JP2022107897A - Reinforced concrete pile structure - Google Patents

Abstract

To provide a reinforced concrete pile structure capable of securing necessary proof strength and having excellent workability with a reduced number of vertical main reinforcements, even when large bending moment is applied to a pile head.SOLUTION: A reinforced concrete pile 1 has a reinforcement cage 4 cylindrically formed by combining multiple vertical main reinforcements 22 and annual and lateral hoop reinforcements 3 and installed inside a concrete column. Partially high-strength bars 2 with at least a part in the longitudinal direction formed in high strength, are included as the multiple vertical main reinforcements 22.SELECTED DRAWING: Figure 1

Description

The present invention relates to a reinforced concrete pile structure.

Mainly in civil engineering and construction of building structures, pile foundations made of reinforced concrete are built in the ground, and building structures are built on them. As a construction method for the above pile foundation, after excavating the ground at the site, a reinforcing bar cage formed in a cylindrical shape by combining multiple vertical main bars and annular horizontal hoop bars is inserted into the excavated hole, and concrete is poured to form a reinforced concrete. There is a cast-in-place pile construction method in which piles are constructed, and a ready-made pile construction method in which reinforced concrete piles made in advance at a factory are driven on site.

On the other hand, when the pile foundation, which is built underground to support the building structure, is subjected to horizontal external forces such as seismic force, plastic hinges occur in the pile foundation and the pile head yields. As a result, bending, cracks, shear cracks, etc. may occur in the pile head and footing. In addition, if a crack occurs in the area where the vertical main reinforcement is anchored in the footing, the anchorage performance of the vertical main reinforcement deteriorates, making it difficult to repair. Even if there is no noticeable damage to the superstructure, the building can continue to be used. sometimes it becomes impossible. Furthermore, when the pile head is sheared, the axial force bearing capacity is reduced, so the building may tilt after the disaster.

Therefore, in consideration of such a situation, in order to increase the bending resistance of the pile head of the reinforced concrete pile, the pile diameter of the pile head is increased, or as shown in FIG. In the reinforcing bar cage 4 formed cylindrically by combining the horizontal hoop bars 3, the number of the vertical main bars 22 on the upper part of the pile 1 is increased compared to the middle part and the lower part of the pile 1.

However, in the case of reinforced concrete piles using the cast-in-place pile method, the minimum distance between vertical main bars is 1.5 times the diameter of the reinforcing bars, 1.25 times the diameter of the coarse aggregate, and 25 mm, whichever is the smallest. Therefore, the pile diameter is determined by the number of longitudinal rebars. That is, there is a problem that if the number of vertical main reinforcing bars is increased, the pile diameter must be designed to be large. Also, in reinforced concrete piles made by the prefabricated pile construction method, there is a problem that if the number of reinforcing bars at the top of the pile increases, the fit of the bar arrangement deteriorates.

In addition, when a large bending moment acts on the pile head of a pile foundation built on soft ground, etc., there is a method to increase the bending resistance by covering only the pile head with a steel pipe and using a steel pipe concrete pile. be. However, this method has the problem that the amount of steel material increases, resulting in an increase in cost.

JP 2018-193751 A

On the other hand, as a method of increasing the amount of vertical rebars while suppressing the increase in pile diameter without using large-diameter rebars, concrete piles using bundled bars have been proposed (Patent Document 1). However, this proposal requires mechanical joints for bundling the vertical main reinforcing bars, resulting in high cost and poor economic efficiency. In addition, if the strength of the vertical main reinforcement is increased, the length of the fixing portion in the footing increases, which causes problems such as deterioration of fitting of the upper portion of the vertical main reinforcement and deterioration of workability.

The present invention has been made in view of the above circumstances, and it is possible to secure the required yield strength with a configuration that reduces the number of vertical main rebars even when a large bending moment acts on the pile head. It is an object of the present invention to provide a reinforced concrete pile structure that has a high workability and is excellent in workability.

The reinforced concrete pile structure of the present invention has been made to solve the above technical problems, and has the following features.

