JP7384645B2 - How to calculate the strength at the joint between a column and a flat beam - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act ▲1▼ Publication date: July 20, 2020 Publication: 2019 Conference (Hokuriku) Academic Lecture Abstracts Architectural Design Presentation Abstracts, pp. 115-116, General Foundation Architectural Institute of Japan ▲2▼ Publication date: July 20, 2020 Publication: 2019 Annual Conference (Hokuriku) Academic Lecture Abstracts Architectural Design Presentation Abstracts, pp. 117-118, Architectural Institute of Japan ▲ 3▼Publication date: September 1, 2020 Publication: Okumura Gumi Technical Annual Report No. 45, pp. 77-84, Okumura Gumi Technical Research Institute Co., Ltd.

The present invention relates to a method for calculating proof strength at a joint between a column and a flat beam.

A flat beam construction method using flat beams having a width wider than the column width has been proposed for buildings with reinforced concrete rigid-frame frames. This flat beam construction method can keep the beam height small and create an open space under the beam, making it possible to lower the overall height of the building while ensuring sufficient interior height. . However, in the flat beam construction method, since the beam height is small, the bending moment that can be supported at the joint between the column and the flat beam is small. Particularly at the end of the beam, the part that protrudes from the column width has low rigidity because it is not connected to the column and is prone to bending deformation.As a result, the bending moment that can be supported by the entire beam is also lower than the result based on normal cross-sectional calculations. becomes smaller.

Therefore, for example, Patent Document 1 describes calculating the ultimate bending strength of a flat beam based on the difference between the beam width and the column width. In addition, Patent Document 2 discloses that the material strength or the amount of main reinforcement of tension main reinforcements (beam main reinforcements) placed outside the column width of a flat beam is reduced to reduce the bending strength of the flat beam located outside the column width. It is described that the flat beam is designed to be lower than the area within the width.

Patent No. 6243238 Patent No. 6267905

However, in the technique disclosed in Patent Document 1, the protruding portion protruding to the outside of the column is not sufficiently integrated into the joint between the column and the flat beam, and as a result, the strength of the protruding portion is poor. However, the bending strength is reduced based on the difference between the column width and the beam width, and does not take into account the difference between when the column is in the center of the beam and when it is closer to one side in the width direction.

Furthermore, in the technique disclosed in Patent Document 2, the material strength or the amount of main reinforcement of the beam main reinforcing bars placed in the protruding portion (the part located outside the column width of the flat beam) is intentionally reduced. Although the strength of the protruding portion is intentionally lowered, only the ultimate bending strength of the protruding portion is considered, and shear strength and the like are not taken into account.

It is considered that the calculation method used to reduce the strength of the projecting portion in this way does not match the actual conditions, and that sufficient evaluation has not been possible.

In view of the above points, an object of the present invention is to provide a method for calculating the proof stress at a joint between a column and a flat beam, taking into consideration the positional relationship of the column with respect to the flat beam.

The present invention provides a method for calculating the yield strength in a joint structure between a column and a flat beam having a beam width wider than the column width of the column, the method comprising: Considering the effect that the stress borne by the beam main reinforcement placed in the column is smaller than the stress borne by the beam main reinforcement placed in the flat beam placed within the column width of the column,Long-term allowable bending moment or short-term allowable bending moment of the flat beam _g M _a (N・mm) by the following formula (1)It is characterized by calculating.
_g M _a =ξ・a _t ・gf _t ・j... (1)
However, a _t is the cross-sectional area of the tensile reinforcement of the flat beam (mm ² ), _g f _t is the long-term or short-term allowable stress of the main beam reinforcement of the flat beam (N/mm ² ), j is the stress center distance (mm) of the flat beam, and the reduction coefficient ξ is a reduction coefficient according to the column-to-beam width ratio α, and when it is 1 or more and less than 2, it is 1-0.15 (α -1), and 0.85-0.1 (α-2) when the column/beam width ratio α is 2 or more and 3 or less.

