JP7201867B1 - METHOD FOR INTRODUCING TENSION AND METHOD FOR PRODUCING PRESTRESSED CONCRETE STRUCTURE - Google Patents

Abstract

Kind Code: A1 A tendon anchoring structure, a tension introducing method, and a prestressed concrete structure that can be anchored by applying prestress stress to a concrete structure by a post-tensioning method with a simple and inexpensive configuration that does not require antirust treatment. Provide a method of manufacturing an object. SOLUTION: In a post-tension type tendon fixing structure for introducing prestress to a concrete structure, an insertion hole is formed in the concrete structure and penetrates end faces of the concrete structure, and the tendon is inserted through the insertion hole. T1 and a grout material G1 filled around the tendon in the insertion hole, and the tension of the tendon tensioned before the grout material is filled, the compressive strength of the grout material is a predetermined compression By being released in a state where the strength is developed, the tension force is transmitted to the concrete structure by the adhesion resistance stress acting between the grout material and the tendon, and is fixed to introduce prestress. [Selection drawing] Fig. 2

Description

TECHNICAL FIELD The present invention relates to a method for introducing tension force and a method for manufacturing a prestressed concrete structure, and more particularly, to a method for applying prestressing force to a concrete structure by a post-tension method without using a conventional fixing device for post-tensioning. It relates to a method for introducing tension force and a method for manufacturing a prestressed concrete structure.

Conventionally, there are two types of methods for introducing tension force into prestressed concrete structures: a post-tension method and a pre-tension method. Since these two methods each have advantages and disadvantages, either method is adopted according to the construction conditions and design conditions of prestressed concrete structures.

In the pretension method, since factory production is advantageous, it is possible to install a tension reaction force device and steam curing equipment to enable efficient tensioning work. No tensioning device is required. In addition, the pretension method has the advantage of being able to economically manufacture the members of the prestressed concrete structure, such as eliminating the need for PC grouting. On the other hand, since the pretension method is basically factory-produced, it is difficult to adopt it in cases where the length of concrete members is long, such as in large-scale bridges, or where it is necessary to join concrete members together. . Therefore, in the case of such construction conditions, the post-tension method is adopted.

On the other hand, in the post-tension method, since tension work is basically performed at the construction site, there is no limit to the length of the concrete members, and it is possible to introduce tension over the entire length of the concrete structure to join the concrete members. is. However, there is a need for a tensioning end of the target concrete structure and an anchoring device for anchoring the tension introduced at the anchoring end to the concrete structure. Although various types of fixing devices are used, they are generally expensive and are made of steel. In the conventional post-tension system, after tension is introduced into the concrete structure through a fixing device, PC grout material is filled around the tendon in the sheath pipe for the purpose of rust prevention of the tendon, and the PC grout material Curing is performed for strength expression.

Conventionally, the post-tension method is an indispensable tensioning method in the construction of prestressed concrete structures such as concrete bridges. However, at the tension end of the prestressed concrete structure by the post-tension method, the fixing device is expensive and needs anti-corrosion treatment. I can't find an example.

For example, Patent Literature 1 discloses a prestressed concrete structure and a method of manufacturing the same that can utilize the respective advantages of the pretension method and the posttension method. In other words, the pretension block 1 manufactured by utilizing the advantages of the economical manufacturing method by the efficient manufacturing method when the length of the member of the pretension method is short, and the post tension method in which the tension construction at the site is superior. has proposed a structure and construction method for a prestressed concrete member that integrates a post tension block 2, which is assumed to be joined on site, by a post tension method (paragraphs [0009] to [0019] of the specification of Patent Document 1. , see FIGS. 1-10 of the drawings).

However, the structure and construction method of the prestressed concrete member of Patent Document 1 does not propose a tension fixing method different from the conventional one for either the pretension method or the post tension method. In the method, it merely followed the conventional fixing method. For this reason, it was not possible to solve the problems of the tension introduction method by the pre-tension method or the post-tension method.

Further, Patent Literature 2 discloses a technique for shortening the required fixing length of a pretension tendon when using a high-strength reinforcing bar as a pretension tendon compared to the conventional fixing length. Specifically, in Patent Document 2, a protruding bump (protrusion) having a diameter of 1.5 times or more of the base material is provided around the base material on the end side of the pretension tendon made of high-strength reinforcing bars. Disclosed is a formed pretension tendon and a method of introducing pretension into concrete using the pretension tendon (paragraphs [0046] to [0086] of the specification of Patent Document 2, FIGS. 7 to 10 of the drawings etc.).

The method of introducing pretension into concrete described in Patent Document 2 is to introduce pretension into concrete by bearing pressure by the nodules of the pretension tendon and adhesion to the concrete at the ends. It is said that the fixing length can be shortened in anticipation of adhesion and bearing force to concrete. However, the method of introducing pretension into concrete using a pretension tendon having bumps (projections) described in Patent Document 2 is merely an extension of the conventional pretension system introduction method. It is limited to the effect of shortening the fixing length, and cannot solve the problems of the above-described tension introduction methods using the pre-tension method and the post-tension method.

Furthermore, Patent Document 3 includes a sleeve 100, a wedge 200, and a cap 300 that are combined along the axial direction (longitudinal direction) of the PC steel material 400, and the sleeve 100 is
In the outer cylindrical surface 120, the male threaded portion 122 is provided on the cap side, and the cap 300 is provided with a female threaded portion 312 that screws into the male threaded portion 122, and a prestress introduction jig provided with a contact end surface 314 that contacts the wedge 200; A pretension-type prestress introducing method using it has been disclosed (see paragraphs [0016] to [0035] of the specification of Patent Document 3, FIGS. 7 to 10 of the drawings, etc.).

The prestress introduction method described in Patent Document 3 is a technique similar to the method of introducing pretension to concrete described in Patent Document 2, and a wedge mechanism is applied when manufacturing a prestressed concrete member by the pretension method. The object is to shorten the fixing length by using a small-sized jig. For this reason, the method for introducing prestress by the pretension method described in Patent Document 3 is similar to the method for introducing pretension to concrete described in Patent Document 2, and the tension force introduction method by the pretension method or the post tension method described above. It was not something that could solve the problem of Moreover, the application target of the tendon of the prestress introduction method described in Patent Document 3 was the PC steel strand.

JP 2016-8441 A JP 2017-203357 A JP 2019-181704 A

SUMMARY OF THE INVENTION Accordingly, the present invention has been devised in view of the above-described problems, and its object is to provide a rust-preventing fixing device that does not require a conventional fixing device for post-tensioning, which is expensive and requires maintenance costs. To provide a tension introducing method and a method for manufacturing a prestressed concrete structure which require no treatment and can introduce and fix prestress stress to a concrete structure by a post-tension method with a simple and inexpensive configuration. be.

