Reinforcement methods for RC bridge piers

Abstract

The present invention provides a method for reinforcing an RC bridge pier having a stepped section, which can improve the seismic performance of the RC bridge pier and improve constructability. [Solution] A method for reinforcing an RC bridge pier having a stepped section, wherein the RC bridge pier is reinforced with a fiber material, and the elastic modulus is 350,000 (N / mm²). 2 The amount of reinforcement using a fiber material with the above-mentioned reinforcing fibers is set so as to cause the failure mode of the RC bridge pier to shift from failure of the stepped portion to bending failure of the base of the RC bridge pier, and the fiber material is bonded to the stepped portion of the RC bridge pier such that at least half of the fiber directions of the reinforcing fibers are aligned with the vertical direction.

Description

[Technical Field]

[0001] The present invention relates to a method for reinforcing reinforced concrete (RC) bridge piers having stepped sections, using a fibrous material. [Background technology]

[0002] In recent years, the risk of large-scale earthquakes, such as a direct hit on the capital, has been increasing. Under these circumstances, seismic reinforcement measures for existing bridges are an extremely important issue, and seismic reinforcement of reinforced concrete bridge piers (hereinafter referred to as RC bridge piers) is currently underway. RC bridge piers designed before the revision of the Road Bridge Specifications in 1980 have stepped sections with a reduced number of main reinforcing bars for economic reasons, and when checked according to the current Road Bridge Specifications, the load-bearing capacity of these stepped sections may be insufficient. Lessons learned from the Great Hanshin Earthquake have shown that failure from the stepped sections transitions to shear failure, causing a rapid decrease in load-bearing capacity. In order to improve the ductility of RC bridge piers and create a tough structure that can withstand large deformations caused by large-scale earthquakes, it is necessary to reinforce the stepped sections and to change the damage mode of the RC bridge pier to a bending failure-first type at the base.

[0003] One method for reinforcing stepped sections is to use lightweight and durable carbon fiber. In this method, carbon fiber sheets are bonded to the concrete surface using adhesive resin to reinforce existing members. There are different types of carbon fiber sheets, such as high-strength and high-elasticity types, based on their physical properties. Non-patent document 1, which describes the design guidelines for this method, states that the use of high-strength type is standard. The elastic modulus of this high-strength type of carbon fiber sheet is lower than that of the high-elasticity type, at 245,000 (N / mm²). 2 ). In order to compensate for the insufficient bending moment in the stepped section with a carbon fiber sheet, the method described in Non-Patent Document 1 determines the amount of reinforcement of the carbon fiber sheet based on the strength of the carbon fiber sheet. Non-Patent Document 2 also describes an example of design calculation for reinforcement of stepped sections using a carbon fiber sheet. In the method described in Non-Patent Document 2 as well, the number of layers is calculated from the strength of the carbon fiber.

[0004] In the reinforcement of the settlement part, in order to make it the base bending fracture precedence type, it is necessary to make the horizontal load when the settlement part yields larger than the horizontal load when the base yields. In this regard, in the methods described in Non-Patent Documents 1 and 2, since there is no investigation of the yield load of the settlement part after reinforcement with a carbon fiber sheet, there is a risk that the settlement of the settlement part will precede.

[0005] Patent Document 1 discloses a reinforcement structure that introduces prestress to a tension member to reinforce the settlement part. However, in the disclosed technique of Patent Document 1, since prestress is introduced to the tension member for reinforcement, construction is more difficult compared to adhesive reinforcement using a carbon fiber sheet.

[0006] Patent Document 2 discloses a concrete structure using a carbon fiber sheet. In the disclosed technique of Patent Document 2, by using a carbon fiber sheet with a modulus of elasticity of 35 tons / mm 2 or more, the rigidity is increased compared to a carbon fiber sheet with a modulus of elasticity of 23.5 tons / mm 2 and it is said that the number of laminated carbon fiber sheets can be reduced. However, in Patent Document 2, no specific reinforcement method for an RC pier having a settlement part has been studied.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0008]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, the present invention has been devised in view of the above circumstances, and its object is to provide a method for reinforcing an RC pier having a scoured section, which can improve the seismic performance of the RC pier and the constructability of the RC pier.

Means for Solving the Problems

[0010] The method for reinforcing an RC pier according to the first invention is a method for reinforcing an RC pier having a scoured section with a fiber material, wherein the reinforcement amount by the fiber material using reinforcing fibers having an elastic modulus of 350,000 (N / mm 2 ) or more is set so as to shift the failure mode of the RC pier from the failure of the scoured section to the flexural failure of the base of the RC pier, and the fiber material is adhered to the scoured section of the RC pier such that at least half of the fiber directions of the reinforcing fibers are along the vertical direction.

[0011] The method for reinforcing an RC pier according to the second invention is characterized in that, in the first invention, the reinforcement amount by the fiber material is set such that the yield load of the scoured section is equal to or greater than the initial yield load or the ultimate load of the base, and the fiber material is adhered to the scoured section of the RC pier such that at least half of the fiber directions of the reinforcing fibers are along the vertical direction.

[0012] The method for reinforcing an RC pier according to the third invention is characterized in that, in the second invention, the yield load of the reinforced scoured section is calculated based on the initial yield bending moment of the reinforced scoured section.

[0013] The method for reinforcing an RC bridge pier according to the fourth invention is characterized in that, in the first invention, the amount of reinforcement by the fiber material is set such that the yield load of the stepped portion is equal to or greater than the ultimate load of the base portion.

[0014] The method for reinforcing an RC bridge pier according to the fifth invention is characterized in that, in the first invention, the fibrous material is bonded as a first reinforcing layer with the fiber direction of the reinforcing fibers aligned vertically, and then a fibrous sheet with the fiber direction aligned horizontally is bonded around the RC bridge pier on top of the first reinforcing layer.

[0015] The method for reinforcing an RC bridge pier according to the sixth invention is characterized in that, in any of the first to fifth inventions, the fibrous material comprises one of the following: a unidirectional reinforcing fiber sheet, a sheet formed by aligning multiple CFRP wires to form a curtain-like structure, and a strip-shaped FRP plate. [Effects of the Invention]

[0016] According to the present invention, the elastic modulus is 350,000 (N / mm²). 2 The amount of reinforcement using a fiber material with reinforcing fibers of 245,000 (N / mm²) or more is set so that the failure mode of the RC bridge pier transitions from failure of the stepped section to bending failure of the base of the RC bridge pier, and the fiber material is bonded to the stepped section of the RC bridge pier such that at least half of the fiber directions of the reinforcing fibers are aligned with the vertical direction. 2 ) has a higher elastic modulus of 350,000 (N / mm²). 2 By using fiber materials with reinforced fibers of ) or higher strength, the reinforcing effect per layer is greatly increased. Therefore, compared to the case of high-strength fiber materials, the amount of fiber material used for reinforcement can be reduced, improving workability on site.

[0017] According to the present invention, the amount of reinforcement by the fiber material is set so as to shift the failure mode of the RC pier from the failure of the collapsed part to the flexural failure of the base of the RC pier. Thereby, without the collapsed part yielding, the flexural failure due to flexural deformation can be shifted to the base. For this reason, the shear failure of the RC pier can be suppressed, and the seismic performance of the RC pier can be improved.

