Note: Descriptions are shown in the official language in which they were submitted.
COMPOSITE STRUCTURE
[Technical Field of the Invention]
[0001]
The present invention relates to a composite structure which can be applied to
a
joint of a steel pipe and a joint object member.
[Related Art]
[0002]
Hitherto, in order to enhance the bond strength between a steel pipe pile and
concrete, a technology in which, protrusions are provided on at least one of
the inner
circumferential surface and the outer circumferential surface of the front end
section of
the steel pipe pile to prevent slippage between the steel pipe pile and the
concrete, is
generally known.
[0003]
In Patent Document 1 mentioned below, in order to enhance the bond strength
between the steek surface and the concrete, a technology in which, annular
protrusions
are provided on the inner circumferential surface of the steel pipe pile along
the
circumferential direction of the steel pipe pile to prevent slippage between
the steel pipe
pile and the concrete, is disclosed.
[0004]
In Patent Documents 2 and 3 mentioned below, in order to enhance the bond
strength between the steek surface and the concrete, a technology in which,
spiral
protrusions are provided on the inner circumferential surface or the outer
circumferential
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surface of the steel pipe pile to prevent slippage between the steel pipe pile
and the
concrete, is disclosed.
[0005]
In Non-Patent Document 1 mentioned below, as a method of manufacturing a
steel pipe pile having spiral protrusions provided on the inner
circumferential surface or
the outer circumferential surface, a method of manufacturing a steel pipe pile
having
spiral protrusions by cold forming a steel strip provided with protrusions in
a spiral form
is disclosed. In Non-Patent Document 1, the bond strength between the steel
pipe pile
and concrete is decreased as an angle in a direction of the spiral protrusions
increases.
Therefore, in order to ensure the enough bond strength between the steel pipe
pile and the
concrete, the angle in the direction of the spiral protrusions is limited to
40 or lower.
[0006]
In Non-Patent Document 2 mentioned below, the results of experiments
conducted to examine the bond strength between a steel pipe having spiral
protrusions
provided on the inner circumferential surface, and concrete are disclosed. The
results of
the experiments show that even when an angle in a direction of the spiral
protrusions is
45 , necessary bond strength between the steel pipe and the concrete can be
ensured.
[Prior Art Document]
[Patent Document]
[0007]
[Patent Document 1] Japanese Unexamined Patent Application, First
Publication No. 2007-51500;
[Patent Document 2] Japanese Unexamined Patent Application, First
Publication No. 2007-32044;
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[Patent Document 3] Japanese Unexamined Patent Application, First
Publication No. H8-284159.
[Non-Patent Document]
[0008]
[Non-Patent Document 1] JIS A 5525 "Steel pipe piles";
[Non-Patent Document 2] "ADHESION PROPERTIES OF LAP JOINT DUE
TO STEEL PIPE WITH RIBS", Proceedings of Annual Conference of the Japan
Society
of Civil Engineers, 5, Vol. 50, pages 880 and 881, 1995.
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[0009]
However, in the steel pipe piles disclosed in Patent Documents 1, 2, and 3,
the
stiffness and the strength of a stiffening region (a region in which the
concrete comes into
contact with the inner circumferential surface of the steel pipe pile) are
significantly
different from those of a raw pipe region (a region in which the concrete does
not come
into contact with the inner circumferential surface of the steel pipe pile).
Particularly, in
the boundary between the stiffening region and the raw pipe region of the
steel pipe pile,
the stiffness and strength of the steel pipe pile are significantly decreased.
[0010]
Therefore, in the steel pipe piles disclosed in Patent Documents 1, 2, and 3,
when an external force such as a bending force, axial force, and/or shear
force is loaded
on the steel pipe pile, stress concentration caused by the external force
occurs near the
boundary between the stiffening region and the raw pipe region of the steel
pipe pile, and
thus there is a possibility that local buckling may occur in the raw pipe
region.
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[0011]
In addition, as described above, when the local buckling occurs in the raw
pipe
region of the steel pipe pile, there is a possibility that, at a junction of
an upper column of
a building structure or the like and the steel pipe pile, the building
structure may not be
insufficiently supported.
[0012]
As one of the methods to prevent local buckling in the raw pipe region of the
steel pipe pile, a method of increasing the plate thickness of the steel pipe
pile is
considered. However, when the method of increasing the plate thickness of the
steel
pipe pile is employed, the weight of the steel pipe pile is increased, and the
material cost
is also increased. Therefore, this method is not reasonable. In addition, as
another
method to prevent local buckling in the raw pipe region of the steel pipe
pile, installing a
stiffening material such as stiffener on the raw pipe region may be
considered. However,
this results in an increase in processing time and effort.
[0013]
The present invention has been made taking the foregoing circumstances into
consideration, and an object thereof is to provide a composite structure
capable of
realizing the enhancement of local buckling resistance in the boundary between
a
stiffening region and a raw pipe region of a steel pipe without increasing the
plate
thickness of the steel pipe and using a stiffening material such as stiffener.
[Measures for Solving the Problem]
[0014]
In order to accomplish the object to solve the problems, the present invention
employs the following measures.
