JP2021055461A - Column-beam frame - Google Patents

Abstract

To provide a column-beam frame of reinforced concrete construction capable of reducing damage of a column-beam joint portion in an earthquake by moving a flexural yielding hinge position of a beam to a beam central portion side than conventional ones.SOLUTION: A column-beam frame 1 comprises a column 10 of reinforced concrete construction and a beam 20 of reinforced concrete construction connected with the column 10. The beam 20 comprises: a first stage beam upper end bar 30A; second stage beam upper end bars 30B, 30C; a first stage beam lower end bar 40A; second stage beam lower end bars 40B, 40C; a stirrup 50; an upper side restraining bar 51 surrounding the beam upper end bars 30A to 30C; and a lower side restraining bar 52 surrounding the beam lower end bars 40A to 40C. The second stage beam upper end bar 30C and the second stage beam lower end bar 40C are cut-off bars arranged only at an end portion side of the beam 20. At a tip of the cut-off bar, a fastening metal fitting 60 is provided.SELECTED DRAWING: Figure 1

Description

The present invention relates to a reinforced concrete column-beam frame.

Conventionally, in the structural design of a reinforced concrete column-beam frame, the yield hinge of the beam is designed to be formed at the interface between the beam end and the column-beam joint (column-beam joint). However, if the difference in bending strength between the column and the beam is small, both the beam main bar and the column main bar may yield in the column-beam joint, and the expected seismic performance may not be obtained.

Non-Patent Document 1 discloses a method of hinge relocation by arranging an additional main bar having a mechanical fixing metal fitting as a second-stage main bar on the beam end side of a reinforced concrete beam. The hinge relocation referred to here is to move the generation position of the yield hinge from the boundary surface between the beam end portion and the beam-column joint portion to the beam center side in order to prevent damage to the column-beam joint portion.
In the beam of Non-Patent Document 1, cracks are concentrated at the yield hinge position, but when the beam is greatly deformed, the damage to the beam end portion is large.
Further, in Patent Document 1, in a reinforced concrete beam, additional reinforcing bars are formed in which the upper reinforcing bars and the lower reinforcing bars arranged at the two-stage reinforcing bars of the upper and lower main reinforcing bars are integrated with each other via an intermediate bent portion. , The method of controlling the yield hinge position of the beam in which the additional reinforcing bars are separately arranged on the left and right sides of the central position of the beam is shown.
In the beam of Patent Document 1, it is necessary to perform a plurality of bending processes on the additional reinforcing bar at a delicate angle, which requires a great deal of cost and labor.

JP-A-2018-145595

Yukitaka Ota et al .: Experimental study on RC beams forming a beam end hinge relocation mechanism using Y-shaped streaks (Part 1 Experimental outline), Architectural Institute of Japan Conference Academic Lecture Abstract, Structure IV, PP.237-238, 2018 September

An object of the present invention is to provide a reinforced concrete beam-column frame capable of moving the bending yield hinge position of a beam toward the center of the beam as compared with the conventional case to reduce damage to the beam-column joint during an earthquake. ..

As a beam-column structure having a hinge relocation mechanism, the present inventors arrange first-stage main reinforcement, second-stage main reinforcement, and shear reinforcing reinforcement on the beam, and on the beam end side, the first-stage main reinforcement and second-stage main reinforcement and second-stage reinforcement. By arranging the upper end restraint bar and the lower end restraint bar surrounding the main bar, the breaking strength of the concrete at the time of crushing increases on the beam end side. This development focused on the fact that damage to the body can be reduced.
The beam-beam structure of the first invention (for example, the beam-beam structure 1 described later) is a beam made of reinforced concrete (for example, a beam 10 described later) and a beam made of reinforced concrete joined to the column (for example, a beam described later). 20), and the beam is a first-stage main bar (for example, first-stage beam upper end bar 30A and first-step beam lower end bar 40A, which will be described later) arranged on the upper and lower end sides of the beam. , The second-stage main bar (for example, the second-stage beam upper end bars 30B and 30C, the second-stage beam lower end bars 40B and 40C) arranged inside the first-stage main bar, the first-stage main bar and the second-stage main bar. A shear reinforcing bar (for example, a stirrup 50 described later) provided surrounding the main bar of the eye is provided, and all or a part of the second step main bar (for example, the second step beam upper end bar 30C described later, the second step). The beam lower end bar 40C) is a cut-off bar arranged only on the end side of the beam, and a fixing metal fitting (for example, a fixing metal fitting 60 described later) is provided at the tip of the cut-off bar. On the end side of the beam, an upper restraint bar (for example, an upper restraint bar 51 described later) surrounding the first step main bar and the second step main bar on the upper side of the beam, and a first step beam main bar on the lower side of the beam. It is characterized in that a lower restraint muscle (for example, a lower restraint muscle 52 described later) surrounding the second-stage main muscle is provided.

