JPS60115717A - Cast-in-place reinforced concrete pile head with double-tubular pile - Google Patents

Abstract

PURPOSE:To lessen bending stress caused by displacement of the ground by a method in which an internal steel tube to be buried in the lower part of a pile as the part for vertical resistance of the pile head and an external steel tube of the pile head consisting of a short steel tube as the part for horizontal resistance are set not to be in contact with an inner steel tube and a lower pile in the portions other than the head. CONSTITUTION:An inner steel tube 6 and head of an outer steel tube 7 are joined with connecting steel plates 8. In portions other than the head of the outer steel tube 7, the lower part of the inner steel tube 6 is buried in a reinforced concrete pile 9 so as not to be touched by the inner steel tube 6 and the reinforced concrete pile 9 of the lower pile. A soft filler 10 is paced into the aperture 11 between the inner steel tube 6 and the outer steel tube 7 to isolate the inner steel tube 6 from the outer steel tube 7. The bending moment of the pile head due to displacement of the ground can thus be lessened without the needs to obtain the same stiffness of the pile head as the expanded head reinforced concrete pile. Even in the case of expanded bottom pile, horizontal forces increased by expanding the bottom can be treated.

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a cast-in-place reinforced concrete pile with a double pipe pile head that can cope with ground displacement due to earthquakes and the like.

When designing a cast-in-place reinforced concrete pile, consider the situation in which a horizontal force P acts on the pile head, as shown in Figure 1, and consider how the pile will react to the bending moment generated by this, as shown in Figure 1. The cross section is designed.In terms of results, a large TC bending moment occurs near the pile cap of pile 1 (for example, in a cast-in-place pile with a pile diameter of 1250, approximately 10rn from the pile cap). Therefore, seismic design was carried out only in the vicinity of the pile cap, and virtually no seismic design was carried out in the middle and lower part of pile 1. In Figure 8'11, (a) shows the pile structure; (b) shows the bending moment distribution of the pile.

Therefore, when an earthquake actually occurs, it is beginning to be observed that bending strains of a magnitude of N are generated in places other than the vicinity of the head. For example, as shown in Figure 2, the -F section is a soft alluvial layer with 0 N, and the diluvial layer with a depth of about 21 m or less is 1,000 N.
A hill 1a with a diameter of 6 on the ground with an N value distribution of >50.
A steel pipe pile with a diameter of 6 (10 mπ and a wall thickness of 12 tnm) is used as the diagonal pile 1b in Fig. 3 (a).
), a total of 64 piles have been driven, and distortions in various parts of the piles have been observed when earthquakes occur on these foundations. The earthquake strength is as shown in Fig. 3 (1)), and the strain as a function of the depth of the sloped pile 1b is shown in Figure 3 (1)), and the strain as a function of the depth of the hill 1a is as shown in (C) for the furnace 1, where the maximum foundation acceleration is 2.4 ga. Become. In other words, the bending strain of the pile head of the mounting portion 1a is at most 15.
4μ, but bending strain of 8.9μ occurs even at the upper end of the support layer, which has not been taken into consideration in conventional seismic design.

Based on this observation, the strength of the earthquake is based on #4: Large acceleration 2
Estimating the strain in the case of 00 ga, e, the results are as shown in Table 1.

Table 1: In this case, the maximum strain of the support layer soil part of the installation part 1a is 1058μ
This causes the problem that the yield point of the pile is exceeded.

In this way, based on the observation results when an earthquake actually occurs, it has become clear that the currently used seismic design methods for piles are insufficient, so we conducted model vibration experiments to examine the distribution of strain that occurs in piles during earthquakes. A detailed investigation revealed the following: As an experimental model, as shown in Figure 4,
Considering the ground, piles, and superstructure, the ground model consists of a surface layer, a soft layer, and an intermediate layer consisting of a sand layer with an N value of about 60.
The structure consists of a soft layer such as clay and a supporting layer, and the actual ground, foundation, and structure satisfy the law of similarity.

Figure 5 shows the above experimental results, and (a) shows the bending strain distribution when using a cast-in-place pile model and applying vibration with an input acceleration of 10 gaps and a ground resonance frequency of 3.31-Iz. , (b) shows the bending strain distribution when a steel pipe pile model is used and vibration is applied at an input acceleration of 10 gal and a ground resonance frequency of 3.2 Hz.

In addition, in the figure, the numerical value of Young's modulus Em is the Young's modulus of each ground layer used as a ground model. As is clear from FIG. 5(a), Φ), the bending strain shows large values at the boundaries of the strata, such as the upper and lower ends of the intermediate layer and the upper end of the supporting layer.

