DEPRES SION-PROVIDED STEEL PIPE AND COMPOSITE PILE
Technical Field
[OOO 11
The present invention relates to a depression-provided steel pipe and a
composite pile used for forming a civil engineering and construction structure.
The present application claims priority based on Japanese Patent Application No.
20 1 1-03 553 5 filed in Japan on February 22,20 11, the disclosures of which are
incorporated herein by reference in their entirety.
Background Art
[0002]
Piles used as foundation for civil engineering and construction structures achieve
a supporting force derived from an end supporting force and a frictional force on the
outer peripheral surface. The end supporting force is a bearing pressure resistance
occurring at an end portion of the pile, which is driven into hard ground to obtain a large
supporting force. The frictional force on the outer peripheral surface occurs from a
frictional force between the pile and the ground. In general, tlte frictional force on the
outer peripheral surface occurring between the steel pipe pile and the ground is small.
[0003]
Thus, the large supporting force is obtained by driving the supporting piles until
they reach the hard supporting layer, or using long or large-di&eter piles to increase the
frictional area on the outer peripheral surface. Thus, in the case where the ground is
weak or the supporting layer is located deeply in the ground, the size of the pile needs to
be increased, resulting in uneconomical design.
[0004]
In order to address these problems, for example, Patent Document 1 discloses a
configuration capable of reaching the piles up to the hard supporting layer, and a
recess-provided steel pipe and a composite pile in which the steel pipe needs not to be
longer or larger in diameter than necessary. This recess-provided steel pipe and the
composite pile have groove portions provided thereto to increase the adhesive force with
the ground or solidified material such as concrete, cement, and soil cement in an
manner, thereby achieving increased supporting force.
Further, for example, Patent Document 2 discloses a technique of inserting a
steel pipe having groove portions formed thereto into a hole formed in the bedrock to fix
the bedrock, and inflating the steel pipe.
Related Art Documents
Patent Documents
[0006]
Patent Document 1 : Japanese Unexamined Patent Application, First Publication
NO. 2008-175055
Patent Document 2: Japanese Unexamined Patent Application, First Publication
NO. 2003-245714
Disclosure of the Invention
Problems to be Solved by the Invention
[0007]
In the steel pipe and the composite pile described in Patent Document 1, the
groove portion provides sufficient adhesive force with the solidified material.
However, the formation of the groove portion on the outer peripheral surface of
the steel pipe possibly leads to a reduction in the compressive strength of the steel pipe
itself. In other words, the strength of the composite pile is evaluated on the basis of the
total of the strength of the steel pipe and the strength of the ground-improved portion
such as the solidified material. Thus, due to the reduction in the compressive strength of
the steel pipe itself, there is a concern of insufficient supporting force of the composite
pile.
[OOOS]
- Further, the technique described in Patent Document 2 above is a technique of
inflating the steel pipe inserted into the bedrock to adhere the bedrock to the steel pipe,
and is intended to increase the frictional force between the steel pipe and the ground,
solidified material and the like.
However, the final shape of the steel pipe cannot be controlled, and although the
* ' pulling-up load increases, the increase in the compressive load, which is important for the
pile, is not guaranteed.
[0009]
In view of the circumstances described above, an object of the present invention
is to provide a depression-provided steel pipe that exhibits excellent adhesive force and
compressive strength by increasing the adhesive force, for example, with the solidified
material while suppressing the reduction in the strength of the steel pipe itself, and
provide a composite pile using the depression-provided steel pipe, thereby obtaining
sufficient supporting force.
Means for Solving the Problems
[OO lo]
The present invention, which is derived to achieve the above object, has the
following aspects.
(1) A first aspect of the present invention provides a depression-provided steel pipe
having plural depressions on an outer peripheral surface, the depressions being formed so
as to form a line along an axial direction of the steel pipe, in which each of the depressed
portions has, inside thereof, a columnar groove portion extending along the axial
direction of the steel pipe and depressed deeper than a bottom surface of these depressed
portions; 0.95 i HA/HB i 1.05 is satisfied, where HA is an average Vickers hardness in
each of the depressed portions, and HB is a Vickers hardness at a portion between the
depressed portions adjacent to each other in the axial direction of the steel pipe; and the
outer peripheral surface is covered with a mill scale.
(2) In the depression-provided steel pipe according to (1) described above, at any
position along an axis of the steel pipe, a percentage of a total circumferential length at
each of the depressed portions of the steel pipe relative to an entire perimeter of the
depression-provided steel pipe may be 50% or less.
(3) In the depression-provided steel pipe according to (1) or (2) described above, the
depressed portions may be arranged so as to form four or more lines in parallel.
(4) In the depression-provid~ds teel pipe according to (3) described above, among
the lines of the depressed portions, lines of the depressed portiqns adjacent in the
* direction of the steel pipe; and the phase difference may be not less than 118 and not more
than 112 of a distance between centers of the depressed portions adjacent in the axial
direction of the steel pipe.
(5) In the depression-provided steel pipe according to (1) or (2) described above, the
depressed portions may be arranged so as to form six or more lines in parallel.
(6) In the depression-provided steel pipe according to (5) described above, among
the lines of the depressed portions, lines of the depressed portions adjacent in the
circumferential direction may be formed so as to have a phase difference in the axial
direction of the steel pipe; and the phase difference may be not less than 118 and not more
than 112 of a distance between centers of the depressed portions adjacent in the axial
direction of the steel pipe.
(7) In the depression-provided steel pipe according to any one of (1) to (6) described
above, each of the depressed portions may have an oval shape with a major axis in
parallel to the axial direction of the steel pipe.
(8) In the depression-provided steel pipe according to any one of (1) to (7) described
above, each of the depressed portions may be formed through hot roll forming using a
steel pipe processing roll having a surface with a raised portion.
(9) In the depression-provided steel pipe according to any one of (1) to (8) described
above, at least one of a plating layer and a resin layer may be formed on a mill scale.
(1 0) A second aspect of the present invention provides a composite pile formed by
integrally driving the depression-provided steel pipe according to any one of (1) to (9)
above into a solidified material.
Effects of the Invention
[OOll]
According to the invention described in (1) above, plural depressed portions are
arranged on the outer peripheral surface of the steel pipe so as to form a line along the
axial direction of the steel pipe, thereby increasing an area where the solidified material
adheres to the outer peripheral surface of the steel pipe. Thus, it is possible to increase
the adhesive force with the solidified material. Further, a columnar groove portion is
formed in each of the depressed portions, thereby increasing the area where the solidified
material adheres to the outer peripheral surface of the steel pipe, and achieving a
P frictional force or shearing force at the interface between the solidified material entering
the columnar groove portion and the surrounding solidified material so as to make the
columnar groove portion function as an anti-slipper, which makes it possible to further
improve the adhesive force. Thus, it is possible to improve the adhesive force with the
solidified material while maintaining increased compressive strength of the steel pipe
itself. Yet further, in the case where there exists a portion of the depression-provided
steel pipe where hardness suddenly increases, this portion exhibits deteriorated toughness
or ductility, and serves as crack-starting point. This crack is more likely to advance,
possibly causing deterioration in the compressive strength. However, by setting HA and
HB SO as to satisfy 0.95 5 HA/HB 5 1.05, it is possible to avoid the deterioration in the
compressive strength described above. In other words, by making the hardness uniform
throughout the steel pipe, it is possible to achieve excellent compressive strength.
Further, by adding the mill scale covering the surface of the depression-provided steel
pipe having the depressed portions and the columnar groove portions provided thereto, it
is possible to increase the adhesive force with the solidified material in a synergistic
manner.
According to the configuration described in (2) above, at any position along the
axis of the steel pipe, the percentage of the total circumferential length at the depressed
portion of the steel pipe relative to the entire perimeter of the depression-provided steel
pipe is set to 50% or less, whereby it is possible to avoid forrning the depressed portions
so as to concentrate on a specific position in the axial direction of the steel pipe.
Although, in the case where a large number of depressed portions are formed in a
concentrated manner in the circumferential direction of the steel pipe at the specific
position in the axial direction of the steel pipe, buckling is more likely to occur at this
position. However, with this configuration described in (2) above, it is possible to avoid
the occurrence of such buckling. Thus, it is possible to reliably suppress the reduction
in the compressive strength caused by the formation of the depressed portions, whereby it
is possible to achieve excellent adhesive force and compressive strength.