Here, the cut-off bar may be the same reinforcing bar as the through bar, or may have a larger diameter or higher strength than the through bar.
According to the present invention, since the cutoff streaks are provided only on the end side of the beam, the number of beam streaks on the end side of the beam is larger than that on the center side of the beam. Therefore, since the position of the bending yield hinge of the beam moves to the center side of the beam more than before, it is possible to prevent cracks in the vicinity of the bending yield hinge from reaching the beam-column joint and prevent the beam-column joint from being destroyed. Sufficient seismic performance can be ensured at the beam-column joint.
Further, since all or a part of the second stage main reinforcing bar is used as a cutoff reinforcing bar and a fixing metal fitting is provided at the tip of this cutoff reinforcing bar, the upper reinforcing bar and the lower reinforcing bar are provided at the center of the beam as in the additional reinforcing bar of Patent Document 1. There is no need to perform multiple bending processes at a delicate angle toward the side. Further, since the cutoff bar does not extend to the center side of the beam, it can be shorter than the additional reinforcing bar of Patent Document 1, and the cost is low.
In addition, the first-stage main reinforcement and the second-stage main reinforcement were doubly surrounded by the upper restraint muscle and the lower restraint muscle in addition to the shear reinforcement. Therefore, on the beam end side, the fracture strength at the time of crushing the concrete increases, so that it is possible to reduce damage to the concrete body at the beam end due to the compressive force generated at the upper and lower ends of the beam end.

The beam-beam structure of the second invention includes a reinforced concrete beam (for example, a beam 10 described later) and a reinforced concrete beam with a floor slab (for example, a beam 20A described later) joined to the beam. A beam structure (for example, a beam structure 1 described later), wherein the beam is a first-stage main bar (for example, a first-stage beam upper end bar 30A described later, a first-stage beam lower end) arranged on the upper and lower end sides of the beam. The bar 40A), the second step main bar (for example, the second step beam upper end bar 30B, 30C, the second step beam lower end bar 40B, 40C) arranged inside the first step main bar, and the first step main bar. And a shear reinforcing bar (for example, a stirrup 50 described later) provided around the second step main bar, and all or a part of the second step main bar (for example, the second step beam upper end bar 30C described later). , Second-stage beam lower end bar 40C) is a cut-off bar arranged only on the end side of the beam, and a fixing metal fitting (for example, a fixing metal fitting 60 described later) is attached to the tip of the cut-off bar. On the end side of the beam, a lower restraint bar (for example, a lower restraint bar 52 described later) surrounding the first-stage beam main bar and the second-step main bar on the lower side of the beam is provided. It is characterized by.