As mentioned above, based on the observation results and model experiment results during actual earthquakes, we have determined the factors that generate the bending moment of the pile, and the horizontal force P at the pile head as shown in Figure 6 (a).
In addition to the strain caused by the earthquake, forced displacement of the pile due to ground displacement during an earthquake as shown in (b) is also greatly affected. Therefore, when designing the earthquake resistance of piles, as shown in (e), (
It is necessary to consider the bending moment that is a combination of the bending moment due to ground displacement shown in C) and the bending moment due to the horizontal force of the pile head shown in (d).

By the way, for conventional site PI reinforced concrete piles, for example, the concrete allowable stress of moving parts is always 60kc.
/d, the allowable bearing capacity of the tip ground is approximately 25 in luta.
kg/cd, so in order to fully utilize the concrete allowable stress of the shaft, the pile tip should be approximately doubled f-,i
The bottom of the pile has been widened and the vertical load supported by the pile increases approximately twice as much. The horizontal force that acts on the pile head during an earthquake is roughly expressed as (continuous vertical load x horizontal vibration), so as the constant vertical load increases, the horizontal force also increases, so the pile head can withstand this horizontal force, so K In this case, it is necessary to increase the amount of reinforcing bars at the pile head, and for this reason, as shown in Figure 7, it is impossible to arrange reinforcement unless the pile head has a diameter of L2. , except for cases where there is something to reduce the horizontal force from the superstructure, the top should be enlarged with a wave crest along with the bottom enlargement.

In addition, in Fig. 7, 1 is a pile, 2 is concrete, and 6 is
4 is an expanded bottom part, 4 is an expanded head part, and 5 is a reinforcing bar.

An example of the pile head bending moment distribution caused by local displacement during an earthquake for this expanded head is shown in Figure 8 (a3 K). The moment distribution is shown, 0) is the enlarged head diameter 1'750mrp,
This figure shows the bending moment distribution due to ground displacement of an expanded cast-in-place reinforced concrete pile with an expanded head length of 8 m and a shaft diameter of 1250y+i. The ground on which the piles were set has approximately 5.5 mm of fine sand with N==7 as shown in the figure Φ). , N=3 silt is about 5m
For about 18 m from the base, the depth is made up of sand and gravel with a diameter of N = 50.

In the example shown in Figure 8(a), the pile cap bending moment is approximately 130t-7+1 for the non-corrugated pile, whereas
When the head is expanded, it is approximately 430 tm. That is,
In the case of an expanded pile head, the bending moment of the pile head caused by ground displacement increases as the bending rigidity of the expanded head increases due to the wave crest.
It becomes several times that of non-wave crest piles. Therefore, for conventional cast-in-place reinforced concrete piles, considering the ground displacement at the time of: The stiffness of the pile head further increases, creating a vicious cycle.

An object of the present invention is to provide a cast-in-place reinforced concrete pile with a double pipe pile cap that solves the above-mentioned problems.

The double-negative pipe pile head according to the present invention, that is, the reinforced concrete,
J-1- Consists of an internal steel pipe or copper JV concrete (hereinafter referred to as internal steel pipe, etc.) to be implanted in the pile, and an external steel pipe whose length is shorter than the internal steel pipe, etc. as a horizontal resistance member, and the external copper pipe is located outside the YFJ section. By installing the pipe so that it does not come into contact with the internal steel pipe and the lower reinforced concrete pile, the generation of bending moment due to ground displacement can be suppressed, and the horizontal force from the upper bar structure and the force of the lead section can be supported. .

Disclaimer: The present invention will be discussed based on the examples.

FIG. 9 shows the vertical I! of the actual addition ff1f11 of the present invention! 'I side view, 6 is internal steel pipe, 7 is row steel pipe, 8 is inner and outer pipe joint steel +p
i and 9 are reinforced concrete piles.

The internal fA pipe 6 and the ν1 part of the external one-chain four-pipe 7 are internally joined by a pipe joining steel plate 8.The pipe length of the external copper pipe 7 is longer than that of the internal one-chain pipe 6, and the external steel (The lower part of the internal pipe 6 should be pushed into the concrete pile 9 of 4 or 1 so that the arm 7 does not come in contact with the internal pipe 6 or the reinforced concrete pile 9 of 1 pile except for the head part.) The gap 11 between the inner steel pipe 6 and the outer steel pipe 7 is filled with a void or a soft filler 1o of soft earth or polyurethane Φ) to meet and cut the inner steel pipe 6 and the outer copper pipe 7. ing.

The internal pot 16 and the reinforced concrete pile 9 act as a vertical resistance member, and the external copper pipe 7 acts as a horizontal resistance member.

