Seismic reinforcement structure and seismic reinforcement method for existing reinforced concrete columnar structures

Abstract

This invention provides a seismic reinforcement structure and method for existing reinforced concrete (RC) columnar structures using a superelastic alloy, which can be applied to seismic reinforcement of existing RC columnar structures, improving their strength and toughness while also suppressing residual displacement. [Solution] In an existing RC columnar structure (RC bridge pier 10) reinforced by adding reinforced concrete (wrapping section 2) around the existing RC columnar structure (RC bridge pier 10), a superelastic alloy (superelastic alloy rod 6) is provided at the hinge section 12a at the bottom of the existing RC columnar structure (RC bridge pier 10), which is mechanically connected to the additional reinforcing bars (main reinforcing bars 3) with a high nut 5.

Description

Technical Field

[0001] The present invention relates to a seismic strengthening structure and method for existing RC columnar structures, and more particularly to a seismic strengthening structure and method for existing RC columnar structures using a superelastic alloy.

Background Art

[0002] Conventionally, seismic strengthening of existing RC columnar structures such as RC bridge piers has been progressing. However, when unexpected seismic forces act on such existing RC columnar structures, there is concern that the use of the structure after the disaster may become impossible due to the collapse of the RC columnar structure or an increase in residual displacement. In that case, it is necessary to demolish and then reconstruct the entire structure supported by the damaged RC columnar structure, resulting in a problem of prolonged recovery. Therefore, there is a demand for a seismic strengthening method with a residual displacement suppression effect that enables early recovery even when unexpected seismic forces or the like act on the RC columnar structure.

[0003] For example, in Patent Document 1 filed by the applicant of the present application, in a residual strain suppression structure 1 of an RC columnar structure (RC bridge pier 10) having a plastic hinge portion 2 in which axial bars (axial steel bars 4) yield due to bending stress acting on the RC columnar structure (RC bridge pier 10) to absorb seismic energy, in order to prevent damage to the core concrete 6 around the central axis of the RC columnar structure (RC bridge pier 10), a core concrete protection material (superelastic alloy bar 7) made of a superelastic alloy that extends vertically along the axial direction from the plastic hinge portion 2 so as to surround the core concrete 6 is provided. A residual strain suppression structure of an RC columnar structure is disclosed (see Claim 1 of the claims of Patent Document 1, Paragraphs

[0032] to

[0057] of the specification, FIGS. 2 and 6 of the drawings, etc.).

[0004] However, the residual strain suppression structure of the RC columnar structure described in Patent Document 1 is a technology applied to the plastic hinge portion of a newly constructed RC columnar structure so that the entire structure does not need to be demolished even when a major earthquake occurs, and it cannot be applied to the seismic strengthening of existing RC columnar structures.

[0005] Furthermore, for example, Patent Document 2 discloses a shear wall in which a superelastic alloy is used in part of the brace (bracing) of a wooden building, and the superelastic alloy portion 11 of the brace 5 yields before the brace body 10, thereby preventing residual strain from occurring in the brace body 10 and reliably preventing buckling of the brace 5 (see Claim 3 of the claims in Patent Document 2, paragraphs

[0057] to

[0076] of the specification, and Figures 1, 5, 7, etc. of the drawings).

[0006] However, the load-bearing wall described in Patent Document 2 involves providing a superelastic alloy portion 11 to the brace (diagonal bracing) of a wooden building, and was not applicable to seismic reinforcement of existing RC columnar structures.

[0007] Furthermore, Patent Document 3 discloses a Cu-Al-Mn-based shape memory alloy molded body in which a threaded portion is formed by rolling, and a method for manufacturing the same (see claims 1 and 9 of the claims section of Patent Document 3, paragraphs

[0020] to

[0044] of the specification, and Figures 1 to 3 of the drawings, etc.).

