Reinforcement structure of cast-in-place pile

Abstract

To provide a reinforcement structure 1 of cast-in-place piles that uses high-strength reinforcements as main reinforcements 10a and 10b to eliminate overcrowding of reinforcing bars.SOLUTION: A reinforcement structure 1 of cast-in-place piles has a plurality of main reinforcements 10a and 10b. The main reinforcements 10a and 10b are formed by joining a plurality of deformed steel bars having a yield point or 0.2% proof stress of 590 (N / mm2) to 785 (N / mm2) using lap joints. A length L of the lap joint is 40d (d is a diameter of a reinforcement) or more when the design standard strength of concrete used in the cast-in-place pile is 30 (N / mm2) to 60 (N / mm2).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a reinforced concrete cast-in-place pile structure. [Background technology]

[0002] Conventionally, a common construction method involves using an excavator to drill a pile hole of a specified diameter and depth into the ground while injecting a stabilizing liquid into the hole to protect the hole walls, erecting a reinforcing bar cage into the hole, and then pouring concrete into the hole to construct a cast-in-place pile (for example, Patent Document 1).

[0003] When assembling the reinforcing bar cage of a cast-in-place pile, the main bars are connected to each other in the longitudinal direction of the reinforcing bar cage by joints according to the depth of the pile hole. Regarding the joint length when the main bars are connected with lap joints, for example, in the scope of application of "Chapter 3 Cast-in-place reinforced concrete piles" in Non-Patent Document 1, it is stated that "When the main bars are connected with lap joints, the joint length is 40d b More than(d b : The numerical value used in the name of the deformed bar) is specified as follows. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3615082 [Non-patent literature]

[0005] [Non-Patent Document 1] "Strength and Deformation Performance of Foundation Members," Architectural Institute of Japan, Published by Architectural Institute of Japan, March 2022, p.61 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the joint length in Non-Patent Document 1 is intended for the types of reinforcing bars described in the scope of application as "SD295, SD345, SD390, SD490 and high-strength shear reinforcement bars certified by the Minister of Land, Infrastructure, Transport and Tourism," and does not include SD590 and SD685, which have been produced in recent years and have a yield point of 490 N / mm 2 Therefore, even now, high-strength reinforcing bars with a yield point of 490N / mm 2 High-strength rebars exceeding this are not used as the main reinforcement for cast-in-place piles.

[0007] On the other hand, in recent years, the number of rebars in cast-in-place piles has increased, leading to overcrowding of the rebars, which affects the filling of concrete and the workability of the rebars.

[0008] Therefore, the present invention provides a reinforced concrete structure for cast-in-place piles that uses high-strength reinforcing bars as the main reinforcement and can eliminate overcrowding of the reinforcement bars. [Means for solving the problem]

[0009] The present invention has been made to solve at least some of the above-mentioned problems, and can be realized in the following aspects or application examples.

[0010] [1] One embodiment of the reinforced concrete structure of the cast-in-place pile according to the present invention is as follows: A reinforced concrete structure of cast-in-place piles having a plurality of main reinforcements, The main reinforcement has a yield point or 0.2% strength of 590 (N / mm 2 )~785(N / mm 2 ) is formed by joining multiple deformed steel bars with lap joints, The length of the lap joint is set so that the design strength of the concrete used for the cast-in-place pile is 30 (N / mm 2 )~60(N / mm 2 ) is 40d (d is the diameter of the reinforcing bar) or more. It is a sign.

[0011] [2] In one embodiment of the above-mentioned cast-in-place pile reinforcement structure, The main reinforcement may be a deformed steel bar of SD590 or SD685 as specified in JIS G3112. Effect of the Invention

[0012] According to one aspect of the reinforcement structure of a cast-in-place pile of the present invention, the number of main bars can be reduced by using high-strength reinforcement bars with an appropriate lap joint length as the main bars, thereby eliminating over-dense reinforcement. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a schematic diagram showing a part of a reinforced concrete structure of a cast-in-place pile according to the present embodiment. [Diagram 2] FIG. 4 is a cross-sectional view taken along the line BB in FIG. 3 of the lap joint length confirmation test of Example 1. [Diagram 3] 3 is a cross-sectional view taken along the line AA in FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Note that the embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are necessarily essential components of the present invention.

[0015] 1.Reinforced concrete structure of cast-in-place piles A reinforced concrete structure 1 for a cast-in-place pile according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing a part of the reinforced concrete structure 1 for a cast-in-place pile according to this embodiment. Fig. 1 is a cross-sectional view in which the main reinforcements 10a, 10b and the tie bars 11 on the front side of the figure are omitted in order to show the lap joints of the main reinforcements 10a, 10b.

