Reinforced concrete structures with FRP hoops

Abstract

To provide a reinforcement concrete structure using FRP hoop reinforcements with workability and economical efficiency better than conventional ones.SOLUTION: A reinforcement structure using FRP hoop reinforcements to solve a problem of the present invention comprises main reinforcements 2, FRP hoop reinforcements 1 surrounding the main reinforcement 2, and concrete covering the main reinforcement 2 and the FRP reinforcements 1, wherein the FRP hoop reinforcements 1 are integrally formed without any seams in an annular shape and arranged with specific intervals in an axial direction of the main reinforcement 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to reinforced concrete structures constructed using FRP (fiber reinforced plastic) hoops. [Background technology]

[0002] In recent years, various methods have been proposed to use high-strength fiber-reinforced plastics as an alternative material to conventional reinforcing bars. For example, Patent Document 1 discloses a structure for constructing a concrete slab using CFRP (carbon fiber-reinforced plastic) reinforcing bars, and Patent Document 2 discloses an invention for shield tunnel segments that achieves both machinability and strength by using segment reinforcing materials made of carbon fibers or the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 2689843 [Patent Document 2] Patent No. 5162125 Summary of the Invention [Problem to be solved by the invention]

[0004] However, although conventional technology has made it possible to replace some reinforcement with fiber-reinforced plastics, there have been insufficient attempts to do so, particularly with hoop reinforcement. In addition, while fiber-reinforced plastics are commercialized and widely used in various industries, the effective use of these by-products has not been fully studied.

[0005] In view of the above-mentioned various problems, an object of the present invention is to provide a reinforced concrete structure using FRP hoops that is easier to construct and more economical than conventional structures. [Means for solving the problem]

[0006] (1) A concrete structure reinforced with FRP hoops, comprising: main bars; FRP hoops surrounding the main bars; and concrete covering the main bars and the FRP hoops, wherein the FRP hoops are formed seamlessly and continuously in a circular ring shape and are arranged in the axial direction of the main bars.

[0007] According to the invention related to (1) above, by using FRP hoops formed continuously and integrally in a circular ring shape without joints instead of conventional hoops made from processed rebars, it is possible to significantly improve the deformation performance of concrete structures. In addition, due to the high strength, it is possible to reduce the amount of conventional shear reinforcement and lateral restraint reinforcement, and it is also possible to improve workability.

[0008] (2) The FRP hoop is a reinforced concrete structure using FRP hoop as described in (1) above, which has a plurality of dowel holes penetrating from the outer peripheral surface to the inner peripheral surface, and a concrete dowel is formed by the dowel holes.

[0009] According to the invention related to (2) above, a concrete dowel is formed through the dowel hole formed in the FRP hoop, making it possible to ensure extremely high adhesive strength.

[0010] (3) The FRP hoop is an FRP hoop reinforced concrete structure described in (1) or (2) above, which is constructed by overlapping one FRP hoop with the other FRP hoop through interlocking reinforcement.

[0011] According to the invention related to (3) above, by overlapping one FRP hoop with the other FRP hoop to form an interlocking arrangement, it is possible to use FRP hoops of a certain size and apply them to structures having cross-sections of any size.

[0012] (4) The FRP hoop is a reinforced concrete structure using FRP hoops as described in any one of (1) to (3) above, which has a liner layer and an FRP layer covering the outer periphery of the liner layer.

[0013] According to the invention related to the above item (4), it is possible to easily and efficiently form an FRP layer by winding a fiber bundle around the liner layer.

[0014] (5) A concrete structure reinforced with an FRP hoop as described in any one of (1) to (4) above, wherein the FRP hoop is a fiber bundle wound helically.

[0015] According to the invention related to (5) above, by helically winding the fiber bundle, even if the FRP hoop is cut out or a hole is drilled, the fibers that run freely in all directions make it possible to firmly maintain its shape.

[0016] (6) The FRP hoop is a concrete structure reinforced with FRP hoops described in any one of (1) to (5) above, which is obtained by cutting an FRP product having a hollow cylindrical shape into a ring shape.

[0017] According to the invention related to the above item (6), by cutting out FRP hoops from hollow cylindrical FRP products scheduled for disposal, it is possible to procure hoops at low cost and to make effective use of resources.

[0018] (7) A concrete structure reinforced with FRP hoops according to any one of (1) to (6) above, in which the FRP hoops are made primarily of CFRP.