According to the present invention, based on the results of experiments conducted by the inventor, it is possible to appropriately calculate on the safe side the proof stress at the joint between a column and a flat beam in a state where the joint and the protruding part are sufficiently integrated. becomes.

In the present invention, on the inner side of the column of the column including the joint between the column and the flat beam, a plurality of beam main reinforcements are provided in the flat beam so as to surround a plurality of beam main reinforcements arranged in the flat beam. A first reinforcing bar is provided, and each of the first reinforcing bars is divided into two and each has a U-shape, and both ends of the U-shape are located inside the column width of the column. It is preferable that the beam reinforcement be fixed to the beam main reinforcement so as to overlap in the width direction of the column.

In this case, since the first reinforcing bars restrain the main beam reinforcements in the joints and the protruding parts, which are the inner parts of the columns of the flat beams, deformation due to shear force and torsion in these parts is suppressed. becomes possible. This makes it possible to particularly suppress deformation due to torsion, and also effectively suppress deformation due to shear force.

Further, in the present invention, a plurality of second reinforcing bars are arranged inside the flat beam on the outside of the column, and the second reinforcing bars are arranged in the plurality of reinforcing bars arranged inside the flat beam. It is preferable that the beam main reinforcement is composed of a surrounding reinforcement that surrounds the outer periphery of the main beam reinforcement, and a plurality of connecting reinforcements that are connected in the direction in which the column extends in the middle of the surrounding reinforcement.

In this case, since the second reinforcing bars are connected in the middle by the core reinforcing bars, it is possible to effectively suppress deformation due to shear force in the part of the flat beam where the second reinforcing bars are installed. .

FIG. 3 is a schematic cross-sectional view in the XY plane of the first column-beam joint structure. FIG. 9 is a schematic cross-sectional view taken along line II-II in FIGS. 1, 5, and 9. FIG. 9 is a schematic cross-sectional view taken along line III-III in FIGS. 1, 5, and 9. FIG. 9 is a schematic cross-sectional view taken along the IV-IV line in FIGS. 1 and 9. FIG. FIG. 4 is a schematic cross-sectional view in the XY plane of the second column-beam joint structure. A schematic cross-sectional view taken along the VI-VI line in FIG. 5. A schematic cross-sectional view taken along line VII-VII in FIG. 5. A schematic cross-sectional view taken along line VIII-VIII in FIG. 5. FIG. 6 is a schematic cross-sectional view in the XY plane of the third beam-column joint structure. A schematic cross-sectional view along the X-X line in FIG. 9. A schematic cross-sectional view taken along the line XI-XI in FIG. 9. 7 is a graph showing a reduction coefficient used in a first calculation method in a method for calculating proof strength at a joint between a column and a flat beam according to an embodiment of the present invention. The graph which shows the reduction coefficient used in the 2nd calculation method in the calculation method of yield strength. The graph which shows the reduction coefficient used in the 2nd calculation method in the calculation method of yield strength.

First, a first column-beam joint structure 100 to which a proof stress calculation method according to an embodiment of the present invention is applied will be described with reference to FIGS. 1 to 4.

The column-beam joint structure 100 includes a joint 40 in which a reinforced concrete (RC) pillar 10 and a flat beam 20 are joined together in a criss-cross pattern. For example, pillar 10 is a central pillar located inside a building.

The flat beam 20 is a flat beam whose beam width Bg is wider than the beam width Dg (not shown), and the beam width Bg is wider than the column width Bc. The ratio of the beam width Bg to the column width Bc (column/beam width ratio) is preferably 3 or less. A portion of the flat beam 20 that extends outward from the side surface of the column 10 in the beam width direction of the flat beam 20 from the joint portion 40 serves as a protruding portion 41 . The dimensions of the portion of the protruding portion 41 that protrudes from the side surface of the column 10 are preferably equal to or less than the column width Bc and column height Dc, and twice or less than the beam depth Dg 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, that is, the case where the column 10 is joined to the flat beam 20 without eccentricity, but even if there is eccentricity, That is, the column 10 may be joined to the flat beam 20 in a manner that is offset to one side. In this case, the beam width Bg when calculating the ratio (column/beam width ratio) is calculated as the sum of twice the larger width of the protruding portion 41 and the width of the column 10.

