JP2018003432A - Double pipe structure of pile head part and design method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce transmission of earthquake time horizontal force to a main pile from an outer pipe in a double pipe structure of a pile head part installed so as to be put on a head part of the main pile for supporting a vertical load, and having the outer pipe for burdening a part of the earthquake time horizontal force.SOLUTION: The top end of a main pile 1-head part is projected more than the top end of an outer pipe 2, the top end of the main pile 1-head part and the top end of the outer pipe 2 are buried in a pile cap 3, and soil cement or water-soil-muddy water or a cavity 8 being 0.1-5.0 N/mmin uniaxial compressive strength is formed between the main pile 1-head part and the outer pipe 2 under the pile cap 3. The lower end of a fixation reinforcement 5 is welded to a top end outer peripheral surface of the outer pipe 2, and this fixation reinforcement 5 is buried in the pile cap 3. The lower end of the fixation reinforcement 4 is welded to the top end outer peripheral surface of the main pile 1-head part, or the lower end of the fixation reinforcement 4 is welded or fixed by a screw to a top end upper surface of the main pile 1-head part, and this fixation reinforcement 4 is buried in the pile cap 3.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a double pipe structure of a pile head that is installed so as to cover an outer pipe that bears a part of the horizontal force during an earthquake on the head of the main pile that supports a vertical load, and a design method thereof.

  In general, this pile that receives a horizontal force during a large earthquake can be selected from SC piles with high earthquake resistance, or the head of the pile can be enlarged, or if the diameter is large, the ready-made pile can be given up and changed to a cast-in-place pile. There was a method, but it left problems in terms of performance and cost.

Therefore, it is possible to consider a structure in which only the pile head is seismically reinforced. For example, under the building foundation, this pile mainly receives vertical loads and has the role of reducing the load of this pile mainly by receiving horizontal loads. Arranging both the horizontal resistance members has already been implemented in various forms.
As the main thing, space saving and construction efficiency are good, so a cylindrical horizontal resistance member is placed on the same center axis as the main pile outside or inside the pile head, and the gap is filled with concrete etc. Such a synthetic structure is preferred.

  However, the conventional composite structure is designed to design the joints between the pile body and the pile cap, assuming that this pile and the horizontal resistance member are integrated, and the design of the pile body is troublesome. There were many design constraints.

And the pile head joint part of the conventional main pile is the pile diameter in the pile cap without installing the fixing bar in the pile outer periphery, the pile top, or the pile body, or without installing the fixing bar. The pile head stress is transmitted to the pile cap by one of the methods of embedding.
In the construction field, the method of installing anchorage is the mainstream. However, when the earthquake horizontal force acting on one pile is large and the pile head stress cannot be transmitted to the pilecap only by installing anchorage, the pile cap The pile head is embedded inside, and the anchoring bar is installed against the stress that reduces the resistance caused by the concrete on the side of the pile.

With respect to such a conventional ready-made pile, in Patent Document 1, the horizontal resistance member is constituted by a tubular body, and is installed so that the pile penetrates inside the tubular body, so that the horizontal force from the upper structure A seismic isolation structure for piles that can prevent pile breakage, particularly at the head of the pile, has been proposed.
In this seismic isolation structure, an elastic material (rubber body) is filled between the pile head and the pipe body.

Further, in Patent Document 2, the vertical force is applied to the main pile, the horizontal force is applied to the outer pipe, the vertical force and the horizontal force are shared, and the periphery of the head of the main pile and the outer pipe are separated. In addition to the structure in which concrete is filled in between, a different-diameter combination pile in which a connecting material for joining the outer tube and the foundation is arranged at the head of the outer tube and a construction method therefor have been proposed.
The pile head joint proposed in Patent Document 2 is considered to resist the stress generated in the pile head as a composite structure in which the main pile and the outer tube are integrated, and resists horizontal force. It is necessary to arrange the amount of reinforcing bars that can be placed in the concrete filled between the main pile and the outer pipe.

  In addition, in the seismic reinforcement structure in which an outer tube is press-fitted with a jack on the outer side of the upper end of the existing main pile, conventionally, the upper end of the main pile and the outer tube are slightly embedded on the basis, and Patent Document 2 Similar to the above, concrete was filled between the main pile and the outer pipe.

