JPH09177072A - Manufacture of centrifugal prestressed concrete pile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart a large elongation performance to a steel product by once stretching a reinforcement with a load exceeding a yield point strength to cause all of its yielding distortions, and then newly placing it under a tensioning state to fix it. SOLUTION: Ten high strength reinforcements obtained by once stretching a high strength reinforcement having a yield point strength of a prescribed value, for example, 75kg/mm<2> , or more with a load exceeding the yield point strength to remove yielding distortions are used as reinforcements 2, and these reinforcements are stretched with a load lower than the yield point load to impart a prestress to concrete 4, whereby a centrifugal prestressed concrete pile 1 is provided. Since the steel quantity to use is relatively increased more than the case of a conventional PC pile when a steel product having a yield point lower than that of the conventional PC pile is used, the initial bending performance is enhanced also against compression force or shearing force, compared with the same PC pile.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ready-made concrete pile used as a foundation pile for civil engineering and building structures, and it is possible to obtain particularly high bending performance and toughness, and at the same time, when the pile is bent. The present invention relates to a method for manufacturing a centrifugal prestressed concrete pile capable of suppressing cracking.

[0002]

2. Description of the Related Art Reinforced concrete piles (RC piles) and prestressed concrete piles (PC piles) have been used as conventional ready-made concrete piles. In the former RC pile of these, it is necessary to increase the amount of rebar in order to improve the bending performance, but since the strength of the rebar is limited, it was necessary to arrange a large amount of rebar in the pile. However, in concrete piles that are molded by centrifugal force, aggregates in the concrete cannot move during molding when the space between the reinforcing bars becomes tight, which may result in defective molding, so there is a limit to the amount of reinforcing bars that can be arranged. .

Therefore, it was not possible to manufacture piles with large bending moments. Moreover, even if the amount of reinforcing bars in the pile was increased, the load at which bending and tensile cracks occurred in the concrete when it was bent, was almost constant, and cracking of the concrete could not be suppressed. For this reason, RC piles have almost never been manufactured recently.

The latter PC pile solves the problem of cracking, which is a major problem of RC piles. This PC
The pile is a PC steel rod (JIS G3 manufactured by hot rolling rolled killed steel, and then subjecting it to stretching, drawing, heat treatment, etc.
109) It is a pile manufactured by using this PC steel rod while tensioning it and placing concrete around it by centrifugal molding. Therefore, this PC pile is characterized in that concrete is pre-stressed with a compressive force (pre-stress), so that tensile cracks are less likely to occur even when the pile is bent.

However, in PC piles, when the amount of PC steel rods arranged for the purpose of improving bending performance is increased, the tensile strength of concrete is improved by prestressing, but the compression side of concrete becomes strict, and PC steel rods that can be arranged are still available. There was also a limit to the amount. Further, the biggest drawback of PC piles is that the bending deformation ability of PC piles is considerably smaller than that of RC piles because the elongation capacity of PC steel rods is considerably smaller than that of rebars, resulting in a so-called brittle pile without toughness. .

As described above, since it is difficult to secure a large bending performance in RC piles and PC piles, PRC piles are the ones that are improved in terms of bending performance. This is one in which a reinforcing bar and a PC steel rod are arranged in one pile, and only the PC steel rod is tensioned to form a prestressed pile. Therefore,
The PRC pile solves the problem of cracking, which was a drawback of RC piles, and improves the bending performance (bending strength) of PC piles, which is a drawback of PC piles.
I was able to raise it more than a stake.

However, even in this PRC pile, since the PC steel bar is used, the problem that the bending deformation capacity (deflection amount), which is a drawback of the PC pile, is small, cannot be solved. Since the PC steel rods are arranged and only the PC steel rods are tensioned, the manufacturing process is complicated and it is a stake that is time-consuming to manufacture.

In order to improve the above-mentioned defects of RC piles, J
An attempt was made to use a steel rod of ISG3112 at a yield strength of 50% or less of the yield strength of the steel rod to produce a prestressed pile, and to increase the toughness of the pile more than RC piles. It is proposed in the official gazette (first known technology). However, even in this case, in order to have bending strength and toughness comparable to PC piles, it is necessary to use about four times the number of steel rods, and furthermore, there is a drawback that cracking cannot be suppressed. It was a thing.