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(1) A composite structure according to an aspect of the present invention
includes: a steel pipe; a joint object member having an end portion inserted
into the steel
pipe; and concrete which fills a space between an inner circumferential
surface of the
steel pipe and the end portion of the joint object member. The steel pipe
includes
protrusions which protrude inward in a radial direction of the steel pipe from
the inner
circumferential surface of the steel pipe and extend in a spiral shape along a
pipe axis
direction of the steel pipe. When a region in which the concrete comes into
contact with
the inner circumferential surface of the steel pipe is defined as a stiffening
region and a
region in which the concrete does not come into contact with the inner
circumferential
surface of the steel pipe is defined as a raw pipe region, the protrusions
extend in the
spiral shape along the pipe axis direction to straddle a boundary between the
stiffening
region and the raw pipe region. An extension length of the protrusion in the
pipe axis
direction in the raw pipe region is equal to or greater than a local buckling
half-
wavelength of the steel pipe. When the local buckling half-wavelength of the
steel pipe
is defined as X, (mm), an outer diameter of the steel pipe is defined as D
(mm), and a plate
thickness of the steel pipe is defined as t (mm), the local buckling half-
wavelength X, is
expressed in the following Expression (1), and a ratio D/t obtained by
dividing the outer
diameter D by the plate thickness t of the steel pipe is 50 or higher and 100
or lower.
[0015]
K (D = t) -(1)
(where, K is a dimensionless constant)
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[0016]
(2) In the composite structure described in (1), when the protrusion is viewed
from the inside in the radial direction of the steel pipe, an angle between a
circumferential
direction of the steel pipe and the protrusion may be 30 or higher and lower
than 90 .
[0017]
(3) In the composite structure described in (1) or (2), when the steel pipe is
viewed in a section parallel to the pipe axis direction, convex sections of
the protrusions
may be arranged with an interval equal to or smaller than the local buckling
half-
wavelength X therebetween along the pipe axis direction.
[Effects of the Invention]
[0018]
According to the composite structure described in (1), the difference in the
stifthess and the strength of this structure between the stiffening region and
the raw pipe
region of the steel pipe is reduced in the boundary between the stiffening
region and the
raw pipe region of the steel pipe, and thus the stiffness and the strength of
the steel pipe
are gradually decreased from the stiffening region to the raw pipe region.
Therefore, it
is possible to prevent rapid decreases in the stiffness and the strength of
the steel pipe.
[0019]
According to the composite structure described in (1), in the boundary between
the stiffening region and the raw pipe region of the steel pipe, rapid
decreases in the
stiffness and strength of the steel pipe are prevented, and thus the
occurrence of stress
concentration on the steel pipe caused by an external force such as a bending
force, axial
force, and/or shear force is prevented. Therefore, it is possible to prevent
the occurrence
of local buckling in the raw pipe region.
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[0020]
According to the composite structure described in (1), the local buckling
resistance of the steel pipe in the boundary between the stiffening region and
the raw pipe
region of the steel pipe can be enhanced, and thus it is possible to
sufficiently support a
building structure or the like at a junction of the steel pipe and the joint
object member.
[0021]
According to the composite structure described in (2), a thin section of the
steel
pipe in which the protrusion is not present is not continuous in a section of
the steel pipe
in the pipe circumferential direction thereof. As a result, the local buckling
resistance of
the steel pipe can be enhanced, and thus it is possible to prevent the
occurrence of the
local buckling in the raw pipe region.
[0022]
In addition, according to the composite structure described in (2), it is
possible
to reliably prevent the occurrence of local buckling in which the pipe wall is
crushed into
a bellows shape in the steel pipe. In addition, the concrete is reliably
adhered to the
inner circumferential surface of the steel pipe, and thus it is possible to
sufficiently ensure
the bond strength between the steel pipe and the concrete.
[0023]
According to the composite structure described in (2), the protrusions
provided
in the stiffening region to enhance the bond strength between the steel pipe
and the
concrete can be extended along the pipe axis direction of the steel pipe.
Therefore, it is
possible to efficiently manufacture a steel pipe having enhanced local
buckling resistance.
[0024]
Particularly, in the related art, in a case where protrusions are provided in
a steel
pipe only for the purpose of ensuring the bond strength between the steel pipe
and
concrete, the protrusions are inclined at about 10 to 20 with respect to the
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circumferential direction of the steel pipe. However, according to the
composite
structure described in (2), a manufacturing process of a steel pipe provided
with
protrusions is directly used to ensure the bond strength between the steel
pipe and
concrete, and the protrusions are inclined at an angle of 300 or higher with
respect to the
circumferential direction of the steel pipe, thereby efficiently providing the
protrusions
that enhance the local buckling resistance of the steel pipe.
[0025]
According to the composite structure described in (3), it is possible to
prevent
the occurrence of local buckling in the raw pipe region due to an external
force loaded on
the steel pipe between the protrusions which are adjacent to each other along
the pipe
axis direction of the steel pipe.
[Brief Description of the Drawings]
[0026]
FIG. 1 is a longitudinal sectional view showing a composite structure 1
according to an embodiment of the present invention.
FIG. 2 is an enlarged view of a region C enclosed by dotted lines in FIG. 1.
FIG. 3 is an enlarged view of a region including the boundary between a
stiffening region B1 and a raw pipe region B2 in FIG. 1.
FIG. 4 is a view schematically showing each of a case where shear force Q is
exerted on a steel pipe pile 10 and a case where axial force N is loaded on
the steel pipe
pile 10.
FIG. 5 shows a graph in which "LN(D=t)" in Table 1 is set as the horizontal
axis,
and "Qõ,./Q0" in Table 1 is set as the vertical axis.
FIG. 6 show a graph in which a protrusion inclination angle 0 in Table 2 is
set
as the horizontal axis, and "Qmax/Q0" in Table 2 is set as the vertical axis.
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FIG. 7 shows a graph in which the protrusion inclination angle 0 in Table 3 is
set
as the horizontal axis, and "Nn,,x/NO" in Table 3 is set as the vertical axis.
FIG. 8 shows a graph in which "S/ AD-0" in Table 4 is set as the horizontal
axis,
and "Qmax/Q0" in Table 4 is set as the vertical axis.
FIG. 9 is a view showing a modification example of the embodiment.
