Shear walls and structures

Abstract

To provide a bearing wall which is excellent in bearing strength and deformation performance while reducing the widths of column parts of the bearing wall.SOLUTION: A bearing wall 10 is made of reinforced concrete, and includes a wall part 20, and column parts 30 which are provided on the end in a horizontal direction of the wall part 20 and extend in a vertical direction. Concrete bodies 21 and 31 of the wall part 20 and the column parts 30 are formed of fiber-reinforced concrete in which 0.3% or more and 1.5% or less of fibers are mixed with respect to a concrete volume. The widths in the wall thickness direction of the wall part 20 of the column parts 30 are 1 time or more and less than twice of the wall thickness of the wall part 20.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a fiber-mixed reinforced concrete shear wall and a structure including the shear wall. [Background technology]

[0002] BACKGROUND ART Conventionally, there has been a bearing wall that includes a wall portion made of reinforced concrete (RC) and a column portion made of RC provided on one end side of the wall portion (see Patent Documents 1 and 2). Patent Document 1 discloses a multi-story earthquake-resistant wall structure for a high-rise building. The multi-story earthquake-resistant wall includes wall panels and auxiliary columns, and a plurality of such walls are arranged vertically in succession. Patent Document 2 shows a reinforced structure for a building that includes a reinforced wall and a column of a concrete building joined to the reinforced wall. The reinforced wall is made of a panel made of a hardened fiber-containing hydraulic composition and a joint formed between the panel and the column. Non-Patent Document 1 describes a method for determining the plastic deformation capacity of RC shear walls made of ordinary concrete. While ductility can be evaluated higher for RC shear walls with auxiliary columns than for RC shear walls without such columns, the width of the auxiliary columns must be at least twice the wall thickness to expect high plastic deformation capacity based on the method. Therefore, in RC shear walls with auxiliary columns, the width of the auxiliary columns is often set to at least twice the wall thickness, which reduces the floor area of ​​the building and can make it difficult to ensure a user-friendly interior space. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 02-248582 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-32192 [Non-patent literature]

[0004] [Non-Patent Document 1] 2020 Edition: Commentary on the Technical Standards for Building Structures Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a bearing wall that has excellent strength and deformation performance while reducing the width of the column portion of the bearing wall, and a structure that uses the bearing wall. [Means for solving the problem]

[0006] The inventors arrived at this invention by noting that by mixing fibers into the concrete that forms the walls and columns of a shear wall in an amount of 0.3% to 1.5% by volume of concrete, the fibers can provide a reinforcing effect equal to or greater than that of shear reinforcement, eliminating the need to densely arrange shear reinforcement in the walls and columns. The shear wall of the first invention (for example, shear wall 10 described below) is a shear wall made of reinforced concrete, and comprises a wall portion made of reinforced concrete (for example, wall portion 20 described below) and a column portion made of reinforced concrete (for example, column portion 30 described below) provided at the horizontal end of the wall portion, and the concrete bodies of the wall portion and the column portion (for example, concrete bodies 21, 31 described below) are formed of fiber-reinforced concrete containing fibers in an amount of 0.3% to 1.5% by volume of concrete, and the width of the column portion is at least 1 time but less than 2 times the wall thickness of the wall portion.

