JP6733905B2 - Double pipe structure of pile head and its designing method - Google Patents

Description

The present invention relates to a pile pipe double pipe structure in which a head portion of a main pile supporting a vertical load is covered with an outer pipe that bears a part of horizontal force during an earthquake, and a design method thereof.

Generally, for the main pile that receives a large horizontal force during an earthquake, select SC piles with high seismic resistance, increase the diameter of the pile head, change the existing pile to a cast-in-place pile if the diameter is large, etc. There was a method, but it left a problem in terms of performance and cost.

Therefore, a structure in which only the pile head is reinforced with earthquake resistance is conceivable. For example, it has a role to reduce the load on the main pile mainly receiving a vertical load and a horizontal load under the building foundation. Arranging both the horizontal resistance member and the horizontal resistance member has already been implemented in various forms.
The main thing is that space saving and construction efficiency are good, so a cylindrical horizontal resistance member is placed on the outside or inside of the pile head as the same central axis as the main pile, and the gap is filled with concrete etc. Such synthetic structures are preferred.

However, the conventional composite structure is one in which the pile and the horizontal resistance member are integrated to design the joint between the pile body and the pile cap, and in addition to the cumbersome design of the pile body, However, there were many design restrictions.

And, the pile head joint part of the conventional main pile is installed with anchorages at the pile periphery, the top of the pile, or inside the pile, or without installing anchorages, the piles are piled inside the pile cap. The pile head stress is transmitted to the pile cap by one of the methods of embedding to some extent.
In the construction field, the method of installing anchorages is the mainstream method. However, if the horizontal stress of one pile is large during an earthquake and it is not possible to transmit the pile head stress to the pile cap only by installing anchorages, the pile cap will be used. The pile heads are embedded in the piles, and anchoring bars are installed for the stress that reduces the resistance due to the concrete on the side of the piles.

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

In Patent Document 2, the vertical force is applied to the main pile and the horizontal force is applied to the outer pipe to share the vertical force and the horizontal force. In addition to a structure in which concrete is filled in between, a different diameter combination pile in which a connecting material for joining the outer pipe and the foundation is arranged on the head of the outer pipe and a construction method thereof 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 pipe are integrated, and resists horizontal force. It is necessary to arrange the amount of rebar that can be formed in the concrete that is filled between the main pile and the outer pipe.

In a seismic retrofit structure in which an outer pipe is press-fitted onto the outside of an upper end of an existing main pile by a jack, conventionally, the flush upper end of the main pile and the outer pipe are slightly embedded in a foundation, and Patent Document 2 Similarly 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 portion of the main pile is slightly embedded in the upper structure, and the concrete structure of the pile head joint portion with the pile cap is not shown. I can't design the department.
Further, in Patent Document 2, only the upper end of the main pile is slightly embedded in the foundation, the amount of reinforcing bars that can be arranged between the main pile and the outer pipe is limited, and the proof stress of the pile head joint is If the outer pipe and the outer pipe are smaller than the proof stress integrated with concrete, the performance of this structure may not be sufficiently exhibited.

And in the structure which filled the elastic material or concrete between the main pile and the outer pipe like patent document 1 or patent document 2, the horizontal force at the time of an earthquake is transmitted to the main pile from an outer pipe through an elastic material or concrete. There is a problem that will be done.

An object of the present invention is to provide a pile head double pipe structure including an outer pipe that is installed so as to cover the head of a main pile that supports a vertical load and bears a part of horizontal force during an earthquake. It is to reduce the transfer of horizontal force from the outer pipe to the main pile.

In order to solve the above problems, the invention described in claim 1 is
A double-pipe structure of a pile head that is installed so as to cover the head of a main pile that supports a vertical load and that has an outer pipe that bears a part of horizontal force during an earthquake,
The main pile is a concrete pile with an outer shell steel pipe, a centrifugal force prestressed reinforced concrete pile or a pretension system centrifugal force high strength prestressed concrete pile,
By projecting the top end of the main pile head from the top end of the outer pipe, and embedding the top end of the main pile head and the top end of the outer pipe in a pile cap,
Soil cement having a uniaxial compressive strength of 0.1 to 5.0 N/mm ² is formed between the pile head under the pile cap and the outer pipe , or water, soil, muddy water or voids are formed. Has been formed ,
The lower end of the fixing streak is welded to the outer peripheral surface of the top end of the outer tube, the fixing streak is embedded in the pile cap, and the depth of the outer tube embedded in the pile cap is welded to the outer tube by the fixing. A value obtained by adding a cover to the required welding length of the streak, and 100 mm or more,
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 screw-fitted to the upper surface of the top end, and the fixing bar is embedded in the pile cap. The depth of embedding into the pile cap is 100 mm or more added to the depth of embedding of the outer tube .