[0008] However, the Cu-Al-Mn-based shape memory alloy molded body and its manufacturing method described in Patent Document 3 are inventions that focus on forming threaded portions in superelastic alloys, and do not even consider the applications of superelastic alloys or their use in seismic reinforcement of existing concrete structures. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2021-179129 [Patent Document 2] Japanese Patent Publication No. 2020-122358 [Patent Document 3] Japanese Patent Publication No. 2020-122209 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Therefore, the present invention was devised in view of the aforementioned problems, and its objective is to provide a seismic reinforcement structure and seismic reinforcement method for existing RC columnar structures using a superelastic alloy that can be applied to seismic reinforcement of existing RC columnar structures, improving load-bearing capacity and toughness while also suppressing residual displacement. [Means for solving the problem]

[0011] The seismic reinforcement structure for an existing RC columnar structure according to the first invention is a seismic reinforcement structure for an existing RC columnar structure in which reinforced concrete is poured around the existing RC columnar structure to reinforce it, characterized in that a superelastic alloy that is mechanically connected to the added reinforcing bars is provided at the hinge portion at the lower part of the existing RC columnar structure.

[0012] The seismic reinforcement structure for an existing RC columnar structure according to the second invention is characterized in that, in the first invention, the lower end of the superelastic alloy is embedded and fixed to the foundation of the existing RC columnar structure.

[0013] The third invention relates to a seismic reinforcement method for an existing RC columnar structure, which involves reinforcing the existing RC columnar structure by pouring additional reinforced concrete around it, comprising: a reinforcement step of arranging reinforcing bars around the existing RC columnar structure; a formwork installation step of assembling and installing formwork around the reinforcing bars assembled in the reinforcement step; and a filler filling step of filling the formwork installed in the formwork installation step with filler, wherein in the reinforcement step, a superelastic alloy that mechanically connects with the additional reinforcing bars is placed at the hinge portion at the lower part of the existing RC columnar structure.

[0014] The seismic reinforcement method for an existing RC columnar structure according to the fourth invention is characterized in that, in the reinforcement step, a hole is drilled in the foundation of the existing RC columnar structure and the superelastic alloy is embedded and fixed in the foundation.

[0015] The fifth invention relates to a seismic reinforcement method for an existing RC columnar structure, which involves reinforcing the existing RC columnar structure by pouring additional reinforced concrete around it, comprising: a reinforcement step of arranging reinforcing bars around the existing RC columnar structure; a steel pipe press-fitting step of press-fitting steel pipes around the reinforcing bars assembled in the reinforcement step; and a filler material filling step of filling the steel pipes installed in the steel pipe press-fitting step with a filler material, wherein in the reinforcement step, a superelastic alloy that mechanically connects with the additional reinforcing bars is placed at the hinge portion at the lower part of the existing RC columnar structure. [Effects of the Invention]

[0016] According to the first to fifth inventions, the seismic reinforcement of existing RC columnar structures can be applied, improving the load-bearing capacity of the existing RC columnar structure before reinforcement, and improving ductility and suppressing residual displacement compared to conventional methods of seismic reinforcement using RC wrapping on existing RC columnar structures. As a result, even if a large seismic force acts on the RC columnar structure, the RC columnar structure will not collapse, and the entire structure supported by the RC columnar structure can be used (shared) sooner. Furthermore, with general RC wrapping reinforcement, the load on the foundation increases due to the improvement in load-bearing capacity from the reinforcement, which may necessitate foundation reinforcement as well. However, according to the first to fifth inventions, deformation performance such as improved ductility and reduced residual displacement can be improved without increasing the load-bearing capacity after reinforcement to the same extent as in conventional methods.

