JP2003343119A - Steel pipe with jointing part and its exchanging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily provide a steel pipe with a jointing part by simplifying the structure. <P>SOLUTION: The steel pipe with a jointing part is provided with a pipe body 1 and a tabular base 2 for jointing provided in the lower end of the pipe body 1. The pipe body 1 can be fixed to another material by attaching bolts to a base 2 from the upper face of the base 2 to bring the under face of the base 2 into contact with the other material. The base 2 is formed of a base body 3 having a flat upper face and a spot facing part 4. Holes 40, 40... for fitting bolts are formed in the spot facings 4. The wall thickness of the base body 3 is made larger than that of the spot facing part 4. In this way, reinforcing rib is removed, the steel pipe is constituted of only the pipe body 1 and the base 2 to simplify the structure. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel pipe with a connecting portion and a method for replacing the steel pipe.

[0002]

2. Description of the Related Art In recent years, circular steel pipes and rectangular steel pipes have been widely used from poles (struts) of works such as road signs, street lights and flag poles to pillars of steel-framed buildings. At that time, the steel pipe pillar installed as a pole of a road sign or a pillar of a building is, for example, as shown in FIGS. 14 (A) and 14 (B), the base plate 2 protruding from the lower end portion of the steel pipe pillar 20.
1 is placed on the concrete foundation 22, and a plurality of anchor bolts 23 projectingly provided on the foundation 22 and inserted into the bolt holes 21a of the base plate 21 and a plurality of fixings screwed into the anchor bolts 23, respectively. It is fixed with a nut 24. Further, since a large bending stress is generated in the column base of the steel pipe column 20, a plurality of stiffening members 25 (reinforcing ribs) such as rib plates are formed on the outer periphery of the column base.
Is attached.

However, the base plate 21 and the stiffener 25
Since all of them have to be attached to the lower end of the steel pipe column 20 by welding, there are many welded parts, and the shape is inevitably complicated, which not only makes the processing and manufacturing troublesome but also causes welding defects and stress concentration. There was a problem such as being easy.
Further, since many stiffening members 26 are projected around the column base, it may hinder walking, especially in the case of a streetlight pole or the like standing upright on a roadside or in a park. There were also challenges. Each member number shown in the "Prior Art" column is used only in this column, and is not related to the member numbers in other columns unless otherwise specified.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems by providing a steel pipe with a connecting portion having a simple structure and easily manufactured, and a method for replacing the steel pipe.

[0005]

A steel pipe with a connecting portion according to a first aspect of the present invention is provided with a pipe main body 1 and a connecting plate-shaped base 2 provided at an end of the pipe main body 1. ,
It is characterized in that a reinforcing rib is not provided between the tube body 1 and the base 2.

A steel pipe with a connecting portion according to the second invention of the present application is
The pipe main body 1 and the plate-shaped base 2 for connection provided at the lower end of the pipe main body 1 are provided, and the lower surface of the base 2 is brought into contact with another to attach bolts from the upper surface of the base 2 to the base 2. As a result, the following configuration is adopted for the one that can fix the pipe body 1 to another. That is, the base 2 is composed of a base body 3 having a flat upper surface and a spot facing portion 4,
Bolt mounting holes 40 ... 40 are provided in the spot facing portion 4, and the thickness of the base body 3 is larger than the thickness of the spot facing portion 4.

A method for exchanging a steel pipe with a connecting portion according to a third aspect of the present invention is a method for exchanging a steel pipe with a connecting portion, which comprises a pipe body 1 and a plate-shaped base 2 for connection provided at an end of the pipe body 1. A method for exchanging an existing ribbed steel pipe with the steel pipe with a connecting portion according to the second invention of the present application, wherein the steel pipe with a connecting portion according to the second invention of the present application is an existing ribbed steel pipe base. Is equal to the thickness of the counterbore part 4 and the thickness of the base body 1 is larger than the thickness of the base, so that it has a strength higher than that of the existing ribbed steel pipe.

