Reinforcement methods for RC bridge piers

Abstract

A method for reinforcing an RC pier with a stepped portion is provided, which can improve the earthquake resistance performance of the RC pier and improve workability. The method for reinforcing RC piers with stepped sections is to reinforce them with fiber materials, and the elastic modulus is 350,000 (N / mm 2 ) or more, is set so that the failure mode of the RC pier shifts from failure at the step-down portion to bending failure at the base of the RC pier, and the fibrous material is adhered to the step-down portion of the RC pier so that the fiber direction of at least half of the reinforcing fibers is along the vertical direction.

Description

[Technical Field]

[0001] The present invention relates to a method for reinforcing RC piers having stepped portions by using a fiber material. [Background technology]

[0002] In recent years, the risk of large-scale earthquakes, such as those occurring directly beneath the capital, has increased. 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 piers) is currently underway. RC piers designed before the 1980 revision of the Highway Bridge Specifications had step-down sections with fewer main reinforcing bars for economic reasons. However, when examined under the current Highway Bridge Specifications, the step-down sections may not have sufficient strength. Lessons learned from the Hyogo-ken Nanbu Earthquake and other studies have revealed that failure at the step-down sections transitions to shear failure, causing a rapid decrease in strength. To improve the ductility of RC piers and ensure their resilience against large deformations caused by large earthquakes, it is necessary to reinforce the step-down sections and ensure that the damage mode of RC piers is preceded by flexural failure at the base.

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

[0004] When reinforcing the stepped-down section, the horizontal load at which the stepped-down section yields must be greater than the horizontal load at which the base yields, in order to make the base bend and fracture first. In this regard, the methods described in Non-Patent Documents 1 and 2 do not examine the yield load of the stepped-down section after reinforcement with carbon fiber sheets, so there is a risk that the stepped-down section will yield first.

[0005] Patent Document 1 discloses a reinforcement structure that reinforces the stepped portion by introducing prestress into the tendons. However, since the technology disclosed in Patent Document 1 involves reinforcing the tendons by introducing prestress, construction is more difficult than adhesive reinforcement using carbon fiber sheets.

[0006] Patent Document 2 discloses a concrete structure using carbon fiber sheets. The technology disclosed in Patent Document 2 uses a concrete structure with an elastic modulus of 35 ton / mm 2 By using the above carbon fiber sheet, the elastic modulus is 23.5 ton / mm 2 It is said that the number of layers of carbon fiber sheets can be reduced because the rigidity is greater than that of carbon fiber sheets used in the past. However, Patent Document 2 does not consider specific reinforcement methods for RC piers with stepped sections. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-40894 [Patent Document 2] Japanese Patent Application Publication No. 7-97460 [Non-patent literature]

[0008] [Non-Patent Document 1] East Nippon Expressway Co., Ltd., Central Nippon Expressway Co., Ltd., West Nippon Expressway Co., Ltd., Design Guidelines Volume 2: Bridge Maintenance, P8-54~P8-61, 2023 [Non-patent document 2] Marine Bridge and Bridge Research Association, Case Studies of Seismic Reinforcement Methods for Existing Bridges, II-71 to II-82, April 2005 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the present invention was devised in consideration of the above-mentioned circumstances, and its purpose is to provide a method for reinforcing RC piers with stepped sections, which can improve the seismic performance of the RC piers and improve workability. [Means for solving the problem]

[0010] The reinforcing method for RC piers according to the first invention is a reinforcing method for RC piers that has a stepped portion and is reinforced with a fiber material, and the reinforcing method is for a RC pier with an elastic modulus of 350,000 (N / mm 2 ) or more, the amount of reinforcement by the fiber material using reinforcing fibers is set so as to shift the failure mode of the RC pier from failure of the step portion to bending failure of the base of the RC pier. and a reinforcing layer forming step of forming a reinforcing layer on the RC pier, wherein the reinforcing layer is made of the fiber material, or is made of the fiber material as a first reinforcing layer and a fiber sheet attached around the RC pier on top of the first reinforcing layer so that the fiber direction is horizontal, and in the setting step, the yield load of the stepped-down portion is calculated based on the elastic coefficient, and the reinforcement amount of the fiber material is set so that the calculated yield load of the stepped-down portion is equal to or greater than the initial yield load of the base or the ultimate load of the base, and in the reinforcing layer forming step, The fiber material is adhered to the stepped portion of the RC pier so that the fiber direction of at least half of the reinforcing fibers is aligned vertically.

[0011] The second invention is a method of reinforcing an RC pier, which is characterized in that, in the first invention, the amount of reinforcement by the fiber material is set so 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, and the fiber material is adhered to the stepped portion of the RC pier so that the fiber direction of at least half of the reinforcing fibers is 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 stepped-down portion is calculated based on the initial yield bending moment of the reinforced stepped-down portion.

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

[0014] The method of reinforcing RC piers according to the fifth invention is characterized in that, in the first invention, the fiber material is adhered as a first reinforcing layer so that the fiber direction of the reinforcing fibers is along the vertical direction, and then a fiber sheet with the fiber direction along the horizontal direction is adhered around the RC pier on top of the first reinforcing layer.

[0015] The method for reinforcing RC piers according to the sixth invention is characterized in that, in any of the first to fifth inventions, the fiber material comprises any of a unidirectional reinforcing fiber sheet, a sheet made by aligning multiple CFRP wires and forming it into a curtain shape, and a rectangular FRP plate. [Effects of the Invention]

[0016] According to the present invention, the elastic modulus is 350,000 (N / mm 2 The reinforcement amount by the fiber material using reinforcing fibers of 245,000 (N / mm) or more is set so that the failure mode of the RC pier transitions from failure of the step-down portion to bending failure of the base of the RC pier, and the fiber material is bonded to the step-down portion of the RC pier so that the fiber direction of at least half of the reinforcing fibers is along the vertical direction. 2 ) with a higher elastic modulus than 350,000 (N / mm 2 ) or more, the reinforcing effect per layer is greater. Therefore, compared to high-strength fiber materials, the amount of reinforcement required 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 failure of the stepped-down portion to flexural failure of the base of the RC pier. This prevents the stepped-down portion from yielding, and allows flexural failure due to flexural deformation to be shifted to the base. This prevents shear failure of the RC pier and improves the seismic performance of the RC pier.

