JP2019015069A - Concrete pile - Google Patents

Abstract

To provide a concrete pile with improved flexural capacity and toughness compared with conventional ones without including an outer shell steel pipe.SOLUTION: A concrete pile comprises a hollow cylindrical pile body which includes concrete in at least a part. The pile body has an outer peripheral surface not covered with metallic material in an intermediate part in an axial direction of the pile body. The pile body satisfies a relationship presented by the following formula: 0.24≤tc/D<0.5, in which D is an outer diameter of the pile body, tc is thickness of the pile body and tc/D is a diameter thickness ratio.SELECTED DRAWING: Figure 11

Description

  The present disclosure relates to hollow concrete piles.

  A concrete pile with an outer shell steel pipe (SC pile), which is a kind of ready-made pile, is generally constituted by an outer shell steel pipe and a hollow and cylindrical concrete covered with the outer shell steel pipe (for example, Patent Documents). 1).

Japanese Patent No. 5265447

Since SC pile has a shell steel pipe, it has higher bending strength and toughness than a normal concrete pile without a shell steel pipe. However, further improvements in bending strength and toughness are desired for such SC piles.
On the other hand, not only SC piles, but also concrete piles such as PRC piles (pre-stressed reinforced high-strength concrete piles) and PHC piles (pre-stressed high-strength concrete piles) that do not have shell steel pipes, Development of means to improve is desired.
In view of the above-described circumstances, an object of at least one embodiment of the present invention is to provide a ready-made concrete pile having improved bending strength and toughness than before.

As a result of various studies to achieve the above object, the present inventor has found that when the concrete pile with outer steel pipe has a predetermined diameter-thickness ratio, the bending strength and toughness are improved. Furthermore, even when the diameter-thickness ratio is applied to a concrete pile not provided with a shell steel pipe, the present inventors have found that bending strength and toughness are improved, and have arrived at the present invention.
(1) A concrete pile according to at least one embodiment of the present invention is:
In a concrete pile provided with a hollow and cylindrical pile body including concrete at least in part,
The pile body has an outer peripheral surface that is not covered with a metal material at an intermediate portion in the axial direction of the pile body,
When the outer diameter of the pile body is D, the thickness of the pile body is tc, and the diameter-thickness ratio is tc / D, the following formula:
0.24 ≦ tc / D <0.5
The relationship indicated by is satisfied.

According to the configuration (1), the diameter-thickness ratio tc / D is less than 0.5, the pile body has a cylindrical shape, is not completely solid, and has a columnar cavity in the radial center. Have. For this reason, when a crack generate | occur | produces in a pile body, a part of inner surface of a pile body may peel off and there exists a possibility that the bending strength and toughness of a concrete pile may fall.
However, according to the above configuration, since the diameter / thickness ratio tc / D is 0.24 or more, the bending strength and toughness are improved as compared with the case where the diameter / thickness ratio tc / D is less than 0.24.
Moreover, since a concrete pile is hollow, the buoyancy which arises when inserting in a pile hole can be reduced. Furthermore, since the weight is lighter than a solid concrete pile, the burden of transportation and pile construction can be reduced.

(2) In some embodiments, in the configuration (1),
The pile body includes two or more cylindrical portions arranged concentrically,
The material constituting the innermost cylindrical portion located in the innermost circumference of the two or more cylindrical portions has a compressive strength smaller than the material constituting the outermost cylindrical portion located in the outermost circumference,
Each of the two or more cylindrical portions is made of a material having a compressive strength of 30 N / mm ² or more.

According to the said structure (2), since the pile body is comprised by the two or more cylindrical parts arrange | positioned concentrically, for example of centrifugal molding, after shaping | molding the outermost cylindrical part, Molding can be performed, and the pile body can be easily molded.
Moreover, according to the said structure (2), since the material which comprises an innermost periphery cylindrical part has compressive strength smaller than the material which comprises an outermost periphery cylindrical part, the material cost of an innermost periphery cylindrical part Can be reduced.
According to the configuration (2), since the compressive strength of the material constituting the outermost peripheral cylindrical portion is larger than the compressive strength of the material constituting the innermost peripheral cylindrical portion, occurrence of cracks in the outermost peripheral cylindrical portion is suppressed, Costs can be reduced while improving bending strength and toughness.
Moreover, according to the said structure (2), since the material which comprises each cylindrical part has the compressive strength of 30 N / mm < ² > or more, the compressive strength of a cylindrical part is not insufficient, bending strength and Toughness can be improved reliably.