[0016] As shown in FIG. 1, the cast-in-place pile reinforcement structure 1 is a cast-in-place pile reinforcement structure having a plurality of main reinforcements 10a, 10b. The cast-in-place pile is a pile made of reinforced concrete constructed on-site. The cast-in-place pile is constructed by excavating the ground, discharging the soil to the surface, erecting a reinforced cage in the excavated hole, and pouring concrete to a specified position. The enlarged base pile method and the steel pipe concrete method explained in the Standard Specifications for Building Construction and Commentary JASS4 Pile, Foundation Work and Foundation Work (Architectural Institute of Japan) can be used for the cast-in-place concrete pile construction. In addition, the construction method of the cast-in-place concrete pile construction can be the earth drill method, the all casing method, the reverse circulation drill method, the BH method, and the deep foundation method explained in the Standard Specifications for Building Construction and Commentary JASS4 Pile, Foundation Work and Foundation Work. The reinforced concrete structure 1 may be assembled at the construction site of the cast-in-place pile, or multiple reinforced concrete cages assembled at a factory may be assembled at the construction site. Although only one set of main reinforcements 10a, 10b is shown at the top and bottom in Fig. 1, multiple sets of main reinforcements 10a, 10b are joined at the top and bottom to match the length of the drilled hole (not shown). The reinforced concrete structure 1 is erected in the drilled hole, and then concrete is poured into the hole to construct the cast-in-place pile.

[0017] The main reinforcements 10a, 10b extend along the longitudinal direction of the cast-in-place pile and are arranged at a specified interval in the circumferential direction. The main reinforcement 10a arranged on the upper side and the main reinforcement 10b arranged on the lower side are connected by a lap joint. In addition, hoops 11 are provided in a ring shape along the circumferential direction on the outside of the main reinforcements 10a, 10b. A plurality of the hoops 11 are arranged at specified intervals in the longitudinal direction of the main reinforcements 10a, 10b. Each of the hoops 11 is fixed to the main reinforcements 10a, 10b by, for example, a tie wire (copper wire, etc.).

[0018] The main reinforcements 10a and 10b have a yield point or 0.2% strength of 590 (N / mm 2 )~785(N / mm 2) by joining multiple deformed steel bars with lap joints. Here, the yield point or 0.2% yield strength is determined in accordance with JIS Z2241 (Metallic Material Tensile Test Method)-1998 using No. 2 or No. 3 test pieces of JIS Z2201 (Metallic Material Tensile Test Pieces)-1998. Here, the yield point or 0.2% yield strength is a value determined using the nominal cross-sectional area. Furthermore, the yield point or 0.2% yield strength is based on the yield point, and when no clear yield point appears, it is the 0.2% yield strength. Note that for such deformed steel bars, the standard strength certified by the Minister of Land, Infrastructure, Transport and Tourism under Article 37, item 2 of the Building Standards Act is 685 (N / mm 2 ) for example USD685, OSD685, etc. or materials with the same strength of 590 (N / mm 2 ) such as USD590 or OSD590. In a lap joint, the main reinforcements 10a, 10b to be joined are arranged parallel to each other for a predetermined length or more, and then wire such as a wire is wound around the overlapping portion to connect them. After concrete is poured, the lap joint becomes one with the concrete, transmitting the force generated in the main reinforcements 10a, 10b.

[0019] Furthermore, the main reinforcements 10a, 10b may be deformed steel bars of SD590 or SD685 as specified in JIS G3112. The deformed steel bars of SD590 or SD685 can satisfy the above-mentioned range of yield point or 0.2% yield strength.

[0020] The length of the lap joint, L, is determined based on the design strength of the concrete used for cast-in-place piles of 30 (N / mm 2 )~60(N / mm 2 ) is 40d (d is the diameter of the reinforcing bar) or more. As shown in the experimental results described later, when high-strength reinforcing bars are used for the main bars 10a, 10b, the allowable bond stress of a specified concrete can be satisfied by adopting an appropriate lap splice length L of 40d or more.

[0021] In this way, according to the cast-in-place pile reinforcement structure 1, high-strength reinforcing bars with an appropriate lap joint length L can be used for the main reinforcements 10a, 10b, thereby reducing the number of main reinforcements 10a, 10b, thereby eliminating over-dense reinforcement. EXAMPLES

[0022] Using the experimental equipment shown in Figures 2 and 3, a pull-out test was conducted to verify the lap joint length.

[0023] The main reinforcements 10a and 10b of the test specimen 2 had a yield point or 0.2% strength of 691.38 (N / mm 2 )~748.06(N / mm 2 The main reinforcements 10a and 10b were deformed steel bars with a rebar diameter of D19. The concrete strength was 30 N / mm 2 The lengths of the main reinforcements 10a and 10b in the case of were 2,110 mm, 2,104 mm, and 2,110 mm and 1,824 mm. 2 In this case, the lengths of the main reinforcements 10a and 10b were 2,110 mm and 1,774 mm. The two deformed steel bars, main reinforcements 10a and 10b, were joined at one location with a lap joint. The length of the lap joint was 2,110 mm and 1,774 mm, respectively, for a concrete strength of 30 N / mm 2 In the case of 55d (1,045mm = 55 x 19mm) and 40d (760mm = 40 x 19mm), concrete strength is 60N / mm 2 In this case, we prepared 38d (722mm = 38 x 19mm).