[0018] According to the present invention, the amount of reinforcement by the fiber material using reinforcing fibers having an elastic modulus of 350,000 (N / mm 2 ) or more is set so that the yield load of the collapsed part of the RC pier is equal to or greater than the initial yield load or the ultimate load of the base of the RC pier, and the fiber material is adhered to the collapsed part of the RC pier so that at least half of the fiber directions of the reinforcing fibers are along the vertical direction. Since a fiber material using reinforcing fibers having an elastic modulus higher than 245,000 (N / mm 2 ), which is the elastic modulus of the high-strength type, that is, 350,000 (N / mm 2 ) or more is used, the reinforcing effect per layer becomes large. For this reason, compared with the case of the high-strength type fiber material, the amount of reinforcement of the fiber material can be reduced, and the workability at the site can be improved. Further, in the conventional method, the amount of reinforcement of the fiber sheet is set only by the strength of the fiber sheet in order to supplement the bending moment insufficient in the collapsed part, and the yield load of the collapsed part after reinforcement by the fiber sheet has not been examined. According to the present invention, since the amount of reinforcement of the fiber material is set after examining the yield load of the collapsed part after reinforcement by the fiber material, the desired reinforcing effect can be more reliably exhibited.

Brief Description of Drawings

[0019] [Figure 1] FIG. 1 is a side cross-sectional view showing an example of an RC pier in the first embodiment. [Figure 2] FIG. 2(a) is a plan cross-sectional view showing an example of the base of the RC pier in the first embodiment, and FIG. 2(b) is a plan cross-sectional view showing an example of the collapsed part of the RC pier in the first embodiment. [Figure 3]Figure 3 is a plan cross-sectional view showing an example of a stepped section of an RC bridge pier in the second embodiment. [Figure 4] Figure 4(a) is a side view showing the specimen of Example 1, and Figure 4(b) is a front view showing the specimen of Example 1. [Figure 5] Figure 5(a) is a plan cross-sectional view showing the base of the specimen of Example 1, and Figure 5(b) is a plan cross-sectional view showing the stepped portion of the specimen of Example 1. [Figure 6] Figure 6 is a perspective view showing the analysis model of the RC bridge pier in Example 2. [Figure 7] Figure 7 is a graph showing the relationship between stress and relative displacement of the interface element of the analysis model of Example 2. Figure 7(a) shows the relationship in the shear direction, and Figure 7(b) shows the relationship in the normal direction. [Figure 8] Figure 8 is a graph showing the relationship between the horizontal displacement of the loading point and the load in Example 2. [Figure 9] Figure 9 is a graph showing the relationship between the position from the bottom surface of the footing in Example 2 and the strain of the reinforcing bars. [Figure 10] Figure 10 shows an overview of the reinforcement arrangement of the specimen in Example 3, where Figure 10(a) is a side view, Figure 10(b) is a front view, Figure 10(c) is a cross-sectional view AA of Figure 10(b), and Figure 10(d) is a cross-sectional view BB of Figure 10(b). [Figure 11] Figure 11 shows an overview of the reinforcement of the carbon fiber sheet in the specimen of Example 3, where Figure 11(a) is a side view, Figure 11(b) is a front view, and Figure 11(c) is a cross-sectional view AA of Figure 11(b). [Figure 12] Figure 12 illustrates the loading cycle in the alternating positive and negative loading test of Example 3. [Figure 13] Figure 13 is a photograph showing the fracture state of Comparative Example 3 after the test of Example 3, where Figure 13(a) shows the stepped portion of the test specimen and Figure 13(b) shows the base of the test specimen. [Figure 14]Figure 14 is a photograph showing the fracture state of the stepped section of Comparative Example 4 after the test of Example 3. Figure 14(a) shows the stepped section before the removal of the carbon fiber sheet, and Figure 14(b) shows the stepped section after the removal of the carbon fiber sheet. [Figure 15] Figure 15 is a photograph showing the fracture state of the base of Comparative Example 4 after the test of Example 3. [Figure 16] Figure 16 is a photograph showing the fracture state of the stepped section of Example 2 of the present invention after the test of Example 3. Figure 16(a) shows the stepped section before the removal of the carbon fiber sheet, and Figure 16(b) shows the stepped section after the removal of the carbon fiber sheet. [Figure 17] Figure 17 is a photograph showing the fracture state of the stepped section of Example 3 of the present invention after testing in Example 3. Figure 17(a) shows the stepped section before the carbon fiber sheet was removed, and Figure 17(b) shows the stepped section after the carbon fiber sheet was removed. [Figure 18] Figure 18(a) is a photograph showing the fracture state of the base of Example 2 of the present invention after the test of Example 3, and Figure 18(b) is a photograph showing the fracture state of the base of Example 3 of the present invention after the test of Example 3. [Figure 19] Figure 19 shows the relationship between the horizontal load and the horizontal displacement at the loading point in the alternating positive and negative loading test of Example 3. Figure 19(a) shows the case for Comparative Example 3, and Figure 19(b) shows the case for Comparative Example 4. [Figure 20] Figure 20 shows the relationship between the horizontal load and the horizontal displacement at the loading point in the alternating positive and negative loading test of Example 3. Figure 20(a) shows the case of Example 2 of the present invention, and Figure 20(b) shows the case of Example 3 of the present invention. [Figure 21] Figure 21 shows the relationship between the horizontal load and the envelope of the horizontal displacement at the loading point at its peak during the alternating positive and negative loading test in Example 3. [Figure 22] Figure 22 shows the relationship between the reinforcement strain in the stepped section and the horizontal displacement at the loading point in Comparative Example 4 during the alternating positive and negative loading test of Example 3. [Figure 23]Figure 23(a) shows the relationship between the reinforcement strain and the horizontal displacement at the loading point of the stepped section of Example 2 of the present invention in the alternating positive and negative loading test of Example 3, and Figure 23(b) shows the relationship between the reinforcement strain and the horizontal displacement at the loading point of the stepped section of Example 3 of the present invention in the alternating positive and negative loading test of Example 3. [Modes for carrying out the invention]

[0020] The following describes in detail, with reference to the drawings, embodiments for implementing the reinforcement method for RC bridge piers to which the present invention is applied.

[0021] <First Embodiment> As shown in Figures 1, 2(a), and 2(b), the RC bridge pier 10 according to the first embodiment has a base 3 having main reinforcement bars 5, and a stepped section 2 having fewer main reinforcement bars 5 than the base 3. A fibrous material 4 is bonded to the stepped section 2 of the RC bridge pier 10.

[0022] Fiber material 4 has an elastic modulus of 350,000 (N / mm²). 2 ) or more, preferably 390,000 (N / mm²) 2 ) or more, more preferably 500,000 (N / mm 2 It is constructed using reinforcing fibers of the following strength. The fiber material 4 is bonded to the stepped portion 2 of the RC bridge pier 10 such that at least half of the fiber directions of the reinforcing fibers are aligned with the vertical direction. The fiber material 4 may also be bonded so that all of the fiber directions of the reinforcing fibers are aligned with the vertical direction.

[0023] The fiber material 4 is composed of reinforcing fibers such as carbon fibers impregnated with resin. The matrix resin constituting the fiber material 4 can be either a thermosetting resin or a thermoplastic resin, but vinyl ester resin or epoxy resin, which are thermosetting resins, are preferred. The reinforcing fibers constituting the fiber material 4 are not limited to carbon fibers as long as they satisfy the aforementioned elastic modulus, and may also be organic fibers such as aramid, PBO (poly(p-phenylene benzbisoxazole), polyamide, polyarylate, polyester, basalt fibers, glass fibers, etc., and various fibers can be used. However, carbon fibers are preferred as reinforcing fibers, and pitch-based carbon fibers are more preferred. Furthermore, the reinforcing fibers are not limited to one type, and multiple types can be selected and used.