(3) In some embodiments, in the configuration (2),
The innermost cylindrical portion is constituted by a grout.
According to the said structure (3), since the innermost peripheral cylindrical part is comprised by the grout which is a sclerosing | hardenable material, formation of an innermost peripheral cylindrical part is easy.

(4) In some embodiments, in any one of the configurations (1) to (3),
The concrete pile is
A tension material that extends inside the pile body in the axial direction of the pile body, and exerts a compressive force on the concrete contained in the pile body,
A first reinforcing member extending in the circumferential direction of the pile body and disposed outside the tendon in the radial direction of the pile body.

  According to the said structure (4), the outer side of a pile body is reinforced with the 1st reinforcement material extended in the circumferential direction of a pile body. As a result, a concrete pile such as a PHC pile having excellent toughness even in a state in which an axial force is acting even if the outer shell steel pipe is not provided.

(5) In some embodiments, in the configuration (4),
The concrete pile is
The inside of the said pile body is further provided with the 2nd reinforcement material extended in the axial direction of the said pile body.

  According to the configuration (5), the second reinforcing member extending in the axial direction of the pile body can increase the bending strength, and a concrete pile such as a PRC pile having higher toughness is provided.

(6) In some embodiments, in the above configuration (4) or (5),
The pile body is
A cylindrical outermost cylindrical portion made of concrete;
A cylindrical innermost cylindrical portion that is located on the inner side in the radial direction of the pile body than the outermost cylindrical portion, and that constitutes the inner peripheral surface of the pile body,
The first reinforcing member is disposed inside the outermost cylindrical portion;
The product of the volume ratio of the first reinforcing material and the yield point in the outermost cylindrical portion is a value greater than 2.45 N / mm ² .

According to the said structure (6), since the product of the volume ratio of the 1st reinforcement in the outermost periphery cylindrical part of a pile body and a yield point is a value larger than 2.45 N / mm < ² >, the outer side of a pile body is ensured. Can be reinforced. As a result, a concrete pile such as a PRC pile or a PHC pile having excellent toughness even in a state in which an axial force is acting, even if the outer shell steel pipe is not provided.

  According to at least one embodiment of the present invention, there is provided a concrete pile having improved bending strength and toughness as compared with the prior art, even if the outer peripheral steel pipe is not provided.

It is a schematic longitudinal cross-sectional view of the concrete pile with an outer shell steel pipe which concerns on one Embodiment of this invention. It is a schematic sectional drawing which follows the II-II line of FIG. It is sectional drawing equivalent to FIG. 2 of the concrete pile with an outer shell steel pipe which concerns on one Embodiment of this invention. It is a figure for demonstrating the effect by setting diameter thickness ratio T / D to 0.24 or more. It is a flowchart which shows the schematic procedure of an example of the manufacturing method of the concrete pile with an outer shell steel pipe shown in FIG. It is a flowchart which shows the schematic procedure of an example of the manufacturing method of the concrete pile with an outer shell steel pipe shown in FIG. It is a figure which shows the schematic structure of the test apparatus of a concrete pile with an outer shell steel pipe with the concrete pile with an outer shell steel pipe. It is a graph which shows the loading step to a test body. It is an envelope diagram of the relationship between the load and center deflection in an example and a comparative example. It is a schematic longitudinal cross-sectional view of the prestressed reinforced high strength concrete pile which concerns on other one Embodiment of this invention. It is a schematic sectional drawing which follows the XI-XI line of FIG. It is a flowchart which shows the schematic procedure of an example of the manufacturing method of the prestressed reinforced high strength concrete pile shown in FIG. It is a schematic longitudinal cross-section of the node pile which is a kind of ready-made concrete pile which concerns on other one Embodiment of this invention. It is a schematic longitudinal cross-sectional view of the diameter-expanded pile which is a kind of ready-made concrete pile which concerns on other one Embodiment of this invention.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Absent.
For example, expressions expressing relative or absolute arrangements such as “in a certain direction”, “along a certain direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” are strictly In addition to such an arrangement, it is also possible to represent a state of relative displacement with an angle or a distance such that tolerance or the same function can be obtained.
For example, an expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also has a tolerance or a difference that can provide the same function. It also represents the existing state.
For example, expressions representing shapes such as quadrangular shapes and cylindrical shapes represent not only geometrically strict shapes such as quadrangular shapes and cylindrical shapes, but also irregularities and chamfers as long as the same effects can be obtained. A shape including a part or the like is also expressed.
On the other hand, the expressions “comprising”, “comprising”, “comprising”, “including”, or “having” one constituent element are not exclusive expressions for excluding the existence of the other constituent elements.

