JP2002201636A - High flexural toughness and high strength pile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high flexural toughness and high strength pile improved in view of the fact that covering concrete of 20 mm or more in thickness required for rust prevention exfoliates in the process of resulting in bending rupture, to cause plastic deformation with the decrease of load resisting capacity caused by lacking in cross section even if flexural toughness is heightened by arranging a horizontal restriction reinforcement at the PHC pile. SOLUTION: A ring body formed of a bundle of carbon fiber reinforced plastic linear material serving as a shear reinforcement is disposed on the outer surface of the pile, and prestressed concrete steel of high uniform elongation is used as a main reinforcement. High prestress of 8 MPa or more is applied to the prestressed concrete steel. A filler such as concrete or mortar is filled in a hollow part of the pile.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a high bending toughness and high strength pile.

[0002]

2. Description of the Related Art JIS A5337 "Pre-tension type centrifugal high strength prestressed concrete pile (PHC)
"Pile)" is a high-strength pile in which a number of PC steels parallel to the axis are embedded in concrete, and the PC steels are tensioned to give prestress to the concrete. This pile has a concrete compressive strength of 80 MPa or more and an effective prestress force of 4 to 10 MPa.

[0003] In the Hyogoken-Nanbu Earthquake, the superstructure of the structure was severely damaged. However, as the damage investigation progressed, a great deal of serious damage was also found on the foundation piles. You are in a required situation. The main points that need improvement are as follows.

[0004] Not only is the pile body damaged near the pile head, but also significant damage such as breakage and cracks is found near the pile tip support and the middle layer. This suggests that it is necessary to use piles with excellent seismic resistance not only for the upper pile but also for the middle and lower piles.

[0005] Damage to the pile body near the pile tip support and the middle layer is caused not only by the horizontal force at the pile head earthquake but also by the pile body being pushed by the ground due to the vibration (shear deformation) of the ground itself and receiving the force. Is recognized.

[0006] The seismic design method of currently used pile foundations specifies an allowable stress design (elastic design) for an earthquake horizontal force having a base shear coefficient of 0.2. In the superstructure, the ultimate strength design is performed for the base shear coefficient of 0.3 or more, but the ultimate limit state design method (design that guarantees strength and toughness) equivalent to this should be promptly shifted to. further,
In order to examine the seismic safety of piles near the pile tip and near the middle layer, it is important to shift to a design method that takes into account pile body stress based on ground deformation due to earthquakes in addition to pile head horizontal force.

[0007] In view of the mode of fracture of PHC pile concrete, there is a question about the mechanical soundness of the autoclave-cured concrete itself used for the pile. The reason is that many microcracks are generated by autoclave curing.

[0008] No shear reinforcing bars are arranged on the JISPHC pile. Although there are assembled bars that assemble the main bars, they are ineffective for shear reinforcement and cannot be called shear reinforcement. Arrangement of shear reinforcement is essential.

As described above, the design of the foundation pile for future seismic force needs to be shifted to a design based on the ultimate limit, and it is necessary to use a toughness type design method combining ultimate strength design and toughness design. .

As a technique for increasing the bending strain of concrete, there is a lateral constraint of the concrete. FIG.
0 and FIG. 11 are explanatory diagrams for explaining this. FIG. 10 is a schematic view showing the mechanism of compression failure of ordinary unconstrained concrete. When a compressive force 41 is applied to the concrete 40, cracks occur as shown in FIG. 10 immediately before compressive fracture, and a cone-shaped concrete mass 42 formed by the oblique cracks near the upper and lower end faces pushes the concrete 43 in the center part right and left. Spread and split, leading to destruction. Therefore, as shown in FIG. 11, when the concrete body is restrained from the side by attaching a reinforcing bar (lateral restraint bar) 44 to the outer peripheral surface of the concrete 40, a compressive force 41 is applied and cracks similar to those in FIG. However, unlike the case of unconstrained concrete, the reinforcing bar hedge 44 prevents the concrete from bulging laterally by the upper and lower cone-shaped concrete blocks 46 by the tightening force 45, and the concrete 40 reduces the compressive stress. While continuing, it is further deformed by compression,
The compression limit strain increases. However, when the lateral restraint muscle 44 yields, the tightening force 45 decreases, so that the lateral restraint effect is reduced by half. According to the study of the present inventor, in order to prevent such yielding of the lateral restraining muscle, a high strength lateral restraining muscle having a yield point strength of 800 MPa must be used. It is usually difficult to prevent the yielding of the lateral restraint bars with ordinary reinforcing bars having a yield point strength of about 400 MPa.

