JPS6046215B2 - How to connect concrete pile cap and footing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention proposes a method for connecting the pile cap and footing of a concrete pile, which is effective in preventing the pile head from being destroyed by horizontal force during an earthquake.

There are two ways to connect the pile cap and footing: by rigid connection and by pins.

When the pile cap and the footing are rigidly connected, the horizontal force generated due to the relative movement between the ground and above-ground structures during an earthquake causes the pile cap to collapse as shown in Figure 1A. However, in the case of a pin, no bending moment acts on the head of the pile, as shown in Figure 1.

Therefore, in order to bring the bending moment of the pile head due to horizontal force during an earthquake as close to zero as possible, it is desirable to bring the pile head condition close to a pin state, but concrete piles such as RC piles, PC piles, and cast-in-place piles However, a method for connecting the pile cap and footing in which the pile cap condition becomes a clear pin from the time the footing is completed has not yet been established.

For example, in the case of a foundation made of PC piles, even if the pile cap is considered to be a pin in the design, the connection between the pile cap and the footing is constructed by removing the pile cap concrete and burying it in the concrete at equal intervals in the circumferential direction. This is usually done by exposing a large number of prestressing steel members and using them as anchoring bars for the footing.

In this method, the connection between the pile cap and the footing is rather rigid, and at least when the construction of the footing is completed, it is not in a clear pin state.

In other words, in the event of an earthquake, it is thought that the pile head will first resist the horizontal force in a fixed state, and the balance will gradually collapse, eventually becoming a pin state, but by the time the footing reaches this pin state, the footing has already The pile heads at the bottom have been destroyed, and as a result, the specified bearing capacity cannot be obtained, but it is fully assumed that this will be a factor in a type of uneven settlement, although there may be differences in degree. In addition, methods to prevent pile heads from being destroyed by horizontal forces during earthquakes include increasing the number of piles, increasing the pile diameter, or integrating pile heads with cast-in-place concrete. Various methods have been proposed in the past, such as locally reinforcing the pile head by pouring concrete around the pile.
This method is based on the idea of increasing the horizontal strength of the pile head, where the largest bending moment acts, and it goes without saying that it is disadvantageous in terms of construction costs.

Therefore, the present invention can connect the pile cap and footing so that the pile cap condition of the concrete pile is in a clear pin state from the time the construction of the footing is completed, and while ensuring a predetermined bearing capacity, the horizontal This method provides a method for connecting the pile cap and footing that can effectively prevent the destruction of the pile head due to force, especially local crushing of the pile head surface due to the load of above-ground structures, and is effective in preventing concrete pile piles. The overhead surface is formed into a spherical shape,
Then, with an anchoring bar for the footing erected only at the apex of this spherical part, concrete for the footing is cast at a position above the lower edge of the spherical part, and the pile cap and footing are connected to the anchoring bar. It is characterized by being connected only through muscle.

In addition, in the present invention, the footing is constructed at a position above the lower edge of the spherical portion so that the footing and the pile cap can move relative to each other without causing damage to the footing bottom or the pile cap as a structure. In this sense, the phrase "located above the lower edge of the spherical portion" should be interpreted substantially.

Embodiments of the present invention will be described below with reference to the drawings.

First, as shown in Figure 2A, after inserting a PC pile 1, which is an example of a concrete pile, into the ground to a predetermined depth,
Fixing to the top plate 2 of the pile 1 a metal fitting 4 whose upper surface is formed into a spherical shape and has one fixing bar 3 erected at the top,
The spherical portion S is treated to reduce frictional force by applying asphalt, coating with Teflon (trade name), or covering it with glass fiber cloth impregnated with Teflon.

I'll keep it. In FIG. 2, a indicates a layer for reducing frictional force. This frictional force reduction process may be performed after the hardware 4 is fixed to the top plate 2, or may be performed prior to the fixation. As shown in FIGS. 3 and 4, the hardware 4 has a hole 5 formed in the center and holes 6 formed at a predetermined pitch around the hole 5.
It has... Then, the fixing bar 3 made of a threaded reinforcing bar or a threaded reinforcing bar is inserted into the hole 5 in the center part, and is attached so as to be prevented from coming out with a pair of nuts 7... and washers 8, and then the hole 6...・Bolt 9 inserted into...
・The screw hole formed in the top plate 2 (it is desirable to use the hole for fixing one end of the PC steel material to the top plate 2 or the hole for applying tensile force to the Pq steel material in the manufacturing process of the PC pile as is) ) and installed as shown in Figure 2 A. Note that the hole 5 in the center is
As shown in the figure, the shape has an inverted conical inner circumferential surface, and the structure is such that the fixing strip 3 can swing within the gap between the inner surface of the hole 5 and the fixing strip 3 and 1. Although this is very preferable in that it can suppress bending of the anchoring strips 3, it is not an essential configuration. Next, as shown in FIG. They are connected via . According to the above configuration, the pile cap and the footing 10 are connected by only one anchoring bar 3, and the pile cap (i.e., the spherical portion S)
Since the frictional force between the footing 10 and the footing 10 is reduced by the layer a, a pin connection is achieved, and relative movement between the footing 10 and the pile cap due to horizontal force during an earthquake is possible.

In addition, since the pile top surface is spherical, when the above-mentioned relative movement occurs, the load of the ground structure transmitted via the footing 10 is distributed over the entire area of the spherical portion S and is evenly supported. Therefore, local crushing can be prevented. FIG. 5 shows another embodiment, in which a flat metal fitting 4'' with fixing bars 3 erected thereon is fixed to the top plate 2 of the PC pile 1, and then mortar swirls 11 are formed on the metal fitting 4''. It is particularly distinctive in that the top surface of the pile is formed into a spherical shape.

FIG. 6 shows another embodiment, which is characterized in that the upper surface of the concrete pile itself is formed into a spherical shape.

Note that, as in each of the above embodiments, it is desirable to perform a frictional force reduction treatment on the spherical portion to ensure the edge cutting with the footing bottom, but this treatment is not always necessary. The present invention has the above-mentioned configuration, and the pile cap and the footing are connected by only one anchoring bar, and the footing bottom is located above the lower edge of the spherical portion of the pile head surface, so the footing A clear pin connection is established from the time construction is completed, which is effective in preventing destruction of the pile head due to horizontal force during an earthquake.Furthermore, since the pile head surface is formed into a spherical shape, the pile head and ground structure are easily connected during an earthquake. When relative movement occurs, the load of the earth structure transmitted through the footing is distributed over the entire area of the pile head and supported evenly, which has the effect of preventing local collapse.

[Brief explanation of the drawing]

Figure 1A is a bending moment diagram; Figure 2A is a vertical sectional view showing an embodiment of the present invention; Figures 3 and 4 are side views of the hardware; Figures 5 and 6 are FIG. 7 is a vertical cross-sectional view of main parts showing different embodiments. 1... Concrete pile (PC pile), 10...
...Footing, S...Spherical part.

Claims (1)

[Claims] 1 The pile head surface of a concrete pile is formed into a spherical shape, and the anchorage for the footing is erected only at the apex of this spherical portion, and the footing is placed above the lower edge of the spherical portion. A method for connecting a pile cap and a footing of a concrete pile, comprising placing concrete and connecting the pile cap and the footing only through the anchor reinforcement.