Further, Japanese Patent Laid-Open No. 60-36108 (second known technique) discloses a pile in which a PC steel material is used instead of a normal steel material without prestressing as in the case of manufacturing an RC pile. Although the toughness of this pile is higher than that of RC piles, it cannot prevent the occurrence of cracks, and cracks occur at an early stage of the bending test of the piles, and it is said that such toughness cannot be expected. There was a flaw.

Further, Japanese Patent Laid-Open No. 62-280418 (third known technique) discloses an expensive PC having a high uniform elongation.
It is proposed to use steel, but in order to maintain toughness, as specified in the specification,
It is necessary to use transverse restraint muscles having a yield stress (toughness) three times or more higher than usual. Even if such an expensive lateral restraint bar is used, as shown in the prior art section of Japanese Patent Application Laid-Open No. 5-98638 (fourth known art), which is the invention of the same inventor, bending of the pile is required. During the test, it was reported that bending deformation was particularly concentrated in one place and the expected toughness was not achieved.

As described above, the method proposed in the third known technique is a pile having a true toughness, in which cracks are initially generated even if an expensive special PC steel material and an expensive special lateral restraint are used. I couldn't do it. And, in the above-mentioned fourth known technique, there is a method of using an expensive PC steel material having a high uniform elongation as a longitudinal streak, and also deformed, and an expensive material having a high uniform elongation as a lateral restraint. It is disclosed.

In the method disclosed in the fourth known technique,
It is necessary to make an expensive material with a high uniform elongation as a PC steel bar into a deformed shape that has been subjected to special processing. Moreover, in the production of ordinary RC piles and ordinary PC piles, spirals are used as lateral restraint bars. It is impossible to use ordinary iron wire that is wound in a shape, it is necessary to use an expensive material for the lateral restraint bar, and in addition to the fact that it requires extremely complicated labor in manufacturing, It became an expensive pile, and there was a problem in commercializing it as a real pile.

[0013]

As mentioned above, the first known technology and the second known technology developed to improve the problems of the conventional PC piles, RC piles and PRC piles and these piles. In the third known technology and the fourth known technology, cracks occur when each concrete pile is bent, problems that it is difficult to obtain large bending performance and toughness at breakage, and special problems Since a deformed PC steel material must be used and an expensive lateral restraint bar must be used, there is a problem that the manufacturing becomes extremely complicated and the cost becomes high.

The method for manufacturing a centrifugal prestressed concrete pile according to the present invention is a completely new technique developed in view of many problems of the prior art, and in particular, it uses a reinforcing bar from which the yield strain is removed in advance, By producing this rebar by pretensioning the concrete by tensioning it with a load less than the yield strength, it is possible to obtain large bending performance and toughness, and to suppress cracking when the pile is bent. It provides a completely new method of manufacturing prestressed concrete piles.

[0015]

The method for manufacturing a centrifugal prestressed concrete pile according to the present invention is a technique that has fundamentally improved many of the above-mentioned conventional problems, and the gist of the invention is the yield strain. The method for producing a centrifugal prestressed concrete pile is characterized in that the rebar from which is removed is tensioned with a load equal to or lower than the yield point strength to prestress the concrete.

As described above, the characteristic of the present invention is that when the reinforcing bar is tensioned, it has a yield strength of 8 as seen in the conventional PC pile.
Instead of just tensioning to 0%, first reinforce the reinforcing bar with a load that exceeds the yield point strength to generate all the yield strain of the reinforcing bar, and then re-tension it to obtain 80% of the yield point strength.
It is to be established in a tense state to some extent.

The yield strength of the reinforcing bar used in the manufacturing method of the present invention is 60 kg / mm ² or more, preferably 75 kg / m.
m ² or more. Normal rebar SD30, 30 kg / mm
² can be used, but the amount of contraction due to prestressing is constant, so high-strength reinforcing bars are more effective.