First, the reinforced concrete pile structure of the present invention is a reinforced concrete pile in which a reinforcing bar cage formed in a cylindrical shape by combining a plurality of vertical main bars and annular horizontal hoop bars is installed inside a concrete column, as the vertical main bar, It is characterized by including a partial high-strength reinforcing bar formed to have high strength at least partly in the longitudinal direction.
Second, in the reinforced concrete pile structure of the first aspect of the invention, a fixing portion is formed at the upper end of the partial high-strength reinforcing bar, and the fixing portion is embedded in a footing provided at the upper end of the reinforced concrete pile. is preferred.
Thirdly, in the reinforced concrete pile structure of the first or second invention, it is preferable that the strength of the partial high-strength reinforcing bars on the upper end side in the longitudinal direction is higher than the strength on the lower end side. .
Fourth, in the first to third reinforced concrete pile structures, the strength of the central part in the longitudinal direction of the partial high-strength reinforcing bars is higher than the strength of the upper end side and the lower end side. preferable.
Fifth, in the reinforced concrete pile structure of the first to fourth inventions, it is preferable that the yield strength of the high-strength region of the partial high-strength reinforcing bars is in the range of 490 to 1275 N/mm ² .
Sixth, in the reinforced concrete pile structure of the first to fifth inventions, the displacement point of the high strength region of the partial high strength reinforcing bar and the strength region lower than the strength of the high strength region is at least from the upper end side It is preferable to set the length within a range of five times the diameter of the reinforced concrete pile.
Seventhly, in the reinforced concrete pile structure of the first to sixth inventions, it is preferable that the vertical main reinforcing bars are composed of a combination of the partial high strength reinforcing bars and the normal strength reinforcing bars.
Eighth, in the reinforced concrete pile structure of the first to seventh inventions, the partial high-strength reinforcing bars in the footing provided at the upper end of the reinforced concrete pile are connected to reinforcing bars of other members. preferable.

According to the pile structure of the present invention, even when a large bending moment acts on the pile head, it is possible to reduce the number of vertical main reinforcements and to secure the required proof stress.
In addition, since the amount of vertical main reinforcement at the pile head can be reduced, it is possible to reduce the crossing of reinforcement with footings and foundation beams, which can be expected to improve workability and quality, as well as reduce costs by shortening the construction period.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a reinforced concrete pile structure of the present invention using partial high-strength vertical reinforcement for the vertical main reinforcement, (A) is a schematic perspective view of the side, and (B) is an AA schematic cross-sectional view of (A). be. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows one Embodiment of the partial high strength vertical main reinforcement used for the reinforced concrete pile structure of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is the side perspective schematic diagram which shows the plastic hinge generating position of a reinforced concrete pile, (A) is the conventional reinforced concrete pile, (B) is the side perspective schematic diagram of the reinforced concrete pile of this invention. FIG. 4 is a schematic diagram showing an embodiment in which the strength of the longitudinal main reinforcement is gradually decreased downward. FIG. 4 is a schematic diagram showing an embodiment in which a fixing portion is provided at the upper end portion of the partial high-strength vertical main reinforcement; It is the schematic which shows the joining structure of embodiment which connected the footing of the reinforced concrete pile which concerns on this invention, and another member. It is a schematic diagram (C) of the soil structure (A) of the simulated ground used in the example, the graph (B) showing the results of the standard penetration test, and the reinforced concrete pile used in the test. 4 is a graph showing results of horizontal ground reaction force coefficient and bending moment distribution with respect to depth. 4 is a graph showing the axial force-bending correlation diagram of a reinforced concrete pile using partial high-strength vertical rebars and a reinforced concrete pile using normal-strength vertical rebars. It is a schematic diagram showing a conventional reinforced concrete pile structure using normal strength reinforcing bars as vertical main bars, (A) is a schematic perspective view of the side, and (B) is a schematic cross-sectional view of BB of (A).

Hereinafter, the reinforced concrete pile structure of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic illustration of one embodiment of a reinforced concrete pile structure according to the present invention.