Hereinafter, the direction in which the axis Og of the flat beam 20 extends is referred to as the X-axis direction, the direction in which the axis Oc of the column 10 extends is referred to as the Z-axis direction, and the direction perpendicular to the X-axis and the Z-axis is referred to as the Y-axis direction. It will be explained as follows.

The column 10 is internally provided with a plurality of column main reinforcements 11 extending in the Z-axis direction and a plurality of hoop reinforcements 12 surrounding the outer periphery of these column main reinforcements 11 and arranged at intervals in the Z-axis direction. There is.

A plurality of beam main reinforcements 21 extending in the X-axis direction are arranged on the flat beam 20. The main beam reinforcements 21 may be arranged at equal intervals in the Y-axis direction, but it is preferable that the main beam reinforcements 21 are arranged so that the intervals are narrower inside the pillar than outside the pillar.

Further, in a portion of the flat beam 20 inside the column, that is, a portion consisting of the joint 40 and the protruding portion 41 between the column 10 and the flat beam 20, a plurality of torsion reinforcements are provided so as to surround the plurality of beam main reinforcements 21. The stripes 22 are arranged at intervals in the X-axis direction. The torsion reinforcing bars 22 correspond to the first reinforcing bars of the present invention.

Each torsion reinforcing bar 22 is divided into two parts each having a U-shape, and specifically, each torsion reinforcing bar 22 is comprised of a base part 22a and two legs 22b extending from both ends of the base part 22a. The base portion 22a is located in contact with the outer side of the end surface of the beam main reinforcement 21 disposed within the end portion of the projecting portion 41, and each foot portion 22b is disposed at intervals in the Y-axis direction. It is located in contact with the upper side of the upper end reinforcement and the lower side of the lower end reinforcement of the main reinforcement 21. The end portion of each leg portion 22b on the side not connected to the base portion 22a is directly or indirectly fixed to the beam main reinforcement 21 so as to have an overlapping portion within the column width.

Each of the torsion reinforcing bars 22 configured in this manner restrains the beam main reinforcements 21 in the joint portion 40 and the projecting portion 41, thereby suppressing deformation due to shear force and torsion in the joint portion 40 and the projecting portion 41. becomes possible.

This makes it possible to particularly suppress deformation due to torsion, and also effectively suppress deformation due to shear force. Furthermore, the bending moment generated in the protruding portion 41 is transmitted to the column 10 as a torsion resistance force by the torsion reinforcing bars 23. Note that the torsion reinforcing bars 22 may be arranged in an amount that makes it possible to suppress deformation due to shear force and torsion at the joint 40 between the column 10 and the flat beam 20 to a desired amount or less.

Furthermore, a plurality of shear reinforcing bars 23 are arranged at intervals in the X-axis direction in a range outside the column of the flat beam 20, that is, in both parts outside the front and rear surfaces of the column 10 in the X-axis direction. has been done. The shear reinforcing bars 23 correspond to the second reinforcing bars of the present invention. Note that the shear reinforcing bars 23 are arranged over the entire outer side of the column of the flat beam 20 in both the positive and negative directions of the X-axis.

The shear reinforcing bars 23 include stirrups 24 surrounding the outer periphery of the plurality of main beam reinforcements 21 and a plurality of core reinforcing bars connected in the direction in which the column 10 extends, that is, the Z-axis direction, in the middle of one stirrup 24. It consists of 25. The stirrup muscles 24 correspond to the surrounding muscles of the present invention, and the core muscles 25 correspond to the connecting muscles of the present invention.