According to the present invention, as in the first invention described above, since the cutoff streaks are provided only on the end side of the beam, the bending yield hinge position of the beam moves to the center side of the beam as compared with the conventional case. It is possible to prevent cracks in the vicinity of the bending yield hinge from reaching the beam-column joint, and to sufficiently secure the seismic performance of the beam-column joint.
Further, since all or a part of the second stage main reinforcing bar is used as a cutoff reinforcing bar and a fixing metal fitting is provided at the tip of this cutoff reinforcing bar, the upper reinforcing bar and the lower reinforcing bar are provided at the center of the beam as in the additional reinforcing bar of Patent Document 1. There is no need to perform multiple bending processes at a delicate angle toward the side. Further, since the cutoff bar does not extend to the center side of the beam, it can be shorter than the additional reinforcing bar of Patent Document 1, and the cost is low.
In addition, the first-stage main bar and the second-stage main bar were doubly surrounded by the lower restraint bar in addition to the shear reinforcing bar. Therefore, on the lower end side of the beam end portion, the fracture strength at the time of crushing the concrete increases, so that it is possible to reduce damage to the concrete body at the beam end portion due to the compressive force generated at the lower end portion of the beam end portion.
Further, since the floor slab is provided on the beam, the floor slab bears the compressive force together with the beam. Therefore, even if the upper restraint bar is omitted, the damage to the beam can be sufficiently suppressed.

In the column-beam frame of the third invention, on the end side of the beam, all or a part of the shear reinforcing bars are arranged in contact with each other to form a bundling bar (for example, a bundling bar 53 described later). It is characterized by being.

According to the present invention, since a plurality of all or part of the shear reinforcing bars are bundled to form a bundled bar on the end side of the beam, many shear reinforcing bars can be arranged on the end side of the beam. Therefore, on the beam end side, the degree of restraint of the concrete body is further increased, so that the fracture strength at the time of crushing the concrete is increased, and the compressive force generated at the upper and lower ends of the beam end reduces the damage to the concrete body of the beam. it can.

According to the present invention, it is possible to provide a reinforced concrete beam-column frame capable of moving the bending yield hinge position of the beam toward the center of the beam as compared with the conventional case to reduce damage to the beam-column joint during an earthquake.

It is a side view of the column beam frame which concerns on one Embodiment of this invention. It is AA cross-sectional view and BB cross-sectional view of the beam shown in FIG. It is a figure which shows the structure of the reinforced concrete beam test piece which concerns on Example of this invention. It is a side view of the force device used for the force test of the reinforced concrete beam test piece. It is a figure which shows the test result of the force test. It is a side view which shows the state of the surface after completion of a force test of a reinforced concrete beam test piece. It is a side view of the column beam frame which concerns on the modification of this invention.

The present invention is a column-beam frame including a column made of reinforced concrete and a beam made of reinforced concrete joined to the column. It is a hinge relocation structure in which closed type reinforcing bars (upper restraint bar, lower restraint bar) are provided to surround the main bar of the beam, and the main bar of the beam is doubly surrounded. Specifically, in a beam of a column-beam frame, a fixing hardware is attached to the tip of a part of the second-stage main bar to form a cut-off bar with the fixing hardware, and the section from the beam end face to the tip of the cut-off bar, the first step. It is characterized in that closed type reinforcing muscles (upper restraint muscle, lower restraint muscle) are arranged so as to surround the main muscle and the second stage main muscle.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a vertical sectional view of a column-beam frame 1 according to an embodiment of the present invention. FIG. 2A is a sectional view taken along the line AA of the column-beam frame 1 of FIG. 1, and FIG. 2B is a sectional view taken along the line BB of the column-beam frame 1 of FIG.
The column-beam frame 1 includes a reinforced concrete column 10 and a reinforced concrete beam 20 joined to the column-beam joint portion 11 of the column 10. As shown in FIG. 2, the floor slab is not joined to the beam 20.
The beam 20 is designated by surrounding the beam upper end bars 30A, 30B, 30C and the beam lower end bars 40A, 40B, 40C, which are arranged in two stages, and the beam upper end bars 30A to 30C and the beam lower end bars 40A to 40C, respectively. Stirrup 50 as shear reinforcing bars provided at intervals, upper restraint bars 51 provided at predetermined intervals on the end side of the beam 20 and surrounding the beam upper end bars 30A to 30C, and on the end side of the beam 20. It is provided with a lower restraint bar 52 that surrounds the lower end bars 40A to 40C of the beam, and a bundling bar 53 that is arranged with two stirrups 50 in contact with each other on the end side of the beam 20.