The prestress stress introduction method according to claim 1 is a tension force introduction method for introducing prestress to a concrete structure by a post-tension method by releasing the tension applied to the tendon, wherein the concrete structure is A tendon inserting step of inserting a tendon into an insertion hole that is formed and penetrates between end faces, and a tendon tensioning of applying a predetermined tension by tightening the tendon inserted in the tendon inserting step with a tension jack a grout material filling process of filling grout material around the insertion hole of the tendon tensioned in the tendon tensioning process; and a predetermined compressive strength of the grout material filled in the grout material filling process. Then, a tension release step of releasing the tension of the tendon, and in the tension release step, prestressing the concrete structure while controlling the release speed of the tension of the tendon with a hydraulic torque wrench. is characterized by introducing

The prestress stress introduction method according to claim 2 is the prestress stress introduction method according to claim 1 , wherein the tension releasing step is performed so that the compressive strength f _gm of the grout material satisfies formula (1). It is characterized by performing after developing the compressive strength of.
f _{gm ≥ 0.5 f'ck} ⁽ 1)
Here, f _gm : Compressive strength of grout material (N/mm ² )
f ^' _ck : Design compression standard strength of concrete structure (N/mm ² )

The method for manufacturing a concrete structure according to claim 3 is characterized in that, in the method for introducing prestress stress according to claim 2 , in the tension release step, the tension release speed of the tendon is equal to the average bond stress degree. The rate of change K ₆₅ is characterized by release to satisfy equation (4).
K65≦ ^0.0897・_fgm2 / _3－0.8219 (4)
Here, K ₆₅ : time rate of change of average bond stress (N/mm ² /sec)
_K65 = _τ65 / _Tr
τ ₆₅ = 0.7P _u /(65πφ ² )
T _r : Release time at the time of the fastest release of tension (sec)
τ ₆₅ : Average adhesion stress (N/mm ² ) at standard fixing length (= 65φ)
P _u : Tensile load of tendon (name for PC steel strand)
Or guaranteed breaking load (name in case of continuous fiber reinforcement) (N)
φ: Diameter of tendon (mm)

A method for manufacturing a prestressed concrete structure according to claim 4 is a method for manufacturing a prestressed concrete structure by introducing prestress to the concrete structure by a post - tension method to manufacture the prestressed concrete structure. or 3 , wherein the prestress is introduced into the concrete structure while controlling the releasing speed of the tension of the tendon.

According to the inventions of claims 1 to 4 , the tension force of the taut tendon is transmitted to the concrete structure via the adhesion resistance stress of the grout material, and as a result, prestress is introduced. . In other words, the advantages of both the pretension method and the posttension method can be utilized, and the posttension fixing device, which is expensive and requires maintenance costs (the conventional device, which is made of metal and requires precise machining There is no need to use a post-tensioning fixture). For this reason, according to the inventions of claims 1 to 4 , not only does rust prevention treatment become unnecessary, but even when the length of the concrete members is increased or when it is necessary to join the concrete members together, With a simple and inexpensive structure, it is possible to introduce and fix prestress stress to concrete structures by the post-tension method.

FIG. 1 is a schematic diagram showing the transmission path of the bond shear stress through which the released tension is transmitted to concrete when the tension of the tendon that has been introduced is released. FIG. 2 is an explanatory diagram showing a tension release construction method in the tension force introduction method according to the first embodiment of the present invention, (a) is a cross-sectional view, and (b) is an A arrow view of (a) It is a diagram. FIG. 3 is an explanatory diagram showing a construction method for tension release in the tension introduction method according to the second embodiment of the present invention. FIG. 4 is an explanatory diagram showing the temporal change in the strain generated on the concrete surface at a position 9φ from the end of the concrete due to the released tension when the tension of the tendon is released in the cutting mode. FIG. 5 is an explanatory diagram showing the temporal change in the strain generated on the concrete surface at a position 9φ from the end of the concrete due to the released tension when the tension of the tendon is released in the jack/torque wrench mode. is. FIG. 6 is a graph showing prestress effectiveness ratio (EPR) versus dimensionless distance from taut end (L/φ) in cutting mode. FIG. 7 is a graph showing the relation of prestress effective ratio (EPR) to dimensionless distance from taut end (L/φ) in jack/torque wrench mode. FIG. 8 is a graph showing the relationship between the 2/3 power of the compressive strength of the grout material in the jack/torque wrench mode and the bond stress time rate of change _K65 . FIG. 9 is a graph showing the relationship between the 2/3 power of the compressive strength of the grout material in the cutting mode and the bond stress time change rate _K65 .

EMBODIMENT OF THE INVENTION Hereinafter, one Embodiment for implementing the prestressed concrete structure by the post-tension system which concerns on this invention is described in detail, referring drawings.

<Problem of fixing method by post-tension method using PC steel strand>
The post-tension prestressing method, which uses PC steel strands as tendons, was originally developed and popularized in Germany and France. In Japan, for example, the VSL method, the Freycinet method, the SE method, etc. have been introduced and put into practical use. Many of the existing prestressed concrete structures in Japan have been basically constructed based on these construction methods. However, there is a problem with the post-tension fixing device (fixer) using the conventional PC steel strand.

Fixing methods for PC steel strands are roughly divided into wedge fixing methods and screw fixing methods. The wedge fixing method is a method of gripping and fixing the PC steel strand at any position by the wedge effect, and the screw fixing method is fixing by crimping the prestressing tendon to the sleeve and threading the sleeve. It is a method of fixing to the bearing plate at an arbitrary position using a lock bolt. There are a fixed end portion and a tension end portion for prestress fixing by the post-tension method, and basically the above two fixing devices are applied.

When a PC steel strand (multiple PC steel wires are twisted together) is applied as a prestressing tendon, the fixing method of the fixed end consists of a wedge, an anchor head, a bearing plate, and a spiral bar (or grid bar). A common method is to fix the tendon at the fixed end by a wedge fixing method. There is also an example of fixing to the bearing plate using a simple fixture in which a steel sleeve called a crimping grip is crimped and fixed to the tendon.

On the other hand, the tensioned ends are fixed to the concrete by either the wedge fixing method or the screw fixing method after tensioning with a tensioning jack. In the wedge-type fixing method, set loss of the wedge may occur at the time of fixing, resulting in a slight tension loss. On the other hand, the screw-type fixing method has no risk, but the manufacturing cost of the fixing device is slightly high.

In any case, the fixing method of the post-tension method when PC steel strand is applied as a prestressing tendon is a wedge-type fixing method that is made of steel and requires precision processing, or a fixing device (or fixing device) that uses a screw-type fixing method. equipment) is applied.