There is a high toughness and high strength PHC pile having improved toughness of a conventional PHC pile. A high-strength lateral restraint having a yield point strength of 800 MPa or more is used for such a high-toughness high-strength PHC pile. In order to dispose the lateral restraint bars on the pile, cover concrete having a thickness of 20 mm or more must be provided for rust prevention. This cover concrete is subjected to bending or bending and compression at the same time and peels off in a process leading to bending failure. Accordingly, a cross-sectional defect occurs, and plastic deformation occurs while reducing the load carrying capacity. In other words, the concrete inside the lateral restraint had to be seismically designed as the final effective section.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to develop and provide a high-bending-toughness high-strength pile that does not require cover concrete.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and is a high bending toughness high strength pile characterized by the following technical means.

That is, the present invention provides a lateral restraining bar (CFRP lateral restraining bar or anticorrosion process) composed of a carbon fiber reinforced plastic (hereinafter referred to as CFRP) wire bundle or a hard steel wire bundle subjected to anticorrosion process as a shear reinforcing bar. A high-bending toughness high-strength pile characterized in that a hardened steel wire rod restraining bar) is disposed on the outer surface of the pile. The CFRP wire bundle has, for example, a diameter of 7
It is a collection of 40 to 80 wire rods in which 12,000 μm carbon fibers are combined with plastic.

CFRP lateral restraint bars have excellent corrosion resistance and basically do not require cover concrete, so that cross-sectional defects due to peeling of cover concrete can be avoided.
The whole section of pile concrete can be used effectively until the end.

The above-mentioned high bending toughness high strength pile is preferable because when the hollow portion is filled with a filler having a uniaxial compressive strength of 10 MPa or more, the strength becomes higher and the effect of improving the toughness of the lateral restraint muscle can be further enhanced. . Uniaxial compressive strength is 10MP
Examples of the filler a or more include concrete, mortar, a mixture of earth and sand and a solidifying agent, and a material in which bentonite is mixed. 10 MPa or more
If it is less than MPa, the effect of filling is poor. Further, in the present invention, a highly uniform stretched PC steel material is used for the main bar, and a high prestress of 8 MPa or more is introduced into the PC steel material, whereby a superior pile having higher bending toughness and higher strength can be obtained. It is. The reason why the pressure is set to 8 MPa or more is that applying at least 8 MPa requires high uniform elongation P
This is because it is necessary for the effect of C steel to be exhibited.
More preferably, the pressure is 20 MPa or more.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the increase in compressive limit strain of a concrete member due to lateral restraint will be described with reference to the drawings. FIG. 12 shows an example of the improvement of the compressive toughness of concrete by the lateral constraint described with reference to FIGS.
The specimen is a 200 × 200 × 600 mm concrete column. It shows the relationship between the degree of compressive stress (MPa) and the compressive strain (%) when compressive force is applied to the specimen, and the relationship between the constraint stress (MPa) and the compressive strain (%).

(A) The unconstrained concrete column indicated by the dashed line in the figure yields at a compressive stress of about 27 MPa and a compressive strain of about 0.15%, leading to destruction.

(B) φ9.2 mm square lateral restraint bars, pitch 50 mm, yield point σ _y = 1275 MPa, volume ratio ρ _w =
As for the 2.7% laterally constrained concrete column, as the compressive strain of the concrete increases, the constraining stress generated in the concrete increases as the compressive strain curve and the constraining stress curve shown by solid lines increase, the yield stress increases, and the compressive strain decreases. Increase.

(C) φ9 mm square lateral restraint, pitch 50
mm, yield point σ _y = 355 MPa, volume ratio ρ _w = 2.5%
The compressive stress curve and restraint stress curve of the laterally constrained concrete column are shown by broken lines. In this case, the yield stress and the compressive strain are increased although the constraint stress is smaller than that of the above (b).

In the above examples (b) and (c), the compressive limit strain of concrete laterally constrained by high-strength bars has reached 3.1%.

Next, a description will be given of an experimental example of a basic study on improvement in toughness of a centrifugally compacted PHC pile using CFRP lateral restraint bars.

[Experimental example 1] As a basic study on improvement of toughness of centrifugally compacted PHC pile by lateral restraint of CFRP, C
In order to confirm the lateral restraint effect of FRP lateral restraint muscle, CFR
Diameter φ200mm x height 300mmH with P lateral restraint
A compression test was performed on a 40 mm thick centrifugally compacted concrete body. At the same time as confirming the effect of improving the toughness of CFRP lateral restraint bars with a cover concrete thickness of 0 mm,
An experiment was also conducted to confirm the effect of filling the hollow portion of the specimen on the toughness improving effect.

