JP7653476B2 - Tendon, prestressed concrete structure and manufacturing method thereof - Google Patents

Description

The present invention relates to a tendon, a prestressed concrete structure, and a manufacturing method thereof.

In recent years, prestressed concrete columns have been widely used as concrete columns for erecting power lines, communication lines, etc. In prestressed concrete columns, PC (Prestressed Concrete) steel materials made of high-strength steel are used as internal reinforcing bars to ensure tensile strength. For example, Patent Document 1 discloses the use of PC steel bars and PC steel wires as PC steel materials.

JP 2011-226138 A

When cracks occur in the concrete body of a prestressed concrete column, hydrogen can penetrate the internal reinforcing bars to which a tensile load is applied, and brittle fracture can occur after a certain amount of time has passed. This type of brittle fracture is called delayed fracture, and to prevent this, it is preferable to use PC steel wire as the internal reinforcing bars. However, because the crystal faces of PC steel wire are arranged in the shape of tree rings, it is difficult to create large irregularities on the surface, which poses the problem that the wire is prone to slipping against the concrete body. This problem is not limited to prestressed concrete columns, but also exists in prestressed concrete structures of other shapes.

The present invention was made based on this background, and aims to provide a tension member used in a prestressed concrete structure that improves the gripping force of the PC steel wire on the concrete body, a prestressed concrete structure equipped with the tension member, and a manufacturing method thereof.

In order to achieve the above object, the tendon according to the present invention comprises:
A tendon embedded in a concrete body of a prestressed concrete structure,
PC steel wire made of high strength steel ;
a wire provided in a peripheral region on at least one end side of the PC steel wire, wound in a spiral shape on the surface of the PC steel wire and bonded with an adhesive, the wire forming irregularities on the surface of the PC steel wire so as to suppress slippage of the PC steel wire relative to the concrete body;
Prepare.

The present invention provides a tension member used in a prestressed concrete structure that improves the gripping force of the PC steel wire against the concrete body, a prestressed concrete structure that includes the tension member, and a method for manufacturing the same.

FIG. 1A is a front view showing the configuration of a prestressed concrete column according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of the prestressed concrete column of FIG. 1A taken along line A-A. FIG. 2 is a diagram showing a configuration of a portion of a tendon according to an embodiment of the present invention. 2 is a flowchart showing the flow of a method for manufacturing a prestressed concrete column according to an embodiment of the present invention. FIG. 13 is a diagram showing a configuration of a portion of a tendon according to a modified example of the present invention. FIG. 2 is a photograph of each test specimen used in the tensile test of the examples. FIG. 2 is a schematic diagram showing a state in which a test specimen is embedded in concrete in a tensile test of the embodiment. FIG. 2 is a photograph of a universal testing machine used in the tensile tests of the examples.

The following describes in detail the tendons, prestressed concrete structures, and manufacturing methods thereof according to the embodiments of the present invention with reference to the drawings. In each drawing, the same or equivalent parts are given the same reference numerals. In the embodiments, the case where a prestressed concrete column is used as the prestressed concrete structure will be described as an example.

The prestressed concrete column according to the embodiment is a concrete column in which a compressive load is applied to a long concrete body by utilizing the force of the embedded tendons trying to shrink while tension (tensile force) is applied to the concrete body. Here, "long" means that the cylindrical object is longer in the longitudinal direction than in the radial direction. In the prestressed concrete column according to the embodiment, the load-bearing capacity is improved by canceling out the tensile load acting on the concrete body.

As shown in FIG. 1(a), a prestressed concrete column 1 has a concrete body 2 formed from hardened concrete, and is formed into a truncated cone shape that gradually tapers from the base end to the end end. Concrete is a material that is a mixture of aggregate, coarse bone, water, cement, etc. The aggregate contains at least one of coarse aggregate such as gravel and fine aggregate such as sand. The concrete may be mortar that does not contain coarse aggregate, or cement that does not contain fine aggregate.