Since these reinforcing bars are not subjected to quenching treatment or the like like PC steel rods, when they reach the yield strength after being subjected to tensile stress, a large yield strain is generated, and then they enter the plastic region and are destroyed. When a load exceeding the yield strength is applied to this rebar, it is reborn as a high-strength rebar from which apparent yield strain is removed.

As a result, the amount of elongation until rupture is reduced by the yield strain, resulting in a reinforcing bar having a small rupture elongation.
Even so, it has an elongation capacity of 5% to 30%, and it is possible to secure a large elongation capacity that does not pose a problem compared to PC steel bars. Thus, according to the present invention, once the reinforcing bar is tensioned with a load exceeding the yield point, the strength of the yield point of the steel material is relatively increased, and at the same time, the reinforcing bar also has a large elongation capability.

Therefore, the load that exceeds the yield point applied to the rebar first may be a load that slightly exceeds the yield point load because it will achieve its purpose if yield strain is generated. When this load increases, the yield strength increases relatively, but the elongation at break decreases, so the initial tensile load may be determined in consideration of this elongation at break.

Further, in the present invention, for the purpose of improving cracking which is a drawback of RC piles, the reinforcing bars are tensioned in the same manner as PC piles to prestress concrete. The larger the amount of prestress given, the higher the rigidity of the pile body, which is desirable. However, if too much is given, there is a limit because it is related to the compressive strength of concrete.

Further, there is a limit to the amount of prestress that can be applied according to the amount of reinforcing bars to be placed. Therefore, it is desirable to make the tension at 90% or less of the yield strength of the reinforcing bar. If the tension is further increased, the steel material approaches the yield point and the steel material may be plastically deformed. Preferably 70% of the yield strength of the rebar
It is selected from the range of 80%.

When the yield strength of the high-strength reinforcing bars used in the present invention is lower than that of the PC steel bar used in ordinary PC piles, in order to make the bending strength of the present invention comparable, Use a large amount of rebar (steel amount) for. In this case, since the amount of steel in the present invention is relatively larger than that of the conventional PC pile, there is an extra note that the compressive strength and shear strength of the pile are higher than those of the conventional PC pile.

Further, the yield point strength of the reinforcing bar used in the present invention is as high as that of the PC steel bar, the less the amount used and the more convenient for manufacturing. On the other hand, if the yield strength is low, the tension and strain per steel material will be relatively small.

As a result, when pre-stress is applied to the reinforcing bar after hardening of the concrete, the initial tension strain is consumed by the contraction of the concrete, and the amount of effective pre-stress is reduced. From the viewpoint of the amount of shrinkage of concrete, the yield strength of the reinforcing bar used should be 60 kg / mm ² or more. However, it is preferably close to PC steel bar, 75 kg / mm
^{2 to} 100 kg / mm ² .

The method of removing the yield strain of the reinforcing bar used in the present invention is most easily carried out at the time of introducing prestress in the pile manufacturing process, but it is also possible to remove it by drawing during the manufacturing of the reinforcing bar. Is. Particularly preferably, the strained reinforcing bar is installed in the concrete pile manufacturing form as it is.

In that state, strain is taken by temporarily tensioning the reinforcing bar with a load exceeding the yield strength, and for example, the reinforcing bar is once strained with a load exceeding the yield strength to sufficiently generate the yield strain, To zero or lower it to below the yield point), and then re-tension and settle until the load below the yield point,
This is a method of prestressing concrete in this state. By carrying out this method, it is possible to remove the yield strain of the reinforcing bar by using the production form and to produce the centrifugal prestressed concrete as it is.

According to the present invention described above, the bending performance of the pile is improved by using the high-strength reinforcing bar from which the yield strain is removed. In particular, it is possible to relatively reduce the bending deformation of the pile after the concrete is cracked by being bent, and it is also possible to increase the load of breaking bending.