Japanese Patent No. 3575733 JP 2001-107356 A

However, in patent document 1, only the upper end part of this pile is slightly embedded in the upper structure, and the concrete structure of the pile head joint part with a pile cap is not shown, but a pile head joint is shown. The part cannot be designed.
Moreover, in patent document 2, only the upper end part of this pile is slightly embedded in the foundation, the amount of reinforcing bars which can be arrange | positioned between this pile and an outer pipe is limited, and the proof stress of a pile head junction part is this pile. If the outer tube is smaller than the yield strength integrated with concrete, the performance of this structure may not be fully demonstrated.

  And, as in Patent Document 1 and Patent Document 2, in the structure in which the elastic material or concrete is filled between the main pile and the outer pipe, the horizontal force during earthquake is transmitted from the outer pipe to the main pile through the elastic material or concrete. There is a problem that will be done.

  The subject of the present invention is a double pipe structure of a pile head provided with an outer pipe that is installed so as to cover the head of the main pile supporting a vertical load and bears a part of the horizontal force at the time of an earthquake. It is to reduce the transmission of horizontal force from the outer pipe to the main pile.

In order to solve the above problems, the invention described in claim 1
It is a double pipe structure of the pile head that is installed so as to cover the head of the main pile that supports the vertical load and has an outer pipe that bears a part of the horizontal force at the time of the earthquake,
The top end of the main pile head protrudes from the top end of the outer pipe, and the top end of the main pile head and the top end of the outer pipe are embedded in a pile cap,
A soil cement or water / soil / muddy water or voids having a uniaxial compressive strength of 0.1 to 5.0 N / mm ² is formed between the main pile head under the pile cap and the outer pipe. And

The invention described in claim 2
The double pipe structure of the pile head according to claim 1,
Welding the lower end of the fixing bar to the outer peripheral surface of the top end of the outer tube, and embedding the fixing bar in the pile cap,
The lower end of the fixing bar is welded to the outer peripheral surface of the top end of the main pile head, or the lower end of the fixing bar is welded or screwed to the upper surface of the upper end, and the fixing bar is embedded in the pile cap. To do.

The invention according to claim 3
The double pipe structure of the pile head according to claim 2,
The main pile is a concrete pile with a shell steel pipe, a centrifugal prestressed reinforced concrete pile or a pretension centrifugal high strength prestressed concrete pile,
The embedding depth of the outer pipe into the pile cap is a value obtained by adding a covering to the necessary welding length of the fixing muscle welded to the outer pipe, and 100 mm or more,
The embedding depth of the main pile into the pile cap is 100 mm or more added to the embedding depth of the outer pipe.

The invention according to claim 4
A method for designing a double pipe structure of a pile head according to claim 2 or 3,
The pile head bending moment M1 of the outer pipe top due to the horizontal load borne by the outer pipe, the pile head joint bending strength T1 of the outer pipe, the tensile compression resistance of the fixing muscle welded to the outer pipe, and the outer pipe In the relationship between the compression resistance A in the vertical direction and the interaction coefficient α, the following equation M1 <T1 = A × α Equation [1]
The design and the number of the fixing bars welded to the outer pipe are determined so as to satisfy the requirements.

The invention described in claim 5
A method for designing a double pipe structure of a pile head according to claim 2 or 3,
The pile head bending moment M2 at the top of the main pile due to the horizontal load borne by the main pile, the pile head joint bending strength T2 of the main pile, and the tensile and compression resistance of the fixing bar welded or screwed to the main pile In relation to the compression resistance B in the vertical direction of the main pile, the side resistance C of the main pile, and the interaction coefficient β, the following formula M2 <T2 = B + C × β Formula [2]
The design and the number of the fixing bars welded or screwed to the main pile and the embedding depth of the main pile are determined and designed so as to satisfy the requirements.

  According to the present invention, in the double pipe structure of the pile head that is installed so as to cover the head of the main pile that supports the vertical load and includes the outer pipe that bears a part of the horizontal force at the time of the earthquake, Transmission of horizontal force from the outer pipe to the main pile can be reduced.

