JPH0426783Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial field of application] This invention relates to joints for power cable conduits, particularly those made of fiber-reinforced plastic (hereinafter referred to as FRP).
The invention relates to flexible joints for power cable conduits manufactured by the Company.

[Prior Art] As a flexible joint for underground conduits, a standard joint conventionally used mainly for power cable conduits is shown in FIG. This standard joint 11 is a simple cylindrical body made of FRP, and has a packing 12 attached to its inner peripheral surface. FIG. 4 shows the bending characteristics of the standard joint 11. The graphs in the figure show the bending characteristics when the axial compressive force Q is changed.

Other common flexible joints include one in which the central flexible portion 13 is bulged into a spherical shape (Japanese Utility Model Publication No. 1983-6809), as shown in FIG. One in which the flexible portion 14 is bent into a bellows shape (Japanese Utility Model Publication No. 12021/1983) is known.

[The problem that the idea aims to solve]

In the field of underground power cable conduits, the 7th
As shown in the figure, when passing the conduit 16 through a manhole 15 or a structure such as a bridge abutment, a first joint 17 made of a flexible joint is connected to the manhole 15 in order to cope with ground subsidence due to earthquakes, etc.
A similar second joint 20 is interposed between the short pipe 18 on the 5 side and the first pipe 19, and a similar second joint 20 is connected between the first pipe 19 and the second pipe 21.
A conduit 16 is interposed between the two.

When the above-mentioned standard joint 11 is used as the above-mentioned first joint 17 and second joint 20, the limit settlement amount δ
Assuming that the length of the first tube 19 is 2 m, the length is 316 mm when the allowable deflection angle is 9°.

However, during an earthquake, depending on the condition of the ground,
Since an even larger amount of subsidence is expected, the conventional standard joint 11 will not be able to adequately cope with the problem, and the pipe line 1
It is predicted that 6 destruction or escape will occur.

On the other hand, the flexible portion 1 bulges into a spherical shape as shown in FIG.
3 has the disadvantage that the flexible portion 13 is considerably larger than the diameter of the conduit, resulting in a reduction in space factor in the case of underground conduits for power cables in which a large number of tubes are arranged side by side vertically and horizontally. Further, in the case of a device having a bellows-shaped flexible portion 14 as shown in FIG. 6, the shear deformation is too large and a step is created in the deformed portion, which causes damage to the internal cable. For this reason, there is a problem in that it is not suitable as a joint for preventing ground subsidence in conduits that accommodate cables.

In order to solve the above-mentioned problems with the conventional technology, this invention prevents underground pipes from breaking or slipping out by changing to follow ground subsidence caused by earthquakes, etc., without creating a step, and also provides the required robustness. An object of the present invention is to provide a flexible joint for a power cable conduit having the following characteristics.

[Means to solve the problem]

In order to solve the above problems, this idea
In a flexible joint for a power cable conduit, in which a flexible part is formed in the center of a cylindrical body made of FRP, and insertion parts for pipe end parts are formed at both ends of the flexible joint, the inner diameter of the flexible part is defined as the inner diameter of the insertion part. By forming the flexible part smaller than the inner diameter, the thickness of the flexible part is made thicker than that of the insertion part, and a groove is formed in the circumferential direction for imparting flexibility to the inner peripheral surface of the flexible part, A groove is also formed in the circumferential direction on the inner circumferential surface of the insertion part to provide flexibility, and an O-ring is fitted into the groove that is closest to the flexible part among the grooves formed in the insertion part. , a gasket is attached to the inner circumferential surface of the end of the insertion portion.

[Effect]

Since the flexible joint having the above configuration is made of FRP, it has appropriate rigidity and elasticity. The number of grooves formed in the flexible portion and the insertion portion is determined in consideration of the properties thereof, and the flexibility of these portions is adjusted.

When a strain load is applied to a buried pipe, the packing initially deforms and absorbs the strain, but when the load exceeds a certain point, the flexible part of the flexible joint bends, and in some cases, the insertion part also bends. Wham.

〔Example〕

The FRP flexible joint of the embodiment shown in FIG. 1 is made of thermosetting unsaturated polyester resin reinforced with glass fibers. It has a cylindrical shape as a whole, with a flexible portion 1 formed in the center and insertion portions 2 at both ends.

The flexible portion 1 is formed to have a smaller inner diameter than the insertion portion 2, and its wall thickness is increased accordingly. Flexible part 1
Grooves 4 for imparting flexibility are formed in the circumferential direction on the inner peripheral surface at regular intervals in the length direction. The cross-sectional shape of the bottom surface of the grooves 4 is arcuate, and the cross-sectional shape of the protrusions 3 formed between the grooves 4 is trapezoidal. At least one groove 4 is formed, and its number, depth, and width are appropriately determined according to the rigidity and flexibility required of the flexible portion 1.

Furthermore, three grooves 5 are formed in the circumferential direction at required intervals to impart flexibility to the inner circumferential surface of the insertion portion 2. The innermost groove 5 is provided at the boundary between the flexible portion 1 and the insertion portion 2, and an O-ring 6 is fitted into the groove 5. A packing 8 is attached to the inner circumferential surface of the insertion portion 2 on the open end side.