The outline of the experiment is as follows.

FIG. 4 shows the shape of a laterally restrained centrifugally compacted specimen 20. FIG.
(A) is a cross-sectional view of the test piece 20, and (b) is a longitudinal cross-sectional view. The specimen 20 has an outer diameter of 200 mm and an inner diameter of 120 m
m, a wall thickness of 40 mm, a height of 300 mm, and a hollow cylindrical specimen made of centrifugally compacted concrete 22 for PHC piles.
Cover the RP lateral restraint 21 with a thickness of 1 mm and a pitch of 50 mm
This is a laterally constrained centrifugal specimen placed in the above. A CFRP laterally constrained centrifugal specimen in which the hollow portion 23 was left hollow and a horizontally constrained centrifugal specimen in which concrete or mortar were filled were prepared, and experiments were performed in three series. In each series, an unrestrained centrifugal specimen was simultaneously manufactured as a standard specimen, and a compression test was performed.

Experiments Experiments were conducted in three series shown in Table 1. In Experiment 1, the stability of the compressive toughness improvement of concrete was confirmed when the CFRP lateral restraint was arranged without cover concrete. In Experiment 2, the presence or absence of the effect of improving the compressive toughness of CFRP lateral restraint muscle of the filled concrete was confirmed. Experiment 3 confirmed the effect of the strength of the filled concrete on the effect of improving the compressive toughness.

Properties of Materials Used The CFRP lateral restraint used was 194 mm in outer diameter and 18 in inner diameter.
A carbon fiber input amount was set to 26 in a ring-shaped CFRP lateral restraining bar having a size of 6 mm and a cross section of 5 mm × 4 mm. This C
The FRP lateral restraint is a CFRP lateral restraint designed to have the same compression elastic rigidity as the 800 MPa class φ4 mm steel lateral restraint.

Table 2 shows the composition of the concrete and the filling concrete of the test piece 20. Φ200 at the time of the experiment
Table 3 and FIG. 5 show the physical properties of the concrete of the x300 mmH unconstrained centrifugally compacted specimen. Table 4 and FIG. 6 show the physical properties of the filled concrete.

The results of Experiment 1 are shown in Table 5 and FIG.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

The following can be seen from Table 5 and FIG.

(1) CFRP Laterally Restrained Specimen No. 1-2
The compressive load (compressive stress) strain curve up to the maximum load reaching point (indicated by 〇 in FIG. 7) of the specimen No. 1-1
Is equivalent to

(2) CFRP Laterally Restrained Specimen No. 1-2
It was shown that, even after reaching the maximum load, the plastic deformation occurred while maintaining the load, and the CFRP lateral restraint stably improved the toughness.

(3) However, since it is a hollow specimen,
When the compressive strain reaches 0.535% (indicated by a mark in FIG. 7), oblique cracks generated in the concrete body (compression fracture slip lines generated in unconstrained concrete) penetrate through the thick part and compress the concrete body. Caused destruction. The CFRP lateral restraint muscle was extremely healthy, with a few broken wires observed by the shock at the time of breaking.

The results of Experiment 2 are shown in Table 6 and FIG.
The results obtained are as follows.

(1) CFRP Lateral Restrained Centrifugal Specimen No. 2-2 is the specimen No. of Experiment 1. 1-2 (FIG. 7), exhibiting a behavior similar to that of FIG. 7, with oblique cracks (slip lines) occurring at a compression strain of 0.588%, which penetrated through the thick part of the main body and led to fracture.

(2) On the other hand, CFRP laterally constrained centrifugal specimen No. 2-
In 3, when the strain at the maximum load of the unconstrained specimen reached, a temporary and slight decrease in the load-carrying capacity due to the peeling of the 3-mm-thick cover concrete occurred. Significant plastic deformation was measured. That is, it was confirmed that the lateral restraint effect of the CFRP lateral restraint bars was significantly improved by placing the middle-filled concrete. In this experiment, the compression strain was 1.206.
%, Did not destroy, and the experiment was stopped.

[0042]

[Table 6]

The results of Experiment 3 are shown in Table 7 and FIG. The results obtained are as follows.