1 is a schematic perspective view of a pile head according to an embodiment of a double pipe structure of a pile head to which the present invention is applied. It is a schematic side view of the partial cross section which shows the whole pile of FIG. It is a graph which shows the bending moment which arises in this pile. It is a schematic side view of the partial cross section which shows the pile head junction structure of Example 1. FIG. It is a schematic side view of the partial cross section which shows the pile head junction structure of Example 2. FIG. It is a flowchart of the design of a pile head reinforcement structure. It is a graph which shows the horizontal load share ratio of this pile and an outer pipe. It is the schematic side view (a) explaining the bending strength calculation of an outer tube, and the top view (b) of a virtual cylinder. It is a graph which shows interaction coefficient (alpha). It is a graph which shows the comparison of pile head bending moment M1 of an outer pipe, and proof stress T1 (experimental value M1 and calculation value T1). It is a flowchart of bending strength calculation of an outer tube. It is the schematic side view (a) explaining the bending strength calculation of this pile, and the top view (b) of a virtual cylinder. It is a graph which shows interaction coefficient (beta). It is a graph which shows the comparison of pile head bending moment M2 and proof stress T2 (experimental value M2 and calculation value T2) of this pile. It is a flowchart of bending strength calculation of this pile.

(Overview)
In the present invention, unlike a pile head joint structure based on a combined structure in which a pile that bears a vertical load and a pile that bears a horizontal load are integrated, the pile and the outer pipe each bear a horizontal force. The pile head joints are designed separately according to the pile head reinforcement structure for demonstrating the performance of the heavy pipe piles and the load horizontal force of the main pile and the outer pipe.

In the present invention, the top of the pile is protruded from the top of the outer pipe, and the anchorage is disposed on the pile head of the main pile and the outer pipe to connect the building foundation, more specifically, the pile head and the building foundation. It is characterized by fixing to a pile cap.
As a result, the main pile and the outer pipe can be structurally designed independently, and the design of the pile head joint, which has been a problem, is facilitated.
Here, the pile head joint portion is composed of a main pile, an outer pipe, and a fixing muscle embedded in a pile cap.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
(Embodiment)
1 and 2 show a configuration of an embodiment of a double pipe structure of a pile head to which the present invention is applied, wherein 1 is a main pile, 2 is an outer pipe, and 3 is a pile cap.

As shown in the figure, an outer pipe 2 made of a steel pipe having a diameter larger than that of the main pile 1 and a length shorter than that of the main pile 1 is provided on the outer periphery of the head of the main pile 1 made of ready-made piles. Is embedded in the pile cap 3.
Then, both the pile 1 and the outer pipe 2 are provided with reinforcing bars 4 and 5 for joining with the pile cap 3. That is, the pile cap 3 is also embedded with a fixing bar 4 provided on the top end or the outer periphery of the main pile 1 and a fixing bar 5 provided on the top end outer peripheral surface of the outer tube 2.

In addition, a root consolidation part 6 is formed at the lower end of the main pile 1 by injecting root solidification liquid and stirring and solidifying. Soil cement or water in which a fixed uniaxial compressive strength is 0.1 to 5.0 N / mm ² after the pile fixed portion 7 is formed and solidified between the head of the main pile 1 and the outer tube 2 -In addition to the formation of soil / mud water 8, it may be composed of soil / voids.

FIG. 3 is a graph showing the bending moment generated in the main pile 1, and as shown in the figure, the earthquake stress (bending moment indicated by the broken line) generated in the main pile 1 of the double pipe pile is generated in the conventional ready-made pile. By reducing the stress (bending moment shown by the solid line), it is possible to design with ready-made concrete piles for earthquake horizontal forces that could not be designed so far.
Moreover, since the specification of a pile or a pile diameter can be reduced compared with the conventional construction method, the cost of a pile can be reduced.

  Next, the concrete specification of the pile head joint structure of this invention is shown in FIG. 4 and FIG.

Example 1
FIG. 4 shows the pile head joint structure of Example 1, and this pile is a case of SC pile (Steel Composite Concrete Piles; concrete pile with shell steel pipe).
In the first embodiment, as shown in the drawing, the lower end of the fixing bar 4 is welded to the top end outer peripheral surface of the head of the main pile 1 or welded or screwed to the upper surface of the top end. The top end of the head 1 and the fixing muscle 4 and the top end of the outer tube 2 and the fixing muscle 5 are embedded in the pile cap 3 by welding the lower end of the fixing muscle 5.