In the reinforced concrete pile structure of the present invention, a reinforcing bar cage 4 formed in a cylindrical shape by combining a plurality of vertical main bars 22 and an annular horizontal hoop bar 3 is installed in a concrete column. Partially high-strength reinforcing bars 2 formed with high strength in at least a part in the longitudinal direction are used.

As the partial high-strength reinforcing bars 2 used in the present invention, deformed steel bars of standards such as SD295A, SD295B, SD345, SD390, and SD490 specified by JIS G 3112:2020 (steel bars for reinforced concrete) can be used. , SD390 can be preferably used from the viewpoint of versatility.

Deformed steel bars similar to the above standards are also available. Examples of the shape of the deformed steel bar include not only general bamboo joints, but also steel bars such as wave joints and threaded reinforcing bars that take into account adhesion to concrete. The diameter of the deformed steel bar to be used can be set as appropriate according to the design of the reinforced concrete pile, but usually about D22 to D38 is used.

The partial high-strength reinforcing bar 2 in the reinforced concrete pile structure of the present invention has a high-strength region 2a formed at least partially in the longitudinal direction of the longitudinal main bar 22. The position and range of the high-strength region 2a may be located at the same location or distributed at a plurality of locations. Also, the length of the high-strength region 2a can be appropriately set according to the overall length of the reinforced concrete pile.

The yield strength of the high-strength region 2a in the partial high-strength reinforcing bar 2 is not limited as long as it is higher than the strength of the normal strength region, but usually it is preferably in the range of 490 to 1275 N/mm ² , 685 to 800 N/mm ² are more preferred. With this range, it is possible to increase the bending strength of the pile while suppressing an increase in the number of vertical main reinforcements 22 . In addition, normal strength reinforcing bars with an overall yield strength of about 295 to 390 N/mm ² are usually used for the vertical main reinforcing bars 22 of the reinforced concrete pile 1, and the normal strength other than the high strength region 2a in the partial high strength reinforcing bars 2 is used. The region 2b is set to a strength equivalent to the yield strength range of the normal strength reinforcing bars.

As a method for forming the high-strength region 2a, the high-strength region 2a can be strengthened by heat-treating the place to be the high-strength region 2a. As a specific heat treatment method, heat treatment using a flame of a gas burner or the like and heat treatment using high frequency waves can be exemplified.

By applying the heat treatment, the heat-treated area becomes the high-strength area 2a, and the non-heat-treated area becomes the normal-strength area 2b. Moreover, as shown in FIG. 2, the boundary between the high intensity region 2a and the normal intensity region 2b may be an intensity transition region 2c in which the intensity gradually changes. As a method for forming such a strength transition region 2c, it is possible to form by performing a heat treatment that gradually weakens from the heat treatment of the high strength region 2a to the normal strength region 2b.

Further, in the reinforced concrete pile structure of the present invention, the high-strength region 2a of the partial high-strength reinforcing bar 2 is preferably provided on the upper end side of the reinforced concrete pile 1. Further, the high-strength region 2a of the partial high-strength reinforcing bar 2, It is preferable that the displacement point of the strength region from the normal strength region 2b is set within a length range of at least five times the diameter of the reinforced concrete pile 1 from the upper end side. If the position of the displacement point is within the above range, it is possible to increase the strength against bending moment and shear force of the pile head to which excessive force is applied due to seismic motion or the like.

Furthermore, the strength switching position of the partial high-strength reinforcing bar 2 uses the bending moment distribution calculated from the ground conditions, the generated stress at the pile head is M _A , the allowable bending strength of the pile head is M ₁ , and the reinforcing bar specification strength is If the generated stress at the position where the strength is switched is M _B and the allowable bending resistance at the strength switching position is M ₂ , the settings may be made so as to satisfy the relationships of M ₁ >M _A and M ₂ =M _B . As a result, the plastic hinge generation position 23 of the reinforced concrete pile 1 is located away from the pile head, so that cracks in the footing 5 can be suppressed, and deterioration of the fixing ability of the vertical main reinforcement 22 can be prevented.