[0017] In particular, according to the second and fourth inventions, since the lower end of the superelastic alloy is embedded and anchored in the foundation of the existing RC columnar structure, even when a large seismic force acts on the RC columnar structure, the superelastic alloy can suppress residual displacement and absorb seismic energy, resulting in a highly ductile structure. [Brief explanation of the drawing]

[0018] [Figure 1] Figure 1(a) is a side view showing the existing structure before reinforcement, and Figure 1(b) is a cross-sectional view taken along line AA in Figure 1(a). [Figure 2]Fig. 2(a) is a side view showing the seismic reinforcement structure of an existing RC columnar structure according to an embodiment of the present invention, and Fig. 2(b) is a cross-sectional view taken along line B-B of Fig. 2(a). [Figure 3] It is a graph showing the relationship between the loading cycle of positive and negative alternating loads and the drift. [Figure 4] Fig. 4 is a view showing an RC specimen, where (a) is a front view and (b) is a cross-sectional view taken along line C-C of (a). [Figure 5] Fig. 5 is a view showing an RC reinforced specimen, where (a) is a front view and (b) is a cross-sectional view taken along line D-D of (a). [Figure 6] Fig. 6 is a view showing a SEA-Long specimen, where (a) is a front view and (b) is a cross-sectional view taken along line E-E of (a). [Figure 7] Fig. 7 is a view showing a SEA-Short specimen, where (a) is a front view and (b) is a cross-sectional view taken along line F-F of (a). [Figure 8] Fig. 8 is a graph showing the horizontal displacement (mm) and drift (%) with respect to the horizontal load (kN) of the RC specimen when a negative alternating load is applied. [Figure 9] Fig. 9 is a graph showing the horizontal displacement (mm) and drift (%) with respect to the horizontal load (kN) of the RC reinforced specimen when a negative alternating load is applied. [Figure 10] Fig. 10 is a graph showing the horizontal displacement (mm) and drift (%) with respect to the horizontal load (kN) of the SEA-Long specimen when a negative alternating load is applied. [Figure 11] Fig. 11 is a graph showing the horizontal displacement (mm) and drift (%) with respect to the horizontal load (kN) of the SEA-Short specimen when a negative alternating load is applied. [Figure 12] Fig. 12 is a line graph showing the relationship between the residual displacement (mm) of each specimen, the horizontal displacement (mm), and the drift (%).

Embodiments for Carrying Out the Invention

[0019] Hereinafter, one embodiment of the seismic reinforcement structure and seismic reinforcement method for existing RC columnar structures according to the present invention will be described in detail with reference to the drawings.

[0020] [Seismic reinforcement structure] An embodiment of the seismic reinforcement structure 1 for an existing RC columnar structure will be described using Figures 1 and 2. In this embodiment, a reinforced concrete bridge pier 10 will be used as an example of an existing RC columnar structure.

[0021] First, let's briefly explain the existing RC bridge pier 10 using Figure 1. Figure 1(a) is a side view showing the existing RC bridge pier 10 structure before reinforcement, and Figure 1(b) is a cross-sectional view of Figure 1(a) along line AA.

[0022] The RC bridge pier 10 is a reinforced concrete structure comprising a foundation 11 with a thickness of D2 and a columnar section 12 with a horizontal cross-section of depth D1 and width W1, erected on the foundation 11. Furthermore, the lower cross-sectional edge of the columnar section 12, which is close to the lower foundation 11, will experience a bending moment exceeding the full plastic moment during a major earthquake, causing the entire cross-section of the member to yield and become a plastic hinge section 12a that loses rotational rigidity like a hinge.

[0023] In the columnar section 12, twelve main reinforcements 13 made of deformed steel bars such as SD295A and SD345 are arranged at approximately equal intervals along the vertical direction as internal concrete reinforcement, and rectangular stirrups 14 made of deformed steel bars are arranged around the main reinforcements 13 at predetermined pitches so that their axes are perpendicular to each other. In this embodiment, the stirrups 14 are arranged at equal intervals of 120 mm across the entire cross-section in the vertical direction.