The invention according to claim 2 is
A method of designing a double pipe structure for a pile head according to claim 1 ,
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 anchoring line welded to the outer pipe, and the outer pipe. In the relationship between the vertical compression resistance A and the interaction coefficient α, the following equation M1<T1=A×α (Equation [1]
The specifications and the number of the fixing bars welded to the outer pipe are determined and designed so as to satisfy the above condition.

The invention according to claim 3 is
A method of designing a double pipe structure for a pile head according to claim 1 ,
A pile head bending moment M2 of the top of the main pile due to a horizontal load borne by the main pile, a bending strength T2 of a pile head joint portion of the main pile, and a tensile compression resistance of the anchor bar welded or screw fitted to the main pile. In the relationship of the vertical compression resistance B of the main pile, the side surface resistance C of the main pile, and the interaction coefficient β, the following formula M2<T2=B+C×β... Formula [2]
The specifications and the number of the anchoring bars welded or screw-fitted to the main pile and the embedding depth of the main pile are determined so as to satisfy the above condition.

ADVANTAGE OF THE INVENTION According to this invention, in the double pipe structure of the pile head provided with the outer pipe which is installed so that it may cover the head of the main pile which supports a vertical load and bears a part of horizontal force at the time of an earthquake, It is possible to reduce the transmission of horizontal force from the outer pipe to the main pile.

1 is a schematic perspective view of a pile head, showing a configuration of 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 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 connection structure of Example 1. It is a schematic side view of the partial cross section which shows the pile head connection structure of Example 2. It is a flowchart of 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 pipe, and the top view (b) of a virtual cylinder. It is a graph which shows interaction coefficient (alpha). 6 is a graph showing a comparison between a pile head bending moment M1 of an outer pipe and a proof stress T1 (experimental value M1 and calculated value T1). It is a flow chart of bending strength calculation of an outer pipe. It is a 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 comparison of pile head bending moment M2 of this pile, and proof stress T2 (experimental value M2 and calculation value T2). It is a flowchart of calculation of bending strength of this pile.

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

The present invention makes the top end of the main pile project from the top end of the outer pipe, and arranges the anchoring lines on the main pile and the pile head of the outer pipe to connect the building foundation, more specifically, the pile head and the building foundation. It is characterized by being fixed to the pile cap.
As a result, the main pile and the outer pipe can be designed independently of each other, which facilitates the design of the pile head joint, which is a problem.
Here, the pile head joint portion is composed of the main pile, the outer pipe, and the anchoring line which are respectively embedded in the pile cap.

Hereinafter, a mode for carrying out the present invention will be described in detail with reference to the drawings.
(Embodiment)
1 and 2 show the structure of an embodiment of a double pipe structure of a pile head to which the present invention is applied, in which 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 larger diameter and a shorter length than the main pile 1 is provided on the outer circumference of the head of the main pile 1 made of ready-made piles, and the top ends of the main pile 1 and the outer pipe 2 are provided. Are embedded in the pile cap 3.
Then, both the main pile 1 and the outer pipe 2 are provided with reinforcing bars 4 and 5 for joining to the pile cap 3. That is, the pile cap 3 is also embedded with the fixing streak 4 provided on the top end or the outer circumference of the main pile 1 and the fixing streak 5 provided on the outer peripheral surface of the top end of the outer tube 2.

In addition, a tip root solidification portion 6 is formed at the lower end of the main pile 1 by injecting a rooting liquid and stirring and solidifying it, and injecting a pile circumference fixing liquid around the main pile 1 and the outer pipe 2 to solidify by stirring. Soil cement or water in which the uniaxial compressive strength after solidification between the head of the main pile 1 and the outer tube 2 is 0.1 to 5.0 N/mm ² by forming the pile peripheral fixing portion 7 formed. -Soil/muddy water 8 may be formed, and 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 shown by the broken line) in the main pile 1 of the double pipe pile is generated in the conventional ready-made pile during the earthquake. By reducing the stress (bending moment shown by the solid line), it is possible to design with ready-made concrete piles even for horizontal forces during earthquakes that could not be designed until now.
Moreover, since the specification of the pile or the diameter of the pile can be reduced as compared with the conventional construction method, the cost of the pile can be reduced.