[0019] According to the invention related to the above (7), by using CFRP as the main component material of the FRP hoop, it is possible to obtain an FRP hoop having superior specific strength, specific elastic modulus, and heat resistance to other fiber reinforced plastics. [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 is a perspective view of a CFRP hoop in one embodiment of the present invention. [Diagram 2] FIG. 1A is a diagram illustrating the cross-sectional configuration of a CFRP hoop in one embodiment of the present invention, and FIG. 1B is a diagram illustrating a manufacturing method of the CFRP hoop. [Diagram 3] 1 shows a table and calculation formula showing the results of a study on concrete dowels. [Figure 4] FIG. 2 is a perspective view showing the arrangement of CFRP hoop reinforcement in one embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic cross-sectional view showing a manufacturing method of a CFRP hoop in one embodiment of the present invention. [Figure 6] FIG. 2 is a perspective view showing the arrangement of CFRP hoop reinforcement in one embodiment of the present invention, showing the arrangement of interlocking reinforcement. [Figure 7] FIG. 2 is a schematic cross-sectional view of a column member showing the arrangement of CFRP hoops in one embodiment of the present invention, showing the interlocking arrangement of four CFRP hoops. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, one embodiment of a reinforced concrete structure using FRP hoops according to the present invention will be described with reference to the drawings.

[0022] An embodiment of the FRP hoop used in the present invention is shown in a perspective view in Figure 1. The FRP hoop of this embodiment, which will be exemplified below, is a hoop made mainly of carbon fiber reinforced plastic (hereinafter referred to as "CFRP") and is formed seamlessly and continuously in an annular shape.

[0023] 2(a) shows the cross-sectional structure of the CFRP hoop 1 of this embodiment. A resin liner 13 having a predetermined thickness is formed on the inner peripheral surface 12 side of the CFRP hoop 1, and its outer periphery is composed of a layer of CFRP 14, and further on the outer periphery of that is a layer of glass fiber reinforced plastic (hereinafter referred to as "GFRP") 15.

[0024] The material strength of CFRP is generally 6 to 10 times that of deformed bar SD345, so by using the CFRP hoop bar 1 of this embodiment, it is possible to reduce the amount of reinforcement required for conventional shear reinforcement bars and lateral restraint bars, thereby improving workability.

[0025] Next, Fig. 2(b) shows an example of a manufacturing method for the CFRP hoop 1 of this embodiment. To explain in more detail, first, resin or the like is poured into a mold to form a cylindrical liner 13 having a predetermined inner diameter and a predetermined length. Then, CFRP 14 impregnated with epoxy resin is wound around the outer periphery of the liner 13 by helical winding. Furthermore, carbon fiber bundles of GFRP 15 impregnated with epoxy resin are wound around the outer periphery of the CFRP 14, and the CFRP 14 and GFRP 15 are hardened by applying hot air.

[0026] As a result, a three-layered cylindrical body 10 is formed as shown in Fig. 2(b). Then, the hardened cylindrical body 10 is cut into rings at a predetermined interval (see the dashed-dotted cutting line in the figure) according to the width dimension of the required CFRP hoop 1. In this way, multiple CFRP hoops 1 can be produced from one cylindrical body 10.

[0027] The CFRP hoop 1 cut out as described above is a circular hoop that efficiently restrains concrete without any breaks or joints, and can improve the deformation performance of the concrete structure. The CFRP hoop 1 of this embodiment exhibits extremely high strength due to the CFRP 14, and furthermore, the CFRP 14 is strongly protected by forming a layer of GFRP 15 around the outer periphery of the CFRP 14 layer.

[0028] In addition, as mentioned above, by helically winding the CFRP 14 around the cylindrical liner 13 having a predetermined length, even if the hardened cylinder 10 is cut into a ring, an integrated, high-strength CFRP hoop 1 can be obtained due to the fibers running freely in all directions.

[0029] In addition, as shown in the perspective view of Fig. 1, the CFRP hoop 1 of this embodiment has a plurality of dowel holes 16 formed through the CFRP hoop 1 from the outer peripheral surface 11 to the inner peripheral surface 12. As a result, after the structural concrete is poured, a concrete dowel is formed by the dowel holes 16.

[0030] More specifically, the CFRP hoop 1 of this embodiment obtained by the above-mentioned manufacturing method has a smooth cut surface, outer peripheral surface 11, and inner peripheral surface 12, which makes adhesion to the concrete structure problematic. Therefore, the above-mentioned dowel holes 16 are drilled and formed in the CFRP hoop 1 to ensure the necessary adhesion strength to the concrete. As described above, the CFRP hoop 1 of this embodiment has CFRP 14 wound by helical winding, so that even if the dowel holes 16 are drilled, the shape can be firmly maintained due to the fibers that run freely in all directions.