FIG. 1 is a longitudinal sectional view schematically showing the configuration of a concrete pile with an outer shell steel pipe (hereinafter also referred to as SC pile) 1 (1A) according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view taken along the line II-II in FIG. FIG. 3 is a cross-sectional view corresponding to FIG. 2 of an SC pile 1 (1B) according to another embodiment of the present invention.
As shown in FIGS. 1-3, SC pile 1 (1A, 1B) is provided with the outer shell steel pipe 3 and the pile body 5 (5A, 5B).
The outer shell steel pipe 3 has a cylindrical shape, and is made of, for example, a general-purpose rolled steel material. The outer shell steel pipe 3 has an outer diameter D of, for example, 300 mm or more and 1500 mm or less, and the outer diameter D of the outer shell steel pipe 3 corresponds to the outer diameter of the SC pile 1 (1A, 1B). Moreover, the outer shell steel pipe 3 has a wall thickness ts of 4.5 mm or more and 25 mm or less, for example.

  The pile body 5 (5A, 5B) is disposed in the outer shell steel pipe 3 in a state of adhering to the inner peripheral surface of the outer shell steel pipe 3, and includes concrete at least partially. The pile body 5 (5A, 5B) has a cylindrical shape and is formed, for example, by curing a curable material, and has a thickness tc as seen in a cross section as shown in FIGS. For example, an annular end plate 7 is attached to both ends of the outer shell steel pipe 3 by welding, and the pile body 5 (5A, 5B) extends between the two end plates 7 in the axial direction of the outer shell steel pipe 3. It extends. In addition, when the end plate 7 is attached, the length L of the SC pile 1 (1A, 1B) is the length between the outer surfaces of the end plate 7. SC pile 1 (1A, 1B) has length L of 2 m or more and 15 m or less, for example.

Here, as shown in FIGS. 2 and 3, the thickness T of the SC pile 1 (1A, 1B) is the thickness ts of the outer shell steel pipe 3 and the thickness tc of the pile body 5 (5A, 5B). The sum (ts + tc), which is half of the difference between the outer diameter D and the inner diameter d of the SC pile 1 (1A, 1B).
And in SC pile 1 (1A, 1B), diameter thickness ratio T / D which is the ratio of thickness T with respect to outer diameter D of SC pile 1 (1A, 1B), in other words, outer shell steel pipe 3 The diameter-thickness ratio T / D, which is the ratio of the total thickness (ts + tc) of the outer shell steel pipe 3 and the pile body 5 (5A, 5B) to the outer diameter D of
0.24 ≦ T / D <0.5
The relationship indicated by is satisfied.

According to the above configuration, the diameter-thickness ratio T / D is less than 0.5, and the pile body 5 (5A, 5B) has a cylindrical shape and is not completely solid, but a columnar shape in the center in the radial direction. With cavities. For this reason, when a crack occurs in the inner peripheral surface of the pile body 5 (5A, 5B), a part of the inner peripheral surface of the pile body 5 (5A, 5B) is peeled off, and the SC pile 1 (1A, 1B) Bending strength and toughness may be reduced.
However, according to the above configuration, since the diameter-thickness ratio T / D is 0.24 or more, the bending strength and toughness are improved as compared with the case where the diameter-thickness ratio T / D is less than 0.24.

Here, FIG. 4A and FIG. 4B are diagrams for explaining an effect obtained by setting the diameter-thickness ratio T / D to 0.24 or more.
As shown in FIG. 4A, when the diameter-thickness ratio T / D is less than 0.24, if a bending moment acts on the SC pile 1 ′, the pile body 5 ′ breaks at 60 degrees, and 60 It is considered that the debris 10 having the apex angle of degree is easy to peel off.

