JPH10292368A - Cast-in-place steel encased reinforced concrete pile resisting and compressive force and constructing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the horizontal strength of a pile, and to prevent the cracks of pile-body concrete by constructing the cast-in-place concrete pile of reinforced concrete and introducing prestress by utilizing a steel frame between a front bearing section and a head-section bearing disk. SOLUTION: Jigs for introducing prestress and jacks are installed to the head-section bearing disk 11 of the upper end face section of a steel encased reinforced concrete construction and an exposed section in the upper section of a pile body of a steel frame 6 after placed concrete 5 displays specified strength, and prestress is introduced to the pile body between the head-section bearing section 11 and a front bearing section 4 by these jigs and jacks. A footing beam 15 is built at the upper end section of the pile body 5. Accordingly, the steel frame 6 such as a permanent structural column is arranged in approximately overall length in the axial direction of the central section of the reinforced-concrete constructed pile body 5, and the cast-in-place SRC pile resisting drawing and compressive force is built.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of steel reinforced concrete piles (hereinafter referred to as "SRC piles") constructed of cast-in-place concrete for supporting buildings and the like. The present invention relates to a cast-in-place SRC pile that strongly resists not only resistance but also pull-out force and a construction method thereof.

[0002]

2. Description of the Related Art Conventionally, buoyancy due to groundwater acts on a building or the like constructed deep underground, so that permanent anchors or the like are installed to take measures to resist pulling out by buoyancy. When a high-rise or super-high-rise building is subjected to the action of a horizontal force due to an earthquake or wind load, the overturning moment may generate a pull-out force, and it is also required to take measures to resist the pull-out force.

Conventionally, when it is assumed that a pulling force acts on a pile supporting a building or the like, the frictional resistance of the ground is evaluated only during an earthquake, and the numerical value is set lower than the actual value. . The reason for this is that, in addition to the uneven evaluation of the peripheral frictional force of the pile, the concrete skeleton is inherently weak to the tensile force. As expected, this measure adds cost and effort. Also, at a level below the groundwater level, if even a small crack is generated in the pile, the groundwater will penetrate, and the proof (corrosion) of the reinforcing steel is likely to decrease the proof stress.

[0004] Accordingly, the shortage of the pull-out force caused by the horizontal force at the time of the earthquake or the pull-out force caused by the buoyancy caused by the rise of the groundwater level causes an increase in the building weight of the building or a permanent ground. Countermeasures such as placing anchors (earth anchors) are being implemented, but this has resulted in a large increase in cost and an increase in the number of steps. In addition, as a problem when a pulling force (pulling force) acts on the pile body, the following matters can be cited. 1 Because tensile force is generated in the pile, it is necessary to consider joint strength and cracks in the pile. 2 Detailed examination of the bending cracking of the joint between the pile and the foundation beam and the transmission mechanism of the tensile force is required.

Next, conventionally known techniques are listed. The cast-in-place pile described in Japanese Patent Publication No. 62-21929 has a configuration in which a ground anchor is installed at the tip of the pile, and prestress is introduced into the pile using the anchor. The prestressed cast-in-place concrete pile described in Japanese Patent Publication No. 19648/1988 has a tensioning casing installed on the outer periphery of the pile, and the tensioning casing receives a reaction force to pull the main reinforcing bar of the pile to form a pile. This is a configuration that introduces prestress. The cast-in-place concrete pile described in JP-A-63-107612 has a structure in which a steel frame is arranged at a pile head portion of the cast-in-place concrete pile, and only that portion is used as an SRC pile to obtain large strength. In the cast-in-place concrete pile described in Japanese Patent Application Laid-Open No. 64-535, a donut-shaped shoe is built together with a tension member at the bottom of the cast-in-place concrete pile, and after the concrete is hardened, the tension member is used. Prestress is introduced into the pile. JP-A-5-247933 and JP-A-7-3445
Each of the cast-in-place concrete piles described in Japanese Patent Publication No. 2 is referred to as a straight pillar in a so-called reverse-casting method, and has a configuration in which a steel frame is inserted only into a pile head portion of the cast-in-place concrete pile. In the foundation concrete pile described in Japanese Patent Application Laid-Open No. Hei 7-34452, a corrosion-resistant pudding is arranged in a pile body,
This is a configuration in which prestress is introduced into the pile body using the corrosion-resistant photoresist. The cast-in-place prestressed concrete pile described in Japanese Patent Publication No. Hei 7-99020 has a configuration in which a PC steel wire is arranged in a U-turn shape in a pile body and prestress is introduced at the pile head using the PC steel wire. It is.