According to the first to third inventions of the present application, the rib for reinforcement is eliminated and the steel pipe is constituted only by the pipe main body 1 and the base 2 to simplify the structure. The steel pipe can be easily provided. Further, in each of the above inventions of the present application, the concentration of stress can be suppressed by eliminating the reinforcing ribs as described above. Further, in the second and third inventions of the present application, the thickness of the base body 1 is set to the counterbore portion 4.
By making the thickness larger than the thickness of the steel pipe, sufficient strength was secured for the steel pipe even if the reinforcing ribs were eliminated. In particular, in the third invention of the present application, while simplifying the structure, a strength equal to or higher than that of the ribbed steel pipe is secured.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. FIG. 1 (A) is a partially cutaway front view showing an installed state of a steel pipe with a connecting portion according to the present invention.
(B) is a plan view of a main part of the steel pipe with the connecting portion. For convenience of description, in each drawing, U indicates the upper side and S indicates the lower side.

This steel pipe with a connecting portion is provided with a pipe main body 1 and a plate-like base 2 for connection provided at the lower end of the pipe main body 1, and the lower surface of the base 2 is brought into contact with the ground g to form a base. The pipe body 1 is fixed to the ground g by mounting the bolt b on the base 2 from the upper surface of 2. Hereinafter, the configuration of each unit will be described in detail.

In the present embodiment, the above-mentioned pipe body 1 is a round steel pipe having a circular cross section. The base 2 is fixed to the base end (lower end) of the pipe body 1 by welding.

The base 2 is a plate-like body made of metal and having a substantially rectangular shape in plan view. The base 2 is composed of a base body 3 having a flat upper surface and a spot facing portion 4. The upper surface 3a of the base body 3 which is a main part of the base 2 is flat, and other members such as reinforcing ribs are not provided. As shown in FIG. 1A, the base body 3 is provided with an insertion hole 30 penetrating from the upper surface 2a to the lower surface a2 of the base. The base end of the pipe body 1 is inserted into the insertion hole 30 and welded. As a result, the tube body 1 and the base 2 are fixed. The above welding is performed along the outer circumference of the pipe body 1 without uneven distribution.

As shown in FIG. 1B, the spot facing portion 4 is a portion to which the bolt b is mounted, and is provided at four corners of the base 2. Each counterbore 4 has a hole 40 for mounting a bolt. As shown in FIG. 1 (A), the bolt b is passed through the hole 40 and the base 2 is fixed to the ground g (the seat surface of the bolt b comes into contact with the upper surface 4a of the counterbore portion 4, and the shaft of the bolt b is fixed). Goes into the ground).

The wall thickness h of the base body 3 is larger than the wall thickness w of the spot facing portion 4. Further, the wall thickness of the spot facing portion is the same as the wall thickness of the base of the conventional steel pipe with a connecting portion (FIG. 14) (wall thickness t of the base plate 21 in FIG. 14). That is, the wall thickness of the base body 3 is larger than the wall thickness of the base of the conventional ribbed steel pipe. Thus, in the steel pipe according to the present invention, the strength of the base is made larger than that of the conventional steel pipe provided with such ribs without providing reinforcing ribs.
Further, by forming the base body 3 having such a large thickness, the insertion hole 30 is extended upward as compared with the conventional one, and the outer periphery of the tube body 1 and the insertion hole when the base end of the tube body 1 is inserted. The contact area between the inner peripheral surface of the tube 30 and the inner peripheral surface of the tube 30 can be secured larger than that of the conventional one, and the fixing strength between the tube body 1 and the base 2 is also improved.

FIG. 2 shows another embodiment. Figure 2 (A)
FIG. 2 is an overall front view of a steel pipe with a connecting portion according to this embodiment, FIG. 2 (B) is a front view of a partially cutaway main portion of the steel pipe with a connecting portion, and FIG. 2 (C) is a main portion thereof. It is a top view.
As shown in FIG. 2C, the base 2 in this steel pipe is
It is a plate-shaped body that is substantially circular in a plan view.

FIG. 3 shows another embodiment. Figure 3
(A) is the whole front view of the steel pipe with a connection part which concerns on this embodiment, FIG.3 (B) is the partially cutaway principal part front view, FIG.3 (C) is the principal part top view. is there. As shown in FIG. 3 (A), in this steel pipe, the pipe body 1 is a rectangular pipe having a substantially rectangular cross section, and a mounting portion 5 for a sign or the like is provided on the upper portion thereof. Corresponding to such a cross-sectional shape of the tube body 1, the shape of the body insertion hole 30 is also rectangular.