On the other hand, as shown in FIG. 4B, when the diameter-thickness ratio T / D is 0.24 or more, the pile body 5 even if a bending moment acts on the SC pile 1 (1A, 1B). It is considered that the 60-degree fracture at (5A, 5B) is suppressed, and peeling of the fragments having a 60-degree apex angle is prevented.
In this way, separation of not only large fragments having apex angles larger than 60 degrees but also small fragments having apex angles of 60 degrees prevents the thickness-thickness ratio T / D from being 0.24. In the above case, it is considered that the bending strength and toughness are improved as compared with the case where the diameter-thickness ratio T / D is less than 0.24.

  In the above embodiment, the lower limit of the diameter-thickness ratio T / D is set to 0.24, but is preferably set to 0.245, more preferably set to 0.25, and even more preferably 0.8. 26.

In some embodiments, as shown in FIG. 3, the pile body 5 </ b> B includes two or more cylindrical portions 9 a and 9 b arranged concentrically. Two or more cylindrical portions 9a and 9b are attached to each other.
Of the two or more cylindrical portions 9a and 9b, the material constituting the innermost circumferential cylindrical portion 9a located at the innermost circumference is smaller in compressive strength than the material constituting the outermost circumferential cylindrical portion 9b located at the outermost circumference. Have
Furthermore, each of the two or more cylindrical portions 9a and 9b is made of a material having a compressive strength of 30 N / mm ² or more.

According to the said structure, since the pile body 5B is comprised by the two or more cylindrical parts 9a and 9b arrange | positioned concentrically, the innermost peripheral cylinder is formed after the outermost peripheral cylindrical part 9b is formed using, for example, centrifugal molding. The portion 9a can be formed, and the pile body 5B can be easily formed.
Moreover, according to the said structure, since the material which comprises the innermost periphery cylindrical part 9a has a compressive strength smaller than the material which comprises the outermost periphery cylindrical part 9b, the material cost of the innermost periphery cylindrical part 9a Can be reduced.

  According to the above configuration, since the compressive strength of the material constituting the outermost peripheral cylindrical portion 9b is larger than the compressive strength of the material constituting the innermost peripheral cylindrical portion 9a, the occurrence of cracks in the outermost peripheral cylindrical portion 9b is suppressed, Costs can be reduced while improving bending strength and toughness.

Moreover, according to the said structure, since the material which comprises each cylindrical part 9a, 9b has the compressive strength of 30 N / mm < ² > or more, the compressive strength of cylindrical part 9a, 9b is not insufficient, Bending strength and toughness can be reliably improved.
In addition, when the pile body 5B is comprised by several cylindrical part 9a, 9b, as shown in FIG. 3, thickness tc of the pile body 5B is thickness tc1, tc2 of each cylindrical part 9a, 9b. The total is (tc1 + tc2).

In some embodiments, the outermost cylindrical portion 9b is made of concrete, and the innermost cylindrical portion 9a is made of grout. The grout is, for example, cement paste or mortar.
According to the said structure, since the innermost periphery cylindrical part 9a is comprised by the grout which is a sclerosing | hardenable material, formation of the innermost periphery cylindrical part 9a is easy. Further, the use of grout can reduce the material cost.

In some embodiments, the innermost cylindrical portion 9a and the outermost cylindrical portion 9b are each made of concrete, and the innermost cylindrical portion 9a is made of concrete having a smaller compressive strength than the outermost cylindrical portion 9b. ing.
According to the said structure, reduction of material cost can be aimed at by applying concrete whose compressive strength is lower than the outermost periphery cylindrical part 9b to the innermost periphery cylindrical part 9a.

  In addition, like the pile body 5B shown in FIG. 3, when the pile body 5B includes two or more cylindrical portions 9a and 9b, the thickness tc2 of the outermost cylindrical portion 9b with respect to the thickness T of the pile body B The ratio tc2 / T is set to 0.4 to 0.6, for example, but is not limited to this.

FIG. 5 is a flowchart showing a schematic procedure of an example of a method for manufacturing SC pile 1 (1A).
As shown in FIG. 5, the pile manufacturing method of SC pile 1 (1A) includes outer shell steel pipe preparation step S1, precast step (first precast step) S2, and centrifugal forming step (first centrifugal forming step) S3. And.

The outer shell steel pipe 3 is prepared in the outer shell steel pipe preparation step S1.
In the precast process S2, the outer shell steel pipe 3 is filled with ready-mixed concrete. This filling is performed by a screw feeder having a diameter that can be inserted into the outer shell steel pipe 3. The screw feeder is filled with ready-mixed concrete while being gradually pulled out when the ready-mixed concrete has been filled to some extent.