When the internal steel f6 has a diameter of 60 (1 steel pipe with a wall thickness of 191 m, the external pipe has a wall thickness of 7 1200 m, the copper pipe has a length of 6 m, and the reinforced concrete pile 9 has a diameter of 125 o1 nm). The bending moment distribution caused by II# fluctuation is shown in Figure 1.The ground conditions are the same as those in Figure 8). In the figure, c.) shows the bending moment distribution of the external steel pipe 7, and ←) shows the bending moment distribution of the internal steel pipe 6 and the reinforced concrete pile 9. Further, a point (E) indicates the boundary between the internal steel pipe 6 and the reinforced concrete pile 9. As is clear from the figure, the pile head bending shaft of the external steel pipe 7 is approximately 40 tm, and has almost the same function as the wave crest/expanded bottom cast-in-place reinforced concrete pile shown in (0) of Figure 8 (a). Despite this, the bending moment generated by the displacement of the plate is extremely small. In other words, in the case of the pile targeted in Figure 10, the bending moment generated at the pile head due to ground displacement during an earthquake is approximately 12
t''-m', about 4 [1t, , , in the external fA tube, i
811 (a) ノ(t-1T) Considering the value of approximately 430 t for the cast-in-place reinforced concrete pile with expanded bottom and wave crest, the economic design of the pile itself and the economic yy total of the girder are rA ) is t with 13+1 white.

In addition,? In Figure 9, t'
Then, join the internal steel IP6 and the external copper pipe 7 and insert them into the footing.
Also, the words ``fiv ri'', ``jf2 conc 11'', and ``go'' are also the same.

Also, Fig. 11 shows the 1. ′ is shown.

In the figure, 9V and the same ministry name indicate the same book 1" composition.

Reference numeral 12 designates a bidding button plate 1e fitted to the lower part of the facing pot 1 pipe 6, which is attached to the reinforcing bar 5 of the reinforced concrete pile 9, making it easier to put together the pile head.

As is clear from the explanation of the soil, if the pile head is almost reinforced concrete pile, it is possible to suppress the f1 head bending moment caused by ground displacement to a small value. Even if the hole is enlarged, the wave bottom will be able to handle the horizontal force that is thicker. ``I can do it, I can do it, I'm going to do it, I'm going to do it.'' is a dog.

4. Simple appearance of the drawing, #J? , 1 [! 1 (al is a model of a cast-in-place pile based on the conventional seismic design method, ■) is the bending moment, the figure on the right,
Copper 2ji 1 is the ground condition diagram when the strain of the pile was observed when the ground earthquake occurred, νj 3 IPl (al is the pile structure diagram 1 when the strain of the pile was measured when the shaft earthquake occurred) )) is the bending strain distribution diagram of the hill section at that time, (C) is the bending strain distribution diagram of the inclined pile, Figure 4 is the model diagram of the model vibration experiment, Figure 5 (a), (
b) is the bending strain distribution diagram of the pile in the model vibration experiment, No. 6
[21 (a) is a frame diagram of a cast-in-place pile, (l]) is a ground displacement diagram, (C) is a bending moment distribution diagram due to ground displacement, and (d) is a bending moment distribution diagram due to horizontal force on the pile head. ,(
e) is a bending moment distribution diagram that combines the two, Figure 7 is a configuration diagram of a cast-in-place concrete pile with a wave crest, Figure 8 (a) is a bending moment distribution diagram due to ground displacement, (
1)) shows the construction of the ground coffin, Fig. 9 shows the structure of the embodiment of the present invention, Fig. 10 shows the bending moment distribution diagram based on the ground position, and Fig. 11 shows the structure of the embodiment of the invention. It is a diagram.

1: Pile, 2: Concrete, 3 = Expanded bottom part, 4: Expanded head part,
5: Reinforcing bars, 6: Internal steel pipes, 7: External steel pipes, 8: Jointed inner and outer pipes, 9: Cast-in-place reinforced concrete agent, patent attorney
Sanro Omura 1st Ward (a) (b) 21 弗3 Figure 4 Figure 6 Figure (b) (a) (c) (d) (e) Figure 5 (0) Figure 5 ( b) Ichinkyokui”L (/-t) Go - 0 sun to 9 0 4 υ to (E) □ Masiya/(E) Figure 9 78 Figure 11 Figure 8

Claims (1)

[Claims] Internal steel pipe or steel pipe conc IJ-) where the pile head is embedded into the lower reinforced concrete pile as a vertical resistance member
(g) (abbreviated as downward section steel pipe, etc.) and an external steel pipe whose pipe length is shorter than the internal #I pipe etc. as a horizontal folding member. A cast-in-place reinforced concrete pile with a double pipe pile cap, which is characterized by being installed in a toe that does not come into contact with the steel pipe or the lower reinforced concrete pile.