As shown in FIG. 1(b), a cavity extending in the longitudinal direction is formed inside the concrete body 2, and its radial cross section is formed in a circular ring shape. Each prestressed concrete column 1 includes tension members 3, non-tension members 4, and spiral reinforcement (not shown) embedded inside the concrete body 2. The numbers of tension members 3, non-tension members 4, and spiral reinforcement may be appropriately selected according to the prestressed concrete specifications.

The tension members 3 extend longitudinally over the entire length of the prestressed concrete column 1 and are embedded in the concrete under tension; the tension is removed after the concrete hardens, applying a compressive load to the concrete body 2. The non-tension members 4 are also called auxiliary reinforcements and are embedded in the concrete body 2 under no tension. The helical reinforcements are also called spiral reinforcements and are embedded in the concrete body 2 wrapped around the tension members 3 and non-tension members 4 at a fixed pitch, preventing the concrete body 2 from being damaged by shear loads.

As shown in FIG. 2, the tension member 3 comprises a PC steel wire 3a and additional members 3b that are provided on at least both ends of the peripheral area of the PC steel wire 3a and create unevenness on the surface of the tension member 3. The PC steel wire 3a is made of high-strength steel and is obtained by rolling, for example, cold rolling. The crystal orientation of the PC steel wire 3a is aligned so that the crystal planes are in the shape of annual rings, and therefore has the advantage that delayed fracture is less likely to occur compared to PC steel bars obtained by subjecting steel bars to quenching and tempering treatments.

Delayed fracture is a type of brittle fracture that occurs suddenly after a certain amount of time has passed, when hydrogen penetrates tiny voids in steel material to which a certain tensile load is applied. PC steel bars are made of martensitic steel, so hydrogen penetrates unevenly and fractures occur at locally brittle areas, whereas PC steel wire 3a is made of pearlitic steel with a layered structure, so hydrogen penetrates evenly within the layers and cracks are less likely to propagate.

The additional member 3b is an example of a slippage prevention means that increases the frictional resistance against the concrete body 2 and prevents the PC steel wire 3a from slipping against the concrete body 2. The deeper the unevenness of the surface of the tendon 3, the greater the gripping force on the concrete body 2. It is preferable that the depth of the unevenness caused by adding the additional member 3b to the surface of the PC steel wire 3a is at least 0.3 mm.

The additional member 3b is, for example, a wire wound in a spiral shape on the surface of the tension member 3. The wire is an example of a rope that is attached in a spirally wrapped state to the surface of the PC steel wire 3a. A metal adhesive may be applied to the surface of the PC steel wire 3a, and in that state, the wire may be wound in a spiral shape and attached to the surface of the PC steel wire 3a. In salt-resistant concrete columns, after removing the coating from both ends of the coated PC steel wire (coated steel wire), a metal adhesive may be applied to the surface of the PC steel wire in a similar manner, and the additional member 3b may be attached on top of the coating.

In addition, because the PC steel wire 3a is very hard, it is difficult to weld metal members to the PC steel wire 3a unless it is subjected to extremely high temperatures. Even if it is possible to weld metal members to the PC steel wire 3a, the PC steel wire 3a is subject to thermal effects from the welding, reducing the strength of the PC steel wire 3a and making it more susceptible to breakage. For this reason, when attaching wire to the surface of the PC steel wire 3a, it is preferable to use a means that does not have a thermal effect, such as an adhesive.

The metal adhesive is an adhesive capable of bonding metals together, for example a two-liquid mixed acrylic resin adhesive. The wire is a metal material stretched into a long, thin thread shape, and is made of, for example, aluminum, iron, copper, or stainless steel, and is preferably made of the same or equivalent material as the PC steel wire 3a. The diameter of the wire is preferably, for example, 3 mm or more. The surface of the wire may be plated with, for example, zinc.