[0031] Figure 3 shows a table comparing the anchorage length of a CFRP hoop 1 cut to a width (D) of 50 mm, with a thickness of 25 mm and a diameter of 300 mm, with dowel holes 16 drilled in, the diameter of the dowel holes 16 being 40 mm and the spacing between them being 79 mm, with that of a commonly used deformed bar (D16). Note that the bond strength in the table was calculated using formula (1) (quoted from Hosaka Tetsuya et al.: "Experimental Study on Shear Properties of Perforated Steel Plate Dowels", Structural Engineering Journal, Vol. 46A, pp. 1593-1604, 2000) adopted in the Standard Specifications for Composite Structures (published by the Japan Society of Civil Engineers).

[0032] From the results of the trial calculation, the anchorage length of the CFRP hoop 1 is 527 mm compared to 505 mm of the deformed bar (D16), and by forming the dowel holes 16 as described above, it is possible to form a hoop with the same adhesion characteristics as the deformed bar (D16). In addition, it is found that the equivalent adhesion strength per unit length of the CFRP hoop 1 is 8.4 to 8.7 times that of the deformed bar (D16).

[0033] Next, FIG. 4 shows an example of the arrangement of the CFRP hoops 1 of this embodiment, and the CFRP hoops 1 are arranged in the axial direction of the main reinforcement 2 at a predetermined interval to achieve the arrangement.

[0034] In the above embodiment, as one aspect of the FRP hoop used in the present invention, the method of manufacturing the CFRP hoop 1 and applying it to a concrete structure has been described. However, the FRP hoop is not necessarily limited to the CFRP hoop 1, and for example, the main component of the FRP hoop can be high-strength glass fiber or aramid fiber, and the same manufacturing method and application to a concrete structure as the above-mentioned CFRP hoop 1 can be realized.

[0035] (Reusing CFRP high-pressure gas tanks) In the above-described embodiment, a form of newly manufacturing the CFRP hoop reinforcement 1 has been described, but the CFRP hoop reinforcement 1 used in the present invention can also be manufactured by reusing a CFRP high-pressure gas tank (waste high-pressure tank) that is scheduled to be discarded and can be filled with hydrogen or the like.

[0036] That is, Fig. 5 shows a schematic cross-sectional view of a CFRP high-pressure gas tank 100, and as shown in the figure, it is possible to manufacture the tank by cutting it along the cutting line of the illustrated dashed line according to the width dimension required for the CFRP hoop 1. The CFRP high-pressure gas tank 100 has a cross-sectional configuration as shown in Fig. 2(a) as in the above-mentioned embodiment, and by cutting it into a ring shape, a seamless, integral, and extremely strong CFRP hoop 1 can be obtained. Furthermore, as in the above-mentioned embodiment, it is also possible to drill a plurality of dowel holes 16 penetrating from the outer peripheral surface 11 to the inner peripheral surface 12 of the CFRP hoop 1, and form a concrete dowel through the dowel holes 16 after the structural concrete is poured.

[0037] According to the Basic Law for High Pressure Gas, the CFRP high pressure gas tank 100 must be disposed of after 15 years even if there is no deterioration. Therefore, by cutting out the CFRP hoop 1 from the CFRP high pressure gas tank 100 to be disposed of as described above, it is possible to procure the hoop at low cost and it leads to effective use of resources.

[0038] On the other hand, the CFRP high-pressure gas tank 100 does not come in a variety of sizes (diameters), and since the manufacturing method involves cutting the CFRP high-pressure gas tank 100 to be discarded into rings and cutting out the CFRP hoop 1, only CFRP hoops 1 of a certain size (diameter) can be manufactured. However, by partially overlapping multiple CFRP hoops 1 to form an interlocking arrangement, it is possible to apply it to structures with cross sections of any size.

[0039] For example, FIG. 6 shows an arrangement in which two CFRP hoops 1 are partially overlapped to form an interlocking arrangement. The CFRP hoops 1 are arranged to surround the main reinforcement 2, and the two CFRP hoops 1 are partially overlapped with an interlocking inner reinforcing bar 3 arranged in the overlapping area.

[0040] Furthermore, Figure 7 shows an example of a 600mm square column designed with four 300mm diameter CFRP hoops 1 arranged in an interlocking manner. In more detail, CFRP hoops 1 with a cross section of 25mm square are arranged at 150mm intervals surrounding the main reinforcement 2, and interlocking inner reinforcing bars 3 thinner than the main reinforcement 2 are arranged in the areas where the CFRP hoops 1 overlap each other.