[0018] According to the present invention, the elastic modulus is 350,000 (N / mm 2 The amount of reinforcement by the fiber material using reinforcing fibers of 245,000 (N / mm) or more is set so that the yield load of the stepped portion of the RC pier is equal to or greater than the initial yield load of the base of the RC pier or the ultimate load of the base, and the fiber material is bonded to the stepped portion of the RC pier so that the fiber direction of at least half of the reinforcing fibers is aligned vertically. 2 ) with a higher elastic modulus than 350,000 (N / mm 2 ) or more, the reinforcing effect per layer is increased. Therefore, the amount of reinforcement of the fiber material can be reduced compared to high-strength fiber materials, improving on-site workability. Furthermore, in conventional methods, the amount of reinforcement of the fiber sheet is determined based solely on the strength of the fiber sheet to compensate for the insufficient bending moment at the stepped-down section, and the yield load of the stepped-down section after reinforcement with the fiber sheet is not verified. However, according to the present invention, the amount of reinforcement of the fiber material is determined after verifying the yield load of the stepped-down section after reinforcement with the fiber material, thereby more reliably achieving the desired reinforcing effect. [Brief explanation of the 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 an RC pier in the first embodiment, and FIG. 2(b) is a plan cross-sectional view showing an example of the stepped portion of an RC pier in the first embodiment. [Figure 3]FIG. 3 is a plan cross-sectional view showing an example of a stepped portion of an RC pier in the second embodiment. [Figure 4] FIG. 4(a) is a side view showing the specimen of Example 1, and FIG. 4(b) is a front view showing the specimen of Example 1. As shown in FIG. [Figure 5] 5(a) is a plan cross-sectional view showing the base of the specimen of Example 1, and FIG. 5(b) is a plan cross-sectional view showing the stepped portion of the specimen of Example 1. As shown in FIG. [Figure 6] FIG. 6 is a perspective view showing an analytical model of the RC pier of Example 2. [Figure 7] 7A and 7B are graphs showing the relationship between stress and relative displacement of the interface element of the analytical model of Example 2, where FIG. 7A shows the relationship in the shear direction and FIG. 7B shows the relationship in the normal direction. [Figure 8] FIG. 8 is a graph showing the relationship between the horizontal displacement of the loading point and the load in Example 2. [Figure 9] FIG. 9 is a graph showing the relationship between the position from the bottom surface of the footing portion and the reinforcing bar strain in Example 2. [Figure 10] Figure 10 shows an overview of the reinforcement of the specimen of Example 3, where Figure 10(a) is a side view, Figure 10(b) is a front view, Figure 10(c) is an AA cross-sectional view of Figure 10(b), and Figure 10(d) is a BB cross-sectional view of Figure 10(b). [Figure 11] FIG. 11 is a diagram showing an outline of the carbon fiber sheet reinforcement of the specimen of Example 3, where FIG. 11(a) is a side view, FIG. 11(b) is a front view, and FIG. 11(c) is a cross-sectional view taken along line AA of FIG. 11(b). [Figure 12] FIG. 12 is a diagram illustrating the loading cycle in the alternating positive and negative loading test of Example 3. [Figure 13] FIG. 13 is a photograph showing the state of destruction of Comparative Example 3 after the test of Example 3, where FIG. 13(a) shows the stepped portion of the specimen, and FIG. 13(b) shows the base of the specimen. [Figure 14]FIG. 14 is a photograph showing the state of destruction of the step-down portion of Comparative Example 4 after the test of Example 3, where FIG. 14(a) shows the step-down portion before the carbon fiber sheet was removed, and FIG. 14(b) shows the step-down portion after the carbon fiber sheet was removed. [Figure 15] FIG. 15 is a photograph showing the state of destruction of the base of Comparative Example 4 after the test of Example 3. [Figure 16] FIG. 16 is a photograph showing the state of damage to the step-down portion of Inventive Example 2 after the test of Example 3, where FIG. 16(a) shows the step-down portion before the carbon fiber sheet was removed, and FIG. 16(b) shows the step-down portion after the carbon fiber sheet was removed. [Figure 17] FIG. 17 is a photograph showing the state of damage to the step-down portion of Inventive Example 3 after the test of Example 3, where FIG. 17(a) shows the step-down portion before the carbon fiber sheet was removed, and FIG. 17(b) shows the step-down portion after the carbon fiber sheet was removed. [Figure 18] FIG. 18(a) is a photograph showing the state of fracture of the base of Inventive Example 2 after the test of Example 3, and FIG. 18(b) is a photograph showing the state of fracture of the base of Inventive Example 3 after the test of Example 3. [Figure 19] FIG. 19 is a diagram showing the relationship between horizontal load and horizontal displacement at the loading point in the alternating positive and negative loading test of Example 3, where FIG. 19(a) shows that of Comparative Example 3 and FIG. 19(b) shows that of Comparative Example 4. [Figure 20] Figure 20 is a diagram showing the relationship between horizontal load and horizontal displacement at the loading point in the alternating positive and negative loading test of Example 3, where Figure 20(a) shows that of Invention Example 2 and Figure 20(b) shows that of Invention Example 3. [Figure 21] FIG. 21 is a diagram showing the relationship between the horizontal load and the peak envelope of the horizontal displacement at the loading point in the alternating positive and negative loading test of Example 3. [Figure 22] FIG. 22 is a diagram showing the relationship between the reinforcing bar strain at the stepped portion of Comparative Example 4 and the horizontal displacement at the loading point in the alternating positive and negative loading test of Example 3. [Figure 23]Figure 23(a) is a diagram showing the relationship between the rebar strain at the stepped-down portion of Example 2 of the present invention and the horizontal displacement at the loading point in the alternating positive and negative loading test of Example 3, and Figure 23(b) is a diagram showing the relationship between the rebar strain at the stepped-down portion of Example 3 of the present invention and the horizontal displacement at the loading point in the alternating positive and negative loading test of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment for carrying out a method for reinforcing an RC pier to which the present invention is applied will be described in detail with reference to the drawings.