According to the configuration described in (3) above, the depressed portions are
arranged so as to form four lines in parallel, whereby it is possible to obtain excellent
adhesive force and compressive strength uniformly in the circumferential direction of the
steel pipe.
li According to the configuration described in (4) above, lines of depressed
portions adjacent in the circumferential direction of the steel pipe are formed so as to
have a phase difference of not less than 118 and not more than 112, whereby it is possible
to avoid the depressed portions being formed in a concentrated manner at the specific
position in the axial direction of the steel pipe. Thus, it is possible to reliably obtain
excellent adhesive force and compressive strength.
According to the configuration described in (5), depressed portions are arranged
so as to form six or more lines in parallel, whereby it is possible to obtain excellent
adhesive force and compressive strength uniformly in the circumferential direction of the
steel pipe.
According to the configuration described in (6), lines of depressed portions
adjacent in the circumferential direction of the steel pipe are formed so as to have a phase
difference of not less than 118 and not more than 112, and hence it is possible to avoid the
depressed portions being formed in a concentrated manner at a specific position in the
axiaI direction of the steel pipe. Thus, it is possible to reliably obtain excellent adhesive
force and compressive strength.
According to the configuration described in (7) above, each of the depressed
portions has an oval shape with a major axis parallel to the axial direction of the steel
pipe, whereby it is possible to increase the supporting force against the load acting in the
vertical direction.
According to the configuration described in (8) above, the depressed portion is
formed through the hot roll forming using a steel pipe processing roll having a surface
provided with the raised portion, whereby it is possible to form the depressed portions at
predetermined intervals along the axial direction of the steel pipe. Further, the mill scale
(hot scaled surface) can be added uniformly on the surface of the steel pipe. Thus, it is
possible to reliably obtain the effect of improving the adhesive force with the solidified
material and the compressive strength.
It should be noted that these effects of the invention are not impaired even if the
plating layer or resin layer is added as described in (9) above.
Further, the composite pile is formed by integrally driving the
depression-provided steel pipe according to any one of (1) to (9) above into the solidified
6 the reduction in the strength of the steel pipe itself while increasing the adhesive force
with the solidified material, whereby it is possible to provide a composite pile having
sufficient supporting force.
Brief Description of the Drawings
[OO 1 21
FIG. 1A is a front view partially illustrating a depression-provided steel pipe 1
according to a first embodiment of the present invention.
FIG. 1B is a sectional view taken along the line A1-A1 in FIG. 1A.
FIG. 1C is a sectional view taken along the line A2-A2 in FIG. 1A.
FIG. 1D is an enlarged view of a portion a in FIG. 1B.
FIG. 2A is a front view partially illustrating a depression-provided steel pipe 2
according to a second embodiment of the present invention.
FIG. 2B is a sectional view taken along the line B-B in FIG. 2A.
FIG. 3A is a front view partially illustrating a depression-provided steel pipe 3
according to a third embodiment of the present invention.
FIG. 3B is a sectional view taken along the line C-C in FIG. 3A.
FIG. 4A is a front view partially illustrating a depression-provided steel pipe 4
according to a fourth embodiment of the present invention.
FIG. 4B is a sectional view taken along the line D-D in FIG. 4A.
FIG. 5A is a front view partially illustrating a depression-provided steel pipe 5
according to a fifth embodiment of the present invention.
FIG. 5B is a sectional view taken along the line E-E in FIG. 5A.
FIG. 6A is a sectional view illustrating a composite pile according to a sixth
embodiment of the present invention.
FIG. 6B is a sectional view taken along the line F-F in FIG. 6A.
FIG. 7 is a graph illustrating a compressive strength of a depression-provided
steel pipe at the time of changing the ratio of the total length of depressed portions in the
circumferential direction of the steel pipe relative to the entire perimeter of the steel pipe.
FIG. 8 is a graph showing measurement results obtained by measuring adhesive
strength of three types of composite piles.
C Embodiments of the Invention
[OO 131
Hereinbelow, embodiments according to the present invention will be described
with reference to the drawings.
It should be noted that, in the present specification and the drawings, the same
reference characters are attached to constituting elements having substantially the same
function, and explanation thereof may not be repeated.
[00 141
[First Embodiment]
Below, with reference to FIG. lA to FIG. ID, a depression-provided steel pipe 1
according to a first embodiment of the present invention will be described.
[00 1 51
FIG. 1 A is a front view partially illustrating the depression-provided steel pipe 1
according to the first embodiment of the present invention. The depression-provided
steel pipe 1 extends in the axial direction of the steel pipe so as to have a predetermined
length, and for the purpose of explanation, part of the depression-provided steel pipe 1 is
illustrated in FIG. 1 A.
[00 1 61
As illustrated in FIG. 1 A, the depression-provided steel pipe 1 according to the
first embodiment of the present invention is formed by a steel pipe body 10 having a
substantially tubular shape. On the outer peripheral surface of this steel pipe body 10,
plural depressed portions 11 are formed. Further, a columnar groove portion 12 is
formed at the center of each of the depressed portions 11.
[00 171
As illustrated in FIG. 1 A, the plural depressed portions 1 1 are arranged at
predetermined intervals along the axial direction of the steel pipe, thereby forming a line
of depressed portions. Thus, as illustrated in FIG. 1B and FIG. 1 C, the
depression-provided steel pipe 1 has a cross-section located at a longitudinal position of
the steel pipe where the circumferential length at the depressed portion 11 of the steel
pipe is the longest, and a cross-section located at a longitudinal position of the steel pipe
where no depressed portion 11 is formed. Note that FIG. 1B is a sectional view taken
along the line AI-AI in FIG. 1 A, and FIG. 1C is a sectional view taken along the line
8/39
@ .
A2-A2 in FIG. 1 A.
[00 1 81
In the depression-provided steel pipe 1 according to this embodiment, only one
line of the depressed portions is provided. The depressed portions 11 are formed so as
to protrude in the direction toward the center of the axis of the steel pipe, in other words,
protrude inwardly of the steel pipe. With the depressed portions 11 being formed, the
solidified material such as concrete, cement, and soil cement enters the inside of the
depressed portions 11, which leads to an increase in the adhesive force.
[00 191
As illustrated in FIG. lA, the depressed portion 11 is formed into an oval shape
, having the major axis extending in parallel to the axial direction of the steel pipe,
whereby it is possible to obtain an effect of increasing the adhesive force while reducing
the circumferential length at the depressed portion 11 of the steel pipe. By setting the
direction of the major axis of the oval shape so as to match the axial direction of the steel
pipe, the circumferential length at the depressed portion 11 of the steel pipe can be
minimized, which makes it possible to suppress the reduction in the compressive strength
caused by the formation of the depressed portion 11 as much as possible. Thus, it is
desirable to form the depressed portion 11 into the oval shape having the major axis
extending in parallel to the axial direction of the steel pipe. The depressed portion 11
may have a circular shape or substantially rectangular shape.
[0020]
Further, the circumferential length L at the depressed portion 11 of the steel pipe
may be set to 50% or less, preferably 40% or less, more preferably 30% or less of the
entire perimeter R of the depression-provided steel pipe 1. More specifically, it is only
necessary that, in any positions in the axial direction of the steel pipe, the percentage of
the circumferential length L at the depressed portion 11 of the steel pipe relative to the
entire perimeter R of the depression-provided steel pipe 1 be 50% or less, preferably 40%
or less, more preferably 30% or less. In this case, it is possible to suppress the reduction
in the strength of the steel pipe itself caused by the formation of the depressed portion.
It should be noted that it is only necessary that the lower limit value at the
position in the axial direction of the steel pipe where the "percentage of the
circumferential length at the depressed portion of the steel pipe relative to the entire
I However, the lower limit value may be set to 10% or more, or 20% or more depending on
required adhesive forces.
[002 11
It should be noted that FIG. 1 D is an enlarged diagram illustrating a portion a in
FIG. 1B. As illustrated in FIG. ID, in this specification, the expression "circumferential
length at the depressed portion of the steel pipe" represents a direct distance L between
tangent points (P, P) of the common tangent line at both ends of the depressed portion in
the circumferential direction of the steel pipe. Further, the "entire perimeter of the
depression-provided steel pipe" represents a distance R along the outer peripheral surface
of the steel pipe at a longitudinal position of the steel pipe where no depressed portion is
formed (in other words, line B-B), or at a longitudinal position of the steel pipe where the
formation of the depressed portion is minimum.
[0022]
Below, description will be made of reasons that, at any positions in the axial
direction of the steel pipe, the percentage of the circumferential length L at the depressed
portion 11 of the steel pipe (in the second to the fifth embodiments, the total at a specific
position in the axial direction of the steel pipe) relative to the entire perimeter R of the '
depression-provided steel pipe 1 is 50% or less.