The problem with the post-tension fixing method using PC steel strands is that the fixing devices for these fixed ends and tension ends are expensive precision-machined steel products, and the overall construction cost of the post-tension method. It is mentioned that it occupies a large proportion of

Another problem with the fixing method by the post-tension method using PC steel strands is that the fixing jig (fixing tool) at the tension end and the fixed end is made of steel, so the fixing tool as a whole is not rust-proof. It is necessary to protect the fixing device by covering the fixing device with an oil seal device or a rust-proof cover material, or by post-casting the entire fixing device with concrete. There is a problem that not only is the equipment cost of the oil seal expensive, but also the maintenance cost of the sealed oil is incurred.

In the post-tension method, a pre-stress stress is introduced into the concrete structure at the stage when tension fixing is completed in order to introduce tension force into the concrete structure after the concrete strength has been developed. After that, the gap between the sheath pipe into which the PC steel strand is inserted is filled with PC grout (grout material). The main purpose of PC grout filling is to prevent corrosion of PC steel strands. In other words, the fixation of the tension force is basically expected from the fixation performance of the post-tension-type fixing devices provided at both ends of the concrete structure.

<Fixing Method by Post-Tension Method Using Continuous Fiber Reinforcing Material and Its Problems>
Next, a post-tension fixing method using a continuous fiber reinforcing material and its problems will be described.

Continuous fiber reinforcing material is made by bundling tens of thousands of continuous fibers such as carbon fiber, aramid fiber, and glass fiber, and then adding thermosetting resin such as epoxy resin and vinyl ester resin, or thermoplastic resin such as polycarbonate and polyvinyl chloride. It is impregnated and cured. The continuous fiber reinforcing material may be configured by bundling a plurality of continuous fibers and twisting the plurality of continuous fiber bundles.

Japan is a leading country in the development of materials for continuous fiber reinforcement. When comparing the continuous fiber reinforcement and the PC steel strand from the viewpoint of the tension fixing device, the biggest difference is that the continuous fiber reinforcement has high strength in the tension direction, but is easily deformed in the transverse direction and has low strength. This is the point. Therefore, as with PC steel strands, wedge or crimp anchoring is not possible. At present, the method of fixing to the continuous fiber reinforcing material by the expansive material sleeve is the most applied fixing method.

When a continuous fiber reinforcing material is applied as a tendon, the fixing method of the fixed end is generally a method of fixing the tendon at the fixed end with an expansive material sleeve and fixing it to the end concrete with a bearing plate. The difference from the PC steel strand is that instead of the wedge+tapered sleeve anchoring method described above, an expansive material sleeve anchoring device is applied.

On the other hand, in the case of applying a continuous fiber reinforcement as a tendon, the method of fixing the tension end is generally to fix the tension on the bearing plate provided at the end of the concrete structure after tensioning on the tension side. applied a lot. In this method, a lock nut is mounted on the outside of the expander sleeve to ultimately transmit tension to the bearing plate through the lock nut. Therefore, the sleeve is threaded on the outside to allow the locknut to function. In addition, a threaded hole into which a tension bar can be screwed is provided on the tension side end in order to tension the expansion material sleeve by the tension jack. Tension is applied to the expansion material sleeve through the tension bar by the center hole jack, and when the predetermined tension is reached, the lock nut attached to the expansion material sleeve in advance is tightened to the bearing plate, and the tension is transmitted to the bearing plate. and tension stress is generated in the concrete structure. After that, the sheath is filled with PC grout, and when the strength is developed, a series of tensioning work is completed.

Problem 1 of the post-tension method using continuous fiber reinforcement is that the length of the concrete structure to be tensioned is limited by the method of fixing the tension force to the bearing plate via the lock nut of the expansion material sleeve. is mentioned. In general, the design stipulates that the tensile strength of the continuous fiber reinforcing material when tensioned should be 70% or less of the guaranteed breaking load. In other words, regardless of the diameter of the continuous fiber reinforcement used, the tensile strain of the continuous fiber reinforcement under tension is 11,000μ to 12,000μ. The amount of elongation ΔL is 110 mm to 120 mm. Inflator sleeves, on the other hand, must be installed at a fixed location on the tendons at the factory. For this reason, the continuous fiber reinforcement is cut to the required length and shipped with the expansion material sleeve installed in place. Since the length of the expansive material sleeve is generally 300 to 400 mm at the longest, the length of the concrete structure may be limited to about 15 m to 20 m in consideration of handling during fixing.

Problem 2 of the post-tension system using continuous fiber reinforcing material is that the outer diameter of the expander sleeve to which the lock nut is generally attached is often larger than the sheath pipe diameter. That is, at the start of tensioning, the end of the expansion material sleeve on the side of the bearing plate is outside the bearing plate. Therefore, when the lock nut is fixed to the bearing plate after tensioning, the expansion sleeve protrudes 300 to 400 mm from the tensioned end. Even in conventional PC steel strand end anchoring, the anchor head may protrude beyond the end. In general, it is not desirable to have members that play an important role in strain management protruding from the strain end. Therefore, it is necessary to install a protective cover device and a rust preventive device for management.

Problem 3 of the post-tension system with continuous fiber reinforcement is that the expansion material sleeve is commercialized by filling it with an expandable cementitious material to control the amount of expansion during the hydration reaction. For this reason, quality control such as temperature and humidity control in the factory is required, and it is limited to factory production. Structures subject to tension are concrete structures. For example, many bridges have a scale of 30m to 50m. error will occur.

Also, in the case of joining precast products, although the precision of the precast products is very high, there is a possibility that errors will be accumulated in the joint part because the work is done on site. Such inaccuracies in the length of the target structure to be strained make it difficult to pre-manufacture the expansion sleeves at the factory. In addition, since conventional PC steel strands are basically fixed by wedges, the tendon is cut on site, and the fixing position can be fixed by wedges at any position. No issues arise.

<Means, configuration, technology and principle of the present invention>
Next, the means, configuration, technique, and problem-solving principle for solving the problems of the present invention will be described.

Currently, prestressing tendons that introduce prestress to concrete by the post-tension method are PC steel strands using piano wire, or continuous wires using carbon fiber, aramid fiber, glass fiber, etc. It is a fiber reinforcement.

Using these prestressing tendons, conventional post-tension fixing methods are based on wedge fixing for PC steel strands and expansion material sleeves for continuous fiber reinforcing materials. In any tendon, it was necessary to have metal anchorage devices at both ends of the prestressed concrete structure. For this reason, the fixing device is expensive, and maintenance costs are required for rust prevention. In contrast to the current situation, the method of fixing tendon according to the present invention has few restrictions on site construction, and can greatly reduce the cost of tensioning devices and tensioning construction.

