB06 GG06

Claims (2)

[Claims] 1. A suspension bridge cable system comprising: two main towers; two main cables respectively bridged between the two main towers; and a bridge girder suspended by the two main cables. A cross cable system for a suspension bridge, wherein the two main cables cross each other at an intermediate position in a bridge axis direction between the main towers. 2. The cross of a suspension bridge according to claim 1, further comprising a hanger rope for suspending the bridge girder by the main cable, wherein the hanger rope is obliquely oriented at the halfway position. Cable system.