On the other hand, the outer circumferential surface of the flexible joint is formed into a cylindrical surface 9 having the same diameter over the front part of the flexible part 1 and most of the insertion part 2, and there is a gentle gap between the cylindrical surface 9 and the opening end. It is formed into a tapered surface 10.

The flexible joint of the example is as described above,
At the power cable conduit burying site, each end of the underground conduit 7 is inserted into the insertion portions 10 at both ends. The tapered surface of the end of the conduit 7 is pressed against the O-ring 6, and the conduit 7 and the flexible joint are centered and maintained straight. Further, the packing 8 is brought into close contact with the outer circumferential surface of the conduit 7 to achieve a seal.

When an external force is applied to the pipe line 7 or the flexible joint during work, the external force is absorbed by the elasticity of the O-ring 6 and packing 8, and the straightness is maintained.

Furthermore, after being buried in the ground, the earth pressure that acts on the flexible joint is supported by the flexible part 1 at the center of the joint, and by the insertion parts 2 at both ends.
and the end of the conduit 7 inserted therein.

When a sudden change in the ground occurs due to an earthquake or uneven subsidence and a large strain load is applied to the pipe line 7, if the strain is relatively small, it will be absorbed by the elasticity of the O-ring 6 and packing 8, but any further strain will occur. When this becomes large, the end of the pipe line 7 comes into contact with the inner circumferential surface of the insertion part 2 and is restrained. If it becomes even larger, the flexible part 1 will bend, and in some cases both the flexible part 1 and the insertion part 2 will bend.

However, in both cases, excessive bending or
There is no shear deformation, and the conduit 7 deforms smoothly and with great flexibility to follow the deformation of the ground.
Therefore, the cable within the conduit 7 will not be damaged.

The test results for the flexible joint with the above structure are shown below.

(1) Test object Total length (including the packing) 451mm Length of flexible part 1 125mm Length of insertion part 2 (including packing) 163mm Inner diameter of protrusion 3 160mm Inner diameter of insertion part 2 184mm Outer diameter of cylindrical part 9 220mm Distance between each groove of flexible part 1 and insertion part 2 35mm Number of protrusions 3 4 (2) Test method As shown in Figures 8 and 9, pipes 22 are connected to both ends of the joint 10 to be tested. And span S
Place the joint 10 in the center on a 1m, 120° opening V-shaped roller support base 23, apply a compressive force Q in the axial direction from both ends, apply a load P to the center of the joint, and calculate the load P and Measure the displacement angle θ.

(3) Test results FIG. 2 shows a bending moment-angle diagram.

(4) Consideration of test results Based on the above test results,
It was found that a subsidence of 700mm can be absorbed when the height of the bridge (see figure) is 2m.

Note that the allowable deflection angle is a allowable value when dealing with sudden ground displacement such as an earthquake, and the allowable deflection angle in the case of slow ground displacement in soft ground or the like is smaller than this.

[Effect of idea]

Since this invention is as described above, it has the following effects.

a Appropriate flexibility is imparted by adjusting the rigidity of the material itself using grooves provided on its inner peripheral surface. Therefore, the conduit follows the ground with great flexibility against ground displacement due to earthquakes, etc., so that the cables inside the conduit can be protected.

(b) By making the thickness of the flexible part larger than the thickness of the insertion part, the rigidity of the flexible part without a conduit can be ensured.

c Since an O-ring is fitted to the insertion part, this O-ring cooperates with the seal to maintain the straightness of the joint and the pipe during the pipe connection work.

[Brief explanation of the drawing]

Figure 1 is a partially vertical front view of the embodiment, Figure 2 is a characteristic graph of test results, Figure 3 is a partial vertical front view of a conventional standard joint, Figure 4 is a characteristic graph of the standard joint, and Figure 5 is a characteristic graph of the standard joint. 6 and 6 are a partially vertical front view of the conventional example, FIG. 7 is a perspective view showing a part of the underground pipe, and FIG.
The figure is a front view of the test device, and FIG. 9 is a side view of FIG. 8. 1...Flexible part, 2...Insertion part, 3...Protrusion,
4...Groove, 5...Groove, 6...O ring, 7...Pipe line, 8...Putskin.

Claims (1)

[Scope of utility model registration request] In a flexible joint for a power cable conduit, which has a flexible part formed in the center of a cylindrical body made of fiber-reinforced plastic, and insertion parts for conduit end parts formed at both ends of the flexible joint, the inner diameter of the flexible part is inserted. The thickness of the flexible part is made thicker than the thickness of the insertion part by forming the inner diameter of the flexible part smaller than the inner diameter of the part, and a groove is formed in the circumferential direction for imparting flexibility to the inner circumferential surface of the flexible part. At the same time, a groove is formed in the circumferential direction on the inner circumferential surface of the insertion part to provide flexibility, and an O-ring is fitted into the groove located in the position closest to the flexible part among the grooves formed in the insertion part. A flexible joint for a power cable conduit, characterized in that a gasket is attached to the inner circumferential surface of the end of the insertion part.