In order to further increase the bending strength in the present invention, it is preferable to increase the amount and strength of the reinforcing bars and at the same time increase the compressive strength of the concrete. When the amount of rebar is increased, the strength on the bending tension side increases, but it does not change because the bending compression side is held by concrete. Therefore, if the compressive strength of concrete is increased according to the amount of rebar, even greater bending performance can be obtained. Conventional compressive strength of concrete is 80
Around 0 kg / cm ² is often used, but when the number of rebars increases, the possible range is 1200 kg.
/ Cm ^{2 It} is desirable to increase to about ² .

The preferred rebars used in the present invention are conventional P
It is a reinforcing bar manufactured by only a hot rolling process so as to manufacture a normal reinforcing bar by adding a part of an alloy without performing quenching and tempering treatment like a C steel bar, and preferably having a high strength. It is a reinforcing bar, not a PC steel rod. This steel rod may be a deformed steel rod having an increased adhesiveness to concrete.

Therefore, unlike the PC steel bar, the strain amount after reaching the maximum strength after reaching the yield strength is about 2 for the PC steel bar.
%, Whereas such high strength rebar reaches 5% to 15%. A high-strength reinforcing bar having such strain is a suitable reinforcing bar used in the present invention.

For example, a reinforcing bar having the strain as described above is used, and after the yield strain is removed, the reinforcing bar is tensioned with a load equal to or lower than the yield point strength to prestress the concrete and prestress the concrete with centrifugal force. To manufacture. As a result, it is possible to obtain high bending toughness like a conventional RC pile while having higher strength than the RC pile.

Further, in the above-described method for manufacturing a pile of the present invention,
As a horizontal bar (spiral bar), the JIS A 5335 iron wire or JIS G 353 that has been used for manufacturing conventional ordinary piles.
You can use ordinary iron wires such as 2 iron wires. According to the manufacturing method of the present invention, even if this normal line is used as a horizontal line, the performance can be sufficiently exhibited.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION First, in the embodiments of the present invention,
The following high-strength reinforcing bars were used. That is, outer diameter 10.0
mm, a yield strength of about 80 kg / mm ² , and a maximum tensile strength of about 108 kg / mm ² were used. The chemical components other than iron contained in this high strength rebar are C: 0.4
4, Si: 0.24, Mn: 1.01, P: 0.01
3, Cu: 0.07, Cr: 0.11, Sn: 0.0
1, Ni: 0.04, V: 0.192, Nb: 0.05
It was one.

The inventors of the present invention used the high-strength reinforcing bar having the above-mentioned composition, and first produced the high-strength reinforcing bar A as it was without taking yield strain. Next, using the same high-strength reinforcing bar as this high-strength reinforcing bar A, 90 kg / mm ² exceeding the yield point
Then, a high-strength reinforcing bar B was prepared by pulling once to remove the yield strain.

Then, the high-strength reinforcing bars A and B having the above-mentioned outer diameter, yield point strength, maximum tensile strength and chemical composition were tested for yield point load, 1% elongation load, 2% elongation load and breaking load, respectively. The results obtained were as shown in the following table and FIG.

[0037]

[Table 1]

As is clear from the above table and FIG. 3, the high strength rebar B from which the yield strain is removed and the high strength rebar A from which the yield is not removed have the same breaking strength and do not change. It is clear that the high strength reinforcing bar B has a relatively higher strength than the high strength reinforcing bar A in terms of strength from the time of the breaking to the breaking.

High strength rebar B from which the yield strain has been removed as described above
Was used to produce a prestressed concrete pile as shown in FIG. That is, in FIG. 1, 1 is a prestressed concrete pile manufactured by the method of the present invention.
The prestressed concrete pile 1 is provided with reinforcing bars 2 made of the above-mentioned high-strength reinforcing bars B. 3 is a spiral muscle (horizontal muscle), and the above-mentioned JISA5335 iron wire is used. Reference numeral 4 is concrete, and end plates 5 are provided at both ends of the prestressed concrete pile 1.

The prestressed concrete pile 1 has an outer diameter of 400 mm, the concrete 4 has a wall thickness of 65 mm, and the prestressed concrete pile 1 has a length of 6000 mm.
Further, the concrete 4 was manufactured with a strength of 850 kg / cm ² . Further, the reinforcing bars 2 used in the prestressed concrete pile 1 had an outer diameter of 10 mm, and 10 bars were arranged in the prestressed concrete pile 1 and a prestress of 45 kg / cm ² was applied.

