JPS6052258B2 - Connection method between piles and footings - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) This invention relates to a footing foundation construction method that is implemented as a pile foundation that is effective against earthquake forces, and more specifically, to a structure that is not subject to pulling force during an earthquake. It relates to the method of connection between the footing (or foundation) and the piles that support it.

(Prior art) Conventionally, the method of connecting piles and footings is approximately as shown in Figure 1~
This was done as shown in Figure 3.

First, in Fig. 1, the bed head 1a of a ready-made concrete pile 1 is made to protrude to a certain height above the foundation bottom surface GL, and a part of the bed head 1a is cut off, so that the reinforcing bars (PC steel material) 3 of the pile 1 itself, 3.Expose the required length and stand it straight. On the other hand, reinforcing bars 5, 5 for connection are fixed to the filling concrete 4 cast into the hollow part of the ready-made concrete pile 1, and are made to stand upright to a required length. Then, after pouring concrete 6 on the foundation bottom surface G-L, pouring concrete for the footing 2, embedding the head 1a in the footing 2, fixing the reinforcing bars 3 and 5 in the footing 2, and fixing it. A completely integral connection between the footing 2 and the ready-made concrete pile 1 is made.
FIG. 2 shows the connection structure between the cast-in-place pile 7 and the footing 2, and FIG. 3 shows the connection structure between the steel pipe pile 9 and the footing 2.

For the former, the reinforcing bars 8, 8 of the cast-in-place pile 7 itself are made to stand straight upright, and for the latter, reinforcing bars 10, 10 of the required length are welded to the pile cap of the steel pipe pile 9 and are made to stand upright, respectively, and are completely integrated with the footing 2. connection is being made. By the way, when the pile cap and footing are completely connected as in the conventional connection method described above, the boundary condition of the pile cap when subjected to horizontal force (earthquake force) must be designed in a fixed state. become.

That is, as shown in the bending moment distribution diagram in Figure 4,
The maximum bending moment Mmaxl will act on the pile cap. Therefore, in order to cope with this maximum bending moment Mmaxl, it is necessary to increase the number of piles or use piles with even greater bending rigidity, resulting in deterioration of economic efficiency. (Objective of the Invention) Therefore, the first object of the present invention is to connect the pile cap and the footing so that the boundary condition when receiving horizontal force is a pin state, thereby reducing the bending moment at the pile cap. A method for connecting piles and footings that has been improved in order to reduce it as much as possible and to make the maximum bending moment acting on the pile itself much smaller than in the case of a boundary condition where the pile head is fixed (constraint). Our goal is to provide the following.

The next object of this invention is to sufficiently reinforce the pile cap in advance when connecting the pile cap and the footing, and to eliminate hair cracks that occur when cutting off the pile cap of a ready-made concrete pile. We provide a method for connecting piles and footings that solves this problem.

(Structure of the first invention) In order to achieve the above object, the method for connecting a pile and a footing according to the present invention provides (a) a method for connecting a pile and a footing that is slightly larger than the diameter of the pile cap protruding above the bottom of the foundation. A step of fitting a reinforcing pipe such as a steel pipe with a large diameter and a certain depth into a concentric arrangement and filling a gap between the outer diameter of the pile and the reinforcing pipe with a filler to integrate the pipe, and (b) the pile head. A step of installing a material made of wood or styrofoam, etc., which has low rigidity and has a substantially conical shape that allows the pile head to form a pin state, on the outer diameter surface of the reinforcing pipe body. and (c) the process of placing concrete and forming footings.

(Structure of the second invention) In order to achieve the above object, the method for connecting a pile and a footing according to the present invention is as follows.
Between the step and the step (c), a step of forming the upper end surface of the pile cap into a substantially horizontal flat surface and applying a release material to this end surface is added.

(Example) Further, details will be explained based on the example shown in FIG. 5 and below.

In the case of the connection method between piles and footings shown in Figure 5,
First, ready-made piles 16 (however, cast-in-place piles or steel pipe piles are also acceptable).

), the upper end of the pile cap 16a protruding above the foundation bottom surface G is partially cut off (completely cut off including the PC steel material), and the height of the remaining pile cap 16a protruding above the foundation bottom surface G is reduced by several d. It is arranged in the range of several tens of centimeters. The pile head 16a
In addition, the inner diameter is approximately 50-WO larger than the diameter of the pile cap 16a, and the length is sufficient to cover the decrease in strength due to hair cracks caused by the cut-off, that is, 0.5 to 2 of the pile diameter. A copper tube 17 equivalent to .0 times is fitted in a concentric arrangement as a reinforcing tube body.