Next, specific specifications of the pile head joint structure of the present invention are shown in FIGS. 4 and 5.

(Example 1)
FIG. 4 shows a pile head joint structure of Example 1, and is a case where this pile is an SC pile (Steel Composite Concrete Piles; concrete pile with steel pipes for outer shell).
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 screw-fitted to the top end upper surface so that the top end outer peripheral surface of the outer pipe 2 is attached. The lower end of the fixing bar 5 is welded, and the top end of the head of the main pile 1 and the fixing bar 4 and the top end of the outer tube 2 and the fixing bar 5 are embedded in the pile cap 3.

(Example 2)
FIG. 5 shows a pile head joint structure of Example 2, in which the main pile is a PRC pile (Pretensioned & Reinforced Spun High Strength Concrete Piles) and a PHC pile (Pretensioned Spun High Strength Concrete Piles). Method 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 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 tube 2. Then, the top end of the head of the main pile 1 and the fixing line 4 and the top end of the outer tube 2 and the fixing line 5 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 is made to protrude from the top end of the outer tube 2 to be embedded in the pile cap 3. The projecting height is 100 mm or more, and is more than the required welding length of the fixing bar 4 installed in the main pile 1.
Here, the depth of embedding the outer tube 2 in the pile cap 3 is set to a value obtained by adding a cover to the required welding length of the fixing streak 5 installed in the outer tube 2 and 100 mm or more.

That is, in the case of the SC pile of Example 1, as shown in FIG. 4, the embedding depth of the main pile 1 into the pile cap 3 is the same as the embedding depth of the outer tube 2, and the anchorages installed in the main pile 1 are as follows. The required welding 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 was 100 mm or more in addition to the embedding depth of the outer tube 2. I shall.

FIG. 6 is a flowchart for designing the pile head reinforcement structure. First, the horizontal load to be applied to the main pile 1 and the outer pipe 2 is calculated (step S1). Next, it is assumed that the specifications and the required number of the fixing muscles 5 of the outer tube 2 are satisfied (step S2). Next, it is assumed that the specifications/required number of anchoring streaks 4 of the main pile 1 and the depth of embedding in the pile cap 3 (step S3). Next, the interaction coefficient α is calculated (step S4). Next, the interaction coefficient β is calculated (step S5). Next, the specifications and the number of the fixing muscles 5 of the outer tube 2 are determined (step S6). Next, the specifications and number of anchoring lines 4 of the main pile 1 and the required 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. Therefore, the effect of the main pile 1 on the outer pipe 2 is an interaction coefficient α. , The effect of the outer pipe 2 on the main pile 1 is defined as the interaction coefficient β.

Here, the pile head joining is performed so that the main pile 1 has a bending proof strength that exceeds a pile head bending moment generated at the top of the main pile 1 due to a horizontal load (50 to 20% of the total load) that the main pile 1 bears. Design the parts (specification/number of anchor lines 4 and depth of embedding into the pile cap 3).

In addition, the outer pipe 2 has a bending resistance that exceeds the pile head bending moment generated at the top of the outer pipe 2 due to the horizontal load (50 to 80%) that the outer pipe 2 bears. Design the number of 5).

Specifically, the structural design of the pile head joint between the main pile 1 and the outer pipe 2 is performed by the following procedure.
Since a horizontal load is applied to each of the main pile 1 and the outer pipe 2 to cause an interaction, the structure design method is to consider the influence.

1) Calculate the load horizontal force of the main pile 1 and the outer pipe 2 (step S1).
Specifications of the main pile 1 (diameter, length, concrete strength, etc.) and specifications of the outer pipe 2 (diameter, length) with respect to the horizontal force at the time of a set of the main pile 1 and the outer pipe 2 having the same center axis , Wall thickness, etc.), a stress analysis model considering the ground condition (geology, depth, N value, etc.) is constructed, and the horizontal load sharing ratio (for example, FIG. 7) between the main pile 1 and the outer pipe 2 is set. Calculate.
Specifically, as a result of actually constructing a pile head reinforcement structure on-site and carrying out a horizontal load 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) Assuming the specifications and the required number of anchoring muscles 5 of the outer tube 2 (step S2).
At the hypothesis stage, for example, the interaction coefficient is ignored, and the specifications and required number of anchorage muscles are assumed according to a general design method.
The depth L1 of embedding the outer tube 2 in the pile cap 3 is set to a value that takes into consideration the welding length of the fixing streak 5 + the overburden and is 100 mm or more.
Here, the above-mentioned general design method means that the bending strength of the reinforced concrete section assuming a virtual cylinder of the outer pipe diameter D2+(100 to 200) mm exceeds the bending moment of the horizontal force borne by the outer pipe 2 so that the bending strength of the rebar is increased. Determine specifications and number.