The present inventors do not remove the yield strain for comparison with the prestressed concrete pile 1 in which the above-mentioned high-strength reinforcing bar B from which the yield strain is removed is used as the reinforcing bar 2 as described above. A prestressed concrete pile 10 was manufactured in which the above-mentioned high-strength reinforcing bar A was used as the reinforcing bar 2 and all other conditions were the same as those of the prestressed concrete pile 1.

Prestressed concrete piles 1 of these
In addition to the prestressed concrete pile 10 and the PHC pile class A pile (PC pile) 20 having the same dimensions, a bending test was carried out by the two-point loading method. The bending test results are shown in FIG. 2 as lines (1), (10) and (20), respectively.
It was as shown by the line. The PC pile 20 used for the test had a yield strength of 130 kg / mm ² , a maximum tensile strength of 145 kg / mm ² , and an outer diameter of 7.1 m.
m PC steel rods were used.

The results of the above-mentioned test are shown in line (1) of FIG.
As is clear from the comparison of the lines (10) and (20),
The prestressed concrete pile 1 manufactured by the manufacturing method of the present invention represented by the line (1) is the P represented by another line (20).
Compared with C pile 20, overwhelmingly large deformation capacity (toughness)
It became clear that it has. That is, when the same load was applied to the prestressed concrete pile 1 and the PC pile 20, the PC steel bar broke at 25 mm in the PC pile 20 and no further displacement was observed, whereas the prestressed concrete pile was not recognized. The pile 1 was found to have a displacement of up to about 70 mm.

Further, (1) manufactured by the manufacturing method of the present invention
Prestressed concrete pile 1 represented by a line and prestressed concrete pile 10 represented by another (10) line
Comparing with, it is clear that the prestressed concrete pile 1 is always superior to the prestressed concrete pile 10 in the load of about 10 kg / mm ² . From these, it is clear that removing the yield strain of the reinforcing bar 2 to be used makes it possible to produce a prestressed concrete pile having a relatively large bending moment, as compared with the case where the yield strain is not removed. is there.

[0045]

Since the method for manufacturing a centrifugal prestressed concrete pile according to the present invention has the above-mentioned structure, it has the following great effects.

(1) The centrifugal prestressed concrete pile manufactured by the manufacturing method of the present invention is the same as the conventional PC described above.
It is possible to obtain a large bending performance and a large deformation capacity (toughness) that could not be achieved with piles and the like. (2) In addition, it is possible to suppress early cracks when they are bent and cracks having a large width, which are the drawbacks of the RC piles.

(3) In the manufacturing method of the present invention, when a steel material lower than the yield point strength of the conventional PC pile is used, the amount of steel used is relatively higher than that of the conventional PC pile. Since it increases, the initial bending performance becomes stronger against the compressive force and the shearing force than the same PC pile.

(4) Since it is not necessary to use an expensive PC steel rod, it can be mass-produced at low cost. (5) According to the manufacturing method of the present invention, the manufactured pile can sufficiently exhibit the above-mentioned performance even if the normal line is used as the horizontal bar. (6) Since the whole manufacturing method is simple, it can be mass-produced.

[Brief description of the drawings]

FIG. 1 is an external view and a cross-sectional view of a pile manufactured according to the present invention.

FIG. 2 is a comparative view in a bending test of a pile and a PC pile made for comparison with a pile manufactured according to the present invention.

FIG. 3 is a strain-strain relationship diagram between the high-strength reinforcing bars used in the present invention and my high-strength reinforcing bars.

[Explanation of symbols]

 1 Prestressed concrete pile 2 Reinforcing bar 3 Spiral bar 4 Concrete 5 End plate 10 Prestressed concrete pile 20 PC pile A, B High strength rebar

Claims (1)

[Claims] 1. A method for manufacturing a centrifugal prestressed concrete pile, comprising manufacturing a reinforcing bar from which yield strain has been removed by tensioning the reinforcing bar with a load equal to or lower than the yield point strength to prestress the concrete.