Under the above conditions, as shown in FIG. 3, the plastic hinge generation position 23 of the reinforced concrete pile can be shifted from the conventional pile head side shown in FIG. 3(A) to the downward direction shown in FIG. 3(B). As a result, there is no area in the footing 5 that lowers the anchoring strength of the upper end portion of the vertical main reinforcement 22 that serves as the anchoring portion, and the seismic performance can be enhanced. In addition, it is possible to enhance the continuous usability of the building after a disaster.

The method of constructing the reinforced concrete pile 1 includes a cast-in-place pile construction method in which an excavated hole is drilled at the site, a reinforcing bar cage 4 is inserted, and concrete is cast to form a pile, and a reinforced concrete pile in which the reinforcing bar cage 4 is internally installed at a factory. Although there is a prefabricated pile construction method in which the pile 1 is manufactured, transported to the site, driven into an excavated hole, and inserted, the reinforced concrete pile 1 according to the present invention can be applied to any construction method.

In the case of the cast-in-place pile construction method, the excavation depth, that is, the length of the reinforced concrete pile 1 is appropriately determined according to the construction design. 4 is formed to a predetermined length by joining the vertical main reinforcements 22 one by one and inserting them while splicing them. The length of the vertical main reinforcing bars 22 of one stage can be appropriately set by the designer, but is generally 5 to 11 m. Also, the vertical main reinforcements 22 are usually joined by lap joints.

The pile diameter of the pile head is usually set in the range of about 1 to 3 m. If the bending moment is not sufficiently reduced in the region formed in , as shown in FIG. A configuration in which the strength is lowered is also possible. Here, a range of about 390 to 490 N/mm ² is considered as the yield strength range of the medium strength region and the low strength region.

Moreover, in the reinforced concrete pile structure of the present invention, it is preferable to provide the fixing portion 21 above the upper end portion of the vertical main reinforcing bar 22 , that is, above the partial high-strength reinforcing bar 2 . The fixing portion 21 may be formed by processing the upper end portion of the vertical main reinforcement 22, or may be formed by attaching and fixing a separate fixing member. The shape of the fixing portion 21 is not particularly limited. Other fixable shapes, such as a letter-shaped hook shape, can be used. Further, as the fixing portion 21 for attaching and processing a separate fixing body to the upper end portion of the vertical main reinforcement 22, a nut-shaped fixing body, an inverted J-shaped hook, an inverted L-shaped hook-shaped fixing body, and the like are used. be. In addition, when the fixing part 21 is formed on the upper end side of the partial high strength reinforcing bar 2, the strength of the upper end side to be formed is not set to high strength, but is set to the yield strength equivalent to that of the normal strength reinforcing bar. preferable. Further, by adjusting the process, the fixing portion 21 may be formed by bending and then heat-treated to partially increase the strength. In that case, it is preferable to perform the heat treatment while avoiding the bent portion.

By embedding the upper end portion side of the partial high-strength reinforcing bar 2 including the fixing portion 21 in the footing 5 provided at the upper end portion of the reinforced concrete pile 1, the partial high-strength reinforcing bar 2 is reliably fixed in the footing 5. It is possible to make a high-strength pile having excellent bearing strength. In addition, it is desirable that the stress load at the time of fixing is such that the linear portion of the partial high-strength reinforcing bar 2 in the footing 5 and the fixing portion 21 formed at the upper end thereof bear the same degree of load. In this case, the length of the partial high-strength reinforcing bars 2 fixed in the footing 5 is approximately the same as the length of the fixing portion 21 as shown in FIG.

In addition, when it is confirmed that the strength in the structural calculation is ensured and that there is no problem in the fitting of the reinforcing bars, the fixing part 21 may not be provided and the vertical main bars 22 may be used for straight fixing. In this case, the fixing length can be appropriately set within a range of about 40 to 60 times the reinforcing bar diameter d above the pile head or the position where the reinforcing bar specification strength is switched.