Then, in the gap between the outer diameter surface of the pile cap 16a and the steel pipe pile 17,
Filler 18 such as concrete or mortar or molten sulfur, which can be expected to have the same strength as the pile body, is densely filled, and the upper end surface of the pile cap 16a is also filled so that it becomes a flat surface. It is solidified and integrated.

Furthermore, unreinforced filling concrete 19 is densely filled within the hollow portion of the pile cap 16a within the length of the steel pipe 17, thereby eliminating the adverse effects caused by the existence of the hollow portion. Continuing on, the entire circumference of the outer diameter surface of the steel pipe pile 17 at the pile cap 16a is made of wood, styrofoam, or the like and has low rigidity (however, it has enough rigidity to withstand the concrete placement pressure of the footing).

) The insert 20 is installed. This inclusion 20 is the pile cap 16a
In the illustrated example, the top surface is the top surface of the pile, and the bottom diameter is 5 C! larger than the outer diameter of the steel pipe 17. It is formed in an annular shape so as to form a conical pedestal with a size of about n~10C71. Furthermore, the footing 12 is formed by applying a release material 21 to the entire flat upper end surface of the pile cap 16a, and then pouring concrete for the footing. Therefore, according to the connection method of this embodiment, firstly, the decrease in strength of the pile cap 16a due to the cut-off is repaired and maintained by the steel pipe 17 and the filler material 18. Second, the pile cap 16a and the footing 1
2 is completely separated by the peeling material 21, and the restraining conditions from the circumferential sides are released by the inserts 20, so the boundary conditions of the pile cap when subjected to horizontal force are completely Achieve a pin state. (Effects) As explained in detail above in conjunction with the examples,
According to the method for connecting piles and footings according to this invention,
The following effects are achieved.

When a horizontal force (earthquake force) is applied to the connection between a single pile and a footing, the boundary condition can be a pin state.

2, the distribution of the bending moment acting on the pile is
As shown in the figure, the maximum bending moment will not act on the pile cap.

In addition, the maximum bending moment Mmaxl is the maximum bending moment Mma under the previous condition of fixing the pile head.
xl (Fig. 4), approximately Mmmax2=1/
The relationship is 1.5Mmax1.

That is, the maximum bending stress generated in the pile can be reduced to about 213 when the pile head is fixed. 3. Therefore, it is possible to reduce the number of piles or use piles with a certain degree of low bending rigidity, thereby enabling economically advantageous design and construction.

4. Strength reduction due to hair cracks, etc. that occur due to cutting off the pile head can be completely eliminated by the reinforcing pipe 17 and filler 18 (and in the case of ready-made piles, including filling concrete 19). By repairing and reinforcing the pile, it is possible to create a highly reliable connection between the pile and the footing without any problems in terms of strength.

[Brief explanation of drawings]

Figures 1 to 3 are cross-sectional views showing an example of the conventional method for connecting piles and footings, Figure 4 is a bending moment distribution diagram acting on a pile with a fixed pile head, and Figure 5 is a diagram showing the bending moment distribution according to the present invention. Cross-sectional view showing an example of the method for connecting the pile and footing, No. 6
The figure is a bending moment distribution diagram that acts on a pile with the pile head in a pinned state.

Claims (1)

[Claims] 1 (a) A reinforcing tube 17 having a diameter slightly larger than the diameter of the pile cap 16a is fitted concentrically to the pile cap 16a protruding onto the foundation bottom surfaces G and L, and the outer diameter surface of the pile is and (b) a step of filling and integrating a filler material 18 into the gap between the reinforcing pipe body 17 and the pile cap 16a. a step of installing a substantially conical shaped interposition 20 with a diameter sufficient to form a pin; (c) a step of pouring concrete to form the footing 12;
A method of connecting piles and footings. 2 (a) A reinforcing tube 17 having a diameter slightly larger than the diameter of the pile cap 16a is placed concentrically on the pile cap 16a protruding above the foundation bottom surfaces G and L, and the reinforcing tube 17 is connected to the outer diameter surface of the pile. A step of filling the gap with the filler 18 and integrating it, and (b) the pile cap 1
6a, a step of installing a substantially conical shaped interposer 20 having low rigidity and a diameter sufficient to make the pile cap into a pin state on the outer diameter surface of the reinforcing pipe body 17, and (c) said pile cap 16a.
A connection between a pile and a footing, which includes the steps of forming the upper end surface into a substantially horizontal flat surface and applying a release material 21 to this end surface, and (d) pouring concrete to form the footing 12. Construction method.