(Means for solving the problems of the present invention)
A brief reference is made to the tendon anchorage mechanism according to the present invention. A predetermined tension is introduced into the tendon, the tensioned state is maintained by a temporary fixing device, and PC grout (grout material) is placed in the gap between the concrete and the tendon of the concrete structure to which prestress is to be introduced. to fill. Once the PC grout reaches the compressive strength of the present invention, the hydraulic torque wrench or tension jack of the present invention is applied to tighten the lock nut on the tension end or the fixed end to a predetermined rate of change in average bond stress over time. Release tension while maintaining a state of contentment. As a result, it is possible to expect a predetermined degree of adhesion resistance stress generated between the PC grout and the tendon, and it is possible to maintain the fixation effect of the tendon over the entire length of the tendon. As a result, a certain prestress is introduced into the concrete structure.

The feature of the fixing method according to the present invention that is greatly different from the conventional fixing method is that the present invention does not use conventional fixing devices such as wedge fixing and expansive material sleeves. In other words, the post-tensioned prestressed concrete structure according to the present invention does not have a metal fixing device at the tension fixing end or the tension end. As such, there is no need for a rust preventive device or maintenance of the taut end anchor. A pre-tensioning method is available as a tensioning method that does not require a fixing device at the tensioning end or the fixed end. However, the present invention is fundamentally different from the prestressed concrete structure by the pretension method.

In the pretension method, concrete is placed in a state in which tension is applied to tendons in advance, and when the strength of the concrete reaches a predetermined level, the tension is released and prestress is introduced. The pretension method is based on the premise that the PC is manufactured in a PC factory because of its manufacturing process. Therefore, the manufactured product is subject to restrictions on member length and size due to transportation restrictions.

On the other hand, in the post-tension method, it is possible to apply pre-stress to a long bridge at the construction site. It is also possible to perform on-site joining of concrete members to each other by post-tensioning.

The present invention is basically a post-tension tendon fixing method, and can construct a large prestressed concrete structure at a construction site.

[Fixation structure of tendons according to the embodiment of the present invention]
The present invention is a post-tensioning tensioning method. However, although there is an idea that the fixing structure (fixing mechanism) is a pretension system, the tendon fixing structure according to the embodiment of the present invention is basically similar to, but different from, the pretension system. be.

In the present invention, the tension is basically released, and the tension is transmitted to the concrete structure around the tendon by the adhesion resistance force generated between the tendon and the PC grout, resulting in a predetermined prestress. is an invention introduced into the entire concrete structure. Some may argue that the qualitative description given above is a publicly known fact disclosed, for example, in the pretension technique. However, the present invention is not a combination of the known facts so far, but also theoretically constructs a concept that cannot be obtained with the known technology.

(1) Transmission of tension force from tendon to concrete After tensioning the tendon, fill the gap between the tendon and concrete with PC grout (grout material). The mechanism of how tension is transmitted when the force is released is an important point in considering the present invention. FIG. 1 shows the transmission path of the tension from the tendon to the concrete by releasing the tension, which is the fixing mechanism of the tendon according to the embodiment of the present invention. FIG. 1 is a schematic diagram showing a transmission path of tension from a tendon to concrete.

Consider the transmission of tension from the surface of tendon T1 to the concrete body (concrete structure CS). The release force generated by releasing the tension force is
1) First, it is transmitted by the adhesive shear stress generated between the surface of tendon T1 and the surface of PC grout G1 (grout material) in contact with that surface.

2) The adhesion shear stress is generated as the shear stress inside the PC grout material itself inside the thin PC grout G1 layer, and the shear resistance stress is generated in the concrete body (concrete structure CS ).

3) The shearing force from the PC grout G1 is transmitted by adhesion shear resistance on the surfaces in contact with the outer circumference of the PC grout G1 and the inner circumference of the concrete body (concrete structure CS). A sheath pipe S1 may exist between the PC grout G1 and the concrete body (concrete structure CS). In that case, the adhesion shear stress is transmitted to the surfaces in contact with the outer circumference of the PC grout G1 layer and the inner surface of the thin sheath pipe, and the outer circumference of the thin sheath pipe and the inner circumference of the concrete body (concrete structure CS).

(2) Analysis of Factors Affecting Release of Tension Bearing in mind the transmission path of the release force shown above, analyze the factors that affect the release of tension. First, the problem is the internal shear stress generated inside the PC grout layer. Both the shear resistance stress of PC grout and the bond shear resistance stress between PC grout and tendon or concrete depend on the compressive strength of PC grout. In other words, when the tension force is released, the compressive strength of the PC grout must be maintained at a constant reference strength.

Next, the adhesion shear resistance between the surface of the tendon and the surface of the PC grout, and between the outer circumference of the PC grout and the inner circumference of the concrete body, or if there is a sheath pipe, the outer circumference of the PC grout and the inner circumference of the sheath pipe surface-to-surface) to compare the adhesive shear resistance. When comparing the adhesion shear resistance areas of both, the inner peripheral surface area of the outer circumference of the PC grout and the concrete body (or the inner peripheral surface area of the sheath pipe) is compared to the inner peripheral surface area of the tendon surface and the PC grout. is generally about 1.5 to 2.0 times larger. That is, when the tension is released, the adhesion shear resistance stress on the surface of the tendon and the inner peripheral surface of the PC grout becomes critical.

As a factor affecting the bond shear resistance stress, firstly, the compressive strength of the PC grout mentioned above has an effect. At the same time, we think that the time rate of change of the bond shear resistance stress when the tension force is released is a major influencing factor. Specifically, as a case where the time rate of change of the bond shear resistance stress is very large, there is a case where the tendon on which the tension force is acting is cut. Depending on the diameter of the tendon, it is possible to cut and release the tension in 1 to 2 seconds to cut a single tendon. In such a case, the time rate of change of bond shear resistance stress on the tendon surface and PC grout inner peripheral surface, which is critical, becomes very large, and as a result, bond shear impact force is generated. Efficiency is greatly reduced. That is, in such a case, since the bond shear impact force is generated and only a small part of the tension force is shear-transmitted to the concrete body, it becomes impossible to introduce sufficient prestress to the concrete body.

However, in the present invention, by pursuing several quantitative conditions for releasing the tension indicated by the above qualitative explanation, the concrete structure, which is the object of the present invention, is subjected to a predetermined prestress. It became possible to introduce stress, and a post-tension concrete structure was realized.

In order to realize the fixing mechanism according to this embodiment, it is necessary to satisfy the following two conditions.

(Compressive strength of PC grout)
The compressive strength of the PC grout (grout material) is directly related to the strength of the bond shear stress between the tendon and the PC grout, so it is an important condition for establishing the fixing mechanism according to the present embodiment. It is better to express the compressive strength of PC grout not by the absolute value of the compressive strength but by the relative relationship with the design compressive strength of the concrete structure to which prestress is introduced.