Specifically, the beam upper end bars 30A to 30C are the four beam upper end bars 30A as the upper first step main bars and the upper second step main bars arranged below and outside the beam upper end bars 30A. It is composed of two beam upper end bars 30B and two beam upper end bars 30C as upper second-stage main bars arranged below and inside the beam upper end bars 30A.
The beam lower end bars 40A to 40C are four beam lower end bars 40A as the lower first step main bars and two beams as the lower second step main bars arranged above and outside the beam lower end bars 40A. It is composed of a lower end bar 40B and two beam lower end bars 40C as lower second-stage main bars arranged above and inside the beam lower end bar 40A.
The beam upper end bars 30A and 30B and the beam lower end bars 40A and 40B are through bars arranged from the end side (column-beam joint 11 side) to the center side of the beam 20. On the other hand, the beam upper end reinforcement 30C and the beam lower end reinforcement 40C are cutoff reinforcements arranged only on the end side (column-beam joint portion 11 side) of the beam 20.
Fixing hardware 60 that extends like a brim is provided at the tips of the beam upper end reinforcement 30C and the beam lower end reinforcement 40C, which are cut-off reinforcements.

The upper restraint bar 51 is provided so as to surround the first-stage beam upper end bar 30A and the second-stage beam upper end bars 30B and 30C. The lower restraint bar 52 is provided so as to surround the first-stage beam lower end bar 40A and the second-stage beam lower end bars 40B and 40C.

The bending moment distribution map of the beam 20 at the time of an earthquake is as shown in FIG.
Beam upper muscle 30A, 30B and the beam bottom muscles 40A, the flexural ultimate strength is calculated as the _{M UHR} at 40B, the flexural ultimate strength is calculated by the beam upper muscle 30A~30C and beams lower muscle 40A~40C and _{M uf} .. Further, the position of the end surface of the beam 20 on the beam end side, that is, the side surface of the column 10 is p, and the position of the tip surface of the fixing hardware 60 is q.
As shown in FIG. 1, at the position q of the beam 20, the bending moment _Muhrf at the time of the earthquake reaches the ultimate bending strength _Muhr , but at the position p of the beam 20, the bending moment _Muhrf at the time of the earthquake reaches the ultimate bending strength M. _Does not reach uf. Therefore, the beam 20 yields at the position q, and this position q is the position where the bending yield hinge is generated.

[Example]
As an example, two test bodies of reinforced concrete beams as shown in Table 1 below were manufactured and a force test was performed. Of these, the test body 1 is formed by arranging the beam upper end reinforcement, the beam lower end reinforcement, the stirrup, and the bundling reinforcement to which the fixing hardware is attached. The test body 2 has a structure similar to that of the beam shown in FIG. 1, and has an upper restraint muscle and a lower restraint muscle arranged in addition to the test body 1.

That is, as shown in FIG. 3A, the shape of the test piece is a rectangular cross section, the beam width is 300 mm, the beam length is 450 mm, the internal length of the test section is 2250 mm, and the shear span ratio (a / D) is 2. It was set to 5. Further, as shown in FIG. 3B, the dimension of the mechanical fixing (fixing hardware) in the test body from the column side surface was set to 225 mm, which is 1/2 of the beam length.
The beam main bar used as the through bar was D19 (SD490) for both the first and second steps, and the beam main bar used as the cutoff bar was D22 (SD490). The bending margin ( _Muf / _Mufrf ) was set to 1.14, reflecting the results of the material test.