[0024] For the test specimen 2, two pairs of main reinforcements 10a, 10b were placed in a formwork measuring 1,200 mm wide x 600 mm deep x 1,090 mm to 1,420 mm high, and the formwork was filled with a stabilizing liquid (a mixture of water, bentonite, and polymer). After the stabilizing liquid was drained from the bottom of the formwork, concrete was filled in with the stabilizing liquid adhering to the surface of the rebars. The concrete had a concrete strength of 30 N / mm 2 Actual strength is 32.4N / mm 2 ~32.8N / mm 2 , concrete strength 60N / mm 2 Actual strength is 69.4N / mm 2 ~69.8N / mm 2 Specimen 2 was prepared. Specimen 2 had a concrete strength of 30 N / mm2 and a lap joint length of 55d (1,045 In the case of 40d (760mm), the main reinforcement 10b protrudes 664mm from the bottom and the main reinforcement 10a protrudes 678mm from the top. In the case of 40d (760mm), the main reinforcement 10b protrudes 664mm from the bottom and the main reinforcement 10a protrudes 958mm from the top. In addition, when the concrete strength is 60N / mm 2 When the lap joint length was 38d (722 mm), the main reinforcement 10b protruded 664 mm from the bottom, and the main reinforcement 10a protruded 1,008 mm from the top.

[0025] For each test specimen 2, both the jack side reinforcing bar (the main reinforcing bar protruding from above) and the reaction floor side reinforcing bar (the main reinforcing bar protruding from below) were fixed via jigs, and after repeated loading within the elastic range, a monotonic pull-out test was carried out up to approximately 95% of the tensile strength of the reinforcing bars, and then the test was completed.

[0026] The results of the pull-out test showed that all test specimens 2 exceeded the standard yield strength (685N / mm 2 ), and the maximum strength exceeded the standard yield strength.

[0027] As a result of this test, the design strength of concrete was 30 (N / mm 2 ) is 40d (d is the diameter of the rebar) or more, the standard yield strength of the rebar (685N / mm 2 ) or more. In addition, it was found that the design strength of concrete is 60 (N / mm 2 ) is 38d or more, the standard yield strength of the rebar (685N / mm 2 ) or more strength can be ensured.

[0028] According to existing formulas and literature (formulas described in "Reinforced Concrete Structural Calculation Standards and Commentary" (Architectural Institute of Japan), "Railway Structure Design Standards and Commentary Concrete Structures" (Railway Technical Research Institute), and the table of straight lap joint lengths described in "Standard Specifications for Building Construction and Commentary JASS5 Reinforced Concrete Construction" (Architectural Institute of Japan), the required lap joint length becomes shorter as the concrete strength increases. Therefore, the results of this tensile test show that, in the stabilizing solution, if the concrete strength is 40d (d is the diameter of the rebar) or more, the standard yield strength of the rebar (685N / mm 2 ) or more strength can be ensured.

[0029] In addition, according to previous calculation formulas and literature, the higher the rebar strength, the longer the required lap splice length. Therefore, even with SD590, which has a lower strength than SD685 used in this experiment, if it is 40d (d is the rebar diameter) or more, the standard yield strength of the rebar (590N / mm 2 ) or more strength can be ensured.

[0030] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention includes configurations that are substantially the same as those described in the embodiments (for example, configurations with the same functions, methods, and results, or configurations with the same purpose and effect). The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that achieve the same effects as the configurations described in the embodiments, or configurations that can achieve the same purpose. The present invention also includes configurations in which publicly known technology is added to the configurations described in the embodiments. [Explanation of symbols]

[0031] 1...reinforced concrete structure, 2...test specimen, 10a, 10b...main bars, 11...hoops, 12...longitudinal bars, 14...horizontal bars, 20...concrete, 30, 32...jig, L...lap splice length

Claims

1. A reinforced concrete structure of cast-in-place piles having a plurality of main reinforcements, The main reinforcement has a yield point or 0.2% strength of 590 (N / mm ２ ) ~ 785 (N / mm ２ ) is formed by joining multiple deformed steel bars with lap joints, The length of the lap joint is set so that the design standard strength of the concrete used for the cast-in-place pile is 30 (N / mm ２ ) to 60 (N / mm ２ ) is a reinforced concrete structure of cast-in-place piles with a diameter of 40d or more (d is the diameter of the reinforcing bar).

2. In the reinforced concrete structure of the cast-in-place pile according to claim 1, The main reinforcement is a deformed steel bar of SD590 or SD685 as specified in JIS G3112, and the reinforced concrete structure of the cast-in-place pile.

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