JPH0222169B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a double pile structure in which an outer pile as a horizontal load pile is provided outside the support pile.

BACKGROUND ART It has been known that when the head of a pile foundation that receives horizontal force is rigidly connected, an extremely larger bending moment is generated at the head than at the other parts.

In addition, there were cases where the head was damaged by the impact of driving during construction.

As a countermeasure, install another steel pipe in a concentric circle on the outside of the pile so that only the upper part wraps around it, keep an appropriate distance between them (for example, 5 to 10 cm), and fill this with concrete or mortar. A composite pile was created that was integrated by the force of attachment.

Examples of this include JP-A No. 53-67905, JP-A No. 48-Sho.
There are 6888.

Problems to be Solved by the Invention When piles are used in the foundations of bridge piers, etc., the edges of the pile group receive the maximum and minimum axial forces due to the horizontal swing of the superstructure due to seismic motion. When it is at its minimum, it is often a negative force, that is, a pull-out force. An extremely larger bending moment occurs at the head of the pile, especially where it connects to the footing, and it is necessary to calculate the stress level based on the combination of this bending moment and the axial force.

Next, the reference chart in Figure 1 will be explained. (This is based on Reference P, 56, Figure 2, 22, which will be mentioned later).If we look at the type C pile, which has the largest amount of reinforcing bars, the resistance bending moment is maximum when the axial force is 0.
Therefore, it is desirable to have a structure in which only bending moment acts on the outer pile and no vertical force acts on it.

Means for Solving the Problems This invention was carried out to solve the above problems, and the outer pile is a pile for resisting only the bending moment for horizontal loads, and the inner pile is a pile for vertical loads. As a solution to create a pile structure that can withstand the combined load of large axial force and relatively small bending moment, we have eliminated the synthetic action, or integration, of the outer and inner piles, and conversely made them non-synthetic. It was solved by doing.

Function In this way, the outer pile can be considered as a member for bending moment except for the slight axial force caused by the friction force between the surface of the pile and the earth and sand. It can be seen that it can withstand much larger bending moments (for example, 1.5 times). Think of the inner pile as a pile for vertical loads,
The bending moment at the cross-sectional change point acting on this pile is a small value far from the head of the pile, and this,
In combination with the axial force of , this resistance force also increases dramatically. Also, from the reference chart (Figure 1), it can be seen that the resistance bending moment decreases rapidly when the axial force is This value is small and no further axial force is generated, so the resistance bending moment does not decrease drastically.

Even if the design standards regarding pile cross-sectional calculations are amended, the overall trends shown in the reference chart (Figure 1) will remain the same for other diameters and types of piles.

Example Next, an example of this construction method will be explained using Figures 2, 3, and 4. First, make stake 1. Next, an outer pile 2 having an inner radius approximately 2 to 3 cm larger than the outer radius of the pile 1 is installed concentrically on the top of the pile 1, and the outer pile 2 is tapped or press-fitted.

The length of outer stake 2 is shorter than that of stake 1, for example, if stake 1 is
When it is 30m, it is 10m. Even if the ground is of uniform soil quality for 30m, if the top 10m is made thicker, it will have the same effect in terms of horizontal load as if the whole length is made of thicker diameter piles, and the soil quality and It depends on the diameter of the pile.
It is generally more than 95% effective. This is based on the first line of Reference P, 57 and P, 68, 2, 3, and 4 (2) below.

A reinforcing bar 3 for fixing is embedded in the outer pile 2 in advance. Next, the earth and sand caught between the pile 1 and the outer pile 2 are not removed, nor is filler such as mortar injected. The effect of this earth and sand is an important point of this construction method, and will be explained in detail in the next section on effects.

Next, concrete 5 is cast (using a suspended formwork when the top of the earth and sand in the pile 1 is low) to complete the pile foundation as shown in Figure 3.

Effects of the invention The non-synthetic double pile construction method according to the invention has the following effects.

1 Pile 1 and outer pile 2 can withstand two types of loads, vertical and horizontal, almost separately.

In other words, the adhesion force of the earth and sand between the two piles and the crushed stones act close to the adhesion force when pouring non-shrinkage mortar, but as long as the horizontal load is small,
This force, that is, adhesion force, etc., is relatively large compared to horizontal loads. Therefore, the swing of superstructures such as bridges is small under running loads and wind loads, but when subjected to large horizontal forces such as large earthquakes and repetitive loads such as vibrations. gradually approaches zero, and the combined effect of pile 1 and outer pile 2 disappears, so that pile 1 becomes a pile for vertical loads, and outer pile 2 becomes a pile for horizontal loads.

Note that although a bending moment also acts on the pile 1, this value is relatively small because it is far from the rigid connection point of the pile. Therefore, in the pile stress calculation, the load combination of bending moment and axial force is reduced, and the ultimate strength is improved.

2. Since there is no work to remove the earth and sand between the pile 1 and the outer pile 2, the construction cost is lower and the construction period is accordingly shorter.

3. When filling concrete between the pile 1 and the outer pile 2, if the space between them is made as thin as 2 to 3 cm, it is difficult to exhibit sufficient strength due to the nature of concrete, and for example, a gap of around 10 cm is required. If this is done, the cross section will change suddenly, which is unfavorable in terms of stress. This is particularly noticeable when the outer pile 2 is a concrete pile. This method is advantageous because it does not require the injection of filler.

4 If the pile 1 and the outer pile 2 are left uncomposed, the moment of inertia of the area, that is, the rigidity, will be smaller than that of the combined pile, and the bending moment of the pile head will be correspondingly smaller.

As described above, the present invention has a number of important effects, has a simple structure, is easy to construct, has extremely high economic effects, and has a very important impact not only on the civil engineering world but also on general society. This seems to be a great invention.

(References) Calculation method and calculation examples for pile structures, written by Yokoyama, published by Sankaido, November 1971.

[Brief explanation of drawings]

Figure 1 is an N-M chart, Figure 2 is an overall explanatory diagram,
Figure 3 is a vertical cross-sectional view, and Figure 4 is a cross-sectional view.
...Earth and sand, 5...Concrete.

Claims (1)

[Claims] 1 Outside the vertical load pile 1, a shorter outer pile 2 for horizontal load is provided concentrically, and the outer pile 2 is provided with reinforcing bars 3 that are fixed to the concrete 5, and the connection between the pile 1 and the outer pile 2 is A non-synthetic double pile construction method in which the piles are spaced approximately evenly apart by a certain distance, and earth and sand 4 are used here without integrating and synthesizing the two as in mortar or concrete.