Cast-in-place concrete piles

Abstract

To provide cast-in-place concrete piles that can be easily constructed. [Solution] A cast-in-place concrete pile 10 comprising a reinforced concrete pile body 12, a steel pipe 18 provided to cover the outer peripheral surface of the upper part of the pile body 12 over a predetermined length from the pile head 22 at the upper end of the pile body 12, and the pile head 22 being embedded in a reinforced concrete pile head joint 24, comprising a plurality of main reinforcement bars 14 provided inside the lower part of the pile body 12 along the axial direction of the pile body 12 and having their upper ends fixed inside the upper part of the pile body 12, a plurality of shear reinforcement bars 16 provided inside the lower part of the pile body 12 along the circumferential direction of the pile body 12 so as to surround the main reinforcement bars 14, and a plurality of connecting bars 20 provided from the upper part of the pile body 12 to the inside of the pile head joint 24 and having their upper ends fixed in the pile head joint 24.

Description

[Technical Field]

[0001] This invention relates to cast-in-place concrete piles. [Background technology]

[0002] Conventionally, one of the widely used and established pile foundation structures is the cast-in-place steel pipe concrete pile, which has a steel pipe attached to the top of the pile body (see, for example, Patent Document 1). Cast-in-place steel pipe concrete piles are preferred along with steel pipe piles when the site is close to adjacent land or in a confined space. Since the pile body is constructed by pouring concrete in muddy water using the ground as formwork, it is necessary to properly control the quality of the pile body concrete.

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

[0004] According to these guidelines, for cast-in-place steel pipe concrete piles, the reduction coefficients β1 and β2 can be set to 1.0 or less regardless of the axial force, eliminating the need to reduce the load-bearing capacity. Furthermore, it is suggested in Chapter 2 of Non-Patent Document 1, "Explanation of Basic Matters," that the scope of application of reduction coefficients β1 and β2 may be expanded in the future after individual experimental or analytical studies. [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 project] [Problems that the invention aims to solve]

[0007] Incidentally, in conventional cast-in-place steel pipe concrete piles, the anchoring reinforcement embedded in the pile head joint had to be directly welded to the outer circumference of the upper part of the steel pipe or attached via a coupler, which made construction time-consuming. Therefore, there was a need for a technology that could simplify 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 be easily constructed. [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 comprises a reinforced concrete pile body and a steel pipe provided to cover the outer peripheral surface of the upper part of the pile body over a predetermined length from the pile head at the upper end of the pile body, wherein the pile head is embedded in a reinforced concrete pile head joint, and is characterized by comprising: a plurality of main reinforcements provided inside the lower part of the pile body along the axial direction of the pile body, with their upper ends anchored inside the upper part of the pile body; a plurality of shear reinforcements provided inside the lower part of the pile body along the circumferential direction of the pile body so as to surround the main reinforcements; and a plurality of connecting reinforcements provided from the upper part of the pile body to the inside of the pile head joint, with their upper ends anchored in the pile head joint.

[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. [Effects of the Invention]

[0011] The cast-in-place concrete pile according to the present invention comprises a reinforced concrete pile body and a steel pipe provided to cover the outer circumferential surface of the upper part of the pile body over a predetermined length from the pile head at the upper end of the pile body, with the pile head embedded in a reinforced concrete pile head joint. The cast-in-place concrete pile comprises a plurality of main reinforcement bars provided inside the lower part of the pile body along the axial direction of the pile body, with their upper ends anchored inside the upper part of the pile body; a plurality of shear reinforcement bars provided inside the lower part of the pile body along the circumferential direction of the pile body so as to surround the main reinforcement bars; and a plurality of connecting bars provided from the upper part of the pile body to the inside of the pile head joint, with their upper ends anchored in the pile head joint. Therefore, the work of attaching anchoring bars to the upper part of the steel pipe can be omitted. For this reason, it has the effect of being easier to construct compared to conventional cast-in-place steel pipe concrete piles.

[0012] 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. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic side cross-sectional view showing an embodiment of the cast-in-place concrete pile according to the present invention. [Modes for carrying out the invention]

[0014] The following describes in detail an embodiment of the cast-in-place concrete pile according to the present invention, based on the drawings. However, this embodiment does not limit the present invention.

[0015] As shown in FIG. 1, the cast-in-place concrete pile 10 according to the 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 in the lower part 12A (lower part) of the pile body 12, a steel pipe 18 provided in the upper part 12B (upper part) of the pile body 12, and connecting bars 20. The pile head 22 at the upper end of the pile body 12 is embedded in a reinforced concrete pile head joint 24. The pile head joint 24 is a portion that joins the pile head 22 and the reinforced concrete foundation structure of a structure (not shown) supported by the cast-in-place concrete pile 10.

[0016] 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.

[0017] The main reinforcement bars 14 are reinforcing bars continuously provided in the vertical direction over the entire length inside the lower part 12A 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 lower part 12A of the pile body 12 and are fixed in the lower region 26 of the upper part 12B of the pile body 12. The main reinforcement bars 14 are provided so as not to be continuous up to the upper region 28 of the upper part 12B of the pile body 12 or the pile head joint 24. The main reinforcement bars 14 may be a part of a well-known steel reinforcement cage used for cast-in-place concrete piles.

