Tendon, pre-stressed concrete structure, and manufacturing method of the same

Abstract

To provide a tendon used in a pre-stressed concrete structure and having improved gripping force of PC steel wires against a concrete body, a pre-stressed concrete structure comprising the tendon, and a manufacturing method of the same.SOLUTION: A tendon 3 embedded in a concrete body of a pre-stressed concrete column comprises a PC steel wire 3a and slippage prevention means provided in a peripheral area of at least one end side of the PC steel wire 3a to prevent the PC steel wire 3a from slipping relative to the concrete body. The slippage prevention means is an additional member 3b which is attached to a surface of the PC steel wire 3a and forms unevenness on the surface of the PC steel wire 3a.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tendon, a prestressed concrete structure, and a manufacturing method thereof. [Background technology]

[0002] In recent years, prestressed concrete columns have been widely used as concrete columns for erecting electric 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 or PC steel wires as PC steel materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-226138 A Summary of the Invention [Problem to be solved by the invention]

[0004] When cracks occur in the concrete body of a prestressed concrete column, hydrogen penetrates the internal reinforcing bars to which a tensile load is applied, and brittle fracture may occur after a certain time has passed. This type of brittle fracture is called delayed fracture, and to prevent this, it is preferable to use PC steel wires as the internal reinforcing bars. However, PC steel wires have crystal faces arranged in the shape of tree rings, making it difficult to create large irregularities on the surface, which makes them slippery against the concrete body. This problem is not limited to prestressed concrete columns, but also exists in prestressed concrete structures with other shapes.

[0005] The present invention has been made against this background, and aims to provide a tendon used in prestressed concrete structures that improves the gripping force of PC steel wires on the concrete body, a prestressed concrete structure equipped with such a tendon, and a manufacturing method thereof. [Means for solving the problem]

[0006] 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, a slippage suppression means provided in a peripheral area on at least one end side of the PC steel wire and suppressing slippage of the PC steel wire relative to the concrete body; Prepare. Effect of the Invention

[0007] According to the present invention, it is possible to provide a tendon used in a prestressed concrete structure and having improved gripping force of PC steel wires on a concrete body, a prestressed concrete structure including the tendon, and a manufacturing method thereof. [Brief description of the drawings]

[0008] [Figure 1] 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. [Diagram 2] FIG. 2 is a diagram showing a configuration of a portion of a tendon according to an embodiment of the present invention. [Diagram 3] 2 is a flowchart showing the flow of a method for manufacturing a prestressed concrete column according to an embodiment of the present invention. [Figure 4] FIG. 13 is a diagram showing a configuration of a portion of a tendon according to a modified example of the present invention. [Diagram 5] FIG. 2 is a photograph of each test specimen used in the tensile test of the examples. [Figure 6]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. [Figure 7] FIG. 2 is a photograph of a universal testing machine used in the tensile tests of the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a tension member, a prestressed concrete structure, and a manufacturing method thereof according to an embodiment of the present invention will be described in detail with reference to the drawings. In each drawing, the same or equivalent parts are given the same reference numerals. In the embodiment, a case where a prestressed concrete column is used as a prestressed concrete structure will be described as an example.

[0010] 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 contract 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 the tensile load acting on the concrete body.

[0011] As shown in FIG. 1(a), a prestressed concrete column 1 includes a concrete body 2 formed from hardened concrete, and is formed into a truncated cone shape that tapers gradually from the butt end to the tail end. Concrete is a material made by mixing 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 may be cement that does not contain fine aggregate.

[0012] 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 tendons 3, non-tensioning members 4, and spiral reinforcement bars (not shown) embedded inside the concrete body 2. The numbers of tendons 3, non-tensioning members 4, and spiral reinforcement bars may be appropriately selected according to the prestressed concrete specifications.

[0013] The tendons 3 extend longitudinally over the entire length of the prestressed concrete column 1, are embedded in the concrete under tension, and are subjected to a compressive load on the concrete body 2 by removing the tension after the concrete has hardened. The non-tensioning 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 tendons 3 and non-tensioning members 4 at a certain pitch, preventing the concrete body 2 from being damaged by shear loads.

[0014] As shown in Fig. 2, the tendon 3 includes a PC steel wire 3a and additional members 3b that are provided on at least both end peripheral regions of the PC steel wire 3a and cause unevenness on the surface of the tendon 3. The PC steel wire 3a is made of high-strength steel and is obtained by rolling, for example, cold rolling. The PC steel wire 3a has a uniform crystal orientation such that the crystal planes are in the shape of tree rings, and therefore has the advantage that delayed fracture is less likely to occur than in a PC steel bar obtained by subjecting a steel bar to quenching and tempering treatment.

