Beam structure and method for constructing a beam structure

Abstract

While maintaining the parallel arrangement of the main reinforcement bars in the beam, the resistance of the beam structure to shear forces is improved, and its ductility is enhanced to accommodate large deformations. [Solution] The reinforced concrete beam structure 100 comprises a plurality of main reinforcements 10 provided across a pair of core walls 4, shear reinforcements 20 provided across the plurality of main reinforcements 10, and concrete 30 covering the plurality of main reinforcements 10 and the plurality of shear reinforcements 20. When the beam depth of the beam structure 100 is D, the shear reinforcement ratio is higher in the range of 1 / 2D from the beam end than in other ranges. When the internal span of the beam structure 100 is Lo, the shear stress of the beam structure 100 is τu, and the strength of the concrete 30 is Fc, 3 ≤ Lo / D τu / Fc≦Lo / (120×D)+1 / 24 It satisfies the requirements.

Description

Technical Field

[0001] The present invention relates to a beam structure and a method for constructing the beam structure.

Background Art

[0002] In a reinforced concrete (RC) structure, for the purpose of reducing column beams, a plurality of walls may be provided as main seismic elements in the core part of the floor plan. In such a building, by connecting the walls in the core part with beams, it becomes possible to absorb seismic energy by utilizing the plastic deformation of the beams. Since large deformations occur in the beams connecting the walls in the core part, a beam structure with enhanced toughness has been proposed (Patent Document 1).

[0003] The beam structure disclosed in Patent Document 1 includes a plurality of main reinforcement bars and concrete covering the plurality of main reinforcement bars. The plurality of main reinforcement bars are arranged in an X shape, and the resistance to the shear force generated in the beam when the building receives a horizontal force such as an earthquake is enhanced by the plurality of main reinforcement bars.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the beam structure disclosed in Patent Document 1, since the main reinforcement bars are arranged in an X shape, the reinforcement work becomes complicated, the constraints on the beam through holes increase, and the usability deteriorates.

[0006] An object of the present invention is to improve the resistance of a beam structure to shear force with the main reinforcement bars of the beam being parallel, and to improve the toughness so as to be able to follow large deformations.

Means for Solving the Problems

[0007] The present invention relates to a reinforced concrete beam structure for connecting a pair of walls or columns in a building, comprising: a plurality of main reinforcements provided across the pair of walls or columns; a plurality of shear reinforcements provided across the plurality of main reinforcements; and concrete covering the plurality of main reinforcements and the plurality of shear reinforcements, wherein, when the beam depth of the beam structure is D, the shear reinforcement ratio is higher in the range of 1 / 2D from the beam end than in other ranges, and when the internal span of the beam structure is Lo, the shear stress of the beam structure is τu, and the strength of the concrete is Fc, 3 ≤ Lo / D τu / Fc≦Lo / (120×D)+1 / 24 It satisfies the requirements.

[0008] Furthermore, the present invention relates to a method for constructing a reinforced concrete beam structure that connects a pair of walls or columns in a building, wherein when the beam depth of the beam structure is D, the internal span of the beam structure is Lo, the shear stress of the beam structure is τu, and the strength of the concrete is Fc, 1.5 ≤ Lo / 2 / D τu / Fc≦Lo / (120×D)+1 / 24 The process includes a setting step of setting the strength Fc, beam depth D, and internal span Lo to satisfy the following conditions: a main reinforcement installation step of installing multiple main reinforcements across a pair of walls or columns based on the beam depth D and internal span Lo set in the setting step; a shear reinforcement installation step of installing multiple shear reinforcements across the multiple main reinforcements; and a pouring step of covering the multiple main reinforcements and multiple shear reinforcements with concrete having the strength Fc set in the setting step, wherein in the shear reinforcement installation step, the shear reinforcement ratio is made higher in the range of 1 / 2D from the beam end than in other ranges. [Effects of the Invention]

[0009] According to the present invention, the objective is to improve the resistance of a beam structure to shear force while maintaining the parallel arrangement of the main reinforcement bars of the beam, and to improve its toughness so that it can follow large deformations. [Brief explanation of the drawing]

[0010] [Figure 1]This is a plan view showing an example of a building equipped with a beam structure according to an embodiment of the present invention. [Figure 2] This is a cross-sectional view along the line II-II shown in Figure 1. [Figure 3] This diagram shows the relationship between the internal span-beam depth ratio and the shear strength-concrete strength ratio. [Modes for carrying out the invention]

[0011] Hereinafter, a beam structure 100 according to an embodiment of the present invention and a method for constructing the beam structure 100 will be described with reference to the drawings.