FIG. 4 shows still another embodiment. Figure 4
(A) is the whole front view of the steel pipe with a connection part which concerns on this Embodiment, FIG.4 (B) is the partial cutaway principal part front view, FIG.4 (C) is the principal part top view. is there. In this steel pipe, the pipe body 1 is a polygonal pipe having an octagonal sectional view. Corresponding to such a cross-sectional shape of the tube body 1, the shape of the body insertion hole 30 is also octagonal. Further, the base 2 is also provided with eight spot facing portions 4.

It is also possible to employ a steel pipe having a polygonal cross-sectional shape other than the above-mentioned quadrangle or octagon. The shape of the main body insertion hole 30 of the main body 3 and the number of counterbore parts may be changed. Further, in each of the above-described embodiments, the tube body 1 is shown to extend straight up and down. In addition, as shown in FIG. 5, the tube body 1 can be implemented even if it has a curved and extending portion. Although not shown, the pipe body 1 can be implemented even if its tip is bifurcated.

In each of the above embodiments, the base 2
Shows the one provided on the base side of the pipe body 1 as the connecting portion with the ground g. In addition, as shown in FIG. 6, a base 2 may be provided at the tip of the pipe body 1 as a connecting portion for connecting the steel pipe to a separate horizontal pipe 10. Further, as the horizontal pipe 10 to be connected, a steel pipe according to the present invention can be used as shown in the drawing. 2 to 6 are the same as those of the embodiment shown in FIG. 1 except for the configuration particularly mentioned. The shape of the base 2 may be an ellipse, an ellipse, or another polygon other than the above-described circle or rectangle. In addition, in each of the above-described embodiments, the base 2 is provided with the spot facing portion 4, but such a spot facing portion 4 is not provided, and the entire base 2 is implemented as the base body 3. Is also possible. The pipe body 1 and the base 2 may be fixed by fillet welding or fixed by butt welding.

The steel pipe according to the present invention can be installed not only when newly installed, but also as an existing steel pipe with ribs.

[0021]

EXAMPLE A steel pipe with a connecting portion shown in FIG. 1 having the following dimensions was taken as an example, and the stress concentration and fatigue were examined. First, regarding the pipe body 1, its outer diameter is 16
An SS400 steel pipe having a thickness of 5 mm and a thickness of 4.8 mm was used. In addition, one side of the square base 2 is 400 mm, the inner diameter of the insertion hole 30 corresponds to the outer diameter of the pipe body 1, the wall thickness h of the base body 3 is 40 mm, and the wall thickness of the spot facing portion 4 is 40 mm. w was set to 20 mm, and the distance between the centers of adjacent holes 4 and 4 was set to 300 mm. Then, as a comparison object, the conventional steel pipe shown in FIG. 14 having four reinforcing ribs was used. About this conventional steel pipe, rib (stiffening material 2
The height of 5) was 200 mm, the thickness was 12 mm, and the wall thickness t of the base (base plate) was 20 mm. The other dimensions of this comparative object were the same as those of the steel pipe of the above-mentioned Example of the present application.

With respect to the steel pipes of the examples and the comparative examples, the stress concentration and the JSS were measured in accordance with "Fatigue design guideline for steel structures / commentary" edited by JSSC Japan Steel Structure Association.
The C fatigue grade was examined. As a result, with respect to the above embodiment,
When the test stress was set to 103 Mpa and vibration with an amplitude of 3 million times was applied, the stress concentration was 0.9 to 1.1, J
The SSC fatigue grade was D grade. On the other hand, in the above comparative example, when the test stress was set to 58 Mpa and vibration was applied with an amplitude number of 198,000 times, the stress concentration was 1.8 to 2.
0, JSSC fatigue grade was G grade. in this way,
The above-described examples of the present invention showed more excellent effects on the conventional ribbed steel pipe as a comparative example under lower severe conditions in terms of low stress concentration and JSSC fatigue grade.
The above-mentioned stress concentration indicates the ratio of the stress generated in the structural calculation and the stress actually generated in the test.

