Cast-in-place concrete piles

Abstract

To provide cast-in-place concrete piles that can suppress cost increases. [Solution] A cast-in-place concrete pile 10 comprising a reinforced concrete pile body 12, the pile head 20 at the upper end of the pile body 12 being embedded in a reinforced concrete pile head joint 22, comprising: a plurality of main reinforcing bars 14 provided inside the pile body 12 along the axial direction of the pile body 12 and anchored to the pile head joint 22; a plurality of shear reinforcing bars 16 provided inside the pile body 12 along the circumferential direction of the pile body 12 so as to surround the main reinforcing bars 14; and a steel pipe 18 provided so as to cover the outer surface of the pile body 12 over a predetermined length from the pile head 20.

Description

Technical Field

[0001] The present invention relates to cast-in-place concrete piles.

Background Art

[0002] Conventionally, as one of the widely spread and established pile foundation structures, a cast-in-place reinforced concrete pile with main reinforcement and shear reinforcement arranged throughout the pile length is known (see, for example, Patent Document 1). The cast-in-place reinforced concrete pile is preferentially selected together with steel pipe piles when adjacent to adjacent land or in a narrow area. Since the pile body is constructed by placing concrete in muddy water using the ground as a formwork, it is necessary to appropriately perform quality control of the pile body concrete.

[0003] In recent years, Non-Patent Document 1 has been published by the Architectural Institute of Japan as a guideline for the design of pile foundation structures. In this guideline, the design limit value R n for pile types based on experimental research data, the reduction coefficient β1 for the design formula, and the reduction coefficient β2 based on deformation performance and axial force retention performance are shown. The value obtained by multiplying each coefficient is the "design bearing capacity" of the pile.

[0004] According to this guideline, for cast-in-place reinforced concrete piles, the reduction coefficient β1 for shear force should be set to 0.9 or less, and when the axial stress degree exceeds (1 / 3)·ξ·F c the reduction coefficients β2 for bending moment and shear force should be set to 0.65 or less, respectively. ξ is a coefficient related to the quality control of construction, and takes a value of 0.75 or less when normal construction quality control is performed. F c is the design standard strength of concrete. Note that the coefficients β1, β2, and ξ can be expanded in the applicable range in the future after individually conducting experimental or analytical studies, as suggested in the explanation of basic matters in Chapter 2 of Non-Patent Document 1.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-37787 [Non-patent literature]

[0006] [Non-Patent Document 1] "Strength and Deformation Performance of Foundation Members," Architectural Institute of Japan, 2022. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In the future, cast-in-place reinforced concrete piles designed in accordance with the above guidelines may have larger pile diameters than conventional designs for the same design stress. Larger pile diameters will increase the cost of pile construction.

[0008] The present invention has been made in view of the above, and aims to provide a cast-in-place concrete pile that can suppress cost increases. [Means for solving the problem]

[0009] To solve the above-mentioned problems and achieve the objective, the cast-in-place concrete pile according to the present invention is a cast-in-place concrete pile comprising a reinforced concrete pile body, wherein the pile head at the upper end of the pile body is embedded in a reinforced concrete pile head joint, and is characterized by comprising: a plurality of main reinforcing bars provided inside the pile body along the axial direction of the pile body and anchored to the pile head joint; a plurality of shear reinforcing bars provided inside the pile body along the circumferential direction of the pile body so as to surround the main reinforcing bars; and a steel pipe provided so as to cover the outer surface of the pile body over a predetermined length from the pile head.

[0010] Furthermore, another cast-in-place concrete pile according to the present invention is characterized in that, in the above-described invention, the steel pipe is provided from the pile head to a length of 3 to 5 times the diameter of the pile body, the thickness of the steel pipe is 6 mm or more, and the diameter-to-thickness ratio is 150 or less.

[0011] Furthermore, in the present invention, another cast-in-place concrete pile is characterized in that, in the above-described invention, the shear reinforcement bars are arranged at intervals in the axial direction of the pile body, and the spacing of the shear reinforcement bars arranged inside the pile body in which the steel pipe is provided is greater than the spacing of the shear reinforcement bars arranged inside the pile body in which the steel pipe is not provided. [Effects of the Invention]

[0012] The cast-in-place concrete pile according to the present invention comprises a reinforced concrete pile body, the pile head at the upper end of the pile body being embedded in a reinforced concrete pile head joint, and includes a plurality of main reinforcements provided inside the pile body along the axial direction of the pile body and anchored to the pile head joint, a plurality of shear reinforcements provided inside the pile body along the circumferential direction of the pile body so as to surround the main reinforcements, and a steel pipe provided to cover the outer surface of the pile body for a predetermined length from the pile head. This makes it possible to reduce the pile diameter and has the effect of suppressing an increase in the cost of constructing the pile.

