JP2651860B2 - Structure of bent part of PC cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a structure of a bent portion of a PC cable used for a cable-stayed bridge, a suspension bridge, and the like, and in particular, a PC cable capable of improving the fatigue strength of the bent portion. The structure of the bent portion of the above.

<Prior art> PC steel wire or PC steel stranded wire (hereinafter referred to as “PC cable”) functions effectively with respect to tensile force, but has weakness in bending.

Therefore, when it is necessary to bend the middle or the end of the PC cable into a gentle arc, a metal pipe that has been bent at a predetermined curvature is usually installed in advance at the expected bending position of the PC cable, A PC cable is inserted through the pipe.

The curvature of the PC cable is regulated by being guided by a metal tube.

<Problems to be Solved by the Present Invention> In many cases, a plurality of PC cables are collectively used, for example, a main cable of a cable-stayed bridge.

In addition, a secondary stress due to bending acts on the bent portions of the plurality of PC cable groups in addition to the primary stress as a pure tensile force.

These stresses act in a direction to strongly press the PC cable group against the inner wall of the metal tube.

For this reason, excessive frictional force is generated between the PC cable group and the hole wall of the curved tube and between the PC cables, and when each PC cable is repeatedly rubbed between these members, metal fatigue occurs, which is very dangerous.

Furthermore, due to factors such as lateral pressure acting on the PC cable group, the fatigue strength at the bent portion of the PC cable group becomes low.

<Object of the present invention> The present invention has been made in order to solve the above problems, and an object of the present invention is to connect a PC cable between PC cables and a PC cable at a bent portion of the PC cable. It is an object of the present invention to provide a structure of a bent portion of a PC cable that can prevent direct contact between the inner surface of a pipe to be guided and prevent a decrease in fatigue strength at the bent portion of the PC cable.

<Configuration of the Present Invention> Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

<B> Structure of the bent portion Fig. 1 shows a vertical section of the tower 1 of the cable-stayed bridge.

In this example, a description will be given of an example of a structure in which the PC cables 2 are arranged on the left and right sides of the tower 1 with continuity.

In the figure, reference numeral 3 denotes a bent guide tube buried in the tower 1 in advance.

The plurality of groups of PC cables 2 are guided by the bent guide tube 3 and bent in an arc shape.

 Hereinafter, each part will be described in detail.

<B> Bending guide tube The bending guide tube 3 is a curved part drawn with a locus of a constant radius r.
31 and a straight line part 32 continuing on both sides of the curved part 31.

The bent guide tube 3 is formed by bending a metal pipe as described above, for example, or its minimum bending radius r is determined in consideration of the required fatigue strength of the PC cable 2.

<C> PC cable The PC cable 2 is a PC steel stranded wire or the like, and a single cable or a plurality of cables are collectively used.

The PC cable 2 covers the mantle tube 4 at least over the range where it is finally bent, that is, the range of the curved portion 31 of the bent guide tube 3.

It is preferable that the mantle tube 4 is covered with a margin more than the range of the curved portion 31.

The mantle tube 4 is a member interposed between the PC cables 2 and between the PC cable 2 and the bent guide tube 3 for the purpose of preventing these members from directly contacting each other. It is preferably formed of a material, for example, a resin such as polyethylene, and has a thickness of about 1.0 to 1.2 mm.

As shown in FIG. 2, a viscous oil 5 for rust prevention is sealed in the mantle tube 4.

 In some cases, the filling of the viscous oil 5 may be omitted.

<D> Structural example 2 (Fig. 3) Fig. 3 shows a horizontal cross section of the tower 1.

In this example, a description will be given of a structural example in which a plurality of groups of PC cables 2 are fixed on the left and right sides of the tower 1 without intersecting.

In this example, the bent guide tube 3a having the curved portion 31 and the straight line portion 32 following the curved portion 31 is buried in the tower 1 alternately changing directions.

Therefore, in the case of this example, the mantle tube 4 may be covered over the range of the curved portion 31 of the bent guide tube 3a on the peripheral surface of the PC cable 2 to be fixed.

<E> Structure Example 3 (FIG. 4) FIG. 4 also shows a horizontal cross section of the tower 1.

This embodiment is an example of a fixing structure in a case where a PC cable 2 inserted from one of the right and left of the tower 1 is branched and fixed in the tower 2.

The bent guide tube 3b has two curved portions 3 at the end of the straight portion 32.
Branches to 1, 31.

Therefore, also in the case of the present example, the mantle tube 4 may be covered over the range of the curved portion 31 of the bent guide tube 3b on the peripheral surface of the PC cable 2 to be fixed.

<Operation> As described above, by covering the mantle tube 4 over the bending range of the PC cable 2, the PC cables 2 come into contact with each other with the mantle tube 4 interposed therebetween. An outer tube 4 is interposed between the bending guide tube 2 and the bent guide tube 3.

Therefore, even when stress acts on the bent portion of the PC cable 2 group, the metals do not come into contact with each other and rub against each other.

That is, the individual PC cables 2 do not directly contact each other, and the outer tubes 4 do contact each other.

The metal PC cables 2 do not directly contact the metal bent guide tubes 3, 3a, 3b, and the non-metal sheath tube 4 and the metal bent guide tubes 3, 3a, 3b are not. Will come in contact.

As a result, in the bent portion of the PC cable 2, metal fatigue due to frictional force and electrical causes due to contact of dissimilar metals hardly occurs.

<Effects of the present invention> As described above, the present invention covers the resin outer jacket over the expected bending range for each PC cable to be bent, so that the metallic PC cables directly contact each other. Or, each PC cable does not directly contact the bent guide tube made of metal.

As a result, the conventional metal fatigue does not occur at the bent portion of the PC cable, and a decrease in fatigue strength can be reliably prevented.

In addition, the bent portion of the PC cable can be made smaller than the conventional bent ratio, which is advantageous in design.

[Brief description of the drawings]

Fig. 1 is an explanatory view of one embodiment of the present invention and is a cross-sectional view of a tower of a cable-stayed bridge. Fig. 2 is a cross-sectional view taken along the line II-II in Fig. 1. Figs. Cross-sectional view of a tower in an explanatory view showing an example of the structure of

Claims (1)

(57) [Claims] In a bent portion of a PC cable using a bent guide tube having only a curved portion or a curved portion and a straight portion following the curved portion, an outer sheath tube different from the bent guide tube over a predetermined bending range of the PC cable. To eliminate the points where the metal members directly contact each other between the PC cables and between the PC cable and the bent guide tube. The structure of the bending part of the PC cable.