[0024] Next, using Figure 2, we will describe the seismic reinforcement structure 1 for an existing RC columnar structure according to an embodiment of the present invention (hereinafter also simply referred to as seismic reinforcement structure 1). Figure 2(a) is a side view showing the seismic reinforcement structure 1 for an existing RC columnar structure according to an embodiment of the present invention, and Figure 2(b) is a cross-sectional view taken along line AA of Figure 2(a), showing the horizontal cross-section of the plastic hinge portion 12a of the columnar portion 12. As shown in Figure 2, the seismic reinforcement structure 1 according to this embodiment is a seismic reinforcement structure that reinforces the existing RC columnar structure, the aforementioned RC bridge pier 10, by wrapping new reinforced concrete around the columnar portion 12 to add a wrapping portion 2 of a predetermined thickness t.

[0025] (Reinforcement: Main reinforcement, stirrups) In the reinforcement section 2, twelve main reinforcements 3 of the same or larger diameter as the main reinforcements 13 are arranged at equal intervals along the vertical direction outside the aforementioned main reinforcements 13, and stirrups 4 are arranged around the main reinforcements 3 at equal intervals of 60 mm, shorter than the intervals of the stirrups 14, and concrete of a predetermined strength is poured in place. As shown in Figure 1(a), the main reinforcements 13 extend from the columnar section 12 to the foundation section 11 and are anchored to the foundation section 11 with hooks.

[0026] As shown in Figures 2(a) and 2(b), the seismic reinforcement structure 1 for existing RC columnar structures according to this embodiment differs from conventional RC casing seismic reinforcement structures in that a superelastic alloy rod 6 made of a superelastic alloy is attached to the outside of the plastic hinge portion 12a, along the axial direction of the main reinforcement 3, connected by a high nut 5 which is a mechanical joint.

[0027] (High nut: Mechanical fitting) The tall nut 5 is a component that is screwed into the threaded portion (not shown) formed on the main reinforcement 3 and the threaded portion (not shown) formed on the superelastic alloy rod 6, respectively, for joining. However, the tall nut 5 is not limited to a tall nut, as long as it is a mechanical joint that mechanically joins the main reinforcement 3 and the superelastic alloy rod 6, and the joint portion does not yield before the main reinforcement 3 or the superelastic alloy rod 6 yield.

[0028] (Superelastic alloy rod material) The superelastic alloy rod 6 is a rod made of a superelastic alloy having approximately the same diameter and strength as the main reinforcement 3. Here, a superelastic alloy (SEA) is a type of shape memory alloy that utilizes phase transformation (stress-induced martensitic transformation) due to the loading and unloading of external forces to exhibit extremely high restoring force (superelastic properties), such that the residual strain after a 6% strain load is 1.0% or less. In other words, superelastic alloys (SEAs) are unique materials with high origin directivity, and even when stretched to about 10 times the elastic range of ordinary metals, there is little to no residual displacement that returns them to their original shape.

[0029] In contrast, with common steel materials such as SD295A and SD345 deformed steel bars (reinforcement bars) for main reinforcement 13 and main reinforcement 3, if a load is applied until a 6% distortion occurs, a residual distortion of about 5% will remain even after the load is removed, and it will not return to its original state.

[0030] The superelastic alloy rod 6 according to this embodiment is made of a Cu-Al-Mn superelastic alloy. Specifically, the superelastic alloy rod 6 has a composition containing 3 to 10 mass% Al, 5 to 20 mass% Mn, and 0 to 5 mass% Ni, with the remainder being Cu and unavoidable impurities, and is made of a Cu-Al-Mn alloy having a recrystallized structure that is substantially β single phase. Note that the superelastic alloy can also be a Ti-Ni alloy and will still perform its function adequately.

[0031] The superelastic alloy rod 6 has a total length of 300 mm and is anchored to the base 11 with a 50 mm embedment, as shown in Figure 2. Of course, the length of the superelastic alloy rod 6 is not limited to 300 mm; it can be shorter than 300 mm, such as 150 mm, as in the SEA-Short specimen described later. However, the embedment length of the superelastic alloy rod 6 to the base 11 must be 50 mm.