A plurality of core bars 25 are arranged at intervals in the Y direction. Although the core reinforcements 25 may be arranged at equal intervals in the Y direction, it is preferable that the core reinforcements 25 are arranged so that the intervals are narrower within the column width than outside the column width.

The shear reinforcing bars 23 configured in this manner restrain the portions of the plurality of beam main reinforcing bars 21 outside the column width. Since the shear reinforcing bars 23 are connected in the middle by the core reinforcing bars 25, it is possible to effectively suppress deformation due to shear force in the portion of the flat beam 20 in which the shear reinforcing bars 23 are installed.

The amount of shear reinforcing bars 23 in the flat beam 20 may be the same as the shear reinforcing bars of a normal beam, and may be equal to or greater than the minimum amount of reinforcement for the cross-sectional area of the flat beam 20 and have a desired allowable shear. The amount of reinforcement may be greater than the minimum amount of reinforcement determined from the stress.

Next, a second column-beam joint structure 200 to which the yield strength calculation method according to the embodiment of the present invention is applied will be described with reference to FIGS. 5 to 8, FIGS. 2 and 3. However, the description of the same configuration as the first beam-column joint structure 100 described above will be omitted.

The beam-column joint structure 200 includes a joint 40 in which a reinforced concrete (RC) column 10 and a flat beam 20 are joined in a T-shape. For example, the pillar 10 is a side pillar located on the side of a building.

The main beam reinforcement 21 arranged in the flat beam 20 has a fixing portion 21a at an end on the outside surface side that is flush with the outside surface of the column 10 of the flat beam 20, that is, at an end on the back surface of the flat beam 20. ing.

Then, the flat beam 20 is divided into two parts so as to surround the plurality of beam main reinforcements 21 in the part inside the column, that is, in the part consisting of the joint 40 and the protruding part 41 between the pillar 10 and the flat beam 20. A plurality of torsion reinforcing bars 22 each having a U-shape are arranged at intervals in the X-axis direction.

Each of the torsion reinforcing bars 22 configured in this manner restrains the beam main reinforcements 21 in the joint portion 40 and the projecting portion 41, thereby suppressing deformation due to shear force and torsion in the joint portion 40 and the projecting portion 41. becomes possible.

Furthermore, a plurality of shear reinforcing bars 23 are arranged at intervals in the X-axis direction in a range of the flat beam 20 that is outside the column, that is, a portion outside the front and rear surfaces of the column 10 in the X-axis direction. There is.

In addition, in the protruding portion 41 of the flat beam 20, U-shaped back reinforcement bars (edge crack reinforcement bars) 26 are spaced apart in the beam width direction (Y-axis direction) and between the beam main reinforcements 21. It is located. The back surface reinforcing bars 26 are arranged on the back surface of the flat beam 20 on the outside of the column width. The presence of such back reinforcement bars 26 makes it possible to suppress the occurrence of cracks on the back surface of the flat beam 20.

The back reinforcement 26 has a U-shape, and specifically includes a base 26a and two legs 26b extending from both ends of the base 26a. The base portion 26a is located in contact with the outer side of the end surface of the beam main reinforcement 21 which is disposed at the portion closest to the rear surface of the protruding portion 41, and the respective foot portions 26b are arranged at intervals in the X-axis direction. The reinforcing bars 22 are fixed in contact with the inner sides of the upper and lower legs of the torsion reinforcing bars 22 at portions that intersect with the torsion reinforcing bars 22. The upper leg portion 26b is disposed at approximately the same height as the upper surface of the upper end reinforcement of the beam main reinforcement 21, and the lower foot portion 26b is located at approximately the same height as the lower surface of the lower end reinforcement of the beam main reinforcement 21. The end portion of each foot portion 26b on the side not connected to the base portion 26a is not particularly fixed to other reinforcing bars.