(1) The CFRP lateral restraint used in Experiment 3 was obtained by reusing the CFRP lateral restraint used in Experiments 1 and 2, and a part of the CFRP strand was broken or damaged. was there. Therefore, the laterally restrained specimen No. 3-2 and No. 3 In 3-3, a compressive load-strain relationship is obtained in which the element wire of the CFRP lateral restraint bar is partially broken at an early stage after reaching the maximum load, and plastic deformation occurs while reducing the proof stress. Specimen No. showing relatively stable plastic deformation behavior Also in 3-4, when the compressive strain reached 0.773%, breakage of the lateral restraint strand occurred, and the lateral restraint effect rapidly decreased, leading to breakage.

(2) However, it is possible to significantly increase the effect of improving the toughness of the CFRP lateral restraint muscle by filling in the middle, particularly, a test piece applied with a low strength filling mortar having a low uniaxial compressive strength of 10 MPa. No. It is noteworthy that even in 3-2, a large increase in the toughness improving effect can be expected.

(3) According to the investigation of the fracture location of the CFRP lateral restraint bar after the test is completed, the wire break occurs near the intersection with the assembled reinforcing bar for the lateral restraint dragon knitting. At this intersection, it is determined that the assembling line presses the CFRP strand locally. In fact, the CFRP strand has a remarkably weak characteristic to the local pressure in the direction perpendicular to the axis of the strand, and it is necessary to pay attention to this point in practical use of the CFRP lateral restraint.

[0047]

[Table 7]

[Explanation of Improvement of Flexural Toughness] Next, improvement of the flexural toughness of the member will be described. FIG. 13 illustrates a basic technique for improving bending toughness, taking a rectangular cross section PC member 30 as an example. FIG. 13A is a cross-sectional view of the rectangular concrete member 30, in which a PC steel material 32 is disposed on the lower edge side in the cross section of the concrete 31. FIG. 13B is an explanatory diagram showing stress and strain in this cross section. In a normal member, a strain represented by a straight line BB ′ occurs in each part of the concrete section of the member due to the action of the bending moment M. Concrete section compressive edge strain ε expressed by AB
_{When c} reaches the limit bending strain ε _cu1 of concrete, the compression side concrete is crushed, and the member is bent.

In order to improve the toughness of this member, it is necessary to improve the value of the critical bending strain of concrete so as to be further increased. In FIG. 13, the cross-sectional strain distribution when the bending and compressive strain limit of unconstrained concrete is improved from AB (strain ε _cu ) to compressive edge strain AC (strain ε _cu2 ) of laterally constrained concrete is indicated by CC ′. is there.

In FIG. 13, the bending compressive strain (compression edge strain) ε _c of the compression-side concrete due to the lateral constraint of the concrete 31 is changed from AB to AC.
In the case of bending fracture, the elongation strain of the tensile-side PC steel 32 at the time of bending fracture further elongates by the elongation strain represented by the length bc from the state at the time of normal bending fracture (elongation strain ε _b given by the length ob), The elongation strain of the PC steel material 32 increases to the elongation strain ε _e represented by the length oc. Therefore, when the maximum elongation strain of the PC steel material 32 is larger than the elongation strain represented by the length oc, the PC steel material 32 is required before the compressive edge strain ε _c of the laterally constrained concrete reaches the bending compressive fracture strain ε _cu1. breaking takes place, the effect of improving the bending compression fracture strain epsilon _cu1 concrete 31 can not be utilized 100% by the lateral restraint. In addition, PC
The breakage of the steel member 32 causes the complete collapse of the PC member 30,
It is the most dangerous form of failure from a structural point of view. Therefore, in order to exert 100% of the lateral restraint effect, it is an essential condition that the PC steel material 32 extends until the compression side concrete is crushed.

Since the conventional PC steel rod has a breaking elongation of at least 7 to 10%, it is easy to judge that the above condition is satisfied. However, the elongation at break is a value that has no meaning in structural design. FIG. 14 is an explanatory diagram of elongation of the PC steel material. FIG. 14A is a side view of a PC steel material 50 in which a drawing (constriction) 51 has been generated by tension, and FIG.
(B) is a graph showing the relationship between tensile stress and tensile strain. When the PC steel material 50 is pulled, it reaches the yield point 52, then undergoes plastic elongation and reaches the maximum tensile strength 53, and thereafter, a part (constriction) 51 is formed in a part of the steel material, leading to fracture. The elongation until reaching the maximum tensile strength 53 is the uniform elongation 55. In the concrete structural member, when the elongation strain of the PC steel material 50 reaches the uniform elongation strain ε _uni of FIG. 14, the fracture occurs. Uniform elongation strain ε _uni is a strain corresponding to the maximum tensile strength 53 in the stress-strain curve of the PC steel material 50, and when the member receives a bending moment, the PC steel material 5
After 0 is stretched to a uniform elongation strain, the PC steel material elongates while the tensile stress applied to the PC steel material is reduced, and the bending moment cannot be borne, and the member at once results in bending failure due to the fracture of the PC steel material. That is, the elongation at break of the PC steel material as viewed from the bending fracture of the member is the strain at the maximum tensile strength 53 in FIG. 14B, not the strain at the break point 54 including the range 56 where the drawing occurs.