[0032] [Methods for seismic reinforcement of existing reinforced concrete columnar structures] Next, a seismic reinforcement method for an existing RC columnar structure according to an embodiment of the present invention will be described using Figures 1 and 2. An example will be given in which seismic reinforcement is carried out by wrapping cast-in-place reinforced concrete around the columnar portion 12 of the aforementioned existing columnar concrete structure, an RC bridge pier 10, as shown in Figure 1, to add a wrapping section 2 of a predetermined thickness t, as shown in Figure 2.

[0033] (1. Reinforcement process) First, in the seismic reinforcement method for existing RC columnar structures according to this embodiment, a reinforcement step is performed in which reinforcing bars are placed around the columnar portion 12 of the RC bridge pier 10.

[0034] Specifically, multiple stirrups 4 are placed around the columnar section 12, and 12 main reinforcement bars 3 are inserted through the multiple stirrups 4. The stirrups 4 are then spread out at equal intervals of 60 mm as described above and fixed to the main reinforcement bars 3 with binding wire or the like.

[0035] Furthermore, in the foundation 11 below the main reinforcement 3, holes are drilled and superelastic alloy rods 6 are pre-placed, with the lower end of the superelastic alloy rods 6 embedded about 50 mm into the foundation 11 and fixed to it with adhesive or the like. Then, a tall nut 5 is screwed onto the threaded portion of the upper end of the superelastic alloy rod 6 fixed to the foundation 11 to connect it to the main reinforcement 3, and the reinforcing bars are assembled and placed around the columnar part 12 of the RC bridge pier 10.

[0036] (2. Formwork installation process) Next, in the seismic reinforcement method for existing RC columnar structures according to this embodiment, a formwork installation step is performed in which formwork is assembled and installed around the reinforcing bars (main reinforcement 3 and stirrup reinforcement 4) assembled in the pre-reinforcement step. Alternatively, after the formwork installation step, a steel pipe press-in step may be performed in which steel pipes are pressed into the existing column instead of formwork.

[0037] (3. Filler filling process) Next, in the seismic reinforcement method for existing RC columnar structures according to this embodiment, a filling material filling step is performed in which a filling material is filled into the formwork installed in the formwork installation step, thereby extending the aforementioned winding section 2.

[0038] Specifically, in the seismic reinforcement method for existing RC columnar structures according to this embodiment, fresh concrete mixed to achieve a predetermined design strength is poured into the formwork as a filling material. However, the filling material according to the present invention is not limited to concrete, and if the thickness t of the casing section 2 is narrow, mortar or grout without coarse aggregate may be used as a filling material. If a steel pipe press-in process is performed instead of a formwork installation process, mortar or grout is filled between the existing RC columnar structure and the pressed-in steel pipe in this process.

[0039] (4. Formwork Removal Process) Next, in the seismic reinforcement method for existing RC columnar structures according to this embodiment, after a predetermined curing period has elapsed and the filling material filled in the pre-filling material filling step has reached a predetermined strength, a formwork removal step is performed in which the formwork installed in the formwork installation step is removed and dismantled. However, if steel pipes are pressed in instead of formwork, this step is unnecessary.

[0040] Upon completion of this process, the seismic reinforcement work for the existing RC columnar structure according to the embodiment of the present invention is completed.

[0041] According to the seismic reinforcement structure 1 for existing RC columnar structures and the seismic reinforcement method for existing RC columnar structures according to this embodiment described above, the load-bearing capacity of the existing RC columnar structure, which is the RC bridge pier 10, can be improved compared to before reinforcement, thereby reinforcing the seismic resistance of the existing RC bridge pier 10. Moreover, according to the seismic reinforcement structure 1 for existing RC columnar structures and the seismic reinforcement method for existing RC columnar structures according to this embodiment, the ductility is improved and residual displacement can be suppressed compared to the conventional method of seismically reinforcing existing RC columnar structures with RC wrapping. Therefore, even if a large seismic force acts on the RC bridge pier 10, the RC bridge pier 10 and the bridge supported by the RC bridge pier 10 will not collapse, and the entire bridge supported by the RC bridge pier 10 will be able to be used for vehicle traffic (shared use) at an early stage, enabling rapid disaster recovery.