[0012] Figure 1 is a plan view showing an example of a building 1 equipped with a reinforced concrete (RC) beam structure 100. As shown in Figure 1, the building 1 comprises a core section 2 and an outer perimeter section 3 located around the core section 2. Multiple core walls 4, which function as the main seismic resistance elements, are installed in the core section 2. The core walls 4 bear the horizontal forces generated in the building 1 by earthquakes and wind, making it possible to reduce the number and cross-section of columns 3a and beams 3b in the outer perimeter section 3. This increases the design flexibility of the building 1.

[0013] The beam structure 100 according to this embodiment connects a pair of core walls 4. When the core walls 4 bear a horizontal force, the beam structure 100 undergoes plastic deformation to absorb input energy from earthquakes and the like. By absorbing input energy from earthquakes and the like, the seismic performance of the core section 2 is further improved, and the number and cross-section of columns 3a and beams 3b in the outer perimeter section 3 can be further reduced.

[0014] In Figure 1, a beam structure 100 connects a pair of core walls 4, but the present invention is also applicable to beams 3b connecting columns 3a, as well as to a pair of walls not shown that do not function as major seismic elements, or to beams not shown that connect the walls not shown to columns 3a.

[0015] FIG. 2 is a cross-sectional view taken along line II-II shown in FIG. 1. As shown in FIG. 2, the beam structure 100 includes a plurality of main reinforcement bars 10 provided across a pair of core walls 4, a plurality of shear reinforcement bars 20 provided across the plurality of main reinforcement bars 10, and concrete 30 covering the plurality of main reinforcement bars 10 and the plurality of shear reinforcement bars 20.

[0016] In order to make the beam structure 100 absorb more input energy due to an earthquake or the like, it is effective to enhance the toughness of the beam structure 100 (the ability to maintain its bearing capacity even when repeated deformation occurs). As a method of enhancing the toughness of the beam structure 100, it is conceivable to arrange the main reinforcement bars 10 in an X shape, but the work of arranging the main reinforcement bars 10 in an X shape is complicated and the workability of the beam structure 100 is impaired.

[0017] As a result of repeatedly performing bending-shear experiments on a beam structure in which the main reinforcement bars 10 are arranged linearly, the inventors obtained the finding that when the span of the beam structure is D, damage concentrates in the range of 1 / 2D from the beam end. Therefore, in the beam structure 100, the shear reinforcement bars 20 are intensively arranged in the end region 100E, which is the range of 1 / 2D from the beam end in the beam structure 100. Specifically, the shear reinforcement ratio in the end region 100E is made higher than the shear reinforcement ratio in the intermediate region 100M located between the end regions 100E in the beam structure 100.

[0018] Here, the "shear reinforcement ratio" is a value obtained by dividing the cross-sectional area of one set of shear reinforcement bars 20 by the product of the spacing between adjacent shear reinforcement bars 20 along the main reinforcement bars 10 and the width of the beam. The higher the cross-sectional area of the shear reinforcement bars 20, the higher the shear reinforcement ratio. Also, the narrower the spacing between adjacent shear reinforcement bars 20, that is, the larger the number of shear reinforcement bars 20, the higher the shear reinforcement ratio. The higher the shear reinforcement ratio, the more intensively the shear reinforcement bars 20 are arranged, which means they are reinforced.

[0019] Hereinafter, the shear reinforcement bars 20 in the end region 100E are also referred to as "end region reinforcement bars 20E", and the shear reinforcement bars 20 in the intermediate region 100M are also referred to as "intermediate region reinforcement bars 20M".

[0020] In the beam structure 100 shown in FIG. 2, by making the spacing of the end-region reinforcement bars 20E narrower than the spacing of the intermediate-region reinforcement bars 20M, the shear reinforcement ratio in the end region 100E is made higher than the shear reinforcement ratio in the intermediate region 100M.

[0021] Although not shown in the figure, by making the cross-sectional area of the end-region reinforcement bars 20E larger than the cross-sectional area of the intermediate-region reinforcement bars 20M, the shear reinforcement ratio in the end region 100E may be made higher than the shear reinforcement ratio in the intermediate region 100M. Also, by making the spacing of the end-region reinforcement bars 20E narrower than the spacing of the intermediate-region reinforcement bars 20M and making the cross-sectional area of the end-region reinforcement bars 20E larger than the cross-sectional area of the intermediate-region reinforcement bars 20M, the shear reinforcement ratio in the end region 100E may be made higher than the shear reinforcement ratio in the intermediate region 100M.