[0024] The fiber material 4 is arranged so that the fiber direction of all carbon fibers is aligned vertically, and includes, for example, a unidirectional reinforced fiber sheet made by aligning carbon fibers in one direction to form a sheet, a sheet made by aligning multiple CFRP (Carbon Fiber Reinforced Plastics) wires to form a curtain-like structure, or an FRP (Fiber Reinforced Plastics) plate made by aligning carbon fibers in one direction to form strips. As the unidirectional reinforced fiber sheet, for example, Tow Sheet (registered trademark) may be used. As the curtain-like sheet, for example, Strand Sheet (registered trademark) may be used. As the FRP plate, for example, Tow Plate (registered trademark) may be used.

[0025] The fiber material 4 may be a grid-like member in which more than half of the carbon fibers are arranged vertically and the remainder horizontally. The grid-like member may be, for example, TowGrid (registered trademark). Furthermore, the fiber material 4 may be a triaxial mesh-like member in which more than half of the carbon fibers are arranged vertically and the remainder horizontally.

[0026] The fiber material 4 may be composed of one or more layers of sheet material such as a unidirectional fiber sheet, a sheet in the shape of a bamboo blind, a plate material such as an FRP plate, or a grid-like member. The amount of reinforcement by the fiber material 4 is set so that the yield load of the stepped portion 2 of the reinforced RC bridge pier 10 is equal to or greater than the yield load of the base portion 3 of the RC bridge pier 10 before reinforcement (hereinafter also referred to as the initial yield load of the base portion 3) or the ultimate load of the base portion 3 of the RC bridge pier 10 before reinforcement. Preferably, it is set to 1.1 times or more the initial yield load of the base portion 3 of the RC bridge pier 10 before reinforcement, and more preferably to 1.2 times or more the initial yield load of the base portion 3 of the RC bridge pier 10 before reinforcement. This is because, even if the initial yield load is exceeded, the RC bridge pier will not completely fail until the ultimate load is reached, and can withstand a certain amount of load increase thereafter. However, this depends on the structure of the existing RC bridge pier, and most preferably, the amount of reinforcement by the fiber material 4 is set so that the yield load of the stepped section 2 of the reinforced RC bridge pier 10 is equal to or greater than the ultimate load of the base 3 of the RC bridge pier 10 before reinforcement.

[0027] The adhesive used to bond the fiber material 4 to the stepped section 2 is a well-known adhesive, such as an organic adhesive like an epoxy adhesive, an inorganic adhesive like a polymer cement mortar, or an adhesive combining these.

[0028] Next, an example of a method for reinforcing an RC bridge pier 10 having a stepped section 2 is described, in which the RC bridge pier 10 is reinforced with a fiber material 4.

[0029] The reinforcement method for RC bridge pier 10 has an elastic modulus of 350,000 (N / mm²). 2 The amount of reinforcement provided by the fiber material 4 using the above-mentioned reinforcing fibers is set so that the failure mode of the RC bridge pier 10 transitions from failure of the stepped section to bending failure of the base of the RC bridge pier.

[0030] The reinforcement method for RC bridge pier 10 has an elastic modulus of 350,000 (N / mm²). 2The amount of reinforcement using fiber material 4 with reinforced fibers of ) or more is set so that the yield load of the stepped section 2 of the RC bridge pier 10 is equal to or greater than the initial yield load of the base 3 of the RC bridge pier 10 or the ultimate load of the base 3. Specifically, first the initial yield load of the base 3 is calculated. Then, the cross-sectional area of ​​the fiber material 4 is set to a predetermined cross-sectional area, and the yield load of the stepped section 2 including the fiber material 4 of the set predetermined cross-sectional area is calculated. If the calculated yield load of the stepped section 2 is less than the calculated initial yield load of the base 3, the set cross-sectional area of ​​the fiber material 4 is increased and the yield load of the stepped section 2 is calculated again. The yield load of the stepped section 2 is repeatedly calculated until the calculated yield load of the stepped section 2 is equal to or greater than the calculated initial yield load of the base 3. If the calculated yield load of the stepped section 2 is equal to or greater than the calculated initial yield load of the base 3, the amount of reinforcement of the fiber material 4 is set based on this predetermined cross-sectional area. In the above, the calculation was based on the initial yield load of the base 3, but the same applies when calculating based on the ultimate load of the base 3. However, the decision of whether to use the initial yield load or the ultimate load is made on a case-by-case basis, considering factors such as the amount of reinforcement of the fiber material 4 and the importance of the structure as a traffic route. The initial yield load of the base 3, the ultimate load of the base 3, and the yield load of the stepped section 2 can be calculated, for example, using general spreadsheet software or specialized software (for example, FORUM8's RC section calculation (old standard)) to perform an RC section calculation assuming plane maintenance, as described later, or by FEM analysis. In this embodiment, the stepped section 2 and base 3 of the RC bridge pier are both described below as having rectangular cross-sections, but in the present invention, the cross-sectional shapes of the base 3 and stepped section 2 of the RC bridge pier may be circular, oval, or the like.

[0031] Yield load P of the stepped portion 2 and base portion 3 in the rectangular cross-section y This can be calculated, for example, based on the following formula (1), assuming plane maintenance. When setting the amount of reinforcement for the fiber material 4, the yield load P of the stepped portion 2 of the RC bridge pier 10 reinforced by the fiber material 4. y This is the initial yield bending moment M of the stepped section 2 of the RC bridge pier 10 reinforced with fiber material 4. y It can be calculated based on this.

number

[0032] Ultimate load P of base 3 in rectangular cross-section cu This can be calculated based on the assumption of plane maintenance, for example, using the following formula (5): Ultimate load P of the stepped section 2 of the RC bridge pier 10 reinforced with fiber material 4 cu This is the initial yield bending moment M of the stepped section 2 of the RC bridge pier 10 reinforced with fiber material 4. cu It can be calculated based on this.

number

[0033] In the method for reinforcing the RC bridge pier 10, a set amount of reinforcing fiber material 4 is bonded to the stepped section 2 of the RC bridge pier 10 such that at least half of the fiber directions of the reinforcing fibers are aligned with the vertical direction.

[0034] According to this embodiment, the elastic modulus is 350,000 (N / mm²). 2 The amount of reinforcement provided by the fiber material 4 using reinforcing fibers of 245,000 (N / mm²) or more is set so that the failure mode of the RC bridge pier 10 transitions from failure of the stepped section 2 to bending failure of the base 3 of the RC bridge pier 10, and the fiber material 4 is bonded to the stepped section 2 of the RC bridge pier 10 so that at least half of the fiber directions of the reinforcing fibers are aligned with the vertical direction. 2 ) has a higher elastic modulus of 350,000 (N / mm²). 2 Since the fiber material 4 using reinforced fibers of the above strength is used, the reinforcing effect per layer is increased. Therefore, compared to the case of high-strength fiber material, the amount of fiber material used for reinforcement can be reduced, improving workability on site.

[0035] According to this embodiment, the amount of reinforcement by the fiber material 4 is set to shift the failure mode of the RC bridge pier 10 from failure of the stepped section 2 to bending failure of the base section 3 of the RC bridge pier 10. This prevents the stepped section 2 from yielding and allows bending failure due to bending deformation to be transferred to the base section 3. As a result, shear failure of the RC bridge pier 10 can be suppressed, and the seismic performance of the RC bridge pier 10 can be improved.