In the reinforced concrete pile structure of the present invention, all of the plurality of vertical main reinforcing bars 22 constituting the reinforcing bar cage 4 may be the partial high strength reinforcing bars 2, but the partial high strength reinforcing bars 2 and the normal strength reinforcing bars without the high strength region 2a The vertical main reinforcing bars 22 may be mixed. In addition, in the case of the cast-in-place pile construction method, the partial high-strength reinforcing bars 2 may be used for the vertical main bars 22 of all the reinforcing bar cages 4 connected in the vertical direction, or the vertical main bars 22 of only the uppermost reinforcing bar cage 4 may be partially A high-strength reinforcing bar 2 may be used. By configuring the vertical main reinforcement 2 as described above, it is possible to adjust the reinforced concrete pile 1 to a desired yield strength.

As described above, the reinforced concrete pile structure of the present invention has been described based on the embodiments, but the reinforced concrete pile structure of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist thereof. is.

For example, in the above embodiment, in the construction of the reinforced concrete pile 1 by the cast-in-place pile construction method, the configuration using the partial high-strength reinforcing bars 2 for the vertical main bars 22 of one reinforcing bar cage 4 has been described, but in the present invention, the entire reinforced concrete pile 1 It is sufficient if the vertical main bars 22 are partial high-strength reinforcing bars 2, for example, only the vertical main bars 22 of the uppermost reinforcing bar cage 4 are the partial high-strength reinforcing bars 2, and the vertical main bars 22 of the reinforcing bar cage 4 below it are It can also be configured as a vertical main reinforcing bar 22 having a yield strength equivalent to that of a normal strength reinforcing bar.

Alternatively, the partial high-strength reinforcing bars 2 of the footing 5 provided at the upper end of the reinforced concrete pile 1 may be connected to the reinforcing bars of other members. The other member is not limited as long as it is a member in which the partial high-strength reinforcing bar 2 having the same configuration as the partial high-strength reinforcing bar 2 according to the present invention is installed. ) and the like can be exemplified. Further, the reinforcing bars of the other members may be high-strength reinforcing bars, partial high-strength reinforcing bars, partial high-strength reinforcing bars having the same strength as the partial high-strength reinforcing bars 2, as well as normal strength reinforcing bars.

FIG. 6 shows a joint structure of an embodiment in which the footing 5 of the reinforced concrete pile 1 according to the present invention and another member 6 are connected. In the joint structure of the embodiment shown in FIG. 6, the partial high-strength reinforcing bars 7 having the high-strength region 7a, the normal-strength region 7b, and the strength transition region 7c are installed in the footing 5 of the reinforced concrete pile 1 as other members. A part of the high-strength region 7a of the partial high-strength reinforcing bar 7 installed in the foundation beam 6 and the upper end of the high-strength region 2a of the partial high-strength reinforcing bar 2 of the reinforced concrete pile 1 It joins with its neighbors. As a result, for example, even if a vertical bending moment is applied to the foundation beam 6, the generated stress can be reliably transmitted to the partial high-strength reinforcing bars 2 of the reinforced concrete piles 1, so that the high-strength steel with excellent yield strength can be used. It can be a joint structure of strength piles and high strength beams.

Hereinafter, the reinforced concrete pile structure of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Reinforced concrete pile 1 constructed using partial high-strength reinforcing bars 2 for vertical main reinforcement 22 shown in FIG. (Fig. 7C) has a total length of 32.6 m and a diameter of 1.5 m (footing 5 diameter: 2.1 m). In addition, the partial high-strength reinforcing bar 2 is heat-treated from the upper end of the vertical main bar 22 to 7.5 m so that the vertical main bar yield strength of the high-strength region 2a is 700 N / mm ² , and the region below that is the normal strength region 2b. The yield strength of the longitudinal main bars was set at 390 N/mm ² . In addition, the graph of a standard penetration test result is shown in FIG.7(B).

For the reinforced concrete pile 1 of the present invention, the bending moment distribution was calculated by a method using Chang's formula. The results are shown in FIG. As a result, the axial downward bending moment distribution of the reinforced concrete pile 1 according to this embodiment is maximized at the uppermost portion connected to the footing 5, and rapidly decreases downward.