In the centrifugal molding step S3, the outer steel tube 3 filled with the ready-mixed concrete is put into a mold of a centrifugal molding apparatus, and the ready-mixed concrete is subjected to centrifugal molding by rotating the mold.
Thereafter, when the ready-mixed concrete exhibits a certain level of strength, the outer steel tube 3 is removed from the mold of the centrifugal molding apparatus, and steam curing is performed to form the cylindrical pile body 5 (5A).

FIG. 6 is a flowchart showing a schematic procedure of an example of a method for producing SC pile 1 (1B).
The SC pile 1 (1B) manufacturing method shown in FIG. 6 is different from the SC pile 1 (1A) manufacturing method shown in FIG. 5 in that it has a second precast step S4 and a second centrifugal molding step S5. Yes. According to the SC pile 1 (1B) manufacturing method shown in FIG. 6, the inside of the ready-mixed concrete molded in the first centrifugal molding step S3 in the second precast step S4 performed after the first centrifugal molding step S3. In addition, fresh concrete is further filled.

In the second centrifugal molding step S5, as in the first centrifugal molding step S3, the outer shell steel pipe 3 further filled with ready-mixed concrete is placed in the mold of the centrifugal molding apparatus, and the ready-mixed concrete is rotated by rotating the mold. Centrifugal molding is performed.
After that, when the ready-mixed concrete filled in the first precast step S2 and the second precast step S4 has developed a certain level of strength, the outer steel tube 3 is removed from the mold of the centrifugal molding apparatus, and steam curing is performed. A shaped pile body 5 (5B) is formed.
Note that the strength of the ready-mixed concrete filled in the first precast step S2 is not necessarily expressed before the second precast step S4.

〔Example〕
Examples will be described below.
1. Preparation of test body First, SC piles having the specifications shown in Tables 1 to 3 below were prepared as test bodies of Comparative Examples 1 and 2 and Examples 1 and 2.

2. Test Method An outline of the test apparatus 20 is shown in FIG. The test was a simple beam type bending test, and unidirectional repeated loading. The test device 20 includes a support device 22 for supporting the SC pile 1 as a test body at a support point, a displacement meter 24 for measuring displacements at both ends and the center of the test body, and a central portion of the test body. A load device (not shown) for applying a load evenly at two locations is provided.

FIG. 8 shows a loading step on the test body. When the member angle was in the range of 2.5 / 1000 rad to 50/1000 rad, the test specimen was repeatedly loaded twice until reaching the member angle. When the member angles were 80/1000 and 100/1000 rad, each specimen was loaded once until each member angle was reached. However, when it did not exceed the load at the time of the previous member angle, the subsequent loading step was set as one loading.
The member angle is a value obtained by dividing the deflection amount at the center of the pile by the distance from the support point to the center of the loading point.

3. Test results As test results, an envelope diagram of the relationship between load and center deflection is shown in FIG. 9, the maximum load and yield strength ratio of each test specimen are shown in Table 4, and the center deflection (residual displacement) of each specimen is 100 mm. Table 5 shows the load and the rate of decrease in yield strength.

As apparent from FIG. 9 and Table 4, in the SC piles of Example 1 and Example 2 having a diameter / thickness ratio T / D of 0.24 or more, Comparative Example 2 having a diameter / thickness ratio T / D of less than 0.24 Compared to the SC piles, a large maximum load is developed. For this reason, it turns out that the SC pile of Example 1 and Example 2 has favorable proof stress compared with the SC pile of Comparative Example 2.
On the other hand, as is clear from FIG. 9 and Table 5, in the SC piles of Example 1 and Example 2 having a diameter / thickness ratio T / D of 0.24 or more, the diameter / thickness ratio T / D is less than 0.24. Compared with the SC pile of Example 2, the load when the center deflection is 100 mm is large, and the yield reduction rate is low as compared with the SC pile of Comparative Example 2. From this, it can be seen that the SC piles of Example 1 and Example 2 have better toughness than the SC pile of Comparative Example 2.

  In particular, in the SC pile of Example 2 having a diameter / thickness ratio T / D of 0.33, even when compared with the SC pile of Comparative Example 1 having a diameter / thickness ratio T / D of 0.50, the same maximum load was developed. In addition, the load when the center deflection is 100 mm is substantially the same, and it can be seen that the SC pile of Example 2 has particularly good proof stress and toughness.