Specifically, assuming that the concrete design standard strength of the prestressed concrete structure is f' _ck and the compressive strength of the PC grout when the tension is released is f _gm , it is necessary to satisfy the condition of formula (1). is.
_ƒgm ≧0.5・_f'ck (1)
This conditional expression is basically considered from various verification experiment data.

(Relationship between time rate of change of bond shear stress and bond shear stress)
The tension fixing mechanism according to the present embodiment is basically greatly influenced by the characteristics of the adhesion shear resistance between the tendon and the PC grout. In addition to the compressive strength of PC grout, the time rate of change of the bond shear resistance stress is a major influencing factor for the bond shear resistance characteristics.

As a method of describing the time rate of change of the bond shear resistance stress, it is necessary to obtain a relational expression that can reflect the influence of differences in the diameter of the tensioned material, the magnitude of the tension force, and the strength of the PC grout. Also, one of the factors affecting the fixing performance when the tendon is released is the compressive strength of the PC grout when it is released, and the related performance of the bond shear stress between the tendon and the PC grout.

On the other hand, regarding the degree of adhesion stress acting on the tendon when released, considering the diameter and tension of the tendon, the length 65φ from the tension end or the fixed end is considered as the "fixation length". Define the average bond stress degree (=τ ₆₅ ) resisting on average at that settlement length. The reason why the fixing length was set to 65φ is shown in the specifications for road bridges and commentary (III Concrete bridges and concrete members), published by the Japan Road Association, p101, November 2017, "Pretension As for the members, the fixing length may be 65 times the diameter of the PC steel stranded wire up to φ15.2.

Also, at the end of prestress introduction, 0.7 P _u is adopted as the load immediately after tension as the maximum tension. Here, P _u is the tensile load of the tendon (designated for PC steel strands) or the guaranteed breaking load (designated for continuous fiber reinforcements). Therefore, the average bond stress (τ ₆₅ ) is given by the following equation (2).
τ ₆₅ = 0.7P _u /(65πφ ² ) (2)

Next, the time rate of change (=K ₆₅ ) of the average bond stress degree at the standard fixing length of 65φ at the time of release is defined by the following equation (3).
_K65 = _τ65 / _Tr (3)
where, _Tr = tension release time (sec)

Note that the tension release time _Tr does not represent the total time from the release of the tension to the end. The compressive strain that occurs in concrete structures due to tension release is a function of location and time. The tension force release time _Tr defined by Equation (3) is defined as the release time at the fastest release occurring during a series of release operations.

The rate of change over time of the average bond stress (=K ₆₅ ) indicates the rate of change over time of the average bond stress with respect to the tension force and the release time at the fastest release at the fixing length of 65φ. . For example, when the time rate of change of the average bond stress (=K ₆₅ ) is large, the release time is short, and the bond shear stress for transmitting the tension changes impulsively. Prestress cannot be introduced into the body.

It is known that the adhesion resistance stress acting on reinforcing materials such as reinforcing bars and tendons is proportional to the 2/3 power of concrete compressive strength. In the present embodiment, this relationship is taken into account to construct the relationship between the time rate of change of the average bond stress (=K ₆₅ ) and the PC grout compressive strength: f _gm . That is, as shown in formula (4), the compressive strength of PC grout: f _gm is considered as an influencing factor, and the time rate of change of the average bond stress degree at the standard anchoring length of 65 φ at the time of release (= K ₆₅ ) is an empirical formula. can be expressed.
_{K65≦A×fgm2 /} ³ +B (4)

Equation (4) has experimental constants A and B, which can be obtained from tension release experiments. The resulting empirical formula makes it possible to express the limit state of whether or not it is possible to introduce a predetermined prestress according to the present invention.

[Method for introducing tension force according to the first embodiment]
Next, the anchoring mechanism according to the embodiment of the present invention can achieve, i.e., introduce pre-stress to the concrete structure in a post-tension manner releasing the tension so as to satisfy the basic concept of the present invention. A tension introduction method according to the first embodiment of the present invention will be described.

In the tensioning force introduction method according to the first embodiment, as in the conventional post-tensioning method of tensioning force introduction method, the end faces, which are the sides of the concrete structure CS, are formed in the concrete structure CS, for example, in the lateral direction. A tendon inserting step of inserting the tendon T1 into the insertion hole penetrating through is performed. In the present embodiment, as a method for forming the insertion hole, for example, a method of embedding a polyethylene sheath pipe in the concrete structure CS, a method of embedding a steel sheath pipe and removing it after concrete is placed, and the like. be.

After that, a tendon tightening step is performed in which the tendon T1 inserted in the tendon inserting step is tightened by a tension jack to apply a predetermined tension to the concrete structure CS.

Then, a grout material filling step is performed in which PC grout G1, which is a grout material, is filled around the tendon T1 strained in the tendon tensioning step, and the compressive strength f _gm of the PC grout satisfies the condition of the above formula (1). Take care of yourself.

After the compressive strength f _gm of the PC grout filled in the grout material filling step develops a predetermined compressive strength that satisfies the condition of the above formula (1), the tendon T1 which is a characteristic part of the tension introduction method according to the present embodiment perform a tension release step to release the tension of

FIG. 2 is an explanatory diagram showing a tension release construction method of the tension introduction method according to the first embodiment of the present invention, (a) is a cross-sectional view, and (b) is a view in the direction of arrow A in (a). is. In the tension release step of the tension introduction method according to the first embodiment, as shown in FIG. 2, the hydraulic torque wrench 2 is used to control the release speed of the tension release. As shown in the basic concept, the tension force introduction method according to the present embodiment is efficient by maintaining the time rate of change of the average bond stress degree (=K ₆₅ ) so as to satisfy the above formula (4). can release tension.

The tension force introduction method according to the present embodiment, in which tension force is introduced into the concrete structure CS as a specific tension release method, uses the hydraulic torque wrench 2 to reduce the time rate of change of the desired average bond stress degree ( = K ₆₅ ) can be easily maintained. In addition, the hydraulic torque wrench is a simple operation that requires only turning on a switch, does not require special skills, and is a construction method that can be done by anyone in a short period of time without fail.

As an example of construction, FIG. 2 shows a method of introducing tension according to the present embodiment for releasing the tension at the tension end. The construction example of FIG. 2 shows the tension release construction method at the tension end. Since the same construction method is used for the construction method for the fixed end portion, the explanation is omitted.

(1) Construction step 1 (strand tensioning process)
The construction method from the tendon tensioning step to the grout filling step will be described with reference to FIG. Although FIG. 3 is originally an explanatory diagram of the tension introduction method according to the second embodiment, it is the same as the explanatory diagram of the tendon tensioning process of the first embodiment, so this will be used instead. First, in the tendon tensioning process, as a tensioning method using the tensioning jack 10, the expansion material sleeve 3 (or the mansion sleeve) is connected to the tension bar 11 via the inner screw provided, and the tensioning bar is connected to the tensioning jack 10 of the center hole. The ram chair 4 is tensioned to a predetermined tension force by the reaction force.