[0052] The uniform elongation strain of the PC steel commonly used for the current PHC pile is about 2%. According to research, a PC steel material having a uniform elongation strain of at least 4 to 5% is required to satisfy the above conditions. Therefore, P
In order to improve the bending toughness of the HC pile, it is important to use a high uniform elongation PC steel having a uniform elongation strain of 4 to 5% simultaneously with the lateral restraint of concrete.

Next, an experimental example for uniform elongation will be described.

[Experimental Example 2] FIGS. 15 to 17 are experimental examples in which the above fact was confirmed by experiments. FIG. 15 shows a D400 mm laterally constrained PHC pile used in the experiment, and FIG.
FIG. 15B is a side view of the bending test specimen 60, and FIG.

FIG. 15A is a side view of the bending test specimen 60, showing a half of the length of the specimen (half to the left from the center position 61). It is supported at two support points 62, a load is applied to two load points 63, and the bending at the center is measured. The dimensions of the specimen are 400 mm outside diameter and 250 m inside diameter
m, length 5000 mm, D9.2 mm as main bar 67
Using 16 PC steel rods of φ5 mm in lateral restraint bars (σy =
(1000 MPa) 68 is wound around the outer periphery. Fulcrum 62
The distance 64 between the specimen and the end of the specimen is 700 mm, the distance 65 between the fulcrum 62 and the load point 63 is 1300 mm, and the distance 66 between the load point 63 and the center position 61 is 500 mm. FIG.
Is a stress-strain curve of a conventional deformed PC steel rod having a uniform elongation of 2% used in the experiment and a high uniform elongation steel rod having a uniform elongation of 5% developed separately. In FIG. 16, the symbol 〇 indicates the yield point, and the symbol ● indicates the tensile strength (uniform elongation). FIG. 17 shows a comparison between the bending moment-curvature curve measurement results of the lateral restraint pile obtained from the pile bending test. The experimental results of FIG. 17 are described as follows.

Unconstrained pile (No. 11) (using a conventional PC steel rod with uniform elongation of 2%) Actual value of curvature at bending failure: 3.5 × 10 ^-4 1 / cm Bending fracture; Lateral restrained pile (No. 12) using PC steel rod without breaking (using a conventional PC steel rod with uniform elongation of 2%): Actual measured value of curvature at bending failure; 5 × 10 ⁻⁴ 1 / cm Bending fracture; Steel rod elongation strain at bending failure;
1.9% lateral restraint pile (No. 13) (high uniform elongation P with uniform elongation 5%)
C steel rod used): Actual value of curvature at bending failure; 16 × 10 ^-4 1 / cm (average of two test piles) Bending fracture;
4.6% (average of two test piles) As is clear from the above experimental results shown in FIG. 17, in all the piles, the tensile side PC steel material was broken, and lateral restraint of concrete and high uniform elongation steel rod were observed. It can be seen that significant improvement in toughness due to lateral restraint cannot be expected unless. By the way,
In this experiment, the curvature toughness improvement rate of the laterally restrained pile (No. 12) at the time of bending fracture was 1.43 times the curvature at the time of bending failure of the unrestrained pile (No. 11), and 4 for the laterally restrained pile (No. 13). .57
It is twice. In the above experiment, in order to confirm the importance of uniform elongation strain of the PC steel rod, a test pile with sufficient lateral restraint muscle mass was used so that bending failure of the pile due to PC steel rod fracture occurred. I have.