[0036] According to this embodiment, the elastic modulus is 350,000 (N / mm²). 2 The amount of reinforcement using fiber material 4 with reinforcing fibers of 245,000 (N / mm²) or more is set so that the yield load of the stepped section 2 of the RC bridge pier 10 is equal to or greater than the initial yield load of the base section 3 of the RC bridge pier 10 or the ultimate load of the base section 3, and the fiber material 4 is bonded to the stepped section 2 of the RC bridge pier 10 so that the fiber direction of at least half of the reinforcing fibers is aligned with the vertical direction. 2 ) has a higher elastic modulus of 350,000 (N / mm²). 2 Since the fiber material 4 uses reinforced fibers of the above strength, the reinforcing effect per layer is increased. Therefore, compared to the case of high-strength fiber material, the amount of reinforcement of the fiber material 4 can be reduced, improving workability on site. Furthermore, in conventional methods, the amount of reinforcement of the fiber sheet is determined solely by the strength of the fiber sheet in order to compensate for the insufficient bending moment in the stepped section, and the yield load of the stepped section after reinforcement with the fiber sheet is not checked. However, according to this embodiment, the amount of reinforcement of the fiber material 4 is set after checking the yield load of the stepped section 2 after reinforcement with the fiber material 4, so that the desired reinforcement effect can be achieved more reliably.

[0037] Furthermore, according to this embodiment, the stepped section 2 does not yield, and bending failure due to bending deformation can be transferred to the base section 3. As a result, shear failure of the RC bridge pier 10 can be suppressed, and the seismic performance of the RC bridge pier 10 can be improved.

[0038] <Second Embodiment> As shown in Figure 3, in the RC bridge pier 10 according to the second embodiment, the fibrous material 4 is used as the first reinforcing layer, and a fibrous sheet 6 with the fiber direction aligned horizontally is bonded to the RC bridge pier 10 in a circumferential manner on top of the first reinforcing layer.

[0039] The fiber sheet 6 is constructed by impregnating reinforcing fibers, such as carbon fibers, with resin. The matrix resin constituting the fiber sheet 6 can be either a thermosetting resin or a thermoplastic resin, but vinyl ester resin or epoxy resin, which are thermosetting resins, are preferred. The reinforcing fibers constituting the fiber sheet 6 are not limited to carbon fibers, but may also be organic fibers such as aramid, PBO (poly(p-phenylenebenzbisoxazole)), polyamide, polyarylate, polyester, basalt fibers, glass fibers, etc., and various types of fibers can be used. Furthermore, the reinforcing fibers are not limited to one type, but can be selected and used in multiple types.

[0040] The fiber sheet 6 is arranged so that the fiber direction of all carbon fibers is aligned horizontally. For example, a unidirectional fiber sheet is used, which is made by aligning raw fibers in one direction to form a sheet. As the unidirectional fiber sheet, for example, Tow Sheet (registered trademark) may be used, or a prepreg sheet in which an adhesive is pre-impregnated into the Tow Sheet (registered trademark). For bonding the wrapped fiber sheet 6, well-known organic adhesives such as epoxy adhesives or acrylic adhesives are preferably used.

[0041] Next, an example of a method for reinforcing an RC bridge pier 10 having a stepped section 2 is described, in which the RC bridge pier 10 is reinforced with a fiber material 4.

[0042] In the method for reinforcing the RC bridge pier 10, a fiber material 4 is bonded as the first reinforcing layer so that the fiber direction of the reinforcing fibers is aligned vertically, and then a fiber sheet 6 with the fiber direction aligned horizontally is bonded around the RC bridge pier 10 on top of the first reinforcing layer.

[0043] According to this embodiment, the fiber sheet 6 is bonded to the RC bridge pier 10 in a circumferential manner. This further reinforces the RC bridge pier 10. [Examples]

[0044] In Example 1, the yield load was compared for a specimen simulating an RC bridge pier when the number of layers of fiber material used as reinforcement was set according to a conventional design method and when it was set according to the method of the present invention. The conventional design method, based on Non-Patent Literature 1, determined the number of layers of reinforcement based on the strength of the carbon fiber sheet used as the fiber material. In the method of the present invention, the yield load of the stepped section after reinforcement with fiber material was set to be at least 1.2 times the initial yield load of the base, the ultimate load of the base, and the initial yield load of the base. The yield load and ultimate load were calculated by RC section calculation assuming plane maintenance.

[0045] Figure 4(a) is a side view showing the specimen 100 in Example 1, and Figure 4(b) is a front view showing the specimen 100 in Example 1. As shown in Figure 4, the specimen 100 has a footing section 11 and a column section extending vertically from the footing section 11. The dimensions of the footing section 11 are 1200 mm in length, 1000 mm in width, and 700 mm in height. The dimensions of the column section are 350 mm in length, 500 mm in width, and 2100 mm in height. The column section has a base section 13 at the root and a stepped section 12 located above 700 mm from the base section 13, with fewer main reinforcement bars than the base section 13.

[0046] As shown in Figure 5, the stepped section 12 has fewer main reinforcement bars 151 and 152 than the base section 13. As shown in Figure 5(a), in the base section 13, nine D16 main reinforcement bars 151 are placed at 52.5 mm intervals in the width direction, and three D13 main reinforcement bars 152 are placed at 67.5 mm intervals in the depth direction. As shown in Figure 5(b), in the stepped section 12, five D16 main reinforcement bars 151 are placed at 105 mm intervals in the width direction, and one D13 main reinforcement bar 152 is placed at a 135 mm interval from an adjacent main reinforcement bar 151 in the depth direction. The shear reinforcement bars 153 are D10 and are placed at 100 mm intervals in the height direction.

[0047] The carbon fiber sheet 14, which is a fibrous material, was bonded to the stepped section 12 from a position 200 mm above the top surface of the footing section 11 to a position 1500 mm above the top surface of the footing section. The size of the carbon fiber sheet 14 was 1300 mm x 500 mm. The design thickness per layer of the carbon fiber sheet 14 was 0.111 mm for the high-strength type and 0.143 mm for the high-elasticity type.

[0048] Table 1 shows the initial yield load at the base, the ultimate load at the base, and the calculated value of 1.2 times the initial yield load at the base. As shown in Table 1, the yield load at the base of the specimen was set to 101.1 kN. Therefore, 1.2 times the yield load at the base is 121.3 kN. The ultimate load at the base was set to 114.0 kN.

[0049] [Table 1]

[0050] Table 2 shows the material properties of the carbon fiber sheets. High-strength and high-elasticity carbon fiber sheets were used. The tensile modulus (elastic modulus) of the high-strength carbon fiber sheet was 245,000 (N / mm²). 2 The tensile modulus (elastic modulus) of the high-elasticity carbon fiber sheet was set to 640,000 (N / mm²). 2 The tensile strength and elongation at break were as shown in Table 2.

[0051] [Table 2]

[0052] [Table 3]

[0053] As shown in Table 3, the design strength of concrete f' ck It is 28 (N / mm 2 ) was set to the yield strength f of the reinforcing steel. sy It is 330 (N / mm 2The verification step was set at a position 700 mm from the base, which is the actual step position. The axial force of the specimen was set to 105 kN. The shear strength S of the specimen was set to 182.7 kN. The distance a from the horizontal force application point to the section under consideration was 1200 mm at the step and 1900 mm at the base for this specimen.

[0054] In Case 0, an unreinforced specimen was used, without reinforcement using carbon fiber sheets. In Cases 1 and 2, the amount of reinforcement was set based on the conventional setting method (strength design). In Cases 3 to 8, the amount of reinforcement was set based on the setting method of the present invention (rigidity design). In Cases 3 and 4, the amount of carbon fiber sheet reinforcement was set so that the yield load of the stepped section was equal to or greater than the initial yield load of the base. In Cases 5 and 6, the amount of carbon fiber sheet reinforcement was set so that the yield load of the stepped section was equal to or greater than the ultimate load of the base. In Cases 7 and 8, the amount of carbon fiber sheet reinforcement was set so that the yield load of the stepped section was 1.2 times or more the initial yield load of the base.

