JP7663531B2 - Beam-column joint structure - Google Patents

Description

The present invention relates to the structure at the joint between a column, a flat beam, and an orthogonal beam.

For buildings with reinforced concrete rigid frame structures, a flat beam construction method has been proposed that uses flat beams that are wider than the columns. With this flat beam construction method, the beam depth can be kept small and an open space can be created under the beams, making it possible to ensure sufficient interior height while keeping the overall height of the building low (see, for example, Patent Document 1).

JP 2021-85189 A

However, with conventional flat beam construction methods, there was a risk of damage such as cracks occurring at the joints where the flat beams and the orthogonal beams intersect due to twisting that occurs between the flat beams and the orthogonal beams during earthquakes, etc.

In view of the above, the present invention aims to provide a column-beam joint structure that can reduce the risk of damage, such as cracks, occurring at the joint where the flat beam and the orthogonal beam intersect due to torsion that occurs between the flat beam and the orthogonal beam during an earthquake, etc.

The present invention is a joint structure in which a column, a flat beam with a beam width wider than the column width, and an orthogonal beam perpendicular to the column and the flat beam and having a beam width equal to or less than the beam depth are connected, and is characterized in that a plurality of orthogonal beam main reinforcements extend linearly in the longitudinal direction of the orthogonal beam continuously through the interior of the column and the orthogonal beam via the joint with the flat beam, and a plurality of auxiliary reinforcements extend linearly in the longitudinal direction of the orthogonal beam from the column to the joint outside the beam width of the flat beam and into the interior of the orthogonal beam.

According to the present invention, the presence of the auxiliary reinforcement makes it possible to suppress damage such as cracks at the joint where the flat beam and the orthogonal beam intersect due to torsion that occurs between the flat beam and the orthogonal beam during an earthquake, etc. In addition, since the auxiliary reinforcement protrudes into the orthogonal beam by a predetermined length beyond the beam width of the flat beam, even if the orthogonal beam is damaged due to torsion, the damaged area is at least a predetermined length away from the joint interface between the flat beam and the orthogonal beam, making it easy to repair the damage.

In the present invention, when the beam depth of the orthogonal beam is D, it is preferable that the auxiliary reinforcement protrudes from the outside of the beam width of the flat beam by a distance of D/10 or more and D or less.

The reason why the protruding length of the reinforcing bars is preferably D/10 is based on the fact that, as described below, the inventors fabricated a test specimen with a protruding length of the reinforcing bars of D/4 and conducted alternating positive and negative load tests on this specimen, and found that no penetrating cracks were found in the orthogonal beams, and that there was still room for cracking in the test specimen.

On the other hand, the protruding length of the auxiliary reinforcement is set to D or less because if the protruding length exceeds D, there is a risk that the torsion of the flat beam will not be sufficiently transmitted to the orthogonal beam.

In addition, in the present invention, when the beam depth of the orthogonal beam is D, it is preferable that the auxiliary reinforcement protrudes from the outside of the beam width of the flat beam by a distance of D/4 or more and D or less.

This is based on the fact that, as mentioned above, when a positive and negative alternating load test was conducted on a specimen with a protruding length of the auxiliary reinforcement of D/4, no through cracks were found in the orthogonal beams.

1 is a schematic cross-sectional view in an XY plane of a column-beam joint structure according to an embodiment of the present invention. FIG. Schematic cross-sectional view taken along line II-II in FIG. Schematic cross-sectional view taken along line III-III in FIG.

The column-beam joint structure 100 according to an embodiment of the present invention will be described with reference to Figs. 1 to 3. Note that Figs. 1 to 3 are diagrams for explaining the present embodiment in a schematic manner, and the dimensions have been exaggerated.

The column-beam joint structure 100 is an integrally constructed reinforced concrete (RC) structure including a column 10, a flat beam 20, an orthogonal beam 30 perpendicular to the column 10, and a joint 40 formed by joining these at their intersection. The column-beam connection structure 100 or a structure including the column-beam connection structure 100 may be made of cast-in-place concrete or half-precast concrete.

The flat beam 20 is a flat beam with a beam width wider than the beam depth, and the beam width is wider than the column width of the column 10. The ratio of the beam width of the flat beam 20 to the column width of the column 10 is preferably 3 or less. The orthogonal beam 30 is a non-flat beam with a beam depth equal to or greater than the beam width. The beam width of the orthogonal beam 30 is preferably 1/3 or less of the beam width of the flat beam 20. In addition, the beam depth of the orthogonal beam 30 is preferably equal to or greater than the beam depth of the flat beam 20.

The part of the flat beam 20 that protrudes outward from the side of the column 10 in the beam width direction of the flat beam 20 from the joint 40 is the protruding part 41. This protruding part 41 corresponds to the joint with the flat beam in the present invention.

The portion of the protruding portion 41 that protrudes outward from the side of the orthogonal beam 30 forms a beam joint 42 formed by the intersection of the flat beam 20 and the orthogonal beam 30. It is preferable that the dimension of the portion of the protruding portion 41 that protrudes from the side of the column 10 is equal to or smaller than the column width and column height, and equal to or smaller than twice the beam height of the flat beam 20.