[0042] Furthermore, according to the seismic reinforcement structure 1 for existing RC columnar structures and the seismic reinforcement method for existing RC columnar structures according to this embodiment, since the lower end of the superelastic alloy rod 6 is embedded and fixed in the foundation 11 of the RC bridge pier 10, even when a large seismic force acts on the RC bridge pier 10, the superelastic alloy rod 6 can suppress residual displacement and absorb seismic energy, resulting in a highly ductile structure (bridge pier).

[0043] Furthermore, in conventional reinforced concrete (RC) walling reinforcement, the load on the foundation increases due to the improved load-bearing capacity resulting from the reinforcement, which may necessitate further reinforcement of the foundation. However, according to the seismic reinforcement structure 1 for existing RC columnar structures and the seismic reinforcement method for existing RC columnar structures according to this embodiment, it is possible to improve the deformation performance of the RC columnar structure, such as improving ductility and reducing residual displacement, without increasing the load-bearing capacity of the reinforced RC columnar structure to the same extent as in conventional methods. Therefore, as a seismic reinforcement method for existing RC columnar structures, it becomes unnecessary to perform additional reinforcement of the foundation even when the deformation performance of the RC columnar structure is improved.

[0044] [Effect verification experiment] Next, we will describe the effectiveness verification experiment conducted to confirm the effects of the present invention. The effectiveness verification experiment involved creating multiple types of test specimens and applying alternating positive and negative loads over a predetermined loading cycle to each specimen, assuming conditions equivalent to the load conditions acting on the bridge piers during an earthquake, in order to understand the durability performance, deformation performance, and progress of damage of the bridge piers. The experiment was conducted by measuring the horizontal displacement (mm) in relation to the horizontal load (kN). Furthermore, drift (%) was defined as the percentage of horizontal displacement (mm) / specimen height (mm), and the applied displacement was given as an integer multiple of a drift of 0.5% (5.5 mm).

[0045] As shown in Figure 3, the loading cycles were as follows: 0.5% to 4.5% → displacement increment of 0.5%, 3 cycles; 0.5% to 4.5% → 5.0% to 5.5% → displacement increment of 0.5%, 1 cycle; 6.0% to 15.0% → displacement increment of 1.0%, 1 cycle.

[0046] <Specimen> Four types of test specimens were prepared: an unreinforced RC specimen (as shown in Figure 4, representing the state before RC reinforcement), a reinforced RC specimen (as shown in Figure 5, representing the state after RC reinforcement), a SEA-Long specimen (as shown in Figure 6, with a 300 mm length of superelastic alloy attached to the hinge), and a SEA-Short specimen (as shown in Figure 7, with a 150 mm length of superelastic alloy attached to the hinge).

[0047] Figure 4 shows an RC specimen, where (a) is a front view and (b) is a CC cross-sectional view of (a). Figure 5 shows an RC reinforced specimen, where (a) is a front view and (b) is a DD cross-sectional view of (a). Figure 6 shows a SEA-Long specimen, where (a) is a front view and (b) is an EE cross-sectional view of (a). Figure 7 shows a SEA-Short specimen, where (a) is a front view and (b) is an FF cross-sectional view of (a).

[0048] As shown in Figure 4, the unreinforced concrete (RC) specimen has a square column section with a depth of D1 = 350 mm and a width of W1 = 350 mm. The reinforcement consists of 12 D10 deformed steel bars as main reinforcement, surrounded by multiple D6 deformed steel bars at 120 mm intervals as stirrups. A load with alternating positive and negative loads is applied at a height of 1100 mm from the foundation. Furthermore, the stirrups of the RC specimen are densely spaced at a pitch of 60 mm to prevent buckling and reinforcement fracture from progressing at the loading point before the plastic hinge section.