After the tensioning jack 10 is used to introduce the desired tension, the locknut 5 on the expander sleeve 3 (for continuous fiber reinforcement) or mansion-type sleeve (for PC steel strands) is turned. By doing so, the reaction force of the tension force is replaced by the ram chair 4. In this state, the tension bar 11 and tension jack 10 can be removed.

(2) Construction step 2 (grout filling process)
In the state where the tension reaction force is taken by the ram chair 4, prestress is introduced into the concrete structure CS. In this state, the gap between the sheath tube S1 and the tendon T1 is filled with the PC grout G1, and after curing, a predetermined compressive strength satisfying the condition of the above formula (1) is obtained.

(3) Construction step 3 (tension release process)
Next, the tension releasing process, which is the construction step for releasing the tension, will be described in detail with reference to FIG. FIG. 2 shows a situation in which the tension reaction force is transmitted to the concrete structure CS via the locknut 5 and the ram chair 4. As shown in FIG. It should be noted that this tension release step is an important point of the tension introduction method according to the embodiment of the present invention. In the tensioning force introduction method according to the present embodiment, first, the hydraulic torque wrench 2 is set so that the reaction force can be taken from the reaction force body 7 provided on the bearing plate 6 in advance. The purpose of setting the reaction force body 7 against the bearing plate 6 is to release the lock nut 5 by actuating the hydraulic torque wrench 2 and releasing the tension acting on the tendon T1. This is because the reaction force from the bearing plate 6 is received as the releasing torque reaction force R1 generated in the hydraulic torque wrench 2 engaged with the .

The resistance force acting when the lock nut 5 is unscrewed is: 1) a frictional force dependent on the tension force acting on the outer thread of the expansion material sleeve 3 and the inner thread of the lock nut 5 due to the tension reaction force; and 2) the frictional force associated with the tension reaction force acting on the contact surface between the upper surface of the ram chair 4 and the lock nut 5 . Therefore, prior to the tensioning operation, a lubricating agent containing, for example, molybdenum is applied in advance to the threaded portion between the expansion material sleeve 3 and the lock nut 5 and the contact surface between the ram chair 4 and the lock nut 5. It is desirable to keep

When setting the hydraulic torque wrench 2, another reaction body 8 is required. The reason for this is that, as explained above, when the lock nut 5 is released, a frictional force that depends on the tension acting on the outer thread of the expansion member sleeve 3 and the inner thread of the lock nut 5 in 1) acts. Therefore, a rotational torque reaction force R2 is generated that rotates the entire expansion material sleeve 3 in the co-rotating direction. This rotational torque reaction force R2 results in twisting the tendon T1. Giving a twist to the tendon T1 damages the tendon, so it is a very dangerous work as tension releasing work. As a countermeasure, it is necessary to remove the reaction force body 7 for preventing the expansion material sleeve 3 from rotating from the bearing plate 6 . As shown in FIG. 2, the direction of the rotational torque reaction force R2 acting on the reaction force 7 is opposite to the direction of the rotational torque reaction force R1 by the hydraulic torque wrench 2. 7 are available.

As an example of how to take the reaction force body 8 to prevent the expansion material sleeve 3 from rotating, an external thread is cut on the outer circumference of the expansion material sleeve 3 and a hard lock nut 9 or the like is attached to it. There is a method of setting a fixed nut to prevent co-rotation, and from this a reaction force is taken by a spanner-shaped reaction force body 8 . As another method, a part of the expansion material sleeve may be provided with two parallel surfaces instead of the hexagonal nut shape, and a wrench may be applied to the two parallel surfaces to transmit the force to the reaction force body 7 .

In the method of introducing tension force according to the present embodiment, a lightweight hydraulic torque wrench 2 with its own weight of about 5 kg is used, so that it is easy to set and remove the device on site. In addition, as a feature of the operation of the hydraulic torque wrench 2, since the rotation angle of the lock nut 5 is automatically stopped after rotating by a certain angle with one switch, the average adhesion stress can be reduced simply by controlling the time interval for pressing the switch. You can easily control the rate of change over time. The tension introduction method according to the present embodiment completes the release of the tension per location in about 1 to 2 minutes.

[Tension introduction method according to the second embodiment]
Next, a tension introduction method according to a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is an explanatory diagram showing a method for releasing tension in the method for introducing tension according to the second embodiment of the present invention. The tensioning force introduction method according to the present embodiment uses the tensioning jack 10 to release the tensioning force so as to satisfy the basic concept presented in the present invention. This is a method of introducing prestress to the concrete structure CS by utilizing the In the first embodiment, the hydraulic torque wrench 2 is used to control the release speed of tension release, but in the second embodiment, the tension jack 10 is used to control the release speed of tension release.

(1) Construction step 1 (strand tensioning process)
The tendon tensioning process of the tensioning force introduction method according to the second embodiment will be described with reference to FIG. First, as a method of tensioning by the tension jack 10, the expansion material sleeve 3 is connected to the tension bar 11 via the external and internal screws provided, and the tension bar 11 is connected to the tension jack 10 of the center hole to the ram chair 4 with a predetermined reaction force. to tense tension.

After the tensioning jack 10 is used to introduce the desired tension, the locknut 5 on the expander sleeve 3 (for continuous fiber reinforcement) or mansion-type sleeve (for PC steel strands) is turned. By doing so, the reaction force of the tension force is replaced by the ram chair 4.

(2) Construction step 2 (grout filling process)
In the state where the tension reaction force is taken by the ram chair 4, prestress is introduced into the concrete structure CS. In this state, the gap between the sheath tube S1 and the tendon T1 is filled with the PC grout G1, and after curing, a predetermined compressive strength satisfying the condition of the above formula (1) is obtained.

(3) Construction step 3 (tension release process)
Next, the tension releasing process, which is the construction step for releasing the tension, will be described in detail. In the tensioning force introduction method according to the second embodiment, the tensioning jack 10 used at the time of tensioning is used without using the hydraulic torque wrench 2 . First, the tension bar 11 is joined to the internal thread provided in the expansive material (mansion) sleeve 3, passed through the center hole of the tension jack 10 used when tensioning, and the tension bar 11 is tightened by the steel wedge/sleeve 13 at the tip of the jack ram 12. fixed.