A force test was performed using a force device as shown in FIG. FIG. 5 shows the test results of the force test, and shows the relationship between the shearing force applied to the test body by the force device and the deformation (member angle R) of the test body. FIG. 6 is a side view showing the state of the surface of the test piece after the force test is completed. 5 (a) and 6 (a) are the test results of the force test on the test body 1, and FIGS. 5 (b) and 6 (b) are the test of the force test on the test body 2. The result.
As shown in FIG. 5, in the test body 1, after the shear force reached the calculated bending strength value, no increase in the shearing force was observed, but in the test body 2, the shearing force reached the calculated bending strength value. After that, an increase in yield strength was observed.
Further, as shown in FIG. 6, since the test body 1 is not provided with the upper end restraint bar and the lower end restraint bar, the concrete is peeled off at the beam end portion, and the damage is caused by shear cracks like the beam of the normal bar arrangement. Is getting fierce. On the other hand, in the test body 2, a slight peeling of concrete was confirmed near the beam end face, but by arranging the upper end restraint bar and the lower end restraint bar, the peeling of concrete at the beam end was reduced and sheared. Damage caused by cracks is also reduced.
Therefore, from FIGS. 5 and 6, it was confirmed that by providing the upper end restraint bar and the lower end restraint bar, the degree of restraint of the concrete body at the end of the test body can be increased and the damage to the test body can be reduced.

According to this embodiment, there are the following effects.
(1) Since the cutoff bars 30C and 40C are provided only on the end side of the beam 20, the number of beam bars on the end side of the beam 20 is larger than that on the central side of the beam 20. Therefore, since the position of the bending yield hinge of the beam 20 moves toward the center of the beam as compared with the conventional case, the crack near the bending yield hinge is suppressed from reaching the beam-column joint 11, and the beam-column joint 11 is destroyed. This can be prevented and the seismic performance of the beam-column joint 11 can be sufficiently ensured.
Further, since the beam upper end bar 30C and the beam lower end bar 40C are used as the cutoff bar and the fixing metal fitting 60 is provided at the tip of the cutoff bar, the upper bar and the lower bar are centered on the beam as in the additional bar of Patent Document 1. It is not necessary to perform multiple bending processes at a delicate angle toward the part side. Further, since the beam upper end bar 30C and the beam lower end bar 40C are not extended to the beam center side unlike the additional reinforcing bar of Patent Document 1, the reinforcing bar material cost can be saved.

(2) The first-stage beam upper end reinforcement 30A and the second-stage beam upper end reinforcements 30B and 30C are doubly surrounded by the upper restraint reinforcement 51 in addition to the stirrup 50, and the first-stage beam lower end reinforcement 40A and the second-stage beam lower end reinforcement 40A and the second-stage beam lower end reinforcement. 40B and 40C were doubly surrounded by a lower restraint muscle 52 in addition to the stirrup 50. Therefore, on the end side of the beam 20, the fracture strength at the time of crushing the concrete increases, so that it is possible to reduce damage to the concrete body of the beam due to the compressive force generated at the upper and lower ends of the beam end.
Further, the upper restraint bar 51 and the lower restraint bar 52, which are closed type reinforcing bars, may have a smaller diameter than the beam upper end bars 30A to 30C and the beam lower end bars 40A to 40C, and the stirrup 50 which is a shear reinforcing bar The same processing effort is required. Therefore, there is no problem in workability, and damage to the concrete body due to the compressive force generated at the upper and lower ends of the beam end can be reduced at low cost.

(3) Two shear reinforcing bars 50 were arranged in contact with each other in the vicinity of the tips of the second-stage beam upper end bar 30C and the second-stage beam lower end bar 40C to form a bundling bar 53. Therefore, many shear reinforcing bars 50 can be arranged on the end side of the beam 20, and the degree of restraint of the concrete body is further increased on the end side of the beam 20, so that the breaking strength at the time of crushing the concrete is increased. It is possible to reduce damage to the concrete body of the beam due to the compressive force generated at the upper and lower ends of the beam end.

The present invention is not limited to the above-described embodiment, and modifications, improvements, and the like within the range in which the object of the present invention can be achieved are included in the present invention.
For example, in the above embodiment, the upper restraint bar 51 is arranged on the upper side of the beam and the lower restraint bar 52 is arranged on the lower side of the beam, but the present invention is not limited to this. That is, as shown in FIG. 7, when the floor slab 21 is provided on the beam 20A, the upper restraint bar may not be arranged and only the lower restraint bar 52 may be arranged. This is because the floor slab 21 is provided on the beam 20A, so that the floor slab 21 bears the compressive force together with the beam 20, so that the upper restraint bar can be omitted.