3) It is assumed that the specifications/required number of anchoring lines 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 specifications and required number of anchoring muscles and the embedding depth are assumed according to a general design method.
The embedding depth L2 of the main pile 1 into the pile cap 3 is, for example, in the case of the SC pile (FIG. 4 ), the embedding depth of the outer tube 2 in consideration of the welding length of the anchoring line 4 to the main pile 1. It is assumed that the required welding length of the fixing bar 4 installed on the main pile 1 and 100 mm or more are added to L1.

In the case of PRC piles/PHC piles (FIG. 5), the embedding depth L2 of the main pile 1 in the pile cap 3 is the embedding depth L1 of the outer tube 2 plus 100 mm or more.
Here, the above-mentioned general design method means that the bending strength of the reinforced concrete section assuming a virtual column of the main pile diameter D1+(100 to 200) mm exceeds the bending moment of the horizontal load borne by the main pile 1 so that Determine specifications and number.

4) Calculate the interaction coefficient α (step S4).
As shown in FIG. 8, the interaction coefficient α, which is the influence coefficient of the main pile 1 on the outer pipe 2, is the depth L1 of embedding the outer pipe 2 in the pile cap 3, and the embedding of the main pile 1 and the outer pipe 2. It is determined based on FIG. 9 from the difference between the depths L2 and L1 (the protruding length from the top of the outer pipe 2 to the top of the main pile 1). This relationship was determined based on the indoor structure experiment of the pile head reinforcement structure composed of the main pile 1 and the outer pipe 2.

In addition, the interaction coefficient α is the pile head joint portion of the outer pipe 2 according to the evaluation formula [1] described later in the indoor structure test result of the pile head reinforcement structure including the main pile 1 and the outer pipe 2. The bending strength T1 was determined to be on the safe side (the experimental result exceeds).

FIG. 10 shows a comparison of the bending strength T1 of the pile head joint by the experimental result and 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 finished (step S13).
In step S12, if the bending strength 1 is less than the design bending moment, the bending strength 2 due to the embedding of the top end of the outer tube 2 into the pile cap 3 is input (step S14), and the bending strength 1 due to the fixing bar 5 is set. The bending proof strength 2 due to the embedding of the outer tube 2 top end into the pile cap 3 is added (step S15), and it is determined whether or not the total bending proof strength 1+2 is greater than or equal to the design bending moment (step S16). If there is, the design is finished (step S17).

If the bending strength 1+2 is less than the design bending moment in step S16, 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 the sum of the bending strength 1+2 is equal to or greater than the design bending moment (step S19), and if it is greater than or equal to the design end (step S20). 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 anchoring bar 5 corresponding to the pile diameter is input (step S11), and so on. Process.

5) Calculate the interaction coefficient β (step S5).
The interaction coefficient β which is the influence coefficient of the outer pipe 2 on the main pile 1 is, as shown in FIG. 8, the depth L1 of embedding the outer pipe 2 into the pile cap 3 and the embedding of the main pile 1 and the outer pipe 2. From the difference between the depths L2 and L1 (protruding length from the top of the outer pipe 2 to the top of the main pile 1), it is determined based on FIG. This relationship was established based on the indoor structural experiment of the pile head reinforcement structure consisting of the main pile and the outer pipe.

In addition, the interaction coefficient β is a pile head joint portion of the main pile 1 according to the evaluation formula [2] described later in the indoor structure test result of the pile head reinforcement structure including the main pile 1 and the outer pipe 2. The bending strength T2 was determined to be on the safe side (the experimental result exceeds).

FIG. 14 shows the comparison between the experimental results and the bending strength T2 of the pile head joint part according to the evaluation formula [2].