The details of the above test will be described below. The test was carried out at Sumitomo Metal Technology Co., Ltd. (1-8 Fuso-cho, Amagasaki City, Hyogo Prefecture), Kashima Division, Technical Sales Office, at the request of the applicant of the present application. It will be described based on the report of the test contents (report of the result of fatigue characteristic investigation of the lighting column base). According to this test, regarding the test material (the above-mentioned embodiment of the present invention) having the improved shape in which the rib existing in the conventional steel pipe with the connection portion (illumination column base) is removed, the deformation behavior and the fatigue property when the bending load is applied investigated. In this study, the stress finally applied to the weld toe was compared with the stress calculated from the shape and bending moment, and the stress concentration was calculated, and the fatigue test of the actual body was carried out based on it. Carried out.

First, the static bending deformation behavior investigation conducted will be described. As shown in FIG. 7, in this survey test, a test body with a base plate (steel pipe with a connecting portion) having a SS400 steel pipe as a pipe main body was examined as the test material 100 in the above-described example of the present application. For the test, the sample 100 is
The test was carried out by horizontally fixing the test body (fixing base v) of the test body installed in the test chamber horizontally (fixing the base 2 of the specimen 100 with bolts). And
1140 mm from the weld toe 101 of this specimen 100
A static bending load p was applied at a position (distance between vibration point and weld toe) 102 (static load was applied upward). Regarding the test conditions, a Shimadzu servo pulsar was used as the tester (not shown). The test temperature was room temperature. The amplitude was one-sided swing (cantilever), and the load was applied every 2.5 kN up to 20 kN. Regarding the dimensions of the test material 100, as described above, the outer diameter was 165 mm and the measured wall thickness was 4.8 mm.

Strain gauges f ... F are attached to the above-mentioned specimen 100 at the positions shown in FIG. That is, the specimen 10
7 points along the axial direction x of the tube body 1 of 0, tube body specimen 1
A strain gauge f was attached at 5 points along the circumferential direction r in the vicinity of the weld toe 101 of the pipe body 1 of No. 00. Regarding the attached position of the strain gauge f in the axial direction x, the distance from the position 10 mm from the weld toe toward the tip of the pipe body 1 is 20.
It was attached at a pitch of 50 mm up to 0 mm, and after that, it was attached at a position 400 mm and 600 mm apart from the weld toe 101 (in the axial direction x toward the tip of the pipe body 1). Regarding the attachment position of the strain gauge f in the circumferential direction r, it was attached at a pitch of 50 mm at a position 10 mm from the weld toe. About the axial direction x,
The strain gauge f closest to the proximal end of the tube body 1 is shared with the one in the circumferential direction r (same strain gauge f).

After the above static deformation behavior evaluation test was conducted, the fatigue characteristics were investigated by applying a load amplitude in the installed state (without the strain gauges f ... f). For this test condition, a servo pulsar manufactured by Shimadzu Corporation was used as a tester. The test temperature was room temperature. The amplitude was one-sided swing (cantilever), and the amplitude was 5 Hz. About the stop condition of the tester, 90% of the initial load,
The test machine was stopped. The excitation point was at the same position as the above position 102, and the excitation direction was also upward.

The above test results will be described in detail. First,
The results of the static bending deformation behavior investigation will be described. Regarding the stress of each part that occurs when a static bending load is applied,
The deformation behavior was confirmed by measurement using multiple strain gauges. In particular, the stress generated in the weld toe and its vicinity where fatigue cracks are likely to occur was measured and compared with the stress value calculated by the shape (the stress generated in the above structural calculation) (the stress mentioned above). I asked for the degree of concentration). The stress calculation based on the shape described above is calculation of the stress of the weld toe portion 101 caused by the bending moment. Regarding the calculation method of stress (calculation of stress from bending moment),
The stress generated in the weld toe 101 where the steel pipes are joined from the applied stress and bending moment is expressed by the equation shown below.

[0028]

## EQU1 ## σ max = M / Z

In the above formula 1, σmax indicates the maximum stress level (N / mm ² ), and M indicates the bending moment (N · m).
m) (converted from N · m 2), and Z represents the section modulus. This section modulus Z is given by the formula shown in the following mathematical expression 2, and has a value of 94019 (mm ³ ) here.