[0006]

According to the above-mentioned conventional techniques, it is apparent that a cast-in-place pile in which prestress is introduced into a pile body is known. However, most of them have a structure in which a prestress is introduced by embedding a main reinforcing bar of an anchor or a pile, a tensile member, a presto, and a PC steel wire in a pile body. Therefore, even if a prestress corresponding to a constant load is introduced into the pile body in the above structure, if a large pulling force acts during an earthquake or the like, there is no means for transmitting the pulling force to the pile body by a structural element. Usually, there is no other way than to bear the burden of the main rebar connected to the foundation beam, and ultimately it is not a cast-in-place pile with high strength.

In the above, only the pile head part has an SRC structure in part, and when a pulling force is applied to the steel frame, no measure is taken against cracks in the pile body, and the pile body is resistant to pulling. It is not structured. Accordingly, an object of the present invention is to improve the horizontal strength and toughness of the pile by making the cast-in-place concrete pile into a steel reinforced concrete structure, and to introduce prestress into the cast-in-place concrete pile part by using the steel frame as a reaction force receiver. The pull-out has been improved so that the pile does not crack under the constant pull-out load, and also strongly and effectively resists the pull-out force and bending shear force during a large earthquake. And a cast-in-place SRC pile resisting compressive forces and a method of constructing the same.

[0008]

As a means for solving the above-mentioned problems, a cast-in-place steel reinforced concrete pile which resists pulling and compressing force according to the present invention is provided at the center of a reinforced concrete pile. A steel frame such as a straight pillar is disposed over substantially the entire length in the axial direction of the steel frame, and a tip supporting portion provided at a tip portion of the steel frame, and a head supporting plate provided at an upper end portion of a hardened reinforced concrete pile body. The prestress is introduced by using a steel frame between them, and the upper part of the steel frame is connected to an upper structure.

According to a second aspect of the present invention, the tip supporting portion of the steel frame according to the first embodiment is provided as a pressure plate or a stud or a combination of the two, and the surface of the steel frame is subjected to an unbonding process. It is characterized by being. According to a third aspect of the present invention, the head support plate provided at the upper end of the reinforced concrete pile body according to the first aspect has an annular shape having a hollow portion having a shape and a size through which a transverse section of a steel frame penetrates. After the prestress is introduced, the stiffener is integrally fixed to the steel frame together with the stiffener.

According to a fourth aspect of the present invention, there is provided a method of constructing a cast-in-place steel reinforced concrete pile which resists pulling and compressing force, into a hole for a pile excavated in the ground, together with a reinforcing bar, with a length covering substantially the entire length of the pile. Insert the steel frame with the tip support section,
After performing each positioning and fixing, the stage of casting concrete into the same hole, and after the cast concrete has developed strength, a head support plate provided at the upper end of the steel reinforced concrete pile body, A stage where a jack is installed between the prestress introduction jig attached to the exposed part of the steel frame and the prestress is introduced using the steel frame, and when the prestress reaches a predetermined size, the introduction state is maintained. The prestress fixing stiffener is fixed to the steel frame while being held, the reaction force of the prestress is changed from the jack together with the head support plate by the stiffener, and the prestress introduction jig and the jack are removed. I do.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Cast-in-place steel reinforced concrete piles resistant to pull-out and compression according to the invention of claim 1, and cast-in-place steel reinforced concrete resistant to pull-out and compression in accordance with the invention of claim 4 The pile construction method is preferably implemented in the form shown in FIG.

FIGS. 1 to 4 show an S according to a fourth aspect of the present invention.
It is a figure showing a key process diagram of a method of constructing an RC pile.
First, in FIG. 1, a steel frame 6 provided with a tip supporting portion 4 with a length substantially covering the entire length of a pile is inserted together with a reinforcing bar 3 into a hole 2 for a pile excavated in the ground 1 to perform positioning and fixing of each. After that, the stage where the concrete 5 is poured into the hole is shown.
As the steel frame 6, as will be described later, an H-shaped steel or a steel pipe generally used as a steel frame column of a structure, or an assembled column material can be suitably used. On the outer surface of the steel frame 6, as shown in detail in FIG.
Is applied, and further subjected to an unbonding process 10 such as attaching a protective sheet or plate 9 to the surface. Further, the structure of the distal end supporting portion 4 of the steel frame 6 is shown in FIG.
A, a flat plate-like supporting plate 4a illustrated in FIG.
A plurality of studs 4b illustrated in FIG. 6, or a structure using the supporting plate 4a and the plurality of studs 4b in combination as illustrated in FIG. 6C can be implemented.

