Slip joint for steel poles or the like

Abstract

A slip joint for steel poles wherein a simple reinforcing means is provided at the overlapping ends of telescoping tubes used in forming the poles, whereupon the strength of the pole including the joint is greatly improved.

Description

This invention relates to slip joints for steel poles, and more particularly used in aesthetic steel poles for transmitting high voltage currents.

Steel structures are known in which slip joints are used for aesthetic steel poles now being increasingly used because of their positive impact on the environment.

Such steel poles are made of hollow tapered tubes of octagonal (or multi-Sided) cross-section so that the lower part of the upper tube may fit in the upper part of the lower tube. It therefore becomes easy to assemble such steel poles at the job site without the need for special joints, and the tubes being thus easy to fabricate and erect.

However, in the above-mentioned slip joint, if the strength of the joint is to be equal to the remainder of the pole, the fitting length at the joint must be about twice as large as the distance between the opposed sides in the cross-section of the pole. Thus, for a pole of a large diameter and large thickness, a large quantity of steel is required thereby rendering such poles uneconomical. For example, when the fitting length is L and the distance between the opposed sides in the cross-section of the pole is D, with L/D .ltoreq.1.7, the lower or inner tube will buckle at the tip on the tension side and will also buckle in that portion in contact with the end surface of the outer tube on the compression side. With D/tu .gtoreq.40 (wherein tu is a pole thickness), the upper or outer tube will crack along the weld joint on the end surface on the compression side.

Although the upper tube of such steel poles will not slip down, it is necessary to individually transport each tapered tube unit forming the steel poles to the job site for assembly and, when transporting them long distances or particularly when exporting them, transportion costs will increase rapidly.

Moreover, during the assembly of each steel pole, it is necesssry to align the upper tube and lower tube with each other and, when assembling the poles vertically, it is necessary to suspend the upper tubes one by one from a helicopter or the like, thereby drastically reducing the working efficiency.

An object of the present invention is to provide a slip joint wherein the fitting length is reduced so that the total weight may be decreased and the above-mentioned drawbacks may be avoided. In carrying out this objective, one or more knot-shaped reinforcing flanges are formed in several steps inside the joining portion of the inner tube so that the inner tube may be prevented from buckling, and the thickness of the joining portion of the outer tube is made larger than the thickness of the body of the outer tube as, for example, by winding a reinforcing band on the outer periphery of the end joining portion of the outer tube so that the outer tube may be prevented from cracking along the weld joint on the end surface on the compression side.

Another object of the present invention is to provide such a slip joint wherein, even if the overlapping length is short, a fixed strength will be achieved, the efficiency during assembly of the steel pole will be improved and the work and cost for long distance transportation or the like will be reduced. The steel pole is formed by pushing up such slip joints from below so that the joining portion is wedged, reinforcing means being provided in the form of reinforcing flanges and/or reinforcing bands.

In the drawings:

FIG. 1 is an elevational view of a steel pole for which slip joints of the first embodiment of the present invention are used;

FIG. 2 is a partly sectioned elevational view of the joint in FIG. 1;

FIG. 3 is a cross-sectional view taken along line III - III of FIG. 2;

FIG. 4 is a partly sectioned elevational view of another embodiment;

FIG. 5 is a cross-sectional view taken along line V - V of FIG. 4;

FIG. 6 is an elevational view of a steel pole for which slip joints of the second embodiment of the present invention are used;

FIG. 7 is a vertically sectioned view of the joining part of the slip joint shown in FIG. 6;

FIG. 8 is a cross-sectional view taken along line VIII - VIII of FIG. 7;

FIG. 9 is an elevational view showing a test sample while being tested; and

FIG. 10 is a graph showing the test results.

In FIG. 1 is shown an aesthetic steel pole for transmitting high voltage currents. This steel pole is formed by joining a plurality of steel tubes 1 which are uniformly tapered outwardly from their upper to their lowr ends, and which are octagonal in the cross-section. Generally the height of each tube is about 45 meters, its thickness is 9 to 16mm., the distance between the opposed sides of the octagon is 600 to 1400mm. and the taper is about one-fortieth to one-seventieth. A required number of arms 2 project outwardly of the upper tubes and conductors (not illustrated) are hung on the outer ends of arms 2 through insulators. The pole is supported at its lower end in a foundation 3.