Here, we will explain the case where the axis Oc of the column 10 and the axis Og of the flat beam 20 intersect, i.e., the column 10 is joined to the flat beam 20 without eccentricity, but there may be eccentricity between them, i.e., the column 10 may be joined to one side relative to the flat beam 20.

Here, we will explain the case where the axis Oc of the column 10 and the axis Or of the orthogonal beam 30 intersect, i.e., the column 10 is joined to the orthogonal beam 30 without eccentricity, but there may be eccentricity between them, i.e., the column 10 may be joined to one side relative to the orthogonal beam 30.

In the following description, the direction in which the axis Og of the flat beam 20 extends is the X-axis direction, the direction in which the axis Oc of the column 10 extends is the Z-axis direction, and the direction in which the axis Or of the orthogonal beam 30 extends, perpendicular to the X-axis and Z-axis, is the Y-axis direction.

The columns 10 are fitted with multiple linear column main reinforcements 11 extending in the Z-axis direction, and multiple square-shaped hoop reinforcements (shear reinforcement) 12 that surround the outer periphery of the column main reinforcements 11 and are spaced apart in the Z-axis direction. The column main reinforcements 11 extend through adjacent columns 10 in the Y-axis direction via joints 40.

The flat beams 20 are provided with multiple linear beam main reinforcements 21 extending in the X-axis direction. The beam main reinforcements 21 may be arranged at equal intervals in the Y-axis direction, but are preferably arranged so that the intervals are narrower inside the column compared to outside the column. The beam main reinforcements 21 extend within adjacent flat beams 20 in the X-axis direction via joints 40 and protruding portions 41.

In addition, the flat beam 20 has multiple square-shaped stirrups (shear reinforcement) 22 arranged around the outer periphery of the beam main reinforcement 21 and spaced apart in the X-axis direction. Although not shown, it is preferable that core reinforcement be arranged in the middle of each stirrup 22 to connect in the Z-axis direction.

Furthermore, in the column 10 and the protruding portion 41, in the portion outside the beam width of the orthogonal beam 30 within the column depth, one torsional reinforcement bar 23 is arranged to surround each of the multiple beam main reinforcements 21. Note that each of the multiple torsional reinforcements 23 may be arranged at intervals in the X-axis direction.

The torsional reinforcement 23 is divided into two pieces, each of which is U-shaped. The torsional reinforcement 23 is arranged so that it extends from the end face of the flat beam 20 on the orthogonal beam 30 side toward the inside of the joint 40 so as to surround the outside of the beam main reinforcement 21.

Furthermore, in the area of the flat beam 20 that is outside the column height, i.e., in the beam joint 42 that is outside the side of the column 10 in the Y-axis direction, multiple square-shaped shear reinforcement bars 24 are arranged at intervals in the X-axis direction to surround the outside of the multiple beam main reinforcements 21.

It is preferable that the shear reinforcement 24 is arranged over the entire outer side of the column height of the flat beam 20, but it may be arranged only within the range of the outer side of the column height of the flat beam 20 that is necessary for cross-sectional calculation.

The orthogonal beams 30 are provided with multiple linear beam main reinforcements 31 that extend continuously in the Y-axis direction throughout the two adjacent orthogonal beams 30, penetrating the joints 40 and the protruding parts 41. The beam main reinforcements 31 correspond to the beam main reinforcements of the present invention. In addition, in the orthogonal beams 30, except for the joints 40 and the protruding parts 41, multiple square-shaped hoop reinforcements (shear reinforcement reinforcements) 32 are provided at intervals in the Y-axis direction, surrounding the outer periphery of the multiple beam main reinforcements 31.

In addition to the beam main reinforcement 31, the orthogonal beam 30 is provided with linear auxiliary reinforcement 33 extending in the Y-axis direction through the joint 40 and the protruding portion 41. The auxiliary reinforcement 33 corresponds to the auxiliary reinforcement of the present invention. The auxiliary reinforcement 33 protrudes into the orthogonal beam 30 by a predetermined length X beyond the beam width of the flat beam 20. For example, when the beam depth of the orthogonal beam 30 is D, the predetermined length X is D/10 or more and D or less, and more preferably D/4 or more and D or less.

The auxiliary bars 33 are spaced apart in the X-axis direction, here at the same intervals as the beam main bars 21, and are spaced apart in the Y-axis direction, here at intervals narrower than the intervals between the beam main bars 31 so that they are positioned between the beam main bars 21. The auxiliary bars 33 have fixing parts 33a at both ends. The amount of reinforcement of the reinforcing bars 33 may be greater than or equal to the minimum amount of reinforcement determined from the desired allowable torsional stress.

In addition, within the protruding portion 41, multiple U-shaped bar bars (torsion reinforcement bars) 34 are arranged at intervals in the Y-axis direction to surround the multiple auxiliary bars 33 and the main beam bars 31. Note that here, the bar bars 34 are arranged so that they extend downward from the upper surface side that contacts the main beam bars 31 at their upper ends to contact the auxiliary bars 33 at their lower ends. However, the bar bars 34 do not have to be arranged.