The area where the additional member 3b is provided is the peripheral area on both ends of the tendon 3. This is because the tendon 3 is prone to slip at both ends of the tendon 3 in prestressed concrete columns. The length of the area where the additional member 3b is provided is, for example, within a range of 10 cm to 50 cm. The additional member 3b may be provided in a peripheral area a certain length away from the tip and base ends of the tendon 3. For example, it may be provided in a range from 10 cm away to 50 cm away from the tip and base ends of the tendon 3. This is because the fixing plates of the fixing device are attached to the end and butt ends of the tendon 3 when the prestressed concrete column is manufactured.

When the additional member 3b is provided to the PC steel wire 3a, the bending load that the PC steel wire 3a can withstand increases by about three to eight times compared to when the additional member 3b is not provided to the PC steel wire 3a, and the gripping force on the concrete body 2 is improved. This makes it possible to use a PC steel wire 3a with a large diameter as the tendon 3 and reduce the number of reinforcements, making it easier to manufacture the prestressed concrete column 1. In addition, coating the surface of the tendon 3 with an adhesive also provides an anti-rust effect.

Below, we will explain why improving the gripping force on the concrete body 2 makes it possible to reduce the number of reinforcing bars in the tendon 3. To ensure the strength of the prestressed concrete column 1, it is necessary to ensure both the allowable tension of the PC steel wire 3a and the gripping force of the PC steel wire 3a on the concrete body 2. The allowable tension of the PC steel wire 3a is proportional to the cross-sectional area of the PC steel wire 3a, and the gripping force on the concrete body 2 is proportional to the surface area of the PC steel wire 3a. For this reason, even if the allowable tension of the PC steel wire 3a is doubled, the gripping force on the concrete body 2 will only be √2 times as large.

In order for the PC steel wire 3a to obtain a gripping force against the concrete body 2, it is necessary to secure the surface area of the PC steel wire 3a, and for this purpose, it is preferable to use PC steel wires that are as thick as possible. However, with thick PC steel wires, problems occur in that the PC steel wires 3a slip against the concrete body 2 when the prestress is converted in the manufacturing process of the prestressed concrete column 1. For this reason, in order to avoid inconveniences during manufacturing, it is necessary to use thin PC steel wires, and in such cases, if an attempt is made to secure the surface area of the PC steel wires 3a, an excessive number of reinforcements is required from the perspective of the allowable tension. If a slip prevention means is provided on the surface of the PC steel wires 3a, the gripping force against the concrete body 2 increases dramatically, so that even if the surface area of the PC steel wires 3a is reduced, the necessary gripping force against the concrete body 2 can be secured, and as a result, the number of reinforcements can be reduced while securing the allowable tension of the PC steel wires 3a.

The same problem occurs in salt-resistant concrete columns because the coated steel wire also slips against the concrete body 2. However, this problem can be solved by removing the coating from the coated steel wire and providing an anti-slip means on the surface of the PC steel wire.
The above is the structure of the prestressed concrete column 1.

(Production method)
Next, a method for manufacturing the prestressed concrete column 1 according to the embodiment will be described with reference to the flow chart of Fig. 3. Hereinafter, the method for manufacturing the prestressed concrete column 1 by the centrifugal molding method will be described as an example.

First, the reinforcing material consisting of the tension members 3, non-tension members 4, and spiral muscles is assembled into a cage shape (step S1). In this process, the fixing plates of the fixing device that applies tension to both ends of the tension members 3 are fixed. The tension members 3 are provided with additional members 3b on the peripheral area on both ends of the PC steel wire 3a, and the additional members 3b are provided on the peripheral area a certain length away from the tip and base end faces of the tension members 3, so that the fixing plates can be fixed to both ends of the PC steel wire 3a.

Next, a formwork for concrete molding is assembled with the cage of reinforcing material assembled in step S1 housed inside (step S2). The formwork, for example, includes a pair of formwork pieces that are separable from each other and opposed in the longitudinal direction, and the cage of reinforcing material can be housed inside one of the formwork pieces by placing the cage of reinforcing material inside one of the formwork pieces and covering the other formwork piece with the cage of reinforcing material.