The present invention is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.
For example, the molding method of the innermost peripheral cylindrical portion 9a is not limited to centrifugal molding, and may be performed by, for example, placing a mold and vibration packing.
Furthermore, the present invention is not limited to SC piles, and can be applied to ready-made concrete piles that do not have a shell steel pipe as described below. In the following description, the same or similar configurations as those of the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified.

  FIG. 10 is a schematic longitudinal sectional view of a PRC pile (prestressed reinforced high strength concrete pile) 30 according to another embodiment of the present invention. FIG. 11 is a schematic cross-sectional view taken along line XI-XI in FIG. 10, and FIG. 10 is a schematic cross-sectional view taken along line XX in FIG.

  As shown in FIGS. 10 and 11, the PRC pile 30 is different from the SC pile 1A in that it does not have a shell steel pipe. On the other hand, the PRC pile 30 includes a plurality of PC steel members (PC steel bars) 32 as tension members, a shear reinforcement bar 34 as a first reinforcement member, and a plurality of deformed reinforcing bars 36 as a second reinforcement member. Yes.

  Each of the plurality of PC steel materials 32 extends inside the pile body 5B in the axial direction of the pile body 5B, and is bridged between end plates 7 and 7 disposed at both ends. The plurality of PC steel materials 32 are arranged concentrically when viewed in the axial direction of the pile body 5B. Both ends of the plurality of PC steel materials 32 are engaged with the end plates 7 and 7, and the plurality of PC steel materials 32 together with the end plates 7 and 7 exert a compressive force on the concrete included in the pile body 5 </ b> B. For example, 6 or more and 24 or less PC steel materials 32 are arranged, and are arranged at equal intervals in the circumferential direction of the pile body 5B. The PC steel material 32 has a diameter of 10 mm or more and 12 mm or less, for example.

The shear reinforcing bar 34 as the first reinforcing member extends inside the pile body 5B in the circumferential direction of the pile body 5B, and is disposed outside the PC steel material 32 in the radial direction of the pile body 5B. In the present embodiment, the shear reinforcement bar 34 extends spirally inside the pile body 5B and extends in the axial direction of the pile body 5B. The shear reinforcing bar 34 has, for example, a diameter of 5.0 mm to 7.5 mm, a strength of 785 N / mm ² , and extends in a spiral shape with a pitch of 50 mm to 100 mm. In addition, the shear reinforcement 34 is good also as providing the ring-shaped thing extended in the circumferential direction of the pile body 5B along the axial direction of the pile body 5B instead of spiral. Moreover, the shear reinforcement bar 34 may be comprised with the round steel and the deformed bar.

  The plurality of deformed reinforcing bars 36 as the second reinforcing members are disposed between the end plates 7 and 7 disposed at both ends, respectively, extending inside the pile body 5B in the axial direction of the pile body 5B. The plurality of deformed reinforcing bars 36 are arranged concentrically in the axial direction of the pile body 5B, and are arranged in the middle of the PC steel material 32 in the circumferential direction of the pile body 5B. For example, the diameter of the circle where the deformed reinforcing bar 36 is arranged is equal to or slightly smaller than the diameter of the circle where the PC steel material 32 is arranged.

The PRC pile 30 has the following formula when the outer diameter of the PRC pile 30, that is, the outer diameter of the pile body 5B is D, the thickness of the pile body 5B is tc, and the diameter-thickness ratio is tc / D:
0.24 ≦ tc / D <0.5
The relationship indicated by is satisfied.

According to the above configuration, the diameter-thickness ratio tc / D is less than 0.5, and the pile body 5B has a cylindrical shape and is not completely solid, and has a columnar cavity at the radial center. For this reason, when a crack generate | occur | produces in the pile body 5B, a part of inner surface of the pile body 5B may peel off and there exists a possibility that the bending strength and toughness of the PRC pile 30 may fall.
However, according to the above configuration, since the diameter / thickness ratio tc / D is 0.24 or more, the bending strength and toughness are improved as compared with the case where the diameter / thickness ratio tc / D is less than 0.24.
Moreover, since the PRC pile 30 is hollow, the buoyancy generated when inserted into the pile hole can be reduced. Furthermore, since the weight is lighter than a solid concrete pile, the burden of transportation and pile construction can be reduced.