FIG. 10 is a view showing a modification example of the embodiment.
[Embodiments of the Invention]
[0027]
Hereinafter, an embodiment of the present invention will be described in
detail
with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a composite structure 1
according to the embodiment of the present invention. As shown in FIG. 1, the
composite structure 1 according to this embodiment includes a steel pipe pile
10 (steel
pipe) which is driven into the ground, H-shaped steel 20 (joint object member)
having an
end portion inserted into the steel pipe pile 10, and concrete 30 which fills
a space
between an inner circumferential surface 11 of the steel pipe pile 10 and the
end portion
of the H-shaped steel 20 (the portion inserted into the steel pipe pile 10).
In addition,
FIG. 1 is a view of the steel pipe pile 10 viewed in a section parallel to a
pipe axis
direction (Y direction in FIG. 1) of the steel pipe pile 10.
[0028]
The H-shaped steel 20 is, for example, a column member of a building structure
(upper structure). In a state where the end portion of the H-shaped steel 20
is inserted
into the steel pipe pile 10 that is driven into the ground as the foundation
structure, the
concrete 30 fills the space between the inner circumferential surface 11 of
the steel pipe
pile 10 and the end portion of the H-shaped steel 20 such that the steel pipe
pile 10 and
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the H-shaped steel 20 are joined together. As showned in FIG. 1, in order to
increase
the joining strength between the steel pipe pile 10 and the H-shaped steel 20,
it is
preferable that a baseplate 21 is joined to a tip of the H-shaped steel 20.
However, the
baseplate 21 is not essential.
[0029]
The steel pipe pile 10 is, for example, a steel pipe having an outer diameter
D of
1000 mm, a plate thickness t of 6.6 mm, and a Poisson's ratio v of 0.28 to
0.30. The
outer diameter D, the plate thickness t, and the Poisson's ratio v of the
steel pipe pile 10
are not limited to the above-mentioned numeral values. However, when the plate
thickness t of the steel pipe pile 10 is too high, there is an advantage in
that the local
buckling resistance of the steel pipe pile 10 is increased, while there is a
disadvantage in
that the weight and material cost of the steel pipe pile 10 is increased.
Therefore, in this
embodiment, in consideration of a balance between the advantage and the
disadvantage
caused by the plate thickness t, the ratio D/t obtained by dividing the outer
diameter D by
the plate thickness t is set to be 50 or higher and 100 or lower.
In a case where a steel material for construction is used as the steel pipe
pile 10
and the ratio D/t obtained by dividing the outer diameter D by the plate
thickness t
becomes less than 50, the strength of the steel pipe pile 10 is reduced due to
local
buckling. Therefore, it is preferable that the lower limit of the ratio D/t is
set to 50.
On the other hand, there is no particular limitation regarding the upper limit
of the ratio
D/t. However, the upper limit of the ratio D/t of a steel pipe which is
manufactured for
construction and is distributed to the market is generally 100. Accordingly,
in this
embodiment, the upper limit of the ratio D/t of the steel pipe pile 10 is also
set to 100.
The steel pipe pile 10 includes protrusions 12 which protrude inward in a
radial
direction of the steel pipe pile 10 (X direction in FIG. 1) from the inner
circumferential
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surface 11 of the steel pipe pile 10 and extend in a spiral shape along the
pipe axis
direction Y of the steel pipe pile 10.
[0030]
FIG. 2 is an enlarged view of a region C enclosed by dotted lines in FIG. 1.
As
shown in FIG. 2, the length of a convex section of the protrusion 12 in the
pipe axis
direction Y of the steel pipe pile 10 is defined as a protrusion width w. In
addition, the
length of the convex section of the protrusion 12 in the radial direction X of
the steel pipe
pile 10 is defined as a protrusion height h. In addition, the distance between
the centers
of the convex sections of the protrusions 12 which are adjacent to each other
along the
pipe axis direction Y is defined as a protrusion interval S. Furthermore, when
the
protrusion 12 is viewed from the inside in the radial direction X of the steel
pipe pile 10,
an angle between a circumferential direction (W direction in FIG. 2) of the
steel pipe pile
10 and the protrusion 12 is defined as a protrusion inclination angle 0.
[0031]
The protrusion width w of the protrusion 12 is, for example, 10 mm. The
protrusion height h of the protrusion 12 is, for example, 4 mm. However, the
protrusion
width w and the protrusion height h of the protrusion 12 are not limited to
the above-
mentioned numerical values. It is preferable that the protrusion inclination
angle 0 is
30 or higher and lower than 90 . In addition, it is most preferable that the
protrusion
inclination angle 0 is 30 or higher and lower than 60 . The reason that it is
preferable
to set the protrusion inclination angle 0 to the above range will be described
later. A
preferable range of the protrusion interval S will be described later. In
addition, in this
embodiment, a case where the protrusions 12 having a rectangular convex
section are
formed on the steel pipe pile 10 is exemplified. However, the shape of the
convex
section of the protrusion 12 may also be a shape other than a rectangular
shape.
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[0032]
The protrusions 12 may be provided on the inner circumferential surface 11 of
the steel pipe pile 10 by rolling of a steel strip or the like, or may also be
provided by a
method of attaching a steel bar through welding or placing weld beads. In
addition,
portions of a plurality of spiral protrusions 12 may be allowed to intersect
each other such
that the plurality of protrusions 12 which are inclined in different
directions from each
other with respect to the circumferential direction W of the steel pipe pile
10 are
combined with each other. In addition, a spiral protrusion 12 and a protrusion
12 which
is parallel to the circumferential direction W of the steel pipe pile 10 may
also be
combined with each other.