[0021] First Embodiment As shown in Figures 1, 2(a) and 2(b), the RC pier 10 according to the first embodiment has a base 3 having main reinforcement 5, and a step-down portion 2 having fewer main reinforcement 5 than the base 3. In the RC pier 10, a fiber material 4 is bonded to the step-down portion 2.

[0022] The fiber material 4 has an elastic modulus of 350,000 (N / mm 2 ) or more, preferably 390,000 (N / mm 2 ) or more, more preferably 500,000 (N / mm 2 ) or more reinforcing fibers. The fiber material 4 is bonded to the stepped portion 2 of the RC pier 10 so that the fiber direction of at least half of the reinforcing fibers is aligned in the vertical direction. The fiber material 4 may also be bonded so that the fiber direction of all of the reinforcing fibers is aligned in the vertical direction.

[0023] The fiber material 4 is formed by impregnating reinforcing fibers such as carbon fibers with a resin. The matrix resin constituting the fiber material 4 can be either a thermosetting resin or a thermoplastic resin, but thermosetting resins such as vinyl ester resin and epoxy resin are preferred. The reinforcing fibers constituting the fiber material 4 are not limited to carbon fibers as long as they satisfy the above-mentioned elastic modulus. For example, various fibers can be used, such as organic fibers such as aramid, PBO (polyparaphenylene benzobisoxazole), polyamide, polyarylate, and polyester, basalt fiber, and glass fiber. However, carbon fibers are preferred as reinforcing fibers, and pitch-based carbon fibers are more preferred. Furthermore, the reinforcing fibers are not limited to a single type, and multiple types can be selected and used.

[0024] The fiber material 4 is arranged so that the fiber direction of the carbon fibers is all along the vertical direction, and may be, for example, a unidirectional reinforced fiber sheet in which carbon fibers are aligned in one direction and formed into a sheet, a sheet in which multiple CFRP (Carbon Fiber Reinforced Plastics) wires are aligned and formed into a blind shape, or an FRP (Fiber Reinforced Plastics) plate in which carbon fibers are aligned in one direction and formed into strips. For example, a Tow Sheet (registered trademark) may be used as the unidirectional reinforced fiber sheet. For example, a Strand Sheet (registered trademark) may be used as the blind-shaped sheet. For example, a Tow Plate (registered trademark) may be used as the FRP plate.

[0025] The fiber material 4 may be a lattice-like member in which more than half of the carbon fibers are oriented vertically and the remainder are oriented horizontally. The lattice-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 oriented vertically and the remainder are oriented at ±45° angles.

[0026] The fiber material 4 may be formed by laminating one or more layers of any of the following: a unidirectional fiber sheet, a sheet material such as a blind-shaped sheet, a plate material such as an FRP plate, or a lattice 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 pier 10 is equal to or greater than the yield load of the base 3 of the RC pier 10 before reinforcement (hereinafter also referred to as the initial yield load of the base 3) or the ultimate load of the base 3 of the RC pier 10 before reinforcement, but is preferably set to be 1.1 times or more the initial yield load of the base 3 of the RC pier 10 before reinforcement, and more preferably 1.2 times or more the initial yield load of the base 3 of the RC pier 10 before reinforcement. This is because even if the initial yield load is exceeded, the RC pier will not completely break down until the ultimate load is reached and can withstand a certain amount of increased load thereafter; however, this may depend on the structure of the existing RC pier, and most preferably, the amount of reinforcement by the fiber material 4 is set so that the yield load of the stepped portion 2 of the RC pier 10 after reinforcement is equal to or greater than the ultimate load of the base 3 of the RC pier 10 before reinforcement.

[0027] The adhesive used to bond the fiber material 4 to the step portion 2 may be a well-known adhesive, such as an organic adhesive such as an epoxy adhesive, an inorganic adhesive such as polymer cement mortar, or a combination of these.

[0028] Next, an example of a method for reinforcing an RC pier 10 having a stepped portion 2 with a fiber material 4 will be described.

[0029] The reinforcement method for the RC pier 10 is such that the elastic modulus is 350,000 (N / mm 2 The amount of reinforcement by the fiber material 4 using the above reinforcing fibers is set so as to shift the failure mode of the RC pier 10 from failure of the stepped portion to bending failure of the base of the RC pier.

[0030] The reinforcement method for the RC pier 10 is such that the elastic modulus is 350,000 (N / mm 2) or more, the cross-sectional area as the amount of reinforcement by the fiber material 4 using reinforcing fibers is set so that the yield load of the stepped-down portion 2 of the RC pier 10 is equal to or greater than the initial yield load of the base 3 of the RC pier 10 or the ultimate load of the base 3. In detail, 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-down portion 2 including the fiber material 4 of the set predetermined cross-sectional area is calculated. If the calculated yield load of the stepped-down portion 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-down portion 2 is calculated again. The yield load of the stepped-down portion 2 is repeatedly calculated until the calculated yield load of the stepped-down portion 2 is equal to or greater than the calculated initial yield load of the base 3. If the calculated yield load of the stepped-down portion 2 is equal to or greater than the calculated initial yield load of the base 3, the amount of reinforcement by the fiber material 4 is set based on this predetermined cross-sectional area. In the above, the calculations were based on the initial yield load of the base 3. However, the calculations based on the ultimate load of the base 3 are similar. However, whether to use the initial yield load or the ultimate load is determined on a case-by-case basis based on the economics of the amount of reinforcement of the fiber material 4, etc., and the importance of the bridge 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 step-down portion 2 can be calculated, for example, using a well-known RC section calculation assuming flatness (described below) using general spreadsheet software or dedicated software (e.g., FORUM8's RC Section Calculation (Old Standard)), or by FEM analysis. In the following description of this embodiment, the step-down portion 2 and base 3 of the RC pier are both rectangular in cross section. However, in the present invention, the cross-sectional shapes of the base 3 and step-down portion 2 of the RC pier may be circular, oval, or the like.