[0023]
The present inventors made a keen study, and found that, for example, in the
case where the depression-provided steel pipe is disposed at the center of the soil cement
pillar, (if a reduction in the strength is approximately 5%,) it is possible to obtain a
strength similar to a soil cement pillar having a diameter approximately ten times larger
than that of the steel pipe, and as compared with a soil cement pillar (improved body)
without any steel pipe being provided, it is possible to reduce the size of the soil cement
pillar to 115 resulting from an effect obtained by providing the depression-provided steel
pipe to secure the similar strength. In many cases, the size of the pillar is determined
according to the adhesive strength between the soil cement and the steel pipe, and even in
the case where the reduction in the strength of the steel pipe is 5% or less, the entire
strength of the soil cement pillar including the steel pipe hardly reduces, and this
reduction only has a slight effect on the entire strength. By reducing the size of the
10 / 39
pillar while maintaining the strength, it is possible to significantly reduce the number of
working processes. Reducing the diameter of the pillar to 115 means a reduction in the
volume of the soil cement pillar to 1/25, which leads to a significant reduction in the
materials and a significant increase in the number of soil cement pillars that can be
manufactured per day. On the other hand, in the case where the reduction in the strength
of the steel pipe largely exceeds 5%, the size of the pillar increases, and the
above-described effect reduces. From these findings, it can be determined that the
allowable reduction in the percentage of the strength (in particular, compressive strength)
of the steel pipe is 5% or less. Thus, by considering the condition for achieving 5% or
less, which is the allowable reduction in the percentage of the strength of the steel pipe, it
is desirable to satisfy L/R 5 0.5. Note that, in Examples described later, the condition
that the reduction in the strength of the steel pipe is 5% or less will be explained using a
graph.
100241
Further, in the depression-provided steel pipe 1 according to this embodiment, it
may be possible to set, to 50% or less, the percentage of the total M2 of the longitudinal
length of the depressed portion 11 of the steel pipe relative to the entire length M1 of the
depression-provided steel pipe 1 in the axial direction of the steel pipe. This is because
the compressive strength of the depression-provided steel pipe 1 tends to decrease in the
case where the total M2 of the longitudinal length of the depressed portion 11 of the steel
pipe exceeds 50% of the entire length M1 of the depression-provided steel pipe 1 in the
axial direction of the steel pipe.
It should be noted that the "longitudinal length of the depressed portion of the
1 steel pipe" represents a direct distance between tangent points of the common tangent line
at both ends of the depressed portion in the axial direction of the steel pipe.
100251
Further, at the center of each of the depressed portion 11, a columnar groove
portion 12 is provided so as to be depressed further deeper than the bottom surface of the
depressed portion 11 and extending along the axial direction of the steel pipe. The
solidified material further enters the columnar groove portion 12. Then, there occurs a
frictional force or shearing force at the interface between the solidified material entering
the columnar groove portion 12 and the solidified material existing in the vicinity, and
11 / 39
1 9 this columnar groove portion 12 functions as an anti-slipper, thereby further improving
the adhesive force in addition to the adhesive force resulting from the depressed portion
11. In other words, due to restriction on relative movement of the solidified material
and the steel pipe in the axial direction (catching effect), it is possible to increase the
adhesive force.
[0026]
The depth H of the columnar groove portion 12 is set in the range of not less
than 0.005D and not more than 0.2D, where D is an outside diameter of the
depression-provided steel pipe 1. In this specification, as illustrated in FIG. ID, the
depth H represents the deepest distance from the common tangent line at both ends of the
depressed portion 11 in the circumferential direction of the steel pipe. By setting the
depth H to 0.005D or more, it is possible to obtain a frictional force between the outer
peripheral surface of the steel pipe and the ground or the solidified material. On the
other hand, in the case where the depth H exceeds 0.2D, the effect of improving the
frictional force saturates.
[0027]
As described above, by forming the columnar groove portion at the center
portion of the depressed portion 11, it is possible to achieve excellent adhesive force and
excellent compressive strength. However, in the case where the depressed portion 11
and the columnar groove portion 12 are formed through cold working, the hardness of the
depressed portion 11 or columnar groove portion 12 significantly increases as compared
with the hardness at the midpoint between the depressed portions 11 and 11 adjacent in
the axial direction of the steel pipe (portion where no depressed portion 11 or columnar
groove portion 12 is formed). In this case, when the depression-provided steel pipe 1
receives a strong load, breakage is more likely to advance from a crack occurring at the
portion where toughness or ductility deteriorates, possibly causing the compressive
strength to deteriorate. For these reasons, in the depression-provided steel pipe 1
according to this embodiment, the depressed portion 11 and the columnar groove portion
12 are formed through hot working, thereby manufacturing the steel pipe such that the
average Vickers hardness HA at the depressed portion 11 and the Vickers hardness HB at
the midpoint between the depressed portions 11 and 11 adjacent to each other in the axial
rb With the HA/HB satisfying the above-described range, the entire steel pipe does
not have any point in which the hardness suddenly changes, and hence, it is possible to
avoid reducing the compressive strength as described above.
[0028]
Further, a mill scale (a hot scaled surface) is provided covering the surface of the
depression-provided steel pipe 1 according to this embodiment. Also, by forming the
mill scale on the depressed portion and the columnar groove portion, it is possible to
further improve the adhesive force of the depression-provided steel pipe 1 to the
solidified material. It is only necessary to apply the mill scale to 95% or more of the
outer peripheral surface of the depression-provided steel pipe 1 in terms of area.
[0029]
Further, on the mill scale, it may be possible to form at least one of a plating
layer and a resin layer.
[0030]
The depression-provided steel pipe 1 according to this embodiment is
manufactured, for example, by (1) with a roll unit for forming and forge welding,
rounding and forming a heated steel plate into a pipe-like shape, and jointing end portions
of the steel plate, thereby forming a steel pipe, and (2) then, under a condition of
temperatures in the range of approximately 600°C to 1350°C, pressing a steel pipe
processing roll having a raised portion corresponding to the depressed portion 11 and the
columnar groove portion 12 provided on the surface of the roll against the outer surface
of the steel pipe, and adding the depressed portion 11 and the columnar groove portion 12
uniformly in the axial direction.
With these processes, it is possible to form the depressed portion 11 and the
columnar groove portion 12 at uniform intervals in the axial direction of the steel pipe,
obtain uniform distribution of hardness, and apply the mill scale.
[003 11
[Second Embodiment]
Below, with reference to FIG. 2A and FIG. 2B, a depression-provided steel pipe 2
according to a second embodiment of the present invention will be described. The
depression-provided steel pipe 2 according to this embodiment is different from the
depression-provided steel pipe 1 according to the first embodiment in that four lines of
P the depressed portions are provided in this embodiment.
[0032]
FIG. 2A is a front view partially illustrating the depression-provided steel pipe 2
according to the second embodiment of the present invention. The depression-provided
steel pipe 2 extends in the axial direction of the steel pipe so as to have a predetermined
length, and for the purpose of explanation, part of the depression-provided steel pipe 2 is
illustrated in FIG. 2A.
[0033]
As illustrated in FIG. 2A, the depression-provided steel pipe 2 according to the
second embodiment of the present invention is formed by a steel pipe body 20 having a
substantially tubular shape. On the outer peripheral surface of the steel pipe body, plural
1 depressed portions 21 (21A to 21D) are formed. Further, at the center of each of the
I ' depressed portions 2 1 (2 1A to 2 ID), a columnar groove portion 22 (22A to 22D) is
I formed.
[0034]
As illustrated in FIG. 2A, these plural depressed portions 21 (21A to 21 D) are
formed at predetermined intervals along the axial direction of the steel pipe, thereby
forming four lines of depressed portions. Thus, as illustrated in FIG. 2B, the ~ depression-provided steel pipe 2 has a cross-section located at a longitudinal position of
the steel pipe where the total circumferential length at the depressed portion 21 of the
steel pipe is longest, and a cross-section located at a longitudinal position of the steel pipe
where no depressed portion is formed. Note that FIG. 2B is a sectional view taken along
the line B-B in FIG. 2A.
[003 51
Each of the depressed portions 2 1 (21A to 21D) is formed so as to protrude in
the direction toward the center of the axis of the steel pipe, in other words, protrude
inwardly of the steel pipe. With these depressed portions 2 1 (2 1A to 2 ID) being formed,
the solidified material such as concrete, cement, and soil cement enters the inside of the
depressed portions 2 1 (2 1A to 2 ID), which leads to an increase in the adhesive force.
[003 63
Further, the depression-provided steel pipe 2 according to this embodiment has
four lines of the depressed portions, which makes it possible to obtain excellent adhesive
@' force and compressive strength uniformly in the circumferential direction of the steel pipe.