[0015] Delayed fracture is a brittle fracture that occurs suddenly after a certain time has passed due to hydrogen penetrating into minute 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 from locally brittle areas, whereas PC steel wires 3a are made of pearlitic steel with a layered structure, so hydrogen penetrates evenly within the layers and cracks do not easily propagate.

[0016] The additional member 3b is an example of a slippage suppression means that increases the frictional resistance against the concrete body 2 and suppresses slippage of the PC steel wire 3a against the concrete body 2. The deeper the unevenness on the surface of the tendon 3, the greater the gripping force on the concrete body 2. The depth of the unevenness caused by adding the additional member 3b to the surface of the PC steel wire 3a is preferably at least 0.3 mm or more.

[0017] The additional member 3b is, for example, a wire wound in a spiral shape on the surface of the tendon 3. The wire is an example of a rope that is attached in a spirally wound 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 on the surface of the PC steel wire 3a and attached thereto. In salt-resistant concrete columns, after the coating at both ends of the coated PC steel wire (coated steel wire) is stripped, 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 thereon.

[0018] In addition, because the PC steel wire 3a is very hard, it is difficult to weld a metal member to the PC steel wire 3a unless it is subjected to a very high temperature. Even if a metal member can be welded to the PC steel wire 3a, the PC steel wire 3a is thermally affected by the welding, which reduces the strength of the PC steel wire 3a and makes it more likely to break. For this reason, when attaching wire to the surface of the PC steel wire 3a, it is preferable to use a means that is not affected by heat, such as an adhesive.

[0019] 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 stretched into a long, thin thread-like material, 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.

[0020] The region where the additional members 3b are provided is the peripheral region on both end sides of the tendon 3. This is because it is at both end portions of the tendon 3 that slippage is likely to occur in a prestressed concrete column. The length of the region where the additional members 3b are provided is, for example, within a range of 10 cm to 50 cm. The additional members 3b may be provided in a peripheral region a certain length away from the tip and base end faces of the tendon 3. For example, the additional members 3b may be provided in a range from a position 10 cm away to a position 50 cm away from the tip and base end faces of the tendon 3. This is because fixing plates of an anchoring device are attached to the end and butt ends of the tendon 3, respectively, during the manufacture of the prestressed concrete column.

[0021] 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, improving the gripping force on the concrete body 2. This makes it possible to reduce the number of reinforcements by using PC steel wires 3a with a large diameter as the tendons 3, facilitating the manufacture of the prestressed concrete column 1. In addition, an anti-rust effect can be obtained by coating the surface of the tendons 3 with an adhesive.

[0022] Below, we will explain why improving the holding strength of 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 wires 3a and the holding strength of the PC steel wires 3a to the concrete body 2. The allowable tension of the PC steel wires 3a is proportional to the cross-sectional area of ​​the PC steel wires 3a, and the holding strength of the PC steel wires 3a to the concrete body 2 is proportional to the surface area of ​​the PC steel wires 3a. For this reason, even if the allowable tension of the PC steel wires 3a is doubled, the holding strength of the concrete body 2 only becomes √2 times.

[0023] 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 as thick as possible. However, with thick PC steel wires, a problem occurs in that the PC steel wire 3a slips 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 this inconvenience during manufacturing, it is necessary to use thin PC steel wires, and in such a case, if an attempt is made to secure the surface area of ​​the PC steel wire 3a, an excessive number of reinforcements is required from the viewpoint of the allowable tension. If a slip prevention means is provided on the surface of the PC steel wire 3a, the gripping force against the concrete body 2 is dramatically increased, so that even if the surface area of ​​the PC steel wire 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 wire 3a.

[0024] 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.

[0025] (Manufacturing 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. The following describes an example in which the prestressed concrete column 1 is manufactured by centrifugal molding.

[0026] First, the reinforcing material consisting of the tendons 3, non-tensioning members 4, and spiral bars is assembled into a cage shape (Step S1). In this process, the anchoring plates of the anchoring device that applies tension to both ends of the tendons 3 are fixed. The tendons 3 are provided with additional members 3b on the circumferential surface area on both ends of the PC steel wire 3a, and the additional members 3b are provided on the circumferential surface area a certain length away from the tip and base end faces of the tendons 3, so that the anchoring plates can be fixed to both ends of the PC steel wire 3a.

[0027] 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 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.

[0028] Next, a traction device is attached to the butt-side anchor plate, and tension is applied to the tension member 3 by pulling the butt-side anchor plate away from the tail-side anchor plate (step S3). Each anchor plate is attached to both ends of the formwork, respectively, and the tension member 3 can be maintained in a state in which tension is applied.