[0031] Yield load P of stepped part 2 and base 3 in rectangular cross section y can be calculated based on the assumption of plane retention, for example, using the following formula (1): When determining the reinforcement amount of the fiber material 4, the yield load P y is the initial yield bending moment M of the stepped part 2 of the RC pier 10 reinforced with the fiber material 4. y It can be calculated based on the following.

number

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

number

[0033] In the method for reinforcing the RC pier 10, a set amount of fiber material 4 is adhered to the stepped portion 2 of the RC pier 10 so that the fiber direction of at least half of the reinforcing fibers is aligned vertically.

[0034] According to this embodiment, the elastic modulus is 350,000 (N / mm 2 The amount of reinforcement by the fiber material 4 using reinforcing fibers of 245,000 (N / mm) or more is set so that the failure mode of the RC pier 10 shifts from failure at the step 2 to bending failure at the base 3 of the RC pier 10, and the fiber material 4 is bonded to the step 2 of the RC pier 10 so that the fiber direction of at least half of the reinforcing fibers is along the vertical direction. 2 ) with a higher elastic modulus than 350,000 (N / mm 2 ) or more, the reinforcing effect per layer is increased. Therefore, compared to high-strength fiber materials, the amount of reinforcement required can be reduced, improving workability on site.

[0035] According to this embodiment, the amount of reinforcement by the fiber material 4 is set so as to shift the failure mode of the RC pier 10 from failure at the stepped-down portion 2 to bending failure at the base 3 of the RC pier 10. This prevents the stepped-down portion 2 from yielding, and allows bending failure due to bending deformation to be shifted to the base 3. This makes it possible to suppress shear failure of the RC pier 10 and improve the seismic performance of the RC pier 10.

[0036] According to this embodiment, the elastic modulus is 350,000 (N / mm 2 The amount of reinforcement by the fiber material 4 using reinforcing fibers of 245,000 (N / mm) or more is set so that the yield load of the stepped portion 2 of the RC pier 10 is equal to or greater than the initial yield load of the base 3 of the RC pier 10 or the ultimate load of the base 3, and the fiber material 4 is bonded to the stepped portion 2 of the RC pier 10 so that the fiber direction of at least half of the reinforcing fibers is aligned vertically. 2 ) with a higher elastic modulus than 350,000 (N / mm 2 ) or more, the reinforcing effect per layer is increased. Therefore, the amount of reinforcement by the fiber material 4 can be reduced compared to high-strength fiber materials, improving on-site workability. Furthermore, in conventional methods, the amount of reinforcement by the fiber sheet is set based solely on the strength of the fiber sheet to compensate for the insufficient bending moment at the step-down portion, and the yield load of the step-down portion after reinforcement with the fiber sheet is not examined. However, according to this embodiment, the yield load of the step-down portion 2 after reinforcement with the fiber material 4 is examined before the reinforcement amount of the fiber material 4 is set, thereby more reliably achieving the desired reinforcing effect.

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

[0038] Second Embodiment As shown in Figure 3, in the RC pier 10 of the second embodiment, a fiber material 4 is used as a first reinforcing layer, and a fiber sheet 6 with its fiber direction aligned horizontally is attached around the RC pier 10 on top of the first reinforcing layer.

[0039] The fiber sheet 6 is formed by impregnating reinforcing fibers such as carbon fibers with a resin. The matrix resin forming the fiber sheet 6 can be either a thermosetting resin or a thermoplastic resin, but thermosetting resins such as vinyl ester resin and epoxy resin are preferred. The reinforcing fibers forming the fiber sheet 6 are not limited to carbon fibers, and various fibers can be used, such as organic fibers such as aramid, PBO (polyparaphenylene benzbisoxazole), polyamide, polyarylate, and polyester, basalt fiber, and glass fiber. Furthermore, the reinforcing fibers are not limited to one type, and multiple types can be selected and used.

[0040] The fiber sheet 6 is arranged so that the fiber direction of the carbon fibers is all horizontal, and for example, a unidirectional fiber sheet made by aligning elementary fibers in one direction and forming a sheet is used. As the unidirectional fiber sheet, for example, a Tow Sheet (registered trademark) may be used, or a prepreg sheet made by pre-impregnating the Tow Sheet (registered trademark) with an adhesive material may be used. The wound fiber sheet 6 is preferably bonded with a well-known organic adhesive such as an epoxy adhesive or an acrylic adhesive.

[0041] Next, an example of a method for reinforcing an RC pier 10 having a stepped portion 2 with a fiber material 4 will be described.

[0042] In the method of reinforcing an RC pier 10, a fiber material 4 is bonded as a first reinforcing layer so that the fiber direction of the reinforcing fibers is along the vertical direction, and then a fiber sheet 6 with the fiber direction along the horizontal direction is bonded around the RC pier 10 on top of the first reinforcing layer.

[0043] According to this embodiment, the fiber sheet 6 is adhered around the RC pier 10. This allows the RC pier 10 to be further reinforced. [Example]

[0044] In Example 1, the yield loads of specimens simulating RC piers were compared between cases where the number of layers of fiber material, as the amount of reinforcement, was set using a setting method in accordance with conventional design guidelines and a setting method in accordance with the present invention. For the setting method in accordance with conventional design guidelines, the number of layers, as the amount of reinforcement, was set based on the strength of the carbon fiber sheets used as the fiber material, with reference to Non-Patent Document 1. For the setting method in accordance with the present invention, the yield load of the stepped portion 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 using RC cross-section calculations assuming flatness.

[0045] FIG. 4(a) is a side view showing the specimen 100 in Example 1, and FIG. 4(b) is a front view showing the specimen 100 in Example 1. As shown in FIG. 4, the specimen 100 has a footing portion 11 and a column portion extending vertically from the footing portion 11. The size of the footing portion 11 was 1200 mm long x 1000 mm wide x 700 mm high. The size of the column portion was 350 mm long x 500 mm wide x 2100 mm high. The column portion has a base portion 13 at the base and a step-down portion 12 that is positioned 700 mm above the base portion 13 and has fewer main reinforcement bars than the base portion 13.