Next, a traction device is attached to the butt-side fixing plate, and tension is applied to the tension member 3 by pulling the butt-side fixing plate away from the tail-side fixing plate (step S3). Each fixing plate is attached to both ends of the formwork, and tension is maintained in the tension member 3.

Next, concrete is poured into the formwork while tension is being applied to the tendons 3, and the formwork is rotated around an axis extending in the longitudinal direction by a centrifuge connected to the formwork, thereby centrifugal compacting the concrete within the formwork (step S4). At this time, the concrete flows in to fill the gap between the PC steel wires 3a and the additional members 3b.

Next, steam curing is performed on the concrete with a circular cross section produced in step S4 (step S5). This results in the concrete body 2 being formed with the reinforcing material embedded in it.

Next, the fixing plates of the fixing device are removed from both ends of the tension member 3 to introduce prestress into the concrete body 2 formed by the tension member 3 (step S6). Since additional members 3b are provided on the peripheral areas on both ends of the tension member 3, the additional members 3b bite into the concrete body 2, suppressing slippage of the tension member 3 relative to the concrete body 2.

Next, the formwork is removed from the concrete body 2 (step S7), and all the steps are completed.
The above is the flow of the manufacturing method for the prestressed concrete column 1.

As described above, the tension member 3 according to the embodiment comprises a PC steel wire 3a and additional members 3b that are provided on at least both ends of the peripheral area of the PC steel wire 3a and suppress slippage of the PC steel wire 3a relative to the concrete body 2. This improves the gripping force of the PC steel wire 3a relative to the concrete body 2. This further suppresses cracking of the concrete body 2 when a bending load is applied to the prestressed concrete column 1.

The present invention is not limited to the above embodiment, and the following modifications are also possible.

(Modification)
In the above embodiment, the additional members 3b are provided on the peripheral areas of both ends of the PC steel wire 3a, but the present invention is not limited to this. The additional members 3b may be provided only on the peripheral area of one end of the PC steel wire 3a, or may be provided on the entire peripheral surface of the PC steel wire 3a. The one end of the PC steel wire 3a may be either the end side or the butt side.

In the above embodiment, a metal adhesive is applied to the surface of the PC steel wire 3a to provide anti-slip means, and wire is wound in a spiral shape on top of the adhesive, but the present invention is not limited to this. For example, instead of wire, a rope that is resistant to corrosion by alkali, such as a rope made of fiber-reinforced plastic, may be wound.

In the above embodiment, the additional member 3b made of a spiral wire is adhered to the PC steel wire 3a as a slip prevention means, but the present invention is not limited to this. For example, the additional member 3b may be a ring-shaped member, and multiple ring-shaped members may be aligned and adhered in the longitudinal direction of the PC steel wire 3a. Also, as shown in FIG. 4, granular material 3c may be used as a slip prevention means. The granular material 3c may be composed of, for example, sand or gravel. To adhere the granular material 3c to the surface of the PC steel wire 3a, a metal adhesive may be applied to the surface of the PC steel wire 3a, and the granular material 3c may be sprinkled on top of it, or the PC steel wire 3a may be rolled in a container containing the granular material 3c.

In the above embodiment, the tension members 3, non-tension members 4, and spiral reinforcement are used as reinforcing materials, but the present invention is not limited to this. For example, if the prestressed concrete column 1 does not require high strength, the non-tension members 4 may be omitted. Also, the non-tension members 4 on the butt end side may be left as they are, and the non-tension members 4 on the tail end side may be omitted.

In the above embodiment, the tendon 3 is applied to a prestressed concrete column, but the present invention is not limited to this. For example, it may be applied to concrete structures other than prestressed concrete columns, such as bridge piers, abutments, and bridge girders.