  In the above embodiment, the lower limit of the diameter-thickness ratio tc / D is set to 0.24, but is preferably set to 0.245, and more preferably set to 0.25.

  Note that the PRC pile 30 may further include a tubular member 38 for protecting the outer peripheral surfaces of both ends of the pile body 5B. Each tubular member 38 is fixed to the end plate 7 by welding, for example, and covers one end portion of the outer peripheral surface of the pile body 5B. That is, the pile body 5B of the PRC pile 30 only needs to have an outer peripheral surface that is not covered with a metal material even in a part in the middle in the axial direction, and a part of the PRC pile 30 is a shell steel pipe. It may be covered with.

  In some embodiments, at least the outermost cylindrical portion 9b of the innermost peripheral cylindrical portion 9a and the outermost peripheral cylindrical portion 9b is made of concrete, and a PC steel material 32 as a tension material, and a shear reinforcement as a first reinforcing material. 34 and the deformed reinforcing bar 36 as the second reinforcing member are disposed inside the outermost cylindrical portion 9b.

In some embodiments, the shear reinforcing bar 34 as the first reinforcing member is disposed inside the outermost cylindrical portion 9b of the pile body 5B, and the volume ratio and the yield point of the first reinforcing member in the outermost cylindrical portion 9b ( The product of yield strength is greater than 2.45 N / mm ² .
According to the said structure, since the product of the volume ratio of the shear reinforcement 34 as a 1st reinforcement in the outermost periphery cylindrical part 9b of the pile body 5B and a yield point is a value larger than 2.45 N / mm < ² >, a pile body The outer side of 5B can be reinforced reliably. As a result, the PRC pile 30 having excellent toughness even in a state where the axial force is acting even if the outer shell steel pipe is not provided is provided.

FIG. 12 is a flowchart schematically showing the procedure of the method for manufacturing the PRC pile 30.
The manufacturing method of the PRC pile 30 includes a reinforcing steel bar preparation step S6 instead of the outer shell steel pipe preparation step S1 when compared with the manufacturing method of the SC pile 1B shown in FIG. In the reinforcing steel bar preparation step S6, a reinforcing steel car made of the PC steel material 32, the shear reinforcing bar 34, and the deformed steel bar 36 is prepared.
Moreover, the manufacturing method of the PRC pile 30 is further provided with the tension | tensile_strength process S7 and the prestress introduction process S8, in order to introduce prestress into the pile body 5B.

The tension step S7 is performed after the first precast step S2. In the tensioning step S7, the PC steel material 32 is pulled in the axial direction by a jack, and is held in a pulled state as it is. Specifically, an adapter is attached to the end plate 7, and the adapter is pulled with a jack. The adapter includes a disc-shaped tension plate fixed to the outer surface of the end plate 7 with a bolt, a tension rod provided integrally with the tension plate and extending through the end surface of the mold, and a tension capable of being screwed to the tension rod. It consists of a nut. While pulling the tension rod with the jack, the PC steel material 32 can be held in a pulled state by screwing the tension nut until it comes into contact with the end face of the mold.
The PC steel material 32 is held in a stretched state during the first centrifugal molding step S3, the second precast step S4, and the second centrifugal molding step S5.

After completion of the second centrifugal molding step S5, steam curing is performed according to a predetermined curing program.
After performing the steam curing for a predetermined time, in the pre-stress introduction step S8, the pulled state of the PC steel material 32 is released. That is, the tension nut is loosened. As a result, the pulled PC steel material 32 tends to shrink, and prestress is introduced into the pile body 5B by the end plates 7 and 7 and the PC steel material 32. That is, before the PRC pile 30 is actually used, a compressive force is applied to the pile body 5B in advance.
Note that the prestress introduction step S8 may be performed between the first centrifugal molding step S3 and the second precast step S4. In this case, prestress is introduced only into the outermost peripheral cylindrical portion 9b of the pile body 5B.

  FIG. 13 is a schematic longitudinal sectional view of a joint pile 40 which is a kind of ready-made concrete pile according to another embodiment of the present invention. The joint pile 40 is different from the PRC pile 30 in that it has one or more joint portions 42 protruding from the outer peripheral surface of the pile body 5B. The node portion 42 is integrally formed with the outermost cylindrical portion 9b by concrete. In the joint pile 40, the position of the cross section that defines the thickness tc and the outer diameter D of the pile body 5B is a position where the joint portion 42 is not provided in the axial direction of the pile body 5B.