[0022] Table 1 shows the results of bending tests conducted on Examples 1 to 3 and Comparative Examples 1 to 3. The bending test was carried out by the four-point bending test method. The end supports were pin-roller supports. The loading was controlled by the member deformation angle. The member deformation angles were changed in the order of 1 / 400 rad, 1 / 200 rad, 1 / 100 rad, 1 / 80 rad, 1 / 40 rad, 1 / 25 rad, 1 / 16.7 rad, 1 / 1 rad, and a total of about 60 repeated loadings were performed.

[0023] [Table 1]

[0024] In Table 1, Lo is the internal span of beam structure 100, Fc is the strength of concrete 30 in beam structure 100, and τaij is the maximum shear stress of beam structure 100. End reinforcement was determined as "present" if the shear reinforcement ratio in the end region 100E was higher than the shear reinforcement ratio in the intermediate region 100M, and as "absent" if the shear reinforcement ratio in the end region 100E was the same as the shear reinforcement ratio in the intermediate region 100M. The determination was made as "good" if the shear strength was 80% or more of the maximum load-bearing capacity even when the member deformation angle reached 1 / 16.7 rad, indicating sufficient ductility, and as "bad" if the shear strength fell below 80% of the maximum load-bearing capacity before the member deformation angle reached 1 / 16.7 rad, indicating insufficient ductility.

[0025] As can be seen from Table 1, good results were obtained in Examples 1-3, which had end reinforcement. In Comparative Examples 1-3, which did not have end reinforcement, the results were unsatisfactory. From the above, the effect of end reinforcement in improving toughness was confirmed.

[0026] In building 1, if excessive shear stress is applied to the beam structure 100, the beam structure 100 may behave differently from that observed in bending shear experiments. Therefore, the magnitude of the shear stress is limited.

[0027] Figure 3 shows the relationship between the internal span-beam depth ratio (Lo / D) and the shear strength-concrete strength ratio (τaij / Fc), and is a graph plotting the values ​​for Examples 1 to 3 shown in Table 1. As can be seen from Figure 3, the internal span-beam depth ratio (Lo / D) and the shear strength-concrete strength ratio (τaij / Fc) are proportional. Therefore, by finding an approximate curve for this proportional relationship, the following equation (1) is obtained. τaij / Fc≦Lo / (120×D)+1 / 24 (Formula 1)

[0028] In Examples 1-3, the internal span-to-beam depth ratio (Lo / D) is 3 or greater, whereas when the internal span-to-beam depth ratio (Lo / D) is less than 3, beam structure 100 may yield results different from those of the bending shear experiment shown in Table 1. Therefore, the internal span-to-beam depth ratio (Lo / D) is set to 3 or greater.

[0029] In Examples 1-3, tests were conducted only when the internal span-beam depth ratio (Lo / D) was 5 or less. However, increasing the internal span-beam depth ratio (Lo / D) means increasing the internal span Lo or decreasing the beam depth D, and the upper limit of the internal span-beam depth ratio (Lo / D) is determined by the size of the building 1. Furthermore, it is common technical knowledge that even if the internal span-beam depth ratio (Lo / D) is 5 or more, the behavior does not change from when the internal span-beam depth ratio (Lo / D) is between 3 and 5. Therefore, it is clear that at the upper limit of the internal span-beam depth ratio (Lo / D) determined by the size of the building 1, the relationship between the internal span-beam depth ratio (Lo / D) and the shear strength-concrete strength ratio (τaij / Fc) is as shown in Equation 1.

[0030] Based on the above, in beam structure 100, the shear stress of beam structure 100 calculated by the structural calculation of building 1 is denoted as τu, 3≦Lo / D ··· (Formula 2) τu / Fc≦Lo / (120×D)+1 / 24 (Formula 3) The goal is to satisfy this condition. To achieve this, the end region 100E of the beam structure 100, which is prone to damage, is intensively reinforced with shear reinforcement bars 20, and the shear stress τu generated in the beam structure 100 is set according to the ratio of the internal span to the beam depth (Lo / D) of the beam structure 100. Thus, resistance to shear force can be increased without arranging the main reinforcement bars 10 in an X shape. This makes it possible to improve the ductility of the beam structure 100 while keeping the main reinforcement bars 10 of the beam parallel.