The back surface reinforcing bars 26 are inserted from the back surface of the flat beam 20 toward the inside, are arranged, and are fixed inside the flat beam 20 . It is desirable that the back reinforcing bars 26 ensure a cover thickness as a reinforcing bar and are arranged as close to the back side as possible.

However, although it is preferable to arrange the amount of reinforcing bars necessary for resisting shear force and torsion, the back reinforcing bars 26 are not taken into account when calculating the proof strength of the joint 40.

Next, a third column-beam joint structure 300 to which the yield strength calculation method according to the embodiment of the present invention is applied will be described with reference to FIGS. 9 to 11 and FIGS. 2 to 4. However, the description of the same configuration as the first and second beam-column joint structures 100 and 200 described above will be omitted.

The column-beam joint structure 300 is a joint formed by joining an integrally constructed reinforced concrete (RC) column 10 and a flat beam 20, and further joining an orthogonal beam 30 orthogonal to the column 10 and the flat beam 20. The structure includes 40. For example, the pillar 10 is a side pillar located on the side of a building. The pillars 10, the flat beams 20, and the orthogonal beams 30 are connected so that one outer surface of each is flush with the other. The outside of the column width of the column 10 on the column 10 side of the protruding portion 41 is a beam joint 42 between the flat beam 20 and the orthogonal beam 30.

The main beam reinforcement 21 arranged in the flat beam 20 has a fixing portion 21a at an end on the outside surface side that is flush with the outside surface of the column 10 of the flat beam 20, that is, at an end on the back surface of the flat beam 20. ing. The fixing part 21a is located at the end of the beam joint 42 on the outer surface side, that is, at the end of the beam joint 42 on the back side.

The orthogonal beam 30 has a plurality of main beam reinforcements 31 extending in the Y-axis direction through the joint 40 and the joint 42 of the beam, and a plurality of main beam reinforcements 31 surrounding the outer periphery of these main beam reinforcements 31 outside the joint 40. , a plurality of hoop muscles 32 are arranged at intervals in the Y-axis direction.

For example, when the upper end surfaces of the flat beam 20 and the orthogonal beam 30 match, either the beam main reinforcement 21 at the upper end of the flat beam 20 or the beam main reinforcement 31 at the upper end of the orthogonal beam 30 at the joint 40 and the beam joint 42 It will be placed above. Since the flat beam 20 has a low beam depth Dg, the beam main reinforcement 21 at the upper end is placed above the beam main reinforcement 31 at the upper end of the orthogonal beam 30 in order to ensure a large effective beam height, which is the distance between the upper and lower beam main reinforcements 21. It is preferable.

In this case, if the main beam reinforcement 21 at the upper end of the flat beam 20 is not restrained by the reinforcing bars, the strength against shear force and twisting at the joint 42 of the beam will decrease. Therefore, in the joint portion 42 of the beam, U-shaped hairpins 33 are arranged between the beam main reinforcements 31 at intervals in the beam width direction (X-axis direction) of the orthogonal beam 30. The hairpin reinforcements 33 are arranged to extend downward from the upper surface side of the beam connection portion 42 in a direction perpendicular to the beam main reinforcements 21 (Z-axis direction).

The hairpin bars 33 are arranged up to just before the fixing part 21a of the main beam reinforcement 21 of the flat beam 20 within the beam connection part 42. For example, when the fixing section 21a is mechanical, the hairpins 33 extend to just before the sleeve section of the fixing plate. Further, in the case where the fixing section 21a is configured to directly join the fixing plate to the tip of the reinforcing bar, the hairpins 33 extend to just before the fixing plate.

The hairpins 33 have a U-shape, and specifically include a base 33a and two legs 33b extending from both ends of the base 33a. The base portion 33a is located in contact with the upper surface of the upper end main beam reinforcement 21 in the joint portion 42 of the beam, and each foot portion 33b is arranged at intervals in the vertical direction (Z-axis direction). located in contact with the outside of the As a result, the hairpin reinforcements 33 surround the beam main reinforcements 21 in the joint portion 42 of the beam in a U-shape. Note that the end of each leg 33b that is not connected to the base 33a may not be fixed to any other reinforcing steel.