[0033]
In the following description, as shown in FIG. 1, a region in which the
protrusions 12 are provided on the inner circumferential surface 11 of the
steel pipe pile
10 is defined as a protrusion region Al, and a region in which the protrusions
12 are not
provided on the inner circumferential surface 11 of the steel pipe pile 10 is
defined as a
flat region A2. In addition, as shown in FIG. 1, a region in which the
concrete 30 comes
into contact with the inner circumferential surface 11 of the steel pipe pile
10 is defined
as a stiffening region Bl, and a region in which the concrete 30 does not come
into
contact with the inner circumferential surface 11 of the steel pipe pile 10 is
defined as a
raw pipe region B2.
[0034]
As shown in FIG. 1, the protrusions 12 extend in a spiral shape along the pipe
axis direction Y to straddle the boundary between the stiffening region B1 and
the raw
pipe region B2. In other words, in the protrusion region Al, at least one
boundary is
present between the stiffening region B1 and the raw pipe region B2. Although
the
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details are described later, there may be a case where two boundaries are
present between
the stiffening region B1 and the raw pipe region B2 in the protrusion region
Al.
[0035]
As shown in FIG. 1, the length of the protrusion 12 which extends from the
boundary between the stiffening region B1 and the raw pipe region B2 toward
the side of
the raw pipe region B2 along the pipe axis direction Y is defined as an
extension length L.
In other words, the extension length L of the protrusion 12 in the raw pipe
region B2 in
the pipe axis direction Y is a length obtained by subtracting the length of
the stiffening
region B1 in the pipe axis direction Y from the length of the protrusion
region Al in the
pipe axis direction Y.
[0036]
FIG. 3 is an enlarged view of a region including the boundary between the
stiffening region B1 and the raw pipe region B2 in FIG. 1. As shown in FIG. 3,
the
extension length L of the protrusion 12 in the raw pipe region B2 in the pipe
axis
direction Y is equal to or greater than a local buckling half-wavelength X of
the steel pipe
pile 10. Here, the local buckling half-wavelength X of the steel pipe pile 10
is the length
of a buckled portion 13 which is generated in the pipe wall of the raw pipe
region B2 due
to an external force such as a bending force M, axial force N, and/or shear
force Q loaded
on the steel pipe pile 10, and is close to the boundary between the stiffening
region B1
and the raw pipe region B2 (see FIG. 3).
[0037]
As described above, when it is defined that the outer diameter of the steel
pipe
pile 10 is D (mm), the plate thickness of the steel pipe pile 10 is t (mm),
and the local
buckling half-wavelength of the steel pipe pile 10 is X (mm), the local
buckling half-
wavelength X is expressed by the following Expression (1). In addition, when
the
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Poisson's ratio of the steel pipe pile 10 is defined as v, a constant K in the
following
Expression (1) is expressed by the following Expression (2).
[0038]
= KII(D t) )
(where, K is a dimensionless constant)
[0039]
1
K= __________________________________ === ( 2 )
4\112(1¨v2) 11 2
[0040]
In addition, as shown in FIG. 3, when the steel pipe pile 10 is viewed in a
section parallel to the pipe axis direction Y, it is preferable that the
convex sections of the
protrusions 12 are arranged with an interval of equal to or smaller than the
local buckling
half-wavelength k therebetween along the pipe axis direction Y. In other
words, it is
preferable that the protrusion interval S between the protrusions 12 is equal
to or smaller
than the local buckling half-wavelength k. That is, it is preferable that the
relationship
between the extension length L. the protrusion interval S, and the local
buckling half-
wavelength X of the protrusions 12 satisfies the following Conditional
Expression (3).
SXL = = .(3)
[0041]
According to the composite structure 1 having the above-described
configuration, it is possible to realize the enhancement of local buckling
resistance in the
boundary between the stiffening region B1 and the raw pipe region B2 of the
steel pipe
pile 10 without increasing the plate thickness of the steel pipe pile 10 and
using a
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stiffening material such as stiffener. That is, according to the composite
structure 1
having the above-described configuration, while satisfying the conditions in
which the
balance between the advantage and the disadvantage caused by the plate
thickness t of the
steel pipe pile 10 (conditions in which the ratio D/t obtained by dividing the
outer
diameter D by the plate thickness t is 50 or higher and 100 or lower), the
local buckling
resistance in the boundary between the stiffening region B1 and the raw pipe
region B2
can be enhanced.
[0042]
Hereinafter, as shown in FIG. 4, in each of a case where shear force Q is
loaded
on the steel pipe pile 10 and a case where axial force N is loaded on the
steel pipe pile 10,
analysis results of the local buckling resistance of the steel pipe pile 10
analyzed through
the finite element method (FEM) using shell elements are described.
[0043]
In the FEM analysis, the outer diameter D of the steel pipe pile 10 was set to
1000 mm, the plate thickness t of the steel pipe pile 10 was set to 6.6 mm,
the Poisson's
ratio v of the steel pipe pile 10 was set to 0.30, the protrusion height h of
the protrusion
12 was set to 4 mm, the protrusion width w of the protrusion 12 was set to 10
mm, the
protrusion inclination angle 0 of the protrusion 12 was set to 30 , and the
protrusion
interval S between the protrusions 12 was set to 100 mm. Under such
conditions, the
local buckling half-wavelength 2,, of the steel pipe pile 10 becomes 199 mm.
Under the above conditions, analysis results of the relationship between the
extension length L of the protrusion 12 and the local buckling resistance
against shear
force Q (the maximum strength against shear force Q) in a case where the
extension
length L of the protrusion 12 was changed in a range of 0 mm to 500 mm, are
shown in
the following Table 1. In addition, in the following Table 1, when the
extension length
L of the protrusion 12 is 199 mm or greater, the condition in which the
extension length L
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of the protrusion 12 is equal to or greater than the local buckling half-
wavelength X of the
steel pipe pile 10 is satisfied.