[0049] As shown in Figure 5, the reinforced RC specimen, which is assumed to be after additional RC reinforcement, is assumed to have a wrap-around section formed around the aforementioned unreinforced RC specimen. For this reason, the columnar section is square in shape with a depth of D3 = 400 mm and a width of W1 = 350 mm, and the reinforcement of the wrap-around section consists of 12 D13 deformed steel bars as main reinforcement, and multiple D6 deformed steel bars are placed around them as stirrups at 60 mm intervals along the entire length.

[0050] As shown in Figure 6, the SEA-Long specimen is designed with the aforementioned seismic reinforcement structure 1 in mind, with the aforementioned superelastic alloy rod 6 placed at the hinge of the winding section 2. The columnar section is square (rectangular) with a depth D3 = 400 mm and a width W1 = 400 mm. The reinforcement of the winding section 2 consists of 12 D13 deformed steel bars as main reinforcement, and several D6 deformed steel bars are placed around them as stirrups at 60 mm intervals along the entire length. In addition, the superelastic alloy rod is connected to the D13 deformed steel bars via a high nut. The superelastic alloy rod has a diameter of 12.4 mm and a total length of 300 mm.

[0051] As shown in Figure 6, the SEA-Short specimen, like the SEA-Long specimen, is designed with the aforementioned seismic reinforcement structure 1 in mind, and the aforementioned superelastic alloy rods 6 are placed at the hinge of the winding section 2. Therefore, the columnar section is square (rectangular) with a depth of D3 = 400 mm and a width of W1 = 400 mm. The reinforcement of the winding section 2 consists of 12 D13 deformed steel bars as main reinforcement, and around them, multiple D6 deformed steel bars are placed at 60 mm intervals along the entire length as stirrups. In addition, the superelastic alloy rods are connected to the D13 deformed steel bars via high nuts. The superelastic alloy rods have a diameter of 12.4 mm and a total length of 150 mm.

[0052] <Experimental Results> Figure 8 is a graph showing the horizontal displacement (mm) and drift (%) with respect to the horizontal load (kN) of an RC specimen when subjected to alternating positive and negative loading. Figure 9 is a graph showing the horizontal displacement (mm) and drift (%) with respect to the horizontal load (kN) of an RC reinforced specimen when subjected to alternating negative loading. Figure 10 is a graph showing the horizontal displacement (mm) and drift (%) with respect to the horizontal load (kN) of a SEA-Long specimen when subjected to alternating negative loading. Figure 11 is a graph showing the horizontal displacement (mm) and drift (%) with respect to the horizontal load (kN) of a SEA-Short specimen when subjected to alternating negative loading. Finally, Figure 12 is a line graph showing the relationship between the residual displacement (mm), horizontal displacement (mm), and drift (%) of each specimen.

[0053] As shown in Figure 8, the unreinforced concrete (RC) specimen failed due to buckling or fracture of the main reinforcement when subjected to a horizontal load of ±80kN or less and a drift of approximately ±5% or less. In contrast, as shown in Figure 9, the RC-reinforced specimen, which was reinforced using conventional RC wrapping, showed increased strength up to approximately ±150kN, but failed similarly to the RC specimen due to buckling or fracture of the main reinforcement when subjected to a drift of approximately 5% or less.

[0054] In contrast, as shown in Figure 10, the SEA-Long specimen, having a superelastic alloy attached to the hinge, had a strength of approximately ±130kN, and drifted by approximately ±15% without fracture. As shown in Figure 11, the SEA-Short specimen, similar to the SEA-Long specimen, also had a superelastic alloy attached to the hinge, resulting in a strength of approximately ±130kN, and drifting by approximately ±10% without fracture.