The hairpins 33 are inserted from the upper surface side of the joint portion 42 of the beams toward the inside, are arranged, and are fixed inside the orthogonal beams 30 . Although it is preferable to arrange the amount of reinforcing bars necessary for resisting shear force and torsion, it is preferable that the barbell reinforcements 33 are not taken into account when calculating the proof strength of the flat beam 20.

The hairline reinforcement 33 configured in this manner makes it possible to restrain the main beam reinforcement 21 of the flat beam 20 within the joint 42 of the beam, so that twisting due to shear force in this part and the upper surface of the joint 42 of the beam can be prevented. It is possible to suppress the occurrence of cracks.

In addition, since the hoop reinforcement 32 in the orthogonal beam 30 is present at the end on the back side of the beam joint 42, this allows the rear surface of the beam joint 42 to be straightened without using the back reinforcement 26. The occurrence of cracks is suppressed.

Note that the above-described column-beam connection structures 100, 200, and 300 or a structure including them may be made of cast-in-place concrete or half precast concrete.

Furthermore, the strength calculation method of the present invention is not limited to those having the above-mentioned column-beam joint structures 100, 200, and 300, and the joint portion 40 and the protruding portion 41 are It can be applied to any joint structure between the column 10 and the flat beam 30 in an integrated state.

Hereinafter, a method of calculating proof strength at a joint between a column and a flat beam according to an embodiment of the present invention will be described. This calculation method was derived by the inventors by conducting strength tests and the like on a large number of test specimens having the above-mentioned beam-column joint structures 100, 200, and 300.

The test specimens used had column-to-beam width ratio α (=Bg/Bc), which is the ratio of beam width Bg to column width Bc, of 1.5, 2.0, and 3.0. Therefore, this calculation method is applicable to those where the column/beam width ratio α is 3 or less.

In addition, the test specimen used was one in which the dimensions of the portion of the protruding portion 41 protruding from the side surface of the column 10 were equal to or less than the column width Bc and column depth Dc, and were equal to or less than twice the beam depth Dg of the flat beam 20. . Therefore, this calculation method is applicable to such a configuration. Note that this calculation method can also be applied to a structure in which the column 10 and the flat beam 20 are joined eccentrically. When constructing the top layer of a building using the flat beams 20, a vertical stub is, in principle, provided.

As a first calculation method, the stress borne by the main beam reinforcement 21 of the flat beam 20 placed outside the column 10 is smaller than the stress borne by the main beam reinforcement 21 of the flat beam 20 placed within the column width of the column 10. In consideration of the influence, the allowable bending moment _{g Ma} of the flat beam 20 is calculated by reducing it according to the column-to-beam width ratio α. Specifically, the long-term allowable bending moment or the short-term allowable bending moment _g M _a (N·mm) is calculated using the following equation (1).
_g M _a = ξ・a _t・_g f _t・j ... (1)

Here, ξ is a reduction coefficient according to the column-to-beam width ratio α, a _t is the cross-sectional area of the tensile reinforcement of the flat beam 20 (mm ² ), and _g f _t is the long-term or short-term tolerance of the main beam reinforcement 21 of the flat beam 20. The degree of stress (N/mm ² ), j is the stress center distance (mm) of the flat beam 20. Then, the reduction coefficient ξ is reduced from 1.00 to 0.75 in accordance with the column-to-beam width ratio α, as shown in the graph shown in FIG.

Note that the reduction coefficient ξ is 1/100 of the flat beam 20 of the joint 40 of each test specimen relative to the column 10, with respect to the ratio of the average strain of all the beam main reinforcements 21 to the average strain of the beam main reinforcements 21 in the column 10. , 1/200, and 1/400 of the deformation angle.