[0030]

[Formula 2] Z = π (D4 −d4) / (32 · D)

In the above formula 2, D represents the outer diameter of the tube body 1 of the specimen 100, and takes a numerical value of 165 mm as described above. Further, d represents the inner diameter of the tube body 1 of the sample 100, which is a value of 155.4 mm obtained by subtracting the thickness 4.8 mm from the outer diameter 165 mm (the thickness 4.8 mm).
For, regarding the above, the average measured value of 4.8 mm was adopted instead of the nominal dimension of 5 mm). Table 1 shows the stress calculation test results of the weld toe portion 101 from the bending moment.

[0032]

[Table 1]

Next, the measurement and analysis results of the stress distribution in the axial direction x will be described. Table 2 shows the results of measuring the stress distribution when a bending stress is applied using a strain gauge attached in the axial direction of the steel pipe. This shows the stress distribution tendency (representative value: conversion from N / mm ² strain amount) of the data acquired from the seven strain gauges f ... F arranged along the axial direction x in FIG. 8.

[0034]

[Table 2]

A graph of Table 2 is shown in FIG. As shown in FIG. 9, unlike the measurement results up to now, the stress does not monotonically increase from the steel pipe end portion to the weld toe portion, but a high stress level is obtained up to about 100 mm away from the weld toe portion. It was confirmed to have. This tendency is remarkable when a high bending load is applied.

Table 3 shows the calculation results of the stress generated at the weld toe. In calculating the stress concentration, the actual measurement value obtained at each bending load is adopted.

[0037]

[Table 3]

The relationship between the bending load and the stress (measured value) generated at the weld toe obtained from Table 3 is shown in the graph of FIG.
Shown to 0. As shown in FIG. 10, 1 from the weld toe
It was confirmed that the stress generation behavior due to bending was different between 00 mm and 100 mm and beyond. Therefore, using 3 points of 10 mm, 50 mm, and 100 mm from the weld toe,
The second-order approximation formula was calculated to calculate the stress generated at the weld toe under each bending stress load due to the exterior. As shown in FIG. 10, there is a substantially linear relationship between the bending load and the generated stress on the low load side, but it does not become linear at 10 kN or more, and it was confirmed that the stress increase behavior of the weld toe due to bending is different. It was Regarding this, it is considered that the stress generated by bending does not occur only at the weld toe as a fulcrum, but as a fulcrum at a region having a certain width and area, it deviates from the linear relationship.

Next, the stress distribution behavior in the circumferential direction r will be described. In this study, it was confirmed that the stress concentration at the weld toe local part tends to decrease due to bending load with a certain width and area near the weld toe. Along with the test for confirming the stress distribution in this axial direction, as described above, strain gauges f ... The state of stress generation) was observed. The test results are shown in Table 4.
And shown in FIG. As shown in these charts, a significant increase in stress is observed within a width of ± 50 mm with increasing load.

[0040]

[Table 4]

The calculation of the stress concentration will be described. From the various data obtained above, the stress concentration was calculated with respect to the stress generated at the weld toe of the shaft center, which is considered to easily cause fatigue cracks. In the calculation, it is calculated as a ratio between the actual measurement value obtained from the strain gauges f ... F and the value obtained from the shape / bending moment. The calculation results are shown in Table 5, and the tendency of the stress concentration degree under bending load is shown in Fig. 1.
Shown in 2. The stress concentration is a value obtained by dividing the value of the weld toe obtained from the strain gauge by the value from the bending moment.

[0042]

[Table 5]

From these figures, the stress concentration is 1.00 or more at 10.0 kN or less, but becomes 1.00 or less at 12.5 kN or more. It is considered that this is because the region where stress concentration occurs spreads widely, so that the load is not concentrated and concentrated at one weld toe. These tendencies are supported by the above-mentioned actual measurement results by the strain gauges f ... F.

Here, the results of the actual fatigue test will be described. Specimen having the above deformation behavior characteristics (specimen 10
Regarding 0), a fatigue test was conducted. The test results are shown in Table 6 and FIG.

[0045]

[Table 6]

As shown in these figures, the stress generated at the weld toe was 103 N / mm ^{2 and} cracking was suppressed,
We were able to satisfy more than 2 million times.