[0055] In the case of study case 0, the yield load of the stepped section was calculated to be 92.8 kN, which was less than the initial yield load of the base. Therefore, in study case 1, there is a concern that the stepped section may fail first.

[0056] In Study Case 1, a high-strength carbon fiber sheet was used. In Study Case 1, only one layer was required. In Study Case 1, the yield load of the stepped section was calculated to be 99.9 kN, which was less than the initial yield load of the base. Therefore, in Study Case 1, there is a concern that the stepped section may fail first.

[0057] In Study Case 2, a high-elasticity carbon fiber sheet was used. In Study Case 2, two layers were required. In Study Case 2, the yield load of the stepped section was calculated to be 140.9 kN, which was higher than the initial yield load of the base (101.1 kN).

[0058] In Case 3, a high-strength carbon fiber sheet was used. In Case 3, two layers were required. In Case 3, the yield load of the stepped section was calculated to be 107.0 kN, which was higher than the initial yield load of the base (101.1 kN).

[0059] In Study Case 4, a highly elastic carbon fiber sheet was used. In Study Case 4, only one layer was required. In Study Case 4, the yield load of the stepped section was calculated to be 116.8 kN, which was greater than the initial yield load of the base (101.1 kN).

[0060] In Case 5, a high-strength carbon fiber sheet was used. In Case 5, three layers were required. In Case 5, the yield load of the stepped section was calculated to be 114.2 kN, which was greater than the ultimate load of the base (114.0 kN).

[0061] In study case 6, a high-elasticity carbon fiber sheet was used. In study case 6, one layer was required. In study case 6, the yield load of the stepped section was calculated to be 116.8 kN, which was greater than the ultimate load of the base (114.0 kN).

[0062] In Study Case 7, a high-strength carbon fiber sheet was used. In Study Case 7, four layers were required. In Study Case 7, the yield load of the stepped section was calculated to be 121.3 kN, which was 1.2 times (121.3 kN) or more than the initial yield load of the base.

[0063] In study case 8, a high-elasticity carbon fiber sheet was used. In study case 8, two layers were required. In study case 8, the yield load of the stepped section was calculated to be 140.9 kN, which was more than 1.2 times (121.3 kN) the initial yield load of the base.

[0064] As described above, in Case 1 of the study, although the structure is reinforced with carbon fiber sheets, there is concern about premature failure of the stepped section. On the other hand, in the setting method of the present invention, a high-elasticity carbon fiber sheet is used, and the amount of reinforcement of the carbon fiber sheet is set so that the yield load of the stepped section is greater than the initial yield load of the base, the ultimate load of the base, or 1.2 times the initial yield load of the base. This prevents the stepped section from yielding and allows the bending deformation to be transferred to the base. As a result, shear failure of the RC bridge pier can be suppressed, and the seismic performance of the RC bridge pier can be improved. In particular, when the amount of reinforcement of the carbon fiber sheet is set so that the yield load of the stepped section is 1.2 times or more the ultimate load of the base or the initial yield load of the base, bending failure due to bending deformation can be more reliably transferred to the base.

[0065] As shown in the cases 3 and 4, when the amount of carbon fiber sheet reinforcement was set so that the yield load of the stepped section was equal to or greater than the initial yield load of the base, two layers were required for high-strength carbon fiber sheets, while only one layer was required for high-elasticity carbon fiber sheets. Therefore, by using high-elasticity carbon fiber sheets compared to high-strength carbon fiber sheets, the number of carbon fiber sheet layers required can be reduced. This improves workability on site.

[0066] As shown in cases 5 and 6, when the amount of carbon fiber sheet reinforcement was set so that the yield load of the stepped section was greater than or equal to the ultimate load of the base, three layers of high-strength carbon fiber sheet were required, compared to only one layer of high-elasticity carbon fiber sheet. Therefore, by using high-elasticity carbon fiber sheet compared to high-strength carbon fiber sheet, the number of carbon fiber sheet layers required can be reduced. This improves workability on site.

[0067] As shown in cases 7 and 8, when the amount of carbon fiber sheet reinforcement was set so that the yield load of the stepped section was 1.2 times or more the initial yield load of the base, four layers were required for high-strength carbon fiber sheets, while only two layers were required for high-elasticity carbon fiber sheets. Therefore, by using high-elasticity carbon fiber sheets compared to high-strength carbon fiber sheets, the number of carbon fiber sheet layers required can be reduced. This improves workability on site. [Examples]

[0068] In Example 2, FEM analysis was performed to compare the yield load and reinforcement strain.

[0069] The general-purpose nonlinear FEM analysis program DIANA (ver. 10.8) was used for the analysis. Figure 6 shows the analysis model. The shape and dimensions of the model were determined so that failure of the stepped section precedes failure of the horizontal load in the unreinforced state. The concrete of the footing and column sections were modeled as solid elements, and the reinforcement was modeled as embedded reinforcement elements that considered adhesive sliding. The height of the column section was 2,200 mm, the loading point was set at a height of 1,900 mm from the top surface of the footing section, and a stepped section was provided at a height of 700 mm from the top surface of the footing section. The adhesion range of the carbon fiber sheet as a fibrous material was set from 200 mm to 1,300 mm from the top surface of the footing section and was installed on two surfaces of the column section. D25 shear reinforcement bars were placed as embedded reinforcement elements in the footing section and D10 shear reinforcement bars in the column section to prevent failure of the footing concrete and shear failure of the column section from preceding each other. The carbon fiber sheet was modeled using plane stress elements, and the interface between the carbon fiber sheet and concrete was modeled using interface elements.

[0070] The load conditions were determined based on previous research (Norio Ogata, Hirofumi Ando, ​​Tetsuo Matsuda, Katsuro Kobata, Ryo Ohno: A Study on Seismic Reinforcement of Existing RC Bridge Piers with Stepped Sections Using Carbon Fiber, Transactions of the Japan Society of Civil Engineers, No. 540 / VI-31, 85-104, 1996), with an axial force P (average compressive stress of the column section of 0.6 N / mm²) corresponding to the dead load of the superstructure. 2A horizontal displacement L was applied while maintaining a constant position by adding ( ). The constraint conditions were that the bottom surface of the footing was fixed in three directions: the first plane direction, the second plane direction perpendicular to the first plane direction, and the height direction perpendicular to both the first and second plane directions.

[0071] The analytical models consisted of three cases: Example 1, Comparative Example 1, and Comparative Example 2. Comparative Example 1 is an unreinforced model without reinforcement using carbon fiber sheets. Comparative Example 2 has an elastic modulus of 245,000 (N / mm²). 2 This model consists of two layers of high-strength carbon fiber sheets, one with the fiber direction oriented vertically and the other with the fiber direction oriented horizontally. Example 1 of the present invention has an elastic modulus of 640,000 (N / mm²). 2 This model consists of a single layer of highly elastic carbon fiber sheet with the fiber direction oriented vertically. In Comparative Example 2, the thickness of the single layer of carbon fiber sheet was 0.111 mm. In Example 1 of the present invention, the thickness of the single layer of carbon fiber sheet was 0.286 mm.

[0072] For the high-strength type (Comparative Example 2), the required thickness of the carbon fiber sheet was calculated using the calculation method shown in the existing design guidelines (Non-Patent Literature 1). For the high-elasticity type (Example 1 of the present invention), the amount of reinforcement was determined so that the horizontal load at the time of yielding at the stepped section (yield load at the stepped section) was 1.2 times the horizontal load at the time of yielding at the base (initial yield load at the base). The yield bending moment during reinforcement was calculated by RC section calculation assuming plane stability and ignoring tensile stress below the neutral axis of the concrete, based on the "Guidelines for Repair and Reinforcement of Structures by FRP Bonding (Draft)" (Japan Society of Civil Engineers, Composite Structure Series 09, 2018). Each material was treated as a linear material, and considering the axial compressive force, the bending moment when the stress of the reinforcement reaches the yield strength was defined as the yield bending moment. The ratio of the elastic modulus of each material was calculated using the elastic modulus of concrete as 28,000 (N / mm²). 2 The yield was calculated by dividing the yield by the elastic modulus of each material shown in Table 4 below. The horizontal load at yield was calculated from the yield bending moment, assuming the lower end of the column was a fixed end.