[0013] Furthermore, according to another cast-in-place concrete pile according to the present invention, the steel pipe is provided from the pile head for a length of 3 to 5 times the diameter of the pile body, the thickness of the steel pipe is 6 mm or more, and the diameter-to-thickness ratio is 150 or less, thus providing the effect of reducing the pile diameter while maintaining the same strength as conventional piles.

[0014] Furthermore, according to another cast-in-place concrete pile according to the present invention, the shear reinforcement bars are arranged at intervals in the axial direction of the pile body, and the spacing of the shear reinforcement bars arranged inside the pile body in which the steel pipe is provided is greater than the spacing of the shear reinforcement bars arranged inside the pile body in which the steel pipe is not provided, thereby having the effect of reducing the quantity of shear reinforcement bars. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic side sectional view showing an embodiment of a cast-in-place concrete pile according to the present invention. [Figure 2] Figure 2 is a comparison diagram of the relationship between the bending moment and the curvature of a cast-in-place concrete pile. [Figure 3] Figure 3 is a comparison diagram of the relationship between the bending moment and the curvature of a cast-in-place concrete pile.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of a cast-in-place concrete pile according to the present invention will be described in detail based on the drawings. Note that the present invention is not limited by these embodiments.

[0017] As shown in Figure 1, a cast-in-place concrete pile 10 according to an embodiment of the present invention includes a reinforced concrete pile body 12 constructed in the ground G, main reinforcement bars 14 and shear reinforcement bars 16 provided inside the pile body 12, and a steel pipe 18 provided on the upper portion of the pile body 12. The pile head portion 20 at the upper end of the pile body 12 is embedded in a reinforced concrete pile head joint portion 22. The pile head joint portion 22 is a portion that joins the pile head portion 20 and a reinforced concrete foundation structure of a structure (not shown) supported by the cast-in-place concrete pile 10.

[0018] The pile body 12 is a cylindrical pile body extending in the vertical up-and-down direction (axial direction). Note that the bottom of the pile body 12 (not shown) has an enlarged diameter and is fixed to the underlying ground support layer.

[0019] The main reinforcement bars 14 are reinforcing bars continuously provided in the vertical direction over the entire length of the pile body 12, and a plurality of them are arranged at predetermined intervals in the circumferential direction of the pile body 12. The upper ends of the main reinforcement bars 14 protrude from the pile head portion 20 and are fixed inside the pile head joint portion 22. The main reinforcement bars 14 may be a part of a well-known steel cage used for cast-in-place concrete piles.

[0020] The shear reinforcement bars 16 are reinforcing bars (hoop bars) that are provided in a substantially horizontal ring shape along the circumferential direction of the pile body 12 so as to surround the main reinforcement bars 14, and multiple bars are arranged at predetermined intervals in the vertical direction. The vertical spacing of the shear reinforcement bars 16 is set so that the spacing L1 of the shear reinforcement bars 16 in the upper part of the pile body 12 where the steel pipe 18 is installed is larger than the spacing L2 of the shear reinforcement bars 16 in the lower part of the pile body 12 where the steel pipe 18 is not installed. In other words, L1 > L2. This makes it possible to reduce the number of shear reinforcement bars 16 inside the steel pipe 18 to the number of shear reinforcement bars 16 in the lower part of the pile body 12 where the steel pipe 18 is not installed, thereby reducing the total number of shear reinforcement bars 16 in the pile body 12. However, the present invention is not limited to this, and the spacing of the shear reinforcement bars 16 may be set at equal intervals along the entire length of the pile body 12. The shear reinforcement bars 16 may be part of a well-known reinforcing cage used in cast-in-place concrete piles.

[0021] The steel pipe 18 is a circular steel pipe installed to cover the outer surface of the pile body 12 over a predetermined length from the pile head 20. The upper part of the steel pipe 18 is embedded in the pile head joint 22. If the diameter of the pile body 12 (pile diameter) is D, it is desirable to set the length H of the steel pipe 18 to about 3 to 5D. The thickness (wall thickness) of the steel pipe 18 should be 6 mm or more, and the diameter-to-thickness ratio, which is the ratio of the pipe diameter to the thickness of the steel pipe 19, should be 150 or less. By doing so, the pile diameter D can be reduced while maintaining the same strength as conventional methods. It is not necessary to provide rib-like protrusions or the like on the inner surface of the steel pipe 18.