The presence of the auxiliary reinforcement 33 and the bar reinforcement 34 in this way makes it possible to prevent damage such as cracks from occurring at the intersection of the flat beam 20 and the orthogonal beam 30 due to twisting that occurs between the flat beam 20 and the orthogonal beam 30 during an earthquake, etc.

In addition, the auxiliary reinforcement 33 protrudes into the orthogonal beam 30 by a predetermined length X beyond the beam width of the flat beam 20. Therefore, even if the orthogonal beam 30 is damaged due to twisting, the damaged area will be at least the predetermined length X away from the joint interface between the flat beam 20 and the orthogonal beam 30, making it easy to repair the damage.

The inventors created a test specimen in which the protruding length X of the reinforcing bars 33 was set to D/4. Then, the flat beams 20 and the orthogonal beams 30 of this test specimen were subjected to 10 cycles of alternating positive and negative load tests of 1/50 rad.

As a result, no through cracks (structural cracks) were found in the orthogonal beam 30, and the maximum crack width was 0.06 mm. This shows that if the protruding length X of the auxiliary reinforcement 33 is D/4, it is possible to sufficiently prevent damage to the orthogonal beam 30 due to twisting. And since there was still room for cracking in the test specimen, it is inferred that if the protruding length X of the auxiliary reinforcement 33 is about D/10, it is possible to prevent damage to the orthogonal beam 30 due to twisting.

On the other hand, if the protruding length X of the auxiliary reinforcement 33 from the flat beam 20 is too long, there is a risk that the torsion of the flat beam 20 will not be sufficiently transmitted to the orthogonal beam 30. Therefore, it is presumed that it is preferable for the protruding length X of the auxiliary reinforcement 33 to be D or less so that the torsion of the flat beam 20 can be sufficiently transmitted to the orthogonal beam 30.

The present invention is not limited to the beam-column joint structure 100 specifically described in the above embodiment, but may be modified as appropriate within the scope of the claims.

For example, although a structure in which the upper surfaces of the flat beam 20 and the orthogonal beam 30 coincide has been described, the present invention may also be applied to a structure in which the lower surfaces of the flat beam 20 and the orthogonal beam 30 coincide. In this case, since the lower end bar of the beam main reinforcement 21 of the flat beam 20 is located lower than the lower end bar of the beam main reinforcement 21 of the orthogonal beam 30, the torsional reinforcement bar can be inserted from the lower surface side of the flat beam 20 to restrain the lower end bar of the beam main reinforcement 21 of the flat beam 20.

In addition, although the structure in which the flat beam 20 and the orthogonal beam 30 intersect in a cross shape in plan view has been described, this may also be applied to a structure in which the flat beam 20 and the orthogonal beam 30 are connected in a U-shape in plan view. In this case, for example, the axis Oc of the column 10 and the axis Or of the orthogonal beam 30 do not intersect, and the outer surfaces of the column 10 and the orthogonal beam 30 are flush with each other. The beam main reinforcement 21 may have an anchoring portion at the end of the outer surface of the flat beam 20 that is flush with the outer surface of the column 10.

Furthermore, it may be applied to a structure in which the flat beam 20 and the orthogonal beam 30 are connected in an L-shape in a plan view. In this case, the auxiliary reinforcement 33 may be protruded from the inside of the column 10 via the protruding portion 41 to one of the orthogonal beams 30 by a predetermined length X.

10...column, 11...main column reinforcement, 12...hoop reinforcement (shear reinforcement), 20...flat beam, 21...main beam reinforcement, 22...stirrup reinforcement (shear reinforcement), 23...torsion reinforcement, 24...shear reinforcement, 30...orthogonal beam, 31...main beam reinforcement, 32...hoop reinforcement (shear reinforcement), 33...auxiliary reinforcement, 34...torsion reinforcement (torsion reinforcement), 40...joint, 41...projection (joint with flat beam), 42...joint of beam, 100...column-beam joint structure, D...beam depth of orthogonal beam, Oc...axis of column, Og...axis of flat beam, Or...axis of orthogonal beam, X...projection length.

Claims (3)

A joint structure in which a column, a flat beam having a beam width wider than the column width of the column, and an orthogonal beam perpendicular to the column and the flat beam and having a beam width equal to or less than the beam depth are connected,
A plurality of beam main reinforcements extending linearly in the longitudinal direction of the orthogonal beam continuously through the joint between the column and the orthogonal beam and the flat beam throughout the entire orthogonal beam;
A column-beam joint structure characterized in that a plurality of auxiliary reinforcements are arranged from the column through the joint, protruding from the outside of the beam width of the flat beam to the inside of the orthogonal beam and extending linearly in the longitudinal direction of the orthogonal beam. The beam-column joint structure described in claim 1, characterized in that the auxiliary reinforcement protrudes from the outside of the beam width of the flat beam by more than D/10 and less than D, where D is the beam depth of the orthogonal beam. The column-beam joint structure described in claim 1, characterized in that the auxiliary reinforcement protrudes from the outside of the beam width of the flat beam by a distance of D/4 or more and D or less, when the beam depth of the orthogonal beam is D.