(Example 2)
FIG. 5 shows a pile head joint structure of Example 2, and this pile is a PRC pile (Pretensioned & Reinforced Spun High Strength Concrete Piles) / PHC pile (Pretensioned Spun High Strength Concrete Piles). This is the case of the centrifugal force high strength prestressed concrete pile).
In the second embodiment, as shown in the figure, the lower end of the fixing bar 4 is welded or screwed to the upper surface of the top end of the head of the main pile 1 and the lower end of the fixing bar 5 is welded to the outer peripheral surface of the outer end of the outer pipe 2. Then, the top end and fixing muscle 4 of the head of the main pile 1 and the top end and fixing muscle 5 of the outer tube 2 are embedded in the pile cap 3.

In the above, as shown in FIGS. 4 and 5, the top end of the main pile 1 protrudes from the top end of the outer tube 2 embedded in the pile cap 3. The protruding height is 100 mm or more and the required welding length of the fixing bars 4 installed on the main pile 1.
Here, the embedding depth of the outer tube 2 in the pile cap 3 is set to a value obtained by adding a covering to the necessary welding length of the fixing bar 5 installed in the outer tube 2 and 100 mm or more.

  That is, in the case of the SC pile of the first embodiment, as shown in FIG. 4, the embedding depth of the main pile 1 in the pile cap 3 is set to the embedding depth of the outer pipe 2 and the fixing bars installed in the main pile 1. The required weld length of 4 and 100 mm or more are added.

  Further, in the case of the PRC pile / PHC pile of Example 2, as shown in FIG. 5, the embedding depth of the main pile 1 in the pile cap 3 is 100 mm or more added to the embedding depth of the outer tube 2. Shall.

FIG. 6 is a flowchart of the design of the pile head reinforcement structure. First, the horizontal load force of the main pile 1 and the outer pipe 2 is calculated (step S1). Next, the specification and the required number of fixing muscles 5 of the outer tube 2 are assumed (step S2). Next, the specification / necessary number of fixing bars 4 of the main pile 1 and the depth of embedding in the pile cap 3 are assumed (step S3). Next, the interaction coefficient α is calculated (step S4). Next, the interaction coefficient β is calculated (step S5). Next, the specification and number of the fixing muscles 5 of the outer tube 2 are determined (step S6). Next, the specification / number of anchoring bars 4 of the main pile 1 and the necessary embedding depth are determined (step S7).
The interaction coefficient means that the main pile 1 and the outer pipe 2 are deformed in the pile cap 3 by bearing a horizontal force, and therefore the influence of the main pile 1 on the outer pipe 2 is expressed by the interaction coefficient α. The influence of the outer tube 2 on the main pile 1 is defined as an interaction coefficient β.

  Here, the main pile 1 is pile head bonded so that it has a bending strength exceeding the pile head bending moment generated at the top of the main pile 1 by the horizontal load (50 to 20% of the total load) borne by the main pile 1. The part (specification / number of fixing muscles 4 and the embedding depth in the pile cap 3) is designed.

  Further, the outer pipe 2 has a pile head joint (fixing muscle) so that the outer pipe 2 has a bending strength exceeding the pile head bending moment generated at the top of the outer pipe 2 by a horizontal load (50 to 80%) borne by the outer pipe 2. 5 etc.).

Specifically, the structural design of the pile head joint between the main pile 1 and the outer pipe 2 is performed according to the following procedure.
In addition, since an interaction arises when a horizontal load acts on each of this pile 1 and the outer tube 2, it is set as the structural design method which considered the influence.

1) The horizontal load force of the main pile 1 and the outer pipe 2 is calculated (step S1).
For the horizontal force during an earthquake experienced by a pair of main pile 1 and outer pipe 2 with the same central axis, specifications of main pile 1 (diameter, length, concrete strength, etc.) and specifications of outer pipe 2 (diameter, length) The stress analysis model considering the ground condition (geology, depth, N value, etc.), and the horizontal load sharing ratio of the main pile 1 and the outer pipe 2 (for example, FIG. 7) Calculate.
Specifically, as a result of actually building a pile head reinforcement structure on site and conducting a horizontal loading test, the horizontal load sharing ratio between the main pile 1 and the outer pipe 2 is as shown in FIG. = 5: 5 to 2: 8. Therefore, the pile head joint between the main pile 1 and the outer pipe 2 is designed based on the stress analysis result with reference to the horizontal load sharing ratio.