A load cell 14 provided in advance at the tip of the tension jack 10 applies a tension of 90 to 95% of the tension applied in the tendon tensioning process of construction step 1 to the tendon. If the tension is applied by 95% or more, it becomes an excessive tension that exceeds the construction control value, and as a result, adhesion stress in the opposite direction to tension fixation occurs between the surface of the tendon T1 and the PC grout G1. . Because of this, the permissible bond shear stress may be exceeded, making it impossible to introduce tension.

As a result of the above, the lock nut 5 can be loosened, and the tension force by the tension jack 10 can be released. In the method of introducing tension force according to the second embodiment, it is necessary to control the time rate of change of the average bond stress degree at the time of release. That is, in the tensioning force introducing method according to the present embodiment, the releasing force is gradually applied while controlling the release hydraulic pressure of the tensioning jack 10 .

(4) Construction step 4
By the method of construction step 3, by releasing the tension force under the constraint conditions of the formulas (1) and (4) presented in the present invention, at least the pretension method can be used to achieve a fixation that is equal to or greater than the introduction of prestress. Effectively, prestress introduction becomes possible. As construction step 4, remove all parts prepared for the concrete stressed end shown in FIG. 2 or FIG. The tendon T1 is cut at the tensioned end face of the concrete structure CS, and the concrete ends are surface-treated.

<Full-scale verification experiment>
Next, a full-scale verification experiment conducted to verify whether or not the theoretical development of the post-tension fixing mechanism of the present invention is correct will be described.

(Overview of full-scale experiment)
(1) Experimental specimens and materials used Overview of experimental specimens: 1) Cross-sectional shape × length = B × H × L = 220 × 210 × 2500 mm, 2) tendons = representative continuous fiber reinforcements, Continuous carbon fiber reinforcing material (referred to as CFCC) using carbon fiber, CFCC diameter φ = 17.2 mm, cross-sectional area = 151.1 mm ² , guaranteed breaking load Pu = 385 kN, elastic modulus = 150 kN/mm ² , 3) PE Sheath: inner diameter φ38 polyethylene sheath, 4) PC grout: ultra-low viscosity non-shrinking PC grout, 5) concrete: design standard strength = 60 N/mm ² , 6) concrete strain measurement = strain gauge from tension end (gauge length 60 mm) ) on the concrete surface along the longitudinal direction.

(2) Experimental level 1) Tension release mode: cutting of tendon, release by hydraulic torque wrench, release by jack.
2) Since the tension force was 0.7 Pu=269.5 kN in all cases, the average bond stress (τ ₆₅ )=4.463 N/mm ² (constant).
3) Since the compressive strength of PC grout affects the fixing effect when released, it was varied in the range of f _gm =22.8 to 110 N/mm ² .
4) The compressive strength of concrete was manufactured based on the design standard strength (60 N/mm ² ).

(3) Effective Prestressing Ratio (EPR)
The definition of the prestress effective rate is important for judging whether or not the predetermined prestress is effectively introduced into the post-tensioned concrete structure according to the present invention.
Prestress Effectiveness Ratio (EPR) is defined by equation (5).
EPR= _εp2 / _εp1 ×100 (%) (5)

Here, ε _p1 is the concrete strain immediately before release, and ε _p2 is the concrete strain immediately after release. For example, if the effective rate (EPR) is 100%, it means that the prestressing stress introduced at that position is evaluated as 100% prestressing stress due to the PC grout fixing. ing.

(4) Determination method of average bond stress rate of change over time _K65 from _experimental data defines a rate. However, in actual experimental data, the time change rate _K65 at the time of release is not constant. Therefore, in experimental data processing, the upper limit of the rate of change with time is taken out and data processing is performed so that the threshold is on the safe side. Specifically, the part that changes linearly at the fastest release time is taken out as experimental data, and it is assumed that this state continues from the beginning to the end when the tension force is released. In other words, since this data processing method evaluates the phenomenon on the safe side, it can be considered that the experimental evaluation formula obtained from this result is also evaluated on the safe side.

FIG. 4 shows the typical elapsed time versus concrete strain variation for tension release in cutting mode. Concrete strain was measured at a position 9φ from the tensioned end where strain variation was large. From FIG. 4, the time change rate _K65 in the cutting mode is obtained by the following equation (7).
Rate of change over time K ₆₅ = τ _max / T _max (6)
Here, ε _p is the concrete strain immediately after tensioning, and since τ _max =τ ₆₅ (ε ₂ -ε ₁ )/ε _p , equation (6) finally becomes equation (7).
Time rate of change K ₆₅ = τ ₆₅ (ε ₂ - ε ₁ )/(ε _p ·T _max ) (7)

FIG. 5 shows the typical elapsed time versus concrete strain change for tension release in jack/torque wrench mode. Although it depends on the tension release method, the relationship between elapsed time and concrete strain is generally represented by a line graph. In order to use the experimental evaluation formula on the safe side, assuming that the strain change at the fastest release (ε ₂ - ε ₁ ) continues to the final release strain (ε ₃ ), the time rate of change K ₆₅ in the cutting mode is It is obtained by the following formula (9).
Rate of change over time K ₆₅ = τ _max / T _total (8)
Here, since T _max =T _total (ε ₂ -ε ₁ )/ε ₃ , equation (8) finally becomes
Time rate of change K ₆₅ = τ ₆₅ (ε ₂ - ε ₁ )/(ε ₃ T _max ) (9)

(5) Variation Factors of Experimental Specimen In the full-scale tension release experiment, the experiments were release by cutting = 10 cases, release by hydraulic torque wrench = 6 cases, and release by jack = 8 cases.

Table 1 shows the release of the cutting mode, and Table 2 shows the experimental conditions for releasing the jack/torque wrench mode, the compressive strength of PC grout during the experiment, the elastic modulus of concrete, and other experimental data. Also, from the time history of the strain data closest to the tension end in the last experiment, the fastest release strain and release time were obtained, and finally from these data, the bond stress time change rate at the fastest release was calculated. .

(6) prestress effectiveness rate (EPR) depending on tension release mode
6 and 7 show relationship diagrams of the prestress effective ratio (EPR) to the dimensionless distance from the taut end (L/φ) in the cutting mode and the jack/torque wrench mode. The legends in the figure are the experiment numbers in Tables 1 and 2.

From these figures, it can be seen that in the cutting mode, it is difficult to achieve an effective rate of 95% at a position near the distance of 65φ from the strained end. Among them, Experimental Case 4-9, in which strands of the continuous fiber reinforcing material are selected and cut, shows relatively good EPS. The cutting method in this case is the result of cutting the CFCC strands one by one and increasing the time rate of change (=K ₆₅ ) of the average bond stress as much as possible.

On the other hand, in the release mode of the jack/torque wrench shown in ^FIG . % or more.

A comparison of FIGS. 6 and 7 reveals that sufficient pre-stress effectiveness ratio (EPR) cannot be achieved when tension release is performed in cutting mode. However, it was shown that sufficient prestress effectiveness ratio (EPR) can be achieved over the entire length of the concrete structure when tension release is performed in the jack/torque wrench release mode.