As a second calculation method, the stress borne by the main beam reinforcement 21 of the flat beam 20 placed outside the column 10 is smaller than the stress borne by the main beam reinforcement 21 of the flat beam 20 placed within the column width of the column 10. The ultimate bending moment _g M _y of the flat beam 20 is calculated by reducing it in accordance with the column-to-beam width ratio α, taking into account the following influence. Specifically, the ultimate bending moment _g M _y (N·mm) is calculated by the following equation (2). In addition, formula (2) is based on the description on pages 651 to 652 of the ``2015 Explanation of Structural Technical Standards for Buildings'' edited by the Building Administration Information Center and the Japan Architectural Disaster Prevention Association. .
_g M _y = β・0.9・a _t・_g σ _y・d ... (2)

Here, β is the reduction coefficient according to the column-to-beam width ratio α, a _t is the cross-sectional area of the tensile reinforcement of the flat beam 20 (mm ² ), and _g σ _y is the yield strength of the main beam reinforcement 21 of the flat beam 20 (N/ mm ² ), d is the effective height (mm) of the flat beam 20. Then, the reduction coefficient β is reduced from 1.00 to 0.85 in accordance with the column-to-beam width ratio α, as shown in the graph shown in FIG.

In addition, when we conducted an experiment on a test specimen with a column-to-beam width ratio α of 2.0, it was confirmed that all the beam main reinforcements 21, including the beam main reinforcements 21 placed outside the columns 10, contributed to the strength. - The reduction coefficient β was set to 1.00 when the beam width ratio α was 2.0. On the other hand, when testing a test specimen with a column-to-beam width ratio α of 3.0, it was confirmed that the stress borne by the beam main reinforcement 21 placed outside the column 10 decreased, so the test result was a value on the safe side. Therefore, the reduction coefficient β was set to 0.85.

As a third calculation method, the stress borne by the main beam reinforcement 21 of the flat beam 20 placed outside the column 10 is smaller than the stress borne by the main beam reinforcement 21 of the flat beam 20 placed within the column width of the column 10. In consideration of the _influence of Specifically, the ultimate shear strength V _ju (N) of the joint 40 is calculated using the following equation (3). In addition, formula (3) is a formula based on the toughness guarantee guideline formula, with the column width and beam width in the formula replaced.
V _ju = γ・κ・φ・F _j・b _j・D _j ... (3)

Here, γ is a reduction coefficient according to the column-to-beam width ratio α, κ is a shape coefficient, φ is a correction coefficient depending on the presence or absence of the orthogonal beam 30, and F _j is a correction coefficient depending on the presence or absence of the orthogonal beam 30 (N/mm ² ) , the yield strength (N/mm ² ) of the beam main reinforcement 21 of the flat beam 20, and D _j is the anchoring length of the beam main reinforcement 20 or the column height Dc (mm). b _j is the effective width (mm) of the joint portion 40, and is calculated using equations (4) and (5).
b _j =B _c +b _a1 +b _a2 ... (4)
b _ai = min (b _i /2, D _c /4) ... (5)

Here, b _i is each distance (mm) in the Y-axis direction from the end face of the column 10 to the end face of the flat beam 30. When the column 10 is connected without eccentricity with respect to the flat beam 30, b ₁ =b ₂ =(Bg-Bc)/2. Dc is the column height (mm) mentioned above.

Then, the reduction coefficient γ is reduced from 1.00 to 0.90 in accordance with the column-to-beam width ratio α, as shown in the graph shown in FIG.

The shape factor κ is 1.0 when the column 10 and the flat beam 20 are joined in a cross shape as in the column-beam joint structure 100, and when the column 10 and the flat beam 20 are joined in a cross-shape as in the column-beam joint structure 200, the shape coefficient κ is 1.0. When the beam 20 is joined in a T-shape, it is 0.7. The correction coefficient φ is 1.0 when the orthogonal beam 30 is joined to the outer side of the column 10 in both column width directions as in the column-beam joint structure 300, and is 0.85 in other cases.