[0007] According to this invention, a bearing wall is constructed including wall sections and columns, and these wall sections and columns are formed from fiber-reinforced concrete containing 0.3% to 1.5% of fiber by volume of concrete. Therefore, since the fiber exerts a reinforcing effect equal to or greater than that of shear reinforcement, there is no need to arrange shear reinforcement bars in the wall sections or columns too densely. As a result, the width of the column can be reduced to between one and two times the thickness of the wall, ensuring a user-friendly interior space while achieving a bearing wall with excellent strength and deformation performance. In addition, the concrete bodies of the walls and columns were constructed using fiber-reinforced concrete instead of ordinary concrete, making construction easy. Furthermore, because the columns are made of fiber-reinforced concrete, their deformation performance is improved, ensuring excellent deformation performance even when the column width is more than one time but less than two times the wall thickness. This eliminates the need to make the column width more than twice the wall thickness as in the conventional regulations shown in Non-Patent Document 1. As a result, it has become easier to plan rooms with regular plan shapes, and the floor area of ​​buildings can be increased compared to conventional methods, making it possible to ensure user-friendly interior spaces. Furthermore, fiber-reinforced concrete can be produced by simply adding fibers to ordinary concrete and mixing the fibers during the concrete mix. This is simpler and easier to work with than the method described in Patent Document 1, in which separate components are installed to ensure toughness and strength. For example, if the ratio of the cross-sectional area of ​​the horizontal and vertical reinforcement to the cross-sectional area of ​​the wall (reinforcement ratio) is 0.3% or 0.59%, and the walls and columns are made of fiber-reinforced concrete with 0.5% or 1.0% steel fiber mixed in with the concrete volume, the shear strength can be increased by approximately 1.1 to 1.18 times compared to when the walls and columns are made of ordinary concrete with no fibers mixed in. In addition, a sudden decrease in strength after the maximum strength can be prevented, and deformation performance can be improved.

[0008] The bearing wall of the second invention is characterized in that the fibers are steel fibers with both ends bent. According to this invention, steel fibers with bent ends are used as the fibers to be mixed into the fiber-reinforced concrete, and therefore the bent portions of the steel fibers improve the adhesion between the concrete and the steel fibers. Furthermore, since the thermal expansion coefficient of steel fibers is approximately equal to that of concrete, it is possible to reduce internal stress caused by temperature changes, and to ensure the integrity of the steel fibers and concrete.

[0009] A structure of the third invention (for example, building 1 described below) is a structure comprising the above-mentioned reinforced concrete shear wall, wherein another shear wall (for example, shear wall 10A described below) is placed above or below the aforementioned shear wall, and the another shear wall comprises a wall section (for example, wall 20 described below) made of reinforced concrete without any fibers mixed in, and a column section (for example, column 30 described below) made of reinforced concrete without any fibers mixed in, provided at the horizontal end of the wall section, and wherein the vertical reinforcement of the wall section of the shear wall (for example, vertical reinforcement 22 described below) is joined to the vertical reinforcement of the wall section of the another shear wall, and the column main reinforcement of the column of the shear wall (for example, column main reinforcement 32 described below) is joined to the column main reinforcement of the column of the another shear wall.

[0010] Here, the load-bearing wall and the other load-bearing wall may be provided on either the ground floor or the basement floor of the structure. According to this invention, a bearing wall made of concrete without fibers is installed above or below a bearing wall made of fiber-reinforced concrete, and the vertical reinforcement and main column reinforcement of both walls are connected to each other. Therefore, even if bearing walls made of fiber-reinforced concrete are not installed on every floor of a structure, by using bearing walls made of fiber-reinforced concrete in areas that are subject to large loads or where toughness is required, a structure with excellent shear strength and deformation performance can be realized. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a bearing wall that has excellent strength and deformation performance while reducing the width of the column portion of the bearing wall, and a structure that uses the bearing wall. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a plan view of a building to which a bearing wall according to an embodiment of the present invention is applied. [Figure 2] FIG. 2 is a cross-sectional view of the building taken along line AA in FIG. 1. [Figure 3] FIG. 1 is a front view of a load-bearing wall of a building. [Figure 4] FIG. 4 is a cross-sectional view of the shear wall of FIG. 3 . [Figure 5] 4A and 4B are cross-sectional views CC and DD of the shear wall of FIG. 3. [Figure 6] 1A to 1C are a front view, a cross-sectional view, and a longitudinal-sectional view showing the structures of specimens No. 1 to No. 3 used in the loading test. [Figure 7] FIG. 7 is an enlarged view of the vertical cross section of the wall and column of the specimen in FIG. 6. [Figure 8] FIG. 7 is an enlarged cross-sectional view of the wall and column of the specimen of FIG. 6. [Figure 9] FIG. 1 is a front view of a force application device used in a force application test. [Figure 10] FIG. 10 is a diagram showing the test results of a loading test (the relationship between a horizontal load Q and a horizontal displacement δ). DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention is a shear wall having wall and column sections made of reinforced concrete with fibers mixed in, and the concrete bodies of these walls and columns are made of fiber-reinforced concrete with fibers mixed in at 0.3% to 1.5% by volume of concrete, so that the width of the columns is at least one time but less than two times the wall thickness of the walls (Figs. 1 to 6). Also, in a structure equipped with the shear wall of the present invention, a shear wall made of reinforced concrete with fibers mixed in is placed above or below another shear wall made of reinforced concrete with no fibers mixed in, and the main column reinforcement bars and vertical wall reinforcement bars that form both shear walls are joined to each other. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a plan view of a predetermined floor of a building 1 as a structure to which a bearing wall 10 according to one embodiment of the present invention is applied. Fig. 2 is a cross-sectional view of the building 1 of Fig. 1 taken along line AA. The building 1 is a reinforced concrete building with multiple floors, and is equipped with multiple columns 2 extending vertically, multiple beams 3 connecting the tops of the multiple columns 2, and a floor (not shown) supported by the multiple beams 3. In plan view, a plurality of shear walls 10, 10A are arranged vertically in succession in the core portion, which is the center of the building 1. These shear walls 10, 10A are arranged across multiple stories to form a multi-story earthquake-resistant wall. Each bearing wall 10 comprises a wall portion 20 and a column portion 30 extending vertically along the end of the wall portion 20. In other words, the column 2 arranged in the core portion is the column portion 30 joined to the wall portion 20.