Further, in the above embodiment, the beam upper end bar 30B and the beam lower end bar 40B arranged outside the second stage are used as through bars, and the beam upper end bar 30C and the beam lower end bar 40C arranged inside the second step are cutoff bars. However, it is not limited to this. That is, all of the beam upper end bar and the beam lower end bar of the second stage may be used as the cutoff bar, or a part of the beam upper end bar and the beam lower end bar of the second step may be used as the cutoff bar.
Further, in the above embodiment, the bundling bar 53 is provided only in the vicinity of the tips of the second-stage beam upper end bar 30C and the second-stage beam lower end bar 40C, but the present invention is not limited to this. That is, all the shear reinforcing bars surrounding the second-stage beam upper end bar 30C and the second-stage beam lower end bar 40C, which are arranged at the beam end, may be used as a bundling bar. In this way, many shear reinforcing bars can be arranged on the beam end side to further increase the fracture strength when the concrete is crushed.
Further, in the above embodiment, the beam upper end reinforcement 30C or the beam lower end reinforcement 40C to be arranged at the beam end is all single reinforcement, but the present invention is not limited to this. That is, a part of the beam upper end bar 30C and the beam lower end bar 40C may be used as a single bar, and a plurality of the rest may be brought into contact with each other for bar arrangement.

1 ... Column-beam frame 10 ... Column 11 ... Column-beam joint 20, 20A ... Beam 21 ... Floor slab 30A ... First-stage beam upper end reinforcement (upper first-stage main reinforcement, through reinforcement)
30B ... Second-stage beam upper end reinforcement (upper second-stage main reinforcement, through reinforcement)
30C ... Second-stage beam upper end reinforcement (upper second-stage main reinforcement, cutoff reinforcement)
40A ... 1st stage beam lower end reinforcement (lower 1st stage main reinforcement, through reinforcement)
40B ... Second-stage beam lower end reinforcement (lower second-stage main reinforcement, through reinforcement)
40C ... Second stage beam lower end reinforcement (lower second stage main reinforcement, cutoff reinforcement)
50 ... Stirrup (shear reinforcement) 51 ... Upper restraint muscle 52 ... Lower restraint muscle 53 ... Bundling muscle 60 ... Fixing hardware

Claims (3)

A column-beam frame including a reinforced concrete column and a reinforced concrete beam joined to the column.
The beam is provided so as to surround the first-stage main bar arranged on the upper and lower end sides of the beam, the second-stage main bar arranged inside the first-stage main bar, the first-stage main bar, and the second-stage main bar. With shear reinforcement,
All or part of the second-stage main bar is a cut-off bar arranged only on the end side of the beam.
A fixing hardware is provided at the tip of the cutoff muscle.
On the end side of the beam, an upper restraint bar surrounding the first and second main bars above the beam and a lower restraint bar surrounding the first and second main bars below the beam. A pillar-beam frame characterized by being provided with. A column-beam frame including a reinforced concrete column and a reinforced concrete beam with a floor slab joined to the column.
The beam is provided so as to surround the first-stage main bar arranged on the upper and lower end sides of the beam, the second-stage main bar arranged inside the first-stage main bar, the first-stage main bar, and the second-stage main bar. With shear reinforcement,
All or part of the second-stage main bar is a cut-off bar arranged only on the end side of the beam.
A fixing hardware is provided at the tip of the cutoff muscle.
A column-beam frame characterized in that a lower restraint bar surrounding the first-stage beam main bar and the second-stage main bar on the lower side of the beam is provided on the end side of the beam. The column-beam frame according to claim 1 or 2, wherein on the end side of the beam, all or a part of the shear reinforcing bars are arranged in contact with each other to form a bundled bar.

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