Then, F _j can be determined by the following equation (6).
F _j =0.8・F _c ^0.7 ... (6)

In addition, experiments were conducted using test specimens with a column-to-beam width ratio α of 2.0 or 3.0, and the reduction coefficient γ was set to 0.90 as a value at which the test result was on the safe side. If the column/beam width ratio α is 1.0, there is no need to reduce it, so the reduction coefficient γ was set to 1.00.

Using the above equations (1) to (3), the supportable bending moment and shear strength of the flat beam 20 and the joint 40 between the column 10 and the flat beam 20 are determined. Equation (1) is an equation for determining the supportable bending moment of the flat beam 10, and is used when designing the allowable stress. Equations (2) and (3) are equations for calculating ultimate strength. Equation (2) is used to calculate the ultimate bending moment of the flat beam 20, and equation (3) is used to calculate the ultimate shear strength of the joint 40 between the flat beam 20 and the column 10.

As a practical calculation method, after confirming that the flat beam 20 can support long-term and short-term allowable bending moments using formula (1), the column 10 and flat beam What is necessary is to find the proof strength of the joint portion 40 with 20 and confirm that this proof stress is larger than the stress generated at the final stage. If any of these conditions is not satisfied, the cross-sectional dimensions of the flat beam 20, etc. may be changed.

Note that the yield strength calculation method of the present invention is not limited to the three calculation methods described above, and can be modified as appropriate within the scope of the claims.

10...Column, 11...Column main reinforcement, 12...Hoop reinforcement, 20...Flat beam, 21...Beam main reinforcement, 22...Torsion reinforcement (first reinforcement), 23...Shear reinforcement (second reinforcement), 24... Stirrups (surrounding bars), 25... Core bars (connecting bars), 26... Back reinforcement bars (second reinforcing bars), 26a... Base, 26b... Foot, 30... Orthogonal beam, 31... Main beam reinforcement , 32... Hoop bar, 33... Hairpin bar, 40... Joint part, 41... Jumping part, 42... Beam joint part, 100, 200, 300... Column beam joint structure.

Claims (3)

A method for calculating proof strength in a joint structure between a column and a flat beam having a beam width wider than the column width of the column, the method comprising:
The stress borne by the beam main reinforcement placed in the flat beam placed outside the column width of the column is borne by the beam main reinforcement placed in the flat beam placed within the column width of the column. Considering the effect that is smaller than the stress,Long-term allowable bending moment or short-term allowable bending moment of the flat beam _g M _a (N・mm) by the following formula (1)A yield strength calculation method characterized by calculating.
_g M _a =ξ・a _t ・gf _t ・j... (1)
However, a _t is the cross-sectional area of the tensile reinforcement of the flat beam (mm ² ), _g f _t is the long-term or short-term allowable stress of the main beam reinforcement of the flat beam (N/mm ² ), j is the stress center distance (mm) of the flat beam, and the reduction coefficient ξ is a reduction coefficient according to the column-to-beam width ratio α, and when it is 1 or more and less than 2, it is 1-0.15 (α -1), and 0.85-0.1 (α-2) when the column/beam width ratio α is 2 or more and 3 or less. A plurality of first reinforcements are provided in the flat beam so as to surround a plurality of beam main reinforcements arranged in the flat beam, on the inside of the column wall of the column including the joint between the column and the flat beam. Each of the first reinforcing bars is divided into two parts each having a U-shape, and on the inside of the width of the column, both ends of the U-shape meet the width of the column. The yield strength calculation method according to claim 1, wherein the strength calculation method is fixed to the beam main reinforcement so as to overlap in a direction. A plurality of second reinforcing bars are arranged inside the flat beam outside the column,
The second reinforcing bars include surrounding bars that surround the outer periphery of a plurality of beam main bars arranged in the flat beam, and a plurality of connecting bars that connect in the direction in which the column extends in the middle of the surrounding bars. 3. The yield strength calculation method according to claim 2, comprising:

Images