[0044]
[Table 1]
L(mm) Lii(Dt) QinsAN) Qmax/00
0 0 794 1
10023 810 1,020
199 2.44 834 1.049
___________________ 250 _______ 3.08_ 834 1.049
500_ 6.15 836 1,053
[0045]
In Table 1, Qm (kN) represents the shear force Q at a point in time when local
buckling finally occurs in the steel pipe pile 10 and the shear force Q
reaches to the
maximum strength in a case where the shear force Q loaded on the upper end
portion of
the steel pipe pile 10 is gradually increased to forcibly deform the steel
pipe pile 10.
That is, Qmax represents the local buckling resistance (the maximum strength
against the
shear force Q) of the steel pipe pile 10 against the shear force Q.
The maximum strength Qmax (=794 kN) when the extension length L is 0 mm,
that is, when the protrusion 12 is not present in the raw pipe region B2, is
defined as a
reference strength QO. Therefore, in Table 1, when the extension length L of
the
protrusion 12 is 0 mm, the ratio (=Qmax/Q0) obtained by dividing the maximum
strength
Qmax by the reference strength QO becomes "1". In Table 1, "Qmax/Q0" is a
dimensionless number representing the ratio of an increase in the maximum
strength Qmax
with respect to a change in the extension length L of the protrusion 12.
[0046]
FIG. 5 shows a graph in which "LN(1).0" in Table 1 is set as the horizontal
axis,
and "Qn,./Q0" in Table 1 is set as the vertical axis. As shown in FIG. 5, when
"Lhi(Dt)"
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becomes 2.44 or higher, "Qmax/Q0" becomes 1.049 or higher. That is, when the
condition in which the extension length L of the protrusion 12 is equal to or
greater than
the local buckling half-wavelength X (=199 mm) of the steel pipe pile 10 is
satisfied, the
ratio of the increase in the maximum strength Qmax of the steel pipe pile 10
against the
shear force Q becomes 4.9% or higher. As described above, it was confirmed
that when
the condition in which the extension length L of the protrusion 12 is equal to
or greater
than the local buckling half-wavelength X of the steel pipe pile 10 is
satisfied, the local
buckling resistance of the steel pipe pile 10 against the shear force Q is
significantly
increased.
[0047]
Next, in the FEM analysis, the outer diameter D of the steel pipe pile 10 was
set
to 1000 mm, the plate thickness t of the steel pipe pile 10 was set to 6.6 mm,
the
Poisson's ratio v of the steel pipe pile 10 was set to 0.30, the protrusion
height h of the
protrusion 12 was set to 4 mm, the protrusion width w of the protrusion 12 was
set to 10
mm, the extension length L of the protrusion 12 was set to 500 mm, and the
protrusion
interval S between the protrusions 12 was set to 100 mm. That is, the
condition in
which the extension length L of the protrusion 12 is equal to or greater than
the local
buckling half-wavelength X (-199 mm) of the steel pipe pile 10 is satisfied.
Under such conditions, analysis results of the relationship between the
protrusion inclination angle 0, the maximum strength Qmaõ of the steel pipe
pile 10
against shear force Q, and "Qmax/QO" in a ease where the protrusion
inclination angle 0 of
the protrusion 12 was changed in a range of 100 to 90 are shown in the
following Table 2.
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[0048]
[Table 2]
e(0 ) omax(kN) orna./00
NIMMIZOMMUSSIMP
814 1.025
819 1.031
836 1.053
45 _____________________________ 855 1.077
60 _____________________________ 849 1.069
75 858 1.081
90 862 1.085
[0049]
5 FIG. 6 shows a graph in which the protrusion inclination angle 0 in
Table 2 is set
as the horizontal axis, and "Qmax/Q0" in Table 2 is set as the vertical axis.
As shown in
FIG. 6, when the protrusion inclination angle 0 becomes 30 or higher,
"Qmax/Q0"
becomes 1.053 to 1.085. That is, when the condition in which the protrusion
inclination
angle 0 is 30 or higher is satisfied, the ratio of the increase in the
maximum strength
10 Q,õ,, of the steel pipe pile 10 against the shear force Q becomes 5.3%
to 8.5. As
described above, it was confirmed that when the condition in which the
extension length
L of the protrusion 12 is equal to or greater than the local buckling half-
wavelength X of
the steel pipe pile 10 is satisfied and the condition in which the protrusion
inclination
angle 0 is 30 or higher is satisfied, the local buckling resistance of the
steel pipe pile 10
15 against the shear force Q is more significantly increased.
[0050]
Next, in the FEM analysis, the outer diameter D of the steel pipe pile 10 was
set
to 1000 mm, the plate thickness t of the steel pipe pile 10 was set to 6.6 mm,
the
Poisson's ratio v of the steel pipe pile 10 was set to 0.30, the protrusion
height h of the
20 protrusion 12 was set to 4 mm, the protrusion width w of the protrusion
12 was set to 10
- 18 -
CA 02920289 2016-02-02
mm, the extension length L of the protrusion 12 was set to 3000 mm, and the
protrusion
interval S between the protrusions 12 was set to 100 mm. That is, the
condition in
which the extension length L of the protrusion 12 is equal to or greater than
the local
buckling half-wavelength X (=199 mm) of the steel pipe pile 10 is satisfied.
In addition,
setting the extension length L of the protrusion 12 to 3000 mm means that the
protrusion
12 is formed over the entire length of the steel pipe pile 10.
Under such conditions, analysis results of the relationship between the
protrusion inclination angle 0 and the local buckling resistance against axial
force N (the
maximum strength against axial force N) in a case where the protrusion
inclination angle
0 of the protrusion 12 was changed in a range of 5 to 90 are shown in the
following
Table 3.