  FIG. 14 is a schematic vertical cross-sectional view of an enlarged-diameter pile (ST pile) 50 which is a kind of ready-made concrete pile according to another embodiment of the present invention. The ST pile 50 is different from the PRC pile 30 in that the outer diameter of one end portion (the enlarged diameter portion 52) of the pile body 5B is larger than the intermediate portion of the pile body 5B. The enlarged diameter portion 52 is integrally formed with the outermost peripheral cylindrical portion 9b by concrete, like the node portion 42. In the ST pile 50, the position of the cross section that defines the thickness tc and the outer diameter D of the pile body 5B is a position where the diameter-expanded portion 52 is not provided in the axial direction of the pile body 5B.

  In addition, although the ST pile 50 of FIG. 14 is diameter-expanded only at one end part, the present invention has a diameter-expanded pile in which both ends of the pile body 5B are expanded, or an intermediate part in the axial direction of the pile body 5B. It can also be applied to expanded intermediate piles. Moreover, although the ST pile 50 of FIG. 14 does not have the node part 42, the ST pile 50 may have the node part 42.

Finally, the present invention is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.
For example, in the above-described embodiment, the PRC pile 30 includes a plurality of deformed reinforcing bars 36 as the second reinforcing material, but may not include the deformed reinforcing bars 36. That is, the present invention can be applied not only to the PRC pile 30 but also to a prestressed high-strength concrete pile (PHC pile) which is a kind of ready-made concrete pile.
Moreover, in the PRC pile 30, each deformed reinforcing bar 36 extends over the entire length of the pile body 5B, but the length of each deformed reinforcing bar 36 may be shorter than the entire length of the pile body 5B.

1 (1A, 1B) Concrete pile with outer shell steel pipe (SC pile)
3 Outer shell 5 (5A, 5B) Pile body 7 End plate 9 Cylindrical portion 9a Innermost cylindrical portion 9b Outermost cylindrical portion 10 Fragment 20 Test device 22 Support device 24 Displacement meter 30 Prestressed reinforced high strength concrete pile (PRC pile) )
32 PC steel (tension material)
34 Shear reinforcement (first reinforcement)
36 Deformed bar (second reinforcement)
38 Tubular material 40 Joint pile 42 Joint section 50 Expanded pile (ST pile)
52 Expanded part

Claims (6)

In a concrete pile provided with a hollow and cylindrical pile body including concrete at least in part,
The pile body has an outer peripheral surface that is not covered with a metal material at an intermediate portion in the axial direction of the pile body,
When the outer diameter of the pile body is D, the thickness of the pile body is tc, and the diameter-thickness ratio is tc / D, the following formula:
0.24 ≦ tc / D <0.5
A concrete pile characterized by satisfying the relationship indicated by. The pile body includes two or more cylindrical portions arranged concentrically,
The material constituting the innermost cylindrical portion located in the innermost circumference of the two or more cylindrical portions has a compressive strength smaller than the material constituting the outermost cylindrical portion located in the outermost circumference,
2. The concrete pile according to claim 1, wherein each of the two or more cylindrical portions is made of a material having a compressive strength of 30 N / mm ² or more.   The concrete pile according to claim 2, wherein the innermost cylindrical portion is made of grout. A tension material that is arranged inside the pile body along the axial direction of the pile body, and exerts a compressive force on the concrete contained in the pile body,
A first reinforcing member disposed inside the pile body along the circumferential direction of the pile body and disposed outside the tendon material in the radial direction of the pile body; The concrete pile according to any one of claims 1 to 3.   The concrete pile according to claim 4, further comprising a second reinforcing member disposed inside the pile body along an axial direction of the pile body. The pile body is
A cylindrical outermost cylindrical portion made of concrete;
A cylindrical innermost circumferential cylindrical portion that is positioned on the inner side in the radial direction of the pile body than the outermost circumferential cylindrical portion, and constitutes an inner circumferential surface of the pile body;
The first reinforcing member is disposed inside the outermost cylindrical portion;
6. The concrete pile according to claim 4, wherein a product of a volume ratio of the first reinforcing member and a yield point in the outermost cylindrical portion is a value larger than 2.45 N / mm ² .

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