[0073] [Table 4]

[0074] For concrete, we used the model by Maekawa, K., and Fukuura, N. (Nonlinear modeling of 3D structural reinforced concrete and seismic performance as-sessment, Infrastructure System for Nuclear Energy, 2014), which models both unloading and reloading conditions. For tensile strength, we used the Hordijk model (Hordijk, DA: Local approach to fatigue of concrete. PhD thesis, Delft University of Technology, 1991), and the tensile strength and tensile fracture energy were calculated using a compressive strength of 28 (N / mm²). 2 The maximum aggregate size was set to 20 mm, and the calculation was based on the "Standard Specifications for Concrete, Design Edition" (Japan Society of Civil Engineers: 2022). The plastic model for reinforcement was the Von-Mises model, and the yield strength was assumed to be 330 (N / mm²), based on the actual yield strength of SD295. 2 The secondary slope after rebar yielding was set to Es / 100 (Es: elastic modulus of the rebar). For the bond slip model, the model proposed by Shima et al. (Hiroshi Shima, Liang Zhou, Hajime Okamura: Bond stress-slip-strain relationship of deformed rebar embedded in massive concrete, Transactions of the Japan Society of Civil Engineers, No. 378 / V-6, 1987) was used. The carbon fiber sheet was modeled as a linear orthotropic anisotropic material, and the elastic modulus in the direction orthogonal to the fibers (horizontal direction) was set to 1 / 100 of the elastic modulus in the fiber direction. The stress-relative displacement relationship of the interface element is shown in Figure 7, and the characteristic values ​​are shown in Table 5 below. The material properties of the interface elements were determined based on previous research (Guangfeng Zhang, Junichi Hoshiguma, Junichi Sakai, Shigeki Unjo: Seismic reinforcement method for RC bridge piers using carbon fiber sheets and steel plates and its effects, Journal of Japan Society of Civil Engineers, Series A1, Vol. 67, No. 2, 430-445, 2011).

[0075] Figure 7 and Table 5 show τ u δ is the adhesion strength,e δ is the relative displacement between the concrete and the carbon fiber sheet when the shear stress reaches the bond strength. u k is the relative displacement between the concrete and the carbon fiber sheet when the carbon fiber sheet is peeled off. n σ is the stiffness gradient in the normal direction, and σ is the normal stress.

[0076] [Table 5]

[0077] The loading conditions involved applying an axial force to the column, followed by loading in the horizontal direction until the horizontal displacement at the loading point reached 25 mm.

[0078] Figure 8 shows the load-horizontal displacement relationship under monotonic loading. Table 6 shows the yield load. The yield load (FEM) in Table 6 is the result of this FEM analysis. Note that the yield load (design) in Table 6 is based on RC section calculations assuming plane stability, with a reinforcement stress of 330 (N / mm²). 2 This shows the load when the following occurs.

[0079] [Table 6]

[0080] As shown in Table 6, the RC cross-sectional calculations assuming plane stability show that in Comparative Example 1, Comparative Example 2, and Example 1 of the Invention, the base yields at 98.4 kN. In Comparative Example 1 and Comparative Example 2, the yield load of the stepped section is less than the initial yield load of the base, suggesting that yielding of the stepped section precedes yielding. In Example 1 of the Invention, the yield load of the stepped section is 1.2 times or more the initial yield load of the base, suggesting that yielding of the base precedes yielding.

[0081] As shown in Figure 8 and Table 6, the FEM analysis results showed that in Comparative Example 1, Comparative Example 2, and Example 1 of the Invention, the base yielded at 108.6 kN. In Comparative Example 1, yielding of the stepped section preceded yielding at 99.0 kN. In Comparative Example 2, the yield load was higher than in Comparative Example 1, but it did not reach the initial yield load of the base, and yielding of the stepped section preceded yielding. In Example 1 of the Invention, yielding of the stepped section did not occur up to a horizontal displacement of 25 mm, and yielding of the base preceded yielding.

[0082] Figure 9 shows the relationship between the position from the bottom surface of the footing and the reinforcement strain, based on FEM analysis. As shown in Figure 9, the reinforcement strain in Comparative Examples 1 and 2 was greater near the stepped section at 1300 mm from the bottom surface of the footing than near the base at 700 mm from the bottom surface of the footing. In Example 1 of the present invention, the reinforcement strain was greater near the base at 700 mm from the bottom surface of the footing than near the stepped section at 1300 mm from the bottom surface of the footing. Therefore, in Example 1 of the present invention, bending failure due to bending deformation can be transferred to the base without yielding at the stepped section.

[0083] As described above, by reinforcing the stepped section with a highly elastic carbon fiber sheet so that the yield load of the stepped section is 1.2 times or more than the yield load of the base, the stepped section does not yield, and bending failure due to bending deformation is transferred to the base. Therefore, shear failure of the RC bridge pier can be suppressed, and the seismic performance of the RC bridge pier can be improved. [Examples]

[0084] In Example 3, to confirm the applicability of fiber materials using high-elasticity carbon fibers, alternating positive and negative loading tests were conducted on RC bridge pier specimens with axial force applied, using carbon fiber type and reinforcement amount as parameters.

[0085] <Materials used> Table 7 shows the property values ​​of the materials used in the test. For the reinforcement, SD295 was used, assuming an RC bridge pier with stepped sections designed before 1980. As the fiber material, two types of carbon fiber sheets were used: a high-strength type and a high-elasticity type (a material with a lower tensile strength than the high-strength type but a large elastic modulus). The high-strength type carbon fiber sheet was an ordinary carbon fiber sheet that was aligned unidirectionally in a dry state (i.e., without resin impregnation). The high-elasticity type carbon fiber sheet was a carbon fiber strand sheet obtained by pre-forming high-elasticity type carbon fibers into a wavy FRP. This is because the carbon fiber strand sheet can have a higher fiber areal density per layer than an ordinary carbon fiber sheet, so the number of sheet layers required to achieve the necessary fiber amount for reinforcement can be reduced, which is expected to improve the workability and economy during on-site construction. For the resin required for the construction of the carbon fiber sheet, such as unevenness correction, impregnation adhesion, and adhesion, all epoxy resins were used. For the adhesion of the high-strength type carbon fiber sheet, an epoxy resin for impregnation adhesion was used, and for the high-elasticity type carbon fiber sheet, an epoxy resin for adhesion was used. Ordinary concrete was used for the concrete, and the specimens were fabricated with a specified compressive strength of 21 N / mm 2 as specified.