For a conventional slip joint, the fitting length is about 1.5 times as large as the distance between the opposed sides in the tube cross-section, the strength of the joint between tubes is lower than the strength of the remainder of the pole, and it has been found as a result of tests that, in order to make the strength of the joint equal to that of the main body, the fitting length must be about twice as large as the distance between the opposed sides in the cross-section. If the fitting length is made about twice as large, the weight of the steel at the joint will increase by about 25 percent.

In the embodiments of the present invention, it is intended to make the strength of the joint equal to the strength of the main body of the pole even when the fitting length is made substantially small such as equal to the distance between the opposed sides in the cross-section. One of the embodiments is shown in FIGS. 2 and 3.

This slip joint comprises an inner or lower tube 4 and an outer or upper tube 5, and each of the tubes is formed by bending a steel plate so as to form tapered tubes of octagonal cross-sections and welding each along one and/or two vertexes.

Knot-shaped reinforcing flanges 6 made of steel plates are secured as by welding to the inside of inner tube 4 near and slightly below its upper end at such locations as to lie within the overlap between tube 4 and part of an outer tube 5. It should be noted that flanges 6 are installed before the steel plate is welded along the vertex or vertexes to form a tubular cross-section.

Further, a reinforcing plate 7 in the form of a steel ring or band is secured as by welding along the outer periphery of the lower end of outer tube 5. Such reinforcing plate 7 may be provided only in the vertex part to be welded.

During the assembling operation, inner tube 4 is fitted into outer tube 5 to be joined thereto. The dimensions and positions of the respective parts of this slip joint will be effective as to manufacture and performance when considering the following:

t.sub.s = (0.5 to 1.5) x t.sub.b,

t.sub.i = (0.5 to 1.5) t.sub.b,

.delta..sub.s = (2 to 10) x t.sub.b,

.delta..sub.i = (-10 to +10) x t.sub.b,

h.sub.s = (5 to 15) x t.sub.s,

h.sub.i = (5 to 15) x t.sub.i,

t.sub.o = (0.2 to 1.0) t.sub.u,

b = (10 to 30) t.sub.o and

.sym..sub.o = (-5 to 5) t.sub.u.

In the above embodiment, a pole of octagonal cross-sections is shown. However, the cross-sections may be circular as shown in FIGS. 4 and 5 or any other polygonal shape without departing from the scope of the invention.

The embodiment shown in FIGS. 6, 7 and 8 is a high voltage current transmitting aesthetic steel pole provided with joining means between its tubes. As compared to the above-mentioned embodiment, this steel pole is formed by joining a plurality of steel tubes 1' which each taper toward their upper portions and are octagonal in cross-section throughout. A required number of arms 2' project outwardly of the upper tubes of the steel pole and conductors (not illustrated) are hung on the tips of arms 2' through insulators. The details of the slip joint of the pole are shown in FIGS. 7 and 8. A plurality of tubes smaller in the distance between the opposed sides are inserted in turn toward the center of the outermost tube in advance at the time of erection and are set perpendicularly to the ground surface on a fixed carriage, the innermost tube being pulled out with a lifting machine, and an oil pressure jack (not illustrated) being interposed between reinforcing flanges 6' of the adjacent tubes. A pressure as, for example, 10 tons in the case of an octagonal pole of a distance of 1 m. between the opposed sides in cross-section, is applied until the overlapping length is reached in a required position and then wedges 11 are inserted with an oil pressure jack or the like into the clearance parts 10 between supporting pieces 9 and the inner wall surface of outer tube 5' in advance by inwardly bending the lower end of inner tube 4' . Notches 8 provided in this lower end at the time of making the tube permit such inward bending. As required, wedges 11 may be fixed to the outer tube with bolts. A sealant 12 is applied to the lower end of inner tube 4' before the assembling in order to prevent dew drops or the like from entering the joining part. Then tubes 4' and 5' are pulled out with a lifting machine or the like and the same step is continued successively to complete the assembly of a steel pole. This steel pole can be assembled also horizontally on the ground by using the same jack or the like as in this embodiment and then erected upright.

The above-mentioned steel pole has been described for octagonal cross-sections, although any other tubes of hexagonal or dodecagonal cross-sections may be used as well. For tubes of hexagonal, circular or dodecagonal cross-sections, the supporting pieces and wedges are provided at three points in the apex directions of the equilateral triangle of the cross-section. For a tube of square cross-section, the supporting piece and wedge are arranged on each side of the cross-section.

In another assembling method, the reinforcing flanges provided in the lower end of each tube are maintained sealed and the inside of the tube is filled with concrete by means of a concrete pump to assemble the pole.