[0022] According to the above configuration, compared to a typical cast-in-place concrete pile, the confining effect of the steel pipe 18 in the upper part of the pile body 12 allows for high axial stress (axial stress (1 / 3)·ξ·F). cAs a result of the improved deformation performance and axial force holding performance described above, the reduction coefficient β2 for bending moment and shear force described in the above guidelines can be raised from 0.65 to 1.0 or less. Therefore, for the same design horizontal force, the pile diameter D can be reduced compared to a typical cast-in-place concrete pile. In addition, the number of shear reinforcements 16 in the section where the steel pipe 18 is provided can be reduced. Thus, according to this embodiment, the increase in the cost of pile construction can be suppressed.

[0023] (Verification of the effects of the present invention) To verify the effects of the present invention, bending experiments were conducted on cast-in-place concrete piles under compressive axial force to investigate the relationship between bending moment and curvature. In the above embodiment, a steel pipe 18 with a thickness of 8 mm was provided on the upper part of the pile body 12 as an embodiment of the present invention, and a pile without the steel pipe 18 was used as a comparative example. The spacing of the shear reinforcement bars 16 was set to 100 mm pitch, and the design compressive strength F of the concrete of the pile body 12 was set. c It is 60 N / mm 2 That's what I decided.

[0024] Figures 2 and 3 show the relationship between bending moment and curvature. Figure 2 shows the case with an axial force ratio of 0.3, and Figure 3 shows the case with an axial force ratio of 0.6. As these figures show, this embodiment exhibits superior deformation performance compared to the comparative example. Therefore, according to this embodiment, even when designing in accordance with the above guidelines, it is possible to reduce the pile diameter of cast-in-place concrete piles supporting high axial forces compared to conventional designs.

[0025] As described above, the cast-in-place concrete pile according to the present invention comprises a reinforced concrete pile body, the pile head at the upper end of the pile body being embedded in a reinforced concrete pile head joint, and includes a plurality of main reinforcements provided inside the pile body along the axial direction of the pile body and anchored to the pile head joint, a plurality of shear reinforcements provided inside the pile body along the circumferential direction of the pile body so as to surround the main reinforcements, and a steel pipe provided to cover the outer surface of the pile body for a predetermined length from the pile head. Therefore, it is possible to reduce the pile diameter and suppress the increase in costs required for pile construction.

[0026] Furthermore, according to another cast-in-place concrete pile according to the present invention, the steel pipe is provided from the pile head for a length of 3 to 5 times the diameter of the pile body, the thickness of the steel pipe is 6 mm or more, and the diameter-to-thickness ratio is 150 or less, so the pile diameter can be reduced while maintaining the same strength as conventional piles.

[0027] Furthermore, according to another cast-in-place concrete pile according to the present invention, the shear reinforcement bars are arranged at intervals in the axial direction of the pile body, and the spacing of the shear reinforcement bars arranged inside the pile body in which the steel pipe is provided is greater than the spacing of the shear reinforcement bars arranged inside the pile body in which the steel pipe is not provided, so the quantity of shear reinforcement bars can be reduced.

[0028] Furthermore, the "Sustainable Development Goals (SDGs)" are among the 17 international goals adopted at the UN Summit in September 2015. The cast-in-place concrete piles according to this embodiment can contribute to achieving some of the 17 SDGs, such as Goal 12, "Responsible Consumption and Production." [Industrial applicability]

[0029] As described above, the cast-in-place concrete pile according to the present invention is useful for cast-in-place concrete piles used as pile foundations for buildings and the like, and is particularly suitable for suppressing cost increases. [Explanation of symbols]

[0030] 10. Cast-in-place concrete piles 12 Pile body 14 Main reinforcement 16 Shear reinforcement bars 18 Steel pipe 20 Pile head 22 Pile cap joint G Ground

Claims

1. A cast-in-place concrete pile comprising a reinforced concrete pile body, wherein the pile head at the upper end of the pile body is embedded in a reinforced concrete pile head joint, A cast-in-place concrete pile characterized by comprising: a plurality of main reinforcing bars provided inside the pile body along the axial direction of the pile body and anchored at the pile head joint; a plurality of shear reinforcing bars provided inside the pile body along the circumferential direction of the pile body so as to surround the main reinforcing bars; and a steel pipe provided so as to cover the outer surface of the pile body over a predetermined length from the pile head.

2. The cast-in-place concrete pile according to claim 1, characterized in that the steel pipe is provided from the pile head for a length of 3 to 5 times the diameter of the pile body, the thickness of the steel pipe is 6 mm or more, and the diameter-to-thickness ratio is 150 or less.

3. The cast-in-place concrete pile according to claim 1 or 2, characterized in that the shear reinforcement bars are arranged at intervals in the axial direction of the pile body, and the spacing of the shear reinforcement bars arranged inside the pile body in which the steel pipe is provided is greater than the spacing of the shear reinforcement bars arranged inside the pile body in which the steel pipe is not provided.

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