[0086]

Table 7

[0087] <Summary of the cyclic loading test on RC bridge piers: Specimen summary> The specimen overview diagrams of Example 3 are shown in Figs. 10(a) to 10(d) and Figs. 11(a) to 11(d). The shape and dimensions of the specimen were determined such that when a horizontal load was applied in the unreinforced state, the failure of the buckling part would occur first. The height of the column part was 2,200 mm, a loading point was provided at a height of 1,900 mm from the top of the footing, and a buckling part was provided at a height of 700 mm from the base. D16 and D13 were used for the main reinforcement. D10 was used for the shear reinforcement bars of the column part, and they were arranged so that the shear failure of the column part would not occur first. Similarly, for the footing concrete, the reinforcement bars were arranged so that the failure of the footing would not occur first. The cross-section of the column part was a rectangular cross-section with a width of 500 mm and a height of 350 mm, and the corners were chamfered with a radius of R50. The carbon fiber sheet used for vertical reinforcement had a length of 1,300 mm starting from a position 200 mm from the base, and was adhered to both the front and back sides with a width of 500 mm with respect to the loading surface. Also, a high-strength type carbon fiber sheet was wound around and reinforced the entire circumference within the same range. Table 8 shows a list of specimen parameters. A total of 4 tests were conducted on 1 non-reinforced specimen (Comparative Example 3), 1 specimen reinforced with a high-strength type carbon fiber sheet (Comparative Example 4), and 2 specimens reinforced with a high-elasticity type carbon fiber sheet (Examples 2 and 3 of the present invention). The reinforced specimens used the type (high-strength type, high-elasticity type) and amount of reinforcement of the carbon fiber sheet for vertical reinforcement as parameters, and all the reinforced specimens were further wound (wound reinforcement) with a high-strength type carbon fiber sheet. Table 8 shows the yield loads of the column base and the hinged part of each specimen obtained by RC cross-section calculation assuming plane retention, and the horizontal displacement δy at the time of yield of the column base obtained from FEM analysis. The compressive strength of the concrete is the result of the compressive test of the concrete cylinder specimens conducted on the test day of each specimen.

[0088]

Table 8

[0089] <Summary of the positive and negative alternating test of RC bridge piers: Method for calculating the amount of carbon fiber reinforcement> For the specimen of Comparative Example 4, the required thickness of the carbon fiber sheet was calculated by the calculation method shown in the existing design guidelines (East Nippon Expressway Company Limited, Central Nippon Expressway Company Limited, West Nippon Expressway Company Limited, Design Guidelines Volume 2, Bridge Maintenance Edition, 2023) to determine the reinforcement amount of the carbon fiber sheet. For the specimens with high-elasticity type reinforcement, based on the criterion that the horizontal load at the time of hinge part yield should be 1.2 times the horizontal load (106 kN) at the time of column base yield, the reinforcement amount was set such that the specimens of Example 2 of the present invention were 1.2 times or more, and the specimens of Example 3 of the present invention were approximately 1.2 times and less than 1.2 times. As a result, for the specimens of Example 2 of the present invention, the horizontal load at the time of hinge part yield was approximately 1.47 times (156 kN) the horizontal load at the time of column base yield. For the specimens of Example 3 of the present invention, the horizontal load at the time of hinge part yield was approximately 1.19 times (126 kN) the horizontal load at the time of column base yield. The yield bending moment during reinforcement was calculated by RC cross-section calculation, assuming plane retention and ignoring the tensile stress below the neutral axis of the concrete, referring to the Guidelines for Repair and Reinforcement of Structures by FRP Bonding (Draft), Composite Structure Series 09 (Japan Society of Civil Engineers, July 2018). Each material was considered a linear material, and considering the axial compressive force, the bending moment when the stress of the reinforcing bar reached the yield strength was defined as the yield bending moment. The elastic modulus ratio of each material was calculated from the compressive strength of the concrete of 21 N / mm 2 to obtain the elastic modulus of 23,500 N / mm 2 and was obtained by dividing by the elastic modulus of each material shown in Table 7. The horizontal load at yield was obtained by dividing the yield bending moment by the distance from the cross-section position under consideration to the horizontal load position.

[0090] <Summary of Reversed Cyclic Tests on RC Bridge Piers: Specimen Reinforcement Procedure> As the construction procedure for the carbon fiber sheet bonding method, first, a disk sander was used to roughen the bonding area. Next, an epoxy primer was applied to the roughened concrete surface, and unevenness was corrected with an epoxy resin for unevenness correction after the primer was touch-dry. Thereafter, the high-strength type carbon fiber sheet of Comparative Example 4 was bonded vertically using an epoxy resin for impregnation bonding. The high-elasticity type carbon fiber strand sheets of Examples 2 and 3 of the present invention were bonded vertically using an epoxy resin for bonding. Finally, the high-strength type carbon fiber sheets used for the circumferential reinforcement of Comparative Example 4, Examples 2 and 3 of the present invention were wound and bonded using an epoxy resin for impregnation bonding.

[0091] <Summary of Reversed Cyclic Tests on RC Bridge Piers: Loading Method> The footing of the specimen was fixed to the reaction floor using PC steel bars, and a loading girder for axial force loading was installed at the top end of the column. Referring to previous studies, the axial force corresponding to the dead load of the superstructure (average compressive stress of the column of 0.6 N / mm 2 ) was applied with a vertical jack through the loading girder, and while keeping the load constant, the horizontal displacement was gradually increased statically in a reversed cyclic manner. The loading cycle is shown in Figure 12. Using the horizontal displacement analysis value δy at yield point at the base of the column for each specimen shown in Table 8 as a reference, the displacement control was repeated three times for each range from 1 to 4δy and once for each range from 4 to 8δy. The test was terminated when the load significantly decreased due to the failure of the specimen, or when the load was applied down to -8δy. During the test, the difference between the displacement gauge installed at the horizontal load application position and the displacement gauge installed on the footing was used as the control displacement. The load was considered positive when the horizontal jack was pushing the specimen. In addition, after the first loading of each cycle, crack sketching and carbon fiber sheet delamination were investigated by impact testing.

[0092] <Test Results: Destruction Status> Figures 13 to 18 show the test conditions of the specimens after the test. Furthermore, after the test, the carbon fiber sheet was removed from the reinforced specimens to check the damage condition on the back of the carbon fiber sheet. The carbon fiber sheet was removed using a hammer drill, but in the process, the surface layer of the concrete was also peeled off, so only cracks with wide crack widths could be visually observed. Figure 13 is a photograph showing the fracture state of Comparative Example 3 after the test of Example 3, where Figure 13(a) shows the stepped portion of the test specimen and Figure 13(b) shows the base of the test specimen. As shown in Figure 13(a), in Comparative Example 3, which was unreinforced, damage was concentrated in the stepped section, and concrete failure occurred due to buckling of the reinforcing bars. On the other hand, as shown in Figure 13(b), bending deformation was concentrated in the stepped section, so no concrete failure occurred at the base of the column. Figure 14 is a photograph showing the fracture state of the stepped section of Comparative Example 4 after the test of Example 3. Figure 14(a) shows the stepped section before the removal of the carbon fiber sheet, and Figure 14(b) shows the stepped section after the removal of the carbon fiber sheet. Figure 15 is a photograph showing the fracture state of the base of Comparative Example 4 after the test of Example 3. As shown in Figures 14(a), 14(b), and 15, the specimen of Comparative Example 4, which was reinforced with a high-strength carbon fiber sheet, showed a difference compared to the unreinforced specimen (Comparative Example 3). Because the stepped section was reinforced, the failure of the concrete occurred due to buckling of the reinforcing bars at the base of the column, rather than the stepped section failing first, and the damage was transferred to the base of the column. However, delamination of the carbon fiber sheet was observed near the stepped section when a load of 4-5δy was applied. Furthermore, after the removal of the carbon fiber sheet, cracks resembling block-like delamination were observed in the concrete cover of the stepped section. Therefore, it is considered that this delamination occurred because the reinforcing bars in the stepped section yielded, and when subjected to compressive force from alternating loading, buckling of the reinforcing bars caused bulging, resulting in a force normal to the bonding surface. Figure 16 is a photograph showing the fracture state of the stepped section of Example 2 of the present invention after the test of Example 3, where Figure 16(a) shows the stepped section before the removal of the carbon fiber sheet, and Figure 16(b) shows the stepped section after the removal of the carbon fiber sheet. Figure 17 is a photograph showing the fracture state of the stepped section of Example 3 of the present invention after the test of Example 3, where Figure 17(a) shows the stepped section before the removal of the carbon fiber sheet, and Figure 17(b) shows the stepped section after the removal of the carbon fiber sheet. Figure 18(a) is a photograph showing the fracture state of the base of Example 2 of the present invention after the test of Example 3, and Figure 18(b) is a photograph showing the fracture state of the base of Example 3 of the present invention after the test of Example 3. As shown in Figure 18, the specimens of Examples 2 and 3 of the present invention, which are reinforced specimens made of highly elastic carbon fiber sheets, were able to transfer damage to the base of the column, similar to the specimen of Comparative Example 4. As shown in Figures 16(a) and 16(b), the specimen of Example 2 of the present invention showed no peeling or breakage of the carbon fiber sheet in the stepped section, and observation after removal of the carbon fiber sheet revealed that the stepped section was in a sound condition with no block formation of the cover concrete. As shown in Figures 17(a) and 17(b), in the specimen of Example 3 of the present invention, delamination of the carbon fiber sheet occurred in a small area at the stepped section when the horizontal displacement was 7δy. However, observation after removal of the carbon fiber sheet showed that it was in a sound condition, similar to the specimen of Example 2 of the present invention. Therefore, it was confirmed that reinforcing the stepped section with a carbon fiber sheet can cause the failure to transition from the stepped section to the column base, regardless of the type of carbon fiber sheet, but that reinforcing with a highly elastic carbon fiber sheet can suppress damage to the stepped section.

