JP3752436B2 - Reinforced cast-in-place concrete pile - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cast-in-place concrete pile reinforced with a reinforcing pipe such as a steel pipe.
[0002]
[Prior art]
As a method for increasing the yield strength of a cast-in-place concrete pile, there is a method in which a steel pipe is installed at the pile head and the concrete and the steel pipe are combined and integrated as disclosed in Japanese Patent Application Laid-Open No. 60-47117. In this pile, ribs, protrusions, stud bolts, dowels, and the like are attached to the inner surface of the steel pipe in order to increase the adhesion of concrete to the steel pipe. In addition, a cast-in-place concrete pile in which multidirectional X-shaped rebars are inserted to prevent concrete shear failure by X-direction reinforcement has been proposed.
On the other hand, in the precast concrete pile, there is a steel pipe concrete composite pile (SC pile) in which expanded concrete is cast and combined inside the steel pipe. (Japanese Patent Laid-Open No. 53-53021)
[0003]
[Problems to be solved by the invention]
When a ribbed steel pipe is installed on the pile head of a cast-in-place concrete pile, and the bond strength between the cast concrete and the steel pipe is increased to integrate the steel pipe and the concrete, ensuring the bending strength, the bending moment acting on the pile Stress concentrates on the ribs, and cracks occur in the concrete from the rib tips. Moreover, the concrete inserted between the ribs breaks, and the adhesion between the steel pipe and the concrete is lost. As a result, a decrease in proof stress and durability as a pile is recognized. In particular, when a repeated load is applied like an earthquake, the tendency is great. Once the concrete breaks, the adhesion cannot be expected, and the meaning of reinforcing the composite with steel and steel pipe is lost.
[0004]
Therefore, when the pile is designed in consideration of the adhesion between the steel pipe and the concrete, it becomes dangerous if the adhesion between the concrete and the steel pipe is lost. That is, when bending stress acts on the pile, concentrated stress is generated from the ribs in the steel pipe and cracks are generated.
[0005]
Thus, the pile which put the steel pipe on the outer peripheral part of the cast-in-place concrete pile and integrated both is easy to break the concrete inserted in the rib. Similarly, the stress is concentrated on the stud bolts and the like, and as a result, the concrete breaks.
The present invention seeks to ensure the toughness of cast-in-place concrete piles at the time of failure without expecting adhesion between steel pipe and concrete.
[0006]
[Means for Solving the Problems]
An anti-adhesion layer for the concrete is provided on the inner wall of the reinforcement pipe to prevent the reinforcement pipe and concrete from adhering to the concrete.In addition, reinforcing steel is added to the concrete to reinforce the cast-in-place concrete pile, increasing the toughness at the end of failure. It is a thing.
[0007]
[Action]
Since there is no adhesion between the steel pipe of the pile head and concrete, the concrete in the reinforcement pipe is restrained from deformation in the radial direction, but the reinforcement pipe and concrete are not integrated in the pile axis direction, and the axial force is applied to the steel pipe. Since it is not burdened, the bending strength of the steel pipe can be greatly increased. Therefore, ultimate toughness that is not found in a concrete pile in which conventional concrete and steel pipe are integrated with ribs or the like can be secured.
Since it does not expect adhesion to steel pipes, there is no decrease in adhesion due to secular change unlike piles of construction methods that expect adhesion, and the toughness of the pile can be secured for many years. Moreover, since an anti-adhesion layer is provided between the concrete and the reinforcing pipe, stress concentration due to the projections attached to the steel pipe and the steel pipe is avoided, so there is no cracking inside the concrete and no breakage of the concrete between the ribs. The stress from the pile head is smoothly transmitted downward through the reinforced concrete.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
FIG. 1 shows a longitudinal section of a reinforced cast-in-place concrete pile of the present invention, and FIG. 2 shows a plan view.
In the reinforced cast-in-place concrete pile 1 of the present invention, a reinforcing bar 20 comprising a reinforcing main reinforcing bar 2 and a hoop bar 21 is arranged in the pile, and a steel pipe 3 is reinforced over the pile head from the pile head to more than five times the pile diameter. It is arranged as a body. The inner surface of the steel pipe 3 is a smooth flat surface on which protrusions such as ribs are not formed, and an adhesion preventing layer (sliding layer) 4 is formed by applying a lubricant such as grease to prevent adhesion between the concrete and the steel pipe. Yes.
[0009]
In order to join with the superstructure, the beard muscle 22 joined to the steel pipe is fixed to the footing 5 as an anchor muscle. In the design of the reinforced cast-in-place concrete pile of the present invention, the inner surface of the steel pipe is not attached to the concrete at all, thereby preventing a decrease in toughness at the end.
[0010]
This will be explained by a model experiment.
Fig. 3 shows a pile of Portland cement concrete placed in a steel pipe with an inner diameter of 195 mm and a thickness of 2.15 mm with a water cement ratio of 55%, a unit water volume of 189 kg / m ³ , a slump of 18 cm and a fine aggregate ratio of 46.1%. In the bending test, the inside of the steel pipe is unstriped. The compressive strength of concrete is 27.8 N / mm ² and the tensile strength is 2.25 N / mm ² . No. No. 1 pile is a steel pipe and concrete integrated by applying an epoxy adhesive inside the steel pipe before placing the concrete. In the pile of No. 2, grease is applied to the inner surface of the steel pipe to completely cut off the adhesion between the concrete and the steel pipe, and further, a polyester film having a thickness of 0.1 mm is applied to form an adhesion preventing layer 4 to adhere the concrete and the steel pipe. There is no such thing.