In order to obtain this effect in a more favorable manner, it is preferable to set the lines of
depressed portions uniformly in the circumferential direction of the steel pipe as
illustrated in FIG. 2B. However, the lines of depressed portions are not necessarily set
uniformly. It may be possible to employ a configuration in which, of the four lines of
depressed portions, two adjacent lines of depressed portions are brought closer to each
other depending on locations where the depression-provided steel pipe 2 is installed, and
in terms of the symmetric position with respect to the axis of this steel pipe, the
remaining two adjacent lines of depressed portions are brought closer to each other, for
example.
[0037]
As illustrated in FIG. 2A, the depressed portions 21 (21A to 2 1D) are formed
into an oval shape having the major axis extending in parallel to the axial direction of the
steel pipe, whereby it is possible to obtain an effect of increasing the adhesive force while
reducing the circumferential length at the depressed portions 2 1 (2 1A to 2 1 D) of the steel
pipe. By setting the direction of the major axis of the oval shape so as to match the axial
direction of the steel pipe, the total circumferential length of the depressed portions 21
(21A to 21D) can be minimized, which makes it possible to suppress the reduction in the
compressive strength caused by the formation of the depressed portions 21 (21A to 21D)
as much as possible. Thus,% is desirable to fonn the depressed portions 21 (2 1A to
21D) into the oval shape ha4ng the major axis extending in parallel to the axial direction
of the steel pipe. The shape of the depressed portions 2 1 (2 1 A to 2 ID) may have a
circular shape or substantially rectangular shape.
[003 81
Further, the circumferential length at the depressed portions 2 1 (2 1 A to 2 1 D) of
the steel pipe may be set such that, at any positions in the axial direction of the steel pipe,
the percentage of the total LTotaol f the circumferential lengths L1 to L4 at the depressed
portions 2 1 (2 1 A to 2 1 D) relative to the entire perimeter R of the depression-provided
steel pipe 2 is 50% or less, preferably 40% or less, more preferably 30% or less. In
other words, the upper limit value of the L T ~ ~is~ s~et/ toR 0 .50 or less, preferably 40%,
more preferably 30%. The reason that "0.50 or less" is preferable has already been
explained in the first embodiment.
In the depression-provided steel pipe 2 according to this embodiment, the total.
LTotaol f the circumferential lengths L1 to L4 at the depressed portions 2 1 (2 1A to 21D) is
maximum at the line B-B in FIG. 2A, more specifically, at the center of each of the
depressed portions 2 1 (21A to 2 ID) in the axial direction of the steel pipe. Thus, in the
I
I
case of the depression-provided steel pipe 2 according to this embodiment, as illustrated
in FIG. 2B, it is only necessary to set the total LTotal of the circumferential lengths L1 to L4
at the depressed portions 2 1 (2 1A to 21D) to 50% or less of the entire perimeter R of the
depression-provided steel pipe 2. If the total LTotaol f the circumferential lengths L1 to
L4 of the steel pipe is 50% or less of the entire perimeter R of the depression-provided
steel pipe, it is possible to suppress the reduction in the strength of the steel pipe caused
by the formation of the depressed portions.
Thus, it is only necessary that the percentage of the total LTotaol f the
circumferential lengths L1 to L4 at the depressed portions of the steel pipe relative to the
entire perimeter R of the depression-provided steel pipe be set to 50% or less at any
positions in the axial direction of the steel pipe.
It should be noted that it is only necessary that the lower limit value at the
position in the axial direction of the steel pipe where "the percentage of the total LTotaol f
the circumferential lengths L1 to L4 at the depressed portions relative to the entire
perimeter R of the depression-provided steel pipe" is the maximum be set to more than
0%. However, the lower limit value may be set to 10% or more, or 20% or more
depending on required adhesive forces.
[0040]
Further, in the depression-provided steel pipe 2 according to this embodiment, it
may be possible to set each of the lines of the depressed portions such that the percentage
of the total M2 of the longitudinal lengths at the depressed portions 21 of the steel pipe
relative to the entire length M1 of the depression-provided steel pipe 2 in the axial
direction of the steel pipe is set to 50% or less. This is because, in the case where the
total M2 of the longitudinal lengths at the depressed portions 21 of the steel pipe exceeds
50% of the entire length M1 of the depression-provided steel pipe 2 in the axial direction
of the steel pipe, the compressive strength of the depression-provided steel pipe 2 tends to
decrease.
16 / 39
Further, at the center of each of the depressed portions 2 1 (2 1A to 2 ID), a
columnar groove portion 22 (22A to 22D) is formed so as to be depressed deeper than the
bottom surface of the depressed portion 21 and extend along the axial direction of the
steel pipe. The solidified material further enters the inside of the columnar groove
portion 22 (22A to 22D). Then, there occurs a frictional force or shearing force at the
interface between the solidified material entering the columnar groove portion 22 (22A to
22D) and the solidified material existing in the vicinity, and this columnar groove portion
22 functions as an anti-slipper, thereby further improving the adhesive force in addition
to the adhesive force resulting from the depressed portion 21. In other words, due to
restriction on relative movement of the solidified material and the steel pipe in the axial
direction (catching effect), it is possible to increase the adhesive force.
[0042]
The depth H of the columnar groove portion 22 (22A to 22D) is set in the range
of not less than 0.005D and not more than 0.2D, where D is an outside diameter of the
depression-provided steel pipe 2. By setting the depth H to 0.005D or more, it is
possible to obtain a frictional force between the outer peripheral surface of the steel pipe
and the ground or the solidified material. On the other hand, in the case where the depth
H exceeds 0.2D, the effect of improving the fictional force saturates.
[0043]
As in the description in the first embodiment, in the depression-provided steel
pipe 2 according to this embodiment, the average Vickers hardness HA at the depressed
portion 21 and the vickers hardness He at the midpoint between the depressed portions
21 and 21 adjacent to each other in the axial direction of the steel.pipe satisfy 0.95 5
HA/HB 5 1.05. With this setting, the entire steel pipe does not have any point in which
the hardness suddenly changes, and hence, it is possible to avoid reducing the
compressive strength.
[0044]
Further, a mill scale is provided covering the surface of the depression-provided
steel pipe'2 according to this embodiment. Also, by forming the mill scale on the
depressed portions and the columnar groove portion, it is possible to further improve the
adhesive force of the depression-provided steel pipe 1 to the solidified material. It is
-
only necessary to apply the mill scale to 95% or more of the outer peripheral surface of
the depression-provided steel pipe 1 in tenns of area.
[0045]
Further, on the mill scale, it may be possible to form at least one of a plating
layer and a resin layer.
[0046]
The depression-provided steel pipe 2 according to this embodiment is
manufactured, for example, by (1) with a roll unit for forming and forge welding,
rounding and forming a heated steel plate into a pipe-like shape, and jointing end portions
of the steel plate, thereby forming a steel pipe, and (2) then, under a condition of
temperatures in the range of approximately 600°C to 1 350°C, pressing four rolls for
forming a steel pipe having a raised portion corresponding to the depressed portion 21
and the columnar groove portion 22 provided on the surface of the roll against the outer
surface of the steel pipe, and adding the depressed portions 21 and the columnar groove
portions 22 uniformly in the axial direction.
With these processes, it is possible to form the depressed portions 2 1 (2 1 A to
21D) and the columnar groove portions 22 (22A to 22D) at uniform intervals in the axial
direction of the steel pipe, obtain uniform distribution of hardness, and apply the mill
scale.
[0047]
[Third Embodiment]
Below, with reference to FIG. 3A and FIG. 3B, a depression-provided steel pipe 3
according to the third embodiment of the present invention will be described. The
depression-provided steel pipe 3 according to this embodiment is different from the
depression-provided steel pipe 2 according to the second embodiment in that lines of the
depressed portions adjacent in the circumferential direction of the steel pipe are provided
so as to have a phase difference in the axial direction of the steel pipe in this embodiment.
Elements that have been already explained will not be repeated.
[0048]
FIG. 3A is a front view partia1Iy illustrating the depression-provided steel pipe 3
according to the third embodiment of the present invention. The depression-provided
steel pipe 3 extends in the axial direction of the steel pipe so as to have a predetermined
-
length, and for the purpose of explanation, part of the depression-provided steel pipe 3 is
illustrated in FIG. 3A.
[0049]
As illustrated in FIG. 3A, the depression-provided steel pipe 3 according to the
third embodiment of the present invention is formed by a steel pipe body 30 having a
substantially tubular shape and including plural depressed portions 3 1 (3 1 A to 3 1 D) and a
columnar groove portion 32 (32A to 32D) formed at the center of each of the depressed
portions 3 1.