The above is the details of the test conducted on the above-described embodiment of the present application and the result thereof. When the test of the same content is compared with the result performed for the above-mentioned comparative example, as described above, the steel pipes of the above-mentioned examples, under the more severe conditions, have a low stress concentration and a fatigue grade as compared with the comparative example. about,
It showed a better effect.

[0048]

By implementing the first to third aspects of the present invention, the steel pipe with the connecting portion can be easily provided by simplifying the structure. Therefore, it is possible to suppress the occurrence of welding defects and stress concentration, and it is easy to manufacture. Furthermore, by eliminating reinforcing ribs for steel pipes that are installed on the ground and used as poles for road signs and columns of buildings, problems such as obstacles to walking could be eliminated.

[Brief description of drawings]

FIG. 1 (A) is a front view of a partially cutaway essential part showing an installed state of a steel pipe with a connecting portion according to an embodiment of the present invention,
(B) is a plan view of a main part of the steel pipe with the connecting portion.

2A is an overall front view of a steel pipe with a connecting portion according to another embodiment, FIG. 2B is a front view of a partially cutaway main portion thereof, and FIG. 2C is a plan view of the main portion thereof. Is.

3A is an overall front view of a steel pipe with a connecting portion according to another embodiment, FIG. 3B is a front view of a partially cutaway essential portion thereof, and FIG. It is a figure.

FIG. 4A is an overall front view of a steel pipe with a connecting portion according to still another embodiment, FIG. 4B is a front view of a partially cutaway main portion thereof, and FIG. It is a figure.

FIG. 5 is an overall front view of a steel pipe with a connecting portion according to still another embodiment.

FIG. 6 is a partially cutaway front view showing a usage state of a steel pipe with a connecting portion according to another embodiment.

FIG. 7 is an explanatory diagram showing test results of an example of the present invention.

FIG. 8 is a schematic front view showing a state of a test for one example of the present invention.

9 is an explanatory view showing a strain gauge mounting position in the embodiment of FIG.

FIG. 10 is an explanatory diagram showing the test results of the above-mentioned embodiment of the present invention.

FIG. 11 is an explanatory diagram showing a test result of the above-described embodiment of the present invention.

FIG. 12 is an explanatory diagram showing the test results of the above-described embodiment of the present invention.

FIG. 13 is an explanatory diagram showing the test results of the above-described embodiment of the present invention.

FIG. 14 (A) is a plan view of a main part of a conventional exchange with a connecting part, and FIG. 14 (B) is a front view of the main part showing its installation state.

[Explanation of symbols]

1 tube body 2 base 3 base body 4 spot facing 40 holes

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2D064 AA11 AA22 CA04 DB07 HA11                       HA13                 2E125 AA04 AA48 AB16 AB17 AC16                       AG03 AG12 CA03

Claims (3)

[Claims] 1. A steel pipe with a connecting part comprising a pipe body (1) and a plate-shaped base (2) for connection provided at an end of the pipe body (1), wherein the pipe body (1) and the base A steel pipe with a connecting part, characterized in that a reinforcing rib is not provided between the steel pipe and the (2). 2. A base comprising a pipe body (1) and a plate-shaped base (2) for connection provided at the lower end of the pipe body (1),
In a steel pipe with a connection part that can fix the pipe body (1) to another by abutting the lower surface of (2) to another and mounting bolts from the upper surface of the base (2) to the base (2). , The base (2) above is a base body (3) with a flat top surface,
It is composed of the spot facing (4), the spot facing (4) is provided with a hole (40) for bolt mounting, and the wall thickness of the base body (3) is different from that of the spot facing (4). Steel pipe with a connecting part characterized by being larger than the wall thickness. 3. A method of exchanging a steel pipe with a connecting portion, comprising: a pipe main body (1); and a connecting plate-like base (2) provided at an end of the pipe main body (1). The steel pipe with a connecting portion according to claim 2 is to be replaced with a steel pipe with a connecting portion according to claim 2, wherein the thickness of the existing ribbed steel pipe base is equal to the thickness of the spot facing portion (4). A method of replacing a steel pipe with a connecting portion, in which the thickness of the base body (1) is greater than that of the base, so that the steel body has strength higher than that of an existing ribbed steel pipe.