In order to elucidate the problems of the conventional slip joint of the steel pole and to confirm the effects of the slip joint of the present invention, the conventional ones and the two of the first embodiment of the present invention were loaded and tested in model of a scale about one-half in size of an actual steel pole. The testing approach used is shown in FIG. 9. A test sample A slip-joined substantially at its middle portion was secured with bolts and nuts to one end part of upper and lower beams 13, a tension steel member 14 was arranged between the other end parts of beams 13 and was tensioned with a tensioning jack 15 to make a bending moment act on test sample A. For making a larger bending moment act on the test sample, a test sample A' was fitted in the position shown in phantom outline.

The results of the above tests are shown in the following table and in FIG. 10.

__________________________________________________________________________ Sample Fitting Ratio Strength: Failure No. Length of Maximum Mode L/D diameter moment Remarks to thick- tm 1 2 3 4 ness D/t __________________________________________________________________________ 1 1.05 80 75.26 0 Reinforced as in FIG. 2 (A) 2 1.01 do. 73.45 0 do. 3 1.01 40 70.25 0 Not reinforced. (B) 4 1.09 60 55.38 0 0 do. 5 1.08 80 44.20 0 0 0 do. 6 1.29 60 70.55 0 do. 7 1.30 80 47.63 0 0 do. 8 1.46 do. 51.05 0 0 do. 9 1.50 do. 50.71 0 do. 10 1.56 do. 54.47 0 do. 11 1.67 do. 62.35 0 do. 12 1.85 do. 66.77 0 do. 13 2.03 do. 71.54 0 do. 14 do. 74.39 0 No slip joint __________________________________________________________________________

Note: Failure Modes.

1. Buckled on the tension side of the tip of the inner tube.

2. Buckled in the part in contact with the end surface of the outer tube on the compression side of the inner tube.

3. Cracked in the welding part of the end surface on the compression side of the outer tube.

4. Buckled on the compression side of the root of the main pole.

In FIG. 10 the A readings are for the first embodiment of the present invention and the B readings are for the ones not reinforced. As understood from FIG. 10, in the test sample B of D/tu =80, in order to obtain the same strength as the durability of the pole body, a fitting length of about twice as large as the distance between the opposed sides in the cross-section is required. On the other hand, in the ones illustrated in FIG. 2, a sufficient strength is obtained with a fitting length substantially small such as equal to the distance between the opposed sides in the cross-section. Further, as evident from the table, when D/t .gtoreq. 40 substantially, it will be necessary to reinforce the outer tube but, when D/t .ltoreq. 40 substantially, it will not be necessary to reinforce it. Further, when L/D .gtoreq. 1.7 substantially, it will not be necessary to reinforce the inner tube. When 1.3 .ltoreq. L/D .ltoreq. 1.7 , such two reinforcing flanges at the tip and on the inside as are shown in FIG. 2 will be required. When L/D .ltoreq. 1.3, the reinforcing flange at the tip will suffice. It is recognized that, in such case, the clearance between the reinforcing flanges at the tip and on the inside will be so narrow that a sufficient end force will be obtained with the reinforcing flange only at the tip.

Although these experiments were made only with the slip joints of the first embodiment of the present invention, the effects of the other embodiments are the same.

Further, according to the present invention, the working efficiency in erecting steel poles is very high, the efficiency in transportation time to the job site is improved, the transporting cost is low, and the joining part of the slip joint is sufficiently durable.

Claims

What is claimed is:

1. In a slip joint located at the overlapping ends of telescoping tubes tapering between a larger end to a smaller end thereof and forming a pole when telescoped together, reinforcing means provided at said overlapping ends, said reinforcing means comprising at least one reinforcing flange secured to substantially the entire inner surface of the inner one of said tube ends and lying wholly within the overlap of said ends, and said flange lying in a plane perpendicular to the longitudinal axis of said tubes, whereby the overlapping length at said ends is reduced and the strength of the pole including the joint is substantially uniform throughout.

2. In the slip joint according to claim 1, said reinforcing means further comprising a reinforcing band provided along the outer periphery of the outer one of said tube ends and lying wholly within the overlap of said ends.

3. In the slip joint according to claim 1, wherein the larger end of one of said tubes fits within the smaller end of another of said tubes, said reinforcing flange being spaced inwardly of said larger end of said one tube, a portion of said one tube located between said flange and said larger end having slits therein to facilitate a clearance between said portion and the inner surface of said another tube, and wedging means located with said clearaance.