[0014] Fig. 3 is a front view of the bearing wall 10. Fig. 4 is a BB cross-sectional view of the bearing wall 10 of Fig. 3. Fig. 5 is a CC cross-sectional view and a DD cross-sectional view of the bearing wall 10 of Fig. 3. The wall portion 20 comprises a concrete body 21 formed of fiber-reinforced concrete mixed with fibers, vertical reinforcement 22 embedded in the concrete body 21 and extending vertically, and horizontal reinforcement 23 embedded in the concrete body 21 and extending horizontally. The column portion 30 comprises a concrete body 31 formed of fiber-reinforced concrete mixed with fibers, column main reinforcements 32 embedded in the concrete body 31 and extending vertically, and hoop reinforcements 33 embedded in the concrete body 31 and wrapped around the column main reinforcements 32. The width of the column portion 30 in the wall thickness direction of the wall portion 20 (column width) is the same as the wall thickness of the wall portion 20. The column depth of the column portion 30 (visible width when viewed from the front) is approximately 0.1 to 0.3 times the total length of the bearing wall 10 including the wall portion 20 and the column portion 30 (total wall length). The concrete bodies 21 of the wall sections 20 and the concrete bodies 31 of the column sections 30 are made of fiber-reinforced concrete in which steel fibers are mixed in an amount of 0.3% to 1.5% by volume of concrete. The steel fibers have hooks on both ends, and the diameter of the steel fibers is preferably about 0.1 mm to 0.6 mm, and the length of the steel fibers is preferably about 20 mm to 50 mm.

[0015] The shear wall 10A is arranged in multiple layers on top of the shear wall 10, and differs from the shear wall 10 in that the concrete body 21 of the wall portion 20 and the concrete body 31 of the column portion 30 are formed from concrete that does not contain fibers, but the rest of the configuration is the same as that of the shear wall 10. The vertical reinforcements 22 and the column main reinforcements 32 of the upper and lower bearing walls 10, 10A are joined to each other.

[0016] [Loading test] Below, four test specimens (No. 1 to No. 4) were fabricated to mimic the above-mentioned shear walls, and a loading test was conducted to apply horizontal force to verify the reinforcing effect of SFRC (steel fiber reinforced concrete). Figure 6 shows a front view, a cross section, and a longitudinal section showing the structure of specimens No. 1 to No. 3. Figure 7 is an enlarged view of the longitudinal section of the wall and column of the specimen in Figure 6. Figure 8 is an enlarged view of the cross section of the wall and column of the specimen in Figure 6. Note that specimen No. 4 has twice the amount of horizontal and vertical reinforcement in the wall as specimens No. 1 to No. 3 in Figures 6 to 8. The test specimens were approximately 1 / 3 to 1 / 4 the size of the actual building, simulating the lower floors of the building. Each specimen was also constructed so that shear failure of the wall preceded flexural yielding at the base of the wall. Specifically, the wall thickness of each specimen was 180 mm, the wall internal length was 1200 mm, the column width was the same as the wall thickness, 180 mm, and the column depth was 500 mm.