2) The specifications and necessary number of fixing muscles 5 of the outer tube 2 are assumed (step S2).
In the hypothesis stage, for example, the interaction coefficient is ignored, and the specification and the necessary number of anchors are assumed according to a general design method.
The embedding depth L1 of the outer tube 2 in the pile cap 3 is set to a value that takes into account the weld length + cover of the fixing bar 5 and 100 mm or more.
Here, the general design method is that the bending strength of the reinforced concrete cross section assuming a virtual cylinder having an outer tube diameter D2 + (100 to 200) mm exceeds the bending moment due to the horizontal force applied to the outer tube 2. Determine the specifications and number.

3) Assuming the specification / necessary number of fixing bars 4 of the main pile 1 and the depth of embedding in the pile cap 3 (step S3).
In the hypothesis stage, for example, the interaction coefficient is ignored, and the specification of the anchorage and the necessary number and embedding depth are assumed according to a general design method.
For example, in the case of an SC pile (FIG. 4), the embedding depth L2 of the main pile 1 in the pile cap 3 is determined by considering the weld length of the fixing bar 4 to the main pile 1. It is assumed that the necessary weld length of the fixing bar 4 installed in the main pile 1 and 100 mm or more are added to L1.

In the case of the PRC pile / PHC pile (FIG. 5), the embedding depth L2 of the main pile 1 in the pile cap 3 is assumed to be 100 mm or more added to the embedding depth L1 of the outer pipe 2.
Here, the general design method is that the bending strength of the reinforced concrete cross section assuming a virtual cylinder with a main pile diameter D1 + (100 to 200) mm exceeds the bending moment due to the horizontal load of the main pile 1. Determine the specifications and number.

4) The interaction coefficient α is calculated (step S4).
As shown in FIG. 8, the interaction coefficient α, which is an influence coefficient of the main pile 1 on the outer pipe 2, is embedded depth L 1 of the outer pipe 2 into the pile cap 3 and the embedding of the main pile 1 and the outer pipe 2. Based on the difference between the depths L2 and L1 (the protruding length from the top end of the outer pipe 2 to the top end of the main pile 1), it is determined based on FIG. This relationship was determined based on an indoor structural experiment of a pile head reinforcing structure composed of the main pile 1 and the outer pipe 2.

  It should be noted that the interaction coefficient α is a pile head joint portion of the outer pipe 2 according to an evaluation formula [1] to be described later with respect to the experimental result in the indoor structure test result of the pile head reinforcing structure composed of the main pile 1 and the outer pipe 2. The bending strength T1 was determined to be on the safe side (experimental result exceeded).

  FIG. 10 shows a comparison between the experimental results and the pile head joint bending strength T1 based on the evaluation formula [1].

FIG. 11 is a flowchart for calculating the bending strength of the outer tube 2. First, the bending strength 1 by the fixing bar 5 is input (step S11), and it is determined whether or not the bending strength 1 is equal to or greater than the design bending moment (step S12). If so, the design is completed (step S13).
In step S12, if the bending strength 1 is less than the design bending moment, the bending strength 2 by embedding the top end of the outer tube 2 in the pile cap 3 is input (step S14), and the bending strength 1 by the fixing bar 5 is input. Add bending strength 2 by embedding outer tube 2 top end into pile cap 3 (step S15), and determine whether or not the sum of bending strength 1 + 2 is greater than the design bending moment (step S16). If so, the design is terminated (step S17).

  In step S16, if the bending strength 1 + 2 is less than the design bending moment, the embedding depth is increased (step S18), and the bending strength 2 corresponding to the embedding depth is added to the bending strength 1. It is determined whether or not the sum bending resistance 1 + 2 is greater than or equal to the design bending moment (step S19). In step S19, if the bending strength 1 + 2 is less than the design bending moment, the pile diameter is increased (step S21), the bending strength 1 by the fixing bar 5 corresponding to the pile diameter is input (step S11), and so on. Perform the process.