[0011]
No. shown in FIG. 3, no. No. 4 stakes both have steel bars placed in the steel pipe. 3 piles are No. Similar to No. 1 pile, an epoxy adhesive is applied to integrate concrete and steel pipe. The 4 piles are made by applying grease to the inner surface of the steel pipe and attaching a polyester film to prevent adhesion. No. The 5 pile is a normal reinforced concrete pile not wound with a steel pipe, and the reinforcement ratio is 1%.
[0012]
No. which adheres to concrete and steel pipe. It can be seen that one pile has good bending strength. No. As for the two piles, the yield strength gradually decreases as the central deflection increases.
For this reason, when the inside of the steel pipe is unreinforced concrete, the presence or absence of adhesion between the concrete and the steel pipe has a great influence on the maximum strength and the decrease in the strength with increasing bending deformation.
[0013]
On the other hand, in the case of a pile in which steel bars are arranged inside the steel pipe shown in FIG. 4, it can be seen that the rigidity until the steel material yields and the load at the time of steel material yield are almost equal, regardless of whether the steel pipe and concrete adhere to each other, It can be seen that when reinforcing bars are placed in the steel pipe, the toughness of the pile body is maintained without being affected by the adhesion between the steel pipe and concrete.
However, no. The three piles gradually increase in yield strength as the deflection increases. The 4 piles are almost constant.
[0014]
Construction Example 1 Simultaneous Excavation As shown in the process in FIG. 5, a steel pipe that becomes a reinforcing pipe is constructed in the ground after excavation is completed or simultaneously with excavation, and concrete is placed in the steel pipe.
When the pile hole is formed by the bentonite mud construction method and the pile hole is completed, the primary bottom processing is performed to remove the slime at the bottom of the pile hole, and the steel pipe 3 and the reinforcing bar 2 are installed in the pile hole. The steel pipe 3 was about 5 times as long as the pile diameter. The pile hole is filled with bentonite mud used during excavation, and bentonite particles are deposited on the inner wall of the steel pipe 3 to form a bentonite film. This film becomes the adhesion preventing layer 4 for preventing adhesion of the cast concrete and the steel pipe.
If necessary, slime treatment (secondary pile bottom treatment) is performed on the bottom of the pile hole, and concrete is cast to complete the cast-in-place pile.
[0015]
It is also possible to use the reinforcing pipe as a casing for ground protection during excavation. In this case, the steel pipe casing 3 is installed in the ground, and the steel pipe casing is connected as the pile hole is deepened by excavating the pile hole. When excavation of the pile hole is completed, a reinforcing bar is installed and concrete is laid.
[0016]
In order to positively attach bentonite in the muddy water to the inner wall of the steel pipe, an anode is connected to the steel pipe 3, a cathode is installed in the muddy water, and negatively charged bentonite particles are attracted and adhered to the inner wall of the steel pipe. The adhesion preventing layer 4 is formed.
[0017]
Construction example 2
As shown in FIG. 6, a cast-in-place concrete pile is built in the ground, and a steel pipe as a reinforcing pipe is press-fitted with a power jack or a vibro hammer before the cast concrete is hardened yet.
[0018]
【The invention's effect】
The present invention provides a flat surface without forming ribs or protrusions on the inner surface of the reinforcing pipe of the cast-in-place concrete pile, forms an adhesion preventing layer between the reinforcing pipe and the concrete, and slips between the inner surface of the reinforcing pipe and the concrete. In order not to cause stress concentration against unexpected external force, the fracture of the concrete in the reinforcing pipe was prevented and the toughness was maintained for many years.
Further, since the adhesion between the concrete and the reinforcing pipe is not expected, it is not necessary to bear the axial force on the reinforcing pipe, so that the bending strength can be increased.
In this way, since protrusions such as ribs are not formed on the inner wall of the reinforcing pipe, a commercially available steel pipe can be used as the reinforcing pipe.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of the present invention.
FIG. 2 is a plan view of the present invention.
FIG. 3 is a graph showing a bending test result and a theoretical value in a state where there is no adhesion of a steel pipe.
FIG. 4 is a graph of toughness when reinforcing bars are inserted into a steel pipe without adhesion.
FIG. 5 is an explanatory diagram of a construction process.
FIG. 6 is an explanatory diagram of a construction process.

Claims (4)

Reinforced cast-in-place concrete piles that are reinforced with reinforcing bars installed on the outer periphery of the pile with a reinforcement pipe with an anti-adhesion layer on the inside. The reinforced cast-in-place concrete pile according to claim 1, wherein a reinforcement pipe is provided at a pile head. The reinforced cast-in-place concrete pile according to claim 1 or 2, wherein a fluororesin is applied to the inner surface of the reinforcing pipe. The reinforced cast-in-place concrete pile according to claim 1 or 2, wherein grease is applied to an inner surface of the reinforcing pipe.

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