[OOSO]
As illustrated in FIG, 3A, the plural depressed portions 3 1 (3 1A to 3 ID) are
formed at predetermined intervals along the axial direction of the steel pipe, thereby
forming four lines of depressed portions. Further, unlike the depression-provided steel
pipe 2 according to the second embodiment, the depression-provided steel pipe 3
according to the third embodiment has the depressed portions 3 1 (3 1A to 3 ID) formed
such that lines of the depressed portions adjacent in the circumferential direction of the
steel pipe are arranged with a 112 phase difference. Thus, the depression-provided steel
pipe 3 has a cross-section located at a longitudinal position of the steel pipe where the
total circumferential length at the depressed portion 3 1 (3 1A to 3 ID) of the steel pipe is
longest (in other words, FIG. 3B), and a cross-section located at a longitudinal position of
the steel pipe where the total circumferential length at the depressed portion 3 1 (3 1A to
3 1D) of the steel pipe is shortest. Note that FIG. 3B is a sectional view taken along the
line C-C in FIG. 3A.
In this specification, the expression "lines of the depressed portions have a phase
difference" means a state in which lines of the depressed portions adjacent in the
circumferential direction are positionally shifted in the axial direction of the steel pipe.
Further, for example, the expression "112 phase difference" means a state in which lines
of the depressed portions adjacent in the circumferential direction are positionally shifted
in the axial direction of the steel pipe by a distance of 112 of a distance between centers of
the depressed portions adjacent in the axial direction of the steel pipe.
[005 11
As described above, in the case where the phase difference is provided, the LTotal
at the position where the LTotails maximum in the axial direction of the steel pipe can be
19 / 39
* suppressed only to the total of L1 and L3 as illustrated in FIG. 3B. Thus, it is possible to
increase the depth of or the circumferential length at the depressed portions 3 1 (3 1A to
3 ID) of the steel pipe while suppressing the value of LTotal/Rto 50% or less. Thus, it is
possible to achieve further excellent compressive strength while achieving the adhesive
force with the same level as that of the depression-provided steel pipe 2 according to the
second embodiment described above.
[0052]
In the depression-provided steel pipe 3 according to this embodiment, although
the lines of the depressed portions adjacent to each other are arranged with the 112 phase
difference, it may be possible to set the phase difference to less than 112, for example to a
114 phase difference, a 116 phase difference, or a 118 phase difference. However, even if
the phase difference of less than 118 is applied, the effect obtained by the application of
the phase difference is small. Thus, in the case where the phase difference is applied, it
is preferable to apply the phase difference in the range of 118 to 112. Further, it may be
' possible to employ a configuration in which, rather than applying the phase difference to
all the four lines of the depressed portions, the phase difference is applied only to one line
of the depressed portions with respect to the other three lines of the depressed portions.
[0053]
[Fourth Embodiment]
Below, with reference to FIG. 4A and FIG. 4B, a depression-provided steel pipe 4
according to a fourth embodiment of the present invention will be described. The
depression-provided steel pipe 4 according to this embodiment is different from the
depression-provided steel pipe 1 according to the first embodiment in that six lines of the
depressed portions are provided in this embodiment.
[0054]
FIG. 4A is a front view partially illustrating the depression-provided steel pipe 4
according to the fourth embodiment of the present invention. The depression-provided
steel pipe 4 extends in the axial direction of the steel pipe so as to have a predetermined
length, and for the purpose of explanation, part of the depression-provided steel pipe 4 is
1
illustrated in FIG. 4A.
[0055]
As illustrated in FIG. 4A, the depression-provided steel pipe 4 according to the
20 / 39
Ib fourth embodiment of the present invention is formed by a steel pipe body 20 having a
substantially tubular shape. On the outer peripheral surface of the steel pipe body, plural
depressed portions 4 1 (4 1 A to 4 1F) are formed. Further, at the center of each of the
depressed portions 4 1 (4 1 A'to 4 1 F), a columnar groove portion 42 (42A to 42F) is
formed.
[0056]
As illustrated in FIG. 4A, these plural depressed portions 41 (41 A to 41 D) are
formed at predetermined intervals alang the axial direction of the steel pipe, thereby
forming six lines of depressed portions. Thus, as illustrated in FIG. 4B, the
depression-provided steel pipe 4 has a cross-section located at a longitudinal position of
the steel pipe where the total circumferential length at the depressed portion 4 1 of the
steel pipe is longest, and a cross-section located at a longitudinal position of the steel pipe
where no depressed portion is formed. Note that FIG. 4B is a sectional view taken along
the line D-D in FIG. 4A.
[0057]
The depressed portions 41 (41A to 41F) are formed so as to protrude in the
direction toward the center of the axis of the sted pipe, in other words, protrude inwardly
of the steel pipe. With the depressed portions 41 (41A to 41F) being formed, the
solidified material such as concrete, cement, and soil cement enters the inside of the
depressed portions 41 (41A to 41F), which leads to an increase in the adhesive force.
[005 81
Further, the depression-provided steel pipe 4 according to this embodiment has
six lines of the depressed portions, which makes it possible to obtain excellent adhesive
force and compressive strength uniformly in the circumferential direction of the steel pipe.
In order to obtain this effect in a more favorable manner, it is preferable to set the lines of
depressed portions uniformly in the circumferential direction of the steel pipe as
illustrated in FIG: 4B. However, the lines of depressed portions are not necessarily set
uniformly. It may be possible to employ a configuration in which, of the six lines of
depressed portions, adjacent three lines of depressed portions are brought closer to each
other depending on locations where the depression-provided steel pipe 4 is placed, and in
terms of the symmetric position with respect to the axis of this steel pipe, the remaining
adjacent three lines of depressed portions are brought closer to each other, for example.
21 I39
As iliustrated in FIG. 4A, the depressed portions 4 1 (4 1 A to 4 1 F) are formed into
an oval shape having the major axis extending in parallel to the axial direction of the steel
pipe, whereby it is possible to obtain an effect of increasing the adhesive force while
reducing the circumferential length at the depressed portion 4 1 (4 1 A to 4 1 F) of the steel
pipe. By setting the direction of the major axis of the oval shape so as to match the axial
direction of the steel pipe, the total circumferential length of the depressed portion 4 1
(41A to 41F) of the steel pipe can be minimized, which makes it possible to suppress the
reduction in the compressive strength caused by the formation of the depressed portions
41 (41A to 41F) as much as possible. Thus, it is desirable to form the depressed portion
41 (41A to 41F) into the oval shape having the major axis extending in parallel to the
axial direction of the steel pipe. The shape of the depressed portion 4 1 (4 1 A to 4 1 F)
may have a circular shape or substantially rectangular shape.
[0060]
Further, the circumferential length at the depressed portions 4 1 (4 1 A to 4 1 F) of
the steel pipe may be set such that, at any positions in the axial direction of the steel pipe,
the percentage of the total LTotaol f the circumferential lengths L1 to L6 at the depressed
portions 4 1 (4 1 A to 4 IF) relative to the entire perimeter R of the depression-provided
steel pipe 4 is 50% or less, preferably 40% or less, more preferably 30% or less. In
other words, the upper limit value of the LTotal/Ris set to 0.50 or less, preferably 40%,
more preferably 30%. The reason that "0.50 or less" is preferable has already been
explained in the first embodiment.
[0061]
In the depression-provided steel pipe 4 according to this embodiment, the total
LTotaol f the circumferential lengths L1 to L6 at the depressed portion 41 (41A to 41F) is
maximum at the line D-D in FIG. 4A, more specifically, at the center of each of the
depressed portions 41 (21A to 21F) in the axial direction of the steel pipe. Thus, in the
case of the depression-provided steel pipe 4 according to this embodiment, as illustrated
in FIG. 4B, it is only necessary to set the total LTotaol f the circumferential lengths L1 to L6
at the depressed portions 4 1 (4 1A to 4 IF) of the steel pipe to 50% or less of the entire
perimeter R of the depression-provided steel pipe 4.
If the total LTotal of the circumferential lengths L1 to L6 of the steel pipe is 50%
or less of the entire perimeter R of the depression-provided steel pipe, it is possible to
suppress the reduction in the strength of the steel pipe caused by the formation of the
depressed portions. Thus, it is only necessary that the percentage of the total LTotaolf
the circumferential lengths L1 to L6 at the depressed portions of the steel pipe relative to
the entire perimeter R of the depression-provided steel pipe be set to 50% or less at any
positions in the axial direction of the steel pipe.