[0031] Although not shown in the diagram, the concrete 30 may contain fibers. In this case, the fibers contained in the concrete 30 disperse bending cracks and shear cracks in the concrete 30. Therefore, the ability of the beam structure 100 to absorb input energy due to earthquakes, etc., can be further increased, and the toughness of the beam structure 100 can be further improved.

[0032] The fibers contained in the concrete 30 are preferably steel fibers or organic fibers (e.g., vinylon fibers, polypropylene fibers, polyethylene fibers). In the case of steel fibers, they are less prone to deterioration compared to organic fibers, and the performance of the beam structure 100 can be maintained for a longer period of time. In the case of organic fibers, it is possible to prevent pitting on the surface of the structure that may occur when the concrete 30 contains steel fibers.

[0033] The method for constructing the beam structure 100 comprises a setting step of setting the strength Fc, beam depth D, and internal span Lo of the concrete 30; a main reinforcement installation step of providing multiple main reinforcements 10 across a pair of core walls 4; a shear reinforcement installation step of providing shear reinforcements 20 across the multiple main reinforcements 10; and a pouring step of covering the multiple main reinforcements 10 and shear reinforcements 20 with concrete 30. In the setting step, the strength Fc, beam depth D, and internal span Lo of the concrete 30 are set to satisfy the above equations 3 and 4. In the main reinforcement installation step, multiple main reinforcements 10 are provided based on the beam depth D and internal span Lo set in the setting step. In the shear reinforcement installation step, the shear reinforcement ratio is made higher in the range of 1 / 2D from the beam end than in other ranges. In the pouring step, concrete 30 having the strength Fc set in the setting step is poured, and the multiple main reinforcements 10 and shear reinforcements 20 are covered with concrete 30.

[0034] In a beam structure 100 constructed using this method, the end regions 100E of the beam structure 100, which are prone to damage, are intensively reinforced with shear reinforcement bars 20, and the shear stress τu generated in the beam structure 100 is set according to the ratio of the internal span to the beam depth (Lo / D) of the beam structure 100. Therefore, resistance to shear force can be increased without arranging the main reinforcement bars 10 in an X shape. This makes it possible to improve the ductility of the beam structure 100 while maintaining the parallel arrangement of the main reinforcement bars 10 of the beam.

[0035] In the concrete placement process, fibers may be included in the concrete 30. The fibers are preferably steel fibers or organic fibers (e.g., vinylon fibers, polypropylene fibers, polyethylene fibers).

[0036] Although embodiments of the present invention have been described above, these embodiments only represent a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments. [Explanation of symbols]

[0037] 100·Beam structure 1...Buildings 4. Wall (core wall) 10...Main reinforcement 20. Shear reinforcement bars 30. Concrete Lo ··Inner span D···Beam τu··shear stress Fc...Concrete Strength

Claims

1. A reinforced concrete beam structure that connects a pair of walls or columns in a building, Multiple main reinforcements provided across the pair of walls or columns, Multiple shear reinforcement bars provided across the multiple main reinforcements, The system comprises concrete covering the plurality of main reinforcements and the plurality of shear reinforcements, When the beam depth of the beam structure is D, the shear reinforcement ratio is higher in the range of 1 / 2D from the beam end than in other ranges. When the internal span of the beam structure is Lo, the shear stress of the beam structure is τu, and the strength of the concrete is Fc, 3 ≤ Lo / D τu / Fc≦Lo / (120×D)+1 / 24 It satisfies, Beam structure.

2. The aforementioned concrete contains fibers. The beam structure according to claim 1.

3. The aforementioned fiber is either a steel fiber or an organic fiber. The beam structure according to claim 2.

4. A method for constructing a reinforced concrete beam structure that connects a pair of walls or columns in a building, When the beam depth of the beam structure is D, the internal span of the beam structure is Lo, the shear stress of the beam structure is τu, and the strength of the concrete is Fc, 1.5≦Lo / 2 / D τu / Fc≦Lo / (120×D)+1 / 24 A setting step of setting the strength Fc, beam depth D, and internal span Lo so as to satisfy the following conditions: A main reinforcement installation step is performed in which multiple main reinforcements are installed across the pair of walls or columns based on the beam depth D and the internal span Lo set in the setting step, A shear reinforcement installation step involves providing multiple shear reinforcement bars across the multiple main reinforcement bars, The process includes a concrete casting step in which the plurality of main reinforcements and the plurality of shear reinforcements are covered with concrete having the strength Fc set in the setting step, In the shear reinforcement installation process, the shear reinforcement ratio is made higher in the 1 / 2D range from the beam end than in other ranges. Method for constructing beam structures.

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