[0046] As shown in Figure 5, the stepped-down section 12 has fewer main reinforcements 151, 152 than the base section 13. As shown in Figure 5(a), in the base section 13, nine D16 main reinforcements 151 were placed at intervals of 52.5 mm in the width direction, and three D13 main reinforcements 152 were placed at intervals of 67.5 mm in the depth direction. As shown in Figure 5(b), in the stepped-down section 12, five D16 main reinforcements 151 were placed at intervals of 105 mm in the width direction, and one D13 main reinforcement 152 was placed at an interval of 135 mm between adjacent main reinforcements 151 in the depth direction. Shear reinforcement 153 was D10 and was placed at intervals of 100 mm in the height direction.

[0047] The carbon fiber sheet 14, which is a fiber material, was adhered to the step-down portion 12 from a position 200 mm above the top surface of the footing portion 11 to a position 1500 mm above the top surface of the footing portion. The size of the carbon fiber sheet 14 was 1300 mm x 500 mm. The designed 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 calculated values ​​for the initial yield load at the base, the ultimate load at the base, and 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 / mm 2 The tensile modulus (elastic modulus) of the high-elasticity carbon fiber sheet was 640,000 (N / mm 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 is 28(N / mm 2 ) The yield strength of the reinforcing bar f sy is 330(N / mm 2) The step-down position to be checked was set at 700 mm from the base, which was the actual step-down position. The axial force of the specimen was set at 105 kN. The shear strength S of the specimen was set at 182.7 kN. For this specimen, the distance a from the position where the horizontal force acts to the examined cross section is 1200 mm at the step-down part and 1900 mm at the base.

[0054] In study case 0, an unreinforced specimen was used, with no reinforcement by carbon fiber sheets. In study cases 1 and 2, the amount of reinforcement was set based on the conventional setting method (strength design). In study cases 3 to 8, the amount of reinforcement was set based on the setting method of the present invention (rigidity design). In study cases 3 and 4, the amount of reinforcement by the carbon fiber sheets was set so that the yield load of the stepped-down portion was equal to or greater than the initial yield load of the base. In study cases 5 and 6, the amount of reinforcement by the carbon fiber sheets was set so that the yield load of the stepped-down portion was equal to or greater than the ultimate load of the base. In study cases 7 and 8, the amount of reinforcement by the carbon fiber sheets was set so that the yield load of the stepped-down portion was equal to or greater than 1.2 times the initial yield load of the base.

[0055] In the case of study case 0, the yield load of the stepped-down 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 concern that the stepped-down 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 portion 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 concern that the stepped portion may fail first.

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

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

[0059] In Study Case 4, a high-elasticity carbon fiber sheet was used. In Study Case 4, the number of layers required was one. In Study Case 4, the yield load of the stepped portion was calculated to be 116.8 kN, which was greater than the initial yield load of the base (101.1 kN).

[0060] In Study Case 5, a high-strength carbon fiber sheet was used. In Study Case 5, the required number of layers was three. In Study Case 5, the yield load of the stepped portion 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, the number of layers required was one. In Study Case 6, the yield load of the stepped portion was calculated and found 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, the required number of layers was four. In Study Case 7, the yield load of the stepped portion was calculated to be 121.3 kN, which was more than 1.2 times (121.3 kN) the initial yield load of the base.

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

[0064] As described above, in Study Case 1, although reinforcement is provided by carbon fiber sheets, there is concern about the possibility of the stepped-down section failing first. In contrast, the setting method of the present invention uses high-elasticity carbon fiber sheets, and the amount of reinforcement of the carbon fiber sheets is set so that the yield load of the stepped-down 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-down section from yielding, allowing bending deformation to be transferred to the base. This suppresses shear failure of the RC pier and improves its seismic performance. In particular, if the amount of reinforcement of the carbon fiber sheets is set so that the yield load of the stepped-down 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 Study 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 of high-strength carbon fiber sheet were required, while one layer of high-elasticity carbon fiber sheet was required. Therefore, compared to when high-strength carbon fiber sheet is used, using high-elasticity carbon fiber sheet reduces the number of layers of carbon fiber sheet required, which improves on-site workability.

[0066] As shown in Study Cases 5 and 6, 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 ultimate load of the base, three layers of high-strength carbon fiber sheet were required, while one layer of high-elasticity carbon fiber sheet was required. Therefore, compared to when high-strength carbon fiber sheet is used, using high-elasticity carbon fiber sheet reduces the number of layers of carbon fiber sheet required, which improves on-site workability.

[0067] As shown in Study 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 of high-strength carbon fiber sheet were required, while two layers of high-elasticity carbon fiber sheet were required. Therefore, compared to when high-strength carbon fiber sheet is used, using high-elasticity carbon fiber sheet reduces the number of layers of carbon fiber sheet required, which improves on-site workability. [Example]

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

[0069] The analysis was performed using the general-purpose nonlinear FEM analysis program DIANA (ver. 10.8). Figure 6 shows the analytical model. The model's shape and dimensions were determined so that failure of the stepped section would occur first when a horizontal load was applied without reinforcement. The concrete in the footing and column sections was modeled using solid elements, and the reinforcing bars were modeled using embedded rebar elements that took bond-slip into account. The column height was 2,200 mm, with the loading point located 1,900 mm above the top of the footing, and the stepped section located 700 mm above the top of the footing. The adhesive range of the carbon fiber sheets used as the fiber material was from 200 mm above the top of the footing to 1,300 mm, and they were installed on two sides of the column. To prevent failure of the concrete in the footing and shear failure in the column from occurring first, D25 shear reinforcement was placed as embedded rebar elements in the footing and D10 shear reinforcement in the column. 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 loading conditions were determined based on previous research (Norio Ogata, Hirofumi Ando, ​​Tetsuo Matsuda, Katsuro Obata, Ryo Ohno: Study on seismic reinforcement of existing RC piers with stepped sections using carbon fiber, Proceedings of the Japan Society of Civil Engineers, No. 540 / VI-31, 85-104, 1996), and the axial force P (average compressive stress of the column 0.6 N / mm) equivalent to the dead load of the superstructure was set. 2) was applied and kept constant while a horizontal displacement L was applied. 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 the first and second plane directions.