[0051]
[Table 3]
( N,õõ'KN) Nnu,õ/NO
M. NOW
None 7581 1
5 6948 0.916
10 7001 0.924
15 6913 0.912
20 ____ 7120 0.939
25 7667 1.011
30 7949 1.049
45 8154 1.076
60 8288 1.093
75 8336 1.100
90 8323 1.098
[0052]
In Table 3, Nnia, (kN) represents the axial force N at a point in time when
local
buckling finally occurs in the steel pipe pile 10 and the axial force N
reaches the
maximum strength in a case where the axial force N loaded on the steel pipe
pile 10 is
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CA 02920289 2016-02-02
gradually increased to forcibly deform the steel pipe pile 10. That is, Nmax
represents
the local buckling resistance (the maximum strength against the axial force N)
of the steel
pipe pile 10 against the axial force N.
The maximum strength Nmax (-7580 kN) when the protrusion inclination angle 0
is "none" (when the protrusion 12 is not present in the steel pipe pile 10) is
defined as a
reference strength NO. Therefore, in Table 3, when the protrusion inclination
angle 0 is
"none", the ratio (Nmax/NO) obtained by dividing the maximum strength Ni,õ, by
the
reference strength NO becomes "1". "Nõ,./NO" is a dimensionless number
representing
the ratio of an increase in the maximum strength Nmax with respect to a change
in the
protrusion inclination angle 0 of the protrusion 12.
[0053]
FIG. 7 shows a graph in which the protrusion inclination angle 0 in Table 3 is
set
as the horizontal axis, and "Nmax/NO" in Table 3 is set as the vertical axis.
As shown in
FIG. 7, when the protrusion inclination angle 0 becomes 300 or higher,
"Nmax/NO"
becomes 1.049 to 1.100. That is, when the condition in which the protrusion
inclination
angle 0 is 30 or higher is satisfied, the ratio of the increase in the
maximum strength
N. of the steel pipe pile 10 against the axial force N becomes 4.9% to 10.0%.
As
described above, it was confirmed that when the condition in which the
extension length
L of the protrusion 12 is equal to or greater than the local buckling half-
wavelength X of
the steel pipe pile 10 is satisfied and the condition in which the protrusion
inclination
angle 0 is 300 or higher is satisfied, the local buckling resistance of the
steel pipe pile 10
against the axial force N is significantly increased.
[0054]
As described above, from the analysis results shown in Tables 2 and 3 (FIGS. 6
and 7), a condition in which the protrusion inclination angle 0 of the
protrusion 12 is 30
or higher and 90 or lower is derived as one of the conditions for further
enhancing the
- 20 -
CA 02920289 2016-02-02
local buckling resistance of the steel pipe pile 10. However, in a case where
the
protrusion inclination angle 0 is 900, the bond strength between the steel
pipe pile 10 and
the concrete 30 cannot be sufficiently obtained. Therefore, in this
embodiment, as one
of the conditions for further enhancing the local buckling resistance of the
steel pipe pile
10, a condition in which the protrusion inclination angle 0 of the protrusion
12 is 30 or
higher and lower than 90 is employed.
[0055]
From the analysis results shown in Tables 2 and 3 (FIGS. 6 and 7), as the most
preferable condition, a condition in which the protrusion inclination angle 0
of the
protrusion 12 is 30 or higher and 60 or lower is derived. Here, as shown in
FIGS. 6
and 7, 300 which is the lower limit of the protrusion inclination angle 0 is a
value at
which the ratios of the increases in the maximum strength Qmax against the
shear force Q
and in the maximum strength N. against the axial force N are significantly
increased.
In addition, 60 which is the upper limit of the protrusion inclination angle
0 is a value at
which the ratios of the increases in the maximum strength ()max against the
shear force Q
and in the maximum strength Nmax against the axial force N are not
significantly
increased even when the protrusion inclination angle 0 is further increased.
[0056]
Next, in the FEM analysis, the outer diameter D of the steel pipe pile 10 was
set
to 1000 mm, the plate thickness t of the steel pipe pile 10 was set to 6.6 mm,
the
Poisson's ratio v of the steel pipe pile 10 was set to 0.30, the protrusion
height h of the
protrusion 12 was set to 4 mm, the protrusion width w of the protrusion 12 was
set to 10
mm, the protrusion inclination angle 0 of the protrusion 12 was set to 45 ,
and the
extension length L of the protrusion 12 was set to 500 mm. That is, the
condition in
which the extension length L of the protrusion 12 is equal to or greater than
the local
buckling half-wavelength X (=199 mm) of the steel pipe pile 10 is satisfied.
- 21 -
CA 02920289 2016-02-02
Under these conditions, analysis results of the relationship between the
protrusion interval S between the protrusions 12 and the local buckling
resistance against
shear force Q (the maximum strength against shear force Q) in a case where the
protrusion interval S between the protrusions 12 was changed in a range of 0
mm to 300
mm are shown in the following Table 4. In addition, in the following Table 4,
when the
protrusion interval S between the protrusions 12 is 199 mm or smaller, a
condition in
which the protrusion interval S between the protrusions 12 is equal to or
smaller than the
local buckling half-wavelength ?\, of the steel pipe pile 10 is satisfied.