[0029] 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 in the formwork (step S4). At this time, the concrete flows in so as to fill the gap between the PC steel wires 3a and the additional members 3b.

[0030] Next, steam curing is performed on the concrete having a circular cross section produced in step S4 (step S5), whereby the concrete body 2 is formed with the reinforcing material embedded therein.

[0031] Next, prestress is introduced into the concrete body 2 formed by the tensioned tendon 3 by removing the anchor plates of the anchoring device from both ends of the tendon 3 (step S6). Since additional members 3b are provided on the peripheral areas on both ends of the tendon 3, the additional members 3b bite into the concrete body 2, suppressing slippage of the tendon 3 relative to the concrete body 2.

[0032] Next, demolding is performed by removing the formwork 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.

[0033] As described above, the tendon 3 according to the embodiment includes the PC steel wires 3a and the additional members 3b that are provided on the peripheral areas of at least both ends of the PC steel wires 3a and that suppress slippage of the PC steel wires 3a relative to the concrete body 2. This can improve the gripping force of the PC steel wires 3a relative to the concrete body 2. This can further suppress cracks in the concrete body 2 when a bending load is applied to the prestressed concrete column 1.

[0034] The present invention is not limited to the above-described embodiment, and the following modifications are possible.

[0035] (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.

[0036] In the above embodiment, the surface of the PC steel wire 3a is coated with a metal adhesive and a wire is wound spirally on top of the adhesive to provide anti-slip means, but the present invention is not limited to this. For example, instead of the wire, a rope that is resistant to corrosion by alkali, such as a rope made of fiber-reinforced plastic, may be wound.

[0037] In the above embodiment, the additional member 3b made of a spiral wire is bonded to the PC steel wire 3a as the slippage suppression means, but the present invention is not limited to this. For example, the additional member 3b may be a ring-shaped member, and a plurality of ring-shaped members may be aligned and bonded to the PC steel wire 3a in the longitudinal direction. Also, as shown in FIG. 4, granular material 3c may be used as the slippage suppression means. The granular material 3c may be composed of, for example, sand or gravel. To bond 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 the adhesive, or the PC steel wire 3a may be rolled in a container containing the granular material 3c.

[0038] In the above embodiment, the tension members 3, non-tension members 4, and spiral reinforcement members are used as reinforcing members, 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.

[0039] 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, the tendon 3 may be applied to a concrete structure other than a prestressed concrete column, such as a bridge pier, abutment, or girder of a bridge.

[0040] The above-mentioned embodiments are merely 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 modifications can be freely combined. In addition, inventions equivalent to the inventions described in the claims are also included in the present invention. EXAMPLES

[0041] The present invention will be specifically described below with reference to examples, although the present invention is not limited to these examples.

[0042] In the examples, specimens of tendons used in prestressed concrete columns were prepared, and tensile tests were performed on each specimen. Specimens A to H used in the tensile tests are shown in Fig. 5. Note that in Fig. 5, two PC steel wires are arranged side by side and appear to be connected to each other, but the two PC steel wires are only temporarily fixed by bands or fixtures for the purpose of photography.

[0043] Specimens A, B, E, and F have a spirally wound wire adhered to the surface of a PC steel wire with adhesive. Specimens A and B and specimens E and F have the same wire diameter. Specimen D has gravel adhered to the surface of a 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 wound around the surface of a PC steel wire without the use of adhesive.

[0044] 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. At this time, the two PC steel wires were arranged so that the ends facing each other were exposed from the concrete. 28 days after the concrete was poured, it was confirmed that the concrete had 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 method) was also shown.

[0045] 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 wires by the large amount of adhesive, resulting in increased resistance. As evidence of this, specimens G and H, which were wrapped with guy wires without adhesive, only achieved a load-bearing capacity not much different from that of specimen C, which was a normal product. [Explanation of symbols]

[0046] 1 Prestressed concrete columns 2. Concrete body 3 Tensors 3a PC steel wire 3b Additional parts 3c Granules

Claims

1. A tendon embedded in a concrete body of a prestressed concrete structure, PC steel wire, A slippage suppression means is provided in a peripheral area of ​​at least one end side of the PC steel wire and suppresses slippage of the PC steel wire relative to the concrete body; Tension material provided.

2. The slip prevention means is an additional member attached to the surface of the PC steel wire and forming unevenness on the surface of the PC steel wire. The tendon according to claim 1 .

3. The additional member is a rope that is spirally wound around the surface of the PC steel wire and adhered thereto. The tendon according to claim 2.

4. The slip prevention means is a granular material adhered to the surface of the PC steel wire. The tendon according to claim 1 .

5. 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:

6. 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:

Images