5) The interaction coefficient β is calculated (step S5).
As shown in FIG. 8, the interaction coefficient β, which is an influence coefficient of the outer pipe 2 on the main pile 1, is embedded depth L 1 of the outer pipe 2 into the pile cap 3 and the embedding of the main pile 1 and the outer pipe 2. It is determined based on FIG. 13 from the difference between the depths L2 and L1 (the protruding length from the top end of the outer pipe 2 to the top end of the main pile 1). This relationship was determined based on an indoor structural experiment of a pile head reinforcement structure consisting of this pile and an outer pipe.

  It should be noted that the interaction coefficient β is a pile head joint portion of the main pile 1 according to an evaluation formula [2] to be described later with respect to the experimental result in the indoor structure experimental result of the pile head reinforcing structure composed of the main pile 1 and the outer pipe 2. The bending strength T2 was determined to be on the safe side (experimental result exceeded).

  FIG. 14 shows a comparison between the experimental results and the pile head joint bending strength T2 based on the evaluation formula [2].

6) The specification and number of the fixing muscles 5 of the outer tube 2 are determined (step S6).
Pile head bending moment M1 at the top of the outer pipe 2 due to the horizontal load borne by the outer pipe 2, the pile head joint bending strength T1 of the outer pipe 2, the tensile compression resistance of the outer pipe anchoring muscle 5 and the vertical compression of the outer pipe 2 In relation to the resistance A and the interaction coefficient α, the specifications and the number of the outer tube anchoring muscles 5 satisfying the following expression [1] are determined.
M1 <T1 = A × α (1)

  However, as shown in FIG. 8, the tensile compression resistance of the outer tube fixing muscle 5 and the vertical compression resistance A of the outer tube 2 are based on a reinforced concrete section assuming a virtual cylinder having an outer tube diameter D2 + (100 to 200) mm. Calculated based on bending strength.

7) The specifications and number of anchoring bars 4 of the main pile 1 and the necessary embedding depth are determined (step S7).
The pile head bending moment M2 at the top of the main pile 1 due to the horizontal load borne by the main pile 1, the pile head joint bending strength T2 of the main pile 1, the tensile compression resistance of the main pile anchoring bar 4, and the vertical compression of the main pile 1 In relation to the resistance B, the main pile side resistance C, and the interaction coefficient β, the specifications and the number of the main pile fixing bars 4 that satisfy the following equation [2] are determined.
M2 <T2 = B + C × β (2)

  However, the tensile compression resistance of the main pile anchoring bar 4 and the vertical compression resistance B of the main pile 1 are based on a reinforced concrete cross section assuming a virtual cylinder with a main pile diameter D1 + (100 to 200) mm, as shown in FIG. Calculated based on bending strength.

Moreover, this pile side resistance C considers the bearing resistance of the side concrete of the part which protruded from the outer pipe 2 top end mainly, as shown in FIG.
That is, the main pile side resistance C is the concrete bearing resistance of the main pile 1 side surface protruding from the top end of the outer pipe 2 and is calculated from the following commonly used equation.
^{C = D × l 2/6} × fc-Q 0 × l / 6
Here, D: main pile diameter, l: protrusion length of the main pile from the top of the outer pipe, fc: short-term allowable compressive stress degree of pile cap concrete (a bearing coefficient may be further considered), Q ₀ : main This is the horizontal force of the pile.

FIG. 15 is a flowchart for calculating the bending strength of the main pile 1. First, the bending strength 1 by the fixing bar 4 is input (step S31), and it is determined whether the bending strength 1 is equal to or greater than the design bending moment (step S32). If so, the design is finished (step S33).
In step S32, if the bending strength 1 is less than the design bending moment, the bending strength 2 by embedding the top end of the main pile 1 in the pile cap 3 is input (step S34), and the bending strength 1 by the fixing bar 4 is input. Add bending strength 2 by embedding main pile 1 in pile cap 3 (step S35), and determine whether or not the sum of bending strength 1 + 2 is greater than the design bending moment (step S36). If so, the design is terminated (step S37).

  In step S36, if the bending strength 1 + 2 is less than the design bending moment, the embedding depth is increased (step S38), and the bending strength 2 corresponding to the embedding depth is added to the bending strength 1. It is determined whether or not the sum bending resistance 1 + 2 is greater than or equal to the design bending moment (step S39), and if so, the design is terminated (step S40). In step S39, if the bending strength 1 + 2 is less than the design bending moment, the pile diameter is increased (step S41), the bending strength 1 by the fixing bar 4 corresponding to the pile diameter is input (step S31), and so on. Perform the process.