FIG. 9 shows the axial force-bending correlation diagram of the reinforced concrete pile 1 using the partial high-strength reinforcing bars 2 and the reinforced concrete pile 1 using the longitudinal main bars 22 having the same yield strength as the normal strength reinforcing bars. From this figure, the compressive strength of the reinforced concrete pile 1 using the partial high-strength reinforcing bars 2 and the bending strength in the state where the compressive stress is generated in the entire pile cross section (state where the compressive axial force is large) are the yield strengths of the normal strength reinforcing bars. It can be seen that there is almost no difference from the conventional reinforced concrete pile using the vertical main reinforcement 22 . In general, there are few cases where the cross-section of a pile is determined by the strength of the compression side, and the fact that the strength of the compression side does not increase is not a problem in design.
On the other hand, in the reinforced concrete pile 1 using the partial high-strength reinforcing bars 2, the limit value of the tensile axial force increases. In addition, it can be seen that the bending resistance from about 0 axial force to the limit value of the tensile axial force increases compared to the conventional reinforced concrete pile.

According to the reinforced concrete pile structure of the present invention, even when a large bending moment acts on the pile head, it is possible to reduce the number of vertical main reinforcements 22 and to secure the necessary yield strength.

Reference Signs List 1 reinforced concrete pile 2 partial high-strength reinforcing bar 2a high-strength region 2b normal-strength region 2c strength transition region 2d medium-strength region 2e low-strength region 21 anchorage (J-shaped hook)
22 Vertical main reinforcement 23 Plastic hinge occurrence position 3 Horizontal hoop reinforcement 4 Reinforcing bar cage 5 Footing 6 Other members (foundation beam)
7 Partial high-strength reinforcing bars 7a High-strength area 7b Normal strength area 7c Strength transition area 8a Area where yield strength is determined by compressive strength of concrete 8b Area where yield strength is determined by tensile strength of reinforcing bars Area where compressive stress acts 8d Pile applied with partial high strength reinforcing bars, area where no compressive stress occurs in concrete 8e Pile applied with normal strength longitudinal rebars, area where yield strength is determined by tensile strength of reinforcing bars

Claims (8)

In a reinforced concrete pile, a reinforcing bar cage formed in a cylindrical shape by combining multiple vertical main bars and annular horizontal hoop bars is installed inside a concrete column.
A reinforced concrete pile structure, wherein the longitudinal main reinforcing bars include partial high-strength reinforcing bars of which at least a portion in the longitudinal direction is formed to have high strength. The reinforced concrete pile structure according to claim 1, wherein an anchorage portion is formed on the upper end of the partial high-strength reinforcing bar, and the anchorage portion is embedded in a footing provided at the upper end of the reinforced concrete pile. The reinforced concrete pile structure according to claim 1 or 2, wherein the partial high-strength reinforcing bars are formed so that the strength on the upper end side in the length direction is higher than the strength on the lower end side. 4. The partial high-strength reinforcing bar according to any one of claims 1 to 3, wherein the strength of the central part in the longitudinal direction of the partial high-strength reinforcing bar is higher than the strength of the upper end side and the lower end side. Reinforced concrete pile structure. The reinforced concrete pile structure according to any one of claims 1 to 4, characterized in that the yield strength of the high-strength region of the partial high-strength reinforcing bars is in the range of 490-1275 N/mm ² . The displacement point between the high-strength region of the partial high-strength reinforcing bars and the strength region lower than the strength of the high-strength region is set within a range of at least five times the diameter of the reinforced concrete pile from the upper end of the reinforced concrete pile. The reinforced concrete pile structure according to any one of claims 1 to 5, characterized in that The reinforced concrete pile structure according to any one of claims 1 to 6, wherein the vertical main reinforcement is composed of a combination of the partial high strength reinforcement and the medium strength reinforcement. The reinforced concrete pile according to any one of claims 1 to 7, wherein the partial high-strength reinforcing bars in the footing provided at the upper end of the reinforced concrete pile are connected to reinforcing bars of other members. structure.

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