[0071] The analysis models were three cases: Invention Example 1, Comparative Example 1, and Comparative Example 2. Comparative Example 1 is an unreinforced model that is not reinforced with a carbon fiber sheet. Comparative Example 2 is a model with an elastic modulus of 245,000 (N / mm 2 This model is made up of two layers of high-strength carbon fiber sheets, one with the fiber direction vertical and the other with the fiber direction horizontal. Inventive Example 1 has an elastic modulus of 640,000 (N / mm 2 The model is a single layer of a high-elasticity carbon fiber sheet (e.g., CFRP) with the fiber direction in the vertical direction. In Comparative Example 2, the thickness of one layer of the carbon fiber sheet was 0.111 mm. In Inventive Example 1, the thickness of one layer of the 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 Document 1). For the high-elasticity type (Invention Example 1), the reinforcement amount was determined so that the horizontal load at the time of yielding of the stepped section (yield load of the stepped section) would be 1.2 times the horizontal load at the time of yielding of the base (initial yield load of the base). The yield bending moment at the time of reinforcement was calculated by RC cross-section calculation, assuming flatness and ignoring tensile stress below the neutral axis of the concrete, with reference to the "Guidelines for Repair and Reinforcement of Structures Using FRP Bonding (Draft)" (Japan Society of Civil Engineers, Composite Structure Series 09, 2018). Each material was considered linear, and the bending moment when the stress level of the reinforcing bars reached the yield strength was taken as the yield bending moment, taking into account axial compressive force. The elastic modulus ratio of each material was calculated using the elastic modulus of concrete of 28,000 (N / mm 2 ) and divided 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 that the bottom end of the column was a fixed end.

[0073] [Table 4]

[0074] The concrete was modeled using the model by Maekawa and Fukuura et al. (Maekawa, K., and Fukuura, N.: Nonlinear modeling of 3D structural reinforced concrete and seismic performance assessment, Infrastructure System for Nuclear Energy, 2014), which also models the unloading and reloading of concrete. The tensile model was 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 / mm 2 ), and the maximum size of the coarse aggregate was set at 20 mm, and calculations were made with reference to the "Standard Specifications for Concrete, Design Edition" (Japan Society of Civil Engineers: 2022). The Von-Mises model was used as the plastic model for the reinforcing bars, and the yield strength was set at 330 (N / mm 2 ) was used. The secondary gradient after yielding of the rebar was Es / 100 (Es: elastic modulus of the rebar). The bond-slip model used was that proposed by Shima et al. (Shima Hiroshi, Shu Reira, Okamura Hajime: Bond stress-slip-strain relationship of deformed rebars embedded in massive concrete, Journal of the Japan Society of Civil Engineers, No. 378 / V-6, 1987). The carbon fiber sheet was modeled as a linear orthotropic material, and the elastic modulus in the direction perpendicular 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 (Zhang Guangfeng, Hoshiguma Junichi, Sakai Junichi, Unjo Shigeki: Earthquake-resistant reinforcement method for RC piers using a combination of carbon fiber sheets and steel plates and its effects, Journal of the Japan Society of Civil Engineers, A1, Vol. 67, No. 2, 430-445, 2011).

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

[0076] [Table 5]

[0077] The loading conditions were that axial force was applied to the column, and then the load was applied horizontally 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 shows the results of this FEM analysis. The yield load (design) in Table 6 is based on an RC cross-section calculation that assumes flatness, and is calculated based on a reinforcing bar stress of 330 (N / mm 2 ) indicates the load when

[0079] [Table 6]

[0080] As shown in Table 6, the results of RC cross-section calculations assuming plane retention show that the base yields at 98.4 kN in Comparative Example 1, Comparative Example 2, and Inventive Example 1. In Comparative Examples 1 and 2, the yield load of the stepped-down section is less than the initial yield load of the base, so it is thought that the stepped-down section yields first. In Inventive Example 1, the yield load of the stepped-down section is 1.2 times or more the initial yield load of the base, so it is thought that the base yields first.

[0081] As shown in Figure 8 and Table 6, the results of the FEM analysis showed that in Comparative Example 1, Comparative Example 2, and Inventive Example 1, the base yielded at 108.6 kN. In Comparative Example 1, the stepped-down section yielded first at 99.0 kN. In Comparative Example 2, the yield load was improved compared to Comparative Example 1, but did not improve to the initial yield load of the base, and the stepped-down section yielded first. In Inventive Example 1, yielding did not occur in the stepped-down section up to a horizontal displacement of 25 mm, and the base yielded first.

[0082] Figure 9 shows the relationship between the position from the bottom of the footing and the rebar strain, based on FEM analysis. As shown in Figure 9, the rebar strain in Comparative Examples 1 and 2 was greater near the stepped portion at 1,300 mm from the bottom of the footing than near the base at 700 mm from the bottom of the footing. The rebar strain in Inventive Example 1 was greater near the base at 700 mm from the bottom of the footing than near the stepped portion at 1,300 mm from the bottom of the footing. Therefore, in Inventive Example 1, bending failure due to bending deformation can be shifted to the base without causing the stepped portion to yield.

[0083] As described above, by reinforcing the step-down section with high-elasticity carbon fiber sheets so that the yield load of the step-down section is 1.2 times or more the yield load of the base, the step-down section will not yield, and bending failure due to bending deformation can be transferred to the base. This makes it possible to suppress shear failure of RC piers and improve their seismic performance. [Example]

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

[0085] <Materials used> The properties of the materials used in the test are shown in Table 7. The reinforcing bars used were SD295, assuming RC piers 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 in one direction in a dry state (i.e., not impregnated with resin), and 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 weight 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, and an improvement in construction workability and economy at the site can be expected. For the resins 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 impregnation adhesion resin was used, and for the high-elasticity type carbon fiber sheet, an adhesive epoxy resin 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 follows.