[0093] <Test Results: Relationship between Horizontal Load and Horizontal Displacement at Loading Point> The horizontal load-horizontal displacement at the loading point relationship for each specimen is shown in Figures 19(a), 19(b), 20(a), and 20(b). The horizontal displacement at the loading point is shown dimensionlessly as the horizontal displacement δy at the yielding point of the column base of each specimen. The peak envelope of the horizontal load-horizontal displacement at the loading point for each specimen is shown in Figure 21. As the loading of each specimen was repeated, the concrete deteriorated and the load decreased. While the maximum load of the unreinforced specimen in Comparative Example 3 was 110kN, the yielding and damage at the stepped section preceded the load, causing it to start decreasing from 3δy, and the test was terminated when the load fell to less than half of the maximum load at 5δy. All reinforced specimens (Comparative Example 4, Invention Example 2, and Invention Example 3) yielded at the base of the column, and therefore the maximum loads were all approximately the same: 122kN, 122kN, and 121kN for Comparative Example 4, Invention Example 2, and Invention Example 3, respectively. For Comparative Example 4, the load began to decrease from 5δy in the positive direction and from -4δy in the negative direction. This is thought to be due to delamination of the carbon fibers at the stepped section at 4-5δy. For Invention Examples 2 and 3, the load began to decrease from 6-7δy, and compared to Comparative Example 4, the load did not decrease until significant deformation occurred, confirming improved toughness. This is thought to be because, when reinforced with a high-elasticity carbon fiber sheet, bending failure could be transferred to the base without damage to the stepped section.

[0094] <Test results: Reinforcement strain in the paragraph section> Figures 22, 23(a), and 23(b) show the strain-horizontal displacement relationship at the loading point of the stepped reinforcement in each reinforced specimen. As shown in Figure 10, strain gauges were installed at a total of four points (points A, B, C, and D in Figure 10(d)) on the reinforcement in the stepped section at a height of 700 mm from the top of the footing. In Figures 22 and 23, AB_ave. and CD_ave. represent the average strains of two points installed on the reinforcement at the bottom and top of the stepped section, respectively. As shown in Figure 22, the specimen of Comparative Example 4 yielded over a period of -1 to -2δy, and the yield strain of D16 was (1,760 × 10⁻¹⁰). -6 The strain increased significantly beyond 10⁻¹⁰. After that, the strain increased to approximately 11,000 × 10⁻¹⁰. -6 ~3,000 x 10 -6 The specimen exhibited alternating behavior within the range. The test specimen of Example 2 of the present invention had a maximum strain of approximately 2,000 × 10⁻⁶. -6 Although it exceeded the yield strain of the reinforcing steel, the strain did not increase significantly as in the specimen of Comparative Example 4. The specimen of Invention Example 3 behaved in roughly the same way as the specimen of Invention Example 2, but at 6-7δy it increased by approximately 4,000 × 10⁻⁶. -6 The strain increased up to a certain point. This is thought to be because partial delamination of the carbon fiber sheet in the stepped section occurred at 7δy.

[0095] Based on the above, it was confirmed that by using a highly elastic carbon fiber sheet to reinforce the stepped section, the yielding of the reinforcing steel can be suppressed without delamination or fracture of the carbon fiber sheet at the stepped section, and the failure can be shifted to bending failure at the base of the column.

[0096] In Example 3, a carbon fiber strand sheet using high-elasticity carbon fibers is used as the fiber material. However, in the present invention, a similar reinforcing effect can be obtained even if a regular carbon fiber sheet using high-elasticity carbon fibers (a carbon fiber sheet that is aligned in one direction while not impregnated with resin (=dry)) is used as the fiber material.

[0097] While embodiments of this invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. Furthermore, this invention can be implemented in various novel forms in addition to the embodiments described above. Therefore, the above embodiments can be omitted, replaced, or modified in various ways without departing from the spirit of this invention. Such novel forms and modifications are included in the scope and spirit of this invention, as well as in the invention described in the claims and its equivalents. [Explanation of Symbols]

[0098] 10: RC bridge pier 2: Paragraph section 3: Base 4: Textile materials 5: Main reinforcement 6: Fiber sheet

Claims

1. A method for reinforcing an RC bridge pier having a stepped section, using a fibrous material, Elastic modulus is 350,000 (N / mm) 2 The amount of reinforcement using the fiber material with the above-mentioned reinforcing fibers is set so that the failure mode of the RC bridge pier transitions from failure of the stepped section to bending failure of the base of the RC bridge pier. The fiber material is bonded to the stepped portion of the RC bridge pier such that at least half of the fiber directions of the reinforcing fibers are aligned with the vertical direction. A method for reinforcing RC bridge piers characterized by the following.

2. The amount of reinforcement of the fiber material is set such that the yield load of the stepped portion is equal to or greater than the initial yield load of the base or the ultimate load of the base. A method for reinforcing an RC bridge pier according to claim 1, characterized by the above.

3. The yield load of the reinforced stepped section is calculated based on the initial yield bending moment of the reinforced stepped section. A method for reinforcing an RC bridge pier according to claim 2, characterized by the above.

4. The amount of reinforcement provided by the aforementioned fiber material is set such that the yield load of the stepped portion is equal to or greater than the ultimate load of the base portion. A method for reinforcing an RC bridge pier according to claim 1, characterized by the above.

5. After bonding the aforementioned fibrous material as the first reinforcing layer so that the fiber direction of the reinforcing fibers is aligned with the vertical direction, A fiber sheet with its fiber direction aligned horizontally is bonded to the RC bridge pier in a circumferential manner on top of the first reinforcing layer. A method for reinforcing an RC bridge pier according to claim 1, characterized by the above.

6. The aforementioned fiber material is Unidirectional reinforced fiber sheet, A sheet made by aligning multiple CFRP wires to form a blind-like structure, and It must have one of the following: a strip-shaped FRP plate. A method for reinforcing an RC bridge pier according to any one of claims 1 to 5, characterized by the above.

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