[0057]

FIG. 3 is a sectional view showing a high-bending toughness high-strength pile having a diameter of 400 mm of the embodiment. This high bending toughness high strength pile has an outer diameter of 400 mm, an inner diameter of 260 mm, and a wall thickness of 70 m.
m, vertical streak diameter φ15.2 of high uniform elongation specification shown in Table 8.
8 mm × 7 post tension strands (sheath inner diameter is 21 mm or more), and D10.7 m shown in Table 9
Four m-high uniform elongation pretension deformed PC steel bars were used. CFR equivalent to φ6mm high-strength steel lateral restraint bar around pile
P lateral restraint bars were arranged at a pitch of 50 mm in the pile axial direction.
A nominal prestress of 20 MPa was introduced.

This pile was subjected to a bending test. FIG. 1 is a graph showing measured values showing the relationship between the applied load and the curvature in the center bending span, and FIG. 2 is a comparison graph showing actually measured values showing the relationship between the applied load and the central deflection curve. For comparison, an unconstrained PHC standard pile having the same specifications is shown by a broken line, and a conventional high bending toughness high strength pile having a high-strength lateral restraint bar having a diameter of φ6 mm arranged at a pitch of 50 mm is shown by a thin line. Further, an example using a CFRP lateral restraint bar equivalent to the conventional high bending toughness high strength pile is shown by a thick line.

The unconstrained PHC standard pile is bent when the applied load reaches the maximum load, has a very small amount of energy absorption, and shows brittle fracture without stickiness. In contrast, conventional piles using lateral restraint bars have large plastic deformation and a large energy absorption capacity, whereas those using the CFRP lateral restraint bars of the examples increase the curvature or increase the central deflection. On the other hand, there is no decrease in load, and the energy absorption ability is larger than that of the conventional pile using lateral restraint bars.

[0060]

[Table 8]

[0061]

[Table 9]

[0062]

As described above, the high-bending toughness high-strength pile of the present invention is constructed as described above, so that it is extremely excellent in seismic resistance and extremely large in energy absorption capacity against a large earthquake as compared with the conventional PHC pile. It has an excellent effect that the contribution is large.

[Brief description of the drawings]

FIG. 1 is a graph showing characteristics of a high bending toughness high strength pile of an example.

FIG. 2 is a graph showing characteristics of a high bending toughness and high strength pile of an example.

FIG. 3 is a sectional view of a high bending toughness high strength pile according to an embodiment.

FIG. 4 is a dimensional view of a specimen.

FIG. 5 is a graph showing test results.

FIG. 6 is a graph showing test results.

FIG. 7 is a graph showing test results.

FIG. 8 is a graph showing test results.

FIG. 9 is a graph showing test results.

FIG. 10 is an explanatory view of compression failure of unreinforced concrete.

FIG. 11 is an explanatory view of compression fracture of laterally reinforced concrete.

FIG. 12 is a graph showing an example of improving the toughness of a laterally reinforced concrete in compressive fracture.

FIG. 13 is an explanatory diagram of the improvement in member bending toughness due to lateral constraint of concrete.

FIG. 14 is an explanatory diagram of uniform elongation.

FIG. 15 is (a) a side view and (b) a cross-sectional view of a test sample.

FIG. 16 is a stress-strain curve of a test PC steel rod.

FIG. 17 is a measured bending moment diagram showing a result of a bending test.

[Explanation of symbols]

 Reference Signs List 20 specimen 21 CFRP lateral restraint streak 22 centrifugal compaction concrete 23 hollow portion 30 rectangular section PC member 31 concrete 32 PC steel 33 center of gravity shaft 40 concrete 41 compressive force 42 cone-shaped concrete block 43 concrete in center portion 44 45) Tightening force 46 Cone-shaped concrete block 50 PC steel 51 Drawing (constriction) 52 Yield point 53 Maximum tensile strength (Maximum stress) 54 Break point 55 Uniform elongation 56 Range where drawing occurs 60 Bending test Specimen 61 Center position 62 Support point 63 Load point 64, 65, 66 Distance 67 Main bar 68 Side restraint bar

Continued on the front page F-term (reference) 2D041 AA02 BA16 CA01 CB06 DB06 DB09

Claims (3)

[Claims] 1. A high-bending-toughness high-strength pile, characterized in that a lateral restraining bar composed of a bundle of carbon fiber reinforced plastic wires or a bundle of hard steel wires subjected to anticorrosion treatment is disposed on the outer surface of a pile as a shear reinforcing bar. 2. The high bending toughness and high strength pile according to claim 1, wherein the hollow portion is filled with a filler having a uniaxial compressive strength of 10 MPa or more. 3. A high uniform elongation PC steel material is used for a main reinforcing bar.
3. The high bending toughness and high strength pile according to claim 1, wherein a high prestress of 8 MPa or more is introduced into the C steel material.