It should be noted that it is only necessary that the lower limit value at the
position in the axial direction of the steel pipe where "the percentage of the total LTotaol f
the circumferential lengths L1 to L6 at the depressed portions relative to the entire
perimeter R of the depression-provided steel pipe" is the maximum be set to more than
0%. However, the lower limit value may be set to 10% or more, or 20% or more
depending on required adhesive forces.
[0062]
Further, in the depression-provided steel pipe 4 according to this embodiment, it
may be possible to set each of the lines of the depressed portions such that the percentage
of the total M2 of the longitudinal lengths at the depressed portions 41 of the steel pipe
relative to the entire length Ml of the depression-provided steel pipe 4 in the axial
direction of the steel pipe is set to 50% or less. This is because, in the case where the
total M2 of the longitudinal lengths at the depressed portions 41 of the steel pipe exceeds
50% of the entire length M1 of the depression-provided steel pipe 4 in the axial direction
of the steel pipe, the compressive strength of the depression-provided steel pipe 4 tends to
decrease.
[0063]
Further, at the center of each of the depressed portions 4 1 (4 1A to 4 1 F), a
columnar groove portion 42 (42A to 42F) is formed so as to be depressed deeper than the
bottom surface of the depressed portion 41 and extend along the axial direction of the
steel pipe. The solidified material further enters the inside of the columnar groove
portion 42 (42A to 42F). Then, there occurs a frictional force or shearing force at the
interface between the solidified material entering the columnar groove portion 42 (42A to
42F) and the solidified material existing in the vicinity, and this columnar groove portion
42 functions as an anti-slipper, thereby further improving the adhesive force in addition
to the adhesive force resulting from the depressed portion 41. In other words, due to
23 / 39
4B restriction on relative movement of the solidified material and the steel pipe in the axial
direction (catching effect), it is possible to increase the adhesive force.
[0064]
The depth H of the columnar groove portion 42 (42A to 42F) is set in the range
of not less than 0.005D and not more than 0.2D, where D is an outside diameter of the
depression-provided steel pipe 4. By setting the depth H to 0.005D or more, it is
possible to obtain a frictional force between the outer peripheral surface of the steel pipe
and the ground or the solidified material. On the other hand, in the ease where the depth
H exceeds 0.2D, the effect of improving the frictional force saturates.
100651
As in the description in the first embodiment, in the depression-provided steel
pipe 4 according to this embodiment, the average'vickers hardness HA at the depressed
portion 41 and the Vickers hardness HB at the midpoint between the depressed portions
41 and 41 adjacent to each other in the axial direction of the steel pipe satisfy 0.95 5
HA/HB 5 1.05. With such a setting, the entire steel pipe does not have any point in
which the hardness suddenly changes, and hence, it is possible to avoid reducing the
compressive strength.
[0066]
Further, a mill scale is provided on the surface of the depression-provided steel
pipe 4 according to this embodiment. Also, by forming the mill scale on the depressed
portions and the columnar groove portions, it is possible to further improve the adhesive
force of the depression-provided steel pipe to the solidified material. It is only
necessary to apply the mill scale to 95% or more of the outer peripheral surface of the
depression-provided steel pipe 1 in terms of area.
[0067]
I Further, on the mill scale, it may be possible to form at least one of a plating
layer and a resin layer.
[0068]
The depression-provided steel pipe 4 according to this embodiment is
manufactured, for example, by (1) with a roll unit for forming and forge welding,
rounding and forming a heated steel plate into a pipe-like shape, and jointing end portions
of the steel plate, thereby forming a steel pipe, and (2) then, pressing six rolls for forming
24 / 39
a steel pipe having a raised portion corresponding to the depressed portion 41 and the
columnar groove portion 42 provided on the surface' of the roll against the outer surface
of the steel pipe, thereby adding the depressed portion 41 and columnar groove portion
42 uniformly in the axial direction.
With these processes, it is possible to form the depressed portions 41 (41A to
41F) and the columnar groove portions 42 (42A to 42F) at uniform intervals in the axial
direction of the steel pipe, obtain uniform distribution of hardness, and apply the mill
scale.
[0069]
[Fifth Embodiment]
Below, with reference to FIG. 5A and FIG. 5B, a depression-provided steel pipe 5
according to a fifth embodiment of the present invention will be described. The
depression-provided steel pipe 5 according to this embodiment is different from the
depression-provided steel pipe 4 according to the fourth embodiment in that lines of
depressed portions adjacent in the circumferential direction of the steel pipe are provided
so as to have a phase difference in the axial direction of the steel pipe in this embodiment.
Elements that have been already described will not be repeated.
[0070]
FIG. 5A is a front view partially illustrating the depression-provided steel pipe 5
according to the fifth embodiment of the present invention. The depression-provided
steel pipe 5 extends in the axial direction of the steel pipe so as to have a predetermined
length, and for the purpose of explanation, part of the depression-provided steel pipe 5 is
illustrated in FIG. 5A.
[0071]
As illustrated in FIG. 5A, the depression-provided steel pipe 5 according to the
fifth embodiment of the present invention is formed by a steel pipe body 50 having a
substantially tubular shape and including plural depressed portions 5 1 (5 1 A to 5 1 F) and a
columnar groove portion 52 (52A to 52D) formed at the center of each of the depressed
portions 5 1.
[0072]
As illustrated in FIG. 5A, the plural depressed portions 5 1 (5 1 A to 5 IF) are
formed at predetermined intervals along the axial direction of the steel pipe, thereby
pipe 4 according to the fourth embodiment, the depression-provided steel pipe 5
according to the fifth embodiment has the depressed portions 5 1 (5 1A to 5 1F) formed
such that lines of the depressed portions adjacent in the circumferential direction of the
steel pipe are arranged with a 116 phase difference. Thus, the depression-provided steel
pipe 5 has a cross-section located at a longitudinal position of the steel pipe where the
total circumferential length at the depressed portion 5 1 (5 1A to 5 IF) of the steel pipe is
longest (in other words, FIG. 5B), and a cross-section located at a longitudinal position of
the steel pipe where the total circumferential length at the depressed portion 5 1 (5 1A to
51F) of the steel pipe is shortest. Note that FIG. 5B is a sectional view taken along the
line E-E in FIG. 5A.
[0073]
As described above, in the case where the phase difference is provided, the LTotal
at the position where the LTotails maximum in the axial direction of the steel pipe can be
suppressed as illustrated in FIG. 5B. Thus, it is possible to increase the depth of or the
circumferential length at the depressed portions 5 1 (5 1A to 5 1F) of the steel pipe while
suppressing the value of LTotal/Rto 50% or less. Thus, it is possible to achieve further
excellent compressive strength while achieving the adhesive force with the same level as
that of the depression-provided steel pipe 4 according to the fourth embodiment described
1 above.
[0074] : In the depression-provided steel pipe 5 according to this embodiment, although
the lines of the depressed portions adjacent to each other are arranged with the 116 phase
difference, it may be possible to set the phase difference, for example, to 112, 114, or 118.
i However, even if the phase difference of less than 118 is applied, the effect obtained by
the application of the phase difference is small. Thus, in the case where the phase
difference is applied, it is preferable to apply the phase difference in the range of 118 to
112. Further, it may be possible to employ a configuration in which, rather than
applying the phase difference to all the six lines of the depressed portions, the phase
difference is applied to only one line of the depressed portions with respect to the other
five lines of the depressed portions.
[0075]
Q, [Sixth Embodiment]
With the depression-provided steel pipes 1 to 5 according to the first to fifth
embodiments, it is possible to form a composite pile used mainly for making a civil
engineering and construction structure, by integrally embedding the depression-provided
steel pipes into the solidified material such as concrete, cement, and soil cement. Below,
as an example, a composite pile 100 using the depression-provided steel pipe according
to the first embodiment will be described.
[0076]
FIG. 6A and FIG. 6B illustrate the composite pile 100 obtained by integrally
embedding the depression-provided steel pipe 1 according to the first embodiment into
soil cement S as the solidified material. FIG. 6A is a schematic sectional view
illustrating a side face of the composite pile 100, and FIG. 6B is a plan sectional view
schematically illustrating the composite pile 100.
[0077]
As illustrated in FIG. 6A and FIG. 6B, the composite pile 100 is configured by
installing the depression-provided steel pipe 1 into the soil cement S in a form 11 0
provided in the ground G, and solidifying the soil cement S.
It should be noted that, in order to obtain sufficient strength, the composite pile
100 needs to have sufficient adhesive strength between the depression-provided steel pipe
1 and the soil cement S.