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

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

7) The specifications and the number of anchoring lines 4 of the main pile 1 and the required 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 bending strength T2 at the pile head joint portion 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 surface resistance C, and the interaction coefficient β, the specifications and the number of the main pile anchoring streaks 4 that satisfy the following expression [2] are determined.
M2<T2=B+C×β... Formula [2]

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

As for the side surface resistance C of the pile, as shown in FIG. 12, the bearing pressure resistance of the side surface concrete of the portion protruding from the top end of the outer tube 2 is mainly considered.
That is, the main pile side surface resistance C is a concrete bearing pressure resistance of the side surface of the main pile 1 protruding from the top end of the outer pipe 2, and is calculated from the following formula that is generally used.
C=D×l ² /6×fc-Q ₀ ×l/6
Here, D: main pile diameter, l: protrusion length of the main pile from the outer pipe top end, fc: short-term permissible compressive stress level of pile cap concrete (there may also be a bearing coefficient), Q ₀ : book It is the horizontal load on 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 or not 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 due to the embedding of the top end of the main pile 1 into the pile cap 3 is input (step S34), and the bending strength 1 due to the fixing bar 4 is set. The bending strength 2 due to the embedding of the top end of the main pile 1 into the pile cap 3 is added (step S35), and it is determined whether or not the bending strength 1+2 of the sum is greater than or equal to the design bending moment (step S36). If there is, the design is finished (step S37).

If the bending strength 1+2 is less than the design bending moment in step S36, 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 bending strength 1+2 of the sum is equal to or greater than the design bending moment (step S39), and if it is greater than or equal to the design end (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 anchoring streak 4 corresponding to the pile diameter is input (step S31), and so on. Process.

8) As shown in FIGS. 11 and 15, when the bending strength of the anchor 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 5, increase the strength of the fixing streak, and increase the depth of embedding in the pile cap 3.
In addition, between the main pile 1 and the outer pipe 2 up 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 becomes possible to reliably transmit the loads carried by the main pile 1 and the outer pipe 2 to the pile cap 3, and also in the vertical/horizontal direction of the double pipe. The burden of power can be secured.

As described above, according to the double-pipe structure of the pile head of the embodiment, the top end of the main pile 1 head is projected more than the top end of the outer pipe 2, and the top end of the main pile 1 head and the outer pipe are formed. The top of No. 2 is embedded in the pile cap 3, and soil cement, water, muddy water, soil, and voids 8 are formed between the head of the main pile 1 under the pile cap 3 and the outer pipe 2. The force transmitted from the outer pipe 2 to the main pile 1 can be reduced.

(Modification)
It is needless to say that other than the above-described embodiment, specific detailed structures and methods can be appropriately changed.

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

Claims (3)

A double-pipe structure of a pile head that is installed so as to cover the head of a main pile that supports a vertical load and that has an outer pipe that bears a part of horizontal force during an earthquake,
The main pile is a concrete pile with an outer shell steel pipe, a centrifugal force prestressed reinforced concrete pile or a pretension system centrifugal force high strength prestressed concrete pile,
By projecting the top end of the main pile head from the top end of the outer pipe, and embedding the top end of the main pile head and the top end of the outer pipe in a pile cap,
Soil cement having a uniaxial compressive strength of 0.1 to 5.0 N/mm ² is formed between the pile head under the pile cap and the outer pipe , or water, soil, muddy water or voids are formed. Has been formed ,
The lower end of the fixing streak is welded to the outer peripheral surface of the top end of the outer tube, the fixing streak is embedded in the pile cap, and the depth of the outer tube embedded in the pile cap is welded to the outer tube by the fixing. A value obtained by adding a cover to the required welding length of the streak and 100 mm or more,
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 screw-fitted to the upper surface of the top end, and the fixing bar is embedded in the pile cap. A pile head double pipe structure , wherein the depth of embedding in the pile cap is 100 mm or more added to the depth of embedding of the outer pipe . A method of designing a double pipe structure for a pile head according to claim 1 ,
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 anchoring line welded to the outer pipe, and the outer pipe. In the relationship between the vertical compression resistance A and the interaction coefficient α, the following equation M1<T1=A×α (Equation [1]
A method of designing a double pipe structure for a pile head, characterized in that the specifications and the number of the anchoring bars welded to the outer pipe are determined and designed so as to satisfy the above condition. A method of designing a double pipe structure for a pile head according to claim 1 ,
The pile head bending moment M2 of 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 portion of the main pile, and the tensile compression resistance of the anchor bar welded or screw-fitted to the main pile. In the relationship of the vertical compression resistance B of the main pile, the side surface resistance C of the main pile, and the interaction coefficient β, the following formula M2<T2=B+C×β... Formula [2]
A method for designing a double pipe structure of a pile head, characterized in that the design and the number of the anchoring bars welded or screw-fitted to the main pile are determined so as to satisfy the above.

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