[0057]
[Table 4]
S(mm) Sir(Dt) Q(kN)
None 794 1
0 ________ 0 940 1.184
60 0.74 871 1.097
100 1.23 854 1.076
150 1.85 821 1.034
199 2.44 811 1.022
1
300 3.69 802
1.010,
[0058]
In Table 4, as in Tables 1 and 2, Qmaõ (kN) represents the shear force Q at a
point
in time when local buckling finally occurs in the steel pipe pile 10 and the
shear force Q
reaches the maximum strength in a case where the shear force Q loaded on the
upper end
portion of the steel pipe pile 10 is gradually increased to forcibly deform
the steel pipe
pile 10. That is, Qmax represents the local buckling resistance (the maximum
strength
against the shear force Q) of the steel pipe pile 10 against the shear force
Q.
The maximum strength Qma, (-794 kN) when the protrusion interval S is "none"
(when the protrusion 12 is not present in the steel pipe pile 10) is defined
as a reference
strength QO. Therefore, in Table 4, when the protrusion interval S is "none",
the ratio
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CA 02920289 2016-02-02
(=Qmax/Q0) obtained by dividing the maximum strength Qmax by the reference
strength
QO becomes "1". In Table 4, "Q/Q0" is a dimensionless number representing the
ratio of an increase in the maximum strength Qmax with respect to a change in
the
protrusion interval S between the protrusions 12.
[0059]
FIG. 8 shows a graph in which "S/(D=t)" in Table 4 is set as the horizontal
axis,
and "Qmax/Q0" in Table 4 is set as the vertical axis. As shown in FIG. 8, when
"SN(Dt)"
becomes 2.44 or lower, "Qmax/QO" becomes 1.022 or higher. That is, when the
condition in which the protrusion interval S between the protrusions 12 is
equal to or
smaller than the local buckling half-wavelength X (=199 mm) of the steel pipe
pile 10 is
satisfied, the ratio of the increase in the maximum strength Qmax of the steel
pipe pile 10
against the shear force Q becomes 2.2% or higher. As described above, it was
confirmed that when the condition in which the extension length L of the
protrusion 12 is
equal to or greater than the local buckling half-wavelength X of the steel
pipe pile 10 is
satisfied and the condition in which the protrusion interval S between the
protrusions 12
is equal to or smaller than the local buckling half-wavelength X of the steel
pipe pile 10
(that is, conditions specified in the above Expression (3)) is satisfied, the
local buckling
resistance of the steel pipe pile 10 against the shear force Q is
significantly increased.
[0060]
As described above, according to the composite structure 1 according to this
embodiment which satisfies the condition (first condition) in which the
extension length
L of the protrusion 12 is equal to or greater than the local buckling half-
wavelength X of
the steel pipe pile 10, the condition (second condition) in which the
protrusion inclination
angle 0 is 30 or higher and lower than 90 , and the condition (third
condition) in which
the protrusion interval S between the protrusions 12 is equal to or smaller
than the local
buckling half-wavelength X of the steel pipe pile 10, it is possible to
realize the
- 23 -
CA 02920289 2016-02-02
enhancement of local buckling resistance in the boundary between the
stiffening region
B1 and the raw pipe region B2 while satisfying the conditions in which the
balance
between the advantage and the disadvantage caused by the plate thickness t of
the steel
pipe pile 10 is optimized (the conditions in which the ratio D/t obtained by
dividing the
outer diameter D by the plate thickness t is 50 or higher and 100 or lower).
[0061]
In addition, as understood from the analysis results, a composite structure
which
satisfies at least the first condition can obtain the above effects. However,
in order to
further enhance the local buckling resistance of the steel pipe pile 10, it is
preferable that
a composite structure which satisfies at least one of the second and third
conditions in
addition to the first condition is employed.
[0062]
Incidentally, in the embodiment, a case where the protrusions 12 are formed
over
the entire section of the stiffening region B1 (that is, a case where the
protrusions 12 are
formed over the entire section of the inner circumferential surface 11 which
comes into
contact with the concrete 30) is exemplified. However, the protrusions 12 do
not need
to be formed over the entire section of the stiffening region B1 as long as at
least the first
condition is satisfied. For example, as shown in FIG. 9, the stiffening region
B1 may
also include a region in which the protrusions 12 are not formed (flat region
A2) and a
region in which the protrusions 12 are formed (protrusion region Al). However,
for
high bond strength of the steel pipe pile 10 and the concrete 30, it is
preferable that the
protrusions 12 are formed over the entire section of the stiffening region Bl.
[0063]
In addition, in the embodiment, a case where one boundary is present between
the stiffening region B1 and the raw pipe region B2 in the protrusion region
Al is
exemplified. However, as shown in FIG. 10, a composite structure in which two
- 24 -
CA 02920289 2016-02-02
boundaries are present between the stiffening region B1 and the raw pipe
region B2 in the
protrusion region Al may also be employed. Even in the composite structure
shown in
FIG. 10, at least the first condition needs to be satisfied. That is, in FIG.
10, both of the
extension length L of the protrusions 12 that extend upward from the upper end
of the
stiffening region B1 in the pipe axis direction Y and the extension length L
of the
protrusions 12 that extend downward from the lower end of the stiffening
region B1 in
the pipe axis direction Y need to be set to a length of equal to or greater
than the local
buckling half-wavelength X, of the steel pipe pile 10.
[0064]
In addition, in the embodiment, the H-shaped steel 20 is exemplified as the
joint
object member joined to the steel pipe pile 10. However, any joint object
member may
be employed as long as the joint object member has a shape that can be
inserted into the
steel pipe pile 10.
In addition, in the embodiment, a case where the protrusions 12 are provided
on
the inner circumferential surface 11 of the steel pipe pile 10 is exemplified.
However,
protrusions which protrude outward in the radial direction of the steel pipe
pile 10 from
the outer circumferential surface of the steel pipe pile 10 and extend in a
spiral shape
along the pipe axis direction Y of the steel pipe pile 10 may also be provided
in addition
to the protrusions 12.