The above embodiments are examples, and the present invention is not limited to these, and various embodiments are possible without departing from the spirit of the invention described in the claims. The components described in the embodiments and variations can be freely combined. Furthermore, inventions equivalent to the inventions described in the claims are also included in the present invention.

The present invention will be specifically explained below with reference to examples. However, the present invention is not limited to these examples.

In the examples, specimens of tendons used in prestressed concrete columns were created, and tensile tests were conducted on each specimen. Specimens A to H used in the tensile tests are shown in Figure 5. Note that in Figure 5, two PC steel wires appear to be lined up and connected to each other, but they are only temporarily secured by bands and fixtures for the purpose of photographing.

Specimens A, B, E, and F have a spirally wound wire attached to the surface of the PC steel wire with adhesive. The diameter of the wire is the same for specimens A and B and specimens E and F. Specimen D has gravel attached to the surface of the PC steel wire with adhesive. Metallock (registered trademark) manufactured by Cemedine Co., Ltd. was used as the adhesive for all specimens. Specimen C is a PC steel wire (normal product) with no additional components. Specimens G and H have a pole support wire wrapped around the surface of the PC steel wire without the use of adhesive.

The specific test procedure is as follows. First, as shown in Figure 6, two PC steel wires were set in parallel in a plastic formwork pipe, and concrete was poured into the formwork pipe and allowed to harden. The two PC steel wires were arranged so that the ends facing each other were exposed from the concrete. 28 days after pouring, the concrete was confirmed to have hardened, and a tensile test was performed on each of the test specimens A to H. In the tensile test, each of the test specimens A to H was attached to the universal testing device shown in Figure 7, and the two PC steel wires arranged in parallel were pulled away from each other to measure the load-bearing capacity of each of the test specimens A to H. The bond strength was calculated by dividing the bond tensile strength by the surface area, and the value calculated according to the Japan Society of Civil Engineers' Standard Specifications for Concrete (Japan Society of Civil Engineers formula) was also shown.

As a result, as shown in Figure 5, it was found that specimens A, B, E, and F, which were wrapped with wire, and specimen D, which was coated with gravel, had a higher load-bearing capacity (adhesive tensile strength) than specimen C, which was a normal product. In addition, when specimens A and B, which were wrapped with wire of the same diameter, were compared with specimens E and F, it was found that the load-bearing capacity was higher when a larger amount of adhesive was used. This was not due to the amount of adhesive itself, but rather to the fact that the components were firmly fixed to the PC steel wire by the large amount of adhesive, resulting in increased resistance. As evidence of this, specimens G and H, which were wrapped with support wires without adhesive, only achieved a load-bearing capacity not much different from that of specimen C, which was a normal product.

1 Prestressed concrete column 2 Concrete body 3 Tendon 3a PC steel wire 3b Additional member 3c Granular material

Claims (6)

A tendon embedded in a concrete body of a prestressed concrete structure,
PC steel wire made of high strength steel ;
a wire provided in a peripheral region on at least one end side of the PC steel wire, wound in a spiral shape on the surface of the PC steel wire and bonded with an adhesive, the wire forming irregularities on the surface of the PC steel wire so as to suppress slippage of the PC steel wire relative to the concrete body;
Tension material provided. The wire is attached only to the peripheral areas on both ends of the PC steel wire.
The tendon according to claim 1 . The wire is a wire,
The adhesive is a metal adhesive.
The tendon according to claim 1 . The metal adhesive is a two-part acrylic resin adhesive.
The tendon according to claim 3. A concrete body,
The tendon according to any one of claims 1 to 4, which is embedded inside the concrete body and applies a compressive load to the concrete body;
A prestressed concrete structure comprising: placing a tendon according to any one of claims 1 to 4 in a formwork;
applying tension to the tendons disposed within the formwork;
A step of pouring concrete into the formwork while applying tension to the tendons and allowing the concrete to harden;
A method for manufacturing a prestressed concrete structure comprising:

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