[0018] The shear reinforcement bars 16 are reinforcing bars (hoop bars) provided in a substantially horizontal annular shape along the circumferential direction of the pile body 12 so as to surround the main reinforcement bars 14, and a plurality of them are arranged at predetermined intervals in the vertical direction. The shear reinforcement bars 16 may be a part of a well-known steel reinforcement cage used for cast-in-place concrete piles.

[0019] The steel pipe 18 is a circular steel pipe installed so as to cover the outer surface of the upper portion 12B of the pile body 12 over a predetermined length from the pile head 22. The upper portion of the steel pipe 18 is embedded in the pile head joint 24. 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 general cast-in-place steel pipe concrete piles. It is not necessary to provide rib-like protrusions on the inner surface of the steel pipe 18. For this reason, in addition to spiral steel pipes (steel pipes with rib-like protrusions arranged spirally on the inner surface) that are commonly used in conventional cast-in-place steel pipe concrete piles, steel pipes with a smooth inner surface can also be used.

[0020] The connecting reinforcement bars 20 are reinforcing bars provided vertically from the inside of the upper portion 12B of the pile body 12 to the inside of the pile head joint 24, and multiple bars are arranged at predetermined intervals around the circumferential direction of the pile body 12. The upper end of the connecting reinforcement bars 20 is anchored inside the pile head joint 24, and the lower end of the connecting reinforcement bars 20 is anchored in the upper region 28 of the upper portion 12B of the pile body 12. The connecting reinforcement bars 20 may also be provided as part of a reinforcing cage. For example, this can be achieved by arranging a reinforcing cage having connecting reinforcement bars 20 with an effective anchorage length from the inside of the upper portion 12B of the pile body 12 to the inside of the pile head joint 24.

[0021] The concrete cover thickness of the connecting reinforcement 20 (the length from the inner surface of the steel pipe 18 to the outer surface of the connecting reinforcement 20) should preferably be 30 mm or more. The horizontal spacing of the connecting reinforcement 20 should preferably be 2.5 times or more the nominal diameter of the reinforcing bars constituting the connecting reinforcement 20. Furthermore, the anchorage length L1 of the connecting reinforcement 20 within the steel pipe 18 should be 1.5D, and the effective anchorage length l d It is desirable to set the value to +0.5D, which is greater than or equal to the maximum of 60% of the shear span. The anchorage length L2 of the joint reinforcement 20 within the pile head joint 24 may be set to be approximately the same as L1. Here, the effective anchorage length l d This is the effective anchorage length of the reinforcing bars that make up the joint reinforcement 20, and can be calculated using the following formula.

[0022] l d = s f t ·A o / (0.8· s f a · r φ) s f t : Design tensile strength of steel bar for short term A o : Cross-sectional area of steel bar s f a : Design bond strength of steel bar to concrete for short term r φ: Perimeter of steel bar

[0023] Next, an example of the method for constructing the cast-in-place concrete pile 10 will be described. First, the ground G is excavated to form a pile hole, and a steel cage having main reinforcement bars 14 and shear reinforcement bars 16 is placed in this pile hole, thereby arranging the main reinforcement bars 14 and the shear reinforcement bars 16 in the lower part of the pile hole. Subsequently, a steel pipe 18 is placed covering the upper end side of the main reinforcement bar 14, and a steel cage having connecting reinforcement bars 20 is placed in the upper part inside the steel pipe 18, thereby arranging the connecting reinforcement bars 20. Thereafter, a tremie pipe is inserted into the pile hole to drive in concrete and fill the pile hole and the steel pipe 18 with concrete. After that, concrete is driven in around and above the pile head 22 to construct the pile head joint 24. By doing so, the cast-in-place concrete pile 10 can be constructed.

[0024] According to the present embodiment, by using the connecting reinforcement bars 20, the work of attaching fixing reinforcement bars to the upper part of the steel pipe 18 can be omitted. Compared with the conventional cast-in-place steel pipe concrete pile, the reinforcement around the pile head 22 is rationalized, so that the construction can be easily performed.

[0025] As described above, the cast-in-place concrete pile according to the present invention comprises a reinforced concrete pile body and a steel pipe provided to cover the outer circumferential surface of the upper part of the pile body over a predetermined length from the pile head at the upper end of the pile body, with the pile head embedded in a reinforced concrete pile head joint. The cast-in-place concrete pile comprises a plurality of main reinforcement bars provided inside the lower part of the pile body along the axial direction of the pile body, with their upper ends anchored inside the upper part of the pile body; a plurality of shear reinforcement bars provided inside the lower part of the pile body along the circumferential direction of the pile body so as to surround the main reinforcement bars; and a plurality of connecting bars provided from the upper part of the pile body to the inside of the pile head joint, with their upper ends anchored in the pile head joint. Therefore, the work of attaching anchoring bars to the upper part of the steel pipe can be omitted. For this reason, construction can be carried out more easily compared to conventional cast-in-place steel pipe concrete piles.

[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, 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]

[0028] 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 facilitating construction. [Explanation of symbols]

[0029] 10. Cast-in-place concrete piles 12 Pile body 12A Lower part (lower part) 12B Upper part (upper part) 14 Main reinforcement 16 Shear reinforcement bars 18 Steel pipe 20 Joint muscle 22 Pile head 24 Pile cap joint G Ground

Claims

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

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.

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