[0086]

Table 7

[0087] <Summary of the positive and negative cyclic test of RC bridge pier: Specimen summary> The specimen schematic diagrams of Example 3 are shown in FIGS. 10(a) to 10(d) and FIGS. 11(a) to 11(d). The size of the specimen was determined in terms of shape and dimensions such that the failure of the buckling part would occur first when a horizontal load was applied in the non-reinforced state. 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 of the column part and was arranged so that the shear failure of the column part would not occur first. Similarly, for the footing concrete, the steel 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 50. The carbon fiber sheet used for vertical reinforcement was set to a length of 1,300 mm starting from a position 200 mm from the base, and was adhered with a width of 500 mm on both the front and back sides with respect to the loading surface. Also, a high-strength type carbon fiber sheet was wound and reinforced around the entire circumference of the same range. A list of specimen parameters is shown in Table 8. 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 reinforcement amount 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 at 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 column base yield obtained from FEM analysis. The compressive strength of the concrete is the result of the compression 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 pier: 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, Second Volume, Bridge Maintenance Edition, 2023) to determine the reinforcement amount of the carbon fiber sheet. For the specimens with high-elasticity type reinforcement, the horizontal load at the time of hinge part yield was set to be 1.2 times the horizontal load (106 kN) at the time of column base yield as a reference. For the specimen of Example 2 of the present invention, the reinforcement amount was set so that it would be 1.2 times or more, and for the specimen of Example 3 of the present invention, the reinforcement amount was set to be approximately 1.2 times, which is less than 1.2 times. As a result, for the specimen 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 specimen 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 regarded as 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 it 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 the Alternating Positive and Negative Tests of RC Bridge Piers: Specimen Reinforcement Procedure> As the construction procedure of the carbon fiber sheet bonding method, first, the concrete surface within the bonding range was roughened using a disk sander. 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 circumferential reinforcement in Comparative Example 4 and Examples 2 and 3 of the present invention were wound circumferentially and bonded using an epoxy resin for impregnation bonding.

[0091] <Summary of the Alternating Positive and Negative Tests of 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 part. The loading was carried out by applying an axial force corresponding to the dead load of the superstructure (average compressive stress of the column part of 0.6 N / mm 2 ) to the vertical jack through the loading girder, and while keeping the load constant, the horizontal displacement was gradually increased statically in an alternating positive and negative manner. The loading cycle is shown in Figure 12. Using the analytical horizontal displacement δy at column base yield for each specimen shown in Table 8 as the reference, displacement control was performed three times at 1 to 4δy and once at 4 to 8δy. The test was terminated when the load dropped significantly due to specimen failure, or until the specimen reached -8δy. During the test, the difference between the displacement meter installed at the horizontal load application position and the displacement meter installed at the footing was used as the control displacement. The load was positive in the direction in which the horizontal jack pushed the specimen. After the first loading of each cycle, crack sketches and hammering tests were conducted to investigate delamination of the carbon fiber sheet.

[0092] <Test results: Destruction status> Figures 13 to 18 show the test conditions of the specimens after the test. After the test, the carbon fiber sheets were removed from the reinforced specimens to check the damage condition on the backside of the carbon fiber sheets. The carbon fiber sheets were removed using a hammer drill or similar tool, but in the process, the surface layer of the concrete was also removed, so only the widest cracks could be visually observed. FIG. 13 is a photograph showing the state of destruction of Comparative Example 3 after the test of Example 3, where FIG. 13(a) shows the stepped portion of the specimen, and FIG. 13(b) shows the base of the specimen. As shown in Figure 13(a), damage was concentrated in the stepped portion of the unreinforced specimen of Comparative Example 3, and the concrete fractured due to buckling of the rebar. On the other hand, as shown in Figure 13(b), the bending deformation was concentrated in the stepped portion, so the concrete at the base of the column did not fracture. Fig. 14 is a photograph showing the state of fracture of the step-down portion of Comparative Example 4 after the test of Example 3, where Fig. 14(a) shows the step-down portion before the carbon fiber sheet was removed, and Fig. 14(b) shows the step-down portion after the carbon fiber sheet was removed. Fig. 15 is a photograph showing the state of fracture 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 high-strength carbon fiber sheets, differed from the unreinforced specimen (Comparative Example 3) in that the reinforced lowering section did not fail first in the lowering section. Instead, the concrete failed due to buckling of the rebar at the column base, causing damage to migrate to the column base. However, peeling of the carbon fiber sheet was observed near the lowering section during loading from 4 to 5δy. Furthermore, after removing the carbon fiber sheet, cracks were observed in the cover concrete at the lowering section, causing it to peel off in block-like pieces. Therefore, it is believed that this peeling was caused by the rebar at the lowering section yielding, and when subjected to compressive force due to alternating loading, the rebar buckled and bulged out, resulting in a force normal to the adhesive surface. Fig. 16 is a photograph showing the fracture state of the step-down portion of Inventive Example 2 after the test of Example 3, where Fig. 16(a) shows the step-down portion before the carbon fiber sheet was removed, and Fig. 16(b) shows the step-down portion after the carbon fiber sheet was removed. Fig. 17 is a photograph showing the fracture state of the step-down portion of Inventive Example 3 after the test of Example 3, where Fig. 17(a) shows the step-down portion before the carbon fiber sheet was removed, and Fig. 17(b) shows the step-down portion after the carbon fiber sheet was removed. Fig. 18(a) is a photograph showing the fracture state of the base portion of Inventive Example 2 after the test of Example 3, and Fig. 18(b) is a photograph showing the fracture state of the base portion of Inventive Example 3 after the test of Example 3. As shown in FIG. 18, in the specimens of Inventive Examples 2 and 3, which were specimens reinforced with high-elasticity carbon fiber sheets, damage was able to be transferred 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 Inventive Example 2 did not experience peeling or breakage of the carbon fiber sheet at the step-down portion, and even after the carbon fiber sheet was removed, the step-down portion was found to be in good condition with no blocking of the cover concrete. 17(a) and 17(b), in the specimen of Inventive Example 3, a small area of ​​the carbon fiber sheet peeled off in the step-down section when the horizontal displacement was 7δy, but observation after removing the carbon fiber sheet showed that the specimen was in a sound state, similar to that of Inventive Example 2. Therefore, it was confirmed that by reinforcing the step-down section with a carbon fiber sheet, it is possible to shift the fracture from the step-down section to the column base regardless of the type of carbon fiber sheet, but that by reinforcing with a high-elasticity carbon fiber sheet, it is possible to suppress damage to the step-down section.