(7) Critical condition of time rate of change of average bond stress (=K ₆₅ ) It is necessary to derive a quantitative critical conditional expression that becomes the limit when releasing the tension force, which is the most important part of the present invention. From the theoretical development so far, using the mortar material with the required strength shown by the formula (1), the time rate of change of the average bond stress (K ₆₅ ) and the compressive strength of the grout material shown by the formula (4) It is considered that sufficient tension is introduced along the entire length of the concrete structure by releasing the tension in a manner that satisfies the relationship to the 2/3 power of .

FIG. 8 shows a plot of the relationship between the 2/3 power of the compressive strength of the mortar material shown in Table 2 and the time rate of change of adhesive stress (K ₆₅ ). From the observation of the experimental data, the limit region where the tension can be fixed is shown by the formula (4), and as the experimental data showing the limit region, A and B are A = 0.0897 and B = -0 .8219. A dashed line shown in FIG. 6 indicates the boundary line.

Also, all data shown in FIG. 9 are plots of the experimental data in Table 1. These experimental data are obtained by releasing the tension force in the cutting mode, and from the results of the prestress effective rate (EPR) at the dimensionless distance 65 shown in FIG. not achievable. The cutting mode experimental data are all above the dashed boundary line of equation (4) shown in FIG. 9, demonstrating the validity of equation (4).

<Applicability of empirical formula depending on the type of tendon>
In verification by a full-scale experiment, a CFCC (Carbon Fiber Composite Cable), in which carbon fiber is applied as a continuous fiber reinforcing material, was applied as a tensile material. As mentioned above, PC steel strands, which have been conventionally applied to tension materials, are also often applied to actual construction. Therefore, it will be examined whether the verification experimental data obtained using CFCC and formulas (1) and (4) are applicable to PC steel strands.

(Strands to be examined)
The guaranteed breaking load Pu of CFCCφ17.2 applied to the verification experiment is 385.0 kN. As a PC steel strand with a tensile load substantially equivalent to this, there is PCφ17.8, and its tensile load Pu is 387.0 kN. A comparison is made of the average bond strength at different strain anchorage lengths when using both upholstery materials.

(1) Physical property values of CFCCφ17.2 and PCφ17.8 CFCCφ17.2: diameter = 17.2 mm, cross-sectional area A _cf = 151.1 mm ² , tension introduction force 0.7 Pu = 269.5 kN
PCφ17.8: diameter = 17.8 mm, cross-sectional area A _PC = 208.4 mm ² , tension introduction force 0.7 Pu = 270.9 kN

(2) Tensile stress of prestressing tendon Tensile stress of CFCCφ17.2 = 1783.6 N/mm ²
Tensile stress of PCφ17.8 = 1300.0 N/mm ²

(Comparison of average bond stress)
At the time of prestress introduction (tension = 0.7 Pu), when the tension anchorage length from the tension end is Nφ, and the average bond stress degree at the tension anchorage length is τ _N , it is obtained by equation (10). be done.
τ _N =0.7 P _u /(Nπφ ² ) (10)

Here, when N=65, Nφ=standard fixing length.
Table 3 shows the average degree of adhesion stress at the time of prestress introduction at the fixing length Nφ of CFCCφ17.2 and PCφ17.8 according to the equation (10).

From the comparison of the average bond stresses shown in Table 3, it can be seen that the average bond stress of PCφ17.8 is about 6% smaller than the average bond stress of CFCCφ17.2. From the comparison results of these two, the average bond stress in the anchoring length is slightly smaller when the tendon is PC steel strand, so the experimental constant obtained from the equation (4) applying the CFCC tendon is the design is on the conservative side.

The fixing structure of the tendon according to the embodiment of the present invention and the tension introducing method according to the first and second embodiments of the present invention have been described above in detail. However, the above-described or illustrated embodiments merely show one embodiment embodied in carrying out the present invention, and the technical scope of the present invention should not be construed to be limited by these. It is.

2: Hydraulic torque wrench 3: Expansion material sleeve 4: Ram chair 5: Lock nut 6: Support plate 7, 8: Reaction body 9: Hard lock nut 10: Tension jack 11: Tension bar 12: Jack ram 13: Steel Wedge/sleeve 14: Load cell CS: Concrete structure (concrete body)
S1: Sheath tube (through hole)
T1: tendon G1: PC grout (grout material)
R1: Rotational torque reaction generated by hydraulic torque wrench R2: Rotational torque reaction generated by co-rotation

Claims (4)

A tension introduction method for introducing prestress to a concrete structure by a post-tension method by releasing the tension of the tendon,
A tendon inserting step of inserting a tendon into an insertion hole formed in the concrete structure and penetrating between end faces;
a tendon tightening step of tensioning the tendon inserted in the tendon inserting step with a tension jack to apply a predetermined tension;
A grout material filling step of filling a grout material around the insertion hole of the tendon tensioned in the tendon tensioning step;
A tension release step of releasing the tension of the tendon after the grout material filled in the grout material filling step exhibits a predetermined compressive strength,
In the tension release step, a prestress is introduced to the concrete structure while controlling the tension release speed of the tendon with a hydraulic torque wrench. The tensioning force introduction method according to claim 1 , wherein the tensioning force releasing step is performed after the compressive strength f _gm of the grout material develops a predetermined compressive strength that satisfies the formula (1).
f _{gm ≥ 0.5 f'ck} ⁽ 1)
Here, f _gm : Compressive strength of grout material (N/mm ² )
f ^' _ck : Design compression standard strength of concrete structure (N/mm ² ) 3. The tension release step is characterized in that the tension release speed of the tendon is released so that the time rate of change _K65 of the average bond stress degree satisfies formula ( 4 ). tension force introduction method.
K65≦ ^0.0897・_fgm2 / _3－0.8219 (4)
Here, K ₆₅ : time rate of change of average bond stress (N/mm ² /sec)
_K65 = _τ65 / _Tr
τ ₆₅ = 0.7P _u /(65πφ ² )
T _r : Release time at the time of the fastest release of tension (sec)
τ ₆₅ : Average adhesion stress (N/mm ² ) at standard fixing length (= 65φ)
P _u : Tensile strength or guaranteed breaking load of tendon (continuous fiber reinforcement) (N)
φ: Diameter of tendon (mm) A method for manufacturing a prestressed concrete structure, wherein a prestress is introduced into the concrete structure by a post-tension method to manufacture the prestressed concrete structure,
A method for manufacturing a prestressed concrete structure, wherein a prestress is introduced into the concrete structure while controlling a releasing speed of the tension of the tendon by the tension introducing method according to claim 2 or 3 .

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