[0041] In this way, even if only a certain size of CFRP hoop 1 can be taken out from the CFRP high pressure gas tank 100, the CFRP hoop 1 can be effectively reused for structures with any size of cross section by interlocking the CFRP hoop 1. This is also true in the case of manufacturing a new CFRP hoop 1 as described above. If a certain size of CFRP hoop 1 is manufactured and interlocked, it is not necessary to prepare many dies according to the size, and it is possible to reduce the manufacturing effort and cost. In addition, it is known that the deformation performance is improved compared to a normal RC structure in the interlocking reinforcement using a circular hoop reinforcing bar or a spiral reinforcing bar, and it is possible to further improve the deformation performance in the CFRP hoop 1 of this embodiment.

[0042] In the above embodiment, one aspect of reusing a CFRP high-pressure gas tank (waste high-pressure tank) has been described. However, the FRP hoop reinforcement can be reused not only for CFRP high-pressure gas tanks (waste high-pressure tanks). In other words, it can be reused for tank products that store low-pressure gas or liquids, not limited to tank products that store high-pressure gas, and further, it can be reused for FRP products that have a hollow cylindrical shape, not limited to tank products, and whose main constituent material is FRP such as CFRP, glass fiber, or aramid fiber, and it is possible to cut the FRP hoop reinforcement into rings and take it out by the same recycling method as the above-mentioned CFRP high-pressure gas tank (waste high-pressure tank).

[0043] The embodiment of the present invention has been described above with reference to the drawings, mainly with respect to a reinforced concrete structure using a CFRP hoop 1, in which the CFRP hoop 1 is manufactured by newly manufacturing the CFRP hoop 1 or by reusing a CFRP high-pressure gas tank 100 that is scheduled to be discarded. However, the specific configuration is not necessarily limited to the embodiment described above.

[0044] For example, the above-mentioned CFRP hoop 1 has a three-layer structure of the liner 13, CFRP 14, and GFRP 15, but it is not necessarily limited to such a cross-sectional structure, and the effects of the present invention can be obtained as long as the structure is mainly made of at least CFRP 14. Similarly, it goes without saying that the CFRP hoop 1 used in the present invention does not necessarily have to be wound by helical winding to obtain the CFRP hoop 1 used in the present invention.

[0045] The liner 13 is not necessarily limited to being made of resin, but may be made of plastic or metal. In addition, for example, the liner 13 is not necessarily limited to being made by a mold, but may be made by extrusion molding.

[0046] In the above embodiment, the dowel holes 16 are drilled in the CFRP hoop 1 to improve the bond strength with the concrete, but the present invention is not necessarily limited to this form. For example, it is also possible to insert a penetrating rebar through the dowel hole 16, or to roughen the outer peripheral surface 11 or the inner peripheral surface 12 of the CFRP hoop 1, or to provide uneven portions on the outer peripheral surface 11 or the inner peripheral surface 12 to improve the bond strength with the concrete.

[0047] The scope of the present invention is defined by the claims, not by the description of the above embodiments, and includes all modifications within the meaning and scope of the claims. The specific materials, dimensions, shapes, etc. described in the above examples can be modified within the scope of the present invention. [Explanation of symbols]

[0048] 1 CFRP hoop reinforcement 2 Main reinforcement 3 Interlocking inner bars 10 Cylinder 11 Outer surface 12 Inner surface 13. Liner 14 CFRP 15. GFRP 16 Dowel hole 100 CFRP high pressure gas tank (abandoned high pressure tank)

Claims

1. The structure includes a main reinforcement, an FRP hoop reinforcement surrounding the main reinforcement, and concrete covering the main reinforcement and the FRP hoop reinforcement, The FRP hoop reinforcement is formed in a continuous, seamless, annular shape, has a plurality of dowel holes penetrating from the outer peripheral surface to the inner peripheral surface, and is arranged in the axial direction of the main reinforcement. The dowel holes form concrete dowels A reinforced concrete structure using FRP hoops.

2. The FRP hoop reinforcement is composed of interlocking reinforcement in which one FRP hoop reinforcement is overlapped with the other FRP hoop reinforcement. A concrete structure reinforced with the FRP hoop of claim 1.

3. The FRP hoop reinforcement is A liner layer and an FRP layer covering the outer periphery of the liner layer. A concrete structure reinforced with the FRP hoop according to claim 1 or 2.

4. The FRP hoop reinforcement is a helically wound fiber bundle. A concrete structure reinforced with the FRP hoop according to any one of claims 1 to 3.

5. The FRP hoop reinforcement is cut into rings from an FRP product having a hollow cylindrical shape. A concrete structure reinforced with the FRP hoop according to any one of claims 1 to 4.

6. The FRP hoop reinforcement has CFRP as its main component. A concrete structure reinforced with the FRP hoop according to any one of claims 1 to 5.

Images