[0093] <Test results: Horizontal load - horizontal displacement relationship at loading point> The relationship between horizontal load and horizontal displacement at the loading point 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 time of yielding of the column base for each specimen. Figure 21 also shows the peak envelope of the horizontal load-horizontal displacement at the loading point for each specimen. As the loading of each specimen was repeated, damage to the concrete progressed and the load decreased. The maximum load for the unreinforced specimen of Comparative Example 3 was 110 kN, but as yielding and damage at the stepped section preceded the load, the load began to decrease from 3δy, and the test was terminated at 5δy when the load fell to less than half of the maximum load. Because all of the reinforced specimens (Comparative Example 4, Inventive Example 2, and Inventive Example 3) experienced yielding at the base of the column, the maximum loads were all similar: 122 kN, 122 kN, and 121 kN for Comparative Example 4, Inventive Example 2, and Inventive Example 3, respectively. For the specimen of 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 in the step-down section between 4 and 5δy. For the specimens of Inventive Examples 2 and 3, the load began to decrease between 6 and 7δy. Compared to the specimen of Comparative Example 4, this load decrease did not occur until a large deformation was reached, confirming improved toughness. This is thought to be because, when reinforced with high-modulus carbon fiber sheets, bending failure was shifted to the base without damage to the step-down section.

[0094] <Test results: Strain of rebar at step> The relationship between the strain on the stepped rebars and the horizontal displacement at the loading point for each reinforced specimen is shown in Figure 22, Figure 23(a) and Figure 23(b). As shown in Figure 10, the strain gauges were installed at four points (four points A, B, C and D in Figure 10(d)) on the stepped rebars at a height of 700 mm from the top of the footing. AB_ave. and CD_ave. in Figures 22 and 23 respectively indicate the average strain at two points installed on the rebars at the bottom and top of the stepped section. As shown in Fig. 22, the specimen of Comparative Example 4 yielded in the rebar over a period of -1 to -2δy, and the yield strain of D16 (1,760 × 10 -6 ), the strain increased significantly. After that, the strain increased to approximately 11,000×10 -6 ~3,000×10 -6 The specimen of Inventive Example 2 exhibited alternating behavior in the range of 2,000 × 10 -6 Although this exceeded the yield strain of the reinforcing bar, the strain did not increase significantly as in the specimen of Comparative Example 4. The specimen of Inventive Example 3 also behaved in a similar manner to the specimen of Inventive Example 2, but at 6 to 7 δy, the strain increased by approximately 4,000 × 10 -6 This is thought to be due to partial delamination of the carbon fiber sheet at the end of the stretch at 7δy.

[0095] From the above, it was confirmed that by using a high-elasticity carbon fiber sheet to reinforce the step-down section, it is possible to suppress yielding of the reinforcing bars at the step-down section without causing peeling or breakage of the carbon fiber sheet, and to shift failure 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, but 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 without being impregnated with resin (= dry)) is used as the fiber material.

[0097] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. Furthermore, the present invention can be embodied in various novel forms in addition to the above-described embodiments. Therefore, various omissions, substitutions, and modifications are possible in the above-described embodiments without departing from the spirit and scope of the present invention. Such novel forms and modifications are included within the scope and spirit of the present invention, as well as within the scope of the inventions set forth in the claims and equivalents of the inventions set forth in the claims. [Explanation of symbols]

[0098] 10: RC pier 2: End of paragraph 3: Base 4: Fiber materials 5: Main reinforcement 6: Fiber sheet

Claims

1. A reinforcement method for an RC pier that has a stepped portion and reinforces it with a fiber material, comprising: Elastic modulus is 350,000 (N / mm 2 ) A setting process of setting the amount of reinforcement by the fiber material using the above reinforcing fibers so that the failure mode of the RC pier shifts from failure of the step-down portion to bending failure of the base of the RC pier; A reinforcing layer forming process of forming a reinforcing layer on the RC pier, The reinforcing layer comprises: or consisting of the above-mentioned fiber material; The fiber material is a first reinforcing layer, and a fiber sheet is attached to the first reinforcing layer in a circumferential direction around the RC pier so that the fiber direction is horizontal, In the setting step, Calculating the yield load of the stepped portion based on the elastic modulus; setting a reinforcement amount of the fiber material so that the calculated yield load of the stepped-down portion is equal to or greater than the initial yield load of the base portion or the ultimate load of the base portion; In the reinforcing layer forming step, the fiber material is bonded to the stepped portion of the RC pier so that the fiber direction of at least half of the reinforcing fibers is along the vertical direction. A reinforcement method for RC bridge piers characterized by the above.

2. The reinforcement amount of the fiber material is set so that the yield load of the stepped portion is equal to or greater than the initial yield load of the base portion or the ultimate load of the base portion.

2. The method for reinforcing an RC pier according to claim 1,

3. Calculating the yield load of the reinforced stepped portion based on the initial yield bending moment of the reinforced stepped portion.

3. The method for reinforcing an RC pier according to claim 2, wherein:

4. The amount of reinforcement by the fiber material is set so that the yield load of the stepped portion is equal to or greater than the ultimate load of the base portion.

2. The method for reinforcing an RC pier according to claim 1,

5. The fiber material is bonded as a first reinforcing layer so that the fiber direction of the reinforcing fibers is aligned vertically, A fiber sheet with horizontal fiber direction is attached around the RC pier on the first reinforcement layer.

2. The reinforcement method for RC piers according to claim 1,

6. The fiber material is Unidirectional reinforced fiber sheet, A sheet formed by aligning a plurality of CFRP wire rods into a curtain shape, and strip-shaped FRP plates. The reinforcement method for an RC pier according to any one of claims 1 to 5, characterized in that:

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