[0017] The configuration of specimens No. 1 to No. 4 is shown in the table below. [Table 1]

[0018] As shown in the table, the concrete used to form the wall and column sections was ordinary concrete for specimen No. 1, and fiber-reinforced concrete (SFRC) containing steel fibers for specimens No. 2 to No. 4. The target strength of the concrete was 60 N / mm 2 The amount of fiber mixed in was 0.5% of the concrete volume for specimens No. 2 and No. 4, and 1.0% of the concrete volume for specimen No. 3. The fibers mixed into the concrete were steel fibers with a diameter of 0.55 mm, a length of 35 mm, an aspect ratio of 65, and a specific gravity of 7.85.These steel fibers had both ends bent into hooks, and were 0.55 mm in diameter and 35 mm in length.

[0019] The main column reinforcement of each specimen was 12-D19 (SD490) with a reinforcement ratio of pg = 3.83% to ensure that shear failure preceded. The vertical and horizontal reinforcement in the wall sections of specimens No. 1 to No. 3 were 2-D6@120 (SD345) with a reinforcement ratio of ps = 0.30%, while specimen No. 4 was 2-D6@60 (SD345) with a reinforcement ratio of ps = 0.59%, aiming for specimens No. 3 and No. 4 to have the same shear strength.

[0020] The above specimens were subjected to loading using the loading device shown in Figure 9. Specifically, while maintaining the axial force applied to the specimen using the loading device, displacement control points were installed on the upper stub of the specimen, and horizontal loads were applied repeatedly from the left and right. The axial force ratio η of the column cross section only was set to 0.15. This axial force ratio η was calculated using the following formula. η=N / (2·Bc·Dc·σB) Here, N is the axial force (for two columns), Bc is the column width (= wall thickness 180 mm), Dc is the column depth (= 500 mm), and σB is the concrete compressive strength (N / mm 2 )

[0021] FIG. 10 is a diagram showing the results of the loading test (the relationship between the horizontal load Q and the horizontal displacement δ). From Figure 10, the maximum horizontal load Q MAX It can be seen that specimen No. 2 is 1.11 times that of specimen No. 1, specimen No. 3 is 1.18 times that of specimen No. 1, and specimen No. 4 is 1.17 times that of specimen No. 1. Furthermore, specimens No. 2 to No. 4 were able to prevent a sudden drop in deformation capacity after the horizontal load Q reached its maximum, compared to specimen No. 1, and showed improved deformation performance. Therefore, when cracks occur in ordinary concrete, they have difficulty bearing the tensile stress, causing the cracks to grow significantly. However, in fiber-reinforced concrete, when cracks occur, the fibers bridging the cracks bear the tensile stress, preventing the cracks from widening, and resulting in smaller crack widths when subjected to the same load or deformation. Furthermore, Figure 10 shows that the load decrease in specimen No. 3 is more gradual than in specimen No. 4, and that even when the shear strength is the same, a larger amount of steel fiber results in greater deformation performance.

[0022] Therefore, from Figure 10, it can be seen that a bearing wall made of fiber-reinforced concrete with a column width equal to the wall thickness and containing 0.5% or 1.0% steel fiber relative to the concrete volume has smaller crack widths and improved ultimate deformation angle (toughness), and is superior in strength and deformation performance, compared to a bearing wall made of ordinary concrete with no steel fiber mixed in. Furthermore, this loading test confirmed that the strength and deformation performance could be improved by mixing 0.5% or 1.0% steel fibers into the concrete volume. In the case of the shear wall of the present invention, the concrete body of the wall and column sections is preferably made of fiber-reinforced concrete with fibers mixed in at 0.3% to 1.5% by volume of concrete. In the fabrication of the specimens for the loading test, the amount of steel fiber was set to 0.5% or 1.0%, an amount that can be easily controlled and mixed into ordinary concrete at the construction site. Furthermore, in the shear wall of the present invention, it is preferable that the width of the column portion is at least 1 time but less than 2 times the wall thickness of the wall portion. In the fabrication of the specimen for this loading test, the width of the column portion was set to be the same as the wall thickness, taking into consideration ease of construction. Furthermore, in the multi-story shear wall equipped with the shear walls of the present invention, one or more layers of fiber-mixed shear walls are arranged, and shear walls without fiber mixed in are arranged on top of these shear walls, as shown in Figure 2. In this way, by arranging the fiber-mixed shear walls in a limited manner, the structural performance of the multi-story shear wall can be improved without having to install fiber-mixed shear walls on every floor of the building.