8) As shown in FIG. 11 and FIG. 15, when the bending strength of the fixing bars 4 and 5 is insufficient for both the outer tube 2 and the main pile 1, as shown in FIG. -Increase the number of 5s, use strong anchoring streaks, or increase the depth of embedding in the pile cap 3.
In addition, between the main pile 1 and the outer pipe 2 to the lower end of the pile cap 3, the soil cement 8 is excavated and discharged, and the same concrete as the pile cap 3 is placed.

  As described above, the pile head stress generated in the main pile 1 and the outer pipe 2 can be reliably transmitted to the pile cap 3.

  By constructing the pile head joint by the above design method, it is possible to reliably transmit the load borne by the main pile 1 and the outer pipe 2 to the pile cap 3, and the vertical and horizontal of the double pipe The burden of power can be secured.

  As mentioned above, according to the double pipe structure of the pile head of the embodiment, the top end of the head of the main pile is protruded from the top end of the outer pipe 2, and the top end of the head of the main pile and the outer pipe 2 is embedded in the pile cap 3, and the soil cement, water, mud, soil, and void 8 are formed between the head of the main pile 1 and the outer pipe 2 under the pile cap 3. Transmission of force from the outer tube 2 to the main pile 1 can be reduced.

(Modification)
In addition to the above-described embodiments, it is needless to say that specific detailed structures and methods can be appropriately changed.

1 Pile 2 Outer pipe 3 Pile cap 4 Pile anchoring muscle 5 Outer pipe anchoring muscle 6 Tip root fixing part 7 Pile circumference fixing part 8 Soil cement or water (or soil, muddy water, void)

Claims (5)

It is a double pipe structure of the pile head that is installed so as to cover the head of the main pile that supports the vertical load and has an outer pipe that bears a part of the horizontal force at the time of the earthquake,
The top end of the main pile head protrudes from the top end of the outer pipe, and the top end of the main pile head and the top end of the outer pipe are embedded in a pile cap,
A soil cement or water / soil / muddy water or voids having a uniaxial compressive strength of 0.1 to 5.0 N / mm ² is formed between the main pile head under the pile cap and the outer pipe. Double pipe structure of the pile head. Welding the lower end of the fixing bar to the outer peripheral surface of the top end of the outer tube, and embedding the fixing bar in the pile cap,
The lower end of the fixing bar is welded to the outer peripheral surface of the top end of the main pile head, or the lower end of the fixing bar is welded or screwed to the upper surface of the upper end, and the fixing bar is embedded in the pile cap. The double pipe structure of the pile head according to claim 1. The main pile is a concrete pile with a shell steel pipe, a centrifugal prestressed reinforced concrete pile or a pretension centrifugal high strength prestressed concrete pile,
The embedding depth of the outer pipe into the pile cap is a value obtained by adding a covering to the necessary welding length of the fixing muscle welded to the outer pipe, and 100 mm or more,
The double pipe structure of the pile head according to claim 2, wherein the embedding depth of the main pile in the pile cap is added to the embedding depth of the outer pipe by 100 mm or more. A method for designing a double pipe structure of a pile head according to claim 2 or 3,
The pile head bending moment M1 of the outer pipe top due to the horizontal load borne by the outer pipe, the pile head joint bending strength T1 of the outer pipe, the tensile compression resistance of the fixing muscle welded to the outer pipe, and the outer pipe In the relationship between the compression resistance A in the vertical direction and the interaction coefficient α, the following equation M1 <T1 = A × α Equation [1]
The design method of the double pipe structure of the pile head characterized by determining and designing the specification and the number of the fixed reinforcements welded to the outer pipe so as to satisfy the above. A method for designing a double pipe structure of a pile head according to claim 2 or 3,
The pile head bending moment M2 at the top of the main pile due to the horizontal load borne by the main pile, the bending strength T2 of the pile head joint of the main pile, and the tensile and compression resistance of the fixing bar welded or screwed to the main pile In relation to the compression resistance B in the vertical direction of the main pile, the side resistance C of the main pile, and the interaction coefficient β, the following formula M2 <T2 = B + C × β Formula [2]
The design method of the double pipe structure of the pile head characterized by determining and designing the specification and the number of the fixing bars welded or screwed to the main pile so as to satisfy the requirements.

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