FIG. 2 shows a head support plate 11 provided on the upper end surface of the steel reinforced concrete pile body after the cast concrete 5 has developed a predetermined strength, and an exposed portion of the steel frame 6 above the pile body. Prestressing jig 12
And a step of introducing a prestress into the pile body between the head support plate 11 and the tip support unit 4 by using the steel frame 6 as a reaction force receiver between the jack 13 and the jack 13. I have. As described above, since the unbonding process 10 is performed on the surface of the steel frame 6, the prestress can be effectively introduced.
Incidentally, as the head support plate 11, a ring-shaped plate body having a hollow portion having substantially the same shape and the same cross-sectional shape as the steel frame 6 in the center portion is preferably used.

FIG. 3 shows that when the introduction of the prestress by the jack 13 reaches a predetermined size, the prestress fixing stiffener 14 is fixed to the steel frame 6 while keeping the introduction state static. The stiffener 14 and the head support plate 11 are used together with the prestress to counteract the reaction force of the prestress from the jack 13 so that the prestress introduction state is structurally and firmly fixed.
3 shows the stage after removal. In FIG. 3, the remaining prestress introducing jig 12 may be removed for convenience or left unattended.

FIG. 4 shows a completed stage in which a foundation beam 15 is constructed at the upper end of the pile body 5 and the steel frame 6 having the foundation beam 15 penetrated vertically upward is connected to an upper structure not shown.
Thus, a steel frame 6 such as a straight pillar is disposed at substantially the entire axial length of the central portion of the reinforced concrete pile 5, and a tip bearing portion 4 provided at the tip of the steel frame 6 and a hardened reinforced concrete pile 5 5 is a cast-in-place SRC in which a prestress is introduced into a pile body using a steel frame 6 as a reaction force receiving member and a head support plate 11 provided at an upper end portion of the pile 5 to resist pulling and compressing force. The stake (the invention of claim 1) is constructed and used.

FIGS. 7A, 7B and 7C show the structure of the introduction of prestress at the pile head and the fixing process when the steel frame is an H-section steel 6a. 7A and 7B show a box-shaped structure in which the prestress introducing jig 12 is fixed to the outer surface of the flange of the H-section steel 6a by a high tension bolt 16. On the other hand, the prestress fixing stiffener 14 is fixed to the web of the H-section steel 6a by two consecutive fillet welds in the vertical direction, and presses the head support plate 11 downward. If necessary, the inner periphery of the head support plate 11 is also fixed to the H-section steel 6a by continuous fillet welding.
FIG. 7C shows that the introduced prestress is replaced with the prestress fixing stiffener 14 and the head support plate 11 to be structurally firmly fixed, and then the prestress introducing jig 12 as well as the jack 13 is used. Shows the stage of removal.

FIGS. 8A, 8B and 8C show the structure of the introduction of prestress at the pile head and the fixing process when the steel frame is a steel pipe 6b. FIG. 8C shows that the prestress introducing jig 12 is composed of two vertical ribs and a bottom plate parallel to the vertical direction, and each is fixed to the outer peripheral surface of the steel pipe 6b by continuous fillet welding. For this reason, after the introduced prestress is replaced by the prestress fixing stiffener 14 and the head support plate 11 so as to be structurally firmly fixed, the jack 13 is removed, but the prestress introducing jig 12 is removed. Is left on the steel pipe 6b if there is no structural problem.

[0018]

ADVANTAGE OF THE INVENTION According to the cast-in-place SRC pile which resists pulling and compressive force and the method of constructing the same according to the present invention, the cast-in-place concrete pile is made of steel reinforced concrete, thereby improving the horizontal strength and toughness of the pile. Prestress was introduced into the cast-in-place concrete pile by using the steel frame as a reaction force receiver, as well as pulling the concrete of the pile until a pullout force of the expected size was applied at all times. Does not occur. And, since only the compressive force is always applied to the pile concrete, it is not necessary to specially examine the strength of the reinforcing steel joint.