[0023] According to this embodiment, the following effects are obtained. (1) The bearing wall 10 is composed of a wall section 20 and a column section 30, and these wall sections 20 and column sections 30 are formed from fiber-reinforced concrete in which steel fibers are mixed in an amount of 0.3% to 1.5% by volume of concrete. Therefore, since the steel fibers have a reinforcing effect equal to or greater than that of shear reinforcement, there is no need to arrange shear reinforcement bars in the wall sections or columns in an overly dense manner. As a result, even if the width of the column portion 30 is the same as the wall thickness of the wall portion 20 without increasing the cross section of the column portion 30, a bearing wall 10 with excellent strength and deformation performance can be realized. Furthermore, the concrete bodies 21, 31 of the wall section 20 and the column section 30 are constructed using fiber-reinforced concrete containing steel fibers, rather than ordinary concrete, which makes construction easy. Furthermore, in a multi-story earthquake-resistant wall equipped with shear walls 10 and 10A, the cost of mixing steel fibers into the concrete in the lower story where shear wall 10 is installed increases, but the deformation performance of shear wall 10 with steel fibers mixed in is improved, which improves the deformation performance of building 1 and reduces the amount of material in the surrounding structure.

[0024] (2) Steel fibers with bent ends are used as the fibers mixed into the fiber-reinforced concrete, so the bond between the concrete and the steel fibers is improved at the bent parts of the steel fibers. Furthermore, since the thermal expansion coefficient of steel fibers is approximately equal to that of concrete, it is possible to reduce internal stress caused by temperature changes, and to ensure the integrity of the steel fibers and concrete. (3) A bearing wall 10A made of concrete without fibers is installed above the bearing wall 10 made of fiber-reinforced concrete, and the vertical reinforcement 22 and main column reinforcement 32 of both walls are joined together. Therefore, even if bearing walls 10 made of fiber-reinforced concrete are not installed on all floors of the building 1, a building 1 with excellent shear strength and deformation performance can be realized.

[0025] The present invention is not limited to the above-described embodiment, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. [Explanation of symbols]

[0026] 1...Building (structure) 2...Column 3...Beam 10...Shear wall 10A...Another shear wall 20...wall section 21...concrete body 22...vertical reinforcement 23...horizontal reinforcement 30...Column section 31...Concrete body 32...Column main reinforcement 33...Hoop reinforcement

Claims

1. A reinforced concrete bearing wall, Reinforced concrete walls and and a reinforced concrete column portion provided at the horizontal end of the wall portion, The concrete bodies of the wall and column portions are formed of fiber-reinforced concrete in which steel fibers with bent ends are mixed in an amount of 0.3% to 1.5% by volume of concrete, A shear wall characterized in that the width of the column portion is greater than or equal to one time but less than two times the wall thickness of the wall portion.

2. A structure comprising the reinforced concrete bearing wall according to claim 1, Another bearing wall is arranged above or below the bearing wall, The other bearing wall comprises a wall section made of reinforced concrete not mixed with fibers, and a column section made of reinforced concrete not mixed with fibers and provided at a horizontal end of the wall section, The vertical reinforcement of the wall portion of the bearing wall is connected to the vertical reinforcement of the wall portion of the other bearing wall, A structure characterized in that the main reinforcement of the column of the bearing wall is connected to the main reinforcement of the column of the other bearing wall.

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