JPH02167906A - Structure of pc cable at crooked part - Google Patents

Abstract

PURPOSE:To prevent occurrence of metallic fatigue in PC cables at crooked parts and to check decrease of fatigue strength by covering each bundle of bending PC cables at a crooked part with mantle tubes made of resin that are applied over a range of the crooked part. CONSTITUTION:A crooked guide sleeve 3 is composed of a curved part 31, formed in a locus of a certain radius (r), and straight-lined parts 32 extending from the opposite ends of the curved part. PC cables 2 are covered with mantle tubes 4 that are stretching over the curved part 31 of the crooked guide sleeve 3. The mantle tubes 4 are interposed between the adjoining PC cables 2 as well as between the PC cables 2 and the interior face of the crooked guide sleeve 3 so that these members may not contact directly one another. Thereby decrease of fatigue strength at the crooked part can be prevented.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to the structure of the bent portion of a PC cable used in cable-stayed bridges, suspension bridges, etc., and more specifically to a PC cable that can improve the fatigue strength of the bent portion. <Conventional technology>PCm''a or PC steel stranded wire, etc. (hereinafter referred to as rPC cable)
Although it functions effectively against tensile force, it has the property of being weak against ribbing.

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

The PC cable is guided by the metal tube [11] "F-
is regulated.

<Problems to be Solved by the Present Invention> For example, a plurality of PC cables are often used together, such as the main cable of a cable-stayed bridge.

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

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

As a result, excessive frictional force is generated between the PC cable group and the hole wall of the curved pipe, and between the PC cables, and each PC
If the cable rubs repeatedly between these parts, it can cause metal fatigue, which is very dangerous.

Furthermore, with the addition of causes 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 its purpose is to reduce the distance between the PC cables and between the PC cables and the PC cable at the bending part of the PC cable.
An object of the present invention is to provide a structure for a bending part of a PC cable that can prevent a decrease in fatigue strength at the bending part of the PC cable by avoiding direct contact between the cable and the inner surface of a tube that guides the cable.

Configuration of the Present Invention> An embodiment of the present invention will be described below with reference to the drawings.

Structure of <A> bend 111] part Fig. 1 shows a longitudinal section of the tower 1 of the cable-stayed bridge.

In this example, a structural example in which the PC cable 2 is disposed continuously on the left and right sides of the tower 1 will be described.

Reference numeral 3 in the figure indicates a bent guide tube that has been buried in the tower 1 in advance.

The plurality of PC cables 2 are guided by the bending guide tube 3 and bent into an arc.

Each part will be explained in detail below.

1111 Guide tube bend The guide tube 3 is drawn with a locus of constant radius r. +To
It consists of a line part 31 and straight parts 32 continuing on both sides of the curved part 31.

The bent guide tube 3 is formed by, for example, bending a metal pipe as described above, and its minimum +11] bending radius r is determined in consideration of the required fatigue strength of the PC cable 2.

＼C) PC cable PC cape, JL 2 is a PC steel stranded wire, etc., and it is used in single or multiple bundles; strained and used once.

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

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

The jacket tube 4 connects the PC cables 2 to each other and connects the PC cables 2 to each other.
This is a member that is interposed between the bending guide tube 3 and the bending guide tube 3 to prevent these parts F from n1 contact.
It is made of a material different from that of the mountain guide tube 3, for example, a resin such as polyethylene, and its wall thickness is preferably about 1.0 to 2 mm.

Further, as shown in FIG. 2, viscous oil 5 for rust prevention is sealed inside the mantle tube 4.

Incidentally, the inclusion of the viscous oil 5 may be omitted in some cases.

<2> Structure example 2 (Figure 3) FIG. 3 shows a horizontal section of the tower 1.

In this example, a structural example will be described in which two groups of plural PC cables are fixed on the left and right sides of the tower 1 without crossing each other.

In this example, bent guide tubes 3a having curved portions 31 and straight portions 32 following the curved portions are buried in the tower I with alternate directions.

Therefore, in a case like this example, it is sufficient to cover the outer tube 4 over the range of the curved portion 31 of the bent guide tube 3a among the peripheral surface of the PC cable 2 to be fixed.

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

This example is an example of a fixing structure in which the PC cable 2 inserted from either the left or right side of the tower 1 is branched into two parts within the tower 2 and fixed.

The bent guide tube 3b branches into two curved sections 31 and 31 at the end of the M-line section 32.

Therefore, in the case of this example as well, it is sufficient to cover the jacket tube 4 over the range of the curved portion 31 where the bent guide tube 3b branches out of the peripheral surface of the PC cable 2 to be fixed.

<Function> As described above, by covering the bending range of the PC cable 2 with the jacket tube 4, the PC cables 2 come into contact with each other with the jacket tube 4 interposed between them, and each P
A mantle tube 4 is also interposed between the C cable 2 and the bending guide tube 3.

Therefore, even if stress is applied to the bent portions of the second group of PC cables, the metals will not come into contact with each other and rub against each other.

That is, the PC cables 2 do not come into direct contact with each other, but the mantle tubes 4 contact with each other.

Moreover, each metal PC cable 2 does not come into direct contact with the metal bending guide tubes 3.3a, 3b, and the nonmetallic jacket tube 4 and the metal bending guide tubes 3.3a, 3b will come into contact.

As a result, at the bent portion of the PC cable 2, metal fatigue caused by frictional force or electrical causes due to contact between dissimilar metals is unlikely to occur.

<Effects of the Invention> As explained above, in the present invention, each PC cable to be bent is coated with a resin jacket tube over the intended bending range, so that the metal PC cables do not come into direct contact with each other. , or each PC cable does not come into direct contact with the metal bending guide tube.

As a result, the bending portion of the PC cable does not suffer from metal fatigue as in the conventional case, and a decrease in fatigue strength can be reliably prevented.

Further, since the bending portion of the PC cable can be made smaller than the conventional bending ratio, it is advantageous in terms of design.

[Brief explanation of the drawing]

Figure 1.2 An explanatory diagram of an embodiment of the present invention, a cross-sectional view of a tower of a cable-stayed bridge. Figure 2: A cross-sectional view taken along ■-■ in Figure 1. Figure 3.4: Other bent parts of PC cables. A cross-sectional view of a tower with an explanatory diagram showing an example of its construction.

Claims (1)

[Claims] (1) At the bending part of a PC cable using a bending guide tube having only a curved part or a curved part and a straight part following it, the bending guide tube and a different mantle tube are covered over the planned bending range of the PC cable. The structure of the bending part of the PC cable eliminates the direct contact between metal parts between the PC cables and between the PC cable and the bending guide tube.