Further, even in the case where a pulling force larger than expected in the event of an earthquake or the like is applied, the steel member 6 used for introducing the pre-stress is used as the tensile material to withstand, in addition to the reinforcing bar 3. No excessive pull-out displacement occurs because the steel column is connected to the steel frame of reinforced concrete. Since a steel frame is present at the joint between the pile head and the superstructure, reinforcement of the bending moment of the pile head is also achieved.

Further, since the load is mainly transmitted to the steel frame at the pile head, the transmission mechanism of the tensile force is clear, which is convenient for design and construction.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an initial stage of a cast-in-place SRC pile construction method of the present invention.

FIG. 2 is a cross-sectional view showing a prestress introduction stage of the cast-in-place SRC pile construction method.

FIG. 3 is a cross-sectional view showing a stage of changing a prestress introduced in a cast-in-place SRC pile construction method.

FIG. 4 is a cross-sectional view showing the stage of completion and use of the cast-in-place SRC pile of the present invention.

FIG. 5 is a detailed view showing an unbonding process of a steel frame.

FIGS. 6A, 6B, and 6C are partial views showing examples of a tip supporting portion of a steel frame.

FIGS. 7A, 7B, and 7C are partial views sequentially showing the processing steps of the pile head when the steel frame is an H-section steel.

FIGS. 8A, 8B, and 8C are partial views sequentially showing processing steps of a pile head when a steel frame is a steel pipe.

[Explanation of symbols]

 Reference Signs List 6 steel frame 4 tip supporting part 5 concrete (pile body) 11 head supporting plate 4a supporting plate 4b stud 10 unbonding treatment 14 stiffener for fixing prestress 2 hole for pile 3 reinforcing bar 13 jack

Continuing from the front page (72) Inventor Masao Maruoka 1-5-1, Otsuka, Inzai City, Chiba Prefecture Inside the Research Institute of Takenaka Corporation (72) Inventor Takahiro Moi 1-5-1, Otsuka, Inzai City, Chiba Pref. Inside Takenaka Corporation Technical Research Institute (72) Inventor Takatoshi Mine 4-1-1-13 Honcho, Chuo-ku, Osaka City Inside Takenaka Corporation Osaka Main Store

Claims (4)

[Claims] 1. A steel frame such as a straight pillar is disposed at substantially the entire axial length of a central portion of a reinforced concrete pile, and a tip bearing portion provided at a tip of the steel frame, and a hardened reinforced concrete pile are provided. Prestress is introduced using a steel frame between the head support plate provided at the upper end of the body, and the upper portion of the steel frame is connected to the upper structure, and the pulling and pulling are performed. Cast-in-place steel reinforced concrete piles that resist compressive forces. 2. The supporting portion of a steel frame according to claim 1, wherein the supporting portion is provided as a supporting plate, a stud, or a combination of both, and the surface of the steel frame is subjected to an unbonding process. Cast-in-place steel reinforced concrete piles, resisting pulling and compressive forces. 3. The head support plate provided at the upper end of the reinforced concrete pile body according to claim 1, is formed in an annular shape having a hollow portion having a shape and a size through which a transverse section of a steel frame penetrates,
Cast-in-place steel-framed reinforced concrete pile that resists pulling and compressive forces, which is integrally fixed to a steel frame together with a stiffener after the introduction of prestress. 4. Inserting a steel frame provided with a tip supporting portion with a length substantially corresponding to the entire length of the pile together with a reinforcing bar into a hole for a pile excavated in the ground, and performing positioning and fixing of each. The stage where concrete is poured into the hole, and after the cast concrete has developed its strength, the head support plate installed at the upper end of the steel-framed reinforced concrete pile and the prestressing device attached to the exposed part of the steel frame Installing a jack between the jig and introducing prestress using a steel frame, and when the prestress reaches a predetermined size, fix the prestressing stiffener to the steel frame while maintaining the introduced state Then, the reaction force of the prestress is changed from the jack together with the head support plate by the stiffener, and the prestress introduction jig and the jack are removed, and the drawing and compression are performed. How to build a cast-in-place steel reinforced concrete piles to resist.