[0055] Furthermore, as shown in Figure 12, in the SEA-Long and SEA-Short specimens, compared to the RC specimens and RC-reinforced specimens, when the reinforcing steel yields at a drift of approximately 4%, the maximum load decreases. However, at that time, the superelastic alloy functions as a fail-safe, and the residual displacement decreases significantly as indicated by the arrow in the figure. In other words, the SEA-Long and SEA-Short specimens suppress residual displacement even with large drifts, showing greater toughness compared to the RC-reinforced specimens.

[0056] The seismic reinforcement structure 1 and seismic reinforcement method for existing RC columnar structures according to embodiments of the present invention have been described in detail above. However, the embodiments described above or illustrated are merely examples of embodiments that have been implemented in carrying out the present invention. Therefore, the technical scope of the present invention should not be interpreted as being limited by these embodiments.

[0057] In particular, while RC bridge piers were used as an example of RC columnar structures in this explanation, the present invention is not limited to RC bridge piers and can also be applied to RC columns in building structures, etc. Furthermore, the diameter and pitch of the main reinforcement and stirrups are examples only and should be determined by structural calculations according to the scale of the RC columnar structure, etc. [Explanation of symbols]

[0058] 1: Seismic reinforcement structure 2: Rolling section 3: Main reinforcement (reinforcement bars) 4: Stirring bars (reinforcement bars) 5: High nut (mechanical fitting) 6: Superelastic alloy rod (superelastic alloy) 10: RC bridge pier (existing RC columnar structure) 11:Foundation part 12: Columnar part 12a: Plastic hinge section 13: Main reinforcement (reinforcement bars) 14: Stirring bars (reinforcement bars)

Claims

1. An existing reinforced concrete columnar structure is reinforced by pouring additional reinforced concrete around the existing reinforced concrete columnar structure, A superelastic alloy is provided at the hinge portion of the lower part of the existing RC columnar structure, which is mechanically connected to the reinforcement bars to be added. A seismic reinforcement structure for existing reinforced concrete columnar structures characterized by the following features.

2. The lower end of the superelastic alloy is embedded and anchored in the foundation of the existing RC columnar structure. The seismic reinforcement structure for an existing RC columnar structure according to claim 1, characterized by the above.

3. A seismic reinforcement method for existing reinforced concrete columnar structures, which involves adding reinforced concrete around the existing reinforced concrete columnar structure to strengthen it, The process of arranging reinforcing bars around the existing RC columnar structure, The formwork installation process involves assembling and installing formwork around the reinforcing bars assembled in the aforementioned reinforcement process, The process includes a filler material filling step in which filler material is filled into the formwork installed in the formwork installation step, In the reinforcement step, a superelastic alloy is placed at the hinge portion at the bottom of the existing RC columnar structure to be mechanically connected to the reinforcement bars to be added. A seismic reinforcement method for existing reinforced concrete columnar structures characterized by the following.

4. In the reinforcement step, drilling holes in the foundation of the existing RC columnar structure and embedding the superelastic alloy into the foundation is performed. A seismic reinforcement method for an existing RC columnar structure according to claim 3, characterized by the above.

5. A seismic reinforcement method for existing reinforced concrete columnar structures, which involves adding reinforced concrete around the existing reinforced concrete columnar structure to strengthen it, The process of arranging reinforcing bars around the existing RC columnar structure, A steel pipe pressing process in which steel pipes are pressed into the area around the reinforcing bars assembled in the aforementioned reinforcement process, The process includes a filler material filling step in which a filler material is filled into the steel pipe installed in the steel pipe press-in step, In the reinforcement step, a superelastic alloy is placed at the hinge portion at the bottom of the existing RC columnar structure to be mechanically connected to the reinforcement bars to be added. A seismic reinforcement method for existing reinforced concrete columnar structures characterized by the following.

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