In the case where the same soil cement S is used, the adhesive strength of the
composite pile 100 depends on the shape of the steel pipe installed. With the
depression-provided steel pipe 1 according to this embodiment, it is possible to obtain
suEcient adhesive strength.
[0078]
With the depression-provided steel pipe 1 described with reference to the
drawings above, it is possible to increase the adhesive force between the steel pipe and
the solidified material while suppressing the reduction in the strength of the steel pipe
itself.
Fmther, with this depression-provided steel pipe 1, it is possible to achieve the
composite pile 100 having sufficient adhesive strength while suppressing the reduction in
the strength of the steel pipe itself.
0
In other words, with the depression-provided steel pipe 1 having sufficient
strength, it is possible to form the composite pile having the adhesive strength (adhesive
force) while minimizing the reduction in the strength thereof, whereby it is possible to
form the civil engineering and construction structure in an economical manner.
[0079]
The above describes examples of the embodiment according to the present
invention. However, the present invention is not limited thereto. For example,
although, in the description above, the number of lines of the depressed portions is set to
1,4, and 6, the number may be set to 2,3,5,7 or more.
While preferred embodiments of the invention have been described and
illustrated above, it should be understood that these are exemplary of the invention and
are not to be considered as limiting. Additions, omissions, substitutions, and other
modifications can be made without departing from the scope of the present invention.
Accordingly, the invention is not to be considered as being limited by the foregoing
description, and is only limited by the scope of the appended claims.
Examples
[0080]
[Example 11
Steel pipes 1 to 14 having a diameter (outside diameter) of 76.3 rnm and a length
in the axial direction of the steel pipe of 300 mm were manufactured from a steel plate
having a thickness of 4.5 mm.
[OOS 11
More specifically, the steel pipe 1 according to an example of the present
invention was manufactured by: with a roll unit for forming and forge welding, rounding
a heated steel plate to form it into a pipe-like shape; jointing end portions of the steel
plate, thereby forming a steel pipe; then, under a condition of a temperature of
approximately 800°C, pressing a steel pipe processing roll having a surface provided with
a raised portion with a shape corresponding to the depressed portion and the columnar
groove portion against the outer surface of the steel pipe formed above, thereby adding
the depressed portion and the columnar groove portion uniformly in the axial direction.
The steel pipe 2 serving as Comparative Example was manufactured by: with a
e roll unit for forming and forge welding, rounding a heated steel plate to form it into a
pipe-like shape; jointing end portions of the steel plate, thereby forming a steel pipe;
cooling the steel pipe; and forming a depressed portion through cold working.
The steel pipe 3 serving as Comparative Example was manufactured by: with a
roll unit for forming and forge welding, rounding a heated steel plate to form it into a
pipe-like shape; jointing end portions of the steel plate, thereby forming a steel pipe.
The steel pipe 4 serving as Comparative Example was manufactured by: with a
roll unit for forming and forge welding, rounding a heated steel plate to form it into a
pipe-like shape; jointing end portions of the steel plate, thereby forming a steel pipe; then,
under a condition of temperatures of approximately 800°C, pressing a roll having a
surface provided with a protrusion having a shape corresponding to the depressed portion
against the outer surface of the steel pipe formed above, thereby adding only the
depressed portions uniformly in the axial direction.
The steel pipes 4 to 12 are examples of the present invention manufactured by
changing the manufacturing conditions applied to the steel pipe 1.
Table 1 and Table 2 show specific manufacturing conditions for the steel pipes 1
to 14.
[Table 11
Method of
forming
depressed
portion
Hot
Cold
Hot
Hot
Hot
Hot
Hot
Hot
Hot
Hot
fiat
Circumferent
ial length
at depressed
porti& of
steel pipe
mm
23
23
23
23
23
23
23
23
23
23
23
Steel
pipe 1
Steel
pipe 2
Steel
pipe 3
Steel
pipe 4
Steel
pipe 5
Steel
pipe 6
Steel
pipe 7
Steel
pipe 8
Steel
pipe 9
Steel
pipe 10
Steel
pipe 11
Steel
pipe 12
Distance
between
centers of
depressed
portion
adjacent in
axial direction
of steel pipe
mm
45
45
45
45
45
45
45
45
45
45
45
Lines of
depressed
portion
8
8
0
8
1
4
6
8
8
8
8
8
Length at
depressed
portion in
the axial
direction of
steel pipe
mm
30
30
30
30
30
30
30
30
30
30
30
Phase
difference
No exist
No exist
No exist
No exist
No exist
112
114
118
111 6
No exist
Shape of
depressed
portion
Oval
Oval
Oval
Oval
Oval
Oval
Oval
Oval
Oval
Oval
Oval
Extending direction of
depressed portion
Axial direction of
steel pipe
Axial direction of
steel pipe
Axial direction of
steel pipe
Axial direction of
steel pipe
Axial direction of
steel pipe
Axial direction of steel
pipe
Axial direction of
steel pipe
Axial direction of
steel pipe
Axial direction of
steel pipe
Axial direction of
steel pipe
45" tilted to Axial
direction of steel pipe
[Table 21
[0084]
For the steel pipes 1 to 14, measurement was made on "average hardness HA of
the depressed portion," "hardness HB at the midpoint between depressed portions adjacent
in the axial direction of the steel pipe," "HA/€-I~,""p resence or absence of mill scale,"
"compressive strength," and "adhesive force." Table 3 shows the results of the
measurement.
Longitudinal
length at
columnar
groove portlon
of steel pipe
mm
20
20
20
20
20
20
20
20
20
20
Steel
PlPe 1
Steel
Pipe 2
Steel
PlPe 3
. Steel
PlPe 4
Steel
, Pipe 5
Steel
Pipe 6
Steel
PiPC 7
Steel
PlPe 8
Steel
Pipe 9
Steel
pipe 10
Steel
pipe 11
Steel
pipe 12
LT~WIR
76 99
76 99
76 99
9 62
38 49
57 74
50 21
46 03
44 35
71 13
109 21
Entire
per~meterR
of steel plpe
mm
239
239
239
239
239
239
239
239
239
239
239
239
Total
circumferential
length LTod at
depressed portion
mm
184
184
184
23
92
138
120
110
106
170
261
Formation
of columnar
groove
portion
Formed
Formed
Not formed
Not formed
Formed
Formed
Formed
Formed
Formed
Formed
Formed
Formed
Depth H of
coIumnar
groove
port~on
mm
2
2
2
2
2
2
2
2
2
2
C~rcurnferential
length at
columnar groove
portion of steel
PlPe
mm
3
3
3
3
3
3
3
3
3
3
[0085]
[Table 31
The "average hardness HA of the depressed portion" and the "hardness HB at the
midpoint between depressed portions adjacent in the axial direction of the steel pipe"
were measured such that a piece including the depression is cut from the target steel pipe
to create a sample, and measuring the thickness center using a hardness meter. Five
points of data were measured, and were averaged as representative data. 10 or more
points of judging data were taken, and the taken data were used to obtain the average
hardness and variation of the hardness.
[0087]
The "presence or absence of mill scale " was obtained through visual
observation.
[0088]
For measurement of the "compressive strength," a steel piece with a length
corresponding to two times the outside diameter of the target steel pipe was cut from the
target steel pipe, and end-surface preparation was applied to obtain a sample. Tests
were conducted by applying static load while paying attention to applying the load
equally on cross-sectional area of the steel pipe with a compressive tester. Three
32 1 39
Steel pipe 1
Steel pipe 2
Steel pipe 3
Steel pipe 4
Steel pipe 5
Steel pipe 6
Steel pipe 7
Steel pipe 8
Steel pipe 9
Steel pipe 10
Steel pipe 11
Steel pipe 12
Average
hardness
HA of
depressed
portion
HV
202
227
-
201
202
201
199
205
202
201
202
203
Hardness HB at
midpoint
between
depressed
portions adjacent
in axial direction
of steel pipe
HV
196
196
196
194
194
199
199
205
199
206
196
HAMB
1.03
1.16
1.03
1.04
1.04
1 .OO
1.03
0.99
1.01
0.98
1.04
Presence or
absence of mill
scale
Exist
No exist
Exist
Exist
Exist
Exist
Exist
Exist
Exist
Exist
Exist
Exist
Compressive
strength
kN
204.3
132.8
232.0
204.3
232.8
228.1
218.9
223.2
225.0
225.9
209.1
166.9
Adhesive force
kNlm
4.1
4.1
0.4
2.5
0.9
2.3
3.2
4.1
4.1
4.1
4.1
4.1
samples were used for each target steel pipe, and were subjected to the tests, and the
, compressive strength was judged on the basis of the average of the maximum values in
the load history through the measurement.