[0065]
As described above, according to the embodiment, by satisfying at least the
first
condition, the difference in the stiffness and the strength of this structure
between the
stiffening region B1 and the raw pipe region B2 is reduced in the boundary
between the
stiffening region B1 and the raw pipe region B2.
- 25 -
CA 02920289 2016-02-02
[0066]
Accordingly, the stiffness and the strength of this structure are gradually
decreased from the stiffening region B1 to the raw pipe region B2 in the
boundary
between the stiffening region B1 and the raw pipe region B2, and thus it is
possible to
prevent rapid decreases in the stiffness and the strength of the steel pipe
(the steel pipe
pile 10). In addition, according to the embodiment, the occurrence of stress
concentration on the steel pipe caused by an external force such as a bending
force M,
axial force N, and/or shear force Q in the boundary between the stiffening
region B1 and
the raw pipe region B2 of the steel pipe is prevented, and thus it is possible
to prevent the
occurrence of local buckling in the raw pipe region B2.
[0067]
In addition, according to the embodiment, the local buckling resistance of the
steel pipe in the boundary between the stiffening region B1 and the raw pipe
region B2 of
the steel pipe can be enhanced, and thus it is possible to sufficiently
support a building
structure or the like at a junction of the steel pipe and the joint object
member.
[0068]
In addition, in the embodiment, when the protrusions (12) of the steel pipe
are
viewed from the inside in the radial direction X of the steel pipe, the angle
between the
circumferential direction W of the steel pipe and the protrusion is set to be
30 or higher
and lower than 90 .
[0069]
Accordingly, in the embodiment, a thin section of the steel pipe in which the
protrusion is not present is not continuous in a section of the steel pipe in
the pipe
circumferential direction thereof. As a result, the local buckling resistance
of the steel
pipe can be enhanced, and thus it is possible to prevent the occurrence of the
local
buckling in the raw pipe region B2.
- 26 -
CA 02920289 2016-02-02
[0070]
In addition, according to the embodiment, the protrusions are provided in a
spiral shape along the pipe axis direction Y of the steel pipe, and thus the
bond strength
between the steel pipe and the concrete (30) can be enhanced. In addition, in
order to
enhance the bond strength between the steel pipe and the concrete, protrusions
provided
in the stiffening region B1 may be provided to extend along the pipe axis
direction Y of
the steel pipe. Therefore, it is possible to efficiently manufacture a steel
pipe having
enhanced local buckling resistance. Furthermore, according to the embodiment,
for
example, in a case where a steel strip provided with protrusions is formed
into a spiral
shape, it is possible to significantly enhance the manufacturing efficiency of
the steel pipe.
[0071]
In the related art, in a case in which it is desired to only ensure the bond
strength
between a steel pipe and concrete, protrusions inclined at about 100 to 20
with respect to
the circumferential direction W of a steel pipe are provided in the steel pipe
by forming a
steel strip provided with the protrusions into a spiral shape, or the like.
[0072]
Contrary to this, according to the embodiment, a manufacturing process of a
steel pipe provided with protrusions is directly used to ensure the bond
strength between
the steel pipe and concrete, and the protrusions are inclined at an angle of
300 or higher
with respect to the circumferential direction W of the steel pipe in order to
enhance the
local buckling resistance of the steel pipe, thereby efficiently providing the
protrusions in
the steel pipe.
[0073]
Particularly, according to the embodiment, by setting the protrusion
inclination
angle 0 to be 30 or higher and lower than 90 (most preferably, 30 <0<60 ),
it is
possible to reliably prevent the occurrence of local buckling, in which the
pipe wall is
- 27 -
CA 02920289 2016-02-02
crushed into a bellows shape, in the steel pipe. In addition, by allowing the
concrete to
be reliably adhered to the inner circumferential surface (11) of the steel
pipe, it is possible
to sufficiently ensure the bond strength between the steel pipe and the
concrete.
[0074]
In addition, in the embodiment, when the steel pipe is viewed in a section
parallel to the pipe axis direction Y, the convex sections of the protrusions
are arranged
with an interval equal to or smaller than the local buckling half-wavelength
2,, of the steel
pipe therebetween along the pipe axis direction Y. That is, the protrusion
interval S
between the protrusions is set to be equal to or smaller than the local
buckling half-
wavelength A, of the steel pipe.
[0075]
Accordingly, it is possible to prevent the occurrence of local buckling in the
raw
pipe region B2 due to an external force loaded on the steel pipe between the
protrusions
which are adjacent to each other along the pipe axis direction Y of the steel
pipe.
[0076]
In addition, by setting the protrusion interval S between the protrusions to
be
equal to or smaller than the local buckling half-wavelength 2, of the steel
pipe, the local
buckling resistance of the steel pipe is further increased. As a result, it is
possible to
significantly enhance the strength of the steel pipe.
[0077]
While the embodiment of the present invention has been described above in
detail, the present invention is not limited to the above-described
embodiment, and the
technical scope of the present invention should not be construed as being
limited by the
embodiment.
- 28 -
CA 02920289 2016-02-02
[0078]
For example, the present invention can also be applied to a beam-column
connection, in which protrusions are provided in a column member or a steel
pipe used as
a sheath pipe, the column member (joint object member) is inserted into the
sheath pipe
to which a beam member is connected, and concrete fills a space between the
sheath pipe
and the column member.
[Brief Description of the Reference Symbols]
[0079]
1 composite structure
12 protrusion
10 steel pipe pile (steel pipe)
H-shaped steel (joint object member)
11 inner circumferential surface of steel pipe pile (steel pipe)
concrete
15 13 buckled portion
extension length
Al protrusion region
A2 flat region
B1 stiffening region
20 B2 raw pipe region
circumferential direction
X radial direction
pipe axis direction
- 29 -