For measurement of the "adhesive force," a soil cement pillar was prepared by
placing the target steel pipe at the center of the soil cement pillar such that the soil cement
pillar has a diameter approximately three times larger than the diameter of the steel pipe
and a length 3.5 times longer than the length of the steel pipe. The top of the steel pipe
protrudes from the soil cement pillar by approximately 50 rnrn, which makes it possible
for the driving load to act only on the steel pipe. The lower part of the soil cement pillar
is suaorted by a base mount while the lower part of the steel pipe is not supported,
which allows only the steel pipe to move when a downward load in the vertical direction
is applikd. After the steel pipe and the soil cement pillar are prepared as described
above, 28 days of maturation period required for solidifying the soil cement was set, and
a load-applying test was performed by applying a static load downwardly pressing to the
top of the steel pipe. Then, the measured compressive load is divided by the outer
peripheral area where the steel pipe is contacted with the soil cement, thereby calculating
the adhesive force. The test was performed for three samples in two-different
compressive strength of soil cement, and the adhesive force was judged.
The steel pipe 1 satisfies all the requirements for the present invention, thereby
achieving excellent compressive strength and adhesive force.
The steel pipe 2 has the depressed portion formed through the cold working,
which generates a portion having the excessively large average hardness HA of the
depressed portion. This leads to a significant reduction in the compressive strength as
compared with the steel pipe 1.
The steel pipe 3 does not have the depressed portion or the columnar groove
portion formed thereto, and hence, the adhesive force significantly reduces as compared
with the steel pipe 1.
The steel pipe 4 only has the depressed portion formed thereto and does not have
the columnar groove portion formed thereto, and hence, the adhesive force reduces as
compared with the steel pipe 1.
Further, the steel pipes 5 to 12, which were manufactured with various
33 1 39
conditions different from that for the steel pipe 1, achieved excellent compressive
strength and adhesive force.
[0090]
[Example 21
As Example 2 according to the present invention, measurement was performed
for the depression-provided steel pipe on how compressive yield strength of the
depression-provided steel pipe changes when the percentage of the total circumferential
length at the depressed portions of the steel pipe relative to the entire perimeter of the
steel pipe is varied.
[0091]
FIG. 7 is a graph showing the compressive strength of the depression-provided
steel pipe when the percentage of the total circumferential length at the depressed
portions of the steel pipe relative to the entire perimeter of the steel pipe is varied. The
vertical axis represents values of the compressive yield strength of the steel pipe, the
values being made non-dimensional by load at the guaranteed yield point of the straight
steel pipe (straight pipe), and the horizontal axis represents percentages of the total
circumferential length at the depressed groove portions of the steel pipe relative to the
entire perimeter of the steel pipe.
As can be clearly understood from FIG. 7, the compressive yield strength of the
steel pipe decreases with the increase in the percentage of the total circumferential length
at the depressed portions relative to the entire perimeter of the steel pipe.
In particular, it is found that, in the case where the percentage of the total
circumferential length at the depressed portions of the steel pipe relative to the entire
perimeter of the steel pipe exceeds 0.5, in other words, in the case where the depressed
portions account for over 50% of the entire perimeter of the steel pipe, the compressive
yield strength of the steel pipe significantly decreases.
[0092]
As described in the embodiments above, for the general steel pipes, the
allowable decrease in the strength (in particular, compressive yield strength) of the steel
pipe is 5% or less.
From the graph shown in FIG. 7, it is obvious that, in the case where the
percentage of the total circumferential length at the depressed portion of the steel pipe
I@
relative to the entire perimeter of the steel pipe exceeds 50%, the compressive yield
strength of the steel pipe is less than 0.95. Thus, it can be understood that it is
preferable to set the percentage of the total circumferential lengths at the depressed
portions relative to the entire perimeter to 50% or less.
[0093]
[Example 31
Further, as Example 3, in order to confirm the advantage in the adhesive strength
in the case where a composite pile is formed using the depression-provided steel pipe,
composite piles with the soil cement were manufactured using three types of steel pipes:
(1) straight steel pipe;
(2) recess-provided steel pipe obtained by machining a part of the surface of the straight
steel pipe through cold working, and forming a recessed portion to form the
recess-provided steel pipe illustrated in FIG. 2A and FIG. 2B; and
(3) depression-provided steel pipe according to the present invention illustrated in FIG.
2A and FIG. 2B.
It 'should be noted that the composite piles manufactured have a configuration as
illustrated in FIG. 6A and FIG. 6B.
[0094]
.FIG 8 is a graph showing measurement results obtained by driving the
above-described three types of steel pipes (straight steel pipe, recess-provided steel pipe
(surface-removed steel pipe), and depression-provided steel pipe) into the soil cement to
manufacture composite piles, and measuring the adhesive strength of these composite
piles.
It should be noted that, in FIG. 8, the vertical axis represents the adhesive force
fs (kN/m) between the steel pipe and the soil cement, and the horizontal axis represents
single-axis compressive strength qu (MPa) of the soil cement.
[0095]
As illustrated in FIG 8, it was confirmed that, of the composite piles
manufactured using the three types of the steel pipes (straight steel pipe, surface-removed
steel pipe, and depression-provided steel pipe), the largest adhesive strength can be
obtained from the composite pile manufactured using the depression-provided steel pipe
(denoted as roll-depressed steel pipe in FIG. 8) and measured on the adhesive strength.
lndustrial Applicability
[0096]
The present invention is applicable to the depression-provided steel pipe and the
composite pile used for forming the civil engineering and construction structure,
Reference Signs List
[0097]
192,3,4,5 Depression-provided steel pipe
lO92O, 30,40, 50 Steel pipe body
l l y 21,31, 419 51 Depressed portion
12,22,32,42, 52 Columnar groove portion
100 Composite pile
110 Form
R Entire perimeter of steel pipe
H Depth at the deepest portion of columnar groove portion
9 Outside diameter of steel pipe
S Soil cement (solidified material)
L Circumferential length at depressed portion of steel pipe
LTotal Total circumferential length at depressed portion of steel pipe

1)
CLAIM
1. A depression-provided steel pipe having plural depressions on an outer
peripheral surface , the depressions being formed so as to form a line along an axial
direction of the steel pipe, whereineach of the depressed portions has, inside thereof, a
columnar groove portion extending along the axial direction of the steel pipe and
depressed deeper than a bottom surface of these depressed portions;
0.95 F HA& F 1.05 is satisfied, where HA is an average Vickers hardness in
each of the depressed portions, and HB is a Vickers hardness at a portion between the
depressed portions adjacent to each other in the axial direction of the steel pipe; and
the outer peripheral surface is covered with a mill scale.
2. The depression-provided steel pipe according to Claim 1, wherein
at any position along an axis of the steel pipe, a percentage of a total
circumferential length at each of the depressed portions of the steel pipe relative to an
entire perimeter of the depression-provided steel pipe is 50% or less.
3. The depression-provided steel pipe according to Claim 1, wherein
the depressed portions are arranged so as to form four or more lines in parallel.
4. The depression-provided steel pipe according to Claim 3, wherein
among the lines of the depressed portions, lines of the depressed portions
adjacent in the circumferential direction are formed so as to have a phase difference in the
axial direction of the steel pipe; and
the phase difference is not less than 118 and not more than 112 of a distance
between centers of the depressed portions adjacent in the axial direction of the steel pipe.
5. The depression-provided steel pipe according to Claim 1, wherein
the depressed portions are arranged so as to form six or more lines in parallel.
6. The depression-provided steel pipe according to Claim 5, wherein
among the lines of the depressed portions, lines of the depressed portions
37 / 39
adjacent in the circumferential direction are formed so as to have a phase difference in the
axial direction of the steel pipe; and
the phase difference is not less than 118 and not more than 112 of a distance
between centers of the depressed portions adjacent in the axial direction of the steel pipe.
7. The depression-provided steel pipe according to Claim 1, wherein
each of the depressed portions has an oval shape with a major axis in parallel to
the axial direction of the steel pipe.
8. The depression-provided steel pipe according to Claim 1, wherein
each of the depressed portions is formed through hot roll forming using a steel
pipe processing roll, the roll having a surface with J raised portion.
9. The depression-provided steel pipe according to Claim 1, wherein
at least one of a plating layer and a resin layer is formed on the mill scale.
10. A composite pile formed by integrally driving the depression-provided steel pipe
according to any one of Claims 1 to 9 into a solidified material.
Dated this 22.07.2013
OF REMFRY & SAGAR
ATTORNEY FOR "THE APPLICANT[S]